Author name code: brown-john
ADS astronomy entries on 2022-09-14
author:"Brown, John Campbell"
------------------------------------------------------------------------
Title: 3D magnetic-field morphology of the Perseus molecular cloud
Authors: Tahani, M.; Lupypciw, W.; Glover, J.; Plume, R.; West, J. L.;
Kothes, R.; Inutsuka, S.; Lee, M. -Y.; Robishaw, T.; Knee, L. B. G.;
Brown, J. C.; Doi, Y.; Grenier, I. A.; Haverkorn, M.
Bibcode: 2022A&A...660A..97T
Altcode: 2022arXiv220104718T
Context. Despite recent observational and theoretical advances in
mapping the magnetic fields associated with molecular clouds, their
three-dimensional (3D) morphology remains unresolved. Multi-wavelength
and multi-scale observations will allow us to paint a comprehensive
picture of the magnetic fields of these star-forming regions.
Aims: We reconstructed the 3D magnetic field morphology associated
with the Perseus molecular cloud and compared it with predictions
of cloud-formation models. These cloud-formation models predict a
bending of magnetic fields associated with filamentary molecular
clouds. We compared the orientation and direction of this field
bending with our 3D magnetic-field view of the Perseus cloud.
Methods: We used previous line-of-sight and plane-of-sky magnetic
field observations as well as Galactic magnetic field models to
reconstruct the complete 3D magnetic field vectors and morphology
associated with the Perseus cloud.
Results: We approximated
the 3D magnetic field morphology of the cloud as a concave arc that
points in the decreasing longitude direction in the plane of the sky
(from our point of view). This field morphology preserves a memory of
the Galactic magnetic field. In order to compare this morphology to
cloud-formation model predictions, we assume that the cloud retains
a memory of its most recent interaction. After incorporating velocity
observations, we find that the line-of-sight magnetic field observations
are consistent with predictions of shock-cloud-interaction models.
Conclusions: To our knowledge, this is the first time that the 3D
magnetic fields of a molecular cloud have been reconstructed. We find
the 3D magnetic field morphology of the Perseus cloud to be consistent
with the predictions of the shock-cloud-interaction model that describes
the formation mechanism of filamentary molecular clouds.
Title: Orion A's complete 3D magnetic field morphology
Authors: Tahani, M.; Glover, J.; Lupypciw, W.; West, J. L.; Kothes, R.;
Plume, R.; Inutsuka, S.; Lee, M. -Y.; Grenier, I. A.; Knee, L. B. G.;
Brown, J. C.; Doi, Y.; Robishaw, T.; Haverkorn, M.
Bibcode: 2022A&A...660L...7T
Altcode: 2022arXiv220308763T
Magnetic fields permeate the interstellar medium and are important
in the star formation process. Determining the three-dimensional (3D)
magnetic fields of molecular clouds will allow us to better understand
their role in the evolution of these clouds and the formation of
stars. We fully reconstruct the approximate 3D magnetic field morphology
of the Orion A molecular cloud (on scales of a few to ∼100 pc) using
Galactic magnetic field models, as well as available line-of-sight
and plane-of-sky magnetic field observations. While previous studies
identified the 3D magnetic field morphology of the Orion A cloud as an
arc shape, in this study we provide the orientation of this arc-shaped
field and its plane-of-sky direction for the first time. We find
that this 3D field is a tilted, semi-convex (from our point of view)
structure and mostly points in the direction of decreasing latitude
and longitude on the plane of the sky from our vantage point. The
previously identified bubbles and events in this region were key in
shaping this arc-shaped magnetic field morphology.
Title: ICARUS: new voyage to sterile neutrino search in the Short
Baseline Program
Authors: Kose, U.; Abratenko, P.; Aduszkiewicz, A.; Akbar, F.; Asaadi,
J.; Babicz, M.; Badgett, W. F.; Bagby, L. F.; Behera, B.; Bellini, V.;
Beltramello, O.; Benocci, R.; Berger, J.; Berkman, S.; Bertolucci,
S.; Betancourt, M.; Biagi, S.; Biery, K.; Bonesini, M.; Boone, T.;
Bottino, B.; Braggiotti, A.; Bremer, J.; Brice, S. J.; Brizzolari,
C.; Brown, J.; Budd, H.; Carneiro, M.; Carranza, H.; Casazza, D.;
Castro, A.; Centro, S.; Cerati, G.; Chalifour, M.; Chatterjee, A.;
Cherdack, D.; Cherubini, S.; Coan, T.; Cocco, A.; Convery, M. R.;
Copello, S.; De Roeck, A.; Di Noto, L.; Di Stefano, C.; Diwan, M.;
Dolan, S.; Domine, L.; Doubnik, R.; Drielsma, F.; Dyer, J.; Dytman, S.;
Fabbri, V.; Fabre, C.; Falcone, A.; Farnese, C.; Fava, A.; Ferrari,
A.; Ferraro, F.; Gallice, N.; Garcia, F.; Geynisman, M.; Gibin, D.;
Gomez Cortes, B.; Gu, W.; Guerzoni, M.; Guglielmi, A.; Hahn, S.;
Heggestuen, A.; Hilgenberg, C.; Howard, B.; Howell, R.; Hrivnak, J.;
James, C.; Jang, W.; Ketchum, W.; Koh, D. H.; Kose, U.; Larkin, J.;
Laurenti, G.; Lukhanin, G.; Marshall, C.; Martynenko, S.; Mauri, N.;
Mazzacane, A.; McFarlan, K. S.; Mendez, D. P.; Menegolli, A.; Meng,
G.; Miranda, O. G.; Mladenov, D.; Moggi, N.; Montanari, C.; Montanari,
A.; Mooney, M.; Moreno Granados, G.; Mueller, J.; Naples, D.; Nessi,
M.; Nichols, T.; Palestini, S.; Pallavicini, M.; Paolone, V.; Papaleo,
R.; Pasqualini, L.; Patrizii, L.; Petrillo, G.; Petta, C.; Pia, V.;
Pietropaolo, F.; Poppi, F.; Pozzato, M.; Prosser, A.; Putnam, G.;
Qian, X.; Rappoldi, A.; Raselli, G. L.; Rechenmacher, R.; Resnati,
F.; Riccobene, G.; Rice, L.; Rigamonti, A.; Rosenberg, M.; Rossella,
M.; Rubbia, C.; Sala, P.; Sapienza, P.; Savage, G.; Scaramelli, A.;
Scarpelli, A.; Schmitz, D.; Schukraft, A.; Sergiampietri, F.; Sirri,
G.; Smedley, J.; Soha, A.; Spanu, M.; Stanco, L.; Stewart, J.; Su, H.;
Suarez, N. B.; Sutera, C.; Tanaka, H.; Tenti, M.; Terao, K.; Terranova,
F.; Torretta, D.; Torti, M.; Tortorici, F.; Tsai, Y. T.; Tufanli,
S.; Usher, T.; Varanini, F.; Ventura, S.; Vignoli, C.; Vincenzi,
M.; Viren, B.; Warner, D.; Williams, Z.; Wilson, R. J.; Wilson, P.;
Wolfs, J.; Wongjirad, T.; Wood, A.; Worcester, E.; Worcester, M.;
Wospakrik, M.; Yu, H.; Yu, J.; Zani, A.; Zennamo, J.; Zettlemoyer,
J.; Zhang, C.; Zucchelli, S.; Zuckerbrot, M.
Bibcode: 2022icrc.confE1071K
Altcode: 2022PoS...395E1071K
No abstract at ADS
Title: A WC/WO star exploding within an expanding carbon-oxygen-neon
nebula
Authors: Gal-Yam, A.; Bruch, R.; Schulze, S.; Yang, Y.; Perley, D. A.;
Irani, I.; Sollerman, J.; Kool, E. C.; Soumagnac, M. T.; Yaron, O.;
Strotjohann, N. L.; Zimmerman, E.; Barbarino, C.; Kulkarni, S. R.;
Kasliwal, M. M.; De, K.; Yao, Y.; Fremling, C.; Yan, L.; Ofek,
E. O.; Fransson, C.; Filippenko, A. V.; Zheng, W.; Brink, T. G.;
Copperwheat, C. M.; Foley, R. J.; Brown, J.; Siebert, M.; Leloudas,
G.; Cabrera-Lavers, A. L.; Garcia-Alvarez, D.; Marante-Barreto, A.;
Frederick, S.; Hung, T.; Wheeler, J. C.; Vinkó, J.; Thomas, B. P.;
Graham, M. J.; Duev, D. A.; Drake, A. J.; Dekany, R.; Bellm, E. C.;
Rusholme, B.; Shupe, D. L.; Andreoni, I.; Sharma, Y.; Riddle, R.;
van Roestel, J.; Knezevic, N.
Bibcode: 2022Natur.601..201G
Altcode: 2021arXiv211112435G
The final fate of massive stars, and the nature of the compact remnants
they leave behind (black holes and neutron stars), are open questions
in astrophysics. Many massive stars are stripped of their outer hydrogen
envelopes as they evolve. Such Wolf-Rayet stars1 emit strong
and rapidly expanding winds with speeds greater than 1,000 kilometres
per second. A fraction of this population is also helium-depleted, with
spectra dominated by highly ionized emission lines of carbon and oxygen
(types WC/WO). Evidence indicates that the most commonly observed
supernova explosions that lack hydrogen and helium (types Ib/Ic)
cannot result from massive WC/WO stars2,3, leading some to
suggest that most such stars collapse directly into black holes without
a visible supernova explosion4. Here we report observations
of SN 2019hgp, beginning about a day after the explosion. Its short
rise time and rapid decline place it among an emerging population of
rapidly evolving transients5-8. Spectroscopy reveals a rich
set of emission lines indicating that the explosion occurred within a
nebula composed of carbon, oxygen and neon. Narrow absorption features
show that this material is expanding at high velocities (greater than
1,500 kilometres per second), requiring a compact progenitor. Our
observations are consistent with an explosion of a massive WC/WO star,
and suggest that massive Wolf-Rayet stars may be the progenitors of
some rapidly evolving transients.
Title: Erratum "The Global Magneto-Ionic Medium Survey: A Faraday
Depth Survey of the Northern Sky Covering 1280-1750 MHz" (2021, AJ,
162, 35)
Authors: Wolleben, M.; Landecker, T. L.; Douglas, K. A.; Gray,
A. D.; Ordog, A.; Dickey, J. M.; Hill, A. S.; Carretti, E.; Brown,
J. C.; Gaensler, B. M.; Han, J. L.; Haverkorn, M.; Kothes, R.; Leahy,
J. P.; McClure-Griffiths, N.; McConnell, D.; Reich, W.; Taylor, A. R.;
Thomson, A. J. M.; West, J. L.
Bibcode: 2021AJ....162..173W
Altcode:
No abstract at ADS
Title: Observations and Orbits of Comets and a/ Objects
Authors: Novichonok, A.; Zhornichenko, A.; Tesi, L.; Bacci, P.;
Maestripieri, M.; Facchini, M.; Corradini, G.; Vilagi, J.; Haver, R.;
Gorelli, R.; Jaeger, M.; Prosperi, E.; Prosperi, S.; Buzzi, L.; Naves,
R.; Campas, M.; Hasubick, W.; Reina, E.; De Pieri, A.; Agarwal, J.;
Kadota, K.; McAndrew, S. G.; Camarasa, M.; Gilmore, A. C.; Kilmartin,
P. M.; Meech, K. J.; Bufanda, E.; Kleyna, J.; Keane, J. V.; Wainscoat,
R.; Januszewski, H.; Burdullis, T.; Micheli, M.; Weryk, R.; Helin,
E. F.; Pravdo, S.; Lawrence, K.; Kuluhiwa, K.; Hicks, M.; Thicksten,
R.; Matson, R.; Balam, D. D.; Spratt, C. E.; Green, D. W. E.; Groeller,
H.; Kowalski, R. A.; Christensen, E. J.; Farneth, G. A.; Fuls, D. C.;
Gibbs, A. R.; Grauer, A. D.; Larson, S. M.; Leonard, G. J.; Pruyne,
T. A.; Rankin, D.; Seaman, R. L.; Shelly, F. C.; Wierzchos, K. W.;
Moritz, N.; Childs, W.; Sheppard, S. S.; Romanov, F. D.; Zoltowski,
F. B.; Ikari, Y.; James, N.; Moreno, J.; Nicolas, J.; Bosch, J. -G.;
Kugel, F.; Shurpakov, S.; Bosch, J. M.; Bryssinck, E.; Soulier, J. -F.;
Diepvens, A.; Aledo, J.; Lindner, P.; Object Wide-field Infrared
Survey Explorer, Near-Earth; Mainzer, A. K.; Bauer, J. M.; Grav, T.;
Masiero, J. R.; Cutri, R. M.; Dailey, J. W.; Kramer, E.; Pittichova,
J.; Wright, E. L.; Smith-Perez, C.; Vanderspek, R.; Brown, J.; Evans,
E.; Main, E.; Rios, R.; Ruprecht, J.; Vaillancourt, J.; Varey, J.;
Viggh, H.; Woods, D.; Wang, Z. X.; Ye, Q. -Z.; Zhao, H. B.; Li, B.;
Zhaori, G.; Hong, R. Q.; Hu, L. F.; Lu, H.; Xu, Z. J.; Takahashi,
T.; Carstens, R.; Drummond, J.; Bulger, J.; Lowe, T.; Schultz, A.;
Willman, M.; Smith, I.; Chambers, K.; Chastel, S.; de Boer, T.;
Denneau, L.; Fairlamb, J.; Flewelling, H.; Huber, M.; Lin, C. -C.;
Magnier, E.; Ramanjooloo, Y.; Weryk, R.; Gao, H.; Dukes, T.; Armstrong,
J. D.; Berrigan, L. H.; Urbanik, M.; van Buitenen, G.; Vincent, J.;
Valvasori, A.; Guido, E.; Kuettner, I.; Degot Longhi, Y.; Banfalvy,
Z.; Pei, W.; Paul, N.; Cortes, E.; Lutkenhoner, B.; Johnson, J. A.;
Matheny, R. G.; Bolin, B. T.; Z. T. F. Collaboration; Ip, W. -H.;
Lin, Z. -Y.; Masci, F. J.; Helou, G.; Kramer, E. A.; Prince, T. A.;
Martin, J. L.; Buczynski, D.; Carrillo, J.; Gonzalez, J.; Ruiz, P.;
Biesiada, M.; Busch, M.; Carsenty, U.; Clerkin, E.; Husar, D.; Knofel,
A.; Koschny, D.; Schwab, E.; Thommes, T.; Tsyhankou, M.; Kresken, R.;
Fohring, D.; Conversi, L.; Hormuth, F.; Hills, K.; Gomez, F.; Garcia,
F.; Temprano, J.; Morales, M.; Demeautis, C.; Bachini, M.; Taccogna,
F.; Fichtl, R.; Ventre, G.; Vandenbulcke, G.; Teseo, A.; Annamelia,
A.; Borisov, G.; Sonka, A.; Nedelcu, A.; Vauquelin, B.; Iozzi, M.;
Morra, G.; Demetz, L.; Galli, G.; Aletti, A.; Feraco, M.; Scarmato,
T.; Gao, X.; Yoshimoto, K.; Yamaguchi, Y.; Ikemura, T.; Sato, H.;
Nohara, H.; Mattiazzo, M.; Prystavski, T.; Conlon, W.; Tonry, J.;
Heinze, A.; Weiland, H.; Fitzsimmons, A.; Robinson, J.; Erasmus,
N.; Kumar, B.; Holbrook, M.; Maikner, J.; Bertesteanu, D.; Popescu,
M.; Deen, S.; Rocchetto, M.; Fulle, M.; Milani, G.; Nassef, C.;
Savini, G.; Virlichie, J. L.; Traverse, P.; Amaral, L. S.; Jacques,
C.; Pimentel, E.; Barros, J.; Holvorcem, P.; Carson, P.; Hale, A.;
Farfan, R.; Wells, G.; Wells, J.; Bamberger, D.
Bibcode: 2021MPEC....R...75N
Altcode:
No abstract at ADS
Title: The Global Magneto-ionic Medium Survey: A Faraday Depth Survey
of the Northern Sky Covering 1280-1750 MHz
Authors: Wolleben, M.; Landecker, T. L.; Douglas, K. A.; Gray,
A. D.; Ordog, A.; Dickey, J. M.; Hill, A. S.; Carretti, E.; Brown,
J. C.; Gaensler, B. M.; Han, J. L.; Haverkorn, M.; Kothes, R.; Leahy,
J. P.; McClure-Griffiths, N.; McConnell, D.; Reich, W.; Taylor, A. R.;
Thomson, A. J. M.; West, J. L.
Bibcode: 2021AJ....162...35W
Altcode: 2021arXiv210600945W
The Galactic interstellar medium hosts a significant magnetic field,
which can be probed through the synchrotron emission produced from its
interaction with relativistic electrons. Linearly polarized synchrotron
emission is generated throughout the Galaxy and, at longer wavelengths,
modified along nearly every path by Faraday rotation in the intervening
magneto-ionic medium. Full characterization of the polarized emission
requires wideband observations with many frequency channels. We have
surveyed polarized radio emission from the Northern sky over the range
1280-1750 MHz, with channel width 236.8 kHz, using the John A. Galt
Telescope (diameter 25.6 m) at the Dominion Radio Astrophysical
Observatory, as part of the Global Magneto-Ionic Medium Survey. The
survey covered 72% of the sky, decl. -30° to +87° at all R.A. The
intensity scale was absolutely calibrated, based on the flux density
and spectral index of Cygnus A. Polarization angle was calibrated using
the extended polarized emission of the Fan Region. Data are presented
as brightness temperatures with angular resolution 40'. Sensitivity
in Stokes Q and U is 45 mK rms in a 1.18 MHz band. We have applied
rotation measure synthesis to the data to obtain a Faraday depth
cube of resolution 150 rad m-2 and sensitivity 3 mK rms of
polarized intensity. Features in Faraday depth up to a width of 110
rad m-2 are represented. The maximum detectable Faraday
depth is ±2 × 104 rad m-2. The survey data
are available at the Canadian Astronomy Data Centre.
Title: VizieR Online Data Catalog: New rotation measures from the CGPS
(Van Eck+, 2021)
Authors: van Eck, C. L.; Brown, J. C.; Ordog, A.; Kothes, R.;
Landecker, T. L.; Cooper, B.; Rae, K. M.; Del Rizzo, D. A.; Gray,
A. D.; Ransom, R.; Reid, R. I.; Uyaniker, B.
Bibcode: 2021yCat..22530048V
Altcode:
The details of the Canadian Galactic Plane Survey (CGPS) 1.4GHz
observations and subsequent processing through to the final images are
reported in full detail by Landecker+ (2010A&A...520A..80L). For
our analysis, we have used the data from the Synthesis Telescope at the
Dominion Radio Astrophysical Observatory (DRAO-ST) only. Observations
for the survey began in 1995 and continued in several phases until
2009. (1 data file).
Title: Revisiting Rotation Measures from the Canadian Galactic Plane
Survey: the Magnetic Field in the Disk of the Outer Galaxy
Authors: Van Eck, C. L.; Brown, J. C.; Ordog, A.; Kothes, R.;
Landecker, T. L.; Cooper, B.; Rae, K. M.; Del Rizzo, D. A.; Gray,
A. D.; Ransom, R.; Reid, R. I.; Uyaniker, B.
Bibcode: 2021ApJS..253...48V
Altcode: 2021arXiv210202856V
Faraday rotation provides a valuable tracer of magnetic fields in the
interstellar medium; catalogs of Faraday rotation measures provide key
observations for studies of the Galactic magnetic field. We present
a new catalog of rotation measures derived from the Canadian Galactic
Plane Survey, covering a large region of the Galactic plane spanning
52° < l < 192°, -3° < b < 5°, along with northern
and southern latitude extensions around l ≍ 105°. We have derived
rotation measures for 2234 sources (4 of which are known pulsars), 75%
of which have no previous measurements, over an area of approximately
1300 deg2. These new rotation measures increase the
measurement density for this region of the Galactic plane by a factor
of 2.
Title: A Fresh Look at Jovian Decametric Radio Emission Occurrence
Probabilities in the CML-Io Phase Plane
Authors: Typinski, D.; Higgins, C. A.; Flagg, R. F.; Greenman, W.;
Sky, J.; Giuntini, R.; Reyes, F. J.; Fung, S. F.; Brown, J.; Ashcraft,
T.; Dodd, L.; Thieman, J.; Garcia, L. N.
Bibcode: 2020AGUFMSM0540001T
Altcode:
The occurrence of Jovian decametric emission (DAM) is sporadic as
observed from ground-based instruments. When the timing intervals of
observed occurrences of Jovian DAM are compared to all periods when
Jupiter was observable, a set of Jovian DAM emission occurrence
probabilities can be created. These probabilities are usefully
plotted as a function of Jovian system III (magnetospheric) central
meridian longitude (CML-III) and Io's phase measured from superior
geocentric conjunction (SGC), producing a CML-Io phase plane. It has
been known since 1964 that Jovian DAM tends to have higher occurrence
probabilities in different regions of the CML-Io phase plane, leading
to the identification of different Io-related and non-Io-related DAM
components. AJ4CO Observatory, located in High Springs, Florida,
USA, has been observing Jupiter when it is within ~4.5 hours of transit
since October, 2013. The primary instrument used for observing Jovian
DAM is a swept-frequency (16 to 32 MHz) dual polarization spectrograph
fed by an eight-element phased array of terminated folded dipoles. A
high-speed digital spectrograph with a tunable 2 MHz bandwidth was also
used from 2013 to 2016 to observe emission at higher time resolution. We analyze the dynamic spectra of Jovian DAM observed at AJ4CO
Observatory from 2013 through 2020 to measure emission timing intervals
and classify the emission into four types: L (for wideband L bursts), S
(for wideband S bursts), N (for narrowband continuous emission), and T
(for narrowband trains of S bursts). For this presentation, we
show CML-Io phase plane probabilities categorized by radio frequency,
polarization, emission type, and emission arc shape. We show how the
various high-probability DAM regions within the phase plane change
with each parameter and with various combinations of parameters. We
present updated definitions of the DAM component phase plane boundaries
and discuss how the DAM components appearing in various parts of the
CML-Io phase plane may differ from one another.
Title: Impact of Paleoclimate Variation on the Settlement History
of the Columbia Plateau
Authors: Brown, J.; Hackenberger, S.; Chatters, J. C.
Bibcode: 2020AGUFMPP0040003B
Altcode:
The settlement history of the Columbia Plateau has been compiled
through the record of riverine villages along the Columbia River
and its many major and minor tributaries. The chronologies that were
established based on the radiocarbon dates obtained from these villages
are the result of large river and dam surveys and data recoveries that
occurred throughout the 20th Century. These chronologies
have seldom been revisited and reanalyzed in the years since their
publications in major syntheses of the 1980s-1990s. Analysis of
these records using modern analytical techniques, such as summed
probability distributions and GIS, will allow for a fuller picture
of past settlement activities. Summed probability distributions have
become the de facto technique for analyzing aggregate radiocarbon
dates. This technique provides an analysis that can be robustly analyzed
for determining high and low points in the distribution that are
"real" and not artifacts of sampling strategies. Additional analysis
of the radiocarbon dates using GIS documents the change in spatial
distribution of dated villages over time, indicating the abandonment
of old villages, establishment of new villages, and the possible
return to old village locations. Comparing the peaks and valleys of
the radiocarbon distributions with paleoclimate records indicates a
correlation between cool periods and the greater intensity of house
occupation. Gaps or valleys that occur in the summed probability
distributions may be indicative of portions of the settlement record
that are not encapsulated in an archaeological database biased toward
riverine settings. These missing components of the settlement history
are thought to be the habitation of upland villages appears to coincide
with warmer periods of time. Notable low points in the radiocarbon
distribution are between 4100-3700 cal BP and 2100-1500 cal BP, these
may be periods in which people were not inhabiting riverine villages
and instead moved into the uplands. Revisiting these chronologies with
modern analytical strategies paired with ever-more-detailed paleoclimate
models allows for a better understanding of the settlement history of
the Columbia Plateau.
Title: Multi-proxy evidence for a millennial expansion of the south
Pacific gyre driven by ENSO/SAM interactions
Authors: Sinclair, D.; Hitt, N. T.; Neil, H.; Komugabe-Dixson, A. K.;
Fallon, S.; Bury, S.; Brown, J.; Sabadel, A.; Delgado, J.; Hellstrom,
J. C.
Bibcode: 2020AGUFMPP034..08S
Altcode:
The South Pacific Gyre (SPG) is the largest ocean gyre on Earth. It
modulates Pacific climate by distributing warm, subtropical waters to
high latitudes along its western limb and returning cool, subpolar
waters back to low latitudes along its eastern limb. In recent
decades, acceleration of the SPG's western boundary currents have
increased temperatures in the SW Pacific by up to 4x the global
average. This has also altered macronutrient distributions and
impacted marine ecology. These recent changes, however, may
not be unprecedented. Here we investigate a possible SPG enhancement
between 2000-3000BP by reconstructing SPG circulation strength and
bioavailable nitrogen distributions using deep-sea black corals from
New Zealand and the Tasman Sea. We use marine radiocarbon reservoir
age (∆R) to track the strength and latitudinal extent of southwest
SPG boundary currents (Hitt et al., submitted; Komugabe-Dixson et al.,
2016). ∆R is low in the subtropical waters and interior of the Gyre
due to a greater exchange of 14CO2 between the
ocean and atmosphere (Key et al., 2004). We use bulk and amino-acid
specific nitrogen isotopes to reconstruct the spatial distribution
of bioavailable nitrogen. POM δ15N in the central Gyre is
high due to complete NO3- utilization and a lower
degree of fractionation during photosynthesis (Somes et al., 2010). We see a reduction in ∆R and increase in δ15N around
between 2000-3000BP, suggesting that Gyre circulation was enhanced
and expanded southward. This thousand-year interval of stronger SPG
circulation corresponds to a period where ENSO and the Southern Annular
Mode (SAM) are coupled (Gomez et al., 2012; Komugabe-Dixson et al.,
2016). Both ENSO and SAM modulate the strength of different currents
in the SW Pacific. ENSO affects the South Equatorial Current and East
Australian Current (EAC) while SAM affects the EAC, EAC Extension and
Tasman Front. We therefore conclude that a coupling between ENSO/SAM
drove a strengthening and expansion of the SPG that is similar to the
Gyre intensification observed in the present day.
Title: Thunderstorms as Possible HF Radiation Sources of Propagation
Teepee Signatures
Authors: Fung, S. F.; Anderson, T.; Ashcraft, T.; Greenman, W.;
Typinski, D.; Brown, J.
Bibcode: 2020AGUFMSA0140015F
Altcode:
Propagation teepee is a type of HF spectral feature often recorded at
15-30 MHz by a group of citizen scientists whose main interest is in
observing radio emissions from Jupiter. The feature is characterized
as spectral enhancements with the frequency of enhancement first
increasing and then decreasing with time, resulting in a "triangular
spectral feature." Its shape is reminiscent of teepee tents (or TPs for
short), the moveable dwellings of some groups of native-Americans. TPs
usually have sharp or well-defined upper frequency limits for both the
leading and trailing edges (see figure). While some TPs are observed
in isolation, they are often seen in groups, distributed either in
time or in apex frequency as a nested group at a particular time. As
reported by Fung et al. [2020], most TPs appear to be diffuse even at
high time resolution, but a few TPs seen at high time resolution reveal
that those TPs consist actually of discrete bursts, strongly suggestive
that the band noise could be produced by lightning storms. TP signatures
are thus believed to be HF signals produced by remote lightning storms
and reflected by the bottom-side ionosphere. By analyzing a few events
with TP signatures detected simultaneously by multiple spectrograph
stations, we will use a relationship between the TP apex frequency and
the distance to its radiation source to identify the lightning storms
responsible for the observed TP signatures.
Title: The complex large-scale magnetic fields in the first Galactic
quadrant as revealed by the Faraday depth profile disparity
Authors: Ma, Y. K.; Mao, S. A.; Ordog, A.; Brown, J. C.
Bibcode: 2020MNRAS.497.3097M
Altcode: 2020arXiv200707893M; 2020MNRAS.tmp.2216M
The Milky Way is one of the very few spiral galaxies known to host
large-scale magnetic field reversals. The existence of the field
reversal in the first Galactic quadrant near the Sagittarius spiral
arm has been well established, yet poorly characterized due to the
insufficient number of reliable Faraday depths (FDs) from extragalactic
radio sources (EGSs) through this reversal region. We have therefore
performed broad-band (1- $2\, {\rm GHz}$ ) spectropolarimetric
observations with the Karl G. Jansky Very Large Array (VLA) to determine
the FD values of 194 EGSs in the Galactic longitude range of 20°-52°
within ±5° from the Galactic mid-plane, covering the Sagittarius arm
tangent. This factor of five increase in the EGS FD density has led to
the discovery of a disparity in FD values across the Galactic mid-plane
in the Galactic longitude range of 40°-52°. Combined with existing
pulsar FD measurements, we suggest that the Sagittarius arm can host
an odd-parity disc field. We further compared our newly derived EGS FDs
with the predictions of three major Galactic magnetic field models, and
concluded that none of them can adequately reproduce our observational
results. This has led to our development of new, improved models of
the Milky Way disc magnetic field that will serve as an important step
towards major future improvements in Galactic magnetic field models.
Title: The Line-of-Sight Magnetic Field Structure in Filamentary
Molecular Clouds
Authors: Tahani, M.; Plume, R.; Brown, J.
Bibcode: 2020IAUGA..30..103T
Altcode:
No abstract at ADS
Title: Nebular spectra of 111 Type Ia supernovae disfavour
single-degenerate progenitors
Authors: Tucker, M. A.; Shappee, B. J.; Vallely, P. J.; Stanek, K. Z.;
Prieto, J. L.; Botyanszki, J.; Kochanek, C. S.; Anderson, J. P.;
Brown, J.; Galbany, L.; Holoien, T. W. -S.; Hsiao, E. Y.; Kumar, S.;
Kuncarayakti, H.; Morrell, N.; Phillips, M. M.; Stritzinger, M. D.;
Thompson, Todd A.
Bibcode: 2020MNRAS.493.1044T
Altcode: 2019arXiv190305115T; 2019MNRAS.tmp.3025T
We place statistical constraints on Type Ia supernova (SN Ia)
progenitors using 227 nebular-phase spectra of 111 SNe Ia. We find no
evidence of stripped companion emission in any of the nebular-phase
spectra. Upper limits are placed on the amount of mass that could go
undetected in each spectrum using recent hydrodynamic simulations. With
these null detections, we place an observational 3σ upper limit on
the fraction of SNe Ia that are produced through the classical H-rich
non-degenerate companion scenario of < 5.5 per cent. Additionally,
we set a tentative 3σ upper limit otan He star progenitor scenarios
of < 6.4 per cent, although further theoretical modelling is
required. These limits refer to our most representative sample
including normal, 91bg-like, 91T-like, and `super-Chandrasekhar'
SNe Ia but excluding SNe Iax and SNe Ia-CSM. As part of our analysis,
we also derive a Nebular Phase Phillips Relation, which approximates
the brightness of an SN Ia from 150 to 500 d after maximum using the
peak magnitude and decline rate parameter Δm15(B).
Title: APOGEE's Serendipitous Variable Stars: a Value Added Catalog
Authors: Cash, J.; Brown, J.; Cabang, T.; Lavender, R.; Beaton, R.;
SDSS-Iv/Apogee-2 Collaboration
Bibcode: 2020AAS...23531306C
Altcode:
The Sloan Digital Sky Survey APOGEE-2 mission obtained near-infrared
spectroscopy for > 400,000 stars throughout the Milky Way
Galaxy. Some of these stars were targeted as known variable stars,
but it is expected that many more variables were serendipitously
targeted by APOGEE. This project supported by the SDSS Faculty and
Student Teams Initiative focused on creating a Value Added Catalog
of the variable stars within the APOGEE-2 dataset by cross-matching
against catalogs of variable stars such as the International Variable
Star Index, the ASAS-SN Variable Star Catalog, the KELT variables,
and the OGLE database. We will present the current progress of the
catalog creation and some initial statistics on the variable stars
that have been identified in the sample. Support for this research
has been provided by the SDSS Faculty and Student Teams Initiative
and the LS-SCAMP program. Additional partial funding for this research
was provided under NSF AST 1901296.
Title: Propagation Teepee: A High Frequency (HF) Radio Spectral
Feature Identified by Citizen Scientists
Authors: Fung, S. F.; Typinski, D.; Flagg, R. F.; Ashcraft, T.;
Greenman, W.; Higgins, C.; Brown, J.; Dodd, L.; Mount, A. S.; Reyes,
F. J.; Sky, J.; Thieman, J.; Garcia, L. N.
Bibcode: 2019AGUFMSA51C3173F
Altcode:
We report on the observations of a high frequency (HF) spectral feature
that appears often in ground-based spectral data at 15-30 MHz. The
feature, likely of terrestrial origin, is often recorded by a group
of amateur radio astronomers, the Spectrograph User Group (SUG), whose
main interest is in observing radio emissions from Jupiter. The feature
appears as spectral enhancements with the frequency of enhancement first
increasing and then decreasing with time, resulting in a "triangular
spectral feature." Its shape is reminiscent of teepee tents (or TPs for
short), the moveable dwellings of some groups of native-Americans. TPs
usually have sharp or well-defined upper frequency limits for both the
leading and trailing edges. While some TPs are observed in isolation,
they are often seen in groups, distributed either in time or in
frequency as a nested group at a particular time. Most TPs appear to be
diffuse even at high time resolution, but a few TPs seen at high time
resolution reveal that those TPs consist actually of discrete bursts,
strongly suggestive that the band noise produced from lightning as
possible radiation sources of the TPs. In this paper, we investigate
the possible generation of TPs as a result of ionospheric reflection
of band noise produced by remote lightning storms.
Title: Could bow-shaped magnetic morphologies surround filamentary
molecular clouds?. The 3D magnetic field structure of Orion-A
Authors: Tahani, M.; Plume, R.; Brown, J. C.; Soler, J. D.;
Kainulainen, J.
Bibcode: 2019A&A...632A..68T
Altcode: 2019arXiv191007619T
Context. A new method based on Faraday rotation measurements recently
found the line-of-sight component of magnetic fields in Orion-A and
showed that their direction changes from the eastern side of this
filamentary structure to its western side. Three possible magnetic
field morphologies that can explain this reversal across the Orion-A
region are toroidal, helical, and bow-shaped morphologies.
Aims:
In this paper, we constructed simple models to represent these three
morphologies and compared them with the available observational data to
find the most probable morphology(ies).
Methods: We compared the
observations with the models and used probability values and a Monte
Carlo analysis to determine the most likely magnetic field morphology
among these three morphologies.
Results: We found that the bow
morphology had the highest probability values, and that our Monte-Carlo
analysis suggested that the bow morphology was more likely.
Conclusions: We suggest that the bow morphology is the most likely
and the most natural of the three morphologies that could explain
a magnetic field reversal across the Orion-A filamentary structure
(i.e., bow, helical and toroidal morphologies).
Title: Book review: Oor Big Braw Cosmos: A cocktail of cosmic science,
imagery & poetry (Brown & Wilson)
Authors: Sawers, A.; Brown, J. C.; Wilson, R.
Bibcode: 2019JBAA..129..238S
Altcode:
No abstract at ADS
Title: Transient Classification Report for 2019-07-08
Authors: Rojas-Bravo, C.; Brown, J.; Dimitriadis, G.; Foley, R. J.;
Stacey, H.; Yao, Y.
Bibcode: 2019TNSCR1175....1R
Altcode:
No abstract at ADS
Title: Spectroscopic Classifications of Optical Transients with the
Lick Shane telescope
Authors: Rojas-Bravo, C.; Brown, J.; Dimitriadis, G.; Foley, R. J.;
Stacey, H.; Yao, Y.
Bibcode: 2019ATel12908....1R
Altcode:
We report the following classifications of optical transients from
spectroscopic observations with the Kast spectrograph on the Shane
telescope. Targets were supplied by ATLAS.
Title: Transient Classification Report for 2019-05-10
Authors: Brown, J.; Siebert, M.; Foley, R.
Bibcode: 2019TNSCR.744....1B
Altcode:
No abstract at ADS
Title: LIGO/Virgo S190425z: Further confirmation for the
classification of PS19qp/AT 2019ebq as a supernova.
Authors: McCully, C.; Hiramatsu, D.; Hiramatsu, D.; Howell, D. A.;
Arcavi, I.; Drout, M.; Burke, J.; Peligrino, C.; de Carvalho,
R.; Forster, F.; Foley, R.; Coulter, D.; Kilpatrick, C.; Sand,
D.; Valenti, S.; Soares-Santos, M.; Rembold, S.; Resti, A.; Kasen,
D.; Metzger, B.; Piro, A.; Quataert, E.; Ramirez-Ruiz, E.; Wheeler,
J. C.; Bauer, F.; Brink, T.; Cooke, J.; Clocchiatti, A.; Filippenko,
A. V.; Freedman, W.; Garnavich, P.; Horvath, J. E.; Jha, S.; Kirshner,
R.; Krisciunas, K.; Lin, H.; Madore, B.; Makler, M.; Prochaska, X.;
Riess, A.; Sturani, R.; Suntzeff, N.; Tanaka, M.; Tucker, D.; Vinko,
J.; Wang, L.; Brown, J.; Contrerasi, C.; D'Andrea, C.; Dimitriadis,
G.; Jones, D.; Lundquist, M.; Narayan, G.; Olivares, F.; Palmese,
A.; Pan, Y. -C.; Scolnic, D.; Zheng, W.; Bernardo, A.; Bostroem, A.;
Berthier, A. M.; Rodriguez, O.; Rojas-Bravo, C.; Siebert, M.; Souza, I.
Bibcode: 2019GCN.24295....1M
Altcode:
No abstract at ADS
Title: New constraints on oscillation parameters from νe
appearance and νμ disappearance in the NOvA experiment
Authors: Acero, M. A.; Adamson, P.; Aliaga, L.; Alion, T.;
Allakhverdian, V.; Anfimov, N.; Antoshkin, A.; Arrieta-Diaz, E.;
Aurisano, A.; Back, A.; Backhouse, C.; Baird, M.; Balashov, N.; Bambah,
B. A.; Bays, K.; Behera, B.; Bending, S.; Bernstein, R.; Bhatnagar,
V.; Bhuyan, B.; Bian, J.; Blackburn, T.; Blair, J.; Bolshakova,
A.; Bour, P.; Bromberg, C.; Brown, J.; Buchanan, N.; Butkevich, A.;
Bychkov, V.; Campbell, M.; Carroll, T. J.; Catano-Mur, E.; Cedeno, A.;
Childress, S.; Choudhary, B. C.; Chowdhury, B.; Coan, T. E.; Colo, M.;
Cooper, J.; Corwin, L.; Cremonesi, L.; Cronin-Hennessy, D.; Davies,
G. S.; Davies, J. P.; De Rijck, S.; Derwent, P. F.; Dharmapalan,
R.; Ding, P.; Djurcic, Z.; Dukes, E. C.; Dung, P.; Duyang, H.;
Edayath, S.; Ehrlich, R.; Feldman, G. J.; Frank, M. J.; Gallagher,
H. R.; Gandrajula, R.; Gao, F.; Germani, S.; Giri, A.; Gomes, R. A.;
Goodman, M. C.; Grichine, V.; Groh, M.; Group, R.; Grover, D.; Guo,
B.; Habig, A.; Hakl, F.; Hartnell, J.; Hatcher, R.; Hatzikoutelis,
A.; Heller, K.; Himmel, A.; Holin, A.; Howard, B.; Huang, J.; Hylen,
J.; Jediny, F.; Judah, M.; Kakorin, I.; Kalra, D.; Kaplan, D. M.;
Keloth, R.; Klimov, O.; Koerner, L. W.; Kolupaeva, L.; Kotelnikov,
S.; Kourbanis, I.; Kreymer, A.; Kulenberg, Ch.; Kumar, A.; Kuruppu,
C.; Kus, V.; Lackey, T.; Lang, K.; Lin, S.; Lokajicek, M.; Lozier,
J.; Luchuk, S.; Maan, K.; Magill, S.; Mann, W. A.; Marshak, M. L.;
Matveev, V.; Méndez, D. P.; Messier, M. D.; Meyer, H.; Miao, T.;
Miller, W. H.; Mishra, S. R.; Mislivec, A.; Mohanta, R.; Moren,
A.; Mualem, L.; Muether, M.; Mufson, S.; Murphy, R.; Musser, J.;
Naples, D.; Nayak, N.; Nelson, J. K.; Nichol, R.; Niner, E.; Norman,
A.; Nosek, T.; Oksuzian, Y.; Olshevskiy, A.; Olson, T.; Paley, J.;
Patterson, R. B.; Pawloski, G.; Pershey, D.; Petrova, O.; Petti,
R.; Phan-Budd, S.; Plunkett, R. K.; Potukuchi, B.; Principato, C.;
Psihas, F.; Radovic, A.; Rameika, R. A.; Rebel, B.; Rojas, P.; Ryabov,
V.; Sachdev, K.; Samoylov, O.; Sanchez, M. C.; Sepulveda-Quiroz, J.;
Shanahan, P.; Sheshukov, A.; Singh, P.; Singh, V.; Smith, E.; Smolik,
J.; Snopok, P.; Solomey, N.; Song, E.; Sousa, A.; Soustruznik, K.;
Strait, M.; Suter, L.; Talaga, R. L.; Tas, P.; Thayyullathil, R. B.;
Thomas, J.; Tiras, E.; Tognini, S. C.; Torbunov, D.; Tripathi, J.;
Tsaris, A.; Torun, Y.; Urheim, J.; Vahle, P.; Vasel, J.; Vinton, L.;
Vokac, P.; Vold, A.; Vrba, T.; Wang, B.; Warburton, T. K.; Wetstein,
M.; Whittington, D.; Wojcicki, S. G.; Wolcott, J.; Yang, S.; Yu, S.;
Zalesak, J.; Zamorano, B.; Zwaska, R.; NOvA Collaboration
Bibcode: 2018PhRvD..98c2012A
Altcode: 2018arXiv180600096N; 2018arXiv180600096A
We present updated results from the NOvA experiment for
νμ→νμ and νμ→νe
oscillations from an exposure of 8.85 ×1020 protons
on target, which represents an increase of 46% compared to
our previous publication. The results utilize significant
improvements in both the simulations and analysis of the data. A
joint fit to the data for νμ disappearance and
νe appearance gives the best-fit point as normal mass
hierarchy, Δ m322=2.44 ×10-3
eV2/c4 , sin2θ23=0.56
, and δCP=1.21 π . The 68.3% confidence intervals
in the normal mass hierarchy are Δ m322
∈[2.37 ,2.52 ]×10-3 eV2/c4 ,
sin2θ23 ∈[0.43 ,0.51 ]∪[0.52 ,0.60 ], and
δCP∈[0 ,0.12 π ]∪[0.91 π ,2 π ]. The inverted mass
hierarchy is disfavored at the 95% confidence level for all choices
of the other oscillation parameters.
Title: Helical magnetic fields in molecular clouds?. A new method
to determine the line-of-sight magnetic field structure in molecular
clouds
Authors: Tahani, M.; Plume, R.; Brown, J. C.; Kainulainen, J.
Bibcode: 2018A&A...614A.100T
Altcode: 2018arXiv180207831T
Context. Magnetic fields pervade in the interstellar medium (ISM)
and are believed to be important in the process of star formation, yet
probing magnetic fields in star formation regions is challenging.
Aims: We propose a new method to use Faraday rotation measurements in
small-scale star forming regions to find the direction and magnitude
of the component of magnetic field along the line of sight. We test
the proposed method in four relatively nearby regions of Orion A,
Orion B, Perseus, and California.
Methods: We use rotation
measure data from the literature. We adopt a simple approach based
on relative measurements to estimate the rotation measure due to the
molecular clouds over the Galactic contribution. We then use a chemical
evolution code along with extinction maps of each cloud to find the
electron column density of the molecular cloud at the position of each
rotation measure data point. Combining the rotation measures produced by
the molecular clouds and the electron column density, we calculate the
line-of-sight magnetic field strength and direction.
Results: In
California and Orion A, we find clear evidence that the magnetic fields
at one side of these filamentary structures are pointing towards us and
are pointing away from us at the other side. Even though the magnetic
fields in Perseus might seem to suggest the same behavior, not enough
data points are available to draw such conclusions. In Orion B, as well,
there are not enough data points available to detect such behavior. This
magnetic field reversal is consistent with a helical magnetic field
morphology. In the vicinity of available Zeeman measurements in OMC-1,
OMC-B, and the dark cloud Barnard 1, we find magnetic field values
of - 23 ± 38 μG, - 129 ± 28 μG, and 32 ± 101 μG, respectively,
which are in agreement with the Zeeman measurements. Tables
1 to 7 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/A100
Title: VizieR Online Data Catalog: Molecular clouds los magnetic
field structure (Tahani+, 2018)
Authors: Tahani, M.; Plume, R.; Brown, J. C.; Kainulainen, J.
Bibcode: 2018yCat..36140100T
Altcode:
We propose a new method to use Faraday rotation measurements in small
scale star forming regions to find the direction and magnitude of
the component of magnetic field along the line-of-sight. We test
the proposed method in four relatively nearby regions of Orion A,
Orion B, California, and Perseus. Tables 1, 3, 4, and 6 show
the result magnetic fields for these regions. Tables 2, 5,
and 7 show the result magnetic fields that do not change direction
within their uncertainty range for Orion A, California, and Perseus
respectively. Negative values indicate magnetic fields pointed away
from the observer and positive values are towards the observer. (7 data files).
Title: The Science of Sungrazers, Sunskirters, and Other Near-Sun
Comets
Authors: Jones, Geraint H.; Knight, Matthew M.; Battams, Karl; Boice,
Daniel C.; Brown, John; Giordano, Silvio; Raymond, John; Snodgrass,
Colin; Steckloff, Jordan K.; Weissman, Paul; Fitzsimmons, Alan; Lisse,
Carey; Opitom, Cyrielle; Birkett, Kimberley S.; Bzowski, Maciej;
Decock, Alice; Mann, Ingrid; Ramanjooloo, Yudish; McCauley, Patrick
Bibcode: 2018SSRv..214...20J
Altcode:
This review addresses our current understanding of comets that venture
close to the Sun, and are hence exposed to much more extreme conditions
than comets that are typically studied from Earth. The extreme solar
heating and plasma environments that these objects encounter change many
aspects of their behaviour, thus yielding valuable information on both
the comets themselves that complements other data we have on primitive
solar system bodies, as well as on the near-solar environment which
they traverse. We propose clear definitions for these comets: We use
the term near-Sun comets to encompass all objects that pass sunward of
the perihelion distance of planet Mercury (0.307 AU). Sunskirters are
defined as objects that pass within 33 solar radii of the Sun's centre,
equal to half of Mercury's perihelion distance, and the commonly-used
phrase sungrazers to be objects that reach perihelion within
3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with
orbits that intersect the solar photosphere are termed sundivers. We
summarize past studies of these objects, as well as the instruments
and facilities used to study them, including space-based platforms that
have led to a recent revolution in the quantity and quality of relevant
observations. Relevant comet populations are described, including the
Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a
brief discussion of their origins. The importance of light curves and
the clues they provide on cometary composition are emphasized, together
with what information has been gleaned about nucleus parameters,
including the sizes and masses of objects and their families, and their
tensile strengths. The physical processes occurring at these objects
are considered in some detail, including the disruption of nuclei,
sublimation, and ionisation, and we consider the mass, momentum, and
energy loss of comets in the corona and those that venture to lower
altitudes. The different components of comae and tails are described,
including dust, neutral and ionised gases, their chemical reactions,
and their contributions to the near-Sun environment. Comet-solar wind
interactions are discussed, including the use of comets as probes of
solar wind and coronal conditions in their vicinities. We address the
relevance of work on comets near the Sun to similar objects orbiting
other stars, and conclude with a discussion of future directions for
the field and the planned ground- and space-based facilities that will
allow us to address those science topics.
Title: ASAS-SN Transient Discovery Report for 2018-01-24
Authors: Brown, J.
Bibcode: 2018TNSTR.112....1B
Altcode:
No abstract at ADS
Title: Search for active-sterile neutrino mixing using neutral-current
interactions in NOvA
Authors: Adamson, P.; Aliaga, L.; Ambrose, D.; Anfimov, N.; Antoshkin,
A.; Arrieta-Diaz, E.; Augsten, K.; Aurisano, A.; Backhouse, C.; Baird,
M.; Bambah, B. A.; Bays, K.; Behera, B.; Bending, S.; Bernstein, R.;
Bhatnagar, V.; Bhuyan, B.; Bian, J.; Blackburn, T.; Bolshakova, A.;
Bromberg, C.; Brown, J.; Brunetti, G.; Buchanan, N.; Butkevich, A.;
Bychkov, V.; Campbell, M.; Catano-Mur, E.; Childress, S.; Choudhary,
B. C.; Chowdhury, B.; Coan, T. E.; Coelho, J. A. B.; Colo, M.; Cooper,
J.; Corwin, L.; Cremonesi, L.; Cronin-Hennessy, D.; Davies, G. S.;
Davies, J. P.; Derwent, P. F.; Dharmapalan, R.; Ding, P.; Djurcic, Z.;
Dukes, E. C.; Duyang, H.; Edayath, S.; Ehrlich, R.; Feldman, G. J.;
Frank, M. J.; Gabrielyan, M.; Gallagher, H. R.; Germani, S.; Ghosh,
T.; Giri, A.; Gomes, R. A.; Goodman, M. C.; Grichine, V.; Groh, M.;
Group, R.; Grover, D.; Guo, B.; Habig, A.; Hartnell, J.; Hatcher,
R.; Hatzikoutelis, A.; Heller, K.; Himmel, A.; Holin, A.; Howard, B.;
Hylen, J.; Jediny, F.; Judah, M.; Kafka, G. K.; Kalra, D.; Kasahara,
S. M. S.; Kasetti, S.; Keloth, R.; Kolupaeva, L.; Kotelnikov, S.;
Kourbanis, I.; Kreymer, A.; Kumar, A.; Kurbanov, S.; Lackey, T.; Lang,
K.; Lee, W. M.; Lin, S.; Lokajicek, M.; Lozier, J.; Luchuk, S.; Maan,
K.; Magill, S.; Mann, W. A.; Marshak, M. L.; Matera, K.; Matveev,
V.; Méndez, D. P.; Messier, M. D.; Meyer, H.; Miao, T.; Miller,
W. H.; Mishra, S. R.; Mohanta, R.; Moren, A.; Mualem, L.; Muether, M.;
Mufson, S.; Murphy, R.; Musser, J.; Nelson, J. K.; Nichol, R.; Niner,
E.; Norman, A.; Nosek, T.; Oksuzian, Y.; Olshevskiy, A.; Olson, T.;
Paley, J.; Patterson, R. B.; Pawloski, G.; Pershey, D.; Petrova, O.;
Petti, R.; Phan-Budd, S.; Plunkett, R. K.; Poling, R.; Potukuchi, B.;
Principato, C.; Psihas, F.; Radovic, A.; Rameika, R. A.; Rebel, B.;
Reed, B.; Rocco, D.; Rojas, P.; Ryabov, V.; Sachdev, K.; Sail, P.;
Samoylov, O.; Sanchez, M. C.; Schroeter, R.; Sepulveda-Quiroz, J.;
Shanahan, P.; Sheshukov, A.; Singh, J.; Singh, J.; Singh, P.; Singh,
V.; Smolik, J.; Solomey, N.; Song, E.; Sousa, A.; Soustruznik, K.;
Strait, M.; Suter, L.; Talaga, R. L.; Tas, P.; Thayyullathil, R. B.;
Thomas, J.; Tian, X.; Tognini, S. C.; Tripathi, J.; Tsaris, A.; Urheim,
J.; Vahle, P.; Vasel, J.; Vinton, L.; Vold, A.; Vrba, T.; Wang, B.;
Wetstein, M.; Whittington, D.; Wojcicki, S. G.; Wolcott, J.; Yadav,
N.; Yang, S.; Zalesak, J.; Zamorano, B.; Zwaska, R.; NOvA Collaboration
Bibcode: 2017PhRvD..96g2006A
Altcode: 2017arXiv170604592N
We report results from the first search for sterile neutrinos
mixing with active neutrinos through a reduction in the rate of
neutral-current interactions over a baseline of 810 km between the
NOvA detectors. Analyzing a 14-kton detector equivalent exposure of
6.05 ×1020 protons-on-target in the NuMI beam at Fermilab,
we observe 95 neutral-current candidates at the Far Detector compared
with 83.5 ±9.7 (stat ) ±9.4 (syst ) events predicted assuming
mixing only occurs between active neutrino species. No evidence for
νμ→νs transitions is found. Interpreting
these results within a 3 +1 model, we place constraints on the mixing
angles θ24<20.8 ° and θ34<31.2 ° at the
90% C.L. for 0.05 eV2≤Δ m412≤0.5
eV2 , the range of mass splittings that produce no
significant oscillations over the Near Detector baseline.
Title: Deposition of steeply infalling debris - pebbles, boulders,
snowballs, asteroids, comets - around stars
Authors: Brown, J. C.; Veras, D.; Gänsicke, B. T.
Bibcode: 2017EPSC...11...51B
Altcode:
When Comet Lovejoy plunged into the Sun, and survived, questions arose
about the physics of infall of small bodies. [1,2] has already described
this infall in detail. However, a more general analysis for any type
of star has been missing. [3] generalized previous studies, with
specific applications to white dwarfs. High-metallicity pollution is
common in white dwarf stars hosting remnant planetary systems. However,
they rarely have detectable debris accretion discs, possibly because
much of the influx is fast steeply infalling debris in star-grazing
orbits, producing a more tenuous signature than a slowly accreting
disc. Processes governing such deposition between the Roche radius
and photosphere have so far received little attention and we model
them here analytically by extending recent work on sun-grazing comets
to white dwarf systems. We find that the evolution of cm-to-km size
infallers most strongly depends on two combinations of parameters,
which effectively measure sublimation rate and binding strength. We
then provide an algorithm to determine the fate of infallers for any
white dwarf, and apply the algorithm to four limiting combinations of
hot versus cool (young/old) white dwarfs with snowy (weak, volatile)
versus rocky (strong, refractory) infallers. We find: (i) Total
sublimation above the photosphere befalls all small infallers across
the entire white dwarf temperature range, the threshold size rising
with it and 100× larger for rock than snow. (ii) All very large
objects fragment tidally regardless of temperature: for rock, a0 ≽
105 cm; for snow, a0 ≽ 103 - 3 × 104
cm across all white dwarf cooling ages. (iii) A considerable range of
infaller sizes avoids fragmentation and total sublimation, yielding
impacts or grazes with cold white dwarfs. This range rapidly narrows
with increasing temperature, especially for snowy bodies. Finally, we
briefly discuss how the various forms of deposited debris may finally
reach the photosphere surface itself.
Title: Three-dimensional structure of the magnetic field in the disk
of the Milky Way
Authors: Ordog, A.; Brown, J. C.; Kothes, R.; Landecker, T. L.
Bibcode: 2017A&A...603A..15O
Altcode: 2017arXiv170408663O
Aims: We present rotation measures (RM) of the diffuse Galactic
synchrotron emission from the Canadian Galactic Plane Survey (CGPS)
and compare them to RMs of extragalactic sources in order to study
the large-scale reversal in the Galactic magnetic field (GMF).
Methods: Using Stokes Q, U and I measurements of the Galactic
disk collected with the Synthesis Telescope at the Dominion Radio
Astrophysical Observatory, we calculate RMs over an extended region
of the sky, focusing on the low longitude range of the CGPS (ℓ =
52° to ℓ = 72°).
Results: We note the similarity in the
structures traced by the compact sources and the extended emission
and highlight the presence of a gradient in the RM map across an
approximately diagonal line, which we identify with the well-known
field reversal of the Sagittarius-Carina arm. We suggest that the
orientation of this reversal is a geometric effect resulting from our
location within a GMF structure arising from current sheets that are
not perpendicular to the Galactic plane, as is required for a strictly
radial field reversal, but that have at least some component parallel
to the disk. Examples of models that fit this description are the
three-dimensional dynamo-based model of Gressel et al. (2013, A&A,
560, A93) and a Galactic scale Parker spiral (Akasofu & Hakamada
1982, ApJ, 253, 552), although the latter may be problematic in terms
of Galactic dynamics.
Conclusions: We emphasize the importance
of constructing three-dimensional models of the GMF to account for
structures like the diagonal RM gradient observed in this dataset.
Title: Deposition of steeply infalling debris around white dwarf stars
Authors: Brown, John C.; Veras, Dimitri; Gänsicke, Boris T.
Bibcode: 2017MNRAS.468.1575B
Altcode: 2017arXiv170205109B
High-metallicity pollution is common in white dwarf (WD) stars hosting
remnant planetary systems. However, they rarely have detectable
debris accretion discs, possibly because much of the influx is fast
steeply infalling debris in star-grazing orbits, producing a more
tenuous signature than a slowly accreting disc. Processes governing
such deposition between the Roche radius and photosphere have so
far received little attention and we model them here analytically by
extending recent work on sun-grazing comets to WD systems. We find that
the evolution of cm-to-km size (a0) infallers most strongly
depends on two combinations of parameters, which effectively measure
sublimation rate and binding strength. We then provide an algorithm
to determine the fate of infallers for any WD, and apply the algorithm
to four limiting combinations of hot versus cool (young/old) WDs with
snowy (weak, volatile) versus rocky (strong, refractory) infallers. We
find: (I) Total sublimation above the photosphere befalls all small
infallers across the entire WD temperature (TWD) range,
the threshold size rising with TWD and 100× larger for
rock than snow. (II) All very large objects fragment tidally regardless
of TWD: for rock, a0 ≽ 105 cm; for
snow, a0 ≽ 103-3 × 104 cm across
all WD cooling ages. (III) A considerable range of a0 avoids
fragmentation and total sublimation, yielding impacts or grazes with
cold WDs. This range rapidly narrows with increasing TWD,
especially for snowy bodies. Finally, we briefly discuss how the
various forms of deposited debris may finally reach the photosphere
surface itself.
Title: Constraints on Oscillation Parameters from νe
Appearance and νμ Disappearance in NOvA
Authors: Adamson, P.; Aliaga, L.; Ambrose, D.; Anfimov, N.; Antoshkin,
A.; Arrieta-Diaz, E.; Augsten, K.; Aurisano, A.; Backhouse, C.; Baird,
M.; Bambah, B. A.; Bays, K.; Behera, B.; Bending, S.; Bernstein, R.;
Bhatnagar, V.; Bhuyan, B.; Bian, J.; Blackburn, T.; Bolshakova, A.;
Bromberg, C.; Brown, J.; Brunetti, G.; Buchanan, N.; Butkevich, A.;
Bychkov, V.; Campbell, M.; Catano-Mur, E.; Childress, S.; Choudhary,
B. C.; Chowdhury, B.; Coan, T. E.; Coelho, J. A. B.; Colo, M.; Cooper,
J.; Corwin, L.; Cremonesi, L.; Cronin-Hennessy, D.; Davies, G. S.;
Davies, J. P.; Derwent, P. F.; Dharmapalan, R.; Ding, P.; Djurcic,
Z.; Dukes, E. C.; Duyang, H.; Edayath, S.; Ehrlich, R.; Feldman,
G. J.; Frank, M. J.; Gabrielyan, M.; Gallagher, H. R.; Germani, S.;
Ghosh, T.; Giri, A.; Gomes, R. A.; Goodman, M. C.; Grichine, V.;
Group, R.; Grover, D.; Guo, B.; Habig, A.; Hartnell, J.; Hatcher,
R.; Hatzikoutelis, A.; Heller, K.; Himmel, A.; Holin, A.; Hylen, J.;
Jediny, F.; Judah, M.; Kafka, G. K.; Kalra, D.; Kasahara, S. M. S.;
Kasetti, S.; Keloth, R.; Kolupaeva, L.; Kotelnikov, S.; Kourbanis,
I.; Kreymer, A.; Kumar, A.; Kurbanov, S.; Lang, K.; Lee, W. M.; Lin,
S.; Liu, J.; Lokajicek, M.; Lozier, J.; Luchuk, S.; Maan, K.; Magill,
S.; Mann, W. A.; Marshak, M. L.; Matera, K.; Matveev, V.; Méndez,
D. P.; Messier, M. D.; Meyer, H.; Miao, T.; Miller, W. H.; Mishra,
S. R.; Mohanta, R.; Moren, A.; Mualem, L.; Muether, M.; Mufson, S.;
Murphy, R.; Musser, J.; Nelson, J. K.; Nichol, R.; Niner, E.; Norman,
A.; Nosek, T.; Oksuzian, Y.; Olshevskiy, A.; Olson, T.; Paley, J.;
Pandey, P.; Patterson, R. B.; Pawloski, G.; Pershey, D.; Petrova,
O.; Petti, R.; Phan-Budd, S.; Plunkett, R. K.; Poling, R.; Potukuchi,
B.; Principato, C.; Psihas, F.; Radovic, A.; Rameika, R. A.; Rebel,
B.; Reed, B.; Rocco, D.; Rojas, P.; Ryabov, V.; Sachdev, K.; Sail,
P.; Samoylov, O.; Sanchez, M. C.; Schroeter, R.; Sepulveda-Quiroz,
J.; Shanahan, P.; Sheshukov, A.; Singh, J.; Singh, J.; Singh, P.;
Singh, V.; Smolik, J.; Solomey, N.; Song, E.; Sousa, A.; Soustruznik,
K.; Strait, M.; Suter, L.; Talaga, R. L.; Tamsett, M. C.; Tas, P.;
Thayyullathil, R. B.; Thomas, J.; Tian, X.; Tognini, S. C.; Tripathi,
J.; Tsaris, A.; Urheim, J.; Vahle, P.; Vasel, J.; Vinton, L.; Vold,
A.; Vrba, T.; Wang, B.; Wetstein, M.; Whittington, D.; Wojcicki,
S. G.; Wolcott, J.; Yadav, N.; Yang, S.; Zalesak, J.; Zamorano, B.;
Zwaska, R.; NOvA Collaboration
Bibcode: 2017PhRvL.118w1801A
Altcode:
Results are reported from an improved measurement of
νμ→νe transitions by the NOvA
experiment. Using an exposure equivalent to 6.05 ×1 020
protons on target, 33 νe candidates are observed with
a background of 8.2 ±0.8 (syst.). Combined with the latest NOvA
νμ disappearance data and external constraints from reactor
experiments on sin22 θ13, the hypothesis of
inverted mass hierarchy with θ23 in the lower octant is
disfavored at greater than 93% C.L. for all values of δC P.
Title: ASAS-SN Transient Discovery Report for 2017-05-05
Authors: Brown, J.
Bibcode: 2017TNSTR.522....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2017-05-16
Authors: Brown, J.
Bibcode: 2017TNSTR.556....1B
Altcode:
No abstract at ADS
Title: Measurement of the Neutrino Mixing Angle θ23
in NOvA
Authors: Adamson, P.; Aliaga, L.; Ambrose, D.; Anfimov, N.; Antoshkin,
A.; Arrieta-Diaz, E.; Augsten, K.; Aurisano, A.; Backhouse, C.; Baird,
M.; Bambah, B. A.; Bays, K.; Behera, B.; Bending, S.; Bernstein, R.;
Bhatnagar, V.; Bhuyan, B.; Bian, J.; Blackburn, T.; Bolshakova, A.;
Bromberg, C.; Brown, J.; Brunetti, G.; Buchanan, N.; Butkevich, A.;
Bychkov, V.; Campbell, M.; Catano-Mur, E.; Childress, S.; Choudhary,
B. C.; Chowdhury, B.; Coan, T. E.; Coelho, J. A. B.; Colo, M.; Cooper,
J.; Corwin, L.; Cremonesi, L.; Cronin-Hennessy, D.; Davies, G. S.;
Davies, J. P.; Derwent, P. F.; Desai, S.; Dharmapalan, R.; Ding,
P.; Djurcic, Z.; Dukes, E. C.; Duyang, H.; Edayath, S.; Ehrlich,
R.; Feldman, G. J.; Frank, M. J.; Gabrielyan, M.; Gallagher, H. R.;
Germani, S.; Ghosh, T.; Giri, A.; Gomes, R. A.; Goodman, M. C.;
Grichine, V.; Group, R.; Grover, D.; Guo, B.; Habig, A.; Hartnell,
J.; Hatcher, R.; Hatzikoutelis, A.; Heller, K.; Himmel, A.; Holin, A.;
Hylen, J.; Jediny, F.; Judah, M.; Kafka, G. K.; Kalra, D.; Kasahara,
S. M. S.; Kasetti, S.; Keloth, R.; Kolupaeva, L.; Kotelnikov, S.;
Kourbanis, I.; Kreymer, A.; Kumar, A.; Kurbanov, S.; Lang, K.; Lee,
W. M.; Lin, S.; Liu, J.; Lokajicek, M.; Lozier, J.; Luchuk, S.; Maan,
K.; Magill, S.; Mann, W. A.; Marshak, M. L.; Matera, K.; Matveev,
V.; Méndez, D. P.; Messier, M. D.; Meyer, H.; Miao, T.; Miller,
W. H.; Mishra, S. R.; Mohanta, R.; Moren, A.; Mualem, L.; Muether,
M.; Mufson, S.; Murphy, R.; Musser, J.; Nelson, J. K.; Nichol, R.;
Niner, E.; Norman, A.; Nosek, T.; Oksuzian, Y.; Olshevskiy, A.;
Olson, T.; Paley, J.; Pandey, P.; Patterson, R. B.; Pawloski, G.;
Pershey, D.; Petrova, O.; Petti, R.; Phan-Budd, S.; Plunkett, R. K.;
Poling, R.; Potukuchi, B.; Principato, C.; Psihas, F.; Radovic, A.;
Rameika, R. A.; Rebel, B.; Reed, B.; Rocco, D.; Rojas, P.; Ryabov, V.;
Sachdev, K.; Sail, P.; Samoylov, O.; Sanchez, M. C.; Schroeter, R.;
Sepulveda-Quiroz, J.; Shanahan, P.; Sheshukov, A.; Singh, J.; Singh,
J.; Singh, P.; Singh, V.; Smolik, J.; Solomey, N.; Song, E.; Sousa,
A.; Soustruznik, K.; Strait, M.; Suter, L.; Talaga, R. L.; Tamsett,
M. C.; Tas, P.; Thayyullathil, R. B.; Thomas, J.; Tian, X.; Tognini,
S. C.; Tripathi, J.; Tsaris, A.; Urheim, J.; Vahle, P.; Vasel, J.;
Vinton, L.; Vold, A.; Vrba, T.; Wang, B.; Wetstein, M.; Whittington,
D.; Wojcicki, S. G.; Wolcott, J.; Yadav, N.; Yang, S.; Zalesak, J.;
Zamorano, B.; Zwaska, R.; NOvA Collaboration
Bibcode: 2017PhRvL.118o1802A
Altcode:
This Letter reports new results on muon neutrino disappearance from
NOvA, using a 14 kton detector equivalent exposure of 6.05 ×1
020 protons on target from the NuMI beam at the Fermi
National Accelerator Laboratory. The measurement probes the muon-tau
symmetry hypothesis that requires maximal θ23 mixing
(θ23=π /4 ). Assuming the normal mass hierarchy, we
find Δ m322 =(2.67 ±0.11 )×10-3
eV2 and sin2θ23 at the two
statistically degenerate values 0.40 4-0.022+0.030
and 0.62 4-0.030+0.022, both at the 68%
confidence level. Our data disfavor the maximal mixing scenario with
2.6 σ significance.
Title: ASAS-SN Transient Discovery Report for 2017-03-29
Authors: Brown, J.
Bibcode: 2017TNSTR.369....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2017-02-21
Authors: Brown, J.
Bibcode: 2017TNSTR.216....1B
Altcode:
No abstract at ADS
Title: Constraints on the Geophysical Detection of Brine within
the Europa Ice Shell From a Synthesis of Dielectric Spectroscopy
Measurements
Authors: Stillman, D. E.; Grimm, R. E.; MacGregor, J. A.;
Sander-Olhoeft, M.; Brown, J.
