Author name code: brosius
ADS astronomy entries on 2022-09-14
author:"Brosius, Jeffrey W."
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Title: First Imaging Spectroscopy of 92-115 Angstrom Solar Soft
X-rays by EUNIS: Implications for Solar Coronal Heating
Authors: Brosius, Jeffrey; Daw, Adrian; Rabin, Douglas; Landi, Enrico;
Schmit, Donald
Bibcode: 2021AGUFMSH12B..04B
Altcode:
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS)
sounding rocket waslaunched from White Sands Missile Range, NM, on
May 18, 2021. The instrumentcomprised a pair of coaligned imaging
spectrographs, one of which observed solarline emission in first
order at wavelengths between 525 and 639 A, and the secondof which
observed line emission in third order at wavelengths between 92 and
115 Aand in first order between 277 and 345 A. Images of AR 12824,
quiet-sun area, andoff-limb area were obtained by rastering the slits
over the selected targets. Thisis the first time that solar imaging
spectroscopy has been performed in the 92-115A soft X-ray range. This
waveband was selected to (1) observe Fe XVIII 93.932 and103.948 A
and Fe XIX 108.355 A line emission in a quiescent active region, and
(2)explore a relatively unobserved portion of the solar electromagnetic
spectrum. Theinstrument performed well during its 6-minute observing
run. We report preliminaryresults on observations of Fe XVIII and Fe
XIX in the quiescent active region, anddiscuss implications for the
nanoflare model of solar coronal heating. EUNIS wassupported by NASA
Heliophysics Low Cost Access to Space award 13-HTIDS13_2-0074.
Title: Evidence For Active Region Coronal Heating By Nanoflares
Based On Time-lag Measurements In EUV Light Curves From EIS
Authors: Brosius, J.; Viall, N.
Bibcode: 2021AAS...23832813B
Altcode:
The nanoflare model of solar coronal heating is based on the idea
that ubiquitous tiny, independent heating events occur on individual
sub-resolution strands within coronal loops. Each heating event raises
its strand plasma to temperatures (6-10 MK) that are greater than the
average active region temperature (about 2 MK). After the impulsive
energy release, the loop strand increases in density and cools by
conduction and radiation. The strand spends more time at higher density
in the radiative cooling phase than it does in any other phase of
the heating and cooling cycle. Thus, even when observed on spatial
scales larger than the unresolvable individual strands, the solar
atmosphere is expected to exhibit an overall cooling trend. Evidence
for this has been presented based on correlations among light curves
from AIA's six EUV channels. While this supports the nanoflare model
of coronal heating, AIA's lack of temperature fidelity means that
precise cooling information for small locations or single events are
less than conclusive. Here we report results from an investigation
of time-lag diagnostics based on EUV light curves derived from stare
spectra obtained with a new EIS study designed to investigate time
lags in non-flaring active regions. This study observes line emission
from ten successive ionization stages of iron (VIII-XVII, 0.45-4 MK),
as well as Fe XXIII (seen in flares and microflares) and lines formed
at lower temperatures. We find evidence of post-nanoflare cooling in
AR 12759 from 2.8 to 0.45 MK, but note that not all locations cool to
temperatures this low, possibly indicating a mixture of medium and
low frequency nanoflares. The AR periphery is cooler than its core,
and exhibits post-nanoflare cooling only from 1.7 to 1.4 MK, suggestive
of higher frequency nanoflares.
Title: Evidence of Solar Coronal Heating by Nanoflares Based on
Time-Lag Measurements in EUV Light Curves from EIS
Authors: Brosius, J. W.; Viall, N. M.
Bibcode: 2020AGUFMSH0370004B
Altcode:
The nanoflare model is a major contender to explain solar coronal
heating. The model is based on the idea that ubiquitous tiny,
independent heating events occur on individual sub-resolution strands
within coronal loops. Each heating event raises its strand plasma to
temperatures (6 - 10 MK) that are greater than the average active
region temperature (~2 MK). Compelling evidence for this mechanism
is pervasive faint emission at flare-like temperatures, such as that
detected in an active region by the EUNIS sounding rocket. After the
impulsive energy release, the loop strand cools by conduction and
radiation, during which it spends more time at higher density and
at colder temperatures than it does at hotter temperatures. Thus,
even when observed on spatial scales larger than the unresolvable
individual strands, the solar atmosphere is expected to exhibit an
overall cooling trend. Evidence for this cooling trend has been sought
and found based on correlations among light curves from AIA's six
EUV channels. While this provides further support for the nanoflare
model of coronal heating, AIA's lack of temperature fidelity means
that precise cooling information for small locations or single events
are less than conclusive. Here we report preliminary results from an
investigation of time-lag diagnostics based on EUV light curves from
Hinode/EIS spectra. We present results for non-flaring active regions
and quiet-sun areas derived from stare spectra obtained with several
different EIS studies that observe unblended emission lines formed
at temperatures that range from 0.14 to 14 MK. We performed time-lag
diagnostics on light curves of Fe XXIII, Fe XVII, Fe XVI, Fe XIV, S X,
Si VII, Mg VI, O IV, and other lines. For example, for a 2014 March 11
observing run on AR 12002, EIS observed fan loops that cooled slowly
between 1.4 and 0.6 MK on timescales of ~3000s; microflares that cooled
from 14 to 2 MK on timescales of ~1000 s; and core loops that cooled
from about 4 to 0.1 MK on timescales ~1500 s. Properties such as peak
temperature, the timescales of the cooling, and a determination of
whether the cooling is full or partial all provide valuable constraints
on nanoflares as a source of coronal heating.
Title: Evidence for Solar Coronal Heating by Nanoflares Based on
Coordinated EUV Spectra Observed with the EUNIS Sounding Rocket
and Hinode/EIS
Authors: Brosius, J. W.; Daw, A. N.; Landi, E.
Bibcode: 2019AGUFMSH53B3373B
Altcode:
The nanoflare model of solar coronal heating has been widely viewed with
increasing favor over the last 5-10 years. According to this model,
the solar atmosphere is heated by numerous impulsive heating events
that are currently too small to be detected individually. Collectively,
however, they produce the corona's 2-3 MK plasma. Widespread faint
emission from lines formed at flare-like temperatures (6-10 MK) is
considered to be strong, "smoking gun" evidence for the nanoflare
model. Previously we reported such evidence in the form of faint
Fe XIX emission observed throughout an active region during the 2013
flight of the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS)
sounding rocket instrument. The instrument recorded spectra in 300-370
and 530-635 A wavebands. Here we present an analysis of coordinated
spectra of that same active region obtained with both EUNIS and the
Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode. EIS
records spectra in 170-210 and 250-290 A wavebands. We investigate
the emission measure of the faint, high-temperature component, slopes
within the emission measure curve, element abundances, nonthermal line
broadening, and bulk velocity flows. This work helps pave the way for
the next EUNIS flight, which records spectra and spectroheliograms
in 90-115 and 530-635 A wavebands. These include, in particular,
strong emission lines of Fe XVIII and Fe XIX, which are among the best
candidates for nanoflare emission identification and analysis.
Title: Localized Quasi-Periodic Fluctuations in C II, Si IV, and
Fe XXI Emission During Chromospheric Evaporation in a Flare Ribbon
Observed by IRIS and RHESSI on 2017 September 9
Authors: Brosius, Jeffrey W.; Inglis, Andrew
Bibcode: 2019AAS...23420403B
Altcode:
We investigate the onset of a GOES M3.7 flare on 2017 September 9
with rapid cadence (9.4 s) ultraviolet stare spectra obtained with
IRIS in five 1-arcsec slit segments. Our analysis is based primarily
on integrated intensities and Doppler velocities of C II at 1334.5
Angstroms (T 0.025 MK), Si IV 1402.7 (0.079 MK), and Fe XXI 1354.1
(11 MK). The four segments within the ribbon show systematically
earlier starting times for the low-T lines (C II and Si IV) than
Fe XXI; further, the velocities derived for Fe XXI are generally
directed upward along the line of sight. This is consistent with the
standard flare model, in which beams of nonthermal particles ionize
and heat the chromosphere, and drive chromospheric evaporation:
as the temperature and ionization stages of the chromospheric plasma
increase, intensities of emission lines also increase, first from lines
in lower stages of ionization, and later from lines in higher stages
of ionization. Where quasi-periodic fluctuations were observed in the
ribbon in both low-T and Fe XXI emission, the peaks in the low-T light
curves preceded those in the Fe XXI light curve, and peaks in the Fe
XXI upward velocity typically also preceded those in the Fe XXI light
curve. Thus the behavior of each individual fluctuation was similar to
that of a standard flare, suggesting that each individual fluctuation
was due to a separate injection of nonthermal particles into the
chromosphere. Based on RHESSI HXR observations, we estimate sufficient
beam energy flux to drive explosive chromospheric evaporation.
Title: Localized Quasi-periodic Fluctuations in C II, Si IV, and
Fe XXI Emission during Chromospheric Evaporation in a Flare Ribbon
Observed by IRIS on 2017 September 9
Authors: Brosius, Jeffrey W.; Inglis, Andrew R.
Bibcode: 2018ApJ...867...85B
Altcode:
We investigate the onset of a GOES M3.7 flare on 2017 September 9 with
rapid-cadence (9.4 s) UV stare spectra obtained with IRIS in five 1″
slit segments. Our analysis is based primarily on integrated intensities
and Doppler velocities of C II λ1334.5 (T ≈ 2.5 × 104
K), Si IV λ1402.7 (7.9 × 104 K), and Fe XXI λ1354.1
(1.1 × 107 K). The four segments within the ribbon show
systematically earlier starting times for the low-T lines (C II and
Si IV) than Fe XXI; further, the velocities derived for Fe XXI are
generally directed upward along the line of sight. This is consistent
with the standard flare model, in which beams of nonthermal particles
ionize and heat the chromosphere and drive chromospheric evaporation:
as the temperature and ionization stages of the chromospheric plasma
increase, intensities of emission lines also increase, first from lines
in lower stages of ionization, and later from lines in higher stages
of ionization. Where quasi-periodic fluctuations were observed in the
ribbon in both low-T and Fe XXI emission, peaks in the low-T intensity
preceded those in the Fe XXI intensity, and peaks in the Fe XXI upward
velocity typically also preceded those in the Fe XXI intensity. Thus,
the behavior of each individual fluctuation was similar to that of a
standard flare, suggesting that each individual fluctuation was due to a
separate injection of nonthermal particles into the chromosphere. Based
on RHESSI hard X-ray observations, we estimate sufficient beam energy
flux (≥1.5 × 1010 erg cm-2 s-1)
to drive explosive chromospheric evaporation.
Title: A 3D Model of AR 11726 Heated by Nanoflares
Authors: Allred, Joel; Daw, Adrian; Brosius, Jeffrey
Bibcode: 2018arXiv180700763A
Altcode:
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) and the
Hinode/ EUV Imaging Spectrometer (EIS) observed AR 11726 on 2013 April
23. We present intensity images in numerous atomic lines constructed
from these observations. These lines are formed over a wide range
of temperatures, and we use their relative intensities to constrain
a parameterization of nanoflare heating. We construct a 3D model of
the magnetic field in this active region by extrapolating the surface
magnetic field into the corona and using SDO/AIA images of coronal
loops to ensure that extrapolated magnetic field lines co-align with
observed coronal loops. We trace 2848 magnetic field lines within the
volume of this active region and model how they fill with hot plasma
in response to nanoflare heating. We perform a parameter study to
determine how the frequency and energy released in nanoflares scale
with magnetic field strength and loop length. From our 3D model, we
construct synthetic images of the lines observed by EUNIS and EIS and
constrain the parameter study by minimizing the difference between
the synthetic and observed images.
Title: The Case for Spectroscopic Observations of Very Hot Plasmas
Authors: Klimchuk, James A.; Daldorff, Lars K. S.; Liu, Yi-Hsin;
Brosius, Jeffrey W.; Daw, Adrian Nigel; Leake, James Edward
Bibcode: 2018tess.conf11003K
Altcode:
Explosive magnetic energy release is responsible for many solar
phenomena, ranging from coronal heating, to jets, to CMEs and
flares. Despite its importance, many of the basic details of how this
works are still not well established. In order to make significant
progress, we must observe the actual energy release process. That means
measuring plasmas at high temperatures (> 5 MK). Most existing
coronal observations are of plasma that has cooled dramatically,
after vital information has been lost, or, worse yet, plasma that has
evaporated from the chromosphere and is only an indirect bi-product of
the energy release. Spectroscopic observations are especially valuable
because of their potential for diagnosing flows, temperatures, and
densities. Furthermore, only with spectroscopy can we disentangle the
disparate plasmas that are invariably present along optically-thin
lines-of-sight. I will discuss these points in more detail, review the
pros and cons of different wavelength regimes, and present preliminary
results on synthetic line profiles from a particle-in-cell (PIC)
simulation of magnetic reconnection.
Title: Explosive Chromospheric Evaporation and Warm Rain in a GOES
C3 Flare Observed by IRIS, Hinode/EIS, and RHESSI
Authors: Brosius, J. W.; Inglis, A. R.
Bibcode: 2017AGUFMSH41A2740B
Altcode:
IRIS and Hinode/EIS observed a C3.1 flare in AR 12002 in stare mode on
2014 March 15.GOES observed the flare to start at 00:21:35 UT and peak
at 00:26:30 UT. The IRIS slitwas pointed near the center of the flare
while the EIS slit was pointed 35 arcsec westof the IRIS slit. About 4
minutes before the GOES flare start, the C II and Si IV lineintensities
observed by IRIS became (and remained) significantly greater than
theirpre-flare average values; this indicates that the flare had begun
and that thechromosphere and transition region were involved. IRIS
first detected significant,blueshifted Fe XXI emission at 00:22:42
UT, by which time the C II and Si IV lineintensities had increased by
factors around 100 and their profiles were significantlyredshifted. This
combination of simultaneous, cospatial blueshifted Fe XXI emissionwith
redshifted C II and Si IV emission indicates explosive chromospheric
evaporation.SDO's HMI observed a localized area of enhanced magnetic
field strength toward thesouthernmost portion of the EIS slit's
position that appears to be connected to theflare site by faint loops
evident in AIA 131 A emission. EIS spectra at this locationreveal
intensity enhancements by factors up to about 1.7 in the Fe XIV and
Fe XVI lineemission, and the emergence of faint Fe XXIII emission
that is too weak to measurevelocities. Emission lines from the two
coronal ions show redshifts of about 9 km/saround 00:24:00 UT. The
density sensitive line intensity ratio of Fe XIV 264.7/274.2observed
by EIS reveals an increase of electron density from (1.03+/-0.20)X10^9
/cm^3before the flare to (3.58+/-0.68)X10^9 /cm^3 during the flare. This
combination ofredshifted coronal line emission and increased coronal
electron density is consistentwith explosively evaporated flare
material observed by IRIS falling as warm rain andaccumulating in the
remote area observed by EIS. A thermal/nonthermal fit to the hardX-ray
spectrum observed by RHESSI yields a nonthermal energy injection rate
of4.9X10^26 ergs/s; combining this with an estimated injection area of
(2.1+/-1.7)X10^17cm^2 based on IRIS slit-jaw images, we estimate a HXR
beam energy flux of(6.7+/-5.5)X10^9 ergs/cm^2/s, a wide range whose
larger values are consistent withexplosive chromospheric evaporation.
Title: Explosive Chromospheric Evaporation and Warm Rain in a C3.1
Flare Observed by IRIS, Hinode/EIS, and RHESSI
Authors: Brosius, Jeffrey W.; Inglis, Andrew R.
Bibcode: 2017ApJ...848...39B
Altcode:
IRIS and EIS observed a GOES C3.1 flare in stare mode on 2014 March
15. The GOES flare started at 00:21:35 and peaked at 00:26:30 UT. The
IRIS slit pointed near the center of the flare, while the EIS slit
pointed 35\prime\prime to its west. About 4 minutes before
the GOES flare start, the IRIS C II and Si IV intensities became (and
remained) greater than their pre-flare averages, indicating that the
flare had begun and that the chromosphere and transition region were
involved. IRIS first detected blueshifted Fe xxi emission at 00:22:42
UT, by which time the C II and Si IV intensities had increased by
factors around 100 and their profiles were redshifted. Simultaneous,
cospatial blueshifted Fe xxi emission with redshifted C II and Si IV
emission indicates explosive chromospheric evaporation. EIS spectra
reveal Fe xxiii emission that is too weak to measure velocities,
and intensity enhancements by factors about 1.7 in the Fe xiv and Fe
xvi emission. Lines from both of these coronal ions show redshifts
≈9 km s-1 around 00:24:00 UT, and the Fe xiv 264.7/274.2
intensity ratio reveals an increase of n e from (1.03+/-
0.20)× {10}9 before to (3.58+/- 0.68)× {10}9
cm-3 during the flare. The redshifted coronal line emission
and increased n e are consistent with warm rain falling
and accumulating in the remote area observed by EIS. A fit to the
RHESSI hard X-ray spectrum yields a nonthermal energy injection rate
of 4.9× {10}26 erg s-1, from which we estimate
a HXR beam energy flux range consistent with explosive evaporation.
Title: Solving the Coronal Heating Problem using X-ray
Microcalorimeters
Authors: Christe, Steven; Bandler, Simon; DeLuca, Edward; Caspi,
Amir; Golub, Leon; Smith, Randall; Allred, Joel; Brosius, Jeffrey W.;
Dennis, Brian; Klimchuk, James
Bibcode: 2017arXiv170100795C
Altcode:
Even in the absence of resolved flares, the corona is heated to several
million degrees. However, despite its importance for the structure,
dynamics, and evolution of the solar atmosphere, the origin of this
heating remains poorly understood. Several observational and theoretical
considerations suggest that the heating is driven by small, impulsive
energy bursts which could be Parker-style "nanoflares" (Parker 1988)
that arise via reconnection within the tangled and twisted coronal
magnetic field. The classical "smoking gun" (Klimchuk 2009; Cargill et
al. 2013) for impulsive heating is the direct detection of widespread
hot plasma (T > 6 MK) with a low emission measure. In recent years
there has been great progress in the development of Transition Edge
Sensor (TES) X-ray microcalorimeters that make them more ideal for
studying the Sun. When combined with grazing-incidence focusing optics,
they provide direct spectroscopic imaging over a broad energy band
(0.5 to 10 keV) combined with extremely impressive energy resolution
in small pixels, as low as 0.7 eV (FWHM) at 1.5 keV (Lee 2015),
and 1.56 eV (FWHM) at 6 keV (Smith 2012), two orders of magnitude
better than the current best traditional solid state photon-counting
spectrometers. Decisive observations of the hot plasma associated
with nanoflare models of coronal heating can be provided by new solar
microcalorimeters. These measurements will cover the most important part
of the coronal spectrum for searching for the nanoflare-related hot
plasma and will characterize how much nanoflares can heat the corona
both in active regions and the quiet Sun. Finally, microcalorimeters
will enable to study all of this as a function of time and space in
each pixel simultaneously a capability never before available.
Title: Coordinated Observations of AR 11726 by Hinode/EIS and
EUNIS-2013
Authors: Ancheta, A. J.; Daw, A. N.; Brosius, J. W.
Bibcode: 2016AGUFMSH31B2558A
Altcode:
The Extreme-Ultraviolet Normal-Incidence Spectrograph (EUNIS) sounding
rocket payload was flown on 2013 April 23 with two independent
channels covering the 300-370 A and 525-635 A wavebands. EUNIS-2013
observed two targets on the solar disk that included quiet sun, active
regions, a flare, and a micro-flare. The active region AR 11726 was
co-observed with the EUV Imaging Spectrometer (EIS) on Hinode. The
radiometric response of EUNIS is measured in the laboratory using a
NIST-calibrated photodiode and hollow cathode discharge lamp. A density-
and temperature- insensitive line intensity ratio technique can be used
to derive an in-flight calibration update of Hinode/EIS. Measurements
of EIS emission lines with respect to EUNIS lines, including Fe X to
Fe XII and Si X, provide a comparison between the calibrations of the
two instruments. The radiometric calibration of EUNIS-2013 is also
validated using the same insensitive ratio technique with emission
lines such as Mg VIII, Fe XI, Fe XVI, and Si IX.
Title: Quasi-Periodic Fluctuations and Chromospheric Evaporation in a
Solar Flare Ribbon Observed by Hinode/EIS, IRIS, RHESSI, and Fermi/GBM
Authors: Brosius, J. W.; Inglis, A. R.; Daw, A. N.
Bibcode: 2016AGUFMSH14B..02B
Altcode:
We obtained rapid cadence (11.2 s) EUV stare spectra of a GOES M7.3
flare ribbonin AR 12036 on 2014 April 18 with Hinode/EIS, along with
coordinated IRIS, RHESSI,and Fermi/GBM observations. Quasi-periodic
(P ≈ 75.6 ± 9.2 s)intensity fluctuations occurred in emission
lines of O IV, Mg VI, Mg VII, Si VII, Fe XIV, and Fe XVI during
the flare's impulsive rise, and ended when the maximumintensity
in Fe XXIII was reached. The profiles of the O IV - Fe XVI lines
revealthat they were all redshifted during most of the interval of
quasi-periodicintensity fluctuations, while the Fe XXIII profile
revealed multiple componentsincluding one or two highly blueshifted
ones. This indicates that the flareunderwent explosive chromospheric
evaporation during its impulsive rise.Fluctuations in the relative
Doppler velocities were detected, but theirsignal-to-noise ratios
were inadequate to extract significant quasi-periodicities.RHESSI
detected 25-100 keV hard X-ray sources in the ribbon near the
EIS slit'spointing position during the peaks in the EIS intensity
fluctuations. We concludethat the series of quasi-periodic intensity
peaks in the EUV light curves wasproduced by a series of nonthermal
electron injections into the chromosphere. Theinjections may be
attributed to MHD oscillations in a magnetic trap, MHDoscillations
in a nearby, non-flaring magnetic loop, or magnetic reconnection in a
large-scale current sheet dominated by repeated formation of magnetic
islands.Electron densities derived with Fe XIV (4.6 × 1010
cm-3) and Mg VII(7.8 × 109 cm-3)
average line intensity ratios during the interval ofquasi-periodic
intensity fluctuations, combined with the radiative loss functionof an
optically thin plasma (derived with CHIANTI), yield radiative cooling
timesof 32 s at 2.0 MK, and 46 s at 0.63 MK; assuming the same density
for Fe XXIIIthat we derived for Fe XIV yields a radiative cooling time
of 1000 s at 14 MK.We speculate that fluctuations are observed in the
lower temperature (but not FeXXIII) lines because at those temperatures
the plasma had sufficient time toradiatively cool between successive
energy injections. Quasi-periodic fluctuationswere observed by IRIS
in the same ribbon, 40 arcsec to the west, where RHESSIdetected no
hard X-ray emission.
Title: Quasi-periodic Fluctuations and Chromospheric Evaporation in
a Solar Flare Ribbon Observed by Hinode/EIS, IRIS, and RHESSI
Authors: Brosius, Jeffrey W.; Daw, Adrian N.; Inglis, Andrew R.
Bibcode: 2016ApJ...830..101B
Altcode:
The Hinode/Extreme-ultraviolet Imaging Spectrometer (EIS) obtained
rapid cadence (11.2 s) EUV stare spectra of an M7.3 flare ribbon in AR
12036 on 2014 April 18. Quasi-periodic (P ≈ 75.6 ± 9.2 s) intensity
fluctuations occurred in emission lines of O IV, Mg VI, Mg vii, Si vii,
Fe xiv, and Fe xvi during the flare's impulsive rise, and ended when
the maximum intensity in Fe xxiii was reached. The profiles of the O
IV-Fe xvi lines reveal that they were all redshifted during most of
the interval of quasi-periodic intensity fluctuations, while the Fe
xxiii profile revealed multiple components including one or two highly
blueshifted ones. This indicates that the flare underwent explosive
chromospheric evaporation during its impulsive rise. Fluctuations in
the relative Doppler velocities were seen, but their amplitudes were
too subtle to extract significant quasi-periodicities. RHESSI detected
25-100 keV hard-X-ray sources in the ribbon near the EIS slit's pointing
position during the peaks in the EIS intensity fluctuations. The
observations are consistent with a series of energy injections into the
chromosphere by nonthermal particle beams. Electron densities derived
with Fe xiv (4.6 × 1010 cm-3) and Mg vii (7.8 ×
109 cm-3) average line intensity ratios during the
interval of quasi-periodic intensity fluctuations, combined with the
radiative loss function of an optically thin plasma, yield radiative
cooling times of 32 s at 2.0 × 106 K, and 46 s at 6.3
× 105 K (about half the quasi-period); assuming Fe xiv's
density for Fe xxiii yields a radiative cooling time of 103
s (13 times the quasi-period) at 1.4 × 107 K.
Title: Evidence for Nanoflare Heating of the Solar Corona from the
EUNIS Sounding Rocket
Authors: Brosius, J. W.; Daw, A. N.; Rabin, D. M.
Bibcode: 2015AGUFMSH31D..01B
Altcode:
We present spatially resolved EUV spectroscopic measurements
ofpervasive, faint Fe XIX 592.2 A line emission in AR 11726,observed
during the 2013 April 23 flight of the Extreme UltravioletNormal
Incidence Spectrograph (EUNIS-13) sounding rocket instrument. With
cooled detectors, high sensitivity, and high spectralresolution,
EUNIS-13 resolves the lines of Fe XIX at 592.2 A (formedat temperature
T around 8.9 MK) and Fe XII at 592.6 A (T around 1.6MK). The Fe XIX
line emission, observed over an area in excess of4920 square arcsec
(2.58x10^9 square km, more than 60% of the activeregion), provides
strong evidence for the nanoflare heating model ofthe solar corona. No
GOES events occurred in the region less than 2hours before the rocket
flight, but a microflare was observed northand east of the region with
RHESSI and EUNIS during the flight. Theabsence of significant upward
velocities anywhere in the region,particularly the microflare, indicates
that the pervasive Fe XIXemission is not propelled outward from the
microflare site, but ismost likely attributed to localized heating (due
to reconnection,wave dissipation, or some other mechanism) consistent
with thenanoflare heating model of the solar corona. We measure average
FeXIX/Fe XII intensity ratios of 0.070 outside the AR core, 0.22 inarea
of bright coronal emission (the area in which the Fe XIIintensity
exceeds half its maximum observed value), and 0.55 in theregion's hot
core. Using the CHIANTI atomic physics database andassuming ionization
equilibrium, we estimate corresponding Fe XIX/FeXII emission measure
ratios of about 0.076, 0.23 and 0.59. Theemission measure ratios must
be viewed with caution in light oflingering uncertainties in the Fe XII
contribution functions.EUNIS-13 was supported by the NASA Heliophysics
Division through itsLow Cost Access to Space program.
Title: Quasi-periodic Fluctuations and Chromospheric Evaporation in
a Solar Flare Ribbon Observed by IRIS
Authors: Brosius, Jeffrey W.; Daw, Adrian N.
Bibcode: 2015ApJ...810...45B
Altcode:
The Interface Region Imaging Spectrograph (IRIS) satellite obtained
rapid cadence (9.4 s) stare spectra of an M7 flare ribbon in
AR 12036 on 2014 April 18. Chromospheric and transition region
line emission exhibited quasi-periodic intensity and velocity
fluctuations in the ribbon prior to the appearance of Fe xxi
emission. Seven intensity peaks were observed in light curves from small
(0\buildrel{\prime\prime}\over{.} 333× 0\buildrel{\prime\prime}\over{.}
333) tracked spatial locations in the ribbon, the first four of which
show variable time separations around 3 minutes, and the last four
of which show variable time separations about half that value, i.e.,
the frequency appears to have doubled. The Fe xxi intensity increased
rapidly and impulsively after the quasi-periodic fluctuations in
chromospheric and transition region lines. The entire Fe xxi line
profile was blueshifted when the line first appeared, corresponding
to an upward velocity around -100 km s-1. This upward
velocity increased to a maximum of about -150 km s-1 before
diminishing to zero around the time of maximum intensity. Simultaneous,
cospatial velocities observed with Si iv line emission were directed
downward, consistent with explosive chromospheric evaporation. During
this flare the Fe xxi line’s profile is well fit with only one
Gaussian component that is either wholly blueshifted or wholly at
rest; no significant secondary blueshifted or redshifted components
are observed. This suggests that IRIS may have sufficient spatial
resolution to resolve loop strands in these flare observations. Under
the assumption that the Fe xxi line is at rest when its width is
thermal, we derive a rest wavelength of 1354.0714 ± 0.0108 Å for
this forbidden line.
Title: EUNIS 2013: Unambiguous Evidence for Impulsive Coronal Heating,
Data Available
Authors: Daw, Adrian; Brosius, Jeffrey; Haas, J. Patrick; Plummer,
Thomas; Rabin, Douglas
Bibcode: 2015TESS....120401D
Altcode:
The broad spectral coverage (303-370 Å, 527-635 Å) and unprecedented
dynamic range of the Extreme Ultraviolet Normal Incidence Spectrograph
(EUNIS) 2013 sounding rocket observations includes emission lines of
ionization stages from He I to Fe XX, and thus a wide temperature range
of 0.03 to 10 MK. Pervasive, faint Fe XIX 592 Å line emission was
observed in active regions. Comparison of observed line intensities
with calculations demonstrates that the Fe XIX emission, formed at
temperatures around 8 MK, is evidence of the faint hot emission
predicted by impulsive heating models of the solar corona (e.g.,
‘nano-flares’). The calibration and availability of the EUNIS-2013
dataset is discussed as well.
Title: Eunis Observation of Pervasive Faint Fe XIX Line Emission
from a Solar Active Region: Evidence for Coronal Heating By Nanoflares
Authors: Brosius, J. W.; Daw, A. N.; Rabin, D. M.
Bibcode: 2014AGUFMSH13C4130B
Altcode:
We present spatially resolved EUV spectroscopic measurements
ofpervasive, faint Fe XIX 592.2 A line emission in an active
regionobserved during the 2013 April 23 flight of the Extreme
UltravioletNormal Incidence Spectrograph (EUNIS-13) sounding
rocket instrument. With cooled detectors, high sensitivity, and
high spectralresolution, EUNIS-13 resolves the lines of Fe XIX at
592.2 A (formedat temperature T around 8.9 MK) and Fe XII at 592.6 A
(T around 1.6MK). The Fe XIX line emission, observed over an area
in excess of4920 square arcsec (2.58x10^9 square km, more than 60%
of the activeregion), provides strong evidence for the nanoflare
heating model ofthe solar corona. No GOES events occurred in the
region less than 2hours before the rocket flight, but a microflare
was observed northand east of the region with RHESSI and EUNIS during
the flight. Theabsence of significant upward velocities anywhere in
the region,particularly the microflare, indicates that the pervasive
Fe XIXemission is not propelled outward from the microflare site, but
ismost likely attributed to localized heating (due to reconnection,wave
dissipation, or some other mechanism) consistent with thenanoflare
heating model of the solar corona. We measure average FeXIX/Fe XII
intensity ratios of 0.070 outside the AR core, 0.22 inarea of bright
coronal emission (the area in which the Fe XIIintensity exceeds half
its maximum observed value), and 0.55 in theregion's hot core. Using
the CHIANTI atomic physics database andassuming ionization equilibrium,
we estimate corresponding Fe XIX/FeXII emission measure ratios of about
0.076, 0.23 and 0.59. Theemission measure ratios must be viewed with
caution in light oflingering uncertainties in the Fe XII contribution
functions.EUNIS-13 was supported by the NASA Heliophysics Division
through itsLow Cost Access to Space program.
