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Author name code: schad
ADS astronomy entries on 2022-09-14
author:"Schad, Thomas Antony"
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Title: Ground-based instrumentation and observational techniques
Authors: Rimmele, Thomas; Kuhn, Jeff; Woeger, Friedrich; Tritschler,
. Alexandra; Lin, Haosheng; Casini, Roberto; Schad, Thomas; Jaeggli,
Sarah; de Wijn, Alfred; Fehlmann, Andre; Anan, Tetsu; Schmidt, Dirk
2022cosp...44.2507R Altcode:
We'll review the current state-of-the-art for ground-based
instrumentation and techniques to achieve high-resolution
observations. We'll use the 4m Daniel K. Inouye Solar Telescope
(DKIST), the European Solar Telescope (EST) and other ground-based
instrumentation as examples to demonstrate instrument designs
and observing techniques. Using adaptive optics and post-facto
image processing techniques, the recently completed DKIST provides
unprecedented resolution and high polarimetric sensitivity that
enables astronomers to unravel many of the mysteries the Sun presents,
including the origin of solar magnetism, the mechanisms of coronal
heating and drivers of flares and coronal mass ejections. Versatile
ground-based instruments provide highly sensitive measurements of solar
magnetic fields, that in the case of DKIST, also include measurements
of the illusive magnetic field of the faint solar corona. Ground-based
instruments produce large and diverse data sets that require complex
calibration and data processing to provide science-ready to a broad
community. We'll briefly touch on ongoing and future instrumentation
developments, including multi-conjugate adaptive optics.
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Title: Science Commissioning of the Diffraction-Limited Near-IR
Spectropolarimter for the Daniel K. Inouye Solar Telescope
Authors: Lin, Haosheng; Schad, Thomas; Kramar, Maxim; Jaeggli, Sarah;
Anan, Tetsu; Onaka, Peter
2022cosp...44.2508L Altcode:
The Diffraction-Limited Near-IR Spectropolarimeter (DL-NIRSP) is one
of the first-generation facility instruments of the Daniel K. Inouye
Solar Telescope (DKIST, or The Inouye Solar Telescope). It is a near-IR
spectropolarimeter optimized to study the magnetism of the dynamic solar
atmosphere, from the photosphere to the corona. DL-NIRSP is equipped
with two integral field units (IFUs) coupled to a high-resolution
grating spectrograph, and is capable of simultaneous measurements
of the full polarized spectra of a 2-dimensional spatial field
without scanning. Large field of view observations are supported by
mosaicking. DL-NIRSP observes simultaneously at three spectral windows,
enabling simultaneous coverage of different atmospheric layers with
carefully selected spectral lines. It can also observe the Sun with
three resolution modes, from diffraction-limited observations with
a spatial sampling of 0.03" to wide-field mode covering a 32"x15"
instantaneous FOV with 0.5" sampling. This paper will present results
from science commissioning observations conducted in late 2021.
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Title: Thomson Scattering above Solar Active Regions and an Ad Hoc
Polarization Correction Method for the Emissive Corona
Authors: Schad, Thomas A.; Jaeggli, Sarah A.; Dima, Gabriel I.
2022ApJ...933...53S Altcode: 2022arXiv220509808S
Thomson-scattered photospheric light is the dominant constituent
of the lower solar corona's spectral continuum viewed off-limb at
optical wavelengths. Known as the K-corona, it is also linearly
polarized. We investigate the possibility of using the a priori
polarized characteristics of the K-corona, together with polarized
emission lines, to measure and correct instrument-induced polarized
crosstalk. First we derive the Stokes parameters of the Thomson
scattering of unpolarized light in an irreducible spherical tensor
formalism. This allows forward synthesis of the Thomson-scattered signal
for the more complex scenario that includes symmetry-breaking features
in the incident radiation field, which could limit the accuracy of our
proposed technique. For this, we make use of an advanced 3D radiative
magnetohydrodynamic coronal model. Together with synthesized polarized
signals in the Fe XIII 10746 Å emission line, we find that an ad hoc
correction of telescope- and instrument-induced polarization crosstalk
is possible under the assumption of a nondepolarizing optical system.
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Title: A Model-based Technique for Ad Hoc Correction of Instrumental
Polarization in Solar Spectropolarimetry
Authors: Jaeggli, Sarah A.; Schad, Thomas A.; Tarr, Lucas A.;
Harrington, David M.
2022ApJ...930..132J Altcode: 2022arXiv220403732J
We present a new approach for correcting instrumental polarization by
modeling the nondepolarizing effects of a complex series of optical
elements to determine physically realizable Mueller matrices. Provided
that the Mueller matrix of the optical system can be decomposed into
a general elliptical diattenuator and general elliptical retarder,
it is possible to model the crosstalk between both the polarized and
unpolarized states of the Stokes vector and then use the acquired
science observations to determine the best-fit free parameters. Here
we implement a minimization for solar spectropolarimetric measurements
containing photospheric spectral lines sensitive to the Zeeman effect
using physical constraints provided by polarized line and continuum
formation. This model-based approach is able to provide an accurate
correction even in the presence of large amounts of polarization
crosstalk and conserves the physically meaningful magnitude of
the Stokes vector, a significant improvement over previous ad hoc
techniques.
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Title: Polarized forbidden coronal line emission in the presence of
active regions
Authors: Schad, Thomas; Dima, Gabriel
2021AGUFMSH15G2087S Altcode:
Photoexcited forbidden lines at visible and infrared wavelengths
provide important diagnostics for the coronal magnetic field via
scattering induced polarization and the Zeeman Effect. In forward
models, the polarized formation of these lines is often treated
assuming a simplified exciting radiation field, consisting only of the
photospheric quiet-sun continuum, which is both cylindrically-symmetric
relative to the solar vertical and unpolarized. Near active regions
in particular, this assumption breaks down, especially due to the
presence of sunspots and other surface features that lead to additional
asymmetries in the continuum radiation field. Here we investigate the
role of symmetry-breaking on the emergent polarized emission within
high resolution models of the active corona simulated by the MURaM
code. We treat the full 3D (unpolarized) continuum radiation field of
the photosphere exciting the coronal ions and compare the cases that
include and ignore the symmetry-breaking effects of the photospheric
features. Our discussion focuses on the key observables soon to be made
available by the National Science Foundation's Daniel K Inouye Solar
Telescope. The results indicate that while symmetry breaking can in
principle have a large effect, its role is relatively minor for the
simulated active region largely due to the low inherent polarization
fraction emitted by forbidden lines in denser active region plasmas.
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Title: pycelp: Python package for Coronal Emission Line Polarization
Authors: Schad, T. A.; Dima, G. I.
2021ascl.soft12001S Altcode:
pyCELP (aka "pi-KELP") calculates Coronal Emission Line Polarization. It
forward synthesizes the polarized emission of ionized atoms formed
in the solar corona and calculates the atomic density matrix elements
for a single ion under coronal equilibrium conditions and excited by a
prescribed radiation field and thermal collisions. pyCELP solves a set
of statistical equilibrium equations in the spherical statistical tensor
representation for a multi-level atom for the no-coherence case. This
approximation is useful in the case of forbidden line emission by
visible and infrared lines, such as Fe XIII 1074.7 nm and Si X 3934 nm.
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Title: Chromospheric Heating Mechanisms in a Plage Region Constrained
by Comparison of Magnetic Field and Mg II h & k Flux Measurements
with Theoretical Studies
Authors: Anan, Tetsu; Schad, Thomas; Kitai, Reizaburo; Dima, Gabriel;
Jaeggli, Sarah; Tarr, Lucas; Collados, Manuel; Dominguez-Tagle,
Carlos; Kleint, Lucia
2021AGUFMSH44A..05A Altcode:
The strongest quasi-steady heating in the solar atmosphere from the
photosphere through the corona occurs in plage regions. As many
chromospheric heating mechanisms have been proposed, important
discriminators of the possible mechanisms are the location of the
heating and the correlation between the magnetic field properties in
the chromosphere and the local heating rate. We observed a plage region
with the He I 1083.0 nm and Si I 1082.7 nm lines on 2018 October 3
using the integral field unit mode of the GREGOR Infrared Spectrograph
(GRIS) installed at the GREGOR telescope. During the GRIS observation,
the Interface Region Imaging Spectrograph (IRIS) obtained spectra of the
ultraviolet Mg II h & k doublet emitted from the same region. In
the periphery of the plage region, within the limited field of view
seen by GRIS, we find that the Mg II radiative flux increases with the
magnetic field in the chromosphere. The positive correlation implies
that magnetic flux tubes can be heated by Alfvén wave turbulence
or by collisions between ions and neutral atoms relating to Alfvén
waves. Within the plage region itself, the radiative flux was large
between patches of strong magnetic field strength in the photosphere, or
at the edges of magnetic patches. On the other hand, we do not find any
significant spatial correlation between the enhanced radiative flux and
the chromospheric magnetic field strength or the electric current. In
addition to the Alfvén wave turbulence or collisions between ions
and neutral atoms relating to Alfvén waves, other heating mechanisms
related to magnetic field perturbations produced by interactions of
magnetic flux tubes could be at work in the plage chromosphere.
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Title: Measurements of Photospheric and Chromospheric Magnetic
Field Structures Associated with Chromospheric Heating over a Solar
Plage Region
Authors: Anan, Tetsu; Schad, Thomas A.; Kitai, Reizaburo; Dima,
Gabriel I.; Jaeggli, Sarah A.; Tarr, Lucas A.; Collados, Manuel;
Dominguez-Tagle, Carlos; Kleint, Lucia
2021ApJ...921...39A Altcode: 2021arXiv210807907A
In order to investigate the relation between magnetic structures and
the signatures of heating in plage regions, we observed a plage region
with the He I 1083.0 nm and Si I 1082.7 nm lines on 2018 October 3
using the integral field unit mode of the GREGOR Infrared Spectrograph
(GRIS) installed at the GREGOR telescope. During the GRIS observation,
the Interface Region Imaging Spectrograph obtained spectra of the
ultraviolet Mg II doublet emitted from the same region. In the periphery
of the plage region, within the limited field of view seen by GRIS,
we find that the Mg II radiative flux increases with the magnetic
field in the chromosphere with a factor of proportionality of 2.38 ×
10<SUP>4</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP> G<SUP>-1</SUP>. The
positive correlation implies that magnetic flux tubes can be heated
by Alfvén wave turbulence or by collisions between ions and neutral
atoms relating to Alfvén waves. Within the plage region itself,
the radiative flux was large between patches of strong magnetic field
strength in the photosphere or at the edges of magnetic patches. On
the other hand, we do not find any significant spatial correlation
between the enhanced radiative flux and the chromospheric magnetic
field strength or the electric current. In addition to the Alfvén
wave turbulence or collisions between ions and neutral atoms relating
to Alfvén waves, other heating mechanisms related to magnetic field
perturbations produced by interactions of magnetic flux tubes could
be at work in the plage chromosphere.
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Title: Polarized Forbidden Coronal Line Emission in the Presence of
Active Regions
Authors: Schad, Thomas; Dima, Gabriel
2021SoPh..296..166S Altcode:
Photoexcited forbidden lines at visible and infrared wavelengths provide
important diagnostics for the coronal magnetic field via scattering
induced polarization and the Zeeman effect. In forward models,
the polarized formation of these lines is often treated assuming a
simplified exciting radiation field consisting only of the photospheric
quiet-Sun continuum, which is both cylindrically-symmetric relative
to the solar vertical and unpolarized. In particular, this assumption
breaks down near active regions, especially due to the presence of
sunspots and other surface features that modify the strength and
anisotropy of the continuum radiation field. Here we investigate
the role of symmetry-breaking on the emergent polarized emission in
high resolution models of the active corona simulated with the MURaM
code. We treat the full 3D unpolarized continuum radiation field of
the photosphere that excites the coronal ions and compare the cases
where the symmetry-breaking effects of the photospheric features are
included or ignored. Our discussion focuses on the key observables soon
to be available by the National Science Foundation's Daniel K Inouye
Solar Telescope. The results indicate that while symmetry breaking can
in principle have a large effect, its role is relatively minor for the
simulated active region, largely due to the low inherent polarization
fraction emitted by forbidden lines in denser active region plasmas.
