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Author name code: judge
ADS astronomy entries on 2022-09-14
author:"Judge, Philip G."
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Title: Thermal and Non-thermal Properties of Active Region Recurrent
Coronal Jets
Authors: Paraschiv, Alin R.; Donea, Alina C.; Judge, Philip G.
2022ApJ...935..172P Altcode: 2022arXiv220712612P
We present observations of recurrent active region coronal jets,
and derive their thermal and non-thermal properties, by studying
the physical properties of the plasma simultaneously at the base
footpoint and along the outflow of jets. The sample of analyzed solar
jets were observed by SDO-AIA in extreme ultraviolet and by RHESSI
in the X-ray domain. The main thermal plasma physical parameters,
such as temperature, density, energy flux contributions, etc.,
are calculated using multiple inversion techniques to obtain the
differential emission measure from extreme-ultraviolet filtergrams. The
underlying models are assessed, and their limitations and applicability
are scrutinized. Complementarily, we perform source reconstruction
and spectral analysis of higher energy X-ray observations to further
assess the thermal structure and identify non-thermal plasma emission
properties. We discuss a peculiar penumbral magnetic reconnection
site, which we previously identified as a "Coronal Geyser." Evidence
supporting cool and hot thermal emission, as well as non-thermal
emission, is presented for a subset of geyser jets. These active
region jets are found to be energetically stronger than their polar
counterparts, but we find their potential influence on heliospheric
energetics and dynamics to be limited. We scrutinize whether the
geyser does fit the non-thermal erupting microflare picture, finding
that our observations at peak flaring times can only be explained by a
combination of thermal and non-thermal emission models. This analysis
of geysers provides new information and observational constraints
applicable to theoretical modeling of solar jets.
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Title: A Spectroscopic Survey of Infrared 1-4 μm Spectra in Regions
of Prominent Solar Coronal Emission Lines of Fe XIII, Si X, and Si IX
Authors: Ali, Aatiya; Paraschiv, Alin Razvan; Reardon, Kevin; Judge,
Philip
2022ApJ...932...22A Altcode: 2022arXiv220308636A
The infrared solar spectrum contains a wealth of physical data about
the Sun and is being explored using modern detectors and technology
with new ground-based solar telescopes. One such instrument will be
the ground-based Cryogenic Near-IR Spectro-Polarimeter of the Daniel
K. Inouye Solar Telescope (DKIST), which will be capable of sensitive
imaging of the faint infrared solar coronal spectra with full Stokes I,
Q, U, and V polarization states. Highly ionized magnetic dipole emission
lines have been observed in galaxies and the solar corona. Quantifying
the accuracy of spectral inversion procedures requires a precise
spectroscopic calibration of observations. A careful interpretation
of the spectra around prominent magnetic dipole lines is essential
for deriving physical parameters and particularly for quantifying the
off-limb solar coronal observations from DKIST. In this work, we aim to
provide an analysis of the spectral regions around the infrared coronal
emission lines of Fe XIII 1074.68 nm, Fe XIII 1079.79 nm, Si X 1430.10
nm, and Si IX 3934.34 nm, aligning with the goal of identifying solar
photospheric and telluric lines that will help facilitate production of
reliable inversions and data products from four sets of solar coronal
observations. The outputs can be integrated in processing pipelines
to produce level 2 science-ready data.
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Title: The mercurial Sun at the heart of our solar system
Authors: Judge, Philip Gordon
2022arXiv220503498J Altcode:
As the powerhouse of our solar system, the Sun's electromagnetic
planetary influences appear contradictory. On the one hand, the Sun
for aeons emitted radiation which was "just right" for life to evolve
in our terrestrial Goldilocks zone, even for such complex organisms
as ourselves. On the other, in the dawn of Earth's existence the Sun
was far dimmer than today, and yet evidence for early liquid water is
written into geology. Now in middle age, the Sun should be a benign
object of little interest to society or even astronomers. However,
for physical reasons yet to be fully understood, it contains a magnetic
machine with a slightly arrhythmic 11 year magnetic heartbeat. Although
these variations require merely 0.1% of the solar luminosity, this power
floods the solar system with rapidly changing fluxes of photons and
particles at energies far above the 0.5eV thermal energy characteristic
of the photosphere. Ejected solar plasma carries magnetic fields into
space with consequences for planets, the Earth being vulnerable to
geomagnetic storms. This chapter discusses some physical reasons why
the Sun suffers from such ailments, and examine consequences through
time across the solar system. A Leitmotiv of the discussion is that
any rotating and convecting star must inevitably generate magnetic
"activity" for which the Sun represents the example par excellence.
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Title: Efficient and Automated Inversions of Magnetically Sensitive
Forbidden Coronal Lines: CLEDB - The Coronal Line Emission DataBase
Magnetic Field Inversion Algorithm
Authors: Paraschiv, Alin Razvan; Judge, Philip Gordon
2022SoPh..297...63P Altcode: 2022arXiv220414111P
We present CLEDB, a "single-point inversion" algorithm for inferring
parameters using I , Q , U , and V Stokes parameters of forbidden
magnetic dipole lines formed in the solar corona. We select lines
of interest and construct databases of Stokes parameters for
combinations of plasma thermal and magnetic configurations. The
size and complexity of such databases are drastically reduced by
taking advantage of symmetries. Using wavelength-integrated line
profiles, each of which might be decomposed beforehand into several
line-of-sight components, we search for nearest matches to observed
Stokes parameters computed for the elongation corresponding to the
observed region. The method is intended to be applied to two or
more lines observed simultaneously. The solutions initially yield
magnetic orientation, thermal properties, and the spatial position of
the emitting plasma in three dimensions. Multiple possible solutions
for each observation are returned, including irreducible degeneracies,
where usually sets of two solutions are compatible with the two input I
, Q , U , and V measurements. In solving for the scattering geometry,
this method avoids an additional degeneracy pointed out by Dima and
Schad (Astrophys. J.889, 109, 2020). The magnetic field strength
is separately derived from the simple ratio of observed to database
Stokes V data, after the thermal properties and scattering geometry
solutions have been determined.
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Title: Study the tortoise, not just the hare
Authors: Judge, P.
2022fysr.confE..50J Altcode:
Darwin encountered enormous Galapagos tortoises in 1835 around the
time that Schwabe was collecting sunspot numbers. The creatures were
slow and easy to study. Of course, fauna from the Galapagos played a
central role in our understanding of evolution of life; genetic records
imprinted in modern animals have since given us pages in the book of
life history. Skumanich's 1972 work represents the first 3 pages in the
book of stellar magnetic evolution, studying (like Darwin) only what was
observable at a given time. The Sun and stars continue to be studied by
politically palatable 1-10 year long missions, measuring short duration
phenomena -- analogous to the peculiar springtime "boxing" of the March
Hare. Stellar activity measurements over multiple decades (sampling
sun-like cycling) are now a part of history, just as their need from
space weather, dynamo theory, exoplanet habitability seems greater
than ever. The communities must support tortoise-like measurements
of stellar chromospheric signatures, extending the record begun in
1965, and used by Andy in 1972. A "palatable path" might be through
development of automated observatories at under-privileged colleges,
I present some ideas along these lines.
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Title: How to Measure the Magnetic Origins of Coronal Dynamics
Authors: Gilbert, Holly; Judge, Philip
2021AGUFMSH12C..03G Altcode:
To identify the origins of coronal dynamics, we have examined
how we might measure magnetic free energy and topology and their
evolution above the solar surface. Given the challenges associated
with extrapolations based upon magnetic field measurements in the
photosphere, we identify a region in the near UV part of the spectrum
as optimal for studying the development of magnetic free energy over
active regions. We demonstrate that the challenges are best met through
a combination of near UV lines of bright Mg II, and lines of Fe II and
Fe I mostly within the 4s-4p transition array. The lines form across
the entire chromosphere and into the lower transition region. Based
upon the recently-reported successful suborbital space measurements
of magnetic fields with the CLASP2 instrument, we argue that a modest
space-borne telescope will be able to make significant advances in
the attempts to predict solar eruptions.
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Title: CLEDB - An Algorithm for Inverting Vector Magnetic Fields in
The Solar Corona
Authors: Paraschiv, Alin; Judge, Philip
2021AGUFMSH42B..06P Altcode:
We present an algorithm capable of inverting coronal vector magnetic
field information from observations of polarized light. The CLEDB
algorithm implements two branches that can process full Stokes IQUV
spectro-polarimetric observations of one or two coronal emission
lines.The 1-line branch uses analytical approximations to derive
line of sight integrated magnetic field products. When posing an
inversion problem, the second branch allows for more degrees of freedom
enabling us to break intrinsic degeneracies. Thus, by utilizing 2-line
Stokes observations, we recover the 3D magnetic fields and volumetric
locations of emitting structures for single-point voxels. In practice,
forward calculation in the order of 107-109 atomic plasma, magnetic,
and geometric configurations are needed in order to satisfy solution
resolution criteria.Forward modelling this many solutions in an
iterative fashion is dreadfully time consuming, rendering such approach
as unfeasible. We bypassed the limitation by building databases, that
store vast sets of synthetic Stokes IQUV signals, via forward modelling
of parameter combinations. Using a 2 fitting approach has proved to
be significantly more robust in matching such databases with Stokes
IQUV observations.Additionally, the database theoretical calculations
gain intrinsic access to otherwise non-observable input parameters,
e.g. atomic alignment, that can be used to break inherent degeneracies
encountered when attempting analytical inversions like in the 1-line
case. The dimensionality of the problem at hand can be further reduced
by 1-2 orders of magnitude by using native symmetries when building
and querying databases. The goal of robustly resolving vector coronal
magnetometry has been hard to achieve. The need for inverting magnetic
fields from solar spectro-polarimetric observations is crucial, as the
next generation of coronal capable instruments like DKIST Cryo-NIRSP,
DL-NIRSP, and UCOMP will become operational. Benchmarks of the CLEDB
algorithm tested against synthetic data are explored, while we wait
for the first ever full Stokes spectro-polarimetric observations to
become available.
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Title: From 1973 to the 2020s, from SKYLAB to 3D vector magnetic
fields in prominences
Authors: Lacatus, Daniela; Judge, Philip; Gilbert, Holly; Paraschiv,
Alin; Berger, Thomas
2021AGUFMSH42B..05L Altcode:
Routine measurement of the vector magnetic fields threading prominences
would mark a significant advance in our ability to determine the
dynamics of the Sun's corona. Gilbert et al. (AGU abstract #849653)
have identified the near-UV (250-281 nm) as a prime region for
measurements of magnetic fields within the chromosphere and lower
transition region. Here, we perform an in depth analysis of the near
UV spectra of all prominences observed by the SKYLAB SO82B instrument
during 1973, for the first time. Using over 100 spectral lines we
process the photographic data from scratch, and solve for plasma
properties of several prominences. Given the known complexity of the
thermal and dynamical conditions within prominence plasma, we develop
a model to find mean electron temperatures, densities and mass columns
which capture each spectrums essential characteristics. Prominence
plasmas are optically thick in the cores of many spectral lines of Fe
II and Mg II present in this spectral region. The different optical
depths probe different surfaces along the line-of-sight, so that
near-UV spectro-polarimetry will uniquely determine vector magnetic
fields within the 3D volume of prominences. Therefore, we show that
this technique offers the best future method for answering critical
problems related to coronal dynamics, not only above active regions
as shown by Gilbert et al., but also in prominence plasmas.
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Title: Atomic Structure Calculations of Landé g Factors of
Astrophysical Interest with Direct Applications for Solar Coronal
Magnetometry
Authors: Schiffmann, Sacha; Brage, Tomas; Judge, Philip Gordon;
Paraschiv, Alin Razvan; Wang, Kai
2021ApJ...923..186S Altcode:
We perform a detailed theoretical study of the atomic structure of
ions with ns <SUP>2</SUP> np <SUP> m </SUP> ground configurations
and focus on departures from LS coupling, which directly affect the
Landé g factors of magnetic dipole lines between levels of the ground
terms. Particular emphasis is given to astrophysically abundant ions
formed in the solar corona (those with n = 2,3) with M1 transitions
spanning a broad range of wavelengths. Accurate Landé g factors are
needed to diagnose coronal magnetic fields using measurements from
new instruments operating at visible and infrared wavelengths, such
as the Daniel K. Inouye Solar Telescope. We emphasize an explanation
of the dynamics of atomic structure effects for nonspecialists.
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Title: The enduring mystery of the solar corona
Authors: Judge, Philip G.
2021PhyW...34...38J Altcode:
Physicists have long known that the Sun's magnetic fields make its
corona much hotter than the surface of the star itself. But how -
and why - those fields transport and deposit their energy is still a
mystery, as Philip G Judge explains.
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Title: Erratum: Spectral Lines for Polarization Measurements of the
Coronal Magnetic Field. II. Consistent Treatment of the Stokes Vector
for Magnetic-dipole Transitions (1999, ApJ, 522, 524)
Authors: Casini, R.; Judge, P. G.
2021ApJ...917...50C Altcode:
No abstract at ADS
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Title: Measuring the Magnetic Origins of Solar Flares, Coronal Mass
Ejections, and Space Weather
Authors: Judge, Philip; Rempel, Matthias; Ezzeddine, Rana; Kleint,
Lucia; Egeland, Ricky; Berdyugina, Svetlana V.; Berger, Thomas; Bryans,
Paul; Burkepile, Joan; Centeno, Rebecca; de Toma, Giuliana; Dikpati,
Mausumi; Fan, Yuhong; Gilbert, Holly; Lacatus, Daniela A.
2021ApJ...917...27J Altcode: 2021arXiv210607786J
We take a broad look at the problem of identifying the magnetic
solar causes of space weather. With the lackluster performance
of extrapolations based upon magnetic field measurements in the
photosphere, we identify a region in the near-UV (NUV) part of the
spectrum as optimal for studying the development of magnetic free energy
over active regions. Using data from SORCE, the Hubble Space Telescope,
and SKYLAB, along with 1D computations of the NUV spectrum and numerical
experiments based on the MURaM radiation-magnetohydrodynamic and
HanleRT radiative transfer codes, we address multiple challenges. These
challenges are best met through a combination of NUV lines of bright Mg
II, and lines of Fe II and Fe I (mostly within the 4s-4p transition
array) which form in the chromosphere up to 2 × 10<SUP>4</SUP>
K. Both Hanle and Zeeman effects can in principle be used to derive
vector magnetic fields. However, for any given spectral line the τ
= 1 surfaces are generally geometrically corrugated owing to fine
structure such as fibrils and spicules. By using multiple spectral
lines spanning different optical depths, magnetic fields across nearly
horizontal surfaces can be inferred in regions of low plasma β, from
which free energies, magnetic topology, and other quantities can be
derived. Based upon the recently reported successful sub-orbital space
measurements of magnetic fields with the CLASP2 instrument, we argue
that a modest space-borne telescope will be able to make significant
advances in the attempts to predict solar eruptions. Difficulties
associated with blended lines are shown to be minor in an Appendix.
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Title: Magnetic Connections across the Chromosphere-Corona Transition
Region
Authors: Judge, Philip
2021ApJ...914...70J Altcode: 2021arXiv210407753J
The plasma contributing to emission from the Sun between the cool
chromosphere (≤10<SUP>4</SUP> K) and hot corona (≥10<SUP>6</SUP> K)
has been subjected to many different interpretations. Here we look at
the magnetic structure of this transition region (TR) plasma, based
upon the implications of CLASP2 data of an active region recently
published by Ishikawa et al., and earlier Interface Region Imaging
Spectrograph (IRIS) and Solar Dynamics Observatory (SDO) data of quiet
regions. Ishikawa et al. found that large areas of sunspot plages
are magnetically unipolar as measured in the cores of Mg II resonance
lines, formed in the lower TR under low plasma-β conditions. Here we
show that IRIS images in the line cores have fibrils that are well
aligned with the overlying coronal loop segments seen in the 171 Å
channel of SDO. When the TR emission in active regions arises from
plasma magnetically and thermally connected to the corona, then the
line cores can provide the first credible magnetic boundary conditions
for force-free calculations extended to the corona. We also re-examine
IRIS images of dynamic TR cool loops previously reported as a major
contributor to TR emission from the quiet Sun. Dynamic cool loops
contribute only a small fraction of the total TR emission from the
quiet Sun.
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Title: On Single-point Inversions of Magnetic Dipole Lines in
the Corona
Authors: Judge, Philip; Casini, Roberto; Paraschiv, Alin Razvan
2021ApJ...912...18J Altcode: 2021arXiv210303824J
Prompted by a recent paper by Dima and Schad, we reconsider the problem
of inferring magnetic properties of the corona using polarimetric
observations of magnetic dipole (M1) lines. Dima and Schad point to a
potential source of degeneracy in a formalism developed by Plowman,
which under some circumstances can lead to the solution being
under-determined. Here we clarify the nature of the problem. Its
resolution lies in solving for the scattering geometry using the
elongation of the observed region of the corona. We discuss some
conceptual problems that arise when casting the problem for inversion in
the observer's reference frame, and satisfactorily resolve difficulties
identified by Plowman, Dima, and Schad.
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Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
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Title: Spectroscopic Inversions & Calibrations for DKIST Coronal
Observations
Authors: Ali, A.; Paraschiv, A.; Reardon, K.; Judge, P. G.
2020AGUFMSH0280014A Altcode:
The Cryo-NIRSP's (Cryogenic Near-IR Spectro-Polarimeter) is one of the
DKIST instruments capable of sensitive imaging of faint infrared coronal
solar spectra, and its primary goal is to measure the full polarization
state (Stokes I, Q, U and V) of spectral lines originating on the Sun
at different wavelengths. Producing data products from off-limb solar
coronal observations from the DKIST telescope is essential when trying
to study its future observations. Quantifying the accuracy of spectral
inversion procedures based on its spectral comparisons to absorption
and telluric calibrated spectra will give insight to interpreting
valid DKIST observations and its ultimate findings. Using simulated
contaminated data of both pure and noisy data sets has allowed us
to compare the wavelength shifts and broadening properties to help
pinpoint where contamination would affect the data set as a whole,
and by how much. In doing so, we developed code that will eventually
be integrated in the DKIST Level-2 pipeline. Working to compare
these findings to absorption and telluric readings will further help
minimize the uncertainties read in through observations, and give
direction on how to reduce the original coronal data in hopes to refine
it. Understanding the origins and magnitude of the contamination would
therefore help refine the original coronal data and make it compatible
for data processing, and would assist the automation of processing
the data observed by the DKIST telescope.
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Title: Spectropolarimetric Insight into Plasma Sheet Dynamics of a
Solar Flare
Authors: French, R.; Judge, P. G.; Matthews, S.; van Driel-Gesztelyi,
L.; Long, D.
2020AGUFMSH045..03F Altcode:
Magnetic reconnection is thought to lie at the heart of energy release
in solar flares, but the process is not yet fully understood. We examine
spectropolarimetric data from the CoMP coronagraph, acquired a few hours
into the evolution of the September 10th 2017 X8.2-class flare. We
find a striking and spatially coherent low polarisation structure,
aligned with the hot plasma sheet observed in EUV. By elimination,
we find the significant depolarisation to be a result of small-scale
sub-pixel magnetic structure along the plasma sheet, consistent with
theory of reconnection instabilities. This interpretation of ongoing
reconnection is supported by further Hinode/EIS observations and AIA
DEMs, from well beyond the impulsive phase of the flare. The plasma
sheet remains visible in CoMP linear polarisation over a day into the
flare's evolution, several hours after its last appearance in EUV. We
conclude that polarisation measurements with new coronagraphs, such
the DKIST CRYO-NIRSP instrument, will further enhance our understanding
of magnetic reconnection during eruptive flares.
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Title: Automated Single Point Inversions of Infrared Forbidden Lines
for DKIST Coronal Observations
Authors: Paraschiv, A.; Judge, P. G.; Ali, A.
2020AGUFMSH0280013P Altcode:
We present preliminary results on an inversion scheme that can be
applied to polarimetric measurements of forbidden lines formed in
the solar corona. <P />We aim to find optimal fits to synthetic CLE
data, delivering information on the vector magnetic field, thermal
properties and line of sight position from a single point in the
corona. We calculate the azimuthal angle from the linear polarization
and estimate the line-of-sight magnetic fields via the magnetograph
formulation. Our method complements these calculations to achieve vector
magnetic fields. We create a database of emergent Stokes profiles from a
Monte Carlo exploration of the parameter space. In building the database
set, we first reduce the line formation problem to an irreducible form,
factoring out linear parameters such as the magnetic field strength,
and using native symmetries in the line formation problem to reduce
the dimensionality of the needed calculations. We "precondition" the
observed data with simple linear transformations and a rotation of
the Stokes profiles around the line-of-sight axis through Sun center,
which affects only the linearly polarized components. We show that
calculations confined to the ecliptic plane are sufficient to explore
the full 3D space. After the best-fit profiles are found, the necessary
transformations are applied in reverse to the matching geometric,
magnetic and thermal parameters to estimate them in 3D space. We then
highlight the natural degeneracies in the analysis and examine their
accuracy and sensitivity to noise.
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Title: Inevitable consequences of ion-neutral damping of intermediate
MHD waves in Sun-like stars
Authors: Judge, Philip G.
2020MNRAS.498.2018J Altcode: 2020MNRAS.tmp.2062J; 2020arXiv200803607J
In the context of the solar atmosphere, we re-examine the role
of neutral and ionized species in dissipating the ordered energy
of intermediate-mode MHD waves into heat. We solve conservation
equations for the hydrodynamics and for hydrogen and helium ionization
stages, along closed tubes of magnetic field. First, we examine the
evolution of coronal plasma under conditions where coronal heating has
abruptly ceased. We find that cool (<10<SUP>5</SUP>K) structures
are formed lasting for several hours. MHD waves of modest amplitude
can heat the plasma through ion-neutral collisions with sufficient
energy rates to support the plasma against gravity. Then we examine
a calculation starting from a cooler atmosphere. The calculation
shows that warm (>10<SUP>4</SUP>) K long (> several Mm) tubes
of plasma arise by the same mechanism. We speculate on the relevance
of these solutions to observe properties of the Sun and similar stars
whose atmospheres are permeated with emerging magnetic fields and
stirred by convection. Perhaps this elementary process might help to
explain the presence of 'cool loops' in the solar transition region
and the production of broad components of transition region lines. The
production of ionized hydrogen from such a simple and perhaps inevitable
mechanism may be an important step towards finding the more complex
mechanisms needed to generate coronae with temperatures in excess of
10<SUP>6</SUP>K, independent of a star's metallicity.
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Title: Dynamics of Late-stage Reconnection in the 2017 September 10
Solar Flare
Authors: French, Ryan J.; Matthews, Sarah A.; van Driel-Gesztelyi,
Lidia; Long, David M.; Judge, Philip G.
2020ApJ...900..192F Altcode: 2020arXiv200713377F
In this multi-instrument paper, we search for evidence of sustained
magnetic reconnection far beyond the impulsive phase of the X8.2-class
solar flare on 2017 September 10. Using Hinode/EIS, CoMP, SDO/AIA,
K-Cor, Hinode/XRT, RHESSI, and IRIS, we study the late-stage evolution
of the flare dynamics and topology, comparing signatures of reconnection
with those expected from the standard solar flare model. Examining
previously unpublished EIS data, we present the evolution of nonthermal
velocity and temperature within the famous plasma sheet structure,
for the first four hours of the flare's duration. On even longer
timescales, we use differential emission measures and polarization data
to study the longevity of the flare's plasma sheet and cusp structure,
discovering that the plasma sheet is still visible in observations
of CoMP linear polarization on 2017 September 11, long after its last
appearance in EUV. We deduce that magnetic reconnection of some form
is still ongoing at this time—27 hr after flare onset.
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Title: New Light on an Old Problem of the Cores of Solar Resonance
Lines
Authors: Judge, Philip G.; Kleint, Lucia; Leenaarts, Jorrit;
Sukhorukov, Andrii V.; Vial, Jean-Claude
2020ApJ...901...32J Altcode: 2020arXiv200801250J
We reexamine a 50+ yr old problem of deep central reversals predicted
for strong solar spectral lines, in contrast to the smaller reversals
seen in observations. We examine data and calculations for the resonance
lines of H I, Mg II, and Ca II, the self-reversed cores of which form
in the upper chromosphere. Based on 3D simulations, as well as data for
the Mg II lines from the Interface Region Imaging Spectrograph (IRIS),
we argue that the resolution lies not in velocity fields on scales in
either of the micro- or macroturbulent limits. Macroturbulence is ruled
out using observations of optically thin lines formed in the upper
chromosphere, and by showing that it would need to have unreasonably
special properties to account for critical observations of the Mg
II resonance lines from the IRIS mission. The power in "turbulence"
in the upper chromosphere may therefore be substantially lower than
earlier analyses have inferred. Instead, in 3D calculations horizontal
radiative transfer produces smoother source functions, smoothing out
intensity gradients in wavelength and in space. These effects increase
in stronger lines. Our work will have consequences for understanding
the onset of the transition region, for understanding the energy in
motions available for heating the corona, and for the interpretation
of polarization data in terms of the Hanle effect applied to resonance
line profiles.
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Title: Automated Single Point Inversions of Infrared Forbidden Lines
for DKIST Coronal Observations
Authors: Paraschiv, A.; Judge, P.
2020SPD....5120302P Altcode:
We present preliminary results on an inversion scheme that can
be applied to polarimetric measurements of forbidden lines formed
in the solar corona. We aim to find optimal fits to synthetic CLE
data, delivering information on the vector magnetic field, thermal
properties and line of sight position from a single point in the
corona. The azimuthal angle is derived from the linear polarization
and the line-of-sight magnetic fields are derived via the magnetograph
formulation. Our method complements these calculations to achieve full
vector magnetic fields. We create a database of emergent Stokes profiles
from a Monte Carlo exploration of the parameter space. In building
the database set, we first reduce the line formation problem to an
irreducible form, factoring out linear parameters such as the magnetic
field strength, and using native symmetries in the line formation
problem to reduce the dimensionality of the needed calculations. We
"precondition" the observed data with simple linear transformations and
a rotation of the Stokes profiles around the line-of-sight axis through
Sun center, which affects only the linearly polarized components. We
show that calculations confined to the ecliptic plane are sufficient
to explore the full 3D space. After the best-fit profiles are found,
the necessary transformations are applied in reverse to the matching
geometric, magnetic and thermal parameters to estimate them in 3D
space. We then highlight the natural degeneracies in the analysis and
examine their accuracy and sensitivity to noise.
---------------------------------------------------------
Title: Spectropolarimetric Insight into Plasma Sheet Dynamics of a
Solar Flare
Authors: French, R.; Judge, P.; Matthews, S.; van Driel-Gesztelyi,
L.; Long, D.
2020SPD....5121102F Altcode:
Magnetic reconnection is thought to lie at the heart of energy release
in solar flares, but the process is not yet fully understood. We examine
spectropolarimetric data from the CoMP coronagraph, acquired a few hours
into the evolution of the September 10th 2017 X8.2-class flare. We
find a striking and spatially coherent low polarisation structure,
aligned with the hot plasma sheet observed in EUV. By elimination,
we find the significant depolarisation to be a result of small-scale
sub-pixel magnetic structure along the plasma sheet, consistent with
theory of reconnection instabilities. This interpretation of ongoing
reconnection is supported by further Hinode/EIS observations and AIA
DEMs, from well beyond the impulsive phase of the flare. The plasma
sheet remains visible in CoMP linear polarisation over a day into the
flare's evolution, several hours after its last appearance in EUV. We
conclude that polarisation measurements with new coronagraphs, such
the DKIST CRYO-NIRSP instrument, will further enhance our understanding
of magnetic reconnection during eruptive flares.
---------------------------------------------------------
Title: A New Facility for Airborne Solar Astronomy: NASA's WB-57 at
the 2017 Total Solar Eclipse
Authors: Caspi, Amir; Seaton, Daniel B.; Tsang, Constantine C. C.;
DeForest, Craig E.; Bryans, Paul; DeLuca, Edward E.; Tomczyk,
Steven; Burkepile, Joan T.; Casey, Thomas "Tony"; Collier, John;
Darrow, Donald "DD"; Del Rosso, Dominic; Durda, Daniel D.; Gallagher,
Peter T.; Golub, Leon; Jacyna, Matthew; Johnson, David "DJ"; Judge,
Philip G.; Klemm, Cary "Diddle"; Laurent, Glenn T.; Lewis, Johanna;
Mallini, Charles J.; Parent, Thomas "Duster"; Propp, Timothy; Steffl,
Andrew J.; Warner, Jeff; West, Matthew J.; Wiseman, John; Yates,
Mallory; Zhukov, Andrei N.; NASA WB-57 2017 Eclipse Observing Team
2020ApJ...895..131C Altcode: 2020arXiv200409658C
NASA's WB-57 High Altitude Research Program provides a deployable,
mobile, and stratospheric platform for scientific research. Airborne
platforms are of particular value for making coronal observations
during total solar eclipses because of their ability both to follow the
Moon's shadow and to get above most of the atmospheric air mass that
can interfere with astronomical observations. We used the 2017 August
21 eclipse as a pathfinding mission for high-altitude airborne solar
astronomy, using the existing high-speed visible-light and near/midwave
infrared imaging suite mounted in the WB-57 nose cone. In this paper,
we describe the aircraft, the instrument, and the 2017 mission;
operations and data acquisition; and preliminary analysis of data
quality from the existing instrument suite. We describe benefits and
technical limitations of this platform for solar and other astronomical
observations. We present a preliminary analysis of the visible-light
data quality and discuss the limiting factors that must be overcome
with future instrumentation. We conclude with a discussion of lessons
learned from this pathfinding mission and prospects for future research
at upcoming eclipses, as well as an evaluation of the capabilities of
the WB-57 platform for future solar astronomy and general astronomical
observation.
---------------------------------------------------------
Title: The Sun: A Very Short Introduction
Authors: Judge, Philip Gordon
2020svsi.book.....J Altcode:
The Sun, as our nearest star, is of enormous importance for life
on Earth - providing the warm radiation and light which allowed
complex life to evolve. The Sun plays a key role in influencing our
climate, whilst solar storms and high-energy events can threaten
our communication infrastructure and satellites. <P />This Very
Short Introduction explores what we know about the Sun, its physics,
its structure, origins, and future evolution. Philip Judge explains
some of the remaining puzzles about the Sun that still confound us,
using elementary physics, and mathematical concepts. Why does the Sun
form spots? Why does it flare? As he shows, these and other nagging
difficulties relate to the Sun's continually variable magnetism,
which converts an otherwise dull star into a machine for flooding
interplanetary space with variable radiation, high-energy particles
and magnetic ejections. Throughout, Judge highlights the many reasons
that the Sun is important, and why scientists engage in solar research.
---------------------------------------------------------
Title: Sun-like Stars Shed Light on Solar Climate Forcing
Authors: Judge, P. G.; Egeland, R.; Henry, G. W.
2020ApJ...891...96J Altcode: 2020arXiv200204633J
Recently published precise stellar photometry of 72 Sun-like stars
obtained at the Fairborn Observatory between 1993 and 2017 is used
to set limits on the solar forcing of Earth's atmosphere of ±4.5
W m<SUP>-2</SUP> since 1750. This compares with the +2.2 ± 1.1 W
m<SUP>-2</SUP> IPCC estimate for anthropogenic forcing. Three critical
assumptions are made. In decreasing order of importance they are:
(a) most of the brightness variations occur within the average time
series length of ≈17 yr; (b) the Sun seen from the ecliptic behaves
as an ensemble of middle-aged solar-like stars; and (c) narrowband
photometry in the Strömgren b and y bands are linearly proportional
to the total solar irradiance. Assumption (a) can best be relaxed and
tested by obtaining more photometric data of Sun-like stars, especially
those already observed. Eight stars with near-solar parameters have
been observed from 1999, and two since 1993. Our work reveals the
importance of continuing and expanding ground-based photometry, to
complement expensive solar irradiance measurements from space.
---------------------------------------------------------
Title: Some thoughts on emission-line spectroscopy
Authors: Judge, Philip G.
2020MNRAS.491..576J Altcode: 2019MNRAS.tmp.2640J
The interpretation of emission lines formed in large astrophysical
plasmas such as the solar atmosphere faces many challenges. Relatively
simple line-ratio estimates of physical parameters, while appealing,
are heavily laden with assumptions. In practical cases, some critical
assumptions are neither defensible from first principles, nor testable
by experiment. Free parameters and functional forms must be defined,
whose numbers of degrees of freedom exceed the number of independent
data points. These issues are illustrated in the particular case of
using lines of Si IV and O IV formed in the solar transition region,
observed for decades, most recently using the IRIS mission. The problems
highlighted are in addition to well-known problems of mathematical
ill-posedness.
---------------------------------------------------------
Title: Spectropolarimetric Insight into Plasma Sheet Dynamics of a
Solar Flare
Authors: French, Ryan J.; Judge, Philip G.; Matthews, Sarah A.;
van Driel-Gesztelyi, Lidia
2019ApJ...887L..34F Altcode: 2019arXiv191112666F
We examine spectropolarimetric data from the Coronal Multi-channel
Polarimeter (CoMP) instrument, acquired during the evolution of the 2017
September 10 X8.2 solar flare on the western solar limb. CoMP captured
linearly polarized light from two emission lines of Fe XIII at 1074.7
and 1079.8 nm, from 1.03 to 1.5 solar radii. We focus here on the hot
plasma sheet lying above the bright flare loops and beneath the ejected
coronal mass ejection. The polarization has a striking and coherent
spatial structure, with unexpectedly small polarization aligned with
the plasma sheet. By elimination, we find that small-scale magnetic
field structure is needed to cause such significant depolarization,
and suggest that plasmoid formation during reconnection (associated
with the tearing-mode instability) creates magnetic structure on scales
below instrument resolution of 6 Mm. We conclude that polarization
measurements with new coronagraphs, such as the upcoming Daniel
K. Inouye Solar Telescope, will further enhance our understanding of
magnetic reconnection and development of turbulence in the solar corona.
---------------------------------------------------------
Title: Coronal Solar Magnetism Observatory Science Objectives
Authors: Gibson, S. E.; Tomczyk, S.; Burkepile, J.; Casini, R.;
DeLuca, E.; de Toma, G.; de Wijn, A.; Fan, Y.; Golub, L.; Judge,
P. G.; Landi, E.; McIntosh, S. W.; Reeves, K.; Seaton, D. B.; Zhang, J.
2019AGUFMSH11C3395G Altcode:
Space-weather forecast capability is held back by our current
lack of basic scientific understanding of CME magnetic evolution,
and the coronal magnetism that structures and drives the solar
wind. Comprehensive observations of the global magnetothermal
environment of the solar atmosphere are needed for progress. When fully
implemented, the COSMO suite of synoptic ground-based telescopes will
provide the community with comprehensive and simultaneous measurements
of magnetism, temperature, density and plasma flows and waves from the
photosphere through the chromosphere and out into the corona. We will
discuss how these observations will uniquely address a set of science
objectives that are central to the field of solar and space physics:
in particular, to understand the storage and release of magnetic energy,
to understand CME dynamics and consequences for shocks, to determine the
role of waves in solar atmospheric heating and solar wind acceleration,
to understand how the coronal magnetic field relates to the solar
dynamo, and to constrain and improve space-weather forecast models.
---------------------------------------------------------
Title: High-Altitude Instrumentation for Infrared Observations of
the Solar Corona
Authors: Samra, J.; Cheimets, P.; DeLuca, E.; Golub, L.; Hannigan,
J. W.; Judge, P. G.; Madsen, C. A.; Marquez, V.; Tañón Reyes, N.;
Tomczyk, S.
2019AGUFMSH43B..07S Altcode:
High-altitude infrared remote sensing is a promising new method for
measuring coronal plasma and magnetic fields. We present new results
from a recent airborne eclipse mission and outline concepts for future
airborne and balloon-based instruments for coronal spectroscopy
and spectro-polarimetry. <P />The airborne infrared spectrometer
(AIR-Spec) was commissioned during the 2017 total solar eclipse,
when it observed five infrared coronal emission lines from the NSF
Gulfstream V research jet. These magnetically sensitive emission lines
of highly ionized magnesium, silicon, sulfur, and iron are promising
candidates for future observations of the coronal magnetic field, and
their characterization is an important first step toward developing
the next generation of instrumentation for coronal magnetometry. The
second AIR-Spec research flight took place during the July 2, 2019
total solar eclipse across the south Pacific. Higher sensitivity and
reduced jitter enabled more precise measurements of emission line
properties and plasma density, temperature, and line-of-sight velocity
up to one solar radius from the solar limb. Atmospheric absorption
was significant, even at altitude, and atmospheric modeling was
required to extract accurate line intensities. <P />AIR-Spec is a slit
spectrometer that measures light over a 1.55 solar radius field of view
in three spectral passbands between 1.4 and 3 microns. The successful
eclipse missions overcame a number of engineering challenges, centered
around maintaining adequate resolution and signal-to-noise ratio in
a compact and inexpensive package on a moving platform. AIR-Spec is a
pathfinder for future infrared spectrometers and spectro-polarimeters,
including a balloon-based coronagraph that will measure the global
coronal magnetic field and an airborne spectrometer that will survey
the infrared emission corona during a future eclipse.
---------------------------------------------------------
Title: Novel observations of the middle corona during the 2017 total
solar eclipse
Authors: Caspi, A.; Seaton, D. B.; Tsang, C.; DeForest, C.; Bryans,
P.; Samra, J.; DeLuca, E.; Tomczyk, S.; Burkepile, J.; Gallagher,
P.; Golub, L.; Judge, P. G.; Laurent, G. T.; West, M.; Zhukov, A.
