Dear Colleagues,
The following paper on EIS+XRT coronal loop DEM analysis has just been published in ApJ:
Deeper by the Dozen: Understanding the Cross-Field Temperature Distributions of Coronal Loops
by Schmelz, J.T., Pathak, S. Jenkins, B.S., Worley, B.T. 2013, ApJ, 764, 53.
https://umdrive.memphis.edu/jschmelz/public/Loops/Dozen_SchmelzEtAl_2013.pdf
Abstract: Spectroscopic analysis of coronal loops has revealed a variety of cross-field temperature distributions. Some loops appear to be isothermal while others require multithermal plasma. The EUV Imaging Spectrometer on Hinode has the spatial resolution and temperature coverage required for differential emission measure (DEM) analysis of coronal loops. Our results also use data from the X-Ray Telescope on Hinode as a high-temperature constraint. Of our 12 loops, two were post-flare loops with broad temperature distributions, two were narrow but not quite isothermal, and the remaining eight were in the mid range. We consider our DEM methods to be a significant advance over previous work, and it is also reassuring to learn that our findings are consistent with results available in the literature. For the quiescent loops analyzed here, 10 MK plasma, a signature of nanoflares, appears to be absent at a level of approximately two orders of magnitude down from the DEM peak. We find some evidence that warmer loops require broader DEMs. The cross-field temperatures obtained here cannot be modeled as single flux tubes. Rather, the observed loop must be composed of several or many unresolved strands. The plasma contained in each of these strands could be cooling at different rates, contributing to the multithermal nature of the observed loop pixels. An important implication of our DEM results involves observations from future instruments. Once solar telescopes can truly resolve X-ray and EUV coronal structures, these images would have to reveal the loop substructure implied by our multithermal results.
Regards,
Joan
>
>
> Subject: new paper on loops
>
> Folks,
>
> The following paper has now been accepted by ApJ. The conclusion
> goes rather against the current consensus: our observations show that at least some coronal separator surfaces and separators are *darker*
> than the corona around them. We have no explanation yet.
>
> Download the paper from: http://solar.physics.montana.edu/martens/Darkbands_Scott_revisions_20130111…
>
> Cheers,
>
> Piet Martens
>
> OUTFLOWS AND DARK BANDS AT ARCADE-LIKE ACTIVE REGION CORE BOUNDARIES
> J. T. Scott, P.C.H. Martens, L. Tarr Dept. of Physics, Montana State
> University Bozeman MT 59717 USA
>
> ABSTRACT
> Observations from the EUV Imaging Spectrometer (EIS) on board Hinode have revealed outflows and non-thermal line broadening in low intensity regions at the edges of active regions (ARs). We use data from Hinode′s EIS, SDO’s AIA and HMI, and the TRACE instrument to investigate the boundaries of arcade like AR cores for NOAA ARs 11112, 10978, and 9077. A narrow, low intensity region that is observed at the core’s periphery as a dark band shows outflows and increased spectral line broadening. This dark band is found to exist for days and appears between the bright coronal loop structures of different coronal topologies. We find a case where the dark band region is formed between magnetic field from emerging flux and the field of the pre-existing flux. A magnetic field extrapolation indicates this dark band is coincident with the spine lines or magnetic separatricies in the extrapolated field. This occurs over unipolar regions where the brightened coronal field is separated in connectivity and topology. This separation does not appear to be infinitesimal and an initial estimate of the minimum distance of separation is found to be ≈ 1.5-3.5 Mm.
>
> Subject headings: Solar Corona, Spectral Line Broadening, Coronal Topology, Coronal Loops
>
>
-------------------------------------------------------------------------------------
Dr. Henry (Trae) Winter III
Astrophysicist Tel: 617-495-7400
Center for Astrophysics Fax: 617-496-7577
60 Garden Street, MS 58 Cell: 617-755-7967
Cambridge, MA 02138 hwinter(a)cfa.harvard.edu
-------------------------------------------------------------------------------------
Hi everyone,
In the spirit of a number of recent papers that have been focused on trying
to determine the dominant components of the emission in the wavelength
channels of imaging instruments (AIA, in particular), Jim and I would like
to share with you all a link to a paper on this very topic that was recently
published in the ApJ Supplement Series:
http://iopscience.iop.org/0067-0049/194/2/26/pdf/apjs_194_2_26.pdf
Our aim in carrying out the work described in this paper was to provide a
large amount of quantitative data from our modeling studies that we hope
will be of use in the analysis of observationally gathered data.
