Author name code: jefferies-stuart
ADS astronomy entries on 2022-09-14
=author:"Jefferies, S.M." OR =author:"Jefferies, Stuart M."
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Title: Moving Speckle Imaging into New Frontiers
Authors: Martinez, Arturo O.; Hope, Douglas A.; Jefferies, Stuart M.;
Howell, Steve B.; Baron, Fabien R.
Bibcode: 2022AAS...24030205M
Altcode:
A common method used in speckle interferometric analysis is based on
a series of temporal correlations between Fourier components of short
exposure images. We present results on the next advancement beyond
speckle interferometry that uses multi-frame blind deconvolution (MFBD)
algorithm to detect closely spaced objects with high-contrast ratios,
such as faint binary companions. MFBD estimates the parameters that
describe the object and the point-spread functions (PSFs) and uses
physical constraints to increase the fidelity of these parameter
estimates. However, detecting faint companions requires large volumes
of data, typically thousands of frames. Numerical algorithms such
as MFBD require minimizing an error metric between the modeled data
and actual imagery which requires solving a set of parameters that
describe the blur in the image and the object scene. In large data sets,
parameter space becomes heavily pocketed with local minima, which can
typically cause MFBD algorithms to stagnate and fail to find reasonable
approximate physical solutions that describe faint companions within
the image. We present a compact MFBD (CMFBD) method as a preliminary
step before using MFBD that uses consistency constraints imposed
on the data from turbulence-induced temporal correlations to move
the parameter space closer to the global minimum. We show images of
various examples of restorations of objects and compare our results to
those produced from conventional speckle interferometric methods. Even
though CMFBD/MFBD is at the frontier of speckle image restoration,
we plan to improve upon the MFBD algorithm in the near future by
introducing the use of alternating direction method of multipliers
(ADMM) to improve object and PSF estimation by enforcing physical
constraints on sparsity and smoothness in the object, and wavelength
diversity as a constraint of the estimated PSFs. ADMM techniques can
cascade penalty functions and can leverage on the PSF in multiple ways,
simultaneously, for better recovery of the true object.
Title: PMODE I: Design and Development of an Observatory for
Characterizing Giant Planet Atmospheres and Interiors
Authors: Shaw, Cody L.; Gulledge, Deborah J.; Swindle, Ryan; Jefferies,
Stuart M.; Murphy, Neil
Bibcode: 2022FrASS...968452S
Altcode:
The giant planets of our Solar System are exotic laboratories,
enshrouding keys which can be used to decipher planetary formation
mysteries beneath their cloudy veils. Seismology provides a direct
approach to probe beneath the visible cloud decks, and has long
been considered a desirable and effective way to reveal the interior
structure. To peer beneath the striking belts and zones of Jupiter and
to complement previous measurements—both Doppler and gravimetric—we
have designed and constructed a novel instrument suite. This set of
instruments is called PMODE—the Planetary Multilevel Oscillations and
Dynamics Experiment, and includes a Doppler imager to measure small
shifts of the Jovian cloud decks; these velocimetric measurements
contain information related to Jupiter's internal global oscillations
and atmospheric dynamics. We present a detailed description of
this instrument suite, along with data reduction techniques and
preliminary results (as instrumental validation) from a 24-day
observational campaign using PMODE on the AEOS 3.6 m telescope atop
Mount Haleakalā, Maui, HI during the summer of 2020, including a
precise Doppler measurement of the Jovian zonal wind profile. Our
dataset provides high sensitivity Doppler imaging measurements of
Jupiter, and our independent detection of the well-studied zonal wind
profile shows structural similarities to cloud-tracking measurements,
demonstrating that our dataset may hold the potential to place future
constraints on amplitudes and possible excitation mechanisms for the
global modes of Jupiter.
Title: Post-AO High-resolution Imaging Using the Kraken Multi-frame
Blind Deconvolution Algorithm
Authors: Hope, Douglas A.; Jefferies, Stuart M.; Li Causi, Gianluca;
Landoni, Marco; Stangalini, Marco; Pedichini, Fernando; Antoniucci,
Simone
Bibcode: 2022ApJ...926...88H
Altcode: 2022arXiv220202178H
In the context of extreme adaptive optics for large telescopes,
we present the Kraken multi-frame blind deconvolution (MFBD)
algorithm for processing high-cadence acquisitions, capable of
providing a diffraction-limited estimation of the source brightness
distribution. This is achieved by a data modeling of each frame in
the sequence driven by the estimation of the instantaneous wave front
at the entrance pupil. Under suitable physical constraints, numerical
convergence is guaranteed by an iteration scheme starting from a compact
MFBD, which provides a very robust initial guess that only employs a few
frames. We describe the mathematics behind the process and report the
high-resolution reconstruction of the spectroscopic binary α And (16.3
mas separation) acquired with the precursor of SHARK-VIS, the upcoming
high-contrast camera in the visible for the Large Binocular Telescope.
Title: A novel approach to identify resonant MHD wave modes in solar
pores and sunspot umbrae: B − ω analysis
Authors: Stangalini, M.; Jess, D. B.; Verth, G.; Fedun, V.; Fleck, B.;
Jafarzadeh, S.; Keys, P. H.; Murabito, M.; Calchetti, D.; Aldhafeeri,
A. A.; Berrilli, F.; Del Moro, D.; Jefferies, S. M.; Terradas, J.;
Soler, R.
Bibcode: 2021A&A...649A.169S
Altcode: 2021arXiv210311639S
The umbral regions of sunspots and pores in the solar photosphere are
generally dominated by 3 mHz oscillations, which are due to p-modes
penetrating the magnetic region. In these locations, wave power is
also significantly reduced with respect to the quiet Sun. However,
here we study a pore where not only is the power of the oscillations
in the umbra comparable to, or even larger than, that of the quiet
Sun, but the main dominant frequency is not 3 mHz as expected, but
instead 5 mHz. By combining Doppler velocities and spectropolarimetry
and analysing the relationship between magnetic field strength and
frequency, the resultant B − ω diagram reveals distinct ridges that
are remarkably clear signatures of resonant magneto-hydrodynamic (MHD)
oscillations confined within the pore umbra. We demonstrate that these
modes, in addition to velocity oscillations, are also accompanied
by magnetic oscillations, as predicted from MHD theory. The novel
technique of B − ω analysis proposed in this article opens up
an exciting new avenue for identifying MHD wave modes in the umbral
regions of both pores and sunspots.