Bibcode: 2016AGUFM.P54B..08S
Altcode:
The numerous chaos regions, lenticulae and double layer ridges on
Europa's surface suggest that pockets of liquid currently exist or did
exist. Here we investigate the sensitivity of ice-penetrating radar
(IPR) and magnetotelluric (MT) methods to the putative electrical
properties of Europa's ice shell, based on a set of plausible ice-shell
scenarios and a synthesis of laboratory dielectric spectroscopy
measurements of hundreds of ice samples. We evaluate models of the
electrical conductivity of the ice shell as a function of impurity
content, temperature and liquid vein network tortuosity. Europa's
ice shell is estimated to be 5-30 km thick. If its thickness exceeds
10 km, the shell likely convects within its bottom 70%, while the
upper part is thermally conductive. These convective downwellings
and upwellings are estimated to have core temperatures of 235 K and
253 K, respectively. Downwellings are so cold that they are below of
eutectic temperature of most Europa-relevant salts, but not below that
of Europa-relevant acids. Given the low temperature of downwelling
ice, IPR is expected to penetrate through it. Warmer upwellings may
possess significant amounts of unfrozen water if the shell is acid-
or salt-rich. The injection of liquid or the melting of acid- or
salt-rich ice will eventually lead to refreezing, as the shell conducts
away this excess heat. As liquid freezes, impurities are rejected and
concentrated in a liquid vein network surrounding relatively pure ice
crystals. These vein networks remain liquid as long as the temperature
is greater than that of the eutectic of the bulk impurities. Therefore,
in upwellings, vein networks should be briny and hence more electrically
conductive. The electrical conductivity of these vein networks depends
on the initial impurity concentration of the liquid, impurity type,
temperature and the tortuosity of any vein networks. The latter property
decreases with increasing ice recrystallization. We conclude that IPR
will likely be able to map the top of the unfrozen zone, assuming
typical marine ice salt concentrations, but not penetrate through
it. MT measurements could complement IPR effectively, because they
could measure a conductivity depth profile within the unfrozen part
of the ice shell, where the electrical conductivity exceeds 0.1 mS/m.
Title: ASAS-SN Transient Classification Report for 2016-12-06
Authors: Brown, J.
Bibcode: 2016TNSCR1009....1B
Altcode:
No abstract at ADS
Title: MDM OSMOS Spectroscopic classification of Supernovae
Authors: Bose, Subhash; Dong, Subo; Chen, Ping; Klusmeyer, J.;
Prieto, Jose Luis; Shappee, B.; Shields, J.; Brown, J.; Stanek, K. Z.;
Kochanek, C.
Bibcode: 2016ATel.9695....1B
Altcode:
We report optical spectroscopic classification of supernova
candidates 2016hgd (ATel #9651), 2016hli (ATel #9685),
CSS161013:015319+171853 and CSS161013:020130+141534
(http://nesssi.cacr.caltech.edu/catalina/AllSN.html).
Title: ASAS-SN Transient Classification Report for 2016-10-27
Authors: Bose, S.; Frank, S.; Shields, J.; Brown, J.; Stanek, K. Z.;
Dong, S.; Prieto, J. L.
Bibcode: 2016TNSCR.837....1B
Altcode:
No abstract at ADS
Title: Spectroscopic classification of Type Ia Supernova 2016guc
Authors: Bose, Subhash; Frank, S.; Shields, J.; Brown, J.; Stanek,
K. Z.; Dong, Subo; Prieto, Jose Luis
Bibcode: 2016ATel.9674....1B
Altcode:
We report optical spectroscopic observation of supernova candidate SN
2016guc UT 2016-10-19.23 with OSMOS (range 398-686 nm) mounted on the
MDM 2.4m telescope at KPNO.
Title: ASAS-SN Transient Discovery Report for 2016-09-08
Authors: Brown, J.
Bibcode: 2016TNSTR.644....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-09-13
Authors: Brown, J.
Bibcode: 2016TNSTR.674....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-08-25
Authors: Brown, J.
Bibcode: 2016TNSTR.590....1B
Altcode:
No abstract at ADS
Title: Shatter Cones, Shock Attenuation and Feldspars: Manicouagan
Impact Structure, Canada
Authors: Thompson, L. M.; Brown, J.; Spray, J. G.
Bibcode: 2016LPICo1921.6531T
Altcode:
We plan to quantify a qualititive shock attenuation scheme based on
the distribution of shatter cones, and associated shock metamorphic
effects within quartz and feldspars at Manicouagan.
Title: ASAS-SN Transient Discovery Report for 2016-07-25
Authors: Brown, J.
Bibcode: 2016TNSTR.484....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-07-07
Authors: Brown, J.
Bibcode: 2016TNSTR.457....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-07-26
Authors: Brown, J.
Bibcode: 2016TNSTR.487....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-07-15
Authors: Brown, J.
Bibcode: 2016TNSTR.472....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-07-05
Authors: Brown, J.
Bibcode: 2016TNSTR.454....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-07-29
Authors: Brown, J.
Bibcode: 2016TNSTR.497....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-06-13
Authors: Brown, J.
Bibcode: 2016TNSTR.420....1B
Altcode:
No abstract at ADS
Title: Amended Results for Hard X-Ray Emission by Non-thermal Thick
Target Recombination in Solar Flares
Authors: Reep, J. W.; Brown, J. C.
Bibcode: 2016ApJ...824...90R
Altcode: 2016arXiv160404607R
Brown & Mallik and the corresponding corrigendum Brown et
al. presented expressions for non-thermal recombination (NTR) in the
collisionally thin- and thick-target regimes, claiming that the process
could account for a substantial part of the hard X-ray continuum in
solar flares usually attributed entirely to thermal and non-thermal
bremsstrahlung (NTB). However, we have found the thick-target
expression to become unphysical for low cut-offs in the injected
electron energy spectrum. We trace this to an error in the derivation,
derive a corrected version that is real-valued and continuous for
all photon energies and cut-offs, and show that, for thick targets,
Brown et al. overestimated NTR emission at small photon energies. The
regime of small cut-offs and large spectral indices involve large
(reducing) correction factors but in some other thick-target parameter
regimes NTR/NTB can still be of the order of unity. We comment on
the importance of these results to flare and microflare modeling and
spectral fitting. An empirical fit to our results shows that the peak
NTR contribution comprises over half of the hard X-ray signal if δ
≳ 6{≤ft(\tfrac{{E}0c}{4{keV}}\right)}0.4.
Title: ASAS-SN Transient Discovery Report for 2016-06-07
Authors: Brown, J.
Bibcode: 2016TNSTR.405....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-06-05
Authors: Brown, J.
Bibcode: 2016TNSTR.403....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-05-16
Authors: Brown, J.
Bibcode: 2016TNSTR.353....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-05-17
Authors: Brown, J.
Bibcode: 2016TNSTR.354....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-05-25
Authors: Brown, J.
Bibcode: 2016TNSTR.371....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-05-26
Authors: Brown, J.
Bibcode: 2016TNSTR.378....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-05-12
Authors: Brown, J.
Bibcode: 2016TNSTR.343....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-04-28
Authors: Brown, J.
Bibcode: 2016TNSTR.319....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-01-20
Authors: Stanek; Bock; Shappee; Brown; Holoien; Kochanek; Godoy-rivera;
Basu; Prieto; Bersier; Dong; Chen; Brimacombe
Bibcode: 2016TNSTR..38....1S
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-01-12
Authors: Stanek; Brown; Holoien; Kochanek; Godoy-Rivera; Basu; Shappee;
Prieto; Bersier; Dong; Chen; Brimacombe
Bibcode: 2016TNSTR..15....1S
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-01-03
Authors: Stanek; Brown; Holoien; Kochanek; Godoy-rivera; Basu; Shappee;
Prieto; Bersier; Dong; Chen; Brimacombe
Bibcode: 2016TNSTR...3....1S
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-01-29
Authors: Brown, J.
Bibcode: 2016TNSTR..63....1B
Altcode:
No abstract at ADS
Title: ASAS-SN Transient Discovery Report for 2016-01-02
Authors: Stanek; Brown; Holoien; Kochanek; Godoy-rivera; Basu; Shappee;
Prieto; Bersier; Dong; Chen; Brimacombe
Bibcode: 2016TNSTR...2....1S
Altcode:
No abstract at ADS
Title: Search for Dark Matter in Events with Missing Transverse
Momentum and a Higgs Boson Decaying to Two Photons in p p Collisions
at √{s }=8 TeV with the ATLAS Detector
Authors: Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.;
Abolins, M.; Abouzeid, O. S.; Abramowicz, H.; Abreu, H.; Abreu, R.;
Abulaiti, Y.; Acharya, B. S.; Adamczyk, L.; Adams, D. L.; Adelman,
J.; Adomeit, S.; Adye, T.; Affolder, A. A.; Agatonovic-Jovin, T.;
Aguilar-Saavedra, J. A.; Ahlen, S. P.; Ahmadov, F.; Aielli, G.;
Akerstedt, H.; Åkesson, T. P. A.; Akimoto, G.; Akimov, A. V.;
Alberghi, G. L.; Albert, J.; Albrand, S.; Alconada Verzini, M. J.;
Aleksa, M.; Aleksandrov, I. N.; Alexa, C.; Alexander, G.; Alexopoulos,
T.; Alhroob, M.; Alimonti, G.; Alio, L.; Alison, J.; Alkire, S. P.;
Allbrooke, B. M. M.; Allport, P. P.; Aloisio, A.; Alonso, A.;
Alonso, F.; Alpigiani, C.; Altheimer, A.; Alvarez Gonzalez, B.;
Álvarez Piqueras, D.; Alviggi, M. G.; Amadio, B. T.; Amako, K.;
Amaral Coutinho, Y.; Amelung, C.; Amidei, D.; Amor Dos Santos, S. P.;
Amorim, A.; Amoroso, S.; Amram, N.; Amundsen, G.; Anastopoulos, C.;
Ancu, L. S.; Andari, N.; Andeen, T.; Anders, C. F.; Anders, G.; Anders,
J. K.; Anderson, K. J.; Andreazza, A.; Andrei, V.; Angelidakis, S.;
Angelozzi, I.; Anger, P.; Angerami, A.; Anghinolfi, F.; Anisenkov,
A. V.; Anjos, N.; Annovi, A.; Antonelli, M.; Antonov, A.; Antos,
J.; Anulli, F.; Aoki, M.; Aperio Bella, L.; Arabidze, G.; Arai,
Y.; Araque, J. P.; Arce, A. T. H.; Arduh, F. A.; Arguin, J. -F.;
Argyropoulos, S.; Arik, M.; Armbruster, A. J.; Arnaez, O.; Arnal, V.;
Arnold, H.; Arratia, M.; Arslan, O.; Artamonov, A.; Artoni, G.; Asai,
S.; Asbah, N.; Ashkenazi, A.; Åsman, B.; Asquith, L.; Assamagan,
K.; Astalos, R.; Atkinson, M.; Atlay, N. B.; Auerbach, B.; Augsten,
K.; Aurousseau, M.; Avolio, G.; Axen, B.; Ayoub, M. K.; Azuelos,
G.; Baak, M. A.; Baas, A. E.; Bacci, C.; Bachacou, H.; Bachas, K.;
Backes, M.; Backhaus, M.; Bagiacchi, P.; Bagnaia, P.; Bai, Y.; Bain,
T.; Baines, J. T.; Baker, O. K.; Balek, P.; Balestri, T.; Balli,
F.; Banas, E.; Banerjee, Sw.; Bannoura, A. A. E.; Bansil, H. S.;
Barak, L.; Barberio, E. L.; Barberis, D.; Barbero, M.; Barillari,
T.; Barisonzi, M.; Barklow, T.; Barlow, N.; Barnes, S. L.; Barnett,
B. M.; Barnett, R. M.; Barnovska, Z.; Baroncelli, A.; Barone, G.; Barr,
A. J.; Barreiro, F.; Barreiro Guimarães da Costa, J.; Bartoldus, R.;
Barton, A. E.; Bartos, P.; Basalaev, A.; Bassalat, A.; Basye, A.;
Bates, R. L.; Batista, S. J.; Batley, J. R.; Battaglia, M.; Bauce,
M.; Bauer, F.; Bawa, H. S.; Beacham, J. B.; Beattie, M. D.; Beau, T.;
Beauchemin, P. H.; Beccherle, R.; Bechtle, P.; Beck, H. P.; Becker,
K.; Becker, M.; Becker, S.; Beckingham, M.; Becot, C.; Beddall,
A. J.; Beddall, A.; Bednyakov, V. A.; Bee, C. P.; Beemster, L. J.;
Beermann, T. A.; Begel, M.; Behr, J. K.; Belanger-Champagne, C.;
Bell, W. H.; Bella, G.; Bellagamba, L.; Bellerive, A.; Bellomo, M.;
Belotskiy, K.; Beltramello, O.; Benary, O.; Benchekroun, D.; Bender,
M.; Bendtz, K.; Benekos, N.; Benhammou, Y.; Benhar Noccioli, E.;
Benitez Garcia, J. A.; Benjamin, D. P.; Bensinger, J. R.; Bentvelsen,
S.; Beresford, L.; Beretta, M.; Berge, D.; Bergeaas Kuutmann, E.;
Berger, N.; Berghaus, F.; Beringer, J.; Bernard, C.; Bernard, N. R.;
Bernius, C.; Bernlochner, F. U.; Berry, T.; Berta, P.; Bertella,
C.; Bertoli, G.; Bertolucci, F.; Bertsche, C.; Bertsche, D.; Besana,
M. I.; Besjes, G. J.; Bessidskaia Bylund, O.; Bessner, M.; Besson, N.;
Betancourt, C.; Bethke, S.; Bevan, A. J.; Bhimji, W.; Bianchi, R. M.;
Bianchini, L.; Bianco, M.; Biebel, O.; Bieniek, S. P.; Biglietti, M.;
Bilbao de Mendizabal, J.; Bilokon, H.; Bindi, M.; Binet, S.; Bingul,
A.; Bini, C.; Black, C. W.; Black, J. E.; Black, K. M.; Blackburn,
D.; Blair, R. E.; Blanchard, J. -B.; Blanco, J. E.; Blazek, T.;
Bloch, I.; Blocker, C.; Blum, W.; Blumenschein, U.; Bobbink, G. J.;
Bobrovnikov, V. S.; Bocchetta, S. S.; Bocci, A.; Bock, C.; Boehler,
M.; Bogaerts, J. A.; Bogdanchikov, A. G.; Bohm, C.; Boisvert, V.; Bold,
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I.; Daya-Ishmukhametova, R. K.; de, K.; de Asmundis, R.; de Castro,
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A.; di Ciaccio, L.; di Domenico, A.; di Donato, C.; di Girolamo,
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M.; Dias, F. A.; Diaz, M. A.; Diehl, E. B.; Dietrich, J.; Diglio,
S.; Dimitrievska, A.; Dingfelder, J.; Dita, P.; Dita, S.; Dittus, F.;
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M.; Farbin, A.; Farilla, A.; Farooque, T.; Farrell, S.; Farrington,
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J.; Whalen, K.; Wharton, A. M.; White, A.; White, M. J.; White, R.;
White, S.; Whiteson, D.; Wickens, F. J.; Wiedenmann, W.; Wielers, M.;
Wienemann, P.; Wiglesworth, C.; Wiik-Fuchs, L. A. M.; Wildauer, A.;
Wilkens, H. G.; Williams, H. H.; Williams, S.; Willis, C.; Willocq, S.;
Wilson, A.; Wilson, J. A.; Wingerter-Seez, I.; Winklmeier, F.; Winter,
B. T.; Wittgen, M.; Wittkowski, J.; Wollstadt, S. J.; Wolter, M. W.;
Wolters, H.; Wosiek, B. K.; Wotschack, J.; Woudstra, M. J.; Wozniak,
K. W.; Wu, M.; Wu, M.; Wu, S. L.; Wu, X.; Wu, Y.; Wyatt, T. R.; Wynne,
B. M.; Xella, S.; Xu, D.; Xu, L.; Yabsley, B.; Yacoob, S.; Yakabe,
R.; Yamada, M.; Yamaguchi, Y.; Yamamoto, A.; Yamamoto, S.; Yamanaka,
T.; Yamauchi, K.; Yamazaki, Y.; Yan, Z.; Yang, H.; Yang, H.; Yang,
Y.; Yao, L.; Yao, W. -M.; Yasu, Y.; Yatsenko, E.; Yau Wong, K. H.;
Ye, J.; Ye, S.; Yeletskikh, I.; Yen, A. L.; Yildirim, E.; Yorita,
K.; Yoshida, R.; Yoshihara, K.; Young, C.; Young, C. J. S.; Youssef,
S.; Yu, D. R.; Yu, J.; Yu, J. M.; Yu, J.; Yuan, L.; Yurkewicz, A.;
Yusuff, I.; Zabinski, B.; Zaidan, R.; Zaitsev, A. M.; Zalieckas, J.;
Zaman, A.; Zambito, S.; Zanello, L.; Zanzi, D.; Zeitnitz, C.; Zeman,
M.; Zemla, A.; Zengel, K.; Zenin, O.; Ženiš, T.; Zerwas, D.; Zhang,
D.; Zhang, F.; Zhang, J.; Zhang, L.; Zhang, R.; Zhang, X.; Zhang,
Z.; Zhao, X.; Zhao, Y.; Zhao, Z.; Zhemchugov, A.; Zhong, J.; Zhou,
B.; Zhou, C.; Zhou, L.; Zhou, L.; Zhou, N.; Zhu, C. G.; Zhu, H.;
Zhu, J.; Zhu, Y.; Zhuang, X.; Zhukov, K.; Zibell, A.; Zieminska, D.;
Zimine, N. I.; Zimmermann, C.; Zimmermann, S.; Zinonos, Z.; Zinser,
M.; Ziolkowski, M.; Živković, L.; Zobernig, G.; Zoccoli, A.; Zur
Nedden, M.; Zurzolo, G.; Zwalinski, L.; Atlas Collaboration
Bibcode: 2015PhRvL.115m1801A
Altcode: 2015arXiv150601081A
Results of a search for new phenomena in events with large missing
transverse momentum and a Higgs boson decaying to two photons are
reported. Data from proton-proton collisions at a center-of-mass
energy of 8 TeV and corresponding to an integrated luminosity of 20.3
fb-1 have been collected with the ATLAS detector at the
LHC. The observed data are well described by the expected standard
model backgrounds. Upper limits on the cross section of events with
large missing transverse momentum and a Higgs boson candidate are also
placed. Exclusion limits are presented for models of physics beyond
the standard model featuring dark-matter candidates.
Title: Destruction and Observational Signatures of Sun-impacting
Comets
Authors: Brown, John C.; Carlson, Robert W.; Toner, Mark P.
Bibcode: 2015ApJ...807..165B
Altcode: 2015arXiv150705062B
Motivated by recent data on comets in the low corona, we discuss
destruction of “Sun-impacting” comets in the dense lower
atmosphere. Perihelion distances q≲ {R}⊙ and masses
{M}o\gg {10}12 g are required to reach such
depths. Extending earlier work on planetary atmosphere impacts to solar
conditions, we evaluate the mechanisms and distribution of nucleus
mass and energy loss as functions of {M}o and q, and of
parameter X=2Q/{C}{{H}}{v}o2. Q is
the total specific energy for ablative mass-loss, {C}{{H}}
the bow-shock heat-transfer efficiency, and {v}o the
solar escape speed (619 km s-1). We discuss factors
affecting Q and {C}{{H}} and conclude that, for solar
{v}o,X is most likely <1 and solar-impactors mostly
ablated before decelerating. Sun-impacting comets have energies
{M}o{v}o2/2∼ 2× {10}30×
({M}o/{10}15 {{g}}) erg, (comparable to magnetic
flares ∼1029-33). This is released as a localized explosive
airburst within a few scale heights H≃ 200 {km} of the photosphere,
depending weakly on {M}o,q and X. For X={10}-2
and {M}o={10}15 {{g}}, a shallow incidence (e.g.,
polar θ ∼ {{cos}}-1(0.01)) Kreutz comet airburst occurs at
atmospheric density n∼ 3× {10}15\{{cm}}-3—a
height of 700 km (3.5 H) above the photosphere (where
n={n}o={10}17 {{cm}}-3). The airburst n
scales as ∼ {({M}oX{{cos}}3θ )}1/2
(while height z( {km})=200{ln}({n}o/n)) so n increases
1000 × (700 km deeper) for vertical entry. Such airbursts drive
flare-like phenomena including prompt radiation, hot rising plumes,
and photospheric ripples, the observability and diagnostic value of
which we discuss.
Title: Distribution of Discontinuous Kaibab Ejecta North of Meteor
Crater, Arizona
Authors: Kring, D. A.; Atwood-Stone, C.; Boyd, A.; Brown, J.;
Corley, L.; Curran, N.; Davis, C.; Korman, K.; Maine, A.; McDonald,
F.; Montalvo, S.; Nuno, R.; Oezdemir, S.; Rathbun, K.; Rhodes, N.;
Susorney, H.; Weiss, D.; Zanetti, M.
Bibcode: 2015LPI....46.1186K
Altcode: 2015LPICo1832.1186K
New mapping indicates there is significant discontinuous Kaibab-rich
ejecta far beyond the area originally mapped by Shoemaker.
Title: Magnetic Fields in the Milky Way Halo
Authors: Mao, S. A.; McClure-Griffiths, N. M.; Gaensler, B. M.; Brown,
J. C.; van Eck, C. L.; Haverkorn, M.; Kronberg, P. P.; Stil, J. M.;
Shukurov, A.; Taylor, A. R.
Bibcode: 2015HiA....16..403M
Altcode:
We present a study of the Milky Way halo magnetic field, determined
from observations of Faraday rotation measure (RM) of extragalactic
radio sources (EGS) in Galactic longitude range 100°-117° within
30° of the Galactic plane. We find negative median RMs in both the
northern and southern Galactic hemispheres for |b|>15°, outside the
latitude range where the disk field dominates. This suggest that the
halo magnetic field towards the outer Galaxy does not reverse direction
across the mid-plane. An azimuthal magnetic field at heights 0.8-2
kpc above/below the Galactic plane between the local and the Perseus
spiral arm can reproduce the observed trend of RM against Galactic
latitude. We propose that the Milky Way could have a halo magnetic
field similar to that observed in M51.
Title: Piezoelectric Dust Detector Design and Calibration for the
Armadillo Program
Authors: Odom, F.; Richter, G.; Brown, J.; Martinsen, B.; Cai, R.;
Fellows, M.; Wolf, A.; Montag, C.; Young, P.; Carmona-Reyes, J. A.;
Schmoke, J.; Cook, M.; Garner, B.; Gravagne, I.; Pin, K.; Shedd, L.;
Groskreutz, T.; Hegle, T.; Mulenos, N.; Stone, J.; Wiley, C.; Yanga,
V.; Eustice, D.; Flachsbart, K.; Steele, N.; Tilley, C.; Friudenberg,
P.; Penshorn, D.; Henderson, L.; Cavazos, E.; Nabili, A.; Cox, E.;
Cox, A.; Wood, J.; Devine, L.; Curran, J.; Mendiola, A.; Falkner, C.;
Laufer, R.; Srama, R.; Schubert, K. E.; Matthews, L. S.; Lightsey,
G.; Hyde, T. W.
Bibcode: 2015LPI....46.2191O
Altcode: 2015LPICo1832.2191O
Design and calibration of piezoelectric dust detector for LEO.
Title: Solar Hard X-Ray Source Sizes in a Beam-heated and Ionized
Chromosphere
Authors: O'Flannagain, Aidan M.; Brown, John C.; Gallagher, Peter T.
Bibcode: 2015ApJ...799..127O
Altcode:
Solar flare hard X-rays (HXRs) are produced as bremsstrahlung
when an accelerated population of electrons interacts with the
dense chromospheric plasma. HXR observations presented by Kontar et
al. using the Ramaty High-Energy Solar Spectroscopic Imager have shown
that HXR source sizes are three to six times more extended in height
than those predicted by the standard collisional thick target model
(CTTM). Several possible explanations have been put forward including
the multi-threaded nature of flare loops, pitch-angle scattering,
and magnetic mirroring. However, the nonuniform ionization (NUI)
structure along the path of the electron beam has not been fully
explored as a solution to this problem. Ionized plasma is known to
be less effective at producing nonthermal bremsstrahlung HXRs when
compared to neutral plasma. If the peak HXR emission was produced in
a locally ionized region within the chromosphere, the intensity of
emission will be preferentially reduced around this peak, resulting in
a more extended source. Due to this effect, along with the associated
density enhancement in the upper chromosphere, injection of a beam of
electrons into a partially ionized plasma should result in an HXR source
that is substantially more vertically extended relative to that for a
neutral target. Here we present the results of a modification to the
CTTM, which takes into account both a localized form of chromospheric
NUI and an increased target density. We find 50 keV HXR source widths,
with and without the inclusion of a locally ionized region, of ~3 Mm
and ~0.7 Mm, respectively. This helps to provide a theoretical solution
to the currently open question of overly extended HXR sources.
Title: Magnetic Fields in a Sample of Nearby Spiral Galaxies
Authors: Van Eck, C. L.; Brown, J. C.; Shukurov, A.; Fletcher, A.
Bibcode: 2015ApJ...799...35V
Altcode: 2014arXiv1411.1386V
Both observations and modeling of magnetic fields in the diffuse
interstellar gas of spiral galaxies are well developed, but the theory
has been confronted with observations for only a handful of individual
galaxies. There is now sufficient data to consider the statistical
properties of galactic magnetic fields. We have collected data from the
literature on the magnetic fields and interstellar media of 20 spiral
galaxies, and tested for various physically motivated correlations
between magnetic field and interstellar medium parameters. Clear
correlations emerge between the total magnetic field strength and
molecular gas density as well as the star formation rate. The magnetic
pitch angle exhibits correlations with the total gas density, the star
formation rate, and the strength of the axisymmetric component of the
mean magnetic field. The total and mean magnetic field strengths exhibit
a noticeable degree of correlation, suggesting a universal behavior
of the degree of order in galactic magnetic fields. We also compare
the predictions of galactic dynamo theory to observed magnetic field
parameters and identify directions in which theory and observations
might be usefully developed.
Title: Solar Hard X-ray Source Sizes in a Beam-Heated and Ionised
Chromosphere
Authors: O'Flannagain, A.; Brown, J. C.; Gallagher, P. T.
Bibcode: 2014arXiv1411.5168O
Altcode:
Solar flare hard X-rays (HXRs) are produced as bremsstrahlung
when an accelerated population of electrons interacts with the
dense chromospheric plasma. HXR observations presented by using
the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) have
shown that HXR source sizes are 3-6 times more extended in height
than those predicted by the standard collisional thick target model
(CTTM). Several possible explanations have been put forward including
the multi-threaded nature of flare loops, pitch-angle scattering,
and magnetic mirroring. However, the nonuniform ionisation (NUI)
structure along the path of the electron beam has not been fully
explored as a solution to this problem. Ionised plasma is known to
be less effective at producing nonthermal bremsstrahlung HXRs when
compared to neutral plasma. If the peak HXR emission was produced in
a locally ionised region within the chromosphere, the intensity of
emission will be preferentially reduced around this peak, resulting in
a more extended source. Due to this effect, along with the associated
density enhancement in the upper chromosphere, injection of a beam of
electrons into a partially ionised plasma should result in a HXR source
which is substantially more vertically extended relative to that for a
neutral target. Here we present the results of a modification to the
CTTM which takes into account both a localised form of chromospheric
NUI and an increased target density. We find 50 keV HXR source widths,
with and without the inclusion of a locally ionised region, of ~3 Mm
and ~0.7 Mm, respectively. This helps to provide a theoretical solution
to the currently open question of overly-extended HXR sources.
Title: Testing the GRACE follow-on triple mirror assembly
Authors: Fleddermann, R.; Ward, R. L.; Elliot, M.; Wuchenich, D. M.;
Gilles, F.; Herding, M.; Nicklaus, K.; Brown, J.; Burke, J.; Dligatch,
S.; Farrant, D. I.; Green, K. L.; Seckold, J. A.; Blundell, M.;
Brister, R.; Smith, C.; Sheard, B. S.; Heinzel, G.; Danzmann, K.;
Klipstein, B.; McClelland, D. E.; Shaddock, D. A.
Bibcode: 2014CQGra..31s5004F
Altcode:
We report on the successful testing of the GRACE follow-on triple
mirror assembly (TMA) prototype. This component serves to route the
laser beam in a proposed follow-on mission to the Gravity Recovery and
Climate Explorer (GRACE) mission, containing an optical instrument for
space-based distance measurement between satellites. As part of this,
the TMA has to meet a set of stringent requirements on both the optical
and mechanical properties. The purpose of the TMA prototype testing
is to establish the feasibility of the design, materials choice and
fabrication techniques. Here we report on co-alignment testing of
this device to the arc second (5 μrad) level and thermal alignment
stability testing to 1 $\mu {\rm rad}\;{{{\rm K}}^{-1}}$ μ rad K - 1 .
Title: Progress on 241Am Production for Use in Radioisotope Power
Systems
Authors: Baker, S. R.; Bell, K. J.; Brown, J.; Carrigan, C.; Carrott,
M. J.; Gregson, C.; Clough, M.; Maher, C. J.; Mason, C.; Rhodes,
C. J.; Rice, T. G.; Sarsfield, M. J.; Stephenson, K.; Taylor, R. J.;
Tinsley, T. P.; Woodhead, D. A.; Wiss, T.
Bibcode: 2014ESASP.719E..17B
Altcode:
Electrical power sources used in outer planet missions are a key
enabling technology for data acquisition and communications. Power
sources generate electricity from the thermal energy from alpha decay
of the radioisotope 238Pu via thermo-electric conversion. Production
of 238Pu requires specialist facilities including a nuclear reactor
and reprocessing plants that are expensive to build and operate,
so naturally, a more economical alternative is attractive to the
industry. Within Europe 241Am is a feasible alternative to 238Pu that
can provide a heat source for radioisotope thermoelectric generators
(RTGs) and radioisotope heating units (RHUs). As a daughter product
of 241Pu decay, 241Am is present at 1000s kg levels within the UK
civil plutonium stockpile.A chemical separation process is required
to extract the 241Am in a pure form and this paper describes such a
process, successfully developed to the proof of concept stage.
Title: Destruction regimes of Sun-skimming and Sun-plunging comets
Authors: Brown, J.; Carlson, R.; Toner, M.
Bibcode: 2014acm..conf...61B
Altcode:
We establish and model destruction regimes for close sun-grazers,
i.e. comets of small enough perihelia (q ≤ a few R_⊙) and large
enough mass (M_o ≥ 10^{13} g) to reach the inner solar corona or
below. These can be divided into sun-skimming and sun-plunging according
to whether their M_o,q values confine them to atmospheric densities
n ≤ 10^{14}cm^{-3} where mass loss is dominated by insolative
sublimation, or let them reach n≥ 10^{14}cm^{-3} where hydrodynamic
interactions with the dense chromosphere take over (bow-shock-heated
ablative mass loss, ram pressure pancaking and deceleration). Being
rare, no sun-plungers have yet been detected but they are of potentially
great interest. Recent years have seen the first direct monitoring of
three sun-skimmers in the low corona by SDO at EUV wavelengths. Both
sun-plungers and sun-skimmers offer novel diagnostics of both cometary
and solar conditions. We show that, due to their much higher
speeds than planetary impacts, sun-plungers are likely dominated by
pancaking and ablative mass-loss, rather than deceleration, even for
quite inefficient bow-shock heat transfer, but we obtain solutions for
ablation- and deceleration-dominated, and for intermediate, cases. All
involve rapid local deposition of nucleus kinetic energy and momentum
within a few 100 km near the photosphere. This occurs at atmospheric
density n_{peak}(cm^{-3})≈3×10^{16}(Xμ_{-2}^3M_{15})^{1/2}
for incident mass M_o=10^{15}M_{15} g, incident angle θ =
cos^{-1}(10^{-2}μ_{-2}) to the vertical, and parameter X ranges from
0.001 up to 1. Break-up into Y fragments reduces n_{peak} by a factor
≈ Y^{-1/3}. This deposition will drive hot rising 'airburst' plumes
and internal helioseismic waves similar to magnetic flare effects. In
the normal ablation-dominated case (small X) the hot airburst will
exhibit essentially cometary abundances (metallicity Gt; solar). Though sun-skimmer nuclei are vaporized by 5800 K (≈ 0.6 eV/photon)
photospheric sunlight, their dissociation, ionization and heating
up to EUV temperatures (10-100 eV) have to involve chromospheric EUV
(10 eV/photon), 2 MK coronal thermal conduction (200 eV/electron) and
conversion of nucleus kinetic energy (2 keV/nucleon). Coronal heat flux
may be important in small sun-skimmers with tenuous comae and tails but
kinetic energy conversion must dominate in large ones like Lovejoy 2011.
Title: The design and construction of a prototype lateral-transfer
retro-reflector for inter-satellite laser ranging
Authors: Ward, R. L.; Fleddermann, R.; Francis, S.; Mow-Lowry, C.;
Wuchenich, D.; Elliot, M.; Gilles, F.; Herding, M.; Nicklaus, K.;
Brown, J.; Burke, J.; Dligatch, S.; Farrant, D.; Green, K.; Seckold,
J.; Blundell, M.; Brister, R.; Smith, C.; Danzmann, K.; Heinzel,
G.; Schütze, D.; Sheard, B. S.; Klipstein, W.; McClelland, D. E.;
Shaddock, D. A.
Bibcode: 2014CQGra..31i5015W
Altcode:
The Gravity Recovery and Climate Experiment (GRACE) mission, launched in
2002, is nearing an end, and a continuation mission (GRACE Follow-on)
is on a fast-tracked development. GRACE Follow-on will include a
laser ranging interferometer technology demonstrator, which will
perform the first laser interferometric ranging measurement between
separate spacecraft. This necessitates the development of lightweight
precision optics that can operate in this demanding environment. In
particular, this beam routing system, called the triple mirror assembly,
for the GRACE Follow-on mission presents a significant manufacturing
challenge. Here we report on the design and construction of a prototype
triple mirror assembly for the GRACE Follow-on mission. Our constructed
prototype has a co-alignment error between the incoming and outgoing
beams of 9 μrad, which meets the requirement that this error must be
less than 10 μrad.
Title: Search for Invisible Decays of a Higgs Boson Produced in
Association with a Z Boson in ATLAS
Authors: Aad, G.; Abajyan, T.; Abbott, B.; Abdallah, J.; Abdel Khalek,
S.; Abdinov, O.; Aben, R.; Abi, B.; Abolins, M.; Abouzeid, O. S.;
Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Acharya, B. S.; Adamczyk, L.;
Adams, D. L.; Addy, T. N.; Adelman, J.; Adomeit, S.; Adye, T.; Aefsky,
S.; Agatonovic-Jovin, T.; Aguilar-Saavedra, J. A.; Agustoni, M.;
Ahlen, S. P.; Ahmad, A.; Ahmadov, F.; Aielli, G.; Åkesson, T. P. A.;
Akimoto, G.; Akimov, A. V.; Alam, M. A.; Albert, J.; Albrand, S.;
Alconada Verzini, M. J.; Aleksa, M.; Aleksandrov, I. N.; Alessandria,
F.; Alexa, C.; Alexander, G.; Alexandre, G.; Alexopoulos, T.; Alhroob,
M.; Alimonti, G.; Alio, L.; Alison, J.; Allbrooke, B. M. M.; Allison,
L. J.; Allport, P. P.; Allwood-Spiers, S. E.; Almond, J.; Aloisio, A.;
Alon, R.; Alonso, A.; Alonso, F.; Altheimer, A.; Alvarez Gonzalez, B.;
Alviggi, M. G.; Amako, K.; Amaral Coutinho, Y.; Amelung, C.; Ammosov,
V. V.; Amor Dos Santos, S. P.; Amorim, A.; Amoroso, S.; Amram, N.;
Amundsen, G.; Anastopoulos, C.; Ancu, L. S.; Andari, N.; Andeen, T.;
Anders, C. F.; Anders, G.; Anderson, K. J.; Andreazza, A.; Andrei, V.;
Anduaga, X. S.; Angelidakis, S.; Anger, P.; Angerami, A.; Anghinolfi,
F.; Anisenkov, A. V.; Anjos, N.; Annovi, A.; Antonaki, A.; Antonelli,
M.; Antonov, A.; Antos, J.; Anulli, F.; Aoki, M.; Aperio Bella, L.;
Apolle, R.; Arabidze, G.; Aracena, I.; Arai, Y.; Arce, A. T. H.;
Arguin, J. -F.; Argyropoulos, S.; Arik, E.; Arik, M.; Armbruster,
A. J.; Arnaez, O.; Arnal, V.; Arslan, O.; Artamonov, A.; Artoni, G.;
Asai, S.; Asbah, N.; Ask, S.; Åsman, B.; Asquith, L.; Assamagan, K.;
Astalos, R.; Astbury, A.; Atkinson, M.; Atlay, N. B.; Auerbach, B.;
Auge, E.; Augsten, K.; Aurousseau, M.; Avolio, G.; Azuelos, G.; Azuma,
Y.; Baak, M. A.; Bacci, C.; Bach, A. M.; Bachacou, H.; Bachas, K.;
Backes, M.; Backhaus, M.; Backus Mayes, J.; Badescu, E.; Bagiacchi,
P.; Bagnaia, P.; Bai, Y.; Bailey, D. C.; Bain, T.; Baines, J. T.;
Baker, O. K.; Baker, S.; Balek, P.; Balli, F.; Banas, E.; Banerjee,
Sw.; Banfi, D.; Bangert, A.; Bansal, V.; Bansil, H. S.; Barak, L.;
Baranov, S. P.; Barber, T.; Barberio, E. L.; Barberis, D.; Barbero, M.;
Barillari, T.; Barisonzi, M.; Barklow, T.; Barlow, N.; Barnett, B. M.;
Barnett, R. M.; Baroncelli, A.; Barone, G.; Barr, A. J.; Barreiro,
F.; Barreiro Guimarães da Costa, J.; Bartoldus, R.; Barton, A. E.;
Bartos, P.; Bartsch, V.; Bassalat, A.; Basye, A.; Bates, R. L.;
Batkova, L.; Batley, J. R.; Battistin, M.; Bauer, F.; Bawa, H. S.;
Beau, T.; Beauchemin, P. H.; Beccherle, R.; Bechtle, P.; Beck, H. P.;
Becker, K.; Becker, S.; Beckingham, M.; Beddall, A. J.; Beddall, A.;
Bedikian, S.; Bednyakov, V. A.; Bee, C. P.; Beemster, L. J.; Beermann,
T. A.; Begel, M.; Behr, K.; Belanger-Champagne, C.; Bell, P. J.;
Bell, W. H.; Bella, G.; Bellagamba, L.; Bellerive, A.; Bellomo, M.;
Belloni, A.; Beloborodova, O. L.; Belotskiy, K.; Beltramello, O.;
Benary, O.; Benchekroun, D.; Bendtz, K.; Benekos, N.; Benhammou,
Y.; Benhar Noccioli, E.; Benitez Garcia, J. A.; Benjamin, D. P.;
Bensinger, J. R.; Benslama, K.; Bentvelsen, S.; Berge, D.; Bergeaas
Kuutmann, E.; Berger, N.; Berghaus, F.; Berglund, E.; Beringer, J.;
Bernard, C.; Bernat, P.; Bernius, C.; Bernlochner, F. U.; Berry, T.;
Berta, P.; Bertella, C.; Bertolucci, F.; Besana, M. I.; Besjes, G. J.;
Bessidskaia, O.; Besson, N.; Bethke, S.; Bhimji, W.; Bianchi, R. M.;
Bianchini, L.; Bianco, M.; Biebel, O.; Bieniek, S. P.; Bierwagen, K.;
Biesiada, J.; Biglietti, M.; Bilbao de Mendizabal, J.; Bilokon, H.;
Bindi, M.; Binet, S.; Bingul, A.; Bini, C.; Bittner, B.; Black, C. W.;
Black, J. E.; Black, K. M.; Blackburn, D.; Blair, R. E.; Blanchard,
J. -B.; Blazek, T.; Bloch, I.; Blocker, C.; Blum, W.; Blumenschein,
U.; Bobbink, G. J.; Bobrovnikov, V. S.; Bocchetta, S. S.; Bocci, A.;
Boddy, C. R.; Boehler, M.; Boek, J.; Boek, T. T.; Bogaerts, J. A.;
Bogdanchikov, A. G.; Bogouch, A.; Bohm, C.; Bohm, J.; Boisvert, V.;
Bold, T.; Boldea, V.; Boldyrev, A. S.; Bolnet, N. M.; Bomben, M.;
Bona, M.; Boonekamp, M.; Borer, C.; Borisov, A.; Borissov, G.; Borri,
M.; Borroni, S.; Bortfeldt, J.; Bortolotto, V.; Bos, K.; Boscherini,
D.; Bosman, M.; Boterenbrood, H.; Bouchami, J.; Boudreau, J.;
Bouhova-Thacker, E. V.; Boumediene, D.; Bourdarios, C.; Bousson, N.;
Boutouil, S.; Boveia, A.; Boyd, J.; Boyko, I. R.; Bozovic-Jelisavcic,
I.; Bracinik, J.; Branchini, P.; Brandt, A.; Brandt, G.; Brandt, O.;
Bratzler, U.; Brau, B.; Brau, J. E.; Braun, H. M.; Brazzale, S. F.;
Brelier, B.; Brendlinger, K.; Brennan, A. J.; Brenner, R.; Bressler,
S.; Bristow, T. M.; Britton, D.; Brochu, F. M.; Brock, I.; Brock,
R.; Broggi, F.; Bromberg, C.; Bronner, J.; Brooijmans, G.; Brooks,
T.; Brooks, W. K.; Brosamer, J.; Brost, E.; Brown, G.; Brown, J.;
Bruckman de Renstrom, P. A.; Bruncko, D.; Bruneliere, R.; Brunet, S.;
Bruni, A.; Bruni, G.; Bruschi, M.; Bryngemark, L.; Buanes, T.; Buat,
Q.; Bucci, F.; Buchholz, P.; Buckingham, R. M.; Buckley, A. G.; Buda,
S. I.; Budagov, I. A.; Budick, B.; Buehrer, F.; Bugge, L.; Bugge,
M. K.; Bulekov, O.; Bundock, A. C.; Bunse, M.; Burckhart, H.; Burdin,
S.; Burghgrave, B.; Burke, S.; Burmeister, I.; Busato, E.; Büscher,
V.; Bussey, P.; Buszello, C. P.; Butler, B.; Butler, J. M.; Butt,
A. I.; Buttar, C. M.; Butterworth, J. M.; Buttinger, W.; Buzatu, A.;
Byszewski, M.; Cabrera Urbán, S.; Caforio, D.; Cakir, O.; Calafiura,
P.; Calderini, G.; Calfayan, P.; Calkins, R.; Caloba, L. P.; Caloi,
R.; Calvet, D.; Calvet, S.; Camacho Toro, R.; Camarri, P.; Cameron,
D.; Caminada, L. M.; Caminal Armadans, R.; Campana, S.; Campanelli,
M.; Canale, V.; Canelli, F.; Canepa, A.; Cantero, J.; Cantrill, R.;
Cao, T.; Capeans Garrido, M. D. M.; Caprini, I.; Caprini, M.; Capua,
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M.; Esch, H.; Escobar, C.; Espinal Curull, X.; Esposito, B.; Etienne,
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K.; Yamamoto, S.; Yamamura, T.; Yamanaka, T.; Yamauchi, K.; Yamazaki,
Y.; Yan, Z.; Yang, H.; Yang, H.; Yang, U. K.; Yang, Y.; Yanush, S.;
Yao, L.; Yasu, Y.; Yatsenko, E.; Yau Wong, K. H.; Ye, J.; Ye, S.;
Yen, A. L.; Yildirim, E.; Yilmaz, M.; Yoosoofmiya, R.; Yorita, K.;
Yoshida, R.; Yoshihara, K.; Young, C.; Young, C. J. S.; Youssef,
S.; Yu, D. R.; Yu, J.; Yu, J. M.; Yu, J.; Yuan, L.; Yurkewicz, A.;
Zabinski, B.; Zaidan, R.; Zaitsev, A. M.; Zaman, A.; Zambito, S.;
Zanello, L.; Zanzi, D.; Zaytsev, A.; Zeitnitz, C.; Zeman, M.; Zemla,
A.; Zengel, K.; Zenin, O.; Ženiš, T.; Zerwas, D.; Zevi Della Porta,
G.; Zhang, D.; Zhang, H.; Zhang, J.; Zhang, L.; Zhang, X.; Zhang, Z.;
Zhao, Z.; Zhemchugov, A.; Zhong, J.; Zhou, B.; Zhou, L.; Zhou, N.; Zhu,
C. G.; Zhu, H.; Zhu, J.; Zhu, Y.; Zhuang, X.; Zibell, A.; Zieminska,
D.; Zimine, N. I.; Zimmermann, C.; Zimmermann, R.; Zimmermann, S.;
Zimmermann, S.; Zinonos, Z.; Ziolkowski, M.; Zitoun, R.; Zobernig,
G.; Zoccoli, A.; Zur Nedden, M.; Zurzolo, G.; Zutshi, V.; Zwalinski,
L.; Atlas Collaboration
Bibcode: 2014PhRvL.112t1802A
Altcode: 2014arXiv1402.3244A
A search for evidence of invisible-particle decay modes of a Higgs boson
produced in association with a Z boson at the Large Hadron Collider is
presented. No deviation from the standard model expectation is observed
in 4.5 fb-1 (20.3 fb-1) of 7 (8) TeV pp collision
data collected by the ATLAS experiment. Assuming the standard model
rate for ZH production, an upper limit of 75%, at the 95% confidence
level is set on the branching ratio to invisible-particle decay modes
of the Higgs boson at a mass of 125.5 GeV. The limit on the branching
ratio is also interpreted in terms of an upper limit on the allowed
dark matter-nucleon scattering cross section within a Higgs-portal dark
matter scenario. Within the constraints of such a scenario, the results
presented in this Letter provide the strongest available limits for
low-mass dark matter candidates. Limits are also set on an additional
neutral Higgs boson, in the mass range 110<mH<400
GeV, produced in association with a Z boson and decaying to invisible
particles.
Title: Determining the resonance strength of the 56Ni
rp-process waiting point through (d,n) with VANDLE and MoNA-LISA
Authors: Peters, W.; Grzywacz, R.; Madurga, M.; Paulauskas, S. V.;
Taylor, S.; Allen, J.; Cizewski, J. A.; Manning, B.; Howard, M. E.;
Smith, J.; Jones, M.; Baumann, T.; Thoennessen, M.; Bardayan, D. W.;
Pain, S. D.; Clement, R. C. C.; Brown, J.; Luther, B.; Ilyushkin,
S.; O'Malley, P. D.; Ikeyama, R.; Kozub, R. L.; Bergstrom, Z. J.;
Deyoung, P. A.; Rogers, W.
Bibcode: 2014APS..APR.K6008P
Altcode:
The rapid proton capture (rp) process of explosive nucleosynthesis
is believed to be the driver of X-ray bursts and creates nuclei
up to around mass 110. Whereas much of this process burns in an
equilibrium determined by half-lives and masses, the waiting point at
56Ni is unique. At this point the process reaches its peak
luminosity and the synthesis of almost all heavier nuclei pass through
the 56Ni(p,γ)57Cu reaction. Since the gamma-decay
width dominates the relevant resonance in 57Cu, a measurement
of its proton partial width can be used to extract the proton-capture
resonance strength. An experiment to do this was performed at the
NSCL using the Versatile Array of Neutron Detectors at Low Energy
(VANDLE) along with the MoNA-LISA neutron detector arrays; and was
the commissioning experiment for VANDLE with a transfer reaction. The
events in the digitizing electronics of VANDLE were event-matched to
the MoNA-LISA-Sweeper data acquisition system. Work supported in
part by U.S. DOE, the NNSA SSAA, and the NSF.
Title: Radio Jove: Jupiter Radio Astronomy for Citizens
Authors: Higgins, Charles; Thieman, J. R.; Flagg, R.; Reyes, F. J.;
Sky, J.; Greenman, W.; Brown, J.; Typinski, D.; Ashcraft, T.; Mount, A.
Bibcode: 2014AAS...22344407H
Altcode:
Radio JOVE is a hands-on educational activity that brings the radio
sounds of the Sun, Jupiter, the Milky Way Galaxy, and terrestrial radio
noise to students, teachers, and the general public. Participants may
build a simple radio telescope kit, make scientific observations, and
interact with professional radio observatories in real-time over the
Internet. Our website (http://radiojove.gsfc.nasa.gov) includes science
information, construction manuals, observing guides, and education
resources for teachers and students. Radio Jove is continually expanding
its participants with over 1800 kits sold to more than 70 countries
worldwide. Recently some of our most dedicated observers have upgraded
their Radio Jove antennas to semi-professional observatories. We have
spectrographs and wide band antennas, some with 8 MHz bandwidth and
some with dual polarization capabilities. In an effort to add to the
science literature, these observers are coordinating their efforts
to pursue some basic questions about Jupiter’s radio emissions
(radio source locations, spectral structure, long term changes,
etc.). We can compare signal and ionosphere variations using the
many Radio Jove observers at different locations. Observers are also
working with members of the Long Wavelength Array Station 1 (LWA1)
radio telescope to coordinate observations of Jupiter; Radio Jove is
planning to make coordinated observations while the Juno Mission is
active beginning in 2015. The Radio Jove program is overviewed, its
hardware and software are highlighted, recent sample observations are
shown, and we demonstrate that we are capable of real citizen science.
Title: Search for Dark Matter in Events with a Hadronically Decaying
W or Z Boson and Missing Transverse Momentum in pp Collisions at
√s =8 TeV with the ATLAS Detector
Authors: Aad, G.; Abajyan, T.; Abbott, B.; Abdallah, J.; Abdel Khalek,
S.; Abdinov, O.; Aben, R.; Abi, B.; Abolins, M.; Abouzeid, O. S.;
Abramowicz, H.; Abreu, H.; Abulaiti, Y.; Acharya, B. S.; Adamczyk,
L.; Adams, D. L.; Addy, T. N.; Adelman, J.; Adomeit, S.; Adye, T.;
Aefsky, S.; Agatonovic-Jovin, T.; Aguilar-Saavedra, J. A.; Agustoni,
M.; Ahlen, S. P.; Ahmad, A.; Ahmadov, F.; Ahsan, M.; Aielli, G.;
Åkesson, T. P. A.; Akimoto, G.; Akimov, A. V.; Alam, M. A.; Albert,
J.; Albrand, S.; Alconada Verzini, M. J.; Aleksa, M.; Aleksandrov,
I. N.; Alessandria, F.; Alexa, C.; Alexander, G.; Alexandre, G.;
Alexopoulos, T.; Alhroob, M.; Aliev, M.; Alimonti, G.; Alio, L.;
Alison, J.; Allbrooke, B. M. M.; Allison, L. J.; Allport, P. P.;
Allwood-Spiers, S. E.; Almond, J.; Aloisio, A.; Alon, R.; Alonso,
A.; Alonso, F.; Altheimer, A.; Alvarez Gonzalez, B.; Alviggi, M. G.;
Amako, K.; Amaral Coutinho, Y.; Amelung, C.; Ammosov, V. V.; Amor
Dos Santos, S. P.; Amorim, A.; Amoroso, S.; Amram, N.; Amundsen, G.;
Anastopoulos, C.; Ancu, L. S.; Andari, N.; Andeen, T.; Anders, C. F.;
Anders, G.; Anderson, K. J.; Andreazza, A.; Andrei, V.; Anduaga, X. S.;
Angelidakis, S.; Anger, P.; Angerami, A.; Anghinolfi, F.; Anisenkov,
A. V.; Anjos, N.; Annovi, A.; Antonaki, A.; Antonelli, M.; Antonov,
A.; Antos, J.; Anulli, F.; Aoki, M.; Aperio Bella, L.; Apolle, R.;
Arabidze, G.; Aracena, I.; Arai, Y.; Arce, A. T. H.; Arfaoui, S.;
Arguin, J. -F.; Argyropoulos, S.; Arik, E.; Arik, M.; Armbruster,
A. J.; Arnaez, O.; Arnal, V.; Arslan, O.; Artamonov, A.; Artoni, G.;
Asai, S.; Asbah, N.; Ask, S.; Åsman, B.; Asquith, L.; Assamagan, K.;
Astalos, R.; Astbury, A.; Atkinson, M.; Atlay, N. B.; Auerbach, B.;
Auge, E.; Augsten, K.; Aurousseau, M.; Avolio, G.; Azuelos, G.; Azuma,
Y.; Baak, M. A.; Bacci, C.; Bach, A. M.; Bachacou, H.; Bachas, K.;
Backes, M.; Backhaus, M.; Backus Mayes, J.; Badescu, E.; Bagiacchi,
P.; Bagnaia, P.; Bai, Y.; Bailey, D. C.; Bain, T.; Baines, J. T.;
Baker, O. K.; Baker, S.; Balek, P.; Balli, F.; Banas, E.; Banerjee,
Sw.; Banfi, D.; Bangert, A.; Bansal, V.; Bansil, H. S.; Barak, L.;
Baranov, S. P.; Barber, T.; Barberio, E. L.; Barberis, D.; Barbero,
M.; Bardin, D. Y.; Barillari, T.; Barisonzi, M.; Barklow, T.; Barlow,
N.; Barnett, B. M.; Barnett, R. M.; Baroncelli, A.; Barone, G.; Barr,
A. J.; Barreiro, F.; Barreiro Guimarães da Costa, J.; Bartoldus, R.;
Barton, A. E.; Bartsch, V.; Bassalat, A.; Basye, A.; Bates, R. L.;
Batkova, L.; Batley, J. R.; Battistin, M.; Bauer, F.; Bawa, H. S.;
Beau, T.; Beauchemin, P. H.; Beccherle, R.; Bechtle, P.; Beck, H. P.;
Becker, K.; Becker, S.; Beckingham, M.; Beddall, A. J.; Beddall,
A.; Bedikian, S.; Bednyakov, V. A.; Bee, C. P.; Beemster, L. J.;
Beermann, T. A.; Begel, M.; Behr, K.; Belanger-Champagne, C.; Bell,
P. J.; Bell, W. H.; Bella, G.; Bellagamba, L.; Bellerive, A.; Bellomo,
M.; Belloni, A.; Beloborodova, O. L.; Belotskiy, K.; Beltramello, O.;
Benary, O.; Benchekroun, D.; Bendtz, K.; Benekos, N.; Benhammou, Y.;
Benhar Noccioli, E.; Benitez Garcia, J. A.; Benjamin, D. P.; Bensinger,
J. R.; Benslama, K.; Bentvelsen, S.; Berge, D.; Bergeaas Kuutmann,
E.; Berger, N.; Berghaus, F.; Berglund, E.; Beringer, J.; Bernard, C.;
Bernat, P.; Bernhard, R.; Bernius, C.; Bernlochner, F. U.; Berry, T.;
Berta, P.; Bertella, C.; Bertolucci, F.; Besana, M. I.; Besjes, G. J.;
Bessidskaia, O.; Besson, N.; Bethke, S.; Bhimji, W.; Bianchi, R. M.;
Bianchini, L.; Bianco, M.; Biebel, O.; Bieniek, S. P.; Bierwagen, K.;
Biesiada, J.; Biglietti, M.; Bilbao de Mendizabal, J.; Bilokon, H.;
Bindi, M.; Binet, S.; Bingul, A.; Bini, C.; Bittner, B.; Black, C. W.;
Black, J. E.; Black, K. M.; Blackburn, D.; Blair, R. E.; Blanchard,
J. -B.; Blazek, T.; Bloch, I.; Blocker, C.; Blocki, J.; Blum, W.;
Blumenschein, U.; Bobbink, G. J.; Bobrovnikov, V. S.; Bocchetta, S. S.;
Bocci, A.; Boddy, C. R.; Boehler, M.; Boek, J.; Boek, T. T.; Boelaert,
N.; Bogaerts, J. A.; Bogdanchikov, A. G.; Bogouch, A.; Bohm, C.; Bohm,
J.; Boisvert, V.; Bold, T.; Boldea, V.; Boldyrev, A. S.; Bolnet, N. M.;
Bomben, M.; Bona, M.; Boonekamp, M.; Bordoni, S.; Borer, C.; Borisov,
A.; Borissov, G.; Borri, M.; Borroni, S.; Bortfeldt, J.; Bortolotto,
V.; Bos, K.; Boscherini, D.; Bosman, M.; Boterenbrood, H.; Bouchami,
J.; Boudreau, J.; Bouhova-Thacker, E. V.; Boumediene, D.; Bourdarios,
C.; Bousson, N.; Boutouil, S.; Boveia, A.; Boyd, J.; Boyko, I. R.;
Bozovic-Jelisavcic, I.; Bracinik, J.; Branchini, P.; Brandt, A.;
Brandt, G.; Brandt, O.; Bratzler, U.; Brau, B.; Brau, J. E.; Braun,
H. M.; Brazzale, S. F.; Brelier, B.; Brendlinger, K.; Brenner, R.;
Bressler, S.; Bristow, T. M.; Britton, D.; Brochu, F. M.; Brock, I.;
Brock, R.; Broggi, F.; Bromberg, C.; Bronner, J.; Brooijmans, G.;
Brooks, T.; Brooks, W. K.; Brosamer, J.; Brost, E.; Brown, G.; Brown,
J.; Bruckman de Renstrom, P. A.; Bruncko, D.; Bruneliere, R.; Brunet,
S.; Bruni, A.; Bruni, G.; Bruschi, M.; Bryngemark, L.; Buanes, T.;
Buat, Q.; Bucci, F.; Buchanan, J.; Buchholz, P.; Buckingham, R. M.;
Buckley, A. G.; Buda, S. I.; Budagov, I. A.; Budick, B.; Buehrer,
F.; Bugge, L.; Bulekov, O.; Bundock, A. C.; Bunse, M.; Burckhart,
H.; Burdin, S.; Burgess, T.; Burke, S.; Burmeister, I.; Busato,
E.; Büscher, V.; Bussey, P.; Buszello, C. P.; Butler, B.; Butler,
J. M.; Butt, A. I.; Buttar, C. M.; Butterworth, J. M.; Buttinger, W.;
Buzatu, A.; Byszewski, M.; Cabrera Urbán, S.; Caforio, D.; Cakir,
O.; Calafiura, P.; Calderini, G.; Calfayan, P.; Calkins, R.; Caloba,
L. P.; Caloi, R.; Calvet, D.; Calvet, S.; Camacho Toro, R.; Camarri,
P.; Cameron, D.; Caminada, L. M.; Caminal Armadans, R.; Campana,
S.; Campanelli, M.; Canale, V.; Canelli, F.; Canepa, A.; Cantero,
J.; Cantrill, R.; Cao, T.; Capeans Garrido, M. D. M.; Caprini, I.;
Caprini, M.; Capua, M.; Caputo, R.; Cardarelli, R.; Carli, T.; Carlino,
G.; Carminati, L.; Caron, S.; Carquin, E.; Carrillo-Montoya, G. D.;
Carter, A. A.; Carter, J. R.; Carvalho, J.; Casadei, D.; Casado,
M. P.; Caso, C.; Castaneda-Miranda, E.; Castelli, A.; Castillo
Gimenez, V.; Castro, N. F.; Catastini, P.; Catinaccio, A.; Catmore,
J. R.; Cattai, A.; Cattani, G.; Caughron, S.; Cavaliere, V.; Cavalli,
D.; Cavalli-Sforza, M.; Cavasinni, V.; Ceradini, F.; Cerio, B.;
Cerny, K.; Cerqueira, A. S.; Cerri, A.; Cerrito, L.; Cerutti, F.;
Cervelli, A.; Cetin, S. A.; Chafaq, A.; Chakraborty, D.; Chalupkova,
I.; Chan, K.; Chang, P.; Chapleau, B.; Chapman, J. D.; Chapman,
J. W.; Charfeddine, D.; Charlton, D. G.; Chavda, V.; Chavez Barajas,
C. A.; Cheatham, S.; Chekanov, S.; Chekulaev, S. V.; Chelkov, G. A.;
Chelstowska, M. A.; Chen, C.; Chen, H.; Chen, K.; Chen, S.; Chen,
X.; Chen, Y.; Cheng, Y.; Cheplakov, A.; Cherkaoui El Moursli, R.;
Chernyatin, V.; Cheu, E.; Chevalier, L.; Chiarella, V.; Chiefari,
G.; Childers, J. T.; Chilingarov, A.; Chiodini, G.; Chisholm,
A. S.; Chislett, R. T.; Chitan, A.; Chizhov, M. V.; Choudalakis, G.;
Chouridou, S.; Chow, B. K. B.; Christidi, I. A.; Chromek-Burckhart,
D.; Chu, M. L.; Chudoba, J.; Ciapetti, G.; Ciftci, A. K.; Ciftci,
R.; Cinca, D.; Cindro, V.; Ciocio, A.; Cirilli, M.; Cirkovic, P.;
Citron, Z. H.; Citterio, M.; Ciubancan, M.; Clark, A.; Clark, P. J.;
Clarke, R. N.; Clemens, J. C.; Clement, B.; Clement, C.; Coadou, Y.;
Cobal, M.; Coccaro, A.; Cochran, J.; Coelli, S.; Coffey, L.; Cogan,
J. G.; Coggeshall, J.; Colas, J.; Cole, B.; Cole, S.; Colijn, A. P.;
Collins-Tooth, C.; Collot, J.; Colombo, T.; Colon, G.; Compostella,
G.; Conde Muiño, P.; Coniavitis, E.; Conidi, M. C.; Consonni, S. M.;
Consorti, V.; Constantinescu, S.; Conta, C.; Conti, G.; Conventi, F.;
Cooke, M.; Cooper, B. D.; Cooper-Sarkar, A. M.; Cooper-Smith, N. J.;
Copic, K.; Cornelissen, T.; Corradi, M.; Corriveau, F.; Corso-Radu,
A.; Cortes-Gonzalez, A.; Cortiana, G.; Costa, G.; Costa, M. J.;
Costanzo, D.; Côté, D.; Cottin, G.; Courneyea, L.; Cowan, G.; Cox,
B. E.; Cranmer, K.; Cree, G.; Crépé-Renaudin, S.; Crescioli, F.;
Cristinziani, M.; Crosetti, G.; Cuciuc, C. -M.; Cuenca Almenar, C.;
Cuhadar Donszelmann, T.; Cummings, J.; Curatolo, M.; Cuthbert, C.;
Czirr, H.; Czodrowski, P.; Czyczula, Z.; D'Auria, S.; D'Onofrio, M.;
D'Orazio, A.; da Cunha Sargedas de Sousa, M. J.; da Via, C.; Dabrowski,
W.; Dafinca, A.; Dai, T.; Dallaire, F.; Dallapiccola, C.; Dam, M.;
Damiani, D. S.; Daniells, A. C.; Dano Hoffmann, M.; Dao, V.; Darbo,
G.; Darlea, G. L.; Darmora, S.; Dassoulas, J. A.; Davey, W.; David,
C.; Davidek, T.; Davies, E.; Davies, M.; Davignon, O.; Davison, A. R.;
Davygora, Y.; Dawe, E.; Dawson, I.; Daya-Ishmukhametova, R. K.; de, K.;
de Asmundis, R.; de Castro, S.; de Cecco, S.; de Graat, J.; de Groot,
N.; de Jong, P.; de La Taille, C.; de la Torre, H.; de Lorenzi, F.;
de Nooij, L.; de Pedis, D.; de Salvo, A.; de Sanctis, U.; de Santo,
A.; de Vivie de Regie, J. B.; de Zorzi, G.; Dearnaley, W. J.; Debbe,
R.; Debenedetti, C.; Dechenaux, B.; Dedovich, D. V.; Degenhardt, J.;
Del Peso, J.; Del Prete, T.; Delemontex, T.; Deliot, F.; Deliyergiyev,
M.; Dell'Acqua, A.; Dell'Asta, L.; Della Pietra, M.; Della Volpe, D.;
Delmastro, M.; Delsart, P. A.; Deluca, C.; Demers, S.; Demichev, M.;
Demilly, A.; Demirkoz, B.; Denisov, S. P.; Derendarz, D.; Derkaoui,
J. E.; Derue, F.; Dervan, P.; Desch, K.; Deviveiros, P. O.; Dewhurst,
A.; Dewilde, B.; Dhaliwal, S.; Dhullipudi, R.; di Ciaccio, A.; di
Ciaccio, L.; di Donato, C.; di Girolamo, A.; di Girolamo, B.; di
Mattia, A.; di Micco, B.; di Nardo, R.; di Simone, A.; di Sipio, R.;
di Valentino, D.; Diaz, M. A.; Diehl, E. B.; Dietrich, J.; Dietzsch,
T. A.; Diglio, S.; Dindar Yagci, K.; Dingfelder, J.; Dionisi, C.;
Dita, P.; Dita, S.; Dittus, F.; Djama, F.; Djobava, T.; Do Vale,
M. A. B.; Do Valle Wemans, A.; Doan, T. K. O.; Dobos, D.; Dobson, E.;
Dodd, J.; Doglioni, C.; Doherty, T.; Dohmae, T.; Doi, Y.; Dolejsi, J.;
Dolezal, Z.; Dolgoshein, B. A.; Donadelli, M.; Donati, S.; Donini, J.;
Dopke, J.; Doria, A.; Dos Anjos, A.; Dotti, A.; Dova, M. T.; Doyle,
A. T.; Dris, M.; Dubbert, J.; Dube, S.; Dubreuil, E.; Duchovni,
E.; Duckeck, G.; Ducu, O. A.; Duda, D.; Dudarev, A.; Dudziak, F.;
Duflot, L.; Duguid, L.; Dührssen, M.; Dunford, M.; Duran Yildiz,
H.; Düren, M.; Dwuznik, M.; Ebke, J.; Edson, W.; Edwards, C. A.;
Edwards, N. C.; Ehrenfeld, W.; Eifert, T.; Eigen, G.; Einsweiler,
K.; Eisenhandler, E.; Ekelof, T.; El Kacimi, M.; Ellert, M.; Elles,
S.; Ellinghaus, F.; Ellis, K.; Ellis, N.; Elmsheuser, J.; Elsing,
M.; Emeliyanov, D.; Enari, Y.; Endner, O. C.; Endo, M.; Engelmann,
R.; Erdmann, J.; Ereditato, A.; Eriksson, D.; Ernis, G.; Ernst, J.;
Ernst, M.; Ernwein, J.; Errede, D.; Errede, S.; Ertel, E.; Escalier,
M.; Esch, H.; Escobar, C.; Espinal Curull, X.; Esposito, B.; Etienne,
F.; Etienvre, A. I.; Etzion, E.; Evangelakou, D.; Evans, H.; Fabbri,
L.; Facini, G.; Fakhrutdinov, R. M.; Falciano, S.; Fang, Y.; Fanti,
M.; Farbin, A.; Farilla, A.; Farooque, T.; Farrell, S.; Farrington,
S. M.; Farthouat, P.; Fassi, F.; Fassnacht, P.; Fassouliotis, D.;
Fatholahzadeh, B.; Favareto, A.; Fayard, L.; Federic, P.; Fedin,
O. L.; Fedorko, W.; Fehling-Kaschek, M.; Feligioni, L.; Feng, C.; Feng,
E. J.; Feng, H.; Fenyuk, A. B.; Fernando, W.; Ferrag, S.; Ferrando, J.;
Ferrara, V.; Ferrari, A.; Ferrari, P.; Ferrari, R.; Ferreira de Lima,
D. E.; Ferrer, A.; Ferrere, D.; Ferretti, C.; Ferretto Parodi, A.;
Fiascaris, M.; Fiedler, F.; Filipčič, A.; Filipuzzi, M.; Filthaut,
F.; Fincke-Keeler, M.; Finelli, K. D.; Fiolhais, M. C. N.; Fiorini, L.;
Firan, A.; Fischer, J.; Fisher, M. J.; Fitzgerald, E. A.; Flechl, M.;
Fleck, I.; Fleischmann, P.; Fleischmann, S.; Fletcher, G. T.; Fletcher,
G.; Flick, T.; Floderus, A.; Flores Castillo, L. R.; Florez Bustos,
A. C.; Flowerdew, M. J.; Fonseca Martin, T.; Formica, A.; Forti, A.;
Fortin, D.; Fournier, D.; Fox, H.; Francavilla, P.; Franchini, M.;
Franchino, S.; Francis, D.; Franklin, M.; Franz, S.; Fraternali, M.;
Fratina, S.; French, S. T.; Friedrich, C.; Friedrich, F.; Froidevaux,
D.; Frost, J. A.; Fukunaga, C.; Fullana Torregrosa, E.; Fulsom, B. G.;
Fuster, J.; Gabaldon, C.; Gabizon, O.; Gabrielli, A.; Gabrielli, A.;
Gadatsch, S.; Gadfort, T.; Gadomski, S.; Gagliardi, G.; Gagnon, P.;
Galea, C.; Galhardo, B.; Gallas, E. J.; Gallo, V.; Gallop, B. J.;
Gallus, P.; Galster, G.; Gan, K. K.; Gandrajula, R. P.; Gao, J.;
Gao, Y. S.; Garay Walls, F. M.; Garberson, F.; García, C.; García
Navarro, J. E.; Garcia-Sciveres, M.; Gardner, R. W.; Garelli, N.;
Garonne, V.; Gatti, C.; Gaudio, G.; Gaur, B.; Gauthier, L.; Gauzzi, P.;
Gavrilenko, I. L.; Gay, C.; Gaycken, G.; Gazis, E. N.; Ge, P.; Gecse,
Z.; Gee, C. N. P.; Geerts, D. A. A.; Geich-Gimbel, Ch.; Gellerstedt,
K.; Gemme, C.; Gemmell, A.; Genest, M. H.; Gentile, S.; George, M.;
George, S.; Gerbaudo, D.; Gershon, A.; Ghazlane, H.; Ghodbane, N.;
Giacobbe, B.; Giagu, S.; Giangiobbe, V.; Giannetti, P.; Gianotti,
F.; Gibbard, B.; Gibson, S. M.; Gilchriese, M.; Gillam, T. P. S.;
Gillberg, D.; Gillman, A. R.; Gingrich, D. M.; Giokaris, N.; Giordani,
M. P.; Giordano, R.; Giorgi, F. M.; Giovannini, P.; Giraud, P. F.;
Giugni, D.; Giuliani, C.; Giunta, M.; Gjelsten, B. K.; Gkialas,
I.; Gladilin, L. K.; Glasman, C.; Glatzer, J.; Glazov, A.; Glonti,
G. L.; Goblirsch-Kolb, M.; Goddard, J. R.; Godfrey, J.; Godlewski,
J.; Goeringer, C.; Goldfarb, S.; Golling, T.; Golubkov, D.; Gomes,
A.; Gomez Fajardo, L. S.; Gonçalo, R.; Goncalves Pinto Firmino da
Costa, J.; Gonella, L.; González de La Hoz, S.; Gonzalez Parra, G.;
Gonzalez Silva, M. L.; Gonzalez-Sevilla, S.; Goodson, J. J.; Goossens,
L.; Gorbounov, P. A.; Gordon, H. A.; Gorelov, I.; Gorfine, G.; Gorini,
B.; Gorini, E.; Gorišek, A.; Gornicki, E.; Goshaw, A. T.; Gössling,
C.; Gostkin, M. I.; Gough Eschrich, I.; Gouighri, M.; Goujdami, D.;
Goulette, M. P.; Goussiou, A. G.; Goy, C.; Gozpinar, S.; Grabas,
H. M. X.; Graber, L.; Grabowska-Bold, I.; Grafström, P.; Grahn,
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Ruzicka, P.; Ryabov, Y. F.; Rybar, M.; Rybkin, G.; Ryder, N. C.;
Saavedra, A. F.; Saddique, A.; Sadeh, I.; Sadrozinski, H. F. -W.;
Sadykov, R.; Safai Tehrani, F.; Sakamoto, H.; Sakurai, Y.; Salamanna,
G.; Salamon, A.; Saleem, M.; Salek, D.; Salihagic, D.; Salnikov, A.;
Salt, J.; Salvachua Ferrando, B. M.; Salvatore, D.; Salvatore, F.;
Salvucci, A.; Salzburger, A.; Sampsonidis, D.; Sanchez, A.; Sánchez,
J.; Sanchez Martinez, V.; Sandaker, H.; Sander, H. G.; Sanders,
M. P.; Sandhoff, M.; Sandoval, T.; Sandoval, C.; Sandstroem, R.;
Sankey, D. P. C.; Sansoni, A.; Santoni, C.; Santonico, R.; Santos,
H.; Santoyo Castillo, I.; Sapp, K.; Sapronov, A.; Saraiva, J. G.;
Sarkisyan-Grinbaum, E.; Sarrazin, B.; Sartisohn, G.; Sasaki, O.;
Sasaki, Y.; Sasao, N.; Satsounkevitch, I.; Sauvage, G.; Sauvan,
E.; Sauvan, J. B.; Savard, P.; Savinov, V.; Savu, D. O.; Sawyer,
C.; Sawyer, L.; Saxon, D. H.; Saxon, J.; Sbarra, C.; Sbrizzi, A.;
Scanlon, T.; Scannicchio, D. A.; Scarcella, M.; Schaarschmidt, J.;
Schacht, P.; Schaefer, D.; Schaelicke, A.; Schaepe, S.; Schaetzel,
S.; Schäfer, U.; Schaffer, A. C.; Schaile, D.; Schamberger, R. D.;
Scharf, V.; Schegelsky, V. A.; Scheirich, D.; Schernau, M.; Scherzer,
M. I.; Schiavi, C.; Schieck, J.; Schillo, C.; Schioppa, M.; Schlenker,
S.; Schmidt, E.; Schmieden, K.; Schmitt, C.; Schmitt, C.; Schmitt,
S.; Schneider, B.; Schnellbach, Y. J.; Schnoor, U.; Schoeffel,
L.; Schoening, A.; Schoenrock, B. D.; Schorlemmer, A. L. S.;
Schott, M.; Schouten, D.; Schovancova, J.; Schram, M.; Schramm,
S.; Schreyer, M.; Schroeder, C.; Schroer, N.; Schuh, N.; Schultens,
M. J.; Schultz-Coulon, H. -C.; Schulz, H.; Schumacher, M.; Schumm,
B. A.; Schune, Ph.; Schwartzman, A.; Schwegler, Ph.; Schwemling,
Ph.; Schwienhorst, R.; Schwindling, J.; Schwindt, T.; Schwoerer,
M.; Sciacca, F. G.; Scifo, E.; Sciolla, G.; Scott, W. G.; Scutti,
F.; Searcy, J.; Sedov, G.; Sedykh, E.; Seidel, S. C.; Seiden, A.;
Seifert, F.; Seixas, J. M.; Sekhniaidze, G.; Sekula, S. J.; Selbach,
K. E.; Seliverstov, D. M.; Sellers, G.; Seman, M.; Semprini-Cesari, N.;
Serfon, C.; Serin, L.; Serkin, L.; Serre, T.; Seuster, R.; Severini,
H.; Sforza, F.; Sfyrla, A.; Shabalina, E.; Shamim, M.; Shan, L. Y.;
Shank, J. T.; Shao, Q. T.; Shapiro, M.; Shatalov, P. B.; Shaw,
K.; Sherwood, P.; Shimizu, S.; Shimojima, M.; Shin, T.; Shiyakova,
M.; Shmeleva, A.; Shochet, M. J.; Short, D.; Shrestha, S.; Shulga,
E.; Shupe, M. A.; Shushkevich, S.; Sicho, P.; Sidorov, D.; Sidoti,
A.; Siegert, F.; Sijacki, Dj.; Silbert, O.; Silva, J.; Silver, Y.;
Silverstein, D.; Silverstein, S. B.; Simak, V.; Simard, O.; Simic,
Lj.; Simion, S.; Simioni, E.; Simmons, B.; Simoniello, R.; Simonyan,
M.; Sinervo, P.; Sinev, N. B.; Sipica, V.; Siragusa, G.; Sircar, A.;
Sisakyan, A. N.; Sivoklokov, S. Yu.; Sjölin, J.; Sjursen, T. B.;
Skinnari, L. A.; Skottowe, H. P.; Skovpen, K. Yu.; Skubic, P.; Slater,
M.; Slavicek, T.; Sliwa, K.; Smakhtin, V.; Smart, B. H.; Smestad,
L.; Smirnov, S. Yu.; Smirnov, Y.; Smirnova, L. N.; Smirnova, O.;
Smith, K. M.; Smizanska, M.; Smolek, K.; Snesarev, A. A.; Snidero,
G.; Snow, J.; Snyder, S.; Sobie, R.; Socher, F.; Sodomka, J.; Soffer,
A.; Soh, D. A.; Solans, C. A.; Solar, M.; Solc, J.; Soldatov, E. Yu.;
Soldevila, U.; Solfaroli Camillocci, E.; Solodkov, A. A.; Solovyanov,
O. V.; Solovyev, V.; Soni, N.; Sood, A.; Sopko, V.; Sopko, B.; Sosebee,
M.; Soualah, R.; Soueid, P.; Soukharev, A. M.; South, D.; Spagnolo,
S.; Spanò, F.; Spearman, W. R.; Spighi, R.; Spigo, G.; Spousta, M.;
Spreitzer, T.; Spurlock, B.; St. Denis, R. D.; Stahlman, J.; Stamen,
R.; Stanecka, E.; Stanek, R. W.; Stanescu, C.; Stanescu-Bellu,
M.; Stanitzki, M. M.; Stapnes, S.; Starchenko, E. A.; Stark, J.;
Staroba, P.; Starovoitov, P.; Staszewski, R.; Stavina, P.; Steele,
G.; Steinbach, P.; Steinberg, P.; Stekl, I.; Stelzer, B.; Stelzer,
H. J.; Stelzer-Chilton, O.; Stenzel, H.; Stern, S.; Stewart, G. A.;
Stillings, J. A.; Stockton, M. C.; Stoebe, M.; Stoerig, K.; Stoicea,
G.; Stonjek, S.; Stradling, A. R.; Straessner, A.; Strandberg, J.;
Strandberg, S.; Strandlie, A.; Strauss, E.; Strauss, M.; Strizenec,
P.; Ströhmer, R.; Strom, D. M.; Stroynowski, R.; Stucci, S. A.;
Stugu, B.; Stumer, I.; Stupak, J.; Sturm, P.; Styles, N. A.; Su, D.;
Subramania, Hs.; Subramaniam, R.; Succurro, A.; Sugaya, Y.; Suhr, C.;
Suk, M.; Sulin, V. V.; Sultansoy, S.; Sumida, T.; Sun, X.; Sundermann,
J. E.; Suruliz, K.; Susinno, G.; Sutton, M. R.; Suzuki, Y.; Svatos,
M.; Swedish, S.; Swiatlowski, M.; Sykora, I.; Sykora, T.; Ta, D.;
Tackmann, K.; Taenzer, J.; Taffard, A.; Tafirout, R.; Taiblum, N.;
Takahashi, Y.; Takai, H.; Takashima, R.; Takeda, H.; Takeshita,
T.; Takubo, Y.; Talby, M.; Talyshev, A. A.; Tam, J. Y. C.; Tamsett,
M. C.; Tan, K. G.; Tanaka, J.; Tanaka, R.; Tanaka, S.; Tanaka, S.;
Tanasijczuk, A. J.; Tani, K.; Tannoury, N.; Tapprogge, S.; Tarem,
S.; Tarrade, F.; Tartarelli, G. F.; Tas, P.; Tasevsky, M.; Tashiro,
T.; Tassi, E.; Tavares Delgado, A.; Tayalati, Y.; Taylor, C.; Taylor,
F. E.; Taylor, G. N.; Taylor, W.; Teischinger, F. A.; Teixeira Dias
Castanheira, M.; Teixeira-Dias, P.; Temming, K. K.; Ten Kate, H.;
Teng, P. K.; Terada, S.; Terashi, K.; Terron, J.; Terzo, S.; Testa,
M.; Teuscher, R. J.; Therhaag, J.; Theveneaux-Pelzer, T.; Thoma, S.;
Thomas, J. P.; Thompson, E. N.; Thompson, P. D.; Thompson, P. D.;
Thompson, A. S.; Thomsen, L. A.; Thomson, E.; Thomson, M.; Thong,
W. M.; Thun, R. P.; Tian, F.; Tibbetts, M. J.; Tic, T.; Tikhomirov,
V. O.; Tikhonov, Yu. A.; Timoshenko, S.; Tiouchichine, E.; Tipton,
P.; Tisserant, S.; Todorov, T.; Todorova-Nova, S.; Toggerson, B.;
Tojo, J.; Tokár, S.; Tokushuku, K.; Tollefson, K.; Tomlinson, L.;
Tomoto, M.; Tompkins, L.; Toms, K.; Tonoyan, A.; Topilin, N. D.;
Torrence, E.; Torres, H.; Torró Pastor, E.; Toth, J.; Touchard,
F.; Tovey, D. R.; Tran, H. L.; Trefzger, T.; Tremblet, L.; Tricoli,
A.; Trigger, I. M.; Trincaz-Duvoid, S.; Tripiana, M. F.; Triplett,
N.; Trischuk, W.; Trocmé, B.; Troncon, C.; Trottier-McDonald, M.;
Trovatelli, M.; True, P.; Trzebinski, M.; Trzupek, A.; Tsarouchas,
C.; Tseng, J. C. -L.; Tsiareshka, P. V.; Tsionou, D.; Tsipolitis, G.;
Tsirintanis, N.; Tsiskaridze, S.; Tsiskaridze, V.; Tskhadadze, E. G.;
Tsukerman, I. I.; Tsulaia, V.; Tsung, J. -W.; Tsuno, S.; Tsybychev,
D.; Tua, A.; Tudorache, A.; Tudorache, V.; Tuggle, J. M.; Tuna, A. N.;
Tupputi, S. A.; Turchikhin, S.; Turecek, D.; Turk Cakir, I.; Turra, R.;
Tuts, P. M.; Tykhonov, A.; Tylmad, M.; Tyndel, M.; Uchida, K.; Ueda,
I.; Ueno, R.; Ughetto, M.; Ugland, M.; Uhlenbrock, M.; Ukegawa, F.;
Unal, G.; Undrus, A.; Unel, G.; Ungaro, F. C.; Unno, Y.; Urbaniec,
D.; Urquijo, P.; Usai, G.; Usanova, A.; Vacavant, L.; Vacek, V.;
Vachon, B.; Vahsen, S.; Valencic, N.; Valentinetti, S.; Valero, A.;
Valery, L.; Valkar, S.; Valladolid Gallego, E.; Vallecorsa, S.;
Valls Ferrer, J. A.; van Berg, R.; van der Deijl, P. C.; van der
Geer, R.; van der Graaf, H.; van der Leeuw, R.; van der Ster, D.;
van Eldik, N.; van Gemmeren, P.; van Nieuwkoop, J.; van Vulpen, I.;
van Woerden, M. C.; Vanadia, M.; Vandelli, W.; Vaniachine, A.; Vankov,
P.; Vannucci, F.; Vari, R.; Varnes, E. W.; Varol, T.; Varouchas, D.;
Vartapetian, A.; Varvell, K. E.; Vassilakopoulos, V. I.; Vazeille, F.;
Vazquez Schroeder, T.; Veatch, J.; Veloso, F.; Veneziano, S.; Ventura,
A.; Ventura, D.; Venturi, M.; Venturi, N.; Vercesi, V.; Verducci, M.;
Verkerke, W.; Vermeulen, J. C.; Vest, A.; Vetterli, M. C.; Viazlo, O.;
Vichou, I.; Vickey, T.; Vickey Boeriu, O. E.; Viehhauser, G. H. A.;
Viel, S.; Vigne, R.; Villa, M.; Villaplana Perez, M.; Vilucchi, E.;
Vincter, M. G.; Vinogradov, V. B.; Virzi, J.; Vitells, O.; Viti, M.;
Vivarelli, I.; Vives Vaque, F.; Vlachos, S.; Vladoiu, D.; Vlasak,
M.; Vogel, A.; Vokac, P.; Volpi, G.; Volpi, M.; Volpini, G.; von der
Schmitt, H.; von Radziewski, H.; von Toerne, E.; Vorobel, V.; Vos,
M.; Voss, R.; Vossebeld, J. H.; Vranjes, N.; Vranjes Milosavljevic,
M.; Vrba, V.; Vreeswijk, M.; Vu Anh, T.; Vuillermet, R.; Vukotic, I.;
Vykydal, Z.; Wagner, W.; Wagner, P.; Wahrmund, S.; Wakabayashi, J.;
Walch, S.; Walder, J.; Walker, R.; Walkowiak, W.; Wall, R.; Waller,
P.; Walsh, B.; Wang, C.; Wang, H.; Wang, H.; Wang, J.; Wang, J.; Wang,
K.; Wang, R.; Wang, S. M.; Wang, T.; Wang, X.; Warburton, A.; Ward,
C. P.; Wardrope, D. R.; Warsinsky, M.; Washbrook, A.; Wasicki, C.;
Watanabe, I.; Watkins, P. M.; Watson, A. T.; Watson, I. J.; Watson,
M. F.; Watts, G.; Watts, S.; Waugh, A. T.; Waugh, B. M.; Webb, S.;
Weber, M. S.; Weber, S. W.; Webster, J. S.; Weidberg, A. R.; Weigell,
P.; Weingarten, J.; Weiser, C.; Weits, H.; Wells, P. S.; Wenaus, T.;
Wendland, D.; Weng, Z.; Wengler, T.; Wenig, S.; Wermes, N.; Werner,
M.; Werner, P.; Wessels, M.; Wetter, J.; Whalen, K.; White, A.;
White, M. J.; White, R.; White, S.; Whiteson, D.; Whittington, D.;
Wicke, D.; Wickens, F. J.; Wiedenmann, W.; Wielers, M.; Wienemann,
P.; Wiglesworth, C.; Wiik-Fuchs, L. A. M.; Wijeratne, P. A.; Wildauer,
A.; Wildt, M. A.; Wilhelm, I.; Wilkens, H. G.; Will, J. Z.; Williams,
E.; Williams, H. H.; Williams, S.; Willis, W.; Willocq, S.; Wilson,
J. A.; Wilson, A.; Wingerter-Seez, I.; Winkelmann, S.; Winklmeier,
F.; Wittgen, M.; Wittig, T.; Wittkowski, J.; Wollstadt, S. J.;
Wolter, M. W.; Wolters, H.; Wong, W. C.; Wosiek, B. K.; Wotschack,
J.; Woudstra, M. J.; Wozniak, K. W.; Wraight, K.; Wright, M.; Wu,
S. L.; Wu, X.; Wu, Y.; Wulf, E.; Wyatt, T. R.; Wynne, B. M.; Xella, S.;
Xiao, M.; Xu, C.; Xu, D.; Xu, L.; Yabsley, B.; Yacoob, S.; Yamada, M.;
Yamaguchi, H.; Yamaguchi, Y.; Yamamoto, A.; Yamamoto, K.; Yamamoto, S.;
Yamamura, T.; Yamanaka, T.; Yamauchi, K.; Yamazaki, Y.; Yan, Z.; Yang,
H.; Yang, H.; Yang, U. K.; Yang, Y.; Yang, Z.; Yanush, S.; Yao, L.;
Yasu, Y.; Yatsenko, E.; Yau Wong, K. H.; Ye, J.; Ye, S.; Yen, A. L.;
Yildirim, E.; Yilmaz, M.; Yoosoofmiya, R.; Yorita, K.; Yoshida, R.;
Yoshihara, K.; Young, C.; Young, C. J. S.; Youssef, S.; Yu, D. R.; Yu,
J.; Yu, J.; Yuan, L.; Yurkewicz, A.; Zabinski, B.; Zaidan, R.; Zaitsev,
A. M.; Zaman, A.; Zambito, S.; Zanello, L.; Zanzi, D.; Zaytsev, A.;
Zeitnitz, C.; Zeman, M.; Zemla, A.; Zenin, O.; Ženiš, T.; Zerwas,
D.; Zevi Della Porta, G.; Zhang, D.; Zhang, H.; Zhang, J.; Zhang, L.;
Zhang, X.; Zhang, Z.; Zhao, Z.; Zhemchugov, A.; Zhong, J.; Zhou, B.;
Zhou, L.; Zhou, N.; Zhu, C. G.; Zhu, H.; Zhu, J.; Zhu, Y.; Zhuang, X.;
Zibell, A.; Zieminska, D.; Zimin, N. I.; Zimmermann, C.; Zimmermann,
R.; Zimmermann, S.; Zimmermann, S.; Zinonos, Z.; Ziolkowski, M.;
Zitoun, R.; Živković, L.; Zobernig, G.; Zoccoli, A.; Zur Nedden,
M.; Zurzolo, G.; Zutshi, V.; Zwalinski, L.; Atlas Collaboration
Bibcode: 2014PhRvL.112d1802A
Altcode:
A search is presented for dark matter pair production in association
with a W or Z boson in pp collisions representing 20.3 fb-1
of integrated luminosity at √s =8 TeV using data recorded with the
ATLAS detector at the Large Hadron Collider. Events with a hadronic
jet with the jet mass consistent with a W or Z boson, and with large
missing transverse momentum are analyzed. The data are consistent
with the standard model expectations. Limits are set on the mass
scale in effective field theories that describe the interaction of
dark matter and standard model particles, and on the cross section
of Higgs production and decay to invisible particles. In addition,
cross section limits on the anomalous production of W or Z bosons with
large missing transverse momentum are set in two fiducial regions.
