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Author name code: benz
ADS astronomy entries on 2022-09-14
author:"Benz, Arnold O."
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Title: Peculiar Radio-X-Ray Relationship in Active Stars
Authors: Vedantham, H. K.; Callingham, J. R.; Shimwell, T. W.; Benz,
A. O.; Hajduk, M.; Ray, T. P.; Tasse, C.; Drabent, A.
2022ApJ...926L..30V Altcode: 2022arXiv220112203V
The empirical relationship between the nonthermal 5 GHz radio luminosity
and the soft X-ray luminosity of active stellar coronae, canonically
called the Güdel-Benz relationship, has been a cornerstone of stellar
radio astronomy, as it explicitly ties the radio emission to the
coronal heating mechanisms. The relationship extends from microflares
on the Sun to the coronae of the most active stars suggesting that
active coronae are heated by a flare-like process. The relationship
is thought to originate from a consistent partition of the available
flare energy into relativistic charges, which emit in the radio-band
via the incoherent gyrosynchrotron mechanism, and heating of the bulk
coronal plasma, which emits in the X-ray band via the Bremsstrahlung
mechanism. Consequently, coherent emission from stellar and substellar
objects is not expected to adhere to this empirical relationship,
as it is observed in ultracool dwarf stars and brown dwarfs. Here we
report a population of radio-detected chromospherically active stars
that surprisingly follow the Güdel-Benz relationship despite their
radio emission being classified as coherent emission by virtue of its
high circularly polarized fraction and high brightness temperature. Our
results prompt a reexamination of the physics behind the Güdel-Benz
relationship, its implication for the mechanism of coronal heating
and particle acceleration in active stars, and the phenomenological
connection between solar and stellar flares.
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Title: STIX X-ray microflare observations during the Solar Orbiter
commissioning phase
Authors: Battaglia, Andrea Francesco; Saqri, Jonas; Massa, Paolo;
Perracchione, Emma; Dickson, Ewan C. M.; Xiao, Hualin; Veronig,
Astrid M.; Warmuth, Alexander; Battaglia, Marina; Hurford, Gordon J.;
Meuris, Aline; Limousin, Olivier; Etesi, László; Maloney, Shane A.;
Schwartz, Richard A.; Kuhar, Matej; Schuller, Frederic; Senthamizh
Pavai, Valliappan; Musset, Sophie; Ryan, Daniel F.; Kleint, Lucia;
Piana, Michele; Massone, Anna Maria; Benvenuto, Federico; Sylwester,
Janusz; Litwicka, Michalina; Stȩślicki, Marek; Mrozek, Tomasz;
Vilmer, Nicole; Fárník, František; Kašparová, Jana; Mann,
Gottfried; Gallagher, Peter T.; Dennis, Brian R.; Csillaghy, André;
Benz, Arnold O.; Krucker, Säm
2021A&A...656A...4B Altcode: 2021arXiv210610058B
Context. The Spectrometer/Telescope for Imaging X-rays (STIX) is the
hard X-ray instrument onboard Solar Orbiter designed to observe solar
flares over a broad range of flare sizes. <BR /> Aims: We report
the first STIX observations of solar microflares recorded during
the instrument commissioning phase in order to investigate the STIX
performance at its detection limit. <BR /> Methods: STIX uses hard
X-ray imaging spectroscopy in the range between 4-150 keV to diagnose
the hottest flare plasma and related nonthermal electrons. This first
result paper focuses on the temporal and spectral evolution of STIX
microflares occuring in the Active Region (AR) AR12765 in June 2020,
and compares the STIX measurements with Earth-orbiting observatories
such as the X-ray Sensor of the Geostationary Operational Environmental
Satellite (GOES/XRS), the Atmospheric Imaging Assembly of the Solar
Dynamics Observatory, and the X-ray Telescope of the Hinode mission. <BR
/> Results: For the observed microflares of the GOES A and B class, the
STIX peak time at lowest energies is located in the impulsive phase of
the flares, well before the GOES peak time. Such a behavior can either
be explained by the higher sensitivity of STIX to higher temperatures
compared to GOES, or due to the existence of a nonthermal component
reaching down to low energies. The interpretation is inconclusive
due to limited counting statistics for all but the largest flare
in our sample. For this largest flare, the low-energy peak time is
clearly due to thermal emission, and the nonthermal component seen at
higher energies occurs even earlier. This suggests that the classic
thermal explanation might also be favored for the majority of the
smaller flares. In combination with EUV and soft X-ray observations,
STIX corroborates earlier findings that an isothermal assumption
is of limited validity. Future diagnostic efforts should focus on
multi-wavelength studies to derive differential emission measure
distributions over a wide range of temperatures to accurately describe
the energetics of solar flares. <BR /> Conclusions: Commissioning
observations confirm that STIX is working as designed. As a rule of
thumb, STIX detects flares as small as the GOES A class. For flares
above the GOES B class, detailed spectral and imaging analyses can
be performed.
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Title: Ion Acceleration and the Development of a Power-law Energy
Spectrum in Magnetic Reconnection
Authors: Che, H.; Zank, G. P.; Benz, A. O.
2021ApJ...921..135C Altcode:
How charged particles are accelerated efficiently and form a power-law
energy spectrum in magnetic reconnection is a problem that is not
well understood. In a previous paper, it was shown that the electron
Kelvin-Helmholtz instability (EKHI) in force-free magnetic reconnection
generates fast-expanding vortices that can accelerate electrons in
a few tens of ion gyroperiods (less than 1 ms in the solar corona)
to form a power-law energy distribution. In this paper, we present
a particle-in-cell (PIC) simulation study of ion acceleration in
force-free magnetic reconnection in the presence of the EKHI-induced
turbulence. We find that ions are not significantly accelerated by the
EKHI-induced stochastic electric field until the magnetic vortices
expand to sizes comparable to the ion gyroradius. The Alfvén waves
generated by the EKHI couple with the magnetic vortices, leading to
resonance between the ions inside the magnetic vortices and Alfvén
waves and enhanced ion heating. The induced Alfvén wave resonance
results in a broken power-law energy spectrum with a breakpoint
at $\sim {m}_{i}{v}_{A}^{2}$ , where v<SUB>A</SUB> is the Alfvén
velocity. We show that the process that forms the nonthermal tail
is a second-order Fermi mechanism and the mean spectral index
is α = (1 + 4a<SUP>2</SUP>D/R)/2, where D is the spatial scale
of the inductive electric field, R is that of vortices, and a =
B<SUB>g</SUB>/B<SUB>0</SUB>, with ratio of guide field B<SUB>g</SUB>
and asymptotic B<SUB>0</SUB>.
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Title: ALMA small-scale features in the quiet Sun and active regions
Authors: Brajša, R.; Skokić, I.; Sudar, D.; Benz, A. O.; Krucker,
S.; Ludwig, H. -G.; Saar, S. H.; Selhorst, C. L.
2021A&A...651A...6B Altcode: 2021arXiv210503644B
<BR /> Aims: The main aim of the present analysis is to decipher (i)
the small-scale bright features in solar images of the quiet Sun and
active regions obtained with the Atacama Large Millimeter/submillimeter
Array (ALMA) and (ii) the ALMA correspondence of various known
chromospheric structures visible in the Hα images of the Sun. <BR
/> Methods: Small-scale ALMA bright features in the quiet Sun region
were analyzed using single-dish ALMA observations (1.21 mm, 248 GHz)
and in an active region using interferometric ALMA measurements (3
mm, 100 GHz). With the single-dish observations, a full-disk solar
image is produced, while interferometric measurements enable the
high-resolution reconstruction of part of the solar disk, including
the active region. The selected quiet Sun and active regions are
compared with the Hα (core and wing sum), EUV, and soft X-ray images
and with the magnetograms. <BR /> Results: In the quiet Sun region,
enhanced emission seen in the ALMA is almost always associated with a
strong line-of-sight magnetic field. Four coronal bright points were
identified, while other small-scale ALMA bright features are most likely
associated with magnetic network elements and plages. In the active
region, in 14 small-scale ALMA bright features randomly selected and
compared with other images, we found five good candidates for coronal
bright points, two for plages, and five for fibrils. Two unclear cases
remain: a fibril or a jet, and a coronal bright point or a plage. A
comparison of the Hα core image and the 3 mm ALMA image of the analyzed
active region showed that the sunspot appears dark in both images
(with a local ALMA radiation enhancement in sunspot umbra), the four
plage areas are bright in both images and dark small Hα filaments are
clearly recognized as dark structures of the same shape also in ALMA.
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Title: Water in star-forming regions: physics and chemistry from
clouds to disks as probed by Herschel spectroscopy
Authors: van Dishoeck, E. F.; Kristensen, L. E.; Mottram, J. C.;
Benz, A. O.; Bergin, E. A.; Caselli, P.; Herpin, F.; Hogerheijde,
M. R.; Johnstone, D.; Liseau, R.; Nisini, B.; Tafalla, M.; van der
Tak, F. F. S.; Wyrowski, F.; Baudry, A.; Benedettini, M.; Bjerkeli,
P.; Blake, G. A.; Braine, J.; Bruderer, S.; Cabrit, S.; Cernicharo,
J.; Choi, Y.; Coutens, A.; de Graauw, Th.; Dominik, C.; Fedele, D.;
Fich, M.; Fuente, A.; Furuya, K.; Goicoechea, J. R.; Harsono, D.;
Helmich, F. P.; Herczeg, G. J.; Jacq, T.; Karska, A.; Kaufman, M.;
Keto, E.; Lamberts, T.; Larsson, B.; Leurini, S.; Lis, D. C.; Melnick,
G.; Neufeld, D.; Pagani, L.; Persson, M.; Shipman, R.; Taquet, V.;
van Kempen, T. A.; Walsh, C.; Wampfler, S. F.; Yıldız, U.; WISH Team
2021A&A...648A..24V Altcode: 2021arXiv210202225V
Context. Water is a key molecule in the physics and chemistry of star
and planet formation, but it is difficult to observe from Earth. The
Herschel Space Observatory provided unprecedented sensitivity as
well as spatial and spectral resolution to study water. The Water In
Star-forming regions with Herschel (WISH) key program was designed
to observe water in a wide range of environments and provide a
legacy data set to address its physics and chemistry. <BR /> Aims:
The aim of WISH is to determine which physical components are traced
by the gas-phase water lines observed with Herschel and to quantify
the excitation conditions and water abundances in each of these
components. This then provides insight into how and where the bulk of
the water is formed in space and how it is transported from clouds to
disks, and ultimately comets and planets. <BR /> Methods: Data and
results from WISH are summarized together with those from related
open time programs. WISH targeted ~80 sources along the two axes of
luminosity and evolutionary stage: from low- to high-mass protostars
(luminosities from <1 to > 10<SUP>5</SUP> L<SUB>⊙</SUB>) and
from pre-stellar cores to protoplanetary disks. Lines of H<SUB>2</SUB>O
and its isotopologs, HDO, OH, CO, and [O I], were observed with the HIFI
and PACS instruments, complemented by other chemically-related molecules
that are probes of ultraviolet, X-ray, or grain chemistry. The analysis
consists of coupling the physical structure of the sources with simple
chemical networks and using non-LTE radiative transfer calculations to
directly compare models and observations. <BR /> Results: Most of the
far-infrared water emission observed with Herschel in star-forming
regions originates from warm outflowing and shocked gas at a high
density and temperature (> 10<SUP>5</SUP> cm<SUP>−3</SUP>,
300-1000 K, v ~ 25 km s<SUP>−1</SUP>), heated by kinetic energy
dissipation. This gas is not probed by single-dish low-J CO lines, but
only by CO lines with J<SUB>up</SUB> > 14. The emission is compact,
with at least two different types of velocity components seen. Water is
a significant, but not dominant, coolant of warm gas in the earliest
protostellar stages. The warm gas water abundance is universally low:
orders of magnitude below the H<SUB>2</SUB>O/H<SUB>2</SUB> abundance
of 4 × 10<SUP>−4</SUP> expected if all volatile oxygen is locked
in water. In cold pre-stellar cores and outer protostellar envelopes,
the water abundance structure is uniquely probed on scales much smaller
than the beam through velocity-resolved line profiles. The inferred
gaseous water abundance decreases with depth into the cloud with an
enhanced layer at the edge due to photodesorption of water ice. All of
these conclusions hold irrespective of protostellar luminosity. For
low-mass protostars, a constant gaseous HDO/H<SUB>2</SUB>O ratio of
~0.025 with position into the cold envelope is found. This value
is representative of the outermost photodesorbed ice layers and
cold gas-phase chemistry, and much higher than that of bulk ice. In
contrast, the gas-phase NH<SUB>3</SUB> abundance stays constant as a
function of position in low-mass pre- and protostellar cores. Water
abundances in the inner hot cores are high, but with variations from
5 × 10<SUP>−6</SUP> to a few × 10<SUP>−4</SUP> for low- and
high-mass sources. Water vapor emission from both young and mature
disks is weak. <BR /> Conclusions: The main chemical pathways of
water at each of the star-formation stages have been identified and
quantified. Low warm water abundances can be explained with shock
models that include UV radiation to dissociate water and modify the
shock structure. UV fields up to 10<SUP>2</SUP>−10<SUP>3</SUP> times
the general interstellar radiation field are inferred in the outflow
cavity walls on scales of the Herschel beam from various hydrides. Both
high temperature chemistry and ice sputtering contribute to the gaseous
water abundance at low velocities, with only gas-phase (re-)formation
producing water at high velocities. Combined analyses of water gas and
ice show that up to 50% of the oxygen budget may be missing. In cold
clouds, an elegant solution is that this apparently missing oxygen
is locked up in larger μm-sized grains that do not contribute to
infrared ice absorption. The fact that even warm outflows and hot
cores do not show H<SUB>2</SUB>O at full oxygen abundance points to
an unidentified refractory component, which is also found in diffuse
clouds. The weak water vapor emission from disks indicates that water
ice is locked up in larger pebbles early on in the embedded Class I
stage and that these pebbles have settled and drifted inward by the
Class II stage. Water is transported from clouds to disks mostly as
ice, with no evidence for strong accretion shocks. Even at abundances
that are somewhat lower than expected, many oceans of water are likely
present in planet-forming regions. Based on the lessons for galactic
protostars, the low-J H<SUB>2</SUB>O line emission (E<SUB>up</SUB> <
300 K) observed in extragalactic sources is inferred to be predominantly
collisionally excited and to originate mostly from compact regions
of current star formation activity. Recommendations for future mid-
to far-infrared missions are made.
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Title: The Formation of Electron Outflow Jets with Power-law Energy
Distribution in Guide-field Magnetic Reconnection
Authors: Che, H.; Zank, G. P.; Benz, A. O.; Tang, B.; Crawford, C.
2021ApJ...908...72C Altcode:
Observationally, electron beams with power-law energy spectra are
commonly associated with solar flares. Previous studies have found that
during magnetic reconnection with a guide field B<SUB>g</SUB> larger
than 0.1 times the asymptotic field B<SUB>0</SUB>, electron beams are
unable to develop due to the strong deflection caused by the guide
field. Using particle-in-cell simulations we show that in force-free
reconnection, the development of an electron Kelvin-Helmholz instability
can suppress the Hall effect and produce a flute-like outflow exhaust,
in which both electrons and ions are nearly frozen-in with the magnetic
field. The coupling of a continuously growing electron velocity shear
and E × B drift drive the electrons out of magnetic vortices and
results in collimated jets with a power-law energy spectrum in the
elongated exhaust. The spatial density of electron jets is comparable
to the background and is highly inhomogeneous, signifying on asymmetric
density structure in guide field reconnection.
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Title: Electron Acceleration and the Development of Power-Law Energy
Spectra in Magnetic Reconnection with A Force-free Current Sheet
Authors: Che, Haihong; Benz, Arnold; Tang, Bofeng; Crawford, Chris
2021APS..GECM13007C Altcode:
Extensive observations have discovered that a huge number of energetic
electrons with energy up to MeV (~0.9c and Lorentz factor ~2) are
produced during solar flares. These very mild relativistic energetic
electrons demonstrate two-stage power-law spectral evolutions. What
mechanism efficiently accelerates non-relativistic particles to
a power-law has been a long-standing “ injection problem” in
particle acceleration theory since Fermi first proposed his famous
Fermi-acceleration model in 1949. In this talk, I will discuss why
particle acceleration in solar flares is an “injection problem” and
what problems are with the previous and current widely invoked models. I
will present a new acceleration mechanism in magnetic reconnection. I
will show how the velocity shear stored naturally in force-free currents
drives an electron Kevin-helmholtz instability (EKHI) during magnetic
reconnection and efficiently acceleration electrons to a power-law
energy spectrum via a two-stage soft-hard-hard evolution. Finally,
I will discuss the potentially broad application of this mechanism
in solar physics and how the complexity of solar flares may impact
the further development of this model. <P />NASA Heliophysics Career
award No. 80NSSC19K1106NSF EPSCoR RII-Track-1 Cooperative Agreement
OIA1655280NSF Grant PHY-1707247.
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Title: The Spectrometer/Telescope for Imaging X-rays (STIX)
Authors: Krucker, Säm; Hurford, G. J.; Grimm, O.; Kögl, S.;
Gröbelbauer, H. -P.; Etesi, L.; Casadei, D.; Csillaghy, A.; Benz,
A. O.; Arnold, N. G.; Molendini, F.; Orleanski, P.; Schori, D.; Xiao,
H.; Kuhar, M.; Hochmuth, N.; Felix, S.; Schramka, F.; Marcin, S.;
Kobler, S.; Iseli, L.; Dreier, M.; Wiehl, H. J.; Kleint, L.; Battaglia,
M.; Lastufka, E.; Sathiapal, H.; Lapadula, K.; Bednarzik, M.; Birrer,
G.; Stutz, St.; Wild, Ch.; Marone, F.; Skup, K. R.; Cichocki, A.; Ber,
K.; Rutkowski, K.; Bujwan, W.; Juchnikowski, G.; Winkler, M.; Darmetko,
M.; Michalska, M.; Seweryn, K.; Białek, A.; Osica, P.; Sylwester, J.;
Kowalinski, M.; Ścisłowski, D.; Siarkowski, M.; Stęślicki, M.;
Mrozek, T.; Podgórski, P.; Meuris, A.; Limousin, O.; Gevin, O.; Le
Mer, I.; Brun, S.; Strugarek, A.; Vilmer, N.; Musset, S.; Maksimović,
M.; Fárník, F.; Kozáček, Z.; Kašparová, J.; Mann, G.; Önel,
H.; Warmuth, A.; Rendtel, J.; Anderson, J.; Bauer, S.; Dionies, F.;
Paschke, J.; Plüschke, D.; Woche, M.; Schuller, F.; Veronig, A. M.;
Dickson, E. C. M.; Gallagher, P. T.; Maloney, S. A.; Bloomfield, D. S.;
Piana, M.; Massone, A. M.; Benvenuto, F.; Massa, P.; Schwartz, R. A.;
Dennis, B. R.; van Beek, H. F.; Rodríguez-Pacheco, J.; Lin, R. P.
2020A&A...642A..15K Altcode:
<BR /> Aims: The Spectrometer Telescope for Imaging X-rays (STIX)
on Solar Orbiter is a hard X-ray imaging spectrometer, which
covers the energy range from 4 to 150 keV. STIX observes hard X-ray
bremsstrahlung emissions from solar flares and therefore provides
diagnostics of the hottest (⪆10 MK) flare plasma while quantifying
the location, spectrum, and energy content of flare-accelerated
nonthermal electrons. <BR /> Methods: To accomplish this, STIX applies
an indirect bigrid Fourier imaging technique using a set of tungsten
grids (at pitches from 0.038 to 1 mm) in front of 32 coarsely pixelated
CdTe detectors to provide information on angular scales from 7 to 180
arcsec with 1 keV energy resolution (at 6 keV). The imaging concept of
STIX has intrinsically low telemetry and it is therefore well-suited
to the limited resources available to the Solar Orbiter payload. To
further reduce the downlinked data volume, STIX data are binned on
board into 32 selectable energy bins and dynamically-adjusted time
bins with a typical duration of 1 s during flares. <BR /> Results:
Through hard X-ray diagnostics, STIX provides critical information
for understanding the acceleration of electrons at the Sun and their
transport into interplanetary space and for determining the magnetic
connection of Solar Orbiter back to the Sun. In this way, STIX serves
to link Solar Orbiter's remote and in-situ measurements.
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Title: Centre-to-Limb Brightness Variations from the Atacama Large
Millimeter-Submillimeter Array (ALMA) Full-Disk Solar Images
Authors: Sudar, Davor; Brajša, Roman; Skokić, Ivica; Benz, Arnold O.
2019SoPh..294..163S Altcode:
Science Verification (SV) data of solar observations with the Atacama
Large Millimeter-submillimeter Array (ALMA) telescope have been
released to the scientific community. Understanding the centre-to-limb
brightness function is necessary to compare features in full-disk
images. Our goals are to find the empirical centre-to-limb brightness
functions in two available spectral bands and create flattened
images with centre-to-limb brightness variations removed. We used a
second-order polynomial fit of the cosine of incidence angle to data
points as a function of radial distance to the centre of the solar
disk. The method also includes iterative removal of outliers based
on the inter-quartile range. Fitting functions for all available
images proved to describe the data adequately with comparatively
small errors in the fitting coefficients. In both bands we found
brightening towards the limb, which is a consequence of the increase
in electron temperature with radial distance in this region of the
solar atmosphere. This study found that the brightness temperature
[T<SUB>b</SUB>] of an active region has about 180 K difference between
estimates with and without the limb brightening at radial distance
≈0.75 <SUB>R⊙</SUB> in Band 6. We also made flattened images with
limb brightening removed. The limb-brightening effect in ALMA images
is significant enough (of the order of 10% for Band 3 and about 15%
in Band 6) that it cannot be neglected in further analyses. Since the
effect of the side lobes was not included in this study, these values
probably represent the lower limit of the limb brightening. The shape
of the limb-brightening function can also be used to constrain electron
densities and temperatures in various layers of the solar atmosphere.
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Title: Centre to limb brightness variations from ALMA full disk
solar images
Authors: Sudar, Davor; Brajša, Roman; Skokić, Ivica; Benz, Arnold O.
2019arXiv190908952S Altcode:
Science Verification (SV) data of solar observations with Atacama Large
Millimeter-submillimeter Array (ALMA) telescope were released to the
scientific community. Understanding the centre to limb brightness
function is necessary to compare features in full disk images. Our
goals are to find the empirical centre to limb brightness functions
in two available spectral bands and create flattened images with
centre to limb brightness variations removed. We used second-order
polynomial fit of the cosine of incidence angle to data points as
a function of radial distance to the centre of the solar disk. The
method also includes iterative removal of outliers based on the
interquartile range. Fitting functions for all available images proved
to adequately describe the data with comparatively small errors in the
fitting coefficients. In both bands we found brightening towards the
limb which is a consequence of increase in electron temperatures with
radial distance in this region of the solar atmosphere. This study
found that the $T_{b}$ of an active region has about 180 K difference
between with and without the limb brightening at radial distance
$\approx$0.75$R_{\odot}$ in Band 6. We also made flattened images with
limb brightening removed. The limb brightening effect in ALMA images
is significant enough (of the order of 10% for Band 3 and about 15%
in Band 6) that it can not be neglected in further analyses. Since the
effect of the side lobes was not included in this study, these values
probably represent the lower limit of the limb brightening. The shape
of the limb brightening function can also be used to constrain electron
densities and temperatures in various layers of the solar atmosphere.
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Title: Observations of the solar chromosphere with ALMA and comparison
with theoretical models
Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold O.;
Kuhar, Matej; Kobelski, Adam; Wedemeyer, Sven; White, Stephen M.;
Ludwig, Hans-G.; Temmer, Manuela; Saar, Steven H.; Selhorst, Caius L.
2018csss.confE..37B Altcode: 2018arXiv181207293B
In this work we use solar observations with the ALMA radio telescope
at the wavelength of 1.21 mm. The aim of the analysisis to improve
understanding of the solar chromosphere, a dynamic layer in the
solar atmosphere between the photosphere andcorona. The study has
an observational and a modeling part. In the observational part
full-disc solar images are analyzed.Based on a modied FAL atmospheric
model, radiation models for various observed solar structures are
developed. Finally, theobservational and modeling results are compared
and discussed.
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Title: First analysis of solar structures in 1.21 mm full-disc ALMA
image of the Sun
Authors: Brajša, R.; Sudar, D.; Benz, A. O.; Skokić, I.; Bárta,
M.; De Pontieu, B.; Kim, S.; Kobelski, A.; Kuhar, M.; Shimojo, M.;
Wedemeyer, S.; White, S.; Yagoubov, P.; Yan, Y.
2018A&A...613A..17B Altcode: 2017arXiv171106130B
Context. Various solar features can be seen in emission or absorption
on maps of the Sun in the millimetre and submillimetre wavelength
range. The recently installed Atacama Large Millimetre/submillimetre
Array (ALMA) is capable of observing the Sun in that wavelength range
with an unprecedented spatial, temporal and spectral resolution. To
interpret solar observations with ALMA, the first important step is to
compare solar ALMA maps with simultaneous images of the Sun recorded in
other spectral ranges. <BR /> Aims: The first aim of the present work
is to identify different structures in the solar atmosphere seen in the
optical, infrared, and EUV parts of the spectrum (quiet Sun, active
regions, prominences on the disc, magnetic inversion lines, coronal
holes and coronal bright points) in a full-disc solar ALMA image. The
second aim is to measure the intensities (brightness temperatures) of
those structures and to compare them with the corresponding quiet Sun
level. <BR /> Methods: A full-disc solar image at 1.21 mm obtained on
December 18, 2015, during a CSV-EOC campaign with ALMA is calibrated and
compared with full-disc solar images from the same day in Hα line, in
He I 1083 nm line core, and with various SDO images (AIA at 170 nm, 30.4
nm, 21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness
temperatures of various structures are determined by averaging over
corresponding regions of interest in the calibrated ALMA image. <BR />
Results: Positions of the quiet Sun, active regions, prominences on
the disc, magnetic inversion lines, coronal holes and coronal bright
points are identified in the ALMA image. At the wavelength of 1.21
mm, active regions appear as bright areas (but sunspots are dark),
while prominences on the disc and coronal holes are not discernible
from the quiet Sun background, despite having slightly less intensity
than surrounding quiet Sun regions. Magnetic inversion lines appear as
large, elongated dark structures and coronal bright points correspond
to ALMA bright points. <BR /> Conclusions: These observational results
are in general agreement with sparse earlier measurements at similar
wavelengths. The identification of coronal bright points represents
the most important new result. By comparing ALMA and other maps,
it was found that the ALMA image was oriented properly and that the
procedure of overlaying the ALMA image with other images is accurate
at the 5 arcsec level. The potential of ALMA for physics of the solar
chromosphere is emphasised.
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Title: Order out of Randomness: Self-Organization Processes in
Astrophysics
Authors: Aschwanden, Markus J.; Scholkmann, Felix; Béthune, William;
Schmutz, Werner; Abramenko, Valentina; Cheung, Mark C. M.; Müller,
Daniel; Benz, Arnold; Chernov, Guennadi; Kritsuk, Alexei G.; Scargle,
Jeffrey D.; Melatos, Andrew; Wagoner, Robert V.; Trimble, Virginia;
Green, William H.
2018SSRv..214...55A Altcode: 2017arXiv170803394A
Self-organization is a property of dissipative nonlinear processes
that are governed by a global driving force and a local positive
feedback mechanism, which creates regular geometric and/or
temporal patterns, and decreases the entropy locally, in contrast
to random processes. Here we investigate for the first time a
comprehensive number of (17) self-organization processes that
operate in planetary physics, solar physics, stellar physics,
galactic physics, and cosmology. Self-organizing systems create
spontaneous " order out of randomness", during the evolution from an
initially disordered system to an ordered quasi-stationary system,
mostly by quasi-periodic limit-cycle dynamics, but also by harmonic
(mechanical or gyromagnetic) resonances. The global driving force
can be due to gravity, electromagnetic forces, mechanical forces
(e.g., rotation or differential rotation), thermal pressure, or
acceleration of nonthermal particles, while the positive feedback
mechanism is often an instability, such as the magneto-rotational
(Balbus-Hawley) instability, the convective (Rayleigh-Bénard)
instability, turbulence, vortex attraction, magnetic reconnection,
plasma condensation, or a loss-cone instability. Physical models
of astrophysical self-organization processes require hydrodynamic,
magneto-hydrodynamic (MHD), plasma, or N-body simulations. Analytical
formulations of self-organizing systems generally involve coupled
differential equations with limit-cycle solutions of the Lotka-Volterra
or Hopf-bifurcation type.
---------------------------------------------------------
Title: Erratum: Correction to: Observations of a Radio-Quiet Solar
Preflare
Authors: Benz, Arnold O.; Battaglia, Marina; Güdel, Manuel
2018SoPh..293...32B Altcode:
Correction to: Solar Physhttps://doi.org/10.1007/s11207-017-1175-3
---------------------------------------------------------
Title: A comparison of solar ALMA observations and model based
predictions of the brightness temperature
Authors: Brajša, R.; Kuhar, M.; Benz, A. O.; Skokić, I.; Sudar,
D.; Wedemeyer, S.; Báarta, M.; De Pontieu, B.; Kim, S.; Kobelski,
A.; Shimojo, M.; White, S.; Yagoubov, P.; Yan, Y.; Ludwig, H. G.;
Temmer, M.; Saar, S. H.; Selhorst, C. L.; Beuc, R.
2018CEAB...42....1B Altcode:
The new facility Atacama Large Millimeter/submillimeter Array (ALMA) is
capable of observing the Sun in the wavelength range from 0.3 mm to 10
mm with an unprecedented spatial, temporal and spectral resolution. The
first aim of the present work is to identify different structures
in the solar atmosphere (quiet Sun, active regions, filaments on the
disc, and coronal holes) in a full disc solar ALMA image at 1.21 mm
obtained on December 18, 2015 during a CSV-EOC campaign. It is compared
with full disc solar images from the same day in the Hα line (Cerro
Tololo Observatory, NISP), and at three EUV wavelengths (30.4 nm,
21.1 nm, 17.1 nm; a composite SDO image). Positions of the quiet Sun
areas, active regions, filaments on the disc, and coronal holes are
identified in the ALMA image. To interpret solar observations with ALMA
it is important to compare the measured and calculated intensities
of various solar structures. So, the second aim of this work is to
calculate the intensity (brightness temperature) for those structures
(quiet Sun, active regions, filaments on the disc, and coronal holes)
for a broad wavelength range (from 0.3 mm to 10 mm), closely related
to that of the ALMA, and to compare the results with available
ALMA observations. Thermal bremsstrahlung is the dominant radiation
mechanism for explanation of the observed phenomena. A procedure for
calculating the brightness temperature for a given wavelength and
model atmosphere, which integrates the radiative transfer equation
for thermal bremsstrahlung, is used. At the wavelength of 1.21 mm
active regions appear as bright areas, while filaments on the disc and
coronal holes are not discernible from the quiet Sun background. The
models generally agree with the observed results: Active regions are
bright primarily due to higher densities, filaments can appear bright,
dark or not at all and coronal holes cannot be easily identified.
---------------------------------------------------------
Title: Flare Observations
Authors: Benz, Arnold O.
2017LRSP...14....2B Altcode:
Solar flares are observed at all wavelengths from decameter radio waves
to gamma-rays beyond 1 GeV. This review focuses on recent observations
in EUV, soft and hard X-rays, white light, and radio waves. Space
missions such as RHESSI, Yohkoh, TRACE, SOHO, and more recently Hinode
and SDO have enlarged widely the observational base. They have revealed
a number of surprises: Coronal sources appear before the hard X-ray
emission in chromospheric footpoints, major flare acceleration sites
appear to be independent of coronal mass ejections, electrons, and ions
may be accelerated at different sites, there are at least 3 different
magnetic topologies, and basic characteristics vary from small to
large flares. Recent progress also includes improved insights into the
flare energy partition, on the location(s) of energy release, tests
of energy release scenarios and particle acceleration. The interplay
of observations with theory is important to deduce the geometry and
to disentangle the various processes involved. There is increasing
evidence supporting magnetic reconnection as the basic cause. While
this process has become generally accepted as the trigger, it is still
controversial how it converts a considerable fraction of the energy
into non-thermal particles. Flare-like processes may be responsible
for large-scale restructuring of the magnetic field in the corona as
well as for its heating. Large flares influence interplanetary space
and substantially affect the Earth's ionosphere. Flare scenarios have
slowly converged over the past decades, but every new observation still
reveals major unexpected results, demonstrating that solar flares,
after 150 years since their discovery, remain a complex problem of
astrophysics including major unsolved questions.
---------------------------------------------------------
Title: Observations of a Radio-Quiet Solar Preflare
Authors: Benz, Arnold O.; Battaglia, Marina; Güdel, Manuel
2017SoPh..292..151B Altcode: 2017arXiv170906417B
The preflare phase of the flare SOL2011-08-09T03:52 is unique in its
long duration, in that it was covered by the Reuven Ramaty High Energy
Solar Spectroscopic Imager (RHESSI) and the Nobeyama Radioheliograph,
and because it showed three well-developed soft X-ray (SXR) peaks. No
hard X-rays (HXR) are observed in the preflare phase. Here we report
that no associated radio emission at 17 GHz was found either, despite
the higher sensitivity of the radio instrument. The ratio between the
SXR peaks and the upper limit of the radio peaks is higher by more
than one order of magnitude than the ratio in regular flares. The
result suggests that the ratio between acceleration and heating in the
preflare phase was different than in regular flares. Acceleration to
relativistic energies, if any, occurred with lower efficiency.
---------------------------------------------------------
Title: Identification of features in solar ALMA images and comparison
with solar atmospheric models
Authors: Skokić, I.; Brajša, R.; Sudar, D.; Kuhar, M.; Benz, A. O.
2017simi.conf..121S Altcode:
Various solar features were identified in the full-disc single-dish ALMA
images taken at wavelength of 1.2 and 2.8 mm and compared with Hα, Ca
II K and EUV images and magnetograms. Assuming thermal bremsstrahlung
as the dominant radiation mechanism, several models were constructed
to calculate the brightness temperature of various solar features
(quiet and active solar regions, filaments and coronal holes) in a
wavelength range from 0.3 to 10 mm. It is found that model predictions
are in a qualitative agreement with ALMA images where active regions
appear brighter, while filaments and coronal holes are not discernible
from the quiet Sun level. It is also found that in ALMA images regions
around magnetic neutral lines appear darker than the quiet Sun. Models
predict a critical frequency below which filaments should appear in
absorption and above it in emission.
---------------------------------------------------------
Title: A comparison of solar ALMA maps with solar images obtained
at other wavelengths
Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold;
Kuhar, Matej; White, Stephen M.
2017SPD....4820403B Altcode:
We use recently released Commissioning and Science Verification
data of the Sun from the observing campaigns perfomed with the ALMA
radio telescope in December 2014 and in December 2015. The dataset
consists of calibrated maps of the Sun recorded in ALMA observing
band 3 (corresponding to a wavelength of 3 mm) and band 6 (1.2 mm)
which show both bright and dark areas and a background of highly
structured pattern. Solar ALMA maps are compared with images in EUV
(SDO/AIA), H-alpha (NISP, Cerro Tololo) and He 1083 nm (NSO/SOLIS),
as well as with magnetograms (SDO/HMI) recorded at times closest
to the ALMA observations. With a special software the images
are overlapped and a correspondence of identified structures is
checked in both ways. The visibility of active regions, sunspots,
inversion lines of global magnetic field, prominences on the disc,
coronal holes and coronal bright points is investigated in ALMA
images at mm wavelengths. Single-dish ALMA images of the Sun reveal
large-scale structures in the solar atmosphere, while high resolution
interferometric images are used to analyse the fine-scale chromospheric
structure. The intensities (the brightness temperatures) of identified
structures were determined and compared with selected model-based
predictions.
---------------------------------------------------------
Title: Hydride Ions, HCO<SUP>+</SUP> and Ionizing Irradiation in
Star Forming Region
Authors: Benz, Arnold O.; Bruderer, Simon; van Dishoeck, Ewine
2016AAS...22830803B Altcode:
Hydrides are fundamental precursor molecules in cosmic chemistry and
many hydride ions have become observable in high quality for the first
time thanks to the Herschel Space Observatory. Ionized hydrides, such as
CH<SUP>+</SUP> and OH<SUP>+</SUP> and also HCO<SUP>+</SUP> affect the
chemistry of molecules such as water. They also provide complementary
information on irradiation by far UV (FUV) or X-rays and gas
temperature.We explore hydrides of the most abundant heavier elements
in an observational survey covering star forming regions with different
mass and evolutionary state. Twelve YSOs were observed with HIFI on
Herschel in 6 spectral settings providing fully velocity-resolved line
profiles. The YSOs include objects of low (Class 0 and I), intermediate,
and high mass, with luminosities ranging from 4 L<SUB>s</SUB> to 2
10<SUP>5</SUP> L<SUB>s</SUB>.The targeted lines of CH<SUP>+</SUP>,
OH<SUP>+</SUP>, H<SUB>2</SUB>O<SUP>+</SUP>, and C<SUP>+</SUP> are
detected mostly in blue-shifted absorption. H<SUB>3</SUB>O<SUP>+</SUP>
and SH<SUP>+</SUP> are detected in emission and only toward some
high-mass objects. For the low-mass YSOs the column density ratios
of CH<SUP>+</SUP>/OH<SUP>+</SUP> can be reproduced by simple chemical
models implying an FUV flux of 2 - 400 times the ISRF at the location
of the molecules. In two high-mass objects, the UV flux is 20 -
200 times the ISRF derived from absorption lines, and 300 - 600
ISRF using emission lines. Upper limits for the X-ray luminosity
can be derived from H<SUB>3</SUB>O<SUP>+</SUP> observations for
some low-mass objects.If the FUV flux required for low-mass objects
originates at the central protostar, a substantial FUV luminosity,
up to 1.5 L<SUB>s</SUB>, is required. For high-mass regions, the FUV
flux required to produce the observed molecular ratios is smaller
than the unattenuated flux expected from the central object(s) at
the Herschel beam radius. This is consistent with an FUV flux reduced
by circumstellar extinction or by bloating of the protostar.The ion
molecules are proposed to form in FUV irradiated cavity walls that are
shocked by the disk wind. The shock region is turbulent, broadening the
lines to some 1 - 12 km/s. It is driven by the outward motion of the
wind to blue shifts of 0 to -10 km/s. The blue-shifted H<SUB>2</SUB>O
emission line (Kristensen et al. 2013) may be related but not coincident
with the CH<SUP>+</SUP> and OH<SUP>+ </SUP>emitting region.
---------------------------------------------------------
Title: Water in star-forming regions with Herschel
(WISH). VI. Constraints on UV and X-ray irradiation from a survey
of hydrides in low- to high-mass young stellar objects
Authors: Benz, A. O.; Bruderer, S.; van Dishoeck, E. F.; Melchior,
M.; Wampfler, S. F.; van der Tak, F.; Goicoechea, J. R.; Indriolo,
N.; Kristensen, L. E.; Lis, D. C.; Mottram, J. C.; Bergin, E. A.;
Caselli, P.; Herpin, F.; Hogerheijde, M. R.; Johnstone, D.; Liseau,
R.; Nisini, B.; Tafalla, M.; Visser, R.; Wyrowski, F.
2016A&A...590A.105B Altcode: 2016arXiv160308721B
Context. Hydrides are simple compounds containing one or a few hydrogen
atoms bonded to a heavier atom. They are fundamental precursor molecules
in cosmic chemistry and many hydride ions have become observable
in high quality for the first time thanks to the Herschel Space
Observatory. Ionized hydrides such as CH<SUP>+</SUP> and OH<SUP>+</SUP>
(and also HCO<SUP>+</SUP>), which affect the chemistry of molecules
such as water, provide complementary information on irradiation by
far-UV (FUV) or X-rays and gas temperature. <BR /> Aims: We explore
hydrides of the most abundant heavier elements in an observational
survey covering young stellar objects (YSOs) with different mass
and evolutionary state. The focus is on hydrides associated with
the dense protostellar envelope and outflows, contrary to previous
work that focused on hydrides in diffuse foreground clouds. <BR />
Methods: Twelve YSOs were observed with HIFI on Herschel in six spectral
settings providing fully velocity-resolved line profiles as part of the
Water in star-forming regions with Herschel (WISH) program. The YSOs
include objects of low (Class 0 and I), intermediate, and high mass,
with luminosities ranging from 4 L<SUB>⊙</SUB> to 2 × 10<SUP>5</SUP>
L<SUB>⊙</SUB>. <BR /> Results: The targeted lines of CH<SUP>+</SUP>,
OH<SUP>+</SUP>, H<SUB>2</SUB>O<SUP>+</SUP>, C<SUP>+</SUP>, and CH are
detected mostly in blue-shifted absorption. H<SUB>3</SUB>O<SUP>+</SUP>
and SH<SUP>+</SUP> are detected in emission and only toward some
high-mass objects. The observed line parameters and correlations suggest
two different origins related to gas entrained by the outflows and to
the circumstellar envelope. The derived column densities correlate with
bolometric luminosity and envelope mass for all molecules, best for
CH, CH<SUP>+</SUP>, and HCO<SUP>+</SUP>. The column density ratios of
CH<SUP>+</SUP>/OH<SUP>+</SUP> are estimated from chemical slab models,
assuming that the H<SUB>2</SUB> density is given by the specific
density model of each object at the beam radius. For the low-mass YSOs
the observed ratio can be reproduced for an FUV flux of 2-400 times the
interstellar radiation field (ISRF) at the location of the molecules. In
two high-mass objects, the UV flux is 20-200 times the ISRF derived from
absorption lines, and 300-600 ISRF using emission lines. Upper limits
for the X-ray luminosity can be derived from H<SUB>3</SUB>O<SUP>+</SUP>
observations for some low-mass objects. <BR /> Conclusions: If the
FUV flux required for low-mass objects originates at the central
protostar, a substantial FUV luminosity, up to 1.5 L<SUB>⊙</SUB>, is
required. There is no molecular evidence for X-ray induced chemistry
in the low-mass objects on the observed scales of a few 1000 AU. For
high-mass regions, the FUV flux required to produce the observed
molecular ratios is smaller than the unattenuated flux expected from
the central object(s) at the Herschel beam radius. This is consistent
with an FUV flux reduced by circumstellar extinction or by bloating of
the protostar. <P />Herschel is an ESA space observatory with science
instruments provided by a European-led Principal Investigator consortia
and with important participation from NASA.
---------------------------------------------------------
Title: Solar Science with the Atacama Large Millimeter/Submillimeter
Array—A New View of Our Sun
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.;
Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu,
B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin,
P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz,
A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.;
Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary,
D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van
der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.;
Selhorst, C. L.; Barta, M.
2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new
powerful tool for observing the Sun at high spatial, temporal, and
spectral resolution. These capabilities can address a broad range
of fundamental scientific questions in solar physics. The radiation
observed by ALMA originates mostly from the chromosphere—a complex
and dynamic region between the photosphere and corona, which plays a
crucial role in the transport of energy and matter and, ultimately,
the heating of the outer layers of the solar atmosphere. Based on
first solar test observations, strategies for regular solar campaigns
are currently being developed. State-of-the-art numerical simulations
of the solar atmosphere and modeling of instrumental effects can help
constrain and optimize future observing modes for ALMA. Here we present
a short technical description of ALMA and an overview of past efforts
and future possibilities for solar observations at submillimeter and
millimeter wavelengths. In addition, selected numerical simulations
and observations at other wavelengths demonstrate ALMA's scientific
potential for studying the Sun for a large range of science cases.
---------------------------------------------------------
Title: ALMA Observations of the Sun in Cycle 4 and Beyond
Authors: Wedemeyer, S.; Fleck, B.; Battaglia, M.; Labrosse, N.;
Fleishman, G.; Hudson, H.; Antolin, P.; Alissandrakis, C.; Ayres, T.;
Ballester, J.; Bastian, T.; Black, J.; Benz, A.; Brajsa, R.; Carlsson,
M.; Costa, J.; DePontieu, B.; Doyle, G.; Gimenez de Castro, G.;
Gunár, S.; Harper, G.; Jafarzadeh, S.; Loukitcheva, M.; Nakariakov,
V.; Oliver, R.; Schmieder, B.; Selhorst, C.; Shimojo, M.; Simões,
P.; Soler, R.; Temmer, M.; Tiwari, S.; Van Doorsselaere, T.; Veronig,
A.; White, S.; Yagoubov, P.; Zaqarashvili, T.
2016arXiv160100587W Altcode:
This document was created by the Solar Simulations for the Atacama
Large Millimeter Observatory Network (SSALMON) in preparation of
the first regular observations of the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA), which are anticipated to start
in ALMA Cycle 4 in October 2016. The science cases presented here
demonstrate that a large number of scientifically highly interesting
observations could be made already with the still limited solar
observing modes foreseen for Cycle 4 and that ALMA has the potential
to make important contributions to answering long-standing scientific
questions in solar physics. With the proposal deadline for ALMA Cycle
4 in April 2016 and the Commissioning and Science Verification campaign
in December 2015 in sight, several of the SSALMON Expert Teams composed
strategic documents in which they outlined potential solar observations
that could be feasible given the anticipated technical capabilities
in Cycle 4. These documents have been combined and supplemented
with an analysis, resulting in recommendations for solar observing
with ALMA in Cycle 4. In addition, the detailed science cases also
demonstrate the scientific priorities of the solar physics community
and which capabilities are wanted for the next observing cycles. The
work on this White Paper effort was coordinated in close cooperation
with the two international solar ALMA development studies led by
T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be
further updated until the beginning of Cycle 4 in October 2016. In
particular, we plan to adjust the technical capabilities of the solar
observing modes once finally decided and to further demonstrate the
feasibility and scientific potential of the included science cases by
means of numerical simulations of the solar atmosphere and corresponding
simulated ALMA observations.
---------------------------------------------------------
Title: SSALMON - The Solar Simulations for the Atacama Large
Millimeter Observatory Network
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson,
H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu,
B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.;
Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.;
Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier,
A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M.
2015AdSpR..56.2679W Altcode: 2015arXiv150205601W
The Solar Simulations for the Atacama Large Millimeter Observatory
Network (SSALMON) was initiated in 2014 in connection with two ALMA
development studies. The Atacama Large Millimeter/submillimeter Array
(ALMA) is a powerful new tool, which can also observe the Sun at
high spatial, temporal, and spectral resolution. The international
SSALMONetwork aims at co-ordinating the further development of solar
observing modes for ALMA and at promoting scientific opportunities
for solar physics with particular focus on numerical simulations,
which can provide important constraints for the observing modes and
can aid the interpretation of future observations. The radiation
detected by ALMA originates mostly in the solar chromosphere - a
complex and dynamic layer between the photosphere and corona, which
plays an important role in the transport of energy and matter and the
heating of the outer layers of the solar atmosphere. Potential targets
include active regions, prominences, quiet Sun regions, flares. Here,
we give a brief overview over the network and potential science cases
for future solar observations with ALMA.
---------------------------------------------------------
Title: Signatures of Accelerated Electrons in Solar and Stellar Flares
Authors: Benz, Arnold O.
2015IAUGA..2254709B Altcode:
Flares energize electrons (and ions) to supra-thermal energies. In
most cases the final distribution in momentum or energy space
is non-Maxwellian. The non-thermal part of the energy can be the
source for various emissions, including hard X-rays, synchrotron
radiation and coherent radio emission. Such non-thermal emissions
may contain information on the acceleration process. Several
acceleration scenarios have been proposed: electric DC field,
stochastic, and shock acceleration. There is observational evidence
for all three scenarios. The new data come from SDO, X-ray (RHESSI),
radio observations (Nobeyama, VLA and e-Callisto). Solar energetic
particles are an additional channel of information.Tiny solar
microflares and huge stellar flares in binary systems (RS CVns) and
dMe dwarfs differ by more than 10 orders of magnitude in released
energy. Yet the relation between peak luminosity in thermal (soft)
X-ray and non-thermal synchrotron (radio) emission is surprisingly
constant. This observational fact indicates that flare acceleration
scales with energy release over a large range. Electron acceleration in
flares seems to be a universal process. The constraint on simultaneous
thermal X-rays and non-thermal (radio) synchrotron emission seems to
select on particular kind of flare. In this subset, there seems to
be only one type of acceleration.Yet, small deviations are noted:
Small solar flares are softer in hard X-rays. Solar nanoflares are
relatively weak in synchrotron emission. The recently noted case of
radio-poor preflares will also be presented. The deviations suggest
that the acceleration is less efficient in small flares and in the
early phase of flares. Larger deviations are reported occasionally for
solar flares and more often from stellar flares, where either thermal
or non-thermal emission seems to be missing completely.The location
of the acceleration in solar flares remains disputed. Observations
suggesting acceleration in the soft X-ray top-tops, above top-tops
and near the loop footpoints are presented. Whereas reconnection is
well understood in MHD, acceleration of electrons (and ions) is not.
---------------------------------------------------------
Title: Formation, Excitation and Destruction of CH<SUP>+</SUP>
under the Influence of Water and Irradiation in Star Forming Regions
Authors: Benz, Arnold O.; Simon, Bruderer; van Dishoeck, Ewine
2015IAUGA..2255589B Altcode:
Simple ionized hydrides were observed for the first time with
Herschel/HIFI towards young star-forming objects of low to high
mass. Of particular interest is CH<SUP>+</SUP>, a fundamental precursor
molecule for carbon hydrides. Gaseous H2O reduces the abundance of
C and C<SUP>+</SUP>, the starting products of CH<SUP>+</SUP>. The
abundances of H<SUB>2</SUB>O and CH<SUP>+</SUP> cannot be enhanced
at the same place. Strong irradiation by FUV or X-rays reduces H2O,
and CH<SUP>+</SUP> gets more abundant. Thus CH<SUP>+</SUP> signals
high irradiation, but low H<SUB>2</SUB>O abundance.CH<SUP>+</SUP> was
observed to be enhanced in most objects to an abundance of typically
10<SUP>-10</SUP> relative to hydrogen. This suggests an internal source
of irradiation. The observed ratio of CH<SUP>+</SUP>/OH<SUP>+</SUP>
is consistent with irradiation by far UV as expected from chemical
modelling. For low-mass objects the required FUV flux is between
1 - 200 times the ISRF at the location of the molecules. If the
FUV flux originates at the central protostar, an FUV luminosity
up to 1.5 L<SUB>sun</SUB> is required. The UV flux in two
high-mass objects is 30 and 90 times the ISRF using absorption
lines, and of the order of 500 ISRF using emission lines. It
is smaller than the unattenuated flux expected from the central
object(s). The observed CH<SUP>+</SUP>/OH<SUP>+</SUP> ratio, and
other ratios such as OH<SUP>+</SUP>/H<SUB>2</SUB>O<SUP>+</SUP> and
CH<SUP>+</SUP>/C<SUP>+</SUP>, can only be modelled for low molecular
hydrogen densities.The targeted lines of CH<SUP>+</SUP>, OH<SUP>+</SUP>,
H<SUB>2</SUB>O<SUP>+</SUP>, and C<SUP>+</SUP> are detected mostly in
blue-shifted absorption. They are proposed to origin in FUV irradiated
cavity walls that are shocked by the disk wind. The shock region is
turbulent, broadening the lines to some 1 - 12 km/s. It is driven by
the outward motion of the wind to blue shifts of 0 to -10 km/s. The
blue-shifted H2O emission line (Kristensen et al. 2013) may be related
but not coincident with the CH<SUP>+</SUP> emitting region.
---------------------------------------------------------
Title: Herschel Survey of Galactic OH<SUP>+</SUP>,
H<SUB>2</SUB>O<SUP>+</SUP>, and H<SUB>3</SUB>O<SUP>+</SUP>: Probing
the Molecular Hydrogen Fraction and Cosmic-Ray Ionization Rate
Authors: Indriolo, Nick; Neufeld, D. A.; Gerin, M.; Schilke, P.; Benz,
A. O.; Winkel, B.; Menten, K. M.; Chambers, E. T.; Black, John H.;
Bruderer, S.; Falgarone, E.; Godard, B.; Goicoechea, J. R.; Gupta,
H.; Lis, D. C.; Ossenkopf, V.; Persson, C. M.; Sonnentrucker, P.; van
der Tak, F. F. S.; van Dishoeck, E. F.; Wolfire, Mark G.; Wyrowski, F.
2015ApJ...800...40I Altcode: 2014arXiv1412.1106I
In diffuse interstellar clouds the chemistry that leads to
the formation of the oxygen-bearing ions OH<SUP>+</SUP>,
H<SUB>2</SUB>O<SUP>+</SUP>, and H<SUB>3</SUB>O<SUP>+</SUP>
begins with the ionization of atomic hydrogen by cosmic rays,
and continues through subsequent hydrogen abstraction reactions
involving H<SUB>2</SUB>. Given these reaction pathways, the observed
abundances of these molecules are useful in constraining both the
total cosmic-ray ionization rate of atomic hydrogen (ζ<SUB>H</SUB>)
and molecular hydrogen fraction (f_H_2). We present observations
targeting transitions of OH<SUP>+</SUP>, H<SUB>2</SUB>O<SUP>+</SUP>,
and H<SUB>3</SUB>O<SUP>+</SUP> made with the Herschel Space Observatory
along 20 Galactic sight lines toward bright submillimeter continuum
sources. Both OH<SUP>+</SUP> and H<SUB>2</SUB>O<SUP>+</SUP> are
detected in absorption in multiple velocity components along every
sight line, but H<SUB>3</SUB>O<SUP>+</SUP> is only detected along
7 sight lines. From the molecular abundances we compute f_H_2 in
multiple distinct components along each line of sight, and find
a Gaussian distribution with mean and standard deviation 0.042
± 0.018. This confirms previous findings that OH<SUP>+</SUP>
and H<SUB>2</SUB>O<SUP>+</SUP> primarily reside in gas with low
H<SUB>2</SUB> fractions. We also infer ζ<SUB>H</SUB> throughout our
sample, and find a lognormal distribution with mean log (ζ<SUB>H</SUB>)
= -15.75 (ζ<SUB>H</SUB> = 1.78 × 10<SUP>-16</SUP> s<SUP>-1</SUP>) and
standard deviation 0.29 for gas within the Galactic disk, but outside
of the Galactic center. This is in good agreement with the mean and
distribution of cosmic-ray ionization rates previously inferred from
H_3^+ observations. Ionization rates in the Galactic center tend to be
10-100 times larger than found in the Galactic disk, also in accord
with prior studies. <P />Herschel is an ESA space observatory with
science instruments provided by European-led Principal Investigator
consortia and with important participation from NASA.
---------------------------------------------------------
Title: Water in star-forming regions with Herschel (WISH)
(Corrigendum). V. The physical conditions in low-mass protostellar
outflows revealed by multi-transition water observations
Authors: Mottram, J. C.; Kristensen, L. E.; van Dishoeck, E. F.;
Bruderer, S.; San José-García, I.; Karska, A.; Visser, R.;
Santangelo, G.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Herpin, F.;
Hogerheijde, M. R.; Johnstone, D.; van Kempen, T. A.; Liseau, R.;
Nisini, B.; Tafalla, M.; van der Tak, F. F. S.; Wyrowski, F.
2015A&A...574C...3M Altcode:
Herschel is an ESA space observatory with science instruments provided
by European-led Principal Investigator consortia and with important
participation from NASA.
---------------------------------------------------------
Title: Water in star-forming regions with Herschel (WISH). V. The
physical conditions in low-mass protostellar outflows revealed by
multi-transition water observations
Authors: Mottram, J. C.; Kristensen, L. E.; van Dishoeck, E. F.;
Bruderer, S.; San José-García, I.; Karska, A.; Visser, R.;
Santangelo, G.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Herpin, F.;
Hogerheijde, M. R.; Johnstone, D.; van Kempen, T. A.; Liseau, R.;
Nisini, B.; Tafalla, M.; van der Tak, F. F. S.; Wyrowski, F.
2014A&A...572A..21M Altcode: 2014arXiv1409.5704M
Context. Outflows are an important part of the star formation process
as both the result of ongoing active accretion and one of the main
sources of mechanical feedback on small scales. Water is the ideal
tracer of these effects because it is present in high abundance
for the conditions expected in various parts of the protostar,
particularly the outflow. <BR /> Aims: We constrain and quantify the
physical conditions probed by water in the outflow-jet system for
Class 0 and I sources. <BR /> Methods: We present velocity-resolved
Herschel HIFI spectra of multiple water-transitions observed towards
29 nearby Class 0/I protostars as part of the WISH guaranteed time key
programme. The lines are decomposed into different Gaussian components,
with each component related to one of three parts of the protostellar
system; quiescent envelope, cavity shock and spot shocks in the jet
and at the base of the outflow. We then use non-LTE radex models to
constrain the excitation conditions present in the two outflow-related
components. <BR /> Results: Water emission at the source position is
optically thick but effectively thin, with line ratios that do not
vary with velocity, in contrast to CO. The physical conditions of the
cavity and spot shocks are similar, with post-shock H<SUB>2</SUB>
densities of order 10<SUP>5</SUP> - 10<SUP>8</SUP> cm<SUP>-3</SUP>
and H<SUB>2</SUB>O column densities of order 10<SUP>16</SUP> -
10<SUP>18</SUP> cm<SUP>-2</SUP>. H<SUB>2</SUB>O emission originates in
compact emitting regions: for the spot shocks these correspond to point
sources with radii of order 10-200 AU, while for the cavity shocks these
come from a thin layer along the outflow cavity wall with thickness of
order 1-30 AU. <BR /> Conclusions: Water emission at the source position
traces two distinct kinematic components in the outflow; J shocks at
the base of the outflow or in the jet, and C shocks in a thin layer
in the cavity wall. The similarity of the physical conditions is in
contrast to off-source determinations which show similar densities
but lower column densities and larger filling factors. We propose
that this is due to the differences in shock properties and geometry
between these positions. Class I sources have similar excitation
conditions to Class 0 sources, but generally smaller line-widths
and emitting region sizes. We suggest that it is the velocity of
the wind driving the outflow, rather than the decrease in envelope
density or mass, that is the cause of the decrease in H<SUB>2</SUB>O
intensity between Class 0 and I sources. <P />Herschel is an ESA
space observatory with science instruments provided by European-led
Principal Investigator consortia and with important participation
from NASA.Appendices are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424267/olm">http://www.aanda.org</A>Reduced
spectra are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/A21">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/A21</A>
---------------------------------------------------------
Title: VizieR Online Data Catalog: H<SUB>2</SUB>O spectra of 29
nearby Class 0/I protostars (Mottram+,
Authors: Mottram, J. C.; Kristensen, L. E.; van Dishoeck, E. F.;
Bruderer, S.; San Jose-Garcia, I.; Karska, A.; Visser, R.; Santangelo,
G.; Benz, A. O.; Bergin, E. A.; Caselli, P.; Herpin, F.; Hogerheijde,
M. R.; Johnstone, D.; van Kempen, T. A.; Liseau, R.; Nisini, B.;
Tafalla, M.; van der Tak, F. F. S.; Wyrowski, F.
2014yCat..35720021M Altcode: 2014yCat..35729021M
This sample was the target of a series of observations of gas-phase
water transitions with the Heterodyne Instrument for the Far-Infrared
(HIFI) on Herschel between March 2010 and October 2011. Three of
the Class I sources (IRAS3A, RCrA-IRS5A and HH100-IRS) were only
observed in the 557GHz H<SUB>2</SUB>O 1<SUB>10</SUB>-1<SUB>01</SUB>
line, which was presented for all sources by Kristensen et
al. (2012A&A...542A...8K). All other sources were observed in
between four and seven H<SUB>2</SUB><SUP>16</SUP>O transitions and
between one and four H<SUB>2</SUB><SUP>18</SUP>O transitions. Additional
data from two OT2 programmes, OT2<SUB>rvisser</SUB>2 and
OT2<SUB>evandish</SUB>4, are also included to augment the WISH data. <P
/>(2 data files).
---------------------------------------------------------
Title: Short-duration Radio Bursts with Apparent Extragalactic
Dispersion
Authors: Saint-Hilaire, P.; Benz, A. O.; Monstein, C.
2014ApJ...795...19S Altcode: 2014arXiv1402.0664S
We present the results of the longest yet undertaken search for
apparently extragalactic radio bursts at the Bleien Radio Observatory
covering 21,000 hr (898 days). The data were searched for events of
less than 50 ms FWHM duration showing a ν<SUP>-2</SUP> drift in the
spectrogram characteristic of the delay of radio waves in plasma. We
have found five cases suggesting dispersion measures between 350
and 400 cm<SUP>-3</SUP> pc while searching in the range of 75-2000
cm<SUP>-3</SUP> pc. Four of the five events occurred between 10:27
and 11:24 a.m. local civil time. The only exception occurred at
night with the full Moon in the beam. It was an event that poorly
fits plasma dispersion, but had the characteristics of a solar Type
III burst. However, we were not able to confirm that it was a lunar
reflection. All events were observed with a log-periodic dipole within
6800 hr, but none with a more directional horn antenna observing the
rest of the time. These properties suggest a terrestrial origin of the
"peryton" type reported before. However, the cause of these events
remains ambiguous.
---------------------------------------------------------
Title: Herschel HIFI Observations of O<SUB>2</SUB> toward Orion:
Special Conditions for Shock Enhanced Emission
Authors: Chen, Jo-Hsin; Goldsmith, Paul F.; Viti, Serena; Snell,
Ronald; Lis, Dariusz C.; Benz, Arnold; Bergin, Edwin; Black, John;
Caselli, Paola; Encrenaz, Pierre; Falgarone, Edith; Goicoechea,
Javier R.; Hjalmarson, Åke; Hollenbach, David; Kaufman, Michael;
Melnick, Gary; Neufeld, David; Pagani, Laurent; van der Tak, Floris;
van Dishoeck, Ewine; Yıldız, Umut A.
2014ApJ...793..111C Altcode: 2014arXiv1408.1962C
We report observations of molecular oxygen (O<SUB>2</SUB>) rotational
transitions at 487 GHz, 774 GHz, and 1121 GHz toward Orion Peak A. The
O<SUB>2</SUB> lines at 487 GHz and 774 GHz are detected at velocities
of 10-12 km s<SUP>-1</SUP> with line widths ~3 km s<SUP>-1</SUP>
however, the transition at 1121 GHz is not detected. The observed line
characteristics, combined with the results of earlier observations,
suggest that the region responsible for the O<SUB>2</SUB> emission is
sime9” (6 × 10<SUP>16</SUP> cm) in size, and is located close to the H
<SUB>2</SUB> Peak 1 position (where vibrationally excited H<SUB>2</SUB>
emission peaks), and not at Peak A, 23” away. The peak O<SUB>2</SUB>
column density is sime1.1 × 10<SUP>18</SUP> cm<SUP>-2</SUP>. The line
velocity is close to that of the 621 GHz water maser emission found
in this portion of the Orion Molecular Cloud, and having a shock with
velocity vector lying nearly in the plane of the sky is consistent with
producing maximum maser gain along the line of sight. The enhanced
O<SUB>2</SUB> abundance compared to that generally found in dense
interstellar clouds can be explained by passage of a low-velocity
C shock through a clump with preshock density 2 × 10<SUP>4</SUP>
cm<SUP>-3</SUP>, if a reasonable flux of UV radiation is present. The
postshock O<SUB>2</SUB> can explain the emission from the source if
its line-of-sight dimension is sime10 times larger than its size on
the plane of the sky. The special geometry and conditions required
may explain why O<SUB>2</SUB> emission has not been detected in the
cores of other massive star-forming molecular clouds.
---------------------------------------------------------
Title: Dense molecular cocoons in the massive protocluster W3 IRS5:
a test case for models of massive star formation
Authors: Wang, K. -S.; Bourke, T. L.; Hogerheijde, M. R.; van der Tak,
F. F. S.; Benz, A. O.; Megeath, S. T.; Wilson, T. L.
2013A&A...558A..69W Altcode: 2013arXiv1308.5151W
Context. Two competing models describe the formation of massive stars
in objects like the Orion Trapezium. In the turbulent core accretion
model, the resulting stellar masses are directly related to the mass
distribution of the cloud condensations. In the competitive accretion
model, the gravitational potential of the protocluster captures gas
from the surrounding cloud for which the individual cluster members
compete. <BR /> Aims: With high resolution submillimeter observations
of the structure, kinematics, and chemistry of the proto-Trapezium
cluster W3 IRS5, we aim to determine which mode of star formation
dominates. <BR /> Methods: We present 354 GHz Submillimeter Array
observations at resolutions of 1″-3″ (1800-5400 AU) of W3 IRS5. The
dust continuum traces the compact source structure and masses of the
individual cores, while molecular lines of CS, SO, SO<SUB>2</SUB>,
HCN, H<SUB>2</SUB>CS, HNCO, and CH<SUB>3</SUB>OH (and isotopologues)
reveal the gas kinematics, density, and temperature. <BR /> Results:
The observations show five emission peaks (SMM1-5). SMM1 and SMM2
contain massive embedded stars (~20 M<SUB>⊙</SUB>); SMM3-5 are
starless or contain low-mass stars (<8 M<SUB>⊙</SUB>). The
inferred densities are high, ≥10<SUP>7</SUP> cm<SUP>-3</SUP>,
but the core masses are small, 0.2-0.6 M<SUB>⊙</SUB>. The detected
molecular emission reveals four different chemical zones. Abundant
(X ~ few 10<SUP>-7</SUP> to 10<SUP>-6</SUP>) SO and SO<SUB>2</SUB> are
associated with SMM1 and SMM2, indicating active sulfur chemistry. A
low abundance (5 × 10<SUP>-8</SUP>) of CH<SUB>3</SUB>OH concentrated
on SMM3/4 suggest the presence of a hot core that is only just turning
on, possibly by external feedback from SMM1/2. The gas kinematics are
complex with contributions from a near pole-on outflow traced by CS,
SO, and HCN; rotation in SO<SUB>2</SUB>, and a jet in vibrationally
excited HCN. <BR /> Conclusions: The proto-Trapezium cluster W3 IRS5
is an ideal test case to discriminate between models of massive star
formation. Either the massive stars accrete locally from their local
cores; in this case the small core masses imply that W3 IRS5 is at
the very end stages (1000 yr) of infall and accretion, or the stars
are accreting from the global collapse of a massive, cluster forming
core. We find that the observed masses, densities and line widths
observed toward W3 IRS 5 and the surrounding cluster forming core are
consistent with the competitive accretion of gas at rates of Ṁ ~
10<SUP>-4</SUP>M<SUB>⊙</SUB> yr<SUP>-1</SUP> by the massive young
forming stars. Future mapping of the gas kinematics from large to
small scales will determine whether large-scale gas inflow occurs and
how the cluster members compete to accrete this material.
---------------------------------------------------------
Title: Neutral and Ionized Hydrides in Star-Forming
Regions. Observations with Herschel/HIFI
Authors: Benz, Arnold O.; Bruderer, Simon; van Dishoeck, Ewine F.;
Stäuber, Pascal; Wampfler, Susanne F.
2013JPCA..117.9840B Altcode: 2013arXiv1308.5556B
The cosmic abundance of hydrides depends critically on high-energy
UV, X-ray, and particle irradiation. Here we study hydrides in
star-forming regions where irradiation by the young stellar object can
be substantial, and density and temperature can be much enhanced over
interstellar values. Lines of OH, CH, NH, and SH and their ions OH+,
CH+, NH+, SH+, H2O+, and H3O+ were observed in star-forming regions by
the HIFI spectrometer onboard the Herschel Space Observatory. Molecular
column densities are derived from observed ground-state lines,
models, or rotational diagrams. We report here on two prototypical
high-mass regions, AFGL 2591 and W3 IRS5, and compare them to chemical
calculations by making assumptions on the high-energy irradiation. A
model assuming no ionizing protostellar emission is compared with
(i) a model assuming strong protostellar X-ray emission and (ii)
a two-dimensional (2D) model including emission in the far UV (FUV,
6-13.6 eV), irradiating the outflow walls that separate the outflowing
gas and infalling envelope material. We confirm that the effect of FUV
in two-dimensional models with enlarged irradiated surfaces is clearly
noticeable. A molecule that is very sensitive to FUV irradiation is
CH+, enhanced in abundance by more than 5 orders of magnitude. The HIFI
observations of CH+ lines agree with the two-dimensional FUV model by
Bruderer et al., which computes abundances, non-LTE excitation, and line
radiative transfer.20 It is concluded that CH+ is a good FUV tracer
in star-forming regions. The effect of potential X-ray irradiation is
not excluded but cannot be demonstrated by the present data.
---------------------------------------------------------
Title: Observational evidence for dissociative shocks in the inner
100 AU of low-mass protostars using Herschel-HIFI
Authors: Kristensen, L. E.; van Dishoeck, E. F.; Benz, A. O.; Bruderer,
S.; Visser, R.; Wampfler, S. F.
2013A&A...557A..23K Altcode: 2013arXiv1307.1710K
<BR /> Aims: Herschel-HIFI spectra of H<SUB>2</SUB>O towards low-mass
protostars show a distinct velocity component not seen in observations
from the ground of CO or other species. The aim is to characterise this
component in terms of excitation conditions and physical origin. <BR />
Methods: A velocity component with an offset of ~10 km s<SUP>-1</SUP>
detected in spectra of the H<SUB>2</SUB>O 1<SUB>10</SUB>-1<SUB>01</SUB>
557 GHz transition towards six low-mass protostars in the "Water
in star-forming regions with Herschel" (WISH) programme is also
seen in higher-excited H<SUB>2</SUB>O lines. The emission from this
component is quantified and local excitation conditions are inferred
using 1D slab models. Data are compared to observations of hydrides
(high-J CO, OH<SUP>+</SUP>, CH<SUP>+</SUP>, C<SUP>+</SUP>, OH) where
the same component is uniquely detected. <BR /> Results: The velocity
component is detected in all six targeted H<SUB>2</SUB>O transitions
(E<SUB>up</SUB> ~ 50-250 K), as well as in CO 16-15 towards one source,
Ser SMM1. Inferred excitation conditions imply that the emission arises
in dense (n ~ 5 × 10<SUP>6</SUP>-10<SUP>8</SUP> cm<SUP>-3</SUP>) and
hot (T ~ 750 K) gas. The H<SUB>2</SUB>O and CO column densities are
≳10<SUP>16</SUP> and 10<SUP>18</SUP> cm<SUP>-2</SUP>, respectively,
implying a low H<SUB>2</SUB>O abundance of ~10<SUP>-2</SUP> with
respect to CO. The high column densities of ions such as OH<SUP>+</SUP>
and CH<SUP>+</SUP> (both ≳10<SUP>13</SUP> cm<SUP>-2</SUP>) indicate
an origin close to the protostar where the UV field is strong enough
that these species are abundant. The estimated radius of the emitting
region is 100 AU. This component likely arises in dissociative shocks
close to the protostar, an interpretation corroborated by a comparison
with models of such shocks. Furthermore, one of the sources, IRAS 4A,
shows temporal variability in the offset component over a period
of two years which is expected from shocks in dense media. High-J
CO gas detected with Herschel-PACS with T<SUB>rot</SUB> ~ 700 K is
identified as arising in the same component and traces the part of
the shock where H<SUB>2</SUB> reforms. Thus, H<SUB>2</SUB>O reveals
new dynamical components, even on small spatial scales in low-mass
protostars. <P />Herschel is an ESA space observatory with science
instruments provided by European-led Principal Investigator consortia
and with important participation from NASA.
---------------------------------------------------------
Title: Water in star-forming regions with Herschel (WISH). IV. A
survey of low-J H<SUB>2</SUB>O line profiles toward high-mass
protostars
Authors: van der Tak, F. F. S.; Chavarría, L.; Herpin, F.; Wyrowski,
F.; Walmsley, C. M.; van Dishoeck, E. F.; Benz, A. O.; Bergin, E. A.;
Caselli, P.; Hogerheijde, M. R.; Johnstone, D.; Kristensen, L. E.;
Liseau, R.; Nisini, B.; Tafalla, M.
2013A&A...554A..83V Altcode: 2013arXiv1304.2949V
Context. Water is a key constituent of star-forming matter, but the
origin of its line emission and absorption during high-mass star
formation is not well understood. <BR /> Aims: We study the velocity
profiles of low-excitation H<SUB>2</SUB>O lines toward 19 high-mass
star-forming regions and search for trends with luminosity, mass,
and evolutionary stage. <BR /> Methods: We decompose high-resolution
Herschel-HIFI line spectra near 990, 1110 and 1670 GHz into three
distinct physical components. Dense cores (protostellar envelopes) are
usually seen as narrow absorptions in the H<SUB>2</SUB>O 1113 and 1669
GHz ground-state lines, the H<SUB>2</SUB>O 987 GHz excited-state line,
and the H<SUB>2</SUB><SUP>18</SUP>O 1102 GHz ground-state line. In a
few sources, the envelopes appear in emission in some or all studied
lines, indicating higher temperatures or densities. Broader features
due to outflows are usually seen in absorption in the H<SUB>2</SUB>O
1113 and 1669 GHz lines, in 987 GHz emission, and not seen in
H<SUB>2</SUB><SUP>18</SUP>O, indicating a lower column density and
a higher excitation temperature than the envelope component. A few
outflows are detected in H<SUB>2</SUB><SUP>18</SUP>O, indicating higher
column densities of shocked gas. In addition, the H<SUB>2</SUB>O 1113
and 1669 GHz spectra show narrow absorptions by foreground clouds
along the line of sight. The lack of corresponding features in the
987 GHz and H<SUB>2</SUB><SUP>18</SUP>O lines indicates a low column
density and a low excitation temperature for these clouds, although
their derived H<SUB>2</SUB>O ortho/para ratios are close to 3. <BR />
Results: The intensity of the ground state lines of H<SUB>2</SUB>O
at 1113 and 1669 GHz does not show significant trends with source
luminosity, envelope mass, or evolutionary state. In contrast,
the flux in the excited-state 987 GHz line appears correlated with
luminosity and the H<SUB>2</SUB><SUP>18</SUP>O line flux appears
correlated with the envelope mass. Furthermore, appearance of the
envelope in absorption in the 987 GHz and H<SUB>2</SUB><SUP>18</SUP>O
lines seems to be a sign of an early evolutionary stage, as probed by
the mid-infrared brightness and the L<SUB>bol</SUB>/M<SUB>env</SUB>
ratio of the source. <BR /> Conclusions: The ground state transitions
of H<SUB>2</SUB>O trace the outer parts of the envelopes, so that
the effects of star formation are mostly noticeable in the outflow
wings. These lines are heavily affected by absorption, so that line
ratios of H<SUB>2</SUB>O involving the ground states must be treated
with caution, especially if multiple clouds are superposed as in the
extragalactic case. The isotopic H<SUB>2</SUB><SUP>18</SUP>O line
appears to trace the mass of the protostellar envelope, indicating
that the average H<SUB>2</SUB>O abundance in high-mass protostellar
envelopes does not change much with time. The excited state line at
987 GHz increases in flux with luminosity and appears to be a good
tracer of the mean weighted dust temperature of the source, which may
explain why it is readily seen in distant galaxies. <P />Herschel
is an ESA space observatory with science instruments provided by
European-led Principal Investigator consortia and with important
participation from NASA.Appendices are available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: OH far-infrared emission from low- and intermediate-mass
protostars surveyed with Herschel-PACS
Authors: Wampfler, S. F.; Bruderer, S.; Karska, A.; Herczeg, G. J.;
van Dishoeck, E. F.; Kristensen, L. E.; Goicoechea, J. R.; Benz,
A. O.; Doty, S. D.; McCoey, C.; Baudry, A.; Giannini, T.; Larsson, B.
2013A&A...552A..56W Altcode: 2012arXiv1212.5033W
Context. The OH radical is a key species in the water chemistry network
of star-forming regions, because its presence is tightly related
to the formation and destruction of water. Previous studies of the
OH far-infrared emission from low- and intermediate-mass protostars
suggest that the OH emission mainly originates from shocked gas and
not from the quiescent protostellar envelopes. <BR /> Aims: We aim
to study the excitation of OH in embedded low- and intermediate-mass
protostars, determine the influence of source parameters on the strength
of the emission, investigate the spatial extent of the OH emission,
and further constrain its origin. <BR /> Methods: This paper presents
OH observations from 23 low- and intermediate-mass young stellar
objects obtained with the PACS integral field spectrometer on-board
Herschel in the context of the "Water In Star-forming regions with
Herschel" (WISH) key program. Radiative transfer codes are used to
model the OH excitation. <BR /> Results: Most low-mass sources have
compact OH emission (≲5000 AU scale), whereas the OH lines in most
intermediate-mass sources are extended over the whole 47.″0 ×
47.″0 PACS detector field-of-view (≳20 000 AU). The strength
of the OH emission is correlated with various source properties
such as the bolometric luminosity and the envelope mass, but also
with the [OI] and H<SUB>2</SUB>O emission. Rotational diagrams for
sources with many OH lines show that the level populations of OH
can be approximated by a Boltzmann distribution with an excitation
temperature at around 70 K. Radiative transfer models of spherically
symmetric envelopes cannot reproduce the OH emission fluxes nor
their broad line widths, strongly suggesting an outflow origin. Slab
excitation models indicate that the observed excitation temperature
can either be reached if the OH molecules are exposed to a strong
far-infrared continuum radiation field or if the gas temperature and
density are sufficiently high. Using realistic source parameters and
radiation fields, it is shown for the case of Ser SMM1 that radiative
pumping plays an important role in transitions arising from upper
level energies higher than 300 K. The compact emission in the low-mass
sources and the required presence of a strong radiation field and/or
a high density to excite the OH molecules points toward an origin in
shocks in the inner envelope close to the protostar. <P />Herschel
is an ESA space observatory with science instruments provided by
European-led Principal Investigator consortia and with important
participation from NASA.Appendices are only available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Water in star-forming regions with Herschel
(WISH). III. Far-infrared cooling lines in low-mass young stellar
objects
Authors: Karska, A.; Herczeg, G. J.; van Dishoeck, E. F.; Wampfler,
S. F.; Kristensen, L. E.; Goicoechea, J. R.; Visser, R.; Nisini, B.;
San José-García, I.; Bruderer, S.; Śniady, P.; Doty, S.; Fedele,
D.; Yıldız, U. A.; Benz, A. O.; Bergin, E.; Caselli, P.; Herpin,
F.; Hogerheijde, M. R.; Johnstone, D.; Jørgensen, J. K.; Liseau,
R.; Tafalla, M.; van der Tak, F.; Wyrowski, F.