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
Bibcode: 2021SoPh..296...70R
Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
Title: A new method for detecting solar atmospheric gravity waves
Authors: Calchetti, Daniele; Jefferies, Stuart M.; Fleck, Bernhard;
Berrilli, Francesco; Shcherbik, Dmitriy V.
Bibcode: 2021RSPTA.37900178C
Altcode: 2020arXiv200800210C
Internal gravity waves have been observed in the Earth's atmosphere
and oceans, on Mars and Jupiter, and in the Sun's atmosphere. Despite
ample evidence for the existence of propagating gravity waves in the
Sun's atmosphere, we still do not have a full understanding of their
characteristics and overall role for the dynamics and energetics of
the solar atmosphere. Here, we present a new approach to study the
propagation of gravity waves in the solar atmosphere. It is based on
calculating the three-dimensional cross-correlation function between
the vertical velocities measured at different heights. We apply this
new method to a time series of co-spatial and co-temporal Doppler
images obtained by SOHO/MDI and Hinode/SOT as well as to simulations
of upward propagating gravity wave-packets. We show some preliminary
results and outline future developments. This article is part of
the Theo Murphy meeting issue `High-resolution wave dynamics in the
lower solar atmosphere'.
Title: Looking into the future of interferometry using free-space
beam propagation
Authors: Martinez, Arturo O.; Abbott, Caleb G.; Jefferies, Stuart M.;
ten Brummelaar, Theo A.; Baron, Fabien R.
Bibcode: 2020SPIE11446E..1BM
Altcode:
We describe a new concept for future interferometric observations. Our
laboratory experiment simulates an interferometer with two telescopes
observing through different volumes of atmospheric turbulence. We
simulate both vertical and horizontal propagation through the
atmosphere; the latter mimics free-space beam propagation without
the need for vacuum pipes or fiber optics. Practically, we simulate
the effects of atmospheric turbulence using numerically calculated
Kolmogorov phase screens injected onto a spatial light modulator. We
correct this distorted wavefront using an adaptive optics system to
determine the range of turbulence conditions over which we can detect
fringes from the two telescopes. Our experiment lays the groundwork for
investigating the potential of having movable telescopes in which light
propagates from the telescopes to the beam combiner through free space.
Title: A versatile turbulence simulator for high-resolution imaging
studies of astronomical targets
Authors: Abbott, Caleb G.; Martinez, Arturo O.; Jefferies, Stuart M.;
ten Brummelaar, Theo; Baron, Fabien R.
Bibcode: 2020SPIE11448E..3TA
Altcode:
We describe versatile turbulence simulator for testing and calibration
of new techniques for high-resolution imaging of objects outside
the Earth's atmosphere using ground-based instrumentation. Examples
here include: dynamic aperture diversity, wave front sensing using
multi-aperture phase retrieval, and free-space beam propagation for
rapidly re-configurable interferometers. Used in the testing of all of
these, the simulator uses a high resolution spatial light modulator in
tandem with a lower resolution deformable mirror to simulate atmospheric
phase distortions over a wide range of turbulence conditions.
Title: Tor Vergata Synoptic Solar Telescope: spectral characterization
of potassium KI D1 MOFs
Authors: Calchetti, Daniele; Viavattene, Giorgio; Terranegra, Luciano;
Pietropaolo, Ermanno; Oliviero, Maurizio; Murphy, Neil; Jefferies,
Stuart M.; Giovannelli, Luca; Del Moro, Dario; Berrilli, Francesco
Bibcode: 2020SPIE11445E..2TC
Altcode:
Synoptic telescopes are fundamental tools in Solar Physics and
Space Weather. Their typical high cadence full-disk observations are
pivotal to assess the physical conditions on the Sun and to forecast
the evolution in time of those conditions. The TSST (Tor vergata
Synoptic Solar Telescope) is a synoptic telescope composed of two
main full-disk instruments: an H-alpha Daystar SR-127 telescope and
a Magneto Optical Filter (MOF)-based telescope in the Potassium KI at
769.90 nm. The MOF consists in a glass cell containing a Potassium vapor
where a longitudinal magnetic field is applied. The MOF-based channel
produces full disk Line-of-Sight magnetic field and velocity maps of
the solar photosphere at 300 km above the solar surface. In this work,
we present the optical setup, the spectral characterization of the
MOF-based telescope, and details on the spectral characterization of the
MOFs cells which is a required test to obtain calibrated magnetograms
and dopplergrams.
Title: Measuring the Dispersion Relation of Acoustic-Gravity Waves
in the Solar Atmosphere
Authors: Fleck, Bernhard; Jefferies, Stuart M.; Murphy, Neil;
Berrilli, Francesco
Bibcode: 2020ASSP...57..141F
Altcode:
We use localized measurements of the dispersion relation for
acoustic-gravity waves to generate the first maps of the spatial
structure of the sound speed, acoustic cut-off frequency, and radiative
damping time in the Sun's lower atmosphere. These maps offer a new
diagnostic for the solar atmosphere.
Title: Observed Local Dispersion Relations for Magnetoacoustic-gravity
Waves in the Sun’s Atmosphere: Mapping the Acoustic Cutoff Frequency
Authors: Jefferies, Stuart M.; Fleck, Bernhard; Murphy, Neil;
Berrilli, Francesco
Bibcode: 2019ApJ...884L...8J
Altcode: 2019arXiv191003198J
We present the observed local dispersion relations for
magnetoacoustic-gravity waves in the Sun’s atmosphere for different
levels of magnetic field strength. We model these data with a
theoretical local dispersion relation to produce spatial maps of the
acoustic cutoff frequency in the Sun’s photosphere. These maps have
implications for the mechanical heating of the Sun’s upper atmosphere,
by magnetoacoustic-gravity waves, at different phases of the solar
magnetic activity cycle.