2019AGUFMSH13A..10C Altcode:
Total solar eclipses offer rare opportunities to study the middle
corona. This intriguing region contains complex interfaces and
transitions between physical regimes, but has historically been
under-observed due to the challenges of observing its dim emission so
close to the bright inner corona and blinding solar disk. The unique
circumstances of a total solar eclipse coupled with a high-altitude
observing platform provide nearly space-quality observing conditions,
including for wavelengths inaccessible by ground-based observatories,
but with availability of ground-quality resources, including high-speed,
high-resolution, wide-field coronography typically inaccessible
from space. We used the 2017 August 21 "Great American" total solar
eclipse to observe the solar corona from ~1.02 to ~3 R<SUB>Sun</SUB>
in both visible (533.9 ± 4.75 nm) and medium-wave infrared (3-5
μm) light using stabilized telescopes on two of NASA's WB-57F
high-altitude research aircraft. This pathfinding mission utilized
existing instrumentation to evaluate the platform performance, guide
instrumentation development, and explore new discovery space for
future studies of the middle corona. <P />We present the high-speed
(30 Hz), high-resolution (3 arcsec/pixel) visible and IR observations
obtained during the eclipse, and analysis of these observations
in the context of coronal structure and dynamics. We discuss the
limitations of the prototype data and pathways forward for future
instrumentation and missions optimized for the range of observable
parameters in the middle corona. We also discuss the benefits of
such eclipse studies to an understanding of the corona as a single,
unified system, from its origins at the solar surface to its extension
into the heliosphere, particularly within the context of a developing
multi- and inter-disciplinary research collaboration, COHERENT (the
"Corona as a Holistic Environment" Research Network).
---------------------------------------------------------
Title: Solar Eclipse Observations from the Ground and Air from 0.31
to 5.5 Microns
Authors: Judge, Philip; Berkey, Ben; Boll, Alyssa; Bryans, Paul;
Burkepile, Joan; Cheimets, Peter; DeLuca, Edward; de Toma, Giuliana;
Gibson, Keon; Golub, Leon; Hannigan, James; Madsen, Chad; Marquez,
Vanessa; Richards, Austin; Samra, Jenna; Sewell, Scott; Tomczyk,
Steven; Vera, Alysha
2019SoPh..294..166J Altcode:
We present spectra and broad-band polarized light data from a novel
suite of instruments deployed during the 21st August 2017 total solar
eclipse. Our goals were to survey solar spectra at thermal infrared
wavelengths during eclipse, and to test new technology for measuring
polarized coronal light. An infrared coronal imaging spectrometer,
flown at 14.3 km altitude above Kentucky, was supported on the ground
by observations from Madras, Oregon (elevation 683 m) and Camp Wyoba
on Casper Mountain, Wyoming (2402 m). In Wyoming we deployed a new
infrared Fourier Transform Spectrometer (FTS), three low-dispersion
spectrometers loaned to us by Avantes, a novel visible-light camera
PolarCam, sensitive to linear polarization, and one of two infrared
cameras from FLIR Systems, the other operated at Madras. Circumstances
of eclipse demanded that the observations spanned 17:19 to 18:26
UT. We analyze spectra of the limb photosphere, the chromosphere,
prominences, and coronal lines from 310 nm to 5.5 μm. We calibrated
data photometrically using the solar disk as a source. Between different
spectrometers, the calibrations were consistent to better than 13%. But
the sensitivities achieved were insufficient to detect coronal lines
from the ground. The PolarCam data are in remarkable agreement with
polarization data from the K-Cor synoptic instrument on Mauna Loa, and
with FLIR intensity data acquired in Madras. We discuss new results,
including a detection of the He I 1083 nm multiplet in emission during
the whole of totality. The combination of the FTS and AIR-Spec spectra
reveals for the first time the effects of the telluric extinction
on the infrared coronal emission lines, to be observed with upcoming
Daniel K. Inouye Solar Telescope.
---------------------------------------------------------
Title: Multiwavelength High-resolution Observations of Chromospheric
Swirls in the Quiet Sun
Authors: Shetye, Juie; Verwichte, Erwin; Stangalini, Marco; Judge,
Philip G.; Doyle, J. G.; Arber, Tony; Scullion, Eamon; Wedemeyer, Sven
2019ApJ...881...83S Altcode:
We report observations of small-scale swirls seen in the solar
chromosphere. They are typically 2 Mm in diameter and last around
10 minutes. Using spectropolarimetric observations obtained by the
CRisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope,
we identify and study a set of swirls in chromospheric Ca II 8542 Å
and Hα lines as well as in the photospheric Fe I line. We have three
main areas of focus. First, we compare the appearance, morphology,
dynamics, and associated plasma parameters between the Ca II and Hα
channels. Rotation and expansion of the chromospheric swirl pattern
are explored using polar plots. Second, we explore the connection to
underlying photospheric magnetic concentration (MC) dynamics. MCs are
tracked using the SWAMIS tracking code. The swirl center and MC remain
cospatial and share similar periods of rotation. Third, we elucidate
the role swirls play in modifying chromospheric acoustic oscillations
and found a temporary reduction in wave period during swirls. We use
cross-correlation wavelets to examine the change in period and phase
relations between different wavelengths. The physical picture that
emerges is that a swirl is a flux tube that extends above an MC in a
downdraft region in an intergranular lane. The rotational motion of
the MC matches the chromospheric signatures. We could not determine
whether a swirl is a gradual response to the photospheric motion or
an actual propagating Alfvénic wave.
---------------------------------------------------------
Title: HAOS-DIPER: HAO Spectral Diagnostic Package For Emitted
Radiation
Authors: Judge, P. G.
2019ascl.soft05009J Altcode:
HAOS-DIPER works with and manipulates data for neutral atoms and
atomic ions to understand radiation emitted by some space plasmas,
notably the solar atmosphere and stellar atmospheres. HAOS-DIPER
works with quantum numbers for atomic levels, enabling it to perform
tasks otherwise difficult or very tedious, including a variety of data
checks, calculations based upon the atomic numbers, and searching and
manipulating data based upon these quantum numbers. HAOS-DIPER handles
conditions from LTE to coronal-like conditions, in a manner controlled
by one system variable !REGIME, and has some capability for estimating
data for which no accurate parameters are available and for accounting
for the effects of missing atomic levels.
---------------------------------------------------------
Title: High-cadence Visible and Infrared Spectra of the Sun during
Eclipse
Authors: Judge, P.; Tomczyk, S.; Hannigan, J.; Sewell, S.
2019ApJ...877...10J Altcode:
We study novel spectra from 310 nm to 5.5 μm obtained during the
2017 August 21 eclipse. Four spectrometers were deployed at Camp
Wyoba (altitude 2402 m) on Casper Mountain, WY. Three low-resolution
({ \mathcal R } ≲ 1000) Avantes spectrometers obtained useful
spectra from 310 nm to 2.3 μm, at cadences from 8 to 500 ms. To
maximize photometric precision, these instruments were fed with
optical fibers placed in the pupil planes of two small (D = 5 cm)
telescopes, thereby integrating all light from the field of view. We
also acquired higher-resolution ({ \mathcal R } ≈ 30000) spectra with
a new infrared Fourier Transform Spectrometer, fed by a Sun-tracking
heliostat, at a 2.5 s cadence. We calibrate the fluxes using counts
obtained during partial eclipse, with known limb-darkened photospheric
intensities. Fluxes of chromospheric lines, including Ca II H, K, and
Hα, obtained near third contact, were measured every 20 ms, a sampling
in height above the limb of 5.6 km. The behavior found corresponds to
that found in traditional (image-plane) flash spectra. Two unknown
chromospheric emission lines are noted. Based upon our measurements
and earlier calculations, we propose new eclipse experiments to uncover
clues to the origin and structure of spicules.
---------------------------------------------------------
Title: COSMO Science
Authors: Gibson, Sarah; Tomczyk, Steven; Burkepile, Joan; Casini,
Roberto; Deluca, Ed; de Toma, Giuliana; deWijn, Alfred; Fan, Yuhong;
Golub, Leon; Judge, Philip; Landi, Enrico; Lin, Haosheng; McIntosh,
Scott; Reeves, Kathy; Seaton, Dan; Zhang, Jie
2019shin.confE..32G Altcode:
Space-weather forecast capability is held back by our current
lack of basic scientific understanding of CME magnetic evolution,
and the coronal magnetism that structures and drives the solar
wind. Comprehensive observations of the global magnetothermal
environment of the solar atmosphere are needed for progress. When fully
implemented, the COSMO suite of synoptic ground-based telescopes will
provide the community with comprehensive and simultaneous measurements
of magnetism, temperature, density and plasma flows and waves from the
photosphere through the chromosphere and out into the corona. We will
discuss how these observations will uniquely address a set of science
objectives that are central to the field of solar and space physics:
in particular, to understand the storage and release of magnetic energy,
to understand CME dynamics and consequences for shocks, to determine the
role of waves in solar atmospheric heating and solar wind acceleration,
to understand how the coronal magnetic field relates to the solar
dynamo, and to constrain and improve space-weather forecast models.
---------------------------------------------------------
Title: Erratum: “Discovery of New Coronal Lines at 2.843 and 2.853
μm” (<A href="http://doi.org/10.3847/2041-8213/aab434">2018,
ApJL, 856, L29</A>)
Authors: Samra, Jenna E.; Judge, Philip G.; DeLuca, Edward E.;
Hannigan, James W.
2019ApJ...873L..25S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Measuring solar surface magnetic fields without ambiguity
Authors: Judge, Philip G.
2019MNRAS.482.5542J Altcode: 2018MNRAS.tmp.2891J
The goal of this paper is to find a method to yield solar surface
magnetic field measurements while inflicting minimal prior assumptions
on the acceptable solutions. A small spacecraft placed at least 0.1
radian away from the Earth-Sun line can, with vector field observations
from the Earth, offer unambiguous determinations of magnetic fields
from the Sun. A telescope of between 10 and 40 cm aperture operating at
ultraviolet (UV) wavelengths can, with a simple Stokes-V polarimeter,
enhance observations made with the suite of large telescopes on the
Earth. A 40 cm aperture can achieve the same diffraction limit at
400 nm that Daniel K. Innouye Solar Telescope (DKIST) might achieve
at 4 microns. Even a 10 cm aperture offers higher signal to noise in
Stokes V than DKIST can Q and U in magnetic fields outside sunspots,
transverse to the line of sight, offering enormous benefits for
understanding magnetic components transverse to the Earth-Sun line. We
identify UV and infrared (IR) lines of Fe I that are useful for joint
spacecraft-DKIST observations. Benefits of space observations also
include line-of-sight fields measured in strong chromospheric lines
in the UV that are free of seeing, such as Ca II H&K and Mg II
h&k. A simple mission devoted to such space measurements will
enhance our understanding of solar magnetism and hence, space weather
and space climate, for decades to come.
---------------------------------------------------------
Title: VizieR Online Data Catalog: UV spectrum of molecular hydrogen
in the Sun (Jaeggli+, 2018)
Authors: Jaeggli, S. A.; Judge, P. G.; Daw, A. N.
2019yCat..18550134J Altcode:
Ultraviolet (UV) lines of molecular hydrogen have been observed in
solar spectra for almost four decades, but the behavior of the molecular
spectrum and its implications for solar atmospheric structure are not
fully understood. Data from the High-Resolution Telescope Spectrometer
(HRTS) instrument revealed that H2 emission forms in particular regions,
selectively excited by a bright UV transition region and chromospheric
lines. We test the conditions under which H2 emission can originate
by studying non-LTE models, sampling a broad range of temperature
stratifications and radiation conditions. Stratification plays the
dominant role in determining the population densities of H2, which
forms in greatest abundance near the continuum photosphere. However,
opacity due to the photoionization of Si and other neutrals determines
the depth to which UV radiation can penetrate to excite the H2. Thus
the majority of H2 emission forms in a narrow region, at about 650km
in standard one-dimensional (1D) models of the quiet Sun, near the
{tau}=1 opacity surface for the exciting UV radiation, generally coming
from above. When irradiated from above using observed intensities of
bright UV emission lines, detailed non-LTE calculations show that the
spectrum of H2 seen in the quiet-Sun Solar Ultraviolet Measurement of
Emitted Radiation atlas spectrum and HRTS light-bridge spectrum can
be satisfactorily reproduced in 1D stratified atmospheres, without
including three-dimensional or time-dependent thermal structures. A
detailed comparison to observations from 1205 to 1550Å is presented,
and the success of this 1D approach to modeling solar UV H2 emission
is illustrated by the identification of previously unidentified lines
and upper levels in HRTS spectra. <P />(3 data files).
---------------------------------------------------------
Title: Chapter 5 - Spectroscopy and Atomic Physics
Authors: Judge, Philip G.
2019sgsp.book..127J Altcode: 2019sgsp.book..127.
A short guide to spectroscopy is given with an emphasis on the
elementary physics needed to understand and begin modeling the radiation
emerging from astrophysical plasmas using the Sun as a guide, without
bias toward a particular region of the Sun's atmosphere. The Sun is the
astronomical body par excellence upon which our tools for exploring
the universe have been most carefully developed. Observable solar
plasmas span a broad range of conditions and consequently extremes
of local thermodynamic equilibrium deep in the atmosphere, to extreme
non-local thermodynamical equilibrium conditions in the corona and wind,
including nonstatistical equilibrium conditions. For brevity, important
subjects are omitted, notably non-Maxwellian electron distributions,
line broadening, polarization, particle diffusion, and high-energy and
collective phenomena of importance, at radio and hard x-ray wavelengths.
---------------------------------------------------------
Title: Eclipse Science from 50,000 Feet: New Coronal Results from
NASA WB-57F High-Altitude Aircraft Observations of the 2017 Total
Solar Eclipse
Authors: Caspi, Amir; Tsang, Constantine; Seaton, Daniel B.; DeForest,
Craig; Bryans, Paul; DeLuca, Edward; Tomczyk, Steven; Burkepile,
Joan; Casey, Thomas Anthony; Collier, John; Darrow, Donald DD; Del
Rosso, Dominic; Durda, Daniel D.; Gallagher, Peter; Gascar, Jasmine;
Golub, Leon; Jacyna, Matthew; Johnson, David DJ; Judge, Philip G.;
Klemm, Cary; Laurent, Glenn Thomas; Lewis, Johanna; Mallini, Charles;
Parent, Thomas Duster; Propp, Timothy; Steffl, Andrew; Warner, Jeff;
West, Matthew John; Wiseman, John; Yates, Mallory; Zhukov, Andrei
2018tess.conf31302C Altcode:
Total solar eclipses present rare opportunities to study the complex
solar corona, down to altitudes of just a few percent of a solar
radius above the surface. Studying the corona is critical to gaining
a better understanding of the dominant driver of space weather that
affects human assets on Earth and elsewhere. For example, it is still
poorly understood how the corona is heated to temperatures of 1-2 MK
globally and up to 5-10 MK above active regions, while the underlying
chromosphere is 100 times cooler. The stability of large-scale coronal
structures and the extent of their reach to the middle and outer corona
are also not well known, limited in large part by sensitivities and
fields of view of existing observations. <P />Airborne observations
during a total eclipse provide unique advantages. By flying in the
stratosphere at altitudes of 50 kft or higher, they avoid all weather,
the seeing quality is enormously improved, and additional wavelengths
such as near-IR also become available due to significantly reduced
water absorption. An airborne observatory can also follow the Moon's
shadow, increasing the total observing time by 50% or more. <P />We
present current results of solar coronal measurements from airborne
observations of the 2017 Great American Total Solar Eclipse using two
of NASA's WB-57 high-altitude research aircraft, each equipped with
two 8.7-inch telescopes feeding high-sensitivity visible (green line
and nearby continuum) and medium-wave IR (3-5 μm) cameras operating
at high cadence (30 Hz) with ∼3 arcsec/pixel platescale and ±3
R<SUB>sun</SUB> fields of view. The two aircraft flew along the eclipse
path, separated by ∼110 km, to observe a total of ∼7.5 minutes
of totality in both visible and MWIR. These observations enable
groundbreaking studies of high-speed coherent motion - including
possible Alfvén waves and nanojets - in the lower and middle corona
that could shed light on coronal heating processes and the formation
and stability of coronal structures. Our MWIR observations of a cool
prominence and hot coronal active region plasma will be combined with
spectra from the AIR-Spec instrument, flown concurrently on NCAR's
HIAPER GV. We review the WB-57 eclipse mission and the current results
of analysis on the visible and IR coronal measurements, along with an
outlook for future analysis and missions.
---------------------------------------------------------
Title: Solar UV Molecular Hydrogen Fluorescence
Authors: Daw, Adrian Nigel; Jaeggli, Sarah Amelia; Judge, Philip G.;
Roueff, Evelyne; Abgrall, Hervé
2018tess.conf21706D Altcode:
Solar observations of ultraviolet molecular hydrogen lines indicate
that H<SUB>2</SUB> emission forms in particular regions, selectively
excited by bright UV transition region and chromospheric lines. IRIS
frequently observes numerous H<SUB>2</SUB> lines during flares and
smaller energetic events, but the diagnostic value of these lines for
probing the structure of the solar atmosphere has heretofore remained
largely unexploited. We present a synthesis method for H<SUB>2</SUB>
emission, using 1-D non-LTE models sampling a broad range of temperature
stratifications and input radiation conditions from the atmosphere
above, and compare the results to observations by IRIS, SUMER and
HRTS from 1205 to 1550 Å. Because opacity due to photoionization of
silicon and other neutrals determines the depth to which UV radiation
can penetrate to excite the H<SUB>2</SUB>, the majority of H<SUB>2</SUB>
emission forms in a narrow region near the tau=1 opacity surface for
the exciting UV radiation, generally coming from above. The success
of this 1-D approach to modeling solar UV H<SUB>2</SUB> emission is
illustrated by the identification of previously unidentified lines and
upper levels. Applications of the observed emission and implications
for solar atmospheric structure are discussed.
---------------------------------------------------------
Title: Discovery of New Coronal Lines at 2.843 and 2.853 μm
Authors: Samra, Jenna E.; Judge, Philip G.; DeLuca, Edward E.;
Hannigan, James W.
2018ApJ...856L..29S Altcode:
Two new emission features were observed during the 2017 August 21
total solar eclipse by a novel spectrometer, the Airborne Infrared
Spectrometer (AIR-Spec), flown at 14.3 km altitude aboard the NCAR
Gulfstream-V aircraft. We derive wavelengths in air of 2.8427 ±
0.00009 μm and 2.8529 ± 0.00008 μm. One of these lines belongs to the
3{{{p}}}<SUP>5</SUP>3{{d}}{}<SUP>3</SUP>{{{F}}}<SUB>3</SUB><SUP>^\circ
</SUP>\to
3{{{p}}}<SUP>5</SUP>3{{d}}{}<SUP>3</SUP>{{{F}}}<SUB>4</SUB><SUP>^\circ
</SUP> transition in Ar-like Fe IX. This appears to be the first
detection of this transition from any source. Minimization of
residual wavelength differences using both measured wavelengths,
together with National Institute of Standards and Technology (NIST)
extreme ultraviolet wavelengths, does not clearly favor assignment to
Fe IX. However, the shorter wavelength line appears more consistent
with other observed features formed at similar temperatures to Fe
IX. The transition occurs between two levels within the excited
3{{{p}}}<SUP>5</SUP>3{{d}} configuration, 429,000 cm<SUP>-1</SUP>
above the ground level. The line is therefore absent in photo-ionized
coronal-line astrophysical sources such as the Circinus Galaxy. Data
from a Fourier transform interferometer (FTIR) deployed from Wyoming
show that both lines are significantly attenuated by telluric
H<SUB>2</SUB>O, even at dry sites. We have been unable to identify
the longer wavelength transition.
---------------------------------------------------------
Title: Formation of the UV Spectrum of Molecular Hydrogen in the Sun
Authors: Jaeggli, S. A.; Judge, P. G.; Daw, A. N.
2018ApJ...855..134J Altcode: 2018arXiv180203779J
Ultraviolet (UV) lines of molecular hydrogen have been observed in
solar spectra for almost four decades, but the behavior of the molecular
spectrum and its implications for solar atmospheric structure are not
fully understood. Data from the High-Resolution Telescope Spectrometer
(HRTS) instrument revealed that H<SUB>2</SUB> emission forms in
particular regions, selectively excited by a bright UV transition
region and chromospheric lines. We test the conditions under which
H<SUB>2</SUB> emission can originate by studying non-LTE models,
sampling a broad range of temperature stratifications and radiation
conditions. Stratification plays the dominant role in determining
the population densities of H<SUB>2</SUB>, which forms in greatest
abundance near the continuum photosphere. However, opacity due to
the photoionization of Si and other neutrals determines the depth to
which UV radiation can penetrate to excite the H<SUB>2</SUB>. Thus
the majority of H<SUB>2</SUB> emission forms in a narrow region,
at about 650 km in standard one-dimensional (1D) models of the quiet
Sun, near the τ = 1 opacity surface for the exciting UV radiation,
generally coming from above. When irradiated from above using observed
intensities of bright UV emission lines, detailed non-LTE calculations
show that the spectrum of H<SUB>2</SUB> seen in the quiet-Sun Solar
Ultraviolet Measurement of Emitted Radiation atlas spectrum and HRTS
light-bridge spectrum can be satisfactorily reproduced in 1D stratified
atmospheres, without including three-dimensional or time-dependent
thermal structures. A detailed comparison to observations from 1205 to
1550 Å is presented, and the success of this 1D approach to modeling
solar UV H<SUB>2</SUB> emission is illustrated by the identification
of previously unidentified lines and upper levels in HRTS spectra.
---------------------------------------------------------
Title: Magnetic Diagnostics of the Solar Corona: Synthesizing Optical
and Radio Techniques
Authors: Casini, R.; White, S. M.; Judge, P. G.
2018smf..book..145C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chasing the Great American 2017 Total Solar Eclipse: Coronal
Results from NASA's WB-57F High-Altitude Research Aircraft
Authors: Caspi, A.; Tsang, C.; DeForest, C. E.; Seaton, D. B.; Bryans,
P.; Burkepile, J.; Casey, T. A.; Collier, J.; Darrow, D.; DeLuca,
E.; Durda, D. D.; Gallagher, P.; Golub, L.; Judge, P. G.; Laurent,
G. T.; Lewis, J.; Mallini, C.; Parent, T.; Propp, T.; Steffl, A.;
Tomczyk, S.; Warner, J.; West, M. J.; Wiseman, J.; Zhukov, A.
2017AGUFMSH24A..05C Altcode:
Total solar eclipses present rare opportunities to study the complex
solar corona, down to altitudes of just a few percent of a solar
radius above the surface, using ground-based and airborne observatories
that would otherwise be dominated by the intense solar disk and high
sky brightness. Studying the corona is critical to gaining a better
understanding of physical processes that occur on other stars and
astrophysical objects, as well as understanding the dominant driver of
space weather that affects human assets at Earth and elsewhere. For
example, it is still poorly understood how the corona is heated to
temperatures of 1-2 MK globally and up to 5-10 MK above active regions,
while the underlying chromosphere is 100 times cooler; numerous theories
abound, but are difficult to constrain due to the limited sensitivities
and cadences of prior measurements. The origins and stability of coronal
fans, and the extent of their reach to the middle and outer corona,
are also not well known, limited in large part by sensitivities and
fields of view of existing observations. Airborne observations during
the eclipse provide unique advantages; by flying in the stratosphere
at altitudes of 50 kft or higher, they avoid all weather, the seeing
quality is enormously improved, and additional wavelengths such as
near- IR also become available due to significantly reduced water
absorption. For an eclipse, an airborne observatory can also follow the
shadow, increasing the total observing time by 50% or more. We present
results of solar coronal measurements from airborne observations of
the 2017 Great American Total Solar Eclipse using two of NASA's WB-57
high-altitude research aircraft, each equipped with two 8.7" telescopes
feeding high-sensitivity visible (green-line) and medium-wave IR (3-5
μm) cameras operating at high cadence (30 Hz) with 3 arcsec/pixel
platescale and ±3 R_sun fields of view. The aircraft flew along the
eclipse path, separated by 110 km, to observe a summed 7.5 minutes of
totality in both visible and NIR, enabling groundbreaking studies of
high-speed wave motions and nanojets in the lower corona, the structure
and extent of coronal fans, and constraints on a potential primordial
dust ring around the Sun. We review the mission, and the results of
analysis on the visible and IR coronal measurements.
---------------------------------------------------------
Title: Formation of the UV Spectrum of Molecular Hydrogen in the Sun
Authors: Jaeggli, S. A.; Judge, P. G.; Daw, A. N.
2017AGUFMSH52B..01J Altcode:
UV lines of molecular hydrogen in the Sun have been observed for almost
four decades, but the behavior of the spectra and their implications
for solar atmospheric structure are not fully understood. Data from the
HRTS instrument revealed that H2 emission forms in particular regions,
selectively excited by bright UV transition region and chromospheric
lines. We test the conditions under which H2 emission can originate
by studying non-LTE models with increasingly complex temperature
stratification. Stratification plays the dominant role in determining
the population densities of H2, which can form in abundance only within
about 700 km of the continuum photosphere where 3D and dynamic structure
generally play secondary roles to stratification. When irradiated
from above using observed intensities of bright UV emission lines,
detailed non-LTE calculations show that the spectrum of H2 can be
satisfactorily modeled in 1D stratified atmospheric models, with no
need to invoke unusual 3D or time dependent thermal structures.
---------------------------------------------------------
Title: Multi-wavelength observations of the solar atmosphere from
the August 21, 2017 total solar eclipse
Authors: Tomczyk, S.; Boll, A.; Bryans, P.; Burkepile, J.; Casini,
R.; DeLuca, E.; Gibson, K. L.; Judge, P. G.; McIntosh, S. W.; Samra,
J.; Sewell, S. D.
2017AGUFMSH24A..04T Altcode:
We will conduct three experiments at the August 21, 2017 total
solar eclipse that we call the Rosetta Stone experiments. First,
we will obtain narrow-bandpass images at infrared wavelengths of the
magnetically sensitive coronal emission lines of Fe IX 2855 nm, Mg VIII
3028 nm and Si IX 3935 nm with a FLIR thermal imager. Information on the
brightness of these lines is important for identifying the optimal lines
for coronal magnetometry. These images will also serve as context images
for the airborne AirSpec IR coronal spectroscopy experiment (Samra et
al). Second, we will obtain linear polarization images of the visible
emission lines of Fe X 637 nm and Fe XI 789 nm as well as the continuum
polarization near 735 nm. These will be obtained with a novel detector
with an integral array of linear micro-polarizers oriented at four
different angles that enable polarization images without the need for
liquid crystals or rotating elements. These measurements will provide
information on the orientation of magnetic fields in the corona and
serve to demonstrate the new detector technology. Lastly, we will obtain
high cadence spectra as the moon covers and uncovers the chromosphere
immediately after 2nd contact and before third contact. This so-called
flash spectrum will be used to obtain information about chromospheric
structure at a spatial resolution higher than is possible by other
means. In this talk, we will describe the instrumentation used in these
experiments and present initial results obtained with them. This work
is supported by a grant from NASA, through NSF base funding of HAO/NCAR
and by generous loans of equipment from our corporate partners, FLIR,
4D Technologies and Avantes.
---------------------------------------------------------
Title: Polarization Observations of the Total Solar Eclipse of August
21, 2017
Authors: Burkepile, J.; Boll, A.; Casini, R.; de Toma, G.; Elmore,
D. F.; Gibson, K. L.; Judge, P. G.; Mitchell, A. M.; Penn, M.; Sewell,
S. D.; Tomczyk, S.; Yanamandra-Fisher, P. A.
2017AGUFMSH13B2477B Altcode:
A total solar eclipse offers ideal sky conditions for viewing the
solar corona. Light from the corona is composed of three components:
the E-corona, made up of spectral emission lines produced by ionized
elements in the corona; the K-corona, produced by photospheric light
that is Thomson scattered by coronal electrons; and the F-corona,
produced by sunlight scattered from dust particles in the near
Sun environment and in interplanetary space. Polarized white light
observations of the corona provide a way of isolating the K-corona to
determine its structure, brightness, and density. This work focuses
on broadband white light polarization observations of the corona
during the upcoming solar eclipse from three different instruments. We
compare coronal polarization brightness observations of the August 21,
2017 total solar eclipse from the NCAR/High Altitude Observatory (HAO)
Rosetta Stone experiment using the 4-D Technology PolarCam camera with
the two Citizen PACA_CATE17Pol telescopes that will acquire linear
polarization observations of the eclipse and the NCAR/HAO K-Cor white
light coronagraph observations from the Mauna Loa Solar Observatory in
Hawaii. This comparison includes a discussion of the cross-calibration
of the different instruments and reports the results of the coronal
polarization brightness and electron density of the corona. These
observations will be compared with results from previous coronal
measurements taken at different phases of the solar cycle. In addition,
we report on the performance of the three different polarimeters. The
4-D PolarCam uses a linear polarizer array, PACA_CATE17Pol uses
a nematic liquid crystal retarder in a single beam configuration
and K-Cor uses a pair of ferroelectric liquid crystal retarders in
a dual-beam configuration. The use of the 4-D PolarCam camera in the
Rosetta Stone experiment is to demonstrate the technology for acquiring
high cadence polarization measurements. The Rosetta Stone experiment
is funded through the NASA award NNH16ZDA001N-ISE. The Citizen Science
approach to measuring the polarized solar corona during the eclipse
is funded through NASA award NNX17AH76G. The NCAR Mauna Loa Solar
Observatory is funded by the National Science Foundation.
---------------------------------------------------------
Title: Surveying the IR corona during the 2017 solar eclipse
Authors: Bryans, P.; Hannigan, J. W.; Sewell, S. D.; Judge, P. G.
2017AGUFMSH13B2479B Altcode:
The spectral emission of the infrared solar corona is the most
promising direct diagnostic of the coronal magnetic field, and
yet remains poorly measured. During the 2017 total solar eclipse,
we will perform the first spectral survey of the IR corona using
the NCAR Airborne Interferometer. This Fourier Transform Infrared
Spectrometer is configured to observe the coronal spectrum from 1.5
to 5.5 microns at R 10,000 from a ground-based site. The location
is atop Casper Mountain, Wyoming (42.73ºN, 106.32ºW, 2400 masl),
8 km from the center-line of totality. In this presentation, we will
outline the need for such measurements, describe the instrument design
and adaptation for the eclipse measurement, observation scheme, and
present preliminary results. We will also discuss implications for
observing infrared coronal lines from the ground, for example with
the upcoming DKIST facility.
---------------------------------------------------------
Title: ASPIRE - Airborne Spectro-Polarization InfraRed Experiment
Authors: DeLuca, E.; Cheimets, P.; Golub, L.; Madsen, C. A.; Marquez,
V.; Bryans, P.; Judge, P. G.; Lussier, L.; McIntosh, S. W.; Tomczyk, S.
2017AGUFMSH13B2480D Altcode:
Direct measurements of coronal magnetic fields are critical for
taking the next step in active region and solar wind modeling and
for building the next generation of physics-based space-weather
models. We are proposing a new airborne instrument to make these key
observations. Building on the successful Airborne InfraRed Spectrograph
(AIR-Spec) experiment for the 2017 eclipse, we will design and build a
spectro-polarimeter to measure coronal magnetic field during the 2019
South Pacific eclipse. The new instrument will use the AIR-Spec optical
bench and the proven pointing, tracking, and stabilization optics. A new
cryogenic spectro-polarimeter will be built focusing on the strongest
emission lines observed during the eclipse. The AIR-Spec IR camera,
slit jaw camera and data acquisition system will all be reused. The
poster will outline the optical design and the science goals for ASPIRE.
---------------------------------------------------------
Title: Efficient Radiative Transfer for Dynamically Evolving
Stratified Atmospheres
Authors: Judge, Philip G.
2017ApJ...851....5J Altcode:
We present a fast multi-level and multi-atom non-local thermodynamic
equilibrium radiative transfer method for dynamically evolving
stratified atmospheres, such as the solar atmosphere. The
preconditioning method of Rybicki & Hummer (RH92) is adopted. But,
pressed for the need of speed and stability, a “second-order
escape probability” scheme is implemented within the framework
of the RH92 method, in which frequency- and angle-integrals are
carried out analytically. While minimizing the computational work
needed, this comes at the expense of numerical accuracy. The iteration
scheme is local, the formal solutions for the intensities are the only
non-local component. At present the methods have been coded for vertical
transport, applicable to atmospheres that are highly stratified. The
probabilistic method seems adequately fast, stable, and sufficiently
accurate for exploring dynamical interactions between the evolving MHD
atmosphere and radiation using current computer hardware. Current 2D
and 3D dynamics codes do not include this interaction as consistently
as the current method does. The solutions generated may ultimately
serve as initial conditions for dynamical calculations including full
3D radiative transfer. <P />The National Center for Atmospheric Research
is sponsored by the National Science Foundation.
---------------------------------------------------------
Title: Eclipse Science Results from the Airborne Infrared Spectrometer
(AIR-Spec)
Authors: Samra, J.; Cheimets, P.; DeLuca, E.; Golub, L.; Judge, P. G.;
Lussier, L.; Madsen, C. A.; Marquez, V.; Tomczyk, S.; Vira, A.
2017AGUFMSH24A..06S Altcode:
We present the first science results from the commissioning flight
of the Airborne Infrared Spectrometer (AIR-Spec), an innovative
solar spectrometer that will observe the 2017 solar eclipse from
the NSF/NCAR High-Performance Instrumented Airborne Platform for
Environmental Research (HIAPER). During the eclipse, AIR-Spec will
image five magnetically sensitive coronal emission lines between 1.4
and 4 microns to determine whether they may be useful probes of coronal
magnetism. The instrument will measure emission line intensity, FWHM,
and Doppler shift from an altitude of over 14 km, above local weather
and most of the absorbing water vapor. Instrumentation includes an image
stabilization system, feed telescope, grating spectrometer, infrared
camera, and visible slit-jaw imager. Results from the 2017 eclipse
are presented in the context of the mission's science goals. AIR-Spec
will identify line strengths as a function of position in the solar
corona and search for the high frequency waves that are candidates
for heating and acceleration of the solar wind. The instrument will
also identify large scale flows in the corona, particularly in polar
coronal holes. Three of the five lines are expected to be strong in
coronal hole plasmas because they are excited in part by scattered
photospheric light. Line profile analysis will probe the origins
of the fast and slow solar wind. Finally, the AIR-Spec measurements
will complement ground based eclipse observations to provide detailed
plasma diagnostics throughout the corona. AIR-Spec will measure infrared
emission of ions observed in the visible from the ground, giving insight
into plasma heating and acceleration at radial distances inaccessible
to existing or planned spectrometers.
---------------------------------------------------------
Title: The Magnetic Future of the Sun
Authors: Judge, Philip G.; Egeland, Ricky; Metcalfe, Travis S.;
Guinan, Edward; Engle, Scott
2017ApJ...848...43J Altcode: 2017arXiv171005088J
We analyze space- and ground-based data for the old (7.0 ± 0.3
Gyr) solar analogs 16 Cyg A and B. The stars were observed with the
Cosmic Origins UV Spectrographs on the Hubble Space Telescope (HST)
on 2015 October 23 and 2016 February 3, respectively, and with the
Chandra X-ray Observatory on 2016 February 7. Time-series data in
Ca II data are used to place the UV data in context. The UV spectra
of 18 Sco (3.7 ± 0.5 Gyr), the Sun (4.6 ± 0.04 Gyr), and α Cen A
({5.4}<SUB>-0.2</SUB><SUP>+1.2</SUP> {Gyr}) appear remarkably similar,
pointing to a convergence of magnetic heating rates for G2 main-sequence
stars older than ≈2-4 Gyr. But the B component’s X-ray (0.3-2.5
keV) flux lies 20× below a well-known minimum level reported by
Schmitt. As reported for α Cen A, the coronal temperature probably
lies below that detectable in soft X-rays. No solar UV flux spectra
of comparable resolution to those of stellar data exist, but they are
badly needed for comparison with stellar data. Center-to-limb variations
are reevaluated for lines such as Ca II through X-rays, with important
consequences for observing activity cycles in such features. We also
call into question work that has mixed solar intensity-intensity
statistics with flux-flux relations of stars.
---------------------------------------------------------
Title: Solar Spectral Lines with Special Polarization Properties
for the Calibration of Instrument Polarization
Authors: Li, W.; Casini, R.; del Pino Alemán, T.; Judge, P. G.
2017ApJ...848...82L Altcode:
We investigate atomic transitions that have previously been identified
as having zero polarization from the Zeeman effect. Our goal is
to identify spectral lines that can be used for the calibration of
instrumental polarization of large astronomical and solar telescopes,
such as the Daniel K. Inouye Solar Telescope, which is currently
under construction on Haleakala. We use a numerical model that
takes into account the generation of scattering polarization and
its modification by the presence of a magnetic field of arbitrary
strength. We adopt values for the Landé factors from spectroscopic
measurements or semi-empirical results, thus relaxing the common
assumption of LS-coupling previously used in the literature. The
mechanisms dominating the polarization of particular transitions are
identified, and we summarize groups of various spectral lines useful
for the calibration of spectropolarimetric instruments, classified
according to their polarization properties.
---------------------------------------------------------
Title: Atomic physics and solar polarimetry
Authors: Judge, P. G.
2017CaJPh..95..847J Altcode: 2017arXiv170707090J
Observational solar physics is entering a new era with the advent of
new 1.5 m class telescopes with adaptive optics, as well as the Daniel
K. Inouye 4 m telescope which will become operational in 2019. Major
outstanding problems in solar physics all relate to the solar magnetic
field. Spectropolarimetry offers the best, and sometimes only, method
for accurate measurements of the magnetic field. In this paper we
highlight how certain atomic transitions can help us provide both
calibration data, as well as diagnostic information on solar magnetic
fields, in the presence of residual image distortions through the
atmosphere close to, but not at the diffraction limits of large and
polarizing telescopes. Particularly useful are spectral lines of
neutrals and singly charged ions of iron and other complex atoms. As
a proof-of-concept, we explore atomic transitions that might be used
to study magnetic fields without the need for an explicit calibration
sequence, offering practical solutions to the difficult challenges
of calibrating the next generation of solar spectropolarimetric
telescopes. Suggestions for additional work on atomic theory and
measurements, particularly at infrared wavelengths, are given. There
is some promise for continued symbiotic advances between solar physics
and atomic physics.
