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Author name code: kobelski
ADS astronomy entries on 2022-09-14
author:"Kobelski, Adam"
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Title: Quiet Sun Center to Limb Variation of the Linear Polarization
Observed by CLASP2 Across the Mg II h and k Lines
Authors: Rachmeler, L. A.; Bueno, J. Trujillo; McKenzie, D. E.;
Ishikawa, R.; Auchère, F.; Kobayashi, K.; Kano, R.; Okamoto,
T. J.; Bethge, C. W.; Song, D.; Ballester, E. Alsina; Belluzzi,
L.; Pino Alemán, T. del; Ramos, A. Asensio; Yoshida, M.; Shimizu,
T.; Winebarger, A.; Kobelski, A. R.; Vigil, G. D.; Pontieu, B. De;
Narukage, N.; Kubo, M.; Sakao, T.; Hara, H.; Suematsu, Y.; Štěpán,
J.; Carlsson, M.; Leenaarts, J.
2022ApJ...936...67R Altcode: 2022arXiv220701788R
The CLASP2 (Chromospheric LAyer Spectro-Polarimeter 2) sounding rocket
mission was launched on 2019 April 11. CLASP2 measured the four Stokes
parameters of the Mg II h and k spectral region around 2800 Å along a
200″ slit at three locations on the solar disk, achieving the first
spatially and spectrally resolved observations of the solar polarization
in this near-ultraviolet region. The focus of the work presented here
is the center-to-limb variation of the linear polarization across these
resonance lines, which is produced by the scattering of anisotropic
radiation in the solar atmosphere. The linear polarization signals of
the Mg II h and k lines are sensitive to the magnetic field from the
low to the upper chromosphere through the Hanle and magneto-optical
effects. We compare the observations to theoretical predictions
from radiative transfer calculations in unmagnetized semiempirical
models, arguing that magnetic fields and horizontal inhomogeneities
are needed to explain the observed polarization signals and spatial
variations. This comparison is an important step in both validating and
refining our understanding of the physical origin of these polarization
signatures, and also in paving the way toward future space telescopes
for probing the magnetic fields of the solar upper atmosphere via
ultraviolet spectropolarimetry.
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Title: Defining the Middle Corona
Authors: West, Matthew J.; Seaton, Daniel B.; Wexler, David B.;
Raymond, John C.; Del Zanna, Giulio; Rivera, Yeimy J.; Kobelski,
Adam R.; DeForest, Craig; Golub, Leon; Caspi, Amir; Gilly, Chris R.;
Kooi, Jason E.; Alterman, Benjamin L.; Alzate, Nathalia; Banerjee,
Dipankar; Berghmans, David; Chen, Bin; Chitta, Lakshmi Pradeep; Downs,
Cooper; Giordano, Silvio; Higginson, Aleida; Howard, Russel A.; Mason,
Emily; Mason, James P.; Meyer, Karen A.; Nykyri, Katariina; Rachmeler,
Laurel; Reardon, Kevin P.; Reeves, Katharine K.; Savage, Sabrina;
Thompson, Barbara J.; Van Kooten, Samuel J.; Viall, Nicholeen M.;
Vourlidas, Angelos
2022arXiv220804485W Altcode:
The middle corona, the region roughly spanning heliocentric altitudes
from $1.5$ to $6\,R_\odot$, encompasses almost all of the influential
physical transitions and processes that govern the behavior of
coronal outflow into the heliosphere. Eruptions that could disrupt
the near-Earth environment propagate through it. Importantly, it
modulates inflow from above that can drive dynamic changes at lower
heights in the inner corona. Consequently, this region is essential
for comprehensively connecting the corona to the heliosphere and for
developing corresponding global models. Nonetheless, because it is
challenging to observe, the middle corona has been poorly studied by
major solar remote sensing missions and instruments, extending back to
the Solar and Heliospheric Observatory (SoHO) era. Thanks to recent
advances in instrumentation, observational processing techniques,
and a realization of the importance of the region, interest in the
middle corona has increased. Although the region cannot be intrinsically
separated from other regions of the solar atmosphere, there has emerged
a need to define the region in terms of its location and extension
in the solar atmosphere, its composition, the physical transitions
it covers, and the underlying physics believed to be encapsulated by
the region. This paper aims to define the middle corona and give an
overview of the processes that occur there.
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Title: A Publicly Available Multiobservatory Data Set of an Enhanced
Network Patch from the Photosphere to the Corona
Authors: Kobelski, Adam R.; Tarr, Lucas A.; Jaeggli, Sarah A.; Luber,
Nicholas; Warren, Harry P.; Savage, Sabrina
2022ApJS..261...15K Altcode: 2022arXiv220501766K
New instruments sensitive to chromospheric radiation at X-ray, UV,
visible, IR, and submillimeter wavelengths have become available that
significantly enhance our ability to understand the bidirectional
flow of energy through the chromosphere. We describe the calibration,
coalignment, initial results, and public release of a new data set
combining a large number of these instruments to obtain multiwavelength
photospheric, chromospheric, and coronal observations capable of
improving our understanding of the connectivity between the photosphere
and the corona via transient brightenings and wave signatures. The
observations center on a bipolar region of enhanced-network
magnetic flux near disk center on SOL2017-03-17T14:00-17:00. The
comprehensive data set provides one of the most complete views to
date of chromospheric activity related to small-scale brightenings
in the corona and chromosphere. Our initial analysis shows a strong
spatial correspondence between the areas of broadest width of the
hydrogen-α spectral line and the hottest temperatures observed in
Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 radio
data, with a linear coefficient of 6.12 × 10<SUP>-5</SUP>Å/K. The
correspondence persists for the duration of cotemporal observations
(≍60 m). Numerous transient brightenings were observed in multiple
data series. We highlight a single, well-observed transient brightening
in a set of thin filamentary features with a duration of 20 minutes. The
timing of the peak intensity transitions from the cooler (ALMA, 7000 K)
to the hotter (XRT, 3 MK) data series.
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Title: Radar observations and characterization of (436724) 2011 UW158
Authors: Naidu, Shantanu; Benner, Lance; Brozovic, Marina; Giorgini,
Jon; Busch, Michael; Taylor, Patrick; Richardson, James; Ghigo, Frank;
Kobelski, Adam; Ford, Linda
2019EPSC...13..737N Altcode:
Near-Earth asteroid (436724) 2011 UW158 made a close approach to the
Earth on 2015 July 19 at a distance of 0.016 au (6.4 lunar distances),
which provided an outstanding opportunity for ground-based radar
imaging. We observed it using the Goldstone X-band (8560 MHz, 3.5 cm)
radar, the Green Bank Telescope (GBT), and Arecibo S-band (2380 MHz,
12.6 cm) radar, between July 13-26. The radar dataset allowed us
to estimate the shape, spin state, and other physical properties of
the object.
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Title: Frequency Agile Solar Radiotelescope
Authors: Bastian, Tim; Bain, H.; Bradley, R.; Chen, B.; Dahlin, J.;
DeLuca, E.; Drake, J.; Fleishman, G.; Gary, D.; Glesener, L.; Guo,
Fan; Hallinan, G.; Hurford, G.; Kasper, J.; Ji, Hantao; Klimchuk,
J.; Kobelski, A.; Krucker, S.; Kuroda, N.; Loncope, D.; Lonsdale,
C.; McTiernan, J.; Nita, G.; Qiu, J.; Reeves, K.; Saint-Hilaire, P.;
Schonfeld, S.; Shen, Chengcai; Tun, S.; Wertheimer, D.; White, S.
2019astro2020U..56B Altcode:
We describe the science objectives and technical requirements for a
re-scoped Frequency Agile Solar Radiotelescope (FASR). FASR fulfills
a long term community need for a ground-based, solar-dedicated, radio
telescope - a next-generation radioheliograph - designed to perform
ultra-broadband imaging spectropolarimetry.
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Title: Transient dynamics and energy transfer from the photosphere
to the low corona: initial results from a coordinated ALMA, DST,
Hinode, IRIS, and SDO observation campaign
Authors: Kobelski, Adam; Tarr, Lucas A.; Jaeggli, Sarah A.; Savage,
Sabrina
2019AAS...23430702K Altcode:
We present initial results from a coordinated observation campaign
to study transient dynamics and energy transfer in the low solar
atmosphere. The observations ran from approximately 2017-03-21 from
13UT to 19UT, and include data from Hinode, IRIS, DST, and ALMA. The
target, a small, magnetically bipolar active area associated with a
coronal bright point, was chosen for showing reasonable dynamics in the
chromosphere (as dictated by AIA 304 data from the day prior), and being
near disk center to better facilitate magnetic field measurement. The
campaign was designed to capture the dynamics of the target with as
rapid a timescale as possible for each instrument. Photospheric dynamics
are available from broadband IBIS data and the HMI. New to this dataset,
the chromospheric dynamics were observed in radio frequencies using ALMA
(Band 3: 92-108GHz) at a 2s cadence. Additional chromospheric data are
spectral H-α from the IBIS instrument at the DST, spectropolarimetic
HeI 10830 from the FIRS instrument at the DST, and the medium linelist
from IRIS; coronal data includes imaging from XRT and spectral data
from EIS. In this first set of results, we discuss the frequency of
transient brightenings observed in each set of imaging data and how
the spatial distribution relates across each data channel and to the
regions magnetic topology.