Title: Oceans and Internal Structures of the Large Icy Satellites
Authors: Vance, S.; Brown, J.; Choukroun, M.; Sotin, C.
Bibcode: 2013AGUFM.P41E1974V
Altcode:
We predict water ice freezing and constrain geothermal gradients
in the interiors of the large icy satellites Ganymede, Callisto, and
Titan using thermodynamic and phase-boundary data for MgSO4 and ammonia
solutions, including new results for ammonia. Accounting for available
measurements of gravitational moments of inertia leads to estimates
of the depths to silicate boundaries. In the case of Ganymede we also
compute the size of an iron-bearing core. The new equations of state
allow us to assess the influence of ocean salinity on the thickness
of layers of ice I-III-V-VI in the interiors of these objects, and on
associated ocean dynamics. Ocean compositions with salt and ammonia have
less high-pressure ice, and can exist in the presence of ice III. In
some model oceans high-pressure ice phases become buoyant relative to
surrounding fluids, implying frazil-like upward snows, interlayered
liquids and ices, and fluids in direct contact with rock. We discuss the
relative roles of dissolved constituents in the large icy satellites,
the consequences for their habitability, and prospects of future
missions for testing these predictions. Schematic of interior structure
for Ganymede showing dense fluids under high pressure ices and directly
in contact with rock. We use available thermodynamic properties for
relevant fluids and solids materials us to calculate self-consistent
depths for the various layers (approximate values shown here).
Title: Hands on Education Through Student-Industry Partnerships
Authors: Brown, J.; Wolfson, M.; Morris, K.
Bibcode: 2013amos.confE.112B
Altcode:
Lockheed Martin Space Systems Company has invested in the future
generation of engineers by partially funding and mentoring CubeSat
projects around the country. One CubeSat in particular, ALL-STAR,
has shown how this industry/university partnership benefits both the
students and their mentors. Students gain valuable insight into aspects
of spacecraft design that aren't taught in classes. They also start
learning about industry processes for designing, building, and testing
satellites before ever working in that environment. Because of this
experience, industry is getting more qualified engineers starting
fresh out of college. In addition Lockheed Martin's partnership
with the university will allow them to use the students to help
build affordable CubeSats for internal and customer's research and
development projects. The mentoring also challenges the engineers to
think differently about similar problems they face every day with their
larger programs in order to make the solution simple and affordable.
Title: CubeSat Integration into the Space Situational Awareness
Architecture
Authors: Morris, K.; Wolfson, M.; Brown, J.
Bibcode: 2013amos.confE..92M
Altcode:
Lockheed Martin Space Systems Company has recently been involved
in developing GEO Space Situational Awareness architectures, which
allows insights into how cubesats can augment the current national
systems. One hole that was identified in the current architecture is
the need for timelier metric track observations to aid in the chain of
custody. Obtaining observations of objects at GEO can be supported by
CubeSats. These types of small satellites are increasing being built and
flown by government agencies like NASA and SMDC. CubeSats are generally
mass and power constrained allowing for only small payloads that cannot
typically mimic traditional flight capability. CubeSats do not have a
high reliability and care must be taken when choosing mission orbits
to prevent creating more debris. However, due to the low costs, short
development timelines, and available hardware, CubeSats can supply
very valuable benefits to these complex missions, affordably. For
example, utilizing CubeSats for advanced focal plane demonstrations
to support technology insertion into the next generation situational
awareness sensors can help to lower risks before the complex sensors
are developed. CubeSats can augment the planned ground and space based
assets by creating larger constellations with more access to areas
of interest. To aid in maintaining custody of objects, a CubeSat
constellation at 500 km above GEO would provide increased point of
light tracking that can augment the ground SSA assets. Key features of
the Cubesat include a small visible camera looking along the GEO belt,
a small propulsion system that allows phasing between CubeSats, and
an image processor to reduce the data sent to the ground. An elegant
communications network will also be used to provide commands to and
data from multiple CubeSats. Additional CubeSats can be deployed on
GSO launches or through ride shares to GEO, replenishing or adding to
the constellation with each launch. Each CubeSat would take images of
the GEO belt, process out the stars, and then downlink the data to the
ground. This data can then be combined with the existing metric track
data to enhance the coverage and timeliness. With the current capability
of CubeSats and their payloads, along with the launch constraints,
the near term focus is to integrate into existing architectures by
reducing technology risks, understanding unique phenomenology, and
augment mission collection capability. Understanding the near term
benefits of utilizing CubeSats will better inform the SSA mission
developers how to integrate CubeSats into the next generation of
architectures from the start.
Title: A Relation between the Warm Neutral and Ionized Media Observed
in the Canadian Galactic Plane Survey
Authors: Foster, T.; Kothes, R.; Brown, J. C.
Bibcode: 2013ApJ...773L..11F
Altcode: 2013arXiv1307.4358F
We report on a comparison between 21 cm rotation measure (RM) and the
optically thin atomic hydrogen column density (N H I (τ →
0)) measured toward unresolved extragalactic sources in the Galactic
plane of the northern sky. H I column densities integrated to the
Galactic edge are measured immediately surrounding each of nearly
2000 sources in 1 arcmin 21 cm line data, and are compared to RMs
observed from polarized emission of each source. RM data are binned
in column density bins 4 × 1020 cm-2 wide,
and one observes a strong relationship between the number of hydrogen
atoms in a 1 cm2 column through the plane and the mean
RM along the same line of sight and path length. The relationship is
linear over one order of magnitude (from 0.8 to 14 × 1021
atoms cm-2) of column densities, with a constant RM/N
H I ~ -23.2 ± 2.3 rad m-2/1021 atoms
cm-2, and a positive RM of 45.0 ± 13.8 rad m-2
in the presence of no atomic hydrogen. This slope is used to calculate
a mean volume-averaged magnetic field in the second quadrant of langB
∥rang ~1.0 ± 0.1 μG directed away from the Sun, assuming
an ionization fraction of 8% (consistent with the warm-neutral medium;
WNM). The remarkable consistency between this field and langBrang = 1.2
μG found with the same RM sources and a Galactic model of dispersion
measures (DMs) suggests that electrons in the partially ionized WNM
are mainly responsible for pulsar DMs, and thus the partially ionized
WNM is the dominant form of the magneto-ionic interstellar medium.
Title: Solar flare X-ray source motion as a response to electron
spectral hardening
Authors: O'Flannagain, A. M.; Gallagher, P. T.; Brown, J. C.; Milligan,
R. O.; Holman, G. D.
Bibcode: 2013A&A...555A..21O
Altcode: 2013arXiv1305.1574O
Context. Solar flare hard X-rays (HXRs) are thought to be produced by
nonthermal coronal electrons stopping in the chromosphere or remaining
trapped in the corona. The collisional thick target model (CTTM)
predicts that more energetic electrons penetrate to greater column
depths along the flare loop. This requires that sources produced by
harder power-law injection spectra should appear further down the
legs or footpoints of a flareloop. Therefore, the frequently observed
hardening of the injected power-law electron spectrum during flare
onset should be concurrent with a descending hard X-ray source.
Aims: We test this implication of the CTTM by comparing its predicted
HXR source locations with those derived from observations of a solar
flare which exhibits a nonthermally-dominated spectrum before the peak
in HXRs, known as an early impulsive event.
Methods: The HXR
images and spectra of an early impulsive C-class flare were obtained
using the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI). Images
were reconstructed to produce HXR source height evolutions for three
energy bands. Spatially integrated spectral analysis was performed to
isolate nonthermal emission and to determine the power-law index of the
electron injection spectrum. The observed height-time evolutions were
then fitted with CTTM-based simulated heights for each energy, using
the electron spectral indices derived from the RHESSI spectra.
Results: The flare emission was found to be dominantly nonthermal
above ~7 keV, with emission of thermal and nonthermal X-rays likely
to be simultaneously observable below that energy. The density
structure required for a good match between model and observed source
heights agreed with previous studies of flare loop densities.
Conclusions: The CTTM has been used to produce a descent of model HXR
source heights that compares well with observations of this event. Based
on this interpretation, downward motion of nonthermal sources should
occur in any flare where there is spectral hardening in the electron
distribution during a flare. However, this is often masked by thermal
emission associated with flare plasma preheating. To date, flare models
that predict transfer of energy from the corona to the chromosphere by
means other than a flux of nonthermal electrons do not predict this
observed source descent. Therefore, flares such as this will be key
in explaining this elusive energy transfer process.
Title: The Weak Wind Stars
Authors: Todt, Helga; Hamann, Wolf-Rainer; Oskinova, Lida;
Huenemoerder, David; Ignace, Richard; Waldron, Wayne L.; Hamaguchi,
Kenji; Kitamoto, Shunji; Assinelli, Joe P.; Brown, J. C.
Bibcode: 2013msao.confE..49T
Altcode:
The hottest and most massive stars on the main sequence have spectral
types O and B. The standard theory of line driven winds predicts
that these stars possess strong stellar winds with mass-loss rates
up to 10^{-5} M_⊙/yr. These predictions have been verified for the
hottest O-stars by means of spectral analyses in the optical, UV, and
radio range - albeit there are still uncertainties due to the effects
of unknown wind inhomogeneities. However, for stars with luminosity
class V (dwarfs) and subtypes between late-O and early-B the same
analysis techniques yield mass-loss rates that are at least one order of
magnitude below the values expected from the wind theory. Thus, there
is a severe discordance, which is often referred to as ``the weak wind
problem'' in the literature. Our new multi-wavelength observations and
their analyses shed new light on this issue. We will present recent
results from X-ray and UV spectroscopy of early B-type stars and the
weak-wind O9V star μ Columbae.
Title: Hot Gas Flows in T Tauri Stars
Authors: Ardila, David R.; Herczeg, G.; Gregory, S. G.; Ingleby, L.;
France, K.; Brown, A.; Edwards, S.; Linsky, J.; Yang, H.; Valenti,
J. A.; Johns-Krull, C. M.; Alexander, R.; Bergin, E. A.; Bethell,
T.; Brown, J.; Calvet, N.; Espaillat, C.; Hervé, A.; Hillenbrand,
L.; Hussain, G.; Roueff, E.; Schindhelm, R.; Walter, F. M.
Bibcode: 2013AAS...22111704A
Altcode:
We describe observations of the hot gas 1e5 K) ultraviolet lines C IV
and He II, in Classical and Weak T Tauri Stars (CTTSs, WTTSs). Our goal
is to provide observational constraints for realistic models. Most of
the data for this work comes from the Hubble proposal “The Disks,
Accretion, and Outflows (DAO) of T Tau stars” (PI Herczeg). The DAO
program is the largest and most sensitive high resolution spectroscopic
survey of young stars in the UV ever undertaken and it provides a rich
source of information for these objects. The sample of high resolution
COS and STIS spectra presented here comprises 35 stars: one Herbig
Ae star, 28 CTTSs, and 6 WTTSs. For CTTSs, the lines consist of two
kinematic components. The relative strengths of the narrow and broad
components (NC, BC) are similar in C IV but in He II the NC is stronger
than the BC, and dominates the line profile. We do not find correlations
between disk inclination and the velocity centroid, width, or shape
of the CIV line profile. The NC of the C IV line in CTTSs increases in
strength with accretion rate, and its contribution to the line increases
from ∼20% to ∼80%, for the accretion rates considered here (1e-10
to 1e-7 Msun/yr). The CTTSs C IV lines are redshifted by ∼20 km/s
while the CTTSs He II are redshifted by ∼10 km/s. Because the He
II line and the C IV NC have the same width in CTTSs and in WTTSs,
but are correlated with accretion, we suggest that they are produced
in the stellar transition region. The accretion shock model predicts
that the velocity of the post-shock emission should be 4x smaller than
the velocity of the pre-shock emission. Identifying the post-shock
emission with the NC and the pre-shock with the BC, we find that this is
approximately the case in 11 out of 23 objects. The model cannot explain
11 systems in which the velocity of the NC is smaller than the velocity
of the BC, or systems in which one of the velocities is negative (five
CTTSs). The hot gas lines in some systems such as HN Tau, RW Aur A, AK
Sco, DK Tau, T Tau N, and V1190 Sco require an outflow contribution,
which may come from jet shocks in the observed outflows. We suggest
that a hot wind is being launched by the Herbig Ae star DX Cha.
Title: Sun-plunging Comets and Cometary Flares
Authors: Brown, J. C.; Carlson, R. W.
Bibcode: 2012AGUFMSH21D..04B
Altcode:
During 2011, NASA's Solar Dynamics Observatory (SDO) made the first ever
direct observations of sun-grazing comet destruction in the inner solar
atmosphere. On July 6, the nucleus material of Comet C/2011 N3 (SOHO)
(perihelion distance q~1.14R_sun) was observed to vaporize, decelerate
and radiate, with total nucleus destruction over a path length ~
R_sun through the lower corona (density n ~ 10^8/cm^3). On Dec. 16,
the much more massive Comet C/2011 W3 (Lovejoy), with similar q~1.17
R_sun), was seen vaporizing until it vanished behind the solar limb
then re-emerging in a much diminished state. A range of current work
on these data is being presented by others in this AGU session. These
two 'sun-skimming' comets had q in the low corona. There, mass loss
is dominated by insolation-driven sublimation, so the physics of their
destruction is largely similar to those with q>> R_sun. However,
Brown et al. (Astron. Astrophys. 535, A71, 2011) showed that mass loss
and destruction is completely different for 'sun-plunging' comets with
q<q*=1.01R_sun, and with large enough mass to survive insolation down
to there. At heliocentric distances r<q*, the density n is very high
(n>n*= 2.5x10^11/cm^3, increasing exponentially with depth on scale
height H~100-500 km). Consequently sun-plunger mass loss and destruction
is dominated by ablation and by ram-pressure-driven explosion. The
very large cometary kinetic energy (2x10^27 erg x (M/10^12) for mass
M g) and its highly localized deposition in time (<10 s) and space
(<6000 km ~ 10") should produce signatures somewhat like solar
magnetic flares. Such 'cometary flare' events should offer wholly new
ways to probe properties both of comets (e.g. element abundances) and of
the low solar atmosphere (e.g magnetic fields). Super-flares produced by
very large sun-plungers could have serious terrestrial consequences. We
will present and discuss results of our current work on sun-plunging
comets and explosive cometary flares, including - - Likely rate of
occurrence of detectable cometary flares, in terms of the statistical
distribution of relevant cometary masses M and of orbital q values. -
Comparison of Brown et al's analytic estimates of their properties with
those from numerical simulations, developed by modifying Carlson et
al's (Icarus 121,228, 1997) Shoemaker-Levy-9 Jupiter impact model. The
much higher comet-sun impact velocity compared to that for SL-9-Jupiter
requires the addition of various effects, including solar, thermal, and
radiative ablation, to hydrodynamic radial expansion of the impactor
,and subsequent fragmentation. The solar atmosphere's much higher
temperature and ionization and lower density than Jupiter's also modify
the "airburst" conditions. - Predictive estimates of the observational
signatures of such explosions and their practical observability.
Title: Broadband Study of GRB 091127: A Sub-energetic Burst at
Higher Redshift?
Authors: Troja, E.; Sakamoto, T.; Guidorzi, C.; Norris, J. P.;
Panaitescu, A.; Kobayashi, S.; Omodei, N.; Brown, J. C.; Burrows,
D. N.; Evans, P. A.; Gehrels, N.; Marshall, F. E.; Mawson, N.;
Melandri, A.; Mundell, C. G.; Oates, S. R.; Pal'shin, V.; Preece,
R. D.; Racusin, J. L.; Steele, I. A.; Tanvir, N. R.; Vasileiou, V.;
Wilson-Hodge, C.; Yamaoka, K.
Bibcode: 2012ApJ...761...50T
Altcode: 2012arXiv1201.4181T
GRB 091127 is a bright gamma-ray burst (GRB) detected by Swift
at a redshift z = 0.49 and associated with SN 2009nz. We present
the broadband analysis of the GRB prompt and afterglow emission
and study its high-energy properties in the context of the GRB/SN
association. While the high luminosity of the prompt emission and
standard afterglow behavior are typical of cosmological long GRBs,
its low-energy release (E γ < 3 × 1049 erg),
soft spectrum, and unusual spectral lag connect this GRB to the class
of sub-energetic bursts. We discuss the suppression of high-energy
emission in this burst, and investigate whether this behavior could
be connected with the sub-energetic nature of the explosion.
Title: New Constraints on the Galactic Halo Magnetic Field Using
Rotation Measures of Extragalactic Sources toward the Outer Galaxy
Authors: Mao, S. A.; McClure-Griffiths, N. M.; Gaensler, B. M.; Brown,
J. C.; van Eck, C. L.; Haverkorn, M.; Kronberg, P. P.; Stil, J. M.;
Shukurov, A.; Taylor, A. R.
Bibcode: 2012ApJ...755...21M
Altcode: 2012arXiv1206.3314M
We present a study of the Milky Way disk and halo magnetic field,
determined from observations of Faraday rotation measure (RM) toward
641 polarized extragalactic radio sources in the Galactic longitude
range 100°-117°, within 30° of the Galactic plane. For |b| <
15°, we observe a symmetric RM distribution about the Galactic
plane. This is consistent with a disk field in the Perseus arm of
even parity across the Galactic mid-plane. In the range 15° <
|b| < 30°, we find median RMs of -15 ± 4 rad m-2
and -62 ± 5 rad m-2 in the northern and southern Galactic
hemispheres, respectively. If the RM distribution is a signature of the
large-scale field parallel to the Galactic plane, then this suggests
that the halo magnetic field toward the outer Galaxy does not reverse
direction across the mid-plane. The variation of RM as a function of
Galactic latitude in this longitude range is such that RMs become more
negative at larger |b|. This is consistent with an azimuthal magnetic
field of strength 2 μG (7 μG) at a height 0.8-2 kpc above (below)
the Galactic plane between the local and the Perseus spiral arm. We
propose that the Milky Way could possess spiral-like halo magnetic
fields similar to those observed in M51.
Title: Electrons Re-Acceleration at the Footpoints of Solar Flares
Authors: Turkmani, R.; Brown, J.
Bibcode: 2012ASPC..454..349T
Altcode: 2010arXiv1011.0756T
Hinode's observations revealed a very dynamic and complex
chromosphere. This require revisiting the assumption that the
chromospheric footpoints of solar flares are areas where accelerated
particles only lose energy due to collisions. Traditionally electrons
are thought to be accelerated in the coronal part of the loop, then
travel to the footpoints where they lose their energy and radiate the
observed hard X-ray. Increasing observational evidence challenges this
assumption. We review the evidence against this assumption and present
the new Local Re-acceleration Thick Target Model (LRTTM) where at the
footpoints electrons receive a boost of re-acceleration in addition
to the usual collisional loses. Such model may offer an alternative
to the standard collisional thick target injection model (TTM) (Brown
1971) of solar HXR burst sources, requiring far fewer electrons and
solving some recent problems with the TTM interpretation. We look at
the different scenarios which could lead to such re-acceleration and
present numerical results from one of them.
Title: An improved map of the Galactic Faraday sky
Authors: Oppermann, N.; Junklewitz, H.; Robbers, G.; Bell, M. R.;
Enßlin, T. A.; Bonafede, A.; Braun, R.; Brown, J. C.; Clarke, T. E.;
Feain, I. J.; Gaensler, B. M.; Hammond, A.; Harvey-Smith, L.; Heald,
G.; Johnston-Hollitt, M.; Klein, U.; Kronberg, P. P.; Mao, S. A.;
McClure-Griffiths, N. M.; O'Sullivan, S. P.; Pratley, L.; Robishaw,
T.; Roy, S.; Schnitzeler, D. H. F. M.; Sotomayor-Beltran, C.; Stevens,
J.; Stil, J. M.; Sunstrum, C.; Tanna, A.; Taylor, A. R.; Van Eck, C. L.
Bibcode: 2012A&A...542A..93O
Altcode: 2011arXiv1111.6186O
We aim to summarize the current state of knowledge regarding Galactic
Faraday rotation in an all-sky map of the Galactic Faraday depth. For
this we have assembled the most extensive catalog of Faraday rotation
data of compact extragalactic polarized radio sources to date. In
the map-making procedure we used a recently developed algorithm that
reconstructs the map and the power spectrum of a statistically isotropic
and homogeneous field while taking into account uncertainties in the
noise statistics. This procedure is able to identify some rotation
angles that are offset by an integer multiple of π. The resulting
map can be seen as an improved version of earlier such maps and is
made publicly available, along with a map of its uncertainty. For the
angular power spectrum we find a power law behavior Cℓ
∝ ℓ-2.17 for a Faraday sky where an overall variance
profile as a function of Galactic latitude has been removed, in
agreement with earlier work. We show that this is in accordance with a
3D Fourier power spectrum P(k) ∝ k-2.17 of the underlying
field neBr under simplifying geometrical and
statistical assumptions.
Title: The Journey of Sungrazing Comet Lovejoy
Authors: Bryans, Paul; A'Hearn, M.; Battams, K.; Biesecker, D.;
Bodewits, D.; Boice, D.; Brown, J.; Caspi, A.; Chodas, P.; Hudson,
H.; Jia, Y.; Jones, G.; Keller, H. U.; Knight, M.; Linker, J.; Lisse,
C.; Liu, W.; McIntosh, S.; Pesnell, W. D.; Raymond, J.; Saar, S.;
Saint-Hilaire, P.; Schrijver, C.; Snow, M.; Tarbell, T.; Thompson,
W.; Weissman, P.; Comet Lovejoy Collaboration Team
Bibcode: 2012AAS...22052507B
Altcode:
Comet Lovejoy (C/2011 W3) was the first sungrazing comet, observed
by space-based instruments, to survive perihelion passage. First
observed by ground-based telescopes several weeks prior to perihelion,
its journey towards the Sun was subsequently recorded by several solar
observatories, before being observed in the weeks after perihelion by
a further array of space- and ground-based instruments. Such a surfeit
of wide-ranging observations provides an unprecedented insight into
both sungrazing comets themselves, and the solar atmosphere through
which they pass. This paper will summarize what we have learnt from the
observations thus far and offer some thoughts on what future sungrazing
comets may reveal about comets, the Sun, and their interaction.
Title: Polarization variability due to clumps in the winds of
Wolf-Rayet stars
Authors: Li, Q.; Cassinelli, J. P.; Brown, J. C.; Ignace, R.
Bibcode: 2012AIPC.1429..168L
Altcode:
Wolf-Rayet (WR) stars are understood to have clumpy winds [1]. Robert
et al. [2] found a statistical relation between the variations of
the polarization and the scattering light intensity, R = σp/σphot ~
0.05. To explain this result, we propose a model in which clumps are
ejected from the surface of WR stars uniformly in space with a Gaussian
time interval distribution. According to the observed R along with the
subpeaks on the emission lines of WR stars, we can obtain the parameters
of the velocity law index β, and of the clump ejection rate in a flow
time N. Also, the fraction η of the total mass loss rate contained
in the clumps can be found from the observed polarization.
Title: Stellar polarimetry: Where are we and where are we going?
Authors: Hoffman, Jennifer L.; Brown, John C.; Nordsieck, Kenneth;
St-Louis, Nicole; Wade, Gregg
Bibcode: 2012AIPC.1429..289H
Altcode: 2012arXiv1205.2159H
On the final day of the Stellar Polarimetry conference, participants
split up into three "breakout sessions" to discuss the future of
the field in the areas of instrumentation, upcoming opportunities,
and community priorities. This contribution compiles the major
recommendations arising from each breakout session. We hope that the
polarimetric community will find these ideas useful as we consider
how to maintain the vitality of polarimetry in the coming years.
Title: Destruction of Sun-Grazing Comet C/2011 N3 (SOHO) Within the
Low Solar Corona
Authors: Schrijver, C. J.; Brown, J. C.; Battams, K.; Saint-Hilaire,
P.; Liu, W.; Hudson, H.; Pesnell, W. D.
Bibcode: 2012Sci...335..324S
Altcode:
Observations of comets in Sun-grazing orbits that survive solar
insolation long enough to penetrate into the Sun's inner corona provide
information on the solar atmosphere and magnetic field as well as on
the makeup of the comet. On 6 July 2011, the Solar Dynamics Observatory
(SDO) observed the demise of comet C/2011 N3 (SOHO) within the low solar
corona in five wavelength bands in the extreme ultraviolet (EUV). The
comet penetrated to within 0.146 solar radius (~100,000 kilometers)
of the solar surface before its EUV signal disappeared. Before that,
material released into the coma - at first seen in absorption - formed
a variable EUV-bright tail. During the final 10 minutes of observation
by SDO's Atmospheric Imaging Assembly, ~6 × 10^8 to 6 × 10^10 grams
of total mass was lost (corresponding to an effective nucleus diameter
of ~10 to 50 meters), as estimated from the tail's deceleration due to
interaction with the surrounding coronal material; the EUV absorption
by the comet and the brightness of the tail suggest that the mass was
at the high end of this range. These observations provide evidence
that the nucleus had broken up into a family of fragments, resulting
in accelerated sublimation in the Sun's intense radiation field.
Title: Exploring Deep Icy World Oceans through New Experimental
Equations of State for Aqueous MgSO4 and NH3
Authors: Vance, S.; Brown, J.
Bibcode: 2011AGUFM.P23D1735V
Altcode:
Observational evidence supports the presence of very deep oceans in
Europa, Ganymede, Callisto, Titan, and Enceladus. Thermal models for
other bodies to be more thoroughly explored also suggest internal liquid
layers in the present or past. Hydrostatic pressure at the bottom oceans
in the three largest of the solar system's icy world oceans exceeds
the formation pressures of high-pressure ice phases. Temperature-
and pressure-dependent thermodynamic effects on fluid transport and
phase stability may have profound geophysical and astrobiological
implications, but experimental constraints on these properties are only
now becoming available. In this context, we present equations of state
for aqueous NH3 and MgSO4 derived from speeds of
sound obtained by the method of impulsive stimulated scattering. Using
these, we provide new constraints on the presence of liquids within
ice layers at the tops and bottoms of icy world oceans.
Title: The EUV Emission in Comet-Solar Corona Interactions
Authors: Bryans, P.; Pesnell, W. D.; Schrijver, C. J.; Brown, J. C.;
Battams, K.; Saint-Hilaire, P.; Liu, W.; Hudson, H. S.
Bibcode: 2011AGUFMSH34B..05B
Altcode:
The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
(SDO) viewed a comet as it passed through the solar corona on 2011 July
5. This was the first sighting of a comet by a EUV telescope. For 20
minutes, enhanced emission in several of the AIA wavelength bands marked
the path of the comet. We explain this EUV emission by considering
the evolution of the cometary atmosphere as it interacts with the
ambient solar atmosphere. Water ice in the comet rapidly sublimates
as it approaches the Sun. This water vapor is then photodissociated,
primarily by Ly-α, by the solar radiation field to create atomic H and
O. Other molecules present in the comet also evaporate and dissociate
to give atomic Fe and other metals. Subsequent ionization of these
atoms can be achieved by a number of means, including photoionization,
electron impact, and charge exchange with coronal protons and other
highly-charged species. Finally, particles from the cometary atmosphere
are thermalized to the background temperature of the corona. Each step
could cause emission in the AIA bandpasses. We will report here on
their relative contribution to the emission seen in the AIA telescopes.
Title: Using the EUV to Weigh a Sun-grazing Comet as it Disappears
in the Solar Corona
Authors: Pesnell, W. D.; Schrijver, C. J.; Brown, J. C.; Battams,
K.; Saint-Hilaire, P.; Hudson, H. S.; Lui, W.
Bibcode: 2011AGUFMSH33A2040P
Altcode:
On July 6, 2011, the Atmospheric Imaging Assembly (AIA) on the
Solar Dynamics Observatory (SDO) observed a comet in most of its
EUV passbands. The comet disappeared while moving through the solar
corona. The comet penetrated to 0.146 solar radii ( ∼~100,000
km) above the photosphere before its EUV faded. Before then, the
comet's coma and a tail were observed in absorption and emission,
respectively. The material in the variable tail quickly fell behind
the nucleus. An estimate of the comet's mass based on this effect,
one derived from insolation, and one using the tail's EUV brightness,
all yield ∼ 50 giga-grams some 10 minutes prior to the end of
its visibility. These unique first observations herald a new era in
the study of Sun-grazing comets close to their perihelia and of the
conditions in the solar corona and solar wind. We will discuss the
observations and interpretation of the comet by SDO as well as the
coronagraph observations from SOHO and STEREO. A search of the SOHO
comet archive for other comets that could be observed in the SDO/AIA
EUV channels will be described.
Title: X-ray emission from massive stars with magnetic fields
Authors: Oskinova, L. M.; Hamann, W. -R.; Cassinelli, J. P.; Brown,
J. C.; Todt, H.
Bibcode: 2011AN....332..988O
Altcode: 2011arXiv1110.5345O
We investigate the connections between the magnetic fields and the X-ray
emission from massive stars. Our study shows that the X-ray properties
of known strongly magnetic stars are diverse: while some comply to
the predictions of the magnetically confined wind model, others do
not. We conclude that strong, hard, and variable X-ray emission may
be a sufficient attribute of magnetic massive stars, but it is not
a necessary one. We address the general properties of X-ray emission
from ``normal'' massive stars, especially the long standing mystery
about the correlations between the parameters of X-ray emission and
fundamental stellar properties. The recent development in stellar
structure modeling shows that small-scale surface magnetic fields
may be common. We suggest a ``hybrid'' scenario which could explain
the X-ray emission from massive stars by a combination of magnetic
mechanisms on the surface and shocks in the stellar wind. The magnetic
mechanisms and the wind shocks are triggered by convective motions in
sub-photospheric layers. This scenario opens the door for a natural
explanation of the well established correlation between bolometric
and X-ray luminosities. Based on observations obtained with \xmm
and \cxo.
Title: Mass loss, destruction and detection of Sun-grazing and
-impacting cometary nuclei
Authors: Brown, J. C.; Potts, H. E.; Porter, L. J.; Le Chat, G.
Bibcode: 2011A&A...535A..71B
Altcode: 2011arXiv1107.1857B
Context. Sun-grazing comets almost never re-emerge, but their
sublimative destruction near the sun has only recently been observed
directly, while chromospheric impacts have not yet been seen, nor
impact theory developed.
Aims: We seek simple analytic models
of comet destruction processes near the sun, to enable estimation of
observable signature dependence on original incident mass Mo
and perihelion distance q.
Methods: Simple analytic solutions are
found for M(r) versus q and distance r for insolation sublimation and,
for the first time, for impact ablation and explosion.
Results:
Sun-grazers are found to fall into three (Mo,q) regimes:
sublimation-, ablation-, and explosion-dominated. Most sun-grazers
have Mo too small (<1011 g) or q too large
(>1.01R⊙) to reach atmospheric densities (n > 2.5 ×
1011/cm3) where ablation exceeds sublimation. Our
analytic results for sublimation are similar to numerical models. For q
< 1.01R⊙,Mo > 1011 g, ablation
initially dominates but results are sensitive to nucleus strength
Pc = 106P6 dyne/cm2
and entry angle φ to the vertical. Nuclei with Mo ≼
1010(P6secφ)3 g are fully ablated
before exploding, though the hot wake itself explodes. For most
sun-impactors secφ ≫ 1 (since q ~ r∗), so for q very
close to r∗ the ablation regime applies to moderate Mo
∼ 1013-16P_6^3 g impactors unless P6
≼ 0.1. For higher masses, or smaller q, nuclei reach densities n
> 2.5 × 1014P6/cm3 where ram
pressure causes catastrophic explosion.
Conclusions: Analytic
descriptions define (Mo,q) regimes where sublimation,
ablation and explosion dominate sun-grazer/-impactor destruction. For
q ≺ 1.01R⊙,Mo ≽ 1011
g nuclei are destroyed by ablation or explosion (depending on
Mocos3φ/Pc) in the chromosphere,
producing flare-like events with cometary abundance spectra. For all
plausible Mo,q and physical parameters, nuclei are destroyed
above the photosphere. This paper is dedicated to the memories of:
Brian G. Marsden, world expert on minor bodies of the solar system and
an irreplaceable friend and colleague; Gerald S. Hawkins who introduced
me to the joys of this field in my (J.C.B.'s) first real (radar meteor)
research experience at HSRAO/CfA in the summer of 1967.
Title: Deducing Electron Properties from Hard X-ray Observations
Authors: Kontar, E. P.; Brown, J. C.; Emslie, A. G.; Hajdas, W.;
Holman, G. D.; Hurford, G. J.; Kašparová, J.; Mallik, P. C. V.;
Massone, A. M.; McConnell, M. L.; Piana, M.; Prato, M.; Schmahl,
E. J.; Suarez-Garcia, E.
Bibcode: 2011SSRv..159..301K
Altcode: 2011arXiv1110.1755K; 2011SSRv..tmp..279K
X-radiation from energetic electrons is the prime diagnostic of
flare-accelerated electrons. The observed X-ray flux (and polarization
state) is fundamentally a convolution of the cross-section for the hard
X-ray emission process(es) in question with the electron distribution
function, which is in turn a function of energy, direction, spatial
location and time. To address the problems of particle propagation
and acceleration one needs to infer as much information as possible on
this electron distribution function, through a deconvolution of this
fundamental relationship. This review presents recent progress toward
this goal using spectroscopic, imaging and polarization measurements,
primarily from the Reuven Ramaty High Energy Solar Spectroscopic
Imager ( RHESSI). Previous conclusions regarding the energy, angular
(pitch angle) and spatial distributions of energetic electrons in
solar flares are critically reviewed. We discuss the role and the
observational evidence of several radiation processes: free-free
electron-ion, free-free electron-electron, free-bound electron-ion,
photoelectric absorption and Compton backscatter (albedo), using both
spectroscopic and imaging techniques. This unprecedented quality of
data allows for the first time inference of the angular distributions
of the X-ray-emitting electrons and improved model-independent
inference of electron energy spectra and emission measures of
thermal plasma. Moreover, imaging spectroscopy has revealed hitherto
unknown details of solar flare morphology and detailed spectroscopy of
coronal, footpoint and extended sources in flaring regions. Additional
attempts to measure hard X-ray polarization were not sufficient to put
constraints on the degree of anisotropy of electrons, but point to the
importance of obtaining good quality polarization data in the future.
Title: Early magnetic B-type stars: X-ray emission and wind properties
Authors: Oskinova, L. M.; Todt, H.; Ignace, R.; Brown, J. C.;
Cassinelli, J. P.; Hamann, W. -R.
Bibcode: 2011MNRAS.416.1456O
Altcode: 2011MNRAS.tmp.1214O; 2011arXiv1106.0508O
We present a comprehensive study of X-ray emission by, and
wind properties of, massive magnetic early B-type stars. Dedicated
XMM-Newton observations were obtained for three early-type B-type stars,
ξ1 CMa, V2052 Oph and ζ Cas, with recently discovered
magnetic fields. We report the first detection of X-ray emission from
V2052 Oph and ζ Cas. The latter is one the softest X-ray sources among
the early-type stars, while the former is one of the X-ray faintest. The
observations show that the X-ray spectra of our programme stars are
quite soft with the bulk of X-ray emitting material having a temperature
of about 1 MK. We compile the complete sample of early B-type stars
with detected magnetic fields to date and existing X-ray measurements,
in order to study whether the X-ray emission can be used as a general
proxy for stellar magnetism. We find that the X-ray properties of early
massive B-type magnetic stars are diverse, and that hard and strong
X-ray emission does not necessarily correlate with the presence of
a magnetic field, corroborating similar conclusions reached earlier
for the classical chemically peculiar magnetic Bp-Ap stars. We
analyse the ultraviolet (UV) spectra of five non-supergiant B stars
with magnetic fields (τ Sco, β Cep, ξ1 CMa, V2052 Oph
and ζ Cas) by means of non-local thermodynamic equilibrium (non-LTE)
iron-blanketed model atmospheres. The latter are calculated with the
Potsdam Wolf-Rayet (PoWR) code, which treats the photosphere as well as
the wind, and also accounts for X-rays. With the exception of τ Sco,
this is the first analysis of these stars by means of stellar wind
models. Our models accurately fit the stellar photospheric spectra in
the optical and the UV. The parameters of X-ray emission, temperature
and flux are included in the model in accordance with observations. We
confirm the earlier findings that the filling factors of X-ray emitting
material are very high. Our analysis reveals that the magnetic
early-type B stars studied here have weak winds with velocities not
significantly exceeding vesc. The mass-loss rates inferred
from the analysis of UV lines are significantly lower than predicted by
hydrodynamically consistent models. We find that, although the X-rays
strongly affect the ionization structure of the wind, this effect is
not sufficient in reducing the total radiative acceleration. When the
X-rays are accounted for at the intensity and temperatures observed,
there is still sufficient radiative acceleration to drive a stronger
mass-loss than we empirically infer from the UV spectral lines.
Title: Early magnetic B-type stars: X-ray emission and wind properties
Authors: Oskinova, Lidia; Todt, Helge; Ignace, Richard; Brown, John;
Cassinelli, Joseph; Hamann, Wolf-Rainer
Bibcode: 2011xru..conf..117O
Altcode:
No abstract at ADS
Title: A VLT-CRIRES 4.7 micron survey of CO emission from young
protoplanetary disks
Authors: Brown, J.; Pontoppidan, K.; van Dishoeck, E. F.; Herczeg, G.
Bibcode: 2011IAUS..280P.105B
Altcode:
The inner regions of protoplanetary disks are thought to be the most
active regions for planet formation and thus potentially hold the key
to understanding the formation of solar systems like our own. Direct
spatial imaging is mainly limited to dust observations. However,
spectroscopic studies probe gas within regions that are inaccessible
to imaging and trace the dominant mass component. CO is an excellent
tracer of the gas being both abundant and easily observable. We have
used the CRIRES spectrograph on the ESO VLT to obtain high resolution
spectra (R~100,000, v=3 km/s) of the 4.7 micron CO v=1-0 fundamental
emission band for a large sample ( 100) young stars with a wide range
of physical properties and in various stages of evolution from young
strongly accreting disks to transition disks, where dust clearing has
begun. Acquisition of such a large sample of CO emission profiles from
protoplanetary disks provides an unprecedented opportunity for a broad
examination of the gas distribution in a wide variety of circumstellar
environments. The high spectral resolution and high dynamic range of
CRIRES spectra is essential to resolve the individual line profiles
so that velocity information can be used to locate the gas within
the disk. CRIRES has the additional advantage of an excellent adaptive
optics system allowing spatial resolution of extended emission as in the
case of IRS 48. We then compare the spatially resolved gas emission to
a Submillimeter Array map of the dust continuum. Detailed knowledge of
dust and gas in the inner regions of disks is a key component needed to
determine the evolutionary process of how circumstellar disks transform
into planetary systems.
Title: Planet-forming Regions at the Highest Spectral and Spatial
Resolution with VLT-CRIRES
Authors: Pontoppidan, K. M.; van Dishoeck, E.; Blake, G. A.; Smith,
R.; Brown, J.; Herczeg, G. J.; Bast, J.; Mandell, A.; Smette, A.;
Thi, W. -F.; Young, E. D.; Morris, M. R.; Dent, W.; Käufl, H. U.
Bibcode: 2011Msngr.143...32P
Altcode:
The inner regions (< 10 AU) of discs surrounding young pre-main
sequence stars are thought to be places of active planet formation. The
disc surfaces are traced by molecular emission lines in the infrared. We
have carried out a spectroscopic 3-5 μm survey at the highest spectral
resolution (as high as R = 100000) using CRIRES on the VLT, and have
used the data to map the dynamics and chemistry of molecular gas, with
the aims of constraining disc evolution and learning more about the
process of planet formation. In this paper, we provide a brief overview
of our CRIRES observing campaign and discuss the results obtained.
Title: Modeling the Magnetic Field in the Galactic Disk Using New
Rotation Measure Observations from the Very Large Array
Authors: Van Eck, C. L.; Brown, J. C.; Stil, J. M.; Rae, K.; Mao,
S. A.; Gaensler, B. M.; Shukurov, A.; Taylor, A. R.; Haverkorn, M.;
Kronberg, P. P.; McClure-Griffiths, N. M.
Bibcode: 2011ApJ...728...97V
Altcode: 2010arXiv1012.2938V
We have determined 194 Faraday rotation measures (RMs) of polarized
extragalactic radio sources using new, multi-channel polarization
observations at frequencies around 1.4 GHz from the Very Large Array
in the Galactic plane at 17° <= l <= 63° and 205° <=
l <= 253°. This catalog fills in gaps in the RM coverage of
the Galactic plane between the Canadian Galactic Plane Survey and
Southern Galactic Plane Survey. Using this catalog we have tested the
validity of recently proposed axisymmetric and bisymmetric models of the
large-scale (or regular) Galactic magnetic field, and found that of the
existing models we tested, an axisymmetric spiral model with reversals
occurring in rings (as opposed to along spiral arms) best matched our
observations. Building on this, we have performed our own modeling,
using RMs from both extragalactic sources and pulsars. By developing
independent models for the magnetic field in the outer and inner Galaxy,
we conclude that in the inner Galaxy, the magnetic field closely follows
the spiral arms, while in the outer Galaxy, the field is consistent with
being purely azimuthal. Furthermore, the models contain no reversals
in the outer Galaxy, and together seem to suggest the existence of a
single reversed region that spirals out from the Galactic center.
Title: The Potential of High Angular Resolution and Contrast FUV
Imagery for Studies of Star and Planetary System Formation
Authors: Grady, C. A.; Brown, A.; Woodgate, B.; Hornbeck, J.; Williger,
G.; Herczeg, G.; Brown, J.; Brittain, S.; Wisniewski, J.; Perrin,
M.; Hamaguchi, K.; Henning, T.; Kamp, I.; Petre, R.; Schneider, G.;
Sitko, M.; Walter, F.; Apai, D.; Ayres, T.
Bibcode: 2011AAS...21734019G
Altcode: 2011BAAS...4334019G
High contrast and high angular resolution imagery has opened new
viewpoints on the formation and early evolution of planetary systems,
revealing features of protoplanetary and young planetary systems which
would go undetected in the integrated measures of the systems. Much
of the power of such studies has resulted from pan-chromatic data, but
the majority of studies to date have been limited to optical and longer
wavelengths, despite the wealth of atomic, ionic, and molecular tracers
of circumstellar material in the FUV. As with high-contrast imaging
at longer wavelengths, realizing the full potential of FUV imagery
of young stars requires subtraction of PSF template data, which are
now available for 3 of the HST ACS/SBC bandpasses. Such imagery has
resulted in the first imagery of the circumstellar disk around the
Herbig Ae star PDS 144S and can trace the geometry of the molecular
gas disk for T Tauri stars. FUV imaging data also provide exquisite
detail for molecular outflows for systems like T Tauri, complementing
studies in the FIR with Herschel. Such data can also reveal the presence
of previously unsuspected disk winds, as seen in GM Aur. Since FUV
imagery is sensitive to extinction, FUV data preferentially detect
circumstellar material on the near side of disks and the approaching
components of outflows, removing ambiguities in disk viewing geometry,
and can map, at the highest angular resolution achievable with HST,
where disks are shadowed. This is a capability which future UV/Optical
telescopes optimized for studies of planetary system formation should
not be without. This study is based on data obtained with the
Hubble Space Telescope under GO programs 10864, 11336, and 12016.
Title: The Magnetic Field of the Milky Way Galaxy
Authors: Brown, J. C.
Bibcode: 2010ASPC..438..216B
Altcode: 2010arXiv1012.2932B
Cosmic magnetic fields are an integral component of the interstellar
medium (ISM), having influence on scales ranging from star formation
to galactic dynamics. While observations of external galaxies offer a
‘birds-eye-view' of magnetic fields within galaxies, it is equally
important to explore the magnetic field of our own Milky Way Galaxy,
which offers a more detailed, albeit more complicated view. Over
the past decade there has been a significant increase in interest in
the Galactic magnetic field, fueled largely by innovations developed
through the Canadian Galactic Plane Survey. In this paper, I review
the current state of understanding of the Galactic magnetic field,
and discuss briefly new and future observations that will provide
exciting new insights about the field.
Title: Constraints on the Galactic Magnetic Field from the Canadian
Galactic Plane Survey
Authors: Rae, K. M.; Brown, J. C.
Bibcode: 2010ASPC..438..229R
Altcode: 2010arXiv1012.2934R
The Galactic magnetic field is important in the dynamics of our
Galaxy. It is believed to play a role in star formation and influence
the structure of the Galaxy. In order to understand how the Galactic
magnetic field originally formed or how it is evolving, we must first
determine its present topology. To this end, we have used observations
from the Canadian Galactic Plane Survey (CGPS) to calculate the highest
source density of rotation measures (RM) to date in the disk of the
Galaxy. Using these data, we estimate the Galactic longitude of the
RM null point in the outer Galaxy (where the RMs of extragalactic
sources are observed to pass through zero, on average, with increasing
Galactic longitude). We have also examined the RM scale height using
the CGPS latitude extension. The values of these parameters offer
critical constraints for modeling the large-scale magnetic field in
the Galactic disk.
Title: Modeling the Galactic Magnetic Field Using Rotation Measure
Observations in the Galactic Disk from the CGPS, SGPS, and the VLA
Authors: van Eck, C. L.; Brown, J. C.
Bibcode: 2010ASPC..438..236V
Altcode: 2010arXiv1012.2936V
Interstellar magnetic fields play critical roles in many astrophysical
processes. Yet despite their importance, our knowledge about magnetic
fields in our Galaxy remains limited. For the field within the Milky
Way, much of what we do know comes from observations of polarisation and
Faraday rotation measures (RMs) of extragalactic sources and pulsars. A
high angular density of RM measurements in several critical areas of the
Galaxy is needed to clarify the Galactic magnetic field structure. Using
observations made with the VLA, we have determined RMs for sources
in regions of the Galactic plane not covered by the Canadian Galactic
Plane Survey (CGPS) and Southern Galactic Plane Survey (SGPS). We have
combined these new RMs with those determined from the CGPS and SGPS and
have produced a new model for the magnetic field of the Galactic disk.
Title: Generation and emplacement of fine-grained ejecta in planetary
impacts
Authors: Ghent, Rebecca R.; Gupta, V.; Campbell, B. A.; Ferguson,
S. A.; Brown, J. C. W.; Fergason, R. L.; Carter, L. M.
Bibcode: 2010Icar..209..818G
Altcode:
We report here on a survey of distal fine-grained ejecta deposits on the
Moon, Mars, and Venus. On all three planets, fine-grained ejecta form
circular haloes that extend beyond the continuous ejecta and other
types of distal deposits such as run-out lobes or ramparts. Using
Earth-based radar images, we find that lunar fine-grained ejecta
haloes represent meters-thick deposits with abrupt margins, and
are depleted in rocks ⩾1 cm in diameter. Martian haloes show low
nighttime thermal IR temperatures and thermal inertia, indicating
the presence of fine particles estimated to range from ∼10 μm to
10 mm. Using the large sample sizes afforded by global datasets for
Venus and Mars, and a complete nearside radar map for the Moon, we
establish statistically robust scaling relationships between crater
radius R and fine-grained ejecta run-out r* for all three
planets. On the Moon, r* ∼ R-0.18 for craters
5-640 km in diameter. For Venus, radar-dark haloes are larger than
those on the Moon, but scale as r* ∼ R-0.49,
consistent with ejecta entrainment in Venus' dense atmosphere. On Mars,
fine-ejecta haloes are larger than lunar haloes for a given crater
size, indicating entrainment of ejecta by the atmosphere or vaporized
subsurface volatiles, but scale as R-0.13, similar to the
ballistic lunar scaling. Ejecta suspension in vortices generated by
passage of the ejecta curtain is predicted to result in ejecta run-out
that scales with crater size as R1/2, and the wind speeds
so generated may be insufficient to transport particles at the larger
end of the calculated range. The observed scaling and morphology of
the low-temperature haloes leads us rather to favor winds generated
by early-stage vapor plume expansion as the emplacement mechanism for
low-temperature halo materials.
Title: Analysis of Unresolved Spectral Infrared Signature for the
Extraction of Invariant Features
Authors: Chaudhary, A.; Payne, T.; Wilhelm, S.; Gregory, S.; Skinner,
M.; Rudy, R.; Russell, R.; Brown, J.; Dao, P.
Bibcode: 2010amos.confE...9C
Altcode:
This paper demonstrates a simple analytical technique for extraction of
spectral radiance values for the solar panel and body from an unresolved
spectral infrared signature of 3-axis stabilized low-earth orbit (LEO)
satellites. It uses data collected by The Aerospace Corporation’s
Broad-band Array Spectrograph System (BASS) instrument at the Air Force
Maui Optical and Supercomputing (AMOS) site. The observation conditions
were such that the signatures were due to the emissive phenomenology and
contribution of earthshine was negligible. The analysis is based on a
two-facet orientation model of the satellite. This model captures the
basic, known behavior of the satellite body and its solar panels. One
facet points to nadir and the second facet tracks the sun. The facet
areas are unknown. Special conditions are determined on the basis of
observational geometry that allows separation of the spectral radiance
values of the solar panel and body. These values remain unchanged
(i.e., are invariant) under steady illumination conditions even if
the signature appears different from one observation to another. In
addition, they provide information on the individual spectral makeup
of the satellite solar panel and body materials.