2013A&A...552A.141K Altcode: 2013arXiv1301.4821K
Context. Understanding the physical phenomena involved in the earlierst
stages of protostellar evolution requires knowledge of the heating
and cooling processes that occur in the surroundings of a young
stellar object. Spatially resolved information from its constituent
gas and dust provides the necessary constraints to distinguish
between different theories of accretion energy dissipation into
the envelope. Aims. Our aims are to quantify the far-infrared line
emission from low-mass protostars and the contribution of different
atomic and molecular species to the gas cooling budget, to determine
the spatial extent of the emission, and to investigate the underlying
excitation conditions. Analysis of the line cooling will help us
characterize the evolution of the relevant physical processes as
the protostar ages. Methods. Far-infrared Herschel-PACS spectra
of 18 low-mass protostars of various luminosities and evolutionary
stages are studied in the context of the WISH key program. For most
targets, the spectra include many wavelength intervals selected to
cover specific CO, H<SUB>2</SUB>O, OH, and atomic lines. For four
targets the spectra span the entire 55-200 μm region. The PACS
field-of-view covers ~47" with the resolution of 9.4". Results. Most
of the protostars in our sample show strong atomic and molecular
far-infrared emission. Water is detected in 17 out of 18 objects (except
TMC1A), including 5 Class I sources. The high-excitation H<SUB>2</SUB>O
8<SUB>18</SUB>-7<SUB>07</SUB> 63.3 μm line (E<SUB>u</SUB>/k<SUB>B</SUB>
= 1071 K) is detected in 7 sources. CO transitions from J = 14-13 up
to J = 49 - 48 are found and show two distinct temperature components
on Boltzmann diagrams with rotational temperatures of ~350 K and
~700 K. H<SUB>2</SUB>O has typical excitation temperatures of ~150
K. Emission from both Class 0 and I sources is usually spatially
extended along the outflow direction but with a pattern that depends on
the species and the transition. In the extended sources, emission is
stronger off source and extended on &≥10,000 AU scales; in the
compact sample, more than half of the flux originates within 1000 AU
of the protostar. The H<SUB>2</SUB>O line fluxes correlate strongly
with those of the high-J CO lines, both for the full array and for
the central position, as well as with the bolometric luminosity and
envelope mass. They correlate less strongly with OH fluxes and not
with [O I] fluxes. In contrast, [O I] and OH often peak together at
the central position. Conclusions. The PACS data probe at least two
physical components. The H<SUB>2</SUB>O and CO emission very likely
arises in non-dissociative (irradiated) shocks along the outflow
walls with a range of pre-shock densities. Some OH is also associated
with this component, most likely resulting from H<SUB>2</SUB>O
photodissociation. UV-heated gas contributes only a minor fraction
to the CO emission observed by PACS, based on the strong correlation
between the shock-dominated CO 24-23 line and the CO 14-13 line. [O
I] and some of the OH emission probe dissociative shocks in the inner
envelope. The total far-infrared cooling is dominated by H<SUB>2</SUB>O
and CO, with the fraction contributed by [O I] increasing for Class
I sources. Consistent with previous studies, the ratio of total
far-infrared line emission over bolometric luminosity decreases with
the evolutionary state. <P />Appendices A-J are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Observing the Sun with ALMA
Authors: Benz, A. O.; Brajsa, R.; Shimojo, M.; Karlicky, M.; Testi, L.
2012IAUSS...6E.205B Altcode:
The Atacama Large Millimeter Array (ALMA) is in the commissioning
phase for solar observations. A filter reduces the solar radiation
to a level suitable for solar observations. First observations
with one antenna have mapped the Sun by scanning. The results look
promising. The image of the quiet chromosphere shows large spatial
variations in emissivity. Interferometry is much more demanding and
not yet achieved. The current state and problems will be summarized. It
is clear that solar ALMA observations will take more developing time,
but will eventually be possible. The goal is subarcsecond resolution
of the quiet and active submillimeter continuum radiation originating
in the chromosphere and possibly in the flaring corona. A limiting
factor will be the temporal variability of the solar emission.
---------------------------------------------------------
Title: Spectrometer Telescope for Imaging X-rays (STIX)
Authors: Benz, A. O.; Gallagher, P.; Veronig, A.; Grimm, O.; Sylwester,
J.; Orleanski, P.; Arnold, N.; Bednarzik, M.; Farnik, F.; Hurford,
G.; Krucker, S.; Limousin, O.; Mann, G.; Vilmer, N.
2012IAUSS...6E.509B Altcode:
The Solar Orbiter Mission has been confirmed within ESA's M-class
Cosmic Vision plan. Launch date is January 2017 into an orbit that
reaches nearly one quarter AU in the perihelion. STIX is one of
the 10 instruments selected for close cooperation. STIX applies
a Fourier-imaging technique using shading tungsten grids. A total
of 32 pixelized CdTe detectors will permit high resolution imaging
spectroscopy. The design has passed ESA's Preliminary Design Review
and will be finalized by the end of 2012. The instrument specification
will be presented and its scientific potential discussed.
---------------------------------------------------------
Title: The spectrometer telescope for imaging x-rays on board the
Solar Orbiter mission
Authors: Benz, A. O.; Krucker, S.; Hurford, G. J.; Arnold, N. G.;
Orleanski, P.; Gröbelbauer, H. -P.; Klober, S.; Iseli, L.; Wiehl,
H. J.; Csillaghy, A.; Etesi, L.; Hochmuth, N.; Battaglia, M.;
Bednarzik, M.; Resanovic, R.; Grimm, O.; Viertel, G.; Commichau, V.;
Meuris, A.; Limousin, O.; Brun, S.; Vilmer, N.; Skup, K. R.; Graczyk,
R.; Stolarski, M.; Michalska, M.; Nowosielski, W.; Cichocki, A.;
Mosdorf, M.; Seweryn, K.; Przepiórka, A.; Sylwester, J.; Kowalinski,
M.; Mrozek, T.; Podgorski, P.; Mann, G.; Aurass, H.; Popow, E.;
Onel, H.; Dionies, F.; Bauer, S.; Rendtel, J.; Warmuth, A.; Woche,
M.; Plüschke, D.; Bittner, W.; Paschke, J.; Wolker, D.; Van Beek,
H. F.; Farnik, F.; Kasparova, J.; Veronig, A. M.; Kienreich, I. W.;
Gallagher, P. T.; Bloomfield, D. S.; Piana, M.; Massone, A. M.;
Dennis, B. R.; Schwarz, R. A.; Lin, R. P.
2012SPIE.8443E..3LB Altcode:
The Spectrometer Telescope for Imaging X-rays (STIX) is one of 10
instruments on board Solar Orbiter, a confirmed Mclass mission of the
European Space Agency (ESA) within the Cosmic Vision program scheduled
to be launched in 2017. STIX applies a Fourier-imaging technique
using a set of tungsten grids (at pitches from 0.038 to 1 mm) in
front of 32 pixelized CdTe detectors to provide imaging spectroscopy
of solar thermal and non-thermal hard X-ray emissions from 4 to 150
keV. The status of the instrument reviewed in this paper is based on
the design that passed the Preliminary Design Review (PDR) in early
2012. Particular emphasis is given to the first light of the detector
system called Caliste-SO.
---------------------------------------------------------
Title: Remnant Gas in Evolved Circumstellar Disks: Herschel PACS
Observations of 10-100 Myr Old Disk Systems
Authors: Geers, Vincent C.; Gorti, Uma; Meyer, Michael R.; Mamajek,
Eric; Benz, Arnold O.; Hollenbach, David
2012ApJ...755....8G Altcode: 2012arXiv1206.1044G
We present Herschel PACS spectroscopy of the [O I] 63 μm gas line
for three circumstellar disk systems showing signs of significant
disk evolution and/or planet formation: HR 8799, HD 377, and RX
J1852.3-3700. [O I] is undetected toward HR 8799 and HD 377 with 3σ
upper limits of 6.8 × 10<SUP>-18</SUP> W m<SUP>-2</SUP> and 9.9 ×
10<SUP>-18</SUP> W m<SUP>-2</SUP>, respectively. We find an [O I]
detection for RX J1852.3-3700 at (12.3 ± 1.8) × 10<SUP>-18</SUP>
W m<SUP>-2</SUP>. We use thermo-chemical disk models to model the gas
emission, using constraints on the [O I] 63 μm and ancillary data to
derive gas mass upper limits and constrain gas-to-dust ratios. For HD
377 and HR 8799, we find 3σ upper limits on the gas mass of 0.1-20 M
<SUB>⊕</SUB>. For RX J1852.3-3700, we find two distinct disk scenarios
that could explain the detection of [O I] 63 μm and CO(2-1) upper
limits reported in the literature: (1) a large disk with gas co-located
with the dust (16-500 AU), resulting in a large tenuous disk with ~16
M <SUB>⊕</SUB> of gas, or (2) an optically thick gas disk, truncated
at ~70 AU, with a gas mass of 150 M <SUB>⊕</SUB>. We discuss the
implications of these results for the formation and evolution of planets
in these three systems. <P />Herschel is an ESA space observatory with
science instruments provided by European-led Principal Investigator
consortia and with important participation from NASA.
---------------------------------------------------------
Title: Submillimeter line emission from LMC 30 Doradus: The impact
of a starburst on a low-metallicity environment
Authors: Pineda, J. L.; Mizuno, N.; Röllig, M.; Stutzki, J.; Kramer,
C.; Klein, U.; Rubio, M.; Kawamura, A.; Minamidani, T.; Benz, A.;
Burton, M.; Fukui, Y.; Koo, B. -C.; Onishi, T.
2012A&A...544A..84P Altcode: 2012arXiv1206.4051P
Context. The 30 Dor region in the Large Magellanic Cloud (LMC)
is the most vigorous star-forming region in the Local Group. Star
formation in this region is taking place in low-metallicity molecular
gas that is exposed to an extreme far-ultraviolet (FUV) radiation
field powered by the massive compact star cluster R136. 30 Dor is
therefore ideally suited to study the conditions in which stars formed
at earlier cosmological times. <BR /> Aims: Observations of (sub)mm
and far-infrared (FIR) spectral lines of the main carbon-carrying
species, CO, [C i] and [C ii], which originate in the surface layers
of molecular clouds illuminated by the FUV radiation of young stars,
can be used to constrain the physical and chemical state of the
star-forming ISM. <BR /> Methods: We used the NANTEN2 telescope to
obtain high-angular resolution observations of the <SUP>12</SUP>CO J =
4 → 3, J = 7 → 6, and <SUP>13</SUP>CO J = 4 → 3 rotational lines
and [C i] <SUP>3</SUP>P<SUB>1</SUB>- <SUP>3</SUP>P<SUB>0</SUB> and
<SUP>3</SUP>P<SUB>2</SUB>- <SUP>3</SUP>P<SUB>1</SUB> fine-structure
submillimeter transitions in 30 Dor-10, the brightest CO and
FIR-emitting cloud at the center of the 30 Dor region. We derived the
physical and chemical properties of the low-metallicity molecular gas
using an excitation/radiative transfer code and found a self-consistent
solution of the chemistry and thermal balance of the gas in the
framework of a clumpy cloud PDR model. We compared the derived
properties with those in the N159W region, which is exposed to a more
moderate far-ultraviolet radiation field compared with 30 Dor-10,
but has similar metallicity. We also combined our CO detections with
previously observed low-J CO transitions to derive the CO spectral-line
energy distribution in 30 Dor-10 and N159W. <BR /> Results: The separate
excitation analysis of the submm CO lines and the neutral carbon fine
structure lines shows that the mid-J CO and [C i]-emitting gas in the
30 Dor-10 region has a temperature of about 160 K and a H<SUB>2</SUB>
density of about 10<SUP>4</SUP> cm<SUP>-3</SUP>. We find that the
molecular gas in 30 Dor-10 is warmer and has a lower beam filling factor
compared to that of N159W, which might be a result of the effect of a
strong FUV radiation field heating and disrupting the low-metallicity
molecular gas. We use a clumpy PDR model (including the [C ii] line
intensity reported in the literature) to constrain the FUV intensity
to about χ<SUB>0</SUB> ≈ 3100 and an average total H density of
the clump ensemble of about 10<SUP>5</SUP> cm<SUP>-3</SUP> in 30 Dor-10.
---------------------------------------------------------
Title: Water in star-forming regions with Herschel
(WISH). II. Evolution of 557 GHz 1<SUB>10</SUB>-1<SUB>01</SUB>
emission in low-mass protostars
Authors: Kristensen, L. E.; van Dishoeck, E. F.; Bergin, E. A.;
Visser, R.; Yıldız, U. A.; San Jose-Garcia, I.; Jørgensen, J. K.;
Herczeg, G. J.; Johnstone, D.; Wampfler, S. F.; Benz, A. O.; Bruderer,
S.; Cabrit, S.; Caselli, P.; Doty, S. D.; Harsono, D.; Herpin, F.;
Hogerheijde, M. R.; Karska, A.; van Kempen, T. A.; Liseau, R.; Nisini,
B.; Tafalla, M.; van der Tak, F.; Wyrowski, F.
2012A&A...542A...8K Altcode: 2012arXiv1204.0009K
Context. Water is a key tracer of dynamics and chemistry in low-mass
star-forming regions, but spectrally resolved observations have so far
been limited in sensitivity and angular resolution, and only data from
the brightest low-mass protostars have been published. <BR /> Aims:
The first systematic survey of spectrally resolved water emission
in 29 low-mass (L < 40 L<SUB>⊙</SUB>) protostellar objects is
presented. The sources cover a range of luminosities and evolutionary
states. The aim is to characterise the line profiles to distinguish
physical components in the beam and examine how water emission changes
with protostellar evolution. <BR /> Methods: H<SUB>2</SUB>O was observed
in the ground-state 1<SUB>10</SUB>-1<SUB>01</SUB> transition at 557 GHz
(E<SUB>up</SUB>/k<SUB>B</SUB> ~ 60 K) as single-point observations with
the Heterodyne Instrument for the Far-Infrared (HIFI) on Herschel in 29
deeply embedded Class 0 and I low-mass protostars. Complementary far-IR
and sub-mm continuum data (including PACS data from our programme)
are used to constrain the spectral energy distribution (SED) of each
source. H<SUB>2</SUB>O intensities are compared to inferred envelope
properties, e.g., mass and density, outflow properties and CO 3-2
emission. <BR /> Results: H<SUB>2</SUB>O emission is detected in
all objects except one (TMC1A). The line profiles are complex and
consist of several kinematic components tracing different physical
regions in each system. In particular, the profiles are typically
dominated by a broad Gaussian emission feature, indicating that
the bulk of the water emission arises in outflows, not in the
quiescent envelope. Several sources show multiple shock components
appearing in either emission or absorption, thus constraining the
internal geometry of the system. Furthermore, the components include
inverse P-Cygni profiles in seven sources (six Class 0, one Class I)
indicative of infalling envelopes, and regular P-Cygni profiles in
four sources (three Class I, one Class 0) indicative of expanding
envelopes. Molecular "bullets" moving at ≳50 km s<SUP>-1</SUP>
with respect to the source are detected in four Class 0 sources; three
of these sources were not known to harbour bullets previously. In the
outflow, the H<SUB>2</SUB>O/CO abundance ratio as a function of velocity
is nearly the same for all line wings, increasing from 10<SUP>-3</SUP>
at low velocities (<5 km s<SUP>-1</SUP>) to ≳10<SUP>-1</SUP> at
high velocities (>10 km s<SUP>-1</SUP>). The water abundance in
the outer cold envelope is low, ≳10<SUP>-10</SUP>. The different
H<SUB>2</SUB>O profile components show a clear evolutionary trend:
in the younger Class 0 sources the emission is dominated by outflow
components originating inside an infalling envelope. When large-scale
infall diminishes during the Class I phase, the outflow weakens and
H<SUB>2</SUB>O emission all but disappears. <P />Herschel is an ESA
space observatory with science instruments provided by European-led
Principal Investigator consortia and with important participation
from NASA.Appendices are available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Multi-line detection of O<SUB>2</SUB> toward ρ Ophuichi A
Authors: Liseau, R.; Goldsmith, P. F.; Larsson, B.; Pagani, L.;
Bergman, P.; Le Bourlot, J.; Bell, T. A.; Benz, A. O.; Bergin, E. A.;
Bjerkeli, P.; Black, J. H.; Bruderer, S.; Caselli, P.; Caux, E.;
Chen, J. -H.; de Luca, M.; Encrenaz, P.; Falgarone, E.; Gerin, M.;
Goicoechea, J. R.; Hjalmarson, Å.; Hollenbach, D. J.; Justtanont,
K.; Kaufman, M. J.; Le Petit, F.; Li, D.; Lis, D. C.; Melnick, G. J.;
Nagy, Z.; Olofsson, A. O. H.; Olofsson, G.; Roueff, E.; Sandqvist,
Aa.; Snell, R. L.; van der Tak, F. F. S.; van Dishoeck, E. F.; Vastel,
C.; Viti, S.; Yıldız, U. A.
2012A&A...541A..73L Altcode: 2012arXiv1202.5637L
Context. Models of pure gas-phase chemistry in well-shielded regions of
molecular clouds predict relatively high levels of molecular oxygen,
O<SUB>2</SUB>, and water, H<SUB>2</SUB>O. These high abundances imply
high cooling rates, leading to relatively short timescales for the
evolution of gravitationally unstable dense cores, forming stars and
planets. Contrary to expectations, the dedicated space missions SWAS
and Odin typically found only very small amounts of water vapour and
essentially no O<SUB>2</SUB> in the dense star-forming interstellar
medium. <BR /> Aims: Only toward ρ Oph A did Odin detect a very weak
line of O<SUB>2</SUB> at 119 GHz in a beam of size 10 arcmin. The line
emission of related molecules changes on angular scales of the order
of some tens of arcseconds, requiring a larger telescope aperture such
as that of the Herschel Space Observatory to resolve the O<SUB>2</SUB>
emission and pinpoint its origin. <BR /> Methods: We use the Heterodyne
Instrument for the Far Infrared (HIFI) aboard Herschel to obtain high
resolution O<SUB>2</SUB> spectra toward selected positions in the ρ
Oph A core. These data are analysed using standard techniques for
O<SUB>2</SUB> excitation and compared to recent PDR-like chemical
cloud models. <BR /> Results: The N<SUB>J</SUB> = 3<SUB>3</SUB> -
1<SUB>2</SUB> line at 487.2 GHz is clearly detected toward all three
observed positions in the ρ Oph A core. In addition, an oversampled map
of the 5<SUB>4</SUB>-3<SUB>4</SUB> transition at 773.8 GHz reveals the
detection of the line in only half of the observed area. On the basis
of their ratios, the temperature of the O<SUB>2</SUB> emitting gas
appears to vary quite substantially, with warm gas ( ≳ 50 K) being
adjacent to a much colder region, of temperatures lower than 30 K. <BR
/> Conclusions: The exploited models predict that the O<SUB>2</SUB>
column densities are sensitive to the prevailing dust temperatures,
but rather insensitive to the temperatures of the gas. In agreement
with these models, the observationally determined O<SUB>2</SUB>
column densities do not seem to depend strongly on the derived gas
temperatures, but fall into the range N(O<SUB>2</SUB>) = 3 to ≳ 6 ×
10<SUP>15</SUP> cm<SUP>-2</SUP>. Beam-averaged O<SUB>2</SUB> abundances
are about 5 × 10<SUP>-8</SUP> relative to H<SUB>2</SUB>. Combining
the HIFI data with earlier Odin observations yields a source size at
119 GHz in the range of 4 to 5 arcmin, encompassing the entire ρ Oph
A core. We speculate that one of the reasons for the generally very low
detection rate of O<SUB>2</SUB> is the short period of time during which
O<SUB>2</SUB> molecules are reasonably abundant in molecular clouds. <P
/>Based on observations with Herschel-HIFI. Herschel is an ESA space
observatory with science instruments provided by European-led Principal
Investigator consortia and with important participation from NASA.
---------------------------------------------------------
Title: Instrument data processing unit for spectrometer/telescope
for imaging x-rays (STIX)
Authors: Skup, Konrad R.; Cichocki, A.; Graczyk, R.; Michalska,
M.; Mosdorf, M.; Nowosielski, W.; Orleański, P.; Przepiórka, A.;
Seweryn, K.; Stolarski, M.; Winkler, M.; Sylwester, J.; Kowalinski,
M.; Mrozek, T.; Podgorski, P.; Benz, A. O.; Krucker, S.; Hurford,
G. J.; Arnold, N. G.; Önel, H.; Meuris, A.; Limousin, O.; Grimm, O.
2012SPIE.8454E..0KS Altcode:
The Spectrometer/Telescope for Imaging X-rays (STIX) is one of 10
instruments on board Solar Orbiter, an M-class mission of the European
Space Agency (ESA) scheduled to be launch in 2017. STIX applies a
Fourier-imaging technique using a set of tungsten grids in front of
32 pixelized CdTe detectors to provide imaging spectroscopy of solar
thermal and non-thermal hard X-ray emissions from 4 to 150 keV. These
detectors are source of data collected and analyzed in real-time by
Instrument Data Processing Unit (IDPU). Besides the data processing
the IDPU controls and manages other STIX's subsystems: ASICs and ADCs
associated with detectors, Aspect System, Attenuator, PSU and HK. The
instrument reviewed in this paper is based on the design that passed the
Instrument Preliminary Design Review (IPDR) in early 2012 and Software
Preliminary Design Review (SW PDR) in middle of 2012. Particular
emphasis is given to the IDPU and low level software called Basic SW
(BSW).
---------------------------------------------------------
Title: Herschel Observations of Interstellar Chloronium
Authors: Neufeld, David A.; Roueff, Evelyne; Snell, Ronald L.;
Lis, Dariusz; Benz, Arnold O.; Bruderer, Simon; Black, John H.;
De Luca, Massimo; Gerin, Maryvonne; Goldsmith, Paul F.; Gupta,
Harshal; Indriolo, Nick; Le Bourlot, Jacques; Le Petit, Franck;
Larsson, Bengt; Melnick, Gary J.; Menten, Karl M.; Monje, Raquel;
Nagy, Zsófia; Phillips, Thomas G.; Sandqvist, Aage; Sonnentrucker,
Paule; van der Tak, Floris; Wolfire, Mark G.
2012ApJ...748...37N Altcode: 2012arXiv1201.2941N
Using the Herschel Space Observatory's Heterodyne Instrument
for the Far-Infrared, we have observed para-chloronium
(H<SUB>2</SUB>Cl<SUP>+</SUP>) toward six sources in the Galaxy. We
detected interstellar chloronium absorption in foreground molecular
clouds along the sight lines to the bright submillimeter continuum
sources Sgr A (+50 km s<SUP>-1</SUP> cloud) and W31C. Both the
para-H<SUP>35</SUP> <SUB>2</SUB>Cl<SUP>+</SUP> and para-H<SUP>37</SUP>
<SUB>2</SUB>Cl<SUP>+</SUP> isotopologues were detected, through
observations of their 1<SUB>11</SUB>-0<SUB>00</SUB> transitions
at rest frequencies of 485.42 and 484.23 GHz, respectively. For an
assumed ortho-to-para ratio (OPR) of 3, the observed optical depths
imply that chloronium accounts for ~4%-12% of chlorine nuclei in
the gas phase. We detected interstellar chloronium emission from two
sources in the Orion Molecular Cloud 1: the Orion Bar photodissociation
region and the Orion South condensation. For an assumed OPR of 3 for
chloronium, the observed emission line fluxes imply total beam-averaged
column densities of ~2 × 10<SUP>13</SUP> cm<SUP>-2</SUP> and ~1.2
× 10<SUP>13</SUP> cm<SUP>-2</SUP>, respectively, for chloronium in
these two sources. We obtained upper limits on the para-H<SUP>35</SUP>
<SUB>2</SUB>Cl<SUP>+</SUP> line strengths toward H<SUB>2</SUB> Peak
1 in the Orion Molecular cloud and toward the massive young star AFGL
2591. The chloronium abundances inferred in this study are typically
at least a factor ~10 larger than the predictions of steady-state
theoretical models for the chemistry of interstellar molecules
containing chlorine. Several explanations for this discrepancy were
investigated, but none has proven satisfactory, and thus the large
observed abundances of chloronium remain puzzling. <P />Herschel is an
ESA space observatory with science instruments provided by European-led
Principal Investigator consortia and with important participation
from NASA.
---------------------------------------------------------
Title: Location of Decimetric Pulsations in Solar Flares
Authors: Benz, Arnold O.; Battaglia, Marina; Vilmer, Nicole
2012esrs.book...57B Altcode:
This work investigates the spatial relation between coronal X-ray
sources and coherent radio emissions, both generally thought to be
signatures of particle acceleration. Two limb events were selected
during which the radio emission was well correlated in time with hard
X-rays. The radio emissions were of the type of decimetric pulsations
as determined from the spectrogram observed by Phoenix-2 of ETH
Zurich. The radio positions were measured from observations with the
Nançay Radioheliograph between 236 and 432 MHz and compared to the
position of the coronal X-ray source imaged with RHESSI. The radio
pulsations originated at least 30 - 240 Mm above the coronal hard X-ray
source. The altitude of the radio emission increases generally with
lower frequency. The average positions at different frequencies are on
a line pointing approximately to the coronal hard X-ray source. Thus,
the pulsations cannot be caused by electrons trapped in the flare
loops, but are consistent with emission from a current sheet above
the coronal source.
---------------------------------------------------------
Title: The Radio-X-ray Relation in Cool Stars: Are We Headed Toward
a Divorce?
Authors: Forbrich, J.; Wolk, S. J.; Güdel, M.; Benz, A.; Osten, R.;
Linsky, J. L.; McLean, M.; Loinard, L.; Berger, E.
2011ASPC..448..455F Altcode: 2011csss...16..455F; 2010arXiv1012.1626F
This splinter session was devoted to reviewing our current knowledge
of correlated X-ray and radio emission from cool stars in order
to prepare for new large radio observatories such as the EVLA. A
key interest was to discuss why the X-ray and radio luminosities of
some cool stars are in clear breach of a correlation that holds for
other active stars, the so-called Güdel-Benz relation. This article
summarizes the contributions whereas the actual presentations can be
accessed on the splinter website.
---------------------------------------------------------
Title: Location of Decimetric Pulsations in Solar Flares
Authors: Benz, Arnold O.; Battaglia, Marina; Vilmer, Nicole
2011SoPh..273..363B Altcode: 2011SoPh..tmp..166B; 2011arXiv1103.5353B; 2011SoPh..tmp..235B;
2011SoPh..tmp...88B
This work investigates the spatial relation between coronal X-ray
sources and coherent radio emissions, both generally thought to be
signatures of particle acceleration. Two limb events were selected
during which the radio emission was well correlated in time with hard
X-rays. The radio emissions were of the type of decimetric pulsations
as determined from the spectrogram observed by Phoenix-2 of ETH
Zurich. The radio positions were measured from observations with the
Nançay Radioheliograph between 236 and 432 MHz and compared to the
position of the coronal X-ray source imaged with RHESSI. The radio
pulsations originated at least 30 - 240 Mm above the coronal hard X-ray
source. The altitude of the radio emission increases generally with
lower frequency. The average positions at different frequencies are on
a line pointing approximately to the coronal hard X-ray source. Thus,
the pulsations cannot be caused by electrons trapped in the flare
loops, but are consistent with emission from a current sheet above
the coronal source.
---------------------------------------------------------
Title: WISHes coming true: water in low-mass star-forming regions
with Herschel
Authors: Kristensen, L. E.; Visser, R.; van Dishoeck, E. F.; Yıldız,
U. A.; Herczeg, G. J.; Doty, S.; Jørgensen, J. K.; van Kempen, T. A.;
Brinch, C.; Wampfler, S.; Bruderer, S.; Benz, A. O.
2011EAS....52..177K Altcode:
Water is a key molecule for tracing physical and chemical processes in
star-forming regions. The key program "Water in star-forming regions
with Herschel" is observing several water transitions towards low-mass
protostars with HIFI. Results regarding the 557 GHz transition of
water are reported here showing that the line is surprisingly broad,
and consists of several different velocity components. The bulk of the
emission comes from shocks, where the abundance is increased by several
orders of magnitude to ~10<SUP>-4</SUP>. The abundance of water in
the outer envelope is determined to ~10<SUP>-8</SUP>, whereas only an
upper limit of 10<SUP>-5</SUP> is derived for the inner, warm envelope.
---------------------------------------------------------
Title: The WADI key project: New insights to photon-dominated regions
from Herschel observations
Authors: Ossenkopf, V.; Röllig, M.; Kramer, C.; Okada, Y.; Fuente,
A.; Akyilmaz Yabaci, M.; Benz, A. O.; Berné, O.; Boulanger, F.;
Bruderer, S.; Dedes, C.; France, K.; Gerin, M.; Goicoechea, J. R.;
Gusdorf, A.; Güsten, R.; Harris, A.; Joblin, C.; Klein, T.; Latter,
W.; Le Petit, F.; Lord, S.; Martin, P. G.; Pilleri, P.; Martin-Pintado,
J.; Mookerjea, B.; Neufeld, D. A.; Phillips, T.; Rizzo, R.; Simon,
R.; Stutzki, J.; van der Tak, F. F. S.; Teyssier, D.; Yorke, H.
2011EAS....52..181O Altcode:
Within the Herschel key project "The Warm And Dense ISM" (WADI) we
systematically observe a number of prominent photon-dominated regions
(PDRs) to measure the impact of varying UV fields on the energy balance,
the chemical and dynamical structure of heated molecular clouds.
---------------------------------------------------------
Title: Tracing FUV Radiation in the Embedded Phase of Star Formation
Authors: Benz, A. O.; Bruderer, S.; van Dishoeck, E. F.; Stäuber,
P.; Wampfler, S. F.; Dedes, C.
2011EAS....52..239B Altcode:
Molecules containing one or a few hydrogen atoms and a heavier atom
(hydrides) have been predicted to trace FUV radiation. In some
chemical models, FUV emission by the central object or protostar
of a star forming region greatly enhances some of the hydride
abundances. Two massive regions, W3 IRS5 and AFGL 2591, have
been observed in hydride lines by HIFI onboard the Herschel Space
Observatory. We use published results as well as new observations of
CH<SUP>+</SUP> towards W3 IRS5. Molecular column densities are derived
from ground state absorption lines, radiative transfer modeling or
rotational diagrams. Models assuming no internal FUV are compared with
two-dimensional models including FUV irradiation of outflow walls. We
confirm that the effect of FUV is clearly noticeable and greatly
improves the fit. The most sensitive molecules to FUV irradiation are
CH<SUP>+</SUP> and OH<SUP>+</SUP>, enhanced in abundance by many orders
of magnitude. Modeling in addition also full line radiative transfer,
Bruderer et al. (2010b) achieve good agreement of a two-dimensional
FUV model with observations of CH<SUP>+</SUP> in AFGL 2591. It is
concluded that CH<SUP>+</SUP> and OH<SUP>+</SUP> are good FUV tracers
in star-forming regions.
---------------------------------------------------------
Title: High-resolution Imaging of Solar Flare Ribbons and Its
Implication on the Thick-target Beam Model
Authors: Krucker, Säm; Hudson, H. S.; Jeffrey, N. L. S.; Battaglia,
M.; Kontar, E. P.; Benz, A. O.; Csillaghy, A.; Lin, R. P.
2011ApJ...739...96K Altcode:
We report on high-resolution optical and hard X-ray observations of
solar flare ribbons seen during the GOES X6.5 class white-light flare
of 2006 December 6. The data consist of imaging observations at 430 nm
(the Fraunhofer G band) taken by the Hinode Solar Optical Telescope
with the hard X-rays observed by the Reuven Ramaty High Energy Solar
Spectroscopic Imager. The two sets of data show closely similar ribbon
structures, strongly suggesting that the flare emissions in white light
and in hard X-rays have physically linked emission mechanisms. While
the source structure along the ribbons is resolved at both wavelengths
(length ~ 30”), only the G-band observations resolve the width of the
ribbon, with values between ~0farcs5 and ~1farcs8. The unresolved
hard X-ray observations reveal an even narrower ribbon in hard
X-rays (the main footpoint has a width perpendicular to the ribbon
of <1farcs1 compared to the G-band width of ~1farcs8) suggesting
that the hard X-ray emission comes from the sharp leading edge of
the G-band ribbon. Applying the thick-target beam model, the derived
energy deposition rate is >5 × 10<SUP>12</SUP> erg s<SUP>-1</SUP>
cm<SUP>-2</SUP> provided by an electron flux of 1 × 10<SUP>20</SUP>
electrons s<SUP>-1</SUP> cm<SUP>-2</SUP> above 18 keV. This requires
that the beam density of electrons above 18 keV be at least 1 ×
10<SUP>10</SUP> cm<SUP>-3</SUP>. Even if field lines converge toward
the chromospheric footpoints, the required beam in the corona has too
high a density to be described as a dilute tail population on top of
a Maxwellian core. We discuss this issue and others associated with
this extreme event, which poses serious questions to the standard
thick target beam interpretation of solar flares.
---------------------------------------------------------
Title: Recent Advances in Understanding Particle Acceleration
Processes in Solar Flares
Authors: Zharkova, V. V.; Arzner, K.; Benz, A. O.; Browning, P.;
Dauphin, C.; Emslie, A. G.; Fletcher, L.; Kontar, E. P.; Mann, G.;
Onofri, M.; Petrosian, V.; Turkmani, R.; Vilmer, N.; Vlahos, L.
2011SSRv..159..357Z Altcode: 2011SSRv..tmp..156Z; 2011SSRv..tmp..249Z; 2011SSRv..tmp..232Z;
2011arXiv1110.2359Z; 2011SSRv..tmp..278Z
We review basic theoretical concepts in particle acceleration,
with particular emphasis on processes likely to occur in regions of
magnetic reconnection. Several new developments are discussed, including
detailed studies of reconnection in three-dimensional magnetic field
configurations (e.g., current sheets, collapsing traps, separatrix
regions) and stochastic acceleration in a turbulent environment. Fluid,
test-particle, and particle-in-cell approaches are used and results
compared. While these studies show considerable promise in accounting
for the various observational manifestations of solar flares, they
are limited by a number of factors, mostly relating to available
computational power. Not the least of these issues is the need to
explicitly incorporate the electrodynamic feedback of the accelerated
particles themselves on the environment in which they are accelerated. A
brief prognosis for future advancement is offered.
---------------------------------------------------------
Title: The Relationship Between Solar Radio and Hard X-ray Emission
Authors: White, S. M.; Benz, A. O.; Christe, S.; Fárník, F.; Kundu,
M. R.; Mann, G.; Ning, Z.; Raulin, J. -P.; Silva-Válio, A. V. R.;
Saint-Hilaire, P.; Vilmer, N.; Warmuth, A.
2011SSRv..159..225W Altcode: 2011SSRv..tmp..263W; 2011SSRv..tmp..244W; 2011SSRv..tmp..164W;
2011arXiv1109.6629W; 2011SSRv..tmp...88W
This review discusses the complementary relationship between radio
and hard X-ray observations of the Sun using primarily results from
the era of the Reuven Ramaty High Energy Solar Spectroscopic Imager
satellite. A primary focus of joint radio and hard X-ray studies of
solar flares uses observations of nonthermal gyrosynchrotron emission
at radio wavelengths and bremsstrahlung hard X-rays to study the
properties of electrons accelerated in the main flare site, since
it is well established that these two emissions show very similar
temporal behavior. A quantitative prescription is given for comparing
the electron energy distributions derived separately from the two
wavelength ranges: this is an important application with the potential
for measuring the magnetic field strength in the flaring region, and
reveals significant differences between the electrons in different
energy ranges. Examples of the use of simultaneous data from the two
wavelength ranges to derive physical conditions are then discussed,
including the case of microflares, and the comparison of images at
radio and hard X-ray wavelengths is presented. There have been puzzling
results obtained from observations of solar flares at millimeter
and submillimeter wavelengths, and the comparison of these results
with corresponding hard X-ray data is presented. Finally, the review
discusses the association of hard X-ray releases with radio emission at
decimeter and meter wavelengths, which is dominated by plasma emission
(at lower frequencies) and electron cyclotron maser emission (at
higher frequencies), both coherent emission mechanisms that require
small numbers of energetic electrons. These comparisons show broad
general associations but detailed correspondence remains more elusive.
---------------------------------------------------------
Title: Herschel Measurements of Molecular Oxygen in Orion
Authors: Goldsmith, Paul F.; Liseau, René; Bell, Tom A.; Black, John
H.; Chen, Jo-Hsin; Hollenbach, David; Kaufman, Michael J.; Li, Di; Lis,
Dariusz C.; Melnick, Gary; Neufeld, David; Pagani, Laurent; Snell,
Ronald; Benz, Arnold O.; Bergin, Edwin; Bruderer, Simon; Caselli,
Paola; Caux, Emmanuel; Encrenaz, Pierre; Falgarone, Edith; Gerin,
Maryvonne; Goicoechea, Javier R.; Hjalmarson, Åke; Larsson, Bengt;
Le Bourlot, Jacques; Le Petit, Franck; De Luca, Massimo; Nagy, Zsofia;
Roueff, Evelyne; Sandqvist, Aage; van der Tak, Floris; van Dishoeck,
Ewine F.; Vastel, Charlotte; Viti, Serena; Yıldız, Umut
2011ApJ...737...96G Altcode: 2011arXiv1108.0441G
We report observations of three rotational transitions of molecular
oxygen (O<SUB>2</SUB>) in emission from the H<SUB>2</SUB> Peak 1
position of vibrationally excited molecular hydrogen in Orion. We
observed the 487 GHz, 774 GHz, and 1121 GHz lines using the Heterodyne
Instrument for the Far Infrared on the Herschel Space Observatory,
having velocities of 11 km s<SUP>-1</SUP> to 12 km s<SUP>-1</SUP>
and widths of 3 km s<SUP>-1</SUP>. The beam-averaged column density is
N(O<SUB>2</SUB>) = 6.5 × 10<SUP>16</SUP> cm<SUP>-2</SUP>, and assuming
that the source has an equal beam-filling factor for all transitions
(beam widths 44, 28, and 19”), the relative line intensities
imply a kinetic temperature between 65 K and 120 K. The fractional
abundance of O<SUB>2</SUB> relative to H<SUB>2</SUB> is (0.3-7.3) ×
10<SUP>-6</SUP>. The unusual velocity suggests an association with a
~5” diameter source, denoted Peak A, the Western Clump, or MF4. The
mass of this source is ~10 M <SUB>sun</SUB> and the dust temperature
is >=150 K. Our preferred explanation of the enhanced O<SUB>2</SUB>
abundance is that dust grains in this region are sufficiently warm (T
>= 100 K) to desorb water ice and thus keep a significant fraction
of elemental oxygen in the gas phase, with a significant fraction
as O<SUB>2</SUB>. For this small source, the line ratios require a
temperature >=180 K. The inferred O<SUB>2</SUB> column density
sime5 × 10<SUP>18</SUP> cm<SUP>-2</SUP> can be produced in Peak A,
having N(H<SUB>2</SUB>) ~= 4 × 10<SUP>24</SUP> cm<SUP>-2</SUP>. An
alternative mechanism is a low-velocity (10-15 km s<SUP>-1</SUP>)
C-shock, which can produce N(O<SUB>2</SUB>) up to 10<SUP>17</SUP>
cm<SUP>-2</SUP>. <P />Herschel is an ESA space observatory with science
instruments provided by European-led Principal Investigator consortia
and with important participation from NASA.
---------------------------------------------------------
Title: First hyperfine resolved far-infrared OH spectrum from a
star-forming region
Authors: Wampfler, S. F.; Bruderer, S.; Kristensen, L. E.; Chavarría,
L.; Bergin, E. A.; Benz, A. O.; van Dishoeck, E. F.; Herczeg, G. J.;
van der Tak, F. F. S.; Goicoechea, J. R.; Doty, S. D.; Herpin, F.
2011A&A...531L..16W Altcode: 2011arXiv1105.5026W
OH is an important molecule in the H<SUB>2</SUB>O chemistry and the
cooling budget of star-forming regions. The goal of the Herschel key
program "Water In Star-forming regions with Herschel" (WISH) is to study
H<SUB>2</SUB>O and related species during protostellar evolution. Our
aim in this Letter is to assess the origin of the OH emission from
star-forming regions and constrain the properties of the emitting
gas. High-resolution observations of the OH {^2Π<SUB>1/2</SUB> J =
3/2-1/2 } triplet at 1837.8 GHz (163.1 μm) towards the high-mass
star-forming region W3 IRS 5 with the Heterodyne Instrument for
the Far-Infrared (HIFI) on Herschel reveal the first hyperfine
velocity-resolved OH far-infrared spectrum of a star-forming
region. The line profile of the OH emission shows two components:
a narrow component (FWHM ≈ 4-5 km s<SUP>-1</SUP>) with partially
resolved hyperfine structure resides on top of a broad (FWHM ≈ 30 km
s<SUP>-1</SUP>) component. The narrow emission agrees well with results
from radiative transfer calculations of a spherical envelope model
for W3 IRS 5 with a constant OH abundance of x<SUB>OH</SUB> ≈ 8 ×
10<SUP>-9</SUP>. Comparison with H<SUB>2</SUB>O yields OH/H<SUB>2</SUB>O
abundance ratios of around 10<SUP>-3</SUP> for T ≳ 100 K and around
unity for T ≲ 100 K, consistent with the current picture of the
dense cloud chemistry with freeze-out and photodesorption. The broad
component is attributed to outflow emission. An abundance ratio of
OH/H<SUB>2</SUB>O ≳ 0.028 in the outflow is derived from comparison
with results of water line modeling. This ratio can be explained by a
fast J-type shock or a slower UV-irradiated C-type shock. <P />Herschel
is an ESA space observatory with science instruments provided by
European-led Principal Investigator consortia and with important
participation from NASA.Appendices are available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Tracing X-ray and FUV Radiation in the Embedded Phase of
Star Formation
Authors: Benz, A. O.; Bruderer, S.; Wampfler, S. F.; Dedes, C.;
van Dishoeck, E. F.
2011IAUS..280P..91B Altcode: 2011arXiv1101.1746B
Molecules containing one (or a few) hydrogen atoms and one heavier
atom (hydrides) are predicted to trace ionizing FUV radiation. In some
chemical models, FUV emission by the central object or protostar of a
star forming region greatly enhances the abundance of some hydrides. Two
massive regions, W3 IRS5 and AFGL 2591, have been observed in hydride
lines by HIFI onboard the Herschel Space Observatory. They both
have Ultra Compact HII regions, indicating the presence of FUV. We
derive molecular column densities from ground state absorption lines,
radiative transfer modeling and/or rotational diagrams. Models assuming
no internal FUV are compared with two-dimensional models including
FUV irradiation of outflow walls. The most sensitive molecules to
FUV irradiation are CH^+, OH^+, SH^+, and NH^+. They are enhanced in
abundance by many orders of magnitude. We confirm that the effect of
FUV is clearly noticeable and greatly improves the fit of observations
with theory (see figure). Modeling in addition also full line radiative
transfer, we report good agreement of a two-dimensional FUV model with
line observations of CH^+ in AFGL 2591. It is concluded that CH^+ and
OH^+ are good and abundant FUV tracers in star-forming regions. Having
confirmed the tracer molecules in cases with known FUV radiation,
we search for that radiation in cases where FUV irradiation is
questionable, such as younger stellar objects and lower mass objects. We
report the results of new Herschel observations of CH^+, OH^+, and CH
in 5 massive YSOs of different age, in 6 low-mass objects of class 0
and I, and an intermediate-mass source. The observations are compared
with chemical and radiative transfer models. For nearby low-mass
YSOs, we discuss also the possibility to indentify protostellar
X-ray irradiation. The conclusion is that high-energy irradiation
has started in all objects observed, thus at a very early phase of
star formation. Its impact on star and planet formation needs to
be investigated.
---------------------------------------------------------
Title: Studying cooling mechanisms in the massive star forming region
IRAS 12326-6245
Authors: Dedes, C.; Herpin, F.; Chavarria, L.; Wampfler, S.;
Wyrowski, F.; van der Tak, F.; Benz, A.; Bruderer, D.; Polehampton,
E.; Melchior, M.
2011IAUS..280P.149D Altcode:
The strong feedback processes of massive stars influence the surrounding
ISM both locally and on large scales. An important question to be
answered is the one of cooling and heating in massive star forming
regions. There, heating is provided mostly by far-UV (FUV) and infra-red
radiation. Cooling is mostly provided by emission in the fine structure
lines of [CII] and [OI]. There are, however, molecular lines such as
CO, OH and H_2O which can become significant coolants in the dense,
embedded regions. To understand the heating and cooling balance, one
has to consider the contributions of various radiative and dynamical
processes such as FUV radiation, shocks, and the PDRs where the
radiation impinges on the molecular material. The tracers of these
processes can be observed in the far-infrared, a wavelength range that
is now accessible at unprecedented high spectral and spatial resolution
with the Herschel Space Observatory. Our approved 3 hour Herschel GT
project was designed to cover all the major coolants in one massive
star forming region, IRAS 12326-6245. H_2O and [CII] were obtained at
high spectral resolution with HIFI, [OI] and OH lines will be observed
with PACS and the CO ladder with SPIRE. This luminous, massive, region,
located at 4.4 kpc, contains a hot core inside a ∼ 1600M<SUB>⊙</SUB>
dust envelope and has one of the most massive outflows observed (Dedes
et al. 2011). In this contribution, we will present first results of the
radiative transfer modeling of the continuum emission, the H_2O lines
modeling, and the derivation of physical conditions of the gas obtained
from CH_3OH, <SUP>13</SUP>CO and C<SUP>18</SUP>O lines. Despite its
apparent simplicity in the ground based CO line profiles, Herschel
observations of the source show a complicated velocity structure
in the water lines, with many lines contributing to absorption from
foreground clouds. High spectral resolution measurements from CH^+
and H_2O^+ are used to assign the velocity components to the source
and foreground material.
---------------------------------------------------------
Title: First hyperfine structure resolved OH FIR spectrum of a
star-forming region
Authors: Wampfler, S. F.; Bruderer, S.; Kristensen, L. E.; Bergin,
E. A.; Benz, A. O.; van Dishoeck, E. F.; Herczeg, G. J.; van der Tak,
F. F. S.; Goicoechea, J. R.; Doty, S. D.; Herpin, F.
2011IAUS..280P.380W Altcode:
Embedded protostars interact with their natal cloud through shocks
and irradiation. The ambient interstellar medium warms up, allowing
icy grain mantles to evaporate and making different chemical routes in
the gas phase available. Water then becomes one of the most abundant
molecular species in the gas phase. The Herschel key program `Water
in Star-Forming Regions with Herschel (WISH)' studies the excitation
and chemistry of water around protostars. Hydroxyl (OH) is of the
cornerstone species in the water chemistry network, because it is
closely linked to both the formation and destruction of water through
the OH + H2 leftrightarrow H2O + H reactions and photodissociation
processes. This poster presents the first OH observation with
resolved hyperfine structure at 163 μm of a star-forming region
obtained using HIFI on Herschel. The OH triplet from the high-mass
star-forming region W3 IRS5 is in emission, with the line profile
revealing a narrow component on top of a broad feature. The broad
component is attributed to outflow emission based on comparison with
molecular lines of other species, whereas the narrow component is in
agreement with radiative transfer results for a spherically symmetric
envelope model. The resolved hyperfine structure allows us to constrain
the excitation temperature and the OH column density in our models
simultaneously. The derived OH/H2O ratios in the envelope are consistent
with the current picture of the water chemistry. In the outer envelope
(T < 100 K), where OH and H2O are released into the gas phase by
photodesorption from the ice mantles of dust grains, we find a ratio of
about unity. Laboratory work by Öberg et al. (2009) demonstrated that
similar amounts of OH and water are released with an expected OH/H2O
ratio of 0.5-1. This ratio is also in agreement with the theoretical
work by Andersson & van Dishoeck (2008). In the inner envelope (T
> 100 K), water is efficiently formed from OH and the OH/H2O ratio
is therefore expected to drop significantly, which is consistent with
the derived value of the order of 10<SUP>-4</SUP>. For the outflow,
a lower limit of OH/H2O > 0.025 is obtained and can be explained
with either a fast J-type shock or a slower UV irradiated C-type shock.
---------------------------------------------------------
Title: Water in Star-forming Regions with the Herschel Space
Observatory (WISH). I. Overview of Key Program and First Results
Authors: van Dishoeck, E. F.; Kristensen, L. E.; Benz, A. O.; Bergin,
E. A.; Caselli, P.; Cernicharo, J.; Herpin, F.; Hogerheijde, M. R.;
Johnstone, D.; Liseau, R.; Nisini, B.; Shipman, R.; Tafalla, M.; van
der Tak, F.; Wyrowski, F.; Aikawa, Y.; Bachiller, R.; Baudry, A.;
Benedettini, M.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine,
J.; Brinch, C.; Bruderer, S.; Chavarría, L.; Codella, C.; Daniel, F.;
de Graauw, Th.; Deul, E.; di Giorgio, A. M.; Dominik, C.; Doty, S. D.;
Dubernet, M. L.; Encrenaz, P.; Feuchtgruber, H.; Fich, M.; Frieswijk,
W.; Fuente, A.; Giannini, T.; Goicoechea, J. R.; Helmich, F. P.;
Herczeg, G. J.; Jacq, T.; Jørgensen, J. K.; Karska, A.; Kaufman,
M. J.; Keto, E.; Larsson, B.; Lefloch, B.; Lis, D.; Marseille, M.;
McCoey, C.; Melnick, G.; Neufeld, D.; Olberg, M.; Pagani, L.; Panić,
O.; Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Salter, D.;
Santiago-García, J.; Saraceno, P.; Stäuber, P.; van Kempen, T. A.;
Visser, R.; Viti, S.; Walmsley, M.; Wampfler, S. F.; Yıldız, U. A.
2011PASP..123..138V Altcode: 2010arXiv1012.4570V
Water In Star-forming regions with Herschel (WISH) is a key program
on the Herschel Space Observatory designed to probe the physical and
chemical structures of young stellar objects using water and related
molecules and to follow the water abundance from collapsing clouds
to planet-forming disks. About 80 sources are targeted, covering a
wide range of luminosities—from low (< 1 L<SUB>⊙</SUB>) to high
(>10<SUP>5</SUP> L<SUB>⊙</SUB>)—and a wide range of evolutionary
stages—from cold prestellar cores to warm protostellar envelopes
and outflows to disks around young stars. Both the HIFI and PACS
instruments are used to observe a variety of lines of H<SUB>2</SUB>O,
H<SUB>2</SUB><SUP>18</SUP>O and chemically related species at the source
position and in small maps around the protostars and selected outflow
positions. In addition, high-frequency lines of CO, <SUP>13</SUP>CO,
and C<SUP>18</SUP>O are obtained with Herschel and are complemented
by ground-based observations of dust continuum, HDO, CO and its
isotopologs, and other molecules to ensure a self-consistent data set
for analysis. An overview of the scientific motivation and observational
strategy of the program is given, together with the modeling approach
and analysis tools that have been developed. Initial science results are
presented. These include a lack of water in cold gas at abundances that
are lower than most predictions, strong water emission from shocks in
protostellar environments, the importance of UV radiation in heating
the gas along outflow walls across the full range of luminosities,
and surprisingly widespread detection of the chemically related
hydrides OH<SUP>+</SUP> and H<SUB>2</SUB>O<SUP>+</SUP> in outflows and
foreground gas. Quantitative estimates of the energy budget indicate
that H<SUB>2</SUB>O is generally not the dominant coolant in the warm
dense gas associated with protostars. Very deep limits on the cold
gaseous water reservoir in the outer regions of protoplanetary disks
are obtained that have profound implications for our understanding of
grain growth and mixing in disks.
---------------------------------------------------------
Title: Heating of the quiet solar corona from measurements of the
FET/TESIS instrument on-board the KORONAS-FOTON satellite
Authors: Rybák, J.; Gömöry, P.; Benz, A.; Bogachev, P.; Brajša, R.
2010nspm.conf..107R Altcode:
The paper presents the first results of the observations of time
evolution of the quiet solar corona brightenings obtained due to
very rapid photography of the corona with full-disk EUV telescopes
of the FET/TESIS instrument onboard the KORONA FOTON satellite. The
measurements were performed simultaneously in the emission of the Fe
IX / X 17.1 and Fe VIII 13.1 spectral lines with 10 second temporal
cadence and spatial scale of 1.7 arc seconds within one hour. This
test observation, carried out on 15 July 2009, was analyzed in order
to determine whether this type of observation can be used to identify
individual microevents in the solar corona heating that are above the
tresholds of spatial and temporal resolutions of the observations
of non-active regions in the solar atmosphere. For this purpose,
a simple method was used involving cross-correlation of the plasma
emission time evolution at different temperatures, each time from
observations of identical elements. The results obtained are confronted
with the expected observable manifestations of the corona heating
via nanoflares. TESIS is a set of instruments for the Sun photography
developed in the Lebedev Physics Institute of the Russian Academy of
Sciences that was launched into orbit in January 2009.
---------------------------------------------------------
Title: Star-forming Dense Cloud Cores in the TeV Gamma-ray SNR
RX J1713.7-3946
Authors: Sano, H.; Sato, J.; Horachi, H.; Moribe, N.; Yamamoto, H.;
Hayakawa, T.; Torii, K.; Kawamura, A.; Okuda, T.; Mizuno, N.; Onishi,
T.; Maezawa, H.; Inoue, T.; Inutsuka, S.; Tanaka, T.; Matsumoto,
H.; Mizuno, A.; Ogawa, H.; Stutzki, J.; Bertoldi, F.; Anderl, S.;
Bronfman, L.; Koo, B. -C.; Burton, M. G.; Benz, A. O.; Fukui, Y.
2010ApJ...724...59S Altcode: 2010arXiv1005.3409S
RX J1713.7-3946 is one of the TeV γ-ray supernova remnants (SNRs)
emitting synchrotron X-rays. The SNR is associated with molecular gas
located at ~1 kpc. We made new molecular observations toward the dense
cloud cores, peaks A, C, and D, in the SNR in the <SUP>12</SUP>CO(J
= 2-1) and <SUP>13</SUP>CO(J = 2-1) transitions at an angular
resolution of 90”. The most intense core in <SUP>13</SUP>CO, peak
C, was also mapped in the <SUP>12</SUP>CO(J = 4-3) transition at an
angular resolution of 38”. Peak C shows strong signs of active star
formation including bipolar outflow and a far-infrared protostellar
source, and has a steep gradient with a r <SUP>-2.2±0.4</SUP>
variation in the average density within radius r. Peak C and the
other dense cloud cores are rim-brightened in synchrotron X-rays,
suggesting that the dense cloud cores are embedded within or on the
outer boundary of the SNR shell. This confirms the earlier suggestion
that the X-rays are physically associated with the molecular gas. We
present a scenario where the densest molecular core, peak C, survived
the blast wave and is now embedded within the SNR. Numerical simulations
of the shock-cloud interaction indicate that a dense clump can indeed
survive shock erosion, since the shock propagation speed is stalled
in the dense clump. Additionally, the shock-cloud interaction induces
turbulence and magnetic field amplification around the dense clump that
may facilitate particle acceleration in the lower-density inter-clump
space leading to enhanced synchrotron X-rays around dense cores.
---------------------------------------------------------
Title: Herschel/HIFI detections of hydrides towards AFGL
2591. Envelope emission versus tenuous cloud absorption
Authors: Bruderer, S.; Benz, A. O.; van Dishoeck, E. F.; Melchior, M.;
Doty, S. D.; van der Tak, F.; Stäuber, P.; Wampfler, S. F.; Dedes,
C.; Yıldız, U. A.; Pagani, L.; Giannini, T.; de Graauw, Th.; Whyborn,
N.; Teyssier, D.; Jellema, W.; Shipman, R.; Schieder, R.; Honingh, N.;
Caux, E.; Bächtold, W.; Csillaghy, A.; Monstein, C.; Bachiller, R.;
Baudry, A.; Benedettini, M.; Bergin, E.; Bjerkeli, P.; Blake, G. A.;
Bontemps, S.; Braine, J.; Caselli, P.; Cernicharo, J.; Codella, C.;
Daniel, F.; di Giorgio, A. M.; Dominik, C.; Encrenaz, P.; Fich, M.;
Fuente, A.; Goicoechea, J. R.; Helmich, F.; Herczeg, G. J.; Herpin,
F.; Hogerheijde, M. R.; Jacq, T.; Johnstone, D.; Jørgensen, J. K.;
Kristensen, L. E.; Larsson, B.; Lis, D.; Liseau, R.; Marseille, M.;
McCoey, C.; Melnick, G.; Neufeld, D.; Nisini, B.; Olberg, M.; Parise,
B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García, J.;
Saraceno, P.; Shipman, R.; Tafalla, M.; van Kempen, T. A.; Visser,
R.; Wyrowski, F.
2010A&A...521L..44B Altcode: 2010arXiv1007.3408B
The Heterodyne Instrument for the Far Infrared (HIFI) onboard
the Herschel Space Observatory allows the first observations
of light diatomic molecules at high spectral resolution and in
multiple transitions. Here, we report deep integrations using HIFI
in different lines of hydrides towards the high-mass star forming
region AFGL 2591. Detected are CH, CH<SUP>+</SUP>, NH, OH<SUP>+</SUP>,
H<SUB>2</SUB>O<SUP>+</SUP>, while NH<SUP>+</SUP> and SH<SUP>+</SUP>
have not been detected. All molecules except for CH and CH<SUP>+</SUP>
are seen in absorption with low excitation temperatures and at
velocities different from the systemic velocity of the protostellar
envelope. Surprisingly, the CH(J<SUB>F,P</SUB> = 3/2<SUB>2,-</SUB>
- 1/2<SUB>1,+</SUB> ) and CH<SUP>+</SUP>(J = 1-0, J = 2-1) lines
are detected in emission at the systemic velocity. We can assign the
absorption features to a foreground cloud and an outflow lobe, while the
CH and CH<SUP>+</SUP> emission stems from the envelope. The observed
abundance and excitation of CH and CH<SUP>+</SUP> can be explained in
the scenario of FUV irradiated outflow walls, where a cavity etched out
by the outflow allows protostellar FUV photons to irradiate and heat
the envelope at larger distances driving the chemical reactions that
produce these molecules. <P />Herschel is an ESA space observatory with
science instruments provided by European-led Principal Investigator
consortia and with important participation from NASA.Apppendices and
Table 1 (pages 6 to 7) are only available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: The origin of the [C II] emission in the S140 photon-dominated
regions. New insights from HIFI
Authors: Dedes, C.; Röllig, M.; Mookerjea, B.; Okada, Y.; Ossenkopf,
V.; Bruderer, S.; Benz, A. O.; Melchior, M.; Kramer, C.; Gerin, M.;
Güsten, R.; Akyilmaz, M.; Berne, O.; Boulanger, F.; de Lange, G.;
Dubbeldam, L.; France, K.; Fuente, A.; Goicoechea, J. R.; Harris,
A.; Huisman, R.; Jellema, W.; Joblin, C.; Klein, T.; Le Petit, F.;
Lord, S.; Martin, P.; Martin-Pintado, J.; Neufeld, D. A.; Philipp,
S.; Phillips, T.; Pilleri, P.; Rizzo, J. R.; Salez, M.; Schieder, R.;
Simon, R.; Siebertz, O.; Stutzki, J.; van der Tak, F.; Teyssier, D.;
Yorke, H.
2010A&A...521L..24D Altcode: 2010arXiv1007.4957D
Using Herschel's HIFI instrument, we observe C ii along a cut through
S140, as well as high-J transitions of CO and HCO<SUP>+</SUP> at
two positions on the cut, corresponding to the externally irradiated
ionization front and the embedded massive star-forming core IRS1. The
HIFI data were combined with available ground-based observations
and modeled using the KOSMA-τ model for photon-dominated regions
(PDRs). We derive the physical conditions in S140 and in particular
the origin of C ii emission around IRS1. We identify three distinct
regions of C ii emission from the cut, one close to the embedded source
IRS1, one associated with the ionization front, and one further into
the cloud. The line emission can be understood in terms of a clumpy
model of PDRs. At the position of IRS1, we identify at least two
distinct components contributing to the [C ii] emission, one of them
a small, hot component, which can possibly be identified with the
irradiated outflow walls. This is consistent with the C ii peak at
IRS1 coinciding with shocked H<SUB>2</SUB> emission at the edges of
the outflow cavity. We note that previously available observations of
IRS1 can be reproduced well by a single-component KOSMA-τ model. Thus,
it is HIFI's unprecedented spatial and spectral resolution, as well as
its sensitivity that has allowed us to uncover an additional hot gas
component in the S140 region. <P />Herschel is an ESA space observatory
with science instruments provided by European-led Principal Investigator
consortia and with important participation from NASA.Acknowledgements
and appendices (pages 5 to 7) are only available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Hydrides in young stellar objects: Radiation tracers in a
protostar-disk-outflow system
Authors: Benz, A. O.; Bruderer, S.; van Dishoeck, E. F.; Stäuber,
P.; Wampfler, S. F.; Melchior, M.; Dedes, C.; Wyrowski, F.; Doty,
S. D.; van der Tak, F.; Bächtold, W.; Csillaghy, A.; Megej, A.;
Monstein, C.; Soldati, M.; Bachiller, R.; Baudry, A.; Benedettini,
M.; Bergin, E.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine, J.;
Caselli, P.; Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio,
A. M.; Dieleman, P.; Dominik, C.; Encrenaz, P.; Fich, M.; Fuente,
A.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.;
Herczeg, G. J.; Herpin, F.; Hogerheijde, M. R.; Jacq, T.; Jellema,
W.; Johnstone, D.; Jørgensen, J. K.; Kristensen, L. E.; Larsson, B.;
Lis, D.; Liseau, R.; Marseille, M.; McCoey, C.; Melnick, G.; Neufeld,
D.; Nisini, B.; Olberg, M.; Ossenkopf, V.; Parise, B.; Pearson,
J. C.; Plume, R.; Risacher, C.; Santiago-García, J.; Saraceno,
P.; Schieder, R.; Shipman, R.; Stutzki, J.; Tafalla, M.; Tielens,
A. G. G. M.; van Kempen, T. A.; Visser, R.; Yıldız, U. A.
2010A&A...521L..35B Altcode: 2010arXiv1007.3370B
Context. Hydrides of the most abundant heavier elements are fundamental
molecules in cosmic chemistry. Some of them trace gas irradiated by
UV or X-rays. <BR /> Aims: We explore the abundances of major hydrides
in W3 IRS5, a prototypical region of high-mass star formation. <BR />
Methods: W3 IRS5 was observed by HIFI on the Herschel Space Observatory
with deep integration (≃2500 s) in 8 spectral regions. <BR />
Results: The target lines including CH, NH, H<SUB>3</SUB>O<SUP>+</SUP>,
and the new molecules SH<SUP>+</SUP>, H<SUB>2</SUB>O<SUP>+</SUP>,
and OH<SUP>+</SUP> are detected. The H<SUB>2</SUB>O<SUP>+</SUP>
and OH<SUP>+</SUP> J = 1-0 lines are found mostly in absorption, but
also appear to exhibit weak emission (P-Cyg-like). Emission requires
high density, thus originates most likely near the protostar. This
is corroborated by the absence of line shifts relative to the young
stellar object (YSO). In addition, H<SUB>2</SUB>O<SUP>+</SUP> and
OH<SUP>+</SUP> also contain strong absorption components at a velocity
shifted relative to W3 IRS5, which are attributed to foreground
clouds. <BR /> Conclusions: The molecular column densities derived
from observations correlate well with the predictions of a model
that assumes the main emission region is in outflow walls, heated
and irradiated by protostellar UV radiation. <P />Herschel is an ESA
space observatory with science instruments provided by a European-led
Principal Investigator consortia and with important participation
from NASA.Appendix (page 5) is only available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Water vapor toward starless cores: The Herschel view
Authors: Caselli, P.; Keto, E.; Pagani, L.; Aikawa, Y.; Yıldız,
U. A.; van der Tak, F. F. S.; Tafalla, M.; Bergin, E. A.; Nisini,
B.; Codella, C.; van Dishoeck, E. F.; Bachiller, R.; Baudry, A.;
Benedettini, M.; Benz, A. O.; Bjerkeli, P.; Blake, G. A.; Bontemps,
S.; Braine, J.; Bruderer, S.; Cernicharo, J.; Daniel, F.; di Giorgio,
A. M.; Dominik, C.; Doty, S. D.; Encrenaz, P.; Fich, M.; Fuente, A.;
Gaier, T.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich,
F.; Herczeg, G. J.; Herpin, F.; Hogerheijde, M. R.; Jackson, B.;
Jacq, T.; Javadi, H.; Johnstone, D.; Jørgensen, J. K.; Kester,
D.; Kristensen, L. E.; Laauwen, W.; Larsson, B.; Lis, D.; Liseau,
R.; Luinge, W.; Marseille, M.; McCoey, C.; Megej, A.; Melnick,
G.; Neufeld, D.; Olberg, M.; Parise, B.; Pearson, J. C.; Plume, R.;
Risacher, C.; Santiago-García, J.; Saraceno, P.; Shipman, R.; Siegel,
P.; van Kempen, T. A.; Visser, R.; Wampfler, S. F.; Wyrowski, F.
2010A&A...521L..29C Altcode: 2010arXiv1007.1248C
<BR /> Aims: Previous studies by the satellites SWAS and Odin
provided stringent upper limits on the gas phase water abundance
of dark clouds (x(H<SUB>2</SUB>O) < 7 × 10<SUP>-9</SUP>). We
investigate the chemistry of water vapor in starless cores beyond the
previous upper limits using the highly improved angular resolution
and sensitivity of Herschel and measure the abundance of water vapor
during evolutionary stages just preceding star formation. <BR />
Methods: High spectral resolution observations of the fundamental
ortho water (o-H<SUB>2</SUB>O) transition (557 GHz) were carried
out with the Heterodyne Instrument for the Far Infrared onboard
Herschel toward two starless cores: Barnard 68 (hereafter B68),
a Bok globule, and LDN 1544 (L1544), a prestellar core embedded
in the Taurus molecular cloud complex. Detailed radiative transfer
and chemical codes were used to analyze the data. <BR /> Results:
The RMS in the brightness temperature measured for the B68 and L1544
spectra is 2.0 and 2.2 mK, respectively, in a velocity bin of 0.59 km
s<SUP>-1</SUP>. The continuum level is 3.5 ± 0.2 mK in B68 and 11.4
± 0.4 mK in L1544. No significant feature is detected in B68 and the
3σ upper limit is consistent with a column density of o-H<SUB>2</SUB>O
N(o-H<SUB>2</SUB>O) < 2.5 × 10<SUP>13</SUP> cm<SUP>-2</SUP>, or a
fractional abundance x(o-H<SUB>2</SUB>O) < 1.3 × 10<SUP>-9</SUP>,
more than an order of magnitude lower than the SWAS upper limit on this
source. The L1544 spectrum shows an absorption feature at a 5σ level
from which we obtain the first value of the o-H<SUB>2</SUB>O column
density ever measured in dark clouds: N(o-H<SUB>2</SUB>O) = (8 ± 4) ×
10<SUP>12</SUP> cm<SUP>-2</SUP>. The corresponding fractional abundance
is x(o-H<SUB>2</SUB>O) ≃ 5 × 10<SUP>-9</SUP> at radii >7000 AU
and ≃2 × 10<SUP>-10</SUP> toward the center. The radiative transfer
analysis shows that this is consistent with a x(o-H<SUB>2</SUB>O)
profile peaking at ≃10<SUP>-8</SUP>, 0.1 pc away from the core center,
where both freeze-out and photodissociation are negligible. <BR />
Conclusions: Herschel has provided the first measurement of water
vapor in dark regions. Column densities of o-H<SUB>2</SUB>O are low,
but prestellar cores such as L1544 (with their high central densities,
strong continuum, and large envelopes) appear to be very promising
tools to finally shed light on the solid/vapor balance of water in
molecular clouds and oxygen chemistry in the earliest stages of star
formation. <P />Herschel is an ESA space observatory with science
instruments provided by European-led Principal Investigator consortia
and with important participation from NASA.
---------------------------------------------------------
Title: Herschel/HIFI spectroscopy of the intermediate mass protostar
NGC 7129 FIRS 2
Authors: Johnstone, D.; Fich, M.; McCoey, C.; van Kempen, T. A.;
Fuente, A.; Kristensen, L. E.; Cernicharo, J.; Caselli, P.; Visser,
R.; Plume, R.; Herczeg, G. J.; van Dishoeck, E. F.; Wampfler,
S.; Bachiller, R.; Baudry, A.; Benedettini, M.; Bergin, E.; Benz,
A. O.; Bjerkeli, P.; Blake, G.; Bontemps, S.; Braine, J.; Bruderer,
S.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik, C.; Doty,
S. D.; Encrenaz, P.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.;
Helmich, F.; Herpin, F.; Hogerheijde, M. R.; Jacq, T.; Jørgensen,
J. K.; Larsson, B.; Lis, D.; Liseau, R.; Marseille, M.; Melnick, G.;
Neufeld, D.; Nisini, B.; Olberg, M.; Parise, B.; Pearson, J.; Risacher,
C.; Santiago-García, J.; Saraceno, P.; Shipman, R.; Tafalla, M.;
van der Tak, F.; Wyrowski, F.; Yıldız, U. A.; Caux, E.; Honingh,
N.; Jellema, W.; Schieder, R.; Teyssier, D.; Whyborn, N.
2010A&A...521L..41J Altcode: 2010arXiv1008.1254J
Herschel/HIFI observations of water from the intermediate mass protostar
NGC 7129 FIRS 2 provide a powerful diagnostic of the physical conditions
in this star formation environment. Six spectral settings, covering
four H<SUB>2</SUB><SUP>16</SUP>O and two H<SUB>2</SUB><SUP>18</SUP>O
lines, were observed and all but one H<SUB>2</SUB><SUP>18</SUP>O line
were detected. The four H<SUB>2</SUB><SUP>16</SUP>O lines discussed
here share a similar morphology: a narrower, ≈6 km s<SUP>-1</SUP>,
component centered slightly redward of the systemic velocity of NGC
7129 FIRS 2 and a much broader, ≈25 km s<SUP>-1</SUP> component
centered blueward and likely associated with powerful outflows. The
narrower components are consistent with emission from water arising
in the envelope around the intermediate mass protostar, and the
abundance of H<SUB>2</SUB>O is constrained to ≈10<SUP>-7</SUP>
for the outer envelope. Additionally, the presence of a narrow
self-absorption component for the lowest energy lines is likely
due to self-absorption from colder water in the outer envelope. The
broader component, where the H<SUB>2</SUB>O/CO relative abundance is
found to be ≈0.2, appears to be tracing the same energetic region
that produces strong CO emission at high J. <P />Herschel is an ESA
space observatory with science instruments provided by European-led
Principal Investigator consortia and with important participation
from NASA. Appendix (page 6) is only available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Herschel/HIFI discovery of interstellar chloronium
(H<SUB>2</SUB>Cl<SUP>+</SUP>)
Authors: Lis, D. C.; Pearson, J. C.; Neufeld, D. A.; Schilke, P.;
Müller, H. S. P.; Gupta, H.; Bell, T. A.; Comito, C.; Phillips,
T. G.; Bergin, E. A.; Ceccarelli, C.; Goldsmith, P. F.; Blake,
G. A.; Bacmann, A.; Baudry, A.; Benedettini, M.; Benz, A.; Black,
J.; Boogert, A.; Bottinelli, S.; Cabrit, S.; Caselli, P.; Castets,
A.; Caux, E.; Cernicharo, J.; Codella, C.; Coutens, A.; Crimier, N.;
Crockett, N. R.; Daniel, F.; Demyk, K.; Dominic, C.; Dubernet, M. -L.;
Emprechtinger, M.; Encrenaz, P.; Falgarone, E.; Fuente, A.; Gerin,
M.; Giesen, T. F.; Goicoechea, J. R.; Helmich, F.; Hennebelle, P.;
Henning, Th.; Herbst, E.; Hily-Blant, P.; Hjalmarson, Å.; Hollenbach,
D.; Jack, T.; Joblin, C.; Johnstone, D.; Kahane, C.; Kama, M.; Kaufman,
M.; Klotz, A.; Langer, W. D.; Larsson, B.; Le Bourlot, J.; Lefloch,
B.; Le Petit, F.; Li, D.; Liseau, R.; Lord, S. D.; Lorenzani, A.;
Maret, S.; Martin, P. G.; Melnick, G. J.; Menten, K. M.; Morris,
P.; Murphy, J. A.; Nagy, Z.; Nisini, B.; Ossenkopf, V.; Pacheco, S.;
Pagani, L.; Parise, B.; Pérault, M.; Plume, R.; Qin, S. -L.; Roueff,
E.; Salez, M.; Sandqvist, A.; Saraceno, P.; Schlemmer, S.; Schuster,
K.; Snell, R.; Stutzki, J.; Tielens, A.; Trappe, N.; van der Tak,
F. F. S.; van der Wiel, M. H. D.; van Dishoeck, E.; Vastel, C.; Viti,
S.; Wakelam, V.; Walters, A.; Wang, S.; Wyrowski, F.; Yorke, H. W.;
Yu, S.; Zmuidzinas, J.; Delorme, Y.; Desbat, J. -P.; Güsten, R.;
Krieg, J. -M.; Delforge, B.
2010A&A...521L...9L Altcode: 2010arXiv1007.1461L
We report the first detection of chloronium,
H<SUB>2</SUB>Cl<SUP>+</SUP>, in the interstellar
medium, using the HIFI instrument aboard the Herschel
Space Observatory. The 2<SUB>12</SUB>-1<SUB>01</SUB>
lines of ortho-H_2<SUP>35</SUP>Cl<SUP>+</SUP> and
ortho-H_2<SUP>37</SUP>Cl<SUP>+</SUP> are detected in absorption
towards NGC 6334I, and the 1<SUB>11</SUB>-0<SUB>00</SUB> transition
of para-H_2<SUP>35</SUP>Cl<SUP>+</SUP> is detected in absorption
towards NGC 6334I and Sgr B2(S). The H<SUB>2</SUB>Cl<SUP>+</SUP>
column densities are compared to those of the chemically-related
species HCl. The derived HCl/H<SUB>2</SUB>Cl<SUP>+</SUP> column
density ratios, ~1-10, are within the range predicted by models
of diffuse and dense photon dominated regions (PDRs). However,
the observed H<SUB>2</SUB>Cl<SUP>+</SUP> column densities, in
excess of 10<SUP>13</SUP> cm<SUP>-2</SUP>, are significantly
higher than the model predictions. Our observations demonstrate
the outstanding spectroscopic capabilities of HIFI for detecting
new interstellar molecules and providing key constraints for
astrochemical models. <P />Herschel is an ESA space observatory with
science instruments provided by European-led Principal Investigator
consortia and with important participation from NASA.Table 1 and
acknowledgments (page 5) are only available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Water abundances in high-mass protostellar envelopes: Herschel
observations with HIFI
Authors: Marseille, M. G.; van der Tak, F. F. S.; Herpin, F.; Wyrowski,
F.; Chavarría, L.; Pietropaoli, B.; Baudry, A.; Bontemps, S.;
Cernicharo, J.; Jacq, T.; Frieswijk, W.; Shipman, R.; van Dishoeck,
E. F.; Bachiller, R.; Benedettini, M.; Benz, A. O.; Bergin, E.;
Bjerkeli, P.; Blake, G. A.; Braine, J.; Bruderer, S.; Caselli, P.;
Caux, E.; Codella, C.; Daniel, F.; Dieleman, P.; di Giorgio, A. M.;
Dominik, C.; Doty, S. D.; Encrenaz, P.; Fich, M.; Fuente, A.; Gaier,
T.; Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.;
Herczeg, G. J.; Hogerheijde, M. R.; Jackson, B.; Javadi, H.; Jellema,
W.; Johnstone, D.; Jørgensen, J. K.; Kester, D.; Kristensen, L. E.;
Larsson, B.; Laauwen, W.; Lis, D.; Liseau, R.; Luinge, W.; McCoey,
C.; Megej, A.; Melnick, G.; Neufeld, D.; Nisini, B.; Olberg, M.;
Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Roelfsema, P.;
Santiago-García, J.; Saraceno, P.; Siegel, P.; Stutzki, J.; Tafalla,
M.; van Kempen, T. A.; Visser, R.; Wampfler, S. F.; Yıldız, U. A.