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Title: He I Spectropolarimetry of a Supersonic Coronal Downflow
Within a Sunspot Umbra
Authors: Schad, Thomas A.; Dima, Gabriel I.; Anan, Tetsu
2021ApJ...916....5S Altcode:
We report spectropolarimetric observations of a supersonic
downflow impacting the lower atmosphere within a large sunspot
umbra. This work is an extension of Schad et al. using observations
acquired in the He I 10830 Å triplet by the Facility Infrared
Spectropolarimeter. Downflowing material accelerating along a cooled
coronal loop reaches peak speeds near 200 km s<SUP>-1</SUP> and exhibits
both high speed emission and absorption within the umbra, which we
determine to be a consequence of the strong height dependence of the
radiatively controlled source function above the sunspot umbra. Strong
emission profiles close to the rest wavelengths but with long redshifted
tails are also observed at the downflow terminus. From the polarized
spectra, we infer longitudinal magnetic field strengths of ~2.4 kG in
the core portion of the He I strong emission, which we believe is the
strongest ever reported in this line. Photospheric field strengths along
the same line of sight are ~2.8 kG as inferred using the Ca I 10839 Å
spectral line. The temperatures of the highest speed He I absorption
and the near-rest emission are similar (~10 kK), while a differential
emission measure analysis using Solar Dynamics Observatory/Atmospheric
Imaging Assembly data indicates significant increases in radiative
cooling for temperatures between ~0.5 and 1 MK plasma associated with
the downflow terminus. Combined we interpret these observations in the
context of a strong radiative shock induced by the supersonic downflow
impacting the low sunspot atmosphere.
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Title: The National Science Foundation's Daniel K. Inouye Solar
Telescope — Status Update
Authors: Rimmele, T.; Woeger, F.; Tritschler, A.; Casini, R.; de Wijn,
A.; Fehlmann, A.; Harrington, D.; Jaeggli, S.; Anan, T.; Beck, C.;
Cauzzi, G.; Schad, T.; Criscuoli, S.; Davey, A.; Lin, H.; Kuhn, J.;
Rast, M.; Goode, P.; Knoelker, M.; Rosner, R.; von der Luehe, O.;
Mathioudakis, M.; Dkist Team
2021AAS...23810601R Altcode:
The National Science Foundation's 4m Daniel K. Inouye Solar Telescope
(DKIST) on Haleakala, Maui is now the largest solar telescope in the
world. DKIST's superb resolution and polarimetric sensitivity will
enable astronomers to unravel many of the mysteries the Sun presents,
including the origin of solar magnetism, the mechanisms of coronal
heating and drivers of flares and coronal mass ejections. Five
instruments, four of which provide highly sensitive measurements
of solar magnetic fields, including the illusive magnetic field of
the faint solar corona. The DKIST instruments will produce large and
complex data sets, which will be distributed through the NSO/DKIST Data
Center. DKIST has achieved first engineering solar light in December
of 2019. Due to COVID the start of the operations commissioning phase
is delayed and is now expected for fall of 2021. We present a status
update for the construction effort and progress with the operations
commissioning phase.
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Title: Forward Synthesis Of The Active Corona In DKIST Coronal Lines
Authors: Schad, T.; Dima, G.
2021AAS...23832801S Altcode:
Large aperture coronagraphic spectropolarimeters offer unique
possibilities to study the off-limb corona using polarized diagnostics,
including those that probe the ill-measured coronal magnetic field
properties. Here, we investigate the formation of the prime coronal
lines targeted by US National Science Foundation's Daniel K Inouye Solar
Telescope. We synthesize observables through advanced, high-resolution,
and finely-structured, 3D MURaM coronal simulations. To do so, we
have built and optimized Python-based synthesis modules that calculate
the polarized line emission for multi-level atoms including the role
of electron and proton collisions. We provide detailed benchmarks of
these modules, in specific against tools provided by the Chianti team
(in the scalar limit), both to validate the code and provide a primer
for the line-dependent aspects of the polarization formation. The
synthetic maps allow us to describe and predict polarized features
within the array of multi-wavelength observables available. In addition,
we comment on the opportunities provided for, as well as the challenges
faced by, the analysis of the apparent polarized fine structures.
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Title: Possibilities and limitations of single-point coronal
magnetometry based on multi-line spectropolarimetric observations
Authors: Dima, G. I.; Schad, T.
2021AAS...23832810D Altcode:
Emission from the solar corona in the visible and infrared is
dominated by magnetic dipole (M1) emission lines. The magnetic and
thermal properties of the coronal plasma influence the polarized
properties of M1 lines and offer an opportunity to directly measure
the coronal magnetic field. While the optically thin nature of the
coronal plasma requires careful interpretation of observations, some
differentiated coronal structures, like coronal loops, may offer
opportunities for 'single-point' inversions to work. Generalizing
the analytical formalism of the 'single-point' inversion approach
introduced by Plowman (2014) for the Fe XIII 10747 / 10798 Å line
pair, we show that some combinations of M1 lines contain degenerate
spectropolarimetric information which prohibits their application for
this technique. Combining polarized atomic modeling based on coronal
loop properties with a sensitivity analysis based on photon noise,
we discuss using the Fe XIII 10747 Å, Si X 14301 Å line pair as
one alternative combination for implementing this technique. We show
that at noise levels around 10<SUP>-4</SUP> of the line intensity,
magnetic fields with sufficient strength (~25 G) and not severely
inclined to the line-of-sight (<35º) can be recovered using this
method. The DKIST will feasibly reach such low noise levels while taking
spectropolarimetric observations of multiple coronal emission lines
at spatial resolutions close to 1 arcsec, comparable to space-based
observatories.
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Title: A Coronal Downflow Induced Radiative Shock In A Sunspot Umbra
Observed With He I Spectropolarimetry
Authors: Schad, T. A.; Dima, G.; Anan, T.
2021AAS...23812703S Altcode:
Downward directed energy deposition into sunspot umbrae may be an
important contributor to the energetics of the umbral transition region
(TR) and upper chromosphere. Supersonic downflows, and their association
with TR bright dots, are now more routinely studied by NASA's Interface
Region Imaging Spectrograph. Observations that trace the impact of
these flows into the lower chromosphere and perhaps lower are less
frequent. Here we report unique spectropolarimetric observations of a
supersonic downflow using the He I 1083 nm triplet observed using the
Facility Infrared Spectropolarimeter at the Dunn Solar Telescope. We
observe downflows reaching speeds near 200 km/s into a sunspot umbra
that present both high-speed absorption and emission profiles. At the
downflow terminus, we also observe a sharp transition from supersonic
speeds to near-rest speeds, which are connected by extended redshifted
line wings of the near-stationary component. Careful analysis,
correcting for straylight, and using spectropolarimetric inversions,
provide a detailed picture of what we interpret as a strong radiative
shock in the sunspot umbra. In particular, we find evidence of very
strong magnetic field strengths in the post-shocked flow that suggests
the flow penetrates into the deeper umbral atmosphere.
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Title: Magnetic field structures associated with chromospheric
heating in a plage region
Authors: Anan, T.; Schad, T.; Kitai, R.; Dima, G.; Jaeggli, S.;
Collados, M.; Dominguez-Tagle, C.; Kleint, L.
2021AAS...23821222A Altcode:
The strongest quasi-steady heating in the solar atmosphere occurs in
the active chromosphere and in particular within plage regions. Our
aim is to investigate the relation between magnetic structures and
the signatures of heating in the plage regions so as to clarify what
mechanisms are at work. We observed a plage region in NOAA active
region 12723 in the near infrared He I triplet and Si I 1082.7 nm
on 2018 October 3 using the Integral Field Unit mode of the GREGOR
Infrared Spectrograph (GRIS) installed at the GREGOR telescope. At the
same time, the Interface Region Imaging Spectrograph (IRIS) obtained
spectra in the ultra-violet Mg II h & k doublet emitted from the
same region. We applied the HAnle and ZEeman Light v2.0 inversion
code (HAZEL v2.0) to the GRIS data to infer the photospheric and
chromospheric magnetic field. We find that the radiative flux of the Mg
II was large between patches of strong magnetic field strength in the
photosphere, or at edges of the magnetic patches. On the other hand,
the spatial correspondences between the Mg II flux and the magnetic
field strength in the chromosphere and between the Mg II flux and the
electric current are not so clear. In conclusion, chromospheric heatings
in the plage region can be related to magnetic field perturbations
produced by interactions of magnetic flux tubes.
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Title: He I spectropolarimetry of a supersonic coronal downflow
within a sunspot umbra
Authors: Schad, Thomas A.; Dima, Gabriel I.; Anan, Tetsu
2021arXiv210512853S Altcode:
We report spectropolarimetric observations of a supersonic downflow
impacting the lower atmosphere within a large sunspot umbra. This
work is an extension of Schad et al. 2016 using observations
acquired in the He I 10830 Angstrom triplet by the Facility Infrared
Spectropolarimeter. Downflowing material accelerating along a cooled
coronal loop reaches peak speeds near 200 km s$^{-1}$ and exhibits
both high speed emission and absorption within the umbra, which
we determine to be a consequence of the strong height dependence
of the radiatively-controlled source function above the sunspot
umbra. Strong emission profiles close to the rest wavelengths but with
long red-shifted tails are also observed at the downflow terminus. From
the polarized spectra, we infer longitudinal magnetic field strengths of
${\sim}2.4$ kG in the core portion of the He I strong emission, which we
believe is the strongest ever reported in this line. Photospheric field
strengths along the same line-of-sight are ${\sim}2.8$ kG as inferred
using the Ca I 10839 Angstrom spectral line. The temperatures of the
highest speed He I absorption and the near rest emission are similar
(${\sim}$10 kK), while a differential emission measure analysis using
SDO/AIA data indicates significant increases in radiative cooling for
temperatures between $\sim$0.5 and 1 MK plasma associated with the
downflow terminus. Combined we interpret these observations in the
context of a strong radiative shock induced by the supersonic downflow
impacting the low sunspot atmosphere.
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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: Single-point coronal magnetometry using multi-line
spectropolarimetric observations
Authors: Dima, Gabriel; Schad, Thomas
2021cosp...43E1788D Altcode:
The US National Science Foundation's Daniel K Inouye Solar Telescope
(DKIST) will soon provide large-aperture coronagraphic observations
of polarized coronal emission lines in the visible and infrared
spectrum at spatial resolutions close to 1 arcsec, comparable to
space-based observatories. Polarized via coherent scattering and the
Zeeman Effect, the targeted emission lines hold diagnostic potential
for the hard-to-measure coronal magnetic field. DKIST provides the
requisite advances in spatial resolution, spectral coverage, and
polarimetric sensitivity in these lines to advance our understand of
coronal magnetic structure; however, techniques for inferring the field
parameters from the observations require careful consideration. Here
we discuss a technique that combines two or more magnetic-dipole (M1)
coronal lines to infer the vector components of the coronal magnetic
field that do not require detailed knowledge of the other intrinsic
plasma state variables. Generalizing the analytical formalism
of the 'single-point' inversion approach introduced by Plowman
(2014) we show that some combinations of M1 lines contain degenerate
spectropolarimetric information which prohibits their application for
this technique. This may include the pair of Fe XIII 10747, 10797 Å
emission lines originally proposed by Plowman. Through a sensitivity
analysis based on photon noise and polarized atomic modeling based
on coronal loop properties, we discuss using the Fe XIII 10747 Å, Si
X 14301 Å line pair as one alternative combination for implementing
this technique. We find that for noise levels around 10$^{-4}$ of the
line intensity, which will be available with DKIST, magnetic fields
with sufficient strength ($\sim$25 G) and not severely inclined to the
line-of-sight (<35$^\circ$) can be recovered with this method. We
discuss potential targets for this method and limitations for it's
applicability.
