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Author name code: doyle
ADS astronomy entries on 2022-09-14
author:"Doyle, J.G."
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Title: Searching for stellar flares from low-mass stars using ASKAP
and TESS
Authors: Rigney, Jeremy; Ramsay, Gavin; Carley, Eoin P.; Doyle,
J. Gerry; Gallagher, Peter T.; Wang, Yuanming; Pritchard, Joshua;
Murphy, Tara; Lenc, Emil; Kaplan, David L.
2022MNRAS.516..540R Altcode: 2022MNRAS.tmp.2052R; 2022arXiv220700405R
Solar radio emission at low frequencies (<1 GHz) can provide
valuable information on processes driving flares and coronal mass
ejections (CMEs). Radio emission has been detected from active M dwarf
stars, suggestive of much higher levels of activity than previously
thought. Observations of active M dwarfs at low frequencies can
provide information on the emission mechanism for high energy flares
and possible stellar CMEs. Here, we conducted two observations with
the Australian Square Kilometre Array Pathfinder Telescope totalling
26 h and scheduled to overlap with the Transiting Exoplanet Survey
Satellite Sector 36 field, utilizing the wide fields of view of both
telescopes to search for multiple M dwarfs. We detected variable
radio emission in Stokes I centred at 888 MHz from four known active
M dwarfs. Two of these sources were also detected with Stokes V
circular polarization. When examining the detected radio emission
characteristics, we were not able to distinguish between the models
for either electron cyclotron maser or gyrosynchrotron emission. These
detections add to the growing number of M dwarfs observed with variable
low-frequency emission.
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Title: Detection of spicules termed rapid blueshifted excursions as
seen in the chromosphere via H α and the transition region via Si
IV 1394 Å line emission
Authors: Vilangot Nhalil, Nived; Shetye, Juie; Doyle, J. Gerry
2022MNRAS.515.2672V Altcode: 2022arXiv220701415V; 2022MNRAS.tmp.1929N
We show signatures of spicules termed rapid blueshifted excursions
(RBEs) in the Si IV 1394 Å emission line using a semi-automated
detection approach. We use the H α filtergrams obtained by the CRISP
imaging spectropolarimeter on the Swedish 1-m Solar Telescope and
co-aligned Interface Region Imaging Spectrograph data using the SJI
1400 Å channel to study the spatiotemporal signature of the RBEs in
the transition region. The detection of RBEs is carried out using
an oriented coronal loop tracing algorithm on H α Dopplergrams at
±35 km s<SUP>-1</SUP>. We find that the number of detected features
is significantly impacted by the time-varying contrast values of the
detection images, which are caused by the changes in the atmospheric
seeing conditions. We detect 407 events with lifetime greater than 32
s. This number is further reduced to 168 RBEs based on the H α profile
and the proximity of RBEs to the large-scale flow. Of these 168 RBEs,
89 of them display a clear spatiotemporal signature in the SJI 1400
Å channel, indicating that a total of $\sim 53{{\ \rm per\ cent}}$
are observed to have co-spatial signatures between the chromosphere
and the transition region.
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Title: Doubling of minute-long quasi-periodic pulsations from
super-flares on a low-mass star
Authors: Doyle, J. Gerry; Irawati, Puji; Kolotkov, Dmitrii Y.; Ramsay,
Gavin; Nhalil, Nived Vilangot; Dhillon, Vik S.; Marsh, Tom R.; Yadav,
Ram Kesh
2022MNRAS.514.5178D Altcode: 2022MNRAS.tmp.1673D; 2022arXiv220608070D
Using the ULTRASPEC instrument mounted on the 2.4-m Thai National
Telescope, we observed two large flares, each with a total energy
close to 10<SUP>34</SUP> erg with sub-second cadence. A combination
of a wavelet analysis, a Fourier transform plus an empirical mode
decomposition, reveals quasi-periodic pulsations (QPPs) that exhibit
an apparent doubling of the oscillation period. Both events showed
oscillations of a few minutes over a interval of several minutes, and
despite the availability of sub-second cadence, there was no evidence
of sub-minute oscillations. The doubling of the QPP periods and shorter
lifetime of shorter-period QPP modes strongly favour resonant dynamics
of magnetohydrodynamic waves in a coronal loop. We estimate loop lengths
to be 0.2-0.7 R<SUB>⋆</SUB>, in agreement with a typical length of
solar coronal loops. These observations presents rare and compelling
evidence for the presence of compact plasma loops in a stellar corona.
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Title: The puzzling story of flare inactive ultra fast rotating M
dwarfs - I. Exploring their magnetic fields
Authors: Doyle, Lauren; Bagnulo, Stefano; Ramsay, Gavin; Doyle,
J. Gerry; Hakala, Pasi
2022MNRAS.512..979D Altcode: 2022arXiv220206889D; 2022MNRAS.tmp..468D
Stars which are rapidly rotating are expected to show high levels of
activity according to the activity-rotation relation. However, previous
TESS studies have found ultra fast rotating (UFR) M dwarfs with periods
less than 1 d displaying low levels of flaring activity. As a result,
in this study, we utilize VLT/FORS2 spectro-polarimetric data of 10 M
dwarf UFR stars between spectral types ~M2-M6 all with P<SUB>rot</SUB>
< 1, to detect the presence of a magnetic field. We divide our sample
into rotation period bins of equal size, with one star having many
more flares in the TESS light curve than the other. We also provide
an analysis of the long-term variability within our sample using
TESS light curves taken during Cycles 1 and 3 (up to 3 yr apart). We
identify 605 flares from our sample which have energies between
2.0 × 10<SUP>31</SUP> and 5.4 × 10<SUP>34</SUP> erg. Although we
find no significant difference in the flare rate between the Cycles,
two of our targets display changes in their light-curve morphology,
potentially caused by a difference in the spot distribution. Overall,
we find five stars (50 per cent) in our sample have a detectable
magnetic field with strengths ~1-2 kG. Of these five, four were the
more flare active stars within the period bins with one being the less
flare active star. It would appear the magnetic field strength may
not be the answer to the lack of flaring activity and supersaturation
or magnetic field configuration may play a role. However, it is clear
the relationship between rotation and activity is more complex than
a steady decrease over time.
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Title: The puzzling story of flare inactive ultra fast rotating M
dwarfs. II. Searching for radial velocity variations
Authors: Ramsay, Gavin; Hakala, Pasi; Doyle, J. Gerry; Doyle, Lauren;
Bagnulo, Stefano
2022MNRAS.511.2755R Altcode: 2022MNRAS.tmp..250R; 2022arXiv220206888R
Observations made using TESS revealed a sample of low-mass stars which
show a periodic modulation on a period <0.2 d. Surprisingly, many
of these ultra fast rotating (UFR) stars showed no evidence of flare
activity which would be expected from such rapidly rotating stars. We
present results from a spectroscopic survey of UFRs using the Nordic
Optical Telescope to search for radial velocity variations which
could reveal evidence for binarity. Our sample of 29 sources have a
photometric period between 0.1-0.2 d, cover spectral classes of M0-4V,
and show no evidence for flares. We detect only one source with clear
radial velocity shifts, with another two having Gaia RUWE values
which suggests they are binaries. Further observations reveal the
former star possibly contains a brown dwarf companion with a mass of
M<SUB>2</SUB> > 58 M<SUB>Jup</SUB> and probability P(M<SUB>2</SUB>
< 90 M<SUB>Jup</SUB>) = 50 per cent. There is no evidence for the
companion in our spectra, strengthening the case for a brown dwarf
companion. We also examine the folded TESS light curves of all our
targets, finding at least two are eclipsing binaries and one which has
been contaminated by a spatially nearby δ Sct star. We estimate that
around 1/4 of our targets may have been contaminated by short period
variable stars. However, the majority of our targets are consistent with
being single, low mass stars whose variability is due to starspots. We
outline the possible reasons why they are not flare active despite
being such rapid rotators.
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Title: Implications of spicule activity on coronal loop heating and
catastrophic cooling
Authors: Nived, V. N.; Scullion, E.; Doyle, J. G.; Susino, R.; Antolin,
P.; Spadaro, D.; Sasso, C.; Sahin, S.; Mathioudakis, M.
2022MNRAS.509.5523N Altcode: 2021arXiv211107967N; 2021MNRAS.tmp.3004N
We report on the properties of coronal loop foot-point heating
with observations at the highest resolution, from the CRisp Imaging
Spectro-Polarimeter located at the Swedish 1-m Solar Telescope and
co-aligned NASA Solar Dynamics Observatory observations, of Type II
spicules in the chromosphere and their signatures in the extreme
ultraviolet (EUV) corona. Here, we address one important issue,
as to why there is not always a one-to-one correspondence, between
Type II spicules and hot coronal plasma signatures, i.e. beyond
TR temperatures. We do not detect any difference in their spectral
properties in a quiet Sun region compared to a region dominated by
coronal loops. On the other hand, the number density close to the
foot-points in the active region is found to be an order of magnitude
higher than in the quiet Sun case. A differential emission measure
analysis reveals a peak at ~5 × 10<SUP>5</SUP> K of the order of
10<SUP>22</SUP> cm<SUP>-5</SUP> K<SUP>-1</SUP>. Using this result as
a constraint, we conduct numerical simulations and show that with an
energy input of 1.25 × 10<SUP>24</SUP> erg (corresponding to ~10 RBEs
contributing to the burst) we manage to reproduce the observation very
closely. However, simulation runs with lower thermal energy input do not
reproduce the synthetic AIA 171 Å signatures, indicating that there
is a critical number of spicules required in order to account for the
AIA 171 Å signatures in the simulation. Furthermore, the higher energy
(1.25 × 10<SUP>24</SUP> erg) simulations reproduce catastrophic cooling
with a cycle duration of ~5 h, matching a periodicity we observe in
the EUV observations.
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Title: The Nature of High-frequency Oscillations Associated with
Short-lived Spicule-type Events
Authors: Shetye, Juie; Verwichte, Erwin; Stangalini, Marco; Doyle,
J. G.
2021arXiv211214486S Altcode:
We investigate high resolution spectroscopic and imaging observations
from the CRisp Imaging SpectroPolarimeter (CRISP) instrument to
study the dynamics of chromospheric spicule type events. It is
widely accepted that chromospheric fine structures are waveguides
for several types of magnetohydrodynamic (MHD) oscillations, which
can transport energy from the lower to upper layers of the Sun. We
provide a statistical study of 30 high frequency waves associated
with spicule type events. These high frequency oscillations have two
components of transverse motions: the plane of sky (POS) motion and
the line of sight (LOS) motion. We focus on single isolated spicules
and track the POS using time distance analysis and in the LOS direction
using Doppler information. We use moment analysis to find the relation
between the two motions. The composition of these two motions suggests
that the wave has a helical structure. The oscillations do not have
phase differences between points along the structure. This may be the
result of the oscillation being a standing mode, or that propagation
is mostly in the perpendicular direction. There is evidence of fast
magnetoacoustic wave fronts propagating across these structures. To
conclude, we hypothesize that the compression and rarefaction of
passing magnetoacoustic waves may influence the appearance of spicule
type events, not only by contributing to moving them in and out of
the wing of the spectral line but also through the creation of density
enhancements and an increase in opacity in the Halpha line.
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Title: First results from the REAL-time Transient Acquisition backend
(REALTA) at the Irish LOFAR station
Authors: Murphy, P. C.; Callanan, P.; McCauley, J.; McKenna, D. J.;
Fionnagáin, D. Ó.; Louis, C. K.; Redman, M. P.; Cañizares,
L. A.; Carley, E. P.; Maloney, S. A.; Coghlan, B.; Daly, M.; Scully,
J.; Dooley, J.; Gajjar, V.; Giese, C.; Brennan, A.; Keane, E. F.;
Maguire, C. A.; Quinn, J.; Mooney, S.; Ryan, A. M.; Walsh, J.; Jackman,
C. M.; Golden, A.; Ray, T. P.; Doyle, J. G.; Rigney, J.; Burton, M.;
Gallagher, P. T.
2021A&A...655A..16M Altcode: 2021arXiv210811251M
Modern radio interferometers such as the LOw Frequency ARray (LOFAR)
are capable of producing data at hundreds of gigabits to terabits per
second. This high data rate makes the analysis of radio data cumbersome
and computationally expensive. While high performance computing
facilities exist for large national and international facilities, that
may not be the case for instruments operated by a single institution or
a small consortium. Data rates for next generation radio telescopes are
set to eclipse those currently in operation, hence local processing
of data will become all the more important. Here, we introduce the
REAL-time Transient Acquisition backend (REALTA), a computing backend
at the Irish LOFAR station (I-LOFAR) which facilitates the recording
of data in near real-time and post-processing. We also present first
searches and scientific results of a number of radio phenomena observed
by I-LOFAR and REALTA, including pulsars, fast radio bursts, rotating
radio transients, the search for extraterrestrial intelligence, Jupiter,
and the Sun.
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Title: The Nature of High-frequency Oscillations Associated with
Short-lived Spicule-type Events
Authors: Shetye, Juie; Verwichte, Erwin; Stangalini, Marco; Doyle,
J. G.
2021ApJ...921...30S Altcode:
We investigate high-resolution spectroscopic and imaging observations
from the CRisp Imaging SpectroPolarimeter (CRISP) instrument to
study the dynamics of chromospheric spicule-type events. It is
widely accepted that chromospheric fine structures are waveguides
for several types of magnetohydrodynamic (MHD) oscillations, which
can transport energy from the lower to upper layers of the Sun. We
provide a statistical study of 30 high-frequency waves associated
with spicule-type events. These high-frequency oscillations have two
components of transverse motions: the plane-of-sky (POS) motion and
the line-of-sight (LOS) motion. We focus on single isolated spicules
and track the POS using time-distance analysis and in the LOS direction
using Doppler information. We use moment analysis to find the relation
between the two motions. The composition of these two motions suggests
that the wave has a helical structure. The oscillations do not have
phase differences between points along the structure. This may be the
result of the oscillation being a standing mode, or that propagation
is mostly in the perpendicular direction. There is evidence of fast
magnetoacoustic wave fronts propagating across these structures. To
conclude, we hypothesize that the compression and rarefaction of passing
magnetoacoustic waves may influence the appearance of spicule-type
events, not only by contributing to moving them in and out of the
wing of the spectral line but also through the creation of density
enhancements and an increase in opacity in the Hα line.
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Title: Transiting Exoplanet Survey Satellite (TESS) Observations
of Flares and Quasi-Periodic Pulsations from Low-Mass Stars and
Potential Impact on Exoplanets
Authors: Ramsay, Gavin; Kolotkov, Dmitrii; Doyle, J. Gerry; Doyle,
Lauren
2021SoPh..296..162R Altcode: 2021arXiv210810670R
We have performed a search for flares and quasi-periodic pulsations
(QPPs) from low-mass M-dwarf stars using Transient Exoplanet Survey
Satellite (TESS) two-minute cadence data. We find seven stars that
show evidence of QPPs. Using Fourier and empirical mode decomposition
techniques, we confirm the presence of 11 QPPs in these seven stars
with a period between 10.2 and 71.9 minutes, including an oscillation
with strong drift in the period and a double-mode oscillation. The
fraction of flares that showed QPPs (7%) is higher than other studies of
stellar flares, but it is very similar to the fraction of solar C-class
flares. Based on the stellar parameters taken from the TESS Input
Catalog, we determine the lengths and magnetic-field strengths of the
flare coronal loops using the period of the QPPs and various assumptions
about the origin of the QPPs. We also use a scaling relationship based
on flares from the Sun and solar-type stars and the observed energy,
plus the duration of the flares, finding that the different approaches
predict loop lengths that are consistent to within a factor of about
two. We also discuss the flare frequency of the seven stars determining
whether this could result in ozone depletion or abiogenesis in any
orbiting exoplanet. Three of our stars have a sufficiently high rate
of energetic flares, which are likely to cause abiogenesis. However,
two of these stars are also in the range where ozone depletion is
likely to occur. We speculate on the implications of the flare rates,
loop lengths, and QPPs for life on potential exoplanets orbiting in
their host star's habitable zone.
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Title: Searching for Quasi Periodic Pulsations in flares from low
mass stars using TESS data
Authors: Ramsay, Gavin; Kolotkov, Dmitrii; Doyle, J. Gerry; Doyle, L.,
2021tsc2.confE..74R Altcode:
We have searched the light curves of low mass stars with TESS 2 min
cadence data in Cycles 1 & 2 for Quasi Periodic Pulsations (QPPs)
in stellar flares. We identified 11 flares from 7 stars which have QPPs
with periods ranging from ~10 min to 70 min. We use several methods for
determining the loop length of the flares and find they can extend to a
handful of stellar radius. Based on scaling relationships we determine
the magnetic field strength in the coronal loops and compare the loop
lengths to distance to the habitable zone for the host star.
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Title: The AstroPath Image Acquisition and Segmentation Workflow
Authors: Green, Benjamin; Berry, Sneha; Giraldo, Nicolas; Cottrell,
Tricia; Engle, Elizabeth; Xu, Haiyang; Ogurtsova, Aleksandra; Wang,
Daphne; Nguyen, Peter; Soto-Diaz, Sigfredo; Loyola, Jose; Doyle,
Joshua; Wilton, Richard; Eminizer, Margaret; Roskes, Jeffrey; Szalay,
Alexander; Taube, Janis
2021wems.confE..12G Altcode:
Multidimensional, spatially resolved analyses of cells from
pathology slides are of great diagnostic and prognostic interest. New
multispectral, multiplex immunofluorescence microscopy platforms
have the potential to facilitate such analyses, and here, we further
improve and standardize the image acquisition and cell classification
workflow. Studies to date on this emerging technology have typically
assessed ~10 operator-dependent high power fields (HPFs) per slide,
which represents a fraction of the tissue available for study. Standard
cell segmentation and classification algorithms often oversegment
larger cells, when they are segmented at the same time as smaller
cells. Here we describe our AstroPath imaging platform, which addresses
each of these considerations. In our study, slides from formalin-fixed
paraffin embedded tissue specimens were stained with an optimized 6-plex
multiplex immunofluorescence (mIF) assay. The slides were then scanned
at 35 unique wavelengths using a multispectral microscope (Vectra 3.0
or Vectra Polaris) with 20% overlap of HPFs in an operator-independent
fashion. An average of 1300 HPFs per slide was required to image the
entire tissue, and each microscope scanned between 2 to 3 slides per
day with this approach. After the images were captured and organized,
overlaps were used to measure, quantify and correct systematics in
the imagery (see Eminizer abstract). The central parts of the images
were used to create a set of seamless "primary" tiles, similar to the
strategy of the Sloan Digital Sky Survey, for a statistically fair pixel
coverage of the whole tissue area (see Roskes abstract). Images were
then linearly unmixed from the 35 wavelengths to 8 component layers
(DAPI, tissue auto-fluorescence, and the 6 added fluorescent dyes)
using inForm Cell Analysis
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Title: Power-law energy distributions of small-scale impulsive events
on the active Sun: results from IRIS
Authors: Vilangot Nhalil, Nived; Nelson, Chris J.; Mathioudakis,
Mihalis; Doyle, J. Gerry; Ramsay, Gavin
2020MNRAS.499.1385V Altcode: 2020MNRAS.tmp.2719N; 2020arXiv200903123V
Numerous studies have analysed inferred power-law distributions
between frequency and energy of impulsive events in the outer solar
atmosphere in an attempt to understand the predominant energy supply
mechanism in the corona. Here, we apply a burst detection algorithm to
high-resolution imaging data obtained by the Interface Region Imaging
Spectrograph to further investigate the derived power-law index, γ,
of bright impulsive events in the transition region. Applying the
algorithm with a constant minimum event lifetime (of either 60 s or
110 s) indicated that the target under investigation, such as Plage
and Sunspot, has an influence on the observed power-law index. For
regions dominated by sunspots, we always find γ < 2; however,
for data sets where the target is a plage region, we often find that
γ > 2 in the energy range (~10<SUP>23</SUP>, ~10<SUP>26</SUP>)
erg. Applying the algorithm with a minimum event lifetime of three
time-steps indicated that cadence was another important factor, with
the highest cadence data sets returning γ > 2 values. The estimated
total radiative power obtained for the observed energy distributions
is typically 10-25 per cent of what would be required to sustain the
corona indicating that impulsive events in this energy range are not
sufficient to solve coronal heating. If we were to extend the power-law
distribution down to an energy of 10<SUP>21</SUP> erg, and assume parity
between radiative energy release and the deposition of thermal energy,
then such bursts could provide 25-50 per cent of the required energy
to account for the coronal heating problem.
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Title: TESS observations of southern ultrafast rotating low-mass stars
Authors: Ramsay, Gavin; Doyle, J. Gerry; Doyle, Lauren
2020MNRAS.497.2320R Altcode: 2020MNRAS.tmp.2138R; 2020arXiv200704071R
In our previous study of low-mass stars using TESS, we found a handful
that show a periodic modulation on a period <1 d but also displayed
no flaring activity. Here we present the results of a systematic search
for ultrafast rotators (UFRs) in the Southern ecliptic hemisphere,
which were observed in 2-min cadence with TESS. Using data from
Gaia DR2, we obtain a sample of over 13 000 stars close to the lower
main sequence. Of these, we identify 609 stars that lie on the lower
main sequence and have a periodic modulation <1 d. The fraction
of stars that show flares appears to drop significantly at periods
<0.2 d. If the periods are a signature of the rotation rate, this
would be a surprise, since faster rotators would be expected to have a
stronger magnetic field and, therefore, produce more flares. We explore
possible reasons for our finding: The flare inactive stars are members
of binaries, in which case the stars rotation rate could have increased
as the binary orbital separation reduced due to angular momentum loss
over time, or that enhanced emission occurs at blue wavelengths beyond
the pass band of TESS. Follow-up spectroscopy and flare monitoring at
blue/ultraviolet wavelengths of these flare inactive stars are required
to resolve this question.
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Title: Velocity Response of the Observed Explosive Events in the
Lower Solar Atmosphere. I. Formation of the Flowing Cool-loop System
Authors: Srivastava, A. K.; Rao, Yamini K.; Konkol, P.; Murawski,
K.; Mathioudakis, M.; Tiwari, Sanjiv K.; Scullion, E.; Doyle, J. G.;
Dwivedi, B. N.
2020ApJ...894..155S Altcode: 2020arXiv200402775S
We observe plasma flows in cool loops using the Slit-Jaw Imager on board
the Interface Region Imaging Spectrometer (IRIS). Huang et al. observed
unusually broadened Si IV 1403 Šline profiles at the footpoints of
such loops that were attributed to signatures of explosive events
(EEs). We have chosen one such unidirectional flowing cool-loop
system observed by IRIS where one of the footpoints is associated
with significantly broadened Si IV line profiles. The line-profile
broadening indirectly indicates the occurrence of numerous EEs below
the transition region (TR), while it directly infers a large velocity
enhancement/perturbation, further causing the plasma flows in the
observed loop system. The observed features are implemented in a
model atmosphere in which a low-lying bipolar magnetic field system
is perturbed in the chromosphere by a velocity pulse with a maximum
amplitude of 200 km s<SUP>-1</SUP>. The data-driven 2D numerical
simulation shows that the plasma motions evolve in a similar manner
as observed by IRIS in the form of flowing plasma filling the skeleton
of a cool-loop system. We compare the spatio-temporal evolution of the
cool-loop system in the framework of our model with the observations,
and conclude that their formation is mostly associated with the velocity
response of the transient energy release above their footpoints in
the chromosphere/TR. Our observations and modeling results suggest
that the velocity responses most likely associated to the EEs could
be one of the main candidates for the dynamics and energetics of the
flowing cool-loop systems in the lower solar atmosphere.
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Title: Superflares and variability in solar-type stars with TESS in
the Southern hemisphere
Authors: Doyle, L.; Ramsay, G.; Doyle, J. G.
2020MNRAS.494.3596D Altcode: 2020MNRAS.tmp.1151D; 2020arXiv200314410D
Superflares on solar-type stars have been a rapidly developing
field ever since the launch of Kepler. Over the years, there have
been several studies investigating the statistics of these explosive
events. In this study, we present a statistical analysis of stellar
flares on solar-type stars made using photometric data in 2-min
cadence from Transiting Exoplanet Survey Satellite of the whole
Southern hemisphere (sectors 1-13). We derive rotational periods for
all the stars in our sample from rotational modulations present in
the light curve as a result of large star-spot(s) on the surface. We
identify 1980 stellar flares from 209 solar-type stars with energies
in the range of 10<SUP>31</SUP>-10<SUP>36</SUP> erg (using the solar
flare classification, this corresponds to X1-X100 000) and conduct an
analysis into their properties. We investigate the rotational phase
of the flares and find no preference for any phase, suggesting the
flares are randomly distributed. As a benchmark, we use GOES data of
solar flares to detail the close relationship between solar flares and
sunspots. In addition, we also calculate approximate spot areas for
each of our stars and compare this to flare number, rotational phase,
and flare energy. Additionally, two of our stars were observed in the
continuous viewing zone with light-curves spanning 1 yr; as a result
we examine the stellar variability of these stars in more detail.
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Title: Exploring Flaring Behaviour on Low Mass Stars, Solar-type
Stars and the Sun
Authors: Doyle, L.; Ramsay, G.; Doyle, J. G.; Wyper, P. F.; Scullion,
E.; Wu, K.; McLaughlin, J. A.
2020IAUS..354..384D Altcode:
We report on our project to study the activity in both the Sun and low
mass stars. Utilising high cadence, Hα observations of a filament
eruption made using the CRISP spectropolarimeter mounted on the
Swedish Solar Telescope has allowed us to determine 3D velocity maps
of the event. To gain insight into the physical mechanism which drives
the event we have qualitatively compared our observation to a 3D MHD
reconnection model. Solar-type and low mass stars can be highly active
producing flares with energies exceeding erg. Using K2 and TESS data
we find no correlation between the number of flares and the rotation
phase which is surprising. Our solar flare model can be used to aid
our understanding of the origin of flares in other stars. By scaling
up our solar model to replicate observed stellar flare energies,
we investigate the conditions needed for such high energy flares.
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Title: On the Observations of Rapid Forced Reconnection in the
Solar Corona
Authors: Srivastava, A. K.; Mishra, S. K.; Jelínek, P.; Samanta,
Tanmoy; Tian, Hui; Pant, Vaibhav; Kayshap, P.; Banerjee, Dipankar;
Doyle, J. G.; Dwivedi, B. N.
2019ApJ...887..137S Altcode: 2019arXiv190107971S
Using multiwavelength imaging observations from the Atmospheric Imaging
Assembly on board the Solar Dynamics Observatory on 2012 May 3, we
present a novel physical scenario for the formation of a temporary
X-point in the solar corona, where plasma dynamics are forced externally
by a moving prominence. Natural diffusion was not predominant; however,
a prominence driven inflow occurred first, forming a thin current sheet,
thereafter enabling a forced magnetic reconnection at a considerably
high rate. Observations in relation to the numerical model reveal that
forced reconnection may rapidly and efficiently occur at higher rates
in the solar corona. This physical process may also heat the corona
locally even without establishing a significant and self-consistent
diffusion region. Using a parametric numerical study, we demonstrate
that the implementation of the external driver increases the rate
of the reconnection even when the resistivity required for creating
normal diffusion region decreases at the X-point. We conjecture that
the appropriate external forcing can bring the oppositely directed
field lines into the temporarily created diffusion region first via the
plasma inflows as seen in the observations. The reconnection and related
plasma outflows may occur thereafter at considerably larger rates.
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Title: Observations and 3D Magnetohydrodynamic Modeling of a Confined
Helical Jet Launched by a Filament Eruption
Authors: Doyle, Lauren; Wyper, Peter F.; Scullion, Eamon; McLaughlin,
James A.; Ramsay, Gavin; Doyle, J. Gerard
2019ApJ...887..246D Altcode: 2019arXiv191202133D
We present a detailed analysis of a confined filament eruption
and jet associated with a C1.5 class solar flare. Multi-wavelength
observations from the Global Oscillations Network Group and Solar
Dynamics Observatory reveal the filament forming over several days
following the emergence and then partial cancellation of a minority
polarity spot within a decaying bipolar active region. The emergence
is also associated with the formation of a 3D null point separatrix
that surrounds the minority polarity. The filament eruption occurs
concurrently with brightenings adjacent to and below the filament,
suggestive of breakout and flare reconnection, respectively. The
erupting filament material becomes partially transferred into a
strong outflow jet (∼60 km s<SUP>-1</SUP>) along coronal loops,
becoming guided back toward the surface. Utilizing high-resolution
Hα observations from the Swedish Solar Telescope/CRisp Imaging
SpectroPolarimeter, we construct velocity maps of the outflows,
demonstrating their highly structured but broadly helical nature. We
contrast the observations with a 3D magnetohydrodynamic simulation
of a breakout jet in a closed-field background and find close
qualitative agreement. We conclude that the suggested model provides
an intuitive mechanism for transferring twist/helicity in confined
filament eruptions, thus validating the applicability of the breakout
model not only to jets and coronal mass ejections but also to confined
eruptions and flares.
---------------------------------------------------------
Title: Probing the origin of stellar flares on M dwarfs using TESS
data sectors 1-3
Authors: Doyle, L.; Ramsay, G.; Doyle, J. G.; Wu, K.
2019MNRAS.489..437D Altcode: 2019arXiv190802698D; 2019MNRAS.tmp.2115D
Detailed studies of the Sun have shown that sunspots and solar
flares are closely correlated. Photometric data from Kepler/K2 has
allowed similar studies to be carried out on other stars. Here, we
utilize Transiting Exoplanet Survey Satellite (TESS) photometric 2-min
cadence of 167 low-mass stars from Sectors 1 to 3 to investigate the
relationship between star-spots and stellar flares. From our sample,
90 per cent show clear rotational modulation likely due to the presence
of a large, dominant star-spot and we use this to determine a rotational
period for each star. Additionally, each low-mass star shows one or more
flares in its light curve and using Gaia Data Release 2 parallaxes and
SkyMapper magnitudes we can estimate the energy of the flares in the
TESS band-pass. Overall, we have 1834 flares from the 167 low-mass stars
with energies from 6.0 × 10<SUP>29</SUP> to 2.4 × 10<SUP>35</SUP>
erg. We find none of the stars in our sample show any preference for
rotational phase, suggesting the lack of a correlation between the
large, dominant star-spot, and flare number. We discuss this finding
in greater detail and present further scenarios to account for the
origin of flares on these low-mass stars.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Stellar parameters of M and K
dwarfs (Houdebine+, 2019)
Authors: Houdebine, E. R.; Mullan, D. J.; Doyle, J. G.; de La
Vieuville, G.; Butler, C. J.; Paletou, F.
2019yCat..51580056H Altcode:
Observations of (R-I)<SUB>C</SUB> (Cousin's photometric system) or
(R-I)<SU photometric system) for our samples of K and M dwarfs
were taken from several papers. We selected eight samples of K and M
dwarfs according to their (R-I)<SUB>C</SUB> colors. This represents
a total sample of 2765 K and M dwarfs. Most stars in this sample
are nearby or large proper motion stars. We also completed these
samples of stars with a ninth sample of stars: the M0-M1 sample,
which includes some stars from the samples of stars from B12 and M15
(see Table 1), as well as several stars initially from the M2 sample,
which were found to have higher temperatures (we included in the M0-M1
sample stars down to the spectral type dM1.5). <P />(3 data files).
---------------------------------------------------------
Title: The Mass-Activity Relationships in M and K Dwarfs. I. Stellar
Parameters of Our Sample of M and K Dwarfs
Authors: Houdebine, Éric R.; Mullan, D. J.; Doyle, J. G.; de La
Vieuville, Geoffroy; Butler, C. J.; Paletou, F.
2019AJ....158...56H Altcode: 2019arXiv190507921H
Empirical correlations between stellar parameters such as rotation
or radius and magnetic activity diagnostics require estimates
of the effective temperatures and the stellar radii. The aim of
this study is to propose simple methods that can be applied to
large samples of stars in order to derive estimates of the stellar
parameters. Good empirical correlations between red/infrared colors
(e.g., (R - I)<SUB> C </SUB>) and effective temperatures have been
well established for a long time. The more recent (R - I)<SUB> C
</SUB> color-T <SUB>eff</SUB> correlation using the data of Mann et
al. (hereafter M15) and Boyajian et al. (hereafter B12) shows that
this color can be applied as a temperature estimate for large samples
of stars. We find that the mean scatter in T <SUB>eff</SUB> relative
to the (R - I)<SUB> C </SUB>-T <SUB>eff</SUB> relationship of B12 and
M15 data is only ±3σ = 44.6 K for K dwarfs and ±3σ = 39.4 K for M
dwarfs. These figures are small and show that the (R - I)<SUB> C </SUB>
color can be used as a first-guess effective temperature estimator
for K and M dwarfs. We derive effective temperatures for about 1910
K and M dwarfs using the calibration of (R - I)<SUB> C </SUB> color-T
<SUB>eff</SUB> from B12 and M15 data. We also compiled T <SUB>eff</SUB>
and metallicity measurements available in the literature using the
VizieR database. We determine T <SUB>eff</SUB> for 441 stars with
previously unknown effective temperatures. We also identified 21 new
spectroscopic binaries and one triple system from our high-resolution
spectra. <P />Based on Gaia DR2 and Hipparcos parallax measurements.
---------------------------------------------------------
Title: Multiwavelength High-resolution Observations of Chromospheric
Swirls in the Quiet Sun
Authors: Shetye, Juie; Verwichte, Erwin; Stangalini, Marco; Judge,
Philip G.; Doyle, J. G.; Arber, Tony; Scullion, Eamon; Wedemeyer, Sven
2019ApJ...881...83S Altcode:
We report observations of small-scale swirls seen in the solar
chromosphere. They are typically 2 Mm in diameter and last around
10 minutes. Using spectropolarimetric observations obtained by the
CRisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope,
we identify and study a set of swirls in chromospheric Ca II 8542 Å
and Hα lines as well as in the photospheric Fe I line. We have three
main areas of focus. First, we compare the appearance, morphology,
dynamics, and associated plasma parameters between the Ca II and Hα
channels. Rotation and expansion of the chromospheric swirl pattern
are explored using polar plots. Second, we explore the connection to
underlying photospheric magnetic concentration (MC) dynamics. MCs are
tracked using the SWAMIS tracking code. The swirl center and MC remain
cospatial and share similar periods of rotation. Third, we elucidate
the role swirls play in modifying chromospheric acoustic oscillations
and found a temporary reduction in wave period during swirls. We use
cross-correlation wavelets to examine the change in period and phase
relations between different wavelengths. The physical picture that
emerges is that a swirl is a flux tube that extends above an MC in a
downdraft region in an intergranular lane. The rotational motion of
the MC matches the chromospheric signatures. We could not determine
whether a swirl is a gradual response to the photospheric motion or
an actual propagating Alfvénic wave.
---------------------------------------------------------
Title: Confined pseudo-shocks as an energy source for the active
solar corona
Authors: Srivastava, Abhishek Kumar; Murawski, Krzysztof; Kuźma,
BlaŻej; Wójcik, Dariusz Patryk; Zaqarashvili, Teimuraz V.;
Stangalini, Marco; Musielak, Zdzislaw E.; Doyle, John Gerard; Kayshap,
Pradeep; Dwivedi, Bhola N.
2018NatAs...2..951S Altcode: 2018NatAs.tmp..138S
The Sun's active corona requires an energy flux of 10<SUP>3</SUP>
W m<SUP>-2</SUP> to compensate for radiative losses and to maintain
its high temperature<SUP>1</SUP>. Plasma moves in the corona through
magnetic loops<SUP>2,3</SUP>, which may be connected with the flows
in and around sunspots<SUP>4-6</SUP>. Global energizing processes
(for example, reconnection) play an important part in heating the
corona<SUP>7-9</SUP>; however, energy and mass transport may also
occur via shocks, waves or flows<SUP>5,10,11</SUP>. A full picture
and the influence of such localized events, which significantly
couple with various layers of the solar upper atmosphere, is still not
clear. Using the Interface Region Imaging Spectrograph temporal image
data of C uc(ii) 1,330 Å, we observed the presence of pseudo-shocks
around a sunspot. Unlike shocks<SUP>12</SUP>, pseudo-shocks exhibit
discontinuities only in the mass density. A two-fluid numerical
simulation reproduces such confined pseudo-shocks with rarefied
plasma regions lagging behind them. We find that these pseudo-shocks
carry an energy of 10<SUP>3</SUP> W m<SUP>-2</SUP>, which is enough
to locally power the inner corona and also generate bulk flows (
10<SUP>-5</SUP> kg m<SUP>-2</SUP> s<SUP>-1</SUP>), contributing to the
localized mass transport. If they are ubiquitous, such energized and
bulky pseudo-shocks above active regions could provide an important
contribution to the heating and mass transport in the overlying
solar corona.
---------------------------------------------------------
Title: A persistent quiet-Sun small-scale tornado. I. Characteristics
and dynamics
Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.; Scullion,
E.; Doyle, J. G.
2018A&A...618A..51T Altcode:
Context. Vortex flows have been extensively observed over a wide range
of spatial and temporal scales in different spectral lines, and thus
layers of the solar atmosphere, and have been widely found in numerical
simulations. However, signatures of vortex flows have only recently
been reported in the wings of the Hα, but never so far in the Hα line
centre. <BR /> Aims: We investigate the appearance, characteristics,
substructure, and dynamics of a 1.7 h persistent vortex flow observed
from the ground and from space in a quiet-Sun region in several
lines/channels covering all atmospheric layers from the photosphere up
to the low corona. <BR /> Methods: We use high spatial and temporal
resolution CRisp Imaging SpectroPolarimeter (CRISP) observations in
several wavelengths along the Hα and Ca II 8542 Å line profiles,
simultaneous Atmospheric Imaging Assembly (AIA) observations in several
Ultraviolet (UV) and Extreme ultraviolet (EUV) channels and Helioseismic
and Magnetic Imager (HMI) magnetograms to study a persistent vortex flow
located at the south solar hemisphere. Doppler velocities were derived
from the Hα line profiles. Our analysis involves visual inspection and
comparison of all available simultaneous/near-simultaneous observations
and detailed investigation of the vortex appearance, characteristics
and dynamics using time slices along linear and circular slits. <BR />
Results: The most important characteristic of the analysed clockwise
rotating vortex flow is its long duration (at least 1.7 h) and its
large radius ( 3″). The vortex flow shows different behaviours in
the different wavelengths along the Hα and Ca II 8542 Å profiles
reflecting the different formation heights and mechanisms of the two
lines. Ground-based observations combined with AIA observations reveal
the existence of a funnel-like structure expanding with height, possibly
rotating rigidly or quasi-rigidly. However, there is no clear evidence
that the flow is magnetically driven as no associated magnetic bright
points have been observed in the photosphere. Hα and Ca II 8542 Å
observations also reveal significant substructure within the flow,
manifested as several individual intermittent chromospheric swirls
with typical sizes and durations. They also exhibit a wide range of
morphological patterns, appearing as dark absorbing features, associated
mostly with mean upwards velocities around 3 km s<SUP>-1</SUP> and
up to 8 km s<SUP>-1</SUP>, and occupying on average 25% of the total
vortex area. The radial expansion of the spiral flow occurs with
a mean velocity of 3 km s<SUP>-1</SUP>, while its dynamics can be
related to the dynamics of a clockwise rigidly rotating logarithmic
spiral with a swinging motion that is, however, highly perturbed by
nearby flows associated with fibril-like structures. A first rough
estimate of the rotational period of the vortex falls in the range of
200-300 s. <BR /> Conclusions: The vortex flow resembles a small-scale
tornado in contrast to previously reported short-lived swirls and
in analogy to persistent giant tornadoes. It is unclear whether
the observed substructure is indeed due to the physical presence
of individual intermittent, recurring swirls or a manifestation of
wave-related instabilities within a large vortex flow. Moreover,
we cannot conclusively demonstrate that the long duration of
the observed vortex is the result of a central swirl acting as an
"engine" for the vortex flow, although there is significant supporting
evidence inferred from its dynamics. It also cannot be excluded that
this persistent vortex results from the combined action of several
individual smaller swirls further assisted by nearby flows or that
this is a new case in the literature of a hydrodynamically driven
vortex flow. <P />The movie associated to Fig. 4 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201833101/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: Investigating the rotational phase of stellar flares on M
dwarfs using K2 short cadence data
Authors: Doyle, L.; Ramsay, G.; Doyle, J. G.; Wu, K.; Scullion, E.
2018MNRAS.480.2153D Altcode: 2018MNRAS.tmp.1870D; 2018arXiv180708592D
We present an analysis of K2 short cadence data of 34 M dwarfs which
have spectral types in the range M0-L1. Of these stars, 31 showed flares
with a duration between ∼10 and 90min. Using distances obtained from
Gaia DR2 parallaxes, we determined the energy of the flares to be in the
range ∼1.2 × 10<SUP>29</SUP>-6 × 10<SUP>34</SUP> erg. In agreement
with previous studies we find rapidly rotating stars tend to show more
flares, with evidence for a decline in activity in stars with rotation
periods longer than ∼10 d. The rotational modulation seen in M dwarf
stars is widely considered to result from a starspot which rotates in
and out of view. Flux minimum is therefore the rotation phase where we
view the main starspot close to the stellar disc centre. Surprisingly,
having determined the rotational phase of each flare in our study
we find none show any preference for rotational phase. We outline
three scenarios which could account for this unexpected finding. The
relationship between rotation phase and flare rate will be explored
further using data from wide surveys such as NGTS and TESS.
---------------------------------------------------------
Title: Signatures of quiet Sun reconnection events in Ca II, Hα,
and Fe I
Authors: Shetye, J.; Shelyag, S.; Reid, A. L.; Scullion, E.; Doyle,
J. G.; Arber, T. D.
2018MNRAS.479.3274S Altcode: 2018MNRAS.tmp.1509S; 2017arXiv170310968S
We use observations of quiet Sun (QS) regions in the Hα 6563 Å, Ca II
8542 Å, and Fe I 6302 Å lines. We observe brightenings in the wings
of the Hα and Ca II combined with observations of the interacting
magnetic concentrations observed in the Stokes signals of Fe I. These
brightenings are similar to Ellerman bombs (EBs), i.e. impulsive
bursts in the wings of the Balmer lines that leave the line cores
unaffected. Such enhancements suggest that these events have similar
formation mechanisms to the classical EBs found in active regions,
with the reduced intensity enhancements found in the QS regions due to
a weaker feeding magnetic flux. The observations also show that the
quiet Sun Ellerman bombs are formed at a higher height in the upper
photosphere than the photospheric continuum level. Using simulations,
we investigate the formation mechanism associated with the events and
suggest that these events are driven by the interaction of magnetic
field lines in the upper photospheric regions. The results of the
simulation are in agreement with observations when comparing the light
curves, and in most cases, we found that the peak in the Ca II 8542
Å wing occurred before the peak in Hα wing. Moreover, in some cases,
the line profiles observed in Ca II are asymmetrical with a raised core
profile. The source of heating in these events is shown by the MURaM
simulations and is suggested to occur 430 km above the photosphere.
---------------------------------------------------------
Title: Searching for the Origin of Flares in M dwarfs
Authors: Doyle, Lauren; Ramsay, Gavin; Doyle, John G.
2018csss.confE..81D Altcode: 2018arXiv181106594D
We present an overview of K2 short cadence observations for 34 M
dwarfs observed in Campaigns 1 - 9 which have spectral types between
M0 - L1. All of the stars in our sample showed flares with the most
energetic reaching 3×10(34) ergs. As previous studies have found,
we find rapidly rotating stars tend to show more flares, with evidence
for a decline in activity in stars with rotation periods longer than
approximately 10 days. We determined the rotational phase of each flare
and performed a simple statistical test on our sample to determine
whether the phase distribution of the flares is random or if there
is a preference for phase. We find, with the exception of one star
which is in a known binary system, that none show a preference for the
rotational phase of the flares. This is unexpected and all stars in our
sample show flares at all rotational phases, suggesting these flares
are not all originating from one dominant starspot on the surface of
the stars. We outline three scenarios which could explain the lack of
a correlation between the number of flares and the stellar rotation
phase. In addition we also highlight preliminary observations of DP
Cnc, observed in campaigns 16 and 18, and is one of the stars in our
extended sample from K2Campaigns 10 -18 which are still to be examined.
---------------------------------------------------------
Title: Energetics of Hi-C EUV brightenings
Authors: Subramanian, Srividya; Kashyap, Vinay L.; Tripathi, Durgesh;
Madjarska, Maria S.; Doyle, John G.
2018A&A...615A..47S Altcode: 2018arXiv180309505S
We study the thermal structure and energetics of the point-like extreme
ultraviolet (EUV) brightenings within a system of fan loops observed
in the active region AR 11520. These brightenings were simultaneously
observed on 2012 July 11 by the High-resolution Coronal (Hi-C) imager
and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
Observatory (SDO). We identified 27 brightenings by automatically
determining intensity enhancements in both Hi-C and AIA 193 Å light
curves. The energetics of these brightenings were studied using the
Differential Emission Measure (DEM) diagnostics. The DEM weighted
temperatures of these transients are in the range log T(K) = 6.2-6.6
with radiative energies ≈10<SUP>24-25</SUP> ergs and densities
approximately equal to a few times 10<SUP>9</SUP> cm<SUP>-3</SUP>. To
the best of our knowledge, these are the smallest brightenings in
EUV ever detected. We used these results to determine the mechanism
of energy loss in these brightenings. Our analysis reveals that the
dominant mechanism of energy loss for all the identified brightenings
is conduction rather than radiation.
---------------------------------------------------------
Title: First Evidence of the Frequency Filtering of Magnetoacoustic
Waves in the Flaring Star EK Dra
Authors: Srivastava, A. K.; Pandey, J. C.; Karmakar, Subhajeet;
Chowdhury, Partha; Moon, Y. -J.; Goossens, Marcel; Jelínek, P.;
Mathioudakis, M.; Doyle, J. G.; Dwivedi, B. N.
2018arXiv180408858S Altcode:
Using the data obtained from XMM-Newton, we show the gradual evolution
of two periodicities of ~4500 s and ~2200 s in the decay phase of the
flare observed in a solar analog EK Dra. The longer period evolves
firstly for first 14 ks, while the shorter period evolves for next
10 ks in the decay phase. We find that these two periodicities are
associated with the magnetoacoustic waves triggered in the flaring
region. The flaring loop system shows cooling and thus it is subjected
to the change in the scale height and the acoustic cut-off period. This
serves to filter the longer period magnetoacoustic waves and enables
the propagation of the shorter period waves in the later phase of
the flare. We provide the first clues of the dynamic behaviour of
EK Dra's corona which affects the propagation of waves and causes
their filtering.
---------------------------------------------------------
Title: Stellar flare oscillations: evidence for oscillatory
reconnection and evolution of MHD modes
Authors: Doyle, J. G.; Shetye, J.; Antonova, A. E.; Kolotkov, D. Y.;
Srivastava, A. K.; Stangalini, M.; Gupta, G. R.; Avramova, A.;
Mathioudakis, M.
2018MNRAS.475.2842D Altcode: 2018MNRAS.tmp...77D
Here, we report on the detection of a range of quasi-periodic
pulsations (20-120 s; QPPs) observed during flaring activity of several
magnetically active dMe stars, namely AF Psc, CR Dra, GJ 3685A,
Gl 65, SDSS J084425.9+513830, and SDSS J144738.47+035312.1 in the
GALEX NUV filter. Based on a solar analogy, this work suggests that
many of these flares may be triggered by external drivers creating
a periodic reconnection in the flare current sheet or an impulsive
energy release giving rise to an avalanche of periodic bursts that
occur at time intervals that correspond to the detected periods, thus
generating QPPs in their rising and peak phases. Some of these flares
also show fast QPPs in their decay phase, indicating the presence of
fast sausage mode oscillations either driven externally by periodic
reconnection or intrinsically in the post-flare loop system during
the flare energy release.
---------------------------------------------------------
Title: Photospheric Observations of Surface and Body Modes in Solar
Magnetic Pores
Authors: Keys, Peter H.; Morton, Richard J.; Jess, David B.; Verth,
Gary; Grant, Samuel D. T.; Mathioudakis, Mihalis; Mackay, Duncan H.;
Doyle, John G.; Christian, Damian J.; Keenan, Francis P.; Erdélyi,
Robertus
2018ApJ...857...28K Altcode: 2018arXiv180301859K
Over the past number of years, great strides have been made in
identifying the various low-order magnetohydrodynamic wave modes
observable in a number of magnetic structures found within the solar
atmosphere. However, one aspect of these modes that has remained
elusive, until now, is their designation as either surface or body
modes. This property has significant implications for how these modes
transfer energy from the waveguide to the surrounding plasma. Here, for
the first time to our knowledge, we present conclusive, direct evidence
of these wave characteristics in numerous pores that were observed to
support sausage modes. As well as outlining methods to detect these
modes in observations, we make estimates of the energies associated
with each mode. We find surface modes more frequently in the data,
as well as that surface modes appear to carry more energy than those
displaying signatures of body modes. We find frequencies in the range
of ∼2-12 mHz, with body modes as high as 11 mHz, but we do not find
surface modes above 10 mHz. It is expected that the techniques we have
applied will help researchers search for surface and body signatures
in other modes and in differing structures from those presented here.
---------------------------------------------------------
Title: Origin of impulsive plasma outflows due to magnetoacoustic
shocks
Authors: Rao, Y. K.; Srivastava, A. K.; Doyle, J. G.; Dwivedi, B. N.
2017MNRAS.470.2449R Altcode:
We study an impulsive plasma outflow in the quiet-Sun using
multiwavelength observations from the Atmospheric Imaging Assembly (AIA)
onboard the Solar Dynamics Observatory (SDO) on 2011 March 30. The
outflow rises to the upper solar atmosphere with a high terminal
speed of 1250 km s<SUP>- 1</SUP>. Emissions from multiple SDO/AIA
channels (log T (K) = 4.7 to log T (K) = 7.0), peak at the same time
indicating its highly impulsive origin. We obtain the line-of-sight
differential emission measure maps and find that the outflow is made
up of multitemperature plasma. Investigation of SDO/HMI magnetic field
data at its footpoint shows that the emerging flux of negative polarity
is oscillating at the period of 442 s. The oscillations are also
observed in the intensity of 1600 Å almost co-temporally at the base
of the outflow with the almost same period (≈416 s). The ∼7.0 min
periodicity in the magnetic flux and 1600 Å flux is present both prior
to and during the onset, and even after the outflows for the duration
of ≈1 h. This indicates that the magnetoacoustic waves are generated
and present at the base of the outflow and interact with the localized
small-scale current sheet and associated X-point. Magnetoacoustic
waves encounter with the discontinuity at the X-point that may further
develop into the fast magnetic shocks leading to the formation of the
observed shock cusp and triggering of the impulsive plasma outflows.
---------------------------------------------------------
Title: Chromospheric Inversions of a Micro-flaring Region
Authors: Reid, A.; Henriques, V.; Mathioudakis, M.; Doyle, J. G.;
Ray, T.
2017ApJ...845..100R Altcode: 2017arXiv170700029R
We use spectropolarimetric observations of the Ca II 8542 Å line, taken
from the Swedish 1 m Solar Telescope, in an attempt to recover dynamic
activity in a micro-flaring region near a sunspot via inversions. These
inversions show localized mean temperature enhancements of ∼1000
K in the chromosphere and upper photosphere, along with co-spatial
bi-directional Doppler shifting of 5-10 km s<SUP>-1</SUP>. This heating
also extends along a nearby chromospheric fibril, which is co-spatial
to 10-15 km s<SUP>-1</SUP> downflows. Strong magnetic flux cancellation
is also apparent in one of the footpoints, and is concentrated in the
chromosphere. This event more closely resembles that of an Ellerman
Bomb, though placed slightly higher in the atmosphere than what is
typically observed.
---------------------------------------------------------
Title: High-frequency torsional Alfvén waves as an energy source
for coronal heating
Authors: Srivastava, Abhishek Kumar; Shetye, Juie; Murawski, Krzysztof;
Doyle, John Gerard; Stangalini, Marco; Scullion, Eamon; Ray, Tom;
Wójcik, Dariusz Patryk; Dwivedi, Bhola N.
2017NatSR...743147S Altcode:
The existence of the Sun’s hot atmosphere and the solar
wind acceleration continues to be an outstanding problem in
solar-astrophysics. Although magnetohydrodynamic (MHD) modes and
dissipation of magnetic energy contribute to heating and the mass
cycle of the solar atmosphere, yet direct evidence of such processes
often generates debate. Ground-based 1-m Swedish Solar Telescope
(SST)/CRISP, Hα 6562.8 Å observations reveal, for the first time,
the ubiquitous presence of high frequency (~12-42 mHz) torsional
motions in thin spicular-type structures in the chromosphere. We
detect numerous oscillating flux tubes on 10 June 2014 between 07:17
UT to 08:08 UT in a quiet-Sun field-of-view of 60” × 60”
(1” = 725 km). Stringent numerical model shows that
these observations resemble torsional Alfvén waves associated
with high frequency drivers which contain a huge amount of energy
(~10<SUP>5</SUP> W m<SUP>-2</SUP>) in the chromosphere. Even after
partial reflection from the transition region, a significant amount of
energy (~10<SUP>3</SUP> W m<SUP>-2</SUP>) is transferred onto the
overlying corona. We find that oscillating tubes serve as substantial
sources of Alfvén wave generation that provide sufficient Poynting
flux not only to heat the corona but also to originate the supersonic
solar wind.
---------------------------------------------------------
Title: Modelling the environment around five ultracool dwarfs via
the radio domain
Authors: Metodieva, Y. T.; Kuznetsov, A. A.; Antonova, A. E.; Doyle,
J. G.; Ramsay, G.; Wu, K.
2017MNRAS.465.1995M Altcode: 2016arXiv161002989M
We present the results of a series of short radio observations of six
ultracool dwarfs made using the upgraded Very Large Array in S (2-4GHz)
and C (4-7GHz) bands. LSR J1835+3259 exhibits a 100 per cent right-hand
circularly polarized burst that shows intense narrow-band features with
a fast negative frequency drift of about -30 MHz s<SUP>-1</SUP>. They
are superimposed on a fainter broad-band emission feature with a
total duration of about 20 min, bandwidth of about 1 GHz, centred
at about 3.5 GHz, and a slow positive frequency drift of about 1
MHz s<SUP>-1</SUP>. This makes it the first such event detected
below 4 GHz and the first one exhibiting both positive and negative
frequency drifts. Polarized radio emission is also seen in 2MASS
J00361617+1821104 and NLTT 33370, while LP 349-25 and TVLM 513-46546
have unpolarized emission and BRI B0021-0214 was not detected. We can
reproduce the main characteristics of the burst from LSR J1835+3259
using a model describing the magnetic field of the dwarf as a tilted
dipole. We also analyse the origins of the quiescent radio emission and
estimate the required parameters of the magnetic field and energetic
electrons. Although our results are non-unique, we find a set of models
that agree well with the observations.
---------------------------------------------------------
Title: Solar Ellerman Bombs in 1D Radiative Hydrodynamics
Authors: Reid, A.; Mathioudakis, M.; Kowalski, A.; Doyle, J. G.;
Allred, J. C.
2017ApJ...835L..37R Altcode: 2017arXiv170104213R
Recent observations from the Interface Region Imaging Spectrograph
appear to show impulsive brightenings in high temperature lines,
which when combined with simultaneous ground-based observations in
Hα, appear co-spatial to Ellerman Bombs (EBs). We use the RADYN
one-dimensional radiative transfer code in an attempt to try and
reproduce the observed line profiles and simulate the atmospheric
conditions of these events. Combined with the MULTI/RH line synthesis
codes, we compute the Hα, Ca II 8542 Å, and Mg II h and k lines for
these simulated events and compare them to previous observations. Our
findings hint that the presence of superheated regions in the
photosphere (>10,000 K) is not a plausible explanation for the
production of EB signatures. While we are able to recreate EB-like
line profiles in Hα, Ca II 8542 Å, and Mg II h and k, we cannot
achieve agreement with all of these simultaneously.
---------------------------------------------------------
Title: Explosive events in active region observed by IRIS and
SST/CRISP
Authors: Huang, Z.; Madjarska, M. S.; Scullion, E. M.; Xia, L. -D.;
Doyle, J. G.; Ray, T.
2017MNRAS.464.1753H Altcode: 2016arXiv160907698H
Transition-region explosive events (EEs) are characterized by
non-Gaussian line profiles with enhanced wings at Doppler velocities
of 50-150 km s<SUP>-1</SUP>. They are believed to be the signature
of solar phenomena that are one of the main contributors to coronal
heating. The aim of this study is to investigate the link of EEs to
dynamic phenomena in the transition region and chromosphere in an active
region. We analyse observations simultaneously taken by the Interface
Region Imaging Spectrograph (IRIS) in the Si IV 1394 Å line and the
slit-jaw (SJ) 1400 Å images, and the Swedish 1-m Solar Telescope
in the Hα line. In total 24 events were found. They are associated
with small-scale loop brightenings in SJ 1400 Å images. Only four
events show a counterpart in the Hα-35 km s<SUP>-1</SUP> and Hα+35
km s<SUP>-1</SUP> images. Two of them represent brightenings in the
conjunction region of several loops that are also related to a bright
region (granular lane) in the Hα-35 km s<SUP>-1</SUP> and Hα+35
km s<SUP>-1</SUP> images. 16 are general loop brightenings that do
not show any discernible response in the Hα images. Six EEs appear
as propagating loop brightenings, from which two are associated with
dark jet-like features clearly seen in the Hα-35 km s<SUP>-1</SUP>
images. We found that chromospheric events with jet-like appearance
seen in the wings of the Hα line can trigger EEs in the transition
region and in this case the IRIS Si IV 1394 Å line profiles are
seeded with absorption components resulting from Fe II and Ni II. Our
study indicates that EEs occurring in active regions have mostly
upper-chromosphere/transition-region origin. We suggest that magnetic
reconnection resulting from the braidings of small-scale transition
region loops is one of the possible mechanisms of energy release that
are responsible for the EEs reported in this paper.
---------------------------------------------------------
Title: On the relationship between magnetic cancellation and UV
burst formation
Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.
2016MNRAS.463.2190N Altcode: 2016arXiv160806505N; 2016MNRAS.tmp.1156N
Burst-like events with signatures in the UV are often observed
co-spatial to strong line-of-sight photospheric magnetic fields. Several
authors, for example, have noted the spatial relationship between
Ellerman bombs (EBs) and moving magnetic features (MMFs), regions of
flux which disconnect from a sunspot or pore before propagating away
in the moat flow and often displaying evidence of cancellation. In
this article, data collected by the Solar Dynamics Observatory's
Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly
are analysed in an attempt to understand the potential links between
such cancellation and UV burst formation. Two MMFs from AR 11579,
three bi-poles from AR 11765, and six bi-poles (four of which were
co-spatial to Interface Region Imaging Spectrograph bursts) in AR 11850
were identified for analysis. All of these cancellation features were
found to have lifetimes of the order hours and cancellation rates of
the order 10<SUP>14</SUP>-10<SUP>15</SUP> Mx s<SUP>-1</SUP>. Hα line
wing data from the Dunn Solar Telescope's Interferometric BIdimensional
Spectrometer were also available for AR 11579 facilitating a discussion
of links between MMFs and EBs. Using an algebraic model of photospheric
magnetic reconnection, the measured cancellation rates are then used
to ascertain estimates of certain quantities (such as upflow speeds,
jet extents, and potential energy releases), which compared reasonably
to the properties of EBs reported within the literature. Our results
suggest that cancellation rates of the order measured here are capable
of supplying enough energy to drive certain UV bursts (including EBs),
however, they are not a guaranteeing condition for burst formation.
---------------------------------------------------------
Title: A prototype of the NFIRAOS to instrument thermo-mechanical
interface
Authors: Hill, Alexis; Byrnes, Peter; Fitzsimmons, Joeleff; Herriot,
Glen; Reshetov, Vlad; Szeto, Kei; Winter, Calvin; Pennec, Yan; Lambert,
Sam; Poulton, Evan; Doyle, Jeffrey
2016SPIE.9912E..02H Altcode:
NFIRAOS is the first light adaptive optics system for the Thirty Meter
Telescope (TMT). NFIRAOS components are maintained at a stable -30°C
+/-0.5°C by embedding an actively cooled refrigeration system in
the walls of the NFIRAOS enclosure. Three instruments are attached
to interface ports in the NFIRAOS enclosure and are required to be
thermally stable while the instrument rotates in place. Additionally,
instruments must be installed and removed while NFIRAOS is cold to avoid
lengthy cool-down cycles. A portion of the actively cooled enclosure
system and the interface has been prototyped at NRC-Herzberg. We
present a description of the design of the interface and results of
testing so far and lessons learned.
---------------------------------------------------------
Title: Magnetic Flux Cancellation in Ellerman Bombs
Authors: Reid, A.; Mathioudakis, M.; Doyle, J. G.; Scullion, E.;
Nelson, C. J.; Henriques, V.; Ray, T.
2016ApJ...823..110R Altcode: 2016arXiv160307100R
Ellerman Bombs (EBs) are often found to be co-spatial with bipolar
photospheric magnetic fields. We use Hα imaging spectroscopy along with
Fe I 6302.5 Å spectropolarimetry from the Swedish 1 m Solar Telescope
(SST), combined with data from the Solar Dynamic Observatory, to study
EBs and the evolution of the local magnetic fields at EB locations. EBs
are found via an EB detection and tracking algorithm. Using NICOLE
inversions of the spectropolarimetric data, we find that, on average,
(3.43 ± 0.49) × 10<SUP>24</SUP> erg of stored magnetic energy
disappears from the bipolar region during EB burning. The inversions
also show flux cancellation rates of 10<SUP>14</SUP>-10<SUP>15</SUP>
Mx s<SUP>-1</SUP> and temperature enhancements of 200 K at the detection
footpoints. We investigate the near-simultaneous flaring of EBs due to
co-temporal flux emergence from a sunspot, which shows a decrease in
transverse velocity when interacting with an existing, stationary area
of opposite polarity magnetic flux, resulting in the formation of the
EBs. We also show that these EBs can be fueled further by additional,
faster moving, negative magnetic flux regions.
---------------------------------------------------------
Title: High-cadence observations of spicular-type events on the Sun
Authors: Shetye, J.; Doyle, J. G.; Scullion, E.; Nelson, C. J.;
Kuridze, D.; Henriques, V.; Woeger, F.; Ray, T.
2016A&A...589A...3S Altcode: 2016arXiv160108087S
Context. Chromospheric observations taken at high-cadence and
high-spatial resolution show a range of spicule-like features,
including Type-I, Type-II (as well as rapid blue-shifted excursions
(RBEs) and rapid red-shifted excursions (RREs) which are thought to
be on-disk counterparts of Type-II spicules) and those which seem to
appear within a few seconds, which if interpreted as flows would imply
mass flow velocities in excess of 1000 km s<SUP>-1</SUP>. <BR /> Aims:
This article seeks to quantify and study rapidly appearing spicular-type
events. We also compare the multi-object multi-frame blind deconvolution
(MOMFBD) and speckle reconstruction techniques to understand if
these spicules are more favourably observed using a particular
technique. <BR /> Methods: We use spectral imaging observations taken
with the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1-m
Solar Telescope. Data was sampled at multiple positions within the Hα
line profile for both an on-disk and limb location. <BR /> Results: The
data is host to numerous rapidly appearing features which are observed
at different locations within the Hα line profile. The feature's
durations vary between 10-20 s and lengths around 3500 km. Sometimes,
a time delay in their appearance between the blue and red wings of
3-5 s is evident, whereas, sometimes they are near simultaneous. In
some instances, features are observed to fade and then re-emerge at
the same location several tens of seconds later. <BR /> Conclusions:
We provide the first statistical analysis of these spicules and suggest
that these observations can be interpreted as the line-of-sight (LOS)
movement of highly dynamic spicules moving in and out of the narrow 60
mÅ transmission filter that is used to observe in different parts of
the Hα line profile. The LOS velocity component of the observed fast
chromospheric features, manifested as Doppler shifts, are responsible
for their appearance in the red and blue wings of Hα line. Additional
work involving data at other wavelengths is required to investigate
the nature of their possible wave-like activity.
---------------------------------------------------------
Title: High Cadence Observations and Analysis of Spicular-type Events
Using CRISP Onboard SST
Authors: Shetye, J.; Doyle, J. G.; Scullion, E.; Nelson, C. J.;
Kuridze, D.
2016ASPC..504..115S Altcode:
We present spectroscopic and imaging observations of apparent ultra-fast
spicule-like features observed with CRisp Imaging SpectroPolarimeter
(CRISP) at the Swedish 1-m Solar Telescope (SST). The data shows
spicules with an apparent velocity above 500 km s<SUP>-1</SUP>,
very short lifetimes of up to 20 s and length/height around 3500
km. The spicules are seen as dark absorption structures in the Hα
wings ±516 mÅ, ±774 mÅ and ±1032 mÅ which suddenly appear and
disappear from the FOV. These features show a time delay in their
appearance in the blue and red wings by 3-5 s. We suggest that their
appearance/disappearance is due to their Doppler motion in and out of
the 60 mÅ filter. See Fig. 1 for the evolution of the event at two
line positions.
---------------------------------------------------------
Title: Solar Science with the Atacama Large Millimeter/Submillimeter
Array—A New View of Our Sun
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.;
Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu,
B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin,
P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz,
A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.;
Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary,
D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van
der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.;
Selhorst, C. L.; Barta, M.
2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new
powerful tool for observing the Sun at high spatial, temporal, and
spectral resolution. These capabilities can address a broad range
of fundamental scientific questions in solar physics. The radiation
observed by ALMA originates mostly from the chromosphere—a complex
and dynamic region between the photosphere and corona, which plays a
crucial role in the transport of energy and matter and, ultimately,
the heating of the outer layers of the solar atmosphere. Based on
first solar test observations, strategies for regular solar campaigns
are currently being developed. State-of-the-art numerical simulations
of the solar atmosphere and modeling of instrumental effects can help
constrain and optimize future observing modes for ALMA. Here we present
a short technical description of ALMA and an overview of past efforts
and future possibilities for solar observations at submillimeter and
millimeter wavelengths. In addition, selected numerical simulations
and observations at other wavelengths demonstrate ALMA's scientific
potential for studying the Sun for a large range of science cases.
---------------------------------------------------------
Title: Evolutionary tradeoffs in cellular composition across diverse
bacteria
Authors: Kempes, Christopher P.; Wang, Lawrence; Amend, Jan P.; Doyle,
John; Hoehler, Tori
2016ISME...10.2145K Altcode:
One of the most important classic and contemporary interests in biology
is the connection between cellular composition and physiological
function. Decades of research have allowed us to understand the
detailed relationship between various cellular components and processes
for individual species, and have uncovered common functionality
across diverse species. However, there still remains the need for
frameworks that can mechanistically predict the tradeoffs between
cellular functions and elucidate and interpret average trends across
species. Here we provide a comprehensive analysis of how cellular
composition changes across the diversity of bacteria as connected
with physiological function and metabolism, spanning five orders of
magnitude in body size. We present an analysis of the trends with cell
volume that covers shifts in genomic, protein, cellular envelope, RNA
and ribosomal content. We show that trends in protein content are more
complex than a simple proportionality with the overall genome size, and
that the number of ribosomes is simply explained by cross-species shifts
in biosynthesis requirements. Furthermore, we show that the largest
and smallest bacteria are limited by physical space requirements. At
the lower end of size, cell volume is dominated by DNA and protein
content—the requirement for which predicts a lower limit on cell
size that is in good agreement with the smallest observed bacteria. At
the upper end of bacterial size, we have identified a point at which
the number of ribosomes required for biosynthesis exceeds available
cell volume. Between these limits we are able to discuss systematic
and dramatic shifts in cellular composition. Much of our analysis
is connected with the basic energetics of cells where we show that
the scaling of metabolic rate is surprisingly superlinear with all
cellular components.
---------------------------------------------------------
Title: First simultaneous SST/CRISP and IRIS observations of a
small-scale quiet Sun vortex
Authors: Park, S. -H.; Tsiropoula, G.; Kontogiannis, I.; Tziotziou,
K.; Scullion, E.; Doyle, J. G.