---------------------------------------------------------
Title: A Novel Strategy to Seek Biosignatures at Enceladus and Europa
Authors: Judge, Philip
2017AsBio..17..852J Altcode: 2017arXiv170707230J
A laboratory experiment is suggested in which conditions similar
to those in the plume ejecta from Enceladus and, perhaps, Europa are
established. Using infrared spectroscopy and polarimetry, the experiment
might identify possible bio-markers in differential measurements of
water from the open-ocean, from hydrothermal vents, and abiotic water
samples. Should the experiment succeed, large telescopes could be
used to acquire sensitive infrared spectra of the plumes of Enceladus
and Europa, as the satellites transit the bright planetary disks. The
extreme technical challenges encountered in so doing are similar to
those of solar imaging spectropolarimetry. The desired signals are
buried in noisy data in the presence of seeing-induced image motion
and a changing natural source. Some differential measurements used
for solar spectropolarimetry can achieve S/N ratios of $10^5$ even in
the presence of systematic errors two orders of magnitude larger. We
review the techniques and likelihood of success of such an observing
campaign with some of the world's largest ground-based telescopes, as
well as the long anticipated James Webb Space Telescope. We discuss
the relative merits of the new 4m Daniel K. Inouye Solar Telescope,
as well as the James Webb Space Telescope and larger ground-based
observatories, for observing the satellites of giant planets. As seen
from near Earth, transits of Europa occur regularly, but transits of
Enceladus will begin again only in 2022.
---------------------------------------------------------
Title: Magnetic Diagnostics of the Solar Corona: Synthesizing Optical
and Radio Techniques
Authors: Casini, R.; White, S. M.; Judge, P. G.
2017SSRv..210..145C Altcode: 2017SSRv..tmp...91C
In this contribution we review the current state-of-the-art of
coronal magnetometry, in both optical and radio domains. We address
the achievable objectives and the challenges of present measurement
techniques and interpretation tools. In particular, we focus on the
role that these observations can play for constraining and validating
numerical models of the global coronal magnetic field. With regard
to optical techniques, we mainly focus on the use of M1 diagnostics,
further developing the theory of the formation of their polarization
signatures in the magnetized corona.
---------------------------------------------------------
Title: On the Fine Structure Splitting of the 3p43d 4D5/2 and 3p43d
4D7/2 Levels of Fe X
Authors: Judge, Philip; Hutton, Roger; Li, Wenxian; Brage, Tomas
2017arXiv170707077J Altcode:
We study UV spectra obtained with the SO82-B slit spectrograph on
board SKYLAB to estimate the fine structure splitting of the Cl-like
3p4 3d 4D J=5/2 and 3p4 3d 4D J=7/2 levels of Fe X. The splitting is
of interest because the Zeeman effect mixes these levels, producing a
"magnetically induced transition" (MIT) from 3p4 3d 4D J=7/2 to 3p5 2Po
J=3/2 for modest magnetic field strengths characteristic of the active
solar corona. We estimate the splitting using the Ritz combination
formula applied to two lines in the UV region of the spectrum close
to 1603.2 Angstrom, which decay from the level 3p4(1D)3d 2G J=7/2
to these two lower levels. The MIT and accompanying spin-forbidden
transition lie near 257 Angstrom. By careful inspection of a deep
exposure obtained with the S082B instrument we derive a splitting of
<~ 7 +/- 3 cm-1. The upper limit arises because of a degeneracy
between the effects of non-thermal line broadening and fine-structure
splitting for small values of the latter parameter. Although the data
were recorded on photographic film, we solved for optimal values of
line width and splitting of 8.3 +/- 0.9 and 3.6 +/- 2.7 cm-1.
---------------------------------------------------------
Title: An Explanation of Remarkable Emission-line Profiles in
Post-flare Coronal Rain
Authors: Lacatus, Daniela A.; Judge, Philip G.; Donea, Alina
2017ApJ...842...15L Altcode: 2017arXiv170707069L
We study broad redshifted emission in chromospheric and transition
region lines that appears to correspond to a form of post-flare
coronal rain. Profiles of Mg II, C II, and Si IV lines were obtained
using IRIS before, during, and after the X2.1 flare of 2015 March 11
(SOL2015-03-11T16:22). We analyze the profiles of the five transitions
of Mg II (the 3p-3s h and k transitions, and three lines belonging to
the 3d-3p transitions). We use analytical methods to understand the
unusual profiles, together with higher-resolution observational data
of similar phenomena observed by Jing et al. The peculiar line ratios
indicate anisotropic emission from the strands that have cross-strand
line center optical depths (k line) of between 1 and 10. The lines
are broadened by unresolved Alfvénic motions whose energy exceeds
the radiation losses in the Mg II lines by an order of magnitude. The
decay of the line widths is accompanied by a decay in the brightness,
suggesting a causal connection. If the plasma is ≲99% ionized,
ion-neutral collisions can account for the dissipation; otherwise, a
dynamical process seems necessary. Our work implies that the motions are
initiated during the impulsive phase, to be dissipated as radiation over
a period of an hour, predominantly by strong chromospheric lines. The
coronal “rain” we observe is far more turbulent than most earlier
reports have indicated, with implications for plasma heating mechanisms.
---------------------------------------------------------
Title: Are All Flare Ribbons Simply Connected to the Corona?
Authors: Judge, Philip G.; Paraschiv, Alin; Lacatus, Daniela; Donea,
Alina; Lindsey, Charlie
2017ApJ...838..138J Altcode: 2017arXiv170707072J
We consider the observational basis for the belief that flare
ribbons in the chromosphere result from energy transport from the
overlying corona. We study ribbons of small flares using magnetic
and intensity data from the Hinode, Solar Dynamics Observatory, and
IRIS missions. While most ribbons appear connected to the corona and
overlie regions of significant vertical magnetic field, we examine
one ribbon with no clear evidence for such connections. Evolving
horizontal magnetic fields seen with Hinode suggest that reconnection
with preexisting fields below the corona can explain the data. The
identification of just one, albeit small, ribbon, with no apparent
connection to the corona, leads us to conclude that at least two
mechanisms are responsible for the heating that leads to flare ribbon
emission. <P />The National Center for Atmospheric Research is sponsored
by the National Science Foundation.
---------------------------------------------------------
Title: Vector Magnetic Field Measurements along a Cooled Stereo-imaged
Coronal Loop
Authors: Schad, T. A.; Penn, M. J.; Lin, H.; Judge, P. G.
2016ApJ...833....5S Altcode: 2016arXiv161005332S
The variation of the vector magnetic field along structures in
the solar corona remains unmeasured. Using a unique combination of
spectropolarimetry and stereoscopy, we infer and compare the vector
magnetic field structure and three-dimensional morphology of an
individuated coronal loop structure undergoing a thermal instability. We
analyze spectropolarimetric data of the He I λ10830 triplet
(1s2s{}<SUP>3</SUP>{S}<SUB>1</SUB>-1s2p{}<SUP>3</SUP>{P}<SUB>{2,1,0</SUB>})
obtained at the Dunn Solar Telescope with the Facility Infrared
Spectropolarimeter on 2011 September 19. Cool coronal loops are
identified by their prominent drainage signatures in the He I data
(redshifts up to 185 km s<SUP>-1</SUP>). Extinction of EUV background
radiation along these loops is observed by both the Atmospheric Imaging
Assembly on board the Solar Dynamics Observatory and the Extreme
Ultraviolet Imager on board spacecraft A of the Solar Terrestrial
Relations Observatory, and is used to stereoscopically triangulate
the loop geometry up to heights of 70 Mm (0.1R <SUB>Sun</SUB>) above
the solar surface. The He I polarized spectra along this loop exhibit
signatures indicative of atomic-level polarization, as well as magnetic
signatures through the Hanle and Zeeman effects. Spectropolarimetric
inversions indicate that the magnetic field is generally oriented
along the coronal loop axis, and provide the height dependence of the
magnetic field intensity. The technique we demonstrate is a powerful
one that may help better understand the thermodynamics of coronal
fine-structure magnetism.
---------------------------------------------------------
Title: Estimates Of Magnetic Plage Filling Factors Using The Cn Band
Authors: Saar, Steven H.; Judge, Philip
2016csss.confE.151S Altcode:
The 388nm CN band (like the better known "G band" of CH) is used in the
Sun to locate strong magnetic concentrations. Magnetic network and plage
are bright in these molecular bands, since the enhanced chromospheric
heating there destroys the molecule, erasing its absorption and allowing
the continuum to shine through. We take advantage of this to estimate
the filling factor of strong fields in active dwarf stars. CN band
depths in active stars can be compared with those of inactive stars of
very similar temperature and metallicity, and after an adjustment for
line-blanketing, used to estimate a magnetic plage filling factor. We
estimate filling factors for a two stars, and compare them to direct
Stokes I line-broadening measurements. Limitations, caveats, and future
directions are briefly considered.
---------------------------------------------------------
Title: On the Fine Structure Splitting of the 3p<SUP>4</SUP>3d
<SUP>4</SUP>D<SUB>5/2</SUB> and 3p<SUP>4</SUP>3d
<SUP>4</SUP>D<SUB>7/2</SUB> Levels of Fe X
Authors: Judge, Philip G.; Hutton, Roger; Li, Wenxian; Brage, Tomas
2016ApJ...833..185J Altcode:
We study UV spectra obtained with the SO82-B slit spectrograph on board
SKYLAB to estimate the fine structure (FS) splitting of the Cl-like
3{{{p}}}<SUP>4</SUP>3{{d}}{}<SUP>4</SUP>{{{D}}}<SUB>5/2</SUB> and
3{{{p}}}<SUP>4</SUP>3{{d}}{}<SUP>4</SUP>{{{D}}}<SUB>7/2</SUB> levels
of Fe x. The splitting is of interest because the Zeeman effect mixes
these levels, producing a “magnetically induced transition” (MIT)
from 3{{{p}}}<SUP>4</SUP>3{{d}}{}<SUP>4</SUP>{{{D}}}<SUB>7/2</SUB> to
3{{{p}}}<SUP>5</SUP>{}<SUP>2</SUP>{{{P}}}<SUB>3/2</SUB><SUP>{{o</SUP>}}
for modest magnetic field strengths characteristic of the
active solar corona. We estimate the splitting using the Ritz
combination formula applied to two lines in the UV region
of the spectrum close to 1603.2 Å, which decay from the level
3{{{p}}}<SUP>4</SUP>{(}<SUP>1</SUP>{{D}})3{{d}}{}<SUP>2</SUP>{{{G}}}<SUB>7/2</SUB>
to these two lower levels. The MIT and accompanying spin-forbidden
transition lie near 257 Å. By careful inspection of a deep exposure
obtained with the S082B instrument, we derive a splitting of ≲ 7+/-
3 cm<SUP>-1</SUP>. The upper limit arises because of a degeneracy
between the effects of non-thermal line broadening and FS splitting for
small values of the latter parameter. Although the data were recorded
on photographic film, we solved for optimal values of line width and
splitting of 8.3 ± 0.9 and 3.6 ± 2.7 cm<SUP>-1</SUP>.
---------------------------------------------------------
Title: An airborne infrared spectrometer for solar eclipse
observations
Authors: Samra, Jenna; Cheimets, Peter; DeLuca, Edward; Galeros,
John; Gauron, Thomas; Golub, Leon; Guth, Giora; Hertz, Edward; Judge,
Philip; Koutchmy, Serge; Marquez, Vanessa
2016SPIE.9908E..5US Altcode:
This paper presents the design of an innovative solar spectrometer
that will y on the NSF/NCAR Gulfstream V High-Performance Instrumented
Airborne Platform for Environmental Research (GV HIAPER) during the
2017 solar eclipse. The airborne infrared spectrometer (AIR-Spec) is
groundbreaking in two aspects: it will image infrared coronal emission
lines that have never been measured, and it will bring high resolution
imaging to GV HIAPER. The instrument development faces the challenges
of achieving adequate resolution and signal-to-noise ratio in a compact
package mounted to a noisy moving platform. To ensure that AIR-Spec
meets its research goals, the instrument is undergoing pre-flight
modeling and testing. The results are presented with reference to the
instrument requirements.
---------------------------------------------------------
Title: An Airborne Infrared Spectrometer for Solar Eclipse
Observations
Authors: Samra, Jenna; DeLuca, Edward; Golub, Leon; Cheimets, Peter;
Judge, Philip
2016shin.confE.155S Altcode:
The airborne infrared spectrometer (AIR-Spec) is an innovative
solar spectrometer that will observe the 2017 solar eclipse from
the NSF/NCAR High-Performance Instrumented Airborne Platform for
Environmental Research (HIAPER). AIR-Spec will image five infrared
coronal emission lines to determine whether they may be useful probes
of coronal magnetism. <P />The solar magnetic field provides the free
energy that controls coronal heating, structure, and dynamics. Energy
stored in coronal magnetic fields is released in flares and coronal mass
ejections and ultimately drives space weather. Therefore, direct coronal
field measurements have significant potential to enhance understanding
of coronal dynamics and improve solar forecasting models. Of particular
interest are observations of field lines in the transitional region
between closed and open flux systems, providing important information
on the origin of the slow solar wind. <P />While current instruments
routinely observe only the photospheric and chromospheric magnetic
fields, AIR-Spec will take a step toward the direct observation of
coronal fields by measuring plasma emission in the infrared at high
spatial and spectral resolution. During the total solar eclipse of
2017, AIR-Spec will search for five magnetically sensitive coronal
emission lines between 1.4 and 4 μm from the HIAPER Gulfstream V at
an altitude above 14.9 km. The instrument will measure emission line
intensity, width, and Doppler shift, map the spatial distribution of
infrared emitting plasma, and search for waves in the emission line
velocities. <P />AIR-Spec consists of an optical system (feed telescope,
grating spectrometer, and infrared detector) and an image stabilization
system, which uses a fast steering mirror to correct the line-of-sight
for platform perturbations. To ensure that the instrument meets its
research goals, both systems are undergoing extensive performance
modeling and testing. These results are shown with reference to the
science requirements.
---------------------------------------------------------
Title: The March 11, 2015 X2.1 flare: peculiar post-flare spectral
signatures
Authors: Lacatus, Daniela Adriana; Donea, A.; Judge, P. G.
2016shin.confE.207L Altcode:
The only X-class flare of 2015 observed by IRIS occurred at 16:22
UT on 11 March 2015, in AR 12297. This flare generated significant
seismic transients in the photosphere at the eastern location of the
flare. IRIS observations of the chromosphere and transition region
help us understand the physics of the sunquake. In this work we will
analyze this event using data from IRIS, SDO, and RHESSI. Unfortunately,
the IRIS rasters scanned the area between the main footpoints of the
solar flare. Whereas, the main X-ray emission dominates the eastern
footprint. Significant enhancements in the chromospheric and TR lines
intensities were measured. The forbidden line of Fe XXI 1354.1 Å
is detected after the flare peak. Important plasma downflows were
identified in the majority of the observed lines, consistent with
magnetic field reconfiguration. An erupting filament develops at 16:12
UT and moves rapidly towards the eastern part of the active region.
---------------------------------------------------------
Title: HST/COS FUV Spectrophotometry of the Key Binary Solar Twins
16 Cyg A&B: Astrophysical Laboratories for the Future Sun and
Older Solar Analogs
Authors: Guinan, Edward F.; Dewarf, Laurence; Engle, Scott G.; Judge,
Philip G.; Metcalfe, Travis S.
2016hst..prop13861G Altcode:
The fortuitous location of the wide G1.5V/G2.5V binary 16 Cyg A&B
as the brightest stars in the Kepler Field is a "game changer,"
permitting the determination of the stars' fundamental properties from
asteroseismolgy analyses. Recent studies returned precise determinations
of the stars' basic properties including masses and age (6.8+/-0.4 Gyr),
along with the rotation periods. Thus, 16 Cyg A&B are now the oldest
solar-mass analogs with reliable ages and physical properties. Only
the Sun has better determined physical properties. 16 Cyg A&B now
serve as old-age anchors for Rotation-Age-Activity-Irradiance relations
(and Gyrochronology studies) for solar-type stars. Extensive Ca II
HK spectrophotometry reveals low levels of chromospheric emission are
below the lowest values for our Sun. These stars serve as critical test
beds for studying solar/stellar dynamos for stars less active than the
Sun. These advances have catapulted 16 Cyg A&B into a prominent
place in solar/stellar astrophysics for studying the evolution,
internal structure, magnetic dynamos, angular momentum loss, and FUV
irradiances of old solar-mass stars. Although 16 Cyg has been observed
from X-ray - IR, there are no observations in the FUV region where
most of the crucial diagnostic chromospheric & transition region
emissions occur. We request COS FUV medium resolution (G130M, G160M)
spectra (six orbits/star). This permits the important FUV (1150-1750A)
line emission strengths, profiles and Doppler shifts to be analyzed
and compared with the Sun and other solar-analogs. This program is
complemented by Ca II HK, high precision uvby observations, and by
proposed Chandra X-ray coronal observations.
---------------------------------------------------------
Title: Airborne Infrared Spectrograph for Eclipse Observations
Authors: Golub, L.; Cheimets, P.; DeLuca, E. E.; Samra, J.; Judge,
P. G.
2015AGUFMSH51C2454G Altcode:
Direct measurements of the coronal magnetic field have significant
potential to enhance our understanding of coronal dynamics, and improve
forecasting models. Of particular interest are observations of coronal
field lines in the Transition Corona, the transitional region between
closed and open flux systems, providing important information on
eruptive instabilities and on the origin of the slow solar wind. While
current instruments routinely observe the photospheric and chromospheric
magnetic fields, the proposed airborne spectrometer will take a step
toward the direct observation of coronal fields by measuring plasma
emission in the infrared at high spatial and spectral resolution. The
targeted lines are five forbidden magnetic dipole transitions between
1.4 and 4 um. The airborne system will consist of a telescope,
grating spectrometer and pointing/stabilization system to be flown
on the NSF/NCAR High-performance Instrumented Airborne Platform for
Environmental Research (HIAPER) during the 21 August 2017 total solar
eclipse. We will discuss the scientific objectives of the 2017 flight,
describe details of the instrument design, and present the observing
program for the eclipse.
---------------------------------------------------------
Title: On Helium 1083 nm Line Polarization during the Impulsive
Phase of an X1 Flare
Authors: Judge, Philip G.; Kleint, Lucia; Sainz Dalda, Alberto
2015ApJ...814..100J Altcode: 2015arXiv151009218J
We analyze spectropolarimetric data of the He i 1083 nm multiplet
(1s2s{}<SUP>3</SUP>{S}<SUB>1</SUB>-1s2p{}<SUP>3</SUP>{P}<SUB>2,1,0</SUB><SUP>o</SUP>)
during the X1 flare SOL2014-03-29T17:48, obtained with the Facility
Infrared Spectrometer (FIRS) at the Dunn Solar Telescope. While scanning
active region NOAA 12017, the FIRS slit crossed a flare ribbon during
the impulsive phase, when the helium line intensities turned into
emission at ≲twice the continuum intensity. Their linear polarization
profiles are of the same sign across the multiplet including 1082.9
nm, intensity-like, at ≲5% of the continuum intensity. Weaker
Zeeman-induced linear polarization is also observed. Only the strongest
linear polarization coincides with hard X-ray (HXR) emission at 30-70
keV observed by RHESSI. The polarization is generally more extended and
lasts longer than the HXR emission. The upper J = 0 level of the 1082.9
nm component is unpolarizable thus, lower-level polarization is the
culprit. We make non-LTE radiative transfer calculations in thermal
slabs optimized to fit only intensities. The linear polarizations
are naturally reproduced, through a systematic change of sign with
wavelength of the radiation anisotropy when slab optical depths of
the 1082.9 component are ≲1. Neither are collisions with beams of
particles needed, nor can they produce the same sign of polarization
of the 1082.9 and 1083.0 nm components. The He i line polarization
merely requires heating sufficient to produce slabs of the required
thickness. Widely different polarizations of Hα, reported previously,
are explained by different radiative anisotropies arising from slabs
of different optical depths.
---------------------------------------------------------
Title: UV Spectra, Bombs, and the Solar Atmosphere
Authors: Judge, Philip G.
2015ApJ...808..116J Altcode: 2015arXiv150608336J
A recent analysis of UV data from the Interface Region Imaging
Spectrograph (IRIS) reports plasma “bombs” with temperatures
near 8 × 10<SUP>4</SUP> K within the solar photosphere. This is a
curious result, first because most bomb plasma pressures p (the largest
reported case exceeds 10<SUP>3</SUP> dyn cm<SUP>-2</SUP>) fall well
below photospheric pressures (\gt 7× {10}<SUP>3</SUP>), and second,
UV radiation cannot easily escape from the photosphere. In the present
paper the IRIS data is independently analyzed. I find that the bombs
arise from plasma originally at pressures between ≤ 80 and 800 dyne
cm<SUP>-2</SUP> before explosion, i.e., between ≥ 850 and 550 km
above {τ }<SUB>500</SUB>=1. This places the phenomenon’s origin in
the low-mid chromosphere or above. I suggest that bomb spectra are
more compatible with Alfvénic turbulence than with bi-directional
reconnection jets.
---------------------------------------------------------
Title: Century-long monitoring of solar irradiance and Earth's albedo
using a stable scattering target in space.
Authors: Judge, P. G.; Egeland, R.
2015MNRAS.448L..90J Altcode: 2015arXiv150101253J
An inert sphere of a few metres diameter, placed in a special stable
geosynchronous orbit in perpetuo, can be used for a variety of
scientific experiments. Ground-based observations of such a sphere,
`GeoSphere', can resolve very difficult problems in measuring the
long-term solar irradiance. GeoSphere measurements will also help us
understand the evolution of Earth's albedo and climate over at least
the next century.
---------------------------------------------------------
Title: Photon Mean Free Paths, Scattering, and Ever-Increasing
Telescope Resolution
Authors: Judge, P. G.; Kleint, L.; Uitenbroek, H.; Rempel, M.;
Suematsu, Y.; Tsuneta, S.
2015SoPh..290..979J Altcode: 2014arXiv1409.7866J; 2015SoPh..tmp....3J
We revisit an old question: what are the effects of observing stratified
atmospheres on scales below a photon mean free path λ? The mean free
path of photons emerging from the solar photosphere and chromosphere
is ≈ 10<SUP>2</SUP> km. Using current 1 m-class telescopes, λ is
on the order of the angular resolution. But the Daniel K. Inoue Solar
Telescope will have a diffraction limit of 0.020″ near the atmospheric
cutoff at 310 nm, corresponding to 14 km at the solar surface. Even
a small amount of scattering in the source function leads to physical
smearing due to this solar "fog", with effects similar to a degradation
of the telescope point spread function. We discuss a unified picture
that depends simply on the nature and amount of scattering in the
source function. Scalings are derived from which the scattering in the
solar atmosphere can be transcribed into an effective Strehl ratio,
a quantity useful to observers. Observations in both permitted (e.g.,
Fe I 630.2 nm) and forbidden (Fe I 525.0 nm) lines will shed light on
both instrumental performance as well as on small-scale structures in
the solar atmosphere.
---------------------------------------------------------
Title: On the Origin of a Sunquake during the 2014 March 29 X1 Flare
Authors: Judge, Philip G.; Kleint, Lucia; Donea, Alina; Sainz Dalda,
Alberto; Fletcher, Lyndsay
2014ApJ...796...85J Altcode: 2014arXiv1409.6268J
Helioseismic data from the Helioseismic Magnetic Imager instrument have
revealed a sunquake associated with the X1 flare SOL2014-03-29T17:48
in active region NOAA 12017. We try to discover if acoustic-like
impulses or actions of the Lorentz force caused the sunquake. We
analyze spectropolarimetric data obtained with the Facility Infrared
Spectrometer (FIRS) at the Dunn Solar Telescope (DST). Fortunately,
the FIRS slit crossed the flare kernel close to the acoustic source
during the impulsive phase. The infrared FIRS data remain unsaturated
throughout the flare. Stokes profiles of lines of Si I 1082.7 nm and He
I 1083.0 nm are analyzed. At the flare footpoint, the Si I 1082.7 nm
core intensity increases by a factor of several, and the IR continuum
increases by 4% ± 1%. Remarkably, the Si I core resembles the classical
Ca II K line's self-reversed profile. With nLTE radiative models of
H, C, Si, and Fe, these properties set the penetration depth of flare
heating to 100 ± 100 km (i.e., photospheric layers). Estimates of the
non-magnetic energy flux are at least a factor of two less than the
sunquake energy flux. Milne-Eddington inversions of the Si I line show
that the local magnetic energy changes are also too small to drive the
acoustic pulse. Our work raises several questions. Have we missed the
signature of downward energy propagation? Is it intermittent in time
and/or non-local? Does the 1-2 s photospheric radiative damping time
discount compressive modes? <P />The National Center for Atmospheric
Research is sponsored by the National Science Foundation.
---------------------------------------------------------
Title: A Flare Observed in Coronal, Transition Region, and Helium
I 10830 Å Emissions
Authors: Zeng, Zhicheng; Qiu, Jiong; Cao, Wenda; Judge, Philip G.
2014ApJ...793...87Z Altcode: 2014arXiv1408.0236Z
On 2012 June 17, we observed the evolution of a C-class flare associated
with the eruption of a filament near a large sunspot in the active
region NOAA 11504. We obtained high spatial resolution filtergrams
using the 1.6 m New Solar Telescope at the Big Bear Solar Observatory
in broadband TiO at 706 nm (bandpass: 10 Å) and He I 10830 Å narrow
band (bandpass: 0.5 Å, centered 0.25 Å to the blue). We analyze the
spatio-temporal behavior of the He I 10830 Å data, which were obtained
over a 90”×90” field of view with a cadence of 10 s. We also analyze
simultaneous data from the Atmospheric Imaging Assembly and Extreme
Ultraviolet Variability Experiment instruments on board the Solar
Dynamics Observatory spacecraft, and data from the Reuven Ramaty High
Energy Solar Spectroscopic Imager and GOES spacecrafts. Non-thermal
effects are ignored in this analysis. Several quantitative aspects
of the data, as well as models derived using the "0D" enthalpy-based
thermal evolution of loops model code, indicate that the triplet
states of the 10830 Å multiplet are populated by photoionization of
chromospheric plasma followed by radiative recombination. Surprisingly,
the He II 304 Å line is reasonably well matched by standard emission
measure calculations, along with the C IV emission which dominates
the Atmosphere Imaging Assembly 1600 Å channel during flares. This
work lends support to some of our previous work combining X-ray, EUV,
and UV data of flares to build models of energy transport from corona
to chromosphere.
---------------------------------------------------------
Title: Detection of Supersonic Downflows and Associated Heating
Events in the Transition Region above Sunspots
Authors: Kleint, L.; Antolin, P.; Tian, H.; Judge, P.; Testa, P.;
De Pontieu, B.; Martínez-Sykora, J.; Reeves, K. K.; Wuelser, J. P.;
McKillop, S.; Saar, S.; Carlsson, M.; Boerner, P.; Hurlburt, N.; Lemen,
J.; Tarbell, T. D.; Title, A.; Golub, L.; Hansteen, V.; Jaeggli, S.;
Kankelborg, C.
2014ApJ...789L..42K Altcode: 2014arXiv1406.6816K
Interface Region Imaging Spectrograph data allow us to study the solar
transition region (TR) with an unprecedented spatial resolution of
0.”33. On 2013 August 30, we observed bursts of high Doppler shifts
suggesting strong supersonic downflows of up to 200 km s<SUP>-1</SUP>
and weaker, slightly slower upflows in the spectral lines Mg II h
and k, C II 1336, Si IV 1394 Å, and 1403 Å, that are correlated
with brightenings in the slitjaw images (SJIs). The bursty behavior
lasts throughout the 2 hr observation, with average burst durations
of about 20 s. The locations of these short-lived events appear to
be the umbral and penumbral footpoints of EUV loops. Fast apparent
downflows are observed along these loops in the SJIs and in the
Atmospheric Imaging Assembly, suggesting that the loops are thermally
unstable. We interpret the observations as cool material falling
from coronal heights, and especially coronal rain produced along the
thermally unstable loops, which leads to an increase of intensity
at the loop footpoints, probably indicating an increase of density
and temperature in the TR. The rain speeds are on the higher end of
previously reported speeds for this phenomenon, and possibly higher
than the free-fall velocity along the loops. On other observing days,
similar bright dots are sometimes aligned into ribbons, resembling
small flare ribbons. These observations provide a first insight into
small-scale heating events in sunspots in the TR.
---------------------------------------------------------
Title: CLE: Coronal line synthesis
Authors: Judge, Philip G.; Casini, Roberto
2014ascl.soft07010J Altcode:
CLE, written in Fortran 77, synthesizes Stokes profiles of forbidden
lines such as Fe XIII 1074.7nm, formed in magnetic dipole transitions
under coronal conditions. The lines are assumed to be optically thin,
excited by (anisotropic) photospheric radiation and thermal particle
collisions.
---------------------------------------------------------
Title: A particular seismic event generated during the solar flare
2014 March 29
Authors: Donea, Alina C.; Judge, P.; Kleint, L.; Sainz-Dalda, Alberto
2014shin.confE..49D Altcode:
The X1.3 solar flare of 2014 March 29 from AR 2017 was extremely well
observed, from both space and the ground. Helioseismic observations
from the Helioseismic Magnetic Imager (HMI) aboard the Solar Dynamics
Observatory (SDO) indicate that this flare generated a weak seismic
transient. All previous strong seismic transients to date have
emanated from sunspot penumbrae, but the source of this transient
lay outside the active-region penumbra close to a magnetic pore. <P
/>Uniquely, Kleint and Sainz Dalda captured ground based imaging
and slit spectropolarimetry of this flare using the IBIS and FIRS
instruments respectively, at the Dunn Solar Telescope in Sunspot,
New Mexico. Here we report only on FIRS data along with space-based
data, IBIS data will be reported elsewhere. The FIRS infrared data
are not saturated even during the flare, which was observed through
the rise and decay phases. We are still investigating the origins of
peculiar, Zeeman-induced polarization in the He I 1083 nm multiplet. <P
/>Using spectropolarimetric data of Si I and He I lines from FIRS, we
investigate the evolution of both photosphere and chromosphere above
and around the seismic source. Together with data from AIA and from
RHESSI, these data offer unique new insight into how the flare energy
is channeled into and through the photosphere into the Sun's interior
as a seismic transient. We present acoustic properties of the seismic
event and their relationship to photospheric and chromospheric plasma
and magnetic fields from FIRS, and to the evolving plasmas seen from
space from UV to X-ray wavelengths.
---------------------------------------------------------
Title: Insights on the solar dynamo from stellar observations
Authors: Egeland, Ricky; Martens, Petrus C.; Judge, Philip G.
2014AAS...22421105E Altcode:
A successful dynamo model should not only explain the broad
characteristics of the magnetic field cycle for the Sun (22-year sunspot
cycle with polarity reversals, migration of active latitudes toward
the poles throughout the cycle, and Joy’s law), but should also be
able to explain the cycling behavior observed in Solar-analog stars,
which are very close to the Sun in essential characteristics. Our aim
is to develop a set of constraints on dynamo models from the observed
behavior of solar-analog stars obtained from a number of long-running
synoptic surveys of cycling activity (Mount Wilson Observatory HK
survey, Lowel Observatory Solar-Stellar Spectrograph, and the Fairborn
Observatory Automatic Photoelectric Telescope survey), in conjuncture
with stellar rotation and differential rotation data obtained by the
Kepler Mission and other sources. By carefully piecing together the
best data available today, we will provide an improved understanding
of the parameter space in which Solar-like dynamos operate.
---------------------------------------------------------
Title: A FLARE OBSERVED IN CORONAL, TRANSITION REGION AND HELIUM I
10830 Å EMISSIONS
Authors: Zeng, Zhicheng; Qiu, Jiong; Cao, Wenda; Judge, Philip G.
2014AAS...22412309Z Altcode:
On June 17, 2012, we observed the evolution of a C-class flare
associated with the eruption of a filament near a large sunspot in
the active region NOAA 11504. We obtained high spatial resolution
filtergrams using the 1.6 m New Solar Telescope at the Big Bear
Solar Observatory in TiO broad-band (bandpass: 10 Å)and He I 10830
Å narrow-band (bandpass: 0.5 Å, centered 0.25 Å to the blue). We
analyze the spatio-temporal behavior of the He I 10830 Å data, which
were obtained over a 90×90 arcsends field of view with a cadence
of 10 sec. We also analyze simultaneous data from the Atmospheric
Imaging Assembly and Extreme Ultraviolet Variability Experiment
instruments on board the Solar Dynamics Observatoryspacecraft, and
data from Reuven Ramaty High Energy Solar Spectroscopic Imager and
GOES spacecrafts. Several quantitative aspects of the data, as well as
models derived using the “0D” Enthalpy-Based Thermal Evolution of
Loops model (EBTEL: Klimchuk et al. 2008) code, indicate that the 10830
Å multiplet is formed primarily by photoionization of chromospheric
plasma followed by radiative recombination. Surprisingly, the He II
304 Å line is reasonably well matched by standard emission measure
calculations, along with the C IV emission which dominates the AIA
1600 Å channel during flares. This work lends support to some of our
previous work combining X-ray, EUV and UV data of flares to buildmodels
of energy transport from corona to chromosphere.
---------------------------------------------------------
Title: Single-point Inversion of the Coronal Magnetic Field
Authors: Plowman, Joseph; Casini, Roberto; Judge, Philip G.; Tomczyk,
Steven
2014AAS...22432324P Altcode:
The Fe XIII 10747 and 10798 Å lines observed in the solar corona
are sensitive to the coronal magnetic field in such a way that,
in principle, the full vector field at a point on the line of sight
can be inferred from their combined polarization signals. This paper
presents analytical inversion formulae for the field parameters and
analyzes the uncertainty of magnetic field measurements made from such
observations, assuming emission dominated by a single region along the
line-of-sight. We consider the case of the current CoMP instrument
as well as the future COSMO and ATST instruments. Uncertainties are
estimated with a direct analytic inverse and with an MCMC algorithm. We
find that (in effect) two components of the vector field can be
recovered with CoMP, and well-recovered with COSMO or ATST, but that
the third component can only be recovered when the solar magnetic
field is strong and optimally oriented.
---------------------------------------------------------
Title: Spectropolarimetric Observations of a Small Active Region
with IBIS
Authors: Tarr, Lucas; Judge, Philip G.
2014AAS...22442204T Altcode:
We have used the Interferometric BI--dimensional Spectrograph (IBIS)
instrument at the Dunn Solar Telescope to measure the polarimetric
Stokes IQUV signals for the small active region, NOAA 11304. We used
three lines generally corresponding to three atmospheric heights ranging
from the photosphere to low corona: Fe I 6302Å, NaI 5896Å, and CaII
8542Å. Each set of profiles has been inverted using the NICOLE code to
determine the vector magnetic field at the three heights throughout the
field of view, or the line--of--sight field, as allowed by the level
of polarization signal. Comparisons are made between the magnetic and
thermal structures with the goal of constraining chromospheric models
with the information obtained at multiple heights.
---------------------------------------------------------
Title: FORWARD: Forward modeling of coronal observables
Authors: Gibson, Sarah E.; Kucera, Therese A.; Casini, Roberto; Dove,
James; Forland, Blake; Judge, Philip; Rachmeler, Laurel
2014ascl.soft05007G Altcode: 2014ascl.soft05007F
FORWARD forward models various coronal observables and can access
and compare existing data. Given a coronal model, it can produce
many different synthetic observables (including Stokes polarimetry),
as well as plots of model plasma properties (density, magnetic field,
etc.). It uses the CHIANTI database (ascl:9911.004) and CLE polarimetry
synthesis code, works with numerical model datacubes, interfaces with
the PFSS module of SolarSoft (ascl:1208.013), includes several analytic
models, and connects to the Virtual Solar Observatory for downloading
data in a format directly comparable to model predictions.
---------------------------------------------------------
Title: The Solar Chromosphere Observed at 1 Hz and 0.”2 Resolution
Authors: Lipartito, Isabel; Judge, Philip G.; Reardon, Kevin; Cauzzi,
Gianna
2014ApJ...785..109L Altcode: 2014arXiv1401.4474L
We recently reported extremely rapid changes in chromospheric fine
structure observed using the IBIS instrument in the red wing of
Hα. Here, we examine data obtained during the same observing run
(2010 August 7), of a mature active region NOAA 11094. We analyze
more IBIS data including wavelength scans and data from the Solar
Dynamics Observatory, all from within a 30 minute interval. Using a
slab radiative transfer model, we investigate the physical nature of
fibrils in terms of tube-like versus sheet-like structures. Principal
Component Analysis shows that the very rapid Hα variations in the
line wings depend mostly on changes of line width and line shift,
but for Ca II 854.2 the variations are dominated by changes in column
densities. The tube model must be rejected for a small but significant
class of fibrils undergoing very rapid changes. If our wing data arise
from the same structures leading to "type II spicules," our analysis
calls into question much recent work. Instead, the data do not reject
the hypothesis that some fibrils are optical superpositions of plasma
collected into sheets. We review how Parker's theory of tangential
discontinuities naturally leads to plasma collecting into sheets,
and show that the sheet picture is falsifiable. Chromospheric fine
structures seem to be populated by both tubes and sheets. We assess the
merits of spectral imaging versus slit spectroscopy for future studies.