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Title: Remote sensing the thermal evolution and magnetic conditions
within coronal thermal nonequilibrium events using ground-based
large-aperture coronagraphic polarimetry
Authors: Schad, Thomas
2021cosp...43E.988S Altcode:
The solar atmosphere provides an unparalleled opportunity to
study the detailed processes governing the onset and evolution of
thermal instabilities in magnetized plasmas. Spectral imaging and
polarimetric capabilities made available by ground-based large-aperture
(coronagraphic) telescopes, in particular the soon-to-be commissioned
US National Science Foundation's Daniel K Inouye Solar Telescope
(DKIST), provide enhanced diagnostics of the thermal evolution and,
uniquely, the magnetic conditions within coronal thermal nonequilibrium
events. Here we demonstrate, using measurements from the MLSO/HAO CoMP
instrument, the potential of linear polarized measurements of forbidden
magnetic-dipole transitions of highly ionized species for studying the
temporal evolution of temperature and density within unstable (cooling)
loops. In addition, we show how DKIST linear and circular polarized
measurements of these lines will provide the possibility for measuring
the magnetic field conditions within the hot loops. As the thermal
instability progresses in such structures and coronal rain is formed,
the enhanced emission within permitted lines like He I and Ca II allow
very detailed imaging of the rain parcels in addition to significant
advantages for polarimetric measurements of coronal magnetism. In some
cases, such rain events can be observed on-disk and traced directly to
the lower atmosphere wherein the influence of the lower atmosphere's
evolution on the instability might be assessed. DKIST provides a very
flexible multi-instrument suite capable of taking advantage of these
many diagnostics of thermal stabilities from the ground, and here we
comment on specific strategies for observations.
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Title: New polarized views of the neutral and ionized solar corona
using the US NSF's Daniel K Inouye Solar Telescope
Authors: Schad, Thomas; Dima, Gabriel
2021cosp...43E1789S Altcode:
This year's commissioning of the US National Science Foundation's
4-meter aperture Daniel K Inouye Solar Telescope (DKIST) on the
island of Maui, in Hawaii, revolutionizes our view of the dynamic
finely-structured solar corona in at least two important ways. First,
its unprecedented spatial resolving power within the solar photosphere
affords our most detailed view yet of the footpoints of coronal
structures as we endeavor to understand the nature of the convective
and magnetic drivers of coronal loop energetics. And second, the
capabilities it provides off-limb for conducting low-scattered light,
multi-wavelength spectropolarimetry of primarily highly ionized species
opens up new remote diagnostic of magnetism directly in the corona, not
only providing critical constraints for the large-scale configuration
of active regions but also the possibility to study scaling relations
between the magnetic field and localized heating and cooling. The
challenges involved in interpreting these optically thin polarized
diagnostics can be severe, as we will summarize; however, we also
demonstrate via observations and simulations the power of multi-spectral
diagnostics, and in particular, the value of neutral helium formation
during corona rain events that make high-resolution coronal polarimetry
of individuated structures a real possibility made available for the
first time by the large-aperture coronagraphy of the DKIST.
---------------------------------------------------------
Title: DKIST and Advances in Chromospheric Polarimetry: Connecting
the Trees with the Forest
Authors: Schad, T. A.
2020AGUFMSH004..04S Altcode:
The chromosphere is comprised of a wondrous taxonomy of multi-scaled
dynamic phenomena. Together, localized features like jets, jet-lets,
fibrils, and spicules, in congress with a vigorous and evolving wave
field, create a rich interconnected forest. Indeed, observers have often
remarked how spicules extending from the limb appear like a forest of
trees, and on-disk, analogous references to fibril canopies are often
invoked. Characterizing these basic chromospheric constituents requires
highly advanced instrumentation pushing the boundaries of spatial,
spectral, and temporal resolution. Yet, pushing for such a microscopic
view is not a case of not seeing the forest for the trees. These dynamic
features trace important, yet poorly understood, physical processes
that are responsible for transporting significant energy from the
sun's magnetized convection and depositing it throughout the global
chromosphere. A key challenge is to connect the energy budget on local
scales with that of the global chromosphere an d lower corona. The US
National Science Foundation's Daniel K Inouye Solar Telescope (DKIST)
is at the forefront of this observational effort. DKIST provides an
extremely versatile facility designed from the ground-up to enable
high-speed, multi-channel imaging, slit- and imaging-based spectroscopy
and spectropolarimetry at the highest resolutions available. It is
uniquely positioned to leverage recent advances in chromospheric
polarimetry for inferring the magnetic fields and electric fields in
chromospheric plasmas. Early operations start soon, and we are already
seeing glimpses of the promise of DKIST. This talk will discuss the
exciting opportunities provided by its first light instrument suite,
in particular, to study non-equilibrium and non-ideal MHD effects in
the Sun's chromospheric forest.
---------------------------------------------------------
Title: The Daniel K. Inouye Solar Telescope - Observatory Overview
Authors: Rimmele, Thomas R.; Warner, Mark; Keil, Stephen L.; Goode,
Philip R.; Knölker, Michael; Kuhn, Jeffrey R.; Rosner, Robert R.;
McMullin, Joseph P.; Casini, Roberto; Lin, Haosheng; Wöger, Friedrich;
von der Lühe, Oskar; Tritschler, Alexandra; Davey, Alisdair; de Wijn,
Alfred; Elmore, David F.; Fehlmann, André; Harrington, David M.;
Jaeggli, Sarah A.; Rast, Mark P.; Schad, Thomas A.; Schmidt, Wolfgang;
Mathioudakis, Mihalis; Mickey, Donald L.; Anan, Tetsu; Beck, Christian;
Marshall, Heather K.; Jeffers, Paul F.; Oschmann, Jacobus M.; Beard,
Andrew; Berst, David C.; Cowan, Bruce A.; Craig, Simon C.; Cross,
Eric; Cummings, Bryan K.; Donnelly, Colleen; de Vanssay, Jean-Benoit;
Eigenbrot, Arthur D.; Ferayorni, Andrew; Foster, Christopher; Galapon,
Chriselle Ann; Gedrites, Christopher; Gonzales, Kerry; Goodrich, Bret
D.; Gregory, Brian S.; Guzman, Stephanie S.; Guzzo, Stephen; Hegwer,
Steve; Hubbard, Robert P.; Hubbard, John R.; Johansson, Erik M.;
Johnson, Luke C.; Liang, Chen; Liang, Mary; McQuillen, Isaac; Mayer,
Christopher; Newman, Karl; Onodera, Brialyn; Phelps, LeEllen; Puentes,
Myles M.; Richards, Christopher; Rimmele, Lukas M.; Sekulic, Predrag;
Shimko, Stephan R.; Simison, Brett E.; Smith, Brett; Starman, Erik;
Sueoka, Stacey R.; Summers, Richard T.; Szabo, Aimee; Szabo, Louis;
Wampler, Stephen B.; Williams, Timothy R.; White, Charles
2020SoPh..295..172R Altcode:
We present an overview of the National Science Foundation's Daniel
K. Inouye Solar Telescope (DKIST), its instruments, and support
facilities. The 4 m aperture DKIST provides the highest-resolution
observations of the Sun ever achieved. The large aperture of
DKIST combined with state-of-the-art instrumentation provide the
sensitivity to measure the vector magnetic field in the chromosphere
and in the faint corona, i.e. for the first time with DKIST we will
be able to measure and study the most important free-energy source
in the outer solar atmosphere - the coronal magnetic field. Over its
operational lifetime DKIST will advance our knowledge of fundamental
astronomical processes, including highly dynamic solar eruptions
that are at the source of space-weather events that impact our
technological society. Design and construction of DKIST took over two
decades. DKIST implements a fast (f/2), off-axis Gregorian optical
design. The maximum available field-of-view is 5 arcmin. A complex
thermal-control system was implemented in order to remove at prime
focus the majority of the 13 kW collected by the primary mirror and
to keep optical surfaces and structures at ambient temperature, thus
avoiding self-induced local seeing. A high-order adaptive-optics
system with 1600 actuators corrects atmospheric seeing enabling
diffraction limited imaging and spectroscopy. Five instruments, four
of which are polarimeters, provide powerful diagnostic capability
over a broad wavelength range covering the visible, near-infrared,
and mid-infrared spectrum. New polarization-calibration strategies
were developed to achieve the stringent polarization accuracy
requirement of 5×10<SUP>−4</SUP>. Instruments can be combined and
operated simultaneously in order to obtain a maximum of observational
information. Observing time on DKIST is allocated through an open,
merit-based proposal process. DKIST will be operated primarily in
"service mode" and is expected to on average produce 3 PB of raw
data per year. A newly developed data center located at the NSO
Headquarters in Boulder will initially serve fully calibrated data to
the international users community. Higher-level data products, such as
physical parameters obtained from inversions of spectro-polarimetric
data will be added as resources allow.
---------------------------------------------------------
Title: The off-limb polarized corona at high-resolution: new synthetic
views for the DKIST era
Authors: Schad, T. A.; Dima, G. I.
2020AGUFMSH0280015S Altcode:
In anticipation of the great advances that the National Science
Foundation's Daniel K. Inouye Solar Telescope will soon provide for
spectropolarimetry of the off limb solar corona, we investigate the
formation of the prime coronal lines targeted by DKIST as synthesized
through advanced, high-resolution, finely-structured, 3D MURaM coronal
simulations. In doing so, we demonstrate a new code developed for
polarized line emission calculations referred to as pyCLE. We provide
detailed benchmarks of pyCLE, in specific against tools provided by
the Chianti team (in the scalar limit), both to validate the code and
provide a primer for the line-dependent aspects of the polarization
formation. Synthetic maps created using pyCLE and the MURaM active
region simulation allow us to describe and predict polarized features
within the array of multi-wavelength observables available. In addition,
we comment on the opportunities provided for, as well as the challenges
faced by, the analysis of the apparent polarized fine structure.
---------------------------------------------------------
Title: Forward Synthesis of Polarized Emission in Target DKIST
Coronal Lines Applied to 3D MURaM Coronal Simulations
Authors: Schad, Thomas; Dima, Gabriel
2020SoPh..295...98S Altcode:
Self-consistent magnetohydrodynamic simulations of the solar corona
with fine (≲10 km) grid scales are now being realized in parallel
to advancements in high-resolution coronal spectropolarimetry provided
by the National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST). We investigate the synthesis of polarized emission in the
presence of apparent coronal fine structure exhibited by 3D MURaM
coronal simulations for the key polarized spectral lines targeted by
DKIST, namely Fe XIVλ 5303 , Fe XIλ 7892 , Fe XIIIλ 10746 , Fe
XIIIλ 10798 , Si Xλ 14301 , and Si IXλ 39343 . To benchmark our
calculations, we provide detailed comparisons between the employed
polarized line formation theory and established scalar line synthesis
tools provided by the CHIANTI database team. To accelerate polarized
synthesis for large simulations, we create efficient lookup tables
based on atomic models significantly larger than previous studies. The
spectral data cubes we describe provide a useful guide for the new
era of multi-spectral DKIST coronal diagnostics as we discuss specific
analysis techniques and challenges.
---------------------------------------------------------
Title: Using Multi-line Spectropolarimetric Observations of Forbidden
Emission Lines to Measure Single-point Coronal Magnetic Fields
Authors: Dima, Gabriel I.; Schad, Thomas A.