2016A&A...586A..25P Altcode: 2015arXiv151206032P
Context. Ubiquitous small-scale vortices have recently been found
in the lower atmosphere of the quiet Sun in state-of-the-art solar
observations and in numerical simulations. <BR /> Aims: We investigate
the characteristics and temporal evolution of a granular-scale vortex
and its associated upflows through the photosphere and chromosphere
of a quiet Sun internetwork region. <BR /> Methods: We analyzed high
spatial and temporal resolution ground- and spaced-based observations
of a quiet Sun region. The observations consist of high-cadence time
series of wideband and narrowband images of both Hα 6563 Å and Ca
II 8542 Å lines obtained with the CRisp Imaging SpectroPolarimeter
(CRISP) instrument at the Swedish 1-m Solar Telescope (SST), as well
as ultraviolet imaging and spectral data simultaneously obtained by
the Interface Region Imaging Spectrograph (IRIS). <BR /> Results:
A small-scale vortex is observed for the first time simultaneously
in Hα, Ca II 8542 Å, and Mg II k lines. During the evolution of the
vortex, Hα narrowband images at -0.77 Å and Ca II 8542 Å narrowband
images at -0.5 Å, and their corresponding Doppler signal maps, clearly
show consecutive high-speed upflow events in the vortex region. These
high-speed upflows with a size of 0.5-1 Mm appear in the shape of
spiral arms and exhibit two distinctive apparent motions in the plane
of sky for a few minutes: (1) a swirling motion with an average speed
of 13 km s<SUP>-1</SUP> and (2) an expanding motion at a rate of
4-6 km s<SUP>-1</SUP>. Furthermore, the spectral analysis of Mg II k
and Mg II subordinate lines in the vortex region indicates an upward
velocity of up to ~8 km s<SUP>-1</SUP> along with a higher temperature
compared to the nearby quiet Sun chromosphere. <BR /> Conclusions:
The consecutive small-scale vortex events can heat the upper
chromosphere by driving continuous high-speed upflows through the lower
atmosphere. <P />Movies associated to Figs. 2 and 3 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201527440/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: SSALMON - The Solar Simulations for the Atacama Large
Millimeter Observatory Network
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson,
H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu,
B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.;
Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.;
Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier,
A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M.
2015AdSpR..56.2679W Altcode: 2015arXiv150205601W
The Solar Simulations for the Atacama Large Millimeter Observatory
Network (SSALMON) was initiated in 2014 in connection with two ALMA
development studies. The Atacama Large Millimeter/submillimeter Array
(ALMA) is a powerful new tool, which can also observe the Sun at
high spatial, temporal, and spectral resolution. The international
SSALMONetwork aims at co-ordinating the further development of solar
observing modes for ALMA and at promoting scientific opportunities
for solar physics with particular focus on numerical simulations,
which can provide important constraints for the observing modes and
can aid the interpretation of future observations. The radiation
detected by ALMA originates mostly in the solar chromosphere - a
complex and dynamic layer between the photosphere and corona, which
plays an important role in the transport of energy and matter and the
heating of the outer layers of the solar atmosphere. Potential targets
include active regions, prominences, quiet Sun regions, flares. Here,
we give a brief overview over the network and potential science cases
for future solar observations with ALMA.
---------------------------------------------------------
Title: Active region upflows. I. Multi-instrument observations
Authors: Vanninathan, K.; Madjarska, M. S.; Galsgaard, K.; Huang,
Z.; Doyle, J. G.
2015A&A...584A..38V Altcode: 2015arXiv150905624V
Context. We study upflows at the edges of active regions, called AR
outflows, using multi-instrument observations. <BR /> Aims: This study
intends to provide the first direct observational evidence of whether
chromospheric jets play an important role in furnishing mass that could
sustain coronal upflows. The evolution of the photospheric magnetic
field, associated with the footpoints of the upflow region and the
plasma properties of active region upflows is investigated with the
aim of providing information for benchmarking data-driven modelling of
this solar feature. <BR /> Methods: We spatially and temporally combine
multi-instrument observations obtained with the Extreme-ultraviolet
Imaging Spectrometer on board the Hinode, the Atmospheric Imaging
Assembly and the Helioseismic Magnetic Imager instruments on board
the Solar Dynamics Observatory and the Interferometric BI-dimensional
Spectro-polarimeter installed at the National Solar Observatory, Sac
Peak, to study the plasma parameters of the upflows and the impact of
the chromosphere on active region upflows. <BR /> Results: Our analysis
shows that the studied active region upflow presents similarly to
those studied previously, i.e. it displays blueshifted emission of 5-20
kms<SUP>-1</SUP> in Fe xii and Fe xiii and its average electron density
is 1.8 × 10<SUP>9</SUP> cm<SUP>-3</SUP> at 1 MK. The time variation
of the density is obtained showing no significant change (in a 3σ
error). The plasma density along a single loop is calculated revealing
a drop of 50% over a distance of ~20 000 km along the loop. We find a
second velocity component in the blue wing of the Fe xii and Fe xiii
lines at 105 kms<SUP>-1</SUP> reported only once before. For the first
time we study the time evolution of this component at high cadence and
find that it is persistent during the whole observing period of 3.5 h
with variations of only ±15 kms<SUP>-1</SUP>. We also, for the first
time, study the evolution of the photospheric magnetic field at high
cadence and find that magnetic flux diffusion is responsible for the
formation of the upflow region. High cadence Hα observations are used
to study the chromosphere at the footpoints of the upflow region. We
find no significant jet-like (spicule/rapid blue excursion) activity
to account for several hours/days of plasma upflow. The jet-like
activity in this region is not continuous and blueward asymmetries
are a bare minimum. Using an image enhancement technique for imaging
and spectral data, we show that the coronal structures seen in the
AIA 193 Å channel are comparable to the EIS Fe xii images, while
images in the AIA 171 Å channel reveal additional loops that are a
result of contribution from cooler emission to this channel. <BR />
Conclusions: Our results suggest that at chromospheric heights there
are no signatures that support the possible contribution of spicules
to active region upflows. We suggest that magnetic flux diffusion is
responsible for the formation of the coronal upflows. The existence of
two velocity components possibly indicates the presence of two different
flows, which are produced by two different physical mechanisms,
e.g. magnetic reconnection and pressure-driven jets. <P />Movies
associated to Figs. A.1-A.3 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201526340/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Searching for I-band variability in stars in the M/L spectral
transition region
Authors: Ramsay, Gavin; Hakala, Pasi; Doyle, J. Gerry
2015MNRAS.453.1484R Altcode: 2015arXiv150707784R
We report on I-band photometric observations of 21 stars with spectral
types between M8 and L4 made using the Isaac Newton Telescope. The
total amount of time for observations which had a cadence of <2.3
min was 58.5 h, with additional data with lower cadence. We test
for photometric variability using the Kruskal-Wallis H-test and find
that four sources (2MASS J10224821+5825453, 2MASS J07464256+2000321,
2MASS J16262034+3925190 and 2MASS J12464678+4027150) were found to be
significantly variable at least on one epoch. Three of these sources
are reported as photometrically variable for the first time. If we
include sources which were deemed marginally variable, the number
of variable sources is 6 (29 per cent). No flares were detected from
any source. The percentage of sources which we found were variable is
similar to previous studies. We summarize the mechanisms which have
been put forward to explain the light curves of brown dwarfs.
---------------------------------------------------------
Title: Magnetospherically driven optical and radio aurorae at the
end of the stellar main sequence
Authors: Hallinan, G.; Littlefair, S. P.; Cotter, G.; Bourke, S.;
Harding, L. K.; Pineda, J. S.; Butler, R. P.; Golden, A.; Basri, G.;
Doyle, J. G.; Kao, M. M.; Berdyugina, S. V.; Kuznetsov, A.; Rupen,
M. P.; Antonova, A.
2015Natur.523..568H Altcode: 2015arXiv150708739H
Aurorae are detected from all the magnetized planets in our Solar
System, including Earth. They are powered by magnetospheric current
systems that lead to the precipitation of energetic electrons into
the high-latitude regions of the upper atmosphere. In the case of the
gas-giant planets, these aurorae include highly polarized radio emission
at kilohertz and megahertz frequencies produced by the precipitating
electrons, as well as continuum and line emission in the infrared,
optical, ultraviolet and X-ray parts of the spectrum, associated
with the collisional excitation and heating of the hydrogen-dominated
atmosphere. Here we report simultaneous radio and optical spectroscopic
observations of an object at the end of the stellar main sequence,
located right at the boundary between stars and brown dwarfs, from which
we have detected radio and optical auroral emissions both powered by
magnetospheric currents. Whereas the magnetic activity of stars like
our Sun is powered by processes that occur in their lower atmospheres,
these aurorae are powered by processes originating much further out in
the magnetosphere of the dwarf star that couple energy into the lower
atmosphere. The dissipated power is at least four orders of magnitude
larger than what is produced in the Jovian magnetosphere, revealing
aurorae to be a potentially ubiquitous signature of large-scale
magnetospheres that can scale to luminosities far greater than those
observed in our Solar System. These magnetospheric current systems may
also play a part in powering some of the weather phenomena reported
on brown dwarfs.
---------------------------------------------------------
Title: Ellerman Bombs with Jets: Cause and Effect
Authors: Reid, A.; Mathioudakis, M.; Scullion, E.; Doyle, J. G.;
Shelyag, S.; Gallagher, P.
2015ApJ...805...64R Altcode: 2015arXiv150305359R
Ellerman Bombs (EBs) are thought to arise as a result of photospheric
magnetic reconnection. We use data from the Swedish 1 m Solar
Telescope to study EB events on the solar disk and at the limb. Both
data sets show that EBs are connected to the foot points of forming
chromospheric jets. The limb observations show that a bright structure
in the Hα blue wing connects to the EB initially fueling it, leading
to the ejection of material upwards. The material moves along a loop
structure where a newly formed jet is subsequently observed in the
red wing of Hα. In the disk data set, an EB initiates a jet which
propagates away from the apparent reconnection site within the EB
flame. The EB then splits into two, with associated brightenings in
the inter-granular lanes. Micro-jets are then observed, extending
to 500 km with a lifetime of a few minutes. Observed velocities of
the micro-jets are approximately 5-10 km s<SUP>-1</SUP>, while their
chromospheric counterparts range from 50 to 80 km s<SUP>-1</SUP>. MURaM
simulations of quiet Sun reconnection show that micro-jets with
properties similar to those of the observations follow the line of
reconnection in the photosphere, with associated Hα brightening at
the location of increased temperature.
---------------------------------------------------------
Title: The view from K2: questioning the traditional view of flaring
on early dM stars
Authors: Ramsay, Gavin; Doyle, J. Gerry
2015MNRAS.449.3015R Altcode: 2015arXiv150302696R
We use K2 short cadence data obtained over a duration of 50 d during
Campaign 0 to observe two M1V dwarf stars, TYC 1330-879-1 and RXJ
0626+2349. We provide an overview of our data analysis, in particular,
making a comparison between using a fixed set of pixels and an aperture
which follows the position of the source. We find that this moving
aperture approach can give fewer non-astrophysical features compared
to a fixed aperture. Both sources shows flares as energetic as observed
from several M4V stars using both Kepler and ground-based telescopes. We
find that the flare energy distribution of the sources shown here are
very similar to the less active M3-M5 stars but are ∼8 times less
likely to produce a flare of a comparable energy to the more active
M0-M5 stars. We discuss the biases and sources of systematic errors when
comparing the activity of stars derived from different instruments. We
conclude that K2 observations will provide an excellent opportunity
to perform a census of flare activity across the full range of M dwarf
spectral class and hence the physical mechanisms which power them.
---------------------------------------------------------
Title: New Upper Limit on the Electron's Electric Dipole Moment
Authors: Doyle, John
2015APS..APR.B8003D Altcode:
The ACME collaboration has measured the electron's electric dipole
moment (eEDM) to be d<SUB>e</SUB> =(- 2 . 1 +/- 3 .7<SUB>stat</SUB> +/-
2 .5<SUB>syst</SUB>) ×10<SUP>-29</SUP> e .cm. This corresponds to an
upper limit of | d<SUB>e</SUB> | < 8 . 7 × 10<SUP>-29</SUP> e .cm
with 90 percent confidence, which represents an order of magnitude
improvement on the previous best limit. We describe our method of
measuring the eEDM using a buffer gas cooled beam of thorium monoxide
(ThO) and discuss our approach to finding and quantifying systematic
effects. This results constrains T-violating physics at the TeV energy
scale. <P />This project is supported by NSF.</p>
---------------------------------------------------------
Title: A coronal wave and an asymmetric eruptive filament in SUMER,
CDS, EIT, and TRACE co-observations
Authors: Madjarska, M. S.; Doyle, J. G.; Shetye, J.
2015A&A...575A..39M Altcode: 2014arXiv1412.1984M
Context. The investigation covers the complex subject of coronal waves
and the phenomena contributing to and/or causing their formation. <BR
/> Aims: The objectives of the present study is to provide a better
physical understanding of the complex inter-relation and evolution
of several solar coronal features comprising a double-peak flare,
a coronal dimming caused by a coronal mass ejection (CME), a
CME-driven compression, and a fast-mode wave. For the first time,
the evolution of an asymmetric eruptive filament is analysed in
simultaneous Solar Ultraviolet Measurement of Emitted Radiation
(SUMER) spectroscopic and Transition Region and Coronal Explorer
(TRACE) and Extreme-ultraviolet Imaging Telescope (EIT) imaging
data. <BR /> Methods: We use imaging observations from EIT and
TRACE in the 195 Å channel and spectroscopic observations from the
Coronal Diagnostic Spectrometer (CDS) in a rastering and SUMER in a
sit-and-stare observing mode. The SUMER spectra cover spectral lines
with formation temperatures from log T(K) ~ 4.0 to 6.1. <BR /> Results:
Although the event was already analysed in two previous studies,
our analysis brings a wealth of new information on the dynamics and
physical properties of the observed phenomena. We found that the dynamic
event is related to a complex flare with two distinct impulsive peaks,
one according to the Geostationary Operational Environmental Satellite
(GOES) classification as C1.1 and the second - C1.9. The first energy
release triggers a fast-mode wave and a CME with a clear CME driven
compression ahead of it. This activity is related to, or possibly
caused, by an asymmetric filament eruption. The filament is observed to
rise with its leading edge moving at a speed of ~300 kms<SUP>-1</SUP>
detected both in the SUMER and CDS data. The rest of the filament body
moves at only ~150 kms<SUP>-1</SUP> while untwisting. No signature is
found of the fast-mode wave in the SUMER data, suggesting that the
plasma disturbed by the wave had temperatures above 600 000 K. The
erupting filament material is found to emit only in spectral lines at
transition region temperatures. Earlier identification of a coronal
response detected in the Mg x 609.79 Å line is found to be caused by
a blend from the O iv 609.83 Å line. <BR /> Conclusions: We present a
unique analysis of the complex phenomenon called "EIT/coronal wave",
confirming its bimodal nature. We suggest that the disintegration of
the dimming/CME and the CME-driven compression are either caused by
a CME-CME interaction taking place in the low solar atmosphere or by
an impulsive CME cavity overexpansion in the low solar atmosphere. <P
/>A movie associated to Fig. A.1 is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424754/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Low-resolution optical spectra of ultracool dwarfs with
OSIRIS/GTC
Authors: Metodieva, Y.; Antonova, A.; Golev, V.; Dimitrov, D.;
García-Álvarez, D.; Doyle, J. G.
2015MNRAS.446.3878M Altcode: 2014arXiv1412.2736M
We present the results of low-resolution optical spectroscopy
with OSIRIS/GTC (Optical System for Imaging and Low Resolution
Integrated Spectroscopy/Gran Telescopio Canarias) for a sample
of ultracool dwarfs. For a subsample of seven objects, based on 2
Micron Sky Survey (2MASS) NIR photometric colours, a `photometric'
spectral type is determined and compared to the results of the optical
spectroscopy. For the stars, showing Hα line in emission, equivalent
widths were measured, and the ratio of Hα to bolometric luminosity
were calculated. We find that two dwarfs show the presence of magnetic
activity over long periods, LP 326-21 - quasi-constant-like, and 2MASS
J17071830+6439331 - variable.
---------------------------------------------------------
Title: A multiwavelength study of the M dwarf binary YY Geminorum
Authors: Butler, C. J.; Erkan, N.; Budding, E.; Doyle, J. G.; Foing,
B.; Bromage, G. E.; Kellett, B. J.; Frueh, M.; Huovelin, J.; Brown,
A.; Neff, J. E.
2015MNRAS.446.4205B Altcode: 2015arXiv150103930B
We review the results of the 1988 multiwavelength campaign on
the late-type eclipsing binary YY Geminorum. Observations include:
broad-band optical and near-infrared photometry, simultaneous optical
and ultraviolet (IUE) spectroscopy, X-ray (Ginga) and radio (VLA)
data. From models fitted to the optical light curves, fundamental
physical parameters have been determined together with evidence for
transient maculations (spots) located near quadrature longitudes and
intermediate latitudes. Eclipses were observed at optical, ultraviolet
and radio wavelengths. Significant drops in 6 cm radio emission near the
phases of both primary and secondary eclipse indicate relatively compact
radio emitting volumes that may lie between the binary components. IUE
observations during secondary eclipse are indicative of a uniform
chromosphere saturated with Mg II emission and an extended volume of
Lyα emission. Profile fitting of high-dispersion Hα spectra confirms
the chromospheric saturation and indicates significant Hα opacity to
heights of a few per cent of the photospheric radius. There is evidence
for an enhanced Hα emission region visible near phase 0.25-0.35
which may be associated with a large spot on the primary and with two
small optical flares which were also observed at other wavelengths:
one in microwave radiation and the other in X-rays. For both flares,
L<SUB>X</SUB>/L<SUB>opt</SUB> is consistent with energy release in
closed magnetic structures.
---------------------------------------------------------
Title: Stellar flares observed by LOFT: implications for the physics
of coronae and for the "space weather" environment of extrasolar
planets
Authors: Drake, S. A.; Behar, E.; Doyle, J. G.; Güdel, M.; Hamaguchi,
K.; Kowalski, A. F.; Maccarone, T.; Osten, R. A.; Peretz, U.; Wolk,
S. J.
2015arXiv150102771D Altcode:
This is a White Paper in support of the mission concept of the Large
Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA
mission. We discuss the potential of LOFT for the study of stellar
flares. For a summary, we refer to the paper.
---------------------------------------------------------
Title: Small-scale Structuring of Ellerman Bombs at the Solar Limb
Authors: Nelson, C. J.; Scullion, E. M.; Doyle, J. G.; Freij, N.;
Erdélyi, R.
2015ApJ...798...19N Altcode: 2014arXiv1410.5715N
Ellerman bombs (EBs) have been widely studied in recent years due to
their dynamic, explosive nature and apparent links to the underlying
photospheric magnetic field implying that they may be formed by
magnetic reconnection in the photosphere. Despite a plethora of
researches discussing the morphologies of EBs, there has been a limited
investigation of how these events appear at the limb, specifically,
whether they manifest as vertical extensions away from the disk. In
this article, we make use of high-resolution, high-cadence observations
of an Active Region at the solar limb, collected by the CRisp Imaging
SpectroPolarimeter (CRISP) instrument, to identify EBs and infer their
physical properties. The upper atmosphere is also probed using the
Solar Dynamic Observatory's Atmospheric Imaging Assembly (SDO/AIA). We
analyze 22 EB events evident within these data, finding that 20 appear
to follow a parabolic path away from the solar surface at an average
speed of 9 km s<SUP>-1</SUP>, extending away from their source by 580
km, before retreating back at a similar speed. These results show strong
evidence of vertical motions associated with EBs, possibly explaining
the dynamical "flaring" (changing in area and intensity) observed
in on-disk events. Two in-depth case studies are also presented that
highlight the unique dynamical nature of EBs within the lower solar
atmosphere. The viewing angle of these observations allows for a direct
linkage between these EBs and other small-scale events in the Hα line
wings, including a potential flux emergence scenario. The findings
presented here suggest that EBs could have a wider-reaching influence
on the solar atmosphere than previously thought, as we reveal a direct
linkage between EBs and an emerging small-scale loop, and other near-by
small-scale explosive events. However, as previous research found,
these extensions do not appear to impact upon the Hα line core,
and are not observed by the SDO/AIA EUV filters.
---------------------------------------------------------
Title: Erratum: Erratum to: Off-limb (Spicule) DEM Distribution from
SoHO/SUMER Observations
Authors: Vanninathan, K.; Madjarska, M. S.; Scullion, E.; Doyle, J. G.
2014SoPh..289.4749V Altcode: 2014SoPh..tmp..127V
No abstract at ADS
---------------------------------------------------------
Title: Explosive Events on a Subarcsecond Scale in IRIS Observations:
A Case Study
Authors: Huang, Zhenghua; Madjarska, Maria S.; Xia, Lidong; Doyle,
J. G.; Galsgaard, Klaus; Fu, Hui
2014ApJ...797...88H Altcode: 2014arXiv1409.6425H
We present a study of a typical explosive event (EE) at subarcsecond
scale witnessed by strong non-Gaussian profiles with blue- and
redshifted emission of up to 150 km s<SUP>-1</SUP> seen in the
transition region Si IV 1402.8 Å, and the chromospheric Mg II
k 2796.4 Å and C II 1334.5 Å observed by the Interface Region
Imaging Spectrograph (IRIS) at unprecedented spatial and spectral
resolution. For the first time an EE is found to be associated with
very small-scale (~120 km wide) plasma ejection followed by retraction
in the chromosphere. These small-scale jets originate from a compact
bright-point-like structure of ~1.”5 size as seen in the IRIS 1330
Å images. SDO/AIA and SDO/HMI co-observations show that the EE lies
in the footpoint of a complex loop-like brightening system. The EE is
detected in the higher temperature channels of AIA 171 Å, 193 Å,
and 131 Å, suggesting that it reaches a higher temperature of log
T = 5.36 ± 0.06 (K). Brightenings observed in the AIA channels with
durations 90-120 s are probably caused by the plasma ejections seen
in the chromosphere. The wings of the C II line behave in a similar
manner to the Si IV'S, indicating close formation temperatures, while
the Mg II k wings show additional Doppler-shifted emission. Magnetic
convergence or emergence followed by cancellation at a rate of 5 ×
10<SUP>14</SUP> Mx s<SUP>-1</SUP> is associated with the EE region. The
combined changes of the locations and the flux of different magnetic
patches suggest that magnetic reconnection must have taken place. Our
results challenge several theories put forward in the past to explain
non-Gaussian line profiles, i.e., EEs. Our case study on its own,
however, cannot reject these theories; thus, further in-depth studies
on the phenomena producing EEs are required.
---------------------------------------------------------
Title: The M4.5V flare star AF Psc as seen in K2 engineering data
Authors: Ramsay, Gavin; Doyle, J. Gerry
2014MNRAS.442.2926R Altcode: 2014arXiv1405.7318R
We present the light curve of the little studied flare star AF Psc
(M4.5V) obtained using engineering data from the K2 mission. Data were
obtained in long-cadence mode giving an effective exposure of 29 min
and nearly 9 d of coverage. A clear modulation on a period of 1.08
d was seen which is the signature of the stellar rotation period. We
identify 14 flares in the light curve, with the most luminous flares
apparently coming from the same active region. We compare the flare
characteristics of AF Psc to two M4V flare stars studied using Kepler
data. The K2 mission will present a unique opportunity to study the
rotation and flare properties of late-type dwarf stars with different
ages and mass.
---------------------------------------------------------
Title: Hα spectroscopy and multiwavelength imaging of a solar flare
caused by filament eruption
Authors: Huang, Z.; Madjarska, M. S.; Koleva, K.; Doyle, J. G.;
Duchlev, P.; Dechev, M.; Reardon, K.
2014A&A...566A.148H Altcode: 2014arXiv1405.2194H
Context. We study a sequence of eruptive events including filament
eruption, a GOES C4.3 flare, and a coronal mass ejection. <BR /> Aims:
We aim to identify the possible trigger(s) and precursor(s) of the
filament destabilisation, investigate flare kernel characteristics,
flare ribbons/kernels formation and evolution, study the interrelation
of the filament-eruption/flare/coronal-mass-ejection phenomena as
part of the integral active-region magnetic field configuration, and
determine Hα line profile evolution during the eruptive phenomena. <BR
/> Methods: Multi-instrument observations are analysed including Hα
line profiles, speckle images at Hα - 0.8 Å and Hα + 0.8 Å from
IBIS at DST/NSO, EUV images and magnetograms from the SDO, coronagraph
images from STEREO, and the X-ray flux observations from Fermi and
GOES. <BR /> Results: We establish that the filament destabilisation
and eruption are the main triggers for the flaring activity. A
surge-like event with a circular ribbon in one of the filament
footpoints is determined as the possible trigger of the filament
destabilisation. Plasma draining in this footpoint is identified as
the precursor for the filament eruption. A magnetic flux emergence
prior to the filament destabilisation followed by a high rate of flux
cancellation of 1.34 × 10<SUP>16</SUP> Mx s<SUP>-1</SUP> is found
during the flare activity. The flare X-ray lightcurves reveal three
phases that are found to be associated with three different ribbons
occurring consecutively. A kernel from each ribbon is selected and
analysed. The kernel lightcurves and Hα line profiles reveal that the
emission increase in the line centre is stronger than that in the line
wings. A delay of around 5-6 min is found between the increase in the
line centre and the occurrence of red asymmetry. Only red asymmetry is
observed in the ribbons during the impulsive phases. Blue asymmetry
is only associated with the dynamic filament. <P />Appendix A and
movie associated to Fig. A.4 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201323097/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Intensity Enhancement of O VI Ultraviolet Emission Lines in
Solar Spectra due to Opacity
Authors: Keenan, F. P.; Doyle, J. G.; Madjarska, M. S.; Rose, S. J.;
Bowler, L. A.; Britton, J.; McCrink, L.; Mathioudakis, M.
2014ApJ...784L..39K Altcode: 2014arXiv1403.1470K
Opacity is a property of many plasmas. It is normally expected that if
an emission line in a plasma becomes optically thick, then its intensity
ratio to that of another transition that remains optically thin
should decrease. However, radiative transfer calculations undertaken
both by ourselves and others predict that under certain conditions the
intensity ratio of an optically thick to an optically thin line can show
an increase over the optically thin value, indicating an enhancement
in the former. These conditions include the geometry of the emitting
plasma and its orientation to the observer. A similar effect can
take place between lines of differing optical depths. While previous
observational studies have focused on stellar point sources, here we
investigate the spatially resolved solar atmosphere using measurements
of the I(1032 Å)/I(1038 Å) intensity ratio of O VI in several regions
obtained with the Solar Ultraviolet Measurements of Emitted Radiation
instrument on board the Solar and Heliospheric Observatory satellite. We
find several I(1032 Å)/I(1038 Å) ratios observed on the disk to be
significantly larger than the optically thin value of 2.0, providing
the first detection (to our knowledge) of intensity enhancement in
the ratio arising from opacity effects in the solar atmosphere. The
agreement between observation and theory is excellent and confirms
that the O VI emission originates from a slab-like geometry in the
solar atmosphere, rather than from cylindrical structures.
---------------------------------------------------------
Title: Excitation of an outflow from the lower solar atmosphere and
a co-temporal EUV transient brightening
Authors: Nelson, C. J.; Doyle, J. G.
2013A&A...560A..31N Altcode: 2013arXiv1310.8490N
<BR /> Aims: We analyse an absorption event within the Hα line wings,
which has been identified as a surge, and the co-spatial evolution
of an EUV brightening, with spatial and temporal scales analogous
to a small blinker. <BR /> Methods: We conduct a multi-wavelength,
multi-instrument analysis using high-cadence, high-resolution data,
collected by the Interferometric BIdimensional Spectrometer on the
Dunn Solar Telescope, as well as the space-borne Atmospheric Imaging
Assembly and Helioseismic and Magnetic Imager instruments on board
the Solar Dynamics Observatory. <BR /> Results: One large absorption
event situated within the plage region trailing the lead sunspot of
AR 11579 is identified within the Hα line wings. This event is found
to be co-spatially linked to a medium-scale (around 4” in diameter)
brightening within the transition region and corona. This ejection
appears to have a parabolic evolution, first forming in the Hα blue
wing before fading and reappearing in the Hα red wing, and comprises a
number of smaller fibril events. The line-of-sight photospheric magnetic
field shows no evidence of cancellation leading to this event. <BR />
Conclusions: Our research has identified clear evidence that at least
a subset of transient brightening events in the transition region is
linked to the influx of cooler plasma from the lower solar atmosphere
during large eruptive events, such as surges. These observations agree
with previous numerical researches on the nature of blinkers and,
therefore, suggest that magnetic reconnection is the driver of the
analysed surge events; however, further research is required to confirm
this. <P />A movie attached to Fig. 2 is available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Ellerman Bombs—Evidence for Magnetic Reconnection in the
Lower Solar Atmosphere
Authors: Nelson, C. J.; Shelyag, S.; Mathioudakis, M.; Doyle, J. G.;
Madjarska, M. S.; Uitenbroek, H.; Erdélyi, R.
2013ApJ...779..125N Altcode: 2013arXiv1310.7756N
The presence of photospheric magnetic reconnection has long been thought
to give rise to short and impulsive events, such as Ellerman bombs (EBs)
and Type II spicules. In this article, we combine high-resolution,
high-cadence observations from the Interferometric BIdimensional
Spectrometer and Rapid Oscillations in the Solar Atmosphere instruments
at the Dunn Solar Telescope, National Solar Observatory, New Mexico,
with co-aligned Solar Dynamics Observatory Atmospheric Imaging Assembly
and Hinode Solar Optical Telescope (SOT) data to observe small-scale
events situated within an active region. These data are then compared
with state-of-the-art numerical simulations of the lower atmosphere
made using the MURaM code. It is found that brightenings, in both the
observations and the simulations, of the wings of the Hα line profile,
interpreted as EBs, are often spatially correlated with increases in
the intensity of the Fe I λ6302.5 line core. Bipolar regions inferred
from Hinode/SOT magnetic field data show evidence of flux cancellation
associated, co-spatially, with these EBs, suggesting that magnetic
reconnection could be a driver of these high-energy events. Through
the analysis of similar events in the simulated lower atmosphere,
we are able to infer that line profiles analogous to the observations
occur co-spatially with regions of strong opposite-polarity magnetic
flux. These observed events and their simulated counterparts are
interpreted as evidence of photospheric magnetic reconnection at scales
observable using current observational instrumentation.
---------------------------------------------------------
Title: Short-duration high-amplitude flares detected on the M dwarf
star KIC 5474065
Authors: Ramsay, Gavin; Doyle, J. Gerry; Hakala, Pasi; Garcia-Alvarez,
David; Brooks, Adam; Barclay, Thomas; Still, Martin
2013MNRAS.434.2451R Altcode: 2013MNRAS.tmp.1831R; 2013arXiv1306.5938R
Using data obtained during the RATS-Kepler project, we identified one
short-duration flare in a 1 h sequence of ground-based photometry of the
dwarf star KIC 5474065. Observations made using Gran Telescopio Canarias
show that it is a star with an M4V spectral type. Kepler observations
made using 1 min sampling show that KIC 5474065 exhibits large-amplitude
(δF/F > 0.4) optical flares which have a duration as short as 10
min. We compare the energy distribution of flares from KIC 5474065
with that of KIC 9726699, which has also been observed using 1-min
sampling, and ground-based observations of other M dwarf stars in the
literature. We discuss the possible implications these short-duration,
relatively low-energy flares would have on the atmosphere of exoplanets
orbiting in the habitable zone of these flare stars.
---------------------------------------------------------
Title: Diagnosing transient ionization in dynamic events
Authors: Doyle, J. G.; Giunta, A.; Madjarska, M. S.; Summers, H.;
O'Mullane, M.; Singh, A.
2013A&A...557L...9D Altcode: 2013arXiv1307.8251D
<BR /> Aims: The present study aims to provide a diagnostic line ratio
that will enable the observer to determine whether a plasma is in
a state of transient ionization. <BR /> Methods: We use the Atomic
Data and Analysis Structure (ADAS) to calculate line contribution
functions for two lines, Si iv 1394 Å and O iv 1401 Å, formed in
the solar transition region. The generalized collisional-radiative
theory is used. It includes all radiative and electron collisional
processes, except for photon-induced processes. State-resolved direct
ionization and recombination to and from the next ionization stage
are also taken into account. <BR /> Results: For dynamic bursts
with a decay time of a few seconds, the Si iv 1394 Å line can be
enhanced by a factor of 2-4 in the first fraction of a second with
the peak in the line contribution function occurring initially at a
higher electron temperature due to transient ionization compared to
ionization equilibrium conditions. On the other hand, the O iv 1401 Å
does not show such any enhancement. Thus the ratio of these two lines,
which can be observed with the Interface Region Imaging Spectrograph,
can be used as a diagnostic of transient ionization. <BR /> Conclusions:
We show that simultaneous high-cadence observations of two lines formed
in the solar transition region may be used as a direct diagnostic of
whether the observed plasma is in transient ionization. The ratio of
these two lines can change by a factor of four in a few seconds owing
to transient ionization alone.
---------------------------------------------------------
Title: Measurement of the Electron's Electric Dipole Moment in
Thorium Monoxide
Authors: Baron, J.; Demille, D.; Doyle, J.; Gabrielse, G.; Hess, P.;
Hutzler, N.; Oleary, B.; Panda, C.; Petrik, E.; Spaun, B.
2013mss..confETF06B Altcode:
Some polar diatomic molecules have large effective internal
electric fields ({E}_{eff}∼10^{11} V/cm that can be used to make
measurements of the electron's electric dipole moment (eEDM) with
unprecedented sensitivity. By performing precision spectroscopy on
the metastable H ^{3}Δ_{1} state of ThO in a cryogenic buffer gas
beam, we have demonstrated a statistical sensitivity to the eEDM of
δ d_{e}≈1×10^{-28} e\cdot cm/√{T/{days}}, which is competitive
with the current experimental limit, |d_{e}|<1.05×10^{-27}e\cdot
cm. The existence of a non-zero eEDM on this level would be evidence
for the existence of interactions that violate parity and time-reversal
symmetries that are not included in the Standard Model. Many extensions
to the Standard Model (in particular supersymmetric theories) predict
the eEDM to be very close to the current experimental limit. We present
an overview and discuss the characterization of systematic errors
in this experiment. <P />E. R. Meyer and J. L. Bohn, Phys. Rev. A
78, 010502 (2008) <P />J. Hudson, D. Kara, J. Smallman, B. Sauer,
M. Tarbutt, E. Hinds, Nature 473 493 (2011) <P />This work is supported
by the NSF.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Radio survey of ultracool dwarfs
(Antonova+, 2013)
Authors: Antonova, A.; Hallinan, G.; Doyle, J. G.; Yu, S.; Kuznetsov,
A.; Metodieva, Y.; Golden, A.; Cruz, K. L.
2013yCat..35490131A Altcode: 2013yCat..35499131A
The observations were conducted with the NRAO Very Large Array in the
period 09 August-09 September 2009 using the standard continuum mode
with 2x50MHz contiguous bands. <P />(1 data file).
---------------------------------------------------------
Title: Statistical Analysis of Small Ellerman Bomb Events
Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.; Huang, Z.;
Madjarska, M. S.; Mathioudakis, M.; Mumford, S. J.; Reardon, K.
2013SoPh..283..307N Altcode: 2013arXiv1301.1351N
The properties of Ellerman bombs (EBs), small-scale brightenings in
the Hα line wings, have proved difficult to establish because their
size is close to the spatial resolution of even the most advanced
telescopes. Here, we aim to infer the size and lifetime of EBs using
high-resolution data of an emerging active region collected using
the Interferometric BIdimensional Spectrometer (IBIS) and Rapid
Oscillations of the Solar Atmosphere (ROSA) instruments as well as
the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO). We develop an algorithm to track EBs through their
evolution, finding that EBs can often be much smaller (around 0.3″)
and shorter-lived (less than one minute) than previous estimates. A
correlation between G-band magnetic bright points and EBs is also
found. Combining SDO/HMI and G-band data gives a good proxy of the
polarity for the vertical magnetic field. It is found that EBs often
occur both over regions of opposite polarity flux and strong unipolar
fields, possibly hinting at magnetic reconnection as a driver of these
events.The energetics of EB events is found to follow a power-law
distribution in the range of a nanoflare (10<SUP>22−25</SUP> ergs).
---------------------------------------------------------
Title: Looking for a Pulse: A Search for Rotationally Modulated
Radio Emission from the Hot Jupiter, τ Boötis b
Authors: Hallinan, G.; Sirothia, S. K.; Antonova, A.; Ishwara-Chandra,
C. H.; Bourke, S.; Doyle, J. G.; Hartman, J.; Golden, A.
2013ApJ...762...34H Altcode: 2012arXiv1210.8259H
Hot Jupiters have been proposed as a likely population of low-frequency
radio sources due to electron cyclotron maser emission of similar nature
to that detected from the auroral regions of magnetized solar system
planets. Such emission will likely be confined to specific ranges of
orbital/rotational phase due to a narrowly beamed radiation pattern. We
report on GMRT 150 MHz radio observations of the hot Jupiter τ Boötis
b, consisting of 40 hr carefully scheduled to maximize coverage of the
planet's 79.5 hr orbital/rotational period in an effort to detect such
rotationally modulated emission. The resulting image is the deepest
yet published at these frequencies and leads to a 3σ upper limit on
the flux density from the planet of 1.2 mJy, two orders of magnitude
lower than predictions derived from scaling laws based on solar system
planetary radio emission. This represents the most stringent upper
limits for both quiescent and rotationally modulated radio emission from
a hot Jupiter yet achieved and suggests that either (1) the magnetic
dipole moment of τ Boötis b is insufficient to generate the surface
field strengths of >50 G required for detection at 150 MHz or (2)
Earth lies outside the beaming pattern of the radio emission from
the planet.
---------------------------------------------------------
Title: Ellerman bombs: small-scale brightenings in the photosphere
Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.; Madjarska, M.;
Mumford, S. J.
2013MmSAI..84..436N Altcode:
Observations of small-scale events in the solar atmosphere are
limited by the spatial and temporal resolutions of the current crop
of observational instruments. Both high-cadence and high-resolution
observations of the photosphere have shown the continued dynamics to
extremely small-scales. Ellerman bombs, brightening events in the
wings of the Halpha line profile, are one example of small-scale,
short-lived events which have been widely studied due to their fast
dynamics in recent years. By combining the Interferometric BIdimensional
Spectrometer (IBIS) instrument with the Helioseismic and Magnetic Imager
(HMI/SDO), we show the small-scale nature of these events, as well as
their link to the background magnetic field. It is found that EBs can
be much smaller and shorter-lived than previous estimates have stated,
implying the continued dynamics of the solar atmosphere below current
observational limits.
---------------------------------------------------------
Title: Volume-limited radio survey of ultracool dwarfs
Authors: Antonova, A.; Hallinan, G.; Doyle, J. G.; Yu, S.; Kuznetsov,
A.; Metodieva, Y.; Golden, A.; Cruz, K. L.
2013A&A...549A.131A Altcode: 2012arXiv1212.3464A
<BR /> Aims: We aim to increase the sample of ultracool dwarfs
studied in the radio domain to allow a more statistically significant
understanding of the physical conditions associated with these
magnetically active objects. <BR /> Methods: We conducted a
volume-limited survey at 4.9 GHz of 32 nearby ultracool dwarfs with
spectral types covering the range M7-T8. A statistical analysis was
performed on the combined data from the present survey and previous
radio observations of ultracool dwarfs. <BR /> Results: Whilst no
radio emission was detected from any of the targets, significant
upper limits were placed on the radio luminosities that are below
the luminosities of previously detected ultracool dwarfs. Combining
our results with those from the literature gives a detection rate for
dwarfs in the spectral range M7-L3.5 of ~9%. In comparison, only one
dwarf later than L3.5 is detected in 53 observations. We report the
observed detection rate as a function of spectral type and the number
distribution of the dwarfs as a function of spectral type and rotation
velocity. <BR /> Conclusions: The radio observations to date point to
a drop in the detection rate toward the ultracool dwarfs. However,
the emission levels of detected ultracool dwarfs are comparable to
those of earlier type active M dwarfs, which may imply that a mildly
relativistic electron beam or a strong magnetic field can exist in
ultracool dwarfs. Fast rotation may be a sufficient condition to
produce magnetic fields strengths of several hundred Gauss to several
kilo Gauss, as suggested by the data for the active ultracool dwarfs
with known rotation rates. A possible reason for the non-detection
of radio emission from some dwarfs is that maybe the centrifugal
acceleration mechanism in these dwarfs is weak (due to a low rotation
rate) and thus cannot provide the necessary density and/or energy of
accelerated electrons. An alternative explanation could be long-term
variability, as is the case for several ultracool dwarfs whose radio
emission varies considerably over long periods with emission levels
dropping below the detection limit in some instances.
---------------------------------------------------------
Title: Nature of Quiet Sun Oscillations Using Data from the Hinode,
TRACE, and SOHO Spacecraft
Authors: Gupta, G. R.; Subramanian, S.; Banerjee, D.; Madjarska,
M. S.; Doyle, J. G.
2013SoPh..282...67G Altcode: 2012arXiv1209.5252G; 2012SoPh..tmp..247G
We study the nature of quiet-Sun oscillations using multi-wavelength
observations from TRACE, Hinode, and SOHO. The aim is to investigate
the existence of propagating waves in the solar chromosphere and
the transition region by analyzing the statistical distribution of
power in different locations, e.g. in bright magnetic (network),
bright non-magnetic and dark non-magnetic (inter-network) regions,
separately. We use Fourier power and phase-difference techniques
combined with a wavelet analysis. Two-dimensional Fourier power maps
were constructed in the period bands 2 - 4 minutes, 4 - 6 minutes, 6 -
15 minutes, and beyond 15 minutes. We detect the presence of long-period
oscillations with periods between 15 and 30 minutes in bright magnetic
regions. These oscillations were detected from the chromosphere to the
transition region. The Fourier power maps show that short-period powers
are mainly concentrated in dark regions whereas long-period powers are
concentrated in bright magnetic regions. This is the first report of
long-period waves in quiet-Sun network regions. We suggest that the
observed propagating oscillations are due to magnetoacoustic waves,
which can be important for the heating of the solar atmosphere.
---------------------------------------------------------
Title: Coronal hole boundaries at small scales. IV. SOT view. Magnetic
field properties of small-scale transient brightenings in coronal
holes
Authors: Huang, Z.; Madjarska, M. S.; Doyle, J. G.; Lamb, D. A.
2012A&A...548A..62H Altcode: 2012arXiv1210.2009H
Context. We study the magnetic properties of small-scale transients
in coronal holes and a few in the quiet Sun identified in X-ray
observations and spectroscopic data in two previous papers. <BR />
Aims: We aim to investigate the role of small-scale transients in the
evolution of the magnetic field in an equatorial coronal hole. <BR />
Methods: Two sets of observations of an equatorial coronal hole and
another two in quiet-Sun regions were analysed using longitudinal
magnetograms taken by the Solar Optical Telescope. An automatic
feature tracking program, SWAMIS, was used to identify and track
the magnetic features. Each event was then visually analysed in
detail. <BR /> Results: In both coronal holes and quiet-Sun regions,
all brightening events are associated with bipolar regions and are
caused by magnetic flux emergence followed by cancellation with the
pre-existing and/or newly emerging magnetic flux. In the coronal
hole, 19 of 22 events have a single stable polarity which does not
change its position in time. In eleven cases this is the dominant
polarity. In the coronal hole, the magnetic features with the largest
flux are those of the dominant polarity, while the opposite polarity is
distributed in weaker features. The number of magnetic features of the
dominant polarity is four times grater than the opposite polarity. The
supergranulation configuration appears to preserve its general shape
during approximately nine hours of observations although the large
concentrations (the dominant polarity) in the network did evolve
and/or were slightly displaced, and their strength either increased or
decreased. The emission fluctuations/radiance oscillations seen in the
X-ray bright points are associated with recurring magnetic cancellation
in the footpoints. Unique observations of an X-ray jet reveal similar
magnetic behaviour in the footpoints, i.e. cancellation of the opposite
polarity magnetic flux. We find that the magnetic flux cancellation rate
during the jet is much higher than in bright points. Not all magnetic
cancellations result in an X-ray enhancement, suggesting that there is
a threshold of the amount of magnetic flux involved in a cancellation
above which brightening would occur at X-ray temperatures. <BR />
Conclusions: Our study demonstrates that the magnetic flux in coronal
holes is continuously processed through magnetic reconnection which
is responsible for the formation of numerous small-scale transient
events. The open magnetic flux forming the coronal-hole phenomenon
is largely involved in these transient features. The question of
whether this open flux is transported as a result of the formation and
evolution of these transient events, however, still remains open. <P
/>Three movies and Appendix A are available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Off-limb (Spicule) DEM Distribution from SoHO/SUMER
Observations
Authors: Vanninathan, K.; Madjarska, M. S.; Scullion, E.; Doyle, J. G.
2012SoPh..280..425V Altcode: 2012SoPh..tmp...88V; 2012arXiv1203.2073V
In the present work we derive a Differential Emission Measure (DEM)
distribution from a region dominated by spicules. We use spectral
data from the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer on-board the Solar Heliospheric Observatory
(SoHO) covering the entire SUMER wavelength range taken off-limb in
the Northern polar coronal hole to construct this DEM distribution
using the CHIANTI atomic database. This distribution is then used to
study the thermal properties of the emission contributing to the 171 Å
channel in the Atmospheric Imaging Assembly (AIA) on-board the Solar
Dynamics Observatory (SDO). From our off-limb DEM we found that the
radiance in the AIA 171 Å channel is dominated by emission from the
Fe IX 171.07 Å line and has sparingly little contribution from other
lines. The product of the Fe IX 171.07 Å line contribution function
with the off-limb DEM was found to have a maximum at logT<SUB>max</SUB>
(K)=5.8 indicating that during spicule observations the emission in
this line comes from plasma at transition region temperatures rather
than coronal. For comparison, the same product with a quiet Sun and
prominence DEM were found to have a maximum at logT<SUB>max</SUB>
(K)=5.9 and logT<SUB>max</SUB> (K)=5.7, respectively. We point out
that the interpretation of data obtained from the AIA 171 Å filter
should be done with foreknowledge of the thermal nature of the observed
phenomenon. For example, with an off-limb DEM we find that only 3.6 %
of the plasma is above a million degrees, whereas using a quiet Sun DEM,
this contribution rises to 15 %.
---------------------------------------------------------
Title: Coronal hole boundaries evolution at small scales. III. EIS
and SUMER views
Authors: Madjarska, M. S.; Huang, Z.; Doyle, J. G.; Subramanian, S.
2012A&A...545A..67M Altcode: 2012arXiv1207.1281M
Context. We report on the plasma properties of small-scale
transient events identified in the quiet Sun, coronal holes and their
boundaries. <BR /> Aims: We aim at deriving the physical characteristics
of events that were identified as small-scale transient brightenings
in XRT images. <BR /> Methods: We used spectroscopic co-observations
from SUMER/SoHO and EIS/Hinode combined with high-cadence imaging
data from XRT/Hinode. We measured Doppler shifts using single and
multiple Gaussian fits of the transition region and coronal lines as
well as electron densities and temperatures. We combined co-temporal
imaging and spectroscopy to separate brightening expansions from
plasma flows. <BR /> Results: The transient brightening events in
coronal holes and their boundaries were found to be very dynamical,
producing high-density outflows at high speeds. Most of these events
represent X-ray jets from pre-existing or newly emerging coronal
bright points at X-ray temperatures. The average electron density of
the jets is log<SUB>10</SUB> N<SUB>e</SUB> ≈ 8.76 cm<SUP>-3</SUP>
while in the flaring site it is log<SUB>10</SUB> N<SUB>e</SUB> ≈ 9.51
cm<SUP>-3</SUP>. The jet temperatures reach a maximum of 2.5 MK but in
the majority of the cases the temperatures do not exceed 1.6 MK. The
footpoints of jets have maximum temperatures of 2.5 MK, though in a
single event scanned a minute after the flaring the measured temperature
was 12 MK. The jets are produced by multiple microflaring in the
transition region and corona. Chromospheric emission was only detected
in their footpoints and was only associated with downflows. The Doppler
shift measurements in the quiet Sun transient brightenings confirmed
that these events do not produce jet-like phenomena. The plasma flows
in these phenomena remain trapped in closed loops. <BR /> Conclusions:
We can conclude that the dynamic day-by-day and even hour-by-hour
small-scale evolution of coronal hole boundaries reported in Paper
I is indeed related to coronal bright points. The XRT observations
reported in Paper II revealed that these changes are associated with
the dynamic evolution of coronal bright points producing multiple jets
during their lifetime until their full disappearance. We demonstrate
here through spectroscopic EIS and SUMER co-observations combined
with high-cadence imaging information that the co-existence of open
and closed magnetic fields results in multiple energy depositions,
which propel high-density plasma along open magnetic field lines. We
conclude from the physical characteristics obtained in this study that
X-ray jets are important candidates for the source of the slow solar
wind. This, however, does not exclude the possibility that these jets
are also the microstreams observed in the fast solar wind, as recently
suggested. <P />Figures A.1, A.2, and movies are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Solar Fine-Scale Structures. I. Spicules and Other Small-Scale,
Jet-Like Events at the Chromospheric Level: Observations and Physical
Parameters
Authors: Tsiropoula, G.; Tziotziou, K.; Kontogiannis, I.; Madjarska,
M. S.; Doyle, J. G.; Suematsu, Y.
2012SSRv..169..181T Altcode: 2012SSRv..tmp...65T; 2012arXiv1207.3956T
Over the last two decades the uninterrupted, high resolution
observations of the Sun, from the excellent range of telescopes aboard
many spacecraft complemented with observations from sophisticated
ground-based telescopes have opened up a new world producing
significantly more complete information on the physical conditions of
the solar atmosphere than before. The interface between the lower solar
atmosphere where energy is generated by subsurface convection and the
corona comprises the chromosphere, which is dominated by jet-like,
dynamic structures, called mottles when found in quiet regions,
fibrils when found in active regions and spicules when observed at
the solar limb. Recently, space observations with Hinode have led to
the suggestion that there should exist two different types of spicules
called Type I and Type II which have different properties. Ground-based
observations in the Ca ii H and K filtergrams reveal the existence of
long, thin emission features called straws in observations close to
the limb, and a class of short-lived events called rapid blue-shifted
excursions characterized by large Doppler shifts that appear only
in the blue wing of the Ca ii infrared line. It has been suggested
that the key to understanding how the solar plasma is accelerated
and heated may well be found in the studies of these jet-like,
dynamic events. However, while these structures are observed and
studied for more than 130 years in the visible, but also in the UV
and EUV emission lines and continua, there are still many questions
to be answered. Thus, despite their importance and a multitude of
observations performed and theoretical models proposed, questions
regarding their origin, how they are formed, their physical parameters,
their association with the underlying photospheric magnetic field, how
they appear in the different spectral lines, and the interrelationship
between structures observed in quiet and active regions on the disk
and at the limb, as well as their role in global processes has not
yet received definitive answers. In addition, how they affect the
coronal heating and solar wind need to be further explored. In this
review we present observations and physical properties of small-scale
jet-like chromospheric events observed in active and quiet regions,
on the disk and at the limb and discuss their interrelationship.
---------------------------------------------------------
Title: The Diagnostic Potential of Transition Region Lines Undergoing
Transient Ionization in Dynamic Events
Authors: Doyle, J. G.; Giunta, A.; Singh, A.; Madjarska, M. S.;
Summers, H.; Kellett, B. J.; O'Mullane, M.
2012SoPh..280..111D Altcode: 2012SoPh..tmp..118D; 2012arXiv1204.6598D
We discuss the diagnostic potential of high cadence UV spectral
data when transient ionization is considered. For this we use high
cadence UV spectra taken during the impulsive phase of a solar flare
(observed with instruments on-board the Solar Maximum Mission) which
showed excellent correspondence with hard X-ray pulses. The ionization
fraction of the transition region ion O V and, in particular, the
contribution function for the O V 1371 Å line are computed within
the Atomic Data and Analysis Structure, which is a collection of
fundamental and derived atomic data and codes to manipulate them. Due
to transient ionization, the O V 1371 Å line is enhanced in the
first fraction of a second with the peak in the line contribution
function occurring initially at a higher electron temperature than in
ionization equilibrium. The rise time and enhancement factor depend
mostly on the electron density. The fractional increase in the O V
1371 Å emissivity due to transient ionization can reach a factor
of two-four and can explain the fast response in the line flux of
transition regions ions during the impulsive phase of flares solely
as a result of transient ionization. This technique can be used to
diagnose the electron temperature and density of solar flares observed
with the forthcoming Interface Region Imaging Spectrograph.
---------------------------------------------------------
Title: Electron-beam-induced Radio Emission from Ultracool Dwarfs
Authors: Yu, S.; Doyle, J. G.; Kuznetsov, A.; Hallinan, G.; Antonova,
A.; MacKinnon, A. L.; Golden, A.
2012ApJ...752...60Y Altcode: 2012arXiv1204.2261Y
We present the numerical simulations for an electron-beam-driven and
loss-cone-driven electron-cyclotron maser (ECM) with different plasma
parameters and different magnetic field strengths for a relatively
small region and short timescale in an attempt to interpret the
recent discovered intense radio emission from ultracool dwarfs. We
find that a large amount of electromagnetic (EM) field energy can be
effectively released from the beam-driven ECM, which rapidly heats the
surrounding plasma. A rapidly developed high-energy tail of electrons
in velocity space (resulting from the heating process of the ECM)
may produce the radio continuum depending on the initial strength
of the external magnetic field and the electron beam current. Both
significant linear polarization and circular polarization of EM waves
can be obtained from the simulations. The spectral energy distributions
of the simulated radio waves show that harmonics may appear from 10 to
70ν<SUB>pe</SUB> (ν<SUB>pe</SUB> is the electron plasma frequency)
in the non-relativistic case and from 10 to 600ν<SUB>pe</SUB> in the
relativistic case, which makes it difficult to find the fundamental
cyclotron frequency in the observed radio frequencies. A wide frequency
band should therefore be covered by future radio observations.
---------------------------------------------------------
Title: Coronal hole boundaries and the slow solar wind from
Hinode/EIS/XRT/SOT and SUMER/SoHO
Authors: Madjarska, M. S.; Huang, Zh.; Doyle, J. G.; Subramanian, S.
2012decs.confE..16M Altcode:
We present a statistical study on outflows at coronal hole boundaries
and inside coronal holes and discuss their role in the slow solar
wind formation in the low solar corona. The outflows are studied in
XRT/Hinode image data taken with the Al_poly filter using an automatic
identification method. A spectroscopic analysis is made using EIS and
SUMER data of spectral lines with formation temperatures in the range
from 10 000 K to 12 MK. The derived plasma parameters of about 60
phenomena will be reported. The longitudinal magnetic field data for
each feature falling in the SOT/Hinode field-of-view (more than 25)
are studied using a magnetic feature tracking procedure and a visual
inspection. The mechanism of the outflow formation and acceleration
will be discussed.
---------------------------------------------------------
Title: What is the true nature of blinkers?
Authors: Subramanian, S.; Madjarska, M. S.; Doyle, J. G.; Bewsher, D.
2012A&A...538A..50S Altcode: 2011arXiv1111.2149S
<BR /> Aims: The aim of this work is to identify the true nature of the
transient EUV brightenings, called blinkers. <BR /> Methods: Co-spatial
and co-temporal multi-instrument data, including imaging (EUVI/STEREO,
XRT and SOT/Hinode), spectroscopic (CDS/SoHO and EIS/Hinode) and
magnetogram (SOT/Hinode) data, of an isolated equatorial coronal hole
were used. An automatic program for identifying transient brightenings
in CDS O v 629 Å, EUVI 171 Å and XRT was applied. <BR /> Results: We
identified 28 blinker groups in the CDS O v 629 Å raster images. All
CDS O v 629 Å blinkers showed counterparts in EUVI 171 Å and 304 Å
images. We classified these blinkers into two categories, one associated
with coronal counterparts and other with no coronal counterparts as seen
in XRT images and EIS Fe xii 195.12 Å raster images. Around two-thirds
of the blinkers show coronal counterparts and correspond to various
events like EUV/X-ray jets, brightenings in coronal bright points
or foot-point brightenings of larger loops. These brightenings occur
repetitively and have a lifetime of around 40 min at transition region
temperatures. The remaining blinker groups with no coronal counterpart
in XRT and EIS Fe xii 195.12 Å appear as point-like brightenings and
have chromospheric/transition region origin. They take place only once
and have a lifetime of around 20 min. In general, lifetimes of blinkers
are different at different wavelengths, i.e. different temperatures,
decreasing from the chromosphere to the corona. <BR /> Conclusions: This
work shows that the term blinker covers a range of phenomena. Blinkers
are the EUV response of various transient events originating at coronal,
transition region and chromospheric heights. Hence, events associated
with blinkers contribute to the formation and maintenance of the
temperature gradient in the transition region and the corona.
---------------------------------------------------------
Title: Comparative Analysis of Two Formation Scenarios of Bursty
Radio Emission from Ultracool Dwarfs
Authors: Kuznetsov, A. A.; Doyle, J. G.; Yu, S.; Hallinan, G.;
Antonova, A.; Golden, A.
2012ApJ...746...99K Altcode: 2011arXiv1111.7019K
Recently, a number of ultracool dwarfs have been found to produce
periodic radio bursts with high brightness temperature and polarization
degree; the emission properties are similar to the auroral radio
emissions of the magnetized planets of the solar system. We simulate
the dynamic spectra of radio emission from ultracool dwarfs. The
emission is assumed to be generated due to the electron-cyclotron
maser instability. We consider two source models: the emission caused
by interaction with a satellite and the emission from a narrow sector
of active longitudes; the stellar magnetic field is modeled by a tilted
dipole. We have found that for the dwarf TVLM 513-46546, the model of
the satellite-induced emission is inconsistent with observations. On
the other hand, the model of emission from an active sector is able
to reproduce qualitatively the main features of the radio light curves
of this dwarf; the magnetic dipole seems to be highly tilted (by about
60°) with respect to the rotation axis.
---------------------------------------------------------
Title: The Response of A Three-dimensional Solar Atmosphere to
Wave-driven Jets
Authors: Scullion, E.; Erdélyi, R.; Fedun, V.; Doyle, J. G.
2011ApJ...743...14S Altcode:
Global oscillations from the solar interior are, mainly, pressure-driven
(p-modes) oscillations with a peak power of a five-minute period. These
oscillations are considered to manifest in many phenomena in the lower
solar atmosphere, most notably, in spicules. These small-scale jets
may provide the key to understanding the powering mechanisms of the
transition region (TR) and lower corona. Here, we simulate the formation
of wave-driven (type-I) spicule phenomena in three dimensions and the
transmission of acoustic waves from the lower chromosphere and into
the corona. The outer atmosphere oscillates in response to the jet
formation, and in turn, we reveal the formation of a circular seismic
surface wave, which we name as a Transition Region Quake (TRQ). The TRQ
forms as a consequence of an upward propelling spicular wave train that
repeatedly punctures and energizes the TR. The steep density gradient
enables the TRQ to develop and radially fan outward from the location
where the spicular plasma column impinges the TR. We suggest the TRQ
formation as a formidable mechanism in continuously sustaining part of
the energy budget of the TR. We present a supporting numerical model
which allow us to determine the level of energy dumping at the TR by
upward-propagating p-modes. Upon applying a wavelet analysis on our
simulations we identify the presence of a chromospheric cavity which
resonates with the jet propagation and leaves behind an oscillatory
wake with a distinctive periodicity. Through our numerical analysis we
also discover type-I spicule turbulence leading to a convection-based
motion in the low corona.
---------------------------------------------------------
Title: Overview of the Southern Andes - ANtarctic GRavity wave
InitiAtive (SAANGRIA)
Authors: Doyle, J.; Fritts, D. C.; Smith, R. B.; Eckermann, S. D.;
Taylor, M. J.
2011AGUFM.A52B..05D Altcode:
An overview of the Southern Andes - ANtarctic GRavity wave InitiAtive
(SAANGRIA) will be presented, which is a comprehensive, airborne and
ground-based measurement and modeling program focused on providing a
new understanding of gravity wave (GW) dynamics and impacts from the
troposphere through the mesosphere and lower thermosphere (MLT). This
program will employ the new NSF/NCAR GV (NGV) research aircraft
from a base near the southern tip of South America in a 10-week field
measurement campaign from late June to early September 2013. The region,
spanning the southern Andes, Drake Passage, and Antarctic Peninsula,
is chosen since all the relevant GW sources occur strongly here and
satellite observations suggest this region in winter contains the
largest GW amplitudes on the planet. Given large-amplitude GWs that
propagate routinely into the MLT, the region offers an ideal natural
laboratory for studying these important GW dynamics and effects
impacting weather and climate over a much deeper atmospheric layer
than previous campaigns have attempted (0-100 km altitude). An overview
will be provided of the airborne and ground based instrumentation and
the suite of GW-focused forecasting and modeling tools that will be
used to guide the NGV.
---------------------------------------------------------
Title: Magnetic reconnection resulting from flux emergence:
implications for jet formation in the lower solar atmosphere?
Authors: Ding, J. Y.; Madjarska, M. S.; Doyle, J. G.; Lu, Q. M.;
Vanninathan, K.; Huang, Z.
2011A&A...535A..95D Altcode: 2011arXiv1109.5606D
<BR /> Aims: We aim at investigating the formation of jet-like features
in the lower solar atmosphere, e.g. chromosphere and transition
region, as a result of magnetic reconnection. <BR /> Methods: Magnetic
reconnection as occurring at chromospheric and transition regions
densities and triggered by magnetic flux emergence is studied using a
2.5D MHD code. The initial atmosphere is static and isothermal, with
a temperature of 2 × 10<SUP>4</SUP> K. The initial magnetic field
is uniform and vertical. Two physical environments with different
magnetic field strength (25 G and 50 G) are presented. In each case,
two sub-cases are discussed, where the environments have different
initial mass density. <BR /> Results: In the case where we have a
weaker magnetic field (25 G) and higher plasma density (N<SUB>e</SUB> =
2 × 10<SUP>11</SUP> cm<SUP>-3</SUP>), valid for the typical quiet Sun
chromosphere, a plasma jet would be observed with a temperature of 2-3
× 10<SUP>4</SUP> K and a velocity as high as 40 kms<SUP>-1</SUP>. The
opposite case of a medium with a lower electron density (N<SUB>e</SUB>
= 2 × 10<SUP>10</SUP> cm<SUP>-3</SUP>), i.e. more typical for the
transition region, and a stronger magnetic field of 50 G, up-flows
with line-of-sight velocities as high as ~90 kms<SUP>-1</SUP> and
temperatures of 6 × 10<SUP>5</SUP> K, i.e. upper transition region -
low coronal temperatures, are produced. Only in the latter case, the low
corona Fe ix 171 Å shows a response in the jet which is comparable to
the O v increase. <BR /> Conclusions: The results show that magnetic
reconnection can be an efficient mechanism to drive plasma outflows
in the chromosphere and transition region. The model can reproduce
characteristics, such as temperature and velocity for a range of jet
features like a fibril, a spicule, a hot X-ray jet or a transition
region jet by changing either the magnetic field strength or the
electron density, i.e. where in the atmosphere the reconnection occurs.
---------------------------------------------------------
Title: Simulation of the rotation-modulated and satellite-induced
radio emissions from brown dwarfs
Authors: Kuznetsov, A. A.; Doyle, J. G.; Yu, S.
2011epsc.conf...90K Altcode: 2011DPS....43...90K
We simulate the dynamic spectra of the radio emission from a brown
dwarf. The emission is produced due to the electron-cyclotron maser
instability. Two source models are considered: the emission caused
by interaction with a satellite and the emission from a sector of
active longitudes. We have found that for the dwarf TVLM513 the model
of an active sector (with a highly tilted magnetic dipole) fits the
observations better.
---------------------------------------------------------
Title: Starspots on the fastest rotators in the β Pictoris moving
group
Authors: García-Alvarez, D.; Lanza, A. F.; Messina, S.; Drake, J. J.;
van Wyk, F.; Shobbrook, R. R.; Butler, C. J.; Kilkenny, D.; Doyle,
J. G.; Kashyap, V. L.
2011A&A...533A..30G Altcode: 2011arXiv1107.5688G
<BR /> Aims: We carried out high-resolution spectroscopy and
BV(I)<SUB>C</SUB> photometric monitoring of the two fastest late-type
rotators in the nearby β Pictoris moving group, HD 199143 (F7V) and
CD-64°1208 (K7V). The motivation for this work is to investigate the
rotation periods and photospheric spot patterns of these very young
stars, with a longer term view to probing the evolution of rotation and
magnetic activity during the early phases of main-sequence evolution. We
also aim to derive information on key physical parameters, such as
rotational velocity and rotation period. <BR /> Methods: We applied
maximum entropy (ME) and Tikhonov regularizing (TR) criteria to derive
the surface spot map distributions of the optical modulation observed in
HD 199143 (F7 V) and CD-64°1208 (K7 V). We also used cross-correlation
techniques to determine stellar parameters such as radial velocities and
rotational velocities. Lomb-Scargle periodograms were used to obtain
the rotational periods from differential magnitude time series. <BR
/> Results: We find periods and inclinations of 0.356 days and 21.5
deg for HD 199143, and 0.355 days and 50.1 deg for CD-64°1208. The
spot maps of HD 199143 obtained from the ME and TR methods are very
similar, although the latter gives a smoother distribution of the
filling factor. Maps obtained at two different epochs three weeks apart
show a remarkable increase in spot coverage amounting to ~7% of the
surface of the photosphere over a time period of only ~20 days. The
spot maps of CD-64°1208 from the two methods show good longitudinal
agreement, whereas the latitude range of the spots is extended to
cover the whole visible hemisphere in the TR map. The distributions
obtained from the first light curve of HD 199143 show the presence of
an extended and asymmetric active longitude with the maximum filling
factor at longitude ~325°. A secondary active longitude is present at
~100°. The spotted area distributions on CD-64°1208 show two active
longitudes separated by about 180°, which is not unusual on such very
active stars. <P />Figures 7-10 are available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Can coronal hole spicules reach coronal temperatures?
Authors: Madjarska, M. S.; Vanninathan, K.; Doyle, J. G.
2011A&A...532L...1M Altcode: 2011arXiv1105.1296M
<BR /> Aims: The present study aims to provide observational evidence
of whether coronal hole spicules reach coronal temperatures. <BR />
Methods: We combine multi-instrument co-observations obtained with
the SUMER/SoHO and with the EIS/SOT/XRT/Hinode. <BR /> Results:
The analysed three large spicules were found to be comprised of
numerous thin spicules that rise, rotate, and descend simultaneously
forming a bush-like feature. Their rotation resembles the untwisting
of a large flux rope. They show velocities ranging from 50 to 250
kms<SUP>-1</SUP>. We clearly associated the red- and blue-shifted
emissions in transition region lines not only with rotating but
also with rising and descending plasmas. Our main result is that
these spicules although very large and dynamic, are not present in
the spectral lines formed at temperatures above 300 000 K. <BR />
Conclusions: In this paper we present the analysis of three Ca ii H
large spicules that are composed of numerous dynamic thin spicules
but appear as macrospicules in lower resolution EUV images. We found
no coronal counterpart of these and smaller spicules. We believe that
the identification of phenomena that have very different origins as
macrospicules is due to the interpretation of the transition region
emission, and especially the He ii emission, wherein both chromospheric
large spicules and coronal X-ray jets are present. We suggest that
the recent observation of spicules in the coronal AIA/SDO 171 Å
and 211 Å channels probably comes from the existence of transition
region emission there. <P />Movie is available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Mapping radio emitting-region on low-mass stars and brown
dwarfs
Authors: Yu, S.; Doyle, J. G.; Hallinan, G.; MacKinnon, A. L.
2011EPJWC..1606013Y Altcode:
Strong magnetic activity in ultracool dwarfs (UCDs, spectral classes
later than M7) have emerged from a number of radio observations,
including the periodic beams. The highly (up to 100%) circularly
polarized nature of the emission point to an effective amplification
mechanism of the high-frequency electromagnetic waves - the electron
cyclotron maser (ECM) instability. Several anisotropic velocity
distibution models of electrons, including the horseshoe distribution,
ring shell distribution and the loss-cone distribution, are able
to generate the ECM instability. A magnetic-field-aligned electric
potential would play an significant role in the ECM process. We are
developing a theoretical model in order to simulate ECM and apply
this model to map the radio-emitting region on low-mass stars and
brown dwarfs.
---------------------------------------------------------
Title: Water vapor intrusions into the High Arctic during winter
Authors: Doyle, J. G.; Lesins, G.; Thackray, C. P.; Perro, C.; Nott,
G. J.; Duck, T. J.; Damoah, R.; Drummond, J. R.
2011GeoRL..3812806D Altcode:
The meridional transport of water vapor into the High Arctic,
accompanied by dry enthalpy and clouds, impacts the surface radiative
forcing. The evolution of one such moist intrusion over 9-11 February
2010 is presented. The event is analyzed using a unique blend of
measurements including a new pan-Arctic retrieval of column water vapor
from the Microwave Humidity Sounders, water vapor profiles from a Raman
lidar and a ground-based microwave radiometer at the Polar Environment
Atmospheric Research Laboratory (PEARL), in Eureka (80°N, 86°W),
on Ellesmere Island in the Canadian High Arctic. A radiation model
reveals the intrusion is associated with a 17 W m<SUP>-2</SUP> average
increase in downwelling longwave irradiance. Optically thin clouds,
as observed by the lidar, contribute a further 20 W m<SUP>-2</SUP> to
the downwelling longwave irradiance at their peak. Intrusion events are
shown to be a regular occurrence in the Arctic winter with implications
for the understanding of the mechanisms driving Arctic Amplification.
