Author name code: casini
ADS astronomy entries on 2022-09-14
author:"Casini, Roberto"
------------------------------------------------------------------------
Title: Effects of spectral resolution on simple magnetic field
diagnostics of the Mg II h & k lines
Authors: Centeno, Rebecca; Rempel, Matthias; Casini, Roberto; del
Pino Aleman, Tanausu
Bibcode: 2022arXiv220807507C
Altcode:
We study the effects of finite spectral resolution on the magnetic
field values retrieved through the weak field approximation (WFA)
from the cores of the Mg II h & k lines. The retrieval of the
line-of-sight (LOS) component of the magnetic field, $B_{\rm LOS}$,
from synthetic spectra generated in a uniformly magnetized FAL-C
atmosphere are accurate when restricted to the inner lobes of Stokes
V. As we degrade the spectral resolution, partial redistribution (PRD)
effects, that more prominently affect the outer lobes of Stokes V,
are brought into the line core through spectral smearing, degrading the
accuracy of the WFA and resulting in an inference bias, which is more
pronounced the poorer the resolution. When applied to a diverse set of
spectra emerging from a sunspot simulation, we find a good accuracy
in the retrieved $B_{\rm LOS}$ when comparing it to the model value
at the height where the optical depth in the line core is unity. The
accuracy is preserved up to field strengths of B~1500 G. Limited
spectral resolution results in a small bias toward weaker retrieved
fields. The WFA for the transverse component of the magnetic field is
also evaluated. Reduced spectral resolution degrades the accuracy of
the inferences because spectral mixing results in the line effectively
probing deeper layers of the atmosphere.
Title: Ultraviolet Spectropolarimetry: Investigating stellar magnetic
field diagnostics
Authors: Folsom, C. P.; Ignace, R.; Erba, C.; Casini, R.; del Pino
Alemán, T.; Gayley, K.; Hobbs, K.; Manso Sainz, R.; Neiner, C.;
Petit, V.; Shultz, M. E.; Wade, G. A.
Bibcode: 2022arXiv220701865F
Altcode:
Magnetic fields are important for stellar photospheres and
magnetospheres, influencing photospheric physics and sculpting stellar
winds. Observations of stellar magnetic fields are typically made in
the visible, although infrared observations are becoming common. Here
we consider the possibility of directly detecting magnetic fields at
ultraviolet (UV) wavelengths using high resolution spectropolarimetry,
specifically considering the capabilities of the proposed Polstar
mission. UV observations are particularly advantageous for studying wind
resonance lines not available in the visible, but they can also provide
many photospheric lines in hot stars. Detecting photospheric magnetic
fields using the Zeeman effect and Least Squares Deconvolution is
potentially more effective in the UV due to the much higher density
of strong lines. We investigate detecting magnetic fields in the
magnetosphere of a star using the Zeeman effect in wind lines, and
find that this could be detectable at high S/N in an O or B star
with a strong magnetic field. We consider detecting magnetic fields
using the Hanle effect in linear polarization, which is complementary
to the Zeeman effect, and could be more sensitive in photospheric
lines of rapid rotators. The Hanle effect can also be used to infer
circumstellar magnetism in winds. Detecting the Hanle effect requires
UV observations, and a multi-line approach is key for inferring
magnetic field properties. This demonstrates that high resolution
spectropolarimetry in the UV, and the proposed Polstar mission, has
the potential to greatly expand our ability to detect and characterize
magnetic fields in and around hot stars.
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
Bibcode: 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.
Title: TIC: A Stokes Inversion Code for Scattering Polarization with
Partial Frequency Redistribution and Arbitrary Magnetic Fields
Authors: Li, H.; del Pino Alemán, T.; Trujillo Bueno, J.; Casini, R.
Bibcode: 2022ApJ...933..145L
Altcode: 2022arXiv220515666L
We present the Tenerife Inversion Code (TIC), which has been developed
to infer the magnetic and plasma properties of the solar chromosphere
and transition region via full Stokes inversion of polarized spectral
lines. The code is based on the HanleRT forward engine, which takes into
account many of the physical mechanisms that are critical for a proper
modeling of the Stokes profiles of spectral lines originating in the
tenuous and highly dynamic plasmas of the chromosphere and transition
region: the scattering polarization produced by quantum level imbalance
and interference (atomic polarization), the effects of frequency
coherence in polarized resonance scattering (partial redistribution),
and the impact of arbitrary magnetic fields on the atomic polarization
and the radiation field. We present first results of atmospheric and
magnetic inversions, and discuss future developments for the project.
Title: Ultraviolet Spectropolarimetry With Polstar: Using Polstar
to test Magnetospheric Mass-loss Quenching
Authors: Shultz, M. E.; Casini, R.; Cheung, M. C. M.; David-Uraz, A.;
del Pino Alemán, T.; Erba, C.; Folsom, C. P.; Gayley, K.; Ignace,
R.; Keszthelyi, Z.; Kochukhov, O.; Nazé, Y.; Neiner, C.; Oksala,
M.; Petit, V.; Scowen, P. A.; Sudnik, N.; ud-Doula, A.; Vink, J. S.;
Wade, G. A.
Bibcode: 2022arXiv220712970S
Altcode:
Polstar is a proposed NASA MIDEX space telescope that will provide
high-resolution, simultaneous full-Stokes spectropolarimetry in the
far ultraviolet, together with low-resolution linear polarimetry in the
near ultraviolet. This observatory offers unprecedented capabilities to
obtain unique information on the magnetic and plasma properties of the
magnetospheres of hot stars. We describe an observing program making use
of the known population of magnetic hot stars to test the fundamental
hypothesis that magnetospheres should act to rapidly drain angular
momentum, thereby spinning the star down, whilst simultaneously reducing
the net mass-loss rate. Both effects are expected to lead to dramatic
differences in the evolution of magnetic vs. non-magnetic stars.
Title: Realizing Comprehensive 3D Observations to Probe Magnetic
Energy Storage and Release in the Corona
Authors: Caspi, A.; Seaton, D. B.; Casini, R.; Downs, C.; Gibson, S.;
Gilbert, H.; Glesener, L.; Guidoni, S.; Hughes, J. M.; McKenzie, D.;
Reeves, K.; Saint-Hilaire, P.; Shih, A. Y.; West, M.
Bibcode: 2022heli.conf.4058C
Altcode:
Understanding impulsive energy release in the solar corona requires
knowledge of the 3D coronal magnetic field and 3D signatures of
energy release through systematic multi-viewpoint observations, in
many wavelengths, including coronal magnetometry.
Title: Scattering Polarization Diagnostic of the UV Corona
Authors: Casini, R.; Gibson, S.; Newmark, J.; Fineschi, S.; Gilbert, H.
Bibcode: 2022heli.conf.4053C
Altcode:
A largely unexplored diagnostic of the coronal magnetic field vector
is offered by the linear polarization signature of the Hanle effect
of far ultraviolet (FUV) resonance lines.
Title: Convolutional Neural Networks and Stokes Response Functions
Authors: Centeno, Rebecca; Flyer, Natasha; Mukherjee, Lipi; Egeland,
Ricky; Casini, Roberto; del Pino Alemán, Tanausú; Rempel, Matthias
Bibcode: 2022ApJ...925..176C
Altcode: 2021arXiv211203802C
In this work, we study the information content learned by
a convolutional neural network (CNN) when trained to carry out the
inverse mapping between a database of synthetic Ca II intensity spectra
and the vertical stratification of the temperature of the atmospheres
used to generate such spectra. In particular, we evaluate the ability
of the neural network to extract information about the sensitivity of
the spectral line to temperature as a function of height. By training
the CNN on sufficiently narrow wavelength intervals across the Ca
II spectral profiles, we find that the error in the temperature
prediction shows an inverse relationship to the response function
of the spectral line to temperature, that is, different regions of
the spectrum yield a better temperature prediction at their expected
regions of formation. This work shows that the function that the CNN
learns during the training process contains a physically meaningful
mapping between wavelength and atmospheric height.
Title: New Approaches to Integrated Mission, Data, and Modeling
Frameworks
Authors: Seaton, D. B.; Caspi, A.; Casini, R.; Downs, C.; Gibson, S.;
Gilbert, H.; Glesener, L.; Guidoni, S.; Hughes, J. M.; McKenzie, D.;
Reeves, K.; Saint-Hilaire, P.; Shih, A.; West, M.
Bibcode: 2022heli.conf.4057S
Altcode:
A new generation of heliophysics missions will require integration of
data from multiple missions with analysis tools and physics-based
models. We discuss strategies to develop a framework for
systems-integrated data and analysis environments.
Title: The Visible Spectro-Polarimeter of the Daniel K. Inouye
Solar Telescope
Authors: de Wijn, A. G.; Casini, R.; Carlile, A.; Lecinski, A. R.;
Sewell, S.; Zmarzly, P.; Eigenbrot, A. D.; Beck, C.; Wöger, F.;
Knölker, M.
Bibcode: 2022SoPh..297...22D
Altcode: 2022arXiv220300117D
The Daniel K. Inouye Solar Telescope (DKIST) Visible Spectro-Polarimeter
(ViSP) is a traditional slit-scanning spectrograph with the ability
to observe solar regions up to a 120 ×78 arcsec2 area. The
design implements dual-beam polarimetry, a polychromatic polarization
modulator, a high-dispersion echelle grating, and three spectral
channels that can be automatically positioned. A defining feature of
the instrument is its capability to tune anywhere within the 380 - 900
nm range of the solar spectrum, allowing for a virtually infinite number
of combinations of three wavelengths to be observed simultaneously. This
enables the ViSP user to pursue well-established spectro-polarimetric
studies of the magnetic structure and plasma dynamics of the solar
atmosphere, as well as completely novel investigations of the solar
spectrum. Within the suite of first-generation instruments at the DKIST,
ViSP is the only wavelength-versatile spectro-polarimeter available to
the scientific community. It was specifically designed as a discovery
instrument to explore new spectroscopic and polarimetric diagnostics
and test improved models of polarized line formation through high
spatial-, spectral-, and temporal-resolution observations of the Sun's
polarized spectrum. In this instrument article, we describe the science
requirements and design drivers of ViSP and present preliminary science
data collected during the commissioning of the instrument.
Title: The COMPLETE mission concept for the Heliophysics Decadal
Survey
Authors: Seaton, Daniel; Caspi, Amir; Casini, Roberto; Downs, Cooper;
Gibson, Sarah; Gilbert, Holly; Glesener, Lindsay; Guidoni, Silvina;
Hughes, Marcus; Reeves, Katharine; Shih, Albert; Tomczyk, Steven;
West, Matthew
Bibcode: 2021AGUFMSH52A..08S
Altcode:
We present the COMPLETE mission concept, currently under study for
the upcoming Heliophysics Decadal Survey. COMPLETE would provide the
first comprehensive measurements of the 3D low-coronal magnetic field
and simultaneous 3D energy release diagnostics from large eruptions
(flares and CMEs) down to small-scale processes (coronal heating and
solar wind outflows). COMPLETE's measurements will finally allow closure
on the long-standing question of exactly how energy is stored, released,
and transported in impulsive events at all scales. COMPLETE comprises
an instrument suite with hard and soft X-ray spectral imagers, gamma-ray
and energetic neutral atom spectral imagers, high-resolution wide-field
EUV filtergram imagers, photospheric Doppler vector magnetographs,
and Hanle-effect UV (Ly-a) coronal magnetographs. Distributed across
three spacecraft at the L1, L4, and L5 Earth-Sun Lagrange points, the
suite on each spacecraft is optimized for the measurements from that
vantage point and for the mission as a whole. Data from all instruments
will be processed to enable systems-level analysis from the entire
observatory. COMPLETE instrument suite is deliberately complementary
across its individual spacecraft, with overlapping fields of view and
optimized capabilities to provide a zone of ideal coverage near the
west limb as viewed from Earth. Within this region COMPLETE provides
comprehensive observations of 3D structures, photospheric and coronal
magnetic fields, and signatures of impulsive energy release within
integrated data products. The COMPLETE mission concept, and the science
and data analysis techniques it espouses, represent a strategic shift
from the nearly ubiquitous current practices of siloed study in isolated
subdisciplines to a comprehensive, unified systems approach to solar,
coronal, and heliophysics.
Title: Understanding the coronal origins of global heliospheric
phenomena through 3D measurements with COMPLETE
Authors: Caspi, Amir; Seaton, Daniel; Casini, Roberto; Downs, Cooper;
Gibson, Sarah; Gilbert, Holly; Glesener, Lindsay; Guidoni, Silvina;
Hughes, Marcus; Reeves, Katharine; Shih, Albert; Tomczyk, Steven;
West, Matthew
Bibcode: 2021AGUFMSH25F2151C
Altcode:
Impulsive solar eruptions (flares, coronal mass ejections) and more
gradual energetic processes (coronal heating in active regions, solar
wind outflows) are powered and governed by the Sun's complex coronal
magnetic field. The evolution of these events in the low and middle
corona has direct impact on global scales throughout the corona and
heliosphere, including as drivers of space weather that affect human
and technological assets, but a coherent understanding of globally
connected behavior necessarily requires understanding its origins at
the Sun. Despite many decades of research, it is still poorly understood
exactly how magnetic energy is stored and impulsively released to power
plasma heating, particle acceleration, and bulk flows. Breakthroughs
have been hindered by two critical limitations: lack of knowledge of
the 3D coronal magnetic field and its evolution, and a similar lack
of insight into how localized energy release manifests and propagates
within 3D coronal structures. Transformative progress to close these
gaps requires systematic observations from multiple viewpoints, in a
variety of wavelengths, and including coronal magnetometry. Recent and
ongoing technological advancements allow us to realize these goals
within a decadal timescale. To that end, we present the COMPLETE
mission concept, currently under study for the upcoming Heliophysics
Decadal Survey. COMPLETEs highly co-optimized and complementary
instrument suite include spectroscopic imagers for X-rays, gamma-rays,
and energetic neutral atoms; high-resolution wide-field EUV filtergram
imagers; photospheric Doppler vector mangetographs; and Hanle-effect UV
(Lyman-alpha) coronal magnetographs. Distributed across three spacecraft
at the L1, L4, and L5 Earth-Sun Lagrange points, COMPLETE would provide
the first comprehensive measurements of the 3D low- and middle-coronal
magnetic field and simultaneous 3D energy-release diagnostics from
large eruptions down to small-scale processes. COMPLETE represents
a strategic shift towards a comprehensive, unified systems approach
to solar, coronal, and heliospheric physics, to enable us to finally
close decades-old questions of how the Suns magnetic field and impulsive
energy release are interrelated, from local to global scales.
Title: The COronal Magnetism Observatory (COMO)
Authors: Casini, Roberto; Newmark, Jeffrey; Fineschi, Silvano;
Burkepile, Joan; Gibson, Sarah; Gilbert, Holly; Raouafi, Nour
Bibcode: 2021AGUFMSH15G2092C
Altcode:
Structuring of solar coronal plasma by the magnetic field is the
key to understanding the fundamental physical processes of energy
dissipation in the corona. The coronal magnetic field is crucial to
understanding coronal dynamics and space weather. We present the
COronal Magnetism Observatory (COMO), a new polarimetric imaging
solar coronagraph for the FUV (H Ly-alpha), to be deployed to the
International Space Station. COMO will provide the first global maps
of the magnetic field and solar wind properties from 1.1 to 3 Rsun.The
instrument will measure the linearly polarized scattered light from
the low through the middle corona with a spatial sampling of 2.8
arcsec/pixel. The science mission relies on a variety of different
polarization diagnostic methods (unsaturated Hanle effect, Doppler
dimming) to infer information on the magnetic state of the active
low corona, and the solar wind velocity/acceleration in the middle
corona. The instrument design is an adaptation of the internally
occulted coronagraph for the Sounding-rocket Coronagraphic Experiment
(SCORE), successfully flown in 2009 as part of the NASA HERSCHEL
experiment, and the dual-beam polarimeter adopts a newly developed,
highly stable, Al-MgF2 multilayer coating for the polarization analyzer.
Title: Ultraviolet Spectropolarimetry With Polstar: Hot Star
Magnetospheres
Authors: Shultz, M. E.; Casini, R.; Cheung, M. C. M.; David-Uraz, A.;
del Pino Alemán, T.; Erba, C.; Folsom, C. P.; Gayley, K.; Ignace,
R.; Keszthelyi, Z.; Kochukhov, O.; Nazé, Y.; Neiner, C.; Oksala,
M.; Petit, V.; Scowen, P. A.; Sudnik, N.; ud-Doula, A.; Vink, J. S.;
Wade, G. A.
Bibcode: 2021arXiv211106434S
Altcode:
Polstar is a proposed NASA MIDEX space telescope that will provide
high-resolution, simultaneous full-Stokes spectropolarimetry in the far
ultraviolet, together with low-resolution linear polarimetry in the
near ultraviolet. In this white paper, we describe the unprecedented
capabilities this observatory would offer in order to obtain unique
information on the magnetic and plasma properties of the magnetospheres
of hot stars. This would enable a test of the fundamental hypothesis
that magnetospheres should act to rapidly drain angular momentum,
thereby spinning the star down, whilst simultaneously reducing the
net mass-loss rate. Both effects are expected to lead to dramatic
differences in the evolution of magnetic vs. non-magnetic stars.
Title: Erratum: Spectral Lines for Polarization Measurements of the
Coronal Magnetic Field. II. Consistent Treatment of the Stokes Vector
for Magnetic-dipole Transitions (1999, ApJ, 522, 524)
Authors: Casini, R.; Judge, P. G.
Bibcode: 2021ApJ...917...50C
Altcode:
No abstract at ADS
Title: The Polstar High Resolution Spectropolarimetry MIDEX Mission
Authors: Scowen, Paul A.; Gayley, Ken; Neiner, Coralie; Vasudevan,
Gopal; Woodruff, Robert; Ignace, Richard; Casini, Roberto; Hull,
Tony; Nordt, Alison; Stahl, H. Philip
Bibcode: 2021SPIE11819E..08S
Altcode: 2021arXiv210810729S
The Polstar mission will provide for a space-borne 60cm telescope
operating at UV wavelengths with spectropolarimetric capability
capturing all four Stokes parameters (intensity, two linear polarization
components, and circular polarization). Polstar's capabilities are
designed to meet its goal of determining how circumstellar gas flows
alter massive stars' evolution, and finding the consequences for the
stellar remnant population and the stirring and enrichment of the
interstellar medium, by addressing four key science objectives. In
addition, Polstar will determine drivers for the alignment of the
smallest interstellar grains, and probe the dust, magnetic fields,
and environments in the hot diffuse interstellar medium, including for
the first time a direct measurement of the polarized and energized
properties of intergalactic dust. Polstar will also characterize
processes that lead to the assembly of exoplanetary systems and that
affect exoplanetary atmospheres and habitability. Science driven
design requirements include: access to ultraviolet bands: where hot
massive stars are brightest and circumstellar opacity is highest;
high spectral resolution: accessing diagnostics of circumstellar gas
flows and stellar composition in the far-UV at 122-200nm, including
the NV, SiIV, and CIV resonance doublets and other transitions such
as NIV, AlIII, HeII, and CIII; polarimetry: accessing diagnostics of
circumstellar magnetic field shape and strength when combined with
high FUV spectral resolution and diagnostics of stellar rotation and
distribution of circumstellar gas when combined with low near-UV
spectral resolution; sufficient signal-to-noise ratios: ~103 for
spectropolarimetric precisions of 0.1% per exposure; ~102 for detailed
spectroscopic studies; ~10 for exploring dimmer sources; and cadence:
ranging from 1-10 minutes for most wind variability studies, to hours
for sampling rotational phase, to days or weeks for sampling orbital
phase. The ISM and exoplanet science program will be enabled by these
capabilities driven by the massive star science.
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
Bibcode: 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.
Title: DKIST First-light Instrumentation
Authors: Woeger, F.; Rimmele, T.; Casini, R.; von der Luehe, O.; Lin,
H.; Kuhn, J.; Dkist Team
Bibcode: 2021AAS...23810602W
Altcode:
The NSF's Daniel K. Inouye Solar Telescope's (DKIST) four meter aperture
and state-of-the-art wavefront correction system and instrumentation
will facilitate new insights into the complexities of the solar
atmosphere. We will describe the details and status of the diverse
first light instruments, including the high order adaptive optics
system, that are being commissioned: The Visible Spectro-Polarimeter
(ViSP), the Visible Broadband Imager (VBI), the Visible Tunable Filter
(VTF), the Diffraction-Limited Spectro-Polarimeter (DL-NIRSP) and the
Cryogenic Spectro-Polarimeter (Cryo-NIRSP). We will present first data
demonstrating the telescope's instrument systems performance.
Title: On Single-point Inversions of Magnetic Dipole Lines in
the Corona
Authors: Judge, Philip; Casini, Roberto; Paraschiv, Alin Razvan
Bibcode: 2021ApJ...912...18J
Altcode: 2021arXiv210303824J
Prompted by a recent paper by Dima and Schad, we reconsider the problem
of inferring magnetic properties of the corona using polarimetric
observations of magnetic dipole (M1) lines. Dima and Schad point to a
potential source of degeneracy in a formalism developed by Plowman,
which under some circumstances can lead to the solution being
under-determined. Here we clarify the nature of the problem. Its
resolution lies in solving for the scattering geometry using the
elongation of the observed region of the corona. We discuss some
conceptual problems that arise when casting the problem for inversion in
the observer's reference frame, and satisfactorily resolve difficulties
identified by Plowman, Dima, and Schad.
Title: Simulating the Solar Minimum Corona in UV Wavelengths with
Forward Modeling II. Doppler Dimming and Microscopic Anisotropy Effect
Authors: Zhao, Jie; Gibson, Sarah E.; Fineschi, Silvano; Susino,
Roberto; Casini, Roberto; Cranmer, Steven R.; Ofman, Leon; Li, Hui
Bibcode: 2021ApJ...912..141Z
Altcode:
In ultraviolet (UV) spectropolarimetric observations of the solar
corona, the existence of a magnetic field, solar wind velocity, and
temperature anisotropies modify the linear polarization associated with
resonant scattering. Unlike previous empirical models or global models,
which present blended results of the above physical effects, in this
work, we forward-model expected signals in the H I Lyα line (121.6 nm)
by adopting an analytic model that can be adjusted to test the roles
of different effects separately. We find that the impact of all three
effects is most evident in the rotation of the linear polarization
direction. In particular, (1) for magnetic fields between ∼10 and
∼100 G, the Hanle effect modifies the linear polarization at low
coronal heights, rotating the linear polarization direction clockwise
(counterclockwise) when the angle between the magnetic field and the
local vertical is greater (less) than the van Vleck angle, which is
consistent with the result of Zhao et al.; (2) solar wind velocity,
which increases with height, has a significant effect through the
Doppler dimming effect at higher coronal heights, rotating the linear
polarization direction in an opposite fashion to the Hanle effect;
and (3) kinetic temperature anisotropies are most significant at
lower heights in open nonradial magnetic field regions, producing
tilt opposite to isotropic Doppler dimming. The fact that the three
effects operate differently in distinct spatial regimes opens up the
possibility for using linear polarization measurements in UV lines to
diagnose these important physical characteristics of the solar corona.
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
Bibcode: 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.
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
Bibcode: 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 5×10−4. 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 Magnetic Sensitivity of the Resonance and Subordinate
Lines of Mg II in the Solar Chromosphere
Authors: del Pino Alemán, T.; Trujillo Bueno, J.; Casini, R.; Manso
Sainz, R.
Bibcode: 2020ApJ...891...91D
Altcode: 2020arXiv200409176D
We carry out a theoretical study of the polarization of the solar Mg
II h-k doublet (including its extended wings) and the subordinate
ultraviolet (UV) triplet around 280 nm. These lines are of great
diagnostic interest, as they encode information on the physical
properties of the solar atmosphere from the upper photosphere to the
chromosphere-corona transition region. We base our study on radiative
transfer calculations of spectral line polarization in one-dimensional
models of quiet and plage regions of the solar atmosphere. Our
calculations take into account the combined action of atomic
polarization, quantum level interference, frequency redistribution,
and magnetic fields of arbitrary strength. In particular, we study the
sensitivity of the emergent Stokes profiles to changes in the magnetic
field through the Zeeman and Hanle effects. We also study the impact
of the chromospheric plasma dynamics on the emergent Stokes profiles,
taking into account the angle-dependent frequency redistribution in the
h-k resonance transitions. The results presented here are of interest
for the interpretation of spectropolarimetric observations in this
important region of the solar UV spectrum.
Title: Coronal Solar Magnetism Observatory Science Objectives
Authors: Gibson, S. E.; Tomczyk, S.; Burkepile, J.; Casini, R.;
DeLuca, E.; de Toma, G.; de Wijn, A.; Fan, Y.; Golub, L.; Judge,
P. G.; Landi, E.; McIntosh, S. W.; Reeves, K.; Seaton, D. B.; Zhang, J.
Bibcode: 2019AGUFMSH11C3395G
Altcode:
Space-weather forecast capability is held back by our current
lack of basic scientific understanding of CME magnetic evolution,
and the coronal magnetism that structures and drives the solar
wind. Comprehensive observations of the global magnetothermal
environment of the solar atmosphere are needed for progress. When fully
implemented, the COSMO suite of synoptic ground-based telescopes will
provide the community with comprehensive and simultaneous measurements
of magnetism, temperature, density and plasma flows and waves from the
photosphere through the chromosphere and out into the corona. We will
discuss how these observations will uniquely address a set of science
objectives that are central to the field of solar and space physics:
in particular, to understand the storage and release of magnetic energy,
to understand CME dynamics and consequences for shocks, to determine the
role of waves in solar atmospheric heating and solar wind acceleration,
to understand how the coronal magnetic field relates to the solar
dynamo, and to constrain and improve space-weather forecast models.
Title: Spectropolarimetry of the Solar Mg II h and k Lines
Authors: Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; McIntosh,
S.
Bibcode: 2019ApJ...883L..30M
Altcode: 2019arXiv190905574M
We report on spectropolarimetric observations across the Mg II h and k
lines at 2800 Å made by the Ultraviolet Spectrometer and Polarimeter
on board the Solar Maximum Mission satellite. Our analysis confirms
the strong linear polarization in the wings of both lines observed
near the limb, as previously reported, but also demonstrates the
presence of a negatively (i.e., radially oriented) polarized signal
between the two lines. We find evidence for fluctuations of the
polarization pattern over a broad spectral range, resulting in some
depolarization with respect to the pure scattering case when observed
at very low spatial and temporal resolutions. This is consistent with
recent theoretical modeling that predicts this to be the result of
redistribution effects, quantum interference between the atomic levels
of the upper term, and magneto-optical effects. A first attempt at a
quantitative exploitation of these signals for the diagnosis of magnetic
fields in the chromosphere is attempted. In active regions, we present
observations of circular polarization dominated by the Zeeman effect. We
are able to constrain the magnetic field strength in the upper active
chromosphere using an analysis based on the magnetograph formula, as
justified by theoretical modeling. We inferred a significantly strong
magnetic field (∼500 G) at the 2.5σ level on an exceptionally active,
flaring region.