2020ApJ...889..109D Altcode: 2020arXiv200106123D
Polarized magnetic dipole (M1) emission lines provide important
diagnostics for the magnetic field dominating the evolution of the
solar corona. This paper advances a multi-line technique using specific
combinations of M1 lines to infer the full vector magnetic field for
regions of optically thin emission that can be localized along a given
line of sight. Our analytical formalism is a generalization of the
"single-point inversion" approach introduced by Plowman. We show that
combinations of M1 transitions for which each is either a $J=1\to 0$
transition or has equal Landé g-factors for the upper and lower levels
contain degenerate spectropolarimetric information that prohibits the
application of the single-point inversion technique. This may include
the pair of Fe XIII lines discussed by Plowman. We identify the Fe
XIII 10747 Å and Si X 14301 Å lines as one alternative combination
for implementing this technique. Our sensitivity analysis, based on
coronal loop properties, suggests that for photon noise levels around
10<SUP>-4</SUP> of the line intensity, which will be achievable with
the National Science Foundation's Daniel K. Inouye Solar Telescope,
magnetic fields with sufficient strength (∼10 G) and not severely
inclined to the line of sight (≲35°) can be recovered with this
method. Degenerate solutions exist, though we discuss how added
constraints may help resolve them or reduce their number.
---------------------------------------------------------
Title: Acceleration of Coronal Mass Ejection Plasma in the Low Corona
as Measured by the Citizen CATE Experiment
Authors: Penn, Matthew J.; Baer, Robert; Walter, Donald; Pierce,
Michael; Gelderman, Richard; Ursache, Andrei; Elmore, David; Mitchell,
Adrianna; Kovac, Sarah; Hare, Honor; McKay, Myles; Jensen, Logan;
Watson, Zachary; Conley, Mike; Powers, Lynn; Lazarova, Marianna;
Wright, Joseph; Young, David; Isberner, Fred; Hart, C. Alexandra;
Sheeley, N. R., Jr.; Penn, Debbie; Allen-Penn, Kate; Alder, Bruce;
Alder, Ryan; Hall-Conley, Geri; Gerdes, David; Weber, Katherine;
Johnson, Jeffrey; Matzek, Gerald; Somes, Steven; Sobnosky, Rob;
McGowen, Robert; Meo, Michael; Proctor, Damani; Wessinger, Charlie;
Schilling, Jeannine; Kerr, Jay; Beltzer-Sweeney, Alexander; Falatoun,
Alex; Higgins, David; Boyce, Grady; Hettick, Jared; Blanco, Philip;
Dixon, Scott; Ardebilianfard, Sepehr; Boyce, Pat; Lighthill, Richard;
Lighthill, Denese; Anderson, David; Anderson, Mine; Schad, Thomas;
Smith, Sonna; Jensen, Declan; Allen, Anthony; Smith, Donavan; Brandon,
Gage; Earp, Joe; Earp, Jane; Blair, Bob; Claver, Chuck F.; Claver,
Jennifer A.; Claver, Ryan H.; Hoops, Danielle; Rivera, Esteban;
Gibson, Llanee; Hiner, Martin; Lann, Rein; Miller, Shaedyn; Briggs,
Burton; Davis, Karan; Jackson, Brian; Kautzsch, Kaleb; Sandidge,
Wesley; Lucas, Russell; Gregg, Duane; Kamenetzky, Julia; Rivera,
Tiffany; Shaw, Joe; Scherrer, Bryan; Sandbak, Dylan; McFate, Richard;
Harris, Wilson; Brasier, Zachery; McNeil, Stephen; Jensen, Jack;
Jensen, Makai; Moore, Mason; Temple, Alexandria; Vanderhorst, Thomas;
Kautz, Richard; Bellorado, Orion; Jenkins, LaVor R.; Pantuso, Corey;
Carey, Marley; Byrnes, Josh; Scholtens, Kyle; Web, Julian; Baker,
Brain; Barngrover, Katie; Hathaway, Drew; Smith, Kallen; Chandler,
Kellyn; Hinkle, Lydia; Chandler, Ione; Gisler, Galen; Benner, Jack;
Mas, Madison; Rogers, Maya; Moore, Prescott; Pelofske, Elijah;
Gulley, Stephen; Short, Beth; Crooker, Isabel; Hammock, Jennifer;
Cardenas, Katsina; Cardenas, Kateri; Wellman, Jennifer; Roy, Mark;
Meyer, Joe; Brough, Jalynne; Brough, Kameron; Nelson, Tim; Nelson,
Zack; Russell, Caleb; Bautz, Theresa; Weitzel, Eric; Team; Wistisen,
Michele; Aagard, Shae; Whipps, Zachary; Neuroth, Logan; Poste, Dawson;
Worthen, Connor; Gosain, Sanjay; Steward, Mark; Gosain, Vanshita;
Gosain, Ruchi; Jorgensen, Janet; Doucette, Eleanor; Doucette, Reba;
Iwen, Elliott; Cochran, Alexus; Stith, James; Scribner, Doug; Kenney,
Austen; Pisciotti, Kolby; Pease, Irene; Cynamon, Samuel; Cynamon,
Charles; Cynamon, Dawn; Tolbert, Bart; Dupree, Jean A.; Weremeichik,
Jeremy; Pindell, Nathan; Stives, Kristen; Simacek, Thomas K.; Simacek,
Yolanta G.; Simacek, Anne L.; Boeck, Wayne; Boeck, Andreea; Ryan,
Austin; Wierzorec, Gabriel; Klebe, Dimitri; Costanza, Bryan; Cerny,
Arnie; Schmale, Trevor; Hoffman, Tessa; Streeter, Sam; Erickson,
Jack; McClellan, Michele; Erickson, Ella; Brettell, Brynn; Shoffner,
Savannah; McClellan, Emilie; VanVoorhis, Julie; Bramhall, Cole; Stelly,
Daniel; Bee, Bentley; Acevedo, Bruno; Kroeger, Madison; Trumpenski,
Ben; Sump, Nolan; Brook, Liam; Ernzen, Jagert; Lewis, Jessica;
Maderak, Ryan; Kennedy, Charles; Dembinski, David; Wright, Rita;
Foster, Michael; Ahmadbasir, Mohammad; Laycox, Monty; Foster, James;
Orr, Ethan; Staab, Ashley; Speck, Angela; Baldridge, Sean; Kegley,
Lucy; Bavlnka, Jordan; Ballew, Thomas; Callen, Bruce; Ojakangas,
Gregory; Bremer, Mark; Angliongto, Maryanne; Redecker, Mark; Bremer,
Chris; Hill, Peggy; Rodgers, Michael; Duncan, Jordan; Fincher, Sam;
Nielsen, Ben; Hasler, Samantha; Shivelbine, Taylor; Howard, Tyler;
Midden, Chris; Patrick, Sean; Glenn, Kerry; Mandrell, Chris; Dawson,
Kyle; Cortez, Margaret; Levsky, Alyssa; Gallaba, Dinuka; Perrone,
Mason; Taylor, Jasmyn; Yanamandra-Fisher, Padma A.; Harper, Howard;
Adams, Lindsay; Springer, Michaela; Menard, BillyJoe; Boggs, Dylan;
Lynch, Caitlin; Watson, Jacob; York, Andi; Matthews, David; Brown,
Kiley; Garrison, Dylan; Mangin, Jonathan; Mangin, Isaac; Birriel,
Jennifer; Birriel, Ignacio; Yess, Capp; Anderson, Jesse; Caudill,
Ethan; Smith, Allyn; Buckner, Spencer; Longhurst, Russ; Fagan, Ben;
Nations, Christian; DiMatties, Jeffrey; Thompson, Patricia; Garrison,
David; Garrison, Thomas; Garrison, William; Kidd, Mary; Baker, Maria;
Ledford, Mary-Beth; Winebarger, Amy; Freed, Michael; Church, Morgyn;
Dickens, Jim; Anderson, Bob; Smith, Ned; Dorsey, Lynne; Justice, Doug;
Zavala, Daniel; Stockbridge, Zach; Brittain, Sean; Jensen, Stanley;
Leiendecker, Harrison; Thompson, Erin; Deady, Michelle; Quinn-Hughes,
Kelly; Slimmer, David; Granger, Valerie; LaRoche, Michael; Hill
LaRoche, Serena; Manspeaker, Rachel; Nguyen, Peter; Smith, Daniel;
Payne, Jim; Zissett, Jerry; Roberts, Arianna M.; Roberts, Gabrielle
W.; Roberts, Harrison; Riddle, Amy; Ursache, Corina; Ursache, Elena
2020PASP..132a4201P Altcode:
The citizen Continental-America Telescopic Eclipse (CATE) Experiment
was a new type of citizen science experiment designed to capture a time
sequence of white-light coronal observations during totality from 17:16
to 18:48 UT on 2017 August 21. Using identical instruments the CATE
group imaged the inner corona from 1 to 2.1 RSun with 1.″43 pixels
at a cadence of 2.1 s. A slow coronal mass ejection (CME) started on
the SW limb of the Sun before the total eclipse began. An analysis
of CATE data from 17:22 to 17:39 UT maps the spatial distribution of
coronal flow velocities from about 1.2 to 2.1 RSun, and shows the CME
material accelerates from about 0 to 200 km s<SUP>-1</SUP> across this
part of the corona. This CME is observed by LASCO C2 at 3.1-13 RSun
with a constant speed of 254 km s<SUP>-1</SUP>. The CATE and LASCO
observations are not fit by either constant acceleration nor spatially
uniform velocity change, and so the CME acceleration mechanism must
produce variable acceleration in this region of the corona.
---------------------------------------------------------
Title: Shock Heating Energy of Umbral Flashes Measured with Integral
Field Unit Spectroscopy
Authors: Anan, Tetsu; Schad, Thomas A.; Jaeggli, Sarah A.; Tarr,
Lucas A.
2019ApJ...882..161A Altcode: 2019arXiv190710797A
Umbral flashes are periodic brightness increases routinely observed in
the core of chromospheric lines within sunspot umbrae and are attributed
to propagating shock fronts. In this work we quantify the shock heating
energy of these umbral flashes using observations in the near-infrared
He I triplet obtained on 2014 December 7 with the SpectroPolarimetric
Imager for the Energetic Sun, which is a novel integral field unit
spectrograph at the Dunn Solar Telescope. We determine the shock
properties (the Mach number and the propagation speed) by fitting
the measured He I spectral profiles with a theoretical radiative
transfer model consisting of two constant-property atmospheric slabs
whose temperatures and macroscopic velocities are constrained by the
Rankine-Hugoniot relations. From the Mach number, the shock heating
energy per unit mass of plasma is derived to be 2 × 10<SUP>10</SUP>
erg g<SUP>-1</SUP>, which is insufficient to maintain the umbral
chromosphere. In addition, we find that the shocks propagate upward with
the sound speed and the Mach number does not depend on the temperature
upstream of the shocks. The latter may imply suppression of the
amplification of the Mach number due to energy loss of the shocks.
---------------------------------------------------------
Title: Shock heating energy in an umbra of a sunspot with integral
field unit spectroscopy
Authors: Anan, Tetsu; Schad, Thomas A.; Jaeggli, Sarah A.; Tarr,
Lucas A.
2019AAS...23421705A Altcode:
On 2014 December 7 we used new integral field spectroscopy techniques
to observe umbral flashes, which are periodic brightness increases
routinely observed in the core of chromospheric lines within sunspot
umbrae and are attributed to propagating shock fronts. In this work
we quantify the shock heating energy of these umbral flashes using
observations in the near infrared HeI triplet obtained with the
SpectroPolarimetric Imager for the Energetic Sun (SPIES), which is
novel integral field unit spectrograph at the Dunn Solar Telescope. We
determine the shock properties (the Mach number and the propagation
speed) by fitting the measured HeI spectral profiles with a theoretical
radiative transfer model using two constant property atmospheric slabs
whose temperatures and macroscopic velocities are constrained by the
Rankine-Hugoniot relations. From the Mach number, the shock heating
energy per unit mass of plasma is derived as 2 x 10<SUP>10</SUP>
erg/g. We conclude that the estimated shock heating energy rate is
less than the amount required to maintain the umbral chromosphere.