---------------------------------------------------------
Title: Modelling the radio pulses of an ultracool dwarf
Authors: Yu, S.; Hallinan, G.; Doyle, J. G.; MacKinnon, A. L.;
Antonova, A.; Kuznetsov, A.; Golden, A.; Zhang, Z. H.
2011A&A...525A..39Y Altcode: 2010arXiv1009.1548Y
Context. Recently, unanticipated magnetic activity in ultracool dwarfs
(UCDs, spectral classes later than M7) has emerged from a number of
radio observations. The highly (up to 100%) circularly polarized
nature and high brightness temperature of the emission have been
interpreted as requiring an effective amplification mechanism of
the high-frequency electromagnetic waves - the electron cyclotron
maser instability (ECMI). <BR /> Aims: We aim to understand the
magnetic topology and the properties of the radio emitting region
and associated plasmas in these ultracool dwarfs, interpreting the
origin of radio pulses and their radiation mechanism. <BR /> Methods:
An active region model was built, based on the rotation of the UCD and
the ECMI mechanism. <BR /> Results: The high degree of variability in
the brightness and the diverse profile of pulses can be interpreted
in terms of a large-scale hot active region with extended magnetic
structure existing in the magnetosphere of TVLM 513-46546. We suggest
the time profile of the radio light curve is in the form of power law
in the model. Combining the analysis of the data and our simulation,
we can determine the loss-cone electrons have a density in the range
of 1.25 × 10<SUP>5</SUP> -5 × 10<SUP>5</SUP> cm<SUP>-3</SUP> and
temperature between 10<SUP>7</SUP> and 5 × 10<SUP>7</SUP> K. The
active region has a size < 1R<SUB>Jup</SUB>, while the pulses
produced by the ECMI mechanism are from a much more compact region
(e.g. ~0.007 R<SUB>Jup</SUB>). A surface magnetic field strength of
≈7000 G is predicted. <BR /> Conclusions: The active region model
is applied to the radio emission from TVLM 513-46546, in which the
ECMI mechanism is responsible for the radio bursts from the magnetic
tubes and the rotation of the dwarf can modulate the integral of flux
with respect to time. The radio emitting region consists of complicated
substructures. With this model, we can determine the nature (e.g. size,
temperature, density) of the radio emitting region and plasma. The
magnetic topology can also be constrained. We compare our predicted
X-ray flux with Chandra X-ray observation of TVLM 513-46546. Although
the X-ray detection is only marginally significant, our predicted flux
is significantly lower than the observed flux. Further multi-wavelength
observations will help us better understand the magnetic field structure
and plasma behavior on the ultracool dwarf.
---------------------------------------------------------
Title: Phase connecting multi-epoch radio data for the ultracool
dwarf TVLM 513-46546
Authors: Doyle, J. G.; Antonova, A.; Marsh, M. S.; Hallinan, G.; Yu,
S.; Golden, A.
2010A&A...524A..15D Altcode:
Context. Radio data obtained for the ultracool dwarf TVLM 513-46546
has indicated a rotation period of ≈1.96 h via regular radio pulses,
but how stable is this period. This has major implications regarding
the stability of the magnetic field structures responsible for the
radio emission from the ultracool dwarf. <BR /> Aims: The aim of
the present work is to investigate the stability of this rotation
period using two datasets taken ≈40 days apart, some 12 months
after the first report of periodical pulses in the radio data. <BR />
Methods: Here we use a Bayesian analysis method which is a statistical
procedure that endeavours to estimate the parameters of an underlying
model probability distribution based on the observed data. <BR />
Results: Periodical pulses are detected in datasets taken in April
and June 2007, with the pulses being confined to a narrow range in
the rotation period. This is in contradiction to a previous report of
only aperiodic activity in the April 2007 dataset, while in fact both
datasets have a periodic signal with a false alarm probability ≪
10<SUP>-12</SUP>. These two datasets are then used to derive a more
accurate period (previously determined to be 1.96 h) of 1.96733 ±
0.00002 h. <BR /> Conclusions: The similarly in the burst structure
in datasets taken several weeks apart point towards the stability of
an electric field structure which is somehow generated and sustained
within the magnetosphere of the ultracool dwarf. The derived period of
1.96733 h is consistent with the period derived via radio and optical
data taken some 12 months prior to the present observations and implies
the near phase constancy of the pulsed emission. This suggest the
presence of stable large-scale magnetic fields on timescales of more
than 1 year. The characteristics of the pulses suggest that they are
produced by the electron cyclotron maser (ECM) instability.
---------------------------------------------------------
Title: A permanently-acting NEA damage mitigation technique via the
Yarkovsky effect
Authors: Hyland, D. C.; Altwaijry, H. A.; Ge, S.; Margulieux, R.;
Doyle, J.; Sandberg, J.; Young, B.; Bai, X.; Lopez, J.; Satak, N.
2010CosRe..48..430H Altcode:
In the later stages of a combined mission of exploration and damage
mitigation of a hazardous Near Earth Asteroid (NEA), sufficiently
detailed tracking, orbit prediction, mass distribution, and physical
properties data have been accumulated. It may be desirable to
implement a “slow push” damage mitigation technique that is
capable of altering the NEA orbit continuously and permanently. This
possibility was suggested in a companion paper that outlined an
archetypal exploration/mitigation mission to the NEA 99942 Apophis,
which is achieved using a novel albedo change approach. The details
and apparatus used in the albedo modification technique are described
in the paper. We describe the design details and the constraints on
particle size (to prevent electrostatic levitation and escape) and on
the dispensing speed (to achieve the desired coverage zone and prevent
particles from orbiting or escaping).
---------------------------------------------------------
Title: A mission template for exploration and damage mitigation of
potential hazard of Near Earth Asteroids
Authors: Hyland, D. C.; Altwaijry, H. A.; Margulieux, R.; Doyle, J.;
Sandberg, J.; Young, B.; Satak, N.; Lopez, J.; Ge, S.; Bai, X.
2010CosRe..48..437H Altcode:
The Apophis Exploratory and Mitigation Platform (AEMP) concept was
developed as a prototype mission to explore and potentially deflect
the Near Earth Asteroid (NEA) 99942 Apophis. Deflection of the asteroid
from the potential 2036 impact will be achieved using a gravity tractor
technique, while a permanent deflection, eliminating future threats,
will be imparted using a novel albedo manipulation technique. This
mission will serve as an archetypal template for future missions to
small NEAs and could be adapted to mitigate the threat of collision
with other potential Earth-crossing objects.
---------------------------------------------------------
Title: Looking for a Radio Pulse from Hot Jupiters
Authors: Hallinan, G.; Sirothia, S.; Chandra, I.; Doyle, J. G.;
Antonova, A.; Golden, A.
2010epsc.conf..413H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Investigating Magnetic Field Strengths and Topologies for
Pulsing Ultracool Dwarfs: The M8.5 Dwarf TVLM 513-46546
Authors: Antonova, A.; Hallinan, G.; Doyle, J. G.; Golden, A.
2010POBeo..90..117A Altcode:
The detection of both quiescent and flaring nonthermal radio emission
from a number of late M-, L-type dwarfs indicates the presence of
magnetic activity in the ultracool dwarf domain. What is more, four
of those dwarfs show periodic, highly circularly polarized pulsing
signatures consistent with electron cyclotron maser emission. The
pulsing emission can be used as a powerful diagnostic of magnetic
field strengths and topologies of very low-mass stars and brown
dwarfs. Here we present our results from multi-epoch VLA observations
of the M8.5 dwarf TVLM 513-46546 which provide evidence of the presence
of stable large-scale magnetic fields with kilogaus strengths, as well
as broadband dynamic spectra of the individual pulses in the emission
of the dwarf obtained using the Arecibo Observatory. We discuss how
such observations can be used for mapping the radio coronae of UCDs.
---------------------------------------------------------
Title: Coronal hole boundaries evolution at small scales. II. XRT
view. Can small-scale outflows at CHBs be a source of the slow
solar wind
Authors: Subramanian, S.; Madjarska, M. S.; Doyle, J. G.
2010A&A...516A..50S Altcode: 2010arXiv1002.1675S
<BR /> Aims: We aim to further explore the small-scale evolution of
coronal hole boundaries using X-ray high-resolution and high-cadence
images. We intend to determine the fine structure and dynamics of the
events causing changes of coronal hole boundaries and to explore the
possibility that these events are the source of the slow solar wind. <BR
/> Methods: We developed an automated procedure for the identification
of transient brightenings in images from the X-ray telescope on-board
Hinode taken with an Al Poly filter in the equatorial coronal holes,
polar coronal holes, and the quiet Sun with and without transient
coronal holes. <BR /> Results: We found that in comparison to the quiet
Sun, the boundaries of coronal holes are abundant with brightening
events including areas inside the coronal holes where closed magnetic
field structures are present. The visual analysis of these brightenings
revealed that around 70% of them in equatorial, polar and transient
coronal holes and their boundaries show expanding loop structures and/or
collimated outflows. In the quiet Sun only 30% of the brightenings show
flows with most of them appearing to be contained in the solar corona
by closed magnetic field lines. This strongly suggests that magnetic
reconnection of co-spatial open and closed magnetic field lines creates
the necessary conditions for plasma outflows to large distances. The
ejected plasma always originates from pre-existing or newly emerging
(at X-ray temperatures) bright points. <BR /> Conclusions: The present
study confirms our findings that the evolution of loop structures known
as coronal bright points is associated with the small-scale changes
of coronal hole boundaries. The loop structures show an expansion
and eruption with the trapped plasma consequently escaping along the
“quasi” open magnetic field lines. These ejections appear to be
triggered by magnetic reconnection, e.g. the so-called interchange
reconnection between the closed magnetic field lines (BPs) and the
open magnetic field lines of the coronal holes. We suggest that
these plasma outflows are possibly one of the sources of the slow
solar wind. <P />4 movies are only available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Chromospheric magnetic reconnection caused by photospheric
flux emergence: implications for jet-like events formation
Authors: Ding, J. Y.; Madjarska, M. S.; Doyle, J. G.; Lu, Q. M.
2010A&A...510A.111D Altcode: 2009arXiv0912.4449D
Magnetic reconnection in the low atmosphere, e.g. chromosphere, is
investigated in various physical environments. Its implications for
the origination of explosive events (small-scale jets) are discussed. A
2.5-dimensional resistive magnetohydrodynamic (MHD) model in Cartesian
coordinates is used. It is found that the temperature and velocity of
the outflow jets as a result of magnetic reconnection are strongly
dependent on the physical environments, e.g. the magnitude of the
magnetic field strength and the plasma density. If the magnetic
field strength is weak and the density is high, the temperature of
the jets is very low (~10<SUP>4</SUP> K) as well as its velocity (~40
km s<SUP>-1</SUP>). However, if environments with stronger magnetic
field strength (40 G) and smaller density (electron density N_e=2×
10<SUP>10</SUP> cm<SUP>-3</SUP>) are considered, the outflow jets
reach higher temperatures of up to 6× 10^5 K and a line-of-sight
velocity of up to 130 km s<SUP>-1</SUP> which is comparable with the
observational values of jet-like events.
---------------------------------------------------------
Title: A spectroscopic analysis of macrospicules .
Authors: Scullion, E.; Doyle, J. G.; Erdélyi, R.
2010MmSAI..81..737S Altcode:
We explore the nature of macrospicule structures, both off-limb
and on-disk, and their possible relation to explosive events in the
mid-solar atmosphere. We use high resolution spectroscopy obtained with
the SoHO/SUMER instrument. We present a highly resolved spectroscopic
analysis and line parameter study of time series data for such jets. We
focus on two interesting off-limb events which rapidly propagate
between the mid-transition region N IV 765 Å line formation (140
000 K) and the lower corona Ne VIII 770 Å line formation (630 000
K). In one example, a strong jet-like event is associated with a cool
feature not present in the Ne VIII 770 Å line radiance or Doppler
velocity maps. Our data reveals fast, repetitive plasma outflows
with blue-shift velocities of ≈ 145 km s<SUP>-1</SUP> in the lower
solar atmosphere. The data suggests a strong role for smaller jets
(spicules), as a precursor to macrospicule formation, which may have
a common origin with explosive events.
---------------------------------------------------------
Title: Statistical Detection of Propagating Waves in a Polar
Coronal Hole
Authors: Gupta, G. R.; O'Shea, E.; Banerjee, D.; Popescu, M.; Doyle,
J. G.
2010ASSP...19..433G Altcode: 2009arXiv0902.4333G; 2010mcia.conf..433G
Waves are important in the heating of the solar corona and the
acceleration of the solar wind. We have examined a long spectral time
series sampling a southern coronal hole, observed on the 25 February
1997 using the SUMER spectrometer onboard SoHO. The observations
used the spectra lines NIV 765Å, formed in the transition region,
and Ne VIII 770Å, formed in the low corona. The spectra indicate
the presence of compressional waves with periods of about 18 min, and
also significant power at shorter periods. Using Fourier techniques,
we measured the phase delays between the intensity as well as the
velocity oscillations in the two lines as a function of frequency. From
these measurements we derive the travel time of the propagating
oscillations and so the propagation speeds of the waves producing
the oscillations. As the measured propagation speeds are subsonic,
we conclude that the observed waves are slow magneto-acoustic ones.
---------------------------------------------------------
Title: Deriving the coronal hole electron temperature: electron
density dependent ionization / recombination considerations
Authors: Doyle, John Gerard; Chapman, Steven; Bryans, Paul;
Pérez-Suárez, David; Singh, Avninda; Summers, Hugh; Savin,
Daniel Wolf
2010RAA....10...91D Altcode: 2009arXiv0909.3195D
Comparison of appropriate theoretically derived line ratios with
observational data can yield estimates of a plasma's physical
parameters, such as electron density or temperature. The usual practice
in the calculation of the line ratio is the assumption of excitation
by electrons/protons followed by radiative decay. Furthermore, it
is normal to use the so-called coronal approximation, i.e. one only
considers ionization and recombination to and from the ground-state. A
more accurate treatment is to include ionization/recombination to and
from metastable levels. Here, we apply this to two lines from adjacent
ionization stages, Mg IX 368 Å and Mg X 625 Å, which has been shown to
be a very useful temperature diagnostic. At densities typical of coronal
hole conditions, the difference between the electron temperature derived
assuming the zero density limit compared with the electron density
dependent ionization/recombination is small. This, however, is not
the case for flares where the electron density is orders of magnitude
larger. The derived temperature for the coronal hole at solar maximum
is around 1.04 MK compared to just below 0.82 MK at solar minimum.
---------------------------------------------------------
Title: Multi-frequency long-term monitoring of the ultracool dwarf
TVLM 513-46546
Authors: Antonova, Antoaneta; Doyle, John Gerard; Hallinan, Gregg;
Golden, Aaron; Bourke, Stephen
2010BlgAJ..14...58A Altcode:
Recently, observations of three ultracool dwarfs have shown that the
emission is in fact due to the electron cyclotron maser instability
operating in the low plasma density, high magnetic field strength
regions above the poles of a large-scale magnetic field, i.e. it is
similar to that of the magnetized planets in the Solar system. The
M8.5 dwarf TVLM 513-46546 is one of the most studied radio emitting
dwarfs. It has been found to display periodic pulses of 100% circularly
polarized radio emission, the periodicity of the bursts being consistent
with the rotational period of the dwarf as confirmed by optical I band
observations . Here we present a systematic review and analysis of all
observations of TVLM 513-46546 conducted in the radio X and C bands,
including our latest VLA and Arecibo observations.
---------------------------------------------------------
Title: Waves in the Transition Region
Authors: Scullion, E.; Erdélyi, R.; Doyle, J. G.
2010ASSP...19..426S Altcode: 2010mcia.conf..426S
Fundamental questions concerning coronal heating and the origin of
the fast solar wind may be answered through greater understanding of
fine structures in the lower solar atmosphere. We present results
from a 2.5-D ideal-MHD simulation from a new numerical code, plus
new supportive observational material. The simulation was run with
the Sheffield Advanced Code (SAC, Shelyag et al. 2008, A&A, 486,
655) and is supported by multi-instrument evidence of a surface wave
obtained from co-alignment of observations with Hinode/EIS and SoHO/MDI.
---------------------------------------------------------
Title: Fine Structure of a Coronal Bright Point as Seen with SoHO,
TRACE, and Hinode
Authors: Pérez-Suárez, D.; Maclean, R. C.; Doyle, J. G.; Madjarska,
M. S.
2009ASPC..415..140P Altcode:
We present a study of a Coronal Bright Point (BPs) where data from
Hinode, SoHO and TRACE are analyzed. Covering a large temperature
range, we study the variation of the BP from the surface to the
corona investigating both the morphology and variation in physical
parameters, such as electron density, Doppler-shift and magnetic field
variability. We obtain excellent correlation between the X-ray light
curve with the positive magnetic flux; also a good agreement is found
between a potential extrapolated magnetic field and the loops seen in
the X-ray images.
---------------------------------------------------------
Title: Jets in Polar Coronal Holes
Authors: Scullion, E.; Popescu, M. D.; Banerjee, D.; Doyle, J. G.;
Erdélyi, R.
2009ApJ...704.1385S Altcode:
Here, we explore the nature of small-scale jet-like structures and
their possible relation to explosive events and other known transient
features, like spicules and macrospicules, using high-resolution
spectroscopy obtained with the Solar and Heliospheric Observatory/Solar
Ultraviolet Measurements of Emitted Radiation instrument. We present
a highly resolved spectroscopic analysis and line parameter study
of time-series data for jets occurring on-disk and off-limb in
both a northern and a southern coronal hole. The analysis reveals
many small-scale transients which rapidly propagate between the
mid-transition region (N IV 765 Å line formation: 140,000 K) and
the lower corona (Ne VIII 770 Å line formation: 630,000 K). In one
example, a strong jet-like event is associated with a cool feature
not present in the Ne VIII 770 Å line radiance or Doppler velocity
maps. Another similar event is observed, but with a hot component,
which could be perceived as a blinker. Our data reveal fast, repetitive
plasma outflows with blueshift velocities of ≈145 km s<SUP>-1</SUP>
in the lower solar atmosphere. The data suggest a strong role for
smaller jets (spicules), as a precursor to macrospicule formation,
which may have a common origin with explosive events.
---------------------------------------------------------
Title: Explosive Events Associated with a Surge
Authors: Madjarska, M. S.; Doyle, J. G.; de Pontieu, B.
2009ApJ...701..253M Altcode: 2009arXiv0906.2544M
The solar atmosphere contains a wide variety of small-scale transient
features. Here, we explore the interrelation between some of them such
as surges, explosive events, and blinkers via simultaneous spectral
and imaging data taken with the TRACE imager, the SUMER and Coronal
Diagnostics Spectrometer (CDS) on board SOHO, and Swedish Vacuum Solar
Telescope La Palma. The features were observed in spectral lines with
formation temperatures from 10,000 K to 1 MK and with the TRACE Fe
IX/X 171 Å filter. The Hα filtergrams were taken in the wings of
the Hα 6365 Å line at ±700 mÅ and ±350 mÅ. The alignment of all
data in both time and solar XY shows that SUMER line profiles, which
are attributed to explosive events, are due to a surge phenomenon. The
surge's up- and downflows, which often appear simultaneously, correspond
to the blue- and redshifted emission of the transition region N V
1238.82 Å and O V 629.77 Å lines as well as radiance increases of
the C I, S I, and S II and Si II chromospheric lines. Some parts of
the surge are also visible in the TRACE 171 Å images which could
suggest heating to coronal temperatures. The surge is triggered,
most probably, by one or more Elerman bombs which are best visible
in Hα ± 350 Å but were also registered by TRACE Fe IX/X 171 Å
and correspond to a strong radiance increase in the CDS Mg IX 368.07
Å line. With the present study, we demonstrate that the division of
small-scale transient events into a number of different subgroups,
for instance explosive events, blinkers, spicules, surges or just
brightenings, is ambiguous, implying that the definition of a feature
based only on either spectroscopic or imaging characteristics as well
as insufficient spectral and spatial resolution can be incomplete.
---------------------------------------------------------
Title: Signatures of Alfvén waves in the polar coronal holes as
seen by EIS/Hinode
Authors: Banerjee, D.; Pérez-Suárez, D.; Doyle, J. G.
2009A&A...501L..15B Altcode: 2009arXiv0906.4600B
Context: We diagnose the properties of the plume and interplume regions
in a polar coronal hole and the role of waves in the acceleration of
the solar wind. <BR />Aims: We attempt to detect whether Alfvén waves
are present in the polar coronal holes through variations in EUV line
widths. <BR />Methods: Using spectral observations performed over a
polar coronal hole region with the EIS spectrometer on Hinode, we study
the variation in the line width and electron density as a function of
height. We use the density sensitive line pairs of Fe xii 186.88 Å
and 195.119 Å and Fe xiii 203.82 Å and 202.04 Å. <BR />Results:
For the polar region, the line width data show that the nonthermal
line-of-sight velocity increases from 26~km s<SUP>-1</SUP> at 10´´
above the limb to 42~km s<SUP>-1</SUP> some 150´´ (i.e. ~110 000
km) above the limb. The electron density shows a decrease from 3.3
× 10^9~cm<SUP>-3</SUP> to 1.9 × 10^8~cm<SUP>-3</SUP> over the same
distance. <BR />Conclusions: These results imply that the nonthermal
velocity is inversely proportional to the quadratic root of the electron
density, in excellent agreement with what is predicted for undamped
radially propagating linear Alfvén waves. Our data provide signatures
of Alfvén waves in the polar coronal hole regions, which could be
important for the acceleration of the solar wind. <P />Table [see full
textsee full textsee full text] and Fig. [see full textsee full textsee
full text] are only available in electronic form at http://www.aanda.org
---------------------------------------------------------
Title: Stellar and galactic environment survey (SAGE)
Authors: Barstow, M. A.; Burleigh, M. R.; Bannister, N. J.; Lapington,
J. S.; Kowalski, M. P.; Cruddace, R. G.; Wood, K. S.; Auchere,
F.; Bode, M. F.; Bromage, G. E.; Gibson, B.; Collier Cameron, A.;
Cassatella, A.; Delmotte, F.; Ravet, M. -F.; Doyle, J. G.; Jeffery,
C. S.; Gaensicke, B.; Jordan, C.; Kappelmann, N.; Werner, K.;
Lallement, R.; de Martino, D.; Matthews, S. A.; Phillips, K. J. H.;
Del Zanna, G.; Orio, M.; Pace, E.; Pagano, I.; Schmitt, J. H. M. M.;
Welsh, B. Y.
2009Ap&SS.320..231B Altcode: 2008Ap&SS.tmp..161B
This paper describes a proposed high resolution soft X-ray and
Extreme Ultraviolet (EUV) spectroscopy mission to carry out a survey
of Stellar and Galactic Environments (SAGE). The payload is based on
novel diffraction grating technology which has already been proven in
a sub-orbital space mission and which is ready to fly on a satellite
platform with minimal development. Much of the technical detail of
the instrumentation has been reported elsewhere and we concentrate
our discussion here on the scientific goals of a SAGE base-line
mission, demonstrating the scientific importance of high resolution
spectroscopy in the Extreme Ultraviolet for the study of stars and
the local interstellar medium.
---------------------------------------------------------
Title: Stellar And Galactic Environment survey (SAGE)
Authors: Barstow, M. A.; Kowalski, M. P.; Cruddace, R. G.; Wood, K. S.;
Auchere, F.; Bannister, N. J.; Bode, M. F.; Bromage, G. E.; Burleigh,
M. R.; Collier Cameron, A.; Cassatella, A.; Delmotte, F.; Doyle, J. G.;
Gaensicke, B.; Gibson, B.; Jeffery, C. S.; Jordan, C.; Kappelmann,
N.; Lallement, R.; Lapington, J. S.; de Martino, D.; Matthews, S. A.;
Orio, M.; Pace, E.; Pagano, I.; Phillips, K. J. H.; Ravet, M. -F.;
Schmitt, J. H. M. M.; Welsh, B. Y.; Werner, K.; Del Zanna, G.
2009ExA....23..169B Altcode: 2008ExA...tmp...25B
This paper describes a proposed high resolution soft X-ray and Extreme
Ultraviolet spectroscopy mission to carry out a survey of Stellar
and Galactic Environments (SAGE). The payload is based on novel
diffraction grating technology which has already been proven in a
sub-orbital space mission and which is ready to fly on a satellite
platform with minimal development. We discuss the goals of a SAGE
base-line mission and demonstrate the scientific importance of high
resolution spectroscopy in the Extreme Ultraviolet for the study of
stars and the local interstellar medium.
---------------------------------------------------------
Title: On the statistical detection of propagating waves in polar
coronal holes
Authors: Gupta, G. R.; O'Shea, E.; Banerjee, D.; Popescu, M.; Doyle,
J. G.
2009A&A...493..251G Altcode: 2009arXiv0902.2676G
Context: Waves are important to the study of dynamical processes
in coronal holes and the acceleration of the fast solar wind. A
spectral time series was taken with the SUMER spectrometer on-board
SoHO on 20 October 1996. The observations were obtained in the N iv
765 Å transition region line and the Ne viii 770 Å line of the low
corona. <BR />Aims: We detect the presence of waves and study their
characteristic properties in terms of their propagation speeds and
direction. Previous statistical studies, undertaken with data from the
CDS spectrometer, report the presence of waves in these regions. We
extend this analysis using SUMER observations. <BR />Methods: Using
Fourier techniques, we measured the phase delays between intensity
oscillations, as well as between velocity oscillations, in our two lines
over the full range of available frequencies. From this, we were able
to measure the travel time of the propagating oscillations, hence the
propagation speeds of the waves that produce the oscillations. <BR
/>Results: We detect the long period oscillations in polar coronal
holes on the disc. For network bright locations within coronal
holes, our results indicate the presence of compressional waves with
a dominant period of ≈25 min. However, we also find power at many
other different frequencies, so we are able to study oscillations over
a full range of frequencies. We find evidence of propagating waves with
a fixed time delay in the coronal hole. We find, moreover, that there
is a difference in the nature of the wave propagation in the bright
(“network”), as opposed to the dark (“internetwork”) regions,
with the latter sometimes showing evidence of downwardly propagating
waves that are not seen in the former. From a measurement of propagation
speeds, we find that all measured waves are subsonic in nature. <BR
/>Conclusions: Waves with different characteristics are found to
be present at different locations in the observed coronal hole. The
measured propagation speeds are subsonic, indicating that the majority
of them are slow magneto-acoustic in nature. These waves, measured
in the lower atmosphere, could accelerate farther at higher altitudes
and may be important for the acceleration of the fast solar wind.
---------------------------------------------------------
Title: On oscillations found in an active region with EIS on Hinode
Authors: O'Shea, E.; Doyle, J. G.
2009A&A...494..355O Altcode:
Aims: Using temporal series (40” slot) data in the ion{Fe}{xii}
195 Å line from the extreme-ultraviolet imaging spectrometer (EIS)
on board the Hinode satellite, we seek to carry out a statistical
study of oscillations in an active region. <BR />Methods: Using wavelet
techniques, we measure the frequency and duration of oscillations found
in the time series data. Stokes I and V data from Hinode's SOT are used
to measure photospheric magnetic fields, while an EIS raster is used to
provide estimates of LOS velocity and electron density. The measured
frequencies are displayed as maps in different bands to aid their
analysis. <BR />Results: Oscillations over a broad range of frequencies
(2-154 mHz) are found throughout the active region at the temperature
of ion{Fe}{xii} (log T=6.1 K). Oscillations with frequencies between 2-8
mHz are concentrated in bright plage areas, while oscillations of higher
frequency preferentially group at the edges of these areas. Evidence
is found for harmonics on the boundary of the active region loop,
indicating the presence of standing waves. From a measurement of
the lengths and electron density of loops appearing in our active
region field-of-view (FOV), together with a knowledge of the periods
(frequencies) of the oscillations within the area of these loops, we
find a magnetic field value of between 12.2±2.08-18.9±3.40 G, assuming
standing fast kink waves. <BR />Conclusions: We conclude that waves,
which the observed oscillations are signatures of, are common in the
active region studied, over a broad range of frequencies. The change in
the distribution of the oscillations present at frequencies less than
8 mHz and those at all frequencies above this indicates a variation of
the wave mode with frequency, e.g., possibly from slow magnetoacoustic
waves in the bright plage regions to fast magnetoacoustic waves at
the boundaries of these regions. The preference for higher frequency
oscillations to cluster on the edges of regions of high magnetic
field is considered indicative of resonant absorption. Based on our
measurements of magnetic field, we conclude that the oscillations
found by us in the active region loop are fast kink waves.
---------------------------------------------------------
Title: The structure and dynamics of a bright point as seen with
Hinode, SoHO and TRACE
Authors: Pérez-Suárez, D.; Maclean, R. C.; Doyle, J. G.; Madjarska,
M. S.
2008A&A...492..575P Altcode: 2008arXiv0810.1020P
Context: Solar coronal bright points have been studied for more than
three decades, but some fundamental questions about their formation and
evolution still remain unanswered. <BR />Aims: Our aim is to determine
the plasma properties of a coronal bright point and compare its magnetic
topology extrapolated from magnetogram data with its appearance in
X-ray images. <BR />Methods: We analyse spectroscopic data obtained with
EIS/Hinode, Ca ii H and G-band images from SOT/Hinode, UV images from
TRACE, X-ray images from XRT/Hinode and high-resolution/high-cadence
magnetogram data from MDI/SoHO. <BR />Results: The BP comprises several
coronal loops as seen in the X-ray images, while the chromospheric
structure consists of tens of small bright points as seen in Ca ii
H. An excellent correlation exists between the Ca ii H bright points
and increases in the magnetic field strength, implying that the Ca
ii H passband is a good indicator for the concentration of magnetic
flux. Furthermore, some of the Ca ii H bright points are the locations
of the loop foot-points as determined from a comparison between the
extrapolated magnetic field configuration and the X-ray images. Doppler
velocities between 6 and 15 km s<SUP>-1</SUP> are derived from the Fe
xii and Fe xiii lines for the bright point region, while for Fe xiv
and Si vii they are in the range from -15 to +15 km s<SUP>-1</SUP>. The
coronal electron density is 3.7 × 10<SUP>9</SUP> cm<SUP>-3</SUP>. An
excellent correlation is found between the positive magnetic flux and
the X-ray light-curves. <BR />Conclusions: The remarkable agreement
between the extrapolated magnetic field configuration and some of the
loops composing the bright point as seen in the X-ray images suggests
that a large fraction of the magnetic field in the bright point is close
to potential. However, some loops in the X-ray images do not have a
counterpart in the extrapolated magnetic field configuration implying
a non-potential component. The close correlation between the positive
magnetic flux and the X-ray emission suggests that energy released by
magnetic reconnection is stimulated by flux emergence or cancellation.
---------------------------------------------------------
Title: Lidar Observations of Volcanic Aerosol Layers Over Halifax,
Canada
Authors: Bitar, L.; Duck, T. J.; Doyle, J.; Perro, C.
2008AGUFM.A53B0272B Altcode:
Lidar measurements of vertical aerosol distributions from late
summer 2008 indicate the presence of unusual aerosol layers in the
upper troposphere and lower stratosphere over Halifax, Nova Scotia
in Eastern Canada (44.64°N, 63.59°W). Trajectory analyses indicate
that the sources of the aerosol layers were the explosive 7-8 August
eruptions of Kasatochi volcano in the Aleutian Volcanic Arc (52.17°N,
175.51°W). The aerosol plumes were detected on multiple days throughout
August and September by the Dalhousie Raman Lidar. A new high-altitude
receiver addition to the lidar system is being used to enhance
investigation of the optical characteristics as well as the vertical
and temporal structures of the observed volcanic aerosol layers.
---------------------------------------------------------
Title: Study of Transition Region Transient Events with Hinode
Authors: Subramanian, S.; Madjarska, M.; Doyle, J. G.
2008ASPC..397..194S Altcode:
We present preliminary results of a study of transient events in the
solar transition region (TR), using observations taken at disk centre
on 9 April, 2007 with SOT, XRT and EIS on-board Hinode; CDS and MDI
on-board SoHO, plus TRACE covering the photosphere to corona.
---------------------------------------------------------
Title: Confirmation of the Electron Cyclotron Maser Instability as
the Dominant Source of Radio Emission from Very Low Mass Stars and
Brown Dwarfs
Authors: Hallinan, G.; Antonova, A.; Doyle, J. G.; Bourke, S.; Lane,
C.; Golden, A.
2008ApJ...684..644H Altcode: 2008arXiv0805.4010H
We report on radio observations of the M8.5 dwarf LSR J1835+3259 and
the L3.5 dwarf 2MASS J00361617+1821104, which provide the strongest
evidence to date that the electron cyclotron maser instability is the
dominant mechanism producing radio emission in the magnetospheres
of ultracool dwarfs. As has previously been reported for the M9
dwarf TVLM 513-46546, periodic pulses of 100% circularly polarized,
coherent radio emission are detected from both dwarfs with periods of
2.84 +/- 0.01 and 3.08 +/- 0.05 hr, respectively, for LSR J1835+3259
and 2MASS J00361617+1821104. Importantly, periodic unpolarized radio
emission is also detected from 2MASS J00361617+1821104, and brightness
temperature limitations rule out gyrosynchrotron radiation as a source
of this radio emission. The unpolarized emission from this and other
ultracool dwarfs is also attributed to electron cyclotron maser
emission, which has become depolarized on traversing the ultracool
dwarf magnetosphere, possibly due to propagations effects such as
scattering. Based on available vsin i data in the literature and
rotation periods derived from the periodic radio data for the three
confirmed sources of electron cyclotron maser emission, TVLM 513-46546,
LSR J1835+3259, and 2MASS J00361617+1821104, we determine that the
rotation axes of all three dwarfs are close to perpendicular to our
line of sight. This suggests a possible geometrical selection effect
due to the inherent directivity of electron cyclotron maser emission,
that may account for the previously reported relationship between radio
activity and vsin i observed for ultracool dwarfs. We also determine
the radius of the dwarf LSR J1835+3259 to be >=0.117 +/- 0.012
R<SUB>⊙</SUB>. The implied size of the radius, together with the
bolometric luminosity of the dwarf, suggests that either LSR J1835 is
a young- or intermediate-age brown dwarf, or that current theoretical
models underestimate the radii of ultracool dwarfs.
---------------------------------------------------------
Title: Magnetic topology of blinkers
Authors: Subramanian, S.; Madjarska, M. S.; Maclean, R. C.; Doyle,
J. G.; Bewsher, D.
2008A&A...488..323S Altcode:
Context: Co-spatial and co-temporal spectroscopic, imaging and
magnetogram data enable us to better understand various solar transient
phenomena. Here, we study brightening events in the transition region
of the quiet Sun, also called “blinkers”. <BR />Aims: We aim
to investigate the physical mechanism responsible for blinkers. <BR
/>Methods: An automated blinker identification procedure (BLIP) is
used to identify blinker events in SoHO/CDS data. The 3D magnetic
topology of the magnetic field in the blinker region is reconstructed
based on SoHO/MDI magnetogram data. <BR />Results: During 3 h of
SoHO/CDS observations on 2006 January 18, 66 blinkers were identified
in the O v 629 Å emission line. Out of them, a group comprising of
16 events were modelled here. They were found to be associated with
the emergence of magnetic flux which gave rise to the appearance of,
and multiple magnetic reconnection events across, an upper atmosphere
(coronal) magnetic null point, along with a loop structure as observed
with TRACE. <BR />Conclusions: This blinker group results from the
release of energy that was accumulated during flux emergence, although
whether all blinkers follow the same formation scenario requires
further investigation using additional multi-instrument/multi-mission
studies. <P />2 movies are only available in electronic form at
http://star.arm.ac.uk/preprints/ and http://www.aanda.org
---------------------------------------------------------
Title: Magnetic Variability of an XRT Bright Point
Authors: Maclean, R. C.; Owens, B. J.; Pérez Suárez, D.; Doyle, J. G.
2008ASPC..397..178M Altcode:
Solar coronal bright points display complex internal structure when
viewed at the high spatial resolutions provided by the instruments
onboard Hinode and SoHO. We study the magnetic evolution of a newly
formed bright point on the 6th of April 2007, using high-resolution
SoHO/MDI magnetogram data as a basis for topological reconstruction
of the 3D magnetic field in the corona. A dynamic network of magnetic
connections exists both within the bright point itself and linking it
with the surrounding magnetic features. When these changes in magnetic
connectivity are compared with Hinode/XRT observations of X-ray loops
and brightenings, we can gain new insights into how changes in the
coronal magnetic field configuration lead to brightenings of magnetic
structures within the bright point, with possible implications for
coronal heating.
---------------------------------------------------------
Title: A mini-survey of ultracool dwarfs at 4.9 GHz
Authors: Antonova, A.; Doyle, J. G.; Hallinan, G.; Bourke, S.;
Golden, A.
2008A&A...487..317A Altcode: 2008arXiv0805.4574A
Context: A selection of ultracool dwarfs are known to be radio active,
with both gyrosynchrotron emission and the electron cyclotron maser
instability being given as likely emission mechanisms. <BR />Aims: We
explore whether ultracool dwarfs previously undetected at 8.5 GHz may
be detectable at a lower frequency. <BR />Methods: We select a sample
of fast rotating ultracool dwarfs with no detectable radio activity at
8.5 GHz, observing each of them at 4.9 GHz. <BR />Results: From the 8
dwarfs in our sample, we detect emission from 2MASS J07464256+2000321,
with a mean flux level of 286 ± 24 μJy. The light-curve of 2MASS
J07464256+2000321, is dominated towards the end of the observation by a
very bright, ≈ 100% left circularly polarized burst during which the
flux reached 2.4 mJy. The burst was preceded by a raise in the level of
activity, with the average flux being ≈160 μJy in the first hour of
observation rising to ≈400 μJy in the 40 min before the burst. During
both periods, there is significant variability. <BR />Conclusions:
The detection of 100% circular polarization in the emission at 4.9
GHz points towards the electron cyclotron maser as the emission
mechanism. However, the observations at 4.9 GHz and 8.5 GHz were not
simultaneous, thus the actual fraction of dwarfs capable of producing
radio emission, as well as the fraction of those that show periodic
pulsations is still unclear, as indeed are the relative roles played
by the electron cyclotron maser instability versus gyrosynchrotron
emission, therefore we cannot assert if the previous non-detection
at 8.5 GHz was due to a cut-off in emission between 4.9 and 8.4 GHz,
or due to long term variability.
---------------------------------------------------------
Title: Small-scale flows in SUMER and TRACE high-cadence
co-observations
Authors: Madjarska, M. S.; Doyle, J. G.
2008A&A...482..273M Altcode: 2008arXiv0802.2477M
Context: We report on the physical properties of small-scale
transient flows observed simultaneously at high cadence with
the SUMER spectrometer and the TRACE imager in the plage area of
an active region. <BR />Aims: Our major objective is to provide a
better understanding of the nature of transient phenomena in the solar
atmosphere by using high-cadence imager and spectrometer co-observations
at similar spatial and temporal resolution. <BR />Methods: A sequence
of TRACE Fe IX/X λ171 Å and high-resolution MDI images were analysed
together with simultaneously obtained SUMER observations in spectral
lines covering a temperature range from 10 000 K to 1 MK. <BR />Results:
We reveal the existence of numerous transient flows in small-scale loops
(up to 30 Mm) observed in the plage area of an active region. These
flows have temperatures from 10 000 K (the low temperature limit
of our observations) to 250 000 K. The coronal response of these
features is uncertain due to a blending of the observed coronal line
Mg x λ624.85 Å. The duration of the events ranges from 60 s to 19
min depending on the loop size. Some of the flows reach supersonic
velocities. <BR />Conclusions: The Doppler shifts often associated with
explosive events or bi-directional jets can actually be identified with
flows (some of them reaching supersonic velocities) in small-scale
loops. Additionally, we demonstrate how a line-of-sight effect can
give misleading information on the nature of the observed phenomena
if only either an imager or a spectrometer is used. <P />An animation
of the TRACE λ171 Å images is only available in electronic form
at http://www.aanda.org
---------------------------------------------------------
Title: Jets or High-Velocity Flows Revealed in High-Cadence
Spectrometer and Imager Co-observations?
Authors: Madjarska, M. S.; Doyle, J. G.; Innes, D. E.; Curdt, W.
2007ApJ...670L..57M Altcode: 2007arXiv0710.2199M
We report on active region EUV dynamic events observed simultaneously
at high cadence with SOHO SUMER and TRACE. Although the features
appear in the TRACE Fe IX/X 171 Å images as jets seen in projection
on the solar disk, the SUMER spectral line profiles suggest that the
plasma has been driven along a curved large-scale magnetic structure,
a preexisting loop. The SUMER observations were carried out in
spectral lines covering a large temperature range from 10<SUP>4</SUP>
to 10<SUP>6</SUP> K. The spectral analysis revealed that a sudden
heating from an energy deposition is followed by a high-velocity
plasma flow. The Doppler velocities were found to be in the range
from 90 to 160 km s<SUP>-1</SUP>. The heating process has a duration
which is below the SUMER exposure time of 25 s while the lifetime of
the events is from 5 to 15 minutes. The additional check on soft X-ray
Yohkoh images shows that the features most probably reach 3 MK (X-ray)
temperatures. The spectroscopic analysis showed no existence of cold
material during the events.
---------------------------------------------------------
Title: Plasma condensation in coronal loops
Authors: O'Shea, E.; Banerjee, D.; Doyle, J. G.
2007A&A...475L..25O Altcode:
Aims:Using temporal series data from the Coronal Diagnostic Spectrometer
(CDS) on SOHO, we seek to investigate plasma condensation through
the use of spectroscopic analysis. <BR />Methods: Using a space-time
(X-T) type plot we show, for a number of transition region (TR) and
coronal lines, the variation of intensity (radiant flux) with time in
an off-limb loop system. Noting a number of pixels where the intensity
shows a sharp jump in value for the TR lines and a corresponding sharp
decrease for the coronal lines, we investigate further and plot the
intensity and velocity for these pixels as a function of time. Using
standard Fourier techniques, together with a pre-whitening method, we
measure all statistically significant frequencies present in the time
series so created. <BR />Results: We find that, for the cooler lines
of He I 584 Å and O V 629 Å, there are sharp increases in intensity,
accompanied by large blueshifted velocities. In the case of O V there
is a substantial rebound to redshifted velocities when the strong
brightening fades. The sharp increase in intensity and blueshifted
velocity in the cooler lines is accompanied by a corresponding decrease
in the intensity of the coronal lines (Mg X 624 Å, Fe XVI 360 Å,
Si XII 520 Å), but with no corresponding change in their velocity
values implying an evacuation of plasma. From the Fourier analysis,
evidence is found for possible 1st and 2nd harmonics in the He I and
O V lines, indicative of standing waves in loops. <BR />Conclusions:
We conclude that what we are seeing is the first spectroscopic evidence
of plasma condensation taking place in coronal loops. <P />A movie is
only available in electronic form at http://www.aanda.org
---------------------------------------------------------
Title: Evidence for wave harmonics in cool loops
Authors: O'Shea, E.; Srivastava, A. K.; Doyle, J. G.; Banerjee, D.
2007A&A...473L..13O Altcode:
Aims:Using temporal series image data from the Coronal Diagnostic
Spectrometer (CDS) on SOHO, we study oscillations found in intensity
(radiance) measurements from the transition region O v 629 line with
the aim of finding evidence of wave harmonics in cool loops. <BR
/>Methods: Using standard Fourier techniques, together with a
pre-whitening method, we measure all statistically significant
frequencies present in oscillations found in flaring active region
loops at the temperature of O v. By measuring the distances travelled
by three Propagating Disturbances (PDs), estimates of their propagation
speeds are calculated. <BR />Results: Evidence is found for harmonics
in the measured oscillations suggesting the presence of standing waves
in the loops. We find that PDs in cool O v active region loops have
sub-sonic velocities of between 12-24 km s<SUP>-1</SUP>, suggesting they
are moved either by slow mode (acoustic or slow magnetoacoustic) wave
propagation or by bulk flows along the loops triggered by the flaring
that also produces the PDs. <BR />Conclusions: We find evidence that
standing waves are present in flaring cool transition region loops. This
evidence comes in the form of oscillations showing harmonic frequencies
that match those expected for standing fast kink waves.
---------------------------------------------------------
Title: Rotational Modulation of M/L Dwarfs due to Magnetic Spots
Authors: Lane, C.; Hallinan, G.; Zavala, R. T.; Butler, R. F.; Boyle,
R. P.; Bourke, S.; Antonova, A.; Doyle, J. G.; Vrba, F. J.; Golden, A.
2007ApJ...668L.163L Altcode: 2007arXiv0709.1045L
We find periodic I-band variability in two ultracool dwarfs,
TVLM 513-46546 and 2MASS J00361617+1821104, on either side of the
M/L dwarf boundary. Both of these targets are short-period radio
transients, with the detected I-band periods matching those found at
radio wavelengths (P=1.96 hr for TVLM 513-46546 and P=3 hr for 2MASS
J00361617+1821104). We attribute the detected I-band periodicities to
the periods of rotation of the dwarfs, supported by radius estimates
and measured vsini values for the objects. Based on the detected
period of rotation of TVLM 513-46546 (M9) in the I band, along with
confirmation of strong magnetic fields from recent radio observations,
we argue for magnetically induced spots as the cause of this periodic
variability. The I-band rotational modulation of the L3.5 dwarf 2MASS
J00361617+1821104 appeared to vary in amplitude with time. We conclude
that the most likely cause of the I-band variability for this object
is magnetic spots, possibly coupled with time-evolving features such
as dust clouds.
---------------------------------------------------------
Title: Sporadic long-term variability in radio activity from a
brown dwarf
Authors: Antonova, A.; Doyle, J. G.; Hallinan, G.; Golden, A.; Koen, C.
2007A&A...472..257A Altcode: 2007arXiv0707.0634A
Context: Radio activity has been observed in a large variety of stellar
objects, including in the last few years, ultra-cool dwarfs. <BR
/>Aims: To explore the extent of long-term radio activity in ultra-cool
dwarfs. <BR />Methods: We use data taken over an extended period of 9
hr from the Very Large Array of the source 2MASS J05233822-1403022 in
September 2006, plus data taken in 2004. <BR />Results: The observation
taken in September 2006 failed to detect any radio activity at 8.46
GHz. A closer inspection of earlier data reveals that the source
varied from a null detection on 3 May 2004, to ≈95 μJy on 17
May 2004, to 230 μJy on 18 June 2004. The lack of detection in
September 2006 suggests at least a factor of ten flux variability
at 8.46 GHz. Three short photometric runs did not reveal any optical
variability. <BR />Conclusions: In addition to the observed pulsing
nature of the radio flux from another ultra-cool source, the present
observations suggests that ultra-cool dwarfs may not just be pulsing
but can also display long-term sporadic variability in their levels of
quiescent radio emission. The lack of optical photometric variability
suggests an absence of large-scale spots at the time of the latest VLA
observations, although small very high latitude spots combined with a
low inclination could cause very low amplitude rotational modulation
which may not be measurable. We discuss this large variability in the
radio emission within the context of both gyrosynchrotron emission
and the electron-cyclotron maser, favoring the latter mechanism.
---------------------------------------------------------
Title: Periodic Bursts of Coherent Radio Emission from an Ultracool
Dwarf
Authors: Hallinan, G.; Bourke, S.; Lane, C.; Antonova, A.; Zavala,
R. T.; Brisken, W. F.; Boyle, R. P.; Vrba, F. J.; Doyle, J. G.;
Golden, A.
2007ApJ...663L..25H Altcode: 2007arXiv0705.2054H
We report the detection of periodic (p=1.96 hr) bursts of extremely
bright, 100% circularly polarized, coherent radio emission from
the M9 dwarf TVLM 513-46546. Simultaneous photometric monitoring
observations have established this periodicity to be the rotation
period of the dwarf. These bursts, which were not present in previous
observations of this target, confirm that ultracool dwarfs can
generate persistent levels of broadband, coherent radio emission,
associated with the presence of kG magnetic fields in a large-scale,
stable configuration. Compact sources located at the magnetic polar
regions produce highly beamed emission generated by the electron
cyclotron maser instability, the same mechanism known to generate
planetary coherent radio emission in our solar system. The narrow beams
of radiation pass our line of sight as the dwarf rotates, producing
the associated periodic bursts. The resulting radio light curves are
analogous to the periodic light curves associated with pulsar radio
emission highlighting TVLM 513-46546 as the prototype of a new class
of transient radio source.
---------------------------------------------------------
Title: On the Signature of MHD Waves in Coronal Holes
Authors: Srivastava, A. K.; Doyle, J. G.; O'Shea, E.
2007nam7.conf...87S Altcode:
Polar coronal holes are the open magnetic field regions of
strongly-reduced emissions at various wavelengths. Recent spectroscopic
analysis provides an evidence for the presence of MHD waves, which may
be one of the possible energy sources in polar coronal holes. We present
our some recent findings which interestedly engaged with the presence
of MHD waves, and discuss their possible roles in polar coronal holes.
---------------------------------------------------------
Title: A statistical study of wave propagation in coronal holes
Authors: O'Shea, E.; Banerjee, D.; Doyle, J. G.
2007A&A...463..713O Altcode:
Aims:To find evidence for propagating magnetoacoustic waves in
equatorial and polar coronal hole locations. <BR />Methods: Using
temporal series data from the Coronal Diagnostic Spectrometer (CDS)
on SOHO, we study oscillations found in radiant flux and velocity
measurements from transition region (O V 629) and coronal lines
(Mg X 624, Si XII 520). We use Fourier techniques to measure phase
delays between flux ("intensity") oscillations and between velocity
oscillations of different transition region-corona and corona-corona
line pairs. We also measure the phase delays between flux and velocity
oscillations (I-V) in the three spectral lines investigated. <BR
/>Results: We find outwardly propagating slow magnetoacoustic waves
in both of the coronal hole regions studied. The propagation speeds
are found to be lower than those found in off-limb locations. We
find evidence for a resonant cavity or "Doppler" effect, whereby the
measured phases are present at fixed integer intervals of f/4 (90°
of phase) and 3f/8 (135° of phase) instead of the expected interval
of f or 360°. We find, in addition, from the I-V phases, evidence for
standing waves at coronal temperatures in the lines of Mg X 624 and Si
XII 520. Correlations are found between the locations where the phases
are measured and localised brightenings in both equatorial and polar
coronal holes. This suggests that the slow magnetoacoustic waves are
originating preferentially from bright areas within the coronal holes
which we take to be the locations of concentrated magnetic field (loops,
bright points). Finally, we find evidence that in these bright regions
along the slit, the measured phases tend to occur at a spectrum of
frequencies, perhaps suggesting the presence of discrete propagating
wave packets. <BR />Conclusions: .We conclude that propagating slow
magnetoacoustic waves are present in equatorial and polar coronal
hole locations and that they occur preferentially in bright regions
that are associated with magnetic field concentrations in the form of
loops or bright points. In addition, we conclude that some resonant
cavity effect is affecting the propagating waves, perhaps resulting
in the standing waves that are found at coronal temperatures.
---------------------------------------------------------
Title: A study of a macro-spicule and a transition region explosive
event in a solar coronal hole
Authors: Popescu, M. D.; Xia, L. D.; Banerjee, D.; Doyle, J. G.
2007AdSpR..40.1021P Altcode:
AimsSpicules and the higher macro-spicules (jet-like structures seen
at the solar limb) are believed to be the dominant mechanism for mass
ejection in the higher solar atmosphere outside active regions. But
what is the connection between them and other small-scale structures
in the Sun's atmosphere, like for example transition region explosive
events, is not known yet. MethodsOur data are temporal series
spectroheliograms of EUV emission lines from two ions (N IV 765 Å
and Ne VIII 770 Å), taken with the SUMER (Solar UV Measurements of
Emitted Radiation) spectrograph on SoHO (the Solar and Heliospheric
Observatory). SUMER's good spatial, spectral and temporal resolution
allowed us to have one of the most detailed studies of these small-scale
structures over a range of transition region temperatures. ResultsOur
study reveals that a macro-spicule seen off-limb looks similar to a
transition region explosive event, especially in the map of the lines'
full-width-at-half-maximum (FWHM). The macro-spicule seen in the low
transition region N IV line (≈140,000 K) is also visible in the
higher temperature Ne VIII line (≈630,000 K). Also, the jet seen
on-disk in the N IV line heats and accelerates plasma to the higher Ne
VIII temperature, traveling probably along the local (presumably open)
magnetic field line.
---------------------------------------------------------
Title: Analysis of power spectra of Doppler shift time series as a
diagnostic tool for quiescent coronal loops
Authors: Taroyan, Y.; Erdélyi, R.; Doyle, J. G.; Bradshaw, S. J.
2007A&A...462..331T Altcode:
Context: Analysing the structure of solar coronal loops is crucial
to our understanding of the processes which heat and maintain the
coronal plasma at multimillion degree temperatures. The determination
of the physical parameters of the loops remains both an observational
and theoretical challenge. <BR />Aims: The present work is aimed at
tackling some of these challenges such as the determination of the
average loop temperature and its distribution along a given loop. <BR
/>Methods: A novel diagnostic technique for quiescent coronal loops
based on the analysis of power spectra of Doppler shift time series
is proposed. It is assumed that the loop is heated randomly both in
space and time by small-scale discrete impulsive events of unspecified
nature. The loop evolution is characterised by longitudinal motions
caused by the random heating events. These random motions can be
represented as a superposition of the normal modes of the loop,
i.e., its standing acoustic wave harmonics. The idea is borrowed
from helioseismology where a similar approach resulted in a deep
understanding of the solar interior. <BR />Results: It is shown that
depending on the heliographic position of the loop and its geometrical
orientation, various harmonics can be identified in the power spectra
of the line shift time series. The highest power peak corresponds
to the fundamental mode. The peaks become smaller as the frequency
increases. The frequencies of the harmonics are determined by the
loop length and temperature and thus are suggested to be used as a
temperature diagnostic tool. It is demonstrated that the analysis of
the power spectra allows the distinction between uniformly heated
loops from loops heated near their footpoints and to estimate the
average energy of a single heating event. The proposed new method
could in principle be used to study the multithermal structure of
coronal loops. <BR />Conclusions: .The power spectrum analysis is a
potentially powerful technique for coronal loop diagnostics.
---------------------------------------------------------
Title: Rotational Modulation of the Radio Emission from the M9
Dwarf TVLM 513-46546: Broadband Coherent Emission at the Substellar
Boundary?
Authors: Hallinan, G.; Antonova, A.; Doyle, J. G.; Bourke, S.; Brisken,
W. F.; Golden, A.
2006ApJ...653..690H Altcode: 2006astro.ph..8556H
The Very Large Array was used to observe the ultracool rapidly rotating
M9 dwarf TVLM 513-46546 simultaneously at 4.88 and 8.44 GHz. The radio
emission was determined to be persistent, variable, and periodic at both
frequencies with a period of ~2 hr. This periodicity is in excellent
agreement with the estimated period of rotation of the dwarf based on
its vsini of ~60 km s<SUP>-1</SUP>. This rotational modulation places
strong constraints on the source size of the radio-emitting region and
hence the brightness temperature of the associated emission. We find
the resulting high brightness temperature, together with the inherent
directivity of the rotationally modulated component of the emission,
difficult to reconcile with incoherent gyrosynchrotron radiation. We
conclude that a more likely source is coherent, electron cyclotron maser
emission from the low-density regions above the magnetic poles. This
model requires the magnetic field of TVLM 513-46546 to take the form of
a large-scale, stable dipole or multipole with surface field strengths
up to at least 3 kG. We discuss a mechanism by which broadband,
persistent electron cyclotron maser emission can be sustained in
the low-density regions of the magnetospheres of ultracool dwarfs. A
second nonvarying, unpolarized component of the emission may be due to
depolarization of the coherent electron cyclotron maser emission or,
alternatively, incoherent gyrosynchrotron or synchrotron radiation from
a population of electrons trapped in the large-scale magnetic field.
---------------------------------------------------------
Title: Transition region counterpart of a moving magnetic feature
Authors: Lin, C. -H.; Banerjee, D.; O'Shea, E.; Doyle, J. G.
2006A&A...460..597L Altcode:
Context: .While moving magnetic features have been studied extensively
at the photospheric level, the effect they have on the upper atmosphere
remains largely unknown, and it is this which we seek to address in this
work.<BR /> Aims: .In this work we aim to investigate the chromospheric
and transition-region dynamics associated with a moving magnetic
monopole by using spectral time-series and images.<BR /> Methods:
.Cross correlation was applied to images taken by different instruments
and at different times in order to spatially correlate brightenings
seen at transition region temperatures with moving magnetic features
seen in magnetograms. We used wavelet analysis to examine and compare
the periodicities of time-series signals in different regions.<BR />
Results: .Oscillations with a multitude of frequencies are found in
the chromospheric and transition-region brightenings associated with
a moving magnetic monopole. The region of the brightenings shows a
tendency to be blue-shifted when compared to the average motion of the
entire field of view. The results indicate the presence of waves and/or
flows carrying energy from the monopole to the higher atmosphere.<BR />
Conclusions: .We studied the influence of a moving magnetic monopole,
as recorded by magnetograms, up to transition region temperatures. This
suggests that the magnetic monopole, despite being small, can influence
dynamics in the upper atmospheric layers.
---------------------------------------------------------
Title: GALEX high time-resolution ultraviolet observations of dMe
flare events
Authors: Welsh, B. Y.; Wheatley, J.; Browne, S. E.; Siegmund, O. H. W.;
Doyle, J. G.; O'Shea, E.; Antonova, A.; Forster, K.; Seibert, M.;
Morrissey, P.; Taroyan, Y.
2006A&A...458..921W Altcode: 2006astro.ph..8254W
Aims.We present near ultraviolet (NUV: 1750-2800 Å) and far ultraviolet
(FUV: 1350-1750 Å) light-curves for flares on 4 nearby dMe-type
stars (GJ 3685A, CR Dra, AF Psc and SDSS J084425.9+513830.5) observed
with the GALEX satellite.<BR /> Methods: .Taking advantage of the
time-tagged events recorded with the GALEX photon counting detectors,
we present high temporal resolution (<0.01 s) analysis of these UV
flare data.<BR /> Results: .A statistical analysis of 700 s of pre-flare
quiescence data for both CR Dra and SDSS J084425.9+513830.5 failed to
reveal the presence of significant micro-flare activity in time bins of
0.2, 1 and 10 s intervals. Using an appropriate differential emission
measure for both the quiescent and flaring state, it is possible
to reproduce the observed FUV:NUV flux ratios. A major determinant
in reproducing this flux ratio is found to be the value of plasma
electron density during the flare. We also searched the count rate
data recorded during each of the four flare events for periodicity
associated with magneto-hydrodynamic oscillations in the active region
coronal loops. Significant oscillations were detected during the flare
events observed on all 4 stars, with periodicities found in the 30 to
40 s range. Flare oscillations with this periodicity can be explained
as acoustic waves in a coronal loop of length of ≈10<SUP>9</SUP> cm
for an assumed plasma temperature of 5-20 × 10<SUP>6</SUP> K. This
suggests a loop length for these M-dwarf flares of less than 1/10th
of the stellar radii. We believe that this is the first detection
of non-solar coronal loop flare oscillations observed at ultraviolet
wavelengths.<BR />
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Title: Observational Clues to the Origin of the Fast Solar Wind
Authors: Popescu, M. D.; Doyle, J. G.; Banerjee, D.
2006ihy..workE..43P Altcode:
It is well known that the fast solar wind originates from coronal
holes, but its source close to the solar 'surface' has been a matter
of debate even in today's era of modern solar observations. Recently,
it has been suggested that the fast solar wind outflow starts at about
10 kilometers per second in coronal funnels, which are located at the
edges of the chromospheric magnetic network inside coronal holes. We
present further evidence that the outflow might also originate from
above 'explosive event' sites. These jets have a lifetime of about
5 minutes and are often seen reoccurring at the same location over
intervals of typically 20-30 minutes. Although the expelled jets
might actually extend high in the Sun's atmosphere, they are not
seen in the intensity on the disk. Some of the transparent features
might nevertheless appear as macrospicules at the Sun's edge. This
observation itself is shedding new light onto another long- standing
question regarding the nature of macrospicules. These results about
the small-scale structures of coronal holes and their consequence on
explaining the nature of the fast solar wind have been derived due
to an innovative way of extracting information from the spectral data
offered by SOHO’s highest resolution detector, SUMER. The 'secret'
of our technique lies in understanding plasma properties from the
signature it leaves in the shape and widths of the spectral lines.
---------------------------------------------------------
Title: Line Broadening of EUV Lines at the Solar Limb Observed with
SUMER/SoHO. Relation to Spicules
Authors: Giannikakis, J.; Tsiropoula, G.; Tziotziou, K.; Antonopoulou,
E.; Doyle, J. G.
2006AIPC..848..115G Altcode:
We study the broadening of EUV line widths as we move from the
disk through and off the solar limb. This broadening maximizes at
approximately 10 Mm above the limb. We use one raster scan and two
time series obtained by SUMER/SoHO to examine a possible correlation
between this phenomenon and spicule activity. It appears that spicule
presence leads to even wider profiles whereas the appearance of
macrospicules extends the broadening to even greater distances above
the limb. We suggest that this correlation might imply that spicules
are responsible for this disk-to-limb behavior even in regions where
they cannot be observed.
---------------------------------------------------------
Title: Off-Limb Coronal Loop Dynamics as Seen from CDS, EIT and TRACE
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.
2006ESASP.617E..83B Altcode: 2006soho...17E..83B
No abstract at ADS
---------------------------------------------------------
Title: The Signature of Moving Magnetic Feature in the Solar
Atmosphere
Authors: Lin, C. -H.; Banerjee, D.; O'Shea, E.; Doyle, J. G.
2006ESASP.617E..97L Altcode: 2006soho...17E..97L
No abstract at ADS
---------------------------------------------------------
Title: Dynamic features in the solar atmosphere with unusual spectral
line enhancements and Doppler-shifts
Authors: Doyle, J. G.; Ishak, B.; Madjarska, M. S.; O'Shea, E.;
Dzifćáková, E.
2006A&A...451L..35D Altcode:
Context.The solar atmosphere contains a wide variety of transient
features, here, we discuss data relating to one such feature. <BR
/>Aims.To explore via simultaneous spectral and imaging data the
nature of high-velocity flow events in the solar transition region. <BR
/>Methods.High spectral and temporal resolution data from SUMER/SoHO
plus high resolution images from TRACE are used. <BR />Results.In the
transient feature discussed, we see a factor of two enhancement in N
v 1238, coupled with a factor of two decrease in O v 629 visible over
3”-4” along the slit. Furthermore, the O v line shows a secondary
component with a down-flow of ≈75 km s<SUP>-1</SUP>, while the
N v line shows only a small additional broadening of the line. <BR
/>Conclusions.Inclusion of an electron density dependent ionization
calculation will increase the N v radiance over that of O v at large
electron densities. We suggest this feature can be explained via a
highly focused jet at the O v/Ovi formation temperature resulting from
reconnection. Also, we believe that this event is not unique but that
their detection depends on the availability of simultaneous spectral
and imaging data of comparable spatial and temporal resolution.
---------------------------------------------------------
Title: Magnetoacoustic wave propagation in off-limb polar regions
Authors: O'Shea, E.; Banerjee, D.; Doyle, J. G.
2006A&A...452.1059O Altcode:
Aims.To find evidence of magnetoacoustic waves in off-limb polar
regions.<BR /> Methods: .Using temporal series data from the Coronal
Diagnostic Spectrometer (CDS) on SOHO, we study oscillations found
in radiant flux and velocity measurements from transition region and
coronal spectral lines. We use Fourier techniques to measure phase
delays between flux (“intensity”) oscillations and between velocity
oscillations of different transition region-corona and corona-corona
line pairs. We also measure the phase delays between flux and velocity
oscillations (I-V).<BR /> Results: .The phase delays measured between
different line pairs, when plotted over a -180 ° to +180 ° range,
line up along diagonal lines corresponding to measurable and fixed
time delays. The slopes of these diagonal lines suggest the outward
propagation of waves. Using the measured time delays, we estimate
propagation speeds for the different line pairs that indicate that
the waves producing the observed phase delays are magnetoacoustic
waves propagating at speeds close to the sound speed. In addition,
we find that the phases occur at fixed integer frequencies of f/4
(90 °) and 3f/16 (67.5 °), instead of the expected interval of f
(360 °), indicating that a “Doppler effect” is acting on the
waves.<BR /> Conclusions: .From I-V measurements, we find evidence
for fast magnetoacoustic waves to be predominantly present at
coronal temperatures, while at transition region temperatures slow
magnetoacoustic waves are more common. We find strong evidence for
outwardly propagating slow magnetoacostic waves in off-limb polar
regions and an indication that these propagating waves are influenced
by some form of resonant cavity through which they pass.
---------------------------------------------------------
Title: Study of a transient siphon flow in a cold loop
Authors: Doyle, J. G.; Taroyan, Y.; Ishak, B.; Madjarska, M. S.;
Bradshaw, S. J.
2006A&A...452.1075D Altcode:
Context: .The nature of loops is still a matter of debate with several
explanations having been put forward. Simultaneous spectral and imaging
data have the capacity to provide a new insight into mass motions,
dynamics and energetics of loops.<BR /> Aims: .We report on spectral
data taken with the Solar Ultraviolet Measurements of Emitted Radiation
spectrograph (SUMER) and imaging data from the Transition Region and
Coronal Explorer (TRACE) of a transient event which occurred in a cold
loop, lasting a few minutes.<BR /> Methods: .A sequence of TRACE images
in the 1550 Å and 171 Å filters show a disturbance which originated
at one foot-point and propagates along the loop. The SUMER slit was
placed at the other foot-point of the loop. In order to interpret the
results, numerical simulations were performed with the results then
converted into observable quantities and compared with the data.<BR />
Results: .During the event a radiance increase and a relative red shift
of ≈ 20~km s<SUP>-1</SUP> was detected in the N v 1238.82 Å line. 1D
numerical simulations are performed and observable quantities derived
from the results of the simulations. The observed dynamic behaviour of
the N v 1238.82 Å line profiles was recovered.<BR /> Conclusions: .The
results suggest that the observations could be interpreted in terms of
a short-lived siphon flow reaching a speed of 120~km s<SUP>-1</SUP>
and driven by a nonlinear heating pulse. The energies required to
drive the observed red-shifts are estimated to be about 10<SUP>25</SUP>
erg. The absence of a significant blue-shift caused by the return flow
is explained.
---------------------------------------------------------
Title: Macrospicules and blinkers as seen in Shutterless EIT 304 Å
Authors: Madjarska, M. S.; Doyle, J. G.; Hochedez, J. -F.; Theissen, A.
2006A&A...452L..11M Altcode:
Aims.Small-scale transient phenomena in the solar atmosphere are
believed to play a crucial role in the coronal heating and solar
wind generation. This study aims at providing new observational
evidence on blinkers and macrospicules appearance in imager data and
in doing so, establish the long disputed relationship between these
phenomena.<BR /> Methods: .We analyse unique high-cadence images in
the transition region He ii 304 Å line obtained in a shutterless mode
of the Extreme-ultraviolet Imaging Telescope on board the Solar and
Heliospheric Observatory. The data have a cadence of approximately 68
s and a pixel size of 2.62 arcsec. The events are identified through
an automatic brightenings identification procedure. Features showing
a jet-like structure seen in projection on the disk were selected
and their light-curve further analysed.<BR /> Results: .The temporal
evolution of the intensity in three events is shown, two of them seen
on-disk as jet-like features and one above the limb. The flux increase,
size and duration derived from the light-curve of the on-disk events
show an identity with the blinker phenomenon.<BR /> Conclusions: .The
light curves of these events suggest that the off-limb and on-disk
features are in fact one and the same phenomenon and therefore that
some blinkers are the on-disk counterparts of macrospicules.
---------------------------------------------------------
Title: Multi-wavelength study of a high velocity event near a sunspot
Authors: Lin, Chia-Hsien; Banerjee, D.; O'Shea, E.; Doyle, J. G.
2006A&A...450.1181L Altcode:
Context: .Jets with velocities higher than 200 km s<SUP>-1</SUP> are
often observed in the X-ray spectral range in the solar atmosphere,
however, very few such objects are observed in the EUV range.<BR />
Aims: .We report on an eruptive event observed in the south-west side of
a sunspot, within active region, AR0554, in a range of spectral lines
formed in the transition region and corona.<BR /> Methods: .The main
data were time-series observations obtained with the Coronal Diagnostic
Spectrometer (CDS), in addition to images from the Michelson Doppler
Imager (MDI) and Extreme ultraviolet Imaging Telescope (EIT) on board
the Solar and Heliospheric Observatory. Additional high resolution
images from the Transition Region and Coronal Explorer (TRACE) were also
used.<BR /> Results: .The event brightened a loop connecting the sunspot
and a bright-point structure, triggering both a high-speed flow in
the loop and a transient, low-speed ambient flow into the sunspot. The
energy released is quickly conducted to the chromosphere, as deduced
from the TRACE 1600 Å images and the light curve of He i 522 Å as seen
by CDS. The results from our multi-wavelength study further indicates
that the effect of the eruptive event may have reached temperatures
higher than 2 × 10<SUP>6</SUP> K. Relative Doppler velocities of
over 300 km s<SUP>-1</SUP> were detected in the transition region
line, O v 629 Å.<BR /> Conclusions: .The multi-wavelength analysis
indicates that the event is likely due to fast magnetic reconnection
in the transition region. The velocities detected are consistent with
the results obtained by the evaporation jet model.