Title: Thermalisation and hard X-ray bremsstrahlung efficiency of
self-interacting solar flare fast electrons
Authors: Galloway, R. K.; Helander, P.; MacKinnon, A. L.; Brown, J. C.
Bibcode: 2010A&A...520A..72G
Altcode: 2010arXiv1003.3263G
Context. Most theoretical descriptions of the production of solar flare
bremsstrahlung radiation assume the collision of dilute accelerated
particles with a cold, dense target plasma, neglecting interactions of
the fast particles with each other. This is inadequate for situations
where collisions with this background plasma are not completely
dominant, as may be the case in, for example, low-density coronal
sources.
Aims: We aim to formulate a model of a self-interacting,
entirely fast electron population in the absence of a dense background
plasma, to investigate its implications for observed bremsstrahlung
spectra and the flare energy budget.
Methods: We derive
approximate expressions for the time-dependent distribution function
of the fast electrons using a Fokker-Planck approach. We use these
expressions to generate synthetic bremsstrahlung X-ray spectra as would
be seen from a corresponding coronal source.
Results: We find
that our model qualitatively reproduces the observed behaviour of some
flares. As the flare progresses, the model's initial power-law spectrum
is joined by a lower energy, thermal component. The power-law component
diminishes, and the growing thermal component proceeds to dominate the
total emission over timescales consistent with flare observations. The
power-law exhibits progressive spectral hardening, as is seen in some
flare coronal sources. We also find that our model requires a factor of
7-10 fewer accelerated electrons than the cold, thick target model to
generate an equivalent hard X-ray flux.
Conclusions: This model
forms the basis of a treatment of self-interactions among flare fast
electrons, a process which affords a more efficient means to produce
bremsstrahlung photons and so may reduce the efficiency requirements
placed on the particle acceleration mechanism. It also provides a useful
description of the thermalisation of fast electrons in coronal sources.
Title: Measurements of Tilt and Focus for Sodium Beacon Adaptive
Optics on the Starfire 3.5 Meter Telescope
Authors: Johnson, R.; Brown, J.; Spinhirne, J.
Bibcode: 2010amos.confE..19J
Altcode:
Telescopes with adaptive optics systems can measure high-order
aberrations using an artificial laser beacon without the need for a
relatively bright object near the object being imaged. Unfortunately,
tilt and focus measurements are difficult to obtain from a laser
beacon. One solution is to use light from the object being imaged
to measure tilt and focus. We characterize the performance of a
Shack-Hartmann wavefront sensor with 2_2 sub-apertures for measuring
tilt and focus. Specifically, we implemented this scheme for the sodium
beacon adaptive optics upgrade to the Starfire Optical Range (SOR)
3.5 meter telescope [1]. We use a wave-optics simulation to predict
the performance of the tilt and focus sensor in the SOR sodium beacon
system, and compare the results to laboratory measurements.
Title: Nonstationary EO/IR Clutter Suppression and Dim Object Tracking
Authors: Tartakovsky, A.; Brown, A.; Brown, J.
Bibcode: 2010amos.confE..20T
Altcode:
We develop and evaluate the performance of advanced algorithms which
provide significantly improved capabilities for automated detection and
tracking of ballistic and flying dim objects in the presence of highly
structured intense clutter. Applications include ballistic missile
early warning, midcourse tracking, trajectory prediction, and resident
space object detection and tracking. The set of algorithms include, in
particular, adaptive spatiotemporal clutter estimation-suppression and
nonlinear filtering-based multiple-object track-before-detect. These
algorithms are suitable for integration into geostationary, highly
elliptical, or low earth orbit scanning or staring sensor suites, and
are based on data-driven processing that adapts to real-world clutter
backgrounds, including celestial, earth limb, or terrestrial clutter. In
many scenarios of interest, e.g., for highly elliptic and, especially,
low earth orbits, the resulting clutter is highly nonstationary,
providing a significant challenge for clutter suppression to or below
sensor noise levels, which is essential for dim object detection and
tracking. We demonstrate the success of the developed algorithms
using semi-synthetic and real data. In particular, our algorithms
are shown to be capable of detecting and tracking point objects with
signal-to-clutter levels down to 1/1000 and signal-to-noise levels
down to 1/4.
Title: Parallel electric field generation by Alfvén wave turbulence
Authors: Bian, N. H.; Kontar, E. P.; Brown, J. C.
Bibcode: 2010A&A...519A.114B
Altcode: 2010arXiv1006.2662B
Aims: This work aims to investigate the spectral structure
of the parallel electric field generated by strong anisotropic
and balanced Alfvénic turbulence in relation with the problem of
electron acceleration from the thermal population in solar flare
plasma conditions.
Methods: We consider anisotropic Alfvénic
fluctuations in the presence of a strong background magnetic
field. Exploiting this anisotropy, a set of reduced equations
governing non-linear, two-fluid plasma dynamics is derived. The
low-β limit of this model is used to follow the turbulent cascade
of the energy resulting from the non-linear interaction between
kinetic Alfvén waves, from the large magnetohydrodynamics (MHD)
scales with k⊥ρ_s≪1 down to the small “kinetic”
scales with k⊥ρs ≫1, ρ_s being the ion
sound gyroradius.
Results: Scaling relations are obtained
for the magnitude of the turbulent electromagnetic fluctuations, as
a function of k⊥ and k∥, showing that the
electric field develops a component parallel to the magnetic field at
large MHD scales.
Conclusions: The spectrum we derive for the
parallel electric field fluctuations can be effectively used to model
stochastic resonant acceleration and heating of electrons by Alfvén
waves in solar flare plasma conditions
Title: Non-thermal recombination - a neglected source of flare hard
X-rays and fast electron diagnostics (Corrigendum)
Authors: Brown, J. C.; Mallik, P. C. V.; Badnell, N. R.
Bibcode: 2010A&A...515C...1B
Altcode:
Brown and Mallik (BM) recently claimed that non-thermal recombination
(NTR) can be a dominant source of flare hard X-rays (HXRs) from hot
coronal and chromospheric sources. However, major discrepancies between
the thermal continua predicted by BM and by the Chianti database as
well as RHESSI flare data, led us to discover substantial errors in
the heuristic expression used by BM to extend the Kramers expressions
beyond the hydrogenic case. Here we present the relevant corrected
expressions and show the key modified results. We conclude that, in
most cases, NTR emission was overestimated by a factor of 1-8 by BM
but is typically still large enough (as much as 20-30% of the total
emission) to be very important for electron spectral inference and
detection of electron spectral features such as low energy cut-offs
since the recombination spectra contain sharp edges. For extreme
temperature regimes and/or if the Fe abundance were as high as some
values claimed, NTR could even be the dominant source of flare HXRs,
reducing the electron number and energy budget, problems such as in
the extreme coronal HXR source cases reported by e.g. Krucker et al.
Title: The Slow Growth of Massive Galaxies in Rapidly Growing Dark
Matter Halos
Authors: Brown, Michael J. I.; Brown
Bibcode: 2010IAUS..262..244B
Altcode: 2010arXiv1001.2368B
In cold dark matter cosmologies, the most massive dark matter halos
are predicted to undergo rapid growth at z < 1. While there is the
expectation that massive galaxies will also rapidly grow via merging,
recent observational studies conclude that the stellar masses of the
most massive galaxies grow by just ~ 30% at z < 1. We have used
the observed space density and clustering of z < 1 red galaxies
in Boötes to determine how these galaxies populate dark matter
halos. In the most massive dark matter halos, central galaxy stellar
mass is proportional to halo mass to the power of a ~1/3 and much of
the stellar mass resides within satellite galaxies. As a consequence,
the most massive galaxies grow slowly even though they reside within
rapidly growing dark matter halos.
Title: Solar X-Ray Processes
Authors: Mallik, P. C. V.; Brown, J. C.; MacKinnon, A. L.
Bibcode: 2010ASSP...19..463M
Altcode: 2010mcia.conf..463M
Past analyses of solar flares have ignored nonthermal recombination
(NTR) emission as a means of producing Hard X-rays (HXRs) in the corona
and chromosphere. However, Brown and Mallik (2008, A&A, 481, 507)
have shown that NTR can be significant and even exceed nonthermal
bremsstrahlung (NTB) emission for certain flare conditions that are
quite common. For hot enough plasma (T > 10 MK), HXR emission of a
few deka-keV has a large contribution from NTR onto highly ionized heavy
elements, especially Fe. Consequently, including NTR has implications
for the magnitude and the form of the inferred electron spectrum,
F(E), and hence for fast-electron density and energy budgets and for
the acceleration mechanisms. We show under what circumstances NTR
dominates in deka-keV HXR emission. It is important to note that at
high temperatures, HXR emission from thermal electrons (recombination
and bremsstrahlung) becomes important. However, NTR dominates over
NTB without being swamped by thermal emission in the photon energy
(ɛ) regime of 20-30 keV and temperature range of 10-25MK (Fig. 1,
left). By integrating the flux for all ɛ > 20keV, i.e., looking at
the source luminosity function above 20 keV, we were able to show that
by including NTR, the acceleration requirements are less demanding
for every event, but to varying degrees based on temperature (T),
spectral index (δ) and electron low-energy cut-off (Ec). Our key
result is that, for T > 10MK and δ ≈ 5, including NTR reduces
the demand for nonthermal electrons by up to 85%. Our paper with these
results will be submitted to ApJ Letters.
Title: The first direct measurement of 17O(α,γ)21Ne and its impact
upon s-process abundances
Authors: Taggart, M.; Hager, U.; Laird, A.; Ruiz, C.; Hutcheon, D.;
Ottewell, D. F.; Fallis, J.; Erikson, L.; Bentley, M.; Brown, J.;
Buchmann, L.; Chen, A. A.; Chen, J.; Chipps, K.; D'Auria, J.; Davids,
B.; Davis, C.; Diget, C. A.; Fox, S. P.; Fulton, B. R.; Galinski,
N.; Greife, U.; Herwig, F.; Hirschi, R.; Howell, D.; Martin, L.;
Mountford, D.; Murphy, A.; Pignatari, M.; Reeve, S.; Ruprecht, G.;
Sjue, S.; Veloce, L.
Bibcode: 2010nuco.confE..45T
Altcode: 2010PoS...100E..45T
No abstract at ADS
Title: Electron reacceleration in flares and resulting modifications
of the 'standard' Thick Target Model of electron beams
Authors: Brown, John C.; Turkmani, Rim
Bibcode: 2010cosp...38.2976B
Altcode: 2010cosp.meet.2976B
A modified Thick Target Model proposed by Brown et al. (2009) and termed
the Local Reac-celeration Thick Target Model (LRTTM) offers a possible
solution of these CTTM problems by invoking reacceleration of electrons
after injection from a coronal primary acceleration region. Various
reacceleration processes are possible, including in current sheet
cascades but, provided the acceleration rate offsets collisional
losses, electron lifetimes and HXR yield are greatly in-creased,
so that the necessary beam density is much reduced, as is the HXR
source electron anisotropy. The total beam power input required in the
LRTTM is, however, no less than in the CTTM and, furthermore it has
predominantly to be released in the chromosphere. This, together with
the longer range of reaccelerated electrons, may affect the vertical
distribution of beam heating with possible consequences for white
light flare production and chromospheric explosive evaporation models.
Title: Local re-acceleration and a modified thick target model of
solar flare electrons
Authors: Brown, J. C.; Turkmani, R.; Kontar, E. P.; MacKinnon, A. L.;
Vlahos, L.
Bibcode: 2009A&A...508..993B
Altcode: 2009arXiv0909.4243B
Context: The collisional thick target model (CTTM) of solar hard
X-ray (HXR) bursts has become an almost “standard model” of
flare impulsive phase energy transport and radiation. However, it
faces various problems in the light of recent data, particularly the
high electron beam density and anisotropy it involves.
Aims: We
consider how photon yield per electron can be increased, and hence fast
electron beam intensity requirements reduced, by local re-acceleration
of fast electrons throughout the HXR source itself, after injection.
Methods: We show parametrically that, if net re-acceleration rates
due to e.g. waves or local current sheet electric (E) fields are a
significant fraction of collisional loss rates, electron lifetimes, and
hence the net radiative HXR output per electron can be substantially
increased over the CTTM values. In this local re-acceleration thick
target model (LRTTM) fast electron number requirements and anisotropy
are thus reduced. One specific possible scenario involving such
re-acceleration is discussed, viz, a current sheet cascade (CSC) in a
randomly stressed magnetic loop.
Results: Combined MHD and test
particle simulations show that local E fields in CSCs can efficiently
accelerate electrons in the corona and and re-accelerate them after
injection into the chromosphere. In this HXR source scenario, rapid
synchronisation and variability of impulsive footpoint emissions can
still occur since primary electron acceleration is in the high Alfvén
speed corona with fast re-acceleration in chromospheric CSCs. It is
also consistent with the energy-dependent time-of-flight delays in
HXR features.
Conclusions: Including electron re-acceleration in
the HXR source allows an LRTTM modification of the CTTM in which beam
density and anisotropy are much reduced, and alleviates theoretical
problems with the CTTM, while making it more compatible with radio and
interplanetary electron numbers. The LRTTM is, however, different in
some respects such as spatial distribution of atmospheric heating by
fast electrons.
Title: Revised Results for Non-thermal Recombination Flare Hard
X-Ray Emission
Authors: Brown, J. C.; Mallik, P. C. V.; Badnell, N. R.
Bibcode: 2009arXiv0912.3385B
Altcode:
Brown and Mallik (BM) recently showed that, for hot sources,
recombination of non-thermal electrons (NTR) onto highly ionised heavy
ions is not negligible compared to non-thermal bremsstrahlung (NTB)
as a source of flare hard X-rays (HXRs) and so should be included in
modelling non-thermal HXR flare emission. In view of major discrepancies
between BM results for the THERMAL continua and those of the Chianti
code and of RHESSI solar data, we critically re-examine and correct
the BM analysis and modify the conclusions concerning the importance
of NTR. Although the analytic Kramers expression used by BM is correct
for the purely hydrogenic recombination cross section, the heuristic
expressions used by BM to extend the Kramers expression beyond the
`bare nucleus' case to which it applies had serious errors. BM results
have therefore been recalculated using corrected expressions, which
have been validated against the results of detailed calculations. At T ~
10-30 MK the dominant ions are Fe 22+, 23+, 24+ for which BM erroneously
overestimated NTR emission by around an order of magnitude. Contrary
to the BM claim, NTR in hot flare plasmas does NOT dominate over NTB,
although in some cases it can be comparable and so still very important
in inversions of photon spectra to derive electron spectra, especially
as NTR includes sharp edge features. The BM claim of dominance of
NTR over NTB in deka-keV emission is incorrect due to a serious error
in their analysis. However, the NTR contribution can still be large
enough to demand inclusion in spectral fitting, the spectral edges
having potentially serious effects on inversion of HXR spectra to
infer fast electron spectra.
Title: Polarization variability arising from clumps in the winds of
Wolf-Rayet stars
Authors: Li, Qing-Kang; Cassinelli, Joseph P.; Brown, John C.;
Ignace, Richard
Bibcode: 2009RAA.....9..558L
Altcode: 2009arXiv0903.3082L
Polarimetric and photometric variability of Wolf-Rayet (WR) stars
as caused by clumps in the winds is revisited. In our model, which
is improved from Li et al., radial expansion of the thickness is
accounted for, but we retain dependence on the β velocity law and
stellar occultation effects. We again search for parameters that can
yield results consistent with observations in regards to the mean
polarization bar p, the ratio R = σP/σphot
of polarimetric to photometric variability and the volume filling
factor fv. Clump generation and spatial distribution
are randomized by the Monte Carlo method so as to produce clumps
which are, in the mean, distributed uniformly in space and have time
intervals that obey a Gaussian distribution. The generated clumps
move radially outward with a velocity law determined by a β index,
and the angular size of clumps is assumed to be fixed. By fitting the
observed σP/σphot and the volume filling factor
fv, clump velocity law index β (~ 2) and clump ejection
rate N (~ 1) are inferred, and are found to be well constrained. In
addition, the subpeak features of broad emission lines seem to support
the clump ejection rate. Meanwhile, the fraction of total mass loss
rate that is contained in clumps is obtained by fitting observed
polarization. We conclude that this picture of the clumps' properties
produces a valuable diagnostic of WR wind structure.
Title: Diagnostics of Solar Flare Energetic Particles
Authors: Mallik, Procheta; Brown, J. C.; MacKinnon, A. L.
Bibcode: 2009SPD....40.3707M
Altcode:
For work on my thesis dissertation, we have been studying some energetic
processes in solar flares. On our work on Hard X-ray (HXR) emission
from flares, we have shown that recombination emission can exceed the
bremsstrahlung HXR flux for certain flare conditions. We will show
some spectral features characteristic of non-thermal recombination
HXR emission and will suggest how it plays a significant role in the
flare HXR continuum, something that has been ignored in the past. It
is important to note that these results could demand a reconsideration
of the numbers of accelerated electrons since recombination can be
much more efficient in producing HXR photons than bremsstrahlung. In
related work on diagnosing particle acceleration in flares, we also
have an interest in studying solar neutrons. To this end, we will
present our work done with new-age neutron detectors developed by
our colleagues at the University of New Hampshire. Using laboratory
and simulated data from the detector to produce its response matrix,
we then employ regularisation and deconvolution techniques to produce
encouraging results for data inversion. As a corollary, we have also
been reconsidering the role of inverse Compton (IC) scattering of
photospheric photons. Gamma-ray observations clearly show the presence
of 100 MeV electrons and positrons in the solar corona, by-products
of GeV energy ions. Here we will present results of IC scattering of
such photons taking proper account of radiation field geometry near the
solar surface. If observed, such radiation would let us determine the
number of secondary positrons produced in large flares, contributing
to a full picture of ion acceleration and to predicting neutron fluxes
to be encountered by future inner heliosphere space missions. This
work is supported by a UK STFC Rolling Grant and a Dorothy Hodgkin's
Scholarship (PM).
Title: Flare Hard X-Ray Sources Dominated by Nonthermal Recombination
Authors: Brown, John C.; Mallik, Procheta C. V.
Bibcode: 2009ApJ...697L...6B
Altcode:
It was recently shown that, in the hottest regions of flare plasma,
nonthermal hard X-ray (HXR) emission in the few deka-keV range from
nonthermal electrons by recombination (NTR) onto heavy ions (especially
Fe) exceeds bremsstrahlung (NTB), contrary to earlier assumptions. Here
we discuss what types of HXR events are so dominated. Though significant
even at temperatures T down to 106 K, the dominance of
such NTR radiation over NTB needs T > 10 MK in order for Fe22+
ions and above to be plentiful. Furthermore, even for an accelerated
fraction of only 0.01, the total hot plasma thermal emission begins
to exceed NTR only for T > 25 MK. The relative NTR contribution is
greatest when the electron flux spectrum is steep and extends to low
energies. Thus, in proper modeling of hot HXR sources, inclusion of NTR
as well as NTB is essential and reduces the HXR electron number and
power requirements by over an order of magnitude in some cases. This
alleviates problems of electron acceleration efficiency, especially
in coronal HXR sources. Even some chromospheric footpoint HXR sources
may be NTR-dominated if the hot soft X-ray (SXR) footpoint plasma
there contains fast electrons. Only a small fraction of the plasma
emission measure observed in SXR footpoints need be in the form of
nonthermals to provide the necessary HXR emission measure. Compared
with the standard cold thick target (bremsstrahlung) model (CTTM),
such a scenario would give fast electrons a lesser role in the flare
energy budget and help solve various problems with the CTTM.
Title: Solar X-ray Processes
Authors: Mallik, Procheta; Brown, J. C.; MacKinnon, A. L.
Bibcode: 2009SPD....40.2004M
Altcode:
We have shown that recombination emission can exceed the bremsstrahlung
Hard X-ray (HXR) flux for certain flare conditions. Here we will
show that particular spectral features may suggest non-thermal
recombination plays a significant part in the flare HXR continuum,
something that has been ignored in the past. It is important to note
that these results could demand a reconsideration of the numbers of
accelerated electrons since recombination can be much more efficient
in producing HXR photons than bremsstrahlung. In related work on
diagnosing flare ion and relativistic electron acceleration, we have
also been reconsidering the role of Inverse Compton (IC) scattering of
photospheric photons. Gamma-ray observations clearly show the presence
of 100 MeV electrons and positrons in the solar corona, by-products
of GeV energy ions. Here we will present results of IC scattering of
such photons taking proper account of radiation field geometry near
the surface. If observed, such radiation would let us determine the
number of secondary positrons produced in large flares, contributing
to a full picture of ion acceleration and to predicting neutron fluxes
to be encountered by future inner heliosphere space missions.
Title: Scattering polarization due to light source
anisotropy. II. Envelope of arbitrary shape
Authors: Ignace, R.; Al-Malki, M. B.; Simmons, J. F. L.; Brown, J. C.;
Clarke, D.; Carson, J. C.
Bibcode: 2009A&A...496..503I
Altcode:
Aims: We consider the polarization arising from scattering in an
envelope illuminated by a central anisotropic source. This work extends
the theory introduced in a previous paper (Al-Malki et al. 1999) in
which scattering polarization from a spherically symmetric envelope
illuminated by an anisotropic point source was considered. Here
we generalize to account for the more realistic expectation of a
non-spherical envelope shape.
Methods: Spherical harmonics are
used to describe both the light source anisotropy and the envelope
density distribution functions of the scattering particles. This
framework demonstrates how the net resultant polarization arises from a
superposition of three basic “shape” functions: the distribution
of source illumination, the distribution of envelope scatterers,
and the phase function for dipole scattering.
Results: Specific
expressions for the Stokes parameters and scattered flux are derived for
the case of an ellipsoidal light source inside an ellipsoidal envelope,
with principal axes that are generally not aligned. Two illustrative
examples are considered: (a) axisymmetric mass loss from a rapidly
rotating star, such as may apply to some Luminous Blue Variables, and
(b) a Roche-lobe filling star in a binary system with a circumstellar
envelope.
Conclusions: As a general conclusion, the combination
of source anisotropy with distorted scattering envelopes leads to more
complex polarimetric behavior such that the source characteristics
should be carefully considered when interpreting polarimetric data.
Title: Signature Intensity Derivative and its Application to Resident
Space Object Typing
Authors: Payne, T.; Chaudhary, A.; Gregory, S.; Brown, J.; Nosek, M.
Bibcode: 2009amos.confE..27P
Altcode:
A key feature of resident space object (RSO) photometric signatures is
change in their brightness and color with time. It has been discovered
that because of the illumination angle dependency of this temporal
nature, time alone is insufficient to characterize the intrinsic
nature of change in signature brightness. In this paper, we present
a derivation of how the first derivative of the photometric intensity
as a function of phase angle is related to the normalized reflectance
spectra of the materials contained in the RSO signature. It is shown
for the case of the geosynchronous orbit satellite and the results
of a test case in this orbit regime are presented. We discuss the
implications on existing characterization algorithms and its potential
for the development of new algorithms that process the photometric
signatures. Finally, we discuss the insights obtained by this analysis
on photometric data collection techniques.
Title: Space Object Characterization Using Time-Frequency Analysis
of Multispectral Measurements from the Magdalena Ridge Observatory
Authors: Alcala, C.; Brown, J.
Bibcode: 2009amos.confE..29A
Altcode:
The interactions between the surface materials and the body dynamics
complicate the characterization of space objects from their optical
signatures. One method for decoupling these two effects on the
observed signature is to obtain simultaneous measurements using
multiple spectral filter bands. The advantage of this approach is
that it provides spectral resolution between the filter bands to
identify the different materials based on their optical properties
as a function of wavelength and temporal resolution between samples
to identify the periodic, quasi-periodic, and transient fluctuations
characteristic of the object motions, including attitude control,
maneuvers, and station-keeping. We have developed algorithms to extract
and to analyze light curve data from unresolved resident space objects
(RSO) collected at the Magdalena Ridge Observatory (MRO) using the
Multi Lens Array (MLA) camera coupled to the 2.4-m telescope. The
MLA camera produces 16 spectrally-filtered and temporally synchronous
sub-images ranging from 414 nm to 845 nm. We have developed a filter
band calibration using a set of stellar observations to remove the
atmospheric refraction and absorption effects and differences in
the optical paths across the different filter bands using catalogued
spectrophotometric data. We apply wavelet analysis to the RSO optical
signature light curves to obtain the time-frequency characteristics
of the signal for each band. This information allows us to obtain
information about the body motions as a function of time. We next
attempt to correlate these characteristics across the different MLA
filter bands to derive constraints on the types of surface materials. In
this presentation, we will present results from several case studies to
demonstrate the effectiveness of our approach and to provide guidance
on the effectiveness of different spectral bands for space object
characterization.
Title: Enhanced Algorithms for EO/IR Electronic Stabilization,
Clutter Suppression, and Track-Before-Detect for Multiple Low
Observable Targets
Authors: Tartakovsky, A.; Brown, A.; Brown, J.
Bibcode: 2009amos.confE..17T
Altcode:
The paper describes the development and evaluation of a suite of
advanced algorithms which provide significantly-improved capabilities
for finding, fixing, and tracking multiple ballistic and flying low
observable objects in highly stressing cluttered environments. The
algorithms have been developed for use in satellite-based staring
and scanning optical surveillance suites for applications including
theatre and intercontinental ballistic missile early warning, trajectory
prediction, and multi-sensor track handoff for midcourse discrimination
and intercept. The functions performed by the algorithms include
electronic sensor motion compensation providing sub-pixel stabilization
(to 1/100 of a pixel), as well as advanced temporal-spatial clutter
estimation and suppression to below sensor noise levels, followed
by statistical background modeling and Bayesian multiple-target
track-before-detect filtering. The multiple-target tracking is performed
in physical world coordinates to allow for multi-sensor fusion,
trajectory prediction, and intercept. Output of detected object cues and
data visualization are also provided. The algorithms are designed
to handle a wide variety of real-world challenges. Imaged scenes may be
highly complex and infinitely varied -- the scene background may contain
significant celestial, earth limb, or terrestrial clutter. For example,
when viewing combined earth limb and terrestrial scenes, a combination
of stationary and non-stationary clutter may be present, including
cloud formations, varying atmospheric transmittance and reflectance
of sunlight and other celestial light sources, aurora, glint off sea
surfaces, and varied natural and man-made terrain features. The targets
of interest may also appear to be dim, relative to the scene background,
rendering much of the existing deployed software useless for optical
target detection and tracking. Additionally, it may be necessary
to detect and track a large number of objects in the threat cloud,
and these objects may not always be resolvable in individual data
frames. In the present paper, the performance of the developed
algorithms is demonstrated using real-world data containing resident
space objects observed from the MSX platform, with backgrounds varying
from celestial to combined celestial and earth limb, with instances
of extremely bright aurora clutter. Simulation results are also
presented for parameterized variations in signal-to-clutter levels
(down to 1/1000) and signal-to-noise levels (down to 1/6) for simulated
targets against real-world terrestrial clutter backgrounds. We also
discuss algorithm processing requirements and C++ software processing
capabilities from our on-going MDA- and AFRL-sponsored development
of an image processing toolkit (iPTK). In the current effort, the
iPTK is being developed to a Technology Readiness Level (TRL) of 6
by mid-2010, in preparation for possible integration with STSS-like,
SBIRS high-like and SBSS-like surveillance suites.
Title: Scattering polarization due to light source anisotropy
Authors: Ignace, R; Al-Malki, M; Simmons, J; Brown, J C; Clarke, D;
Carson, J
Bibcode: 2008arXiv0812.2772I
Altcode:
We consider the polarization arising from scattering in an envelope
illuminated by a central anisotropic source. Spherical harmonics are
used to describe both the light source anisotropy and the envelope
density distribution functions of the scattering particles. This
framework demonstrates how the net resultant polarization arises from
a superposition of three basic "shape" functions: the distribution
of source illumination, the distribution of envelope scatterers,
and the phase function for dipole scattering. Specific expressions
for the Stokes parameters and scattered flux are derived for the
case of an ellipsoidal light source inside an ellipsoidal envelope,
with principal axes that are generally not aligned. Two illustrative
examples are considered: (a) axisymmetric mass loss from a rapidly
rotating star, such as may apply to some Luminous Blue Variables, and
(b) a Roche-lobe filling star in a binary system with a circumstellar
envelope. As a general conclusion, the combination of source anisotropy
with distorted scattering envelopes leads to more complex polarimetric
behavior such that the source characteristics should be carefully
considered when interpreting polarimetric data.
Title: Science with ASKAP. The Australian square-kilometre-array
pathfinder
Authors: Johnston, S.; Taylor, R.; Bailes, M.; Bartel, N.; Baugh,
C.; Bietenholz, M.; Blake, C.; Braun, R.; Brown, J.; Chatterjee,
S.; Darling, J.; Deller, A.; Dodson, R.; Edwards, P.; Ekers, R.;
Ellingsen, S.; Feain, I.; Gaensler, B.; Haverkorn, M.; Hobbs, G.;
Hopkins, A.; Jackson, C.; James, C.; Joncas, G.; Kaspi, V.; Kilborn,
V.; Koribalski, B.; Kothes, R.; Landecker, T.; Lenc, E.; Lovell, J.;
Macquart, J. -P.; Manchester, R.; Matthews, D.; McClure-Griffiths,
N.; Norris, R.; Pen, U. -L.; Phillips, C.; Power, C.; Protheroe, R.;
Sadler, E.; Schmidt, B.; Stairs, I.; Staveley-Smith, L.; Stil, J.;
Tingay, S.; Tzioumis, A.; Walker, M.; Wall, J.; Wolleben, M.
Bibcode: 2008ExA....22..151J
Altcode: 2008arXiv0810.5187J; 2008ExA...tmp...49J
The future of cm and m-wave astronomy lies with the Square Kilometre
Array (SKA), a telescope under development by a consortium of 17
countries. The SKA will be 50 times more sensitive than any existing
radio facility. A majority of the key science for the SKA will be
addressed through large-area imaging of the Universe at frequencies
from 300 MHz to a few GHz. The Australian SKA Pathfinder (ASKAP)
is aimed squarely in this frequency range, and achieves instantaneous
wide-area imaging through the development and deployment of phase-array
feed systems on parabolic reflectors. This large field-of-view
makes ASKAP an unprecedented synoptic telescope poised to achieve
substantial advances in SKA key science. The central core of ASKAP
will be located at the Murchison Radio Observatory in inland Western
Australia, one of the most radio-quiet locations on the Earth and one
of the sites selected by the international community as a potential
location for the SKA. Following an introductory description of ASKAP,
this document contains 7 chapters describing specific science programmes
for ASKAP. In summary, the goals of these programmes are as follows:
The detection of a million galaxies in atomic hydrogen emission
across 75% of the sky out to a redshift of 0.2 to understand galaxy
formation and gas evolution in the nearby Universe.
Title: Magnetically Fed Hot Star Keplerian Disks with Slow Outflow
Authors: Brown, J. C.; Cassinelli, J. P.; Maheswaran, M.
Bibcode: 2008ApJ...688.1320B
Altcode:
The puzzle of the origin of Be star disks is discussed. Contrary
to recently published claims, it is argued that the magnetically
torqued disk (MTD) type models of Cassinelli et al. offer a viable
scenario for a successful model with all the key ingredients. MTD
models involve disk compression by equatorial collision of stellar
wind streams that are steered and torqued by a dipole-like magnetic
field. While the growing disk density tends to lead to the gas breaking
out centrifugally from the field, it is proposed that the onset of
viscous effects can lead to an eventual stable, slowly outflowing,
Keplerian disk. It is then shown that the resulting very dense
(wind compressed) disk need have only a very slow subsonic outflow
to satisfy mass continuity. Consequently, line profile data do not
preclude steadily expanding disks of high density. It is also shown
that the time taken to reach the steady state would typically be of
the order of 104 wind flow times R/v∞. This
is far longer than the run times of recent numerical MHD simulations
that displayed bursty breakout behavior, which may therefore only be
transients induced by unrealistic initial conditions.
Title: Fast spectral fitting of hard X-ray bremsstrahlung from
truncated power-law electron spectra
Authors: Brown, J. C.; Kašparová, J.; Massone, A. M.; Piana, M.
Bibcode: 2008A&A...486.1023B
Altcode: 2008arXiv0802.0621B
Context: Hard X-ray bremsstrahlung continuum spectra, such as from solar
flares, are commonly described in terms of power-law fits, either to the
photon spectra themselves or to the electron spectra responsible for
them. In applications various approximate relations between electron
and photon spectral indices are often used for energies both above
and below electron low-energy cutoffs.
Aims: We examine the
form of the exact relationships in various situations, and for various
cross-sections, showing that empirical relations sometimes used can be
highly misleading especially at energies below the low-energy cutoff,
and consider how to improve fitting procedures.
Methods: We
obtain expressions for photon spectra from single, double and truncated
power-law electron spectra for a variety of cross-sections and for
the thin and thick target models and simple analytic expressions for
the non-relativistic Bethe-Heitler case.
Results: We show that
below the low-energy cutoff Kramers and other constant spectral index
forms commonly used are very poor approximations to accurate results,
but that our analytical forms are a good match; and that above a
low-energy cutoff, the Kramers and non-relativistic Bethe-Heitler
results match reasonably well with results for up to energies around
100 keV.
Conclusions: Analytical forms of the non-relativistic
Bethe-Heitler photon spectra from general power-law electron spectra
are good match to exact results for both thin and thick targets and
they enable much faster spectral fitting than evaluation of the full
spectral integrations.
Title: RHESSI Microflares: II. Implications for Loop Structure
and Evolution
Authors: Stoiser, S.; Brown, J. C.; Veronig, A. M.
Bibcode: 2008SoPh..250..315S
Altcode: 2008SoPh..tmp..127S
We present simple analytic models which predict the peak X-ray
emission measure and temperature attained in flares in which the
chromospheric evaporation process takes place either in a single
`monolithic' loop or in a loop consisting of several filaments that
are created successively as the energy release process proceeds
in time. As possible mechanisms driving chromospheric evaporation
we consider both classical heat conduction from the loop top and
non-thermal electron beams. The model predictions are tested for a
set of 18 well studied RHESSI microflares. The results suggest beam
driven evaporation in filamented loops as being capable of accounting
for the observed emission measures and temperatures though there are
issues with the very high beam densities needed. On the other hand,
estimates of the emission measures achieved by conductive evaporation
which are derived by using the Rosner - Tucker - Vaiana (RTV) scaling
law are much larger than the observed ones. Possible reasons for this
discrepancy are discussed.
Title: Thermohaline circulation of shallow tidal seas
Authors: Hill, A. E.; Brown, J.; Fernand, L.; Holt, J.; Horsburgh,
K. J.; Proctor, R.; Raine, R.; Turrell, W. R.
Bibcode: 2008GeoRL..3511605H
Altcode:
The mechanisms controlling the temperature and salinity structure of
shallow continental shelf seas have been understood for over thirty
years, yet knowledge of what drives their large-scale circulation has
remained relatively unknown. Here we describe a decade long programme of
measurements, using satellite-tracked drifting buoys on the northwest
European shelf, to draw attention to a striking picture of highly
organised thermohaline circulation consisting of narrow, near surface,
fast flowing jets. These are ubiquitous above sharp horizontal gradients
in bottom temperatures and/or salinities. The circulation phenomena
we describe are likely to be prevalent on all similar, wide, tidally
energetic continental shelves including those off north-eastern China,
Argentina and parts of the Arctic. The robust, repeatable observation
of the key role of jets above bottom fronts results in a fundamental
reassessment of how we view the dynamics of shelf seas.
Title: The Outer Scale of Turbulence in the Magnetoionized Galactic
Interstellar Medium
Authors: Haverkorn, M.; Brown, J. C.; Gaensler, B. M.;
McClure-Griffiths, N. M.
Bibcode: 2008ApJ...680..362H
Altcode: 2008arXiv0802.2740H
We analyze Faraday rotation and depolarization of extragalactic
radio point sources in the direction of the inner Galactic plane to
determine the outer scale and amplitude of the rotation measure power
spectrum. Structure functions of rotation measure show lower amplitudes
than expected when extrapolating electron density fluctuations to
large scales assuming a Kolmogorov spectral index. This implies an
outer scale of those fluctuations on the order of a parsec, much
smaller than commonly assumed. Analysis of the partial depolarization
of point sources independently indicates a small outer scale of a
Kolmogorov power spectrum. In the Galaxy's spiral arms, no rotation
measure fluctuations on scales above a few parsecs are measured. In
the interarm regions fluctuations on larger scales than in spiral arms
are present, and show power-law behavior with a shallow spectrum. These
results suggest that in the spiral arms stellar sources such as stellar
winds or protostellar outflows dominate the energy injection for
the turbulent energy cascade on parsec scales, while in the interarm
regions supernova and superbubble explosions are the main sources of
energy on scales on the order of 100 pc.
Title: The c2d Spitzer Spectroscopic Survey of Ices around Low-Mass
Young Stellar Objects. I. H2O and the 5-8 μm Bands
Authors: Boogert, A. C. A.; Pontoppidan, K. M.; Knez, C.; Lahuis, F.;
Kessler-Silacci, J.; van Dishoeck, E. F.; Blake, G. A.; Augereau,
J. -C.; Bisschop, S. E.; Bottinelli, S.; Brooke, T. Y.; Brown, J.;
Crapsi, A.; Evans, N. J., II; Fraser, H. J.; Geers, V.; Huard, T. L.;
Jørgensen, J. K.; Öberg, K. I.; Allen, L. E.; Harvey, P. M.; Koerner,
D. W.; Mundy, L. G.; Padgett, D. L.; Sargent, A. I.; Stapelfeldt, K. R.
Bibcode: 2008ApJ...678..985B
Altcode: 2008arXiv0801.1167B
To study the physical and chemical evolution of ices in
solar-mass systems, a spectral survey is conducted of a sample
of 41 low-luminosity YSOs (L ~ 0.1-10 L⊙) using 3-38
μm Spitzer and ground-based spectra. The sample is complemented
with previously published Spitzer spectra of background stars and
with ISO spectra of well-studied massive YSOs (L ~ 105
L⊙). The long-known 6.0 and 6.85 μm bands are detected
toward all sources, with the Class 0-type YSOs showing the deepest
bands ever observed. The 6.0 μm band is often deeper than expected
from the bending mode of pure solid H2O. The additional
5-7 μm absorption consists of five independent components, which,
by comparison to laboratory studies, must be from at least eight
different carriers. Much of this absorption is due to simple species
likely formed by grain surface chemistry, at abundances of 1%-30%
for CH3OH, 3%-8% for NH3, 1%-5% for HCOOH,
~6% for H2CO, and ~0.3% for HCOO- relative to
solid H2O. The 6.85 μm band has one or two carriers, of
which one may be less volatile than H2O. Its carrier(s)
formed early in the molecular cloud evolution and do not survive in
the diffuse ISM. If an NH4+-containing salt is
the carrier, its abundance relative to solid H2O is ~7%,
demonstrating the efficiency of low-temperature acid-base chemistry
or cosmic-ray-induced reactions. Possible origins are discussed for
enigmatic, very broad absorption between 5 and 8 μm. Finally, the
same ices are observed toward massive and low-mass YSOs, indicating
that processing by internal UV radiation fields is a minor factor in
their early chemical evolution.
Title: Non-thermal recombination - a neglected source of flare hard
X-rays and fast electron diagnostic
Authors: Brown, J. C.; Mallik, P. C. V.
Bibcode: 2008A&A...481..507B
Altcode: 2007arXiv0706.2823B
Context: Flare Hard X-rays (HXRs) from non-thermal electrons
are commonly treated as solely bremsstrahlung (free-free = f-f),
recombination (free-bound = f-b) being neglected. This assumption is
shown to be substantially in error, especially in hot sources, mainly
due to recombination onto Fe ions.
Aims: We analyse the effects
on HXR spectra J(ɛ) and electron diagnostics by including non-thermal
recombination onto heavy elements in our model.
Methods: Using
Kramers hydrogenic cross sections with effective Z=Z_eff, we calculate
f-f and f-b spectra for power-law electron spectra within both thin
and thick target limits and for Maxwellians with summation over all
important ions.
Results: We find that non-thermal electron
recombination, especially onto Fe, must, in general, be included with
f-f for reliable spectral interpretation, when the HXR source is hot,
such as occulted loops containing high ions of Fe (f-b cross-section
∝ Z^4). The f-b contribution is greatest when the electron spectral
index δ is large and any low energy cut-off Ec is small,
because the electron flux spectrum F(E) emitting f-b photon energy
ɛ is ∝ (E=ɛ-V_Z)-δ (VZ is the ionisation
potential) and not ∝ (E=ɛ)-δ+1 as for f-f. The f-b
spectra recombination edges mean a cut-off Ec in F(E)
appears as an HXR feature at ɛ = Ec + V_Z, offering an
Ec diagnostic. For thick target sources, the presence of
Ec appears as edges in J'(ɛ), not in J(ɛ), but it is
still detectable. Including f-b lowers the F(E) needed for prescribed
HXR fluxes greatly in some cases; and even when small, it seriously
distorts F(E) as inferred by inversion or forward fitting of J(ɛ)
based on f-f alone.
Conclusions: The f-b recombination from
non-thermal electrons can be an important contributor to HXR spectra,
so it should be included in spectral analyses, especially for hot
sources. Accurate results will require use of better cross sections
than ours and consideration of source ionisation structure.
Title: Volcano Topography and Apparent Viscosity of the Crust on Mars
Authors: Brown, J.; Li, Q.
Bibcode: 2008LPI....39.1409B
Altcode:
This project explores the potential viscous deformation of the crust
on Mars by focusing on the major volcanos of the planet in addition
to placing constraints on the average apparent crustal viscosity.
Title: X-Ray Emission from Magnetically Torqued Disks of Oe/Be Stars
Authors: Li, Q.; Cassinelli, J. P.; Brown, J. C.; Waldron, W. L.;
Miller, N. A.
Bibcode: 2008ApJ...672.1174L
Altcode: 2007arXiv0710.2633L
The near-main-sequence B stars show a sharp dropoff in their
X-ray-to-bolometric luminosity ratio in going from B1 to later spectral
types. Here we focus attention on the subset of these stars that are
also Oe/Be stars, to test the concept that the disks of these stars form
by magnetic channeling of wind material toward the equator. Calculations
are made of the X-rays expected from the magnetically torqued disk
(MTD) model for Be stars discussed by Cassinelli et al., Maheswaran,
and Brown et al. In this model, the wind outflow from Be stars is
channeled and torqued by a magnetic field such that the flows from
the upper and lower hemispheres of the star collide as they approach
the equatorial zone. X-rays are produced by the material that enters
the shocks above and below the disk region and radiatively cools
and compresses while moving toward the MTD central plane. The model
predictions are compared with ROSAT observations obtained for an O9.5
star, ζ Oph, by Berghöfer et al. and for seven Be stars from Cohen
et al. Two types of fitting models are used to compare predictions
with observations of X-ray luminosity versus spectral type. Extra
consideration is also given here to the well-studied Oe star ζ Oph,
for which we have Chandra observations of the X-ray line profiles
of the triad of He-like lines from the ion Mg XI. Thus, the X-ray
properties add to the list of observables that can be explained within
the context of the MTD concept. This list already includes the Hα
equivalent widths and white-light polarization of Be stars.
Title: XMM-Newton X-ray study of early type stars in the Carina
OB1 association
Authors: Antokhin, I. I.; Rauw, G.; Vreux, J. -M.; van der Hucht,
K. A.; Brown, J. C.
Bibcode: 2008A&A...477..593A
Altcode: 2007arXiv0711.3612A
Aims:X-ray properties of the stellar population in the Carina
OB1 association are examined with special emphasis on early-type
stars. Their spectral characteristics provide some clues to
understanding the nature of X-ray formation mechanisms in the winds
of single and binary early-type stars.
Methods: A timing and
spectral analysis of five observations with XMM-Newton is performed
using various statistical tests and thermal spectral models.
Results: 235 point sources have been detected within the field of
view. Several of these sources are probably pre-main sequence stars
with characteristic short-term variability. Seven sources are possible
background AGNs. Spectral analysis of twenty four sources of type OB
and WR 25 was performed. We derived spectral parameters of the sources
and their fluxes in three energy bands. Estimating the interstellar
absorption for every source and the distance to the nebula, we derived
X-ray luminosities of these stars and compared them to their bolometric
luminosities. We discuss possible reasons for the fact that, on average,
the observed X-ray properties of binary and single early type stars are
not very different, and give several possible explanations. Based
on observations obtained with XMM-Newton, an ESA science mission with
instruments and contributions directly funded by ESA Member States and
the USA (NASA). The X-ray catalogue and its cross-identification with
infra-red and optical catalogues (Tables [see full textsee full textsee
full textsee full textsee full textsee full textsee full textsee full
textsee full textsee full text] and [see full textsee full textsee
full textsee full textsee full textsee full textsee full textsee full
textsee full textsee full text]) 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/477/593 Sample
Tables [see full textsee full textsee full textsee full textsee full
textsee full textsee full textsee full textsee full textsee full text]
and [see full textsee full textsee full textsee full textsee full
textsee full textsee full textsee full textsee full textsee full text]
are only available in electronic form at http://www.aanda.org
Title: Unmixing the Materials and Mechanics Contributions in
Non-resolved Object Signatures
Authors: Chaudhary, A.; Birkemeier, C.; Gregory, S.; Payne, T.;
Brown, J.
Bibcode: 2008amos.confE..39C
Altcode:
Temporal behavior of a non-resolved resident space object [RSO]
signature is a function of the abundance of its contributing
materials. These abundances are, in turn, a function of the orbital
behavior of the RSO. For example, in case of a spin-stabilized RSO,
the abundances display a cyclic behavior. The present work uses
a positive matrix factorization technique to extract the temporal
variation of material abundances from hyperspectral or multi-spectral
time-resolved signatures. A Fourier analysis of temporal variation
of material abundance provides knowledge about the mechanics of the
space object. This paper describes the unmixing and Fourier analysis
process that, taken together, extract information about materials
and mechanics from non-resolved RSO signatures. Unmixing results
are presented for simulated hyperspectral signatures and for three-
or four-color Johnson BVRI photometry observations data. These two
situations cover the range of optics and sensor capabilities that
may be available from a premier site for optical observations to a
commercial-off-the-shelf small-aperture telescope site.
Title: Space Object Characterization with 16-Visible-Band Measurements
at Magdalena Ridge Observatory
Authors: Dao, P.; McNicholl, P.; Brown, J.; Cowley, J.; Kendra, M.;
Crabtree, P.; Dentamaro, A.; Ryan, E.; Ryan, W.
Bibcode: 2008amos.confE..57D
Altcode:
Data was collected at the Magdalena Ridge Observatory (MRO)
with the Multi Lens Array (MLA) camera coupled to the MRO 2.4 m
telescope. MRO is located at 33.985oN, 252.811oE at an altitude of
3193 m, approximately 30 miles West of Socorro, NM. The MRO facilities
are intended for both astronomical research and Resident Space Object
(RSO) characterization. The purpose of the measurement campaign was
to collect both resolved images and unresolved signatures of RSOs in
16 spectral bands, ranging from 414 nm to 845 nm. During the campaign,
observations were made over five sessions for the period 21-27 September
2007. During that time we succeeded in observing and collecting data
for 18 different calibration stars and 40 different RSOs, mostly
those in Low Earth Orbit (LEO). A major objective of the measurement
campaign is to collect RSO data that can be used to select spectral
bands optimized for estimating surface material composition. The
analysis results help determine the nominal spectral differences for
typical RSO materials. The paper will discuss the potential of using
a multiband camera for RSO identification and characterization.
Title: Science with the Australian Square Kilometre Array Pathfinder
Authors: Johnston, S.; Bailes, M.; Bartel, N.; Baugh, C.; Bietenholz,
M.; Blake, C.; Braun, R.; Brown, J.; Chatterjee, S.; Darling, J.;
Deller, A.; Dodson, R.; Edwards, P. G.; Ekers, R.; Ellingsen, S.;
Feain, I.; Gaensler, B. M.; Haverkorn, M.; Hobbs, G.; Hopkins, A.;
Jackson, C.; James, C.; Joncas, G.; Kaspi, V.; Kilborn, V.; Koribalski,
B.; Kothes, R.; Landecker, T. L.; Lenc, E.; Lovell, J.; Macquart,
J. -P.; Manchester, R.; Matthews, D.; McClure-Griffiths, N. M.; Norris,
R.; Pen, U. -L.; Phillips, C.; Power, C.; Protheroe, R.; Sadler, E.;
Schmidt, B.; Stairs, I.; Staveley-Smith, L.; Stil, J.; Taylor, R.;
Tingay, S.; Tzioumis, A.; Walker, M.; Wall, J.; Wolleben, M.
Bibcode: 2007PASA...24..174J
Altcode: 2007arXiv0711.2103J
The future of centimetre and metre-wave astronomy lies with the Square
Kilometre Array (SKA), a telescope under development by a consortium
of 17 countries that will be 50 times more sensitive than any existing
radio facility. Most of the key science for the SKA will be addressed
through large-area imaging of the Universe at frequencies from a
few hundred MHz to a few GHz. The Australian SKA Pathfinder (ASKAP)
is a technology demonstrator aimed in the mid-frequency range, and
achieves instantaneous wide-area imaging through the development and
deployment of phased-array feed systems on parabolic reflectors. The
large field-of-view makes ASKAP an unprecedented synoptic telescope
that will make substantial advances in SKA key science. ASKAP will be
located at the Murchison Radio Observatory in inland Western Australia,
one of the most radio-quiet locations on the Earth and one of two
sites selected by the international community as a potential location
for the SKA. In this paper, we outline an ambitious science program
for ASKAP, examining key science such as understanding the evolution,
formation and population of galaxies including our own, understanding
the magnetic Universe, revealing the transient radio sky and searching
for gravitational waves.
Title: Electron-Electron Bremsstrahlung Emission and the Inference
of Electron Flux Spectra in Solar Flares
Authors: Kontar, Eduard P.; Emslie, A. Gordon; Massone, Anna Maria;
Piana, Michele; Brown, John C.; Prato, Marco
Bibcode: 2007ApJ...670..857K
Altcode: 2007arXiv0707.4225K
Although both electron-ion and electron-electron bremsstrahlung
contribute to the hard X-ray emission from solar flares, the latter
is normally ignored. Such an omission is not justified at electron
(and photon) energies above ~300 keV, and inclusion of the additional
electron-electron bremsstrahlung in general makes the electron
spectrum required to produce a given hard X-ray spectrum steeper at
high energies. Unlike electron-ion bremsstrahlung, electron-electron
bremsstrahlung cannot produce photons of all energies up to the electron
energy involved. The maximum possible photon energy depends on the angle
between the direction of the emitting electron and the emitted photon,
and this suggests a diagnostic for an upper cutoff energy and/or for
the degree of beaming of the accelerated electrons. We analyze the
large event of 2005 January 17 and show that the upward break around
400 keV in the observed hard X-ray spectrum is naturally accounted for
by the inclusion of electron-electron bremsstrahlung. Indeed, the mean
source electron spectrum recovered through a regularized inversion
of the hard X-ray spectrum, using a cross section that includes both
electron-ion and electron-electron terms, has a relatively constant
spectral index δ over the range from electron kinetic energy E=200 keV
to E=1 MeV. Such a spectrum is indicative of an acceleration mechanism
without a characteristic energy or corresponding scale.
Title: VizieR Online Data Catalog: X-ray properties of Carina OB1
association (Antokhin+, 2008)
Authors: Antokhin, I. I.; Rauw, G.; Vreux, J. -M.; van der Hucht,
K. A.; Brown, J. C.
Bibcode: 2007yCat..34770593A
Altcode:
X-ray catalogue of sources detected with XMM-Newton in the Carina OB1
association is presented. X-ray count rates in three energy bands and
the X-ray variability status are given. Cross-identifications of X-ray
sources with optical and infrared catalogues are also presented. (2 data files).
Title: Meeting contribution: Abra Cad Astra
Authors: Brown, J.
Bibcode: 2007JBAA..117..212B
Altcode:
No abstract at ADS
Title: Joint Discussion 1 Particle acceleration from solar system
to AGN
Authors: Karlický, Marian; Brown, John C.
Bibcode: 2007HiA....14...79K
Altcode:
The scene is set for IAU JD01 on Cosmic Particle Acceleration: from
Solar System to AGNs
Title: Volcano Topography and Apparent Viscosity of the Crust on Mars
Authors: Brown, J.; Li, Q.
Bibcode: 2007lpii.conf....7B
Altcode:
No abstract at ADS
Title: Rotation Measures of Extragalactic Sources behind the Southern
Galactic Plane: New Insights into the Large-Scale Magnetic Field of
the Inner Milky Way
Authors: Brown, J. C.; Haverkorn, M.; Gaensler, B. M.; Taylor, A. R.;
Bizunok, N. S.; McClure-Griffiths, N. M.; Dickey, J. M.; Green, A. J.
Bibcode: 2007ApJ...663..258B
Altcode: 2007arXiv0704.0458B
We present new Faraday rotation measures (RMs) for 148
extragalactic radio sources behind the southern Galactic
plane (253deg<=l<=356deg,
|b|<=1.5deg), and use these data in combination with
published data to probe the large-scale structure of the Milky Way's
magnetic field. We show that the magnitudes of these RMs oscillate
with longitude in a manner that correlates with the locations of the
Galactic spiral arms. The observed pattern in RMs requires the presence
of at least one large-scale magnetic reversal in the fourth Galactic
quadrant, located between the Sagittarius-Carina and Scutum-Crux
spiral arms. To quantitatively compare our measurements to other
recent studies, we consider all available extragalactic and pulsar RMs
in the region we have surveyed, and jointly fit these data to simple
models in which the large-scale field follows the spiral arms. In the
best-fitting model, the magnetic field in the fourth Galactic quadrant
is directed clockwise in the Sagittarius-Carina spiral arm (as viewed
from the north Galactic pole), but is oriented counterclockwise in
the Scutum-Crux arm. This contrasts with recent analyses of pulsar
RMs alone, in which the fourth-quadrant field was presumed to be
directed counterclockwise in the Sagittarius-Carina arm. Also in
contrast to recent pulsar RM studies, our joint modeling of pulsar
and extragalactic RMs demonstrates that large numbers of large-scale
magnetic field reversals are not required to account for observations.
Title: Probing the inner accretion disk using Spitzer c2d mid-infrared
spectra
Authors: Olofsson, J.; Augereau, J. -C.; Kessler-Silacci, J. E.; Evans,
N. J., II; Dullemond, C. P.; Merín, B.; Geers, V. C.; van Dishoeck,
E. F.; Blake, G. A.; Brown, J.
Bibcode: 2007sf2a.conf..541O
Altcode:
Mid-infrared emission from silicates grains around young stars arises
from the inner disks regions (at distances smaller than a few AU),
and can serve to probe the dust content and disk structure close to
the inner disk edge. We obtained more than a hundred of Spitzer/IRS
spectra in a 5-35 μm range, as part of the Cores to Disks (c2d)
Legacy Program. The sample consists of mostly Class II objects (T
Tauri) and they all show silicate emission features. In addition,
a large fraction of them (∼ 80%, Olofsson et al. in prep) show
at least one crystalline silicate feature which could be attributed
to crystalline Mg-rich silicates (forsterite or enstatite) or other
crystalline components (diopside, etc). A statistical study, led by
Kessler-Silacci et al. (2006, 2007), evidenced a correlation between
the spectral type of the central star and the silicate grain size. This
correlation finds an explanation considering the illumination from the
star (the 10 μm emission zone is closer to the star for less luminous
sources; less than a tenth of AU for a star luminosity smaller than
∼ 0.01 L&odotB}) and by the fact that the grains are,
on average, expected to be larger at smaller radii. These results
were obtained using the CGPlus two-layer disk model, therefore only
geometrical considerations were studied. Future modelling including
more details of grain coagulation, thermal processing and accretion
events will be needed to strengthen this study. But the complexity of
such modelling is beyond the scope of this poster.
Title: Hard X-ray spectra and positions of solar flares observed by
RHESSI: photospheric albedo, directivity and electron spectra
Authors: Kašparová, J.; Kontar, E. P.; Brown, J. C.
Bibcode: 2007A&A...466..705K
Altcode: 2007astro.ph..1871K
Aims:We investigate the signature of the photospheric albedo
contribution in solar flare hard X-ray spectra, the effect of low
energy cutoffs in electron spectra, and the directivity of hard X-ray
emission.
Methods: Using Ramaty High Energy Solar Spectroscopic
Imager (RHESSI) flare data we perform a statistical analysis of
spatially integrated spectra and positions of solar flares.
Results: We demonstrate clear centre-to-limb variation of photon
spectral indices in the 15-20 keV energy range and a weaker dependency
in the 20-50 keV range which is consistent with photospheric albedo as
the cause. The results also suggest that low-energy cutoffs sometimes
inferred in mean electron spectra are an artefact of albedo. We also
derive the anisotropy (ratio of downward/observer directed photons)
of hard X-ray emission in the 15-20 keV range for various heliocentric
angles.
Title: Probing Protoplanetary Disks with Silicate Emission: Where
Is the Silicate Emission Zone?
Authors: Kessler-Silacci, J. E.; Dullemond, C. P.; Augereau, J. -C.;
Merín, B.; Geers, V. C.; van Dishoeck, E. F.; Evans, N. J., II;
Blake, G. A.; Brown, J.
Bibcode: 2007ApJ...659..680K
Altcode: 2006astro.ph.12450K
Recent results indicate that the grain size and crystallinity
inferred from observations of silicate features may be correlated
with the spectral type of the central star and/or disk geometry. In
this paper, we show that grain size, as probed by the 10 μm
silicate feature peak-to-continuum and 11.3 to 9.8 μm flux
ratios, is inversely proportional to logL*. These
trends can be understood using a simple two-layer disk model for
passive irradiated flaring disks, CGPLUS. We find that the radius,
R10, of the 10 μm silicate emission zone in the disk goes as
(L*/Lsolar)0.56, with slight variations
depending on disk geometry (flaring angle and inner disk radius). The
observed correlations, combined with simulated emission spectra of
olivine and pyroxene mixtures, imply a dependence of grain size on
luminosity. Combined with the fact that R10 is smaller for
less luminous stars, this implies that the apparent grain size of the
emitting dust is larger for low-luminosity sources. In contrast, our
models suggest that the crystallinity is only marginally affected,
because for increasing luminosity, the zone for thermal annealing
(assumed to be at T>800 K) is enlarged by roughly the same factor as
the silicate emission zone. The observed crystallinity is affected by
disk geometry, however, with increased crystallinity in flat disks. The
apparent crystallinity may also increase with grain growth due to a
corresponding increase in contrast between crystalline and amorphous
silicate emission bands.
Title: First Results from the Stopped RISING Campaign at GSI: The
Mapping of Isomeric Decays in Highly Exotic Nuclei
Authors: Regan, P. H.; Garnsworthy, A. B.; Steer, S. J.; Pietri, S.;
Podolyák, Zs.; Rudolph, D.; Górska, M.; Caceres, L.; Werner-Malento,
E.; Gerl, J.; Wollersheim, H. J.; Becker, F.; Bednarczyk, P.;
Doornenbal, P. D.; Geissel, H.; Grawe, H.; GreBosz, J.; Hoischen,
R.; Kelic, A.; Kojouharov, I.; Kurz, N.; Montes, F.; Prokopowicz,
W.; Saito, T.; Schaffner, H.; Tashenov, S.; Heinz, A.; Pfützner,
M.; Kurtukian-Nieto, T.; Benzoni, G.; Hellström, M.; Jungclaus,
A.; Andersson, L. -L.; Atanasova, L.; Balabanski, D. L.; Bentley,
M. A.; Blank, B.; Blazhev, A.; Brandau, C.; Brown, J.; Bruce, A. M.;
Camera, F.; Catford, W. N.; Cullen, I. J.; Dombradi, Zs.; Estevez,
E.; Fahlander, C.; Gelletly, W.; Ilie, G.; Johansson, E. K.; Jolie,
J.; Jones, G. A.; Kmiecik, M.; Kondev, F. G.; Lalkovski, S.; Liu,
Z.; Maj, A.; Myalski, S.; Schwertel, S.; Shizuma, T.; Simons, A. J.;
Walker, P. M.; Wieland, O.
Bibcode: 2007AIPC..899...19R
Altcode:
The first results from the Stopped Beam RISING experimental
campaign performed at the GSI laboratory in Darmstadt, Germany, are
presented. RISING (Rare ISotope INvestigations at GSI) constitutes a
major new experimental program in European nuclear structure physics
research aimed at using relativistic-energy, projectile-fragmentation
reactions to study nuclei with exotic proton-to-neutron ratios. This
paper introduces the physics aims of the Stopped RISING collaboration
and presents some technical details and initial results from experiments
using the RISING array to study decays from metastable nuclear states
in both proton and neutron-rich nuclei.
Title: Birth and evolution of a dense coronal loop in a complex
flare region
Authors: Bone, L.; Brown, J. C.; Fletcher, L.; Veronig, A.; White, S.
Bibcode: 2007A&A...466..339B
Altcode:
Context: During the 14th/15th of April 2002, several flares occurred
in NOAA active region complex 9893/9910. Two of these were previously
interpreted as having anomalously high coronal column densities.
Aims: We develop a scenario using multiwavelength observations
to explain the high coronal column density (≈1020
cm-2) present at the onset of the 14th April 2002 M3.7
hard X-ray event.
Methods: Prior to this event a series of
flares occurred in close temporal and spatial proximity. We observe
the sequence of flares in a multiwavelength regime from radio to hard
X-rays. This allows us to study the particle acceleration and plasma
evaporation in these events.
Results: The observations of these
flares lead us to propose a sequence of reconnections between multiple
systems of loops in a 3 dimensional field geometry. We suggest that
the dense loops in the M3.7 event can be explained as being already
filled with plasma from the earlier events; these loops then themselves
become unstable or reconnect leading to particle acceleration into
an overdense coronal environment. We explore the possibility that a
high-beta disruption is behind the instability of these dense loops,
leading to the 14th April 2002 M3.7 event and the observation of hard
X-rays in the corona at energies up to ≈50 keV.
Title: SAMM-2: A Rapid, Modular and Extensible All-Altitude VIS-IR
Background Scene Generator
Authors: Panfili, R.; Dothe, H.; Gruninger, J.; Duff, J.; Brown, J.
Bibcode: 2007amos.confE..34P
Altcode:
This talk describes recent upgrades to SAMM-2, a background radiance
and transmission code. SAMM-2 incorporates all of the major components
necessary for background scene generation at all altitudes: atmospheric
characterization, solar irradiance, molecular chemical kinetics and
molecular spectroscopic data. In addition, it seamlessly combines
MODTRAN, a standard low-altitude local thermodynamic equilibrium
model (LTE), with SAMM-1 and SHARC, standard high-altitude non-local
thermodynamic equilibrium models (NLTE) to form a single, unified
code with comprehensive coverage in the .4 to 40 micron (250 to 25,000
wavenumber) wavelength region for arbitrary lines-of-sight in the 0 to
300 kilometer altitude regime. Efforts are currently underway to
upgrade SAMM-2 from a code primarily used for line-of-sight computations
to an efficient scene generator. The inclusion of new, high-efficiency
radiation transport (RT) algorithms is central to this upgrade. To this
end, Spectral Sciences, Inc. (SSI) has developed an NLTE correlated-k RT
model which provides a factor-of-100 speed increase over the existing
line-by-line model (QBL) in SAMM-2. This model is able to simulate
atmospheric stochastic structure as defined by a temperature and
density fluctuation model in addition to clear atmosphere radiance
and transmission. In addition, a new NLTE band model developed by SSI
provides a factor-of-1000 speed increase over the QBL model. The
proliferation of RT algorithms within SAMM-2 provides the impetus to
open SAMM-2 to a wider developer community. SAMM-2 will communicate with
its RT algorithms through a well-defined interface. This interface will
guarantee inter-operability while allowing for independent development
of SAMM-2 and the third-party algorithms in the future. This approach
will allow cutting-edge RT algorithms can be rapidly incorporated
without the need to develop new atmospheric characterization and
molecular chemistry components.
Title: RHESSI Results Time for a Rethink?
Authors: Brown, J. C.; Kontar, E. P.; Veronig, A. M.
Bibcode: 2007LNP...725...65B
Altcode: 2006astro.ph..7440B
Hard X-rays and γ-rays are the most direct signatures of energetic
electrons and ions in the sun’s atmosphere which is optically thin at
these energies and their radiation involves no coherent processes. Being
collisional they are complementary to gyro-radiation in probing
atmospheric density as opposed to magnetic field and the electrons
are primarily 10 100~keV in energy, complementing the (>100 keV)
electrons likely responsible for microwave bursts. The pioneering
results of the Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
are raising the first new major questions concerning solar energetic
particles in many years. Some highlights of these results are discussed
primarily around RHESSI topics on which the authors have had direct
research involvement particularly when they are raising the need for
re-thinking of entrenched ideas. Results and issues are broadly divided
into discoveries in the spatial, temporal and spectral domains, with the
main emphasis on flare hard X-rays/fast electrons but touching also on
γ-rays/ions, non-flare emissions, and the relationship to radio bursts.
Title: A Steady, Radiative-Shock Method for Computing X-Ray Emission
from Colliding Stellar Winds in Close, Massive Star Binaries
Authors: Antokhin, I. I.; Owocki, S. P.; Brown, J. C.
Bibcode: 2007ASPC..367..165A
Altcode:
We present a practical, efficient semi-analytic formalism for
computing steady-state X-ray emission from radiative shocks from
colliding stellar winds in relatively close (orbital period up to
order tens of days), massive-star, binary systems. Our simplified
approach idealizes the individual wind flows as smooth and steady,
ignoring the intrinsic instabilities and associated structure thought
to occur in such flows. By also suppressing thin-shell instabilities
for wind-collision radiative shocks, our steady-state approach avoids
the extensive structure and mixing that has thus far precluded reliable
computation of X-ray emission spectra from time-dependent hydrodynamical
simulations of close-binary, wind-collision systems; but in ignoring the
unknown physical level of such mixing, the luminosity and hardness of
X-ray spectra derived here represent upper limits to what is possible
for a given set of wind and binary parameters.
Title: Stereoscopic Electron Spectroscopy of Solar Hard X-Ray Flares
with a Single Spacecraft
Authors: Kontar, Eduard P.; Brown, John C.
Bibcode: 2006ApJ...653L.149K
Altcode: 2006astro.ph.11170K
Hard X-ray (HXR) spectroscopy is the most direct method of diagnosing
energetic electrons in solar flares. Here we present a technique that
allows us to use a single HXR spectrum to determine an effectively
stereoscopic electron energy distribution. Considering the Sun's
surface to act as a ``Compton mirror'' allows us to look at emitting
electrons also from behind the source, providing vital information
on downward-propagating particles. Using this technique we determine
simultaneously the electron spectra of downward- and upward-directed
electrons for two solar flares observed by the Ramaty High Energy
Solar Spectroscopic Imager (RHESSI). The results reveal surprisingly
near-isotropic electron distributions, which contrast strongly with
the expectations from the standard model that invokes strong downward
beaming, including a collisional thick-target model.
Title: 'Where have all the observers gone'
Authors: Markham, Tony; Brown, John; Heath, Alan W.
Bibcode: 2006JBAA..116..271M
Altcode:
No abstract at ADS
Title: Measurement of the Gamow-Teller strength distribution in Co58
via the Ni58(t,He3) reaction at 115 MeV/nucleon
Authors: Cole, A. L.; Akimune, H.; Austin, Sam M.; Bazin, D.; van
den Berg, A. M.; Berg, G. P. A.; Brown, J.; Daito, I.; Fujita, Y.;
Fujiwara, M.; Gupta, S.; Hara, K.; Harakeh, M. N.; Jänecke, J.;
Kawabata, T.; Nakamura, T.; Roberts, D. A.; Sherrill, B. M.; Steiner,
M.; Ueno, H.; Zegers, R. G. T.
Bibcode: 2006PhRvC..74c4333C
Altcode: 2006nucl.ex...3019C
Electron capture and β decay play important roles in the evolution of
presupernovae stars and their eventual core collapse. These rates are
normally predicted through shell-model calculations. Experimentally
determined strength distributions from charge-exchange reactions
are needed to test modern shell-model calculations. We report on the
measurement of the Gamow-Teller strength distribution in Co58 from
the Ni58(t,He3) reaction with a secondary triton beam of an intensity
of ~106 pps at 115 MeV/nucleon and a resolution of ~250
keV. Previous measurements with the Ni58(n,p) and the Ni58(d,He2)
reactions were inconsistent with each other. Our results support the
latter. We also compare the results to predictions of large-scale
shell-model calculations using the KB3G and GXPF1 interactions
and investigate the impact of differences between the various
experiments and theories in terms of the weak rates in the stellar
environment. Finally, the systematic uncertainties in the normalization
of the strength distribution extracted from Ni58(He3, t) are described
and turn out to be nonnegligible due to large interferences between
the ΔL=0,ΔS=1 Gamow-Teller amplitude and the ΔL=2,ΔS=1 amplitude.