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Title: Radio Propagation Diagnostics of the Inner Heliosphere in
the Era of the Parker Solar Probe
Authors: Kobelski, Adam; Bastian, Timothy S.; Vourlidas, Angelos
2019AAS...23410706K Altcode:
The solar wind offers and extraordinary laboratory for studying
turbulence, turbulent dissipation, and heating. The Parker Solar Probe
(PSP) was launched in August 2018 to study these and other important
processes in the inner heliosphere. One type of observation that will
complement those of PSP are radio propagation measurements of solar
wind turbulence in the outer corona and the inner heliosphere. This
type of observation can provide measurements of the angular broadening
of distant spatially coherent background sources that transilluminate
the foreground solar wind plasma. This well-known technique can be used
to measure the spatial spectrum of electron density inhomogeneities in
the solar wind on scales of 100s of meters to 10s of kilometers inside
of 10-15 solar radii over a wide range of position angles. <P />Here
we report the results of a pilot study of background sources using the
Jansky Very Large Array (JVLA) in summer 2015. Unlike previous studies
of this kind, the JVLA's much greater sensitivity allows fainter
and more numerous sources to be used as probes of the foreground
medium. We observed 11 background sources in 16 sessions at apparent
radial distances of 2-7 solar radii. We confirm previous findings:
that the spectrum is flatter than Kolmogorov and that is highly
anisotropic. Unlike previous studies we find breaks into steeper spectra
for some sources on short spatial scales, suggestive of a transition to
dissipation. <P />Looking forward, we describe observations planned in
August 2019 in support of the third PSP perihelion passage (35.7 solar
radii). The VLA will be used to observe the corona and inner heliosphere
along 70 pierce points <10 solar radii. These observations will not
only provide global context about the state of the inner heliosphere
at time of perihelion passage, they will also baseline key solar wind
parameters that can be compared directly with PSP measurements. These
include turbulence level, spectral index, degree of anisotropy, and
the orientation of the magnetic field. The PSP measurements will, in
turn, provide measurements that will validate key assumptions made in
interpreting the radio data.
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Title: High Frequency Solar Observing at the Green Bank Observatory
Authors: Kobelski, Adam
2019BAAS...51c.533K Altcode: 2019astro2020T.533K
Here we discuss the utility of performing high frequency observations of
the solar chromosphere with the 100 m Green Bank Telescope at 100 GHz.
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Title: Radio Observational Constraints on Turbulent Astrophysical
Plasmas
Authors: Bastian, Tim; Cordes, James; Kasper, Justin; Kobelski,
Adam; Korreck, Kelly; Howes, Gregory; Salem, Chadi; Spangler, Steve;
Vourlidas, Angelos
2019astro2020T.307B Altcode: 2019arXiv190405807B
Using radio observations of background sources, scattering phenomena
may be used to characterize the properties of foreground turbulent
plasma. We discuss the potential of such techniques to explore
turbulence in the solar wind and interstellar medium. The Next
Generation VLA will be an ideal instrument to exploit these techniques.
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Title: Observations of the solar chromosphere with ALMA and comparison
with theoretical models
Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold O.;
Kuhar, Matej; Kobelski, Adam; Wedemeyer, Sven; White, Stephen M.;
Ludwig, Hans-G.; Temmer, Manuela; Saar, Steven H.; Selhorst, Caius L.
2018csss.confE..37B Altcode: 2018arXiv181207293B
In this work we use solar observations with the ALMA radio telescope
at the wavelength of 1.21 mm. The aim of the analysisis to improve
understanding of the solar chromosphere, a dynamic layer in the
solar atmosphere between the photosphere andcorona. The study has
an observational and a modeling part. In the observational part
full-disc solar images are analyzed.Based on a modied FAL atmospheric
model, radiation models for various observed solar structures are
developed. Finally, theobservational and modeling results are compared
and discussed.
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Title: Probing the Inner Heliosphere Using Radio Diagnostic Techniques
Authors: Bastian, Tim; Kobelski, Adam
2018shin.confE..38B Altcode:
A variety of radio propagation techniques - angular and spectral
broadening, scintillation, and Faraday rotation - can be used to probe
regions in the corona and solar wind that are otherwise inaccessible to
direct observation. We present some recent pilot observations made by
the Jansky Very Large Array to illustrate their potential for deducing
key properties of solar wind turbulence in the inner heliosphere. We
discuss prospects for exploiting these techniques in a more systematic
way in the era of the Parker Solar Probe and the Solar Obiter.
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Title: Searching for Supra Arcade Downflows in the Earth's Magnetotail
and Dipolarization Fronts in Solar Flares
Authors: Kobelski, Adam; Savage, Sabrina L.; Malaspina, David
2018tess.conf10207K Altcode:
Pinpointing the location of a single reconnection event in the corona
is difficult due to observational constraints, although features
directly resulting from this rapid reconfiguration of the field lines
can be observed beyond the reconnection site. One set of such features
are outflows in the form of post-reconnection loops, which have been
linked to observations of supra-arcade downflows (SADs). SADs appear
as sunward-traveling, density-depleted regions above flare arcades
that develop during long duration eruptions. The limitations of
remote sensing methods inherently results in ambiguities regarding the
interpretation of SAD formation. Of particular interest is how these
features are related to post-reconnection retracting magnetic field
lines. <P />In planetary magnetospheres, similar events to solar flares
occur in the form of substorms, where reconnection in the anti-sunward
tail of the magnetosphere causes field lines to retract toward the
planet. Using data from the Time History of Events and Macroscopic
Interactions during Substorms (THEMIS), we compare one particular
aspect of substorms, dipolarization fronts, to SADs. Dipolarization
fronts are observed as rapid but temporary changes in the magnetic
field of the magnetotail plasma sheet into a more potential-like,
dipolar shape. These dipolarization fronts are believed to be retracting
post-reconnection field lines. We combine data sets to show that the
while the densities and magnetic fields involved vary greatly between
the regimes, the plasma βs and Alfvén speeds are similar. These
similarities allow direct comparison between the retracting field lines
and their accompanying wakes of rarified plasma observed with THEMIS
around the Earth to the observed morphological density depletions
visible with XRT and AIA on the Sun. These results are an important
source of feedback for models of coronal current sheets.
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Title: First analysis of solar structures in 1.21 mm full-disc ALMA
image of the Sun
Authors: Brajša, R.; Sudar, D.; Benz, A. O.; Skokić, I.; Bárta,
M.; De Pontieu, B.; Kim, S.; Kobelski, A.; Kuhar, M.; Shimojo, M.;
Wedemeyer, S.; White, S.; Yagoubov, P.; Yan, Y.
2018A&A...613A..17B Altcode: 2017arXiv171106130B
Context. Various solar features can be seen in emission or absorption
on maps of the Sun in the millimetre and submillimetre wavelength
range. The recently installed Atacama Large Millimetre/submillimetre
Array (ALMA) is capable of observing the Sun in that wavelength range
with an unprecedented spatial, temporal and spectral resolution. To
interpret solar observations with ALMA, the first important step is to
compare solar ALMA maps with simultaneous images of the Sun recorded in
other spectral ranges. <BR /> Aims: The first aim of the present work
is to identify different structures in the solar atmosphere seen in the
optical, infrared, and EUV parts of the spectrum (quiet Sun, active
regions, prominences on the disc, magnetic inversion lines, coronal
holes and coronal bright points) in a full-disc solar ALMA image. The
second aim is to measure the intensities (brightness temperatures) of
those structures and to compare them with the corresponding quiet Sun
level. <BR /> Methods: A full-disc solar image at 1.21 mm obtained on
December 18, 2015, during a CSV-EOC campaign with ALMA is calibrated and
compared with full-disc solar images from the same day in Hα line, in
He I 1083 nm line core, and with various SDO images (AIA at 170 nm, 30.4
nm, 21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness
temperatures of various structures are determined by averaging over
corresponding regions of interest in the calibrated ALMA image. <BR />
Results: Positions of the quiet Sun, active regions, prominences on
the disc, magnetic inversion lines, coronal holes and coronal bright
points are identified in the ALMA image. At the wavelength of 1.21
mm, active regions appear as bright areas (but sunspots are dark),
while prominences on the disc and coronal holes are not discernible
from the quiet Sun background, despite having slightly less intensity
than surrounding quiet Sun regions. Magnetic inversion lines appear as
large, elongated dark structures and coronal bright points correspond
to ALMA bright points. <BR /> Conclusions: These observational results
are in general agreement with sparse earlier measurements at similar
wavelengths. The identification of coronal bright points represents
the most important new result. By comparing ALMA and other maps,
it was found that the ALMA image was oriented properly and that the
procedure of overlaying the ALMA image with other images is accurate
at the 5 arcsec level. The potential of ALMA for physics of the solar
chromosphere is emphasised.