---------------------------------------------------------
Title: Where Are the Roots of the Fast Solar Wind? .
Authors: Popescu, Miruna Daniela; Doyle, John Gerard
2006RoAJ...16S.195P Altcode: 2006RoAJS..16..195P
No abstract at ADS
---------------------------------------------------------
Title: Repetitive occurrence of explosive events at a coronal hole
boundary
Authors: Doyle, J. G.; Popescu, M. D.; Taroyan, Y.
2006A&A...446..327D Altcode:
SUMER/SoHO data taken at a coronal hole boundary show a repetitive
explosive event occurrence rate of around 3 min increasing to over 5
min towards the end of the activity. We suggest that the neighbouring
oppositely directed closed and open field lines at the coronal hole
boundary undergo repetitive reconnection seen as a sequence of explosive
events. The repetitive reconnection may be triggered by transverse
oscillations of the flux tubes in the closed field line region. These
oscillations periodically separate and bring together the closed and
open field lines on the two sides of the coronal hole boundary. An
important indicator favouring the interpretation in terms of a kink
mode is the observed increase in the oscillation period.
---------------------------------------------------------
Title: Off-limb coronal loop dynamics as seen from CDS, EIT and TRACE
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.
2006cosp...36..780B Altcode: 2006cosp.meet..780B
Observations have revealed the existence of weak transient disturbances
in extended coronal loop systems These propagating disturbances PDs
originate from small scale brightenings at the footpoints of the loops
and propagate upward along the loops In all cases observed the projected
propagation speed is close to but below the expected sound speed in the
loops This suggest that the PDs could be interpreted as slow mode MHD
waves Interpreting the oscillation in terms of different wave modes and
or plasma motions always depend on the line of sight as we observe in
the limb or on the center of the disk The JOP 165 campaign will address
some of these questions MDI and TRACE photospheric and UV imaging of
TRACE and SPIRIT have been acquired simultaneously with high temporal
and spatial coverage along with the spectroscopic data from CDS EIT was
operated in the shutterless mode to achieve high Cadence Some of the
off-limb active region dynamics and oscillations observed during this
JOP campaign will be focussed in this presentation Plasma condensations
and temporal variations in active region loops will be also addressed
---------------------------------------------------------
Title: Polar and equatorial Coronal holes and the solar wind
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.
2006cosp...36..771B Altcode: 2006cosp.meet..771B
Coronal holes are low density regions where the solar magnetic field
is open to interplanetary space thus provides the sun s magnetic
connection to the heliosphere The fast solar wind is believed to be
originating from coronal holes We study the variation of the line width
and electron density as a function of height above coronal holes from
forbidden spectral lines of Si VIII The spectra were obtained with the
Solar Ultraviolet Measurements of Emitted Radiation spectrometer flown
on the it Solar and Heliospheric Observatory spacecraft The observations
concentrate on the dark regions outside the plumes which are believed to
be the locations where the fast solar wind originates We also examine
long spectral time series with the Coronal Diagnostic Spectrometer CDS
on-board SoHO The observations were obtained with several transition
region and coronal lines We study the dynamics of coronal holes in
the polar regions and also in the equatorial regions on the disk From
a study of the phase delays between flux and velocity measurements I-V
we find evidence for magnetoacoustic waves Measurements of phase delays
between different line pairs reveals that the measured phases tend to
line up along diagonal lines corresponding to fixed time delays From the
orientation of the slopes of these diagonal lines we can infer that the
higher temperature lines lag the cooler temperature lines suggesting
the outward propagation of waves From estimates of the formation
heights of the lines and using the measured time delays we estimate
---------------------------------------------------------
Title: Nanoflare heating of coronal loops: hydrodynamic response
and observational consequences
Authors: Taroyan, Y.; Bradshaw, S. J.; Doyle, J. G.
2006A&A...446..315T Altcode:
The plasma response inside a semicircular coronal loop heated by
nanoflares is examined. The loop is thermally and gravitationally
stratified. The losses due to thermal conduction and radiation
are balanced by localised energy pulses randomly deposited along
the loop. The initial stage of the loop evolution during which the
temperature along the loop gradually increases from chromospheric to
coronal values is completed about 20 minutes after the start of the
heating. The random heating produces a thin transition region which is
in a continuous motion. The profiles of the C IV, O VI, Ne VIII and Mg
X resonance lines, which have peak formation temperatures covering the
upper transition region and lower corona, are synthesised. The line
shifts and the average shifts are calculated and compared with the
observations. It is shown that the nanoflare heating mechanism may
reproduce the observed dynamics of the transition region lines. The
calculated and previously measured average Doppler shift values are
in good agreement for the studied spectral lines except for the C IV
line. Possible reasons for this discrepancy are discussed. The study
also shows that the nanoflares could contribute to the oscillation
power often seen in the mHz ranges. The power peak of the resulting
oscillations is near 2 mHz.
---------------------------------------------------------
Title: The extent of 3-min oscillations in regions other than
sunspot plumes
Authors: Lin, C. -H.; Banerjee, D.; Doyle, J. G.; O'Shea, E.
2005A&A...444..585L Altcode:
The active region, AR0554, was observed with NIS/CDS on board SoHO
to examine the extent and range of oscillations from a range of
features. Among all the NIS spectral lines analysed, significant
oscillations were found in Si xii 520 Å, Mg x 625 Å, O v 629 Å,
and He i 522 Å. The periods of the strongest oscillations in these
lines were ≈10-20 min. After the dominant 10-20 min oscillations
were filtered out from these lines, only O v 629 Å showed
significant (i.e. above the 95% significance level) shorter-period
oscillations. Specifically, we found that weak but significant 3-min
oscillations are not confined to the umbra/plume but can be seen in many
bright locations. The duration of these non-umbral 3-min oscillations
is mostly ≈20 min. In contrast, the 3-min oscillations within the
umbra are strong and stable for longer than 50 min. The duration could
be related to the size of the oscillating source region, rather than
the lifetime of the oscillation. To find the possible sources of these
3-min oscillations outside of the umbra, we compared the oscillations
of single pixels in different regions. The results of our comparison
indicate a possible connection between the magnetic fields and the
oscillations. Therefore, we suggest that 3-min oscillations may exist
in many magnetic structures, but are often too weak to be seen in an
unfiltered signal.
---------------------------------------------------------
Title: Variation of Line Widths in Polar Off-Limb Regions
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.
2005ESASP.600E..43B Altcode: 2005dysu.confE..43B; 2005ESPM...11...43B
No abstract at ADS
---------------------------------------------------------
Title: Study of a Transient Siphon Flow in a Cold Loop
Authors: Taroyan, Y.; Doyle, J. G.; Ishak, B.; Madjarska, M. S.;
Bradshaw, S. J.
2005ESASP.600E..25T Altcode: 2005ESPM...11...25T; 2005dysu.confE..25T
No abstract at ADS
---------------------------------------------------------
Title: Optical and EUV observations of solar flare kernels
Authors: García-Alvarez, D.; Johns-Krull, C. M.; Doyle, J. G.;
Ugarte-Urra, I.; Madjarska, M. S.; Butler, C. J.
2005A&A...444..593G Altcode:
We present high-resolution spectral observations, covering the entire
optical region (3800-9000 Å), of a solar flare observed during
a multi-wavelength campaign. The flare, recorded on 2002 January
11, was a medium solar flare event (GOES class C7.5). The spectral
observations were carried out using the Hamilton echelle spectrograph on
the coudé auxiliary telescope at Lick Observatory and with the Coronal
Diagnostic Spectrometer (CDS) on board SoHO. The high signal-to-noise
optical spectra are analysed using the same techniques as we applied to
stellar flare data. Hα images obtained at Big Bear Solar Observatory
(BBSO), plus magnetograms obtained with the Michelson Doppler Imager
(MDI) on board SoHO and Transition Region And Coronal Explorer (TRACE)
1600 Å were used in the flare analysis. We observe stellar-like
behaviour in the main solar chromospheric activity indicators, which
show either filling-in or emission during the flare. We find that the
Balmer and Ca II lines show asymmetric profiles, with red-shifted
wings and blue-shifted cores. This behaviour could be explained by
material expanding. During the flare, the Mg i and Fe i lines show
a filling-in of the line profile indicating that the flare affected
the lower atmosphere. There is some evidence for pre-flare heating
as seen in Fe xix 592 Å. Furthermore, O v 629 Å shows an increase
in flux some 10 min. before the coronal lines, perhaps indicating
particle beam heating in the initial stages of the flare. We have
also determined the main physical parameters at flare maximum. The
electron densities and electron temperatures found for the flare imply
that the Balmer emitting plasma originates in the chromosphere. The
physical parameters obtained for the modelled flare are consistent
with previously derived values for solar flares.
---------------------------------------------------------
Title: Very long period activity at the base of solar wind streams
Authors: Popescu, M. D.; Banerjee, D.; O'Shea, E.; Doyle, J. G.; Xia,
L. D.
2005A&A...442.1087P Altcode:
Using time series data of spectral lines originating from a wide
range of temperatures in the solar transition region, above a polar
coronal hole, from SUMER (Solar Ultraviolet Measurements of Emitted
Radiation) on SoHO (Solar and Heliospheric Observatory), we report on
the detection of very long (≈170 min) periodic intensity fluctuations,
above the limb. Our data also reveal long periodicities (10 90 min),
previously observed with other SoHO instruments. With the acoustic
cut-off frequency implying a maximum allowable period of ≈90 min,
it is unclear whether these intensity fluctuations are due to waves
or are the result of a recurrent magnetic reconnection process.
---------------------------------------------------------
Title: Detection of Waves in the Equatorial Coronal Holes
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.
2005ESASP.596E..41B Altcode: 2005ccmf.confE..41B
No abstract at ADS
---------------------------------------------------------
Title: Spicules and Blinkers as Seen in Shutterless EIT 304 Å
Authors: Madjarska, M. S.; Doyle, J. G.; Hochedez, J. F.; Theissen, A.
2005ESASP.596E..73M Altcode: 2005ccmf.confE..73M
No abstract at ADS
---------------------------------------------------------
Title: Evidence for explosive event activity originating in the
chromosphere
Authors: Doyle, J. G.; Ishak, B.; Ugarte-Urra, I.; Bryans, P.; Summers,
H. P.
2005A&A...439.1183D Altcode:
We report on a joint SUMER, CDS, TRACE study, concentrating on
a region which shows prolonged EUV explosive event (EE) activity
in the transition region line N v 1238 Å, yet little evidence of
such activity in another transition region line O v 629 Å (formed
at a similar temperature) which was observed simultaneously. A
possible explanation for the lack of major activity in the O v line
in several explosive events could be that they originate in the lower
chromosphere. This is consistent with the enhancements in the C i 1249
Å line and with the findings of another study which reported time
delays between the chromospheric and transition region lines in some
EE's using high cadence observations (10 s exposure time) obtained
with the SUMER spectrometer in H i Ly 6 (20 000 K) and S vi (200 000
K). Using the generalized collisional-radiative picture, including
the population of metastable levels, we derive the density dependent
contribution function for both N v 1238 and O v 629 for four values
of the electron density; 10<SUP>6</SUP> cm<SUP>-3</SUP> representing
the low density limit, 10<SUP>9</SUP> cm<SUP>-3</SUP> for a typical
quiet Sun electron density plus 10<SUP>11</SUP> cm<SUP>-3</SUP> and
10<SUP>12</SUP> cm<SUP>-3</SUP> for an active region. These calculations
show that with increasing electron density, both lines shift to slightly
lower temperatures. However, the major difference is in the relative
increase in the line flux with increasing density. For N v, increasing
the density to 10<SUP>11</SUP> cm<SUP>-3</SUP> results in a 60%
increase in the line flux, while O v shows a 30% decrease. Increasing
the electron density to 10<SUP>12</SUP> cm<SUP>-3</SUP> results in a
factor of two decrease in the O v flux, thus making it difficult to
detect explosive event activity in this line if the event is formed
in the chromosphere. Other explosive events which show simultaneous
activity in both lines are probably formed in the transition region. In
one such event, activity is observed in both N v and O v, yet nothing
in C i. In this event we also observe an increase in the TRACE 173
emission, delayed by ≈40 s compared to the transition region lines.
---------------------------------------------------------
Title: On the Connection Between the Disk and Limb Events Observed
by Soho
Authors: Xia, L. D.; Popescu, M. D.; Chen, Y.; Doyle, J. G.
2005ESASP.592..575X Altcode: 2005soho...16E.110X; 2005ESASP.592E.110X
No abstract at ADS
---------------------------------------------------------
Title: Electron density along a coronal loop observed with CDS/SOHO
Authors: Ugarte-Urra, I.; Doyle, J. G.; Walsh, R. W.; Madjarska, M. S.
2005A&A...439..351U Altcode:
The analysis of a coronal loop observed by CDS and EIT on board SOHO
is presented. The loop was situated above the North-East limb at
a latitude of ~48°, being clearly visible in the hottest lines of
the dataset, Fe xvi 360.76 Å, i.e. greater than 2 000 000 K. The
cooler lines in the sample (i.e. O v 629.73 Å and He i 584.35 Å)
showed only a brightening at the footpoints location. Based on
the Fe xiv 353.84/334.17 line ratio, the electron density along
the loop was determined following three different approaches for
the background subtraction. No differences, within the error bars,
can be found between the three methods. At the apex, the density is
0.9×10<SUP>9</SUP> cm<SUP>-3</SUP>, while at the footpoint it is
50% greater, i.e. 1.4×10<SUP>9</SUP> cm<SUP>-3</SUP>. The inferred
filling factor values along the loop, at the formation temperature
of the lines, are in the range 0.2-0.9. One dimensional hydrodynamic
modelling of the loop along a given field line, gravity neglected,
was performed. A minimum χ<SUP>2</SUP> analysis results in a best fit
case where the total energy input is directed preferentially to the loop
footpoint (the heating rate is three times larger at the base than at
the apex). An isochoric solution can not be ruled out completely. The
exercise illustrates the necessity of accurate spectral diagnostics
in order to derive definite conclusions from theoretical models and
suggests the need for simultaneous density and temperature diagnostics.
---------------------------------------------------------
Title: Time series study of EUV spicules observed by SUMER/SoHO
Authors: Xia, L. D.; Popescu, M. D.; Doyle, J. G.; Giannikakis, J.
2005A&A...438.1115X Altcode:
Here we study the dynamic properties of EUV spicules seen at the
solar limb. The selected data were obtained as time series in polar
coronal holes by SUMER/SoHO. The short exposure time and the almost
fixed position of the spectrometer's slit allow the analysis of spicule
properties such as occurrence, lifetime and Doppler velocity. Our data
reveal that spicules occur repeatedly at the same location with a birth
rate of around 0.16/min as estimated at 10´´ above the limb and a
lifetime ranging from 15 down to ≈3 min. We are able to see some
spicules showing a process of “falling after rising” indicated by
the sudden change of the Doppler velocity sign. A periodicity of ≈5
min is sometimes discernible in their occurrence. Most spicules have
a height between 10´´ and 20´´ above the limb. Some can stretch
up to 40´´; these “long macro-spicules” seem to be comprised of
a group of high spicules. Some of them have an obvious periodicity in
the radiance of ≈5 min.
---------------------------------------------------------
Title: Footpoint excitation of standing acoustic waves in coronal
loops
Authors: Taroyan, Y.; Erdélyi, R.; Doyle, J. G.; Bradshaw, S. J.
2005A&A...438..713T Altcode:
A new theoretical model for the study of slow standing sausage mode
oscillations in hot (T > 6 MK) active region coronal loops is
presented. These oscillations are observed by the SUMER spectrometer on
board the SoHO satellite. The model contains the transition region and
the upper chromosphere which enables us to study the entire process of
hot loop oscillations - from the impulsive footpoint excitation phase
to the rapid damping phase. It is shown that standing acoustic waves
can be excited by an impulsive heat deposition at the chromospheric
footpoint of a loop if the duration of the pulse matches the fundamental
mode period. The pulse is immediately followed by a standing wave
consistent with the SUMER observations in hot loops. The amount of
released energy determines the oscillation amplitude. The combined
effects of thermal conduction and radiation on the behaviour of the
standing acoustic waves in hot gravitationally stratified loops are
investigated. In addition to damping, these effects lead to downflows
which are superimposed on the oscillations. The implications of the
results in coronal seismology are discussed.
---------------------------------------------------------
Title: Comparison Between Explosive Events of Two Transition Region
Lines of Similar Temperatures
Authors: Ishak, B.; Doyle, J. G.; Ugarte-Urra, I.
2005PADEU..15...21I Altcode:
We present the difference in behavior of two transition region lines at
very close temperatures, observed with SUMER/SoHO. N v 1238.82 A shows
a series of explosive events with broadenings mostly shifted to the
blue. This is not seen in O v 629.73 A, the behavior of which remains
"quiet" throughout most of the time series.
---------------------------------------------------------
Title: Electron densities in EUV coronal bright points
Authors: Ugarte-Urra, I.; Doyle, J. G.; Del Zanna, G.
2005A&A...435.1169U Altcode:
Electron density measurements of six coronal bright points have been
obtained using line ratio diagnostics of four ions in the temperature
range 1.3-2.0 × 10<SUP>6</SUP> K. The results suggest that BP plasma
has more similarities to active region plasma than to quiet Sun
plasma. Nevertheless, they do not show the exact same behaviour: the
increase of electron density at temperatures over log~T<SUB>e</SUB> ~
6.2, observed in the core of active regions, has not been detected. The
Fe XII results based on new atomic data, although in better agreement
decreasing more than a factor of two the densities obtained with older
calculations, are still in some instances higher than those from Si
X. This could be a consequence of the inhomogeneity of the plasma in
the observed volume. New measurements with a better constriction of
the volumetric properties seem necessary to rule out the influence of
other factors and confirm whether there is an inconsistency between
the ions, perhaps due to line blending problems in the Fe XII lines.
---------------------------------------------------------
Title: On the widths and ratios of Mg X 609.79 and 624.94 Å lines
in polar off-limb regions
Authors: O'Shea, E.; Banerjee, D.; Doyle, J. G.
2005A&A...436L..35O Altcode:
Using measurements of Mg X 609.78 and 624.94 Å lines from the Coronal
Diagnostic Spectrometer (CDS) on board SOHO, we seek to examine the
variation of line width and line ratio in regions far off-limb at the
Northern pole of the Sun. It is found that above ≈1150´´ the ratio
of the two coronal Mg X resonance lines reduces to values that might be
expected for a more radiatively dominant excitation mode. A comparison
of the line widths with these ratios indicates that the line widths
start to show a decrease in their values at the location where the
dominant excitation changes from being collisionally to radiatively
dominant, that is, at ≈1150´´. We suggest that the decrease in
the line widths above ≈1150´´ is likely to be due to a reduction
in the non-thermal component of the line widths caused by a damping
of upwardly propagating Alfvén waves.
---------------------------------------------------------
Title: Blinker/macro-spicule activity in an off-limb polar region
Authors: O'Shea, E.; Banerjee, D.; Doyle, J. G.
2005A&A...436L..43O Altcode:
Using measurements of O V 629.73 Å from the Coronal Diagnostic
Spectrometer (CDS) on board SOHO we report on blinker activity in
off-limb regions above the Northern pole of the Sun. The blinkers are
found to be occurring above a region showing strong dynamic activity,
with evidence for evacuation of plasma. The presence of blinkers is
discussed in terms of the heating of spicular material.
---------------------------------------------------------
Title: Coronal oscillations in the vicinity of a sunspot as observed
by GIS/CDS
Authors: Lin, C. -H.; Banerjee, D.; Doyle, J. G.; O'Shea, E.; Foley,
C. R.
2005A&A...434..751L Altcode:
In this paper, we present results from a time series analysis of
data from the Grazing Incidence Spectrometer (GIS), onboard SoHO. Our
observations were concentrated at the boundary between the quiet Sun and
an active region, close to a sunspot plume. The dominant oscillations
in all the lines studied are of periods longer than 5 min. Although
our observations were not taken directly above the sunspot, the 3-min
oscillations, which are normally associated with the umbra, are seen
in several spectral lines, suggesting some leakage perhaps via plume
structures. The oscillations of coronal lines form wavepackets, and
are intermittent with no obvious decay. The average time scale of the
intermittence is of the order of 20 min, which would correspond to a
source size of 2 arcsec.
---------------------------------------------------------
Title: Northern Adriatic Response to a Wintertime Bora Wind Event
Authors: Lee, Craig M.; Askari, Farid; Book, Jeff; Carniel, Sandro;
Cushman-Roisin, Benoit; Dorman, Clive; Doyle, James; Flament, Pierre;
Harris, Courtney K.; Jones, Burton H.; Kuzmic, Milivoj; Martin, Paul;
Ogston, Andrea; Orlic, Mirko; Perkins, Henry; Poulain, Pierre-Marie;
Pullen, Julie; Russo, Aniello; Sherwood, Christopher; Signell,
Richard P.; Thaler, Dietmar
2005EOSTr..86..157L Altcode:
During winters, the northern Adriatic Sea experiences frequent, intense
cold-air outbreaks that drive oceanic heat loss and imprint complex but
predictable patterns in the underlying waters. This strong, reliable
forcing makes this region an excellent laboratory for observational
and numerical investigations of air-sea interaction, sediment and
biological transport, and mesoscale wind-driven flow. Narrow sea
surface wind jets, commonly known as “bora,” occur when cold, dry air
spills through gaps in the Dinaric Alps (the mountain range situated
along the Adriatic's eastern shore). Horizontal variations in these
winds drive a mosaic of oceanic cyclonic and anticyclonic cells that
draw coastal waters far into the middle basin. The winds also drive
intense cooling and overturning, producing a sharp front between dense,
vertically homogenous waters (North Adriatic Dense Water, or NAdDW) in
the north and the lighter (colder, fresher), stratified waters of the
Po River plume. Once subducted at the front, the NAdDW flows southward
in a narrow vein following the isobaths (contours of constant depth)
of the Italian coast. In addition to governing the basin's general
circulation, these processes also influence sediment transport and
modulate biological and optical variability.
---------------------------------------------------------
Title: Line broadening of EUV lines across the Solar limb: A spicule
contribution?
Authors: Doyle, J. G.; Giannikakis, J.; Xia, L. D.; Madjarska, M. S.
2005A&A...431L..17D Altcode:
Spectral lines formed in the solar transition region show an increase
in the line width, peaking at ≈10 000 km above the limb. Looking at
a region off-limb with no obvious spicules, the non-spicule region has
a significantly smaller line width above 6000 km compared those taken
in a spicule region. We suggest that this increase in line broadening
is not due to small scale random motions but rather to unresolved line
shifts due to spicules and/or macro-spicules activity.
---------------------------------------------------------
Title: Searching for the Origins of the Fast Solar Wind
Authors: Popescu, M. D.; Doyle, J. G.
2005ASSL..320..235P Altcode: 2005smp..conf..235P
No abstract at ADS
---------------------------------------------------------
Title: The effect of metastable level populations on the ionization
fraction of Li-like ions
Authors: Doyle, J. G.; Summers, H. P.; Bryans, P.
2005A&A...430L..29D Altcode:
Lines from Li-like ions have been known to produce theoretical
intensities under-estimated compared to lines of a similar formation
temperature. Here we investigate this anomalous behaviour whereby the
ionization fractions are calculated using the ADAS code considering
the electron density dependence of dielectronic recombination coupled
with collisional ionization from metastable levels. For the lines
investigated, the line contribution functions show a clear dependence
with increasing electron density. For example, C IV 1548 Å shows
over a factor of three enhancement for N<SUB>e</SUB> = 10<SUP>12</SUP>
cm<SUP>-3</SUP>. The increase in the higher temperature lines is lower,
but are still in the range of 30 to 60%. Furthermore, all the lines have
their peak contribution shifted to lower temperature. Calculating the
total radiative power output at an electron density of 10<SUP>11</SUP>
cm<SUP>-3</SUP>, we find that the difference in the transition region
is 10-15% while above 10<SUP>6</SUP> K the difference is around 30%
compared to the low density value.
---------------------------------------------------------
Title: Impulse Excitation and Damping of Slow Standing Mode
Oscillations in Hot Coronal Loops
Authors: Taroyan, Y.; Erdélyi, R.; Doyle, J. G.
2004ESASP.575..443T Altcode: 2004soho...15..443T
No abstract at ADS
---------------------------------------------------------
Title: Detection of Long Periodwaves in the Polar Coronal Holes
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.; Poedts, S.
2004ESASP.575..136B Altcode: 2004soho...15..136B
No abstract at ADS
---------------------------------------------------------
Title: Temporal Evolution of the Magnetic Network in Polar Coronal
Holes
Authors: Popescu, M. D.; Xia, L. D.; Doyle, J. G.
2004ESASP.575..513P Altcode: 2004soho...15..513P
No abstract at ADS
---------------------------------------------------------
Title: Joint Observing Program 166: Multi-Instrumental Study of
Extreme-Ultraviolet Coronal Bright Points
Authors: Ugarte-Urra, I.; Doyle, J. G.
2004ESASP.575..535U Altcode: 2004soho...15..535U
No abstract at ADS
---------------------------------------------------------
Title: Coronal Oscillations in the Vicinity of a Sunspot as Observed
by GIS/CDS
Authors: Lin, C. H.; Banerjee, D.; Doyle, J. G.; O'Shea, E.
2004ESASP.575..416L Altcode: 2004soho...15..416L
No abstract at ADS
---------------------------------------------------------
Title: Determining the Temperature Profile Along a Plasma Loop Iii:
Spectrometers Verus Imagers
Authors: Walsh, R. W.; Ugarte-Urra, I.; Doyle, J. G.; Noglik, J. B.
2004ESASP.575..567W Altcode: 2004soho...15..567W
No abstract at ADS
---------------------------------------------------------
Title: Dynamic Properties of Solar Spicules Observed by SUMER/SOHO
Authors: Xia, L. D.; Popescu, M. D.; Doyle, J. G.
2004ESASP.575..362X Altcode: 2004soho...15..362X
No abstract at ADS
---------------------------------------------------------
Title: Transition region small-scale dynamics as seen by SUMER on SOHO
Authors: Teriaca, L.; Banerjee, D.; Falchi, A.; Doyle, J. G.;
Madjarska, M. S.
2004A&A...427.1065T Altcode:
High spectral, spatial and temporal resolution UV observations
of the quiet Sun transition region show a highly structured and
dynamical environment where transient supersonic flows are commonly
observed. Strongly non-Gaussian line profiles are the spectral
signatures of these flows and are known in the literature as explosive
events. In this paper we present a high spatial resolution (≈ 1”)
spectroheliogram of a 273”× 291” area of the quiet Sun acquired with
SUMER/SOHO in the O VI spectral line at λ103.193 nm. The extremely high
quality of these observations allows us to identify tens of explosive
events from which we estimate an average size of 1800 km and a birthrate
of 2500 s<SUP>-1</SUP> over the entire Sun. Estimates of the kinetic and
enthalpy fluxes associated with these events show that explosive events
are not important as far as solar coronal heating is concerned. The
relationship with the underlying photospheric magnetic field is also
studied, revealing that explosive events generally occur in regions
with weak (and, very likely, mixed polarity) magnetic flux. By studying
the structure of upward and downward flows exceeding those associated
to average quiet Sun profiles, we find a clear correlation between
the “excess” flows and the magnetic network. However, although
explosive events are always associated with flow patterns often
covering areas larger than the explosive event itself, the contrary is
not true. In particular, almost all flows associated with the stronger
concentrations of photospheric magnetic flux do not show non-Gaussian
line profiles. In some cases, non-Gaussian line profiles are associated
with supersonic flows in small magnetic loops. The case of a small
loop showing a supersonic siphon-like flow of ≈130 km s<SUP>-1</SUP>
is studied in detail. This is, to our knowledge, the first detection
of a supersonic siphon-like flow in a quiet Sun loop. In other cases,
the flow patterns associated with explosive events may suggest a
relation with UV spicules.
---------------------------------------------------------
Title: CDS wide slit time-series of EUV coronal bright points
Authors: Ugarte-Urra, I.; Doyle, J. G.; Nakariakov, V. M.; Foley, C. R.
2004A&A...425.1083U Altcode:
Wide slit (90<SUP>”</SUP>×240<SUP>”</SUP>) movies of four Extreme
Ultraviolet coronal bright points (BPs) obtained with the Coronal
Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric
Observatory (SoHO) have been inspected. The wavelet analysis of the He
I 584.34 Å, O V 629.73 Å and Mg VII/IX 368 Å time-series confirms
the oscillating nature of the BPs, with periods ranging between
600 and 1100 s. In one case we detect periods as short as 236 s. We
suggest that these oscillations are the same as those seen in the
chromospheric network and that a fraction of the network bright points
are most likely the cool footpoints of the loops comprising coronal
bright points. These oscillations are interpreted in terms of global
acoustic modes of the closed magnetic structures associated with BPs.
---------------------------------------------------------
Title: Network boundary origins of fast solar wind seen in the low
transition region?
Authors: Popescu, M. D.; Doyle, J. G.; Xia, L. D.
2004A&A...421..339P Altcode:
We present a study of a high spatial resolution raster acquired on-disk
with the SUMER (Solar Ultraviolet Measurements of Emitted Radiation)
grating spectrograph on SoHO (the Solar and Heliospheric Observatory)
in a polar Coronal Hole (CH) region. We analyse two EUV emission lines,
representing the properties of solar plasma in the low transition region
(TR), O III 703.87 Å (maximum electron temperature, T<SUB>e</SUB>≈
8× 10<SUP>4</SUP> K), as well as in the corona, Mg IX 706.02 Å
(T<SUB>e</SUB>≈ 10<SUP>6</SUP> K). For Mg IX, we find that low CH
intensities correspond to negative Doppler velocities (outflows) of
≈5 km s<SUP>-1</SUP>. Along the quiet Sun (QS)/CH boundaries, the
coronal plasma begins to be more red-shifted. A coronal bright point
(BP) located within the CH is blue-shifted in the coronal line. In
the TR line, the outer region of the BP is red-shifted at ≈5 km
s<SUP>-1</SUP>, but, towards its middle, the shift is around zero. The
O III line, although it shows predominant downward motion of ≈5.5 km
s<SUP>-1</SUP> in the CH and ≈6 km s<SUP>-1</SUP> in the QS, it also
has blue-shifts arranged in a small-scale network pattern with average
negative values of 3.5 km s<SUP>-1</SUP> in CH and 3 km s<SUP>-1</SUP>
in the QS. The blue-shifts are caused either by plasma outflows of a
few km s<SUP>-1</SUP>, or by transient events such as bi-directional
jets which dislocate plasma to upward velocities even higher than
100 km s<SUP>-1</SUP>. The outflows originate predominantly from the
intersection between the magnetic network and the inter-network cells
(network boundaries). The bi-directional jets are found along the
CH/QS boundaries, and, moreover, in locations where the plasma seen in
the Mg IX line is blue-shifted, but very close to small red-shifted
regions. Another interesting change in behaviour is observed at the
QS/CH boundaries, in the O III line, where plasma from the network
changes its velocity sign, becoming red-shifted. Our results constitute
the lowest-in-altitude observed signature of plasma outflows from the
chromospheric network boundaries inside a CH. We have derived this
conclusion from direct correlation between Doppler velocity and the
intensity of the O III 702.87 Åline.
---------------------------------------------------------
Title: Solar Oscillations and the Magnetic Atmosphere
Authors: Taroyan, Y.; Doyle, J. G.
2004PADEU..14..129T Altcode:
With the launch of the SOHO and TRACE satellites two new branches of
solar physics have emerged: time-distance helioseismology and coronal
seismology. In time-distance helioseismology the travel time of the
acoustic waves between different points on the solar surface is measured
to infer the local structure and properties of the subsurface layers of
the Sun. The travel time changes due to the atmospheric magnetic field
are evaluated theoretically. Coronal seismology utilises MHD waves in
solar coronal structures as a tool to diagnose the physical parameters
of the coronal plasma. Theoretical modelling of recently observed slow
standing mode oscillations in stratified loops is presented. It is
shown that large-amplitude resonant standing waves can be driven by
small-amplitude oscillations at the chromospheric footpoints of the
loops. The periods and the behaviour of these waves are different
from those predicted by the classical theory of isothermal loop
oscillations. The possible relationsheep between the oscillations
studied in time-distance helioseismology and in coronal seismology
is addressed.
---------------------------------------------------------
Title: Coronal response of Bi-directional Jets
Authors: Doyle, J. G.; Madjarska, M. S.; DzifČÁkovÁ, E.; Dammasch,
I. E.
2004SoPh..221...51D Altcode:
EUV bi-directional jets are a prominent class of phenomena
characterizing the solar transition region. Using simultaneously
obtained SUMER observations in the chromospheric Si ii 1251.16 Å
and C i 1251.17 Å, transition region N v 1238.8 Å and coronal Mg x
625 Å lines we show an example of a bi-directional jet observed in
the chromospheric and the transition region lines but not showing
any detectable signature in the coronal line. The phenomenon,
however, was also clearly detected by the TRACE imager with the 171
Å filter. This discrepancy is explained here with a non-Maxwellian
electron distribution which makes a significant fraction of the plasma
in the TRACE 171 Å pass-band to be derived from temperatures around ≈
300 000 K, as opposed to ≈ 800 000 K. This could have implications
for other phenomena observed in the TRACE pass-bands, including the
transition region `moss' and the 3- and 5-min oscillations.
---------------------------------------------------------
Title: New insight into the blinker phenomenon and the dynamics of
the solar transition region
Authors: Doyle, J. G.; Roussev, I. I.; Madjarska, M. S.
2004A&A...418L...9D Altcode:
We present, for the first time, blinker phenomena being associated
with brightenings in pre-existing coronal loops registered by the
Extreme-ultraviolet Imaging Telescope (EIT) in Fe XII 195 Å. The
brightenings occur during the emergence of new magnetic flux as
registered by the Big Bear Solar Observatory (BBSO) magnetograph. The
blinkers were identified using simultaneous observations obtained
with the Coronal Diagnostic Spectrometer (CDS) and Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrograph. In light of
the new observational results, we present one possible theoretical
interpretation of the blinker phenomenon. We suggest that the
blinker activity we observe is triggered by interchange reconnection,
serving to provide topological connectivity between newly emerging
flux and pre-existing flux. The EIT images show the existence of loop
structures prior to the onset of the blinker activity. Based on the
available spatial resolution the blinker occurs within, or nearby,
an existing coronal loop. The temperature interfaces created in the
reconnection process between the cool plasma of the newly emerging
loop and the hot plasma of the existing loop are what we suggest to
causes the observed activity seen in both the SUMER and CDS data. As
the temperature interfaces propagate with the characteristic speed of a
conduction front, they heat up the cool chromospheric plasma to coronal
temperatures, an increasing volume of which brightens at transition
region temperatures. We believe this new interpretation gives further
qualitative understanding about the evolution of newly emerging flux
on the Sun. This also provides new insight into the dynamic nature of
the solar transition region.
---------------------------------------------------------
Title: Signature of oscillations in coronal bright points
Authors: Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S.; O'Shea, E.
2004A&A...418..313U Altcode:
A detailed study of two consecutive bright points observed
simultaneously with the Coronal Diagnostic Spectrometer (CDS),
the Extreme ultraviolet Imaging Telescope (EIT) and the Michelson
Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory
(SOHO) is presented. The analysis of the evolution of the photospheric
magnetic features and their coronal counterpart shows that there is
a linear dependence between the EIT Fe XII 195 Å flux and the total
magnetic flux of the photospheric bipolarity. The appearance of the
coronal emission is associated with the emergence of new magnetic
flux and the disappearance of coronal emission is associated with
the cancellation of one of the polarities. In one of the cases the
disappearance takes place ∼3-4 h before the full cancellation of
the weakest polarity. <P />The spectral data obtained with CDS show
that one of the bright points experienced short time variations in
the flux on a time scale of 420-650 s, correlated in the transition
region lines (O V 629.73 Å and O III 599.60 Å) and also the He I
584.34 Å line. The coronal line (Mg IX 368.07 Å) undergoes changes
as well, but on a longer scale. The wavelet analysis of the temporal
series reveals that many of these events appear in a random fashion and
sometimes after periods of quietness. However, we have found two cases
of an oscillatory behaviour. A sub-section of the O V temporal series
of the second bright point shows a damped oscillation of five cycles
peaking in the wavelet spectrum at 546 s, but showing in the latter few
cycles a lengthening of that period. The period compares well with that
detected in the S VI 933.40 Å oscillations seen in another bright point
observed with the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer, which has a period of 491 s. The derived electron
density in the transition region was 3×10<SUP>10</SUP> cm<SUP>-3</SUP>
with some small variability, while the coronal electron density was
5×10<SUP>8</SUP> cm<SUP>-3</SUP>.
---------------------------------------------------------
Title: Evidence of Magnetic Reconnection along Coronal Hole Boundaries
Authors: Madjarska, M. S.; Doyle, J. G.; van Driel-Gesztelyi, L.
2004ApJ...603L..57M Altcode:
The present study reveals for the first time the existence of
bidirectional jets, which are a signature of magnetic reconnection,
occurring along coronal hole boundaries. The Solar Ultraviolet
Measurement of Emitted Radiation spectrometer observations obtained
in the N IV 765.15 Å (1.3×10<SUP>5</SUP> K) and Ne VIII 770.42
Å (6×10<SUP>5</SUP> K) emission lines in an equatorial extension
of a polar coronal hole, known as the “Elephant's Trunk” coronal
hole, show small regions of a few arcseconds size with strong blue-
and redshifted emission reaching Doppler shifts of up to 150 km
s<SUP>-1</SUP>, i.e., bidirectional jets. The jets' number density
along coronal hole boundaries was found to be about 4-5 times higher
with respect to the quiet Sun.
---------------------------------------------------------
Title: Bi-Directional Jets at Coronal Hole Boundaries
Authors: Madjarska, M. S.; Doyle, J. G.; van Driel-Gesztelyi, L.
2004ESASP.547..397M Altcode: 2004soho...13..397M
Our study reveals, for the first time, the presence of bi-directional
jets which are considered to be signatures of magnetic reconnection
occurring along coronal hole boundaries. The SUMER observations obtained
in Ne VIII 770.42 Å (6 10 K) and N IV 765.15 Å (1.3 10 K) show small
regions of a few arcsec size with strong blueand red-shifted emission
reaching Doppler shifts up to 150 km s which appear along the coronal
hole boundaries where evolving loop systems are present.
---------------------------------------------------------
Title: A Study of Transition Region and Coronal Doppler Shifts in
a Solar Coronal Hole
Authors: Popescu, M. D.; Doyle, J. G.
2004ESASP.547..363P Altcode: 2004soho...13..363P
We present a study of a high spatial resolution raster scan taken
on-disk with the SoHO/SUMER spectrograph in a solar polar Coronal
Hole (CH) region. We have analysed the line shifts and widths of two
EUV emitting ions, O III 703.87 Å and Mg IX 706.02 Å. Our results
confirm plasma outflows from CHs. In particular, the correlation
between the intensity and the Doppler velocity in the case of the O
III line constitute the lowest precise indication of fast wind streams
seen originating from the network boundaries in the transition region.
---------------------------------------------------------
Title: Time-Distance Helioseismology and the Magnetic Atmosphere of
the Sun
Authors: Taroyan, Y.; Erdélyi, R.; Doyle, J. G.
2004ESASP.547...33T Altcode: 2004soho...13...33T
No abstract at ADS
---------------------------------------------------------
Title: Oscillations in Coronal Bright Points
Authors: Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S.; O'Shea, E.
2004ESASP.547..329U Altcode: 2004soho...13..329U
No abstract at ADS
---------------------------------------------------------
Title: Coronal Oscillations above Sunspots?
Authors: Doyle, J. G.; Dzifćáková, E.; Madjarska, M. S.
2003SoPh..218...79D Altcode:
Observational data clearly indicate the presence of 3-min oscillations
in sunspots in spectral lines covering a vast temperature range
from the low chromosphere to those lines normally associated with
coronal temperatures. We show that after folding in the sunspot
plume emission measure distribution, the contribution functions for
lines normally formed just below 1×10<SUP>6</SUP> K are shifted to
lower temperatures. For example, the Fe ix 171 Å line is shifted to
6×10<SUP>5</SUP> K for a Maxwellian distribution and to less than
5×10<SUP>5</SUP> K with a non-Maxwellian distribution. Other lines
such as Mg ix 368 Å will also be affected. This then questions some
previous work regarding the suggested detection of 3-min oscillations
in the corona above sunspots.
---------------------------------------------------------
Title: MUSICOS 1998: Observations of Rotational Modulation and Flares
on the RS CVn Binary HR1099
Authors: García-Alvarez, D.; Foing, B. H.; Montes, D.; Oliveira,
J.; Doyle, J. G.; MUSICOS 98 Collaboration
2003csss...12..958G Altcode: 2001astro.ph..9235G
We present simultaneous and continuous observations of Hα, Hβ,
ion{Na}{1} D<SUB>1</SUB>, D<SUB>2</SUB>, ion{He}{1} D<SUB>3</SUB>
and ion{Ca}{2} H & K lines of the chromospherically active
binary HR 1099. We have observed HR 1099 for more than 3 weeks almost
continuously and monitored two flares. An increase in Hα and ion{Ca}{2}
H & K, Hβ and ion{He}{1} D<SUB>3</SUB> and a strong filling-in
of the ion{Na}{1} D<SUB>1</SUB>, D<SUB>2</SUB> during the flares are
observed. We have found that the flares took place at the same phase
(0.85) of the binary orbit, and both of them seems to occur near
the limb.
---------------------------------------------------------
Title: Line Shift Variations in Solar Transition Region Lines
Authors: Doyle, J. G.; Madjarska, M.; Giamikakis, J.; Teriaca, L.;
Roussev, I.
2003csss...12..619D Altcode:
Two high time cadence datasets, taken in C III 977Å and O VI 1032Å
were analysed in an effort to establish the extent of the variability
in the Doppler-shift of typical mid-transition region lines. In C
III, the shortest time-scale variability seems to occur in the network
boundary regions where the line-shift can vary by 7-8 km s<SUP>-1</SUP>
in less than 1 min. The internetwork region also shows variability
although this tends to be longer lived, ∼2-3 mins. The average C III
line-shift in all regions is for a red-shift of ∼ 8 km s<SUP>-1</SUP>
in very good agreement with that derived by others. Furthermore, there
does not seem to be any obvious difference in the average line-shift
in network and internetwork regions. On a few rare occasions, the C
III line was blue-shifted. The O VI line was also red-shifted with the
network region showing evidence for a periodicity. These observations
were compared to model line profiles based on the response of a 2D MHD
environment representing the solar transition region to micro-scale
energy depositions. A variety of temperatures at which the energy
deposition takes place as well as the amount of energy deposited
was examined.
---------------------------------------------------------
Title: Sunspot plume observations in the EUV. The gas pressure
differential between the umbra and surrounding region
Authors: Doyle, J. G.; Madjarska, M. S.
2003A&A...407L..29D Altcode:
The electron density over a bright sunspot plume region was evaluated
using lines within the O V 760 Å multiplet. The plume showed an
intensity enhancement factor of ~9 in the O V lines compared to regions
outside the sunspot umbra. Internal agreement between the various
ratios is excellent which would suggest that the O V lines do not
suffer from blending problems. The derived mean electron densities for
the sunspot plume is log N<SUB>e</SUB>/cm<SUP>-3</SUP> ~ 9.9 compared
to log N<SUB>e</SUB>/cm<SUP>-3</SUP> ~ 10.20-10.45 in the surrounding
area. The derived gas pressure in the plume compared to that outside
leads weight to the suggestion that it is plasma flowing from outside
the spot into the umbra at transition region temperatures that is the
main cause of the down-flows. The plume non-thermal velocities are 5 to
10 km ; s<SUP>-1</SUP> smaller than those measured in regions external
to the spot, suggesting significantly less turbulence within the umbra.
---------------------------------------------------------
Title: Simultaneous observations of solar transition region blinkers
and explosive events by SUMER, CDS and BBSO. Are blinkers, explosive
events and spicules the same phenomenon?
Authors: Madjarska, M. S.; Doyle, J. G.
2003A&A...403..731M Altcode:
The SoHO discovery of the new “blinker” phenomena focused our study on
the search of its relation to already known phenomena such as explosive
events and spicules. The study was performed using a specially planned
joint observing program involving the Coronal Diagnostic Spectrometer
(CDS), Solar Ultraviolet Measurements of Emitted Radiation spectrograph
(SUMER) and Big Bear Solar Observatory (BBSO) magnetograph. Within
each blinker, the SUMER data reveal the presence of small-scale (3
arcsec-5 arcsec), short-lived (2-3 min) bright features not seen in
the CDS data which has sometimes being interpreted as oscillations in
SUMER data. With this data we have clearly identified UV explosive
events in CDS data. The explosive events show a size close to the
small-scale brightenings forming the blinker core. However, they appear
in the SUMER data with their typical strong blue and red wings while
the blinker shows at best only a small increase in the emission of
the blue and red wings and in most instances the typical transition
region red-shift in the center of the line. In all cases the explosive
events cover one pixel in CDS corresponding to a size of 4arcsec x
4arcsec -6arcsec . All identified explosive events were located at
the border of the bright network i.e. the blinker, in the network or
even in the internetwork. From this data, we believe that blinkers and
explosive events are two separate phenomena not directly related or
triggering each other. In this study, the Doppler shift was derived in
a blinker phenomenon for the first time. It ranges from -5 to 25 km ;
s<SUP>-1</SUP> and is predominantly red-shifted. The observed magnetic
flux increase during the blinker phenomena seems to play a crucial
role in the development of this event. We suggest that “blinkers”
maybe the on-disk signature of spicules.
---------------------------------------------------------
Title: Doppler images of the RS CVn binary HR 1099 (V711 Tau) from
the MUSICOS 1998 campaign
Authors: García-Alvarez, D.; Barnes, J. R.; Collier Cameron, A.;
Doyle, J. G.; Messina, S.; Lanza, A. F.; Rodonò, M.
2003A&A...402.1073G Altcode: 2003astro.ph..3154G
We present Doppler Images of the RS CVn binary system HR 1099
(V711 Tau) from spectra taken in two different sites, KPNO and MSO,
during the MUSICOS 1998 campaign. Contemporaneous APT photometry is
used to constrain the Doppler Images. The resulting maximum entropy
reconstructions based on the least-squares deconvolved profiles,
derived from ~ 2000 photospheric absorption lines, reveal the presence
of starspots at medium-high latitudes. We have obtained maps for both
components of the binary system for the first time. The predominant
structure in the primary component is an off-centered polar spot,
confirming previous works on the same target by using independent
codes. The result is verified by using both data sets independently. The
lower spectral resolution data set gives a less detailed map for the
MSO data set. The images obtained for the secondary component show a
low latitude spot around orbital phase 0.7. This spot seems to mirror
the structure seen on the primary. It might suggest that tidal forces
may influence the spot distribution on this binary system. <P />Based
on observations obtained during the MUSICOS 98 MUlti-SIte COntinuous
Spectroscopic campaign from Kitt Peak National Observatory, USA,
and Mt. Stromlo Observatory, Australia.
---------------------------------------------------------
Title: An EUV Bright Point as seen by SUMER, CDS, MDI and EIT
on-board SoHO
Authors: Madjarska, M. S.; Doyle, J. G.; Teriaca, L.; Banerjee, D.
2003A&A...398..775M Altcode:
This paper presents the formation, evolution and decay of a coronal
bright point via a spectroscopic analysis of its transition region
counterpart and the evolution of the underlying magnetic bipole during
3 days of almost continuous observations. The data were obtained with
various instruments on-board SoHO, including the SUMER spectrograph
in the transition region line S VI 933.40 Å, CDS in the He I 584.33,
O V 629.73 and Mg IX 368.06 Å lines, plus MDI and EIT. The existence
of the coronal feature is strongly correlated with the evolution of
the underlying bipolar region. The lifetime of the bright point from
the moment when it was first visible in the EIT images until its
complete disappearance was ~ 18 hrs. Furthermore, the bright point
only became visible at coronal temperatures when the two converging
opposite magnetic polarities were ~ 7000 km apart. As far as the
temporal coverage of the data permits, we found that the bright point
disappeared at coronal temperatures after a full cancellation of one of
the magnetic polarities. The spectroscopic analysis reveals the presence
of small-scale ( ~ 6 arcsec) transient brightenings within the bright
point with a periodicity of ~ 6 min. The Doppler shift in the bright
point was found to be in the range of -10 to 10 km ; s<SUP>-1</SUP>
although it is dominated by a red-shifted emission which is associated
with regions characterized by stronger “quiet” Sun photospheric
magnetic flux. Small-scale brightenings within the bright point show
velocity variations in the range 3-6 km ; s<SUP>-1</SUP>. In general
the bright point has a radiance ~ 4 times higher than that of the
network. No relation was found between the bright point and the UV
explosive event phenomena.
---------------------------------------------------------
Title: Simultaneous optical and X-ray observations of flares and
rotational modulation on the RS CVn binary HR 1099 (V711 Tau) from
the MUSICOS 1998 campaign
Authors: García-Alvarez, D.; Foing, B. H.; Montes, D.; Oliveira,
J.; Doyle, J. G.; Messina, S.; Lanza, A. F.; Rodonò, M.; Abbott, J.;
Ash, T. D. C.; Baldry, I. K.; Bedding, T. R.; Buckley, D. A. H.; Cami,
J.; Cao, H.; Catala, C.; Cheng, K. P.; Domiciano de Souza, A., Jr.;
Donati, J. -F.; Hubert, A. -M.; Janot-Pacheco, E.; Hao, J. X.; Kaper,
L.; Kaufer, A.; Leister, N. V.; Neff, J. E.; Neiner, C.; Orlando, S.;
O'Toole, S. J.; Schäfer, D.; Smartt, S. J.; Stahl, O.; Telting, J.;
Tubbesing, S.
2003A&A...397..285G Altcode: 2002astro.ph.10230G
We present simultaneous and continuous observations of the Hα, Hβ,
He I D<SUB>3</SUB>, Na I D<SUB>1</SUB>, D<SUB>2</SUB> doublet and the
Ca II H & K lines for the RS CVn system HR 1099. The spectroscopic
observations were obtained during the MUSICOS 1998 campaign involving
several observatories and instruments, both echelle and long-slit
spectrographs. During this campaign, HR 1099 was observed almost
continuously for more than 8 orbits of 2.8 deg. Two large optical
flares were observed, both showing an increase in the emission of Hα,
Ca II H & K, Hβ and He I D<SUB>3</SUB> and a strong filling-in
of the Na I D<SUB>1</SUB>, D<SUB>2</SUB> doublet. Contemporary
photometric observations were carried out with the robotic telescopes
APT-80 of Catania and Phoenix-25 of Fairborn Observatories. Maps
of the distribution of the spotted regions on the photosphere of
the binary components were derived using the Maximum Entropy and
Tikhonov photometric regularization criteria. Rotational modulation
was observed in Hα and He I D<SUB>3</SUB> in anti-correlation with
the photometric light curves. Both flares occurred at the same binary
phase (0.85), suggesting that these events took place in the same
active region. Simultaneous X-ray observations, performed by ASM on
board RXTE, show several flare-like events, some of which correlate
well with the observed optical flares. Rotational modulation in the
X-ray light curve has been detected with minimum flux when the less
active G5 V star was in front. A possible periodicity in the X-ray
flare-like events was also found. <P />Based on observations obtained
during the MUSICOS 98 MUlti-SIte COntinuous Spectroscopic campaign from
Observatoire de Haute-Provence, France, Kitt Peak National Observatory,
USA, ESO La Silla, Chile, Mt. Stromlo Observatory, Australia, Xinglong
National Observatory, China, Isaac Newton Telescope, Spain, Laboratório
Nacional de Astrofísica, Brazil, and South African Astronomical
Observatory, South Africa. Contemporaneous observations from Catania,
Italy and Fairborn Observatories, USA, and on data obtained with the
Rossi X-ray Timing Explorer.
---------------------------------------------------------
Title: Transition region small-scale dynamics: UV explosive events
Authors: Teriaca, L.; Falchi, A.; Doyle, J. G.; Madjarska, M. S.;
Banerjee, D.
2002ESASP.506..777T Altcode: 2002ESPM...10..777T; 2002svco.conf..777T
High spectral, spatial and temporal resolution UV observations of the
quiet Sun transition region show a highly structured and dynamical
environment where transient events such as brightenings, blinkers
and explosive events occur continuously. In particular explosive
events are characterized by strongly non-Gaussian line profiles
witnessing velocities up to 200 km s<SUP>-1</SUP>. The high kinetic
and enthalpy fluxes associated with these events could be important
in the energy balance of the transition region and, perhaps, of the
whole corona. In this paper we present a high spatial resolution (~1")
spectroheliogram of a 270×290 arcsec<SUP>2</SUP> wide area of the
quiet Sun acquired with SUMER/SoHO in the O VI 1032 spectral line. The
extremely high quality of these observations allows us to identify
tens of explosive events and to study their relationship with the
underlying photospheric magnetic field. Moreover, the behaviour of lines
emitted by plasma at chromospheric (2×10<SUP>4</SUP>K) and coronal
(10<SUP>6</SUP>K) temperatures during transition region explosive
events is investigated. We conclude that those events do not contribute
significantly to the energy balance of the corona and seems typical
of structure not obviously connected to the T≥10<SUP>6</SUP>K corona.
---------------------------------------------------------
Title: Temporal variability in the Doppler-shift of solar transition
region lines
Authors: Doyle, J. G.; Madjarska, M. S.; Roussev, I.; Teriaca, L.;
Giannikakis, J.
2002A&A...396..255D Altcode:
High cadence datasets taken in C III 977 Å, O VI 1032 Å and Ne
VIII 720 Å were analysed in an effort to establish the extent
of the variability in the Doppler-shift of typical mid-transition
region lines. The shortest time-scale variability seems to occur
in the network boundary regions where the line-shift can vary by
7-8 km s<SUP>-1</SUP> in less than 1 min. The internetwork region
also shows variability although this tends to be longer lived, ~
2-3 min. The average line-shift in C III is a red-shift which ranges
from ~ 2 km s<SUP>-1</SUP> to ~ 20 km s<SUP>-1</SUP> with an average
value for all regions selected being around 10 km s<SUP>-1</SUP>
in very good agreement with that derived by others. The red-shift
values indicate a clear difference between network and internetwork
regions, with the largest red-shift being present at the network
boundary. For O VI, this gives an average red-shift ranging from 5 to
10 km s<SUP>-1</SUP>. For Ne VIII, there is a 13 km s<SUP>-1</SUP>
difference between internetwork and bright network plasma with the
bright network being more red-shifted. This could imply that the
bright network regions are dominated by spicule down-flow.\ In the
second part we present results from 2-dimensional (2D) dissipative
magnetohydrodynamic (MHD) simulations of the response of the solar
transition region to micro-scale energy depositions. A variety of
temperatures at which the energy deposition takes place as well as the
amount of energy deposited are examined. This work is a continuation
of previous related simulations where small-scale energy depositions
were modelled in 1D hydrodynamics. The observable consequences of
such transient events are then computed for three transition region
lines, namely C IV 1548 Å, O VI 1032 Å, and Ne VIII 770 Å, under
the consideration of non-equilibrium ionization.
---------------------------------------------------------
Title: On the nature of umbral oscillations: theory and observation
by CDS/SoHO
Authors: Banerjee, D.; O'Shea, E.; Goossens, M.; Poedts, S.; Doyle,
J. G.
2002ESASP.506..427B Altcode: 2002ESPM...10..427B; 2002svco.conf..427B
We will present solutions for magneto-acoustic-gravity (or MAG)
waves. The possible wave modes in the 3-5 min range will be
discussed. We will then present observations of sunspots performed
in the EUV wavelength range with the Coronal Diagnostic Spectrometer
(CDS) on SoHO. We examine the time series for the line intensities
and relative velocities and calculate their power spectrum using
wavelet transforms. We find oscillations in the chromosphere and
transition region above the sunspots in the temperature range logT =
4.6 -5.4. Most of the spectral power above the umbra is contained in
the 5-7 mHz frequency range. When the CDS slit crosses the sunspot
plume a clear 3 min oscillation is observed. The observations are
interpreted in terms of slow magnetoacoustic waves propagating upwards.
---------------------------------------------------------
Title: MUSICOS 1998: Optical and X-rays Observations of Flares on
the RS CVn Binary HR 1099
Authors: García-Alvarez, D.; Doyle, J. G.; Foing, B. H.; Oliveira,
J. M.; Montes, D.
2002ASPC..277..479G Altcode: 2001astro.ph.10305G; 2002sccx.conf..479G
We present simultaneous and continuous observations of H_alpha, H_beta,
NaI D_1, D_2 and HeI D_3 lines of the chromospherically active binary HR
1099. We have observed HR 1099 for more than 3 weeks almost continuously
and monitored two flares. An increase in H_alpha, CaII H & K,
H_beta, HeI D_3 and HeI lambda6678 and a strong filling-in of the NaI
D_1, D_2 and MgI b triplet during one of the flares are observed. We
have found that the flares took place at the same phase (0.85) of the
binary orbit, and both of them seems to occur near the limb. Several
X-rays flares were also detected by ASM on board RXTE. Rotational
modulation in the X-rays light curve has been detected with maximum
flux when the active K1IV star is in front.
---------------------------------------------------------
Title: The OIV and SIV intercombination lines in the ultraviolet
spectra of astrophysical sources
Authors: Keenan, F. P.; Ahmed, S.; Brage, T.; Doyle, J. G.; Espey,
B. R.; Exter, K. M.; Hibbert, A.; Keenan, M. T. C.; Madjarska, M. S.;
Mathioudakis, M.; Pollacco, D. L.
2002MNRAS.337..901K Altcode:
New electron density diagnostic line ratios are presented for
the OIV 2s<SUP>2</SUP>2p <SUP>2</SUP>P-2s2p<SUP>24</SUP>P and SIV
3s<SUP>2</SUP>3p <SUP>2</SUP>P-3s3p<SUP>24</SUP>P intercombination
lines around 1400Å. A comparison of these with observational data
for the symbiotic star RR Telescopii (RR Tel), obtained with the
Space Telescope Imaging Spectrograph (STIS), reveals generally
very good agreement between theory and observation. However the
SIV<SUP>2</SUP>P<SUB>3/2</SUB>-<SUP>4</SUP>P<SUB>1/2</SUB> transition
at 1423.824Å is found to be blended with an unknown feature at
1423.774Å. The linewidth for the latter indicates that the feature
arises from a species with a large ionization potential. In addition,
the SIV<SUP>2</SUP>P<SUB>1/2</SUB>-<SUP>4</SUP>P<SUB>3/2</SUB>
transition at 1398.044Å is identified for the first time (to
our knowledge) in an astrophysical source other than the Sun,
and an improved wavelength of 1397.166 Å is measured for the
OIV<SUP>2</SUP>P<SUB>1/2</SUB>-<SUP>4</SUP>P<SUB>3/2</SUB> line. The
OIV and SIV line ratios in a sunspot plume spectrum, obtained with
the Solar Ultraviolet Measurements of the Emitted Radiation (SUMER)
instrument on the Solar and Heliospheric Observatory, are found to be
consistent, and remove discrepancies noted in previous comparisons of
these two ions.
---------------------------------------------------------
Title: On the theory of MAG waves and a comparison with sunspot
observations from CDS/SoHO
Authors: Banerjee, D.; O'Shea, E.; Goossens, M.; Doyle, J. G.;
Poedts, S.
2002A&A...395..263B Altcode:
We examine the influence of non-adiabatic effects on the modes of an
isothermal stratified magnetic atmosphere. We present new solutions for
magneto-acoustic-gravity (or MAG) waves in the presence of a radiative
heat exchange based on Newton's law of cooling. An analytic expression
for the dispersion relation is derived, which allows the effect of a
weak magnetic field on the modes to be studied. The insight so gained
proves useful in extending the computations to the moderate-high field
case. In the second part we present observations of two sunspots
obtained in the EUV wavelength range with the Coronal Diagnostic
Spectrometer (CDS) on SoHO. We examine the time series for the line
intensities and relative velocities and calculate their power spectra
using wavelet transforms. We find oscillations in the chromosphere
and transition region above the sunspots in the temperature range
log T = 4.6-5.4 K. Most of the spectral power above the umbra is
contained in the 5-7 mHz frequency range. When the CDS slit crosses
the sunspot umbra a clear 3 min oscillation is observed. The observed
oscillation frequencies are compared with the computed frequencies and
the observations are interpreted in terms of the slow magneto-acoustic
waves.
---------------------------------------------------------
Title: Magnetic properties of ultraviolet transient phenomena. Are
blinkers and explosive events the same phenomenon?
Authors: Madjarska, M. S.; Doyle, J. G.
2002ESASP.505..489M Altcode: 2002solm.conf..489M; 2002IAUCo.188..489M
Simultaneous 'quiet' Sun observations were performed on 2001 October 23
with the SUMER and CDS spectrometers on-board SoHO together with the Big
Bear Solar Observatory magnetograph. The aim was to study the magnetic
properties and distinct nature of the transition region phenomena
such as explosive events and blinkers. The different appearance of the
two phenomena in both spectrometer observations was analysed. Blinker
phenomena were clearly associated with bipolar magnetic regions with
always one polarity stronger than the other one. Higher resolution
observations are needed in order to associate explosive events with
any particular magnetic field changes.
---------------------------------------------------------
Title: Electron density variation in off-limb solar corona structures
Authors: Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S.
2002ESASP.505..595U Altcode: 2002IAUCo.188..595U; 2002solm.conf..595U
We present a study of the electron density variation for off
limb observations with the Coronal Diagnostic Spectrometer (CDS)
on board SoHO using the density sensitive coronal line ratio Si X
(356.0/347.4). The analysis is divided into three parts: the latitudinal
variation from 1.01 < r/R<SUB>solar</SUB> < 1.09, the temporal
variation in successive rasters, and the electron density along a hot
coronal loop found in one of the rasters.
---------------------------------------------------------
Title: Explosive events and associated periodicities
Authors: Giannikakis, I.; Doyle, J. G.; Antonopoulou, E.
2002ESASP.505..413G Altcode: 2002IAUCo.188..413G; 2002solm.conf..413G
We studied an explosive event which occurred in the transition region
line O VI, in particular we investigate whether this event produced
periodicities in the line intensity during its evolution.
---------------------------------------------------------
Title: Slow MAG waves in the sunspot umbra as observed by CDS/SOHO
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.; Goossens, M.;
Poedts, S.
2002ESASP.505..187B Altcode: 2002solm.conf..187B; 2002IAUCo.188..187B
We present observations, in the EUV wavelength range, of two
sunspots, carried out by the Coronal Diagostic Spectrometer (CDS)
on SoHO. We examine the time series for the line intensities and
relative velocities and calculate their power spectrum using wavelet
transforms. We find oscillations in the chromosphere and transition
region above the sunspots in the temperature range logT = 4.6 -
5.4. Most of the spectral power above the umbra are contained in the
5 - 7 mHz frequency range. When the CDS slit croses the sunspot plume
a clear 3 in oscillation is observed. We also present new solutions
for magnetic-acoustic-gravity (or MAG) waves in the presence of
radiative heat exchange based on Newton's law of cooling. The observed
oscillation frequencies are compared with the computed frequencies. The
observations are interpreted in terms of slow magnetoacoustic waves
propagating upwards.
---------------------------------------------------------
Title: Transition region explosive events: Do they have a coronal
counterpart?
Authors: Teriaca, L.; Madjarska, M. S.; Doyle, J. G.
2002A&A...392..309T Altcode:
EUV explosive events are a prominent class of phenomena characterizing
the solar transition region. Their correct location in the wider
frame-work of the outer solar atmosphere can provide important insight
on the nature of the transition region itself and its relationship
with the hotter corona and the cooler chromosphere. In this paper
we present new high-cadence SUMER observations of the “quiet”
Sun obtained simultaneously in the mid-transition region N V 1238.8
Å line (1.8x 10<SUP>5</SUP> K) and in the coronal Mg X 625 Å line
(1.1x 10<SUP>6</SUP> K). These observations are aimed at providing
information on the behaviour of the coronal plasma during EUV
transition region explosive events detected in N V 1238.8 Å. None of
the events observed in N V shows any detectable signature in the Mg
X line profile or in its integrated intensity. The analysis of 1996
observations obtained simultaneously in N V 1238.8 Å and S II 1253.8
Å (3.5x 10<SUP>4</SUP> K) shows, instead, a weak but clear presence
of enhanced wings in the S II line profile during a series of events
observed in N V. These results suggest that EUV explosive events are
not directly relevant in heating the corona and are characteristic of
structures not obviously connected with the upper corona. The evidence
of a chromospheric response suggests that, contrary to some previous
suggestions, explosive events have a chromospheric origin.
---------------------------------------------------------
Title: Transition region counterpart of X-ray/EUV coronal bright
points registered by SUMER, CDS, EIT and MDI/SOHO
Authors: Madjarska, M. S.; Doyle, J. G.
2002ESASP.508..311M Altcode: 2002soho...11..311M
We present a spectroscopic analysis of the transition region counterpart
of Coronal Bright Points (BPs). Simultaneous observations obtained
with the SUMER spectrometer in the S VI 933.38 Å and Ly 6 930.75
&Aring lines, CDS in the He I 584.33, O V 629.73 and Mg IX 368.06
Å MDI and EIT Fe XII 195 Å on-board SoHO were analysed. The dataset
obtained on 1996 October 16, 17 & 18 reveals a complete picture
of the formation, temporal evolution and decay of a bright point. The
nature of the intensity variations in a BP, its Doppler velocities
and its relation to transient phenomena such as explosive events and
blinkers are discussed.
---------------------------------------------------------
Title: Observations and modelling of a large optical flare on AT
Microscopii
Authors: García-Alvarez, D.; Jevremović, D.; Doyle, J. G.; Butler,
C. J.
2002A&A...383..548G Altcode: 2001astro.ph.12224G
Spectroscopic observations covering the wavelength range 3600-4600
Å are presented for a large flare on the late type M dwarf AT Mic
(dM4.5e). A procedure to estimate the physical parameters of the flaring
plasma has been used which assumes a simplified slab model of the flare
based on a comparison of observed and computed Balmer decrements. With
this procedure we have determined the electron density, electron
temperature, optical thickness and temperature of the underlying source
for the impulsive and gradual phases of the flare. The magnitude and
duration of the flare allows us to trace the physical parameters of
the response of the lower atmosphere. In order to check our derived
values we have compared them with other methods. In addition, we have
also applied our procedure to a stellar and a solar flare for which
parameters have been obtained using other techniques.
---------------------------------------------------------
Title: Dynamics and Diagnostics of Explosive Events and Blinkers
Authors: Madjarska, M. S.; Doyle, J. G.; Teriaca, L.
2002mwoc.conf...69M Altcode:
The knowledge of the main physical parameters of UV explosive events
and blinkers, such as density and temperature, is of great importance
for the better understanding of the true nature of these transient
events. In this context, density and temperature diagnostics based on
lines belonging to O iv 1400Å and O iii multiplets is presented for
both kind of events. The dynamics of the solar transient phenomena
is revealed through their temporal and spatial evolution as observed
in spectral lines covering a wide temperature range. The results
are obtained using SUMER, CDS, MDI and EIT aboard SoHO, TRACE and
Big Bear Solar Observatory observations and are aimed to give more
information about the main properties of these phenomena. The events
are also studied in connection with the evolution of the underlying
magnetic field, searching for observational evidences of their further
propagation higher in the solar corona.
---------------------------------------------------------
Title: Temporal evolution of different temperature plasma during
explosive events
Authors: Madjarska, M. S.; Doyle, J. G.
2002A&A...382..319M Altcode:
High cadence observations (10 s exposure time) obtained with the SUMER
spectrometer on-board SoHO in the Ly 6 (20 000 K) and S VI (200 000 K)
lines reveal new insight on the nature of explosive events. A time
delay in the response of the S VI line with respect to the Ly 6 line
has been observed, with the Ly 6 line responding with about 20-40
s earlier. A temporal series obtained with 30 s exposure time and
covering the entire Lyman series plus O I, C II and S VI (temperature
range from 15 000 to 200 000 K) has also been explored showing the
response of all these lines during transient phenomena. New common
features linking explosive events and blinkers were found. During
explosive events, the central intensity increases between 1.6 and 2.0
times the pre-event value while the same range of intensity increase
was already reported during blinker phenomena. On the other hand the
maximum intensity increase in Ly 6 was only 13%.