---------------------------------------------------------
Title: Coronagraphic Observations of Si X λ14301 and Fe XIII λ10747
Linearly Polarized Spectra Using the SOLARC Telescope
Authors: Dima, Gabriel I.; Kuhn, Jeffrey R.; Schad, Thomas A.
2019ApJ...877..144D Altcode:
The forbidden Si X emission line at 14301 Å has been identified
as a potentially valuable polarized diagnostic for solar coronal
magnetic fields; however, the only polarized Si X measurements
achieved to date have been during eclipses and at comparatively low
spatial and spectral resolution. Here we report spectropolarimetric
observations of both the Si X 14301 Å and more well-established Fe
XIII 10747 Å coronal lines acquired with the 0.45 m aperture SOLARC
coronagraph atop Haleakalā. Using its fiber-based integral field
spectropolarimeter, we derive observations sampled at radial intervals
of 0.05 {R}<SUB>⊙ </SUB> (i.e., ∼50″) with a spectral resolving
power of ≈36,000. Results for both lines, which represent averages
over different active and nonactive regions of the corona, indicate a
relatively flat radial variation for the line widths and line centers
and a factor of ≈2-3 decrease in polarized brightness between 1.05
and 1.45 {R}<SUB>⊙ </SUB>. Averaging over all the measurements the
mean and standard deviations of line properties for Si X 14301 Å and
Fe XIII 10747 Å are, respectively, FWHM of 3.0 ± 0.4 Å and 1.6 ±
0.1 Å, line-integrated polarized brightness of 0.07 ± 0.03 and 0.3
± 0.3 erg s<SUP>-2</SUP> cm<SUP>-2</SUP> sr<SUP>-1</SUP>, where the
uncertainty quoted reflects a large sample variance, and line center
wavelengths 14300.7 ± 0.2 Å and 10746.3 ± 0.1 Å. The polarized
brightness for both lines may be underestimated by up to a factor of
5 due to limitations in the photometric calibration. When accounting
for this uncertainty we find consistency between our observations
and previous measurements of the two lines as well as theoretical
calculations and affirm the potential of the Si X line as a polarized
diagnostic of the solar corona.
---------------------------------------------------------
Title: Polarimetric observations of the SiX and Fe XIII infrared
coronal emission lines using the SOLARC telescope
Authors: Dima, Gabriel; Kuhn, Jeffrey Richard; Schad, Thomas A.
2019AAS...23411704D Altcode:
The forbidden Si X emission line at 14301 Å has been identified as a
potentially valuable polarized diagnostic for solar coronal magnetic
fields; however, the only polarized Si X measurements achieved to
date have been during eclipses and at comparatively low spatial and
spectral resolution. Here we report spectropolarimetric observations
of both the Si X 14301 Å and more well-established FeXIII 10747 Å
coronal lines acquired with the 0.45 m aperture SOLARC coronagraph
atop Haleakala. Results for both lines, which represent averages over
different active and non-active regions of the corona, indicate a
relatively flat radial variation for the line widths and line centers
and a factor of 2-3 decrease in polarized brightness between 1.05 and
1.45 R<SUB>⊙</SUB>. Averaging over all the measurements the mean
and standard deviations of line properties for Si X 14301 Å and Fe
XIII 10747 Å are respectively: FWHM of 3.0±0.4 Å and 1.6±0.1,
line-integrated polarized brightness of 0.07±0.03 and 0.3±0.3 erg
s<SUP>-2</SUP> cm<SUP>-2</SUP> sr<SUP>-1</SUP> where the uncertainty
quoted reflects a large sample variance, and line center wavelengths
14300.7±0.2 Å and 10746.3±0.1 Å. The polarized brightness for both
lines may be underestimated by up to a factor of 5 due to limitations
in the photometric calibration. When accounting for this uncertainty
we find consistency between our observations and previous measurements
of the two lines as well as theoretical calculations and affirm the
potential of the Si X line as a polarized diagnostic of the solar
corona.
---------------------------------------------------------
Title: Multi-line diagnostics of the coronal magnetic field with DKIST
Authors: Dima, Gabriel; Schad, Thomas A.
2019AAS...23410601D Altcode:
Full-stokes polarimetric observations of multiple coronal emission
lines can in principle be used to infer the vector magnetic field in
the solar corona assuming the emission is all coming from a single
location in space. The Fe XIII line pair at 10747 / 10798 Å has
already been identified as a prime candidate for multi-line inversions;
although such measurements are sensitive to uncertainties and biases
that must be carefully assessed. That said, this technique may have
additional utility when expanded to other multi-line observations
planned for the National Science Foundation's Daniel K Inouye Solar
Telescope (DKIST). This work investigates, in particular, the use
of the Fe XIII 10747 / Si X 14301 Å line pair, and its benefits for
probing the magnetic conditions in cooler coronal loops formed near
1.4 MK. We discuss the advantages and limitations of the Fe XIII / Si
X line pair as well as possible observing scenarios with the DL-NIRSP
and Cryo-NIRSP instruments on the DKIST.
---------------------------------------------------------
Title: Neutral Helium Triplet Spectroscopy of Quiescent Coronal
Rain with Sensitivity Estimates for Spectropolarimetric Magnetic
Field Diagnostics
Authors: Schad, Thomas A.
2018ApJ...865...31S Altcode: 2018arXiv180902252S
On account of its polarizability and magnetic field sensitivity,
as well as the role of neutral helium in partially ionized solar
environments, the neutral helium triplet (orthohelium) system
provides important, yet underutilized, diagnostics of solar coronal
rain. This work describes off-limb observations of coronal rain in
NOAA Active Region 12468 obtained in the He I 10830 Å triplet using
the Massively MultipleXed Imaging Spectrograph experiment at the Dunn
Solar Telescope along with cotemporal observations from NASA’s Solar
Dynamics Observatory and the Interface Region Imaging Spectrograph
(IRIS). We detect rain simultaneously in the IRIS 1400 and 2796 Å
channels and in He I 10830 Å. The large degree of spatial coherence
present between all channels agrees with previous observations of the
multitemperature nature of coronal rain. A statistical analysis of
He I spectral profiles for rain identified via automated detection
indicates that He I line radiances are, on average, 10<SUP>4</SUP>
erg cm<SUP>-2</SUP> s<SUP>-1</SUP> sr<SUP>-1</SUP> the average
translational velocity is 70 km s<SUP>-1</SUP>, and Doppler widths
are distributed around 10 km s<SUP>-1</SUP>. Based on these results,
forward models of expected He I polarized signals allow us to estimate,
using synthetic observables and an inversion algorithm including fits
for the scattering angle constraining the material’s location along
the line of sight, the magnetic sensitivity of the upcoming National
Science Foundation’s Daniel K. Inouye Solar Telescope. We predict
that joint observations of the He I 10830 and 5876 Å multiplets using
first-light instrumentation will provide inverted magnetic field
errors of ±3.5 G (2σ) for spatial scales of 0.″5 (∼360 km),
assuming dynamically limited integration times of 5.5 s.
---------------------------------------------------------
Title: Magnetic Diagnostics of Coronal Rain using the DKIST
Authors: Schad, Thomas
2018cosp...42E3005S Altcode:
The routine production of coronal rain in the outer solar atmosphere
provides one of the finest probes we have of the coronal plasma
environment and its apparent structuring. Despite the range of
phenomena discovered with imaging observations, the magnetic environment
hosting and marshaling rain production remains poorly constrained by
observations. With the dawn of the DKIST and its advanced suite of
five facility instruments, this is primed to change. The large DKIST
aperture (4 meter) provides a collecting area capable of combining
rapid exposure imaging diagnostics and spectroscopic observations of
coronal rain with meaningful spectropolarimetric observations, which
to date have been rarely achieved for coronal rain. The brightness
of coronal rain in key chromospheric diagnostics (as compared to hot
infrared coronal lines) offers a very significant photon advantage
for conducting "cool" coronal magnetometry. This talk will discuss the
building blocks for an observational framework to study coronal rain at
DKIST, including how to coordinate VBI imaging, VISP spectropolarimetry,
VTF 2D spectro-imaging, and DL-NIRSP IFU-based spectropolarimetry. This
discussion will be guided by recent observations of neutral helium
production within coronal rain that allow us to much better predict
DKIST capabilities for coronal rain polarimetry. In addition, automated
analysis techniques based on the Rolling Hough Transform have been
developed that assist with these techniques. Coronal rain is a critical
use case for early science at DKIST when it becomes operational in 2020.
---------------------------------------------------------
Title: Status of the Daniel K. Inouye Solar Telescope: unraveling
the mysteries the Sun.
Authors: Rimmele, Thomas R.; Martinez Pillet, Valentin; Goode, Philip
R.; Knoelker, Michael; Kuhn, Jeffrey Richard; Rosner, Robert; Casini,
Roberto; Lin, Haosheng; von der Luehe, Oskar; Woeger, Friedrich;
Tritschler, Alexandra; Fehlmann, Andre; Jaeggli, Sarah A.; Schmidt,
Wolfgang; De Wijn, Alfred; Rast, Mark; Harrington, David M.; Sueoka,
Stacey R.; Beck, Christian; Schad, Thomas A.; Warner, Mark; McMullin,
Joseph P.; Berukoff, Steven J.; Mathioudakis, Mihalis; DKIST Team
2018AAS...23231601R Altcode:
The 4m Daniel K. Inouye Solar Telescope (DKIST) currently under
construction on Haleakala, Maui will be the world’s largest solar
telescope. Designed to meet the needs of critical high resolution and
high sensitivity spectral and polarimetric observations of the sun,
this facility will perform key observations of our nearest star that
matters most to humankind. DKIST’s superb resolution and sensitivity
will enable astronomers to address many of the fundamental problems
in solar and stellar astrophysics, including the origin of stellar
magnetism, the mechanisms of coronal heating and drivers of the
solar wind, flares, coronal mass ejections and variability in solar
and stellar output. DKIST will also address basic research aspects of
Space Weather and help improve predictive capabilities. In combination
with synoptic observations and theoretical modeling DKIST will unravel
the many remaining mysteries of the Sun.The construction of DKIST is
progressing on schedule with 80% of the facility complete. Operations
are scheduled to begin early 2020. DKIST will replace the NSO
facilities on Kitt Peak and Sac Peak with a national facility with
worldwide unique capabilities. The design allows DKIST to operate as
a coronagraph. Taking advantage of its large aperture and infrared
polarimeters DKIST will be capable to routinely measure the currently
illusive coronal magnetic fields. The state-of-the-art adaptive optics
system provides diffraction limited imaging and the ability to resolve
features approximately 20 km on the Sun. Achieving this resolution
is critical for the ability to observe magnetic structures at their
intrinsic, fundamental scales. Five instruments will be available at
the start of operations, four of which will provide highly sensitive
measurements of solar magnetic fields throughout the solar atmosphere
- from the photosphere to the corona. The data from these instruments
will be distributed to the world wide community via the NSO/DKIST data
center located in Boulder. We present examples of science objectives
and provide an overview of the facility and project status, including
the ongoing efforts of the community to develop the critical science
plan for the first 2-3 years of operations.