Title: Regularized Reconstruction of the Differential Emission
Measure from Solar Flare Hard X-Ray Spectra
Authors: Prato, M.; Piana, M.; Brown, J. C.; Emslie, A. G.; Kontar,
E. P.; Massone, A. M.
Bibcode: 2006SoPh..237...61P
Altcode: 2006SoPh..tmp....6P
We address the problem of how to test whether an observed solar hard
X-ray bremsstrahlung spectrum (I(∊)) is consistent with a purely
thermal (locally Maxwellian) distribution of source electrons, and,
if so, how to reconstruct the corresponding differential emission
measure (ξ(T)). Unlike previous analysis based on the Kramers and
Bethe-Heitler approximations to the bremsstrahlung cross-section,
here we use an exact (solid-angle-averaged) cross-section. We show
that the problem of determining ξ(T) from measurements of I(∊)
invOlves two successive inverse problems: the first, to recover the
mean source-electron flux spectrum ($\overline{F}$(E)) from I(∊)
and the second, to recover ξ(T) from $\overline{F}$(E). We discuss
the highly pathological numerical properties of this second problem
within the framework of the regularization theory for linear inverse
problems. In particular, we show that an iterative scheme with
a positivity constraint is effective in recovering δ-like forms
of ξ(T) while first-order Tikhonov regularization with boundary
conditions works well in the case of power-law-like forms. Therefore,
we introduce a restoration approach whereby the low-energy part of
$\overline{F}$ (E), dominated by the thermal component, is inverted by
using the iterative algorithm with positivity, while the high-energy
part, dominated by the power-law component, is inverted by using
first-order regularization. This approach is first tested by using
simulated $\overline{F}$(E) derived from a priori known forms of ξ(T)
and then applied to hard X-ray spectral data from the Reuven Ramaty
High Energy Solar Spectroscopic Imager (RHESSI).
Title: The (t,He3) and (He3, t) reactions as probes of Gamow-Teller
strength
Authors: Zegers, R. G. T.; Akimune, H.; Austin, Sam M.; Bazin, D.;
van den Berg, A. M.; Berg, G. P. A.; Brown, B. A.; Brown, J.; Cole,
A. L.; Daito, I.; Fujita, Y.; Fujiwara, M.; Galès, S.; Harakeh,
M. N.; Hashimoto, H.; Hayami, R.; Hitt, G. W.; Howard, M. E.; Itoh,
M.; Jänecke, J.; Kawabata, T.; Kawase, K.; Kinoshita, M.; Nakamura,
T.; Nakanishi, K.; Nakayama, S.; Okumura, S.; Richter, W. A.; Roberts,
D. A.; Sherrill, B. M.; Shimbara, Y.; Steiner, M.; Uchida, M.; Ueno,
H.; Yamagata, T.; Yosoi, M.
Bibcode: 2006PhRvC..74b4309Z
Altcode: 2005nucl.ex..12025Z
It is shown via a study on a Mg26 target that the (t,He3) reaction
at 115 MeV/nucleon reaction is an accurate probe for extracting
Gamow-Teller transition strengths. To do so, the data are complemented
by results from the Mg26(He3, t) reaction at 140 MeV/nucleon that
allows for a comparison of T=2 analog states excited via the mirror
reactions. Extracted Gamow-Teller strengths from Mg26(t,He3) and
Mg26(He3, t) are compared with those from Mg26(d,He2) and Mg26(p,n)
studies, respectively. A good correspondence is found, indicating
probe independence of the strength extraction. Furthermore, we
test shell-model calculations using the new USD-05B interaction
in the sd-model space and show that it reproduces the experimental
Gamow-Teller strength distributions well. In anticipation of further
(t,He3) experiments on medium-heavy nuclei aimed at determining
weak-interaction rates of relevance for stellar evolution, a second
goal of this work is to improve the understanding of the (t,He3) and
(He3, t) reaction mechanisms at intermediate energies because detailed
studies are scarce. The distorted-wave Born approximation is employed,
taking into account the composite structures of the He3 and triton
particles. The reaction model provides the means to explain systematic
uncertainties at the 10% 20% level in the extraction of Gamow-Teller
strengths as being because of interference between Gamow-Teller
ΔL=0,ΔS=1 and ΔL=2,ΔS=1 amplitudes that both contribute to
transitions from 0+ to 1+ states.
Title: The Neupert Effect in Filamented versus Monolithic Solar
Flare Loop Structures
Authors: Stoiser, Sigrid; Brown, J. C.; Veronig, A. M.
Bibcode: 2006SPD....37.1304S
Altcode: 2006BAAS...38R.241S
In many flares, the soft X-ray light curves resemble the time integral
of the corresponding hard X-ray lightcurves, a phenomenon called the
Neupert effect. The favoured explanation is that non-thermal electrons
which emit bremsstrahlung in hard X-rays deposit the bulk of their
energy in collisions in the dense chromosphere. In turn, the cool plasma
in the chromosphere is heated to high temperatures and evaporated into
the corona, which is discernible as a rise of the soft X-ray light
curve and the emission measure.We have investigated if we can attribute
the observed emission measure enhancement at the flare peaks to the
described process of beam driven chromospheric evaporation using a set
of RHESSI microflares (GOES class < C1.4). In contrast, we consider
the case of a thermal flare origin, i.e. if the peak emission measures
of the analysed events agree with the theoretically expected values from
chromospheric evaporation driven by heat conduction. For both cases,
we consider a single loop and a filamentary loop model. We do not
use detailed hydromodelling but use simple analytic expressions. The
work is intended to find explanations for problems encountered when
comparing the empirical to the theoretical Neupert effect as well as
to distinguish between possible formation processes of the analysed
flares. The parameters involved (peak emission measure, temperature,
electron spectral indices, flare geometry variables) are determined
from RHESSI spectroscopy and TRACE 1600 A data in combination with
RHESSI imaging.
Title: Evaluation of Algorithms for Reconstructing Electron Spectra
from Their Bremsstrahlung Hard X-Ray Spectra
Authors: Brown, John C.; Emslie, A. Gordon; Holman, Gordon D.;
Johns-Krull, Christopher M.; Kontar, Eduard P.; Lin, Robert P.;
Massone, Anna Maria; Piana, Michele
Bibcode: 2006ApJ...643..523B
Altcode:
The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has
yielded solar flare hard X-ray spectra with unprecedented resolution,
enabling reconstruction of mean source electron energy spectra F(E) by
deconvolution of photon energy spectra I(ɛ). While various algorithms
have been proposed, the strengths and weaknesses of each have yet to
be explored in a systematic fashion. For real data F(E) is unknown,
so these various algorithms must instead be tested on simulated data
for which the ``true'' F(E) is known. Accordingly, we devised several
forms of F(E) with ``interesting'' features, generated the corresponding
(noise-added) I(ɛ), and recovered F(E) using a variety of algorithms,
including zero- and first-order Tikhonov regularizations, triangular
matrix row elimination, and forward fitting using a parametric
form consisting of a double power law with low/high cutoffs plus an
isothermal component. All inversion methods reconstructed the general
magnitude and form of F(E) well, suffering only from (1) blurring of
sharp features and (2) poor recovery at low electron energies E in
cases in which F'(E) was positive and large. Addition of a
steep thermal component at low E did not prevent recovery of features
at higher values of E. Forward fitting did recover large-scale forms
and features well but, inevitably, failed to recover local features not
expressible within the parametric used. This confirms that inversions
are the most dependable way to discover such features. However,
examination of the pattern of I(ɛ) residuals can suggest feature
locations and so help refine the parametric form used. Since quite
smooth F(E) forms do reproduce the observed I(ɛ) form with relatively
small residuals, it appears that sharp features may be uncommon in
actual flares.
Title: Compton backscattered and primary X-rays from solar flares:
angle dependent Green's function correction for photospheric albedo
Authors: Kontar, E. P.; MacKinnon, A. L.; Schwartz, R. A.; Brown, J. C.
Bibcode: 2006A&A...446.1157K
Altcode: 2005astro.ph.10167K
The observed hard X-ray (HXR) flux spectrum I(ɛ) from solar flares is a
combination of primary bremsstrahlung photons I_P(ɛ) with a spectrally
modified component from photospheric Compton backscatter of downward
primary emission. The latter can be significant, distorting or hiding
the true features of the primary spectrum which are key diagnostics
for acceleration and propagation of high energy electrons and of their
energy budget. For the first time in solar physics, we use a Green's
function approach to the backscatter spectral deconvolution problem,
constructing a Green's matrix including photoelectric absorption. This
approach allows spectrum-independent extraction of the primary spectrum
for several HXR flares observed by the Ramaty High Energy Solar
Spectroscopic Imager (RHESSI). We show that the observed and primary
spectra differ very substantially for flares with hard spectra close
to the disk centre. We show in particular that the energy dependent
photon spectral index γ (ɛ)=-d log I/d log ɛ is very different for
I_P(ɛ) and for I(ɛ) and that inferred mean source electron spectra
F(E) differ greatly. Even for a forward fitting of a parametric F(E) to
the data, a clear low-energy cutoff required to fit I(ɛ) essentially
disappears when the fit is to I_P(ɛ) - i.e. when albedo correction
is included. The self-consistent correction for backscattered photons
is thus shown to be crucial in determining the energy spectra of flare
accelerated electrons, and hence their total number and energy.
Title: Observation, Prediction, and Modeling Atmospheric Structure
Effects on EO/IR Systems
Authors: Kendra, M.; Griffin, J.; Snell, H.; Donatelli, D.; Brown, J.
Bibcode: 2006amos.confE..94K
Altcode:
EO/IR sensors observing the battlespace environment through the
earth's atmosphere can be adversely affected by spatial and temporal
variations in atmospheric radiance and transmission along the
sensor line of sight (LOS). The physics of stochastic fluctuations
is largely understood, and the radiation transport theory and models
that include stochastic effects exhibit high fidelity when compared
to corresponding sensor measurements. Deterministic structure is not
as well understood, however, and the associated radiance levels and
variability are often significantly higher than those of the benign,
stochastic background. Since the radiance measured by the sensor
comes from both the object of interest and the radiating atmosphere
and it can also be attenuated by the atmosphere along the optical
path, atmospheric structure and clutter affect target acquisition,
identification, discrimination, and tracking in ways that are difficult
to assess. We ranked MSX SPIRIT III radiometer measurements
by radiance and clutter levels for a number of altitudes and sensor
bands, and the atmospheric phenomena responsible for elevated levels
were identified. Many of these high altitude atmospheric structures
are not included in current IR radiance codes, and we describe recent
efforts to extract and characterize these features using models such as
MODTRAN, SHARC, and SAMM2. Our process involves identifying scenes with
suitable structure, determining ambient model background conditions for
a sufficiently large number of runs where the sensor, line of sight,
and geophysical conditions are duplicated, and extracting radiance
enhancements due to this structure on a pixel by pixel basis. We
present a number of examples where extraction techniques have been
successfully applied to scenes from the MSX SPIRIT III radiometer,
including phenomena such as aurora, polar mesospheric clouds (PMC),
and stratospheric warmings. The extracted structure features are
then recombined with new ambient model background scenes such that
they are properly located in the global/geophysical environment,
accounting for the dependence of specific types of atmospheric
structure on time, latitude, and season, in order to ensure real world
fidelity. There are several limitations to this approach, so we
used existing model capabilities to address these limitations. In the
case of aurora, we show how auroral observations in the infrared by
the MSX SPIRIT III radiometer can be used to determine valid model
inputs. In the case of stratospheric warmings, we use measured scenes
to determine stratospheric temperature enhancements. We demonstrate
that proper combination of validated model inputs allows simulation
of complex scenes in a real world context, and that prediction can
be extended to other IR bands. The goal of this effort is to
develop real time nowcast and forecast capability to estimate EO/IR
sensor impairment levels on SSA systems due to geophysical effects on
atmospheric structure, and we will discuss plans to develop real time
data assimilation capabilities to support operational application.
Title: Solar flare hard X-ray spectra possibly inconsistent with
the collisional thick target model
Authors: Kontar, Eduard P.; Brown, John C.
Bibcode: 2006AdSpR..38..945K
Altcode: 2005astro.ph..8418K
Recent progress in solar hard X-ray (HXR) observations with RHESSI data
and methods for spectral inversion allow us to study model-independent
mean electron flux spectra in solar flares. We report several hard
X-ray events observed by RHESSI in which the photon spectra I(γ) are
such that the inferred source mean electron spectra are not consistent
with the standard model of collisional transport in solar flares. The
observed photon spectra are so flat locally that the recovered mean
electron flux spectra show a dip around 17 31 keV. While we note that
alternative explanations, unrelated to electron transport, have not
been ruled out, we focus on the physical implications of this tentative
result for the collisional thick target model.
Title: Enhanced Small-Scale Faraday Rotation in the Galactic
Spiral Arms
Authors: Haverkorn, M.; Gaensler, B. M.; Brown, J. C.; Bizunok, N. S.;
McClure-Griffiths, N. M.; Dickey, J. M.; Green, A. J.
Bibcode: 2006ApJ...637L..33H
Altcode: 2005astro.ph.12456H
We present an analysis of the rotation measures (RMs) of polarized
extragalactic point sources in the Southern Galactic Plane Survey. This
work demonstrates that the statistics of fluctuations in RM differ
for the spiral arms and the interarm regions. Structure functions
of RM are flat in the spiral arms, while they increase in the
interarms. This indicates that there are no correlated RM fluctuations
in the magnetoionized interstellar medium in the spiral arms on scales
larger than ~0.5d, corresponding to ~17 pc in the nearest spiral arm
probed. The nonzero slopes in interarm regions imply a much larger scale
of RM fluctuations. We conclude that fluctuations in the magnetoionic
medium in the Milky Way spiral arms are not dominated by the mainly
supernova-driven turbulent cascade in the global ISM but are probably
due to a different source, most likely H II regions.
Title: Angular and energy distributions of energetic electrons in
solar flares: results with RHESSI
Authors: Kontar, E. P.; Brown, J. C.
Bibcode: 2006cosp...36.1013K
Altcode: 2006cosp.meet.1013K
X-ray spectroscopy of solar flares is the key tool in diagnostics of
high-energy particles in the low solar atmosphere However an observed
X-ray spectrum is the convolution of radiation propagation effects as
well as the instrumental response Specifically Compton back-scattering
from the photosphere can account for 30-90 of the observed flux at
energies 30-50 keV Starting with RHESSI Hard X-ray spectra and using
recently developed inversion tools we compute the spectra of energetic
electrons The angular and energy distribution of energetic electrons
can be viewed as acceleration and propagation model fingerprints The
electron spectra inferred from RHESSI solar flare spectra put new
tighter observational constrains on possible acceleration propagation
models
Title: Multiwavelength Observations of a Partially Occulted Solar
Flare
Authors: Bone, L.; Brown, J. C.; Fletcher, L.
Bibcode: 2005ESASP.600E..38B
Altcode: 2005ESPM...11...38B; 2005dysu.confE..38B
No abstract at ADS
Title: Analysis of Selected Rhessi Microflares
Authors: Stoiser, S.; Veronig, A. M.; Brown, J. C.; McTiernan, J. M.;
Hanslmeier, A.
Bibcode: 2005ESASP.600E.142S
Altcode: 2005dysu.confE.142S; 2005ESPM...11..142S
No abstract at ADS
Title: Effects of Magnetic Fields on Winds and Disks
Authors: Brown, J. C.; Cassinelli, J. P.
Bibcode: 2005ASPC..337...88B
Altcode:
The problems facing magnetically guided wind models for the
generation of stellar disks are outlined, particularly in relation
to Be stars. Various parametric, analytic and numerical treatments
have been published; some with and some without rotation, but all
considering dipole like magnetic fields that can steer the star's
wind to create a compressed equatorial region, variously termed;
Magnetically Torqued Disk ( MTD), Magnetically Rigidized Disk, or
Magnetically Confined Wind Shocked Disk. The essential issues are A)
What field and rotation are required to create a MTD that is dense
enough to generate emission line Equivalent Widths, the observed level
of intrinsic polarization, and IR excesses? B) Can semi-corotational
velocity fields be reconciled with observed line profiles and with the
long term V/R variations normally attributed to spiral density waves in
a Keplerian disk? C) What limits the lifetime of such a disk? D) Can
the Keplerian disks model be reconciled with the fact that recently
observed B fields in some early B type stars are large enough for
MTD production. E) Can any other model predict as well as MTD does,
the range of Spectral types in which disks are observed. F) What are
the critical observations that might test the MTD model?
Title: Weak interaction strengths for supernovae calculations via the
(t,3He) reaction on medium-heavy nuclei
Authors: Zegers, R. G. T.; Cole, A. L.; Akimune, H.; Austin, S. M.;
Bazin, D.; van den Berg, A. M.; Berg, G. P. A.; Brown, J.; Daito,
I.; Fujita, Y.; et al.
Bibcode: 2005NuPhA.758...67Z
Altcode:
The 58Ni(t,3He)58Co reaction at
112 MeV/nucleon was measured to identify strength associated with
Gamow-Teller transitions in the Tz=+1 direction. The
experiment is a test case for future similar studies. The main aim of
such studies is to test theoretical models used to predict Gamow-Teller
strength distributions that serve as input for supernovae evolution
calculations. The results indicate that the (t,3He) reaction
is indeed a powerful tool to perform such tests.
Title: Enhanced magneto-ionic fluctuations in the Milky Way's
spiral arms
Authors: Haverkorn, M.; Gaensler, B.; Brown, J.; McClure-Griffiths,
N.; Dickey, J.; Green, A.
Bibcode: 2005mpge.conf...80H
Altcode:
The 1.4 GHz polarized continuum data of the Southern Galactic Plane
Survey are ideally suited to study spatial variations in the turbulent
properties of the magneto-ionic interstellar medium. Statistical
analysis of rotation measures in the inner Galactic plane suggests
an additional source of fluctuations in electron density and/or
magnetic field in the Galaxy's spiral arms, with an outer scale of
a few parsecs. A probable source for this additional component of
structure is HII regions from relatively late-type stars, which are
sufficiently abundant and of the appropriate size to account for the
additional structure.
Title: Comparison of Algorithms for Reconstructing Electron Spectra
from Solar Flare Hard X-Ray Spectra
Authors: Emslie, G.; Brown, J. C.; Holman, G. D.; Johns-Krull, C.;
Kontar, E. P.; Massone, A. M.; Piana, M.
Bibcode: 2005AGUSMSP21A..05E
Altcode:
The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is yielding
solar flare hard X-ray (HXR) spectra with unprecedented resolution and
precision. Such spectra enable the reconstruction of the effective
mean source electron spectrum F?(E) by deconvolution of the photon
spectrum I(ɛ) through the bremsstrahlung cross-section Q(ɛ,E). In
this paper we report on an evaluation of three distinct "inverting"
reconstruction techniques and one forward fitting procedure. We
synthesized a variety of hypothetical F?(E) forms, with a variety
of empirical features designed to represent diagnostics of electron
acceleration and transport processes, generated the corresponding I(ɛ)
with realistic random noise added, and performed "blind" (i.e. without
knowledge of F?[E] in advance) recoveries of F?(E) for comparison with
the originally assumed forms. In most cases the inversion methods
gave very good reconstructions of F?(E). The forward fitting method
did well in recovering large-scale features but, somewhat inevitably,
failed to recover features outwith the parametric forms of F?(E),
such as dips, bumps and positive slopes. However, examination of the
distribution of photon spectrum residuals over ɛ should in principle
permit refinement of the parametric form used.
Title: Physics of the Neupert Effect: Estimates of the Effects of
Source Energy, Mass Transport, and Geometry Using RHESSI and GOES Data
Authors: Veronig, Astrid M.; Brown, John C.; Dennis, Brian R.;
Schwartz, Richard A.; Sui, Linhui; Tolbert, A. Kimberley
Bibcode: 2005ApJ...621..482V
Altcode:
The ``empirical Neupert effect'' (ENE) is the observed temporal
correlation of the hard X-ray (HXR) flux FHXR(t) with the
time derivative of the soft X-ray (SXR) flux F˙SXR(t) in
many flares. This is widely taken to mean that the energetic electrons
responsible for FHXR(t) by thick-target collisional
bremsstrahlung are the main source of heating and mass supply (via
chromospheric evaporation) of the SXR-emitting hot coronal plasma. If
this interpretation were correct, one would expect better correlation
between the beam power supply Pbeam(t), inferred from the HXR
spectrum, and the actual power Pin(t) required to explain
the SXR flux and spectrum, allowing for variations in both emission
measure (EM) and temperature T, for radiative and conductive cooling
losses, and for complexities of geometry like multiple loops. We call
this the ``theoretical Neupert effect'' (TNE). To test if it is true
that Pbeam(t) and Pin(t) inferred from data are
better correlated than FHXR(t) and F˙SXR(t),
we use an approximate approach for a simple single-loop geometry
and rough estimates of the particle and energy transport and apply
the model to RHESSI and GOES data on four flares. We find that if
the beam low cutoff energy E1 is taken as constant, the
correlation of Pbeam(t), Pin(t) is no better
than that of FHXR(t),F˙SXR(t). While our
modeling contains many approximations to cooling and other physics,
ignored entirely from ENE data considerations, there seems to be no
reason why their order-of-magnitude inclusion should make the TNE worse
rather than better, although this should be checked by more accurate
simulations. These results suggest that one or more of the following
must be true: (1) fast electrons are not the main source of SXR plasma
supply and heating, (2) the beam low cutoff energy varies with time, or
(3) the TNE is strongly affected by source geometry. These options are
discussed in relation to possible future directions for TNE research.
Title: Determination of Electron Flux Spectra in a Solar Flare with
an Augmented Regularization Method: Application to Rhessi Data
Authors: Kontar, Eduard P.; Emslie, A. Gordon; Piana, Michele; Massone,
Anna Maria; Brown, John C.
Bibcode: 2005SoPh..226..317K
Altcode: 2004astro.ph..9691K
Kontar et al. (2004) have shown how to recover mean source electron
spectra $\bar F(E)$ in solar flares through a physical constraint
regularization analysis of the bremsstrahlung photon spectra I(ε) that
they produce. They emphasize the use of non-square inversion techniques,
and preconditioning combined with physical properties of the spectra
to achieve the most meaningful solution to the problem. Higher-order
regularization techniques may be used to generate $\bar F(E)$ forms with
certain desirable properties (e.g., higher-order derivatives). They
further note that such analysis may be used to infer properties of
the electron energy spectra at energies well above the maximum photon
energy observed. In this paper we apply these techniques to data from
a solar flare observed by RHESSI on 26 February, 2002. Results using
different orders of regularization are presented and compared for
various time intervals. Clear evidence is presented for a change in the
value of the high-energy cutoff in the mean source electron spectrum
with time. We also show how the construction of the injected electron
spectrum F0(E0) (assuming that Coulomb collisions
in a cold target dominate the electron transport) is facilitated by
the use of higher-order regularization methods.
Title: Applications of a phoswich-based detector for fast (∼1 10
MeV) solar neutrons for missions to the inner heliosphere
Authors: McKibben, R. B.; Connell, J. J.; Macri, J. R.; McConnell,
M. L.; Ryan, J. M.; Flückiger, E. O.; Moser, M. R.; Brown, J. C.;
McKinnon, A. L.
Bibcode: 2005AdSpR..36.1432M
Altcode:
We describe a phoswich-based detector concept for studies of low
energy (∼1-10 MeV) solar neutrons in the innermost heliosphere ( R
<∼ 0.5 AU). The detector has applications both as a very low mass
(<∼1 kg), low power (∼1-2 W) stand-alone instrument, and as a
component to enhance the capabilities of more sophisticated instruments,
for example, the fast neutron imaging telescope instrument described by
Moser et al. [Moser, M.R., Flückiger, E.O., Ryan, J.M., et al. A fast
neutron imaging telescope for inner heliosphere missions. Adv. Space
Res., in press, this issue, doi:10.1016/j.asr.2005.03.037]. In its
most basic form, the detector consists of a small volume (∼1 cm
3) of fast organic scintillator completely surrounded
by a slow inorganic scintillator. The dimensions of the organic
scintillator are chosen to minimize multiple n-p scatterings while
retaining adequate sensitivity. The inorganic scintillator provides
anti-coincidence protection against energetic charged particles. A
single PM tube views light from both scintillators. Pulse shape analysis
identifies as potential neutrons those events where only the organic
scintillator contributes to the signal. The signal size corresponds to
the energy of the recoil proton from an n-p elastic scatter, on average
half the energy of the incident neutron. An instrument based on this
concept would provide measurements of the neutron flux and, through
statistical analysis of recoil proton energies, basic information
about the neutron spectrum.
Title: Evidence for a solar coronal thick-target hard X-ray source
observed by RHESSI
Authors: Veronig, Astrid M.; Brown, John C.; Bone, Laura
Bibcode: 2005AdSpR..35.1683V
Altcode:
We study a solar flare hard X-ray (HXR) source observed by the Reuven
Ramaty high energy solar spectroscopic imager (RHESSI) in which the
HXR emission is almost entirely in a coronal loop so dense as to be
collisionally thick at electron energies up to ∼45-60 keV. This
contrasts with most events previously reported in which the HXR
emission is primarily from the loop footpoints in the collisionally
dense chromosphere. In particular, we show that the high loop column
densities inferred from the GOES and RHESSI soft X-ray emission
measure and the volume of the flare loop are consistent with the
coronal thick-target interpretation of the HXR images and spectra. The
high column densities observed already at the very beginning of the
impulsive phase are explained by chromospheric evaporation during a
preflare which, as Nobeyama 17 GHz radio images reveal, took place in
the same set of nested loops as the main flare.
Title: Testing the Neupert Effect
Authors: Veronig, A. M.; Brown, J. C.; Dennis, B. R.; Schwartz, R. A.;
Sui, L.; Tolbert, A. K.
Bibcode: 2005ASSL..320..263V
Altcode: 2005smp..conf..263V
No abstract at ADS
Title: High Energy Radiation from the Sun
Authors: Brown, J. C.
Bibcode: 2005ASSL..320...87B
Altcode: 2005smp..conf...87B
No abstract at ADS
Title: Problems and progress in flare fast particle diagnostics
Authors: Brown, John C.; Kontar, Eduard P.
Bibcode: 2005AdSpR..35.1675B
Altcode: 2005astro.ph..8417B
Recent progress in the diagnosis of flare fast particles is
critically discussed with the main emphasis on high resolution
hard X-ray (HXR) data from RHESSI and coordinated data from other
instruments. Spectacular new photon data findings are highlighted
as are advances in theoretical aspects of their use as fast particle
diagnostics, and some important comparisons made with interplanetary
particle data. More specifically the following topics are addressed:
RHESSI data on HXR (electron) versus gamma-ray line (ion) source
locations. RHESSI hard X-ray source spatial structure in relation
to theoretical models and loop density structure. Energy budget
of flare electrons and the Neupert effect. Spectral deconvolution
methods including blind target testing and results for RHESSI HXR
spectra, including the reality and implications of dips inferred
in electron spectra. The relation between flare in situ and
interplanetary particle data.
Title: Spitzer IRS observations of protoplanetary disks around
low-mass stars
Authors: Kessler-Silacci, J. E.; Geers, V. C.; Augereau, J. -C.;
Boogert, A. C. A. B.; Blake, G. A.; Brown, J.; van Dishoeck, E. F.;
Evans, N. J.; Knez, C.; Lahuis, F.; Pontoppidan, K.
Bibcode: 2004AAS...20517407K
Altcode: 2005AAS...20517407K; 2005BAAS...37..378K
This work is part of the c2d Spitzer legacy program designed to
study the evolution of circumstellar matter 'From Molecular Cores to
Planet-Forming Disks.' This program utilizes the improved sensitivity
of the Spitzer InfraRed Spectrograph (IRS) to greatly expand the study
of infrared emission features in solar-mass stars, which previously
were restricted primarily to ground based studies in the 10 micron
region. Through the observation of 5--35 micron spectra toward a
variety of solar-type PMS stars, a database analogous to ISO studies
of high/intermediate mass stars will be created. To date, near to
mid infrared spectra have been obtained for 50 T Tauri stars with
circumstellar disks (class II) with ages up to 5 Myr. These spectra
probe the changing physical conditions of disks and the chemical
structure of silicates and polycyclic aromatic hydrocarbons (PAHs)
as grains evolve and grow into planetesimals. In the spectra observed
thus far, PAH emission is observed toward 10 stars, among which the 11.2
micron feature is most prominent and 6.2 to 8.6 micron features are not
frequently observed. The connection between the observed PAH features
and interstellar/circumstellar environment is being explored. Silicate
emission is observed at 10 and 20 microns toward a large fraction of
the sample and appears to arise from primarily amorphous silicates
with grain sizes between 0.1 and 5 microns. The spectral SEDs will
be compared to the categories established for intermediate mass
Herbig Ae/Be s tars to explore the connections between the dust
size/composition and disk geometry (Meeus et al. 2001). The
c2d Spitzer Legacy project is funded through NASA contract number
1407. JEK-S is supported by NASA through the Spitzer Postdoctoral
Fellowship Program, under award 1256316.
Title: Layering and Double-Diffusion Style Convection in Europa's
Ocean
Authors: Vance, S.; Brown, J.
Bibcode: 2004AGUFM.P31A0966V
Altcode:
We assess the effects of fluid composition and depth-dependent
hydrostatic pressure on dynamics in Europa's ocean for aqueous Na2SO4
and MgSO4. We observe a salinity- and pressure-dependent check on
buoyancy in putative upwellings, which may act as mechanism for
storing heat in the ocean's base. For either sodium or magnesium,
a small excess in salinity of an initially buoyant parcel of water,
even for low average ambient salinity, causes upwellings to lose
buoyancy before reaching the base of the overlying ice. The result is
a two-layer convecting system with a characteristic lifetime dependent
on the properties of Europa's ocean, including the balance of heat
flow through the system and details of pressure effects on thermal
expansion and volumes of mixing. When volume of mixing is neglected
plume rise remains dependent on temperature and pressure effects
alone. Stratification develops as bottom water continually acquires
heat and salt. The added mass of the salt dominates over the thermal
expansion. As the rise in temperature becomes sufficient to overcome
the salinity effect, upwellings rise to a terminal height determined
by the pressure dependence of thermal expansion of the fluid, and by
differences in the fluid's temperature and salinity. This regime is
similar to double-diffusive convecting systems observed in the Red
Sea and Lake Vanda over the last forty years. In the Red Sea, boundary
layers separating convecting zones have been observed to move upward
as the lower layer acquires heat and salt. By analogy using reasonable
parameters for Europa's ocean, we estimate a time scale on the order of
10 Myr for the upward progress of a lower convecting layer saturated
with MgSO4, which could correlate with recently inferred change in
surface alteration style over the last 70-80 Myr.
Title: Generalized Regularization Techniques with Constraints for
the Analysis of Solar Bremsstrahlung X-ray Spectra
Authors: Kontar, Eduard P.; Piana, Michele; Massone, Anna Maria;
Emslie, A. Gordon; Brown, John C.
Bibcode: 2004SoPh..225..293K
Altcode: 2004astro.ph..9688K
Hard X-ray spectra in solar flares provide knowledge of the electron
spectrum that results from acceleration and propagation in the solar
atmosphere. However, the inference of the electron spectra from solar
X-ray spectra is an ill-posed inverse problem. Here, we develop and
apply an enhanced regularization algorithm for this process making
use of physical constraints on the form of the electron spectrum. The
algorithm incorporates various features not heretofore employed in
the solar flare context: Generalized Singular Value Decomposition
(GSVD) to deal with different orders of constraints; rectangular form
of the cross-section matrix to extend the solution energy range;
regularization with various forms of the smoothing operator; and
"preconditioning" of the problem. We show by simulations that this
technique yields electron spectra with considerably more information
and higher quality than previous algorithms.
Title: Anisotropic Bremsstrahlung Emission and the Form of Regularized
Electron Flux Spectra in Solar Flares
Authors: Massone, Anna Maria; Emslie, A. Gordon; Kontar, Eduard P.;
Piana, Michele; Prato, Marco; Brown, John C.
Bibcode: 2004ApJ...613.1233M
Altcode:
The cross section for bremsstrahlung photon emission in solar flares is,
in general, a function of the angle θ between the incoming electron
and the outgoing photon directions. Thus the electron spectrum required
to produce a given photon spectrum is a function of this angle, which
is related to the position of the flare on the solar disk and the
direction(s) of the precollision electrons relative to the local solar
vertical. We compare mean electron flux spectra for the flare of 2002
August 21 using cross sections for parameterized ranges of the angle
θ. Implications for the shape of the mean source electron spectrum
and for the injected power in nonthermal electrons are discussed.
Title: Magnetic field connected fast line profile variability in
spectra of bright O supergiants
Authors: Kholtygin, A.; Brown, J.; Fabrika, S.; Surkov, A.
Bibcode: 2004mast.conf..250K
Altcode:
Results of study of fast line profile variability (lpv) in the spectra
of selected bright O-stars are reported. A regular component of lpv
in the spectra of the star λ Ori A with estimated period P≈ 3 d
have been detected. We suppose that the formation of long time-scale
regular components of lpv can be explained in the framework of the
magnetically confined wind-shock (MCWS) model of Babel & Montmerle
(1997a). In the context of testing the MCWS model the program of
searching for weak magnetic fields in bright O and early B stars is
outlined. The possibility of measuring weak longitudinal magnetic fields
(Bl ≈ 100 G) is demonstrated.
Title: Measurement of Gamow-Teller Strength via (t,^3He)
Authors: Cole, A. L.; Austin, S. M.; Bazin, D.; Hitt, G. W.; Sherrill,
B. M.; Steiner, M.; Zegers, R.; Akimune, H.; van den Berg, A. M.; Berg,
G. P. A.; Harakeh, M. N.; Fujita, Y.; Ueno, H.; Daito, I.; Fujiwara,
M.; Hara, K.; Kawabata, T.; Nakamura, T.; Jänecke, J.; Brown, J.
Bibcode: 2004APS..DNP.DC006C
Altcode:
Electron capture and beta decay play important roles in the evolution
of pre-supernovae stars and their collapse. Recent predictions for weak
interactions in modern large-scale shell model calculations that include
residual interactions differ greatly from earlier rates determined
from independent particle models. We report preliminary results for
the measurement of the GT strength in ^58Co via the ^58Ni(t,^3He)
reaction with a secondary triton beam of intensity ∼10^6pps at 112
MeV/nucleon. In preparation for future (t,^3He) measurements, we have
performed test experiments that demonstrate enhancements in the triton
beam intensity by an order of magnitude to ∼10^7pps.
Title: Optically thick clumps - not the solution to the Wolf-Rayet
wind momentum problem?
Authors: Brown, J. C.; Cassinelli, J. P.; Li, Q.; Kholtygin, A. F.;
Ignace, R.
Bibcode: 2004A&A...426..323B
Altcode: 2004astro.ph..6685B
The hot star wind momentum problem η=\dot{M} ǎrv∞/(L/c)
≫ 1 is revisited, and it is shown that the conventional belief,
that it can be solved by a combination of clumping of the wind and
multiple scattering of photons, is not self-consistent for optically
thick clumps. Clumping does reduce the mass loss rate \dot{M}, and
hence the momentum supply, required to generate a specified radio
emission measure ǎrepsilon, while multiple scattering increases the
delivery of momentum from a specified stellar luminosity L. However,
in the case of thick clumps, when combined the two effects act in
opposition rather than in unison since clumping reduces multiple
scattering. From basic geometric considerations, it is shown that
this reduction in momentum delivery by clumping more than offsets the
reduction in momentum required, for a specified ǎrepsilon. Thus the
ratio of momentum deliverable to momentum required is maximal for
a smooth wind and the momentum problem remains for the thick clump
case. In the case of thin clumps, all of the benefit of clumping in
reducing η lies in reducing \dot{M} for a given ǎrepsilon so that
extremely small filling factors f≈ 10-4 are needed. It is
also shown that clumping affects the inference of \dot{M} from radio
ǎrepsilon not only by changing the emission measure per unit mass but
also by changing the radio optical depth unity radius Rrad,
and hence the observed wind volume, at radio wavelengths. In fact,
for free-free opacity ∝ n2, contrary to intuition,
Rrad increases with increasing clumpiness.
Title: A Steady, Radiative-Shock Method for Computing X-Ray Emission
from Colliding Stellar Winds in Close, Massive-Star Binaries
Authors: Antokhin, I. I.; Owocki, S. P.; Brown, J. C.
Bibcode: 2004ApJ...611..434A
Altcode:
We present a practical, efficient, semianalytic formalism for computing
steady state X-ray emission from radiative shocks between colliding
stellar winds in relatively close (orbital period up to order tens of
days) massive-star, binary systems. Our simplified approach idealizes
the individual wind flows as smooth and steady, ignoring the intrinsic
instabilities and associated structure thought to occur in such
flows. By also suppressing thin-shell instabilities for wind-collision
radiative shocks, our steady state approach avoids the extensive
structure and mixing that has thus far precluded reliable computation of
X-ray emission spectra from time-dependent hydrodynamical simulations
of close-binary, wind-collision systems; but in ignoring the unknown
physical level of such mixing, the luminosity and hardness of X-ray
spectra derived here represent upper limits to what is possible for a
given set of wind and binary parameters. A key feature of our approach
is the separation of calculations for the small-scale shock-emission
from the ram-pressure-balance model for determining the large-scale,
geometric form of the wind-wind interaction front. Integrating the
localized shock emission over the full interaction surface and using
a warm-absorber opacity to take account of attenuation by both the
smooth wind and the compressed, cooled material in the interaction
front, the method can predict spectra for a distant observer at any
arbitrary orbital inclination and phase. We illustrate results for a
sample selection of wind, stellar, and binary parameters, providing
both full X-ray light curves and detailed spectra at selected orbital
phases. The derived spectra typically have a broad characteristic
form, and by synthetic processing with the standard XSPEC package,
we demonstrate that they simply cannot be satisfactorily fitted with
the usual attenuated single- or two-temperature thermal-emission
models. We conclude with a summary of the advantages and limitations
of our approach and outline its potential application for interpreting
detailed X-ray observations from close, massive-star binary systems.
Title: The effect of rotational gravity darkening on magnetically
torqued Be star discs
Authors: Brown, J. C.; Telfer, D.; Li, Q.; Hanuschik, R.; Cassinelli,
J. P.; Kholtygin, A.
Bibcode: 2004MNRAS.352.1061B
Altcode: 2004astro.ph..7039B; 2004MNRAS.tmp..166B
In the magnetically torqued disc (MTD) model for hot star discs,
as proposed and formulated by Cassinelli et al., stellar wind mass
loss was taken to be uniform over the stellar surface. Here account
is taken of the fact that as the stellar spin rate is increased, and
the stellar equator is gravity darkened, the equatorial mass flux and
terminal speed are reduced, compared with the poles, for a given total
. As a result, the distribution of equatorial disc density, determined
by the impact of northbound and southbound flows, is shifted further
out from the star. This results, for high So(>~0.5), in a
fall in the disc mass and emission measure, and hence in the observed
emission line equivalent width, scattering polarization and infrared
emission. Consequently, contrary to expectations, critical rotation
So-> 1 is not the optimum for creation of hot star discs
which, in terms of emission measure for example, is found to occur in
a broad peak around So~ 0.5-0.6 depending slightly on the
wind velocity law. The relationship of this analytic quasi-steady
parametric MTD model to other work on magnetically guided winds is
discussed. In particular, the failures of the MTD model for Be-star
discs alleged by Owocki and ud-Doula are shown to revolve largely
around open observational tests, rather than in the basic MTD physics,
and around their use of insufficiently strong fields.
Title: Kinematic model inversions of hot star recurrent DAC data -
tests against dynamical CIR models
Authors: Krtička, J.; Barrett, R. K.; Brown, J. C.; Owocki, S. P.
Bibcode: 2004A&A...417.1039K
Altcode: 2004astro.ph..1383K
The Discrete Absorption Components (DACs) commonly observed in
the ultraviolet lines of hot stars have previously been modelled
by dynamical simulations of Corotating Interaction Regions (CIRs)
in their line-driven stellar winds. Here we apply the kinematic DAC
inversion method of Brown et al. to the hydrodynamical CIR models
and test the reliability of the results obtained. We conclude that
the inversion method is able to recover valuable information on the
velocity structure of the mean wind and to trace movement of velocity
plateaux in the hydrodynamical data, though the recovered density
profile of the stream is correct only very near to the stellar surface.
Title: A Coronal Thick-Target Interpretation of Two Hard X-Ray
Loop Events
Authors: Veronig, Astrid M.; Brown, John C.
Bibcode: 2004ApJ...603L.117V
Altcode:
We report a new class of solar flare hard X-ray (HXR) sources in
which the emission is mainly in a coronal loop so dense as to be
collisionally thick at electron energies up to >~50 keV. In most
of the events previously reported, most of the emission is at the
dense loop footpoints, although sometimes with a faint high-altitude
component. HXR RHESSI data on loop dimensions and nonthermal electron
parameters and GOES soft X-ray data on hot loop plasma parameters
are used to model coronal thick-target physics for two ``discovery''
events (2002 April 14 [23:56 UT] and 2002 April 15 [23:05 UT]). We
show that loop column densities N are consistent with (1) a nonthermal
coronal thick-target interpretation of the HXR image and spectrum;
(2) chromospheric evaporation by thermal conduction from the hot loop
rather than by electron beam heating; and (3) the hot loop temperature
being due to a balance of thick-target collisional heating and (mainly)
conductive cooling.
Title: Heat Source Neutron Emission Rate Reduction Studies - Water
Induced HF Liberation
Authors: Matonic, John; Brown, John; Foltyn, Liz; Garcia, Lawrence;
Hart, Ron; Herman, David; Huling, Jeff; Pansoy-Hjelvik, M. E. Lisa;
Sandoval, Fritz; Spengler, Diane
Bibcode: 2004AIPC..699..242M
Altcode:
Plutonium-238 oxide (238PuO2) is used in the fabrication
of general purpose heat sources (GPHS) or light-weight radioisotope
heater units (LWRHUs). The heat sources supply the thermal energy
used in radioisotope thermoelectric generators to power spacecraft
for deep space missions and to heat critical components in the cold
environs of space. Los Alamos National Laboratory has manufactured
heat sources for approximately two decades. The aqueous purification
of 238PuO2 is required, due to rigorous total Pu-content,
actinide and non-actinide metal impurity, and neutron emission rate
specifications. The 238PuO2 aqueous purification process
is a new capability at Los Alamos National Laboratory as previously,
aqueous purified 238PuO2 occurred at other DOE complexes. The
Pu-content and actinide and non-actinide metal impurity specifications
are met well within specification in the Los Alamos process, though
reduction in neutron emission rates have been challenging. High
neutron emission rates are typically attributed to fluoride content
in the oxide. The alpha decay from 238Pu results in α,n
reactions with light elements such as 17O, 18O,
and 19F resulting in high neutron emission rates in the
purified 238PuO2. Simple 16O-exchange takes
care of the high NER due to 17O, and 18O. A
new method to reduce the NER due to 19F in the purified
238PuO2 is presented in this paper. The method involves
addition of water to purified 238PuO2, followed by heating
to remove the water and liberating fluoride as HF.
Title: An Explanation for the Different Locations of Electron and
Ion Acceleration in Solar Flares
Authors: Emslie, A. Gordon; Miller, James A.; Brown, John C.
Bibcode: 2004ApJ...602L..69E
Altcode:
RHESSI observations of the 2002 July 23 solar flare have shown that
hard X-rays and gamma rays are produced in different locations within
the flare volume. The gamma-ray emission, which is a diagnostic of
ion acceleration, appears to originate in the vicinity of large loops,
while the hard X-ray emission, a diagnostic of electron acceleration,
originates near shorter loops. The tendency for a stochastic
acceleration model based on cascading MHD turbulence to favor ion
acceleration in larger acceleration regions has been previously
noted. Here we evaluate this effect quantitatively and show that such
a model is consistent with the RHESSI observations.
Title: Inference of hot star density stream properties from data
on rotationally recurrent DACs
Authors: Brown, J. C.; Barrett, R. K.; Oskinova, L. M.; Owocki, S. P.;
Hamann, W. -R.; de Jong, J. A.; Kaper, L.; Henrichs, H. F.
Bibcode: 2004A&A...413..959B
Altcode:
The information content of data on rotationally periodic
recurrent discrete absorption components (DACs) in hot star
wind emission lines is discussed. The data comprise optical
depths τ(w,φ) as a function of dimensionless Doppler velocity
w=(Δλ/λ0)(c/v&infy) and of time expressed
in terms of stellar rotation angle φ. This is used to study the
spatial distributions of density, radial and rotational velocities, and
ionisation structures of the corotating wind streams to which recurrent
DACs are conventionally attributed. The simplifying assumptions
made to reduce the degrees of freedom in such structure distribution
functions to match those in the DAC data are discussed and the problem
then posed in terms of a bivariate relationship between τ(w,φ) and
the radial velocity vr(r), transverse rotation rate Ω(r)
and density ρ(r,φ) structures of the streams. The discussion applies
to cases where: the streams are equatorial; the system is seen edge
on; the ionisation structure is approximated as uniform; the radial
and transverse velocities are taken to be functions only of radial
distance but the stream density is allowed to vary with azimuth. The
last kinematic assumption essentially ignores the dynamical feedback
of density on velocity and the relationship of this to fully dynamical
models is discussed. The case of narrow streams is first considered,
noting the result of Hamann et al. (\cite{Ham01}) that the apparent
acceleration of a narrow stream DAC is higher than the acceleration
of the matter itself, so that the apparent slow acceleration of DACs
cannot be attributed to the slowness of stellar rotation. Thus DACs
either involve matter which accelerates slower than the general wind
flow, or they are formed by structures which are not advected with the
matter flow but propagate upstream (such as Abbott waves). It is then
shown how, in the kinematic model approximation, the radial speed
of the absorbing matter can be found by inversion of the apparent
acceleration of the narrow DAC, for a given rotation law. The
case of broad streams is more complex but also more informative. The
observed τ(w,φ) is governed not only by vr(r) and Ω(r)
of the absorbing stream matter but also by the density profile across
the stream, determined by the azimuthal (φ0) distribution
function F0(φ0) of mass loss rate around the
stellar equator. When F0(φ0) is fairly wide
in φ0, the acceleration of the DAC peak τ(w,φ) in w
is generally slow compared with that of a narrow stream DAC and the
information on vr(r), Ω(r) and F0(φ0)
is convoluted in the data τ(w,φ). We show that it is possible,
in this kinematic model, to recover by inversion, complete information
on all three distribution functions vr(r), Ω(r) and
F0(φ0) from data on τ(w,φ) of sufficiently
high precision and resolution since vr(r) and Ω(r) occur
in combination rather than independently in the equations. This
is demonstrated for simulated data, including noise effects, and is
discussed in relation to real data and to fully hydrodynamic models. Figures \ref{fig:results1}, \ref{fig:results2}, \ref{fig:results7},
\ref{fig:results8}, \ref{fig:results13}, \ref{fig:results14},
\ref{fig:rotation1} and \ref{fig:rotation2} are only available in
electronic form at http://www.edpsciences.org
Title: The Sun as a Stellar Laboratory: Unsolved Problems
Authors: Brown, J. C.
Bibcode: 2004IAUS..219....1B
Altcode: 2003IAUS..219E.155B
The past decade has seen major adances in short wavelength observations
of solar and stellar atmospheres. In the case of the sun SoHOYohKoh
TRACE Compton GRO Granat etc and now RHESSI have provided a wealth of
new data and ideas while Chandra XMM-Newton FUSE etc are taking stellar
data into the precision plasma diagnostic realms already familiar
to solar astronomers. Selected highlights of these results will be
presented and discussed in terms of stellar/solar cross-fertilisation
of ideas. Special attention will be paid to the answers and puzzles
being presented by recent data from RHESSI concerning the dynamic
solar atmosphere and by Chandra XMM-Newton and other data on flare
stars and on hot star wind structure.
Title: Progress and problems in flare particle diagnostics
Authors: Brown, J. C.
Bibcode: 2004cosp...35.4230B
Altcode: 2004cosp.meet.4230B
Recent solar maxima saw major progress in remote diagnosis of flare
particles at the sun via advances in ground and space instrumentation
and in coordinated observing campaigns, including in situ measurements
of related space plasma particles, waves, and fields. This review
discusses aspects of where we stand with regard to remote particle
diagnostics, emphasising recent progress and new problems. Special
attention is paid to interpretation of `hard' [hard X-ray (HXR) and
gamma-ray (GR)] photon data from the Ramaty High Energy Spectrometric
Imager (RHESSI) and emphasising their implications for the basic
physics problems of acceleration, propagation, and flare energy
transport budget. In particular the following are discussed: - a) HXR
SPECTRAL INVERSION Progress in numerical regularisation algorithms
incorporating physical constraints Real thin and thick target and
thermal model electron distribution recovery Testing/exclusion
of models by application of these to RHESSI data Interpretive
complications - e.g. albedo, directivity, energy dispersion b) HXR
SPECTROSCOPIC IMAGE INTERPRETATION Image reconstruction algorithms
- 2-D to 3-D ambiguity Source sizes and physics implications Source sizes and locations compared with TRACE, radio and other
data Beam energy losses, and atmospheric density structure -
e.g. coronal thick targets Evidence for and implications of
complex versus simple loop structure Diffuse source (e.g. albedo
patch) detection c) HXR ANISOTROPY AND POLARISATION d) GR-LINE SPECTRA
AND IMAGES AND OTHER ION DIAGNOSTICS Implications for MEV ion
acceleration sites, propagation, and energy budget Low energy ion
diagnostics e) FLARE ENERGY BUDGET Real evidence for low energy
cut-offs in particle spectra Neupert effect and status of the
single loop particle heated model
Title: Applications of a phoswich-based detector for fast (~1-10 MeV)
solar neutrons for missions to the inner heliosphere
Authors: McKibben, R. B.; Connell, J. J.; Macri, J. R.; McConnell,
M. L.; Ryan, J. M.; Flückiger, E. O.; Moser, M. R.; Brown, J. C.;
McKinnon, A. L.
Bibcode: 2004cosp...35.3099M
Altcode: 2004cosp.meet.3099M
We describe a phoswich-based detector concept for measurement
of low energy (~1-10 MeV) solar neutron fluxes on missions to the
innermost heliosphere (~0.5 AU or less from the Sun). The detector has
applications both as a very low mass, low power stand-alone instrument
to provide basic information about the neutron flux and spectrum, and
as a component of more powerful and sophisticated instruments. In its
most basic form, the detector consists of a small volume (~1 cm3) of
fast organic scintillator embedded within and completely surrounded by a
slow inorganic scintillator. The dimensions of the organic scintillator
are such that no more than one n-p elastic scatter is likely in the
scintillator, and the inorganic scintillator provides anti-coincidence
protection against energetic charged particles. A single PM tube views
light from both scintillators. A potential neutron is then identified
by pulse shape analysis as having produced a signal only in the
fast organic scintillator. The size of the signal corresponds to the
energy of the recoil proton from an n-p elastic scatter, on average
half the energy of the incident neutron. A minimal instrument based
on this concept would require very little mass and power to provide
measurements of the neutron flux and, through statistical analysis
of the energies of the recoil protons, basic information about the
neutron spectrum. For more advanced applications, the phoswich detector
concept can be incorporated into more sophisticated instrument designs
to provide significant enhancements of their capabilities. As an
example we discuss a concept for an advanced neutron telescope based
on addition of a phoswich-based detector to the Fast Neutron Imaging
Telescope (FNIT) described by Moser et al. in an accompanying paper.
Title: Regularized mean and accelerated electron flux spectra in
solar flares
Authors: Kontar, E. P.; Emslie, A. G.; Piana, M.; Massone, A. M.;
Brown, J. C.
Bibcode: 2004cosp...35.3941K
Altcode: 2004cosp.meet.3941K
Hard X-ray spectra in solar flares permit, through knowledge of
the bremsstrahlung cross-section, inference of the mean source
electron spectrum that results from acceleration and propagation
of electrons in the solar atmosphere. Here we develop and apply an
enhanced regularization algorithm for this process which makes use of
a variety of physical constraints on the possible form of the electron
spectrum. The algorithm incorporates various features not heretofore
employed in the solar flare context, such as the use of Generalized
Singular Value Decomposition (GSVD), a rectangular representation of the
discretized problem (so that the electron and photon energy ranges used
are not necessarily the same), regularization using various smoothing
operators. The use of non-square inversion techniques, with physical
properties of the spectra to achieve the most meaningful solution
to the problem. We apply these techniques to data from a few solar
flares observed by RHESSI. Results using different regularization are
presented and compared for various time intervals. We further note
that such analyses may be used to infer properties of the electron
energy spectrum that lie at energies well above the maximum photon
energy observed. We also show how the construction of the accelerated
(injected) electron spectrum (assuming that Coulomb collisions in a
cold target dominate the electron energetics) is facilitated by the
use of higher-order regularization methods. Clear evidence is presented
for a change in the value of the high-energy cutoff in the mean source
electron spectrum with time.
Title: RHESSI discovery of solar coronal thick target hard X-ray
sources
Authors: Veronig, A.; Brown, J.
Bibcode: 2004cosp...35.1393V
Altcode: 2004cosp.meet.1393V
We report the discovery of a new class of solar flare hard X-ray (HXR)
source observed by the Reuven Ramaty High Energy Solar Spectroscopic
Imager (RHESSI) in which the HXR emission is almost entirely in
a coronal loop so dense as to be collisionally thick at electron
energies up to ≳50 keV. This contrasts with most events previously
reported in which the bulk of emission is at the loop footpoints in
the collisionally dense chromosphere though sometimes with a faint high
altitude component such as in Masuda `above the loop-top' sources. We
use HXR data from RHESSI to infer loop dimensions and nonthermal
electron parameters and soft X-ray (SXR) data from GOES to obtain
hot loop plasma parameters. These are used to model the physics of
coronal thick target loops for the 14 and 15 April 2002 `discovery'
events both of which have very steep HXR spectra. In particular we
show that: [(a)] the loop column density N derived from the SXR
emission measure and loop geometry is consistent with the coronal thick
target interpretation of the HXR image, [(b)] this N is consistent
with chromospheric evaporation by thermal conduction flux from the hot
coronal plasma rather than by electron beam heating, and [(c)]
the temperature of the hot loop plasma (and hence the conductively
driven N value) is consistent with thick target collisional heating
balanced by (mainly) conductive cooling.
Title: Radio Frequency Interference: Projects and Activities Developed
for the High School Earth Science, Astronomy, and Physics Classroom
Authors: Dunn, S. K.; Brown, J.
Bibcode: 2003AAS...203.5906D
Altcode: 2003BAAS...35.1305D
Radio Frequency Interference: Projects and Activities Developed for
the High School Earth Science, Astronomy, and Physics Classroom Susan
Dunn Tewksbury Memorial High School Jason Brown Tyngsboro High School
Preethi Pratap MIT Haystack Observatory The Research Experiences
for Teachers (RET) program, funded by the NSF, brings teachers into
research environments to interact with scientists and translate the
experience into the classroom. We will describe a RET experience at the
MIT Haystack Observatory which involved using an AR3000A communications
receiver and a discone antenna as the basis for an Earth Science,
Astronomy, and Physics classroom unit. The projects and activities
in this unit were developed to help foster student learning and
understanding of radio astronomy, the electromagnetic spectrum,
wave dynamics, signal propagation, meteor detection, and radio
frequency interference. Additionally, this RET project utilizes the
SEARFE (Students Examining Australia???s Radio Frequency Environment)
software developed for use with the AR3000A communications receiver to
scan and monitor frequencies across the radio bandwidth to determine
areas of low and high usage in the radio spectrum. Classroom activities
include Scanning Protected Radio Astronomy Bandwidths, Investigating the
Radio Environment, Time Variation of Signal Strength, Signal Strength
vs. Location Studies, Detecting Meteors using the AR300A Receiver,
Mapping the RFI Environment of Your School, AM Radio Interference,
and Signal Propagation Effects. The primary focus of the unit???s
activities is to address the Massachusetts State Science Frameworks for
electromagnetic radiation, waves, cosmology, and matter and energy
in the Earth system and foster an understanding of how everyday
communications devices may cause radio frequency interference with
sensitive radio astronomy equipment. The projects and activities in
the unit will be used in the classroom, amended, and the results of
the classroom experience will be discussed.
Title: Permafrost: An International Approach to 21th Century
Challenges
Authors: Brown, J.
Bibcode: 2003AGUFM.C11A..02B
Altcode:
Whereas glaciers are easily discernible to the human eye and
satellites, permafrost terrains and their physical components are not
easily detected from the surface without supplemental knowledge and
measurements. In the Northern Hemisphere, approximately 17 million
km2 of exposed land contains some extent of permafrost or
ground that remains frozen for more than two years. The vast majority,
or 11 million km2, of permafrost terrain has temperatures
of 5° C or below, with perennially frozen ground underlying
essentially all ground surfaces to considerable depths. Permafrost
in the remaining regions, including mid-latitude mountains, is both
warmer and is spatially variable (discontinuous). As climate warms
the uppermost permafrost is subjected to increase thaw with resulting
ground subsidence, accelerated erosion, and related biogeochemical
modifications. The challenging questions to geocryologists, modelers
and the public relate to the rate of change and the spatial variability
of the projected thaw, particularly in the warmer zones where actual
areal and subareal distribution of permafrost is poorly known. An
international network of active layer measurements and borehole
sites now exists under the Global Climate Observing System (GCOS),
but requires additional sites for representative coverage. This
Global Terrestrial Network for Permafrost (GTN-P) is coordinated by
the 24-member, International Permafrost Association. At the Eighth
International Conference on Permafrost (ICOP) in Zurich in July 2003,
the IPA Council agreed on the scope of new activities for the next
five years, many of which will be undertaken in cooperation with other
international organizations (e.g. WCRP/CliC; ICSI, IASC, SCAR, IGU,
IUGS). Examples of the activities of the IPA Working Groups are:
1. Antarctic Permafrost and Periglacial Environments (active
layer processes, maps, database). 2. Coastal and Offshore
Permafrost (sediment and organic transfers, subsea permafrost
dynamics). 3. Cryosol (Antarctic soil map, soil database). 4. Glacier and Permafrost Hazards in High Mountains (interaction of
ice and permafrost on slopes). 5. Isotopes and Geochemistry of
Permafrost (paleo-reconstruction, modern processes). 6. Mapping
and Modelling of Mountain Permafrost (standardize map legends and
maps, multi-dimensional models). 7. Periglacial Processes
and Environments (past and present processes, field manual of
measurements). 8. Permafrost and Climate (monitoring, impact
assessments, inter-comparisons of models). 9. Permafrost
Astrobiology (survivability of life on planets and analogous Earth
environments). 10. Permafrost Engineering (case studies, climate
impacts on infrastructure). The Data Committee facilitates
recovery of data, web access, and CD data production. These activities
will provide added insight into past, present and future occurrences
and responses of permafrost to climate change. They can contribute to
activities of the International Polar Year. Results will be reported at
the Ninth ICOP in Fairbanks, Alaska, in summer 2008. Current information
is available on the IPA web site and in annual issues of Frozen Ground.
Title: Regularized Electron Flux Spectra in the 2002 July 23 Solar
Flare
Authors: Piana, Michele; Massone, Anna Maria; Kontar, Eduard P.;
Emslie, A. Gordon; Brown, John C.; Schwartz, Richard A.
Bibcode: 2003ApJ...595L.127P
Altcode:
By inverting the Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI) hard X-ray photon spectrum with the Tikhonov regularization
algorithm, we infer the effective mean electron source spectrum for
a time interval near the peak of the 2002 July 23 event. This inverse
approach yields the smoothest electron flux spectrum consistent with the
data while retaining real features, such as local minima, that cannot
be found with forward model-fitting methods that involve only a few
parameters. A significant dip in the recovered mean source electron
spectrum near E=55 keV is noted, and its significance briefly discussed.
Title: An Explanation for Non-Power-Law Behavior in the Hard X-Ray
Spectrum of the 2002 July 23 Solar Flare
Authors: Kontar, Eduard P.; Brown, John C.; Emslie, A. Gordon;
Schwartz, Richard A.; Smith, David M.; Alexander, R. Calum
Bibcode: 2003ApJ...595L.123K
Altcode:
High-resolution Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI) data reveal that solar flare hard X-ray spectra show systematic
deviations from power-law behavior. Even for injection of a power-law
electron spectrum, such deviations are expected because of a number
of effects, including nonuniform target ionization and solar albedo
backscattering of the primary hard X-ray flux. In this Letter, we
examine 1 keV resolution hard X-ray spectra for the intense 2002 July
23 event, corrected for the effects of decimation, pulse pileup,
and background. We find that the observed spectra indeed deviate
from a power-law behavior in a manner consistent with the effects
of nonuniform target ionization. Further, this interpretation of
the observed deviations requires that the amount of coronal material
increases during the initial phase of the flare. The implications of
this discovery for models of atmospheric response to flare heating
are discussed.
Title: The Determination and Use of Mean Electron Flux Spectra in
Solar Flares
Authors: Brown, John C.; Emslie, A. Gordon; Kontar, Eduard P.
Bibcode: 2003ApJ...595L.115B
Altcode:
Hard X-ray spectra in solar flares provide information on electron
acceleration and propagation processes. We here point out that
the inference of these processes involves two distinct steps: (1)
the model-independent deconvolution of the hard X-ray spectrum to
obtain the effective mean electron spectrum F(E) in the source and (2)
the model-dependent interpretation of this mean spectrum in terms of
physical processes operating in that source. Thus, the mean electron
spectrum is a natural ``middle ground'' on which to compare the
predictions of models with observations, and we urge the presentation
of results, both from analysis of photon spectra and from modeling
of candidate physical processes, in the form of F(E) spectra. We
consider the constraints that various source models impose on F(E),
and we present explicit forms for an illustrative F(E) corresponding
to the injection of a power-law spectrum of electrons into a thick
target with a nonuniform ionization level.
Title: XMM-Newton observations of the nitrogen-rich Wolf-Rayet star
WR 1
Authors: Ignace, R.; Oskinova, L. M.; Brown, J. C.
Bibcode: 2003A&A...408..353I
Altcode:
We present XMM-Newton results for the X-ray spectrum from the N-rich
Wolf-Rayet (WR) star WR 1. The EPIC instrument was used to obtain a
medium-resolution spectrum. The following features characterize this
spectrum: (a) significant emission ``bumps'' appear that are coincident
with the wavelengths of typical strong lines, such as MgXI, SiXIII,
and SXV; (b) little emission is detected above 4 keV, in contrast to
recent reports of a hard component in the stars WR 6 and WR 110 which
are of similar subtype; and (c) evidence for sulfur K-edge absorption
at about 2.6 keV, which could only arise from absorption of X-rays by
the ambient stellar wind. The lack of hard emission in our dataset is
suggestive that WR 1 may truly be a single star, thus representing
the first detailed X-ray spectrum that isolates the WR wind alone
(in contrast to colliding wind zones). Although the properties of the
S-edge are not well-constrained by our data, it does appear to be real,
and its detection indicates that at least some of the hot gas in WR
1 must reside interior to the radius of optical depth unity for the
total absorptive opacity at the energy of the edge.
Title: Implications of solar flare hard X-ray ``knee'' spectra
observed by RHESSI
Authors: Conway, A. J.; Brown, J. C.; Eves, B. A. C.; Kontar, E.
Bibcode: 2003A&A...407..725C
Altcode:
We analyse the RHESSI photon spectra of four flares that exhibit
significant deviations from power laws - i.e. changes in the ``local''
Hard X-ray spectral index. These spectra are characterised by two
regions of constant power law index connected by a region of changing
spectral index - the ``knee''. We develop theoretical and numerical
methods of describing such knees in terms of variable photon spectral
indices and we study the results of their inversions for source mean
thin target and collisional thick target injection electron spectra. We
show that a particularly sharp knee can produce unphysical negative
values in the electron spectra, and we derive inequalities that
can be used to test for this without the need for an inversion to
be performed. Such unphysical features would indicate that source
model assumptions were being violated, particularly strongly for
the collisional thick target model which assumes a specific form for
electron energy loss. For all four flares considered here we find that
the knees do not correspond to unphysical electron spectra. In the
three flares that have downward knees we conclude that the knee can be
explained in terms of transport effects through a region of non-uniform
ionisation. In the other flare, which has an upward knee, we conclude
that it is most likely a feature of the accelerated spectrum.
Title: On Large-Scale Magnetic Field Reversals in the Outer Galaxy
Authors: Brown, J. C.; Taylor, A. R.; Wielebinski, R.; Mueller, P.
Bibcode: 2003ApJ...592L..29B
Altcode:
We combine the observations of rotation measures of extragalactic
radio sources from the Canadian Galactic Plane Survey and pulsars to
investigate the question of magnetic field reversals in the outer
Galaxy. Our results are consistent with there being no reversal in
the Galactic magnetic field beyond the solar radius. We reconcile our
conclusions with the results of previous studies that have been used
to argue the presence of such reversals.
Title: Coronal scattering as a source of flare-associated polarized
hard X-rays
Authors: Hudson, H. S.; Hurford, G. J.; Brown, J. C.
Bibcode: 2003SoPh..214..171H
Altcode:
We consider the scattering of flare-associated X-rays above 1
keV at coronal heights, particularly from regions of enhanced
density. This includes a discussion of the polarization of the
scattered X-rays. Although the scattered radiation would not be
bright by comparison with the total hard X-ray flux from a flare,
its detectability would be enhanced for events located a few degrees
behind the limb for which the dominant `footpoint' hard X-ray sources
are occulted. Thus we predict that major flares occurring beyond the
solar limb may be detectable via scattering in density enhancements
that happen to be visible above the limb, and that such sources
may be strongly polarized. Since thin-target bremsstrahlung will
generally greatly exceed the scattered thick-target flux in flare loops
themselves, these considerations apply only to coronal structures that
do not contain significant populations of non-thermal electrons.
Title: On multicomponent effects in stellar winds of stars at
extremely low metallicity
Authors: Krtička, J.; Owocki, S. P.; Kubát, J.; Galloway, R. K.;
Brown, J. C.
Bibcode: 2003A&A...402..713K
Altcode: 2003astro.ph..3026K
We calculate multicomponent line-driven wind models of stars at
extremely low metallicity suitable for massive first generation
stars. For most of the models we find that the multicomponent wind
nature is not important for either wind dynamics or for wind temperature
stratification. However, for stars with the lowest metallicities we
find that multicomponent effects influence the wind structure. These
effects range from pure heating to possible fallback of the nonabsorbing
wind component. We present a simple formula for the calculation of
metallicity for which the multicomponent effects become important. We
show that the importance of the multicomponent nature of winds of
low metallicity stars is characterised not only by the low density of
driving ions, but also by lower mass-loss rate.
Title: The conspicuous absence of X-ray emission from carbon-enriched
Wolf-Rayet stars
Authors: Oskinova, L. M.; Ignace, R.; Hamann, W. -R.; Pollock,
A. M. T.; Brown, J. C.
Bibcode: 2003A&A...402..755O
Altcode: 2003astro.ph..3025O
The carbon-rich WC5 star WR 114 was not detected during a 15.9
ksec XMM-Newton, observation, implying an upper limit to the
X-ray luminosity of LX <∼ 2.5x 1030 erg
s-1 and to the X-ray to bolometric luminosity ratio of
LX/Lbol <∼ 4*E-9. This confirms
indications from earlier less sensitive measurements that there has
been no convincing X-ray detection of any single WC star. This lack
of detections is reinforced by XMM-Newton, and CHANDRA observations
of WC stars. Thus the conclusion has to be drawn that the stars
with radiatively-driven stellar winds of this particular class are
insignificant X-ray sources. We attribute this to photoelectronic
absorption by the stellar wind. The high opacity of the metal-rich and
dense winds from WC stars puts the radius of optical depth unity at
hundreds or thousands of stellar radii for much of the X-ray band. We
believe that the essential absence of hot plasma so far out in the
wind exacerbated by the large distances and correspondingly high
ISM column densities makes the WC stars too faint to be detectable
with current technology. The result also applies to many WC stars in
binary systems, of which only about 20% are identified X-ray sources,
presumably due to colliding winds.
Title: Rotation Measures of Compact Sources in the Canadian Galactic
Plane Survey
Authors: Brown, J. C.; Taylor, A. R.; Jackel, B. J.
Bibcode: 2003ApJS..145..213B
Altcode:
The Canadian Galactic Plane Survey is providing new rotation measures
(RMs) for compact extragalactic sources in the Galactic plane at a
solid-angle density of roughly 1 source per square degree. To date,
we have derived reliable RM values for 380 sources along lines of sight
through the disk of the Galaxy in the first and second quadrants. The
purpose is to provide a data set useful for studies of the magneto-ionic
component of the Galactic interstellar medium (ISM). We present the
method used to obtain the measurements and the resulting RMs.
Title: VizieR Online Data Catalog: Rotation measures of compact
sources in CGPS (Brown+, 2003)
Authors: Brown, J. C.; Taylor, A. R.; Jackel, B. J.