---------------------------------------------------------
Title: Long-Period Oscillations in Polar Coronal Holes as Observed
by CDS on SOHO
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.; Goossens, M.
2002mwoc.conf...19B Altcode:
We examine spectral time series of the coronal line Mg ix 368Å,
the transition region line O v 629Å, and the chromospheric line He
i 584Å observed during several periods of 2000, with the Coronal
Diagnostic Spectrometer (CDS) onboard the SoHO spacecraft. We study
different parts of coronal holes, plumes and inter-plumes (off-limb)
as a separate study. We report here on a time series analysis, using
wavelet methods, of small individual regions in the polar coronal
hole. The wavelet analysis allows us to derive the duration as well
as the periods of the oscillations. The statistical significance of
the oscillations was estimated by using a randomisation method. Our
observations indicate the presence of compressional waves with periods
of 20-30 minutes or longer. These slow magneto-acoustic waves may
provide enough energy flux for the acceleration of the fast solar wind.
---------------------------------------------------------
Title: Signatures of very long period waves in the polar coronal holes
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.; Goossens, M.
2001A&A...380L..39B Altcode:
We examine long spectral time series of a coronal hole observed on
the 7th March 2000 with the Coronal Diagnostic Spectrometer (CDS)
on-board SoHO. The observations were obtained in the chromospheric He
I, and a series of higher temperature oxygen lines. In this letter we
report on the presence of long period oscillations in a polar coronal
hole region on the disk. Our observations indicate the presence of
compressional waves with periods of 20-30 min or longer.
---------------------------------------------------------
Title: Modelling of solar explosive events in 2D
environments. III. Observable consequences
Authors: Roussev, I.; Doyle, J. G.; Galsgaard, K.; Erdélyi, R.
2001A&A...380..719R Altcode:
We examine the response via line synthesis of two representative
transition region lines, namely C IV 1548.2 Å and O VI 1031.9 Å,
in various physical environments representing the “quiet” Sun to
magnetic reconnection events. Our calculations of ion populations allow
for departures from equilibrium ionization (EI), which is critical
in studies of transient events. Both lines reveal highly blue- and
red-shifted Doppler components, and some of the results are examined in
the context of solar explosive events. The observable consequences of
magnetic reconnection are subtle in the various physical circumstances
examined here and differ from one emission line to another, because
of the difference in their formation temperatures.
---------------------------------------------------------
Title: Oxygen abundance in polar coronal holes
Authors: Teriaca, L.; Poletto, G.; Falchi, A.; Doyle, J. G.
2001AIPC..598...65T Altcode: 2001sgc..conf...65T
Fast solar wind is known to emanate from polar coronal holes. However,
only recently attention has been given to the problem of where,
within coronal holes, fast wind originates. Information on whether the
fast solar wind originates from plumes or interplume regions may be
obtained by comparing the elemental abundances in these regions with
those characterizing the fast wind. Here we present a first attempt
to determine the oxygen abundance in the interplume regions by using
spectra taken at times of minimum in the solar cycle (when it is
easier to identify these structures) by the SUMER spectrograph aboard
SoHO. To this end, we analyze spectra taken in 1996 in polar regions,
at altitudes ranging between 1.05 and 1.3 R<SUB>solar</SUB>, finding a
value >=8.5 for the oxygen abundance in the interplume regions. From
the analysis of the O VI 1032 to 1037 line intensity ratio we also find
no evidence of outflow velocities below 1.2 solar radii in interplume
regions, while there are indications that outflow motions start to be
significant above 1.5 solar radii. The method used and the assumptions
made are discussed in light of the derived values. Our values are
compared with previous determinations in the corona and solar wind. .
---------------------------------------------------------
Title: Long period oscillations in the inter-plume regions of the Sun
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.; Goossens, M.
2001A&A...377..691B Altcode:
We examine long spectral time series of inter-plume lanes observed on
the 14th and 15th March 2000 with the Coronal Diagnostic Spectrometer
(CDS) on-board SoHO. The observations were obtained in lines over a wide
temperature range, from the chromosphere to the corona. The statistical
significance of the oscillations was estimated by using a randomisation
method. Our observations indicate the presence of compressional waves
with periods of 20-50 min or longer, both off-limb and on-disk and up
to 70 min further out to at least 25 arcsec off-limb. To our knowledge
this is the first time that long period oscillations in the inter-plume
regions close to the limb of the Sun have been detected. We interpret
these oscillations as outward propagating slow magneto-acoustic waves
which may contribute significantly to the heating of the lower corona
by compressive dissipation and which may also provide some of the
enough energy flux required for the acceleration of the fast solar
wind. These slow waves may have been produced at the network boundaries
in the coronal hole.
---------------------------------------------------------
Title: Temporal evolution of explosive events as observed in Lyman
and S VI lines
Authors: Madjarska, M. S.; Doyle, J. G.
2001ESASP.493..279M Altcode: 2001sefs.work..279M
No abstract at ADS
---------------------------------------------------------
Title: Temporal Variability in Transition Region Line .
Authors: Giannikakis, I.; Doyle, J. G.; Antonopoulou, E.; Madjarska, M.
2001hell.confE..41G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Explosive Events and associated Periodicities
Authors: Giannikakis, I.; Doyle, J. G.; Antonopoulou, E.
2001hell.confE..20G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Modelling of explosive events in the solar transition region
in a 2D environment. II. Various MHD experiments
Authors: Roussev, I.; Galsgaard, K.; Erdélyi, R.; Doyle, J. G.
2001A&A...375..228R Altcode:
We examine the response of various physical environments representing
the solar atmosphere to a magnetic reconnection event. The reconnection
is driven by a localized increase of the magnetic diffusivity in the
current concentration formed between two magnetic fluxes of opposite
polarity. The time dependent evolution is then followed by numerically
solving the 2-dimensional (2D) dissipative magnetohydrodynamic (MHD)
equations, including also effects of thermal conduction, radiative
losses, and volumetric heating.\ This work continues a previous related
study (Roussev et al. 2001a), and compares results obtained from
exploring different initial states. The choice of the initial states
is found to be crucial to the dynamics of the reconnection jets. The
numerical experiments are aimed at modelling transient events on the
quiet Sun, with an emphasis on explosive events. The 2D reconnection
experiments presented in this paper are the basis for a detailed
analysis on the line synthesis in transition region resonant lines,
presented by Roussev et al. (\cite{rou01b}).
---------------------------------------------------------
Title: The nature of network oscillations
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.; Goossens, M.
2001A&A...371.1137B Altcode:
We examine time-series of spectral data obtained from the Coronal
Diagnostic Spectrometer (CDS) and the Solar Ultraviolet Measurements
of Emitted Radiation instrument (SUMER) onboard the Solar Heliospheric
Observatory (SOHO) spacecraft, in the period 30-31 July 1996. The
observations were obtained in lines, ranging in temperature from
12 000 K to 10<SUP>6</SUP> K, covering the low chromosphere to the
corona. We report here on a time series analysis, using wavelet methods,
of small individual network regions in the quiet Sun. The wavelet
analysis allows us to derive the duration as well as the periods of
the oscillations. The statistical significance of the oscillations
was estimated by using a randomisation method. The oscillations are
considered to be due to waves, which are produced in short bursts with
coherence times of about 10-20 min. The low chromospheric and transition
region lines show intensity and velocity power in the 2-4 mHz range. The
coronal line Mg x does not show any statistically significant power
in this range. In general, it is thought likely that the chromosphere
and possibly the transition region oscillates in response to forcing
by the p-modes, but they are also influenced strongly by the presence
of magnetic fields. The observed 2-4 mHz network oscillations can
thus be interpreted in terms of kink and sausage waves propagating
upwards along thin magnetic flux tubes. We perform a linear numerical
computation comparing the results with our observations.
---------------------------------------------------------
Title: Electron density variations during ultraviolet transient events
Authors: Teriaca, L.; Madjarska, M. S.; Doyle, J. G.
2001SoPh..200...91T Altcode:
% High-resolution temporal observations performed with the SUMER
spectrometer on SOHO provide an opportunity to investigate the electron
density variations in the `quiet-Sun' solar transition region due to
UV transient events. Two datasets obtained in the density sensitive
lines belonging to the O iv 1400 Å multiplet were searched for such
events, leading to the identification of two explosive events, on 10
July 1996 and 31 May 1997. In both cases, the O iv 1401.16/1404.81
density-sensitive line intensity ratio shows a clear variation,
corresponding to enhancements in the electron density by factors of
∼3. This is fully consistent with recent 2.5D MHD simulations. The
10 July 1996 dataset also provided us with the opportunity to monitor
the behavior of the electron density through an UV blinker. Despite
an increase of a factor of two in the line intensities, no variation
of the electron density was found. This suggests that the intensity
enhancement is due to an increase in the filling factor.
---------------------------------------------------------
Title: Numerical Modeling of the Transition Region Dynamics
Authors: Teriaca, L.; Doyle, J. G.
2001ASSL..259..307T Altcode: 2001dysu.conf..307T
We explore the idea that the occurrence of nano-flares in a magnetic
loop around the O VI formation temperature could explain the observed
red-shift of mid-low transition region lines as well as the blue-shift
observed in low coronal lines (T > 6 times 10<SUP>5</SUP>
K). Observations are compared to numerical simulations of the
response of the solar atmosphere to an energy perturbation of 4 times
10<SUP>24</SUP> ergs representing an energy release during magnetic
reconnection in a 1-D semi-circular flux tube. The temporal evolution
of the thermodynamic state of the loop is finally converted into C
III 977, C IV 1548, O V 630, O VI 1032, Ne VII 465 and Ne VIII 770
line profiles in non-equilibrium ionization. Performing an integration
over the entire period of simulation, redshifts of 8.5, 6.1 and 1.7 km
s<SUP>-1</SUP>, are found in C III, C IV, and O V while blue-shifts
of -1.8, -3.9 and -10.7 km s<SUP>-1</SUP> were derived for O VI,
Ne VII and Ne VIII respectively, in good agreement with observations.
---------------------------------------------------------
Title: Modelling of explosive events in the solar transition region
in a 2D environment. I. General reconnection jet dynamics
Authors: Roussev, I.; Galsgaard, K.; Erdélyi, R.; Doyle, J. G.
2001A&A...370..298R Altcode:
The aim of the present study is to investigate the reconnection
jets formed during the process of magnetic flux cancellation
in the physical environment of the solar transition region. The
emission properties of these jets are then computed for two resonance
transition region lines, C iv 1548.2 Å and O vi 1031.9 Å, under the
assumption of non-equilibrium ionization. The numerical modelling
involves 2-dimensional (2D) dissipative, radiative, nonlinear
magnetohydrodynamics. The nonlinear anisotropic thermal conduction,
radiative losses, and volumetric heating are taken into account in order
to assess their role in the physical situation examined. This work is a
continuation of previous related simulations where small-scale energy
depositions were modelled in 1D radiative hydrodynamics. Having an
X-point reconnection in the mid-transition region gives blue-shifts
of the order of ~ 100 km s<SUP>-1</SUP>, however, the red-shift can
be up to one order of magnitude less.
---------------------------------------------------------
Title: Solar Mn I 5432/5395 Å line formation explained
Authors: Doyle, J. G.; Jevremović, D.; Short, C. I.; Hauschildt,
P. H.; Livingston, W.; Vince, I.
2001A&A...369L..13D Altcode:
We present a solution for the long standing problem concerning the
“chromospheric” behaviour of the Mn i 5395/5432 Å lines in the
solar spectrum using multi-line/multi-species NLTE modelling. Using
comprehensive spectral line formation modelling, we show that the
Mn i lines are very sensitive to optical pumping in a transition
which overlaps with Mg ii k. It therefore follows that one has to be
careful with the choice of lines as temperature indicators and for
the determination of the Mn abundances although on the other hand,
due to the formation process of these lines they may be useful as a
solar and stellar activity diagnostic.
---------------------------------------------------------
Title: Active region oscillations
Authors: O'Shea, E.; Banerjee, D.; Doyle, J. G.; Fleck, B.; Murtagh, F.
2001A&A...368.1095O Altcode:
We report here on an investigation of high frequency oscillations in
active regions, carried out using high cadence observations of O V
629 Å, Mg Ix 368 Å and Fe Xvi 335 Å, with the Coronal Diagnostic
Spectrometer (cds) on soho. Using the techniques of wavelet analysis
on various temporal series datasets, we find that certain oscillation
frequencies are favoured for each line. We find furthermore that
a ~ 5 min oscillation signature is commonly present in all lines,
suggesting a coupling of the photospheric driver with the transition
region and coronal loop modes. We report on the tendency for higher
frequency oscillations to be present at lower intensity values,
suggesting that higher frequency oscillations occur in interloop
regions or at loop boundaries, possibly as a result of some resonant
absorption process. In addition, we find that the coronal lines of
Fe Xvi and Mg Ix show more significant oscillations in the velocity
than in the intensity, which suggests that in the velocity we measure
additional non-compressive wave modes not visible in the intensity. As
this effect is not seen in the transition region line of O V it would
seem that these additional non-compressive modes are produced in and
limited to the corona. We suggest that there are two main mechanisms
responsible for the observed oscillations; either resonant Alfvén
and/or fast kink waves or propagating slow magnetoacoustic waves,
both present in coronal loops.
---------------------------------------------------------
Title: On the nature of network oscillations
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.; Goossens, M.;
Fleck, B.
2001ESASP.464..175B Altcode: 2001soho...10..175B
We examine time-series of spectral data obtained from the Solar
Ultraviolet Measurements of Emitted Radiation instrument (SUMER), on
board SOHO in the period 10-31 July 1996. Observations were obtained
in lines, ranging in temperature from 12,000 K to 10<SUP>6</SUP>K,
covering the low chromosphere to the corona. In this short contribution
we report on the time series analysis on one of these dataset, using
wavelet methods, of small individual network regions in the quiet
Sun. The wavelet analysis allows us to derive the duration as well
as the periods of the oscillations. The statistical significance of
the oscillations was estimated by using a randomisation method. The
oscillations are considered to be due to waves, which are produced
in short bursts with coherence times of about 10-20 minutes. The
low chromospheric and transition region lines show intensity and
velocity power in the 2.4 mHz range. The observed 2-4 mHz network
oscillations can be interpreted in terms of kink and sausage waves
propagating upwards along thin magnetic flux tubes. The kink waves can
be generated by random foot-point motions, e.g. by exploding granules,
at the photospheric level. As they propagate within flux tubes, their
amplitude grows exponentially with height and becomes non-linear. The
waves can thereby undergo a mode transformation and become sausage
type waves, which are more easily detected on the disk.
---------------------------------------------------------
Title: Electron Density Enhancement During an UV Explosive Event
Authors: Madjarska, M. S.; Doyle, J. G.; Teriaca, L.
2001IAUS..203..407M Altcode:
High resolution temporal observations performed with the SUMER
spectrometer on SOHO provide us the opportunity to investigate the
electron density variations in the solar mid transition region due
to explosive event-like phenomena. The O IV 1401.16/1404.81 density
sensitive line intensity ratio shows a clear increase during a strong
explosive event, corresponding to an electron density enhancement of
a factor of ~ 3.5 respect to pre-event values. This is consistent
with recent MHD simulations (2.5 D) carried out by Karpen et
al. (1998). Karpen J. T., Antiochos S. K., DeVore C. R. and Golub L.,
1998, ApJ 495, 491.
---------------------------------------------------------
Title: SUMER Observations of the Solar Transition Region: Spatial
and Temporal Behaviour
Authors: Teriaca, L.; Doyle, J. G.; Banerjee, D.
2001IAUS..203..425T Altcode:
In this paper we examine the spatial and temporal behaviour of the quiet
Sun transition region using high resolution SUMER observations in O VI
1032. The observations are devoted to the study of the variability in
the transition region and consists of four raster scans of the same
area followed by a long series of spectra taken in the same position
with high temporal cadence. A detailed study of the raster images
allows us to differentiate the network and internetwork through
Doppler shift and line width measurements. We have also identified
several explosive-events like phenomena toghether with an UV bright
point. We also show evidence for a possible formation of a shock front
after one partcular bright point appearence. The oscillatory nature
of the transition region is finally investigated using the wavelet
analysis and particular attention has been paid to the effect due to
the occurrence of explosive events.
---------------------------------------------------------
Title: Long Period Oscillations in Polar Plumes as observed by CDS
on SoHO
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.; Goossens, M.
2001IAUS..203..244B Altcode:
We examine spectral time series of coronal line Mg IX 368 Å and
transition region line O V 629 Å, observed with the Coronal Diagnostic
Spectrometer (CDS) onboard the SOHO spacecraft. Primarily we were
looking for intensity and velocity oscillations in polar plumes,
however by chance we detected a giant macro-spicule at the limb and
were able to follow its dynamical structure. Blue and red-shifted
emission in the O V line indicates that it is probably a rotating
twisted magnetic jet. Emission is also detected in the Mg IX 368
Å line, at a temperature of 1 million K. Both Fourier and wavelet
transforms have been applied independently to the analysis of the
oscillations in order to find the most reliable periods. We report
here on the existence of long period oscillations in the polar plumes
as observed in the O V 629 Å line. Our observations indicate the
presence of compressional waves with periods of 20-25 minutes.
---------------------------------------------------------
Title: Environment of Two RS CVn Stars (CD-ROM Directory:
contribs/ozeren)
Authors: Özeren, F. F.; Doyle, J. G.; Jevromovic, D.; Gunn, A. G.
2001ASPC..223.1036O Altcode: 2001csss...11.1036O
No abstract at ADS
---------------------------------------------------------
Title: A spectroscopic study of the eclipsing binaries SV
Camelopardalis and XY Ursae Majoris
Authors: Özeren, F. F.; Gunn, A. G.; Doyle, J. G.; Jevremović, D.
2001A&A...366..202O Altcode:
High-resolution spectroscopic observations of the eclipsing RS CVn-type
active close binaries SV Camelopardalis and XY Ursae Majoris reveal
excess emission components in the Hα and Hβ lines. We have used the
spectral subtraction technique to separate the excess emission from
the photospheric background and find that in both stars the excess
emission is associated with the secondary, cooler component. Analysis
of the EW<SUB>Hα</SUB>/EW<SUB>Hβ</SUB> ratio indicates that in both
cases the emission is probably associated with surface plage regions
or prominences viewed against the stellar disks. We find no evidence
of excess absorption features associated with extended prominence-like
material in these systems. Based on observations made at Observatoire
de Haute Provence (CNRS), France.
---------------------------------------------------------
Title: A Quiescent Atmosphere of AD Leo (CD-ROM Directory:
contribs/jevrem2)
Authors: Jevremović, D.; Doyle, J. G.; Butler, C. J.
2001ASPC..223..815J Altcode: 2001csss...11..815J
No abstract at ADS
---------------------------------------------------------
Title: Active region oscillations
Authors: O'Shea, E.; Banerjee, D.; Doyle, J. G.; Fleck, B.; Murtagh, F.
2001ESASP.464..223O Altcode: 2001soho...10..223O
We report here on an investigation of high frequency oscillations in
active regions, carried out using high cadence observations of O V
629 Å, Mg IX 368 Å and Fe XVI 335 Å with the Coronal Diagnostic
Spectrometer (CDS) on SoHO. Using the techniques of wavelet analysis
on various temporal series datasets, we find that certain bands of
oscillation frequency are favoured for each line. We report on the
tendency for higher frequency oscillations to correspond to lower
intensity values, suggesting that higher frequency oscillations occur in
inter-loop regions or at loop boundaries, and further that some resonant
absorption process is perhaps at work at these locations. We suggest
that there are two possible mechanisms for the observed oscillations;
either resonant Alfvén waves or resonant fast kink waves in coronal
loops.
---------------------------------------------------------
Title: A Role of Isotropic Turbulence in Atmospheres of Late Type
Stars (CD-ROM Directory: contribs/jevrem1)
Authors: Jevremović, D.; Doyle, J. G.; Short, C. I.
2001ASPC..223..809J Altcode: 2001csss...11..809J
No abstract at ADS
---------------------------------------------------------
Title: Electron density diagnostics for solar ultraviolet lines of O V
Authors: O'Shea, E.; O'Neill, T.; Keenan, F. P.; Doyle, J. G.
2000SoPh..196..321O Altcode:
We determine the electron densities for a range of solar features using
new calculations for the O v line ratio, R=I(λ761.1)/I(λ760.4), in
conjunction with observational data obtained with the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) instrument on the Solar
and Heliospheric Observatory (SOHO). The densities obtained from this
diagnostic are in good agreement with earlier measured values. This
provides support for the theoretical diagnostics presented in this
paper, and hence the atomic data used in their derivation. We conclude
from these results that this particular O v ratio is a useful diagnostic
for many types of solar features.
---------------------------------------------------------
Title: Long period oscillations in the polar plumes
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.; Goossens, M.
2000AIPC..537..160B Altcode: 2000wdss.conf..160B
We examine spectral time series of the transition region line O v
629 Å, observed with the Coronal Diagnostic Spectrometer (CDS) on
the SoHO spacecraft. Both Fourier and wavelet transforms have been
applied independently to the analysis of plume oscillations in order
to find the most reliable periods. The wavelet analysis enables us to
derive the duration as well as the periods of the oscillations. Our
observations indicate the presence of compressional waves with periods
of 10-20 minutes. We have also detected a 10+/-2 minute periodicity
in the network regions of the north polar coronal hole. The waves
are produced in short bursts with coherence times of about 20-30
minutes. We interpret these oscillations as outward propagating slow
magneto-acoustic waves, which may contribute significantly to the
heating of the lower corona by compressive dissipation and which may
also provide enough energy flux for the acceleration of the fast solar
wind. The data support the idea that the same driver is responsible
for the network and plume oscillations with the network providing the
magnetic channel through which the waves propagate upwards from the
lower atmosphere to the plumes. .
---------------------------------------------------------
Title: Long-Period Oscillations in Polar Plumes as Observed by cds
on Soho
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.
2000SoPh..196...63B Altcode:
We examine spectral time series of the transition region line O v 629Å,
observed with the Coronal Diagnostic Spectrometer (CDS) on the SOHO
spacecraft in July 1997. Both Fourier and wavelet transforms have been
applied independently to the analysis of plume oscillations in order
to find the most reliable periods. The wavelet analysis allows us to
derive the duration as well as the periods of the oscillations. Our
observations indicate the presence of compressional waves with periods
of 10-25 min. We have also detected a 11±1 min periodicity in the
network regions of the north polar coronal hole. The waves are produced
in short bursts with coherence times of about 30 min. We interpret
these oscillations as outward propagating slow magneto-acoustic waves,
which may contribute significantly to the heating of the lower corona
by compressive dissipation and which may also provide enough energy
flux for the acceleration of the fast solar wind. The data support
the idea that the same driver is responsible for the network and
plume oscillations with the network providing the magnetic channel
through which the waves propagate upwards from the lower atmosphere
to the plumes.
---------------------------------------------------------
Title: Modelling near-IR spectra and mid-IR dust emission of Mira
variables at different phases
Authors: Lobel, A.; Bagnulo, S.; Doyle, J. G.; Power, C.
2000MNRAS.317..391L Altcode:
We model the spectral changes of late oxygen-rich Miras observed in
different pulsation phases. From a combination of variable near-IR
spectra and UKIRT spectro-photometry of the 9.7-μm silicate dust
emission feature in different phases we study the influence of
the changing atmospheric circumstances on the conditions in the
circumstellar dust shell. From a detailed modelling of TiO and VO
bands in the near-IR spectra, we determine changes of the effective
temperature and the effective atmospheric acceleration of the
central star. The corresponding model spectral energy distribution is
redistributed through the dust shell by means of radiative transfer
calculations in order to perform a detailed modelling of shape
changes observed in the silicate feature. We show that the latter
are mainly caused by changes in the flux distribution of the incident
radiation field with stellar pulsation, whereas intensity changes of
the dust emission result from stellar luminosity changes as they are
enshrouded by very optically thin dust shells. In the case of the
Mira o Cet we compute that the effective temperature increases from
T<SUB>eff</SUB>=2400K in the minimum phase to 3000K (+/-100K) around
the maximum phase. The amplified momentum transfer around maximum
light enhances the acceleration of the dust outflow near the dust
condensation radius of ~6R*. This produces variations of the terminal
dust outflow velocity with phase (Δv<SUB>∞</SUB>~=5kms<SUP>-1</SUP>)
at larger distance from the star. The corresponding small
changes in flux mean opacity and gas mass-loss rates (from 2.8 to
3.2×10<SUP>-7</SUP>M<SUB>solar</SUB>yr<SUP>-1</SUP>) are sufficient
to model the shape changes observed in the dust emission feature. A
comparison with the modelling results for another long period Mira,
U Ori, is also provided.
---------------------------------------------------------
Title: Physical parameters of EUV explosive events
Authors: Pérez, M. E.; Doyle, J. G.
2000A&A...360..331P Altcode:
Previously published results of EUV explosive events and electron
density enhancements in the solar transition region are revised. An
attempt has been made to correlate both observational phenomena, and to
associate the observed density enhancements to magnetic reconnection
sites. The corresponding local magnetic field strength in these sites
is estimated. These values are of the same order as previously measured
in photospheric cancelling flux regions.
---------------------------------------------------------
Title: Rotational modulation and flares on RS CVn and BY Dra
stars. XX. Photometry and spectroscopy of CC Eri in late 1989
Authors: Amado, P. J.; Doyle, J. G.; Byrne, P. B.; Cutispoto, G.;
Kilkenny, D.; Mathioudakis, M.; Neff, J. E.
2000A&A...359..159A Altcode:
The active flaring binary CC Eri was studied via multi-wavelength
observations involving multi-based photometry and ground- and
space-based spectroscopy. Combining early spectroscopic data with
the present implies an orbital period of P=1.5615 days. Furthermore,
the spectroscopic data suggests spectral types of K7 and M3 for the
system. The optical photometry indicated a small spot coverage in
late 1989, consistent with data taken a year later which showed CC Eri
entering its brightest-to-date phase. Two flares were detected in the
ultraviolet spectral data. These flares radiated 2.7 10<SUP>31</SUP>
erg and 1.6 10<SUP>31</SUP> erg in the C Iv line alone, each with a
total estimated radiative energy budget of ~ 10<SUP>36</SUP> erg. For
the higher-temperature lines, such as C Iv, there was no systematic
variability with phase. The lower-temperature lines show a slight
indication of rotational modulation. However, there is a much larger
scatter in the individual measurements of the Mg Ii and C Iv fluxes
than would be expected from measurement errors alone, consistent with
an atmosphere showing continual small-scale activity.
---------------------------------------------------------
Title: The contribution of the micro-turbulent velocity on the
modelling of chromospheric lines in late type dwarfs
Authors: Jevremović, D.; Doyle, J. G.; Short, C. I.
2000A&A...358..575J Altcode:
We discuss the influence of the non-thermal velocity (micro-turbulence)
on the formation of chromospheric lines in the atmospheres of late
type dwarfs. A review of previous work shows a variety of different
approaches to the problem leading to different atmospheric structures
and consequently different computed line profiles. In that light,
we re-examine the formation of the Hydrogen Balmer lines and Na i D
lines using twelve different distributions of the micro-turbulent
velocity throughout the atmosphere. Our results show a wide range
of possible line shapes. Using the analogy with the solar case and
the latest results of the non-thermal component widths as derived
from instruments on-board SOHO we model Hα and the Na i D lines in
an active dMe star Gl 616.2. Based in part on observations made at
Observatoire de Haute Provence (CNRS), France and SOHO
---------------------------------------------------------
Title: Polar Plumes and Inter-plume regions as observed by SUMER
on SOHO
Authors: Banerjee, D.; Teriaca, L.; Doyle, J. G.; Lemaire, P.
2000SoPh..194...43B Altcode:
We present observations of O vi 1032 Å line profiles obtained
with the SUMER instrument on SOHO extending from the solar
disk to 1.5 R<SUB>⊙</SUB> above the limb in the north polar
coronal hole. Variations of the intensity and linewidth in the
polar plume and inter-plume regions are investigated. We find an
anti-correlation between the intensity and the linewidth in the plume
and inter-plume regions with detailed plume structures been seen out
to 1.5 R<SUB>⊙</SUB>. Possible implications regarding the magnetic
topologies of these two regions and related heating mechanisms are
discussed. The O vi linewidth measurements are combined with UVCS output
to provide an overview of its variations with height extending up to
3.5 R<SUB>⊙</SUB>. We find a linear increase of the linewidth from
1 to 1.2 R<SUB>⊙</SUB>, then a plateau followed by a sharp increase
around 1.5 R<SUB>⊙</SUB>.
---------------------------------------------------------
Title: Photometric modelling of starspots - II. The fortran code
spotpic
Authors: Amado, P. J.; Doyle, J. G.; Byrne, P. B.
2000MNRAS.314..489A Altcode:
A fortran code which computes synthetic light and colour curves of
active, spotted stars has been developed. The main feature of this
code is that it can simultaneously model the V light curve and the
(V-R)<SUB>c</SUB>, (V-I)<SUB>c</SUB>, (V-K) colour data. It also uses
new effective temperature-colour and Barnes-Evans-like calibrations,
temperature and gravity-dependent limb darkening coefficients and
different effective surface gravities for the spotted and unspotted
photosphere. The code allows for two-component spots, i.e. spots
with umbral and penumbral components. Various problematic spot
configurations were investigated and we conclude that, in order
to be able to differentiate spots with various thermal structures
(umbrae, penumbrae, faculae) or polar spots from equatorial bands,
the modelling of the infrared colours, especially (V-I)<SUB>c</SUB>
and (V-K), is needed.
---------------------------------------------------------
Title: Solar transition region line broadening: Limb to limb
measurements
Authors: Doyle, J. G.; Teriaca, L.; Banerjee, D.
2000A&A...356..335D Altcode:
Full disk images from SUMER/SoHO taken in He I, C IV and Ne VIII are
used to investigate whether there exists a center-to-limb variation
in the line width. Both C IV and He I show such a variation but the
higher temperature Ne VIII line is relatively constant. For C IV,
this corresponds to ~ 3 km s<SUP>-1</SUP> difference while He I
is significantly larger particularly at the limb. This work may
suggest that the non-thermal motions are slightly non-isotropic in
the transition region and upper chromosphere, with the horizontal
unresolved motions exceeding those in the vertical plane however a more
probable explanation is that the lines are broadened due to opacity
effects. The more slower variation in the C IV 1548 Ä line width could
be explained by increasing the opacity from zero at disk center to ~ 1
at the limb. For He I the opacity is significantly grater than unity at
the limb. This therefore implying all mass motions in the chromosphere,
transition region and corona are isotropic.
---------------------------------------------------------
Title: Giant macro-spicule as observed by CDS on SOHO
Authors: Banerjee, D.; O'Shea, E.; Doyle, J. G.
2000A&A...355.1152B Altcode:
We examine spectral time series of coronal line Mg ix 368 Ä and
transition region line O v 629 Ä, observed with the Coronal Diagnostic
Spectrometer (CDS) onboard the SOHO spacecraft. Primarily we were
looking for intensity and velocity oscillations in polar plumes,
however by chance we detected a giant macro-spicule at the limb and
were able to follow its dynamical structure. Blue and red-shifted
emission in the O v line indicates that it is probably a rotating
twisted magnetic jet. Emission is also detected in the Mg ix 368
Ä line, at a temperature of 1 million K. Both Fourier and wavelet
transforms have been applied independently to the analysis of the
oscillations in order to find the most reliable periods. We report
here on the existence of long period oscillations in the polar plumes
as observed in the O v 629 Ä line. Our observations indicate the
presence of compressional waves with periods of 20-25 minutes.
---------------------------------------------------------
Title: Modelling of Explosive Events in the Solar Transition Region:
Importance of Radiative Losses and Thermal Conduction
Authors: Roussev, I.; Erdélyi, R.; Doyle, J. G.; Galsgaard, K.
1999ESASP.448..641R Altcode: 1999mfsp.conf..641R; 1999ESPM....9..641R
No abstract at ADS
---------------------------------------------------------
Title: New Insight in Transition Region Dynamics as Derived from
SUMER Observations and Numerical Modelling
Authors: Teriaca, L.; Doyle, J. G.; Erdélyi, R.; Sarro, L. M.;
Banerjee, D.
1999ESASP.448..379T Altcode: 1999ESPM....9..379T; 1999mfsp.conf..379T
No abstract at ADS
---------------------------------------------------------
Title: New insight into transition region dynamics via SUMER
observations and numerical modelling
Authors: Teriaca, L.; Doyle, J. G.; Erdélyi, R.; Sarro, L. M.
1999A&A...352L..99T Altcode:
We explore the idea that the occurrence of nano-flares in a magnetic
loop around the O vi formation temperature could explain the
observed red-shift of mid-low transition region lines as well as the
blue-shift observed in low coronal lines (T > 6x 10<SUP>5\</SUP>
K). Observations are compared to numerical simulations of the response
of the solar atmosphere to an energy perturbation of 4x 10<SUP>24</SUP>
ergs representing an energy release during magnetic reconnection
in a 1-D semi-circular flux tube. The temporal evolution of the
thermodynamic state of the loop is converted into C iv 1548, O vi 1032
and Ne viii 770 line profiles in non-equilibrium ionization. Performing
an integration over the entire period of simulations, a redshift of ~
6\ km\ s<SUP>-1</SUP> is found in C iv, while a blue-shift of ~ 2\ km\
s<SUP>-1</SUP> and ~ 10\ km\ s<SUP>-1</SUP> were derived for O vi and
Ne viii, respectively, in reasonable agreement with observations.
---------------------------------------------------------
Title: SUMER Measurements of Electron Density Enhancements in the
Solar Transition Region
Authors: Pérez, M. E.; Doyle, J. G.; O'Shea, E.; Keenan, F.
1999ESASP.448..629P Altcode: 1999mfsp.conf..629P; 1999ESPM....9..629P
No abstract at ADS
---------------------------------------------------------
Title: Temporal variability in the electron density at the solar
transition region
Authors: Pérez, M. E.; Doyle, J. G.; O'Shea, E.; Keenan, F. P.
1999A&A...351.1139P Altcode:
The electron density as measured in the transition region of a coronal
hole, a `quiet' Sun region at disk center plus an active region shows
variations of up to a factor of two at T_e ~ 1.5 10<SUP>5</SUP> K,
lasting at most only a few minutes. There is remarkable agreement
between the number of such variations, their temporal variability
and duration in the coronal hole and `quiet' Sun datasets, consistent
with an earlier bright point study. There appears to be evidence of
super-granular cells, with the increases in electron density occurring
along the network boundaries. At some locations, periodicities of
between 8 and 16 min are visible in the electron density variations. We
associate these variations with the sites of explosive events.
---------------------------------------------------------
Title: Modelling explosive events in the solar atmosphere
Authors: Sarro, L. M.; Erdélyi, R.; Doyle, J. G.; Pérez, M. E.
1999A&A...351..721S Altcode:
High-resolution ultraviolet (UV) spectra of the outer solar
atmosphere show transient brightenings often referred to as explosive
events. These are localized regions of small spatial extent that
show sudden enhancements in the intensities of lines formed between
20,000 and 200,000 K, accompanied by strong non-gaussian profiles. The
present work is an attempt to extract observational consequences from
computational simulations of the dynamic response of a coronal loop to
energy perturbations. Explosive events are simulated in semi-circular
magnetic flux tubes. Thermal energy perturbations drive flows along
the flux tube giving rise to thermodynamic phenomena. The temporal
evolution of the thermodynamic state of the loop is converted into C iv
lambda 1548.2 Ä line profiles in (non)-equilibrium ionization. Time
dependent carbon ion populations are obtained in the non-equilibrium
conditions derived from the thermodynamic variables by means of
an adaptive grid code. Most important, departures from ionization
equilibrium are assessed for the first time under conditions such as
those encountered in explosive events.
---------------------------------------------------------
Title: The Wilson-Bappu relation for RS CVn stars
Authors: Özeren, F. F.; Doyle, J. G.; Jevremovic, D.
1999A&A...350..635O Altcode:
We investigate the extent to which the Wilson-Bappu relationship holds
for chromospherically active binaries using the Mg ii h&k lines of
41 RS CVn stars observed with IUE. The resulting fits are different
from the relationships obtained for single, less active stars. The
parallax used were those from the hipparcos catalogue, these give a
much better correlation than the magnitudes taken from CABS. Within a
particular luminosity class the relationship is good, however it tends
to break down when we incorporate objects ranging in luminosity from
class i to v. From model calculations there is very little dependence
of the Mg ii line width on effective temperature. The line width does
however depend on the column mass at the transition region boundary
showing increased line width at lower column mass. There is also a
dependence on the column mass adopted for the temperature minimum,
however, the major and dominant parameter is the surface gravity
scaling as g(-1/4) . Within a luminosity class more active objects
will show larger lines widths reflecting a higher column mass deeper
in the atmosphere, e.g. at the temperature minimum level.
---------------------------------------------------------
Title: SUMER Observations of Line Shifts in the Quiet Sun and in an
Active Region
Authors: Teriaca, L.; Banerjee, D.; Doyle, J. G.; Erdély, R.
1999ESASP.446..645T Altcode: 1999soho....8..645T
The UV spectral lines formed at transition region temperatures in the
solar atmosphere, shows a prevailing redshifted emission. Using the
Solar Ultraviolet Measurements of Emitted Radiation spectrometer
flown on the Solar and Heliospheric Observatory spacecraft, we
measure the amount of line shift as a function of the temperature
for several spectral lines formed in the range between 10<SUP>4</SUP>
and 10<SUP>6</SUP> K. We analyze spectrograms relative to the quiet
Sun and to the active region NOAA 7946. The velocities derived are
increasing from a redshift of ~ 0 km/s at ~ 20000 K to 10 km/s
at 1.9x10<SUP>5</SUP> K for the quiet Sun, and to ~ 15 km/s at
10<SUP>5</SUP> K for the active region. At higher temperature an
opposite behaviour is observed. In the quiet Sun a blueshift of ~ -2
km/s is observed at the Ne viii formation temperature (6x10<SUP>5</SUP>
K), while in the active region, a blue-shifted value around -8 km/s is
observed for the same spectral line. By 10<SUP>6</SUP> K the blueshift
is ~ -10 km/s in the active region as measured by Fe xii 1242.
---------------------------------------------------------
Title: The Nature Of Network Oscillations In The Solar Chromosphere
Authors: Banerjee, D.; Doyle, J. G.; O'Shea, E.
1999ESASP.446..161B Altcode: 1999soho....8..161B
We examine the simultaneous time-series spectral data for NI 1319 deg
and CII 1335 deg and CII and OVI obtained from the SUMER instrument
on the SOHO spacecraft. The observed 4-5 min network oscillations
can be interpreted in terms of kink and sausage waves propagating
upwards along thin magnetic flux tubes. Transverse kink waves can be
generated by random foot-point motions driven by exploding granules at
the photospheric level. As they propagate within flux tubes, their
amplitude grows exponentially with height and become non-linear,
thereby undergoing a mode transformation becomes longitudinal sausage
type. We propose that for the network bright regions these sausage waves
are responsible for the 3.5 mHz power peak. Numerical results based
on thin flux tube equations will be compared with observations. Our
two layer isothermal atmospheric model predicts a coupled oscillator
frquency which matches fairly well with the network observations.
---------------------------------------------------------
Title: Coronal Hole Diagnostics out to 8 solar radii
Authors: Doyle, J. G.; Teriaca, L.; Banerjee, D.; Fludra, A.
1999ESASP.446..281D Altcode: 1999soho....8..281D
The line width measurements (from Si VIII) and N<SUB>e</SUB> estimates
(from Si VIII and Si IX) based on SUMER and CDS observations are
combined with LASCO and UVCS output to provide an overview of its
variations with height above a polar coronal hole. From the combined
dataset we find a radial dependence of the electron density, in the
range 1-2 solar radii as r-8, from 2 to 4 solar radii as r-4 and then
as r-2. Combining the Si VIII half width at 1/e of the peak intensity
with the UVCS O VI half width, we find a small increase of the half
width from 1 to 1.2 solar radii, then a plateau until 1.5 solar radii,
thereafter a sharp increase until 2 solar radii, finally a more gradual
increase reaching 550 km/s at 3.5 solar radii. Our data suggests that
the MHD waves responsible for the excess line broadening tends to
become non-linear as it reaches 1.2 solar radii.
---------------------------------------------------------
Title: SUMER observations of Doppler shift in the quiet Sun and in
an active region
Authors: Teriaca, L.; Banerjee, D.; Doyle, J. G.
1999A&A...349..636T Altcode:
The UV spectral lines formed at transition region temperatures in the
solar atmosphere, show a prevailing redshifted emission. Using the Solar
Ultraviolet Measurements of Emitted Radiation spectrometer flown on the
Solar and Heliospheric Observatory spacecraft, we measure the amount
of line shift as a function of the temperature for several spectral
lines formed in the range between 10(4) and 10(6) \ K. We analyze
spectrograms relative to the quiet Sun and to the active region NOAA\
7946. The velocities derived are increasing from a redshift of ~ \
0 \ km ; s(-1) at ~ 20000\ K to 10\ km ; s(-1) at 1.9\ 10(5) \ K for
the quiet Sun, and to ~ 15 \ km ; s(-1) at 10(5) \ K for the active
region. At higher temperature an opposite behaviour is observed. In
the quiet Sun a blueshift of ~ \ -2 \ km ; s(-1) is observed at the
Ne viii formation temperature (6.3\ 10(5) \ K), while in the active
region, a blue-shifted value around -8\ km ; s(-1) is observed for
the same spectral line. The finding of blueshift in Ne viii is due to
the adoption of a new rest wavelength of 770.428 Ä. By 10(6) \ K the
blueshift is ~ \ -10 \ km ; s(-1) in the active region as measured by
Fe xii 1242.
---------------------------------------------------------
Title: Coronal hole diagnostics out to 8R<SUB>sun</SUB>
Authors: Doyle, J. G.; Teriaca, L.; Banerjee, D.
1999A&A...349..956D Altcode:
The Si viii line width measurements and N_e estimates based on SUMER
observations are combined with LASCO and UVCS output to provide an
overview of its variations with height above a polar coronal hole. From
the combined dataset we find a radial dependence of the electron
density, in the range 1-2 R<SUB>sun</SUB> as r(-8) , from 2 to 4
R<SUB>sun</SUB> as r(-4) and then as r(-2) . Combining the Si viii half
width at 1/e of the peak intensity with the UVCS O vi half width, we
find a small increase of the half width from 1 to 1.2 R<SUB>sun</SUB>,
then a plateau until 1.5 R<SUB>sun</SUB>, thereafter a sharp increase
until 2 R<SUB>sun</SUB>, finally a more gradual increase reaching 550
km s(-1) at 3.5 R<SUB>sun</SUB>. Our data suggests that the MHD waves
responsible for the excess line broadening tends to become non-linear
as it reaches 1.2 R<SUB>sun</SUB>.
---------------------------------------------------------
Title: Electron densities above a polar coronal hole based on improved
SI IX density diagnostics
Authors: Doyle, J. G.; Keenan, F. P.; Ryans, R. S. I.; Aggarwal,
K. M.; Fludra, A.
1999SoPh..188...73D Altcode:
Using new close-coupling excitation rates for the C-like ion Si ix,
density-diagnostic ratios based on Si ix lines have been re-evaluated
and applied to a sequence of CDS observations taken above a polar
coronal hole. The derived electron densities are in excellent agreement
with previous values of N<SUB>e</SUB>estimated from the N-like ion Si
viii for another coronal hole. The confirmed trend is for a fall-off
of one order of magnitude within the first 0.3 R<SUB>⊙</SUB>above the
limb. These densities are well fitted with an analytic formula for the
density profile out to at least 8 R<SUB>⊙</SUB>, by which stage the
electron density has fallen to ∼4×10<SUP>3</SUP> cm<SUP>−3</SUP>,
from 1.5×10<SUP>8</SUP> cm<SUP>−3</SUP>at 1.0 R<SUB>⊙</SUB>.
---------------------------------------------------------
Title: Exploring the dynamical nature of the lower solar chromosphere
Authors: Doyle, J. G.; van den Oord, G. H. J.; O'Shea, E.; Banerjee, D.
1999A&A...347..335D Altcode:
We examine spectral time-series of two lower-chromospheric lines (N i
1319 Ä and C ii 1335 Ä) observed with the SUMER instrument on the SOHO
spacecraft. We point out differences between (intensity and velocity)
power spectra of network and internetwork regions and argue that the
behaviour resembles that of Ca ii power spectra. No significant phase
differences are found between the intensities of both lines. However,
when phase spectra are averaged along the slit there is some evidence
that the C ii intensity lags that of N i by 16 sec near 3 mHz. Intensity
power spectra of C ii are affected at higher frequencies by streams
of emitting structures. Using contrast-enhanced time slices we show
that 1) there exists a grain-like pattern which is found in both
network and internetwork regions; 2) streams of supersonically moving
structures probably outline a wave interference pattern; 3) the sizes
of structures observed in N i are smaller than when observed in C ii. At
various points our findings disagree with earlier results from SUMER. A
cookbook formalism is presented to derive confidence levels for power,
phase, gain and coherency spectra.
---------------------------------------------------------
Title: Alfvén waves in the solar polar coronal holes
Authors: Banerjee, D.; Teriaca, L.; Doyle, J. G.; Wilhelm, K.
1999AIPC..471..289B Altcode: 1999sowi.conf..289B
We study the variation of the line width and electron density as a
function of height above two coronal holes from forbidden spectral
lines of Si VIII. The spectra were obtained with the Solar Ultraviolet
Measurements of Emitted Radiation spectrometer flown on the Solar and
Heliospheric Observatory spacecraft. The observations concentrate on the
dark regions outside the plumes, which are believed to be the location,
where the fast solar wind originates. The line width data show that
the non-thermal line-of-sight velocity increases from 20 km s-1 at
27 arc sec above the limb to 37 km s-1 some 370 arc sec (i.e. ~1.38
R<SUB>solar</SUB>) above the limb. The electron density shows a
decrease from 3.5 10<SUP>8</SUP> cm<SUP>-3</SUP> to 1.6 10<SUP>7</SUP>
cm<SUP>-3</SUP> over the same distance. This data implies that the
non-thermal velocity is inversely proportional to the quadratic root of
the electron density in the range 1-1.2 R<SUB>solar</SUB>, in excellent
agreement with that predicted for undamped radially propagating Alfvén
waves. Beyond 1.2 R<SUB>solar</SUB> our data suggests an effective
breakdown of linear theory for the propagation of Alfvén waves.
---------------------------------------------------------
Title: Eclipsing behaviour of the radio emission in the Algol system
V505 Sagittarii
Authors: Gunn, A. G.; Brady, P. A.; Migenes, V.; Spencer, R. E.;
Doyle, J. G.
1999MNRAS.304..611G Altcode:
We present radio interferometric observations of the EA2 Algol-type
binary system V505 Sagittarii made with the ATNF Compact Array at
6 and 3.6 cm over one orbital cycle (1.18 d). We have obtained a
strong detection of the source (1.5 mJy at 6 cm and 1.4 mJy at 3.6 cm)
and derive a brightness temperature for the emitting region of T_b ~
2.7 x 10_9 K, a magnetic field strength of 17 < B < 170 G and
an electron density of N_e ~ 3.7 x 10_8 cm_-3. The radio flux density
levels show a clear modulation with evidence of eclipses of the emission
region at both conjunctions of the binary. The form of the light
curve implies that the radio source involves at least some enhanced
emission in the intra-binary region. This has important consequences
for the details of coronal formation and field interaction in active
close binary stars. We discuss some scenarios for the formation of
intra-binary active regions in Algol-type binary systems.
---------------------------------------------------------
Title: Modelling the spectral energy distribution and SED variability
of the Carbon Mira R Fornacis
Authors: Lobel, A.; Doyle, J. G.; Bagnulo, S.
1999A&A...343..466L Altcode:
We have developed a new method to determine the physical properties
and the local circumstances of dust shells surrounding Carbon- and
Oxygen-rich stars for a given pulsation phase. The observed mid-IR
dust emission feature(s), in conjunction with IRAS BB photometry and
coeval optical and near-IR BB photometry, are modelled from radiative
transport calculations through the dust shell using a grid of detailed
synthetic model input spectra for M-S-C giants. From its application
to the optical Carbon Mira R For we find that the temperature of the
inner shell boundary exceeds 1000 K, ranging between 1200 K and 1400
K. The optical depth of the shell at 11.3 mu m is determined at tau_
{11 microns }=0.105 with T_eff=3200+/-200 K for the central star in
the considered phase of variability. By-products of the analysis are
the shell composition of 90% amorphous carbon and only 10% SiC grains
with rather small average radii of 0.05+/-0.02 mu m. The dust density
distribution assumes a power law of r(-2) for a steady-state wind with a
geometrical thickness ranging between 10(4) and 5 10(4) times the inner
boundary shell radius and with a high gas mass-loss rate of 3-4 10(-6)
M<SUB>sun</SUB> y(-1) derived by radiation pressure onto the dust. We
show that the optical and near-IR light curves are strongly affected by
small changes of T_eff and of the shell optical depth with pulsation. A
comparison of high resolution optical spectra of R For and medium/low
resolution spectra of other carbon stars with the selected model input
spectrum is also provided. Based on observations taken at UKIRT, CST,
JCMT, SAAO, AAO and the IRAS Pointsource Catalogue
---------------------------------------------------------
Title: Explosive events in the solar atmosphere
Authors: Pérez, M. E.; Doyle, J. G.; Erdélyi, R.; Sarro, L. M.
1999A&A...342..279P Altcode:
Two examples of explosive events observed with SUMER in transition
region spectral lines are reported here; one detected in C iv 1548
Angstroms, in a region within the northern polar coronal hole, and the
other in O vi 1032 Angstroms, in an active region. The event measured
in C iv lasted ~ 3 min and extended approximately a region of 8 arc sec
along the slit (N-S) and 8 arc sec in the E-W direction. Velocities
reached around 150 km s(-1) in the blue wing and 100 km s(-1) in the
red wing. The active region events were more energetic and in total
lasted ~ 6 min. At the point of maximum activity, a region of 8 arc
sec along the slit is covered by one explosive event located in the
northern section of the observed region, while in the southern section
we observe two events very closely located and extended over a maximum
of 14 arc sec along the slit. More precisely, in the northern section
we have at least two consecutive events occurring in a short time
interval ( ~ 12 min) separated by ~ 3 arc sec. In the E-W direction
the raster length covered by each of these events was approximately
4 arc sec. The explosive events seen in O vi showed a very complex
structure of subsonic and supersonic velocity flows, both red-shifted
and blue-shifted. The apparent maximum velocity reached in the blue
wing was approximately 250 km s(-1) and 215 km s(-1) in the red wing.
---------------------------------------------------------
Title: Line Width Variations above a Coronal Hole: Implications
for Heating
Authors: Doyle, J. G.; Teriaca, L.; Banerjee, D.
1999ASPC..158..366D Altcode: 1999ssa..conf..366D
No abstract at ADS
---------------------------------------------------------
Title: Solar and Stellar Activity: Similarities and Differences
Authors: Butler, C. J.; Doyle, J. G.
1999ASPC..158.....B Altcode: 1999ssa..conf.....B
No abstract at ADS
---------------------------------------------------------
Title: Turbulent Bursts in the Solar Transition Region
Authors: O'Shea, E.; Doyle, J. G.
1999ASPC..158..383O Altcode: 1999ssa..conf..383O
No abstract at ADS
---------------------------------------------------------
Title: Observations of Explosive Events in the Solar Atmosphere
Authors: Pérez, M. E.; Doyle, J. G.
1999ASPC..158..387P Altcode: 1999ssa..conf..387P
No abstract at ADS
---------------------------------------------------------
Title: Oscillations in Chromospheric Network Bright Points
Authors: Banerjee, D.; Doyle, J. G.; O'Shea, E.
1999ASPC..158..297B Altcode: 1999ssa..conf..297B
No abstract at ADS
---------------------------------------------------------
Title: Observations and Modelling of a Flare on AD Leo
Authors: Jevremovic, D.; Butler, C. J.; Doyle, J. G.
1999ASPC..158..222J Altcode: 1999ssa..conf..222J
No abstract at ADS
---------------------------------------------------------
Title: SUMER Observations of Doppler Shifts in the Quiet Sun and an
Active Region
Authors: Teriaca, L.; Doyle, J. G.; Banerjee, D.
1999ASPC..158..362T Altcode: 1999ssa..conf..362T
No abstract at ADS
---------------------------------------------------------
Title: Dynamical Nature of the Quiet Solar Outer Atmosphere
Authors: Banerjee, D.; Doyle, J.; O'Shea, E.; van den Oord, G.
1999ASPC..183..389B Altcode: 1999hrsp.conf..389B
No abstract at ADS
---------------------------------------------------------
Title: Modelling of Explosive Events in the Solar Transition Region
Authors: Roussev, I.; Erdélyi, S.; Doyle, J. G.; Galsgaard, K.
1999RoAJ....9S..57R Altcode:
We present preliminary results of modelling 2D magnetic reconnection
in the solar transition region environment. Compressible
magnetohydrodynamic (MHD) simulations are performed by using a 2D
MHD code based on staggered meshes. The present work is an attempt
to numerically simulate magnetic reconnection that occurs between
newly emerging magnetic flux and the pre-existing network field,
which is widely believed to cause explosive events observed in the
solar atmosphere. The formation of asymmetric reconnection jets is
demonstrated in this study. Nonlinear anisotropic thermal conduction,
radiative losses, and volumetric heating are included in the energy
equation in order to investigate the formation of reconnection jets
more precisely, as these processes are of fundamental importance at
that region. The role of both nonlinear anisotropic thermal conduction
and radiative losses is found to be significant in the solar transition
region.
---------------------------------------------------------
Title: The Wilson-Bappu Relation for RS CVn Stars
Authors: Özeren, F. F.; Doyle, J. G.
1999ASPC..158..315O Altcode: 1999ssa..conf..315O
No abstract at ADS
---------------------------------------------------------
Title: The oscillatory nature of the upper solar atmosphere.
Authors: O'Shea, E.; Doyle, J. G.; Banerjee, D.; van den Oord, G. H. J.
1999joso.proc..128O Altcode:
The authors examine time series spectral data obtained by the SUMER
instrument onboard SOHO. Lines of N V 1242 Å, Si II 1533 Å, C IV 1548
Å, C II 1037 Å and O VI 1037.6 Å were measured and found to show
intensity oscillations. The oscillations were usually observed to occur
in small regions along the slit, limited to a few arcsec. N V 1242 Å
typically showed frequencies of between 1 - 2 mHz. The Si II and C IV
lines observed simultaneously were found to have differing oscillation
frequency ranges of 2 - 8 mHz and 2 - 4 mHz respectively. The C II
and O VI lines also measured simultaneously were both found to have
oscillation frequency ranges of 2 - 4 mHz. In addition a time lag
of ≡50 seconds was measured between the intensity oscillations in
these two lines, perhaps signifying a propagating wave from the low
temperature C II line region to the higher temperature O VI region of
the atmosphere.
---------------------------------------------------------
Title: Observations of explosive events in the solar atmosphere.
Authors: Pèrez, M. E.; Doyle, J. G.
1999joso.proc..178P Altcode:
Two examples of explosive events observed with SUMER in transition
region spectral lines are reported here; one detected in C IV 1548 Å,
in a region within the northern polar coronal hole, and the other in O
VI 1032 Å, in an active region located in the solar disk. The event
measured in C IV lasts over 3 min and extends approximately over
a region of 8 arcsec along the slit (N-S) and 8 arcsec in the E-W
direction. Velocities reach values of around 150 km s<SUP>-1</SUP>
in the blue wing and 100 km s<SUP>-1</SUP> in the red wing. The
active region events are more energetic and in total they last over
6 minutes. These explosive events seen in O VI showed a very complex
structure of subsonic and supersonic velocity flows, both redshifted and
blueshifted. The largest apparent maximum velocity reached in the blue
wing was approximately 250 km s<SUP>-1</SUP> and 215 km s<SUP>-1</SUP>
in the red wing.
---------------------------------------------------------
Title: Solar and Stellar Activity: Similarities and Differences
Authors: Butler, C. J.; Doyle, J. G.; Bailey, M. E.
1998PASP..110.1513B Altcode:
Conference was held in Armagh, Northern Ireland, in 1998
September. Proceedings will be edited by C. J. Butler and J. G. Doyle
and published in the ASP Conference Series.
---------------------------------------------------------
Title: Broadening of SI VIII lines observed in the solar polar
coronal holes
Authors: Banerjee, D.; Teriaca, L.; Doyle, J. G.; Wilhelm, K.
1998A&A...339..208B Altcode:
We study the variation of the line width and electron density as a
function of height above two coronal holes from forbidden spectral
lines of Si viii. The spectra were obtained with the Solar Ultraviolet
Measurements of Emitted Radiation spectrometer flown on the Solar and
Heliospheric Observatory spacecraft. The observations concentrate on the
dark regions outside the plumes, which are believed to be the locations,
where the fast solar wind originates. The line width data show that
the non-thermal line-of-sight velocity increases from 27 {km s}(-1) at
27 arc sec above the limb to 46 {km s}(-1) some 250 arc sec ({i.e. } ~
180,000 km) above the limb. The electron density shows a decrease from
1.1 10(8) {cm}(-3) to 1.6 10(7) {cm}(-3) over the same distance. This
data implies that the non-thermal velocity is inversely proportional
to the quadratic root of the electron density, in excellent agreement
with that predicted for undamped radially propagating Alfven waves. We
show that the energy flux associated with these hydromagnetic waves
is sufficient to drive the high speed solar wind streams.
---------------------------------------------------------
Title: The solar transition region: a time-varying interface between
the chromosphere and corona?
Authors: O'Shea, E.; Doyle, J. G.; Keenan, F. P.
1998A&A...338.1102O Altcode:
Using joint observations taken with the CDS and SUMER instruments
onboard SOHO, we re-examine the solar transition region in an attempt
to determine whether it is de-coupled from the over-lying coronal
region. Line ratios calculated from temporal series observations of
O iv and Fe xiii spectral lines were converted to electron density,
and hence electron pressure using theoretical line ratios. Little or no
evidence was found to support the constant electron density assumption,
and instead a constant electron pressure is found between the transition
region and corona. This lends support to the idea that the transition
region is a time varying interface between the chromosphere and corona,
and is not formed in unresolved fine-structures that are disconnected
from the corona.
---------------------------------------------------------
Title: Center-to-limb line width measurements of solar chromospheric,
transition region and coronal lines
Authors: Erdelyi, R.; Doyle, J. G.; Perez, M. E.; Wilhelm, K.
1998A&A...337..287E Altcode:
Line widths derived from observational data obtained by SUMER
onboard SOHO in August 1996 at disk center and at the limb are used
to confront those derived via assuming Alfven and/or magneto-acoustic
wave heating. The observational data clearly shows a center-to-limb
variation in the upper chromospheric and transition region lines,
with only a marginal difference in the coronal lines in the sense of
additional broadening further from disk center. Numerical estimations
based on linear MHD, favour the existence of Alfven wave heating
over magneto-acoustic heating, although further calculations are
required. For example, non-linear effects could change the wave
characteristics which in turn can have a major effect on the overall
line broadening.
---------------------------------------------------------
Title: Chromospheric modelling of the Hα and NA I D lines in five
M dwarfs of low to high activity level
Authors: Short, C. I.; Doyle, J. G.
1998A&A...336..613S Altcode:
We have obtained simultaneous high resolution Hα and Na I D spectra
of five dwarf M stars that span a wide range in chromospheric activity
level. The observed Na I D lines exhibit behavior that is qualitatively
similar to that of more well established diagnostics such as the Ca
II HK lines: as the activity level, as indicated by the Hα line,
increases, the absorption core brightens and then develops an emission
reversal. We compare the observed profiles with computed non-LTE
profiles from a grid of chromospheric/transition region models. We
find that the Hα and Na I D lines tend to be in general agreement
as indicators of approximate chromospheric activity level. However,
the Hα line systematically indicates a value for the mass loading
at the onset of the Transition Region and the location of T_min that
is 0.4 dex lower in column mass density than that indicated by Na I
D. Therefore, the profile of both lines cannot be simultaneously well
fit for all but one of our stars. We also find, in agreement with
the pioneering study of Andretta et al. (\cite{adb}), that for dMe
stars the shape of the Na I D emission cores is a much more sensitive
indicator of chromospheric thickness (or, equivalently, chromospheric
steepness) than is Hα , and, therefore, provides a powerful diagnostic
complement to Hα . Finally, we investigate the dependence of the
predicted line profiles on the values of the stellar parameters and
conclude that the inferred chromospheric pressure is sensitive to the
choice of T_eff and log g, especially among dMe stars. Specifically,
among dMe stars, a model in which the value of T_eff is too small
or too large by approximately 200 K, or in which the value of log g
is too large or too small by 0.5 dex, will give rise to closest fit
values of the column mass density at the location of the Transition
Region and T_min that are too small or too large, respectively, by
approximately 0.3 dex. As a result, discrepancies between the stellar
parameters of our photospheric model and those of the program objects
allow us to extract only upper or lower limits for the values of the
column mass density at critical points in the chromospheric structure
---------------------------------------------------------
Title: Waves in the solar transition region
Authors: Doyle, J. G.; van den Oord, G. H. J.; O'Shea, E.; Banerjee, D.
1998SoPh..181...51D Altcode:
The power spectra for line intensities of several lines formed in the
upper transition region around 100000 to 250000 K are presented. A
period of ∼5 min is clearly present in lines due to Oiii, Oiv,
and Ov. In one dataset a period approaching 10 min is present for
∼40 min. The size of the emitting features is limited to ∼7 arc
sec squared. In all datasets examined, there is excess power below 4
mHz everywhere along the slit, although the observed periods do not
always come from the most intense regions. In ∼40% of instances clear
periods are observable in the 2-5 mHz range with the largest power peak
at 3.0 mHz. In all regions, the 5.0 mHz power peak is smaller. For the
frequencies investigated there are no significant time delays in any of
the datasets examined. This finding may not be entirely unexpected as
the formation temperatures of Oiii (∼100000 K) and Ov (∼250000 K)
may be too close in order to result in an observable phase shift.
---------------------------------------------------------
Title: Coronal line-width variations
Authors: Doyle, J. G.; Banerjee, D.; Perez, M. E.
1998SoPh..181...91D Altcode:
Line-width measurements of the coronal ion Siviii confirm earlier
observations which show an increase in the non-thermal velocity above
the solar limb. The present data, taken at the equatorial limb, show an
increase from 24 km s<SUP>-1</SUP> at the limb to 28 km s<SUP>-1</SUP>
some 25000 km above the limb. The electron density as measured from
the Siviii line pair shows a decrease from 3.5 × 10<SUP>8</SUP>
cm<SUP>-3</SUP> to 1.8 × 10<SUP>8</SUP> cm<SUP>-3</SUP> over the
same distance. These data imply that the non-thermal velocity is
inversely proportional to the quadratic root of the electron density,
in excellent agreement with that predicted for undamped radially
propagating Alfvén waves.
---------------------------------------------------------
Title: Observations and modelling of spectral energy distributions
of carbon stars with optically thin envelopes
Authors: Bagnulo, S.; Doyle, J. G.; Andretta, V.
1998MNRAS.296..545B Altcode:
We present broad-band photometry in the optical, near-infrared and
submillimetre, and mid-infrared spectrophotometry of a selection of
carbon stars with optically thin envelopes. Most of the observations
were carried out simultaneously. Beside the emission feature at 11.3mum
due to silicon carbide grains in the circumstellar environment, many
of our mid-infrared spectra show an emission feature at 8.6mum. All
the observed spectral energy distributions exhibit a very large
far-infrared flux excess. Both these features are indeed common to
many carbon stars surrounded by optically thin envelopes. We have
modelled the observed spectral energy distributions by means of a
full radiative transfer treatment, paying particular attention to the
features quoted above. The peak at 8.6mum is usually ascribed to the
presence of hydrogenated amorphous carbon grains. We find also that
the feature at 8.6mum might be reproduced by assuming that the stars
have a circumstellar environment formed of both carbon- and oxygen-rich
dust grains, although this is in contrast with what one should expect
in a carbon-rich environment. The far-infrared flux excess is usually
explained by the presence of a cool detached dust shell. Following
this hypothesis, our models suggest a time-scale for the modulation
of the mass-loss rate of the order of some 10^3yr.
---------------------------------------------------------
Title: On the rotation-activity correlation for active binary stars
Authors: Gunn, A. G.; Mitrou, C. K.; Doyle, J. G.
1998MNRAS.296..150G Altcode:
We present an investigation of rotation-activity correlations using
International Ultraviolet Explorer (IUE) SWP measurements of the
Civ emission line at 1550Angstroms for 72 active binary systems. We
use a standard stellar evolution code to derive non-empirical Rossby
numbers, R_0, for each star in our sample and compare the resulting
Civ rotation-activity correlation to that found for empirically derived
values of the Rossby number and that based on rotation alone. For dwarf
stars our values of R_0 do not differ greatly from empirical ones and
we find a corresponding lack of improvement in correlation. Only a
marginal improvement in correlation is found for evolved components
in our sample. We discuss possible additional factors, other than
rotation or convection, that may influence the activity levels in active
binaries. Our observational data imply, in contrast to the theoretical
predictions of convective motions, that activity is only weakly related
to mass in evolved stars. We conclude that current dynamo theory is
limited in its application to the study of active stars because of the
uncertainty in the angular velocity-depth profile in stellar interiors
and the unknown effects of binarity and surface gravity.
---------------------------------------------------------
Title: Pa-beta as a chromospheric diagnostic in M dwarfs
Authors: Short, C. I.; Doyle, J. G.
1998A&A...331L...5S Altcode:
We have obtained, for the first time, a high resolution near-infrared
spectrum in the region of Pabeta of a chromospherically active M dwarf
(AU Mic). We demonstrate that both Pabeta and Hα can be fit with a
model of large chromospheric pressure, but that the two lines indicate
clearly different values of the exact pressure. There are several
important types of missing physics that need to be included in the
calculations before the importance of this apparent discrepancy can
be assessed. Nevertheless, the approximate agreement of the two lines
lends support to an earlier theoretical result that the Paschen series
is a useful chromospheric diagnostic in M dwarfs.
---------------------------------------------------------
Title: The photosphere and chromosphere of the RS Canum Venaticorum
star, II Pegasi. II. A multi-wavelength campaign in August/September
1992
Authors: Byrne, P. B.; Abdul Aziz, H.; Amado, P. J.; Arevalo, M. J.;
Avgoloupis, S.; Doyle, J. G.; Eibe, M. T.; Elliott, K. H.; Jeffries,
R. D.; Lanzafame, A. C.; Lazaro, C.; Murphy, H. M.; Neff, J. E.;
Panov, K. P.; Sarro, L. M.; Seiradakis, J. H.; Spencer, R. E.
1998A&AS..127..505B Altcode:
We describe multi-wavelength, simultaneous observations of the RS
CVn star, II Pegasi, most of which were obtained during the first
three weeks of September 1992. These observations were made using
optical and infra-red broad-band photometry, ultraviolet and optical
spectroscopy and microwave monitoring. We have detected photospheric
spots and chromospheric flares, as well as deriving a description
of mean conditions in the quiet chromosphere. One of the flares,
observed in optical photometry and ultraviolet spectroscopy is one of
the most energetic ever observed on this star. We demonstrate that in
its “quiescent” state II Peg is continually variable in most of its
chromospheric emissions, as well as in its coronal output.
---------------------------------------------------------
Title: Explosive events modelled in the view of SOHO observations
Authors: Erdélyi, R.; Sarro, L. B.; Doyle, J. G.
1998ESASP.421..207E Altcode: 1998sjcp.conf..207E
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric and coronal activity levels in the nearby faint
M dwarf GL 105B
Authors: Doyle, J. G.; Short, C. I.; Byrne, P. B.; Amado, P. J.
1998A&A...329..229D Altcode:
Monitoring with the HRI onboard ROSAT failed to detect the nearby
faint M dwarf star Gl 105B (a star of anomalously low chromospheric and
coronal activity), implying log L_x < 26.1. High resolution optical
data for Caii HK indicate a surface flux of ~ 6.5 \ 10(3) \ erg \
cm(-2) \ s(-1) , in good agreement with the previously measured Mg ii
hk flux. Based on chromospheric modelling, both the Hα and Caii K line
profiles indicate an atmospheric structure which is intermediate between
that of an intermediate dM chromosphere and a basal chromosphere. Also,
the modelling indicates that a better fit is obtained using a model
atmosphere which has T<SUB>min</SUB> less than 2650 K, and a thin,
steep chromosphere. Furthermore, the Caii HK radiative losses may only
be ~ 5% of the radiative losses in the UV continuum, implying total
chromospheric losses in excess of 10(5) erg cm(-2) s(-1) .
---------------------------------------------------------
Title: Observations of Explosive Events in the Solar Atmosphere
Authors: Perez, E. P.; Doyle, J. G.; Erdelyi, R.