2010A&A...521L..32M Altcode: 2010arXiv1007.4119M
<BR /> Aims: We derive the dense core structure and the water abundance
in four massive star-forming regions in the hope of understanding
the earliest stages of massive star formation. <BR /> Methods:
We present Herschel/HIFI observations of the para-H<SUB>2</SUB>O
1<SUB>11</SUB>-0<SUB>00</SUB> and 2<SUB>02</SUB>-1<SUB>11</SUB>
and the para-H_2<SUP>18</SUP>O 1<SUB>11</SUB>-0<SUB>00</SUB>
transitions. The envelope contribution to the line profiles is
separated from contributions by outflows and foreground clouds. The
envelope contribution is modeled with Monte-Carlo radiative transfer
codes for dust and molecular lines (MC3D and RATRAN), and the water
abundance and the turbulent velocity width as free parameters. <BR />
Results: While the outflows are mostly seen in emission in high-J lines,
envelopes are seen in absorption in ground-state lines, which are almost
saturated. The derived water abundances range from 5×10<SUP>-10</SUP>
to 4×10<SUP>-8</SUP> in the outer envelopes. We detect cold clouds
surrounding the protostar envelope, thanks to the very high quality
of the Herschel/HIFI data and the unique ability of water to probe
them. Several foreground clouds are also detected along the line
of sight. <BR /> Conclusions: The low H<SUB>2</SUB>O abundances
in massive dense cores are in accordance with the expectation that
high densities and low temperatures lead to freeze-out of water on
dust grains. The spread in abundance values is not clearly linked
to physical properties of the sources. <P />Herschel is an ESA
space observatory with science instruments provided by European-led
Principal Investigator consortia and with important participation of
NASA.Appendix (pages 6 to 7) is only available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Herschel observations in the ultracompact HII region Mon
R2. Water in dense photon-dominated regions (PDRs)
Authors: Fuente, A.; Berné, O.; Cernicharo, J.; Rizzo, J. R.;
González-García, M.; Goicoechea, J. R.; Pilleri, P.; Ossenkopf,
V.; Gerin, M.; Güsten, R.; Akyilmaz, M.; Benz, A. O.; Boulanger, F.;
Bruderer, S.; Dedes, C.; France, K.; García-Burillo, S.; Harris, A.;
Joblin, C.; Klein, T.; Kramer, C.; Le Petit, F.; Lord, S. D.; Martin,
P. G.; Martín-Pintado, J.; Mookerjea, B.; Neufeld, D. A.; Okada,
Y.; Pety, J.; Phillips, T. G.; Röllig, M.; Simon, R.; Stutzki, J.;
van der Tak, F.; Teyssier, D.; Usero, A.; Yorke, H.; Schuster, K.;
Melchior, M.; Lorenzani, A.; Szczerba, R.; Fich, M.; McCoey, C.;
Pearson, J.; Dieleman, P.
2010A&A...521L..23F Altcode: 2010arXiv1007.1523F
Context. Monoceros R2, at a distance of 830 pc, is the only
ultracompact H ii region (UC H ii) where the photon-dominated region
(PDR) between the ionized gas and the molecular cloud can be resolved
with Herschel. Therefore, it is an excellent laboratory to study
the chemistry in extreme PDRs (G<SUB>0</SUB> > 10<SUP>5</SUP> in
units of Habing field, n > 10<SUP>6</SUP> cm<SUP>-3</SUP>). <BR
/> Aims: Our ultimate goal is to probe the physical and chemical
conditions in the PDR around the UC H ii Mon R2. <BR /> Methods: HIFI
observations of the abundant compounds <SUP>13</SUP>CO, C<SUP>18</SUP>O,
o-H<SUB>2</SUB><SUP>18</SUP>O, HCO<SUP>+</SUP>, CS, CH, and NH have
been used to derive the physical and chemical conditions in the
PDR, in particular the water abundance. The modeling of the lines
has been done with the Meudon PDR code and the non-local radiative
transfer model described by Cernicharo et al. <BR /> Results: The
<SUP>13</SUP>CO, C<SUP>18</SUP>O, o-H_2<SUP>18</SUP>O, HCO<SUP>+</SUP>
and CS observations are well described assuming that the emission
is coming from a dense (n = 5 × 10<SUP>6</SUP> cm<SUP>-3</SUP>,
N(H<SUB>2</SUB>)> 10<SUP>22</SUP> cm<SUP>-2</SUP>) layer of
molecular gas around the H ii region. Based on our o-H_2<SUP>18</SUP>O
observations, we estimate an o-H<SUB>2</SUB>O abundance of ≈2 ×
10<SUP>-8</SUP>. This is the average ortho-water abundance in the
PDR. Additional H_2<SUP>18</SUP>O and/or water lines are required
to derive the water abundance profile. A lower density envelope
(n ~ 10<SUP>5</SUP> cm<SUP>-3</SUP>, N(H<SUB>2</SUB>) = 2-5 ×
10<SUP>22</SUP> cm<SUP>-2</SUP>) is responsible for the absorption in
the NH 1_1→ 0_2 line. The emission of the CH ground state triplet
is coming from both regions with a complex and self-absorbed profile
in the main component. The radiative transfer modeling shows that the
<SUP>13</SUP>CO and HCO<SUP>+</SUP> line profiles are consistent with
an expansion of the molecular gas with a velocity law, v<SUB>e</SUB> =
0.5 × (r/R<SUB>out</SUB>)<SUP>-1</SUP> km s<SUP>-1</SUP>, although the
expansion velocity is poorly constrained by the observations presented
here. <BR /> Conclusions: We determine an ortho-water abundance of ≈2
× 10<SUP>-8</SUP> in Mon R2. Because shocks are unimportant in this
region and our estimate is based on H_2<SUP>18</SUP>O observations
that avoids opacity problems, this is probably the most accurate
estimate of the water abundance in PDRs thus far. <P />Herschel is an
ESA space observatory with science instruments provided by European-led
Principal Investigator consortia and with important participation from
NASA.Figures 1 and 4 (page 5) are only available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Herschel/HIFI observations of high-J CO lines in the NGC 1333
low-mass star-forming region
Authors: Yıldız, U. A.; van Dishoeck, E. F.; Kristensen, L. E.;
Visser, R.; Jørgensen, J. K.; Herczeg, G. J.; van Kempen, T. A.;
Hogerheijde, M. R.; Doty, S. D.; Benz, A. O.; Bruderer, S.; Wampfler,
S. F.; Deul, E.; Bachiller, R.; Baudry, A.; Benedettini, M.; Bergin,
E.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine, J.; Caselli, P.;
Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik,
C.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.; Goicoechea,
J. R.; de Graauw, Th.; Helmich, F.; Herpin, F.; Jacq, T.; Johnstone,
D.; Larsson, B.; Lis, D.; Liseau, R.; Liu, F. -C.; Marseille, M.;
McCoey, C.; Melnick, G.; Neufeld, D.; Nisini, B.; Olberg, M.; Parise,
B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García, J.;
Saraceno, P.; Shipman, R.; Tafalla, M.; Tielens, A. G. G. M.; van
der Tak, F.; Wyrowski, F.; Dieleman, P.; Jellema, W.; Ossenkopf, V.;
Schieder, R.; Stutzki, J.
2010A&A...521L..40Y Altcode: 2010arXiv1008.0867Y
Herschel/HIFI observations of high-J lines (up to J<SUB>u</SUB> = 10)
of <SUP>12</SUP>CO, <SUP>13</SUP>CO and C<SUP>18</SUP>O are presented
toward three deeply embedded low-mass protostars, NGC 1333 IRAS 2A,
IRAS 4A, and IRAS 4B, obtained as part of the Water In Star-forming
regions with Herschel (WISH) key program. The spectrally-resolved HIFI
data are complemented by ground-based observations of lower-J CO and
isotopologue lines. The <SUP>12</SUP>CO 10-9 profiles are dominated
by broad (FWHM 25-30 km s<SUP>-1</SUP>) emission. Radiative transfer
models are used to constrain the temperature of this shocked gas to
100-200 K. Several CO and <SUP>13</SUP>CO line profiles also reveal a
medium-broad component (FWHM5-10 km s<SUP>-1</SUP>), seen prominently
in H<SUB>2</SUB>O lines. Column densities for both components are
presented, providing a reference for determining abundances of other
molecules in the same gas. The narrow C<SUP>18</SUP>O 9-8 lines probe
the warmer part of the quiescent envelope. Their intensities require
a jump in the CO abundance at an evaporation temperature around 25 K,
thus providing new direct evidence for a CO ice evaporation zone around
low-mass protostars. <P />Herschel is an ESA space observatory with
science instruments provided by European-led Principal Investigator
consortia and with important participation from NASA.Appendices and
acknowledgements (pages 5 to 7) are only available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Herschel observations of the hydroxyl radical (OH) in young
stellar objects
Authors: Wampfler, S. F.; Herczeg, G. J.; Bruderer, S.; Benz,
A. O.; van Dishoeck, E. F.; Kristensen, L. E.; Visser, R.; Doty,
S. D.; Melchior, M.; van Kempen, T. A.; Yıldız, U. A.; Dedes, C.;
Goicoechea, J. R.; Baudry, A.; Melnick, G.; Bachiller, R.; Benedettini,
M.; Bergin, E.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine,
J.; Caselli, P.; Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio,
A. M.; Dominik, C.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.;
de Graauw, Th.; Helmich, F.; Herpin, F.; Hogerheijde, M. R.; Jacq,
T.; Johnstone, D.; Jørgensen, J. K.; Larsson, B.; Lis, D.; Liseau,
R.; Marseille, M.; McCoey, C.; Neufeld, D.; Nisini, B.; Olberg, M.;
Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García,
J.; Saraceno, P.; Shipman, R.; Tafalla, M.; van der Tak, F. F. S.;
Wyrowski, F.; Roelfsema, P.; Jellema, W.; Dieleman, P.; Caux, E.;
Stutzki, J.
2010A&A...521L..36W Altcode: 2010arXiv1007.2198W
<BR /> Aims: “Water In Star-forming regions with Herschel” (WISH)
is a Herschel key program investigating the water chemistry in young
stellar objects (YSOs) during protostellar evolution. Hydroxyl (OH)
is one of the reactants in the chemical network most closely linked
to the formation and destruction of H<SUB>2</SUB>O. High-temperature
(T ⪆ 250 K) chemistry connects OH and H<SUB>2</SUB>O through the OH +
H<SUB>2</SUB> Leftrightarrow H<SUB>2</SUB>O + H reactions. Formation
of H<SUB>2</SUB>O from OH is efficient in the high-temperature
regime found in shocks and the innermost part of protostellar
envelopes. Moreover, in the presence of UV photons, OH can be produced
from the photo-dissociation of H<SUB>2</SUB>O through H<SUB>2</SUB>O +
γ<SUB>UV</SUB> Rightarrow OH + H. <BR /> Methods: High-resolution
spectroscopy of the 163.12 μm triplet of OH towards HH 46 and NGC
1333 IRAS 2A was carried out with the Heterodyne Instrument for the Far
Infrared (HIFI) on board the Herschel Space Observatory. The low- and
intermediate-mass protostars HH 46, TMR 1, IRAS 15398-3359, DK Cha, NGC
7129 FIRS 2, and NGC 1333 IRAS 2A were observed with the Photodetector
Array Camera and Spectrometer (PACS) on Herschel in four transitions of
OH and two [O i] lines. <BR /> Results: The OH transitions at 79, 84,
119, and 163 μm and [O i] emission at 63 and 145 μm were detected with
PACS towards the class I low-mass YSOs as well as the intermediate-mass
and class I Herbig Ae sources. No OH emission was detected from the
class 0 YSO NGC 1333 IRAS 2A, though the 119 μm was detected in
absorption. With HIFI, the 163.12 μm was not detected from HH 46 and
only tentatively detected from NGC 1333 IRAS 2A. The combination of
the PACS and HIFI results for HH 46 constrains the line width (FWHM
⪆ 11 km s<SUP>-1</SUP>) and indicates that the OH emission likely
originates from shocked gas. This scenario is supported by trends
of the OH flux increasing with the [O i] flux and the bolometric
luminosity, as found in our sample. Similar OH line ratios for most
sources suggest that OH has comparable excitation temperatures despite
the different physical properties of the sources. <P />Herschel is an
ESA space observatory with science instruments provided by European-led
Principal Investigator consortia and with important participation from
NASA.Appendices (page 6) are only available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Water in massive star-forming regions: HIFI observations of
W3 IRS5
Authors: Chavarría, L.; Herpin, F.; Jacq, T.; Braine, J.; Bontemps,
S.; Baudry, A.; Marseille, M.; van der Tak, F.; Pietropaoli, B.;
Wyrowski, F.; Shipman, R.; Frieswijk, W.; van Dishoeck, E. F.;
Cernicharo, J.; Bachiller, R.; Benedettini, M.; Benz, A. O.; Bergin,
E.; Bjerkeli, P.; Blake, G. A.; Bruderer, S.; Caselli, P.; Codella,
C.; Daniel, F.; di Giorgio, A. M.; Dominik, C.; Doty, S. D.; Encrenaz,
P.; Fich, M.; Fuente, A.; Giannini, T.; Goicoechea, J. R.; de Graauw,
Th.; Hartogh, P.; Helmich, F.; Herczeg, G. J.; Hogerheijde, M. R.;
Johnstone, D.; Jørgensen, J. K.; Kristensen, L. E.; Larsson, B.;
Lis, D.; Liseau, R.; McCoey, C.; Melnick, G.; Nisini, B.; Olberg, M.;
Parise, B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García,
J.; Saraceno, P.; Stutzki, J.; Szczerba, R.; Tafalla, M.; Tielens, A.;
van Kempen, T. A.; Visser, R.; Wampfler, S. F.; Willem, J.; Yıldız,
U. A.
2010A&A...521L..37C Altcode: 2010arXiv1007.3986C
We present Herschel observations of the water molecule in the
massive star-forming region W3 IRS5. The o-H_2<SUP>17</SUP>O
1<SUB>10</SUB>-1<SUB>01</SUB>, p-H_2<SUP>18</SUP>O
1<SUB>11</SUB>-0<SUB>00</SUB>, p-H<SUB>2</SUB>O
2<SUB>02</SUB>-1<SUB>11</SUB>, p-H<SUB>2</SUB>O
1<SUB>11</SUB>-0<SUB>00</SUB>, o-H<SUB>2</SUB>O
2<SUB>21</SUB>-2<SUB>12</SUB>, and o-H<SUB>2</SUB>O
2<SUB>12</SUB>-1<SUB>01</SUB> lines, covering a frequency range
from 552 up to 1669 GHz, have been detected at high spectral
resolution with HIFI. The water lines in W3 IRS5 show well-defined
high-velocity wings that indicate a clear contribution by
outflows. Moreover, the systematically blue-shifted absorption
in the H<SUB>2</SUB>O lines suggests expansion, presumably
driven by the outflow. No infall signatures are detected. The
p-H<SUB>2</SUB>O 1<SUB>11</SUB>-0<SUB>00</SUB> and o-H<SUB>2</SUB>O
2<SUB>12</SUB>-1<SUB>01</SUB> lines show absorption from the cold
material (T ~ 10 K) in which the high-mass protostellar envelope
is embedded. One-dimensional radiative transfer models are used
to estimate water abundances and to further study the kinematics
of the region. We show that the emission in the rare isotopologues
comes directly from the inner parts of the envelope (T ≳ 100 K)
where water ices in the dust mantles evaporate and the gas-phase
abundance increases. The resulting jump in the water abundance
(with a constant inner abundance of 10<SUP>-4</SUP>) is needed to
reproduce the o-H_2<SUP>17</SUP>O 1<SUB>10</SUB>-1<SUB>01</SUB>
and p-H_2<SUP>18</SUP>O 1<SUB>11</SUB>-0<SUB>00</SUB> spectra
in our models. We estimate water abundances of 10<SUP>-8</SUP> to
10<SUP>-9</SUP> in the outer parts of the envelope (T ≲ 100 K). The
possibility of two protostellar objects contributing to the emission
is discussed. <P />Herschel is an ESA space observatory with science
instruments provided by European-led Principal Investigator consortia
and with important participation from NASA.
---------------------------------------------------------
Title: Sensitive limits on the abundance of cold water vapor in the
DM Tauri protoplanetary disk
Authors: Bergin, E. A.; Hogerheijde, M. R.; Brinch, C.; Fogel,
J.; Yıldız, U. A.; Kristensen, L. E.; van Dishoeck, E. F.; Bell,
T. A.; Blake, G. A.; Cernicharo, J.; Dominik, C.; Lis, D.; Melnick,
G.; Neufeld, D.; Panić, O.; Pearson, J. C.; Bachiller, R.; Baudry,
A.; Benedettini, M.; Benz, A. O.; Bjerkeli, P.; Bontemps, S.; Braine,
J.; Bruderer, S.; Caselli, P.; Codella, C.; Daniel, F.; di Giorgio,
A. M.; Doty, S. D.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.;
Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herczeg, G. J.; Herpin,
F.; Jacq, T.; Johnstone, D.; Jørgensen, J. K.; Larsson, B.; Liseau,
R.; Marseille, M.; McCoey, C.; Nisini, B.; Olberg, M.; Parise, B.;
Plume, R.; Risacher, C.; Santiago-García, J.; Saraceno, P.; Shipman,
R.; Tafalla, M.; van Kempen, T. A.; Visser, R.; Wampfler, S. F.;
Wyrowski, F.; van der Tak, F.; Jellema, W.; Tielens, A. G. G. M.;
Hartogh, P.; Stützki, J.; Szczerba, R.
2010A&A...521L..33B Altcode: 2010arXiv1007.2129B
We performed a sensitive search for the ground-state emission lines
of ortho- and para-water vapor in the DM Tau protoplanetary disk
using the Herschel/HIFI instrument. No strong lines are detected
down to 3σ levels in 0.5 km s<SUP>-1</SUP> channels of 4.2 mK
for the 1<SUB>10</SUB>-1<SUB>01</SUB> line and 12.6 mK for the
1<SUB>11</SUB>-0<SUB>00</SUB> line. We report a very tentative
detection, however, of the 1<SUB>10</SUB>-1<SUB>01</SUB> line in the
wide band spectrometer, with a strength of T<SUB>mb</SUB> = 2.7 mK,
a width of 5.6 km s<SUP>-1</SUP> and an integrated intensity of 16.0 mK
km s<SUP>-1</SUP>. The latter constitutes a 6σ detection. Regardless
of the reality of this tentative detection, model calculations indicate
that our sensitive limits on the line strengths preclude efficient
desorption of water in the UV illuminated regions of the disk. We
hypothesize that more than 95-99% of the water ice is locked up in
coagulated grains that have settled to the midplane. <P />Herschel
is an ESA space observatory with science instruments provided by
European-led Principal Investigator consortia and with participation
important from NASA.
---------------------------------------------------------
Title: Gas morphology and energetics at the surface of PDRs: New
insights with Herschel observations of NGC 7023
Authors: Joblin, C.; Pilleri, P.; Montillaud, J.; Fuente, A.;
Gerin, M.; Berné, O.; Ossenkopf, V.; Le Bourlot, J.; Teyssier,
D.; Goicoechea, J. R.; Le Petit, F.; Röllig, M.; Akyilmaz, M.;
Benz, A. O.; Boulanger, F.; Bruderer, S.; Dedes, C.; France, K.;
Güsten, R.; Harris, A.; Klein, T.; Kramer, C.; Lord, S. D.; Martin,
P. G.; Martin-Pintado, J.; Mookerjea, B.; Okada, Y.; Phillips, T. G.;
Rizzo, J. R.; Simon, R.; Stutzki, J.; van der Tak, F.; Yorke, H. W.;
Steinmetz, E.; Jarchow, C.; Hartogh, P.; Honingh, C. E.; Siebertz,
O.; Caux, E.; Colin, B.
2010A&A...521L..25J Altcode: 2010arXiv1008.1315J
Context. We investigate the physics and chemistry of the gas and dust
in dense photon-dominated regions (PDRs), along with their dependence
on the illuminating UV field. <BR /> Aims: Using Herschel/HIFI
observations, we study the gas energetics in NGC 7023 in relation
to the morphology of this nebula. NGC 7023 is the prototype of
a PDR illuminated by a B2V star and is one of the key targets of
Herschel. <BR /> Methods: Our approach consists in determining the
energetics of the region by combining the information carried by the
mid-IR spectrum (extinction by classical grains, emission from very
small dust particles) with that of the main gas coolant lines. In
this letter, we discuss more specifically the intensity and line
profile of the 158 μm (1901 GHz) [C ii] line measured by HIFI and
provide information on the emitting gas. <BR /> Results: We show that
both the [C ii] emission and the mid-IR emission from polycyclic
aromatic hydrocarbons (PAHs) arise from the regions located in the
transition zone between atomic and molecular gas. Using the Meudon
PDR code and a simple transfer model, we find good agreement between
the calculated and observed [C ii] intensities. <BR /> Conclusions:
HIFI observations of NGC 7023 provide the opportunity to constrain the
energetics at the surface of PDRs. Future work will include analysis of
the main coolant line [O i] and use of a new PDR model that includes
PAH-related species. <P />Herschel is an ESA space observatory with
science instruments provided by European-led Principal Investigator
consortia and with important participation from NASA.
---------------------------------------------------------
Title: Herschel spectral surveys of star-forming regions. Overview
of the 555-636 GHz range
Authors: Ceccarelli, C.; Bacmann, A.; Boogert, A.; Caux, E.; Dominik,
C.; Lefloch, B.; Lis, D.; Schilke, P.; van der Tak, F.; Caselli,
P.; Cernicharo, J.; Codella, C.; Comito, C.; Fuente, A.; Baudry, A.;
Bell, T.; Benedettini, M.; Bergin, E. A.; Blake, G. A.; Bottinelli,
S.; Cabrit, S.; Castets, A.; Coutens, A.; Crimier, N.; Demyk, K.;
Encrenaz, P.; Falgarone, E.; Gerin, M.; Goldsmith, P. F.; Helmich,
F.; Hennebelle, P.; Henning, T.; Herbst, E.; Hily-Blant, P.; Jacq, T.;
Kahane, C.; Kama, M.; Klotz, A.; Langer, W.; Lord, S.; Lorenzani, A.;
Maret, S.; Melnick, G.; Neufeld, D.; Nisini, B.; Pacheco, S.; Pagani,
L.; Parise, B.; Pearson, J.; Phillips, T.; Salez, M.; Saraceno, P.;
Schuster, K.; Tielens, X.; van der Wiel, M. H. D.; Vastel, C.; Viti,
S.; Wakelam, V.; Walters, A.; Wyrowski, F.; Yorke, H.; Liseau, R.;
Olberg, M.; Szczerba, R.; Benz, A. O.; Melchior, M.
2010A&A...521L..22C Altcode:
High resolution line spectra of star-forming regions are mines of
information: they provide unique clues to reconstruct the chemical,
dynamical, and physical structure of the observed source. We present
the first results from the Herschel key project “Chemical HErschel
Surveys of Star forming regions”, CHESS. We report and discuss
observations towards five CHESS targets, one outflow shock spot and four
protostars with luminosities bewteen 20 and 2 × 10<SUP>5</SUP> L_⊙:
L1157-B1, IRAS 16293-2422, OMC2-FIR4, AFGL 2591, and NGC 6334I. The
observations were obtained with the heterodyne spectrometer HIFI on
board Herschel, with a spectral resolution of 1 MHz. They cover the
frequency range 555-636 GHz, a range largely unexplored before the
launch of the Herschel satellite. A comparison of the five spectra
highlights spectacular differences in the five sources, for example
in the density of methanol lines, or the presence/absence of lines
from S-bearing molecules or deuterated species. We discuss how these
differences can be attributed to the different star-forming mass or
evolutionary status. <P />Herschel is an ESA space observatory with
science instruments provided by European-led principal Investigator
consortia and with important participation from NASA.Figures [see
full textsee full text]-[see full textsee full text] and Tables
3, 4 (pages 6 to 8) are only available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: First detection of ND in the solar-mass protostar
IRAS16293-2422
Authors: Bacmann, A.; Caux, E.; Hily-Blant, P.; Parise, B.; Pagani,
L.; Bottinelli, S.; Maret, S.; Vastel, C.; Ceccarelli, C.; Cernicharo,
J.; Henning, T.; Castets, A.; Coutens, A.; Bergin, E. A.; Blake,
G. A.; Crimier, N.; Demyk, K.; Dominik, C.; Gerin, M.; Hennebelle, P.;
Kahane, C.; Klotz, A.; Melnick, G.; Schilke, P.; Wakelam, V.; Walters,
A.; Baudry, A.; Bell, T.; Benedettini, M.; Boogert, A.; Cabrit, S.;
Caselli, P.; Codella, C.; Comito, C.; Encrenaz, P.; Falgarone, E.;
Fuente, A.; Goldsmith, P. F.; Helmich, F.; Herbst, E.; Jacq, T.;
Kama, M.; Langer, W.; Lefloch, B.; Lis, D.; Lord, S.; Lorenzani,
A.; Neufeld, D.; Nisini, B.; Pacheco, S.; Pearson, J.; Phillips,
T.; Salez, M.; Saraceno, P.; Schuster, K.; Tielens, X.; van der Tak,
F. F. S.; van der Wiel, M. H. D.; Viti, S.; Wyrowski, F.; Yorke, H.;
Faure, A.; Benz, A.; Coeur-Joly, O.; Cros, A.; Güsten, R.; Ravera, L.
2010A&A...521L..42B Altcode: 2010arXiv1007.4691B
Context. In the past decade, much progress has been made in
characterising the processes leading to the enhanced deuterium
fractionation observed in the ISM and in particular in the cold, dense
parts of star forming regions such as protostellar envelopes. Very
high molecular D/H ratios have been found for saturated molecules and
ions. However, little is known about the deuterium fractionation in
radicals, even though simple radicals often represent an intermediate
stage in the formation of more complex, saturated molecules. The
imidogen radical NH is such an intermediate species for the ammonia
synthesis in the gas phase. Many of these light molecules however
have their fundamental transitions in the submillimetre domain and
their detection is hampered by the opacity of the atmosphere at these
wavelengths. Herschel/HIFI represents a unique opportunity to study the
deuteration and formation mechanisms of species not observable from
the ground. <BR /> Aims: We searched here for the deuterated radical
ND in order to determine the deuterium fractionation of imidogen and
constrain the deuteration mechanism of this species. <BR /> Methods:
We observed the solar-mass Class 0 protostar IRAS16293-2422 with
the heterodyne instrument HIFI in Bands 1a (480-560 GHz), 3b (858-961
GHz), and 4a (949-1061 GHz) as part of the Herschel key programme CHESS
(Chemical HErschel Survey of Star forming regions). <BR /> Results: The
deuterated form of the imidogen radical ND was detected and securely
identified with 2 hyperfine component groups of its fundamental
transition (N = 0-1) at 522.1 and 546.2 GHz, in absorption against the
continuum background emitted from the nascent protostar. The 3 groups
of hyperfine components of its hydrogenated counterpart NH were also
detected in absorption. The absorption arises from the cold envelope,
where many deuterated species have been shown to be abundant. The
estimated column densities are ~2 × 10<SUP>14</SUP> cm<SUP>-2</SUP>
for NH and ~ 1.3 × 10<SUP>14</SUP> cm<SUP>-2</SUP> for ND. We derive a
very high deuterium fractionation with an [ND]/[NH] ratio of between 30
and 100%. <BR /> Conclusions: The deuterium fractionation of imidogen
is of the same order of magnitude as that in other molecules, which
suggests that an efficient deuterium fractionation mechanism is at
play. We discuss two possible formation pathways for ND, by means
of either the reaction of N<SUP>+</SUP> with HD, or deuteron/proton
exchange with NH. <P />Herschel is an ESA space observatory with
science instruments provided by European-led principal Investigator
consortia and with important participation from NASA.
---------------------------------------------------------
Title: Variations in H<SUB>2</SUB>O<SUP>+</SUP>/H<SUB>2</SUB>O ratios
toward massive star-forming regions
Authors: Wyrowski, F.; van der Tak, F.; Herpin, F.; Baudry, A.;
Bontemps, S.; Chavarria, L.; Frieswijk, W.; Jacq, T.; Marseille,
M.; Shipman, R.; van Dishoeck, E. F.; Benz, A. O.; Caselli, P.;
Hogerheijde, M. R.; Johnstone, D.; Liseau, R.; Bachiller, R.;
Benedettini, M.; Bergin, E.; Bjerkeli, P.; Blake, G.; Braine, J.;
Bruderer, S.; Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio,
A. M.; Dominik, C.; Doty, S. D.; Encrenaz, P.; Fich, M.; Fuente, A.;
Giannini, T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herczeg,
G. J.; Jørgensen, J. K.; Kristensen, L. E.; Larsson, B.; Lis, D.;
McCoey, C.; Melnick, G.; Nisini, B.; Olberg, M.; Parise, B.; Pearson,
J. C.; Plume, R.; Risacher, C.; Santiago, J.; Saraceno, P.; Tafalla,
M.; van Kempen, T. A.; Visser, R.; Wampfler, S.; Yıldız, U. A.;
Black, J. H.; Falgarone, E.; Gerin, M.; Roelfsema, P.; Dieleman, P.;
Beintema, D.; de Jonge, A.; Whyborn, N.; Stutzki, J.; Ossenkopf, V.
2010A&A...521L..34W Altcode: 2010arXiv1007.4370W
Early results from the Herschel Space Observatory revealed the water
cation H<SUB>2</SUB>O<SUP>+</SUP> to be an abundant ingredient of
the interstellar medium. Here we present new observations of the
H<SUB>2</SUB>O and H<SUB>2</SUB>O<SUP>+</SUP> lines at 1113.3 and
1115.2 GHz using the Herschel Space Observatory toward a sample of
high-mass star-forming regions to observationally study the relation
between H<SUB>2</SUB>O and H<SUB>2</SUB>O<SUP>+</SUP>. Nine out
of ten sources show absorption from H<SUB>2</SUB>O<SUP>+</SUP>
in a range of environments: the molecular clumps surrounding the
forming and newly formed massive stars, bright high-velocity outflows
associated with the massive protostars, and unrelated low-density
clouds along the line of sight. Column densities per velocity
component of H<SUB>2</SUB>O<SUP>+</SUP> are found in the range of
10<SUP>12</SUP> to a few 10<SUP>13</SUP> cm<SUP>-2</SUP>. The highest
N(H<SUB>2</SUB>O<SUP>+</SUP>) column densities are found in the outflows
of the sources. The ratios of H<SUB>2</SUB>O<SUP>+</SUP>/H<SUB>2</SUB>O
are determined in a range from 0.01 to a few and are found to differ
strongly between the observed environments with much lower ratios in
the massive (proto)cluster envelopes (0.01-0.1) than in outflows and
diffuse clouds. Remarkably, even for source components detected in
H<SUB>2</SUB>O in emission, H<SUB>2</SUB>O<SUP>+</SUP> is still seen
in absorption. <P />Herschel is an ESA space observatory with science
instruments provided by European-led Principal Investigator consortia
and with important participation from NASA.
---------------------------------------------------------
Title: A high-resolution line survey of IRC +10216 with
Herschel/HIFI. First results: Detection of warm silicon dicarbide
(SiC{_2})
Authors: Cernicharo, J.; Waters, L. B. F. M.; Decin, L.; Encrenaz, P.;
Tielens, A. G. G. M.; Agúndez, M.; De Beck, E.; Müller, H. S. P.;
Goicoechea, J. R.; Barlow, M. J.; Benz, A.; Crimier, N.; Daniel, F.;
di Giorgio, A. M.; Fich, M.; Gaier, T.; García-Lario, P.; de Koter,
A.; Khouri, T.; Liseau, R.; Lombaert, R.; Erickson, N.; Pardo, J. R.;
Pearson, J. C.; Shipman, R.; Sánchez Contreras, C.; Teyssier, D.
2010A&A...521L...8C Altcode: 2010arXiv1008.1199C
We present the first results of a high-spectral-resolution survey
of the carbon-rich evolved star IRC+10216 that was carried out
with the HIFI spectrometer onboard Herschel. This survey covers
all HIFI bands, with a spectral range from 488 to 1901 GHz. In
this letter we focus on the band-1b spectrum, in a spectral range
554.5-636.5 GHz, where we identified 130 spectral features with
intensities above 0.03 K and a signal-to-noise ratio >5. Detected
lines arise from HCN, SiO, SiS, CS, CO, metal-bearing species and,
surprisingly, silicon dicarbide (SiC<SUB>2</SUB>). We identified
55 SiC<SUB>2</SUB> transitions involving energy levels between
300 and 900 K. By analysing these rotational lines, we conclude
that SiC<SUB>2</SUB> is produced in the inner dust formation zone,
with an abundance of ~ 2 × 10<SUP>-7</SUP> relative to molecular
hydrogen. These SiC<SUB>2</SUB> lines have been observed for the
first time in space and have been used to derive an SiC<SUB>2</SUB>
rotational temperature of ~204 K and a source-averaged column density
of ~ 6.4 × 10<SUP>15</SUP> cm<SUP>-2</SUP>. Furthermore, the high
quality of the HIFI data set was used to improve the spectroscopic
rotational constants of SiC<SUB>2</SUB>. <P />Herschel is an ESA
space observatory with science instruments provided by European-led
Principal Investigator consortia and with important participation
from NASA.Appendix (pages 6, 7) is only available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Water in low-mass star-forming regions with Herschel . HIFI
spectroscopy of NGC 1333
Authors: Kristensen, L. E.; Visser, R.; van Dishoeck, E. F.;
Yıldız, U. A.; Doty, S. D.; Herczeg, G. J.; Liu, F. -C.; Parise,
B.; Jørgensen, J. K.; van Kempen, T. A.; Brinch, C.; Wampfler, S. F.;
Bruderer, S.; Benz, A. O.; Hogerheijde, M. R.; Deul, E.; Bachiller, R.;
Baudry, A.; Benedettini, M.; Bergin, E. A.; Bjerkeli, P.; Blake, G. A.;
Bontemps, S.; Braine, J.; Caselli, P.; Cernicharo, J.; Codella, C.;
Daniel, F.; de Graauw, Th.; di Giorgio, A. M.; Dominik, C.; Encrenaz,
P.; Fich, M.; Fuente, A.; Giannini, T.; Goicoechea, J. R.; Helmich,
F.; Herpin, F.; Jacq, T.; Johnstone, D.; Kaufman, M. J.; Larsson, B.;
Lis, D.; Liseau, R.; Marseille, M.; McCoey, C.; Melnick, G.; Neufeld,
D.; Nisini, B.; Olberg, M.; Pearson, J. C.; Plume, R.; Risacher, C.;
Santiago-García, J.; Saraceno, P.; Shipman, R.; Tafalla, M.; Tielens,
A. G. G. M.; van der Tak, F.; Wyrowski, F.; Beintema, D.; de Jonge, A.;
Dieleman, P.; Ossenkopf, V.; Roelfsema, P.; Stutzki, J.; Whyborn, N.
2010A&A...521L..30K Altcode: 2010arXiv1007.3031K
“Water In Star-forming regions with Herschel” (WISH) is a key
programme dedicated to studying the role of water and related
species during the star-formation process and constraining the
physical and chemical properties of young stellar objects. The
Heterodyne Instrument for the Far-Infrared (HIFI) on the Herschel
Space Observatory observed three deeply embedded protostars in the
low-mass star-forming region NGC 1333 in several H_2<SUP>16</SUP>O,
H_2<SUP>18</SUP>O, and CO transitions. Line profiles are resolved for
five H_2<SUP>16</SUP>O transitions in each source, revealing them to
be surprisingly complex. The line profiles are decomposed into broad
(>20 km s<SUP>-1</SUP>), medium-broad (~5-10 km s<SUP>-1</SUP>),
and narrow (<5 km s<SUP>-1</SUP>) components. The H_2<SUP>18</SUP>O
emission is only detected in broad 1<SUB>10</SUB>-1<SUB>01</SUB>
lines (>20 km s<SUP>-1</SUP>), indicating that its physical origin
is the same as for the broad H_2<SUP>16</SUP>O component. In one of
the sources, IRAS4A, an inverse P Cygni profile is observed, a clear
sign of infall in the envelope. From the line profiles alone, it is
clear that the bulk of emission arises from shocks, both on small
(⪉1000 AU) and large scales along the outflow cavity walls (~10
000 AU). The H<SUB>2</SUB>O line profiles are compared to CO line
profiles to constrain the H<SUB>2</SUB>O abundance as a function of
velocity within these shocked regions. The H<SUB>2</SUB>O/CO abundance
ratios are measured to be in the range of ~0.1-1, corresponding
to H<SUB>2</SUB>O abundances of ~10<SUP>-5</SUP>-10<SUP>-4</SUP>
with respect to H<SUB>2</SUB>. Approximately 5-10% of the gas
is hot enough for all oxygen to be driven into water in warm
post-shock gas, mostly at high velocities. <P />Herschel is an ESA
space observatory with science instruments provided by European-led
Principal Investigator consortia and with important participation from
NASA.Tables 2 and 3 (page 6) are only available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Physical Processes in Magnetically Driven Flares on the Sun,
Stars, and Young Stellar Objects
Authors: Benz, Arnold O.; Güdel, Manuel
2010ARA&A..48..241B Altcode:
The first flare on the Sun was observed exactly 150 years ago. During
most of the long history, only secondary effects have been noticed, so
flares remained a riddle. Now the primary flare products, high-energy
electrons and ions, can be spatially resolved in hard X-rays (HXRs)
and gamma rays on the Sun. Soft X-rays (SXRs) are observed from most
stars, including young stellar objects. Structure and bulk motions of
the corona are imaged on the Sun in high temperature lines and are
inferred from line shifts in stellar coronae. Magnetic reconnection
is the trigger for reorganization of the magnetic field into a lower
energy configuration. A large fraction of the energy is converted into
nonthermal particles that transport the energy to higher density gas,
heating it to SXR-emitting temperatures. Flares on young stars are
several orders of magnitude more luminous and more frequent; they
significantly ionize protoplanetary disks and planetary ionospheres.
---------------------------------------------------------
Title: Multidimensional Chemical Modeling of Young Stellar
Objects. III. The Influence of Geometry on the Abundance and
Excitation of Diatomic Hydrides
Authors: Bruderer, S.; Benz, A. O.; Stäuber, P.; Doty, S. D.
2010ApJ...720.1432B Altcode:
The Herschel Space Observatory enables observations in the far-infrared
at high spectral and spatial resolution. A particular class of molecules
will be directly observable: light diatomic hydrides and their ions
(CH, OH, SH, NH, CH<SUP>+</SUP>, OH<SUP>+</SUP>, SH<SUP>+</SUP>,
NH<SUP>+</SUP>). These simple constituents are important both for
the chemical evolution of the region and as tracers of high-energy
radiation. If outflows of a forming star erode cavities in the envelope,
protostellar far-UV (FUV; 6 < E <SUB>γ</SUB> < 13.6 eV) radiation
may escape through such low-density regions. Depending on the shape of
the cavity, the FUV radiation then irradiates the quiescent envelope
in the walls along the outflow. The chemical composition in these
outflow walls is altered by photoreactions and heating via FUV photons
in a manner similar to photo-dominated regions. In this work, we study
the effect of cavity shapes, outflow density, and of a disk with the
two-dimensional chemical model of a high-mass young stellar object
introduced in the second paper in this series. The model has been
extended with a self-consistent calculation of the dust temperature
and a multi-zone escape probability method for the calculation of the
molecular excitation and the prediction of line fluxes. We find that the
shape of the cavity is particularly important in the innermost part of
the envelope, where the dust temperatures are high enough (gsim100 K)
for water ice to evaporate. If the cavity shape allows FUV radiation to
penetrate this hot-core region, the abundance of FUV-destroyed species
(e.g., water) is decreased. On larger scales, the shape of the cavity is
less important for the chemistry in the outflow wall. In particular,
diatomic hydrides and their ions CH<SUP>+</SUP>, OH<SUP>+</SUP>,
and NH<SUP>+</SUP> are enhanced by many orders of magnitude in the
outflow walls due to the combination of high gas temperatures and rapid
photodissociation of more saturated species. The enhancement of these
diatomic hydrides is sufficient for a detection using the HIFI and
PACS instruments on board Herschel. The effect of X-ray ionization on
the chemistry is found to be small, due to the much larger luminosity
in FUV bands compared to X-rays.
---------------------------------------------------------
Title: Water cooling of shocks in protostellar outflows. Herschel-PACS
map of L1157
Authors: Nisini, B.; Benedettini, M.; Codella, C.; Giannini, T.;
Liseau, R.; Neufeld, D.; Tafalla, M.; van Dishoeck, E. F.; Bachiller,
R.; Baudry, A.; Benz, A. O.; Bergin, E.; Bjerkeli, P.; Blake, G.;
Bontemps, S.; Braine, J.; Bruderer, S.; Caselli, P.; Cernicharo, J.;
Daniel, F.; Encrenaz, P.; di Giorgio, A. M.; Dominik, C.; Doty, S.;
Fich, M.; Fuente, A.; Goicoechea, J. R.; de Graauw, Th.; Helmich,
F.; Herczeg, G.; Herpin, F.; Hogerheijde, M.; Jacq, T.; Johnstone,
D.; Jørgensen, J.; Kaufman, M.; Kristensen, L.; Larsson, B.; Lis,
D.; Marseille, M.; McCoey, C.; Melnick, G.; Olberg, M.; Parise, B.;
Pearson, J.; Plume, R.; Risacher, C.; Santiago, J.; Saraceno, P.;
Shipman, R.; van Kempen, T. A.; Visser, R.; Viti, S.; Wampfler, S.;
Wyrowski, F.; van der Tak, F.; Yıldız, U. A.; Delforge, B.; Desbat,
J.; Hatch, W. A.; Péron, I.; Schieder, R.; Stern, J. A.; Teyssier,
D.; Whyborn, N.
2010A&A...518L.120N Altcode: 2010arXiv1005.4517N
Context. The far-IR/sub-mm spectral mapping facility provided by the
Herschel-PACS and HIFI instruments has made it possible to obtain,
for the first time, images of H<SUB>2</SUB>O emission with a spatial
resolution comparable to ground based mm/sub-mm observations. <BR
/> Aims: In the framework of the Water In Star-forming regions with
Herschel (WISH) key program, maps in water lines of several outflows
from young stars are being obtained, to study the water production in
shocks and its role in the outflow cooling. This paper reports the first
results of this program, presenting a PACS map of the o-H<SUB>2</SUB>O
179 μm transition obtained toward the young outflow L1157. <BR />
Methods: The 179 μm map is compared with those of other important
shock tracers, and with previous single-pointing ISO, SWAS, and Odin
water observations of the same source that allow us to constrain the
H<SUB>2</SUB>O abundance and total cooling. <BR /> Results: Strong
H<SUB>2</SUB>O peaks are localized on both shocked emission knots
and the central source position. The H<SUB>2</SUB>O 179 μm emission
is spatially correlated with emission from H<SUB>2</SUB> rotational
lines, excited in shocks leading to a significant enhancement of the
water abundance. Water emission peaks along the outflow also correlate
with peaks of other shock-produced molecular species, such as SiO and
NH<SUB>3</SUB>. A strong H<SUB>2</SUB>O peak is also observed at the
location of the proto-star, where none of the other molecules have
significant emission. The absolute 179 μm intensity and its intensity
ratio to the H<SUB>2</SUB>O 557 GHz line previously observed with
Odin/SWAS indicate that the water emission originates in warm compact
clumps, spatially unresolved by PACS, having a H<SUB>2</SUB>O abundance
of the order of 10<SUP>-4</SUP>. This testifies that the clumps have
been heated for a time long enough to allow the conversion of almost
all the available gas-phase oxygen into water. The total H<SUB>2</SUB>O
cooling is ~10<SUP>-1</SUP> L_⊙, about 40% of the cooling due to
H<SUB>2</SUB> and 23% of the total energy released in shocks along the
L1157 outflow. <P />Herschel is an ESA space observatory with science
instruments provided by European-led Principal Investigator consortia
and with important partecipation from NASA.
---------------------------------------------------------
Title: HIFI observations of warm gas in DR21: Shock versus radiative
heating
Authors: Ossenkopf, V.; Röllig, M.; Simon, R.; Schneider, N.;
Okada, Y.; Stutzki, J.; Gerin, M.; Akyilmaz, M.; Beintema, D.; Benz,
A. O.; Berne, O.; Boulanger, F.; Bumble, B.; Coeur-Joly, O.; Dedes,
C.; Diez-Gonzalez, M. C.; France, K.; Fuente, A.; Gallego, J. D.;
Goicoechea, J. R.; Güsten, R.; Harris, A.; Higgins, R.; Jackson,
B.; Jarchow, C.; Joblin, C.; Klein, T.; Kramer, C.; Lord, S.; Martin,
P.; Martin-Pintado, J.; Mookerjea, B.; Neufeld, D. A.; Phillips, T.;
Rizzo, J. R.; van der Tak, F. F. S.; Teyssier, D.; Yorke, H.
2010A&A...518L..79O Altcode: 2010arXiv1005.2517O
Context. The molecular gas in the DR21 massive star formation region
is known to be affected by the strong UV field from the central star
cluster and by a fast outflow creating a bright shock. The relative
contribution of both heating mechanisms is the matter of a long
debate. <BR /> Aims: By better sampling the excitation ladder of
various tracers we provide a quantitative distinction between the
different heating mechanisms. <BR /> Methods: HIFI observations of
mid-J transitions of CO and HCO<SUP>+</SUP> isotopes allow us to
bridge the gap in excitation energies between observations from the
ground, characterizing the cooler gas, and existing ISO LWS spectra,
constraining the properties of the hot gas. Comparing the detailed line
profiles allows to identify the physical structure of the different
components. <BR /> Results: In spite of the known shock-excitation of
H<SUB>2</SUB> and the clearly visible strong outflow, we find that
the emission of all lines up to ⪆2 THz can be explained by purely
radiative heating of the material. However, the new Herschel/HIFI
observations reveal two types of excitation conditions. We find hot
and dense clumps close to the central cluster, probably dynamically
affected by the outflow, and a more widespread distribution of cooler,
but nevertheless dense, molecular clumps. <P />Herschel is an ESA space
observatory with science instruments provided by European-led Principal
Investigator consortia and with important participation from NASA.
---------------------------------------------------------
Title: Water abundance variations around high-mass protostars:
HIFI observations of the DR21 region
Authors: van der Tak, F. F. S.; Marseille, M. G.; Herpin, F.; Wyrowski,
F.; Baudry, A.; Bontemps, S.; Braine, J.; Doty, S.; Frieswijk, W.;
Melnick, G.; Shipman, R.; van Dishoeck, E. F.; Benz, A. O.; Caselli,
P.; Hogerheijde, M.; Johnstone, D.; Liseau, R.; Bachiller, R.;
Benedettini, M.; Bergin, E.; Bjerkeli, P.; Blake, G.; Bruderer, S.;
Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik,
C.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini, T.; Goicoechea, J.;
de Graauw, Th.; Helmich, F.; Herczeg, G.; Jørgensen, J.; Kristensen,
L.; Larsson, B.; Lis, D.; McCoey, C.; Neufeld, D.; Nisini, B.; Olberg,
M.; Parise, B.; Pearson, J.; Plume, R.; Risacher, C.; Santiago, J.;
Saraceno, P.; Tafalla, M.; van Kempen, T.; Visser, R.; Wampfler, S.;
Yıldız, U.; Ravera, L.; Roelfsema, P.; Siebertz, O.; Teyssier, D.
2010A&A...518L.107V Altcode: 2010arXiv1005.2903V
Context. Water is a key molecule in the star formation process, but its
spatial distribution in star-forming regions is not well known. <BR />
Aims: We study the distribution of dust continuum and H<SUB>2</SUB>O and
<SUP>13</SUP>CO line emission in DR21, a luminous star-forming region
with a powerful outflow and a compact H ii region. <BR /> Methods:
Herschel-HIFI spectra near 1100 GHz show narrow <SUP>13</SUP>CO 10-9
emission and H<SUB>2</SUB>O 1<SUB>11</SUB>-0<SUB>00</SUB> absorption
from the dense core and broad emission from the outflow in both
lines. The H<SUB>2</SUB>O line also shows absorption by a foreground
cloud known from ground-based observations of low-J CO lines. <BR />
Results: The dust continuum emission is extended over 36” FWHM, while
the <SUP>13</SUP>CO and H<SUB>2</SUB>O lines are confined to ≈24” or
less. The foreground absorption appears to peak further North than the
other components. Radiative transfer models indicate very low abundances
of ~2×10<SUP>-10</SUP> for H<SUB>2</SUB>O and ~8×10<SUP>-7</SUP> for
<SUP>13</SUP>CO in the dense core, and higher H<SUB>2</SUB>O abundances
of ~4×10<SUP>-9</SUP> in the foreground cloud and ~7×10<SUP>-7</SUP>
in the outflow. <BR /> Conclusions: The high H<SUB>2</SUB>O abundance
in the warm outflow is probably due to the evaporation of water-rich
icy grain mantles, while the H<SUB>2</SUB>O abundance is kept down
by freeze-out in the dense core and by photodissociation in the
foreground cloud. <P />Herschel is an ESA space observatory with
science instruments provided by European-led Principal Investigator
consortia and with important participation from NASA.
---------------------------------------------------------
Title: Origin of the hot gas in low-mass protostars. Herschel-PACS
spectroscopy of HH 46
Authors: van Kempen, T. A.; Kristensen, L. E.; Herczeg, G. J.; Visser,
R.; van Dishoeck, E. F.; Wampfler, S. F.; Bruderer, S.; Benz, A. O.;
Doty, S. D.; Brinch, C.; Hogerheijde, M. R.; Jørgensen, J. K.;
Tafalla, M.; Neufeld, D.; Bachiller, R.; Baudry, A.; Benedettini, M.;
Bergin, E. A.; Bjerkeli, P.; Blake, G. A.; Bontemps, S.; Braine, J.;
Caselli, P.; Cernicharo, J.; Codella, C.; Daniel, F.; di Giorgio,
A. M.; Dominik, C.; Encrenaz, P.; Fich, M.; Fuente, A.; Giannini,
T.; Goicoechea, J. R.; de Graauw, Th.; Helmich, F.; Herpin, F.; Jacq,
T.; Johnstone, D.; Kaufman, M. J.; Larsson, B.; Lis, D.; Liseau, R.;
Marseille, M.; McCoey, C.; Melnick, G.; Nisini, B.; Olberg, M.; Parise,
B.; Pearson, J. C.; Plume, R.; Risacher, C.; Santiago-García, J.;
Saraceno, P.; Shipman, R.; van der Tak, F.; Wyrowski, F.; Yıldız,
U. A.; Ciechanowicz, M.; Dubbeldam, L.; Glenz, S.; Huisman, R.; Lin,
R. H.; Morris, P.; Murphy, J. A.; Trappe, N.
2010A&A...518L.121V Altcode: 2010arXiv1005.2031V
<BR /> Aims: “Water In Star-forming regions with Herschel” (WISH)
is a Herschel key programme aimed at understanding the physical and
chemical structure of young stellar objects (YSOs) with a focus on water
and related species. <BR /> Methods: The low-mass protostar HH 46 was
observed with the Photodetector Array Camera and Spectrometer (PACS) on
the Herschel Space Observatory to measure emission in H<SUB>2</SUB>O,
CO, OH, [O i], and [C ii] lines located between 63 and 186 μm. The
excitation and spatial distribution of emission can disentangle the
different heating mechanisms of YSOs, with better spatial resolution
and sensitivity than previously possible. <BR /> Results: Far-IR line
emission is detected at the position of the protostar and along the
outflow axis. The OH emission is concentrated at the central position,
CO emission is bright at the central position and along the outflow,
and H<SUB>2</SUB>O emission is concentrated in the outflow. In addition,
[O i] emission is seen in low-velocity gas, assumed to be related to the
envelope, and is also seen shifted up to 170 km s<SUP>-1</SUP> in both
the red- and blue-shifted jets. Envelope models are constructed based on
previous observational constraints. They indicate that passive heating
of a spherical envelope by the protostellar luminosity cannot explain
the high-excitation molecular gas detected with PACS, including CO
lines with upper levels at >2500 K above the ground state. Instead,
warm CO and H<SUB>2</SUB>O emission is probably produced in the walls
of an outflow-carved cavity in the envelope, which are heated by UV
photons and non-dissociative C-type shocks. The bright OH and [O i]
emission is attributed to J-type shocks in dense gas close to the
protostar. In the scenario described here, the combined cooling by
far-IR lines within the central spatial pixel is estimated to be 2
× 10<SUP>-2</SUP> L_⊙, with 60-80% attributed to J- and C-type
shocks produced by interactions between the jet and the envelope. <P
/>Herschel is an ESA space observatory with science instruments provided
by European-led Principal Investigator consortia and with important
participation from NASA.Table 2 is only available in electronic form
at <A href="http//www.aanda.org">http//www.aanda.org</A>
---------------------------------------------------------
Title: Herschel-PACS spectroscopy of the intermediate mass protostar
NGC 7129 FIRS 2
Authors: Fich, M.; Johnstone, D.; van Kempen, T. A.; McCoey, C.;
Fuente, A.; Caselli, P.; Kristensen, L. E.; Plume, R.; Cernicharo, J.;
Herczeg, G. J.; van Dishoeck, E. F.; Wampfler, S.; Gaufre, P.; Gill,
J. J.; Javadi, H.; Justen, M.; Laauwen, W.; Luinge, W.; Ossenkopf,
V.; Pearson, J.; Bachiller, R.; Baudry, A.; Benedettini, M.; Bergin,
E.; Benz, A. O.; Bjerkeli, P.; Blake, G.; Bontemps, S.; Braine, J.;
Bruderer, S.; Codella, C.; Daniel, F.; di Giorgio, A. M.; Dominik,
C.; Doty, S. D.; Encrenaz, P.; Giannini, T.; Goicoechea, J. R.;
de Graauw, Th.; Helmich, F.; Herpin, F.; Hogerheijde, M. R.; Jacq,
T.; Jørgensen, J. K.; Larsson, B.; Lis, D.; Liseau, R.; Marseille,
M.; Melnick, G.; Nisini, B.; Olberg, M.; Parise, B.; Risacher, C.;
Santiago, J.; Saraceno, P.; Shipman, R.; Tafalla, M.; van der Tak,
F.; Visser, R.; Wyrowski, F.; Yıldız, U. A.
2010A&A...518L..86F Altcode: 2010arXiv1006.0210F
<BR /> Aims: We present preliminary results of the first Herschel
spectroscopic observations of NGC 7129 FIRS2, an intermediate mass
star-forming region. We attempt to interpret the observations in the
framework of an in-falling spherical envelope. <BR /> Methods: The
PACS instrument was used in line spectroscopy mode (R = 1000-5000)
with 15 spectral bands between 63 and 185 μm. This provided good
detections of 26 spectral lines seen in emission, including lines
of H<SUB>2</SUB>O, CO, OH, O I, and C II. <BR /> Results: Most of
the detected lines, particularly those of H<SUB>2</SUB>O and CO,
are substantially stronger than predicted by the spherical envelope
models, typically by several orders of magnitude. In this paper we
focus on what can be learned from the detected CO emission lines. <BR />
Conclusions: It is unlikely that the much stronger than expected line
emission arises in the (spherical) envelope of the YSO. The region hot
enough to produce such high excitation lines within such an envelope
is too small to produce the amount of emission observed. Virtually all
of this high excitation emission must arise in structures such as as
along the walls of the outflow cavity with the emission produced by
a combination of UV photon heating and/or non-dissociative shocks. <P
/>Herschel is an ESA space observatory with science instruments provided
by European-led Principal Investigator consortia and with important
participation from NASA.Figure 3 is only available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: HIFI observations of water in the atmosphere of comet C/2008 Q3
(Garradd)
Authors: Hartogh, P.; Crovisier, J.; de Val-Borro, M.;
Bockelée-Morvan, D.; Biver, N.; Lis, D. C.; Moreno, R.; Jarchow,
C.; Rengel, M.; Emprechtinger, M.; Szutowicz, S.; Banaszkiewicz,
M.; Bensch, F.; Blecka, M. I.; Cavalié, T.; Encrenaz, T.; Jehin,
E.; Küppers, M.; Lara, L. -M.; Lellouch, E.; Swinyard, B. M.;
Vandenbussche, B.; Bergin, E. A.; Blake, G. A.; Blommaert, J. A. D. L.;
Cernicharo, J.; Decin, L.; Encrenaz, P.; de Graauw, T.; Hutsemekers,
D.; Kidger, M.; Manfroid, J.; Medvedev, A. S.; Naylor, D. A.; Schieder,
R.; Thomas, N.; Waelkens, C.; Roelfsema, P. R.; Dieleman, P.; Güsten,
R.; Klein, T.; Kasemann, C.; Caris, M.; Olberg, M.; Benz, A. O.
2010A&A...518L.150H Altcode: 2010arXiv1005.2969H
High-resolution far-infrared and sub-millimetre spectroscopy of water
lines is an important tool to understand the physical and chemical
properties of cometary atmospheres. We present observations of several
rotational ortho- and para-water transitions in comet C/2008 Q3
(Garradd) performed with HIFI on Herschel. These observations have
provided the first detection of the 2<SUB>12</SUB>-1<SUB>01</SUB>
(1669 GHz) ortho and 1<SUB>11</SUB>-0<SUB>00</SUB> (1113 GHz)
para transitions of water in a cometary spectrum. In addition,
the ground-state transition 1<SUB>10</SUB>-1<SUB>01</SUB> at
557 GHz is detected and mapped. By detecting several water lines
quasi-simultaneously and mapping their emission we can constrain the
excitation parameters in the coma. Synthetic line profiles are computed
using excitation models which include excitation by collisions, solar
infrared radiation, and radiation trapping. We obtain the gas kinetic
temperature, constrain the electron density profile, and estimate the
coma expansion velocity by analyzing the map and line shapes. We derive
water production rates of 1.7-2.8 × 10<SUP>28</SUP> s<SUP>-1</SUP>
over the range r<SUB>h</SUB> = 1.83-1.85 AU. <P />Herschel is an ESA
space observatory with science instruments provided by European-led
Principal Investigator consortia and with important participation
from NASA.Figure 5 is only available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Detection of interstellar oxidaniumyl: Abundant
H<SUB>2</SUB>O<SUP>+</SUP> towards the star-forming regions DR21,
Sgr B2, and NGC6334
Authors: Ossenkopf, V.; Müller, H. S. P.; Lis, D. C.; Schilke,
P.; Bell, T. A.; Bruderer, S.; Bergin, E.; Ceccarelli, C.; Comito,
C.; Stutzki, J.; Bacman, A.; Baudry, A.; Benz, A. O.; Benedettini,
M.; Berne, O.; Blake, G.; Boogert, A.; Bottinelli, S.; Boulanger,
F.; Cabrit, S.; Caselli, P.; Caux, E.; Cernicharo, J.; Codella,
C.; Coutens, A.; Crimier, N.; Crockett, N. R.; Daniel, F.; Demyk,
K.; Dieleman, P.; Dominik, C.; Dubernet, M. L.; Emprechtinger,
M.; Encrenaz, P.; Falgarone, E.; France, K.; Fuente, A.; Gerin, M.;
Giesen, T. F.; di Giorgio, A. M.; Goicoechea, J. R.; Goldsmith, P. F.;
Güsten, R.; Harris, A.; Helmich, F.; Herbst, E.; Hily-Blant, P.;
Jacobs, K.; Jacq, T.; Joblin, Ch.; Johnstone, D.; Kahane, C.; Kama, M.;
Klein, T.; Klotz, A.; Kramer, C.; Langer, W.; Lefloch, B.; Leinz, C.;
Lorenzani, A.; Lord, S. D.; Maret, S.; Martin, P. G.; Martin-Pintado,
J.; McCoey, C.; Melchior, M.; Melnick, G. J.; Menten, K. M.; Mookerjea,
B.; Morris, P.; Murphy, J. A.; Neufeld, D. A.; Nisini, B.; Pacheco,
S.; Pagani, L.; Parise, B.; Pearson, J. C.; Pérault, M.; Phillips,
T. G.; Plume, R.; Quin, S. -L.; Rizzo, R.; Röllig, M.; Salez, M.;
Saraceno, P.; Schlemmer, S.; Simon, R.; Schuster, K.; van der Tak,
F. F. S.; Tielens, A. G. G. M.; Teyssier, D.; Trappe, N.; Vastel,
C.; Viti, S.; Wakelam, V.; Walters, A.; Wang, S.; Whyborn, N.; van
der Wiel, M.; Yorke, H. W.; Yu, S.; Zmuidzinas, J.
2010A&A...518L.111O Altcode: 2010arXiv1005.2521O
<BR /> Aims: We identify a prominent absorption feature at 1115
GHz, detected in first HIFI spectra towards high-mass star-forming
regions, and interpret its astrophysical origin. <BR /> Methods: The
characteristic hyperfine pattern of the H<SUB>2</SUB>O<SUP>+</SUP>
ground-state rotational transition, and the lack of other known
low-energy transitions in this frequency range, identifies the feature
as H<SUB>2</SUB>O<SUP>+</SUP> absorption against the dust continuum
background and allows us to derive the velocity profile of the absorbing
gas. By comparing this velocity profile with velocity profiles of other
tracers in the DR21 star-forming region, we constrain the frequency of
the transition and the conditions for its formation. <BR /> Results: In
DR21, the velocity distribution of H<SUB>2</SUB>O<SUP>+</SUP> matches
that of the [C ii] line at 158 μm and of OH cm-wave absorption,
both stemming from the hot and dense clump surfaces facing the H
ii-region and dynamically affected by the blister outflow. Diffuse
foreground gas dominates the absorption towards Sgr B2. The integrated
intensity of the absorption line allows us to derive lower limits to
the H<SUB>2</SUB>O<SUP>+</SUP> column density of 7.2 × 10<SUP>12</SUP>
cm<SUP>-2</SUP> in NGC 6334, 2.3 × 10<SUP>13</SUP> cm<SUP>-2</SUP>
in DR21, and 1.1 × 10<SUP>15</SUP> cm<SUP>-2</SUP> in Sgr B2. <P
/>Herschel is an ESA space observatory with science instruments provided
by European-led Principal Investigator consortia and with important
participation from NASA.
---------------------------------------------------------
Title: The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI)
Authors: de Graauw, Th.; Helmich, F. P.; Phillips, T. G.; Stutzki,
J.; Caux, E.; Whyborn, N. D.; Dieleman, P.; Roelfsema, P. R.; Aarts,
H.; Assendorp, R.; Bachiller, R.; Baechtold, W.; Barcia, A.; Beintema,
D. A.; Belitsky, V.; Benz, A. O.; Bieber, R.; Boogert, A.; Borys, C.;
Bumble, B.; Caïs, P.; Caris, M.; Cerulli-Irelli, P.; Chattopadhyay,
G.; Cherednichenko, S.; Ciechanowicz, M.; Coeur-Joly, O.; Comito, C.;
Cros, A.; de Jonge, A.; de Lange, G.; Delforges, B.; Delorme, Y.; den
Boggende, T.; Desbat, J. -M.; Diez-González, C.; di Giorgio, A. M.;
Dubbeldam, L.; Edwards, K.; Eggens, M.; Erickson, N.; Evers, J.; Fich,
M.; Finn, T.; Franke, B.; Gaier, T.; Gal, C.; Gao, J. R.; Gallego,
J. -D.; Gauffre, S.; Gill, J. J.; Glenz, S.; Golstein, H.; Goulooze,
H.; Gunsing, T.; Güsten, R.; Hartogh, P.; Hatch, W. A.; Higgins,
R.; Honingh, E. C.; Huisman, R.; Jackson, B. D.; Jacobs, H.; Jacobs,
K.; Jarchow, C.; Javadi, H.; Jellema, W.; Justen, M.; Karpov, A.;
Kasemann, C.; Kawamura, J.; Keizer, G.; Kester, D.; Klapwijk, T. M.;
Klein, Th.; Kollberg, E.; Kooi, J.; Kooiman, P. -P.; Kopf, B.; Krause,
M.; Krieg, J. -M.; Kramer, C.; Kruizenga, B.; Kuhn, T.; Laauwen, W.;
Lai, R.; Larsson, B.; Leduc, H. G.; Leinz, C.; Lin, R. H.; Liseau,
R.; Liu, G. S.; Loose, A.; López-Fernandez, I.; Lord, S.; Luinge,
W.; Marston, A.; Martín-Pintado, J.; Maestrini, A.; Maiwald, F. W.;
McCoey, C.; Mehdi, I.; Megej, A.; Melchior, M.; Meinsma, L.; Merkel,
H.; Michalska, M.; Monstein, C.; Moratschke, D.; Morris, P.; Muller,
H.; Murphy, J. A.; Naber, A.; Natale, E.; Nowosielski, W.; Nuzzolo,
F.; Olberg, M.; Olbrich, M.; Orfei, R.; Orleanski, P.; Ossenkopf,
V.; Peacock, T.; Pearson, J. C.; Peron, I.; Phillip-May, S.; Piazzo,
L.; Planesas, P.; Rataj, M.; Ravera, L.; Risacher, C.; Salez, M.;
Samoska, L. A.; Saraceno, P.; Schieder, R.; Schlecht, E.; Schlöder,
F.; Schmülling, F.; Schultz, M.; Schuster, K.; Siebertz, O.; Smit,
H.; Szczerba, R.; Shipman, R.; Steinmetz, E.; Stern, J. A.; Stokroos,
M.; Teipen, R.; Teyssier, D.; Tils, T.; Trappe, N.; van Baaren, C.;
van Leeuwen, B. -J.; van de Stadt, H.; Visser, H.; Wildeman, K. J.;
Wafelbakker, C. K.; Ward, J. S.; Wesselius, P.; Wild, W.; Wulff, S.;
Wunsch, H. -J.; Tielens, X.; Zaal, P.; Zirath, H.; Zmuidzinas, J.;
Zwart, F.
2010A&A...518L...6D Altcode:
<BR /> Aims: This paper describes the Heterodyne Instrument for the
Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space
Observatory in May 2009. <BR /> Methods: The instrument is a set of 7
heterodyne receivers that are electronically tuneable, covering 480-1250
GHz with SIS mixers and the 1410-1910 GHz range with hot electron
bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises
a Ka-band synthesizer followed by 14 chains of frequency multipliers
and 2 chains for each frequency band. A pair of auto-correlators and a
pair of acousto-optical spectrometers process the two IF signals from
the dual-polarization, single-pixel front-ends to provide instantaneous
frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz
to 1 MHz) that are better than 0.1 km s<SUP>-1</SUP>. <BR /> Results:
After a successful qualification and a pre-launch TB/TV test program,
the flight instrument is now in-orbit and completed successfully
the commissioning and performance verification phase. The in-orbit
performance of the receivers matches the pre-launch sensitivities. We
also report on the in-orbit performance of the receivers and some first
results of HIFI's operations. <P />Herschel is an ESA space observatory
with science instruments provided by European-led Principal Investigator
consortia and with important participation from NASA.
---------------------------------------------------------
Title: Multidimensional Chemical Modeling. III. Abundance and
excitation of diatomic hydrides
Authors: Bruderer, Simon; Benz, Arnold O.; Stäuber, P.; Doty,
Steven D.
2010arXiv1007.3261B Altcode:
The Herschel Space Observatory opens the sky for observations in the far
infrared at high spectral and spatial resolution. A particular class of
molecules will be directly observable; light diatomic hydrides and their
ions (CH, OH, SH, NH, CH+, OH+, SH+, NH+). These simple constituents are
important both for the chemical evolution of the region and as tracers
of high-energy radiation. If outflows of a forming star erode cavities
in the envelope, protostellar far UV (FUV; 6 < E_gamma < 13.6 eV)
radiation may escape through such low-density regions. Depending on the
shape of the cavity, the FUV radiation then irradiates the quiescent
envelope in the walls along the outflow. The chemical composition in
these outflow walls is altered by photoreactions and heating via FUV
photons in a manner similar to photo dominated regions (PDRs). In
this work, we study the effect of cavity shapes, outflow density,
and of a disk with the two-dimensional chemical model of a high-mass
young stellar object introduced in the second paper in this series. We
find that the shape of the cavity is particularly important in the
innermost part of the envelope, where the dust temperatures are high
enough (> 100 K) for water ice to evaporate. If the cavity shape
allows FUV radiation to penetrate this hot-core region, the abundance
of FUV destroyed species (e.g. water) is decreased. In particular,
diatomic hydrides and their ions CH$+, OH+ and NH+ are enhanced by
many orders of magnitude in the outflow walls due to the combination
of high gas temperatures and rapid photodissociation of more saturated
species. The enhancement of these diatomic hydrides is sufficient for
a detection using the HIFI and PACS instruments onboard Herschel. The
effect of X-ray ionization on the chemistry is found to be small,
due to the much larger luminosity in FUV bands compared to X-rays.
---------------------------------------------------------
Title: Strong CH<SUP>+</SUP> J = 1-0 emission and absorption in DR21
Authors: Falgarone, E.; Ossenkopf, V.; Gerin, M.; Lesaffre, P.; Godard,
B.; Pearson, J.; Cabrit, S.; Joblin, Ch.; Benz, A. O.; Boulanger, F.;
Fuente, A.; Güsten, R.; Harris, A.; Klein, T.; Kramer, C.; Lord,
S.; Martin, P.; Martin-Pintado, J.; Neufeld, D.; Phillips, T. G.;
Röllig, M.; Simon, R.; Stutzki, J.; van der Tak, F.; Teyssier, D.;
Yorke, H.; Erickson, N.; Fich, M.; Jellema, W.; Marston, A.; Risacher,
C.; Salez, M.; Schmülling, F.
2010A&A...518L.118F Altcode: 2010arXiv1007.1420F
We report the first detection of the ground-state rotational
transition of the methylidyne cation CH<SUP>+</SUP> towards the
massive star-forming region DR 21 with the HIFI instrument onboard the
Herschel satellite. The line profile exhibits a broad emission line,
in addition to two deep and broad absorption features associated with
the DR 21 molecular ridge and foreground gas. These observations allow
us to determine a <SUP>12</SUP>CH<SUP>+</SUP>J = 1-0 line frequency of
ν = 835 137 ± 3 MHz, in good agreement with a recent experimental
determination. We estimate the CH<SUP>+</SUP> column density to be a
few 10<SUP>13</SUP> cm<SUP>-2</SUP> in the gas seen in emission, and
>10<SUP>14</SUP> cm<SUP>-2</SUP> in the components responsible for
the absorption, which is indicative of a high line of sight average
abundance [CH<SUP>+</SUP>] /[H] > 1.2 × 10<SUP>-8</SUP>. We show
that the CH<SUP>+</SUP> column densities agree well with the predictions
of state-of-the-art C-shock models in dense UV-illuminated gas for
the emission line, and with those of turbulent dissipation models in
diffuse gas for the absorption lines. <P />Herschel is an ESA space
observatory with science instruments provided by European-led Principal
Investigator consortia and with important participation from NASA.
---------------------------------------------------------
Title: Temperature and Density in the Foot Points of the Molecular
Loops in the Galactic Center; Analysis of Multi-J Transitions of
<SUP>12</SUP>CO (J = 1--0, 3--2, 4--3, 7--6), <SUP>13</SUP>CO (J =
1--0), and C<SUP>18</SUP>O (J = 1--0)
Authors: Torii, Kazufumi; Kudo, Natsuko; Fujishita, Motosuji; Kawase,
Tokuichi; Okuda, Takeshi; Yamamoto, Hiroaki; Kawamura, Akiko; Mizuno,
Norikazu; Onishi, Toshikazu; Machida, Mami; Takahashi, Kunio; Nozawa,
Satoshi; Matsumoto, Ryoji; Ott, Jürgen; Tanaka, Kunihiko; Yamaguchi,
Nobuyuki; Ezawa, Hajime; Stutzki, Jürgen; Bertoldi, Frank; Koo,
Bon-Chul; Bronfman, Leonardo; Burton, Michael; Benz, Arnold O.; Ogawa,
Hideo; Fukui, Yasuo
2010PASJ...62..675T Altcode: 2009arXiv0909.2073T
<A >Fukui et al.(2006)</A> (<A >Fukui et
al.(2006)</A>, Science, 314, 106) discovered two molecular loops
in the Galactic center, and argued that the foot points of the molecular
loops, two bright spots at both loop ends, represent gas accumulated by
the falling motion along the loops, subsequent to magnetic flotation by
the Parker instability. We have carried out sensitive CO observations
of the foot points toward l = 356° at a few pc resolution in the six
rotational transitions of CO: <SUP>12</SUP>CO (J = 1--0, 3--2, 4--3,
7--6), <SUP>13</SUP>CO (J = 1--0), and C<SUP>18</SUP>O (J = 1--0). A
high-resolution image of <SUP>12</SUP>CO (J = 3--2) has revealed the
detailed distribution of the high-excitation gas, including U shapes,
the outer boundary of which shows sharp intensity jumps accompanying
strong velocity gradients. An analysis of the multi-J CO transitions
shows that the temperature is in the range from 30 to 100 K and
the density is around 10<SUP>3</SUP>-10<SUP>4</SUP>cm<SUP>-3</SUP>,
confirming that the foot points have high temperature and density,
although there is no prominent radiative heating source, such
as high-mass stars in or around the loops. We argue that the
high temperature is likely due to shock heating under the C-shock
condition caused by magnetic flotation. We made a comparison of the gas
distribution with theoretical numerical simulations, and note that the
U shape is consistent with numerical simulations. We also find that the
region of highest temperature of ∼100 K or higher inside the U shape
corresponds to the spur having an upward flow, additionally heated up
either by magnetic reconnection or bouncing in the interaction with
the narrow neck at the bottom of the U shape. We note that these new
findings further reinforce the magnetic floatation interpretation.
---------------------------------------------------------
Title: Observing Solar Hard X-rays from Heliospheric Orbits
Authors: Hurford, Gordon J.; Benz, A.; Dennis, B.; Krucker, S.;
Limousin, O.; Lin, R.; Vilmer, N.
2010AAS...21640416H Altcode: 2010BAAS...41Q.902H
The coming decade provides two opportunities to acquire a different
observational perspective on solar hard x-ray emission. Both ESA's Solar
Orbiter and NASA's Solar Probe Plus missions will be in heliocentric
orbits with perihelia of 0.28 au and 0.05 au respectively. This
poster indicates the unique scientific advantages of hard x-ray
imaging/spectroscopy observations from such platforms. <P />These
advantages stem from three factors: First, in combination with other
payload elements, the hard x-rays provide the ability to observationally
link accelerated electrons at the Sun to radio observations of
the propagating electrons and to direct observations of in situ
electrons. Second, the substantial gain in sensitivity afforded by
close-in vantage points enables exploration of the origin of non-flare
associated SEP events to be studied and the character of quiescent
active-region heating and electron acceleration to be evaluated. Third,
the different observational perspectives provided by the heliocentric
orbits compared to low-Earth orbits enable improved separation of
coronal and footpoint sources as well as measurements of the isotropy
of the x-ray emission. <P />Despite the limited payload resources
(mass, power, telemetry) afforded by such missions, scientifically
effective hard x-ray imaging spectroscopy from 5 keV to 150 keV is
still feasible. The Spectrometer/Telescope for Imaging X-rays (STIX),
accepted as part of the Solar Orbiter payload, combines high spectral
resolution ( 1 keV FWHM at 10 keV) with spatial resolution as good
as 1500 km, and can efficiently encode the data for several hundred
optimized images per hour within a modest telemetry allocation and
4 kg / 4 watt budget. The X-ray Imaging Spectrometer (XIS) proposed
for Solar Probe Plus, views the Sun through its thermal shield. It
also features high spectral resolution from 6 to 150 keV and spatial
resolution of 1500 km at perihelion. The poster describes the imaging
principles and current configurations of both instruments.