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Title: Exploring the Sun with ALMA
Authors: Bastian, T. S.; Bárta, M.; Brajša, R.; Chen, B.; Pontieu,
B. D.; Gary, D. E.; Fleishman, G. D.; Hales, A. S.; Iwai, K.; Hudson,
H.; Kim, S.; Kobelski, A.; Loukitcheva, M.; Shimojo, M.; Skokić,
I.; Wedemeyer, S.; White, S. M.; Yan, Y.
2018Msngr.171...25B Altcode:
The Atacama Large Millimeter/submillimeter Array (ALMA) Observatory
opens a new window onto the Universe. The ability to perform continuum
imaging and spectroscopy of astrophysical phenomena at millimetre and
submillimetre wavelengths with unprecedented sensitivity opens up new
avenues for the study of cosmology and the evolution of galaxies, the
formation of stars and planets, and astrochemistry. ALMA also allows
fundamentally new observations to be made of objects much closer
to home, including the Sun. The Sun has long served as a touchstone
for our understanding of astrophysical processes, from the nature of
stellar interiors, to magnetic dynamos, non-radiative heating, stellar
mass loss, and energetic phenomena such as solar flares. ALMA offers
new insights into all of these processes.
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Title: A comparison of solar ALMA observations and model based
predictions of the brightness temperature
Authors: Brajša, R.; Kuhar, M.; Benz, A. O.; Skokić, I.; Sudar,
D.; Wedemeyer, S.; Báarta, M.; De Pontieu, B.; Kim, S.; Kobelski,
A.; Shimojo, M.; White, S.; Yagoubov, P.; Yan, Y.; Ludwig, H. G.;
Temmer, M.; Saar, S. H.; Selhorst, C. L.; Beuc, R.
2018CEAB...42....1B Altcode:
The new facility Atacama Large Millimeter/submillimeter Array (ALMA) is
capable of observing the Sun in the wavelength range from 0.3 mm to 10
mm with an unprecedented spatial, temporal and spectral resolution. The
first aim of the present work is to identify different structures
in the solar atmosphere (quiet Sun, active regions, filaments on the
disc, and coronal holes) in a full disc solar ALMA image at 1.21 mm
obtained on December 18, 2015 during a CSV-EOC campaign. It is compared
with full disc solar images from the same day in the Hα line (Cerro
Tololo Observatory, NISP), and at three EUV wavelengths (30.4 nm,
21.1 nm, 17.1 nm; a composite SDO image). Positions of the quiet Sun
areas, active regions, filaments on the disc, and coronal holes are
identified in the ALMA image. To interpret solar observations with ALMA
it is important to compare the measured and calculated intensities
of various solar structures. So, the second aim of this work is to
calculate the intensity (brightness temperature) for those structures
(quiet Sun, active regions, filaments on the disc, and coronal holes)
for a broad wavelength range (from 0.3 mm to 10 mm), closely related
to that of the ALMA, and to compare the results with available
ALMA observations. Thermal bremsstrahlung is the dominant radiation
mechanism for explanation of the observed phenomena. A procedure for
calculating the brightness temperature for a given wavelength and
model atmosphere, which integrates the radiative transfer equation
for thermal bremsstrahlung, is used. At the wavelength of 1.21 mm
active regions appear as bright areas, while filaments on the disc and
coronal holes are not discernible from the quiet Sun background. The
models generally agree with the observed results: Active regions are
bright primarily due to higher densities, filaments can appear bright,
dark or not at all and coronal holes cannot be easily identified.
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Title: Supra Arcade Downflows in the Earth's Magnetotail
Authors: Kobelski, A.; Savage, S. L.; Malaspina, D.
2017AGUFMSH41A2752K Altcode:
Pinpointing the location of a single reconnection event in the corona
is difficult due to observational constraints, although features
directly resulting from this rapid reconfiguration of the field lines
can be observed beyond the reconnection site. One set of such features
are outflows in the form of post-reconnection loops, which have been
linked to observations of supra-arcade downflows (SADs). SADs appear
as sunward-traveling, density-depleted regions above flare arcades
that develop during long duration eruptions. The limitations of
remote sensing methods inherently results in ambiguities regarding the
interpretation of SAD formation. Of particular interest is how these
features are related to post-reconnection retracting magnetic field
lines. In planetary magnetospheres, similar events to solar flares
occur in the form of substorms, where reconnection in the anti-sunward
tail of the magnetosphere causes field lines to retract toward the
planet. Using data from the Time History of Events and Macroscopic
Interactions during Substorms (THEMIS), we compare one particular aspect
of substorms, dipolarization fronts, to SADs. Dipolarization fronts
are observed as rapid but temporary changes in the magnetic field
of the magnetotail plasma sheet into a more potential-like dipolar
shape. These dipolarization fronts are believed to be retracting
post-reconnection field lines. We combine data sets to show that the
while the densities and magnetic fields involved vary greatly between
the regimes, the plasma βs and Alfvén speeds are similar. These
similarities allow direct comparison between the retracting field lines
and their accompanying wakes of rarified plasma observed with THEMIS
around the Earth to the observed morphological density depletions
visible with XRT and AIA on the Sun. These results are an important
source of feedback for models of coronal current sheets.
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Title: Large Scale Coordination of Small Scale Structures
Authors: Kobelski, Adam; Tarr, Lucas A.; Jaeggli, Sarah A.; Savage,
Sabrina
2017SPD....4820005K Altcode:
Transient brightenings are ubiquitous features of the solar atmosphere
across many length and energy scales, the most energetic of which
manifest as large-class solar flares. Often, transient brightenings
originate in regions of strong magnetic activity and create strong
observable enhancements across wavelengths from X-ray to radio, with
notable dynamics on timescales of seconds to hours.The coronal aspects
of these brightenings have often been studied by way of EUV and X-ray
imaging and spectra. These events are likely driven by photospheric
activity (such as flux emergence) with the coronal brightenings
originating largely from chromospheric ablation (evaporation). Until
recently, chromospheric and transition region observations of these
events have been limited. However, new observational capabilities have
become available which significantly enhance our ability to understand
the bi-directional flow of energy through the chromosphere between the
photosphere and the corona.We have recently obtained a unique data set
with which to study this flow of energy through the chromosphere via
the Interface Region Imaging Spectrograph (IRIS), Hinode EUV Imaging
Spectrometer (EIS), Hinode X-Ray Telescope (XRT), Hinode Solar Optical
Telescope (SOT), Solar Dynamics Observatory (SDO) Atmospheric Imaging
Assembly (AIA), SDO Helioseismic and Magnetic Imager (HMI), Nuclear
Spectroscopic Telescope Array (NuStar), Atacama Large Millimeter Array
(ALMA), and Interferometric BIdimensional Spectropolarimeter (IBIS)
at the Dunn Solar Telescope (DST). This data set targets a small active
area near disk center which was tracked simultaneously for approximately
four hours. Within this region, many transient brightenings detected
through multiple layers of the solar atmosphere. In this study, we
combine the imaging data and use the spectra from EIS and IRIS to
track flows from the photosphere (HMI, SOT) through the chromosphere
and transition region (AIA, IBIS, IRIS, ALMA) into the corona (EIS,
XRT, AIA).
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Title: High-cadence Hinode/XRT observations for studying coronal
events with very short timescales
Authors: McKenzie, David Eugene; Kobelski, Adam; Savage, Sabrina
2017SPD....4830406M Altcode:
The Hinode X-Ray Telescope’s capability for high time cadence
observations makes it an excellent tool for probing highly variable
conditions in the corona, including wave-like activity, dynamic
plasma motions, and short-duration transient events. XRT is capable
of producing images at cadences faster than one image per 10 seconds,
which is comparable to the energy release timescales, and/or ionization
evolution timescales, predicted by a range of models of coronal
activity. In the present work, we demonstrate XRT’s high-cadence
capability through observations of active region AR 10923 (2006
November), with cadences of 6-20 seconds. The image sequences, made
sequentially with multiple analysis filters, reveal many transient
brightenings (i.e., microflares), for which we derive heating and
cooling timescales. We also forward model the observed light curves to
estimate the temperature, density, filling factors, and lengths of the
observed loops. These estimates allow us to prioritize different heating
mechanisms, and to better understand the unresolved structures within
the observations. This study provides a test of capabilities, which
have still not yet been fully utilized by the ten-year-old Hinode X-Ray
Telescope, and thus provides a starting point for future investigations
of short-timescale/high-frequency variations in coronal X-ray intensity.
