Dear all,
here is a link to another paper, accepted for publication on ApJ, presenting
an analysis of Chandra high-resolution stellar spectra to test the
accuracy and
completeness of the atomic data of CHIANTI 6 for SDO analyses
http://adsabs.harvard.edu/abs/2011arXiv1110.4611T
cheers,
Paola
"Testing EUV/X-ray Atomic Data for the Solar Dynamics Observatory"
Paola Testa, Jeremy J. Drake, Enrico Landi
ABSTRACT
The Atmospheric Imaging Assembly (AIA) and the Exteme-ultraviolet
Variability Experiment (EVE) onboard the Solar Dynamics Observatory
include spectral windows in the X-ray/EUV band. Accuracy and
completeness of the atomic data in this wavelength range is essential
for interpretation of the spectrum and irradiance of the solar corona,
and of SDO observations made with the AIA and EVE instruments. Here we
test the X-ray/EUV data in the CHIANTI database to assess their
completeness and accuracy in the SDO bands, with particular focus on the
94A and 131A AIA passbands. Given the paucity of solar observations
adequate for this purpose, we use high-resolution X-ray spectra of the
low-activity solar-like corona of Procyon obtained with the Chandra Low
Energy Transmission Grating Spectrometer (LETGS). We find that while
spectral models overall can reproduce quite well the observed spectra in
the soft X-ray range <~ 50A, and at the EUV wavelengths >~ 130A, they
significantly underestimate the observed
flux in the 50-130A wavelength range. The model underestimates the
observed flux by a variable factor ranging from ~1.5, at short
wavelengths below ~50A, up to ~5-7 in the ~70−125A range. In the AIA
bands covered by LETGS, i.e. 94A and 131A , we find that the observed
flux can be underestimated by large factors (~3 and ~1.9 respectively,
for the case of Procyon presented here). We discuss the consequences for
analysis of AIA data and possible empirical corrections to the AIA
responses to model more realistically the coronal emission in these
passbands.
Dear all,
Here is a link to a preprint, accepted for publication in A&A,
presenting new calculations of Fe VIII & Fe IX atomic data relevant to
the SDO AIA 94 A channel.
http://www.damtp.cam.ac.uk/user/astro/bo234/publications/17926.pdf
Best regards,
Brendan O'Dwyer
Dear coronal loopers,
I'm pleased to share a preprint on loop oscillations observed with AIA
that has been accepted for publication in ApJ.
Share and enjoy,
Cheers,
Markus
Aschwanden,M.J. and Schrijver,C.J. 2011, The Astrophysical Journal, ... (in press)
URL1="http://www.lmsal.com/~aschwand/eprints/2011_aia_osc.pdf" - _movies/"
Coronal loop oscillations observed with AIA : Kink-mode with cross-sectional and density oscillation
_______________________________________
Dr. Markus J. Aschwanden
Solar & Astrophysics Laboratory
Lockheed Martin Advanced Techology Center
Org. ADBS, Bldg. 252
3251 Hanover St., Palo Alto, CA 94304, USA
Phone: 650-424-4001, FAX: 650-424-3994
URL: http://www.lmsal.com/~aschwand/
e-mail: aschwanden(a)lmsal.com
_______________________________________
Dear all,
here is the link to another paper, which will appear in ApJ Letters,
presenting calculations of FeIX atomic data relevant to the 94A AIA
passband:
http://adsabs.harvard.edu/abs/2011arXiv1107.0470F
cheers,
Paola
Dear colleagues
please find at the following link the preprint of a work accepted
for publication on the ApJ Letters, showing new strong evidence of
finely-structured loops with impulsive nanoflare activity in active regions:
http://arxiv.org/abs/1106.1591
The abstract is below.
Best regards
Fabio Reale
Solar Dynamics Observatory discovers thin high temperature strands in
coronal active regions
Authors: Fabio Reale, Massimiliano Guarrasi, Paola Testa, Edward E.
DeLuca, Giovanni
Peres, Leon Golub
<http://arxiv.org/find/astro-ph/1/au:+Golub_L/0/1/0/all/0/1>
Abstract: One scenario proposed to explain the million degrees solar
corona is a finely-stranded corona where each strand is heated by a
rapid pulse. However, such fine structure has neither been resolved
through direct imaging observations nor conclusively shown through
indirect observations of extended superhot plasma. Recently it has
been shown that the observed difference in appearance of cool and
warm coronal loops (~1 MK, ~2-3 MK, respectively) -- warm loops
appearing "fuzzier" than cool loops -- can be explained by models of
loops composed of subarcsecond strands, which are impulsively heated
up to ~10 MK. That work predicts that images of hot coronal loops
(>~6 MK) should again show fine structure. Here we show that the
predicted effect is indeed widely observed in an active region with
the Solar Dynamics Observatory, thus supporting a scenario where
impulsive heating of fine loop strands plays an important role in
powering the active corona.