---------------------------------------------------------
Title: From Forbidden Coronal Lines to Meaningful Coronal Magnetic
Fields
Authors: Judge, P. G.; Habbal, S.; Landi, E.
2013SoPh..288..467J Altcode: 2013arXiv1304.3863J
We review methods to measure magnetic fields within the corona using
the polarized light in magnetic-dipole (M1) lines. We are particularly
interested in both the global magnetic-field evolution over a solar
cycle, and the local storage of magnetic free energy within coronal
plasmas. We address commonly held skepticisms concerning angular
ambiguities and line-of-sight confusion. We argue that ambiguities are,
in principle, no worse than more familiar remotely sensed photospheric
vector fields, and that the diagnosis of M1 line data would benefit
from simultaneous observations of EUV lines. Based on calculations and
data from eclipses, we discuss the most promising lines and different
approaches that might be used. We point to the S-like [Fe XI] line
(J=2 to J=1) at 789.2 nm as a prime target line (for the Advanced
Technology Solar Telescope (ATST) for example) to augment the hotter
1074.7 and 1079.8 nm Si-like lines of [Fe XIII] currently observed by
the Coronal Multi-channel Polarimeter (CoMP). Significant breakthroughs
will be made possible with the new generation of coronagraphs, in three
distinct ways: i) through single-point inversions (which encompasses
also the analysis of MHD wave modes), ii) using direct comparisons of
synthetic MHD or force-free models with polarization data, and iii)
using tomographic techniques.
---------------------------------------------------------
Title: Using large telescopes to answer: why must the Sun have a
chromosphere and corona?
Authors: Judge, P.; Casini, R.
2012IAUSS...6E.106J Altcode:
I will discuss the potential for ground-based telescopes such as
the ATST to make breakthrough discoveries about the long standing
mysteries of the solar chromosphere and corona. The biggest advances
will hinge upon the ability to diagnose magnetic fields through high
s/n spectropolarimetry.
---------------------------------------------------------
Title: Removal of Spectro-polarimetric Fringes by Two-dimensional
Pattern Recognition
Authors: Casini, R.; Judge, P. G.; Schad, T. A.
2012ApJ...756..194C Altcode: 2012arXiv1208.5104C
We present a pattern-recognition-based approach to the problem of
the removal of polarized fringes from spectro-polarimetric data. We
demonstrate that two-dimensional principal component analysis can
be trained on a given spectro-polarimetric map in order to identify
and isolate fringe structures from the spectra. This allows us,
in principle, to reconstruct the data without the fringe component,
providing an effective and clean solution to the problem. The results
presented in this paper point in the direction of revising the way
that science and calibration data should be planned for a typical
spectro-polarimetric observing run.
---------------------------------------------------------
Title: Analysis of Seeing-induced Polarization Cross-talk and
Modulation Scheme Performance
Authors: Casini, R.; de Wijn, A. G.; Judge, P. G.
2012ApJ...757...45C Altcode: 2011arXiv1107.0367C
We analyze the generation of polarization cross-talk in Stokes
polarimeters by atmospheric seeing, and its effects on the noise
statistics of spectropolarimetric measurements for both single-beam
and dual-beam instruments. We investigate the time evolution of
seeing-induced correlations between different states of one modulation
cycle and compare the response to these correlations of two popular
polarization modulation schemes in a dual-beam system. Extension of
the formalism to encompass an arbitrary number of modulation cycles
enables us to compare our results with earlier work. Even though we
discuss examples pertinent to solar physics, the general treatment
of the subject and its fundamental results might be useful to a wider
community.
---------------------------------------------------------
Title: Confronting a solar irradiance reconstruction with solar and
stellar data
Authors: Judge, P. G.; Lockwood, G. W.; Radick, R. R.; Henry, G. W.;
Shapiro, A. I.; Schmutz, W.; Lindsey, C.
2012A&A...544A..88J Altcode:
Context. A recent paper by Shapiro and colleagues (2011, A&A,
529, A67) reconstructs spectral and total irradiance variations of
the Sun during the holocene. Aims. In this note, we comment on why
their methodology leads to large (0.5%) variations in the solar TSI on
century-long time scales, in stark contrast to other reconstructions
which have ∼ 0.1% variations. Methods. We examine the amplitude
of the irradiance variations from the point of view of both solar
and stellar data. Results. Shapiro et al.'s large amplitudes arise
from differences between the irradiances computed from models A and C
of Fontenla and colleagues, and from their explicit assumption that
the radiances of the quiet Sun vary with the cosmic ray modulation
potential. We suggest that the upper photosphere, as given by model A,
is too cool, and discuss relative contributions of local vs. global
dynamos to the magnetism and irradiance of the quiet Sun. We compare
the slow (>22 yr) components of the irradiance reconstructions with
secular changes in stellar photometric data that span 20 years or less,
and find that the Sun, if varying with such large amplitudes, would
still lie within the distribution of stellar photometric variations
measured over a 10-20 year period. However, the stellar time series
are individually too short to see if the reconstructed variations will
remain consistent with stellar variations when observed for several
decades more. Conclusions. By adopting model A, Shapiro et al. have
over-estimated quiet-Sun irradiance variations by about a factor of
two, based upon a re-analysis of sub-mm data from the James Clerk
Maxwell telescope. But both estimates are within bounds set by current
stellar data. It is therefore vital to continue accurate photometry of
solar-like stars for at least another decade, to reveal secular and
cyclic variations on multi-decadal time scales of direct interest to
the Sun.
---------------------------------------------------------
Title: Evidence for Sheet-like Elementary Structures in the Sun's
Atmosphere?
Authors: Judge, Philip G.; Reardon, Kevin; Cauzzi, Gianna
2012ApJ...755L..11J Altcode:
Narrow, thread-like structures in the Sun's chromosphere are currently
understood to be plasma guided along narrow tubes of magnetic flux. We
report on 1 s cadence imaging spectroscopic measurements of the Hα
line with the IBIS Fabry-Pérot instrument at the Dunn Solar Telescope,
obtained +0.11 nm from line center. Rapid changes grossly exceeding
the Alfvén speed are commonly seen along the full extent of many
chromospheric threads. We argue that only an optical superposition
effect can reasonably explain the data, analogous to striations of
curtains blowing in the wind. Other explanations appear to require
significant contrivances to avoid contradicting various aspects of
the data. We infer that the absorbing plasma exists in two-dimensional
sheet-like structures within the three-dimensional magnetofluid, related
perhaps to magnetic tangential discontinuities. This interpretation
demands a re-evaluation of basic assumptions about low-β solar plasmas,
as advocated by Parker, with broader implications in astrophysics
and plasma physics. Diverse, high-cadence observations are needed to
further define the relationship between magnetic field and thermal
fine structure.
---------------------------------------------------------
Title: Solar and stellar activity: diagnostics and indices
Authors: Judge, Philip G.; Thompson, Michael J.
2012IAUS..286...15J Altcode: 2012arXiv1201.4625J
We summarize the fifty-year concerted effort to place the “activity”
of the Sun in the context of the stars. As a working definition of solar
activity in the context of stars, we adopt those globally-observable
variations on time scales below thermal time scales, of ~10<SUP>5</SUP>
yr for the convection zone. So defined, activity is dominated by
magnetic-field evolution, including the 22-year Hale cycle, the typical
time it takes for the quasi-periodic reversal in which the global
magnetic-field takes place. This is accompanied by sunspot variations
with 11 year periods, known since the time of Schwabe, as well as faster
variations due to rotation of active regions and flaring. “Diagnostics
and indices” are terms given to the indirect signatures of varying
magnetic-fields, including the photometric (broad-band) variations
associated with the sunspot cycle, and variations of the accompanying
heated plasma in higher layers of stellar atmospheres seen at special
optical wavelengths, and UV and X-ray wavelengths. Our attention is
also focussed on the theme of the Symposium by examining evidence for
deep and extended minima of stars, and placing the 70-year long solar
Maunder Minimum into a stellar context.
---------------------------------------------------------
Title: Spectropolarimetry of a Limb Active Region and its Cool
Coronal Structures
Authors: Judge, Philip G.; Kleint, L.; Casini, R.; Schad, T.
2012AAS...22052119J Altcode:
During the SDO mission we have regularly used the IBIS and FIRS
spectropolarimeters at the Dunn Solar Telescope to measure magnetic
fields and plasma parameters from photosphere up to the coronal
base. Here we analyze data of a region at and above the east limb (later
named NOAA 11302) obtained on September 22nd 2011. The measurements
show an erupting prominence, remarkably uniform cool plumes and some
material seemingly draining into the active region along post-flare
loops. The imaging Fabry-Perot instrument IBIS obtained 30 scans of
intensity spectra (30s cadence) and 40 scans of Stokes parameters
(90s cadence) in lines of Fe I 630 nm, Na I 596 nm, Ca II 852 nm and
H-alpha 656 nm, with an angular resolution near 0.2", over a 40"x80"
field of view. The FIRS slit was scanned across the solar image to
obtain Stokes profiles including lines of Si I 1028.7 nm and He I 1083
nm. We obtained 3 FIRS scans covering a 90"x75" area with cadences of
between half an hour and an hour simultaneously with IBIS, at a lower
angular resolution. Simultaneous broad band Ca II K and G-band data
were obtained with a cadence of 5s. We discuss the vector magnetic
fields and plasma properties of NOAA 11302, with emphasis on cool <P
/>plasma structures extending many Mm into the corona.
---------------------------------------------------------
Title: Radiating Current Sheets in the Solar Chromosphere
Authors: Goodman, Michael L.; Judge, Philip G.
2012ApJ...751...75G Altcode: 2014arXiv1406.1211G
An MHD model of a hydrogen plasma with flow, an energy equation,
NLTE ionization and radiative cooling, and an Ohm's law with
anisotropic electrical conduction and thermoelectric effects
is used to self-consistently generate atmospheric layers over a
50 km height range. A subset of these solutions contains current
sheets and has properties similar to those of the lower and middle
chromosphere. The magnetic field profiles are found to be close to
Harris sheet profiles, with maximum field strengths ~25-150 G. The
radiative flux F<SUB>R</SUB> emitted by individual sheets is ~4.9 ×
10<SUP>5</SUP>-4.5 × 10<SUP>6</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>,
to be compared with the observed chromospheric emission rate of
~10<SUP>7</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>. Essentially all
emission is from regions with thicknesses ~0.5-13 km containing the
neutral sheet. About half of F<SUB>R</SUB> comes from sub-regions with
thicknesses 10 times smaller. A resolution <~ 5-130 m is needed to
resolve the properties of the sheets. The sheets have total H densities
~10<SUP>13</SUP>-10<SUP>15</SUP> cm<SUP>-3</SUP>. The ionization
fraction in the sheets is ~2-20 times larger, and the temperature is
~2000-3000 K higher than in the surrounding plasma. The Joule heating
flux F<SUB>J</SUB> exceeds F<SUB>R</SUB> by ~4%-34%, the difference
being balanced in the energy equation mainly by a negative compressive
heating flux. Proton Pedersen current dissipation generates ~62%-77%
of the positive contribution to F<SUB>J</SUB> . The remainder of this
contribution is due to electron current dissipation near the neutral
sheet where the plasma is weakly magnetized.
---------------------------------------------------------
Title: Radiating Current Sheets in the Solar Chromosphere
Authors: Goodman, Michael L.; Judge, P. G.
2012AAS...22052116G Altcode:
An MHD model of a Hydrogen plasma with flow, an energy equation,
NLTE ionization and radiative cooling, and an Ohm's law with
anisotropic electrical conduction and thermoelectric effects is used
to self-consistently generate atmospheric layers over a 50 km height
range. A subset of these solutions contain current sheets, and have
properties similar to those of the lower and middle chromosphere. The
magnetic field profiles are found to be close to Harris sheet profiles,
with maximum field strengths 25-150 G. The radiative flux F_R emitted
by individual sheets is 4.9 x 10^5 - 4.5 x 10^6 ergs-cm^{-2}-s^{-1},
to be compared with the observed chromospheric emission rate of 10^7
ergs-cm^{-2}-s^{-1}. Essentially all emission is from regions with
thicknesses 0.5 - 13 km containing the neutral sheet. About half of F_R
comes from sub-regions with thicknesses 10 times smaller. A resolution
< 5-130 m is needed to resolve the properties of the sheets. The
sheets have total H densities 10^{13}-10^{15} cm^{-3}. The ionization
fraction in the sheets is 2-20 times larger, and the temperature is
2000-3000 K higher than in the surrounding plasma. The Joule heating
flux F_J exceeds F_R by 4-34 %, the difference being balanced
in the energy equation mainly by a negative compressive heating
flux. Proton Pedersen current dissipation generates 62-77 % of the
positive contribution to F_J. The remainder of this contribution
is due to electron current dissipation near the neutral sheet where
the plasma is weakly magnetized. These solutions represent the first,
first principles theoretical proof of the existence of radiating current
sheets under chromospheric conditions. The existence of these solutions
suggests the existence of sub-resolution, horizontal current sheets
in the chromosphere that are sites of strong Joule heating driven
radiative emission.
---------------------------------------------------------
Title: Key- or tomb- stones in the bridge from photosphere to corona?
Authors: Judge, Philip G.
2012decs.confE..28J Altcode:
The Sun's atmosphere must get from photospheric pressures of 10(5)
dyn cm(-2) , where gas pressures and Reynolds stresses dominate, to
coronal pressures of 10(-1) dyne cm(-2) , where magnetic stresses become
dominant, within a mere 2000km. Outside of sunspots, the photospheric
boundary layer exhibits hydrodynamic turbulent structure. The low
pressure chromosphere- corona transition, while poorly understood,
is clearly ordered by magnetic fields. Across the intervening scale
heights, the richness of coupled magneto- hydrodynamics in a partially
ionized atmosphere out of LTE, within which ions become magnetized,
somehow leads to what we observe as the "magnetic chromosphere". We
understand only the overall thermal structure of the chromosphere,
it behaves as a thermostat: in response to heating energy is stored
in latent heat of ionization and lost to radiation. But in terms of
the magnetic structure, we must deal with: interaction with the plasma
including multi-fluid effects, especially ion-neutral damping; effects
of stratification on coupling wave modes; the existence of weak,
discontinuous solutions to the MHD equations (current sheets). To
generate discussion, I will argue that we have little idea what the
chromosphere does to the incoming flux of EM energy from beneath,
and that current generations of MHD models are far from providing
this understanding. We must not let apparent "successes" of, e.g.,
potential field models on large scales seduce us into thinking we
understand how the Sun makes the photosphere-corona transition.
---------------------------------------------------------
Title: The Connection of Type II Spicules to the Corona
Authors: Judge, Philip G.; de Pontieu, Bart; McIntosh, Scott W.;
Olluri, Kosovare
2012ApJ...746..158J Altcode: 2011arXiv1112.6174D; 2011arXiv1112.6174J
We examine the hypothesis that plasma associated with "Type II"
spicules is heated to coronal temperatures, and that the upward
moving hot plasma constitutes a significant mass supply to the solar
corona. One-dimensional hydrodynamical models including time-dependent
ionization are brought to bear on the problem. These calculations
indicate that heating of field-aligned spicule flows should produce
significant differential Doppler shifts between emission lines formed
in the chromosphere, transition region, and corona. At present,
observational evidence for the computed 60-90 km s<SUP>-1</SUP>
differential shifts is weak, but the data are limited by difficulties
in comparing the proper motion of Type II spicules with spectral
and kinematic properties of an associated transition region and
coronal emission lines. Future observations with the upcoming infrared
interferometer spectrometer instrument should clarify if Doppler shifts
are consistent with the dynamics modeled here.
---------------------------------------------------------
Title: Spectropolarimetry Of The Footpoints Of A C-class Flare In
The Chromosphere
Authors: Kleint, Lucia; Judge, P.
2011SPD....42.0308K Altcode: 2011BAAS..43S.0308K
Flares are well-known solar phenomena but have rarely been
imaged in high resolution polarimetry and even less often in the
chromosphere. We observed the declining phase of a C-class flare in
NOAA 10940 on January 29, 2007 with the IBIS instrument (0.17"/px),
taking quasi-simultaneous spectropolarimetric images in the chromosphere
(8542 [[Unable to Display Character: &#506]]) and in the photosphere
(6302 [[Unable to Display Character: &#506]]). <P />Only the inner
wings and core of the chromospheric line are seen to brighten in IBIS,
the underlying photosphere remaining undisturbed. TRACE images reveal
the connectivity of the chromospheric flaring plasma to the overlying
corona: IBIS fortuitously captured the chromospheric flares associated
with both footpoints of a loop systems seen in TRACE. <P />Our hour-long
image sequence shows the evolution and weakening of the chromospheric
flare, and reveals unresolved opposite magnetic field components with
large velocities with respect to the average Sun. In the chromosphere,
we find redshifted components but in the photosphere we see observe
blueshifts. We will present high resolution movies of the flaring
plasma seen in both footpoints of the loop system. We will discuss the
implications of these measurements for models of the storage and release
of energy for this class of small flare, and possible connections to
the formation of the penumbra that appears later at this location.
---------------------------------------------------------
Title: A Ring of Polarized Light: Evidence for Twisted Coronal
Magnetism in Cavities
Authors: Dove, J. B.; Gibson, S. E.; Rachmeler, L. A.; Tomczyk, S.;
Judge, P.
2011ApJ...731L...1D Altcode:
Coronal prominence cavities may be manifestations of twisted or sheared
magnetic fields capable of storing the energy required to drive solar
eruptions. The Coronal Multi-Channel Polarimeter (CoMP), recently
installed at Mauna Loa Solar Observatory, can measure polarimetric
signatures of current-carrying magnetohydrodynamic (MHD) systems. For
the first time, this instrument offers the capability of daily full-Sun
observations of the forbidden lines of Fe XIII with high enough
spatial resolution and throughput to measure polarimetric signatures of
current-carrying MHD systems. By forward-calculating CoMP observables
from analytic MHD models of spheromak-type magnetic flux ropes, we show
that a predicted observable for such flux ropes oriented along the line
of sight is a bright ring of linear polarization surrounding a region
where the linear polarization strength is relatively depleted. We
present CoMP observations of a coronal cavity possessing such a
polarization ring.
---------------------------------------------------------
Title: Thermal Fine Structure and Magnetic Fields in the Solar
Atmosphere: Spicules and Fibrils
Authors: Judge, Philip G.; Tritschler, Alexandra; Chye Low, Boon
2011ApJ...730L...4J Altcode: 2011arXiv1102.1517J
The relationship between observed structures in the solar atmosphere
and the magnetic fields threading them is known only for the solar
photosphere, even then imprecisely. We suggest that some of the fine
structures in the more tenuous chromosphere and corona—specifically
some populations of spicules and fibrils—correspond to warps
in two-dimensional sheet-like structures, as an alternative to
conventional interpretations in terms of tube-like structures. The
sheets are perhaps related to magnetic tangential discontinuities,
which Parker has argued arise naturally in low-β conditions. Some
consequences of this suggestion, if it can be confirmed, are discussed.
---------------------------------------------------------
Title: A ring of polarized light: evidence for twisted coronal
magnetism in cavities (Invited)
Authors: Dove, J.; Rachmeler, L.; Gibson, S. E.; Judge, P. G.;
Tomczyk, S.
2010AGUFMSH54A..01D Altcode:
Determining coronal magnetic fields is crucial to modeling the processes
that power and trigger solar flares and coronal mass ejections. Coronal
prominence cavities have been modeled as magnetic flux ropes, and have
been observed to erupt bodily as coronal mass ejections. One promising
technique for establishing the magnetic morphology of cavities is to
use spectropolarimetry of the infrared (IR) forbidden lines of Fe XIII
(at 1074.7 nm and 1079.8 nm). The Coronal Multi-Channel Polarimeter is
currently situated at the Mauna Loa Solar Observatory (MLSO), and has
begun taking daily full-Sun observations of line-of-sight integrated
Stokes parameters for these lines. For a variety of analytic coronal
magnetohydrodynamic models, we have determined forward-calculations
of CoMP observables using the formalism of Judge and Casini (2001). We
show that different MHD models and orientations do yield distinguishing
observational characteristics. In particular, a common characteristic
for spheroidal flux ropes oriented along the observational line of
sight is a ring of linear polarization surrounding a region where
the linear polarization strength is relatively depleted (the heart of
darkness). Such a polarization ring has been found in an observation
of a coronal cavity taken by CoMP in April 2005 from Sacramento
Peak. Cavities are ubiquitous features, particularly at this time of
the solar cycle. The daily observations to be taken by CoMP at MLSO
will allow us to further probe these structures, constraining models
of coronal magnetism and providing a testbed for future capabilities
of the proposed Coronal Solar Magnetism Observatory (COSMO).
---------------------------------------------------------
Title: Magnetic Field Measurements at the Photosphere and Coronal Base
Authors: Judge, P. G.; Centeno, R.; Tritschler, A.; Uitenbroek, H.;
Jaeggli, S.; Lin, H.
2010AGUFMSH31A1783J Altcode:
We have obtained vector polarimetric measurements in lines of Fe I
(630nm), Ca II (854nm) and He I (1083nm) of several active regions
during 3-14 June 2010. The measurements were made at the Dunn Solar
Telescope at Sacramento Peak Observatory, using the FIRS and IBIS
instruments simultaneously. We discuss these and SDO data for NOAA
11076. The seeing was very good or excellent and the adaptive
optics system functioned well. In this preliminary analysis we
compare extrapolations of photospheric fields with the constraints
available from Stokes polarimetry, including the morphology and
kinematic properties of fibrils. Connections to the corona will also be
discussed. The implications for field extrapolations from photospheric
measurements will be discussed. We will make the reduced data freely
available on the web for interested researchers.
---------------------------------------------------------
Title: Discovery of a 1.6 Year Magnetic Activity Cycle in the
Exoplanet Host Star ι Horologii
Authors: Metcalfe, T. S.; Basu, S.; Henry, T. J.; Soderblom, D. R.;
Judge, P. G.; Knölker, M.; Mathur, S.; Rempel, M.
2010ApJ...723L.213M Altcode: 2010arXiv1009.5399M
The Mount Wilson Ca HK survey revealed magnetic activity variations in
a large sample of solar-type stars with timescales ranging from 2.5
to 25 years. This broad range of cycle periods is thought to reflect
differences in the rotational properties and the depths of the surface
convection zones for stars with various masses and ages. In 2007, we
initiated a long-term monitoring campaign of Ca II H and K emission
for a sample of 57 southern solar-type stars to measure their magnetic
activity cycles and their rotational properties when possible. We report
the discovery of a 1.6 year magnetic activity cycle in the exoplanet
host star ι Horologii and obtain an estimate of the rotation period
that is consistent with Hyades membership. This is the shortest activity
cycle so far measured for a solar-type star and may be related to the
short-timescale magnetic variations recently identified in the Sun
and HD 49933 from helioseismic and asteroseismic measurements. Future
asteroseismic observations of ι Hor can be compared to those obtained
near the magnetic minimum in 2006 to search for cycle-induced shifts in
the oscillation frequencies. If such short activity cycles are common
in F stars, then NASA's Kepler mission should observe their effects
in many of its long-term asteroseismic targets.
---------------------------------------------------------
Title: A Chromospheric Conundrum?
Authors: Judge, Philip; Knölker, Michael; Schmidt, Wolfgang;
Steiner, Oskar
2010ApJ...720..776J Altcode: 2010arXiv1007.1203J
We examine spectra of the Ca II H line, obtained under good seeing
conditions with the VTT Echelle Spectrograph in 2007 June, and
higher resolution data of the Ca II λ8542 line from Fabry-Pérot
instruments. The VTT targets were areas near disk center which included
quiet Sun and some dispersed plage. The infrared data included quiet
Sun and plage associated with small pores. Bright chromospheric network
emission patches expand little with wavelength from line wing to line
center, i.e., with increasing line opacity and height. We argue that
this simple observation has implications for the force and energy
balance of the chromosphere, since bright chromospheric network
emission is traditionally associated with enhanced local mechanical
heating which increases temperatures and pressures. Simple physical
considerations then suggest that the network chromosphere may not be
able to reach horizontal force balance with its surroundings, yet the
network is a long-lived structure. We speculate on possible reasons for
the observed behavior. By drawing attention to a potential conundrum,
we hope to contribute to a better understanding of a long-standing
unsolved problem: the heating of the chromospheric network.
---------------------------------------------------------
Title: On the Solar Chromosphere Observed at the LIMB with Hinode
Authors: Judge, Philip G.; Carlsson, Mats
2010ApJ...719..469J Altcode: 2010arXiv1004.1398J
Broadband images in the Ca II H line, from the Broadband Filter Imager
(BFI) instrument on the Hinode spacecraft, show emission from spicules
emerging from and visible right down to the observed limb. Surprisingly,
little absorption of spicule light is seen along their lengths. We
present formal solutions to the transfer equation for given (ad hoc)
source functions, including a stratified chromosphere from which
spicules emanate. The model parameters are broadly compatible with
earlier studies of spicules. The visibility of Ca II spicules down
to the limb in Hinode data seems to require that spicule emission
be Doppler shifted relative to the stratified atmosphere, either by
supersonic turbulent or organized spicular motion. The non-spicule
component of the chromosphere is almost invisible in the broadband BFI
data, but we predict that it will be clearly visible in high spectral
resolution data. Broadband Ca II H limb images give the false impression
that the chromosphere is dominated by spicules. Our analysis serves
as a reminder that the absence of a signature can be as significant
as its presence.
---------------------------------------------------------
Title: Magnetic field measurements at the photosphere and coronal base
Authors: Judge, Philip; Centeno, R.; Tritschler, A.; Uitenbroek, H.;
Jaeggli, S.; Lin, H.
2010shin.confE..56J Altcode:
We have obtained vector polarimetric measurements in lines of Fe I
(630nm), Ca II (854nm) and He I (1083) of several active regions during
3-14 June 2010. The measurements were made at the Dunn Solar Telescope
at Sacramento Peak Observatory, using the FIRS and IBIS instruments
simultaneously. We discuss data for NOAA 11076 observed on 4 June
2010. The seeing was very good or excellent and the adaptive optics
system functioned well. In this preliminary analysis we compare linear
extrapolations of photospheric fields with the constraints available
from Stokes polarimetry, including the morphology and kinematic
properties of fibrils. The implications for field extrapolations from
photospheric measurements will be discussed. We will make the reduced
data freely available on the web for interested researchers.
---------------------------------------------------------
Title: Forward modeling of spectropolarimetric data to interpret
coronal magnetic features
Authors: Rachmeler, Laurel A.; Gibson, S. E.; Dove, J.; Judge, P. G.
2010shin.confE..53R Altcode:
We present a forward model that creates various forms of coronal
observational data from simulated systems. Along with plane of
sky parameter slices and integrated emission images, this model
calculates the full Stokes vectors from forbidden infrared lines. It
is clear that photospheric magnetograph data is not sufficient to
ascertain coronal magnetic fields. The coronal Stokes vectors provide
additional information about the magnetic morphology above the solar
limb, specifically the relative strength of the integrated plane of
sky and line of sight field. Our forward model helps to determine
which physical features can be identified in the observations as a
specific component of a theoretical model, without requiring a full
3D inversion of the Stokes profiles. We have found that flux ropes
are theoretically identifiable in the simulated data, and we use this
technique to explore the disambiguation of pre-CME filament structure.
---------------------------------------------------------
Title: Historical Eclipses and the Recent Solar Minimum Corona
Authors: Judge, P. G.; Burkepile, J.; de Toma, G.; Druckmüller, M.
2010ASPC..428..171J Altcode: 2010arXiv1001.5278J
We have studied the corona as seen at the eclipses of 1878, 1900, 1901,
and others. These eclipses occurred during extended sunspot minimum
conditions. We compare these data with those of the recent solar minimum
corona, using data from the eclipses of July 22, 2009 and August 1,
2008. An attempt to characterize the global solar magnetic fields is
made. We speculate on the origin of the non-dipolar structure seen in
the 2008 and 2009 eclipse images.
---------------------------------------------------------
Title: Fabry-Pérot Versus Slit Spectropolarimetry of Pores and
Active Network: Analysis of IBIS and Hinode Data
Authors: Judge, Philip G.; Tritschler, Alexandra; Uitenbroek, Han;
Reardon, Kevin; Cauzzi, Gianna; de Wijn, Alfred
2010ApJ...710.1486J Altcode: 2010arXiv1001.0561J
We discuss spectropolarimetric measurements of photospheric (Fe I
630.25 nm) and chromospheric (Ca II 854.21 nm) spectral lines in and
around small magnetic flux concentrations, including a pore. Our
long-term goal is to diagnose properties of the magnetic field
near the base of the corona. We compare ground-based two-dimensional
spectropolarimetric measurements with (almost) simultaneous space-based
slit spectropolarimetry. We address the question of noise and crosstalk
in the measurements and attempt to determine the suitability of Ca II
measurements with imaging spectropolarimeters for the determination
of chromospheric magnetic fields. The ground-based observations
were obtained 2008 May 20, with the Interferometric Bidimensional
Spectrometer (IBIS) in spectropolarimetric mode operated at the Dunn
Solar Telescope at Sunspot, NM. The space observations were obtained
with the Spectro-Polarimeter of the Solar Optical Telescope aboard the
Japanese Hinode satellite. The agreement between the near-simultaneous
co-spatial IBIS and Hinode Stokes-V profiles at 630.25 nm is
excellent, with V/I amplitudes compatible to within 1%. The IBIS QU
measurements are affected by residual crosstalk from V, arising from
calibration inaccuracies, not from any inherent limitation of imaging
spectroscopy. We use a Principal Component Analysis to quantify the
detected crosstalk. QU profiles with V crosstalk subtracted are in
good agreement with the Hinode measurements, but are noisier owing to
fewer collected photons. Chromospheric magnetic fields are notoriously
difficult to constrain by polarization of Ca II lines alone. However,
we demonstrate that high cadence, high angular resolution monochromatic
images of fibrils in Ca II and Hα, seen clearly in IBIS observations,
can be used to improve the magnetic field constraints, under conditions
of high electrical conductivity. Such work is possible only with time
series data sets from two-dimensional spectroscopic instruments such
as IBIS, under conditions of good seeing.
---------------------------------------------------------
Title: Coronal Emission Lines as Thermometers
Authors: Judge, Philip G.
2010ApJ...708.1238J Altcode: 2009arXiv0911.4085J
Coronal emission-line intensities are commonly used to measure electron
temperatures using emission measure and/or line ratio methods. In the
presence of systematic errors in atomic excitation calculations and
data noise, the information on underlying temperature distributions
is fundamentally limited. Increasing the number of emission lines
used does not necessarily improve the ability to discriminate between
different kinds of temperature distributions.
---------------------------------------------------------
Title: The chromosphere: gateway to the corona? ...Or the purgatory
of solar physics?
Authors: Judge, P. G.
2010MmSAI..81..543J Altcode:
I argue that one should attempt to understand the solar chromosphere not
only for its own sake, but also if one is interested in the physics of:
the corona; astrophysical dynamos; space weather; partially ionized
plasmas; heliospheric UV radiation; the transition region. I outline
curious observations which I personally find puzzling and deserving
of attention.
---------------------------------------------------------
Title: Activity Cycles of Southern Asteroseismic Targets
Authors: Metcalfe, Travis S.; Judge, P. G.; Basu, S.; Henry, T. J.;
Soderblom, D. R.; Knoelker, M.; Rempel, M.
2010AAS...21542416M Altcode: 2010BAAS...42..333M
The Mount Wilson Ca HK survey revealed magnetic activity variations in
a large sample of solar-type stars with timescales ranging from 2.5
to 25 years. This broad range of cycle periods is thought to reflect
differences in the rotational properties and the depths of the surface
convection zones for stars with various masses and ages. Asteroseismic
data will soon provide direct measurements of these quantities for
individual stars, but many of the most promising targets are in the
southern sky (e.g., alpha Cen A & B, beta Hyi, mu Ara, tau Cet,
nu Ind), while long-term magnetic activity cycle surveys are largely
confined to the north. In 2007 we began using the SMARTS 1.5-m telescope
to conduct a long-term monitoring campaign of Ca II H & K emission
for a sample of 57 southern solar-type stars to measure their magnetic
activity cycles and their rotational properties when possible. This
sample includes the most likely southern asteroseismic targets to be
observed by the Stellar Oscillations Network Group (SONG), currently
scheduled to begin operations in 2012. We present selected results from
the first two years of the survey, and from the longer time baseline
sampled by a single-epoch survey conducted in 1992.
---------------------------------------------------------
Title: New Perspectives on the Photosphere/Corona Interface (Keynote)
Authors: Judge, P. G.
2009ASPC..415....7J Altcode:
I review the role of the chromosphere as the lower boundary for the
corona. I highlight the need for measurements of the chromospheric
magnetic field as the plasma regimes change from β >1 to <1,
using a striking observational example. I also review some physical
processes which can alter the magnetic free energy as it traverses the
chromosphere. Multi-fluid effects appear to be important in determining
the supply of mass, momentum and energy into the overlying corona. Such
effects have been only partly studied in the literature. I re-iterate
the obvious conclusion, often ignored, that one must understand specific
chromospheric processes if one is to have hope of addressing the nature
of the supply of mass, momentum, and energy into the corona.
---------------------------------------------------------
Title: Activity Cycles of Southern Asteroseismic Targets
Authors: Metcalfe, T. S.; Judge, P. G.; Basu, S.; Henry, T. J.;
Soderblom, D. R.; Knoelker, M.; Rempel, M.
2009arXiv0909.5464M Altcode:
The Mount Wilson Ca HK survey revealed magnetic activity variations in
a large sample of solar-type stars with timescales ranging from 2.5
to 25 years. This broad range of cycle periods is thought to reflect
differences in the rotational properties and the depths of the surface
convection zones for stars with various masses and ages. Asteroseismic
data will soon provide direct measurements of these quantities for
individual stars, but many of the most promising targets are in the
southern sky (e.g., alpha Cen A & B, beta Hyi, mu Ara, tau Cet,
nu Ind), while long-term magnetic activity cycle surveys are largely
confined to the north. In 2007 we began using the SMARTS 1.5-m telescope
to conduct a long-term monitoring campaign of Ca II H & K emission
for a sample of 57 southern solar-type stars to measure their magnetic
activity cycles and their rotational properties when possible. This
sample includes the most likely southern asteroseismic targets to be
observed by the Stellar Oscillations Network Group (SONG), currently
scheduled to begin operations in 2012. We present selected results from
the first two years of the survey, and from the longer time baseline
sampled by a single-epoch survey conducted in 1992.
---------------------------------------------------------
Title: Mining a Massive Brightpoint Database for Science
Authors: McIntosh, Scott W.; Sitongia, L.; Markel, R.; Judge, P. G.;
Davey, A. R.
2009SPD....40.1525M Altcode:
We update the analysis of McIntosh & Gurman [2005, Sol. Phys.,
228, 285] to incorporate changes to the automatic EUV Bright Point
(BP) detection algorithm of data from the Extreme-ultraviolet
Imaging Telescope (EIT) on the Solar and Heliospheric Observatory
(SOHO). We discuss the implementation of the BP catalog as a searchable
database for the community and some of the basic manipulations on
that database. We present the multi-wavelength differential rotation
rates for the previous solar cycle and make an initial foray into the
connection of this most ubiquitous coronal structure and the larger
scale magnetic dynamo.
---------------------------------------------------------
Title: On magnetic field “reconstruction”
Authors: Judge, P. G.
2009A&A...493.1121J Altcode:
Context: Solanki and colleagues have presented intriguing 3D
“reconstructions” of magnetic fields from the vector polarimetry
of the He I 1083 nm multiplet. <BR />Aims: In this Research Note I
re-examine the reconstruction technique used. <BR />Methods: Using
a simple dipole field, I examine the reconstruction technique as
applied to the theoretical fields. I assume that the He line forms in
two locations, (1) along the magnetic loops and (2) in a horizontal
plane. <BR />Results: The planar interpretation can account for all
aspects of the data, but the loop interpretation has geometrical and
physical problems. <BR />Conclusions: The data by themselves are not
sufficient to determine which picture is more applicable. Nevertheless
I argue that the planar interpretation makes more physical sense and
that the early reconstructions lead to spurious results. I suggest
additional tests that might help constrain the problem further.
---------------------------------------------------------
Title: The Solar Chromosphere: Old Challenges, New Frontiers
Authors: Ayres, T.; Uitenbroek, H.; Cauzzi, G.; Reardon, K.; Berger,
T.; Schrijver, C.; de Pontieu, B.; Judge, P.; McIntosh, S.; White,
S.; Solanki, S.
2009astro2010S...9A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Physics of the chromosphere and the lower coronal boundary
conditions
Authors: Judge, P.
2008AGUFMSH51C..03J Altcode:
I will review observations and theoretical work concerning the role
of the chromosphere as the lower boundary for the corona. I will
highlight the need for measurements of the chromospheric magnetic
field as the plasma regimes change from beta > 1 to < 1, using
a striking observational example. I will review some of the important
physical processes occurring within the partially ionized chromosphere
which can greatly alter the conditions at the coronal base from those
expected based only upon photospheric measurements. I will re-iterate
the obvious conclusion, but one often ignored, that one must understand
specific chromospheric processes if one is to have hope of addressing
the nature of the supply of mass, momentum and energy into the corona.