---------------------------------------------------------
Title: Pipeline development for routine chromospheric magnetic field
inversions of DST/FIRS observations
Authors: Wang, Shuo; Schad, Thomas A.; Mcateer, R. T. James
2018tess.conf30819W Altcode:
The Facility Infrared Spectropolarimeter (FIRS) at the Dunn Solar
Telescope (DST) provides efficient mapping of the full Stokes vector
in the chromospheric He I triplet at 1083 nm across solar targets. The
inversion of this type of data to achieve measurements of the magnetic
field vector plays a key role in understanding chromospheric active
region topologies and is especially useful in studying solar filaments
and prominences. As a baseline supporting future synoptic magnetic
observations of solar filaments at the DST, we demonstrate first
steps in implementing a new pipeline that inverts FIRS data using
the "Hanle and Zeeman Light" (HAZEL) code, which incorporates all the
relevant atomic-level and Zeeman effect mechanisms. Inverted wide-field
observations (170” x 70”) of NOAA AR 12470 on December 14, 2015,
exhibit our ability to recover reliable field measurements using
multiple parallel FIRS slits. Using this pipeline, further analysis
of active region magnetic fields may shed light on the formation and
eruption processes of active region filaments.
---------------------------------------------------------
Title: Inference of chromospheric magnetic fields in a sunspot
derived from spectropolarimetry of Ca II 8542 A
Authors: Abdelkawy, Ali G. A.; Shaltout, Abdelrazek M. K.; Beheary,
M. M.; Schad, T. A.
2017arXiv171206829A Altcode:
We analyze spectropolarimetric observations of the chromospheric Ca II
8542 A line taken by the Interferometric Bidimensional Spectrometer
(IBIS) at the Dunn Solar Telescope. The data were observed on
2012 January 29 for the NOAA active region 11408. Adopting the
center-of-gravity (COG) approach we obtain the line-of-sight (LOS)
field strength for the chromospheric IBIS data of Ca II 8542 A line. The
LOS strength of the magnetic field is determined in the target active
region inside a field of view 45 x 95 arcsec. The LOS field values
were found to be increase up to 800 G inside the umbral region and
decrease systematically toward the edges of a sunspot. Under the weak
field approximation (WFA), the horizontal, vertical magnetic field
components and azimuthal field vector are obtained.
---------------------------------------------------------
Title: Infrared Imaging Spectroscopy Using Massively Multiplexed
Slit-Based Techniques and Sub-Field Motion Correction
Authors: Schad, Thomas; Lin, Haosheng
2017SoPh..292..158S Altcode: 2018arXiv180905132S
Targeting dynamic spatially extended phenomena in the upper
solar atmosphere, a new instrument concept has been developed
and demonstrated at the Dunn Solar Telescope in New Mexico, USA,
which provides wide-field, rapid-scanning, high-resolution imaging
spectroscopy of the neutral helium λ 10830 spectral triplet. The
instrument combines a narrowband imaging channel with a novel
cospatial grating-based spectrograph with 17 parallel long slits
that are simultaneously imaged on a single HgCdTe detector. Over a
175<SUP>″</SUP>×125<SUP>″</SUP> field of view, a temporal cadence
of 8.5 s is achieved between successive maps that critically sample the
diffraction limit of the Dunn Solar Telescope at 1083 nm (1.22 λ /D
=0.36<SUP>″</SUP>) and provide a resolving power (R =λ /δ λ ) up
to ≈25 ,000 with a 1 nm bandwidth (i.e.275 kms−<SUP>1</SUP> Doppler
coverage). Capitalizing on the strict simultaneity of the narrowband
channel relative to each spectral image (acquired at a rate of 9.53
Hz), this work demonstrates that sub-field image motion introduced by
atmospheric seeing may be corrected post-facto in each mapped spectral
data cube. This instrument furnishes essential infrared spectral imaging
capabilities for current investigations while pioneering techniques
for high-resolution wide-field time-domain solar astronomy.
---------------------------------------------------------
Title: Automated Spatiotemporal Analysis of Fibrils and Coronal Rain
Using the Rolling Hough Transform
Authors: Schad, Thomas
2017SoPh..292..132S Altcode: 2018arXiv180903635S
A technique is presented that automates the direction characterization
of curvilinear features in multidimensional solar imaging datasets. It
is an extension of the Rolling Hough Transform (RHT) technique
presented by Clark, Peek, and Putman (Astrophys. J.789, 82, 2014),
and it excels at rapid quantification of spatial and spatiotemporal
feature orientation even for applications with a low signal-to-noise
ratio. It operates on a pixel-by-pixel basis within a dataset and
reliably quantifies orientation even for locations not centered on
a feature ridge, which is used here to derive a quasi-continuous map
of the chromospheric fine-structure projection angle. For time-series
analysis, a procedure is developed that uses a hierarchical application
of the RHT to automatically derive the apparent motion of coronal rain
observed off-limb. Essential to the success of this technique is the
formulation presented in this article for the RHT error analysis as
it provides a means to properly filter results.
---------------------------------------------------------
Title: Critical Infrared Science with the Daniel K. Inouye Solar
Telescope
Authors: Schad, Thomas A.; Fehlmann, Andre; Jaeggli, Sarah A.; Kuhn,
Jeffrey Richard; Lin, Haosheng; Penn, Matthew J.; Rimmele, Thomas R.;
Woeger, Friedrich
2017SPD....4811703S Altcode:
Critical science planning for early operations of the Daniel K. Inouye
Solar Telescope is underway. With its large aperture, all-reflective
telescope design, and advanced instrumentation, DKIST provides
unprecedented access to the important infrared (IR) solar spectrum
between 1 and 5 microns. Breakthrough IR capabilities in coronal
polarimetry will sense the coronal magnetic field routinely for the
first time. The increased Zeeman resolution near the photospheric
opacity minimum will provide our deepest and most sensitive measurement
of quiet sun and active region magnetic fields to date. High-sensitivity
He I triplet polarimetry will dynamically probe the chromospheric
magnetic field in fibrils, spicules, and filaments, while observations
of molecular CO transitions will characterize the coolest regions
of the solar atmosphere. When combined with the longer timescales
of good atmospheric seeing compared with the visible, DKIST infrared
diagnostics are expected to be mainstays of solar physics in the DKIST
era. This paper will summarize the critical science areas addressed
by DKIST infrared instrumentation and invite the community to further
contribute to critical infrared science planning.
---------------------------------------------------------
Title: Wide-field, dynamic, slit-based spectroscopy of neutral helium
in coronal rain
Authors: Schad, T. A.
2016AGUFMSH43C2581S Altcode:
Building upon the Massively Multiplexed Spectrograph (mxSPEC)
instrument concept [Lin, H. SPIE Vol. 9147 (2014)], we report
dynamical observations of off-limb coronal rain in the neutral
orthohelium lines at 1083 nm using an experiment that combines a
narrowband imaging channel with a co-spatial, 17 parallel-long-slit,
grating-based, spectrograph on a single HgCdTe detector. Over a 170”
x 120” field of view, a temporal cadence of 8.5 seconds is achieved
between successive maps that critically sample the diffraction limit
of the Dunn Solar Telescope (1.22λ/D = 0.36”) while providing a
spectral resolution (R = λ/δλ) of 40000 and a bandwidth of 1 nm
(i.e. 275 km/sec Doppler coverage). The strict simultaneity of the
narrowband channel relative to the each spectra (acquired at a rate
of 10 Hz) allows a robust assessment (and/or compensation) of the
atmospheric seeing. Due to the relatively high helium abundance, the
magnetic sensitivity of the helium triplet, and the expected important
role of neutral helium atoms in partially ionized environments, the
He I triplet is an important diagnostic of coronal rain that will
be made available by the Daniel K Inouye Solar Telescope (DKIST),
currently under construction on Haleakala, Maui, Hawaii. This report
will introduce the modified mxSPEC observing technique, discuss the
dynamics observed in the He I spectra, and compare these dynamics with
coordinated slit-jaw measurements at 1400 and 2796 Angstrom from the
Interface Region Imaging Spectrograph (IRIS).
---------------------------------------------------------
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: Student artistry sparks eclipse excitement on Maui: NSO/DKIST
EPO for the 2016 Partial Solar Eclipse
Authors: Schad, Thomas A.; Penn, Matthew J.; Armstrong, James
2016SPD....47.0501S Altcode:
Local creativity and artistry is a powerful resource that enhances
education programs and helps us generate excitement for science
within our communities. In celebration of the 2016 Solar Eclipse,
the National Solar Observatory (NSO) and its Daniel K Inouye Solar
Telescope (DKIST) project were pleased to engage with students across
Maui County, Hawai`i, via the 2016 Maui Eclipse Art Contest. With
the help of the Maui Economic Development Board and the University
of Hawai'is Institute for Astronomy, we solicited art entries from
all K-12 schools in Maui County approximately 6 months prior to the
eclipse. Along with divisional prizes, a grand prize was selected
by a panel of local judges, which was subsequently printed on 25,000
solar eclipse viewing glasses and distributed to all Maui students. We
found that the impact of a locally-sourced glasses design cannot be
understated. Overall, the success of this program relied upon reaching
out to individual teachers, supplying educational flyers to all schools,
and visiting classrooms. On the day of the eclipse, all of the art
entries were prominently displayed during a community eclipse viewing
event at Kalama Beach Park in Kihei, HI, that was co-hosted by NSO
and the Maui Science Center. This eclipse art contest was integral to
making local connections to help promote science education on Maui,
and we suggest that it could be adapted to the solar community's EPO
activities for the upcoming 2017 Great American Solar Eclipse.
---------------------------------------------------------
Title: He I Vector Magnetic Field Maps of a Sunspot and Its
Superpenumbral Fine-Structure
Authors: Schad, T. A.; Penn, M. J.; Lin, H.; Tritschler, A.
2015SoPh..290.1607S Altcode: 2015arXiv150505567S; 2015SoPh..tmp...60S
Advanced inversions of high-resolution spectropolarimetric observations
of the He I triplet at 1083 nm are used to generate unique maps of
the chromospheric magnetic field vector across a sunspot and its
superpenumbral canopy. The observations were acquired by the Facility
Infrared Spectropolarimeter (FIRS) at the Dunn Solar Telescope (DST)
on 29 January 2012. Multiple atmospheric models are employed in the
inversions because superpenumbral Stokes profiles are dominated by
atomic-level polarization, while sunspot profiles are Zeeman-dominated,
but also exhibit signatures that might be induced by symmetry-breaking
effects of the radiation field incident on the chromospheric
material. We derive the equilibrium magnetic structure of a sunspot in
the chromosphere and furthermore show that the superpenumbral magnetic
field does not appear to be finely structured, unlike the observed
intensity structure. This suggests that fibrils are not concentrations
of magnetic flux, but are instead distinguished by individualized
thermalization. We also directly compare our inverted values with a
current-free extrapolation of the chromospheric field. With improved
measurements in the future, the average shear angle between the inferred
magnetic field and the potential field may offer a means to quantify
the non-potentiality of the chromospheric magnetic field to study the
onset of explosive solar phenomena.
---------------------------------------------------------
Title: Polarization properties of a birefringent fiber optic image
slicer for diffraction-limited dual-beam spectropolarimetry
Authors: Schad, Thomas; Lin, Haosheng; Ichimoto, Kiyoshi; Katsukawa,
Yukio
2014SPIE.9147E..6ES Altcode:
The birefringent fiber optic image slicer design, or BiFOIS,
adapts integral field spectroscopy methods to the special needs of
high-sensitivity, spatially-resolved spectropolarimetry. In solar
astronomy these methods are of particular importance, as dynamic
magnetism lies at the heart of various multi-scaled phenomena in the
solar atmosphere. While integral field units (IFU) based on fiber
optics have been in continual development for some time, standard
stock multimode fibers do not typically preserve polarization. The
importance of a birefringent fiber optic IFU design stems from the
need for dual-beam spatio-temporal polarimetric modulation to correct
for spurious polarization signals induced either by platform jitter or
atmospheric seeing. Here we characterize the polarization response of a
second generation BiFOIS IFU designed for solar spectropolarimetry. The
unit provides 60 × 64 spatial imaging pixels in a densely-packed,
high filling factor configuration. Particular attention is placed on
the spatial uniformity of the IFU polarization response. Calibrated
first-light solar observations are also presented to demonstrate the
performance of the device in a real application.