Title: PolStar - An Explorer-Class FUV Spectropolarimetry Mission
to Map the Environments of Massive Stars
Authors: Scowen, Paul; Ignace, Richard; Neiner, Coralie; Wade, Gregg;
Beasley, Matt; Bjorkman, Jon; Bouret, Jean-Claude; Casini, Roberto;
del Pino Alemán, Tanausu; Edgington, Samantha; Gayley, Ken; Guinan,
Ed; Hoffman, Jennifer; Howarth, Ian; Hull, Tony; Manso Sainz, Rafael;
Naze, Yael; Nordt, Alison; Owocki, Stan; Petrinec, Steve; Prinja,
Raman; Sana, Hugues; Shultz, Matt; Sparks, William; St-Louis, Nicole;
Tillier, Clem; Trujillo Bueno, Javier; Vasudevan, Gopal; Woodruff, Bob
Bibcode: 2019BAAS...51g.167S
Altcode: 2019astro2020U.167S; 2019arXiv191106724S
PolStar is an Explorer-class far ultraviolet (FUV) spectropolarimetry
mission designed to target massive stars and their environments. PolStar
will take advantage of resonance lines only available in the FUV to
measure for the first time the magnetic and wind environment around
massive stars to constrain models of rotation and mass loss.
Title: Simulating the Solar Corona in the Forbidden and Permitted
Lines with Forward Modeling. I. Saturated and Unsaturated Hanle
Regimes
Authors: Zhao, Jie; Gibson, Sarah E.; Fineschi, Silvano; Susino,
Roberto; Casini, Roberto; Li, Hui; Gan, Weiqun
Bibcode: 2019ApJ...883...55Z
Altcode:
The magnetic field in the corona is important for understanding solar
activity. Linear polarization measurements in forbidden lines in the
visible/IR provide information about coronal magnetic direction and
topology. However, these measurements do not provide a constraint on
coronal magnetic field strength. The unsaturated, or critical regime
of the magnetic Hanle effect is potentially observable in permitted
lines for example in the UV, and would provide an important new
constraint on the coronal magnetic field. In this paper we present
the first side-by-side comparison of forbidden versus permitted linear
polarization signatures, examining the transition from the unsaturated
to the saturated regime. In addition, we use an analytic 3D flux rope
model to demonstrate the Hanle effect for the line-of-sight versus
plane-of-sky (POS) components of the magnetic field. As expected, the
linear polarization in the unsaturated regime will vary monotonically
with increasing magnetic field strength for regions where the magnetic
field is along the observer’s line of sight. The POS component of
the field produces a linear polarization signature that varies with
both the field strength and direction in the unsaturated regime. Once
the magnetic field is strong enough that the effect is saturated, the
resulting linear polarization signal is essentially the same for the
forbidden and permitted lines. We consider how such observations might
be used together in the future to diagnose the coronal magnetic field.
Title: Investigating Coronal Magnetism with COSMO: Science on
the Critical Path To Understanding The ``Weather'' of Stars and
Stellarspheres
Authors: McIntosh, Scott; Tomczyk, Steven; Gibson, Sarah E.; Burkepile,
Joan; de Wijn, Alfred; Fan, Yuhong; deToma, Giuliana; Casini, Roberto;
Landi, Enrico; Zhang, Jie; DeLuca, Edward E.; Reeves, Katharine K.;
Golub, Leon; Raymond, John; Seaton, Daniel B.; Lin, Haosheng
Bibcode: 2019BAAS...51g.165M
Altcode: 2019astro2020U.165M
The Coronal Solar Magnetism Observatory (COSMO) is a unique ground-based
facility designed to address the shortfall in our capability to measure
magnetic fields in the solar corona.
Title: Egidio Landi: A Life in the Science and Teaching of Polarimetry
Authors: Casini, R.
Bibcode: 2019ASPC..526....3C
Altcode:
This is inevitably a very personal and perhaps even biased account of
the work of Prof. Egidio Landi Degl'Innocenti, during his nearly 45
years long scientific career, in the field of polarimetry as it applies
to the investigation of solar processes, as well as in the broader
context of astrophysics. Despite the breadth of Egidio's contributions
to scientific research and teaching, I will not be providing (nor
would I have been able to) a complete account of his work. I instead
made the choice to emphasize Egidio's style in approaching new science
challenges as well as revisiting older problems. This style is first of
all a product of both personal discipline and deeply rooted curiosity,
but also a legacy of the cultural and academic ambient where Egidio
spent his formative years, that is, Florence and its University.
Title: Magnetic Field Diagnostics with Strong Chromospheric Lines
Authors: Manso Sainz, R.; del Pino Alemán, T.; Casini, R.
Bibcode: 2019ASPC..526..145M
Altcode: 2017arXiv171004155M
The complex spectropolarimetric patterns around strong chromospheric
lines, the result of subtle spectroscopic and transport mechanisms,
are sensitive, sometimes in unexpected ways, to the presence of magnetic
fields in the chromosphere, which may be exploited for diagnostics. We
apply numerical polarization radiative transfer implementing partially
coherent scattering by polarized multi-term atoms, in the presence
of arbitrary magnetic fields, in plane-parallel stellar atmospheres
to study a few important spectroscopic features: Mg II h-k doublet;
Ca II H-K doublet and IR triplet. We confirm the importance of partial
redistribution effects in the formation of the Mg II h-k doublet in
magnetized atmospheres, as previously pointed out for the non-magnetic
case. Moreover, we show, numerically and analytically, that a magnetic
field produces measurable modifications of the broadband linear
polarization even for relatively small field strengths, while circular
polarization remains well represented by the magnetograph formula. We
note that this phenomenon has already (unknowingly) been observed by
UVSP/SMM, and the interest and possibility of its observation in stars
other than the Sun. The interplay between partial redistribution in the
H-K doublet of Ca II and metastable level polarization in its IR triplet
allow diagnosing the chromospheric magnetic field at different layers
and strengths. Our results suggest several new avenues to investigate
empirically the magnetism of the solar and stellar chromospheres.
Title: COSMO Science
Authors: Gibson, Sarah; Tomczyk, Steven; Burkepile, Joan; Casini,
Roberto; Deluca, Ed; de Toma, Giuliana; deWijn, Alfred; Fan, Yuhong;
Golub, Leon; Judge, Philip; Landi, Enrico; Lin, Haosheng; McIntosh,
Scott; Reeves, Kathy; Seaton, Dan; Zhang, Jie
Bibcode: 2019shin.confE..32G
Altcode:
Space-weather forecast capability is held back by our current
lack of basic scientific understanding of CME magnetic evolution,
and the coronal magnetism that structures and drives the solar
wind. Comprehensive observations of the global magnetothermal
environment of the solar atmosphere are needed for progress. When fully
implemented, the COSMO suite of synoptic ground-based telescopes will
provide the community with comprehensive and simultaneous measurements
of magnetism, temperature, density and plasma flows and waves from the
photosphere through the chromosphere and out into the corona. We will
discuss how these observations will uniquely address a set of science
objectives that are central to the field of solar and space physics:
in particular, to understand the storage and release of magnetic energy,
to understand CME dynamics and consequences for shocks, to determine the
role of waves in solar atmospheric heating and solar wind acceleration,
to understand how the coronal magnetic field relates to the solar
dynamo, and to constrain and improve space-weather forecast models.
Title: Solar Polarization Workshop 8
Authors: Belluzzi, L.; Casini, R.; Romoli, M.; Trujillo Bueno, J.
Bibcode: 2019ASPC..526.....B
Altcode:
No abstract at ADS
Title: Comparison of Scattering Polarization Signals Observed by
CLASP: Possible Indication of the Hanle Effect
Authors: Ishikawa, R.; Trujillo Bueno, J.; Uitenbroek, H.; Kubo, M.;
Tsuneta, S.; Goto, M.; Kano, R.; Narukage, N.; Bando, T.; Katsukawa,
Y.; Ishikawa, S.; Giono, G.; Suematsu, Y.; Hara, H.; Shimizu, T.;
Sakao, T.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.;
Auchère, F.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso
Sainz, R.; De Pomtieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R.
Bibcode: 2019ASPC..526..305I
Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP; Kano et
al. 2012; Kobayashi et al. 2012; Kubo et al. 2014) observed, for the
first time, the linear polarization produced by scattering processes
in the hydrogen Lyman-α (121.57 nm) and Si III (120.56 nm) lines of
the solar disk radiation. The complexity of the observed scattering
polarization (i.e., conspicuous spatial variations in Q/I and U/I
at spatial scales of 10″-20″ and the absence of center-to- limb
variation at the Lyman-α center; see Kano et al. 2017) motivated us
to search for possible hints of the operation of the Hanle effect by
comparing: (a) the Lyman-α line center signal, for which the critical
field strength (BH) for the onset of the Hanle effect is
53 G, (b) the Lyman-α wing, which is insensitive to the Hanle effect,
and (c) the Si III line, whose BH = 290 G. We focus on four
regions with different total unsigned photospheric magnetic fluxes
(estimated from SDO/HMI observations), and compare the corresponding
U/I spatial variations in the Lyman-α wing, Lyman-α center, and Si III
line. The U/I signal in the Lyman-α wing shows an antisymmetric spatial
distribution, which is caused by the presence of a bright structure in
all the selected regions, regardless of the total unsigned photospheric
magnetic flux. In an internetwork region, the Lyman-α center shows an
antisymmetric spatial variation across the selected bright structure,
but it does not show it in other more magnetized regions. In the Si III
line, the spatial variation of U/I deviates from the above-mentioned
antisymmetric shape as the total unsigned photospheric magnetic flux
increases. We argue that a plausible explanation of this differential
behavior is the operation of the Hanle effect. This work, presented
in an oral contribution at this Workshop, has been published on The
Astrophysical Journal (Ishikawa et al. 2017).
Title: Removal of Spectro-polarimetric Fringes by Two-dimensional
Principal Component Analysis
Authors: Casini, R.; Li, W.
Bibcode: 2019ApJ...872..173C
Altcode:
We investigate the application of two-dimensional Principal Component
Analysis (2D PCA) to the problem of removal of polarization fringes
from spectro-polarimetric data sets. We show how the transformation
of the PCA basis through a series of carefully chosen rotations allows
us to confine polarization fringes (and other stationary instrumental
effects) to a reduced set of basis “vectors,” which at the same time
are largely devoid of the spectral signal from the observed target. It
is possible to devise algorithms for the determination of the optimal
series of rotations of the PCA basis, thus opening the possibility of
automating the procedure of defringing of spectro-polarimetric data
sets. We compare the performance of the proposed method with the more
traditional Fourier filtering of Stokes spectra.
Title: Experimental Testing of Scattering Polarization Models
Authors: Li, W.; Casini, R.; Tomczyk, S.; Landi Degl'Innocenti, E.;
Marsell, B.
Bibcode: 2018ApJ...867L..22L
Altcode: 2018arXiv181107090L
We realized a laboratory experiment to study the scattering polarization
of the Na I D-doublet at 589.0 and 589.6 nm in the presence of a
magnetic field. This work was stimulated by solar observations of
that doublet, which have proven particularly challenging to explain
through available models of polarized line formation, even to the
point of casting doubts on our very understanding of the underlying
physics. The purpose of the experiment was to test a quantum theory
for the polarized scattering of spectrally flat incident radiation, on
which much of the current magnetic diagnostics of stellar atmospheres
is based. The experiment has confirmed the predictions of that theory,
and its adequacy for the modeling of scattering polarization under
flat-spectrum illumination.
Title: Removal of Spectro-Polarimetric Fringes by 2D PCA
Authors: Casini, Roberto; Li, Wenxian
Bibcode: 2018arXiv181103211C
Altcode:
We investigate the application of 2-dimensional Principal Component
Analysis (2D PCA) to the problem of removal of polarization fringes
from spectro-polarimetric data sets. We show how the transformation of
the PCA basis through a series of carefully chosen rotations allows
to confine polarization fringes (and other stationary instrumental
effects) to a reduced set of basis "vectors", which at the same time
are largely devoid of the spectral signal from the observed target. It
is possible to devise algorithms for the determination of the optimal
series of rotations of the PCA basis, thus opening the possibility of
automating the procedure of de-fringing of spectro-polarimetric data
sets. We compare the performance of the proposed method with the more
traditional Fourier filtering of Stokes spectra.
Title: CLASP Constraints on the Magnetization and Geometrical
Complexity of the Chromosphere-Corona Transition Region
Authors: Trujillo Bueno, J.; Štěpán, J.; Belluzzi, L.; Asensio
Ramos, A.; Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; Ishikawa,
R.; Kano, R.; Winebarger, A.; Auchère, F.; Narukage, N.; Kobayashi,
K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara,
H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.;
Cirtain, J.; Champey, P.; De Pontieu, B.; Carlsson, M.
Bibcode: 2018ApJ...866L..15T
Altcode: 2018arXiv180908865T
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a
suborbital rocket experiment that on 2015 September 3 measured
the linear polarization produced by scattering processes in the
hydrogen Lyα line of the solar disk radiation. The line-center
photons of this spectral line radiation mostly stem from the
chromosphere-corona transition region (TR). These unprecedented
spectropolarimetric observations revealed an interesting surprise,
namely that there is practically no center-to-limb variation (CLV) in
the Q/I line-center signals. Using an analytical model, we first show
that the geometric complexity of the corrugated surface that delineates
the TR has a crucial impact on the CLV of the Q/I and U/I line-center
signals. Second, we introduce a statistical description of the solar
atmosphere based on a 3D model derived from a state-of-the-art radiation
magnetohydrodynamic simulation. Each realization of the statistical
ensemble is a 3D model characterized by a given degree of magnetization
and corrugation of the TR, and for each such realization we solve the
full 3D radiative transfer problem taking into account the impact
of the CLASP instrument degradation on the calculated polarization
signals. Finally, we apply the statistical inference method presented
in a previous paper to show that the TR of the 3D model that produces
the best agreement with the CLASP observations has a relatively weak
magnetic field and a relatively high degree of corrugation. We emphasize
that a suitable way to validate or refute numerical models of the upper
solar chromosphere is by confronting calculations and observations
of the scattering polarization in ultraviolet lines sensitive to the
Hanle effect.
Title: A Statistical Inference Method for Interpreting the CLASP
Observations
Authors: Štěpán, J.; Trujillo Bueno, J.; Belluzzi, L.; Asensio
Ramos, A.; Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; Kano, R.;
Winebarger, A.; Auchère, F.; Ishikawa, R.; Narukage, N.; Kobayashi,
K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara,
H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.;
Cirtain, J.; Champey, P.; De Pontieu, B.; Carlsson, M.
Bibcode: 2018ApJ...865...48S
Altcode: 2018arXiv180802725S
On 2015 September 3, the Chromospheric Lyman-Alpha SpectroPolarimeter
(CLASP) successfully measured the linear polarization produced by
scattering processes in the hydrogen Lyα line of the solar disk
radiation, revealing conspicuous spatial variations in the Q/I and U/I
signals. Via the Hanle effect, the line-center Q/I and U/I amplitudes
encode information on the magnetic field of the chromosphere-corona
transition region, but they are also sensitive to the three-dimensional
structure of this corrugated interface region. With the help of a simple
line-formation model, here we propose a statistical inference method
for interpreting the Lyα line-center polarization observed by CLASP.
Title: Construction update of the Daniel K. Inouye Solar Telescope
project
Authors: Warner, Mark; Rimmele, Thomas R.; Martinez Pillet, Valentin;
Casini, Roberto; Berukoff, Steve; Craig, Simon C.; Ferayorni, Andrew;
Goodrich, Bret D.; Hubbard, Robert P.; Harrington, David; Jeffers,
Paul; Johansson, Erik M.; Kneale, Ruth; Kuhn, Jeff; Liang, Chen; Lin,
Haosheng; Marshall, Heather; Mathioudakis, Mihalis; McBride, William
R.; McMullin, Joseph; McVeigh, William; Sekulic, Predrag; Schmidt,
Wolfgang; Shimko, Steve; Sueoka, Stacey; Summers, Rich; Tritschler,
Alexandra; Williams, Timothy R.; Wöger, Friedrich
Bibcode: 2018SPIE10700E..0VW
Altcode:
Construction of the Daniel K. Inouye Solar Telescope (DKIST) is
well underway on the Haleakalā summit on the Hawaiian island of
Maui. Featuring a 4-m aperture and an off-axis Gregorian configuration,
the DKIST will be the world's largest solar telescope. It is designed
to make high-precision measurements of fundamental astrophysical
processes and produce large amounts of spectropolarimetric and
imaging data. These data will support research on solar magnetism
and its influence on solar wind, flares, coronal mass ejections,
and solar irradiance variability. Because of its large aperture, the
DKIST will be able to sense the corona's magnetic field—a goal that
has previously eluded scientists—enabling observations that will
provide answers about the heating of stellar coronae and the origins
of space weather and exo-weather. The telescope will cover a broad
wavelength range (0.35 to 28 microns) and operate as a coronagraph
at infrared (IR) wavelengths. Achieving the diffraction limit of
the 4-m aperture, even at visible wavelengths, is paramount to these
science goals. The DKIST's state-of-the-art adaptive optics systems
will provide diffraction-limited imaging, resolving features that are
approximately 20 km in size on the Sun. At the start of operations,
five instruments will be deployed: a visible broadband imager (VTF),
a visible spectropolarimeter (ViSP), a visible tunable filter (VTF),
a diffraction-limited near-IR spectropolarimeter (DLNIRSP), and a
cryogenic near-IR spectropolarimeter (cryo-NIRSP). At the end of
2017, the project finished its fifth year of construction and eighth
year overall. Major milestones included delivery of the commissioning
blank, the completed primary mirror (M1), and its cell. Commissioning
and testing of the coudé rotator is complete and the installation
of the coudé cleanroom is underway; likewise, commissioning of the
telescope mount assembly (TMA) has also begun. Various other systems and
equipment are also being installed and tested. Finally, the observatory
integration, testing, and commissioning (IT&C) activities have
begun, including the first coating of the M1 commissioning blank and
its integration within its cell assembly. Science mirror coating and
initial on-sky activities are both anticipated in 2018.
Title: Instrument prototypes of miniature near-UV imaging
spectro-polarimeters for observations of solar magnetism
Authors: Oakley, P. H. H.; Casini, R.; Sewell, S.; Ela, N.
Bibcode: 2018SPIE10699E..38O
Altcode:
This paper summarizes our current instrument prototyping efforts
of miniature near-UV imaging spectro-polarimeters to probe
the thermodynamics and magnetism of the solar Chromosphere and
Transition Region. This includes our high altitude balloon piggyback
instruments DIMS-RADIANCE and DIMS-STOUT, which are scheduled to fly
in 2018. These payloads are CubeSat sized instruments designed around
commercial off-the-shelf miniaturized spectrographs. Additionally
we detail a new optical concept and proposed CubeSat mission called
SolarCube. This instrument will be capable of "snapshot polarimetry"
with simultaneous 2D imaging, spectroscopy, and linear polarization
without mechanisms or scanning. This concept utilizes an integral
field unit, diffraction grating, and unique polarization sensitive
detector. The design, capabilities, current prototyping efforts, and
future plans are discussed. The design goal is to observe the spatially
resolved polarization signature of the Mg II h-k doublet at 280nm over
the full solar disk.
Title: Current State of UV Spectro-Polarimetry and its Future
Direction
Authors: Ishikawa, Ryohko; Sakao, Taro; Katsukawa, Yukio; Hara,
Hirohisa; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Kubo, Masahito;
Auchere, Frederic; De Pontieu, Bart; Winebarger, Amy; Kobayashi,
. Ken; Kano, Ryouhei; Narukage, Noriyuki; Trujillo Bueno, Javier;
Song, Dong-uk; Manso Sainz, Rafael; Asensio Ramos, Andres; Leenaarts,
Jorritt; Carlsson, Mats; Bando, Takamasa; Ishikawa, Shin-nosuke;
Tsuneta, Saku; Belluzzi, Luca; Suematsu, Yoshinori; Giono, Gabriel;
Yoshida, Masaki; Goto, Motoshi; Del Pino Aleman, Tanausu; Stepan,
Jiri; Okamoto, Joten; Tsuzuki, Toshihiro; Uraguchi, Fumihiro; Champey,
Patrick; Alsina Ballester, Ernest; Casini, Roberto; McKenzie, David;
Rachmeler, Laurel; Bethge, Christian
Bibcode: 2018cosp...42E1564I
Altcode:
To obtain quantitative information on the magnetic field in low beta
regions (i.e., upper chromosphere and above) has been increasingly
important to understand the energetic phenomena of the outer
solar atmosphere such as flare, coronal heating, and the solar wind
acceleration. In the UV range, there are abundant spectral lines that
originate in the upper chromosphere and transition region. However,
the Zeeman effect in these spectral lines does not give rise to easily
measurable polarization signals because of the weak magnetic field
strength and the larger Doppler broadening compared with the Zeeman
effect. Instead, the Hanle effect in UV lines is expected to be a
suitable diagnostic tool of the magnetic field in the upper atmospheric
layers. To investigate the validity of UV spectro-polarimetry and
the Hanle effect, the Chromospheric Lyman-Alpha Spectro-Polarimeter
(CLASP), which is a NASA sounding- rocket experiment, was launched at
White Sands in US on September 3, 2015. During its 5 minutes ballistic
flight, it successfully performed spectro-polarimetric observations
of the hydrogen Lyman-alpha line (121.57 nm) with an unprecedentedly
high polarization sensitivity of 0.1% in this wavelength range. CLASP
observed the linear polarization produced by scattering process in VUV
lines for the first time and detected the polarization signals which
indicate the operation of the Hanle effect. Following the success
of CLASP, we are confident that UV spectro-polarimetry is the way
to proceed, and we are planning the second flight of CLASP (CLASP2:
Chromospheric LAyer SpectroPolarimeter 2). For this second flight we
will carry out spectro-polarimetry in the Mg II h and k lines around
280 nm, with minimum modifications of the CLASP1 instrument. The linear
polarization in the Mg II k line is induced by scattering processes and
the Hanle effect, being sensitive to magnetic field strengths of 5 to 50
G. In addition, the circular polarizations in the Mg II h and k lines
induced by the Zeeman effect can be measurable in at least plage and
active regions. The combination of the Hanle and Zeeman effects could
help us to more reliably infer the magnetic fields of the upper solar
chromosphere. CLASP2 was selected for flight and is being developed for
launch in the spring of 2019.Based on these sounding rocket experiments
(CLASP1 and 2), we aim at establishing the strategy and refining the
instrument concept for future space missions to explore the enigmatic
atmospheric layers via UV spectro-polarimetry.
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
Bibcode: 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: Experimental testing of scattering polarization models
Authors: Li, Wenxian; Casini, Roberto; Tomczyk, Steven; Landi
Degl'Innocenti, Egidio; Marsell, Brandan
Bibcode: 2018AAS...23212305L
Altcode:
We realized a laboratory experiment to study the polarization of the Na
I doublet at 589.3 nm, in the presence of a magnetic field. The purpose
of the experiment is to test the theory of scattering polarization for
illumination conditions typical of astrophysical plasmas. This work
was stimulated by solar observations of the Na I doublet that have
proven particularly challenging to reproduce with current models of
polarized line formation, even casting doubts on our very understanding
of the physics of scattering polarization on the Sun. The experiment
has confirmed the fundamental correctness of the current theory, and
demonstrated that the "enigmatic'' polarization of those observations
is exclusively of solar origin.
Title: Magnetic Diagnostics of the Solar Corona: Synthesizing Optical
and Radio Techniques
Authors: Casini, R.; White, S. M.; Judge, P. G.
Bibcode: 2018smf..book..145C
Altcode:
No abstract at ADS
Title: Multi-wavelength observations of the solar atmosphere from
the August 21, 2017 total solar eclipse
Authors: Tomczyk, S.; Boll, A.; Bryans, P.; Burkepile, J.; Casini,
R.; DeLuca, E.; Gibson, K. L.; Judge, P. G.; McIntosh, S. W.; Samra,
J.; Sewell, S. D.
Bibcode: 2017AGUFMSH24A..04T
Altcode:
We will conduct three experiments at the August 21, 2017 total
solar eclipse that we call the Rosetta Stone experiments. First,
we will obtain narrow-bandpass images at infrared wavelengths of the
magnetically sensitive coronal emission lines of Fe IX 2855 nm, Mg VIII
3028 nm and Si IX 3935 nm with a FLIR thermal imager. Information on the
brightness of these lines is important for identifying the optimal lines
for coronal magnetometry. These images will also serve as context images
for the airborne AirSpec IR coronal spectroscopy experiment (Samra et
al). Second, we will obtain linear polarization images of the visible
emission lines of Fe X 637 nm and Fe XI 789 nm as well as the continuum
polarization near 735 nm. These will be obtained with a novel detector
with an integral array of linear micro-polarizers oriented at four
different angles that enable polarization images without the need for
liquid crystals or rotating elements. These measurements will provide
information on the orientation of magnetic fields in the corona and
serve to demonstrate the new detector technology. Lastly, we will obtain
high cadence spectra as the moon covers and uncovers the chromosphere
immediately after 2nd contact and before third contact. This so-called
flash spectrum will be used to obtain information about chromospheric
structure at a spatial resolution higher than is possible by other
means. In this talk, we will describe the instrumentation used in these
experiments and present initial results obtained with them. This work
is supported by a grant from NASA, through NSF base funding of HAO/NCAR
and by generous loans of equipment from our corporate partners, FLIR,
4D Technologies and Avantes.
Title: Polarization Observations of the Total Solar Eclipse of August
21, 2017
Authors: Burkepile, J.; Boll, A.; Casini, R.; de Toma, G.; Elmore,
D. F.; Gibson, K. L.; Judge, P. G.; Mitchell, A. M.; Penn, M.; Sewell,
S. D.; Tomczyk, S.; Yanamandra-Fisher, P. A.
Bibcode: 2017AGUFMSH13B2477B
Altcode:
A total solar eclipse offers ideal sky conditions for viewing the
solar corona. Light from the corona is composed of three components:
the E-corona, made up of spectral emission lines produced by ionized
elements in the corona; the K-corona, produced by photospheric light
that is Thomson scattered by coronal electrons; and the F-corona,
produced by sunlight scattered from dust particles in the near
Sun environment and in interplanetary space. Polarized white light
observations of the corona provide a way of isolating the K-corona to
determine its structure, brightness, and density. This work focuses
on broadband white light polarization observations of the corona
during the upcoming solar eclipse from three different instruments. We
compare coronal polarization brightness observations of the August 21,
2017 total solar eclipse from the NCAR/High Altitude Observatory (HAO)
Rosetta Stone experiment using the 4-D Technology PolarCam camera with
the two Citizen PACA_CATE17Pol telescopes that will acquire linear
polarization observations of the eclipse and the NCAR/HAO K-Cor white
light coronagraph observations from the Mauna Loa Solar Observatory in
Hawaii. This comparison includes a discussion of the cross-calibration
of the different instruments and reports the results of the coronal
polarization brightness and electron density of the corona. These
observations will be compared with results from previous coronal
measurements taken at different phases of the solar cycle. In addition,
we report on the performance of the three different polarimeters. The
4-D PolarCam uses a linear polarizer array, PACA_CATE17Pol uses
a nematic liquid crystal retarder in a single beam configuration
and K-Cor uses a pair of ferroelectric liquid crystal retarders in
a dual-beam configuration. The use of the 4-D PolarCam camera in the
Rosetta Stone experiment is to demonstrate the technology for acquiring
high cadence polarization measurements. The Rosetta Stone experiment
is funded through the NASA award NNH16ZDA001N-ISE. The Citizen Science
approach to measuring the polarized solar corona during the eclipse
is funded through NASA award NNX17AH76G. The NCAR Mauna Loa Solar
Observatory is funded by the National Science Foundation.