---------------------------------------------------------
Title: GT1_abenz_1: Completing the OH ladder for HH 46
Authors: Benz, A.
2010hers.prop..586B Altcode:
First results from PACS observations towards the low-mass protostar HH
46 show surprisingly bright OH lines. The hydroxyl radical OH plays
important roles in the water and oxygen chemistry of star-forming
regions and their cooling. Furthermore, the hydroxyl-to-water line
ratios are interesting tracers for ionizing radiation. We propose a
nearly complete observation of the OH ladder in low-mass star formation
for the first time. Four OH transitions in the class I object HH 46
were detected by PACS. We propose complementary observations towards
the source in PACS line spectroscopy mode at 53, 56, 65, 71, 96,
115 and 135 micron. We gain insight in the origin and formation of OH
from the PACS spatial information. The completeness of the OH ladder
allows a reliable determination of the OH abundance and thus constrains
water chemistry and cooling contribution more precisely. In addition,
we propose HIFI observations of the OH transition at 163.4 micron to
resolve the three hyperfine components for the first time. This will
allow to determine optical depths of OH and test the hypothesis of
asymmetries between the two closely spaced triplets, as the second
triplet will be observed within the HIFI priority science program. <P
/>Note: This proposal is submitted under the Swiss part of the HIFI
guaranteed time program; HIFI PI: Frank Helmich, HIFI Swiss Lead CoI:
Arnold O. Benz
---------------------------------------------------------
Title: Warm and Dense Molecular Gas in the N 159 Region:
<SUP>12</SUP>CO J = 4-3 and <SUP>13</SUP>CO J = 3-2 Observations
with NANTEN2 and ASTE
Authors: Mizuno, Yoji; Kawamura, Akiko; Onishi, Toshikazu; Minamidani,
Tetsuhiro; Muller, Erik; Yamamoto, Hiroaki; Hayakawa, Takahiro;
Mizuno, Norikazu; Mizuno, Akira; Stutzki, Jürgen; Pineda, Jorge L.;
Klein, Uli; Bertoldi, Frank; Koo, Bon-Chul; Rubio, Monica; Burton,
Michael; Benz, Arnold; Ezawa, Hajime; Yamaguchi, Nobuyuki; Kohno,
Kotaro; Hasegawa, Tetsuo; Tatematsu, Ken'ichi; Ikeda, Masafumi; Ott,
Jürgen; Wong, Tony; Hughes, Annie; Meixner, Margaret; Indebetouw,
Remy; Gordon, Karl D.; Whitney, Barbara; Bernard, Jean-Philippe;
Fukui, Yasuo
2010PASJ...62...51M Altcode: 2009arXiv0910.0309M
New 12CO J=4-3 and 13CO J=3-2 observations of the N159 region in the
Large Magellanic Cloud have been made. The 12CO J=4-3 distribution
is separated into three clumps. These new measurements toward the
three clumps are used in coupled calculations of molecular rotational
excitation and line radiation transfer, along with other transitions of
the 12CO as well as the isotope transitions of 13CO. The temperatures
and densities are determined to be ~70-80K and ~3x10^3 cm-3 in
N159W and N159E and ~30K and ~1.6x10^3 cm-3 in N159S. These results
are compared with the star formation activity. The N159E clump is
associated with embedded cluster(s) as observed at 24 micron and the
derived high temperature is explained as due to the heating by these
sources. The N159E clump is likely responsible for a dark lane in a
large HII region by the dust extinction. The N159W clump is associated
with embedded clusters mainly toward the eastern edge of the clump
only. These clusters show offsets of 20"-40" from the 12CO J=4-3 peak
and are probably responsible for heating indicated by the derived high
temperature. The N159W clump exhibits no sign of star formation toward
the 12CO J=4-3 peak position and its western region. We suggest that
the N159W peak represents a pre-star-cluster core of ~105M_sol which
deserves further detailed studies. Note that recent star formation took
place between N159W and N159E as indicated by several star clusters
and HII regions, while the natal molecular gas toward the stars have
already been dissipated by the ionization and stellar winds of the
OB stars. The N159S clump shows little sign of star formation as is
consistent with the lower temperature and somewhat lower density. The
N159S clump is also a candidate for future star formation.
---------------------------------------------------------
Title: Initial results from the Herschel Oxygen Project
Authors: Goldsmith, Paul; Encrenaz, Pierre; Liseau, R.; Bell, T. A.;
Bergin, T.; Black, J.; Benz, A.; Caselli, P.; Caux, E.; Falgarone,
E.; Gerin, M.; Goicoechea, J. R.; Hjalmarson, A.; Hollenbach, D.;
Kaufman, M.; Larsson, B.; Le Bourlot, J.; Le Petit, F.; Li, D.; Lis,
D.; Melnick, G.; Neufeld, D.; Pagani, L.; Roueff, E.; Sandqvist, A.;
Snell, R.; Vastel, C.; van Dishoeck, E.; Viti, S.; van der Tak, F.
2010cosp...38.2480G Altcode: 2010cosp.meet.2480G
Initial Results from the Herschel Oxygen Project (HOP) Oxygen is
the third most abundant element in the cosmos, but can be found in
many forms. In the gas phase, oxygen can be ionized, atomic, or in
molecular form, and it is also incorporated into grains. The molecular
form is expected to dominate in cold, well-shielded regions, and in
such molecular clouds, oxygen can be found in key species including
carbon monoxide and water. Gas phase chemistry models predict molecular
oxygen (O2) to be almost as abundant as CO. A number of searches for
rotational transitions of O2 have been carried out. These include
ground-based searches for the isotopologue 16O18O and searches for
16O2 in galaxies with red shift sufficient to move the line away from
terrestrial atmospheric absorption. Searches for Galactic 16O2 carried
out with the SWAS and Odin spacecraft have yielded upper limits on
the abundance of molecular oxygen typically 1 to 2 orders of magnitude
below those predicted by gas-phase models. There has been a statistical
detection of O2 in one source, again at a low abundance. A variety of
new models have been proposed to explain this low abundance, which
involve grain surface and photo effects. To address this important
problem in astro-chemistry and molecular cloud structure, we have
developed the Open Time Key Project HOP (Herschel Oxygen Project),
which exploits the high angular resolution and sensitivity of the HIFI
instrument on Herschel to observe 3 rotational transitions of O2 in
a broad sample of molecular clouds. We report on the status of HOP
and present early results available from Priority Science Phase and
Science Definition Phase observations.
---------------------------------------------------------
Title: High Spectral Resolution Observation of Decimetric Radio Spikes
Emitted by Solar Flares - First Results of the Phoenix-3 Spectrometer
Authors: Benz, Arnold O.; Monstein, Christian; Beverland, Michael;
Meyer, Hansueli; Stuber, Bruno
2009SoPh..260..375B Altcode: 2009arXiv0909.4137B
A new multichannel spectrometer, Phoenix-3, is in operation having
capabilities to observe solar flare radio emissions in the 0.1 -
5 GHz range at an unprecedented spectral resolution of 61.0 kHz with
high sensitivity. The present setup for routine observations allows
measuring circular polarization, but requires a data compression
to 4096 frequency channels in the 1 - 5 GHz range and to a temporal
resolution of 200 ms. First results are presented by means of a well
observed event that included narrowband spikes at 350 - 850 MHz. Spike
bandwidths are found to have a power - law distribution, dropping
off below a value of 2 MHz for full width at half maximum (FWHM). The
narrowest spikes have a FWHM bandwidth less than 0.3 MHz or 0.04% of
the central frequency. The smallest half-power increase occurs within
0.104 MHz at 443.5 MHz, which is close to the predicted natural width
of maser emission. The spectrum of spikes is found to be asymmetric,
having an enhanced low-frequency tail. The distribution of the total
spike flux is approximately an exponential.
---------------------------------------------------------
Title: Correlation between decimetric radio emission and hard X-rays
in solar flares
Authors: Dabrowski, B. P.; Benz, A. O.
2009A&A...504..565D Altcode: 2009A&A...504..565B
Aims: The emission of decimetric flare radiation, in particular
narrowband spikes and pulsations, is generally considered to originate
in accelerated, non-thermal particles. On the other hand, non-thermal
hard X-rays are also understood to be products of this acceleration. Do
radio emission and hard X-ray signatures originate from the same
acceleration process? A strong correlation between the light curves in
the radio and HXR ranges may help answer this question. <BR />Methods:
The delay between the radio and hard X-ray emission was determined
by cross-correlation. The time profiles of X-ray and radio emission
include a wide range of energies and frequencies. Thus, correlation is
not simply a yes/no question, but must be systematically searched for
in various ranges. The high spectral resolution of RHESSI ensured that
it was possible to carefully choose the energy range, excluding thermal
emission. The broad bandwidth of Phoenix-2 allowed the selection of any
emission in the full decimetre range. The energy range and duration in
hard X-rays, and the frequency range in radio spectrograms were chosen
to optimize the correlation. The cross-correlation coefficient was
then analyzed by a Gaussian fitting method. <BR />Results: The measured
delays have a distribution of FWHM 4.9 s and 4.7 s for pulsations and
spikes, respectively, evaluated from such a Gaussian fitting method. The
mean delay for pulsations was found to be -1.4± 0.9 s (minus indicates
that hard X-ray emission comes first), and for narrowband spikes
to -2.5±2.5 s. There are broad wings in the distribution, which we
interpret as chance coincidences. The delays do not depend on centre
frequency, cross-correlation coefficient, duration of the correlating
sequence, and position on the disk. However, we find an increase in
the delay for the spikes with GOES magnitude (peak soft X-ray emission)
of the flare and with peak hard X-ray flux. This was not the case for
pulsations. <BR />Conclusions: In contrast to previous reports, the
average delays for all pulsations and all spike groups are consistent
with zero. Thus, correlated decimetric pulsations and spikes are,
on average, concomitant with non-thermal X-rays.
---------------------------------------------------------
Title: Evidence of warm and dense material along the outflow of a
high-mass YSO
Authors: Bruderer, S.; Benz, A. O.; Bourke, T. L.; Doty, S. D.
2009A&A...503L..13B Altcode:
Context: Outflow cavities in envelopes of young stellar objects (YSOs)
have been predicted to allow far-UV (FUV) photons to escape far from
the central source, with significant observable effects, especially
if the protostar is a forming high-mass star suspected of emitting a
copious amount of FUV radiation. Indirect evidence of this picture has
been provided by models and unresolved single-dish observations, but
direct high-resolution data are necessary for confirmation. Previous
chemical modeling has suggested that CS and HCN are good probes of the
local FUV field, so make good target species. <BR />Aims: We directly
probe the physical conditions of the material in the outflow walls to
test this prediction. <BR />Methods: Interferometric observations of
the CS(7-6) and HCN(4-3) rotational lines in the high-mass star-forming
region <ASTROBJ>AFGL 2591</ASTROBJ> are carried out in the compact
and extended configuration of the SubMillimeter Array (SMA). The
velocity structure was analyzed, and integrated maps compared to
K-band near-IR observations. A chemical model predicts abundances of
CS and HCN for a gas under protostellar X-ray and FUV irradiation,
and was used in conjunction with the data to distinguish between
physical scenarios. <BR />Results: CS and HCN emission was found in
spatial coincidence in extended sources displaced up to 7 arcsec from
the position of the young star. Their line widths are small, excluding
major shocks. Chemical model calculations predict an enhanced abundance
of the two molecules in warm, dense, and FUV irradiated gas. Hot dust
observed between the molecular emission and the outflow accounts
for the necessary attenuation to prevent photodissociation of the
molecules. <BR />Conclusions: The SMA data suggest that the outflow
walls are heated and chemically altered by the FUV emission of the
central high-mass object, providing the best direct evidence yet of
large-scale direct irradiation of outflow walls. <P />Appendix is only
available in electronic form at http://www.aanda.org
---------------------------------------------------------
Title: Chemical Modeling of Young Stellar Objects. I. Method and
Benchmarks
Authors: Bruderer, S.; Doty, S. D.; Benz, A. O.
2009ApJS..183..179B Altcode: 2009arXiv0906.0584B
Upcoming facilities such as the Herschel Space Observatory or Atacama
Large Millimeter Array will deliver a wealth of molecular line
observations of young stellar objects (YSOs). Based on line fluxes,
chemical abundances can then be estimated by radiative transfer
calculations. To derive physical properties from abundances,
the chemical network needs to be modeled and fitted to the
observations. This modeling process is however computationally
exceedingly demanding, particularly if in addition to density and
temperature, far-UV (FUV) irradiation, X-rays, and multi-dimensional
geometry have to be considered. We develop a fast tool, suitable
for various applications of chemical modeling in YSOs. A grid of the
chemical composition of the gas having a density, temperature, FUV
irradiation and X-ray flux is pre-calculated as a function of time. A
specific interpolation approach is developed to reduce the database
to a feasible size. Published models of AFGL 2591 are used to verify
the accuracy of the method. A second benchmark test is carried out
for FUV sensitive molecules. The novel method for chemical modeling
is more than 250,000 times faster than direct modeling and agrees
within a mean factor of 1.35. The tool is distributed for public
use. Main applications are (1) fitting physical parameters to observed
molecular line fluxes and (2) deriving chemical abundances for two-
and three-dimensional models. They will be presented in two future
publications of this series. In the course of developing the method,
the chemical evolution is explored: we find that X-ray chemistry
in envelopes of YSOs can be reproduced by means of an enhanced
cosmic-ray ionization rate with deviations less than 25%, having
the observational consequence that molecular tracers for X-rays are
hard to distinguish from cosmic-ray ionization tracers. We provide
the detailed prescription to implement this total ionization rate
approach in any chemical model. We further find that the abundance of
CH<SUP>+</SUP> in low-density gas with high ionization can be enhanced
by the recombination of doubly ionized carbon (C<SUP>++</SUP>) and
suggest a new value for the initial abundance of the main sulfur
carrier in the hot core.
---------------------------------------------------------
Title: Multidimensional Chemical Modeling of Young Stellar
Objects. II. Irradiated Outflow Walls in a High-Mass Star-Forming
Region
Authors: Bruderer, S.; Benz, A. O.; Doty, S. D.; van Dishoeck, E. F.;
Bourke, T. L.
2009ApJ...700..872B Altcode: 2009arXiv0906.0588B
Observations of the high-mass star-forming region AFGL 2591 reveal a
large abundance of CO<SUP>+</SUP>, a molecule known to be enhanced by
far-ultraviolet (FUV) and X-ray irradiation. In chemical models assuming
a spherically symmetric envelope, the volume of gas irradiated by
protostellar FUV radiation is very small due to the high extinction by
dust. The abundance of CO<SUP>+</SUP> is thus underpredicted by orders
of magnitude. In a more realistic model, FUV photons can escape through
an outflow region and irradiate gas at the border to the envelope. Thus,
we introduce the first two-dimensional axisymmetric chemical model
of the envelope of a high-mass star-forming region to explain the
CO<SUP>+</SUP> observations as a prototypical FUV tracer. The model
assumes an axisymmetric power-law density structure with a cavity
due to the outflow. The local FUV flux is calculated by a Monte Carlo
radiative transfer code taking scattering on dust into account. A grid
of precalculated chemical abundances, introduced in the first part
of this series of papers, is used to quickly interpolate chemical
abundances. This approach allows us to calculate the temperature
structure of the FUV-heated outflow walls self-consistently with
the chemistry. Synthetic maps of the line flux are calculated using
a raytracer code. Single-dish and interferometric observations are
simulated and the model results are compared to published and new JCMT
and Submillimeter Array (SMA) observations. The two-dimensional model
of AFGL 2591 is able to reproduce the JCMT single-dish observations
and also explains the nondetection by the SMA. We conclude that
the observed CO<SUP>+</SUP> line flux and its narrow width can be
interpreted by emission from the warm and dense outflow walls irradiated
by protostellar FUV radiation.
---------------------------------------------------------
Title: Do solar decimetric spikes originate in coronal X-ray sources?
Authors: Battaglia, M.; Benz, A. O.
2009A&A...499L..33B Altcode: 2009arXiv0904.4146B
Context: In the standard solar flare scenario, a large number of
particles are accelerated in the corona. Nonthermal electrons emit
both X-rays and radio waves. Thus, correlated signatures of the
acceleration process are predicted at both wavelengths, coinciding
either close to the footpoints of a magnetic loop or near the coronal
X-ray source. <BR />Aims: We attempt to study the spatial connection
between coronal X-ray emission and decimetric radio spikes to determine
the site and geometry of the acceleration process. <BR />Methods:
The positions of radio-spike sources and coronal X-ray sources are
determined and analyzed in a well-observed limb event. Radio spikes
are identified in observations from the Phoenix-2 spectrometer. Data
from the Nançay radioheliograph are used to determine the position
of the radio spikes. RHESSI images in soft and hard X-ray wavelengths
are used to determine the X-ray flare geometry. Those observations
are complemented by images from GOES/SXI. <BR />Results: We find
that the radio emission originates at altitudes much higher than the
coronal X-ray source, having an offset from the coronal X-ray source
amounting to 90´´ and to 113´´ and 131´´ from the two footpoints,
averaged over time and frequency. <BR />Conclusions: Decimetric spikes
do not originate from coronal X-ray flare sources contrary to previous
expectations. However, the observations suggest a causal link between
the coronal X-ray source, related to the major energy release site,
and simultaneous activity in the higher corona.
---------------------------------------------------------
Title: Observations of conduction driven evaporation in the early
rise phase of solar flares
Authors: Battaglia, M.; Fletcher, L.; Benz, A. O.
2009A&A...498..891B Altcode: 2009arXiv0903.2754B
Context: The classical flare picture features a beam of electrons, which
were accelerated in a site in the corona, hitting the chromosphere. The
electrons are stopped in the dense chromospheric plasma, emitting
bremsstrahlung in hard X-rays. The ambient material is heated by the
deposited energy and expands into the magnetic flare loops, a process
termed chromospheric evaporation. In this view hard X-ray emission from
the chromosphere is succeeded by soft-X-ray emission from the hot plasma
in the flare loop, the soft X-ray emission being a direct consequence
of the impact of the non-thermal particle beam. However, observations
of events exist in which a pronounced increase in soft X-ray emission
is observed minutes before the onset of the hard X-ray emission. Such
pre-flare emission clearly contradicts the classical flare picture. <BR
/>Aims: For the first time, the pre-flare phase of such solar flares
is studied in detail. The aim is to understand the early rise phase of
these events. We want to explain the time evolution of the observed
emission by means of alternative energy transport mechanisms such as
heat conduction. <BR />Methods: RHESSI events displaying pronounced
pre-flare emission were analyzed in imaging and spectroscopy. The time
evolution of images and full sun spectra was investigated and compared
to the theoretical expectations from conduction driven chromospheric
evaporation. <BR />Results: The pre-flare phase is characterized by
purely thermal emission from a coronal source with increasing emission
measure and density. After this earliest phase, a small non-thermal
tail to higher energies appears in the spectra, becoming more and
more pronounced. However, images still only display one X-ray source,
implying that this non-thermal emission is coronal. The increase of
emission measure and density indicates that material is added to the
coronal region. The most plausible origin is evaporated material from
the chromosphere. Energy provided by a heat flux is capable of driving
chromospheric evaporation. We show that the often used classical Spitzer
treatment of the conductive flux is not applicable. The conductive
flux is saturated. During the preflare-phase, the temperature of the
coronal source remains constant or increases. Continuous heating in the
corona is necessary to explain this observation. <BR />Conclusions:
The observations of the pre-flare phase of four solar flares are
consistent with chromospheric evaporation driven by a saturated heat
flux. Additionally, continuous heating in the corona is necessary to
sustain the observed temperature.
---------------------------------------------------------
Title: A World-Wide Net of Solar Radio Spectrometers: e-CALLISTO
Authors: Benz, A. O.; Monstein, C.; Meyer, H.; Manoharan, P. K.;
Ramesh, R.; Altyntsev, A.; Lara, A.; Paez, J.; Cho, K. -S.
2009EM&P..104..277B Altcode: 2009EM&P..tmp....2B
Radio spectrometers of the CALLISTO type to observe solar flares have
been distributed to nine locations around the globe. The instruments
observe automatically, their data is collected every day via internet
and stored in a central data base. A public web-interface exists
through which data can be browsed and retrieved. The nine instruments
form a network called e-CALLISTO. It is still growing in the number
of stations, as redundancy is desirable for full 24 h coverage of
the solar radio emission in the meter and low decimeter band. The
e-CALLISTO system has already proven to be a valuable new tool for
monitoring solar activity and for space weather research.
---------------------------------------------------------
Title: Millimetron—a large Russian-European submillimeter space
observatory
Authors: Wild, Wolfgang; Kardashev, Nikolay S.; Likhachev, S. F.;
Babakin, N. G.; Arkhipov, V. Y.; Vinogradov, I. S.; Andreyanov,
V. V.; Fedorchuk, S. D.; Myshonkova, N. V.; Alexsandrov, Y. A.;
Novokov, I. D.; Goltsman, G. N.; Cherepaschuk, A. M.; Shustov, B. M.;
Vystavkin, A. N.; Koshelets, V. P.; Vdovin, V. F.; de Graauw, Th.;
Helmich, F.; Vd Tak, F.; Shipman, R.; Baryshev, A.; Gao, J. R.;
Khosropanah, P.; Roelfsema, P.; Barthel, P.; Spaans, M.; Mendez, M.;
Klapwijk, T.; Israel, F.; Hogerheijde, M.; Vd Werf, P.; Cernicharo,
J.; Martin-Pintado, J.; Planesas, P.; Gallego, J. D.; Beaudin,
G.; Krieg, J. M.; Gerin, M.; Pagani, L.; Saraceno, P.; di Giorgio,
A. M.; Cerulli, R.; Orfei, R.; Spinoglio, L.; Piazzo, L.; Liseau, R.;
Belitsky, V.; Cherednichenko, S.; Poglitsch, A.; Raab, W.; Guesten,
R.; Klein, B.; Stutzki, J.; Honingh, N.; Benz, A.; Murphy, A.; Trappe,
N.; Räisänen, A.
2009ExA....23..221W Altcode: 2008ExA...tmp...17W
Millimetron is a Russian-led 12 m diameter submillimeter and
far-infrared space observatory which is included in the Space Plan of
the Russian Federation for launch around 2017. With its large collecting
area and state-of-the-art receivers, it will enable unique science
and allow at least one order of magnitude improvement with respect
to the Herschel Space Observatory. Millimetron will be operated in
two basic observing modes: as a single-dish observatory, and as an
element of a ground-space very long baseline interferometry (VLBI)
system. As single-dish, angular resolutions on the order of 3 to 12
arc sec will be achieved and spectral resolutions of up to a million
employing heterodyne techniques. As VLBI antenna, the chosen elliptical
orbit will provide extremely large VLBI baselines (beyond 300,000 km)
resulting in micro-arc second angular resolution.
---------------------------------------------------------
Title: A Venus Flagship Mission: Report of the Venus Science and
Technology Definition Team
Authors: Bullock, M. A.; Senske, D. A.; Balint, T. S.; Benz, A.;
Campbell, B. A.; Chassefiere, E.; Colaprete, A.; Cutts, J. A.; Glaze,
L.; Gorevan, S.; Grinspoon, D. H.; Hall, J.; Hashimoto, G. L.; Head,
J. W.; Hunter, G.; Johnson, N.; Kerzhanovich, V. V.; Kiefer, W. S.;
Kolawa, E. A.; Kremic, T.; Kwok, J.; Limaye, S. S.; Mackwell, S. J.;
Marov, M. Y.; Ocampo, A.; Schubert, G.; Stofan, E. R.; Svedhem, H.;
Titov, D. V.; Treiman, A. H.
2009LPI....40.2410B Altcode:
The Venus STDT has defined the goals, objectives, mission architecture,
science investigations and payload for a Flagship-class mission to
Venus. The mission puts advanced exploration capabilities in orbit,
in the atmosphere, and on the surface.
---------------------------------------------------------
Title: Construction of AN E-Callisto Station in Korea
Authors: Bong, Su-Chan; Kim, Yeon-Han; Roh, Hee-Seon; Cho, Kyung-Suk;
Park, Young-Deuk; Choi, Seong-Hwan; Baek, Ji-Hye; Monstein, Christian;
Benz, Arnold O.; Moon, Yong-Jae; Kim, Sung-Soo S.
2009JKAS...42....1B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radio Emission of the Quiet Sun
Authors: Benz, Arnold O.
2009LanB...4B..103B Altcode: 2009LanB...4B.4116B
No abstract at ADS
---------------------------------------------------------
Title: Solar Differential Rotation Determined by Tracing Low and
High Brightness Temperature Regions at 8 mm
Authors: Romštajn, I.; Brajša, R.; Wöhl, H.; Benz, A. O.; Temmer,
M.; Roša, D.; Ruždjak, V.
2009CEAB...33...79R Altcode:
At the wavelength of 8 mm absorption features (Low brightness
Temperature Regions, LTRs) and emission features (High brightness
Temperature Regions, HTRs) can be traced for determination of solar
rotation. From earlier studies it is known that about two thirds of LTRs
are associated with Hα filaments. The goal of the present analysis is
to determine the heights of these solar structures and their rotational
velocities. We used the method for the simultaneous determination of
the solar synodic rotation velocity and the height of tracers. The
rotation velocities were determined by the linear least-square fit of
their central meridian distances as a function of time. The mean value
of the low brightness temperature regions' heights is about 45 600
km. The results of solar rotation determined by tracing LTRs and HTRs
are mutually compared and also compared with the results using other
tracers and methods. The method for the simultaneous determination
of the solar synodic rotation velocity and the height of the tracers
could be applied properly only on LTRs, since a wide distribution
over latitudes and central meridian distances of a large data set is
necessary, which was not available for HTRs. Observational findings that
HTRs rotate systematically faster than LTRs and the possibility that
they can be observed at and outside the solar limb are consistent with
relatively high altitudes of HTRs. It was concluded that the radiation
mechanism of HTRs is thermal bremsstrahlung, probably associated with
flaring active regions.
---------------------------------------------------------
Title: On the Relation Between Decimetric and Hard X-ray Emissions
in the Impulsive Flare Phase
Authors: Dabrowski, B. P.; Benz, A. O.
2009CEAB...33..221D Altcode:
The emission of decimetric flare radiation, in particular narrowband
spikes and pulsations, is generally considered to originate from
accelerated, non-thermal particles. On the other hand, non-thermal hard
X-rays (HXR) are well accepted results of such acceleration. Are radio
emissions and HXR signatures of the same acceleration process? Good
correlation of the light curves in the radio and HXR range may evidence
it. <P />The correlation of decimetric radio emission and HXR in solar
flares was analysed using data from the RHESSI spacecraft and the
Phoenix-2 spectrometer in Bleien (Switzerland). For the first time we
have the possibility of a systematic search on the radio-HXR relation
in the range from 100 MHz to 4 GHz. <P />The measured delays have a
distribution with a FWHM of 4.9 s and 4.7 s for pulsations and spikes,
respectively, evaluated from a Gauss fitting method. The mean delay
for pulsations was found to be -1.4± 0.9 seconds (minus indicates
that hard X-rays emission comes first), and for narrowband spikes
to -2.5±2.5 seconds. The delays do not depend on centre frequency,
cross-correlation coefficient, duration of the correlating sequence
and position on the disc. However, we find an increase in delay for
the spikes with GOES magnitude (peak soft X-ray emission) of the flare
and with peak hard X-ray flux.
---------------------------------------------------------
Title: Radio Bursts of the Non-Thermal Sun
Authors: Benz, Arnold O.
2009LanB...4B..189B Altcode: 2009LanB...4B.4128B
No abstract at ADS
---------------------------------------------------------
Title: Heights of solar tracers observed at 8 mm and an interpretation
of their radiation
Authors: Brajša, R.; Romštajn, I.; Wöhl, H.; Benz, A. O.; Temmer,
M.; Roša, D.
2009A&A...493..613B Altcode:
Context: At the wavelength of 8 mm, emissive features (high
brightness-temperatrue regions, HTRs) and absorptive features
(low brightness-temperature regions, LTRs) can be traced for the
determining the solar rotation. From earlier studies it is known
that about two thirds of LTRs are associated with Hα filaments. <BR
/>Aims: Thermal bremsstrahlung and gyromagnetic (cyclotron) radiation
mechanism can be important for explaining the observed phenomena,
so we determine the heights of solar structures and interpret their
radiation mechanism(s). <BR />Methods: We use the method of simultaneous
determination of the solar synodic rotation velocity and the height
of tracers. The rotation velocities were determined by the linear
least-square fit of their central meridian distance as a function of
time. We used a procedure for calculating the brightness temperature for
a given wavelength and model atmosphere, which integrates the radiative
transfer equation for the thermal bremsstrahlung. <BR />Results:
The mean value of the low brightness-temperature regions' heights
is about 45 600 km. This height was used as input for constructing
prominence and coronal condensation models, which, when assuming thermal
bremsstrahlung as the radiation mechanism, yield a decrease in the
brightness temperature of 2-14%, in agreement with observations. If the
same radiation mechanism is considered, the models of the solar corona
above active regions give an increase in the brightness temperature of
5-19%, also in agreement with observations. In this case an indirect
indication (from the rotational analysis) that the HTRs are located
higher in the solar atmosphere than the LTRs was taken into account. <BR
/>Conclusions: The method for simultaneously determining the solar
synodic rotation velocity and the height of tracers could have only
been properly applied on LTRs, since a homogeneous distribution over
latitudes and central meridian distances of a large enough data set is
necessary. Thermal bremsstrahlung can explain both the LTR (prominences
and coronal condensations) and HTR (ordinary active regions) phenomena
observed at 8 mm. At this wavelength, thermal gyromagnetic emission
is almost surely excluded as a possible radiation mechanism.
---------------------------------------------------------
Title: Flare Observations
Authors: Benz, Arnold O.
2008LRSP....5....1B Altcode:
Solar flares are observed at all wavelengths from decameter radio waves
to gamma-rays at 100 MeV. This review focuses on recent observations
in EUV, soft and hard X-rays, white light, and radio waves. Space
missions such as RHESSI, Yohkoh, TRACE, and SOHO have enlarged widely
the observational base. They have revealed a number of surprises:
Coronal sources appear before the hard X-ray emission in chromospheric
footpoints, major flare acceleration sites appear to be independent of
coronal mass ejections (CMEs), electrons, and ions may be accelerated at
different sites, there are at least 3 different magnetic topologies, and
basic characteristics vary from small to large flares. Recent progress
also includes improved insights into the flare energy partition, on
the location(s) of energy release, tests of energy release scenarios
and particle acceleration. The interplay of observations with theory
is important to deduce the geometry and to disentangle the various
processes involved. There is increasing evidence supporting reconnection
of magnetic field lines as the basic cause. While this process has
become generally accepted as the trigger, it is still controversial
how it converts a considerable fraction of the energy into non-thermal
particles. Flare-like processes may be responsible for large-scale
restructuring of the magnetic field in the corona as well as for its
heating. Large flares influence interplanetary space and substantially
affect the Earth's lower ionosphere. While flare scenarios have slowly
converged over the past decades, every new observation still reveals
major unexpected results, demonstrating that solar flares, after 150
years since their discovery, remain a complex problem of astrophysics
including major unsolved questions.
---------------------------------------------------------
Title: A Venus Flagship Mission: Exploring a World of Contrasts
Authors: Senske, D.; Bullock, M.; Balint, T.; Benz, A.; Campbell,
B.; Chassefiere, E.; Colaprete, A.; Cutts, J.; Glaze, L.; Gorevan,
S.; Grinspoon, D.; Hall, J.; Hasimoto, G.; Head, J.; Hunter, G.;
Johnson, N.; Kiefer, W.; Kolawa, E.; Kremic, T.; Kwok, J.; Limaye,
S.; Mackwell, S.; Marov, M.; Peterson, C.; Schubert, G.; Spilker,
T.; Stofan, E.; Svedhem, H.; Titov, D.; Treiman, A.
2008AGUFM.P22A..08S Altcode:
Results from past missions and the current Venus Express Mission show
that Venus is a world of contrasts, providing clear science drivers
for renewed exploration of this planet. In early 2008, NASA's Science
Mission Directorate formed a Science and Technology Definition Team
(STDT) to formulate science goals and objectives, mission architecture
and a technology roadmap for a flagship class mission to Venus. This
3- to 4 billon mission, to launch in the post 2020 timeframe, should
revolutionize our understanding of how climate works on terrestrial
planets, including the close relationship between volcanism, tectonism,
the interior, and the atmosphere. It would also more clearly elucidate
the geologic history of Venus, including the existence and persistence
of an ancient ocean. Achieving these objectives will provide a basis
to understand the habitability of extra solar terrestrial planets. To
address a broad range of science questions this mission will be composed
of flight elements that include an orbiter that is highlighted by an
interferometric SAR to provide surface topographic and image information
at scales one to two orders of magnitude greater than that achieved by
any previous spacecraft to Venus. Two balloons with a projected lifetime
of weeks will probe the structure and dynamics of the atmosphere at an
altitude of 50 to 70-km. In addition, two descent probes will collect
data synergistic to that from the balloon and analyze the geochemistry
of surface rocks over a period of hours. The technology road map
focuses on key areas of science instruments and enabling engineering
to provide greater in situ longevity in the hostile Venus environment.
---------------------------------------------------------
Title: The Pre-flare Phase: Key to Understanding Energy and Mass
Transport in Flare Loops
Authors: Battaglia, M.; Fletcher, L.; Benz, A. O.
2008ESPM...12.2.85B Altcode:
In the classical solar flare scenario, the chromosphere is heated by an
incident beam of supra-thermal electrons that were accelerated in the
corona, then precipitated downward along the field lines of a magnetic
loop. The hot chromospheric plasma expands and fills the magnetic
loops. This process has been termed chromospheric evaporation. The
classical scenario causes characteristic emission in soft- and hard
X-rays, both from the corona and the chromosphere. The time evolution of
this emission follows a specific pattern known as the Neupert effect. <P
/>Recent observations indicate that this scenario is only applicable for
about half of the observed flares (Veronig et al. 2002). The early rise
phase of many events is dominated by increasing soft X-ray emission up
to minutes before the onset of the hard X-ray emission. This pre-heating
clearly contradicts the classical Neupert scenario and indicates that
other mechanisms of energy transport such as thermal conduction have
to be at work. It also implies that the pre-flare energy release is
dominated by heating, not acceleration. While energy transport by
thermal conduction and subsequent chromospheric evaporation has been
studied in some detail for the decay phase of solar flares, we present
the first comprehensive study of the early phases of 4 pre-heating
events. We analyze the time evolution of those events in imaging and
spectroscopy using data from the RHESSI satellite and demonstrate how
this can improve our understanding of heating and evaporation processes
in coronal loops and the initiation of particle acceleration.
---------------------------------------------------------
Title: Correlation of Decimetric Radio Emission and Hard X-rays in
Solar Flares
Authors: Dabrowski, B.; Benz, A. O.
2008ESPM...122.106D Altcode:
The emission of decimetric radiation, in particular narrowband spikes
and pulsations, is generally considered to originate from particle
acceleration processes in solar flares. On the other hand, non-thermal
hard X-rays are well accepted results of such acceleration. Are
radio emissions and hard X-rays signatures of the same acceleration
process? Good correlation of the light curves in the radio and HXR range
may evidence it. <P />The correlation of decimetric radio emission and
hard X-rays in solar flares was analyzed using data from the RHESSI
spacecraft and the Phoenix-2 spectrometer of ETH Zürich. The Phoenix-2
spectrometer in Bleien (Switzerland) records the solar radio emission
from 100 MHz to 4 GHz. We found 169 well observed joint decimetric
events in the complete list of observations from February 2002 (date
launch of the RHESSI satellite) to December 2006. About hundred radio
events were of the type of pulsations, and in around thirty events
we found were spikes. For the detailed analysis, 33 groups (26 radio
events) of pulsations and 12 groups (11 radio events) of spikes were
chosen. <P />The delay between the radio and hard X-rays emission
was determined by cross-correlation. The time profiles of X-ray and
radio emission differ much in energy and frequency. Thus correlation
is not simply a yes/no question, but must be systematically searched in
various ranges. The high spectral resolution of RHESSI made it possible
to carefully choose the energy range, excluding thermal emission. The
broad bandwidth of Phoenix-2 allowed selecting any emission in the
full decimeter range. The energy range and duration in hard X-rays,
and the frequency range in radio spectrograms were chosen to optimize
the correlation. The cross-correlation coefficient was then analyzed by
Gauss fit in delay for each event. <P />The mean delay for pulsations
evaluated from Gauss fitting was found to be -1.50 seconds (minus
indicates that hard X-rays emission comes first). The mean delay
for narrowband spikes evaluated from Gauss fitting amounts to -2.25
seconds. The delays do not depend on position on the disk, duration
of the correlating sequence and maximum value of cross-correlation
coefficient. However, we find an increase in delay for the spikes with
GOES magnitude (peak soft X-ray emission) of the flare and with peak
hard X-ray flux. This was not the case for pulsations.
---------------------------------------------------------
Title: Spectral Hardening in Large Solar Flares
Authors: Grigis, P. C.; Benz, A. O.
2008ApJ...683.1180G Altcode: 2007arXiv0708.2472G
Observations by the Ramaty High Energy Solar Spectroscopic Imager
(RHESSI) are used to quantitatively study the hard X-ray evolution
in five large solar flares selected for spectral hardening in the
course of the event. The X-ray bremsstrahlung emission from nonthermal
electrons is characterized by two spectroscopically distinct phases:
impulsive and gradual. The impulsive phase usually consists of several
emission spikes following a soft-hard-soft spectral pattern, whereas
the gradual stage manifests itself as spectral hardening while the
flux slowly decreases. Both the soft-hard-soft (impulsive) phase and
the hardening (gradual) phase are well described by piecewise linear
dependence of the photon spectral index on the logarithm of the hard
X-ray flux. The different linear parts of this relation correspond
to different rise and decay phases of emission spikes. The temporal
evolution of the spectra is compared with the configuration and motion
of the hard X-ray sources in RHESSI images. These observations reveal
that the two stages of electron acceleration causing these two different
behaviors are closely related in space and time. The transition
between the impulsive and gradual phase is found to be smooth and
progressive rather than abrupt. This suggests that they arise because
of a slow change in a common accelerator rather than being caused by
two independent and distinct acceleration processes. We propose that
the hardening during the decay phase is caused by continuing particle
acceleration with longer trapping in the accelerator before escape.
---------------------------------------------------------
Title: Observational evidence for return currents in solar flare loops
Authors: Battaglia, M.; Benz, A. O.
2008A&A...487..337B Altcode: 2008arXiv0806.1701B
Context: The common flare scenario comprises an acceleration site
in the corona and particle transport to the chromosphere. Using
satellites available to date it has become possible to distinguish
between the two processes of acceleration and transport, and study the
particle propagation in flare loops in detail, as well as complete
comparisons with theoretical predictions. <BR />Aims: We complete a
quantitative comparison between flare hard X-ray spectra observed by
RHESSI and theoretical predictions. This enables acceleration to be
distinguished from transport and the nature of transport effects to be
explored. <BR />Methods: Data acquired by the RHESSI satellite were
analyzed using full sun spectroscopy as well as imaging spectroscopy
methods. Coronal source and footpoint spectra of well observed
limb events were analyzed and quantitatively compared to theoretical
predictions. New concepts are introduced to existing models to resolve
discrepancies between observations and predictions. <BR />Results:
The standard thin-thick target solar flare model cannot explain the
observations of all events. In the events presented here, propagation
effects in the form of non-collisional energy loss are of importance to
explain the observations. We demonstrate that those energy losses can
be interpreted in terms of an electric field in the flare loop. One
event seems consistent with particle propagation or acceleration in
lower than average density in the coronal source. <BR />Conclusions:
We find observational evidence for an electric field in flare loops
caused by return currents.
---------------------------------------------------------
Title: The Herschel-Heterodyne Instrument for the Far-Infrared
(HIFI): instrument and pre-launch testing
Authors: de Graauw, Thijs; Whyborn, Nick; Helmich, Frank; Dieleman,
Pieter; Roelfsema, Peter; Caux, Emmanuel; Phillips, Tom; Stutzki,
Jürgen; Beintema, Douwe; Benz, Arnold; Biver, Nicolas; Boogert,
Adwin; Boulanger, Francois; Cherednichenko, Sergey; Coeur-Joly, Odile;
Comito, Claudia; Dartois, Emmanuel; de Jonge, Albrecht; de Lange, Gert;
Delorme, Ian; DiGiorgio, Anna; Dubbeldam, Luc; Edwards, Kevin; Fich,
Michael; Güsten, Rolf; Herpin, Fabrice; Honingh, Netty; Huisman,
Robert; Jacobs, Herman; Jellema, Willem; Kawamura, Jon; Kester,
Do; Klapwijk, Teun; Klein, Thomas; Kooi, Jacob; Krieg, Jean-Michel;
Kramer, Carsten; Kruizenga, Bob; Laauwen, Wouter; Larsson, Bengt;
Leinz, Christian; Liseau, Rene; Lord, Steve; Luinge, Willem; Marston,
Anthony; Merkel, Harald; Moreno, Rafael; Morris, Patrick; Murphy,
Anthony; Naber, Albert; Planesas, Pere; Martin-Pintado, Jesus; Olberg,
Micheal; Orleanski, Piotr; Ossenkopf, Volker; Pearson, John; Perault,
Michel; Phillip, Sabine; Rataj, Mirek; Ravera, Laurent; Saraceno,
Paolo; Schieder, Rudolf; Schmuelling, Frank; Szczerba, Ryszard;
Shipman, Russell; Teyssier, David; Vastel, Charlotte; Visser, Huib;
Wildeman, Klaas; Wafelbakker, Kees; Ward, John; Higgins, Roonan;
Aarts, Henri; Tielens, Xander; Zaal, Peer
2008SPIE.7010E..04D Altcode: 2008SPIE.7010E...2D
This paper describes the Heterodyne Instrument for the Far-Infrared
(HIFI), to be launched onboard of ESA's Herschel Space Observatory,
by 2008. It includes the first results from the instrument level
tests. The instrument is designed to be electronically tuneable over a
wide and continuous frequency range in the Far Infrared, with velocity
resolutions better than 0.1 km/s with a high sensitivity. This will
enable detailed investigations of a wide variety of astronomical
sources, ranging from solar system objects, star formation regions to
nuclei of galaxies. The instrument comprises 5 frequency bands covering
480-1150 GHz with SIS mixers and a sixth dual frequency band, for the
1410-1910 GHz range, with Hot Electron Bolometer Mixers (HEB). The
Local Oscillator (LO) subsystem consists of a dedicated Ka-band
synthesizer followed by 7 times 2 chains of frequency multipliers,
2 chains for each frequency band. A pair of Auto-Correlators and a
pair of Acousto-Optic spectrometers process the two IF signals from
the dual-polarization front-ends to provide instantaneous frequency
coverage of 4 GHz, with a set of resolutions (140 kHz to 1 MHz),
better than < 0.1 km/s. After a successful qualification program,
the flight instrument was delivered and entered the testing phase
at satellite level. We will also report on the pre-flight test and
calibration results together with the expected in-flight performance.
---------------------------------------------------------
Title: Concluding remarks
Authors: Benz, Arnold O.
2008IAUS..247..366B Altcode: 2007IAUS..247..366B
Waves in solar and stellar atmospheres have been proposed more than
fifty years ago to heat the chromosphere and the corona. Their
usefulness as a means to explain an important phenomenon gave
wave science its initial impetus. However, since then, waves and
oscillations have become a great astrophysical topic of their own. In
an inhomogeneous medium, waves occur in immense variety. The theory of
waves explores this complexity and highlights modes and properties that
are important in stellar atmospheres. We have seen steady progress in
this fundamental endeavour that has recently been accelerated through
the use of numerical simulations. The discovery, three decades ago,
of waves in the solar and stellar interiors and later in the corona,
although at low energy levels, opened a new field: the diagnostic use
of waves. Seismology of the interior has become a booming field of
solar and stellar physics, and observed oscillations have been used
to derive the magnetic field strength and to explore the corona.
---------------------------------------------------------
Title: New Evidence for Return Currents in Solar Flare Loops
Authors: Battaglia, M.; Benz, A. O.
2008AGUSMSH51C..07B Altcode:
The common flare scenario comprises particle acceleration in the
corona and transport to the chromosphere along the field lines of
magnetic loops. This leads to characteristic hard X-ray emission from
the corona (coronal source) and the chromosphere (footpoints). Simple
models presume that both emissions are caused by the same electron
population. Assuming thin target bremsstrahlung emission from the
coronal source and thick target bremsstrahlung from the footpoints,
the shape and relations between the hard X-ray spectra of the distinct
sources can be computed. With RHESSI, it has become possible to
observe hard X-ray spectra both from the corona as well as from the
footpoints with high spectral resolution. Therefore the so-called
thin-thick target model can be tested directly. We analyzed coronal
source and footpoint spectra of well observed RHESSI limb events and
quantitatively compared them to theoretical predictions. In the analyzed
flares, the difference in spectral hardness between the coronal and
footpoint sources differs significantly from the theoretically expected
value. Transport effects in the form of non-collisional energy loss
were introduced to the thin-thick target model to account for the
discrepancy. We show that those energy losses can be interpreted by an
electric field and associated return current. This is direct evidence
for return currents in solar flare loops.
---------------------------------------------------------
Title: The Results of Sub-mm Observations in the Large Magellanic
Cloud with the NANTEN2 Telescope
Authors: Mizuno, Yoji; Mizuno, N.; Kawamura, A.; Onishi, T.; Fukui,
Y.; Ogawa, H.; Stutzki, J.; Bertoldi, F.; Koo, B. C.; Rubio, M.;
Burton, M.; Benz, A.
2008ASSP....5..313M Altcode: 2008glv..book..313M
No abstract at ADS
---------------------------------------------------------
Title: Prospectives of Herschel PDR observations
Authors: Ossenkopf, V.; Gerin, M.; Güsten, R.; Benz, A.; Berne, O.;
Boulanger, F.; Bruderer, S.; France, K.; Fuente, A.; Goicoechea, J.;
Harris, A.; Joblin, C.; Klein, T.; Lord, S.; Kramer, C.; Martin,
P.; Martin-Pintado, J.; Mookerjea, B.; Neufeld, D.; Le Petit, F.;
Phillips, T.; Poelman, D.; Rizzo, R.; Röllig, M.; Simon, R.; Spaans,
M.; Stutzki, J.; Teyssier, D.; Yorke, H.
2008EAS....31..193O Altcode:
Observations using the HIFI and PACS instruments aboard the Herschel
satellite provide a unique way to study the chemical inventory,
the dynamics, and the energy balance in dense interstellar clouds
heated by UV radiation. We propose a comprehensive observing program
to reveal the details of the interaction of massive young stars with
their parental molecular clouds.
---------------------------------------------------------
Title: Division II: Sun and Heliosphere
Authors: Webb, David F.; Melrose, Donald B.; Benz, Arnold O.; Bogdan,
Thomas J.; Bougeret, Jean-Louis; Klimchuk, James A.; Martinez-Pillet,
Valentin
2007IAUTB..26..101W Altcode:
Division II provides a forum for astronomers studying a wide range of
problems related to the structure, radiation and activity of the Sun,
and its interaction with the Earth and the rest of the solar system.
---------------------------------------------------------
Title: Spectral Hardening of Large Solar Flares
Authors: Grigis, P. C.; Benz, A. O.
2007AGUFMSH53A1062G Altcode:
We present quantitative studies of the hard X-ray spectral evolution
of large solar flares featuring hardening trends, using RHESSI high
cadence spectroscopy observations. The temporal evolution of the
spectra is compared with the configuration and motion of the hard
X-ray sources in RHESSI images. Both soft-hard-soft (impulsive)
phases and hardening (gradual) phases are observed during the events
and are well described by piecewise linear dependence of the spectral
index on the logarithm of the flux. In particular, we investigate
whether two different acceleration mechanisms are responsible for the
impulsive and gradual phases, finding evidence that points toward a
single acceleration mechanism acting in the two phases, rather than
two different separated mechanisms, because the impulsive and gradual
phases are closely interconnected in time and space.
---------------------------------------------------------
Title: Energetic radiation and the sulfur chemistry of protostellar
envelopes: submillimeter interferometry of AFGL 2591
Authors: Benz, A. O.; Stäuber, P.; Bourke, T. L.; van der Tak,
F. F. S.; van Dishoeck, E. F.; Jørgensen, J. K.
2007A&A...475..549B Altcode: 2007arXiv0709.0215B
Context: The chemistry in the inner few thousand AU of accreting
envelopes around young stellar objects is predicted to vary greatly with
far-UV and X-ray irradiation by the central star. <BR />Aims: We search
for molecular tracers of high-energy irradiation by the protostar in
the hot inner envelope. <BR />Methods: The Submillimeter Array (SMA)
has observed the high-mass star forming region AFGL 2591 in lines of
CS, SO, HCN, HCN(ν<SUB>2</SUB> = 1), and HC<SUP>15</SUP>N with 0.6”
resolution at 350 GHz probing radial scales of 600-3500 AU for an
assumed distance of 1 kpc. The SMA observations are compared with
the predictions of a chemical model fitted to previous single-dish
observations. <BR />Results: The CS and SO main peaks are extended in
space at the FWHM level, as predicted in the model assuming protostellar
X-rays. However, the main peak sizes are found smaller than modeled
by nearly a factor of 2. On the other hand, the lines of CS, HCN, and
HC<SUP>15</SUP>N, but not SO and HCN(ν<SUB>2</SUB> = 1), show pedestal
emissions at radii ⪉3500 AU that are not predicted. All lines except
SO show a secondary peak within the approaching outflow cone. A dip or
null in the visibilities caused by a sharp decrease in abundance with
increasing radius is not observed in CS and only tentatively in SO. <BR
/>Conclusions: The emission of protostellar X-rays is supported by the
good fit of the modeled SO and CS amplitude visibilities including an
extended main peak in CS. The broad pedestals can be interpreted by
far-UV irradiation in a spherically non-symmetric geometry, possibly
comprising outflow walls on scales of 3500-7000 AU. The extended CS
and SO main peaks suggest sulfur evaporation near the 100 K temperature
radius. The effects of the corresponding abundance jumps may be reduced
in visibility plots by smoothing due to inhomogeneity at the evaporation
radius, varying by ±10% or more in different directions. <P />The
FITS files of SMA data are only available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/475/549
---------------------------------------------------------
Title: An Interpretation of the Coronal Holes' Visibility in the
Millimeter Wavelength Range
Authors: Brajša, R.; Benz, A. O.; Temmer, M.; Jurdana-Šepić, R.;
Šaina, B.; Wöhl, H.
2007SoPh..245..167B Altcode:
Various observations indicate that coronal holes generally appear as low
brightness temperature regions (LTRs) in the centimeter and millimeter
wavelength ranges. However, within their borders local enhancements of
radiation, that is, high brightness temperature regions (HTRs), often
occur. The theory behind the described behavior is not fully understood
and therefore we analyze full-disk solar images obtained at a wavelength
of 8 mm at Metsähovi Radio Observatory and compare them with data
simultaneously taken in other wavelength ranges. The observational
finding that the average brightness temperature of coronal holes is
not much different from the quiet-Sun level (with localized deviations
toward higher and lower intensities on the order of a few percent)
is compared with theoretical models of the thermal bremsstrahlung
radiation originating in the solar chromosphere, transition region,
and corona. Special attention is devoted to the interpretation of the
localized enhancements of radiation observed inside coronal holes at
millimeter wavelengths. The main conclusion is that the most important
contribution to the brightness temperature comes from an increased
density in the transition region and low corona (i.e., at the heights
where the temperature is below 10<SUP>6</SUP> K). This can explain
both the LTRs and HTRs associated with coronal holes.
---------------------------------------------------------
Title: VizieR Online Data Catalog: AFGL 2591 maps in CS, SO and HCN
lines (Benz+, 2007)
Authors: Benz, A. O.; Stauber, P.; Bourke, T. L.; van Det Tak,
F. F. S.; van Dishoeck, E. F.; Jorgensen, J. K.
2007yCat..34750549B Altcode:
The chemistry in the inner few thousand AU of accreting envelopes
around young stellar objects is predicted to vary greatly with far-UV
and X-ray irradiation by the central star. <P />We search for molecular
tracers of high-energy irradiation by the protostar in the hot inner
envelope. <P />The Submillimeter Array (SMA) has observed the high-mass
star forming region AFGL 2591 in lines of CS, SO, HCN, HCN(nu2=1), and
HC<SUP>15</SUP>N with 0.6" resolution at 350GHz probing radial scales
of 600-3500AU for an assumed distance of 1kpc. The SMA observations are
compared with the predictions of a chemical model fitted to previous
single-dish observations. <P />(2 data files).
---------------------------------------------------------
Title: Electron acceleration in solar flares: observations versus
numerical simulations
Authors: Benz, Arnold O.; Grigis, Paolo C.; Battaglia, Marco
2007HiA....14...87B Altcode:
We use RHESSI hard X-ray observations to constrain acceleration of
solar flare electrons, generally considered to be a primary recipient
of the released energy.
---------------------------------------------------------
Title: Tracing high energy radiation with molecular lines near deeply
embedded protostars
Authors: Stäuber, P.; Benz, A. O.; Jørgensen, J. K.; van Dishoeck,
E. F.; Doty, S. D.; van der Tak, F. F. S.
2007A&A...466..977S Altcode: 2006astro.ph..8393S
Aims:The aim is to probe high energy radiation emitted by deeply
embedded protostars. <BR />Methods: Submillimeter lines of CN,
NO, CO<SUP>+</SUP> and SO^+, and upper limits on SH<SUP>+</SUP>
and N2O are observed with the James Clerk Maxwell Telescope in
two high-mass and up to nine low-mass young stellar objects and
compared with chemical models. <BR />Results: Constant fractional
abundances derived from radiative transfer modeling of the line
strengths are x(CN) ≈ a few ×10<SUP>-11</SUP>-10<SUP>-8</SUP>,
x(NO) ≈ 10<SUP>-9</SUP>-10<SUP>-8</SUP> and x(CO^+) ≈
10<SUP>-12</SUP>-10<SUP>-10</SUP>. SO<SUP>+</SUP> has abundances of
a few × 10<SUP>-11</SUP> in the high-mass objects and upper limits
of ≈10<SUP>-12</SUP>-10<SUP>-11</SUP> in the low-mass sources. All
abundances are up to 1-2 orders of magnitude higher if the molecular
emission is assumed to originate mainly from the inner region (≲1000
AU) of the envelope. For high-mass sources, the CN, SO<SUP>+</SUP> and
CO<SUP>+</SUP> abundances and abundance ratios are best explained by
an enhanced far-ultraviolet (FUV) field impacting gas at temperatures
of a few hundred K. The observed column densities require that this
region of enhanced FUV has scales comparable to the observing beam,
such as in a geometry in which the enhanced FUV irradiates outflow
walls. For low-mass sources, the required temperatures within the
FUV models of T ≳ 300 K are much higher than found in models, so
that an X-ray enhanced region close to the protostar (r ≲ 500 AU)
is more plausible. Gas-phase chemical models produce more NO than
observed, suggesting an additional reduction mechanism not included
in current models. <BR />Conclusions: The observed CN, CO<SUP>+</SUP>
and SO<SUP>+</SUP> abundances can be explained with either enhanced
X-rays or FUV fields from the central source. High-mass sources
likely have low opacity regions that allow the FUV photons to reach
large distances from the central source. X-rays are suggested to be
more effective than FUV fields in the low-mass sources. The observed
abundances imply X-ray fluxes for the Class 0 objects of L<SUB>X</SUB>
≈ 10<SUP>29</SUP>-10<SUP>31</SUP> erg s<SUP>-1</SUP>, comparable to
those observed from low-mass Class I protostars. Spatially resolved
data are needed to clearly distinguish the effects of FUV and X-rays
for individual species. <P />Appendices are only available in electronic
form at http://www.aanda.org
---------------------------------------------------------
Title: Exploring the connection between coronal and footpoint sources
in a thin-thick target solar flare model
Authors: Battaglia, M.; Benz, A. O.
2007A&A...466..713B Altcode: 2007astro.ph..2309B
Context: Hard X-ray emission of coronal sources in solar flares has been
observed and studied since its discovery in Yohkoh observations. Several
models have been proposed to explain the physical mechanisms causing
this emission and the relations between those sources and simultaneously
observed footpoint sources. <BR />Aims: We investigate and test one
of the models (intermediate thin-thick target model) developed on the
basis of Yohkoh observations. The model makes precise predictions on the
shape of coronal and footpoint spectra and the relations between them,
that can be tested with new instruments such as RHESSI. <BR />Methods:
RHESSI observations of well observed events are studied in imaging and
spectroscopy and compared to the predictions from the intermediate
thin-thick target model. <BR />Results: The results indicate that
such a simple model cannot account for the observed relations between
the non-thermal spectra of coronal and footpoint sources. Including
non-collisional energy loss of the electrons in the flare loop due to
an electric field can solve most of the inconsistencies.
---------------------------------------------------------
Title: Division II: Sun and Heliosphere
Authors: Webb, David F.; Melrose, Donald B.; Benz, Arnold O.; Bogdan,
Thomas J.; Bougeret, Jean-Louis; Klimchuk, James A.; Martinez Pillet,
Valentin
2007IAUTA..26...69W Altcode:
Division II of the IAU provides a forum for astronomers studying a wide
range of phenomena related to the structure, radiation and activity
of the Sun, and its interaction with the Earth and the rest of the
solar system. Division II encompasses three Commissions, 10, 12 and
49, and four working groups. During the last triennia the activities
of the division involved some reorganization of the division and its
working groups, developing new procedures for election of division and
commission officers, promoting annual meetings from within the division
and evaluating all the proposed meetings, evaluating the division's
representatives for the IAU to international scientific organizations,
and participating in general IAU business.
---------------------------------------------------------
Title: Commission 10: Solar Activity
Authors: Melrose, Donald B.; Klimchuk, James A.; Benz, A. O.; Craig,
I. J. D.; Gopalswamy, N.; Harrison, R. A.; Kozlovsky, B. Z.; Poletto,
G.; Schrijver, K. J.; van Driel-Gesztelyi, L.; Wang, J. -X.
2007IAUTA..26...75M Altcode:
Commission 10 aims at the study of various forms of solar activity,
including networks, plages, pores, spots, fibrils, surges, jets,
filaments/prominences, coronal loops, flares, coronal mass ejections
(CMEs), solar cycle, microflares, nanoflares, coronal heating etc.,
which are all manifestation of the interplay of magnetic fields and
solar plasma. Increasingly important is the study of solar activities
as sources of various disturbances in the interplanetary space
and near-Earth "space weather".Over the past three years a major
component of research on the active Sun has involved data from the
RHESSI spacecraft. This review starts with an update on current and
planned solar observations from spacecraft. The discussion of solar
flares gives emphasis to new results from RHESSI, along with updates on
other aspects of flares. Recent progress on two theoretical concepts,
magnetic reconnection and magnetic helicity is then summarized, followed
by discussions of coronal loops and heating, the magnetic carpet
and filaments. The final topic discussed is coronal mass ejections
and space weather.The discussions on each topic is relatively brief,
and intended as an outline to put the extensive list of references
in context.The review was prepared jointly by the members of the
Organizing Committee, and the names of the primary contributors to
the various sections are indicated in parentheses.
---------------------------------------------------------
Title: Are There Radio-quiet Solar Flares?
Authors: Benz, Arnold O.; Brajša, Roman; Magdalenić, Jasmina
2007SoPh..240..263B Altcode: 2007astro.ph..1570B
Some 15% of solar flares having a soft X-ray flux above GOES class C5
are reported to lack coherent radio emission in the 100 - 4000 MHz
range (type I - V and decimetric emissions). A detailed study of 29
such events reveals that 22 (76%) of them occurred at a radial distance
of more than 800″ from the disk center, indicating that radio waves
from the limb may be completely absorbed in some flares. The remaining
seven events have statistically significant trends to be weak in GOES
class and to have a softer non-thermal X-ray spectrum. All of the
non-limb flares that were radio-quiet above 100 MHz were accompanied by
metric type III emission below 100 MHz. Out of 201 hard X-ray flares,
there was no flare except near the limb (R>800″) without coherent
radio emission in the entire meter and decimeter range. We suggest
that flares above GOES class C5 generally emit coherent radio waves
when observed radially above the source.
---------------------------------------------------------
Title: On the Visibility of Coronal Holes in Microwaves
Authors: Brajša, R.; Benz, A. O.; Temmer, M.; Jurdana-Šepić, R.;
Šaina, B.; Wöhl, H.; Ruždjak, V.
2007CEAB...31..219B Altcode:
Previous observations indicate that coronal holes generally appear as
low brightness temperature regions in microwaves. However, within their
borders local enhancements of radiation often occur. This is confirmed
by comparing a full-disc solar image obtained at 37 GHz on 27 May 1993
with full-disc solar images obtained at various wavelengths. Microwave
brightness temperatures of three coronal holes are determined and
interpreted.
---------------------------------------------------------
Title: Are there Radio-quiet Solar Flares?
Authors: Benz, Arnold O.; Brajsa, Roman; Magdalenic, Jasmina
2007astro.ph..1566B Altcode:
This submission has been withdrawn by arXiv administrators because it
is a duplicate of astro-ph/0701570.
---------------------------------------------------------
Title: Electron acceleration in solar flares: theory of spectral
evolution
Authors: Grigis, P. C.; Benz, A. O.
2006A&A...458..641G Altcode: 2006astro.ph..6339G
Context: .Stochastic acceleration is thought to be a key mechanism in
the energization of solar flare electrons.<BR /> Aims: .We study whether
stochastic acceleration can reproduce the observed soft-hard-soft
evolution of the spectral features of the hard X-ray emitted by
suprathermal electrons. We pay special attention to the effects of
particle trapping and escape.<BR /> Methods: .The Fokker-Planck
equation for the electron distribution is integrated numerically
using the coefficients derived by Miller et al. for transit-time
damping acceleration. The electron spectra are then converted to
photon spectra for comparison with RHESSI observations of looptop
sources.<BR /> Results: .The presence of particle escape softens the
model spectra computed in the stochastic acceleration framework. The
ratio between the efficiency of trapping and acceleration controls the
spectral evolution which follows a soft-hard-soft pattern. Furthermore,
a pivot point (that is, a common crossing point of the accelerated
particle spectra at different times) is found at around 10 keV. It
can be brought into agreement with the observed value of 20 keV by
enhanced trapping through an electric potential.<BR /> Conclusions:
.The model proposed here accounts for the key features observed in
the spectral evolution of hard X-ray emission from looptop sources.
---------------------------------------------------------
Title: Relations between concurrent hard X-ray sources in solar flares
Authors: Battaglia, M.; Benz, A. O.
2006A&A...456..751B Altcode: 2006astro.ph..6353B
Context: .Solar flares release a large fraction of their energy into
non-thermal electrons, but it is not clear where and how. Bremsstrahlung
X-rays are observed from the corona and chromosphere. <BR /> Aims:
.We aim to characterize the acceleration process by the coronal
source and its leakage toward the footpoints in the chromosphere. The
relations between the sources reflect the geometry and constrict the
configuration of the flare.<BR /> Methods: .We studied solar flares of
GOES class larger than M1 with three or more hard X-ray sources observed
simultaneously in the course of the flare. The events were observed
with the X-ray satellite RHESSI from February 2002 until July 2005. We
used imaging spectroscopy methods to determine the spectral evolution
of each source in each event. The images of all of the five events
show two sources visible only at high energies (footpoints) and one
source only visible at low energies (coronal or looptop source, in two
cases situated over the limb). <BR /> Results: . We find soft-hard-soft
behavior in both, coronal source and footpoints. The coronal source is
nearly always softer than the footpoints. The footpoint spectra differ
significantly only in one event out of five.<BR /> Conclusions: .The
observations are consistent with acceleration in the coronal source
and an intricate connection between the corona and chromosphere.
---------------------------------------------------------
Title: NANTEN2 Project: CO and CI Survey of the Southern Sky
Authors: Fukui, Y.; Onishi, T.; Mizuno, N.; Mizuno, A.; Ogawa, H.;
Yonekura, Y.; Stutzki, J.; Graf, U.; Kramer, C.; Simon, R.; Bertoldi,
F.; Klein, U.; Bensch, F.; Koo, B. C.; Park, Y. S.; Bronfman, L.;
May, J.; Burton, M.; Benz, A.
2006IAUSS...1E..21F Altcode:
We present a project overview and science goals of the upcoming NANTEN2
project. This is an upgrade of the 4-m mm telescope, NANTEN, which was
operated at Las Campanas Observatory, Chile. We have been carrying out
extensive molecular cloud surveys in the Galaxy as well as toward the
Magellanic system for seven years. The upgrade started by moving NANTEN
from Las Campanas to Atacama in Northern Chile at an altitude of 4,800m
in 2004 to realize a large-scale survey at sub-mm wavelengths. In this
new project, we will make large-scale surveys toward the Galaxy and
the nearby galaxies including the Magellanic Clouds. We will reveal
the physical and chemical states of interstellar gas in various
density regions with the highly excited CO (carbon-monoxide) and CI
(neutral carbon) spectra in the sub-millimeter wavelength (100 - 800
GHz). With thorough extensive surveys, we will make studies of star
formation process in the Local Group and investigate the dynamical
effects of energetic explosive events like supernovae and supershells
on the interstellar matter. The installation started at the beginning
of 2004. The highest observing frequencies will be covered by KOSMA
SMART (Sub-Millimeter Array Receivers for Two frequencies) receiver,
a new multi-beam receiver capable of observing both 490 GHz and 800
GHz radiation simultaneously and speedily. The NANTEN2 observations
provide a large database of interstellar matter in the Galaxy and the
Magellanic Clouds. This database must be a useful guide for the future
science with ALMA.
---------------------------------------------------------
Title: Electron Acceleration in Solar Flares: Observations versus
Numerical S imulations
Authors: Benz, A. O.; Grigis, P. C.; Battaglia, M.
2006IAUJD...1E...6B Altcode:
We use RHESSI hard X-ray observations to constrict electron acceleration
in solar flares, generally considered as a primary recipient of the
released energy. X-ray sources in the corona have been previously
discovered and tentatively associated with bremsstrahlung emission of
the acceleration site. RHESSI imaging spectroscopy can temporally
resolve the non-thermal spectrum of the coronal source for the
first time. We compare the time behaviour with the predictions of
stochastic acceleration, as described by transit-time damping of
MHD turbulence excited by reconnection. The results in 5 limb events
indicate soft-hard-soft (shs) behaviour of the coronal source emission
in the course of an X-ray peak (the more intense, the harder the
spectrum). The shs behaviour thus constitutes a conspicuous property of
the acceleration process. The temporal behaviour of the spectrum can be
quantitatively described a pivot point near a photon energy of 20 keV
at which the spectrum remains constant in time. We solve a diffusion
equation for the interaction of waves and particles including trapping,
escape and particle replenishment. The solution yields a spectrum that
is approximately a power-law in the observed range of energies, having a
spectral index in the observed range. However, the theoretically derived
pivot point is generally at energy lower than observed. For this reason
we include transport effects, such as produced by an electric potential,
or scattering in the coronal source (trapping) to bring the pivot energy
up to the observed value. Escaping particles propagate to the base of
the loop in the dense chromosphere. These precipitating particles are
identified as origin of the observed hard X-ray footpoints. Observations
and simulations show that solar flare electron acceleration is a process
that involves interactions with the connecting loop. The observations
are consistent with stochastic acceleration in a relatively dense
medium (up to 10^11 cm^-3) and high wave energy densities (up to 0.001
magnetic). The comparison also constrains the global flare geo-metry,
requiring coupling between the coronal source and the footpoints.
---------------------------------------------------------
Title: Water destruction by X-rays in young stellar objects
Authors: Stäuber, P.; Jørgensen, J. K.; van Dishoeck, E. F.; Doty,
S. D.; Benz, A. O.
2006A&A...453..555S Altcode: 2006astro.ph..2114S
Aims.We study the H2O chemistry in star-forming environments under
the influence of a central X-ray source and a central far ultraviolet
(FUV) radiation field. The X-ray models are applied to envelopes around
low-mass Class 0 and I young stellar objects (YSOs).<BR />Methods.The
gas-phase water chemistry is modeled as a function of time, hydrogen
density and X-ray flux. To cover a wide range of physical environments,
densities between n<SUB>H</SUB> = 10^4-10<SUP>9</SUP> cm<SUP>-3</SUP>
and temperatures between T=10-1000 K are studied.<BR />Results.Three
different regimes are found: for T<100 K, the water abundance is of
order 10<SUP>-7</SUP>-10<SUP>-6</SUP> and can be somewhat enhanced or
reduced due to X-rays, depending on time and density. For 100 K ≲ T
≲ 250 K, H2O is reduced from initial x(H_2O) ≈ 10<SUP>-4</SUP>
following ice evaporation to x(H_2O) ≈ 10<SUP>-6</SUP> for
F<SUB>X</SUB> ≳ 10<SUP>-3</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP>
(t=10<SUP>4</SUP> yr) and for F<SUB>X</SUB> ≳ 10<SUP>-4</SUP>
erg s<SUP>-1</SUP> cm<SUP>-2</SUP> (t=10<SUP>5</SUP> yr). At higher
temperatures (T ≳ 250 K) and hydrogen densities, water can persist
with x({H_2O}) ≈ 10<SUP>-4</SUP> even for high X-ray fluxes. Water is
destroyed in both Class 0 and I envelopes on relatively short timescales
(t ≈ 5000 yr) for realistic X-ray fluxes, although the effect is
less prominent in Class 0 envelopes due to the higher X-ray absorbing
densities there. FUV photons from the central source are not effective
in destroying water.<BR />Conclusions.X-rays reduce the water abundances
especially in regions where the gas temperature is T ≲ 250-300
K for fluxes F<SUB>X</SUB> ≳ 10<SUP>-5</SUP>-10<SUP>-4</SUP> erg
s<SUP>-1</SUP> cm<SUP>-2</SUP>. The affected regions can be envelopes,
disks or outflow hot spots. The average water abundance in Class I
sources for L<SUB>X</SUB> ≳ 10<SUP>27</SUP> erg s<SUP>-1</SUP> is
predicted to be x(H_2O) ≲ 10<SUP>-6</SUP>. Central UV fields have
a negligible influence, unless the photons can escape through cavities.
---------------------------------------------------------
Title: Comparison of Electron Stochastic Acceleration Models with
RHESSI Hard X-Ray Observations of Solar Flares.
Authors: Grigis, Paolo C.; Benz, A. O.
2006SPD....37.2802G Altcode: 2006BAAS...38..254G
Acceleration of charged particles in a plasma by means of stochastic
interactions with turbulent waves is very efficient and therefore is
often invoked as the key mechanism acting in solar flare electron
acceleration. We compare the photon spectra produced by electrons
accelerated using the Transit Time Damping (TTD) mechanism with the
detailed hard X-ray observations provided by RHESSI for looptop sources,
showing the soft-hard-soft behavior in the spectral evolution. The
TTD model with a simple leaky box escape term shows the observed
correlation between the photon spectral index and flux but requires too
large variations in photon flux over the range of observed spectral
indices. We discuss more realistic models and further modifications
needed to reproduce the RHESSI observations.
---------------------------------------------------------
Title: Relations Between Concurrent Hard X-ray Sources In Solar Flares
Authors: Battaglia, Marina; Benz, A. O.
2006SPD....37.2801B Altcode: 2006BAAS...38..254B
Solar flares release a large fraction of their energy into non-thermal
electrons,but it is not clear where and how. Bremsstrahlung
X-rays are observed from the corona (coronal or looptop source) and
chromosphere (footpoints).The spectral time evolution of the sources
and the relations between themreflect the geometry and constrict the
configuration of the flare.We studied solar flares of GOES class larger
than M1 with three hard X-raysources observed simultaneously in the
course of the flare. The events whereselected from observations with
the X-ray satellite RHESSI from February 2002 until July 2005.We used
imaging spectroscopy methods to determine the spectral time evolution
ofeach source in each event. The images of all of the five events show
twosources visible only at high energies (footpoints) and one source
onlyvisible at low energies (coronal source).We find soft-hard-soft
behavior in both, coronal source and footpoints. Thisis a strong
indication that soft-hard-soft is a feature of the accelerationmechanism
rather than a transport effect.The coronal source is nearly always
softer than the footpoints. The footpointspectra differ significantly
only in one event out of five.
---------------------------------------------------------
Title: RHESSI observation of flare elements
Authors: Grigis, Paolo C.; Benz, Arnold O.
2006astro.ph..2302G Altcode:
RHESSI observations of elementary flare bursts are presented. These
solar flare elements are distinct emission peaks of a duration of
some tens of seconds present in the hard X-ray light curves. They are
characterized by consistent soft-hard-soft spectral behavior, which can
be described in a quantitative way and compared which predictions from
acceleration models. A detailed analysis of hard X-ray images for an M5
class flare shows that elementary flare bursts do not occur at distinct
locations, but as twin X-ray sources move smoothly along an arcade of
magnetic loops. This observation apparently contradicts the predictions
of standard translation invariant 2.5-dimensional reconnection models.
---------------------------------------------------------
Title: Radio Emission of Solar Flare Particle Acceleration
Authors: Benz, A. O.
2006pre6.conf..325B Altcode: 2006pre4.conf..325B
The solar corona is a very dynamic plasma on time scales of decades to
a few milliseconds. Radio missions provide diagnostic tools particularly
suited for the analysis of non-thermal electron distributions, enhanced
levels of various kinds of plasma waves and plasma phenomena related
to electron acceleration in flares. Very intense coherent emissions
are observed at frequencies below about 3 GHz, weaker ones up to 9
GHz. They are caused by plasma instabilities driving various wave modes
that in turn may emit observable radio waves. The focus here is on Type
III and stationary type IV bursts from about 0.2 to 4 GHz. Type III
bursts can be traced back in the corona to the acceleration region of
electron beams. Less known are radio emissions from magnetically trapped
electrons driving loss-cone unstable waves. This is the interpretation
usually given to type IV emission. It is a very powerful radiation
probably also observed in stars and possibly related to acceleration
after the main flare energy release phase. The comparison of the radio
emissions with hard X-rays reveals surprisingly that the two emissions
often do not correlate in time and thus must originate from different
electron acceleration processes. In combination with other wavelengths
and their recent imaging capabilities, exciting new possibilities may
soon open for radio diagnostics.
---------------------------------------------------------
Title: Extended decimeter radio emission after large solar flares
Authors: Benz, A. O.; Perret, H.; Saint-Hilaire, P.; Zlobec, P.
2006AdSpR..38..951B Altcode:
The large solar flares of October and November 2003 were accompanied
by extremely intense radio emissions at decimeter wavelengths. The
radio emission continued long after the main phase of the flares and
reached an unprecedented peak flux density at 410 MHz of 6.3(±0.7)
× 10<SUP>5</SUP> solar flux units on 2003, October 28. The unusual
number of large flares from the same active regions yields a homologous
set ideal for statistical analysis. We have compared the coherent radio
emissions (as observed by the Zurich and Trieste instruments) with the
X-rays measured by RHESSI and GOES. As major results, we find that
the total duration, the peak flux, and radiated energy of the radio
emissions correlate with the flare energy released (measured in soft
X-rays). Enhanced hard X-rays (>12 keV) are always observed during
the time of enhanced radio emission. In 27% of the radio subpeaks
covered by RHESSI, we find X-ray subpeaks. The most intense radio
emissions are not due to electron beams, but are post-flare emissions
apparently not directly related to the primary energy release and
acceleration process. These radio emissions, generally classified as
Type IV and DCIM bursts, have previously been interpreted by loss-cone
emission of trapped electrons. However, radio and hard X-ray subpeaks
do not show a detailed correlation or Neupert effect, and long-term
trapping can be excluded. Possible acceleration mechanisms after the
main flare phase are discussed and compared with the observations.
---------------------------------------------------------
Title: Rhessi Observation of Flare Elements
Authors: Grigis, P. C.; Benz, A. O.
2005ESASP.600E..35G Altcode: 2005ESPM...11...35G; 2005dysu.confE..35G
No abstract at ADS
---------------------------------------------------------
Title: A broadband FFT spectrometer for radio and millimeter astronomy
Authors: Benz, A. O.; Grigis, P. C.; Hungerbühler, V.; Meyer, H.;
Monstein, C.; Stuber, B.; Zardet, D.