---------------------------------------------------------
Title: Tools for 3D Spectropolarimetry - A Birefringent Fiber Optic
Image Slicer
Authors: Schad, Thomas A.; Lin, Haosheng
2014AAS...22412358S Altcode:
Image-slicing technology benefits astronomical spectropolarimetry by
transposing a three-dimensional informational set--two spatial and one
spectral dimension--into a format more amenable to simultaneous coverage
by conventional spectrographs. To probe, for example, the magnetism
of the fine-scaled, dynamic chromosphere, methods beyond slit-based
spectropolarimetry are essential. Fiber optic integral field units
(IFUs) present one promising solution. The importance of a birefringent
fiber-optic IFU design stems from the need of spatio-temporal modulation
to correct for spurious polarization signals induced either by platform
jitter or atmospheric seeing. Standard stock fibers do not typically
preserve polarization. Here we characterize the polarization response of
a close-packed IFU based on rectangular optical fibers, currently under
development for the Diffraction-Limited Near-IR Spectropolarimeter,
a facility instrument of the Advanced Technology Solar Telescope. Solar
observations utilizing this device will be presented.
---------------------------------------------------------
Title: From static to dynamic mapping of chromospheric magnetism -
FIRS and SPIES
Authors: Schad, Thomas A.; Lin, Haosheng
2014AAS...22430204S Altcode:
Advancements in theoretical forward modeling and observational
techniques now allow the mapping of the chromospheric magnetic field
vector in some regions. We report on full maps of the chromospheric
magnetic field vector across a sunspot and its superpenumbra within
NOAA AR 11408. These maps are derived from full Stokes observations of
the He I triplet at 1083 nm, which show both Zeeman and atomic-level
polarization signatures. Yet, due to the long time to acquire these
observations with the slit-based Facility Infrared Spectropolarimeter
(FIRS), our measurements primarily probe long-lived chromospheric
structures, albeit at very high polarization sensitivity. The fast
temporal scales remain difficult to probe with conventional slit-based
spectropolarimeters. Alternatively, SPIES is an instrument based on a
birefringent fiber optic IFU, designed to multiplex a two-dimensional
spatial field with high spectral resolution spectropolarimetry, and is
an ideal tool for probing small-scale, dynamic magnetic features. We
will present movies of the dynamic chromosphere acquired from SPIES
across a sunspot and its fine-scaled superpenumbra.
---------------------------------------------------------
Title: On the Collective Magnetic Field Strength and Vector Structure
of Dark Umbral Cores Measured by the Hinode Spectropolarimeter
Authors: Schad, T. A.
2014SoPh..289.1477S Altcode: 2015arXiv150505581S
We study 7530 sunspot umbrae and pores measured by the Hinode
Spectropolarimeter (SP) between November 2006 and November 2012. We
primarily seek confirmation of the long term secular decrease in
the mean magnetic field strength of sunspot umbrae found by Penn
and Livingston (IAU Symp.273, 126, 2011) between 1998 and 2011. The
excellent SP photometric properties and full vector magnetic field
determinations from full-Stokes Milne-Eddington inversions are used
to address the interrelated properties of the magnetic field strength
and brightness temperature for all umbral cores. We find non-linear
relationships between magnetic field strength and umbral temperature
(and continuum contrast), as well as between umbral radius and magnetic
field strength. Using disambiguated vector data, we find that the
azimuths measured in the umbral cores reflect an organization weakly
influenced by Joy's law. The large selection of umbrae displays a
log-normal size spectrum similar to earlier solar cycles. Influenced by
the amplitude of the solar cycle and the non-linear relationship between
umbral size and core magnetic field strength, the distribution of core
magnetic field strengths, fit most effectively with a skew-normal
distribution, shows a weak solar cycle dependence. Yet, the mean
magnetic field strength does not show a significant long term trend.
---------------------------------------------------------
Title: He I Vector Magnetometry of Field-aligned Superpenumbral
Fibrils
Authors: Schad, T. A.; Penn, M. J.; Lin, H.
2013ApJ...768..111S Altcode: 2013arXiv1303.4463S
Atomic-level polarization and Zeeman effect diagnostics in the neutral
helium triplet at 10830 Å in principle allow full vector magnetometry
of fine-scaled chromospheric fibrils. We present high-resolution
spectropolarimetric observations of superpenumbral fibrils in the
He I triplet with sufficient polarimetric sensitivity to infer
their full magnetic field geometry. He I observations from the
Facility Infrared Spectropolarimeter are paired with high-resolution
observations of the Hα 6563 Å and Ca II 8542 Å spectral lines from
the Interferometric Bidimensional Spectrometer from the Dunn Solar
Telescope in New Mexico. Linear and circular polarization signatures
in the He I triplet are measured and described, as well as analyzed
with the advanced inversion capability of the "Hanle and Zeeman Light"
modeling code. Our analysis provides direct evidence for the often
assumed field alignment of fibril structures. The projected angle of
the fibrils and the inferred magnetic field geometry align within an
error of ±10°. We describe changes in the inclination angle of these
features that reflect their connectivity with the photospheric magnetic
field. Evidence for an accelerated flow (~40 m s<SUP>-2</SUP>) along
an individual fibril anchored at its endpoints in the strong sunspot
and weaker plage in part supports the magnetic siphon flow mechanism's
role in the inverse Evershed effect. However, the connectivity of the
outer endpoint of many of the fibrils cannot be established.
---------------------------------------------------------
Title: He I Spectropolarimetry with FIRS: Towards Vector Magnetometry
of Chromospheric Fibrils Plus New Diagnostics of Coronal Rain
Authors: Schad, T. A.; Penn, M. J.; Lin, H.; Tritschler, A.
2012ASPC..463...25S Altcode:
At the Dunn Solar Telescope, the Interferometric Bidimensional
Spectrometer (IBIS) can measure the full Stokes vector of the Ca II
854.2 nm spectral line while the Facility Infrared Spectropolarimeter
(FIRS) measures the Stokes vector of the He I triplet at 1083
nm. We analyze the He I triplet observed in two widely different
features above NOAA AR 11295 on 19 September 2011 - thin (< 1″)
chromospheric fibrils and a large-scale loop hosting a high-velocity
coronal rain event. These two features are shown to first demonstrate
the diagnostic potential of the He I triplet for magnetic fields in the
chromosphere/transition region and second to stress the need to pair
large-aperture facilities with flexible instrumentation. Inversions of
the He I triplet near the penumbral boundary return azimuthal directions
of the magnetic field aligned with fine-scale fibrils observed in the
line core of Ca II. The coronal rain event shows Doppler velocities
up to 195 km s<SUP>-1</SUP>, among the largest reported. We observe
measurable polarization within the raining material, which may be a
good magnetic diagnostic of chromospheric-like material higher in the
corona within condensating loops.
---------------------------------------------------------
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: 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: Multi-wavelength Spectropolarimetry Of A Sunspot Superpenumbra
With Firs And Ibis
Authors: Schad, Thomas A.; Tritschler, A.; Penn, M. J.
2012AAS...22020302S Altcode:
Extending nearly radially from magnetic field concentrations like
sunspot umbrae or pores, threadlike fibrils observed in the chromosphere
and transition region host a variety of dynamic behavior and have long
been considered local tracers for the magnetic field. Morphologically,
fibrils are similar to spicules seen on the limb. The connectivity
of fibrils outside of the magnetic field concentrations with the
photosphere and/or corona is not well understood, and probing the
magnetic field in these features remains challenging. In this
contribution we describe multi-wavelength spectropolarimetric
observations from the Dunn Solar Telescope in New Mexico using the
Facility Infrared Spectropolarimeter (FIRS) and the Interferometric
BiDimensional Spectropolarimeter (IBIS). FIRS performs high resolution
slit spectropolarimetry in the He I triplet at 1083 nm, which is a
promising diagnostic of chromospheric vector fields. Significant
progress has been made to boost the accuracy and sensitivity of
these measurements. Here we present measurements of an active region
sunspot at a spatial resolution of 0.3 arcsec and an RMS noise in
Stokes Q,U,V spectra down to 0.0003 in units of the local continuum
(SNR > 3300). We perform full inversions of these spectra taking
into account both Zeeman and Hanle effects. Initial results lend
support for field-aligned fibrils near the penumbral boundary of a
sunspot. Jointly with the FIRS observations, we use IBIS to observe the
Stokes vectors of Ca II 854.2 nm and Fe I 617.3 nm and the intensity
spectrum of H-alpha 656.3 nm. As a spectral imaging instrument, IBIS
rapidly scans through the three spectral lines over a 45” by 95” FOV
at an overall cadence of 50 seconds, allowing a much better description
the dynamics of fibrils observed by both FIRS and IBIS.
---------------------------------------------------------
Title: Coronal Rain Observed On-disk with He I Spectropolarimetry
from DST/FIRS
Authors: Schad, Thomas A.; Penn, M. J.; Pietarila, A.
2012AAS...22031005S Altcode:
Coronal rain refers to cool, dense blobs of plasma that presumably
condense near the apex of hot coronal loops and then "rain" down upon
the chromosphere traveling along curved loop-like paths. Considered
to be the result of a thermal instability known as "catastrophic
cooling", coronal rain places constraints on heating mechanisms for
coronal loops. Nearly all observational studies of coronal rain,
however, have been limited to the solar limb where cooler material
within hot coronal loops is more readily identified. Here, we report
observations of what we interpret to be the on-disk counterpart of
coronal rain. Scanned spectropolarimetric observations in the He I
triplet (1083 nm) from the Facility Infrared Spectropolarimeter (FIRS)
reveal highly-redshifted material displaying an acceleration along
curved trajectories terminating within a large sunspot (located at
N17W21). Line-of-sight velocities in the He I triplet peak near 190
km/s, which can be consider high in relation to most coronal rain
observations. This is also the largest redshift ever reported in the
He I triplet. These curved loops correspond to an overarching loop
structure seen in SDO/AIA anchored at its ends by a large sunspot and
a group of pores. The loops observed with SDO/AIA display significant
cooling as dark (EUV absorptive) blobs begin to form near the loop
apex and then traverse along the same trajectories observed in the He
I FIRS observations. Although the EUVI instrument of STEREO-A/SECCHI
has a reduced temporal resolution compared to SDO/AIA, we are able
to confidently match rain features in both spacecraft and thus
stereoscopically reconstruct the three-dimensional trajectory to
confirm the material is raining upon the solar surface.
---------------------------------------------------------
Title: Sunspot Dynamics as seen with CO 4666nm Spectroscopy
Authors: Penn, Matthew J.; Schad, T.
2012AAS...22020610P Altcode:
High resolution adaptive-optics corrected spectroscopy of sunspots using
strong CO absorption lines at 4666nm was performed at the McMath-Pierce
Solar Telescope using the NSO Array Camera. Active region NOAA 11158
was observed after the X-class flare on 17 Feb 2011. Several hours of
rapid cadence scans reveal changes in umbral bright points, Evershed
flows, flows along a sheer zone and penumbral fibrils as seen with the
cool CO lines. Solar oscillations are studied, and the chromospheric
structure associated with the regions of CO absorption are examined
using 854.2nm Ca spectroscopy.
---------------------------------------------------------
Title: Probing the Solar Atmosphere Using Oscillations of Infrared
CO Spectral Lines
Authors: Penn, M. J.; Schad, T.; Cox, E.