1998ASPC..154..666P Altcode: 1998csss...10..666P
Two ultraviolet explosive events are reported here; one which lasted
over 2 mins and was detected in a region within the northern polar
coronal hole and a second event which lasted over 4 mins and was
detected within an active region. The coronal hole event first showed
a mass upflow, followed by blue and red-shifted plasma, then finally
a red-shifted plasma. Velocities reached ~120 km s^{-1}. The active
region event was more energetic, showing a second injection after
about 2 mins. The maximum velocity reached 300 km s^{-1}. Towards the
end of each of these events, the location of the mass upflow/downflow
had shifted by 3-4 arcsec compared to the initial location.
---------------------------------------------------------
Title: In Memoriam of P. Brendan Byrne
Authors: Doyle, J. G.
1998ASPC..154..127D Altcode: 1998csss...10..127D
No abstract at ADS
---------------------------------------------------------
Title: Modeling of Explosive Events in the Solar Atmosphere
Authors: Sarro, L. M.; Doyle, J. G.; Montesinos, B.; Erdelyi, R.;
de Sterck, H.
1998ASPC..154..693S Altcode: 1998csss...10..693S
High-resolution ultraviolet (UV) spectra show transient brightenings ---
often referred to as explosive events --- in the solar atmosphere. The
present work describes the progress made on their numerical
simulations. Using semi-circular magnetic flux tubes we find that
thermal energy perturbations drive flows along the flux tube. The time
evolution of our simulations first shows a sudden rise in temperature
at the perturbation site followed by the ejection of cool dense gas
bullets and the generation of sound waves. This is then followed by
the appearance of “new” transition regions moving at different
velocities. Our computational results are converted into UV line
profiles in (non)-equilibrium ionization. Observational signatures
(e.g., emission measures) are calculated as a function of time at
different locations on the solar disk.
---------------------------------------------------------
Title: Modelling the Spectral Energy Distribution of Carbon and
Oxygen-rich stars from stellar model spectra
Authors: Lobel, A.; Doyle, J. G.; Bagnulo, S.
1998IAUS..191P.307L Altcode:
We have developed a new method to determine the physical properties
and the local circumstances of dust shells surrounding Carbon- and
Oxygen-rich stars for a given pulsation phase. The observed mid-IR
dust emission feature(s), in conjunction with IRAS BB photometry and
coeval optical and near-IR BB photometry, are modelled from radiative
transport calculations through the dust shell using a grid of detailed
synthetic model input spectra for M-S-C giants to the DUSTY code. From
its application to the optical Carbon Mira R For we find that the
temperature of the inner shell boundary exceeds 1000 K, ranging between
1200 K and 1400 K. The optical depth of the shell at 11.3 microns is
determined at tau<SUB>11</SUB> = 0.105 with T<SUB>eff</SUB> = 3200
+- 200 K for the central star in the considered phase of variability
(Jul.-Aug. '95). By-products of the analysis are the shell composition
of 90% amorphous carbon and only 10% SiC grains with rather small
average radii of 0.05 +- 0.02 microns. The dust density distribution
follows a power law of r^{-2} for a steady-state wind with a geometrical
thickness ranging between 10^4 and 5 10^4 times the inner boundary
shell radius. The density gradient of r^{-2} results from the full
dynamic radiative transport calculations which include the momentum
transfer from the radiation field. This elaborate method enables
the modelling of the variable shape of the silicate feature of o Cet
and other oxygen-rich stars in conjunction with the SED observed at
various pulsation phases. We discuss the changes in the CSE and the
related ranges of the mass-loss rate and terminal outflow velocity. A
brief comparison of high-resolution optical spectra of R For, o Cet
and spectra of other carbon- and oxygen-rich stars, with the selected
model input spectra is also provided.
---------------------------------------------------------
Title: The Dynamical Nature of the Chromosphere
Authors: Banerjee, D.; Doyle, J. G.; O'Shea, E.
1998ESASP.417..333B Altcode: 1998cesh.conf..333B
No abstract at ADS
---------------------------------------------------------
Title: Transition Region Variability: Evidence for Oscillation
Authors: O'Shea, E.; Doyle, J. G.
1998ASPC..154..798O Altcode: 1998csss...10..798O
The data reported here was obtained with the Coronal Diagnostic
Spectrometer (CDS) in a sit-and-stare mode using a 4 x 240 arcsec
slit. Using integration times ranging from 15 to 20 sec, two different
types of observing sequences were obtained, the first involved the
observation of three oxygen lines due to O 3 599 AA, O 4 554 AA and
O 5 630 AA. These lines have temperature of formation ranging from
100,000 K to 250,000 K. The second type of sequence involved four lines,
He 1 584 AA formed below 100,000 K, O 4 554 AA and O 5 630 AA formed
between 150,000 K to 250,000 K, and Mg 10 610 AA formed at 1,000,000
K. Using a FFT technique, the resulting power spectra reveals periods
ranging from 4 to 10 minutes for plasma around the 150,000 to 250,000
K region. These periods were present for ~40 minutes covering a region
of ~7 arcsec^2. Excess power was present below 5 mHz in most datasets
in He 1 line data. For about 10-15% of the slit a single period was
detected. No periods were found in the Mg 10 line, although this may
be related to the fact that Mg 10 was rather weak in our data.
---------------------------------------------------------
Title: On the Rotation-Activity Correlation in Active Binaries
Authors: Gunn, A. G.; Mitrou, C. K.; Doyle, J. G.
1998ASPC..154.1257G Altcode: 1998csss...10.1257G
We present an investigation of rotation-activity correlations using
IUE SWP measurements of the C 4 emission line at 1550 AA for 72 active
binary systems. We use a standard stellar evolution code to derive
non-empirical Rossby numbers for each star in our sample and compare
the resulting C 4 rotation-activity correlation to that found for
empirically derived values of Rossby number. We find only a marginal
improvement in the correlation which suggests an additional factor
other than rotation or convective motion influencing the activity
levels in evolved stars. We conclude that current dynamo theory is
limited in its application to the study of active stars because of the
uncertainty in the angular velocity-depth profile in stellar interiors
and the unknown effects of binarity and surface gravity.
---------------------------------------------------------
Title: Chromospheric Line Blanketing and the H I Spectrum in dM Stars
Authors: Short, C. I.; Doyle, J. G.
1998ASPC..154..865S Altcode: 1998csss...10..865S
We present non-LTE calculations of the H 1 spectrum in a grid of
chromospheric models that represents a dM0 star in which the activity
level ranges from quiescent to very active. We investigate three
different treatments of the background opacity: 1) continuous opacity
only, 2) blanketing due to lines that form in the photosphere below
T_min, and 3) blanketing by lines that form throughout the entire
outer atmosphere. We show that the predicted peak flux of Hα in very
active (dMe) stars is reduced by ~15% by the inclusion of background
line opacity. We compare the synthetic Hα profiles with observed Hα
spectra of six early dM stars that span a range of activity level. A
consistent treatment of line blanketing that includes the effect of
the chromospheric and transition region temperature structure in the
calculation of background line opacity is necessary for the accurate
calculation of Hα in high activity stars.
---------------------------------------------------------
Title: Line Width Variations in the Solar Polar Coronal Holes
Authors: Teriaca, L.; Banerjee, D.; Doyle, J. G.
1998ESASP.417..329T Altcode: 1998cesh.conf..329T
No abstract at ADS
---------------------------------------------------------
Title: Randomly sampling the chromospheric peak power distribution.
Authors: Doyle, J. G.; van den Oord, G. H. J.; O'Shea, E.
1997A&A...327..365D Altcode:
We have analyzed the UV continuum light curves of 2535 pixels
obtained during fifteen separate observations of active regions
with the Ultraviolet Spectrometer and Polarimeter (UVSP) on board
the solar maximum mission in 1989. Specifically we have looked for
periodicities. In the power spectra of 738 light curves (i.e., 29%),
evidence was found for periodicities at multiple frequencies. For
each power spectrum, containing significant power, we determined the
frequency at which the maximum power is found. The distribution N(ν),
which describes the number of pixels having maximum power at frequency
ν, is strongly concentrated in the 2-5mHz band with a distinct maximum
at 3-3.5mHz. No pixels had their maximum power above 10mHz and only
a few had their maximum power in the 5-10mHz range. The oscillations
in the 2-5mHz range are probably related to evanescent acoustic waves
driven by the photospheric five minute oscillations. In the 2-5mHz band,
the distribution N(ν) resembles very much the power spectra as have
been observed near the temperature minimum. This suggests that the
photospheric power distribution can be interpreted as a probability
distribution for finding a given frequency in the UV continuum light
curves. In the 2-5mHz band the spread of the maximum powers and the
spread of the count rates, at any frequency, is much larger than above
5mHz where both are relatively constant. No clear correlation is found
between the maximum power and the count rate in a pixel. Furthermore,
no evidence is found for emission from the shocks which have recently
been invoked to explain the formation of CaII grains. Whether this is
due to temperature effects is unclear. Our general procedure adopted to
estimate the confidence level in the power spectrum of a light curve
containing photon noise can be equally applied to SUMER and CDS data
from SOHO.
---------------------------------------------------------
Title: Chromospheric line blanketing and the hydrogen spectrum in
M dwarfs.
Authors: Short, C. I.; Doyle, J. G.
1997A&A...326..287S Altcode:
We present non-LTE calculations of the HI spectrum in a grid of
chromospheric models that represents a dM0 star in which the activity
level ranges from quiescent to very active. We investigate three
different treatments of the background opacity: 1) continuous opacity
only, 2) blanketing due to lines that form in the photosphere below
T_min_, and 3) blanketing by lines that form throughout the entire
outer atmosphere. We show that the predicted W<SUB>lambda</SUB>_ of
Lyα in all models is reduced by as much as a factor of =~4, and that
of Hα in very active (dMe) stars is enhanced by a factor of about two
by the inclusion of background line opacity. A consistent treatment
of line blanketing that includes the effect of the chromospheric and
transition region temperature structure in the calculation of background
line opacity is necessary for the accurate calculation of Lyα, and
in some cases Hα, in these stars. The Hα line in less active models,
and the Paβ line in all models, is negligibly affected by the treatment
of background opacity. We also show that, in addition to the expected
suppression of emergent flux in the visible by line blanketing, the
broad-band continuum flux in regions where λ<2000A is increased by
as much as a factor of three in some models by the inclusion of line
blanketing. This reduces the equivalent width of the Lyman series by a
factor of four and is due to the veil of background lines going into
emission in the UV, and to the stronger coupling of the background
source function to the Planck function in the presence of blanketing
by thermal lines. We confirm the results of earlier calculations that
suggest the dominance of the continuum emission in the radiative cooling
of the chromosphere. Therefore, any proposed heating mechanisms must
supply at least an order of magnitude more non-radiative heating than
would be required on the basis of an analysis in which only emission
line cooling is considered. We also include a preliminary assessment of
non-LTE effects in the background opacity on the emergent UV continua.
---------------------------------------------------------
Title: The CaI 4227 line as a chromospheric diagnostic for M dwarfs.
Authors: Short, C. I.; Doyle, J. G.; Byrne, P. B.
1997A&A...324..196S Altcode:
In M dwarfs the CaI 4227 line is saturated, therefore, the line
core forms at a relatively small column mass density. As a result,
the line is a potential diagnostic of chromospheric structure in
these stars. We have calculated line profiles out of LTE for a grid
of early M dwarf atmospheric models that spans the range from low to
high chromospheric pressure and covers a range of observed activity
levels. We have found that this line is sensitive to the detailed
structure of the chromosphere in the same way as well studied strong
lines such as Hα and CaII HK: as the chromospheric pressure increases,
the line changes from absorption to strong emission with a central
double reversal. Therefore, observations of the CaI 4227 line in M
dwarfs would provide a useful additional constraint on the structure
of the outer atmosphere. We also calculate consistently the line
blanketing in the upper atmosphere of models with a chromosphere and
transition region and investigate the effect of its inclusion on CaI
4227. Finally, we demonstrate that the effects of Partial Frequency
Redistribution must be taken into account if the CaI 4227 is to be
used as an accurate diagnostic of the T_min_ region in dMe stars.
---------------------------------------------------------
Title: Nonthermal Velocities in the Solar Transition Zone and Corona
Authors: Doyle, J. G.; O'Shea, E.; Erdélyi, R.; Dere, K. P.; Socker,
D. G.; Keenan, F. P.
1997SoPh..173..243D Altcode:
Nonthermal velocities are presented for spectral lines covering the
temperature range 10 4-10 6 K, measured from high-spectral-resolution
data for several solar features observed at the limb by the high
resolution telescope and spectrograph (HRTS), including a coronal hole,
`quiescent regions' and several small-scale active regions. These
results are compared with predictions based on acoustic waves and
heating via Alfvén waves. It is likely that more than one mechanism is
operating simultaneously, in particular, resonant Alfvén wave heating,
which is very sensitive to background plasma motions.
---------------------------------------------------------
Title: Observations and Modelling of Spectral Energy Distributions
of Asymptotic Giant Branch Stars
Authors: Bagnulo, S.; Doyle, J. G.
1997Ap&SS.251..177B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The NaI λλ5890,5896 resonance doublet as chromospheric
diagnostics in M dwarfs.
Authors: Andretta, V.; Doyle, J. G.; Byrne, P. B.
1997A&A...322..266A Altcode:
The Nai D lines at 5890/5896Å are very prominent features in the
spectrum of late-type stars. Nevertheless, little attention has
been devoted to the potential use of those lines as chromospheric
diagnostics. As a case study, we explore the dependence on chromospheric
activity of the D lines in a star with T_eff_=3700K, logg=4.7 and solar
metallicity. The results are compared with the better studied hydrogen
spectrum. We find that the D lines seem to be a promising diagnostic
of the lower-middle chromosphere, that can complement the information
given by lines like Hα. We also find that, for detailed quantitative
studies, it is necessary to include a proper treatment of the background
opacities. Less important, instead, is the need of careful treatment
of transitions induced by collisions with hydrogen atoms. Finally,
our calculations make it clear that, for the most active stars, the
level of coronal emission should also be taken into account.
---------------------------------------------------------
Title: Carbon stars with detached dust shells: the circumstellar
envelope of UU Aurigae.
Authors: Bagnulo, S.; Skinner, C. J.; Doyle, J. G.; Camphens, M.
1997A&A...321..605B Altcode:
We have modelled the spectral energy distribution of the carbon-rich
star UU Aurigae, which shows an excess flux in the far infrared and
sub-millimeter regions, in terms of a detached shell generated by an
episode of higher (than the current) mass loss rate. Two different
compositions for the detached shell were used: oxygen-rich and
carbon-rich dust grains. By assuming that at longer wavelengths the
extinction coefficients of the oxygen-rich grains follow a λ^-2^
law, and those of the amorphous carbon follow a λ^-1.3^ law, we show
that the model including a detached carbon-rich shell produces a more
satisfactory fit to the observational data compared to the model with
a detached oxygen-rich shell. Moreover, we derived a relatively small
value for the distance of the detached shell from the central star,
which implies that the episode of high mass loss rate ended only few
hundred years ago. The results of our analysis are consistent with
the scenario for the stellar evolution on the asymptotic giant branch
which predicts a short time-scale modulation of the mass loss rate
induced by repeated Helium shell-flashes.
---------------------------------------------------------
Title: Radio and extreme-ultraviolet observations of CF Tucanae
Authors: Gunn, A. G.; Migenes, V.; Doyle, J. G.; Spencer, R. E.;
Mathioudakis, M.
1997MNRAS.287..199G Altcode:
We present contemporaneous EUV and radio observations obtained for
the totally eclipsing chromospherically active RS CVn-type binary CF
Tucanae. Observations were made with the ATNF Compact Array at 6 and
3.6cm over one complete orbital cycle of the system, and with the EUVE
Deep Survey/Spectrometer telescope over five orbital cycles. We obtained
a strong detection of the source (1.9mJy at 6cm and 1.1mJy at 3.6cm)
in the radio. Both EUV and radio flux levels appear to show a clear
modulation at the orbital period with a maximum at phase 0.5 which
indicates the existence of an intra-binary region of activity. This
has important consequences for the details of coronal formation and
field interaction in active close binary stars. We interpret the EUV
emission as an isotropically radiating thermal source; on the other
hand, the radio emission shows evidence of intrinsic gyromagnetic
directivity. We also demonstrate that contemporaneous EUV and radio
observations are not sufficient to determine the characteristics of
the gyro-emission electron population.
---------------------------------------------------------
Title: Constraints on mass loss from dMe stars: theory and
observations.
Authors: van den Oord, G. H. J.; Doyle, J. G.
1997A&A...319..578V Altcode:
We show that the flux distribution of a wind from a cool star
differs considerably from what is predicted by the theory for mass
loss from hot stars. The differences are caused by the facts that 1)
the mass loss rates are lower, resulting in smaller optical depths
in the wind, and 2) for winds from cool stars the temperature of the
wind is higher than the temperature of the star while for winds from
hot stars the reverse holds. These differences result in substantial
modifications of the flux distribution and imply that care must be
exercised when applying the flux predictions by e.g. Wright and Barlow
(1975MNRAS.170...41W) to winds from cool stars. By using observational
constraints we show that the mass loss from cool dwarf stars equals at
most 10^-12^M<SUB>sun</SUB>_/yr. This is a factor hundred lower than
previous estimates. At this rate the mass loss from dMe stars is of
little importance for the enrichment of the interstellar medium. By
solving the radiative transfer equations for stellar winds from dMe
stars, we show that the inferred power-law flux distributions, based
on radio, JCMT and IRAS data, cannot be reconciled with the flux
distributions from a stellar wind of 10^-10^M<SUB>sun</SUB>_/yr as
was previously assumed. The maximum allowable mass loss rate is at
most a few times 10^-12^M<SUB>sun</SUB>_/yr which implies that the
fluxes observed with JCMT, IRAS, and in the future with ISO, require
a different interpretation than free-free emission from a stellar wind.
---------------------------------------------------------
Title: Environments of active close binaries. II. GK Hydrae and
TY Pyxidis.
Authors: Gunn, A. G.; Doyle, J. G.; Houdebine, E. R.
1997A&A...319..211G Altcode:
High-resolution spectroscopic observations were obtained for two
eclipsing active close binary systems, GK Hydrae and TY Pyxidis. For
GK Hya excess emission was observed in the Balmer lines and Mg I b
lines while TY Pyx showed excess emission in the Balmer lines and
Ca ii H&K lines. The emission from GK Hya arises from a global
phenomenon associated solely with the secondary component. The lack
of significant He I D_3_ excess absorption and an analysis of the
flux ratio in the Balmer lines suggest that the emission originates
in prominence-like material seen off the limb of the star. A marginal
broad excess absorption band centered around the Balmer emission peaks
may be caused by this material absorbing the stellar continuum against
the disk with high (350km/s) line-of-sight turbulent velocities. The
inference that plage-like regions and associated star-spots are
not substantial on this star is in agreement with the lack of spot
modulation in the photometric light curve. For TY Pyx the majority
of the Hβ excess and a larger proportion of the Ca ii core emission
could be attributed to a global phenomenon on the primary. Analysis
suggests that very large volumes are responsible for the emission,
however, there is no observational evidence for the existence of
discrete extended structures around TY Pyx.
---------------------------------------------------------
Title: M VIII Diagnostic Line Ratios in SKYLAB Solar Observations
Authors: Foster, V. J.; Keenan, F. P.; Reid, R. H. G.; Doyle, J. G.;
Zhang, H. L.; Pradhan, A. K.; Widing, K. G.
1997SoPh..170..217F Altcode:
Recent calculations of Mgviii electron and proton impact
excitations rates are used to derive theoretical electron temperature
(T<SUB>e</SUB>)- and density (N<SUB>e</SUB>)-sensitive emission line
ratios involving transitions in the 315-782 Å wavelength range. Some
of these ratios are presented in the form of ratio-ratio diagrams,
which should in principle allow both N<SUB>e</SUB> and T<SUB>e</SUB>
to be deduced. These results are compared with solar observational data
from Skylab, but agreement between theory and observation is very poor,
probably due to blending.
---------------------------------------------------------
Title: The intrinsic LY α to H α ratio in M dwarf stars.
Authors: Doyle, J. G.; Mathioudakis, M.; Andretta, V.; Short, C. I.;
Jelinsky, P.
1997A&A...318..835D Altcode:
Using Ly α line profiles generated from a grid of M
dwarf model atmospheres we calculate the attenuation factor
[i.e. Lyα(obs)/Lyα(intrin)] due to the interstellar medium as
a function of hydrogen column density. Then using selected model
atmospheres, attenuation factors were calculated for those M dwarfs with
available Ly α observations. The prime motivation in this work has been
to look afresh at the intrinsic Ly α to H α flux ratio, an important
constraint in the radiative transfer modelling of M dwarfs. For those
active dMe stars where both lines were observed, the intrinsic ratio
is ~3-5 (with ~50% variation). The major uncertainty in this work has
been the interstellar hydrogen column density, emphasizing the need
for further work in this area and in particular an accurate model of
its variation in all directions.
---------------------------------------------------------
Title: An active K0 IV-V star and a hot white dwarf (EUVE J0702+129)
in a wide binary.
Authors: Vennes, S.; Christian, D. J.; Mathioudakis, M.; Doyle, J. G.
1997A&A...318L...9V Altcode:
We present far ultraviolet and optical spectroscopy of the Extreme
Ultraviolet Explorer (EUVE) survey source EUVE J0702+129 revealing
a composite K0 star plus DA white dwarf spectrum. The International
Ultraviolet Explorer spectra show continuum emission from a hot white
dwarf (Teff=30-40,000K) and a rising contribution from the K0 star
at λ>2500Å. High resolution optical spectroscopy uncovers a high
level of activity with strong Hα and Ca H&K emission; application
of the Wilson-Bappu relation indicates that the secondary star is
slightly above the main sequence (K0 IV-V). Both objects are found at
a distance of ~130pc and they likely constitute a physical pair. The
EUV emission is dominated by the white dwarf, but the late-type star
certainly contributes at higher energy. An interesting parallel is
drawn with other DA+K0 pairs with moderately active secondaries such
as HD 18131 and HR 1608. The present discovery as well as other recent
ones demonstrate the existence of a large population of white dwarfs
hidden by evolved companions (III-IV).
---------------------------------------------------------
Title: EUV Emission from RS Canum Venaticorum binaries.
Authors: Mitrou, C. K.; Mathioudakis, M.; Doyle, J. G.; Antonopoulou,
E.
1997A&A...317..776M Altcode:
We performed a study of 104 RS CVn systems in the extreme ultraviolet
(EUV) using the all-sky survey data obtained by the Extreme Ultraviolet
Explorer (EUVE). The present sample includes several new RS CVn
detections; 11 more than in the published EUVE catalogs, and 8 more
than in the ROSAT Wide Field Camera catalog. The ratio of detections to
non-detections remained constant throughout the sky, implying that our
detections are not limited by the exposure time but are most likely
limited by absorption from the interstellar medium. A general trend
of increasing Lex/B (50-180Å) flux with decreasing rotational period
is clear. The dwarf systems exhibit a leveling-off for the faster
rotators. In contrast, the evolved systems exhibit no such effect. For
the RS CVn systems the losses in the EUV represent a smaller fraction
of the coronal radiative losses, as compared to active late-type dwarfs.
---------------------------------------------------------
Title: Environments of active close binaries. I. ER Vulpeculae.
Authors: Gunn, A. G.; Doyle, J. G.
1997A&A...318...60G Altcode:
High-resolution observations of the eclipsing active close binary
system ER Vulpeculae have revealed excess emission in the Hα, the Ca
II IRT and the Mg I b lines and excess absorption in the He I D_3_
line. The emission appears to be from a global phenomenon with the
secondary component the more active. Analysis has revealed that the
emission arises in plage-like material covering perhaps half of the
secondary's surface. This gives credence to X-ray and UV studies
which have indicated that ER Vul is near the saturation limit for
dynamo-induced activity. No firm spectroscopic evidence for the
existence of extended material around ER Vul was found. A consistent
velocity offset of ~10km/s was observed in the excess Hα emission from
the secondary component which may be associated with active regions
such as spicules. If so this represents the first observation of the
equivalent of solar spicule emission in a stellar system other than
the Sun.
---------------------------------------------------------
Title: MHD Waves Observed (?) by SOHO: MHD Wave Heating
Authors: Erdélyi, R.; Perez, E. P.; Doyle, J. G.
1997ESASP.404..357E Altcode: 1997cswn.conf..357E
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric line blanketing and the CA I 4227 line in
M dwarfs
Authors: Short, C. I.; Doyle, J. G.
1997IrAJ...24...35S Altcode:
In M dwarfs the Ca I 4227 line is saturated, therefore, the line core
forms at a relatively small column mass density. As a result, the line
is a potential diagnostic of chromospheric structure in these stars. We
have calculated line profiles out of LTE for a grid of early M dwarf
atmospheric models that spans the range from low to high chromospheric
pressure and covers a range of observed activity levels. We have
found that this line is sensitive to the detailed structure of the
chromosphere in the same way as well studied strong lines such as
H alpha and Ca II HK: as the chromospheric pressure increases, the
line changes from absorption to strong emission with a central double
reversal. Therefore, observations of the Ca I 4227 line in M dwarfs
would provide a useful additional constraint on the structure of the
outer atmosphere. We also calculate consistently the line blanketing
in the upper atmosphere of models with a chromosphere and transition
region and investigate the effect of its inclusion on Ca I 4227.
---------------------------------------------------------
Title: Explosive Events Observed by SOHO
Authors: Erdélyi, R.; Perez, E. P.; Doyle, J. G.
1997ESASP.404..353E Altcode: 1997cswn.conf..353E
No abstract at ADS
---------------------------------------------------------
Title: Modelling of Explosive Events in the Solar Atmosphere
Authors: Sarro, I. M.; de Sterk, H.; Erdélyi, R.; Montesinos, B.;
Doyle, J. G.
1997ESASP.404..657S Altcode: 1997cswn.conf..657S
No abstract at ADS
---------------------------------------------------------
Title: In memorian: Patrick Brendan Byrne (28 September 1947 -
16 September 1997)
Authors: Doyle, J. G.; Butler, C. J.; Bailey, M. E.
1997MmSAI..68..945D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A non-empirical rotation--activity correlation for active
binaries
Authors: Gunn, A. G.; Mitrou, C. K.; Doyle, J. G.
1997jena.confE.145G Altcode:
We present an investigation of rotation-activity correlations using
IUE SWP measurements of the CIV emission line at 1550AA for 72 active
binary systems. We use a standard stellar evolution code to derive
non-empirical Rossby numbers for each system. We compare the resulting
rotation--CIV activity correlation to that found for empirically derived
Rossby numbers and to the one based on period only. The marginal only
improvement in the correlation that we find, is surprising considering
that the empirically derived Rossby numbers were for main-sequence
stars and should not be appropriate for evolved stars. This suggests
an additional factor (other than rotation and convective motion)
influencing the activity levels. Our observational data imply that
activity is only weakly related to mass in evolved stars, in contrast
to the theoretical predictions of convection zone motions. We conclude
that current dynamo theory is limited in its application to the study of
active stars, because of the uncertainty in the angular velocity--depth
profile in stellar interiors and the unknown effects of binarity and
surface gravity.
---------------------------------------------------------
Title: Chromospheric Line Blanketing and the Hydrogen Spectrum of
dM Stars
Authors: Short, C. I.; Doyle, J. G.
1996AAS...189.8109S Altcode: 1996BAAS...28.1383S
We present non-LTE calculations of the Hi spectrum in a grid of
chromospheric models that represents a dM0 star in which the activity
level ranges from quiescent to very active. We investigate three
different treatments of the background opacity: 1) continuous opacity
only, 2) blanketing due to lines that form in the photosphere below
T<SUB>min</SUB>, and 3) blanketing by lines that form throughout the
entire outer atmosphere. We show that the predicted W_lambda of Lyalpha
in all models, and of Hα in very active (dMe) stars, is reduced by as
much as a factor of ~ 4 by the inclusion of background line opacity. A
consistent treatment of line blanketing that includes the effect of
the chromospheric and transition region temperature structure in the
calculation of background line opacity is necessary for the accurate
calculation of Lyalpha , and in some cases Hα , in thes e stars. The
Hα line in less active models, and the Pabeta line in all models,
is negligibly affected by the treatment of background opacity. We also
show that the broad-band continuum flux in regions where lambda <
2000 A is increased by as much as a factor of ~ 3 in some models by
the inclusion of chromospheric line blanketing.
---------------------------------------------------------
Title: Comprehensive Multiwavelength Observations of the 1992 January
7 Solar Flare
Authors: Silva, Adriana V. R.; White, Stephen M.; Lin, Robert P.;
de Pater, Imke; Gary, Dale E.; McTiernan, James M.; Hudson, Hugh S.;
Doyle, J. Gerry; Hagyard, Mona J.; Kundu, Mukul R.
1996ApJS..106..621S Altcode:
Observations of a solar flare that occurred at 2022 UT on 1992
January 7, during the 1991 December/1992 January Max `91 campaign,
are presented. This flare was observed simultaneously in Hα, radio
(at microwave and millimeter wavelengths), and soft and hard X-rays
(by the Yohkoh spacecraft) with high spatial and moderate spectral
resolution. A comparison of magneto grams before and after the flare
shows evidence of the emergence of new magnetic flux of opposite
polarity at the flare site. Although this flare was only of moderate
size (GOES classification C8.9 and Hα importance SF), it exhibited
several distinct bursts and at least 10 spatially distinct hard/soft
X-ray sources. Cospatial Hα brightenings suggest that most of the
X-ray sources are located at footpoints of magnetic loops. Two of the
hard X-ray sources have no Hα counterparts and are therefore believed
to be located at loop tops. The flare consisted of three bursts
of particle acceleration followed by a purely thermal phase. High
spectral resolution Ca XIX line profiles indicate upflows shortly
after the second acceleration phase. Analysis of the microwave/hard
X-ray/soft X-ray emission from individual sources provides information
on the radio emission mechanisms, the energetic electron population,
the magnetic field strength, and the plasma density. These parameters
were estimated for the two microwave sources observed during the
third acceleration burst; these sources were simultaneously detected
in soft X-rays, and one of the sources is also seen in hard X-ray
maps. Although the microwave emission is consistent with the gyro
synchrotron mechanism, the millimeter emission, which peaks during the
thermal phase when all nonthermal activity has ceased, is likely due
to thermal bremsstrahlung from the soft X-ray emitting hot plasma. The
energy lost to collisions by the energetic (>15 keV) electrons
and the energy contained in the thermal plasma are calculated for
each source. The energy injected by the nonthermal electrons from all
sources is estimated to be 10<SUP>30</SUP> ergs. Only the soft X-ray
sources with gradual time profiles seem to show the Neupert effect.
---------------------------------------------------------
Title: Flare energetics: analysis of a large flare on YZ Canis
Minoris observed simultaneously in the ultraviolet, optical and radio.
Authors: van den Oord, G. H. J.; Doyle, J. G.; Rodono, M.; Gary,
D. E.; Henry, G. W.; Byrne, P. B.; Linsky, J. L.; Haisch, B. M.;
Pagano, I.; Leto, G.
1996A&A...310..908V Altcode:
The results of coordinated observations of the dMe star YZ CMi
at optical, UV and radio wavelengths during 3-7 February 1983 are
presented. YZ CMi showed repeated optical flaring with the largest
flare having a magnitude of 3.8 in the U-band. This flare coincided
with an IUE exposure which permits a comparison of the emission measure
curves of YZ CMi in its flaring and quiescent state. During the flare a
downward shift of the transition zone is observed while the radiative
losses in the range 10^4^-10^7^K strongly increase. The optical flare
is accompanied with a radio flare at 6cm, while at 20cm no emission
is detected. The flare is interpreted in terms of optically thick
synchrotron emission. We present a combined interpretation of the
optical/radio flare and show that the flare can be interpreted within
the context of solar two-ribbon/white-light flares. Special attention
is paid to the bombardment of dMe atmospheres by particle beams. We
show that the characteristic temperature of the heated atmosphere is
almost independent of the beam flux and lies within the range of solar
white-light flare temperatures. We also show that it is unlikely that
stellar flares emit black-body spectra. The fraction of accelerated
particles, as follows from our combined optical/radio interpretation
is in good agreement with the fraction determined by two-ribbon flare
reconnection models.
---------------------------------------------------------
Title: Estimating the total radiative power output from the hot outer
layers of late-type stellar atmospheres: how many lines are required?
Authors: Doyle, J. G.
1996A&A...307..162D Altcode:
The total radiative power output from the hot outer layers of six
late-type stars (of different spectral types and luminosity class)
is derived via an emission measure technique. This analysis was
based on observational data from the spectral range 100A to 3000A
obtained as a result of three separate satellite missions, i.e. Hubble
Space Telescope, International Ultraviolet Explorer and the Extreme
Ultraviolet Explorer. Solar observational data of active regions,
coronal holes, sunspots, `quiescent' regions and flares were also
used. Based on the derived total power output from all of these
different plasma, it is shown that a linear relationship involving
a single transition region line can be used to provide an accurate
estimate of the total power output as previously shown for the Sun. The
derived relationship does not include losses due to hydrogen, nor the
UV continuum which can be a large contributor, particularly for very
active stars.
---------------------------------------------------------
Title: EUV emission lines of O IV observed in solar spectra by the
S-055 instrument on Skylab.
Authors: O'Shea, E.; Foster, V. J.; Keenan, F. P.; Doyle, J. G.;
Reid, R. H. G.; Zhang, H. L.; Pradhan, A. K.
1996A&A...306..621O Altcode:
Recent calculations of electron and proton impact excitation rates
in O IV are used to derive the intensity ratios of lines in the
~340-1350A wavelength range as a function of electron temperature
(T_e_) and density (N_e_). These results are presented in the form of
ratio-ratio diagrams, which should in principle allow both N_e_ and T_e_
to be deduced for the O IV line emitting region of a plasma. Electron
temperatures derived from ratio-ratio diagrams involving the 790A/554A
ratio, in conjunction with observational data for several solar
features obtained with the Harvard S-055 spectrometer on board Skylab,
are found to be in reasonable agreement with the value of T_e_ expected
from ionization equilibrium calculations. This provides some support
for the theoretical diagnostics presented in this paper, and hence
the atomic data used in their derivation. However other temperature
and density sensitive ratios involving the O IV multiplets at 609A,
625A and 787A could not be used to derive plasma parameters from the
ratio-ratio diagrams, due to blending with lines of Mg X and S V.
---------------------------------------------------------
Title: Basic Stellar Parameter Determination for Active Cool
Eclipsing Binaries
Authors: Budding, E.; Butler, C. J.; Doyle, J. G.; Etzel, P. B.;
Oláh, K.; Zeilik, M.; Brown, D.
1996Ap&SS.236..215B Altcode:
We examine procedures for the determination of reliable parameter
sets characterizing stars in short period eclipsing binary systems
of later dwarf, generally sunlike, spectral types. These stars have
magnetodynamically active components and form a useful “extension
to the solar laboratory”. Their much more rapid rotation than
that of the Sun implies correspondingly enhanced indications of
activity-particularly with relatively large maculation effects in
broadband data. We concentrate on five such systems, for which we
discuss new data and analyses-CG Cyg, ER Vul, YY Gem, BH Vir and
UV Psc. Our main aim is to enable more reliable absolute comparisons
between the basic properties of such stars and the Sun. Some indications
of the ages of these binaries can also provide further pointers to
the relative importance of different parameters (e.g. rotation, age,
etc.), in determining stellar activity.
---------------------------------------------------------
Title: On IV diagnostic line ratios in solar EUV spectra.
Authors: Foster, V. J.; O'Shea, E.; Keenan, F. P.; Doyle, J. G.;
Reid, R. H. G.; Zhang, H. L.; Pradhan, A. K.
1996uxsa.conf..425F Altcode: 1996uxsa.coll..425F
Recent calculations of electron and proton impact excitation rates in
O IV are used to derive the intensity ratios of lines in the ≡340
- 1350 Å wavelength range as a function of electron temperature
(T<SUB>e</SUB>) and density (N<SUB>e</SUB>). These results are
presented in the form of ratio-ratio diagrams, which should in
principle allow both N<SUB>e</SUB> and T<SUB>e</SUB> to be deduced
for the O IV line emitting region of a plasma. Electron temperatures
derived from ratio-ratio diagrams involving the 790 Å/554 Å ratio,
in conjunction with observational data for several solar features
obtained with the Harvard S-055 spectrometer on board Skylab, are
found to be in reasonable agreement with the value of T<SUB>e</SUB>
expected from ionization equilibrium calculations. This provides
some support for the theoretical diagnostics presented in this paper,
and hence the atomic data used in their derivation.
---------------------------------------------------------
Title: Cross-correlation radial velocity measurements of
chromospherically active binaries.
Authors: Gunn, A. G.; Hall, J. C.; Lockwood, G. W.; Doyle, J. G.
1996A&A...305..146G Altcode:
We present observational radial velocity curves for 12 chromospherically
active binary systems and individual measurements for a further
5 systems. These binaries are LX Per, V 471 Tau, EI Eri, OU Gem,
GK Hya, TY Pyx, Z Her, MM Her, V772 Her, ER Vul, BD-004234, MY Cyg,
AR Lac, KZ And, RT And, SZ Psc and EZ Peg. Six of our target binaries
do not agree with published ephemerides or orbital parameters. We also
present a rigorous derivation of the resolution limit for binary star
cross-correlation radial velocities. Using synthetic spectral data we
investigate the errors induced by rotational broadening, signal-to-noise
ratio, spectral-type mismatch and luminosity ratio.
---------------------------------------------------------
Title: On the diagnostic contents of NA I lines in M dwarfs
Authors: Andretta, V.; Byrne, P. B.; Doyle, J. G.
1996ASPC..109..559A Altcode: 1996csss....9..559A
No abstract at ADS
---------------------------------------------------------
Title: Environments of active binaries
Authors: Gunn, A. G.; Doyle, J. G.
1996ASPC..109..649G Altcode: 1996csss....9..649G
No abstract at ADS
---------------------------------------------------------
Title: Observation and modelling of main sequence star
chromospheres. V. Ultraviolet excess emission in active M dwarfs.
Authors: Houdebine, E. R.; Mathioudakis, M.; Doyle, J. G.; Foing, B. H.
1996A&A...305..209H Altcode:
The variation in the continuum intensity (50-5000nm) of late-type
M dwarfs is investigated via two grids of model atmospheres with
different temperature minima. It is shown that the (E)UV intensity
is mostly dependent on the transition region pressure, although the
temperature minimum also plays an important role. We also observe
a significant frequency redistribution of the photospheric flux when
changing the minimum temperature, and a black-body type of emission from
the lower chromosphere. We examine the formation of the continuum and
point out that, although some differences appear for very low or very
high activity levels, in general the global picture is much alike the
Sun. We show that the UV continua are very good diagnostics of cool
dwarf atmospheres, from the temperature minimum to the transition
region. Our calculations give a good overview of the domains where
physical parameters and spectral signatures are most likely observed. We
compute the UBV(RIJKL)_J_ broad band fluxes for our models and conclude
that the chromospheric contribution should be detectable in the U
band and possibly also in the B band. We compare our calculations to
recent high resolution observations for selected stars in a narrow
spectral range ((R-I)_K_=0.875+/-0.05); we show that Hα line profiles
behave as expected, with a tight correlation between the line width
and equivalent width. Hα emission line stars show an excess in U-B
color but not in B-V. They are also more luminous than their less
active absorption line counterparts, which indicates that active dwarfs
have not yet reached the main sequence and are intermediate between T
Tauri stars and main sequence stars. The anomalously large proportion
of active stars towards late spectral types is attributed to the very
slow contraction phase for low mass stars. We calculate the fluxes in
the Extreme Ultraviolet Explorer Sn/SiO band (500-740A) and show that
they are compatible with observed upper limits. We further compare
our results for the upper activity range to pre-main sequence models
and observations. They strongly support the case for a chromospheric
contribution to Hα and the blue/UV excess for those objects (T
Tauris, naked T Tauris, YSOs). An important conclusion is that at
high pressures, corresponding to active dMe stellar atmospheres,
the chromosphere becomes a very efficient radiator at continuum
wavelengths. From log(M)~-5 (column mass), radiative losses in the
continuum rise exponentially and faster than in Hydrogen spectral lines
because of their larger optical depths. As a consequence, Hi spectral
lines have a small or negligible contribution to the total Hi (lines and
continua) and white light radiative budget. We show that the hydrogen
series dominate the radiative cooling in spectral lines (from 40% to
90%) for Hα emission line stars. The cooling in the (E)UV continuum
overwhelms the total radiative budget and is much larger than that
in outstanding chromospheric and transition region lines (e.g. CaII,
MgII, HI Lyman and Balmer). We propose this as a possible contribution
for the apparent saturation observed in some spectral lines, therefore
questioning the suggestion of saturation in magnetic activity levels.
---------------------------------------------------------
Title: Radio Eclipse Imaging of CF Tucanae
Authors: Gunn, A. G.; Doyle, J. G.; Migenes, V.; Spencer, R. E.
1996ASPC...93..321G Altcode: 1996ress.conf..321G
No abstract at ADS
---------------------------------------------------------
Title: Nonthermal velocities in the solar transition and coronal
region observed with the high-resolution telescope and spectrograph
Authors: O'Shea, E.; Doyle, J. G.; Dere, K. P.; Keenan, F. P.
1996ASPC..109..145O Altcode: 1996csss....9..145O
No abstract at ADS
---------------------------------------------------------
Title: The silicate-like mid-infrared spectrum of the C-rich star
R SCULPTORIS
Authors: Bagnulo, S.; Doyle, J. G.; Barlow, M. J.; Skinner, C. J.
1996ASPC..109..517B Altcode: 1996csss....9..517B
No abstract at ADS
---------------------------------------------------------
Title: Accumulative coronal, chromospheric and transition region
radiative power output from late-type stars
Authors: Doyle, J. G.
1996ASPC..109..601D Altcode: 1996csss....9..601D
No abstract at ADS
---------------------------------------------------------
Title: Surface inhomogeneities on YY Geminorum
Authors: Butler, C. J.; Doyle, J. G.; Budding, E.
1996ASPC..109..589B Altcode: 1996csss....9..589B
No abstract at ADS
---------------------------------------------------------
Title: The RS CVn binaries seen through the Eye of IRAS
Authors: Mitrou, C. K.; Doyle, J. G.; Mathioudakis, M.; Antonopoulou,
E.
1996hell.conf..301M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: EM distribution and radiative losses of II Peg and lambda And
Authors: Mitrou, C. K.; Doyle, J. G.; Mathioudakis, M.; Antonopoulou,
B.
1996ASPC..109..275M Altcode: 1996csss....9..275M
No abstract at ADS
---------------------------------------------------------
Title: SKYLAB Observations of Temperature and Density Sensitive
Emission Line Ratios in NE VI
Authors: Greer, C. J.; Foster, V. J.; Keenan, F. P.; Reid, R. H. G.;
Doyle, J. G.; Zhang, H. L.; Pradhan, A. K.
1996aeu..conf..537G Altcode: 1996IAUCo.152..537G
No abstract at ADS
---------------------------------------------------------
Title: The emission of the RS CVn binaries in the IRAS passbands.
Authors: Mitrou, C. K.; Doyle, J. G.; Mathioudakis, M.; Antonopoulou,
E.
1996A&AS..115...61M Altcode:
In the literature, there is an ambiguity pertaining to the existence
of a far-IR excess in RS CVn systems. In the current paper we undertook
a study of the behaviour of 103 such systems in the IRAS passbands. We
found 72 acceptable detections in the 12μm band, and 40 in the 25μm
band (50% more than the IRAS Point Source Catalog). Although our
findings may be interpreted as indicating towards the existence of an
excess beyond 12μm for some systems, the evidence is not conclusive
in all but two cases. These are systems GX Lib and HR 7428, with
Capella being the only system where the IRAS fluxes in all four bands
originate from the stellar photosphere. Given the accuracy of the data
we did not find 12μm excess for any system. We argue that the IRAS
data alone cannot settle the issue, as their uncertainty is, in many
cases, higher than what the Signal-to-Noise ratio of each observation
implies. Furthermore, at the higher wavelength bands the IRAS angular
resolution drops from 0.5' at 12μm to 2' at 100μm and the background
becomes very complex, so one cannot be certain about the origin of
the observed flux. The existence of IR excess in the RS CVn stars is
important as far as the evolutionary scenarios for these systems are
concerned. Future missions such as the Infrared Space Observatory will
return more sensitive and accurate measurements and the ambiguity can
be removed. The fluxes we quote will be helpful when planning these
future observations, as we provide more accurate photometry and for
a larger selection of sources than the IRAS Point Source Catalog.
---------------------------------------------------------
Title: Evolution of two small solar flares.
Authors: Fludra, A.; Doyle, J. G.; Metcalf, T.; Lemen, J. R.; Phillips,
K. J. H.; Culhane, J. L.; Kosugi, T.
1995A&A...303..914F Altcode:
Data from the YOHKOH satellite have been analysed for two small flares
(GOES class C) of total duration of 10 and 60 minutes. Upflows in S
XV, Ca XIX and Fe XXV lines were compared and the presence of a range
of upflow velocities was found. Emission from flare loop footpoints
corresponding to plasma moving with a typical velocity of 200-400km/s
is seen in soft X-ray images. In one of these events (23 June 1992),
which occurred in sheared loops being part of a sparse magnetic arcade,
with initial energy release taking place near one of the footpoints, a
large proportion of upflowing plasma was seen at least 1 minute before
the first peak in hard X-rays. In the second event (13 July 1992), the
increase of soft X-ray emission began more than 3 minutes before, and
weak mass upflows one minute before the rapid increase of temperature
and the onset of the detectable hard X-ray emission. This event was
probably triggered by emerging magnetic flux and accompanied by heating
and restructuring of two nearby magnetic loops. In both events the
emission measure of upflowing plasma is present simultaneously to,
and is very well correlated in time with the hard X-ray flux in the
14-23keV band. Differential emission measure in the temperature range
5-60x10^6^K was derived from S XV, Ca XIX and Fe XXV line and continuum
fluxes, and from images in two broad band soft X-ray filters, and
used to analyse the thermal contribution to the hard X-ray emission. A
non-thermal component of the hard X-ray emission is found at the peak
of the 23 June 1992 flare. The hard X-ray emission in the 13 July 1992
flare is primarily thermal, however, a possibility of an enhanced tail
of the electron energy distribution above 14keV is also indicated. The
chromospheric evaporation in these flares was driven both by electron
beams and thermal conduction, with conduction predominating during most
of the rise phase of the 13 July 1992 flare. In both events, the soft
X-ray emission measure at flare maximum was a few times 10^48^cm^-3^
with an electron temperature 19 and 24x10^6^K; the estimated lower
limit of the electron density is ~10^11^cm^-3^. The broadening of
Ca XIX spectral lines in the decay phase of these flares indicates
persisting random motions with a velocity of 60km/s, which is very
similar to the non-thermal broadening observed previously by SMM in
M and X class flares.
---------------------------------------------------------
Title: Optical identification of EUV sources: the secrets of EUVE
J2056-17.1.
Authors: Mathioudakis, M.; Drake, J. J.; Craig, N.; Kilkenny, D.;
Doyle, J. G.; Sirk, M. M.; Dupuis, J.; Fruscione, A.; Christian,
C. A.; Abbott, M. J.
1995A&A...302..422M Altcode:
We present optical, ultraviolet (UV), and extreme ultraviolet (EUV)
results for a new active late-type dwarf star discovered by the Extreme
Ultraviolet Explorer (EUVE). A large flare with an energy in excess of
10^35^erg and duration of ~1.1 days was detected in the EUVE Lex/B band
(60-200A). The energetics of the event indicate that radiative losses in
the EUV are a significant contributor to the energy budget in stellar
flares. The "quiescent" EUV emission of the source is similar to the
most active flare stars with the "quiescent" optical spectrum showing
strong Hα, Ca II H & K, and Mg II h & k emission. A strong
Li I 6707.8A absorption line is also present in the spectrum. We have
estimated a Li abundance of log N(Li)=2.5+/-0.4. Although the high
Li abundance suggests that EUVE J2056-17.1 is a young object having
recently arrived on the main sequence; the high flare activity favours
an interpretation where the enhanced Li is sustained by spallation
reactions.
---------------------------------------------------------
Title: Observation and modelling of main sequence star
chromospheres. IV. The chromospheric contribution to LiI lines in
active dwarfs.
Authors: Houdebine, E. R.; Doyle, J. G.
1995A&A...302..861H Altcode:
In magnetically active stars, non-thermal heating and magnetic fields
result in inhomogeneous outer atmospheres (plages) and photospheres
(dark and bright spots). So as to gauge the importance of these
phenomena on "normal photospheric lines", we investigate the influence
of the chromosphere on the Lithium I lines in M dwarfs. We choose this
element because LiI 6708A is often used as an age indicator. Solving
the NLTE-radiation transfer problem for a grid of model atmospheres
that mimic the effect of magnetic activity (from basal to saturated
chromospheres), we show that the Lithium lines are in fact activity
sensitive. This dependence commences at rather high activity levels,
i.e. when H<SUB>alpha</SUB>_ goes into emission. As in the solar case,
this chromospheric plage effect weakens the line equivalent widths
and may cancel the photospheric spot effect on disc integrated
measurements. The ionisation balance and line formation remain
photoionisation controlled throughout the known pressure range in M
star chromospheres. Changes in the line profiles and equivalent widths
are due to the non-photospheric UV continuum that further ionises
neutral lithium and depletes the line optical depths, whereas in solar
plages collisional ionisation is the driving mechanism. In K dwarfs,
both would compete to yield a similar effect. Therefore, great care
must be exercised in the use of Li 6708A in both abundance and age
calculations for active stars. We found that the 6708A to 6104A line
ratio is less sensitive to magnetic activity than the line equivalent
widths and should be a better age indicator.
---------------------------------------------------------
Title: A study of the size and composition of dust grains in the
circumsteller envelope of IRC +10 216.
Authors: Bagnulo, S.; Doyle, J. G.; Griffin, I. P.
1995A&A...301..501B Altcode:
We utilise a modelling technique in which a generalised two-stream
Eddington approximation is applied to the problem of the radiative
transfer in a spherically symmetric dust shell. We calculate
the emerging flux taking into account the effect of non-isotropic
scattering, absorption and thermal reemission for a multiple grain size,
multiple grain component distribution. We have applied our technique
to the well known carbon-rich star IRC +10 216; we have considered a
model with grains of amorphous carbon and silicon carbide, and we have
studied how different grain size distributions affect the transport
coefficients and the calculated flux. In agreement with previous works,
we reproduce quite well the general spectral characteristics, spanning
from λ=0.55μm to 2cm, assuming the dust envelope composed of small
grains (with radius ~10^-2<SUP>mu</SUP>m) of amorphous carbons. The
presence of silicon carbide cannot be excluded, but it is not required
to explain the feature at 11.4μm observed in the IRAS Low Resolution
Spectrum: a one-component model including only amorphous carbons fits
both the general characteristics and the feature at 11.4μm
---------------------------------------------------------
Title: Theoretical emission line intensity ratios for NE ^44^Sc VI
compared to EUV solar observations.
Authors: Keenan, F. P.; Foster, V. J.; Reid, R. H. G.; Doyle, J. G.;
Zhang, H. L.; Pradhan, A. K.
1995A&A...300..534K Altcode:
Recent calculations of electron and proton impact excitation rates
in Ne ^44^Sc VI are used to derive the intensity ratios of lines in
the ~402-1006A wavelength range as a function of electron temperature
(T_e_) and density (N_e_). These results are presented in the form
of ratio-ratio diagrams, which should in principle allow both N_e_
and T_e_ to be deduced for the Ne ^44^Sc VI line emitting region of a
plasma. Electron temperatures and densities derived from ratio-ratio
diagrams involving the 562.7, 997.4, 999.6 and 1006.1A lines, in
conjunction with observational data for a sunspot obtained with
the Harvard S-055 spectrometer on board Skylab, are found to be
compatible, and in good agreement with plasma parameters determined
using other methods. This provides some support for the diagnostic
calculations presented in this paper, and hence the atomic data used
in their derivation. However agreement between theory and observation
is very poor for other Ne ^44^Sc VI lines in the sunspot spectrum,
and for most transitions observed in S-055 active region and flare
data, which is probably due to blending with lines from N ^44^Sc III,
Mg ^44^Sc VI and Mg ^44^Sc VII.
---------------------------------------------------------
Title: Discovery of a white dwarf companion (EUVE J0254-053) to the
K0 IV star HD18131
Authors: Vennes, S.; Mathioudakis, M.; Doyle, J. G.; Thorstensen,
J. R.; Byrne, P. B.
1995A&A...299L..29V Altcode:
New ultraviolet (UV) observations of late-type stars detected in
the Extreme Ultraviolet Explorer (EUVE) all-sky survey revealed
an unsuspected white dwarf companion to the K0 star HD18131. The
International Ultraviolet Explorer (IUE) spectrum show a composite of a
white dwarf and a late-type star. The white dwarf dominates the emission
below 2000A while the K0 star prevails at longer wavelengths. A model
atmosphere analysis of the new ultraviolet spectrophotometry and of
the extreme ultraviolet (EUV) photometry reveals a hot, hydrogen-rich
(DA) white dwarf (Teff~30000K) that is the most likely source of the
EUV emission (EUVE J0254-053). We estimate a distance to the white
dwarf of 70-90pc. The K0 star shows a modest level of chromospheric
activity with the detection of Mg II h and k emission in the IUE
spectrum. Optical spectroscopy revealed that the K0 star is a subgiant
(K0 IV). The star is located at a distance of ~70pc, consistent with
the estimated distance of the white dwarf. Therefore, it most likely
constitutes a physical pair with the white dwarf. Until results of a
radial velocity study are made available we cannot establish whether
the pair is wide or close. In earlier works the strong EUV emission was
attributed to the K0 star; however, our multiwavelength observations
show the white dwarf as the most likely source. This discovery has
important implications for the EUV white dwarf population survey and,
in particular, for the binary frequency.
---------------------------------------------------------
Title: The O IV and S IV Intercombination Lines in Solar and Stellar
Ultraviolet Spectra
Authors: Cook, J. W.; Keenan, F. P.; Dufton, P. L.; Kingston, A. E.;
Pradhan, A. K.; Zhang, H. L.; Doyle, J. G.; Hayes, M. A.
1995ApJ...444..936C Altcode:
New calculations of O IV electron density diagnostic emission-line
ratios involving the 1399.8, 1401.2, 1404.8, and 14076.4 A transitions
are presented. A comparison of these calculations with observational
data from a quiet solar region, a sunspot, and an active region obtained
with the High Resolution Telescope and Spectrograph (HRTS), two flares
observed with the SO82B spectrograph on board Skylab, and Hubble Space
Telescope (HST) observations by the Goddard High Resolution Spectrograph
(GHRS) of Capella, gives good results using the ratio R<SUB>1</SUB> =
I(1407.4 A)/I(1401.2 A). However, the electron density obtained using
the ratio R<SUB>2</SUB> = I(1407.4 A)/I(1404.8 A) is often an order
of magnitude smaller. The O IV 1404.8 A line is blended with the S
IV 1404.8 A line, and we investigate whether this ratio may still be
used as a density diagnostic if the S IV 1406.1 A line intensity is
used to correct for the presence of S IV 1404.8 A, using previous S
IV calculations by Dufton et al. We still find systematic differences
compared to density determinations from line ratios that do not involve
the O IV 1404.8 A line, which we suggest are due to errors in earlier
theoretical calculations of the S IV atomic data, and also possibly
to previously unconsidered fluorescent pumping of the upper level of
the S IV 1404.8 A transition.
---------------------------------------------------------
Title: Book-Review - Discovering the Secrets of the Sun
Authors: Kippenhahn, R.; Doyle, J. G.
1995Obs...115...96K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Which size distribution is best for IRC +10°216?
Authors: Bagnulo, S.; Doyle, J. G.; Griffin, I. P.
1995Ap&SS.224..425B Altcode:
A generalized two-streamed Eddington aproximation is applied to the
problem of radiative transfer in a spherically symmetric dust shell. We
investigate whether our technique allows us to draw conclusions about
the size distribution of the grains.
---------------------------------------------------------
Title: Observation and modelling of main sequence star
chromospheres. III. Differential analysis of hydrogen lines versus
activity level in M dwarfs.
Authors: Houdebine, E. R.; Doyle, J. G.; Koscielecki, M.
1995A&A...294..773H Altcode:
In two previous papers we investigated in detail the formation
of hydrogen lines in high pressure dMe stellar chromospheres,
constraining the possible structures over a two orders of magnitude
pressure range. In another study, we modeled the low activity M dwarf
spectra. Here, we use these constraints at the extremes in magnetic
activity level to simulate the effect of varying magnetic non-thermal
heating in dM and dMe chromospheres by varying the transition region
pressure and temperature minimum. We built four grids of model
atmospheres with temperature minimum either at 2,660K or 3,000K, and
a range of transition region pressure. We found that when decreasing
the transition region pressure (i.e. the chromospheric temperature
gradient), the Balmer lines change rapidly from emission to strong
absorption, then the profiles weaken and become narrower until they
disappear totally (zero H<SUB>alpha</SUB>_ stars). The Paschen and
Brackett series exhibit a qualitatively similar behaviour, but the
"emission domain" is at a higher column mass: log(M)>-4.4gcm^-2^,
log(M)>-4.2gcm^-2^ and log(M)>-3.8gcm^-2^ respectively for the
Balmer, Paschen and Brackett series. The Brackett lines never really
develop a strong absorption. In opposition with other series, the
Lyman lines show a monotonous decrease and even change to absorption
for very low density models. These differences are useful spectral
diagnostics for M dwarf atmospheres. All hydrogen series, except the
Lyman series for intermediate and high pressures, are sensitive to
the temperature minimum when large changes are considered. We also
investigated the effect of the temperature break zone and found it is
important only for high pressure atmospheres. We show that the continuum
emission shortward of 4000A is highly dependent on the atmospheric
pressure and rises sharply in the Balmer emission domain. Our grids of
models successfully reproduce all types of observed H<SUB>alpha</SUB>_
profiles: (i) high activity with strong emission and weak self-reversal,
(ii) filled in intermediate activity with inner wings in emission and
the core in absorption, (iii) intermediate activity with strong and
broad absorption, (iv) low activity with weak and narrow absorption,
(v) "zero activity" with an undetectable profile. We discuss the
line characteristics over this wide range of physical conditions. We
analyse the ionisation fraction and electron density for our series
of chromospheres. Changes in the ionisation fraction are important
throughout the pressure range. Heavy elements are the main electron
donor in the photosphere for all models, and in the chromosphere for
low pressure models. Back-ionisation by the chromospheric continuum
emission and direct ionisation by the photospheric radiation field are
taking place at about the temperature minimum. Finally, we compare
the chromospheric density regimes for main sequence stars (M, K and
G dwarfs) for the quiescent and flare states.
---------------------------------------------------------
Title: Determination of the neutron lifetime using magnetically
trapped neutrons
Authors: Doyle, J.
1995dmcc.conf..519D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Energetic Flare on at Microscopium
Authors: Gunn, A. G.; Doyle, J. G.
1995IrAJ...22...31G Altcode:
In this paper we present and discuss observations of an energetic mass
flow event associated with a chromospheric flare on AT Mic. AT Mic is
a dM4.5e star at 8.8 pc. The spectroscopic observations were made in
May 1992 using the SAAO 1.9m telescope. The useful wavelength range
covered was 3750 Angstroms to 4150 Angstroms incorporating the higher
Balmer lines and Ca II H and K lines. Simple models were applied to
derive order of magnitude estimates for the mass and kinetic energy
budget of the flare for assumed electron density, ionization fraction
and temperature values. It is found that the kinetic energy of the
flare plasma is two orders of magnitude less than the radiative
energy release.
---------------------------------------------------------
Title: Models for M-Dwarf Basal Atmospheres
Authors: Houdebine, E. R.; Doyle, J. G.
1995IrAJ...22...25H Altcode:
We performed NLTE-radiation transfer calculations in an attempt to
reproduce M dwarf spectra with zero H alpha and low Ca II emission
lines. We found that zero H alpha can be produced by a range of
models and that the Ca II flux is dramatically affected by the
temperature minimum value. We show that it is possible to reproduce the
observations with low pressure transition region and low temperature
minimum models. Such models provide important constraints for modelling
acoustic heating mechanisms.
---------------------------------------------------------
Title: Quaternionic generalisation of the Mandelbrot set.
Authors: Gomatam, J.; Doyle, J.; Steves, B.
1995ASIB..336..557G Altcode: 1995fntc.conf..557G
The complex quadratic map leading to the celebrated Mandelbrot set
is generalised in a natural way to R<SUP>4</SUP> using the framework
of quaternions. Calculations are presented with the aid of Pauli spin
matrices. Stability analyses of 3-cycles are summarised, with explicit
expressions for generalised Mandelbrot domains in R<SUP>4</SUP>. It
is conjectured that similar expressions hold for stability domains
of k-cycles.
---------------------------------------------------------
Title: An orbital period study of SZ Piscium.
Authors: Kalimeris, A.; Mitrou, C. K.; Doyle, J. G.; Antonopoulou,
E.; Rovithis-Livaniou, H.
1995A&A...293..371K Altcode:
The variations of the orbital period of the RS CVn-type binary system SZ
Psc are examined through a detailed description of the O-C diagram and
the use of a new analysis technique. Continuous changes of very large
magnitude have been found. They are considered as short-timescale
variations whose character is investigated for periodicity or as
short-timescale variation of periodic or non-periodic behaviour
eventually carried by an underlying long-timescale variation. The
prospective physical mechanisms that could have modulated the orbital
period in the observed way, have been examined for both cases. A
combination of a magnetic activity cycle mechanism and an enhanced
stellar wind are found to reproduce satisfactorily the period changes.
---------------------------------------------------------
Title: On the Power Output from Late-Type Stars
Authors: Doyle, J. G.
1995IrAJ...22...29D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: UV Observations of Selected EUV Late-Type Objects
Authors: Doyle, J. G.
1995iue..prop.4997D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A multi-wavelength campaign on YY Geminorum.
Authors: Butler, C. J.; Doyle, J. G.; Budding, E.; Foing, B.
1995mscs.conf..207B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Surface inhomogeneities on SZ Piscium.
Authors: Doyle, J. G.; Mitrou, C. K.; Mathioudakis, M.; Avgoloupis,
S.; Mavridis, L. N.; Varvoglis, P. P.; Graos, F.; Antonopoulou, E.
1994A&A...291..135D Altcode:
Ultraviolet and optical data are used to look at surface inhomogeneities
on the active close binary system SZ Piscium. Lower chromospheric
emission lines such as Mg II h&k, and to a lesser extend the
upper chromospheric/lower transition region lines of O I 1305A and C
II 1335A show a pronounced decrease when the F star is eclipsing the
K sub-giant. However, higher temperature lines such as the resonance
line of C IV 1550A do not show any change in flux. This suggests the
presence of a plage with a high contrast at lower temperatures with
a Mg II plage-to-K-star ratio of 5. Alternative explanations are
explored. Monitoring of this system in the optical U-band and the
ultraviolet lines such as C IV 1550A, indicates frequent high energy
(10^35^-10^36^erg) flares.
---------------------------------------------------------
Title: Interferometer observations of RS Canum Venaticorum binaries.
Authors: Gunn, A. G.; Spencer, R. E.; Abdul Aziz, H.; Doyle, J. G.;
Davis, R. J.; Pavelin, P. E.
1994A&A...291..847G Altcode:
We present radio flux measurements at 5 GHz for a sample of RS CVn-type
chromospherically active binary systems made from 1988 to 1992 using the
NRAL broad-band interferometer (BBI). The derived radio luminosities
are consistent with previous observations but show that radio flaring
is a common feature which will affect the results of rotation-activity
studies. The mean brightness temperature for our sample, assuming
a radio source size equal to twice the radius of the active stellar
component, is consistent with a gyrosynchrotron emission process from
mildly relativistic electrons.
---------------------------------------------------------
Title: Observation and modelling of main sequence star chromospheres
I. Modelling of the hydrogen spectrum in dMe stars.
Authors: Houdebine, E. R.; Doyle, J. G.
1994A&A...289..169H Altcode:
In this new series we present observations and modelling of spectral
lines formed in main sequence star chromospheres (from G0 to M8). In
this paper, we discuss the Hydrogen line formations in very active
dMe stellar chromospheres. We present the conclusions drawn from
our modelling approach to the AU Mic (dM2e) spectrum. Our final
model atmosphere is described in detail in the next paper in this
series. Here, we investigate the effects of some stellar (T_eff_, vsin
i) and atmospheric (turbulence, temperature structure) parameters on
the line formation. We found that observations are best reproduced by
a chromospheric structure including a constant temperature gradient
(in a log(M) scale) in the chromosphere and transition region. We
show that a very thin transition region is required to account for
the observed Ly<SUB>alpha</SUB>_ to H<SUB>alpha</SUB>_ surface flux
ratio. Then, to drive the Balmer lines into emission and reproduce
the H<SUB>alpha</SUB>_ and H<SUB>beta</SUB>_ self-reversal and FWHM,
the chromospheric gradient and transition region pressure must be
quite high for the most active stars. We put forward a complete set
of important constraints on the possible structures of such active
region atmospheres from 5,000 K to 50,000 K. Notably we show that:
(i) the chromosphere/transition region temperature break zone must
be located at about 8,200 +/-~200 K, implying that there is rather
little plasma above this temperature, (ii) the temperature break zone
is central to the formation of Lyman and Balmer lines, it should be
smooth and contained in a small column mass domain, (iii) the transition
region must be very thin and at a high column mass, log(M)~-3, (iv)
the temperature break demarcates the temperature domains of formation
of Lyman and other Hydrogen series, (v) backwarming due to the Lyman
and Balmer radiation fields occurs at the top of the chromosphere,
(vi) turbulence and rotational broadening have little effect on the
line profiles and fluxes, (vii) rotational broadening should not
however be neglected because H<SUB>alpha</SUB>_ self-reversal is a
major constraint to the modelling, (viii) the profiles are weakly
dependant on the stellar effective temperature whose uncertainties
can be neglected in first approximation. Finally, we further compare
our results to observations and propose some general properties that
could be tested with future observations.
---------------------------------------------------------
Title: Modelling of the atmospheric environment on and around cool
M giants and dwarfs
Authors: Doyle, J. G.; Griffin, I. P.
1994IrAJ...21..255D Altcode:
A numerical method involving radiative transfer techniques has been
developed to model the gas/dust environment around cool red giants. The
method provides a large amount of information as to the physical
conditions within the model dust shell, such as the temperature gradient
and intensity distributions throughout the shell, as well as predicting
the emergent fluxes. Although the method has so far been applied only
to a few examples of carbon-rich and oxygen-rich stars, it is apparent
from the results that they are an improvement upon previous work. We
suggest here where further enhancements in the technique are possible.
---------------------------------------------------------
Title: Observation and modelling of main sequence star chromospheres
II. Modelling of the AU MIC (dM2.5e) hydrogen spectrum.
Authors: Houdebine, E. R.; Doyle, J. G.
1994A&A...289..185H Altcode:
We present the first successful attempt in modelling simultaneously
the H<SUB>alpha</SUB>_ and H<SUB>beta</SUB>_ high resolution profiles
and the H<SUB>alpha</SUB>_ to Ly<SUB>alpha</SUB>_ flux ratio for a
dMe star (AU Mic, dM2.5e). We show that a very high transition region
pressure and a thin transition region are simultaneously required
to reproduce our observations. We give evidence that lower pressure
model chromospheres can also reproduce the Balmer line profiles,
but give Lyman surface fluxes overestimated by more than an order
of magnitude. Our model also reproduces the Balmer decrements,
the Ly<SUB>alpha</SUB>_ full width half maximum (upper limit) and
the Balmer jump which is weak. Discrepancies in the profiles between
observations and our model point to possible systematic upward flows in
active stellar chromospheres. We obtain the Paschen lines in emission
and Paschen decrements as large as 41 for Pa<SUB>beta</SUB>_. For our
model, we obtain a transition region column mass of 1.2610^-3^g/cm^2^
(log(M)=~-2.9) which should be a lower limit (with the present modelling
approximations). This large pressure chromosphere yields too large
equivalent widths by a factor of 3.3. We believe that this points
to the inhomogeneous character of the star's chromosphere. In this
context, the plage filling factor is about 30%. This disagrees with
the concept of homogeneous atmospheres back-heated by large coronal
X-ray radiation and suggests that additional non-thermal heating is
taking place in active regions. The electron density at the top of the
chromosphere is in the 10^12^-5 10^12^ cm^-3^ range, in agreement with
previous estimates based on the Balmer decrements. The pressure is 6.3
Pa, of the same order as the current estimates for coronal pressures
(~10 Pa). Discordant results for the HI Lyman and the HeI lines for
our model atmosphere imply conflicting filling factors for these lines
which indicates that, like the Sun, stellar transition regions are
quite inhomogeneous. Formation of all Hydrogen series is collisionally
controlled and takes place in a rather thin layer at the top of the
chromosphere (Balmer, Paschen, and Brackett) or in the transition region
(Lyman). The temperature break acts as a disjunction in the domains
of formation of the Lyman and other series. High electron density
and collisional control is a necessary condition to drive the Balmer
lines into emission in M dwarf atmospheres. Because of particularly
low electron temperature and density in the middle chromosphere down
to the photosphere, the Balmer, Paschen and Brackett source functions
are photoionisation controlled in this region. We compare our model to
other dMe, dKe and solar model chromospheres. It shares common physical
properties with solar flare models, thus implying a large and continuous
chromospheric heating rate. The temperature break at 8200 K is very
close to values obtained for the quiet Sun, plages, flares and other
stellar models. This emphasizes that this temperature is constrained by
the plasma ability to radiate in the Hydrogen lines, over a wide range
of the plasma and stellar parameters. The total radiative cooling in the
Hydrogen lines and continua is about 1.22x10^8^erg/m^2^/s, of which 66%
arise from the Balmer series and continuum. The radiative cooling is
dominated by the Lyman series and the Balmer series respectively in
the transition region and the chromosphere. Cooling is dominated by
the Paschen lines in the lower chromosphere. The short penetration
of the Lyman radiation field produces a net backwarming in the upper
chromosphere, while other series penetrate deeper and backwarm the
lower chromosphere and the temperature minimum.