Title: Recurrence Quantification Analysis as a Post-processing
Technique in Adaptive Optics High-contrast Imaging
Authors: Stangalini, M.; Li Causi, G.; Pedichini, F.; Antoniucci,
S.; Mattioli, M.; Christou, J.; Consolini, G.; Hope, D.; Jefferies,
S. M.; Piazzesi, R.; Testa, V.
Bibcode: 2018ApJ...868....6S
Altcode: 2018arXiv181000714S
In this work we explore the possibility of using recurrence
quantification analysis (RQA) in astronomical high-contrast imaging to
statistically discriminate the signal of faint objects from speckle
noise. To this end, we tested RQA on a sequence of high frame rate
(1 kHz) images acquired with the SHARK-VIS forerunner at the Large
Binocular Telescope. Our tests show promising results in terms of
detection contrasts at angular separations as small as 50 mas,
especially when RQA is applied to a very short sequence of data
(2 s). These results are discussed in light of possible science
applications and with respect to other techniques such as, for example,
angular differential imaging and speckle-free imaging.
Title: The MOTH II Doppler-Magnetographs and Data Calibration Pipeline
Authors: Forte, Roberta; Jefferies, Stuart M.; Berrilli, Francesco;
Del Moro, Dario; Fleck, Bernhard; Giovannelli, Luca; Murphy, Neil;
Pietropaolo, Ermanno; Rodgers, Wayne
Bibcode: 2018IAUS..335..335F
Altcode:
The calibration pipeline of the level zero images obtained from
the Magneto-Optical filters at Two Heights (MOTH II) instrument is
presented. MOTH II consists of two 20 cm aperture instruments, each
using a Magneto-Optical Filter (MOF): one at 5896 Å (Na D2-line), the
other one at 7700 Å (K I-line). MOTH II instruments thus provide full
disk line-of-sight Doppler velocity and magnetic field measurements at
two heights in the solar atmosphere. The developed MOTH II pipeline
employs a set of standard calibration corrections, a correction for
signal leakage, due to the non-ideal behavior of the polarizers, and
the geometrical registration between the eight images acquired by four
CMOS cameras, relative to two components of the signal in two circular
polarization states, in each of the two channels. MOTH II data are used
to investigate atmospheric dynamics (e.g., internal gravity waves and
magneto-acoustic portals) and Space Weather phenomena. Particularly,
flare forecasting algorithms, based on the detection of magnetic active
regions (ARs) and associated flare probability estimation, are currently
under development. The possible matching of MOTH II data with SDO/HMI
and SDO/AIA images into a flux rope model, developed in collaboration
between Harvard-Smithsonian CfA and MIT Laboratory for Nuclear Science,
is being tested.
Title: Recurrence quantification analysis as a post-processing
technique in adaptive optics high contrast imaging
Authors: Stangalini, M.; Li Causi, G.; Pedichini, F.; Antoniucci,
S.; Mattioli, M.; Christou, J.; Consolini, G.; Hope, D.; Jefferies,
S. M.; Piazzesi, R.; Testa, V.
Bibcode: 2018SPIE10703E..2VS
Altcode:
Recurrence Quantification Analysis (RQA) is a non-linear time
series analysis technique widely employed in many different research
fields. Among the many applications of this method, it has been shown
that it can be successfully employed in the detection of small signals
embedded into noise. In this work we explore the possibility of using
the RQA in astronomical high contrast imaging, for the detection of
faint objects nearby bright sources in very high frame rate (1 KHz)
data series. For this purpose, we used a real 1 kHz image sequence of a
bright star, acquired with the SHARK-VIS forerunner at LBT. Our results
show excellent performances in terms of detection contrasts even with a
very short data sequence (a few seconds). The use of RQA in astronomical
high contrast imaging is discussed in light of the possible science
applications and with respect to other techniques like, for example,
the angular differential imaging (ADI) or the Speckle-Free ADI (SFADI).
Title: The Importance of Long-Term Synoptic Observations and Data
Sets for Solar Physics and Helioseismology
Authors: Elsworth, Yvonne; Broomhall, Anne-Marie; Gosain, Sanjay;
Roth, Markus; Jefferies, Stuart M.; Hill, Frank
Bibcode: 2017hdsi.book..143E
Altcode:
No abstract at ADS
Title: Image Restoration from Limited Data
Authors: Hope, D.; Hart, M.; Swindle, T. R.; Jefferies, S. M.
Bibcode: 2017amos.confE..86H
Altcode:
Ground-based imagery of satellites is a cornerstone of SSA. The
resolution of this imagery is fundamentally limited by turbulence in
the atmosphere. Full resolution can be restored by using advanced
multi-frame blind deconvolution (MFBD) algorithms which, applied
to sequences of short-exposure images, estimate the object scene and
point spread functions (PSFs) that characterize the turbulence. Because
there are always more variables to estimate than measurements, MFBD is
an ill-posed problem. Furthermore, in the regime of limited data, for
example a satellite with a rapidly changing pose, the problem is also
ill-conditioned because of the lack of diversity in the PSFs. These
challenges typically lead to poor quality restorations. The Daylight
Object Restoration Algorithm (DORA) overcomes this problem, by using
additional simultaneous measurements from a wave-front sensor, along
with a frozen flow model of the atmosphere, to achieve high-resolution
estimates of space objects from limited data sets. The improvement in
image resolution achieved by DORA when compared to current state of
the art MFBD algorithms is demonstrated using real data.
Title: Daylight operation of a sodium laser guide star for adaptive
optics wavefront sensing
Authors: Hart, Michael; Jefferies, Stuart M.; Murphy, Neil
Bibcode: 2016JATIS...2d0501H
Altcode:
We report contrast measurements of a sodium resonance guide star against
the daylight sky when observed through a tuned magneto-optical filter
(MOF). The guide star was created by projection of a laser beam at
589.16 nm into the mesospheric sodium layer and the observations
were made with a collocated 1.5-m telescope. While MOFs are used with
sodium light detecting and ranging systems during the day to improve
the signal-to-noise ratio of the measurements, they have not so far
been employed with laser guide stars to drive adaptive optics (AO)
systems to correct atmospherically induced image blur. We interpret
our results in terms of the performance of AO systems for astronomy,
with particular emphasis on thermal infrared observations at the next
generation of extremely large telescopes now being built.