---------------------------------------------------------
Title: On the Magnetic Structure of the Solar Transition Region
Authors: Judge, Philip; Centeno, Rebecca
2008ApJ...687.1388J Altcode: 2008arXiv0805.1436J
We examine the hypothesis that cool loops dominate emission from solar
transition region plasma below temperatures of 2 × 10<SUP>5</SUP>
K. We compare published VAULT images of H Lyα, a lower transition
region line, with nearly contemporaneous magnetograms from Kitt Peak,
obtained during the second flight (VAULT-2) on 2002 June 14. The
measured surface fields and potential extrapolations suggest that there
are too few short loops and that Lyα emission is associated with
the base regions of longer, coronal loops. VAULT-2 data of network
boundaries have an asymmetry on scales larger than supergranules,
also indicating an association with long loops. We complement the
Kitt Peak data with very sensitive vector polarimetric data from the
spectropolarimeter on board Hinode to determine the influence of very
small magnetic concentrations on our analysis. From these data, two
classes of behavior are found. Within the cores of strong magnetic
flux concentrations (>5 × 10<SUP>18</SUP> Mx) associated with
active network and plage, small-scale mixed fields are absent, and
any short loops can connect just the peripheries of the flux to cell
interiors. Core fields return to the surface via longer, most likely
coronal, loops. In weaker concentrations, short loops can connect
concentrations and produce mixed fields within network boundaries,
as suggested by Dowdy and colleagues. The VAULT-2 data that we
examined are associated with strong concentrations. We conclude that
the cool-loop model applies only to a small fraction of the VAULT-2
emission, but we cannot discount a significant role for cool loops in
quieter regions. We suggest a physical picture for how network Lyα
emission may occur through the cross-field diffusion of neutral atoms
from chromospheric into coronal plasma.
---------------------------------------------------------
Title: An Explanation of the Solar Transition Region
Authors: Judge, Philip
2008ApJ...683L..87J Altcode: 2008arXiv0807.1706J
Prompted by high-resolution observations, I propose an explanation
for the 40+ year old problem of structure and energy balance in
the solar transition region. The ingredients are simply cross-field
diffusion of neutral atoms from cool threads extending into the corona,
and the subsequent excitation, radiation, and ionization of these
atoms via electron impact. The processes occur whenever chromospheric
plasma is adjacent to coronal plasma, and are efficient even when ion
gyrofrequencies exceed collision frequencies. Cool threads—fibrils
and spicules perhaps—grow slowly in thickness as a neutral, ionizing
front expands across the magnetic field into coronal plasma. Radiative
intensities estimated for H Lyα are within an order of magnitude of
those observed, with no ad hoc parameters; only thermal parameters and
geometric considerations are needed. I speculate that the subsequent
dynamics of the diffused material might also explain observed properties
of trace elements.
---------------------------------------------------------
Title: The Fainting of α Centauri A, Resolved
Authors: Ayres, Thomas R.; Judge, Philip G.; Saar, Steven H.; Schmitt,
Jürgen H. M. M.
2008ApJ...678L.121A Altcode:
Beginning in 2003, XMM-Newton snapshot monitoring of α Centauri (HD
128620, 128621: G2 V, K1 V) documented a steady fading of the primary's
X-ray corona, which had all but disappeared by early 2005. The steep
decline in L<SUB>X</SUB> was at odds with the previous two decades
of high-energy measurements, which showed only modest variability of
the Sun-like star. A Chandra LETGS spectrum in 2007 June, however,
fully resolved the source of the curious X-ray darkening: a depletion
of plasma above ~2 MK had substantially depressed the line spectrum
where the XMM-Newton response peaks (λ lesssim 30 Å), even though the
overall coronal luminosity, dominated by longer wavelength emissions,
had declined only slightly. This is reminiscent of the Sun's magnetic
activity cycle, where the 2-3 MK active regions of sunspot maximum
give way to the spatially pervasive, but cycle-independent, 1 MK
"quiet corona" at minimum. This emphasizes that any discussion of
cyclic coronal variability in low-activity stars will depend crucially
on the energy coverage of the measurements.
---------------------------------------------------------
Title: An Instrument to Measure Coronal Emission Line Polarization
Authors: Tomczyk, S.; Card, G. L.; Darnell, T.; Elmore, D. F.; Lull,
R.; Nelson, P. G.; Streander, K. V.; Burkepile, J.; Casini, R.; Judge,
P. G.
2008SoPh..247..411T Altcode: 2008SoPh..tmp....3T
We have constructed an instrument to measure the polarization of light
emitted by the solar corona in order to constrain the strength and
orientation of coronal magnetic fields. We call this instrument the
Coronal Multichannel Polarimeter (CoMP). The CoMP is integrated into
the Coronal One Shot coronagraph at Sacramento Peak Observatory and
employs a combination birefringent filter and polarimeter to form
images in two wavelengths simultaneously over a 2.8R<SUB>⊙</SUB>
field of view. The CoMP measures the complete polarization state at
the 1074.7 and 1079.8 Fe XIII coronal emission lines, and the 1083.0
nm He I chromospheric line. In this paper we present design drivers
for the instrument, provide a detailed description of the instrument,
describe the calibration methodology, and present some sample data
along with estimates of the uncertainty of the measured magnetic field.
---------------------------------------------------------
Title: Instruments: HRC
Authors: Kraft, Ralph; Kenter, Almus; Ayres, Thomas R.; Judge, Philip
G.; Saar, Steven H.; Schmitt, Jurgen H. M. M.; Anderson, Gemma;
Gaensler, Bryan; Chicago Team
2008ChNew..15...13K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The COronal Solar Magnetism Observatory
Authors: Burkepile, J.; Tomczyk, S.; Lin, H.; Zurbuchen, T.; Judge,
P.; Casini, R.
2007AGUFMSH53A1070B Altcode:
Measurements of coronal and chromospheric magnetic fields are
arguably the most important observables required for advances in
our understanding of the emergence of magnetic flux into the solar
atmosphere and the processes responsible for the production of solar
activity, coronal heating and coronal dynamics. The COronal Solar
Magnetism Observatory (COSMO) is a proposed ground-based suite of
instruments designed for routine study of coronal and chromospheric
magnetic fields and their environment. The facility consists of 3
instruments: 1) a meter-class aperture coronal magnetometer devoted
to obtaining the highest quality polarimetric data of forbidden lines
of Fe XIII 1074.7 and 1079.8 nm.; 2) a chromosphere and prominence
magnetometer devoted primarily to measurements of lines of helium
(D3, 1083 nm) and perhaps Halpha, that will provide full disk vector
magnetic field observations; 3) a white-light polarized-brightness (pB)
coronagraph that will observe down to 1.05 solar radii at very high
time cadence (15 seconds) at high signal-to-noise. This new facility
will be operated by the High Altitude Observatory of the National
Center for Atmospheric Research (HAO/NCAR) in collaboration with the
University of Hawaii and the University of Michigan. COSMO will enhance
the value of existing and new observatories on the ground (SOLIS, ATST,
and FASR) and in space (SOHO, TRACE, GOES, SOLAR-B, STEREO, SDO) by
providing unique and crucial observations of the global coronal and
chromospheric magnetic field and its evolution.
---------------------------------------------------------
Title: Alfven Waves in the Solar Corona
Authors: Tomczyk, S.; McIntosh, S. W.; Keil, S. L.; Judge, P. G.;
Schad, T.; Seeley, D. H.; Edmondson, J.
2007AGUFMSH21A0289T Altcode:
We present observations of the coronal intensity, line-of-sight
velocity, and linear polarization obtained in the FeXIII 1074.7 nm
coronal emission line with the Coronal Multi-channel Polarimeter
(CoMP) instrument. Analysis of these observations reveal ubiquitous
upward propagating waves with phase speeds of 1-4 Mm/s and trajectories
consistent with the direction of the magnetic field inferred from the
linear polarization measurements. We can definitively identify these
as Alfvén waves. An estimate of the energy carried by the waves that
we spatially resolve indicates that they are unable to heat the solar
corona, however, unresolved waves may carry sufficient energy.
---------------------------------------------------------
Title: Alfvén Waves in the Solar Corona
Authors: Tomczyk, S.; McIntosh, S. W.; Keil, S. L.; Judge, P. G.;
Schad, T.; Seeley, D. H.; Edmondson, J.
2007Sci...317.1192T Altcode:
Alfvén waves, transverse incompressible magnetic oscillations, have
been proposed as a possible mechanism to heat the Sun’s corona
to millions of degrees by transporting convective energy from the
photosphere into the diffuse corona. We report the detection of
Alfvén waves in intensity, line-of-sight velocity, and linear
polarization images of the solar corona taken using the FeXIII
1074.7-nanometer coronal emission line with the Coronal Multi-Channel
Polarimeter (CoMP) instrument at the National Solar Observatory, New
Mexico. Ubiquitous upward propagating waves were seen, with phase speeds
of 1 to 4 megameters per second and trajectories consistent with the
direction of the magnetic field inferred from the linear polarization
measurements. An estimate of the energy carried by the waves that we
spatially resolved indicates that they are too weak to heat the solar
corona; however, unresolved Alfvén waves may carry sufficient energy.
---------------------------------------------------------
Title: Asteroseismic signatures of stellar magnetic activity cycles
Authors: Metcalfe, T. S.; Dziembowski, W. A.; Judge, P. G.; Snow, M.
2007MNRAS.379L..16M Altcode: 2007MNRAS.tmpL..50M; 2007arXiv0704.1606M
Observations of stellar activity cycles provide an opportunity to study
magnetic dynamos under many different physical conditions. Space-based
asteroseismology missions will soon yield useful constraints on the
interior conditions that nurture such magnetic cycles, and will be
sensitive enough to detect shifts in the oscillation frequencies due to
the magnetic variations. We derive a method for predicting these shifts
from changes in the MgII activity index by scaling from solar data. We
demonstrate this technique on the solar-type subgiant β Hyi, using
archival International Ultraviolet Explorer spectra and two epochs of
ground-based asteroseismic observations. We find qualitative evidence
of the expected frequency shifts and predict the optimal timing for
future asteroseismic observations of this star.
---------------------------------------------------------
Title: The Outer Solar Atmosphere during the Maunder Minimum:
A Stellar Perspective
Authors: Judge, Philip G.; Saar, Steven H.
2007ApJ...663..643J Altcode:
By comparing solar data with data of “flat activity” stars at UV and
soft X-ray wavelengths, we estimate solar chromospheric, transition
region, and coronal emission as it might have existed during the
Maunder minimum (1645-1715), the most recent of several episodes of
persistently weak sunspot activity. Several flat activity stars from
the Mount Wilson S-index survey have been observed with the Hubble
Space Telescope and ROSAT. Drawing on published data, we reassess
the criteria by which a star may be considered as a Maunder minimum
candidate. Of our targets, HD 10700 and HD 143761 are the most likely
such candidates. Solar UV spectra from the SOHO and UARS spacecraft, and
soft X-ray data from the SNOE spacecraft are compared with the stellar
UV and X-ray data. The comparison suggests that the radiative output
of the Maunder minimum chromosphere, transition region, and corona
were similar to (or at least not much less than) those observed under
conditions close to current solar minima. In turn, this suggests that
the emitting structures (which on the Sun at sunspot minimum are small
scale, <<R<SUB>solar</SUB>), including the magnetic network,
were also similar. These results have implications for the nature
of the surface magnetic fields and irradiance during the Maunder and
other magnetic minima, and for the solar dynamo.
---------------------------------------------------------
Title: Spectral Lines for Polarization Measurements of the Coronal
Magnetic Field. V. Information Content of Magnetic Dipole Lines
Authors: Judge, P. G.
2007ApJ...662..677J Altcode:
Stokes profiles of typical magnetic dipole coronal emission lines
contain information on the embedded magnetic fields, but the
interpretation of the lines is subject to ambiguities. The present
study illuminates the information content of coronal emission line
measurements that include all four Stokes parameters. The simplest
case of localized emission along the line of sight, such as that
from a single bright loop, is scrutinized. Knowledge of the “atomic
alignment” is central to the diagnosis of magnetic fields beyond
determining the field's azimuth projected on the plane of the sky. For
localized emission, a method to determine the atomic alignment is
presented, combining Stokes I, Q, and U observations and statistical
equilibrium calculations, related to work by Querfeld. The method
yields the sign of the alignment under conditions that might exist
25% of the time, thereby reducing the Van Vleck ambiguity from one of
90° to 180°. Even then, the magnitude of the alignment is sometimes
ambiguous. With measurements of Stokes V, unambiguous knowledge of
the alignment also yields the vector field B with just an ambiguity
of 180° in the plane of the sky. In other, more general cases,
neither the sign nor the magnitude of the atomic alignment can be
uniquely determined. Suggestions are made as to how these more serious
ambiguities might be ameliorated by assuming continuity of magnetic
fields underlying the polarization maps, an idea first expressed by
House in 1972. Some conclusions are offered concerning the relative
merits of formal inversions, diagnosis of magnetic properties from a
localized region, tomography using solar rotation, and forward modeling.
---------------------------------------------------------
Title: Observations of the Solar Chromosphere
Authors: Judge, P.
2006ASPC..354..259J Altcode:
I summarize observational properties of the solar chromosphere with
emphasis on some of Bob Stein's continuing interests, with an historical
slant. Bob's interests always concern basic physical processes, so I
try to identify some basic facts about the chromosphere from the myriads
of observations from radio to UV wavelengths. The observations suggest
a simple demarcation between the “low” chromosphere and “high”
chromosphere which depends on the local plasma-β. Relatively simple
properties are exhibited in high-β regions (hydrostatic equilibrium,
three-minute compressive oscillations), and obviously complex thermal
properties of the “fine structure” observed for many decades,
arise in low-β chromospheric regions. The latter appears to share
properties more in common with the intermingled lower corona, where
the energetically dominant magnetic structure is arguably simpler
than the high-β regions. But like the coronal heating problem, the
thermal structure of the upper chromosphere is far more complex and
is manifested as fine structure.
---------------------------------------------------------
Title: The Coronal Solar Magnetic Observatory (COSMO)
Authors: Tomczyk, S.; Zurbuchen, T.; Kuhn, J.; Lin, H.; Judge, P.;
Burkepile, J.; Casini, R.
2006AGUFMSM12A..03T Altcode:
Measurement of magnetic fields in the corona is arguably the most
important observable required for advances in our understanding of
the emergence of magnetic flux into the solar atmosphere and the
processes responsible for the production of solar activity, coronal
heating and coronal dynamics. We discuss plans for the COronal Solar
Magnetic Observatory (COSMO), which is a proposed ground-based suite
of instruments designed to routinely study coronal magnetic fields and
their environment. The core of the facility includes a meter-class
coronagraph with instrumentation dedicated to measuring the coronal
magnetic field using the polarization of forbidden emission lines in
the infrared. Supporting instruments focus on prominence magnetometry
and the dynamics of the electron-scattered corona (K-corona) and
chromosphere. In addition to acquiring routine synoptic observations
of coronal magnetic fields, the COSMO project will include the
establishment of a community-based user advisory panel to accept
observational campaigns submitted by members of the scientific community
at-large. COSMO will enhance the value of existing and new observatories
on the ground (SOLIS, ATST, FASR) and in space (SOHO, TRACE, GOES,
Solar-B, STEREO and SDO) by providing unique and crucial observations
of the global coronal magnetic field and its evolution and dynamics.
---------------------------------------------------------
Title: Spectral Lines for Polarization Measurements of the Coronal
Magnetic Field. IV. Stokes Signals in Current-carrying Fields
Authors: Judge, P. G.; Low, B. C.; Casini, R.
2006ApJ...651.1229J Altcode:
We present the first theoretical, forward calculations of the Stokes
profiles of several magnetic dipole (“M1”) coronal emission lines
produced in current-carrying magnetic structures. An idealized coronal
model of Low, Fong, and Fan is used, which describes a spherically
symmetric, hydrostatic background atmosphere, isothermal at a
coronal temperature of 1.6×10<SUP>6</SUP> K. Embedded is a global,
axisymmetric magnetic field that is everywhere potential except
at a quiescent prominence, consisting of an infinitesimally thin,
equatorial current sheet whose weight is supported by the outward
discrete Lorentz force in the sheet. This model contains a physically
nontrivial, localized magnetic structure, although the atmospheric
plasma is thermally of the simplest stratification possible. The
calculated M1 coronal lines show clear and distinct signatures of
the presence and magnitude of this localized magnetic structure,
in both linear and circular polarizations, even though the thermal
structure is almost homogeneous. The morphology of maps of linear
polarization is particularly sensitive to the existence and strength
of the current sheets, as field lines wrap around them according to
the Biot-Savart law, and the linear polarization responds to different
projections of field line directions onto local radius vectors. Of the
M1 lines studied, those of Fe XIII (1074.7 nm) and Si X (1430.1 nm)
are especially promising because of their relatively strong linear
polarization. These forward calculations provide a basis for optimism
that emission-line measurements may reveal the presence and nature of
current systems in the corona, and provide motivation for developing
instruments capable of routinely measuring polarized light in forbidden
coronal lines.
---------------------------------------------------------
Title: Observational aspects of sunspot oscillations
Authors: Bogdan, T. J.; Judge, P. G.
2006RSPTA.364..313B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Wavelet Phase Coherence Analysis: Application to a Quiet-Sun
Magnetic Element
Authors: Bloomfield, D. Shaun; McAteer, R. T. James; Lites, Bruce W.;
Judge, Philip G.; Mathioudakis, Mihalis; Keenan, Francis P.
2004ApJ...617..623B Altcode:
A new application of wavelet analysis is presented that utilizes
the inherent phase information residing within the complex Morlet
transform. The technique is applied to a weak solar magnetic network
region, and the temporal variation of phase difference between TRACE
1700 Å and SOHO/SUMER C II 1037 Å intensities is shown. We present,
for the first time in an astrophysical setting, the application of
wavelet phase coherence, including a comparison between two methods
of testing real wavelet phase coherence against that of noise. The
example highlights the advantage of wavelet analysis over more
classical techniques, such as Fourier analysis, and the effectiveness
of the former to identify wave packets of similar frequencies but
with differing phase relations is emphasized. Using cotemporal,
ground-based Advanced Stokes Polarimeter measurements, changes in the
observed phase differences are shown to result from alterations in
the magnetic topology.
---------------------------------------------------------
Title: Evaluation of Seeing-Induced Cross Talk in Tip-Tilt-Corrected
Solar Polarimetry
Authors: Judge, Philip G.; Elmore, David F.; Lites, Bruce W.; Keller,
Christoph U.; Rimmele, Thomas
2004ApOpt..43.3817J Altcode:
We reanalyze the effects of atmosphere-induced image motions on the
measurement of solar polarized light using a formalism developed by
Lites. Our reanalysis is prompted by the advent of adaptive optics (AO)
systems that reduce image motion and higher-order aberrations, by the
availability of liquid crystals as modulation devices, and by the need
to understand how best to design polarimeters for future telescopes
such as the Advanced Technology Solar Telescope. In this first attempt
to understand the major issues, we analyze the influence of residual
image motion (tip-tilt) corrections of operational AO systems on the
cross talk between Stokes parameters and present results for several
polarization analysis schemes. Higher-order wave-front corrections are
left for future research. We also restrict our discussion to the solar
photosphere, which limits several important parameters of interest,
using some recent magnetoconvection simulations.
---------------------------------------------------------
Title: A Comparison of the Outer Atmosphere of the “Flat Activity”
Star τ Ceti (G8 V) with the Sun (G2 V) and α Centauri A (G2 V)
Authors: Judge, Philip G.; Saar, Steven H.; Carlsson, Mats; Ayres,
Thomas R.
2004ApJ...609..392J Altcode:
Driven by the desire to understand the roles of acoustic and
magnetic mechanisms in heating the outer atmospheres of Sun-like
stars, we compare solar UV spectra with archival STIS spectra from
the Hubble Space Telescope of α Cen A (G2 V) and new STIS spectra
of the extremely inactive dwarf star τ Cet (G8 V, V=3.5). The
activity of τ Cet shows occasional rotational modulations but no
long-term cyclic variation. It may be in a phase analogous to the
solar Maunder minimum. Solar disk center intensities from both the
HRTS instrument and the SUMER instrument on SOHO were converted to
Sun-as-a-star fluxes by using center-to-limb data from Dammasch and
colleagues. The derived solar flux spectrum represents conditions
near the minimum of the solar magnetic activity cycle. We find that
the τ Cet line profiles differ systematically from those of the Sun
and α Cen A. While lines formed in the middle chromospheres appear
similar, the entire emission from the upper chromosphere to the middle
transition region of τ Cet has lower flux densities by factors of
~2, the line widths are significantly narrower, and, uniquely, the
transition region lines are not significantly redshifted. The soft
X-ray surface flux of τ Cet, measured between 0.1 and 2.4 keV, is
~9×10<SUP>3</SUP> ergs cm<SUP>-2</SUP> s<SUP>-1</SUP>, several times
smaller than the median solar value. We also find that the UV spectrum
of α Cen serves as a proxy for a Sun-as-a-star spectrum when the Sun
is in an intermediate phase of its activity cycle but that its coronal
emission may be somewhat smaller. We discuss the implications of these
results for magnetic fields and heating mechanisms in the stars and
speculate that τ Cet's UV spectrum might represent the solar spectrum
during a grand minimum phase.
---------------------------------------------------------
Title: Background-Induced Measurement Errors of the Coronal Intensity,
Density, Velocity, and Magnetic Field
Authors: Penn, M. J.; Lin, H.; Tomczyk, S.; Elmore, D.; Judge, P.
2004SoPh..222...61P Altcode:
The effect of a background signal on the signal-to-noise ratio is
discussed, with particular application to ground-based observations of
emission lines in the solar corona with the proposed Advanced Technology
Solar Telescope. The concepts of effective coronal aperture and
effective coronal integration time are introduced. Specific expressions
are developed for the 1σ measurement errors for coronal intensity,
coronal electron density, coronal velocity, and coronal magnetic field
measurements using emission lines and including a background.
---------------------------------------------------------
Title: On the Formation of Extreme-Ultraviolet Helium Lines in the
Sun: Analysis of SOHO Data
Authors: Judge, Philip G.; Pietarila, Anna
2004ApJ...606.1258J Altcode:
The resonance lines of helium in the Sun are several times stronger than
expected, relative to lines of other ions. To explore the origins of
this “helium enhancement,” we have studied data from the SUMER, CDS,
MDI, and EIT instruments on the Solar and Heliospheric Observatory
(SOHO). Time series data obtained in a quiet region and a coronal
hole indicate that the spatio-temporal properties of the He I 584
Å, and He II 304 and 1084 Å lines are qualitatively unlike other
chromospheric and transition region lines. Helium line intensities
vary slowly compared to chromospheric oscillations and to transient
transition region brightenings seen in other lines, yet they vary
rapidly (both spatially and temporally) compared to the coronal
radiation. This suggests that photoionization/recombination plays a
minor excitation role in these lines. The Doppler shift of the 584 Å
line shows a remarkably clear 4-8 mHz oscillation, with no accompanying
line intensity oscillation. Transient brightenings are used to show
that nonradial photon scattering might explain the previously found
diffuse appearance of the network but cannot account for the reduced
network/internetwork intensity contrast in the 584 Å line. We propose
a new enhancement mechanism, based on arguments in a companion paper,
in which predominantly neutral species such as helium diffuse across
magnetic field lines into regions of hot coronal plasma, but charged
ions do not. The enhanced internetwork helium emission may arise
from the diffusion of helium atoms across the chromospheric canopy;
the enhanced network emission may have contributions from diffusion
from spicules. This mechanism may naturally explain why the 584 Å
line shows Doppler shift, but not intensity, oscillations. Finally,
if a mechanism such as “velocity redistribution” dominates helium
emission, spectroheliograms of helium lines will be bright in regions of
large temperature gradients parallel to the magnetic field. Differences
between helium and other spectroheliograms may then reveal the relative
contributions of “classical” and “cool loop” models to the observed
emission.
---------------------------------------------------------
Title: Solar Physics at Evergreen
Authors: Zita, E. J.; Bogdan, T. J.; Carlsson, M.; Judge, P.; Heller,
N.; Johnson, M.; Petty, S.
2004APS..NWS.C1005Z Altcode:
We have recently established a solar physics research program at
The Evergreen State College. Famed for its cloudy skies, the Pacific
Northwest is an ideal location for solar physics research activities
that do not require local observations. Collaborators from the High
Altitude Observatory (HAO) at the National Center for Atmospheric
Research have shared solar data from satellite-borne instruments such
as TRACE and SUMER. HAO colleagues also share data from computer
simulations of magneto-hydrodynamics (MHD) in the chromosphere,
generated by the Institute for Theoretical Astrophysics (ITA) at
the University of Oslo. Evergreen students and faculty learned to
analyze data from satellites and simulations, in Boulder and Oslo, and
established an infrastructure for continuing our analyses in Olympia. We
are investigating the role of magnetic waves in heating the solar
atmosphere. Comparing data from satellites and simulations shows that
acoustic oscillations from the photosphere cannot effectively propagate
into the chromosphere, but that magnetic waves can carry energy up
toward the hot, thin corona. We find that acoustic waves can change into
magnetic waves, especially near the magnetic "canopy," a region where
the sound speed is comparable to magnetic wave speeds. Understanding
MHD wave transformations and their role in energy transport can help
answer outstanding questions about the anomalous heating of the solar
atmosphere. Ref: Waves in the magnetized solar atmosphere II: Waves
from localized sources in magnetic flux concentrations. Bogdan et al.,
2003, ApJ 597
---------------------------------------------------------
Title: On the Formation of the Resonance Lines of Helium in the Sun
Authors: Pietarila, Anna; Judge, Philip G.
2004ApJ...606.1239P Altcode:
To investigate the cause of anomalously bright resonance lines of
helium in the Sun, we have studied the magnitude of the enhancements and
some proposals made to explain them. Calculations in new semiempirical
solar models indicate that the resonance lines of helium are enhanced
by factors of 2-5 for He I and between 2 and 9 for He II, depending on
the elemental abundances assumed. These enhancements are substantially
less than earlier work has suggested, with the differences arising
from radiative transfer not only in helium lines but also in lines of
less abundant elements. Photon scattering, even with small line center
optical depths (of order unity or less) throughout the transition
region, is shown to significantly modify line intensities and their
center-to-limb variation. This effect has important consequences
both for our analysis and also for the analysis of solar EUV lines in
general, including emission measure analyses. We have re-examined some
proposals to explain the enhancements based on the “ionizing plasma”
picture. The proposals include explicit heating (the “burst” picture)
and heating via advection (diffusive and/or flowing models and the
“velocity redistribution” [VR] proposal). We argue that the original
VR mechanism must be modified to include kinetic effects for helium
atoms, which reduce the effects of VR. The VR mechanism also naturally
predicts helium lines that are blue-shifted relative to lines less
sensitive to VR, which contradicts observations for the He I 584 Å
line. Ionizing plasma models also potentially lead to enhancement of
Δn>=1 transitions (n is the principal quantum number) in other
atoms and ions. Existing observational evidence for enhanced Δn>=1
transitions in other ions is weak. We conclude that the ionizing plasma
scenarios are not the sole cause of the helium enhancement. Instead,
in a companion paper, we propose that the thermodynamic properties
of noble gases in the upper chromosphere will lead to enhancement of
their spectral lines if cross-field diffusion into coronal plasma is
important. Finally, we show that, surprisingly, multifluid flows of
the kind computed by Fontenla and colleagues can reproduce observed
intensities of several lines of C and Si and may contain a resolution
to the helium enhancement problem.
---------------------------------------------------------
Title: Initial Magnetic Field Measurements from The Coronal
Multi-Channel Polarimeter
Authors: Tomczyk, S.; Card, G. L.; Darnell, T.; Elmore, D. F.; Casini,
R.; Judge, P. G.; Burkepile, J.
2004AAS...204.2002T Altcode: 2004BAAS...36..686T
We have constrcted a filter-based polarimeter optimized for the
measurement of magnetic fileds in the solar corona. The instrument will
observe the coronal emission lines of FeXIII at 1074.7 and 1079.8 nm as
well as the chromospheric HeI emission line at 1083 nm. The instrument
consists of a polarimeter allowing complete Stokes I,Q,U,V measurement
followed by a Lyot birefringent filter with dual passbands of 0.14
nm width. Both the polarimeter and filter employ liquid crystals for
rapid electro-optical tuning. This instrument was deployed to the
20-cm One Shot coronagraph at NSO's Sacramento Peak Observatory in
January of 2004. <P />Measurement of the longitudinal Zeeman effect
provides information on the strength of the line-of-sight component
of the magnetic field while the observation of resonance scattering
will constrain the plane-of-sky field direction. Precise measurement
of plasma velocity is also possible. Such measurements are critical
for addressing many outstanding problems in coronal physics. <P />The
operation and performance of the instrument will be described. We
will also describe the methodology for the coronal magnetic field
measurement. Initial measurements taken with the instrument will be
presented. This research was supported by the NSF.
---------------------------------------------------------
Title: Chromospher-corona transition region line emissions
Authors: Fontenla, J.; Judge, P.
2004cosp...35..668F Altcode: 2004cosp.meet..668F
We study the effects of diffusion and flows on the transition region
trace-species emission lines and the radiative losses produced by
them and compare them with observations. We find that mass flows can
have dramatic effects on the line emissions through the effect on
non-local ionization and in this way completely alter the radiative
losses and the structure of the transition regions. Also, in static
cases thermal diffusion can have a very significant effect on the
elemental abundance variation that in turn affects the line emissions
and radiative losses leading to reduced abundances of trace species at
temperatures around 10^5 K, and the details this effect is dependent on
the first-ionization-potential. This is due to the combination of large
temperature gradient and increased mean free path and is expected to
occur for all species. However, the mass flows would reduce this effect
and especially in the case of downflows the thermal diffusion can have
complex results. Also, species diffusion flows can arise from specific
boundary conditions and may not be directly related to a simultaneous
mass flow. We discuss several scenarios that may arise in typical
dynamic cases that have been observed. We show that the transition
region emissions have the large fluctuations in space and time, much
more than the chromospheric emissions, and that the radiated energy
can be easily explained in terms of the downward energy flow from the
corona coupled with enthalpy and ionization energy carried by the up
and down mass flows often observed.
---------------------------------------------------------
Title: Oscillatory Signatures above Quiet Sun Magnetic Elements
Authors: Bloomfield, D. S.; McAteer, R. T. J.; Lites, B. W.; Judge,
P. G.; Mathioudakis, M.; Keenan, F. P.
2004ESASP.547...51B Altcode: 2004soho...13...51B
A new application of wavelet analysis is presented. The data used are
part of Joint Observing Proposal 72 between SoHO and TRACE, obtained on
1998 May 16 with accompanying groundbased data taken with the Dunn Solar
Telescope at Sacramento Peak, New Mexico. A weak magnetic network region
is studied and the temporal variation of phase difference between TRACE
1700 Å and SoHO/SUMER C II intensities is shown. The example clearly
highlights the advantages of wavelet analysis over more classical
techniques such as Fourier analysis, where the effectiveness of the
technique to identify wavepackets with differing phase difference
relations is emphasised.
---------------------------------------------------------
Title: A Coronal Multi Channel Polarimeter For Magnetic Field
Measurements
Authors: Darnell, T.; Tomczyk, S.; Card, G.; Judge, P. G.; Casini,
R.; Burkepile, J.
2003AGUFMSH42B0505D Altcode:
The Coronal Multi-channel Polarimeter (CoMP) is a filter-based
polarimeter designed to provide quantitative measurements of magnetic
fields in the solar corona. It will measure the Stokes parameters
at the 1074.7 and 1079.8 FeXIII coronal emission lines (1.67 x 106
degrees K), and the 1083.0 nm HeI chromospheric line. The CoMP is
based on a four stage birefringent filter and is designed such that
the corona is imaged in two wavelengths simultaneously. The strength of
the line-of-sight component of the coronal magnetic field is inferred
from the measured amplitude of the Stokes V profile and an estimate of
the plane-of-sky direction is made from the Stokes U/Q ratio. Further,
inference of line-of-sight velocities can be made from Stokes I (red and
blue wing) amplitudes. Finally, it may be possible to obtain a coronal
density diagnostic capability from the ratio of the 1074.7/1079.8
amplitudes. This poster will present the latest test results as well
as any preliminary data that have been obtained.
---------------------------------------------------------
Title: On the Origin of the Basal Emission from Stellar Atmospheres:
Analysis of Solar C II Lines
Authors: Judge, Philip G.; Carlsson, Mats; Stein, Robert F.
2003ApJ...597.1158J Altcode:
Combining a variety of data with radiation hydrodynamic simulations,
we examine the heating of the Sun's internetwork chromosphere
and the hypothesis that the chromospheric “basal” emission
arises because of acoustic wave dissipation. We focus on the
2s2p<SUP>2</SUP><SUP>2</SUP>D-2s<SUP>2</SUP>2p<SUP>2</SUP>P<SUP>o</SUP>
multiplet of C II near 1335 Å, whose basal level of chromospheric
emission has been reliably determined for stars and the Sun by
Schrijver and colleagues. By accounting for center-to-limb variations
and the different spectral bandpasses of the instruments used, we find
that Schrijver's C II solar basal intensity substantially exceeds
stellar values, and that it can be identified with intensities seen
in typical internetwork regions with the SUMER instrument on the SOHO
spacecraft. Some time-series data sets of internetwork regions are
then examined and compared with simulations made specifically for a
typical observational data set, with vertical velocities at the lower
boundaries fixed from observations with the MDI instrument on SOHO. The
simulations can qualitatively account for the observed internetwork UV
continuum fluctuations seen with SUMER, formed 0.6-0.85 Mm above the
photosphere. However, they fail to capture almost any property of the
observed internetwork C II multiplet, which is formed substantially
higher. The time-averaged simulations can account for between 1/7
and 1/4 of the C II basal intensities; they predict oscillatory power
between 5 and 10 mHz, whereas internetwork observations are dominated by
low-frequency (<2 mHz) power of solar origin. The average simulated
C II intensities, which have a large contribution from the transition
region heated by conduction down from a coronal upper boundary,
fall short even of the smaller stellar basal intensities by a factor
of >=2. Together with known properties of weak, internetwork
photospheric magnetic fields, we conclude that the internetwork
upper chromosphere is probably dominated by magnetic heating. Thus,
the solar basal (and internetwork) intensities of the C II 1335 Å
multiplet originate from magnetic, and not acoustic, mechanisms,
in contradiction to the commonly accepted picture
---------------------------------------------------------
Title: The Sun As A Guide To The Stars
Authors: Judge, P.
2003csss...12..158J Altcode:
I review the “Sun as a guide to the stars” with emphasis on solar
magnetism: its origins and effects. I do not present an in-depth
review but instead try to highlight the current status of relevant
solar physics. The first half of the discussion focuses on what we have
learned about dynamo process on both large (ℓ ≈ R<SUB>sun</SUB>)
and small (ℓ ≪ R<SUB>sun</SUB>) scales. The second half focuses on
the observed effects of the emerging magnetic fields, especially the
problem of atmospheric heating. I make no attempt to be complete in
referencing, but instead try to point to some key references (mostly
reviews) as appropriate. Some WWW resources are listed.
---------------------------------------------------------
Title: An Estimate of the Sun's ROSAT-PSPC X-Ray Luminosities Using
SNOE-SXP Measurements
Authors: Judge, Philip G.; Solomon, Stanley C.; Ayres, Thomas R.
2003ApJ...593..534J Altcode:
Using solar soft X-ray irradiance measurements from the SXP instrument
on the SNOE satellite, we relate the solar surface flux densities and
their variability to those of stars as measured with the PSPC instrument
on ROSAT. We translate SNOE-SXP measurements into equivalent ROSAT-PSPC
counts using model spectra calculated from the CHIANTI package. Using
the SNOE-SXP measurements has significant advantages over earlier
studies: the absolute calibration is known to +/-25%, SNOE measures the
Sun as if it were an unresolved star, it has operated over a significant
fraction of the solar cycle, and its three wavelength channels overlap
substantially with that of the ROSAT-PSPC instrument. The predicted
solar X-ray luminosities and surface flux densities are compared with
measurements from the ROSAT database. We find that we can estimate
the luminosity of the Sun as seen in the 0.1-2.4 keV (“RASS”)
passband of ROSAT-PSPC to within +/-50%, not counting sources of
systematic uncertainty mentioned in an appendix: the result lies
between 10<SUP>27.1</SUP> and 10<SUP>27.75</SUP> ergs s<SUP>-1</SUP>
(measured in the existing data set, only partially covering a full
solar cycle) and between 10<SUP>26.8</SUP> and 10<SUP>27.9</SUP>
ergs s<SUP>-1</SUP> (extrapolated to the full activity range of a
typical solar cycle). The solar luminosities lie close to the median
behavior found for a volume-limited (d<13 pc) sample of G stars
studied in 1997 by Schmitt, revealing the Sun to be a normal or
slightly inactive G dwarf. A factor of 1.5 peak-to-peak variation in
the RASS passband is predicted due simply to rotational modulations
(i.e., those filtered to include periods P<81 days). The ratio of
maximum/minimum RASS luminosities from the magnetic activity cycle
(filtered to include periods P>81 days) are estimated to be 0.7-0.8
in log10L<SUB>RASS</SUB>, a ratio of 5 or 6. These variations are much
smaller than both recent estimates of solar X-ray variability and
the range of X-ray luminosities seen within Schmitt's sample. It is
suggested that the reported absence of “solar-like” cyclic emission
in stellar X-rays might partly arise because the Sun is less variable
than assumed in some earlier work. Repeated ROSAT observations of
α Cen A during 1995-1998 show X-ray behavior reminiscent of the Sun
during activity minimum conditions.
---------------------------------------------------------
Title: Investigating the role of plasma topography on chromospheric
oscillations observed by TRACE
Authors: McIntosh, S. W.; Fleck, B.; Judge, P. G.
2003A&A...405..769M Altcode:
We present the results of an investigation into the interaction of
the topographic structure of the solar chromospheric plasma with the
wave modes manifesting themselves in the UV continua formed there. We
show that there is a distinct correlation between the inferred
plasma topography, the phase-differences between and suppression of
oscillations in different levels of the solar atmosphere. We interpret
these factors as evidence of interaction between the oscillations and
the extended magnetic “canopy”. This work is based on the analysis of
joint observations made by the Solar and Heliospheric Observatory (SOHO)
spacecraft and the Transition Region and Coronal Explorer (TRACE).