Title: Pervasive Faint Fe XIX Emission from a Solar Active Region
Observed with EUNIS-13: Evidence for Nanoflare Heating
Authors: Brosius, Jeffrey W.; Daw, Adrian N.; Rabin, D. M.
Bibcode: 2014ApJ...790..112B
Altcode:
We present spatially resolved EUV spectroscopic measurements
of pervasive, faint Fe XIX 592.2 Å line emission in an active
region observed during the 2013 April 23 flight of the Extreme
Ultraviolet Normal Incidence Spectrograph (EUNIS-13) sounding
rocket instrument. With cooled detectors, high sensitivity, and high
spectral resolution, EUNIS-13 resolves the lines of Fe XIX at 592.2 Å
(formed at temperature T ≈ 8.9 MK) and Fe XII at 592.6 Å (T ≈
1.6 MK). The Fe XIX line emission, observed over an area in excess
of 4920 arcsec2 (2.58 × 109 km2,
more than 60% of the active region), provides strong evidence for the
nanoflare heating model of the solar corona. No GOES events occurred
in the region less than 2 hr before the rocket flight, but a microflare
was observed north and east of the region with RHESSI and EUNIS during
the flight. The absence of significant upward velocities anywhere in
the region, particularly the microflare, indicates that the pervasive
Fe XIX emission is not propelled outward from the microflare site, but
is most likely attributed to localized heating (not necessarily due
to reconnection) consistent with the nanoflare heating model of the
solar corona. Assuming ionization equilibrium we estimate Fe XIX/Fe
XII emission measure ratios of ~0.076 just outside the AR core and
~0.59 in the core.
Title: Further Analysis of Active Region Thermal Structure from
EUNIS-13
Authors: Rabin, Douglas M.; Landi, Enrico; Daw, Adrian N.; Brosius,
Jeffrey W.
Bibcode: 2014AAS...22432339R
Altcode:
The 2013 April 23 flight of the Extreme Ultraviolet Normal Incidence
Spectrograph (EUNIS) sounding rocket instrument returned high-quality
spectra in two wavelength bands, 30.0-37.0 nm and 52.7-63.5 nm, sampling
three active regions (11723, 11724, and 11726). The spectral lines
in these bands probe a wide temperature range, 0.03 MK to 8 MK. We
have demonstrated that the differential emission measure (DEM) varies
significantly between different sub-regions of AR 11726. We extend
this analysis to ARs 11723 and 11724 and include a wider selection of
spectral lines to delineate better the variations in thermal structure.
Title: Evidence for Impulsive Coronal Heating from EUNIS 2013
Authors: Daw, Adrian N.; Brosius, Jeffrey W.; Rabin, Douglas M.;
Landi, Enrico; Klimchuk, James A.
Bibcode: 2014AAS...22431204D
Altcode:
Pervasive, faint Fe XIX 592 Å line emission was observed in active
regions by the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS)
sounding rocket instrument on 23 April 2013. The broad spectral coverage
(303-370 Å, 527-635 Å) and unprecedented dynamic range of the EUNIS
observations includes emission lines of ionization stages from He I to
Fe XX, and thus a wide temperature range of 0.03 to 10 MK. Comparison
of observed line intensities with calculations demonstrates that the
Fe XIX emission, formed at temperatures around 8 MK, is evidence of
the faint hot emission predicted by impulsive heating models of the
solar corona (such as nanoflares).
Title: Rapid Evolution of the Solar Atmosphere during the Impulsive
Phase of a Microflare Observed with the Extreme-ultraviolet
Imaging Spectrometer aboard Hinode: Hints of Chromospheric Magnetic
Reconnection
Authors: Brosius, Jeffrey W.
Bibcode: 2013ApJ...777..135B
Altcode:
We obtained rapid cadence (11.2 s) EUV stare spectra of a solar
microflare with the Extreme-ultraviolet Imaging Spectrometer aboard
Hinode. The intensities of lines formed at temperatures too cool to
be found in the corona brightened by factors around 16 early during
this event, indicating that we observed a site of energy deposition in
the chromosphere. We derive the density evolution of the flare plasma
at temperature around 2 MK from the intensity ratio of Fe XIV lines
at 264.789 Å and 274.204 Å. From both lines we removed the bright
pre-flare quiescent emission, and from 274.204 we removed the blended
emission of Si VII λ274.180 based on the Si VII λ274.180/275.361
intensity ratio, which varies only slightly with density. In this
way the flare electron density is derived with emission from only
the flare plasma. The density increased by an order of magnitude from
its pre-flare quiescent average of (3.43 ± 0.19) × 109
cm-3 to its maximum impulsive phase value of (3.04 ±
0.57) × 1010 cm-3 in 2 minutes. The fact that
this rapid increase in density is not accompanied by systematic,
large upward velocities indicates that the density increase is not
due to the filling of loops with evaporated chromospheric material,
but rather due to material being directly heated in the chromosphere,
likely by magnetic reconnection. The density increase may be due to a
progression of reconnection sites to greater depths in the chromosphere,
where it has access to larger densities, or it may be due to compression
of 2 MK plasma by the 10 MK plasma as it attempts to expand against
the high-density chromospheric plasma.
Title: EUNIS 2013 and Beyond: Resolving the AIA 94 and 131 Å
Bandpasses
Authors: Daw, Adrian N.; Brosius, J. W.; Haas, J. P.; Landi, E.;
Plummer, T.; Rabin, D. M.; Wang, T.
Bibcode: 2013SPD....44...10D
Altcode:
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding
rocket instrument is a two-channel imaging spectrograph that observes
the solar corona and transition region with high spectral resolution
and a rapid cadence made possible by unprecedented sensitivity. The
2013 flight on 23 April at 17:30 UT incorporated a new wavelength
channel covering the range 525-630 Å, the previously-flown 300-370
Å channel, and the first flight demonstration of cooled active
pixel sensor (APS) arrays, resulting in high-signal-to-noise spectral
coverage spanning a wide temperature range of 0.025 to 10 MK. Absolute
radiometric calibration of the two channels is performed using a hollow
cathode discharge lamp and NIST-calibrated AXUV-100G photodiode. For
the 2013 flight, EUNIS co-observed dynamic coronal phenomena with
DST/IBIS, SoHO/CDS, SDO/AIA and Hinode/EIS and contributes to the
absolute radiometric calibrations of these instruments. Plans for
future wavelength channels to cover the AIA 94 and 131 Å bandpasses
and address the currently unresolved spectral lines (and therefore
temperature responses) within them are presented.
Title: First Results from the EUNIS 2013 Sounding Rocket Campaign
Authors: Daw, Adrian N.; Rabin, D. M.; Brosius, J. W.; Haas, J. P.;
Plummer, T.; Cauzzi, G.; Reardon, K. P.; Beck, C.
Bibcode: 2013SPD....4410501D
Altcode:
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS)
sounding rocket launched 23 April 2013 at 17:30 UT, as part of a
campaign including co-ordinated observations with the Dunn Solar
Telescope/IBIS, Hinode/EIS, SoHO/CDS, RHESSI and SDO. EUNIS obtained
the highest-resolution observations of the solar spectrum from 52-63 nm
observed to date, as well as observations with the previously-flown
waveband from 30-37 nm. The broad spectral coverage of the EUV
observations includes emission lines of ionization stages from He I to
Fe XIX, and thus a wide temperature range of 0.025 to 10 MK. Absolute
radiometric calibration of EUNIS provides underflight calibration of
CDS, EIS and AIA. Spectra were obtained with a 1.3 s cadence as the
660-arcsec long slit was rastered across two different regions. The
observations captured a B-class flare in active region NOAA 11726 as
well as active regions 11723, 11724, off-limb, quiet sun and a coronal
hole. We discuss first results from anaysis of this rich and extensive
data set.
Title: Chromospheric Evaporation in Solar Flare Loop Strands Observed
with the Extreme-ultraviolet Imaging Spectrometer on Board Hinode
Authors: Brosius, Jeffrey W.
Bibcode: 2013ApJ...762..133B
Altcode:
The entire profile of the Fe XXIII line at 263.8 Å, formed at
temperature ≈14 MK, was blueshifted by an upward velocity -122 ± 33
km s-1 when it was first detected by the Extreme-ultraviolet
Imaging Spectrometer operating in rapid cadence (11.18 s) stare mode
during a C1 solar flare. The entire profile became even more blueshifted
over the next two exposures, when the upward velocity reached its
maximum of -208 ± 14 km s-1 before decreasing to zero
over the next 12 exposures. After that, a weak, secondary blueshifted
component appeared for five exposures, reached a maximum upward velocity
of -206 ± 33 km s-1, and disappeared after the maximum
line intensity (stationary plus blueshifted) was achieved. Velocities
were measured relative to the intense stationary profile observed near
the flare's peak and early during its decline. The initial episode
during which the entire profile was blueshifted lasted about 156 s,
while the following episode during which a secondary blueshifted
component was detected lasted about 56 s. The first episode likely
corresponds to chromospheric evaporation in a single loop strand,
while the second corresponds to evaporation in an additional strand,
as described in multi-strand flare loop models proposed by Hori et
al. and Warren & Doschek. Line emission from progressively cooler
ions (Fe XVII, XVI, and XIV) brightened at successively later times,
consistent with cooling of flare-heated plasma.
Title: Rapid Cadence Dual Slit EUV Spectroscopic Observation of
Episodic Chromospheric Evaporation in a Solar Flare Loop
Authors: Brosius, J. W.
Bibcode: 2012AGUFMSH43B2164B
Altcode:
We observed a C1 flare in rapid cadence stare mode simultaneously
with Hinode's EIS (11.2 s) and SOHO's CDS (10 s) on 2012 March 7. The
pointings of the two slits were offset about 25 arcsec, so that EIS
observed the leg and CDS the apex of the flaring loop. EIS observed the
Fe XXIII line at 263.8 A, formed at temperatures around 14 MK, to emerge
abruptly above the background noise at 18:49:36 UT. The line's intensity
peaked at 18:53:09 UT. After its emergence the Fe XXIII line's entire
profile became increasingly blueshifted over the next 3 exposures,
reached a maximum upward velocity of -208 km/s, and then became
decreasingly blueshifted toward zero velocity while the line's intensity
continued to increase over the next 12 exposures. The bulk of the Fe
XXIII emission remained stationary after that. A secondary blueshifted
component of the Fe XXIII line profile appeared at 18:52:24 UT, endured
for 5 exposures, and reached a maximum upward velocity of -206 km/s. We
interpret this sudden, brief re-appearance of rapid upward velocity in
Fe XXIII emission as evidence for ongoing reconnection following the
flare's initial, impulsive phase. The structure of the loop and its
strand footpoints seen in the AIA 131 and 94 A images reveal changes
possibly due to the cutting and rearrangement of individual strands
during reconnection. Emission lines of Fe XVII, formed at temperatures
around 4 MK, and Fe XVI, formed around 2.7 MK, brightened significantly
starting about 3.3 and 7.1 minutes after the first appearance of Fe
XXIII emission, likely due to cooling of plasma previously heated to
temperatures appropriate for Fe XXIII emission. Neither Fe XVII nor
Fe XVI showed significant relative Doppler velocities. None of the
transition region lines observed by EIS participated in the event. CDS
spectra were contaminated by a particle storm at SOHO during the flare,
but we were able to salvage roughly 1/3 of the exposures by visually
inspecting individual line profiles and discarding those that appeared
affected. The intensity of the Fe XIX line at 592.2 A, formed at 8 MK,
reached its maximum value at the location of the CDS slit near the
flare loop apex about 4.6 minutes after the Fe XXIII line reached its
peak intensity. This work was supported by NASA grant NNX10AC08G.
Title: Extreme-ultraviolet Spectroscopic Observation of Direct
Coronal Heating during a C-class Solar Flare
Authors: Brosius, Jeffrey W.
Bibcode: 2012ApJ...754...54B
Altcode:
With the Coronal Diagnostic Spectrometer operating in rapid cadence
(9.8 s) stare mode during a C6.6 flare on the solar disk, we observed
a sudden brightening of Fe XIX line emission (formed at temperature T
≈ 8 MK) above the pre-flare noise without a corresponding brightening
of emission from ions formed at lower temperatures, including He I
(0.01 MK), O V (0.25 MK), and Si XII (2 MK). The sudden brightening
persisted as a plateau of Fe XIX intensity that endured more than 11
minutes. The Fe XIX emission at the rise and during the life of the
plateau showed no evidence of significant bulk velocity flows, and
hence cannot be attributed to chromospheric evaporation. However, the
line width showed a significant broadening at the rise of the plateau,
corresponding to nonthermal velocities of at least 89 km s-1
due to reconnection outflows or turbulence. During the plateau He I,
O V, and Si XII brightened at successively later times starting about
3.5 minutes after Fe XIX, which suggests that these brightenings were
produced by thermal conduction from the plasma that produced the Fe XIX
line emission; however, we cannot rule out the possibility that they
were produced by a weak beam of nonthermal particles. We interpret an
observed shortening of the O V wavelength for about 1.5 minutes toward
the middle of the plateau to indicate new upward motions driven by the
flare, as occurs during gentle chromospheric evaporation; relative to
a quiescent interval shortly before the flare, the O V upward velocity
was around -10 km s-1.
Title: EUV Rapid Cadence Spectroscopic Observation of Direct Coronal
Heating During a C-class Solar Flare
Authors: Brosius, Jeffrey W.
Bibcode: 2012AAS...22020421B
Altcode:
With CDS operating in rapid cadence (9.8 s) stare mode during a
C6.6 flare on the solar disk, we observed a sudden brightening
of Fe XIX line emission (formed at temperature around 8 MK)
above the pre-flare noise without a corresponding brightening of
emission from ions formed at lower temperatures, including He I
(0.01 MK), O V (0.25 MK), and Si XII (2 MK). The sudden brightening
persisted as a plateau of Fe XIX intensity that endured more than
11 minutes. The Fe XIX emission at the rise and during the life of
the plateau showed no evidence of significant bulk velocity flows,
and hence cannot be attributed to chromospheric evaporation. However,
the line width showed a significant broadening at the rise of the
plateau, corresponding to nonthermal velocities of at least 89 km/s
due to reconnection outflows or turbulence. During the plateau He I,
O V, and Si XII brightened at successively later times starting about
3.5 minutes after Fe XIX, which suggests that these brightenings were
produced by thermal conduction from the plasma producing Fe XIX line
emission; however, we cannot rule out the possibility that they were
produced by a weak beam of nonthermal particles. O V showed an upward
velocity around -10 km/s for about 2 minutes toward the middle of the
plateau, indicating gentle chromospheric evaporation. This work
is supported by NASA grant NNX10AC08G.
Title: Using SDO's AIA to investigate energy transport from a flare's
energy release site to the chromosphere
Authors: Brosius, J. W.; Holman, G. D.
Bibcode: 2012A&A...540A..24B
Altcode:
Context. Coordinated observations of a GOES B4.8 microflare with SDO's
Atmospheric Imaging Assembly (AIA) and the Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) on 2010 July 31 show that emission in
all seven of AIA's EUV channels brightened simultaneously nearly 6 min
before RHESSI or GOES detected emission from plasma at temperatures
around 10 MK.
Aims: To help interpret these and AIA flare
observations in general, we characterized the expected temporal
responses of AIA's 94, 131, 171, 193, 211, and 335 Å channels to
solar flare brightenings by combining (1) AIA's nominal temperature
response functions available through SSWIDL with (2) EUV spectral
line data observed in a flare loop footpoint on 2001 April 24 with
the Coronal Diagnostic Spectrometer (CDS) on timescales comparable to
AIA's image cadence.
Methods: The nine emission lines observed
by CDS cover a wide range of formation temperature from about 0.05 to
8 MK. Line brightenings observed early during the CDS flare occurred at
temperatures less than about 0.7 MK, with the largest values around 0.1
MK. These brightenings were consistent with the flare's energy transport
being dominated by nonthermal particle beams. Because all of AIA's EUV
channels are sensitive to emission from plasma in the 0.1 to 0.7 MK
temperature range, we show that all of AIA's EUV channels will brighten
simultaneously during flares like this, in which energy transport is
dominated by nonthermal particle beams.
Results: The 2010 July 31
flare observed by AIA and RHESSI displays this behavior, so we conclude
that such beams likely dominated the flare's energy transport early
during the event. When thermal conduction from a reconnection-heated,
hot (~10 MK) plasma dominates the energy transport, the AIA channels
that are sensitive to emission from such temperatures (particularly
the 94 and 131 Å channels) will brighten earlier than the channels
that are not sensitive to such temperatures (171 and 211 Å).
Conclusions: Thus, based on the differences expected between AIA's
response to flares whose energy transport is dominated by nonthermal
particle beams from those whose energy transport is dominated by thermal
conduction, AIA can be used to determine the dominant energy transport
mechanism for any given event. Movie is available in electronic
form at http://www.aanda.org
Title: Underflight Calibration of SOHO/CDS and Hinode/EIS with
EUNIS-07
Authors: Wang, Tongjiang; Thomas, Roger J.; Brosius, Jeffrey W.; Young,
Peter R.; Rabin, Douglas M.; Davila, Joseph M.; Del Zanna, Giulio
Bibcode: 2011ApJS..197...32W
Altcode: 2011arXiv1109.6598W
Flights of Goddard Space Flight Center's Extreme Ultraviolet
Normal Incidence Spectrograph (EUNIS) sounding rocket in 2006
and 2007 provided updated radiometric calibrations for Solar and
Heliospheric Observatory/Coronal Diagnostic Spectrometer (SOHO/CDS)
and Hinode/Extreme Ultraviolet Imaging Spectrometer (Hinode/EIS). EUNIS
carried two independent imaging spectrographs covering wavebands of
300-370 Å in first order and 170-205 Å in second order. After each
flight, end-to-end radiometric calibrations of the rocket payload were
carried out in the same facility used for pre-launch calibrations of
CDS and EIS. During the 2007 flight, EUNIS, SOHO/CDS, and Hinode/EIS
observed the same solar locations, allowing the EUNIS calibrations to
be directly applied to both CDS and EIS. The measured CDS NIS 1 line
intensities calibrated with the standard (version 4) responsivities with
the standard long-term corrections are found to be too low by a factor
of 1.5 due to the decrease in responsivity. The EIS calibration update
is performed in two ways. One uses the direct calibration transfer of
the calibrated EUNIS-07 short wavelength (SW) channel. The other uses
the insensitive line pairs, in which one member was observed by the
EUNIS-07 long wavelength (LW) channel and the other by EIS in either the
LW or SW waveband. Measurements from both methods are in good agreement,
and confirm (within the measurement uncertainties) the EIS responsivity
measured directly before the instrument's launch. The measurements also
suggest that the EIS responsivity decreased by a factor of about 1.2
after the first year of operation (although the size of the measurement
uncertainties is comparable to this decrease). The shape of the EIS SW
response curve obtained by EUNIS-07 is consistent with the one measured
in laboratory prior to launch. The absolute value of the quiet-Sun
He II 304 Å intensity measured by EUNIS-07 is consistent with the
radiance measured by CDS NIS in quiet regions near the disk center
and the solar minimum irradiance recently obtained by CDS NIS and the
Solar Dynamics Observatory/Extreme Ultraviolet Variability Experiment.
Title: Using AIA on SDO to Investigate the Transport of Flare Energy
From Its Release Site to the Chromosphere
Authors: Brosius, J. W.; Holman, G.
Bibcode: 2011AGUFMSH44A..03B
Altcode:
Coordinated AIA and RHESSI observations of a GOES B4.8 flare on 2010
July 31 show that emission in all seven of AIA's EUV channels brightened
nearly six minutes before RHESSI or GOES detected any emission from
plasma at temperatures around 10 MK. To help interpret these and AIA
flare observations in general, we characterized the expected temporal
responses of AIA's 94, 131, 171, 193, 211, and 335 Angstrom channels
to solar flare brightenings by combining (1) AIA's nominal temperature
response functions available through SSWIDL (Boerner et al. 2011)
with (2) existing EUV spectral line flare data obtained on timescales
comparable to AIA's image cadence. For the latter we use CDS stare
spectra of a flare loop footpoint reported by Brosius and Phillips
(2004). These spectra were observed at a cadence of 9.8 s, and their
nine emission lines cover a wide range of formation temperature from
about 0.05 to 8 MK. The line brightenings that were observed early
during the CDS flare occurred at temperatures less than about 0.7 MK,
with the largest brightenings around 0.1 MK; this indicates that
the flare's energy transport was dominated by nonthermal particle
beams. Because all of AIA's EUV channels are sensitive to emission
from plasma in this temperature range (0.1 - 0.7 MK), we show that
all of AIA's EUV channels are expected to brighten simultaneously
during flares like this, in which energy transport is dominated by
nonthermal particle beams. Since the 2010 July 31 flare observed by
AIA and RHESSI displays this expected behavior, we conclude that such
beams began to drive chromospheric evaporation during this event nearly
six minutes before flare temperatures around 10 MK were reached. When
thermal conduction from a directly-heated, hot (~10 MK) plasma is
the dominant energy transport mechanism, the AIA channels that are
sensitive to emission from such temperatures (particularly the 94
and 131 channels) will brighten earlier than the channels that are
not sensitive to such temperatures (171 and 211). Thus, based on the
differences that we expect in AIA's response to flares whose energy
transport is dominated by nonthermal particle beams from those whose
energy transport is dominated by thermal conduction, AIA may be able to
determine the dominant energy transport mechanism for any given event.
Title: Coronal Bright Points and Quiet Sun Areas Observed with
EUNIS-07 and EIS
Authors: Brosius, Jeffrey W.; Wang, T. J.; Rabin, D. M.; Thomas,
R. J.; Landi, E.
Bibcode: 2011SPD....42.1828B
Altcode: 2011BAAS..43S.1828B
The Extreme-Ultraviolet Normal-Incidence Spectrograph is a
sounding rocket instrument with two independent but co-pointing
imaging spectrographs. One spectrograph observes emission lines in a
long-wavelength (LW) channel (300-370 A), while a second observes lines
in a short-wavelength (SW) channel (170-205 A). The instrument was last
flown on 6 November 2007 (EUNIS-07), when there were no active regions
on the solar disk. After the flight, the absolute radiometric responses
of both channels were derived from laboratory measurements obtained
in the same facility used for pre-flight calibrations of SOHO/CDS and
Hinode/EIS. Coordinated EUNIS-07 and EIS observations of quiet sun area
near disk center reveal that the sensitivity of both EIS wavebands had
diminished to 82% of their pre-launch values (Wang et al. 2011). Here
we use the combined EUNIS-07 and EIS spectra to investigate quiet sun
areas and small bright points observed by both instruments, as well
as a larger, brighter bright point that was observed only by EUNIS-07.
Title: New Capabilities of the EUNIS Sounding Rocket Instrument
Authors: Daw, Adrian N.; Brosius, J.; Criscuolo, E.; Davila, J.;
Haas, J. P.; Hilton, G.; Linard, D.; Plummer, T.; Rabin, D.; Thomas,
R.; Varney, D.; Wang, T.
Bibcode: 2011SPD....42.1502D
Altcode: 2011BAAS..43S.1502D
The upcoming flight of the Extreme Ultraviolet Normal Incidence
Spectrograph (EUNIS) sounding rocket instrument, a two-channel imaging
spectrograph that observes the solar corona and transition region
with high spectral resolution and a rapid cadence made possible by
unprecedented sensitivity, will incorporate a new wavelength channel
and cooling of the active pixel sensor (APS) arrays. The new 52.4-63.0
nm channel incorporates a Toroidal Varied Line Space (TVLS) grating
coated with B4C/Ir, providing broad spectral coverage and
a wide temperature range of 0.025 to 10 MK. The APS arrays for both
the 52-63 nm and 30-37 nm channels will be cooled to -20 C to reduce
dark current noise. With the resulting read-noise limited performance,
over a dozen new diagnostic line pairs become available in the two
wavelength channels. To our knowledge, this will be the first flight
demonstration of cooled APS arrays. EUNIS will co-observe dynamic
coronal phenomena with SDO/AIA and Hinode/EIS and will contribute to
the absolute radiometric calibrations of these instruments. EUNIS
is supported by NASA through the Low Cost Access to Space Program in
Solar and Heliospheric Physics.
Title: An Investigation of Solar Coronal Bright Points Based on EUV
Spectra Obtained with EUNIS-07
Authors: Schaefer, R.; Brosius, J. W.; Bruhweiler, F.; Rabin, D. M.;
Thomas, R.; Wang, T.
Bibcode: 2010AGUFMSH31C1805S
Altcode:
The EUNIS sounding rocket instrument is a two-channel imaging
spectrograph that observes the solar corona with a rapid cadence made
possible by unprecedented sensitivity. The instrument was successfully
flown on 2006 April 12 (EUNIS-06) and 2007 November 6 (EUNIS-07),
providing hundreds of spectra in the wavelength ranges 170-205 A and
300-370 A with sustained cadences as fast as 1.3 s. The EUNIS-07
data have provided the first on-orbit radiometric calibration of
Hinode's EIS and STEREO's SECCHI/EUVI. Although there were no active
regions on the solar disk during this flight, EUNIS-07 repeatedly
scanned across several small coronal bright points within a large
area of quiet Sun near disk center. We fitted Gaussian profiles to
emission lines formed at temperatures ranging from 0.05 MK to 2 MK
(with particular attention to He II 304 A, Mg IX 368 A, and Fe XIV
334 A) in the spatially resolved EUV spectra. The resulting line
profile fits are used to derive a series of bright point images that
we investigate for brightness variations on time scales of one minute,
as well as relative Doppler velocities. Evolution of the bright points
on time scales of hours are investigated with magnetograms from SOHO's
MDI. EUNIS is supported by the NASA Heliophysics Division through its
Low Cost Access to Space Program in Solar and Heliospheric Physics,
and is scheduled to fly again in 2011. EUNIS data are freely available
to the solar physics community. RS acknowledges support under NSF/REU
grant ATM-00552671 to CUA. JWB is supported by NASA grant NNX10AK45G.
Title: Solar flare impulsive phase observations from SDO and other
observatories
Authors: Chamberlin, P. C.; Woods, T. N.; Schrijver, C. J.; Warren,
H. P.; Milligan, R. O.; Christe, S.; Brosius, J. W.
Bibcode: 2010AGUFMSH23A1832C
Altcode:
With the start of normal operations of the Solar Dynamics Observatory
in May 2010, the Extreme ultraviolet Variability Experiment (EVE)
and the Atmospheric Imaging Assembly (AIA) have been returning the
most accurate solar XUV and EUV measurements every 10 and 12 seconds,
respectively, at almost 100% duty cycle. The focus of the presentation
will be the solar flare impulsive phase observations provided by EVE
and AIA and what these observations can tell us about the evolution
of the initial phase of solar flares. Also emphasized throughout
is how simultaneous observations with other instruments, such as
RHESSI, SOHO-CDS, and HINODE-EIS, will help provide a more complete
characterization of the solar flares and the evolution and energetics
during the impulsive phase. These co-temporal observations from the
other solar instruments can provide information such as extending
the high temperature range spectra and images beyond that provided
by the EUV and XUV wavelengths, provide electron density input into
the lower atmosphere at the footpoints, and provide plasma flows of
chromospheric evaporation, among other characteristics.
Title: Using AIA, RHESSI, EVE, and CDS Observations to Investigate
the Temperature-Dependent Response of the Solar Atmosphere to Flares
Authors: Brosius, J. W.; Holman, G.; Chamberlin, P. C.
Bibcode: 2010AGUFMSH21C..05B
Altcode:
We combine SDO/AIA multi-channel EUV images obtained during GOES B, C,
and M-class flares with EVE spectra, RHESSI hard X-ray observations,
and/or CDS rapid cadence EUV stare spectra to investigate the
temperature- dependent response of solar active region atmospheres to
flare energy input. In particular we investigate temperature-dependent
differences in flare onset times based on emission from plasma
temperatures that range from 0.05 MK to 20 MK. Preliminary results
from observations of a GOES B4.8 flare that occurred in AR 11092 on
31 July 2010 reveal no significant onset time differences among the
various AIA wavebands, with all of the AIA light curves revealing
a precursor-like brightening that began 6 minutes before the start
of the flare was observed with either GOES or RHESSI, and a rapid,
impulsive rise that began about 1 minute before the flare was observed
with GOES or RHESSI. Similar behavior is observed in a secondary burst
that occurred at a different spatial location during the same small
flare. Preliminary results based on observations of a GOES M1.0 flare
that occurred in AR 11093 on 7 August 2010 again reveal simultaneous
early brightenings in all of the AIA channels, but in this case we note
subsequent decreases in the 211 and 335 Angstrom emission at several
locations after the flare was already well developed, and while it
showed increasing emission in the 94 and 131 Angstrom channels. This
work is supported by NASA grant NNX10AC08G.
Title: Early Chromospheric Response During a Solar Microflare Observed
With SOHO's CDS and RHESSI
Authors: Brosius, Jeffrey W.; Holman, Gordon D.
Bibcode: 2010ApJ...720.1472B
Altcode:
We observed a solar microflare with RHESSI and SOHO's Coronal Diagnostic
Spectrometer (CDS) on 2009 July 5. With CDS we obtained rapid cadence
(7 s) stare spectra within a narrow field of view toward the center
of AR 11024. The spectra contain emission lines from ions that
cover a wide range of temperature, including He I (<0.025 MK),
O V (0.25 MK), Si XII (2 MK), and Fe XIX (8 MK). The start of a
precursor burst of He I and O V line emission preceded the steady
increase of Fe XIX line emission by about 1 minute and the emergence
of 3-12 keV X-ray emission by about 4 minutes. Thus, the onset of the
microflare was observed in upper chromospheric (He I) and transition
region (O V) line emission before it was detected in high-temperature
flare plasma emission. Redshifted O V emission during the precursor
suggests explosive chromospheric evaporation, but no corresponding
blueshifts were found with either Fe XIX (which was very weak) or Si
XII. Similarly, in subsequent microflare brightenings the O V and He
I intensities increased (between 49 s and almost 2 minutes) before
emissions from the hot flare plasma. Although these time differences
likely indicate heating by a nonthermal particle beam, the RHESSI
spectra provide no additional evidence for such a beam. In intervals
lasting up to about 3 minutes during several bursts, the He I and O V
emission line profiles showed secondary, highly blueshifted (~-200 km
s-1) components; during intervals lasting nearly 1 minute
the velocities of the primary and secondary components were oppositely
directed. Combined with no corresponding blueshifts in either Fe XIX
or Si XII, this indicates that explosive chromospheric evaporation
occurred predominantly at either comparatively cool temperatures (<2
MK) or within a hot temperature range to which our observations were
not sensitive (e.g., between 2 and 8 MK).
Title: Absolute Radiometric Calibration Of EUNIS, And Calibration
Updates For Hinode/EIS And SOHO/CDS
Authors: Wang, Tongjiang; Thomas, R. J.; Brosius, J. W.; Young, P. R.;
Rabin, D. M.; Davila, J. M.