Bibcode: 2003yCat..21450213B
Altcode:
The Canadian Galactic Plane Survey is providing new rotation measures
(RMs) for compact extragalactic sources in the Galactic plane at a
solid-angle density of roughly 1 source per square degree. To date,
we have derived reliable RM values for 380 sources along lines of sight
through the disk of the Galaxy in the first and second quadrants. The
purpose is to provide a data set useful for studies of the magneto-ionic
component of the Galactic interstellar medium (ISM). We present the
method used to obtain the measurements and the resulting RMs. (1
data file).
Title: Do Magnetically Torqued Disks (MTDs) Exist Around Early-Type
Stars?
Authors: Brown, J. C.; Telfer, D. C.; Hanuschik, R. W.; Cassinelli,
J. P.
Bibcode: 2003ASPC..305..285B
Altcode: 2003mfob.conf..285B
No abstract at ADS
Title: X-ray Aureola of Central Stars
Authors: Oskinova, L.; Brown, J. C.
Bibcode: 2003IAUS..209..425O
Altcode:
No abstract at ADS
Title: Emission Line Profiles from Be Stars - A Test of the MTD Model
Authors: Telfer, D.; Brown, J. C.; Hanuschik, R.; Cassinelli, J. P.
Bibcode: 2003ASPC..305..291T
Altcode: 2003mfob.conf..291T
No abstract at ADS
Title: Energetic Particles in Solar and Stellar Coronae
Authors: Brown, J. C.; O'Malley, L.; Smolkin, S.
Bibcode: 2002ASPC..277..135B
Altcode: 2002sccx.conf..135B
No abstract at ADS
Title: Flare electron energy budgets - what is RHESSI telling us?
Authors: Brown, J. C.; Kontar, E.; MacKinnon, A. L.; Aschwanden, M. J.
Bibcode: 2002ESASP.506..253B
Altcode: 2002ESPM...10..253B; 2002svco.conf..253B
We address the idea that energetic particles may play a key role in the
dissipation and transport of energy in flares. After three decades of
predictions of spatial, spectral and temporal distributions of hard X-
and γ-rays, the various models can now be quantitatively tested against
RHESSI high resolution spectral imaging data. It is shown that RHESSI
results for a number of HXR flares are in very good agreement with
predictions of the basic thick target model (Brown 1971) regarding
source height as a function of energy and of global HXR spectrum. A
single power-law injection spectrum and purely collisional transport
(no wave generation) fit well the decrease of source peak height
with increasing energy for very plausible chromospheric density
structures. When the target ionisation drop across the transition one
is included, the global HXR spectrum agrees well with observed "knee"
spectra without any feature added to a scale-less power-law electron
injection spectrum. This result favours statistically distributed, as
opposed to single large scale, E-field acceleration. Whether energetic
electron beams actually dominate flare energy transport still depends
on accurate inference of the low energy thermal/nonthermal spectral
transition though RHESSI results to date support the idea. The ion
energy budget is also briefly mentioned.
Title: X-rays from Wolf-Rayet Stars
Authors: Ignace, R.; Oskinova, L. M.; Pollock, A. M. T.; Brown, J. C.;
Hamann, W. -R.
Bibcode: 2002AAS...201.3308I
Altcode: 2002BAAS...34.1156I
We describe observations of several apparently single Wolf-Rayet stars
that have now been observed with the XMM-Newton instrument. Prior
to this, the X-ray data of Wolf-Rayet stars consisted primarily of
ROSAT passband detections (many of which were marginal). Data for
the nitrogen-rich stars WR 6 (EZ CMa; HD50896) and WR 110 have been
described by Skinner etal, who unexpectedly found a hard component in
the spectra. We report on a third WN star, WR 1, which also shows the
hint of a hard tail. In our program we also observed the carbon-rich
star WR 114. Even after 19000 seconds of integration, we were unable
to detect this star, which places a 1-sigma upper limit to the ratio
of X-ray to Bolometric luminosity of 10-8.4, about 25 times
smaller than typical O stars. (This research has been supported by
NASA grant NAG5-12557.)
Title: Empirical correction of RHESSI spectra for photospheric albedo
and its effect on inferred electron spectra
Authors: Alexander, R. Calum; Brown, John C.
Bibcode: 2002ESASP.506..271A
Altcode: 2002ESPM...10..271A; 2002svco.conf..271A
Photospheric Compton backscatter (albedo) makes a significant
contribution to observed hard X-ray (HXR) spectral fluxes over the
RHESSI energy range and should be allowed for in spatially integrated
HXR spectral interpretation. The high HXR spectral resolution of RHESSI
creates the chance for precise study of source electron spectra provided
the observed spectra are well corrected for non-primary effects at the
sun including albedo, directivity, source ionisation variations and
the like. However the full correction problem is nonlinear and messy
but we offer a simple approximate first order correction procedure
for global HXR spectra based upon empirical fits to published albedo
simulations. We also illustrate the impact of this correction on
inferred electron spectra for the thin and thick target models with
the Kramers cross-section.
Title: X-ray observations with RHESSI and collisional thick target
model with nonuniform target ionisation
Authors: Kontar, Eduard P.; Brown, John C.; McArthur, Guillian K.
Bibcode: 2002ESASP.506..311K
Altcode: 2002ESPM...10..311K; 2002svco.conf..311K
Past analysis of the flare Hard X-Ray (HXR) spectra have largely ignored
the effect of nonuniform ionisation along the electron paths in the
thick target model, though it is very significant for well-resolved
spectra. The fit to RHESSI data on four flares for a single powerlaw
F0(E0) is much improved when ionisation structure
is included. The expression involves the column depth N*
of the transition region in the flare loop as one of the parameters.
Title: Chromospheric density and height measurements of the
2002-Feb-20 flare observed with RHESSI
Authors: Aschwanden, Markus J.; Brown, John C.; Kontar, Eduard P.
Bibcode: 2002ESASP.506..275A
Altcode: 2002ESPM...10..275A; 2002svco.conf..275A
We present the first chromospheric density and height measurements
made with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
spacecraft during the flare of 2002-Feb-22, 11:06 UT. Thanks to the
high energy resolution of the germanium-cooled hard X-ray detectors on
RHESSI we can measure the flare source positions with a high accuracy
as a function of energy. Using a forward-fitting algorithm for image
reconstruction, we find a systematic decrease in the altitudes of the
source centroids z(ɛ) as a function of increasing hard X-ray energy
ɛ, as expected in the thick-target bremsstrahlung model of Brown. The
altitude of hard X-ray emission as a function of photon energy ɛ can
be characterized by a powerlaw function in the ɛ = 15-50 keV energy
range, viz. z(ɛ) ≍ 2.3 (ɛ/20 keV)-1.3 Mm. Based on a
purely collisional 1-D thick-target model, this height dependence can
be inverted into a chromospheric density model n(z), which follows
the powerlaw function ne(z) = 1.25×1013 (z/1
Mm)-2.5 cm-3. This density is comparable with
models based on optical/UV spectrometry in the chromospheric height
range, while at a height of h≍1000-2500 km, it is more consistent
with the "spicular extended-chromosphere model" inferred from radio
sub-mm observations. In coronal heights of the flare loop, the RHESSI
inferred desities are comparable with soft X-ray and radio observations.
Title: The Pressure Factor in Europa's Aqueous Evolution
Authors: Vance, S.; Brown, J.; Kargel, J. S.
Bibcode: 2002AGUFM.P72B0508V
Altcode:
Equation of state data at high pressure need to be incorporated into
computational efforts to understand the evolution of the composition of
Europa's ocean. These efforts also have applications to other planetary
bodies and for Earth's deep oceans. While investigators refer to some
experimental constraints in consideration of the likely effects of
high pressures on the relevant aqueous geochemistry, calculations have
not yet taken them into account. Specific processes requiring a better
understanding of the role of high pressures include devolatilization
within the rocky interior, the evolution of volatiles released into the
ocean, metamorphism of hydrated salts on the seafloor, and temperature
oscillations of the system in response to changes in tidal heating. We
derive chemical potentials for aqueous solutions from speeds of sound
measured as functions of pressure and temperature. These parameters are
determined in our laboratory through the method of impulsive stimulated
scattering. A complete equation of state for aqueous sodium sulfate up
to 34 kbar and 573 K is reported in terms of activity coefficients and
volumes of mixing. Systematic trends within this important chemical
system provide guidance in constructing the overall framework of
aqueous geochemistry in multicomponent systems at elevated pressures.
Title: Detecting a liquid and solid H2O layer by geophysical methods
Authors: Yoshikawa, K.; Romanovsky, V.; Tsapin, A.; Brown, J.
Bibcode: 2002AGUFM.P71A0450Y
Altcode:
The objective is to detect the hydrological and cryological structure of
the cold continuous permafrost subsurface using geophysical methods. We
believe that a lot of water potentially exists as solid and liquid
phases underground on Mars. It is likely that the liquid fluid would
be high in saline concentration (brine). The ground freezing process
involves many hydrological processes including enrichment of the brine
layer. The brine layer is an important environment for ancient and/or
current life to exist on terrestrial permafrost regions. The existence
of a Martian brine layer would increase the possibility of the existence
of life, as on Earth. In situ electric resistivity measurement will be
the most efficient method to determine brine layer as well as massive
H2O ice in the permafrost. However, the wiring configuration is unlikely
to operate on the remote planetary surface. Satellite-born Radar
and/or EM methods will be the most accessible methods for detecting
the hydrological and cryological structure. We are testing several
geophysical methods at the brine layer site in Barrow and massive
pingo ice site in Fairbanks, Alaska. The radar system is affected by
the dielectric properties of subsurface materials, which allows for
evidence of liquid phase in the frozen ground. The dielectric constant
varies greatly between liquid water and frozen ground. The depth of the
terrestrial (and probably Martian) brine layer is frequently located
deeper than the maximum detecting depth of the impulse type of the
ground penetrating radar system. Once we develop a radar system with
a deeper penetrating capability (Lower frequency), the dispersion of
the ground ice will be the key function for interpretation of these
signals. We will improve and use radar signals to understand the
hydrological and cryological structure in the permafrost. The core
samples and borehole temperature data validate these radar signals.
Title: Chromospheric Height and Density Measurements in a Solar
Flare Observed with RHESSI II. Data Analysis
Authors: Aschwanden, Markus J.; Brown, John C.; Kontar, Eduard P.
Bibcode: 2002SoPh..210..383A
Altcode:
We present an analysis of hard X-ray imaging observations from one
of the first solar flares observed with the Reuven Ramaty High-Energy
Solar Spectroscopic Imager (RHESSI) spacecraft, launched on 5 February
2002. The data were obtained from the 22 February 2002, 11:06 UT flare,
which occurred close to the northwest limb. Thanks to the high energy
resolution of the germanium-cooled hard X-ray detectors on RHESSI
we can measure the flare source positions with a high accuracy as
a function of energy. Using a forward-fitting algorithm for image
reconstruction, we find a systematic decrease in the altitudes of
the source centroids z(ε) as a function of increasing hard X-ray
energy ε, as expected in the thick-target bremsstrahlung model of
Brown. The altitude of hard X-ray emission as a function of photon
energy ε can be characterized by a power-law function in the ε=15-50
keV energy range, viz., z(ε)≈2.3(ε/20 keV)−1.3
Mm. Based on a purely collisional 1-D thick-target model, this
height dependence can be inverted into a chromospheric density model
n(z), as derived in Paper I, which follows the power-law function
ne(z)=1.25×1013(z/1 Mm)−2.5
cm−3. This density is comparable with models based on
optical/UV spectrometry in the chromospheric height range of h≲1000
km, suggesting that the collisional thick-target model is a reasonable
first approximation to hard X-ray footpoint sources. At h≈1000-2500
km, the hard X-ray based density model, however, is more consistent
with the `spicular extended-chromosphere model' inferred from radio
sub-mm observations, than with standard models based on hydrostatic
equilibrium. At coronal heights, h≈2.5-12.4 Mm, the average flare
loop density inferred from RHESSI is comparable with values from
hydrodynamic simulations of flare chromospheric evaporation, soft
X-ray, and radio-based measurements, but below the upper limits set
by filling-factor insensitive iron line pairs.
Title: Chromospheric Height and Density Measurements in a Solar
Flare Observed with RHESSI I. Theory
Authors: Brown, John C.; Aschwanden, Markus J.; Kontar, Eduard P.
Bibcode: 2002SoPh..210..373B
Altcode:
We obtain a theoretical description of the height (z) distribution
of flare hard X-rays in the collisional thick-target model as a
function of photon energy ε. This depends on the target atmosphere
density structure n(z) and on the beam spectral index δ. We
show that by representing the data in terms of the 1-D function
z(ε) defining where the emission peaks as a function of ε it is
possible to derive n(z) from data on z(ε). This is done first on
the basis of a simple stopping depth argument then refined to allow
for the dependence on spectral index δ. The latter is worked out
in detail for the case of a parameterization n(z)=n0
(z/z0)−b which yields numerical results for
z(ε) well fit by z(ε)∼ε−α, with α dependent on δ,
which is also found to fit well to actual observations. This enables
derivation of flare loop n(z) in terms of n0,b from RHESSI
data in an entirely novel way, independent of other density diagnostic
methods, and also of how n(z) varies with time in flares such as by
evaporation, as detailed in companion Paper II.
Title: Empirical correction of RHESSI spectra for photospheric albedo
and its effect on inferred electron spectra
Authors: Alexander, R. Calum; Brown, John C.
Bibcode: 2002SoPh..210..407A
Altcode:
Photospheric Compton backscatter (albedo) makes a significant
contribution to observed hard X-ray (HXR) spectral fluxes over
the RHESSI energy range and should be allowed for in HXR spectral
interpretation. The full correction problem is nonlinear and messy
but we offer a simple approximate first-order correction procedure
for global HXR spectra based upon empirical fits to published albedo
simulations. We also illustrate the impact of this correction on
inferred electron spectra for the thin- and thick-target models.
Title: Nonuniform Target Ionization and Fitting Thick Target Electron
Injection Spectra to RHESSI Data
Authors: Kontar, Eduard P.; Brown, John C.; McArthur, Guillian K.
Bibcode: 2002SoPh..210..419K
Altcode:
Past analyses of flare hard X-ray (HXR) spectra have largely
ignored the effect of nonuniform ionization along the electron
paths in the thick-target model, though it is very significant
for well-resolved spectra. The inverse problem (photon spectrum
to electron injection spectrum F0(E0)) is
disturbingly non-unique. However, we show that it is relatively simple
to allow for the effect in forward fitting of parametric models of
F0(E0)) and provide an expression to evaluate it
for the usual single power-law form of F0(E0)).The
expression involves the column depth N* of the transition
region in the flare loop as one of the parameters so data fitting can
enable derivation of N* (and its evaporative evolution)
as part of the fitting procedure. The fit to RHESSI data on four
flares for a single power law F0(E0)) is much
improved when ionization structure is included compared to when the
usual fully ionized approximation is used. This removes the need, in
these events at least, to invoke broken power laws, or other forms,
of the acceleration spectrum F0(E0)) to explain
the observed photon spectrum
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.
Bibcode: 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 (>107) 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: A Magnetically Torqued Disk Model for Be Stars
Authors: Cassinelli, J. P.; Brown, J. C.; Maheswaran, M.; Miller,
N. A.; Telfer, D. C.
Bibcode: 2002ApJ...578..951C
Altcode: 2002astro.ph..7370C
Despite extensive study, the mechanisms by which Be star disks acquire
high densities and angular momentum while displaying variability on
many timescales are still far from clear. In this paper, we discuss
how magnetic torquing may help explain disk formation with the observed
quasi-Keplerian (as opposed to expanding) velocity structure and their
variability. We focus on the effects of the rapid rotation of Be stars,
considering the regime where centrifugal forces provide the dominant
radial support of the disk material. Using a kinematic description of
the angular velocity, vφ(r), in the disk and a parametric
model of an aligned field with a strength B(r), we develop analytic
expressions for the disk properties that allow us to estimate the
stellar surface field strength necessary to create such a disk for
a range of stars on the main sequence. The fields required to form a
disk are compared with the bounds previously derived from photospheric
limiting conditions. The model explains why disks are most common for
main-sequence stars at about spectral class B2 V. The earlier type stars
with very fast and high-density winds would require unacceptably strong
surface fields (>103 G) to form torqued disks, while the
late B stars (with their low mass-loss rates) tend to form disks that
produce only small fluxes in the dominant Be diagnostics. For stars at
B2 V the average surface field required is about 300 G. The predicted
disks provide an intrinsic polarization and a flux at Hα comparable to
observations. The radial extent of our dense quasi-Keplerian disks is
compatible with typical estimates. We also discuss whether the effect
on field containment of the time-dependent accumulation of matter in
the flux tubes/disk can help explain some of the observed variability
of Be star disks.
Title: What Do "Filling Factors" of Wind X-Ray Sources Tell Us?
Authors: Oskinova, L. M.; Brown, J. C.; Cassinelli, J. P.; Ignace, R.
Bibcode: 2002ASPC..260..205O
Altcode: 2002iwms.conf..205O
No abstract at ADS
Title: The Structure of the Magnetic Field in the Outer Galaxy from
Rotation Measure Observations through the Disk
Authors: Brown, J. C.; Taylor, A. R.
Bibcode: 2001ApJ...563L..31B
Altcode:
High-resolution 21 cm polarization data from the Canadian Galactic Plane
Survey are yielding radio sources with well-defined rotation measures
(RMs) at a solid angle density of roughly 1 source deg-2,
approximately 10 times greater than previous RM surveys in the plane
of the Galaxy. The predominance of negative RMs in the second quadrant
suggests, in contradiction to previous work, that there is no global
magnetic field reversal between the solar circle and the Perseus
arm. In addition, these data reveal details in the magnetoionic medium
not previously observed and suggest that the random component of the
magnetic field may be preferentially aligned to the uniform component,
in contrast to the common assumption of an isotropic distribution.
Title: The effect of wave generation on HXR bremsstrahlung spectra
from flare thick-target beams
Authors: Haydock, E. L.; Brown, J. C.; Conway, A. J.; Emslie, A. G.
Bibcode: 2001SoPh..203..355H
Altcode:
Fast electrons in the solar atmosphere are detected by their hard X-ray
bremsstrahlung and by type III radio bursts caused by `bump-on-tail'
plasma wave generation. This paper investigates empirically the effect
of wave generation on the HXR spectrum. Purely collisional propagation
of an electron beam generates a bump in the distribution function, due
to stopping of low-velocity electrons. The consequent positive gradient
means there is a possibility of wave generation, production of type
III radio bursts, and energy redistribution of the electron beam. We
have represented this relaxation parametrically and calculated the
global bremsstrahlung HXR emission spectrum. We show that for a range
of relaxed forms, with different local electron spectral shapes, the
bremsstrahlung spectrum integrated over the whole target is identical
in shape to the purely collisionally evolved beam. Our results show
that spatially integrated HXR spectral measurements would be unable to
distinguish between the presence or absence of relaxation effects. Only
spatially resolved hard X-ray spectra, such as anticipated from the
HESSI mission, will be able to remove this ambiguity in HXR diagnostics
of beam relaxation.
Title: On the wavelength drift of spectral features from structured
hot star winds
Authors: Hamann, W. -R.; Brown, J. C.; Feldmeier, A.; Oskinova, L. M.
Bibcode: 2001A&A...378..946H
Altcode:
Spectral lines formed in stellar winds from OB stars are observed
to exhibit profile variations. Discrete Absorption Components (DACs)
show a remarkably slow wavelength drift with time. In a straightforward
interpretation, this is in sharp contradiction to the steep velocity
law predicted by the radiation-driven wind theory, and by semi-empirical
profile fitting. In the present paper we re-discuss the interpretation
of the drift rate. We show that the Co-rotating Interaction Region (CIR)
model for the formation of DACs does not explain their slow drift rate
as a consequence of rotation. On the contrary, the apparent acceleration
of a spectral CIR feature is even higher than for the corresponding
kinematical model without rotation. However, the observations can
be understood by distinguishing between the velocity field of the
matter flow, and the velocity law for the motion of the patterns in
which the DAC features are formed. If the latter propagate upstream
against the matter flow, the resulting wavelength drift mimics a much
slower acceleration although the matter is moving fast. Additional
to the DACs, a second type of recurrent structures is present in
observed OB star spectra, the so-called modulations. In contrast to
the DACs, these structures show a steep acceleration compatible with
the theoretically predicted velocity law. We see only two possible
consistent scenarios. Either, the wind is accelerated fast, and the
modulations are formed in advected structures, while the DACs come
from structures which are propagating upstream. Or, alternatively,
steep and shallow velocity laws may co-exist at the same time in
different spatial regions or directions of the wind.
Title: An Empirical Method to Determine Electron Energy Modification
Rates from Spatially Resolved Hard X-Ray Data
Authors: Emslie, A. Gordon; Barrett, Richard K.; Brown, John C.
Bibcode: 2001ApJ...557..921E
Altcode:
We discuss a technique for determining the energy loss (or gain) rates
affecting high-energy electrons from spatially resolved observations
of the hard X-ray bremsstrahlung signature that they produce. The
procedure involves two main steps-determining the local electron
flux spectrum from inversion of the hard X-ray spectrum using a
matrix technique, and evaluating the changes (due to energy losses)
in the electron flux spectra at different positions in the source
via the continuity equation for total electron flux. In order to
test the viability of this numerical technique, we generate a set of
simulated hard X-ray photon count spectra, corresponding to different
models of electron energy loss, characterized parametrically through
an exponent α in the energy loss rate equation, including the case
α=1, which corresponds to the electrons losing energy solely through
Coulomb collisions in an ionized target. We then add Poisson noise in
the hard X-ray count rate spectra, based on a nominal detector area
and observation integration interval, and use the above procedure on
this simulated noisy data set to determine the energy-loss rate as
a function of energy in each model. For count rates associated with
large flares, the procedure reproduces well the collisional energy
loss profile for electron energies up to about 40 keV, even when no
statistical smoothing (regularization) methodology is applied. Above
this energy, the method breaks down due to the data noise present, but
the method could be extended to higher energies by use of a suitable
regularized inversion technique. When other (noncollisional) models
of energy loss are used to generate the simulated hard X-ray data,
the procedure produces energy loss forms that are demonstrably and
quantifiably different from the purely collisional case. This shows
that even using a simple, unregularized inversion procedure, spatially
resolved hard X-ray spectra can indeed be used to compare models of
energy transport in solar flares. We discuss our results with reference
to the forthcoming High Energy Solar Spectroscopic Imager mission,
which will provide data of the necessary quality for the application
of our technique.
Title: Modelling X-ray variability in the structured atmospheres of
hot stars
Authors: Oskinova, L. M.; Ignace, R.; Brown, J. C.; Cassinelli, J. P.
Bibcode: 2001A&A...373.1009O
Altcode: 2001astro.ph..4413O
We describe X-ray production in the atmospheres of hot, early-type stars
in the framework of a ``stochastic shock model''. The extended envelope
of a star is assumed to possess numerous X-ray emitting ``hot'' zones
that are produced by shocks and embedded in the ambient ``cold'' medium
in dynamical equilibrium. It is shown that the apparent lack of X-ray
variability on short ( ~ hours) timescales do not contradict a shock
model for X-ray production. The character of the X-ray variability is
found to depend on the frequency with which hot zones are generated,
the cool wind opacity to X-rays, and the wind flow parameters, such
as mass loss rate and terminal speed.
Title: An Empirical Method to Determine Electron Energy Modification
Rates from Spatially Resolved Hard X-ray Data
Authors: Emslie, A. G.; Barrett, R. K.; Brown, J. C.
Bibcode: 2001AGUSM..SP42A04E
Altcode:
We discuss a technique for determining the energy loss (or gain) rates
affecting high-energy electrons from spatially-resolved observations
of the hard X-ray bremsstrahlung signature that they produce. The
procedure involves two main steps -- determining the local electron
flux spectrum from inversion of the hard X-ray spectrum using a
matrix technique, and evaluating the changes (due to energy losses)
in the electron flux spectra at different positions in the source via
the continuity equation for total electron flux. In order to test the
viability of this numerical technique, we generate a set of simulated
hard X-ray photon count spectra, corresponding to different models
of electron energy loss, characterized parametrically through an
exponent α in the energy loss rate equation, including the case α
=1, which corresponds to the electrons losing energy solely through
Coulomb collisions in an ionized target. We then add Poisson noise in
the hard X-ray count rate spectra, based on a nominal detector area
and observation integration interval, and use the above procedure on
this simulated noisy data set to determine the energy loss rate as
a function of energy in each model. For count rates associated with
large flares, the procedure reproduces well the collisional energy
loss profile for electron energies up to about 40~keV, even when no
statistical smoothing (regularization) methodology is applied. Above
this energy, the method breaks down due to the data noise present, but
the method could be extended to higher energies by use of a suitable
regularized inversion technique. When other (non-collisional) models
of energy loss are used to generate the simulated hard X-ray data,
the procedure produces energy loss forms which are demonstrably
and quantifiably different from the purely collisional case. This
shows that even using a simple, unregularized inversion procedure,
spatially resolved hard X-ray spectra can indeed be used to compare
models of energy transport in solar flares. We discuss our results with
reference to the forthcoming High Energy Solar Spectroscopic Imager
(HESSI) mission, which will provide data of the necessary quality for
the application of our technique.
Title: Mechanisms for Coronal Mass Supply by Evaporative Micro-Events
Authors: Brown, J. C.; Krucker, S.; Güdel, M.; Benz, A. O.
Bibcode: 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: Photometric Examination of Possible Sub-Stellar Companions
of HD155826 and HD68456
Authors: Brown, J.; Bennum, D.; Rodrigue, M.; Schultz, A. B.; Backman,
D.; Vener, P.; Rosenthal, E.; Perriello, B.; Chen, H.; Ho, P. T. P.;
Burrows, A.; Schneider, G.; Lisse, C.; Christian, D.; Gorjian, V.
Bibcode: 2000AAS...197.1103B
Altcode: 2000BAAS...32.1416B
A low-mass stellar and substellar companion search program has
been completed using the Near-Infrared Camera and Multi-Object
Spectrometer (NICMOS) Camera 2 coronagraph aboard the Hubble Space
Telescope (HST). Coronagraphic observations of seven targets were
obtained with the F165M, F171M, F180M, and F207M filters. Of the seven
IR-excess stars observed, two ( HD155826 and HD68456 ) were found to
have potential companions within 4" from the parent star. We report
photometric measurements of the suspected companions and compare their
photometry to Gliese 229B. Support for this work was provided by NASA
through grant number G0-07385.03-96A from the Space Telescope Science
Institute (STScI).
Title: Hard X-Rays from Neutralized Ion Beams in Solar Flares
Authors: Brown, J. C.; Karlický, M.; Mandzhavidze, N.; Ramaty, R.
Bibcode: 2000ApJ...541.1104B
Altcode:
Under suitable conditions, hard X-rays (HXRs) may be emitted by a
neutralized proton beam due to the ``heating'' of the electrostatically
dragged electrons in collisions with a nearly neutral background
atmosphere. A simple estimate is made generalizing this HXR
emission mechanism to heavier ions dragging a neutralizing electron
current. Recent gamma-ray results on the energy content of flare ions
of >=1 MeV nucleon-1 are used to estimate the total HXR
yield above 20 keV or so which would be expected from these processes,
and in 19 flares the results are compared with HXR data in the same
events. It is found that only in two flares are the neutral beam HXRs
clearly important and that in a few others they may be significant. In
most events, however, the neutral beam HXR contribution is small,
though the ion energy is comparable with that of electrons.
Title: Mechanisms for dynamic coronal mass supply via evaporative
solar ``micro-events''
Authors: Brown, J. C.; Krucker, S.; Güdel, M.; Benz, A. O.
Bibcode: 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: NICMOS Search for Circumstellar Dust and Substellar Companions
around Six Nearby Main Sequence Stars
Authors: Vener, P. C.; Brown, J.; Bennum, D.; Rothstein, D.; Gurwell,
M.; Ho, P.; Schneider, G.; Schultz, A.; Backman, D.
Bibcode: 2000AAS...196.0205V
Altcode: 2000BAAS...32..676V
We report preliminary results from an HST/NICMOS search for planetary
debris and companions around six nearby stars. Each target system
has a far-IR excess indicating thermal emission from optically thin
dust. Observations were obtained in two modes, direct imaging and with
the NICMOS Camera 2 coronagraphic mode. Data reduction and analysis
were performed using both IRAF and the IDL/IDP3 software routines
developed by the NICMOS IDT. Our tenative results place limits on the
detectability of disks via near-IR scattered light as well as on the
brightness and location of point-source companions.
Title: Wolf-Rayet wind structure and optical variability
Authors: Li, Q.; Brown, J. C.; Ignace, R.; Cassinelli, J. P.; Oskinova,
L. M.
Bibcode: 2000A&A...357..233L
Altcode:
Results are presented on the expected variability of Wolf-Rayet
(WR) stars in broad-band optical polarimetry and photometry, and in
emission line profiles, due to an inhomogeneous random distribution
of blobs in spherical geometry. Time dependent 3-D simulations are
carried out with blob ejection random in time and direction, and the
radiation properties are evaluated in the optically thin limit. In
contrast with previous purely statistical analyses, inclusion in
the present treatment of a beta velocity law and stellar occultation
effects can yield results consistent with observations of the mean
polarisation bar p and the ratio R=sigma_p /sigma_phot of polarimetric
to photometric variability. Such consistency puts constraints on model
parameters. Indeed by considering combinations of the three observables
sigma_p , sigma_phot , and bar p it is possible to infer reasonably good
estimates of three wind-blob parameters - the beta of their velocity
law, the total mass loss rate dot M in blobs and the total number N
of blobs emitted per wind flow time ({R_*}/{v_{\infty}}), provided
the blobs are reasonably localised in angular and radial extent. It
is found that typical data requires beta >= 1.5, {cal N} ~ 20-50
and dot M ~ 10-4 M_\odot/year. The N estimate is consistent
with the number of observed narrow features on emission lines. Smaller
values of beta are excluded. This improved model shows that data do
not after all demand very dense blobs as previously suggested, and
offers a valuable diagnostic of WR wind structure parameters.
Title: Hot star polarimetric variability and the nature of wind
inhomogeneities
Authors: Brown, J. C.; Ignace, R.; Cassinelli, J. P.
Bibcode: 2000A&A...356..619B
Altcode:
The problem is addressed of how much hot star polarisation variability
can result from density redistribution processes within the wind as
opposed to localised enhancement of stellar mass loss rate, such
as ejections of wind inhomogeneities. For optically thin electron
scattering, we present a theory for the relative polarisation arising
from particle redistribution and consider several specific cases
relevant to interpreting observations of wind variability. It is
concluded that, allowing for partial cancellation of the contribution
from compressed and evacuated regions, density redistribution internal
to the wind can produce significant polarisation but only for processes
that redistribute wind material over relatively large radial or angular
scales. This conclusion favors extended spatial structures (e.g.,
from strong radiatively driven shocks) over localised condensations
(e.g., from radiative instabilities).
Title: Preconditioning the Differential Emission Measure
(Te) Inverse Problem
Authors: McIntosh, S. W.; Charbonneau, P.; Brown, J. C.
Bibcode: 2000ApJ...529.1115M
Altcode:
In an inverse problem of any kind, poor conditioning of the inverse
operator decreases the numerical stability of any unregularized
solution in the presence of data noise. In this paper we show that
the numerical stability of the differential emission measure (DEM)
inverse problem can be considerably improved by judicious choice of
the integral operator. Specifically, we formulate a combinatorial
optimization problem where, in a preconditioning step, a subset of
spectral lines is selected in such a way as to minimize explicitly the
condition number of the discretized integral operator. We tackle this
large combinatorial optimization problem using a genetic algorithm. We
apply this preconditioning technique to a synthetic data set comprising
of solar UV/EUV emission lines in the SOHO SUMER/CDS wavelength
range. Following which we test the same hypothesis on lines observed by
the Harvard S-055 EUV spectroheliometer. On performing the inversion
we see that the temperature distribution in the emitting region of
the solar atmosphere is recovered with considerably better stability
and smaller error bars when our preconditioning technique is used,
in both synthetic and ``real'' cases, even though this involves
the analysis of fewer spectral lines than in the ``All-lines''
approach. The preconditioning step leads to regularized inversions
that compare favorably to inversions by singular value decomposition,
while providing greater flexibility in the incorporation of physically
and/or observationally based constraints in the line selection process.
Title: Hard X-Rays from MeV Neutral Beams
Authors: Brown, J. C.; Karlicky, M.; Mandzhavidze, N.; Ramaty, R.
Bibcode: 2000ASPC..206..210B
Altcode: 2000hesp.conf..210B
No abstract at ADS
Title: Flare hard X-rays from neutral beams
Authors: Karlický, Marian; Brown, John C.; Conway, Andrew J.;
Penny, Gail
Bibcode: 2000A&A...353..729K
Altcode:
A new mechanism is presented for the production of bremsstrahlung
radiation from neutral beams (p+,e-) and its
possible relevance to flare heating and production of hard x-ray bursts
is discussed. Beam electrons lag behind the protons, due to differential
drag in collisions with the background, but their longitudinal
velocities are closely tied to the protons by the electric field
generated. However, collisions with the background also scatter the beam
electrons resulting in rms (quasi-thermal) transverse velocities well
in excess of the proton speed. We demonstrate the initial development
of this effect using an electrostatic particle simulation with scaled
collision rate and then study its full development using an approximate
analytic treatment. In particular, the heating of the beam electrons
under the bombardment effect of the background is limited by the warm
target effect but mean electron energies (`temperatures') of up to
E_e =~ 0.02Ep0 result during the propagation of a neutral
beam of initial proton energy Ep0. Thus, for example, HXR
bremsstrahlung in the range 20-200 keV can be generated by protons
in the range 1MeV-10MeV. The energy efficiency of the bremsstrahlung
production is also limited by the warm target effect but, depending on
the HXR spectrum, can exceed =~ 0.2 of the efficiency of the standard
thick target electron beam model. This suggests that the MeV neutral
beam model is, in terms of power requirements, unlikely to be the
source of `HXR-rich' flare bursts but that neutral beams able to
provide the impulsive flare heating will yield easily detectable HXR
burst signatures. Also, while the neutral beam model needs more power
( =~ 5x) than an electron beam to yield a given HXR burst flare, it
requires a much smaller beam number flux ( =~ 0.07 x). The issue of
the HXR spectral distribution expected from the neutral beam model is
also discussed.
Title: A Search for Substellar Companions of β Pic- and Vega-like
Stars Using HST/NICMOS
Authors: Brown, J.; Bennum, D.; Schultz, A. B.; Rodrigue, M.; Backman,
D.; Vener, P.; Rosenthal, E.; Perriello, B.; Chen, H.; Ho, P. T. P.;
Burrows, A.
Bibcode: 1999AAS...195.7801B
Altcode: 1999BAAS...31R1487B
We report preliminary results for a low-mass stellar and substellar
companion search program using the Near Infrared and Multi-Object
Spectrometer (NICMOS). The NICMOS Camera 2 coronagraph was used
to search in a region approximately 0.4\arcsec-4\arcsec from the
target stars. Targets were selected to take advantage of the onboard
acquisition software and were observed with single orbit visits. Seven
IR-excess stars were observed: HD10476, HD218396, HD48682, HD155826,
HD68456, HD87696, HD84117. Support for this work was provided by NASA
through grant number G0-07835.03-96A from the Space Telescope Science
Institute (STScI).
Title: A non-uniqueness problem in solar hard x-ray spectroscopy
Authors: Piana, M.; Barrett, R.; Brown, J. C.; McIntosh, S. W.
Bibcode: 1999InvPr..15.1469P
Altcode:
We consider the hard x-ray emission process by interaction between
the electrons and the ions in the solar atmosphere. We provide the
integral equations describing this process as an inverse problem
in the case of uniform ionization of the plasma and of a simple but
rather realistic approximation of non-uniform conditions. The singular
system of the integral operators is computed analytically in the
continuous case for the uniform ionization model and numerically in
the case of discrete data for both uniform and non-uniform ionization
conditions. By analytical arguments and analysis of the singular
spectrum we point out that non-uniform ionization results in an
ambiguous interpretation of the solution of the integral equation,
this solution not being unique. Finally, we briefly recall that this
analysis facilitates methods for recovering unique and regularized
solutions from high-resolution hard x-ray spectral data soon to be
forthcoming from the HESSI space mission.
Title: Revealing the galactic magnetic field in the plane of the
galaxy.
Authors: Brown, J. C.; Taylor, A. R.
Bibcode: 1999JRASC..93..177B
Altcode:
No abstract at ADS
Title: The Canadian Galactic Plane Survey - Phase 2.
Authors: Landecker, T. L.; Knee, L. B. G.; Brunt, C.; Dewdney, P. E.;
Dougherty, S. M.; Galt, J. A.; Gray, A. D.; Higgs, L. A.; Kothes, R.;
Purton, C. R.; Roger, R. S.; Tapping, K.; Wallace, B. J.; Willis,
A. G.; Brown, J. C.; Gibson, S. J.; Leahy, D. A.; Peracaula, M.;
Taylor, A. R.; Wilder, S.; Foster, T.; Routledge, D.; Vaneldik, J. F.;
McCutcheon, W. H.; Basu, S.; Johnstone, D. I.; Kerton, C.; Martin,
P. G.; Cazzolato, F.; Gagnon, E.; Germain, S.; Ghazzali, N.; Godbout,
S.; Joncas, G.; Maschenko, S. Y.; Miville-Deschènes, M. -A.; Pineault,
S.; Carignan, C.; St-Louis, N.; Christie, R. A.; Irwin, J. A.; Brar,
R.; Fich, M.; Zhang, X. -Z.; Heiles, C. E.; Normandeau, M.; Terebey,
S.; Heyer, M. H.; Wendker, H. J.; Beichman, C. A.; Moriarty-Schieven,
G. H.; Green, D. A.; Duric, N.; English, J.
Bibcode: 1999JRASC..93..182L
Altcode:
No abstract at ADS
Title: Casting a shadow.
Authors: Brown, J.
Bibcode: 1999Ast....27...80B
Altcode:
What happens in the sky when the Sun and Moon play hide-and-seek.
Title: Scattering polarization due to light source
anisotropy. I. Large spherical envelope
Authors: Al-Malki, M. B.; Simmons, J. F. L.; Ignace, R.; Brown, J. C.;
Clarke, D.
Bibcode: 1999A&A...347..919A
Altcode:
Expressions are developed for the flux and polarization of radiation
scattered by a spherically symmetric envelope for a central point
stellar light source that radiates anisotropically. These are obtained
in terms of the components of the spherical harmonics of the flux
anisotropy from the source. Such anisotropy can arise from stellar
spots, or from distortion of the star through rotation, pulsation,
or magnetic effects. Explicit expressions for the Stokes parameters
are obtained in the case of an ellipsoidal star of uniform surface
brightness. It is thus shown that even when the scattering envelope is
spherical, observationally significant polarization can arise from stars
with physically realistic degrees of distortion. The time dependence
of the polarization is computed for models of ellipsoidal stars in the
cases of pure rotation, pure pulsation, and both rotation and pulsation.
Title: Life in a Stormy Universe
Authors: Brown, J. C.
Bibcode: 1999IrAJ...26...21B
Altcode:
This paper represents a summary of the Robinson Lecture given in Armagh
in November 1998. I describe briefly some of the great hierarchy of
cosmic `storms' in increasing order of energy, indicating the processes
involved and their positive and negative impacts on Earth and on life.
Title: Inverse Spectropolarimetric Modelling of Hot Star Wind
Structure and Variability
Authors: Brown, John C.; Ignace, Richard; Piana, M.
Bibcode: 1999LNP...523..111B
Altcode: 1999vnss.conf..111B; 1999IAUCo.169..111B
No abstract at ADS
Title: The Interstellar Magnetic Field in the Ionized Filament CXR 11
Authors: Brown, J. C.; Taylor, A. R.; Peracaula, M.
Bibcode: 1999ASPC..168..223B
Altcode: 1999npim.conf..223B
No abstract at ADS
Title: The interstellar magnetic field of CXR 11
Authors: Brown, J. C.; Taylor, A. R.; Peracaula, M.
Bibcode: 1999gfp..work...34B
Altcode:
No abstract at ADS
Title: On the role of beam driven return current instabilities in
white-light flares
Authors: Matthews, S. A.; Brown, J. C.; van Driel-Gesztelyi, L.
Bibcode: 1998A&A...340..277M
Altcode:
It has been shown previously that the low ionization levels in the
deep chromosphere of solar flares can cause the return current driven
by a thick target electron beam to be unstable to ion aoustic wave
generation, contrary to conventional wisdom. We investigate, using
Yohkoh data, the possibility that anomalous heating as a result of
this instability is capable of producing sufficient heating, in the
right places at the right times, to account for the enhanced continuum
emission actually observed in white-light flares. The Soft X-ray
Telescope (SXT) onboard \it Yohkoh incorporates an aspect camera which,
prior to its failure in 1992, provided white-light images at 431 nm with
a bandpass of 3 nm. A number of white-light flares were observed during
its operational lifetime for which there was coincident hard X-ray data
from the Hard X-ray Telescope (HXT), providing suitable candidates for
study. Four such events are discussed, and the model found to be viable.
Title: A neural network prediction of solar cycle 23
Authors: Conway, A. J.; Macpherson, K. P.; Blacklaw, G.; Brown, J. C.
Bibcode: 1998JGR...10329733C
Altcode:
We examine the use of feed forward neural networks in the long term
(i.e., years ahead) prediction of sunspot number. First, we briefly
review the history of the time series and also some previous attempts
to predict it. We outline our neural network method and discuss
how the reliability of the data affects training. We conclude that
earlier data should not be used to train neural networks that are
intended to make predictions at the current epoch. We then use this
understanding of the data in training neural networks, testing many
different configurations to see which provides the best 1-6 year ahead
prediction accuracies. By looking at the distribution of residuals,
an estimate of the uncertainty is placed on the best networks'
predictions. According to our predictions of yearly sunspot number,
the maximum of cycle 23 will occur in the year 2001 and will have an
annual mean sunspot number of 130 with an uncertainty of +/-30-80%
confidence. Finally, we discuss our result in relation to others and
comment on how neural networks may be used in future work.
Title: The Electron Injection Function and Energy-dependent Delays
in Thick-Target Hard X-Rays
Authors: Brown, John C.; Conway, Andrew J.; Aschwanden, Markus J.
Bibcode: 1998ApJ...509..911B
Altcode:
We analytically and numerically study the relationship
between an energy-dependent electron injection spectrum,
F0(E0, t), and the resulting bremsstrahlung
photon spectrum, J(ɛ, t), with the goal of exploring whether injection
functions could explain energy-dependent time delays observed in
solar flare hard X-rays (HXRs) without any time-of-flight effects. We
calculate the inversion of the bremsstrahlung photon spectrum (for
the Kramers cross section) and find that the timing of the electron
injection function depends on the time derivative of the second spectral
derivative of the photon spectrum. To match the observed delays, a
systematic softening of the electron injection spectrum is required
over the duration (~1 s) of individual HXR pulses. This requirement
is exactly the same as that which occurs in the time-of-flight model,
except there the softening is due to spatial dispersion of injected
electrons of different energy E0. We show that such a
softening injection rate is not consistent with acceleration models
where the electron acceleration times are comparable with the HXR pulse
lengths, but it can be consistent with models where the acceleration
times are very short since the injection spectrum variations are
then governed by spectral variations in the acceleration rate. We
conclude that acceleration mechanisms cannot be ruled out on the
basis of HXR light curves alone as an alternative to time-of-flight
effects. Observations of HXR images and of the relationship of HXRs to
soft X-ray loops strongly suggest, however, that time-of-flight effects
must be important and must be included in attempts to infer primary
accelerator properties from HXR light curves. We also conclude that the
agreement of the time-of-flight model with observed energy-dependent
HXR delays, and the properties of any acceleration model contributing
to this trend, puts strong constraints on the timescales involved in
the accelerator.
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
Bibcode: 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: Wide field imaging polarimetry as a probe of the interstellar
medium.
Authors: Brown, J. C.; Taylor, A. R.; Gray, A. D.; Landecker, T. L.;
Dewdney, P. E.
Bibcode: 1998JRASC..92R..27B
Altcode:
No abstract at ADS
Title: Optimal inversion of hard X-ray bremsstrahlung spectra. I. SVD
analysis
Authors: Piana, M.; Brown, J. C.
Bibcode: 1998A&AS..132..291P
Altcode:
The instability properties of bremsstrahlung spectrum inversion
to yield source electron spectra in flares are examined in terms
of singular value decomposition (SVD) for the cases of thin- and
thick-target models for different bremsstrahlung cross-sections. It is
shown that, for the Kramers and Bethe-Heitler cross-sections, analytic
expressions can be obtained for evaluation of the Gram matrix. These
allow quantitative comparison of the instability of inversion for
each case and hence assessment of the accuracy and resolution of the
electron source function recovery. Based on this analysis we find that:
(a) the solution instability is worse for the Bethe-Heitler than for
the Kramers approximation; care must therefore be taken in real data
analysis to use the most accurate possible cross-section to avoid over-
or under-estimating the maximum precision and resolution achievable in
the recovered electron spectrum; (b) instability is worse in recovering
thick-target injection spectra than thin-target mean source spectra,
as expected because of the double deconvolution involved in the former;
(c) such SVD analysis should form an important part of future analysis
of high resolution flare data such as from the HESSI Mission.
Title: Generation of solar Hα impact polarization by fragmented
evaporative upflows
Authors: Fletcher, L.; Brown, J. C.
Bibcode: 1998A&A...338..737F
Altcode:
In this paper a novel mechanism is proposed for the generation of Hα
impact polarization observed during some solar flares. Rather than
being generated by the primary particle beams transporting energy from
the chromosphere to the corona, we suggest that following heating,
the solar chromosphere evaporates in a fragmented manner, and that
impact excitations in the regions of interaction of hot evaporating
and cool non-evaporating material locally generates impact-polarized
Hα emission. This thermal upflow model is more consistent with
the large areas and times over which polarization is observed than
are beam models. A simple model for the process is given, and the
resulting polarization is calculated and compared with observations,
under two assumptions about the number density of neutral particles
in the interaction regions.
Title: Spectral decomposition by genetic forward modelling
Authors: McIntosh, S. W.; Diver, D. A.; Judge, P. G.; Charbonneau,
P.; Ireland, J.; Brown, J. C.
Bibcode: 1998A&AS..132..145M
Altcode:
We discuss the analysis of real and simulated line spectra using
a genetic forward modelling technique. We show that this Genetic
Algorithm (GA) based technique experiences none of the user bias
or systematic problems that arise when faced with poorly sampled or
noisy data. An important feature of this technique is the ease with
which rigid a priori constraints can be applied to the data. These
constraints make the GA decomposition much more accurate and stable,
especially at the limit of instrumental resolution, than decomposition
algorithms commonly in use.
Title: Inference of steady stellar wind v(r) laws from optically thin
emission lines. III. Inversion of total line intensity distributions
Authors: Ignace, R.; Brown, J. C.; Milne, J. E.; Cassinelli, J. P.
Bibcode: 1998A&A...337..223I
Altcode:
The variation with wavelength for a sequence of total intensities of
stellar wind lines is considered as a basis for deriving the wind
velocity law v(r). In particular, we focus on the case where the
continuum formation in the wind is dominated by the free-free opacity
so that the inner radius increases with wavelength, as is realized in
some massive winds like those of the Wolf-Rayet stars. The line emission
in the wind occurs exterior to the continuum photosphere, hence lines
observed at different wavelengths probe different regions of the wind
acceleration. A major consequence of these physical conditions is the
opportunity to infer v(r), even if non-monotonic. Numerical examples
are given to test the method, in which smooth and non-smooth monotonic
v(r), non-monotonic v(r), and the effects of noise are addressed. In
the absence of noise, the inversion of the simulated data for radius
r(lambda ) and expansion velocity v(lambda ) is excellent. Even
with noise at the 15% level, the recovery for r(lambda ) remains
reasonably robust, though the results for v(lambda ) are more strongly
affected. Although more sophisticated techniques are required to
infer v(lambda ) from noisy data, the simpler considerations presented
here provide a basic theoretical framework for applying the inversion
and indicate the potential of the method for deriving the wind flow
structure.
Title: Inversion of Thick Target Bremsstrahlung Spectra from
Nonuniformly Ionised Plasmas
Authors: Brown, John C.; McArthur, Guillian K.; Barrett, Richard K.;
McIntosh, Scott W.; Emslie, A. Gordon
Bibcode: 1998SoPh..179..379B
Altcode:
The effects of non-uniform plasma target ionisation on the spectrum of
thick-target HXR bremsstrahlung from a non-thermal electron beam are
analysed. In particular the effect of the target ionisation structure on
beam collisional energy losses, and hence on inversion of an observed
photon spectrum to yield the electron injection spectrum, is considered
and results compared with those obtained under the usual assumption
of a fully ionised target.
Title: The relation between line ratio and emission measure analyses
Authors: McIntosh, S. W.; Brown, J. C.; Judge, P. G.
Bibcode: 1998A&A...333..333M
Altcode:
Spectroscopic diagnosis of the temperature and density structure of
hot optically thin plasmas from emission line intensities is usually
described in two ways. The simplest approach, the `line ratio' method,
uses an observed ratio of emission line intensities to determine a
`spectroscopic mean' value of electron temperature < T_e >
or electron density < ne>. The mean value is chosen
to be the theoretical value of T_e or ne which matches the
observed value. The line ratio method is stable, leading to well defined
values of < T_e > or < n_e > for each line pair but, in the
realistic case of inhomogeneous plasmas, these are hard to interpret
since each line pair yields different mean parameter values. The more
general `differential emission measure' (DEM) method recognizes that
observed plasmas are better described by distributions of temperature
or density along the line of sight, and poses the problem in inverse
form. It is well known that the DEM function is the solution to the
inverse problem, which is a function of T_e, n_e, or both. Derivation of
DEM functions, while more generally applicable, is unstable to noise
and errors in spectral and atomic data. The mathematical relation
between these two approaches has never been precisely defined. In
this paper we demonstrate the formal equivalence of the approaches,
and discuss some potentially important applications of methods based
upon combining the line ratio and DEM approaches.
Title: Predicting the maximum of solar cycle 23
Authors: Conway, Andrew; MacPherson, Keith; Brown, John
Bibcode: 1998A&G....39b..22C
Altcode:
No abstract at ADS
Title: The Canadian Galactic Plane Survey
Authors: English, J.; Taylor, A. R.; Irwin, J. A.; Dougherty, S. M.;
Basu, S.; Beichman, C.; Brown, J.; Cao, Y.; Carignan, C.; Crabtree,
D.; Dewdney, P.; Duric, N.; Fich, M.; Gagnon, E.; Galt, J.; Germain,
S.; Ghazzali, N.; Gibson, S. J.; Godbout, S.; Gray, A.; A. Green, D.;
Heiles, C.; Heyer, M.; Higgs, L.; Jean, S.; Johnstone, D.; Joncas,
G.; Landecker, T.; Langer, W.; Leahy, D.; Martin, P.; Matthews, H.;
McCutcheon, W.; Moriarity-Scheiven, G.; Pineault, S.; Purton, C.;
Roger, R.; Routledge, D.; St-Louis, N.; Tapping, K.; Terebey, S.;
Vaneldik, F.; Watson, D.; Wendker, H.; Willis, T.; Zhang, X.
Bibcode: 1998PASA...15...56E
Altcode:
The Dominion Radio Astrophysical Observatory (DRAO) is carrying out a
survey as part of an international collaboration to image the northe,
at a common resolution, in emission from all major constituents of
the interstellar medium; the neutral atomic gas, the molecular gas,
the ionised gas, dust and relativistic plasma. For many of these
constituents the angular resolution of the images (1 arcmin) will
be more than a factor of 10 better than any previous studies. The
aim is to produce a publicly-available database of high resolution,
high-dynamic range images of the Galaxy for multi-phase studies of
the physical states and processes in the interstellar medium. We
will sketch the main scientific motivations as well as describe some
preliminary results from the Canadian Galactic Plane Survey/Releve
Canadien du Plan Galactique (CGPS/RCPG).
Title: Electrostatic effects during neutral beam propagation through
plasmas
Authors: Brown, John C.; Karlicky, Marian; Conway, Andrew J.;
Martland, Suzanne
Bibcode: 1998A&A...331.1147B
Altcode:
In this paper several aspects of the interaction of 1-D neutral beams
with plasmas are considered. In order to clearly understand the dual
roles of a background plasma in collisionally decelerating the beam
and its response to the consequently generated E-field, we examine two
cases: an artificial unresponsive background plasma, that corresponds
closely to the case of an unionized gas; and a realistic background
plasma, whose charges respond to the presence of any E-field. In the
former case, the electric field results solely in extremely small scale
oscillation of the beam electrons about the protons as both decelerate
collisionally and, although electron runaway is possible, the numbers
involved are found to be negligibly small. However, collisional
separation of the beam electrons and protons does occur in the case
of a realistic background plasma, since E easily drives a neutralizing
dense plasma electron current. Despite the charge separation, runaway
is found to be impossible in this case because of the masking effect
that the background plasma electrons have on the separated charges
unless the plasma is extremely tenuous compared to the beam, where the
plasma behaviour is close to that of a near-neutral gas. These effects
are shown by approximate analytic mean particle solutions and confirmed
by simulations from an electrostatic particle code, which can deal with
collective effects. Additional numerical simulations are also performed
to investigate the generation of Langmuir waves by a neutral beam. The
consequences of these results are discussed for flare neutral beams and
corresponding radiation signatures. As regards hard X-ray production
by runaways, although some very high energy electrons may result,
the number is far too small to be relevant to solar flare HXR burst
production. The beam and plasma oscillations may however be relevant
to radio bursts.
Title: Analytic description of collisionally evolving fast electrons,
and solar loop-top hard X-ray sources
Authors: Conway, A. J.; MacKinnon, A. L.; Brown, J. C.; McArthur, G.
Bibcode: 1998A&A...331.1103C
Altcode:
We present a new approach to the problem of particle transport described
by the linearised Fokker-Planck equation. Instead of attempting to solve
for the distribution function directly, exact and analytic expressions
for the moments of the distribution are derived from the equivalent
stochastic differential equation. Although the moments themselves
will be of greatest use, we also show how these moments can be used to
construct an exact, analytic solution to the Fokker-Planck equation. In
addition, we explain how mean scattering theory naturally emerges from
the first order moments. The derivation of the second (and higher)
order moments means that the spatial spreading of electrons due to the
changing pitch angle distribution can be described analytically for any
injected pitch angle - previously, such a description was not possible
with mean scattering and, in general, numerical simulation was the only
method available. The treatment also explicitly reveals a simple scaling
relationship between the distribution of particles along the magnetic
field and the square of the particle's injection energy. We check our
results against numerical simulations and point out how the results
here can be extended to more general cases. Uses of these results are
illustrated in relation to the spatial distribution of Hard X-Ray (HXR)
emission and its relevance to solar HXR ``above the loop top" sources.
Title: Inference of steady stellar wind v(r) laws from optically
thin emission lines. II. Occultation effects and the determination
of intrinsic stellar properties
Authors: Ignace, R.; Brown, J. C.; Richardson, L. L.; Cassinelli, J. P.
Bibcode: 1998A&A...330..253I
Altcode:
This paper extends previous work on the inversion of line profiles to
obtain wind velocity laws to a case that includes the occultation of
light from the far side of the star. The velocity law v(r) is assumed to
be from a wind that is steady and spherically symmetric. The wind is
also assumed to be optically thin in the emission line profile. The
major result here is the derivation of an analytic inversion
formula. The effects of stellar occultation are shown to produce a
significant change in the analysis from paper I, and by accounting
for the occultation, the red-shifted emission of P Cygni profiles can
be used to obtain v(r). Using simulated line profiles as generated
from a radiation transport code to test the procedure, the inversion
technique based on optically thin lines successfully recovers v(r)
distributions for weak LTE H_alpha profiles from hot star winds. Even in
the case of NLTE H_alpha lines, the technique is seen to reproduce the
model velocity distribution quite well. Our inversion technique thus
remains robust outside the scope of our assumptions, owing primarily
to an empirical approach for applying the method. An important aspect
of our empirical approach is the possibility of estimating intrinsic
stellar and wind properties, such as the mass-loss rate {dot M},
photospheric radius R, and the stellar distance D. As an example,
photospheric stellar radii are derived from the model profiles and
found to be in good agreement with the input values, with typical
errors of about 5%. Even in the NLTE case, the photospheric radii are
underestimated by only 10-20%.
Title: Using ISO to Probe the Acceleration of Wolf-Rayet Winds
Authors: Ignace, R.; Cassinelli, J. P.; Morris, P.; Brown, J. C.
Bibcode: 1998cvsw.conf...29I
Altcode:
No abstract at ADS
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.
Bibcode: 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: Differential Emission Measures-Can we do more??
Authors: McIntosh, S. W.; Brown, J. C.; Judge, P. G.
Bibcode: 1997BAAS...29.1120M
Altcode:
No abstract at ADS
Title: Inference of steady stellar wind v(r) laws from optically
thin emission lines. I. Idealised analysis for the profile of a
single line.
Authors: Brown, J. C.; Richardson, L. L.; Cassinelli, J. P.; Ignace, R.
Bibcode: 1997A&A...325..677B
Altcode:
The form of the profile Flambda_0__({DELTA}λ) of an
emission line from a steady spherical wind of velocity profile
v(r) is derived for the case when optical depths are small, when
stellar occultation of the wind is neglected, and when v(r) is highly
supersonic. It is shown how the resulting integral equation for v(r),
given Flambda_0__ ({DELTA}λ), can be inverted to yield
v(r) if the line emissivity function j(r) is known. Solutions are
demonstrated for simulated data in the case of a recombination line
(j{prop.to}n^2^) for various trial forms of v(r). The solution is
unique provided dv/dr does not change sign anywhere and is remarkably
stable against noise in the Flambda_0__({DELTA}λ) data. The
analysis is idealised in the sense that the stellar mass loss rate ˙(M)
and distance D are assumed known, the solution being then carried out
in scaled dimensionless variables. The absolute r-scale of the solution
for given Flambda_0__({DELTA}λ) scales as (˙(M/D))^2^. If
this quantity is known the method also yields the stellar radius.
Title: Coulomb Energy Losses in the Solar Corona and the Proton
Energy Budget in Flares
Authors: Emslie, A. Gordon; Brown, John C.; MacKinnon, Alexander L.
Bibcode: 1997ApJ...485..430E
Altcode:
It has recently been proposed, on the basis of measurements of the
flux in the 20Ne 1.634 MeV line, that the energy budget for
nonthermal protons in solar flares may be significantly larger than
previously assumed. The argument is founded on the fact that the 1.634
MeV feature has a (proton) excitation threshold energy significantly
lower than that of the C and O lines in the 4-6 MeV range. Hence the
observed enhanced level of emission in the 1.634 MeV line requires
a higher flux of low-energy (~1 MeV) protons than would be obtained
from a backward extrapolation of the ~10 MeV spectrum using canonical
(i.e., modified Bessel function) spectral forms and so a greater overall
energy content. In this paper we check the effects on this conclusion of
two significant factors omitted from the previous analysis, which was
based on a ``cold'' chromospheric target model. While such a model may
be appropriate for protons of ~10 MeV energies, protons of ~1 MeV may
undergo a significant part of their energy loss in the hot corona, which
is ionized and also ``warm'' for beam protons of these energies. The
ionization results in a Coulomb logarithm (and energy loss rate) almost
3 times higher than in the neutral chromosphere. On the other hand, the
warm target effect results in energy losses a factor of 1-10 times lower
than in a cold target. Thus, if beam protons underwent a substantial
part of their energy loss in the corona (depending on the column
density encountered), previous conclusions from the 20Ne
line flux could be either enhanced or negated, depending on which
effect dominates. We show that for likely flare coronal temperatures
and column densities that the net consequences for the 20Ne
flux are in fact small, unless the low-energy protons are preferentially
trapped in an improbably hot dense magnetic island.
Title: Inversion of Thick-target Bremsstrahlung Spectra from
Nonuniformly Ionized Plasmas
Authors: Emslie, A. Gordon; Brown, John C.; McArthur, Guillian K.;
Barrett, Richard K.; McIntosh, Scott W.
Bibcode: 1997SPD....28.0158E
Altcode: 1997BAAS...29..890E
The energy loss rate of bremsstrahlung-producing electrons is strongly
dependent on the ionization level of the target with which they
interact. Electrons injected from the corona toward the chromosphere
suffer reduced energy losses, and therefore become more efficient
at bremsstrahlung production, when they enter the near-neutral
chromospheric layers. Thus the electron spectrum inferred from
a uniform target model (as hitherto universally applied to data)
causes a serious overestimate of the number of injected electrons,
particularly at the low energies appropriate to the electrons as they
enter the chromosphere. We here demonstrate how to derive the correct
injected electron spectrum from that derived from a uniform target
model. Significantly, we find that the correct spectrum is not unique,
even for perfect (noise-free) hard X-ray data. The implications of
this result for the interpretation of hard X-ray spectral data, and a
possible method of determining the location of the corona/chromosphere
ionization jump using information on the evolution of the hard X-ray
spectrum throughout the flare, are discussed.
Title: Fundamental Limitations of Emission-Line Spectra as Diagnostics
of Plasma Temperature and Density Structure
Authors: Judge, P. G.; Hubeny, Veronika; Brown, John C.
Bibcode: 1997ApJ...475..275J
Altcode:
We discuss the problem of determining plasma structure from optically
thin emission lines whose emission coefficients and frequency-integrated
intensities are dependent on temperature T and electron density n. We
cast the problem into the inverse form discussed by Hubeny & Judge
(1995). Three properties of the kernels in the integral equations
lead to fundamental limitations in trying to determine the source
term μ(T, n), the ``emission measure differential in temperature and
density,'' from a set of emission-line intensities. First, the kernels
are rather weakly dependent on n. Second, they have asymptotically
identical dependencies on n. The inverse problem is therefore very
poorly conditioned in the density dimension. Third, the kernels cannot
(and may never) be calculated with an accuracy better than +/-10%. These
properties set limits on the accuracy of all solutions, independent of
the accuracy of observed line intensities. This concurs with earlier
but less general work by Brown et al. (1991). We try to determine
solutions for μ(T, n), using specific target sources and numerical
algorithms. Using realistic uncertainties, calculations indicate that
meaningful inverse solutions for μ(T, n) cannot be obtained owing to
the severe propagation of kernel errors, irrespective of the quality of
observational data. Solutions for the ``emission measure differential
in temperature'' ξ(T) = \smallint μ(T, n)dn are more robust against
instabilities driven by poor conditioning. Since traditional
``emission-line diagnostic ratios'' can only be defined through μ(T,
n) (or some generalization thereof), our analysis casts doubt on
the meaning of plasma properties derived from such line ratios, and
illustrates the severe nonuniqueness of any equivalent ``inverse''
solution. This work may be important for studying a wide variety of
atomic and ionic emission-line spectra, including work with instruments
on SOHO and the Hubble Space Telescope.
Title: Department of Physics and Astronomy, University of
Glasgow. Report for the period 1995 January to 1995 December.
Authors: Brown, J. C.; Clarke, D.; Hough, J.
Bibcode: 1996QJRAS..37..819B
Altcode:
No abstract at ADS
Title: A Possible Mechanism Governing the Production and Evolution
of Ellerman Bombs
Authors: Diver, Declan A.; Brown, John C.; Rust, David M.
Bibcode: 1996SoPh..168..105D
Altcode:
A hydrodynamic-magnetofluid hybrid analysis of lower chromospheric
shear flows in the Sun may explain the occurrence and time development
of Ellerman bombs. The analysis assumes that the erupting material
forming the bomb is driven initially by the Kelvin-Helmholtz fluid
instability applied to the interface between two atmospheric fluid
layers, characterized by a steep density change across the boundary
and driven by flow fields around sunspots. The ensuing instability
eventually evolves into a magnetofluid phenomenon by virtue of the
trapping and bending of the interfacial magnetic field, giving rise
to a dense globule of material entering, and persisting in, the upper
layers and due to Ohmic dissipation having a significantly enhanced
temperature compared with ambient material.
Title: Optimal inference of episodic stellar mass loss rates from
real polarimetric and absorption data with noise and sparse sampling.
Authors: Calvini, P.; Bertero, M.; Brown, J. C.
Bibcode: 1996A&A...309..235C
Altcode:
The inverse problem of evaluating the axisymmetric stellar mass loss
rate and oblateness during an episodic event, from observations of broad
band scattering polarization and absorption spectrum line strength,
is analyzed. In particular, a new inversion algorithm is developed to
provide the optimal approach to the inversion problem in realistic
cases where the data are noisy and sparsely sampled. Implementation
of the method is presented for simulated data and for real data on a
mass loss episode for the star ω Orionis.
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.
Bibcode: 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: Hard X-ray bremsstrahlung emission and polarization in a
flaring loop affected by electron beams
Authors: Zharkova, V. V.; Brown, J. C.; Syniavskii, D. V.
Bibcode: 1996AdSpR..17d..81Z
Altcode: 1996AdSpR..17...81Z
Using a kinetic approach the hard X-ray bremsstrahlung emission
and polarization produced by an electron beam injected, with an
power law energy distribution from the corona into the chromosphere
are investigated. The time-dependent kinetic equation was solved
numerically in a flaring loop taking into account the energy losses and
anisotropy of electron scattering for the following channels: Coulomb
collisions and inelastic ones with neutral atoms, Ohmic dissipation
and adiabatic scattering in a converging magnetic field. The temporal
hard X-ray bremsstrahlung emission profiles are symmetric ones which
resemble the observations for events with the timescale around a few
seconds. The intensity of the X-ray bremsstrahlung emission increases
and its directivity decreases with the time of a beam injection. The
polarization is found to vary noticeably with the emergent photon
energies below 40 keV being up to 30% and down to -10% for different
angles of view. Harder X-ray polarization is almost constant with
increase of photon energy, within a fixed angle of view.
Title: Prominence and flare fine structure from cross-field thermal
conduction.
Authors: Gray, N.; Brown, J. C.
Bibcode: 1996A&A...307..955G
Altcode: 1995astro.ph..9011G
Thermal conduction across a magnetic field is strongly suppressed
compared with conduction along the field. However, if a flare is heated
by a highly filamented beam directed along the field, then the array
of heated cells in a cross-section of the flare will result in both
small spatial scales (with consequently large temperature gradients)
and a large surface area for the heated volume, providing a geometrical
enhancement of the total cross-field energy flux. To investigate the
importance of this filamentary geometry, we present a simple model of a
single heated filament surrounded by an optically thin radiating shell,
obtain an analytical expression for the stable equilibrium temperature
profile within the shell, and use this to impose limits on the size
of filament for which this model is appropriate. We find that this
mechanism by itself is capable of transporting a power of the same
order as a large flare, with a moderate range of filament sizes. The
length scales are substantially smaller than can be resolved at present,
although they should be regarded as underestimates.
Title: Polarimetric versus photometric variability and the density
of WR star wind inhomogeneities.
Authors: Richardson, L. L.; Brown, J. C.; Simmons, J. F. L.
Bibcode: 1996A&A...306..519R
Altcode:
Intensive broad band observations of Wolf-Rayet (WR) stars by
Moffat et al. reveal photometric and polarimetric fluctuations
on timescales of hours, similar to the timescale of variation of
narrow spectral features on emission lines. These are attributed
to localised density enhancements (blobs) in the general wind. The
r.m.s. fluctuations in the two observing modes are found to be in the
ratio R=σ_pol_/σ_phot_=~0.05 whereas if both were due to electron
scattering of starlight in single optically thin blobs far from the
star, the ratio should be around unity. It has been suggested that the
smallness of R may be attributed to cancellation of the polarisation
contributions of significant numbers, N, of blobs emitted in different
directions. We prove that this explanation of the small σ ratio is
untenable, by calculating the expected values of σ_pol_ and σ_phot_
due to random fluctuations in N and in blob positions. This is done
analytically in a simplified case and numerically in the general
case. No value of N can yield the observed R. We conclude that the
discrepancy must result from a substantial photometric contribution from
broad band light emitted in the blobs and/or substantial reduction in
the polarisation by multiple scattering in the blobs. Either explanation
demands that the blobs be very dense, with n_e_> 5x10^13^ cm^-3^,
when the blobs are at distances from the WR centre of around 10^12^ cm.
Title: Derivation of Accelerated Electron Spectra by Inversion of
Bremsstrahlung Spectra from a Thick Target of Nonuniform Ionisation
Authors: Brown, John C.; McArthur, Guillian K.; McIntosh, Scott W.
Bibcode: 1996ASPC..111..292B
Altcode: 1997ASPC..111..292B
The problem of inferring flare electron spectra at the acceleration site
from their HXR bremsstrahlung spectra is considered for the case when
they are injected into a thick target in which the plasma ionisation
x varies with depth. The correction formulae derived will be useful
and convenient for application to future high resolution HXR spectra.
