34 research outputs found
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
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 A 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
Differential Emission Measures from the Regularized Inversion of Hinode and SDO data
We develop and apply an enhanced regularization algorithm, used in RHESSI
X-ray spectral analysis, to constrain the ill-posed inverse problem that is
determining the DEM from solar observations. We demonstrate this
computationally fast technique applied to a range of DEM models simulating
broadband imaging data from SDO/AIA and high resolution line spectra from
Hinode/EIS, as well as actual active region observations with Hinode/EIS and
XRT. As this regularization method naturally provides both vertical and
horizontal (temperature resolution) error bars we are able to test the role of
uncertainties in the data and response functions. The regularization method is
able to successfully recover the DEM from simulated data of a variety of model
DEMs (single Gaussian, multiple Gaussians and CHIANTI DEM models). It is able
to do this, at best, to over four orders of magnitude in DEM space but
typically over two orders of magnitude from peak emission. The combination of
horizontal and vertical error bars and the regularized solution matrix allows
us to easily determine the accuracy and robustness of the regularized DEM. We
find that the typical range for the horizontal errors is log and this is dependent on the observed signal to noise, uncertainty in
the response functions as well as the source model and temperature. With
Hinode/EIS an uncertainty of 20% greatly broadens the regularized DEMs for both
Gaussian and CHIANTI models although information about the underlying DEMs is
still recoverable. When applied to real active region observations with
Hinode/EIS and XRT the regularization method is able to recover a DEM similar
to that found via a MCMC method but in considerably less computational time.Comment: 15 pages, 17 figures, accepted for publication in A&
The X-ray spectra of the flaring and quiescent states of AT Microscopii observed by XMM-Newton
The X-ray spectrum of the late-type M-dwarf binary AT Mic (dM4.5e+dM4.5e) is
observed in the wavelength range 1 - 40 Angstrom by means of rgs and epic-mos
on board XMM-Newton. During the exposure a flare occured. We have performed a
3-temperature fit and a DEM-modeling to the flaring and quiescent part of the
spectrum. We report the coronal temperature distribution, emission measures,
and abundances of the flaring and quiescent state of this bright X-ray source.
The temperature range stretches from about 1 to 60 MK. The total volume
emission measure in this temperature interval is ~12.2*10^51 cm^-3 for the
quiescent state and ~19.5*10^51 cm^-3 for the flare state. This difference is
due to the contribution of the hot temperature component. The high-resolution
spectrum of AT Mic, obtained by rgs, is dominated by the H- and He-like
transitions of C, N, O, and Ne and by Fe XVII lines, produced by the plasma
with temperatures from 1 to 10 MK. The epic-mos spectrum below 10 Angstrom
shows H- and He-like Ne, Si and the iron K-shell transitions. They are produced
by the hot component (30 MK). The iron K-shell is more prominent in the flare
state. The abundance pattern in the quiescent state of AT Mic shows the
depletion of low-FIP elements relative to high-FIP elements, indicating the
presence of an I(nverse)FIP effect in this active star. In the flare state,
however, some flattening of this IFIP effect is present.Comment: 7 pages, 11 figures ordered as: 1, 2ab, 3, 4abc, 5ab, 6a
EIT and TRACE responses to flare plasma
Aims: To understand the contribution of active region and flare plasmas to
the 195 channels of SOHO/EIT (Extreme-ultraviolet Imaging Telescope)
and TRACE (Transition Region and Coronal Explorer).
Methods: We have analysed an M8 flare simultaneously observed by the Coronal
Diagnostic Spectrometer (CDS), EIT, TRACE and RHESSI. We obtained synthetic
spectra for the flaring region and an outer region using the differential
emission measures (DEM) of emitting plasma based on CDS and RHESSI observations
and the CHIANTI atomic database. We then predicted the EIT and TRACE count
rates.
Results: For the flaring region, both EIT and TRACE images taken through the
195 filter are dominated by Fe (formed at about 20 MK).
However, in the outer region, the emission was primarily due to the Fe, with substantial contributions from other lines. The average count rate
for the outer region was within 25% the observed value for EIT, while for TRACE
it was a factor of two higher. For the flare region, the predicted count rate
was a factor of two (in case of EIT) and a factor of three (in case of TRACE)
higher than the actual count rate.
