keil

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Author name code: keil
ADS astronomy entries on 2022-09-14
=author:"Keil, S.L." OR =author:"Keil, Stephen L." OR =author:"Keil, Stephen" OR =author:"Keil, Steve"

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Title: The Daniel K. Inouye Solar Telescope - Observatory Overview
Authors: Rimmele, Thomas R.; Warner, Mark; Keil, Stephen L.; Goode,
Philip R.; Knölker, Michael; Kuhn, Jeffrey R.; Rosner, Robert R.;
McMullin, Joseph P.; Casini, Roberto; Lin, Haosheng; Wöger, Friedrich;
von der Lühe, Oskar; Tritschler, Alexandra; Davey, Alisdair; de Wijn,
Alfred; Elmore, David F.; Fehlmann, André; Harrington, David M.;
Jaeggli, Sarah A.; Rast, Mark P.; Schad, Thomas A.; Schmidt, Wolfgang;
Mathioudakis, Mihalis; Mickey, Donald L.; Anan, Tetsu; Beck, Christian;
Marshall, Heather K.; Jeffers, Paul F.; Oschmann, Jacobus M.; Beard,
Andrew; Berst, David C.; Cowan, Bruce A.; Craig, Simon C.; Cross,
Eric; Cummings, Bryan K.; Donnelly, Colleen; de Vanssay, Jean-Benoit;
Eigenbrot, Arthur D.; Ferayorni, Andrew; Foster, Christopher; Galapon,
Chriselle Ann; Gedrites, Christopher; Gonzales, Kerry; Goodrich, Bret
D.; Gregory, Brian S.; Guzman, Stephanie S.; Guzzo, Stephen; Hegwer,
Steve; Hubbard, Robert P.; Hubbard, John R.; Johansson, Erik M.;
Johnson, Luke C.; Liang, Chen; Liang, Mary; McQuillen, Isaac; Mayer,
Christopher; Newman, Karl; Onodera, Brialyn; Phelps, LeEllen; Puentes,
Myles M.; Richards, Christopher; Rimmele, Lukas M.; Sekulic, Predrag;
Shimko, Stephan R.; Simison, Brett E.; Smith, Brett; Starman, Erik;
Sueoka, Stacey R.; Summers, Richard T.; Szabo, Aimee; Szabo, Louis;
Wampler, Stephen B.; Williams, Timothy R.; White, Charles
2020SoPh..295..172R Altcode:
We present an overview of the National Science Foundation's Daniel
K. Inouye Solar Telescope (DKIST), its instruments, and support
facilities. The 4 m aperture DKIST provides the highest-resolution
observations of the Sun ever achieved. The large aperture of
DKIST combined with state-of-the-art instrumentation provide the
sensitivity to measure the vector magnetic field in the chromosphere
and in the faint corona, i.e. for the first time with DKIST we will
be able to measure and study the most important free-energy source
in the outer solar atmosphere - the coronal magnetic field. Over its
operational lifetime DKIST will advance our knowledge of fundamental
astronomical processes, including highly dynamic solar eruptions
that are at the source of space-weather events that impact our
technological society. Design and construction of DKIST took over two
decades. DKIST implements a fast (f/2), off-axis Gregorian optical
design. The maximum available field-of-view is 5 arcmin. A complex
thermal-control system was implemented in order to remove at prime
focus the majority of the 13 kW collected by the primary mirror and
to keep optical surfaces and structures at ambient temperature, thus
avoiding self-induced local seeing. A high-order adaptive-optics
system with 1600 actuators corrects atmospheric seeing enabling
diffraction limited imaging and spectroscopy. Five instruments, four
of which are polarimeters, provide powerful diagnostic capability
over a broad wavelength range covering the visible, near-infrared,
and mid-infrared spectrum. New polarization-calibration strategies
were developed to achieve the stringent polarization accuracy
requirement of 5×10−4. 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.

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Title: The Advanced Technology Solar Telescope Construction Status
Report
Authors: McMullin, Joseph P.; Rimmele, T. R.; Warner, M.; Berger,
T.; Keil, S. L.
2013SPD....4440001M Altcode:
The Advanced Technology Solar Telescope (ATST) will provide observing
capabilities in the visible through infrared wavelengths with
unprecedented resolution and sensitivity. Designed to study solar
magnetism that controls the solar wind, flares, CMEs and variability in
the Sun's output, the ATST will be capable of detecting and spatially
resolving the fundamental astrophysical processes at their intrinsic
scales throughout the solar atmosphere. The 4-m class facility is
currently under construction in Maui, HI on the Haleakala Observatories
site with a scheduled completion of July 2019. Since the start of
site construction in December of 2012, significant progress has been
made toward the development of the observatory buildings (excavation,
foundations, working towards the steel erection). In addition, off-site,
the major subsystems of the telescope have been contracted, designs are
complete and fabrication is underway. We review the science drivers,
design details, technical challenges, and provide a construction status
update on the subsystems and their integration.

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Title: Solar Cycle Variability and Surface Differential Rotation
from Ca II K-line Time Series Data
Authors: Scargle, Jeffrey D.; Keil, Stephen L.; Worden, Simon P.
2013ApJ...771...33S Altcode: 2013arXiv1303.6303S
Analysis of over 36 yr of time series data from the NSO/AFRL/Sac Peak
K-line monitoring program elucidates 5 components of the variation of
the 7 measured chromospheric parameters: (a) the solar cycle (period
~ 11 yr), (b) quasi-periodic variations (periods ~ 100 days), (c) a
broadband stochastic process (wide range of periods), (d) rotational
modulation, and (e) random observational errors, independent of
(a)-(d). Correlation and power spectrum analyses elucidate periodic
and aperiodic variation of these parameters. Time-frequency analysis
illuminates periodic and quasi-periodic signals, details of frequency
modulation due to differential rotation, and in particular elucidates
the rather complex harmonic structure (a) and (b) at timescales in
the range ~0.1-10 yr. These results using only full-disk data suggest
that similar analyses will be useful for detecting and characterizing
differential rotation in stars from stellar light curves such as
those being produced by NASA's Kepler observatory. Component (c)
consists of variations over a range of timescales, in the manner
of a 1/f random process with a power-law slope index that varies
in a systematic way. A time-dependent Wilson-Bappu effect appears
to be present in the solar cycle variations (a), but not in the
more rapid variations of the stochastic process (c). Component (d)
characterizes differential rotation of the active regions. Component
(e) is of course not characteristic of solar variability, but the fact
that the observational errors are quite small greatly facilitates
the analysis of the other components. The data analyzed in this
paper can be found at the National Solar Observatory Web site <A
href="http://nsosp.nso.edu/cak_mon/">http://nsosp.nso.edu/cak_mon/</A>,
or by file transfer protocol at <A
href="ftp://ftp.nso.edu/idl/cak.parameters">ftp://ftp.nso.edu/idl/cak.parameters</A>.

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Title: Solar Differential Rotation in Calcium II K Line Spectra
Supported with Spectroheliogram Analysis
Authors: Behm, Tyler; Keil, S. L.
2013SPD....44...05B Altcode:
Two recent papers report on measuring differential rotation in data that
views the Sun as a star. Unlike using tracers at different latitudes
to measure the differential rotation, disk-integrated light averages
over many latitudes and can only work if the features both exist at a
dominate latitude that changes with the solar cycle and they persist
long enough to affect the measured rotation rate. Bertello, Pevtsov,
and Pietarila (2012, ApJ 761, pg 11) use disk-integrated Ca II K-line
data from the SOLIS/ISS instrument to show that a change in rotation
rate is clearly visible at the beginning of the current solar cycle
in the disk-integrated K-line. Scargle, Keil, and Worden (2013, ApJ in
press, arXiv:1303.6303) use the Sacramento Peak K-line series to look at
the last current and previous three cycles with fairly strong evidence
that the differential rotation is visible in cycle 22, but much harder
to see in cycles 21 and 23. In order to understand the differences in
the three cycles we report on solar differential rotation measurements
in both the Sacramento Peak disk-integrated, Ca II K spectral time
series (1977-2012) and full-disk, Ca II K spectroheliogram time series
(1977-2002) observed at the Evans Solar Facility. The former data set
is the same as used by Scargle et al (2013) and averages about 2-3
measurements per week. For the disk-integrated spectra, we use two
interpolation schemes to fill in missing days (regression and singular
value decomposition with proxy data sets) and use two methods (power
spectra and autocorrelation) to find the rotation rates. We find a clear
signature of solar differential rotation for solar cycle 21 and 22 and
a partial signature for cycle 23. We test this result by measuring
differential rotation using the Ca II K spectroheliograms using
phase analysis between longitudinal bands. We have also explored the
image features that lead to changes in the disk-integrated spectrum's
signal-to-noise. The data analyzed in this presentation can be found at
the National Solar Observatory web site http://nsosp.nso.edu/cak_mon/ ,
or by file transfer protocol at ftp://ftp.nso.edu/idl/cak.parameters and
ftp://diglib.nso.edu/Evans_spectroheliograms/.Abstract (2,250 Maximum
Characters): Two recent papers report on measuring differential rotation
in data that views the Sun as a star. Unlike using tracers at different
latitudes to measure the differential rotation, disk-integrated light
averages over many latitudes and can only work if the features both
exist at a dominate latitude that changes with the solar cycle and they
persist long enough to affect the measured rotation rate. Bertello,
Pevtsov, and Pietarila (2012, ApJ 761, pg 11) use disk-integrated Ca
II K-line data from the SOLIS/ISS instrument to show that a change
in rotation rate is clearly visible at the beginning of the current
solar cycle in the disk-integrated K-line. Scargle, Keil, and Worden
(2013, ApJ in press, arXiv:1303.6303) use the Sacramento Peak K-line
series to look at the last current and previous three cycles with fairly
strong evidence that the differential rotation is visible in cycle 22,
but much harder to see in cycles 21 and 23. In order to understand the
differences in the three cycles we report on solar differential rotation
measurements in both the Sacramento Peak disk-integrated, Ca II K
spectral time series (1977-2012) and full-disk, Ca II K spectroheliogram
time series (1977-2002) observed at the Evans Solar Facility. The former
data set is the same as used by Scargle et al (2013) and averages about
2-3 measurements per week. For the disk-integrated spectra, we use two
interpolation schemes to fill in missing days (regression and singular
value decomposition with proxy data sets) and use two methods (power
spectra and autocorrelation) to find the rotation rates. We find a clear
signature of solar differential rotation for solar cycle 21 and 22 and
a partial signature for cycle 23. We test this result by measuring
differential rotation using the Ca II K spectroheliograms using
phase analysis between longitudinal bands. We have also explored the
image features that lead to changes in the disk-integrated spectrum's
signal-to-noise. The data analyzed in this presentation can be found at
the National Solar Observatory web site http://nsosp.nso.edu/cak_mon/
, or by file transfer protocol at ftp://ftp.nso.edu/idl/cak.parameters
and ftp://diglib.nso.edu/Evans_spectroheliograms/.

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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
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.

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Title: The Advanced Technology Solar Telescope: design and early
construction
Authors: McMullin, Joseph P.; Rimmele, Thomas R.; Keil, Stephen L.;
Warner, Mark; Barden, Samuel; Bulau, Scott; Craig, Simon; Goodrich,
Bret; Hansen, Eric; Hegwer, Steve; Hubbard, Robert; McBride, William;
Shimko, Steve; Wöger, Friedrich; Ditsler, Jennifer
2012SPIE.8444E..07M Altcode:
The National Solar Observatory’s (NSO) Advanced Technology Solar
Telescope (ATST) is the first large U.S. solar telescope accessible
to the worldwide solar physics community to be constructed in more
than 30 years. The 4-meter diameter facility will operate over a broad
wavelength range (0.35 to 28 μm ), employing adaptive optics systems to
achieve diffraction limited imaging and resolve features approximately
20 km on the Sun; the key observational parameters (collecting area,
spatial resolution, spectral coverage, polarization accuracy, low
scattered light) enable resolution of the theoretically-predicted,
fine-scale magnetic features and their dynamics which modulate the
radiative output of the sun and drive the release of magnetic energy
from the Sun’s atmosphere in the form of flares and coronal mass
ejections. In 2010, the ATST received a significant fraction of its
funding for construction. In the subsequent two years, the project has
hired staff and opened an office on Maui. A number of large industrial
contracts have been placed throughout the world to complete the detailed
designs and begin constructing the major telescope subsystems. These
contracts have included the site development, AandE designs, mirrors,
polishing, optic support assemblies, telescope mount and coudé
rotator structures, enclosure, thermal and mechanical systems, and
high-level software and controls. In addition, design development
work on the instrument suite has undergone significant progress;
this has included the completion of preliminary design reviews (PDR)
for all five facility instruments. Permitting required for physically
starting construction on the mountaintop of Haleakalā, Maui has also
progressed. This paper will review the ATST goals and specifications,
describe each of the major subsystems under construction, and review
the contracts and lessons learned during the contracting and early
construction phases. Schedules for site construction, key factory
testing of major subsystems, and integration, test and commissioning
activities will also be discussed.