---------------------------------------------------------
Title: BD +22 4409 : a rapidly rotating, low-mass member of the
Local Association.
Authors: Jeffries, R. D.; Byrne, P. B.; Doyle, J. G.; Anders, G. J.;
James, D. J.; Lanzafame, A. C.
1994MNRAS.270..153J Altcode:
We present spectroscopic and photometric observations of BD +2204409,
a nearby, low-mass star which, on the basis of its Galactic space
motions and high EUV-tobolometric luminosity ratio, has been previously
assigned membership of the young kinematic group known as the Local
Association. Our observations show that BD +2204409 is a single,
K5V-K7V, chromospherically active ultrafast rotator, with a probable
period of 10.1710.10 h and a projected equatorial velocity of 691 1 km 1
It has a comparatively high photo spheric lithium abundance of N(Li) =
1.3010.25, and this, combined with our photometry and a trigonometric
parallax, leads to the conclusion that the star is young, although
probably no younger than 20-30 Myr, and is a prime Local Association
candidate in all respects. Considerable variability is seen in the
rotationally broadened H a emission line, and can be interpreted
in terms of transient flare activity at very high latitudes or the
combination of a rotationally modulated, high-latitude active region
and a rather smaller flare at an unconstrained latitude. In either
case, the flare radiative losses in the H a line are at least 2 x 1032
erg. There is no evidence for the corotating cool prominences that
have been seen at some distance from the surfaces of other late-type
rapid rotators. This may be interpreted as a geometric effect,
whereby the low inclination deduced for BD +2204409, of 5001 100,
combined with a centrifugal flattening of any cloud system towards
the equatorial plane, renders clouds unobservable as Ha absorption
transients. Spot modelling of the photometric light curves yields
an asymmetric spot component, covering at least 4 per cent of the
total stellar surface. Variability of 1013 per cent is seen in the
strength of the Lii 6708-A line over 7 h of a rotation period, in the
sense that the peak Li I equivalent width correlates with the time of
maximum spot coverage deduced from the shapes of photospheric line
profiles. This result is consistent with calculations of the effect
of starspots on the Li I equivalent width, once projection effects
and limb-darkening are taken into account. Enhanced molecular bands
may also play a role, but very cool atmospheric models are required to
investigate this question fully. Key words: stars: abundances - stars:
activity - stars: individual: BD +2204409 - stars: late-type - stars:
rotation - open clusters and associations: general.
---------------------------------------------------------
Title: Multiwavelength Observations of a Solar Flare
Authors: White, S. M.; Silva, A.; de Pater, I.; Lin, R. P.; Gary,
D. E.; Hudson, H. S.; Doyle, J. G.; Hagyard, M. J.; Kundu, M. R.
1994kofu.symp..203W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Lower chromospheric activity in low activity M dwarfs
Authors: Doyle, J. G.; Houdebine, E. R.; Mathioudakis, M.; Panagi,
P. M.
1994A&A...285..233D Altcode:
Four low activity dM(e) stars Gl 105B, Gl 643, Gl 813 and Gl 821
were observed spectroscopically in the optical and ultraviolet
regions. Despite relatively long integrations, only one of the four
had detectable Ca II K&H emission, Gl 821, which had an observed
flux of 9 10^-15^ erg/cm2/s, giving a surface flux of only 0.8 10^4^
erg/cm2/s. Similarly, the IUE observations implied very weak Mg II
emission. In one of these stars, Gl 813, the Mg II h&k surface
flux was less than 0.4 10^4^ erg/cm2/s, which is a factor of two
less than the previous known weakest dM(e) star, Gl 105B. Using
radiative transfer techniques the Ca II H&K fluxes have been
derived for a range of model atmospheres. The zero Hα flux can be
produced by a range of models, this line is therefore a rather poor
constraint for the lower atmosphere. On the other hand, the Ca II K
flux can be dramatically effected by simply varying the temperature
minimum. Comparing our calculations to the observational data, we find
that the Ca II H&K surface fluxes cannot be reproduced with T_min_
3000K. However, decreasing the temperature minimum by less than 400K
produces Ca II H&K fluxes of the order of 10^3^ erg/cm2/s, in very
good agreement with the weakest dM(e) stars.
---------------------------------------------------------
Title: High-velocity evaporation during a flare on AT Microscopii
Authors: Gunn, A. G.; Doyle, J. G.; Mathioudakis, M.; Houdebine,
E. R.; Avgoloupis, S.
1994A&A...285..489G Altcode:
We present and discuss observations of a flare event on the dM4.5e star
AT Mic (Gl 799AB). These data show evidence of an energetic flare with
a radiated energy of 3 10^31^erg in the range 3600-4200A. The Balmer
emission lines display a prominent blue asymmetry which has been used
to constrain the velocity of the associated bulk plasma motion. Simple
models were applied to derive order of magnitude estimates for the mass
and kinetic energy budget of the flare for assumed electron density,
ionization fraction and temperature values. It is found that the
kinetic energy of the flare plasma is two orders of magnitude less
than the radiative energy release. The chromospheric Ca II H &
K lines are also observed to have a blue-shifted component which has
not been observed prior to these results. We suggest that this is
evidence of a very energetic particle beam penetrating to the cooler
atmospheric layers where Ca II H & K is formed.
---------------------------------------------------------
Title: An optical flare on YZ Canis Minoris
Authors: Gunn, A. G.; Doyle, J. G.; Mathioudakis, M.; Avgoloupis, S.
1994A&A...285..157G Altcode:
We present and discuss observations of an energetic optical flare on
the dM4.5e star YZ CMi (Gl 285). The flux-time variations and energy
release of the flare are fully consistent with previous observations
of this star. The observations have also revealed a symmetric excess
emission in the bases of the chromospheric Balmer lines. If due to a
bulk plasma motion event, the maximum extension in the Balmer wings
represents a Doppler velocity of ~ 250 km/s.
---------------------------------------------------------
Title: Theoretical Emission Line Strengths for OV Compared to Extreme
Ultraviolet Solar Observations
Authors: Keenan, F. P.; Warren, G. A.; Doyle, J. G.; Berrington,
K. A.; Kingston, A. E.
1994SoPh..150...61K Altcode:
Recent R-matrix calculations of electron impact excitation
rates in OV are used to derive the emission line intensity
ratios (in energy units) R<SUB>1</SUB> = I(2s2p<SUP>3</SUP>P -
2p<SUP>2</SUP><SUP>3</SUP>P)/I(2s<SUP>2</SUP><SUP>1</SUP>S<SUB>0</SUB>
- 2s2p<SUP>1</SUP>P<SUB>1</SUB> = I(761.1 A)/I(629.7 A),
R<SUB>2</SUB> = I(2s<SUP>2</SUP><SUP>1</SUP>S<SUB>0</SUB> -
2s2p<SUP>3</SUP>P<SUB>1</SUB>/I(2s<SUP>2</SUP><SUP>1</SUP>S<SUB>0</SUB>
- 2s2p<SUP>1</SUP>P<SUB>1</SUB> = I(1218.4 A)/I(629.7
A), and R<SUB>3</SUB> = I(2s2p<SUP>1</SUP>)P<SUB>1</SUB> -
2p<SUP>2</SUP><SUP>1</SUP>S<SUB>0</SUB>/I(2s<SUP>2</SUP><SUP>1</SUP>S<SUB>0</SUB>
- 2s2p<SUP>1</SUP>P<SUB>1</SUB>) = I(774.5 A)/I(629.7 A) as
a function of electron temperature (T<SUB>e</SUB>) and density
(N<SUB>e</SUB>). These results are presented as plots of R<SUB>1</SUB>
vsR<SUB>2</SUB>, andR<SUB>1</SUB> vsR<SUB>3</SUB>, which should
allowboth N<SUB>e</SUB> andT<SUB>e</SUB> to be deduced for the OV
line emitting region of a plasma. Electron densities derived from the
(R<SUB>1</SUB>,R<SUB>2</SUB>) and (R<SUB>1</SUB>,R<SUB>3</SUB>) diagrams
in conjunction with observational data for several solar features
obtained with the Harvard S-055 spectrometer on boardSkylab are found
to be compatible, and in good agreement with values ofN<SUB>e</SUB>
estimated from line ratios in species formed at similar electron
temperatures to OV. In addition, values ofT<SUB>e</SUB> determined
from (R<SUB>1</SUB>,R<SUB>2</SUB>) and (R<SUB>1</SUB>,R<SUB>3</SUB>)
are generally close to that expected theoretically. These results
provide experimental support for the accuracy of the diagnostic
calculations presented in this paper, and hence the atomic data used
in their derivation.
---------------------------------------------------------
Title: Ultraviolet flare activity on the eclipsing binary SZ Piscium.
Authors: Doyle, J. G.; Mitrou, C. K.; Mathioudakis, M.; Antonopoulou,
E.
1994A&A...283..522D Altcode:
The estimated total chromospheric, transition region and coronal
losses for a flare observed on the eclipsing binary SZ Psc with the
International Ultraviolet Explorer (IUE) satellite on 6 July 1990 is
of the order of 4.5 10<SUP>36</SUP> ergs. This estimate is similar to
that derived by Doyle et al. (1989) for an ultraviolet flare on another
RS CVn star, II Peg, and is a substantial fraction of the total amount
that is possible to store on these stars without having to evoke the
presence of kiloGauss fields.
---------------------------------------------------------
Title: NLTE-Radiation Transfer Modelling of Li I Lines in dM
Atmospheres
Authors: Houdebine, E. R.; Doyle, J. G.
1994ASPC...64..285H Altcode: 1994csss....8..285H
No abstract at ADS
---------------------------------------------------------
Title: Effect of the Star Effective Temperature on the Hydrogen and
Calcium Spectra in M-G Dwarfs
Authors: Houdebine, E. R.; Doyle, J. G.
1994ASPC...64..423H Altcode: 1994csss....8..423H
No abstract at ADS
---------------------------------------------------------
Title: Circumstellar Material in the RS CVn System SZ Psc
Authors: Doyle, J. G.
1994iue..prop.4926D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Dynamics of a Low Energetic Solar Flare
Authors: Doyle, J. G.; Fludra, A.; Bentley, R. D.; Culhane, J. L.;
Metcalf, T.; Lemen, J. R.; Kosugi, T.
1994ASPC...64..402D Altcode: 1994csss....8..402D
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet Spectroscopy of the DA + dM Binary Feige 24 Near
Inferior Conjunction:
Authors: Doyle, J. G.
1994iue..prop.4927D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Eclipse Observations of Active Binary Systems
Authors: Gunn, A. G.; Doyle, J. G.; Houdebine, E. R.
1994ASPC...64..702G Altcode: 1994csss....8..702G
No abstract at ADS
---------------------------------------------------------
Title: Coordinated HST-EUVE-IUE Observations of YZ Cmi
Authors: Doyle, J. G.
1994iue..prop.4871D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Models for M Dwarf Basal Atmospheres
Authors: Houdebine, E. R.; Doyle, J. G.
1994ASPC...64..420H Altcode: 1994csss....8..420H
No abstract at ADS
---------------------------------------------------------
Title: Low Activity M Dwarfs
Authors: Doyle, J. G.; Houdebine, E. R.; Mathioudakis, M.
1994ASPC...64..557D Altcode: 1994csss....8..557D
No abstract at ADS
---------------------------------------------------------
Title: Far infrared properties of late type dwarfs. Infrared fluxes
of K and M dwarfs.
Authors: Mathioudakis, M.; Doyle, J. G.
1993A&A...280..181M Altcode:
IRAS fluxes/upper limits are presented for a large sample of K
and M dwarfs. Good agreement is found between the 12 micrometer
fluxes and those derived from the photospheric models of Mould
(1976). Relationships between the optical and infrared colors are
derived. The active dMe/dKe stars appear systematically brighter
in the infrared compared with the less active dM/dK stars, which
could be attributed to more efficient nonradiative heating in their
atmosphere. Any systematic differences found in our results when
compared with those obtained from previous studies are attributed to
the different analysis packages used.
---------------------------------------------------------
Title: Rotational modulation and flares on the RS Canum Venaticorum
binary II Pagasi in July/September 1990 : spots and flares on II Peg.
Authors: Doyle, J. G.; Mathioudakis, M.; Murphy, H. M.; Avgoloupis,
S.; Mavridis, L. N.; Seiradakis, J. H.
1993A&A...278..499D Altcode:
During ultraviolet spectroscopic observations of the RS CVn star II
Peg in September 1990 a long duration (greater than or = 3 hrs.) flare
was observed. During the early stage of the event, a feature at 1354
A was present, however, within the spectral resolution of the data
it is not possible to identify this line. A contribution from the
hot coronal ion Fe XXI is suspected. From line diagnostic ratios, the
electron pressure at flare peak was estimated to be 10<SUP>17</SUP>/cu
cm K, decreasing to 10<SUP>16</SUP>/cu cm K towards the end of the
flare. One other flare was observed with IUE, and three optical flares
(unfortunately none of these were observed simultaneously). The
chromospheric and transition region losses from the larger of
the two IUE flares was approx. 3 x 10<SUP>31</SUP> erg/s at flare
maximum, with total chromospheric/transition region radiative losses
over the duration of the event being approx. 1.5 x 10<SUP>35</SUP>
erg. Continuum radiative losses over the wavelength region 1150A to
1950A were approximately 3% of the above figure. At flare maximum,
the N V 1240 A line showed an enhancement factor of approx. 3 over the
preflare value compared to 9 for the C IV 1550 A line. We interpret this
difference as due to an underabundance of nitrogen during the flare,
possibly related to photoionization of lower chromospheric material
by soft X-ray photons sometime prior to the flare. No evidence of
rotational modulation was present in any of the transition region lines,
although the chromospheric lines did show a phase variation. However,
these lines (H-alpha, Ca II K and Mg II h&k) were not consistent
with one another although it is clear that the H-alpha equivalent
width showed variations faster than the star's rotation period, being
perhaps related to the decay/activation of individual active regions.
---------------------------------------------------------
Title: Dynamics of flares on late-type dMe stars. III. Kinetic energy
and mass momentum budget of a flare on AD Leonis.
Authors: Houdebine, E. R.; Foing, B. H.; Doyle, J. G.; Rodono, M.
1993A&A...278..109H Altcode:
In two previous publications (Paper I and II in this series), we
described the spectral line Doppler shifts and asymmetries observed
during a large flare on AD Leo, and interpreted those in terms of
mass motions. Here, in order to further constrain the plasma physical
properties and estimate the amount of energy released under mass
motions, we developed simple methods so as to infer lower limits to the
plasma cross-section, volume, column density, mass, average emissivity
and optical depth. This allows us to derive the first kinetic energy
and momentum budget of a stellar flare spectral signatures at visible
wavelengths. The investigation of the line flux variation along the
Balmer series indicates that up to 40% or more of the CaII H emission is
likely to arise from radiative pumping by the Balmer H-epsilon line. For
the preflare motion of the solar like 'dark filament', we estimate that
its minimum mass, kinetic energy and radius are respectively about 6.4
10<SUP>13</SUP> kg, 2.7 10<SUP>32</SUP> erg and 5 10<SUP>7</SUP> m. The
impulsive phase downward motion which attains deep photospheric layers
in 'kernels' is believed to carry a mass of only 1.3 10<SUP>13</SUP> kg
and energy 2.4 10<SUP>32</SUP> erg. The area/extent values we inferred
from the Balmer and the CaII lines using escape probability methods
agree well with NLTE-radiation transfer modelling. We obtain a minimum
kernel area of approximately 6 10<SUP>13</SUP> sq m and an estimated
area of approximately 10<SUP>14</SUP> sq m. A flaring prominence whose
spectral signature is oscillatory Doppler shifts has an estimated mass
and radius of respectively 1.2 10<SUP>13</SUP> kg and 2 10<SUP>7</SUP>
m. The minimum kinetic energy associated with its motion is about 2.9
10<SUP>31</SUP> erg. We find that the kinetic energy associated with
the detected mass motions strongly depends on the localization of the
flare on the stellar disc. Ignoring or taking into account this possible
projection factor for the velocities gives a total kinetic energy of
respectively approximately 3 10<SUP>30</SUP> erg and approximately
6 10<SUP>32</SUP> erg (without the impulsive phase CME). The latter
figure is about a factor of 3 times more than the energy radiated in the
U-band and 2.3 times less than the 'missing energy' in the K band. This
points to an interesting aspect of stellar flare energetics, that is,
for this flare the kinetic energy may be a significant fraction of the
total energy budget. Along the same lines, our results also indicate
that possibly only a small fraction of the kinetic energy is carried by
cool plasmas and that most mass motions may occur in coronal plasmas at
a higher temperature regime. This important aspect of flare energetics
should be assessed by simultaneous observations in optical and UV/EUV
spectroscopy with a higher time resolution.
---------------------------------------------------------
Title: Effect of interstellar absorption on the MG II H &
K profiles and fluxes of RS CVn stars
Authors: Houdebine, E. R.; Doyle, J. G.; Butler, C. J.
1993IrAJ...21..102H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Tuned Solar and Stellar Oscillations?
Authors: Andrews, A. D.; Doyle, J. G.
1993IrAJ...21...83A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Productivity of Armagh Observatory Compared to a Range of
Institutions in the USA
Authors: Doyle, J. G.
1993IrAJ...21..153D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Dynamics of flares on late type dMe stars. II. Mass motions
and prominence oscillations during a flare on AD Leonis.
Authors: Houdebine, E. R.; Foing, B. H.; Doyle, J. G.; Rodono, M.
1993A&A...274..245H Altcode:
On 28 March 1984 at 3:22 UT, a 2.1 magnitude flare in the U-band was
observed simultaneously in several wavelength regions, including low
resolution spectrophotometry in the wavelength range 3600-4400Å. This
flare displayed enhanced emission in chromospheric lines for a duration
of about 50 min. By studying in detail the emission line centroid
displacements and asymmetries, we discovered several new exciting
phenomena. In this paper we present evidence for complex velocity
fields. A deeper investigation of the plasma physical parameters and
the kinetic energy associated with these mass motions is discussed
by Houdebine et al. (1993). <P />Prior to the flare onset, weak
P-Cygni profiles were observed in the Call resonance lines which
we interpret as evidence for the preflare motion of a solar like
"dark filament". The loop radius is estimated to be of the order of
5 1O<SUP>7</SUP> m. During the impulsive phase, a high velocity mass
ejection was observed (Houdebine et al. 1990, Paper I) with red-shifts
in the Balmer line cores, the CaII K and HeI 4026Å. This latter event
is interpreted as the downward motion of chromospheric condensations
initiated by highly energetic particle beams (in the MeV range)
and a subsequent chromospheric evaporation. The inferred minimum
energy flux deposited by the beam in the transition region is about
9 10<SUP>10</SUP> which corresponds to the energy of a large flare
on the Sun. Later during the flare, a 2.68 min periodic oscillation
occurred in the line centroids with a peak to peak amplitude up to ∼
95 km s<SUP>-1</SUP>. We show that it is most likely the signature
of periodic motions in a prominence that may have been initiated by
flare-born disturbances. This prominence (whose minimum radius and apex
magnetic field strength are 2 1O<SUP>7</SUP>m and 20G respectively)
expanded slowly during the gradual phase, and finally disrupted,
ejecting part of its mass higher in the corona. The loop disruption
signatures are well defined reversed P-Cygni profiles that are sustained
for several minutes. During the post-flare stage, we found clues for
clouds of plasma spread across the stellar disc with a minimum filling
factor of 17%.
---------------------------------------------------------
Title: Rotational modulation and flares on RS Canum Venaticorum and
BY Draconis stars. XVII. UV spectroscopy and optical photometry of
AU Microscopii in 1986.
Authors: Quin, D. A.; Doyle, J. G.; Butler, C. J.; Byrne, P. B.;
Swank, J. H.
1993A&A...272..477Q Altcode:
We present IUE spectroscopy and optical photometry of the active
late type star AU Mic. The UV spectroscopy allow us to measure
the chromospheric and transition region line fluxes. No detectable
variations attributable to rotational modulation were evident in
either the chromospheric lines or optical bands. We have produced
an emission measure curve for the quiescent state of AU Mic, which
spans a temperature range 4.0 ≤ log T<SUB>e</SUB> ≤ 7.6 when
coupled with previous X-ray flux measurements. The quiescent radiative
losses per unit surface area over the above temperature range is ≍8
1O<SUP>7</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>
---------------------------------------------------------
Title: Chromospheric Heating in K &M Dwarfs
Authors: Doyle, J. G.; Mathioudakis, M.
1993ASSL..183..471D Altcode: 1993pssc.symp..471D
No abstract at ADS
---------------------------------------------------------
Title: Emission up to 18 ke V in the Quiescent X-ray Spectrum of
II Peg
Authors: Doyle, J. G.; van den Oord, G. H. J.; Kellett, B. J.
1993ASSL..183..311D Altcode: 1993pssc.symp..311D
No abstract at ADS
---------------------------------------------------------
Title: The Nature of M Dwarfs with a Zero H Alpha Flux
Authors: Doyle, J. G.
1993iue..prop.4657D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar O IV and S IV lines from the High Resolution Telescope
and Spectrograph (HRTS) and the S082B spectrograph on board Skylab.
Authors: Keenan, F. P.; Cook, J. W.; Doyle, J. G.; Dufton, P. L.;
Hayes, M. A.; Kingston, A. E.
1993uxrs.conf..345K Altcode: 1993uxsa.conf..345K
A comparison of theoretical O IV electron density diagnostics with
observational data from a quiet solar region, a sunspot and an active
region obtained with the High Resolution Telescope and Spectrograph
(HRTS), and a flare observed with the S082B instrument on board Skylab,
reveals that the O IV 1404.8 Å line is not only blended with the S IV
1404.8 Å transition, but also with an unknown feature that contributes
a significant amount to the blend. It is therefore suggested that
line ratios which include the O IV 1404.8 Å transition should not be
employed as density diagnostics.
---------------------------------------------------------
Title: Mass Loss from Cool Dwarfs: Limits on Detectability
Authors: Doyle, J. G.; Mullan, D. J.
1993ASSL..183..401D Altcode: 1993pssc.symp..401D
No abstract at ADS
---------------------------------------------------------
Title: Dynamic phenomena on the RS Canum Venaticorum binary II Pegasi
in August 1989. I. Observational data.
Authors: Doyle, J. G.; Kellett, B. J.; Butler, C. J.; Byrne, P. B.;
Neff, J. E.; Brown, A.; Fox, D.; Linsky, J. L.; Bromage, G. E.;
Avgoloupis, S.; Mavridis, L. N.; Seiradakis, J. H.; Mathioudakis,
M.; Murphy, H. M.; Krzesinski, J.; Pajdosz, G.; Dadonas, V.;
Sperauskas, J.; van Wyk, F.; Marang, F.; Olah, K.; Collier Cameron,
A.; Antonomoulos, E.; Rovithis, P.; Rovithis-Livaniou, H.
1992A&AS...96..351D Altcode:
Observational results are given for two flares in Pi Pegasi that were
detected by the GINGA and IUE satellites, as well as by ground-based
Johnson U-band photometry and optical spectroscopy. The best-fitting
results were obtained for a combination of a single-temperature
plasma together with a power law; for a two-temperature model, the
temperature of the second component was very high due to the tail in
the photon distribution.
---------------------------------------------------------
Title: A recalculation of the line emissivities for the strongest
UV and extreme-UV lines in the 400-2800 A wavelength range
Authors: Doyle, J. G.; Keenan, F. P.
1992A&A...264..173D Altcode:
Using the most recent atomic data we re-calculate line emissivities
for the strongest transitions in the 400-2800 A region. These line
emissivities may be used to construct emission measure curves for
either observed ultraviolet/extreme ultraviolet solar features or
ultraviolet observations of stellar sources. The new tables contain
several lines not in the original Raymond and Doyle tables.
---------------------------------------------------------
Title: Limits on Detectability of Mass Loss from Cool Dwarfs
Authors: Mullan, D. J.; Doyle, J. G.; Redman, R. O.; Mathioudakis, M.
1992ApJ...397..225M Altcode:
Recent spectroscopic evidence supports the theoretical expectation
that certain cool dwarfs may have stellar winds with M-dot values
several orders of magnitude larger than the solar rate. For large
enough values of M-dot, the emission from the wind is expected to have
a spectrum which, at low enough frequencies, becomes a power law,
S(v) about v exp alpha with alpha about 0.7. Data from IRAS and VLA
suggest that such a spectrum may in fact occur in certain M dwarfs:
a key test of the wind spectrum would be provided if the stars could
be detected at lambda about 1 mm. We show that the M-dot required to
ensure power-law emission is a few times 10 exp -10 solar mass/yr. With
M-dot of this order, fluxes at lambda about 1 mm would be tens of
mJy. Using the James Clerk Maxwell Telescope, we have tested this
prediction on several stars: the data are suggestive but are near the
limits of detection. Confirmation of our estimates will be important
for evolution and for interstellar medium (ISM) physics: if even a
few percent of all M dwarfs are losing mass at the above rates, the
mass balance of the ISM will be dominated by M dwarfs.
---------------------------------------------------------
Title: Chromspheric diagnostics in M dwarfs
Authors: Mathioudakis, M.; Doyle, J. G.
1992IrAJ...20..272M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric heating in late-type dwarfs : acoustic or
magnetic ?
Authors: Mathioudakis, M.; Doyle, J. G.
1992A&A...262..523M Altcode:
Mg II h and k fluxes for 69 K and 88 M dwarfs have been analyzed. An
empirical lower limit is found in the Mg II flux, extended down to
the latest spectral types. Based on the data presented here it is the
magnetic component that dominates the emission from the atmosphere of
cool dwarfs, especially the M dwarfs. It, however, coexists with an
acoustically heated component, which can only be identified in the
stars with the lowest fluxes in the flux-color diagram, these stars
possibly being the slowest rotators. Data for the dM(e) stars, i.e.,
those stars with zero H-alpha, show that these are divided into two
classes: (1) an inactive M dwarf star with very weak chromospheric
heating, perhaps only by acoustic waves; and (2) an intermediate
chromospheric activity star dominated by magnetic heating.
---------------------------------------------------------
Title: Dynamic phenomena on the RS Canum Venaticorum binary II Pegasi
in August 1989. II. an interpretation.
Authors: Doyle, J. G.; van den Oord, G. H. J.; Kellett, B. J.
1992A&A...262..533D Altcode:
An analysis of the quiescent X-ray and radio observations and of the
X-ray observations of a major flare of II Pegasi is presented. For both
the flare and the quiescent emission, photometric, and spectroscopic
optical data are also discussed. The quiescent X-ray emission shows
a power-law tail up to 18 keV. It is shown that an interpretation
in terms of free-free emission by nonthernal particles requires
unrealistically large values for the number of particles involved
and for the energy input required to maintain the population. Basic
flare parameters like volume, loop length, and typical magnetic field
strength are derived. The observed flare decay on II Peg is compared
with the observed flare decay on Sigma CrB and Algol. It is shown
that the behavior of the temperature and emission measure during the
II Peg flare differs significantly from the observed behavior during
the Algol/sigma CrB flares.
---------------------------------------------------------
Title: AI II as an electron density diagnostic for the upper
chromosphere/lower transition region in late-type stars.
Authors: Doyle, J. G.; Keenan, F. P.; Harra, L. K.; Aggarwal, K. M.;
Tayal, S. S.
1992A&A...261..285D Altcode:
The ratio of the Al II resonance line 3s2 1S-3sp 1P1 at 1670 A to the
inter-system line 3s2 1S-3s3p 3P1 at 2669 A is a useful electron density
diagnostic for N(e) greater than 10 exp 10/cu cm. However, it is also
sensitive to the adopted electron temperature, and, in fact, should
be a useful electron temperature diagnostic when Ne is not greater
than 10 exp 9/cu cm. In particular, we present observational data for
the RS CVn star II Peg and show that this ratio implies an electron
pressure substantially less than that implied from other diagnostic
line ratios but in good agreement with the pressure derived from the
C III 1176/C III 1908 ratio. We suggest additional observational and
theoretical work that may be required.
---------------------------------------------------------
Title: Book Review: The sun and cool stars: activity, magnetism,
dynamos / Springer-Verlag, 1991
Authors: Doyle, J. G.
1992Obs...112..133D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Limits on detectability of mass loss from cool dwarfs
Authors: Mullan, D. J.; Doyle, J. G.; Mathioudakis, M.; Redman, R. O.
1992AAS...180.6006M Altcode: 1992BAAS...24..826M
Recent spectroscopic evidence supports the theoretical expectation
that certain cool dwarfs may have stellar winds with dot {M} values
several orders of magnitude larger than the solar rate. For large
enough values of dot {M}, the emission from the wind is expected to
have a spectrum which, at low enough frequencies, becomes a power law,
S_ν ~ nu (alpha ) with alpha ~ 0.7. Data from IRAS and VLA suggest
that such a spectrum may in fact occur in certain M dwarfs: a key
test of the wind spectrum would be provided if the stars could be
detected at lambda ~ 1 mm. We show that the dot {M} required to ensure
power law emission is a few times 10(-10) M<SUB>sun</SUB> \ yr(-1)
. With dot {M} of this order, fluxes at lambda ~ 1 mm would be tens
of mJy. Using the James Clerk Maxwell Telescope, we have tested this
prediction on several stars: the data are suggestive but are near the
limits of detection. Confirmation of our estimates will be important
for studies of evolution of low mass stars and for interstellar medium
(ISM) physics: if even a few percent of all M dwarfs are losing mass
at the above rates, the mass balance of the ISM will be dominated by
M dwarfs. Moreover, if flares on these stars are accompanied by mass
ejecta, the ISM may become contaminated with deuterium produced in
the surface layers of the star by energetic protons.
---------------------------------------------------------
Title: The Sun as a Star: High Spectral Resolution Solar Data Degraded
to Low-Dispersion IUE Resolution
Authors: Doyle, J. G.; Cook, J. W.
1992ApJ...391..393D Altcode:
High spectral resolution (about 0.06 A) solar data for an active region
and a large two-ribbon flare degraded to the typical resolution
of low-dispersion (about 5 A) spectra of the IUE satellite are
presented. This clearly shows the amount of detail yet to be acquired
in stellar spectra and indicates the main spectral regions where line
blending is a problem.
---------------------------------------------------------
Title: Excitation of the solar flare far-ultraviolet continuum by
line irradiation
Authors: Doyle, J. G.; Phillips, K. J. H.
1992A&A...257..773D Altcode:
Observations of the FUV (wavelength less than 1682 A) continuum by
Skylab during an intense solar flare confirm previous calculations that
the excitation of this continuum is due to the ionization of neutral
silicon atoms near the temperature minimum region irradiated by UV line
radiation emitted by the upper chromosphere or transition region. The
evidence is an observed proportionality of the continuum intensity
with the intensities of C IV (1548/51 A) and C II (1335/36 A) lines.
---------------------------------------------------------
Title: Who Needs an X-Ray Satellite when we have IUE
Authors: Doyle, J. G.
1992IrAJ...20..209D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: So you Think Solar Abundances are Constant
Authors: Doyle, J. G.
1992IrAJ...20..208D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Optical flares on the RS CVn binary II Peg.
Authors: Mathioudakis, M.; Doyle, J. G.; Avgoloupis, V.; Mavridis,
L. N.; Seiradakis, J. H.
1992MNRAS.255...48M Altcode:
During 57.4 hr of optical monitoring in the Johnson U- and B-bands of
the RS CVn binary II Peg, 10 flares were detected. The absolute energies
of these events are in the range 1-180 x 10 exp 33 erg. This implies
a flare activity in the U-band of 0.17 flares per hour, compared with
0.12 flares per hour from UV C IV data. A double power-law distribution
is required to fit the cumulative flare-frequency distribution of the
U-band flares.
---------------------------------------------------------
Title: The Origin of the Far-Ultraviolet Continuum in Solar and
Stellar Flares
Authors: Phillips, K. J. H.; Bromage, G. E.; Doyle, J. G.
1992ApJ...385..731P Altcode:
A continuum in the far-ultraviolet region observed in IUE spectra
of dMe stars in a flaring state is discussed and compared with that
observed in solar flares. Similar continuous emission observed in
solar flare far-ultraviolet spectra has been identified with neutral
silicon recombination radiation excited by intense lines. This also
appears to be the case for stellar flares, as is deduced here from
the proportionality of far-ultraviolet line and continuum power for
several flares on dMe stars, two flares on an RS CVn star (II Peg),
and the spotted active binary BY Dra. The only solar flare observation
available, from Skylab, obeys this same linear relation. Other emission
mechanisms are considered, but they are unlikely to give the observed
continuum flux.
---------------------------------------------------------
Title: High Spectral Resolution Solar Data Degraded to Low Dispersion
lUE Resolution
Authors: Doyle, J. G.; Cook, J. W.
1992ASPC...26...49D Altcode: 1992csss....7...49D
No abstract at ADS
---------------------------------------------------------
Title: A MN I Emission Line at 4032 A During a Flare on the RS CVn
Star II Peg
Authors: Doyle, J. G.; Panagi, P. M.; Butler, C. J.
1992ASPC...26..300D Altcode: 1992csss....7..300D
No abstract at ADS
---------------------------------------------------------
Title: The Quiescent X-ray Spectrum of the RS CVn Binary II Peg in
August 1989
Authors: Doyle, J. G.; Byrne, P. B.; van den Oord, G. H. J.; Kellett,
B. J.; Bromage, G. E.
1992ASPC...26..356D Altcode: 1992csss....7..356D
No abstract at ADS
---------------------------------------------------------
Title: Millimeter; Sub-Millimeter Emission from Flare Stars
Authors: Mullan, D. J.; Doyle, J. G.; Mathioudakis, M.; Redman, R. O.
1992ASPC...26..328M Altcode: 1992csss....7..328M
No abstract at ADS
---------------------------------------------------------
Title: GL 890 - The Magnetic Brake?
Authors: Byrne, P. B.; Doyle, J. G.; Mathioudakis, M.
1992ASPC...26..438B Altcode: 1992csss....7..438B
No abstract at ADS
---------------------------------------------------------
Title: Modelling of the Large X-ray Flare on II Peg Observed with
GINGA
Authors: Kellett, B. E.; Doyle, J. G.; Bromage, G. E.; Byrne, P. B.
1992LNP...397..289K Altcode: 1992sils.conf..289K
No abstract at ADS
---------------------------------------------------------
Title: Optical Flares on II Peg
Authors: Mathioudakis, M.; Doyle, J. G.; Avgoloupis, S.; Mavridis,
L. N.; Seiradakis, J. H.
1992ASPC...26..303M Altcode: 1992csss....7..303M
No abstract at ADS
---------------------------------------------------------
Title: The Nature of M Dwarfs with a Zero H Alpha Flux
Authors: Doyle, J.
1992iue..prop.4345D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The August 1989 Spot Lightcurve of II Peg and Related Flare
Activity
Authors: Avgoloupis, S.; Doyle, J. G.; Mavridis, L. N.; Seiradakis,
J. H.; Mathioudakis, M.
1992LNP...397..247A Altcode: 1992sils.conf..247A
No abstract at ADS
---------------------------------------------------------
Title: Short Time-scale Changes in the V-band Light Curve of II Peg:
Flare Companion or Prominence?
Authors: Doyle, J. G.; Bromage, G. E.; Collier Cameron, A.; Kilkenny,
D. W.; Krzesinski, J.; Murphy, H. M.; Neff, J. E.; Pajdosz, G.;
van Wyk, F.
1992LNP...397..276D Altcode: 1992sils.conf..276D
No abstract at ADS
---------------------------------------------------------
Title: A study of the flaring and quiscent X-ray and UV emission
from II Pegasi.
Authors: Tagliaferri, G.; White, N. E.; Doyle, J. G.; Culhane, J. L.;
Hassall, B. J. M.; Swank, J. H.
1991A&A...251..161T Altcode:
An investigation has been conducted of the rotational modulation of the
transition-region UV and coronal X-ray emission for the RS CVn system II
Pegasi. The X-ray light curve is dominated by a strong flare detected at
orbital phase, where the minimum of the photometric wave occurred. The
flare parameters derived show that the flare originates with a height
greater than half the stellar radius. The characteristics of the flare
are similar to those of a solar two-ribbon flare; a comparison of the
midtransition region density with that in the coronal region shows a
very steep pressure gradient.
---------------------------------------------------------
Title: A comparison of theoretical Fe xii emission line strengths
with EUV observations of a solar active region
Authors: Keenan, F. P.; Doyle, J. G.; Tayal, S. S.; Henry, R. J. W.
1991SoPh..135..353K Altcode:
New theoretical electron-density-sensitive Fe XII emission line
ratios R<SUB>1</SUB> = I(3s<SUP>2</SUP>3p<SUP>34</SUP>S<SUB>3/2</SUB> -
3s3p<SUP>44</SUP>P<SUB>5/2</SUB>)/I(3s<SUP>2</SUP>3p<SUP>32</SUP>P<SUB>3/2</SUB>
- 3s3p<SUP>4</SUP>D<SUB>5/2</SUB> and R<SUB>2</SUB>
= I(3s<SUP>2</SUP>3p<SUP>32</SUP>P<SUB>3/2</SUB> -
3s3p<SUP>42</SUP>D<SUB>5/2</SUB>)/I(3s<SUP>2</SUP>3p<SUP>34</SUP>S<SUB>3/2</SUB>
- 3s3p<SUP>2</SUP>P<SUB>3/2</SUB>) are derived using R-matrix electron
impact excitation rate calculations. We have identified the FeXII and
transitions in an active region spectrum obtained with the Harvard
S-055 spectrometer on board Skylab at wavelengths of 364.0, 382.8,
1241.7, and 1349.4 Å, respectively. Electron densities determined
from the observed values of R<SUB>1</SUB> (log N<SUB>e</SUB> ≃ 11.0)
and R<SUB>2</SUB>(log N<SUB>e</SUB> ≃ 11.4) are significantly larger
than the typical active region measurements, but are similar to those
derived from some active region spectra observed with the Skylab 2082A
instrument, which provides observational support for the atomic data
adopted in the line ratio calculations, and also for the identification
of the Fe XII transitions in the S-055 spectrum. However the observed
value of R<SUB>3</SUB> = I(1349.4 Å)/I(1241.7 Å) is approximately
a factor of two larger than one would expect from theory which,
considering that the 1349.4 Å line lies at the edge of the S-055
wavelength coverage, may reflect errors in the instrument efficiency
curve. Another possibility is that the 1349.4 Å transition is blended,
probably with Si II 1350.1 Å.
---------------------------------------------------------
Title: The Sun as a Star - High Spectral Resolution Solar Data
Degraded to Low Dispersion IUE Resolution
Authors: Doyle, J. G.
1991IrAJ...20...95D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Sun as a Star: High Spectral Resolution Solar Data Degraded
to Low Dispersion IUE Resolution
Authors: Cook, J. W.; Doyle, J. G.
1991BAAS...23.1384C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A gas-dynamic model for a flare on YZ CMi : interpretation
of high-temporal-resolution spectroscopic data.
Authors: Katsova, M. M.; Livshits, M. A.; Butler, C. J.; Doyle, J. G.
1991MNRAS.250..402K Altcode:
The 3600-4400 A spectra obtained for the March 4, 1985 flare spectra
of YZ CMi are analyzed on the basis of a gasdynamic model whose U-band
optical radiation is generated by a condensation formed during the
gasdynamic process. The source of the optical radiation is a dense,
cool plasma with small height; this source is responsible for the
radiation from the higher Balmer lines when they are at maximum
intensity, as presently demonstrated by the hydrogen plasma kinetics
of an 'eight-levels-plus-continuum' model atom. It is demonstrated
that the low slope of the Balmer decrement is due to a combination
of a large population in the second level of the hydrogen atom, in
conjunction with a photon escape probability decrease from the medium,
at the higher Balmer line frequencies.
---------------------------------------------------------
Title: Rotationalmodulation and flares on RS Canum Venaticorum and BY
Draconis stars. XVI. IUE spectroscopy and VLA observations of GL 182
(=V 1005 Orionis) in October 1983.
Authors: Mathioudakis, M.; Doyle, J. G.; Rodono, M.; Gibson, D. M.;
Byrne, P. B.; Avgoloupis, S.; Linsky, J. L.; Gary, D.; Mavridis,
L. N.; Varvoglis, P.
1991A&A...244..155M Altcode:
A large flare was detected simultaneously with IUE and VLA on Gl 182 on
October 5, 1983, this event showing the largest C IV flare enhancement
yet observed by IUE. A smaller flare was also detected on October 4,
although only with the IUE satellite. Line ratio and emission measure
techniques are used to derive various physical parameters of the
flares. The radiative losses in the temperature region log T(e) =
4.3-5.4 in the two flares are 2.9 x 10 to the 33rd and 8.4 x 10 to
the 32nd ergs, respectively. Total radiative losses over the whole
temperature range log T(e) = 4.0-8.0 are estimated to be of the order
of 6.4 x 10 to the 34th and 1.1 x 10 to the 34th ergs, respectively. In
the October 5, flare, a very strong ultraviolet continuum is present
with a total energy of 1.9 x 10 to the 33rd ergs over the wavelength
range 1250-1950 A.
---------------------------------------------------------
Title: Active M-type stars from the ultraviolet to the infrared.
Authors: Mathioudakis, M.; Doyle, J. G.
1991A&A...244..433M Altcode:
Fluxes at 12 microns are presented for a group of seven active dMe
stars. Five of these stars are considered as significant detections
at 25 microns, while only two stars were detected at 60 microns and
only one at 100 microns. Comparing with previous results it is found
that the fluxes are systematically lower by 7-50 percent depending on
the band. Above 60 microns there is a definite excess over a blackbody
radiation curve.
---------------------------------------------------------
Title: Chromospheric diagnostics in late-type stars.
Authors: Mathioudakis, M.; Doyle, J. G.
1991A&A...244..409M Altcode:
Moderate and low resolution spectroscopic observations of late type
dwarfs covering a broad range of activity are presented. The strength of
the TiO band in 4762 A is used for spectral classification. Calibrated
fluxes for the Balmer and the Ca II H and K lines are derived. H-alpha
equivalent widths are given for those stars where the line is in
absorption as well as those in emission. It is confirmed that stars
with no detectable or very weak H-alpha do exist. It is also shown
that stars with very weak or no detectable emission in Ca II H and K
also exist, this occurring preferentially in late M dwarfs. Although
this can be explained in terms of reduced nonradiative heating in
the chromosphere, the results cannot be conclusive due to the limited
resolution of the data.
---------------------------------------------------------
Title: Book-Review - the Sun - an Introduction
Authors: Stix, M.; Doyle, J. G.
1991IrAJ...20...49S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Millimetre Continuum Emission from Flare Stars
Authors: Doyle, J. G.
1991IrAJ...20Q..47D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Introduction to Stellar Astrophysics - VOL.1 -
Basic Stellar Observations and Data
Authors: Bohm-Vitense, E.; Doyle, J. G.
1991IrAJ...20...50B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Mni Emission Line at 4032A during a Flare on the Rs-Canum
Star II-Pegasi
Authors: Doyle, J. G.
1991IrAJ...20R..47D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Simultaneous detection of a large flare in the X-ray and
optical regions on the RS CVn-type star II Peg.
Authors: Doyle, J. G.; Kellett, B. J.; Byrne, P. B.; Avgoloupis,
S.; Mavridis, L. N.; Seiradakis, J. H.; Bromage, G. E.; Tsuru, T.;
Makishima, K.; Makishima, K.; McHardy, I. M.
1991MNRAS.248..503D Altcode:
Results are presented for a large flare detected simultaneously on the
RS CVn star II Peg by the X-ray satellite GINGA and from ground-based
Johnson U-band measurements. The total U-band flare energy is estimated
to be at least 6.6 x 10 to the 34th erg. This compares with at least
4.6 x 10 to 34th erg in the 1-10 keV energy range. These values
are lower limits to the true radiative output, since the U-band data
relates only to the rise phase of the flare, while the X-ray data were
obtained during part of the decay phase. Using a 'smooth-burst model',
the combined U-band plus X-ray radiative output is estimated to be
about 3 x 10 to the 34th erg.
---------------------------------------------------------
Title: Millimeter continuum emission from flare stars.
Authors: Doyle, J. G.; Mathioudakis, M.
1991A&A...241L..41D Altcode:
The first detection of continuum emission in the millimeter region
for two dwarf M flare stars is reported. The observed flux at 1.1 and
2 mm is weak, being just above background, but above that based on a
black-body curve. This confirms the impression gained from infrared
fluxes at 60 and 100 microns, which indicated excess emission at
these wavelengths.
---------------------------------------------------------
Title: Multiwavelength Observations of Stellar Flares
Authors: Doyle, J.
1991iue..prop.4064D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Comparison of solar and stellar flare ultraviolet continua
Authors: Phillips, K. J. H.; Bromage, G. E.; Doyle, J. G.
1991VA.....34..277P Altcode:
It is proposed that there is a strong connection between the continua
formed in the ultraviolet spectra of stellar flares with that seen
in solar spectra, and that the mechanism of formation believed to
occur in the latter — silicon recombination radiation excited by
photo-ionization due to ultraviolet line emission — is the same as
in stellar flares.
---------------------------------------------------------
Title: The Nature of M Dwarfs with a Zero H Alpha Flux
Authors: Doyle, J.
1991iue..prop.4059D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chrpmosphere Radiative Losses in M Dwarfs
Authors: Doyle, J.
1991iue..prop.4126D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric/Coronal Emission Correlations in 'Quiescent'
and Eruptive Phenomena in M-Dwarf Stars (With 1 Figure)
Authors: Mathioudakis, M.; Doyle, J. G.
1991mcch.conf..279M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Discovery of flare activity on the dwarf M stars, GL 375 and
GL 431.
Authors: Doyle, J. G.; Mathioudakis, M.; Panagi, P. M.; Butler, C. J.
1990A&AS...86..403D Altcode:
Optical and infrared photometry plus spectroscopic data is present
for two new flare stars, Gl 375 and Gl 431. Both of these stars have
the hydrogen Balmer lines strongly in emission. Several flares were
detected on Gl 375 implying a high level of flare activity. The H-alpha
surface flux of 1.0 x 10 to the 6th erg/sq cm per sec for both stars
is similar to that of other active flare stars. Fluxes are given for
several of the higher Balmer lines.
---------------------------------------------------------
Title: Chromospheric/coronal emission correlations in "quiscent"
and eruptive phenomena in M-dwarf stars.
Authors: Mathioudakis, M.; Doyle, J. G.
1990A&A...240..357M Altcode:
A power correlation between 'quiescent' and flaring H-gamma and
X-ray emission is presented for a group of active dwarf M stars. The
relationship holds for both 'quiescent' and flaring conditions for
several orders of magnitude change in energy. Explanations in terms
of X-ray back-heating and microflaring are discussed.
---------------------------------------------------------
Title: Activity in late-type stars. VII. Chromospheric and transition
region line fluxes in 2 dM and dM(e) stars.
Authors: Byrne, P. B.; Doyle, J. G.
1990A&A...238..221B Altcode:
Ultraviolet spectra of the two dM stars Gl380 and Gl411 and the dM(e)
Gl900 are presented. The dM stars show mean surface fluxes in a variety
of emission lines arising throughout the chromosphere and the lower
transition region which are very similar to those of the quiet sun. In
the one star in which it could be determined the electron density at
log T(e) was roughly 4.75, also within a factor of roughly 2.5 that of
the solar value. Results for a single dM(e) star indicate higher mean
surface fluxes in these same lines, consistent with the view that they
are intermediate between the dM and the dMe stars.
---------------------------------------------------------
Title: A Giant X-ray/optical Flare on II Peg
Authors: Byrne, P. B.; Doyle, J. G.; Tsuru, T.; Avgoloupis, S.;
Mavridis, L. N.; Seiridakis, J. H.; Kilkenny, D. W.; Laing, J. D.;
Marang, F.
1990IrAJ...19..150B Altcode:
The paper presents a preliminary account of a large X-ray flare
recorded by an X-ray satellite (it was also recorded in broadband
optical light and in hydrogen Balmer emission) as a part of a campaign
to monitor the RS CVn system II Peg with ground-based optical photometry
and spectroscopy and satellite ultraviolet and X-ray spectroscopy. Two
X-ray flares observed are described: the first one is relatively weak in
X-rays, while the second flare which is the subject of the discussion,
was present when the source was reacquired after earth occultation on
August 17, 1989. Flare energy, temperature, and emission measure and
volume are analyzed, and emphasis is placed on the observation of a
line feature at approximately 6.8 keV, coinciding in energy to the
position of the H-like FeXXVI line at 1.79 A.
---------------------------------------------------------
Title: Ultraviolet continuum in solar and dMe star flares
Authors: Phillips, K. J. H.; Bromage, G. E.; Doyle, J. G.
1990ESASP.310..427P Altcode: 1990eaia.conf..427P
No abstract at ADS
---------------------------------------------------------
Title: Optical and infrared photometry of dwarf M and K stars.
Authors: Doyle, J. G.; Butler, C. J.
1990A&A...235..335D Altcode:
Absolute U, B, V, R, I, J, H, K, and L photometry are given for a group
of dwarf M and K stars. Using black-body fits to the data, bolometric
luminosities and radii are derived. The derived bolometric luminosities
are good to + or - 10 percent and the effective temperatures to +
or - 100 K. A comparison is made with the values derived by other
authors. The derived radii are 14 percent smaller than those derived
from the revised Barnes et al. (1978) relation involving (V - R).
---------------------------------------------------------
Title: A Comparison of Theoretical SV Emission Line Strengths with
Extreme Ultraviolet Observations of a Sunspot
Authors: Keenan, F. P.; Doyle, J. G.
1990SoPh..128..345K Altcode: 1990IAUCo.121P.345K
Electron impact excitation rates for transitions in the S v ion,
calculated with theR-matrix code, are used to derive the electron
temperature sensitive emission line ratiosR<SUB>1</SUB> =I(854.8
Å)/I(786.9 Å),R<SUB>2</SUB> =I(852.2 Å)/I(786.9 Å),R<SUB>3</SUB>
=I(849.2 Å)/I(786.9 Å), andR<SUB>4</SUB> =I(1199.1 Å)/I(786.9 Å),
which are found to be significantly different from previous estimates. A
comparison of the present results with observational data for a sunspot
obtained with the Harvard S-055 spectrometer on boardSkylab reveals
generally good agreement between theory and experiment, except in the
case ofR<SUB>1</SUB>, which is probably due to blending in the 854.8
Å feature. The possible effects of Lyman continuum absorption on the
observed line ratios is briefly discussed.
---------------------------------------------------------
Title: A periodicity in the flaring rate on the eclipsing binary
YY Geminorum.
Authors: Doyle, J. G.; Butler, C. J.; van den Oord, G. H. J.; Kiang, T.
1990A&A...232...83D Altcode:
Five flares were observed on the late-type binary YY Gem in March 1988
during a total monitoring time of 408 min. The flares were unusual
in that there is a periodicity in the occurrence of four of them,
these being separated by 48 + or - 3 min. Considering the flares to
be formed as a stochastic process, it is found that the probability
of these events occurring by chance is 0.5 percent. Modeling indicates
that for quite reasonable input parameters, the flare periodicity can
be explained in terms of filament oscillations. The only requirement
is that there should be a filament at these heights where the magnetic
field drops inversely proportional to the height.
---------------------------------------------------------
Title: IUE observations of GL 644 AB (=Wolf 630) in the wavelength
region 1150-1950 A, in June 1981.
Authors: Mathioudakis, M.; Doyle, J. G.
1990A&A...232..114M Altcode:
IUE short wavelength observations of the flare star Gl 644, obtained
in June 1981 are presented. A flare was detected in one of the spectra
as a strong increase in C IV, He II, and continuum fluxes. The electron
density of the flaring plasma, determined using line ratio techniques,
is 4 x 10 to the 10th/cu cm, which is an increase by a factor of
2.7 above the quiescent. The radiative losses of the flare are at
least 1.3 x 10 to the 32nd erg and 4.0 x 10 to the 33rd erg over the
temperature range log Te between 4.3 and 5.4 and log Te between 4.0
and 8.0, respectively. This compares with continuum losses of 8.1 x
10 to the 31st erg over the wavelength region 1250-1950 A.
---------------------------------------------------------
Title: An X-ray flare observed from van Biesbroeck 8.
Authors: Tagliaferri, G.; Doyle, J. G.; Giommi, P.
1990A&A...231..131T Altcode:
An X-ray flare was detected on the previously unknown flare-star van
Biesbroeck 8 ( = Gl 644 C). The total energy of the event in the 0.05-2
keV energy range was 8 x 10 to the 31st erg/s with a mean luminosity of
1.8 x 10 to 28th erg/s. This implies an emission measure of about 6 x 10
to the 50th/cu cm, and adopting a simple loop model an electron density
of 10 to the 11th/cu cm or greater. It is estimated that the flare
covered 1-4 percent of the stellar surface. Quiescent X-ray emission
from VB 8 was detected during an Einstein-HRI observation. These
properties of VB 8 suggest that stars later than M 5 can be very active
X-ray emitters.
---------------------------------------------------------
Title: Mass ejections from the rapidly rotating M dwarf star GL 890.
Authors: Doyle, J. G.; Collier Cameron, A.
1990MNRAS.244..291D Altcode:
Mg II line fluxes from the rapidly rotating single M dwarf Gliese
890 show a 'dip' lasting less than 120 min. H-alpha spectra obtained
simultaneously show systematic profile changes during the Mg II 'dip':
the line bisector of the H-alpha emission feature shows at first a
red then a blue displacement. The behavior of both the H-alpha line
bisector and the Mg II emission 'dip' is consistent with a model in
which a cloud of mainly neutral hydrogen passes in front of the disk of
the star. Similar behavior has been observed in the rapidly rotating
single K dwarf AB Doradus. The projected area of the Gl 890 cloud is
0.25-0.40 times that of the stellar disk.
---------------------------------------------------------
Title: 1973 September 7 Two-Ribbon Flare. I. Morphology and Loop
Expansion
Authors: Doyle, J. G.; Widing, K. G.
1990ApJ...352..754D Altcode:
XUV data are presented for a two-ribbon flare of H-alpha class 2B and
X-ray class X1 which occurred on September 7, 1973. The morphology
and loop expansion rates observed in coronal lines of Fe XIV and Ca
XVII are compared with data from the chromospheric line H-alpha. The
loop arcades at different temperatures and different loops in a given
arcade show different expansion rates. Consideration is given to the
relationship of the observed arcade loop system to various surface
features. The loop aspect ratio and electron density are derived as
a function of position along the loop for the coronal plasma. These
values are used to derive the energy density and to discuss scaling
laws relating loop length, temperature, and pressure. The observed
radiative cooling times for individual loops are compared to times
calculated from radiative conductive and enthalpy cooling times. Also,
the observed energy density is compared with that calculated from a
reconnection model.
---------------------------------------------------------
Title: 1973 September 7 Two-Ribbon Flare. II. Physical Properties
of the Loops in the Arcade
Authors: Widing, K. G.; Doyle, J. G.
1990ApJ...352..760W Altcode:
Spectral data of selected lines between 170 and 340 Å for a large
two-ribbon flare of 1973 September 7 are presented. The flare
arcade consisted of four prominent loops. Loop intensities and
densities decreased by approximately a factor of 2 during one hour of
observations, beginning 15 minutes after Solrad flux maximum suggesting
that the mass and energy supply are strongly maintained during the
early hours of the gradual phase. Observed emission measures in Ca
XVII loops give N<SUB>e</SUB> = 7 × 10<SUP>10</SUP> cm<SUP>-3</SUP>
compared with 2 × 10<SUP>10</SUP> cm<SUP>-3</SUP> in Fe XIV loops. The
Fe XIV density sensitive 219/211 line ratio gives similar densities
implying a filling factor of ≍50% near flare maximum to unity 1
hour later. These results imply that the upper and outer parts of
the rising loop system are hotter and denser than the lower and inner
parts of the arcade. Electron densities at the loop apex were ∼50%
greater than those at the loop footpoints. The loop aspect ratio
(i.e., the ratio of the loop cross section diameter to the loop
foot-point separation) varies from 0.1 to 0.3, being largest for the
higher temperature lines. The derived loop parameters are compared
with scaling laws. Loop cooling rates are calculated and compared
with observed cooling times. Finally, the observed energy density is
compared with that calculated from a reconnection model.
---------------------------------------------------------
Title: Lyman-alpha and MG II H and K fluxes in a sample of dwarf
M stars.
Authors: Doyle, J. G.; Panagi, P.; Byrne, P. B.
1990A&A...228..443D Altcode:
Ly-alpha and Mg II fluxes are given for a group of M dwarfs. The
Ly-alpha and Mg II lines were extracted from low resolution spectra
taken with the IUE satellite. The Ly-alpha line is shown to be an
important source of radiative losses in dMe chromospheres, being at
least a factor of two more important than Mg II. Overall it contributes
approximately 25 percent of the total chromospheric losses, about
the same as the more commonly observed H-alpha line. In order to have
approximately equal contributions from these lines, one requires either
a plateau region in the lower transition region or different filling
factors for the two lines. In dM stars, Ly-alpha is approximately the
same magnitude as Mg II.
---------------------------------------------------------
Title: Flare activity and orbital rotation of YY Geminorum.
Authors: Doyle, J. G.; Mathioudakis, M.
1990A&A...227..130D Altcode:
The observed flare activity on the eclipsing binary star YY Geminorum,
as determined by the time-average flare energy, is more than as order
of magnitude greater out-of-eclipse than that during eclipses. The
out-of-eclipse value is however, heavily biased by four large
flares. In the cumulative distribution diagram these larger flares
have a substantially different statistical occurrence rate than the
remainder of the flares. It is suggested that the small separation
between the two stars leads to significantly enhanced magnetic field
between the two components and thus to the occurrence of energetic
flares, observable when the stars are out of eclipse.
---------------------------------------------------------
Title: A Model for the Observed Periodicity in the Flaring Rate
on Yy-Geminorum
Authors: Doyle, J. G.; van den Oord, G. H. J.; Butler, C. J.; Kiang, T.
1990IAUS..137..325D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Optical spectroscopy of nova LMC 1988 No 2 during its early
decline stage.
Authors: Sekiguchi, K.; Kilkenny, D.; Winkler, H.; Doyle, J. G.
1989MNRAS.241..827S Altcode:
This paper presents the results obtained from optical spectroscopy of
Nova LMC 1988 No. 2 made at the SAAO. It was a very fast nova (t_2_=5d)
of large amplitude ({DELTA}m>11.2 mag) and the visual maximum
reached m_V_=10.3 on 1988 October 13.75 UT. A spectrogram taken 1.34d
after the maximum showed strong Balmer, He I and Fe II lines with P Cyg
profiles. The broad (FWZI>4000 km s^-1^) emission features extend
to +3000 km s^-1^. Two principle absorption systems at ~-1700 km s^-1^
and ~-2500 km s^-1^ and higher velocity diffuse-enhanced absorption
systems extending to -4000 km s^-1^ were seen. By 1988 December 2
(50d after the maximum) the nova had developed into the early nebular
phase and showed very strong [Ne III] emissions. The characteristics
of the nova closely resemble those of V1500 Cyg and V1370 Aql.
---------------------------------------------------------
Title: Flux-flux relation : MG II H and K versus X-rays in dwarf M
and K stars.
Authors: Mathioudakis, M.; Doyle, J. G.
1989A&A...224..179M Altcode:
Surface X-ray and Mg II h and k fluxes are presented for a group of
dMe, dKe, dM, and dK stars. No correlation is apparent between the
fluxes for the group of stars as a whole, although a good correlation
is present for a subgroup, i.e., the dMe/dKe's. The Mg II and X-ray
luminosities for these active stars define an upper boundary, which
is dependent upon the stellar radii. The Mg II luminosity from the
less active dM/dK stars are also radii-dependent, but this is not the
case for the X-ray luminosity. This may indicate a difference in the
heating mechanisms for the chromosphere and corona, with acoustic wave
heating being an important contributor in the chromosphere and/or a
difference in the plage filling factors in the two regions.
---------------------------------------------------------
Title: Ultraviolet flares on II Pegasi.
Authors: Doyle, J. G.; Byrne, P. B.; van den Oord, G. H. J.
1989A&A...224..153D Altcode:
UV spectroscopic observations of the RS CVn star, II Peg, were obtained
in February 1983. The observations show evidence for flare activity
in greatly enhanced chromospheric and transition region emission
lines. The flare radiation is isolated and the electron pressures of
the mean quiescent atmosphere and the two flares are derived from the
intersystem line flux ratios. Estimates are given of the total flare
power output over the whole atmosphere and the surface filling factor
for the flares. The implications of the observations for studies of
flares on RS CVn stars are considered.
---------------------------------------------------------
Title: Rotational modulation and flares on RS CVn and BY Draconis
stars. XIII. IUE spectroscopy and photometry of II Pegasi during
September 1986.
Authors: Doyle, J. G.; Butler, C. J.; Byrne, P. B.; Rodono, M.; Swank,
J.; Fowles, W.
1989A&A...223..219D Altcode:
UV spectroscopy obtained for the RS CVn star II Pegasi in September,
1986, indicates the presence of a rotational modulation effect for the
Mg II h and k and O I 1305 A lines; the largest flux is observed when
the primary spot concentration is nearly on the opposite hemisphere,
and the rotational modulation is noted to be of opposite sense to that
observed in 1981. Optical photometry shows the largest concentration
of spots on one hemisphere ever observed on II Peg, implying a spot
group covering over 50 percent of the projected area of one hemisphere.
---------------------------------------------------------
Title: H-alpha versus X-ray luminosity in dwarf M stars.
Authors: Doyle, J. G.
1989A&A...218..195D Altcode:
A power-law correlation is presented between the excess chromospheric
H-alpha emission and the coronal X-ray emission for a group of dM
and dMe stars. This excess emission was calculated by subtracting the
maximum (i.e., saturated) observed H-alpha absorption equivalent width
for a star of a similar color. Heating of the chromosphere through
X-ray back-heating is not the dominant component of chromospheric
heating in dM stars, although in the very active late-type stars its
contribution could be about 50 percent.
---------------------------------------------------------
Title: An estimate of the total chromospheric, transition region
and coronalradiative losses in late-type stars.
Authors: Doyle, J. G.
1989A&A...214..258D Altcode:
An estimate is made of the total radiative losses between 10,000 and
100 million K in several late-type stars. Using a relationship between
the CIV 1548-A line flux and the total power losses in the atmosphere
above 10,000 K developed for solar plasmas, it is shown that this
relation also holds for these stars. For the active dMe and dKe stars,
total radiative losses of 30-40 Merg/sq cm sec above 10,000 K are
calculated, being slightly greater than that calculated for the sun
if it were covered by active regions.
---------------------------------------------------------
Title: Rotational modulation and flares on RS Canum Venaticorum and
BY Draconis stars. XII. Near-to-simultaneous high resolution UV and
optical observations of II Pegasi during July 1984.
Authors: Byrne, P. B.; Panagi, P.; Doyle, J. G.; Englebrecht, C. A.;
McMahan, R.; Marang, F.; Wegner, G.
1989A&A...214..227B Altcode:
Nearly simultaneous high resolution ground-based optical and IUE
satellite UV spectroscopy and an optical light curve of the RS CVn
star II Peg are presented. It is shown that the chromospheric and
transition region radiative losses of the star in July 1984 are lower
than previously recorded means. The flux in the Lyman-alpha line is
estimated and evidence is given for variability in all of the emission
lines. This variability appears to be correlated with the optical
spots. Line profiles at two rotational phases for the principal UV
emission lines show an excess broadening over and above the combined
instrumental plus Doppler broadening.
---------------------------------------------------------
Title: Spectroscopic and photometric observations of SN 1987A-
V. Days 386-616.
Authors: Catchpole, R. M.; Whitelock, P. A.; Menzies, J. W.; Feast,
M. W.; Marang, F.; Sekiguchi, K.; van Wyk, F.; Roberts, G.; Balona,
L. A.; Egan, J. M.; Carter, B. S.; Laney, C. D.; Laing, J. D.;
Spencer Jones, J. H.; Glass, I. S.; Winkler, H.; Fairall, A. P.;
Lloyd Evans, T. H. H.; Cropper, M. S.; Shenton, M.; Hill, P. W.;
Payne, P.; Jones, K. N.; Wargau, W.; Mason, K. O.; Jeffery, C. S.;
Hellier, C.; Parker, Q. A.; Chini, R.; James, P. A.; Doyle, J. G.;
Butler, C. J.; Bromage, G.
1989MNRAS.237P..55C Altcode:
We present spectroscopic and UBV(RI)_c_JHKLM photometric observations
of SN 19S7A in the Large Magellanic Cloud made at the Sutherland
observatory of the SAAO between days 386 and 616 after the Kamiokande-II
neutrino event. During this period the bolometric flux from the
supernova measured over the U to M wavelength range has continued to
decline faster than the ^56^Co decay rate. By day 56O the flux in this
wavelength range accounts for only half of that expected from ^56^Co
decay. The estimated total flux (including X-ray and γ-ray data)
is consistent with ^56^Co remaining the sole energy source of the
supernova over the period considered.
---------------------------------------------------------
Title: Activity in late-type dwarfs. III. Chromospheric and transition
region line fluxes for two dM stars.
Authors: Byrne, P. B.; Doyle, J. G.
1989A&A...208..159B Altcode:
Weak upper-chromospheric and transition-region emission from
two dM stars (Gl 784 and Gl 825) has been observed using deep UV
spectroscopy. Ly-alpha fluxes for the two stars were also determined
for the first time. Using these results it is shown that the transition
from weakly active dM to active dMe star is probably due to increasing
surface coverage by solarlike active regions. Also discussed are the
relative importance of Ly-alpha and Mg II as chromospheric coolants
in the M dwarfs and how this changes between dM and dMe stars. The
interrelationship between X-ray, He II (1640-A) and C IV (1550-A)
fluxes is discussed in the light of these results, and it is shown
that all three are tightly related over three orders of magnitude
in each. Several flux-period relationships are used to predict the
rotation periods of the two stars.
---------------------------------------------------------
Title: Flares on RS CVn Stars
Authors: Doyle, J.
1989iue..prop.3519D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Optical flares from the dwarf M star V577 MON (Gliese 234 AB =
Ross 614).
Authors: Doyle, J. G.; van den Oord, G. H. J.; Butler, C. J.
1989A&A...208..208D Altcode:
The paper describes a search for flaring on the Balmer emission line
star, Gliese 234 AB. Ten flares were detected in a total monitoring time
of 4.6 h, implying a very high level of activity. The time-averaged
flare energy in the Johnson U-band is slightly greater than measured
previously but due to the small number of hours of observations it
is best to use the mean of these two measurements. Relative energies
are given for the U, B, V, R, and I bands for a 3.8 mag U-band flare
which had a 45 s rise time and 20 min decay time. Of the various models
fitted to the flare data, bound-free emission seems the most promising.
---------------------------------------------------------
Title: September 7, 1973 two-ribbon flare.
Authors: Doyle, J. G.; Widing, K. G.
1989sasf.confP.199D Altcode: 1988sasf.conf..199D; 1989IAUCo.104P.199D
The flare images show a compact, nearly cylindrical arcade centered
along the filament channel and composed of 4 prominent loops. The loop
systems of Fe XII (T<SUB>e</SUB> = 1.7×10<SUP>6</SUP>K) and Fe XIV
(T<SUB>e</SUB> = 2.3×10<SUP>6</SUP>K) are smaller than, and lie nested
within, the arcades of Fe XVI (T<SUB>e</SUB> = 3×10<SUP>6</SUP>K)
and Ca XVII (T<SUB>e</SUB> = 5×10<SUP>6</SUP>K). The loop arcades
at different temperatures, as well as different loops within a
given arcade, show different expansion rates. These vary from 6 -
8 km s<SUP>-1</SUP> for Fe XIV shortly after flare maximum to 0.5 -
1 km s<SUP>-1</SUP> late in the decay phase. For hotter ions, such
as Ca XVII, the velocities are approximately constant at 2 - 3 km
s<SUP>-1</SUP> during the whole of the observations.