---------------------------------------------------------
Title: Towards the Measurement of Coronal Magnetic Fields
Authors: Judge, P. G.
2003ASPC..307..437J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Determination of Hyperfine-Induced Transition Rates from
Observations of a Planetary Nebula
Authors: Brage, Tomas; Judge, Philip G.; Proffitt, Charles R.
2002PhRvL..89B1101B Altcode: 2002PhRvL..89.1101B
Observations of the planetary nebula NGC3918 made with the
STIS instrument on the Hubble Space Telescope reveal the first
unambiguous detection of a hyperfine-induced transition 2s2p
<PRE><SUP>3</SUP></PRE>P<SUP>o</SUP><SUB>0</SUB>→2s<SUP>2</SUP>
<PRE><SUP>1</SUP></PRE>S<SUB>0</SUB> in the berylliumlike emission line
spectrum of N IV at 1487.89Å. A nebular model allows us to confirm a
transition rate of 4×10<SUP>-4</SUP> sec(<SUP>-1</SUP>±33% for this
line. The measurement represents the first independent confirmation
of the transition rate of hyperfine-induced lines in low ionization
stages, and it provides support for the techniques used to compute
these transitions for the determination of very low densities and
isotope ratios.
---------------------------------------------------------
Title: Observational and Interpretational Challenges
Authors: Judge, P.
2002ASPC..277...45J Altcode: 2002sccx.conf...45J
No abstract at ADS
---------------------------------------------------------
Title: Spectroscopic Detection of the 3.934 Micron Line of Si IX in
the Solar Corona
Authors: Judge, P. G.; Tomczyk, S.; Livingston, W. C.; Keller, C. U.;
Penn, M. J.
2002ApJ...576L.157J Altcode:
We report the detection of the
2s<SUP>2</SUP>2p<SUP>2</SUP><SUP>3</SUP>P<SUB>1-->0</SUB> line of
Si IX using the McMath-Pierce telescope on Kitt Peak. Observations
were made of the solar disk and at various heights above the limb
between 2002 May 13 and 17, under nonideal sky conditions, using the
13.5 m vertical spectrograph and an InSb single-diode detector. We
report a new rest wavelength for the line and discuss its potential
use as a diagnostic of coronal magnetic fields using ground-based
telescopes. Our observations give λ<SUB>rest</SUB>=3.93434+/-0.00007
μm, consistent with earlier less accurate values, but it places the
blue wing of the line under a strong telluric N<SUB>2</SUB>O line. In
the active regions observed, the line's intensity is comparable to or
larger than predicted in earlier work for the quiet Sun.
---------------------------------------------------------
Title: Challenges of Measuring Coronal Magnetic Fields
Authors: Judge, P.
2002AAS...200.3406J Altcode: 2002BAAS...34..691J
Measurements of components of the vector magnetic field in the solar
corona can potentially yield information critical to our understanding
of coronal structure, dynamics and heating. I will review techniques
for making such measurements, in particular those that can be applied
outside of active regions. Forbidden coronal emission lines appear
to have the highest potential to address outstanding problems in
coronal physics, especially those related to the storage and release
of magnetic free energy. Measurements of the full Stokes vector of
M1 lines of magnetic dipole (M1) character can constrain both the
line-of-sight field strength, B<SUB>&|slash</SUB>, through the
longitudinal Zeeman effect seen in Stokes V profiles, and the direction
of the vector field projected onto the plane-of-the-sky, through the
analysis of resonance scattering-induced linear polarization seen in
Stokes Q and U, in the so-called “strong field” regime of the Hanle
effect. Coupled with additional data and models, accurate polarimetry
can reveal information on coronal magnetic fields, including current
systems, unobtainable by other means available now or in the near
future. I will discuss the current challenges presented by such
measurements for both for the ATST project and in more general terms.
---------------------------------------------------------
Title: Physical consequences of the inclusion of anomalous resistivity
in the dynamics of 2D magnetic reconnection
Authors: Roussev, I.; Galsgaard, K.; Judge, P. G.
2002A&A...382..639R Altcode:
The aim of the present paper is to explore the role of anomalous
resistivity on the dynamics of magnetic reconnection in a 2D
environment of relevance to the solar transition region. We adopt an
ad hoc but explicit form of the anomalous resistivity, motivated by a
streaming instability, in which the resistivity jumps suddenly as the
electron drift velocity exceeds some fraction of the mean electron
thermal speed. Experiments have been conducted to investigate the
impact of various critical speeds and arbitrary scaling constants
of the resistivity level on the time-dependent evolution of the
magnetic reconnection process. The specific threshold value is found
to influence the dynamics of the reconnection, with higher values
providing a localised on-off effect of patchy diffusion. For a given
normalised value of the anomalous resistivity, the amount of Joule
heating released scales inversely with the threshold value. The total
energy release is found to be above the lower limit of “quiet”
Sun nano-flares required to maintain a hot corona. The reconnection
events discussed here may be important to the energy balance of the
solar transition region and overlying corona, as already suggested in
earlier work based on SUMER observations.
---------------------------------------------------------
Title: On the Nature of Magnetic Shadows in the Solar Chromosphere
Authors: McIntosh, S. W.; Judge, P. G.
2001ApJ...561..420M Altcode:
Recent multi-instrument spacecraft studies of the solar photosphere
and chromosphere have uncovered a feature-a “magnetic shadow”-not
previously discussed in the literature. A region of the midchromosphere
neighboring, but not within, a network magnetic element exhibits
a suppression of both the mean UV line/continuum intensity and the
characteristic 3 minute oscillation that is clearly observed elsewhere
in apparently similar internetwork regions. The clearest cases appear
to occur rarely, and their properties stand in obvious contrast to the
well-known “aureoles” of enhanced variability seen surrounding some
plage regions. It is imperative to understand more clearly the nature
of the shadow region, not least because the suppressed atmospheric
heating within it has implications for heating processes elsewhere
in the chromosphere that are dependent on, or at least related to,
the 3 minute oscillation. Based on the measured photospheric magnetic
field, its upward extrapolation, and the appearance of spectral features
formed above the midchromosphere, we suggest that a shadow occurs when
magnetic structures, in a relatively weak background field, “close”
locally within the chromosphere, suppressing the upward propagation
of magnetoatmospheric waves into the chromosphere.
---------------------------------------------------------
Title: A Study of Chromospheric Oscillations Using the SOHO and
TRACE Spacecraft
Authors: Judge, Philip G.; Tarbell, Theodore D.; Wilhelm, Klaus
2001ApJ...554..424J Altcode:
We analyze line and continuum time-series data of the solar atmosphere,
with between 10 and 60 s cadence, using the MDI and SUMER instruments
on the SOHO spacecraft and the UV bandpasses on the TRACE satellite. The
co-aligned data sets sample spectral features formed from photosphere to
the middle transition region, spanning five decades in pressure, under
quiet-Sun and plage conditions. We discuss power, phase difference,
and coherence spectra, and examine data in the time domain. The
observed photospheric and chromospheric oscillations are strongly
coupled for frequencies between 2 and 8 mHz. Phase coherences decrease
with increasing height, with only occasional periods and locations of
observable coherence up to heights where transition region emission
lines are formed. The middle chromosphere (in the SUMER continua)
oscillates in several megameter (Mm) diameter coherent patches
with power predominantly in the 5-7 mHz range. The TRACE data,
formed in the upper photosphere, show smaller patterns superimposed
on these large-scale oscillations, resulting (at least in part)
from granulation. At the observed spatial scales, all the observed
properties point to p-modes, especially the “pseudomodes” just above
the acoustic cutoff frequency, as the dominant mode of the chromospheric
dynamics. Smaller scale “acoustic event” drivers, associated
with granular dynamics, appear to be less important. The predominant
internetwork chromospheric oscillations arise from regions much larger
horizontally than vertically. If propagating largely vertically, this
can naturally explain why the one-dimensional simulations of Carlsson
& Stein might be more successful than expected. The chromospheric
response to the p-mode driving is, however, intermittent in space and
time. Some of the intermittency appears to result from the interaction
of the upward-propagating waves with magnetic fields. Evidence for this
includes suppressed intensities and oscillations near quiet-Sun network
elements (which we dub “magnetic shadows”), absence of oscillations
in internetwork regions neighboring plage magnetic fields, and a change
in character of the quiet-Sun internetwork oscillations between the
119 and 104 nm continua formed at 1 and 1.2 Mm. The latter might be
caused by canopy fields that form between these heights under typical
quiet-Sun conditions. A SUMER-only data set reported by Wikstøl et
al. has a factor of 3 more oscillatory power in the 104 nm continuum
than the data analyzed here, with stronger coherences extending into
the solar transition region. Together, these data support the general
picture that the chromosphere oscillates primarily in response to
forcing by the p-modes, they are therefore large-scale (several Mm
across) waves, and they are often strongly influenced by magnetic
effects (internetwork fields, or the overlying canopy), before the
oscillations even reach the transition region.
---------------------------------------------------------
Title: An Observational Manifestation of Magnetoatmospheric Waves
in Internetwork Regions of the Chromosphere and Transition Region
Authors: McIntosh, S. W.; Bogdan, T. J.; Cally, P. S.; Carlsson, M.;
Hansteen, V. H.; Judge, P. G.; Lites, B. W.; Peter, H.; Rosenthal,
C. S.; Tarbell, T. D.
2001ApJ...548L.237M Altcode:
We discuss an observational signature of magnetoatmospheric waves in
the chromosphere and transition region away from network magnetic
fields. We demonstrate that when the observed quantity, line or
continuum emission, is formed under high-β conditions, where β is
the ratio of the plasma and magnetic pressures, we see fluctuations in
intensity and line-of-sight (LOS) Doppler velocity consistent with the
passage of the magnetoatmospheric waves. Conversely, if the observations
form under low-β conditions, the intensity fluctuation is suppressed,
but we retain the LOS Doppler velocity fluctuations. We speculate that
mode conversion in the β~1 region is responsible for this change in
the observational manifestation of the magnetoatmospheric waves.
---------------------------------------------------------
Title: Towards a Global Picture: Observable Effects Induced by or
Related to Magnetic Fields
Authors: Judge, P. G.; Charbonneau, P.
2001ASPC..248..659J Altcode: 2001mfah.conf..659J
No abstract at ADS
---------------------------------------------------------
Title: Coronal Magnetometry: A Feasibility Study
Authors: Judge, P. G.; Casini, R.; Tomczyk, S.; Edwards, D. P.;
Francis, E.
2001STIN...0227999J Altcode:
Measurements of components of the vector magnetic field in the
solar corona can potentially yield information critical to our
understanding of coronal structure, dynamics and heating. In this
report we re-examine various techniques for such measurements,
in particular those that can be applied outside of active regions,
to investigate issues critical to the development of a new 'coronal
magnetometer,' and to lay down some foundations upon which a suitable
instrument may be developed for synoptic observations. The well-known
forbidden coronal emission lines of magnetic dipole (M1) character
appear to have the highest potential to address outstanding problems in
coronal physics, especially those related to the storage and release
of magnetic free energy. Measurements of the full Stokes vector of
M1 lines can constrain both the line-of-sight (LOS) field strength,
through the longitudinal Zeeman effect seen in Stokes V profiles, and
the direction of the vector field projected onto the plane-of-the-sky
(POS), through the analysis of resonance scattering-induced linear
polarization seen in Stokes Q and U, in the so-called 'strong field'
regime of the Hanl effect.
---------------------------------------------------------
Title: A Synthesis Code for Forbidden Coronal Lines
Authors: Judge, P. G.; Casini, R.
2001ASPC..236..503J Altcode: 2001aspt.conf..503J
No abstract at ADS
---------------------------------------------------------
Title: Spectral Lines for Polarization Measurements of the Coronal
Magnetic Field. III. Atomic Data for Si IX
Authors: Brage, Tomas; Judge, Philip G.; Jönsson, Per; Edwards, D. P.
2000ApJ...540.1114B Altcode:
We report on large-scale ab initio multiconfiguration
Dirac-Fock (MCDF) calculations for spectral lines
of Si IX, with emphasis on the forbidden transitions
2p<SUP>2</SUP> <SUP>3</SUP>P<SUB>J-->J<SUP>'</SUP></SUB>. The
J=0-->J<SUP>'</SUP>=1 transition at 3.9346 μm holds promise as a
diagnostic of coronal magnetic fields if and when future coronagraphic
instruments can measure the polarized light at this wavelength.
---------------------------------------------------------
Title: Erratum: Spectral Lines for Polarization Measurements of the
Coronal Magnetic Field. II. Consistent Treatment of the Stokes Vector
for Magnetic-Dipole Transitions
Authors: Casini, R.; Judge, P. G.
2000ApJ...533..574C Altcode:
In the paper “Spectral Lines for Polarization Measurements
of the Coronal Magnetic Field. II. Consistent Treatment of the
Stokes Vector for Magnetic-Dipole Transitions,” by R. Casini and
P. G. Judge (ApJ, 522, 524 [1999]), several typographical errors
were introduced during the production process. The corrections
are as follows: 1. In the second entry of the fourth panel of
Table 1, sqrt(3)/2 cosϑ should read sqrt(3/2) cosϑ 2. The
left-hand sides of equations (23a) and (23b) should be as in
the left-hand sides of equations (22a) and (22b). 3. In equations
(24c) and (24e), ρ<SUP>K<SUP>'</SUP></SUP><SUB>0</SUB>(αJ) should read
ρ<SUP>K<SUP>'</SUP></SUP><SUB>0</SUB><SUP>K<SUP>'</SUP></SUP>(α<SUP>'</SUP>J<SUP>'</SUP>)
4. In equations (24e) and (24f),
J<SUP>K<SUP>”</SUP></SUP><SUB>0</SUB>(ω<SUB>α<SUP>'</SUP>J,αJ<SUP>'</SUP></SUB>)
should read
J<SUP>K<SUP>”</SUP></SUP><SUB>0</SUB>(ω<SUB>α<SUP>'</SUP>J<SUP>'</SUP>,αJ</SUB>)
5. The very first sentence in the legend of Figure 5 should be
deleted. The Press sincerely apologizes for these errors. A last
typographical error, which instead is the complete responsibility of
the authors, is the absence of a minus sign in front of the right-hand
sides of equations (43a) and (43b).
---------------------------------------------------------
Title: Chromospheric and Transition Region Internetwork Oscillations:
A Signature of Upward-propagating Waves
Authors: Wikstøl, Ø.; Hansteen, V. H.; Carlsson, M.; Judge, P. G.
2000ApJ...531.1150W Altcode:
We analyze spectral time series obtained on 1997 April 25 with
the SUMER instrument on SOHO. Line and continuum data near 1037
Å were acquired at a cadence of 16 s. This spectral region was
chosen because it contains strong emission lines of C II, formed
in the upper chromosphere/lower transition region; O VI, formed
in the upper transition region; and neighboring continuum emission
formed in the middle chromosphere. The time series reveal oscillatory
behavior. Subsonic (3-5 km s<SUP>-1</SUP> amplitude) Doppler velocity
oscillations in the C II and O VI lines, with periods between 120
and 200 s, are prominent. They are seen as large-scale coherent
oscillations, typically of 3-7 Mm length scale, occasionally approaching
15 Mm, visible most clearly in internetwork regions. The Doppler
velocity oscillations are related to oscillations seen in the continuum
intensity, which precede upward velocity in C II by 40-60 s. The C II
Doppler shift precedes the O VI Doppler shift by 3-10 s. Oscillations
are also present in the line intensities, but the intensity amplitudes
associated with the oscillations are small. The continuum intensity
precedes the C II intensity by 30-50 s. Phase difference analysis
shows that there is a preponderance of upward-propagating waves in the
upper chromosphere that drive an oscillation in the transition region
plasma, thus extending the evidence for upward-propagating waves from
the photosphere up to the base of the corona.
---------------------------------------------------------
Title: On Spectroscopic Filling Factors and the Solar Transition
Region
Authors: Judge, P. G.
2000ApJ...531..585J Altcode:
The concept of spectroscopic filling factors is examined by assuming
that observable astrophysical plasmas are inhomogeneous and must
therefore be described using functions ζ(n), the emission measure
differential in electron density n. Using a formal definition for the
spectroscopic filling factor (f<SUB>s</SUB>) and simple distribution
functions, it is shown that (1) f<SUB>s</SUB> differs from the
geometric filling factor f unless the plasma is truly homogeneous
[ζ(n)=ζ<SUB>0</SUB>δ(n-n<SUB>0</SUB>)], (2) f<SUB>s</SUB> depends
on the choice of line pairs for the same ζ(n), (3) f<SUB>s</SUB>
systematically underestimates f, and (4) f<SUB>s</SUB> departs
more from f the broader the distribution ζ(n). Implications for
the particular case of the unresolved solar transition region are
discussed. A dynamic “classical” transition region model appears
to satisfy observed properties, including tiny filling factors
(10<SUP>-5</SUP>-10<SUP>-2</SUP>) as well as filamentary models. This
work highlights the nonunique interpretation of spectral data in terms
of unresolved plasma structure.
---------------------------------------------------------
Title: Non-Uniqueness of Atmospheric Modeling
Authors: Judge, Philip G.; McIntosh, Scott W.
1999SoPh..190..331J Altcode:
We focus on the deceptively simple question: how can we use the emitted
photons to extract meaningful information on the transition region and
corona? Using examples, we conclude that the only safe way to proceed
is through forward models. In this way, inherent non-uniqueness is
handled by adding information through explicit physical assumptions
and restrictions made in the modeling procedure. The alternative,
`inverse' approaches, including (as a restricted subset) many standard
'`spectral diagnostic techniques', rely on more subjective choices
that have, as yet, no clear theoretical support. Emphasis is on the
solar transition region, but necessarily discussing the corona, and
with implications for more general problems concerning the use of
photons to diagnose plasma conditions.
---------------------------------------------------------
Title: Transition Region Oscillations
Authors: Hansteen, V. H.; Wisktol, O.; Carlsson, M.; Judge, P. G.
1999ESASP.446..351H Altcode: 1999soho....8..351H
We analyze time series data obtained April 25th 1997 with the SUMER
instrument on SOHO. Line and continuum data near 1037 were acquired at
a cadence of 16s. This spectral region was chosen because it contains
strong emission lines of C II, formed in the upper chromosphere/lower
transition region, O VI, formed in the upper transition region, as well
as neighboring continuum emission formed in the middle chromosphere. The
dataset reveals oscillatory behavior containing valuable information
on the physical structure of the chromosphere and transition
region. Prominent in the data are subsonic (3-5 km/s amplitude)
velocity oscillations with periods between 120 and 200 sec. They
are seen as large scale coherent oscillations, typically of 3--7 Mm
length scale but sometimes approaching 15Mm, visible most clearly
in internetwork regions. The oscillations are present in C II and O
VI velocities, as well as in the continuum intensity. The continuum
intensity precedes upward velocity in the C II line by 40-60s and the C
III velocity precedes the O VI velocity by 3-10s. The oscillations are
also present in the intensities of the two lines, but the intensity
amplitudes associated with the oscillations are small. We find that
the continuum intensity precedes the C II intensity by 30-50s. These
phase shifts indicate that there are upward propagating waves in the
upper chromosphere that drive an oscillation in the transition region
plasma. The oscillations seem to be present in most internetwork areas
at any time, thus they are the dominant resolvable dynamical feature
of the internetwork chromosphere and transition region.
---------------------------------------------------------
Title: On the Doppler Shifts of Solar Ultraviolet Emission Lines
Authors: Peter, H.; Judge, P. G.
1999ApJ...522.1148P Altcode:
We examine emission-line profiles observed with the Solar Ultraviolet
Measurement of Emitted Radiation (SUMER) instrument during the roll
of the SOHO spacecraft on 1997 March 20. SUMER data were acquired in
selected wavelength bands including lines from the low chromosphere to
the corona. Our main aim is to determine the center-to-limb behavior
of emission lines formed in the chromosphere, transition region,
and corona, especially of the observed Doppler shifts, to try to
form a consistent picture of the basic kinematic properties of the
emitting plasmas. To achieve this we combine the roll data with data
from the full disk discussed elsewhere and fitted Gaussian profiles
to the cores of the line profiles. The Doppler-shift data at large
spatial scales (>50") clearly reveal center-to-limb redshift
behavior consistent with a cosϑ variation in all transition region
lines. The three “coronal” lines in the data set (of Ne VIII and
Mg X) reveal center-to-limb behavior consistent with disk-center
blueshifts, in contradiction to some previous work. The redshift
to blueshift transition occurs at electron temperatures of about
5×10<SUP>5</SUP> K. Furthermore, we present evidence for an outflow
of the fast solar wind from the coronal holes throughout the whole
transition region. These results confirm and extend earlier work and
point toward a (re-) measurement of rest wavelengths of lines formed at
coronal temperatures in the laboratory. Together these results provide
a firmer observational foundation for the development of classes of
models to account for the well-known redshifts and point to the need
to develop models that can also account for the coronal-line blueshifts.
---------------------------------------------------------
Title: Spectral Lines for Polarization Measurements of the Coronal
Magnetic Field. II. Consistent Treatment of the Stokes Vector
forMagnetic-Dipole Transitions
Authors: Casini, R.; Judge, P. G.
1999ApJ...522..524C Altcode:
We present a compact, self-consistent formulation for the description
of polarized radiation from magnetic-dipole transitions occurring
in the magnetized solar corona. This work differs from earlier
treatments by Sahal-Bréchot and House in the 1970s, in that the
radiative emission coefficients for the four Stokes parameters, I,
Q, U, and V, are treated to first order in a Taylor expansion of the
line profile in terms of the Larmor frequency of the coronal magnetic
field. In so doing, the influence on the scattered radiation of both
atomic polarization, induced through anisotropic irradiation, and
the Zeeman effect is accounted for in a consistent way. It is found
that the well-known magnetograph formula, relating the V profile to
the frequency derivative of the I profile, must be corrected in the
presence of atomic alignment produced by anisotropic irradiation. This
correction is smallest for lines where collisions and cascades dominate
over excitation by anisotropic radiation, but it systematically
increases with height above the solar limb (up to a theoretical
maximum of 100%, in the collisionless regime and in the limit of
vanishing longitudinal magnetic field). Although the correction to
the magnetograph formula must be calculated separately for each line
as a function of heliocentric distance, it is likely to be small for
some lines of practical interest, along lines of sight close to the
solar limb.
---------------------------------------------------------
Title: Probable Detection of a Bright Infrared Coronal Emission Line
of Si IX near 3.93 Microns
Authors: Kuhn, J. R.; MacQueen, R. M.; Streete, J.; Tansey, G.; Mann,
I.; Hillebrand, P.; Coulter, R.; Lin, H.; Edmunds, D.; Judge, P.
1999ApJ...521..478K Altcode:
We report here the probable detection of an emission line of Si
IX that was observed from an open C130 aircraft over the Pacific
Ocean during the 1998 total solar eclipse. Although the IR data
themselves are inconclusive because of the uncertainty in the precise
central wavelengths of the narrowband filters during the eclipse,
the consistency of the measured IR limb excess with simultaneous EUV
emission measured by SOHO/Coronal Diagnostic Spectrometer and the EUV
Imager Telescope support our detection claim. This line appears to
be the brightest IR coronal line yet observed, and its existence may
significantly improve future prospects for obtaining optical coronal
magnetic field measurements.
---------------------------------------------------------
Title: TRACE Images of the Solar Chromosphere, Transition Region,
and Low Corona at High Cadence and High Spatial Resolution
Authors: Tarbell, T. D.; Handy, B. N.; Judge, P. G.
1999AAS...194.7801T Altcode: 1999BAAS...31..960T
We present TRACE images and movies showing C IV emission (transition
region at 80,000 degrees) and UV continuum (temperature minimum
region) of quiet and active regions. TRACE images using the 1550,
1600, and 1700 Angstroms filters can be combined to estimate the total
emission in the C IV 1548 and 1550 lines and the UV continuum. These
are supplemented in different observations with MDI magnetograms, TRACE
171 Angstroms images (Fe IX/X and perhaps O VI), and SUMER spectra of
chromospheric and transition region lines from SOHO JOP 72. In quiet
sun, bright C IV transients are seen in the vicinity of flux emergence,
flux cancellation, and less dramatic interactions of small magnetic
structures. Some of these are accompanied by high-velocity explosive
events seen in SUMER spectra. The C IV emission can be well-separated
from the photospheric magnetic footpoints, suggesting that it takes
place on current sheets higher in the atmosphere separating different
flux systems. In active regions, both bright and dark fibrils or loops
are seen in C IV. Many nano/micro/sub flares are seen, some but not
all of which are associated with emerging flux. The C IV emission of
"moss" regions, footpoints of hot coronal loops, is contrasted with
that of similar plage which does not have hot loops above it. This work
was supported by the NASA contracts and grants for TRACE, MDI, and SOHO.
---------------------------------------------------------
Title: Lines of OIV and SIV in the Goddard High-Resolution
Spectrograph spectrum of RR Tel: constraints on atomic data
Authors: Harper, G. M.; Jordan, C.; Judge, P. G.; Robinson, R. D.;
Carpenter, K. G.; Brage, T.
1999MNRAS.303L..41H Altcode:
High signal-to-noise ratio spectra of RR Tel obtained at medium
resolution with the Goddard High-Resolution Spectrograph (GHRS) on the
Hubble Space Telescope (HST) are used to test available atomic data for
the OIV 2s^22p ^2P-2s2p^2 ^4P multiplet (UV 0.01). The fine-structure
intervals of the 2s2p^2 ^4P term given by Moore (1983) appear to need
revision. The flux ratios of lines within multiplet UV (0.01), which
have a common upper level, depend only on transition probabilities. The
observed flux ratio of lines from the ^4P_3/2 level differs from that
predicted by theory, but this difference cannot be attributed to a
blend with a line of SIV]. At the electron densities in the RR Tel
nebula, other flux ratios give information on the relative electron
excitation rates between the ^2P and ^4P fine-structure levels. Using
the collision strengths calculated by Zhang, Graziani & Pradhan,
the rate to the ^4P_5/2 level, relative to the rates to the other J
states, appears to be underestimated by ~ 10 per cent, which is within
the expected uncertainty of 20 per cent. We also discuss the SIV 3s^23p
^2P-3s3p^2 ^4P multiplet.
---------------------------------------------------------
Title: Spectral decomposition by genetic forward modelling
Authors: McIntosh, S. W.; Diver, D. A.; Judge, P. G.; Charbonneau,
P.; Ireland, J.; Brown, J. C.
1998A&AS..132..145M Altcode:
We discuss the analysis of real and simulated line spectra using
a genetic forward modelling technique. We show that this Genetic
Algorithm (GA) based technique experiences none of the user bias
or systematic problems that arise when faced with poorly sampled or
noisy data. An important feature of this technique is the ease with
which rigid a priori constraints can be applied to the data. These
constraints make the GA decomposition much more accurate and stable,
especially at the limit of instrumental resolution, than decomposition
algorithms commonly in use.
---------------------------------------------------------
Title: Evidence in Support of the “Nanoflare” Picture of Coronal
Heating from SUMER Data
Authors: Judge, P. G.; Hansteen, V.; Wikstøl, Ø.; Wilhelm, K.;
Schühle, U.; Moran, T.
1998ApJ...502..981J Altcode:
We study high signal-to-noise profiles of O IV emission lines obtained
using the SUMER instrument on SOHO. Data for the quiet Sun obtained
close to the disk center and at the solar limb were acquired. After
careful data processing in which disk data were analyzed differentially
against limb data, we find a systematic correlation between a
density-sensitive emission-line ratio and Doppler shift across the
same emission-line profiles. While unidentified blended lines cannot be
completely discounted, the data suggest that the effects of such blends
are small. Based on theoretical results in an earlier paper, we argue
that if wave motions are responsible for the observed behavior, then
the data reveal evidence for compressive waves propagating downward
from the corona to the chromosphere. This analysis naturally lends
support to the dominance of the “nanoflare” mechanism for coronal
heating over other theories that invoke upward wave propagation,
but other mechanisms capable of generating downward-propagating waves
cannot be discounted. If, instead, steady flows are the cause of the
observed behavior, such as return flows from spicules, then they must
be such that the density is higher in the downflowing plasma. While
these particular data do not allow us to discriminate between waves
or steady flows, additional data from SOHO should be able to address
this problem. This work required and achieved very accurate wavelength
calibrations (better than 1/5 of a pixel on the detectors), taking
SUMER close to its observational capabilities. We therefore present
the elements of the analysis and calibration of SUMER data that may
be of interest to other users.
---------------------------------------------------------
Title: On Inferring the Properties of Dynamic Plasmas from Their
Emitted Spectra: The Case of the Solar Transition Region
Authors: Wikstøl, Øivind; Judge, P. G.; Hansteen, Viggo
1998ApJ...501..895W Altcode:
We reexamine the issue of inferring physical properties of solar
plasmas using EUV and UV observations. We focus on the question of
whether one can determine if typical structures seen as bright in
typical “transition-region” lines are formed in the thermal interface
between the coronal and chromospheric plasmas. Since 1983, Feldman and
colleagues have proposed, based upon Skylab and other data, that much
of the transition-region emission is formed in so-called unresolved
fine structures (UFS) that are magnetically and thermally disconnected
from the corona. This has led others to consider theoretical models of
the transition region that differ from classical models. We examine the
evidence cited in support of the UFS picture, specifically by relaxing
the implicit assumption of a static atmospheric structure. Noting
that observational data alone do not contain the information necessary
to infer essential properties of the emitting plasmas, we argue that
additional information must be added through forward calculations using
physical models. MHD models of coronal flux tubes are then examined
with explicit assumptions and boundary conditions, not as an attempt to
“fit” observed data, but in order to study the formation of emission
lines in dynamically evolving plasmas that are unresolved in space
and time. We show that incorrect conclusions can be drawn by applying
reasonable and traditional diagnostic methods to spectral data when
unresolved dynamic evolution of the emitting plasma is important but
not accounted for. In the particular case of the transition region,
we show that the UFS interpretation is not unique, and is likely to
be incorrect in the presence of unresolved dynamics. Most or all of
the evidence for UFS is amenable to a different, equally reasonable
interpretation, in which the transition-region emission is at all times
formed in the time-varying thermal interface between the corona and the
chromosphere. This work is likely to be important for a wider range of
astrophysical plasmas than simply in the solar transition region. At
stake is our basic ability to correctly diagnose physical conditions
of plasmas for which heating mechanisms are not yet understood, but
which are likely to be time dependent.
---------------------------------------------------------
Title: Hyperfine Induced Transitions as Diagnostics of Isotopic
Composition and Densities of Low-Density Plasmas
Authors: Brage, Tomas; Judge, Philip G.; Aboussaïd, Abdellatif;
Godefroid, Michel R.; Jönsson, Per; Ynnerman, Anders; Froese Fischer,
Charlotte; Leckrone, David S.
1998ApJ...500..507B Altcode:
The J = 0 --> J' = 0 radiative transitions, usually viewed
as allowed through two-photon decay, may also be induced by the
hyperfine (HPF) interaction in atoms or ions having a nonzero
nuclear spin. We compute new and review existing decay rates for the
nsnp <SUP>3</SUP>P<SUP>o</SUP><SUB>J</SUB> --> ns<SUP>2</SUP>
<SUP>1</SUP>S<SUB>J'=0</SUB> transitions in ions of the Be (n =
2) and Mg (n = 3) isoelectronic sequences. The HPF induced decay
rates for the J = 0 --> J' = 0 transitions are many orders of
magnitude larger than those for the competing two-photon processes,
and when present are typically 1 or 2 orders of magnitude smaller
than the decay rates of the magnetic quadrupole (J = 2 --> J'
= 0) transitions for these ions. Several HPF induced transitions
are potentially of astrophysical interest in ions of C, N, Na, Mg,
Al, Si, K, Cr, Fe, and Ni. We highlight those cases that may be of
particular diagnostic value for determining isotopic abundance ratios
and/or electron densities from UV or EUV emission-line data. We
present our atomic data in the form of scaling laws so that, given
the isotopic nuclear spin and magnetic moment, a simple expression
yields estimates for HPF induced decay rates. We examine some UV and
EUV solar and nebular data in light of these new results and suggest
possible applications for future study. We could not find evidence
for the existence of HPF induced lines in the spectra we examined,
but we demonstrate that existing data have come close to providing
interesting upper limits. For the planetary nebula SMC N2, we derive
an upper limit of 0.1 for <SUP>13</SUP>C/<SUP>12</SUP>C from Goddard
High-Resolution Spectrograph data obtained by Clegg. It is likely that
more stringent limits could be obtained using newer data with higher
sensitivities in a variety of objects.
---------------------------------------------------------
Title: Spectral Lines for Polarization Measurements of the Coronal
Magnetic Field. I. Theoretical Intensities
Authors: Judge, P. G.
1998ApJ...500.1009J Altcode:
Infrared emission lines are potentially sensitive probes of components
of the coronal vector magnetic field, through the Zeeman effect,
and on its direction projected onto the plane of the sky, through
fluorescent polarization of scattered photospheric light. Prompted
by the advent of sensitive infrared array detectors, existing atomic
data were reexamined to compile a complete list of coronal lines that
may yield a detectable Zeeman effect, through careful differential
measurements of Stokes profiles, at typical coronal field strengths
of order 10 G. “Average” intensities were computed for a subset of
promising forbidden coronal lines. A representative coronal density
structure was used. The distribution of plasma with temperature was,
at all heights in the corona, assumed to be that described by a standard
differential emission measure from extreme-ultraviolet observations of
the solar disk. Effects of excitation by photospheric radiation were
included, as well as cascades from collisionally excited higher levels
having the same principal quantum number as the ground levels. The
largest source of error in the computed intensities lies in the form
assumed for the emission measure distribution. The assumed density
and temperature structure is too simple for detailed comparisons
with observations of a particular coronal structure. Nevertheless,
existing observed intensities are consistent with the calculations,
which suggests that the theoretical intensities of (as yet) unobserved
lines can be used as a basis for further study. The strongest predicted
lines arise from magnetic dipole transitions within the ground terms
of the 2s<SUP>m</SUP>2p<SUP>n</SUP> and 3s<SUP>m</SUP>3p<SUP>n</SUP>,
m = 1, 2, n = 1, ..., 5, configurations. The most promising lines lie
between 1 and 10 μm, the lower limit being set by the need to detect
small field strengths. The upper limit is set by the small Einstein
A-coefficients and the smaller intensities of the exciting photospheric
light, both of which lead to smaller forbidden line intensities. The
most promising lines include [Fe XIII] 1.0747, 1.0798 μm [Si X]
1.43 μm [Si IX] 2.58, 3.93 μm [Mg VIII] 3.03 μm and [Mg VII]
5.50, 9.03 μm. An aircraft experiment is being prepared to obtain
targeted portions of the coronal spectrum between 1 and 10 μm during
the 1998 February 26 eclipse, with the goal of detecting some of these
promising lines. This work will help toward the planning and development
of efficient magnetographs, perhaps space-borne, for the routine
measurement of coronal magnetic fields in the quiet and active Sun.
---------------------------------------------------------
Title: The relation between line ratio and emission measure analyses
Authors: McIntosh, S. W.; Brown, J. C.; Judge, P. G.
1998A&A...333..333M Altcode:
Spectroscopic diagnosis of the temperature and density structure of
hot optically thin plasmas from emission line intensities is usually
described in two ways. The simplest approach, the `line ratio' method,
uses an observed ratio of emission line intensities to determine a
`spectroscopic mean' value of electron temperature < T_e >
or electron density < n<SUB>e</SUB>>. The mean value is chosen
to be the theoretical value of T_e or n<SUB>e</SUB> which matches the
observed value. The line ratio method is stable, leading to well defined
values of < T_e > or < n_e > for each line pair but, in the
realistic case of inhomogeneous plasmas, these are hard to interpret
since each line pair yields different mean parameter values. The more
general `differential emission measure' (DEM) method recognizes that
observed plasmas are better described by distributions of temperature
or density along the line of sight, and poses the problem in inverse
form. It is well known that the DEM function is the solution to the
inverse problem, which is a function of T_e, n_e, or both. Derivation of
DEM functions, while more generally applicable, is unstable to noise
and errors in spectral and atomic data. The mathematical relation
between these two approaches has never been precisely defined. In
this paper we demonstrate the formal equivalence of the approaches,
and discuss some potentially important applications of methods based
upon combining the line ratio and DEM approaches.
---------------------------------------------------------
Title: The Structure of the Chromosphere Properties Pertaining to
Element Fractionation
Authors: Judge, P. G.; Peter, H.
1998SSRv...85..187J Altcode:
We review the structure and dynamics of the solar chromosphere with
emphasis on the quiet Sun and properties that are relevant to element
fractionation mechanisms. Attention is given to the chromospheric
magnetic field, its connections to the photosphere, and to the dynamical
evolution of the chromosphere. While some profound advances have been
made in the “unmagnetized” chromosphere, our knowledge of the
magnetically controlled chromosphere, more relevant for the discussion
of element fractionation, is limited. Given the dynamic nature of the
chromosphere and the poorly understood magnetic linkage to the corona,
it is unlikely that we will soon know the detailed processes leading
to FIP fractionation.
---------------------------------------------------------
Title: On Chromospheric Heating Mechanisms of “Basal Flux” Stars
Authors: Judge, P. G.; Carpenter, K. G.