Bibcode: 2010AAS...21640704W
Altcode: 2010BAAS...41..860W
The Extreme-Ultraviolet Normal-Incidence Spectrograph sounding rocket
payload was flown in 2006 (EUNIS-06) and 2007 (EUNIS-07), each time
carrying two independent imaging spectrographs covering wave bands
of 300-370 Angstrom in first order and 170-205 Angstrom in second
order. For each flight, the absolute radiometric response of the EUNIS
long-wavelength (LW) channel was directly measured in the same facility
used for pre-flight calibrations of SOHO/CDS and Hinode/EIS. The
wavelength range of the EUNIS LW channel overlaps that of CDS/NIS-1,
and so can provide a direct calibration update for it. The EUNIS-06
observation shows that the efficiency of CDS/NIS-1 has decreased by
a factor about 1.7 compared to that of the previously implemented
calibration. Here we present an update to the absolute calibration for
Hinode/EIS derived with a technique that combines a direct comparison
of line intensities observed in cospatial EUNIS-07 and EIS spectra,
along with density- and temperature-insensitive line intensity ratios.
Title: Fast Cold Upflows During a Solar Microflare Observed with
RHESSI and SOHO's CDS
Authors: Brosius, Jeffrey W.; Holman, G. D.
Bibcode: 2010AAS...21640418B
Altcode: 2010BAAS...41..902B
A GOES B1.8 microflare was observed with RHESSI and SOHO's CDS between
about 16:25 and 17:00 UT on 2009 July 5. The event occurred in NOAA AR
11024, the only active region on the solar disk at the time. With CDS
we obtained rapid cadence (7 s) stare spectra within a narrow field of
view toward the center of the region. Spectra contain emission lines
from ions that cover a wide range of temperature, including He I (0.01
MK), O V (0.25 MK), Si XII (2 MK), and Fe XIX (8 MK). The start of a
burst in He I and O V line emission preceded the emergence of Fe XIX
line emission by about 1 minute, and the emergence of 3-12 keV X-ray
emission by about 4 minutes. Thus the onset of the flare is observed in
upper chromospheric (He I) and transition region (O V) line emission
before it is detected in high temperature flare plasma emission. This
may indicate the presence of a nonthermal particle beam early during
the microflare. Similarly, in subsequent bursts the O V and He I
intensities increase before emissions from the hot flare plasma. In
intervals lasting up to about 3 minutes during several bursts, the He
I and O V emission line profiles show secondary, highly blueshifted
( 200 km/s) components; during intervals lasting nearly 1 minute the
velocities of the primary and secondary components are oppositely
directed, suggesting explosive chromospheric evaporation. This work
is supported by NASA through SR&T grant NNX07AI09G.
Title: Emission lines of FeXI in the 257-407Å wavelength region
observed in solar spectra from EIS/Hinode and SERTS
Authors: Keenan, F. P.; Milligan, R. O.; Jess, D. B.; Aggarwal, K. M.;
Mathioudakis, M.; Thomas, R. J.; Brosius, J. W.; Davila, J. M.
Bibcode: 2010MNRAS.404.1617K
Altcode: 2010MNRAS.tmp..299K; 2010arXiv1001.3627K
Theoretical emission-line ratios involving FeXI transitions in the
257-407Å wavelength range are derived using fully relativistic
calculations of radiative rates and electron impact excitation
cross-sections. These are subsequently compared with both long
wavelength channel Extreme-Ultraviolet Imaging Spectrometer (EIS)
spectra from the Hinode satellite (covering 245-291Å) and first-order
observations (~235-449Å) obtained by the Solar Extreme-ultraviolet
Research Telescope and Spectrograph (SERTS). The 266.39, 266.60 and
276.36Å lines of FeXI are detected in two EIS spectra, confirming
earlier identifications of these features, and 276.36Å is found to
provide an electron density (Ne) diagnostic when ratioed
against the 257.55Å transition. Agreement between theory and
observation is found to be generally good for the SERTS data sets,
with discrepancies normally being due to known line blends, while the
257.55Å feature is detected for the first time in SERTS spectra. The
most useful FeXI electron density diagnostic is found to be the
308.54/352.67 intensity ratio, which varies by a factor of 8.4 between
Ne = 108 and 1011cm-3,
while showing little temperature sensitivity. However, the
349.04/352.67 ratio potentially provides a superior diagnostic,
as it involves lines which are closer in wavelength, and varies
by a factor of 14.7 between Ne = 108 and
1011cm-3. Unfortunately, the 349.04Å line is
relatively weak, and also blended with the second-order FeX 174.52Å
feature, unless the first-order instrument response is enhanced.
Title: Absolute Radiometric Calibration of the EUNIS-06 170-205
Å Channel and Calibration Update for Coronal Diagnostic
Spectrometer/Normal-Incidence Spectrometer
Authors: Wang, Tongjiang; Brosius, Jeffrey W.; Thomas, Roger J.;
Rabin, Douglas M.; Davila, Joseph M.
Bibcode: 2010ApJS..186..222W
Altcode: 2009arXiv0912.2328W
The Extreme-Ultraviolet Normal-Incidence Spectrograph sounding-rocket
payload was flown on 2006 April 12 (EUNIS-06), carrying two independent
imaging spectrographs covering wavebands of 300-370 Å in first order
and 170-205 Å in second order, respectively. The absolute radiometric
response of the EUNIS-06 long-wavelength (LW) channel was directly
measured in the same facility used to calibrate Coronal Diagnostic
Spectrometer (CDS) prior to the Solar and Heliospheric Observatory
(SOHO) launch. Because the absolute calibration of the short-wavelength
(SW) channel could not be obtained from the same lab configuration,
we here present a technique to derive it using a combination of solar
LW spectra and density- and temperature-insensitive line intensity
ratios. The first step in this procedure is to use the coordinated,
cospatial EUNIS and SOHO/CDS spectra to carry out an intensity
calibration update for the CDS NIS-1 waveband, which shows that its
efficiency has decreased by a factor about 1.7 compared to that of the
previously implemented calibration. Then, theoretical insensitive line
ratios obtained from CHIANTI allow us to determine absolute intensities
of emission lines within the EUNIS SW bandpass from those of cospatial
CDS/NIS-1 spectra after the EUNIS LW calibration correction. A total
of 12 ratios derived from intensities of 5 CDS and 12 SW emission
lines from Fe X to Fe XIII yield an instrumental response curve for
the EUNIS-06 SW channel that matches well to a relative calibration
which relied on combining measurements of individual optical
components. Taking into account all potential sources of error, we
estimate that the EUNIS-06 SW absolute calibration is accurate to ±20%.
Title: Conversion from Explosive to Gentle Chromospheric Evaporation
During a Solar Flare
Authors: Brosius, Jeffrey W.
Bibcode: 2009ApJ...701.1209B
Altcode:
A GOES M1.5 solar flare was observed in NOAA AR 10652 on 2004 July
27 around 20:00 UT with the Coronal Diagnostic Spectrometer (CDS)
aboard the Solar and Heliospheric Observatory (SOHO) spacecraft. Images
obtained with SOHO's Extreme-ultraviolet Imaging Telescope and with
the Transition Region And Coronal Explorer satellite show that the
CDS slit was positioned within the flare, whose emission extended 1
arcmin along the slit. Rapid cadence (9.8 s) stare spectra obtained
with CDS include emission from the upper chromosphere (He I at 584.3
Å), transition region (O V at 629.7 Å), corona (Si XII at 520.7 Å),
and hot flare plasma (Fe XIX at 592.2 Å), and reveal that (1) the
flare brightened in its southern parts before it did so in the north;
(2) chromospheric evaporation was "explosive" during the first rapid
intensity increase observed in Fe XIX, but converted to "gentle"
during the second; (3) chromospheric evaporation did not occur in
the northern portion of the flare observed by CDS: the brightening
observed there was due to flare material moving into that location
from elsewhere. We speculate that the initial slow, steady increase
of Fe XIX intensity that was observed to start several minutes before
its rapid increase was due to direct coronal heating. The change from
explosive to gentle evaporation was likely due to either an increased
absorption of beam energy during the gentle event because the beam
passed through an atmosphere modified by the earlier explosive event,
or to a weakening of the coronal magnetic field's ability to accelerate
nonthermal particle beams (via reconnection) as the flare progressed,
or both.
Title: Analysis of Active Region and Quiet Sun Spectra from SERTS-99
Observations
Authors: Coyner, Aaron J.; Davila, J. M.; Brosius, J. W.; Ofman, L.
Bibcode: 2009SPD....40.1216C
Altcode:
The Solar EUV Research Telescope and Spectrograph is a rocket-based
instrument that uses high resolution extreme ultraviolet spectra to
investigate features in the solar corona and transition region. The 1999
flight occurred on 24 June 1999 and obtained spectra from both active
regions and quiet sun regions on the solar disk covering a spectral
bandpass 300-355 angstroms We report here the calibrated intensities
and measured linewidths determined from the spatially-averaged spectra
of both active regions and quiet sun regions respectively. In addition,
we determine a distribution of non-thermal velocity components from the
measured linewidths of the identified lines. This distribution provides
a quantitative constraint on the available energy of non-thermal origin
in the observed regions which is available for coronal heating.
Title: Observation of the Conversion From Explosive to Gentle
Chromospheric Evaporation During a Solar Flare
Authors: Brosius, Jeffrey W.
Bibcode: 2009SPD....40.3603B
Altcode:
A GOES M1.5 solar flare was observed in NOAA AR 10652 on 27 July
2004 around 20:00 UT with SOHO. EIT images show that the CDS slit was
positioned within the flare, whose emission extended 1 arcmin along
the slit. Rapid cadence (9.8 s) stare spectra obtained with CDS include
emission from the chromosphere (He I at 584.3 A), transition region (O
V at 629.7 A), corona (Si XII at 520.7 A), and hot flare plasma (Fe XIX
at 592.2 A), and reveal that (1) the flare brightened in its southern
parts before it did so in the north; (2) chromospheric evaporation was
"explosive" during the first rapid intensity increase observed in Fe
XIX, but converted to "gentle" during the second; (3) chromospheric
evaporation did not occur in the northern portion of the flare observed
by CDS: the brightening observed there was due to flare material moving
into that location from elsewhere. The initial slow, steady increase
of Fe XIX intensity that was observed to start several minutes before
its rapid increase may have been due to direct coronal heating. The
change from explosive to gentle evaporation was likely due to either
an increased absorption of beam energy during the gentle event because
the beam passed through an atmosphere modified by the earlier explosive
event, or to a weakening of the coronal magnetic field's ability to
accelerate nonthermal particle beams (via reconnection) as the flare
progressed, or both. This work is supported by NASA grant NNX07AI09G.
Title: Observations of the Thermal and Dynamic Evolution of a Solar
Microflare
Authors: Brosius, Jeffrey W.; Holman, Gordon D.
Bibcode: 2009ApJ...692..492B
Altcode:
We observed a solar microflare over a wide temperature range with three
instruments aboard the SOHO spacecraft (Coronal Diagnostic Spectrometer
(CDS), Extreme-ultraviolet Imaging Telescope (EIT), and Michelson
Doppler Imager (MDI)), TRACE (1600 Å), GOES, and RHESSI. The
microflare's properties and behavior are those of a miniature
flare undergoing gentle chromospheric evaporation, likely driven by
nonthermal electrons. Extreme-ultraviolet spectra were obtained at a
rapid cadence (9.8 s) with CDS in stare mode that included emission
lines originating from the chromosphere (temperature of formation
Tm ≈ 1 × 104 K) and transition region
(TR), to coronal and flare (Tm ≈ 8 × 106
K) temperatures. Light curves derived from the CDS spectra and
TRACE images (obtained with a variable cadence ≈34 s) reveal two
precursor brightenings before the microflare. After the precursors,
chromospheric and TR emission are the first to increase, consistent
with energy deposition by nonthermal electrons. The initial slow rise
is followed by a brief (20 s) impulsive EUV burst in the chromospheric
and TR lines, during which the coronal and hot flare emission gradually
begin to increase. Relative Doppler velocities measured with CDS are
directed upward with maximum values ≈20 km s-1 during
the second precursor and shortly before the impulsive peak, indicating
gentle chromospheric evaporation. Electron densities derived from an
O IV line intensity ratio (Tm ≈ 1.6 × 105 K)
increased from 2.6 × 1010 cm-3 during quiescent
times to 5.2 × 1011 cm-3 at the impulsive
peak. The X-ray emission observed by RHESSI peaked after the impulsive
peak at chromospheric and TR temperatures and revealed no evidence of
emission from nonthermal electrons. Spectral fits to the RHESSI data
indicate a maximum temperature of ≈13 MK, consistent with a slightly
lower temperature deduced from the GOES data. Magnetograms from MDI
show that the microflare occurred in and around a growing island
of negative magnetic polarity embedded in a large area of positive
magnetic field. The microflare was compact, covering an area of 4 ×
107 km2 in the EIT image at 195 Å, and appearing
as a point source located 7'' west of the EIT source in the RHESSI
image. TRACE images suggest that the microflare filled small loops.
Title: Emission lines of FeX in active region spectra obtained with
the Solar Extreme-ultraviolet Research Telescope and Spectrograph
Authors: Keenan, F. P.; Jess, D. B.; Aggarwal, K. M.; Thomas, R. J.;
Brosius, J. W.; Davila, J. M.
Bibcode: 2008MNRAS.389..939K
Altcode: 2008MNRAS.tmp..860K; 2008arXiv0806.3354K
Fully relativistic calculations of radiative rates and electron
impact excitation cross-sections for FeX are used to derive
theoretical emission-line ratios involving transitions in
the 174-366Å wavelength range. A comparison of these with
solar active region observations obtained during the 1989
and 1995 flights of the Solar Extreme-ultraviolet Research
Telescope and Spectrograph (SERTS) reveals generally very good
agreement between theory and experiment. Several FeX emission
features are detected for the first time in SERTS spectra, while the
3s23p52P3/2-3s23p4(1S)3d
2D3/2 transition at 195.32Å is identified for
the first time (to our knowledge) in an astronomical source. The most
useful FeX electron density (Ne) diagnostic line ratios are
assessed to be 175.27/174.53 and 175.27/177.24, which both involve lines
close in wavelength and free from blends, vary by factors of 13 between
Ne = 108 and 1011cm-3,
and yet show little temperature sensitivity. Should these lines
not be available, then the 257.25/345.74 ratio may be employed
to determine Ne, although this requires an accurate
evaluation of the instrument intensity calibration over a relatively
large wavelength range. However, if the weak 324.73Å line of FeX
is reliably detected, the use of 324.73/345.74 or 257.25/324.73
is recommended over 257.25/345.74. Electron densities deduced from
175.27/174.53 and 175.27/177.24 for the stars Procyon and α Cen,
using observations from the Extreme-Ultraviolet Explorer (EUVE)
satellite, are found to be consistent and in agreement with the values
of Ne determined from other diagnostic ratios in the EUVE
spectra. A comparison of several theoretical extreme-ultraviolet
FeX line ratios with experimental values for a θ-pinch, for which
the plasma parameters have been independently determined, reveals
reasonable agreement between theory and observation, providing some
independent support for the accuracy of the adopted atomic data.
Title: Transition Region Velocity Oscillations Observed by EUNIS-06
Authors: Jess, D. B.; Rabin, D. M.; Thomas, R. J.; Brosius, J. W.;
Mathioudakis, M.; Keenan, F. P.
Bibcode: 2008ApJ...682.1363J
Altcode: 2008arXiv0804.1629J
Spectroscopic measurements of NOAA AR 10871, obtained with the Extreme
Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding rocket
instrument on 2006 April 12, reveal velocity oscillations in the He
II 303.8 Å emission line formed at T ≈ 5 × 104 K. The
oscillations appear to arise in a bright active region loop arcade
about 25'' wide which crosses the EUNIS slit. The period
of these transition region oscillations is 26 +/- 4 s, coupled with
a velocity amplitude of ±10 km s-1, detected over four
complete cycles. Similar oscillations are observed in lines formed at
temperatures up to T ≈ 4 × 105 K, but we find no evidence
for the coupling of these velocity oscillations with corresponding
phenomena in the corona. We interpret the detected oscillations as
originating from an almost purely adiabatic plasma, and infer that
they are generated by the resonant transmission of MHD waves through
the lower active region atmospheres. Through the use of seismological
techniques, we establish that the observed velocity oscillations display
wave properties most characteristic of fast body global sausage modes.
Title: Rapid Cadence EUNIS-06 Observations of a He II Transient
Brightening in the Quiet Sun
Authors: Brosius, Jeffrey W.; Rabin, Douglas M.; Thomas, Roger J.
Bibcode: 2008ApJ...682..630B
Altcode:
We observed a transient brightening in the quiet Sun at rapid cadence
(2.10 s) with the Extreme Ultraviolet Normal Incidence Spectrograph
(EUNIS-06) sounding rocket instrument on 2006 April 12. The transient
was visible only in He II at 303.78 Å (T ≈ 5 × 104 K),
and its maximum temperature T was <4 × 105 K. Taking
its linear extent along the EUNIS slit to be the diameter of a circular
feature, the transient's solar surface area was 7.8 × 107
km2. EUNIS observed the brightening to begin at 18:12:52
and peak at 18:13:29 UT; coordinated observations with SOHO's EIT
confirm that EUNIS observed the onset of the brightening. EUNIS
spectra yield maximum and average He II intensity enhancements
of 2.09 and 1.46, respectively, relative to the pre-event quiet
Sun. He II line profiles from EUNIS reveal that relative upflows
were persistent during the transient (with a maximum speed around
20 km s-1) and that the upflow speed and intensity were
positively correlated. Variations in the observed He II intensity
and relative Doppler velocity were neither abrupt not impulsive, but
occurred slowly compared to the EUNIS cadence. The local photospheric
longitudinal magnetic field strength measured with SOHO's MDI revealed
no significant variability. The transient's measured properties are
consistent with its identification as a blinker or an elementary
blinker, and its observed behavior suggests a formation mechanism
involving gentle chromospheric evaporation.
Title: EUNIS-07: First Look
Authors: Rabin, D. M.; Thomas, R. J.; Brosius, J. W.
Bibcode: 2008AGUSMSP51A..07R
Altcode:
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding
rocket instrument is a two-channel imaging spectrograph that observes
the solar corona with high spectral resolution and a rapid cadence
made possible by unprecedented sensitivity. EUNIS flew for the
first time on 2006 April 12 (EUNIS-06), returning over 140 science
exposures at a cadence of 2.1 s; each exposure comprises six 1K x 1K
active pixel sensor (APS) images, three for each wavelength channel
(170-205 Å and 300-370 Å. Analysis of EUNIS-06 data has so far shed
new light on the nature of coronal bright points, cool transients, and
coronal loop arcades and has enabled calibration updates for TRACE and
SOHO's CDS and EIT. EUNIS flew successfully again on 2007 November 6
(EUNIS-07). Because the APS arrays were operated in video rather than
snapshot mode, a faster cadence of 1.3 s was possible (97% duty cycle),
resulting in 276 science exposures. We present an overview of the
EUNIS-07 spectra and describe the coordinated observing program executed
by the Hinode Extreme ultraviolet Imaging Spectrograph (EIS) that will,
in conjunction with the absolute radiometric calibration of EUNIS-07,
result in the first on-orbit radiometric calibration of EIS. EUNIS data
are freely available to the solar physics community. EUNIS is supported
by the NASA Heliophysics Division through its Low Cost Access to Space
Program in Solar and Heliospheric Physics.
Title: EUNIS-06 Rapid Cadence Observations of a He II Transient
Brightening in the Quiet Sun
Authors: Brosius, J. W.; Rabin, D. M.; Thomas, R. J.
Bibcode: 2008AGUSMSP51A..06B
Altcode:
We observed a transient brightening in the quiet Sun at rapid cadence
(2.10 s) with the Extreme Ultraviolet Normal Incidence Spectrograph
(EUNIS-06) sounding rocket instrument on 2006 April 12. The transient
was visible only in He II at 303.78 Å (T ≍ 5 × 104 K), and its
maximum temperature T was < 4 × 105 K. Taking its linear extent
along the EUNIS slit to be the diameter of a circular feature, the
transient's solar surface area was 7.8 × 107 km2. EUNIS observed the
brightening to begin at 18:12:52 and peak at 18:13:29 UT; coordinated
observations with SOHO's EIT confirm that EUNIS observed the onset
of the brightening. EUNIS spectra yield maximum and average He II
intensity enhancements of 2.09 and 1.46, respectively, relative to
the pre-event quiet Sun. He II line profiles from EUNIS reveal that
relative upflows were persistent during the transient (with a maximum
speed around 20 km s-1) and that the upflow speed and intensity were
positively correlated. Variations in the observed He II intensity
and relative Doppler velocity were neither abrupt not impulsive, but
occurred slowly compared to the EUNIS cadence. The local photospheric
magnetic flux measured with SOHO's MDI revealed no significant
variability. The transient's measured properties are consistent with
its identification as a blinker or an elementary blinker, and its
observed behavior suggests a formation mechanism involving gentle
chromospheric evaporation. The EUNIS program is supported by NASA's
Heliophysics Division through its Low Cost Access to Space Program in
Solar and Heliospheric Physics.
Title: EUNIS Underflight Calibrations of CDS, EIT, TRACE, EIS,
and EUVI
Authors: Thomas, R.; Wang, T.; Rabin, D. M.; Jess, D. B.; Brosius,
J. W.
Bibcode: 2008AGUSMSP51B..04T
Altcode:
The Extreme-Ultraviolet Normal-Incidence Spectrograph (EUNIS) is a
sounding rocket instrument that obtains imaged high-resolution solar
spectra. It has now had two successful flights, on 2006 April 12 and
2007 November 16, providing data to support underflight calibrations
for a number of orbiting solar experiments on both occasions. A regular
part of each campaign is the end-to-end radiometric calibration of
the rocket payload carried out at RAL in the UK, using the same
facility that provided pre-flight CDS and EIS calibrations. The
measurements, traceable to primary radiometric standards, can establish
the absolute EUNIS response within a total uncertainty of 10% over
its full longwave bandpass of 300--370Å. During each EUNIS flight,
coordinated observations are made of overlapping solar locations by
all participating space experiments, and identified by subsequent
image co-registrations, allowing the EUNIS calibrations to be applied
to these other instruments as well. The calibration transfer is
straightforward for wavelengths within the EUNIS LW bandpass, and is
extended to other wavelengths by means of a series of temperature-
and density-insensitive line-ratios, with one line of each pair in
the calibrated band and the other in the transfer band. In this way,
the EUNIS-06 flight is able to update the radiometric calibrations of
CDS NIS1 (and 2nd-order NIS2 near 2x304Å), all four channels of EIT,
and the three EUV channels of TRACE. The EUNIS-07 flight will further
update those missions, as well as both channels of Hinode/EIS and all
four channels of STEREO/SECCHI/EUVI. Future EUNIS flights have been
proposed that will continue this underflight calibration service. EUNIS
is supported by the NASA Heliophysics Division through its Low Cost
Access to Space Program in Solar and Heliospheric Physics.
Title: Analysis of a Solar Coronal Bright Point Extreme Ultraviolet
Spectrum from the EUNIS Sounding Rocket Instrument
Authors: Brosius, Jeffrey W.; Rabin, Douglas M.; Thomas, Roger J.;
Landi, Enrico
Bibcode: 2008ApJ...677..781B
Altcode:
We present a well-calibrated EUV spectrum of a solar coronal bright
point observed with the Extreme Ultraviolet Normal Incidence
Spectrograph (EUNIS) sounding rocket instrument on 2006 April
12. The coronal bright point brightened around 06:30 UT during a
period of emerging magnetic flux and remained bright at least until
the rocket flight around 18:12 UT, while the magnetic flux merged
and canceled. Density-sensitive line intensity ratios yield mutually
consistent coronal electron densities (Ne in cm-3)
of log Ne ≈ 9.4. The differential emission measure
(DEM, in cm-5 K-1) curve derived from the
spectrum yields a peak of log DEM ≈ 20.70 at log T ≈ 6.15 and a
local minimum of log DEM ≈ 20.15 at log T ≈ 5.35. Photospheric
(not coronal) element abundances are required to achieve equality
and consistency in the DEM derived from lines of Mg V, Mg VI, Mg VII,
and Ca VII (with a low first ionization potential, or FIP) and lines
from Ne IV and Ne V (with a high FIP) formed at transition region
temperatures. The bright point's photospheric abundance is likely
produced by reconnection-driven chromospheric evaporation, a process
that is not only central to existing bright point models, but also
consistent with measurements of relative Doppler velocities.
Title: Analysis of a Bright Point Spectrum From the Extreme
Ultraviolet Normal Incidence Spectrograph (EUNIS) Sounding Rocket
Instrument
Authors: Brosius, J. W.; Rabin, D. M.; Thomas, R. J.
Bibcode: 2007AGUFMSH21B..04B
Altcode:
We present a well-calibrated spectrum of a bright point observed with
EUNIS on 2006 April 12. Coordinated observations with SOHO's EIT and
MDI were also obtained. The bright point brightened around 06:30 UT
during a period of emerging magnetic flux, and remained bright at least
until the rocket flight around 18:12 UT while the magnetic flux merged
and canceled. Density-sensitive line intensity ratios yield mutually
consistent coronal electron densities log Ne ~ 9.5. Based on the method
of Landi & Landini (1997), the differential emission measure (DEM)
curve derived from the spectrum yields a peak of log DEM ~ 20.70 at log
T ~ 6.15, and a local minimum of log DEM ~ 20.15 at log T ~ 5.35. We
find that photospheric (not coronal) element abundances are required to
achieve equality and consistency in the DEM derived from lines of Mg V,
Mg VI, Mg VII, Ca VII (with a low first ionization potential, or FIP)
and lines from Ne IV and Ne V (with a high FIP) formed at transition
region temperatures. The bright point's photospheric abundance is
likely produced by reconnection-driven chromospheric evaporation,
a process that is not only central to existing bright point models
(e.g., Priest, Parnell, & Martin 1994; Longcope 1998), but also
consistent with measurements of relative Doppler velocities (e.g.,
± 26 km/s for Fe XIV, ± 35 km/s for Fe XVI) previously presented by
Brosius, Rabin, & Thomas (2007). The EUNIS program is supported
by NASA's Heliophysics Division through its Low Cost Access to Space
Program in Solar and Heliospheric Physics. We thank the entire EUNIS
team for the concerted effort that led to a successful first flight.
Title: Radiometric Calibration of EUNIS-06 With Theoretical Predicted
`Insensitive' Line Ratios
Authors: Wang, T.; Brosius, J. W.; Thomas, R. J.; Rabin, D. M.
Bibcode: 2007AGUFMSH53A1049W
Altcode:
The Extreme-Ultraviolet Normal-Incidence Spectrograph (EUNIS) is a
sounding-rocket payload that obtains imaged high-resolution spectra
of solar active and quiet-Sun regions, providing information about
the corona and upper transition region. EUNIS incorporates two
independent, co-pointing imaging spectrographs, one covering EUV
lines between 300 and 370 Å\ seen in first order (the longwave
[LW] channel), and a second covering lines between 170 and 205 Å\
seen in second order (the shortwave [SW] channel). Shortly after
the payload's initial successful flight on 2006 April 12, a complete
end-to-end radiometric calibration of its LW bandpass was carried out
at the Rutherford Appleton Laboratory in England. Here we develop and
apply a technique for deriving the absolute radiometric calibration
of its SW bandpass from these direct LW results by means of density-
and temperature-insensitive line intensity ratios. The first step
is to use the EUNIS LW calibration to get absolute intensities for
EUV lines recorded from solar positions along its LW slit during the
2006 flight. Then co-registered SOHO/CDS images taken within minutes
of the flight are used to transfer these absolute values to solar
locations observed by the EUNIS SW slit, spatially offset by about 1
arcmin. Finally, theoretical `insensitive' line ratios obtained from
CHIANTI allow us to determine absolute intensities of emission lines
within the EUNIS SW bandpass from those observed in its LW channel. A
total of 29 ratios composed of 11 LW and 15 SW emission lines from Fe~X
- Fe~XIII yield an instrumental response curve that matches very well
to a relative calibration which relied on combining measurements of
individual optical components. The second EUNIS flight, now scheduled
for 2007 October 30, will make coordinated observations and provide
similar calibration updates for Hinode/EIS. We will also present some
preliminary results from the new observations. EUNIS is supported by
the NASA Heliophysics Division through its Low Cost Access to Space
Program in Solar and Heliospheric Physics.
Title: EUNIS And SOHO Observations Of A Cool Transient Brightening
In The Quiet Sun
Authors: Brosius, Jeffrey W.; Rabin, D. M.; Thomas, R. J.
Bibcode: 2007AAS...210.2507B
Altcode: 2007BAAS...39..132B
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding
rocket instrument observed a cool transient brightening in the quiet
Sun during its first flight on 2006 April 12. The brightening appeared
in emission from He II, formed at temperatures around 50,000 K (log
T = 4.7), but was not evident in emission from ions formed at greater
temperatures, including Mg VI (log T = 5.6), Mg IX (log T = 6.0), and
Fe XIV (log T = 6.3). Of these and other lines in the EUNIS spectra,
only lines from He II and Mg IX were strong enough in the quiet Sun
to measure relative Doppler velocities during this transient; He II
revealed continuous upflows around 15 km/s while Mg IX revealed no
significant velocities. The average He II intensity enhancement factor
observed with EUNIS was 1.34, and its maximum was 1.84. Coordinated
observations with SOHO's EIT reveal a source area of 3.3x10^7 km^2,
in which the average He II intensity enhancement factor was 1.39 and
its maximum was 1.81; the transient did not appear in EIT's hotter
wavebands. Variations in the local magnetic field strength measured with
SOHO's MDI were marginal. The EUNIS program is supported by NASA through
its Low Cost Access to Space Program in Solar and Heliospheric Physics.
Title: EUNIS Results on He II 304 Å Line Formation
Authors: Jordan, S. D.; Brosius, J. W.
Bibcode: 2007ASPC..368..183J
Altcode:
The first flight of the Goddard Extreme Ultraviolet Normal Incidence
Spectrograph (EUNIS) took place from White Sands Missile Range at
18:10 UT on April 12, 2006. Observations of the He II 304 Å principal
resonance line were obtained with a cadence of ∼ 2 seconds along
an eleven arc-minute slit. Corresponding EIT images of this line, and
additional EUNIS observations of the strong coronal line of Fe XVI at
335.4 Å, were used to assess the role of the photoionizing coronal
flux in the formation of the He II line. In agreement with previous
work of these authors and others, the results support formation by the
collisional excitation mechanism by thermal electrons in the quiet Sun.
Title: Chromospheric Evaporation In A Remote Solar Flare-Like
Transient Observed At High Time Resolution With SOHO’s CDS And
RHESSI
Authors: Holman, Gordon D.; Brosius, J. W.
Bibcode: 2007AAS...210.9313H
Altcode: 2007BAAS...39Q.213H
We present EUV light curves and Doppler velocity measurements for a
small, remote flare-like transient observed at high time resolution
(9.8 s) with SOHO’s CDS during a GOES M1.6 solar flare. The EUV
observations include a brief precursor and an impulsive peak followed
by a more gradual rise and decline of emission. Hard X-ray light
curves obtained with RHESSI reveal a small burst just before the EUV
impulsive rise, and another burst at the time of the more gradual
EUV peak. RHESSI images show no emission at the location of the EUV
transient due to limitations in dynamic range. During the impulsive
phase we measure simultaneous, cospatial downward velocities ∼
30 km s-1 in the chromospheric line of He I
at 584.3 Å and the transition region line of O V at 629.7 Å, and
upward velocities ∼ 20 km s-1 in the coronal
line of Si XII at 520.7 Å. Fe XIX emission at 592.2 Å emerged during
the impulsive phase, and revealed upward velocities approaching 150
km s-1. These observations demonstrate that
flare-like explosive chromospheric evaporation occurred at a location
remote from the primary region of particle acceleration, apparently
driven by electron beams from the primary acceleration region. This
investigation was supported by NASA’s Heliophysics Guest Investigator
and Solar and Heliospheric Physics Programs and by the RHESSI Project.