Title: Rayleigh Scattering in Spectral Series with L-term Interference
Authors: Casini, R.; Manso Sainz, R.; del Pino Alemán, T.
Bibcode: 2017ApJ...850..162C
Altcode: 2017arXiv171011491C
We derive a formalism to describe the scattering of polarized radiation
over the full spectral range encompassed by atomic transitions belonging
to the same spectral series (e.g., the H I Lyman and Balmer series,
the UV multiplets of Fe I and Fe II). This allows us to study the role
of radiation-induced coherence among the upper terms of the spectral
series, and its contribution to Rayleigh scattering and the polarization
of the solar continuum. We rely on previous theoretical results for
the emissivity of a three-term atom of the Λ-type, taking into account
partially coherent scattering, and generalize its expression in order
to describe a “multiple Λ” atomic system underlying the formation
of a spectral series. Our study shows that important polarization
effects must be expected because of the combined action of partial
frequency redistribution and radiation-induced coherence among the
terms of the series. In particular, our model predicts the correct
asymptotic limit of 100% polarization in the far wings of a complete
(i.e., {{Δ }}L=0,+/- 1) group of transitions, which must be expected
on the basis of the principle of spectroscopic stability.
Title: Explicit Form of the Radiative and Collisional Branching
Ratios in Polarized Radiation Transport with Coherent Scattering
Authors: Casini, R.; del Pino Alemán, T.; Manso Sainz, R.
Bibcode: 2017ApJ...848...99C
Altcode: 2017arXiv170900126C
We consider the vector emissivity of the polarized radiation transfer in
a Λ-type atomic transition, which we recently proposed to account for
both complete frequency redistribution (CRD) and partial redistribution
(PRD) contributions to the scattered radiation. This expression
can concisely be written as ɛ = ( ɛ ( 1 ) - ɛ f . s . ( 2 ) )
+ ɛ ( 2 ) , where {{\boldsymbol{\varepsilon }}}(1) and
{{\boldsymbol{\varepsilon }}}(2) are the emissivity terms
describing, respectively, one-photon and two-photon processes in a
Λ-type atom, and where “f.s.” means that the corresponding term
must be evaluated assuming an appropriate “flat spectrum” average
of the incident radiation across the spectral line. In this follow-up
study, we explicitly consider the expressions of these various terms
for the case of a polarized multi-term atom to derive the algebraic
forms of the branching ratios between the CRD and PRD contributions
to the emissivity. In the limit of a two-term atom with non-coherent
lower term, our results are shown to be in full agreement with those
recently derived by Bommier.
Title: Solar Spectral Lines with Special Polarization Properties
for the Calibration of Instrument Polarization
Authors: Li, W.; Casini, R.; del Pino Alemán, T.; Judge, P. G.
Bibcode: 2017ApJ...848...82L
Altcode:
We investigate atomic transitions that have previously been identified
as having zero polarization from the Zeeman effect. Our goal is
to identify spectral lines that can be used for the calibration of
instrumental polarization of large astronomical and solar telescopes,
such as the Daniel K. Inouye Solar Telescope, which is currently
under construction on Haleakala. We use a numerical model that
takes into account the generation of scattering polarization and
its modification by the presence of a magnetic field of arbitrary
strength. We adopt values for the Landé factors from spectroscopic
measurements or semi-empirical results, thus relaxing the common
assumption of LS-coupling previously used in the literature. The
mechanisms dominating the polarization of particular transitions are
identified, and we summarize groups of various spectral lines useful
for the calibration of spectropolarimetric instruments, classified
according to their polarization properties.
Title: Magnetic Diagnostics of the Solar Corona: Synthesizing Optical
and Radio Techniques
Authors: Casini, R.; White, S. M.; Judge, P. G.
Bibcode: 2017SSRv..210..145C
Altcode: 2017SSRv..tmp...91C
In this contribution we review the current state-of-the-art of
coronal magnetometry, in both optical and radio domains. We address
the achievable objectives and the challenges of present measurement
techniques and interpretation tools. In particular, we focus on the
role that these observations can play for constraining and validating
numerical models of the global coronal magnetic field. With regard
to optical techniques, we mainly focus on the use of M1 diagnostics,
further developing the theory of the formation of their polarization
signatures in the magnetized corona.
Title: Solar Spectral Lines with Special Polarization Properties
for the Calibration of Instrument Polarization
Authors: Li, Wenxian; Casini, Roberto; Judge, Phil; del Pino Alemná,
Tanausú
Bibcode: 2017SPD....4811104L
Altcode:
We investigate atomic transitions that have previously been identified
as having zero polarization from the Zeeman effect. Our goal is
to identify spectral lines that can be used for the calibration of
instrumental polarization of large astronomical and solar telescopes,
such as the Daniel K. Inouye Solar Telescope, which is currently under
construction on Haleakala. We use a numerical model that takes into
account the generation of scattering polarization and its modification
by the presence of a magnetic field (Hanle effect, Zeeman effect,
and incomplete Paschen-Back effect). We adopt values for the Landé
factors from spectroscopic measurements or semi-empirical results,
thus relaxing the common assumption of LS-coupling previously used in
the literature. The mechanisms dominating the polarization of particular
transitions are identified, and we summarize groups of various spectral
lines useful for the polarization calibration of spectro-polarimetric
instruments, classified according to their polarization properties.
Title: Indication of the Hanle Effect by Comparing the Scattering
Polarization Observed by CLASP in the Lyα and Si III 120.65 nm Lines
Authors: Ishikawa, R.; Trujillo Bueno, J.; Uitenbroek, H.; Kubo, M.;
Tsuneta, S.; Goto, M.; Kano, R.; Narukage, N.; Bando, T.; Katsukawa,
Y.; Ishikawa, S.; Giono, G.; Suematsu, Y.; Hara, H.; Shimizu, T.;
Sakao, T.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.;
Auchère, F.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso
Sainz, R.; De Pontieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R.
Bibcode: 2017ApJ...841...31I
Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter is a sounding
rocket experiment that has provided the first successful measurement
of the linear polarization produced by scattering processes in
the hydrogen Lyα line (121.57 nm) radiation of the solar disk. In
this paper, we report that the Si III line at 120.65 nm also shows
scattering polarization and we compare the scattering polarization
signals observed in the Lyα and Si III lines in order to search for
observational signatures of the Hanle effect. We focus on four selected
bright structures and investigate how the U/I spatial variations vary
between the Lyα wing, the Lyα core, and the Si III line as a function
of the total unsigned photospheric magnetic flux estimated from Solar
Dynamics Observatory/Helioseismic and Magnetic Imager observations. In
an internetwork region, the Lyα core shows an antisymmetric spatial
variation across the selected bright structure, but it does not show
it in other more magnetized regions. In the Si III line, the spatial
variation of U/I deviates from the above-mentioned antisymmetric
shape as the total unsigned photospheric magnetic flux increases. A
plausible explanation of this difference is the operation of the Hanle
effect. We argue that diagnostic techniques based on the scattering
polarization observed simultaneously in two spectral lines with very
different sensitivities to the Hanle effect, like Lyα and Si III,
are of great potential interest for exploring the magnetism of the
upper solar chromosphere and transition region.
Title: Polarization Calibration of the Chromospheric Lyman-Alpha
SpectroPolarimeter for a 0.1% Polarization Sensitivity in the VUV
Range. Part II: In-Flight Calibration
Authors: Giono, G.; Ishikawa, R.; Narukage, N.; Kano, R.; Katsukawa,
Y.; Kubo, M.; Ishikawa, S.; Bando, T.; Hara, H.; Suematsu, Y.;
Winebarger, A.; Kobayashi, K.; Auchère, F.; Trujillo Bueno, J.;
Tsuneta, S.; Shimizu, T.; Sakao, T.; Cirtain, J.; Champey, P.; Asensio
Ramos, A.; Štěpán, J.; Belluzzi, L.; Manso Sainz, R.; De Pontieu,
B.; Ichimoto, K.; Carlsson, M.; Casini, R.; Goto, M.
Bibcode: 2017SoPh..292...57G
Altcode:
The Chromospheric Lyman-Alpha SpectroPolarimeter is a sounding
rocket instrument designed to measure for the first time the linear
polarization of the hydrogen Lyman-α line (121.6 nm). The instrument
was successfully launched on 3 September 2015 and observations were
conducted at the solar disc center and close to the limb during the
five-minutes flight. In this article, the disc center observations are
used to provide an in-flight calibration of the instrument spurious
polarization. The derived in-flight spurious polarization is consistent
with the spurious polarization levels determined during the pre-flight
calibration and a statistical analysis of the polarization fluctuations
from solar origin is conducted to ensure a 0.014% precision on the
spurious polarization. The combination of the pre-flight and the
in-flight polarization calibrations provides a complete picture of
the instrument response matrix, and a proper error transfer method
is used to confirm the achieved polarization accuracy. As a result,
the unprecedented 0.1% polarization accuracy of the instrument in the
vacuum ultraviolet is ensured by the polarization calibration.
Title: Discovery of Scattering Polarization in the Hydrogen Lyα
Line of the Solar Disk Radiation
Authors: Kano, R.; Trujillo Bueno, J.; Winebarger, A.; Auchère, F.;
Narukage, N.; Ishikawa, R.; Kobayashi, K.; Bando, T.; Katsukawa, Y.;
Kubo, M.; Ishikawa, S.; Giono, G.; Hara, H.; Suematsu, Y.; Shimizu,
T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.; Goto, M.; Belluzzi, L.;
Štěpán, J.; Asensio Ramos, A.; Manso Sainz, R.; Champey, P.;
Cirtain, J.; De Pontieu, B.; Casini, R.; Carlsson, M.
Bibcode: 2017ApJ...839L..10K
Altcode: 2017arXiv170403228K
There is a thin transition region (TR) in the solar atmosphere where
the temperature rises from 10,000 K in the chromosphere to millions
of degrees in the corona. Little is known about the mechanisms that
dominate this enigmatic region other than the magnetic field plays a
key role. The magnetism of the TR can only be detected by polarimetric
measurements of a few ultraviolet (UV) spectral lines, the Lyα line
of neutral hydrogen at 121.6 nm (the strongest line of the solar UV
spectrum) being of particular interest given its sensitivity to the
Hanle effect (the magnetic-field-induced modification of the scattering
line polarization). We report the discovery of linear polarization
produced by scattering processes in the Lyα line, obtained with
the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) rocket
experiment. The Stokes profiles observed by CLASP in quiet regions of
the solar disk show that the Q/I and U/I linear polarization signals are
of the order of 0.1% in the line core and up to a few percent in the
nearby wings, and that both have conspicuous spatial variations with
scales of ∼10 arcsec. These observations help constrain theoretical
models of the chromosphere-corona TR and extrapolations of the
magnetic field from photospheric magnetograms. In fact, the observed
spatial variation from disk to limb of polarization at the line core
and wings already challenge the predictions from three-dimensional
magnetohydrodynamical models of the upper solar chromosphere.
Title: A Note on the Radiative and Collisional Branching Ratios in
Polarized Radiation Transport with Coherent Scattering
Authors: Casini, R.; del Pino Alemán, T.; Manso Sainz, R.
Bibcode: 2017ApJ...835..114C
Altcode: 2016arXiv161203440C
We discuss the implementation of physically meaningful branching
ratios between the CRD and partial redistribution contributions to
the emissivity of a polarized multi-term atom in the presence of
both inelastic and elastic collisions. Our derivation is based on
a recent theoretical formulation of partially coherent scattering,
and it relies on a heuristic diagrammatic analysis of the various
radiative and collisional processes to determine the proper form of
the branching ratios. The expression we obtain for the emissivity
is {\boldsymbol{\varepsilon }}=[{{\boldsymbol{\varepsilon
}}}(1)-{{\boldsymbol{\varepsilon
}}}{{f}.{{s}}.}(2)]+{{\boldsymbol{\varepsilon
}}}(2), where {{\boldsymbol{\varepsilon }}}(1) and
{{\boldsymbol{\varepsilon }}}(2) are the emissivity terms for
the redistributed and partially coherent radiation, respectively, and
where “f.s.” implies that the corresponding term must be evaluated
assuming a flat-spectrum average of the incident radiation. This result
is shown to be in agreement with prior literature on the subject in
the limit of the unpolarized multi-level atom.
Title: Discovery of Ubiquitous Fast-Propagating Intensity Disturbances
by the Chromospheric Lyman Alpha Spectropolarimeter (CLASP)
Authors: Kubo, M.; Katsukawa, Y.; Suematsu, Y.; Kano, R.; Bando,
T.; Narukage, N.; Ishikawa, R.; Hara, H.; Giono, G.; Tsuneta, S.;
Ishikawa, S.; Shimizu, T.; Sakao, T.; Winebarger, A.; Kobayashi, K.;
Cirtain, J.; Champey, P.; Auchère, F.; Trujillo Bueno, J.; Asensio
Ramos, A.; Štěpán, J.; Belluzzi, L.; Manso Sainz, R.; De Pontieu,
B.; Ichimoto, K.; Carlsson, M.; Casini, R.; Goto, M.
Bibcode: 2016ApJ...832..141K
Altcode:
High-cadence observations by the slit-jaw (SJ) optics system of the
sounding rocket experiment known as the Chromospheric Lyman Alpha
Spectropolarimeter (CLASP) reveal ubiquitous intensity disturbances
that recurrently propagate in either the chromosphere or the transition
region or both at a speed much higher than the speed of sound. The
CLASP/SJ instrument provides a time series of two-dimensional images
taken with broadband filters centered on the Lyα line at a 0.6 s
cadence. The multiple fast-propagating intensity disturbances appear in
the quiet Sun and in an active region, and they are clearly detected in
at least 20 areas in a field of view of 527″ × 527″ during the 5
minute observing time. The apparent speeds of the intensity disturbances
range from 150 to 350 km s-1, and they are comparable
to the local Alfvén speed in the transition region. The intensity
disturbances tend to propagate along bright elongated structures away
from areas with strong photospheric magnetic fields. This suggests
that the observed fast-propagating intensity disturbances are related
to the magnetic canopy structures. The maximum distance traveled by
the intensity disturbances is about 10″, and the widths are a few
arcseconds, which are almost determined by a pixel size of 1.″03. The
timescale of each intensity pulse is shorter than 30 s. One possible
explanation for the fast-propagating intensity disturbances observed
by CLASP is magnetohydrodynamic fast-mode waves.
Title: Laboratory Frequency Redistribution Function for the Polarized
Λ -type Three-term Atom
Authors: Casini, R.; Manso Sainz, R.
Bibcode: 2016ApJ...833..197C
Altcode: 2016arXiv161204362C
We present the frequency redistribution function for a polarized
three-term atom of the Λ-type in the collisionless regime, and we
specialize it to the case where both the initial and final terms of
the three-state transition are metastable (I.e., with infinitely sharp
levels). This redistribution function represents a generalization of
the well-known R II function to the case where the lower
terms of the transition can be polarized and carry atomic coherence,
and it can be applied to the investigation of polarized line formation
in tenuous plasmas, where collisional rates may be low enough that
anisotropy-induced atomic polarization survives even in the case of
metastable levels.
Title: Daniel K. Inouye Solar Telescope: High-resolution observing
of the dynamic Sun
Authors: Tritschler, A.; Rimmele, T. R.; Berukoff, S.; Casini, R.;
Kuhn, J. R.; Lin, H.; Rast, M. P.; McMullin, J. P.; Schmidt, W.;
Wöger, F.; DKIST Team
Bibcode: 2016AN....337.1064T
Altcode:
The 4-m aperture Daniel K. Inouye Solar Telescope (DKIST) formerly
known as the Advanced Technology Solar Telescope (ATST) is currently
under construction on Haleakalā (Maui, Hawai'i) projected to
start operations in 2019. At the time of completion, DKIST will be
the largest ground-based solar telescope providing unprecedented
resolution and photon collecting power. The DKIST will be equipped
with a set of first-light facility-class instruments offering unique
imaging, spectroscopic and spectropolarimetric observing opportunities
covering the visible to infrared wavelength range. This first-light
instrumentation suite will include: a Visible Broadband Imager (VBI) for
high-spatial and -temporal resolution imaging of the solar atmosphere; a
Visible Spectro-Polarimeter (ViSP) for sensitive and accurate multi-line
spectropolarimetry; a Fabry-Pérot based Visible Tunable Filter
(VTF) for high-spatial resolution spectropolarimetry; a fiber-fed
Diffraction-Limited Near Infra-Red Spectro-Polarimeter (DL-NIRSP)
for two-dimensional high-spatial resolution spectropolarimetry
(simultaneous spatial and spectral information); and a Cryogenic Near
Infra-Red Spectro-Polarimeter (Cryo-NIRSP) for coronal magnetic field
measurements and on-disk observations of, e.g., the CO lines at 4.7
μm. We will provide an overview of the DKIST's unique capabilities
with strong focus on the first-light instrumentation suite, highlight
some of the additional properties supporting observations of transient
and dynamic solar phenomena, and touch on some operational strategies
and the DKIST critical science plan.
Title: Magnetic Diagnostics of the Solar Chromosphere with the Mg
II h-k Lines
Authors: del Pino Alemán, T.; Casini, R.; Manso Sainz, R.
Bibcode: 2016ApJ...830L..24D
Altcode: 2016arXiv160705683D
We investigated the formation of the Mg II h-k doublet in a weakly
magnetized atmosphere (20-100 G) using a newly developed numerical
code for polarized radiative transfer in a plane-parallel geometry,
which implements a recent formulation of partially coherent scattering
by polarized multi-term atoms in arbitrary magnetic-field regimes. Our
results confirm the importance of partial redistribution effects in
the formation of the Mg II h and k lines, as pointed out by previous
work in the non-magnetic case. We show that the presence of a magnetic
field can produce measurable modifications of the broadband linear
polarization even for relatively small field strengths (∼10 G), while
the circular polarization remains well represented by the classical
magnetograph formula. Both these results open an important new window
for the weak-field diagnostics of the upper solar atmosphere.
Title: Construction status of the Daniel K. Inouye solar telescope
Authors: McMullin, Joseph P.; Rimmele, Thomas R.; Warner, Mark;
Martinez Pillet, Valentin; Casini, Roberto; Berukoff, Steve; Craig,
Simon C.; Elmore, David; Ferayorni, Andrew; Goodrich, Bret D.;
Hubbard, Robert P.; Harrington, David; Hegwer, Steve; Jeffers, Paul;
Johansson, Erik M.; Kuhn, Jeff; Lin, Haosheng; Marshall, Heather;
Mathioudakis, Mihalis; McBride, William R.; McVeigh, William; Phelps,
LeEllen; Schmidt, Wolfgang; Shimko, Steve; Sueoka, Stacey; Tritschler,
Alexandra; Williams, Timothy R.; Wöger, Friedrich
Bibcode: 2016SPIE.9906E..1BM
Altcode:
We provide an update on the construction status of the Daniel
K. Inouye Solar Telescope. This 4-m diameter facility is designed to
enable detection and spatial/temporal resolution of the predicted,
fundamental astrophysical processes driving solar magnetism at
their intrinsic scales throughout the solar atmosphere. These data
will drive key research on solar magnetism and its influence on
solar winds, flares, coronal mass ejections and solar irradiance
variability. The facility is developed to support a broad wavelength
range (0.35 to 28 microns) and will employ state-of-the-art adaptive
optics systems to provide diffraction limited imaging, resolving
features approximately 20 km on the Sun. At the start of operations,
there will be five instruments initially deployed: Visible Broadband
Imager (VBI; National Solar Observatory), Visible SpectroPolarimeter
(ViSP; NCAR High Altitude Observatory), Visible Tunable Filter (VTF
(a Fabry-Perot tunable spectropolarimeter); Kiepenheuer Institute for
Solarphysics), Diffraction Limited NIR Spectropolarimeter (DL-NIRSP;
University of Hawaii, Institute for Astronomy) and the Cryogenic NIR
Spectropolarimeter (Cryo-NIRSP; University of Hawaii, Institute for
Astronomy). As of mid-2016, the project construction is in its 4th
year of site construction and 7th year overall. Major milestones in
the off-site development include the conclusion of the polishing of
the M1 mirror by University of Arizona, College of Optical Sciences,
the delivery of the Top End Optical Assembly (L3), the acceptance of
the Deformable Mirror System (Xinetics); all optical systems have been
contracted and are either accepted or in fabrication. The Enclosure
and Telescope Mount Assembly passed through their factory acceptance
in 2014 and 2015, respectively. The enclosure site construction
is currently concluding while the Telescope Mount Assembly site
erection is underway. The facility buildings (Utility and Support
and Operations) have been completed with ongoing work on the thermal
systems to support the challenging imaging requirements needed for the
solar research. Finally, we present the construction phase performance
(schedule, budget) with projections for the start of early operations.
Title: Scientific objectives and capabilities of the Coronal Solar
Magnetism Observatory
Authors: Tomczyk, S.; Landi, E.; Burkepile, J. T.; Casini, R.; DeLuca,
E. E.; Fan, Y.; Gibson, S. E.; Lin, H.; McIntosh, S. W.; Solomon,
S. C.; Toma, G.; Wijn, A. G.; Zhang, J.
Bibcode: 2016JGRA..121.7470T
Altcode:
Magnetic influences increase in importance in the solar atmosphere
from the photosphere out into the corona, yet our ability to routinely
measure magnetic fields in the outer solar atmosphere is lacking. We
describe the scientific objectives and capabilities of the COronal Solar
Magnetism Observatory (COSMO), a proposed synoptic facility designed
to measure magnetic fields and plasma properties in the large-scale
solar atmosphere. COSMO comprises a suite of three instruments chosen
to enable the study of the solar atmosphere as a coupled system: (1)
a coronagraph with a 1.5 m aperture to measure the magnetic field,
temperature, density, and dynamics of the corona; (2) an instrument
for diagnostics of chromospheric and prominence magnetic fields and
plasma properties; and (3) a white light K-coronagraph to measure
the density structure and dynamics of the corona and coronal mass
ejections. COSMO will provide a unique combination of magnetic field,
density, temperature, and velocity observations in the corona and
chromosphere that have the potential to transform our understanding
of fundamental physical processes in the solar atmosphere and their
role in the origins of solar variability and space weather.
Title: Frequency Redistribution of Polarized Light in the Λ-Type
Multi-Term Polarized Atom
Authors: Casini, R.; Manso Sainz, R.
Bibcode: 2016ApJ...824..135C
Altcode: 2016arXiv160207173C
We study the effects of Rayleigh and Raman scattering on the formation
of polarized spectral lines in a Λ-type multi-term atom. We fully
take into account the partial redistribution of frequency and the
presence of atomic polarization in the lower states of the atomic
model. Problems that can be modeled with this formalism include, for
example, the formation of the Ca II H-K and IR triplet, the analogous
system of Ba II, and the Lyβ-Hα system of hydrogenic ions.
Title: What’s New at the Mauna Loa Solar Observatory
Authors: Burkepile, Joan; de Toma, Giuliana; Galloy, Michael; Kolinski,
Don; Berkey, Ben; Stueben, Allen; Tomczyk, Steven; De Wijn, Alfred;
Casini, Roberto; Card, Greg; Larson, Brandon; Stanger, Andrew; Oakley,
Phil; Gallagher, Dennis; Waters, Lisa; Rose, Greg; Sewell, Scott
Bibcode: 2016SPD....47.0801B
Altcode:
The Mauna Loa Solar Observatory (MLSO) is located at 3440 meters
on the island of Hawaii. The site provides the dark, clear skies
required for observing the solar corona. The National Center for
Atmosphere Research (NCAR) High Altitude Observatory (HAO) operates two
coronagraphs at the site: the Coronal Multi-Channel Polarimeter (CoMP)
and the COSMO K-Coronagraph (K-Cor). CoMP is designed to study coronal
magnetic fields by observing full Stokes polarimetry of two forbidden
emission lines of FeXIII at 1074.7 and 1079.8 nm. CoMP also observes
active and erupting prominences over the solar limb in neutral Helium
emission at 1083.nm. The K-Cor is designed to study the onset and early
evolution of coronal mass ejections (CMEs). It is the only white light
coronagraph to routinely view the low corona down to 1.05 solar radii
in order to capture the formation of CMEs. Information is provided on
new Helium data products of active and erupting prominences observed
by the CoMP instrument as well as results from the K-Cor observations
of CMEs. Information on current and upcoming upgrades to the MLSO
facility, instrument hardware, and calibrations are reported along
with an accounting of new data products, tools and services from the
MLSO website.
Title: Construction Status and Early Science with the Daniel K. Inouye
Solar Telescope
Authors: McMullin, Joseph P.; Rimmele, Thomas R.; Warner, Mark;
Martinez Pillet, Valentin; Craig, Simon; Woeger, Friedrich; Tritschler,
Alexandra; Berukoff, Steven J.; Casini, Roberto; Goode, Philip R.;
Knoelker, Michael; Kuhn, Jeffrey Richard; Lin, Haosheng; Mathioudakis,
Mihalis; Reardon, Kevin P.; Rosner, Robert; Schmidt, Wolfgang
Bibcode: 2016SPD....4720101M
Altcode:
The 4-m Daniel K. Inouye Solar Telescope (DKIST) is in its seventh
year of overall development and its fourth year of site construction
on the summit of Haleakala, Maui. The Site Facilities (Utility
Building and Support & Operations Building) are in place with
ongoing construction of the Telescope Mount Assembly within. Off-site
the fabrication of the component systems is completing with early
integration testing and verification starting.Once complete this
facility will provide the highest sensitivity and resolution for study
of solar magnetism and the drivers of key processes impacting Earth
(solar wind, flares, coronal mass ejections, and variability in solar
output). The DKIST will be equipped initially with a battery of first
light instruments which cover a spectral range from the UV (380 nm)
to the near IR (5000 nm), and capable of providing both imaging and
spectro-polarimetric measurements throughout the solar atmosphere
(photosphere, chromosphere, and corona); these instruments are being
developed by the National Solar Observatory (Visible Broadband Imager),
High Altitude Observatory (Visible Spectro-Polarimeter), Kiepenheuer
Institute (Visible Tunable Filter) and the University of Hawaii
(Cryogenic Near-Infrared Spectro-Polarimeter and the Diffraction-Limited
Near-Infrared Spectro-Polarimeter). Further, a United Kingdom consortium
led by Queen's University Belfast is driving the development of high
speed cameras essential for capturing the highly dynamic processes
measured by these instruments. Finally, a state-of-the-art adaptive
optics system will support diffraction limited imaging capable of
resolving features approximately 20 km in scale on the Sun.We present
the overall status of the construction phase along with the current
challenges as well as a review of the planned science testing and the
transition into early science operations.