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Title: Solar Cycle Fine Structure and Surface Rotation from Ca II
K-Line Time Series Data
Authors: Scargle, Jeff; Keil, Steve; Worden, Pete
2011sdmi.confE..77S Altcode:
Analysis of three and a half decades of data from the NSO/AFRL/Sac Peak
K-line monitoring program yields evidence for four components to the
variation: (a) the solar cycle, with considerable fine structure and
a quasi-periodicity of 122.4 days; (b) a stochastic process, faster
than (a) and largely independent of it, (c) a quasi-periodic signal
due to rotational modulation, and of course (d) observational errors
(shown to be quite small). Correlation and power spectrum analyses
elucidate periodic and aperiodic variation of these chromospheric
parameters. Time-frequency analysis is especially useful for
extracting information about differential rotation, and in particular
elucidates the connection between its behavior and fine structure of
the solar cycle on approximately one-year time scales. These results
further suggest that similar analyses will be useful at detecting and
characterizing differential rotation in stars from stellar light-curves
such as those being produced by NASA's Kepler observatory. Component (b)
consists of variations over a range of timescales, in the manner of a
"1/f" random process. A time-dependent Wilson-Bappu effect appears to
be present in the solar cycle variations (a), but not in the stochastic
process (b). The data can be found at the National Solar Observatory
web site http://nsosp.nso.edu/data/cak_mon.html, or by file transfer
protocol at ftp://ftp.nso.edu/idl/cak.parameters.

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Title: Solar Polarization Workshop 6
Authors: Kuhn, J. R.; Harrington, D. M.; Lin, H.; Berdyugina, S. V.;
Trujillo-Bueno, J.; Keil, S. L.; Rimmele, T.
2011ASPC..437.....K Altcode:
No abstract at ADS

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Title: ATST: The Largest Polarimeter
Authors: Keil, S. L.; Rimmele, T. R.; Wagner, J.; Elmore, D.; ATST Team
2011ASPC..437..319K Altcode:
The Advanced Technology Solar Telescope's large collecting area,
combined with diffraction limited images delivered by adaptive optics,
will give it the ability to measure solar magnetic fields down to
scales of a few 20-30 km in the solar photosphere and the ability to
measure chromospheric and coronal magnetic fields.

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Title: Tracked Motions of G-band Bright Points
Authors: Telford, Olivia; Keil, S. L.
2011AAS...21715503T Altcode: 2011BAAS...4315503T
Abstract Bright points (BPs) are magnetic elements in the
photosphere observable in the CN G-band at 4305 Å. High-speed speckle
images were taken with the Dunn Solar Telescope in Sunspot, NM with a
80 frame burst every 32 seconds, achieving a resolution of 0.1422” in
the reconstructed images. The BPs were tracked by hand and velocities
and curls (vorticity) were derived at each time step. Small-scale
motions were also tracked using a FFT local correlation tracking
algorithm. The velocities obtained from correlation tracking were
generally smaller by factors of 2 to 5 than the hand tracked motion in
agreement with previous results, however, the hand-tracked BPs tended to
move in the direction of the local correlation tracking velocities. The
velocities of the BPs were used to estimate the energy associated with
these motions, which was found to vary between 1 to 3*1017
erg cm-1 based on observed velocities between 2 to 7 km
s-1. This amount of energy could provide a source of heat for
the corona, which has a minimum energy requirement of 106
erg cm-2 s-1. In some cases, BPs were seen to
travel at 7 km s-1, and changed their direction of motion
after collisions with granules. These supersonic speeds could generate
shockwaves, which in turn could transfer energy from the BPs to the
magnetic field. BPs often spiral around each other, possibly entangling
the associated magnetic field providing a mechanism by which energy
could be transported to the corona. This research was funded by
the National Science Foundation as part of its REU program.

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Title: Advanced Technology Solar Telescope: A status report
Authors: Keil, S. L.; Rimmele, T. R.; Wagner, J.; ATST Team
2010AN....331..609K Altcode:
Magnetic fields control the inconstant Sun. The key to understanding
solar variability and its direct impact on the Earth rests with
understanding all aspects of these magnetic fields. The Advanced
Technology Solar Telescope (ATST) has been design specifically for
magnetic remote sensing. Its collecting area, spatial resolution,
scattered light, polarization properties, and wavelength performance
all insure ATST will be able to observe magnetic fields at all heights
in the solar atmosphere from photosphere to corona. After several
years of design efforts, ATST has been approved by the U.S. National
Science Foundation to begin construction with a not to exceed cost cap
of approximately $298M. Work packages for major telescope components
will be released for bid over the next several months. An application
for a building permit has been submitted.

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Title: The Advanced Technology Solar Telescope: Science Goals,
Design and Project Status. (Invited)
Authors: Rimmele, T.; Keil, S. L.; Wagner, J.
2009AGUFMSH53B..10R Altcode:
The 4m Advance Technology Solar Telescope (ATST) on Haleakala will be
the most powerful solar telescope and the world’s leading resource
for studying solar magnetism that controls the solar wind, flares,
coronal mass ejections and variability in the Sun’s output. The
project is about to enter the construction phase and is expected to
be fully commissioned in 2017. 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
will during which the technical and engineering challenges the ATST
project faces will be discussed. ATST will provide high resolution and
high sensitivity observations of the dynamic solar magnetic fields
throughout the solar atmosphere, including the corona. With its 4 m
aperture, ATST will resolve features at 0.”03 (20km on the sun)
at visible wavelengths. The science requirement for polarimetric
sensitivity (10-5 relative to intensity) and accuracy (5x10-4
relative to intensity) place strong constraints on the polarization
analysis and calibration units. 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 Coude lab facility. A
few examples of the many unique science capabilities of the 4m ATST
will be discussed. The initial set of first generation instruments
includes: 1: the Visible Broadband Imager will provide images at
the highest possible spatial and temporal resolution at a number
of specified wavelengths in the range from 390 nm to 860 nm. 2:
the Visible Spectro-Polarimeter will provide precision vector field
measurements simultaneously at diverse wavelengths in the visible
spectrum and thus deliver quantitative diagnostics of the magnetic
field vector as a function of height in the solar atmosphere, along
with the associated variation of the thermodynamic properties. 3: the
Diffraction-Limited Near-Infrared Spectro-Polarimeter will record with
high temporal cadence the full polarization state of spectral lines
in the near infrared wavelength regime from 900 nm to 2300 nm. 4:
the Cryogenic Near Infrared-Spectro-Polarimeter will measure solar
magnetic fields over a large field-of-view at infrared wavelengths
from 1000 nm to 5000 nm in the solar corona. 5: the Visible Tunable
Filter will provide two-dimensional spectroscopy and polarimetry
by recording diffraction-limited narrow-bandpass images with high
temporal resolution.

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Title: Advanced Technology Solar Telescope
Authors: Keil, Stephen L.; Rimmele, Thomas R.; Wagner, Jeremy
2009EM&P..104...77K Altcode: 2008EM&P..tmp...37K
High-resolution studies of the Sun’s magnetic fields are needed for a
better understanding of the fundamental processes responsible for solar
variability. The generation of magnetic fields through dynamo processes,
the amplification of fields through the interaction with plasma flows,
and the destruction of fields are poorly understood. There is incomplete
insight into physical mechanisms responsible for chromospheric and
coronal structure and heating, causes of variations in the radiative
output of the Sun, and mechanisms that trigger flares and coronal mass
ejections. Progress in answering these critical questions requires
study of the interaction of the magnetic field and convection
with a resolution sufficient to observe scale fundamental to these
processes. The planned 4 m aperture ATST will be a unique scientific
tool, with excellent angular resolution, a large wavelength range,
and low scattered light. With its integrated adaptive optics, the
ATST will achieve a spatial resolution nearly 10 times better than
any existing solar telescope. The ATST design and development phase
began in 2001 and it is now ready to begin construction in 2009.

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Title: Generation, Evolution and Destruction of Solar Magnetic Fields
Authors: Keil, Stephen; Rimmele, Thomas; DeForest, Craig
2009astro2010S.153K Altcode:
No abstract at ADS

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Title: Ca II H &amp; K Spectra From The National Solar Observatory
Authors: Livingston, W. C.; Giampapa, M. S.; Harvey, J. W.; Keil,
S. L.; Toussaint, R. M.
2008AGUSMSP53B..04L Altcode:
When the Sun is observed as a star (i.e., spatially integrated full
disk) the cores of the chronospheric H and K resonance lines of
singly ionized calcium show the greatest cycle variability (up to
40% peak-to-peak) accessible from the ground. Synoptic archives are
available at monthly intervals from 1974 (Kitt Peak) and for K only
at almost a daily cadence from 1984 (Sacramento Peak). We discuss
these time series and compare them with, for example, sunspot numbers
and magnetic fields. Less frequent are center disk observations in
which the activity cycle is found to be absent, implying the quiet
basal atmosphere is constant and not, say, heated by cycle magnetic
activity. New, near daily, spatially integrated full disk solar data
from the SOLIS Integrated Sunlight Spectrometer (ISS)agree well with
the older work. We now propose to produce calibrated (Houtgast 1970;
Solar Phys 15, 273, high points: 387.5, 395.3, and 402.0 nm), low
dispersion full disk spectra that may be directly compared with that
from solar-type stars.

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Title: Alfven Waves in the Solar Corona
Authors: Tomczyk, S.; McIntosh, S. W.; Keil, S. L.; Judge, P. G.;
Schad, T.; Seeley, D. H.; Edmondson, J.
2007AGUFMSH21A0289T Altcode:
We present observations of the coronal intensity, line-of-sight
velocity, and linear polarization obtained in the FeXIII 1074.7 nm
coronal emission line with the Coronal Multi-channel Polarimeter
(CoMP) instrument. Analysis of these observations reveal ubiquitous
upward propagating waves with phase speeds of 1-4 Mm/s and trajectories
consistent with the direction of the magnetic field inferred from the
linear polarization measurements. We can definitively identify these
as Alfvén waves. An estimate of the energy carried by the waves that
we spatially resolve indicates that they are unable to heat the solar
corona, however, unresolved waves may carry sufficient energy.