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Title: Reconnection Outflows in the Extended Corona and Magnetotail
Authors: Savage, Sabrina; Kobelski, Adam
2017SPD....4830303S Altcode:
Observational signatures of reconnection have been studied extensively
in the lower corona for decades, successfully providing insight into
energy release mechanisms in the region above post-flare arcade
loops and below 1.5 solar radii. During large eruptive events,
however, energy release continues to occur well beyond the presence of
reconnection signatures at these low heights. Supra-arcade downflows
(SADs) and downflowing loops (SADLs) are particularly useful measures of
continual reconnection in the corona as they may indicate the presence
and path of retracting post-reconnection loops. SADs and SADLs have
been observed for days beyond the passage of corona mass ejections
through the SOHO/LASCO field of view and for nearly a week after an
eruption on 14 October 2014. The association of these features with
magnetic reconnection increases the significance of understanding
their genesis. SADs have been interpreted as wakes behind newly
reconnected and outflowing loops (SADLs). Models have shown the
plausibility of this interpretation, though this interpretation has
not yet been fully accepted. We will present a preliminary study of
complementary observations of magnetic reconnection detected via in situ
instruments in the magnetosphere. These observations, provided by five
THEMIS spacecraft, reveal similar structures and conditions to those
related to SADs. We compare data from multiple SADs and dipolarization
fronts to test the similarity between these plasma regimes, strongly
favoring the interpretation of SADs as instabilities trailing retracting
loops. We will also use these observations to strengthen the case for
the development of an EUV wide-field coronal imager.
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Title: Observational Signatures of Magnetic Reconnection in the
Extended Corona
Authors: Savage, Sabrina L.; West, Matthew; Seaton, Daniel; Kobelski,
Adam
2017shin.confE..40S Altcode:
Observational signatures of reconnection have been studied extensively
in the lower corona for decades, successfully providing insight into
energy release mechanisms in the region above post-flare arcade
loops and below 1.5 solar radii. During large eruptive events,
however, energy release continues to occur well beyond the presence of
reconnection signatures at these low heights. Supra-arcade downflows
(SADs) and downflowing loops (SADLs) are particularly useful measures
of continual reconnection in the corona as they may indicate the
presence and path of retracting post-reconnection loops. SADs and
SADLs have been faintly observed up to 18 hours beyond the passage
of corona mass ejections through the SOHO/LASCO field of view, but a
recent event from 2014 October 14 associated with giant arches provides
very clear observations of these downflows for days after the initial
eruption. We report on this unique event and compare these findings
with observational signatures of magnetic reconnection in the extended
corona for more typical eruptions.
---------------------------------------------------------
Title: Observing the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA): High-Resolution Interferometric
Imaging
Authors: Shimojo, M.; Bastian, T. S.; Hales, A. S.; White, S. M.;
Iwai, K.; Hills, R. E.; Hirota, A.; Phillips, N. M.; Sawada, T.;
Yagoubov, P.; Siringo, G.; Asayama, S.; Sugimoto, M.; Brajša, R.;
Skokić, I.; Bárta, M.; Kim, S.; de Gregorio-Monsalvo, I.; Corder,
S. A.; Hudson, H. S.; Wedemeyer, S.; Gary, D. E.; De Pontieu, B.;
Loukitcheva, M.; Fleishman, G. D.; Chen, B.; Kobelski, A.; Yan, Y.
2017SoPh..292...87S Altcode: 2017arXiv170403236S
Observations of the Sun at millimeter and submillimeter wavelengths
offer a unique probe into the structure, dynamics, and heating of the
chromosphere; the structure of sunspots; the formation and eruption
of prominences and filaments; and energetic phenomena such as jets
and flares. High-resolution observations of the Sun at millimeter and
submillimeter wavelengths are challenging due to the intense, extended,
low-contrast, and dynamic nature of emission from the quiet Sun,
and the extremely intense and variable nature of emissions associated
with energetic phenomena. The Atacama Large Millimeter/submillimeter
Array (ALMA) was designed with solar observations in mind. The
requirements for solar observations are significantly different from
observations of sidereal sources and special measures are necessary
to successfully carry out this type of observations. We describe the
commissioning efforts that enable the use of two frequency bands,
the 3-mm band (Band 3) and the 1.25-mm band (Band 6), for continuum
interferometric-imaging observations of the Sun with ALMA. Examples of
high-resolution synthesized images obtained using the newly commissioned
modes during the solar-commissioning campaign held in December 2015
are presented. Although only 30 of the eventual 66 ALMA antennas
were used for the campaign, the solar images synthesized from the
ALMA commissioning data reveal new features of the solar atmosphere
that demonstrate the potential power of ALMA solar observations. The
ongoing expansion of ALMA and solar-commissioning efforts will continue
to enable new and unique solar observing capabilities.
---------------------------------------------------------
Title: Observing the Sun with the Atacama Large
Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping
Authors: White, S. M.; Iwai, K.; Phillips, N. M.; Hills, R. E.; Hirota,
A.; Yagoubov, P.; Siringo, G.; Shimojo, M.; Bastian, T. S.; Hales,
A. S.; Sawada, T.; Asayama, S.; Sugimoto, M.; Marson, R. G.; Kawasaki,
W.; Muller, E.; Nakazato, T.; Sugimoto, K.; Brajša, R.; Skokić, I.;
Bárta, M.; Kim, S.; Remijan, A. J.; de Gregorio, I.; Corder, S. A.;
Hudson, H. S.; Loukitcheva, M.; Chen, B.; De Pontieu, B.; Fleishmann,
G. D.; Gary, D. E.; Kobelski, A.; Wedemeyer, S.; Yan, Y.
2017SoPh..292...88W Altcode: 2017arXiv170504766W
The Atacama Large Millimeter/submillimeter Array (ALMA) radio
telescope has commenced science observations of the Sun starting
in late 2016. Since the Sun is much larger than the field of view
of individual ALMA dishes, the ALMA interferometer is unable to
measure the background level of solar emission when observing the
solar disk. The absolute temperature scale is a critical measurement
for much of ALMA solar science, including the understanding of energy
transfer through the solar atmosphere, the properties of prominences,
and the study of shock heating in the chromosphere. In order to provide
an absolute temperature scale, ALMA solar observing will take advantage
of the remarkable fast-scanning capabilities of the ALMA 12 m dishes
to make single-dish maps of the full Sun. This article reports on the
results of an extensive commissioning effort to optimize the mapping
procedure, and it describes the nature of the resulting data. Amplitude
calibration is discussed in detail: a path that uses the two loads in
the ALMA calibration system as well as sky measurements is described
and applied to commissioning data. Inspection of a large number of
single-dish datasets shows significant variation in the resulting
temperatures, and based on the temperature distributions, we derive
quiet-Sun values at disk center of 7300 K at λ =3 mm and 5900 K at
λ =1.3 mm. These values have statistical uncertainties of about 100
K, but systematic uncertainties in the temperature scale that may be
significantly larger. Example images are presented from two periods
with very different levels of solar activity. At a resolution of about
25<SUP>″</SUP>, the 1.3 mm wavelength images show temperatures on
the disk that vary over about a 2000 K range. Active regions and plages
are among the hotter features, while a large sunspot umbra shows up as
a depression, and filament channels are relatively cool. Prominences
above the solar limb are a common feature of the single-dish images.
---------------------------------------------------------
Title: Supra Arcade Downflows in the Corona Informed by Magnetospheric
Dipolarization Fronts with THEMIS
Authors: Kobelski, A.; Savage, S. L.; Malaspina, D.
2016AGUFMSM33A2500K Altcode:
Magnetic reconnection rapidly reconfigures the magnetic
field of the corona, accelerating plasma through the site of
reconnection. Ambiguities (such as line-of-sight effects) due to
the nature of the remote sensing instruments available to study the
corona complicate the interpretation of observations of the inflowing
and outflowing plasma in reconnecting regions. In particular, the
interpretation of sunward moving density depletions above flare arcades
(known as Supra Arcade Downflows — SADs) is still debated. SADs have
been interpreted as wakes behind newly reconnected and outflowing loops
(Supra Arcade Downflowing Loops — SADLs). Hinode/XRT and SDO/AIA
have provided a wealth of observations for SADs and helped inform
our current understanding of these structures. Models have shown the
plausibility of the interpretation of SADs as wakes behind loops,
though this interpretation has not yet been fully accepted. We present
here observations of newly reconnected outflowing loops observed
via in situ instruments in the magnetosphere. These observations,
provided by up to five THEMIS spacecraft, show that around retracting
loops (dipolarization fronts in this context), similar temperature and
density structures as seen in SADs. We compare data from multiple SADs
and dipolarization fronts to show that the observational signatures
implied in the corona can be directly observed in similar plasma regimes
in the magnetosphere, strongly favoring the interpretation of SADs as
wakes behind retracting loops.
---------------------------------------------------------
Title: Observational Signatures of Magnetic Reconnection in the Corona
Authors: Savage, S. L.; West, M. J.; Seaton, D. B.; Kobelski, A.