Title: Spectro-polarimetric observation in UV with CLASP to probe
the chromosphere and transition region
Authors: Kano, Ryouhei; Ishikawa, Ryohko; Winebarger, Amy R.; Auchère,
Frédéric; Trujillo Bueno, Javier; Narukage, Noriyuki; Kobayashi,
Ken; Bando, Takamasa; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-Nosuke; Giono, Gabriel; Hara, Hirohisa; Suematsu, Yoshinori;
Shimizu, Toshifumi; Sakao, Taro; Tsuneta, Saku; Ichimoto, Kiyoshi;
Goto, Motoshi; Cirtain, Jonathan W.; De Pontieu, Bart; Casini, Roberto;
Manso Sainz, Rafael; Asensio Ramos, Andres; Stepan, Jiri; Belluzzi,
Luca; Carlsson, Mats
Bibcode: 2016SPD....4710107K
Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a NASA
sounding-rocket experiment that was performed in White Sands in
the US on September 3, 2015. During its 5-minute ballistic flight,
CLASP successfully made the first spectro-polarimetric observation in
the Lyman-alpha line (121.57 nm) originating in the chromosphere and
transition region. Since the Lyman-alpha polarization is sensitive
to magnetic field of 10-100 G by the Hanle effect, we aim to infer
the magnetic field information in such upper solar atmosphere with
this experiment.The obtained CLASP data showed that the Lyman-alpha
scattering polarization is about a few percent in the wings and
the order of 0.1% in the core near the solar limb, as it had been
theoretically predicted, and that both polarization signals have a
conspicuous spatio-temporal variability. CLASP also observed another
upper-chromospheric line, Si III (120.65 nm), whose critical field
strength for the Hanle effect is 290 G, and showed a measurable
scattering polarization of a few % in this line. The polarization
properties of the Si III line could facilitate the interpretation of
the scattering polarization observed in the Lyman-alpha line.In this
presentation, we would like to show how the upper chromosphere and
transition region are seen in the polarization of these UV lines and
discuss the possible source of these complicated polarization signals.
Title: Waves and Magnetism in the Solar Atmosphere (WAMIS)
Authors: Ko, Yuan-Kuen; Moses, John; Laming, John; Strachan, Leonard;
Tun Beltran, Samuel; Tomczyk, Steven; Gibson, Sarah; Auchere, Frederic;
Casini, Roberto; Fineschi, Silvano; Knoelker, Michael; Korendyke,
Clarence; McIntosh, Scott; Romoli, Marco; Rybak, Jan; Socker, Dennis;
Vourlidas, Angelos; Wu, Qian
Bibcode: 2016FrASS...3....1K
Altcode:
Comprehensive measurements of magnetic fields in the solar corona have
a long history as an important scientific goal. Besides being crucial
to understanding coronal structures and the Sun’s generation of space
weather, direct measurements of their strength and direction are also
crucial steps in understanding observed wave motions. In this regard,
the remote sensing instrumentation used to make coronal magnetic field
measurements is well suited to measuring the Doppler signature of waves
in the solar structures. In this paper, we describe the design and
scientific values of the Waves and Magnetism in the Solar Atmosphere
(WAMIS) investigation. WAMIS, taking advantage of greatly improved
infrared filters and detectors, forward models, advanced diagnostic
tools and inversion codes, is a long-duration high-altitude balloon
payload designed to obtain a breakthrough in the measurement of
coronal magnetic fields and in advancing the understanding of the
interaction of these fields with space plasmas. It consists of a 20 cm
aperture coronagraph with a visible-IR spectro-polarimeter focal plane
assembly. The balloon altitude would provide minimum sky background and
atmospheric scattering at the wavelengths in which these observations
are made. It would also enable continuous measurements of the strength
and direction of coronal magnetic fields without interruptions from
the day-night cycle and weather. These measurements will be made
over a large field-of-view allowing one to distinguish the magnetic
signatures of different coronal structures, and at the spatial and
temporal resolutions required to address outstanding problems in
coronal physics. Additionally, WAMIS could obtain near simultaneous
observations of the electron scattered K-corona for context and to
obtain the electron density. These comprehensive observations are not
provided by any current single ground-based or space observatory. The
fundamental advancements achieved by the near-space observations of
WAMIS on coronal field would point the way for future ground based
and orbital instrumentation.
Title: Waves and Magnetism in the Solar Atmosphere (WAMIS)
Authors: Strachan, L.; Ko, Y. -K.; Moses, J. D.; Laming, J. M.;
Auchere, F.; Casini, R.; Fineschi, S.; Gibson, S.; Knoelker, M.;
Korendyke, C.; Mcintosh, S.; Romoli, M.; Rybak, J.; Socker, D.;
Tomczyk, S.; Vourlidas, A.; Wu, Q.
Bibcode: 2015IAUS..305..121S
Altcode:
Magnetic fields in the solar atmosphere provide the energy for most
varieties of solar activity, including high-energy electromagnetic
radiation, solar energetic particles, flares, and coronal mass
ejections, as well as powering the solar wind. Despite the fundamental
role of magnetic fields in solar and heliospheric physics, there
exist only very limited measurements of the field above the base of
the corona. What is needed are direct measurements of not only the
strength and orientation of the magnetic field but also the signatures
of wave motions in order to better understand coronal structure, solar
activity, and the role of MHD waves in heating and accelerating the
solar wind. Fortunately, the remote sensing instrumentation used to make
magnetic field measurements is also well suited to measure the Doppler
signature of waves in the solar structures. We present here a mission
concept for the Waves And Magnetism In the Solar Atmosphere (WAMIS)
experiment which is proposed for a NASA long-duration balloon flight.
Title: CLASP: A UV Spectropolarimeter on a Sounding Rocket for
Probing theChromosphere-Corona Transition Regio
Authors: Ishikawa, Ryohko; Kano, Ryouhei; Winebarger, Amy; Auchere,
Frederic; Trujillo Bueno, Javier; Bando, Takamasa; Narukage,
Noriyuki; Kobayashi, Ken; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-nosuke; Giono, Gabriel; Tsuneta, Saku; Hara, Hirohisa; Suematsu,
Yoshinori; Shimizu, Toshifumi; Sakao, Taro; Ichimoto, Kiyoshi;
Cirtain, Jonathan; De Pontieu, Bart; Casini, Roberto; Manso Sainz,
Rafael; Asensio Ramos, Andres; Stepan, Jiri; Belluzzi, Luca
Bibcode: 2015IAUGA..2254536I
Altcode:
The wish to understand the energetic phenomena of the outer solar
atmosphere makes it increasingly important to achieve quantitative
information on the magnetic field in the chromosphere-corona
transition region. To this end, we need to measure and model the
linear polarization produced by scattering processes and the Hanle
effect in strong UV resonance lines, such as the hydrogen Lyman-alpha
line. A team consisting of Japan, USA, Spain, France, and Norway has
been developing a sounding rocket experiment called the Chromospheric
Lyman-alpha Spectro-Polarimeter (CLASP). The aim is to detect the
scattering polarization produced by anisotropic radiation pumping in
the hydrogen Lyman-alpha line (121.6 nm), and via the Hanle effect to
try to constrain the magnetic field vector in the upper chromosphere
and transition region. In this talk, we will present an overview
of our CLASP mission, its scientific objectives, ground tests made,
and the latest information on the launch planned for the Summer of 2015.
Title: DKIST: Observing the Sun at High Resolution
Authors: Tritschler, A.; Rimmele, T. R.; Berukoff, S.; Casini, R.;
Craig, S. C.; Elmore, D. F.; Hubbard, R. P.; Kuhn, J. R.; Lin, H.;
McMullin, J. P.; Reardon, K. P.; Schmidt, W.; Warner, M.; Woger, F.
Bibcode: 2015csss...18..933T
Altcode:
The 4-m aperture Daniel K. Inouye Solar Telescope (DKIST) formerly
known as the Advanced Technology Solar Telescope (ATST) and currently
under construction on Haleakalā (Maui, Hawai'i) will be the largest
solar ground-based telescope and leading resource for studying the
dynamic Sun and its phenomena at high spatial, spectral and temporal
resolution. Accurate and sensitive polarimetric observations at
high-spatial resolution throughout the solar atmosphere including the
corona is a high priority and a major science driver. As such the DKIST
will offer a combination of state-of-the-art instruments with imaging
and/or spectropolarimetric capabilities covering a broad wavelength
range. This first-light instrumentation suite will include: a Visible
Broadband Imager (VBI) for high-spatial and -temporal resolution
imaging of the solar atmosphere; a Visible Spectro-Polarimeter (ViSP)
for sensitive and accurate multi-line spectropolarimetry; a double
Fabry-Pérot based Visible Tunable Filter (VTF) for high-spatial
resolution spectropolarimetry; a fiber-fed 2D Diffraction-Limited Near
Infra-Red Spectro-Polarimeter (DL-NIRSP); and a Cryogenic Near Infra-Red
Spectro-Polarimeter (Cryo-NIRSP) for coronal magnetic field measurements
and on-disk observations of e.g. the CO lines at 4.7 microns. We
will provide a brief overview of the DKIST's unique capabilities to
perform spectroscopic and spectropolarimetric measurements of the solar
atmosphere using its first-light instrumentation suite, the status of
the construction project, and how facility and data access is provided
to the US and international community.
Title: Waves and Magnetism in the Solar Atmosphere (WAMIS)
Authors: Ko, Y. K.; Auchere, F.; Casini, R.; Fineschi, S.; Gibson,
S. E.; Knoelker, M.; Korendyke, C.; Laming, J. M.; Mcintosh, S. W.;
Moses, J. D.; Romoli, M.; Rybak, J.; Socker, D. G.; Strachan, L.;
Tomczyk, S.; Vourlidas, A.; Wu, Q.
Bibcode: 2014AGUFMSH53B4221K
Altcode:
Magnetic fields in the solar atmosphere provide the energy for most
varieties of solar activity, including high-energy electromagnetic
radiation, solar energetic particles, flares, and coronal mass
ejections, as well as powering the solar wind. Despite the fundamental
role of magnetic fields in solar and heliospheric physics, there
exists only very limited measurements of the field above the base of
the corona. What is needed are direct measurements of not only the
strength and orientation of the magnetic field but also the signatures
of wave motions in order to better understand coronal structure,
solar activity and the role of MHD waves in heating and accelerating
the solar wind. Fortunately, the remote sensing instrumentation used
to make magnetic field measurements is also well suited for measuring
the Doppler signature of waves in the solar structures. With this
in mind, we are proposing the WAMIS (Waves and Magnetism in the
Solar Atmosphere) investigation. WAMIS will take advantage of greatly
improved infrared (IR) detectors, forward models, advanced diagnostic
tools and inversion codes to obtain a breakthrough in the measurement
of coronal magnetic fields and in the understanding of the interaction
of these fields with space plasmas. This will be achieved with a high
altitude balloon borne payload consisting of a coronagraph with an IR
spectro-polarimeter focal plane assembly. The balloon platform provides
minimum atmospheric absorption and scattering at the IR wavelengths in
which these observations are made. Additionally, a NASA long duration
balloon flight mission from the Antarctic can achieve continuous
observations over most of a solar rotation, covering all of the key
time scales for the evolution of coronal magnetic fields. With these
improvements in key technologies along with experience gained from
current ground-based instrumentation, WAMIS will provide a low-cost
mission with a high technology readiness leve.
Title: A Sounding Rocket Experiment for the Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP)
Authors: Kubo, M.; Kano, R.; Kobayashi, K.; Bando, T.; Narukage, N.;
Ishikawa, R.; Tsuneta, S.; Katsukawa, Y.; Ishikawa, S.; Suematsu, Y.;
Hara, H.; Shimizu, T.; Sakao, T.; Ichimoto, K.; Goto, M.; Holloway,
T.; Winebarger, A.; Cirtain, J.; De Pontieu, B.; Casini, R.; Auchère,
F.; Trujillo Bueno, J.; Manso Sainz, R.; Belluzzi, L.; Asensio Ramos,
A.; Štěpán, J.; Carlsson, M.
Bibcode: 2014ASPC..489..307K
Altcode:
A sounding-rocket experiment called the Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP) is presently under development to measure
the linear polarization profiles in the hydrogen Lyman-alpha (Lyα)
line at 121.567 nm. CLASP is a vacuum-UV (VUV) spectropolarimeter to aim
for first detection of the linear polarizations caused by scattering
processes and the Hanle effect in the Lyα line with high accuracy
(0.1%). This is a fist step for exploration of magnetic fields in
the upper chromosphere and transition region of the Sun. Accurate
measurements of the linear polarization signals caused by scattering
processes and the Hanle effect in strong UV lines like Lyα are
essential to explore with future solar telescopes the strength
and structures of the magnetic field in the upper chromosphere and
transition region of the Sun. The CLASP proposal has been accepted by
NASA in 2012, and the flight is planned in 2015.
Title: Magnetic and Electric Field Diagnostics of Chromospheric Jets
by Spectropolarimetric Observations of the HI Paschen Lines
Authors: Anan, T.; Casini, R.; Ichimoto, K.
Bibcode: 2014ASPC..489...67A
Altcode:
In order to study the magnetic and electric fields of chromospheric
jets, we observed the full Stokes spectra of the Paschen series of
neutral hydrogen in active region jets that took place at the solar limb
on May 5, 2012. For the observations, we used the spectropolarimeter
of the Domeless Solar Telescope at Hida observatory, Japan. Inversion
of the Stokes spectra taking into account the effect of magnetic
field on the energy structure and polarization of the hydrogen
levels (including the Hanle effect and level-crossing effects)
elucidates the magnetic field approximately aligned with the visible
structure of the jets. In addition to the magnetic field, the energy
structure and the polarization of the hydrogen levels is sensitive
to electric field through the Stark effect, electric Hanle effect
(analogous effect with the Hanle effect by magnetic field), and the
level-crossing effects. Since, we found no definitive evidence of the
polarization produced by the effect of electric field in the observed
Stokes profiles, we derived upper limits of electric field felt by
neutral atom moving across the magnetic field, and conclude that the
velocity of the neutral atom perpendicular to the magnetic field was
below several percents of the velocity bulk plasma motion.
Title: On the instrument profile of slit spectrographs
Authors: Casini, R.; de Wijn, A. G.
Bibcode: 2014JOSAA..31.2002C
Altcode: 2014arXiv1409.0137C
We derive an analytic expression for the instrument profile of a
slit spectrograph, also known as the line spread function. While
this problem is not new, our treatment relies on the operatorial
approach to the description of diffractive optical systems, which
provides a general framework for the analysis of the performance of
slit spectrographs under different illumination conditions. Based on
our results, we propose an approximation to the spectral resolution of
slit spectrographs, taking into account diffraction effects and sampling
by the detector, which improves upon the often adopted approximation
based on the root-sumsquare of the individual contributions from the
slit, the grating, and the detector pixel.
Title: Frequency Redistribution Function for the Polarized Two-term
Atom
Authors: Casini, R.; Landi Degl'Innocenti, M.; Manso Sainz, R.;
Landi Degl'Innocenti, E.; Landolfi, M.
Bibcode: 2014ApJ...791...94C
Altcode: 2014arXiv1406.6129C
We present a generalized frequency redistribution function for the
polarized two-term atom in an arbitrary magnetic field. This result is
derived within a new formulation of the quantum problem of coherent
scattering of polarized radiation by atoms in the collisionless
regime. The general theory, which is based on a diagrammatic treatment
of the atom-photon interaction, is still a work in progress. However,
the results anticipated here are relevant enough for the study of the
magnetism of the solar chromosphere and of interest for astrophysics in
general. The National Center for Atmospheric Research is sponsored
by the National Science Foundation.
Title: Construction status of the Daniel K. Inouye Solar Telescope
Authors: McMullin, Joseph P.; Rimmele, Thomas R.; Martínez Pillet,
Valentin; Berger, Thomas E.; Casini, Roberto; Craig, Simon C.; Elmore,
David F.; Goodrich, Bret D.; Hegwer, Steve L.; Hubbard, Robert P.;
Johansson, Erik M.; Kuhn, Jeffrey R.; Lin, Haosheng; McVeigh, William;
Schmidt, Wolfgang; Shimko, Steve; Tritschler, Alexandra; Warner,
Mark; Wöger, Friedrich
Bibcode: 2014SPIE.9145E..25M
Altcode:
The Daniel K. Inouye Solar Telescope (DKIST, renamed in December 2013
from the Advanced Technology Solar Telescope) will be the largest
solar facility built when it begins operations in 2019. Designed
and developed to meet the needs of critical high resolution and high
sensitivity spectral and polarimetric observations of the Sun, the
observatory will enable key research for the study of solar magnetism
and its influence on the solar wind, flares, coronal mass ejections
and solar irradiance variations. The 4-meter class facility will
operate over a broad wavelength range (0.38 to 28 microns, initially
0.38 to 5 microns), using a state-of-the-art adaptive optics system to
provide diffraction-limited imaging and the ability to resolve features
approximately 25 km on the Sun. Five first-light instruments will be
available at the start of operations: Visible Broadband Imager (VBI;
National Solar Observatory), Visible SpectroPolarimeter (ViSP; NCAR High
Altitude Observatory), Visible Tunable Filter (VTF; Kiepenheuer Institut
für Sonnenphysik), Diffraction Limited Near InfraRed SpectroPolarimeter
(DL-NIRSP; University of Hawai'i, Institute for Astronomy) and the
Cryogenic Near InfraRed SpectroPolarimeter (Cryo-NIRSP; University of
Hawai'i, Institute for Astronomy). As of mid-2014, the key subsystems
have been designed and fabrication is well underway, including the
site construction, which began in December 2012. We provide an update
on the development of the facilities both on site at the Haleakalā
Observatories on Maui and the development of components around the
world. We present the overall construction and integration schedule
leading to the handover to operations in mid 2019. In addition, we
outline the evolving challenges being met by the project, spanning the
full spectrum of issues covering technical, fiscal, and geographical,
that are specific to this project, though with clear counterparts to
other large astronomical construction projects.
Title: Performance of polarization modulation and calibration optics
for the Daniel K. Inouye Solar Telescope
Authors: Elmore, David F.; Sueoka, Stacey R.; Casini, Roberto
Bibcode: 2014SPIE.9147E..0FE
Altcode:
The Daniel K. Inouye Solar Telescope (formerly Advanced Technology Solar
Telescope) will be the world's largest solar telescope and polarimeter
when completed in 2019. Efficient use of the telescope to address key
science priorities calls for polarization measurements simultaneously
over broad wavelength ranges and calibration of the telescope and
polarimeters to high accuracy. Broadband polarization modulation
and calibration optics utilizing crystal optics have been designed
for this application. The performance of polarization modulators and
calibration retarders is presented along with a discussion of the unique
challenges of this application. Polarimeters operate over the ranges
of 0.38-1.1 microns, 0.5-2.5 microns, and 1.0-5.0 microns. Efficient
polarization modulation over these broad ranges led to modulators
utilizing multiple wave plates and that are elliptical, rather than
linear, retarders. Calibration retarders are linear retarders and
are constructed from the same sub-component wave plate pairs as the
polarization modulators. Polarization optics must address efficiency
over broad wavelength ranges while meeting beam deflection, transmitted
wave front error, and thermal constraints and doing so with designs
that, though large in diameter, can be affordably manufactured.
Title: CLE: Coronal line synthesis
Authors: Judge, Philip G.; Casini, Roberto
Bibcode: 2014ascl.soft07010J
Altcode:
CLE, written in Fortran 77, synthesizes Stokes profiles of forbidden
lines such as Fe XIII 1074.7nm, formed in magnetic dipole transitions
under coronal conditions. The lines are assumed to be optically thin,
excited by (anisotropic) photospheric radiation and thermal particle
collisions.
Title: The Daniel K. Inouye Solar Telescope first light instruments
and critical science plan
Authors: Elmore, David F.; Rimmele, Thomas; Casini, Roberto; Hegwer,
Steve; Kuhn, Jeff; Lin, Haosheng; McMullin, Joseph P.; Reardon, Kevin;
Schmidt, Wolfgang; Tritschler, Alexandra; Wöger, Friedrich
Bibcode: 2014SPIE.9147E..07E
Altcode:
The Daniel K. Inouye Solar Telescope is a 4-meter-class all-reflecting
telescope under construction on Haleakalā mountain on the island of
Maui, Hawai'i. When fully operational in 2019 it will be the world's
largest solar telescope with wavelength coverage of 380 nm to 28 microns
and advanced Adaptive Optics enabling the highest spatial resolution
measurements of the solar atmosphere yet achieved. We review the
first-generation DKIST instrument designs, select critical science
program topics, and the operations and data handling and processing
strategies to accomplish them.
Title: Single-point Inversion of the Coronal Magnetic Field
Authors: Plowman, Joseph; Casini, Roberto; Judge, Philip G.; Tomczyk,
Steven
Bibcode: 2014AAS...22432324P
Altcode:
The Fe XIII 10747 and 10798 Å lines observed in the solar corona
are sensitive to the coronal magnetic field in such a way that,
in principle, the full vector field at a point on the line of sight
can be inferred from their combined polarization signals. This paper
presents analytical inversion formulae for the field parameters and
analyzes the uncertainty of magnetic field measurements made from such
observations, assuming emission dominated by a single region along the
line-of-sight. We consider the case of the current CoMP instrument
as well as the future COSMO and ATST instruments. Uncertainties are
estimated with a direct analytic inverse and with an MCMC algorithm. We
find that (in effect) two components of the vector field can be
recovered with CoMP, and well-recovered with COSMO or ATST, but that
the third component can only be recovered when the solar magnetic
field is strong and optimally oriented.
Title: Diagnosis of Magnetic and Electric Fields of Chromospheric
Jets through Spectropolarimetric Observations of H I Paschen Lines
Authors: Anan, T.; Casini, R.; Ichimoto, K.
Bibcode: 2014ApJ...786...94A
Altcode: 2014arXiv1402.4903A
Magnetic fields govern the plasma dynamics in the outer layers
of the solar atmosphere, and electric fields acting on neutral
atoms that move across the magnetic field enable us to study the
dynamical coupling between neutrals and ions in the plasma. In order
to measure the magnetic and electric fields of chromospheric jets,
the full Stokes spectra of the Paschen series of neutral hydrogen
in a surge and in some active region jets that took place at the
solar limb were observed on 2012 May 5, using the spectropolarimeter
of the Domeless Solar Telescope at Hida observatory, Japan. First,
we inverted the Stokes spectra taking into account only the effect of
magnetic fields on the energy structure and polarization of the hydrogen
levels. Having found no definitive evidence of the effects of electric
fields in the observed Stokes profiles, we then estimated an upper
bound for these fields by calculating the polarization degree under
the magnetic field configuration derived in the first step, with the
additional presence of a perpendicular (Lorentz type) electric field
of varying strength. The inferred direction of the magnetic field on
the plane of the sky approximately aligns to the active region jets
and the surge, with magnetic field strengths in the range 10 G <
B < 640 G for the surge. Using magnetic field strengths of 70, 200,
and 600 G, we obtained upper limits for possible electric fields of
0.04, 0.3, and 0.8 V cm-1, respectively. This upper bound
is conservative, since in our modeling we neglected the possible
contribution of collisional depolarization. Because the velocity of
neutral atoms of hydrogen moving across the magnetic field derived
from these upper limits of the Lorentz electric field is far below
the bulk velocity of the plasma perpendicular to the magnetic field
as measured by the Doppler shift, we conclude that the neutral atoms
must be highly frozen to the magnetic field in the surge.
Title: FORWARD: Forward modeling of coronal observables
Authors: Gibson, Sarah E.; Kucera, Therese A.; Casini, Roberto; Dove,
James; Forland, Blake; Judge, Philip; Rachmeler, Laurel
Bibcode: 2014ascl.soft05007G
Altcode: 2014ascl.soft05007F
FORWARD forward models various coronal observables and can access
and compare existing data. Given a coronal model, it can produce
many different synthetic observables (including Stokes polarimetry),
as well as plots of model plasma properties (density, magnetic field,
etc.). It uses the CHIANTI database (ascl:9911.004) and CLE polarimetry
synthesis code, works with numerical model datacubes, interfaces with
the PFSS module of SolarSoft (ascl:1208.013), includes several analytic
models, and connects to the Virtual Solar Observatory for downloading
data in a format directly comparable to model predictions.
Title: Prominence Science with ATST Instrumentation
Authors: Rimmele, Thomas; Berger, Thomas; Casini, Roberto; Elmore,
David; Kuhn, Jeff; Lin, Haosheng; Schmidt, Wolfgang; Wöger, Friedrich
Bibcode: 2014IAUS..300..362R
Altcode:
The 4m Advance Technology Solar Telescope (ATST) is under construction
on Maui, HI. With its unprecedented resolution and photon collecting
power ATST will be an ideal tool for studying prominences and filaments
and their role in producing Coronal Mass Ejections that drive Space
Weather. The ATST facility will provide a set of first light instruments
that enable imaging and spectroscopy of the dynamic filament and
prominence structure at 8 times the resolution of Hinode. Polarimeters
allow high precision chromospheric and coronal magnetometry at visible
and infrared (IR) wavelengths. This paper summarizes the capabilities
of the ATST first-light instrumentation with focus on prominence and
filament science.
Title: Improved Search of Principal Component Analysis Databases
for Spectro-polarimetric Inversion
Authors: Casini, R.; Asensio Ramos, A.; Lites, B. W.; López Ariste, A.
Bibcode: 2013ApJ...773..180C
Altcode: 2013arXiv1307.0061C
We describe a simple technique for the acceleration of
spectro-polarimetric inversions based on principal component analysis
(PCA) of Stokes profiles. This technique involves the indexing of the
database models based on the sign of the projections (PCA coefficients)
of the first few relevant orders of principal components of the
four Stokes parameters. In this way, each model in the database can
be attributed a distinctive binary number of 24n bits,
where n is the number of PCA orders used for the indexing. Each of
these binary numbers (indices) identifies a group of "compatible"
models for the inversion of a given set of observed Stokes profiles
sharing the same index. The complete set of the binary numbers so
constructed evidently determines a partition of the database. The
search of the database for the PCA inversion of spectro-polarimetric
data can profit greatly from this indexing. In practical cases it
becomes possible to approach the ideal acceleration factor of 24n
as compared to the systematic search of a non-indexed database
for a traditional PCA inversion. This indexing method relies on the
existence of a physical meaning in the sign of the PCA coefficients
of a model. For this reason, the presence of model ambiguities and of
spectro-polarimetric noise in the observations limits in practice the
number n of relevant PCA orders that can be used for the indexing.
Title: Chromospheric Lyman Alpha SpectroPolarimeter: CLASP
Authors: Kobayashi, Ken; Kano, R.; Trujillo Bueno, J.; Winebarger,
A. R.; Cirtain, J. W.; Bando, T.; De Pontieu, B.; Ishikawa, R.;
Katsukawa, Y.; Kubo, M.; Narukage, N.; Sakao, T.; Tsuneta, S.;
Auchère, F.; Asensio Ramos, A.; Belluzzi, L.; Carlsson, M.; Casini,
R.; Hara, H.; Ichimoto, K.; Manso Sainz, R.; Shimizu, T.; Stepan,
J.; Suematsu, Y.; Holloway, T.