Title: The Importance of Long-Term Synoptic Observations and Data
Sets for Solar Physics and Helioseismology
Authors: Elsworth, Yvonne; Broomhall, Anne-Marie; Gosain, Sanjay;
Roth, Markus; Jefferies, Stuart M.; Hill, Frank
Bibcode: 2015SSRv..196..137E
Altcode: 2015SSRv..tmp..106E
A casual single glance at the Sun would not lead an observer to conclude
that it varies. The discovery of the 11-year sunspot cycle was only
made possible through systematic daily observations of the Sun over
150 years and even today historic sunspot drawings are used to study
the behavior of past solar cycles. The origin of solar activity is
still poorly understood as shown by the number of different models
that give widely different predictions for the strength and timing
of future cycles. Our understanding of the rapid transient phenomena
related to solar activity, such as flares and coronal mass ejections
(CMEs) is also insufficient and making reliable predictions of these
events, which can adversely impact technology, remains elusive. There
is thus still much to learn about the Sun and its activity that requires
observations over many solar cycles. In particular, modern helioseismic
observations of the solar interior currently span only 1.5 cycles,
which is far too short to adequately sample the characteristics of
the plasma flows that govern the dynamo mechanism underlying solar
activity. In this paper, we review some of the long-term solar and
helioseismic observations and outline some future directions.
Title: ADAHELI: exploring the fast, dynamic Sun in the x-ray, optical,
and near-infrared
Authors: Berrilli, Francesco; Soffitta, Paolo; Velli, Marco; Sabatini,
Paolo; Bigazzi, Alberto; Bellazzini, Ronaldo; Bellot Rubio, Luis
Ramon; Brez, Alessandro; Carbone, Vincenzo; Cauzzi, Gianna; Cavallini,
Fabio; Consolini, Giuseppe; Curti, Fabio; Del Moro, Dario; Di Giorgio,
Anna Maria; Ermolli, Ilaria; Fabiani, Sergio; Faurobert, Marianne;
Feller, Alex; Galsgaard, Klaus; Gburek, Szymon; Giannattasio, Fabio;
Giovannelli, Luca; Hirzberger, Johann; Jefferies, Stuart M.; Madjarska,
Maria S.; Manni, Fabio; Mazzoni, Alessandro; Muleri, Fabio; Penza,
Valentina; Peres, Giovanni; Piazzesi, Roberto; Pieralli, Francesca;
Pietropaolo, Ermanno; Martinez Pillet, Valentin; Pinchera, Michele;
Reale, Fabio; Romano, Paolo; Romoli, Andrea; Romoli, Marco; Rubini,
Alda; Rudawy, Pawel; Sandri, Paolo; Scardigli, Stefano; Spandre,
Gloria; Solanki, Sami K.; Stangalini, Marco; Vecchio, Antonio;
Zuccarello, Francesca
Bibcode: 2015JATIS...1d4006B
Altcode:
Advanced Astronomy for Heliophysics Plus (ADAHELI) is a project concept
for a small solar and space weather mission with a budget compatible
with an European Space Agency (ESA) S-class mission, including launch,
and a fast development cycle. ADAHELI was submitted to the European
Space Agency by a European-wide consortium of solar physics research
institutes in response to the "Call for a small mission opportunity
for a launch in 2017," of March 9, 2012. The ADAHELI project builds
on the heritage of the former ADAHELI mission, which had successfully
completed its phase-A study under the Italian Space Agency 2007 Small
Mission Programme, thus proving the soundness and feasibility of
its innovative low-budget design. ADAHELI is a solar space mission
with two main instruments: ISODY: an imager, based on Fabry-Pérot
interferometers, whose design is optimized to the acquisition of
highest cadence, long-duration, multiline spectropolarimetric images
in the visible/near-infrared region of the solar spectrum. XSPO: an
x-ray polarimeter for solar flares in x-rays with energies in the 15
to 35 keV range. ADAHELI is capable of performing observations that
cannot be addressed by other currently planned solar space missions,
due to their limited telemetry, or by ground-based facilities, due to
the problematic effect of the terrestrial atmosphere.
Title: Modeling Solar Oscillation Power Spectra. II. Parametric
Model of Spectral Lines Observed in Doppler-velocity Measurements
Authors: Vorontsov, Sergei V.; Jefferies, Stuart M.
Bibcode: 2013ApJ...778...75V
Altcode: 2013arXiv1310.7924V
We describe a global parametric model for the observed power spectra
of solar oscillations of intermediate and low degree. A physically
motivated parameterization is used as a substitute for a direct
description of mode excitation and damping as these mechanisms remain
poorly understood. The model is targeted at the accurate fitting of
power spectra coming from Doppler-velocity measurements and uses an
adaptive response function that accounts for both the vertical and
horizontal components of the velocity field on the solar surface
and for possible instrumental and observational distortions. The
model is continuous in frequency, can easily be adapted to intensity
measurements, and extends naturally to the analysis of high-frequency
pseudomodes (interference peaks at frequencies above the atmospheric
acoustic cutoff).
Title: Observations of the Interaction of Acoustic Waves and
Small-scale Magnetic Fields in a Quiet Sun
Authors: Chitta, Lakshmi Pradeep; Jain, Rekha; Kariyappa, R.;
Jefferies, Stuart M.
Bibcode: 2012ApJ...744...98C
Altcode: 2012ApJ...744...98P
The effect of the magnetic field on photospheric intensity and
velocity oscillations at the sites of small-scale magnetic fields
(SMFs) in a quiet Sun near the solar disk center is studied. We use
observations made by the G-band filter in the Solar Optical Telescope
on board Hinode for intensity oscillations; Doppler velocity, magnetic
field, and continuum intensity are derived from an Ni I photospheric
absorption line at 6767.8 Å using the Michelson Doppler Imager on
board the Solar and Heliospheric Observatory. Our analysis shows that
both the high-resolution intensity observed in the G band and velocity
oscillations are influenced by the presence of a magnetic field. While
intensity oscillations are suppressed at all frequencies in strong
magnetic field regions compared to weak magnetic field regions,
velocity oscillations show an enhancement of power in the frequency
band 5.5-7 mHz. We find that there is a drop of 20%-30% in the p-mode
power of velocity oscillations within the SMFs when compared to the
regions surrounding them. Our findings indicate that the nature of the
interaction of acoustic waves with the quiet Sun SMFs is similar to
that of large-scale magnetic fields in active regions. We also report
the first results of the center-to-limb variation of such effects
using the observations of the quiet Sun from the Helioseismic and
Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO). The
independent verification of these interactions using SDO/HMI suggests
that the velocity power drop of 20%-30% in p-modes is fairly constant
across the solar disk.