2016AGUFMSM33A2501S Altcode:
Observational signatures of reconnection have been studied extensively
in the lower corona for decades, successfully providing insight into
energy release mechanisms in the region above post-flare arcade
loops and below 1.5 solar radii. During large eruptive events,
however, energy release continues to occur well beyond the presence of
reconnection signatures at these low heights. Supra-arcade downflows
(SADs) and downflowing loops (SADLs) are particularly useful measures
of continual reconnection in the corona as they may indicate the
presence and path of retracting post-reconnection loops. SADs and
SADLs have been faintly observed up to 18 hours beyond the passage
of corona mass ejections through the SOHO/LASCO field of view, but a
recent event from 2014 October 14 associated with giant arches provides
very clear observations of these downflows for days after the initial
eruption. We report on this unique event and compare these findings
with observational signatures of magnetic reconnection in the extended
corona for more typical eruptions.
---------------------------------------------------------
Title: Observational Signatures of Magnetic Reconnection in the
Extended Corona
Authors: Savage, Sabrina; West, Matthew; Seaton, Daniel B.; Kobelski,
Adam
2016SPD....4730703S Altcode:
Observational signatures of reconnection have been studied extensively
in the lower corona for decades, successfully providing insight into
energy release mechanisms in the region above post-flare arcade
loops and below 1.5 solar radii. During large eruptive events,
however, energy release continues to occur well beyond the presence of
reconnection signatures at these low heights. Supra-arcade downflows
(SADs) and downflowing loops (SADLs) are particularly useful measures
of continual reconnection in the corona as they may indicate the
presence and path of retracting post-reconnection loops. SADs and
SADLs have been faintly observed up to 18 hours beyond the passage
of corona mass ejections through the SOHO/LASCO field of view, but a
recent event from 2014 October 14 associated with giant arches provides
very clear observations of these downflows for days after the initial
eruption. We report on this unique event and compare these findings
with observational signatures of magnetic reconnection in the extended
corona for more typical eruptions.
---------------------------------------------------------
Title: Solar Observations with the Atacama Large
Millimeter/submillimeter Array (ALMA)
Authors: Kobelski, A.; Bastian, T. S.; Bárta, M.; Brajša, R.; Chen,
B.; De Pontieu, B.; Fleishman, G.; Gary, D.; Hales, A.; Hills, R.;
Hudson, H.; Hurford, G.; Loukitcheva, M.; Iwai, K.; Krucker, S.;
Shimojo, M.; Skokić, I.; Wedemeyer, S.; White, S.; Yan, Y.; ALMA
Solar Development Team
2016ASPC..504..327K Altcode:
The Atacama Large Millimeter/Submillimeter Array (ALMA) is a
joint North American, European, and East Asian project that opens
the mm-sub mm wavelength part of the electromagnetic spectrum for
general astrophysical exploration, providing high-resolution imaging
in frequency bands currently ranging from 84 GHz to 950 GHz (300
microns to 3 mm). It is located in the Atacama desert in northern
Chile at an elevation of 5000 m. Despite being a general purpose
instrument, provisions have been made to enable solar observations
with ALMA. Radiation emitted at ALMA wavelengths originates mostly
from the chromosphere, which plays an important role in the transport
of matter and energy, and the in heating the outer layers of the solar
atmosphere. Despite decades of research, the solar chromosphere remains
a significant challenge: both to observe, owing to the complicated
formation mechanisms of currently available diagnostics; and to
understand, as a result of the complex nature of the structure and
dynamics of the chromosphere. ALMA has the potential to change the
scene substantially as it serves as a nearly linear thermometer at
high spatial and temporal resolution, enabling us to study the complex
interaction of magnetic fields and shock waves and yet-to-be-discovered
dynamical processes. Moreover, ALMA will play an important role in
the study of energetic emissions associated with solar flares at
sub-THz frequencies.
---------------------------------------------------------
Title: Measuring the Solar Magnetic Field with STEREO A Radio
Transmissions: Faraday Rotation Observations using the 100m Green
Bank Telescope
Authors: Kobelski, A.; Jensen, E.; Wexler, D.; Heiles, C.; Kepley,
A.; Kuiper, T.; Bisi, M.
2016ASPC..504...99K Altcode:
The STEREO mission spacecraft recently passed through superior
conjunction, providing an opportunity to probe the solar corona using
radio transmissions. Strong magnetic field and dense plasma environment
induce Faraday rotation of the linearly polarized fraction of the
spacecraft radio carrier signal. Variations in the Faraday rotation
signify changes in magnetic field components and plasma parameters,
and thus can be used to gain understanding processes of the quiescent
sun as well as active outbursts including coronal mass ejections. Our
2015 observing campaign resulted in a series of measurements over
several months with the 100m Green Bank Telescope (GBT) to investigate
the coronal Faraday rotation at various radial distances. These
observations reveal notable fluctuations in the Faraday rotation of
the signal in the deep corona, and should yield unique insights into
coronal magnetohydrodynamics down to a 1.5 solar radius line-of-sight
solar elongation.
---------------------------------------------------------
Title: Probing Solar Wind Turbulence with the Jansky Very Large Array
Authors: Kobelski, A.; Bastian, T. S.; Betti, S.
2016ASPC..504...97K Altcode:
The solar wind offers an extraordinary laboratory for studying MHD
turbulence, turbulent dissipation, and heating. Radio propagation
phenomena can be exploited as probes of the solar wind in regions that
are generally inaccessible to in situ spacecraft measurements. Here,
we have undertaken a study with the Jansky Very Large Array (VLA)
to observe point-like sources drawn from the JVAS catalog, and 3 VLA
calibrator sources, to trans-illuminate the outer corona/inner solar
wind. In doing so, we will exploit angular broadening and refractive
scintillation to deduce properties of the solar wind along ≍23 lines
of sight within 7 solar radii of the Sun and a wide range of position
angles. By fitting the complex visibilities using well-known techniques
we can deduce or constrain a number of key parameters. In particular,
we fit the visibilities to a function of the known source flux,
displacement of the source due to refraction, source broadening due to
an elliptical structure function, spectral slope of the turbulence, and
the coherence scale. Of particular interest is α, the spectral slope of
the turbulence which we probe at both small (km to 10s of km) and large
(thousands of km) scales. This will help us determine the presence
and evolution of an inner scale, measure the degree of anisotropy,
and constrain the topology of the global coronal magnetic field. The
inner scale is of particular interest for constraining current theories
of turbulence dissipation and heating. Initial analysis show the
visibilities vary notably on timescales of individual integrations
(2 seconds) and that the source is not uniformly broadened. All
sources appear to preferentially broaden perpendicular to the magnetic
field, consistent with theories of kinetic Alfvén waves. This type
of observation will also help to interpret data from the upcoming
Solar Probe Plus and Solar Orbiter missions. A full set of results
and analysis is forthcoming. More details on previous results can be
found in Bastian (1999), which used the previous generation VLA.
---------------------------------------------------------
Title: High-Resolution Bistatic Radar Imaging of Near-Earth Asteroids
in 2015 using New Capabilities of Goldstone and Green Bank Telescopes
Authors: Naidu, S.; Benner, L.; Brozovic, M.; Giorgini, J. D.; Jao,
J. S.; Lee, C. G.; Busch, M.; Ghigo, F. D.; Ford, A.; Kobelski, A.;
Marshall, S.
2015AGUFM.P53G..07N Altcode:
We present new results from bistatic Goldstone to Green Bank
Telescope (GBT) high-resolution radar imaging of near-Earth asteroids
(NEAs). Previously, most radar observations used either the 305-m
Arecibo radar or the 70-m DSS-14 radar at Goldstone. Following the
installation of new data-taking equipment at the GBT in late 2014,
the number of bistatic Goldstone/GBT observations has increased
substantially. Receiving Goldstone radar echoes at the 100-m GBT
improves the signal-to-noise ratios (SNRs) two- to three-fold relative
to monostatic reception at DSS-14. The higher SNRs allow us to obtain
higher resolution images than is possible with DSS-14 both transmitting
and receiving. Thus far in 2015, we have used the GBT receiver in
combination with the 450 kW DSS-14 antenna and a new low-power 80kW
transmitter on the 34-m DSS-13 antenna at the Goldstone complex
to image five and two NEAs respectively. Asteroids 2005 YQ96, 2004
BL86, and 1994 AW1 are binary systems. 2011 UW158 has a spin period
of 36 minutes that is unusually fast among asteroids its size (~500
m). 1999 JD6 is a deeply bifurcated double-lobed object. 2015 HM10 is
an elongated 80 m asteroid with a spin period of 22 minutes. Our best
images of these objects resolve the surface with resolutions of 3.75 m
and reveal numerous features. Such images are useful to estimate the 3D
shape, spin state, and other physical and dynamical properties of the
objects. This knowledge is of particular interest for spacecraft mission
planning, impact threat assessment, and resource utilization. Over the
long term, such observations will help answer fundamental questions
regarding the origin of the diversity in asteroid morphologies,
the importance of spin-up mechanisms and collisional influences,
the interior structure and thermal properties of asteroids, and the
variety of dynamical states.