2005A&A...442..767B Altcode: 2005astro.ph..9671B
The core architecture, tests in the lab and first results of a Fast
Fourier Transform (FFT) spectrometer are described. It is based
on a commercially available fast digital sampler (AC240) with an
on-board Field Programmable Gate Array (FPGA). The spectrometer works
continuously and has a remarkable total bandwidth of 1 GHz, resolved
into 16,384 channels. The data is sampled with 8 bits, yielding a
dynamic range of 48 dB. An Allan time of more than 2000 s and an SFDR of
37 dB were measured. First light observations with the KOSMA telescope
show a perfect spectrum without internal or external spurious signals.
---------------------------------------------------------
Title: X-Ray emission from high-mass protostar AFGL 2591
Authors: Benz, Arnold
2005cxo..prop.1902B Altcode: 2005chan.prop.1835B; 2005cxo..prop.1835B
AFGL 2591 is a prototypical, deeply embedded high-mass protostar,
but is crucially and unusually for high-mass YSOs isolated from the
irradiation of associated protostars. We have observed and modeled
line emissions of X-ray sensitive molecules. The observed abundance
of these molecules can only be interpreted by strong X-ray emission of
the central object. Our models indicate that the X-ray emission must be
at a level that is observable in a 30 ks observation. A non-detection
would be a strong disagreement. A detection would be the first X-ray
emission inferred by indirect means and a crucial test of the chemical
modeling of the impact of high-energy radiation on the environment of
young stars.
---------------------------------------------------------
Title: Temporal Correlation of Hard X-Rays and Meter/Decimeter Radio
Structures in Solar Flares
Authors: Arzner, Kaspar; Benz, Arnold O.
2005SoPh..231..117A Altcode: 2005astro.ph..3145A
We investigate the relative timing between hard X-ray (HXR) peaks and
structures in metric and decimetric radio emissions of solar flares
using data from the RHESSI and Phoenix-2 instruments. The radio events
under consideration are predominantly classified as type III bursts,
decimetric pulsations and patches. The RHESSI data are demodulated using
special techniques appropriate for a Phoenix-2 temporal resolution of
0.1 s. The absolute timing accuracy of the two instruments is found to
be about 170 ms, and much better on the average. It is found that type
III radio groups often coincide with enhanced HXR emission, but only a
relatively small fraction (∼20%) of the groups show close correlation
on time scales < 1 s. If structures correlate, the HXRs precede
the type III emissions in a majority of cases, and by 0.69 ± 0.19 s
on the average. Reversed drift type III bursts are also delayed, but
high-frequency and harmonic emission is retarded less. The decimetric
pulsations and patches (DCIM) have a larger scatter of delays, but
do not have a statistically significant sign or an average different
from zero. The time delay does not show a center-to-limb variation
excluding simple propagation effects. The delay by scattering near
the source region is suggested to be the most efficient process on
the average for delaying type III radio emission.
---------------------------------------------------------
Title: X-ray chemistry in the envelopes around young stellar objects
Authors: Stäuber, P.; Doty, S. D.; van Dishoeck, E. F.; Benz, A. O.
2005A&A...440..949S Altcode: 2005astro.ph..6306S
We present chemical models of the envelope of a young stellar object
(YSO) exposed to a central X-ray source. The models are applied
to the massive star-forming region AFGL 2591 for different X-ray
fluxes. Model results for this region show that the X-ray ionization
rate with and without the effects of Compton scattering differs by only
a few percent and the influence of Compton scattering on the chemistry
is negligible. The total X-ray ionization rate is dominated by the
“secondary” ionization rate of H2 resulting from fast electrons. The
abundance profiles of several molecular and atomic species are shown to
depend on the X-ray luminosity and on the distance from the source. The
carbon, sulphur and nitrogen chemistries are discussed. It is found that
He<SUP>+</SUP> and H3<SUP>+</SUP> are enhanced and trigger a peculiar
chemistry. Several molecular X-ray tracers are found and compared to
tracers of the far ultraviolet (FUV) field. Like ultraviolet radiation
fields, X-rays enhance simple hydrides, ions and radicals. In contrast
to ultraviolet photons, X-rays can penetrate deep into the envelope and
affect the chemistry even at large distances from the source. Whereas
the FUV enhanced species cover a region of ≈ 200{-}300 AU, the
region enhanced by X-rays is ≳ 1000 AU. We find that N2O, HNO, SO,
SO^+, HCO^+, CO^+, OH^+, N2H^+, SH<SUP>+</SUP> and HSO<SUP>+</SUP>
(among others) are more enhanced by X-rays than by FUV photons even
for X-ray luminosities as low as L<SUB>X</SUB> ≈ 10<SUP>30</SUP>
erg s<SUP>-1</SUP>. CO2 abundances are reduced in the gas-phase
through X-ray induced FUV photons. For temperatures T ≲ 230 K, H2O is
destroyed by X-rays with luminosities L<SUB>X</SUB> ≳ 10<SUP>30</SUP>
erg s<SUP>-1</SUP>. Best-fit models for AFGL 2591 predict an X-ray
luminosity L<SUB>X</SUB> ≳ 10<SUP>31</SUP> erg s<SUP>-1</SUP>
with a hard X-ray spectrum T<SUB>X</SUB> ≳ 3 × 10<SUP>7</SUP>
K. This is the first time that the X-ray flux of a highly obscured
source has been estimated by its envelope chemistry. Furthermore,
we find L<SUB>X</SUB>/L<SUB>bol</SUB> ≈ 10<SUP>-6</SUP>. The
chemistry of the bulk of the envelope mass is dominated by cosmic-ray
induced reactions rather than by X-ray induced ionization for X-ray
luminosities L<SUB>X</SUB> ≲ 10<SUP>33</SUP> erg s<SUP>-1</SUP>. The
calculated line intensities of HCO<SUP>+</SUP> and HCS<SUP>+</SUP>
show that high-J lines are more affected than lower J lines by the
presence of X-rays due to their higher critical densities, and that
such differences are detectable even with large aperture single-dish
telescopes. Future instruments such as Herschel-HIFI or SOFIA will
be able to observe X-ray enhanced hydrides whereas the sensitivity
and spatial resolution of ALMA is well-suited to measure the size and
geometry of the region affected by X-rays.
---------------------------------------------------------
Title: Size dependence of solar X-ray flare properties
Authors: Battaglia, M.; Grigis, P. C.; Benz, A. O.
2005A&A...439..737B Altcode: 2005astro.ph..5154B
Non-thermal and thermal parameters of 85 solar flares of GOES class
B1 to M6 (background subtracted classes A1 to M6) have been compared
to each other. The hard X-ray flux has been measured by RHESSI and a
spectral fitting provided flux and spectral index of the non-thermal
emission, as well as temperature and emission measure of the thermal
emission. The soft X-ray flux was taken from GOES measurements. We
find a linear correlation in a double logarithmic plot between the
non-thermal flux and the spectral index. The higher the acceleration
rate of a flare, the harder the non-thermal electron distribution. The
relation is similar to the one found by a comparison of the same
parameters from several sub-peaks of a single flare. Thus small flares
behave like small subpeaks of large flares. Thermal flare properties
such as temperature, emission measure and the soft X-ray flux also
correlate with peak non-thermal flux. A large non-thermal peak flux
entails an enhancement in both thermal parameters. The relation between
spectral index and the non-thermal flux is an intrinsic feature of the
particle acceleration process, depending on flare size. This property
affects the reported frequency distribution of flare energies.
---------------------------------------------------------
Title: The Evolution of Reconnection along an Arcade of Magnetic Loops
Authors: Grigis, Paolo C.; Benz, Arnold O.
2005ApJ...625L.143G Altcode: 2005astro.ph..4436G
RHESSI observations of a solar flare showing continuous motions of
double hard X-ray sources interpreted as footpoints of magnetic
loops are presented. The temporal evolution shows many distinct
emission peaks of duration of some tens of seconds (“elementary
flare bursts”). Elementary flare bursts have been interpreted as
instabilities or oscillations of the reconnection process leading to
an unsteady release of magnetic energy. These interpretations based on
two-dimensional concepts cannot explain these observations, showing
that the flare elements are displaced in a third dimension along the
arcade. Therefore, the observed flare elements are not a modulation of
the reconnection process but originate as this process progresses along
an arcade of magnetic loops. Contrary to previous reports, we find no
correlation between footpoint motion and hard X-ray flux. This flare
apparently contradicts the predictions of the standard translation
invariant 2.5-dimensional reconnection models.
---------------------------------------------------------
Title: The spectral evolution of impulsive solar X-ray
flares. II. Comparison of observations with models
Authors: Grigis, P. C.; Benz, A. O.
2005A&A...434.1173G Altcode: 2005astro.ph..1431G
We study the evolution of the spectral index and the normalization
(flux) of the non-thermal component of the electron spectra observed by
RHESSI during 24 solar hard X-ray flares. The quantitative evolution is
confronted with the predictions of simple electron acceleration models
featuring the soft-hard-soft behaviour. The comparison is general in
scope and can be applied to different acceleration models, provided
that they make predictions for the behavior of the spectral index as a
function of the normalization. A simple stochastic acceleration model
yields plausible best-fit model parameters for about 77% of the 141
events consisting of rise and decay phases of individual hard X-ray
peaks. However, it implies unphysically high electron acceleration
rates and total energies for the others. Other simple acceleration
models such as constant rate of accelerated electrons or constant
input power have a similar failure rate. The peaks inconsistent with
the simple acceleration models have smaller variations in the spectral
index. The cases compatible with a simple stochastic model require
typically a few times 10<SUP>36</SUP> electrons accelerated per second
beyond a threshold energy of 18 keV in the rise phases and 24 keV in
the decay phases of the flare peaks.
---------------------------------------------------------
Title: Absence of linear polarization in Hα emission of solar flares
Authors: Bianda, M.; Benz, A. O.; Stenflo, J. O.; Küveler, G.;
Ramelli, R.
2005A&A...434.1183B Altcode: 2005astro.ph..2263B
High sensitivity observations of Hα polarization of 30 flares of
different sizes and disk positions are reported. Both filter and
spectrographic techniques have been used. The ZIMPOL system eliminates
spurious polarizations due to seeing and flat-field effects. We didn't
find any clear linear polarization signature above our sensitivity
level which was usually better than 0.1%. The observations include an
X17.1 flare with gamma-ray lines reported by the RHESSI satellite. These
results cast serious doubts on previous claims of linear polarization at
the one percent level and more, attributed to impact polarization. The
absence of linear polarization limits the anisotropy of energetic
protons in the Hα emitting region. The likely causes are isotropization
by collisions with neutrals in the chromosphere and defocusing by the
converging magnetic field.
---------------------------------------------------------
Title: Thermal and non-thermal energies of solar flares
Authors: Saint-Hilaire, P.; Benz, A. O.
2005A&A...435..743S Altcode:
The energy of the thermal flare plasma and the kinetic energy of the
non-thermal electrons in 14 hard X-ray peaks from 9 medium-sized solar
flares have been determined from RHESSI observations. <P />The emissions
have been carefully separated in the spectrum. <P />The turnover or
cutoff in the low-energy distribution of electrons has been studied
by simulation and fitting, yielding a reliable lower limit to the
non-thermal energy. <P />It remains the largest contribution to the
error budget. <P />Other effects, such as albedo, non-uniform target
ionization, hot target, and cross-sections on the spectrum have been
studied. <P />The errors of the thermal energy are about equally
as large. <P />They are due to the estimate of the flare volume,
the assumption of the filling factor, and energy losses. <P />Within
a flare, the non-thermal/thermal ratio increases with accumulation
time, as expected from loss of thermal energy due to radiative cooling
or heat conduction. <P />Our analysis suggests that the thermal and
non-thermal energies are of the same magnitude. <P />This surprising
result may be interpreted by an efficient conversion of non-thermal
energy to hot flare plasma.
---------------------------------------------------------
Title: Thermal and non-thermal energies in solar flares
Authors: Saint-Hilaire, Pascal; Benz, Arnold O.
2005astro.ph..3078S Altcode:
The energy of the thermal flare plasma and the kinetic energy of the
non-thermal electrons in 14 hard X-ray peaks from 9 medium-sized solar
flares have been determined from RHESSI observations. The emissions have
been carefully separated in the spectrum. The turnover or cutoff in the
low-energy distribution of electrons has been studied by simulation
and fitting, yielding a reliable lower limit to the non-thermal
energy. It remains the largest contribution to the error budget. Other
effects, such as albedo, non-uniform target ionization, hot target,
and cross-sections on the spectrum have been studied. The errors of
the thermal energy are about equally as large. They are due to the
estimate of the flare volume, the assumption of the filling factor, and
energy losses. Within a flare, the non-thermal/thermal ratio increases
with accumulation time, as expected from loss of thermal energy due
to radiative cooling or heat conduction. Our analysis suggests that
the thermal and non-thermal energies are of the same magnitude. This
surprising result may be interpreted by an efficient conversion of
non-thermal energy to hot flare plasma.
---------------------------------------------------------
Title: Callisto A New Concept for Solar Radio Spectrometers
Authors: Benz, Arnold O.; Monstein, Christian; Meyer, Hansueli
2005SoPh..226..143B Altcode: 2004astro.ph.10437B
A new radio spectrometer, CALLISTO, is presented. It is a dual-channel
frequency-agile receiver based on commercially available consumer
electronics. Its major characteristic is the low price for hardware
and software, and the short assembly time, both two or more orders of
magnitude below existing spectrometers. The instrument is sensitive at
the physical limit and extremely stable. The total bandwidth is 825
MHz, and the width of individual channel is 300 kHz. A total of 1000
measurements can be made per second. The spectrometer is well suited
for solar low-frequency radio observations pertinent to space weather
research. Five instruments of the type were constructed until now and
put into operation at several sites, including Bleien (Zurich) and
NRAO (USA). First results in the 45-870 MHz range are presented. Some
of them were recorded in a preliminary setup during the time of high
solar activity in October and November 2003.
---------------------------------------------------------
Title: Survey on Solar X-ray Flares and Associated Coherent Radio
Emissions
Authors: Benz, Arnold O.; Grigis, Paolo C.; Csillaghy, AndrÉ;
Saint-Hilaire, Pascal
2005SoPh..226..121B Altcode: 2004astro.ph.10436B
The radio emission during 201 selected X-ray solar flares was
surveyed from 100 MHz to 4 GHz with the Phoenix-2 spectrometer of ETH
Zürich. The selection includes all RHESSI flares larger than C5.0
jointly observed from launch until June 30, 2003. Detailed association
rates of radio emission during X-ray flares are reported. In the
decimeter wavelength range, type III bursts and the genuinely decimetric
emissions (pulsations, continua, and narrowband spikes) were found
equally frequently. Both occur predominantly in the peak phase of
hard X-ray (HXR) emission, but are less in tune with HXRs than the
high-frequency continuum exceeding 4 GHz, attributed to gyrosynchrotron
radiation. In 10% of the HXR flares, an intense radiation of the above
genuine decimetric types followed in the decay phase or later. Classic
meter-wave type III bursts are associated in 33% of all HXR flares,
but only in 4% are they the exclusive radio emission. Noise storms
were the only radio emission in 5% of the HXR flares, some of them
with extended duration. Despite the spatial association (same active
region), the noise storm variations are found to be only loosely
correlated in time with the X-ray flux. In a surprising 17% of the HXR
flares, no coherent radio emission was found in the extremely broad
band surveyed. The association but loose correlation between HXR and
coherent radio emission is interpreted by multiple reconnection sites
connected by common field lines.
---------------------------------------------------------
Title: Time Evolution of the Spectral Index in Solar Flares
Authors: Grigis, P. C. :; Buser, D.; Benz, A. O.
2005ASSL..320..199G Altcode: 2005smp..conf..199G
No abstract at ADS
---------------------------------------------------------
Title: X-ray chemistry in the envelopes around young stellar objects
Authors: Stäuber, Pascal; Benz, A. O.; Doty, S. D.; van Dishoeck,
E. F.
2005ESASP.577..413S Altcode: 2004astro.ph.12281S; 2005dmu..conf..413S
We have studied the influence of X-rays from a massive young stellar
object (YSO) on the chemistry of its own envelope by extending the
models of Doty et al. (2002) and Stäuber et al. (2004). The models are
applied to the massive star-forming region AFGL 2591 for different X-ray
luminosities and plasma temperatures. Enhanced column densities for
several species are predicted. In addition we present first detections
of CO<SUP>+</SUP> and SO<SUP>+</SUP> toward AFGL 2591. These molecular
ions are believed to be high-energy tracers. Herschel-HIFI will be
able to observe other tracers like CH and CH<SUP>+</SUP> whereas ALMA
is well suited to measure the size and geometry of the emitting region.
---------------------------------------------------------
Title: The spectral evolution of impulsive solar X-ray flares
Authors: Grigis, P. C.; Benz, A. O.
2004A&A...426.1093G Altcode: 2004astro.ph..7431G
The time evolution of the spectral index and the non-thermal flux in
24 impulsive solar hard X-ray flares of GOES class M was studied in
RHESSI observations. The high spectral resolution allows for a clean
separation of thermal and non-thermal components in the 10-30 keV
range, where most of the non-thermal photons are emitted. Spectral
index and flux can thus be determined with much better accuracy than
before. The spectral soft-hard-soft behavior in rise-peak-decay
phases is discovered not only in the general flare development,
but even more pronounced in subpeaks. An empirically found power-law
dependence between the spectral index and the normalization of the
non-thermal flux holds during the rise and decay phases of the emission
peaks. It is still present in the combined set of all flares. We find
an asymmetry in this dependence between rise and decay phases of the
non-thermal emission. There is no delay between flux peak and spectral
index minimum. The soft-hard-soft behavior appears to be an intrinsic
signature of the elementary electron acceleration process.
---------------------------------------------------------
Title: Influence of UV radiation from a massive YSO on the chemistry
of its envelope
Authors: Stäuber, P.; Doty, S. D.; van Dishoeck, E. F.; Jørgensen,
J. K.; Benz, A. O.
2004A&A...425..577S Altcode: 2004astro.ph..6540S
We have studied the influence of far ultraviolet (UV) radiation
(6 < hν < 13.6 eV) from a massive young stellar object (YSO)
on the chemistry of its own envelope by extending the models of Doty
et al. (\cite{Doty}) to include a central source of UV radiation. The
models are applied to the massive star-forming region AFGL 2591 for
different inner UV field strengths. Depth-dependent abundance profiles
for several molecules are presented and discussed. We predict enhanced
column densities for more than 30 species, especially radicals and
ions. Comparison between observations and models is improved with a
moderate UV field incident on the inner envelope, corresponding to
an enhancement factor G<SUB>0</SUB> ≈ 10-100 at 200 AU from the
star with an optical depth τ ≈ 15-17. The chemical networks of
various species are explored. Subtle differences are found compared
with traditional models of Photon Dominated Regions (PDRs) because of
the higher temperatures and higher gas-phase H<SUB>2</SUB>O abundance
caused by evaporation of ices in the inner region. In particular,
the CN/HCN ratio is not a sensitive tracer of the inner UV field, in
contrast with the situation for normal PDRs: for low UV fields, the
extra CN reacts with H<SUB>2</SUB> in the inner dense and warm region
and produces more HCN. It is found that the CH<SUP>+</SUP> abundance
is strongly enhanced and grows steadily with increasing UV field. In
addition, the ratio CH<SUP>+</SUP>/CH is increased by a factor of
10<SUP>3</SUP>-10<SUP>5</SUP> depending on the inner UV flux. High-J
lines of molecules like CN and HCN are most sensitive to the inner
dense region where UV radiation plays a role. Thus, even though the
total column density affected by UV photons is small, comparison
of high-J and low-J lines can selectively trace and distinguish the
inner UV field from the outer one. In addition, future Herschel-HIFI
observations of hydrides can sensitively probe the inner UV field.
---------------------------------------------------------
Title: Decimeter Burst Emission and Particle Acceleration
Authors: Benz, Arnold O.
2004ASSL..314..203B Altcode:
The radio emission of solar flares at decimeter wavelengths includes
a variety of emission processes of a plasma thought to have a high
beta. Very intense coherent emissions are observed at frequencies
smaller than about 9 GHz. They are caused by plasma instabilities
driving various wave modes that in turn may emit observable radio
waves. Particularly important are type III bursts, caused by electron
beams exciting Langmuir waves. Their sources may be used to trace
the path of the electrons back in the corona to the acceleration
region. Less known are radio emissions from trapped electrons driving
loss-cone unstable waves, suspected for type IV bursts. These types
of coherent radio emission give clues on the geometry and plasma
parameters near the acceleration region.
---------------------------------------------------------
Title: Thermal and non-thermal energies of solar flares
Authors: Saint-Hilaire, P.; Benz, A. O.
2004AAS...204.4715S Altcode: 2004BAAS...36R.740S
The energy of the thermal flare plasma and the kinetic energy of the
non-thermal electrons in 9 medium-sized and 1 X-class solar flares
have been determined from RHESSI observations. The emissions in the
spectrum have been carefully separated. A reliable lower limit to
the non-thermal energy, and the various errors of this estimate have
been studied. The effects of albedo, non-uniform target ionization,
hot target, and electron cross-section on the spectrum have been
estimated. The turn-over or cut-off in the low-energy distribution of
electrons remains the largest contribution to the error budget. About
equally large are the errors of the thermal energy. They are due to the
estimate of the flare volume, the assumption of the filling factor, and
energy losses. Within a flare, the non-thermal/thermal ratio increases
with accumulation time, as expected from loss of thermal energy due
to radiative cooling or heat conduction. Our analysis suggests that
the thermal and non-thermal energies are of the same magnitude. This
surprising result may be interpreted by an efficient conversion of
non-thermal energy to hot flare plasma or by additional energy input
of high-energy ions, or by other flare energy input additional to the
non-thermal electron channel.
---------------------------------------------------------
Title: Electron Trapping, Reconnection, or Shock Acceleration? Radio
Afterglows in the 12X-Events of Oct/Nov 2003
Authors: Benz, A. O.; Perret, H.; Saint-Hilaire, P.; Zlobec, P.
2004cosp...35..345B Altcode: 2004cosp.meet..345B
The large solar flares of October and November 2003 have been
accompanied by unusually intense radio emissions at decimeter
wavelengths. The emissions even had direct effects on terrestrial
activities such as radar and navigation. The radio emissions continued
long after the main phase of the flares. The unusual number of large
flares from the same active regions allow for a detailed comparison. The
radio emissions are not due to electron beams and do not seem to be
related to the primary energy release and acceleration processes. We
have compared the radio emissions (as observed by Phoenix-2, Callisto,
Trieste, and Nançay RH) with the X-rays measured by RHESSI and
GOES. The intensity and duration of the radio emission seem to be
generally related to the energy released as seen in X-rays, but there
are large differences between the three active regions involved. The
lack of X-rays during some times of the radio emission is confirmed. It
has previously been taken for evidence that the radio "afterglow" (type
IV burst) is caused by trapped electrons. We present evidence that this
interpretation is not likely, but that electrons are accelerated long
after the impulsive phase. The possible mechanisms of acceleration
and the reasons for the absence of bremsstrahlung are compared with
the observations.
---------------------------------------------------------
Title: Stars as suns : activity, evolution and planets
Authors: Dupree, Andrea K.; Benz, Arnold O.
2004IAUS..219.....D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nanoflares and the Heating of the Solar Corona
Authors: Benz, A. O.
2004IAUS..219..461B Altcode: 2003IAUS..219E.193B
There is a simmering dispute on the heating of the solar corona. Waves
or flares that is the question. New observational signatures
of the heating process(es) have been revealed by observations of
SoHO TRACE Yohkoh and RHESSI. The evidence for heating in the quiet
corona active region loops and the solar wind are different and must
be distinguished. Prime indications come from the distribution of
temperature and radiation loss in relation to height the correlation
of magnetic flux and brightness nanoflares and other fluctuations line
broadening and waves. The reported microevents in the quiet regions
are about 3 orders of magnitude smaller than microevents reported in
active regions. The effects from localized energy release regardless
of the energy source must be considered. In particular the reaction
of the chromosphere on energy release by evaporation has an important
effect on the corona. A further requirement for the heating process
is to deposit most of the heat in the low corona but heat the upper
corona to even higher temperature. Finally the heating process(es)
must be able to account for the coronae of more active stars showing
coronal emissions at levels of more than 3 orders of magnitude higher
than the Sun
---------------------------------------------------------
Title: Time evolution of the spectral hardness in solar hard X-ray
flares
Authors: Grigis, P. C.; Benz, A. O.
2004cosp...35.1096G Altcode: 2004cosp.meet.1096G
The non-thermal emission from hard X-Ray flares shows high variability
in the flux and spectral hardness. It has been known for a long time
that in the impulsive phase a soft-hard-soft (SHS) pattern is usually
observed. The behaviour of the spectral index is of crucial importance
for the estimation of the non-thermal energy content of flares and is a
direct signature of the electron acceleration process. We present RHESSI
observation of 20 M-class flares for which the time evolution of the
photon spectral index was measured over the whole impulsive phase. The
non-thermal flux and the spectral index are clearly anti-correlated in
most flares. The photon spectral index vs. flux relation can be fitted
by a power-law model. The observed time evolution of the spectral
index can be used to put constraints on electron acceleration models,
which must be able to account for the SHS behaviour.
---------------------------------------------------------
Title: Variations in Solar X-ray Flux and its Relevance to the
Coronal Heating Problem
Authors: Benz, A. O.; Grigis, P. C.; Krucker, S.
2004cosp...35..343B Altcode: 2004cosp.meet..343B
The thermal X-ray and EUV emissions of the solar corona are known
to fluctuate in time and space. The fluctuations seem to be of a
similar nature as the flares and thus are termed microflares or
nanoflares. Several forms of such small events have been observed
in the solar corona by SoHO, TRACE, Yohkoh, and RHESSI. The reported
nanoevents in the quiet regions are about 3 orders of magnitude smaller
than microevents reported in active regions and are radio-poor. Magnetic
energy dissipation by small flares is one of the scenarios for coronal
heating. These micro-events obviously increase the energy in the corona
and are signatures of coronal heating, the question is whether they
dominate coronal heating and are the cause of the existence of the
corona. The main uncertainty in determining the role of flare heating
is the flare energetics, in particular the forms of energy into which
the magnetic energy is dissipated. A large fraction becomes observable
in electrons having energies of some tens of keV. Another less known
fraction is thought to be associated with the reconnection jets and
MHD waves. The heating process(es) must be able to account for the
coronae of the quiet sun including coronal holes, active regions,
as well as more active stars showing coronal emissions at levels of
more than 3 orders of magnitude higher than the Sun.
---------------------------------------------------------
Title: Thermal vs. non-thermal energies in solar flares
Authors: Saint-Hilaire, P.; Benz, A. O.
2004cosp...35.1576S Altcode: 2004cosp.meet.1576S
The energy of the thermal flare plasma and the kinetic energy of
the non-thermal electrons in 9 medium-sized solar flares have
been determined from RHESSI observations. The emissions in the
spectrum have been carefully separated. A reliable lower limit to
the non-thermal energy, and the various errors of this estimate have
been studied. The effects of albedo, non-uniform target ionization,
hot target, and electron cross-section on the spectrum have been
estimated. The turn-over or cut-off in the low-energy distribution of
electrons remains the largest contribution to the error budget. About
equally large are the errors of the thermal energy. They are due to the
estimate of the flare volume, the assumption of the filling factor,
and energy losses. Within a flare, the non-thermal/thermal ratio
increases with accumulation time, as expected from loss of thermal
energy due to radiative cooling or heat conduction. Our analysis
suggests that the thermal and non-thermal energies are of the same
magnitude. This surprising result may be interpreted by an efficient
conversion of non-thermal energy to hot flare plasma or by additional
energy input of high-energy ions, or by another flare energy input,
additional to the non-thermal electron channel.
---------------------------------------------------------
Title: First Detection of Hard X-ray Emission From Solar Type III
Radio Bursts
Authors: Christe, S.; Krucker, S.; Lin, R. P.; Arzner, K.; Benz, A. O.
2003AGUFMSH11D1131C Altcode:
We present the first detection of non-flare related hard X-ray
emission from type III radio bursts as observed by the Reuven Ramaty
High Energy Solar Spectroscopic Imager (RHESSI). During a period of
15 minutes on 19 July 2002 14:23-14:35 UT, the WAVES instrument on
the Wind spacecraft observed interplanetary type III radio bursts
approximately every 2 minutes and each was accompanied by a 12-15 keV
X-ray brightening observed by RHESSI. The radio and X-rays fluxes were
found to be strongly correlated. No flares were reported in the SEC
solar event reports during this time and only the strongest brightening
is associated with a detectable enhancement in the GOES levels (A3
above a B8 background). Phoenix-2, a ground-based radio spectrometer,
observed each interplanetary type III to extend down to 300 MHz
(0.1 R<SUB>sun</SUB>) The strongest type III was also accompagnied
by a cluster of decimetric radio emission in the frequency range 1
to 2 GHz. A close correlation is found between X-ray fluxes and the
decimetric fluxes. X-ray spectra show non-thermal emission (9-30 keV)
with an electron spectral power-law index of ∼4, from the footpoint
of a TRACE loop observed in FeXII (195 Å). Subsequently, jets are
seen to originate from the RHESSI footpoint emission travelling with
apparent speeds of ∼ 100 km s<SUP>-1</SUP>. The observed RHESSI hard
X-ray fluxes require ∼10<SUP>33</SUP> electrons above 10 keV. This
work was supported by NASA contract NAS5-98033.
---------------------------------------------------------
Title: High-Energy Radiation Probes of Protostellar Envelopes
Authors: Stäuber, P.; Benz, A. O.; Doty, S. D.; van Dishoeck, E. F.;
Jørgensen, J. K.
2003astro.ph.11022S Altcode:
We present observations of molecular high-energy radiation probes
and report the first detections of CO+ toward W3 IRS5, a source
containing ultracompact HII regions. UV radiation and X-rays from
the central objects may enhance molecules due to photodissociation
and ionization processes. To study the effects on the immediate YSO
environment, we are developing time- and depth-dependant chemical
models containing UV and X-ray chemistry, by extending the models of
Doty et al. (2002). Molecules like CO+ or NO may be used as tracers
of very early X-ray emission in regions of high extinction, from which
no X-ray photons can be detected.
---------------------------------------------------------
Title: Micro-events in the active and quiet solar corona
Authors: Benz, A. O.; Grigis, P. C.
2003AdSpR..32.1035B Altcode: 2003astro.ph..8323B
The content of hot material in the corona is not constant. Soft X-ray
and high-temperature EUV line observations show that new material,
apparently heated and evaporated from the chromosphere, is frequently
injected into the corona both in active and quiet regions. Active
regions are found to exhibit transient brightenings, termed here
microflares, due to such enhancements in emission measure. They appear
at a rate of up to 10 per hour in RHESSI observations of 3-15 keV
X-rays, occurring even during the periods of lowest solar activity so
far in the mission. The RHESSI observations combined with measurements
at other wavelengths yield estimates of the energy input into the
corona. These observations suggest that the models for coronal heating
must be complemented with respect to continuous replenishing the lower
corona by chromospheric material heated to coronal temperatures. The
observed micro-events are secondary phenomena, and do not represent
the primary energy release, nor its total amount. Nevertheless, they
are an interesting source of information on the heating process(es) of
the corona. The micro-events are compared to events in quiet regions,
termed here nanoflares, which seem to be a different population,
well separated in temperature and emission measure from microflares.
---------------------------------------------------------
Title: Hard X-rays, ejecta, and their associated decimetric radio
emission in solar flares
Authors: Saint-Hilaire, Pascal; Benz, Arnold O.
2003SoPh..216..205S Altcode:
We investigate temporal and spatial correlations in solar flares of
hard X-rays (HXR) and decimetric continuum emissions, ejecta, and
CMEs. The focus is on three M-class flares, supported by observations
from other flares. The main conclusions of our observations are that (1)
major hard X-ray flares are often associated with ejecta seen in soft
X-rays or EUV. (2) Those ejecta seem to start before HXR or related
decimetric radio continua (DCIM emission). (3) DCIM occurring nearly
simultaneously with the first HXR peak are located very close to the HXR
source. Later in the flare, DCIM generally becomes stronger, drifts to
lower frequency and occurs far from the HXR source. Thus the positions
at high frequency are generally closer to the HXR source. DCIM emission
consists of pulses that drift in frequency. The very high and sometimes
positive drift rate suggests spatially extended sources or type III
like beams in an inhomogeneous source. Movies of selected flares used
in this study can be found on the CD-ROM accompanying this volume.
---------------------------------------------------------
Title: VLBI observations of T Tauri South
Authors: Smith, K.; Pestalozzi, M.; Güdel, M.; Conway, J.; Benz, A. O.
2003A&A...406..957S Altcode: 2003astro.ph..5543S
We report observations of the T Tauri system at 8.4 GHz with a VLBI
array comprising the VLBA, VLA and Effelsberg 100 m telescopes. We
detected a compact source offset approximately 40 mas from the best
infrared position of the T Tau Sb component. This source was unresolved,
and constrained to be less than 0.5 mas in size, corresponding to 0.07
AU or 15 R<SUB>sun</SUB> at a distance of 140 pc. The other system
components (T Tau Sa, T Tau N) were not detected in the VLBI data. The
separate VLA map contains extended flux not accounted for by the compact
VLBI source, indicating the presence of extended emission on arcsecond
scales. The compact source shows rapid variability, which together
with circular polarization and its compact nature indicate that the
observed flux arises from a magnetically-dominated region. Brightness
temperatures in the MK range point to gyrosynchrotron as the emission
mechanism for the steady component. The rapid variations are accompanied
by dramatic changes in polarization, and we record an at times 100%
polarized component during outbursts. This strongly suggests a coherent
emission process, most probably an electron cyclotron maser. With
this assumption it is possible to estimate the strength of the local
magnetic field to be 1.5-3 kilogauss.
---------------------------------------------------------
Title: Resolving the Magnetosphere of T Tauri South B
Authors: Smith, K. W.; Pestalozzi, M.; Conway, J.; Güdel, M.; Benz,
A. O.
2003ANS...324R..70S Altcode: 2003ANS...324..P46S
No abstract at ADS
---------------------------------------------------------
Title: Coronal Heating and Microflares in Solar Active and Quiet
Regions
Authors: Benz, Arnold O.
2003ANS...324....8B Altcode: 2003ANS...324..B02B
No abstract at ADS
---------------------------------------------------------
Title: Test particle simulation of the Electron Firehose instability
Authors: Paesold, G.; Benz, A. O.
2003A&A...401..711P Altcode:
In the course of the energization of { electrons to energies of
some tens of keV during the impulsive phase of a solar flare,
the velocity distribution function of the electrons is predicted
to become anisotropic with T<SUP>e</SUP><SUB>parallel</SUB>
>T<SUP>e</SUP><SUB>perpendicular</SUB> to (Here, parallel and
perpendicular to denote directions with respect to the background
magnetic field). Such a configuration can become unstable to the
so-called Electron Firehose instability (EFI). Left hand circularly
polarized electromagnetic waves propagating along the magnetic field
are excited via a non-resonant mechanism: electrons non-resonantly
excite the waves while the protons are in resonance and carry
the wave. The non-resonant nature of the instability raises the
question of the response of the electron population to the growing
waves. Test particle simulations are carried out to investigate the
pitch-angle development of electrons injected to single waves and wave
spectra. To interpret the simulation results, a drift kinetic approach
is developed. The findings in the case of single wave simulations show
the scattering to larger pitch-angles in excellent agreement with the
theory. The situation dramatically changes when assuming a spectrum of
waves. Stochasticity is detected at small initial parallel velocities
resulting in significant deviations from drift kinetic theory. It
enhances the scattering rate of electrons with initial parallel velocity
below to the mean thermal perpendicular velocity. Increased scattering
is also noticed for electrons having initial parallel velocity within an
order of magnitude of the resonance velocity. The resulting pitch-angle
scattering is proposed to be an important ingredient in Fermi-type
electron acceleration models, particularly transit-time acceleration
by compressional MHD waves.
---------------------------------------------------------
Title: The Reuven Ramaty High-Energy Solar Spectroscopic Imager
(RHESSI) - Mission Description and Early Results
Authors: Lin, R. P.; Dennis, B. R.; Benz, A. O.
2003rrhe.conf.....L Altcode:
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
satellite was launched on 5 February 2002. Its objective is to
study the energy release and particle acceleration in solar flares
through observations of X-rays and gamma rays. Two novel technologies
are combined to obtain both spectra and images over a broad energy
range. For the spectroscopy, cooled hyperpure germanium detectors are
used to cover the energy range from 3 keV to 17 MeV with unprecedented
keV-class resolution. Since focusing optics are not possible for
making images with such high energy photons, tungsten and molybdenum
absorbing grids are used to modulate the X-rays and gamma-rays coming
from the Sun as the spacecraft rotates. This allows the spatial Fourier
components of the source to be determined so that images can be made
in spectral ranges where astronomical images have never been produced
before. These new instrumental techniques require equally innovative
software to reconstruct X-ray and gamma-ray spectra and images from the
observations. Ample solar activity, abundant observations, and an open
data policy have attracted many researchers. Astronomers face in the
RHESSI mission an exciting new scientific potential. It has unusually
broad possibilities for improving our understanding of the enigmatic
solar flare phenomenon that is becoming increasingly important as
society depends more and more on space-based technologies. In this
volume, the functioning of RHESSI is explained, the data analysis
techniques including spectroscopy and image reconstruction are
introduced, and the experiences of the first few months of operation
are summarized. First scientific results are presented that provide
the essential base for more extended studies using RHESSI data and
complementary observations by instruments on other spacecraft and at
ground-based solar observatories. The accompanying CD-ROM contains
X-ray and EUV movies showing the dynamics of several solar flares. It
also contains color versions of the graphics in the printed papers
and additional material. Scientists and students will find here the
latest discoveries in solar flare research, as well as inspiration
for future work. The papers will serve as references for the many
new discoveries to come from the continuing RHESSI observations. <P
/>http://www.wkap.nl/prod/b/1-4020-1107-5
---------------------------------------------------------
Title: The Magnetosphere of T Tauri South
Authors: Smith, Kester; Pestalozzi, Michele; Guedel, Manuel; Conway,
John; Benz, Arnold
2003IAUS..221P.166S Altcode:
We report observations of the T Tauri system at 8.4 GHz with a VLBI
array comprising the VLBA VLA and Effelsberg 100m telescopes. We
detected a compact source offset approximately 40mas from the best
optical position of the T Tau Sb component. The other system components
(T Tau Sa T Tau N) were not detected in the VLBI data. The compact
source is constrained to be less than 10 solar radii in size. The
VLA lightcurve shows rapid variability which together with circular
polarization and its compact nature indicate that the observed flux
arises from a magnetically-dominated region. One flare was observed to
have 100% right-hand circular polarization suggestive of a coherent
emission process most probably an electron cyclotron maser. With
this assumption it is possible to estimate the strength of the local
magnetic field to be 1.5-3 kilogauss. Using the assumption that the
steady gyrosynchrotron emission must have brightness temperature less
than 10 billion Kelvin we argue that this field must be large in size
compared to the star.
---------------------------------------------------------
Title: Division II: The Sun and heliosphere (Soleil et héliosphère)
Authors: Benz, Arnold O.
2003IAUTA..25...73B Altcode: 2003IAUTr..25A..73B
No abstract at ADS
---------------------------------------------------------
Title: International low-frequency very-long-baseline interferometry
network project milestones
Authors: Molotov, I.; Lipatov, B.; Dementiev, A.; Antipenko, A.;
Snegirev, S.; Nechaeva, M.; Reznikovak, V.; Altunin, V.; Benz, A.;
Mantovani, F.; Stanghellini, C.; Gridin, A.; Ananthakrishnan, S.;
Balasubramanian, V.; Sankararaman, M.; Hong, X.; Huang, X.; Shiguang,
L.; Dougherty, S.; Del Rizzo, D.; Fink, A.; Liu, X.; Na, W.; Zhang,
J.; Kus, A.; Borkowski, K.; Quick, J.; Nicolson, G.; Shmeld, I.;
Koyama, Y.; Sekido, M.; Gorshenkov, Yu.; Poperechenko, B.; Saurin,
V.; Ozolins, G.; Bezrukov, D.; Zhang, X.; Kovalenko, A.; Samodurov,
V.; Tuccari, G.; Konovalenko, A.; Falkovich, I.
2003A&AT...22..743M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar flare electron acceleration: Comparing theories and
observations
Authors: Benz, A. O.; Saint-Hilaire, P.
2003AdSpR..32.2415B Altcode: 2003astro.ph..8321B
A popular scenario for electron acceleration in solar flares is
transit-time damping of low-frequency MHD waves excited by reconnection
and its outflows. The scenario requires several processes in sequence
to yield energetic electrons of the observed large number. Until
now there was very little evidence for this scenario, as it is even
not clear where the flare energy is released. RHESSI measurements of
bremsstrahlung by non-thermal flare electrons yield energy estimates as
well as the position where the energy is deposited. Thus quantitative
measurements can be put into the frame of the global magnetic field
configuration as seen in coronal EUV line observations. We present
RHESSI observations combined with TRACE data that suggest primary energy
inputs mostly into electron acceleration and to a minor fraction into
coronal heating and primary motion. The more sensitive and lower energy
X-ray observations by RHESSI have found also small events (C class)
at the time of the acceleration of electron beams exciting meter
wave Type III bursts. However, not all RHESSI flares involve Type III
radio emissions. The association of other decimeter radio emissions,
such as narrowband spikes and pulsations, with X-rays is summarized
in view of electron acceleration.
---------------------------------------------------------
Title: Radio Diagnostics of Flare Energy Release
Authors: Benz, A. O.
2003LNP...612...80B Altcode: 2003ecpa.conf...80B
The radio emission of flares at wavelengths from millimeter to decameter
waves includes a large variety of emission processes. They can be
considered as different diagnostic tools particularly suited for
the analysis of non-thermal electron distributions, enhanced levels
of various kinds of plasma waves and plasma phenomena. Incoherent
gyrosynchrotron emission at millimeter and centimeter waves provides
higher sensitivity for observing MeV electrons than existing hard X-ray
(HXR) and gamma-ray satellites. Very intense coherent emissions are
observed at wavelengths longer than about 10 cm, weaker ones from about
4 cm. They are caused by plasma instabilities driving various wave modes
that in turn may emit observable radio waves. Particularly important
are type III bursts, caused by electron beams exciting Langmuir
waves. Their trace in the corona points back to the acceleration
region of the electrons. Less known are radio emissions from trapped
electrons driving loss-cone unstable waves. This is the interpretation
usually given to decimetric type IV emission. These types of coherent
radio emission give clues on the geometry and plasma parameters near
the acceleration region. More speculative are emissions that are
directly produced by the acceleration process. A possible group of
such phenomena are narrowband, short peaks of emission. Narrowband
spikes are seen sometimes at frequencies above the start of metric
type III events. There is mounting evidence for the hypothesis that
these spikes coincide with the energy release region. Much less clear
and highly controversial is the situation for decimetric spikes, which
are associated with HXR flares. More frequently than spikes, however,
there is fluctuating broadband decimetric emission during the HXR phase
of flares. The use of these coherent radio emissions as a diagnostic
tool for the primary energy release requires a solid understanding
of the emission process. At the moment we are still far away from
an accepted theory. Only careful comparisons with complementary
observations of energetic electrons and the thermal coronal background
in EUV lines and soft X-rays can put coherent emissions into context
and test the different scenarios. The comparison with HXR, millimeter
and centimeter observations will be necessary to derive quantitative
results on energy release. In combination with other wavelengths and
their recent imaging capabilities, exciting new possibilities are now
opening for radio diagnostics.
---------------------------------------------------------
Title: Acceleration and Enrichment of <SUP>3</SUP>He in Impulsive
Solar Flares by Electron Firehose Waves
Authors: Paesold, G.; Kallenbach, R.; Benz, A. O.
2003ApJ...582..495P Altcode: 2002astro.ph..9135P
A new mechanism for acceleration and enrichment of <SUP>3</SUP>He during
impulsive solar flares is presented. Low-frequency electromagnetic
plasma waves excited by the electron firehose instability (EFI) can
account for the acceleration of ions up to 1 MeV amu<SUP>-1</SUP>
energies as a single-stage process. The EFI arises as a direct
consequence of the free energy stored in a temperature anisotropy
(T<SUP>e<SUB>∥</SUB></SUP>>T<SUP>e<SUB>⊥</SUB></SUP>) of the
bulk energized electron population during the acceleration process. In
contrast to other mechanisms that require special plasma properties,
the EFI is an intrinsic feature of the acceleration process of the
bulk electrons. Being present as a side effect in the flaring plasma,
these waves can account for the acceleration of <SUP>3</SUP>He and
<SUP>4</SUP>He while selectively enhancing <SUP>3</SUP>He as a result
of the spectral energy density built up from linear growth. Linearized
kinetic theory, analytic models, and test particle simulations have
been applied to investigate the ability of the waves to accelerate and
fractionate. As waves grow in both directions parallel to the magnetic
field, they can trap resonant ions and efficiently accelerate them to
the highest energies. Plausible models have been found that can explain
the observed energies, spectra, and abundances of <SUP>3</SUP>He and
<SUP>4</SUP>He.
---------------------------------------------------------
Title: Preface
Authors: Lin, R.; Dennis, B.; Benz, A.; Harvey, J.; Engvold, O.;
švestka, Z.
2002SoPh..210....1L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The RHESSI Experimental Data Center
Authors: Saint-Hilaire, Pascal; von Praun, Christoph; Stolte, Etzard;
Alonso, Gustavo; Benz, Arnold O.; Gross, Thomas
2002SoPh..210..143S Altcode:
The RHESSI Experimental Data Center (HEDC) at ETH Zürich aims
to facilitate the use of RHESSI data. It explores new ways to
speed up browsing and selecting events such as solar flares. HEDC
provides pre-processed data for on-line use and allows basic data
processing remotely over the Internet. In this article, we describe
the functionality and contents of HEDC, as well as first experiences
by users. HEDC can be accessed at http://www.hedc.ethz.ch. Additional
graphical material and color versions of most figures are available
on the CD-ROM accompanying this volume.
---------------------------------------------------------
Title: Energy budget and imaging spectroscopy of a compact flare
Authors: Saint-Hilaire, Pascal; Benz, Arnold O.
2002SoPh..210..287S Altcode: 2002astro.ph.10023S
We present the analysis of a compact flare that occurred on 26 February
2002 at 10:26 UT, seen by both RHESSI and TRACE. The size of the nearly
circular hard X-ray source is determined to be 5.6 (±0.8)”, using
different methods. The power-law distribution of non-thermal photons
is observed to extend down to 10 keV without flattening, and to soften
with increasing distance from the flare kernel. The former indicates
that the energy of the precipitating flare electron population is larger
than previously estimated: it amounts to 2.6 (±0.8)×10<SUP>30</SUP>
erg above 10 keV, assuming thick-target emission. The thermal energy
content of the soft X-ray source (isothermal temperature of 20.8 (±0.9)
MK) and its radiated power were derived from the thermal emission at
low energies. TRACE has observed a low-temperature ejection in the
form of a constricted bubble, which is interpreted as a reconnection
jet. Its initial energy of motion is estimated. Using data from both
satellites, an energy budget for this flare is derived. The kinetic
energy of the jet bulk motion and the thermal and radiated energies
of the flare kernel were more than an order of magnitude smaller than
the derived electron beam energy. A movie is available on the CD-ROM
accompanying this volume.
---------------------------------------------------------
Title: Microflares and hot component in solar active regions
Authors: Benz, Arnold O.; Grigis, Paolo C.
2002SoPh..210..431B Altcode: 2002astro.ph.10024B
Open-shutter RHESSI observations of 3-15 keV X-rays are found to
exhibit active-region transient brightenings and microflares at a rate
of a least 10 per hour occurring even during the periods of lowest
solar activity so far in the mission. A thermal component fitted by
temperatures of 6-14 MK dominates from 3 keV to about 9 keV, but can
be traced up to 14 keV in some cases, and has an average duration
of 131(±103) s at 7-8 keV. The duration increases with decreasing
photon energy. The peak count rate defined by cross-correlation is
delayed at low energies. The temperature peaks early in the event and
then decreases, whereas the emission measure increases throughout
the event. The properties are consistent with thermal conduction
dominating the evolution. In some of the bigger events, a second
component was found in the 11-14 keV range extending down to 8 keV in
some cases. The duration is typically 3 times shorter and ends near the
peak time of the thermal component consistent with the Neupert effect
of regular flares. Therefore the second component is suggested to be of
non-thermal origin, presumably causing the beam-driven evaporation of
the first component. The two components can be separated and analyzed
in detail for the first time. Low-keV measurements allow a reliable
estimate of the energy input by microflares necessary to assess their
relevance for coronal heating.
---------------------------------------------------------
Title: The Reuven Ramaty High-Energy Solar Spectroscopic Imager
(RHESSI)
Authors: Lin, R. P.; Dennis, B. R.; Hurford, G. J.; Smith, D. M.;
Zehnder, A.; Harvey, P. R.; Curtis, D. W.; Pankow, D.; Turin, P.;
Bester, M.; Csillaghy, A.; Lewis, M.; Madden, N.; van Beek, H. F.;
Appleby, M.; Raudorf, T.; McTiernan, J.; Ramaty, R.; Schmahl, E.;
Schwartz, R.; Krucker, S.; Abiad, R.; Quinn, T.; Berg, P.; Hashii,
M.; Sterling, R.; Jackson, R.; Pratt, R.; Campbell, R. D.; Malone,
D.; Landis, D.; Barrington-Leigh, C. P.; Slassi-Sennou, S.; Cork, C.;
Clark, D.; Amato, D.; Orwig, L.; Boyle, R.; Banks, I. S.; Shirey,
K.; Tolbert, A. K.; Zarro, D.; Snow, F.; Thomsen, K.; Henneck,
R.; Mchedlishvili, A.; Ming, P.; Fivian, M.; Jordan, John; Wanner,
Richard; Crubb, Jerry; Preble, J.; Matranga, M.; Benz, A.; Hudson,
H.; Canfield, R. C.; Holman, G. D.; Crannell, C.; Kosugi, T.; Emslie,
A. G.; Vilmer, N.; Brown, J. C.; Johns-Krull, C.; Aschwanden, M.;
Metcalf, T.; Conway, A.
2002SoPh..210....3L Altcode:
RHESSI is the sixth in the NASA line of Small Explorer (SMEX)
missions and the first managed in the Principal Investigator mode,
where the PI is responsible for all aspects of the mission except
the launch vehicle. RHESSI is designed to investigate particle
acceleration and energy release in solar flares, through imaging and
spectroscopy of hard X-ray/gamma-ray continua emitted by energetic
electrons, and of gamma-ray lines produced by energetic ions. The
single instrument consists of an imager, made up of nine bi-grid
rotating modulation collimators (RMCs), in front of a spectrometer
with nine cryogenically-cooled germanium detectors (GeDs), one behind
each RMC. It provides the first high-resolution hard X-ray imaging
spectroscopy, the first high-resolution gamma-ray line spectroscopy,
and the first imaging above 100 keV including the first imaging of
gamma-ray lines. The spatial resolution is as fine as ∼ 2.3 arc sec
with a full-Sun (≳ 1°) field of view, and the spectral resolution
is ∼ 1-10 keV FWHM over the energy range from soft X-rays (3 keV)
to gamma-rays (17 MeV). An automated shutter system allows a wide
dynamic range (>10<SUP>7</SUP>) of flare intensities to be handled
without instrument saturation. Data for every photon is stored in a
solid-state memory and telemetered to the ground, thus allowing for
versatile data analysis keyed to specific science objectives. The
spin-stabilized (∼ 15 rpm) spacecraft is Sun-pointing to within ∼
0.2° and operates autonomously. RHESSI was launched on 5 February
2002, into a nearly circular, 38° inclination, 600-km altitude orbit
and began observations a week later. The mission is operated from
Berkeley using a dedicated 11-m antenna for telemetry reception and
command uplinks. All data and analysis software are made freely and
immediately available to the scientific community.
---------------------------------------------------------
Title: Plasma Astrophysics, second edition
Authors: Benz, Arnold
2002ASSL..279.....B Altcode: 2002plas.book.....B
This thoroughly revised textbook is a basic introduction to plasma
phenomena in solar and stellar coronae emphasizing non-MHD aspects. The
natural way in which the author unifies observations and theory gives
a wide perspective to the subject. An important feature is the lucidly
written presentation of the fundamentals of plasma physics. The basic
theory thus developed is then extended to some exemplary and important
observations of coronal dynamics, such as coronal currents, particle
acceleration, propagation of particle beams, and shocks. The book has
grown from teaching introductory courses on plasma astrophysics at
the Swiss Federal Institute of Technology (ETH). It addresses advanced
undergraduates and first-year graduate students without a background in
plasma physics. It will also be of interest to more senior research
workers involved in coronal physics of the Sun and other stars,
solar/stellar winds, and various other fields of plasma astrophysics.
---------------------------------------------------------
Title: The solar coronal origin of a slowly drifting decimetric-metric
pulsation structure
Authors: Khan, J. I.; Vilmer, N.; Saint-Hilaire, P.; Benz, A. O.
2002A&A...388..363K Altcode:
We report observations associated with a short duration, slowly
drifting decimetric-metric pulsation structure seen by the Phoenix-2
Radio Spectrometer on 2000 August 25. The range of frequencies over
which this drifting radio feature occurred included frequencies
observed by the Nançay Radioheliograph enabling the spatial location
and development of such a radio source to be determined for the first
time. The radio feature was closely associated with a solar flare. This
flare was observed by the Yohkoh Soft X-ray Telescope (SXT) allowing
us to compare the radio locations with the development of coronal
structures seen in soft X-rays. The Yohkoh SXT images reveal two main
soft X-ray features: a small flaring kernel region consisting of one
or more bright loops located low in the corona and much fainter soft
X-ray ejecta observed above the flare kernel region. The radio sources
of the drifting pulsation structure moved outward with the soft X-ray
ejecta. Our results indicate that the drifting decimetric-metric burst
for this event was closely associated with the soft X-ray ejecta.
---------------------------------------------------------
Title: Acceleration and Enrichment of <SUP>3</SUP>He in Impulsive
Solar Flares by Electron Firehose Waves
Authors: Paesold, G.; Kallenbach, R.; Benz, A. O.
2002AGUSMSH32B..02P Altcode:
A new mechanism for acceleration and enrichment of <SUP>3</SUP>He during
impulsive solar flares is presented. Low-frequency electromagnetic
plasma waves excited by the Electron Firehose Instability (EFI)
account for the acceleration of ions up to 1; {MeV;amu}<SUP>-1</SUP>
energies as a single stage process. The EFI arises as a direct
consequence of the free energy stored in a temperature anisotropy
(T<SUP>e_∥</SUP>/T<SUP>e_perpendicular</SUP> to >1) of the bulk
energized electron population during the acceleration process. In
contrast to other mechanisms which require special plasma properties,
the EFI is an intrinsic feature of the acceleration process of the
bulk electrons. Being present as a side effect in the flaring plasma,
these waves can account for the acceleration of <SUP>3</SUP>He and
<SUP>4</SUP>He while selectively enhancing <SUP>3</SUP>He due to
the spectral energy density obtained from linear growth. Linearized
kinetic theory, analytic models and test-particle simulations have
been applied to investigate the ability of the waves to accelerate
and fractionate. Plausible models have been found that can explain
the observed energies, spectra and abundances of <SUP>3</SUP>He and
<SUP>4</SUP>He.
---------------------------------------------------------
Title: Energy Distribution of Microevents in the Quiet Solar Corona
Authors: Benz, Arnold O.; Krucker, Säm
2002ApJ...568..413B Altcode: 2001astro.ph..9027B
Recent imaging observations of EUV line emissions have shown evidence
for frequent flarelike events in a majority of the pixels in quiet
regions of the solar corona. The changes in coronal emission
measure indicate impulsive heating of new material to coronal
temperatures. These heating or evaporation events are candidate
signatures of “nanoflares” or “microflares” proposed to interpret
the high temperature as well as the very existence of the corona. The
energy distribution of these microevents reported in the literature
differ widely, and so do the estimates of their total energy input into
the corona. Here we analyze the assumptions of the different methods,
compare them by using the same data set, and discuss their results. We
also estimate the different forms of energy input and output, keeping
in mind that the observed brightenings are most likely secondary
phenomena. A rough estimate of the energy input observed by EIT on the
SOHO satellite is of the order of 10% of the total radiative output in
the same region. It is considerably smaller for the two reported TRACE
observations. The discrepancy can be explained by flare selection and
different thresholds for flare detection. There is agreement on the
slope and the absolute value of the distribution if the same methods
are used and a numerical error is corrected. The extrapolation of the
power law to unobserved energies that are many orders of magnitude
smaller remains questionable. Nevertheless, these microevents and
unresolved smaller events are currently the best source of information
on the heating process of the corona.
---------------------------------------------------------
Title: Das Plasma-Universum
Authors: Benz, Arnold
2002Orion..60a...4B Altcode: 2002Orion.308....4B
No abstract at ADS
---------------------------------------------------------
Title: Location of narrowband spikes in solar flares
Authors: Benz, A. O.; Saint-Hilaire, P.; Vilmer, N.
2002A&A...383..678B Altcode: 2001astro.ph.12442B
Narrowband spikes of the decimeter type have been identified in dynamic
spectrograms of Phoenix-2 of ETH Zurich and located in position with
the Nançay Radioheliograph at the same frequency. The spike positions
have been compared with the location of hard X-ray emission and the
thermal flare plasma in soft X-rays and EUV lines. The decimetric
spikes are found to be single sources located some 20 arcsec to 400
arcsec away from the flare site in hard or soft X-rays. In most cases
there is no bright footpoint nearby. In at least two cases the spikes
are near loop tops. These observations do not confirm the widely held
view that the spike emission is produced by some loss-cone instability
masering near the footpoints of flare loops. On the other hand, the
large distance to the flare sites and the fact that these spikes are
all observed in the flare decay phase make the analyzed spike sources
questionable sites for the main flare electron acceleration. They
possibly indicate coronal post-flare acceleration sites.
---------------------------------------------------------
Title: Low Frequency VLBI Project
Authors: Molotov, I. E.; Likhachev, S. F.; Chuprikov, A. A.;
Dementiev, A.; Lipatov, B.; Nechaeva, M.; Snegirev, S.; Dugin, N.;
Ananthakrishnan, S.; Balasubramanian, V.; Benz, A.; Mantovani, F.; Liu,
X.; Hong, X.; Kus, A.; Molotov, E. P.; Ignatov, S. P.; Poperechenko,
B. A.; Gorshenkov, Y. N.; Konovalenko, A. A.
2002IAUS..199..492M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Micro-events in the Quiet Solar Corona
Authors: Benz, A.; Krucker, S.
2002cosp...34E1929B Altcode: 2002cosp.meetE1929B
The content of coronal material in the quiet Sun is not constant as
soft X-ray and high-temperature EUV line observations have shown. New
material, probably heated and evaporated from the chromosphere is
occasionally injected even in the faintest parts above the magnetic
network cell interiors. We discuss the characteristics of the largest
of these events, based on simultaneous transition region observations
(in EUV and radio) and the observed analogies to flares. Assuming that
the smaller events follow the same pattern, we estimate the total
mass input and compare it to the requirements observed in the solar
wind. A rough estimate of the energy input observed by EIT on the SoHO
satellite is of the order of 10% of the total radiative output in the
same region. The simulation indicates that the extrapolation to smaller
events is problematic and that smaller events may play an even more
decisive role than previously assumed. The hypothesis of nanoflare
heating is consistent with these observations if the lower corona is
not just heated, but continuously replenished by chromospheric material
heated to coronal temperatures. These micro-events are currently the
best source of information on the heating process of the corona.
---------------------------------------------------------
Title: Resolving the magnetosphere of T Tauri south B.
Authors: Smith, K. W.; Pestalozzi, M.; Conway, J.; Guedel, M.; Benz,
A. O.
2002AGAb...19Q..94S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flare electrons: comparing theories and observations
Authors: Benz, A.
2002cosp...34E1930B Altcode: 2002cosp.meetE1930B
The prevailing scenario for electron acceleration in solar flares is
transit-time damping of low-frequency waves excited by reconnection
and its outflows. The scenario requires many processes following
each other in order to end up with energetic electrons of the
observed large number. Until now there was very little evidence
for this scenario, as it was even not clear where the reconnection
takes place. RHESSI measurements of bremsstrahlung of non-thermal
flare electrons yield energy estimates as well as the position where
the energy is deposited. Thus quantitative measurements can be put
into the frame of the global magnetic field configuration as seen in
Fe-line observations. I present RHESSI observations combined with TRACE
data that indicate a low reconnection site and a considerable energy
input into motions. Some type III emissions are clearly secondary
acceleration processes. Their propagation path points to a secondary,
higher acceleration site. Nevertheless, some energy X-rays have been
found at the time of the acceleration of electron beams exciting
type III bursts. They are generally at lower photon energies. The
association of decimetric radio emissions and X-rays is summarized in
view of electron acceleration.
---------------------------------------------------------
Title: The Solar Coronal Origin of a Slowly Drifting Radio Pulsation
Feature
Authors: Khan, J. I.; Vilmer, N.; Saint-Hilaire, P.; Benz, A. O.
2002mwoc.conf..285K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Source Regions of Impulsive Solar Electron Events
Authors: Benz, Arnold O.; Lin, Robert P.; Sheiner, Olga A.; Krucker,
Säm; Fainberg, Joe
2001SoPh..203..131B Altcode:
Low-energy (2-19 keV) impulsive electron events observed in
interplanetary space have been traced back to the Sun, using
their interplanetary type III radiation and metric/decimetric
radio-spectrograms. For the first time we are able to study the
highest frequencies and thus the radio signatures closest to the source
region. All the selected impulsive solar electron events have been found
to be associated with an interplanetary type III burst. This allows
to time the particle events at the 2 MHz plasma level and identify
the associated coronal radio emissions. Except for 5 out of 27 cases,
the electron events were found to be associated with a coronal type
III burst in the metric wavelength range. The start frequency yields a
lower limit to the density in the acceleration region. We also search
for narrow-band spikes at the start of the type III bursts. In about
half of the observed cases we find metric spikes or enhancements of
type I bursts associated with the start of the electron event. If
interpreted as the plasma emission of the acceleration process, the
observed average frequency of spikes suggests a source density of the
order of 3×10<SUP>8</SUP> cm<SUP>−3</SUP> consistent with the energy
cut-off observed.
---------------------------------------------------------
Title: On the reliability of peak-flux distributions, with an
application to solar flares
Authors: Isliker, H.; Benz, A. O.
2001A&A...375.1040I Altcode: 2001astro.ph..6158I
Narrow-band radio spikes have been recorded during a solar flare with
unprecedented resolution. This unique example allows us to study the
effect of low resolution in previously published peak-flux distributions
of radio spikes. We give a general, analytical expression for how an
actual peak-flux distribution is changed in shape if the peaks are
determined with low temporal and/or frequency resolution. It turns out
that, generally, low resolution tends to cause an exponential behavior
at large flux values if the actual distribution is of a power-law
shape. The distribution may be severely altered if the burst-duration
depends on the peak-flux. The derived expression is applicable also
to peak-flux distributions derived at other wavelengths (e.g. soft
and hard X-rays, EUV). We show that for the analyzed spike-event the
resolution was sufficient for a reliable peak flux distribution. It
can be fitted by generalized power-laws or by an exponential.
---------------------------------------------------------
Title: On-the-Disk Development of the Halo Coronal Mass Ejection on
1998 May 2
Authors: Pohjolainen, S.; Maia, D.; Pick, M.; Vilmer, N.; Khan, J. I.;
Otruba, W.; Warmuth, A.; Benz, A.; Alissandrakis, C.; Thompson, B. J.
2001ApJ...556..421P Altcode:
A halo coronal mass ejection (CME) was observed at 15:03 UT on 1998 May
2 by the Solar and Heliospheric Observatory Large-Angle Spectrometric
Coronagraph. The observation of the CME was preceded by a major soft
X-ray flare in NOAA Active Region 8210, characterized by a delta spot
magnetic configuration and some activity in region 8214. A large
transequatorial interconnecting loop (TIL) seen in the soft X-rays
connected AR 8210 to a faint magnetic field region in the periphery
of region 8214. Smaller loop systems were also connecting AR 8210 to
other fainter bipolar magnetic structures, the interconnecting loop
(IL) east of AR 8210 being one of the most visible. We present here
a multiwavelength analysis of the large- and small-scale coronal
structures associated with the development of the flare and of the
CME, with emphasis placed on radio-imaging data. In the early phases
of the flare, the radio emission sources traced the propagation paths
of electrons along the TIL and the IL, which are accelerated in the
vicinity of AR 8210. Furthermore, jetlike flows were observed in soft
X-rays and in Hα in these directions. Significantly, the TIL and
IL loop systems disappeared at least partially after the CME. An EUV
Imaging Telescope (EIT) dimming region of similar size and shape to the
soft X-ray TIL, but noticeably offset from it, was also observed. During
the “flash” phase of the flare, new radio sources appeared, presenting
signatures of destabilization and reconnection at discrete locations of
the connecting loops. We interpret these as possible signatures of the
CME liftoff on the disk. An Hα Moreton wave (blast wave) and an “EIT
wave” were also observed, originating from the flaring AR 8210. The
signatures in radio, after the wave propagated high into the corona,
include type II-like emissions in the spectra. The radio images link
these emissions to fast-moving sources, presumably formed at locations
where the blast wave encounters magnetic structures. The opening of
the CME magnetic field is revealed by the radio observations, which
show large and expanding moving sources overlying the later-seen EIT
dimming region.
---------------------------------------------------------
Title: A nanoflare heating model for the quiet solar corona
Authors: Mitra-Kraev, U.; Benz, A. O.
2001A&A...373..318M Altcode: 2001astro.ph..4218M
The energy input into the lower solar corona by flare evaporation
events has been modeled according to the available observations for
quiet regions. The question is addressed whether such heating events
can provide the observed average level of the coronal emission measure
and thus of the observed flux of extreme ultraviolet (EUV) and X-ray
emission without contradicting the observed average power spectrum of
the emission measure, the typical emission measure variations observed
for individual pixels and the observed flare energy distribution. As
the assumed flare height influences the derived flare energy,
the mathematical foundations of nanoflare distributions and their
conversion to different height assumptions are studied first. This
also allows a comparison with various published energy distributions
differing in height assumptions and to relate the observations to
the input parameters of the heating model. An analytic evaluation of
the power spectrum yields the relationship between the average time
profile of nanoflares (or microflares), assumed to be self-similar in
energy, and the power spectrum. We find that the power spectrum is very
sensitive to the chosen time profile of the flares. Models are found
by numerical simulation that fit all available observations. They are
not unique but severely constrained. We concentrate on a model with a
flare height proportional to the square root of the flare area. The
existence of a fitting model demonstrates that nanoflare heating of
the corona is a viable and attractive mechanism.
---------------------------------------------------------
Title: Are Heating Events in the Quiet Solar Corona Small Flares?
Authors: Krucker, S.; Benz, A. O.
2001AGUSM..SP52B03K Altcode:
Temporary enhancements of the coronal emission measure in a quiet
region have been shown to constitute a significant energy input. Here
some relatively large events (Yohkoh, EIT Observations) are discussed
and tested for characteristics known from full-sized impulsive flares
in active regions. The differences to active region flares seem to be
mainly quantitative, and the analyzed heating events may in principle
be considered as microflares or large nanoflares, thus small versions
of regular flares. In this presentation we focus on the following
questions: (1) Are there related events seen in transient region lines
(CDS/SUMER observations)? (2) What are the relative contributions
of the thermal, potential, and expansion energy to the total energy
released in these events. (3) Are the reported flare temperatures in
quiet regions of 1-2 MK possibly higher (3-5 MK)?
---------------------------------------------------------
Title: Spatial analysis of solar type III events associated with
narrow band spikes at metric wavelengths
Authors: Paesold, G.; Benz, A. O.; Klein, K. -L.; Vilmer, N.
2001A&A...371..333P Altcode: 2001astro.ph..3491P
The spatial association of narrow band metric radio spikes with
type III bursts is analyzed. The analysis addresses the question
of a possible causal relation between the spike emission and the
acceleration of the energetic electrons causing the type III burst. The
spikes are identified by the Phoenix-2 spectrometer (ETH Zurich)
from survey solar observations in the frequency range from 220 MHz
to 530 MHz. Simultaneous spatial information was provided by the
Nançay Radioheliograph (NRH) at several frequencies. Five events
were selected showing spikes at one or two and type III bursts at
two or more Nançay frequencies. The 3-dimensional geometry of the
single events has been reconstructed by applying different coronal
density models. As a working hypothesis it is assumed that emission
at the plasma frequency or its harmonic is the responsible radiation
process for the spikes as well as for the type III bursts. It has been
found that the spike source location is consistent with the backward
extrapolation of the trajectory of the type III bursts, tracing a
magnetic field line. In one of the analyzed events, type III bursts
with two different trajectories originating from the same spike source
could be identified. These findings support the hypothesis that narrow
band metric spikes are closely related to the acceleration region.
---------------------------------------------------------
Title: A Nanoflare Heating Model for the Quiet Solar Corona
Authors: Mitra Kraev, U.; Benz, A. O.
2001AGUSM..SP41A02M Altcode:
The energy input into the lower solar corona by flare evaporation
events has been modeled according to the available observations for
quiet regions. The question is addressed whether such heating events
can provide the observed average level of the coronal emission measure
and thus of the observed flux of extreme ultraviolet (EUV) and X-ray
emission without contradicting the observed average power spectrum of
the emission measure, the typical emission measure variations observed
for individual pixels and the observed flare energy distribution. As
the assumed flare height influences the derived flare energy,
the mathematical foundations of nanoflare distributions and their
conversion to different height assumptions are studied first. This
also allows a comparison with various published energy distributions
differing in height assumptions and to relate the observations to
the input parameters of the heating model. An analytic evaluation of
the power spectrum yields the relationship between the average time
profile of nanoflares (or microflares), assumed to be self-similar in
energy, and the power spectrum. We find that the power spectrum is very
sensitive to the chosen time profile of the flares. Models are found
by numerical simulation that fit all available observations. They are
not unique but severely constrained. We concentrate on a model with a
flare height proportional to the square root of the flare area. The
existence of a fitting model demonstrates that nanoflare heating of
the corona is a viable and attractive mechanism.
---------------------------------------------------------
Title: Heating the Quiet Corona by Nanoflares: Evidence and Problems
Authors: Benz, A. O.
2001AGUSM..SP51C06B Altcode:
Recent imaging observations of coronal EUV line emission have shown
evidence for frequent flare-like events in a majority of the pixels in
quiet regions. The changes in the coronal emission measure indicate the
impulsive heating of new material to coronal temperatures. Estimates of
the energy input into the corona by these "nanoflares" differ widely
in the literature. Here we discuss the proposed methods and interpret
the different results by the various recent analyses. The results
using similar EUV data from EIT/SOHO and TRACE basically agree on the
power-law exponent when the same method is used. The extrapolation of
the power law to energies that are many orders of magnitude smaller
remains doubtful, however. Nevertheless, the inferred energy input
into the corona by the micro-events in the observable range has been
reported to be of the order of 10 percent of the observed radiation
output by EIT observations. It is considerably smaller for TRACE. The
discrepancy can be explained only partially by different thresholds
for flare detection. It is pointed out that the deviation between the
different analyses in the number of nanoflares per energy and time
unit is more serious than the widely discussed differences in the
power law index.
---------------------------------------------------------
Title: Astronomy: Brown dwarf is a radio star
Authors: Benz, Arnold O.
2001Natur.410..310B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Division II: Sun and Heliosphere
Authors: Benz, Arnold O.; Bogdan, T.; Foukal, P. V.; Melrose, D. B.;
Solanki, S.; Vandas, M.; Webb, D. F.
2001IAUTB..24..110B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Heating the Quiet Corona by Nanoflares: Evidence and Problems
Authors: Benz, A. O.; Krucker, S.
2001IAUS..203..471B Altcode: 2000astro.ph.12106B
The content of coronal material in the quiet Sun is not constant as
soft X-ray and high-temperature EUV line observations have shown. New
material, probably heated and evaporated from the chromosphere is
occasionaly injected even in the faintest parts above the magnetic
network cell interiors. We discuss the characteristics of the largest
of these events, based on simultaneous transition region observations
(in EUV and radio) and the observed analogies to flares. Assuming
that the smaller events follow the same pattern, we estimate the
total energy input. Various recent analyses are compared and briefly
discussed. Finally we present the results of a simulation, extrapolating
the observed range of microflares to smaller energies. The simultation
indicates that the extrapolation to smaller events is problematic and
that smaller events may play an even more decisive role than previously
assumed. The hypothesis of nanoflare heating is consistent with these
observations if the lower corona is not just heated, but continuously
replenished by chromospheric material heated to coronal temperatures.
---------------------------------------------------------
Title: High-sensitivity observations of solar flare decimeter
radiation
Authors: Benz, A. O.; Messmer, P.; Monstein, C.
2001A&A...366..326B Altcode: 2000astro.ph.12093B
A new acousto-optic radio spectrometer has observed the 1-2 GHz radio
emission of solar flares with unprecedented sensitivity. The number
of detected decimeter type III bursts is greatly enhanced compared
to observations by conventional spectrometers observing only one
frequency at the time. The observations indicate a large number of
electron beams propagating in dense plasmas. For the first time,
we report weak, reversed drifting type III bursts at frequencies
above simultaneous narrowband decimeter spikes. The type III bursts
are reliable signatures of electron beams propagating downward in the
corona, apparently away from the source of the spikes. The observations
contradict the most popular spike model that places the spike sources at
the footpoints of loops. Conspicuous also was an apparent bidirectional
type U burst forming a fish-like pattern. It occurs simultaneously with
an intense U-burst at 600-370 MHz observed in Tremsdorf. We suggest
that it intermodulated with strong terrestrial interference(cellular
phones) causing a spurious symmetric pattern in the spectrogram at 1.4
GHz. Symmetric features in the 1-2 GHz range, some already reported
in the literature, therefore must be considered with utmost caution.
---------------------------------------------------------
Title: Mechanisms for Coronal Mass Supply by Evaporative Micro-Events
Authors: Brown, J. C.; Krucker, S.; Güdel, M.; Benz, A. O.
2001IAUS..203..498B Altcode:
There is extensive evidence from SoHO and other data that
“micro-events” play an important role in sustaining at least
some components of the solar corona. These are often termed coronal
micro-“heating events” though a major part of their role is feeding
coronal loops through chromospheric evaporation. We consider what can
be learnt from these data concerning the energy release and transport
mechanisms driving the evaporation, including thermal conduction and
fast particles, and what model constraints are available from other
data (such as hard X-rays and radio events). We conclude, from one
large event and the statistics of many small ones, that conductive
evaporation alone does not fit observations and that fast particles or
some other nonthermal driver must be involved. As well as the problem
of single loop events, we consider the global implications for supply
of the corona and wind.
---------------------------------------------------------
Title: Solar Flare Observations
Authors: Benz, A.
2000eaa..bookE2049B Altcode:
Flares are caused by the release of magnetic energy up to some 1027 J in
the solar atmosphere within a few minutes (figure 1). The energy input
causes a myriad of phenomena including the flaring up of the region
and its surroundings at all wavelengths from radio to gamma rays,
the acceleration of elementary particles to relativistic energies and
the launch of a shock wave. Flares may be responsib...
---------------------------------------------------------
Title: Solar flare radio pulsations as a signature of dynamic
magnetic reconnection
Authors: Kliem, B.; Karlický, M.; Benz, A. O.
2000A&A...360..715K Altcode: 2000astro.ph..6324K
Decimetric radio observations of the impulsive solar flare on October 5,
1992, 09:25 UT show a long series of quasi-periodic pulsations deeply
modulating a continuum in the 0.6-2 GHz range that is slowly drifting
toward lower frequencies. We propose a model in which the pulsations
of the radio flux are caused by quasi-periodic particle acceleration
episodes that result from a dynamic phase of magnetic reconnection in
a large-scale current sheet. The reconnection is dominated by repeated
formation and subsequent coalescence of magnetic islands (known as
"secondary tearing" or "impulsive bursty" regime of reconnection),
while a continuously growing plasmoid is fed by newly coalescing
islands. Such a model, involving a current sheet and a growing plasmoid,
is consistent with the Yohkoh observations of the same flare (Ohyama
& Shibata ?). We present two-dimensional MHD simulations of dynamic
magnetic reconnection that support the model. Within the framework of
the proposed interpretation, the radio observations reveal details of
plasmoid formation in flares.
---------------------------------------------------------
Title: Mechanisms for dynamic coronal mass supply via evaporative
solar “micro-events”
Authors: Brown, J. C.; Krucker, S.; Güdel, M.; Benz, A. O.