1998ApJ...494..828J Altcode:
Several pieces of evidence have been pieced together over recent years
to support the notion that the chromospheric emission measured from
stars with convection zones results in part from the upward propagation
and dissipation of acoustic waves. One argument, based on a statistical
analysis of available UV data of such stars across the H-R diagram,
suggests the presence of an omnipresent “basal” level of chromospheric
heating, which has been postulated as resulting from nonlinear acoustic
wave heating. <P />However, with few exceptions, no studies have been
made that test more directly the intrinsically dynamic nature of this
shock-heating mechanism. Therefore, in order to search for more direct
signatures of such upward-propagating shock waves in lines of C II,
we examined Goddard High-Resolution Spectrograph spectra of several
evolved stars that have “basal” levels of activity. No evidence is
found to support the presence of such waves as a dominant component
of the heating mechanism. Instead, behavior reminiscent of the solar
transition region is seen, suggesting a magnetic heating mechanism
for these stars. <P />We conclude that upward-propagating shock waves
do not dominate the observed radiative losses from chromospheres of
stars exhibiting typical “basal” behavior, and we suggest that the
nonmagnetic origin of the basal components of all convective stars
must be called into question. New solar data from the SUMER instrument
on SOHO also suggest problems with the acoustic-wave interpretation,
although further work is warranted. <P />In the course of this work,
we also found a simple explanation for previously noted discrepancies
between calculated and observed ratios of C II lines in the spectrum
of α Ori. <P />Based on observations with the NASA/ESA Hubble Space
Telescope, which is operated by the Association of Universities for
Research in Astronomy, Inc., under NASA contract NAS 5-26555.
---------------------------------------------------------
Title: The Structure of the Chromosphere
Authors: Judge, P. G.; Peter, H.
1998sce..conf..187J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: SUMER Observations of the Quiet Solar Atmosphere: The Network
Chromosphere and Lower Transition Region
Authors: Judge, Philip; Carlsson, Mats; Wilhelm, Klaus
1997ApJ...490L.195J Altcode:
We examine spectral properties of the network chromosphere and lower
transition region from the SUMER instrument on the SOHO spacecraft,
using time-series data sets discussed in an accompanying Letter by
Carlsson, Judge, & Wilhelm. The data were obtained early in the
mission with no tracking of solar features and so cannot generally
be used to examine intrinsic variations in features on timescales
in excess of 383 s. Upon examination of the temporal variations and
some preliminary power spectrum analysis, we find the following:
(1) Transition region lines show more redshift in network regions
than in internetwork regions and also a correlation between line
intensity brightenings and increased redshift. (2) The internetwork
“Ca II grain” phenomenon is not seen in He I λ584 or in lines
of Si III and C III. (3) Very rapid changes are seen in the network
for transition region lines with no obvious correspondence with the
underlying chromosphere. (4) He I λ584 line profiles show very slow
time variations. (5) Small-amplitude (2-5 km s<SUP>-1</SUP>) coherent
oscillations of 5"-10" scale length and ~130 s period are seen in
Doppler shifts of Si III between regions of bright network elements. (6)
Essentially all blueshifts or redshifts are substantially less than line
widths. We conclude that upward-propagating acoustic shock waves do not
contribute significantly to the heating of the lower transition region,
and that ionization equilibrium is likely to fail for the interpretation
of certain emission lines. The spatial coherency of the Si III velocity
oscillations indicates that the quiet Sun's magnetic field topology
is more uniform than emission-line intensity data alone might suggest.
---------------------------------------------------------
Title: Differential Emission Measures-Can we do more??
Authors: McIntosh, S. W.; Brown, J. C.; Judge, P. G.
1997BAAS...29.1120M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: SUMER Observations Confirm the Dynamic Nature of the Quiet
Solar Outer Atmosphere: The Internetwork Chromosphere
Authors: Carlsson, Mats; Judge, P. G.; Wilhelm, K.
1997ApJ...486L..63C Altcode: 1997astro.ph..6226C
On 1996 March 12, during the commissioning phase of the SOHO mission, we
obtained observations of the quiet-Sun with the SUMER instrument. The
observations were sequences of 15-20 s exposures of ultraviolet
emission-line profiles and of the neighboring continua. These data
contain signatures of the dynamics of the solar chromosphere that are
uniquely useful because of wavelength coverage, moderate signal-to-noise
ratios, and image stability. <P />We focus on data for the internetwork
chromosphere. The dominant observed phenomenon is an oscillatory
behavior that is analogous to the 3 minute oscillations seen in CaII
lines. The oscillations appear to be coherent over 3"-8" diameter
areas. At any time they occur over about 50% of the area studied,
and they appear as large perturbations in the intensities of lines
and continua. The oscillations are most clearly seen in intensity
variations in the ultraviolet (λ > 912 Å) continua, and they are
also seen in the intensities and velocities of chromospheric lines of
CI, NI, and OI. Intensity brightenings are accompanied by blueshifts
of typically 5 km s<SUP>-1</SUP>. Phase differences between continuum
and line intensities also indicate the presence of upward propagating
waves. The detailed behavior is different between different lines,
sometimes showing phase lags. The 3 minute intensity oscillations
are occasionally seen in second spectra (CII λ1335) but never in
third spectra (CIII and SiIII). Third spectra and HeI λ584 show
oscillations in velocity that are not simply related to the 3 minute
oscillations. The continuum intensity variations are consistent with
recent simulations of chromospheric dynamics (Carlsson and Stein),
while the line observations indicate that important ingredients are
missing at higher layers in the simulations. <P />The data show that
time variations are crucial for our understanding of the chromosphere
itself and for the spectral features formed there--the quiet-Sun's
chromosphere is very dynamic and not “quiet.” The implications of
these data should be considered when planning chromospheric work with
instruments such as those on SOHO.
---------------------------------------------------------
Title: Signatures of Acoustic and Magnetic Waves in Solar and
Stellar Coronae
Authors: Wikstøl, Øivind; Judge, Philip G.; Hansteen, Viggo H.
1997ApJ...483..972W Altcode:
Time-dependent dynamical calculations of the radiating gas in solar
coronal flux tubes are used to identify features of UV spectral-line
profiles that can reveal the direction in which wave energy flows
through the solar transition region. The profile features survive
spatial and temporal averaging through nonlinear dependencies of
line emission coefficients on thermal properties of the plasma
that are correlated with fluid velocities. This approach can be
applied to stellar and other unresolved sources, as well as the
solar atmosphere. It can be regarded as a new angle of attack on the
long-standing problem of determining coronal heating mechanisms. The
approach requires low noise data of high spectral resolution. Therefore,
it can take advantage of some unique properties of the SUMER instrument
on SOHO. We make specific predictions for SUMER data that, in principle,
can test whether energy propagates upward or downward in coronal flux
tubes, thus allowing one to discriminate between competing theories of
coronal heating. We are acquiring SUMER data in an attempt to do this.
---------------------------------------------------------
Title: Evidence in Support of the “Nanoflare Picture” of Coronal
Heating from SUMER Data
Authors: Judge, P.; Wikstol, O.; Hansteen, V.
1997SPD....28.0505J Altcode: 1997BAAS...29..909J
We study high signal\--to\--noise profiles of O 4 emission lines
obtained using the SUMER instrument on SoHO. Data for the quiet Sun
obtained close to disk center and at the solar limb were acquired. After
careful data processing in which disk data were analyzed differentially
against limb data, we find a systematic correlation between a
density sensitive emission line ratio and Doppler shift across the
same emission line profiles. Based upon theoretical results in an
earlier paper, we argue that if wave motions are responsible for
the observed behavior, then the data reveal evidence for compressive
waves propagating downwards from the corona to the chromosphere. This
analysis therefore lends support to the dominance of the “nanoflare”
mechanism for coronal heating (\cite{Parker1988}) over other theories
that invoke upward wave propagation. If instead steady flows are the
cause of the observed behavior, such as return flows from spicules,
then they must be such that the density is higher in the downflowing
plasma. We present time series data of other transition region lines
from SoHO that suggest that episodic heating such as may occur through
nanoflares is a more reasonable picture of heating mechanisms than
models based upon steady flows.
---------------------------------------------------------
Title: Working Group 1: Non-Stationary Processes
Authors: Judge, P. G.
1997ESASP.404..125J Altcode: 1997cswn.conf..125J
No abstract at ADS
---------------------------------------------------------
Title: SUMER Observations Detecting Downward Propagating Waves in
the Solar Transition Region
Authors: Wiskstøl, Ø.; Judge, P. G.; Hansteen, V.; Wilhelm, K.;
Schühle, U.; Moran, T.
1997ESASP.404..731W Altcode: 1997cswn.conf..731W
No abstract at ADS
---------------------------------------------------------
Title: Observational signatures of nanoflare heated solar stellar
coronae
Authors: Wikstøl, Ø.; Judge, P. G.; Hansteen, V. H.
1997AdSpR..20.2289W Altcode:
Using time-dependent dynamical models of the radiating gas in coronal
flux tubes, we identify features in UV spectral line profiles
that can reveal the direction in which energy flows through the
solar transition region, in observations without temporal or spatial
resolution. The profile features survive spatial and temporal averaging
through non-linear dependencies of the line emission coefficients
on thermal properties of the plasma that are correlated with the
material velocity. This approach requires only low noise data of high
spectral resolution and could naturally be applied to stars as well as
the solar corona. We make predictions for the SUMER instrument that
can in principle test whether energy propagates upwards or downwards
in coronal flux tubes, suggesting a new angle of attack on the long
standing problem of determining coronal heating mechanisms.
---------------------------------------------------------
Title: Fundamental Limitations of Emission-Line Spectra as Diagnostics
of Plasma Temperature and Density Structure
Authors: Judge, P. G.; Hubeny, Veronika; Brown, John C.
1997ApJ...475..275J Altcode:
We discuss the problem of determining plasma structure from optically
thin emission lines whose emission coefficients and frequency-integrated
intensities are dependent on temperature T and electron density n. We
cast the problem into the inverse form discussed by Hubeny & Judge
(1995). <P />Three properties of the kernels in the integral equations
lead to fundamental limitations in trying to determine the source
term μ(T, n), the “emission measure differential in temperature and
density,” from a set of emission-line intensities. First, the kernels
are rather weakly dependent on n. Second, they have asymptotically
identical dependencies on n. The inverse problem is therefore very
poorly conditioned in the density dimension. Third, the kernels cannot
(and may never) be calculated with an accuracy better than +/-10%. These
properties set limits on the accuracy of all solutions, independent of
the accuracy of observed line intensities. This concurs with earlier
but less general work by Brown et al. (1991). <P />We try to determine
solutions for μ(T, n), using specific target sources and numerical
algorithms. Using realistic uncertainties, calculations indicate that
meaningful inverse solutions for μ(T, n) cannot be obtained owing to
the severe propagation of kernel errors, irrespective of the quality of
observational data. Solutions for the “emission measure differential
in temperature” ξ(T) = \smallint μ(T, n)dn are more robust against
instabilities driven by poor conditioning. <P />Since traditional
“emission-line diagnostic ratios” can only be defined through μ(T,
n) (or some generalization thereof), our analysis casts doubt on
the meaning of plasma properties derived from such line ratios, and
illustrates the severe nonuniqueness of any equivalent “inverse”
solution. This work may be important for studying a wide variety of
atomic and ionic emission-line spectra, including work with instruments
on SOHO and the Hubble Space Telescope.
---------------------------------------------------------
Title: The Ultraviolet Spectrum of a 3B Class Flare Observed with
SOLSTICE
Authors: Brekke, P.; Rottman, G. J.; Fontenla, J.; Judge, P. G.
1996ApJ...468..418B Altcode:
An observation of the ultraviolet spectrum (1200-1800 Å) during the
impulsive phase of a very extended 3B-X3 class solar flare on 1992
February 27 was obtained with the Solar-Stellar Irradiance Comparison
Experiment (SOLSTICE). This observation is combined with ground-based
Hα, magnetogram, and microwave data as well as hard X-ray measurements
from the Ulysses spacecraft. This flare shows a dramatic enhancement of
lines formed in the solar transition region. The irradiance (emitted
flux density from the entire solar disk) of the resonance lines of
C iv and Si iv increased by a factor of 12-13 during the impulsive
phase of the flare. These irradiance enhancements are comparable
with those measured during stellar flares. By taking into account the
emitting flare area we infer that the radiance (specific intensity)
of the flaring plasma was at least a factor of 15,000 brighter than the
average solar disk radiance just prior to the event. Assuming the flare
site's initial radiance was that of a typical active region, it then
must have brightened by a factor of at least 3400. Such enhancement
far exceeds previous published values (e.g., OSO 8, Skylab, and SMM)
and indicates that many observations were affected by limited dynamic
range. Thus, the SOLSTICE observation may be the first measurement of
the true UV enhancement during the impulsive phase of very bright solar
flares. <P />The Si III multiplet near 1295 Å also shows remarkable
enhancement, but other allowed lines of C II, Si III (1206 Å), N V,
and He II show more moderate enhancements, the weakest being H I Lyα,
the irradiance of which increases only 6%. Some of the differences
between the various enhancements are certainly caused by the timing of
the observations since the scanning spectrometer observed different
spectral features over periods of 4 minutes. Other differences due
to line formation processes are being investigated but are consistent
with density effects in the line emission coefficients. The inferred
Lyα radiance enhancement is consistent with current post-impulsive
phase flare models. However, the formation of the C IV and Si IV lines,
formed during the impulsive phase of the flare, remains unknown. During
the impulsive phase of the flare the strong transition region lines
are systematically redshifted by 50 km s<SUP>-1</SUP>.
---------------------------------------------------------
Title: Intercombinations and Allowed Transitions in O IV
Authors: Brage, Tomas; Judge, P. G.; Brekke, P.
1996ApJ...464.1030B Altcode:
We report on large-scale ab initio multiconfiguration Hartree-Fock
calculations for important multiplets including the UV 0.01
multiplet, 2s<SUP>2</SUP>2p<SUP>2</SUP>P<SUB>J</SUB>-2s2p<SUP>2</SUP>
<SUP>4</SUP>P<SUB>j'</SUB>, in O IV. The resulting transition
probabilities should be accurate to ±5%-10% for intersystem lines and
1% or better for permitted lines. <P />We present new calculations
of line emission coefficients using these transition probabilities
and collisional rate coefficients published by Zhang, Graziani, &
Pradhan in 1994. We readdress the use of these lines as diagnostics
of electron densities, paying particular attention to uncertainties
in density determinations. We find (1) the absolute uncertainties in
derived densities are difficult to assess, but are at least ±40%
controlled by uncertainties in collision strengths; (2) our new
calculations bring observed and computed line ratios into better
agreement (earlier papers yielding systematically different densities
make the agreement worse); (3) there is additional evidence for strong
blends in the 1404.8 emission feature, as argued by other authors,
and/or evidence for inaccurate laboratory wavelengths; and (4) the
computed branching ratios are in good agreement with observed ratios to
within observational uncertainties of ±7%. <P />We determine electron
densities in a variety of solar features from HRTS data from the first
and second flights of this instrument. The derived electron densities
vary remarkably little between quiet Sun network and active regions,
but resonance line intensities vary dramatically, and we discuss reasons
for this. Finally, we discuss how new high-quality data from the SUMER
instrument to be flown on Solar and Heliosphereic Observatory (SO HO)
could be used to address outstanding problems concerning blends and
heating of the solar transition region.
---------------------------------------------------------
Title: Hyperfine induced transitions as diagnostics of low density
plasmas and isotopic abundance ratios.
Authors: Brage, T.; Judge, P. G.; Aboussaid, A.; Godefroid, M. R.;
Jönsson, P.; Leckrone, D. S.
1996BAAS...28..832B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hyperfine Induced Transitions as Diagnostics of Low Density
Plasmas and Isotopic Abundance ratios.
Authors: Brage, T.; Judge, P. G.; Aboussaid, A.; Godefroid, M. R.;
Jonsson, P.; Leckrone, D. S.
1996AAS...188.0705B Altcode: 1996BAAS...28V.832B
We propose a new diagnostics of isotope abundance ratios and electron
densities for low density plasmas, in the form of J = 0 ->
J(') = 0 radiative transitions. These are usually viewed as being
allowed only through two-photon decay, but they may also be induced
by the hyperfine (HPF) interaction in atomic ions. This predicts a
companion line to the E1] and M2 lines in the UV0.01 multiplet of
ions isoelectronic to beryllium (e.g. C III, N IV, O V and Fe XXII)
or magnesium (e.g. Si II, Ca IX, Fe XV and Ni XVII). As an example
the companion line to the well known lambda lambda 1906.7,1908.7 lines
in C III will be at 1909.597 Angstroms, but only present in the (13)
C isotope (which has nuclear spin different from zero). We present
new and accurate decay rates for the nsnp (3P^o<SUB>J</SUB>) ->
ns(2) (1S_{J('}=0)) transitions in ions of the Be (n=2) and Mg (n=3)
isoelectronic sequences. We show that the HPF induced decay rates for
the J = 0 -> J(') = 0 transitions are many orders of magnitude
larger than those for the competing two-photon processes and, when
present, are typically one or two orders of magnitude smaller than
the decay rates of the magnetic quadrupole ( J = 2-> J(') = 0)
transitions for these ions. We show that several of these HPF-induced
transitions are of potential astrophysical interest, in ions of C, N,
Na, Mg, Al, Si, K, Cr, Fe and Ni. We highlight those cases that may
be of particular diagnostic value for determining isotopic abundance
ratios and/or electron densities from UV or EUV emission line data. We
present our atomic data in the form of scaling laws so that, given the
isotopic nuclear spin and magnetic moment, a simple expression yields
estimates for HPF induced decay rates. We examine some UV solar and
nebular data in the light of these new results and suggest possible
cases for future study. We could not find evidence for the existence
of HPF induced lines in the spectra we examined, but we demonstrate
that existing data have come close to providing interesting upper
limits. For the planetary nebula SMC N2 we derive an upper limit of
(13) C/(12) C of 0.1 from GHRS data obtained by Clegg. It is likely
that more stringent limits could be obtained with newer data with
higher sensitivities in a variety of objects.
---------------------------------------------------------
Title: Ultraviolet (1200 to 1800 Angstroms) Emission during the
Impulsive Phase of a Class 3B-X3 Solar Flare Observed with SOLSTICE
Authors: Brekke, P.; Rottman, C. J.; Fontenla, J.; Judge, P. G.
1996mpsa.conf..213B Altcode: 1996IAUCo.153..213B
No abstract at ADS
---------------------------------------------------------
Title: The UV "sun as a star" flare spectrum observed with SOLSTICE
Authors: Brekke, P.; Rottman, G. J.; Fontenla, J.; Judge, P. G.
1996ASPC..109..111B Altcode: 1996csss....9..111B
No abstract at ADS
---------------------------------------------------------
Title: Atomic calculations inspired by the Hubble Space Telescope:
intercombination and forbidden lines.
Authors: Fleming, J.; Brage, T.; Harper, G.; Bell, K. L.; Hibbert,
A.; Judge, P. G.; Leckrone, D. S.
1996BAAS...28.1203F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Failure of Standard Emission Measure Analysis for
Solar Extreme-Ultraviolet and Ultraviolet Irradiance Spectra
Authors: Judge, P. G.; Woods, T. N.; Brekke, P.; Rottman, G. J.
1995ApJ...455L..85J Altcode:
We perform emission measure analysis of new and accurate UV ( lambda
> 1200 A) and extreme-ultraviolet (EUV) ( lambda <= 1200 A)
irradiance ("Sun-as-a-star") emission-line spectra of the Sun. Our
data consist of (1) daily averaged UV irradiances from the SOLSTICE on
the UARS spacecraft and (2) EUV irradiances obtained on the same date
from a \frac {1}{4} m spectrograph flown on a sounding rocket. Both
instruments have a spectral resolution of roughly 1 A. The absolute
uncertainties in these data are at most +/-15% (+/-2 sigma ), one
of the highest photometric accuracies yet achieved. We find large,
highly significant and systematic discrepancies in the emission measure
analysis of transition region lines which can only be accounted for by
a breakdown of one or more standard assumptions. All strong lines above
1000 A, which are from the Li and Na isoelectronic sequences, are too
strong by factors of between 2.5 and 7 compared with their counterparts
in the EUV region. Previous studies were tantalizingly close to finding
these discrepancies, but those data lacked the wavelength coverage and
relative photometric precision necessary for definitive conclusions. We
argue that either dynamical effects, inaccurate treatments of atomic
processes, and/or Lyman continuum absorption are the culprits. However,
we favor the former explanation. In any event, this study should have
implications for models of the solar transition region, for observing
programs with the CDS and SUMER instruments on SOHO, and for analysis of
UV spectra for stars across the cool half of the H-R diagram. Finally,
the discrepancy is not seen for the "coronal" Li-like ions.
---------------------------------------------------------
Title: Solution to the Bivariate Integral Inversion Problem: The
Determination of Emission Measures Differential in Temperature
and Density
Authors: Hubeny, Veronika; Judge, Philip G.
1995ApJ...448L..61H Altcode:
We present a general solution to the inversion problem of determining
the "source function" f(t, n) from integral equations of the form
g<SUB>i</SUB> = \int \limits \int \limits K<SUB>i</SUB>(t,n)f(t,n)dt
dn. The function f(t, n) represents the most information that can be
extracted from a set of observables {gi} for a source for which the
kernel functions Ki(t, n), depending on the two independent variables
t and n, can be calculated a priori. Our specific application is to
the inversion of the equations for a set of optically thin emission
line intensities gi with kernel functions Ki(t, n) which depend
on both the electron density n and the temperature t, a problem
defined by Jefferies and colleagues in the early 1970s. We determine
"regularized" solutions [those for which derivatives of f(t, n)
are minimized to constrain the allowed solutions] for f(t, n) from
which the usual emission measure differential in temperature xi
(t) = ∫f(t, n) dn can be obtained. Unlike some recent work, our
solution is fully two-dimensional and is not restricted to cases
where functional dependences are assumed to exist between t and n in
f(t, n). We compare our solutions for the source terms (derived from
inversions of calculated intensities from input source functions)
with input source functions, for typical extreme-ultraviolet and UV
lines formed in the solar transition region. Details, refinements,
and applications are left to a later paper. This work is likely to
be relevant to other areas of astrophysics, and can aid in planning
observations with spacecraft such as the Hubble Space Telescope and
the upcoming SOHO mission.
---------------------------------------------------------
Title: GHRS Observations of Cool, Low-Gravity Stars. II. Flow
and Turbulent Velocities in the Outer Atmosphere of gamma Crucis
(M3.4 III)
Authors: Carpenter, Kenneth G.; Robinson, Richard D.; Judge, Philip G.
1995ApJ...444..424C Altcode:
The Goddard High Resoulution Spectrograph (GHRS) on the Hubble Space
Telescope (HST) has been used to obtain medium (R = 20,000) and high
(R = 85,000) resoultion UV spectra of chromosphere emission features
for the M3.4 III star gamma Cru. Small Science Aperture (SSA) G270M and
Echelle-B spectra of selected regions in the 2300-2850 A range were
obtained to determine the kinematics of the chromosphere using lines
of C2), Fe2, Co2, Si1/2), Ni2, Mn2, and Mg2. Profiles of C2) (UV 0.01)
lines and fluorescently excited lines of low optical depth indicate
average turbulent velocities (Doppler FWHM) of 30.2 +/- 1.3 and 28.8 +/-
1.3 km/s, respectively. The fluorescent emission lines (mean RV = 21.3
+/- 0.9 km/s) and the wings of the emission components of Fe2 lines
(mean RV = 22.8 +/- 0.4 km/s) are approximately at rest relative to
the radial velocity of the star (21 km/s), while the C2) lines show
a modest inflow (mean RV = 23.1 +/- 0.9 km/s). The more opaque lines
of Fe2 and Mg2 exhibit complex profiles resulting from line formation
in an optically thick, extended expanding atmosphere. The emission
wings of these lines are broadened by multiple scattering, and they are
centered near the photospheric radial velocity. Closer to line center,
these strong lines show a strong blueshifted self-absorption feature
(already seen in IUE data), indicative of formation in an expanding
chromosphere, and a previously unseen dip in the profiles on the red
side of line center. The absorption components, when extracted using
simple Gaussian fits, show strong correlations with the relative
optical depths of the lines. The derived absorption flow velocities
converge to the photospheric velocity as one examines spectra features
formed deeper in the atmosphere. The blueward abosrption velocity
increases in magnitude from about 7 to 14 km/s with increasing line
optical depth - the strong absorptions directly map the acceleration
of the outflowing stellar wind, while the interpretation of the
weaker redshifted absorptions is more ambiguous, indicating either an
inflow of material or formation in an extended, spherically expanding
outflow. The Mg2 and Fe2 profiles, taken together, imply that the wind
speed decreases between the atmospheric layers where the Mg2 and Fe2
self-absorption components are formed. Interstellar absorptions are seen
in the resonance lines of Mg2 (UV 1) and Fe2 (UV1) with zero-volt lower
levels, at about -3 km/s, consistent with models of the interstellar
medium in the direction of gamma Cru. Finally, we have detected the Mg2
'satellite lines' seen in solar spectra obtained above the limb. In
gamma Cru these lines are probably fluorescently excited by H Ly beta.
---------------------------------------------------------
Title: Transition Probabilities for the UV0.01 Multiplet in N III
Authors: Brage, Tomas; Fischer, Charlotte Froese; Judge, Philip G.
1995ApJ...445..457B Altcode:
We report on large-scale ab initio multiconfiguration
Hartree-Fock calculations for the UV0.01 multiplet,
2s<SUP>2</SUP>2p<SUP>2</SUP>P<SUB>J</SUB> - 2s2p<SUP>2 4</SUP>P<SUB>J
prime</SUB>, in N III. The resulting transition probabilities agree
very well with recent semiempirical calculations, and the lifetimes for
two of the three upper levels agree with experiments. The deviation for
the third level is discussed. Comparisons made with the highest quality
IUE echelle spectra available -- those of RR Tel and V1016 Cyg (both
photoionized sources with electron densities below 10<SUP>8</SUP>/cu
cm) -- show that computed branching ratios of lines sharing a common
upper level are in agreement with observations to within uncertainties
of +/- 10%. High-quality solar limb data or stellar data from the
Hubble Space Telescope (HST) could, in principle, be used to determine
whether the theoretical or measured lifetimes for the discrepant level
are in error. Unfortunately, stellar data for high-density plasmas
(N<SUB>e</SUB> greater than 10<SUP>11</SUP>/cu cm are needed) do not
yet exist, and existing solar data lack the photometric precision to
address this problem.
---------------------------------------------------------
Title: The Transition Regions of Capella
Authors: Linsky, Jeffrey L.; Wood, Brian E.; Judge, Philip; Brown,
Alexander; Andrulis, Catherine; Ayres, Thomas R.
1995ApJ...442..381L Altcode:
We have used the Goddard High Resolution Spectrometer (GHRS) to observe
the spectoscopic binary system Capella (G8 III + G1 III). Exposures
with the G140L, G140M, G160M, G200M, and echelle gratings provide
emission line profiles with unprecedented signal-to-noise and spectral
resolving power (lambda/Delta-lambda) up to 92,000. Multi-Gaussin fits
to the line profiles show that the hotter star contributes 60%-70% of
the total flux in the chromospheric O I and Mg II resonance lines, but
about 90% of the flux in the Si III, Si IV, and C IV lines formed in the
transition region at T less than or = 10<SUP>5</SUP> K. We find clear
evidence that the emission lines from the hotter star are systemtically
redshifted relative to the photosphere with Doppler shifts of 5 +/-
1 km/s for the +9 +/- 3 km/s in the chromospheric Mg II and O I lines,
respectively, increasing to +24 +/- 5 km/s for the transition region Si
IV 1393.8A line. The multi-Gaussian fits to permitted transition region
lines of SI III, Si IV, C IV, and N V indicate the presence of three
components: moderately broad lines formed in the transition region of
the hotter star (component H), narrow lines formed in the transition
region of the cooler star (component C), and very broad lines that we
think are formed in microflares on the hotter star (component B). The
He II 1640.4 A feature has an broad profile, which indicates that it
is formed by collisional excitation primarily from the hotter star,
and a weak narrow component that we interpret as due to radiative
recombination on the cooler star. We observed spin-forbidden emission
lines of C III), O III), Si III), O IV), O V), and S IV) that are
sensitive to electron density. Fainter members of the O IV) multiplet
and all of the S IV) lines have never before been seen in any star than
the Sun. We determine electron densities in the transition regions
of the Capella stars using lines ratios of O IV) lines and emission
measure analysis. The emission measures are self-consistent only when
the fluxes from each emitting component are considered separately. In
particular, the transition region abundance distributions appear to
be different on the two stars, and the spin-forbidden lines were not
detected in the B component. The emission measures for component
H (the G1 star) are consistent with a constant electron pressure
(or hydrostatic equilibrium) transition region with P<SUB>e</SUB> =
10<SUP>15 + 0.1</SUP>/cu cm K and possibly solar 'coronal' abundances.
---------------------------------------------------------
Title: Excitation of O i Lines in the Solar Chromosphere
Authors: Athay, R. Grant; Judge, Philip G.
1995ApJ...438..491A Altcode:
Observations of O I lines in the solar spectrum are examined to
determine whether differences in behavior of lines of the quintet
and triplet term systems are consistent with collisional excitation
and/or photoexcitation of both quintets and triplets. Intensities,
I<SUB>IR</SUB>, in near-infrared emission lines observed above the
limb at total eclipse decrease exponentially with height h. The
inverse scale heights (d In I<SUB>IR</SUB>/dh) for the triplet
lines at 844.6 nm and quintet lines at 777.2 nm are found to be
in the ration of 1.45. Ultraviolet O I emission-line intensities
I<SUB>UV</SUB> observed on the solar disk show strong variations, and
the distributions of triplet (130.4 nm) and quintet line intensities
about the means are different. Variances in In I<SUB>UV</SUB> are
found to have a triplet-to-quintet ratio of 1.50, in close agreement
with the ratio of d In I<SUB>IR</SUB>/dh. It is shown that the simple
assumption of collisional excitation of quintets and triplets coupled
with collisional de-excitation of the quintets leads to the correct
ratios for both the UV variances and d In I<SUB>IR</SUB>/dh. Also,
under this assumption d In I<SUB>IR</SUB>/dh for the quintet lines
is predicted to have the same value as d In I/dh at the head of the
hydrogen Balmer continuum, which, in fact, it does. On the other hand,
Carlsson & Judge (1993) have shown that collision rates computed
from the Vernazza, Avrett, & Loeser (1981, hereafter VAL) model
chromosphere using current estimates of O I collision strengths are
too low to produce the observed mean intensity in O I 130.4 nm. In
a similar sense, we find that the predicted intensity of O I 130.4
nm is much too weak relative to O I 135.6 nm, and that the VAL mean
models A-F cannot reproduce the observed behavior of these lines,
even including photoexcitation by H Ly-beta. These difficulties are
removed by increasing specific electron-atom collision rates. Such
increases could reflect large errors in atomic cross sections close
to threshold and/or the inadequacy of the assumptions made by VAL for
predicting line intensities. The latter alternative a likely factor. We
conclude that the O I UV lines are very sensitive to inhomogeneities,
much more than more traditional chromospheric lines (e.g., Mg II k)
which are formed over similar regions of the chromosphere. Such lines
could therefore provide valuable diagnostics of departures of the
chromopsheric plasma from mean models and thereby place constraints
upon heating mechanisms, once accurate atomic data become available.
---------------------------------------------------------
Title: Consolidation and Verification of EUVE's Lunar Observing
Program
Authors: Judge, Philip G.
1995euve.prop...32J Altcode:
EUVE has been providing valuable spectrometer data of the moon
for the duration of the EUVE mission. Our primary goal has been to
provide solar irradiance variability data at a time when such data
are extremely scarce. This proposal asks for additional measurements
to consolidate, calibrate and verify our program to date. The proposal
differs from previous years in that an EUV spectrograph built by co-I
Woods will fly on the METEOR satellite (launch October 1995) that will
monitor the solar EUV irradiance on a daily basis. We therefore ask
for 1 observation a day for 14 days around full moon to accurately
define the phase function, and for 1 observation a month for 1 year
to provide needed overlap (and redundancy, in the case of failure)
with the METEOR experiment. Very short exposures are required (<
30 min each) for a total of roughly 40 Ksec.
---------------------------------------------------------
Title: GHRS Spectra of alpha Tau
Authors: Carpenter, K.; Robinson, R.; Judge, P.
1994AAS...185.4509C Altcode: 1994BAAS...26.1380C
Goddard High Resolution Spectrograph (GHRS) observations of the K5 giant
alpha Tau were obtained on 8 April 1994. Spectra of approximately 40
Angstroms-wide regions centered near 1300, 1550, 1660, 1995, 2340, 2760,
and 2800 Angstroms were obtained through the Small Science Aperture
(SSA) with medium resolution (R=20,000) gratings. These data provide
high-precision profiles of a variety of lines formed in the stellar
chromosphere and transition region, including O I, Fe II, C I, C II],
Si II], Mg II, and C IV. Self-reversed emission from O I, Fe II,
and Mg II provide information on the wind flow velocities, with all
three ions showing both red and blue-shifted absorption components,
as seen previously in the Fe II emission from the later-type giants
gamma Cru and mu Gem. The first evidence for hot plasma in the outer
atmosphere of alpha Tau is seen in the G160M spectrum centered near
1550 Angstroms@. This spectrum shows very broad, but distinct features
due to the C IV (UV 1) doublet, as well as a myriad of much narrower
emissions formed at cooler temperatures, such as (fluorescent) Fe II and
perhaps Ni II and C I. C I (UV 2) is seen in emission and a comparison
of its flux with that in C I (UV 32) will allow an estimation of the C
I chromospheric column density. Multiple observations of the C II] (UV
0.01) intercombination multiplet were obtained to search for evidence
of shocks and/or propagating waves. Results of that search will be
presented. Finally, very high-resolution (R=85,000) echelle spectra
were obtained of the Mg II resonance doublet near 2800 Angstroms@. These
emission features show strong interstellar, stellar, and circumstellar
absorption components at, above, and below the stellar rest velocity.
---------------------------------------------------------
Title: The `HAO spectral diagnostics package' (HAOS-Diaper)
Authors: Judge, P. G.; Meisner, R. W.
1994ESASP.373...67J Altcode: 1994soho....3...67J
No abstract at ADS
---------------------------------------------------------
Title: The “Monochromatic Density Diagnostic” Technique: First
Detection of Multiple Density Components in the Chromosphere of
alpha Tauri
Authors: Judge, P. G.
1994ApJ...430..351J Altcode:
Emission line profiles of the red giant alpha Tau, obtained by Carpenter
et al. (1991) using the echelle and medium dispersion gratings of
the Goddard High Resolution Spectrograph are re-examined. Ratios of
monochromatic flux densities of lines of the C II) 2s<SUP>2</SUP>
2p(2)P<SUP>0</SUP> goes to 2s2p<SUP>2</SUP> (4)P multiple near 2325 A,
well-known diagnostics of electron densities in the chromospheres of
cool evolved stars, change systematically with relative wavelength
across the line profiles. With the justifiable assumption that these
lines are optically thin, this implies that the electron density
varies sytematically across the lines profiles. This is the first
time that traditional electron density diagostic line ratios have
been successfully applied to monochromatic line flux densities in
cool stars. this work clearly demonstrates the power of very high
signal-to-noise, high-resolution spectra in the UV. The monochromatic
density diagonstic technique holds promise as a powerful tool for
studying flows in a variety of astrophysical objects, including the
Sun. The paper concludes with a compliation of ions from the boron and
aluminum sequences for which this technique can be expected to produce
valuable results using astronomical data from the GHRS and solar data
from instruments on the Solar and Heliospheric Observatory (SOHO).
---------------------------------------------------------
Title: The Transition Regions of Capella
Authors: Linsky, J. L.; Wood, B. E.; Brown, A.; Andrulis, C.; Judge,
P.; Ayres, T. R.
1994ASPC...64...62L Altcode: 1994csss....8...62L
No abstract at ADS
---------------------------------------------------------
Title: GHRS Observations and Analysis of the 0 I and C I Resonance
Lines in the UV Spectrum of alpha ORI (M2 Iab)
Authors: Carpenter, Kenneth G.; Robinson, Richard D.; Judge, Philip
G.; Ebbets, Dennis C.; Brandt, John C.
1994ASPC...64...56C Altcode: 1994csss....8...56C
No abstract at ADS
---------------------------------------------------------
Title: Structures in Transition Region Plasma of Active Regions
Authors: Judge, Philip G.; Brekke, Paal
1994ASPC...68..321J Altcode: 1994sare.conf..321J
No abstract at ADS
---------------------------------------------------------
Title: Solar Variability, Lunar Spectroscopy , and Earth's Upper
Atmosphere
Authors: Judge, Philip G.
1994euve.prop...55J Altcode:
Solar EUV radiation and its variability is of central importance to the
earths upper atmosphere. Variability of the earths upper atmosphere
is a major concern to NASAs satellite missions. This proposal asks
for continued measurments of solar EUV variability using EUVE to
observe solar light scattered from the moon. Analysis of EUVE lunar
data shows unambiguous evidence that we have detected and can quantify
solar variability. We can therefore enhance our understanding of the
physics of the upper atmosphere at a time when solar EUV measurements
are scarce. Our aims include: (i) to understand phase and polarization
dependences of solar light scattered from the moon, (ii) to better
quantify variations in solar EUV irradiance, (iii) to re-calibrate
these data with a rocket--launched EUV payload (already successfully
achieved, but a re-observation is desirable), and (iv) to use these
data with simultaneous UV measurements from UARS as inputs to upper
atmospheric models. Very short exposures (< 30min.) are required. We
request observations twice a lunar month, and some other observations
to permit us to take the necessary steps towards converting lunar
intensity data to absolute solar irradiances. The total requested time
is roughly 60 Ksec.
---------------------------------------------------------
Title: On the Weakness of C I and O I Resonance Line Emission from
the Chromosphere of alpha Ori.
Authors: Carpenter, K.; Robinson, R.; Judge, P.; Ebbets, D.; Brandt, J.