Bibcode: 2013SPD....44..142K
Altcode:
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a VUV
spectropolarimeter optimized for measuring the linear polarization of
the Lyman-alpha line (121.6 nm). The Lyman-alpha line is predicted to
show linear polarization caused by atomic scattering in the chromosphere
and modified by the magnetic field through the Hanle effect. The
Hanle effect is sensitive to weaker magnetic fields than Zeeman
effect, and is not canceled by opposing fields, making it sensitive
to tangled or unresolved magnetic field structures. These factors make
the Hanle effect a valuable tool for probing the magnetic field in the
chromosphere above the quiet sun. To meet this goal, CLASP is designed
to measure linear polarization with 0.1% polarization sensitivity
at 0.01 nm spectral resolution and 10" spatial resolution. CLASP is
scheduled to be launched in 2015.
Title: Calibrating the Prominence Magnetometer (ProMag)
Authors: Fox, Lewis; Casini, R.
Bibcode: 2013SPD....44..139F
Altcode:
The Prominence Magnetometer (ProMag) is a dual-channel, dual-beam,
slit-scanning, full Stokes spectro-polarimeter designed by the High
Altitude Observatory at the National Center for Atmospheric Research
(HAO/NCAR) for the study of the magnetism of solar prominences and
filaments. It was deployed in August 2009 at the 40 cm coronagraph of
the Evans Solar Facility (ESF) of the National Solar Observatory on
Sacramento Peak (NSO/SP). In its standard mode of operation it acquires
spectro-polarimetric maps of solar targets simultaneously in the two
chromospheric lines of He I at 587.6 nm and 1083.0 nm. Since August 2011
ProMag has operated in “patrol mode” with a dedicated observer. We
aim to routinely measure the vector magnetic field in prominences. The
electro-optic modulator and polarization analyzer are integrated into a
single mechanical unit located at the coude feed of the telescope. This
location was necessary for proper co-alignment of the dual beams,
but complicates the precise polarimeter calibration necessary to
achieve the sensitivity required for prominence measurements (<
10^-3). At this sensitivity, small variations in optical alignment
can become significant. We present a calibration method for ProMag,
using a polarizer and retarder at coronagraph prime focus. Calibrations
are recorded before and after observations. We discuss the success of
this method and its limitations.
Title: The Advanced Technology Solar Telescope: Science Drivers and
Construction Status
Authors: Rimmele, Thomas; Berger, Thomas; McMullin, Joseph; Keil,
Stephen; Goode, Phil; Knoelker, Michael; Kuhn, Jeff; Rosner, Robert;
Casini, Roberto; Lin, Haosheng; Woeger, Friedrich; von der Luehe,
Oskar; Tritschler, Alexandra; Atst Team
Bibcode: 2013EGUGA..15.6305R
Altcode:
The 4-meter Advance Technology Solar Telescope (ATST) currently
under construction on the 3000 meter peak of Haleakala on Maui,
Hawaii will be the world's most powerful solar telescope and the
leading ground-based resource for studying solar magnetism. The
solar atmosphere is permeated by a 'magnetic carpet' that constantly
reweaves itself to control solar irradiance and its effects on Earth's
climate, the solar wind, and space weather phenomena such as flares and
coronal mass ejections. Precise measurement of solar magnetic fields
requires a large-aperture solar telescope capable of resolving a few
tens of kilometers on the solar surface. With its 4 meter aperture,
the ATST will for the first time resolve magnetic structure at the
intrinsic scales of plasma convection and turbulence. The ATST's
ability to perform accurate and precise spectroscopic and polarimetric
measurements of magnetic fields in all layers of the solar atmosphere,
including accurate mapping of the elusive coronal magnetic fields,
will be transformative in advancing our understanding of the magnetic
solar atmosphere. The ATST will utilize the Sun as an important astro-
and plasma-physics "laboratory" demonstrating key aspects of omnipresent
cosmic magnetic fields. The ATST construction effort is led by the US
National Solar Observatory. State-of-the-art instrumentation will be
constructed by US and international partner institutions. The technical
challenges the ATST is facing are numerous and include the design of the
off-axis main telescope, the development of a high order adaptive optics
system that delivers a corrected beam to the instrument laboratory,
effective handling of the solar heat load on optical and structural
elements, and minimizing scattered light to enable observations
of the faint corona. The ATST project has transitioned from design
and development to its construction phase. The project has awarded
design and fabrication contracts for major telescope subsystems. Site
construction has commenced following the successful conclusion of
the site permitting process. Science goals and construction status of
telescope and instrument systems will be discussed.
Title: Tools for 3D Solar Magnetic Field Measurement
Authors: Casini, R.
Bibcode: 2012ASPC..463..193C
Altcode:
In this paper we describe some of the challenges that solar physicists
face in the application of polarized radiative transfer to the modeling
of the emergent radiation from the outer layers of the solar atmosphere,
where the plane-parallel approximation breaks down, and 3D atmospheric
modeling becomes essential. We review the various plasma conditions
occurring in the photosphere, chromosphere, and corona, which determine
the different regimes of atomic excitation of these regions. Depending
on the relative importance of anisotropic irradiation of the gas over
collisional thermalization of the atomic populations, the description of
the atomic excitation states may necessitate a full quantum-statistical
treatment, which exacerbates the numerical complexity of an already
computationally intensive problem. Special emphasis is placed on forward
modeling and inversion techniques that mitigate this difficulty, making
feasible the interpretation of polarization signals in terms of the
magnetic field and its connectivity throughout the solar atmosphere.
Title: Interpreting Coronal Polarization Observations
Authors: Rachmeler, L. A.; Casini, R.; Gibson, S. E.
Bibcode: 2012ASPC..463..227R
Altcode:
Solar coronal polarization observations are an underused data product
because of the difficulties in interpreting the data and in calculating
an inversion.The physics of the polarization is well understood and
documented in the literature. The purpose of this paper is to present
a general overview on how to interpret polarization signals without
calculating an inversion. This is intended to introduce the data to
those who are unfamiliar to polarization, and in so doing, make the
data more accessible.
Title: Construction of the Advanced Technology Solar Telescope
Authors: Rimmele, T. R.; Keil, S.; McMullin, J.; Knölker, M.; Kuhn,
J. R.; Goode, P. R.; Rosner, R.; Casini, R.; Lin, H.; Tritschler,
A.; Wöger, F.; ATST Team
Bibcode: 2012ASPC..463..377R
Altcode:
The 4m Advance Technology Solar Telescope (ATST) will be the most
powerful solar telescope and the world's leading ground-based resource
for studying solar magnetism that controls the solar wind, flares,
coronal mass ejections and variability in the Sun's output. The
project has entered its construction phase. Major subsystems have
been contracted. As its highest priority science driver ATST shall
provide high resolution and high sensitivity observations of the
dynamic solar magnetic fields throughout the solar atmosphere,
including the corona at infrared wavelengths. With its 4m aperture,
ATST will resolve features at 0.″03 at visible wavelengths and
obtain 0.″1 resolution at the magnetically highly sensitive near
infrared wavelengths. A high order adaptive optics system delivers a
corrected beam to the initial set of state-of-the-art, facility class
instrumentation located in the Coudé laboratory facility. The initial
set of first generation instruments consists of five facility class
instruments, including imagers and spectro-polarimeters. The high
polarimetric sensitivity and accuracy required for measurements of
the illusive solar magnetic fields place strong constraints on the
polarization analysis and calibration. Development and construction
of a four-meter solar telescope presents many technical challenges,
including thermal control of the enclosure, telescope structure and
optics and wavefront control. A brief overview of the science goals
and observational requirements of the ATST will be given, followed by a
summary of the design status of the telescope and its instrumentation,
including design status of major subsystems, such as the telescope
mount assembly, enclosure, mirror assemblies, and wavefront correction
Title: Using large telescopes to answer: why must the Sun have a
chromosphere and corona?
Authors: Judge, P.; Casini, R.
Bibcode: 2012IAUSS...6E.106J
Altcode:
I will discuss the potential for ground-based telescopes such as
the ATST to make breakthrough discoveries about the long standing
mysteries of the solar chromosphere and corona. The biggest advances
will hinge upon the ability to diagnose magnetic fields through high
s/n spectropolarimetry.
Title: Chromospheric Lyman-alpha spectro-polarimeter (CLASP)
Authors: Kano, Ryouhei; Bando, Takamasa; Narukage, Noriyuki; Ishikawa,
Ryoko; Tsuneta, Saku; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-nosuke; Hara, Hirohisa; Shimizu, Toshifumi; Suematsu, Yoshinori;
Ichimoto, Kiyoshi; Sakao, Taro; Goto, Motoshi; Kato, Yoshiaki; Imada,
Shinsuke; Kobayashi, Ken; Holloway, Todd; Winebarger, Amy; Cirtain,
Jonathan; De Pontieu, Bart; Casini, Roberto; Trujillo Bueno, Javier;
Štepán, Jiří; Manso Sainz, Rafael; Belluzzi, Luca; Asensio Ramos,
Andres; Auchère, Frédéric; Carlsson, Mats
Bibcode: 2012SPIE.8443E..4FK
Altcode:
One of the biggest challenges in heliophysics is to decipher the
magnetic structure of the solar chromosphere. The importance of
measuring the chromospheric magnetic field is due to both the key role
the chromosphere plays in energizing and structuring the outer solar
atmosphere and the inability of extrapolation of photospheric fields to
adequately describe this key boundary region. Over the last few years,
significant progress has been made in the spectral line formation
of UV lines as well as the MHD modeling of the solar atmosphere. It
is found that the Hanle effect in the Lyman-alpha line (121.567 nm)
is a most promising diagnostic tool for weaker magnetic fields in
the chromosphere and transition region. Based on this groundbreaking
research, we propose the Chromospheric Lyman-Alpha Spectro-Polarimeter
(CLASP) to NASA as a sounding rocket experiment, for making the first
measurement of the linear polarization produced by scattering processes
and the Hanle effect in the Lyman-alpha line (121.567 nm), and making
the first exploration of the magnetic field in the upper chromosphere
and transition region of the Sun. The CLASP instrument consists
of a Cassegrain telescope, a rotating 1/2-wave plate, a dual-beam
spectrograph assembly with a grating working as a beam splitter, and
an identical pair of reflective polarization analyzers each equipped
with a CCD camera. We propose to launch CLASP in December 2014.
Title: Removal of Spectro-polarimetric Fringes by Two-dimensional
Pattern Recognition
Authors: Casini, R.; Judge, P. G.; Schad, T. A.
Bibcode: 2012ApJ...756..194C
Altcode: 2012arXiv1208.5104C
We present a pattern-recognition-based approach to the problem of
the removal of polarized fringes from spectro-polarimetric data. We
demonstrate that two-dimensional principal component analysis can
be trained on a given spectro-polarimetric map in order to identify
and isolate fringe structures from the spectra. This allows us,
in principle, to reconstruct the data without the fringe component,
providing an effective and clean solution to the problem. The results
presented in this paper point in the direction of revising the way
that science and calibration data should be planned for a typical
spectro-polarimetric observing run.
Title: Analysis of Seeing-induced Polarization Cross-talk and
Modulation Scheme Performance
Authors: Casini, R.; de Wijn, A. G.; Judge, P. G.
Bibcode: 2012ApJ...757...45C
Altcode: 2011arXiv1107.0367C
We analyze the generation of polarization cross-talk in Stokes
polarimeters by atmospheric seeing, and its effects on the noise
statistics of spectropolarimetric measurements for both single-beam
and dual-beam instruments. We investigate the time evolution of
seeing-induced correlations between different states of one modulation
cycle and compare the response to these correlations of two popular
polarization modulation schemes in a dual-beam system. Extension of
the formalism to encompass an arbitrary number of modulation cycles
enables us to compare our results with earlier work. Even though we
discuss examples pertinent to solar physics, the general treatment
of the subject and its fundamental results might be useful to a wider
community.
Title: The Hydromagnetic Interior of a Solar Quiescent
Prominence. II. Magnetic Discontinuities and Cross-field Mass
Transport
Authors: Low, B. C.; Liu, W.; Berger, T.; Casini, R.
Bibcode: 2012ApJ...757...21L
Altcode:
This second paper of the series investigates the transverse response
of a magnetic field to the independent relaxation of its flux tubes
of fluid seeking hydrostatic and energy balance, under the frozen-in
condition and suppression of cross-field thermal conduction. The
temperature, density, and pressure naturally develop discontinuities
across the magnetic flux surfaces separating the tubes, requiring the
finite pressure jumps to be compensated by magnetic-pressure jumps in
cross-field force balance. The tangentially discontinuous fields are
due to discrete currents in these surfaces, δ-function singularities
in the current density that are fully admissible under the rigorous
frozen-in condition but must dissipate resistively if the electrical
conductivity is high but finite. The magnetic field and fluid must
thus endlessly evolve by this spontaneous formation and resistive
dissipation of discrete currents taking place intermittently in
spacetime, even in a low-β environment. This is a multi-dimensional
effect in which the field plays a central role suppressed in the
one-dimensional (1D) slab model of the first paper. The study begins
with an order-of-magnitude demonstration that of the weak resistive
and cross-field thermal diffusivities in the corona, the latter is
significantly weaker for small β. This case for spontaneous discrete
currents, as an important example of the general theory of Parker, is
illustrated with an analysis of singularity formation in three families
of two-dimensional generalizations of the 1D slab model. The physical
picture emerging completes the hypothesis formulated in Paper I that
this intermittent process is the origin of the dynamic interiors of
a class of quiescent prominences revealed by recent Hinode/SOT and
SDO/AIA high-resolution observations.
Title: Preliminary design of the visible spectro-polarimeter for
the Advanced Technology Solar Telescope
Authors: de Wijn, Alfred G.; Casini, Roberto; Nelson, Peter G.;
Huang, Pei
Bibcode: 2012SPIE.8446E..6XD
Altcode: 2012arXiv1207.0976D
The Visible Spectro-Polarimeter (ViSP) is one of the first light
instruments for the Advanced Technology Solar Telescope (ATST). It is
an echelle spectrograph designed to measure three different regions
of the solar spectrum in three separate focal planes simultaneously
between 380 and 900 nm. It will use the polarimetric capabilities
of the ATST to measure the full Stokes parameters across the line
profiles. By measuring the polarization in magnetically sensitive
spectral lines the magnetic field vector as a function of height in the
solar atmosphere can be obtained, along with the associated variation of
the thermodynamic properties. The ViSP will have a spatial resolution
of 0.04 arcsec over a 2 arcmin field of view (at 600 nm). The minimum
spectral resolving power for all the focal planes is 180,000. The
spectrograph supports up to 4 diffraction gratings and is fully
automated to allow for rapid reconfiguration.
Title: Resonance scattering polarization in the magnetosphere
of Mercury
Authors: López Ariste, A.; Leblanc, F.; Casini, R.; Manso Sainz,
R.; Gelly, B.; Le Men, C.
Bibcode: 2012Icar..220.1104L
Altcode:
The conditions of the exosphere of Mercury constitute a prime example
of a magnetosphere subject to space weather. We aim at improving the
diagnostic of the physical conditions of Na atoms in the exosphere of
Mercury, with particular emphasis in the possibility of inferring the
magnetic field through polarimetry of the Na D emission lines. We
performed spectropolarimetry of the Na D emission lines in the
exosphere of Mercury at two different ranges of phases of the planet
and interpreted them under present models of resonance scattering
polarization applied to the Na atom. We measured successfully the
polarization of the Na D2 line while no polarization
was seen in D1, as expected. The measured polarization
varies with the phase angle but it is roughly a factor two smaller
than expected from an isolated emitting atom. Depolarization due to
the presence of optical depth explains this factor two and is the
most probable explanation for this discrepancy. A framework for the
observation of polarization in the emission lines of the exosphere and
its interpretation is laid. This opens the possibility to use these
measurements for diagnostic of the physical conditions in the exosphere
of Mercury, and eventually to infer the magnetic field of Mercury and
its variability from observations made with ground telescopes.
Title: The Hydromagnetic Interior of a Solar Quiescent
Prominence. I. Coupling between Force Balance and Steady Energy
Transport
Authors: Low, B. C.; Berger, T.; Casini, R.; Liu, W.
Bibcode: 2012ApJ...755...34L
Altcode: 2012arXiv1203.1056L
This series of papers investigates the dynamic interiors of quiescent
prominences revealed by recent Hinode and SDO/AIA high-resolution
observations. This first paper is a study of the static equilibrium
of the Kippenhahn-Schlüter diffuse plasma slab, suspended vertically
in a bowed magnetic field, under the frozen-in condition and subject
to a theoretical thermal balance among an optically thin radiation,
heating, and field-aligned thermal conduction. The everywhere-analytical
solutions to this nonlinear problem are an extremely restricted subset
of the physically admissible states of the system. For most values
of the total mass frozen into a given bowed field, force balance
and steady energy transport cannot both be met without a finite
fraction of the total mass having collapsed into a cold sheet of zero
thickness, within which the frozen-in condition must break down. An
exact, resistive hydromagnetic extension of the Kippenhahn-Schlüter
slab is also presented, resolving the mass-sheet singularity into
a finite-thickness layer of steadily falling dense fluid. Our
hydromagnetic result suggests that the narrow, vertical prominence
Hα threads may be falling across magnetic fields, with
optically thick cores much denser and ionized to much lower degrees than
conventionally considered. This implication is discussed in relation
to (1) the recent SDO/AIA observations of quiescent prominences that
are massive and yet draining mass everywhere in their interiors, (2)
the canonical range of 5-60 G determined from spectral polarimetric
observations of prominence magnetic fields over the years, and (3)
the need for a more realistic multi-fluid treatment.
Title: The Chromospheric Magnetometer ChroMag
Authors: Bethge, Christian; de Wijn, A. G.; McIntosh, S. W.; Tomczyk,
S.; Casini, R.
Bibcode: 2012AAS...22013506B
Altcode:
We present the Chromosphere Magnetometer (ChroMag), which is part of
the Coronal Solar Magnetism Observatory (COSMO) proposed by the High
Altitude Observatory (HAO) in collaboration with the University of
Hawaii and the University of Michigan. ChroMag will perform routine
measurements of chromospheric magnetic fields in a synoptic manner. A prototype is currently being assembled at HAO. The main component of
the instrument is a Lyot-type filtergraph polarimeter for both on-disk
and off-limb polarization measurements in the spectral lines of
H alpha at 656.3 nm, Fe I 617.3 nm, Ca II 854.2 nm, He I 587.6 nm,
and He I 1083.0 nm. The Lyot filter is tunable at a fast rate. This
allows to determine line-of-sight velocities in addition to the
magnetic field measurements. The instrument has a field-of-view of
up to 2.5 solar radii and will acquire data at a cadence of less than
1 minute and at a spatial resolution of 2 arcsec. The community will
have open access to the data as well as to a set of inversion tools
for an easier interpretation of the measurements. We show an overview
of the proposed instrument and first results from the protoype.
Title: Spectropolarimetry of a Limb Active Region and its Cool
Coronal Structures
Authors: Judge, Philip G.; Kleint, L.; Casini, R.; Schad, T.
Bibcode: 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 plasma structures extending many Mm into the corona.
Title: Solar magnetism eXplorer (SolmeX). Exploring the magnetic
field in the upper atmosphere of our closest star
Authors: Peter, Hardi; Abbo, L.; Andretta, V.; Auchère, F.; Bemporad,
A.; Berrilli, F.; Bommier, V.; Braukhane, A.; Casini, R.; Curdt,
W.; Davila, J.; Dittus, H.; Fineschi, S.; Fludra, A.; Gandorfer, A.;
Griffin, D.; Inhester, B.; Lagg, A.; Landi Degl'Innocenti, E.; Maiwald,
V.; Sainz, R. Manso; Martínez Pillet, V; Matthews, S.; Moses, D.;
Parenti, S.; Pietarila, A.; Quantius, D.; Raouafi, N. -E.; Raymond, J.;
Rochus, P.; Romberg, O.; Schlotterer, M.; Schühle, U.; Solanki, S.;
Spadaro, D.; Teriaca, L.; Tomczyk, S.; Trujillo Bueno, J.; Vial, J. -C.
Bibcode: 2012ExA....33..271P
Altcode: 2011arXiv1108.5304P; 2011ExA...tmp..134P
The magnetic field plays a pivotal role in many fields of
Astrophysics. This is especially true for the physics of the solar
atmosphere. Measuring the magnetic field in the upper solar atmosphere
is crucial to understand the nature of the underlying physical
processes that drive the violent dynamics of the solar corona—that
can also affect life on Earth. SolmeX, a fully equipped solar space
observatory for remote-sensing observations, will provide the first
comprehensive measurements of the strength and direction of the
magnetic field in the upper solar atmosphere. The mission consists
of two spacecraft, one carrying the instruments, and another one in
formation flight at a distance of about 200 m carrying the occulter to
provide an artificial total solar eclipse. This will ensure high-quality
coronagraphic observations above the solar limb. SolmeX integrates two
spectro-polarimetric coronagraphs for off-limb observations, one in
the EUV and one in the IR, and three instruments for observations on
the disk. The latter comprises one imaging polarimeter in the EUV for
coronal studies, a spectro-polarimeter in the EUV to investigate the low
corona, and an imaging spectro-polarimeter in the UV for chromospheric
studies. SOHO and other existing missions have investigated the emission
of the upper atmosphere in detail (not considering polarization),
and as this will be the case also for missions planned for the near
future. Therefore it is timely that SolmeX provides the final piece of
the observational quest by measuring the magnetic field in the upper
atmosphere through polarimetric observations.
Title: The Hydromagnetic Nature of Quiescent Prominences
Authors: Low, B. C.; Berger, T.; Casini, R.; Liu, W.
Bibcode: 2012decs.confE..84L
Altcode:
High-resolution observations of quiescent prominences with Hinode
and SDO have revealed within their interiors the ever-¬present
descent at less than free-fall speeds of cool, vertical dense
filaments interspersed among upward, narrow streams at comparable
speeds of heated, low-density plasma. We address the physical nature
of this dynamical state. Despite the high magnetic Reynolds numbers
characterizing this hydromagnetic environment, magnetic reconnection
takes place via spontaneous formation and dissipation of current sheets
by the coupled effects of highly-anisotropic thermal conduction,
gravity, optically-thin radiation, heating, and high electrical
conductivity. In this interesting new version of the theory of Parker
(1994, Spontaneous current sheets in magnetic fields, Cambridge U
Press), pervasive reconnections produce a perennial local descent of
dense condensations under gravity along newly reconnected magnetic field
lines and a concurrent turbulent rise of buoyant pockets of heated
magnetized plasma through the large-scale magnetic structure. This
mechanism may explain the massive downward drainage through a quiescent
prominence observed recently (Liu et al. 2012 ApJ 745, L21) and, in
the broader context, relate the quiescent prominence to the surrounding
chromosphere/corona as a novel, large-scale, magneto-thermal convective
phenomenon (Berger et al. 2011, Nature 472, 197).
Title: Forward modeling of coronal polarization
Authors: Gibson, Sarah E.; Casini, Roberto; Dove, James; Tomczyk, Steve
Bibcode: 2012decs.confE...6G
Altcode:
Coronal polarization measurements from the Coronal Multichannel
Polarimeter (CoMP) instrument provide quantitative information about the
magnetic field above the solar limb. Inversion of these measurements
is difficult due to the optically thin nature of the plasma. Our
forward technique can be used with both local and global models to
obtain quantitative comparisons between models and observations of
the coronal magnetic field. We have used the forward technique to
study the magnetic nature of quiescent coronal cavities. We present
results from the cavity analysis as well as ways to interpret the
coronal polarization data without calculating inversions.
Title: The Chromosphere and Prominence Magnetometer
Authors: de Wijn, Alfred; Bethge, Christian; McIntosh, Scott; Tomczyk,
Steven; Casini, Roberto
Bibcode: 2012decs.confE..63D
Altcode:
ChroMag is an imaging polarimeter designed to measure on-disk
chromosphere and off-disk prominence magnetic fields using the
spectral lines of He I (587.6 and 1083 nm). It is part of the planned
CoSMO suite, which includes two more instruments: a large 1.5-m
refracting coronagraph for coronal magnetic field measurements, and
the K-Coronagraph for measurement of the coronal density. ChroMag
will provide insights in the energetics of the solar atmosphere,
how prominences are formed, and how energy is stored and released
in the magnetic field structure of the atmosphere. An essential
part of the ChroMag program is a commitment to develop and provide
community access to the "inversion" tools necessary to interpret the
measurements and derive the magneto-hydrodynamic parameters of the
plasma. A prototype instrument is currently under construction at the
High Altitude Observatory. We will present an overview of the ChroMag
instrument concept, target science, and prototype status.
Title: Synoptic measurements of chromospheric and prominence magnetic
fields with the Chromosphere Magnetometer ChroMag
Authors: Bethge, C.; de Wijn, A. G.; McIntosh, S. W.; Tomczyk, S.;
Casini, R.
Bibcode: 2012decs.confE..62B
Altcode:
The Chromosphere Magnetometer is part of the Coronal Solar Magnetism
Observatory (COSMO) proposed by the High Altitude Observatory (HAO)
in collaboration with the University of Hawaii and the University of
Michigan. Routine measurements of chromospheric and coronal magnetic
fields are vital if we want to understand fundamental problems like
the energy and mass balance of the corona, the onset and acceleration
of the solar wind, the emergence of CMEs, and how these phenomena
influence space weather. ChroMag is designed as a Lyot-type filtergraph
polarimeter with an FOV of 2.5 solar radii, i.e., it will be capable of
both on-disk and off-limb polarimetric measurements. The Lyot filter
- currently being built at HAO - is tunable at a fast rate, which
allows to determine line-of-sight velocities. This will be done in
the spectral lines of H alpha at 656.3 nm, Fe I 617.3 nm, Ca II 854.2
nm, He I 587.6 nm, and He I 1083.0 nm at a high cadence of less than
1 minute, and at a moderate spatial resolution of 2 arcsec. ChroMag
data will be freely accessible to the community, along with inversion
tools for an easier interpretation of the data. A protoype instrument
for ChroMag is currently being assembled at HAO and is expected to
perform first measurements at the Boulder Mesa Lab in Summer 2012. We
present an overview of the ChroMag instrument and the current status
of the protoype.
Title: The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP)j
Authors: Kobayashi, K.; Tsuneta, S.; Trujillo Bueno, J.; Bando, T.;
Belluzzi, L.; Casini, R.; Carlsson, M.; Cirtain, J. W.; De Pontieu,
B.; Hara, H.; Ichimoto, K.; Ishikawa, R.; Kano, R.; Katsukawa, Y.;
Kim, T.; Kubo, M.; Manso Sainz, R.; Narukage, N.; Asensio Ramos,
A.; Robinson, B.; Sakao, T.; Shimizu, T.; Stepan, J.; Suematsu, Y.;
Watanabe, H.; West, E.; Winebarger, A. R.