Best wishes,
Steve
-----Original Message-----
From: loops-bounces(a)solar.physics.montana.edu
[mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Paola Testa
Sent: Tuesday, September 20, 2011 10:00 AM
To: A mailing list for scientists involved in the observation and modeling
of solar loop structures
Cc: Juan Martinez Sykora
Subject: [Loops] Forward modeling of emission in SDO/AIA passbands from
dynamic 3D simulations
Hello all,
here is a link to a preprint of a paper, accepted for publication on ApJ,
that is also discussing issues related to the interpretation of AIA
observations:
http://adsabs.harvard.edu/abs/2011arXiv1109.0704M
cheers,
Paola
On 9/9/11 12:03 PM, Giulio Del Zanna wrote:
>
> Dear colleagues,
>
> here is a link to a preprint that discusses various
> (important) issues related to the interpretation of AIA data:
>
> http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=15555
>
> Those of you that were present at the excellent Mallorca meeting might
> recall the issues we raised there. The paper, which follows on from
> O'Dwyer et al., contains more.
>
> I encourage all to follow the example in the Appendix to calculate
> your own AIA responses using CHIANTI. We will soon release v.7, but do
> not expect huge differences.
> We are working to try and improve the atomic data for AIA, more to come.
>
>
> best wishes,
_______________________________________________
Loops mailing list
Loops(a)solar.physics.montana.edu
https://mithra.physics.montana.edu/mailman/listinfo/loops
Dear All,
We were informed that "your manuscript, "Prominence-cavity regions
observed using SWAP 174A filtergrams and simultaneous eclipse flash
spectra", by Bazin, C. Koutchmy, S. and Tavabi, E. has been accepted for
publication in Solar Physics."
A preprint is available at:
http://arxiv.org/abs/1207.1857
Note it is the 1st time that prominences and the so-called cavity often
seen above eclipse prominences are analyzed using a high spectral
resolution near the HeI and the HeII lines simultaneously with high S/N
ratio SWAP filtergrams at 174A and with EIT filtergrams, shedding some
light on the prominence-corona interacting region physics.
Please find after an abstract of the paper.
Feel free to contact the authors in case some additional material is
needed.
Enjoy!
Best,
Serge
-------------------------------------------------------------
At the occasion of the last solar total eclipse of 11th July, 2010, we
studied SWAP filtergrams (from the PROBA2 mission) taken at 17.4 nm in
the Fe IX/X lines with simultaneous slitless flash spectra in the
spectral region of 470 nm. These eclipse flash spectra showed many faint
low excitation emission lines with He I 471.3 nm and He II 468.6 nm
Paschen {\alpha} chromospheric lines, and correspond to off-limb
prominences regions observed with space-borne imagers. We aligned and
stacked 80 individual spectra to study some modulations intensities
along the continuum between the monochromatic images of the prominences
without parasitic scattered light. We observed intensity depressions
around the continuum between prominences in both eclipse and SWAP
images. The prominence cavities are associated with a depression of the
plasma density, produced in the interface regions between the corona and
the prominences. Photometric measurements are shown at different scales
and different narrow spectral intervals, for both the prominences and
the coronal background.
Comments: 20 pages, 15 figures.
Dear all,
Just wanted to let you know about our new paper just published in the
Astrophysical Journal.
Is Active Region Core Variability age dependent?