---------------------------------------------------------
Title: Arecibo and Goldstone Radar Observations of the
First-Recognized Binary Near-Earth Asteroid: (385186) 1994 AW1
Authors: Richardson, James E.; Taylor, Patrick A.; Rivera-Valentin,
Edgard G.; Rodriguez-Ford, Linda A.; Benner, Lance A. M.; Naidu,
Shantanu P.; Giorgini, Jon D.; Busch, Michael W.; Ghigo, Frank d.;
Kobelski, Adam; Warner, Brian D.; Springmann, Alessondra; Marshall,
Sean E.; Steckloff, Jordan K.; Sharkey, Benjamin
2015DPS....4730808R Altcode:
Near-Earth asteroid (385186) 1994 AW1 was discovered at Palomar
Observatory on 11 January 1994. Subsequent observations of this Amor
family, Sa-class asteroid also identified it as the first candidate
binary NEA, as indicated by multiple periodicities and possible
mutual eclipsing/occulting events in the object’s lightcurve. On 15
July 2015 this asteroid made its closest approach to Earth since its
discovery, coming within 0.065 AU (25 lunar distances), and prompting
an extended observation campaign using both the JPL-Goldstone and
Arecibo Observatory planetary radars. Goldstone observations covered
the 14-19 July period of closest approach (0.066-0.070 AU) while the
object remained below Arecibo’s observing horizon, with Arecibo
picking up the observations between 20-30 July, as the object moved
from 0.075 to 0.126 AU distance. At Goldstone, we were able to observe
this object with range resolutions of 150 m using a Goldstone (DSS-14)
to Green Bank Telescope (GBT) bistatic configuration, while at Arecibo,
we conducted monostatic observations of 1994 AW1 using the 2380 MHz
(12.6 cm) radar at resolutions of 30 m and 75 m.As a result, and
twenty years after its discovery, these observations have confirmed
the binary nature of 1994 AW1, showing the primary body to be about
600 m in diameter, the secondary body to be about half the diameter
of the primary, with the two orbiting a common center of mass at a
distance of about 1.2 km apart. Delay-Doppler image comparisons of the
primary over the course of six nights (at 30 m resolution) confirm a
lightcurve-derived rotation period of 2.518 +/- 0.002 hr, as >90%
longitude coverage was achieved, revealing a slightly elongated,
irregular surface morphology. Delay-Doppler images of the secondary
reveal an elongated, irregular body which appears to be tidally
locked, with its long axis pointed towards the primary as it orbits
with a period of about 22 hr (also consistent with the lightcurve
analysis). These very early results point to a total system mass of
(1.6 +/- 0.5) x 10^11 kg and a crude, mean system density estimate
of 1400 +/- 500 kg/m^3. Additional analysis and shape-modeling will
be presented.
---------------------------------------------------------
Title: Potentially Hazardous Asteroid (85989) 1999 JD6: Radar,
Infrared, and Lightcurve Observations and a Preliminary Shape Model
Authors: Marshall, Sean E.; Howell, Ellen S.; Brozović, Marina;
Taylor, Patrick A.; Campbell, Donald B.; Benner, Lance A. M.; Naidu,
Shantanu P.; Giorgini, Jon D.; Jao, Joseph S.; Lee, Clement G.;
Richardson, James E.; Rodriguez-Ford, Linda A.; Rivera-Valentin,
Edgard G.; Ghigo, Frank; Kobelski, Adam; Busch, Michael W.; Pravec,
Petr; Warner, Brian D.; Reddy, Vishnu; Hicks, Michael D.; Crowell,
Jenna L.; Fernandez, Yanga R.; Vervack, Ronald J.; Nolan, Michael C.;
Magri, Christopher; Sharkey, Benjamin; Bozek, Brandon
2015DPS....4720409M Altcode:
We report observations of potentially hazardous asteroid (85989) 1999
JD6, which passed 0.048 AU from Earth (19 lunar distances) during
its close approach on July 25, 2015. During eleven days between July
15 and August 4, 2015, we observed 1999 JD6 with the Goldstone Solar
System Radar and with Arecibo Observatory's planetary radar, including
bistatic reception of some Goldstone echoes at Green Bank. We obtained
delay-Doppler radar images at a wide range of latitudes, with range
resolutions varying from 7.5 to 150 meters per pixel, depending on
the observing conditions. We acquired near-infrared spectra from the
NASA InfraRed Telescope Facility (IRTF) on two nights in July 2015, at
wavelengths from 0.75 to 5.0 microns, showing JD6's thermal emission. We
also obtained optical lightcurves from Ondrejov Observatory (in 1999),
Table Mountain Observatory (in 2000), and Palmer Divide Station
(in 2015). Previous observers had suggested that 1999 JD6 was most
likely an elongated object, based on its large lightcurve amplitude of
1.2 magnitudes (Szabo et al. 2001; Polishook and Brosch 2008; Warner
2014). The radar images reveal an elongated peanut-shaped object, with
two lobes separated by a sharp concavity. JD6's maximum diameter is
about two kilometers, and its larger lobe is approximately 50% longer
than its smaller lobe. The larger lobe has a concavity on its end. We
will present more details on the shape and rotation state of 1999 JD6,
as well as its surface properties from optical and infrared data and
thermal modeling.
---------------------------------------------------------
Title: Radar observations of near-Earth asteroid (436724) 2011 UW158
using the Arecibo, Goldstone, and Green Bank Telescopes
Authors: Naidu, Shantanu P.; Benner, Lance A. M.; Brozovic, Marina;
Giorgini, Jon D.; Jao, Joseph S.; Busch, Michael W.; Taylor, Patrick
A.; Richardson, James E.; Rivera-Valentin, Edgard G.; Ford, Linda A.;
Ghigo, Frank D.; Kobelski, Adam
2015DPS....4720408N Altcode:
Near-Earth asteroid (436724) 2011 UW158 made a close approach
to the Earth on 2015 July 19 at a distance of 0.016 au (6.4 lunar
distances). We observed it between July 13-26 using the Arecibo S-band
(2380 MHz, 12.5 cm) radar, the Goldstone X-band (8560 MHz, 3.5 cm)
radar, and the Green Bank Telescope (GBT). Arecibo delay-Doppler
observations achieved range resolutions as fine as 7.5 m. At the GBT,
we used a newly installed radar backend to record the radar echoes,
which improved signal-to-noise ratios (SNRs) two-fold relative to
monostatic reception at the 70-m DSS-14 antenna at Goldstone. The higher
SNRs allowed us to obtain images with range resolutions comparable to
those at Arecibo that reveal the asteroid’s surface topography with
great detail. The visible extents of the asteroid in the radar images
suggest an elongated object with dimensions of about 600 x 300 m. The
shape of the object is angular with a facet on one side that spans the
entire length of the asteroid. Three parallel radar-bright features
are visible when the asteroid is oriented broadside and may represent
ridges. These features cause unusually large brightness variations in
the echo as the asteroid rotates. There are other radar-bright regions
that suggest small-scale (tens of meters) topography. Repetition of
the leading edge profiles in the images indicates a spin period of
~37 minutes, which is consistent with the period that was previously
reported using lightcurves (B. Gary, T. Lister, H. K. Moon, P. Pravec,
and B. D. Warner, pers. comm.). This spin period is unusually fast
among asteroids its size and suggests that the object has relatively
high cohesive strength. 2011 UW158 has a relatively low delta-V
for spacecraft missions and is on NASA’s Near-Earth Object Human
Accessible Targets Study list.
---------------------------------------------------------
Title: The versatile GBT astronomical spectrometer (VEGAS): Current
status and future plans
Authors: Prestage, Richard M.; Bloss, Marty; Brandt, Joe; Chen, Hong;
Creager, Ray; Demorest, Paul; Ford, John; Jones, Glenn; Kepley,
Amanda; Kobelski, Adam; Marganian, Paul; Mello, Melinda; McMahon,
David; McCullough, Randy; Ray, Jason; Roshi, D. Anish; Werthimer,
Dan; Whitehead, Mark
2015ursi.confE...4P Altcode:
The VEGAS multi-beam spectrometer (VEGAS) was built for the Green
Bank Telescope (GBT) through a partnership between the National
Radio Astronomy Observatory (NRAO) and the University of California
at Berkeley. VEGAS is based on a Field Programmable Gate Array (FPGA)
frontend and a heterogeneous computing backend comprised of Graphical
Processing Units (GPUs) and CPUs. This system provides processing
power to analyze up to 8 dual-polarization or 16 single-polarization
inputs at bandwidths of up to 1.25 GHz per input. VEGAS was released
for "shared-risk" observing in March 2014 and it became the default
GBT spectral line backend in August 2014. Some of the early VEGAS
observations include the Radio Ammonia Mid-Plane Survey, mapping of
HCN/HCO+ in nearby galaxies, and a variety of radio-recombination
line and pulsar projects. We will present some of the latest VEGAS
science highlights.