Title: The intensity effect in magneto-optical filters
Authors: Oliviero, M.; Severino, G.; Berrilli, F.; Moretti, P. F.;
Jefferies, S. M.
Bibcode: 2011SPIE.8148E..0VO
Altcode: 2011SPIE.8148E..27O
We used a laser system for determining the bandpasses of the two
vapour cells, the Magneto-Optical Filter (MOF) and the Wing Selector
(WS), which are the core of solar narrow-band filters based on the
MOF technology. A new result, which we called the Intensity Effect,
was found: the MOF and WS bandpasses depend not only on the temperature
at which the cell is heated and the external magnetic field in which
the cell is embedded, but also on the radiation intensity entering
the cell. A theoretical interpretation of the Intensity Effect is
proposed in terms of the kinetic equilibrium of the potassium atomic
populations inside the vapour cell. We need to take the Intensity
Effect into account for setting-up MOF based instruments for solar and
stellar observations as well as for modelling the MOF and WS spectral
transmissions.
Title: DIMMI-2h a MOF-based instrument for Solar Satellite ADAHELI
Authors: Stangalini, M.; Moretti, P. F.; Berrilli, F.; Del Moro, D.;
Jefferies, S. M.; Severino, G.; Oliviero, M.
Bibcode: 2011SPIE.8148E..0US
Altcode: 2011SPIE.8148E..26S
The Doppler-Intensity-Magnetograms with a Magneto-optical filter
Instrument at two heights (DIMMI-2h) is a double channel imager using
Magneto Optical Filters (MOF) in the potassium 770 nm and sodium
589 nm lines. The instrument will provide simultaneous dopplergrams
(velocity fields), continuum intensity and longitudinal magnetic flux
images at two heights in the solar atmosphere corresponding to low
and high photosphere. Dimmi- 2h is the possible piggy-back payload on
ADAHELI satellite. The spatial resolution (approximately 4 arcsec) and
the high temporal cadence (15 s) will permit to investigate low and
medium oscillating modes (from 0 to below 1000) up to approximately
32 mHz in the frequency spectrum. The acquisition of long-term
simultaneous velocity, intensity and magnetic information up to these
high frequencies will permit also the study of the propagation and
excitation of the waves with a frequency resolution never obtained
before.
Title: MHD wave transmission in the Sun's atmosphere
Authors: Stangalini, M.; Del Moro, D.; Berrilli, F.; Jefferies, S. M.
Bibcode: 2011A&A...534A..65S
Altcode: 2011arXiv1108.4576S
Magnetohydrodynamics (MHD) wave propagation inside the Sun's atmosphere
is closely related to the magnetic field topology. For example, magnetic
fields are able to lower the cutoff frequency for acoustic waves,
thus allowing the propagation of waves that would otherwise be trapped
below the photosphere into the upper atmosphere. In addition, MHD
waves can be either transmitted or converted into other forms of waves
at altitudes where the sound speed equals the Alfvén speed. We take
advantage of the large field-of-view provided by the IBIS experiment
to study the wave propagation at two heights in the solar atmosphere,
which is probed using the photospheric Fe 617.3 nm spectral line and
the chromospheric Ca 854.2 nm spectral line, and its relationship to
the local magnetic field. Among other things, we find substantial
leakage of waves with five-minute periods in the chromosphere at
the edges of a pore and in the diffuse magnetic field surrounding
it. By using spectropolarimetric inversions of Hinode SOT/SP data,
we also find a relationship between the photospheric power spectrum
and the magnetic field inclination angle. In particular, we identify
well-defined transmission peaks around 25° for five-minute waves and
around 15° for three-minute waves. We propose a very simple model
based on wave transmission theory to explain this behavior. Finally,
our analysis of both the power spectra and chromospheric amplification
spectra suggests the presence of longitudinal acoustic waves along
the magnetic field lines.
Title: Deconvolution of astronomical images using SOR with adaptive
relaxation
Authors: Vorontsov, S. V.; Strakhov, V. N.; Jefferies, S. M.; Borelli,
K. J.
Bibcode: 2011OExpr..1913509V
Altcode:
No abstract at ADS
Title: Solar Oscillations And Acoustic Power Measured In H-alpha
Authors: Jackiewicz, Jason; Balasubramaniam, K.; McAteer, R.;
Jefferies, S. M.
Bibcode: 2011SPD....42.1731J
Altcode: 2011BAAS..43S.1731J
We present initial studies of the evidence of acoustic power in H alpha
data observed with the ISOON telescope. Uninterrupted times series
were obtained at 1-minute cadence of the H alpha intensity and Doppler
velocity signals of both quiet and active regions on the Sun. Spatial
and temporal power maps show enhanced contributions from a flaring
active region that is a strong function of frequency. Cross-correlations
and wave travel times are computed and give indications of the presence
of running waves below the acoustic cut-off frequency.
Title: Future instrumentation for solar physics: a double channel
MOF imager on board ASI Space Mission ADAHELI
Authors: Moretti, P. F.; Berrilli, F.; Bigazzi, A.; Jefferies, S. M.;
Murphy, N.; Roselli, L.; di Mauro, M. P.
Bibcode: 2010Ap&SS.328..313M
Altcode: 2010Ap&SS.tmp...12M
A Magneto-Optical Filter-based system has been proposed as an optional
payload for ASI’s low-budget Solar Mission ADAHELI, which has
completed its Phase A feasibility study. The instrument is capable
of providing simultaneous Dopplergrams, intensity and magnetic solar
full-disk maps using the potassium 770 nm and sodium 589 nm solar
Fraunhofer lines. The instrument is a version, re-designed for a
space environment, of the one which has run an observing campaign at
the South Pole in 2008 with unprecedented performance. The MOF-based
system we present here is a low-cost, low-weight instrument, thus
particularly fit to space applications, capable of providing stability
and sensitivity of signals on long-term observations. The instrument
will explore regions of the oscillation spectrum not available to
other missions’ instruments.