2000A&A...359.1185B Altcode:
The idea that the corona is at least in part supplied by chromospheric
evaporation in loop “micro-events" is quantified in terms of the
power requirements of evaporation mechanisms, using recent analyses of
data on such events in high temperature EUV lines from the SoHO EIT
instrument. Estimates are derived for the pre-event and event values
of loop density and temperature and it is shown, using the conductive
scaling law, that the event emission measure enhancements are too large
to be accounted for solely by enhanced conductive flux from coronal
heating. That is, observations demand that supply of coronal mass by
evaporation events need a mechanism which enhances upper chromospheric
heating and not just conductively driven evaporation. Thus coronal mass
supply in transients is inextricably linked to direct chromospheric
heating processes. Using parametric models of a chromospheric heating
function and of the pre-event chromosphere, an estimate is made of the
extra power required to yield the emission measure enhancement of a
large event evaporatively. The dependence of the result on just how the
EUV solar images are interpreted is emphasised and observational tests
are discussed for the case of heating by fast particles. Implications
of the results in terms of the global supply of the hot corona and
wind mass loss are briefly mentioned.
---------------------------------------------------------
Title: Bidirectional Type III Solar Radio Bursts
Authors: Robinson, P. A.; Benz, A. O.
2000SoPh..194..345R Altcode:
Bidirectional coronal type III bursts are modeled by combining
a model of coronal electron heating and beam generation via
time-of-flight effects with semiquantitative estimates of quasilinear
relaxation. Electromagnetic emissivities are estimated by extending
the recently developed theory of interplanetary type III bursts to
coronal emissions, including its features of stochastic Langmuir-wave
growth and three-wave interactions. The results are investigated for
heating on open and closed coronal field lines and are compared with
observations of normal, reverse-slope, bidirectional, and inverted-J
and -U coronal type III radio bursts. Harmonic emission is predicted
to dominate at plasma frequencies above roughly 100 MHz where the
efficiency of fundamental emission falls off steeply, while its
free-free reabsorption rises. The model also explains the observed
trends in the likelihood of occurrence of normal, reverse-slope,
and bidirectional coronal type III bursts.
---------------------------------------------------------
Title: Coronal Replenishment and Heating
Authors: Benz, A. O.; Krucker, S.; Mitra Kraev, U.
2000SPD....31.0217B Altcode: 2000BAAS...32..814B
The content of coronal material in the quiet Sun is not constant as
soft X-ray and high-temperature EUV line observations have shown. New
material, probably heated and evaporated from the chromosphere is
occasionaly injected even in the faintest parts above the magnetic
network cell interiors. We discuss the characteristics of the largest
of these events, based on simultaneous transition region observations
(in EUV and radio) and the observed analogies to flares. Assuming
that the smaller events follow the same pattern, we estimate the
total mass input and compare it to the requirements observed in
the solar wind. Various recent analyses are compared and briefly
discussed. Finally we present the results of a simulation, extrapolating
the observed range of microflares to smaller energies. The simultation
indicates that the extrapolation to smaller events is problematic and
that smaller events may play an even more decisive role than previously
assumed. The hypothesis of nanoflare heating is consistent with these
observations if the lower corona is not just heated, but continuously
replenished by chromospheric material heated to coronal temperatures.
---------------------------------------------------------
Title: Are Heating Events in the Quiet Solar Corona Small
Flares? Multiwavelength Observations of Individual Events
Authors: Krucker, Säm; Benz, Arnold O.
2000SoPh..191..341K Altcode: 1999astro.ph.12501K
Temporary enhancements of the coronal emission measure in a quiet region
have been shown to constitute a significant energy input. Here some
relatively large events are studied for simultaneous brightenings in
transition region lines and in radio emission. Associated emissions
are discussed and tested for characteristics known from full-sized
impulsive flares in active regions. Heating events and flares are found
to have many properties in common, including (i) associated polarized
radio emission, which usually precedes the emission measure peak
(Neupert effect) and sometimes has a non-thermal spectrum, and (ii)
associated and often preceding peaks in O v and He i emission. On
the other hand, heating events also differ from impulsive flares:
(i) In half of the cases, their radio emission at centimeter waves
shows a spectrum consistent with thermal radiation, (ii) the ratio
of the gyro-synchrotron emission to the estimated thermal soft X-ray
emission is smaller than in flares, and (iii) the associated emission
in the O v transition region line shows red shifts and blue shifts,
indicating upflows in the rise phase and downflows in the decay
phase, respectively. Nevertheless, the differences seem to be mainly
quantitative, and the analyzed heating events with thermal energies
around 10<SUP>26</SUP> erg may in principle be considered as microflares
or large nanoflares, thus small versions of regular flares.
---------------------------------------------------------
Title: The Minimum bandwidth of narrowband spikes in solar flare
decimetric radio waves
Authors: Messmer, Peter; Benz, Arnold O.
2000A&A...354..287M Altcode: 1999astro.ph.12502M
The minimum and the mean bandwidth of individual narrowband spikes
in two events in decimetric radio waves is determined by means
of multi-resolution analysis. Spikes of a few tens of millisecond
duration occur at decimetric/microwave wavelength in the particle
acceleration phase of solar flares. A first method determines the
dominant spike bandwidth scale based on their scalegram, the mean
squared wavelet coefficient at each frequency scale. This allows
to measure the scale bandwidth independently of heuristic spike
selection criteria, e.g. manual selection. The major drawback is
a low resolution in the bandwidth. To overcome this uncertainty,
a feature detection algorithm and a criterion for spike shape in the
time-frequency plane is applied to locate the spikes. In that case,
the bandwidth is measured by fitting an assumed spike profile into
the denoised data. The smallest FWHM bandwidth of spikes was found at
0.17% and 0.41% of the center frequency in the two events. Knowing
the shortest relevant bandwidth of spikes, the slope of the Fourier
power spectrum of this two events was determined and no resemblance to
a Kolmogorov spectrum detected. Additionally the correlation between
spike peak flux and bandwidth was examined.
---------------------------------------------------------
Title: VLBI observations of single stars, spatial resolution and
astrometry
Authors: Pestalozzi, M.; Benz, A. O.; Conway, J. E.; Gudel, M.;
Smith, K.
2000evn..conf..167P Altcode:
VLBI studies can both spatially resolve single dMe stars and measure
their positions at submilliarcsecond accuracy. The spatial resolution
gives the brightness temperature and allows us to draw co nclusions
about the nature of the emitting processes. In particular it is possib
le to distinguish between thermal or non-thermal emission. The position
accuracy gives better knowledge about the astrometric properties
(like proper motion and parallax) especially for nearby stars. In this
contribution recent results of c ontinuum VLBI observations towards
two dMe stars (YZ CMi and AD Leo) at 8.4 GHz are presented. For YZ
CMi an estimate of the size of the coronal emission is giv en (0.98
mas in diameter or 0.7 ±0.3 R<SUB>star</SUB> above the photosphere
where R<SUB>star</SUB> refers to the photospheric radius). For AD Leo
an upper limit is gi ven, i.e. the emitting region is shown to be <
0.8 R<SUB>star</SUB>. The position o f YZ CMi is found to differ by 32
mas form the Hipparcos catalogue, a discrepanc y mostly due to large
errors in the listed proper motion (Pestalozzi et al. 2000 ).
---------------------------------------------------------
Title: VLBI observations of two single dMe stars: spatial resolution
and astrometry
Authors: Pestalozzi, M. R.; Benz, A. O.; Conway, J. E.; Güdel, M.
2000A&A...353..569P Altcode: 1999astro.ph.12159P
We report on 3.6 cm VLA and VLBA observations of <ASTROBJ>YZ
CMi</ASTROBJ> and <ASTROBJ>AD Leo</ASTROBJ>, two nearby dMe stars. We
resolve YZ CMi and can fit a circular symmetrical gaussian component of
FWHP of 0.98 +/-0.2 mas, corresponding to an extent of the corona above
the photosphere of 1.77 x 10<SUP>10</SUP> +/-8.8 x 10<SUP>9</SUP> cm or
0.7 +/-0.3 R_star (R_star refers to the photospheric radius). We obtain
an estimate of the brightness temperature of 7.3 x 10<SUP>7</SUP>
K, which is consistent with that expected from gyrosynchrotron
emission. For AD Leo the emitting region is unresolved. We therefore set
a conservative upper limit to its diameter of 1.8 times the photosphere
diameter, which leads to an extent of the corona above the photosphere
of <2.8x 10<SUP>10</SUP>cm or <0.8 R_star . We compare the radio
emitting dMe stars with measured sizes with the Sun and conclude that
these active stars have much more extended coronal radio emission than
the Sun. The VLBA position of YZ CMi has been found to differ by 32
mas from the positions calculated from the Hipparcos catalogue. The
discrepancy is caused by large errors in the listed proper motion. An
improved value is given.
---------------------------------------------------------
Title: Investigations of the Acceleration Region of Energetic
Electrons Associated with Decimetric Type III and X-Ray Bursts
Authors: Fernandes, F. C. R.; Sawants, H. S.; Meléndez, J. L.; Benz,
A. O.; Kane, S. R.
2000AdSpR..25.1813F Altcode:
Preliminary results of the association between type III decimetric
bursts, mainly having center frequency above 1000 MHz and recorded by
Phoenix radio spectrometer, and seven hard X-ray flares observed by the
Yohkoh/HXT from September, 1992 to October, 1993 are reported here. (a)
For an assumed improved density model of the solar chromosphere, an
average electron beam velocity (~ 0.16 c) and hence an average electron
energy (~ 7 keV) was inferred from the average frequency drift rate (~
1350 MHz/s) of 160 isolated type III bursts. Assuming the electrons
lose energy primarily by collisions, the height of injection of the
energetic electrons was estimated (1.2 × 10<SUP>9</SUP> - 4.5 ×
10<SUP>9</SUP> cm). (b) In two flares at the onset of the bursts, the
correlation between X-rays and radio was better at lower frequencies
(<= 500 MHz). However, during the time evolution of those flares,
the correlation improved for higher and higher frequencies (>= 800
MHz), suggesting that the acceleration region was displaced towards
the photosphere. The estimated velocity of the acceleration region is
~ 3 × 10<SUP>3</SUP> - 8 × 10<SUP>3</SUP> km/s. (c) In two flares,
the enhancement of the radio decimetric emission above 500 MHz started
earlier (~ 10 s) than the X-ray emissions, suggesting in case of these
two flares that the acceleration region is located near to where the
decimetric emission is generated
---------------------------------------------------------
Title: The first VLBI observations with the Ventspils 32m radio
telescope under the LFVN project
Authors: Shmeld, I.; Benz, A.; Dementjev, A.; Lipatov, B.; Molotov,
I.; Ryabov, B.; Sika, Z.
2000evn..conf..247S Altcode:
The first Low frequency VLBI test sessions with 32 m radio telescope
of Ventspils International Radioastronomy center were carried out
on November 10 -14, 1999 and July 15-17, 2000 at 92 cm wavelength. A
total of 39 sources plus the Sun were observed. A brief description
of Ventspils radio telescope and equipment, of the Low Frequency VLBI
Network and obtained results are given.
---------------------------------------------------------
Title: Commission 10: Solar Activity: (Activite Solaire)
Authors: Ai, G.; Benz, A.; Dere, K. P.; Engvold, O.; Gopalswamy, N.;
Hammer, R.; Hood, A.; Jackson, B. V.; Kim, I.; Marten, P. C.; Poletto,
G.; Rozelot, J. P.; Sanchez, A. J.; Shibata, K.; van Driel-Geztelyi, L.
2000IAUTA..24...67A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Division II: The Sun and Heliosphere: (Le Soleil et
Heliosphere)
Authors: Foukal, Peter; Ai, Guoxiang; Benz, Arnold; Engvold, Oddbjorn;
Solanki, Sami; Vandas, Marek; Verheest, Frank
2000IAUTA..24...65F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Heating Events Observed in the Quiet Corona
Authors: Benz, A. O.; Krucker, S.
1999ESASP.448..547B Altcode: 1999ESPM....9..547B; 1999mfsp.conf..547B
No abstract at ADS
---------------------------------------------------------
Title: Heating Events in the Quiet Solar Corona
Authors: Krucker, S.; Benz, A. O.
1999spro.proc...25K Altcode:
Sensitive observations of the quiet Sun provided by (1) the SXT on
board the Yohkoh satellite, (2) the EIT on board the SoHO spacecraft in
high-temperature iron line emission, and (3) the Very Large Array (VLA)
in the centimeter radio range are investigated in view of the coronal
heating problem. The observed enhancements in coronal emission measure
are interpreted as heating events (microflares) bringing chromospheric
material to coronal temperatures, whereas the radio observations
show the existence of non-thermal emission related to some of these
heating events. Assuming an effective height of 5000~km, the thermal
energy inputs by such microflares have been found in the range from
8× 10<SUP>24</SUP> erg to 1.6× 10<SUP>26</SUP> erg, and the total
energy input amounts to about 16% of the average radiated power of
the coronal plasma in the quiet corona. The frequency distribution of
microflares is an approximate power-law of the form f(E) = f<SUB>0</SUB>
E<SUP>-δ</SUP> with a power-law index δ between 2.3 and 2.6. As the
low-energy cutoff is due to sensitivity limitations and the power-law
index is steeper than 2, these observations demonstrate the possibility
that microflares dominate the energy input into the quiet corona.
---------------------------------------------------------
Title: Electron Firehose instability and acceleration of electrons
in solar flares
Authors: Paesold, Gunnar; Benz, Arnold O.
1999A&A...351..741P Altcode: 2000astro.ph..1262P
An electron distribution with a temperature anisotropy T_parallel
/T_perpendicular to >1 can lead to the Electron Firehose instability
(Here parallel and perpendicular to denote directions relative to the
background magnetic field B_0). Since possible particle acceleration
mechanisms in solar flares exhibit a preference of energizing particles
in parallel direction, such an anisotropy is expected during the
impulsive phase of a flare. The properties of the excited waves and
the thresholds for instability are investigated by using linearized
kinetic theory. These thresholds were connected to the pre-flare plasma
parameters by assuming an acceleration model acting exclusively in
parallel direction. For usually assumed pre-flare plasma conditions the
electrons become unstable during the acceleration process and lefthand
circularly polarized waves with frequencies of about ~ |Omega_p |
are excited at parallel propagation. Indications have been found,
that the largest growth rates occur at oblique propagation and the
according frequencies lie well above the proton gyrofrequency.
---------------------------------------------------------
Title: Radio counterparts to extreme X-ray YSO's
Authors: Smith, Kester; Güdel, Manuel; Benz, A. O.
1999A&A...349..475S Altcode:
We search for radio counterparts to two recently-detected strong
X-ray sources associated with highly embedded young stellar objects
(SVS4/EC 95 and SVS16). We detect a radio source (S68-2) consistent
with the position of EC95. We fail to detect a counterpart for SVS16,
and place upper limits on its quiescent radio brightness. For S68-2,
we show that the radio source has a falling spectrum, suggestive of
a gyrosynchrotron emission mechanism, and that it is variable on
a timescale of years. We search for, but do not detect, evidence
for flaring activity on timescales of minutes to hours. We also
search for, but do not detect, circular polarisation. We derive
the radio luminosity and compare the object to an empirical X-ray -
radio luminosity relationship established for dMe stars. We find that
the object is consistent with the dwarfs relation, but is unusually
X-ray rich compared to other high-luminosity coronal sources. By
comparing the objects to a sample of active galactic nuclei in the
L<SUB>X</SUB>-L<SUB>R</SUB> diagram, we rule out the possibility that
either object is a background AGN. We discuss the ways in which a
normal stellar coronal model might be modified to explain the strong,
X-ray rich characteristics of the source, which appears to be the most
extreme stellar corona yet found.
---------------------------------------------------------
Title: Interactive image retrieval in large astronomical archives:
the ASPECT system
Authors: Csillaghy, A.; Benz, A. O.
1999SoPh..188..203C Altcode:
We present a method to access efficiently and effectively images in
large astronomical archives. This method allows users to interactively
participate in the retrieval process. They may virtually 'navigate'
through the archive for choosing images that are relevant for their
purposes. The navigation process is performed by switching back and
forth between three retrieval-system modes: a query mode, a browse
mode and an inspection mode. The method has been applied to an image
retrieval system to access solar radio spectrograms archived at ETH
in Zurich. The system, called ASPECT, allows access to over 50 000
data sets on-line.
---------------------------------------------------------
Title: PHOENIX-2: A New Broadband Spectrometer for Deci- metric and
Microwave Radio Bursts First Results
Authors: Messmer, Peter; Benz, Arnold O.; Monstein, Christian
1999SoPh..187..335M Altcode:
A broadband radio spectrometer has been put into operation at Bleien,
Switzerland, to register the flare emission of the full Sun. In the
frequency range of operation, 0.1 to 4.0 GHz, both modes of circular
polarization are recorded continuously. The new system, Phoenix-2,
has been developed from the experience with the previous Phoenix
spectrometer. Improved, computer-controlled focal hardware allows now a
complete daily calibration, a more sophisticated calibration procedure,
and monitoring of all essential instrumental and environmental
parameters. Calibrated data are now usually available the day after
observation and are accessible through the Internet. The scientific
improvements include a larger frequency range of observation, a larger
number of completely recorded events due to full-day registration,
more accurate measurements, particularly in circular polarization,
and more reliable operation. First observations are presented and
quantitative results comparing the calibration with single frequency
instruments are reported.
---------------------------------------------------------
Title: Statistical analysis of high-frequency decimetric type
III bursts
Authors: Meléndez, J. L.; Sawant, H. S.; Fernandes, F. C. R.; Benz,
A. O.
1999SoPh..187...77M Altcode:
Here we report the statistical analysis of 160 isolated decimetric type
III bursts, a majority of them (74%) having central frequency above
1000 MHz, observed in 8 flares by the spectrometer Phoenix. The most
important finding of the detailed analysis is: 67% of all the bursts
are reverse slope, 38% normal and 5% bi-directional. Also, we obtained
the following results: (a) the best fits for the average half power
duration and for the average drift rate as a function of frequency
are given by t<SUB>1/2</SUB>=1.7×10<SUP>4</SUP>f<SUP>−0.60</SUP>and
/df/dt|=(0.09±0.03)f<SUP>(1.35 ± 0.10)</SUP>, respectively; (b) the
frequency range of most of the type III bursts is less than 250 MHz; (c)
the number of bursts decreases with increasing starting frequency and
flux; (d) peak flux decreases with increasing frequency. The relations
obtained fit well for higher frequency observations. Assuming an
improved density model and type III emission at 2<SUP>nd</SUP>harmonic,
the beam parameters of type III bursts are determined.
---------------------------------------------------------
Title: Large-scale structure and coronal dynamics from joint radio,
SOHO/EIT and coronagraph observations
Authors: Pick, M.; Maia, D.; Vourlidas, A.; Benz, A. O.; Howard, R.;
Thompson, B. J.
1999AIPC..471..649P Altcode: 1999sowi.conf..649P
This study presents joint observations of an `halo' coronal mass
ejection from the EIT telescope and LASCO coronagraphs on SOHO, from
the Nançay Radioheliograph (NRH) and the Zurich ETH radiospectrograph
(Phoenix-2). This event includes different manifestations: a coronal
wave and a dimming region detected by EIT, a CME showing bright discrete
portions above east and west limbs. Radio signatures of all these
manifestations are found and the interpretation is briefly discussed.
---------------------------------------------------------
Title: Quantitative results on heating events in the quiet corona
Authors: Benz, Arnold O.; Krucker, Säm
1999AIPC..471...67B Altcode: 1999sowi.conf...67B
The emission measure of the quiet corona, defined by the plasma
hotter than one million degrees, is fluctuating in nearly every 1900
km×1900 km pixel observed by EIT on SoHO. In the average, the larger
the emission measure in a pixel, the more it fluctuates. Increases
in emission measure constitute a major energy input into the corona,
suggesting that the lower corona is not just heated, but continuously
replenished by chromospheric material heated to coronal temperatures.
---------------------------------------------------------
Title: Phase-reference mapping of nearby stars: status report.
Authors: Alef, W.; Benz, A.; Conway, J.; Beasley, T.
1999evga.conf..241A Altcode:
The authors have observed radio emitting stars in phase-referenced
mode with both the VLBA and the EVN in order to map their brightness
distributions and to determine precise astrometric parameters. While the
VLBA correlator uses the CALC 8 model, the older MK3 correlator model
is not sufficient to make phase-referenced mapping possible using the
visibility amplitude and residual phase. In the raw MK3 correlated data
they have successfully replaced the correlator model with the CALC 8
model. They have shown that phase-reference mapping is possible with
MK3 data for source separations of 2 to 3 degrees. At present the
authors are exploring the possibility of removing ionospheric and
atmospheric contributions, which are not modelled at all in CALC 8,
and which decrease the SNR in phase-reference maps in general by a
factor of 2 to 3.
---------------------------------------------------------
Title: Heating events in the quiet solar corona: multiwavelength
correlations
Authors: Benz, Arnold O.; Krucker, Säm
1999A&A...341..286B Altcode:
Coronal, transition region and chromospheric lines and centimeter
radio emission of the quiet Sun have been simultaneously observed
by SoHO and the VLA. The corona above the magnetic network has a
higher pressure and is more variable than above the interior of
supergranular cells. The Fourier transform in time is found to have
steeper spectra in the corona and upper chromosphere than in the
transition region. The temporal sequence of brightenings has been
determined by cross-correlations of identical picture elements in
different emissions. The method allows to study statistically the
faintest fluctuations in the corona and relate them to the layers
below. The cross-correlations yield that (i) the first emissions to
peak in time are O V and He I originating in the transition region
and the upper chromosphere, respectively. (ii) The coronal line of Fe
XII lags by about 5 minutes and Fe IX/X peaks a further half a minute
later in the average, latest of all emissions. The interpretation of
these lags follows readily from analogy with regular flares in active
regions, where O V and He I correlate closely with hard X-rays emitted
by beam electrons impinging on the chromosphere. The coronal iron lines
are then emitted by the evaporating plasma expanding into the corona
and cooling by conducting part of the energy to increase the emission
in Fe IX. (iii) The radio emission peaks before the coronal emission
measure, similar to the Neupert effect in flares, but shows considerable
variation relative to O V. It is proposed that there are two emission
processes at work radiating both thermal emission and non-thermal
gyrosynchrotron emission at various fluxes. These statistical results
show that the coronal heating events follow the properties of regular
solar flares and thus may be interpreted as microflares or nanoflares.
---------------------------------------------------------
Title: High-Energy Solar Spectroscopic Imager (HESSI) Small Explorer
mission for the next (2000) solar maximum
Authors: Lin, Robert P.; Hurford, Gordon J.; Madden, Norman W.;
Dennis, Brian R.; Crannell, Carol J.; Holman, Gordon D.; Ramaty,
Reuven; von Rosenvinge, Tycho T.; Zehnder, Alex; van Beek, H. Frank;
Bornmann, Patricia L.; Canfield, Richard C.; Emslie, A. Gordon; Hudson,
Hugh S.; Benz, Arnold; Brown, John C.; Enome, Shinzo; Kosugi, Takeo;
Vilmer, Nicole; Smith, David M.; McTiernan, Jim; Hawkins, Isabel;
Slassi-Sennou, Said; Csillaghy, Andre; Fisher, George; Johns-Krull,
Chris; Schwartz, Richard; Orwig, Larry E.; Zarro, Dominic; Schmahl,
Ed; Aschwanden, Markus; Harvey, Peter; Curtis, Dave; Pankow, Dave;
Clark, Dave; Boyle, Robert F.; Henneck, Reinhold; Michedlishvili,
Akilo; Thomsen, K.; Preble, Jeff; Snow, Frank
1998SPIE.3442....2L Altcode:
The primary scientific objective of the High Energy Solar Spectroscopic
Imager (HESSI) Small Explorer mission selected by NASA is to investigate
the physics of particle acceleration and energy release in solar
flares. Observations will be made of x-rays and (gamma) rays from
approximately 3 keV to approximately 20 MeV with an unprecedented
combination of high resolution imaging and spectroscopy. The HESSI
instrument utilizes Fourier- transform imaging with 9 bi-grid rotating
modulation collimators and cooled germanium detectors. The instrument
is mounted on a Sun-pointed spin-stabilized spacecraft and placed
into a 600 km-altitude, 38 degrees inclination orbit.It will provide
the first imaging spectroscopy in hard x-rays, with approximately
2 arcsecond angular resolution, time resolution down to tens of ms,
and approximately 1 keV energy resolution; the first solar (gamma)
ray line spectroscopy with approximately 1-5 keV energy resolution;
and the first solar (gamma) -ray line and continuum imaging,with
approximately 36-arcsecond angular resolution. HESSI is planned for
launch in July 2000, in time to detect the thousands of flares expected
during the next solar maximum.
---------------------------------------------------------
Title: Heating Events in the Quiet Solar Corona
Authors: Benz, Arnold O.; Krucker, Säm
1998SoPh..182..349B Altcode:
Sensitive observations of the quiet Sun observed by EIT on the SOHO
satellite in high-temperature iron-line emission originating in the
corona are presented. The thermal radiation of the quiet corona is
found to fluctutate significantly, even on the shortest time scale of
2 min and in the faintest pixels. The power spectrum of the emission
measure time variations is approximately a power law with an exponent
of 1.79±0.08 for the brightest pixels and 1.69±0.08 for the average
and the faintest pixels. The more prominent enhancements are identified
with previously reported X-ray network flares (Krucker et al., 1997)
above the magnetic network of the quiet chromosphere. In coronal
EUV iron lines they are amenable to detailed analysis suggesting
that the brightenings are caused by additional plasma injected from
below and heated to slightly higher temperature than the preexisting
corona. Statistical investigations are consistent with the hypothesis
that the weaker emission measure enhancements originate from the
same parent population. The power input derived from the impulsive
brightenings is linearly proportional to the radiative loss in the
observed part of the corona. The absolute amount of impulsive input
is model-dependent. It cannot be excluded that it can satisfy the
total requirement for heating. These observations give strong evidence
that a significant fraction of the heating in quiet coronal regions
is impulsive.
---------------------------------------------------------
Title: Kulturelle Kontakte zu Außerirdischen?
Authors: Benz, A.
1998A&R....35...17B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A stochastic model for solar type III bursts
Authors: Isliker, H.; Vlahos, L.; Benz, A. O.; Raoult, A.
1998A&A...336..371I Altcode:
A stochastic model for type III bursts is introduced, discussed,
and compared to observations. The active region is assumed to be
inhomogeneous, with a large number of emerging magnetic fibers. At
their bases, random energy release events take place, in the course of
which electrons are accelerated, travel along the fibers and eventually
undergo the bump-on-tail instability. In the non-linear regime, the
formed Langmuir waves induce strong turbulence in the ambient plasma,
with secondary electrostatic waves appearing. Wave-wave scattering
finally leads to the emission of transverse electro-magnetic waves at
the fundamental and the harmonic of the local plasma-frequency. The
superposition of the emissions from all the fibers yields a model
spectrogram for type III bursts (flux as a function of frequency
and time). Peak-flux distributions of the model are compared to the
ones of five observations of type III bursts. It turns out that,
in a statistical sense, the model is largely compatible with the
observations: the majority of the observations can be considered
generated by a process which corresponds with the presented model. The
details of the different sub-processes constituting the model play no
decisive role concerning the statistical properties of the generated
spectrograms, to describe them approximately by randomizing the unknown
elements is sufficient. Therewith, the correspondence of the model
with the data is not unique. Likewise, intrinsic shortness of observed
type III events does not allow a strict enough discrimination between
different possible sub-processes of the model through statistical
tests. With that, the conclusion is that the observations are compatible
with a model which assumes (i) a randomly structured active region,
(ii) a flare-particle acceleration-process which is fragmented into a
large number of sub-processes, (iii) a distribution of the accelerated
particles which is a random fraction of the ambient density and of
power-law form with random index, and (iv) the fragmentary acceleration
events to occur randomly in time, i.e. the temporal structure of
type III events to be random, without any correlations between the
individual bursts.
---------------------------------------------------------
Title: Energy Distribution of Heating Processes in the Quiet Solar
Corona
Authors: Krucker, Säm; Benz, Arnold O.
1998ApJ...501L.213K Altcode:
We have determined the variations in the emission measure of the solar
corona using EUV Imaging Telescope/Solar and Heliospheric Observatory
observations of iron lines in a quiet region of the Sun. The
emission measure is found to vary significantly in at least 85%
of all the pixels within 42 minutes. The variations are interpreted
as heating events that bring chromospheric material above the one
million degree threshold of the observed lines and that cool the
coronal plasma below that limit. A method to assess heating events
has been developed. The thermal energy input by such microflares is
calculated from the observed increases in emission measure and the
derived temperature. Heating events have been found in the range from
8×10<SUP>24</SUP> to 1.6×10<SUP>26</SUP> ergs. The energy input
by >=3 σ events of the emission measure increase the amounts to
about 16% of the average radiated power of the coronal plasma in
the quiet corona. The frequency distribution of microflares is an
approximate power law of the form f(E)=f<SUB>0</SUB>E<SUP>-δ</SUP>,
with a power-law index δ between 2.3 and 2.6. Since the low-energy
cutoff is due to sensitivity limitations and the power-law index
is steeper than 2, these observations demonstrate the possibility
that microflares dominate the energy input into the quiet corona. The
observed power law would have to continue to about 3×10<SUP>23</SUP>
ergs in order to match the observed minimum heating requirement.
---------------------------------------------------------
Title: A multiwavelength analysis of an electron-dominated gamma-ray
event associated with a disk solar flare
Authors: Trottet, Gerard; Vilmer, Nicole; Barat, Claude; Benz, Arnold;
Magun, Andreas; Kuznetsov, Alexandr; Sunyaev, Rachid; Terekhov, Oleg
1998A&A...334.1099T Altcode:
This paper reports the first comparison of hard X-ray (HXR), gamma-ray
(GR), centimetric-millimetric and metric-decimetric spectral and imaging
radio observations obtained during an electron-dominated gamma-ray
burst. This impulsive event,which occurred on 1990 June 11 at ~ 0943
UT, was associated with a H<SUB>alpha</SUB> 2B flare, located close
to the disk center. The time evolution of the HXR emission consists
of successive peaks of ~ 10 s duration. Several of these peaks show
GR emission up to a few MeV and one of them up to ~ 56 MeV. For each
of these peaks, the photon spectrum significantly hardens above a
break energy varying in the 0.4-0.7 MeV range. No significant GR line
(GRL) emission is detected. The main results of our analysis are:
(i) even if no significant GRL emission is detected, the upper limit
of the energy content in > 1MeV/nucl. ions is comparable with
the energy content in > 20 keV electrons ( a few 10(29) ergs),
as it is found for GRL flares; (ii) during the whole event, the
centimetric-millimetric emission is radiated by ga 0.4-0.7 MeV electrons
which have been accelerated since the very beginning of the flare;
(iii) the different HXR/GR peaks are associated with step-wise changes
of the magnetic structures to which metric-decimetric radio producing
electrons have access. This latter characteristic of the 1990 June 11
burst is globally similar to the behaviour reported in the literature
for GRL events, but the energy in accelerated particles is about one
order of magnitude lower. Finally, the electron-dominated emitting peak
with emission up to ~ 56 MeV is interpreted as a signature of an upward
moving population of relativistic electrons which is strongly beamed
along the magnetic field and which does not contribute significantly
to the centimetric-millimetric and la 0.2 MeV HXR emissions. The
metric-decimetric radio observations indicate that this happens when
electrons have suddenly access to large-scale magnetic structures.
---------------------------------------------------------
Title: Intermediate drift bursts and the coronal magnetic field
Authors: Benz, Arnold O.; Mann, Gottfried
1998A&A...333.1034B Altcode:
We have analyzed 12 decimetric continuum (type IV) events during solar
flares showing intermediate drift (IMD) fine structures in the 1 - 3
GHz band. This is the first time IMD patterns have been reported above
1 GHz and that the full spectrum of both continuum and IMD bursts has
been covered. The IMD pattern was usually shifted to higher frequency
and tends to occur later than the continuum. Average drift rates of
IMD bursts per event were found by cross-correlation yielding dot
nu /nu = -0.167 to -0.046 s(-1) . The average second derivative of
individual IMD bursts expressed as ddot nu dot nu (-2) nu is 0.42
to 4.19. Normalized by the mean frequency, these high-frequency IMD
bursts are found to be identical in their characteristics with this
type of bursts below 1 GHz. The derived burst parameters require an
important change in one of the two existing theories.
---------------------------------------------------------
Title: Logistic Avalanche Processes, Elementary Time Structures,
and Frequency Distributions in Solar Flares
Authors: Aschwanden, Markus J.; Dennis, Brian R.; Benz, Arnold O.
1998ApJ...497..972A Altcode:
We analyze the elementary time structures (on timescales of ~0.1-3.0
s) and their frequency distributions in solar flares using hard X-ray
(HXR) data from the Compton Gamma Ray Observatory (CGRO) and radio data
from the radio spectrometers of Eidgenoessische Technische Hochschule
(ETH) Zurich. The four analyzed data sets are gathered from over
600 different solar flares and include about (1) 10<SUP>4</SUP>
HXR pulses at >=25 and >=50 keV, (2) 4000 radio type III
bursts, (3) 4000 pulses of decimetric quasi-periodic broadband
pulsation events, and (4) 10<SUP>4</SUP> elements of decimetric
millisecond spike events. <P />The time profiles of resolved
elementary time structures have a near-Gaussian shape and can be
modeled with the logistic equation, which provides a quantitative
measurement of the exponential growth time τ<SUB>G</SUB> and the
nonlinear saturation energy level W<SUB>S</SUB> of the underlying
instability. Assuming a random distribution (Poisson statistics)
of saturation times t<SUB>S</SUB> (with an e-folding constant
t<SUB>Se</SUB>), the resulting frequency distribution of saturation
energies W<SUB>S</SUB> or peak energy dissipation rates F<SUB>S</SUB> =
(dW/dt)<SUB>t=t<SUB>S</SUB></SUB> has the form of a power-law function,
i.e., N(F<SUB>S</SUB>)~F<SUP>-α</SUP><SUB>S</SUB>, where the power-law
index α is directly related to the number of e-folding amplifications
by the relation α = (1 + τ<SUB>G</SUB>/t<SUB>Se</SUB>). The same
mathematical formalism is used to generate power-law distributions,
as in Rosner & Vaiana, but the distribution of energies released
in elementary flare instabilities is not related to the global energy
storage process. We assume Poissonian noise for the unamplified
energy levels in unstable flare cells, implying an exponential
frequency distribution of avalanche energies W<SUB>S</SUB> or fluxes
F<SUB>S</SUB> in the absence of coherent amplifications. Also, in
the case of coherent amplification, the Poissonian noise introduces
exponential rollovers of the power law at the low and high ends of the
frequency distributions. <P />We fit both power-law and exponential
functions to the observed frequency distributions of elementary pulse
fluxes N(F) in each flare separately. For HXR pulses, one-half of
the flares are better fitted with power-law frequency distributions,
demanding coherent amplification of the underlying energy dissipation
mechanism, e.g., current exponentiation occurring in the magnetic
tearing instability. The majority of type III burst flares are best
fitted with power-law distributions, consistent with the interpretation
in terms of beam-driven coherent emission. The frequency distributions
of decimetric pulsations and decimetric millisecond spikes are found to
fit exponential functions, in contrast to the expected power laws for
coherent emission mechanisms generally proposed for these radio burst
types. A coherent emission mechanism can be reconciled with the observed
exponential frequency distributions only if nonlinear saturation occurs
at a fixed amplification factor for all elementary pulses or spikes,
for example, if it is produced by an oscillatory compact source (in the
case of decimetric pulsations) or by a fragmented source with similar
spatial cell sizes (in the case of decimetric millisecond spikes).
---------------------------------------------------------
Title: First VLBI images of a main-sequence star
Authors: Benz, Arnold O.; Conway, John; Gudel, Manuel
1998A&A...331..596B Altcode:
The binary system UV Cet A and B has been observed with the VLBA/VLA
at 3.6 cm wavelength. Both dMe stars have been detected. The stronger,
steady radio emitter of the two, UV Cet B, is resolved into at least
two spatial components. Their relative intensities change during the
6.3 hours of observing time. One of the components is more stable and
resolved, the other is possibly unresolved. The resolved component has a
half-power diameter of 2.4x 10(10) cm, exceeding the size of the stellar
photosphere. The separation of the two components of UV Cet B is 4.4
(+/-0.4)x 10(10) cm or 4 - 5 stellar radii. The alignment of the two
components is along the axis of the binary orbit and thus parallel and
very likely close to the stellar rotation axis. The apparent trapping
of the gyrosynchrotron emitting energetic electrons requires large
coronal loops extending to several stellar radii. At the more variable
source a magnetic field between 15 and 130 G is derived.
---------------------------------------------------------
Title: Remote Radio Tracking of CMEs from Wind and ULYSSES
Authors: Benz, A. O.; Reiner, M. J.
1998cee..workE..15B Altcode:
Some interplanetary shocks associated with coronal mass ejections
(CMEs) generate type II radio emissions at the local plasma frequency
and/or its harmonic. These type II radio emissions provide a means of
remotely tracking CMEs from the solar corona out to 1 AU and beyond. We
have developed new analysis techniques for tracking CME associated
radio emissions that inherently reveal the dynamics of a CME as it
propagates through the interplanetary medium. The analyses make use
of dynamic spectral plots of the radio intensity as a function of
1/frequency versus time. Since the interplanetary density falls off
as 1/R<SUP>2</SUP> (R = heliocentric distance), on these plots the
frequency drifting type II emissions are organized along straight
lines that converge to the solar liftoff time. The slopes of the lines
vary as the ratio of the shock speed to the square root of the plasma
density, normalized to 1 AU. The values of the slopes corresponding
to fundamental radio emissions lie between 1-2 times 10^{-7} kHz^{-1}
s^{-1} for the kilometric type II radio events so far examined from
Ulysses and Wind. When in-situ measurements are also made, the method of
analysis determines unequivocally whether the type II emissions occurred
at the fundamental or harmonic of the local plasma frequency in the
upstream or downstream regions of the CME-driven shock. Additional
radio tracking is provided by the direction-finding capabilities on
Wind/WAVES and Ulysses/URAP. They allow identification of specific
structures in the interplanetary medium where the type II emissions were
generated. We will illustrate the new techniques by using examples of
type II events observed by Wind and Ulysses. Some examples show very
weak diffuse emission at the harmonic frequencies and more intense,
sporadic emission at the fundamental frequencies. For a very unusual
event that occurred on 8--11 January 1997, we have determined that some
of the type II emission was generated as the CME-driven shock passed
through a corotating interaction region ( Reiner et al., 1998). Other
examples indicate simultaneous type II radio emissions from regions
of different densities along the shock front. All cases that we have
so far examined are consistent with the fundamental and/or harmonic
type II radio emissions being generated in the upstream region of the
CME-driven shock.
---------------------------------------------------------
Title: Radio Emission from Solar Flares
Authors: Bastian, T. S.; Benz, A. O.; Gary, D. E.
1998ARA&A..36..131B Altcode:
Radio emission from solar flares offers a number of unique diagnostic
tools to address long-standing questions about energy release,
plasma heating, particle acceleration, and particle transport
in magnetized plasmas. At millimeter and centimeter wavelengths,
incoherent gyrosynchrotron emission from electrons with energies of
tens of kilo electron volts (keV) to several mega electron volts (MeV)
plays a dominant role. These electrons carry a significant fraction
of the energy released during the impulsive phase of flares. At
decimeter and meter wavelengths, coherent plasma radiation can play a
dominant role. Particularly important are type III and type III-like
radio bursts, which are due to upward- and downward-directed beams
of nonthermal electrons, presumed to originate in the energy release
site. With the launch of Yohkoh and the Compton Gamma-Ray Observatory,
the relationship between radio emission and energetic photon emissions
has been clarified. In this review, recent progress on our understanding
of radio emission from impulsive flares and its relation to X-ray
emission is discussed, as well as energy release in flare-like phenomena
(microflares, nanoflares) and their bearing on coronal heating.
---------------------------------------------------------
Title: A search for prompt radio emission of gamma-ray bursts
Authors: Benz, Arnold O.; Paesold, Gunnar
1998A&A...329...61B Altcode:
A conducting fireball expanding at relativistic speed into an ambient
magnetic field generates a rapidly changing electric current which
emits coherent electromagnetic radiation at radio frequencies. The
critical frequency (upper limit of the emission) strongly depends on
the Lorentz factor of the expansion. We have searched for simultaneous
radio emission in the data of solar radio spectrographs at times when
BATSE reported a non-solar gamma-ray burst (GRB) within the beams of the
radio telescopes. Solar spectrographs are less sensitive than single
frequency receivers, but yield a broad overview on the spectrum ideal
for discriminating against atmospheric and man-made interference. In 7
well-observed cases no radio emission was found. This puts upper and
lower limits on the Lorentz factor of the fireball expansion in GRBs
if the source distance is less than 1 kpc, i.e. if GRBs are local. The
coherent expansion radiation is not observable with current instruments
if the GRB sources are at >= 1 kpc.
---------------------------------------------------------
Title: PHOENIX-2: A Broadband Spectrometer for Decimetric and
Microwave Radio Bursts: First Results
Authors: Messmer, P.; Benz, A. O.; Monstein, C.; Zmoos, C.
1998cee..workE..55M Altcode:
Phoenix-2, a new spectrometer to register solar flare radio emission in
the 0.1 to 4 GHz band, has become operational. It is a frequency-agile
system for measuring either both senses of circular polarization or
linear polarization in Dicke mode. Spectra are obtained by sweeping
through a set of frequency channels. The number of channels, their
frequencies and their bandwidth are user defined. The temporal
resolution has to be compromised with the number of frequency
channels and can be in the range of 0.5 ms to 1 s for 1 to 2000
channels. The possibility to chose channels at any frequency in the
observed band allows to detect and avoid frequencies with man made
interference. Recording period for the spectra is from sunrise to
sunset. The observation schedule and the interruption of observations
by calibration measurements are user defined. During the night,
the spectral data is automatically transfered from the observatory
location (Bleien, about 50 km from Zurich) through the Internet to
the Institute of Astronomy in Zurich, where all the calibration,
archiving and feature extraction tasks are performed. This allows
to access the spectral data one day after its measurement. Phoenix-2
incorporates parts of the old Zurich Spectrometer 'Phoenix', (Benz et
al, 1991) namely the antenna, the antenna control hardware and some
high-frequency components. The most important new capabilities of
Phoenix-2 are: 1. Observations up to 4 GHz instead of 3 GHz 2. Larger
spectra with up to 2000 different frequency channels instead of 500
3. Continuous recording from sunrise to sunset, instead of 90 minutes
maximum continuous recording time during bursts 4. More accurate,
automatic calibration 5. Immediate evaluation of the data instead
of manual tape transport 6. Online archive of all calibrated data
for later processing with more advanced feature detection methods
7. Monitoring focus instrumentation (pre-amplifier, noise source)
and environmental data (weather station) During normal surveillance
operation, Phoenix-2 measures broadband spectra with 200 channels,
10 MHz bandwidth and 0.1 s time resolution. Bursts are detected either
manually or by searching for a set of channels exceeding a threshold
value. First bursts are detected and demonstrate the functionality of
the system. At the time of writing this abstract, the full qualification
of the instrument was subject of ongoing research.
---------------------------------------------------------
Title: High Frequency Decimetric Type III Bursts
Authors: Fernandes, F. C. R.; Melendez, J. L.; Sawant, H. S.; Benz,
A. O.
1998cee..workE..36F Altcode:
To our knowledge, there is a lack of investigations of the decimetric
type III bursts above 1000 MHz. In this paper, we have carried out
statistical investigations of the type III decimertic bursts, a majority
(74 %) of them having central frequency above 1000 MHz, observed by
the radio spectrometer Phoenix of ETH, Zurich, from September 1992 to
October 1993, associated with 8 hard X-ray flares observed by the Yohkoh
satellite. We found 160 isolated type III bursts suitable for detailed
analysis out of 416 bursts. By using digital data we have adjusted
a gaussian profile for a given frequency, considering the level of 3
sigma above the noise background, and we derived peak flux and time,
corresponding to a gaussian center and half power duration of gaussian
(t_{1/2}). Also, we derived the starting and ending frequencies. The
frequency drift rate (df/dt) was determined from a linear regression of
the maxima in the frequency - time plane. The highlights of the analysis
are: (i) frequency range of most of the type III bursts is less than
250 MHz; (ii) the number of bursts decreases with increasing starting
frequency and flux; (iii) flux decreases with increasing frequency;
(iv) in the bursts we analysed, 64 % are reverse slope, 36 % normal and
5 % bidirectional. The best fits for the average half power duration
and for the average drift rate as a function of frequency are given by
t_{1/2} = 1.7 times 10^4 f^{-0.60} and mid df/dt mid = 0.09 f^{1.35},
respectively. These relations fit well at high frequency. Assuming
an improved density model and type III emission at 2nd harmonic,
following beam parameters of type III bursts are derived: (a) average
electron beam velocity, v<SUB>b</SUB> ~= 0.16 c(~7 keV); (b) beam
electron density, N_b ~= 6 times 10^4 cm^{-3}; (c) total number of
electrons per beam, {N} ~= 6 times 10<SUP>31</SUP>. One bidirectional
drifting type III burst starting at 1700 MHz was observed, suggesting
that ocassionally, acceleration region can be located where the plasma
density is ~10<SUP>11</SUP> cm^{-3}.
---------------------------------------------------------
Title: Radio Wave and Soft X-ray Diagnostics of Heating Events in
the Quiet Solar Corona
Authors: Krucker, S.; Benz, A. O.
1998cee..workE...7K Altcode:
Sensitive observations of the quiet Sun observed by (1) SXT on the
Yohkoh satellite, (2) EIT on the SoHO satellite in high-temperature iron
line emission, (3) CDS on the SoHO satellite in the He I and O V line
emission, and (4) the Very Large Array (VLA) in the centimeter radio
range are investigate in the view of the coronal heating problem. The
observed enhancements are interpreted as heating events (mircoflares)
bringing chromospheric material to coronal temperatures. The thermal
energy inputs by such microflares have been found in the range from
8 times 10<SUP>24</SUP>erg to 1.6 times 10<SUP>26</SUP>erg, and the
total energy input amounts to about 16% of the average radiated power
of the coronal plasma in the quiet corona. The frequency distribution
of microflares is an approximate power-law of the form f(E) = f_0
E^{-delta} with a power-law index delta between 2.3 and 2.6. As the
low-energy cutoff is due to sensitivity limitations and the power-law
index is steeper than 2, these observations demonstrate the possibility
that microflares dominate the energy input into the quiet corona.
---------------------------------------------------------
Title: Logistic Avalanche Processes, Elementary Time Structures,
Frequency Distributions, and Wavelet Analysis of Solar Flares
Authors: Aschwanden, M. J.; Dennis, B. R.; Schwartz, R. A.; Benz,
A. O.; Kliem, B.; Schwarz, U.; Kurths, J.
1998cee..workE..10A Altcode:
Do elementary time scales exist in solar flares that could provide
us a clue on the spatial fragmentation of the primary energy
release process? Or is there a continuous distribution, composed
of a hierarchy of unresolved time structures? We present results
of two recent studies on these fundamental questions. We applied a
multi-resolution analysis (using triangle-shaped wavelet transforms)
to 647 solar flares observed with the COMPTON Gamma Ray Observatory
(CGRO) at hard X-ray energies of >= 25 keV with a time resolution
of 64 ms. From the wavelet scalegrams we infer a distribution of time
scales N(T) for each flare and find a cutoff for the shortest detected
time scales T<SUB>min</SUB> that is independent of the Poisson noise for
strong flares. These shortest time scales T<SUB>min</SUB> are found to
correlate with the flare loop radius r (Fig.1), i.e. T<SUB>min</SUB> =
0.5 (r/10^9 cm)s (measured with Yohkoh) and the collisional deflection
time, T<SUB>min</SUB> > ~t<SUP>Defl</SUP>(n_e), (determined from the
electron density n_e of trapped electrons by measuring energy-dependent
time delays detected with CGRO). From these observations we infer
spatial sizes of r<SUB>acc</SUB> = 75-750 km for elementary acceleration
cells. In a second study we determined the frequency distributions
of elementary time structures in over 600 flares, based on some
10^4 hard X-ray pulses at 25 and 50 keV, 4000 radio type III bursts,
4000 decimetric quasi-periodic broadband pulsation events, and 10^4
decimetric millisecond spike events. All elementary time structures
have a quasi-Gaussian shape and can be modeled with the logistic
equation, which describes the exponential growth phase and nonlinear
saturation (caused by the limited amount of available free energy) of a
general instability. We derive a theoretical description of frequency
distributions in terms of this logistic avalanche model and find that
the power-law slope of observed frequency distributions provides a
powerful diagnostic on coherent versus incoherent instabilities.
---------------------------------------------------------
Title: First Image of the Corona of a Main-Sequence Star
Authors: Benz, Arnold O.; Gudel, Manuel; Conway, John
1998ASPC..154.1942B Altcode: 1998csss...10.1942B
The binary system UV Cet A and B has been observed with the VLBA/VLA
at 3.6 cm wavelength. Both dMe stars have been detected. The stronger,
steady radio emitter of the two, UV Cet B, is resolved into at least
two spatial components. Their relative intensities change during the
6.3 hours of observing time. One of the components is relatively stable
and resolved, the other is possibly unresolved. The resolved component
has a half-power diameter of about the size of the stellar photosphere
or 2 x 10<SUP>10</SUP> cm. The separation of the two components of UV
Cet B is 4.4 (+/-0.4) x 10<SUP>10</SUP> cm or 4-5 stellar radii. The
alignment of the two components is along the axis of the binary orbit
and thus probably close to the stellar rotation axis. The apparent
trapping of the gyrosynchrotron emitting energetic electrons requires
large coronal loops extending to several stellar radii. At the more
variable source a magnetic field between 20 and 130 G is derived.
---------------------------------------------------------
Title: What should we call a spike burst?
Authors: Benz, A. O.
1998cee..workE..16B Altcode:
Short, narrowband spikes at decimetric wavelengths have been found to
correlate with hard X-rays. For this reason they have become interesting
as possible diagnostics for particle acceleration in flares. There
are two competing views: one puts the spike sources at the footpoints
of coronal magnetic fields where they could be caused by a loss-cone
instability, the other relates it more directly with the acceleration
process and predicts them to be located in the acceleration region. All
we need to decide is an image of spikes and a simultaneous X-ray image
showing loops or their footpoints. Unfortunately a considerable
confusion has developed on the definition of spikes. 'Spikes'
are reported at nearly all radio frequencies now from meter waves
to millimeter, even in UV and X-ray observations people talk about
'spikes'. Worst of all, however, is the use of 'spikes' for any short
burst in the decimeter wavelength range, where other short burst types
have been reported, including type IV finestructures, type III and
pulsations. In particular the most frequent decimetric type, type
III bursts, have been reported in the literature as 'spikes'. They
are not always correlated with hard X-rays. Their position is also
interesting but has a completely different meaning. 'Spike' has become
a synonym for 'burst' in decimeter waves. I strongly suggest that we
reserve the word 'spike' for the narrowband bursts which correlate
well with hard X-rays. However, if the word 'decimetric spike' or
'microwave spike' cannot be reserved for this well-defined, restricted
type, we better change to 'decimetric type I bursts' or similar. Of
course, a reliable classification is only possible with a high time
resolution spectrometer. We have long come to accept that fact for
the meter wave burst classification. Since the 1950's, the type I -
V bursts are interpreted by different emission processes, and the word
'burst' would not be a valid identification. This same is the case
for decimetric range, where we have different types of bursts. A
radio image of an unclassified burst in coherent emission at any
wavelength is rather useless. Fortunately, narrowband spikes have a
very short duration which decreases with wavelength. The decay time
of spikes follows a well defined relation. An rough classification is
therefore possible with sufficient time resolution alone. If we do not
keep to some careful classification that keeps apart what seems to
be physically different, there will not be progress in the field of
coherent decimetric radiation. I would like to bring up the problem
to the CESRA participants, discuss it in public and come to a joint
conclusion. It may be necessary to have a small discussion group at
the present meeting.
---------------------------------------------------------
Title: The High Energy Solar Spectroscopic Imager (HESSI): A Small
Explorer for the Start of the New Millennium
Authors: Holman, G. D.; Lin, R. P.; Dennis, B. R.; Crannell, C. J.;
Ramaty, R. R.; Rosenvinge, T. T.; Canfield, R. C.; Emslie, A. G.;
Hudson, H. S.; Hurford, G. J.; Madden, N. W.; van Beek, H. F.; Benz,
A.; Bornmann, P. L.; Brown, J. C.; Enome, S.; Kosugi, T.; Vilmer,
N.; Zehnder, A.
1997AAS...191.7416H Altcode: 1997BAAS...29R1326H
The High Energy Solar Spectroscopic Imager (HESSI) has been selected
for launch in mid 2000, at the peak of the solar activity cycle. The
primary scientific objective of HESSI is to understand particle
acceleration and explosive energy release in the magnetized plasma at
the Sun. HESSI will provide the first high-spectral-resolution x-ray and
gamma -ray images of the Sun. It will obtain the first imaging above
100 keV, the first imaging of solar gamma -ray lines, and the first
high-resolution spectroscopy of solar gamma -ray lines, including the
first determination of line shapes. In two years HESSI is expected to
obtain observations of tens of thousands of microflares, thousands of
hard x-ray flares, and of order a hundred gamma -ray line flares. HESSI
will also monitor and provide high-spectral-resolution observations of
cosmic and terrestrial hard x-ray and gamma -ray transients, as well
as imaging of the Crab Nebula. HESSI's high spectral, spatial, and
temporal resolution and dynamic range will allow the first detailed
studies of the evolution of both accelerated particles and hot,
thermal plasma in solar flares.
---------------------------------------------------------
Title: X-Ray Network Flares of the Quiet Sun
Authors: Krucker, Säm; Benz, Arnold O.; Bastian, T. S.; Acton,
Loren W.
1997ApJ...488..499K Altcode:
Temporal variations in the soft X-ray (SXR) emission and the radio
emission above the solar magnetic network of the quiet corona are
investigated using Yohkoh SXR images with deep exposure and VLA
observations in the centimeter radio range. The SXR data show several
brightenings, with an extrapolated occurrence probability of one
brightening per 3 seconds on the total solar surface. During the roughly
10 minutes of enhanced flux, total radiative losses of the observed
plasma are around 10<SUP>25</SUP> ergs per event. These events are more
than an order of magnitude smaller than previously reported X-ray bright
points or active region transient brightenings. For all of the four
SXR events with simultaneous radio observations, a corresponding radio
source correlating in space and time can be found. There are several
similarities between solar flares and the SXR/radio events presented in
this paper. (1) Variations in temperature and emission measure during
the SXR enhancements are consistent with evaporation of cooler material
from the transition region and the chromosphere. (2) The ratio of the
total energies radiated in SXR and radio frequencies is similar to
that observed in flares. (3) At least one radio event shows a degree
of polarization as high as 35%. (4) In three out of four substructures
the centimeter radio emission peaks several tens of seconds earlier
than in the SXR emission. (5) The associated radio emission tends to
be more structured and to have faster rise times. These events thus
appear to be flare-like and are called network flares.
---------------------------------------------------------
Title: The dispersion of radio waves in the solar corona.
Authors: Benz, A. O.; Pianezzi, P.
1997A&A...323..250B Altcode:
Different arrival times of the two magnetoionic modes in solar
radio bursts have been detected. The bursts are from four decimetric
radio events showing narrowband millisecond spikes. They have been
observed with 2ms and 0.5ms time resolution, respectively, by the
Ikarus and Phoenix spectrometers of ETH Zurich. The four events have
been selected because of their low polarization. The arrival times
of the left and right circularly polarized modes have been compared
by cross-correlation. In all cases the weaker mode is delayed by a
fraction of a millisecond. Several tests have been carried out to
ensure the significance of the delay. The delay is interpreted by the
difference in group velocity of the two modes due to dispersion in
the coronal plasma. Simple models show that the observed difference in
travel time is consistent with this interpretation. It suggests that
the radiation is polarized in the ordinary mode at the location where
the polarization originates. If the polarization originates in the
original source region, the possible emission processes are limited to
the ones radiating in ordinary mode. More likely, the polarization seems
to originate at higher altitude e.g. in a quasi-transverse region. In
both cases the delay is proportional to the longitudinal component of
the magnetic field in the medium of propagation.
---------------------------------------------------------
Title: Decimetric Type III Radio Bursts with High Starting Frequencies
and the Associated Solar Flare Hard X-Ray Emission
Authors: Fernandes, F. C. R.; Sawant, H. S.; Melendez-Moreno, J. L.;
Benz, A. O.; Yoshimori, M.; Kane, S. R.; McTiernan, J. M.
1997SPD....28.0172F Altcode: 1997BAAS...29..892F
We have examined the characteristics of 160 isolated type III decimetric
(100-3000 MHz) radio bursts which occurred during the period September
1992 - October 1993. Bursts associated with 13 hard X-ray flares were
examined in detail. The radio observations were made with the PHOENIX
solar radio spectrometer in Zurich. The X-ray flares were observed by
the Hard X-ray Spectrometer (HXS) on the Yohkoh satellite. Type III
radio bursts with normal, reverse as well as bi-directional drifts
were observed. Characteristic parameters such as starting frequency,
bandwidth, total duration, and frequency drift rate were determined
for the radio bursts. Similarly power law photon spectra were fitted
to the hard X-ray emission. For an assumed model of ambient density
vs. height above the photosphere, the electron beam velocity and hence
the electron energy was inferred from the frequency drift rate of the
radio burst. Assuming that the energy loss of the energetic electrons
is caused primarily by collisions, the height of injection for the
radio emitting electrons was deduced. For comparison, characteristics
of the energetic electrons were also inferred from the thick target
model for the hard X-ray source. Implications of the results with
respect to the acceleration and propagation of energetic electrons in
solar flares will be discussed.
---------------------------------------------------------
Title: Electron Densities in Solar Flare Loops, Chromospheric
Evaporation Upflows, and Acceleration Sites
Authors: Aschwanden, Markus J.; Benz, Arnold O.
1997ApJ...480..825A Altcode:
We compare electron densities measured at three different locations
in solar flares: (1) in soft X-ray (SXR) loops, determined from SXR
emission measures and loop diameters from Yohkoh Soft X-Ray Telescope
maps [n<SUP>SXR</SUP><SUB>e</SUB>=(0.2-2.5)×10<SUP>11</SUP>
cm<SUP>-3</SUP>] (2) in chromospheric evaporation upflows,
inferred from plasma frequency cutoffs of decimetric radio
bursts detected with the 0.1-3 GHz spectrometer Phoenix of ETH
Zürich [n<SUP>upflow</SUP><SUB>e</SUB>=(0.3-11)×10<SUP>10</SUP>
cm<SUP>-3</SUP>] and (3) in acceleration sites, inferred from
the plasma frequency at the separatrix between upward-accelerated
(type III bursts) and downward-accelerated (reverse-drift bursts)
electron beams [n<SUP>acc</SUP><SUB>e</SUB>=(0.6-10)×10<SUP>9</SUP>
cm<SUP>-3</SUP>]. <P />The comparison of these density measurements,
obtained from 44 flare episodes (during 14 different flares),
demonstrates the compatibility of flare plasma density diagnostics with
SXR and radio methods. The density in the upflowing plasma is found to
be somewhat lower than in the filled loops, having ratios in a range
n<SUP>upflow</SUP><SUB>e</SUB>/n<SUP>SXR</SUP><SUB>e</SUB>=0.02-1.3,
and a factor of 3.6 higher behind the upflow front. The acceleration
sites are found to have a much lower density than the SXR-bright flare
loops, i.e., n<SUP>acc</SUP><SUB>e</SUB>/n<SUP>SXR</SUP><SUB>e</SUB>=
0.005-0.13, and thus must be physically displaced from the SXR-bright
flare loops. The scaling law between electron time-of-flight distances
l' and loop half-lengths s, i.e., l'/s = 1.4 +/- 0.3, recently
established by Aschwanden et al. suggests that the centroid of the
acceleration region is located above the SXR-bright flare loop, as
envisioned in cusp geometries (e.g., in magnetic reconnection models).
---------------------------------------------------------
Title: Chromospheric Events in the Quiet Network
Authors: Keller, C.; Bastian, T.; Benz, A.; Krucker, S.
1997SPD....28.1304K Altcode: 1997BAAS...29..917K
Time sequences of a quiet network region close to disk center have
been simultaneously recorded with the VLA, various instruments on SOHO,
and the solar telescopes on Kitt Peak. The analysis of the Hα spectra
obtained at the McMath-Pierce telescope revealed down-flows with
apparent velocities of more than 2.5 km/s associated with magnetic
field structures in the quiet network. During such events, the Hα
spectra show a pronounced asymmetry. The photospheric magnetic field was
determined from rapid scans in three iron lines with the Zurich Imaging
Stokes Polarimeter. Up- and down-flow velocity excursions outside of
magnetic field regions are compatible with chromospheric waves. We
describe the properties of these events as seen in the observations
of the visible part of the spectrum and their signatures at radio
and UV wavelengths. The final goal of this study is the construction
of a time-dependent 3-D picture of the quiet solar atmosphere and the
understanding of the dynamical coupling of photospheric magnetic fields
with the chromosphere and the corona.
---------------------------------------------------------
Title: Fine structure of the X-ray and radio emissions of the quiet
solar corona.
Authors: Benz, A. O.; Krucker, S.; Acton, L. W.; Bastian, T. S.
1997A&A...320..993B Altcode:
Two deep soft X-ray exposures of a quiet region on the Sun were made
with the SXT telescope on board the Yohkoh satellite on 20 Feb 1995. We
report on the spatial X-ray fine structure. Regions of enhanced X-ray
emission, more than two orders of magnitude fainter than previously
reported X-ray bright points, are loosely associated with bipolar
regions in the magnetic network. The power spectrum of quiet X-ray
images at small spatial scales is similar to that of active regions,
but exhibits a kink at a scale of =~25,000km, possibly connected to
the supergranular structure. The spatial X-ray structures in the
time averaged image amount to an rms amplitude which is 6% of the
mean value. The X-ray structures correlate with contemporaneous radio
maps obtained by the VLA at wavelengths of 1.3, 2.0, and 3.6cm. The
amplitude of the brightness variations in the images increases with
radio wavelength, i.e., with increasing height. The cross-correlation
coefficient with the absolute magnetic field strength, however,
generally decreases with height, consistent with the idea of bipolar
regions in the network and of the magnetic field deviating from
vertical in the upper chromosphere. The X-ray observations require an
enhanced pressure in the corona above the magnetic network, but suggest
similar temperatures. Model calculations show that, under a constant
temperature, an rms density increase (relative to that in the cell
interior) ranging from about 20% in the chromosphere to 60% in the low
corona is sufficient to explain the observed standard deviations due
to the spatial structures in radio waves and soft X-rays, respectively.
---------------------------------------------------------
Title: VLBI measurement of the size of dMe stars.
Authors: Alef, W.; Benz, A. O.; Guedel, M.
1997A&A...317..707A Altcode:
The binary system YY Gem, which consists of two dM1e stars, has
been observed during an eclipse using intercontinental Very Long
Baseline Interferometry (VLBI) at 1.6GHz. The stellar emission was
at a low, quiescent level at all observing periods. The correlated
flux decreases slightly with baseline length, indicating that the
source is resolved at the longest baselines. This is confirmed by
model fits, which give a FWHM size of 0.94(+/-0.24)mas (2.0x10^11^cm
or 2.1 photospheric diameters) for the radio emitting source. A lower
limit to the size derived from the lack of observable eclipse effects
is consistent with this value. The resulting brightness temperature
of 1.1x10^9^K is compatible with gyrosynchrotron emission. Deviations
from circular symmetry are not significant. The loops that trap the
radio emitting electrons reaching an altitude of probably more than
a stellar radius appear to be distributed isotropically within the
limits of the resolution.
---------------------------------------------------------
Title: Energy Release Processes in Active Regions
Authors: Benz, A. O.
1997LNP...489..201B Altcode: 1997shpp.conf..201B
A standard model of impulsive energy release has emerged during the
recent years: Magnetic energy is dumped into coronal electrons (and
possibly ions) accelerating them to some tens of keV. These particles
mostly precipitate into the chromosphere, radiate hard X-rays and heat
it to millions of degrees. The hot chromospheric material is ejected
into the corona and produces the soft X-ray flare. The theory behind
the energy release is reconnection, proposed for various geometries.
---------------------------------------------------------
Title: Coronal EUV and Radio Variability and Heating
Authors: Krucker, S.; Benz, A. O.; Delaboudinière, J. -P.
1997ESASP.404..465K Altcode: 1997cswn.conf..465K
No abstract at ADS
---------------------------------------------------------
Title: X-Ray/Radio Network Flares of the Quiet Sun
Authors: Benz, Arnold O.; Krucker, Sam; Acton, Loren W.; Bastian, T. S.
1997IAUJD..19E...1B Altcode:
The temporal variations in the soft X-ray (SXR) emission and the
radio emission above the solar magnetic network of the quiet corona
have been investigated using Yohkoh SXR images with deep exposure and
VLA observations in the centimetric radio range. The SXR data show
several brightenings with an extrapolated occurrence probability of
one brightening per 3 seconds on the total solar surface. During the
roughly 10 minutes of enhanced flux, the total radiative losses of
the observed plasma are betwee () n 0.6 and 2.4 cdot 10<SUP>26</SUP>
erg per event. These events are more than an order of magnitude smaller
than previously reported X-ray bright points or active region transient
brightenings. For all of the four SXR events with simultaneous radio
observations, a corresponding radio source correlating in space
and time can be found. There are several similarities between these
SXR/radio events and regular solar flares. These events thus appear
to be flare-like and are called network flares. We will report also
on very recent work using SOHO's EIT and CDS experiments combined with
VLA and Kitt Peak observations.
---------------------------------------------------------
Title: YOHKOH observation of the source regions of solar narrowband,
millisecond spike events.
Authors: Krucker, S.; Benz, A. O.; Aschwanden, M. J.
1997A&A...317..569K Altcode:
The source regions of metric spike events are investigated on Yohkoh
soft X-ray (SXR) maps. The spikes are identified by the spectrometer
Phoenix between 300MHz and 360MHz and are associated with groups of
type III bursts at lower frequencies reaching also the decametric
range. The Very Large Array (VLA) provides simultaneously spatial
information at 333MHz, 1446MHz and 4866MHz. Similar to the previous
VLA observation of a metric spike event, the new data are consistent
with a high altitude of the spike sources of about 5x10^10^cm above
the photosphere. The additionally available SXR data for one of the
presented events give the following new informations: (i) The spike
sources occur near open field lines and near regions of a slightly
enhanced SXR flux relative to the ambient plasma. (ii) Contrary to SXR
observations of type III bursts without metric spike activity, no SXR
jet is observed. (iii) At low altitude, a weak SXR enhancement occurs,
peaking about 60 s after the spike event. The SXR source and the spike
sources can be connected by potential field lines. The observations
corroborate a model in which a metric spike event is attributed to
an energy release region at high altitude, while upwards propagating
electrons produce type III bursts and downward moving electrons are
responsible for SXR emission of heated plasma.
---------------------------------------------------------
Title: The Neupert Effect in Active Stellar Coronae: Chromospheric
Evaporation and Coronal Heating in the dMe Flare Star Binary UV Ceti
Authors: Guedel, Manuel; Benz, Arnold O.; Schmitt, Juergen H. M. M.;
Skinner, Stephen L.
1996ApJ...471.1002G Altcode:
Evidence for coronal heating by chromospheric evaporation in flares
of active dMe stars is presented through observations of the Neupert
effect in high-frequency microwaves and soft X-rays. The Neupert
effect, as originally found in solar flares, manifests itself in
a close similarity between the soft X-ray light curve and the time
integral of the simultaneous microwave light curve. It is interpreted
as the signature of the accumulation of hot plasma due to heating
by accelerated electrons in the chromosphere. <P />We used the ROSAT
and ASCA soft X-ray observatories and the Very Large Array (VLA) radio
telescope (at 6 cm and 3.6 cm wavelengths) to monitor simultaneously the
nearby dMe flare star binary Gliese 65 A + B = UV Ceti during 9 hours
on each of two consecutive days. We find several weakly polarized
radio events that start contemporaneously (within a few minutes)
with X-ray flares and then peak and decay as the X-ray flares develop
gradually. A striking similarity to the temporal evolution of solar
gradual events is found. We argue that the Neupert effect is best
observed in relatively hard bands of the soft X-ray emission, but that
its presence can be inferred from the much softer bands commonly used
for stellar observations by use of the solar analogy. Together with
spectral hardness observations of soft X-rays, the data suggest the
operation of chromospheric evaporation on UV Cet. The observations
thus indicate a causal relation between the nonthermal and thermal
energies of the underlying electron populations. <P />We find that
stellar flares are, relative to solar flares, X-ray-weak. The ratio
between the total energy radiated into the radio and the soft X-ray
bands closely matches the corresponding ratio between the quiescent
luminosities of active stars, perhaps implying similar mechanisms and
similar efficiencies for the quiescent emission and for larger, single
flares. Estimating the total kinetic energy in the electrons from
the radio flux, we find that only a part is observed in soft X-rays,
a discrepancy well known from solar flares.
---------------------------------------------------------
Title: Metric spikes and electron acceleration in the solar corona.
Authors: Benz, A. O.; Csillaghy, A.; Aschwanden, M. J.
1996A&A...309..291B Altcode:
Short and narrowband spikes near the starting frequency of metric
type III bursts have been searched and analyzed in Zurich radio
spectrometer data. We find that the probability for the occurrence
of metric spikes is related to the starting frequency of type III
bursts; the association rate increases to 34% for groups of type
III bursts with starting frequencies below 500MHz. The frequency
channel containing most of spikes has been cross-correlated in time
with the frequency channels of type III bursts. The correlation is
significant in all selected cases and is caused by the association
of individual type III bursts with groups of spikes, proving beyond
doubt that spikes and type III bursts are physically related. The
cross-correlation also defines the average drift rate of the type
III maximum and its relation to spikes. In the average, the peak
time of metric spikes coincides with the correlated type III burst,
extrapolated to the same frequency. This may be interpreted as the
spike radiation being emitted at the same characteristic frequency
as the type III emission. The generally higher polarization of spikes
helps to distinguish them from type III bursts. Contrary to spikes at
higher (decimetric) frequencies, 60% of metric spike events have the
same sign of circular polarization as the associated type III bursts,
33% are opposite, while the polarization was not measurable for the
rest of the type III bursts. Some of the metric spike events are
associated with weak flare activity in H<SUB>alpha</SUB>_, but none
has been found to be closely associated with a hard X-ray burst or
a microwave event. Metric spikes are consistent with energy release
at high altitudes producing low energy electron beams. If the spikes
are caused by the same electron population as the type III bursts,
its acceleration site must be below or in close proximity to the
spike source.
---------------------------------------------------------
Title: The High Energy Solar Spectroscopic Imager - HESSI
Authors: Dennis, B. R.; Crannell, C. J.; Holman, G. D.; Ramaty,
R.; von Rosenvinge, T. T.; Benz, A.; Bornmann, P. L.; Brown, J. C.;
Canfield, R. C.; Emslie, A. G.; Enome, S.; Kosugi, T.; Hudson, H. S.;
Hurford, G. J.; Lin, R. P.; Ling, J. C.; Madden, N. W.; van Beek,
H. F.; Vilmer, N.
1996AAS...188.7016D Altcode: 1996BAAS...28..941D
HESSI will investigate the physics of particle acceleration and energy
release in solar flares through an unprecedented combination of high
resolution imaging and spectroscopy of X-rays and gamma rays from 2
keV to 20 MeV during the next solar maximum. It uses Fourier-transform
imaging with 12 bi-grid modulation collimators and cooled germanium and
silicon detectors mounted on a Sun-pointed spin-stabilized spacecraft in
a low-altitude equatorial orbit. HESSI will carry out the first imaging
spectroscopy in hard X-rays with 2 arcseconds angular resolution, time
resolution to tens of ms, and ~ 1 keV energy resolution; the first
gamma-ray line spectroscopy from a spacecraft with ~ 1 keV energy
resolution; and the first gamma-ray line and continuum imaging with
20 arcseconds angular resolution.
---------------------------------------------------------
Title: Prompt Radio Emission of Supernovae: Plasma Radiation
Alternative?
Authors: Benz, A. O.; Hafliger, P. D.
1996ASPC...93..150B Altcode: 1996ress.conf..150B
No abstract at ADS
---------------------------------------------------------
Title: Soft X-Ray (Yohkoh) and Radio (VLA) Observations of Solar
Narrowband, Millisecond Spike Events
Authors: Krucker, Sam; Benz, Arnold O.; Aschwanden, Markus J.
1996ASPC..111..129K Altcode: 1997ASPC..111..129K
The source regions of metric spike events are investigated on Yohkoh
soft X-ray (SXR) maps. The spikes are identified by the spectrometer
Phoenix between 300 MHz and 360 MHz and are associated with groups
of type III bursts at lower frequencies reaching also the decametric
range. The Very Large Array (VLA) provides simultaneously spatial
information at 333 MHz and 1445 MHz. Similar to the previous VLA
observation of a metric spike event, the new data are consistent with a
high altitude of the spike sources of about 5×10<SUP>10</SUP>cm above
the photosphere. The additionally available SXR data for one of the
presented events give the following new information: (i) The spike
sources occur near open field lines and near regions of a slightly
enhanced SXR flux relative to the ambient plasma. (ii) Contrary to SXR
observations of type III bursts without metric spike activity, no SXR
jet is observed. (iii) At low altitude, a weak SXR enhancement occurs,
peaking about 60 s after the spike event. The SXR source and the spike
sources can be connected by potential field lines. The observations
corroborate a model in which a metric spike event is attributed to
an energy release region at high altitude, while upwards propagating
electrons produce type III bursts and downward moving electrons are
responsible for SXR emission of heated plasma.
---------------------------------------------------------
Title: Coherent Radio Emission of Solar Flares in the Decimeter Range
(0.3-3 GHz)
Authors: Benz, A. O.
1996ASPC...93..347B Altcode: 1996ress.conf..347B
No abstract at ADS
---------------------------------------------------------
Title: Nonthermal Microwave Emission from F Dwarfs: 71 Tau; alpha For;
and Open Cluster/Moving Group Membership
Authors: Gudel, M.; Benz, A. O.; Guinan, E. F.; Schmitt, J. H. M. M.
1996ASPC...93..306G Altcode: 1996ress.conf..306G
No abstract at ADS
---------------------------------------------------------
Title: Very long baseline interferometry of solar microwave radiation.
Authors: Benz, A. O.; Graham, D.; Isliker, H.; Andersson, C.;
Koehnlein, W.; Mantovani, F.; Umana, G.
1996A&A...305..970B Altcode:
The solar 2.297 GHz radiation has been observed and investigated by
very long baseline interferometry (VLBI). The radio observatories of
Medicina, Noto, Onsala, and Weilheim were involved yielding baselines
between 360km and 3800km and a nominal resolution of 0.09"to 0.008"or
70 to 6km on the Sun. This solar VLBI network operated successfully
with at least one useful baseline for 167 hours during five campaigns
at the maximum of the most recent activity cycle in 1989 and 1990. The
Phoenix spectrometer at Zurich was used to detect and classify the
radio bursts. A total of 59 solar radio bursts were observed at the
VLBI frequency, of which 26 events were analyzed, including narrowband
millisecond spikes, type III bursts, patches, pulsations, and diffuse
broadband (gyrosynchrotron) emission. Neither during bursts nor in
quiet times significant fringes were detected. All sources were well
resolved including the narrowband spikes. We interpret the result
in terms of relatively large radio sources and/or by scattering to
apparent source sizes larger than the lowest resolution and by the
lack of `speckles'. The results are consistent with scattering of
the radio emission in the corona. The upper and lower limits of the
source size of spikes are discussed. For the apparent source size,
l_a_, we find 65km<l_a_<16000km, and for the original source
size before scattering l<~200km.
---------------------------------------------------------
Title: The Enigmatic FOV Star 47 CAS
Authors: Gudel, M.; Benz, A. O.; Guinan, E. F.; Schmitt, J. H. M. M.
1996ASPC...93..309G Altcode: 1996ress.conf..309G
No abstract at ADS
---------------------------------------------------------
Title: Radio Spectra of dMe and dKe Stars
Authors: Gudel, M.; Benz, A. O.
1996ASPC...93..303G Altcode: 1996ress.conf..303G
No abstract at ADS
---------------------------------------------------------
Title: Variability of UV Ceti in Radio and Soft X-ray Emission
Authors: Benz, A. O.; Gudel, M.; Schmitt, J. H. M. M.