2011ApJ...734...47P Altcode: 2010arXiv1012.2371P
Oscillations were observed across the whole solar disk using the Doppler
shift and line center intensity of spectral lines from the CO molecule
near 4666 nm with the National Solar Observatory's McMath/Pierce
solar telescope. Power, coherence, and phase spectra were examined,
and diagnostic diagrams reveal power ridges at the solar global mode
frequencies to show that these oscillations are solar p-modes. The
phase was used to determine the height of formation of the CO lines by
comparison with the IR continuum intensity phase shifts as measured in
Kopp et al. we find that the CO line formation height varies from 425
km < z < 560 km as we move from disk center toward the solar limb
1.0 > μ > 0.5. The velocity power spectra show that while the
sum of the background and p-mode power increases with height in the
solar atmosphere as seen in previous work, the power in the p-modes
only (background subtracted) decreases with height. The CO line center
intensity weakens in regions of stronger magnetic fields, as does the
p-mode oscillation power. Across most of the solar surface the phase
shift is larger than the expected value of 90° for an adiabatic
atmosphere. We fit the phase spectra at different disk positions
with a simple atmospheric model to determine that the acoustic cutoff
frequency is about 4.5 mHz with only small variations, but that the
thermal relaxation frequency drops significantly from 2.7 to 0 mHz at
these heights in the solar atmosphere.
---------------------------------------------------------
Title: High-Resolution He I Spectropolarimetry of Chromospheric
Fibrils
Authors: Schad, Thomas A.; Penn, M. J.
2011SPD....42.0305S Altcode: 2011BAAS..43S.0305S
Of spectral diagnostics for the magnetic field in the solar
chromosphere, the He I triplet at 1083 nm offers a comparatively
simple means to determine both the magnitude and direction of the field
vector. The triplet forms over a narrow range of heights when compared
to strong optical lines, and recently the mechanisms that influence its
polarization have been well characterized, thus allowing inversions of
the magnetic field from observed Stokes profiles. We discuss recent work
with the Facility Infrared Spectropolarimeter (FIRS) at the Dunn Solar
Telescope (DST), New Mexico, USA to measure and infer the magnetic
field vector of chromospheric fibrils. FIRS is designed to perform
fast diffraction-limited dual-beam spectropolarimetry simultaneously
at visible and infrared wavelengths through the use of multiple slits
and narrowband filters. It can be operated in congress with the High
Order Adaptive Optics (HOAO) system of the DST as well as with the
Interferometric BiDimensional Spectropolarimeter (IBIS). Here we present
high-resolution FIRS observations of chromospheric fibrils which employ
the HOAO system under great seeing. We calibrate these observations
for the full effect of the FIRS-DST combined analysis system on the
Stokes vector which allow us to define the observed Stokes geometry
with respect to solar coordinates. Full inversions of our measurements
incorporating the effects of atomic polarization, the Hanle effect, and
the Zeeman effect will be presented showing support for chromospheric
fibrils that are aligned with the magnetic field direction.
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Title: Probing the Solar Atmosphere Using Oscillations of Infrared
CO Spectral Lines
Authors: Penn, Matthew J.; Schad, T.; Cox, E.
2011SPD....42.1702P Altcode: 2011BAAS..43S.1702P
Oscillations were observed across the whole solar disk using the Doppler
shift and line center intensity of spectral lines from the CO molecule
near 4666 nm with the National Solar Observatory's McMath/Pierce
solar telescope. Power, coherence, and phase spectra were examined,
and diagnostic diagrams reveal power ridges at the solar global mode
frequencies to show that these oscillations are solar p-modes. The
phase was used to determine the height of formation of the CO lines by
comparison with the IR continuum intensity phase shifts as measured in
Kopp et al., 1992; we find the CO line formation height varies from
425 < z < 560 km as we move from disk center towards the solar
limb 1.0 > mu > 0.5. The velocity power spectra show that while
the sum of the background and p-mode power increases with height in the
solar atmosphere as seen in previous work, the power in the p-modes only
(background subtracted) decreases with height. The CO line depth weakens
in regions of stronger magnetic fields, as does the p-mode oscillation
power. Across most of the solar surface the phase shift is larger than
the expected value of 90 degrees for an adiabatic atmosphere. We fit
the phase spectra at different disk positions with a simple atmospheric
model to determine that the acoustic cutoff frequency is about 4.5 mHz
with only small variations, but that the thermal relaxation frequency
drops significantly from 2.7 to 0 mHz at these heights in the solar
atmosphere.
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Title: Spectropolarimetry of Chromospheric Magnetic and Velocity
Structure Above Active Regions
Authors: Schad, T. A.; Jaeggli, S. A.; Lin, H.; Penn, M. J.
2011ASPC..437..483S Altcode: 2011arXiv1101.0631S
Active regions often host large-scale gas flows in the
chromosphere presumably directed along curved magnetic field
lines. Spectropolarimetric observations of these flows are critical to
understanding the nature and evolution of their anchoring magnetic
structure. We discuss recent work with the Facility Infrared
Spectropolarimeter (FIRS) located at the Dunn Solar Telescope in New
Mexico to achieve high-resolution imaging-spectropolarimetry of the Fe
I lines at 630 nm, the Si I line at 1082.7 nm, and the He I triplet at
1083 nm. We present maps of the photospheric and chromospheric magnetic
field vector above a sunspot as well as discuss characteristics of
surrounding chromospheric flow structures.
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Title: IR spectroscopy of COmosphere dynamics with the CO first
overtone band
Authors: Schad, T. A.; Penn, M. J.
2010AN....331..589S Altcode: 2010arXiv1008.5375S
We discuss observations of the weak first overtone (\Delta\nu=2) CO
absorption band near 2300 nm with the U.S. National Solar Observatory
Array Camera (NAC), a modern mid-infrared detector. This molecular
band provides a thermal diagnostic that forms lower in the atmosphere
than the stronger fundamental band near 4600 nm. The observed
center-to-limb increase in CO line width qualitatively agrees with
the proposed higher temperature shocks or faster plasma motions higher
in the COmosphere. The spatial extent of chromospheric shock waves is
currently at or below the diffraction limit of the available CO lines at
existing telescopes. Five minute period oscillations in line strength
and measured Doppler shifts are consistent with the p-mode excitation
of the photospheric gas. We also show recent efforts at direct imaging
at 4600 nm. We stress that future large-aperture solar telescopes must
be teamed with improved, dynamic mid-infrared instruments, like the NAC,
to capitalize on the features that motivate such facilities.
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Title: Structural Invariance of Sunspot Umbrae over the Solar Cycle:
1993 - 2004
Authors: Schad, T. A.; Penn, M. J.
2010SoPh..262...19S Altcode: 2010SoPh..tmp...22S; 2009arXiv0912.2370S
Measurements of maximum magnetic flux, minimum intensity, and size
are presented for 12 967 sunspot umbrae detected on the National
Aeronautics and Space Administration/National Solar Observatory
(NASA/NSO) spectromagnetograms between 1993 and 2004 to study
umbral structure and strength during the solar cycle. The umbrae
are selected using an automated thresholding technique. Measured
umbral intensities are first corrected for center-to-limb intensity
dependence. Log-normal fits to the observed size distribution confirm
that the size-spectrum shape does not vary with time. The intensity
- magnetic-flux relationship is found to be steady over the solar
cycle. The dependence of umbral size on the magnetic flux and minimum
intensity are also independent of the cycle phase and give linear and
quadratic relations, respectively. While the large sample size does show
a low-amplitude oscillation in the mean minimum intensity and maximum
magnetic flux correlated with the solar cycle, this can be explained
in terms of variations in the mean umbral size. These size variations,
however, are small and do not substantiate a meaningful change in the
size spectrum of the umbrae generated by the Sun. Thus, in contrast to
previous reports, the observations suggest the equilibrium structure,
as manifested by the invariant size-magnetic field relationship,
as well as the mean size (i.e., strength) of sunspot umbrae do not
significantly depend on the solar-cycle phase.
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Title: Evershed Outflow During Solar Cycle 23
Authors: Penn, Matthew J.; Schad, T.
2009SPD....40.0907P Altcode:
We analyze several thousand Doppler observations of Evershed outflow
in sunspot penumbrae taken at the National Solar Observatory's Kitt
Peak Vacuum Telescope from 1993 to 2003. We compare the mean penumbral
flow vector components with properties of the sunspot, latitude of the
sunspot, and search for evolution of the components as a function of
time. We discuss how our findings relate to measurements of sunspot
magnetic helicity.
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Title: Solar Cycle Dependence of Umbral Magneto-Induced Line
Broadening
Authors: Schad, T. A.; Penn, M. J.
2008AGUSMSP41B..06S Altcode:
Studies of the solar cycle dependence of peak umbral magnetic field
strength have focused upon measurements of continuum intensity and
the Zeeman splitting of infrared spectral lines. Here we extend the
discussion into a measurement of effective line width using eleven years
of spectromagnetograms from the Kitt Peak Vacuum Telescope (KPVT). The
KPVT observed the 868.8 nm Fe I absorption line in opposing states of
circular polarization between 1992 and 2003, deriving full-disk images
of line-of-sight (LOS) velocity, LOS magnetic flux, continuum intensity,
equivalent line width, and central line depth. We determine an effective
spectral line width through a relation of the measured equivalent line
widths and central line depths. Developing a basic model of the Stokes
line profiles using the Seares formalism, we illustrate that a change in
the effective line width within the umbra as determined using the KPVT
data is consistent with the change in the Zeeman splitting. We discuss
the effect of observed distance from disk center, stray light, and the
unknown inclination angle of the magnetic field. Within individual
sunspots observed near disk center, the determined effective line
width decreases with distance from the umbral core consistent with the
studied magnetic field gradient. Measurements of different sunspots
show a clear dependence on umbral size consistent with previous studies
of the umbral magnetic field. Using this effective line width as a
diagnostic for magnetic field, we examine the dependence of maximum
magnetic field strength on the phase of the solar cycle. We present
a comprehensive statistical analysis using a sample size of over 3500
umbral measurements.
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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.
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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.
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Title: Coronal Seismology: The Search for Propagating Waves in
Coronal Loops
Authors: Schad, Thomas A.; Seeley, D.; Keil, S. L.; Tomczyk, S.
2007AAS...210.9113S Altcode: 2007BAAS...39Q.206S
We report on Doppler observations of the solar corona obtained in
the Fe XeXIII 1074.7nm coronal emission line with the HAO Coronal
Multi-Channel Polarimeter (CoMP) mounted on the NSO Coronal One Shot
coronagraph located in the Hilltop Facility of NSO/Sacramento Peak. The
COMP is a tunable filtergraph instrument that records the entire corona
from the edge of the occulting disk at approximately 1.03 Rsun out to
1.4 Rsun with a spatial resolution of about 4” x 4”. COMP can be
rapidly scanned through the spectral line while recording orthogonal
states of linear and circular polarization. The two dimensional spatial
resolution allows us to correlate temporal fluctuations observed in one
part of the corona with those seen at other locations, in particular
along coronal loops. Using cross spectral analysis we find that the
observations reveal upward propagating waves that are characterized
by Doppler shifts with rms velocities of 0.3 km/s, peak wave power
in the 3-5 mHz frequency range, and phase speeds 1-3 Mm/s. The wave
trajectories are consistent with the direction of the magnetic field
inferred from the linear polarization measurements. We discuss the phase
and coherence of these waves as a function of height in the corona and
relate our findings to previous observations. The observed waves appear
to be Alfvenic in character. <P />"Thomas Schad was supported through
the National Solar Observatory Research Experiences for Undergraduate
(REU) site program, which is co-funded by the Department of Defense in
partnership with the National Science Foundation REU Program." Daniel
Seeley was supported through the National Solar Observatory Research
Experience for Teachers (RET) site program, which is funded by the
National Science Foundation RET program.