Title: On the Origin of High-Frequency "Acoustic'' Power in
Photospheric and Chromospheric Velocity Power Spectra
Authors: Fleck, Bernard; Straus, T.; Carlsson, M.; Jefferies, S. M.;
Severino, G.; Tarbell, T. D.
Bibcode: 2010AAS...21640309F
Altcode: 2010BAAS...41..879F
In a recent paper (Fleck et al., 2010) we compared observed Dopplergram
time series from Hinode with results from 3-D numerical simulations
based on the Oslo "Stagger” and CO5BOLD codes. Given the rapid falloff
of atmospheric modulation transfer functions at high frequencies due
to the extended widths of typical velocity response functions, one
would expect the high-frequency tail of Doppler power spectra to drop
significantly below those of actual velocities at the corresponding
heights in the simulations. Surprisingly, our analysis of power spectra
of Doppler shifts of simulated line profiles did not reveal such a
steep falloff at high frequencies. Instead, they are comparable to
(and in some cases even larger than) those of the actual velocities,
making estimates of the energy flux of high frequency acoustic
waves questionable, in particular those that apply atmospheric MTF
corrections. In this work we study the cause of this unexpected
behavior in detail, with particular emphasis on the role of rapidly
changing velocity response functions in a dynamic atmosphere with
strong vertical velocity gradients.
Title: High frequency waves in the solar atmosphere?.
Authors: Fleck, B.; Straus, T.; Carlsson, M.; Jefferies, S. M.;
Severino, G.; Tarbell, T. D.
Bibcode: 2010MmSAI..81..777F
Altcode: 2010arXiv1002.3285F
The present study addresses the following questions: How representative
of the actual velocities in the solar atmosphere are the Doppler
shifts of spectral lines? How reliable is the velocity signal derived
from narrowband filtergrams? How well defined is the height of the
measured Doppler signal? Why do phase difference spectra always pull
to 0o phase lag at high frequencies? Can we actually observe
high frequency waves (P< 70 s)? What is the atmospheric MTF of high
frequency waves? How reliably can we determine the energy flux of high
frequency waves? We address these questions by comparing observations
obtained with Hinode/NFI with results from two 3D numerical simulations
(Oslo Stagger and CO5BOLD). Our results suggest that the
observed high frequency Doppler velocity signal is caused by rapid
height variations of the velocity response function in an atmosphere
with strong velocity gradients and cannot be interpreted as evidence of
propagating high frequency acoustic waves. Estimates of the energy flux
of high frequency waves should be treated with caution, in particular
those that apply atmospheric MTF corrections.
Title: On the detection of fast moving upflows in the quiet solar
photosphere.
Authors: Straus, Th.; Fleck, B.; Jefferies, S. M.; Carlsson, M.;
Tarbell, T. D.
Bibcode: 2010MmSAI..81..751S
Altcode: 2010arXiv1002.3305S
In our studies of the dynamics and energetics of the solar atmosphere,
we have detected, in high-quality observations from Hinode SOT/NFI,
ubiquitous small-scale upflows which move horizontally with supersonic
velocities in the quiet Sun. We present the properties of these fast
moving upflows (FMUs) and discuss different interpretations.
Title: Toward Eliminating Systematic Errors in Intermediate-Degree
p-Mode Measurements
Authors: Vorontsov, S. V.; Jefferies, S. M.; Giebink, C.; Schou, J.
Bibcode: 2009ASPC..416..301V
Altcode:
We report new measurements of p-mode frequency splittings from Michelson
Doppler Imager (MDI) in which systematic errors, previously seen,
appear to have been eliminated. We identify neglect of the effects
of mode coupling by differential rotation as a major source of the
systematic errors.
Title: On the Role of Acoustic-Gravity Waves in the Energetics of
the Solar Atmosphere
Authors: Straus, T.; Fleck, B.; Jefferies, S. M.; McIntosh, S. W.;
Severino, G.; Steffen, M.; Tarbell, T. D.
Bibcode: 2009ASPC..415...95S
Altcode: 2010arXiv1003.3773S
In a recent paper (Straus et al. 2008) we determined the energy
flux of internal gravity waves in the lower solar atmosphere using
a combination of 3D numerical simulations and observations obtained
with the IBIS instrument operated at the Dunn Solar Telescope and
the Michelson Doppler Imager (MDI) on SOHO. In this paper we extend
these studies using coordinated observations from SOT/NFI and SOT/SP
on Hinode and MDI. The new measurements confirm that gravity waves
are the dominant phenomenon in the quiet middle/upper photosphere and
that they transport more mechanical energy than the high-frequency
(> 5 mHz) acoustic waves, even though we find an acoustic flux 3-5
times larger than the upper limit estimate of Fossum & Carlsson
(2006). It therefore appears justified to reconsider the significance of
(non-M)HD waves for the energy balance of the solar chromosphere.
Title: On The Interpretation Of Hinode NFI Filtergrams
Authors: Fleck, Bernard; Straus, T.; Jefferies, S. M.; Severino, G.;
Tarbell, T. D.
Bibcode: 2009SPD....40.0927F
Altcode:
Phase difference spectra between the velocity signals at two
different heights represent a powerful tool to study the propagation
characteristics of acoustic-gravity waves in the solar atmosphere. In
our efforts to study the dynamics and energetics of these waves we
have acquired high-resolution, high-cadence time series with Hinode
SOT/NFI at two different levels in the Mg b2 or Na D1 lines. The
observed phase spectra between the velocity signals derived from the
"wing" and "core" filtergrams of these lines do not show the expected
behavior. This points to (a) a fundamental lack of understanding of
the propagation characteristics of acoustic waves, which may be more
complex than commonly assumed, or (b) significant difficulties in
interpreting filtergrams taken at fixed wavelengths in the wings of an
absorption line, possibly limiting the diagnostic potential of Doppler
"velocity" measurements from such filtergrams. The present work aims
at disentangling these effects with the help of numerical simulations.