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Title: Obituary: Richard B. Dunn, 1927-2005
Authors: Keil, Stephen L.; Dooling, David
2007BAAS...39.1056K Altcode:
Dr. Richard B. Dunn, astronomer emeritus at the National Solar
Observatory, died of a heart attack on September 29, 2005. He was
recognized as one of the foremost experimental solar physicists. His
innovative designs for telescopes and instruments led to many
important discoveries in solar physics. Born in Baltimore,
Maryland, in 1927 and raised in Minneapolis, Minnesota, Dick's parents
were Dr. Halbert L. Dunn and Katherine Brandner. Halbert (MD, Ph.D.,
F.A.P.H.A.) was an physician who became Chief of the National Office
of Vital Statistics, Public Health Service. He published a paper
"High Level Wellness for Man and Society" that became the founding
paper of the field of wellness health care. After their divorce in
1942, Katherine moved to New York and became a social worker. Dick
had two older brothers who died before him, Halbert (born in 1921,
who became a civil engineer) and Robert (born in 1924, who became an
architect). Dick earned a BS in mechanical engineering and an MS
in astronomy at the University of Minnesota. At the end of World War II
he served in the United States Army in Japan. For his master's degree,
Dick undertook the design and construction of a Lyot-type birefringent
filter for observations of solar prominences. This early work led to
his acceptance at Harvard, where Professor Donald Menzel encouraged
him to continue his work with the 15-inch Cambridge telescope. In
1951 he conducted part of his doctoral thesis work at the fledgling
Sacramento Peak Observatory in southern New Mexico. The observatory
director, Dr. John Evans, was impressed with Dick's outstanding
instrumental talents and invited him to join as one of the first
scientific staff members. During his first few years at Sac Peak,
Dick developed two more birefringent filter systems including one
with an integrated coronagraph. With this system, he produced the best
prominence and spicule observations ever obtained. Dick's career
was dedicated to obtaining solar observations of the highest possible
spatial resolution, having unparalleled quality that would reveal the
underlying physics. Only by studying the small magnetic structures
near the surface, he thought, could we understand such phenomena as
the solar flares that periodically disturb the Earth. Many of his
instruments were designed with this aim in mind and he was proven
correct in the end. Preeminent in Dick's achievements is the
design concept for the Vacuum Tower Telescope, which was commissioned
in 1969. It is a completely novel telescope that incorporates several
daring engineering concepts. It was the first tower telescope with an
evacuated light path, to eliminate internal seeing. It was one of the
first to utilize an alt-azimuth mount, under computer control. Upon his
retirement in 1998, the telescope was rededicated in his honor as the
Richard B. Dunn Solar Telescope (DST). In the DST, Dick pioneered
the concept of the telescope as an integrated observing system; it was
the first to incorporate telescope guidance and control and digital
data recording operations in a single computer control system. Dick
appreciated the advantages of such computer control a decade before
the astronomical community generally accepted these concepts. His
innovations led the way to similar advances in astronomy as a whole. The DST achieved Dick's aim of providing high-resolution solar
images and great flexibility in combining analyzing instruments. The
DST continued as the preeminent high-resolution solar telescope in the
world for the next three decades and remains a powerful and versatile
system that allows simultaneous measurements using multiple cameras to
record high-resolution imaging of solar features and activity, as well
as high-sensitivity spectral, polarimetric and other kinds of data,
and now incorporates a very effective adaptive optical system. Another of Dick's major projects was the design of a U.S. Air
Force network of solar telescopes. These five identical systems were
deployed around the world to give continuous monitoring of solar
activity. He was involved with many other instruments, projects and
systems. Notable among these was the design of an early solar space
telescope and pioneering work in solar adaptive optics. Dick
made several important discoveries with his novel instruments. His
early narrow-band filter observations with the DST showed that solar
spicules cover only a small area of the solar surface and reside
mainly on the super-granule network. He discovered that photospheric
magnetic fields emerge in kilogauss strength from sub-arcsecond
"filigree." Dick gained an international reputation for his
design expertise and his willingness to help other astronomers. His
advice and direct help were eagerly sought, and freely given. One can
hardly visit any solar observatory in the world without hearing,"Yes,
that was a Dick Dunn design." He was awarded the Hale Prize by the
Solar Physics Division of the American Astronomical Society in 1998,
"For his bold and imaginative innovation of instrumentation for solar
physics, his discovery of important new phenomena on the Sun, and
the impact of his contributions on solar physicists worldwide." But Dick's life and work at the observatory constitute far more
than simply that of a skilled experimenter who carried out new kinds
of groundbreaking observations with his special instruments. He was
the embodiment of those rare individuals with scientific instrumental
skills who generate totally new types of systems, their work marked
by extremely clever, creative and innovative ideas. In Dick's case,
this profile was coupled with the ability to apply enormous energy,
patience, commitment and enthusiasm to any instrumental challenge. Over
the years his contributions advanced the careers of a whole generation
of solar astronomers. Dick died in his home in Las Cruces, New
Mexico, after a long fight with Parkinson disease. Dick is survived
by his wife of 55 years, Alice Dunn. Alice was very involved in music
and had a beautiful voice. She did Russian translations, worked with
the blind (which got Dick interested in developing the translator and
printer mentioned below, and remains highly involved in the music scene
in Las Cruces. Dick was a person of many talents and interests,
including music, sculpture and sailing, and for example, worked hard
to develop an automated Braille translator and Braille printer. He was
fascinated with renaissance musical instruments, acquiring a substantial
collection, which he later donated to the El Paso Symphony Orchestra. He
achieved much enjoyment from his hurdy-gurdy, happily entertaining
anyone within earshot! Dick built several musical banks that would
play elaborate tunes when a coin was inserted. The coin then rolled
along ramps, striking a note each time it fell to the next level,
with the length of the ramps determining the timing between notes.

---------------------------------------------------------
Title: Alfvén Waves in the Solar Corona
Authors: Tomczyk, S.; McIntosh, S. W.; Keil, S. L.; Judge, P. G.;
Schad, T.; Seeley, D. H.; Edmondson, J.
2007Sci...317.1192T Altcode:
Alfvén waves, transverse incompressible magnetic oscillations, have
been proposed as a possible mechanism to heat the Sun’s corona
to millions of degrees by transporting convective energy from the
photosphere into the diffuse corona. We report the detection of
Alfvén waves in intensity, line-of-sight velocity, and linear
polarization images of the solar corona taken using the FeXIII
1074.7-nanometer coronal emission line with the Coronal Multi-Channel
Polarimeter (CoMP) instrument at the National Solar Observatory, New
Mexico. Ubiquitous upward propagating waves were seen, with phase speeds
of 1 to 4 megameters per second and trajectories consistent with the
direction of the magnetic field inferred from the linear polarization
measurements. An estimate of the energy carried by the waves that we
spatially resolved indicates that they are too weak to heat the solar
corona; however, unresolved Alfvén waves may carry sufficient energy.

---------------------------------------------------------
Title: Coronal Seismology: The Search for Propagating Waves in
Coronal Loops
Authors: Schad, Thomas A.; Seeley, D.; Keil, S. L.; Tomczyk, S.
2007AAS...210.9113S Altcode: 2007BAAS...39Q.206S
We report on Doppler observations of the solar corona obtained in
the Fe XeXIII 1074.7nm coronal emission line with the HAO Coronal
Multi-Channel Polarimeter (CoMP) mounted on the NSO Coronal One Shot
coronagraph located in the Hilltop Facility of NSO/Sacramento Peak. The
COMP is a tunable filtergraph instrument that records the entire corona
from the edge of the occulting disk at approximately 1.03 Rsun out to
1.4 Rsun with a spatial resolution of about 4” x 4”. COMP can be
rapidly scanned through the spectral line while recording orthogonal
states of linear and circular polarization. The two dimensional spatial
resolution allows us to correlate temporal fluctuations observed in one
part of the corona with those seen at other locations, in particular
along coronal loops. Using cross spectral analysis we find that the
observations reveal upward propagating waves that are characterized
by Doppler shifts with rms velocities of 0.3 km/s, peak wave power
in the 3-5 mHz frequency range, and phase speeds 1-3 Mm/s. The wave
trajectories are consistent with the direction of the magnetic field
inferred from the linear polarization measurements. We discuss the phase
and coherence of these waves as a function of height in the corona and
relate our findings to previous observations. The observed waves appear
to be Alfvenic in character. "Thomas Schad was supported through
the National Solar Observatory Research Experiences for Undergraduate
(REU) site program, which is co-funded by the Department of Defense in
partnership with the National Science Foundation REU Program." Daniel
Seeley was supported through the National Solar Observatory Research
Experience for Teachers (RET) site program, which is funded by the
National Science Foundation RET program.

---------------------------------------------------------
Title: High Resolution Optical Spectroscopy, Spectropolarimetry and
Spectral Imaging of Filament and Flaring Atmospheres
Authors: Keil, S. L.; Balasubramaniam, K. S.
2005AGUFMSH41B1129K Altcode:
Narrow-band spectral imaging, and Zeeman Stokes polarimetry of the
photosphere and chromosphere helps to understand the nature of twisted
magnetic fields and their propagation into the chromosphere. We will
discuss high resolution, multi-spectral diagnostics using optical
spectroscopy, imaging and spectropolarimetric techniques as applied
to filament and flaring atmospheres. We trace the twists in magnetic
fields through the trail of evidence it leaves at various levels of the
atmosphere, as it propagates upward of the photosphere. The diagnostic
tools used for this purpose include magnetic and velocity fields at
the photosphere and lower chromosphere (Hα), and velocities in the
upper chromosphere (Ca II~K line). We deduce the structure of magnetic
fields, their relationship to the formation of the filament structure,
and magnetic channels.

---------------------------------------------------------
Title: Overview and Status Report on the Advanced Technology Solar
Telescope
Authors: Keil, S. L.; Rimmele, T.; Wagner, J.; ATST Team
2005AGUSMSP34A..01K Altcode:
The ATST is a 4-m aperture, off-axis solar telescope with integrated
adaptive optics, low-scattered light, infrared, coronagraphic, and
polarimetric capabilities. It will resolve the essential, fine-scale
magnetic features and their dynamics that dictate the varying release
of energy from the Sun's atmosphere. The ATST design is optimized in
terms of throughput, scattered light, and instrumental polarization
properties to perform precision vector magnetic field measurements down
to its diffraction limit (0.03 arcsec at 500 nm) and throughout the
solar atmosphere. Its collecting area, which is a factor of 16 greater
than today's solar telescopes, will provide the sensitivity to measure
both weak fields and rapidly evolving stronger fields. It has a factor
of 64 greater collecting area than the largest existing coronagraph,
and will provide the sensitivity and coronagraphic capability needed
to measure the weak, fine-scale coronal magnetic fields. With adaptive
optics and a set of facility class instrumentation the ATST will be
the worlds leading resource for studying solar magnetism. ATST will
be the successor to the solar telescopes built in the 1960s and 1970s,
and is a natural complement to planned space missions. Starting in late
2001, ATST began a design and development phase. To date the D&amp;D
phase has produced and refined a science requirements document and a
conceptual design that would meet those requirements. A conceptual
design review was held in August of 2003. Following the review, a
construction proposal, including a complete work breakdown structure
and cost, was submitted in early 2004 and was successfully peer
reviewed. NSF astronomy is now in the process of submitting ATST to
the NSF Major Research Equipment and Facilities Construction program
review process. During the D&amp;D phase, a thorough site survey was
also conducted resulting in Haleakala as the site best able to fulfill
the ATST science requirements. We present a brief overview of the ATST
program, how it fits into the broader picture of solar facilities and
capabilities, and discuss the current status of the ATST project and
plans for constructing and commissioning the ATST.

---------------------------------------------------------
Title: The Solar Mass-Ejection Imager (SMEI) Mission
Authors: Jackson, B. V.; Buffington, A.; Hick, P. P.; Altrock, R. C.;
Figueroa, S.; Holladay, P. E.; Johnston, J. C.; Kahler, S. W.; Mozer,
J. B.; Price, S.; Radick, R. R.; Sagalyn, R.; Sinclair, D.; Simnett,
G. M.; Eyles, C. J.; Cooke, M. P.; Tappin, S. J.; Kuchar, T.; Mizuno,
D.; Webb, D. F.; Anderson, P. A.; Keil, S. L.; Gold, R. E.; Waltham,
N. R.
2004SoPh..225..177J Altcode:
We have launched into near-Earth orbit a solar mass-ejection imager
(SMEI) that is capable of measuring sunlight Thomson-scattered from
heliospheric electrons from elongations to as close as 18∘
to greater than 90∘ from the Sun. SMEI is designed to
observe time-varying heliospheric brightness of objects such as coronal
mass ejections, co-rotating structures and shock waves. The instrument
evolved from the heliospheric imaging capability demonstrated by the
zodiacal light photometers of the Helios spacecraft. A near-Earth
imager can provide up to three days warning of the arrival of a mass
ejection from the Sun. In combination with other imaging instruments
in deep space, or alone by making some simple assumptions about the
outward flow of the solar wind, SMEI can provide a three-dimensional
reconstruction of the surrounding heliospheric density structures.

---------------------------------------------------------
Title: Advanced Technology Solar Telescope: conceptual design
and status
Authors: Keil, Stephen; Oschmann, Jacobus M., Jr.; Rimmele, Thomas R.;
Hubbard, Rob; Warner, Mark; Price, Ron; Dalrymple, Nathan; Goodrich,
Bret; Hegwer, Steven; Hill, Frank; Wagner, Jeremy
2004SPIE.5489..625K Altcode:
The Advance Technology Solar Telescope (ATST) has finished its
conceptual design stage, submitted a proposal for construction funding
and is working towards a system level preliminary design review later
this year. The current concept (including integrated adaptive optics
and instrumentation) will be reviewed with concentration on solutions
to the unique engineering challenges for a four meter solar telescope
that have been previously presented. The overall status will be given
with a concentration on near term milestones and impact on final
completion targeted in 2012.

