1,486 research outputs found
Active region evolution in the chromosphere and transtition region
Images in the C IV 1548 A and the Si II 1526 S lines taken with the ultraviolet spectrometer polarimeter (UVSP) instrument on board the Solar Maximum Mission (SMM) satellite were combined into movies showing the evolution of active regions and the neighboring supergranulation over several days. The data sets generally consist of 240 by 240 arc second rasters with 3 arc second pixels taken one per orbit (about every 90 minutes). The images are projected on a latitude/longitude grid to remove the forshortening as the region rotates across the solar disk and further processed to remove jitter and gain variations. Movies were made with and without differential rotation. Although there are occasional missing orbits, these series do not suffer from the long nighttime gaps that occur in observations taken at a single groundbased observatory and are excellent for studying changes on time scales of several hours. The longest sequence processed to date runs from 20 Oct. 1980 to 25 Oct. 1980. This was taken during an SMM flare buildup study on AR 2744. Several shorter sequences taken in 1980 and 1984 will also be shown. The results will be presented on a video disk which can be interactively controlled to view the movies
Using Coronal Loops to Reconstruct the Magnetic Field of an Active Region Before and After a Major Flare
The shapes of solar coronal loops are sensitive to the presence of electrical
currents that are the carriers of the nonpotential energy available for
impulsive activity. We use this information in a new method for modeling the
coronal magnetic field of AR 11158 as a nonlinear force-free field (NLFFF). The
observations used are coronal images around time of major flare activity on
2011/02/15, together with the surface line-of-sight magnetic field
measurements. The data are from the Helioseismic and Magnetic Imager and
Atmospheric Imaging Assembly (HMI and AIA, respectively) onboard the Solar
Dynamics Observatory (SDO). The model fields are constrained to approximate the
coronal loop configurations as closely as possible, while also subject to the
force-free constraints. The method does not use transverse photospheric
magnetic field components as input, and is thereby distinct from methods for
modeling NLFFFs based on photospheric vector magnetograms. We validate the
method using observations of AR 11158 at a time well before major flaring, and
subsequently review the field evolution just prior to and following an X2.2
flare and associated eruption. The models indicate that the energy released
during the instability is about erg, consistent with what is
needed to power such a large eruptive flare. Immediately prior to the eruption
the model field contains a compact sigmoid bundle of twisted flux that is not
present in the post-eruption models, which is consistent with the observations.
The core of that model structure is twisted by full turns about
its axis.Comment: ApJ, in pres
A stellar view of the Sun
This invited memoir looks back on my scientific career that straddles the
solar and stellar branches of astrophysics, with sprinklings of historical
context and personal opinion. Except for a description of my life up to my
Ph.D. phase, the structure is thematic rather than purely chronological,
focusing on those topics that I worked on throughout substantial parts of my
life: stars like the Sun and the Sun-as-a-star, surface field evolution,
coronal structure and dynamics, heliophysics education, and space weather. Luck
and a broadly inquisitive frame of mind shaped a fortunate life on two
continents, taking me from one amazing mentor, colleague, and friend to
another, working in stimulating settings to interpret data from
state-of-the-art space observatories.Comment: Invited memoir, accepted for publication in Solar Physic
Bright hot impacts by erupted fragments falling back on the Sun: UV redshifts in stellar accretion
A solar eruption after a flare on 7 Jun 2011 produced EUV-bright impacts of
fallbacks far from the eruption site, observed with the Solar Dynamics
Observatory. These impacts can be taken as a template for the impact of stellar
accretion flows. Broad red-shifted UV lines have been commonly observed in
young accreting stars. Here we study the emission from the impacts in the
Atmospheric Imaging Assembly's UV channels and compare the inferred velocity
distribution to stellar observations. We model the impacts with 2D hydrodynamic
simulations. We find that the localised UV 1600A emission and its timing with
respect to the EUV emission can be explained by the impact of a cloud of
fragments. The first impacts produce strong initial upflows. The following
fragments are hit and shocked by these upflows. The UV emission comes mostly
from the shocked front shell of the fragments while they are still falling, and
is therefore redshifted when observed from above. The EUV emission instead
continues from the hot surface layer that is fed by the impacts. Fragmented
accretion can therefore explain broad redshifted UV lines (e.g. C IV 1550A) to
speeds around 400 km/s observed in accreting young stellar objects.Comment: 12 pages, 4 figures (movies available upon request), accepted for
publicatio
Thermal Diagnostics with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions
We present a new method for performing differential emission measure (DEM)
inversions on narrow-band EUV images from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO). The method yields positive
definite DEM solutions by solving a linear program. This method has been
validated against a diverse set of thermal models of varying complexity and
realism. These include (1) idealized gaussian DEM distributions, (2) 3D models
of NOAA Active Region 11158 comprising quasi-steady loop atmospheres in a
non-linear force-free field, and (3) thermodynamic models from a
fully-compressible, 3D MHD simulation of AR corona formation following magnetic
flux emergence. We then present results from the application of the method to
AIA observations of Active Region 11158, comparing the region's thermal
structure on two successive solar rotations. Additionally, we show how the DEM
inversion method can be adapted to simultaneously invert AIA and XRT data, and
how supplementing AIA data with the latter improves the inversion result. The
speed of the method allows for routine production of DEM maps, thus
facilitating science studies that require tracking of the thermal structure of
the solar corona in time and space.Comment: 21 pages, 18 figures, accepted for publication in Ap
- …