Bibcode: 2011AGUFM.P14C..05K
Altcode:
We present an overview of the Chromospheric Lyman-Alpha
SpectroPolarimeter (CLASP) program. CLASP is a proposed sounding rocket
experiment currently under development as collaboration between Japan,
USA and Spain. The aim is to achieve the first measurement of magnetic
field in the upper chromosphere and transition region of the Sun
through the detection and measurement of Hanle effect polarization
of the Lyman alpha line. The Hanle effect (i.e. the magnetic field
induced modification of the linear polarization due to scattering
processes in spectral lines) is believed to be a powerful tool for
measuring the magnetic field in the upper chromosphere, as it is more
sensitive to weaker magnetic fields than the Zeeman effect, and also
sensitive to magnetic fields tangled at spatial scales too small to be
resolved. The Lyman-alpha (121.567 nm) line has been chosen because
it is a chromospheric/transition-region line, and because the Hanle
effect polarization of the Lyman-alpha line is predicted to be sensitive
to 10-250 Gauss, encompassing the range of interest. Hanle effect is
predicted to be observable as linear polarization or depolarization,
depending on the geometry, with a fractional polarization amplitude
varying between 0.1% and 1% depending on the strength and orientation of
the magnetic field. This quantification of the chromospheric magnetic
field requires a highly sensitive polarization measurement. The
CLASP instrument consists of a large aperture (287 mm) Cassegrain
telescope mated to a polarizing beamsplitter and a matched pair
of grating spectrographs. The polarizing beamsplitter consists
of a continuously rotating waveplate and a linear beamsplitter,
allowing simultaneous measurement of orthogonal polarizations and
in-flight self-calibration. Development of the instrument is underway,
and prototypes of all optical components have been tested using a
synchrotron beamline. The experiment is proposed for flight in 2014.
Title: Overview of Chromospheric Lyman-Alpha SpectroPolarimeter
(CLASP)
Authors: Narukage, Noriyuki; Tsuneta, Saku; Bando, Takamasa; Kano,
Ryouhei; Kubo, Masahito; Ishikawa, Ryoko; Hara, Hirohisa; Suematsu,
Yoshinori; Katsukawa, Yukio; Watanabe, Hiroko; Ichimoto, Kiyoshi;
Sakao, Taro; Shimizu, Toshifumi; Kobayashi, Ken; Robinson, Brian; Kim,
Tony; Winebarger, Amy; West, Edward; Cirtain, Jonathan; De Pontieu,
Bart; Casini, Roberto; Trujillo Bueno, Javier; Stepan, Jiri; Manso
Sainz, Rafael; Belluzzi, Luca; Asensio Ramos, Andres; Carlsson, Mats
Bibcode: 2011SPIE.8148E..0HN
Altcode: 2011SPIE.8148E..16N
The solar chromosphere is an important boundary, through which all of
the plasma, magnetic fields and energy in the corona and solar wind
are supplied. Since the Zeeman splitting is typically smaller than
the Doppler line broadening in the chromosphere and transition region,
it is not effective to explore weak magnetic fields. However, this is
not the case for the Hanle effect, when we have an instrument with
high polarization sensitivity (~ 0.1%). "Chromospheric Lyman- Alpha
SpectroPolarimeter (CLASP)" is the sounding rocket experiment to detect
linear polarization produced by the Hanle effect in Lyman-alpha line
(121.567 nm) and to make the first direct measurement of magnetic
fields in the upper chromosphere and lower transition region. To
achieve the high sensitivity of ~ 0.1% within a rocket flight (5
minutes) in Lyman-alpha line, which is easily absorbed by materials,
we design the optical system mainly with reflections. The CLASP
consists of a classical Cassegrain telescope, a polarimeter and a
spectrometer. The polarimeter consists of a rotating 1/2-wave plate
and two reflecting polarization analyzers. One of the analyzer also
works as a polarization beam splitter to give us two orthogonal linear
polarizations simultaneously. The CLASP is planned to be launched in
2014 summer.
Title: The Hanle Effect of the Hydrogen Lyα Line for Probing the
Magnetism of the Solar Transition Region
Authors: Trujillo Bueno, Javier; Štěpán, Jiří; Casini, Roberto
Bibcode: 2011ApJ...738L..11T
Altcode: 2011arXiv1107.4787T
We present some theoretical predictions concerning the amplitude and
magnetic sensitivity of the linear-polarization signals produced by
scattering processes in the hydrogen Lyα line of the solar transition
region. To this end, we have calculated the atomic-level polarization
(population imbalances and quantum coherences) induced by anisotropic
radiation pumping in semiempirical and hydrodynamical models of the
solar atmosphere, taking into account radiative transfer and the
Hanle effect caused by the presence of organized and random magnetic
fields. The line-center amplitudes of the emergent linear-polarization
signals are found to vary typically between 0.1% and 1%, depending
on the scattering geometry and the strength and orientation of the
magnetic field. The results shown here encourage the development of UV
polarimeters for sounding rockets and space telescopes with the aim
of opening up a diagnostic window for magnetic field measurements in
the upper chromosphere and transition region of the Sun.
Title: SDO/AIA Observations of Coronal Condensation Leading to
Prominence Formation
Authors: Liu, Wei; Berger, T.; Low, B. C.; Casini, R.
Bibcode: 2011SPD....42.2119L
Altcode: 2011BAAS..43S.2119L
Coronal condensation takes place when million degree coronal plasma
undergoes radiative cooling instability. Direct observation of coronal
condensation in prominences has been difficult in the past, but with the
launch of the Hinode/SOT and SDO/AIA instruments, numerous observations
of plasma condensing "out of nowhere" high up in quiescent prominences
have been captured. We present here one such event seen with SDO/AIA. On
25-Nov-2010, a prominence above the southwest limb is swept away by
a nearby eruption, and for next a few hours there is no visible 304
A material in the local corona. Then, a portion of the coronal loops
at the same location progressively sags and forms a local dip, where
the first sign of new, cool material appears, 7.5 hours after the
eruption. This is a clear indication of coronal condensation, and the
gradual sag of the loops is likely a result of increasing weight of
the condensed material that has been accumulated at the dip. Similar
condensation occurs nearby at a larger rate and leads to the formation
of a moderate-size prominence. The estimated prominence mass increases
linearly for about 7 hours at a rate of 2.6e10 grams/sec and reaches
approximately 6e14 grams. Simultaneously, the prominence drains through
vertical flows of approximately 32 km/s, bringing the mass back to the
chromosphere. We estimate the mass drain rate to be 2.7e10 grams/sec,
which, together with the estimated mass accumulation rate, implies a
coronal condensation rate of approximately 5.3e10 grams/sec. This study
can provide critical information about the coupling between condensation
energetics and MHD, prominence mass cycles, and coronal mass ejections
initiated by loss of anchoring prominence mass (e.g., Low 2001).
Title: The Visible Spectro-Polarimeter (ViSP) for the ATST: Science
Objectives and Design Concepts
Authors: Casini, Roberto
Bibcode: 2011SPD....42.0805C
Altcode: 2011BAAS..43S.0805C
(this presentation is for the special ATST session of the SPD meeting)
The ViSP will be the slit-based spectro-polarimeter for the
ATST. It is designed to be a wavelength versatile research instrument,
multi-line capable (up to three lines simultaneously) between
380 and 900 nm, and providing high spectral, spatial, and temporal
resolution, and large FOV, to satisfy the science needs of the solar
community. The design effort has emphasized the high throughput of the
instrument necessary for precision polarimetry science, and automated
configurability, in order to increase the scientific opportunities of
the instrument during daily operations. In this talk we present the
design characteristics of the instrument, its expected performance,
and an example of instrument configuration for a typical science case.
Title: Wavelength-diverse Polarization Modulators for Stokes
Polarimetry
Authors: de Wijn, A. G.; Tomczyk, S.; Casini, R.; Nelson, P. G.
Bibcode: 2011ASPC..437..413D
Altcode:
An increasing number of astronomical applications depend on the
measurement of polarized light. For example, our knowledge of solar
magnetism relies heavily on our ability to measure and interpret
polarization signatures introduced by magnetic field. Many new
instruments have consequently focused considerable attention
on polarimetry. For solar applications, spectro-polarimeters in
particular are often designed to observe the solar atmosphere in
multiple spectral lines simultaneously, thus requiring that the
polarization modulator employed is efficient at all wavelengths of
interest. We present designs of polarization modulators that exhibit
near-optimal modulation characteristics over broad spectral ranges. Our
design process employs a computer code to optimize the efficiency of
the modulator at specified wavelengths. We will present several examples
of modulator designs based on rotating stacks of Quartz waveplates and
ferroelectric liquid crystals (FLCs). An FLC-based modulator of this
design was recently deployed for the ProMag instrument at the Evans
Solar Facility of NSO/SP.
Title: A Sounding Rocket Experiment for Spectropolarimetric
Observations with the Lyα Line at 121.6 nm (CLASP)
Authors: Ishikawa, R.; Bando, T.; Fujimura, D.; Hara, H.; Kano,
R.; Kobiki, T.; Narukage, N.; Tsuneta, S.; Ueda, K.; Wantanabe,
H.; Kobayashi, K.; Trujillo Bueno, J.; Manso Sainz, R.; Stepan, J.;
de Pontieu, B.; Carlsson, M.; Casini, R.
Bibcode: 2011ASPC..437..287I
Altcode:
A team consisting of Japan, USA, Spain, and Norway is developing a
high-throughput Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP),
which is proposed to fly with a NASA sounding rocket in 2014. CLASP will
explore the magnetism of the upper solar chromosphere and transition
region via the Hanle effect of the Lyα line for the first
time. This experiment requires spectropolarimetric observations with
high polarimetric sensitivity (∼0.1%) and wavelength resolution
(0.1 Å). The final spatial resolution (slit width) is being discussed
taking into account the required high signal-to-noise ratio. We have
demonstrated the performance of the Lyα polarimeter by
extensively using the Ultraviolet Synchrotron ORbital Radiation Facility
(UVSOR) at the Institute for Molecular Sciences. In this contribution,
we report these measurements at UVSOR together with the current status
of the CLASP project.
Title: The Chromospheric Lyman Alpha SpectroPolarimeter (CLASP)
Authors: Kobayashi, K.; Tsuneta, S.; Trujillo Bueno, J.; Cirtain,
J. W.; Bando, T.; Kano, R.; Hara, H.; Fujimura, D.; Ueda, K.; Ishikawa,
R.; Watanabe, H.; Ichimoto, K.; Sakao, T.; de Pontieu, B.; Carlsson,
M.; Casini, R.
Bibcode: 2010AGUFMSH11B1632K
Altcode:
Magnetic fields in the solar chromosphere play a key role in the
energy transfer and dynamics of the solar atmosphere. Yet a direct
observation of the chromospheric magnetic field remains one of the
greatest challenges in solar physics. While some advances have been
made for observing the Zeeman effect in strong chromospheric lines,
the effect is small and difficult to detect outside sunspots. The
Hanle effect offers a promising alternative; it is sensitive to weaker
magnetic fields (e.g., 5-500 G for Ly-Alpha), and while its magnitude
saturates at stronger magnetic fields, the linear polarization signals
remain sensitive to the magnetic field orientation. The Hanle effect
is not only limited to off-limb observations. Because the chromosphere
is illuminated by an anisotropic radiation field, the Ly-Alpha line is
predicted to show linear polarization for on-disk, near-limb regions,
and magnetic field is predicted to cause a measurable depolarization. At
disk center, the Ly-Alpha radiation is predicted to be negligible
in the absence of magnetic field, and linearly polarized to an order
of 0.3% in the presence of an inclined magnetic field. The proposed
CLASP sounding rocket instrument is designed to detect 0.3% linear
polarization of the Ly-Alpha line at 1.5 arcsecond spatial resolution
(0.7’’ pixel size) and 10 pm spectral resolution. The instrument
consists of a 30 cm aperture Cassegrain telescope and a dual-beam
spectropolarimeter. The telescope employs a ``cold mirror’’ design
that uses multilayer coatings to reflect only the target wavelength
range into the spectropolarimeter. The polarization analyzer consists of
a rotating waveplate and a polarizing beamsplitter that comprises MgF2
plates placed at Brewster’s Angle. Each output beam of the polarizing
beamsplitter, representing two orthogonal linear polarizations, is
dispersed and focused using a separate spherical varied-line-space
grating, and imaged with a separate 512x512 CCD camera. Prototypes
of key optical components have been fabricated and tested. Instrument
design is being finalized, and the experiment will be proposed for a
2014 flight aboard a NASA sounding rocket.
Title: The polychromatic polarization modulator
Authors: de Wijn, Alfred G.; Tomczyk, Steven; Casini, Roberto; Nelson,
Peter G.
Bibcode: 2010SPIE.7735E..4AD
Altcode: 2010SPIE.7735E.143D
An increasing number of astronomical applications depend on the
measurement of polarized light. For example, our knowledge of solar
magnetism relies heavily on our ability to measure and interpret
polarization signatures introduced by magnetic field. Many new
instruments have consequently focused considerable attention on
polarimetry. For solar applications, spectro-polarimeters in particular
are often designed to observe the solar atmosphere in multiple spectral
lines simultaneously, thus requiring that the polarization modulator
employed is efficient at all wavelengths of interest. We present
designs of polarization modulators that exhibit near-optimal modulation
characteristics over broad spectral ranges. Our design process employs a
computer code to optimize the efficiency of the modulator at specified
wavelengths. We will present several examples of modulator designs
based on rotating stacks of Quartz waveplates and Ferroelectric Liquid
Crystals (FLCs). An FLC-based modulator of this design was recently
deployed for the ProMag instrument at the Evans Solar Facility of
NSO/SP. We show that this modulator behaves according to its design.
Title: The Visible Spectro-Polarimeter (ViSP) for the Advanced
Technology Solar Telescope
Authors: Nelson, Peter G.; Casini, Roberto; de Wijn, Alfred G.;
Knoelker, Michael
Bibcode: 2010SPIE.7735E..8CN
Altcode: 2010SPIE.7735E.271N
The Visible Spectro-Polarimeter (ViSP) is one of the first light
instruments for the Advanced Technology Solar Telescope (ATST). It is
an echelle spectrograph designed to measure three different regions
of the solar spectrum in three separate focal planes simultaneously
between 380 and 1600nm. It will use the polarimetric capabilities
of the ATST to measure the full Stokes parameters across the line
profiles. By measuring the polarization in magnetically sensitive
spectral lines the magnetic field vector as a function of height
in the solar atmosphere, along with the associated variation of
the thermodynamic properties can be obtained. The ViSP will have a
spatial resolution of 0.04 arc seconds over a 2 minute field of view
(at 600nm). The minimum resolving power for all the focal planes is
180,000. The spectrograph supports up to 5 diffraction gratings and
is fully automated to allow for rapid reconfiguration.
Title: NCAR COSMO K-Coronagraph and Chromospheric Magnetometer
Authors: Burkepile, Joan T.; Tomczyk, Steve; Nelson, Pete; de Wijn,
Alfred; Sewell, Scott; Casini, Roberto; Elmore, David; McIntosh,
Scott; Kolinski, Don; Summers, Rich
Bibcode: 2010shin.confE...3B
Altcode:
We discuss the status of the COronal Solar Magnetism Observatory
(COSMO), a proposed facility dedicated to studying coronal and
chromospheric magnetic fields and their role in driving solar
activity such as coronal mass ejections (CMEs). COSMO is comprised of
3 instruments: 1) a 1.5 m coronagraph dedicated to the study of coronal
magnetic fields; 2) a chromospheric and prominence magnetometer; and 3)
a K-coronagraph designed to study the formation of CMEs and the density
structure of the low corona. The National Center for Atmospheric
Research (NCAR) is fully funding the COSMO K-coronagraph which will
be deployed at the end of 2012. It will observe the white light solar
corona from 1.05 to 3 solar radii at 15 second time cadence in order to
the formation of coronal mass ejections (CMEs) and their interactions
with surrounding coronal structures and related activity (e.g. flares,
prominence eruptions and shock waves). The COSMO K-coronagraph will
replace the aging Mauna Loa Solar Observatory (MLSO) K-coronameter which
has been in operation since 1980. The High Altitude Observatory
(HAO) is funding the design and fabrication of the prototype for the
chromospheric magnetometer. This prototype will include the narrow-band
fully tunable Lyot filter capable of observing from the optical
into the near infrared that is required by the COSMO Chromospheric
Magnetometer. The prototype for the COSMO 1.5 m coronagraph is
the Coronal Multi-Channel Polarimeter (CoMP), designed and funded by
HAO and NCAR. Scientific results from this fully operational prototype
have been reported (e.g. Tomczyk et al. 2007). CoMP has recently been
deployed to MLSO for full time operations (see poster by Sitongia et
al.) The COSMO facility will be designed, built and operated by
the High Altitude Observatory of the National Center for Atmospheric
Research in collaboration with the University of Hawaii and the
University of Michigan. It will replace the current Mauna Loa Solar
Observatory which has been collecting observations of the corona,
chromosphere and photosphere since 1945. NCAR science is supported by
the National Science Foundation (NSF).
Title: Wavelength-diverse polarization modulators for Stokes
polarimetry
Authors: Tomczyk, Steven; Casini, Roberto; de Wijn, Alfred G.; Nelson,
Peter G.
Bibcode: 2010ApOpt..49.3580T
Altcode: 2010arXiv1006.3581T
Information about the three-dimensional structure of solar magnetic
fields is encoded in the polarized spectra of solar radiation by a host
of physical processes. To extract this information, solar spectra must
be obtained in a variety of magnetically sensitive spectral lines at
high spatial, spectral, and temporal resolution with high precision. The
need to observe many different spectral lines drives the development
of Stokes polarimeters with a high degree of wavelength diversity. We
present a new paradigm for the design of polarization modulators that
operate over a wide wavelength range with near optimal polarimetric
efficiency and are directly applicable to the next generation of
multi-line Stokes polarimeters. These modulators are not achromatic
in the usual sense because their polarimetric properties vary with
wavelength, but they do so in an optimal way. Thus we refer to
these modulators as polychromatic. We present here the theory behind
polychromatic modulators, illustrate the concept with design examples,
and present the performance properties of a prototype polychromatic
modulator.
Title: Scattering Polarization in the Fe I 630 nm Emission Lines at
the Extreme Limb of the Sun
Authors: Lites, B. W.; Casini, R.; Manso Sainz, R.; Jurčák, J.;
Ichimoto, K.; Ishikawa, R.; Okamoto, T. J.; Tsuneta, S.; Bellot
Rubio, L.
Bibcode: 2010ApJ...713..450L
Altcode:
Spectro-polarimetric observations with the Solar Optical Telescope
onboard Hinode reveal the emission spectrum of the Fe I 630 nm lines
at the solar limb. The emission shell extends for less than 1'' thereby
making it extremely difficult to detect from ground-based observatories
viewing the limb through the Earth's atmosphere. The linear polarization
signal is clearly due to scattering and it is predominantly oriented
in the radial direction. Using a comprehensive atomic model of
iron, we are able to interpret qualitatively the observed signals,
including the radial orientation of the linear polarization. The Hanle
effect causes the linear polarization of the Fe I 630 nm lines to be
sensitive to magnetic fields between ~0.1 G and ~40 G, and also to
be sensitive to the field's topology for stronger fields. The overall
degree of observed polarization can be reproduced by randomly oriented
horizontal magnetic fields of strength ≈2 G. The discovery of their
scattering polarization signals thus opens a new diagnostic opportunity
for these lines.
Title: Observations of Large-Scale Dynamic Bubbles in Prominences
Authors: de Toma, G.; Casini, R.; Berger, T. E.; Low, B. C.; de Wijn,
A. G.; Burkepile, J. T.; Balasubramaniam, K. S.
Bibcode: 2009ASPC..415..163D
Altcode:
Solar prominences are very dynamic objects, showing continuous motions
down to their smallest resolvable spatial and temporal scales. However,
as macroscopic magnetic structures, they are remarkably stable during
their quiescent phase. We present recent ground-based and Hinode
observations of large-scale bubble-like, dynamic sub-structures that
form within and rise through quiescent prominences without disrupting
them. We investigate the similarities and differences of the Hinode
and ground-based observations and discuss their implications for models
of prominences.
Title: Multi-Line Stokes Inversion for Prominence Magnetic-Field
Diagnostics
Authors: Casini, R.; López Ariste, A.; Paletou, F.; Léger, L.
Bibcode: 2009ApJ...703..114C
Altcode: 2009arXiv0906.2144C
We present test results on the simultaneous inversion of the Stokes
profiles of the He I lines at 587.6 nm (D3) and 1083.0 nm
in prominences (90° scattering). We created data sets of synthetic
Stokes profiles for the case of quiescent prominences (B < 200 G),
assuming a conservative value of 10-3 of the peak intensity
for the polarimetric sensitivity of the simulated observations. In
this work, we focus on the error analysis for the inference of the
magnetic field vector, under the usual assumption that the prominence
can be assimilated to a slab of finite optical thickness with uniform
magnetic and thermodynamic properties. We find that the simultaneous
inversion of the two lines significantly reduces the errors on the
inference of the magnetic field vector, with respect to the case of
single-line inversion. These results provide a solid justification for
current and future instrumental efforts with multi-line capabilities
for the observations of solar prominences and filaments.
Title: Polarimetric Diagnostics of Unresolved Chromospheric Magnetic
Fields
Authors: Casini, R.; Manso Sainz, R.; Low, B. C.
Bibcode: 2009ApJ...701L..43C
Altcode: 2008arXiv0811.0512C
For about a decade, spectropolarimetry of He I λ10830 has been applied
to the magnetic diagnostics of the solar chromosphere. This resonance
line is very versatile as it is visible both on disk and in off-limb
structures, and it has a good sensitivity to both the weak-field
Hanle effect and the strong-field Zeeman effect. Recent observations
of an active-region filament showed that the linear polarization was
dominated by the transverse Zeeman effect, with very little or no
hint of scattering polarization. This is surprising, since the He I
levels should be significantly polarized in a conventional scattering
scenario. To explain the observed level of atomic depolarization by
collisional or radiative processes, one must invoke plasma densities
larger by several orders of magnitude than currently known values
for prominences. We show that such depolarization can be explained
quite naturally by the presence of an unresolved, highly entangled
magnetic field, which averages to give the ordered field inferred
from spectropolarimetric data, over the typical temporal and spatial
scales of the observations. We present a modeling of the polarized He I
λ10830 in this scenario, and discuss its implications for the magnetic
diagnostics of prominences and spicules, and for the general study of
unresolved magnetic field distributions in the solar atmosphere.
Title: Magnetic field strength of active region filaments
Authors: Kuckein, C.; Centeno, R.; Martínez Pillet, V.; Casini, R.;
Manso Sainz, R.; Shimizu, T.
Bibcode: 2009A&A...501.1113K
Altcode: 2009arXiv0904.4876K
Aims: We study the vector magnetic field of a filament observed over a
compact active region neutral line.
Methods: Spectropolarimetric
data acquired with TIP-II (VTT, Tenerife, Spain) of the 10 830
Å spectral region provide full Stokes vectors that were analyzed
using three different methods: magnetograph analysis, Milne-Eddington
inversions, and PCA-based atomic polarization inversions.
Results:
The inferred magnetic field strengths in the filament are around 600-700
G by all these three methods. Longitudinal fields are found in the
range of 100-200 G whereas the transverse components become dominant,
with fields as high as 500-600 G. We find strong transverse fields
near the neutral line also at photospheric levels.
Conclusions:
Our analysis indicates that strong (higher than 500 G, but below kG)
transverse magnetic fields are present in active region filaments. This
corresponds to the highest field strengths reliably measured in these
structures. The profiles of the helium 10 830 Å lines observed in
this active region filament are dominated by the Zeeman effect.
Title: Rise of a Dark Bubble through a Quiescent Prominence
Authors: de Toma, G.; Casini, R.; Burkepile, J. T.; Low, B. C.
Bibcode: 2008ApJ...687L.123D
Altcode:
We report on a dynamical event observed in a quiescent prominence on
2007 November 8: a well-formed dark "bubble" with a bright core rose
vertically through the prominence without causing it to erupt. This
event was observed in Hα and He I 1083 nm with the instruments of
the Mauna Loa Solar Observatory. The dark bubble had a size of over
40'' and rose from the prominence base, at an average speed of ~12 km
s-1, forming a bright compression front as it traversed the
prominence. It finally assumed a "keyhole" shape before fading. The
bright core embedded in the dark bubble was observed to rise from the
solar limb, accelerating from ~12 to ~20 km s-1, leaving a
thin trail of material behind. Subsequent observations indicate that
this was not an exceptional event, but rather that similar disturbances
do occur occasionally in prominences without disrupting them. In this
Letter we present the November 8 observations, and propose a possible
interpretation of the physical mechanism behind these dynamic events.
Title: A new spectro-polarimeter for solar prominence and filament
magnetic field measurements
Authors: Elmore, David F.; Casini, Roberto; Card, Greg L.; Davis,
Marc; Lecinski, Alice; Lull, Ron; Nelson, Peter G.; Tomczyk, Steven
Bibcode: 2008SPIE.7014E..16E
Altcode: 2008SPIE.7014E..39E
We are constructing a spectro-Âpolarimeter using the 40-Âcm
coronagraph at the Evans Solar Facility of the National Solar
Observatory in Sunspot, NM for the purpose of measuring the vector
magnetic field in prominences and filaments. The Prominence Magnetometer
(ProMag) is comprised of a polarization modulation package and a
spectrograph. The modulation optics are located at the prime focus
of the coronagraph along with calibration optics and a beamsplitter
that creates two beams of orthogonal Stokes states. The spectrograph
resides at the coude focus of the coronagraph. The polarizations of the
two chromospheric lines of neutral helium, at 587.6 nm and 1083.0 nm,
are to be observed simultaneously. We present details of the design
of the spectro-Âpolarimeter.
Title: An Instrument to Measure Coronal Emission Line Polarization
Authors: Tomczyk, S.; Card, G. L.; Darnell, T.; Elmore, D. F.; Lull,
R.; Nelson, P. G.; Streander, K. V.; Burkepile, J.; Casini, R.; Judge,
P. G.
Bibcode: 2008SoPh..247..411T
Altcode: 2008SoPh..tmp....3T
We have constructed an instrument to measure the polarization of light
emitted by the solar corona in order to constrain the strength and
orientation of coronal magnetic fields. We call this instrument the
Coronal Multichannel Polarimeter (CoMP). The CoMP is integrated into
the Coronal One Shot coronagraph at Sacramento Peak Observatory and
employs a combination birefringent filter and polarimeter to form
images in two wavelengths simultaneously over a 2.8R⊙
field of view. The CoMP measures the complete polarization state at
the 1074.7 and 1079.8 Fe XIII coronal emission lines, and the 1083.0
nm He I chromospheric line. In this paper we present design drivers
for the instrument, provide a detailed description of the instrument,
describe the calibration methodology, and present some sample data
along with estimates of the uncertainty of the measured magnetic field.
Title: Absorption Line Profiles for Differentially Rotating Stellar
Models
Authors: MacGregor, Keith B.; Casini, R.; Flanagan, W.; Jackson, S.;
Skumanich, A.