---------------------------------------------------------
Title: Advanced Technology Solar Telescope: a progress report
Authors: Oschmann, Jim; Dalrymple, Nathan; Warner, Mark; Price, Ron;
Hill, Frank; Hubbard, Rob; Rimmele, Thomas R.; Keller, Christoph U.;
Keil, Stephen
2004SPIE.5171..160O Altcode:
The 4m ATST will be the most powerful solar telescope in the world,
providing a unique scientific tool to study the Sun and other
astronomical objects. The design and development phase for the Advance
Technology Solar Telescope (ATST) is progressing. The conceptual design
review (CoDR) for the ATST is scheduled for August 2003. We present a
brief description of the science requirements of ATST, and remind the
reader of some of the technical challenges of building a 4-m solar
telescope. We will discuss some of the design strategies that will
allow us to achieve the required performance specifications, present
conceptual designs for the ATST, and summarize the results of trades
we have made on our path to the CoDR. The thermal impacts to local,
self-induced seeing with respect to some of our system level trades
that have been completed will be discussed.

---------------------------------------------------------
Title: Science Goals and Development of the Advanced Technology
Solar Telescope
Authors: Keil, S. L.; Rimmele, T. R.; Oschmann, J.; Hubbard, R.;
Warner, M.; Price, R.; Dalrymple, N.; Atst Team
2004IAUS..223..581K Altcode: 2005IAUS..223..581K
The Advanced Technology Solar Telescope (ATST) will perform
high-resolution studies of the Sun's magnetic fields needed to
understand their role in the fundamental processes responsible for solar
variability. The generation of magnetic fields through dynamo processes,
the amplification of fields through the interaction with plasma flows,
and the destruction of fields remain poorly understood. There is
incomplete insight as to what physical mechanisms are responsible for
heating the corona, what causes variations in the radiative output
of the Sun, and what mechanisms trigger flares and coronal mass
ejections. Progress in answering these critical questions requires
study of the interaction of the magnetic field and convection with a
resolution sufficient to observe scales fundamental to these processes.

---------------------------------------------------------
Title: Synergy of Research and EPO Programs at NSO
Authors: Balasubramaniam, K. S.; Keil, S. L.; Penn, M. J.; Dooling,
D.; Piano, P.; Diehl, J.; Hunter, R.
2003AGUFMED51C1215B Altcode:
The National Solar Observatory with its facilities at Sunspot, NM and
Tucson, AZ runs an extensive education and public outreach effort. Much
of these efforts are coupled research and education efforts aimed
across a spectrum that spans through school teachers, school students,
undergraduate and graduate researchers, and the public. In this paper,
we will describe the benefits and challenges the NSO program faces,
and future prospects of these programs.

---------------------------------------------------------
Title: Design and development of the Advanced Technology Solar
Telescope (ATST)
Authors: Keil, Stephen L.; Rimmele, Thomas; Keller, Christoph U.;
Hill, Frank; Radick, Richard R.; Oschmann, Jacobus M.; Warner, Mark;
Dalrymple, Nathan E.; Briggs, John; Hegwer, Steven L.; Ren, Dauxing
2003SPIE.4853..240K Altcode:
High-resolution studies of the Sun's magnetic fields are needed for
a better understanding of solar magnetic fields and the fundamental
processes responsible for solar variability. The generation of magnetic
fields through dynamo processes, the amplification of fields through
the interaction with plasma flows, and the destruction of fields
are still poorly understood. There is still incomplete insight as
to what physical mechanisms are responsible for heating the corona,
what causes variations in the radiative output of the Sun, and what
mechanisms trigger flares and coronal mass ejections. Progress in
answering these critical questions requires study of the interaction
of the magnetic field and convection with a resolution sufficient to
observe scales fundamental to these processes. The 4m aperture Advanced
Technology Solar Telescope (ATST) will be a unique scientific tool,
with excellent angular resolution, a large wavelength range, and low
scattered light. With its integrated adaptive optics, the ATST will
achieve a spatial resolution nearly 10 times better than any existing
solar telescope. Building a large aperture telescope for viewing the
sun presents many challenges, some of the more difficult being: · Heat
control and rejection · Contamination and scattered light control ·
Control of telescope and instrument polarization · Site selection
This talk will present a short summary of the scientific questions
driving the ATST design, the design challenges faced by the ATST, and
the current status of the developing design and siting considerations

---------------------------------------------------------
Title: Technical challenges of the Advanced Technology Solar Telescope
Authors: Rimmele, Thomas R.; Keil, Stephen L.; Keller, Christoph
U.; Hill, Frank; Briggs, John; Dalrymple, Nathan E.; Goodrich, Bret
D.; Hegwer, Steven L.; Hubbard, Rob; Oschmann, Jacobus M.; Radick,
Richard R.; Ren, Deqing; Wagner, Jeremy; Wampler, Stephen; Warner, Mark
2003SPIE.4837...94R Altcode:
The 4m Advance Technology Solar Telescope (ATST) will be the most
powerful solar telescope in the world, providing a unique scientific
tool to study the Sun and possibly other astronomical objects, such
as solar system planets. We briefly summarize the science drivers and
observational requirements of ATST. The main focus of this paper is on
the many technical challenges involved in designing a large aperture
solar telescope. The ATST project has entered the design and development
phase. Development of a 4-m solar telescope presents many technical
challenges. Most existing high-resolution solar telescopes are designed
as vacuum telescopes to avoid internal seeing caused by the solar heat
load. The large aperture drives the ATST to an open-air design, similar
to night-time telescope designs, and makes thermal control of optics
and telescope structure a paramount consideration. A heat stop must
reject most of the energy (13 kW) at prime focus without introducing
internal seeing. To achieve diffraction-limited observations at visible
and infrared wavelengths, ATST will have a high order (order 1000
DoF) adaptive optics system using solar granulation as the wavefront
sensing target. Coronal observations require occulting in prime focus,
a Lyot stop and contamination control of the primary. An initial set of
instruments will be designed as integral part of the telescope. First
telescope design and instrument concepts will be presented.

---------------------------------------------------------
Title: Innovative Telescopes and Instrumentation for Solar
Astrophysics
Authors: Keil, Stephen L.; Avakyan, Sergey V.
2003SPIE.4853.....K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Science Objectives and Technical Challenges of the Advanced
Technology Solar Telescope (Invited review)
Authors: Rimmele, T.; Keil, S. L.; Keller, C.; Hill, F.; Penn, M.;
Goodrich, B.; Hegwer, S.; Hubbard, R.; Oschmann, J.; Warner, M.;
Dalrymple, N.; Radick, R.; Atst Team
2003ASPC..286....3R Altcode: 2003ctmf.conf....3R
No abstract at ADS

---------------------------------------------------------
Title: The Advanced Technology Solar Telescope
Authors: Keller, C. U.; Rimmele, T. R.; Hill, F.; Keil, S. L.;
Oschmann, J. M.; ATST Team
2002AN....323..294K Altcode:
The Advanced Technology Solar Telescope is the largest solar optical
facility currently under development. The National Solar Observatory
and its partners have just started the design and development phase
with first light being planned for late this decade. The 4-m telescope
will provide an angular resolution down to 0.025 arcsec, a large photon
flux for precise magnetic and velocity field measurements, and access
to a broad set of diagnostics from 0.3 to 28 mu m. We summarize the
currently envisioned scientific capabilities of the telescope and its
suite of instruments along with a glimpse at some of the early concepts.

---------------------------------------------------------
Title: The Advanced Technology Solar Telescope
Authors: Rimmele, T. R.; Keil, S. L.; Keller, C. U.; Hill, F.;
Oschmann, J. M.; Warner, M.; Dalrymple, N. E.; ATST Team
2002AAS...200.3408R Altcode: 2002BAAS...34..691R
The 4m aperture Advance Technology Solar Telescope (ATST) will be the
most powerful solar telescope in the world and a unique scientific tool
to study the Sun and other astronomical objects, such as planets. The
ATST will replace major existing national solar facilities at the end
of this decade. The ATST project has entered the design and development
phase. We present an overview of the ATST science drivers and discuss
preliminary design concepts and technical challenges. The ATST science
goals lead to the following general requirements for the ATST facility:
- Diffraction limited angular resolution in the visible and infrared
to study fundamental astrophysical processes with unprecedented
resolution enabling verification of model predictions. - A high photon
flux for accurate measurements of physical parameters throughout
the solar atmosphere, such as magnetic strength and direction,
temperature and velocity. - Access to a new diagnostics at relatively
unexplored infrared wavelength. - Low scattered light to enable
coronal observations. - Low instrumental polarization for accurate
measurements of magnetic fields. Development of a 4m solar telescope
presents many technical challenges. The large aperture drives the ATST
to an open-air design and makes thermal control of optics and telescope
structure a paramount consideration. To achieve diffraction-limited
observations at visible and infrared wavelength ATST will have a high
order solar adaptive optics system. Coronal observations require,
occulting in prime focus, a Lyot stop and contamination control of the
primary. An initial set of instruments will be designed as integral
part of the telescope. Preliminary telescope and instrument concepts
will be discussed.

---------------------------------------------------------
Title: Calcium II K Spectroheliograms and Disk integrated Spectra
Authors: Raffauf, E.; Eydenberg, M.; Keil, S. L.
2001AGUSM..SP21A01R Altcode:
We compare spatially resolved Calcium II K spectroheliograms and disk
integrated Ca II K spectra. Both data sets are obtained at the Evans
Solar Facility at the National Solar Observatory Sacramento Peak
on a daily basis. An understanding of the relationship between the
spatially resolved and disk integrated data can aid in interpreting
spatially unresolved solar and stellar observations, solar irradiance
studies in which the Ca II K line serves as a ground-based proxy for
solar UV and EUV lines, and differential rotation studies of stars. We
present correlations between plage parameters (area and intensity)
calculated from the spectroheliograms and various spectral line
parameters computed from the disk integrated spectra. We also present
a preliminary comparison of rotation curves obtained from the spatially
resolved data with rotation rates seen in the disk integrated data.

---------------------------------------------------------
Title: The Advanced Technology Solar Telescope -- Science Goals and
Instrument Description.
Authors: Rimmele, T. R.; Keil, S. L.; Keller, C. U.; Hill, F.
2001AGUSM..SH31D08R Altcode:
High-resolution studies of the Sun's magnetic fields are needed for
a better understanding of solar magnetic fields and the fundamental
processes responsible for solar variability. The generation of magnetic
fields through dynamo processes, the amplification of fields through
the interaction with plasma flows, and the destruction of fields are
still poorly understood. There is still incomplete insight as to what
physical mechanisms are responsible for heating the corona, what causes
variations in the radiative output of the Sun, and what mechanisms
trigger flares and coronal mass ejections. Progress in answering
these critical questions requires study of the interaction of the
magnetic field and convection with a resolution sufficient to observe
physical scales fundamental to these processes. The 4m aperture ATST
will be a unique scientific tool, with excellent angular resolution,
a large wavelength range, and low scattered light. With its integrated
adaptive optics, the ATST will achieve a spatial resolution nearly 10
times better than any existing solar telescope. The ATST will provide:
Unprecedented angular resolution of 0.03 arcsec in the visible and
0.08 arcsec at 1.6 microns to enable us to clearly resolve and study the
fundamental astrophysical processes on their intrinsic scales and to
verify model predictions. A high photon flux for accurate and precise
measurements of physical parameters, such as magnetic field strength
and direction, temperature and velocity, on the short time scales
involved. Access to a broad set of diagnostics, from visible to thermal
infrared wavelengths. Low scattered light observations and coronagraphic
capabilities in the infrared, allowing measurements of coronal magnetic
fields. The ATST has been highly ranked by the latest Decadal Survey
of Astronomy and Astrophysics and the NAS/NRC study of ground-based
solar astronomy. A large part of the solar community will participate
in the design and development of the ATST. A strawman telescope design,
design challenges and instrument concepts will be discussed. Examples
of recent high resolution observations with adaptive optics, that
demonstrate the potential of this new technology will be shown.