1996ASPC...93..291B Altcode: 1996ress.conf..291B
No abstract at ADS
---------------------------------------------------------
Title: Radio Emission of Dwarf Novae
Authors: Benz, A. O.; Gudel, M.; Mattei, J. A.
1996ASPC...93..188B Altcode: 1996ress.conf..188B
No abstract at ADS
---------------------------------------------------------
Title: Location of Type I Radio Continuum and Bursts on YOHKOH Soft
X-ray Maps
Authors: Krucker, S.; Benz, A. O.; Aschwanden, M. J.; Bastian, T. S.
1996mpsa.conf..441K Altcode: 1996IAUCo.153..441K
No abstract at ADS
---------------------------------------------------------
Title: Radio Astronomical Diagnostics
Authors: Benz, A. O.
1996LNP...468..213B Altcode: 1996plas.conf..213B
A brief introduction into the diagnostic capabilities and
results of radio waves from coronal plasmas of the Sun and other
late-type stars is presented. These coronal emissions show that the
plasma is in a dynamic state with time scale down to a few tens of
microseconds. Gyrosynchrotron emission in flares reveal the presence of
relativistic electrons, which, in active stars, seem to persist even
during quasi-quiet (quiescent) intervals. Coherent emissions of solar
electron beams by the two-stream instability has been discovered up to
8 GHz. Particularly efficient emitters are trapped electrons having
a loss-cone distribution. This is probably the most frequent cause
of highly polarized stellar radio flares. Of greatest interest are
emissions by unstable currents and shocks, which have been identified
in the solar corona. A general introduction into some basic theories,
but not a review, is given, illustrated with recent observations. A
more extended introduction can be found in Benz (1993).
---------------------------------------------------------
Title: Solar Electron Beams Detected in Hard X-Rays and Radio Waves
Authors: Aschwanden, Markus J.; Benz, Arnold O.; Dennis, Brian R.;
Schwartz, Richard A.
1995ApJ...455..347A Altcode:
We present a statistical survey of electron beam signatures that are
detected simultaneously at hard X-ray (HXR) and radio wavelengths
during solar flares. For the identification of a simultaneous event we
require a type III (normal-drifting or reverse-slope-drifting) radio
burst that coincides (within ± 1 s) with a significant (≥ 3 σ HXR
pulse of similar duration (≥ 1 s). Our survey covers all HXRBS/SMM and
BATSE/CGRO flares that were simultaneously observed with the 0.1-1 GHz
spectrometer Ikarus or the 0.1-3 GHz spectrometer Phoenix of ETH Zurich
during 1980-1993. The major results and conclusions are as follows:
<P />1. We identified 233 HXR pulses (out of 882) to be correlated with
type III-like radio bursts: 77% with normal-drifting type III bursts,
34% with reverse-slope (RS)-drifting bursts, and 13% with oppositely
drifting (III + RS) burst pairs. The majority of these cases provide
evidence for acceleration of bidirectional electron beams. <P />2. The
detailed correlation with type III-like radio bursts suggests that most
of the subsecond fluctuations detectable in ≥ 25 keV HXR emission
are related to discrete electron injections. This is also supported
by the proportionality of the HXR pulse duration with the radio burst
duration. The distribution of HXR pulse durations W<SUB>X</SUB> is
found to have an exponential distribution, i.e., N(W<SUB>X</SUB>) ∝
exp (-W<SUB>X</SUB>/0.25 s) in the measured range of W<SUB>X</SUB> ≍
0.5-1.5 s. <P />3. From oppositely drifting radio burst pairs we infer
electron densities of n<SUB>e</SUB> = 10<SUP>9</SUP>-10<SUP>10</SUP>
cm<SUP>-3</SUP> at the acceleration site. From the absence of a
frequency gap between the simultaneous start frequencies of upward and
downward drifting radio bursts, we infer an upper limit of L ≤ 2000
km for the extent of the acceleration site and an acceleration time of
Δt ≤ 3 ms for the (≥ 5 keV) radio-emitting electrons (in the case
of parallel electric fields). <P />4. The relative timing between HXR
pulses and radio bursts is best at the start frequency (of earliest
radio detection), with a coincidence of ≲0.1 s in the statistical
average, while the radio bursts are delayed at all other frequencies
(in the statistical average). The timing is consistent with the scenario
of electron injection at a mean coronal height of h ≍ 10<SUP>4</SUP>
km. The radio-emitting electrons are found to have lower energies
(≳ 5 keV) than the ≥ 25 keV HXR-emitting electrons. <P />5. The
modulated HXR flux that correlates with electron beam signatures
in radio amounts to 2%-6% of the total HXR count rate (for BATSE
flares). The associated kinetic energy in electrons is estimated to be E
= 4 × 10<SUP>22</SUP>-10<SUP>27</SUP> ergs per beam, or N<SUB>e</SUB>
= 4 × 10<SUP>28</SUP>-10<SUP>33</SUP> electrons per beam, considering
the spread from the smallest to the largest flare detected by HXRBS. <P
/>6. The average drift rate of propagating electron beams is found
here to be [dv/dt] = 0.10ν<SUP>1.4</SUP> MHz km s<SUP>-1</SUP> in
the frequency range of ν = 200-3000 MHz, which is lower than expected
from the Alvarez & Haddock relation for frequencies ≤ 550 MHz. <P
/>7. The frequency distributions of HXR fluxes (F<SUB>x</SUB>) and radio
type III burst fluxes (F<SUB>R</SUB>), which both can be characterized
by a power law, are found to have a significantly different slope,
i.e., N(F<SUB>x</SUB>) ∝ F<SUB>x</SUB><SUP>-1.87</SUP> versus
N(F<SUB>R</SUB>) ∝ F<SUB>R</SUB><SUP>-1.28</SUP>. The difference
in the slope is attributed to the fundamental difference between
incoherent and coherent emission processes. <P />In summary, these
findings suggest a flare scenario in which bidirectional streams of
electrons are accelerated during solar flares at heights of 10 km
above the photosphere in rather compact regions (L ≲ 2000 km). The
acceleration site is likely to be located near the top of flare loops
(defined by HXR double footpoints) or in the cusp above, where electrons
have also access to open field lines or larger arches. The observed
bidirectionality of electron beams favors acceleration mechanisms with
oppositely directed electric fields or stochastic acceleration in an
X-type reconnection geometry.
---------------------------------------------------------
Title: First VLA observation of a solar narrowband, millisecond
spike event.
Authors: Krucker, S.; Aschwanden, M. J.; Bastian, T. S.; Benz, A. O.
1995A&A...302..551K Altcode:
The first spatially resolved observation of solar, narrowband spikes
in two dimensions is presented. The 'metric' spikes around 333MHz
are classified by the broadband spectrometer Phoenix (ETH Zuerich),
whereas the simultaneously observing Very Large Array (VLA) provides
high angular resolution images of the solar disc. At lower frequencies,
a group of associated type III bursts is detected. The spikes occur
at high altitude (=~4.5x10^10^cm above the photosphere), and at least
3 separated locations of emission can be identified. The different
spike sources are separated by up to 130" and show different degrees of
polarization. Spikes and type III bursts have the same sense of circular
polarization, and according to the extrapolated potential field lines,
the polarization of the different spike sources is in x-mode. With
a delay of 42s, a thermal source appears on the same extrapolated
potential field lines as the spikes at the second frequency of the
VLA (1446MHz). The location of the energy release relative to the
spikes source is discussed. A scenario is proposed where the energy
is released in or near the spike source, and in which the spikes,
the type III bursts and the thermal source originate from the same
energy release. Hot electrons expanding along the field lines generate
a type III burst (upward direction) and heat the underlying dense plasma
(thermal source).
---------------------------------------------------------
Title: Microwave emission from X-ray bright solar-like stars: the
F-G main sequence and beyond.
Authors: Guedel, M.; Schmitt, J. H. M. M.; Benz, A. O.
1995A&A...302..775G Altcode:
A sample of F and G main sequence stars and slightly evolved F and G
stars, selected as the apparently strongest X-ray sources in their class
as detected in the ROSAT All-Sky Survey (RASS), has been observed in
microwaves to search for coronae with strong heating and populations
of nonthermal particles. The microwave flux densities were observed
with the VLA at 8.4GHz. Radio emission has been detected from nine
targets, in both luminosity classes V and IV. Since known or unknown
cool companions in binary systems may cause spurious results, we have
checked the available spectroscopic and astrometric data, including
unpublished CORAVEL observations. There is at least one detected object
in each of the four spectral and luminosity classes of stars, FIV,
FV, GIV, and GV for which no known companion can be made responsible
for the observed emission. A very luminous X-ray and radio source is
identified with the F0 V star HD 12230, a member of the Pleiades Moving
Group with an age of the order of 50-70Myr. HD 129333 (EK Dra), a G0 V
target presumably of the same age, is detected also, and the X-ray and
radio modulations agree with the optically measured rotation. On the
other hand, three very old stars that are leaving the main sequence
and are moving towards the subgiant luminosity class are found to be
strong X-ray and radio emitters; in the case of HD 20010, an F8 IV star,
the hypothetical existence of an unknown spectroscopic companion would
contradict astrometric data. These stars appear to define a new class
of radio-luminous coronal stars. The observed microwave flux densities
agree with the ratio of radio to X-ray fluxes of other active coronal
stars. We report sensitive upper limits for all non-detections, up to an
order of magnitude lower than in previous surveys. These observations
yield first systematic evidence that stars close to the solar spectral
type can maintain considerable nonthermal electron populations in their
coronae, possibly due to a mechanism that involves coronal heating. They
provide the crucial link between the study of the solar corona and
of active coronal stars (the "solar-stellar connection"), and bridge
the remaining gaps on the radio main sequence between the cooler stars
and chemically peculiar Ap stars. Further, they support the view that
young, near-Zero-Age Main-Sequence (ZAMS) stars are able to continually
produce luminous radio emission after their arrival on the ZAMS. The
strong activity resurgence in the sample of old stars moving off the
main sequence may be related to an increase in convective turnover time
as the internal structuring of the stars changes; this is of potential
interest for the study of the stellar interior of evolved stars.
---------------------------------------------------------
Title: The corona of the young solar analog EK Draconis.
Authors: Guedel, M.; Schmitt, J. H. M. M.; Benz, A. O.; Elias,
N. M., II
1995A&A...301..201G Altcode:
First coronal microwave and new soft X-ray observations of the
very active, near-Zero-Age Main-Sequence (ZAMS) dG0e star EK Dra =
HD 129333 show that this analog of the young Sun is more luminous
in both emissions than most single M-dwarf flare stars. Variations
in the 8.4GHz flux include modulation with the optically determined
rotation period of 2.7 days. This result points to a non-uniform
filling of the corona with energetic electrons due to an incomplete
coverage of the surface with active regions and a source volume
that is not concentric with the star. The radio luminosity varying
between logL_R_=13.6 and 14.6 (L_R_ in erg/s/Hz) shows evidence for
unpolarized gyrosynchrotron flares, while strongly polarized flares
were absent during the observations. This star is the first young,
truly solar-like main sequence G star discovered in microwaves. Having
just arrived on the main sequence, it conclusively proves that young,
solar-like G stars can maintain very high levels of radio emission
after their T Tau phase. The X-ray observations were obtained from the
ROSAT All-Sky Survey (RASS). The average X-ray luminosity amounts to
logL_X_=29.9 (L_X_ in erg/s). A Raymond-Smith type plasma model fit
yields two plasma components at temperatures of 1.9 and 10MK, with
volume emission measures of 1.2 and 2.5.10^52^cm^-3^, respectively. The
X-ray light curve is significantly variable, with the photon count rate
from the cooler plasma being strongly modulated by the rotation period;
the emission from the hotter plasma is only weakly variable. Modeling
of the source distribution in the stellar corona yields electron
densities of the order of 4.10^10^cm^-3^ or higher for the cool plasma
component. It indicates that a considerable portion of EK Dra's high
X-ray luminosity is due to high-density plasma rather than large
emission volume. Parameters for an X-ray flare indicate an electron
density of 1.75.10^11^cm^-3^ and a source height of (1-2).10^10^cm,
compatible with a few times the scale height of the cooler plasma
component.
---------------------------------------------------------
Title: Location of Type I Radio Continuum and Bursts on YOHKOH Soft
X-Ray Maps
Authors: Krucker, S.; Benz, A. O.; Aschwanden, M. J.; Bastian, T. S.
1995SoPh..160..151K Altcode:
A solar type I noise storm was observed on 30 July, 1992 with the
radio spectrometer Phoenix of ETH Zürich, the Very Large Array (VLA)
and the soft X-ray (SXR) telescope on board theYohkoh satellite. The
spectrogram was used to identify the type I noise storm. In the VLA
images at 333 MHz a fully left circular polarized (100% LCP) continuum
source and several highly polarized (70% to 100% LCP) burst sources
have been located. The continuum and the bursts are spatially separated
by about 100″ and apparently lie on different loops as outlined
by the SXR. Continuum and bursts are separated in the perpendicular
direction to the magnetic field configuration. Between the periods of
strong burst activities, burst-like emissions are also superimposed
on the continuum source. There is no obvious correlation between the
flux density of the continuum and the bursts. The burst sources have
no systematic motion, whereas the the continuum source shows a small
drift of ≈ 0.2″ min<SUP>−1</SUP> along the X-ray loop in the
long-time evolution. The VLA maps at higher frequency (1446 MHz) show
no source corresponding to the type I event. The soft X-ray emission
measure and temperature were calculated. The type I continuum source
is located (in projection) in a region with enhanced SXR emission,
a loop having a mean density of «n<SUB>e</SUB>» = (1.5 ± 0.4) ×
10<SUP>9</SUP> cm<SUP>−3</SUP> and a temperature ofT = (2.1 ± 0.1)
× 10<SUP>6</SUP> K. The centroid positions of the left and right
circularly polarized components of the burst sources are separated
by 15″-50″ and seem to be on different loops. These observations
contradict the predictions of existing type I theories.
---------------------------------------------------------
Title: VLBI observations of single main-sequence M stars.
Authors: Benz, A. O.; Alef, W.; Guedel, M.
1995A&A...298..187B Altcode:
Single dMe stars have been observed at 18cm wavelength by
intercontinental very long baseline interferometry (VLBI). Here we
report on two stars, EQ Peg B and AD Leo, that have been detected
during flares, and one of them also at a relatively low (`quiescent')
state. There are no indications that any of the stars has been spatially
resolved. Upper limits on the size of the radio sources are less than
1.9 stellar diameters for flares and less than 3.7 stellar diameters
for quiescence. This yields directly observed brightness temperatures
beyond 2x10^10^K for flares and 2x10^9^K in quiescence. The observations
suggest that the size of the closed corona is less than predicted from
pressure equilibrium between plasma and magnetic field. An extent of the
order of one density scale height is compatible with the observations.
---------------------------------------------------------
Title: Sequences of Correlated Hard X-Ray and Type III Bursts during
Solar Flares
Authors: Aschwanden, Markus J.; Montello, Maria L.; Dennis, Brian R.;
Benz, Arnold O.
1995ApJ...440..394A Altcode:
Acceleration and injection of electron beams in solar flares can be
traced from radio type III (or type U) bursts and correlated hard
X-ray pulses with similar timescales and nonthermal spectra. We
perform a systematic survey of such correlated radio and hard X-ray
(HXR) pulses with timescales of less than or approximately 2 s in
flares simultaneously observed with the radio spectrometer Ikarus and
the Hard X-Ray Burst Spectrometer (HXRBS) on solar maximum mission
(SMM). We applied an epoch-folding technique to enhance correlated
time patterns in burst sequences at the two wavelengths. We present
the results from the strongest (10) flares with a HXRBS count
rate greater than or = 3000 counts/s, which have a satisfactory
signal-to-noise ratio for subsecond pulses. The major findings of
this study are presented. These observations strongly suggest that
particle acceleration in solar flares occurs in a pulsed mode where
electron beams are simultaneously injected in upward and downward
directions. Since the sequences of correlated HXR and radio bursts
show identical durations and intervals at the two wavelengths, they
are believed to reflect most directly the temporal dynamics of the
underlying common accelerator. As a consequence, thick-target models
should be reconsidered under the aspect of electron injection with
pulse durations of 0.2-2.0 s and duty cycles of approximately = 50%.
---------------------------------------------------------
Title: A bright X-ray and radio corona on the F0V star 47 Cas?
Authors: Guedel, M.; Schmitt, J. H. M. M.; Benz, A. O.
1995A&A...293L..49G Altcode:
X-ray and microwave observations of the nearby A7-F0V star 47 Cas
reveal indications for extraordinarily strong coronal activity,
characterised by X-ray and radio luminosities of L_X_=2.9x10^30^erg/s
and L_R_=1.1x10^15^erg/s/Hz, respectively, and the presence of
very strong X-ray flares. The rapidly rotating star is not known
to possess a spectroscopic companion that may be held responsible
for the observed emissions. Interpreting the X-ray modulation as
rotational modulation and combining the value of the rotation period
with the optically determined vsini, the stellar radius is found to
be consistent with the photometrically determined radius. This may
be the first non-interacting, early F V star discovered as a strong,
nonthermal radio source. From kinematic arguments, 47 Cas is a likely
member of the Pleiades Moving Group, and may thus be very young.
---------------------------------------------------------
Title: Chromospheric Evaporation and Decimetric Radio Emission in
Solar Flares
Authors: Aschwanden, Markus J.; Benz, Arnold O.
1995ApJ...438..997A Altcode:
We have discovered decimetric signatures of the chromospheric
evaporation process. Evidence for the radio detection of chromospheric
evaporation is based on the radio-inferred values of (1) the electron
density, (2) the propagation speed, and (3) the timing, which are
found to be in good agreement with statistical values inferred from
the blueshifted Ca XIX soft X-ray line. The physical basis of our
model is that free-free absorption of plasma emission is strongly
modified by the steep density gradient and the large temperature
increase in the upflowing flare plasma. The steplike density increase
at the chromospheric evaporation front causes a local discontinuity
in the plasma frequency, manifested as almost infinite drift rate in
decimetric type III bursts. The large temperature increase of the
upflowing plasma considerably reduces the local free-free opacity
(due to the T<SUP>-3/2</SUP> dependence) and thus enhances the
brightness of radio bursts emitted at the local plasma frequency near
the chromospheric evaporation front, while a high-frequency cutoff
is expected in the high-density regions behind the front, which can
be used to infer the velocity of the upflowing plasma. From model
calculations we find strong evidence that decimetric bursts with a
slowly drifting high-frequency cutoff are produced by fundamental plasma
emission, contrary to the widespread belief that decimetric bursts
are preferentially emitted at the harmonic plasma level. We analyze
21 flare episodes from 1991-1993 for which broadband (100-3000 MHz)
radio dynamic spectra from Pheonix, hard X-ray data from (BATSE/CGRO)
and soft X-ray data from Burst and Transient Source Experiment/Compton
Gamma Ray Observatory (GOES) were available.
---------------------------------------------------------
Title: Coronal Magnetic Energy Releases
Authors: Benz, Arnold O.; Krüger, Albrecht
1995LNP...444.....B Altcode: 1995cmer.conf.....B
This book brings together a variety of review articles on dynamical
phenomena in the solar corona in order to work out the unifying
aspects of magnetic energy releases. The experimental data from
groundbased methods of radio astronomy as well as from satellites are
also discussed. The book addresses researchers in astrophysics, and
planetary science but should also be accessible to graduate students.
---------------------------------------------------------
Title: Radio Emission from Flares in Single Late-type Stars
Authors: Benz, Arnold O.
1995LNP...454...23B Altcode: 1995IAUCo.151...23B; 1995LNP...454...21B; 1995flfl.conf...23B
Radio observations provide the most direct information on nonthermal
electrons in stellar flares and in the coronae of late-type
stars. Radio emissions of single main-sequence F, G, and of many K
stars have recently been discovered, in addition to the well-known
dwarf M stars. Their long-duration radio flares with low circular
polarization, slow variations and broad bandwidth can be attributed
to gyrosynchrotron emission of mildly relativistic electrons. The
same holds for the low-level (quiescent) radio emission. On the other
hand, highly polarized radio flares of M stars have been interpreted
by coherent emissions from loss-cone instabilities of magnetically
trapped electrons. These conjectures are consistent with recent VLBI
observations. The identification of the radio emission process allows
to estimate the high-energy component of the flare and compare it to
the total flare energy. The weakly polarized radio emission may serve
as a proxy for hard X-ray signatures of relativistic electrons. The
fraction of primary energy released into energetic electrons then
appears to be large and similar to solar flares.
---------------------------------------------------------
Title: Flares and Coronal Heating in the Sun and Stars
Authors: Benz, A. O.
1995LNP...444....1B Altcode: 1995cmer.conf....1B
Many forms of energy input into coronae have been proposed as the
dominant heating mechanism. Here I review topical aspects of impulsive
releases of magnetic energy. Several solar phenomena from bright
points to coronal mass ejections are attributed to free magnetic energy
apparently available in the corona. The possibility that magnetic energy
release is the dominant energy input into the corona is discussed for
the Sun with special emphasis on small radio events, with negative
results. The evidence is better, however, for active stars where a
correlation between thermal radiation and gyrosynchrotron emission
by energetic electrons has been found recently. It suggests that a
flare-like release of magnetic energy is the dominant coronal heating
process of active, rapidly rotating stars. However, the required cadence
of flares has not (yet) been found. The link between stellar coronal
heating and magnetic energy release is not clear as long as the various
flare-like phenomena in the solar corona are not better understood.
---------------------------------------------------------
Title: Stellar Remnants
Authors: Benz, A. O.; Courvoisier, T. J. -L.
1995stre.conf.....B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Plasma Astrophysics
Authors: Benz, A. O.; van Oss, R. F.
1994SoPh..154..203B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Electron beams in solar flares
Authors: Aschwanden, Markus J.; Dennis, Brian R.; Benz, Arnold O.
1994umd..reptR....A Altcode:
A list of publications resulting from this program includes 'The
Timing of Electron Beam Signatures in Hard X-Ray and Radio: Solar
Flare Observations by BATSE/Compton Gamma-Ray Observatory and PHOENIX';
'Coherent-Phase or Random-Phase Acceleration of Electron Beams in Solar
Flares'; 'Particle Acceleration in Flares'; 'Chromospheric Evaporation
and Decimetric Radio Emission in Solar Flares'; 'Sequences of Correlated
Hard X-Ray and Type 3 Bursts During Solar Flares'; and 'Solar Electron
Beams Detected in Hard X-Rays and Radiowaves.' Abstracts and reprints
of each are attached to this report.
---------------------------------------------------------
Title: Discovery of Microwave Emission from Four Nearby Solar-Type
G Stars
Authors: Gudel, Manuel; Schmitt, Jurgen H. M. M.; Benz, Arnold O.
1994Sci...265..933G Altcode:
Radio waves from the sun were detected 50 years ago, but the
microwave detection of other single solar-type stars has remained
a challenge. Here, the discovery of four solar-type radio stars is
reported. These "solar twin" G stars are radio sources up to 3000 times
stronger than the quiet sun. The microwaves most likely originate from
a large number of relativistic electrons, possibly produced along
with coronal heating, a process that is not understood. Two of the
stars are younger than the sun and rotate more rapidly; the dynamo
process in the stellar interior is therefore presumably more vigorous,
resulting in enhanced coronal activity. One of the detections, however,
is an old, metal-deficient G dwarf.
---------------------------------------------------------
Title: Coherent-Phase or Random-Phase Acceleration of Electron Beams
in Solar Flares
Authors: Aschwanden, Markus J.; Benz, Arnold O.; Montello, Maria L.
1994ApJ...431..432A Altcode:
Time structures of electron beam signatures at radio wavelengths
are investigated to probe correlated versus random behavior in solar
flares. In particular we address the issue whether acceleration and
injection of electron beams is coherently modulated by a single source,
or whether the injection is driven by a stochastic (possibly spatially
fragmented) process. We analyze a total of approximately = 6000 type III
bursts observed by Ikarus (Zurich) in the frequency range of 100-500
MHz, during 359 solar flares with simultaneous greater than or = 25
keV hard X-ray emission, in the years 1890-1983. In 155 flares we find
a total of 260 continuous type III groups, with an average number of
13 +/- 9 bursts per group, a mean duration of D = 12 +/- 14 s, a mean
period of P = 2.0 +/- 1.2 s, with the highest burst rate at a frequency
of nu = 310 +/- 120 MHz. Pulse periods have been measured between 0.5
and 10 s, and can be described by an exponential distribution, i.e.,
N(P) varies as e <SUP>-P/1.0s</SUP>. The period shows a frequency
dependence of P(nu)=46(exp-0.6)<SUB>MHz</SUB>s for different flares,
but is invariant during a particular flare. We measure the mean
period P and its standard deviation sigma <SUB>p</SUB> in each type
III group, and quantify the degree of periodicity (or phase-coherence)
by the dimensionless parameter sigma <SUB>p</SUB>P. The representative
sample of 260 type III burst groups shows a mean periodicity of sigma
<SUB>p/P</SUB> = 0.37 +/- 0.12, while Monte Carlo simulations of an
equivalent set of truly random time series show a distinctly different
value of sigma <SUB>p</SUB>P = 0.93 +/- 0.26. This result indicates
that the injection of electron beams is coherently modulated by a
particle acceleration source which is either compact or has a global
organization on a timescale of seconds, in contrast to an incoherent
acceleration source, which is stochastic either in time or space. We
discuss the constraints on the size of the acceleration region resulting
from electron beam propagation delays and from Alfvenic synchronization
during a pulse period. We discuss two periodic processes in flares,
which potentially control quasi-periodic particle acceleration: (1)
MHD oscillations, and (2) current sheets with oscillatory dynamics.
---------------------------------------------------------
Title: Particle Acceleration in Flares
Authors: Benz, A. O.; Kosugi, T.; Aschwanden, M. J.; Benka, S. G.;
Chupp, E. L.; Enome, S.; Garcia, H.; Holman, G. D.; Kurt, V. G.;
Sakao, T.; Stepanov, A. V.; Volwerk, M.
1994SoPh..153...33B Altcode:
Particle acceleration is intrinsic to the primary energy release in
the impulsive phase of solar flares, and we cannot understand flares
without understanding acceleration. New observations in soft and hard
X-rays, γ-rays and coherent radio emissions are presented, suggesting
flare fragmentation in time and space. X-ray and radio measurements
exhibit at least five different time scales in flares. In addition,
some new observations of delayed acceleration signatures are also
presented. The theory of acceleration by parallel electric fields is
used to model the spectral shape and evolution of hard X-rays. The
possibility of the appearance of double layers is further investigated.
---------------------------------------------------------
Title: Directivity of the Radio Emission from the K1 Dwarf Star
AB Doradus
Authors: Lim, Jeremy; White, Stephen M.; Nelson, Graam J.; Benz,
Arnold O.
1994ApJ...430..332L Altcode:
We present measurements of the spectrum and polarization of the
flaring radio emission from the K1 dwarf star AB Doradus, together with
previously reported single frequency measurements (with no polarization
information) on 3 other days. On all 4 days spanning a 6 month period,
the emission was strong and, when folded with the stellar rotation
period, showed similar time variations with two prominant peaks
at phase 0.35 and 0.75. These peaks coincide in longitude with two
large starspots identified from the stellar optical light curve and
have half-powe widths as small as 0.1 rotations and no larger than
0.2 rotations. The modulated emission shows no measurable circular
polarization, and its two peaks have different turnover frequencies.
---------------------------------------------------------
Title: Plasma diagnostics of the solar corona using decimetric radio
waves (review)
Authors: Benz, A. O.
1994R&QE...37..525B Altcode:
The solar corona is a very dynamic plasma on time scales down to a few
tens of microseconds. The various emissions at decimetric wavelength
are briefly reviewed. Several of them seem to be caused by energetic
(non-thermal) electrons accelerated in flares or flare-like processes
releasing free magnetic energy. The use of decimetric radiation
as diagnostics of the acceleration process, the ambient plasma,
and the non-thermal particles requires a solid understanding of the
emission process. Although we are still far from this in most cases,
some information can already be derived from the observations.
---------------------------------------------------------
Title: X-ray/microwave ratio of flares and coronae
Authors: Benz, A. O.; Guedel, M.
1994A&A...285..621B Altcode:
We have carried out plasma diagnostics of solar flares using soft X-ray
(SXR) and simultaneous microwave observations and have compared the
ratio of X-ray to microwave luminosities of solar flares with various
active late-type stars available in the published literature. Both
the SXR low-level (`quiescent') emission from stellar coronae and the
flaring emission from the Sun and stars are generally interpreted
as thermal radiations of coronal plasmas. On the other hand, the
microwave emission of stars and solar flares is generally attributed
to an extremely hot or nonthermal population of electrons. Solar flare
SXR are conventionally measured in a narrower and harder passband
than the stellar sources. Observations of the GOES-2 satellite in
two energy channels have been used to estimate the luminosity of
solar flares as it would appear in the ROSAT satellite passband. The
solar and stellar flare luminosities fit well at the lower end of the
active stellar coronae. The flare SXR/microwave ratio is similar to
the ratio for stellar coronae. The average ratio follows a power-law
relation L_X_{prop.to}L_R_^0.73+/-0.03^ over 10 orders of magnitude
from solar microflares to RS CVn and FK Com-type coronae. Dwarf Me
and Ke stars, and RS CVn stars are also compatible with a linear
SXR/microwave relation, but the ratio is slightly different for each
type of star. Considering the differences between solar flares, stellar
flares and the various active stellar coronae, the similarity of the
SXR/microwave ratios is surprising. It suggests that the energetic
electrons in low-level stellar coronae observed in microwaves are
related in a similar way to the coronal thermal plasma as flare
electrons to the flare thermal plasma, and, consequently, that the
heating mechanism of active stellar coronae is a flare-like process.
---------------------------------------------------------
Title: Multiple frequency spike emission during solar flares
Authors: Krucker, S.; Benz, A. O.
1994SSRv...68..247K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Periodic or random acceleration in solar flares?
Authors: Aschwanden, Markus J.; Benz, Arnold O.
1994SSRv...68..193A Altcode:
The issue whether acceleration and injection of electron beams is
coherently modulated by a single quasi-periodic source, or whether the
injection is driven by a stochastic process in time or (eventually
fragmented) in space, is investigated by menas of a periodicity
analysis of metric type III bursts. We analyze 260 continuous type
III groups observed byIkarus (ETH Zurich) in the frequency range
of 100 500 MHz during 359 solar flares with simultaneous ≥25 keV
hard X-ray emission, in the years 1980 1983. Pulse periods have been
measured between 0.5 and 10 s, and can be described by an exponential
distribution, i.e.N(P) ∝e <SUP>-P/1.0s</SUP>. We measure the mean
periodP and its standard deviation σp in each type III group, and
quantify the degree of periodicity by the dimensionless parameter
σp/P. The representative sample of 260 type III burst groups shows a
mean periodicity of σp/P=0.37±0.12, while Monte-Carlo simulations
of an equivalent set of truly random time series show a distinctly
different value of σp/P=0.93±0.26. This result suggests that the
injection of electron beams is periodically modulated by a particle
acceleration source which is either compact or has a global organization
on a time scale of seconds.
---------------------------------------------------------
Title: On deterministic chaos, stationarity, periodicity and
intermittency in coronal bursts and flares
Authors: Isliker, H.; Benz, A. O.
1994SSRv...68..185I Altcode:
Solar and stellar flares are highly structured in space and in time,
as is indicated for example by their radio signatures: the narrowband
spikes, type III, type II and IV, and pulsation events. Structured in
time are also the not flare related type I events (noise storms). The
nature of this observationally manifest fragmentation is still
not clear. Either, it can be due to stochastic boundary or initial
conditions of the respective processes, such as inhomogeneities in the
coronal plasma. Or else, a deterministic non-linear process is able to
cause complicated patterns of these kinds. We investigate the nature
of the fragmentation in time. The properties of processes we enquire
are stationarity, periodicity, intermittency, and, with dimension
estimating methods, we try to discriminate between stochastic and
low-dimensional deterministic processes. Since the measured time
series are rather short, the dimension estimate methods have to be
used with care: we have developed an extended dimension estimate
procedure consisting of five steps. Among others, it comprises again
the questions of stationarity and intermittency, but also the more
technical problems of temporal correlations, judging scaling and
convergence, and limited number of data points (statistical limits). We
investigate 3 events of narrowband spikes, 13 type III groups, 10 type
I storms, 3 type II bursts and 1 type IV event of solar origin, and
3 pulsation-like events of stellar origin. They have in common that
all of them have stationary phases, periodicities are rather seldom,
and intermittency is quite abundant. However, the burst types turn out
to have different characteristics. None of the investigated time series
reveals a low-dimensional behaviour. This implies that they originate
from complex processes having dimensions (degrees of freedom) larger
than about 4 to 6, which includes infinity,i. e. stochasticity. The
lower limit of the degrees of freedom is inferred from numerical
experiments with known chaotic systems, using time series of similar
lengths, and it depends slightly on the burst types.
---------------------------------------------------------
Title: The frequency ratio of bands of microwave spikes during
solar flares
Authors: Krucker, S.; Benz, A. O.
1994A&A...285.1038K Altcode:
The frequency ratio of narrowband millisecond spikes during 17
solar flares has been measured and analyzed. The observations have
been made in the frequency range 0.3-3 GHz with the ETH Zuerich
spectrometers. The events have been selected from spectrograms for
their harmonic structure. Auto-correlation in frequency yields the
following major results: (i) The ratio of the harmonic spike groups
is not integer, and therefore the term 'harmonic' is strictly speaking
inappropriate. (ii) The ratios are independent of frequency. (iii) The
ratios range from 1.06 to 1.54 with a prominent peak at 1.39+/-0.01. The
cross-correlation of the time profile of harmonic groups peaks at
zero lag, demonstrating a tight relation between individual spikes in
associated groups. The results require an emission mechanism that can
produce harmonic emission at a ratio 5:7 or 1:1.4 and vary significantly
from this value. In several cases 3, and in one case 4 harmonic bands
have been observed. Previously proposed interpretations of harmonic
spike emission are discussed in view of the new observations.
---------------------------------------------------------
Title: Foreword
Authors: van den Oord, Bert; Kuijpers, Jan; Kuperus, Max; Benz, A. O.;
Brown, J. C.; Einaudi, G.; Kuperus, M.; Raadu, M. A.; Trottet, G.;
van den Oord, G. H. J.; Vlahos, L.; Zheleznyakov, V. V.; Wijburg,
Marion; Fletcher, Lyndsay; Volwerk, Martin
1994SSRv...68D..17V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Analysis of solar spike evengs by means of symbolic dynamics
methods
Authors: Schwarz, U.; Kurths, J.; Witt, A.; Benz, A. O.
1994SSRv...68..245S Altcode:
We have searched for interrelations of spikes emitted simultaneously
at different frequencies during the impulsive phase of flare events
(Fig.1). As the spikes are related to the flare energy release and
are interpreted as emissions that originate at different sites having
different magnetic field strengths, any relation in frequency is
interpretated as a relation in space. Quantities of symbolic dynamics,
such as mutual information, Shannon information and algorithmic
complexity are appropriate to characterize such spatiotemporal patterns,
whereas the popular estimate of fractal dimensions can be applied
to low-dimensional systems only. The goal is to decide between two
possible types of fragmentation depending on the energy release and
emission processes, which we callglobal andlocal organization. In the
global organization the whole region becomes supercritical, and the
energy is released in independent, small regions. The alternative local
scenario requires a trigger that spreads from initial localized events
and ignites nearby regions. Mutual information which is a generalization
of correlation indicates a relation in frequency beyond the bandwidth
of individual spikes. The scans in the spectrograms with large mutual
information also show a low level of Shannon information and algorithmic
complexity, indicating that the simultaneous appearance of spikes at
other frequencies is not a completely stochastic phenomenon (white
noise). It may be caused by a nonlinear deterministic system or by a
Markov process. By means of mutual information we find a memory over
frequency intervals up to 60 MHz (Fig. 2). Shannon information and
algorithmic complexity, however, describe spike events as a whole,
i.e. a global source region. A global organization is also apparent
in quasi-periodic changes of the Shannon information and algorithmic
complexity in the range of 2 8 seconds (Fig. 3). This findings
is compatible with a scenario of local organization in which the
information of one spike event spreads spatially and hence triggers
further spike events at different places. The region is not an ensemble
of independently flashing sources, each representing a system that
cascades in energy after an initial trigger. On the contrary, there is
a causal connection between the sources at any time. The analysis of
four spike events suggests that the simultaneous appearance of spikes is
not stochastically independent but a process in which spikes at nearby
locations are simultaneously triggered by a common exciter. We have
shown in the case in the case of spikes that quantities from nonlinear
dynamics used in this paper are helpful in detecting structural
properties of complex spatio-temporal patterns. This approach seems
to be promising also for several other astrophysical applications.
---------------------------------------------------------
Title: Non-linear properties of the dynamics of bursts and flares
in the solar and stellar coronae
Authors: Isliker, H.; Benz, A. O.
1994A&A...285..663I Altcode:
Solar and stellar flares are highly structured in space and in time,
as is indicated for example by their radio signatures: the narrowband
spikes, type III, type II and IV, and pulsation events. Structured in
time are also the not flare related type I events (noise storms). The
nature of this fragmentation is still not clear. Either, it can be
due to stochastic boundary or initial conditions of the respective
processes, such as inhomogeneities in the coronal plasma. Or else,
a deterministic non-linear process is able to cause complicated
patterns of these kinds. We investigate the nature of the fragmentation
in time. The properties of processes we enquire are stationarity,
periodicity, intermittency, and, with dimension estimating methods,
we try to discriminate between stochasticism and low-dimensional
determinism. Since the measured time series are rather short,
the dimension estimate methods have to be used with care: we have
developed an extended dimension estimate procedure consisting of five
steps. Among others, it comprises again the questions of stationarity
and intermittency, but also the more technical problems of temporal
correlations, judging scaling and convergence, and few data points
(statistical limits). We investigate 3 events of narrowband spikes, 13
type III groups, 10 type I storms, 3 type II bursts and 1 type IV event
of solar origin, and 3 pulsation-like events of stellar origin. They
have in common that all of them have stationary phases, periodicities
are rather seldom, and intermittency is quite abundant. However, the
burst types turn out to have different characteristics. None of the
investigated time series reveals a low-dimensional behaviour. This
implies that they originate from complex processes having dimensions
(degrees of freedom) greater than about 4 to 6, which includes infinity,
i.e. stochasticity. The lower limit of the degrees of freedom is
inferred from numerical experiments with known chaotic systems,
using time series of similar lengths, and it depends slightly on the
burst types.
---------------------------------------------------------
Title: Observations of fragmented energy release
Authors: Benz, A. O.
1994SSRv...68..135B Altcode:
Energy release into coronal plasmas is observable in the forms
of heating and acceleration. In flares and active stars, heating
and acceleration have been found to be related as indicated by an
approximately constant ratio of microwave (synchrotron) and soft
X-ray (thermal) emission. The discovery suggests a flare-like heating
process for the quiescent coronae of active stars. The energy release
in solar flares involves several time scales: (i) The largest is the
rate of homologous flares in an active region of the order of one per
five hours. (ii) Hard X-ray andH α emissions suggest a total flare
duration of ten minutes, (iii) with individual episodes of contiguous
acceleration of one minute. (iv) Elementary hard X-ray peaks have 5
10 s duration, corresponding to groups of beams observable as type III
radio bursts. (v) The effective injection time of these beams is of the
order 0.1 s. (vi) The smaller time scale is observed in narrowband radio
spikes in the 0.2 8 GHz range with durations of a few times 0.01 s.
---------------------------------------------------------
Title: Catalogue of 1-3 GHz solar flare radio emission
Authors: Isliker, H.; Benz, A. O.
1994A&AS..104..145I Altcode:
Solar flares frequently radiate in the 1-3 GHz range, the lowest
frequency microwaves, but not much is known about the spectral shape of
these emissions. We present a catalogue of selected bursts observed with
a new spectrometer at ETH Zurich in the years 1989-1993. The original
data set includes 268 events of various types. Featureless broadband
continua generally attributed to gyrosynchrotron emission are often
observed, but they are usually much weaker than the structured emissions
probably caused by coherent processes. The selection emphasizes the
latter class of events. The events show a rich variety of size and
structures in time and frequency. Most events can be grouped into five
major classes with some overlap and transitions. The samples of this
catalogue have been selected to show the breadth of each class without
stressing the extremes.
---------------------------------------------------------
Title: Pulsed Acceleration in Solar Flares
Authors: Aschwanden, Markus J.; Benz, Arnold O.; Dennis, Brian R.;
Kundu, Mukul R.
1994ApJS...90..631A Altcode: 1994IAUCo.142..631A
We study the nonlinear dynamics of particle acceleration in solar flares
by analyzing the time series of various quasi-periodic radio signatures
during flares. In particular we present the radio and hard X-ray data
of three flares which suppport the following tentative conclusions:
(1) Particle acceleration and injection into magnetic structures
occurs intrinsically in a pulsed mode (with a typical period of
1-2 s), produced by a single, spatially coherent, nonlinear system,
rather than by a stochastic system with many spatially independent
components ('statistical flare' produced by a fragmented primary energy
release). (2) The nonlinear (quasi-periodic) mode of pulsed particle
acceleration and injection into a coronal loop can be stabilized by
phase locking with an MHD wave (oscillation) mode, if both periods
are close to each other. (3) Pulsed injection of electron beams into
a coronal loop may trigger nonlinear relaxational oscillations of
wave-particle interactions. This is particularly likely when the limit
cycles of both systems are similar.
---------------------------------------------------------
Title: Books-Received - Plasma Astrophysics - Kinetic Processes in
Solar and Stellar Coronae
Authors: Benz, A.
1994Sci...263R.842B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: ROSAT Observations of Solar-Type G Stars
Authors: Gudel, Manuel; Schmitt, Jurgen H. M. M.; Kurster, Martin;
Benz, Arnold O.
1994ASPC...64...86G Altcode: 1994csss....8...86G
No abstract at ADS
---------------------------------------------------------
Title: Plasma astrophysics. Lecture notes 1994.
Authors: Benz, A. O.; Courvoisier, T. J. -L.
1994paln.book.....B Altcode:
The three contributions to this book are intended as brief but
thorough introductions to important aspects of plasma astrophysics
for astronomers and graduate students.
---------------------------------------------------------
Title: Plasma Astrophysics
Authors: Kirk, J. G.; Melrose, D. B.; Priest, E. R.; Benz, A. O.;
Courvoisier, T. J. -L.
1994plas.conf.....K Altcode: 1994QB462.7.K57....; 1994plas.conf.....B
This volume presents the lecture notes of the 24th Advanced Course
of the Swiss Society for Astrophysics and Astronomy in March 1994 at
Les Diablerets. In three lectures on magnetohydrodynamics, on kinetic
plasma physics and on particle acceleration leading experts describe
the physical basis of their subjects and extend the discussion to
several applications in modern problems of astrophysics. In style and
presentation the texts are well-suited for graduate work in plasma
astrophysics, one of the very important tools of modern astronomy. The
themes developed in this book will be helpful in understanding many
processes in the universe from the solar corona to active galaxies.
---------------------------------------------------------
Title: The Timing of Electron Beam Signatures in Hard X-Ray and Radio:
Solar Flare Observations by BATSE/Compton Gamma-Ray Observatory
and PHOENIX
Authors: Aschwanden, Markus J.; Benz, Arnold O.; Schwartz, Richard A.
1993ApJ...417..790A Altcode:
We analyzed two solar flares of 1992 September 5 and 6, using the high
time resolution (64 ms) hard X-ray data from BATSE/CGRO, and 100-3000
MHz radio (100 ms) dynamic spectra from PHOENIX. The broadband radio
data reveal a separatrix frequency (at 620 and 750 MHz in the two
flares) between normal- and reverse-drifting radio bursts, indicating
a compact acceleration source where electron beams are injected in
both the upward and downward direction. We find a mean injection rate
of 1.2 bursts s<SUP>-1</SUP> in one flare and more than 0.7 bursts
s<SUP>-1</SUP> in the other. From 12 broad-band, reverse-drifting radio
bursts we find in five cases an unambiguous one-to-one correlation
between the reverse-drifting radio bursts and hard X-ray (HXR) pulses
of similar duration (400±220 ms). The high significance (15±6 σ) of
the HXR pulses and the small scatter (±150 ms) in the relative timing
strongly supports a close causal connection. The cross-correlation
between HXR and radio pulses shows that the HXR pulses are coincident
(within the instrumental time resolution) with the reverse-drifting
bursts at the injection frequency (880±50 MHz), and lead the radio
bursts by 270±150 ms at the highest observable frequency (1240±100
MHz). The average drift time of the downward propagating radio bursts
is measured to 150 ms, corresponding to a drift rate of 2350 MHz
s<SUP>-1</SUP>. <P />We examined various effects to model the observed
timing of radio and HXR pulses (propagation delays, radio wave growth
and damping, group velocity delays, radio wave scattering, radio wave
ducting, light path differences, etc.). Assuming an exciter velocity
of υ<SUB>R</SUB>/c = 0.2±0.1 for the reverse-drifting radio bursts,
we infer an altitude difference of H = 8000±3000 km between the
injection site and the HXR source. The most likely explanation for the
retarded radio emission seems to be a combination of the following two
effects: (1) HXR-emitting (>25 keV) and radio-emitting electrons have
different energies (the exciter velocity of the reverse-drifting radio
bursts is associated with ≲5 keV electrons), and (2) a low (marginal)
growth rate for plasma emission at the second harmonics. Delay effects
caused by group velocity, collisional damping, wave scattering, and
wave ducting are found to be minor (<30 ms each).
---------------------------------------------------------
Title: Quasi-periodic Particle Injection into Coronal Loops
Authors: Aschwanden, Markus J.; Benz, Arnold O.; Dennis, Brian R.;
Gaizauskas, Victor
1993ApJ...416..857A Altcode:
We present observations of the flare of 1989 June 22, 1445 UT (in active
region NOAA 5555), obtained with the Hard X-Ray Burst Spectrometer
(HXRBS) on SMM at energies >52 keV, and with the broad-band radio
spectrometer PHOENIX at ETH/Zurich in the frequency range of 100-2800
MHz. The radio emission is dominated by a ≲100% polarized decimetric
continuum at 400-1400 MHz, peaking at 750 MHz. The decimetric radio
flux is highly correlated with the 50-150 keV hard X-ray flux but
is delayed by 3.5-5.4 s with respect to the hard X-rays. The HXR
emission shows an excess of ≳10 fast (≳100 ms) spikes (according to
Poisson statistics). The radio emission exhibits weak fine structure,
consisting of ≍45 quasi-periodic pulses with a mean period of 1.6
s. The frequency-time drift pattern of this fine structure is found
to be consistent with segments of inverted-U type bursts, suggesting
quasi-periodic injection of electron beams into a loop system. The loop
system has an average height of 68,000 km and expands with a velocity of
200 km s<SUP>-1</SUP> due to flare heating. Chromospheric evaporation
enhances the electron density near the footpoints. The type III-
exciting electrons have a mean velocity of υ/c = 0.30±0.10 (22 keV)
and propagate along inverted-U burst trajectories with a mean duration
of 2.5 s. For those electrons which reach the mirror point near the
opposite footpoint of the loop system, we calculate (from the density
and loop length) a low energy cutoff of ≥ 8 keV due to collisional
deflection, yielding a propagation velocity of v/c = 0.18 and a
propagation delay of 5.1±1.0 s, which agrees well with the observed
delay of 5.16 s between the cross-correlated HXR and radio flux. The
≥ 8 keV electrons provide free energy for a loss cone instability
near the secondary footpoint, which is observed as decimetric continuum
polarized in the same sense of circular polarization as the type III
bursts. The constraints from the Hα flare position and the magnetic
potential field extrapolation indicate that the loss cone emission is
produced in the diverging field region above the umbra of the leading
sunspot, which has a photospheric field strength of -1600 G. <P />This
flare allows us to deconvolve quasi-periodic particle injection and
subsequently triggered coherent radio emission from trapped particles
in flare-associated loops. It demonstrates that quasi-periodic modes
of particle acceleration, particle dynamics in mirror loops, and
the resulting plasma instabilities can be efficiently diagnosed from
correlated hard X-ray and radio signatures.
---------------------------------------------------------
Title: Analysis of solar spike events by means of symbolic dynamics
methods
Authors: Schwarz, U.; Benz, A. O.; Kurths, J.; Witt, A.
1993A&A...277..215S Altcode:
Using quantities of symbolic dynamics, such as mutual information,
Shannon information and algorithmic complexity, we have searched for
interrelations of spikes emitted simultaneously at different frequencies
during the impulsive phase of a flare event. As the spikes are related
to the flare energy release and are interpreted as emissions originating
at different sites having different magnetic field strengths, any
relation in frequency is interpreted as a relation in space. This
approach is appropriate to characterize such spatio-temporal patterns,
whereas the popular estimate of fractal dimensions can be applied to
low-dimensional systems only. <P />Depending on the energy release
and emission processes, two types of fragmentation are possible: a
scenario of global organization (spikes are emitted in a succession of
similar events by the same system) or a scenario of local organization
(many systems triggered by an initial event). <P />Mutual information
which is a generalization of correlation indicates a relation in
frequency beyond the bandwidth of individual spikes. The scans in
the spectrograms with large mutual information also show a low level
of Shannon information and algorithmic complexity, indicating that
the simultaneous appearance of spikes at other frequencies is not a
completely stochastic phenomenon (white noise). It may be caused by
a nonlinear deterministic system or by a Markov process. By means
of mutual information we find a memory over frequency intervals up
to 60 MHz. Shannon information and algorithmic complexity concern
the whole frequency region, i.e. the global source region. A global
organization is also apparent in quasi- periodic changes of the
Shannon information and algorithmic complexity in the range of 2 -
8 seconds. <P />The finding is compatible with a scenario of local
organization in which the information of one event spreads spatially
and triggers further events at different places. The region is not an
ensemble of independently flashing sources, each representing a system
that cascades in energy after an initial trigger. On the contrary,
there is a causal connection between the sources at any time. The
analysis of the four spike events suggests that the structure in
frequency is not stochastic but a process in which spikes at nearby
locations are simultaneously triggered by a common exciter.
---------------------------------------------------------
Title: The bandwidth of millisecond radio spikes in solar flares
Authors: Csillaghy, A.; Benz, A. O.
1993A&A...274..487C Altcode:
The bandwidth of 196 individual millisecond spikes has been measured
and analyzed. The spikes occurred in the impulsive phase of eight solar
flares in different active regions. The measurements have been made
at various frequency resolutions and spectral windows in the range
from 0.1 to 8.5 GHz. The major results are (i) that the individual
bandwidths show a scatter of a factor 2-3 or more within an event,
(ii) that the mean bandwidth differs significantly from event to
event at the same center frequency, (iii) that the mean bandwidth
increases only slightly with the center frequency and (iv) that there
is no qualitative difference between spikes in decimeter waves and
spikes in microwaves. The results show that there is no intrinsic
bandwidth of spikes, suggesting that accidental source parameters are
responsible for the width of the emission. The observed decrease of
the mean Δν/ν with frequency is interpreted as a decrease of the
mean source diameter at lower source altitude.
---------------------------------------------------------
Title: Similar X-Ray/Microwave Ratios in Solar Flares and Coronae
of Active Stars
Authors: Benz, A. O.; Gudel, M.
1993AAS...182.4606B Altcode: 1993BAAS...25..874B
We have compared the soft X-ray/microwave ratio of solar and stellar
flares with the ratio of the corresponding `quiescent' emissions
of active M and K stars and other active stars. Solar flare X-ray
observations by the GOES satellite have been converted into total
luminosities (erg/s) using the inferred temperature and emission
measure, and standard X-ray model spectra. Microwave luminosities
(erg/sHz) near the spectral peak of gyrosynchrotron emission (5-10
GHz) have been selected. The average ratio is 10({15.9+/-) 0.2} Hz for
impulsive and gradual flares, and slightly more for microflares. Highly
polarized stellar flare microwave emission is probably of different
origin and cannot be compared. The only simultaneous observation of
stellar flare X-rays and unpolarized microwaves in the literature
has a luminosity ratio of 10(15.5) Hz. The average ratio between
`quiescent' X-ray and microwave luminosities of young, rapidly rotating
M and K stars has previously been reported to be 10(15.5) Hz. It is
only slightly smaller for Algols, RS CVn binaries and post T Tauri
stars. The observation of comparable ratios between thermal X-rays
and gyrosynchrotron emission in the `quiescent' active coronae and
solar/stellar flares suggests that the coronal heating mechanism and
the flare energy release are similar physical processes. In particular,
the heating process of active stellar coronae seems to be associated
by acceleration of electrons. This research is supported by the Swiss
National Science Foundation, NASA, the University of Colorado, and NIST.
---------------------------------------------------------
Title: Strong Microwave Radiation from “Solar-Twin” GV Stars
Authors: Gudel, M.; Schmitt, J. H. M. M.; Benz, A. O.
1993AAS...182.4607G Altcode: 1993BAAS...25..874G
We report the detection of four solar-type main-sequence G stars
as strong, steady 8.5 GHz VLA microwave sources. The targets were
X-ray selected based on a previously reported relation between
quiescent X-ray and microwave luminosities (L_X and L_R) of active
stars. L_X was obtained from the ROSAT All-Sky Survey. The fluxes of
the radio detections (6<= sigma <= 13) match our predictions
within ~ 0.05 -- 0.2 dex (for age estimates, see references below):
\begin{tabular}{lllllll} star & spect. & d(pc) & flux (mJy)
& logL_R & logL_X & age (yrs) & & & & &
& Gl 97 & G1V & 13 & 0.28+/-0.035 & 13.8 &
28.9 & ~ 2* 10(9) Gl 755 & G5V & 19 & 0.19+/-0.031
& 13.9 & 29.4 & ... Gl 559.1 & dG0e & 21 &
0.34+/-0.025 & 14.3 & 29.6 & ~ 0.07* 10(9) HR 9107 &
G2V & 29 & 0.19+/-0.030 & 14.3 & 29.5 & ~ 10*
10(9) Gl 97 (see, e.g., Soderblom ApJS 53,1) and Gl 755 are single
MS stars. Gl 559.1 is a very rapidly rotating, chromospherically
extremely active young star probably just settling on the main sequence
(Soderblom & Clements AJ 93, 920; Elias & Dorren AJ 100,
818). A widely separated companion has been suspected (Duquennoy &
Mayor A&A 248, 485), but we reason that the radio emission comes
from the G star. The surprise detection is HR 9107, a metal-deficient,
high space velocity, old-disk population star just leaving the MS
(see Deliyannis et al. ApJS 73, 21). Brightness temperature estimates
based on an optically thin plasma likely suggest nonthermal emission,
probably gyrosynchrotron as on other active stars. These detections
extend the dichotomy between active and inactive stars into the range of
solar-type stars. We are currently proposing detailed investigations of
these stars. This research is supported by the Swiss National Science
Foundation, NASA, CU, and NIST; the NRAO VLA is supported by Associated
Universities, Inc. and the US NSF.
---------------------------------------------------------
Title: X-Ray/Microwave Relation of Different Types of Active Stars
Authors: Guedel, Manuel; Benz, Arnold O.
1993ApJ...405L..63G Altcode:
Coronal active stars of seven classes between spectral types F and M,
single and double, are compared in their quiescent radio and X-ray
luminosities L(R) and L(X). We find, largely independent of stellar
class, log L(X) is less than about log L(R) + 15.5. This general
relation points to an intimate connection between the nonthermal,
energetic electrons causing the radio emission and the bulk plasma
of the corona responsible for thermal X-rays. The relation, observed
over six orders of magnitude, suggests that the heating mechanism
necessarily involves particle acceleration. We derive requirements
for simple models based on optically thin gyrosynchrotron emission
of mildly relativistic electrons and thermal X-rays from the bulk
plasma. We discuss the possibility that a portion of the accelerated
particles heats the ambient plasma by collisions. More likely, plasma
heating and particle acceleration may occur in parallel and in the
same process, but at a fixed ratio.
---------------------------------------------------------
Title: Plasma astrophysics: Kinetic processes in solar and stellar
coronae
Authors: Benz, Arnold O.
1993ASSL..184.....B Altcode: 1993pakp.book.....B; 1993QB529.B46......
No abstract at ADS
---------------------------------------------------------
Title: VLBI Observations of a stellar flare
Authors: Alef, W.; Benz, A. O.; Güdel, M.; de Vicente, P.
1993sara.conf...28A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A General Correlation between X-Ray and Radio Luminosities
of Active Stars
Authors: Gudel, M.; Benz, A. O.
1992AAS...181.5109G Altcode: 1992BAAS...24.1206G
We have studied the relation between the quiescent radio and X-ray
luminosities L_6cm and L_X of a variety of late-type active stars
(M and K dwarfs, BY Dra binaries, RS CVn binaries, Algol binaries,
FK Comae stars, weak-lined T Tau stars). We find a general relation
logL_X <= logL_R + 15.5 that is valid over 6 orders of magnitude
in luminosity. RS CVn's, Algols, FK Com stars, and WTTS tend to be
“microwave-rich”. This relation points to an intimate connection
between the nonthermal, energetic electrons causing the radio emission
and the coronal bulk plasma responsible for thermal X-rays. We have
tested the hypothesis that particles accelerated in quasi-continuous
flare-like processes emit synchrotron radiation during their lifetime
and finally lose energy in collisions, thereby heating the coronal
plasma. This scenario requires commonly assumed values for the magnetic
field strength (100 G) and produces acceptable electron lifetimes.
---------------------------------------------------------
Title: Electron Beams in the Low Corona
Authors: Benz, A. O.; Magun, A.; Stehling, W.; Su, H.
1992SoPh..141..335B Altcode:
Selected high-resolution spectrograms of solar fast-drift bursts in the
6.2-8.4 GHz range are presented. The bursts have similar characteristics
as metric and decimetric type III bursts: rise and decay in a few
thermal collision times, total bandwidth ≳3% of the center frequency,
low polarization, drift rate of the order of the center frequency per
second, and flare association. They appear in several groups per flare,
each group consisting of some tens of single bursts. Fragmentation is
also apparent in frequency; there are many narrowband bursts randomly
scattered in the spectrum. The maximum frequency of the bursts is
highly variable.
---------------------------------------------------------
Title: Millisecond microwave spikes at 8 GHz during solar flares
Authors: Benz, A. O.; Su, H.; Magun, A.; Stehling, W.
1992A&AS...93..539B Altcode:
Highly circularly polarized spikes have been observed during solar
flares up to 8 GHz. The typical half-power bandwidth was 120 MHz, and
the duration was less than the time resolution of 100 ms. A group of
46 spikes in the 6.5 - 8.0 GHz range has been observed at the maximum
of an H-alpha flare and within 3 s of the peak of microwave emission
observed at 2.7 GHz by other observatories. The peak flux of the spikes
reached 60 sfu above background. These emissions closely resemble
the spikes previously reported at lower frequency. If interpreted
as second harmonic of the electron gyrofrequency, a magnetic field
exceeding 1400 G would be requested in the corona.
---------------------------------------------------------
Title: Decimetric Solar Type U Bursts: VLA and PHOENIX Observations
Authors: Aschwanden, Markus J.; Bastian, T. S.; Benz, A. O.; Brosius,
J. W.
1992ApJ...391..380A Altcode:
Observations of type U bursts, simultaneously detected by the VLA at
1.446 GHz and by the broadband spectrometer Phoenix in the 1.1-1.7
GHz frequency band on August 13, 1989 are reported. Extrapolations
of the coronal magnetic field, assuming a potential configuration,
indicate that the VLA 20 cm source demarcates an isodensity level. The
source covers a wide angle of diverging magnetic field lines whose
footpoints originate close to a magnetic intrusion of negative polarity
into the main sunspot group of the active region with dominant positive
polarity. The centroid of the 20-cm U-burst emission, which corresponds
to the turnover frequency of the type U bursts and remains stationary
during all U bursts, coincides with the apex of extrapolated potential
field lines at a height of about 130,000 km. It is demonstrated
that the combination of radio imaging and broadband dynamic spectra,
combined with the magnetic field reconstruction from magnetograms,
can constrain all physical parameters of a magnetic loop system.
---------------------------------------------------------
Title: VLA, PHOENIX and BATSE observations of an X1 flare.
Authors: Willson, Robert F.; Aschwanden, Markus J.; Benz, Arnold O.
1992NASCP3137..515W Altcode: 1992como.work..515W
The authors present observations of an X1 flare (Jul 18, 1991) detected
simultaneously with the VLA, the PHOENIX Digital Radio Spectrometer
and the Burst and Transient Source Experiment (BATSE) aboard the Gamma
Ray Observatory. The VLA was used to produce snapshot maps of the
impulsive burst emission on timescales of 1.7 sec at both 20 and 91
cm. The results indicate electron acceleration in the higher corona
several minutes before the onset of the hard X-ray burst detected
by BATSE. Comparisons with high spectral and temporal observations
by PHOENIX reveal a variety of radio bursts at 20 cm, such as type
III bursts, intermediate drift bursts, and quasi-periodic pulsations
during different stages of the X1 flare. The described X1 flare is
unique in the sense that it appeared at the east limb, providing the
most accurate information on the vertical structure of different flare
tracers visible in radio wavelengths.
---------------------------------------------------------
Title: Characteristics of the impulsive phase of flares
Authors: Benz, A. O.; Aschwanden, M. J.
1992LNP...399..106B Altcode: 1992esf..coll..106B; 1992LNP...399..106A; 1992IAUCo.133..106B
The impulsive phase of flares is an observational concept, characterized
by spiky emissions from -rays to radio waves. It is generally
agreed that during this time a large fraction of the. original flare
energy resides in energetic particles which are manifested in these
emissions. Here we concentrate on recent decimeter and microwave
observations that indicate a high level of fragmentation of this
energy release when related to hard X-ray (HXR) flux. Recent attempts
to characterize the flare and the distribution of the radio bursts in
time and frequency by statistical methods are also reviewed.
---------------------------------------------------------
Title: VLA, PHOENIX and BATSE observations of an X1 flare
Authors: Willson, Robert F.; Aschwanden, Marcus J.; Benz, Arnold O.
1992STIN...9227935W Altcode:
We present observations of an X1 flare detected simultaneously with
the Very Large Array (VLA), the PHOENIX Digital Radio Spectrometer,
and the Burst and Transient Source Experiment (BATSE) aboard the Gamma
Ray Observatory (GRO). The VLA was used to produce snapshot maps of
the impulsive burst emission in the higher corona on timescales of 1.7
seconds at both 20 and 01 cm. Our results indicate electron acceleration
several minutes before the onset of the hard X-ray burst detected
by BATSE. Comparisons with high spectral and spatial observations by
PHOENIX reveal a variety of radio bursts at 20 cm, such as type III
bursts, intermediate drift bursts, and quasi-periodic pulsations during
different stages of the X1 flare. From the drift rates of these radio
bursts we derive information on local density scale heights, the speed
of radio exciters, and the local magnetic field. Radio emission at 90
cm shows a type IV burst moving outward with a constant velocity of 240
km/sec. The described X1 flare is unique in the sense that it appeared
at the east limb (N06/E88 providing the most accurate information on
the vertical structure of different flare tracers visible in radio
wavelengths.
---------------------------------------------------------
Title: VLBI observations of YZ CMi - a single dMe star.
Authors: Benz, A. O.; Alef, W.
1991A&A...252L..19B Altcode:
The quiescent (nonflaring) radio emission of the single dMe star
YZ CMi was detected in an intercontinental VLBI experiment at 1.7
GHz. A radio diameter of the star of 1.0 + or - 0.5 mas was found,
statistically compatible with zero. The formal value corresponds to
1.7 optical stellar diameters and yields a brightness temperature
of 1.7 x 10 exp 9 K with a lower limit of 4 x 10 exp 8 K. This high
brightness strongly suggests emission by nonthermal particles by the
gyrosynchrotron mechanism or an incoherent process.
---------------------------------------------------------
Title: The association of solar millisecond radio spikes with hard
X-ray emission
Authors: Guedel, M.; Benz, A. O.; Aschwanden, M. J.
1991A&A...251..285G Altcode:
Conventional observational data regarding solar millisecond spikes
are compared with data gathered simultaneously in the hard X-ray
band by means of a statistical analysis. The analysis considers
the association rate, correlation degree, and relative time delays
between hard X-ray emissions (in the 25-438 keV range) and radio-spike
events. About 95 percent of the radio-spike bursts occur during
impulsive hard X-ray bursts, and approximately 43 percent of the
compared events are characterized by hard X-ray time profiles that
mimic the concentration of simultaneous radio spikes. The delay of
the radio emission with respect to the hard X-ray bursts puts some
constraints on the acceleration and propagation of particles. The time
delays and the quantization into discrete radio events are theorized
to be caused by the operation of the accelerator.
---------------------------------------------------------
Title: The attractor dimension of solar decimetric radio pulsations
Authors: Kurths, J.; Benz, A. O.; Aschwanden, M. J.
1991A&A...248..270K Altcode:
The temporal characteristics of decimetric pulsations and related
radio emissions during solar flares are analyzed using statistical
methods recently developed for nonlinear dynamic systems. The results
of the analysis is consistent with earlier reports on low-dimensional
attractors of such events and yield a quantitative description of their
temporal characteristics and hidden order. The estimated dimensions
of typical decimetric pulsations are generally in the range of 3.0 +
or - 0.5. Quasi-periodic oscillations and sudden reductions may have
dimensions as low as 2. Pulsations of decimetric type IV continua have
typically a dimension of about 4.
---------------------------------------------------------
Title: A broadband spectrometer for decimetric and microwave radio
bursts: First results
Authors: Benz, A. O.; Guedel, M.; Isliker, H.; Miszkowicz, S.;
Stehling, W.
1991SoPh..133..385B Altcode:
A new spectrometer has been put into operation that registers
solar flare radio emission in the 0.1 to 3 GHz band. It is a
frequency-agile system which can be fully programmed to measure both
senses of circular polarization at any frequency within that range at
selectable bandwidth. The time resolution has to be compromized with
the number of frequency channels and can be in the range of 0.5 ms to
250 ms for 1 to 500 channels. First results mainly from the 1-3 GHz
band are presented, a spectral region that has never been observed
with high-resolution spectrometers. Most noteworthy are the frequent
appearances of myriads of narrowband, fast-drifting bursts (microwave
type III), diffuse patches of continuum emission, and broad clusters
of millisecond spikes sometimes extending from 0.3 to 3 GHz.
---------------------------------------------------------
Title: Coordinated VLA-PHOENIX-SMM Observations: Microwave Type
U-Bursts
Authors: Aschwanden, M. J.; Bastian, T. S.; Benz, A. O.; Dennis, B. R.
1991BAAS...23.1065A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Mechanism for Producing Plasma Radiation in the Gigahertz
Range by Precipitating High Energy Protons
Authors: Smith, D. F.; Benz, A. O.
1991SoPh..131..351S Altcode:
Gamma-ray observations are discussed to determine the density of
protons of about 1 MeV precipitating to the photosphere. It is shown
that Coulomb collisions will produce a positive slope in the proton
distribution for energies less than 0.1 MeV for traversed column depths
greater than 10<SUP>18</SUP> cm <SUP>−2</SUP>. This could lead
to plasma wave emission and radiation near the plasma frequency for
densities ∼ 3.1 × 10<SUP>10</SUP> cm<SUP>−3</SUP> and temperatures
∼ 4.0 × 10<SUP>4</SUP> K where collisional and collisionless damping
of the plasma waves is sufficiently weak. It is expected that these
conditions will only be satisfied sporadically which leads to stationary
radio emission limited in frequency and time. Recent radio observations
of impulsive phase non-drifting patches in the 1-3 GHz range with
duration 2-4 s are presented which could be produced by this mechanism.
---------------------------------------------------------
Title: Coronal Radio Emission (With 7 Figures)
Authors: Benz, A. O.
1991mcch.conf..140B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The dynamic sun.
Authors: Benz, A. O.
1991EN.....22...19B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Simultaneous Radio and Hard X-ray Observations by
PHOENIX/Zurich and HXRBS/SMM during Max'91 (June 1989)
Authors: Aschwanden, M. J.; Dennis, B. R.; Benz, A. O.
1991max..conf..234A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar flare microwave observations with high spectral
resolution
Authors: Bruggmann, G.; Magun, A.; Benz, A. O.; Stehling, W.
1990A&A...240..506B Altcode:
The solar flare radio emission in the 6-8 GHz range was observed with
a high resolution spectrometer. The observed band corresponds to the
plasma frequencies and gyrofrequencies of the transition region and
the lowest part of the corona in active regions. Most of the emissions
were found to be broadbanded, as expected from the gyrosynchrotron
mechanism. In eight out of 46 observed events, spectral structures of
three types were detected: spikes below the time resolution of 100 ms,
slowly drifting broadband structures, and a narrow bandwidth patch of
continuum emission. These first narrowband bursts spectrally recorded
in the 6-8 GHz range are generally weak. Slowly drifting structures are
the only type compatible with the gyrosynchrotron emission mechanism. A
simple argument based on free-free absorption shows that plasma emission
can only be propagated if the radiation originates in a dense region
with a small density-scale length. The same holds for maser emission
at a low harmonic of the electron gyrofrequency. Possible emission
mechanisms and diagnostic capabilities are discussed.
---------------------------------------------------------
Title: Hard X-Rays and Associated Weak Decimetric Bursts
Authors: Sawant, H. S.; Lattari, C. J. B.; Benz, A. O.; Dennis, B. R.
1990SoPh..130...57S Altcode:
In previous attempts to show one-to-one correlation between type III
bursts and X-ray spikes, there have been ambiguities as to which of
several X-ray spikes are correlated with any given type III burst. Here,
we present observations that show clear associations of X-ray bursts
with RS type III bursts between 16:46 UT and 16:52 UT on July 9,
1985. The hard X-ray observations were made at energies above 25 keV
with HXRBS on SMM and the radio observations were made at 1.63 GHz
using the 13.7m Itapetinga antenna in R and L polarization with a time
resolution of 3 ms.
---------------------------------------------------------
Title: Flare fragmentation and type III productivity in the 1980
June 27 flare
Authors: Aschwanden, M. J.; Benz, A. O.; Schwartz, R. A.; Lin, R. P.;
Pelling, R. M.; Stehling, W.
1990SoPh..130...39A Altcode:
We present observations of the solar flare on 1980 June 27, 16:14-16:33
UT, which was observed by a balloon-borne 300 cm<SUP>2</SUP> phoswich
hard X-ray detector and by the IKARUS radio spectrometer. This flare
shows intense hard X-ray (HXR) emission and an extreme productivity of
(at least 754) type III bursts at 200-400 MHz. A linear correlation
was found between the type III burst rate and the HXR fluence, with a
coefficient of ≈ 7.6 × 10<SUP>27</SUP> photons keV<SUP>−1</SUP> per
type III burst at 20 keV. The occurrence of ≈ 10 type III bursts per
second, and also the even higher rate of millisecond spikes, suggests
a high degree of fragmentation in the acceleration region. This high
quantization of injected beams, assuming the thick-target model,
shows up in a linear relationship between hard X-ray fluence and the
type III rate, but not as fine structures in the HXR time profile.
---------------------------------------------------------
Title: Preface
Authors: Benz, A. O.; Magun, A.
1990SoPh..130....1B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Time Delays Between Decimetric Type-Iii Bursts and Associated
Hard X-Rays
Authors: Sawant, H. S.; Lattari, C. J. B.; Benz, A. O.; Dennis, B. R.
1990RMxAA..21..562S Altcode:
. In July, 1985 radio observations were made at 1.6 GHz using 13.7
m Itapetinga antenna with time resolution of 3 ms. The hard X-ray
observations were obtained from HXRBS on SMM. Comparison of 1.6 GHz
observations with dynamic spectra in the frequency range of (1000 -
100) MHz and hard X-rays shows the following results: i) In 12 cases,
we identify continuation of type Ill-RD bursts up to 1.6 GHz suggesting
presence of type Ill-RD bursts at 1.6 GHz. ii) For the first time, we
have idetified hard X-ray peaks delayed in comparison to decimetric
type Ill-RD bursts. These dalays are longer - 1 5 - than expected (
100 ms) and have been interpreted assuming that the decimetric emission
is at 2 nd harmonic and caused by the leading edge of the exciter,
whereas peaks of X-rays have been attributed to entire entry of the
exciter into the X-ray producing region. Keq : SUN BURSTS - SUN-
---------------------------------------------------------
Title: Alfven wave solitons and solar intermediate drift bursts
Authors: Treumann, R. A.; Guedel, M.; Benz, A. O.
1990A&A...236..242T Altcode:
Stationary resolutions for Alfven solitons propagating obliquely in a
homogeneous magnetic field are investigated. Due to their dispersive
nature, kinetic Alfven waves can evolve into solitonlike structures
which propagate at velocities of the order of the Alfven velocity in
a direction inclined to the magnetic field. In a first model, a cold
plasma with beta less than m(e)/m(i) is considered. In the second
model, the plasma contains two electron components, a hot one and a
cold one. Differential equations are derived for the plasma density,
and examples of numerical solutions for the plasma density profiles
are presented. Kinetic Alfven solitons can propagate in both cases at
Mach numbers M greater than 1 or M less than 1, as rarefactions or as
compressions of the plasma density. It is found that, in both models,
rarefaction and compressional solitons are uniquely determined by beta
and the propagation velocity vector. Interactions between the hot and
cold electron components turn out to be significant for rarefactions of
the cold component. Conditions are given for the existence of soliton
solutions. The super-Alfven kind of solitary waves are applied to solar
intermediate drift radio bursts. With a model of the emission process,
they can be used to determine the magnetic field and the electron
density of the source.
---------------------------------------------------------
Title: VLA-PHOENIX Observations of Coronal Activity
Authors: Willson, R. F.; Lang, K. R.; Benz, A. O.
1990BAAS...22.1196W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Statistical Study of the Correlation of Hard X-Ray and Type
III Radio Bursts in Solar Flares
Authors: Hamilton, Russell J.; Petrosian, Vahe; Benz, A. O.
1990ApJ...358..644H Altcode:
A large number of hard X-ray events which occurred during the
maximum of solar cycle 21 have been analyzed in order to study their
correlation with type III bursts. It is found that the distribution of
occurrences of hard X-ray bursts correlated with type III radio bursts
is significantly different from the distribution of all hard X-ray
bursts. This result is consistent with the assumption that the hard
X-ray and type III intensities are somewhat correlated. A bivariate
distribution function of the burst intensities is fitted to the data
and is used to determine that the typical ratio of X-ray intensity
to type II intensity is about 10 and that the ratio of the number of
X-ray producing-electrons to type III-producing electrons is about
1000. Three models which have been proposed to explain the relation
between the accelerated hard X-ray and type III-producing electrons
are examined in the context of these observations.
---------------------------------------------------------
Title: Book-Review - Instabilities in Space and Laboratory Plasmas
Authors: Melrose, D. B.; Benz, A. O.
1990SoPh..128..427M Altcode: 1990IAUCo.121P.427M
No abstract at ADS
---------------------------------------------------------
Title: Book reviews
Authors: Rayrole, J.; Benz, A. O.
1990SoPh..128..427R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Time profiles of solar radio spikes
Authors: Guedel, M.; Benz, A. O.
1990A&A...231..202G Altcode:
High-resolution observations are carried out to study the time
profiles of individual solar radio spikes. The time profiles show
a characteristic exponential decay with frequency dependent decay
rates. On the assumption of the plasma hypothesis, the following
empirical relation between T and the electron density n was found the
emitting region.
---------------------------------------------------------
Title: Enhanced Radiation Driven by a DC Electric Field
Authors: Tajima, T.; Benz, A. O.; Thaker, M.; Leboeuf, J. N.
1990ApJ...353..666T Altcode:
Direct radiation by runaway electrons under a constant (dc) electric
field is investigated. In a one-and-two-halves-dimensional relativistic
EM code, an electron beam propagates along the external magnetic
field parallel to the dc field and quickly decays into a runaway tail
sustained by the dc field. Electrostatic and transverse waves are
observed at various (fixed for each particular run) angles of wave
propagation. Both plasma waves and EM radiation are strongly enhanced
by the runaway tail. In the linear and early nonlinear beam stages,
the EM wave energy is slightly enhanced as the associated electrostatic
component of the waves (together with the dc field) traps and detraps
electrons. In the late nonlinear (runaway) stage and with sufficiently
large observing angle, bursts of EM wave energy occur, accompanied
by fast perpendicular spreading of the distribution function, and
they coincide with clamping of runaway electron momenta. A possible
application is to msec radio spikes associated with solar flares. In
this situation, the possibility of the present mechanism yielding
radiation temperatures in excess of 10 to the 15th K is not out of
the question.