Conclusions: During a solar flare, both TRACE and EIT 195 channels
are found to be dominated by Fe emission. Reasonable agreement
between predictions and observations is found, however some discrepancies need
to be further investigated.Comment: 6 pages, 4 figure
Coronal properties of G-type stars in different evolutionary phases
We report on the analysis of XMM-Newton observations of three G-type stars in
very different evolutionary phases: the weak-lined T Tauri star HD 283572, the
Zero Age Main Sequence star EK Dra and the Hertzsprung-gap giant star 31 Com.
They all have high X-ray luminosity (10^31 erg/s for HD 283572 and 31 Com and
10^30 erg/s for EK Dra). We compare the Emission Measure Distributions (EMDs)
of these active coronal sources, derived from high-resolution XMM-Newton
grating spectra, as well as the pattern of elemental abundances vs. First
Ionization Potential (FIP). We also perform time-resolved spectroscopy of a
flare detected by XMM from EK Dra. We interpret the observed s as the
result of the emission of ensembles of magnetically confined loop-like
structures with different apex temperatures. Our analysis indicates that the
coronae of HD 283572 and 31 Com are very similar in terms of dominant coronal
magnetic structures, in spite of differences in the evolutionary phase, surface
gravity and metallicity. In the case of EK Dra the distribution appears to be
slightly flatter than in the previous two cases, although the peak temperature
is similar.Comment: 15 pages, 13 Postscript figures, to be published in A&
Coronal properties of the EQ Peg binary system
The activity indicators of M dwarfs are distinctly different for early and
late types. The coronae of early M dwarfs display high X-ray luminosities and
temperatures, a pronounced inverse FIP effect, and frequent flaring to the
extent that no quiescent level can be defined in many cases. For late M dwarfs,
fewer but more violent flares have been observed, and the quiescent X-ray
luminosity is much lower. To probe the relationship between coronal properties
with spectral type of active M dwarfs, we analyze the M3.5 and M4.5 components
of the EQ Peg binary system in comparison with other active M dwarfs of
spectral types M0.5 to M5.5. We investigate the timing behavior of both
components of the EQ Peg system, reconstruct their differential emission
measure, and investigate the coronal abundance ratios based on emission-measure
independent line ratios from their Chandra HETGS spectra. Finally we test for
density variations in different states of activity. The X-ray luminosity of EQ
Peg A (M3.5) is by a factor of 6-10 brighter than that of EQ Peg B (M4.5). Like
most other active M dwarfs, the EQ Peg system shows an inverse FIP effect. The
abundances of both components are consistent within the errors; however, there
seems to be a tendency toward the inverse FIP effect being less pronounced in
the less active EQ Peg B when comparing the quiescent state of the two stars.
This trend is supported by our comparison with other M dwarfs. As the X-ray
luminosity decreases with later spectral type, so do coronal temperatures and
flare rate. The amplitude of the observed abundance anomalies, i.e. the inverse
FIP effect, declines; however, clear deviations from solar abundances remain.Comment: 14 pages, accepted by A&
Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling
This review paper outlines background information and covers recent advances
made via the analysis of spectra and images of prominence plasma and the
increased sophistication of non-LTE (ie when there is a departure from Local
Thermodynamic Equilibrium) radiative transfer models. We first describe the
spectral inversion techniques that have been used to infer the plasma
parameters important for the general properties of the prominence plasma in
both its cool core and the hotter prominence-corona transition region. We also
review studies devoted to the observation of bulk motions of the prominence
plasma and to the determination of prominence mass. However, a simple inversion
of spectroscopic data usually fails when the lines become optically thick at
certain wavelengths. Therefore, complex non-LTE models become necessary. We
thus present the basics of non-LTE radiative transfer theory and the associated
multi-level radiative transfer problems. The main results of one- and
two-dimensional models of the prominences and their fine-structures are
presented. We then discuss the energy balance in various prominence models.
Finally, we outline the outstanding observational and theoretical questions,
and the directions for future progress in our understanding of solar
prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a
better resolution in the published version. New version reflects minor
changes brought after proof editin
Numeri caratteristici definitivi dei flocculi di calcio per l'Anno Geofisico Internazionale
The definitive character figures of the Ca bright flocculi<br />for the International Geophysical Year are given. The observational material<br />used has been collected at Arcetri World Date Center for the Ca bright<br />flocculi, as a part of the I G Y international programme.<br />These character figures take the place of those already published (6- 7)<br />according to the only observations carried out at the Arcetri solar tower