---------------------------------------------------------
Title: Forward Modeling Transient Brightenings and Microflares around
an Active Region Observed with Hi-C
Authors: Kobelski, Adam R.; McKenzie, David E.
2014ApJ...794..119K Altcode: 2014arXiv1408.5440K
Small-scale flare-like brightenings around active regions are among
the smallest and most fundamental of energetic transient events in
the corona, providing a testbed for models of heating and active
region dynamics. In a previous study, we modeled a large collection
of these microflares observed with Hinode/X-Ray Telescope (XRT) using
EBTEL and found that they required multiple heating events, but could
not distinguish between multiple heating events on a single strand,
or multiple strands each experiencing a single heating event. We
present here a similar study, but with extreme-ultraviolet data of
Active Region 11520 from the High Resolution Coronal Imager (Hi-C)
sounding rocket. Hi-C provides an order of magnitude improvement to
the spatial resolution of XRT, and a cooler temperature sensitivity,
which combine to provide significant improvements to our ability to
detect and model microflare activity around active regions. We have
found that at the spatial resolution of Hi-C (≈0.”3), the events
occur much more frequently than expected (57 events detected, only 1
or 2 expected), and are most likely made from strands of the order
of 100 km wide, each of which is impulsively heated with multiple
heating events. These findings tend to support bursty reconnection as
the cause of the energy release responsible for the brightenings.
---------------------------------------------------------
Title: Calibrating Data from the Hinode/X-Ray Telescope and Associated
Uncertainties
Authors: Kobelski, Adam R.; Saar, Steven H.; Weber, Mark A.; McKenzie,
David E.; Reeves, Katharine K.
2014SoPh..289.2781K Altcode: 2013arXiv1312.4850K; 2014SoPh..tmp...27K
The X-Ray Telescope (XRT) onboard the Hinode satellite, launched 23
September 2006 by the Japan Aerospace Exploration Agency (JAXA), is a
joint mission of Japan, the United States, and the United Kingdom to
study the solar corona. In particular, XRT was designed to study solar
plasmas with temperatures between 1 and 10 MK with ≈ 1″ pixels
(≈ 2″ resolution). Prior to analysis, the data product from this
instrument must be properly calibrated and data values quantified to
accurately assess the information contained within. We present here
the standard methods of calibration for these data. The calibration
was performed on an empirical basis that uses the least complicated
correction that accurately describes the data while suppressing
spurious features. By analyzing the uncertainties remaining in the
data after calibration, we conclude that the procedure is successful,
because the remaining uncertainty after calibration is dominated by
photon noise. This calibration software is available in the SolarSoft
software library.
---------------------------------------------------------
Title: The Heating of Active Regions Using Active Region Transient
Brightenings Observed with XRT and Hi-C
Authors: Kobelski, Adam; McKenzie, David Eugene
2014AAS...22431201K Altcode:
Active region transient brightentings (ARTBs) are among the smallest
and most fundamental of energetic transient events in the corona; as
such, they provide a testbed for models of heating and active region
dynamics. We have modeled a large collection of ARTBs observed with
Hinode/XRT and with Hi-C as both (a) multi-stranded loops and (b)
monolithic loops which experience multiple heating events, to explore
the energetic ramifications and characteristics in active region
dynamics. Even for these small, short-lived transients, our modeling
indicates that multiple heating events are required for each ARTB. We
compare the quality of model fits for two different temporal envelopes
of the heating function, and discuss whether the results more strongly
favor nanoflare or wave-absorption heating.
---------------------------------------------------------
Title: Modeling Active Region Transient Brightenings Observed with
X-Ray Telescope as Multi-stranded Loops
Authors: Kobelski, Adam R.; McKenzie, David E.; Donachie, Martin
2014ApJ...786...82K Altcode: 2014arXiv1403.7834K
Strong evidence exists that coronal loops as observed in extreme
ultraviolet and soft X-rays may not be monolithic isotropic structures,
but can often be more accurately modeled as bundles of independent
strands. Modeling the observed active region transient brightenings
(ARTBs) within this framework allows for the exploration of the
energetic ramifications and characteristics of these stratified
structures. Here we present a simple method of detecting and modeling
ARTBs observed with the Hinode X-Ray Telescope (XRT) as groups of
zero-dimensional strands, which allows us to probe parameter space to
better understand the spatial and temporal dependence of strand heating
in impulsively heated loops. This partially automated method can be
used to analyze a large number of observations to gain a statistical
insight into the parameters of coronal structures, including the number
of heating events required in a given model to fit the observations. In
this article, we present the methodology and demonstrate its use in
detecting and modeling ARTBs in a sample data set from Hinode/XRT. These
initial results show that, in general, multiple heating events are
necessary to reproduce observed ARTBs, but the spatial dependence of
these heating events cannot yet be established.
---------------------------------------------------------
Title: Empirical studies on the initiation of impulsive heating in
coronal loops
Authors: Kobelski, Adam Robert
2014PhDT........78K Altcode: 2014PhDT.......546K
The heating of the solar corona is an important topic both
for scientists and modern society. One of the most fundamental of
structures in the corona are bundles of plasma confined to the magnetic
field, loops. Here we perform empirical studies to better understand
the mechanisms responsible for heating loops. We observe loops in
X-rays with XRT and model the observations as bundles of independent
strands, showing that the mechanisms instigating the heating of loops
is likely impulsive, yet requires multiple heating events to match
observations. We also observe and model very small loops with Hi-C,
exploiting the high resolution to show that the frequency with which
small loops are heated is larger than expected. This study also puts
constraints on the size of the heating events. We also perform a
study on the initiation of magnetic reconnection between neighboring
active regions, in hopes of understanding how magnetic fields interact,
evolve and heat coronal loops. We close with a discussion on calibrating
the data from a solar X-ray telescope and interpret the uncertainties
within.
---------------------------------------------------------
Title: Fixing the Leak: Empirical Corrections for the Small Light
Leak in Hinode XRT
Authors: Saar, Steven H.; DeLuca, E. E.; McCauley, P.; Kobelski, A.
2013SPD....44...93S Altcode:
On May 9, 2012, the the straylight level of XRT on Hinode suddenly
increased, consistent with the appearance of a pinhole in the entrance
filter (possibly a micrometeorite breach). The effect of this event
is most noticeable in the optical G band data, which shows an average
light excess of ~30%. However, data in several of the X-ray filters is
also affected, due to low sensitivity "tails" of their filter responses
into the visible. Observations taken with the G band filter but with
the visible light shutter (VLS) closed show a weak, slightly shifted,
out-of-focus image, revealing the leaked light. The intensity of
the leak depends on telescope pointing, dropping strongly for images
taken off-disk. By monitoring light levels in the corners of full-Sun
Ti-poly filter images, we determine the approximate time of the event:
~13:30 UT. We use pairs of images taken just-before and after the filter
breach to directly measure the leakage in two affected X-ray filters. We
then develop a model using a scaled, shifted, and smoothed versions
of the VLS closed images to remove the contamination. We estimate
the uncertainties involved in our proposed correction procedure. This
research was supported under NASA contract NNM07AB07C for Hinode XRT.
---------------------------------------------------------
Title: Modeling Active Region Transient Brightenings Observed with
XRT as Multistranded Loops
Authors: Kobelski, Adam; McKenzie, D. E.
2013SPD....44...77K Altcode:
Strong evidence exists that coronal loops as observed in EUV and soft
X-rays are not monolithic isotropic structures, but are more accurately
modeled as bundles of independent strands. Modeling the observed
active region transient brightenings (ARTBs) within this framework
allows exploration of the energetic ramifications and characteristics
of these stratified structures. Here we present a simple method of
detecting and modeling ARTBs observed with the Hinode X-Ray Telescope
(XRT) as groups of simple 0-dimensional strands. We probe parameter
space to understand better the spatial and temporal dependence of
strand heating in impulsively heated loops. We present results from
using this partially automated method to analyze observations and gain
a statistical insight into the heating of these structures.
---------------------------------------------------------
Title: Inferring Nonthermal Particle Characteristics from Thermal
Emission Signatures
Authors: Kobelski, A. R.; McKenzie, D. E.; Winter, H. D.
2012ASPC..454..333K Altcode:
Much work has been done in characterizing the nonthermal particle
beams found in flares. Most of this work has concentrated on the
interpretation of hard X-ray (HXR) emission. While HXR emission does
have a direct connection to the nonthermal particle beam, there
are other emission mechanisms that can also provide insight into
the nature of the nonthermal beam. In the impulsive phase of solar
flares the primary source of plasma heating is collisions between
the nonthermal particles and the ambient, thermal plasma in the flare
loop. The properties of the nonthermal particle beam directly affect
the heating of the thermal plasma. Thus the thermal emission (e.g.,
soft X-rays) can also yield clues to the properties of the nonthermal
beam. Recent flare modeling in the dissertation of Winter (2009)
makes specific predictions about the behavior of the soft X-ray (SXR)
emission from the flaring loop, depending on the properties of the
nonthermal particle beam. As an initial test of the applicability of
these predictions to real flares, we have undertaken a comparison to HXR
and SXR observations from the Yohkoh mission. We present preliminary
results from the analysis of Yohkoh-observed solar flares, which show
consistent temporal profiles in the apex to footpoint ratio.