Title: High Frequency Acoustic Waves in the Sun's Atmosphere
Authors: Fleck, B.; Jefferies, S. M.; McIntosh, S. W.; Severino, G.;
Straus, T.; Tarbell, T. D.
Bibcode: 2008ESPM...12.2.39F
Altcode:
This year marks the 60th anniversary of two pioneering papers by
Schwarzschild (1948) and Biermann (1948), who independently proposed
that acoustic waves generated in the turbulent convection zone play
an important role in the heating of the chromosphere and corona. High
frequency acoustic waves have remained one of the leading contenders
for solving the heating problem of the non-magnetic chromospheres of
the Sun and late-type stars ever since. Earlier attempts to determine
the acoustic energy flux from ground were compromised by atmospheric
seeing, which has its biggest effect on the high frequency parts
of the observed signal. Recently, based on a comparison of TRACE
observations and 1-D simulations, Fossum & Carlsson (2005, 2006)
concluded that high-frequency acoustic waves are not sufficient
to heat the solar chromosphere. The same conclusion was reached by
Carlsson et al. (2007) from an analysis of Hinode SOT/BFI Ca II H and
blue continuum observations. Other authors (e.g. Cuntz et al. 2007;
Wedemeyer-Boehm et al. 2007, Kalkofen 2007), however, questioned
these results for a number of reasons. Because of its limited spatial
resolution and limited sensitivity there are inherent difficulties
when comparing TRACE observations with numerical simulations. Further,
intensity oscillations are difficult to interpret, as they result from
a phase-sensitive mix of temperature and pressure fluctuations, and
non-local radiation transfer effects may complicate the picture even
more. Here we revisit the role of high frequency acoustic waves in the
dynamics and energetics of the Sun's atmosphere using high cadence,
high resolution Doppler velocity measurements obtained with SOT/SP
and SOT/NFI on Hinode.
Title: On the Role of Acoustic-gravity Waves in the Energetics of
the Solar Atmosphere
Authors: Straus, T.; Fleck, B.; Jefferies, S. M.; Cauzzi, G.; McIntosh,
S. W.; Reardon, K.; Severino, G.; Steffen, M.; Suter, M.; Tarbell,
T. D.
Bibcode: 2008ESPM...12.2.11S
Altcode:
We revisit the dynamics and energetics of the solar atmosphere, using a
combination of high-quality observations and 3D numerical simulations
of the overshoot region of compressible convection into the stable
photosphere. We discuss the contribution of acoustic-gravity waves
to the energy balance of the photosphere and low chromosphere. We
demonstrate the presence of propagating internal gravity waves at
low frequencies (< 5mHz). Surprisingly, these waves are found
to be the dominant phenomenon in the quiet middle/upper photosphere
and to transport a significant amount of mechanical energy into the
atmosphere outweighing the contribution of high-frequency (> 5mHz)
acoustic waves by more than an order of magnitude. We compare the
properties of high-frequency waves in the simulations with results
of recent high cadence, high resolution Doppler velocity measurements
obtained with SOT/SP and SOT/NFI on Hinode. Our results seem to be in
conflict with the simple picture of upward propagating sound waves. We
discuss the implications of our findings on the energy flux estimate
at high-frequencies.
Title: The Energy Flux of Internal Gravity Waves in the Lower Solar
Atmosphere
Authors: Straus, Thomas; Fleck, Bernhard; Jefferies, Stuart M.;
Cauzzi, Gianna; McIntosh, Scott W.; Reardon, Kevin; Severino, Giuseppe;
Steffen, Matthias
Bibcode: 2008ApJ...681L.125S
Altcode:
Stably stratified fluids, such as stellar and planetary atmospheres,
can support and propagate gravity waves. On Earth these waves,
which can transport energy and momentum over large distances and can
trigger convection, contribute to the formation of our weather and
global climate. Gravity waves also play a pivotal role in planetary
sciences and modern stellar physics. They have also been proposed
as an agent for the heating of stellar atmospheres and coronae, the
exact mechanism behind which is one of the outstanding puzzles in solar
and stellar physics. Using a combination of high-quality observations
and 3D numerical simulations we have the first unambiguous detection
of propagating gravity waves in the Sun's (and hence a stellar)
atmosphere. Moreover, we are able to determine the height dependence of
their energy flux and find that at the base of the Sun's chromosphere it
is around 5 kW m-2. This amount of energy is comparable to
the radiative losses of the entire chromosphere and points to internal
gravity waves as a key mediator of energy into the solar atmosphere.
Title: High Frequency Acoustic Waves in the Sun's Atmosphere
Authors: Fleck, B.; Jefferies, S. M.; McIntosh, S. W.; Straus, T.;
Tarbell, T. D.
Bibcode: 2008AGUSMSP41B..04F
Altcode:
This year marks the 60th anniversary of two pioneering papers by
Schwarzschild (1948) and Biermann (1948), who independently proposed
that acoustic waves generated in the turbulent convection zone play
an important role in the heating of the chromosphere and corona. High
frequency acoustic waves have remained one of the leading contenders
for solving the heating problem of the non-magnetic chromospheres of
the Sun and late-type stars ever since. Earlier attempts to determine
the acoustic energy flux from ground were compromised by atmospheric
seeing, which has its biggest effect on the high frequency parts
of the observed signal. Recently, based on a comparison of TRACE
observations and 1-D simulations, Fossum & Carlsson (2005, 2006)
concluded that high-frequency acoustic waves are not sufficient to heat
the solar chromosphere. The same conclusion was reached by Carlsson et
al. (2007) from an analysis of Hinode SOT/BFI Ca II H and blue continuum
observations. Other authors (e.g. Cuntz et al. 2007; Wedemeyer-Boehm
et al. 2007, Kalkofen 2007), however, questioned these results for
a number of reasons. Because of its limited spatial resolution and
limited sensitivity there are inherent difficulties when comparing TRACE
observations with numerical simulations. Further, intensity oscillations
are difficult to interpret, as they result from a phase-sensitive mix of
density, temperature, and pressure fluctuations, and radiation transfer
effects may complicate the picture even more. Here we revisit the role
of high frequency acoustic waves in the Sun's atmosphere using high
cadence, high resolution Doppler velocity measurements obtained with
SOT/SP and SOT/NFI on Hinode.