Dear Colleagues,
Lisa Rightmire's MS thesis paper on EIS & XRT observations of a warm active region loop has been accepted for publication in ApJ. Please click here for a copy:
https://umdrive.memphis.edu/jschmelz/public/Loops/RightmireThesisPaper.pdf
Warm and Fuzzy: Temperature and Density Analysis of an Fe XV EIS Loop
Abstract: The Hinode EUV Imaging Spectrometer (EIS) and X-Ray Telescope (XRT) were designed in part to work together. They have the same spatial resolution and cover different but overlapping coronal temperature ranges. These properties make a combined data set ideal for multithermal analysis, where EIS provides the best information on the cooler corona (Log T $<$ 6.5) and XRT provides the best information on the hotter corona (Log T $>$ 6.5). Here, we analyze a warm non-flaring loop detected in images made in a strong EIS Fe XV emission line with a wavelength of 284.16 \AA\ and peak formation temperature of Log T $=$ 6.3. We perform Differential Emission Measure (DEM) analysis in three pixels at different heights above the footpoint and find multithermal results with the bulk of the emission measure in the range 6.0 $<$ Log T $<$ 6.6. Analysis with the EIS lines alone gave a DEM with huge amounts of emission measure at very high temperatures (Log T $>$7.2); analysis with XRT data alone resulted in a DEM that was missing most of the cooler emission measure required to produce many of the EIS lines. Thus both results were misleading and unphysical. It was only by combining the EIS and XRT data that we were able to produce a reasonable result, one without ad hoc assumptions on the shape and range of the DEM itself.
Regards,
Joan
Dear Loops Group,
It was a pleasure to see so many of you in Mallorca!
One of the papers I talked about has just been accepted for publication in ApJ:
Isothermal and Multithermal Analysis of Coronal Loops Observed with AIA: II. 211 A Selected Loops
Abstract: An important component of coronal loop analysis involves conflicting results on the cross-field temperature distribution. Are loops isothermal or multithermal? The Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory was designed in part to answer this question. AIA has a series of coronal filters that peak at different temperatures and cover the entire active region temperature range. These properties should make AIA ideal for multithermal analysis, but recent results have shown that the response functions of two of the filters, AIA 94 and 131 \AA, are missing a significant number of low-temperature emission lines. Here we analyze coronal loops from several active regions that were chosen in the 211 \AA\ channel of AIA, which has a peak response temperature of log T $=$ 6.3. The Differential Emission Measure (DEM) analysis of the 12 loops in our sample reveals that using data from the 131 \AA\ AIA filter distorts the results, and we have no choice but to do the analysis without these data. The 94 \AA\ data do not appear to be as important, simply because the chosen loops are not visible in this channel. If we eliminate the 131 \AA\ data, however, we find that our DEM analysis is not well-constrained on the cool temperature end of six of our loops. The information revealed by our 211-selected loops indicates that additional atomic data is required in order to pin down the cross-field temperature distribution.
Copies are available here:
https://umdrive.memphis.edu/jschmelz/public/Loops/AIA2_SchmelzEtAl.pdf
Regards,
Joan
Talks from Coronal Loops V Workshop can be found at
http://web.me.com/inigo.arregui/Iñigo_Arregui/LOOPS-talks.html
Regards. JLBallester
Dr. J. L. Ballester
Departament de Física
Universitat Illes Balears
E-07122 Palma de Mallorca (Spain)
phone: 34 971 173228
Fax: 34 971 173426
joseluis.ballester(a)uib.es
dfsjlb0(a)uib.es
jlballester(a)me.com
The list of participants in Coronal Loops V has been updated in the website: www.loops2011.org. Also, the pictures of the meeting can be found at http://gallery.me.com/inigo.arregui/100490.
Dr. J. L. Ballester
Departament de Física
Universitat Illes Balears
E-07122 Palma de Mallorca (Spain)
phone: 34 971 173228
Fax: 34 971 173426
joseluis.ballester(a)uib.es
dfsjlb0(a)uib.es
jlballester(a)me.com
Dear Colleagues,
Our paper 'Patterns of Nanoflare Storm Heating Exhibited by an Active Region Observed with SDO/AIA' was recently accepted for publication in ApJ.
Please find the paper at:
http://arxiv.org/abs/1106.4196
Authors: Nicholeen Viall and James Klimchuk
Abstract:
It is largely agreed that many coronal loops---those observed at a temperature of about 1 MK--- are bundles of unresolved strands that are heated by storms of impulsive nanoflares. The nature of coronal heating in hotter loops and in the very important but largely ignored diffuse component of active regions is much less clear. Are these regions also heated impulsively, or is the heating quasi steady? The spectacular new data from the Atmospheric Imaging Assembly (AIA) telescopes on the Solar Dynamics Observatory (SDO) offer an excellent opportunity to address this question. We analyze the light curves of coronal loops and the diffuse corona in 6 different AIA channels and compare them with the predicted light curves from theoretical models. Light curves in the different AIA channels reach their peak intensities with predictable orderings as a function the nanoflare storm properties. We show that while some sets of light curves exhibit clear evidence of cooling after nanoflare storms, other cases are less straightforward to interpret. Complications arise because of line-of-sight integration through many different structures, the broadband nature of the AIA channels, and because physical properties can change substantially depending on the magnitude of the energy release. Nevertheless, the light curves exhibit predictable and understandable patterns consistent with impulsive nanoflare heating.
Cheers,
Nicki
************************
Nicholeen Viall
Code 671
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
Email: Nicholeen.M.Viall(a)nasa.gov<mailto:Nicholeen.M.Viall@nasa.gov%3cmailto:Nicholeen.M.Viall@nasa.gov>
Phone: 301-286-4054