---------------------------------------------------------
Title: Correlation of solar radio pulsations with hard X-ray emission
Authors: Aschwanden, M. J.; Benz, A. O.; Kane, S. R.
1990A&A...229..206A Altcode:
A systematic study of the correlation of quasi-periodic broad-band
decimetric pulsations with hard X-ray (HXR) emission is carried out. It
is found that, in 11 out of 56 simultaneously observed events, the
decimetric quasi-periodic pulsations in the impulsive phase of flares
are correlated. If events with concurring type III bursts are included,
19 cases of radio pulsations are correlated with HXR.
---------------------------------------------------------
Title: A plasma radiation model for the prompt radio emission of
supernova 1987A.
Authors: Benz, A. O.; Spicer, D. S.
1990A&A...228L..13B Altcode:
We propose that the prompt radio emission of supernova 1987A a few days
after the explosion is the result of a plasma interaction between the
ejecta and the presupernova circumstellar matter. The emission frequency
then is determined by the electron density in the front of the ejecta
and the radio flux density mainly depends on the velosity of the ejecta
and the circumstellar electron density. Free-free absorptions in the
interaction region and by the circumstellar medium limit the emission
on the high, respectively low frequency side and inhabit observable
emission in the first two days.
---------------------------------------------------------
Title: Broadband Spectral Radio Observations of Flare Stars
Authors: Benz, A. O.; Guedel, M.; Bastian, T. S.; Fuerst, E.; Simnett,
G. M.; Pointon, L.
1990IAUS..137..139B Altcode:
The first broadband spectrometer observation of a stellar flare
event is reanalyzed and discussed. Rough estimates of the stellar
source parameters are given, including the source size, exciter drift
velocity, and source magnetic field. An interpretation in terms of
coherent cyclotron emission is presented.
---------------------------------------------------------
Title: The Attractor Dimension of Solar Decimetric Radio Pulsations
Authors: Kurths, J.; Benz, A. O.; Aschwanden, M. J.
1990PDHO....7..196K Altcode: 1990dysu.conf..196K; 1990ESPM....6..196K
The authors have analyzed the temporal characteristics of decimetric
pulsations and related radio emissions during solar flares.
---------------------------------------------------------
Title: Alfven wave solitons and solar intermediate drift bursts
Authors: Treumann, R. A.; Guedel, M.; Benz, A. O.
1990STIN...9029287T Altcode:
Stationary solutions for the Alfven solitons propagating obliquely in
a homogeneous magnetic field are investigated. Due to their dispersive
nature kinetic Alfven waves can evolve into soliton like structures
which propagate at velocities of the order of the Alfven velocity in
a direction inclined to the magnetic field. In a first model, a cold
plasma with beta less than (m<SUB>e/m</SUB> sub i) is considered. In the
second model the plasma contains two electron components, a hot one and
a cold one. Differential equations for the plasma density are derived
and examples of numerical solutions for the plasma density profiles are
presented. Kinetic Alfven solitons can propagate in both cases at Mach
numbers M greater or less than 1, as rarefactions or as compressions
of the plasma density. In both models rarefaction and compressional
solitons are uniquely determined by beta and the propagation velocity
vector. Interaction between the hot and cold electron components turn
out to be significant for rarefactions of the cold component. Conditions
for the existence of soliton solutions are given. The super-Alfvenic
kind of solitary waves are applied to solar intermediate drift radio
bursts. With a model of the emission process they can be used to
determine the magnetic field and the electron density of the source.
---------------------------------------------------------
Title: Particle beams in the solar atmosphere.
Authors: Benz, A. O.; Magun, Andreas
1990pbsa.book.....B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Vla-Phoenix Observations of a Narrow-Band Decimetric Burst
Authors: Willson, Robert F.; Benz, Arnold O.
1990IAUS..142..525W Altcode:
A discussion is conducted regarding observations of a highly-circularly
polarized multiply-impulsive microwave burst detected by the Very
Large Array and the Phoenix Digital Radio Spectrometer. The VLA was
used to resolve the burst in two dimensions, while Phoenix provided
high-time-resolution information about its spectral properties. During
part of the burst, positive frequency drifts were detected, suggesting
inwardly propagating beams of electrons emitting type-III-like
radiation.
---------------------------------------------------------
Title: Broadband spectral observations of a dMe star radio flare.
Authors: Gudel, M.; Benz, A. O.; Bastian, T. S.; Furst, E.; Simnett,
G. M.; Davis, R. J.
1989A&A...220L...5G Altcode:
A flare on the dMe star AD Leonis was simultaneously observed with
the radio telescopes in Effelsberg, Jodrell Bank, and Arecibo using
spectrometers at 1665, 1666, and 1415 MHz with bandwidths of 25,
100, and 40 MHz, respectively. The time coincidence confirms the
stellar origin of the radiation. The flare emission was resolved into a
multitude of broadband pulsations. Their e-folding rise and decay times
were of the order of the time resolution of the Effelsberg data (125
ms), or less. The circular polarization was about 100 percent. Similar
bursts, but 4 orders of magnitude less powerful, have been observed
from the sun at lower frequencies.
---------------------------------------------------------
Title: VLA detection of radio emission from a dwarf nova.
Authors: Benz, A. O.; Guedel, M.
1989A&A...218..137B Altcode:
Radio emission was detected at 4.9 GHz from a dwarf nova for the first
time with the Very Large Array. This confirms earlier reports based
on single or binary dish observations. Radio emission in only one
out of eight dwarf novae was detected. The radio source is EM Cyg,
an eclipsing binary system. It is variable on the scale of days and
is circularly polarized. EM Cyg had an optical outburst, but was not
eclipsed during the observations. If interpreted by synchrotron emission
the observed radiation requires a source size larger than the binary
separation and relatively large magnetic fields. Maser emission of
nonthermal electrons reflected in the magnetic field of the white dwarf
is a possibly more attractive alternative. A source field of 800-2000
Gauss then is required depending on the most efficient maser mode.
---------------------------------------------------------
Title: Radio continuum emission from the pre-main sequence Herbig
AE star ABAurigae.
Authors: Guedel, M.; Benz, A. O.; Catala, C.; Praderie, F.
1989A&A...217L...9G Altcode:
Two Herbig Ae stars have been observed in the radio range with the
Very Large Array for the first time. One of these stars, HD 250550,
was not detected, while the other object, AB Aur, was detected twice at
3.6 cm and once at 6 cm. A slight time variation was found at 3.6 cm,
and its flux agrees with free-free emission of a thermal wind source
having M-dot = 1.5 x 10 to the -8th solar mass/yr (assuming an expansion
velocity of 400 km/s) compatible with quasi-simultaneous optical line
observations. The radio spectrum, however, deviates from a simple nu
exp 0.6-law, showing excess radiation at 6 cm. The possibility exists
that it originates from nonthermal electrons emitting synchrotron
radiation in a magnetic field.
---------------------------------------------------------
Title: Broad-band spectrum of dMe star radio emission.
Authors: Guedel, M.; Benz, A. O.
1989A&A...211L...5G Altcode:
The dMe star UV Ceti was observed at the VLA in all available frequency
bands (90, 20, 6, 3.6, 2, and 1.3 cm) on two dates separated by about
one week. Beside confirming former reports about quiescent emission at
6 and at 20 cm, nonflaring radio emission has also been discovered at
all smaller wavelengths. The radio spectra show a minimum or break at
the 3.6 cm band. The radio spectra show a minimum or break at the 3.6
cm band. This behavior is unexpected if the low-frequency emission is
synchrotron radiation, as generally believed. It may be interpreted
as a different emission increasing to millimetric waves from the well
known microwave component. The high frequency component is shown to be
compatible with cyclotron radiation of the X-ray emitting plasma. The
new component then would require magnetic fields in the source varying
from at least 600 up to 2070 Gauss. This suggests nu(B)/nu(p) = 1...10
in the corona of UV Ceti.
---------------------------------------------------------
Title: Radio Emission of Dwarf Novae
Authors: Benz, A. O.
1989ASSL..156..113B Altcode: 1989admf.proc..113B
The processes giving rise to the radio emission from dwarf novae is
discussed. The radiation, which is variable within days and highly
polarized, is probably caused by some gyromagnetic process. If it
is synchrotron emission, the magnetic field strength in the source
is of the order of 40 G. If the emission is due to a cyclotron maser
process, the magnetic field is 800-1800 G depending on which harmonic
of the local gyrofrequency is emitted. The radio emission appears high
compared to the number of available energetic electrons. The particles
thus appear to be accelerated by or near the prime source of energy,
the accretion disk.
---------------------------------------------------------
Title: Alfvén wave solitons and solar intermediate drift bursts.
Authors: Guedel, M.; Benz, A. O.; Treumann, R. A.
1989plap.work...95G Altcode:
The authors investigate stationary solutions for Alfvén solitons
propagating obliquely in a homogeneous magnetic field. Due to their
dispersive nature kinetic Alfvén waves can evolve into soliton like
structures which propagate at velocities of the order of the Alfvén
velocity in a direction inclined to the magnetic field. In the first
model one keeps the plasma β < m<SUB>e</SUB>/m<SUB>i</SUB>. Kinetic
Alfvén solitons in this case can propagate at Mach numbers M > 1
or M < 1 as dilutions or as compressions of the plasma density. In
the second model the plasma contains two electron components, a
hot one and a cold one. The authors derive differential equations
for the plasma density and present examples of numerical solutions
for the plasma density profiles. They find that both dilutive and
compressional solitons are uniquely determined by β and the propagation
velocity vector. Conditions are given for the existence of soliton
solutions. Interactions between the hot and the cold electron component
turn out to be significant for dilutions of the cold component. The
authors apply this kind of solitary density waves to solar intermediate
drift radio bursts.
---------------------------------------------------------
Title: Particle acceleration.
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Alissandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1989epos.conf..127V Altcode:
Contents: 1. Introduction. 2. Phenomena associated with
mildly-relativistic electrons. 3. Phenomena associated with ions and
relativistic electrons in solar flares. 4. Theoretical studies of
particle acceleration. 5. Achievements - outstanding questions.
---------------------------------------------------------
Title: Solar and stellar flares
Authors: Benz, A. O.
1989HiA.....8..539B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Extended coronal shock waves and electron acceleration during
solar flares.
Authors: Klein, K. -L.; Trottet, G.; Benz, A. O.; Kane, S. R.
1989plap.work..157K Altcode:
Extended shock waves in the solar corona have long been thought to
be responsible for the electrons of the highest observable energies
during big flares where large amounts of electromagnetic radiation
from hard X-rays to decametric radio waves are observed. The authors
have undertaken a detailed study of the radio signature of such shock
waves and of its relation to energetic electrons in the low solar
atmosphere, using hard X-ray and wide-band radio observations with high
time resolution. The results suggest that the extended coronal shock
wave plays a minor part in the acceleration of relativistic electrons
observed in the low corona.
---------------------------------------------------------
Title: A catalogue of decimetric solar flare radio emission
Authors: Guedel, M.; Benz, A. O.
1988A&AS...75..243G Altcode:
Decimetric radio emission is frequently observed during solar
flares. This catalogue exhibits a representative selection of typical
bursts observed with the ETH high resolution digital spectrometer in the
years 1979 - 1983. The data set is confined to the spectral range of 300
- 1000 MHz and to a type of events known to generally occur during the
impulsive phase of flares (thus excluding the well-known fine structures
of post-flare, decimetric type IV bursts). Most events can be grouped
into four major classes, which however show considerable variety. The
samples of this catalogue have been selected to display the observed
range of multiformity by a commensurate number of typical events.
---------------------------------------------------------
Title: A Plasma Radiation Model for the Prompt Radio Emission of
Supernova 1987A
Authors: Benz, A. O.; Spicer, D. S.
1988BAAS...20Q.961B Altcode: 1988BAAS...20Z.961B; 1988BAAS...20..961B
No abstract at ADS
---------------------------------------------------------
Title: On the Electron-Cyclotron Maser Instability. II. Pulsations
in the Quasi-stationary State
Authors: Aschwanden, M. J.; Benz, A. O.
1988ApJ...332..466A Altcode:
In the previous paper we have studied the electron-cyclotron maser
instability of a source in quasi-equilibrium. In a situation of weak
diffusion such a state will remain for a limited time regardless of the
particular loss-cone instability involved. Here our major interest is in
oscillations set up by small disturbances around the steady state. Both
the linear growth as well as the coupled diffusion rate are subject
to a common oscillation period, since wave growth and diffusion are
interlocked by a Lotka-Volterra type of coupled equations. Periods
in the limit of small amplitude (limit cycle) of the self-organizing
wave-particle system are investigated for the magnetoionic X- and O-mode
and for harmonic numbers s = 1, 2 of the maser instability. Pulsation
periods in the order of 1 s, as observed in the decimetric range of
solar flare emission are found exist for (1) fundamental (s = 1) O-mode
for 0.3 < ω<SUB>p</SUB>/Ω<SUB>e</SUB> ≲ 1.0, and (2) harmonic
(s = 2) X-mode (for 1.0 ≲ ω<SUB>p</SUB>/Ω<SUB>e</SUB> 1.4). The
period is sensitive to variations of the shape of the loss-cone and
therefore not stable. The proposed model provides an interpretation
of the observed quasi-periodic decimetric solar pulsations as well as
some of similar stellar phenomena.
---------------------------------------------------------
Title: On the Electron-Cyclotron Maser Instability. I. Quasi-linear
Diffusion in the Loss Cone
Authors: Aschwanden, M. J.; Benz, A. O.
1988ApJ...332..447A Altcode:
Emission and quasi-linear velocity diffusion by the electron-cyclotron
maser instability are studied under conditions of continuous
operation. For the first time, the maser-induced quasi-linear
diffusion is computed with the same accuracy as the well-known linear
growth rates, including integration along the actual resonance
space in k-space. This permits the feedback of the emission on
the particle distribution to be quantified. A novel result is the
discovery of relatively long diffusion time scales for typical solar
conditions. Oscillations set up by small disturbances around the
steady state are considered. Periods in the limit of small amplitude
of the self-organizing wave-particle system are investigated for the
magnetoionic X- and O-mode and for harmonic numbers s = 1, 2 of the
maser instability. Pulsation periods in the order of 1 s, as observed
in the decimetric range of solar flare emission, are found to exist
for fundamental O-mode and for harmonic X-mode.
---------------------------------------------------------
Title: Radio emission of coronal shock waves
Authors: Benz, A. O.; Thejappa, G.
1988A&A...202..267B Altcode:
The "backbone" emission of shock initiated coronal (metric) type II
solar radio bursts is considered. The source has extremely narrow
bandwidth and appears to be stationary in relation to the shock. The
increasingly complete understanding of the phenomena associated with
the Earth's bow shock is tapped for suggestions on the responsible
particles, their energies and the emission mechanism of radio waves. The
authors propose that the radiation originates from electrons and ions
of a few keV energy, the dominant populations of accelerated particles
upstream of the bow shock. A model is developed which can explain
the major observed features by wave-wave coupling between electron
plasma waves themselves and with ion waves. Observational tests at
interplanetary and bow shock waves are proposed.
---------------------------------------------------------
Title: Book-Review - Radio Continua during Solar Flares
Authors: Benz, A. O.
1988ApL&C..26..376B Altcode: 1988ApL....26..376B
No abstract at ADS
---------------------------------------------------------
Title: Stochastic Acceleration of Electrons in Solar Flares
Authors: Benz, A. O.; Smith, D. F.
1987SoPh..107..299B Altcode:
The generation of lower-hybrid waves by cross-field currents is
applied to reconnection processes proposed for solar flares. Recent
observations on fragmentation of energy release and acceleration, and
on hard X-ray (HXR) spectra are taken into account to develop a model
for electron acceleration by resonant stochastic interactions with
lower-hybrid turbulence. The continuity of the velocity distribution is
solved including collisions and escape from the turbulence region. It
describes acceleration as a diffusion process in velocity space. The
result indicates two regimes that are determined by the energy of the
accelerating electrons which may explain the double power-law often
observed in HXR spectra. The model further predicts an anticorrelation
between HXR flux and spectral index in agreement with observations.
---------------------------------------------------------
Title: Small-scale structure in solar flare radio emission.
Authors: Benz, A. O.
1987ESASP.275..105B Altcode: 1987sspp.symp..105B
High resolution radio observations of type 3 solar flares and spike
bursts are presented. Considerable fragmentation appears in time
and spectrum, indicating that many, small sources are involved. The
structure in type 3 emission requires more than 100 distinct injections
or acceleration events in a flare studied. There are suggestions of
orders of magnitude higher fragmentation in the acceleration process
from type 3 bursts and spikes. Small scale structures in flares may
control the energy release and its time scale.
---------------------------------------------------------
Title: Book-Review - Radio Continua during Solar Flares
Authors: Benz, A. O.; Brown, J. C.
1987Obs...107..134B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Radio Continua during Solar Flares - Workshop -
Duino, Italy - 1985MAY
Authors: Benz, A. O.
1987S&T....73Q.395B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spectra of stellar radio flares
Authors: Benz, Arnold O.
1987Natur.326..643B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Acceleration and Energization by Currents and Electric Fields
Authors: Benz, A. O.
1987SoPh..111....1B Altcode:
The acceleration of the influential ≲ 100 keV electrons in
flares observed in hard X-rays and several radio emissions is
unknown. Shock-waves and MHD turbulence, successfully applied to
interprete interplanetary energetic particles, have recently been
called in question concerning energetic flare electrons and ions. Other
possible mechanisms are considered which are closely related to the
primary flare energy release. In particular, runaway acceleration by
the electric field of the reconnection current sheet, bulk heating by
microturbulence, and cross-field ion currents due to bulk motion as a
primary result of reconnection are reviewed. All three are likely to
occur in some way. Their relative importance cannot be definitively
assessed due to the lack of information on non-thermal, low energy
protons.
---------------------------------------------------------
Title: Harmonic Emission and Polarization of Millisecond Radio Spikes
Authors: Benz, A. O.; Guedel, M.
1987SoPh..111..175B Altcode:
The spectral distribution of millisecond radio spikes observed by the
Zürich spectrometers in the 200-1100 MHz range has been studied. In
one event out of a total of 36 we have found clearly developed harmonic
structure. The ratio between the two bands of emission was 1:1.39
± 0.01. We have also determined the sense of circular polarization
of the spike events and compared it to the magnetic polarity of the
leading spot of the flaring active region. According to the `Leading
Spot Rule' the majority of the events (10 out of 13) were emitted in
the ordinary mode.
---------------------------------------------------------
Title: Microwave emission of solar electron beams
Authors: Staehli, M.; Benz, A. O.
1987A&A...175..271S Altcode:
Studying the microwave and decimetric emissions of solar flares the
authors have found drifting microwave fine structures in the range
3100 - 5205 MHz, clearly different from millisecond spikes. Their half
power duration is between 25 and 200 ms. The bandwidth is usually
greater than 150 MHz, and they are slightly circularly polarized. A
comparison of these microwave structures with decimetric blips (Benz
et al., 1983) and with metric type III bursts shows the similarity
between these three phenomena concerning frequency drift, time scale,
bandwidth and polarization. The authors therefore believe that the
drifting microwave bursts are also signatures of travelling electron
beams. Several emission mechanisms are possible. However, the observed
similarities suggest a common process for the new microwave phenomena,
decimetric blips and type III bursts. The most favourable mechanism
then is harmonic plasma radiation.
---------------------------------------------------------
Title: Are solar radio fluctuations real?
Authors: Benz, A. O.; Fuerst, E.
1987A&A...175..282B Altcode:
Coordinated measurements of fluctuations of the microwave radiation of
the Sun have been made using the Arecibo and Effelsberg telescopes. At
4.75 GHz they have comparable beamwidths. The two outputs of
nearly identical regions on the Sun generally turned out to be
different. Significant correlation was found in only one run. No
discrete periodic oscillation remained after cross-correlation. The
possibly common part of the continuous fluctuation spectrum was
extracted by the sample cross-correlation. These fluctuations were
of amplitudes up to 500 Jy. A coherence length of 90 s was found. The
suggestion is made that they may originate from jets recently observed
in coronal EUV and that they may be of possible relevance to coronal
heating.
---------------------------------------------------------
Title: Book-Review - Radio Continua during Solar Flares
Authors: Benz, A. O.
1987Sci...235R.494B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Phenomena Associated with Ions and Relativistic Electrons
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1986epos.conf.2.30V Altcode: 1986epos.confB..30V
No abstract at ADS
---------------------------------------------------------
Title: Mechanisms for Particle Accleration in Flares
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1986epos.conf.2.42V Altcode: 1986epos.confB..42V
No abstract at ADS
---------------------------------------------------------
Title: Phenomena Associated with Mildly Relativistic Electrons
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1986epos.conf..2.2V Altcode: 1986epos.confB...2V
No abstract at ADS
---------------------------------------------------------
Title: The role of metric and decimetric radio emission in the
understanding of solar flares
Authors: Simnett, G. M.; Benz, A. O.
1986A&A...165..227S Altcode:
The metric and decimetric radio emission from large X-ray and gamma
ray flares are examined with the aim of clarifying the role of electron
beams in the primary energy transfer process during the impulsive phase
of solar flares. It is found that a significant fraction, ≡15%, of
the flares have no detectable radio emission at these wavelengths at
current levels of instrument sensitivity. In addition, for the gamma
ray flares a further 43% had the start of type III burst activity
delayed by 60 s or more from the onset of the hard X-ray burst. The
production and propagation of type III radiation is briefly reviewed
and it is concluded that modern ground-based radio telescopes should be
sensitive to a beam of electrons containing ⪆10<SUP>29</SUP>electrons
above 20 keV. It is concluded that in the type III-quiet flares there
is evidence against such beams. A consequence of this conclusion is
that non-thermal electron beams cannot be the dominant energy transfer
mechanism during the impulsive phase in at least some flares.
---------------------------------------------------------
Title: Solar radio signatures suggestive of proton beams
Authors: Benz, A. O.; Simnett, G. M.
1986Natur.320..508B Altcode:
Electron beams propagating in the solar corona excite the ambient
plasma to emit radio waves at the local plasma frequency and/or its
harmonic. This general interpretation of type III radio bursts is
well confirmed by in situ measurements. The rate at which peak flux
drifts in frequency and time is a measure of the velocity of the
exciter. Here we report a class of radio bursts with a significantly
lower drift than normal; consequently, we show that they defy the usual
interpretation. Possible exciters are slowly moving beams of protons.
---------------------------------------------------------
Title: The frequency-time drift of pulsations.
Authors: Aschwanden, M. J.; Benz, A. O.
1986A&A...158..102A Altcode:
A set of 1270 digitally recorded type III bursts and pulsations in
the frequency range of 100 - 1000 MHz was analyzed by a structure
recognizing program. Numerical fitting methods determined the drift
rate with much higher accuracy than previous analysis of analog
data. The analysis of the drift of solar radio bursts in frequency
vs. time provides information not only about the dynamical parameters
of the source but also reveals atmospherical properties. Type III
events and pulsations are clearly distinguished in their drift
distribution. Pulsations statistically exhibit 3 times higher drift
rates than type III events, thus requiring considerably shorter
local scale heights. The source direction of the type III bursts is
preferentially upwards oriented, the pulsations show a downwards
oriented anisotropy. Evidence is given that the pulsations have
a different origin than the common type III burst, concerning the
coronal environment as well as the emission mechanism. Outlines to
construct models of decimetric pulsations are discussed.
---------------------------------------------------------
Title: Preface
Authors: Benz, Arnold O.
1986SoPh..104D...7B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Electron Acceleration in Flares Inferred from Radio and Hard
X-Ray Emissions
Authors: Benz, A. O.; Kane, S. R.
1986SoPh..104..179B Altcode:
Properties of electron acceleration in flares, especially the density
structure in the acceleration region, are deduced from a correlation
study between decimetric type III, spike, and hard X-ray (HXR)
bursts. The high association rate found (71%) strongly suggests that
spikes also originate from energetic electrons. Spikes and type III
bursts have been found to be easily identified by their different
polarizations. The two types of emission generally do not overlap
in frequency. A reliable lower limit to the density is derived from
the starting frequency of type III and U bursts. The spike emission
very likely yields an upper limit. The density inhomogeneity in the
acceleration region spans more than one order of magnitude and is more
than one order of magnitude larger in the associated type U sources. A
peak-to-peak correlation does not always exist between type III,
spike and HXR bursts. This discrepancy can be interpreted in terms of
the different source conditions and propagation properties. Whereas
spikes need special conditions to become visible, type III and peaks
of HXR may be the product of many elementary accelerations.
---------------------------------------------------------
Title: Millisecond Radio Spikes
Authors: Benz, A. O.
1986SoPh..104...99B Altcode:
Millisecond spikes of the solar radio emission are known for more
than two decades. They have recently seen a surge in interest of
theoreticians who are fascinated by their high brightness temperature of
up to 10<SUP>15</SUP> K, their association with hard X-ray bursts, and
a possibly very intimate relation to electron acceleration. This review
is intended to bridge the gap that presently seems to separate theory
and observations. The wide range of spike observations is summarized
and brought into the perspective of recent models. It is concluded
that spikes yield a considerable potential for the diagnostics of
energetic particles, their origin, and history in astrophysical plasmas.
---------------------------------------------------------
Title: Radio continua during solar flares : selected contributions
to the workshop held at Duino, Italy, May, 1985
Authors: Benz, A. O.
1986SoPh..104.....B Altcode:
The conference presents papers on radio continua during flares,
the fine structure in continua, the coronal environment of radio
emission, radio millisecond spikes, the timing of radio emission in
relation to other flare radiation, and new technologies for the next
solar cycle. Particular attention is given to the relation between
flare-related metric continuum bursts and coronal mass ejections,
fast pulsations in flare continua, the polarization of decimetric
pulsations, interplanetary phenomena and solar radio bursts, the
characteristics of type IV-associated spikes at metric wavelengths,
hollow beam distribution of energetic electrons and higher harmonics
of electron cyclotron maser, and a model of ultrafast fine structures
of microwave bursts. Papers are also presented on type IV bursts and
coronal mass ejections, electron acceleration in flares inferred from
radio and hard X-ray emissions gyrosynchrotron emission of solar flares,
microwave diagnostics of energetic electrons in flares and decimeter
continuum radio emission from a postflare loop.
---------------------------------------------------------
Title: Extremely rapid radio spikes in flares.
Authors: Benz, A. O.
1986NASCP2449..133B Altcode: 1986rfsf.nasa..133B
Radio spikes of a few to tens of milliseconds of the solar radio
emission have a high brightness temperature of up to 10<SUP>15</SUP>K,
are associated with hard X-ray bursts, and are related to electron
acceleration. Their bandwidth and global distribution in frequency have
quantitatively been measured only recently. This review is intended
to emphasize the considerable extend of old and new observational
knowledge which is hardly touched upon by theory. The wide range of
spike observations is summarized and brought into the perspective
of recent models. It is concluded that spikes yield a considerable
potential for the diagnostics of energetic particles, their origin,
and history in astrophysical plasmas.
---------------------------------------------------------
Title: Radio emission of cataclysmic variable stars.
Authors: Fuerst, E.; Benz, A.; Hirth, W.; Kiplinger, A.; Geffert, M.
1986A&A...154..377F Altcode:
Eight cataclysmic variable stars were observed at 6 cm wavelength using
the Very Large Array (VLA). The objects were: CN Ori, SS Aur, YZ Cnc,
SU UMa, Z Cam, V603 Aql, EM Cyg, and RZ Sge. Most of these objects
were in optical high stage, but none were detected beyond flux limits
between 0.1 and 0.3 mJy.
---------------------------------------------------------
Title: Particle acceleration.
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1986NASCP2439....2V Altcode:
Contents: 1. Introduction. 2. Phenomena associated with
mildly-relativistic electrons: soft and hard X-ray source structure,
location and development, microwave source structure, location and
development, time structures and time delays in radio and hard X-rays,
microwave rich flares, decimetric - metric observations and comparison
with X-ray observations, discussion of models for X-ray and microwave
emission. 3. Phenomena associated with ions and relativistic electrons:
gamma-ray observations, neutron observations, implications of gamma-ray
and neutron observations, interplanetary charged-particle observations,
acceleration mechanisms. 4. Mechanisms for particle acceleration
in flares: particle acceleration in reconnecting magnetic fields,
electron acceleration along the magnetic field with sub-Dreicer electric
fields, lower hybrid waves, Fermi acceleration and MHD turbulence,
shock acceleration, acceleration of electrons by intense radio waves,
preferential acceleration of heavy ions. 5. Achievements - outstanding
questions.
---------------------------------------------------------
Title: Correlation of Solar Decimetric Radio Bursts with X-Ray Flares
Authors: Aschwanden, M. J.; Wiehl, H. J.; Benz, A. O.; Kane, S. R.
1985SoPh...97..159A Altcode:
Several hundred radio bursts in the decimetric wavelength range
(300-1000 MHz) have been compared with simultaneous soft and hard X-ray
emission. Long lasting (type IV) radio events have been excluded. The
association of decimetric emission with hard X-rays has been found
to be surprisingly high (48%). The association rate increases with
bandwidth, duration, number of structural elements, and maximum
frequency. Type III-like bursts are observed up to the upper limit of
the observed band. This demonstrates that the corona is transparent up
to densities of about 10<SUP>10</SUP> cm<SUP>−3</SUP>, contrary to
previous assumptions. This can only be explained in an inhomogeneous
corona with the radio source being located in a dense structure. The
short decimetric bursts generally occur during the impulsive phase,
i.e. simultaneously with hard X-rays. The times of maximum flux are
well correlated (within 2 s). The HXR emission lasts 4 times longer then
the radio emission in the average. This work finds a close relationship
between decimetric and HXR emission with sufficient statistics offering
additional information on the flare process.
---------------------------------------------------------
Title: Radio Spikes and the Fragmentation of Flare Energy Release
Authors: Benz, A. O.
1985SoPh...96..357B Altcode:
Decimetric radio events with large numbers of spikes during the
impulsive phase of flares have been selected. In the observing range
of 100 to 1000 MHz some flares have of the order of 10000 spikes or
more. The average half-power bandwidth of spikes has been measured
to be only 1.5% of the spike frequency. Since the emission frequency
is determined by some source parameter (such as plasma frequency or
gyrofrequency) the source dimension must be a small fraction of the
scale length. From the flare configuration a typical upper limit of
the dimension of 200 km is found. The observed fragmentation in the
radio emission cannot be explained by a patchy emission mechanism of
a single and much larger source without an additional (and unknown)
assumption. It is proposed that the fragmentation already occurs in
the exciter.
---------------------------------------------------------
Title: Polarization of solar noise storm continuum and plasma wave
density in the corona
Authors: Benz, A. O.; Zolliker, P.
1985A&A...144..227B Altcode:
A statistical method for background subtraction of polarization
observations has been developed. It separates the signal from a
background with a much larger time constant. The method has been applied
to the continuum component of a noise storm at various frequencies. The
circular polarization was found to be constant in frequency within
the statistical error. Its average value in time and frequency was
89.0±1.5%. Well accepted assumptions are used to determine the fraction
of the radiation emitted at the harmonic of the plasma frequency from
observations. The resulting flux of the harmonic is not significantly
different from zero. The observed flux of the fundamental is used to
derive the plasma wave density in the source of the noise storm and
to predict the flux at the harmonic from theory.
---------------------------------------------------------
Title: Different time constants of solar decimetric bursts in the
range 100 1000 MHz
Authors: Wiehl, H. J.; Benz, A. O.; Aschwanden, M. J.
1985SoPh...95..167W Altcode:
Between 1980, January 1 and 1981, December 31 a total of 664 `decimetric
pulsation' events, abbreviated DCIM, were observed with the Zürich
spectrometers in the frequency range 100 to 1000 MHz. All of these
events were recorded on film, allowing an effective resolution in
time of 0.5 s, and 5 MHz in frequency. Some of these events were also
recorded digitally with higher time and frequency resolution.
---------------------------------------------------------
Title: First Detection of Radio Emission From a Dwarf Nova
Authors: Benz, A. O.; Furst, E.; Kiplinger, A. L.
1985ASSL..113..331B Altcode: 1985cvlm.proc..331B
The authors describe a search for radio emission at 4.75 GHz from
dwarf novae that has been carried out with the 100-m telescope at
Effelsberg, F.R. Germany. They have searched for radio emission from
six dwarf novae and a source was discovered at the position of SU
UMa. The source could only be detected during optical outburst and
was below the threshold during quiescence. The authors suggest that
the radio emission arises from a non-thermal process.
---------------------------------------------------------
Title: High Resolution in Astronomy
Authors: Benz, A. O.; Huber, M.; Mayor, Michel
1985hra..conf.....B Altcode: 1985SAAS...15.....B
No abstract at ADS
---------------------------------------------------------
Title: Decimetric Radio Emission During Solar Flares
Authors: Benz, A. O.; Aschwanden, M. J.; Wiehl, H. J.
1985spit.conf..597B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Synchrotron or plasma emission in solar microwave flares?
Authors: Benz, A. O.
1984SoPh...94..161B Altcode:
The spectral indices of microwave and hard X-ray emissions of a solar
flare are found to correlate. Their observed values are in agreement
with the expected relation from synchrotron and bremsstrahlung
theory. These results are considered as strong evidence for the
synchrotron mechanism in the microwave flare, contrary to recent
alternative suggestions.
---------------------------------------------------------
Title: Decimetric gyrosynchrotron emission during a solar flare
Authors: Batchelor, D. A.; Benz, A. O.; Wiehl, H. J.
1984ApJ...280..879B Altcode:
The implications of high time-resolution observations of a decimetric,
microwave, and hard X-ray burst during a solar flare in which the
900-998 MHz, 8.4 GHz, and 10.4 GHz peak fluxes fit the optically
thick spectrum of a homogeneous, thermal gyrosynchrotron source
are reported and discussed. The hard X-ray spectrum from 30 to 463
keV is well represented by a thermal bremsstrahlung function, and a
temperature derived from this spectrum is used to find the source area
of about 10 to the 18th sq cm. An electron density of less than about
7 x 10 to the 9th/cu cm and a magnetic field of roughly 120 gauss are
deduced from elementary plasma physics considerations and the lack of
Razin-Tsytovich absorption of the 900-998 MHz flux. These conditions
place the gyrosynchrotron source at high altitude in a coronal loop,
in agreement with VLA observations of other flares.
---------------------------------------------------------
Title: A Multiwavelength Study of a Double Impulsive Flare
Authors: Strong, K. T.; Benz, A. O.; Dennis, B. R.; Leibacher, J. W.;
Mewe, R.; Poland, A. I.; Schrijver, J.; Simnett, G.; Smith, J. B.,
Jr.; Sylwester, J.
1984SoPh...91..325S Altcode:
Extensive data from the Solar Maximum Mission (SMM) and ground-based
observatories are presented for two flares; the first occurred at
12:48 UT on 31 August, 1980 and the second just 3 min later. They were
both compact events located in the same part of the active region. The
first flare appeared as a typical X-ray flare: the CaXIX X-ray lines
were broadened (≡ 190±40 km s<SUP>-1</SUP>) and blue shifted (≡
60±20 km s<SUP>-1</SUP>) during the impulsive phase, and there was
a delay of about 30 s between the hard and soft X-ray maxima. The
relative brightness of the two flares was different depending on
the spectral region being used to observe them, the first being the
brighter at microwave and hard X-ray wavelengths but fainter in soft
X-rays. The second flare showed no significant mass motions, and the
impulsive and gradual phases were almost simultaneous. The physical
characteristics of the two flares are derived and compared. The main
difference between them was in the pre-flare state of the coronal plasma
at the flare site: before the first flare it was relatively cool (3 ×
10<SUP>6</SUP> K) and tenuous (4 × 10<SUP>9</SUP> cm<SUP>-3</SUP>),
but owing to the residual effects of the first flare the coronal plasma
was hotter (5 × 10<SUP>6</SUP> K) and more dense (3 × 10<SUP>11</SUP>
cm<SUP>-3</SUP>) at the onset of the second flare. We are led to believe
from these data that the plasma filling the flaring loops absorbed most
of the energy released during the impulsive phase of the second flare,
so that only a fraction of the energy could reach the chromosphere to
produce mass motions and turbulence.
---------------------------------------------------------
Title: On coronal oscillations
Authors: Roberts, B.; Edwin, P. M.; Benz, A. O.
1984ApJ...279..857R Altcode:
Magnetoacoustic oscillations in a solar coronal inhomogeneity
(e.g., coronal loop) are shown to take place with two distinct
periodicities, one on an acoustic (long) time scale and the other
on an Alfvenic (short) time scale. The short period modes - fast
magnetoacoustic waves - are trapped in regions of low Alfven speed:
typically, this corresponds to high density loops or dense open field
regions. Their periods may be on the order of seconds. The form of the
fast oscillations is discussed for both standing modes in a closed
loop and impulsively generated disturbances in a loop or open field
structure. Impulsively generated waves in a density enhancement exhibit
both periodic and quasi-periodic phases. Symmetric oscillations (sausage
modes) are analogous to Pekeris waves in oceanography; asymmetrical
(kink) disturbances are akin to Love waves in seismology. It is
suggested that fast magnetoacoustic waves may explain the observed
pulsations in Type IV radio events, the sausage waves providing the
desired 1 s periodicities. Magnetoacoustic oscillations provide a
potentially useful diagnostic tool for determining physical conditions
in the inhomogeneous corona.
---------------------------------------------------------
Title: Decimetric Type-Iii Radio Bursts and Associated Hard X-Ray
Spikes
Authors: Dennis, B. R.; Benz, A. O.; Ranieri, M.; Simnett, G. M.
1984SoPh...90..383D Altcode:
A detailed comparison is made between hard X-ray spikes and decimetric
type III radio bursts for a relatively weak solar flare on 1981 August 6
at 10: 32 UT. The hard X-ray observations were made at energies above 30
keV with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission
and with a balloon-born coarse-imaging spectrometer from Frascati,
Italy. The radio data were obtained in the frequency range from 100
to 1000 MHz with the analog and digital instruments from Zürich,
Switzerland. All the data sets have a time resolution of ∼ 0.1 s or
better. The dynamic radio spectrum shows many fast drift type III radio
bursts with both normal and reverse slope, while the X-ray time profile
contains many well resolved short spikes with durations of ≤ 1 s. Some
of the X-ray spikes appear to be associated in time with reverse-slop
bursts suggesting either that the electron beams producing the radio
bursts contain two or three orders of magnitude more fast electrons than
has previously been assumed or that the electron beams can trigger or
occur in coincidence with the acceleration of additional electrons. One
case is presented in which a normal slope radio burst at ∼ 600 MHz
occurs in coincidence with the peak of an X-ray spike to within 0.1
s. If the coincidence is not merely accidental and if it is meaningful
to compare peak times, then the short delay would indicate that the
radio signal was at the harmonic and that the electrons producing the
radio burst were accelerated at an altitude of ∼4 × 10<SUP>9</SUP>
cm. Such a short delay is inconsistent with models invoking cross-field
drifts to produce the electron beams that generate type III bursts
but it supports the model incorporating a MASER proposed by Sprangle
and Vlahos (1983).
---------------------------------------------------------
Title: The polarization of the noise storm continuum and the upper
limit on harmonic emission.
Authors: Benz, A. O.; Zolliker, P.
1984ost1.conf..167B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Orages solaires de type I: Abbaye de Senanque, Gordes,
France, 17-21 March 1980
---------------------------------------------------------
Title: Orages solaires de type I: Abbaye
de Senanque, Gordes, France, 17-21 March 1980
---------------------------------------------------------
Title: Solar storms
of type I Senanque Abbey, Gordes, France.
Authors: Bougeret, J. L.; Benz, A. O.
1984ost1.conf.....B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal evolution and solar type I radio bursts: an
ion-acoustic wavemodel.
Authors: Benz, A. O.; Wentzel, D. G.
1984ost1.conf..127B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Zukunft der Astronomie.
Authors: Benz, A.
1984Orion..42....6B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the spatial and temporal correlation of type I radio bursts
and soft X-rays.
Authors: Benz, A. O.; Jaeggi, M.; Mosher, J. M.; Nelson, G. J.
1984ost1.conf..145B Altcode:
The authors have compared type I radio burst positions and intensities
with spatially resolved soft X-ray observations. The spatial coincidence
is generally good, but not exact. There seems to be a time lag of about
one day between maximum X-ray brightness and maximum type I activity.
---------------------------------------------------------
Title: Noise storms and their place in the solar radio zoo.
Authors: Benz, A. O.
1984ost1.conf...35B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Decimetric gyrosynchrotron emission during a solar flare
Authors: Batchelor, D. A.; Benz, A. O.; Wiehl, H. J.
1983STIN...8416107B Altcode:
A decimetric, microwave, and hard X-ray burst was observed during
a solar flare in which the radio spectrum below peak flux fits an
f+2 power law over more than a decade in frequency. The spectrum
is interpreted to mean that the radio emission originated in a
homogeneous, thermal, gyrosynchrotron source. This is the first
time that gyrosynchrotron radiation has been identified at such low
decimetric frequencies (900-998) MHz). The radio emission was cotemporal
with the largest single hard X-ray spike burst ever reported. The
spectrum of the hard X-ray burst can be well represented by a thermal
bremsstrahlung function over the energy range from 30 to 463 keV at
the time of maximum flux. The temporal coincidence and thermal form
of both the X-ray and radio spectra suggest a common source electron
distribution. The unusual low-frequency extent of the single-temperature
thermal radio spectrum and its association with the hard X-ray burst
imply that the source had an area approx. 10(18) sq cm a temperature
approx 5x10(8) K, an electron density approx. 7.10(9) cu cm and a
magnetic field of approx. 120 G. H(alpha) and 400-800 MHz evidence
suggest that a loop structure of length 10,000 km existed in the flare
active region which could have been the common, thermal source of the
observed impulsive emissions.
---------------------------------------------------------
Title: Fast pulsations in the solar corona
Authors: Roberts, B.; Edwin, P. M.; Benz, A. O.
1983Natur.305..688R Altcode:
Pulsations in radio emission from the solar coronal plasma have
been detected for over a decade<SUP>1-9</SUP>. The oscillations are
quasiperiodic, with periods of typically a second or so. Recently,
sub-second time structures have been found in hard X rays<SUP>10</SUP>,
and simultaneously in hard X rays and microwaves<SUP>11</SUP>. Here
we examine whether magnetohydrodynamical oscillations in a density
enhancement, treated for simplicity as a straight magnetic slab, can
explain the observed short periods. A dense region in the corona (for
example, a loop) can act as a wave trap, and symmetrical oscillations
within that trap must be of short wavelength with correspondingly short
period. An impulsive source (such as a flare) naturally gives rise to
a quasiperiodic disturbance. Such oscillations are closely akin to
the Pekeris modes of oceanography, the Love waves of seismology and
the dielectric waves of fibre optics.
---------------------------------------------------------
Title: Radio blips and hard X-rays in solar flares
Authors: Benz, A. O.; Bernold, T. E. X.; Dennis, B. R.
1983ApJ...271..355B Altcode:
The properties of short, narrow-band spikes occurring in groups at
decimetric wavelengths have been extensively analyzed. The bursts,
termed blips in the literature, have been found to appear in the
impulsive phase of flares. They are associated with hard X-ray
emission in 40 percent of all cases with simultaneous coverage. The
correspondence between blips and X-ray spikes is generally not
one-to-one, blips being more numerous than X-ray spikes. In some
cases, however, close correlations between single events have been
found. Blips have been discovered to drift in frequency and to decay
in time similarly to type III bursts at lower frequency. They also
resemble type III bursts in polarization. An analysis of starting
frequencies, however, clearly shows that blips and type III bursts
belong to different statistical populations. The narrow bandwidth of
blips, the major qualitative difference with respect to type III bursts,
suggests that blips are the signature of electron beams which either
decay rapidly or have a locally enhanced emission due to the presence
of some low-frequency wave. Blips have been shown to be an impulsive
phase phenomenon occurring at densities of one to three billion per
cu cm in the low corona.
---------------------------------------------------------
Title: First detection of radio emission from a dwarf nova
Authors: Benz, A. O.; Fuerst, E.; Kiplinger, A. L.
1983Natur.302...45B Altcode:
The dwarf novae represent a class of cataclysmic variable stars that
typically exhibit random optical outbursts of 2-6 mag with mean outburst
periods of 10-150 days. Dwarf novae are close binary systems composed
of a late-type star which fills its critical Roche lobe and a white
dwarf companion. The white dwarf is surrounded by a luminous accretion
disk sustained by mass transfer from the late-type star. The disk is
the seat of the eruptions. Although radiation has been detected from
dwarf novae from IR through X-ray energies, radio emission has never
been reported from these objects. We describe here a search for radio
emission at 4.75 GHz from dwarf novae that has been carried out with
the 100-m telescope at Effelsberg, West Germany. We have searched for
radio emission from six dwarf novae and a source was discovered at the
position of SU UMa. The source could only be detected during optical
outbursts and was below the threshold during quiescence. We suggest
here that the radio emission arises from a non-thermal process.
---------------------------------------------------------
Title: X-Ray and Radio Emissions in the Early Stages of Solar Flares
Authors: Benz, A. O.; Barrow, C. H.; Dennis, B. R.; Pick, M.; Raoult,
A.; Simnett, G.
1983SoPh...83..267B Altcode:
Radio and X-ray observations are presented for three flares which show
significant activity for several minutes prior to the main impulsive
increase in the hard X-ray flux. The activity in this `pre-flash'
phase is investigated using 3.5 to 461 keV X-ray data from the Solar
Maximum Mission, 100 to 1000 MHz radio data from Zürich, and 169 MHz
radio-heliograph data from Nançay. The major results of this study
are as follows: Decimetric pulsations, interpreted as plasma emission
at densities of 10<SUP>9</SUP>-10<SUP>10</SUP> cm<SUP>−3</SUP>,
and soft X-rays are observed before any Hα or hard X-ray increase.
---------------------------------------------------------
Title: Solar 'blips' and the heating of X-ray areas
Authors: Hirth, W.; Fuerst, E.; Benz, A. O.
1983KlBer..26..189H Altcode:
Radioastronomy observations of the sun provide significant information
regarding the processes which occur above the photosphere. The 100-m
telescope in Effelsberg, West Germany, makes it possible to observe
the transition layer between chromosphere and corona. This transition
layer is important in connection with energy transfer to the corona. The
Zuerich spectrograph, on the other hand, with its operational range from
200 to 1000 MHz, is suited for observing processes in the corona. The
present investigation is concerned with observations involving very
small radiation bursts, called 'blips'. It is believed that a relation
exists between these phenomena and the heating of coronal areas. These
blips can now be studied on the basis of data simultaneously obtained
on March 2, 1979, in three different wavelength ranges. Data in the
decimetric range were obtained with the Zuerich spectrograph, while
the Effelsberg telescope provided data at 2.8 cm. Observations in the
X-ray range were obtained with the aid of the GOES 2 satellite. The
significance of the data is evaluated.
---------------------------------------------------------
Title: Solar radio storms. Proceedings of the 4th CESRA workshop on
solar noise storms, held at Trieste, Italy, August 9 - 13, 1982.
Authors: Benz, A. O.; Zlobec, P.; Wentzel, D. G.; House, L. L.; Dulk,
G. A.; Tlamicha, A.; Melrose, D. B.
1983srs..work.....B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Millisecond structures in noise storms and other solar radio
emission.
Authors: Barrow, C. H.; Benz, A. O.; Bernold, T. E. X.; Perrenoud,
M. R.
1983srs..work..109B Altcode:
Preliminary results of a high time-resolution (≡8 msec) fine structure
study are reported. Fine structures, having durations of some 10 to 40
msec, have been observed in solar noise storms and also associated with
type III, type IV, and type V bursts. These very short duration bursts,
referred to here as solar S-bursts, have been seen to occur individually
as well as in small groups where they may display a quasi-periodicity
of a few milliseconds. Generally, the S-bursts are not very intense
relative to the associated background emission.
---------------------------------------------------------
Title: Langmuir wave energy density in radio storm sources.
Authors: Benz, A. O.
1983srs..work...38B Altcode:
An enhanced level of Langmuir wave energy density is postulated in all
plasma wave models of radio storm emission. Three different methods are
described to measure this quantity: radar, observations of harmonics,
and polarization measurements. These methods have been applied to solar
noise storm sources. The results are presented. The best upper limit of
the ratio of wave energy density to thermal (kinetic) energy density
is 5×10<SUP>-6</SUP> for bursts and about an order of magnitude less
for the continuum.
---------------------------------------------------------
Title: Electron acceleration in impulsive solar flares
Authors: Kane, S. R.; Benz, A. O.; Treumann, R. A.
1982ApJ...263..423K Altcode:
Physical parameters relevant to the acceleration and propagation of
energetic electrons during the impulsive phase of a solar flare are
studied in hard X-ray, microwave and both type III and decimetric radio
bursts associated with the December 4, 1978 solar flare. A one-to-one
association between single type III bursts and hard X-ray peaks is
established, along with a burst delay with respect to the peaks of 0.5
sec. The observed increase of the high frequency cutoff of the metric
type III bursts during the impulsive phase is examined in terms of the
decreasing altitude of the electron acceleration/injection region,
increasing electron spectrum hardness, and decreasing acceleration
time. A pulsating decimetric continuum was found to be present during
and before the impulsive phase whose high frequency cutoff also
systematically increased during the rise of the impulsive phase.
---------------------------------------------------------
Title: Fine structure near the starting frequency of solar type III
radio bursts
Authors: Benz, A. O.; Jaeggi, M.; Zlobec, P.
1982A&A...109..305B Altcode:
An analysis of the period in time and frequency adjacent to the
beginning of type III bursts digitally recorded at Bleien, Switzerland,
during the second half of 1980 is presented. It is found that a high
percentage (10%, possibly more than 20%) of the type III bursts
show fine structure in the form of narrow-banded spikes of 0.05
s and less duration. These spikes form 'clusters' of relatively
large bandwidth. They are not totally polarized and are uniformly
distributed over the disk. Individual spikes often exhibit highly
variable polarization, which may even change sense. The average degree
of polarization of the clouds is found to have a wider distribution
than that of the associated type III bursts but to have generally the
same sign. It is noted that the spikes are considerably different from
type I bursts. The spikes are then classified on the basis of their
occurrence in relation to the beginning of type III bursts.
---------------------------------------------------------
Title: The Relation Between the Surges and Solar Radio Emission
Authors: Garczynska, I. N.; Rompolt, B.; Benz, A. O.; Slottje, C.;
Tlamicha, A.; Zanelli, C.
1982SoPh...77..277G Altcode:
The 120 limb surges which have been observed by means of Wrocław
Observatory coronagraph from September 1966 to November 1977 are
investigated. The evolution of surges was compared with the radio
data during the surges. A correlation between radio bursts and the
surges was found, particularly with chains of type I radio bursts,
which is the first reliable correlation found of these bursts with
non-radio events. The type I correlation only applied for surges
without accompanying flare, of which 43% are correlated with this type
of radio emission. In 23 of 30 associated events the start of a surge
coincided within 5 minutes with the start or an enhancement of the type
I storm. If flares were present, the association was not significant.
---------------------------------------------------------
Title: Evidence of primary and secondary bursts in solar type III
emission
Authors: Benz, A. O.; Treumann, R.; Vilmer, N.; Mangeney, A.; Pick,
M.; Raoult, A.
1982A&A...108..161B Altcode:
Simultaneous observations of groups of metric type III radio bursts at
high spectral, spatial, and temporal resolution are presented. They
have occurred on different days and above the photospheric limb. It
is found that they tend to be clustered in pairs. The two bursts in
each pair have considerably different properties. The primary bursts
have generally higher frequency drifts, stronger polarization, higher
starting frequency, smaller size, and sometimes larger distance from the
center of the sun. The hypothesis of fundamental and harmonic emission
encounters serious difficulties. The observations fit better with
electron beams propagating along two different (primary and secondary)
paths. This suggests a model where the secondary beam originates from
electrons with a different acceleration region being triggered by
the first energy release and having a smaller energy input and thus
smaller beam velocity.
---------------------------------------------------------
Title: Search for harmonic emission in solar type I radio bursts
Authors: Jaeggi, M.; Benz, A. O.
1982A&A...107...88J Altcode:
A statistical analysis is made of the harmonic emission of type I
bursts, which is based on the latest plasma wave theories for the
emission mechanism. No systematic harmonic emission is detected,
although in a few single cases emission is found at the harmonic
frequency, which is attributed to chance hits of an independent activity
present at that frequency. An upper limit for the Langmuir wave energy
density is derived, and the consequences for plasma emission theories
are discussed.
---------------------------------------------------------
Title: About the relation between radio and soft X-ray emission in
case of very weak solar activity
Authors: Fuerst, E.; Benz, A. O.; Hirth, W.
1982A&A...107..178F Altcode:
Centimeter and decimeter observations of very small solar soft
X-ray events detected by the GOES-2 satellite on March 2, 1979,
are reported. The radio events are labeled 'blips' because of their
faintness at cm-wavelengths combined with fast variation of the flux
and because of unusual narrow-band emission at dm-wavelengths. The
blips occur mainly in the rise phase of the X-ray emission. Analysis
of the blips shows that nonthermal radiation of fast electrons is the
origin of their emission. The energy of fast electrons necessary to
explain the cm-blip flux is roughly equal to the heat energy of the
X-ray source. This is seen as a hint that the X-ray source is heated by
the excess energy of the fast electrons. The X-ray source is assumed to
resemble an emerging flux region with a size typical of X-ray kernels.
---------------------------------------------------------
Title: Solar Radio Storms
Authors: Benz, A. O.; Zlobec, P.
1982srs..work.....B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Millisecond structures in noise storms and other solar radio
emission
Authors: Barrow, C. H.; Benz, A. O.; Bernold, T. E. X.; Perrenoud,
M. R.
1982srs..work..109B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Langmuir wave energy density in radio storm sources (review)
Authors: Benz, A. O.
1982srs..work...38B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar type I noise storms and newly emerging magnetic flux
Authors: Spicer, D. S.; Benz, A. O.; Huba, J. D.
1982A&A...105..221S Altcode:
A new model of solar type I radio bursts is presented based on the
assumption that newly emerging magnetic flux can become, on occasion,
weakly super-Alfvenic and thus capable of driving weak collisionless
shocks in the front of the flux as it emerges. Using the assumption
that the collisionless shock is maintained near marginal stability
with respect to various collisionless flute like instabilities, we
compute the microturbulence level of lower hybrid waves excited by the
shock. It is then argued that these obliquely propagating lower hybrid
waves are capable of accelerating electrons in the wake of the weak
shock. These accelerated electrons are then utilized to excite upper
hybrid waves via a loss-cone instability. The resulting mode coupling
between lower hybrid and upper hybrid waves is then suggested as a
radiation mechanism for the type I bursts.
---------------------------------------------------------
Title: The microwave solar radar experiment. I - Observations
Authors: Fitze, H. R.; Benz, A. O.
1981ApJ...250..782F Altcode:
The first solar radar experiment in microwaves, carried out
with the 300-m dish in Arecibo using a 250 kW transmitter, is
described. Receiving at a displaced frequency from the transmitted radar
frequency makes it possible to probe the Langmuir (plasma) wave energy
density of the corona in the 170-270 MHz range. No echo is found in
various regions on the sun. It is pointed out that this contradicts some
models of type I radio bursts and a proposed scattering mechanism of
metric solar radar echos. Neither is any echo produced in an alternative
experiment, in which reception is at the transmitted frequency. It is
noted that the reflectivity of the sun in microwaves is more than four
orders of magnitude below the reflectivity in meter waves.
---------------------------------------------------------
Title: Solar radio blips and X-ray kernels
Authors: Benz, A. O.; Perrenoud, M. R.; Fuerst, E.; Hirth, W.
1981Natur.291..210B Altcode:
Hudson<SUP>1</SUP> proposed that the primary flare energy release goes
into fast electrons. Others<SUP>2,3</SUP> found the flare soft X-ray
emission to consist of bright, small kernels (knots and loops) embedded
in a more diffuse halo. These kernels with a typical size of 5' arc s
and a temperature of 6-12 × 10<SUP>6</SUP>K emit in radio waves at 3.7
and 11 cm (ref. 4). The discovery of a radio brightness temperature
equal to the temperature derived from the X rays and the radio size
larger than in X rays shows that the observed radio emission is thermal
(free-free) and the source optically thick at λ > 3.7 cm. Therefore,
Kundu et al.<SUP>4</SUP> did not observe the fast electrons expected
to heat the kernels. Here we present high time resolution measurements
at 2.8 cm from the Effelsberg 100-m telescope and at decimetric and
metric wavelengths with the ETH Zurich spectrometers. Both instruments
have detected signatures of non-thermal particles.
---------------------------------------------------------
Title: Optical and radio observations of the 1980 March 29, April 30,
and June 7 flares
Authors: Rust, D. M.; Benz, A.; Hurford, G. J.; Nelson, G.; Pick,
M.; Ruzdjak, V.
1981ApJ...244L.179R Altcode:
Ground-based solar observations are analyzed for three of the flares
discussed in the accompanying Solar Maximum Mission reports. The
principal conclusions are that H-alpha begins to brighten several
minutes before the impulsive, hard X-ray bursts, that the preflare
heating and impulsive phases of the three flares occurred in loop-shaped
structures of about 3500 km semidiameter, and that after the impulsive
phase a much larger volume (about 200 times) of flare plasma was
present for the flare main phase. Evidence is presented for the escape
of 100-500 keV electrons into the larger volume and into the corona
during the impulsive phase. For the April 30 flare, the inferred origin
of the hard X-ray burst is near the feet of the magnetic loops.
---------------------------------------------------------
Title: Über die solaren Minibursts
Authors: Fürst, E.; Hirth, W.; Benz, A.
1981MitAG..52...66F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Quasi-periodic short-term modulations during a moving type
IV burst
Authors: Trottet, G.; Kerdraon, A.; Benz, A. O.; Treumann, R.
1981A&A....93..129T Altcode:
The Nancay Radioheliograph and the E.T.H. spectrometer measurements
of a pulsating emission at the start of a moving type IV continuum
indicated that the modulation is not strictly periodic and that the
brightness temperature of the pulsating source is greater than 10
to the 9th K. The source shows two types of motions observed by the
heliograph which correspond to two negative frequency drifts visible
on the spectrometer: the first is a global motion with a velocity
of 350 km/s typical of moving type IV, and the second has a much
higher velocity of 100,000 km/s. Analysis of modulation and emission
processes involving perturbations of the loss cone distribution of
trapped electrons demonstrate that they provide an alternative for
the interpretation of the observed characteristics.
---------------------------------------------------------
Title: Coronal evolution and solar type I radio bursts - an
ion-acoustic wave model
Authors: Benz, A. O.; Wentzel, D. G.
1981A&A....94..100B Altcode:
A model is proposed for type I burst emission that can accommodate
both the main burst observations and an origin for the continuum. It
is assumed that ion-acoustic waves are generated in the burst source
by a current that is related to the coronal magnetic evolution, in
particular to magnetic nonequilibrium caused by photospheric changes
(e.g. emerging magnetic field) in active regions. Radio emission
arises from coalescence of ion-acoustic and plasma waves. Contrary
to other plasma wave models, emission at the harmonic of the plasma
frequency is below the present detection threshold (not greater
than 0.1%). The ion-acoustic wave density, having a high saturation
value, determines the optical depth, which reaches unity within a
few meters. The brightness temperature is thus entirely given by
the level of Langmuir waves. These waves may be produced by trapped
non-thermal electrons from previous burst sources. The same population
also provides sufficient plasma waves for the type I continuum, which
may arise from interactions with low-frequency waves present in the
corona during times of type I activity.
---------------------------------------------------------
Title: Activity and outer atmospheres of the sun and stars. Eleventh
Advanced Course of the Swiss Society of Astronomy and Astrophysics,
held in Saas-Fee, Switzerland, March 30 - April 4, 1981.
Authors: Benz, A. O.; Chmielewski, Y.; Huber, M. C. E.; Nussbaumer, H.
1981aoas.book.....B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Impulsive Solar Flare at 0918 UT on 1980 March 29
Authors: Crannell, C. J.; Trombka, J. I.; Benz, A.; Magun, A.; Matzler,
C.; Wiehl, H.; Ryan, J. M.
1980BAAS...12..889C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Electron trapping in the solar magnetic field and emission
of decimetric continuum radio bursts.
Authors: Benz, A. O.
1980ApJ...240..892B Altcode:
The conditions for confinement of energetic electrons in the solar
corona are studied with respect to the influence of electrostatic waves,
which have been suggested to cause type IV(dm) decimetric continuum
emission. A hydrodynamic approach is taken for simplicity. The
unstable growth of these waves is found to be effectively limited
by a change of the particle gyroperiod in the electric field of the
wave detuning the resonance. Saturation of wave energy density occurs
at a low level, which is proportional to the fraction of energetic
particles. The low wave level excludes induced scattering on thermal
ions for the hydrodynamic instability. A new model is proposed based
on conversion by interaction with low-frequency waves, in particular,
lower hybrid waves, which are known to exist in loss-cone situations
of the magnetosphere. The fraction of energetic particles of the plasma
necessary for the observed radio flux allows trapping times of the order
of minutes. Oscillations of the saturation wave amplitude are found.
---------------------------------------------------------
Title: First solar radar observations in microwaves
Authors: Benz, A. O.; Fitze, H. R.
1980IAUS...86..247B Altcode:
The first microwave radar experiment probing solar radio emission
source regions is presented. The 300-m dish telescope at Arecibo was
used to scatter 2380-MHz pulsed signals on coronal Langmuir waves with
frequencies from 170 to 270 MHz in source regions of type I emission,
and the radio signal produced by the nonlinear interaction of the two
wave modes was monitored at 2600 MHz at a bandwidth of 100 MHz. The
experiment has performed as expected, with a threshold sensitivity
on the order of 1 Jy, however no echo has yet been detected. An upper
limit to the Langmuir wave energy density of 0.0005 nKT is thus obtained
from the wave-wave interaction coefficient for a source temperature
of 5,000,000 K, size of 10 to the 28th cu cm and an isotropic and flat
Langmuir wave spectrum.
---------------------------------------------------------
Title: Solar Radar Observations
Authors: Benz, A. O.
1980IAUS...91..135B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Type-I Radio Bursts - an Ion-Acoustic Wave Model
Authors: Benz, A. O.; Wentzel, D. G.
1980IAUS...86..251B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sonnenforschung mit Radiowellen.
Authors: Benz, A.
1980Orion..38....9B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sonnenforschung mit Radiowellen an der ETH.
Authors: Benz, A.
1980Orion..38...77B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The evolution of polarization in type U solar radio bursts.
Authors: Benz, A. O.; Urbarz, H. W.; Zlobec, P.
1979A&A....79..216B Altcode:
Surmary. We have analyzed the polarization of type U solar radio bursts
from 16 active regions. Only two of them produced events which changed
sign between ascending and descending branch. These observations lead to
the suggestion of weak mode coupling in quasi-transverse regions in the
low corona, in contradiction to measurements at higher altitudes. The
sign of polarization corresponds to ordinary emission in the field
of the leading spot, which suggests an asymmetric magnetic loop with
stronger field in the ascending leg. This agrees with the observed
higher polarization in the ascending branch of the U-burst. Spikes in
polarization in the descending branch have been found to occur before
maximum flux similar to the ascending branch in contradiction to the
expectation from theory. A new interpretation of the phenomenon is given
in terms of the phase velocity shift of the Langinuir waves during the
passage of the beam at a given place (for fundamental emission). Key
words: solar radio emission - polarization of U-bursts - mode coupling -
Langmuir wave phase velocity
---------------------------------------------------------
Title: Microwave radar observations of the sun.
Authors: Benz, A. O.; Fitze, H. R.
1979A&A....76..354B Altcode:
A pilot experiment on microwave radar observations of the sun has been
conducted with the Arecibo 300-m telescope. Data obtained at 2600 MHz
with a bandwidth of 100 MHz are presented. This frequency is shifted
from the transmitted frequency by the expected Langmuir waves in
the range from 170 to 270 MHz. The results show the absence of such
waves in the corona with energy densities above about 0.0006, 0.08,
and 0.02 nKT for a possible type I radio source region, a prominence,
and streamer, respectively.
---------------------------------------------------------
Title: Type I Solar Radio Bursts
Authors: Benz, A. O.; Wentzel, D. G.
1979BAAS...11..441B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Plasma instabilities of trapped particles in solar magnetic
fields.
Authors: Berney, M.; Benz, A. O.
1978A&A....65..369B Altcode:
Electromagnetic whistler and electrostatic (hydrodynamic) instabilities
in a magnetized plasma are studied with reference to the loss-cone
velocity distribution function of particles. In the electrostatic
case, maximum growth rate and marginal stability are considered. For
whistler waves, the area of instability is spatially limited by the
extent of the loss-cone distribution. Thus, while the growth rate
for the whistler instability peaks at the feet of the arches, the
electrostatic instability is restricted to zones near places where
the upper hybrid frequency of the background particles is an integer
multiple of the electron cyclotron frequency. It is noted that the
electrostatic instability will become saturated, i.e., in a state of
quasi-equilibrium, with the losses of untrapped particles. Whistler
growth, however, is limited by field curvature in a twisted magnetic
field, or by refraction.
---------------------------------------------------------
Title: An extremely narrow-band solar type IV<SUB>dm</SUB> burst
with fine structure.
Authors: Tarnstrom, G. L.; Benz, A. O.
1978A&A....63..147T Altcode:
A decimetric type IV solar burst occurring with a halfpower bandwidth
of only 40 MHz is analyzed; the concurrent fine structure of the burst
is concluded to be a signature for plasma wave emission rather than
synchrotron emission. With plasma wave emission assumed and the most
widely spread interpretation of the fine structure adopted, coronal
magnetic field strengths in the range of 5.5 + or - 1.5 gauss have
been computed. The magnetic field values are about half those computed
for the associated type II split-band event, suggesting that entirely
different conditions in two well separated sources have been detected.
---------------------------------------------------------
Title: Correlation between drift rate and polarization in solar type
III radio bursts.
Authors: Benz, A. O.; Zlobec, P.
1978A&A....63..137B Altcode:
A statistically significant correlation between polarization and
frequency drift rate has been found in an analysis of 463 solar
type III radio bursts. The correlation is particularly marked for
high degrees of polarization, small total bandwidths, or for cases
involving a polarization spike before maximum intensity. It is argued
that the correlation arises naturally from fundamental emission, and
is due to a direct influence of drift velocity on polarization. The
lack of correlation observed at low polarization may be interpreted
by reference to the predominance of second harmonic emission.
---------------------------------------------------------
Title: Observations of the type I continuum radiation on July 9-13,
1978 at Dürnten
Authors: Mätzler, C.; Perrenoud, M. R.; Benz, A. O.
1978cesra...7...18M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transient Aspects of the Corona including Flare Related Events
Authors: Benz, A. O.
1978pfsl.conf..267B Altcode: 1978ESPM....2..267B
No abstract at ADS
---------------------------------------------------------
Title: On the scattering hypothesis for type V radio bursts.
Authors: Pilipp, W. G.; Benz, A. O.
1977A&A....56...39P Altcode:
The possibility is considered that the energetic electrons producing
a type III burst may excite electromagnetic instabilities which
subsequently lead to scattering of the electrons and the generation
of a type V burst. The nonrelativistic dispersion relation is solved
for circularly polarized electromagnetic waves propagating parallel
to the magnetic field in a system consisting of a thermal plasma and
a uniform electron beam. It is shown that for certain beam and plasma
parameters, an instability with respect to lefthand polarized waves
occurs which is driven to a large extent by a 'resonant electron'
instability that could result in scattering of resonant beam electrons
without the need for preexisting plasma turbulence. Observations are
discussed which indicate that type V bursts are preferably produced
under conditions that are in qualitative agreement with those for
which the present calculations yield an instability.
---------------------------------------------------------
Title: The polarization of U-shaped solar radio bursts.
Authors: Benz, A. O.; Berney, M.; Santin, P.
1977A&A....56..123B Altcode:
Circular-polarization measurements of 11 U-shaped solar radio bursts
observed at 237 MHz are reported which contradict the expectation
that the received polarization should have different signs in the two
branches. The mean polarization of these bursts is found to be about 7%
righthanded for the ascending branch and about 6% in the same sense
for the descending branch. An attempt is made to discuss the observed
constancy of the sign of polarization in terms of coronal propagation
properties above the source region.
---------------------------------------------------------
Title: Circular Polarization and Frequency Drift Rate Correlated in
Solar Type III Radio Bursts.
Authors: Benz, A. O.; Zlobec, P.
1977BAAS....9..369B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the kinetics of solar wind acceleration.
Authors: Benz, A. O.; Gold, T.
1977A&A....55..229B Altcode:
A two-stream model of solar-wind hydrogen-plasma expansion is outlined
in which protons at any one level of flux generation are divided into
those that collide rapidly relative to their expansion times and those
that leave the sun without significant relaxation. Proton evaporation
is explicitly taken into account along with momentum and energy gains
due to friction with escaping protons. This model is investigated
numerically by an iteration technique, assuming a lateral expansion
of the solar wind. It is found that for very low temperatures, proton
acceleration is caused mainly by a lack of fast-particle collisions
and that the collisional population is more accelerated and denser
at higher temperatures. The results also show that evaporation over a
large extent of height reduces the solar-wind heating requirements to
the region of the low corona. Examination of the physical stability of
the solar-wind plasma in this model indicates that no electrostatic
two-stream instability can arise, the firehose-instability condition
could be satisfied only with very low temperatures near the level of
full evaporation, and a point of serious instability with respect to
magnetosonic whistlers occurs at a heliocentric distance of about 10
solar radii.
---------------------------------------------------------
Title: Spectral features in solar hard X-ray and radio events and
particle acceleration.
Authors: Benz, A. O.
1977ApJ...211..270B Altcode:
Hard X-ray and radio intensities of two major solar outbursts are
found to anticorrelate in time with their spectral indices, which,
furthermore, are in satisfactory correlation with each other. The
radio emission must be synchrotron radiation from the same electron
population that causes the X-ray bremsstrahlung. A delay of temporal
features, increasing with energy, is clearly observed in one of
the X-ray events. The observations are interpreted with a simple
model, which assumes ion-acoustic instability in a current sheet,
transformation of turbulence energy into Langmuir waves, and their
escape into the ambient plasma where they accelerate particles. A
power-law index of the electron energy distribution is derived for
acceleration being balanced by escape of particles. Anticorrelation of
intensity and spectral index then follows naturally from variations of
the spectral wave energy density or the dimension of the acceleration
region. The finite collision time in the acceleration region and its
increase with energy introduce a perturbation which can explain the
observed drift of temporal features.
---------------------------------------------------------
Title: Short, drifting spikes in the cm-dm wavelength radiation of
the active sun
Authors: Benz, A. O.
1977KlBer..20...31B Altcode:
Data of the October 25, 1972, radio outburst were analyzed in the
cm and dm range. They are interpreted in terms of drifting spikes. A
synchrotron model is proposed in which the source magnetic field changes
either because of expansion or mirror point motion. Absorption on the
low frequency side is proposed to be by gyroresonance.
---------------------------------------------------------
Title: New Features in Hard X-Ray and Radio Spectra of Solar Outbursts
and Implications on Particle Acceleration
Authors: Benz, A. O.
1976BAAS....8..374B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Synchrotron or plasma process emission in narrow-band type
IV<SUB>dm</SUB> bursts?
Authors: Benz, A. O.; Tarnstrom, G. L.
1976ApJ...204..597B Altcode:
Extremely narrow-banded type IVdrn events have been selected to
test the various proposed emission mechanisms. Emphasis is put on
the observed spectral shape and rapid variations in intensity, and
plasma-physical stability of the source model. Synchrotron emission in
quasi- vacuum is excluded by the observed steep low-frequency spectral
sfope. Free-free absorption of incoherent synchrotron emission is
negligible compared with the Razin effect suppression. However,
Razin-suppressed synchrotron emission would lead to unstably high
concentrations of energetic electrons. A low-frequency cutoff due to
cyclotron-resonance absorption is unlikely. The coherent synchrotron
processes are shown to require either an excessively large number of
relativistic electrons or an unstable pitch angle anisotropy. Plasma
processes seem to be the necessary explanation for the bursts under
consideration. Subject headings: plasmas - Sun: radio radiation
synchrotron radiation
---------------------------------------------------------
Title: Type IV dm bursts: onset and sudden reductions.
Authors: Benz, A. O.; Kuijpers, J.
1976SoPh...46..275B Altcode:
The effect of collisions of suprathermal electrons with a thermal
background plasma is investigated and is shown to cause flattening of a
monotonically descending velocity distribution of fast particles. As a
result flare-produced energetic electrons that are trapped in a coronal
magnetic arch and that are initially distributed in energy according to
a power-law, can give rise to an instability of Langmuir waves in the
background plasma and the subsequent emission of continuum radiation
as observed in type IV dm bursts.
---------------------------------------------------------
Title: Simulation of analog spectrograms of solar radio bursts
Authors: Benz, A. O.; Asper, H. K.
1976KlBer..19..383B Altcode:
Analog spectrograms are simulated for a well-documented solar radio
burst by numerical transformation of digital data recorded on magnetic
tape by a radio spectrograph. The simulations were carried out to
observe how different and sometimes erroneous classifications of radio
bursts may result from instrumental characteristics, such as threshold,
noise figure, gain, film blackening, and frequency response. Simulated
spectrograms are presented which illustrate the effects of different
logarithmic compression rates and different receiver frequency
responses. It is shown that suprising effects are possible with
different logarithmic compression rates, that a frequency-dependent
sensitivity may considerably change the drift rate of type III bursts,
and that different relations between solar flux and grey level on the
film can alter the morphology of a burst to a remarkable extent and
result in different classifications. It is concluded that a moderately
uneven frequency response has little effect on a burst shape in the
frequency-time plane if the received burst signal is not near threshold.
---------------------------------------------------------
Title: The New Digitalized Solar Radio Spectrograph in Durnten.
Authors: von Arx, B.; Benz, A. O.; Tarnstrom, G. L.
1975BAAS....7..407V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Type IVdm Bursts vs. the Razin Effect.
Authors: Benz, A. O.; Tarnstrom, G. L.
1975BAAS....7..439B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: First digital observation with the Duernten radio spectrograph.
Authors: Perrenoud, M. R.; Benz, A. O.; Tarnstrom, G. L.
1975MmArc.105..121P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: First digital observation with the Dürnten radio spectrograph
Authors: Perrenoud, M. R.; Benz, A. O.; Tarnstrom, G. L.
1975cesra...5..121P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A possible Mechanism for Type V Bursts
Authors: Benz, A. O.
1974cesra...4..157B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Complex Radio Burst of May 3, 1973
Authors: Benz, A. O.; Tlamicha, A.; Urbarz, H.
1974cesra...4..191B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Harmonic Structure in a Solar Type V Burst
Authors: Benz, A. O.
1973NPhS..242...38B Altcode: 1973Natur.242...38B
WHEN type V bursts were first identified as a distinct class in 1958,
their seemingly featureless continuum radiation was interpreted as
synchrotron emission<SUP>1</SUP>. Later it was observed<SUP>2</SUP>,
however, that the source positions at different frequencies were
not identical. It has then been suggested<SUP>2,3</SUP> that type
V bursts are most likely due to Čerenkov radiation from coherent
plasma waves caused by fast electrons (speed ≍ 1/3 c) which are
magnetically trapped in the corona<SUP>4</SUP>. In the plasma wave
theory radiation is emitted near the local plasma frequency and/or
its integer multiples. In spite of the hindering large bandwidth,
one would nevertheless expect to recognize (at least sporadically)
harmonic structure in the spectra of type V bursts. This is generally
considered to be an observational confirmation of any plasma wave
emission theory. So far it has not been observed in type V bursts,
save for one inconclusive indication (on May 8, 1959)<SUP>2</SUP>.
---------------------------------------------------------
Title: The Acceleration of Solar Wind Protons and Heavy Ions.
Authors: Benz, Arnold Otto
1973PhDT.........8B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetically Trapped Particles in the Lower Solar Atmosphere
Authors: Benz, A. O.; Gold, T.
1971SoPh...21..157B Altcode:
The trapping of energetic electrons and protons in a simple,
arched magnetic field imbedded in the lower solar atmosphere was
considered. The lifetime of electrons with kinetic energies up to about
1.5 MeV was found to be completely determined by the motion of the
mirror points, provided the gyro-synchrotron loss can be neglected. The
same motion also influences the lifetimes of more energetic electrons,
up to 10 MeV. This was not found to be the case for protons in the range
from 1 MeV to 100 GeV. Some fluid and streaming instabilities were also
considered; they pull the particles upward, raise their mirror points,
and increase their lifetime. The emission of gyro-synchrotron radiation
and bremsstrahlung in this model has been related to observations. Using
the duration of non-thermal X-ray peaks given by Kane (1969), the
altitude of injection of energetic particles was estimated.