---------------------------------------------------------
Title: The Advanced Technology Solar Telescope
Authors: Keil, S. L.; Rimmele, T. R.; Keller, C. U.; Atst Team
2001ASPC..236..597K Altcode: 2001aspt.conf..597K
No abstract at ADS

---------------------------------------------------------
Title: The Advanced Solar Telescope
Authors: Keil, S. L.; Rimmele, T. R.; Keller, C.; Hill, F.
2000AAS...197.1710K Altcode: 2000BAAS...32.1433K
The planned Advanced Technology Solar Telescope (ATST) will be a 4-m
aperture general-purpose solar telescope with integrated adaptive
optics and versatile post focus instrumentation. The ATST will achieve
an angular resolution of 0.03 arcsec (20 km on the solar surface)
in the visible, which is almost an order of magnitude better than
what is achieved with current solar telescopes. This will make it
possible to resolve the fundamental astrophysical hydrodynamic and
magnetohydrodynamic processes and structures in the solar atmosphere
such as the building blocks of solar magnetic fields that are believed
to be responsible for solar irradiance variations and the heating of the
outer solar atmosphere. The ATST will cover the wavelength range from
0.35 to 35 ?m and minimize scattered light. The initial set of post
focus instruments will exploit the unique capabilities of the ATST to
study magnetic fields at the highest spatial resolution in the visible
and near-infrared parts of the spectrum. The ATST was highly recommended
by the recent Decadal Study. A proposal for a four-year Design and
Development phase has just been submitted to the NSF. Construction is
expected to start in FY2005. The National Solar Observatory is operated
by the Associated Universities for Research in Astronomy and is funded
by the National Science Foundation under a cooperative agreement.

---------------------------------------------------------
Title: Comparison of Disk-Integrated Ca II K-line Spectra and K-line
Spectroheliograms
Authors: Catanzariti, S. P.; Keil, S. L.
2000SPD....3102119C Altcode:
We compare changes in disk-integrated Ca-II K-line spectra with changes
observed in full-disk K-line spectroheliograms. Disk-integrated K-line
spectra have been obtained on a synoptic basis by the National
Solar Observatory (NSO) at both its Kitt Peak and Sacramento
Peak sites for the past two solar cycles. NSO also records Ca II
K-line spectroheliograms on a daily basis at Sacramento Peak. The
disk-integrated observations have been used as a proxy for changes
in solar UV and EUV lines that can only be measured from space, as
a predictor of satellite drag, to compare the Sun to other active
and variable stars and to measure solar differential rotation on
the Sun when viewed as a star. The goal of the comparison with the
spectroheliograms is to understand and calibrate the causes of change in
the disk-integrated spectra. For the past nine months, we have obtained
the disk-integrated spectra and spectroheliograms simultaneously,
using the Evans Facility to help eliminate sky transparency changes
as a source of noise. We have also investigated several methods of
normalizing the spectroheliograms before extracting plage area and
brightness changes. Correlation between changes in the disk-integrated
intensity and changes in the so-called emission index (an integral of
the intensity over a one-angstrom band centered on the K-line) with
changes in plage area and plage brightness integrated over the solar
disk will be presented. Funding for this project was provided by the
National Science Foundation and the Air Force Office of Scientific
Research.

---------------------------------------------------------
Title: Comparison of disk-integrated Ca II K-line spectra and K-line
spectroheliograms.
Authors: Catanzariti, S. P.; Keil, S. L.
2000BAAS...32Q.832C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Velocities in Solar Pores
Authors: Keil, S. L.; Balasubramaniam, K. S.; Smaldone, L. A.;
Reger, B.
1999ApJ...510..422K Altcode:
We use high spatial and spectral resolution filtergrams to examine the
three-dimensional morphology and velocity fields associated with solar
pores in a region of newly emerged magnetic flux. The observed amplitude
of the horizontal surface velocities decreases near the pores. Most of
the pores exhibit a downflow in the surrounding region. Time-averaged
line-of-sight velocities in and near the pores increased with the
strength of the associated magnetic field. The LOS velocities are
such that the maximum downflow is not centered about the continuum
intensity and sometimes traces an annulus ringlike structure around
the pore. From a time sequence of continuum images, it appears that
some pores shed flux at the photospheric level. “Cork movies” of the
surface velocities show that the “corks” are advected toward weak
downflows near the pore locations and that the loci of the advected
corks trace boundaries that resemble mesogranular and supergranular
flows. We analyze the vertical velocity structure in pores and show that
the downflow decreases exponentially with height, with a scale height
that is a factor of 2 smaller than the photospheric scale height for
granules. The line-of-sight flow associated with the pores appears
to expand with height. Our observations are compared with previous
measurements of flows in and around pores that were based on both
spectrograms and filtergrams. Finally, we provide a phenomenological
description for pores.

---------------------------------------------------------
Title: H alpha Synoptic Observations of Flare-Filament Eruption
Complex 1997 April 6 - 7
Authors: Balasubramaniam, K. S.; Milano, L.; Keil, S. L.
1998ASPC..140..189B Altcode: 1998ssp..conf..189B
No abstract at ADS

---------------------------------------------------------
Title: NSO/AFRL/Sac Peak K-line Monitoring Program
Authors: Keil, Stephen L.; Henry, Timothy W.; Fleck, Bernhard
1998ASPC..140..301K Altcode: 1998ssp..conf..301K
No abstract at ADS

---------------------------------------------------------
Title: Variability of the Solar Call K Line over the 22 Year Hale
Cycle
Authors: White, O. R.; Livingston, W. C.; Keil, S. L.; Henry,
Timothy W.
1998ASPC..140..293W Altcode: 1998ssp..conf..293W
No abstract at ADS

---------------------------------------------------------
Title: Stokes Profile Asymmetries in Solar Active Regions
Authors: Balasubramaniam, K. S.; Keil, S. L.; Tomczyk, S.
1997ApJ...482.1065B Altcode:
Asymmetries in Stokes polarization spectral line profiles can be
attributed to the existence of gradients in the velocity (and magnetic
field) over the line-forming region. Models that solve the Stokes
radiative transfer equations have incorporated both line-of-sight
gradients and gradients perpendicular to the line of sight over the
resolution element to produce the observed asymmetries. There have been
only a few systematic studies of how these Stokes profile asymmetries
vary across spatial structures and as a function of the amplitude of the
velocity and magnetic fields, and very little statistical information
is available. We present observational results from high spectral and
spatial resolution Stokes V profile measurements made in an active
region located near disk center and present correlations between the
amplitude of the Stokes V asymmetry, the magnetic field strength, and
line shifts and line asymmetries observed in the Stokes I profile. In
regions where the field strength exceeds a few hundred gauss, we find
a good correlation between the amplitude of the measured asymmetry
in Stokes V and the observed shifts of the Stokes I profile. We also
find a correlation between the asymmetry of the Stokes I profile and
the amplitude of the Stokes V profile asymmetry.

---------------------------------------------------------
Title: Design for the Solar Mass Ejection Imager (SMEI)
Authors: Keil, S. L.; Altrock, R. C.; Kahler, S. W.; Jackson, B. V.;
Buffington, A.; Hick, P. L.; Simnett, G.; Eyles, C.; Webb, D. F.;
Anderson, P.
1997SPD....28.0227K Altcode: 1997BAAS...29..897K
The Solar Mass Ejection Imager (SMEI) experiment is designed to detect
and measure transient plasma features in the heliosphere, including
coronal mass ejections (CMEs), shock waves, and structures such as
streamers which corotate with the Sun. SMEI will provide measurements
of the propagation of solar plasma clouds and high-speed streams
which can be used to forecast their arrival at Earth from one to
three days in advance. Data from SMEI will be used to develop models
and techniques that will, for the first time, allow us to predict the
onset and magnitude of geomagnetic storms that disrupt space operations
and affect communications and surveillance activities. We will present
the current design and observational plans for SMEI. SMEI is currently
under construction with instrument completion expected in 1999. We
plan to launch SMEI near the next solar maximum and will make the data
available to the scientific and space weather forecast communities.

---------------------------------------------------------
Title: Near Infrared Vector Magnetograph Development
Authors: Gullixson, Craig; Balasubramaniam, K. S.; Keil, Stephen
1997SPD....28.0226G Altcode: 1997BAAS...29..897G
We have developed a two etalon, narrow-band, tunable infrared filter
system and are using it to make solar vector magnetograms in the Fe
I lines at 1.5648 microns. We present results on the spectral and
polarization resolution of the filter system and show maps of the
magnetic field in both quiet regions of the solar atmosphere and
in a region with a growing sunspot. We will discuss the magnetic
sensitivity of the instrument. This system is a prototype instrument
for a operational vector magnetograph that will monitor the evolution
of solar magnetic fields preceding solar activity.

---------------------------------------------------------
Title: Solar Mass Ejection Imager (SMEI)
Authors: Keil, Stephen L.; Altrock, Richard C.; Kahler, Stephen;
Jackson, Bernard V.; Buffington, Andrew; Hick, Paul; Simnett, George
M.; Eyles, Christopher J.; Webb, David; Anderson, Peter
1996SPIE.2804...78K Altcode:
The Solar Mass Ejection Imager (SMEI) experiment is designed to
detect and measure transient plasma features in the heliosphere,
including coronal mass ejections, shock waves, and structures such as
streamers which corotate with the Sun. SMEI will provide measurements
of the propagation of solar plasma clouds and high-speed streams
which can be used to forecast their arrival at Earth from one to
three days in advance. The white light photometers on the HELIOS
spacecraft demonstrated that visible sunlight scattered from the free
electrons of solar ejecta can be sensed in interplanetary space with
an electronic camera baffled to remove stray background light. SMEI
promises a hundred-fold improvement over the HELIOS data, making
possible quantitative studies of mass ejections. SMEI measurements
will help predict the rate of energy transfer into the Earth's
magnetospheric system. By combining SMEI data with solar, interplanetary
and terrestrial data from other space and ground-based instruments, it
will be possible to establish quantitative relationships between solar
drivers and terrestrial effects. SMEI consists of three cameras, each
imaging a 60 degree(s) X 3 degree(s) field of view for a total image
size of 180 degree(s) X 3 degree(s). As the satellite orbits the earth,
repeated images are used to build up a view of the entire heliosphere.

---------------------------------------------------------
Title: Flare Genesis Experiment
Authors: Murphy, Graham A.; Rust, David M.; Strohbehn, Kim; Eaton,
Harry A.; Keil, Stephen L.; Keller, Christoph U.; Wiborg, P. H.
1996SPIE.2804..141M Altcode:
In January 1996, the Flare Genesis Experiment was carried for 19
days by a 29.4 M cu. ft helium-filled balloon in the stratosphere
above Antarctica, during which over 14000 images of the Sun were
recorded. Long-duration ballooning provides a relatively inexpensive
means to observe the Sun under near-space conditions and to develop
instrumentation and techniques that will be used on future solar space
missions. The purpose of the flight was to improve understanding of
the mechanisms involved in many different types of solar activity,
particularly flares and solar filament eruptions. Achieving this goal
demanded the development of a platform for an 80-cm F/1.5 optical
telescope that would be stable to 10 arcseconds. In addition, we
developed an image motion compensation system capable of holding the
Sun's image to better than the system's 0.2 arcsecond diffraction
limit. Other key elements on board included a lithium-niobate
Fabry-Perot etalon filter to provide a tunable 0.016-nm bandpass over
a wide wavelength range, a fast 1534 X 1024-pixel Kodak CCD camera,
and 180 GBytes of on-board storage. There was also a system for
sending commands and receiving telemetry and a high-speed downlink
for sending images during periods when the payload was in line of
sight of the ground station. On- board computers provided a command
and control system capable of near-autonomous operation. During most
of the flight, contact with the payload was sporadic, so operation
was primarily under autonomous control.