1993AAS...183.1504C Altcode: 1993BAAS...25Q1313C
The resonance lines from multiplets UV 2 of both O I and C I are
typically quite strong in emission in the far-UV spectrum of cool
stars. However, in the prototypical M-supergiant alpha Ori, these lines
are remarkably weak, although other transitions from the same upper
energy levels, O I (UV 146) and C I (UV 32), are observed in strong
emission despite their much weaker intrinsic strengths. Due to the
presence of many lines from other species in the regions around the UV
2 multiplets of O I and C I near 1302 Angstroms and 1655 Angstroms, the
lines of interest suffer severe blending and progress in understanding
this flux deficiency is difficult based on low resolution IUE and
GHRS data. We have therefore obtained medium resolution (R=10,000)
GHRS spectra of alpha Ori of these complex spectral regions, as well
as the regions around the O I (UV 146) and C I (UV 32) lines near 1640
Angstroms and 1993 Angstroms, respectively, to resolve the various
contributors and allow detailed study of this phenomenon. In this
paper, we present the spectra and discuss the formation of the O I,
C I, Fe II, and S I lines which they clearly resolve. Semi-empirical
modeling of the outer atmosphere of alpha Ori and detailed radiative
transfer calculations are used to study the creation and destruction
of O I and C I photons.
---------------------------------------------------------
Title: Chromospheric Heating by Acoustic Shocks: A Confrontation of
GHRS Observations of alpha Tauri (K5 III) with AB Initio Calculations
Authors: Judge, P. G.; Cuntz, M.
1993ApJ...409..776J Altcode:
We compare ab initio calculations of semiforbidden C II line profiles
near 2325 A with recently published observations of the inactive red
giant Alpha Tau (K5 III) obtained using the GHRS on board the Hubble
Space Telescope. Our one-dimensional, time-dependent calculations assume
that the chromosphere is heated by stochastic acoustic shocks generated
by photospheric convection. We calculate various models using results
from traditional (mixing length) convection zone calculations as input
to hydrodynamical models. The semiforbidden C II line profiles and
ratios provide sensitive diagnostics of chromospheric velocity fields,
electron densities, and temperatures. We identify major differences
between observed and computed line profiles which are related to
basic gas dynamics and which are probably not due to technical
modeling restrictions. If the GHRS observations are representative
of chromospheric conditions at all epochs, then one (or more) of
our model assumptions must be incorrect. Several possibilities are
examined. We predict time variability of semiforbidden C II lines for
comparison with observations. Based upon data from the IUE archives,
we argue that photospheric motions associated with supergranulation
or global pulsation modes are unimportant in heating the chromosphere
of Alpha Tau.
---------------------------------------------------------
Title: Solar EUV Variability Measurements From Lunar Observations
With EUVE
Authors: Judge, P.; et al.
1993AAS...182.4129J Altcode: 1993BAAS...25..865J
No abstract at ADS
---------------------------------------------------------
Title: Line Profile Variations in M Giants: Clues to Mass-Loss and
Chromospheric Heating Mechanisms
Authors: Judge, P. G.; Luttermoser, D. G.; Neff, D. H.; Cuntz, M.;
Stencel, R. E.
1993AJ....105.1973J Altcode:
Analysis is presented of time-series, high dispersion spectra of
the Mg II, k, Ca II H, and K lines of the semiregular giants Rho Per
(M4 II-III, periodicity of about 50 days), R Lyr (M5 III, period of
about 46 days), and g Her (M6 III, period of about 90 days). The fine
error sensor on the IUE satellite and ground based UBV photometry was
used to relate line profile variations to photospheric variations. The
above mentioned stars were selected to study the relative importance
of convective motions and global stellar pulsations in determining
the structure of the outer atmospheres. Small amplitude changes, but
substantial changes in the profiles of Mg II and Ca II lines were
detected. It is contended that the observed variability is due to
changes in chromospheric conditions and not variations within the
circumstellar shell. The picture of a steady state chromosphere,
which is modulated on long time scales, is corroborated by these
observations. Localized heating is found in g Her.
---------------------------------------------------------
Title: On i Lines in the Sun and Stars. I. Understanding the
Resonance Lines
Authors: Carlsson, M.; Judge, P. G.
1993ApJ...402..344C Altcode:
The use of O I lines as spectral diagnostics of conditions in the
chromospheres of the sun and cool stars is addressed, focusing on
the resonance lines. The important processes influencing these lines
are identified and an attempt it made to understand the detailed line
transfer calculations in terms of simpler analytical models. How the
lines respond to changes in uncertain atomic parameters is illustrated,
and it is shown how the O I line flux densities depend simply and
sensitively on the radiative transfer solution for hydrogen. Approximate
analytical formulas are derived for the O I line flux densities in
terms of the hydrogen number densities.
---------------------------------------------------------
Title: Solar Variability, Lunar Spectroscopy and Earth's Upper
Atmosphere
Authors: Judge, Philip G.
1993euve.prop...31J Altcode:
Solar EUV radiation and its variability is of central importance to
the earths upper atmosphere. Variability of the earths upper atmosphere
is a major concern to NASAs satellite missions. This LARGE PROJECT (2
year) proposal asks for continued measurments of solar EUV variability
using EUVE to observe solar light scattered from the moon. Existing
EUVE data prove that we can enhance ourunderstanding of the physics
of the upper atmosphere at a time when solar EUV measurements are
scarce. Our aims include: (i) to understand the phase and polarization
dependence of solar light scattered from the moon, (ii) to quantify
variations in solar EUV irradiance, (iii) to calibrate these data
with a rocket--launched EUV payload, and (iv) to use these data with
simultaneous UV measurements from UARS as inputs to upper atmospheric
models. Very short exposures (<30 min) are required. We request TYPE
2 observations twice a lunar month, and a variety of TYPE 1 observations
to permit us to take the necessary steps towards converting lunar
intensity data to absolute solar irradiances.
---------------------------------------------------------
Title: The Search for Acoustically-Driven Mass-Loss in Evolved Stars
Authors: Stencel, R. E.; Brown, A.; Carpenter, K. G.; Cuntz, M.;
Judge, P.
1992AAS...181.3603S Altcode: 1992BAAS...24.1175S
Recent ab-initio calculations of stochastic stellar wind models by
Cuntz (1992 in Cool Stars VII, ASP Conf. Ser. 26, p.383) have proven
remarkably robust in predicting observed chromospheric flow patterns
including possible variabilities with time in selected cool, evolved
stars. The calculations solve the equations of hydrodynamics using
the method of characteristics and assume: (i) saw-tooth shock wave
profiles, and (ii) wave periods were changed stochastically while
keeping the wave amplitudes constant (see Cuntz 1990 Ap.J. 349,
p.141). Among the results of fitting chromospheric flow velocities is
the implication that the permitted range of acoustic wave periods for
a given star is constrained. We made use of the IUE satellite during
August and September 1992 to repeatedly observe two stars, the yellow
giant Aldebaran (K5 III) and the red supergiant, Betelgeuse (M2 Iab),
in order to sample variations in their atmospheres on timescales of ~
10(4) to ~ 10(6) seconds, which bracket the predicted mean acoustic wave
periods for these objects. In particular, we obtained deep exposures
in order to measure density-sensitive line ratios within the C II]
intercombination features near 2325A (cf. Lennon et al. 1985 Ap.J. 294,
p.200) to test the hypothesis that density fluctuations could be
measured as a consequence of these acoustic waves. The results of
these observations will be presented and discussed in terms of the
number and amplitude of acoustic waves contributing to chromospheric
heating and mass loss from these stars, as well as the wave origins in
the evolving oscillatory structure of these stellar interiors. We are
pleased to acknowledge IUE--NASA grant NAG5-2103 for partial support
of this effort.
---------------------------------------------------------
Title: Fe II Emission Lines. II. Excitation Mechanisms in Cool Stars
Authors: Judge, P. G.; Jordan, C.; Feldman, U.
1992ApJ...384..613J Altcode:
Excitation mechanisms are discussed for the 'resonance' transitions
(between the 3d(6)4s, 3d7, and 3d(6)4p configurations) of Fe II observed
in emission in the near-UV spectra of cool stars. The analysis is
based upon: (1) emission measure analysis of previously measured
lines in IUE spectra of cool giants; (2) discussion of the behavior
of Fe II lines observed above the solar limb from Skylab spectra; (3)
approximate radiative-transfer calculations in a 59 level Fe-II model
atom using mean escape probabilities and a parameterization of optical
radiation fields; and (4) accurate radiative transfer calculations in
a smaller atomic model. The solar spectra show unambiguous evidence
that electron collisions are responsible for most of the Fe-II emission
observed above the white-light limb. The terms leading to UV multiplets
3-6, 34-36, and 61-64 are excited by electron excitation of metastable
quartet terms below about 4 eV, followed by photoexcitation in lines at
optical wavelengths by photospheric radiation. A 'cool-star' diagnostic
diagram is constructed showing the regimes in which electron collisions
and continuum photoexcitation are important in the chromospheres of
cool stars.
---------------------------------------------------------
Title: The Unusual Ultraviolet Chromospheric Spectrum of the R
Coronae Borealis Star, V854 Centauri (NSV 6708), at Minimum Light
Authors: Clayton, Geoffrey C.; Whitney, Barbara A.; Stanford, S. A.;
Drilling, John S.; Judge, P. G.
1992ApJ...384L..19C Altcode:
Results are presented of IUE observations of a decline of the recently
discovered R CrB star, V854 Cen. These observations are of particular
interest because they include spectra taken at 7 mag below maximum
light. The 'chromospheric' emission spectra show striking differences
from UV spectra of other R CrB stars in decline. Strong emission appears
in several lines not normally seen in R CrB emission-line spectra,
in particular at semiforbidden C II 2326, Mg I 2852, and C I 2965,
2967. Spectral evolution similar to that seen in visible spectra of R
CrB stars is clearly seen in the UV. It is argued that the differences
between V854 Cen and other R CrB stars are related to known abundance
differences or to different temperature and density conditions in the
emission-line regions of the various R CrB stars. The emission may
also be significantly affected by the presence of dust in or near the
emitting region.
---------------------------------------------------------
Title: SI II emission line diagnostics.
Authors: Judge, P. G.; Carpenter, K. G.; Harper, G. M.
1991MNRAS.253..123J Altcode:
The present study compares ratios of Si II UV emission lines in a
variety of objects with computations based on recently published
collisional data of Dufton and Kingston (1991). A high-quality
spectrum of Alpha Tau (K5 III) obtained by Carpenter et al. (1991) is
analyzed using the G270M mode of the GHRS on the HST, in addition to
high-dispersion data from Skylab and IUE. Agreement between observation
and theory is satisfactory for most lines. A blend with a line of
Ni II accounts partially for the discrepancies and solves a problem
with semiforbidden S II emission measures. Disagreement exists between
certain observed flux ratios and computed values using recent atomic
data for the intersystem lines. The discrepancy is most significant
for Alpha Tau. The computed atomic collision strengths within the
intersystem multiplet itself are argued as a possible cause of the
discrepancy.
---------------------------------------------------------
Title: Coordinated IUE/HST Observations of the Flare Star AU mic:
Results from IUE
Authors: Carpenter, K. G.; Maran, S. P.; Brown, A.; Linsky, J. L.;
Robinson, R. D.; Byrne, P. B.; Judge, P. G.
1991BAAS...23.1383C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fe II Emission Lines. I. Chromospheric Spectra of Red Giants
Authors: Judge, P. G.; Jordan, C.
1991ApJS...77...75J Altcode:
A 'difference filtering' algorithm developed by Ayers (1979) is used
to construct high-quality high-dispersion long-wavelength IUE spectra
of three giant stars. Measurements of all the emission lines seen
between 2230 and 3100 A are tabulated. The emission spectrum of Fe II is
discussed in comparison with other lines whose formation mechanisms are
well understood. Systematic changes in the Fe II spectrum are related
to the different physical conditions in the three stars, and examples
are given of line profiles and ratios which can be used to determine
conditions in the outer atomspheres of giants. It is concluded that
most of the Fe II emission results from collisional excitation and/or
absorption of photospheric photons at optical wavelengths, but some
lines are formed by fluorescence, being photoexcited by other strong
chromospheric lines. Between 10 and 20 percent of the radiative losses
of Fe II arise from 10 eV levels radiatively excited by the strong
chromospheric H Ly-alpha line.
---------------------------------------------------------
Title: Evolution of the Chromospheres and Winds of Low- and
Intermediate-Mass Giant Stars
Authors: Judge, P. G.; Stencel, R. E.
1991ApJ...371..357J Altcode:
Results are presented of an empirical analysis of the global
thermodynamical requirements of the winds in the outer atmospheres of a
representative sample of red giant stars of low- and intermediate-mass
range. Results indicate that the mass-loss rates in these stars are
not strongly dependent on the actual physical processes driving the
winds. It is suggested that nonlinear processes act to regulate wind
energy fluxes. Possible mechanisms responsible for the chromospheric
heating and the mass loss in the low- and intermediate-mass giant
stars are discussed.
---------------------------------------------------------
Title: Radio Continuum Observations of a Variety of Cool Stars
Authors: Drake, S. A.; Linsky, J. L.; Judge, P. G.; Elitzur, M.
1991AJ....101..230D Altcode:
Radio-continuum observations at 2 and 6 cm are presented for 26
cool stars (F0 and later), including 10 F-K main-sequence stars and
16 F-M giant and supergiant stars. The detection of two M giants,
g Her and R Lyr, is reported for the first time; a redetection of
the unusual infrared carbon star IRC + 10216 is also reported. Some
general conclusions are made concerning the radio-emission properties
of the various types of cool stars observed. For both the detected and
nondetected stars, constraints are obtained on the ionized component
of their mass-loss rates.
---------------------------------------------------------
Title: The Mira/Semi-Regular Connection
Authors: Judge, Philip G.
1991iue..prop.3983J Altcode:
Substantial mass-loss for stars on the asymptotic giant branch has
been inferred for Mira stars for some time. Mass-loss mechanisms
involving the coupled action of stellar pulsations and dust formation
have been shown to account or the observed mass-loss rates by Bowen and
colleagues. Mechanisms for stars with substantial massloss, but which
are not regular pulsators, are not yet identified or understood. An
important goal of this proposal is to obtain the data needed to identify
the mass-loss mechanism for the semi-regular stars. The Mg II line
fluxes are sensitive indicators of non-radiative processes occuring
in layers of evolved giants where energy and momentum is imparted to
the wind. We propose to monitor the Mg II line fluxes with the LWP
camera at low dispersion, for a sample of semi-regular giant stars,
This sample differs from previously studied stars because the stars
have far infrared excesses similar to those of Miras. Simultaneous
ground based photometry will be obtained to help identify the phase
of tile variation of the Mg II lines. We will compare our findings
with our earlier similar studies of Miras and with our study of high
dispersion Mg II line profiles of "non-dusty" semi-regulars obtained
during the present (twelfth) round of IUE observations. Using the IRAS
database and other constraints, we will study the relations between
Mira-like behavior and the semi-regulars, both SRa and SRb types. From
this study we will learn about the nature of the mass-loss process from
cool giants, and obtain strong constraints on models of the evolution of
the circumstellar envelopes, and hence of stellar evolution on the AGB.
---------------------------------------------------------
Title: Feii Emission Line Diagnostics of the Sun and Stars
Authors: Judge, P.
1991ASIC..341..291J Altcode: 1991sabc.conf..291J
No abstract at ADS
---------------------------------------------------------
Title: The Mira/Semi-Regular Connection II
Authors: Judge, Philip G.
1991iue..prop.3984J Altcode:
We propose to extend the present 1 year program LGMPJ, "the
Mira/Semi-Regular Connection" for an extra year. The purpose is to
obtain a better understanding of mass-loss mechanisms by studying
the behavior of the Mg II h and k line fluxes in a more complete
sample of pulsating stars. In program LGMPJ, the allotted observing
time was insufficient to permit more than a preliminary study
of 3 stars. Important classes of stars of various infrared and
variability properties have therefore remained unstudied. The Mg
II line fluxes are sensitive indicators of non-radiative processes
occuring in layers of giants where energy and momentum is imparted to
the wind. We will compare our findings with our earlier IUE studies
of Miras and "non-dusty" semi-regulars. Using the IRAS database and
other constraints, we will learn about the nature of the mass-loss
process from cool giants, and obtain strong constraints on models of
the evolution of the circumstellar envelopes, and hence of stellar
evolution on the AGB.
---------------------------------------------------------
Title: Stringent Limits on the Ionized Mass Loss from A and F Dwarfs
Authors: Brown, Alexander; Veale, Anthony; Judge, Philip; Bookbinder,
Jay A.; Hubeny, Ivan
1990ApJ...361..220B Altcode:
Following the suggestion of Willson et al. (1987) that A- and
F-type main-sequence stars might undergo significant mass loss due to
pulsationally driven winds, upper limits to the ionized mass loss from A
and F dwarfs have been obtained using VLA observations. These stringent
upper limits show that the level of ionized mass loss would have at
most only a small effect on stellar evolution. Radiative-equilibrium
atmospheric and wind models for early A dwarfs indicate that it is
highly likely that a wind flowing from such stars would be significantly
ionized. In addition, late A and early F dwarfs exhibit chromospheric
emission indicative of significant nonradiative heating. The present
mass-loss limits are thus representative of the total mass-loss rates
for these stars. It is concluded that A and F dwarfs are not losing
sufficient mass to cause A dwarfs to evolve into G dwarfs.
---------------------------------------------------------
Title: On the disappearance of OI in some high-luminosity cool stars
Authors: Carpenter, K. G.; Norman, D.; Robinson, R.;
Fernandez-Villacanas, J. L.; Jordan, C.; Judge, P.
1990ESASP.310..307C Altcode: 1990eaia.conf..307C
No abstract at ADS
---------------------------------------------------------
Title: Fe II Emission Lines: Chromospheric Spectra of Red Giants
Authors: Judge, P. G.; Jordan, C.
1990BAAS...22..848J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Interpretation of Chromospheric Emission Lines
Authors: Judge, P. G.
1990ApJ...348..279J Altcode:
This paper reexamines the formation of ultraviolet emission lines in
stellar chromospheres, using detailed radiative transfer calculations
and relatively simple methods based on approximate line cooling rates,
including escape probabilities. Approximations for the cooling integrals
are demonstrated to work well for 'effectively thin' chromospheric
lines. Two cases are identified, whose behavior can be understood using
Ayres's (1979) chromospheric scaling laws relating the chromospheric
structure to stellar properties: those of inactive stars, like cool
giants, and more active stars like the sun.
---------------------------------------------------------
Title: Radiative Cooling Functions Below 2X10/4K
Authors: Judge, P. G.; Neff, D. H.
1990ASPC....9...57J Altcode: 1990csss....6...57J
No abstract at ADS
---------------------------------------------------------
Title: Toward Mapping the Ultraviolet Circumstellar Shells of
Late-Type Stars
Authors: Stencel, Robert E.; Judge, Philip G.; Carpenter, Kenneth G.
1990ASPC....9..467S Altcode: 1990csss....6..467S
Detection of spatially resolved circumstellar matter surrounding
selected cool stars, using off-source observations made with the
International Ultraviolet Explorer satellite, is reported. The data
demonstrate that: (1) the instrumental scattered light profile of
IUE appears to depend on the ultraviolet color temperature of the
star observed, and (2) certain red stars show signal in excess of the
instrumental levels, at spatial offsets of 10 to 20 arc-seconds from
the star.
---------------------------------------------------------
Title: The Evolution of Chromospheres and Winds of Low and
Intermediate Mass Giant Stars
Authors: Judge, P. G.; Stencel, R. E.
1990ASPC....9..411J Altcode: 1990csss....6..411J
No abstract at ADS
---------------------------------------------------------
Title: Mass Loss Upper Limits for a and F Dwarfs
Authors: Brown, A.; Veale, A.; Judge, P.; Bookbinder, J.; Hubeny, I.
1990ASPC....9..183B Altcode: 1990csss....6..183B
The upper limits of the ionized mass losses of A- and F-type main
sequence stars are obtained with the VLA to investigate the theory that
pulsationally driven winds contribute to substantial mass loss in the
stars. The upper limits are found to be at least one order of magnitude
lower than the mass-loss loci proposed by Willson et al. (1987). Because
any wind flowing from the stars should be detectable, the notion that
A dwarfs are evolving into G dwarfs cannot be supported by the amount
of mass that A and F dwarfs are shown to be losing.
---------------------------------------------------------
Title: How Consistent are Ab-Initio Models of Giant Star Chromospheres
with Observations
Authors: Cuntz, M.; Judge, P. G.
1990ASPC....9...61C Altcode: 1990csss....6...61C
No abstract at ADS
---------------------------------------------------------
Title: Radiative Transfer in ab-initio Chromospheric Models
Authors: Cuntz, M.; Judge, P. G.
1989BAAS...21Q1101C Altcode: 1989BAAS...21.1101C
No abstract at ADS
---------------------------------------------------------
Title: Chromospheres of Chemically Peculiar Giant Stars (invited
Paper)
Authors: Judge, P. G.
1989eprg.proc..303J Altcode: 1989IAUCo.106..303J
The chromospheres of evolved stars with peculiar chemical abundances
are reviewed, emphasizing the dependence of chromospheric properties
on the evolutionary status of the stars. A sample of intermediate
mass stars observed in the radio, IR and UV wavelength regions is
compiled. The chromospheres of MS, S, and C stars are compared with
one another. The sample is used to study the relationship between
stellar parameters and chromospheric heating. The results are used to
construct a scenario for AGB evolution.
---------------------------------------------------------
Title: Cycle-Dependent Studies of Semi-Regular Giant Stars
Authors: Judge, Philip G.
1989iue..prop.3423J Altcode:
We propose to monitor the chromospheres and winds of the semi-regular
giants Rho Per (M4 II-III, P ~ 50 days) and g Her (M6 III, P ~ 90
days) as a function of their cyclic photospheric variability using
LWP observations coordinated with ground based spectroscopy and
photometry. We have recently studied a sample of 42 stars covering
various phases of evolution on the redand asymptoticgiant branches. We
have discovered that as a star evolves from a photometrically
"constant" early M stax to a semi-regular (SRb) stax near spectral
type M5 III, important changes in the response of the outer atmosphere
to the photospheric mechanical energy generation occur. The energy
fluxes are dominated in the early phases by chromospheric heating and
radiative losses, and by mass loss in the later phases. "Non-variable"
and semi-regular K and M stars lose mass by a currently unidentified
process. The present proposal aims to follow the response of the
chromosphere and wind, via the emission and absorption components in
the Mg II and Ca II resonance lines, to the underlying photospheric
variability in SRb-type M stars. In this way we can test whether
global photospheric variability on a long timescale (>= weeks,
i.e. > acoustic cutoff period) is responsible for the enhanced
massloss and dust formation in non-Mira stars later than M5 and
whether the energy generated by these pulsations is related to the
(observationally-inferred) chromospheric heating. Previous monitoring
studies with IUE of SRb stars reveal variability but they have neither
adequate phase coverage nor the ground-based support required for
our study. Our study will help to provide a link between the outer
atmospheres of the "non-variable" and Mira phases of stellar evolution:
current theory indicates that the Miras (P > 150 days, DeltaV >
2.5 mag.) lose substantial mass because of the propagation and decay of
global acoustic shocks, accompanied by dust formation, generated by the
regular photospheric pulsations. Our recent study and theoretical work
suggest that similar processes may be occuring in the shorterperiod,
smaller amplitude SRb stars. The proposed IUE observations will help
to clarify the relation of stellar winds and chromospheres to the
variability properties of stars evolving up the giant branches.
---------------------------------------------------------
Title: Direct UV observations of the circumstellar envelope of
alpha Orionis.
Authors: Stencel, R. E.; Carpenter, K. G.; Pesce, J. E.; Skinner,
S.; Brown, A.; Judge, P.
1988ESASP.281a.249S Altcode: 1988uvai....1..249S; 1988IUE88...1..249S
Observations were made in the IUE LWP camera, low dispersion mode, with
alpha Ori being offset various distances from the center of the Long
Wavelength Large Aperture along its major axis. Signal was acquired
at all offset positions and is comprised of unequal components of
background/dark counts, telescope-scattered light, and scattered light
emanating from the extended circumstellar shell. The star is known from
optical and infrared observations to possess an extended, arc-minute
sized, shell of cool material. Attempts to observe this shell with the
IUE are described, although the deconvolution of the stellar signal
from the telescope scattered light requires further calibration effort.
---------------------------------------------------------
Title: The excitation of SI emission lines in chromospheres of
late-type giant stars.
Authors: Judge, P. G.
1988MNRAS.231..419J Altcode:
Constraints on the structure of the chromospheres of Alpha Boo,
Alpha Tau, and Beta Gru derived from high-resolution IUE spectra
are used to investigate the excitation mechanisms of emission lines
of neutral sulfur, which are prominent in IUE spectra of late-type
giant and supergiant stars. Observational data for the S I lines
from other studies are collected and discussed together with data
for the prototype M supergiant Alpha Ori. The physical conditions
under which the emission lines are excited are summarized, and the
atomic processes and models required to interpret the line fluxes are
addressed. The processes leading to emission in Alpha Tau, Alpha Boo,
and Beta Gru are identified. The requirements for more accurate atomic
and spectroscopic data are discussed, and the potential diagnostic
value of the various emission lines is assessed.
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Title: Spectroscopy of Cool Stars from IUE Data
Authors: Judge, P. G.
1988IAUS..132..163J Altcode:
IUE has revolutionized our knowledge of the outer atmospheres of cool
stars, largely through the study of spectral lines, and now we possess a
quite detailed knowledge of stellar chromospheres, transition regions,
coronae and winds in the cool half of the HR-diagram. The aim of the
present review is to highlight advances in this field using IUE data
with high signal-to-noise ratios.
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Title: A Very Deep SWP Echellogram of Aldebaran
Authors: Judge, Philip G.
1988iue..prop.3335J Altcode:
No abstract at ADS
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Title: Understanding the ultraviolet spectra of cool stars.
Authors: Jordan, C.; Judge, P. G.
1988CoAMP..21...97J Altcode:
No abstract at ADS
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Title: Modelling the outer atmospheres and winds of K giant stars.
Authors: Judge, P. G.
1987IAUS..122..323J Altcode:
It is shown how empirically derived constraints affect models of the
outer atmospheres and winds of K giants, taking α Boo (K2 III) as
an example. The importance of empirical approaches prior to making
semi-empirical models is stressed. The reliability of recent wind
models is assessed.
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Title: Delta Andromedae (K3III) : an IRAS source with an unusual
ultraviolet spectrum.
Authors: Judge, P. G.; Jordan, C.; Rowan-Robinson, M.
1987MNRAS.224...93J Altcode:
The IRAS survey has revealed anomalous cool infrared emission from
a number of otherwise apparently normal K stars. IUE spectra of the
brightest of these stars, Delta And, which is a spectroscopic binary
and optical standard K3 III star, is obtained. The IUE spectra show the
unexpected presence of C IV in emission, implying hot material (about
100,000 K), and evidence for a strong, high-velocity wind. It is argued
that the unusual ultraviolet spectrum arises solely from the primary
star and that it is another example of a 'hybrid' K star. The infrared
excess appears to be caused by a primordial dust shell extending
from about 1 to 30 arcsec from the primary. One of the companions of
Delta And lies close to the inner edge of the shell and another one
(possibly two) lies close to the outer edge, so that interesting
dynamical interactions between the companions and the dust shell may
be expected. The dust shell may be analogous to the Oort cometary
cloud in the Solar System or to a scaled-up version of Saturn's rings.
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Title: δ Andromedae (K3 III): a hybrid giant in an extended dust
shell.
Authors: Jordan, C.; Judge, P. G.; Rowan-Robinson, M.
1987IAUS..122..321J Altcode:
Spectra of δ And have been obtained with the International Ultraviolet
Explorer in both the long and short wavelength regions. These spectra
show several features unusual in a K giant as cool as δ And, in
particular. The IRAS observations are interpreted in terms of a cool
(≡100 K) dust cloud surrounding δ And - a spectroscopic binary
system - and a third component at 1200 A.U.
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Title: Re-examining the "Corona-Wind Dividing Line" Diagnostics of
"Non-Coronal" Atmospheres (Invited review)
Authors: Judge, P. G.
1987LNP...291..294J Altcode: 1987csss....5..294J; 1987LNP87.291..294J
A review of observations and analyses of the outer atmospheres of
"non-coronnl" stars is given, with an emphasis on spectroscopic
diagnostics. These stars, lying to the right of the "corona-wind
division" in the HR diagram, have no detectable material above
temperatures of ∼ 2×10<SUP>4</SUP> K, and instead of solar-like
transition regions and coronae, they possess relatively massive winds
and expanding "basal-flux" chromospheres. The discussion is restricted
to "normal", single, red giants, i.e. oxygen-rich stars which have
not evolved as far as the asymptotic giant branch, and which have not
yet developed massive, dusty molecular outflows. The methods described
can in principle be applied to cool star chromospheres in general.
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Title: High-Dispersion Observations of Alpha Bootis (K1 III) with
the International Ultraviolet Explorer
Authors: Ayres, T. R.; Judge, P.; Jordan, C.; Brown, A.; Linsky, J. L.
1986ApJ...311..947A Altcode:
The authors have obtained very deeply exposed IUE echelle spectrograms
of the bright, early-K giant Arcturus. They did not detect significant
flux in the most prominent high-excitation species of a solar-like
transition zone, C IV λ1548.2. The presence of a weak feature of
Si III] λ1892.0, and possibly also Si IV λ1393.8, indicates the
existence of a small amount of plasma at temperatures as hot as
6×10<SUP>4</SUP>K. Measurements of C II] multiplet UV0.01 near 2325
Å provide a lower limit of about 5×10<SUP>9</SUP>cm<SUP>-3</SUP> for
the electron density in the chromospheric layers. C II UV1 (1335 Å)
emission is very weak. These results confirm that the "coronal" activity
of the old red giants is considerably diminished from that of even the
"quietest" of their main-sequence predecessors, stars like the Sun.
---------------------------------------------------------
Title: Constraints on the outer atmospheric structure of late-type
giants stars with IUE : application to alpha Tau (K5III) and beta Gru
(M5III).
Authors: Judge, P. G.
1986MNRAS.223..239J Altcode:
Empirical constaints on the outer atmospheric structures of α Tau and
β Gru are derived using high resolution spectra from the International
Ultraviolet Explorer (IUE) satellite, with methods which have been
described and applied to α Boo (K2III) in an earlier paper. These
stars have IUE spectra which are typical of giant stars later than ∼K0
which lie on the 'wind' side of the 'corona/wind division' in the H-R
diagram. The methods are based on the interpretation of emission-line
fluxes and profiles, combining emission measures, column density
measurements from opacity-sensitive line ratios and electron-density
measurements from C II] line ratios. Many of the conclusions derived
earlier for α Boo are confirmed for the later type stars considered
here: radiative processes are vitally important in determining the
observed spectra because of the low particle densities in red giants. A
consistent set of constraints is derived only when such processes are
taken into account. There is no evidence from IUE that the emission
regions are significantly extended in the sense suggested by previous
workers. For α Tau the constraints are used to examine the reliability
of an earlier chromospheric model of Kelch et al. Finally the general
implications of this work on the outer atmospheres of late-type giant
stars are discussed.
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Title: Formation of Emission Lines in the Outer Atmosphere of Arcturus
(Alpha Boo K2 III)
Authors: Judge, P. G.; Avrett, E. H.; Loeser, R.
1986BAAS...18..982J Altcode:
No abstract at ADS
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Title: The outer atmospheres of late-type giant stars.
Authors: Judge, P. G.
1986ESASP.263..189J Altcode: 1986niia.conf..189J; 1986NIA86......189J
Results of recent work with IUE on the structure of the outer
atmospheres of late-type giant stars are summarized, based on empirical
constraints derived from emission lines in α Boo (K2 III), α Tau
(K5 III) and β Gru (M5 III), observed with deep exposures in the
high resolution mode of IUE. These stars have IUE spectra typical
of giant stars on the "wind" side of the "corona-wind division" in
the HR diagram. Particular attention is paid to the structure of the
emitting regions, including densities, temperatures, inhomogeneities,
geometric extents and velocity fields. Comparisons are made with
earlier chromospheric models and with other spectroscopic work, and
trends with stellar parameters are examined. Finally, the implications
of this work for modelling the winds of red giants are discussed.
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Title: Constraints on the outer atmospheric structure of late-type
giant stars with IUE : methods and application to Arcturus (alpha
Boo K2III).
Authors: Judge, P. G.
1986MNRAS.221..119J Altcode:
Methods for empirically analyzing the emission lines formed in the outer
atmospheres of late-type low-gravity stars are described and applied
to the K2III star Alpha Boo. The methods are based on electron-density
measurements, emission-measure analysis, and determination of the
optical depths of emission lines. The reduction and measurement of
IUE data of Alpha Boo is described. The important atomic and radiative
processes which determine the emission-line fluxes of the 'diagnostic'
emission lines in late-type giant stars are identified, and the effects
of the scattering of radiation in optically thick lines are examined
using results from probabilistic radiative transfer theory, and models
for line excitation are obtained. Empirical constraints on the outer
atmospheric structure of Alpha Boo are derived using the observed line
fluxes and widths and the previously described models.
---------------------------------------------------------
Title: Empirical Constraints on the Outer Atmospheres of Late-Type
Giant Stars with IUE
Authors: Judge, P. G.
1986IrAJ...17..300J Altcode:
Useful constraints on the outer atmospheric structure of late-type
giant stars can be obtained using emission lines observed with the
IUE satellite if all important processes in the atomic excitation
calculations are included. Carpenter et al. (1985) did not include
such effects, and therefore overestimated the geometric extent of
the emission regions. The Ayres and Linsky (1975) model for Alpha Boo
satisfies most of the constraints derived below 8000 K, but the model
has electron densities and linewidths that are a factor of about 2
smaller than those observed.
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Title: Ultraviolet Observations of Young Stars in the Chameleon
1 Association
Authors: Brown, A.; Linsky, J. L.; Walter, F.; Jordan, C.; Judge,
P.; Gahm, G.; Feigelson, E. D.
1985BAAS...17R.837B Altcode: 1985BAAS...17..837B
No abstract at ADS
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Title: Emission Line Variability of RY Tau, DR Tau and SU Aur
Authors: Brown, A.; Walter, F. M.; Carpenter, K. G.; Jordan, C.;
Judge, P.
1985BAAS...17..556B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet spectroscopy of late-type giant and supergiant
stars
Authors: Judge, Philip Gordon
1985PhDT........44J Altcode:
No abstract at ADS
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Title: A progress report on the analysis of long exposure SWP high
resolution spectra of cool stars.
Authors: Linsky, J. L.; Ayres, T. R.; Brown, A.; Carpenter, K.;
Jordan, C.; Judge, P.; Gustafsson, B.; Eriksson, K.; Saxner, M.;
Engvold, O.; Jensen, E.; Moe, O. K.; Simon, T.
1984NASCP2349..445L Altcode: 1984fiue.rept..445L; 1984IUE84......445L
The IUE is the first experiment with sufficient sensitivity to obtain
high resolution spectra (lambda/delta lambda is approximately 10,000)
of many cool stars in the vitally important 1200 to 2000 A spectral
region. These data provide qualitatively new information with
which to understand the properties of and structures in the outer
atmospheres of these stars. Also, these cool star spectra will be
extremely useful in planning for the Space Telescope High Resolution
Spectrograph, which will be 1000 times more sensitive than IUE but will
be hampered by limited observing time and limited spectral bandwidth
in each exposure. Very long exposure, high disperson SWP spectra of
many stars located throughout the cool half of the HR diagram were
obtained. These 12 to 21 hour exposures were obtained by combining
NASA and Vilspa shifts so as to obtain the longest possible exposures
at times of low background. Included are dwarf stars of spectral type
G0 V to M2 V, G9.5 III to M5 II giants, G2 Ib to M2 Iab supergiants,
a number of RS CVn-type systems, and Barium stars.
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Title: Precise measurements of radial velocities of emission lines
in the far-ultraviolet spectra of late-type stars.
Authors: Ayres, T. R.; Engvold, O.; Moe, D. K.; Simon, T.; Jordan,
C.; Judge, P.; Brown, A.; Linsky, J. L.
1984NASCP2349..468A Altcode: 1984fiue.rept..468A; 1984IUE84......468A
The radial velocities of emission lines in deep short wave prime camera
echelle exposures of several late-type dwarf and giant stars were
measured. The goal was to search for absolute and differential Doppler
shifts of emission lines formed at different temperatures in the stellar
outer atmospheres analogous to the redshifts of C IV lambda 1548 (10
to the 5th power K) which occur in the solar transition zone. Existing
images, taken without the precise radial velocity precautions, of five
dwarf stars, four giant stars, and three supergiants are reanalyzed.
---------------------------------------------------------
Title: Ultraviolet Spectroscopy of Cool Stars from IUE (invited Paper)
Authors: Jordan, C.; Judge, P.; Johansson, S.
1984uxsa.coll...51J Altcode: 1984IAUCo..86...51J; 1984uxsa.conf...51J
No abstract at ADS
---------------------------------------------------------
Title: Radiative processes in cool star chromospheres.
Authors: Jordan, C.; Judge, P.
1984PhST....8...43J Altcode: 1984PhyS....8...43J
Observations made with the IUE satellite between 1200 Å and 3000 Å
have shown that the spectra of giant and supergiant stars later than
about K0 are dominated by emission from neutral atoms and singly charged
ions. The cool star spectra show many examples of photo-excitation,
line-leaking and fluorescent processes, some of which are discussed
here. There is evidence that the H Ly α and H Ly β lines play an
important role in the production of emission from O I, S I and Fe
II. Some lines which remain without satisfactory explanations in both
the stellar and solar spectra are discussed.