Title: Beam Driven Return Current Instabilities and White-Light Flares
Authors: Matthews, S. A.; Brown, J. C.; van Driel-Gesztelyi, L.
Bibcode: 1996ASPC..111..304M
Altcode: 1997ASPC..111..304M
It has been shown that the low ionization levels in the deep
chromosphere of solar flares can cause the return current driven by a
thick target flare beam to be unstable to ion acoustic wave generation,
contrary to previous conventional wisdom. The authors investigate the
possibility that anomalous heating as a result of this instability
may produce sufficient heating to power the white-light flare. Four
white-light flares observed by Yohkoh are examined: 1991 Oct 27,
1991 Nov 15, 1992 Jan 26, and 1992 Feb 14.
Title: Instability of beam-driven return currents in the deep
chromosphere of solar flares.
Authors: Matthews, S. A.; Brown, J. C.; Melrose, D. B.
Bibcode: 1996A&A...305L..49M
Altcode:
It i shown that, contrary to previous thinking, the return current
driven by a thick target flare beam may be unstable to ion sound
wave generation in the deep chromosphere, particularly for intense
hard beams and early in the flare. This is so despite the strong
collisional attenuation of the beam and the high plasma density in
the chromosphere because the low ionisation there results in a high
drift velocity of the few free electrons available to carry the return
current. The resulting ion acoustic wave generation will enhance local
beam heating and affect diagnostics through the presence of enhanced
microscopic and return current electric fields.
Title: Electron beam dynamics and hard X-ray bremsstrahlung
polarization in a flaring loop with return current and converging
magnetic field.
Authors: Zharkova, V. V.; Brown, J. C.; Syniavskii, D. V.
Bibcode: 1995A&A...304..284Z
Altcode:
In a kinetic approach the electron beam dynamics and its effect on the
hard X-ray bremsstrahlung emission are investigated in flaring loops
with the atmospheres taken from previously calculated hydrodynamical
models. The electron beam is assumed to have a power law distribution
in energy and to precipitate from the top of the loop in the corona
into the chromosphere. The time dependent kinetic equation was solved
numerically, taking into account the anisotropy of electrons scattering,
for the following channels of energy loss and pitch angle change:
Coulomb collisions and collisions with neutral atoms, Ohmic dissipation
and magnetic field convergence. The evolution with depth and in time of
the electron beam energy distribution functions, as well as the X-ray
bremsstrahlung emission and polarization were evaluated and compared
with observations. The electron beam distribution functions are shown
to be strongly dependent on depth, energy and pitch angle cosine,
in relation to the initial beam parameters at the injection site,
and weakly dependent on the magnetic field convergence. The last,
along with the induced electrical field, produces a preferential
scattering along the field lines which is rather important for
the electron beam precipitation at lower chromospheric levels. The
temporal hard X-ray bremsstrahlung emission profiles are symmetrical
ones and resemble observations for events with timescales around a few
seconds. Polarization varies noticeably with emergent photon energy
below 40keV, being up to 30% and down to -10% for different angles
of view; these variations cover the range of observed magnitudes. The
harder X-ray radiation has almost constant polarization with increasing
photon energy, for a fixed angle of view.
Title: Department of Physics and Astronomy, University of
Glasgow. Report for the period 1994 January 1 to 1994 December 31.
Authors: Brown, J. C.; Clarke, D.; Hough, J.; Laing, E. W.
Bibcode: 1995QJRAS..36..417B
Altcode: 1995QJRAS..36..417.
No abstract at ADS
Title: Prediction of solar and geomagnetic activity data using
neural networks
Authors: Macpherson, K. P.; Conway, A. J.; Brown, J. C.
Bibcode: 1995JGR...10021735M
Altcode:
Accurate predictions of the future behavior of the solar activity
cycle have been sought for many years. Several classes of prediction
approach have been proposed, with many variations in each class, and
have achieved varying degrees of success. However, considerable room
for improvement still remains. Artificial neural network models enjoyed
a resurgence in popularity as prediction tools during the late 1980s,
as a consequence of the discovery of the back propagation of errors
learning algorithm. Initial investigations have been carried out
into their potential for predicting solar activity (e.g., Koons and
Gorney, 1990; Williams, 1991; Macpherson, 1993a, b). In this paper, we
investigate in detail the effect different neural network architectures
and learning parameters have on the prediction accuracy of various
networks trained on smoothed monthly sunspot and solar 10.7-cm flux
data. The importance of obtaining the best generalization capability of
a neural network is stressed. Prediction of the geomagnetic aa index
is also considered. Finally, in order to validate the usefulness
of this technique, the results are compared with a variant of the
well-established McNish and Lincoln method (McNish and Lincoln, 1949)
and are found to be superior in terms of prediction accuracy.
Title: Inverse problems in astrophysical spectrometry
Authors: Brown, J. C.
Bibcode: 1995InvPr..11..783B
Altcode:
No abstract at ADS
Title: Overview of topical issue on inverse problems in astronomy
Authors: Brown, J. C.
Bibcode: 1995InvPr..11..635B
Altcode:
No abstract at ADS
Title: Joint spectral and polarimetric analysis of accelerated hot
star wind transients
Authors: Piana, M.; Brown, J. C.; Calvini, P.
Bibcode: 1995InvPr..11..961P
Altcode:
No abstract at ADS
Title: Particle acceleration and entropy considerations.
Authors: Brown, J. C.; Beekman, G.; Gray, N.; MacKinnon, A. L.
Bibcode: 1995A&A...299..629B
Altcode: 1995astro.ph..1083B
Possible entropy constraints on particle acceleration spectra
are discussed. Solar flare models invoke a variety of initial
distributions of the primary energy release over the particles of the
flare plasma - ie., the partition of the energy between thermal and
nonthermal components. It is suggested that, while this partition
can take any value as far as energy is concerned, the entropy of a
particle distribution may provide a useful measure of the likelihood
of its being produced for a prescribed total energy. The Gibbs'
entropy is calculated for several nonthermal isotropic distribution
functions f, for a single particle species, and compared with that
of a Maxwellian, all distributions having the same total number and
energy of particles. Speculations are made on the relevance of some
of the results to the cosmic ray power-law spectrum, on their relation
to the observed frequency distribution of nonthermal flare hard X-ray
spectrum parameters and on the additional energy release required to
achieve lower entropy fs.
Title: The Visual and Ultraviolet Polarimetric Data of alpha
Camelopardalis and kappa Cassiopeia: Evidence of Shocked Regions
Authors: Fox, Geoffrey K.; Brown, John C.; Bjorkman, Karen S.
Bibcode: 1995ApJ...447..889F
Altcode:
The OB supergiants α Cam and κ Cas are intrinsically very similar
stars at comparable distances. Apart from a constant offset in the
polarization of ≃0.2%, both stars exhibit the same polarimetric
variation between 140° and 800° Å. Several possible mechanisms to
explain the polarimetric observations are investigated. We propose
that the polarization mechanism may be due to grain formation in an
extended shell where the stellar wind and the interstellar medium
interact. If this interpretation is correct, then it implies that
the physical process giving rise to grain formation is not strongly
correlated to the stellar wind parameters.
Title: The optical 'bullets' of SS 433 as a radiative instability
phenomenon.
Authors: Brown, J. C.; Mundell, C. G.; Petkaki, P.; Jenkins, G.
Bibcode: 1995A&A...296L..45B
Altcode:
The fact that the transient 'bullet' phenomenon nd major variability
seen in the optical spectrum of SS 433 are essentially absent in
X-ray data from the 'inner' jets seems to preclude their being 'true'
bullets - i.e. comprising intermittent large mass ejections. We propose
instead that they are a radiative instability phenomenon occurring
when minor variations in the jet filling factor (or other parameters
such as jet mass loss rate or opening angle) take the jet through
a critical threshold only below which can jet cooling to optical
temperatures occur. At other times the jet remains hot until cooled
solely by expansion, by which time the optical emission measure is
small. The effect is analysed for the case where the jets are heated
by interaction with the stellar wind from the companion star. The
parameter criticality of this threshold could also help explain the
rarity of detected SS 433s.
Title: Combined spectrometric, photometric and polarimetric
diagnostics for `blobs' in WR star winds.
Authors: Brown, J. C.; Richardson, L. L.; Antokhin, I.; Robert, C.;
Moffat, A. F. J.; St-Louis, N.
Bibcode: 1995A&A...295..725B
Altcode:
The quantitative interpretation of photometric, spectrometric and
polarimetric data on transient features in WR stars is discussed and
the diagnostic potential of detailed simultaneous coverage in all three
modes emphasised. Our main conclusions/suggestions are : (i) Narrow
emission line features are due to localised density enhancements in the
mean near spherical wind structure; (ii) Broad-band photo-/polari-metric
transients are due to both scattering of starlight and emission in the
blobs; (iii) The amplitude of a polarisation transient is an indicator
of the mass of a single blob. Combined with the narrow feature width
or the narrow feature luminosity, this allows blob density estimation;
(iv) The dense blobs cannot form in the visible part of the wind since
redistribution of electrons in a localised blob would not result in
a continuum polarimetric transient - rather they must form inside the
effective photosphere; (v) Star-blobs distance indicators include, for a
single blob, the ratio of polarimetric to photometric transient feature
amplitudes and the rate of change of polarisation; (vi) When many
blobs are present, if blob broad-band emission is significant, or if
there is multiple scattering in the blobs, the polarimetric/photometric
variation amplitude is reduced (as observed). This makes blob distance
determination more difficult; (vii) Narrow feature widths variation
with feature shift is an indicator of blob velocity structure. If this
is attributed to the general wind velocity gradient then the feature
width ratio is only compatible with statistical observations of bullet
acceleration/velocity trajectories for winds with substantial initial
speed (at the effective photospheric surface). If the wind speed is low
at the effective photosphere, explanation of the feature width variation
requires either significant electron scattering optical depth within
radially elongated blobs or strong differential motion within the blobs.
Title: The 8Li(α, n) 11B reaction and
primordial nucleosynthesis
Authors: Gu, X.; Boyd, R. N.; Farrell, M. M.; Kalen, J. D.; Mitchell,
C. A.; Kolata, J. J.; Belbot, M.; Lamkin, K.; Ashktorab, K.; Becchetti,
F. D.; Brown, J.; Roberts, D.; Kimura, K.; Tanihata, I.; Yoshida,
K.; Islam, M. S.
Bibcode: 1995PhLB..343...31G
Altcode:
The cross section for the 8Li(α, n)11B reaction,
of importance to primordial nucleosynthesis in the inhomogeneous
models, has been measured using a 8Li radioactive beam. The
center-of-mass energy range studied was 0.64-2.2 MeV. The cross
section to all 11B states is found to exceed that for
8Li(α, n) 11B(g.s.) by a factor of at least
five over the entire energy region studied.
Title: Cross sections and reaction rates of d + 8Li
reactions involved in Big Bang nucleosynthesis
Authors: Balbes, M. J.; Farrell, M. M.; Boyd, R. N.; Gu, X.; Hencheck,
M.; Kalen, J. D.; Mitchell, C. A.; Kolata, J. J.; Lamkin, K.; Smith,
R.; Tighe, R.; Ashktorab, K.; Becchetti, F. D.; Brown, J.; Roberts,
D.; Wang, T. -F.; Humphrey, D.; Vourvopoulos, G.; Islam, M. S.
Bibcode: 1995NuPhA.584..315B
Altcode:
We have measured angular distributions of the 2H(
8Li, 7Li) 3H and 2H(
8Li, 9Be)n reactions at Ec.m.
= 1.5 to 2.8 MeV using an 8Li- radioactive-beam
technique. Astrophysical S-factors and reaction rates were calculated
form the measured cross sections. Although the 2H(
8Li, 9Be)n cross section is small, it
can contribute to 9Be synthesis. The 2H(
8Li, 7Li) 3H reaction has a
sufficiently large cross section to destroy 8Li, which
may decrease the synthesis of heavier elements. No products from
the 2H( 8Li, 9Li)p reaction were
detected. We also present the results of calculations using the
inhomogeneous model of primordial nucleosynthesis in several regions
of parameter space.
Title: Thermal Bremsstrahlung Hard X-Rays and Primary Energy Release
in Flares
Authors: Piana, M.; Brown, J. C.; Thompson, A. M.
Bibcode: 1995SoPh..156..315P
Altcode:
Various methods are explored for obtaining regularized solutions of
the severely ill-posed Laplace inversion problem involved in deriving
plasma temperature (T) structure (differential emission measureξ(T))
from bremsstrahlung spectra. Inversions of simulated data show that
zero-order regularisation (Tikhonov regularisation inL2
space) is very unsatisfactory even with weighting, while first-order
regularisation (Tikhonov regularisation in Sobolev space) yields
reasonable results.
Title: Joint spectral and polarimetric analysis of hot star wind
transients
Authors: Calvini, P.; Bertero, M.; Brown, J. C.
Bibcode: 1995InvPr..11...79C
Altcode:
No abstract at ADS
Title: Solar flare Hα impact polarization from high energy electrons?
Authors: Fletcher, L.; Brown, J. C.
Bibcode: 1995A&A...294..260F
Altcode:
In this paper we investigate the possibility of obtaining Hα line
linear polarization in solar flares following the excitation of
neutral hydrogen by energetic electron beams with a large initial
pitch angle. We compare the factors affecting the sign, magnitude and
intensity of polarized radiation collisionally excited by electron
and proton beams and present a calculation of the polarization which
could be observed from an electron beam, using a stochastic simulation
to solve the Fokker-Planck evolution equation for the electron beam in
the collisionally thick chromosphere, in the presence of a converging
magnetic field. We find that polarization from electron beams is
possible but requires extreme energy fluxes which are unlikely to be
present for any length of time during solar flares.
Title: Wolf-Rayet star variability and wind inhomogeneities
Authors: Brown, J. C.; Richardson, L. L.
Bibcode: 1995IAUS..163..186B
Altcode:
No abstract at ADS
Title: Polarimetric versus photometric variability of Wolf-Rayet
star winds
Authors: Richardson, L. L.; Brown, J. C.
Bibcode: 1995IAUS..163..258R
Altcode:
No abstract at ADS
Title: Department of Physics and Astronomy, University of
Glasgow. Report for the period 1993 January to 1993 December.
Authors: Brown, J. C.; Clarke, D.; Hough, J.; Laing, E. W.
Bibcode: 1994QJRAS..35..529B
Altcode: 1994QJRAS..35..529.
No abstract at ADS
Title: The effect of the ambient heating function on the XUV emission
of flaring atmospheres
Authors: Zharkova, V. V.; Brown, J. C.
Bibcode: 1994ESASP.373...61Z
Altcode: 1994soho....3...61Z
No abstract at ADS
Title: Effect of electron thermal motions on Thomson scattered line
profiles from hot circumstellar envelopes.
Authors: Wood, Kenneth; Brown, John C.
Bibcode: 1994A&A...291..202W
Altcode:
The effect of electron thermal motions on the polarisation of light
single Thomson scattered in an optically thin circumstellar envelope
is investigated. When the central star is a point source of continuum
radiation it is found that the scattered continuum polarisation is
unaffected by the electron thermal motions and the familiar single
scattering results dependent on envelope shape and stellar inclination
are obtained. However when the central star is a point source of
line radiation the Doppler redistribution in frequency, due to the
thermal motions of the isothermal envelope electrons, of scattered
line radiation yields a symmetrically broadened spectropolarimetric
line profile (in the absence of envelope bulk motion). These effects
are illustrated and directly compared with previous analysis of line
polarisation arising through the Doppler redistribution of scattered
radiation due to the bulk motions of the scattering material. It is
shown that for early type stars, which possess slow (a few hundred km/s)
winds, the "thermal smearing" effect cannot be ignored.
Title: Spectropolarimetric Modelling of Hot Star Wind Structure
Authors: Brown, John C.
Bibcode: 1994Ap&SS.221..357B
Altcode:
A short overview is given of some recent progress in the theory of
spectropolarimetry as a diagnostic of axisymmetric hot star wind density
and velocity structure, covering the inferences possible from broad band
polarimetry, from polarimetric light curves and simultaneous absorption
line data, and from spectropolarimetric line profiles. Recent work
on joint spectro-, photo-, and polari-metric study of the properties
of wind inhomogeneities is also summarised. One of the most important
conclusions is that the blobs necessary in WR winds to produce narrow
emission line features cannot also produce polarimetric light curve
features unless they originate in enhanced mass loss sources at the
stellar surface rather than solely in density redistribution processes,
such as turbulence, in the wind itself.
Title: Inversion of Thomson scattered spectropolarimetric line
profiles to yield the velocity structure of rotating or expanding
circumstellar discs
Authors: Brown, J. C.; Wood, K.
Bibcode: 1994A&A...290..634B
Altcode:
Using previous analytic expressions for the Stokes fluxes of a narrow
line scattered in a moving disc, we formulate the cases of disc rotation
only and disc expansion only as integral equations relating the unknown
density and gradient weighted disk bulk velocity distribution to the
observed Stokes flux line profiles. It is shown how these equations can
be solved analytically for the weighted velocity distributions and the
system inclination, for exact data. In the case of real noisy data the
analytic forms of the integral equations provides a convenient basis
for methods of statistical inversion.
Title: Energy Release in Solar Flares
Authors: Brown, John C.; Correia, Emilia; Farnik, Frantisek; Garcia,
Howard; Henoux, Jean-Claude; Larosa, Ted N.; Machado, Marcos E.;
Nakajima, Hiroshi; Priest, Eric R.
Bibcode: 1994SoPh..153...19B
Altcode:
Team 2 of the Ottawa FLARES 22 Workshop dealt with observational and
theoretical aspects of the characteristics and processes of energy
release in flares. Main results summarized in this article stress
the global character of the flaring phenomenon in active regions, the
importance of discontinuities in magnetic connectivity, the role of
field-aligned currents in free energy storage, and the fragmentation
of energy release in time and space.
Title: Book Review: Plasma astrophysics. Kinetic processes in solar
and stellar coronae / Kluwer, 1993
Authors: Brown, J. C.
Bibcode: 1994Obs...114..124B
Altcode:
No abstract at ADS
Title: Parametric determination of the inclination, velocity and
density structure of circumstellar discs from spectropolarimetric
profiles of scattered lines
Authors: Wood, K.; Brown, J. C.
Bibcode: 1994A&A...285..220W
Altcode:
An analytic treatment is presented which determines the
spectropolarimetric line profiles resulting from single Thomson
scattering of monochromatic stellar emission or absorption line
radiation in a moving thin circumstellar disc. Expressions are obtained
for the scattered Stokes fluxes in terms of the disc velocity and
density profiles and the inclination of its rotation axis to the line
of sight. The shape of the scattered polarimetric line profile contains
information on the inclination and velocity and density distributions
of the disc. It is shown that, under certain parametrisations of these
distributions, analysis of spectropolarimetric line data yields the
disc inclination and most of the other parameters of the system.
Title: Glasgow's new link to the Stars
Authors: Brown, John
Bibcode: 1994StarB..13....3B
Altcode:
No abstract at ADS
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
Bibcode: 1994SSRv...68D..17V
Altcode:
No abstract at ADS
Title: Spatial fragmentation of solar flare plasma and beams
Authors: Brown, John C.; Gray, Norman
Bibcode: 1994SSRv...68...93B
Altcode:
The observational and theoretical arguments for spatial fragmentation
of the bulk of the thermal and non-thermal components of solar flare
plasma are summarised. Observational aspects considered include
XUV filling factors, EUV centre to limb variations, andH α impact
polarisation. Theoretical points addressed are the high flare inductance
and beam/return current closure at the acceleration site. A high degree
of beam/plasma filamentation implies strong transverse temperature
gradients so that cross-field conduction must be included in energy
transport modelling. Preliminary results are described for a simple
two-component model.
Title: Astronomy at Oundle School
Authors: McKim, R. J.; Brown, J.
Bibcode: 1994JBAA..104...36M
Altcode:
There must be many school observatories in this country. Here is
a short historical account of the observatory at Oundle School,
in Northamptonshire, with details of some of the highlights and
disasters of the school's Astronomy Society and of Astronomy teaching
at the school.
Title: Parametric determination of the inclination, velocity and
density structure of circumstellar discs from spectropolarimetric
profiles of scattered lines
Authors: Wood, Kenneth; Brown, John C.
Bibcode: 1994SPIE.2010..126W
Altcode:
An analytic treatment is presented which determines the
spectropolarimetric line profiles resulting from single Thomson
scattering of monochromatic stellar line radiation in a moving thin
circumstellar disc. Expressions are obtained for the scattered Stokes
fluxes in terms of the disc velocity and density profiles and the
inclination of its rotation axis to the line of sight. The shape of
the scattered polarimetric line profile contains information on the
inclination and velocity and density distributions of the disc. It
is shown that, under certain parametrizations of these distributions,
analysis of spectropolarimetric line data yields the disc inclination
and most of the other parameters of the system. The analysis presented
may be applied to the Thomson scattering of any photospheric absorption
or emission lines in circumstellar discs.
Title: Entropy and the Thermal/nonthermal Flare Debate
Authors: Brown, J. C.
Bibcode: 1994xspy.conf..147B
Altcode:
No abstract at ADS
Title: Department of Physics and Astronomy, University of
Glasgow. Report for the period 1991 September to 1992 December.
Authors: Brown, J. C.; Clarke, D.; Hough, J.; Laing, E. W.
Bibcode: 1993QJRAS..34..531B
Altcode: 1993QJRAS..34..531.
No abstract at ADS
Title: 2H induced reactions on 8Li and
primordial nucleosynthesis
Authors: Balbes, M. J.; Farrell, M. M.; Boyd, R. N.; Gu, X.; Hencheck,
M.; Kalen, J. D.; Mitchell, C. A.; Kolata, J. J.; Lamkin, K.; Smith,
R.; Tighe, R.; Ashktorab, K.; Becchetti, F. D.; Brown, J.; Roberts,
D.; Wang, T. -F.; Humphreys, D.; Vourvopoulos, G.; Islam, M. S.
Bibcode: 1993PhRvL..71.3931B
Altcode:
Cross sections for the 8Li(d,n)9Be (ground state)
and 8Li(d,t)7Li reactions, both important to
primordial nucleosynthesis in the inhomogeneous models, have been
measured using a radioactive beam technique. The cross section for
the former reaction is found to be small, so it is important only for
synthesis of 9Be. The cross section for the latter reaction,
however, is found to be large enough to destroy significant quantities
of 8Li, and thus could affect predictions of primordial
nucleosynthesis yields.
Title: Book-Review - Guide to the Sun
Authors: Phillips, K. J. H.; Brown, J. C.
Bibcode: 1993Obs...113..148P
Altcode:
No abstract at ADS
Title: Polarimetric line profiles from optically thin Thomson
scattering circumstellar envelopes
Authors: Wood, K.; Brown, J. C.; Fox, G. K.
Bibcode: 1993A&A...271..492W
Altcode:
Frequency dependent expressions are derived for the degree of linear
polarisation and position angle for the case of pure Thomson scattering
off of electrons in non-relativistic bulk motion in an optically
thin circumstellar region. A preliminary investigation has
been made into the variation in linear polarisation and polarimetric
position angle across an emission line Thomson scattered in a rotating,
expanding planar disc. The linear polarisation is found to be asymmetric
about the line centre and stronger in the red wing unless there is no
disc expansion. This red-shifting of spectral features is similar to
numerical results previously reported for the case of dust scattering
in an expanding shell. Changes in position angle across the line occur
through the symmetry-breaking effects of stellar occultation of the
scattering material and the combination of rotation and expansion of
the disc.
Title: On the Gaseous Evolution of Globular Clusters
Authors: Burkert, A.; Brown, J.; Truran, J. W.
Bibcode: 1993ASPC...48..656B
Altcode: 1993gcgc.work..656B
No abstract at ADS
Title: Book-Review - the Sun - a Laboratory for Astrophysics
Authors: Schmelz, J. T.; Brown, J. C.; Rutten, R. J.
Bibcode: 1993SSRv...65..370S
Altcode:
No abstract at ADS
Title: Department of Physics and Astronomy, University of
Glasgow. Report for the period 1986 August to 1991 September.
Authors: Brown, J. C.; Clarke, D.; Hough, J.
Bibcode: 1992QJRAS..33..387B
Altcode:
No abstract at ADS
Title: Derivation of episodic mass loss functions for hot stars from
polarimetric and absorption line data.
Authors: Brown, J. C.; Wood, K.
Bibcode: 1992A&A...265..663B
Altcode:
Expressions are derived for the time-dependent continuum polarization
of starlight after (single) Thomson scattering in an axisymmetric
envelope, and for the strength of an absorption line, in terms of
integrals over the angular distribution and previous history of the
stellar mass loss rate. Under the approximation of constant envelope
expansion speed, and parametrizing the mass loss angular distribution
in terms of a time dependent equatorial concentration shape factor,
it is shown that the resulting pair of integral equations has an
explicit Fourier solution for the time dependence of the mass loss
rate and shape, in terms of the polarization and line strength 'light
curves'. The method is illustrated for the simpler case of no 'shape'
variations using both simulated data and for real data.
Title: Book-Review - the Sun - a Laboratory for Astrophysics
Authors: Schmelz, J. T.; Brown, J. C.; Staude, J.
Bibcode: 1992AN....313..348S
Altcode:
No abstract at ADS
Title: Inference of non-thermal electron energy distributions from
hard X-ray spectra.
Authors: Thompson, A. M.; Brown, J. C.; Craig, I. J. D.; Fulber, C.
Bibcode: 1992A&A...265..278T
Altcode:
Hard X-ray Bremsstrahlung Radiation provides a powerful diagnostic for
the behaviour of non-thermal electrons in solar flares. The derivation
of the source electron energy distribution from the bremsstrahlung
radiation that it emits does however require to solve an ill-posed
inverse problem. Johns and Lin (1991) have proposed a method of solving
this using a least squares appraoch. In this paper, the authors examine
this method in detail and show that contrary to the assertions of Johns
and Lin this method makes a priori assumptions about the electron
energy distribution by limiting the minimum width that any feature
in the solution may have. A strategy is suggested for selecting the
size of each bin in the Johns and Lin procedure which ensures that the
fractional error in each bin of the reconstruction is approximately
constant. The authors compare and contrast the Johns and Lin approach
with the more commonly used regularisation (or Bayesian) approach. It
is shown that the method of Johns and Lin does no better than the
regularisation techniques. In particular, it is demonstrated that the
way regularisation can adjust the resolution to produce the "best"
overall solution rather than obtaining a solution with a specified
resolution or noise level can lead to significantly better estimates
of the underlying source function.
Title: Book-Review - Superstrings - a Theory of Everything
Authors: Davies, P. C. W.; Brown, J.
Bibcode: 1992Sci...258.1017D
Altcode:
No abstract at ADS
Title: H-alpha polarization of wind-heated optical bullets in SS 433.
Authors: Brown, J. C.; Fletcher, L.
Bibcode: 1992A&A...259L..43B
Altcode:
Mechanisms for energy supply to the optical bullets are discussed. It is
pointed out that in the case of heating by bullet collisions with the
system wind, recently shown to be a likely heating candidate, impact
polarization of the H-alpha line should be generated. An estimate
shows that this line polarization should be at least 0.2 percent and
orthogonal to the jet, precessing with it on the sky. This should be
observable and is proposed as a diagnostic of the wind heating model,
in contrast to turbulent internal heating.
Title: Book Review: Advances in solar system magnetohydrodynamics /
Cambridge U Press, 1991
Authors: Brown, J. C.
Bibcode: 1992Obs...112...74B
Altcode:
No abstract at ADS
Title: 2H induced reactions on 8Li and
primordial nucleosynthesis.
Authors: Farrell, M. M.; Boyd, R. N.; Kalen, J. D.; Gu, X.; Kolata,
J. J.; Lamkin, K.; Smith, R.; Tighe, R.; Ashktorab, K.; Becchetti,
F. D.; Brown, J.; Roberts, D.; Wang, T. F.
Bibcode: 1992rnb..conf..287F
Altcode:
Cross sections for the 8Li(d, n)9Be and
8Li(d, t)7Li reactions, both of potential
importance to predictions of primordial nucleosynthesis in inhomogeneous
models, have been measured using a radioactive beam technique. The cross
section for the former reaction to the 9Be(ground state)
is found to be small, so it could be important only for synthesis
of 9Be. The latter reaction, however, is found to have
a large cross section. Thus it can destroy significant quantities
of 8Li, and so must be considered in predictions of
nucleosynthesis of nuclides heavier than C in the inhomogeneous models.
Title: The Sun: A Laboratory for Astrophysics
Authors: Schmelz, J. T.; Brown, J. C.
Bibcode: 1992ASIC..373.....S
Altcode: 1992sla..conf.....S
No abstract at ADS
Title: Opening Address
Authors: Brown, J. C.
Bibcode: 1992ASIC..373....1B
Altcode: 1992sla..conf....1B
No abstract at ADS
Title: Constraints on the Physical Properties of Optical Bullets in
SS 433
Authors: Brown, John C.; Cassinelli, Joseph P.; Collins, George W., II
Bibcode: 1991ApJ...378..307B
Altcode:
The present study discusses possible mechanisms for continuously
heating the H-alpha emitting bullets of SS 433 out to distances of
5 x 10 to the 14th cm and for turning off this emission at 10 to the
15th. Various observational contraints are used to establish bounds
on permissible solutions in terms of the two key bullet parameters,
mass, and angular radius seen from the central source. The analysis is
carried out for the mathematically simplest case of uniform spherical
bullets. For radiative heat of such bullets by starlight, solutions
are found to exist only for the very massive bullets with about 0.03
radians, which are highly implausible on the grounds of the large
implied mean kinetic luminosity of about 10 to the 41st ergs/s. It is
concluded that collisional interaction is the most likely mechanism for
heating the optical bullets of SS 433. The effects of these constraints
being fragmented rather than uniform, and being elongated rather than
spherical are discussed.
Title: The interpretation of density sensitive line diagnostics from
inhomogeneous plasmas. II - Non-isothermal plasmas
Authors: Brown, J. C.; Dwivedi, B. N.; Sweet, P. A.; Almleaky, Y. M.
Bibcode: 1991A&A...249..277B
Altcode:
The formulation of the problem of inferring density structure in
inhomogeneous nonisothermal plasmas is generalized here to cases where
both the density n and temperature T are inhomogeneous. It is shown how
the concepts of emission measure differential in T and n can be extended
to arbitrary plasmas. It is demonstrated how in the special degenerate
case where surfaces of constant T and constant n coincide it is possible
to utilize jointly data on temperature and density-sensitive line
ratios to draw conclusions concerning the plasma pressure distribution.
Title: Luminosity Indicators for Warm Carbon Stars: Dwarfs Among
the Giants
Authors: Green, P. J.; Margon, B.; Brown, J.; MacConnell, D. J.
Bibcode: 1991BAAS...23.1385G
Altcode:
No abstract at ADS
Title: Interrelation of Soft and Hard X-Ray Emissions during Solar
Flares. II. Simulation Model
Authors: Winglee, R. M.; Dulk, G. A.; Bornmann, P. L.; Brown, J. C.
Bibcode: 1991ApJ...375..382W
Altcode:
Two-dimensional electrostatic particle simulations are presented which
incorporate the effect of quasi-static electric fields on particle
dynamics as well as effects associated with wave-particle interactions
induced by the accelerated particles. The properties of the soft and
hard X-ray and microwave emissions from such systems are examined. In
particular, it is shown that acceleration by quasi-static electric
fields and heating via wave-particle interactions produces electron
distributions with a broken-power law, similar to those inferred from
hard X-ray spectra. Also, heating of the ambient plasma gives rise to
a region of hot plasma propagating down to the chromosphere at about
the ion sound speed.
Title: Stellar Occultation of Polarized Light from Circumstellar
Electrons. II. Flat Envelopes Viewed at Arbitrary Inclination
Authors: Fox, Geoffrey K.; Brown, John C.
Bibcode: 1991ApJ...375..300F
Altcode:
We extend the treatment given in Paper I for the linear polarization
produced from a flat circumstellar envelope with a finite-size light
source viewed edge-on to the case of arbitrary inclination. We
find that for an axisymmetric disk scattering region viewed at low
inclination, stellar occultation enhances the net polarization, while
for high inclination the polarization is reduced by occultation. We apply our analysis to the polarimetric variations expected from a
rotating binary system in which the scattering material consists of a
one-dimensional plume superposed on an axisymmetric disk and show that
this allows the determination of the inclination of the system and
the radial structure of the plume for sufficiently high inclinations
(i > 60°). The extent to which this method can be generalized
to an arbitrarily distributed two-dimensional scattering region is
also analyzed via Fourier analysis. It is found that the inclination
of the system is largely insensitive to the density distribution when
the distribution function is of a simple power-law form.
Title: Inference of 'bumps' in electron energy spectra from high
resolution X-ray bremsstrahlung spectra
Authors: Brown, J. C.; MacKinnon, A. L.; van den Oord, G. H. J.;
Trottet, G.
Bibcode: 1991A&A...242L..13B
Altcode:
Regions of positive slope in an electron speed distribution function
fs(v) are shown to result in sharp downward 'knees' (spectral
index increases) in the emitted bremsstrahlung spectra. For Kramers'
cross-section, a criterion is established for the detectability of such
a 'bump' in the source electron spectrum from the photon spectrum,
realizable from state of the art X-ray spectrometry, and applying a
fortiori for more exact cross-sections. Inference of bumps in the thick
target injection spectrum, however, demands spectral resolution far
beyond present capabilities. Physical implications of bumps in fs(v)
are discussed.
Title: Density diagnostics and inhomogeneous non-isothermal plasmas
Authors: Almleaky, Y. M.; Brown, J. C.; Dwivedi, B. N.; Sweet, P. A.
Bibcode: 1991AdSpR..11a.311A
Altcode: 1991AdSpR..11..311A
The problem of interpreting densities in inhomogeneous non-isothermal
plasmas has been discussed. It is shown how the concepts of emission
measures differential in density ζ (n) and in temperature ξ (T)
can be generalised to analyse arbitrary plasmas. In the special case
where surfaces of constant temperature ST and of constant
density Sn coincide, the possibility of deriving the
density distribution as a function of temperature has been developed,
provided ξ(T) is known. It is then investigated whether and when
the predicted line strength of a set of sources with different n(T)
but with the same ξ(T) would be distinguishable, using measurements
of density sensitive lines and an empirical model of the form n(T)
α T-δ. The technique can be extended, and the model form
for n(T) tested, by comparing for consistency the value of δ and
ηO obtained for three or more line ratios.
Title: Energetic particles in solar flares: theory and diagnostics.
Authors: Brown, J. C.
Bibcode: 1991psf..conf..413B
Altcode:
Recent progress and future prospects in diagnostics of energetic
electrons and ions in the flares are reviewed, together with the roles
they play in the flare as a whole. Most of the discussion centres on
hard X-ray and gamma-ray and thermal plasma emission data, rather than
on radio sources.
Title: On self-enrichment models for the halo globular clusters.
Authors: Truran, J. W.; Brown, J.; Burkert, A.
Bibcode: 1991ASPC...13...78T
Altcode: 1991fesc.book...78T
Recent spectroscopic studies of the detailed abundance patterns
characterizing globular cluster stars are briefly reviewed. Guided
by the current knowledge of nucleosynthesis as a function of stellar
mass occurring in stars and supernovae, the authors identify some
interesting constraints that these combined observational and
theoretical considerations impose on the nature and timescale of
the early chemical evolution of the Milky Way globular clusters. The
authors are led to the conclusion that the abundance patterns observed
in the halo clusters are very likely a consequence of self-enrichment. A
model for such self-enrichment is presented.
Title: Effect of Electron Beams during Solar Flares
Authors: Aboudarham, J.; Henoux, J. C.; Brown, J. C.; van den Oord,
G. H. J.; van Driel-Gesztelyi, L.; Gerlei, O.
Bibcode: 1990SoPh..130..243A
Altcode:
Electron bombardment of the solar atmosphere has two effects: one is
to enhance hydrogen recombination emission, the other is to increase
the opacity via an increase of H− population. The first
effect is the most important in the upper part of the atmosphere and
the second in the lower part. We predict that, when enhanced absorption
dominates in the part of the atmosphere where radiation originates,
there will be a decrease in the white-light emission, leading to a
`negative flare', or what we call a `Black-Light Flare'. This phenomenon
occurs only for a short duration, not more than ∼ 20 s. `Black-Light
Flares' have already been observed in the case of flare stars and we
suggest here that they could also be present on the Sun, just prior
to a White-Light Flare.
Title: Return Current and Collisional Effects in Nonthermal Electron
Beams with Pulsed Injection
Authors: Karlicky, M.; Alexander, D.; Brown, J. C.; MacKinnon, A. L.
Bibcode: 1990SoPh..129..325K
Altcode:
The evolution of a pulse of nonthermal electrons, with a truncated
power-law spectrum, injected into a uniformly dense coronal plasma,
is studied by the 1-D particle simulation of return current and direct
collisional effects. The beam pulse injection profile varies gradually
enough for total current neutrality, and a steady-state Ohm's law for
the return current, to apply at each point and time. Quasi-linear
relaxation of the beam is deliberately ignored in order to isolate
the modification of return current effects by pulsed injection.
Title: Comet Mueller (1990j)
Authors: Mueller, J.; Mendenhall, J. D.; Holt, H. E.; Holt, H. R.;
Olmstead, C. M.; Brown, J.
Bibcode: 1990IAUC.5091....1M
Altcode:
Jean Mueller reports her discovery of a comet on a plate taken in the
course of the second Palomar Sky Survey. The following observations were
measured by Mueller: 1990 UT R.A. (1950) Decl. m1 Observer Sept.15.34653
0 44 43.68 +12 33 54.8 17 Mueller 15.40299 0 44 42.90 +12 33 44.1 "
16.39253 0 44 23.93 +12 29 06.9 17 Holt 16.42795 0 44 23.21 +12 28
54.0 " J. Mueller and J. D. Mendenhall (Palomar). 1.2-m Oschin Schmidt
Telescope. Beginning and end measurements of trail. Tail visible toward
south-southwest. H. E. Holt, H. R. Holt, C. M. Olmstead, and J. Brown
(Palomar). 0.46-m Schmidt telescope. Central condensation reasonably
dark; fan tail toward southwest.
Title: The Dynamics of Solar Sails with a Non-Point Source of
Radiation Pressure
Authors: McInnes, Colin R.; Brown, John C.
Bibcode: 1990CeMDA..49..249M
Altcode:
The form of the solar radiation pressure on a heliocentric orbiting
solar sail is obtained for a finite angular sized and limb darkened
solar disk by the use of the radiation pressure tensor. It is found
that the usual inverse square variation of the solar radiation pressure
is modified by the finite angular size, and to a lesser extent by
the solar limb darkening. The actual magnitude of the modification
is in itself small, except at close heliocentric distances. However,
its existence has implications for the dynamical stability of solar
sails both in parked and circular orbital configurations and for the
accuracy of trajectory calculations, particularly for sails in the
inner solar system.
Title: Black and white flares?
Authors: Henoux, J. -C.; Aboudarham, J.; Brown, J. C.; van den Oord,
G. H. J.; van Driel-Gesztelyi, L.
Bibcode: 1990A&A...233..577H
Altcode:
It is shown that the nonthermal ionization of a solar flare atmosphere
by beam bombardment can result, in the initial stages of a flare, in
dimunitions in the continuum solar flare brightness (termed 'black
light flares'). The most favorable conditions for observing this
diagnostic phenomenon are investigated in terms of flare location and
wavelength. In terms of bombarding beam parameters, electron beams
of large peak flux are shown to be the most favorable as are target
atmospheres with minimal preheating.
Title: Implications of the solar flare gamma-ray limb-brightening
observations for particle acceleration and the flare magnetic
environment. II - Numerical results for a class of loop models
Authors: MacKinnon, A. L.; Brown, J. C.
Bibcode: 1990A&A...232..544M
Altcode:
A previous, analytical discussion of the directivity of the greather
than 10 MeV continuum is extended by performing numerical calculations
of the directivity expected from electrons injected, with varying
degrees of anisotropy, into magnetic loops. The three-dimensional
loop models employed are semicircular in the corona and strengthen
according to a simple, empirical form between the base of the corona
and the top of the photosphere. It is shown that the observed burst
distribution, taken at face value, places useful constraints on the
region of the solar atmosphere where the field increases, the amount
by which the field increases between the corona and the photosphere,
the radius and orientation of individual flux tubes, and the extent
to which the electrons are initially 'beamed' along the field. The
potential diagnostic importance of observing the flux from disk center
bursts is discussed.
Title: On Removal of the Gradual Component in Analyses of Solar
Impulsive Bursts
Authors: Costa, J. E. R.; Brown, J. C.; Correia, E.; Kaufmann, P.
Bibcode: 1990ApJS...73..191C
Altcode:
Three methods are considered for the removal of the gradual
component in solar flare time profiles. It is emphasized that a
time-dependent gradual component can introduce apparent delays between
impulsive extrema which may be misinterpreted in terms of physical
processes. Running mean subtraction always produces negligible delays
in comparison with the period of the fast component; thus, it has major
advantages compared with second derivatives and Fourier filtering for
recovering the impulsive component.
Title: Beam Heating in Solar Flares: Electrons or Protons?
Authors: Brown, J. C.; Karlicky, M.; MacKinnon, A. L.; van den Oord,
G. H. J.
Bibcode: 1990ApJS...73..343B
Altcode:
The current status of electron and proton beam models as candidates for
the impulsive phase heating of solar flares is discussed in relation to
observational constants and theoretical difficulties. It is concluded
that, while the electron beam model for flare heating still faces
theoretical and observational problems, the problems faced by low
and high energy proton beam models are no less serious, and there are
facets of proton models which have not yet been studied. At the present,
the electron beam model remains the most viable and best developed of
heating model candidates.
Title: Asymmetric Flux Loops in Active Regions - Part Two
Authors: Petrovay, K.; Brown, J. C.; van Driel-Gesztelyi, L.; Fletcher,
L.; Marik, M.; Stewart, G.
Bibcode: 1990SoPh..127...51P
Altcode:
We propose that magnetic flux loops in the subphotospheric layers
of the Sun are seriously asymmetrical as a consequence of the drag
force exerted on them because of the different rotational rate of the
surrounding plasma. In numerical models of stationary slender flux
loops in the plane parallel approximation we show that a serious
tilt is both possible and probable. Observational facts (see van
Driel-Gesztelyi and Petrovay, 1989; Paper I) strongly support the case
for high asymmetry. The different stability of p and f spots may also
be related to such an asymmetry.
Title: Negative Flares on the Sun
Authors: van Driel-Gesztelyi, L.; Brown, J. C.; Hénoux, J. -C.;
Aboudarham, J.; van den Oord, G. H. J.; Gerlei, O.; Fárnik, F.
Bibcode: 1990PDHO....7..202V
Altcode: 1990dysu.conf..202V; 1990ESPM....6..202V
The authors showed that under certain conditions at the beginning
of a solar white-light flare (WLF) event an electron beam can cause
a transient darkening before the WLF emission starts. They propose
optimal conditions for possible observation of solar negative flares and
present an observation, which may be the first identified observation
of such events.
Title: Stellar Occultation of Polarized Light from Circumstellar
Electrons. I. Flat Envelopes Viewed Edge-on
Authors: Brown, John C.; Fox, Geoffrey K.
Bibcode: 1989ApJ...347..468B
Altcode:
The depolarizing and occultation effects of a finite spherical light
source on the polarization of light Thomson-scattered from a flat
circumstellar envelope seen edge-on are analyzed. The analysis shows
that neglect of the finite size of the light source leads to a gross
overestimate of the polarization for a given disk geometry. By including
occultation and depolarization, it is found that B-star envelopes
are necessarily highly flattened disk-type structures. For a disk
viewed edge-on, the effect of occultation reduces the polarization
more than the inclusion of the depolarization factor alone. Analysis
of a one-dimensional plume leads to a powerful technique that permits
the electron density distribution to be explicitly obtained from the
polarimetric data.
Title: Density diagnostics and inhomogeneous plasmas. I - Isothermal
plasmas
Authors: Almleaky, Y. M.; Brown, J. C.; Sweet, P. A.
Bibcode: 1989A&A...224..328A
Altcode:
The problem of interpreting density-sensitive line strengths from
an isothermal plasma of inhomogeneous density is addressed. In the
case of two observed lines, the results may be expressed in terms of a
spectroscopic mean density which is the density of a homogeneous plasma
with the same line ratio. The spectroscopic mean density value will
vary for different line pairs, and differ from the volumetric mean and
emissivity mean unless the plasma is actually homogeneous. Illustrative
diagnosis of an exponential atmosphere model demonstrates how large a
variation in density ratio can occur and how this variation serves to
measure the plasma inhomogeneity. This effect explains the different
densities commonly inferred for the same source by application of
different diagnostic line pairs. As the number of lines observed is
increased, in principle a complete solution for the plasma structure
and correct total volume is approached.
Title: Book-Review - Supernovae
Authors: Syunyaev, R. A.; Brown, J. C.
Bibcode: 1989Obs...109Q.198S
Altcode:
No abstract at ADS
Title: Book Review: The sun: an introduction / Springer-Verlag
Authors: Brown, J. C.
Bibcode: 1989Natur.341R.580B
Altcode:
No abstract at ADS
Title: Book Review: The atmosphere of the sun. / Adam Hilger, 1988
Authors: Syunyaev, R. A.; Brown, J. C.
Bibcode: 1989Obs...109R.198S
Altcode:
No abstract at ADS
Title: Book Review: The restless sun / Smithsonian Institution
Press, 1989
Authors: Brown, J. C.
Bibcode: 1989Natur.341Q.580B
Altcode:
No abstract at ADS
Title: Book-Review - Astrophysical Plasma
Authors: Syunyaev, R. A.; Brown, J. C.
Bibcode: 1989Obs...109S.198S
Altcode:
No abstract at ADS
Title: On the Bremsstrahlung Efficiency of Nonthermal Hard X-Ray
Source Models
Authors: MacKinnon, A. L.; Brown, J. C.
Bibcode: 1989SoPh..122..303M
Altcode:
It has often been stated, but never rigorously proven, that interpreting
observed hard X-ray emission in terms of a thick-target source gives a
lower limit to the flux of electrons which have to be injected into the
source. The truth of this statement, for theburst-integrated emission,
is rigorously established here. Also an explicit inversion for the
injected electron flux in terms of the photon spectrum is given, for the
case where all electrons traverse a single value of column density. This
generalises the previous results for the thick- and thin-target limits.
Title: Finite Source Depolarization Factors for Circumstellar
Scattering
Authors: Brown, John C.; Carlaw, Vivette A.; Cassinelli, Joseph P.
Bibcode: 1989ApJ...344..341B
Altcode:
A single scattering theory is used to directly derive the D(r) result
of Cassinelli et al (1987) and to investigate the extent to which it
can be generalized to nonuniform spherical light sources, nonspherical
light sources, arbitrary spatial distributions of scattering electrons,
and scattering particles other than electrons. Expressions are also
obtained for the factor by which the total scattered (as well as
polarized) intensity is modified by finite size light sources, which
is relevant to the case where the much stronger direct unpolarized
starlight is eclipsed.
Title: Implications of the solar flare gamma-ray limb-brightening
observations for particle acceleration and the flare magnetic
environment. I - Approximate, analytical treatment
Authors: MacKinnon, A. L.; Brown, J. C.
Bibcode: 1989A&A...215..371M
Altcode:
Gamma-ray continuum limb brightening has been interpreted in terms of
the transport and bremsstrahlung of relativistic electrons. A simple
one-dimensional vertically stratified model of field strength and
density variation in the atmosphere is employed which allows qualitative
determination of the influences of atmospheric structure and accelerated
particle anisotropy on the distribution of burst occurrence. Three
limb-brightening mechanisms are identified: (1) the variation with
viewing angle of the column depth along the line of sight; (2) the
combined effects of the loss-cone and the drastic density decrease
above the transition region; and (3) the relationship between the
field strength and ambient density throughout the atmosphere.
Title: Self-similar Lagrangian Hydrodynamics of Beam-heated Solar
Flare Atmospheres
Authors: Brown, John C.; Emslie, A. Gordon
Bibcode: 1989ApJ...339.1123B
Altcode:
The one-dimensional hydrodynamic problem in Lagrangian coordinates (Y,
t) is considered for which the specific energy input Q has a power-law
dependence on both Y and t, and the initial density distribution is
rho(0) which is directly proportional to Y exp gamma. In regimes where
the contributions of radiation, conduction, quiescent heating, and
gravitational terms in the energy equation are negligible compared to
those arising from Q, the problem has a self-similar solution, with the
hydrodynamic variables depending only on a single independent variable
which is a combination of Y, t, and the dimensional constants of the
problem. It is then shown that the problem of solar flare chromospheric
heating due to collisional interaction of a beam of electrons (or
protons) with a power-law energy spectrum can be approximated by such
forms of Q(Y, t) and rho(0)(Y), and that other terms are negligible
compared to Q over a restricted regime early in the flare.
Title: Book-Review - the Atmosphere of the Sun
Authors: Durrant, C. J.; Brown, J. C.
Bibcode: 1989Natur.338..179D
Altcode:
No abstract at ADS
Title: The local star
Authors: Brown, J. C.
Bibcode: 1989Natur.338..179B
Altcode: 1989Natur.338..179Z
No abstract at ADS
Title: Book-Review - Superstrings - a Theory of Everything
Authors: Davies, P. C. W.; Brown, J.
Bibcode: 1989S&T....77..273D
Altcode:
No abstract at ADS
Title: Polarimetric analysis of mass transfer in the X-ray transient
A 0538-66.
Authors: Clayton, Geoffrey C.; Brown, John C.; Thompson, Ian B.; Fox,
Geoffrey K.
Bibcode: 1989MNRAS.236..901C
Altcode:
New observations are reported of the optical polarimetric variation of
the recurrent X-ray transient A0538-66 during outburst 99 (1982 April)
These are utilized, together with data from outburst 75, to study the
redistribution of gas in the system during periastron passage. The
observations exhibit a rapid ~90^deg^ change in polarimetric position
angle φ and a large increase in the degree of polarization p very
close to periastron, both changes persisting much longer than the
photometric decay time. A number of interpretations are excluded by
these data. In particular the slow decay of {DELTA}p and {DELTA}φ are
incompatible with the predominance of scattering of light from one star
off material around the other, due to the rapid geometric changes the
highly eccentric orbit and regardless of the orbital elements. It is
shown that the data are broadly compatible with the polarization arising
from light predominantly from the primary (Be-star) neighborhood which
is scattered off a Be-star type disc and a large gas cloud created
near periastron by the neutron star passage. This cloud, which has a
mass comparable to that accreted by the neutron star to produce the
X-ray burst, has to persist near the periastron direction for longer
than the Keplerian rotation time of the inner Be-star disc. An orbit
inclined to the Be-star disc plane. suggested by several authors,
is not demanded by the available data, but is not exclude either.
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
Bibcode: 1989epos.conf..225C
Altcode:
The work of this group was concerned with how the energy released
in a solar flare is transported through the solar atmosphere before
escaping in the form of radiant and mechanical energy.
Title: Return current instability in flares.
Authors: Cromwell, D.; McQuillan, P.; Brown, J. C.
Bibcode: 1989sasf.confP.313C
Altcode: 1989IAUCo.104P.313C; 1988sasf.conf..313C
The authors consider the problem of ion-acoustic wave generation, and
resultant anomalous Joule heating, by a return current driven unstable
by a small-area thick-target electron beam in solar flares. They find
that, contrary to the usual assumption, the hard X-ray bremsstrahlung
emission may actually be enhanced in comparison to conventional
thick-target models.
Title: Book-Review - Superstrings - a Theory of Everything
Authors: Davies, P. C. W.; Brown, J.; Mahoney, T.
Bibcode: 1988JBAA...98..367D
Altcode:
No abstract at ADS
Title: Superstrings - a Theory of Everything
Authors: Davies, P. C. W.; Brown, J.
Bibcode: 1988Sci...242.1714D
Altcode:
No abstract at ADS
Title: Book-Review - Principles of Plasma Diagnostics
Authors: Hutchinson, I. H.; Brown, J. C.
Bibcode: 1988Obs...108..186H
Altcode:
No abstract at ADS
Title: Book-Review - Superstrings - a Theory of Everything
Authors: Davies, P. C. W.; Brown, J.
Bibcode: 1988JBAA...98..316D
Altcode:
No abstract at ADS
Title: Beam-Driven Return Current Instability and Anomalous Plasma
Heating in Solar Flares
Authors: Cromwell, D.; McQuillan, P.; Brown, J. C.
Bibcode: 1988SoPh..115..289C
Altcode:
We consider the problem of ion-acoustic wave generation, and resultant
anomalous Joule heating, by a return current driven unstable by a
small-area thick-target electron beam in solar flares. With a prescribed
beam current evolution, jb(t) (and, therefore, a prescribed
return current jp(t) = −jb(t)), and using an
approximate local treatment with a two component Maxwellian plasma,
and neglecting energy losses, we demonstrate the existence of two
quite distinct types of ion-acoustic unstable heating regimes. First,
marginally stable heating occurs when the onset of instability occurs
at electron-ion temperature ratios Te/Ti >
4.8. Secondly, there exists a `catastrophic' heating regime for which
marginally stable evolution is impossible, when the onset of instability
occurs at Te/Ti < 4.8.
Title: Analytic Limits on the Forms of Spectra Possible from Optically
Thin Collisional Bremsstrahlung Source Models
Authors: Brown, John C.; Emslie, A. Gordon
Bibcode: 1988ApJ...331..554B
Altcode:
The constraints on hard X-ray bremsstrahlung spectral forms required in
order for them to correspond to physically acceptable (nonnegative)
electron distributions in thin-target, thick-target, and thermal
source models are discussed. The extent to which various spectra
can be attributed to the different models is examined, showing that
many possible spectra cannot be described by all, or in some cases,
any of the models. It is shown that for any bremsstrahlung cross
section, the thick-target and thermal models require that successively
higher derivatives of the thin-target constraint have the appropriate
sign. It is found that thermal models are the most restrictive, and
that thin-target models are the least restrictive. Explicit analytic
constraint expressions are derived for all three cases for the Kramers
cross section and examples of acceptable and unacceptable spectra are
given. Application of these criteria to the testing and exclusion of
models is discussed.
Title: Problems with Non Thermal Models for the Narrow Line Gamma-Rays
Reported from SS:433
Authors: Brown, J. C.; Carlaw, V. A.; Cawthorne, T. V.; Icke, V.
Bibcode: 1988Ap&SS.143..153B
Altcode:
The jet/grain model proposed by Ramatyet al. (1984, hereafter
abbreviated as RKL) for production of the narrow gamma-ray lines
reported from SS433 is examined and shown to be untenable on numerous
grounds. Most importantly: (a) The huge Coulomb collisional
losses (W c≳2×1041 erg s-1) from
the jet, which would necessarily accompany non-thermal production of
the gamma rays, demands a jet acceleration/collimation process acting
over a very long range and with a power at least 102 times
the Eddington limit for any stellar object. (b) There is a
collisional thick target limit (irrespective of jet mass) to the gamma
ray yield per interstellar proton. Consequently, the gamma-ray data
demand an improbably high interstellar density (≳109
cm-3). (c) For the grains to be kept cool
enough (≲3000 K) to survive the heating rateW c either
by radiation or jet expansion would demand a ‘jet’ wider than
its length and so inconsistent with narrow lines. In the case of
radiative cooling, the resultant IR flux would exceed the observed
values by a factor ≳104. (d) Light scattered
on the jet grain mass required would be highly polarized, contrary
to observations, unless the jet was optically thick to grains, again
precluding their radiative cooling. (e) To avoid unacceptable
precessional broadening of the gamma-ray lines demands an emitting jet
length ≲0.5 days atv=0.26c. This increases the necessary mass loss
rate by a factor ≅10 over the values obtained by RKL who assumed a
4-day ‘flare’. (f) The model also predicts rest energy
gamma-ray lines which are not observed.
Title: Self-Similar Hydrodynamics of Electron-Heated Flare Atmospheres
Authors: Emslie, A. G.; Brown, J. C.
Bibcode: 1988BAAS...20..739E
Altcode:
No abstract at ADS
Title: Superstrings. A theory of everything?
Authors: Davies, P. C. W.; Brown, J.
Bibcode: 1988ste..book.....D
Altcode:
The first part of this book presents an introduction, in nonmathematical
terms, to the basic ideas of superstring theoryand its potential
physical and cosmological implications. This part is written by
P. C. W. Davies. The second part of the book presents transcripts
of interviews with theoretical physicists involved in developing
superstring theory. These interviews were originally broadcast in
a BBC Radio science documentary. The book includes the text of the
interviews with the physicists John Schwarz, Edward Witten, Michael
Green, David Gross, John Ellis, Abdus Salam, Sheldon Glashow, Richard
Feynman and Steven Weinberg.
Title: The relation between the visual polarization and UV narrow
absorptionlines in irregular Be star variations.
Authors: Brown, J. C.; Henrichs, H. F.
Bibcode: 1987A&A...182..107B
Altcode:
The data and conclusions of Sonneborn et al. (1987) concerning the
Omega Ori are analyzed using the general formulation of continuum
polarization in Be-star envelopes of Brown and McLean (1977). The
ratio of variability amplitude in narrow UV lines to that in
optical polarization and the time dependence of these amplitudes
are examined. Model-equation-derived data are found to support the
conclusions that: (1) the line-profile variability in the UV line does
not correlate with the visual continuum polarization; (2) the visual
color and continuum fluxes correspond with the polarization; and (3)
the H-alpha variations are weakly related to the polarization.
Title: Interpretation of fast ripple structure in solar impulsive
bursts
Authors: Loran, J. M.; Brown, J. C.; Correia, E.; Kaufmann, P.
Bibcode: 1987STIN...8728494L
Altcode:
The hypothesis that solar impulsive bursts are comprised of
quasi-quantized ultrarapid pulses convoluted with a variable
pulse repetition rate R(t) is investigated by comparison of typical
observations with numerical simulations. It is found that the ripple
amplitude at burst peak increases rapidly with increase in the ratio
delta-t/T of pulse separation to pulse width. Consequently, pulse
widths T are generally much larger than the observed period delta-t
of small amplitude ripples. It is also found that, in order to give
a ripple amplitude of at least a few percent at burst peak together
with reasonable burst rise and fall times without unreasonable ripple
amplitude during rise and fall, the individual pulse shape must be
sharply peaked but have substantial wings while the repetition rate R(t)
must fall gradually away from its peak value cut off rapidly in its
wings. As a specific example, a simulation is presented of the fast
ripple structures observed in the impulsive 22 GHz burst of December
18, 1980. The relevance of these conclusions to physical modeling is
briefly discussed.
Title: Book-Review - Radio Continua during Solar Flares
Authors: Benz, A. O.; Brown, J. C.
Bibcode: 1987Obs...107..134B
Altcode:
No abstract at ADS
Title: Collisional and Return Current Heating Functions for
Beam-Heated Models of Solar Flares
Authors: Brown, J. C.; McClymont, A. N.
Bibcode: 1987Ap&SS.133..297B
Altcode:
In beam-heated models of solar flares, the bulk of the energy deposited
in the flare atmosphere resides in the low-energy end of the electron
spectrum. Since the shape of the spectrum at low energy is not well
determined observationally, various forms of low-energy cut-off have
been assumed in theoretical modelling. Certain results of such modelling
may depend strongly on the assumed spectrum. We derive the heating
distributions for various spectra, both for collisional energy loss
and for Ohmic dissipation of the return current, and show that none of
the spectra are fully satisfactory, according to the criteria that for
both collisional and Ohmic heating, the heating rate should be bounded,
continuous, and smooth, and have a tractable functional form. A simple
form of electron spectrum is suggested, which satisfies these criteria.
Title: Project Leap: Lunar Ecosystem and Architectural Prototype
Authors: Winisdoerffer, F.; Brown, J.; Ximenes, S.
Bibcode: 1987LPI....18.1090W
Altcode:
No abstract at ADS
Title: Impulsive Phase Observations and Their Interpretation
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
Bibcode: 1986epos.conf..3.4C
Altcode: 1986epos.confC...4C
No abstract at ADS
Title: Theoretical Studies of Transport Processes
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
Bibcode: 1986epos.conf.3.34C
Altcode: 1986epos.confBC.34C
No abstract at ADS
Title: Impulsive phase transport
Authors: Canfield, Richard C.; Bely-Dubau, Francoise; Brown, John C.;
Dulk, George A.; Emslie, A. Gordon; Enome, Shinzo; Gabriel, Alan H.;
Kundu, Mukul R.; Melrose, Donald; Neidig, Donald F.
Bibcode: 1986epos.conf..3.1C
Altcode: 1986epos.confC...1C
The transport of nonthermal electrons is explored. The thick-target
electron beam model, in which electrons are presumed to be accelerated
in the corona and typically thermalized primarily in the chromosphere
and photosphere, is supported by observations throughout the
electromagnetic spectrum. At the highest energies, the anisotropy
of gamma-ray emission above 10 MeV clearly indicates that these
photons are emitted by anisotropically-directed particles. The timing
of this high-energy gamma-radiation with respect to lower-energy
hard X-radiation implies that the energetic particles have short
life-times. For collisional energy loss, this means that they are
stopped in the chromosphere or below. Stereoscopic (two-spacecraft)
observations at hard X-ray energies (up to 350 keV) imply that these
lower-energy (but certainly nonthermal) electrons are also stopped deep
in the chromosphere. Hard X-ray images show that, in spatially resolved
flares whose radiation consists of impulsive bursts, the impulsive
phase starts with X-radiation that comes mostly from the foot-points
of coronal loops whose coronal component is outlined by microwaves.
Title: The inverse Compton interpretation of fast-time structures
in solar microwave and hard X-ray bursts
Authors: McClements, K. G.; Brown, J. C.
Bibcode: 1986A&A...165..235M
Altcode:
It has been proposed that recently observed solar microwave and hard
X-ray bursts can be interpreted in terms of a synchrotron/inverse
Compton mechanism and that the very fast time structures associated
with such events are determined by the inverse Compton radiative
lifetime. The feasibility of the inverse Compton interpretation is
analysed in detail. With particular reference to the simultaneous
microwave and hard X-ray observations of a solar burst it is shown
that the model is self-consistent for a narrow range of marginally
plausible parameters if it is assumed that the short timescales are
determined by processes other than radiative losses.
Title: Book-Review - Solar Radiophysics
Authors: McLean, D. J.; Labrum, N. R.; Brown, J. C.
Bibcode: 1986Obs...106..117M
Altcode:
No abstract at ADS
Title: Bombardment solutions to the "soft X-ray puzzle" in radial
white dwarf accretion.
Authors: Thompson, A. M.; Brown, J. C.; Kuijpers, J.
Bibcode: 1986A&A...159..202T
Altcode:
The problem of the observed low ratio of hard to soft X-rays in
accreting white dwarfs, with low accretion rate (e.g. AM Her), is
discussed in terms of models where the accreting matter is treated as
a nonthermal stream bombarding a static atmosphere cooled by optically
thin radiation (Kuijpers and Pringle, 1982). It is shown that the
proton collisional mean free path used by Kuijpers and Pringle (1982)
was inappropriate for the inferred temperature regime and that when
the correct expression is used the global mean temperature of a steady
state bombardment solution is much lower (about 10 to the 5 K) and much
closer to observations. It is seen that no steady state solution is
possible without invoking some other kind of energy transport mechanism;
such bombardment models cannot explain the 'soft X-ray puzzle'. The
shock solution of Frank and King (1984) - and its failure to solve
the puzzle - are discussed.
Title: The quasi-linear relaxation of thick-target electron beams
in solar flares.
Authors: McClements, K. G.; Brown, J. C.; Emslie, A. G.
Bibcode: 1986NASCP2449..373M
Altcode: 1986rfsf.nasa..373M
The effects of quasi-linear interactions on thick-target electron
beams in the solar corona are investigated. Coulomb collisions produce
regions of positive gradient in electron distributions. In the corona,
the timescale for this quasi-linear relaxation is very short compared
to the collision time. It is therefore possible to model the effects
of quasi-linear relaxation by replacing any region of positive slope
in the distribution by a plateau at each time step, in such a way as
to conserve particle number. The X-ray bremsstrahlung and collisional
heating rate produced by a relaxed beam are evaluated.
Title: The effect of beam-driven return current instability on solar
hard X-ray bursts.
Authors: Cromwell, D.; McQuillan, P.; Brown, J. C.
Bibcode: 1986NASCP2449..327C
Altcode: 1986rfsf.nasa..327C
The problem of electrostatic wave generation by a return current
driven by a small area electron beam during solar hard X-ray bursts is
discussed. Preliminary results of calculations attempting to determine
the effect of such return current instability on hard X-ray bursts
during solar flares are described.
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
Bibcode: 1986NASCP2439....3C
Altcode:
Contents: 1. Introduction: motivation for transport studies, historical
perspective, overview of the chapter. 2. Impulsive phase observations
and their interpretation: gamma-ray emission above 10 MeV, hard
X-ray and microwave morphology, combined soft and hard X-ray spectra,
iron Kα emission, ultraviolet and hard X-ray emission, white light
emission, Hα emission. 3. Theoretical studies of transport processes:
electron beams and reverse currents, proton transport, radiative energy
transport by amplified decimetric waves. 4. Summary.
Title: Inverse problems in astronomy. A guide to inversion strategies
for remotely sensed data
Authors: Craig, I. J. D.; Brown, J. C.
Bibcode: 1986ipag.book.....C
Altcode:
After introducing the essential character of integral inversion problems
and the bases of their occurrence in astronomy, attention is given to
standard integral equations arising in astronomical situations. The
main analytic properties of integral inversion problems are presented,
and the naive 'classical' approach to inversion for numerical data
is illustrated to demonstrate the intrinsic instability of this
approach. This instability is overcome by nonclassical regularization
techniques; the application of methods incorporating 'smoothness
constraints' and 'nonnegativity' to several numerical case studies
for contemporary astronomical research problems is demonstrated.
Title: Plasma turbulence and impulsive UV line emission in solar
flares.
Authors: Brown, John C.
Bibcode: 1986NASCP2449..311B
Altcode: 1986rfsf.nasa..311B
Observations show that hard X-ray burst and UV lines rise and fall
simultaneously on time scales of seconds. Hydrodynamic simulations
of beam-heated atmospheres, based on collisional transport, however,
produce only a gradual fall in UV emission, when the beam flux falls,
due to the long time scale of conductive relaxation. It is suggested
that this discrepancy might be explained by onset of plasma turbulence
driven by the strong heat flux or by the beam return current going
unstable.
Title: Evidence for and against electron beams in solar flares.
Authors: Brown, J. C.; Rust, D.
Bibcode: 1986lasf.conf..431B
Altcode: 1986lasf.symp..431B
The theoretical and observational evidence for the interpretation
of hard X-ray bursts as non-thermal bremsstrahlung from a
collision-dominated thick target electron beam is reviewed critically
as on this interpretation rests the extensive work being done on beam
heating of solar flares. It is concluded that the thick target model
cannot be rejected but that it poses a number of problems too serious
to be lightly dismissed.
Title: A Lower Limit to the Field Strength in Magnetic Reconnection
Sites in Solar Flares Inferred from Hard X-Ray Bursts
Authors: Loran, J. M.; Brown, J. C.
Bibcode: 1985Ap&SS.117..173L
Altcode:
It is shown how the hard X-ray burst count rate and itse-folding ime can
be used to estimate the minimum magnetic fieldB min required
in a flare magnetic reconnection site for the burst to be interpreted
in terms of a thick target model. Application of the method to data
from the Solar Maximum Mission (HXRBS) indicates absolute minimum
fields well in excess of 100 G, and impossibly high values for some
reconnection geometries.
Title: Beams and jets in astrophysical plasmas
Authors: Brown, J. C.
Bibcode: 1985PPCF...27.1359B
Altcode:
Consideration is given to the plasma physical aspects of intense
astrophysical particle streams from a variety of sources. A survey is
presented of observations of outflowing jets in active galactic nuclei;
streams of infalling matter onto gravitationally compact stars; and
intense charged beams in solar flares. The contribution of rotational
energy transfer in black holes to the development of relativistic jets
is discussed in detail.
Title: Quantitative analysis of hard X-ray `footpoint' flares observed
by the Solar Maximum Mission
Authors: MacKinnon, A. L.; Brown, J. C.; Hayward, J.
Bibcode: 1985SoPh...99..231M
Altcode:
We describe the instrumental corrections which have to be incorporated
for reliable correction and deconvolution of images obtained in
the 16-22 keV and 22-30 keV energy bands of the Hard X-Ray Imaging
Spectrometer (HXIS) aboard the Solar Maximum Mission (SMM). These
corrections include amplifier gain and collimator hole size variations
across the field of view, amplifier/filter efficiency, variation in
effective collimator hole size and angular response with photon energy,
dead-time, and hard X-ray plate transmission. We also emphasise the
substantial Poisson noise in these energy bands, and describe the
maximum entropy deconvolution/correction routine we have developed to
establish the spatial structure which can be reliably inferred from
HXIS data.