---------------------------------------------------------
Title: Flare energetics.
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veck, N. J.
1989epos.conf..377W Altcode:
The authors have sought to establish a comprehensive and self-consistent
picture of the sources and transport of energy within a flare. To
achieve this goal, they chose five flares in 1980 that were well
observed with instruments on the Solar Maximum Mission, and with other
space-borne and ground-based instruments. The events were chosen to
represent various types of flares. Details of the observations available
for them and the corresponding physical parameters derived from these
data are presented. The flares were studied from two perspectives,
the impulsive and gradual phases, and then the results were compared
to obtain the overall picture of the energetics of these flares. The
authors also discuss the role that modeling can play in estimating the
total energy of a flare when the observationally determined parameters
are used as the input to a numerical model. Finally, a critique of
our current understanding of flare energetics and the methods used to
determine various energetics terms is outlined, and possible future
directions of research in this area are suggested.
---------------------------------------------------------
Title: High Velocity MgII Wings in II Peg
Authors: Doyle, J.
1989iue..prop.3582D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An analysis of the continuum light in the 3500 - 8500 Å region
from a flare observed on the dwarf M star Gliese 234AB (= V577 Mon).
Authors: Doyle, J. G.; van den Oord, G. H. J.; Butler, C. J.
1989sasf.confP..91D Altcode: 1989IAUCo.104P..91D; 1988sasf.conf...91D
Relative energies are given for the U,B,V,R and I bands for a 3.8
magnitude U-band flare observed on the dwarf dMe star Gl 234 AB on 28
Feb. 1985. This flare had a 45 second rise time and 20 minute decay
time. The total flare energy from all five bands during the flare
was 7×10<SUP>31</SUP>erg, 34% of this total was from the U-band
and 20% from the two near infrared R and I bands. The energy density
(per frequency interval) implied a rising continuum towards the red,
however this only lasted for approximately 20 - 40 seconds, i.e. during
the impulsive phase, afterwhich the excess flare emission could not
be detected in the near infrared bands. Of the various models fitted
to the flare data (i.e. optical synchrotron, bound-free emission and
free-free emission), bound-free emission seems the most promising.
---------------------------------------------------------
Title: Multiwavelength Observations of Stellar Flares
Authors: Doyle, J.
1989iue..prop.3633D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Energetic flares on RS CVn stars.
Authors: Doyle, J. G.; Byrne, P. B.; van den Oord, G. H. J.
1989sasf.confP.115D Altcode: 1988sasf.conf..115D; 1989IAUCo.104P.115D
Ultraviolet spectroscopic observations of the RS CVn star II Peg in
February 1983 show evidence for flare activity in greatly enhanced
chromospheric and transition region emission lines. The total
radiative losses from the chromosphere and transition region during
the flare is 3.1×10<SUP>35</SUP>erg. Over the whole atmosphere the
authors estimate total radiative losses of 2.4×10<SUP>36</SUP>erg,
(excluding hydrogen line radiation). At flare peak, the flare radiated
1.5×10<SUP>32</SUP>erg s<SUP>-1</SUP>. Adopting a two-ribbon flare
model, where the filament is located between the two stars of the
system, one can have 10<SUP>39</SUP>(l/R<SUB>sun</SUB>) erg of magnetic
energy available, where l is the filament length. Therefore, only a
small fraction of this magnetic energy need be converted into heating
of the flare plasma.
---------------------------------------------------------
Title: A gas-dynamic model for a flare on YZ CMi: interpretation of
spectroscopic observations with high temporal resolution.
Authors: Katsova, M. M.; Livshits, M. A.; Butler, C. J.; Doyle, J. G.
1989sasf.confP..87K Altcode: 1989IAUCo.104P..87K; 1988sasf.conf...87K
The spectra of a flare on YZ CMi, obtained with a temporal resolution
of 60 seconds on March 4, 1985 and over the range 3600 - 4400 Å,
are analysed using a gas-dynamic model. In this model, the optical
radiation in the U-band, outside of flare maximum, is produced
by a condensation formed during the gas-dynamic process. With
the optical continuum described by a Planck function for a
temperature of T ≍ 10<SUP>4</SUP>K, the emitting source area S ≥
5×10<SUP>17</SUP>cm<SUP>2</SUP>. The hydrogen plasma kinetics of an
"8 levels plus continuum" model atom are calculated, and it is shown
that the low slope of the Balmer decrement, just after the flare
maximum, is connected with a large population in the second level of
the hydrogen atom.
---------------------------------------------------------
Title: X-Ray/Optical Flares on RS CVn Stars
Authors: Doyle, J. G.
1988IBVS.3250....1D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Theoretical Si iv line ratios compared to extreme ultraviolet
solar observations
Authors: Keenan, F. P.; Doyle, J. G.
1988SoPh..115..229K Altcode:
New theoretical electron temperature sensitive emission line
ratios in SiIV involving the 3d<SUP>2</SUP>D − 3p<SUP>2</SUP>P and
4s<SUP>2</SUP>S − 3p<SUP>2</SUP>P multiplets at ∼1125 and 816 Å,
respectively, are derived using recent R-matrix electron excitation
rate calculations. A comparison of these with observational data
for a solar active region at the limb obtained with the Harvard
S-055 spectrometer on board Skylab reveals that there is good
agreement between theory and observation for ratios that include
the <SUP>2</SUP>D<SUB>3/2, 5/2</SUB> − <SUP>2</SUP>P<SUB>3/2</SUB>
transition at 1128.3 Å. This is in contrast to the findings of Keenan,
Dufton, and Kingston (1986) and provides support for the atomic data
adopted in the calculations. However, the <SUP>2</SUP>D<SUB>3/2</SUB>
− <SUP>2</SUP>P<SUB>1/2</SUB> line at 1122.5 Å appears to be
severely blended, as suggested previously by Burton and Ridgeley (1970)
and Feldman and Doschek (1977), as it leads to electron temperature
estimates that differ significantly from that expected in ionisation
equilibrium. The fact that the I(1122.5 Å)/I(1128.3 Å) intensity
ratios determined from several flare spectra are closer to theory than
that for the active region indicates that the blending is probably due
to species with relatively low ionization potentials, as noted by Flower
and Nussbaumer (1975). Electron temperatures deduced for a sunspot are
much lower than that predicted from ionisation balance calculations,
in agreement with earlier results, and imply that a cooling flow may
be present.
---------------------------------------------------------
Title: The Mechanical Energy Budget in Stellar Flares
Authors: Doyle, J. G.
1988IBVS.3244....1D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transition regions of dM stars
Authors: Byrne, P. B.; Doyle, J. G.
1988ESASP.281a.319B Altcode: 1988uvai....1..319B; 1988IUE88...1..319B
Weak upper-chromospheric and transition region (TR) emission from two dM
stars (Gl784 and Gl825) were observed using deep IUE SWP exposures. In
addition to the usual TR lines, Lyman alpha fluxes for the two stars
were also determined. The relative importance of Lyman alpha and Mg II
as chromospheric coolants in the M dwarfs and the status of the X-ray/He
II (1640A) relationship in the light of these results are discussed.
---------------------------------------------------------
Title: UV flares on II Peg
Authors: Doyle, J. G.; Byrne, P. B.
1988ESASP.281a.307D Altcode: 1988uvai....1..307D; 1988IUE88...1..307D
Observations by IUE of the RS CVn star II Peg in the upper chromospheric
and transition regions lines Mg II k, C IV, and He II in Feb. 1983 show
evidence for flare activity. The electron pressure derived from the mean
of two different line ratios produces good agreement between the allowed
and intersystem lines in the differential emission measure curves. The
total radiative losses from the chromosphere and transition region for
the first flare on Feb. 2 is 2.46 times 10 to the 35th power erg, and
at least 1.91 times 10 to the 34th power erg, for the flare on Feb. 4.
---------------------------------------------------------
Title: EUV emission line ratios for Si IV in the solar transition
region.
Authors: Keenan, F. P.; Doyle, J. G.
1988JPhys..49..227K Altcode: 1988IAUCo.102..227K
Theoretical electron temperature sensitive emission line ratios in Si IV
involving the 3d <SUP>2</SUP>D - 3p <SUP>2</SUP>P and 4s <SUP>2</SUP>S
- 3p <SUP>2</SUP>P multiplets at ≡1125 Å and 816 Å respectively
are derived using R-matrix electron excitation rate calculations. A
comparison of these with observational data for a solar active
region obtained with the Harvard S-055 spectrometer on board Skylab
reveals that there is good agreement between theory and observation
for the ratio that includes the <SUP>2</SUP>D<SUB>3/2,5/2</SUB> -
<SUP>2</SUP>P<SUB>3/2</SUB> transition at 1128.3 Å.
---------------------------------------------------------
Title: Rotational modulation and flares on RS CVn and BY DRA
systems. VII. simultaneous X-ray, radio and optical data for the
dMe star YZ CMi on 4/5 March 1985.
Authors: Doyle, J. G.; Butler, C. J.; Bryne, P. B.; van den Oord,
G. H. J.
1988A&A...193..229D Altcode:
Broad-band photometric observations of YZ CMi show a 1.2mag U-band flare
at 19:55 UT on 4 March 1985, however, simultaneous X-ray observations
from EXOSAT show no detectable increase. Two possible explanations
for the lack of an X-ray flare may be i) a flare occurring low in the
chromosphere, where the chromosphere may not have been coupled to
the transition region and therefore the corona via magnetic fields
or ii) proton beam heating as opposed to electron beams. During the
flare, optical spectra show excess emission in the wings of all the
hydrogen Balmer lines. Interpreted in terms of mass flows would imply
material moving at ∼300 km s<SUP>-1</SUP> simultaneously to the
blue and red or alternatively random mass motions with a velocity
of a similar magnitude. At flare maximum, all the Balmer lines show
excess emission in the wings with Hγ and Hσ showing symmetrically
broadened lines while higher members of the series such as Hζ and
Hη show predominately red shifted material. Assuming a single loop
flare, an interpretation in terms of directed mass flows would imply a
loop of length ∼2-3 10<SUP>9</SUP> cm, however this would place the
material in the corona where we should have observed it in X-rays. An
alternative explanation, also assuming directed mass flows could
involve several small flare kernels, which brighten successively,
thus producing a broadened profile. An explanation similar to this
has been suggested to explain the excess emission seen in the wings
of Hα during solar flares. The total optical flare energy was ∼6
10<SUP>31</SUP> erg in this event, with the Balmer lines contributing
∼10% to the energy in the U-band during the flare. Many short-lived
bursts or micro-flares were detected in both the Johnson U-band and the
Balmer emission lines. The probability for a correlation between these
two data-sets to have occurred by chance was less than 10<SUP>-5</SUP>
. The coronal X-ray flux show only a moderate dependence on Balmer
line emission and none on the U-band variations. Thus for YZ CMi not
only does the large optical flare at 19:55 UT produce no significant
X-ray emission but also the low level optical flares, which are seen
almost continuously, are similarly absent in soft X-rays. Several X-ray
flares/micro-flares were observed, however the majority of these did not
show an optical counter-part. The largest of these X-ray events were at
18:00 UT and 23:30 UT, lasting an hour and 1 1/2 h respectively. Their
energy in the 0.02-2 keV range were 9.1 10<SUP>31</SUP> erg and 2.1
10<SUP>32</SUP> erg respectively. No optical data was available for
the first large X-ray flare, while the second event had only limited
coverage. The photometric data implied an optical energy of at least
2.6 10<SUP>31</SUP> erg. The Balmer line contribute at least 10%
to the U-band energy in both the 19:55 UT and 23:30 UT flares. Radio
observations at 326 MHz give an upper limit of 4 mJy for the flux.
---------------------------------------------------------
Title: An active hemisphere on II Peg.
Authors: Doyle, J. G.
1988A&A...192..281D Altcode:
IUE observations of the RS CVn star II Peg in the upper chromospheric
and transition regions lines Mg II k, C IV, and He II in 1981, 1983
and 1985 shows evidence for increased activity at certain phases. The
Mg II k line flux shows an above average value between phases 0.0
and 0.5. This is largely biased by the 1981 and 1983 data-sets,
although the 1985 data is consistent with a flux increase in this
phase interval. The C IV and He II flux show quite clear evidence of
an active hemisphere, although the 1985 data is less convincing than
the combined 1981 and 1983. This is perhaps explained by the reduced
number of observations in 1985, although an alternative explanation
may be a more even distribution of plages during 1985. The above would
therefore imply the presence of a long-lived plage region. The optical
spot migration rate from late 1981 to early 1986 was only 0.03 rotations
per year. The increase in the ultraviolet emission level occurs at the
time of the minimum in the optical light curve, therefore implying a
hot plage region overlying one of the cool optical spots.
---------------------------------------------------------
Title: Large photometric variations on II Peg in Sept/Nov 1986 :
implications for the starspot hypothesis.
Authors: Doyle, J. G.; Butler, C. J.; Morrison, L. V.; Gibbs, P.
1988A&A...192..275D Altcode:
Large cyclic photometric variations of ΔV= 0.5 mag are observed on
II Peg in late 1986. Modelled in terms of starspots, this implies a
large spot group covering at least 40% (and perhaps as much as 55%)
of the projected area of one hemisphere.
---------------------------------------------------------
Title: Rotational modulation and flares on RS CVn and BY DRA
systems. VIII. Simultaneous EXOSAT and H alpha observations of a
flare on the dMe star GL 644 AB (Wolf 630) on 24/25 August 1985.
Authors: Doyle, J. G.; Butler, C. J.; Callanan, P. J.; Tagliaferri,
G.; de La Reza, R.; White, N. E.; Torres, C. A.; Quast, G.
1988A&A...191...79D Altcode:
A large flare was detected simultaneously in X-rays and H-alpha on
the visual binary Gl 644 AB at about 00:15 UT on August 25, 1985. The
flare was detected with both the low (0.05-2 keV) and medium energy
(2-7 keV) experiments onboard Exosat, with the flare rise time being
similar in both the low and medium energy ranges, although in the low
energy the peak occurred about 30 s later. This was followed a few
minutes later by a second burst. The flare decay time lasted about 10
minutes longer in the low energy band than in the medium energy. The
integrated flare energy detected was 11.9 x 10 to the 32nd and 4.15
x 10 to the 32nd erg respectively in the low and medium energy X-rays
and 7 x 10 to the 31st erg in H-alpha. This gives an H-alpha flux of
approximately 4 percent of the total X-ray flux detected from the flare
or 6 percent of the low X-ray flare energy, similar to that observed in
a compact solar flare. Based on the observed cooling time, the flare
was estimated to have 2-3 loops of height about 10 to the 9th cm and
electron density of about 10 to the 12th/cu cm.
---------------------------------------------------------
Title: Coordinated photometry, spectroscopy and X-ray observations
of flare stars
Authors: Butler, C. J.; Doyle, J. G.; Foing, B. H.; Rodono, M.
1988ASSL..143..167B Altcode: 1988acse.conf..167B
The authors have compared the characteristics of flare activity in
UV Ceti and YZ CMi. Almost continuous variability is seen in Hγ and
U-band flux in both stars but only in UV Ceti does this correlate
strongly with soft X-rays. The relative fluxes in the Balmer emission
lines indicates higher densities in the chromospheres of these two
dMe stars as compared to the Sun.
---------------------------------------------------------
Title: Activity in late-type dwarfs. II. Flares and SPOT variations
on GL 867A (=FK Aqr) in 1981.
Authors: Byrne, P. B.; Doyle, J. G.
1987A&A...186..268B Altcode:
We present optical photometry of flares and spot variations on the
flare/BY Draconis star G1 867A (= FK Aqr). Time-integrated rates
of energy lost by optical flaring are derived and compared with
previously published results. No evidence of season-to-season changes
are evident. No spot variations were detected but there is an unusually
large scatter in the mean light curve.
---------------------------------------------------------
Title: Rotational modulation and flares on RS CVn and BY Dra-type
stars. V. EXOSAT and IUE observations of a flare on EQ Pegasi.
Authors: Haisch, B. M.; Butler, C. J.; Doyle, J. G.; Rodono, M.
1987A&A...181...96H Altcode:
Time-trailed UV spectra and a soft X-ray lightcurve were obtained
during a flare on the binary dMe star EQ Peg AB. On the basis of solar
flare Mg II surface fluxes and an about 70-percent enhancement in
the disk-integrated flux during the flare on EQ Peg, it is estimated
that the chromospheric flare covered about 1.5 percent of the stellar
surface. The size scale is estimated to be comparable to that of a solar
two-ribbon flare. This unusual flare is noted to exhibit a low-energy
soft X-ray rise phase which is longer than that of most flares; it
is longer than the decay phase and peaks much later than the medium
energy light curve. Evidence of variable Fe II emission and variable
continuum emission in select UV bands during the flare is noted.
---------------------------------------------------------
Title: Rotational modulation and flares on RS CVn and BY DRA
stars. VI. Physical parameters of the chromospheres/transition
regions of V711 Tau (HR 1099), II Peg and AR Lac during october 1981.
Authors: Byrne, P. B.; Doyle, J. G.; Brown, A.; Linsky, J. L.;
Rodono, M.
1987A&A...180..172B Altcode:
Ground-based optical and IUE satellite-ultraviolet observations of
three RS CVn stars are combined with density sensitive line ratios
and differential emission measure curves to describe the physical
conditions in their outer atmospheres. Solar-like densities are found
to be representative of average conditions on two of the stars, V 711
Tau and AR Lac. The total radiative losses from these two stars are
estimated and found to be larger than the sun by at least two orders of
magnitude. Consideration of the volume emitting in two of the principal
transition region lines suggests a possible relation between the disk
'filling factor' for these two lines and the dynamo-related Rossby
number. Only one hemisphere of the star II Peg, the one showing least
evidence of starspots, is similar. On the opposite hemisphere the
presence of a discrete emitting region is deduced which is almost
coincident in phase with the passage of the dominant optical spot
group across the visible disk. The dimensions of this region, and an
illustrative interpretation in terms of a large emitting magnetic loop,
are discussed. It is compared to large active region loops on the sun.
---------------------------------------------------------
Title: A rotational modulation effect in the flare frequency on
EV Lac.
Authors: Doyle, J. G.
1987A&A...177..201D Altcode:
Flare monitoring data in the Johnson B-band for the years 1973 to
1982 are discussed in terms of a rotational modulation effect. For
the period from 1973 to 1976, a correlation between flare frequency
and rotation period is evident, in the sense that a larger than
expected number of flares occurs on one hemisphere and a smaller
than expected on the other. This correlation is not evident in later
years. Photometric observations carried out during the years 1974/76
did not show any evidence of a wavelike variation in the light-curve,
which was apparent in later years.
---------------------------------------------------------
Title: Rotational modulation and flares on RS CVn and BY DRA
stars. III. IUEobserations of V711 Tau = (HR 1099), II Peg and AR Lac.
Authors: Rodono, M.; Byrne, P. B.; Neff, J. E.; Linsky, J. L.; Simon,
T.; Butler, C. J.; Catalano, S.; Cutispoto, G.; Doyle, J. G.; Andrews,
A. D.; Gibson, D. M.
1987A&A...176..267R Altcode:
The authors present observations of three RS CVn stars, which
were obtained over the stellar rotation cycles with the IUE
satellite. Emission lines from high-temperature transition regions
and chromospheres analogous to those observed in the solar spectrum
were observed. However, the stellar line surface fluxes are hundreds
of times the solar values. The only visible component of II Peg and
both components of V711 Tau and AR Lac appear to be chromospherically
active. The emission line fluxes for II Peg and, marginally, for the
other two systems were observed to vary in anti-phase with the optical
varations at the time of the authors' IUE observations. By comparing
the results of two-spot models from Paper I with the variation of UV
line flux, the authors find evidence of a close spatial correlation
between spot and plage-like features. They interpret these correlations
in terms of large spot areas in the stellar photospheres with overlying
magnetic loops, which form plages in the outer atmosphere.
---------------------------------------------------------
Title: A 155-DAY Period in Solar Flare Frequency
Authors: Doyle, J. G.
1987IrAJ...18...55D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotational modulation and flares on RS CVn and BY DRA
systems. II. IUE observations of BY Draconis and AU Microscopii.
Authors: Butler, C. J.; Doyle, J. G.; Andrews, A. D.; Byrne, P. B.;
Linsky, J. L.; Bornmann, P. L.; Rodono, M.; Pazzani, V.; Simon, T.
1987A&A...174..139B Altcode:
The modulation of the strong chromospheric and transition region lines
over one cycle of the optical light curves of BY Dra and AU Mic is
studied using IUE observations. The IUE observations were made from
October 2-5, 1981 and include 7 short wavelength (SW) spectra and 13
long wavelength (LW) spectra. The integrated line flux data reveal that
for BY Dra in the SW spectra there is modulation in the C IV, C II, O
I, and He II lines and nonflare surface fluxes; and in the LW spectra,
flares are detected in the Mg II and Fe II bands. It is observed that
there is no modulation in AU Mic, and the optical photometry data reveal
a poor correlation between optical flare strength and UV emission line
enhancements. The differential emission measure curves for BY Dra and
AU Mic are compared with solar curves. It is noted that both stars
show the presence of hot material throughout their rotation period.
---------------------------------------------------------
Title: Identification of forbidden lines from the N I-like ions SI
VIII, S X and AR XII
Authors: Doyle, J. G.
1987A&A...173..408D Altcode:
Line identification are given for several forbidden lines from
ions in the N I isoelectronic sequence, in particular Si VIII, S X
and Ar XII. Ratios for several of the observed lines were compared
with predicated values derived from the best atomic data currently
available. Due to the rather poor spectral resolution of the data,
the wavelengths cannot be considered better than ±0.5 Å.
---------------------------------------------------------
Title: An activity-rotation relationship in F-M dwarfs from MG II
H and K flux.
Authors: Doyle, J. G.
1987MNRAS.224P...1D Altcode:
Mg II h and k fluxes are given for late-type dwarfs whose rotation
periods are known. A good correlation between an activity parameter
R<SUB>hk</SUB> (represented by the ratio of Mg II h and k luminosity
to bolometric luminosity) versus the Rossby-number is found for
main-sequence stars F to late M. Both single and binary stars are
found to follow the same relation. A saturation of R<SUB>hk</SUB>
occurs at rotation periods of approximately 4 day, it is suggested that
stars whose rotation period is close to or shorter than this value are
completely covered by active plage regions, although an alternative
explanation may be saturation of the dynamo itself.
---------------------------------------------------------
Title: Proton Excitation Rate Coefficients and Cross Sections among
the Fine-Structure Levels of the (2s2p)<SUP>3</SUP> P State in
Be-like Ions
Authors: Doyle, J. G.
1987ADNDT..37..441D Altcode:
Proton excitation cross sections and rate coefficients are given
for the fine-structure transitions in the (2 s2 p) <SUP>3</SUP>P
state in the Be-like ions C III, N IV, O V, F VI, Ne VII, Mg IX, Si
XI, S XIII, Ar XV, Ca XVII, and Fe XXIII. In the low-energy region
we used the semiclassical Coulomb excitation method, while for the
intermediate-energy range, we used a close-coupling impact parameter
method. For the temperatures tabulated here, the rate coefficients
for all the transitions are better than 5%.
---------------------------------------------------------
Title: X-ray and optical observations of the flare star Wolf 630 AB
and of VB 8 G.
Authors: Tagliaferri, G.; White, N. E.; Giommi, P.; Doyle, J. G.
1987LNP...291..176T Altcode: 1987LNP87.291..176T; 1987csss....5..176T
Results from three EXOSAT observations of Wolf 630 AB are reported. Two
X-ray flares have been detected, one simultaneous with an Hα
flare. During the second observation a large increase in the X-ray
flux from the nearby star VB 8 was also detected.
---------------------------------------------------------
Title: Evidence for an Additional Source of Opacity During the
Impulsive Phase of Stellar Flares
Authors: Murphy, M.; Doyle, J. G.; Byrne, P. B.
1987LNP...291..170M Altcode: 1987LNP87.291..170M; 1987csss....5..170M
Broad-band photometric observations of YZ CMi show a 1.2 magnitude
U-band flare at 19:55 UT on 4 March 1985. During the flare the Ca I
feature at 4227A changed dramatically. In the spectrum taken during
the rise phase, Ca I was both narrower and weaker than that of either
the preflare spectrum or spectra taken later in the flare. We interpret
this as evidence that the photospheric flare continuum observed here is
a combination of a normal dM4.5e continuum plus an overlying continuum
with a temperature of less than 4000 - 5000 K and a pressure of at
least an order of magnitude less than the photosphere of a dM4.5e star.
---------------------------------------------------------
Title: A Survey of Ly Alpha and Mg II Fluxes for a Sample of Dwarf
M Stars
Authors: Doyle, J.
1987iue..prop.3009D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Broadening of Hydrogen Balmer Lines During a Flare on the
dMe Star YZ CMi
Authors: Doyle, J. G.; Byrne, P. B.
1987LNP...291..173D Altcode: 1987csss....5..173D; 1987LNP87.291..173D
Broad-band photometric observations of YZ CMi show a 1.2 magnitude
U-band flare at 19:55 UT on 4 March 1985. During the flare, optical
spectra show excess emission in the wings of all the hydrogen Balmer
lines. Interpreted in terms of mass flows would imply material
moving at ∼300 km s<SUP>-1</SUP> simultaneously to the blue and
red or alternatively random mass motions with a velocity of a similar
magnitude. At flare maximum, all the Balmer lines show excess emission
in the wings with H α and 11 δ showing symmetrically broadened
lines while higher members of the series such as H ζ and H η show
predominately red shifted material.
---------------------------------------------------------
Title: Active Phases on II Peg
Authors: Panagi, P.; Doyle, J. G.
1987LNP...291..488P Altcode: 1987csss....5..488P; 1987LNP87.291..488P
Analysis of HE data for 1981, 1983 and 1985 II Peg show evidence
of a long-lived plage region in Mg II k, C IV and He II. This UV
enhancement is in anti-correlation with the maximum spot visibility
and would imply a hot plage region overlying the cool photospheric
spot. The optical spot migration rate from late 1981 to early 1986
was only 0.03 rotations per year.
---------------------------------------------------------
Title: Characterization of the Total Flare Energy
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veek, N. J.
1986epos.conf.5.41W Altcode: 1986epos.confE..41W
No abstract at ADS
---------------------------------------------------------
Title: Energetics of the Impulsive Phase
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veek, N. J.
1986epos.conf..5.5W Altcode: 1986epos.confE...5W
No abstract at ADS
---------------------------------------------------------
Title: Energetics of the Gradual Phase
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veek, N. J.
1986epos.conf.5.20W Altcode: 1986epos.confE..20W
No abstract at ADS
---------------------------------------------------------
Title: Review of Impulsive Phase Phenomena
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veek, N. J.
1986epos.conf.5.60W Altcode: 1986epos.confE..60W
No abstract at ADS
---------------------------------------------------------
Title: Flares Chosen for Energetics Study
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veek, N. J.
1986epos.conf.5.47W Altcode: 1986epos.confE..47W
No abstract at ADS
---------------------------------------------------------
Title: Relationships among the Phases
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veek, N. J.
1986epos.conf.5.39W Altcode: 1986epos.confE..39W
No abstract at ADS
---------------------------------------------------------
Title: Simultaneous X-ray and optical monitoring of the flare star
YZ CMi.
Authors: Doyle, J. G.; Butler, C. J.; Haisch, B. M.; Rodono, M.
1986MNRAS.223P...1D Altcode:
Broad-band photometric observations of YZ CMi show a 1.2 mag U-band
flare, however, simultaneous X-ray observations from EXOSAT show no
detectable increase. It is suggested that the event could have occurred
low down in a part of the chromosphere, which may not have been coupled
to the transition region and corona via magnetic fields. However,
a more plausible explanation may have been absorption of the X-rays
by an over-lying dense prominence. Several short-lived enhancements
(micro-flares) were detected in both the Johnson U-band and the Balmer
emission lines.
---------------------------------------------------------
Title: Rotational modulation and flares on RS CVn and BY Dra-type
stars. I. Photometry and SPOT models for BY Dra, AU Mic, AR Lac,
II Peg and V711 Tau (=HR 1099).
Authors: Rodono, M.; Cutispoto, G.; Pazzani, V.; Catalano, S.;
Byrne, P. B.; Doyle, J. G.; Butler, C. J.; Andrews, A. D.; Blanco,
C.; Marilli, E.; Linsky, J. L.; Scaltriti, F.; Busso, M.; Cellino,
A.; Hopkins, J. L.; Okazaki, A.; Hayashi, S. S.; Zeilik, M.; Helston,
R.; Henson, G.; Smith, P.; Simon, T.
1986A&A...165..135R Altcode:
Multicolor wide-band photometry of five active stars is presented. The
observations were carried out at several places before, during and
after the period of IUE observations for the purpose of determining
the location, sizes, and evolution of photospheric spots at the time
when chromospheric, transition region, and coronal activity data were
obtained from UV and radio observations. II Peg, BY Dra, and AU Mic
show fairly stable quasi-sinusoidal light curves, while AR Lac and V
711 Tau show double-peaked light curves. For V 711 Tau, a remarkable
evolution of the spotted area extent and/or longitude distribution
is found. Small, but definite color variations that are consistent
with the cool spot hypothesis have also been detected for BY Dra,
II Peg and V 711 Tau.
---------------------------------------------------------
Title: Optical photometry and spectroscopy for five dwarf M stars.
Authors: Doyle, J. G.; Byrne, P. B.; Menzies, J. W.
1986MNRAS.220..223D Altcode:
The authors report on a search for flaring and BY Dra (spotted)
variations on five M-dwarf stars, Gliese 1, 461, 825, 899 and 908. The
results for Gl 461 and 825 are compared with predictions of activity
levels based on the measured quiescent X-ray flux. The chromospheric
radiative loss rate in the Ca H and K lines are determined for Gl 461.
---------------------------------------------------------
Title: Plasma densities from the He-like ion NE IX
Authors: Doyle, J. G.; Keenan, F. P.
1986A&A...157..116D Altcode:
The authors present line emissivity data for the three principal lines
of the He-like ion Ne IX. This data is compared with high resolution
solar flare observations from the Solar Maximum Mission. During the
rise phase of flares it is shown that the forbidden line is blended
with a high temperature line, as opposed to the intercombination line
suggested by McKenzie (1985). It is suggested that the electron density
during the rise phase of flares be determined from the intercombination
to resonance line ratio which the authors have integrated over a
multi-thermal plasma and is shown to be only slightly dependent on
the assumed differential emission measure distribution. Scattering
of resonance line photons from the line-of-sight is shown to be
unimportant.
---------------------------------------------------------
Title: Coordinated IUE and ground-based observations of stellar
flares: YZ CMi, Proxima Cen and AD Leo.
Authors: Foing, B. H.; Rodono, M.; Cutispoto, G.; Catalano, S.; Linsky,
J. L.; Gibson, D. M.; Brown, A.; Haisch, B. M.; Butler, C. J.; Byrne,
P. B.; Andrews, A. D.; Doyle, J. G.; Gary, D. E.; Henry, G. W.; Russo,
G.; Vittone, A.; Scaltriti, F.
1986RMxAA..12..213F Altcode:
Coordinated observations of stellar flares were obtained with lUE
and several ground-based facilities in March 1984.The simultaneous
observations allowed it to cover a wide range of wavelengths from ii5nm
to 6cm.We intend to study the effect ofthe observed flares at different
atmospheric heights in order to estimate the energy budget,the time
scales and the cooling processes.Our observations includetime-resolved
IUE spectroscopy at SWP(115-195nm) and LWP(190-320nm),optical
spectroscopy at the ESO 3.6m+IDS (355-440nm),high resolution
spectroscopy at the ESO 1.4m CAT+CES(653-659nm),narrow band H alpha
and wide band optical photometry, infrared photometry at 2.2microns
and microwave observations at 2,6 and 20 cm We present for some
flare events,among the results,the first detection of infrared flux
decrease -or "negative flare"-in coincidence with the flux increase
at the other wavelengths:the broadening and changes of the Balmer H
lines,He and high excitation lines;the appearance of higher members
of the Balmer serie;the enhancements of Mg II doublet and Fe II blend
(260nm);and the flare detection at 2cm and 6cm
---------------------------------------------------------
Title: Broadening of soft X-ray lines during the impulsive phase of
solar flares - Random or directed mass motions?
Authors: Doyle, J. G.; Bentley, R. D.
1986A&A...155..278D Altcode:
The authors present spectroscopic data for three flares obtained with
the Bent Crystal Spectrometer flown in the Solar Maximum Mission in
1980. This data is concerned with the structure of the Ca XIX resonance
line at 3.176 Å during the impulsive phase of flares. On the basis of
high time resolution (6s.) data, the authors suggest that the previous
published results concerned with the excess broadening of the resonance
line being due to bulk random mass motions may give an over-simplified
picture. Instead the authors suggest that during this stage of the
flare, the resonance line consists of many discrete features, which
are interpreted as mass flows.
---------------------------------------------------------
Title: Trajectory Determinations and Collection of Micrometeoroids
on the Space Station
Authors: Doyle, J. G.; Byrne, P. B.; Butler, C. J.
1986A&A...156..283D Altcode:
We report on a search for flaring and BY Draconis type variability on
the M-dwarf Balmer emission line star, Gliese 867 B. The time-averaged
flare energy in the Johnson U-band is similar to that measured in 1977
and 1978. A typical wave4ike variation of 0.15 magnitudes, seemingly
due to rotational modulation of large spotted areas, was observed in
the V-band with a period 1.95 days.
---------------------------------------------------------
Title: Correlation of the Mg II h & k flux versus rotational
period in late-type stars
Authors: Doyle, J. G.
1986LNP...254...33D Altcode: 1986csss....4...33D
A correlation between the Mg h & k flux and the rotation period
for main-sequence F to K stars has been extended to include all dMe
stars with known rotational periods. It is shown that the relationship
proposed by Hartmann et al for F to K stars does extend to the dMe
stars, although there is more scatter. This is in part due to our
inability to use the parameter representing the convective-overturn
time.
---------------------------------------------------------
Title: Faint optical flares from the dwarf M star Gliese 812
(Ross 193).
Authors: Doyle, J. G.; Byrne, P. B.
1986A&A...154..370D Altcode:
The authors report on a search for flaring on the Balmer emission line
star, Gliese 812. Three flares were detected in a total monitoring
time of 11.66 h. The time-averaged flare energy in the Johnson U-band
is substantially smaller than in other stars of similar absolute U
magnitude, such as AD Leo, EQ Peg and EV Lac.
---------------------------------------------------------
Title: Flare activity and by-Draconis type variability on the
late-type dMe star gliese 867B
Authors: Doyle, J. G.; Byrne, P. B.; Butler, C. J.
1986LNP...254..231D Altcode: 1986csss....4..231D
We report on an analysis of flaring and BY-Draconis type variability
on the Balmer emission line star, Gliese 867B. The time-averaged flare
energy in the Johnson 1-band is similar to that measured in 1977 and
1978. A variation of 0.15 magnitudes was observed in the V-band with
a period l.95 days.
---------------------------------------------------------
Title: Simultaneous X-Ray and Photometric Observations of the Flare
Star YZ CMi
Authors: Doyle, J. G.; Butler, C. J.
1986LNP...254..228D Altcode: 1986csss....4..228D
Broad-band photometric observations of YZ CMi show a 1.2 magnitude
U-band flare, however, simultaneous X-ray observations from EXOSAT show
no detectable increase. It is suggested that the energy was dissipated
before reaching the corona. Two long duration U-band enhancements
detected during the optical monitoring may have been the result of
back-heating from an enhanced coronal X-ray flux.
---------------------------------------------------------
Title: IUE Observations of Surface Structures on II PEG
Authors: Doyle, J.
1986iue..prop.2681D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flare energetics.
Authors: Wu, S. T.; de Jager, C.; Dennis, B. R.; Hudson, H. S.;
Simnett, G. M.; Strong, K. T.; Bentley, R. D.; Bornmann, P. L.; Bruner,
M. E.; Cargill, P. J.; Crannell, C. J.; Doyle, J. G.; Hyder, C. L.;
Kopp, R. A.; Lemen, J. R.; Martin, S. F.; Pallavicini, R.; Peres,
G.; Serio, S.; Sylwester, J.; Veck, N. J.
1986NASCP2439....5W Altcode:
In this investigation of flare energetics, the authors establish a
comprehensive and self-consistent picture of the sources and transport
of energy within a flare. They chose five flares in 1980 that were
well observed with instruments on the SMM, and with other space-borne
and ground-based instruments. Details of the observations available
for them and the corresponding physical parameters derived from these
data are presented. The flares were studied from two perspectives,
the impulsive and gradual phases, and then the results were compared
to obtain the overall picture of the energetics of these flares. The
authors also discuss the role that modeling can play in estimating the
total energy of a flare when the observationally determined parameters
are used as the input to a numerical model.
---------------------------------------------------------
Title: The extreme ultraviolet spectrum of sunspot plumes. I -
Observations
Authors: Noyes, R. W.; Raymond, J. C.; Doyle, J. G.; Kingston, A. E.
1985ApJ...297..805N Altcode:
A complete extreme ultraviolet spectrum of a sunspot plume by the Skylab
S-055 spectroheliometer is presented, and the relevant observational
details are discussed. Identifications and intensities are given for
emission lines and continua in the 303-1343 A range. The emission from
lines found between 100,000 and a million K are enhanced by up to a
factor of 40 compared with quiet and active region spectra. The emission
measure curve for the mean spectrum shows a high double peak at log T
= 5.7 and 6.0, reflecting the very inhomogeneous spatial structure of
the sunspot plumes. The extremely high signal to noise of the spectrum
is used to investigate the electron density and ionization stage of
the gas based on line ratio techniques. A model of line emission from
a gas cooling by radiation alone at constant density is presented,
and the observations are compared with various semiempirical and
theoretical models.
---------------------------------------------------------
Title: The Extreme Ultraviolet Spectrum of Sunspot Plumes - Part Two -
Spectral Diagnostics and Implications for Cooling
Authors: Doyle, J. G.; Raymond, J. C.; Noyes, R. W.; Kingston, A. E.
1985ApJ...297..816D Altcode:
The extreme ultraviolet emission-line spectrum of very intense sunspot
plumes is analyzed. Several of the standard density diagnostics
suggest a constant density, rather than constant pressure, emitting
region. Temperature diagnostic line ratios of several ions yield
temperatures below those expected in ionization equilibrium (and
observed in the quiet Sun). This provides strong evidence for the
suggestion that the internal energy of cooling, falling gas accounts for
the observed radiation. The lack of such departures from equilibrium in
the quiet Sun demonstrates that downflows are not the dominant source
of energy at transition region temperatures. We assess the accuracy
of several atomic rate coefficients.
---------------------------------------------------------
Title: Interpretation of EUV spectra from loop structures in an
active region at the limb
Authors: Doyle, J. G.; Mason, H. E.; Vernazza, J. E.
1985A&A...150...69D Altcode:
EUV spectral scans and rasters of an active region observed at
the limb are analyzed. These were obtained with the Harvard EUV
spectroheliometer on the Apollo Telescope Mount. The spectra were
taken following a small flare and an H-alpha surge. Diagnostic line
ratios are used to determine electron densities and temperatures from
the spectral scans. An electron pressure of 10 to the 15th/cu cm K
is derived at 200,000 K. The temperatures derived from the diagnostic
ratios indicate that the plasma is in ionization equilibrium, although
mass flows of a few kilometers per s could be present. Rasters of
the active region taken later show well defined loop structures. The
parameters derived from the low temperature lines (100,000 K) and the
rasters are inconsistent with those inferred from scaling laws based
on static loop models. However, better agreement between the derived
parameters and the models is achieved if use is made of the electron
density derived from the emission measure of Mg X, and it is assumed
that it remains constant up to 5-million K.
---------------------------------------------------------
Title: Flare Activity and the Quiescent X-ray Emission in dMe Stars
Authors: Doyle, J. G.; Butler, C. J.
1985ASSL..116..237D Altcode: 1985rst..conf..237D
Einstein observations of the X-ray flux of quiescent dwarf Me stars
are correlated with the time-averaged energy emitted by flares in the
Johnson U band. It is shown that the energy emitted by the coronae of
these stars in X-rays is about an order of magnitude greater than the U
band flare energy. From an estimate of the ratio of the total radiation
emitted to the U band flux, it seems possible that if a similar amount
of mechanical energy was dissipated in the stellar atmosphere, then
the observed flare events can provide sufficient energy to heat the
coronae of these stars.
---------------------------------------------------------
Title: Energetics of a double flare on November 8, 1980
Authors: Doyle, J. G.; Byrne, P. B.; Dennis, B. R.; Emslie, A. G.;
Poland, A. I.; Simnett, G. M.
1985SoPh...98..141D Altcode:
Here we complete an energy balance analysis of a double impulsive
hard X-ray flare. From spatial observations, we deduce both
flares probably occur in the same loop within the resolution of the
data. For the first flare, the energy in the fast electrons (assuming
a thick-target model) is comparable to the convective up-flow energy,
suggesting that these are related successive modes of energy storage and
transfer. The total energy lost through radiation and conduction, 2.0 ×
10<SUP>28</SUP> erg, is comparable to the energy in fast electrons 2.5
× 10<SUP>28</SUP> erg. For the second flare, the energy in the fast
electrons is more than one order of magnitude greater than the energy
of the convective up-flow. Total energy losses are within a factor
of two lower than the calculated fast electron energy. We interpret
the observations as showing that the first flare occurred in a small
loop with fast electrons heating the chromosphere and resulting in
chromospheric evaporation increasing the density in the loop. For the
second flare most of the heating occurred at the electron acceleration
site. The two symmetrical components of the Ca XIX resonance line and a
high velocity down-flow of 115 km s <SUP>−1</SUP> observed at the end
of the second hard X-ray burst are consistent with the flare eruption
(reconnection) region being high in the flare loop. The estimated
altitude of the acceleration site is 5500 km above the photosphere.
---------------------------------------------------------
Title: Optical photometry and spectroscopy of the flare star Gliese
229 (=HD42581).
Authors: Byrne, P. B.; Doyle, J. G.; Menzies, J. W.
1985MNRAS.214..119B Altcode:
The authors present optical flare photometry and a search for spotted
variations on the star Gl 229. These results rule out the presence of
a large-scale asymmetric spot distribution and indicate a low level of
flare activity. This is in agreement with other indicators of stellar
activity including coronal X-ray emission and radiative losses from
the lower chromosphere as gauged from the strength of Ca H and K and
the Balmer lines.
---------------------------------------------------------
Title: Ultrviolet Radiation from Stellar Flares and its Relation to
the Coronal X-Ray Emission for dMe Stars
Authors: Doyle, J. G.; Butler, C. J.
1985IrAJ...17...19D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet radiation from stellar flares and the coronal
X-ray emission for dwarf-Me stars
Authors: Doyle, J. G.; Butler, C. J.
1985Natur.313..378D Altcode:
The origin of chromospheric and coronal emission is thought
to derive ultimately from magnetic fields generated by a
dynamo mechanism involving the interaction of rotation and
convection<SUP>1</SUP>. Although these magnetic fields are difficult to
detect directly, the dramatic stellar flares, believed to be the result
of magnetic reconnection, have been observed for many years on dwarf
Me (dMe) stars. Here we correlate Einstein observations of the X-ray
flux of quiescent dMe stars with the time-averaged energy emitted by
flares in the Johnson-U band, showing that the X-ray energy emitted
by the coronae of these stars is about an order of magnitude greater
than the U-band flare energy. From our estimate of the ratio of the
total radiation emitted to the U-band flux, it is possible that, if
a similar amount of energy were dissipated in the stellar atmosphere,
then the observed flare events could heat the coronae of these stars.
---------------------------------------------------------
Title: Optical photometry and UV spectroscopy of the flare star GL
735 (=V1285 Aql).
Authors: Byrne, P. B.; Doyle, J. G.; Butler, C. J.; Andrews, A. D.
1984MNRAS.211..607B Altcode:
The authors present optical photometry of flares and possible spot
variations on the star Gl 735. Consideration of the energetics of the
optical flares suggests that the star may be underactive when compared
to other flare stars of the same spectral type. This conclusion is
not supported however by an estimate of the radiative loss rate from
the lower chromosphere due to Mg II h and k. Radiative losses from the
upper chromosphere, transition zone and corona are also normal for a
flare star of its spectral type.
---------------------------------------------------------
Title: Erratum - Solar Maximum Mission Observations of a Compact
Flare - Interpretation and Theoretical Implications for Flare Theory
Authors: Doyle, J. G.; Byrne, P. B.
1984IrAJ...16..286D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Mg ix and Si xi line ratios in the sun
Authors: Keenan, F. P.; Kingston, A. E.; Dufton, P. L.; Doyle, J. G.;
Widing, K. G.
1984SoPh...94...91K Altcode:
New theoretical emission line ratios for the Be-sequence ions
MgIX and SiXI are presented. A comparison with observational
data for two solar flares and an active region loop obtained
with the Harvard EUV spectrometer and NRL XUV spectroheliograph
aboard Skylab reveals that these plasmas are in ionization
equilibrium at coronal temperatures. Unfortunately most of the
density diagnostics are not particularly useful under solar plasma
conditions, as they vary only slightly over the electron density
range 10<SUP>8</SUP>-10<SUP>13</SUP>cm<SUP>−3</SUP>. However
the SiXI ratioI(<SUP>3</SUP>P<SUP>e</SUP><SUB>2</SUB>
-<SUP>3</SUP>P<SUP>o</SUP><SUB>2</SUB>)/I(<SUP>3</SUP>P<SUP>o</SUP><SUB>1</SUB>
-<SUP>1</SUP>S<SUP>e</SUP><SUB>0</SUB>) is density sensitive in the
range 10<SUP>8</SUP> to 10<SUP>10</SUP>cm<SUP>−3</SUP>, which is
representative of electron densities found in solar active regions or
small flares.
---------------------------------------------------------
Title: Rotational modulation of spots and plages on RS CVn stars.
Authors: Byrne, P. B.; Doyle, J. G.; Andrews, A. D.; Butler, C. J.;
Marstad, N.; Linsky, J. L.; Simon, T.; Rodono, M.; Catalano, S.;
Blanco, C.; Marilli, E.; Pazzani, V.
1984ESASP.218..343B Altcode: 1984iue..conf..343B
Observations of three RS CVn stars made with the IUE satellite are
presented. Emission line fluxes are found to vary in anti-phase with the
stars' optical variations. The authors interpret these correlations in
terms of large-scale spots in the stellar photospheres with overlying
magnetic loops, giving rise to non-thermal heating of the layers above
the spots. Evidence of nonthermal gas motions is also presented which
appear to be associated with the most active regions of the stars.
---------------------------------------------------------
Title: Atmospheric Structure of RS CVN Stars
Authors: Doyle, J.
1984iue..prop.2022D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coordinated IUE and ground-based observations of active stars:
flare events on YZ CMi, V1005 Ori, AD Leo and AR Lac.
Authors: Rodonò, M.; Cutispoto, G.; Catalano, S.; Linsky, J. L.;
Gibson, D. M.; Brown, A.; Haisch, B. M.; Butler, C. J.; Byrne, P. B.;
Andrews, A. D.; Doyle, J. G.; Gary, D. E.; Henry, G. W.; Russo, G.;
Vittone, A.; Scaltriti, F.; Foing, B.
1984ESASP.218..247R Altcode: 1984iue..conf..247R
Observations of stellar flares were obtained with IUE and ground-based
facilities simultaneously over a wide range of wavelengths in order
to study the effect of the flare radiation at different atmospheric
levels. Observations include time-resolved IUE and optical spectroscopy,
narrow and wide-band optical photometry, IR photometry, and microwave
observations. Results include detection of IR flux decrease, or negative
flare, in coincidence with flux increase at all other wavelengths.
---------------------------------------------------------
Title: IUE observations of BY Draconis.
Authors: Butler, C. J.; Doyle, J. G.; Andrews, A. D.; Byrne, P. B.;
Linsky, J. L.; Simon, T.; Marstad, N. C.; Rodono, M.; Pazzani, V.;
Cutispoto, C.
1984ESASP.218..243B Altcode: 1984iue..conf..243B
Phased IUE low resolution observations of BY Draconis are
discussed. They show no significant modulation of the prominent
SWP emission lines over one rotation period. However a marginally
significant anticorrelation of the MgII flux, and the flux in the LWR
continuum, with the V light curve is observed, and is interpreted as
due to plage type areas over the photospheric spots. Two SWP spectra
show sporadic enhancements of the emission lines, as seen in other
IUE spectra of flares.
---------------------------------------------------------
Title: Derivation of ionization balance for calcium XVIII/XIX using
XRP solar X-ray data
Authors: Antonucci, E.; Gabriel, A. H.; Doyle, J. G.; Dubau, J.;
Faucher, P.; Jordan, C.; Veck, N.
1984A&A...133..239A Altcode:
Spectra of calcium from solar flares are used in an attempt to derive
an ionization balance for Ca XVIII/Ca XIX. The isothermal assumption
inherent in this derivation is shown not to introduce errors, by
modelling a number of hypothetical nonisothermal plasmas. The unresolved
blend of calcium and argon lines prevents a definitive determination of
the results, owing to uncertainties in the ratio of abundances of these
elements. The resulting ionization balance curves are presented as a
function of the solar argon/calcium abundance ratio. The theoretical
ionization balance of Doyle and Raymond is consistent with the data. To
within the expected accuracy of the atomic theories, there is no reason
to assume that the flare plasma is other than close to steady-state
ionization balance.
---------------------------------------------------------
Title: SMM Observations of a Compact Flare.Interpretation and
Theoretical Implications of Flare Theory
Authors: Doyle, J. G.; Byrne, P. B.
1984IrAJ...16..226D Altcode:
In the present completion of an energy balance analysis for a
double impulsive, hard X-ray flare, it is deduced on the basis
of spatial observations that both flares occurred in the same
loop. From observations of the Ca XIX resonance line during the
second flare's hard X-ray burst, it appears that two symmetrically
displaced components are moving apart at thermal velocities of about
60 km/sec. These are interpretable in terms of in situ heating, where
most of the fast electrons are stopped in the loop close to the site
of the acceleration (and long before they reach the chromosphere)
to produce the 'evaporated' up-flow. The two symmetrical components,
and a high velocity downflow of 115 km/sec observed at the end of
the second hard X-ray burst, are consistent with the flare eruption
region's location high in the flare loop.
---------------------------------------------------------
Title: Optical photometry and ultraviolet spectroscopy of the flare/BY
DRA star GL 182(V 1005 Ori).
Authors: Byrne, P. B.; Doyle, J. G.; Butler, C. J.
1984MNRAS.206..907B Altcode:
G1 182 was previously reported to be a rapidly rotating BY Dra star
which flares at an anomalously high rate. The present observations
confirm its BY Dra nature but revise the rotation period, such that it
is shown to rotate much more slowly. The time-averaged energy output
in flares is shown to be normal for a flare star of its spectral type,
and its rate of flaring is normal. IUE spectra show chromospheric
features whose surface fluxes compare with those of BY Dra itself.
---------------------------------------------------------
Title: Flare parameters for the 7 September, 1973 two-ribbon flare
Authors: Doyle, J. G.; Raymond, J. C.
1984SoPh...90...97D Altcode:
A study is made of the relative importance of the various energy loss
mechanisms for the long-decay event of 7 September, 1973, using spectral
scans in the 400 Å-1335 Å range. This spectral range contains many of
the important electron density and temperature diagnostic line ratios
for the solar transition zone. We refine earlier analyses of the flare
energy budget using more detailed emission measure curves and density
diagnostics. We examine the constant pressure assumptions used in
both coronal loop models and in the interpretation of observations in
terms of flare energetics. We find that much of the upper transition
region emission originates in cooling loops. Radiative losses are
found to dominate.
---------------------------------------------------------
Title: Compte rendu du Symposium de l'I. U. A. A. à Charleroi,
18-20 février 1983
Authors: Doyle, J.
1984C&T...100...34D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Line ratios for solar ultra-violet lines of O v
Authors: Doyle, J. G.; Dufton, P. L.; Keenan, F. P.; Kingston, A. E.
1983SoPh...89..243D Altcode:
New O V rate coefficients are used to calculate the ratio of the
intensity of the 760 Å multiplet to that of the 630 Å line. Results
are given for a range of electron densities and temperatures. The
theoretical ratios are compared with observed line ratios for different
solar regions.
---------------------------------------------------------
Title: A line identification list for the solar flare of 7 September,
1973 in the wavelength range 1335 Å 380 Å
Authors: Doyle, J. G.
1983SoPh...89..115D Altcode:
A wavelength list is presented for the solar flare of 7 September,
1973 in the spectral range 1335 Å-380 Å. The ions observed suggest
a range of temperatures in the flare plasma from 8 × 10<SUP>3</SUP>
K to 10<SUP>7</SUP> K. This wavelength range contains many of the
important electron density diagnostics lines for the solar transition
zone and corona. The line list should also be of potential use in the
identification and comparison with stellar spectra.
---------------------------------------------------------
Title: CA XVII line ratios in solar flares
Authors: Dufton, P. L.; Kingston, A. E.; Doyle, J. G.; Widing, K. G.
1983MNRAS.205...81D Altcode:
New electron impact collision rates are presented for transitions
between the 10 lowest states of Ca XVII. These data are then used
to predict Ca XVII level populations and emission-line intensity
ratios for electron densities and temperatures appropriate to solar
flares. A comparison is made with observations obtained with the NRL
spectroheliograph aboard Skylab. For the intercombination to resonance
line ratio the agreement is good. For other triplet to singlet ratios
agreement is less satisfactory, possibly due to uncertainties in the
observational data.
---------------------------------------------------------
Title: X-ray line ratios from helium-like ions - Updated theory and
SMM flare observations
Authors: Wolfson, C. J.; Leibacher, J. W.; Doyle, J. G.; Phillips,
K. J. H.
1983ApJ...269..319W Altcode:
The potential which the conduction of measurements of the three
principal lines emitted from helium-like ions has for the determination
of plasma electron density was initially pointed out by Gabriel and
Jordan (1969). The diagnostic technique is based on the fact that
the ratio, R, of the intensity of a forbidden line to the intensity
of an intercombination line decreases as electron density increases
due to collisional excitation of levels. In the present investigation
a further refinement of this procedure is provided by specifically
calculating the effects of cascades from levels with principal quantum
numbers up to n=6. Two improved spectrometers recently placed in
operation include the SOLEX instrument on the satellite P78-1 and the
X-ray Polychromator (XRP) instrument on the NASA Solar Maximum Mission
satellite. Measurements obtained with one of the spectrometers making up
the XRP are presented, taking into account the emission from Ne IX ions.
---------------------------------------------------------
Title: Line ratios for O VII
Authors: Doyle, J. G.; Tayal, S. S.; Kingston, A. E.
1983MNRAS.203P..31D Altcode:
New theoretical rates for electron excitation of the transitions
1<SUP>1</SUP>S-2<SUP>3</SUP>S and 1<SUP>1</SUP>S-2<SUP>3</SUP>P in O
VII are used to calculate the line ratios R<SUB>0</SUB> (forbidden
line to intercombination line) and G<SUB>0</SUB> (forbidden plus
intercombination lines to resonance line). The authors' theoretical
value of R<SUB>0</SUB> are slightly larger than earlier calculations
but their values of G<SUB>0</SUB> are significantly lower than the
earlier calculations. With their results the value of G<SUB>0</SUB>
= 1.0, from the solar observations of McKenzie & Landecker, would
predict an electron temperature of 2.0×10<SUP>6</SUP>K, which is in
good agreement with the temperature of 1.8×10<SUP>6</SUP>K predicted
by recombination-ionization equilibrium calculations.
---------------------------------------------------------
Title: IUE spectra of the BY Dra/flarestar AU MIC
Authors: Butler, C. J.; Andrews, A. D.; Doyle, J. G.; Byrne, P. B.;
Linsky, J. L.; Simon, T.; Marstad, N.; Rodono, M.; Pazzani, V.
1983ASSL..102..249B Altcode: 1983ards.proc..249B; 1983IAUCo..71..249B
Ground-based optical and IUE observations of BY Dra variables undertaken
to follow the spectral variation of these stars over one cycle are
discussed. It is noted that in the first series, 20 LWR and 19 SWP
trailed spectra were taken of AU Mic over a three-day period, August
4-6, 1980. The mean integrated flux are shown here for the strong
emission lines in th SWP spectra of AU Mic over the observed phase
interval of 0.14 to 0.8, together with an approximate V light curve
determined by the FES and IUE. Several points emerge from comparing
the emission line intensities and FES magnitudes. The first is that
the light curve at this time had at least three and possibly four
minima. If this is to be interpreted as deriving from the rotation of
a spotted star, several spotted regions would be required, distributed
in stellar longitude. The second point is that repeated flaring of AU
Mic makes it difficult to perceive any clearly defined modulation of
the emission line intensities owing to plage regions in the vicinity
of the spots. The third point is that following flare activity during
SWP 9695 and WP 9698, it appears that the intensity of the HeII and
SiII lines has remained high for some time after the drop in intensity
of the CIV line.
---------------------------------------------------------
Title: The interpretation of EUV spectra of sunspots
Authors: Doyle, J. G.; Raymond, J. C.; Noyes, R. W.; Kingston, A. E.
1983ASSL..102..325D Altcode: 1983ards.proc..325D; 1983IAUCo..71..325D
EUV observations of a sunspot made on Skylab are discussed. For the
60,000-300,000 K temperature range, a constant electron density of
10 billion/cu cm fits the data, while for the million K plasma the
density decreases by an order of magnitude and a constant pressure
approximation. Temperature diagnostic line ratios show temperatures
lower than the equilibrium temperature and lower than the temperatures
observed in the averaged quiet sun. The observed departure from
ionization equilibrium is consistent with those expected for a
radiatively cooling gas. A model which assumes a constant density
and a constant velocity flow of 7 km/s beginning in ionization
equilibrium at log T = 5.8 matches the overall energetic needs for
the transition region and accounts for the observed shift away from
ionization equilibrium.
---------------------------------------------------------
Title: An Emission Measure Analysis of Two Sunspots Observed by the
UVSP Instrument on the SMM Spacecraft
Authors: Kingston, A. E.; Doyle, J. G.; Dufton, P. L.; Gurman, J. B.
1982SoPh...81...47K Altcode:
The EUV observations from the SMM satellite of two sunspots are
presented here. These observations show the sunspots (a) to be
regions of lower intensity than the surrounding plage, contrary to
that found by previous authors, and (b) to have line intensities
which vary little over a period of several hours. An upper limit to
mass flows of 2km s<SUP>-1</SUP> is derived, indicating a relatively
simple energy balance for the chromosphere-corona transition zone
with thermal conduction being balanced by radiative losses. Electron
densities derived from NIV to CIV line ratios imply electron pressures
(log N<SUB>e</SUB>T<SUB>e</SUB>) of 15.0 to 15.3.
---------------------------------------------------------
Title: Solar Maximum Mission Workshops
Authors: Doyle, J. G.
1982IrAJ...15..338D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of the occultation of HD 197999 by the Minor
planet 105 Artenis.
Authors: Byrne, P. B.; Coulson, I. M.; Doyle, J. G.; Taylor, G. E.
1982MNRAS.200P..65B Altcode:
A minimum value of 110 km for the diameter Artemis is derived from
observations of its occultation of a star.
---------------------------------------------------------
Title: Electron density diagnostic line ratios from the N = 3 lines
of O V
Authors: Widing, K. G.; Doyle, J. G.; Dufton, P. L.; Kingston, E. A.
1982ApJ...257..913W Altcode:
New atomic physics calculations are presented for electron excitation
rates for transitions between the n = 2 and n = 3 levels of O v. These
are used to calculate theoretical line intensity ratios for the 192
A, 215 A, 220 A, and 248 A lines of O v. These line intensity ratios
are electron density sensitive and provide valuable diagnostics at
an electron temperature of approximately 200,000 for small impulsive
flare events in which the transition zone ions are enhanced relative
to the coronal ions. Two flares observed by the NRL spectroheliograph
on Skylab, on December 22, 1973, and January 21, 1974, are studied,
with electron densities of approximately 3 x 10 to the 11th per cu cm
being deduced.
---------------------------------------------------------
Title: Impulsive Phase of Flares in Soft X-Ray Emission
Authors: Antonucci, E.; Gabriel, A. H.; Acton, L. W.; Culhane, J. L.;
Doyle, J. G.; Leibacher, J. W.; Machado, M. E.; Orwig, L. E.; Rapley,
C. G.
1982SoPh...78..107A Altcode:
Observations using the Bent Crystal Spectrometer instrument on the
Solar Maximum Mission show that turbulence and blue-shifted motions
are characteristic of the soft X-ray plasma during the impulsive phase
of flares, and are coincident with the hard X-ray bursts observed
by the Hard X-ray Burst Spectrometer. A method for analysing the
Ca XIX and Fe XXV spectra characteristic of the impulsive phase
is presented. Non-thermal widths and blue-shifted components in the
spectral lines of Ca XIX and Fe XXV indicate the presence of turbulent
velocities exceeding 100 km s<SUP>-1</SUP> and upward motions of
300-400 km s<SUP>-1</SUP>.
---------------------------------------------------------
Title: Cercle Scientifique de Charleroi: Journées de l'astronomie
Authors: Doyle, J.
1982C&T....98..305D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: I. U. A. A.: une invitation
Authors: Doyle, J.
1982C&T....98..303D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IUE Spectra of Active Stars in Binary Systems.
Authors: Butler, C. J.; Andrews, A. D.; Byrne, P. B.; Doyle, J. G.;
Linsky, J. L.; Marstad, N.; Simon, T.; Rodono, M.; Blanco, C.;
Catalano, S.; Pazzani, E.; Marilli, V.
1982uxsa.coll...14B Altcode: 1982IAUCo..73...14B
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet spectra of dwarf solar neighbourhood stars. I.
Authors: Butler, C. J.; Byrne, P. B.; Andrews, A. D.; Doyle, J. G.
1981MNRAS.197..815B Altcode:
Short-wavelength IUE spectra of three nearby M-type dwarfs are
presented. Two of these stars, Gliese 867 A and AU Mic, are active UV
Ceti flare stars and their UV spectra exhibit strong emission lines,
characteristic of active chromospheres. The third star, Gliese 825,
is a low-activity flare star and its spectrum reveals no chromospheric
lines. A strong UV continuum exists in one of the spectra of Gliese 867
A and it is deduced that a flare took place during the exposure. A
spectrum of the flare light is extracted and compared with the
predictions of various flare models.
---------------------------------------------------------
Title: New ionization fractions for the lithium- and helium-like
ionization stages of calcium and iron
Authors: Doyle, J. G.; Raymond, J. C.
1981MNRAS.196..907D Altcode:
A reinterpretation of the high resolution X-ray spectra of Ca XIX and Fe
XXV, observed during a solar flare on March 25, 1979, is presented. New
ionization fractions for Ca XVIII, Ca XIX, Fe XXIV, and Fe XXV are
used, and it is shown that the new calculations substantially change
the interpretation of the spectra. It is implied that the flare plasma
was ionizing during the early phases of the flare, and recombining
during the decay phase.
---------------------------------------------------------
Title: The energy balance in coronal holes and average quiet-sun
regions
Authors: Raymond, J. C.; Doyle, J. G.
1981ApJ...247..686R Altcode:
Emission measure curves are presented for average coronal hole and
quiet-sun spectra taken during the Skylab mission by Vernazza and Reeves
(1978), and the curves are used to discuss the energy balance in each
region. Close-coupling calculations are used for the Be sequence,
assuming a 10 level ion; for B sequence ions mainly distorted
wave calculations in an 11 level ion are used, but close-coupling
cross sections are used for some ions; for C and Mg sequence ions,
distorted wave calculations are used with 15 and 10 level ions,
respectively, and close-coupling results are used for Li-like ions
with two levels. Results are presented and include the following: the
coronal hole spectrum shows a smaller slope in the emission measure
distribution, consistent with the expected outflow effects. It is
concluded that the simple constant pressure models of static coronal
loops of constant cross section are basically able to match the observed
emission measure distribution of the average quiet sun between 1,000,000
and 10,000,000 K. However, the cell center and network distributions
are respectively steeper and shallower than predicted by the detailed
cooling curve.
---------------------------------------------------------
Title: Emissivities of strong ultraviolet lines
Authors: Raymond, J. C.; Doyle, J. G.
1981ApJ...245.1141R Altcode:
Using atomic data published during the last few years for Li to Mg
sequence ions, we have carried out multilevel calculations over a
range of electron pressures to obtain absolute intensities for spectral
lines in the UV and EUV regions of the electromagnetic spectrum. Both
the pressure dependence of the ionization balance and the dependence of
line emissivities on the populations of metastable levels are taken into
account. These line emissivities may be used to obtain plane-parallel
model atmospheres for different solar transition region structures,
and in general for other late-type stars which have observable lines
over a wide range of excitation potentials.
---------------------------------------------------------
Title: Transition probabilities and line intensity ratios of
transitions within the ground-state configuration of O III
Authors: Baluja, K. L.; Doyle, J. G.
1981JPhB...14L..11B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An approximate calculation of the effect of opacity in the
solar spectral lines of C III
Authors: Doyle, J. G.; McWhirter, R. W. P.
1980MNRAS.193..947D Altcode:
The paper applies the fact that the intensity ratio between two
spectral lines arising from the same upper level can depend on opacity,
to determine the optical thickness of the solar atmosphere to C III
radiation. The analysis is based on observations taken near the sun's
limb during the Skylab mission with the Naval Research Laboratory's
spectrograph. By introducing the measured abundance of carbon and the
results of ionization balance calculations, an estimate is made of the
line-of-sight physical thickness of the regions emitting C III lines
at the disk center.
---------------------------------------------------------
Title: Proton excitation rates for fine structure transitions in C
III, O V, and NE VII in the sun
Authors: Doyle, J. G.; Kingston, A. E.; Reid, R. H.
1980A&A....90...97D Altcode:
The close-coupled impact parameter method is used to calculate the
proton excitation rates for fine structure transitions in the levels
(2s, 2p) 3P and (2p)2 3P of the ions C III, O V, and Ne VII. By the use
of these proton rates and recently calculated electron collision rates,
the effect of these proton rates on line ratios involving these fine
structure levels has been studied at electron temperatures and densities
appropriate to the solar transition region. Theoretical estimates of the
strength of the (2s, 2p) 3P (2s)2 1S line are only slightly affected
by the inclusion of proton rates. The estimate of the strength of the
multiplet is decreased by 10% in the case of O V and Ne VII at the
temperature of maximum abundance and 25% for higher temperatures.
---------------------------------------------------------
Title: Soft X-ray Emission During the Impulsive Phase of a Flare
Authors: Antonucci, E.; Gabriel, A. H.; Doyle, J. G.
1980BAAS...12..900A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal Flare Densities
Authors: Wolfson, C. J.; Doyle, J. G.; Phillips, K. J. H.
1980BAAS...12..912W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The interpretation of C V and O VII emission line ratios in
the sun
Authors: Doyle, J. G.
1980A&A....87..183D Altcode:
Recent theoretical atomic data for the collisional and radiative rates
is used in a reinterpretation of the observed C V and O VII emission
line ratios in the solar corona/transition region. In the calculations,
transitions between the five lowest states of the He-like ion are
considered. From C V an electron density of 4.5 x 10 to the 9th power
per cu cm, and an electron temperature of 3.0 x 10 to the 5th power
K are derived, while in the region of O VII emission lines, an upper
limit of 2.0 x 10 to the 9th power per cu cm is found for the electron
density, and an upper limit of 1.6 x 10 to the 15th power per cu cm
K is derived for the electron pressure.
---------------------------------------------------------
Title: A study of solar ultraviolet and X-ray spectra
Authors: Doyle, John Gerard Gerry
1980PhDT.......157D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The interpretation of N IV and Ne VII emission line ratios
in the sun.
Authors: Dufton, P. L.; Doyle, J. G.; Kingston, A. E.
1979A&A....78..318D Altcode:
Summary. Using new atomic data -for electron impact collision rates, the
observed N Iv and Ne vIl emission line ratios in the solar transition
region have been interpreted. For N Iv, the ratio I(3Pe 3P0)/I(1P0 1S )
indicates an electron density of 1.51010 for the quiet sun, while the
active region results are anomalous, possibly due to blending. From
the ratio !(` D `P0)/I(3Pj0 -1 1S ) in N Iv, an electron temperature of
1.0 l0 K is deduced for the quiet sun, in agreement with that expected
in steady-state ionization equilibrium. For Ne vII, the ratio I(3Pj-1
lSe)!i(1F0 1S ) is an excellent electron temperature diagnostic. For
the quiet sun a value of 5 10 K is found, again in agreement with
that expected in steady state ionization equilibrium while higher
electron temperatures are found for coronal holes (8 l0 K) and active
regions (1.2 106 K). Key words: collision rates - transition region -
Be sequence - plasma diagnostics -