Title: Chromospheric Evaporation in a Remote Solar Flare-like
Transient Observed at High Time Resolution with SOHO's CDS and RHESSI
Authors: Brosius, Jeffrey W.; Holman, Gordon D.
Bibcode: 2007ApJ...659L..73B
Altcode:
We present EUV light curves and Doppler velocity measurements for a
small, remote flarelike transient observed at high time resolution (9.8
s) with SOHO's CDS during a GOES M1.6 solar flare. The EUV observations
include a brief precursor and an impulsive peak followed by a more
gradual rise and decline of emission. Hard X-ray light curves obtained
with RHESSI reveal a small burst just before the EUV impulsive rise,
and another burst at the time of the more gradual EUV peak. RHESSI
images show no emission at the location of the EUV transient due to
limitations in dynamic range. During the impulsive phase we measure
simultaneous, cospatial downward velocities ~30 km s-1 in
the chromospheric line of He I at 584.3 Å and the transition region
line of O V at 629.7 Å, and upward velocities ~20 km s-1
in the coronal line of Si XII at 520.7 Å. Fe XIX emission at 592.2
Å emerged during the impulsive phase and revealed upward velocities
approaching 150 km s-1. These observations demonstrate that
flarelike explosive chromospheric evaporation occurred at a location
remote from the primary region of particle acceleration, apparently
driven by electron beams from the primary acceleration region.
Title: Fe XIII emission lines in active region spectra obtained with
the Solar Extreme-Ultraviolet Research Telescope and Spectrograph
Authors: Keenan, F. P.; Jess, D. B.; Aggarwal, K. M.; Thomas, R. J.;
Brosius, J. W.; Davila, J. M.
Bibcode: 2007MNRAS.376..205K
Altcode: 2006astro.ph.12493K; 2007MNRAS.tmp...38K
Recent fully relativistic calculations of radiative
rates and electron impact excitation cross-sections
for Fe XIII are used to generate emission-line ratios
involving 3s23p2-3s3p3 and
3s23p2-3s23p3d transitions in
the 170-225 and 235-450 Å wavelength ranges covered by the Solar
Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS). A
comparison of these line ratios with SERTS active region observations
from rocket flights in 1989 and 1995 reveals generally very good
agreement between theory and experiment. Several new Fe XIII emission
features are identified, at wavelengths of 203.79, 259.94, 288.56 and
290.81 Å. However, major discrepancies between theory and observation
remain for several Fe XIII transitions, as previously found by Landi
and others, which cannot be explained by blending. Errors in the adopted
atomic data appear to be the most likely explanation, in particular for
transitions which have 3s23p3d 1D2
as their upper level. The most useful Fe XIII electron-density
diagnostics in the SERTS spectral regions are assessed, in terms of
the line pairs involved being (i) apparently free of atomic physics
problems and blends, (ii) close in wavelength to reduce the effects
of possible errors in the instrumental intensity calibration, and
(iii) very sensitive to changes in Ne over the range
108-1011 cm-3. It is concluded that
the ratios which best satisfy these conditions are 200.03/202.04 and
203.17/202.04 for the 170-225 Å wavelength region, and 348.18/320.80,
348.18/368.16, 359.64/348.18 and 359.83/368.16 for 235-450 Å.
Title: Doppler Velocities Measured in Coronal Emission Lines from
a Bright Point Observed with the EUNIS Sounding Rocket
Authors: Brosius, Jeffrey W.; Rabin, Douglas M.; Thomas, Roger J.
Bibcode: 2007ApJ...656L..41B
Altcode:
Spectroscopic measurements of a coronal bright point obtained with
the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding
rocket instrument on 2006 April 12 show both upflows and downflows in
all five of the best observed emission lines. Relative velocities on
opposite sides of the feature were found to be +/-15 km s-1
in the line of He II 303.8 Å (formed at T~5×104 K),
+/-14 km s-1 in Mg IX 368.1 Å (T~9.5×105 K),
+/-26 km s-1 in Fe XIV 334.2 Å (T~2.0×106
K), and +/-35 km s-1 in both Fe XVI 335.4 and 360.8 Å
(T~2.5×106 K). The latter are the hottest lines for which
Doppler velocities have been reported in a bright point. Photospheric
longitudinal magnetograms reveal that the photospheric magnetic
fields underlying the bright point were canceling during the EUNIS
observation. Based on existing bright point models, this suggests that
the observed hot flows were associated with magnetic reconnection.
Title: Radio Measurements of the Height of Strong Coronal Magnetic
FieldsAbove Sunspots at the Solar Limb
Authors: Brosius, Jeffrey W.; White, S.
Bibcode: 2006SPD....37.0125B
Altcode: 2006BAAS...38Q.219B
We measure coronal magnetic field strengths of 1750 G at a height of
8000 km above a large sunspot in NOAA Active Region 10652 at the west
solar limb on 2004 July 29 using coordinated observations with the
VLA, TRACE, and three instruments (CDS, EIT, MDI) aboard SOHO. This
observation is the first time that coronal radio brightness temperatures
have been analyzed in a 15 GHz solar radio source projected above the
limb. Observations at 8 GHz yield coronal magnetic field strengths of
960 G at a height of 12,000 km. The field strength measurements combine
to yield a magnetic scale height of 6900 km. The radio brightness
temperature maxima are located away from a sunspot plume that appears
bright in EUV line emission formed at temperatures around several
hundred thousand K. This work is supported by NASA and NSF.
Title: Radio Measurements of the Height of Strong Coronal Magnetic
Fields Above Sunspots at the Solar Limb
Authors: Brosius, Jeffrey W.; White, Stephen M.
Bibcode: 2006ApJ...641L..69B
Altcode:
We measure coronal magnetic field strengths of 1750 G at a height of
8000 km above a large sunspot in NOAA AR 10652 at the west solar limb on
2004 July 29 using coordinated observations with the Very Large Array,
the Transition Region and Coronal Explorer, and three instruments
(CDS, EIT, MDI) aboard the Solar and Heliospheric Observatory. This
observation is the first time that coronal radio brightness temperatures
have been analyzed in a 15 GHz solar radio source projected above the
limb. Observations at 8 GHz yield coronal magnetic field strengths
of 960 G at a height of 12,000 km. The field strength measurements
combine to yield a magnetic scale height LB=6900 km. The
radio brightness temperature maxima are located away from a sunspot
plume that appears bright in EUV line emission formed at temperatures
around several ×105 K. We use the density-sensitive
emission-line intensity ratio of O IV 625.8 Å/554.5 Å to derive
an electron density ne (in units of cm-3) of
logne=10.1+/-0.2 at the base of the plume.
Title: Thermal Composition and Doppler Velocities in a Transequatorial
Loop at the Solar Limb
Authors: Brosius, Jeffrey W.
Bibcode: 2006ApJ...636L..57B
Altcode:
We observed a transequatorial loop (TEL) connecting NOAA Active
Regions 10652 and 10653 at the west solar limb on 2004 July 29 with the
Extreme-Ultraviolet Imaging Telescope (EIT) and the Coronal Diagnostic
Spectrometer (CDS) aboard the Solar and Heliospheric Observatory. Only
the loop's northern leg was observed with CDS. The loop appeared
bright and cospatial in extreme-ultraviolet emission lines from ions
formed over a wide range of temperature (T, in kelvins), including He
I (logT=4.0), O III (logT=4.9), O IV (5.2), O V (5.4), Ne VI (5.6),
Ca X (5.9), Mg X (6.1), and Fe XII (logT=6.1). This indicates that
the loop plasma was multithermal and covered roughly 2 orders of
magnitude in temperature. Our measurement of He I, O III, and O IV
line emission reveals the coolest plasma ever detected in a TEL. The
most likely explanation for the wide range of cospatial temperatures
in the TEL is that it consisted of numerous sub-resolution strands,
all at different temperatures. Each of the lines that are formed at
temperatures less than 106 K exhibited relative Doppler
blueshifts in the TEL that correspond to velocities toward the observer
larger than 30 km s-1, where the two strongest cool lines
(He I at 584.3 Å and O V at 629.7 Å) yielded maximum values of 37
and 41 km s-1, respectively. The presence of cool plasma
in the TEL at heights several times those of the cool ions' scale
heights suggests that the loop remained visible at low temperatures
by maintaining a steady flow of cool plasma.
Title: First Results From EUNIS 2005
Authors: Rabin, D. M.; Thomas, R. J.; Davila, J. M.; Brosius, J. W.;
Swartz, M.; Jordan, S. D.
Bibcode: 2005AGUFMSH41B1122R
Altcode:
The Extreme Ultraviolet Normal-Incidence Spectrograph (EUNIS) is
a sounding rocket experiment to investigate the energetics of the
solar corona and hotter transition region through high-resolution
imaging spectroscopy with a rapid (2 second) cadence. Pre-flight
characterization of throughput has demonstrated that EUNIS is the
most sensitive solar EUV spectrograph in existence, having over
100 times the throughput of its predecessor, the Solar Extreme
ultraviolet Research Telescope and Spectrograph (SERTS). We report
initial results from the first flight in November 2005 from White
Sands Missile Range. The main scientific goal of the first EUNIS
flight is to extend the investigation of transient phenomena, such as
nanoflares and blinkers, to shorter timescales than has been possible
with previous EUV spectrographs. The two independent optical systems
of EUNIS record spatially co-aligned spectra over two passbands
(170--205 Å and 300--370 Å) simultaneously with spectral resolution
of 60 mÅ or 120 mÅ, respectively. The longwave passband includes
He II 304 Å and strong lines from Fe XI--XVI. The shortwave passband
has a sequence of very strong Fe IX--XIII lines. Together, the EUNIS
telescopes furnish a wide range of temperature and density diagnostics
and enable underflight calibration of instrumental passbands on the
SOHO, TRACE, Solar-B, and STEREO missions.
Title: High Time Resolution EUV Spectroscopy of Chromospheric
Evaporation and Other Solar Phenomena
Authors: Brosius, J. W.; Phillips, K. J.
Bibcode: 2005AGUFMSH44A..07B
Altcode:
We present light curves and Doppler velocity measurements for a
solar flare observed at high time resolution with SOHO's CDS (9.8
s) and Yohkoh's BCS (9.0 s). CDS was able to perform rapid cadence
spectroscopy because it was operated in sit-and-stare mode. Coordinated
imagery from EIT and TRACE reveal that the CDS slit was positioned
directly over the location of flare onset. Emission lines formed
at transition region temperatures exhibited upflows of 40 km/s
during precursor brightenings, which suggests gentle chromospheric
evaporation during those events. The same lines showed downflows of
40 km/s during the flare impulsive phase, when emission lines formed
at temperatures around 10 MK exhibited blueshifts. We interpret this
to indicate momentum balance between the hot upflowing plasma and
the cool downflowing material during chromospheric evaporation. In
our quest for rapid cadence EUV spectra during big solar flares,
we have also observed numerous less energetic events like nanoflares
and blinkers. JWB acknowledges support through NASA grant NAG5-11757;
KJHP acknowledges support through an NRC Research Associateship.
Title: Properties of a Sunspot Plume Observed With the Coronal
Diagnostic Spectrometer Aboard the Solar and Heliospheric Observatory
Authors: Brosius, Jeffrey W.; Landi, Enrico
Bibcode: 2005ApJ...632.1196B
Altcode:
We used three instruments (CDS, EIT, MDI) aboard the Solar and
Heliospheric Observatory spacecraft to observe the large sunspot in
NOAA Active Region 8539 on 1999 May 9 and 13. The spot contained
a bright plume, most easily seen in EUV emission lines formed
at 5.2<~logT<~5.7 (where T is the temperature in K), in its
umbra on both dates. The plume's differential emission measure (DEM)
exhibited one and only one broad peak, centered around logT~5.8 on May
9 and around logT~5.6 on May 13, and exceeded the DEM of the quiet
Sun by more than an order of magnitude at these temperatures. The
high-temperature portion of the plume's DEM resembled that of nearby
quiet-Sun areas. Intensity ratios of the O IV lines at 625.8 and 554.5
Å yield logne (where ne is the electron density
in cm-3) of 9.6+0.3-0.6 in the plume
on May 9 and 9.7+0.2-0.2 on May 13; values of
9.4+0.3-0.9 and 9.4+0.2-0.3
were obtained in the quiet-Sun areas on the same dates. Based on
abundance enhancements derived from transition region emission lines of
Ca, an element with low first ionization potential, elemental abundances
in the plume appear to be coronal rather than photospheric. The plume
plasma reveals a bipolar Doppler velocity flow pattern, in which
maximum downflows in excess of 37 km s-1 are observed in
the northeast portion of the plume, and maximum upflows that exceed
52 km s-1 are observed in the northwest.
Title: Fe XI Emission Lines in a High-Resolution Extreme-Ultraviolet
Active Region Spectrum Obtained by the Solar Extreme Ultraviolet
Research Telescope and Spectrograph
Authors: Keenan, F. P.; Aggarwal, K. M.; Ryans, R. S. I.; Milligan,
R. O.; Bloomfield, D. S.; Brosius, J. W.; Davila, J. M.; Thomas, R. J.
Bibcode: 2005ApJ...624..428K
Altcode: 2005astro.ph..4106K
New calculations of radiative rates and electron impact excitation cross
sections for Fe XI are used to derive emission-line intensity ratios
involving 3s23p4-3s23p33d
transitions in the 180-223 Å wavelength range. These ratios are
subsequently compared with observations of a solar active region
obtained during the 1995 flight of the Solar Extreme Ultraviolet
Research Telescope and Spectrograph (SERTS). The version of SERTS flown
in 1995 incorporated a multilayer grating that enhanced the instrumental
sensitivity for features in the ~170-225 Å wavelength range, observed
in second order between 340 and 450 Å. This enhancement led to the
detection of many emission lines not seen on previous SERTS flights,
which were measured with the highest spectral resolution (0.03 Å)
ever achieved for spatially resolved active region spectra in this
wavelength range. However, even at this high spectral resolution,
several of the Fe XI lines are found to be blended, although the sources
of the blends are identified in the majority of cases. The most useful
Fe XI electron density diagnostic line intensity ratio is I(184.80
Å)/I(188.21 Å). This ratio involves lines close in wavelength
and free from blends, and it varies by a factor of 11.7 between
Ne=109 and 1011 cm-3
yet shows little temperature sensitivity. An unknown line in the
SERTS spectrum at 189.00 Å is found to be due to Fe XI, the first
time (to our knowledge) this feature has been identified in the solar
spectrum. Similarly, there are new identifications of the Fe XI 192.88,
198.56, and 202.42 Å features, although the latter two are blended
with S VIII/Fe XII and Fe XIII, respectively.
Title: Scientific Studies Using MACS: Coronal Reconnection
Measurements and Solar Wind Acceleration Diagnostics
Authors: St. Cyr, O. C.; Davila, J. M.; Reginald, N. L.; Brosius,
J.; Moran, T.
Bibcode: 2005AGUSMSP51B..03S
Altcode:
We have developed an instrument and an observational technique that
exploits the shape of the K-coronal visible spectrum, 380-450 nm,
to determine simultaneously both the thermal electron temperature and
its bulk flow speed (see Reginald et al poster, this conference). For
a given electron density along the line of sight, the shape of the
K-coronal visible spectrum is influenced by the thermal electron
temperature and its bulk flow speed. The bulk flow speed of the coronal
electrons in the solar wind causes a Doppler-shift in the shape of
the K-coronal spectrum depending on the magnitude of the speed. The
simple reason for the red shift is that the wavelength-independent
Thomson scattered coronal electrons observe a red-shifted photosphere
as they move away from the Sun at the bulk flow speed. In addition,
recent models have shown that identical streamers could be distinguished
through their influence on the shape of the K-coronal visible spectrum
in different wavelength regions. Modeling efforts have expanded to
include a scenario where the observing line of sight passes through
a coronal reconnection area. Using realistic parameters for the
reconnection, and assuming that it produces bulk electron flows both
toward and away from the Sun, our preliminary results indicate that the
resulting red and blue-shifted K-coronal spectrum should be detectable
with the MACS instrument.
Title: MACS for global measurements of the thermal electron
temperature and its bulk flow speed in the low solar corona through
ground based experiments
Authors: Reginald, N. L.; Davila, J. M.; St. Cyr, C.; Brosius, J. W.;
Moran, T.; Thomas, R.
Bibcode: 2005AGUSMSP51B..04R
Altcode:
The determination of the radial and latitudinal temperature and wind
profiles of the solar corona is of immense importance in understanding
the coronal heating mechanism and the dynamics of the coronal
features. We have built MACS-1 (Multi Aperture Coronal Spectrometer);
a fiber optic based spectrograph, to study the coronal properties
during the total solar eclipses of August 1999 in Elazig, Turkey and
June 2001 in Lusaka, Zambia, through the measurement of the K-coronal
spectrum. In these experiments we have successfully demonstrated the
feasibility of simultaneously measuring both the thermal electron
temperature and its bulk flow speed at multiple locations on the solar
corona. Measurement of these properties radially in the solar corona
could provide valuable information on the solar wind acceleration in the
low corona. We are now in the process of conducting a similar experiment
on the low solar corona with an advanced spectrograph MACS-2 interfaced
with the SolarC coronagraph at the Mees Solar Observatory in Haleakala,
Hawaii. This if proven successful would provide an ability to measure
simultaneously and globally the above coronal properties on demand.
Title: Elemental Abundances in a Sunspot Plume Observed With SERTS
Authors: Brosius, J. W.; Landi, E.; Thomas, R. J.
Bibcode: 2005AGUSMSP11A..03B
Altcode:
We present an EUV spectrum of a sunspot plume obtained with the SERTS
sounding rocket experiment. The spectrum contains emission lines from
various ionization stages of elements with a low (less than 10 eV) first
ionization potential (low FIP: Al, Ca, Fe, Mg, Ni, Si) and a high FIP
(C, He, Ne, O). The plume appears much brighter than its surroundings
in lines formed at log T around 5.6, i.e., lines of high-FIP Ne VI
and low-FIP Mg VI. Based upon the differential emission measure (DEM)
derived from all of the lines available, we are able to compare the
abundances of low-FIP and high-FIP elements in the plume. Results
indicate whether plume plasma abundances are photospheric or coronal.
Title: Mass Flows in a Disappearing Sunspot Plume
Authors: Brosius, Jeffrey W.
Bibcode: 2005ApJ...622.1216B
Altcode:
We observed a large sunspot in NOAA Active Region 9535 on 2001 July
12, 15, 17, and 19 with three instruments (CDS, EIT, and MDI) on board
SOHO. EUV emission lines of O IV (formed at logarithmic temperature of
5.2), O V (5.4), Ne IV (5.2), Ne V (5.5), Ne VI (5.6), Ne VII (5.7),
and Ca X (5.9) revealed a large bright plume within the sunspot penumbra
on July 12 and 15, a smaller, dimmer plume on July 17, and no plume
on July 19. Downflows of 25 km s-1 or more were measured
within the sunspot plume on July 12 and 15. By July 17 the downflow
area had shrunk in size, the downflows had diminished in magnitude,
and upflows were measured in the umbra and parts of the penumbra
outside the plume. By July 19 downflows were no longer observed, but
had been replaced entirely with upflows of 15-25 km s-1
in the umbra and portions of the penumbra. This is the first time
that the disappearance of a sunspot plume has been observed to occur
simultaneously with a dramatic change in flow velocity pattern in the
sunspot plume and umbra. On July 12 upflows northeast of the sunspot
were observed along with the downflows in the plume. Electron density
measurements based on intensity ratios of the O IV lines at 625.8
and 554.5 Å indicate a significantly greater value in the upflow
zone than in the plume, consistent with siphon flow as the driver of
the observed velocities; however, the line at 625.8 Å is very weak
and blended in the red wing of the Mg X line at 624.9 Å, so derived
densities are highly uncertain.
Title: Emission lines of FeXV in spectra obtained with the Solar
Extreme-Ultraviolet Research Telescope and Spectrograph
Authors: Keenan, F. P.; Aggarwal, K. M.; Milligan, R. O.; Ryans,
R. S. I.; Bloomfield, D. S.; Srigengan, V.; O'Mullane, M. G.; Lawson,
K. D.; Msezane, A. Z.; Brosius, J. W.; Davila, J. M.; Thomas, R. J.
Bibcode: 2005MNRAS.356.1592K
Altcode: 2004MNRAS.tmp..752K
Recent R-matrix calculations of electron impact excitation rates
in Mg-like FeXV are used to derive theoretical emission-line ratios
involving transitions in the 243-418 Åwavelength range. A comparison
of these with a data set of solar active region, subflare and off-limb
spectra, obtained during rocket flights by the Solar Extreme-Ultraviolet
Research Telescope and Spectrograph (SERTS), reveals generally
very good agreement between theory and observation, indicating that
most of the FeXV emission lines may be employed with confidence as
electron density diagnostics. In particular, the 312.55-Åline of
FeXV is not significantly blended with a CoXVII transition in active
region spectra, as suggested previously, although the latter does
make a major contribution in the subflare observations. Most of the
FeXV transitions which are blended have had the species responsible
clearly identified, although there remain a few instances where
this has not been possible. We briefly address the long-standing
discrepancy between theory and experiment for the intensity ratio of
the 3s21S-3s3p 3P1 intercombination
line at 417.25 Åto the 3s21S-3s3p 1P resonance
transition at 284.16 Å.
Title: Extreme-Ultraviolet and X-Ray Spectroscopy of a Solar Flare
Loop Observed at High Time Resolution: A Case Study in Chromospheric
Evaporation
Authors: Brosius, Jeffrey W.; Phillips, Kenneth J. H.
Bibcode: 2004ApJ...613..580B
Altcode:
We present extreme-ultraviolet (EUV) and X-ray light curves and Doppler
velocity measurements for a GOES class M2 solar flare observed in
NOAA Active Region 9433 on 2001 April 24 at high time resolution
with the Coronal Diagnostic Spectrometer (CDS) on board the Solar
and Heliospheric Observatory (SOHO) satellite (9.83 s) and the
Bragg Crystal Spectrometer (BCS) and Hard X-Ray Telescope (HXT) on
board the Yohkoh satellite (9.00 s). Coordinated imagery with SOHO's
Extreme-ultraviolet Imaging Telescope and the Transition Region and
Coronal Explorer satellite reveal that the CDS slit was centered on the
flare commencement site; coordinated magnetograms from SOHO's Michelson
Doppler Imager are consistent with this site being the footpoint
of a flare loop anchored in positive magnetic field near the outer
edge of a sunspot's penumbra. CDS observations include the preflare
quiescent phase, two precursors, the flare impulsive and peak phases,
and its slow decline. We find that (1) the average wavelengths of O
III, O IV, O V, Ne VI, and He II lines measured during the preflare
quiescent phase are equal (within the measurement uncertainties) to
those measured during the late decline phase, indicating that they
can be used as reference standards against which to measure Doppler
velocities during the flare; (2) the EUV lines of O III, O IV, O V,
and He II exhibit upflow velocities of ~40 km s-1 during both
precursor events, suggestive of small-scale chromospheric evaporation;
(3) the Fe XIX EUV intensity rises and stays above its preflare noise
level during the second (later) precursor; (4) the maximum upflow
velocities measured in Fe XIX with CDS (64 km s-1) and in
Ca XIX (65 km s-1) and S XV (78 km s-1) with BCS
occur during the flare impulsive phase and are simultaneous within the
instrumental time resolutions; (5) the Fe XIX EUV intensity begins its
impulsive rise nearly 90 s later than the rise in intensities of the
cooler lines; (6) hard X-ray emission arises nearly 60 s after the cool
EUV lines begin their impulsive intensity rise; and (7) the EUV lines
of O III, O IV, O V, and He II exhibit downflow velocities of ~40 km
s-1 during the flare impulsive phase, suggesting momentum
balance between the hot upflowing material and the cool downflowing
material. Our observations are consistent with energy transport by
nonthermal particle beams in chromospheric evaporation theory.
Title: Coronal Diagnostics with Coordinated Radio and EUV/Soft
X-Ray Observations
Authors: Brosius, Jeffrey W.
Bibcode: 2004ASSL..314..265B
Altcode:
A brief review is provided of what has been learned about the
solar corona from existing coordinated radio and EUV (or soft
X-ray) observations. Topics include: introduction to radio thermal
bremsstrahlung and thermal gyroemission; two-dimensional coronal
magnetography measurements; measurements of coronal elemental
abundances; measurements of physical properties of quasitransverse
(QT) layers in the coronal magnetic field; and three-dimensional
coronal magnetography measurements (the primary subject of this
Chapter). Results from these studies are used to help focus on coronal
diagnostics that can be performed with similar coordinated observations
involving FASR, as well as to recommend FASR instrument requirements.
Title: EUV and X-Ray Spectroscopy of a Solar Flare: a Case Study in
Chromospheric Evaporation
Authors: Brosius, J. W.; Phillips, K. J. H.
Bibcode: 2004AAS...204.5412B
Altcode: 2004BAAS...36..759B
We present light curves and Doppler velocity measurements for a GOES
class M2 solar flare observed at high time resolution with SOHO's CDS
(9.8 s) and Yohkoh's BCS (9.0 s) in NOAA Region 9433 on 2001 April
24. Coordinated imagery with SOHO's EIT and the TRACE satellite reveal
that the CDS slit was centered on the flare commencement site. EUV
spectra from CDS include the preflare quiescent phase, two precursors,
the flare's impulsive and peak phases, and its slow decline. Soft X-ray
spectra from BCS were obtained during the impulsive through decline
phases. We find that (1) the average wavelengths of O III, O IV, O V,
Ne VI, and He II lines measured during the preflare quiescent phase are
equal (within the measurement uncertainties) to those measured during
the late decline phase, indicating that they can be used as reference
standards against which to measure Doppler velocities during the flare;
(2) the EUV lines of O III, O IV, O V, and He II exhibit upflows
around 40 km/s during both precursor events, suggesting small-scale
chromospheric evaporation; (3) the Fe XIX EUV intensity rises and stays
above its preflare noise level during the precursors; (4) the maximum
upflow velocities measured in Fe XIX with CDS (64 km/s) and in Ca XIX
(65 km/s) and S XV (78 km/s) with BCS occur during the flare impulsive
phase, and are simultaneous within the instrumental time resolutions;
(5) the EUV lines of O III, O IV, O V, and He II exhibit downflows
around 40 km/s during the flare impulsive phase, suggesting momentum
balance between the hot upflowing material and the cool downflowing
material. Our observations are consistent with energy transport by
nonthermal particle beams in chromospheric evaporation theory. JWB
acknowledges NASA support through grant NAG5-11757; KJHP acknowledges
support through an NRC Research Associateship.
Title: Technique for simultaneous and global measurements of coronal
electron temperature and solar wind speed in the lower corona
Authors: Reginald, N. L.; Davila, J. M.; St. Cyr, O. C.; Brosius, J. W.
Bibcode: 2004AAS...204.7302R
Altcode: 2004BAAS...36..800R
We have successfully demonstrated the feasibility of measuring both the
coronal electron temperature and its radial flow speed simultaneously at
multiple locations in the lower solar corona. This experiment was
conducted in conjunction with the total solar eclipse of 21 June 2001
using multiple fiber optic spectroscopic technique. Here one end of
the multiple fibers was located at fixed radii at different latitudes
in the focal plane of the telescope. The coronal light gathered by
these fibers was then simultaneously fed to a spectroscope. The
required results were obtained by isolating the K-coronal spectrum in
the 350-450 nm regions. Our future plans are to locate fibers along
radii to measure the acceleration of the electron flow speed in the
lower corona. For this we intend to use this methodology in conjunction
with the SolarC coronagraph at the Mees Solar Observatory in Haleakala,
Hawaii. This would enable us to overcome the time constraints associated
with eclipse observations. The new design for the spectrograph
envisages all reflective optics to minimize scattering, specialized
chemical coatings to maximize capture of signal in the 350-450 nm
regions and to pass the beam through a polarizer to account for the
F-coronal component.
Title: A Comparison of Theoretical Si <Emphasis
Type="SmallCaps">VIII</Emphasis> Emission Line Ratios with
Observations from Serts
Authors: Keenan, F. P.; Katsiyannis, A. C.; Ramsbottom, C. A.; Bell,
K. L.; Brosius, J. W.; Davila, J. M.; Thomas, R. J.
Bibcode: 2004SoPh..219..251K
Altcode:
Recent R-matrix calculations of electron impact excitation rates in
N-like Si VIII are used to derive theoretical emission line intensity
ratios involving 2s22p3-2s2p4
transitions in the 216-320 Å wavelength range. A comparison of these
with an extensive dataset of solar active region, quiet-Sun, sub-flare
and off-limb observations, obtained during rocket flights of the Solar
EUV Research Telescope and Spectrograph (SERTS), indicates that the
ratio R1= I(216.94 Å)/I(319.84 Å) may provide a usable
electron density diagnostic for coronal plasmas. The ratio involves
two lines of comparable intensity, and varies by a factor of about
5 over the useful density range of 108-1011
cm−3. However R2= I(276.85 Å)/I(319.84 Å)
and R3=I(277.05 Å)/I(319.84 Å) show very poor agreement
between theory and observation, due to the severe blending of the 276.85
and 277.05 Å lines with Si VII and Mg VII transitions, respectively,
making the ratios unsuitable as density diagnostics. The 314.35 Å
feature of Si VIII also appears to be blended, with the other species
contributing around 20% to the total line flux.
Title: Close Association of an Extreme-Ultraviolet Sunspot Plume
with Depressions in the Sunspot Radio Emission
Authors: Brosius, Jeffrey W.; White, Stephen M.
Bibcode: 2004ApJ...601..546B
Altcode:
We obtained coordinated observations of the large sunspot in NOAA
Region 8539 on 1999 May 9 and 13 with the Very Large Array and
three instruments (CDS, EIT, MDI) aboard the Solar and Heliospheric
Observatory satellite. The EUV observations reveal a plume in the
sunspot umbra on both observing dates. The plume appears brightest
in emission lines formed at temperatures between 1.6×105
and 5.0×105 K. Radio emission from the sunspot umbra is
dominated by thermal gyroemission from the plume, which accounts for
radio brightness temperatures <1×106 K in the umbra on
both dates, as well as umbral brightness temperature depressions in the
4.535 and 8.065 GHz observations on May 13. A compact 14.665 GHz source
persists near the umbra/penumbra boundary during our observing period,
indicating a long-lived, compact flux tube with coronal magnetic field
strength of at least 1748 G. It occurs in a portion of the sunspot
that appears very dark in EUV emission.
Title: Coronal Magnetic Fields in a Sunspot Plume at the Limb
Authors: Brosius, J. W.; White, S. M.