---------------------------------------------------------
Title: The Flare Genesis Experiment
Authors: Rust, D. M.; Murphy, G. A.; Strohbehn, K.; Keil, S. L.;
Keller, C. U.
1996AAS...188.6705R Altcode: 1996BAAS...28Q.934R
The goal of the Flare Genesis Experiment is to make solar observations
at the highest practicable resolution in order to improve understanding
of the mechanisms involved in many different types of solar activity,
particularly flares and solar filament eruptions. Achieving this goal
demanded the development of a balloon-borne platform for an 80-cm F/1.5
optical telescope that could maintain 10 arcsec pointing stability. The
first flight of the Flare Genesis Experiment took place in January
1996. In the stratosphere, 37 km above Antarctica, for more than 19
days, the Flare Genesis telescope pointed at the Sun with the planned
stability. While the primary science objective, to measure the vector
magnetic fields using two liquid crystal polarization modulators, was
not achieved on this flight, 18,000 continuum images were obtained. They
demonstrate that the major engineering challenges for such a flight
were overcome. In addition, we developed an image motion compensation
system capable of limiting the motion of the Sun's image on the focal
plane to less than the system's 0.2 arcsec diffraction limit. Other key
elements on board included a lithium-niobate Fabry-Perot etalon filter
to provide a tunable 0.016-nm bandpass over a wide wavelength range,
a 1538 x 1024- pixel CCD camera and 100 GBytes of on-board storage. We
will describe the payload design and how the instruments performed. We
will discuss how the constraints of long duration Antarctic ballooning
guided the final design and impacted the results. Two more flights
are planned before the next solar maximum. Such long-duration balloon
flights provide a relatively inexpensive means to observe the Sun at
the highest resolution and to develop instrumentation and techniques
for future space missions.

---------------------------------------------------------
Title: Velocities in Solar Pores
Authors: Balasubramaniam, K. S.; Keil, S. L.; Smaldone, L. A.
1996AAS...188.0203B Altcode: 1996BAAS...28..820B
We investigate the three dimensional structure of solar pores and
their surroundings using high spatial and spectral resolution data. We
present evidence that surface velocities decrease around pores with
a corresponding increase in the line-of-sight (LOS) velocities. LOS
velocities in pores increase with the strength of the magnetic
field. Surface velocities show convergence toward a weak downflow which
appear to trace boundaries resembling meso-granular and super granular
flows. The observed magnetic fields in the pores appear near these
boundaries. We analyze the vertical velocity structure in pores and show
that they generally have downflows decreasing exponentially with height,
with a scale height of about 90 km. Evidence is also presented for the
expanding nature of flux tubes. Finally we describe a phenomenological
model for pores. This work was supported by AFOSR Task 2311G3. LAS was
partially supported by the Progetto Nazionale Astrofisica e Fisica
Cosmica of MURST and Scambi Internazionali of the Universita degli
Studi di Napoli Frederico II. National Solar Observatory, NOAO, is
operated for the National Science Foundation by AURA, Inc.

---------------------------------------------------------
Title: Design Considerations for a Near Infrared Imaging Vector
Magnetograph
Authors: Gullixson, C. A.; Keil, S. L.; Balasubramaniam, K. S.
1996AAS...188.5603G Altcode: 1996BAAS...28R.911G
We present a preliminary design for an imaging vector magnetograph at
15648 Angstroms. This instrument is intended as a potential source
of vector magnetic field measurments for the USAF and NOAA solar
activity prediction programs. It will consist of a blocking filter, two
Fabry-Perot Etalons in tandem, a near-IR (10000 -- 17000 Angstroms)
camera and associated polarization optics. Initial test results
of the optical characteristics of this instrument and its expected
performance characteristics will be described. We are exploring designs
for operational vector magnetographs in the near-IR as a way to simplify
vector magnetic field measurements while improving their accuracy. This
work was supported by AFOSR Task 2311G3. National Solar Observatory,
NOAO, is operated for the National Science Foundation by AURA, Inc.

---------------------------------------------------------
Title: Solar drivers of the interplanetary and terrestrial
disturbances
Authors: Balasubramaniam, K. S.; Keil, Stephen L.; Smartt, Raymond N.
1996ASPC...95.....B Altcode: 1996sdit.conf.....B
No abstract at ADS

---------------------------------------------------------
Title: The Solar Mass Ejection Imager (SMEI): Development and Use
in Space Weather Forecasting
Authors: Keil, S. L.; Altrock, R. C.; Kahler, S. W.; Jackson, B. V.;
Buffington, A.; Hick, P. L.; Simnett, G.; Eyles, C.; Webb, D. F.;
Anderson, P.
1996ASPC...95..158K Altcode: 1996sdit.conf..158K
No abstract at ADS

---------------------------------------------------------
Title: A search for large-scale photospheric flows as drivers of
mass ejections
Authors: Balasubramaniam, K. S.; Keil, S. L.
1996ASPC...95..189B Altcode: 1996sdit.conf..189B
No abstract at ADS

---------------------------------------------------------
Title: Restored Solar Velocity Measurements Obtained from the May 10,
1994 Annular Solar Eclipse
Authors: Keil, S. L.; Balasubramaniam, K. S.; Ljungberg, S. K.;
Smaldone, L. A.; Rimmele, T. R.
1995SPD....26..202K Altcode: 1995BAAS...27..951K
No abstract at ADS

---------------------------------------------------------
Title: Stokes Profile Asymmetries in Active Regions
Authors: Balasubramaniam, K. S.; Keil, S. L.; Tomczyk, S.; Bernasconi,
P.
1995SPD....26..205B Altcode: 1995BAAS...27..951B
No abstract at ADS

---------------------------------------------------------
Title: Solar and Stellar Chromospheric Contrast - Part One
Authors: Donahue, Robert A.; Restaino, Sergio R.; Keil, Stephen L.
1994SoPh..149..257D Altcode:
We present an analysis of disk-integrated spectra of the CaII K line
(3933.68 å). The selection of parameters in the line profile, and
the correlations between them, follow the work of Smith (1960), but
represent an innovative aspect in the fact that our data are spatially
integrated. Therefore, the subsequent identification of correlations
between line-profile parameters in disk-integrated solar spectra may be
useful in identifying similar correlations in high-resolution spectra
of solar-like stars.

---------------------------------------------------------
Title: Active Region Development: Results from the JHU/APL Vector
Magnetograph
Authors: Rust, D. M.; Murphy, G.; Balasubramaniam, K. S.; Gullixson,
C. A.; Henry, T.; Coulter, R. L.; Keil, S. L.
1994ASPC...68..263R Altcode: 1994sare.conf..263R
No abstract at ADS

---------------------------------------------------------
Title: Dynamics of Small Flux Tubes
Authors: Reger, Bernard; Keil, Stephen L.; Smaldone, Luigi A.; Cauzzi,
Gianna; Balasubramaniam, K. S.
1994ASPC...68..157R Altcode: 1994sare.conf..157R
No abstract at ADS

---------------------------------------------------------
Title: Simultaneous Filter and Spectrograph Observations of Active
Regions with the Advanced Stokes Polarimeter
Authors: Tomczyk, S.; Balasubramaniam, K. S.; Keil, Stephen L.
1994ASPC...68..262T Altcode: 1994sare.conf..262T
No abstract at ADS

---------------------------------------------------------
Title: Observations of Active Region Dynamics: Preflare Flows and
Field Observations
Authors: Keil, Stephen L.; Balasubramaniam, K. S.; Bernasconi, Pietro;
Smaldone, Luigi A.; Cauzzi, Gianna
1994ASPC...68..265K Altcode: 1994sare.conf..265K
No abstract at ADS

---------------------------------------------------------
Title: Change in the radiative output of the Sun in 1992 and its
effect in the thermosphere
Authors: White, O. R.; Rottman, G. J.; Woods, T. N.; Knapp, B. G.;
Keil, S. L.; Livingston, W. C.; Tapping, K. F.; Donnelly, R. F.;
Puga, L. C.
1994JGR....99..369W Altcode:
Ground and space measurements of the solar spectral irradiance at radio,
visible, UV, and X ray wavelengths show a large decline in the first 6
months of 1992. This sustained drop in the solar output is important
in understanding the connection between the emergent magnetic flux
on the Sun and the radiative output as well as in understanding the
effects of such change in the upper atmosphere of the earth. We present
preliminary estimates of the observed changes as the means to spur
inquiry into this solar event in the declining phase of solar cycle
22. Typical decreases are 15% in Lyman alpha and 40% in 10.7-cm radio
flux. Mass spectrometer and incoherent scatter model calculations at
600 km in the thermosphere indicate a 30% decrease in the temperature
and a 3X decrease in the density of the thermosphere near the altitude
where both the Upper Atmosphere Research Satellite (UARS) and Hubble
Space Telescope (HST) are flying. Decrease of the orbital period of
the UARS shows the expected effect of decreasing density at flight
altitude. Work in progress indicates that the output change results
from the decline in solar magnetic flux to a lower level of activity
in the southern hemisphere of the Sun.

---------------------------------------------------------
Title: On the calibration of line-of-sight magnetograms
Authors: Cauzzi, G.; Smaldone, L. A.; Balasubramaniam, K. S.; Keil,
S. L.
1993SoPh..146..207C Altcode:
Inference of magnetic fields from very high spatial, spectral, and
temporal resolution polarized images is critical in understanding the
physical processes that form and evolve fine scale structures in the
solar atmosphere. Studying high spectral resolution data also helps
in understanding the limits of lower resolution spectral data. We
compare three different methods for calibrating the line-of-sight
component of the magnetic field. Each method is tested for varying
degrees of spectral resolution on both synthetic line profiles computed
for known magnetic fields and real data. The methods evaluated are:
(a) the differences in the center of gravity of the right and left
circular components for different spectral resolution, (b) conversion
of circular polarization, at particular wavelengths, to magnetic
fields using model-dependent numerical solutions to the equations of
polarized radiative transfer, and (c) the derivative method using
the weak field approximation. Each method is applied to very high
spatial and spectral resolution circular polarization images of an
active region, acquired in the FeI 5250 å Zeeman-sensitive spectral
line. The images were obtained using the 20 må pass-band tunable
filter at NSO/Sacramento Peak Observatory Vacuum Tower Telescope. We
find that the center-of-gravity separation offers the best way of
inferring the longitudinal magnetic field.

---------------------------------------------------------
Title: C Class Flares: Dynamics at Multiple Heights in the Solar
Atmosphere
Authors: Balasubramaniam, K. S.; Keil, S. L.
1993BAAS...25R1214B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Calibrations of the JHU/APL-NSO-USAF Vector Magnetograph
Authors: Balasubramaniam, K. S.; Keil, S. L.
1993BAAS...25.1205B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Sun in a Non-Cycling State
Authors: White, O. R.; Skumanich, A.; Lean, J.; Livingston, W. C.;
Keil, S. L.
1992PASP..104.1139W Altcode:
Using the Baliunas and Jastrow (1990) study of cyclic variability in
solar-type stars, we transform existing solar data to the stellar HK
irradiance scale and examine the state of the solar chromosphere when a
solar-type star shows little cyclic variability and surface magnestis
m. To reduce the chromospheric emission to levels for G-type stars
showing no chromospheric activity cycles, no only must the sun be
free of plages and network; the brightness of the quiet chromosphere
in the K line must be reduced to levels seen only in 15% of the quiet
Sun area today. In contrast, the present day level of K emission from
the sun places it in the class of most active solar-type stars, far
removed from a non-cycling state. (SECTION: Stars)

---------------------------------------------------------
Title: Solar Ca II K Measurements and Activity Cycles in Solar-Type
Stars
Authors: White, O. R.; Livingston, W. C.; Keil, S. L.
1992sers.conf..160W Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High-Frequency Acoustic Waves and Effects of Magnetic Fields
on Wave Propagation in the Solar Photosphere
Authors: Reardon, K. W.; Keil, S. L.
1991BAAS...23.1389R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Narrow Bandpass Filter Solar Observations
Authors: Smaldone, L. A.; Cauzzi, G.; Keil, S. L.
1991BAAS...23.1057S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the Fractal Dimension of Granulation
Authors: Newbury, J.; Keil, S. L.
1991BAAS...23Q1048N Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Structure and oscillations in quiescent filaments from
observations in He i λ10830 å
Authors: Yi, Zhang; Engvold, Oddbjorn; Keil, Stephen L.
1991SoPh..132...63Y Altcode: 1991SoPh..132...63Z
Observations of two quiescent filaments show oscillatory variations
in Doppler shift and central intensity of the He I λ10830 Å line.