Bibcode: 2007AAS...21110310M
Altcode: 2007BAAS...39..921M
We have computed absorption line profiles for rapidly rotating 2
solar-mass stars, using structural models of chemically homogeneous,
uniformly and differentially rotating stars of this mass to specify
photospheric physical conditions. The models were constructed
with a recent reformulation of the self-consistent field method, an
iterative procedure yielding two-dimensional, axisymmetric, equilibrium
configurations that are consistent solutions to the stellar structure
equations and Poisson's equation for the gravitational potential,
for a specified conservative angular velocity distribution. The
simulated line profiles display a variety of shapes, with morphological
characteristics that depend on the properties of the surface rotational
velocity distribution, the angle of inclination of the line of sight
relative to the rotation axis, and on rotational modifications to the
structure of the star, including the difference between the surface
temperatures of the poles and the equator and deviations of the stellar
shape from sphericity. Some features of the Doppler-broadened profiles
reflect details of the distribution of the projected rotation speed
over the visible surface of the star, and may thus provide the means
for distinguishing between uniform and differential rotation of the
stellar photosphere. For example, differentially rotating models can
exhibit absorption profiles with flat or even convex-upward bottoms, as
opposed to the rounded, concave-upward profiles that are indicative of
uniform rotation. We present preliminary results from an ongoing effort
to use simulated line profiles in conjunction with the techniques of
Principal Component Analysis to infer stellar rotational properties
from observations.
Title: The COronal Solar Magnetism Observatory
Authors: Burkepile, J.; Tomczyk, S.; Lin, H.; Zurbuchen, T.; Judge,
P.; Casini, R.
Bibcode: 2007AGUFMSH53A1070B
Altcode:
Measurements of coronal and chromospheric magnetic fields are
arguably the most important observables required for advances in
our understanding of the emergence of magnetic flux into the solar
atmosphere and the processes responsible for the production of solar
activity, coronal heating and coronal dynamics. The COronal Solar
Magnetism Observatory (COSMO) is a proposed ground-based suite of
instruments designed for routine study of coronal and chromospheric
magnetic fields and their environment. The facility consists of 3
instruments: 1) a meter-class aperture coronal magnetometer devoted
to obtaining the highest quality polarimetric data of forbidden lines
of Fe XIII 1074.7 and 1079.8 nm.; 2) a chromosphere and prominence
magnetometer devoted primarily to measurements of lines of helium
(D3, 1083 nm) and perhaps Halpha, that will provide full disk vector
magnetic field observations; 3) a white-light polarized-brightness (pB)
coronagraph that will observe down to 1.05 solar radii at very high
time cadence (15 seconds) at high signal-to-noise. This new facility
will be operated by the High Altitude Observatory of the National
Center for Atmospheric Research (HAO/NCAR) in collaboration with the
University of Hawaii and the University of Michigan. COSMO will enhance
the value of existing and new observatories on the ground (SOLIS, ATST,
and FASR) and in space (SOHO, TRACE, GOES, SOLAR-B, STEREO, SDO) by
providing unique and crucial observations of the global coronal and
chromospheric magnetic field and its evolution.
Title: COSMO: The Coronal Solar Magnetism Observatory
Authors: Burkepile, Joan; Tomczyk, S.; Lin, H.; Zurbuchen, T.;
Casini, R.
Bibcode: 2007AAS...210.2519B
Altcode: 2007BAAS...39..134B
The COronal Solar Magnetism Observatory (COSMO) is a proposed
ground-based suite of instruments designed to study coronal magnetic
fields and their environment using the polarization of forbidden
emission lines in the infrared. Supporting instruments focus on
prominence and chromospheric magnetometry and imaging and the evolution
of the electron scattered corona (K-corona). COSMO will address
one of the least understood problems in Sun-Earth connections: the
coronal magnetic field using breakthrough techonologies that have been
successfully demonstrated with proof-of-concept instrumentation. We will
present information about COSMO and science results from the prototype
instruments, including the detection of Alfven waves in the corona.
Title: A suite of community tools for spectro-polarimetric analysis .
Authors: Lites, B.; Casini, R.; Garcia, J.; Socas-Navarro, H.
Bibcode: 2007MmSAI..78..148L
Altcode:
The National Center for Atmospheric Research (NCAR) has undertaken a
3-year initiative to develop the Community Spectro-polarimetric Analysis
Center (CSAC). The goal of this effort is to provide the community
with standardized tools for extracting the solar magnetic field
vector and related atmospheric parameters from spectro-polarimetric
observations. The emphasis will be to develop portable, efficient, and
well-documented procedures for analysis of data from the many new and
upcoming observational facilities, both ground- and space-based. The
initial focus of CSAC will be the development of robust methods
for inversion of Stokes spectral data, starting with a standard
Milne-Eddington inversion that has been the workhorse for analysis of
data from e.g. the Advanced Stokes Polarimeter. Upon completion of that
code, the program will move to more sophisticated methods that embrace
more realistic and detailed models of the solar atmosphere. Very
fast methods for inversion (neural networks or pattern recognition
techniques, for example) are also candidates. Finally, the CSAC is
intended to eventually provide standardized methods for resolution of
the 180-degree field azimuth ambiguity, and for visualization of the
resulting magnetic field vector maps. CSAC is formulated as a community
effort, and as such will receive guidance and input from the community.
Title: Quiet-Sun Magnetism Seen with a Mn Line: Km-Sized Magnetic
Structures
Authors: López Ariste, A.; Ramírez Vélez, J. C.; Tomczyk, S.;
Casini, R.; Semel, M.
Bibcode: 2006ASPC..358...54L
Altcode:
We observed Manganese lines with large hyperfine structure and used them
to disentangle strength from flux in the measurement of photospheric
magnetic fields. In observations of the quiet sun with both ASP and
THEMIS, we measure flux from the amplitude of Stokes V in Fe lines, and
the Mn line, crudely analyzed, places the field strength either above
or below a threshold of 600 G, which is set by the atomic structure. In
the case of THEMIS observations, having determined magnetic flux and
field strength for every pixel, one can estimate filling factors of
the magnetic field and determine characteristic scales. Structures at
scales smaller than 50 km are revealed.
Title: Inference of the Magnetic Field in Spicules from
Spectro-Polarimetry of He I D3
Authors: López Ariste, A.; Casini, R.
Bibcode: 2006ASPC..358..443L
Altcode:
Spectro-polarimetric observations of the He I D3 line in
spicules over the solar limb have been analyzed, and the magnetic field
direction determined. Up to a 90° ambiguity the field appears to be
aligned with the visible spicular structures. The anomalous broadening
of the observed line prevents the retrieval of other information at
this stage. The only further constraint we were able to place was on
the field strength: fields stronger than 40 G must be statistically
present in our observations, but not much stronger than that.
Title: The Effect of Turbulent Electric Fields on the Scattering
Polarization of Hydrogen Lines
Authors: Casini, R.; Manso Sainz, R.
Bibcode: 2006ASPC..358..429C
Altcode:
We reviewed the polarization properties of hydrogen lines in the
presence of electric and magnetic fields. We first considered the
case of completely depolarized hydrogen atoms. Under this assumption,
the hydrogen lines manifest complex polarization signatures due to
the combined Stark and Zeeman effect tep{c0 CL93}. One can derive
convenient analytic expressions for the 1st and 2nd-order moments
of the Stokes profile, which nicely summarize the fundamental
properties of hydrogen polarization for both cases of deterministic
and micro-turbulent electric and magnetic fields tep{c0 CL94,c0
CL95,c0 Ca97}. In particular, it is demonstrated the ``additivity''
of the Stark and Zeeman effects on such integral properties of the
line polarization emitted by a gas of depolarized hydrogen atoms. We
then generalized the problem to include the possibility of atomic
polarization induced in the hydrogen atoms by anisotropic excitation
mechanisms (e.g., in chromospheric and coronal plasmas). The complexity
of the problem makes it intractable by analytic means, and one must
resort to numerical tools. The results show that, in the presence of
atomic polarization, the ``additivity'' of the electric and magnetic
effects is lost, and an intricated interplay of the two effects occurs
tep{c0 Ca05}. In particular, we considered two hydrogen lines of
diagnostic relevance-Lyα and Hα-formed in a magnetized plasma, and
demonstrated the modifications of the scattering polarization that are
induced by the additional presence of turbulent, electric microfields
of various strengths (typically, the normal field strength of the
Holtsmark theory, for various electron densities of the plasma). We
showed that the additional presence of these electric microfields can
significantly enhance the amount of net circular polarization (NCP) of
the Hα line for a given magnetic strength, which can be produced by the
so-called alignment-to-orientation transfer mechanism tep[e.g.,][]{c0
La82,c0 Ke84,c0 LL04}, even if the electric microfield distribution is
perfectly isotropic tep[see Fig. ref{c0 NCP};][]{c0 CM06}. We argued
that this mechanism could explain the large levels of NCP that have
recently been detected in several quiescent prominences tep{c0 LA05},
and discussed the implications of this study for the diagnostics of
magnetic fields in the solar atmosphere using hydrogen lines.
Title: The Coronal Solar Magnetic Observatory (COSMO)
Authors: Tomczyk, S.; Zurbuchen, T.; Kuhn, J.; Lin, H.; Judge, P.;
Burkepile, J.; Casini, R.
Bibcode: 2006AGUFMSM12A..03T
Altcode:
Measurement of magnetic fields in the corona is arguably the most
important observable required for advances in our understanding of
the emergence of magnetic flux into the solar atmosphere and the
processes responsible for the production of solar activity, coronal
heating and coronal dynamics. We discuss plans for the COronal Solar
Magnetic Observatory (COSMO), which is a proposed ground-based suite
of instruments designed to routinely study coronal magnetic fields and
their environment. The core of the facility includes a meter-class
coronagraph with instrumentation dedicated to measuring the coronal
magnetic field using the polarization of forbidden emission lines in
the infrared. Supporting instruments focus on prominence magnetometry
and the dynamics of the electron-scattered corona (K-corona) and
chromosphere. In addition to acquiring routine synoptic observations
of coronal magnetic fields, the COSMO project will include the
establishment of a community-based user advisory panel to accept
observational campaigns submitted by members of the scientific community
at-large. COSMO will enhance the value of existing and new observatories
on the ground (SOLIS, ATST, FASR) and in space (SOHO, TRACE, GOES,
Solar-B, STEREO and SDO) by providing unique and crucial observations
of the global coronal magnetic field and its evolution and dynamics.
Title: Solar Polarization 4
Authors: Casini, R.; Lites, B. W.
Bibcode: 2006ASPC..358.....C
Altcode:
No abstract at ADS
Title: Spectral Lines for Polarization Measurements of the Coronal
Magnetic Field. IV. Stokes Signals in Current-carrying Fields
Authors: Judge, P. G.; Low, B. C.; Casini, R.
Bibcode: 2006ApJ...651.1229J
Altcode:
We present the first theoretical, forward calculations of the Stokes
profiles of several magnetic dipole (``M1'') coronal emission lines
produced in current-carrying magnetic structures. An idealized coronal
model of Low, Fong, and Fan is used, which describes a spherically
symmetric, hydrostatic background atmosphere, isothermal at a
coronal temperature of 1.6×106 K. Embedded is a global,
axisymmetric magnetic field that is everywhere potential except
at a quiescent prominence, consisting of an infinitesimally thin,
equatorial current sheet whose weight is supported by the outward
discrete Lorentz force in the sheet. This model contains a physically
nontrivial, localized magnetic structure, although the atmospheric
plasma is thermally of the simplest stratification possible. The
calculated M1 coronal lines show clear and distinct signatures of
the presence and magnitude of this localized magnetic structure,
in both linear and circular polarizations, even though the thermal
structure is almost homogeneous. The morphology of maps of linear
polarization is particularly sensitive to the existence and strength
of the current sheets, as field lines wrap around them according to
the Biot-Savart law, and the linear polarization responds to different
projections of field line directions onto local radius vectors. Of the
M1 lines studied, those of Fe XIII (1074.7 nm) and Si X (1430.1 nm)
are especially promising because of their relatively strong linear
polarization. These forward calculations provide a basis for optimism
that emission-line measurements may reveal the presence and nature of
current systems in the corona, and provide motivation for developing
instruments capable of routinely measuring polarized light in forbidden
coronal lines.
Title: Star tracker scan mode capability for the New Horizons mission
Authors: Haley, David; Strikwerda, Thomas; Ailinger, Kevin; Casini,
Roberto; Landi, Andrea; Bettarini, Rossano
Bibcode: 2006AcAau..59..956H
Altcode:
The New Horizons mission to Pluto and the Kuiper Belt is scheduled
for launch in early 2006. The overall mission design requires a star
tracker that operates autonomously both in a standard “staring”
mode and in a star scanning mode. With the support of APL and the New
Horizons Program, Galileo Avionica S.p.A. has redesigned the software
for their A-STR star tracker to use time-delayed integration techniques
(TDI) to provide autonomous spacecraft attitude estimates at 10 Hz
and at spacecraft spin rates up to 10 RPM. This paper will present
the design considerations and operating modes for the modified A-STR
tracker, as well as expected accuracy performance.
Title: Scattering polarization of hydrogen lines in the presence of
turbulent electric fields
Authors: Casini, R.; Manso Sainz, R.
Bibcode: 2006JPhB...39.3241C
Altcode: 2005astro.ph.11148C
We study the broadband polarization of hydrogen lines produced by
scattering of radiation, in the presence of isotropic electric
fields. In this paper, we focus on two distinct problems: (a)
the possibility of detecting the presence of turbulent electric
fields by polarimetric methods and (b) the influence of such fields
on the polarization due to a macroscopic, deterministic magnetic
field. We found that isotropic electric fields decrease the degree
of linear polarization in the scattered radiation, with respect to
the zero-field case. On the other hand, a distribution of isotropic
electric fields superimposed onto a deterministic magnetic field can
increase significantly the degree of magnetic-induced, net circular
polarization. This phenomenon has important implications for the
diagnostics of magnetic fields in plasmas using hydrogen lines,
because of the ubiquitous presence of the Holtsmark microscopic
electric field from neighbouring ions. In particular, previous solar
magnetographic studies of the Balmer lines of hydrogen may need to be
revised because they neglected the effect of turbulent electric fields
on the polarization signals. In this work, we give explicit results
for the Lyman α and Balmer α lines.
Title: Quiet sun magnetic field diagnostics with a Mn line
Authors: López Ariste, A.; Tomczyk, S.; Casini, R.
Bibcode: 2006A&A...454..663L
Altcode:
Context: .The Mn line at 553 nm shows strong spectral features in both
intensity and polarization profiles due to the hyperfine structure of
the atom. These features, their presence or absence, are known to be
dependent on the magnetic regime to which the Mn atom is subject.
Aims: .Our objective is to disentangle strong kilo-Gauss (kG)
fields from relatively weak hecto-Gauss (hG) fields in the quiet sun,
and compute relative filling factors on the resolution element.
Methods: .We observed the 553 nm Mn line in a quiet sun area with the
Advanced Stokes Polarimeter, and we introduce an in-line ratio between
different spectral features. Filling factors can be retrieved from
the measurement of this ratio and the total longitudinal flux.
Results: .In the photospheric network the kG dominate the magnetic flux,
although out of the higher concentration areas the hG fields dominate in
surface coverage. For the internetwork (granules and lanes confounded)
the hG are dominant both in surface and total flux.
Title: High Resolution Spectropolarimetry of Penumbral Formation
with IBIS
Authors: Reardon, Kevin; Casini, R.; Cavallini, F.; Tomczyk, S.;
Rouppe van der Voort, L.; Van Noort, M.; Woeger, F.; Socas Navarro,
H.; IBIS Team
Bibcode: 2006SPD....37.3503R
Altcode: 2006BAAS...38..260R
We present the results of first spectropolarimetric observations
made with the Interferometric Bidimensional Spectrometer (IBIS)
at the NSO/Dunn Solar Telescope. The use of narrowband imaging and
post-facto reconstruction techniques allows for observations close
to the diffraction limit of the vector magnetic field. We will show
observations of the the formation of an individual penumbral filament
around a small pore. We measure the magnetic field and velocity field
of the forming penumbral filament. The spectropolarimetric mode of
IBIS will be available to the community in the fall of 2006.
Title: The scientific case for spectropolarimetry from space:
a novel diagnostic window on cosmic magnetic fields
Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Casini, R.;
Martínez Pillet, V.
Bibcode: 2005ESASP.588..203T
Altcode: 2005tssc.conf..203T
No abstract at ADS
Title: Magnetic Fields Measured in Spicules.
Authors: López Ariste, A.; Casini, R.
Bibcode: 2005ESASP.596E..21L
Altcode: 2005ccmf.confE..21L
No abstract at ADS
Title: The Scientific Case for Quantum Spectropolarimetry from Space
Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Casini, R.;
Martínez Pillet, V.
Bibcode: 2005ESASP.596E...4T
Altcode: 2005ccmf.confE...4T
No abstract at ADS
Title: Inference of the magnetic field in spicules from
spectropolarimetry of He I D3
Authors: López Ariste, A.; Casini, R.
Bibcode: 2005A&A...436..325L
Altcode:
We present observations of spicules in the He I D3 line with full-Stokes
spectropolarimetry, which were done with the Advanced Stokes Polarimeter
at the Dunn Solar Telescope of the Sacramento Peak Observatory. The line
profiles appear to be significantly broadened by non-thermal processes,
which we interpret using the hypothesis of a distribution of velocities
inside the spicule. The possibility of inferring the magnetic field
in those conditions is tested on synthetic data, and the results are
generalized to the interpretation of the observed data. We conclude
that the magnetic field is aligned with the visible structure of the
spicule, with strengths above 30 G in some cases (for heights between
3000 and 5000 km above the photosphere).
Title: Line Formation Theory for the Multiterm Atom with Hyperfine
Structure in a Magnetic Field
Authors: Casini, R.; Manso Sainz, R.
Bibcode: 2005ApJ...624.1025C
Altcode:
Within the framework of the quantum theory of polarized line
formation, in the limit of complete frequency redistribution and of
the collisionless regime, we derive explicit formulae describing the
statistical equilibrium and the radiative emission of a multiterm
atom with hyperfine structure, in the presence of an external
magnetic field. The formulae we obtained for the radiative rates
of the statistical equilibrium equations and for the radiative
coefficients of the transfer equation for polarized radiation can be
applied to investigate the formation of spectral lines for which both
fine-structure and hyperfine-structure effects are important (e.g.,
the D1 and D2 lines of Na I in the solar atmosphere).
Title: Principal Component Analysis of the He I D3
Polarization Profiles from Solar Prominences
Authors: Casini, R.; Bevilacqua, R.; López Ariste, A.
Bibcode: 2005ApJ...622.1265C
Altcode:
In this paper we discuss some general aspects of Stokes profile
inversion in prominences using principal component analysis
(PCA). First, we address the problem of departure of the formation of
He I D3 from the optically thin approximation, dealing in
a heuristic way with the inversion of the two visible components of
the line, which are differently affected by radiative transfer. This
modified inversion does not alter recently published results on
the magnetic structure of quiescent prominences, in particular
confirming the presence of magnetic fields significantly larger than
average in limited regions. Second, we investigate the effect of
line-of-sight integration of the polarization signals from different
magnetic configurations, to determine whether PCA inversion could
interpret an observed signal in terms of a single magnetic model
with unrealistically large field strength. Our results show that this
possibility is not statistically significant, and in addition the few
models that are wrongly inverted show very peculiar geometries that
are not found in our inversion of real data. This result also supports
the reality of stronger than average fields in prominences. Finally,
we further investigated the importance of full Stokes inversion for
a correct diagnostic of magnetic fields in prominences. We show how
the exclusion of Stokes V induces the appearance of a 90° ambiguity
in the position angle of the magnetic field in the plane of the sky
(in addition to the well-known 180° ambiguity). Inclusion of Stokes V
proves to be important at all field strengths, even though Stokes Q and
U should in theory be sufficient to retrieve the complete vector field
information for field strengths in the Hanle depolarization regime. We
also show how the inversion noise determined by the discreteness of
the PCA database may be an additional source of the 90° ambiguity,
even in the presence of Stokes V, therefore imposing a lower bound on
the model density of the database.
Title: Full Stokes Spectropolarimetry of Hα in Prominences
Authors: López Ariste, A.; Casini, R.; Paletou, F.; Tomczyk, S.;
Lites, B. W.; Semel, M.; Landi Degl'Innocenti, E.; Trujillo Bueno,
J.; Balasubramaniam, K. S.
Bibcode: 2005ApJ...621L.145L
Altcode:
We report on spectropolarimetric observations of Hα in prominences
made with the Télescope Héliographique pour l'Etude du Magnétisme et
des Instabilités Solaires and the High Altitude Observatory/Advanced
Stokes Polarimeter. Stokes Q and U show the expected profile shape from
resonance scattering polarization and the Hanle effect. In contrast,
most of the time, Stokes V does not show the antisymmetric profile shape
typical of the Zeeman effect but a profile that indicates the presence
of strong atomic orientation in the hydrogen levels, to an extent that
cannot be explained by invoking the alignment-to-orientation transfer
mechanism induced by the prominence magnetic field. We found that the
largest signal amplitudes of Stokes V (comparable to that of Stokes
Q and U) could be produced by a process of selective absorption of
circularly polarized radiation from the photosphere, which requires
that the prominence be in the vicinity of an active region. Although
recent observations of active region filaments indicate such a
selective absorption mechanism as a plausible explanation of the
anomalous signals observed, the particular set of conditions that
must be met suggest that a different explanation may be required
to explain the almost ubiquitous symmetric V signal observed in Hα
prominences. Therefore, we speculate that an alternative mechanism
inducing strong atomic orientation at the observed level could be due
to the presence of electric fields inducing an electric Hanle effect
on Hα. Although we are still working toward a careful modeling of
this effect, including both electric and magnetic fields, we present
some preliminary considerations that seem to support this possibility.
Title: Initial Magnetic Field Measurements from The Coronal
Multi-Channel Polarimeter
Authors: Tomczyk, S.; Card, G. L.; Darnell, T.; Elmore, D. F.; Casini,
R.; Judge, P. G.; Burkepile, J.
Bibcode: 2004AAS...204.2002T
Altcode: 2004BAAS...36..686T
We have constrcted a filter-based polarimeter optimized for the
measurement of magnetic fileds in the solar corona. The instrument will
observe the coronal emission lines of FeXIII at 1074.7 and 1079.8 nm as
well as the chromospheric HeI emission line at 1083 nm. The instrument
consists of a polarimeter allowing complete Stokes I,Q,U,V measurement
followed by a Lyot birefringent filter with dual passbands of 0.14
nm width. Both the polarimeter and filter employ liquid crystals for
rapid electro-optical tuning. This instrument was deployed to the
20-cm One Shot coronagraph at NSO's Sacramento Peak Observatory in
January of 2004. Measurement of the longitudinal Zeeman effect
provides information on the strength of the line-of-sight component
of the magnetic field while the observation of resonance scattering
will constrain the plane-of-sky field direction. Precise measurement
of plasma velocity is also possible. Such measurements are critical
for addressing many outstanding problems in coronal physics. The
operation and performance of the instrument will be described. We
will also describe the methodology for the coronal magnetic field
measurement. Initial measurements taken with the instrument will be
presented. This research was supported by the NSF.
Title: A Coronal Multi Channel Polarimeter For Magnetic Field
Measurements
Authors: Darnell, T.; Tomczyk, S.; Card, G.; Judge, P. G.; Casini,
R.; Burkepile, J.
Bibcode: 2003AGUFMSH42B0505D
Altcode:
The Coronal Multi-channel Polarimeter (CoMP) is a filter-based
polarimeter designed to provide quantitative measurements of magnetic
fields in the solar corona. It will measure the Stokes parameters
at the 1074.7 and 1079.8 FeXIII coronal emission lines (1.67 x 106
degrees K), and the 1083.0 nm HeI chromospheric line. The CoMP is
based on a four stage birefringent filter and is designed such that
the corona is imaged in two wavelengths simultaneously. The strength of
the line-of-sight component of the coronal magnetic field is inferred
from the measured amplitude of the Stokes V profile and an estimate of
the plane-of-sky direction is made from the Stokes U/Q ratio. Further,
inference of line-of-sight velocities can be made from Stokes I (red and
blue wing) amplitudes. Finally, it may be possible to obtain a coronal
density diagnostic capability from the ratio of the 1074.7/1079.8
amplitudes. This poster will present the latest test results as well
as any preliminary data that have been obtained.
Title: Magnetic maps of prominences
Authors: Casini, R.; Lopez Ariste, A.; Tomczyk, S.; Lites, B.
Bibcode: 2003AGUFMSH42D..05C
Altcode:
We present the first magnetic maps of a prominence obtained by applying
our PCA inversion approach to prominence spectropolarimetric data
in the He I D3 line. Our results indicate the presence of organized
structures in the prominence plasma embedded in magnetic field that are
significantly larger than average (50 G and higher). We reaffirm the
need for a Hanle-based diagnostics of prominence magnetism using full
Stokes spectropolarimetry, and the importance of improved, multi-line
observations, ideally involving both He I D3 and 10830.
Title: Magnetic Maps of Prominences from Full Stokes Analysis of
the He I D3 Line
Authors: Casini, R.; López Ariste, A.; Tomczyk, S.; Lites, B. W.
Bibcode: 2003ApJ...598L..67C
Altcode:
We present the first magnetic maps of a prominence, derived from
inversion of spectropolarimetric data in He I D3 using the principal
component analysis of all four Stokes profiles. This prominence,
along with several others, was observed in 2002 May using the Dunn
Solar Telescope of the National Solar Observatory/Sacramento Peak
Observatory, equipped with the High Altitude Observatory Advanced
Stokes Polarimeter. The use of an unocculted instrument allowed us to
map the prominence magnetic fields down to the chromospheric limb. Our
analysis indicates that the average magnetic field in prominences
is mostly horizontal and varies between 10 and 20 G, thus confirming
previous findings. However, our maps show that fields significantly
stronger than average, even as large as 60 or 70 G, can often be found
in clearly organized plasma structures of the prominence.
Title: Star tracker scan mode capability for the New Horizons mission
Authors: Haley, Davis; Strikwerda, Thomas; Ailinger, Kevin; Casini,
Roberto; Landi, Andrea; Bettarini, Rossano
Bibcode: 2003ESASP.542..299H
Altcode: 2003lcpm.conf..299H
The New Horizons mission to Pluto and the Kuiper Belt is scheduled for
launch in early 2006. Overall mission design requires a star tracker
that operates autonomously both in a standard "staring" mode and in
a star scanning mode. With the support of APL and the New Horizons
Program, Galileo Avionica S.p.A. has redesigned the software for their
A-STR star tracker to use time-delayed integration techniques (TDI)
to provide autonomous spacecraft attitude estimates at 10 Hz and at
spacecraft spin rates up to 10 RPM. This paper will present the design
considerations and operating modes for the modified A-STR tracker,
as well as expected accuracy performance.
Title: The effect of atomic polarization on early estimates of
prominence magnetic field strengths
Authors: Brown, A.; López Ariste, A.; Casini, R.