Bibcode: 2003AGUFMSH42B0507B
Altcode:
We obtained coordinated EUV and radio observations of NOAA Active
Region 10139 on 2002 October 14 when the region was on the west limb
of the Sun. Observations were obtained with the Very Large Array (VLA)
and three instruments aboard the Solar and Heliospheric Observatory
(SOHO) satellite, including the Coronal Diagnostic Spectrometer (CDS),
the Extreme-ultraviolet Imaging Telescope (EIT), and the Michelson
Doppler Imager (MDI). A sunspot plume is clearly seen in EUV emission
lines formed at temperatures between about 0.2 and 0.5 MK. Polarized
8 GHz radio emission from the plume suggests 4th harmonic gyroemission
(from 760 Gauss fields) above the limb, and 3rd harmonic gyroemission
(from 960 Gauss fields) on the disk.
Title: Electron Temperature and Speed Measurements in the Low Solar
Corona: Results From the 2001 June Eclipse
Authors: Reginald, Nelson L.; Cyr, O. C. St.; Davila, Joseph M.;
Brosius, Jeffrey W.
Bibcode: 2003ApJ...599..596R
Altcode:
We present measurements of electron temperature and bulk flow speed
low in the solar corona derived from white-light spectra obtained
during the total solar eclipse of 2001 June 21. Observations were
obtained at two locations in the solar corona, one within a helmet
streamer at the east limb and the second in a streamer cluster
in the southwest. Both points were at an altitude of about 1.1
Rsolar from the solar center. The east limb and southwest
locations yielded electron temperatures of 0.96+/-0.05 and 1.2+/-0.2
MK and bulk flow speeds of 72.0+281.0-72.0
and 257.0+443.0-257.0 km s-1,
respectively. These measurements are unique in that they simultaneously
provide both the electron temperature and its bulk flow speed;
few previous measurements of electron parameters in the corona are
available. The results presented here demonstrate the potential for
this technique: if the instrument were used with a coronagraph, it
would provide routine synoptic maps of electron temperature and bulk
flow speed.
Title: Emission lines of Na-like ions in spectra obtained with the
Solar EUV Research Telescope and Spectrograph (SERTS)
Authors: Keenan, F. P.; Katsiyannis, A. C.; Brosius, J. W.; Davila,
J. M.; Thomas, R. J.
Bibcode: 2003MNRAS.342..513K
Altcode:
Theoretical emission-line ratios involving transitions in the 236-412
Å wavelength range are presented for the Na-like ions ArVIII, CrXIV,
MnXV, FeXVI, CoXVII, NiXVIII and ZnXX. A comparison of these with an
extensive data set of the solar active region, quiet-Sun, subflare and
off-limb observations, obtained during rocket flights by the Solar
EUV Research Telescope and Spectrograph (SERTS), reveals generally
very good agreement between theory and experiment. This indicates
that most of the Na-like ion lines are reliably detected in the
SERTS observations, and hence may be employed with confidence in
solar spectral analyses. However, the features in the SERTS spectra
at 236.34 and 300.25 Å, originally identified as the NiXVIII 3p
2P3/2-3d 2D3/2 and
CrXIV 3p 2P3/2-3d 2D5/2
transitions, respectively, are found to be due to emission lines of
ArXIII (236.34 Å) and possibly SV or NiVI (300.25 Å). The CoXVII
3s 2S-3p 2P3/2 line at 312.55 Å is
always badly blended with an FeXV feature at the same wavelength, but
MnXV 3s 2S-3p 2P1/2 at 384.75 Å may
not always be as affected by second-order emission from FeXII 192.37
Å as previously thought. On the other hand, we find that the ZnXX 3s
2S-3p 2P3/2 transition can sometimes
make a significant contribution to the ZnXX/FeXIII 256.43-Å blend, and
hence care must be taken when using this feature as an FeXIII electron
density diagnostic. A line in the SERTS-89 active region spectrum at
265.00 Å has been re-assessed, and we confirm its identification as
the FeXVI 3p 2P3/2-3d 2D3/2
transition.
Title: Electron Temperature and Speed Measurements in the Lower
Solar Corona: Results from the June 2001 Eclipse
Authors: Reginald, N. L.; St. Cyr, O. C.; Davila, J. M.; Brosius, J. W.
Bibcode: 2003SPD....34.0408R
Altcode: 2003BAAS...35..811R
The determination of the radial and latitudinal temperature and solar
wind speed profiles of the solar corona is of immense importance
in understanding the coronal heating mechanism and the dynamics of
the coronal features. Cram (Sol. Phys, 48, 3, 1976) provided the
theory for the formation of the K-coronal spectrum and a method for
determining the radial profile of the coronal temperature. We
have modified Cram's theory to incorporate the role of the solar wind
in the formation of the K-corona and have identified both temperature
and speed sensitive intensity ratios. We built MACS (Multi Aperture
Coronal Spectrometer); a fiber optic based spectrograph to study
the total solar eclipse of June 2001 in Lusaka, Zambia. In this
instrument one end of the five fiber-optic tips at the focal plane of
the telescope were positioned to see different latitudes at the same
radii on the solar corona. The other ends of the fibers were vertically
aligned and placed at the primary focus of the collimating lens of
the spectrograph. We have succeeded in isolating the K-corona
from the spectral observations made through two different fibers
in MACS to match the theoretical K-coronal profiles for different
temperatures and wind speeds. Results were obtained at two locations
in the solar corona, one within a helmet streamer at the east limb
and the second in a streamer cluster in the southwest. Both points
were at an altitude of about 0.1-0.2 Rsun above the solar
limb. The east limb location at the edge of a helmet streamer and the
southwest location yielded electron temperatures of 0.94 +/- 0.01 MK
and 1.28 +/- 0.02 MK and bulk flow speeds of 124.0 +/- 48.0 km/sec
and 149.0 +/- 59.0 km/sec, respectively. This mechanism provides for
simultaneous measurement of both the temperature and wind speed in the
field of view of an exposed fiber to the corona. We will also present
the details of this experiment.
Title: Chromospheric Evaporation and Warm Rain During a Solar Flare
Observed with SOHO's CDS
Authors: Brosius, J. W.
Bibcode: 2003SPD....34.1621B
Altcode: 2003BAAS...35R.836B
We present EUV light curves, Doppler shifts, and line broadening
measurements for a flaring solar active region obtained with SOHO's
CDS under conditions of (1) comprehensive temporal coverage (including
the quiescent preflare, impulsive, and gradual decline phases), (2)
high time resolution (9.83 s), and (3) narrow field of view (4''
x 20''). The GOES class M6 flare occurred in NOAA Region 9502 on
2001 June 15. The four strong lines of O III at 599.587 Å, O V at
629.732 Å, Mg X at 624.937 Å, and Fe XIX at 592.225 Å are analyzed,
and provide diagnostics of plasma dynamics for 4.9 <= log T <=
6.9. Wavelengths and widths measured during the preflare and late
decline phases provide standards against which Doppler shifts and excess
line broadening are measured during the impulsive and early decline
phases. The entire profile of all four lines is blueshifted early during
the impulsive rise of the flare, but only the O III, O V, and Mg X lines
subsequently exhibit multiple components and downflows. These downflows
provide evidence of ``warm rain" due to cooling coronal flare plasma
following chromospheric evaporation during the impulsive phase. O III
and O V exhibit a pronounced precursor brightening during which the
Fe XIX emission emerges above the noise; this, combined with the fact
that the O III and O V intensities begin their impulsive rise earlier
than do those of Mg X and Fe XIX, is consistent with the transport
of coronal flare energy to the chromosphere by nonthermal particle
beams. This work is supported by NASA grant NAG5-11757.
Title: Electron Temperature and Speed Measurements In the Low Solar
Corona: Results from the June 2001 Eclipse
Authors: Reginald, N. L.; St. Cyr, O. C.; Davila, J. M.; Brosius, J. W.
Bibcode: 2003EAEJA....11383R
Altcode:
The determination of the radial and latitudinal temperature and solar
wind speed profiles of the solar corona is of immense importance in
understanding the coronal heating mechanism and the dynamics of the
coronal features. Cram (Sol. Phys, 48,3, 1976) provided the theory for
the formation of the K-coronal spectrum and a method for determining the
radial profile of the coronal temperature. A slit-based spectroscopic
study was performed by Ichimoto et.al (PASJ, 48, 545, 1996) on the solar
corona in conjunction with the total solar eclipse of 1994 to evaluate
the temperature profiles of the solar corona. We have modified Cram's
theory to incorporate the role of the solar wind in the formation of
the K-corona and have identified both temperature and speed sensitive
intensity ratios. We built MACS (Multi Aperture Coronal Spectrometer);
a fiber optic based spectrograph to study the total solar eclipse of
June 2001 in Lusaka, Zambia. In this instrument one end of the five
fiber-optic tips at the focal plane of the telescope were positioned to
see different latitudes at the same radii on the solar corona. The other
ends of the fibers were vertically aligned and placed at the primary
focus of the collimating lens of the spectrograph. We have succeeded in
isolating the K-corona from the spectral observations made through two
different fibers in MACS to match the theoretical K-coronal profiles
for different temperatures and wind speeds. Results were obtained at
two locations in the solar corona, one within a helmet streamer at the
east limb and the second in a streamer cluster in the southwest. Both
points were at an altitude of about 0.1-0.2 RSun above the
solar limb. The east limb location at the edge of a helmet streamer and
the southwest location yielded electron temperatures of 0.94 ± 0.01
MK and 1.28 ± 0.02 MK and bulk flow speeds of 124.0 ± 48.0 km/sec
and 149.0 ± 59.0 km/sec, respectively. This mechanism provides for
simultaneous measurement of both the temperature and wind speed in the
field of view of an exposed fiber to the corona. We will also present
the details of this experiment.
Title: Chromospheric Evaporation and Warm Rain during a Solar
Flare Observed in High Time Resolution with the Coronal Diagnostic
Spectrometer aboard the Solar and Heliospheric Observatory
Authors: Brosius, Jeffrey W.
Bibcode: 2003ApJ...586.1417B
Altcode:
We present EUV light curves, Doppler shifts, and line-broadening
measurements for a flaring solar active region obtained with the
Coronal Diagnostic Spectrometer (CDS) aboard the NASA ESA Solar and
Heliospheric Observatory (SOHO) under conditions of (1) comprehensive
temporal coverage (including the quiescent preflare, impulsive, and
gradual decline phases), (2) high time resolution (9.83 s), and (3)
narrow field of view (4''×20''). The four strong
lines of O III at 599.587 Å, O V at 629.732 Å, Mg X at 624.937 Å,
and Fe XIX at 592.225 Å are analyzed and provide diagnostics of plasma
dynamics for 4.9<=logT<=6.9. Wavelengths and widths measured
during the preflare and late decline phases provide standards against
which Doppler shifts and excess line broadening are measured during
the impulsive and early decline phases. The entire profile of all four
lines is blueshifted early during the impulsive rise of the flare,
but only the O III, O V, and Mg X lines subsequently exhibit multiple
components and downflows. These downflows provide evidence of ``warm
rain'' due to cooling coronal flare plasma following chromospheric
evaporation during the impulsive phase. O III and O V exhibit a
pronounced precursor brightening during which the Fe XIX emission
emerges above the noise; this, combined with the fact that the O III
and O V intensities begin their impulsive rise earlier than do those
of Mg X and Fe XIX, is consistent with the transport of coronal flare
energy to the chromosphere by nonthermal particle beams.
Title: Si IX Emission Lines in Spectra Obtained with the Solar euv
Research Telescope and Spectrograph (Serts)
Authors: Keenan, F. P.; Katsiyannis, A. C.; Aggarwal, K. M.;
Mathioudakis, M.; Brosius, J. W.; Davila, J. M.; Thomas, R. J.
Bibcode: 2003SoPh..212...65K
Altcode:
Theoretical electron-density-sensitive emission line ratios involving
2s22p2-2s2p3 transitions in Si ix
between 223 and 350 Å are presented. A comparison of these with
an extensive dataset of solar-active-region, quiet-Sun, subflare
and off-limb observations, obtained during rocket flights by the
Solar EUV Research Telescope and Spectrograph (SERTS), reveals
generally very good agreement between theory and experiment. This
provides support for the accuracy of the line-ratio diagnostics,
and hence the atomic data on which they are based. In particular,
the density-sensitive intensity ratio I(258.10 Å)/I(349.87 Å)
offers an especially promising diagnostic for studies of coronal
plasmas, as it involves two reasonably strong emission lines and
varies by more than an order of magnitude over the useful density
range of 109-1011 cm−3. The
2s22p2 1S0-2s2p3
1P1 transition at 259.77 Å is very marginally
identified for the first time in the SERTS database, although it has
previously been detected in solar flare observations.
Title: Measurements of Three-dimensional Coronal Magnetic Fields
from Coordinated Extreme-Ultraviolet and Radio Observations of a
Solar Active Region Sunspot
Authors: Brosius, Jeffrey W.; Landi, Enrico; Cook, John W.; Newmark,
Jeffrey S.; Gopalswamy, N.; Lara, Alejandro
Bibcode: 2002ApJ...574..453B
Altcode:
We observed NOAA Active Region 8108 around 1940 UT on 1997 November 18
with the Very Large Array and with three instruments aboard the NASA/ESA
Solar and Heliospheric Observatory satellite, including the Coronal
Diagnostic Spectrometer, the EUV Imaging Telescope, and the Michelson
Doppler Imager. We used the right-hand and left-hand circularly
polarized components of the radio observing frequencies, along with
the coordinated EUV observations, to derive the three-dimensional
coronal magnetic field above the region's sunspot and its immediate
surroundings. This was done by placing the largest possible harmonic
(which corresponds to the smallest possible magnetic field strength)
for each component of each radio frequency into appropriate atmospheric
temperature intervals such that the calculated radio brightness
temperatures at each spatial location match the corresponding
observed values. The temperature dependence of the derived coronal
magnetic field, B(x,y,T), is insensitive to uncertainties on the
observed parameters and yields field strengths in excess of 580 G
at 2×106 K and in excess of 1500 G at 1×106
K. The height dependence of the derived coronal magnetic field,
B(x,y,h), varies significantly with our choice of magnetic scale height
LB. Based on LB=3.8×109 cm derived
from the relative displacements of the observed radio centroids, we
find magnetic field strengths in excess of 1500 G at heights of 15,000
km and as great as 1000 G at 25,000 km. By observing a given target
region on several successive days, we would obtain observations at a
variety of projection angles, thus enabling a better determination of
LB and, ultimately, B(x,y,h). We compare coronal magnetic
fields derived from our method with those derived from a potential
extrapolation and find that the magnitudes of the potential field
strengths are factors of 2 or more smaller than those derived from our
method. This indicates that the sunspot field is not potential and that
currents must be present in the corona. Alfvén speeds between 25,000
and 57,000 km s-1 are derived for the 1×106
K plasma at the centroids of the radio observing frequencies. Filling
factors between 0.003 and 0.1 are derived for the 1×106
K plasma at the centroids of the radio observing frequencies.
Title: New Measurements of 3-D Sunspot Coronal Magnetic Fields From
Coordinated SOHO EUV and VLA Radio Observations
Authors: Brosius, J. W.; White, S. M.; Landi, E.; Cook, J. W.; Newmark,
J. S.; Gopalswamy, N.; Lara, A.
Bibcode: 2002AAS...200.0307B
Altcode: 2002BAAS...34..642B
Three-dimensional sunspot coronal magnetograms were derived from
coordinated extreme-ultraviolet (EUV) and radio observations of NOAA
regions 8108 (N21E18 on 1997 November 18) and 8539 (N20W12 on 1999 May
13). The EUV spectra and images, obtained with the Coronal Diagnostic
Spectrometer (CDS) and the Extreme-ultraviolet Imaging Telescope (EIT)
aboard the Solar and Heliospheric Observatory (SOHO) satellite, were
used to derive the differential emission measure (DEM) and the plasma
electron density for each spatial pixel (along each line of sight)
within both regions. These were subsequently used to calculate maps
of the expected thermal bremsstrahlung brightness temperature at the
Very Large Array (VLA) radio observing frequencies of 1.4, 4.9, 8.4,
and 15 GHz. The thermal bremsstrahlung maps reproduce neither the
structure nor the intensity of the observed maps, and indicate that
thermal gyroemission must dominate the observed radio emission. The
radio observations were used to constrain the magnetic scale height and
the gross temperature structure of the atmosphere. These, along with
the DEM, electron density, and observed radio brightness temperature
maps, were used to derive the temperature distribution of the coronal
magnetic field strength B(T) that reproduced simultaneously the observed
right-hand and left-hand circularly polarized emission at the radio
observing frequencies for each spatial pixel in the images. Magnetic
field strengths corresponding to 3rd harmonic gyroemission at 4.9 GHz
(580 Gauss) are found in coronal plasmas at temperatures as high as
3.2 MK, while magnetic field strengths corresponding to 3rd harmonic
gyroemission at 15 GHz (1800 Gauss) are found in coronal plasmas at
temperatures as high as 1.6 MK. B(T) was ultimately converted to B(h)
and compared with extrapolations from photospheric magnetograms.
Title: A Comparison of Theoretical mg vi Emission Line Strengths
with Active-Region Observations From Serts
Authors: Keenan, F. P.; Mathioudakis, M.; Katsiyannis, A. C.;
Ramsbottom, C. A.; Bell, K. L.; Thomas, R. J.; Brosius, J. W.
Bibcode: 2002SoPh..205..265K
Altcode:
R-matrix calculations of electron impact excitation
rates in N-like Mg vi are used to derive theoretical
electron-density-sensitive emission line ratios involving
2s22p3−2s2p4transitions in
the 269-403 Å wavelength range. A comparison of these with
observations of a solar active region, obtained during the
1989 flight of the Solar EUV Rocket Telescope and Spectrograph
(SERTS), reveals good agreement between theory and observation for the
2s22p34S−2s2p44Ptransitions
at 399.28, 400.67, and 403.30 Å, and the
2s22p32P−2s2p42Dlines
at 387.77 and 387.97 Å. However, intensities for the other lines
attributed to Mg vi in this spectrum by various authors do not match the
present theoretical predictions. We argue that these discrepancies are
not due to errors in the adopted atomic data, as previously suggested,
but rather to observational uncertainties or mis-identifications. Some
of the features previously identified as Mg vi lines in the SERTS
spectrum, such as 291.36 and 293.15 Å, are judged to be noise, while
others (including 349.16 Å) appear to be blended.
Title: Search for Evidence of Alpha Particle Beams during a Solar
Flare
Authors: Brosius, Jeffrey W.
Bibcode: 2002mwoc.conf..283B
Altcode:
We observed NOAA Region 9090 (N13 W39) with SOHO's CDS and EIT between
18:17 and 21:09 UT on 24 July 2000 to search for evidence of alpha
particle beams during solar flares. The GOES satellite reports a
C3.8 event in this region from 19:57 to 20:05 UT. Theoretically,
an alpha particle beam will manifest itself during the impulsive
phase of a flare through an enhancement in the red wing of the He II
Lyalpha (303.782 AA) emission line, without a corresponding blue wing
enhancement. This enhancement is due to downstreaming nonthermal alpha
particles undergoing charge exchange with chromospheric neutral hydrogen
atoms to form downstreaming nonthermal He II ions. Lyalpha radiation
emitted from these downstreaming ions is Doppler-shifted into the red
wing of the Lyalpha line. Our CDS observing program acquired high time
resolution (9.7 s) 4'' times 4' slit spectra between 590 and 630 AA,
where we observed He II Lyalpha in second order (607.564 AA). We fit the
spectral background and emission line profiles for each CDS spectrum in
our observed sequence. Density- and temperature-insensitive intensity
ratios of O IV and Mg X lines generally agree with their theoretical
values before and after the flare, but differ significantly from their
theoretical values during the flare. This may indicate line blending
with unknown components, line blending with second order C IV and Fe
XV lines, or loss of ionization equilibrium. Most important, however,
we find that although the red wing and blue wing backgrounds for He II
Lyalpha remain relatively constant during most of our observation, the
blue wing undergoes a more significant enhancement during the flare than
does the red wing. This effect is opposite that expected in the presence
of an alpha particle beam. Further, blended spectral line features that
mimic the expected nonthermal redshifted He II Lyalpha beam signal are
understood in terms of well known emission line components. Thus we
find no evidence for the presence of alpha particle beams in this case.
Title: Electron Densities in the Coronae of the Sun and Procyon from
Extreme-Ultraviolet Emission Line Ratios in Fe XI
Authors: Pinfield, D. J.; Keenan, F. P.; Mathioudakis, M.; Widing,
K. G.; Gallagher, P. T.; Gupta, G. P.; Tayal, S. S.; Thomas, R. J.;
Brosius, J. W.
Bibcode: 2001ApJ...562..566P
Altcode:
New R-matrix calculations of electron impact excitation rates for Fe
XI are used to determine theoretical emission line ratios applicable
to solar and stellar coronal observations. These are subsequently
compared to solar spectra of the quiet Sun and an active region made
by the Solar EUV Rocket Telescope and Spectrograph (SERTS-95), as well
as Skylab observations of two flares. Line blending is identified,
and electron densities of 109.3, 109.7,
>=1010.8, and >=1011.3 cm-3
are found for the quiet Sun, active region, and the two flares,
respectively. Observations of the F5 IV-V star Procyon, made with
the Extreme Ultraviolet Explorer (EUVE) satellite, are compared and
contrasted with the solar observations. It is confirmed that Procyon's
average coronal conditions are very similar to those seen in the quiet
Sun, with Ne=109.4 cm-3. In addition,
although the quiet Sun is the closest solar analog to Procyon, we
conclude that Procyon's coronal temperatures are slightly hotter than
solar. A filling factor of 25+38-12% was derived
for the corona of Procyon.
Title: Search for Evidence of Alpha-Particle Beams during a Solar
Flare Observed by the Coronal Diagnostic Spectrometer aboard the
Solar and Heliospheric Observatory
Authors: Brosius, Jeffrey W.
Bibcode: 2001ApJ...555..435B
Altcode:
We observed NOAA Active Region 9090 (N13°, W39°) with the Coronal
Diagnostic Spectrometer (CDS) and the Extreme-Ultraviolet Imaging
Telescope (EIT) aboard the Solar and Heliospheric Observatory
spacecraft between 18:17 and 21:09 UT on 2000 July 24 to search for
evidence of alpha-particle beams during solar flares. Theoretically,
an alpha-particle beam will manifest itself during the impulsive
phase of a flare through an enhancement in the red wing of the He
II Lyα (λ303.782) emission line without a corresponding blue wing
enhancement. This enhancement is due to downstreaming nonthermal alpha
particles undergoing charge-exchange with chromospheric neutral hydrogen
atoms to form downstreaming nonthermal He II ions. Lyα radiation
emitted from these downstreaming ions is Doppler-shifted into the
red wing of the Lyα line. Our CDS observing program acquired high
time resolution (9.7 s) 4''×4' slit spectra
between 590 and 630 Å, where we observed He II Lyα in second order
(λ607.564). The CDS and EIT observations reveal that AR 9090 underwent
significant intensity fluctuations prior to a sudden drastic increase
(impulsive phase) around 20:00 UT. The GOES satellite reports a C3.8
event in this region from 19:57 to 20:05 UT. We fitted the spectral
background and emission-line profiles for each CDS spectrum in our
observed sequence. Density- and temperature-insensitive intensity
ratios of O IV and Mg X lines generally agree with their theoretical
values before and after the sudden intensity increase, which supports
a reliable relative radiometric calibration for CDS, but differ
significantly from their theoretical values during the flare impulsive
phase. This may indicate line blending with unknown components,
line blending with second-order C IV and Fe XV lines, or loss of
ionization equilibrium. Most important, however, we find that although
the red and blue wing backgrounds for He II Lyα remain relatively
constant during most of our observation, the blue wing undergoes a
more significant enhancement during the impulsive phase than does the
red wing. This effect is opposite to that expected in the presence of
an alpha-particle beam. Furthermore, blended spectral line features
that mimic the expected nonthermal redshifted He II Lyα beam signal
are understood in terms of well-known emission-line components. Thus,
we find no evidence for the presence of alpha-particle beams in our
observations. We estimate an upper limit of ~250 ergs cm-2
s-1 sr-1 Å-1 for the nonthermal
redshifted peak spectral intensity due to an alpha-particle beam prior
to the impulsive phase.
Title: A comparison between theoretical and solar FeXII UV line
intensity ratios UV line intensity ratios
Authors: Binello, A. M.; Landi, E.; Mason, H. E.; Storey, P. J.;
Brosius, J. W.
Bibcode: 2001A&A...370.1071B
Altcode:
A new set of radiative and electron collisional data for Fe XII
was presented in two earlier papers. In the present work, we derive
level populations and theoretical line intensities for a range of
plasma densities and temperatures. Observations of Fe XII lines
obtained with the Solar EUV Rocket Telescope and Spectrograph are
analysed both as a check the quality of the new atomic data and
to determine the electron density in active regions and the quiet
Sun. The discrepancy between the electron density values determined
from Fexii line intensity ratios and those obtained from other ions
is investigated. Tables 2-5 are also available in electronic form
at the CDS via anonymous ftp to cdarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/370/1071}
Title: Measurements of 3-D Sunspot Coronal Magnetic Fields From
Coordinated SOHO EUV and VLA Radio Observations
Authors: Brosius, J. W.; Landi, E.; Cook, J. W.; Newmark, J.;
Gopalswamy, N.; Lara, A.
Bibcode: 2001AGUSM..SH32C02B
Altcode:
Three-dimensional sunspot coronal magnetograms were derived from
coordinated extreme-ultraviolet (EUV) and radio observations of
NOAA region 8108 (N21 E18) on 1997 November 18. The EUV spectra
and images, obtained with the Coronal Diagnostic Spectrometer (CDS)
and the Extreme-ultraviolet Imaging Telescope (EIT) aboard the Solar
and Heliospheric Observatory (SOHO) satellite, were used to derive
differential emission measure (DEM) distributions for each spatial
pixel (i.e., along each line of sight) of the region's images. These
were subsequently used to calculate maps of the expected thermal
bremsstrahlung brightness temperature at the Very Large Array
(VLA) radio observing frequencies of 4.9 and 8.4 GHz. The thermal
bremsstrahlung maps reproduce neither the structure nor the intensity
of the observed maps, and indicate that thermal gyroemission must
also contribute to the observed radio emission. Under the assumptions
of a monotonic increase in temperature and a monotonic decrease in
magnetic field strength with height above the sunspot, we derived
the temperature distribution of the coronal magnetic field strength
that reproduced simultaneously the observed right-hand and left-hand
circularly polarized radio emission at 4.9 and 8.4 GHz for each
spatial pixel in the sunspot maps. This was done by placing harmonics
of the radio observing frequencies in appropriate plasma temperature
intervals, integrating along the line of sight, and iterating until
a solution was obtained. Magnetic field strengths corresponding to
3rd harmonic gyroemission at 4.9 GHz (580 Gauss) are found in coronal
plasmas at temperatures as high as 2.2*E6 K, while magnetic
field strengths corresponding to 2nd harmonic gyroemission at 8.4 GHz
(1500 Gauss) are found in coronal plasmas at temperatures as high as
1.1*E6 K.
Title: VizieR Online Data Catalog: Fe XII UV line intensity ratios
(Binello+, 2001)
Authors: Binello, A. M.; Landi, E.; Mason, H. E.; Storey, P. J.;
Brosius, J. W.
Bibcode: 2001yCat..33701071B
Altcode:
A new set of radiative and electron collisional data for Fe XII
was presented in two earlier papers. In the present work, we derive
level populations and theoretical line intensities for a range of
plasma densities and temperatures. Observations of Fe XII lines
obtained with the Solar EUV Rocket Telescope and Spectrograph are
analysed both as a check on the quality of the new atomic data and
to determine the electron density in active regions and the quiet
Sun. The discrepancy between the electron density values determined
from Fe XII line intensity ratios and those obtained from other ions
is investigated. (2 data files).
Title: The Absolute Abundance of Iron in the Solar Corona (CD-ROM
Directory: contribs/white)
Authors: White, S. M.; Thomas, R. J.; Brosius, J. W.; Kundu, M. R.
Bibcode: 2001ASPC..223.1361W
Altcode: 2001csss...11.1361W
No abstract at ADS
Title: S xi Emission Lines in Active Region Spectra Obtained with
the Solar euv Rocket Telescope and Spectrograph (Serts)
Authors: Keenan, F. P.; Pinfield, D. J.; Mathioudakis, M.; Aggarwal,
K. M.; Thomas, R. J.; Brosius, J. W.
Bibcode: 2000SoPh..197..253K
Altcode:
Theoretical electron density sensitive emission line ratios involving
a total of eleven 2s22p2-2s2p3
transitions in S xi between 187 and 292 Å are presented. A
comparison of these with solar active region observations obtained
during rocket flights by the Solar EUV Rocket Telescope and
Spectrograph (SERTS) reveals generally good agreement between
theory and experiment. However, the 186.87 Å line is masked by
fairly strong Fe xii emission at the same wavelength, while 239.83
Å is blended with an unknown feature, and 285.58 Å is blended with
possibly N iv 285.56 Å. In addition, the 191.23 Å line appears to
be more seriously blended with an Fe xiii feature than previously
believed. The presence of several new S xi lines is confirmed in the
SERTS spectra, at wavelengths of 188.66, 247.14 and 291.59 Å, in
excellent agreement with laboratory measurements. In particular, the
detection of the 2s22p23P1
-2s2p33P0,1 transitions at 242.91
Å is the first time (to our knowledge) that this feature has been
identified in the solar spectrum. The potential usefulness of the S xi
line ratios as electron density diagnostics for the solar transition
region and corona is briefly discussed.
Title: Analysis of a Solar Active Region Extreme-Ultraviolet Spectrum
from SERTS-97
Authors: Brosius, Jeffrey W.; Thomas, Roger J.; Davila, Joseph M.;
Landi, Enrico
Bibcode: 2000ApJ...543.1016B
Altcode:
Goddard Space Flight Center's Solar EUV Research Telescope and
Spectrograph was flown on 1997 November 18, carrying an intensified
CCD detector and a multilayer-coated toroidal diffraction grating
with enhanced sensitivity over that of a standard gold-coated grating
throughout the instrument's 299-353 Å spectral bandpass. Spectra
and spectroheliograms of NOAA Active Region 8108 (N21°, E18°)
were obtained with a spectral resolution (instrumental FWHM) of
115 mÅ. Nearly 100 emission lines were observed in the spatially
averaged active region spectrum. Spectra and spectroheliograms of
quiet areas south of the region were also obtained. An end-to-end
radiometric calibration of the rocket instrument was carried out at
the Rutherford-Appleton Laboratory in the same facility that was used
to calibrate the Coronal Diagnostic Spectrometer experiment on SOHO
and using the same EUV light source. The accuracy of this calibration
is confirmed by the excellent agreement between the measured and
theoretical values of density- and temperature-insensitive line
intensity ratios. Nine emission lines of Fe XV are identified in
our spectrum; however, large differences between wavelengths in the
CHIANTI database and some of the measured solar wavelengths, as well
as inconsistencies of various theoretical intensity ratios, suggest
a need for improvement in the Fe XV atomic physics parameters and/or
the presence of unidentified blending lines. Density-sensitive line
intensity ratios of Fe XI λλ308.55/352.67, Fe XII λλ338.27/352.11,
Fe XIII λλ320.80/312.17, and Fe XV λλ321.78/327.03 yield logarithmic
electron densities (in cm-3) of 9.92+/-0.28, 9.74+/-0.28,
9.52+/-0.30, and 9.62+/-0.26, respectively. Using the strongest emission
line observed for each ionization stage of Fe from X through XVI and Ni
XVIII, we find that all of the measured nonthermal line widths yield
velocities consistent with 35 km s-1. The differential
emission measure curve derived from the observed line intensities
exhibits a relative minimum at logT~5.7, a broad maximum centered
around logT~6.3, and a rapid decline for temperatures above logT~6.6.