---------------------------------------------------------
Title: Elemental Abundances as a New Source of Uncertainty of the
Hinode/XRT Filter-ratio T and EM Analysis
Authors: Takeda, A.; Kobelski, A.; McKenzie, D. E.; Yoshimura, K.
2012ASPC..456..133T Altcode:
We calculated the Hinode/XRT temperature response functions with
different assumptions of elemental abundances. The enhancement of
the low FIP elements significantly affects the amplitude of the XRT
response curves. This yields a significant difference in the emission
measures calculated from the filter ratio method, while the effect on
derived temperatures is relatively small.
---------------------------------------------------------
Title: Photometric Uncertainties within Hinode XRT
Authors: Kobelski, Adam; Saar, S. H.; Weber, M. A.; McKenzie, D. E.;
Reeves, K. K.
2012AAS...22020126K Altcode:
We have developed estimates of the systematic uncertainties for
the X-Ray Telescope (XRT) on Hinode. These estimates are included
as optional returns from the standard XRT data reduction software,
xrt_prep.pro. Included in these software estimates are uncertainties
from instrument vignetting, dark current subtraction, split bias
leveling, Fourier filtering and JPEG compression. Sources of uncertainty
that rely heavily on models of plasma radiation or assumptions of
elemental abundances, such as photon noise, are discussed, but not
included in the software. It will be shown that the photon noise
is much larger than the systematic uncertainty. <P />This work is
supported by NASA under contract NNM07AB07C with the Harvard-Smithsonian
Astrophysical Observatory
---------------------------------------------------------
Title: Multi-Stranded Coronal Loops - A Statistical Forward Model
Authors: Kobelski, Adam; McKenzie, D. E.
2012AAS...22020431K Altcode:
Strong evidence currently exists that coronal loops as observed in
EUVs and soft X-rays are not monolithic structures, but actually exist
as bundles of independent strands. It is of significant importance
to determine the size and number density of these strands in order
to better understand the spatial and temporal scales of magnetic
reconnection in the corona. In order to empirically estimate these
parameters, we have developed software to forward model the cooling
of flaring loops as bundles of strands in order to estimate their
observational signatures. By applying this forward model to a large
database of flares observed by Yohkoh/SXT, we employ a statistical
analysis to constrain the parameters in flaring coronal plasma. Results
of this analysis will be presented.
---------------------------------------------------------
Title: Measuring Uncertainties in the Hinode X-Ray Telescope
Authors: Kobelski, A.; Saar, S.; McKenzie, D. E.; Weber, M.; Reeves,
K.; DeLuca, E.
2012ASPC..456..241K Altcode:
We have developed estimates of the systematic photometric uncertainties
the X-Ray Telescope (Kano et al. (2008)) on Hinode (Kosugi et
al.(2007)). These estimates are included as optional returns from the
standard XRT data reduction software, xrt_prep.pro. Included in the
software estimates are uncertainties from instrument vignetting, dark
current subtraction, split bias leveling, fourier filtering and JPEG
compression. We show that these uncertainties are generally smaller
than the photon counting uncertainty. However, due to the reliance
on assumptions of plasma radiation models and elemental abundances,
photon counting is not included in the software.
---------------------------------------------------------
Title: Forward Modeling for Unresolved Flaring Loops
Authors: Kobelski, Adam; McKenzie, D. E.
2011SPD....42.1824K Altcode: 2011BAAS..43S.1824K
The apparent width of observed coronal loops can have
significant effects on the perceived evolution of flaring active
regions. Frequently, comparing a model flare to observation requires an
estimate of the filling factor of loops contributing to the signal. If
the analysis assumes the loops are resolved, the cooling times
derived from the observations are often much longer than predicted
by models. We have developed software to forward model the cooling
of flaring loops, and estimate their observational signatures. This
allows exploration of the physical parameters necessary within a given
model to reproduce the observations. We can then estimate the number of
unresolved strands contained within the observed flare loop. We will
present early results from this study using data from Yohkoh/SXT. The
implementation of Hinode/XRT observations to improve our spatial
resolution and thermal range will also discussed. <P />This work is
supported by NASA under contract NNM07AB07C with the Harvard-Smithsonian
Astrophysical Observatory. Yohkoh data are provided courtesy of the
NASA-supported Yohkoh Legacy Archive at Montana State University.
---------------------------------------------------------
Title: Inferring Nonthermal Particle Characteristics from Thermal
Emission Signatures: Temperature Evolution
Authors: Kobelski, Adam; Winter, H.; McKenzie, D. E.
2010AAS...21640422K Altcode: 2010BAAS...41..903K
In the impulsive phase of solar flares the primary source of plasma
heating is collisions between the nonthermal particles and the ambient,
thermal plasma in the flare loop. Thus the thermal emission (e.g.,
soft X-rays) can yield clues to the properties of the nonthermal
beam. We have undertaken a study of the nonthermal particle signatures
contained within the thermal emission of a flaring coronal loop to
test predictions modeled in the dissertation of Winter (2009). Here we
study loops as observed in thermal soft X-ray (SXR) emission by the
Yohkoh satellite. We present the temperature evolution as viewed in
SXR to that predicted by the model, and continue an analysis of the
temporal profile of the SXR emission.
---------------------------------------------------------
Title: Inferring Nonthermal Particle Characteristics from Thermal
Emission Signatures
Authors: Kobelski, A.; Winter, H. D.; McKenzie, D. E.
2009AGUFMSH23A1528K Altcode:
Much work has been done in characterizing the nonthermal particle
beams found in flares. Most of this work has concentrated on the
interpretation of hard X-ray (HXR) emission. While HXR emission does
have a direct connection to the nonthermal particle beam, there
are other emission mechanisms that can also provide insight into
the nature of the nonthermal beam. In the impulsive phase of solar
flares the primary source of plasma heating is collisions between
the nonthermal particles and the ambient, thermal plasma in the flare
loop. The properties of the nonthermal particle beam directly affect
the heating of the thermal plasma. Thus the thermal emission (e.g.,
soft X-rays) can also yield clues to the properties of the nonthermal
beam. Recent flare modeling in the dissertation of Winter (2009)
makes specific predictions about the behavior of the soft X-ray (SXR)
emission from the flaring loop, depending on the properties of the
nonthermal particle beam. As an initial test of the applicability of
these predictions to real flares, we have undertaken a comparison to HXR
and SXR observations from the Yohkoh mission. We present preliminary
results from the analysis of Yohkoh-observed solar flares, pursuant
to the predictions of the model.
---------------------------------------------------------
Title: Thermal Evolution of Hyperon-Mixed Neutron Stars
Authors: Tsuruta, S.; Sadino, J.; Kobelski, A.; Teter, M. A.; Liebmann,
A. C.; Takatsuka, T.; Nomoto, K.; Umeda, H.
2009ApJ...691..621T Altcode:
With the impressive amount of data that have poured out from Chandra
and XMM/Newton X-ray space missions, as well as the lower energy band
observations, we are now in the position where careful comparison of
neutron star thermal evolution theories with observations will help
us to distinguish among various competing theories. For instance,
the latest theoretical and observational developments probably will
contradict with the direct Urca cooling of neutron stars without some
exotic particles. In this paper, we investigate one of the remaining
possible fast cooling scenarios—direct Urca cooling of neutron stars
in the hyperon-mixed phase. We conclude that this cooling scenario is
a valid process if hyperon superfluidity is not too weak.
---------------------------------------------------------
Title: Sloan/Johnson-Cousins/2MASS Color Transformations for Cool
Stars
Authors: Davenport, James R. A.; West, Andrew A.; Matthiesen, Caleb
K.; Schmieding, Michael; Kobelski, Adam
2006PASP..118.1679D Altcode: 2006astro.ph.11087D
We present multicolor transformations and photometric parallaxes for
a sample of 40 low-mass dwarfs selected from the Sloan Digital Sky
Survey (SDSS) and the General Catalogue of Trigonometric Stellar
Parallaxes. Our sample was reobserved at the Manastash Ridge
Observatory (MRO) using both Sloan and Johnson-Cousin filters,
and color transformations between the two photometric systems were
derived. A subset of the sample had previously measured Johnson-Cousins
photometry and parallaxes as well as 2MASS photometry. We observed
these stars at MRO using Sloan filters and used these data to derive
photometric parallax relations as well as SDSS/Johnson-Cousins/2MASS
color transformations. We present the data and derived transformations
for use in future low-mass-star studies.