---------------------------------------------------------
Title: A Search for Polarization in Ellerman Bombs
Authors: Rust, D. M.; Keil, S. L.
1991BAAS...23R1029R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Variations of the Solar Calcium K-line 1976-1989
Authors: Keil, S. L.; Fleck, B.
1989BAAS...21.1185K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Line asymmetries and vertical velocities observed with a
narrow-band filter
Authors: Keil, S. L.; Bonaccini, D.; Tamblyn, P.; November, L. J.
1989hsrs.conf..272K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observations of High Frequency Waves in the Solar Atmosphere
Authors: Keil, S. L.; Mossman, A.
1989ASIC..263..333K Altcode: 1989ssg..conf..333K
No abstract at ADS

---------------------------------------------------------
Title: Observation and Interpretation of Photospheric Line Asymmetry
Changes near Active Regions
Authors: Keil, S. L.; Roudier, Th.; Cambell, E.; Koo, B. C.;
Marmolino, C.
1989ASIC..263..273K Altcode: 1989ssg..conf..273K
No abstract at ADS

---------------------------------------------------------
Title: U.S. Observing Facilities
Authors: Keil, Stephen L.
1988Sci...240.1263K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observational Results in Solar Astronomy with the Improved
Lockheed Active Mirror System
Authors: Smithson, R. C.; Acton, D. S.; Peri, M. L.; Sharbaugh, R. J.;
Dunn, R. B.; van der Lühe, O.; Keil, S. L.
1988BAAS...20R.710S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Effects of Magnetic Structures in the Solar Photosphere
on Energy Transport Mechanisms
Authors: Keil, S. L.
1987BAAS...19..940K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Vertical motions in quiescent prominences observed in the He
I λ10830 Å line.
Authors: Engvold, Oddbjorn; Keil, Stephen L.
1986NASCP2442..169E Altcode: 1986copp.nasa..169E
The observations contain two-dimensional spectral scans of a total
of 17 different prominences on the solar disk from the period 3 to 9
May 1981, using the main spectrograph of the solar vacuum telescope at
Sacramento Peak. The following conclusions may be drawn from the data:
(1) Blue shifts are much more common than red shifts. In many cases more
than 90 per cent of the projected prominence area is associated with
blue shifts. (2) The darkest prominence regions show the largest blue
shift (v less than 3 km s-1). (3) Red shifts are most commonly seen
at prominence edges. (4) The general pattern of prominence velocity
persists for several hours. On the scale of about 10 arcsec and less,
changes are detectable in the course of 2 to 5 minutes. The observed
predominance of the blue shifts is largely in agreement with earlier
results from H alpha (cf. Martres et al. 1981). It cannot, however,
be concluded definitely that the observed shift really represents a
net flow of matter. The situation could possibly be analogous to that
of the solar transition region where lines such as C IV lambda 1548
angstroms seem to indicate a net inflow, which can hardly be true,
at velocities greater than 4 km s(-1) in the quiet Sun (Athay et
al. 1983; Gurman and Athay 1983). If the typical structure element
of the prominence is sub-resolution, i.e., 2 to 3 arcsec or worse,
as in the present case, an apparent net shift could result if the
ascending and the decending elements have different temperature and/or
pressure. Different lines could then indicate different flow velocities
and even opposite directions.

---------------------------------------------------------
Title: Diagnostics for Propagating Waves in the Solar Photosphere
Authors: Keil, Stephen L.; Marmolino, Ciro
1986ApJ...310..912K Altcode:
The effects of pure acoustic waves of different frequencies on a
number of Fe I lines formed in the photosphere are investigated. A
dynamical model of the waves which considers velocity, temperature, and
pressure fluctuations as functions of time is used to compute the line
profiles. The extent to which the waves cause the lines to fluctuate,
the time-averaged properties of the line profiles, and the measurability
of vertical phase differences are all determined as functions of the
frequency of the propagating wave. It is concluded that there is no
intrinsic radiative limit, for frequencies of current observational
interest, on ability to measure phase differences. The asymmetry induced
by the propagation of acoustic waves in the photosphere is found to
depend on the frequency of the waves. Acoustic waves contribute only
marginally to line broadening.

---------------------------------------------------------
Title: A Stabilized Spectral Time Sequence of High-Frequency
Propagating Waves in the Solar Atmosphere
Authors: Keil, S. L.
1986BAAS...18..934K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Initial Solar Observations at Sacramento Peak Using the
Lockheed Active Optics System
Authors: Smithson, R. C.; Sharbaugh, R. J.; Ramsey, H. E.; Acton,
D. S.; Pari, M.; Keil, S. L.; Radick, R. R.; Simon, G. W.; von der
Luehe, O.; Zirker, J. B.
1986BAAS...18..933S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Some Effects of Propagating Wave Packets on Solar Spectral
Lines
Authors: Keil, S. L.; Koo, B. C.
1986BAAS...18Q.702K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Activity Measurement Experiment (SAMEX)
Authors: Keil, Stephen L.; Neidig, Donald F.
1986aiaa.meetQ....K Altcode:
SAMEX is the first step in providing the Air Force with a Solar Activity
Forecasting and Monitoring System in Space (SAFMSS). SAMEX will provide
the test bed for a high spatial resolution soft X-ray/EUV imager (20-150
A) and a high resolution vector magnetograph. The proposed payload
will be flown as part of the Space Test Program and subsequently used
to form the kernel of a Solar Activity Monitoring Satellite (SAMSAT)
that has been proposed by the Air Weather Service.

---------------------------------------------------------
Title: How Should Observers Prepare for the SOT / Solar Optical
Telescope / Hydrodymanic Experiments
Authors: Keil, S. L.
1985tphr.conf...30K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Steady flows in active regions observed with the HeI 10830
Å line
Authors: Lites, B. W.; Keil, S. L.; Scharmer, G. B.; Wyller, A. A.
1985SoPh...97...35L Altcode:
We show that the He I 10830 A line gives reliable Doppler shift
measurements in the upper chromosphere above active regions. Persistent
flow patterns in active regions observed near the solar limb show
features previously noted in Dopplergrams using the CIV transition
region ultraviolet emission line. Unlike the CIV measurements, however,
the He I absorption shows a strong correlation with the line-of-sight
velocity images in certain regions of some active regions.

---------------------------------------------------------
Title: A search for long-lived velocity fields at the solar poles
Authors: Durney, B. R.; Lytle, D. M.; Cram, L. E.; Guenther, D. B.;
Keil, S. L.
1985ApJ...292..752D Altcode:
A search has been made in the polar regions of the sun for large-scale
(50-200 Mm) velocity fields with lifetimes of the order of the solar
rotation period (approximately equal to or greater than 30 days). The
observations show that any such large-scale, long-lived velocity
patterns in the polar regions must have an amplitude less than 5
m/s. Marginally significant detections (at the 2-3 sigma level) were
made of two kinds of structures with amplitudes of order 3 m/s. One has
a rotation period approximately 38 days (close to the polar rotation
period at the sun's surface), and a scale approximately 150 Mm; the
other has a period approximately 24 days and a scale approximately
100 Mm. Tentatively, the first structure is interpreted as being of
supergranular origin. The second structure is interpreted as the
overshooting of the dominant convective mode of the lower solar
convection zone - the giant granulation.

---------------------------------------------------------
Title: Effects of Magnetic Fields on the Asymmetry of Photospheric
Line Profiles
Authors: Keil, S. L.
1985BAAS...17..642K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Stellar Convection. (Book Reviews: The Solar Granulation)
Authors: Keil, Stephen L.
1985Sci...227..512B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Stellar Convection. (Book Reviews: The Solar Granulation)
Authors: Keil, Stephen L.
1985Sci...227..512K Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Steady flows in active regions observed with the He I 10830
Å line.
Authors: Lites, B. W.; Keil, S. L.; Scharmer, G. B.; Wyller, A. A.
1985cdm..proc..287L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: How should observers prepare for the SOT hydrodynamic
experiments.
Authors: Keil, S. L.
1985MPARp.212...30K Altcode:
The author concentrates on the need to improve observations. He
discusses some of the things observers should be doing and some of
the problems they must consider to prepare for SOT (Solar Optical
Telescope). The author also discusses a few ongoing programs as
examples of the type of work that needs to be continued to prepare
observationally for SOT.

---------------------------------------------------------
Title: Time-resolved spectral observations of spicule velocities at
several heights
Authors: Sirajul Hasan, S.; Keil, S. L.
1984ApJ...283L..75S Altcode: 1984ApJ...283L..75H
The vacuum telescope of the National Solar Observatory, Sacramento
Peak was used to obtain H-alpha spectral observations of spicules. A
set of spectra corresponding to five slit positions above the solar
limb were recorded every 8 s in order to study the temporal variation
of spicules at several heights with high space and time resolution. The
short time interval (less than 2 s) between exposures at each height is
a new feature of these observations. A typical flow event in a spicule
was found to last 10-15 minutes. During this period the velocity did
not reverse sign. The temporal behavior of the velocity at different
heights in a spicule appeared to show a high correlation, with a time
lag less than 7 s, implying signal propagation speeds greater than
300 km/s. Finally, no significant variation of spicule velocity with
height in the chromosphere was noticed.

---------------------------------------------------------
Title: On the rotation rate of polar features in the sun
Authors: Durney, B. R.; Lytle, D. M.; Keil, S. L.
1984ApJ...281..455D Altcode:
The authors evaluate the rotation rate of solar features in the
vicinity of the poles with the help of a correlation procedure. The
average rotation rates for both poles are systematically smaller than
those predicted by Howard and Harvey's formula, but not in serious
disagreement with their results.

---------------------------------------------------------
Title: Observations of High Frequency Waves Using a CCD Array
Authors: Melroy, P. A.; Keil, S. L.
1984ssdp.conf...19M Altcode:
The authors have measured phase shifts between line displacement
fluctuations at various intensity levels in Fe I 5576 and 6302 for
frequencies up to 40 mHz. Waves with frequencies between 4.2 mHz and 10
mHz are propagating upwards with propagation velocities near the sound
speed. The amplitude of the fluctuations corresponds to approximately
100 m/sec. Although the authors measure power in the fluctuations
above 10 mHz, the phase shifts drop to zero for higher frequencies. The
authors find some evidence for periodic ripples in the high frequency
tail of temporal power spectra of the line displacements as reported
earlier by Deubner (1976), but these could result from atmospheric
and instrumental effects.

---------------------------------------------------------
Title: Line Asymmetries of Partially Resolved Granular Profiles
Authors: Keil, S. L.
1984ssdp.conf..148K Altcode:
A time series of high-spatial resolution spectrograms made in the solar
photospheric line Fe I 5576 is used to extract line profiles formed
in bright granular regions and dark intergranular lanes. The author
forms various mean profiles to generate representative granular and
intergranular profiles. The asymmetry of these mean profiles is compared
with asymmetries predicted from models of the granulation flow. The
observations are compatible with penetrating convective elements having
velocity scale heights of approximately 100 km in the photosphere.

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Title: Variations in the solar calcium K line 1976-1982
Authors: Keil, S. L.; Worden, S. P.
1984ApJ...276..766K Altcode:
Chromospheric variability between 1976 and 1982 as evidenced in Ca
II K line observations obtained at Sacramento Peak Observatory is
reported. The data on solar variability are compared to similar data
collected at Kitt Peak by White and Livingston (1981). The measurement
of solar rotation as reflected in the K index was attempted. Partial
success was achieved in this second objective, based on limited
results in early 1977 and early 1981-1982. While there is good long
term (about 6 months) correlation between the K line and the number
of plages and sunspots during the rising phase of solar activity,
the short term correlation (about 1 week) is poor.

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Title: Small-scale dynamical processes in quiet stellar
atmospheres. Proceedings of a workshop, held at Sunspot, New Mexico,
USA, 25 - 29 July 1983.
Authors: Keil, S. L.
1984ssdp.conf.....K Altcode:
High-resolution observations of small-scale solar dynamics are
discussed, taking into account the phase relations of high degree
p-modes, power spectra of short-period oscillations, observations of
high frequency waves using CCD array, dynamic signatures of quiet
sun magnetic fields, and small-scale dynamical processes in the
solar chromosphere. Other topics explored are related to projected
improvements to high-resolution measurements, interpretation of
high-resolution measurements, modelling of small-scale dynamical
processes, convection and wave generation, interaction between solar
convection and magnetism, low-resolution observations bearing on
small-scale dynamical processes in the sun, the interpretation of
low resolution observations, the accuracy of models obtained from
low-resolution observations, and observations and interpretations of
small-scale dynamical processes in stellar atmospheres. Attention is
given to the observation of stellar granulation, and Zeeman broadening
in solar type stars.