Title: Six emission lines in spectra obtained with the Solar EUV
Rocket Telescope and Spectrograph (SERTS)
Authors: Keenan, F. P.; O'Shea, E.; Thomas, R. J.; Brosius, J. W.;
Katsiyannis, A.; Ryans, R. S. I.; Reid, R. H. G.; Pradhan, A. K.;
Zhang, H. L.
Bibcode: 2000MNRAS.315..450K
Altcode:
New R-matrix calculations of electron impact excitation rates
for transitions among the 2s22p, 2s2p2 and
2p3 levels of Six are presented. These data are subsequently
used, in conjunction with recent estimates for proton excitation rates,
to derive theoretical electron density sensitive emission-line ratios
involving transitions in the ~253-356Å wavelength range. A comparision
of these with observations of a solar active region and subflare,
obtained during the 1989 flight of the Solar EUV Rocket Telescope and
Spectrograph (SERTS), reveals that the electron densities determined
from most of the Six line ratios are consistent with one another for
both solar features. In addition, the derived densities are also in good
agreement with the values of Ne estimated from diagnostic
lines in other species formed at similar electron temperatures to Six,
such as Fexii and Fexiii. These results provide observational support
for the general accuracy of the adopted atomic data, and hence line
ratio calculations, employed in the present analysis. However, we find
that the Six 256.32-Å line is blended with the Heii transition at
the same wavelength, while the feature at 292.25Å is not due to Six,
but currently remains unidentified. The intensity of the 253.81-Å line
in the SERTS active region spectrum is about a factor of 3 larger than
expected from theory, but the reason for this is unclear, and requires
additional observations to explain the discrepancy.
Title: The Absolute Abundance of Iron in the Solar Corona
Authors: White, S. M.; Thomas, R. J.; Brosius, J. W.; Kundu, M. R.
Bibcode: 2000ApJ...534L.203W
Altcode: 2000astro.ph..4007W
We present a measurement of the abundance of Fe relative to H
in the solar corona using a technique that differs from previous
spectroscopic and solar wind measurements. Our method combines EUV line
data from the Coronal Diagnostic Spectrometer (CDS) on the Solar and
Heliospheric Observatory with thermal bremsstrahlung radio data from
the VLA. The coronal Fe abundance is derived by equating the thermal
bremsstrahlung radio emission calculated from the EUV Fe line data to
that observed with the VLA, treating the Fe/H abundance as the sole
unknown. We apply this technique to a compact cool active region and
find Fe/H=1.56×10-4, or about 4 times its value in the solar
photosphere. Uncertainties in the CDS radiometric calibration, the VLA
intensity measurements, the atomic parameters, and the assumptions
made in the spectral analysis yield net uncertainties of ~20%. This
result implies that low first ionization potential elements such as
Fe are enhanced in the solar corona relative to photospheric values.
Title: The Role of Velocity Redistribution in Enhancing the Intensity
of the HE II 304 Å Line in the Quiet-Sun Spectrum
Authors: Andretta, Vincenzo; Jordan, Stuart D.; Brosius, Jeffrey W.;
Davila, Joseph M.; Thomas, Roger J.; Behring, William E.; Thompson,
William T.; Garcia, Adriana
Bibcode: 2000ApJ...535..438A
Altcode:
We present observational evidence of the effect of small-scale
(``microturbulent'') velocities in enhancing the intensity of the
He II λ304 line with respect to other transition region emission
lines, a process we call ``velocity redistribution,''. We first show
results from the 1991 and 1993 flights of SERTS (Solar EUV Rocket
Telescope and Spectrograph). The spectral resolution of the SERTS
instrument was sufficient to infer that, at the spatial resolution
of 5", the line profile is nearly Gaussian both in the quiet Sun and
in active regions. We were then able to determine, for the quiet Sun,
a lower limit for the amplitude of nonthermal motions in the region of
formation of the 304 Å line of the order of 10 km s-1. We
estimated that, in the presence of the steep temperature gradients
of the solar transition region (TR), velocities of this magnitude
can significantly enhance the intensity of that line, thus at least
helping to bridge the gap between calculated and observed values. We
also estimated the functional dependence of such an enhancement on
the relevant parameters (nonthermal velocities, temperature gradient,
and pressure). We then present results from a coordinated campaign,
using SOHO/CDS and Hα spectroheliograms from Coimbra Observatory,
aimed at determining the relationship between regions of enhanced
helium emission and chromospheric velocity fields and transition region
emission in the quiescent atmosphere. Using these data, we examined
the behavior of the He II λ304 line in the quiet-Sun supergranular
network and compared it with other TR lines, in particular with O III
λ600. We also examined the association of 304 Å emission with the
so-called coarse dark mottle, chromospheric structures seen in Hα
red-wing images and associated with spicules. We found that all these
observations are consistent with the velocity redistribution picture.
Title: The Absolute Abundance of Iron in the Solar Corona
Authors: White, S. M.; Thomas, R. J.; Brosius, J. W.; Kundu, M. R.
Bibcode: 2000SPD....31.1301W
Altcode: 2000BAAS...32Q.845W
We present a measurement of the abundance of Fe relative to H in the
solar corona using a technique which differs from previous spectroscopic
and solar wind measurements. Our method combines EUV line data from the
CDS spectrometer on SOHO with thermal bremsstrahlung radio data from
the VLA. The coronal Fe abundance is derived by equating the thermal
bremsstrahlung radio emission calculated from the EUV Fe line data to
that observed with the VLA, treating the Fe/H abundance as the sole
unknown. We apply this technique to a compact cool active region and
find Fe/H = 1.56 x 10-4, or about 4 times its value in the
solar photosphere. Uncertainties in the CDS radiometric calibration, the
VLA intensity measurements, the atomic parameters, and the assumptions
made in the spectral analysis yield net uncertainties of order 20%. This
result implies that low first ionization potential elements such as
Fe are enhanced in the solar corona relative to photospheric values.
Title: Analysis of an Active Region EUV Spectrum from SERTS-97
Authors: Brosius, J. W.; Thomas, R. J.; Davila, J. M.; Landi, E.
Bibcode: 2000SPD....31.0214B
Altcode: 2000BAAS...32..813B
Goddard Space Flight Center's Solar EUV Research Telescope and
Spectrograph (SERTS) was flown on 1997 November 18, carrying
a CCD-intensified detector and a multilayer-coated toroidal
diffraction grating that enhanced the sensitivity over that of a
standard gold-coated grating throughout the instrument's first-order
waveband (299 -- 353 Angstroms). Spectra and spectroheliograms of NOAA
active region 8108 (N21 E18) were obtained with a spectral resolution
(instrumental FWHM) ~ 118 m Angstroms. Spectra and spectroheliograms
of quiet areas southeast of the active region were also obtained. An
end-to-end radiometric calibration of the rocket instrument was
carried out at Rutherford-Appleton Laboratory in the same facility
used to calibrate the Coronal Diagnostic Spectrometer (CDS) on the
Solar and Heliospheric Observatory (SOHO) satellite, using the same
EUV light source. The accuracy of this calibration is confirmed by
the excellent agreement between measured and theoretical values of
density- and temperature-insensitive line intensity ratios among some
of the nearly 100 spectral lines observed in the spatially averaged
active region spectrum. We present the spectrum itself, and discuss
measurements of the plasma density, non-thermal mass motions, relative
wavelength shifts, and the differential emission measure. This work
is supported by NASA through RTOP grants and contract NAS5-99145.
Title: SERTS-97 Measurements Of Relative Wavelength Shifts In Coronal
Emission Lines Across A Solar Active Region
Authors: Brosius, J. W.; Thomas, R. J.; Davila, J. M.; Thompson, W. T.
Bibcode: 2000SoPh..193..117B
Altcode:
We used slit spectra from the 18 November 1997 flight of Goddard Space
Flight Center's Solar EUV Rocket Telescope and Spectrograph (SERTS-97)
to measure relative wavelength shifts of coronal emission lines as a
function of position across NOAA active region 8108. The shifts are
measured relative to reference wavelengths derived from spectra of the
region's nearby quiet surroundings (not necessarily at rest) because
laboratory rest wavelengths for the coronal EUV lines have not been
measured to sufficient accuracy for this work. An additional benefit
to this approach is that any systematic uncertainties in the wavelength
measurements are eliminated from the relative shifts by subtraction. We
find statistically significant wavelength shifts between the spatially
resolved active region slit spectra and the reference spectrum. For
He ii 303.78 Å the maximum measured relative red shift corresponds
to a Doppler velocity ∼+13 km s−1, and the maximum
relative blue shift corresponds to a Doppler velocity ∼−3 km
s−1. For Si x 347.40 Å, Si xi 303.32 Å, Fe xiv 334.17
Å, and Fe xvi 335.40 Å the corresponding maximum relative Doppler
velocities are ∼+19 and ∼−14, ∼+23 and ∼−7, ∼+10 and
∼−10, and ∼+13 and ∼−5 km s−1, respectively. The
active region appears to be divided into two different flow areas;
hot coronal lines are predominantly red-shifted in the northern half
and either blue-shifted or nearly un-shifted in the southern half. This
may be evidence that material flows up from the southern part of the
region, and down into the northern part. Qualitatively similar relative
wavelength shifts and flow patterns are obtained with SOHO/CDS spectra.
Title: Using Temporal Variations of the Nonthermal Redshifted
Ly-Alpha Emission to Deduce Properties of Proton Beams Injected into
a Stellar Atmosphere
Authors: Brosius, J. W.; Woodgate, B. E.
Bibcode: 2000ASPC..206..175B
Altcode: 2000hesp.conf..175B
No abstract at ADS
Title: Does Velocity Redistribution Really Enhance the He 304Å Line
to Observed Intensities?
Authors: Jordan, S.; Andretta, V.; Garcia, A.; Brosius, J.; Behring, W.
Bibcode: 1999ESASP.448..303J
Altcode: 1999mfsp.conf..303J; 1999ESPM....9..303J
No abstract at ADS
Title: SERTS-95 Measurements of Wavelength Shifts in Coronal Emission
Lines Across a Solar Active Region
Authors: Brosius, Jeffrey W.; Thomas, Roger J.; Davila, Joseph M.
Bibcode: 1999ApJ...526..494B
Altcode:
We used slit spectra from the 1995 flight of Goddard Space Flight
Center's Solar EUV Rocket Telescope and Spectrograph (SERTS-95) to
measure wavelength shifts of coronal emission lines in the core of
NOAA active region 7870 relative to its immediate surroundings (its
``edge''). This method circumvents the unavailability of reliable
laboratory rest wavelengths for the observed lines by using wavelengths
from the edge spectrum as references. We derived the SERTS-95
wavelength calibration from measurements of a post-flight laboratory
spectrum containing 28 He II and Ne II EUV standard wavelengths known
to high accuracy. Wavelength measurements for lines of He I, Ne III,
and additional lines of Ne II in the laboratory calibration spectrum
provide more accurate values than were previously available, enabling
these lines also to serve as future calibration standards. Six solar
lines were chosen for this study, namely, He II at 303.78 Å, Fe XII at
193.51 Å, Fe XIII at 202.05 Å, Fe XIV at 211.33 Å, Fe XV at 284.15
Å, and Fe XVI at 335.41 Å. Because these lines are free from known
blends in the SERTS-95 spectra and are either intrinsically strong or
near the SERTS-95 peak sensitivity, they are our most reliable lines
for measuring relative wavelength shifts in the spatially resolved
active-region core spectra. The iron ions are the hottest ions ever
used for this type of analysis. All six lines reveal statistically
significant spatial variations in their measured relative wavelength
shifts in the active-region core, including mixtures of blueshifts and
redshifts (each with maximum values corresponding to relative Doppler
velocities ~15 km s-1), indicating a dynamic, turbulent
corona. For each of these lines we calculated weighted-average relative
Doppler velocities from the wavelength shifts in the spatially resolved
core spectra by weighting the shifts in the individual spatial pixels
with their respective measurement uncertainties. This yields velocities
of 3.3+/-1.1 km s-1 for He II, 5.2+/-1.6 km s-1
for Fe XII, 0.7+/-1.5 km s-1 for Fe XIII, -2.1+/-1.4 km
s-1 for Fe XIV, 1.0+/-1.1 km s-1 for Fe XV,
and -1.1+/-0.8 km s-1 for Fe XVI. We also calculated
intensity-weighted relative Doppler velocities from the wavelength
shifts in the spatially averaged core spectrum, obtaining corresponding
values of 5.8+/-0.6 km s-1, 5.7+/-0.9 km s-1,
0.4+/-0.7 km s-1, -2.1+/-1.0 km s-1, 0.8+/-0.8
km s-1, and -1.1+/-0.5 km s-1. Combining the
above six lines with several additional ones that are strong enough
in both the edge and average core spectra to provide reliable centroid
measurements, we find statistically significant net relative redshifts
for lines of He II, Fe X, Fe XI, and Fe XII; lines of Fe XIII and Fe XV
show no significant shift while lines of Si XI, Fe XIV, and Fe XVI show
a small net relative blueshift. Where multiple lines are available for
a given ion, the directions (red or blue) and magnitudes (except for Fe
XI) of the relative shifts are mutually consistent. The net relative
blueshift observed in the hottest active-region coronal lines in our
sample, combined with the net relative redshift observed in the cooler
active-region coronal lines, suggests a net upflow of heated material
cospatially and cotemporally with a net downflow of cooler material.
Title: Emission Measure Distribution for an Active Region Using
Coordinated SERTS and YOHKOH SXT Observations
Authors: Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.; Winter, H. D.;
Brosius, J. W.
Bibcode: 1999ApJ...523..432S
Altcode:
Often the derived temperature of an active region reflects the
method and the nature of the instrument used in its measurement. The
emission measure (i.e., the amount of emitting material) derived
from spectroscopic observations usually depends on assumptions about
the absolute elemental abundances and ionization fractions of the
emitting ions. Yet establishing the distribution of emission measure
with temperature is the first step needed to proceed with most of the
interesting physics of active regions--including heating processes,
cooling timescales, and loop stability. Accurately characterizing
the thermal distribution of the coronal plasma requires data which
can resolve multithermal features and constrain both low- and
high-temperature emission. To model the temperature distribution
of NOAA Active Region 7563, we have combined broadband filter
data from the Yohkoh Soft X-Ray Telescope (SXT) with simultaneous
spectral line data from the Goddard Solar EUV Rocket Telescope and
Spectrograph (SERTS) taken during its flight on 1993 August 17. We
have used a forward-folding technique to determine the emission
measure distribution of the active region loops. We have found that
(1) the SXT response functions are sensitive to both the elemental
abundances and the ionization fractions assumed to compute the solar
spectrum that is folded through the instrument effective area; (2) the
relative calibration between the SERTS and the SXT instruments must
be adjusted by a factor of 2 (a value consistent with the absolute
measurement uncertainty of the 1993 SERTS flight) no matter which
abundances or iron ionization fractions are used; (3) the two-peaked
differential emission measure previously determined using SERTS data
alone is not consistent with the SXT data: including the SXT data
as a high-temperature constraint in the analysis requires that the
emission above about 3 MK drop off steeply rather than extending out to
6 MK. The sensitivity of the SXT filter response functions to elemental
abundance and iron ionization fraction could have a major impact on
many routine analyses of SXT data. The emission measures can be greatly
affected (up to a factor of 7) and temperatures derived from filter
ratios can be significantly altered (up to at least 40%) by adopting
different sets of commonly used elemental and ionic abundances. The
results of our multithermal analysis imply that using broadband SXT
data or a comparable high-temperature constraint in conjunction with
high-resolution spectra covering a wide lower temperature range to study
solar active regions can significantly improve the information derived
from either data set alone. In this study, the revised multithermal
distribution reduces the thermal energy content of the region by about
a factor of 2 and the required heating by about a factor of 5, which
in turn relaxes some constraints on possible heating models.
Title: The Role of Velocity Redistribution in Enhancing the Intensity
of the He II 304 A Line in the Quiet Sun Spectrum
Authors: Andretta, Vincenzo; Jordan, Stuart D.; Brosius, Jeffrey W.;
Davila, Joseph M.; Thomas, Roger J.; Behring, William E.; Thompson,
William T.; Garcia, Adriana
Bibcode: 1999STIN...9909151A
Altcode:
We present observational evidence of the effect of small scale
("microturbulent") velocities in enhancing the intensity of the He
II lambda304 line with respect to other transition region emission
lines, a process we call "velocity redistribution". We first show
results from the 1991 and 1993 flights of SERTS (Solar EUV Rocket
Telescope and Spectrograph). The spectral resolution of the SERTS
instrument was sufficient to infer that, at the spatial resolution
of 5", the line profile is nearly gaussian both in the quiet Sun and
in active regions. We were then able to determine, for the quiet Sun,
a lower limit for the amplitude of non-thermal motions in the region
of formation of the 304 A line of the order of 10 km/s. We estimated
that, in the presence of the steep temperature gradients of the solar
Transition Region (TR), velocities of this magnitude can significantly
enhance the intensity of that line, thus at least helping to bridge
the gap between calculated and observed values. We also estimated the
functional dependence of such an enhancement on the relevant parameters
(non-thermal velocities, temperature gradient, and pressure). We then
present results from a coordinated campaign, using SOHO/CDS and H-alpha
spectroheliograms from Coimbra Observatory, aimed at determining
the relationship between regions of enhanced helium emission and
chromospheric velocity fields and transition region emission in the
quiescent atmosphere. Using these data, we examined the behavior of
the He II lambda304 line in the quiet Sun supergranular network and
compared it with other TR lines, in particular with O III lambda600. We
also examined the association of 304 A emission with the so-called
"coarse dark mottle", chromospheric structures seen in H-alpha red
wing images and associated with spicules. We found that all these
observations are consistent with the velocity redistribution picture.
Title: Velocity Redistribution as a He II 304 Intensity Enhancement
Mechanism
Authors: Jordan, S. D.; Andretta, V.; Brosius, J. W.; Behring, W. E.;
Garcia, A.
Bibcode: 1999AAS...194.9310J
Altcode: 1999BAAS...31..990J
Both Skylab and SOHO observations show that the total intensity in
the He II 304 Angstroms line exceeds that predicted by standard NLTE
models by at least a factor of 5. However, the NLTE models do not
include the effect of flows. Carole Jordan showed that a 'velocity
redistribution' of the He II ions in the presence of a sharp temperature
gradient could provide the required enhancement. In earlier studies,
we have reported evidence from the Goddard SERTS sounding rocket for
small-scale nonthermal velocities large enough to enhance the emission
by the required amount if the temperature gradient is large enough
(as given by current transition region models). Here, we assess the
correlation of regions of strong Sun-center quiet-Sun 304 emission
observed with the CDS instrument on SOHO and the dark coarse mottles
observed in the red wing of H-alpha observed at the Coimbra Solar
Observatory. The significant positive correlation supports the picture
of greater velocity mixing in the quiet-Sun regions producing the
highest line intensity. Support for this research is provided by NASA
grant 682-344-17-38 and the Coimbra Solar Observatory.
Title: SERTS-95 Measurements of Wavelength Shifts in Coronal Emission
Lines Across a Solar Active Region
Authors: Brosius, J. W.; Thomas, R. J.; Davila, J. M.
Bibcode: 1999AAS...19410004B
Altcode: 1999BAAS...31..997B
We used slit spectra from the 1995 flight of Goddard Space Flight
Center's Solar EUV Rocket Telescope and Spectrograph (SERTS-95) to
measure wavelength shifts of coronal emission lines across the core of
NOAA active region 7870 relative to its immediate surroundings (its
``edge"). This method circumvents the absence of reliable laboratory
wavelengths for the observed lines by using lines from the edge spectrum
as effective standards. We derived the SERTS-95 wavelength calibration
from measurements of a post-flight laboratory spectrum containing 28 He
II and Ne II EUV standard wavelengths known to high accuracy. Wavelength
measurements for lines of He I, Ne III, and additional lines of Ne II
in the laboratory calibration spectrum provide more accurate values
than were previously available, enabling these lines also to serve
as future calibration standards. Six solar lines were chosen for
this study because they are free from known blends and are either
intrinsically strong or near the SERTS-95 peak sensitivity: He II
at 303.78 Angstroms, Fe XII at 193.51 Angstroms, Fe XIII at 202.05
Angstroms, Fe XIV at 211.33 Angstroms, Fe XV at 284.15 Angstroms, and
Fe XVI at 335.41 Angstroms. The iron ions are the hottest ions ever
used for this type of analysis. All six lines reveal statistically
significant variations in their measured wavelength shifts across the
active region core, including mixtures of blueshifts and redshifts,
indicating a dynamic, turbulent corona. For each line we calculated
weighted-average Doppler velocities, obtaining 3.3 +/- 1.1 km s(-1)
for He II, 5.2 +/- 1.6 km s(-1) for Fe XII, 0.7 +/- 1.5 km s(-1) for
Fe XIII, -2.1 +/- 1.4 km s(-1) for Fe XIV, 1.0 +/- 1.1 km s(-1) for Fe
XV, and -1.1 +/- 0.8 km s(-1) for Fe XVI. This suggests a net upflow
of heated material cospatially and cotemporally with a net downflow
of cooler material. We acknowledge NASA support for this research.
Title: Using Temporal Variations of the Nonthermal Redshifted
Lyα Emission to Deduce Properties of Proton Beams Injected into a
Stellar Atmosphere
Authors: Brosius, Jeffrey W.; Woodgate, Bruce E.
Bibcode: 1999ApJ...514..430B
Altcode:
We present theoretical calculations of temporal variations in the
nonthermal redshifted Lyα emission due to time-invariant proton beams
injected into a stellar atmosphere during the impulsive phase of a
flare. The computations are performed for a power-law spectrum of
nonthermal proton energies injected into a model stellar atmosphere
consisting of pure hydrogen in local thermodynamic equilibrium;
beam-induced variations in temperature and particle densities at all
depths and for all times are calculated with the Saha equation. We
characterized the injected model proton beams with the total energy flux
\Fscr and the power-law index δ and computed time-dependent nonthermal
redshifted Lyα emission profiles for five different values of \Fscr and
three different values of δ. Based upon trends evident in the resulting
emission, proton beam properties can be deduced from sufficiently
high-quality observations of the nonthermal redshifted Lyα profile. The
beam penetration depth initially decreases with time, but in most cases
it increases again after reaching some minimum value. This behavior is
due to changes in the ionization and temperature of the atmosphere. The
Lyα intensity also initially decreases with time, but in most cases
it reaches a relative minimum, increases again to a secondary relative
maximum, and then slowly but steadily decreases thereafter. Observable
properties of this time-dependent emission, such as the ratio of the
profile's peak spectral intensity at relative minimum to that at beam
onset (Irelmin/I0), the difference between the
profile's width at beam onset and that at the secondary relative maximum
(FWHM0-FWHMrelmax), and the difference between the
profile's centroid wavelength shift at beam onset and that at relative
minimum (Δλ0-Δλrelmin) can be used to deduce
δ. Once δ is known, \Fscr can be deduced from other observable
properties such as I0 and the times since beam onset at
which the Lyα intensity reaches its relative minimum and secondary
relative maximum values (trelmin and trelmax).
Title: The SERTS-97 rocket experiment to study activity on the Sun:
flight 36.167-GS on 1997 November 18.
Authors: Swartz, Marvin; Condor, Charles E.; Davila, Joseph M.; Haas,
J. Patrick; Jordan, Stuart D.; Linard, David L.; Miko, Joseph J.;
Nash, I. Carol; Novello, Joseph; Payne, Leslie J.; Plummer, Thomas
B.; Thomas, Roger J.; White, Larry A.; Brosius, Jeffrey W.; Thompson,
William T.
Bibcode: 1999sret.book.....S
Altcode:
This paper describes mainly the 1997 version of the Solar EUV Rocket
Telescope and Spectrograph (SERTS-97), a scientific experiment that
operated on NASA's suborbital rocket flight 36.167-GS. Its function
was to study activity on the Sun and to provide a cross calibration
for the CDS instrument on the SOHO satellite.
Title: Coronal Magnetography of Solar Active Regions Using Coordinated
SOHO/CDS and VLA Observations
Authors: Brosius, Jeffrey W.
Bibcode: 1999STIN...0032789B
Altcode:
The purpose of this project is to apply the coronal magnetographic
technique to SOHO (Solar Heliospheric Observatory) /CDS (Coronal
Diagnostic Spectrometer) EUV (Extreme Ultraviolet Radiation) and
coordinated VLA microwave observations of solar active regions to
derive the strength and structure of the coronal magnetic field. A CDS
observing plan was developed for obtaining spectra needed to derive
active region differential emission measures (DEMs) required for coronal
magnetography. VLA observations were proposed and obtained. SOHO
JOP 100 was developed, tested, approved, and implemented to obtain
coordinated CDS (Coronal Diagnostic Spectrometer)/EIT (Ultraviolet
Imaging Telescope)/ VLA (Very Large Array)/ TRACE (Transition Region and
Coronal Explorer)/ SXT (Solar X Ray Telescope) observations of active
regions on April 12, May 9, May 13, and May 23. Analysis of all four
data sets began, with heaviest concentration on COS data. It is found
that 200-pixel (14 A in NIS1) wavelength windows are appropriate for
extracting broadened Gaussian line profile fit parameters for lines
including Fe XIV at 334.2, Fe XVI at 335.4, Fe XVI at 360.8, and Mg
IX at 368.1 over the 4 arcmin by 4 arcmin CDS field of view. Extensive
efforts were focused on learning and applying were focused on learning
and applying CDS software, and including it in new IDL procedures
to carry out calculations relating to coronal magnetography. An
important step is to extract Gaussian profile fits to all the lines
needed to derive the DEM in each spatial pixel of any given active
region. The standard CDS absolute intensity calibration software was
applied to derived intensity images, revealing that ratios between
density-insensitive lines like Fe XVI 360.8/335.4 yield good agreement
with theory. However, the resulting absolute intensities of those
lines are very high, indicating that revisions to the CDS absolute
intensity calibrations remain to be included in the CDS software, an
essential step to deriving reliable coronal magnetograms. With lessons
learned and high quality data obtained during the past year, coronal
magnetography will be successfully pursued under my new SOHO GI program.
Title: Does Velocity Redistribution Really Enhance the HE 304 A Line
to Observed Intensities?
Authors: Jordan, Stuart; Andretta, Vincenzo; Garcia, Adriana; Brosius,
Jeffrey; Behring, William
Bibcode: 1999STIN...9909149J
Altcode:
Previous work by this group has demonstrated that small-scale
nonthermal velocities probably play a significant role in enhancing the
intensity of the He II 304 A line above values predicted by the static
atmosphere NLTE theories, and more in conformity with Skylab and SOHO
observations. This presentation briefly summarizes the evidence for this
conclusion, emphasizing SOHO and correlated groundbased observations,
of which examples are presented. However, in contrast to the previous
studies, the tact taken here is more critical, asking the question
"Can velocity redistribution fully explain the observations of the 304 A
line, and what counter-indications and problems remain?" The conclusion
reached is that, while velocity redistribution plays a significant
role in the intensity enhancement, it may not be the whole story. Some
other mechanism, associated with velocity filtration, may be at work.
Title: Solar Active Region and Quiet-Sun Extreme-Ultraviolet Spectra
from SERTS-95
Authors: Brosius, Jeffrey W.; Davila, Joseph M.; Thomas, Roger J.
Bibcode: 1998ApJS..119..255B
Altcode:
Goddard Space Flight Center's Solar EUV Rocket Telescope and
Spectrograph was flown on 1995 May 15 (SERTS-95), carrying a
multilayer-coated toroidal diffraction grating that enhanced the
instrumental sensitivity in its second-order wave band (171-225
Å). Spectra and spectroheliograms of NOAA active region 7870 (N09 W22)
were obtained in this wave band with a spectral resolution (instrumental
FWHM) ~30 mÅ and in the first-order wave band (235-335 Å) with a
spectral resolution ~55 mÅ. Spectra and spectroheliograms of quiet-Sun
areas northeast of the active region were also obtained. We derived
the SERTS-95 relative radiometric calibration directly from flight
data by means of density- and temperature-insensitive line intensity
ratios. Most theoretical values for such ratios were obtained from the
CHIANTI database. A total of 44 different lines were used to derive
the relative radiometric calibration in the two spectral orders,
most of them coming from seven (Fe X-Fe XVI) of the nine (Fe IX-Fe
XVII) observed ionization stages of iron. The resulting relatively
calibrated line intensities agree well with their corresponding
normalized theoretical values. This supports the overall accuracy
of the atomic physics parameters and demonstrates the power of the
technique. The present work extends earlier work by Brosius, Davila,
& Thomas, who determined the SERTS-95 second-order response
using this technique. Many of the ratios employed here can be used to
carry out a similar calibration exercise on spectra from the Coronal
Diagnostic Spectrometer (CDS) aboard the Solar and Heliospheric
Observatory (SOHO). We placed the line intensities onto an absolute
scale by forcing our quiet-Sun He II λ303.8 + Si XI λ303.3 intensity
to match that from previous observations. The resulting active region
and quietSun absolutely calibrated line lists contain 127 and 20 lines,
respectively. Active region densities derived from density-sensitive
line intensity ratios of Fe X, XI, XIII, and XIV are mutually consistent
with log ne ~ 9.4 +/- 0.2; densities derived from Fe XII
are significantly greater (log ne ~ 10).
Title: Using Strong Solar Coronal Emission Lines as Coronal Flux
Proxies
Authors: Falconer, David A.; Jordan, Stuart D.; Brosius, Jeffrey W.;
Davila, Joseph M.; Thomas, Roger J.; Andreatta, Vicenzo; Hara, Hirohisa
Bibcode: 1998SoPh..180..179F
Altcode:
We investigate the possibility that strong EUV lines observed with the
Goddard Solar EUV Rocket Telescope and Spectrograph (SERTS) provide
good proxies for estimating the total coronal flux over shorter
wavelength ranges. We use coordinated SERTS and Yohkoh observations
to obtain both polynomial and power-law fits relating the broad-band
soft X-ray fluxes to the intensities of Fexvi 335 Ú and 361 Ú, Fexv
284 Ú and 417 Ú, and Mgix 368 Ú measured with SERTS. We found that
the power-law fits best cover the full range of solar conditions from
quiet Sun through active region, though not surprisingly the `cooler'
Mgix 368 Ú line proves to be a poor proxy. The quadratic polynomial
fits yield fair agreement over a large range for all but the Mgix
line. However, the linear fits fail conspicuously when extrapolated
into the quiet-Sun regime. The implications of this work for the Heii
304 Ú line formation problem are also briefly considered.
Title: Calibration of the SERTS-95 Spectrograph from Iron Line
Intensity Ratios
Authors: Brosius, Jeffrey W.; Davila, Joseph M.; Thomas, Roger J.