Bibcode: 2003SoPh..215..295B
Altcode:
In this paper we present our results of the application of the
magnetograph formula to synthetic Stokes V profiles in prominences. We
investigate both the Zeeman and atomic-polarization signatures within
the V profile and question why previous attempts to determine magnetic
field strength, on average, were correct, even if the magnetograph
formula does not apply in general.
Title: Hyperfine Structure as a Diagnostic Tool of Solar Magnetic
Fields
Authors: López Ariste, A.; Tomczyk, S.; Casini, R.
Bibcode: 2003ASPC..307..115L
Altcode:
No abstract at ADS
Title: PCA Inversion of Stokes Profiles in Solar Prominences
Authors: Casini, R.; López Ariste, A.
Bibcode: 2003ASPC..307..109C
Altcode:
No abstract at ADS
Title: Improved Estimate of the Magnetic Field in a Prominence
Authors: López Ariste, A.; Casini, R.
Bibcode: 2003ApJ...582L..51L
Altcode:
We present new results on the inversion of spectropolarimetric data
of the He I D3 line in a prominence. These data were taken with the
High Altitude Observatory Stokes II polarimeter on 1980 August 5. Full
Stokes profiles in I, Q, U, and V were recorded at 13 locations of a
prominence at the northeast limb. This prominence erupted 3 hr later,
giving rise to the day of year 218 Solar Maximum Mission coronal
transient. The data were originally analyzed in a paper by Querfeld
et al. Here we analyze the data using the new inversion algorithm
proposed by López Ariste & Casini based on pattern recognition
techniques. This method employs full Stokes profiles, and in tests
on synthetic data, it proved to be much more precise than previous
diagnostic procedures. When applied to the Stokes data of the prominence
under study, it gives magnetic field strengths at least 2 times larger
than previous estimates.
Title: Hyperfine Structure as a Diagnostic of Solar Magnetic Fields
Authors: López Ariste, A.; Tomczyk, S.; Casini, R.
Bibcode: 2002ApJ...580..519L
Altcode:
We propose the use of the Zeeman effect of the hyperfine structure
(HFS) as a diagnostic of solar photospheric magnetic fields. The HFS
induces unique signatures in the polarized spectra of particular atoms,
which can be used to directly get information on the magnetic field
strength. To explore the effects of HFS, we adopt a numerical model of
line formation and radiative transfer of polarized light in a magnetized
Milne-Eddington atmosphere. We concentrate our studies on several lines
of Mn I, which show particularly striking HFS signatures in the solar
atlas. For these lines, anomalous Stokes profiles are produced for
fields in the range 0-1000 G. The presence of these unusual profiles
for weak magnetic fields constitutes a novel and potentially powerful
diagnostic of the strength of solar magnetic fields in the quiet
photosphere and plages.
Title: Magnetic Fields in Prominences: Inversion Techniques for
Spectropolarimetric Data of the He I D3 Line
Authors: López Ariste, A.; Casini, R.
Bibcode: 2002ApJ...575..529L
Altcode:
We propose the use of principal component analysis (PCA) to invert
spectropolarimetric data from prominences. Observation of the
full Stokes profiles in prominences is very important for a deeper
understanding of magnetic-field topology in these solar structures,
and for the testing of theoretical models. The line formation problem,
however, is complicated by the special conditions of prominences:
anisotropy of light, low magnetic intensities, temperature and density
ranges, etc. We created a code to solve this problem in the limit of
optically thin plasma and of a collisionless regime, and use it in
combination with PCA techniques to invert synthetic data. The results
show that inversion is feasible.
Title: On the Atomic Polarization of the Ground Level of Na I
Authors: Casini, Roberto; Landi Degl'Innocenti, Egidio; Landolfi,
Marco; Trujillo Bueno, Javier
Bibcode: 2002ApJ...573..864C
Altcode: 2002astro.ph..4341C
In a recent Letter, we showed the remarkable result that the atomic
alignment of the levels P1/2 and S1/2 of the
D1 line of Na I is practically destroyed in the presence of
magnetic fields sensibly larger than 10 G, irrespective of the field
direction. In this paper, we analytically demonstrate that this property
is a consequence of the decoupling of the electronic and nuclear angular
momenta J and I in the excited state P3/2, which is achieved
when the Zeeman splitting from the local magnetic field becomes much
larger than the typical hyperfine separation for that level.
Title: New Polarization Diagnostics for the Solar Atmosphere
Authors: Casini, R.; López Ariste, A.; Tomczyk, S.; Lites, B.
Bibcode: 2002AAS...200.3403C
Altcode: 2002BAAS...34..690C
We present relatively new diagnostics of ``weak" magnetic fields in the
solar atmosphere. The first diagnostic is suggested by recent advances
in the inversion of Stokes profiles of lines formed by resonance
scattering in the weakly magnetized plasma of prominences (Hanle
effect and level-crossing; 0 to 100 G). Use of pattern recognition
techniques (PCA) in this field has marked a sensible progress with
respect to previous diagnostic procedures. The second diagnostic is
the modelling of hyperfine structured (HFS) lines that can be observed
in the spectrum of the quiet photosphere. This allows to investigate
relatively weak photospheric fields (200 G to 1000 G), in which regime
the HFS induces peculiar signatures in the Stokes profiles, including
the appearance of subcomponents and net circular polarization. The third
diagnostic is suggested by interesting polarization properties of the
Na I D1 line formed by resonance scattering: the atomic polarization
in the upper level of D1, which is responsible of a characteristic
antisymmetric (i.e., V-like) signature in the core of Stokes Q, is
rapidly suppressed for B > 10 G, irrespective of the magnetic field
direction. A common denominator of these three diagnostics is their
sensitivity to the actual strength of the magnetic field, instead
of the magnetic flux within the resolution element. Another common
aspect is that all require (or would profit from) high polarization
sensitivity, which will be one of the strengths of ATST. For the
diagnostics of prominence magnetic fields, the possibility of multiline
spectropolarimetry could be decisive. Simultaneous observations of
He I D3 (5876A) and 10830A, or of He I D3 and the Na I D lines (all
within a 20A spectral range!), would increase the inversion accuracy
of PCA. The high spatial resolution capabilities of ATST would be
advantageous mostly to diagnose weak photospheric fields, already at
the present time. Because of the complexity of radiative transfer in
complicated structures like prominences, high spatial resolution in
these structures is not the highest priority. However, we hope that
when ATST will become operative, this complicated problem will have
been attacked succesfully.
Title: A Classical Model for the Damped, Magnetic Dipole Oscillator
Authors: Casini, Roberto; Lin, Haosheng
Bibcode: 2002ApJ...571..540C
Altcode:
We propose a simple classical model for the damped, magnetic dipole
oscillator based on a circuit analogy. The solution for the dynamical
equation of the associated magnetic moment is found to be similar
in form to the well-known solution for the damped, electric dipole
oscillator, but with the magnetic vector of the incident electromagnetic
wave as the forcing field, instead of the electric vector. This
model has been successfully applied to a classical derivation of the
polarization properties of the forbidden (M1) coronal emission lines.
Title: The Hanle Effect of the Two-Level Atom in the Weak-Field
Approximation
Authors: Casini, R.
Bibcode: 2002ApJ...568.1056C
Altcode:
We apply the weak-field approximation of the line profiles,
ωB<<Δω (ωB being the Larmor frequency
and Δω the width of the line profile), adopting a second-order
Taylor expansion in the Larmor frequency, to the polarized emission
coefficients of the resonance transition in a two-level atom with values
of the total angular momentum Ju and Jl, for the
upper and lower levels, respectively. Using methods of Racah's algebra,
we then derive rather compact algebraic expressions for the Stokes
parameters of the radiation scattered locally in this transition. The
advantage of using a second-order Taylor expansion of the emission
coefficients is that the contributions of the Hanle effect and the
Zeeman effect to the Stokes vector of the scattered radiation are
easily identified and their respective roles in determining the
polarization properties of the line better understood. Under the
further assumption of unpolarized lower level, these expressions can
be applied to derive explicit diagnostic formulae for polarized,
resonance-scattering radiation, in terms of the relative geometry
of the observer with respect to the solar magnetic field at the
scattering center. The typical case of a spinless, two-level atom
with Ju=1 and Jl=0 is explicitly worked out,
and the corresponding diagnostic formulae are used to clarify some
interesting properties of the Hanle effect. Finally, we compare these
results, derived from the quantum-mechanical theory of line formation,
with a recently proposed, classical formulation of the Hanle effect.
Title: The Physical Origin of the Scattering Polarization of the Na
I D Lines in the Presence of Weak Magnetic Fields
Authors: Trujillo Bueno, Javier; Casini, Roberto; Landolfi, Marco;
Landi Degl'Innocenti, Egidio
Bibcode: 2002ApJ...566L..53T
Altcode: 2002astro.ph..1389T
We demonstrate that the atomic alignment of the hyperfine-structure
components of the ground-level S1/2 of Na I and of the
upper-level P1/2 of the D1 line are practically
negligible for magnetic strengths B>10 G and virtually zero
for B>~100 G. This occurs independently of the magnetic field
inclination on the stellar surface (also, in particular, for vertical
fields). Consequently, the characteristic antisymmetric linear
polarization signature of the scattered light in the D1
line is practically suppressed in the presence of magnetic fields
larger than 10 G, regardless of their inclination. Remarkably, we
find that the scattering polarization amplitude of the D2
line increases steadily with the magnetic strength, for vertical
fields above 10 G, while the contribution of the alignment to the
polarization of the D1 line rapidly decreases. Therefore,
we suggest that spectropolarimetric observations of the ``quiet''
solar chromosphere showing significant linear polarization peaks in
both D1 and D2 cannot be interpreted in terms
of one-component magnetic field models, implying that the magnetic
structuring of the solar chromosphere could be substantially more
complex than previously thought.
Title: Coronal Magnetometry: A Feasibility Study
Authors: Judge, P. G.; Casini, R.; Tomczyk, S.; Edwards, D. P.;
Francis, E.
Bibcode: 2001STIN...0227999J
Altcode:
Measurements of components of the vector magnetic field in the
solar corona can potentially yield information critical to our
understanding of coronal structure, dynamics and heating. In this
report we re-examine various techniques for such measurements,
in particular those that can be applied outside of active regions,
to investigate issues critical to the development of a new 'coronal
magnetometer,' and to lay down some foundations upon which a suitable
instrument may be developed for synoptic observations. The well-known
forbidden coronal emission lines of magnetic dipole (M1) character
appear to have the highest potential to address outstanding problems in
coronal physics, especially those related to the storage and release
of magnetic free energy. Measurements of the full Stokes vector of
M1 lines can constrain both the line-of-sight (LOS) field strength,
through the longitudinal Zeeman effect seen in Stokes V profiles, and
the direction of the vector field projected onto the plane-of-the-sky
(POS), through the analysis of resonance scattering-induced linear
polarization seen in Stokes Q and U, in the so-called 'strong field'
regime of the Hanl effect.
Title: A Synthesis Code for Forbidden Coronal Lines
Authors: Judge, P. G.; Casini, R.
Bibcode: 2001ASPC..236..503J
Altcode: 2001aspt.conf..503J
No abstract at ADS
Title: A Classical Theory of Coronal Emission Line Polarization
Authors: Lin, Haosheng; Casini, Roberto
Bibcode: 2000ApJ...542..528L
Altcode:
We present a classical theory of formation for polarized, magnetic
dipole emission lines in the magnetized solar corona. Because of the
small Einstein A-coefficients of forbidden lines and the expected
magnetic field strengths in the corona, coherences between different
magnetic substates can be neglected, so the observed Stokes vector
for these lines is the result of the incoherent superposition of
the Stokes vectors emitted in the de-excitation of the individual
magnetic substates of the transition's upper level. Using classical
electrodynamics and a weak-field expansion formalism, we could derive
the main polarization properties of the transition J=1 to J=0, in the
collisionless regime. In particular, we derived the correct amount
of atomic alignment in the upper level, induced by the anisotropic,
unpolarized illumination from the photosphere, and the dependence of
Stokes Q and U linear polarization on the magnetic field direction
in the plane of the sky. The influence of atomic alignment on the V
profile is also correctly reproduced. This work provides a classical
interpretation of the physical process that generates atomic alignment
in the radiating ion and how the associated Van Vleck effect in
resonance-scattering linear polarization and the alignment contribution
to Zeeman effect circular polarization come about.
Title: Erratum: Spectral Lines for Polarization Measurements of the
Coronal Magnetic Field. II. Consistent Treatment of the Stokes Vector
for Magnetic-Dipole Transitions
Authors: Casini, R.; Judge, P. G.
Bibcode: 2000ApJ...533..574C
Altcode:
In the paper ``Spectral Lines for Polarization Measurements
of the Coronal Magnetic Field. II. Consistent Treatment of the
Stokes Vector for Magnetic-Dipole Transitions,'' by R. Casini and
P. G. Judge (ApJ, 522, 524 [1999]), several typographical errors
were introduced during the production process. The corrections
are as follows: 1. In the second entry of the fourth panel of
Table 1, sqrt(3)/2 cosϑ should read sqrt(3/2) cosϑ 2. The
left-hand sides of equations (23a) and (23b) should be as in
the left-hand sides of equations (22a) and (22b). 3. In equations
(24c) and (24e), ρK'0(αJ) should read
ρK'0K'(α'J')
4. In equations (24e) and (24f),
JK''0(ωα'J,αJ')
should read
JK''0(ωα'J',αJ)
5. The very first sentence in the legend of Figure 5 should be
deleted. The Press sincerely apologizes for these errors. A last
typographical error, which instead is the complete responsibility of
the authors, is the absence of a minus sign in front of the right-hand
sides of equations (43a) and (43b).
Title: Spectral Lines for Polarization Measurements of the Coronal
Magnetic Field. II. Consistent Treatment of the Stokes Vector
forMagnetic-Dipole Transitions
Authors: Casini, R.; Judge, P. G.
Bibcode: 1999ApJ...522..524C
Altcode:
We present a compact, self-consistent formulation for the description
of polarized radiation from magnetic-dipole transitions occurring
in the magnetized solar corona. This work differs from earlier
treatments by Sahal-Bréchot and House in the 1970s, in that the
radiative emission coefficients for the four Stokes parameters, I,
Q, U, and V, are treated to first order in a Taylor expansion of the
line profile in terms of the Larmor frequency of the coronal magnetic
field. In so doing, the influence on the scattered radiation of both
atomic polarization, induced through anisotropic irradiation, and
the Zeeman effect is accounted for in a consistent way. It is found
that the well-known magnetograph formula, relating the V profile to
the frequency derivative of the I profile, must be corrected in the
presence of atomic alignment produced by anisotropic irradiation. This
correction is smallest for lines where collisions and cascades dominate
over excitation by anisotropic radiation, but it systematically
increases with height above the solar limb (up to a theoretical
maximum of 100%, in the collisionless regime and in the limit of
vanishing longitudinal magnetic field). Although the correction to
the magnetograph formula must be calculated separately for each line
as a function of heliocentric distance, it is likely to be small for
some lines of practical interest, along lines of sight close to the
solar limb.
Title: The Second-Order Moments of Pressure-broadened Hydrogen Lines
in the Quasi-static Approximation
Authors: Casini, Roberto
Bibcode: 1998ApJ...498..479C
Altcode:
We provide an approximate formula for the calculation of second-order
moments of pressure-broadened hydrogen lines in the quasi-static
approximation. Our derivation is based on the results of previous
investigations of the algebraic second-order moments of polarized
hydrogen lines in the presence of Stark broadening mechanisms. The
approximation involved consists in considering a limited spectral range
for the estimate of the second-order moment of the line profile. The
problem of the formal divergence of the second-order moments of
pressure-broadened hydrogen lines because of the infinite contribution
from the wings is so avoided. The approximation we present seems to
be robust enough for setting up a very direct diagnostics of charged
perturber density in low-density plasmas, like solar prominences,
based on the analysis of hydrogen line widths, if the conditions
for a quasi-static treatment of pressure broadening are sufficiently
well verified.
Title: Erratum: Application of the Second-Order Moments of Polarized
Hydrogen Lines to the Investigation of Pressure Broadening and the
Motional Stark Effect
Authors: Casini, Roberto
Bibcode: 1998ApJ...492..855C
Altcode:
In the paper ``Application of the Second-Order Moments of
Polarized Hydrogen Lines to the Investigation of Pressure
Broadening and the Motional Stark Effect'' by Roberto Casini
(ApJ, 487, 967 [1997]),
the argument leading to equation (A5) in the Appendix has a
flaw. Nonetheless, the result expressed by this equation is still
true, so the results presented in the paper are not affected by
the error. In this paper, the author followed D. Mihalas &
B. Mihalas (Foundations of Radiation Hydrodynamics [New York: Oxford
Univ. Press] [1984]) to establish the transformation law for the line
profile, φ(ω), between two frames of reference in relative motion,
φ'(ω')=(ω'/ω)3φ(ω)=γ3(1-βμ)3φ(ω)
, (1)where, with the notation of the paper, ω'=γ(1-βμ)ω
,γ=(1-β2)-1/2(β≡v/c, μ≡cos ϑ)
. According to Mihalas & Mihalas (1984), this transformation
law holds when the profile φ(ω) [and φ'(ω')] has the
dimensions of radiation intensity. In his paper, instead, the
author assumed that the profile φ(ω) was normalized, having the
dimensions of ω-1. So equation (1) does not represent
the correct transformation law for the normalized profile. If equation (1) is integrated over frequency, in fact, one finds
φ'(ω')dω'=γ3(1-βμ)3
φ(ω)(dω'/dω)dω=γ4(1-βμ)4
φ(ω)dω , so the transformation law between
normalized profiles is (φ'(ω'))/(
φ'(ω')dω')=1/γ(1-βμ) φ(ω)/(
φ(ω)dω) . (2)The above equation simply restates the condition
φ'(ω')dω' = φ(ω)dω between normalized profiles. Following
the notation of the paper, equations (A4) and (A5) should then read
<ωq>λ= φ'(ω'
λ)(ω'-ω¯)qdω'
(A4)[the profile φ'(ω' λ) now is normalized], and dωφ(ω
λ)(ω-ω¯)q= dω'φ'(ω'
λ)[ω(ω')-ω¯]q=
dω'φ'(ω'
λ)[(ω')/γ(1-βμ)-ω¯]q=1/(γq(1-βμ)q)
dω'φ'(ω'
λ){ω'-ω+[1-γ(1-βμ)]ω¯}q≡1/(γq(1-βμ)q)
Σn=0q
(q/n)ω¯n[1-γ(1-βμ)]n<ωq-n>λ
. (A5)
Title: Application of the Second-Order Moments of Polarized Hydrogen
Lines to the Investigation of Pressure Broadening and the Motional
Stark Effect
Authors: Casini, Roberto
Bibcode: 1997ApJ...487..967C
Altcode:
We present direct applications of the previously investigated
algebraic second-order moments of polarized hydrogen lines to the
study of pressure broadening (by charged perturbers) and of the
motional Stark effect. These problems are of relevant interest for the
diagnostics of electric and magnetic fields in solar plasmas. Pressure
broadening is investigated under the simple assumption that the charged
perturbers produce an isotropic electric field following the Holtsmark
distribution. The corresponding line width turns out to be a simple
function of the transition levels. In the investigation of the motional
Stark effect, it is assumed that the hydrogen atoms follow an isotropic,
Maxwellian velocity distribution. It is found that the effect of the
motional electric fields on the dispersion of the Stokes profiles
is analogous to that of an effective magnetic field, B*
= χB, where χ depends only on the transition levels and the plasma
temperature, plus an additional line-dependent broadening mechanism
that affects the intensity profile only.
Title: Theoretical polarization profiles of optically-thick hydrogen
lines from slabs in the presence of electric and magnetic fields
Authors: Casini, R.; Landi Degl'Innocenti, E.
Bibcode: 1997A&AS..122..149C
Altcode:
The theory of formation of hydrogen lines in the presence of stationary
electric and magnetic fields is applied to the calculation of the
emerging Stokes profiles from a slab of hydrogen plasma, for different
optical thicknesses of the slab. The calculations are performed assuming
different analytical dependences of the source function on the optical
depth. Typical results for hydrogen lines of interest in solar plasmas
investigation are then shown.
Title: (Erratum) LTE radiative transfert for polarized hydrogen
lines in the weak-field regime.
Authors: Casini, R.; Landi Degl'Innocenti, E.
Bibcode: 1996A&A...313.1027C
Altcode:
Erratum to Astron. Astrophys. 308, 335-344 (1996).
Title: LTE radiative transfer for polarized hydrogen lines in the
weak-field regime.
Authors: Casini, R.; Landi Degl'Innocenti, E.
Bibcode: 1996A&A...308..335C
Altcode:
In this paper we investigate the radiative-transfer problem for
polarized hydrogen lines in the regime of weak electric and magnetic
fields, and under the hypothesis of LTE. A standard perturbation method
is applied which reduces the vector radiative-transfer equation to
a set of four de-coupled ODEs for each order of approximation. Our
derivation enables us to use previous results for the first- and
second-order moments of the polarization profiles of hydrogen lines in
the presence of electric and magnetic fields, also accounting for the
fine structure contribution. We then get to a generalization of the
weak-field solution for the purely magnetic case, which had already
been obtained in the literature under the same hypotheses and through
the same perturbation approach.
Title: On the linear-polarization modulation of hydrogen lines.
Authors: Casini, R.
Bibcode: 1996A&A...307..653C
Altcode:
In this paper we further develop the concept of modulation of the
linear-polarization signals of hydrogen lines, which was defined
in a previous work. After discussing some general properties of the
modulation, we consider the application to two problems of particular
concern in solar physics, namely, the distinction between the cases
of parallel and perpendicular electric and magnetic fields, and the
definition of a Stark-sensitivity parameter for hydrogen lines.
Title: The first and second order moments of the polarization profiles
of hydrogen lines
Authors: Casini, R.; Landi Degl'Innocenti, E.
Bibcode: 1996SoPh..164...91C
Altcode:
The main properties of the first- and second-order moments of polarized
hydrogen lines, forming in the presence of stationary electric and
magnetic fields, are reviewed. The analytical results presented
here apply directly to the case of optically-thin emission lines
in the LTE regime. Some applications of such results to electric-
and magnetic-field diagnostics in (solar) plasmas are then briefly
considered.
Title: Calculated profiles of H I lines of interest for solar plasma
electric field measurements
Authors: Casini, Roberto; Foukal, Peter
Bibcode: 1996SoPh..163...65C
Altcode:
We present calculated Stark-polarized line profiles for a number of
H I lines observed in the visible and infrared emission spectrum of
solar prominences and other limb activity. For use in measurements
of possible electric fields in these structures, we also calculate
curves giving the difference in line width between the 1/2 (I ± Q)
profiles as a function of electric-field intensity. Our calculations
take into account magnetic fields in these structures, and incorporate
typical observed values of Doppler broadening. These calculations
explicitly consider the H I fine structure neglected in previous
work, and thus are more accurate in the range of low to intermediate
electric-field intensity likely to be encountered in solar plasmas
(E < 103 V cm−1). Our results enable us to
compare behavior when E and B are parallel, or perpendicular. We draw
particular attention to the high electric-field sensitivity of the
transitions between high levels such as 12-8 and 15-9 in H I, observed
in prominences at wavelengths around 11μ. Their sensitivity is roughly
an order of magnitude larger than that of the high Paschen-series
lines used in solar plasma electric field studies so far.
Title: Coefficients for calculating the second-order moments of the
polarization profiles of hydrogen lines.
Authors: Casini, R.
Bibcode: 1995A&AS..114..363C
Altcode:
In this paper we provide extensive tables of the coefficients that
are needed in the calculation of the second-order moments of the
polarization profiles of hydrogen lines. We cover all the transitions
up to the level n=50, which is enough for many astrophysical
applications. We also provide formulae which allow the calculation
of the line and oscillator strengths and of the Einstein coefficients
for the tabulated transitions.
Title: Properties of the second-order moments of the polarization
profiles of hydrogen lines.
Authors: Casini, R.; Landi Degl'Innocenti, E.
Bibcode: 1995A&A...300..309C
Altcode:
In this paper we give the expressions for the second-order moments of
the polarization profiles, for any hydrogen line which is formed in the
presence of external electric and magnetic fields. These quantities
are directly related to the dispersions of the polarization profiles
and are useful whenever the centers-of-gravity method cannot be
applied, as in the case of the linear Stark effect or, more generally,
when investigating the linear-polarization profiles. An analytical
definition of the modulation of the polarization signals is given in
order to provide an unambiguous way to estimate the sensitivity of a
line to the electric and magnetic fields. Then, relevant properties of
the modulations are examined in typical regimes of the external fields.
Title: VizieR Online Data Catalog: Polarization profiles of H lines
(Casini 1995)
Authors: Casini, R.
Bibcode: 1995yCat..41140363C
Altcode:
In this paper we provide extensive tables of the coefficients that
are needed in the calculation of the second-order moments of the
polarization profiles of hydrogen lines. We cover all the transitions
up to the level n=50, which is enough for many astrophysical
applications. We also provide formulae which allow the calculation
of the line and oscillator strengths and of the Einstein coefficients
for the tabulated transitions. (1 data file).
Title: Properties of the first-order moments of the polarization
profiles of hydrogen lines.
Authors: Casini, R.; Landi Degl'Innocenti, E.
Bibcode: 1994A&A...291..668C
Altcode:
In this article, we investigate some noteworthy properties of the
first-order moments of the polarization profiles of hydrogen lines in
the presence of external electric and magnetic fields. These properties
are useful in testing the applicability of the centers-of-gravity
method for the estimate of magnetic fields, whenever electric fields
are also present. A criticism is also raised about the effective
Lande factor in hydrogen lines as previously calculated by different
authors. In addition, we achieve a better insight into the problem of
the numerical precision of the software package which has been developed
for the calculation of the polarization properties of hydrogen lines,
a problem already approached in a previous paper.
Title: (Erratum) The polarized spectrum of hydrogen in the presence
of electric and magnetic fields
Authors: Casini, R.; Landi Degl'Innocenti, E.
Bibcode: 1994A&A...287..692C
Altcode:
Erratum to Astron. Astrophys. 276, 289-302 (1993)
Title: The polarized spectrum of hydrogen in the presence of electric
and magnetic fields
Authors: Casini, R.; Landi Degl'Innocenti, E.
Bibcode: 1993A&A...276..289C
Altcode:
The polarization properties of a beam of radiation interacting with a
hydrogen atom subject to simultaneous stationary electric and magnetic
fields are investigated, assuming no constraints on the direction of
the two fields. The problem of determining the energy eigenstates is
solved within the theory of Rayleigh-Schroedinger for the stationary
perturbations (the contributions of the fine and hyperfine structure
of the energy spectrum are also accounted for). Then the polarized
transition rates (for absorption, spontaneous emission and stimulated
emission) are evaluated according to the methods of non-relativistic
quantum electrodynamics, adopting the density matrix formalism which
allows one to deal with partially polarized states of the atomic and
the radiation field systems. Typical results are then shown.
Title: New concepts on SDS: a double beam telescope
Authors: Casini, R.; Greco, V.; Molesini, G.; Quercioli, F.; Reconditi,
M.; Righini, A.
Bibcode: 1993MmSAI..64..255C
Altcode:
No abstract at ADS