14 research outputs found
Fast Differential Emission Measure Inversion of Solar Coronal Data
We present a fast method for reconstructing Differential Emission Measures
(DEMs) using solar coronal data. On average, the method computes over 1000 DEMs
per second for a sample active region observed by the Atmospheric Imaging
Assembly (AIA) on the Solar Dynamics Observatory (SDO), and achieves reduced
chi-squared of order unity with no negative emission in all but a few test
cases. The high performance of this method is especially relevant in the
context of AIA, which images of order one million solar pixels per second. This
paper describes the method, analyzes its fidelity, compares its performance and
results with other DEM methods, and applies it to an active region and loop
observed by AIA and by the Extreme-ultraviolet Imaging Spectrometer (EIS) on
Hinode.Comment: 22 Pages, 11 Figures; submitted to The Astrophysical Journal. This
version (2) includes clarifications in the text and reflects improvements to
the DEM cod
Coronal Loop Expansion Properties Explained Using Separators
One puzzling observed property of coronal loops is that they are of roughly
constant thickness along their length. Various studies have found no consistent
pattern of width variation along the length of loops observed by TRACE and
SOHO. This is at odds with expectations of magnetic flux tube expansion
properties, which suggests that loops are widest at their tops, and
significantly narrower at their footpoints. Coronal loops correspond to areas
of the solar corona which have been preferentially heated by some process, so
this observed property might be connected to the mechanisms that heat the
corona. One means of energy deposition is magnetic reconnection, which occurs
along field lines called separators. These field lines begin and end on
magnetic null points, and loops forming near them can therefore be relatively
wide at their bases. Thus, coronal energization by magnetic reconnection may
replicate the puzzling expansion properties observed in coronal loops. We
present results of a Monte Carlo survey of separator field line expansion
properties, comparing them to the observed properties of coronal loops.Comment: 16 pages, 9 figures, to be submitted to Ap
A Spherical Shells Model of Atmospheric Absorption for Instrument Calibration
We present a model for atmospheric absorption of solar ultraviolet (UV)
radiation. The initial motivation for this work is to predict this effect and
correct it in Sounding Rocket (SR) experiments. In particular, the Full-sun
Ultraviolet Rocket Spectrograph (FURST) is anticipated to launch in mid-2023.
FURST has the potential to observe UV absorption while imaging solar spectra
between 120-181 nm, at a resolution of R > 2x10 ( V < 15
km/s), and at altitudes of between 110-255 km. This model uses estimates for
density and temperature, as well as laboratory measurements of the absorption
cross-section, to predict the UV absorption of solar radiation at high
altitudes. Refraction correction is discussed and partially implemented but is
negligible for the results presented. Absorption by molecular Oxygen is the
primary driver within the UV spectral range of our interest. The model is built
with a wide range of applications in mind. The primary result is a method for
inversion of the absorption cross-section from images obtained during an
instrument flight, even if atmospheric observations were not initially
intended. The potential to obtain measurements of atmospheric properties is an
exciting prospect, especially since sounding rockets are the only method
currently available for probing this altitude in situ. Simulation of noisy
spectral images along the FURST flight profile is performed using data from the
High-Resolution Telescope and Spectrograph (HRTS) SR and the FISM2 model for
comparison. Analysis of these simulated signals allows us to capture the
Signal-to-Noise Ratio (SNR) of FURST and the capability to measure atmospheric
absorption properties as a function of altitude. Based on the prevalence of
distinct spectral features, our calculations demonstrate that atmospheric
absorption may be used to perform wavelength calibration from in-flight data.Comment: To be Published in JPCS. Submitted December 2022. Accepted February
202
Evidence of Non-Thermal Particles in Coronal Loops Heated Impulsively by Nanoflares
The physical processes causing energy exchange between the Sun's hot corona
and its cool lower atmosphere remain poorly understood. The chromosphere and
transition region (TR) form an interface region between the surface and the
corona that is highly sensitive to the coronal heating mechanism. High
resolution observations with the Interface Region Imaging Spectrograph (IRIS)
reveal rapid variability (about 20 to 60 seconds) of intensity and velocity on
small spatial scales at the footpoints of hot dynamic coronal loops. The
observations are consistent with numerical simulations of heating by beams of
non-thermal electrons, which are generated in small impulsive heating events
called "coronal nanoflares". The accelerated electrons deposit a sizable
fraction of their energy in the chromosphere and TR. Our analysis provides
tight constraints on the properties of such electron beams and new diagnostics
for their presence in the nonflaring corona.Comment: Published in Science on October 17:
http://www.sciencemag.org/content/346/6207/1255724 . 26 pages, 10 figures.
Movies are available at: http://www.lmsal.com/~ptesta/iris_science_mov
Wavelength Calibration of the Full-Sun Ultraviolet Rocket SpecTrometer (FURST)
No abstract availabl