Bibcode: 1998ApJ...497L.113B
Altcode:
Goddard Space Flight Center's Solar EUV Rocket Telescope and
Spectrograph was flown on 1995 May 15 (SERTS-95), carrying a
multilayer-coated toroidal diffraction grating which enhanced the
instrumental sensitivity within its second-order wave band (170-225
Å). Spectra and spectroheliograms of NOAA Active Region 7870 (N09/W22)
were obtained in this wave band with a spectral resolution (instrumental
FWHM) ~30 mÅ. We developed and applied a technique for deriving the
relative radiometric calibration independent of laboratory calibration
measurements by employing a method proposed by Neupert & Kastner for
monitoring variations in the sensitivities of orbiting EUV spectrometers
by means of density- and temperature-insensitive line intensity
ratios. Numerous ratios of emission lines from Fe X-XIV are mutually
consistent and yield an instrumental response curve that matches the
design characteristics of the multilayer coating. This supports the
accuracy of the atomic physics parameters and demonstrates the power
of the technique. Many of the ratios employed here can be used to
carry out a similar calibration exercise on spectra from the Coronal
Diagnostic Spectrometer's Grazing Incidence Spectrograph (CDS/GIS)
aboard the Solar and Heliospheric Observatory. Because they are
relatively free from blending with nearby strong lines, the following
density-sensitive ratios are particularly well suited for analysis
with the GIS: Fe X λ175.265/λ174.526, Fe X λ175.265/λ184.534,
Fe XII λ186.867/λ195.117, Fe XIII λ203.820/λ202.042, Fe XIII
λ200.017/λ202.042, and Fe XIV λ219.121/λ211.317. Densities derived
from Fe X, XIII, and XIV yield log ne~9.4+/-0.2.
Title: 3-Dimensional Models of Active Region Loops
Authors: Aschwanden, M. J.; Neupert, W. M.; Newmark, J.; Thompson,
B. J.; Brosius, J. W.; Holman, G. D.; Harrison, R. A.; Bastian, T. S.;
Nitta, N.; Hudson, H. S.; Zucker, A.
Bibcode: 1998ASPC..155..145A
Altcode: 1998sasp.conf..145A
No abstract at ADS
Title: Coordinated Observations with SOHO/CDS and SERTS
Authors: Thompson, W. T.; Thomas, R. J.; Davila, J. M.; Jordan, S. D.;
Brosius, J. W.
Bibcode: 1998AAS...191.7316T
Altcode: 1998BAAS...30..758T
On November 18, 1997, coordinated observations were made between the
Coronal Diagnostic Spectrometer (CDS) aboard the Solar and Heliospheric
Observatory (SOHO), and with the Solar Extreme-ultraviolet Rocket
Telescope and Spectrograph (SERTS). One of the primary goals of this
sounding rocket flight was to serve as a calibration underflight
for SOHO. SERTS observes resolved spectra over most of the short
wavelength channel of the CDS Normal Incidence Spectrograph, as well
as the He II 304 Angstroms line which is observed by CDS in second
order in the long wavelength channel. Observations were also made of
the full sun with the SOHO Extreme ultraviolet Imaging Telescope (EIT)
in its 304 Angstroms channel, allowing coalignment between all three
instruments. EIT also serves as a transfer standard of the alignment
to other full-sun observations. We will report on the status of the
data analysis from the SERTS-97 flight, and its comparison to CDS.
Title: The Measurement of Solar Active Region Properties with EUV
Spectra and Spectroheliograms from SERTS
Authors: Brosius, J. W.; Davila, J. M.; Thomas, R. J.; White, S. M.
Bibcode: 1997AAS...191.7315B
Altcode: 1997BAAS...29.1323B
The Goddard Space Flight Center's Solar EUV Rocket Telescope and
Spectrograph (SERTS) was successfully flown on six different occasions,
and results from several of those flights are presented here. For the
flight of 1995 May 15, SERTS included a multilayer coated toroidal
diffraction grating which enhanced the throughput above that of a
standard gold coated grating for wavelengths between about 170 and
220 Angstroms, with a peak response around 192 Angstroms. Emission
lines in this wavelength range are seen in second order. First order
lines between about 235 and 335 Angstroms are also detected. A total
of nearly 140 lines are identifiable in the combined first and second
order wavebands. These include lines from several ionization stages of
Ca, Mg, Ni, S, and Si, as well as lines from at least nine ionization
stages of Fe (IX -- XVII). Many of the lines are useful for calibration
verification, plasma diagnostics, or both. Results from analyses
of the high spectral resolution (30 m Angstroms in second order,
and 55 m Angstroms in first), spatially resolved (4.4 arcsec spatial
resolution) active region spectra are presented. For the flight of 1993
August 17, SERTS included a multilayer coated grating which enhanced
the instrumental sensitivity within the first order waveband. For
this flight we also obtained coordinated Very Large Array (VLA) radio
observations at 20 and 6 cm wavelengths. Because the radio emission is
sensitive to the coronal magnetic field while the EUV emission is not,
we were able to derive solar coronal magnetograms from the combined
SERTS and VLA observations. (This work was supported by NASA grants
NASW-96006 and NASW-4933.)
Title: Coronal Magnetography of a Solar Active Region Using
Coordinated SERTS and VLA Observations
Authors: Brosius, Jeffrey W.; Davila, Joseph M.; Thomas, Roger J.;
White, Stephen M.
Bibcode: 1997ApJ...488..488B
Altcode:
We observed NOAA region 7563 simultaneously with Goddard Space Flight
Center's Solar EUV Rocket Telescope and Spectrogaph (SERTS) and with
the Very Large Array (VLA) on 1993 August 17. SERTS obtained spectra
in the 280-420 Å wavelength range, and images in the lines of Mg IX
λ368.1, Fe XV λ284.1, and Fe XVI λ335.4. The VLA obtained microwave
images at 20 and 6 cm wavelengths. The microwave emission depends upon
the coronal temperature, density, column emission measure, and magnetic
field; therefore, the coronal magnetic field can be derived when all of
these other quantities are measured. Here we demonstrate this approach
by using the SERTS data to derive all the relevant plasma parameters and
then fitting the radio observations to a magnetic field model in order
to determine the magnetic field structure. We used the method of
Monsignori-Fossi & Landini and the coronal elemental abundances of
Feldman et al. to derive the differential emission measure (DEM) curve
for region 7563 from numerous EUV emission lines in spatially averaged
SERTS spectra. A similar curve was estimated for each point (i.e.,
each pixel or each spatial location) in the two-dimensional region by
scaling the average DEM curve with corresponding pixel intensities
in the Mg IX, Fe XV, and Fe XVI images. We integrated each such DEM
over narrow temperature ranges to obtain the column emission measure
(CEM) as a function of temperature, CEM(T). We also obtained electron
density measurements from EUV line intensity ratios in the spatially
averaged spectrum for several ionization stages of iron. These were
used to derive a functional relation between density and temperature,
ne(T). We derived the temperature dependence of the
coronal magnetic field [B(T)] at each point in the two-dimensional
region by incorporating CEM(T) and ne(T) into expressions for
the thermal bremsstrahlung and the gyroresonance opacities, and varying
B(T) so as to minimize the difference between the calculated and the
observed microwave intensities. The resulting calculated 20 and 6 cm
microwave intensity images reproduce the observed images very well. We
found that thermal bremsstrahlung alone is not sufficient to produce
the observed microwave intensities: gyroemission is required. Further,
contrary to several earlier studies, we found no evidence for cool,
absorbing plasma in the solar corona above the active region. The
coronal magnetic fields derived with our method typically exceed the
coronal fields extrapolated with a simple potential model, suggesting
the presence of coronal electric currents. However, in the diminutive
sunspot which dominates the 6 cm emission this difference is relatively
small, suggesting that the sunspot magnetic field itself is nearly
potential. Although we cannot firmly establish the uniqueness of our
solution in this particular case, the method is quite powerful and
should be repeated with other similar data sets. Variations in the
coronal elemental abundances could affect the determination of the
microwave emission mechanism(s), introduce evidence for the presence
of cool coronal plasma, and alter the strengths of the derived coronal
magnetic fields.
Title: Using Temporal Variations of the Nonthermal Redshifted
Ly-Alpha Emission to Deduce Properties of Proton Beams Injected into
a Stellar Atmosphere
Authors: Brosius, J. W.; Woodgate, B. E.
Bibcode: 1997AAS...190.2514B
Altcode: 1997BAAS...29R.808B
We present theoretical calculations of temporal variations in the
nonthermal redshifted Ly-alpha emission due to proton beams injected
into a stellar atmosphere during the impulsive phase of a flare. The
computations are performed for a power law spectrum of nonthermal proton
energies between 20 and 120 keV injected into a model stellar atmosphere
consisting of pure hydrogen in local thermodynamic equilibrium. We
calculate the beam-induced variations in temperature and particle
densities by assuming that these quantities satisfy the Saha equation
at all depths and for all times. We characterized the injected model
proton beams with the total energy flux and the power law index, and
computed time-dependent nonthermal redshifted Ly-alpha emission profiles
for five different values of the flux and three different values of
the index. Based upon trends evident in the resulting emission, it is
possible to deduce proton beam properties from sufficiently high quality
observations of the nonthermal redshifted Ly-alpha profile. The beam
penetration depth initially decreases with time, but in most cases
it increases again after reaching some minimum value. This behavior
is attributed to changes in the ionization and temperature of the
atmosphere. The nonthermal redshifted Ly-alpha intensity also initially
decreases with time, but in most cases it reaches a relative minimum,
increases again to a relative maximum, and then slowly but steadily
decreases thereafter. We describe how observable properties of the
time-dependent nonthermal redshifted Ly-alpha emission, such as the
ratio of the profile's peak intensity at relative minimum to that
at beam onset, and the times since beam onset at which the intensity
reaches its relative minimum and relative maximum values, can be used
to deduce the power law index and the total beam energy flux.
Title: Coronal Magnetography of a Solar Active Region Using
Coordinated SERTS and VLA Observations
Authors: Brosius, J. W.; Davila, J. M.; Thomas, R. J.; White, S. M.
Bibcode: 1997SPD....28.0135B
Altcode: 1997BAAS...29..885B
We observed NOAA region 7563 simultaneously with Goddard Space Flight
Center's Solar EUV Rocket Telescope and Spectrograph (SERTS) and with
the Very Large Array (VLA) on 1993 August 17. SERTS obtained spectra
in the 280 to 420 Angstroms wavelength range, and images in the lines
of Mg IX lambda 368.1, Fe XV lambda 284.1, and Fe XVI lambda 335.4. The
VLA obtained microwave images at 20 and 6 cm wavelengths. The microwave
emission depends upon the coronal temperature, density, column emission
measure, and magnetic field; therefore, the coronal magnetic field can
be derived when all of these other quantities are measured. Here we
demonstrate this approach by using the SERTS data to derive all the
relevant plasma parameters and then fitting the radio observations
to a magnetic field model in order to determine the magnetic field
structure. We derived the temperature dependence of the coronal magnetic
field (B(T)) at each point (i.e., each pixel or each spatial location)
in the two dimensional region by incorporating the corresponding
column emission measure (CEM(T)) and electron density (n_e(T)) into
expressions for the thermal bremsstrahlung and gyroresonance opacities,
and varying B(T) so as to minimize the difference between the calculated
and the observed microwave intensities. The resulting calculated 20
and 6 cm microwave intensity images reproduce the observed images very
well. Thermal bremsstrahlung emission alone is not sufficient to produce
the observed microwave intensities: gyroemission is required. Further,
contrary to several earlier studies, we found no evidence for cool,
absorbing plasma in the solar corona above the active region. The
coronal magnetic fields derived with our method typically exceed the
coronal fields extrapolated with a simple potential model, suggesting
the presence of coronal electric currents. However, in the diminutive
sunspot which dominates the 6 cm emission this difference is relatively
small, suggesting that the sunspot magnetic field itself is nearly
potential. (This work was supported by NASA grant NASW-4933.)
Title: The Structure and Properties of Solar Active Regions and
Quiet-Sun Areas Observed in Soft X-Rays with Yohkoh/SXT and in the
Extreme-Ultraviolet with SERTS
Authors: Brosius, Jeffrey W.; Davila, Joseph M.; Thomas, Roger J.;
Saba, Julia L. R.; Hara, Hirohisa; Monsignori-Fossi, Brunella C.
Bibcode: 1997ApJ...477..969B
Altcode:
We observed two solar active regions (NOAA regions 7563 and 7565),
quiet-Sun areas, and a coronal hole region simultaneously with Goddard
Space Flight Center's Solar EUV Rocket Telescope and Spectrograph
(SERTS) and with the Yohkoh Soft X-ray Telescope (SXT) on 1993 August
17. SERTS provided spatially resolved active region and quiet-Sun slit
spectra in the 280 to 420 Å wavelength range, and images in the lines
of He II λ303.8, Mg IX λ368.1, Fe XV λ284.1, and Fe XVI λλ335.4
and 360.8 SXT provided images through multiple broadband filters in both
the full-frame imaging mode and the partial-frame imaging mode. The
SERTS images in Fe XV (log Tmax = 6.33, where Tmax
is the temperature which maximizes the fractional ion abundance in
the available ionization equilibrium calculations, i.e., the formation
temperature) and Fe XVI (log Tmax = 6.43) exhibit remarkable
morphological similarity to the SXT images. Whereas the Fe XV and XVI
images outline the loop structures seen with SXT, the cooler He II
(log Tmax = 4.67) and Mg IX (log Tmax = 5.98)
images outline loop footpoints. In addition, the Mg IX emission
outlines other structures not necessarily associated with the hot
loops; these may be cool (T <~ 1 × 106 K) loops. From the spatially resolved slit spectra, we obtained emission-line
profiles for lines of He II λ303.8, Mg IX λ368.1, Fe XIII λ348.2,
Si XI λ303.3, Fe XIV λ334.2, Fe XV λ284.1, and Fe XVI λ335.4
for each spatial position. Based upon the spatial variations of the
line intensities, active region 7563 systematically narrows when
viewed with successively hotter lines, and appears narrowest in the
broadband soft X-ray emission. The active region width (full width at
half-maximum intensity) diminishes linearly with log Tmax;
the linear fit yields an extrapolated effective log Tmax
of 6.51 +/- 0.01 for the X-ray emission. The most intense, central core
straddles the magnetic neutral line. Active region and quiet-Sun
one-dimensional temperature scans were derived from intensity ratios
of spatially resolved SERTS slit spectral lines, and from coregistered
SXT filter ratios. The highest plasma temperatures were measured in the
most intense, central core of region 7563. The temperatures derived
from Fe XVI λ335.4/Fe XV λ284.1 and Fe XVI λ335.4/Fe XIV λ334.2
vary significantly (based upon the measurement uncertainties) but not
greatly (factors of less than 1.5) across the slit. The average log
T values derived from the above two ratios for region 7563 are 6.39
+/- 0.04 and 6.32 +/- 0.02, respectively. Somewhat larger systematic
variations were obtained from all available SXT filter ratios. The
average active region log T values derived from the SXT AlMgMn/thin
Al, thick Al/thin Al, and thick Al/AlMgMn filter ratios are 6.33 +/-
0.03, 6.45 +/- 0.02, and 6.49 +/- 0.03, respectively. Active
region and quiet-Sun one-dimensional density scans were derived from
intensity ratios of spatially resolved SERTS slit spectral lines of
Fe XIII and Fe XIV. The derived densities show neither systematic nor
significant variations along the slit in either the active region or
the quiet-Sun, despite the fact that the intensities themselves vary
substantially. This indicates that the product of the volume filling
factor and the path length (fΔl) must be greater by factors of 3-5 in
the active region core than in the outskirts. Furthermore, the derived
active region densities are ~2 times the quiet-Sun densities. This
density difference is adequate to explain the factor of ~4 intensity
difference in Fe XII and Fe XIII between the active and quiet areas,
but it is not adequate to explain the factor of ~8 intensity difference
in Fe XIV between the active and quiet areas. We attribute the latter
to a greater fΔl in the active regions. Statistically significant
Doppler shifts are not detected in region 7563 or in the quiet-Sun
with any of the EUV lines.
Title: The structure of the solar corona as observed by the Solar
Extreme Ultraviolet Rocket Telescope and Spectrograph
Authors: Davila, Joseph M.; Thomas, Roger J.; Brosius, Jeffrey;
Poland, Arthur
Bibcode: 1997AdSpR..20.2293D
Altcode:
Data from the Solar Extreme-ultraviolet Rocket Telescope and
Spectrograph (SERTS) have been used to address a number of important
scientific problems. The primary strength of the SERTS data is the
fact that this spectral range is rich with emission lines. Over 270
lines are seen in the SERTS active Sun spectrum, from 57 different
ions. For example, multiple (>= 4) lines are observed for all
ionization states of iron from Fe IX to Fe XVII. Temperatures and
densities have been derived for a number of active and quiet Sun
regions, the coronal magnetic field strength has been estimated for
both a plage region and an active region.
Title: Measuring Active and Quiet-Sun Coronal Plasma Properties with
Extreme-Ultraviolet Spectra from SERTS
Authors: Brosius, Jeffrey W.; Davila, Joseph M.; Thomas, Roger J.;
Monsignori-Fossi, Brunella C.
Bibcode: 1996ApJS..106..143B
Altcode:
We obtained high-resolution extreme-ultraviolet (EUV) spectra of solar
active regions, quiet-Sun areas, and off-limb areas during 1991 May
7 and 1993 August 17 flights of NASA/Goddard Space Flight Center's
Solar EUV Rocket Telescope and Spectrograph (SERTS). The 1991 flight
was the first time a multilayer coated diffraction grating was ever
used in space. Emission lines from the eight ionization stages of iron
between Fe+9 (Fe x) and Fe+16 (Fe XVII) were
observed. Values of numerous density- and temperature-insensitive line
intensity ratios agree with their corresponding theoretical values. Intensity ratios among various lines originating in a common stage of
ionization provide measurements of coronal electron density. Numerous
density-sensitive ratios are available for Fe xiii, and they yield
active region density (cm-3) logarithms of 9.66±0.49
and 9.60±0.54 for the 1993 and 1991 flights, respectively, and a
quiet-Sun density of 9.03±0.28 for the 1993 flight. Filling factors,
calculated from the derived densities assuming a path length of 1 ×
109 cm, range from several thousandths to nearly unity. Intensity ratios among lines originating in different ionization
stages of iron yield measurements of coronal electron temperature in the
isothermal approximation. The line ratios yield temperatures ranging
from 1.1 × 106 to 5.2 × 106 K for the active regions,
and 1.0 × 106 to 2.1 × 106 K for the quiet Sun, depending
upon the ionization stages used. The derived temperature diminishes
with decreasing ionization stages. Fe XVII emission, detected in the
active regions but not in the quiet areas, accounts for the higher
maximum active region temperature. Derived active region temperatures
are greater than their quiet-Sun counterparts for ratios that include
lines from Fe xiv through Fe XVI; however, the derived active region and
quiet-Sun temperatures are not statistically significantly different for
line intensity ratios that involve only Fe x through Fe xiii. The latter
similarity in derived temperatures suggests the presence of similar
thermal structures in all the areas observed, although the active
regions also harbor hotter material. Differential emission measure
(DEM) distributions were constructed for the active region and quiet-
Sun observations obtained during both flights. The two quiet-Sun DEM
curves and the 1993 active region DEM curve all show peaks between log
T = 6.1 and 6.2. The 1993 active region DEM has a second peak between
log T = 6.6 and 6.7, and the 1991 active region DEM has only one peak,
between log T = 6.5 and 6.6. Thus, the 1993 active region DEM curve
appears, in some sense, to be a composite of the quiet-Sun DEM curve
and the 1991 active region DEM curve. The 1991 active region exhibited
flaring activity, yielded higher line ratio temperatures, and contained
greater photo spheric magnetic fields than the 1993 active region.
Title: The Structure and Properties of Solar Active Regions and
Quiet Sun Areas Observed With SERTS and YOHKOH
Authors: Brosius, J. W.; Davila, J. M.; Thomas, R. J.; Hara, H.
Bibcode: 1996AAS...188.3715B
Altcode: 1996BAAS...28..880B
We observed solar active regions, quiet sun areas, and a coronal hole
simultaneously with Goddard Space Flight Center's Solar EUV Rocket
Telescope and Spectrograph (SERTS), and with the Yohkoh Soft X-Ray
Telescope (SXT) on 1993 August 17. SERTS provided spatially resolved
active region and quiet sun spectra in the 280 to 420 Angstroms
wavelength range, and images in the lines of He II 304 Angstroms,
Mg IX 368 Angstroms, Fe XV 284 Angstroms, and Fe XVI 335 Angstroms
and 360 Angstroms. The SERTS waveband is accessible to CDS, SUMER,
and EIT on SOHO. SXT provided images through multiple broadband
filters. The SERTS images in Fe XV (T=2 MK) and XVI (T=2.5 MK) exhibit
remarkable morphological similarity to the SXT images. Whereas the
Fe XV and XVI images outline the loop structures seen with SXT, the
cooler He II (T=0.1 MK) and Mg IX (T=1 MK) images seem to outline loop
footpoints. From the spatially resolved spectra, we obtained emission
line profiles for lines of Fe X (1 MK) through Fe XVI, and Mg IX and
Ni XVIII (3.2 MK) for each spatial position. Based upon the spatial
variations of the line intensities, the active region systematically
narrows as it is viewed with successively hotter lines. The active
region appears narrowest in the X-ray emission, which is consistent
with our understanding that Yohkoh is most sensitive to the hottest
plasma in its line of sight. EUV emission from Fe XVII (T=5 MK) is weak
but detectable in the active region core. The most intense, central
core straddles the magnetic neutral line. Temperature maps obtained
with SERTS image ratios and with SXT filter ratios are compared. Line
intensity ratios indicate that the active region temperature is greatest
in the central core, but that the density varies very little across the
region. Significant Doppler shifts are not detected in the EUV lines.
Title: Measurements of Active and Quiet Sun Coronal Plasma Properties
with SERTS EUV Spectra
Authors: Brosius, J. W.; Davila, J. M.; Thomas, R. J.;
Monsignori-Fossi, B. C.; Saba, J. L. R.
Bibcode: 1996mpsa.conf..421B
Altcode: 1996IAUCo.153..421B
No abstract at ADS
Title: Solar EUV spectroscopy with serts: measurements of active
and quiet Sun properties.
Authors: Brosius, J. W.; Davila, J. M.; Thomas, R. J.; Jordan, S. D.;
Monsignori-Fossi, B. C.
Bibcode: 1996uxsa.conf...83B
Altcode: 1996uxsa.coll...83B
The Solar EUV Rocket Telescope and Spectrograph (SERTS) was developed
by the Laboratory for Astronomy and Solar Physics at NASA/Goddard
Space Flight Center. It was successfully flown in 1989, 1991, 1993, and
(very recently) 1995, providing spectra and images of a variety of solar
features on each occasion. SERTS data have been used to address numerous
problems in solar physics, of which the following are discussed below:
(1) measurement of coronal temperature and density, (2) derivation
of differential emission measure distribution, (3) verification of
atomic physics parameters, (4) determination of relative elemental
abundances, (5) formation of the He II 304 Å line, (6) mass flows,
and (7) coronal magnetography.
Title: Plasma Properties and Magnetic Field Structure of the Solar
Corona, Based on Coordinated Max 1991 Observations from SERTS,
the VLA, and Magnetographs
Authors: Brosius, Jeffrey W.
Bibcode: 1996hstx.rept.....B
Altcode: 1996hstx.reptQ....B; 1996hstx.reptR....B
The purposes of this investigation are to determine the plasma
properties and magnetic field structure of the solar corona using
coordinated observations obtained with NASA/GSFC's Solar EUV Rocket
Telescope and Spectrograph (SERTS), the Very Large Array (VLA), and
magnetographs. The observations were obtained under the auspices of
NASA's Max '91 program. The methods of achieving the stated purposes are
to use SERTS spectra and spectroheliograms to determine coronal plasma
properties such as temperature, density, and emission measure. These
properties are subsequently used to calculate the intensity of the
thermal bremsstrahlung microwave emission from the coronal plasma (the
minimum microwave intensity expected from the emitting plasma). This,
in turn, can be used to establish which emission mechanism(s) contribute
to the observed microwave emission. Because both mechanisms that may
contribute to quiescent active region microwave emission (thermal
bremsstrahlung and thermal gyroemission) depend upon the coronal
magnetic field in known ways, this information can ultimately be used
to derive the coronal magnetic field. Ideally, three-dimensional models
of the coronal plasma and magnetic field which are consistent with all
of the EUV spectra and spectroheliograms, as well as with the intensity
and polarization maps at all of the microwave observing frequencies,
can be derived. For completeness, the coronal magnetic field derived
from the coordinated multiwaveband observations must be compared with
extrapolations from photospheric magnetograms.
Title: Measurements of Active and Quiet Sun Coronal Plasma Properties
with SERTS EUV Spectra
Authors: Brosius, J. W.; Davila, J. M.; Thomas, R. J.;
Monsignori-Fossi, B. C.
Bibcode: 1995SPD....26..607B
Altcode: 1995BAAS...27..962B
No abstract at ADS
Title: Heating and Ionization of Stellar Chromospheres by Nonthermal
Proton Beams: Implications for Impulsive Phase, Redshifted Lyman-
alpha Radiation in Stellar Flares
Authors: Brosius, Jeffrey W.; Robinson, Richard D.; Maran, Stephen P.
Bibcode: 1995ApJ...441..385B
Altcode:
We investigate the physical basis for the timescale of impulsive-phase,
redshifted Lyman-alpha emission in stellar flares on the assumption
that it is determined by energy losses in a nonthermal proton beam that
is penetrating the chromosphere from above. The temporal evolution
of ionization and heating in representative model chromospheres
subjected to such beams is calculated. The treatment of 'stopping'
of beam protons takes into account their interactions with (1)
electrons bound in neutral hydrogen, (2) nuclei of neutral hydrogen,
(3) free electrons, and (4) ambient thermal protons. We find that, for
constant incident beam flux, the system attains an equilibrium with the
beam energy input to the chromosphere balanced by radiative losses. In
equilibrium, the beam penetration depth is constant, and erosion of the
chromosphere ceases. If the redshifted, impulsive-phase stellar flare
Lyman-alpha emission is produced by downstreaming hydrogen formed
through charge exchange between beam protons and ambient hydrogen,
then the emission should end when the beam no longer reaches neutral
hydrogen. The durations of representative emission events calculated
on this assumption range from 0.1 to 14 s. The stronger the beam, the
shorter the timescale over which the redshifted Lyman-alpha emission
can be observed.
Title: Plasma properties and magnetic field structure of the solar
corona, based on coordinated Max 1991 observations from SERTS,
the VLA, and magnetographs
Authors: Brosius, Jeffrey W.
Bibcode: 1995hstx.reptQ....B
Altcode:
The purposes of this investigation are to determine the plasma
properties and magnetic field structure of the solar corona using
coordinated observations obtained with NASA/GSFC's Solar EUV
rocket Telescope and Spectrograph (SERTS), the Very Large Array
(VLA), and magnetographs. The observations were obtained under
the auspices of NASA's Max '91 program. The methods of achieving
the stated purposes of this investigation are: (1) to use SERTS
spectra and spectroheliograms to determine coronal plasma properties
such as temperature, density, and emission measure; (2) to use
the coronal plasma properties to calculate the intensity of the
thermal bremsstrahlung microwave emission from the coronal plasma
(the minimum microwave intensity expected from the emitting plasma);
(3) to establish which emission mechanism(s) contribute to the observed
microwave emission by comparing the calculated thermal bremsstrahlung
intensity with the observed microwave intensity; (4) to derive the
coronal magnetic field for regions in which gyroemission contributes
to the microwave emission by determining the appropriate harmonic of
the local electron gyrofrequency; (5) to derive the coronal magnetic
field for regions in which thermal bremsstrahlung emission alone is
responsible for the observed microwave emission by calculating the
magnetic field which yields the observed microwave polarization;
(6) to derive three-dimensional models of the coronal plasma and
magnetic field which are consistent with all of the EUV spectra and
spectroheliograms, as well as with the intensity and polarization
maps at all of the microwave observing frequencies; and (7) to compare
the coronal magnetic field derived from the coordinated multiwaveband
observations with extrapolations from photospheric magnetograms.
Title: Coronal Magnetic Structures Observing Campaign. III. Coronal
Plasma and Magnetic Field Diagnostics Derived from Multiwaveband
Active Region Observations
Authors: Schmelz, J. T.; Holman, G. D.; Brosius, J. W.; Willson, R. F.
Bibcode: 1994ApJ...434..786S
Altcode:
Simultaneous soft X-ray, microwave, and photospheric magnetic
field observations were taken during the Coronal Magnetic Structures
Observing Campaign (CoMStOC '87). The plasma electron temperature and
emission measures determined from the X-ray data are used to predict the
free-free emission expected at 20 and 6 cm. Comparing these predictions
with the microwave observations, it is found that the predicted 20 cm
brightness temperatures are higher than the observed, requiring cool
absorbing material between the hot X-ray plasma and the observer. The
model that is most consistent with all the observations and minimizes
the required coronal fields indicates that this 20 cm emission is
either free-free or a combination of free-free and fourth harmonic
cyclotron emanating from the X-ray plasma with an electron temperature
of approximately 3.1 x 106 K and an emission measure of
approximately 1.3 x 1029/cm5. The observed 20
cm polarization requires a field strength of greater than or equal
to 150 G. In addition, the 6 cm emission is free-free, emanating
from cooler plasma with an electron temperature of approximately
1.5 x 106 K and an emission measure of approximately 3-6
x 1029/cm5. This model is consistent with the
rather unusual combination of high 20 cm and low 6 cm polarization as
well as the low extrapolated coronal fields.
Title: Solar Coronal Temperature Diagnostics Using Emission Lines
from Multiple Stages of Ionization of Iron
Authors: Brosius, Jeffrey W.; Davila, Joseph M.; Thomas, Roger J.;
Thompson, William T.
Bibcode: 1994ApJ...425..343B
Altcode:
We obtained spatially resolved extreme-ultraviolet (EUV) spectra
of AR 6615 on 1991 May 7 with NASA/ Goddard Space Flight Center's
Solar EUV Rocket Telescope and Spectrograph (SERTS). Included are
emission lines from four different stages of ionization of iron:
Fe(+15) lambda 335 A, Fe(+14) lambda 327 A, Fe(+13) lambda 334 A,
and Fe(+12) lambda 348 A. Using intensity ratios from among these
lines, we have calculated the active region coronal temperature along
the Solar Extreme Ultraviolet Telescope and Spectrograph (SERTS)
slit. Temperatures derived from line ratios which incorporate adjacent
stages of ionization are most sensitive to measurement uncertainties
and yield the largest scatter. Temperatures derived from line ratios
which incorporate nonadjacent stages of ionization are less sensitive to
measurement uncertainties and yield little scatter. The active region
temperature derived from these latter ratios has an average value of
2.54 x 106 K, with a standard deviation approximately 0.12
x 106 K, and shows no significant variation with position
along the slit.
Title: Evidence of mass outflow in the low corona over a large sunspot
Authors: Neupert, W. M.; Brosius, J. W.; Thomas, R. J.; Thompson, W. T.