Ignacio Ugarte-Urra and Harry P. Warren
The presence of both steady and transient loops in active region cores
has been reported from soft X-ray and extreme-ultraviolet observations
of the solar corona. The relationship between the different loop
populations, however, remains an open question. We present an
investigation of the short-term variability of loops in the core of two
active regions in the context of their long-term evolution. We take
advantage of the nearly full Sun observations of /STEREO/ and /Solar
Dynamics Observatory/ spacecraft to track these active regions as they
rotate around the Sun multiple times. We then diagnose the variability
of the active region cores at several instances of their lifetime using
EIS//Hinode/ spectral capabilities. We inspect a broad range of
temperatures, including for the first time spatially and temporally
resolved images of Ca XIV and Ca XV lines. We find that the active
region cores become fainter and steadier with time. The significant
emission measure at high temperatures that is not correlated with a
comparable increase at low temperatures suggests that high-frequency
heating is viable. The presence, however, during the early stages, of an
enhanced emission measure in the "hot" (3.0-4.5 MK) and "cool" (0.6-0.9
MK) components suggests that low-frequency heating also plays a
significant role. Our results explain why there have been recent studies
supporting both heating scenarios.
http://iopscience.iop.org/0004-637X/761/1/21/
Best regards,
Ignacio
--
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ Ignacio Ugarte-Urra ~
Naval Research Laboratory. Code 7681.
4555 Overlook Ave SW. Washington, DC 20375
phone: (+1) 202 404 1779
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Dear all,
A new paper concerning the time-dependence of active region heating based on emission measures has just been published in ApJ.
Diagnosing the time-dependence of active region core heating from the emission measure. I. Low-frequency nanoflares
Bradshaw, S. J., Klimchuk, J. A., & Reep, J. W. 2012, ApJ, 758, 53
http://iopscience.iop.org/0004-637X/758/1/53/pdf/0004-637X_758_1_53.pdf
Abstract:
Observational measurements of active region emission measures contain clues to the time dependence of the underlying heating mechanism. A strongly nonlinear scaling of the emission measure with temperature indicates a large amount of hot plasma relative to warm plasma. A weakly nonlinear (or linear) scaling of the emission measure indicates a relatively large amount of warm plasma, suggesting that the hot active region plasma is allowed to cool and so the heating is impulsive with a long repeat time. This case is called low-frequency nanoflare heating, and we investigate its feasibility as an active region heating scenario here.We explore a parameter space of heating and coronal loop properties with a hydrodynamic model. For each model run, we calculate the slope α of the emission measure distribution EM(T ) ∝ T α. Our conclusions are: (1) low-frequency nanoflare heating is consistent with about 36% of observed active region cores when uncertainties in the atomic data are not accounted for; (2) proper consideration of uncertainties yields a range in which as many as 77% of observed active regions are consistent with low-frequency nanoflare heating and as few as zero; (3) low-frequency nanoflare heating cannot explain observed slopes greater than 3; (4) the upper limit to the volumetric energy release is in the region of 50 erg cm−3 to avoid unphysical magnetic field strengths; (5) the heating timescale may be short for loops of total length less than 40Mm to be consistent with the observed range of slopes; (6) predicted slopes are consistently steeper for longer loops.
Best wishes,
Steve
Dr Stephen J. Bradshaw
Department of Physics and Astronomy, MS-108,
Rice University,
6100 Main Street,
Houston,
TX 77005,
USA.
Tel: +1 713 348 4045
Email: stephen.bradshaw(a)rice.edu
Dear Loop Group,
The following paper has just come out in ApJ:
The Cold Shoulder: Emission Measure Distributions of Active Region Cores
By Schmelz, J. T. & Pathak, S.
2012, ApJ, 756, 126
http://adsabs.harvard.edu/abs/2012ApJ...756..126S
Abstract
The coronal heating mechanism for active region core loops is difficult to determine because these loops are often not resolved and cannot be studied individually. Rather, we concentrate on the "inter-moss" areas between loop footpoints. We use observations from the Hinode EUV Imaging Spectrometer and the X-Ray Telescope to calculate the emission measure distributions of eight inter-moss areas in five different active regions. The combined data sets provide both high- and low-temperature constraints and ensure complete coverage in the temperature range appropriate for active regions. For AR 11113, the emission can be modeled with heating events that occur on timescales less than the cooling time. The loops in the core regions appear to be close to equilibrium and are consistent with steady heating. The other regions studied, however, appear to be dominated by nanoflare heating. Our results are consistent with the idea that active region age is an important parameter in determining whether steady or nanoflare heating is primarily responsible for the core emission, that is, older regions are more likely to be dominated by steady heating, while younger regions show more evidence of nanoflares.