Title: The numerical inversion of synchrotron spectra and the Crab
nebula ASA synchrotron source.
Authors: Craig, I. J. D.; McClements, K. G.; Thompson, A. M.; Brown,
J. C.
Bibcode: 1985A&A...149..171C
Altcode:
The photon spectrum from the Crab nebula is interpreted in terms of the
synchrotron emission mechanism. It is emphasised that the inference
of the relativistic electron spectrum in the source by inversion of
the measured photon spectrum is a backward problem that is inherently
unstable and which cannot be solved in any classical sense. The authors
show however, by invoking a variety of classical and non-classical
inversion techniques, that a plausible "minimum structure" solution
can be determined from the raw data. The sensitivity of this solution
to local data perturbations and to global changes in the form of the
measured data function is then investigated in detail.
Title: Hard X-ray bremsstrahlung production in solar flares by
high-energy proton beams
Authors: Emslie, A. G.; Brown, J. C.
Bibcode: 1985ApJ...295..648E
Altcode:
The possibility that solar hard X-ray bremsstrahlung is produced
by acceleration of stationary electrons by fast-moving protons,
rather than vice versa, as commonly assumed, was investigated. It
was found that a beam of protons which involves 1836 times fewer
particles, each having an energy 1836 times greater than that of the
electrons in the equivalent electron beam model, has exactly the same
bremsstrahlung yield for a given target, i.e., the mechanism has an
energetic efficiency equal to that of conventional bremsstrahlung
models. Allowance for the different degrees of target ionization
appropriate to the two models (for conventional flare geometries) makes
the proton beam model more efficient than the electron beam model, by
a factor of order three. The model places less stringent constraints
than a conventional electron beam model on the flare energy release
mechanism. It is also consistent with observed X-ray burst spectra,
intensities, and directivities. The altitude distribution of hard X-rays
predicted by the model agrees with observations only if nonvertical
injection of the protons is assumed. The model is inconsistent with
gamma-ray data in terms of conventional modeling.
Title: Bombardment Models of White Dwarf Accretion Columns
Authors: Thompson, A. M.; Brown, J. C.; Kuijpers, J.
Bibcode: 1985ASSL..116...43T
Altcode: 1985rst..conf...43T
The problem of the observed low ratio of hard to soft X-rays in
accreting white dwarfs, with low accretion rates, (e.g. AM Her) is
discussed in terms of models where the accreting matter is treated as
a non-thermal stream bombarding a static atmosphere cooled by optically
thin radiation (Kuijpers & Pringle, 1982).
Title: Interpretation of Fast Ripple Structure in Solar Impulsive
Bursts
Authors: Loran, J. M.; Brown, J. C.; Correia, E.; Kaufmann, P.
Bibcode: 1985SoPh...97..363L
Altcode:
The hypothesis that solar impulsive bursts are comprised of
quasi-quantised ultrarapid pulses convoluted with a variable
pulse repetition rate R(t) is investigated by comparison of typical
observations with numerical simulations. It is found that: The ripple
amplitude at burst peak increases rapidly with increase in the ratio
Δ/T of pulse separation to pulse width. Consequently pulse widths
T are generally much larger than the observed period Δt of small
amplitude ripples.
Title: The shortest time scales present in solar hard X-ray bursts
Authors: Brown, J. C.; Loran, J. M.; MacKinnon, A. L.
Bibcode: 1985A&A...147L..10B
Altcode:
It is pointed out that isolated transient features in solar hard X-ray
burst light curves, recently announced as having time scales of order 10
ms, have not yet been shown to be inconsistent with extreme statistical
fluctuations in the Poisson counting noise. It is then shown that as
far as persistent rapid time variations (white noise) are concerned,
the available data do not demand the existence of any intrinsic solar
time scales shorter than about 100 ms. This conclusion is supported by
the fact that the high frequency power level of the Fourier transformed
data approaches the Poisson noise expectation value above about 10 Hz
and that the correlation of time scales calculated in widely separated
energy channels deteriorates as the integration time used approaches
100 ms.
Title: Bremsstrahlung spectra from thick-target electron beams with
noncollisional energy losses
Authors: Brown, J. C.; MacKinnon, A. L.
Bibcode: 1985ApJ...292L..31B
Altcode:
A generalization of the Brown's (1971) formulation of the
relationship between bremsstrahlung spectrum and mean electron spectrum
(electrons in the range 10-100 keV) is presented with an objective of
demonstrating the information content of bremsstrahlung spectra from
a thick target. It is shown that the observed photon spectrum can be
inverted to yield an integral functional of the electron spectrum
and the effective energy loss rate. Furthermore, if observational
or theoretical electron injection spectrum is known, an effective
'phenomenological' energy loss function can be obtained.
Title: Coulomb and Ohmic Flare Heating by Nonthermal Electrons
Authors: McClymont, A. N.; Canfield, R. C.; Brown, J. C.
Bibcode: 1985BAAS...17..635M
Altcode:
No abstract at ADS
Title: Solar Hard X-Ray Bremsstrahlung Production by Proton Beams?
Authors: Emslie, A. G.; Brown, J. C.
Bibcode: 1985BAAS...17..609E
Altcode:
No abstract at ADS
Title: The restricted 3-body problem with radiation pressure
Authors: Simmons, J. F. L.; McDonald, A. J. C.; Brown, J. C.
Bibcode: 1985CeMec..35..145S
Altcode:
The restricted 3-body problem is generalised to include the effects of
an inverse square distance radiation pressure force on the infinitesimal
mass due to the large masses, which are both arbitrarily luminous. A
complete solution of the problems of existence and linear stability of
the equilibrium points is given for all values of radiation pressures of
both liminous bodies, and all values of mass ratios. It is shown that
the inner Lagrange point, L1, can be stable, but only when
both large masses are luminous. Four equilibrium points, L6,
L7, L8, and L9 can exist out of the
orbital plane when the radiation pressure of the smaller mass is very
high. Although L8 and L9 are always linearly
unstable, L6 and L7 are stable for a small range
of radiation pressures provided that both large masses are luminous.
Title: Possible evidence for stochastic acceleration of electrons
in solar hard X-ray bursts observed by SMM
Authors: Brown, J. C.; Loran, J. M.
Bibcode: 1985MNRAS.212..245B
Altcode:
It is shown that the dynamic, hard X-ray spectra of the events of
1980 March 29 and June 7 observed by the Solar Maximum Mission (HXRBS)
exhibit an anticorrelation of photon flux and spectral steepness. This
is exhibited in terms of systematic loci followed by the event in the
plane (flux I, spectral index γ). These observations are compared
with a theoretical model, developed from Benz, involving injection
of electrons into a thick target region from a fluctuating slab in
which they are stochastically accelerated. The data are found to be
in reasonable accord with the model predictions and are used to obtain
constraints on plasma conditions in the acceleration site. Theoretical
implications of this result are discussed, as are possible sources of
deviation between the data and the theory.
Title: An exploratory eccentric orbit 'Roche Lobe' overflow model
for recurrent X-ray transients.
Authors: Brown, J. C.; Boyle, C. B.
Bibcode: 1984A&A...141..369B
Altcode:
The mass transfer rate (M) variations which could occur with orbital
phase in an eccentric, semidetached binary star system is estimated by
means of calculations which assume that the rate can be instantaneously
described in terms of overflow through a Roche lobe nozzle in the
neighborhood of the inner Lagrange point. The primary envelope,
in the neighborhood of the effective Roche lobe, is taken to have an
exponential distribution of density with scale height. Orbital variation
of the binary separation then results in a dynamic variation in M. A
correction factor is estimated for the effect of M of the instantaneous
motion of the effective Roche surface; this factor makes the peak in
M precede periastron.
Title: Multiple Energetic Injections in a Strong Spike like Solar
Burst
Authors: Kaufmann, P.; Correia, E.; Costa, J. E. R.; Dennis, B. R.;
Hurford, G. J.; Brown, J. C.
Bibcode: 1984SoPh...91..359K
Altcode:
An intense and fast spike-like solar burst was observed with high
sensitivity in microwaves and hard X-rays, on December 18,1980,
at 19h21m20s UT. It is shown that
the burst was built up of short time scale structures superimposed
on an underlying gradual emission, the time evolution of which showed
remarkable proportionality between hard X-ray and microwave fluxes. The
finer time structures were best defined at mm-microwaves. At the peak
of the event the finer structures repeat every 30-60 ms (displaying an
equivalent repetition rate of 16-20 s-1). The more slowly
varying component with a time scale of about 1 s was identified in
microwaves and hard X-rays throughout the burst duration. Similarly
to what has been found for mm-microwave burst emission, we suggest
that X-ray fluxes might also be proportional to the repetition rate of
basic units of energy injection (quasi-quantized). We estimate that one
such injection produces a pulse of hard X-ray photons with about 4 ×
1021 erg, for ɛ ≳ 25 keV. We use this figure to estimate
the relevant parameters of one primary energy release site both in
the case where hard X-rays are produced primarily by thick-target
bremsstrahlung, and when they are purely thermal, and also discuss
the relation of this figure to global energy considerations. We find,
in particular, that a thick-target interpretation only becomes possible
if individual pulses have durations larger than 0.2 s.
Title: Spectral characteristics of microwave emission from solar
flare thermal hard X-ray models
Authors: MacKinnon, A. L.; Brown, J. C.
Bibcode: 1984A&A...132..229M
Altcode:
The very close temporal correlation of hard X-ray and microwave
emission from solar flares implies a common origin for radiation at
these wavelengths. Here, an analysis is conducted of the spectral
characteristics of microwave emission from a 'multiple kernel' type
of hard X-ray model, where several impulsively heated hot sources are
bounded by conduction fronts and expand at the ion-sound speed. The
properties of a single kernel are considered first; these are found
to be compatible in intensity with observations, but to be limited in
their compatibility with spectra. Extension of the model to include
a spread in kernel parameters (in particular to high temperatures) is
shown to be successful in explaining high frequency spectral indices,
but lower frequencies require some additional effect, such as time
varying magnetic field. It is concluded that microwave observations
do not rule out the multiple kernel thermal model.
Title: Electrodynamics effects in beam/return current systems and
their implications for solar impulsive bursts
Authors: Brown, J. C.; Bingham, R.
Bibcode: 1984A&A...131L..11B
Altcode:
The electrodynamics of electron beam neutralisation in solar
flares is discussed in order to resolve recent controversy over
the origin and evolution of the return current. It is demonstrated
that return currents are established electrostatically and that the
large radii of flare beams imply a resistive time scale so long that
inductive effects are negligible along the finite beam length, even
for anomalous conductivities. Consequently the commonly used steady
state electrostatic (Knight and Sturrock) treatment of return current
dissipation in flares is amply justified.
Title: The importance of particle beam momentum in beam-heated models
of solar flares
Authors: Brown, J. C.; Craig, I. J. D.
Bibcode: 1984A&A...130L...5B
Altcode:
It is shown that, in electron heated flare models, the momentum
transport in the beam itself should be incorporated in the equation
of motion. For moderately intense beams, the atmospheric acceleration
by the beam momentum far exceeds solar gravity, so demanding revision
of hydrostatic models, and is comparable with the effect of thermal
pressure gradients in hydrodynamic models. It is also pointed out that a
20 keV proton beam, of energy flux only 4 percent of the electron flux
at 20 keV, would produce comparable atmospheric accelerations. The
relevant expression is calculated for correction of existing flare
model codes for heating by an electron beam with power law spectrum.
Title: A Comparison of the Thick Target Model with Stereo Data on
the Height Structure of Solar Hard X-Ray Bursts
Authors: Brown, J. C.; Carlaw, V. A.; Cromwell, D.; Kane, S. R.
Bibcode: 1983SoPh...88..281B
Altcode:
The height structure of a thick-target solar hard X-ray source is
predicted for a beam injected vertically downward with a power-law
spectrum and dominated by Coulomb collisional energy losses. This
structure is characterised by the ratio of hard X-ray flux from an upper
part of the source to that from the entire source, and is essentially a
function only of the atmospheric column density ΔN (cm−2)
in the upper region. These predictions are compared with the flux ratios
at 150 keV and 350 keV observed by two spacecraft for five events in
which the solar limb occults part of the source for one spacecraft.
Title: Multiple energetic injections in a strong spike-like solar
burst
Authors: Kaufmann, P.; Correia, E.; Costa, J. E. R.; Dennis, B. R.;
Hurford, G. H.; Brown, J. C.
Bibcode: 1983STIN...8335983K
Altcode:
An intense and fast spike-like solar burst was built up of short time
scale structures superimposed on an underlying gradual emission, the
time evolution of which shows remarkable proportionality between hard
X-ray and microwave fluxes. The finer time structure were best defined
at mm-microwaves. At the peak of the event, the finer structures repeat
every 30x60ms. The more slowly varying component with a time scale
of about 1 second was identified in microwave hard X-rays throughout
the burst duration. It is suggested that X-ray fluxes might also be
proportional to the repetition rate of basic units of energy injection
(quasi-quantized). The relevant parameters of one primary energy release
site are estimated both in the case where hard X-rays are produced
primarily by thick-target bremsstrahlung, and when they are purely
thermal. The relation of this figure to global energy considerations
is discussed.
Title: Dissipative thermal models for impulsive microwave burst delays
Authors: Brown, John C.
Bibcode: 1983SoPh...86..227B
Altcode:
Microwave emission is analysed for a source heated by magnetic
dissipation. As the temperature rises and the field falls, the resulting
variation in microwave optical depth results in time delays between
emission features at different frequencies. A single such source can,
however, only explain events exhibiting small delays (∼-1sec) and
with lower frequencies peaking later. Continuous production of many such
heated regions (multiple kernel model) can, however, explain long delays
and produce either advancement or retardation of lower frequencies.
Title: Conference Summary
Authors: Brown, J. C.
Bibcode: 1983SoPh...86..458B
Altcode:
No abstract at ADS
Title: Dissipative thermal models for solar microwave burst delays
Authors: Brown, J. C.; MacKinnon, A. L.; Zodi, A. M.; Kaufmann, P.
Bibcode: 1983A&A...123...10B
Altcode:
The microwave emission properties are analysed for a plasma region
heated by dissipation of magnetic energy. The rising temperature
and falling magnetic field produce a variation in microwave optical
depth which can introduce time delays in event features at different
frequencies. However, for a single heated region the effect is always
that of retardation of lower frequencies and, for plausible physical
parameters, it is feasible to explain only events with small delays (a
few seconds) and maximum peak frequency ⪉25 GHz. Intense events with
long delays (⪆10 s) and high peak frequencies cannot be explained. The
analysis is extended to the case where many such single annihilation
regions of varying magnetic field strength, each of short lifetime,
are produced continuously throughout the burst. This multiple kernel
model is capable of producing either advancement or retardation of lower
frequencies and also of explaining intense events with large delays.
Title: Inversion of Synchrotron Spectra
Authors: Brown, J. C.; Craig, I. J. D.; Melrose, D. B.
Bibcode: 1983Ap&SS..92..105B
Altcode:
The problem of synchrotron radiation spectra is treated from the
viewpoint of deconvolving the spectrum of ultrarelativistic source
electrons from the observed photon spectrum. It is shown that for
homogeneous sources the problem amounts to inversion of a Meijer
transform with a modified Bessel finction kernel. A precise analytic
inversion is only possible in the complex plane but Meijer transform
tables are available for a wide range of functions. More convenient
inversion formulae prove possible by use of a Laplace transform
approximation or by analysing the spectra in terms of their integral
moments. The filtering property of the transform is also established
showing that the contribution to the synchrotron spectrum of high
frequency components in the electron spectrum declines exponentially
with their frequency. Thus, as with other Laplace-like transforms,
only a few terms in an electron spectrum expansion can be deconvolved
for any plausible noise level in the synchrotron spectrum.
Title: The effect of precipitation on diagnostics for electron trap
models of solar hard X-ray bursts
Authors: MacKinnon, A. L.; Brown, J. C.; Trottet, G.; Vilmer, N.
Bibcode: 1983A&A...119..297M
Altcode:
Some extended hard X-ray bursts exhibit increasing delays in peak times
with photon energy. These delays have been interpreted in terms of the
energy dependence of collisional decay time of energetic electrons in a
magnetic trap and used to infer the trap density. This study considers
the effect on such analyses of the inevitable collisional precipitation
of electrons from the trap to the thick target chromosphere, which has
been neglected previously. It is found that although precipitation
does influence burst time profiles, in particular shortening burst
decay times for a given trap density, it has very little effect on
the relative delays of burst peak with energy. Consequently, values
of trap density previously inferred neglecting precipitation should
be essentially correct.
Title: Solar flares: The evaporating Sun?
Authors: Brown, John C.
Bibcode: 1983Natur.302..292B
Altcode:
No abstract at ADS
Title: Inference of nebular density and luminosity structure from
polarization maps
Authors: Brown, J. C.
Bibcode: 1982MNRAS.201..735B
Altcode:
The problem of deriving the structure of circumstellar nebulae from
polarimetric maps is discussed as a process of deconvolving the nebular
structure from the observed distribution of Stokes' parameters on the
sky. The basic formulation and assumptions involved in the arbitrary
scattering mechanism are described in an attempt to determine the
nebular geometry, and it is shown how an inverse solution can be
obtained for any scattering function by means of an integral moment
representation. The equations involved are of the Volterra type;
the kernels depend on the nature of the spherical scatterers. In the
particular case of Rayleigh scattering, it is found that the equations
can be reduced to Abel's integral equation for which the analytic
inversion formula is well known. The solutions, in both cases include
emission as well as scattering of light by the nebula.
Title: A Review Of Blagg's Formula In The Light Of Recently Discovered
Planetary Moons And Rings
Authors: Lobban, G. G.; Roy, A. E.; Brown, J. C.
Bibcode: 1982JBAA...92..260L
Altcode:
No abstract at ADS
Title: Multiple Energetic Injections in a Strong Spike-Like Solar
Burst
Authors: Kaufmann, P.; Correia, E.; Costa, J. E. R.; Dennis, B. R.;
Hurford, G. J.; Brown, J. C.
Bibcode: 1982BAAS...14..921K
Altcode:
No abstract at ADS
Title: Dissipation and Stability of Return Currents in Solar-Flares
Authors: Brown, J. C.; Hayward, J.
Bibcode: 1982SoPh...80..129B
Altcode:
The dynamics of an electron beam, under the effects of Coulomb
collisions and classical Ohmic dissipation of the return current,
is analysed for a background plasma with a temperature which is time
dependent due to the heating effect of beam dissipation offset by
thermal conductive cooling. It is shown that the plasma is heated
toward a steady state, in time scales short compared to typical flare
beam switch on times, and that in this steady state only two regimes
of beam dynamics arise.
Title: Progress and prospects in solar physics
Authors: Brown, J. C.
Bibcode: 1982Natur.296..784B
Altcode:
No abstract at ADS
Title: Book-Review - Solar Active Regions
Authors: Orrall, F. Q.; Brown, J. C.
Bibcode: 1982Natur.296..784O
Altcode:
No abstract at ADS
Title: Carbon Isotope Ratios in Two Giants in M67
Authors: Brown, J.
Bibcode: 1982BAAS...14..650B
Altcode:
No abstract at ADS
Title: The effect of orbital eccentricity on polarimetric binary
diagnostics.
Authors: Brown, J. C.; Aspin, C.; Simmons, J. F. L.; McLean, I. S.
Bibcode: 1982MNRAS.198..787B
Altcode:
It is found that first and third harmonics are added when eccentricity
does not equal zero, where previously only second harmonic variations
of polarization were present, when (1) the assumption of corotation
implicit in all earlier models of phase-locked polarization variations
from close binaries is relaxed, and (2) the simple case of a localized
scattering region in an eccentric orbit about a point light source
is developed. It is demonstrated that such erroneous model parameter
values as the orbital inclination can occur, if a circular-orbit model
is assumed in the analysis of data from an eccentric-orbit binary. The
extension of the equations to the fitting of noisy data is illustrated
through application to the polarimetric data for Cygnus X-1, and it
is found that while polarimetric variations observed in Cygnus X-1
cannot be solely caused by any orbital eccentricity, it may contain
a contribution due to it.
Title: Bias of polarimetric estimators for binary star inclinations.
Authors: Simmons, J. F. L.; Aspin, C.; Brown, J. C.
Bibcode: 1982MNRAS.198...45S
Altcode:
It is shown that the polarimetric 'modelling' used by previous authors
to obtain the least squares fit to polarimetric binary data will
tend to yield inferred values of inclination greater than the true
value. This statistical bias is most pronounced at high noise levels and
low inclinations when the inferred value and the formal linear error
will have no bearing on the actual value. As noise levels increase
this inferred inclination approaches 90 deg. This complication in the
parameter determination using the canonical model and least squares
procedure has been obscured by the fact that the binaries observed
tend, through selection effects, to have high inclinations. Errors for
inclination which are established by formal techniques are seriously
over optimistic except at extremely low noise levels.
Title: Height Structure of Thermal Hard X-Ray Sources on the Sun
Authors: Brown, J. C.; Hayward, J.
Bibcode: 1981SoPh...73..121B
Altcode:
The height distribution of hard X-ray bremsstrahlung is predicted
for dissipative thermal models, involving rapid heating of many small
(tearing mode) islands near the top of a magnetic arch. Emission at
low energies (ɛ) originates mainly at high altitudes in the heated
kernels themselves while high energy emission comes from the Maxwellian
tail electrons escaping to the chromosphere.
Title: F. Maurice, L. Meny and R. Fixier (Editors), Microanalyse
et Microscopie Electronique à Bayalage and its English translation
Microanalysis and Scanning Electron Microscopy
Authors: Brown, J.
Bibcode: 1981XRS....10..153B
Altcode:
No abstract at ADS
Title: Solar flare theory.
Authors: Spicer, D. S.; Brown, J. C.
Bibcode: 1981NASSP.450..413S
Altcode: 1981suas.nasa..413S
Solar flare models are briefly reviewed with emphasis on the physical
mechanisms invoked to explain the flare. The physics of each mechanism
and their interrelations are discussed in detail. Mechanisms are
classified by their drivers (the source of energy on which they
feed). The application of these mechanisms to coronal heating is
evaluated.
Title: Solar flare observations and their interpretations.
Authors: Brown, J. C.; Smith, D. F.; Spicer, D. S.
Bibcode: 1981NASSP.450..181B
Altcode: 1981suas.nasa..181B
A solar flare has a characteristic spatial extent of 10,000 to
100,000 km. It develops rapidly, with a characteristic time scale of
100 to 1000 s but its manifestations can be observed for hours after
onset. A solar flare is the source of highly energetic particles with
energies that extend into the GeV range; it produces copious amounts
of electromagnetic radiation from gamma-rays to wavelengths of 10 km;
and it produces violent magnetohydrodynamic phenomena such as shocks
and fast mass ejections. The three basic phases of a flare are described
and are: the precursor (preflare) phase, lasting for minutes to hours;
the flash phase, lasting for 1 to 5 minutes; and the main (gradual)
phase, lasting, on occasion, for hours.
Title: Discrepancies between theoretical and empirical models of
the flaring solar chromosphere and their possible resolution
Authors: Emslie, A. G.; Brown, J. C.; Machado, M. E.
Bibcode: 1981ApJ...246..337E
Altcode:
Possible sources of pronounced discrepancy between empirical and
theoretical models of the solar chromosphere during flares are
discussed. It is noted that a principal source of uncertainty in
empirical models is the inhomogeneity of the spectral data on which
they are based. With theoretical models, probably the most important
source of error is neglect of the radiative coupling of upper and lower
chromospheric regions. A new procedure for studying flare energy input
is suggested wherein the required input is derived from the empirical
model chromosphere. This procedure is applied to the electron-heated
case, and it is found that the integral equation defining the flare
energy deposition rate can be inverted analytically to yield the
injected electron flux energy spectrum from knowledge of the energy
balance in the empirical atmosphere. Recent empirical model results
are analyzed in this manner, and the calculated injected electron
flux spectrum is compared with that needed for hard X-ray bursts in
moderately large flares.
Title: Thick Target Beam Interpretation of Stereo Observations of
a Solar Hard X-Ray Burst
Authors: Brown, J. C.; Hayward, J.; Spicer, D.
Bibcode: 1981ApJ...245L..91B
Altcode:
No abstract at ADS
Title: Orbital signature of interglacials
Authors: Kukla, G.; Berger, A.; Lotti, R.; Brown, J.
Bibcode: 1981Natur.290..295K
Altcode:
A specific orbital configuration-high obliquity combined with the June
perihelion-marked the beginning of the past three interglacials. This
suggests that the primary cause of the glacial cycle may be
astronomical. An astronomical climate index (ACLIN) is introduced which
combines the three orbital variables in the time-lag bivariant model
designed to predict the major climate changes in the late and middle
Pleistocene, and in the near future. ACLIN closely correlates with the
major climatic events revealed by independently dated proxy climate
indicators of the past 130,000 yr. It successfully differentiates the
interglacials, and displays a 100,000-yr periodicity. It predicts an
early end of the present inter glacial and the start of a new one in
114,000 yr.
Title: Polarimetric Accuracy Required for the Determination of
Binary Inclinations
Authors: Aspin, C.; Simmons, J. F. L.; Brown, J. C.
Bibcode: 1981MNRAS.194..283A
Altcode:
An analysis is made of the required accuracy of measurement of the
linear polarization Stokes parameters (Q, U) variations from close
binary stars in order to obtain a useful estimate of the orbital
inclination i, based on the analytic canonical model involving single
Thomson scattering in a corotating circumstellar envelope. The procedure
comprises evaluation of the confidence interval of i for which the model
yields an acceptable χ2 fit to simulated (Q, U) data when
optimized over the other free parameters involved. In particular,
results are presented for the maximum polarimetric standard deviation,
σnec permissible on observations for the determination of
i to ±5° in this model at a significance of 10 per cent. The results
depend on the true binary inclination, and (weakly) on the geometry. In particular the required accuracy of polarimetric observations
is found to be significantly greater for low true inclinations. As an example of the application of our computations the results
are applied to data for the binary U Sagittae. it is found that the
size of the error on the polarimetric Q, U data, after phase binning
of the observations, is some five times larger than the maximum error
allowing satisfactory inclination determination for a true inclination
of > 60°. This factor increases rapidly as lower values of i are
considered. Possible complications are discussed which arise when
the data contains noise due to intrinsic variations in the binary system
(i.e. non-corotation, long period changes in the scattering geometry).
Title: Limits on the streaming and escape of electrons in thermal
models for solar hard X-ray emission
Authors: Smith, D. F.; Brown, J. C.
Bibcode: 1980ApJ...242..799S
Altcode:
Upper limits on the number of fast electrons streaming through and
escaping from a plasma whose electrons have been heated to approximately
100 billion K and confined by a collisionless ion-acoustic thermal
conduction front are determined. It is shown that such a front is
fairly transparent to fast electrons with velocities much larger than
the thermal velocity because the anisotropic ion-acoustic waves cannot
scatter them, making them collisionless on a scale much larger than the
thickness of the front. The collisionless analog of the collisional
thermoelectric field is derived self-consistently and shown to offer
a significant impediment to fast electrons because they must climb
over a larger potential barrier than in the collisional case. The
only factors limiting the escape of electrons able to surmount this
barrier are their rate of production and the requirement that they
carry less heat flux than the maximum heat flux allowable. The rate
of production is determined for the case of a Maxwellian whose tail
is being filled collisionally.
Title: A critique of the polarimetric evidence on the nature of
CYG X-1.
Authors: Simmons, J. F. L.; Aspin, C.; Brown, J. C.
Bibcode: 1980A&A....91...97S
Altcode:
An analytical method for determining the effect of data noise on
the evaluation of models for binary star systems from their linear
polarimetric variability was applied to Cyg X-1. The method makes it
possible to fit the constrained optimum to the data using parameters of
a canonical model for polarimetric binaries. The model provides a chi
square value acceptable at the 10% significance level for inclinations
in the 85 to 150 deg range; the spectrophotometrically determined
inclination of Cyg X-1 of 30 deg is within the 90% confidence interval
when applied to noisy polarimetric measurements. The best fit value of
other canonical model parameters shows that the scattering envelope
mass is at least 10 to the 24th g, which is comparable to the mass
accretion per orbital period required to fuel the X-ray source.
Title: Discrepancies between empirical and theoretical models of
the flaring solar chromosphere and their possible resolution
Authors: Emslie, G. A.; Brown, J. C.; Machado, M. E.
Bibcode: 1980STIN...8119989E
Altcode:
Models of the solar chromosphere during flaring deduced theoretically
or empirically are compared. Marked discrepancies are noted and various
reasons are offered to explain their existence. A means is presented
for testing theoretical heating models (electron heating) by analyzing
the net energy loss rates in (observed) empirical atmospheres and
inverting the flare energy equation to deduce the parameters of the
supposed heating mechanism.
Title: A Classification Scheme for Solar Flare Models
Authors: Spicer, D. S.; Brown, J. C.
Bibcode: 1980SoPh...67..385S
Altcode:
We present a classification scheme for solar flare models that utilize
magnetic free energycurrents. The classification scheme is geometry
independent and delineates models into two categories: those models
utilizing currents flowing parallel to B and those utilizing currents
flowing perpendicular to B. This delineation of drivers allows us
to specify what kinds of plasma-magnetic field configurations should
be expected for a given current driver. Further, the delineation of
drivers will allow us to identify both the strengths and the weaknesses
of the various models.
Title: Dynamic Spectral Characteristics of Thermal Models for Solar
Hard X-Ray Bursts
Authors: Brown, J. C.; Craig, I. J. D.; Karpen, J. T.
Bibcode: 1980SoPh...67..143B
Altcode:
The dynamic spectral characteristics of the thermal model for solar
hard X-ray bursts recently proposed by Brown et al. (1979) (BMS) are
investigated. It is pointed out that this model, in which a single
source is heated impulsively and cooled by anomalous conduction across
an ion-acoustic turbulent thermal front, predicts that the total source
emission measure should rise as the temperature falls. This prediction,
which is common to all conductively cooled single-source models, is
contrary to observations of many simple spike bursts. It is proposed,
therefore, that the hard X-ray source may consist of a distribution
of many small impulsively-heated kernels, each cooled by anomalous
conduction, with lifetimes shorter than current burst data temporal
resolution. In this case the dynamic spectra of bursts are governed
by the dynamic evolution of the kernel production process, such as
magnetic-field dissipation in the tearing mode. An integral equation
is formulated, the solution of which yields information on this kernel
production process, from dynamic burst spectra, for any kernel model.
Title: Inference of Relativistic Electron Spectra from Measurements
of Inverse Compton Radiation
Authors: Craig, I. J. D.; Brown, J. C.
Bibcode: 1980Ap&SS..70..425C
Altcode:
The inference of relativistic electron spectra from spectral
measurement of inverse Compton radiation is discussed for the case
where the background photon spectrum is a Planck function. The problem
is formulated in terms of an integral transform that relates the
measured spectrum to the unknown electron distribution. A general
inversion formula is used to provide a quantitative assessment of
the information content of the spectral data. It is shown that the
observations must generally be augmented by additional information
if anything other than a rudimentary two or three parameter model
of the source function is to be derived. It is also pointed out that
since a similar equation governs the continuum spectra emitted by a
distribution of black-body radiators, the analysis is relevant to the
problem of stellar population synthesis from galactic spectra.
Title: Flares without acceleration, or acceleration without flares?
Authors: Brown, John C.
Bibcode: 1980Natur.285..613B
Altcode:
No abstract at ADS
Title: The polarization and directivity of solar-flare hard X-ray
bremsstrahlung from a thermal source
Authors: Emslie, A. G.; Brown, J. C.
Bibcode: 1980ApJ...237.1015E
Altcode:
The polarization and directivity of hard X-ray bremsstrahlung from a
thermal source consisting of a region in which a thermal flux drives
a pair of steel collisionless conduction fronts were evaluated. The
conduction fronts are symmetrically driven from a central region,
heated by the flare energy dissipation process. By comparing results
with similar calculations based on a nonthermal thick-target electron
beam model of the source, it was aimed to determine the degree to which
the observed polarization and directivity of solar flare hard X-rays
favor either model. Results which exhibit significant polarization
and directivity of the hard X-ray radiation emitted by the source are
produced by using Maxwellian electron-phase-space distribution functions
modified to take into account a directional heat flux and a steady
direct current in the X-ray source, and a fully relativistic treatment
of the bremsstrahlung emission process. The results are consistent
with solar hard X-ray anisotropy and polarization observations to date,
although these observations are too crude to be conclusive.
Title: Limits on the Streaming and Escape of Electrons in Thermal
Models for Solar Hard X-ray Bursts
Authors: Smith, D. F.; Brown, J. C.
Bibcode: 1980BAAS...12..481S
Altcode:
No abstract at ADS
Title: The hard X-ray Sun in stereo
Authors: Brown, John C.
Bibcode: 1980Natur.283..814B
Altcode:
No abstract at ADS
Title: REVIEW ARTICLE: Solar flares
Authors: Brown, J. C.; Smith, D. F.
Bibcode: 1980RPPh...43..125B
Altcode:
The current observational and theoretical problem of the
intense and complex release of energy in large solar flares is
reviewed. Observations of thermal radiation at temperatures below and
above 100,000 K and of nonthermal radiation and particles including
flare gamma rays, interplanetary Langmuir waves, soft and hard X rays
and radio bursts are presented. Theories of primary energy release
mechanisms are discussed in terms of magnetic configurations, plasma
instabilities and the trigger mechanism and dissipation mechanisms. The
secondary redistribution of the primary magnetic energy released
through the atmosphere is then considered, taking into account models
for the flash and decay phases in cool and hot regimes of the solar
atmosphere and in interplanetary space. Interpretations of the hard
X-ray data concerning particle acceleration in flares are assessed,
and it is argued that the most likely mechanism for accelerating
nonrelativistic electrons is stochastic acceleration by resonant
interaction with Langmuir waves. Areas in which progress in the theory
and observation of solar flares may be expected are also indicated.
Title: A Critique of the Polarimetric Evidence on the Nature of
Close Binary Systems
Authors: Simmons, J. F. L.; Aspin, C.; Brown, J. C.
Bibcode: 1980IAUS...88..343S
Altcode:
No abstract at ADS
Title: The chromosphere and transition region
Authors: Canfield, R. C.; Brown, J. C.; Craig, I. J. D.; Brueckner,
G. E.; Cook, J. W.; Doschek, G. A.; Emslie, A. G.; Machado, M. E.;
Henoux, J. -C.; Lites, B. W.
Bibcode: 1980sfsl.work..231C
Altcode: 1980sofl.symp..231C
The physical processes occurring as a result of the transfer of
energy and momentum from the primary solar flare energy release site
in the corona to the underlying chromosphere and transition region
during the course of the flare are investigated through a comparison
of theoretical models and observational data. Static, dynamic and
hydrodynamic models of the lower-temperature chromospheric flare are
reviewed. The roles of thermal conduction, radiation, fast particles
and mass motion in chromosphere-corona interactions are analyzed on
the basis of Skylab UV, EUV and X-ray data, and empirical and synthetic
models of the chromospheric and upper photospheric responses to flares
are developed. The canonical model of chromospheric heating during
flares as a result of primary energy release elsewhere is found to be
justified in the chromosphere as a whole, although not entirely as the
temperature minimum, and a simplified model of horizontal chromospheric
flare structure based on results obtained is presented.
Title: The Effect of Orbital Eccentricity on Polarimetric Binary
Diagnostics
Authors: Aspin, C.; Brown, J. C.; Simmons, J. F. L.
Bibcode: 1980IAUS...88...71A
Altcode:
No abstract at ADS
Title: Application of the treap-plus-precipitation hard X-ray burst
model to the flare of August 4, 1972.
Authors: Emslie, A. G.; McCaig, M. G.; Brown, J. C.
Bibcode: 1979SoPh...63..175E
Altcode:
We apply the theory of Melrose and Brown (1976), concerning the X-ray
spectrum resulting from the combined precipitation and within-trap
acceleration of non-thermal electrons, to the large solar flare of
August 4, 1972, using high time resolution hard X-ray data from the ESRO
TD-1A scintillation counter for the calculations. By so doing, we infer
the time behavior of the electron source function Q(E, t), as a function
of energy E and of the mean ambient trap densityn (cm−3).
Title: Applicability of Betatron Acceleration to Two-Stage Hard-ray
Events
Authors: Karpen, J. T.; Frost, K. J.; Brown, J.
Bibcode: 1979BAAS...11Q.436K
Altcode:
No abstract at ADS
Title: Production of a collisionless conduction front by rapid
coronal heating and its role in solar hard X-ray bursts.
Authors: Brown, J. C.; Melrose, D. B.; Spicer, D. S.
Bibcode: 1979ApJ...228..592B
Altcode:
The theoretical and observational evidence for and against an
impulsively heated thermal bremsstrahlung source of solar hard X-ray
bursts is briefly reviewed. In particular, it is noted that in a
collision-dominated plasma of any reasonable density the collisional
relaxation time would be much longer, and the conductive cooling time
much shorter, than typical burst durations (cf. Kahler). It is then
shown, however, that free expansion of impulsively heated electrons
into a cool surrounding plasma will generate an ion-sound turbulent
front which efficiently scatters the electrons, thus bottling up
their heat flux. The conductive cooling time is thus increased by
a factor (mt/me)112 over its free expansion limit, compatible with
observations. The front thickness is less than about 1 km. Interaction
with the turbulence permits the bulk of the electrons to reach a relaxed
distribution, without the need for high densities, hence providing an
efficient source of hard X-rays. Electrons of U > 2.6Ue, however,
are not scattered by the ion-sound turbulence but do not necessarily
escape freely either, because of the action of the thermoelectric field
present. Finally, some brief remarks are directed to the mechanism of
heating and to the compatibility of these conditions in the hard X-ray
source with other flare observations. Subject headings: hydromagnetics -
Sun: corona - Sun: X-rays
Title: Analysis of bremsstrahlung source spectra in terms of integral
moments.
Authors: Brown, J. C.
Bibcode: 1978ApJ...225.1076B
Altcode:
The problems of deriving temperature structure for thermal hard
X-ray sources and electron spectra for nonthermal sources, from
their bremsstrahlung continuum spectra, are briefly reviewed and the
dangers of model-fitting are reiterated. A more satisfactory approach
is developed in terms of the evaluation of integral moments of the
distribution function. Using thermal analysis of the impulsive solar
hard X-ray burst of 1970 March 1 as an illustration, the integral
moment method is shown to give a rapid assessment of the real
information content of a bremsstrahlung spectrum. In particular it is
shown that due to limitations of bandwidth and, to a lesser extent,
of spectral resolution, current hard X-ray spectrometry alone is
incapable of distinguishing isothermal, multithermal, and nonthermal
sources. Criteria are established for the spectrometer needed to define
a thermal source distribution to within some specified accuracy.
Title: On the theoretical significance of density measurements in
XUV flare kernels.
Authors: Brown, J. C.; Nakagawa, Y.
Bibcode: 1978ApJ...225L.153B
Altcode:
Current methods of diagnosis of soft X-ray kernels in flares often
indicate electron densities in excess of 1 trillion per cu cm. In
particular, use of the forbidden-to-intercombination line-intensity
ratio in He-like ions leads to electron densities of at least 10 to
the 14th power per cu cm. The physical implications of these high
densities are discussed in terms of the energetics and dynamics
of flare mechanisms, and it is concluded that an electron density
of around 10 to the 14th power per cu cm is impossible. Possible
sources of error in the forbidden-line method are then discussed,
and it is concluded that neither radiation nor plasma turbulence can
explain the high-density results, though each can play a role in some
transition rates. This leaves transient ionization equilibrium as the
only possible explanation and implies that kernels represent direct
evidence of a dynamic field-dissipation process in flares.
Title: Polarisation by Thomson scattering in optically thin stellar
envelopes. III. A statistical study of the oblateness and rotation
of Be star envelopes.
Authors: McLean, I. S.; Brown, J. C.
Bibcode: 1978A&A....69..291M
Altcode:
Summary. The two statistical problems of interpreting the intrinsic
circumstellar polarisations R = p sin2 i and the apparent rotation
speeds U = V sin i for a group of Be stars with randomly oriented
axial inclinations (i) are discussed. Each can be reduced to Abel's
integral equation for the true distribution of the actual polarisation
parameter p (an effective oblateness . Brown and McLean, Paper I) and
of the actual equatorial rotation speed V The difficulties of accurate
inversion of this equation are briefly discussed and it is proposed that
this is best done in terms of moment analysis of the distributions along
the lines of Chandrasekhar and Miinch (1950). Such a moment analysis
is carried out for a sample of 67 Be stars, for which R and U data are
available, this being the largest list of its type. The results are
discussed in terms of the physics of the objects and the V distribution
compared to earlier conclusions. In particular the p distribution is
found to be very skew toward small values where the polarisations are
hardest to measure and to separate from the interstellar component. Key
words: stellar envelopes - polarisation - stellar rotations - Be stars
Title: Polarisation by Thomson scattering in optically thin
stellar envelopes. II. Binary and multiple star envelopes and the
determination of binary inclinations.
Authors: Brown, J. C.; McLean, I. S.; Emslie, A. G.
Bibcode: 1978A&A....68..415B
Altcode:
A general expression is derived for the linear polarization (i.e.,
the Stokes parameters) arising from scattering in any optically thin
envelope illuminated by any number of unpolarized point sources. The
result is applied to a binary system with a circular orbit and a
corotating (but otherwise arbitrary) envelope. Methods of diagnosing
the geometric properties of the envelope from the observed Stokes
parameters are described, and consequences of both finite star size
and a lack of corotation are considered. The method outlined is used
to analyze published data on the binary systems AO Cas, Sigma Ori E,
and Cyg X-1. It is shown that the polarization variations of AO Cas
and Sigma Ori E are reasonably consistent with scattering in optically
thin circumstellar material, while those of Cyg X-1 yield contradictory
results for the system's orbital inclination.
Title: The structure of the temperature minimum region in solar
flares and its significance for flare heating mechanisms.
Authors: Machado, M. E.; Emslie, A. G.; Brown, J. C.
Bibcode: 1978SoPh...58..363M
Altcode:
We analyze Ca II K-line profiles of one flare and EUV continuum
observations of two other flares in order to infer values for the
temperature enhancements (over active region values) produced in the
upper photosphere around and above the temperature minimum region. The
results, obtained through a partial redistribution calculation of the Ca
II K-line profiles and an LTE approach to the continuum observations,
show that the flare temperature minimum is depressed some two scale
heights below its preflare level, and that substantial temperature
enhancements are produced even at this depth. Estimates for the energy
release in these photospheric layers are given, and are found to be
comparable with that released in chromospheric Hα and Lα emission.
Title: Hα profiles from electron-heated solar flares
Authors: Brown, John C.; Canfield, Richard C.; Robertson, Matthew N.
Bibcode: 1978SoPh...57..399B
Altcode:
We briefly review the status of models of optical flare heating
by electron bombardment. We recompute Brown's (1973a) flare
model atmospheres using considerably revised radiative loss
rates, based on Canfield's (1974b) method applied to α, Lα,
and H−. Profiles of α are computed and compared with
observation. The computed profiles agree satisfactorily with those
observed during the large 1972 August 7 flare, if spatial and velocity
inhomogeneities are assumed. The electron injection rate inferred
from α is one order of magnitude less than that inferred from hard
X-rays, for this event. This may be due to either (1) the neglect of
a mechanism that reduces the thick-target electron injection rate or
(2) failure to incorporate important radiative loss terms.
Title: The inter-relationship of hard X-ray and EUV bursts during
solar flares.
Authors: Emslie, A. G.; Brown, J. C.; Donnelly, R. F.
Bibcode: 1978SoPh...57..175E
Altcode:
A comparison is made between the flux-versus-time profile in the EUV
band and the thick target electron flux profile as inferred from hard
X-rays for a number of moderately large solar flares. This complements
Kane and Donnelly's (1971) study of small flares. The hard X-ray data
are from ESRO TD-1A and the EUV inferred from SFD observations.
Title: Tunguska's comet and non-thermal C-14 production in the
atmosphere
Authors: Brown, J. C.; Hughes, D. W.
Bibcode: 1977Natur.268..512B
Altcode:
In connection with the non-observance of a comet before impact and
the subsequent enhancement of radiocarbon in the atmosphere, the
possibility had been considered that the explosion on June 30, 1908,
over Tunguska, Siberia, had to be explained by assuming the occurrence
of an event other than the impact of a comet. An investigation is
conducted concerning the significance of the various observations
made in connection with the Tunguska event. It is concluded that the
number of neutrons expected in the Tunguska impact, as scaled from
solar flares, is in remarkably good agreement with the radiocarbon
data requirements. Also the low mass of the comet and its position in
the dawn sky, just before impact, makes its prior discovery extremely
unlikely. These points strongly support the suggestion that the Tunguska
explosion was caused by an impacting small comet.
Title: Introductory Talk (Proceedings of the Meeting `How Can Flares
be Understood?', held during the 16th General Assembly of the IAU
in Grenoble, France, on 27 August, 1976.)
Authors: Brown, J. C.
Bibcode: 1977SoPh...53..263B
Altcode:
Present studies of chromospheric flare heating mechanisms are at best
preliminary. Until the above problems have been solved to an adequate
first approximation, refined treatments of individual aspects are
unproductive in the understanding of the flare problem.
Title: Polarisation by Thomson Scattering in Optically Thin Stellar
Envelopes. I. Source Star at Centre of Axisymmetric Envelope
Authors: Brown, J. C.; McLean, I. S.
Bibcode: 1977A&A....57..141B
Altcode:
Summary. Expressions are derived for the scattered flux and polarisation
of starlight from an electron envelope with axial symmetry and
centred on the source star but otherwise of entirely general density
distribution and at an arbitrary inclination i. It is shown that
all such envelopes produce a polarisation P, of the scattered light,
given by P = sin2 i/(2oc + sin2 i) with oc =(1 +y)/(l - 3y) where y
is a "shape factor", defined by the ratio of two moments (integrals)
of the density distribution function in spherical coordinates, and
related to the oblateness (or prolateness) of the envelope. The residual
polarisation PR, after addition of the unpolarised direct starlight,
is then PR T(l - 3y) sin2 i where T is a mean scattering optical depth
(assumed small) for the envelope. The shape factor y is evaluated for
four particular models of the density distribution as illustrative
cases of our general result. These are: a thin spherical shell with
density varying exponentially about the equator; a uniform thick
ellipsoidal shell (Zellner, 1971); a uniform rotated circular sector
(Kruszewski et al., 1968); and a uniform annular cylinder of finite
length. The last corrects errors in the analysis of the same geometry
by Poeckert and Marlborough (1976) which is in fact only correct for a
cylinder of zero height (i.e. a plane annulus). Implications of these
results for the interpretation of early type shell star observations
are considered. In particular it is pointed out that PR depends on too
many parameters (y, i, ?t) for polarisation data alone to be capable of
establishing or testing any envelope model, especially as infinitely
many models have the same y. Finally the effects of absorption and
emission within the shell are briefly discussed. Key words: stellar
envelopes - Thomson scattering polarisation shell stars
Title: Collective plasma effects and the electron number problem in
solar hard X-ray bursts.
Authors: Brown, J. C.; Melrose, D. B.
Bibcode: 1977SoPh...52..117B
Altcode:
Due to the relatively high stream densities involved, collective
interactions with the ambient plasma are likely to be important
for the electrons producing solar hard X-ray bursts. In thick-
and thin-target bremsstrahlung models the most relevant process is
limitation of the invoked electron beams by ion sound wave generation
in the neutralizing reverse current established in the atmosphere. For
the thick target model it is shown that typical electron fluxes are
near the maximum permitted by stability of the reverse current so
that ion-sound wave generation may be the process which limits the
electron injection rate. On the other hand the chromospheric reverse
current is sufficient to supply the large total number of electrons
which have to be accelerated in the corona. For the thin target the
low density of the corona severely limits the possible reverse current
so that the maximum upward flux of fast electrons is probably much
too small to explain X-ray bursts but compatible with observations of
interplanetary electrons.
Title: Why measure astrophysical X-ray spectra?
Authors: Craig, I. J. D.; Brown, J. C.
Bibcode: 1976Natur.264..340C
Altcode:
MANY of the interesting results of X-ray astronomy such as the
presence of compact sources in close binary systems, have been derived
from light curve studies1, obtained with quite simple
detectors. On the other hand, a high resolution spectrometer, one of
the most sophisticated pieces of instrumentation, is almost invariably
included in solar X-ray satellites, and is used increasingly in cosmic
studies2. Here we wish to stress that even spectra of the
highest resolution are of limited applicability in many important
astrophysical problems and also perhaps to indicate the value of
cost-effective planning of expensive instrumentation in general.
Title: Oscillation of coronal electron traps inferred from hard
X-ray data.
Authors: Brown, J. C.; McClymont, A. N.
Bibcode: 1976SoPh...49..329B
Altcode:
The work of Brown and Hoyng (1975) on the betatron acceleration of hard
X-ray source electrons trapped in a vibrating flux tube is generalised
to include Fermi acceleration by the varying transverse field. This
development can explain the trajectory of bursts in a plot of equivalent
thick-target electron flux versus spectral index γ as inferred from
observations obtained by ESRO TD1A. Specifically the loops observed
in this , λ diagram, unexplained in Brown and Hoyng's anslysis are
accounted for by a changing phase relationship between the varying
field strength f(t) and magnetic scale length g(t)- Application of
the formalism to the detailed TD1A observations of the large events
of 1972, August 4 and 7, allows inference of the evolution of f(t),
g(t) in these events.
Title: Precipitation in trap models for solar hard X-ray bursts.
Authors: Melrose, D. B.; Brown, J. C.
Bibcode: 1976MNRAS.176...15M
Altcode:
Precipitation of electrons due to collisions necessarily occurs
in trap models for hard X-ray bursts, and the thick-target emission
from the precipitating electrons produces an X-ray spectrum similar in
intensity and spectral shape to that from the trapped electrons. Such a
trap-plus-precipitation model combines attractive features and removes
some of the difficulties of thick-target and simple trap models. The
evolution of the trap-plus-precipitation model is amenable to an
analytical description, which is presented, including inversion, to
find the injection electron spectrum from the X-ray spectrum. Streaming
instabilities are unlikely to be important. Resonant scattering is also
probably not important for the electrons which emit most of the X-rays,
but may well be important for the higher-energy electrons which generate
microwave bursts.
Title: High time resolution analysis of solar hard X-ray flares
observed on board the ESRO TD-1A satellite.
Authors: Hoyng, Peter; Brown, John C.; van Beek, H. Frank
Bibcode: 1976SoPh...48..197H
Altcode:
The Utrecht solar hard X-ray spectrometer S-100 on board the ESRO TD-1A
satellite covers the energy range above 25 keV with 12 logarithmically
spaced channels. Continuous sun-pointing is combined with high time
resolution: 1.2 s for the four low energy channels (25-90 keV) and
4.8 s for the others. It is emphasized that the instrument design and
calibration yield data virtually free of pile-up and other instrumental
defects.
Title: Fundamental limitations of X-ray spectra as diagnostics of
plasma temperature structure.
Authors: Craig, I. J. D.; Brown, J. C.
Bibcode: 1976A&A....49..239C
Altcode:
The problem of deriving the temperature distribution in hot
optically thin plasmas from their X-ray spectra is discussed, and
it is argued that X-ray spectral data are fundamentally insensitive
to the thermal structure of the source, regardless of the spectral
resolution of the observations. The problem is formulated in terms of
the integral equation which relates both line and continuous spectra
to the differential emission measure of the source. The mathematical
difficulties underlying the solution of such integral equations are
outlined, emphasizing the key role of the kernel function. Continuous
bremsstrahlung spectra are considered, and it is shown that the
kernel involved (the Laplace transform) is highly unstable to small
perturbations in the spectrum due to the flatness of the kernel
function. The line-spectrum problem is examined, and gross errors
in the solution are shown to result from very small observational
errors. A specific example for solar active regions demonstrates
that most existing models for the differential emission measure are
likely to be spurious. Suggestions are made for the most realistic
and economic approach to analysis of existing spectra as well as for
designs of future spectrometers.
Title: The Interpretation of Hard and Soft X-rays from Solar Flares
Authors: Brown, J. C.
Bibcode: 1976RSPTA.281..473B
Altcode: 1976RSLPT.281..473B
The present status of observations of hard X-ray bursts is reviewed
in terms of the light they shed on alternative source models and on
general characteristics of electron acceleration in flares. Special
attention is given to the requirements of total energy release,
and the time scale of its release, into energetic electrons on the
basis of the normal bremsstrahlung interpretation of bursts. It is
particularly emphasized that, since these electrons may dominate
the energy balance in many flares, they provide on the one hand an
attractive heating mechanism for the thermal flare but, on the other,
put severe demands on acceleration mechanisms. A reassessment of the
relative merits of synchrotron and inverse Compton source mechanisms
is suggested, along with other possibilities, as an escape from this
apparent difficulty. Observational characteristics of soft X-ray flares
are cursorily reviewed. The importance of a non-isothermal approach to
the physics of the soft X-ray plasma is then illustrated in terms of
flare energy flow. It is argued however, that high spectral resolution
is not the key to this problem since ill conditioning of the problem
prevents useful inference of temperature structure. Instead high
resolution imaging with moderate spectral resolution is advocated.
Title: High resolution X-ray spectra of the sun.
Authors: Brown, J. C.; Parkinson, J. H.
Bibcode: 1976RSPTA.281..375B
Altcode:
No abstract at ADS
Title: High Resolution X-Ray Spectra of the Sun: Discussion
Authors: Brown, J. C.; Parkinson, J. H.; Gabriel, A. H.
Bibcode: 1976RSPTA.281..382B
Altcode:
No abstract at ADS
Title: Betatron acceleration in a large solar hard X-ray burst.
Authors: Brown, J. C.; Hoyng, P.
Bibcode: 1975ApJ...200..734B
Altcode:
The problem of diagnosing flare particle acceleration mechanisms from
hard X-ray bursts is discussed, and it is argued that the electron
trap model of bursts is more amenable to observational investigation
at present than models of thick-target type. It is then shown that
data for the large X-ray burst of 1972 August 4 are consistent with
the source electrons being trapped in a very large vibrating coronal
magnetic bottle. Furthermore, the observations show that the burst time
profile is not dominated by collisional losses. It is proposed instead
that the entire profile is essentially determined by betatron action
of the varying trap field on the electrons. This betatron model is
then analyzed in detail and shown to predict very well the observed
correlation of electron flux and spectral index in this event when
it is supposed that the electrons are initially produced by runaway
in a direct electric field. Comparison of the model with observations
permits inference of the approximate form of magnetic field evolution
in the trap. Finally the physics behind this field evolution is briefly
considered. Subject headings: flares, solar - X-rays, solar
Title: Determination of the height of hard X-ray sources in the
solar atmosphere by measurement of photospheric albedo photons.
Authors: Brown, J. C.; van Beek, H. F.; McClymont, A. N.
Bibcode: 1975A&A....41..395B
Altcode:
The importance and difficulties of determining the altitude of hard
X-ray sources in the solar atmosphere are discussed. It is argued that
the only unambiguous means of making this measurement is by utilizing
the photospherically scattered component of the radiation. Specifically,
it is proposed that this can be done by measurement of the angular
distribution of the large patch of photospheric albedo X-rays which is
shown to accompany bright point primary X-ray sources. Quantitative
predictions are made of the brightness distribution of this albedo
'image' and the practical feasibility of observing it is demonstrated in
terms of the hard X-ray imaging spectrometer currently under development
at the Space Research Laboratory in Utrecht.
Title: The Height Distribution of Flare Hard X-Rays in Thick and
Thin Target Models
Authors: Brown, J. C.; McClymont, A. N.
Bibcode: 1975SoPh...41..135B
Altcode:
The current controversy between thick and thin target models
of hard X-ray flares is reviewed and it is concluded that the
most promising method of distinguishing them is in terms of the
differences in the distribution of the source with height in the
solar atmosphere. Quantitative predictions are made of this height
distribution for both models and the results discussed in relation to
observations of hard X-ray emission from flares behind the limb. It
is concluded that the thick target model is as compatible with such
events as the thin target whereas the latter is in general much less
satisfactory in terms of energy requirements and of flare observations
at other wavelengths. Other source models are also briefly considered.
Title: Determination of the Height of Hard X-Ray Sources in the
Solar Atmosphere by Measurement of Photospheric Albedo Photons
Authors: Brown, J. C.; van Beek, H. F.
Bibcode: 1975IAUS...68..239B
Altcode:
No abstract at ADS
Title: The Interpretation of Spectra, Polarization, and Directivity
of Solar Hard X-Rays
Authors: Brown, J. C.
Bibcode: 1975IAUS...68..245B
Altcode:
Basic observational features of solar hard X-ray bursts are reviewed,
and analytic as well as numerical inversions of the X-ray spectrum
to infer the flare electron spectrum are discussed. Although
it is found that electron spectra cannot be unambiguously and
accurately inferred from bremsstrahlung emission, consideration
of directional, albedo, and model-dependent effects indicates that
none of the X-ray data are inconsistent with a power-law electron
acceleration spectrum. Characteristics of thick-target, thin-target,
and electron-trap models of hard X-ray sources are discussed
quantitatively, and the ability of these models to fit observational
data is examined. It is concluded that the thick-target model may be
capable of explaining all burst features, including behind-the-limb
occurrences and interplanetary electron spectra.
Title: High Time Resolution Analysis of Solar Flares Observed on
the ESRO Td-Ia Satellite
Authors: Hoyng, P.; Brown, J. C.; Stevens, G.; van Beek, H. F.
Bibcode: 1975IAUS...68..233H
Altcode:
No abstract at ADS
Title: Hard X-ray coverage of the Skylab period by Utrecht's S-100
instrument on board ESRO TD-1A
Authors: Brown, J. C.
Bibcode: 1975xtcg.work...89B
Altcode:
The type of data obtained by the S-100 hard-X-ray spectrometer aboard
the ESRO TD-1A satellite is discussed with respect to the potential
importance of the data in the theoretical interpretation of flares
when combined with observations at other wavelengths. The spectrometer
is briefly described along with the data reduction technique. It
is shown that high-time-resolution hard-X-ray data, when combined
with simultaneous optical and radio observations, will be crucial in
testing the feasibility of overall flare models in which the thermal
flare phenomena are produced due to heating of the solar atmosphere
by the nonthermal electrons responsible for the hard-X-ray bursts.
Title: High time resolution analysis of solar flares observed on
the ESRO TD-1A satellite.
Authors: Hoyng, P.; Brown, J. C.; Stevens, G.; van Beek, H. F.
Bibcode: 1975IAUS...68Q.233H
Altcode:
No abstract at ADS
Title: High time resolution analysis of solar flares observed on
the ESRO TD-1A satellite.
Authors: Hoyng, P.; Brown, J. C.; Stevens, G.; van Beek, H. F.
Bibcode: 1975IAUS...68R.233H
Altcode:
No abstract at ADS
Title: Determination of the height of hard X-ray sources in the
solar atmosphere by measurement of photospheric albedo photons.
Authors: Brown, J. C.; van Beek, H. F.
Bibcode: 1975IAUS...68R.239B
Altcode:
No abstract at ADS
Title: Hard X-ray coverage of the Skylab period by Utrecht's S-100
instrument on board ESRO TD-1A.
Authors: Brown, J. C.
Bibcode: 1975MmArc.104...89B
Altcode:
No abstract at ADS
Title: Determination of the height of hard X-ray sources in the
solar atmosphere by measurement of photospheric albedo photons.
Authors: Brown, J. C.; van Beek, H. F.
Bibcode: 1975IAUS...68Q.239B
Altcode:
No abstract at ADS
Title: Comments on the Role of Conduction in Optical Flare Heating
Authors: Brown, John C.
Bibcode: 1974SoPh...36..371B
Altcode:
No abstract at ADS
Title: Interpretation of Solar Hard X-ray Burst Polarisation
Measurements
Authors: Brown, J. C.; McClymont, A. N.; McLean, I. S.
Bibcode: 1974Natur.247..448B
Altcode:
TINDO et al. (refs 1 to 3 and unpublished results) have reported the
first observations of polarisation of solar flare emission in the hard
X-ray band (around 15 keV) and have made a preliminary interpretation
of these3. Their results depend, however, on the removal
of systematic differences in sensitivity of the detectors used in
the Intercosmos Thomson-scattering polarimeters, by calibration on an
`unpolarised' source. We point out here that the results as presented
by Tindo et al. are in fact in error since their calibration was based
on the assumption that the hard X-ray flux from the flare itself tends
to zero polarisation in its final stages of decay. This assumption is
invalidated by the presence, in the total flux, of a large polarised
contribution from photospheric albedo photons4,5. We further
consider how much this calibration error may affect interpretation
of the Intercosmos results in terms of flare particles and suggest
how further theoretical work, combined with results from a laboratory
calibrated polarimeter, can yield information on the spatial location
of hard X-ray flares as well as on their true polarisation.
Title: On the Thermal Interpretation of Hard X-Ray Bursts from
Solar Flares
Authors: Brown, J. C.
Bibcode: 1974IAUS...57..395B
Altcode:
No abstract at ADS
Title: Temporal Fine Structure of X-Rays from Trapped Electrons in
Solar Flares
Authors: Brown, John C.
Bibcode: 1973SoPh...32..227B
Altcode:
No abstract at ADS
Title: The Temperature Structure of Chromospheric Flares Heated by
Non-Thermal Electrons
Authors: Brown, John C.
Bibcode: 1973SoPh...31..143B
Altcode:
Heating of the deep chromosphere by a vertically descending beam of
non-thermal electrons with power-law energy spectrum, in flares, is
analysed. In lower regions of the flare, radiative losses can balance
the energy input and the flare structure is described in terms of
instantaneous quasi-steady temperature/depth profiles. Motion of the
optical flare material is at constant pressure and is constrained to
be purely vertical by a vertical magnetic field. The ionisation of
hydrogen is determined by the same non-LTE processes as in the quiet
chromosphere. Temperature profiles are obtained for a wide range
of electron beam intensities and spectral indices and are discussed
in terms of optical flare observations. Due to the steepness of the
electron spectra, typical densities in the optical flare vary only
over a narrow range, despite the diversity of beam intensities, in
agreement with observation.
Title: Observations of Saturn
Authors: Cambridge Unverisity Astronomical Society; Papp, Janos;
Brown, John; Brown, Allan; Cooke, John A.
Bibcode: 1973Astr....9..243C
Altcode:
No abstract at ADS
Title: On the Ionisation of Hydrogen in Optical Flares
Authors: Brown, John C.
Bibcode: 1973SoPh...29..421B
Altcode:
Non-steady state and non-LTE effects on the ionisation equilibrium
of hydrogen in optical flares are considered in terms of a two-level
hydrogen atom. It is shown that, just as in the quiet low chromosphere,
the ionisation equation is controlled by spontaneous recombination to
the second level and by photoionisation from this level by photospheric
radiation, and is independent of the nature of the flare energy input
mechanism.
Title: The role of high energy electrons in solar x-ray and optical
flare emission
Authors: Brown, John Campbell
Bibcode: 1973PhDT.......150B
Altcode:
No abstract at ADS
Title: Thick Target X-Ray Bremsstrahlung from Partially Ionised
Targets in Solar Falres
Authors: Brown, John C.
Bibcode: 1973SoPh...28..151B
Altcode:
The effect of partial ionisation of a thick target bremsstrahlung
source on the emitted X-ray intensity is analysed. It is shown that
a totally ionised target produces an X-ray burst only about one third
as intense as that from an unionised target.
Title: Solar hard X-ray and gamma -ray bursts in the interpretation
of solar cosmic ray acceleration in flares.
Authors: Brown, J. C.
Bibcode: 1973skli.conf...36B
Altcode:
No abstract at ADS
Title: The sixteenth Herstmonceux conference, 1972 April 5 - 6. Cosmic
X-ray sources.
Authors: Pounds, K. A.; Miley, G. K.; Murdin, P.; Webster, B. L.;
Pacini, F.; Pringle, J. E.; Jackson, J. C.; Morrison, L. V.; Culhane,
J. L.; Sciama, D. W.; Fabian, A. C.; Brown, J. C.; Gabriel, A. H.;
Bingham, R. G.; Lategan, A. H.; Pagel, B. E. J.
Bibcode: 1972Obs....92..193P
Altcode:
No abstract at ADS
Title: The Directivity and Polarisation of Thick Target X-Ray
Bremsstrahlung from Solar Flares
Authors: Brown, John C.
Bibcode: 1972SoPh...26..441B
Altcode:
The directivity and polarisation of solar hard X-ray bursts is discussed
in terms of two bremsstrahlung source models. These involve continuous
and impulsive injection of electrons respectively, as described widely
in the literature.
Title: The Decay Characteristics of Models of Solar Hard X-Ray Bursts
Authors: Brown, John C.
Bibcode: 1972SoPh...25..158B
Altcode:
Models of solar hard X-ray bursts are considered in which non-thermal
electrons are impulsively injected into a coronal magnetic
trap. Recognising that the ends of the trap are likely to be rooted
in the photosphere and that the density of the ambient atmosphere may
thus be highly non-uniform along the field lines, it is shown that
the X-ray spectra will initially soften with time, due to collisions,
when this non-uniformity is strong enough. This removes a well-known
discrepancy in models with uniform density.
Title: The Deduction of Energy Spectra of Non-Thermal Electrons in
Flares from the Observed Dynamic Spectra of Hard X-Ray Bursts
Authors: Brown, John C.
Bibcode: 1971SoPh...18..489B
Altcode:
The derivation of dynamic spectra of high energy electrons in flares
from high resolution hard X-ray observations is considered. It is shown
that the Bethe-Heitler formula for the electronproton bremsstrahlung
cross-section over the 20-100 keV range of energies admits of a
general analytic solution for the electron spectrum in terms of the
X-ray spectrum, in a form convenient for computation. The bearing of
this analysis on different models of flare conditions is considered. In
examining the hypothesis that the X-rays are produced in regions of high
ambient density, the duration of the burst being governed by modulation
of the electron source rather than by the decay of trapped electrons
injected impulsively, it is emphasised that the energy spectrum of the
electrons at their source is different from their effective spectrum
in the X-ray emitting region. This spectrum, at the source, is found
to be much steeper than that in the X-ray region which means that the
entire energy of the flare could reside in the injected electrons.
Title: a Comprehensive Study of the Characteristics of Meteor Echoes
- I
Authors: Hawkins, G. S.; Brown, J. C.
Bibcode: 1967SAOSR.254.....H
Altcode:
A system of classification of the shapes of meteor echoes is
established, and a recording on punch cards of this classification
with data on the meteors' physical properties is described. A simple
velocity-computation method is described, and a number of statistical
relations of shapes and physical properties are computed. The survey
covers about 1000 meteors with a comprehensive study of all echo
types. It shows some characteristics of the stations and selection
effects in the established reduction program.
Title: Additional Rocket-Borne Mass Spectrometer Measurements of
the Dissociation of Oxygen
Authors: Schaefer, Edward J.; Brown, John
Bibcode: 1964JGR....69.1455S
Altcode:
An earlier letter [Schaefer, 1963] described an experiment to
measure the ambient neutral composition of the upper atmosphere by a
rocket-borne `massenfilter' [Schaefer and Nichols, 1961]. Preliminary
curves of the ratio of the O1 current to the O2
current were presented. The experiment was repeated using a similar
instrument with the same open ion source aboard a Nike-Apache rocket
launched at 0255 EST, March 28, 1963, at Wallops Island, Virginia.
Title: Mineral Composition of Some Drainage Waters from Arctic Alaska
Authors: Brown, J.; Grant, C. L.; Ugolini, F. C.; Tedrow, J. C. F.
Bibcode: 1962JGR....67.2447B
Altcode:
Columns of synthetic ion-exchange resin were used to sample the
exchangeable cations in drainage waters of northern Alaska. Details
of the sampling and analytical procedures are presented. For the
elements Na, K, Mg, Ca, Sr, and Ba, an average recovery of 96 percent
was realized on a typical sample. However, recoveries were quite low
for most trace elements. Sampling was necessarily diversified, but
results for major cations closely follow the lithology of the sample
area. The concentrations observed were similar to those reported for
many areas of North America.
Title: The Departure of Swallows
Authors: Brown, J.
Bibcode: 1896Natur..55R...6B
Altcode:
``E. P.'' mentions in NATURE of October 22, a date, somewhere about
October 20, I presume, which he considers is an unusual one for
swallows. Now, though the bulk of the swallows have left by this time,
it is by no means unusual to see them later on in the year. In 1894 I
saw swallows in Kent, in the neighbourhood of Tonbridge, on October 20,
21, 25 and 27, and the last one on November 11; it was flitting about
a village in a bewildered sort of way, with a crowd of village boys
throwing mud and clods of earth at it.
Title: Observations of the Great Comet
Authors: Home, E., Sir; Brown, J.
Bibcode: 1845MNRAS...6..210H
Altcode:
No abstract at ADS