Bibcode: 1994AdSpR..14d..61N
Altcode: 1994AdSpR..14Q..61N
An extreme ultraviolet (EUV) imaging spectrograph designed for soundings
rocket flight has been used to search for velocity fields in the low
solar corona. During a flight in May, 1989, we obtained emission line
profile measurements along a chord through an active region on the
Sun. Relative Doppler velocities were measured in emissions lines of Mg
IX, Fe XV, and Fe XVI with a sensitivity of 2-3 km s-1 at
350 A. The only Doppler shift appreciably greater than this level was
observed in the line of Mg IX at 368.1 A over the umbra of the large
sunspot. The maximum shift measured at that location corresponded to
a velocity toward the observer of 14 +/- 3km s-1 relative
to the mean of measurements in that emission line made elsewhere over
the active region. The magnetic field in the low corona was aligned
to within 10° of the line of sight at the location of maximum Doppler
shift. Depending on the magnetic field geometry, this mass outflow could
either re-appear as a downflow of material in distant footpoints of
closed coronal loops or, if along open field lines, could contribute to
the solar wind. The site of the sunspot was near a major photospheric
magnetic field boundary. Such boundaries have been associated with
low-speed solar wind as observed in interplanetary plasmas.
Title: Observing Stellar Coronae with the Goddard High Resolution
Spectrograph. I. The dMe Star AU Microscopii
Authors: Maran, S. P.; Robinson, R. D.; Shore, S. N.; Brosius, J. W.;
Carpenter, K. G.; Woodgate, B. E.; Linsky, J. L.; Brown, A.; Byrne,
P. B.; Kundu, M. R.; White, S.; Brandt, J. C.; Shine, R. A.; Walter,
F. M.
Bibcode: 1994ApJ...421..800M
Altcode:
We report on an observation of AU Mic taken with the Goddard High
Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope. The
data consist of a rapid sequence of spectra covering the wavelength
range 1345-1375 A with a spectral resolution of 10,000. The observations
were originally intended to search for spectral variations during
flares. No flares were detected during the 3.5 hr of monitoring. A
method of reducing the noise while combining the individual spectra
in the time series is described which resulted in the elimination of
half of the noise while rejecting only a small fraction of the stellar
signal. The resultant spectrum was of sufficient quality to allow the
detection of emission lines with an integrated flux of 10-15
ergs/sq cm(sec) or greater. Lines of C I, O I, O V, Cl I, and Fe XXI
were detected. This is the first indisputable detection of the 1354
A Fe XXI line, formed at T approximately = 107 K, on a
star other than the Sun. The line was well resolved and displayed
no significant bulk motions or profile asymmetry. From the upper
limit on the observed line width, we derive an upper limit of 38 km/s
for the turbulent velocity in the 107 K plasma. An upper
limit is derived for the flux of the 1349 A Fe XII line, formed at T
approximately = 1.3 x 106 K. These data are combined with
contemporaneous GHRS and International Ultraviolet Explorer (IUE) data
to derive the volume emission measure distribution of AU Mic over the
temperature range 104-107 K. Models of coronal
loops in hydrostatic equilibrium are consistent with the observed
volume emission measures of the coronal lines. The fraction of the
stellar surface covered by the footprints of the loops depends upon the
loop length and is less than 14% for lengths smaller than the stellar
radius. From the upper limit to the estimated width of the Fe XXI line
profile we find that the we cannot rule out Alfven wave dissipation
as a possible contributor to the required quiescent loop heating rate.
Title: Lyman-Alpha Emission as a Diagnostic of Superthermal Proton
Properties in Stellar Flares
Authors: Brosius, J. W.; Robinson, R. D.; Maran, S. P.
Bibcode: 1994ASPC...64..360B
Altcode: 1994csss....8..360B
No abstract at ADS
Title: Simultaneous Observations of Solar Plage with the Solar
Extreme Ultraviolet Rocket Telescope and Spectrograph (SERTS),
the VLA, and the Kitt Peak Magnetograph
Authors: Brosius, Jeffrey W.; Davila, Joseph M.; Thompson, William T.;
Thomas, Roger J.; Holman, Gordon D.; Gopalswamy, N.; White, Stephen
M.; Kundu, Mukul R.; Jones, Harrison P.
Bibcode: 1993ApJ...411..410B
Altcode:
We obtained simultaneous images of solar plage on 1991, May 7
with SERTS, the VLA,4 and the NASA/National Solar Observatory
spectromagnetograph at the NSO/Kitt Peak Vacuum Telescope. Using
intensity ratios of Fe XVI to Fe XV emission lines, we find that the
coronal plasma temperature is (2.3-2.9) x 10 exp 6 K throughout the
region. The column emission measure ranges from 2.5 x 10 exp 27 to
l.3 x 10 exp 28 cm exp -5. The calculated structure and intensity
of the 20 cm wavelength thermal bremsstrahlung emission from the hot
plasma observed by SERTS is quite similar to the observed structure and
intensity of the 20 cm microwave emission observed by the VLA. Using
the Meyer (1991, 1992) revised coronal iron abundance, we find no
evidence either for cool absorbing plasma or for contributions from
thermal gyroemission. Using the observed microwave polarization and the
SERTS plasma parameters, we calculate a map of the coronal longitudinal
magnetic field. The resulting values, about 30-60 G, are comparable
to extrapolated values of the potential field at heights of 5000 and
10,000 km.
Title: Solar Coronal Plasma and Magnetic Field Diagnostics Using
SERTS and Coordinated VLA Observations
Authors: Brosius, J. W.; Davila, J. M.; Thompson, W. T.; Thomas, R. J.;
Holman, G. D.; Gopalswamy, N.; White, S. M.; Kundu, M. R.; Jones, H. P.
Bibcode: 1993BAAS...25.1224B
Altcode:
No abstract at ADS
Title: Analysis of EUV, Microwave and Magnetic Field Observations
of Solar Plage
Authors: Brosius, J. W.; Davila, J. M.; Jones, H. P.; Thompson, W. T.;
Thomas, R. J.; Holman, G. D.; White, S. W.; Gopalswamy, N.; Kundu,
M. R.
Bibcode: 1993ASPC...46..291B
Altcode: 1993mvfs.conf..291B; 1993IAUCo.141..291B
No abstract at ADS
Title: Extreme ultraviolet observation of mass flow in the low corona
over a large sunspot.
Authors: Neupert, W. M.; Brosius, J. W.; Thomas, R. J.; Thompson, W. T.
Bibcode: 1993uxrs.conf..361N
Altcode: 1993uxsa.conf..361N
The authors have used an extreme ultraviolet (EUV) imaging spectrograph
(SERTS) covering the spectral range from 235 to 450 Å to study
velocity fields in the low solar corona. During a flight in May, 1989,
they obtained emission line profile measurements along a chord through
an active region on the Sun, including the corona over a sunspot and
the initial stage of a small flare. Relative Doppler velocities were
measured in the lines of Mg IX, Fe XV, and Fe XVI with a sensitivity
of 2-3 km s-1 at 350 Å. The only significant Doppler shift
observed was in the emission line of Mg IX at 368.1 Å over the umbra
of the large sunspot. The maximum detected shift corresponded to a
peak velocity toward the observer of 14±3 km s-1 relative
to the mean of measurements in this emission line made elsewhere over
the active region. The magnetic field in the low corona was aligned to
within 10° of the line of sight at the location of maximum Doppler
shift. Depending on the closure of the field, such a mass flow could
either contribute to the solar wind or re-appear as a downflow of
material in distant regions on the solar surface.
Title: Coronal Magnetic Structures Observing Campaign. II. Magnetic
and Plasma Properties of a Solar Active Region
Authors: Schmelz, J. T.; Holman, G. D.; Brosius, J. W.; Gonzalez, R. D.
Bibcode: 1992ApJ...399..733S
Altcode:
Simultaneous soft X-ray, microwave, and photospheric magnetic field
observations were taken during the Coronal Magnetic Structures
Observing Campaign. The plasma electron temperatures and emission
measures determined from the X-ray data are used to predict the
intensity and structure of the thermal bremsstrahlung emission at 20
and 6 cm. Comparing these predictions with the microwave observations,
it is found that the 20 cm structure is very similar to that expected
from the X-rays, but a substantial amount of the 6 cm emission was
resolved out. The predicted 20 cm brightness temperatures are higher
than the observed, requiring cool absorbing material (not greater
than 500,000 K) between the hot X-ray plasma and the observer. The
absorption mechanism in the cool plasma at 20 cm is most likely
thermal bremsstrahlung, requiring coronal magnetic fields as high as
150 G. 'Coronal Magnetograms', made by extrapolating the photospheric
longitudinal field using the Sakurai code, show that appropriate values
of the total field are reached at heights of 6000-10,000 km above the
photosphere (at many but not all locations).
Title: Underneath coronal loops: MSDP observations coordinated with
SERTS 4 and NIXT flights.
Authors: Schmieder, B.; Mein, N.; Golub, L.; Davila, J. M.; Thomas,
R.; Brosius, J.
Bibcode: 1992ESASP.348..257S
Altcode: 1992cscl.work..257S
Ground-based coordinated observations with the multichannel subtractive
double pass spectrograph (MSDP) allowed to portray the chromospheric
intensity and velocity fields below coronal structures during recent
launchs of sounding rockets. During SERTS 4 observations (May 7,
1991), two different active regions presenting flare and filament have
been coaligned with UV structures. In July 11, 1991 (eclipse day)
large Hα ejection material in AR 6713 was detected during the NIXT
flight. Preliminary results are displayed.
Title: Evidence for Mass Outflow in the Low Solar Corona over a
Large Sunspot
Authors: Neupert, Werner M.; Brosius, Jeffrey W.; Thomas, Roger J.;
Thompson, William T.
Bibcode: 1992ApJ...392L..95N
Altcode:
Spatially resolved EUV coronal emission-line profiles have been
obtained in a solar active region, including a large sunspot, using an
EUV imaging spectrograph. Relative Doppler velocities were measured in
the lines of Mg IX, Fe XV, and Fe XVI with a sensitivity of 2-3 km/s
at 350 A. The only significant Doppler shift occurred over the umbra of
the large sunspot, in the emission line of Mg IX (at Te of about 1.1 x
10 exp 6 K). The maximum shift corresponded to a peak velocity toward
the observer of 14 +/- 3 km/s relative to the mean of measurements
in this emission line made elsewhere over the active region. The
magnetic field in the low corona was aligned to within 10 deg of the
line of sight at the location of maximum Doppler shift. Depending on
the closure of the field, such a mass flow could either contribute
to the solar wind or reappear as a downflow of material in distant
regions on the solar surface. The site of the source, near a major
photospheric field boundary, was consistent with origins of low-speed
solar wind typically inferred from interplanetary plasma observations.
Title: Decimetric Solar Type U Bursts: VLA and PHOENIX Observations
Authors: Aschwanden, Markus J.; Bastian, T. S.; Benz, A. O.; Brosius,
J. W.
Bibcode: 1992ApJ...391..380A
Altcode:
Observations of type U bursts, simultaneously detected by the VLA at
1.446 GHz and by the broadband spectrometer Phoenix in the 1.1-1.7
GHz frequency band on August 13, 1989 are reported. Extrapolations
of the coronal magnetic field, assuming a potential configuration,
indicate that the VLA 20 cm source demarcates an isodensity level. The
source covers a wide angle of diverging magnetic field lines whose
footpoints originate close to a magnetic intrusion of negative polarity
into the main sunspot group of the active region with dominant positive
polarity. The centroid of the 20-cm U-burst emission, which corresponds
to the turnover frequency of the type U bursts and remains stationary
during all U bursts, coincides with the apex of extrapolated potential
field lines at a height of about 130,000 km. It is demonstrated
that the combination of radio imaging and broadband dynamic spectra,
combined with the magnetic field reconstruction from magnetograms,
can constrain all physical parameters of a magnetic loop system.
Title: Analysis of EUV, Microwave, and Magnetic Field Observations
of a Solar Active Region
Authors: Brosius, J. W.; Davila, J. M.; Jones, H. P.; Thompson, W. T.;
White, S. M.; Gopalswamy, N.; Kundu, M. R.
Bibcode: 1992AAS...180.4002B
Altcode: 1992BAAS...24R.792B
No abstract at ADS
Title: CoMStOC '92: The Coronal Magnetic Structures Observing Campaign
Authors: Schmelz, J. T.; Holman, G. D.; Brosius, J. W.
Bibcode: 1992AAS...180.4511S
Altcode: 1992BAAS...24..804S
A primary goal of CoMStOC '92 is to directly measure the magnetic
field strength and determine its structure in the solar corona,
especially for pre- and post-flare active regions. New instrumentation
and analysis techniques were combined with experience gained during
a previous campaign to improve the observing strategies and data
interpretation. 15 days of VLA observation were scheduled between 03
April -- 12 May 1992. Observations were also obtained by the instruments
on the Japanese Yohkoh spacecraft, ground-based magnetographs, and
the Owens Valley Radio Observatory. At the time of writing, the Solar
Plasma Diagnostics Experiment rocket payload (M. Bruner, Lockheed)
planned to launch and the Tunable Filter (T. Tarbell, Lockheed)
planned to observe during the campaign. The basic CoMStOC method
for determining the magnetic field is as follows: When the microwave
emission is dominated by gyroresonance, the magnetic field strength
is B(Gauss) = 357times nu (GHz)/n, where nu is the microwave observing
frequency and n is the harmonic. When thermal bremsstrahlung dominates,
the field is determined by the microwave polarization. Maps of the
electron temperature and emission measure of the coronal plasma are
made from images taken with the Soft X-ray Telescope on Yohkoh; these
maps are then used to calculate which microwave emission mechanism
dominates. Once this dominant mechanism is known, the magnetic field
strength can be calculated. The values obtained using this method are
then compared with extrapolations photospheric magnetograms into the
corona. (*) NAS/NRC Resident Research Associate
Title: Coronal Magnetic Structures Observing
Campaign. IV. Multiwaveband Observations of Sunspot and
Plage-associated Coronal Emission
Authors: Brosius, Jeffrey W.; Willson, Robert F.; Holman, Gordon D.;
Schmelz, Joan T.
Bibcode: 1992ApJ...386..347B
Altcode:
Results of simultaneous observations of an active region located near
the central meridian obtained on December 18, 1987, are presented. An
asymmetric looplike structure connects the strong leading sunspot
with a nearby region of opposite polarity. Both 6- and 20-cm emission
lie along this structure, rather than over the sunspot, with higher
frequency emission originating closer to the footpoint inside the
sunspot. The 20-cm emission is due to a superposition of second- and
third-harmonic gyroemission, where the field strength is 160-300 G,
while the 6-cm emission is due to third-harmonic gyroemission from a
region where the magnetic field strength ranges from 547 to 583 G. X-ray
data associated with an area of trailing plage are used to predict
the brightness temperature structure due to thermal bremsstrahlung
emission in the 6- and 20-cm wavebands.
Title: CoMStOC 4: Multiwaveband observations of sunspot and
plage-associated coronal emission
Authors: Brosius, Jeffrey W.; Willson, Robert F.; Holman, Gordon D.;
Schmelz, Joan T.
Bibcode: 1992tuft.rept.....B
Altcode:
Simultaneous observations of an active region located near the central
meridian were obtained with the Very Large Array, the Solar Maximum
Mission X-ray Polychromator, and the Beijing Observatory magnetograph
on 18 December 1987, during the Coronal Magnetic Structures Observing
Campaign (COMSTOC). An asymmetric loop-like structure connects the
strong leading sunspot with a nearby region of opposite polarity. Both
6 and 20 cm emission lies along this structure, rather than over
the sunspot, with higher frequency emission originating closer to
the footpoint inside the sunspot. The 20 cm emission is due to a
superposition of 2nd and 3rd harmonic gyroemission, where the field
strength is 16- G- 300 G, while the 6 cm emission is due to the 3rd
harmonic gyroemission from a region where the magnetic field strength
ranges from 547 583 G. A high value of the Alfven speed of 40,000
km/sec, is obtained at the location of the 6 cm source, with somewhat
lower values of 10,000 - 20,000 km/sec, at the location of the 20 cm
emission. At the location of the 6 cm source, the plasma temperature
diminishes with height from 2,500,000 K at 5000 km to 1,300,000 K at
15,000 km.
Title: Microwave polarization inversion observed
Authors: Brosius, Jeffrey W.; Holman, Gordon D.; Schmelz, Joan T.
Bibcode: 1991EOSTr..72..449B
Altcode:
Observations of an inversion of solar-active-region microwave
polarization are described as they occurred during the Coronal
Magnetic Structures Observing Campaign. Data regarding the microwave
frequencies, soft X-ray emissions, brightness temperatures, and column
emissions are obtained with the observations. The data are employed
in the potential-field extrapolation procedure by Sakurai (1982)
to calculate the coronal magnetic-field vector, and the microwave
polarization observations yield reasonable coronal densities and
evidence of an inversion.
Title: Simultaneous EUV, Microwave, and Magnetic Field Observations
of Solar Active Regions
Authors: Brosius, J. W.; Davila, J. M.; Thompson, W. T.; Gopalswamy,
N.; White, S. M.; Jones, H. P.; Metcalf, T. R.
Bibcode: 1991BAAS...23.1388B
Altcode:
No abstract at ADS
Title: Coronal Magnetic Structures Observing Campaign. I. Simultaneous
Microwave and Soft X-Ray Observations of Active Regions at the
Solar Limb
Authors: Nitta, N.; White, S. M.; Kundu, M. R.; Gopalswamy, N.; Holman,
G. D.; Brosius, J. W.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
Bibcode: 1991ApJ...374..374N
Altcode:
Using simultaneous microwave and soft X-ray measurements made with
the Very Large Array (VLA) at 6 and 20 cm and the X-ray Polychromator
(XRP) aboard the Solar Maximum Mission (SMM), we have studied two
active regions near the solar limb. These observations were taken as
part of the Coronal Magnetic Structures Observing Campaign (CoMStOC),
a collaboration designed to study the magnetic field in the solar
corona. The images in soft X-rays and at 20 cm wavelength are similar:
both show peaks above the active regions and extended bridge of
emission 200,000 km long connecting the two regions. The brightness
temperature of the 20 cm emission is lower than that predicted from the
X-ray emitting material, however; it can be attributed to free-free
emission in cooler (<106 K) plasma not visible to XRP,
with an optical depth ∼1. The 6 cm emission is concentrated at lower
altitudes and in a ∼160,000 km long bundle of loops in the northern
active region. Comparison of the 6 cm map with the potential magnetic
field lines computed from photospheric magnetic fields (measured 2 days
earlier) indicates that the 6 cm emission is associated with fields
of less than ∼200 G. Such fields would be too weak to attribute the
observed 6 cm emission to gyroresonance radiation. Analysis of the
6 cm loop bundle indicates that it is strongly asymmetric, with the
magnetic field in the northern leg ∼2 times stronger than in the
southern leg; the 6 cm emission most likely arises from a combination
of hot ( ≥ 2 × 106 K) and cool plasmas, while the 20 cm
emission becomes optically thick in the cooler (∼9 × 103
K) plasma. We estimate an Alfvén speed ∼7000 km s-1
and ratio of electron gyrofrequency to plasma frequency ∼1.0 in the
northern leg of the 6 cm loop.
Title: Coronal Mass Flows and Turbulence from High Resolution Extreme
Ultraviolet Observations
Authors: Neupert, W. M.; Brosius, J. W.; Thompson, W. T.; Thomas, R. J.
Bibcode: 1991BAAS...23.1062N
Altcode:
No abstract at ADS
Title: Comparison of SERTS Spectroheliograms with Ground-Based
Observations
Authors: Thompson, W. T.; Neupert, W. M.; Brosius, J. W.; Jones,
H. P.; Schmieder, B.
Bibcode: 1991BAAS...23R1061T
Altcode:
No abstract at ADS
Title: On the Polarization of Microwave Emission from Active Regions:
Results from CoMStOC
Authors: Holman, G. D.; Brosius, J. W.; Schmelz, J. T.; Willson, R. F.
Bibcode: 1991BAAS...23.1045H
Altcode:
No abstract at ADS
Title: A Comparison of SERTS EUV Spectroheliograms with Solar Active
Region and Quiet Sun Magnetic Field Structure
Authors: Brosius, J. W.; Thompson, W. T.; Neupert, W. M.
Bibcode: 1991BAAS...23.1061B
Altcode:
No abstract at ADS
Title: CoMStOC III: Measuring Magnetic Fields in Active Region
Coronal Plasma
Authors: Schmelz, J. T.; Holman, G. D.; Brosius, J. W.; Willson, R. F.
Bibcode: 1991BAAS...23R1045S
Altcode:
No abstract at ADS
Title: Microwave polarization inversion observed
Authors: Brosius, J. W.; Holman, G. D.; Schmelz, J. T.
Bibcode: 1991EOSTr..72R.449B
Altcode:
No abstract at ADS
Title: CoMStOCI: Physical Properties of an Active Region Loop Observed
at the Solar Limb
Authors: Holman, G. D.; Brosius, J. W.; Nitta, N.; White, S. M.; Kundu,
M. R.; Gopalswamy, N.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
Bibcode: 1990BAAS...22..899H
Altcode:
No abstract at ADS
Title: CoMStOCIV: Interpretation of Multiwavelength Observations of
a Sunspot and Plage
Authors: Brosius, J. W.; Holman, G. D.; Willson, R. F.; Schmelz, J. T.
Bibcode: 1990BAAS...22..794B
Altcode:
No abstract at ADS
Title: The Structure of the Microwave Emission from Sunspot Magnetic
Fields
Authors: Brosius, Jeffrey W.; Holman, Gordon D.
Bibcode: 1989ApJ...342.1172B
Altcode:
Theoretical microwave intensity and polarization maps have been
obtained for a sunspot model which incorporates a point dipole buried
below the photosphere, a 2000-km thick transition region separating the
chromosphere from the corona, a coronal temperature of 2.5 x 10 to the
6th K, and a coronal density of about 10 to the 9th/cu cm. The present
code includes both thermal bremsstrahlung and thermal gyroemission
at the 1st-5th harmonics of the local electron gyrofrequency. The
maps are shown to accurately reproduce many of the observed sunspot
features. Significant changes in the I and V maps are found over closely
spaced frequencies in the 5-GHz band which would be detectable with
the VLA.
Title: Interpretation of Multiwavelength Observations of Solar Active
Regions Obtained During CoMStOC
Authors: Brosius, J. W.; Holman, G. D.; Nitta, N.; White, S. M.; Kundu,
M. R.; Gopalswamy, N.; Schmelz, J. T.; Saba, J. R. L.; Willson, R.
Bibcode: 1989BAAS...21..838B
Altcode:
No abstract at ADS
Title: Simultaneous Microwave and Soft X-ray Observations of Active
Regions at the Solar Limb
Authors: Nitta, N.; White, S.; Kundu, M.; Gopalswamy, N.; Holman,
G.; Brosius, J.; Schmelz, J.; Saba, J.; Strong, K.
Bibcode: 1989BAAS...21..828N
Altcode:
No abstract at ADS
Title: Largescale Magnetic Field Phenomena
Authors: Harrison, R. A.; Bentley, R. D.; Brosius, J.; Dwivedi,
B. N.; Jardine, M.; Klimchuk, J. A.; Kundu, M. R.; Pearce, G.; Saba,
J.; Sakurai, T.; Schmahl, E. J.; Schmelz, J.; Sime, D. G.; Steele,
C. D. C.; Sun, M. T.; Tappin, S. J.; Waljeski, K.; Wang, A. H.; Wu,
S. T.
Bibcode: 1989tnti.conf....1H
Altcode:
No abstract at ADS
Title: Theoretical Models of Free-free Microwave Emission from Solar
Magnetic Loops
Authors: Brosius, Jeffrey W.; Holman, Gordon D.
Bibcode: 1988ApJ...327..417B
Altcode:
The free-free microwave emission is calculated from a series of model
magnetic loops. The loops are surrounded by a cooler external plasma,
as required by recent simultaneous X ray and microwave observations,
and a narrow transition zone separating the loops from the external
plasma. To be consistent with the observational results, upper limits
on the density and temperature scale lengths in the transition zone
are found to be 360 km and 250 km, respectively. The models which best
produce agreement with X-ray and microwave observations also yielded
emission measure curves which agree well with observational emission
measure curves for solar active regions.
Title: Numerical Computations of the Microwave Emission from Model
Solar Magnetic Loops
Authors: Holman, G. D.; Brosius, J. W.; Pfarr, B. B.
Bibcode: 1988BAAS...20Q.713H
Altcode:
No abstract at ADS
Title: Numerical Computations of the Microwave Emission from Model
Sunspots
Authors: Brosius, J. W.; Holman, G. D.; Pfarr, B. B.
Bibcode: 1988BAAS...20..713B
Altcode:
No abstract at ADS
Title: The cause of two plasma-tail disconnection events in comet
P/Haley during the ICE-Halley radial period
Authors: Brosius, J. W.; Holman, G. D.; Niedner, M. B.; Brandt, J. C.;
Slavin, J. A.; Smith, E. J.
Bibcode: 1987A&A...187..267B
Altcode:
The causes of two plasma-tail disconnection events (DEs), which occurred
in Halley's comet on March 20-22 and April 11-12, 1986, during the
ICE-Halley radial period, are analyzed using the ICE magnetometer
and electron plasma data. It is concluded that the DE of March 20-22
was most likely caused by an IMF polarity reversal. The DE of April
11-12 on the other hand, is attributed to either a compression region
in the solar wind, an IMF polarity reversal, or a combination of the
two. Assuming that the two DEs are due to frontside reconnection after
an IMF reversal, it was estimated that the time period between the onset
of reconnection and the final disconnection of the tail is between 0.1
and 0.6 day, suggesting that the average speed at which reconnection
proceeds through the cometary magnetic field pile-up region is between
1 and 6 km/sec, or several tenths of the local Alfven speed.
Title: Theoretical models of free-free microwave emission from solar
magnetic loops
Authors: Brosius, Jeffrey W.; Holman, Gordon D.
Bibcode: 1986NASCP2442..303B
Altcode: 1986copp.nasa..303B
The free-free microwave emission is calculated from a series of model
magnetic loops. The loops are surrounded by a cooler external plasma,
as required by recent simultaneous X ray and microwave observations,
and a narrow transition zone separating the loops from the external
plasma. To be consistent with the observational results, upper limits
on the density and temperature scale lengths in the transition zone
are found to be 360 km and 250 km, respectively. The models which best
produce agreement with X ray and microwave observations also yielded
emission measure curves which agree well with observational emission
measure curves for solar active regions.
Title: Theoretical models of free-free microwave emission from solar
magnetic loops.
Authors: Brosius, J. W.; Holman, G. D.
Bibcode: 1986NASCP2442..301B
Altcode:
No abstract at ADS
Title: Large-Scale Plasma Activity in Halley During the ICE Radial
Interval: 1986 March 20-April 15
Authors: Niedner, M. B.; Brosius, J. W.; Holman, G. D.; Brandt, J. C.;
Smith, E. J.; Bame, S. J.
Bibcode: 1986BAAS...18R.819N
Altcode:
No abstract at ADS
Title: Theoretical Models of the Microwave Emission from Solar
Magnetic Loops
Authors: Brosius, J. W.; Holman, G. D.
Bibcode: 1986BAAS...18..677B
Altcode:
No abstract at ADS
Title: Models of Transition Regions in Hybrid Stars
Authors: Brosius, J. W.; Mullan, D. J.
Bibcode: 1986ApJ...301..650B
Altcode:
Models for the transition regions of six hybrid stars, four bright
giants and two supergiants, are calculated. The models include mass
loss and prescribe Alfven waves as the source of mechanical energy. The
momentum and energy deposition rates required at each level of the
atmosphere are evaluated. The final models for all six stars have
mass loss rates lying below the current VLA upper limits by factors
of two to ten, and have densities which agree with those derived by
density-sensitive line ratios. The density vs. temperature structure in
Alpha TrA agree well with that derived by Hartmann et al. (1985). Wave
amplitudes and magnetic field strengths are derived as functions of
height, and the amplitudes are found to agree well with the observed
line widths in Alpha TrA.
Title: Rotational modulation of chromospheric emission in cool giants
and "hybrid" stars.
Authors: Brosius, J. W.; Mullan, D. J.; Stencel, R. E.
Bibcode: 1985ApJ...288..310B
Altcode:
Archival data from the International Ultraviolet Explorer have been
used to study temporal variations of the Mg II h and k emission lines
in eight late-type giants. Evidence is presented that the variations
are periodic in nature. It is argued that the periodicities can be
interpreted in terms of rotation. It is found that the four fastest
rotators in the sample are 'hybrid' stars.
Title: A Study of Hybrid Atmosphere Stars: Transition Region Modeling
and Chromospheric Emission Variability
Authors: Brosius, J. W.
Bibcode: 1985PhDT.........8B
Altcode: 1986DiAbI..46.3089B
We present models of the transition regions of six "hybrid"
atmosphere stars. The models include mass loss, and are based on
an analysis of IUE data. The equations which we use to describe the
mass loss are sufficiently general that we can evaluate the momentum
and energy deposition rates which are required at each level of the
atmosphere. This approach allows us to apply a self-consistency check
on the model at the critical point in the flow, thereby restricting
the acceptable models to a small region of parameter space. Our
final models for all 6 stars have mass loss rates which lie below
the current VLA upper limits by factors of 2 -10. Our models have
densities which agree with those derived by density-sensitive line
ratios. Our density-versus-temperature structure in (alpha) TrA agrees
well with that derived by Hartmann et al in a recent independent study:
the latter work did not incorporate mass loss. Our transition region
models are rather extended (0.1-0.5 R(,*)). We choose to identify the
source of mechanical energy with Alfven waves, although we have not
attempted to solve the initial value problem, including injection and
dissipation: we simply ascribe the momentum/energy deposition which our
models require to Alfven waves. This allows us to derive wave amplitudes
and magnetic field strengths as functions of height. We find that our
wave amplitudes agree well with the observed line widths in (alpha)
TrA. Moreover, the outflow velocity predicted by our model for (alpha)
TrA at the level of CIV formation is only 30 km/sec: since the FWHM
is 150-200 km/sec, such a small predicted outflow is consistent with
the lack of measurable Doppler shift in CIV in (alpha) TrA. We have
also used IUE data to study temporal variations of the Mg II h and k
emission lines in the hybrids and two additional late-type giants. We
show that the observed variations are significantly higher than the
noise levels, and use a newly-developed technique, in addition to
the periodogram method, to show that the variations are periodic in
nature. Periods ranging from 56 to 430 days are obtained. We argue
that the periodicities can be interpreted in terms of rotation. This
conclusion is supported by its consistency with observed absorption
line broadening, the rotation -activity connection, and rotational
velocities for stars of similar spectral type reported by various other
authors. The four fastest rotators in our sample are "hybrid" stars,
suggesting that "hybrid" atmospheres are linked to rapid rotation.
Title: A study of hybrid atmosphere stars: Transition region modeling
and chromospheric emission variability
Authors: Brosius, Jeffrey W.
Bibcode: 1985PhDT.......210B
Altcode:
No abstract at ADS
Title: Rotational modulation of chromospheric emission in cool giants
and "hybrid" stars.
Authors: Brosius, J. W.; Mullan, D. J.; Stencel, R. E.
Bibcode: 1984NASCP2349..476B
Altcode: 1984fiue.rept..476B; 1984IUE84......476B
The authors have used IUE archival data to study temporal variations of
the Mg II h and k emission lines in 8 late-type giants. They present
evidence that the variations are periodic in nature. They argue that
the periodicities can be interpreted in terms of rotation and find
that the four fastest rotators in their sample are "hybrid" stars.
Title: Rotational Modulation of Chromospheric Emission in Cool Giants
and `Hybrid' Stars
Authors: Brosius, J. W.; Mullan, D. J.; Stencel, R. E.
Bibcode: 1984BAAS...16..491B
Altcode:
No abstract at ADS