Comments welcome.
Regards,
Joan
Dear all,
our paper on testing the MCMC DEM reconstruction method by using 3D MHD
simulations has just been accepted for publication on ApJ. You can find
a preprint at:
http://folk.uio.no/bdp/papers/3dEMD_ptesta.pdf
(It will also appear soon on astro-ph but in an abridged version due to
the length of the paper and astro-ph restrictions on submission size)
Please find the title and abstract below.
cheers,
Paola
Title: "Investigating the reliability of coronal emission measure distribution
diagnostics using 3D radiative MHD simulations"
Authors: Paola Testa, Bart De Pontieu, Juan Martinez-Sykora,
Viggo Hansteen, Mats Carlsson
Abstract:
Determining the temperature distribution of coronal plasmas can provide
stringent constraints on coronal heating. Current observations with the Extreme
ultraviolet Imaging Spectrograph onboard Hinode and the Atmospheric Imaging
Assembly onboard the Solar Dynamics Observatory provide diagnostics of the
emission measure distribution (EMD) of the coronal plasma.
Here we test the reliability of temperature diagnostics using 3D radiative
MHD simulations. We produce synthetic observables from the models, and apply
the Monte Carlo Markov chain EMD diagnostic. By comparing the derived EMDs with
the ``true'' distributions from the model we assess the limitations of the
diagnostics, as a function of the plasma parameters and of the signal-to-noise
of the data.
We find that EMDs derived from EIS synthetic data reproduce some general
characteristics of the true distributions, but usually show differences from
the true EMDs that are much larger than the estimated uncertainties suggest,
especially when structures with significantly different density overlap along
the line-of-sight. When using AIA synthetic data the derived EMDs reproduce the
true EMDs much less accurately, especially for broad EMDs. The differences
between the two instruments are due to the: (1) smaller number of constraints
provided by AIA data, (2) broad temperature response function of the AIA
channels which provide looser constraints to the temperature distribution.
Our results suggest that EMDs derived from current observatories may often
show significant discrepancies from the true EMDs, rendering their
interpretation fraught with uncertainty. These inherent limitations to the
method should be carefully considered when using these distributions to
constrain coronal heating.
Dear Loop Enthusiasts,
There is a workshop coming up that will be of interest to many of you Nov 27-Dec 2nd: Solar in Sonoma, Tracing the Connections in Solar Eruptive Events. For those attending AGU, this workshop runs the 5 days before AGU. The abstract and early registration deadline are September 14th, and the workshop information can all be found here http://hessi.ssl.berkeley.edu/petaluma/index.shtml. In particular to this community, Iain and I are leading a working group on possible connections between microflares and nanoflares (see description below), and encourage your participation.
We hope to see many of you there!
Nicki
**************
Nicholeen Viall
Code 671
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
Email: Nicholeen.M.Viall(a)nasa.gov<https://mail02.ndc.nasa.gov/owa/UrlBlockedError.aspx>
Phone: 301-286-4054
'Working Group 7: Microflares and Nanoflares
Group Leaders: Iain Hannah, Nicki Viall
Flaring energy release occurs over a vast range of scales in the solar atmosphere. The largest X-Class flares down to microflares (A, B-Class) are exclusively active region phenomena and demonstrate similar characteristics of particle acceleration and plasma heating. One can easily envisage that energetically smaller flares beyond the current observational limits also exist due to smaller scale magnetic reconnection events. Indeed, theories to explain certain observational signatures of heating throughout the corona involve such so-called 'nanoflare' events. The power law frequency distribution of flares suggests that there are common features over all energy scales that could also extend to nanoflares. However, unlike microflares and larger flares, nanoflares are not directly observable with current observations, so the question remains: is it accurate to extrapolate the physical features of large flares down to those of nanoflares? What can we learn from such extrapolations, given that the power law distributions are subject to different bias effects and have unknown cut-offs? In this working group we welcome contributions from both observational and theoretical/numerical studies of microflares and nanoflares as well as possible relationships between them.