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Title: Detection of Propagating Waves in the Solar Photosphere
Authors: Keil, S. L.; Marmolino, C.
1983BAAS...15Q.971K Altcode:
No abstract at ADS

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Title: The characteristic size and brightness of facular points in
the quietphotosphere.
Authors: Muller, R.; Keil, S. L.
1983SoPh...87..243M Altcode: 1983SoPh...87..243K
Using two very high resolution, white-light plates of the solar
granulation, we measure a characteristic size and intensity for
facular points. The plates were obtained with the 50 cm refractor
at Pic-du-Midi Observatory using a 60 Å bandpass filter center at
5750 Å. After adjustment for atmospheric and instrumental smearing,
we find a characteristic size of 0.22 arc sec and a characteristic
intensity of 1.3 to 1.5 times the mean continuum intensity.

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Title: Observations of Polar Velocity Fields
Authors: Durney, B. R.; Lytle, D. M.; Cram, L. E.; Guenther, D. B.;
Keil, S. L.
1983BAAS...15..716D Altcode:
No abstract at ADS

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Title: High Frequency Waves in the Photosphere
Authors: Keil, S. L.; Melroy, P. A.
1983BAAS...15R.705K Altcode:
No abstract at ADS

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Title: Solar Rotation and Variability Observed in the Ca II K Line
Authors: Keil, S. L.; Worden, S. P.
1982BAAS...14..623K Altcode:
No abstract at ADS

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Title: A Search for Granular Induced Wave Modes
Authors: Keil, S. L.
1981BAAS...13R.911K Altcode:
No abstract at ADS

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Title: Photospheric Line Asymmetry and Granular Velocity Models
Authors: Keil, S. L.; Yackovich, F. H.
1981SoPh...69..213K Altcode:
We analyze spectral line profiles obtained from regions of the solar
surface exhibiting either an upflow or a downflow on a spatial and
temporal scale corresponding to the white-light granulation. The
differences between their line bisectors are measured to quantify
changes in the asymmetry of the profile resulting from granular
motion. The observed bisector differences are compared with differences
predicted using conflicting granular models. Models, in which the
motion of large, long-lived granules decreases rapidly with increasing
height in the photosphere, are compatible with the observed line
profile asymmetries.

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Title: Dynamical models of convective penetration and high-spatial
resolution observations.
Authors: Keil, S. L.
1980BAAS...12..747K Altcode:
No abstract at ADS

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Title: The structure of solar granulation. I - Observations of the
spatial and temporal behavior of vertical motions. II - Models of
vertical motion
Authors: Keil, S. L.
1980ApJ...237.1024K Altcode:
The height dependence of the granular contribution to observed
photospheric line shifts were deduced using a temporal sequence of
spectroscopic measurements each covering a large horizontal distance
on the solar disk. The deduced height variations represent the most
accurate determination to date because individual granules can be
isolated in both time and space simultaneously in several spectral
lines. The previous attempts to deduce the height dependence,
based on spectrograms having only one spatial resolution which led
to conflicting pictures of the granular velocities are discussed;
it is shown that a purely spatial separation of oscillatory and
granular motions such as used by Mattig and Schlebbe and Durrant et
al. (1979) is inadequate for determining granular velocities. Granules
are predominant source of line shifts in the photosphere; much of the
line-shift fluctuation power at small spatial scales in the stronger
lines, which some authors incorrectly attributed to granules, results
from high-frequency oscillations.

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Title: The Structure of Solar Granulation - Part Two - Models of
Vertical Motion
Authors: Keil, S. L.
1980ApJ...237.1035K Altcode:
Several models proposed for the height dependence of the vertical
motion associated with granules are used to compute photo spheric
line shifts. These predicted line shifts are compared with recent
observations of line shifts resulting from granular motion in a number
of lines whose heights of formation span the photosphere and low
chromosphere. An empirical model of the granular flow giving agreement
between predicted and observed line shifts is deduced. At a height
100 km above τ5000 Å = 1 the amplitude of the granular
flow is approximately 2 km s-1, and an appropriate scale
height for the granular flow at this altitude is ∼80 km.

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Title: The interpretation of solar line shift observations
Authors: Keil, S. L.
1980A&A....82..144K Altcode:
The accuracy of height-dependent photospheric velocity fields inferred
from observed line shifts by the use of velocity weighting (response)
functions is evaluated. Several Fe I profiles for lines near 5150
A are synthesized by using an atmospheric model which includes
horizontal fluctuations in temperature and velocity as well as a
vertical differential velocity field. For assumed geometries of the
granular and oscillatory motions, root-mean-square velocity fluctuations
are synthesized and compared with predictions based on the velocity
weighting functions. It is found that the line synthesis analysis
required larger amplitude granular velocity fluctuations deep in the
photosphere and a more rapid fall off with height than those obtained
by analyzing the same data with velocity weighting functions. Simple
models for the height dependence of the velocity field are used to
determine when the assumptions upon which the use of velocity weighting
functions are based are no longer valid.

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Title: Sources of noise in solar limb definitions
Authors: Keil, S. L.; Worden, S. P.
1980LNP...125..219K Altcode: 1980nnsp.work..219K
A test series of spectroheliograms has been used to evaluate
the hypothesis that the rotation and evolution of solar surface
structure can function as a source of noise in solar limb definition
measurements. The study confirms the hypothesis, and results demonstrate
the amount of variation in solar limb position which is attributable
to evolutionary changes in solar surface structure.

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Title: Some effects of acoustic waves on spectral-line profiles.
Authors: Cram, L. E.; Keil, S. L.; Ulmschneider, P.
1979ApJ...234..768C Altcode:
The paper discusses the formation of spectral lines in the presence of
short-period, nonlinear, radiatively damped acoustic waves propagating
through a model of the solar atmosphere. The temperature and pressure
perturbations associated with the wave strongly influence the line
profile. Although their wavelength is less than the depth of the
velocity response function of photospheric spectral lines, the
acoustic waves produce large (greater than 100 m/s), short-period
line shifts. Acoustic waves of sufficient amplitude to account for
chromospheric heating do not significantly increase the equivalent
widths of photospheric lines and therefore are probably not responsible
for photospheric microturbulence.

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Title: Line Asymmetries Due to Granular Motion
Authors: Keil, S. L.
1979BAAS...11..711K Altcode:
No abstract at ADS

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Title: Some Comments on the Interpretation of Photospheric Line Shifts
Authors: Keil, S. L.
1979BAAS...11..407K Altcode:
No abstract at ADS

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Title: Sources of Noise in Solar Limb Definitions.
Authors: Worden, S. P.; Keil, S. L.
1979BAAS...11..399W Altcode:
No abstract at ADS

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Title: The Height Variation of Velocity and Temperature Fluctuations
in the Solar Photosphere
Authors: Keil, S. L.; Canfield, R. C.
1978A&A....70..169K Altcode:
Summary. The Vacuum Tower Telescope of Sacramento Peak Observatory is
used to observe intensity and velocity fluctuations in several Fe I
lines as functions of heliocentric angle. We derive the vertical and
horizontal components of the velocity fluctuations, using the technique
developed by Canfield (1976) to separate granular and oscillatory
velocities. We also find a set of height dependent temperature
perturbations which are capable of reproducing the observed intensity
fluctuations. The horizontal component of the granular velocity is found
to be between one and two km 1 greater than the vertical component
(depending on height in the atmosphere). A temperature perturbation
(constant with height) of 175 1 25 K in the upper layers of the
atmosphere [Tsooo 0.1] is sufficient to reproduce the intensity
fluctuations in the strong lines. In deeper layers the temperature
perturbations must increase rapidly with depth to reproduce the observed
intensity fluctuations in the continuum and weak lines. Key words: solar
atmosphere - solar velocity fluctuations - solar temperature structure

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Title: Dynamical Processes in the Solar Atmosphere: Observational
and theoretical results concerning the nature of "turbulence"
Authors: Keil, S. L.; Cram, L. E.
1978BAAS...10..638K Altcode:
No abstract at ADS

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Title: The Height Dependence of Solar Velocity Fluctuations.
Authors: Keil, S. L.
1978BAAS...10..415K Altcode:
No abstract at ADS

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Title: A new measurement of the center-to-limb variation of the rms
granular contrast.
Authors: Keil, S. L.
1977SoPh...53..359K Altcode:
The center-to-limb variation of the root-mean-square granular
contrast at 5520 Å is deduced from a set of high-spatial-resolution
filtergrams obtained with the Sacramento Peak Observatory Vacuum Tower
Telescope. The rms contrast is observed to decrease monotonically
between μ = 1.0 and 0.6, and then increase slightly at μ = 0.4. This
result is compared with the results of Edmonds (1962) and with the
results of Pravdjuk et al. (1974).

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Title: Intensity, velocity and temperature fluctuations in the upper
solar atmosphere.
Authors: Altrock, R. C.; Keil, S. L.
1977A&A....57..159A Altcode:
High-spatial-resolution photographic spectra of the Mg I 4571-A line
at 10 solar disk positions from center to limb are reduced to yield
intensity and velocity (line-shift) fluctuations along the spectrograph
slit for a height of about 300 km above the continuum level. The data
obtained are used to compute rms intensity and velocity fluctuations
corrected for instrument smearing. Comparison of the results with
those of Cannon and Wilson (1971) reveals a flatter distribution of
the rms intensity fluctuation as a function of heliocentric angle
and a 60% larger fluctuation at the disk center. It is inferred that
the correlation between velocity and intensity fluctuations exhibits
a large-scale random structure. The intensity-fluctuation data are
analyzed by calculating the emergent intensity from a three-dimensional
atmosphere having a sinusoidal checkerboard pattern of temperature
with a height-dependent amplitude, taking into account fluctuations in
electron pressure. The range of solutions for temperature fluctuations
is found to indicate that there are causes other than oscillations
for the temperature fluctuations in the upper photosphere.

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Title: Photospheric Inhomogeneities: Continuum Fluctuations
Authors: Keil, S. L.
1976BAAS....8..324K Altcode:
No abstract at ADS

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Title: Models of Solar Granular Structure and the Interpretation of
Photospheric Observations.
Authors: Keil, S. L.
1974PhDT.........3K Altcode:
Research data show that standard methods of deriving solar atmospheric
models do not necessarily yield good average models. Data are given
on: (1) standard one-dimensional calculations and observations
which show these calculations can be misleading, (2) problems of
radiation transfer in a two-dimensional two component atmosphere,
and calculations of limitations on possible structure and magnitude
of horizontal temperature fluctuation using the observed root mean
square brightness distribution as a boundary condition, (3) computation
of possible effects of weak solar magnetic fields on the granulation
pattern, and (4) the examination of possible physical interpretations
of granular models obtained.

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Title: Solar Granulation, Limb Flux, and Oblateness
Authors: Kandel, Robert S.; Keil, Stephen L.
1973SoPh...33....3K Altcode:
The radiation field, emergent from an inhomogeneous atmosphere,
may differ significantly from that calculated using a mean model for
such an atmosphere. In the solar case, horizontal anisotropy of the
granulation pattern leads to azimuthal dependence of the emergent
intensity, and this appears as a latitude-dependent limb flux
which may mimic oblateness. We examine this latitude-dependence for
several two and three-dimensional models of the inhomogeneous solar
atmosphere, with varying degrees of anisotropy in the granulation
pattern. Elongation along an east-west axis of about 7% would yield
a signal somewhat imperfectly mimicking an excess oblateness of 4 ×
10−5. Using the Babcock-Leighton model of the general
solar magnetic field we show that some stretching of granules, of
this order of magnitude, should be expected. However, it may vary
with the solar activity cycle, and in any case the result is very
sensitive to the parameters adopted. Even if study of granulation
observations should exclude elongations as high as 7%, smaller
essentially undetectable elongations may exist. We find that 1 %
elongation can account for 25-50 % of a signal corresponding to excess
oblateness 4 × 10−5. We conclude that anisotropy of
the granulation pattern may influence oblateness determinations; when
this is considered together with other effects, much of the claimed
oblateness may be eliminated.

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Title: Granulation Patterns and Solar Oblateness.
Authors: Kandel, R. S.; Keil, S. L.
1971BAAS....3R.376K Altcode:
No abstract at ADS