Title: Multi-Spectral Analysis of Acoustic Mode Characteristics in
Active Regions
Authors: Jain, K.; Hill, F.; Tripathy, S. C.; González-Hernández,
I.; Armstrong, J. D.; Jefferies, S. M.; Rhodes, E. J., Jr.; Rose, P.
Bibcode: 2008ASPC..383..389J
Altcode:
We study the relative differences in acoustic mode parameters
in regions of high magnetic fields at different heights in the
solar atmosphere. The data sets include simultaneous Dopplergrams
obtained with the Ni I 676.8~nm from Global Oscillation Network Group
(GONG+) and K I 769.9 nm from Magneto-Optical Filters at Two Heights
(MOTH). The technique used here is the ring-diagram analysis, which has
been proven to be a powerful tool to study the localized regions on the
solar surface. We find that there is a difference in power suppression
and relative changes in frequencies in active regions with increasing
height. This is explained in terms of the expanding magnetic flux tubes.
Title: High-resolution imaging through strong turbulence
Authors: Hope, Douglas A.; Jefferies, Stuart M.; Giebienk, Cindy
Bibcode: 2007SPIE.6697E..0CH
Altcode: 2007SPIE.6697E..12H
Random fluctuations in the index of refraction, caused by differential
heating and cooling of the atmosphere, can severely limit the quality of
ground-based observations of space objects. Techniques such as adaptive
optics can help compensate for the deleterious effects that turbulence
has on the images by deforming the telescope mirror and thus correcting
the wave-front. However, when imaging through strong turbulence such
techniques may not adequately correct the wave-front. In such cases
blind restoration techniques - which estimate both the atmospheric
turbulence characterized by the atmospheric point-spread-function and
the object that is being observed - must be used. We demonstrate high
quality blind restorations of object scenes, obtained when observing
through strong turbulence, by using a sequence of images obtained
simultaneously at different wavelengths and prior information on
the distribution of the sources of regions of low spectral power in
the data.
Title: Observational signatures of the interaction between acoustic
waves and the solar magnetic canopy
Authors: Moretti, P. F.; Jefferies, S. M.; Armstrong, J. D.; McIntosh,
S. W.
Bibcode: 2007A&A...471..961M
Altcode:
Aims:We show that the spatial distribution (and its variation
with frequency) of the power spectra of the velocity and intensity
signals, in and around solar active regions, is a manifestation of the
interaction of acoustic waves at the magnetic canopy.
Methods:
We analysed 6 h of simultaneous, full-disk, velocity and intensity
images obtained using the MOTH instrument tuned in the Na D2 line at
589 nm and K D1 line at 770 nm, and full-disk velocity images from
the SOHO/MDI experiment using the Ni line at 677 nm.
Results:
We propose that more than one type of magneto-acoustic-gravity wave
is required to explain the well-known phenomena of p-mode absorption
and power halos.
Title: Suppression Of Acoustic Power In Solar Active Regions: An
Analysis At Different Heights
Authors: Tripathy, Sushanta; Jain, K.; Hill, F.; Gonzalez-Hernandez,
I.; Armstrong, J. D.; Jefferies, S. M.; Rhodes, E. J., Jr.; Rose, P. J.
Bibcode: 2007AAS...210.2411T
Altcode: 2007BAAS...39..130T
The presence of enhanced magnetic fields in active regions is known to
suppress acoustic power and modify oscillation frequencies. Applying
the ring diagram technique to data from three different spectral lines
at different heights in the solar atmosphere, we analyze the variation
of the acoustic power with height. The data sets include simultaneous
Dopplergrams obtained with the Ni I 676.8 nm from Global Oscillation
Network Group (GONG), K I 769.9 nm from Magneto-Optical Filters at Two
Heights (MOTH) and Na I 589.0 nm from MOTH and Mount Wilson Observatory
(MWO). It should be noted that the Ni and K lines are formed in the
photosphere while Na line is formed in lower chromosphere. Preliminary
results suggest a difference in power suppression with increasing
height, which can be explained in terms of the expanding magnetic
flux tubes.
Title: On the observation of traveling acoustic waves in the solar
atmosphere using a magneto-optical filter
Authors: Haberreiter, M.; Finsterle, W.; Jefferies, S. M.
Bibcode: 2007AN....328..211H
Altcode:
In contrast to low-frequency waves that are trapped in the cavity of the
Sun, high-frequency waves can travel freely in the solar atmosphere. By
modelling the observed intensity signal in the red and blue wings of K I
7699 Å and Na I 5890 Å, we aim to better understand the measurements
carried out with the Magneto-Optical Filter at Two Heights (MOTH)
experiment. We model the observed intensity signal with radiative
transfer calculations carried out with the COde for Solar Irradiance
(COSI). Furthermore, we derive the formation height of the lines
in order to analyze to what extent the contribution functions are
modulated by the acoustic waves. We find a phase lag between the red
and blue filter for acoustic waves with a frequency above ≈7 mHz
and conclude that a frequency dependent data analysis is required for
higher frequencies.
Title: A comparison of acoustic mode parameters using multi-spectral
data
Authors: Jain, K.; Hill, F.; Tripathy, S. C.; Antia, H. M.; Armstrong,
J. D.; Jefferies, S. M.; Rhodes, E. J., Jr.; Rose, P. J.
Bibcode: 2006ESASP.624E.103J
Altcode: 2006soho...18E.103J
No abstract at ADS
Title: Toward improving the seismic visibility of the solar tachocline
Authors: Jefferies, S. M.; Vorontsov, S. V.; Giebink, C.
Bibcode: 2006ESASP.624E...7J
Altcode: 2006soho...18E...7J
No abstract at ADS
Title: Does the inference of solar subsurface flow change with choice
of the spectral line?
Authors: Jain, K.; Hill, F.; González Hernández, I.; Toner, C. G.;
Tripathy, S. C.; Armstrong, J. D.; Jefferies, S. M.
Bibcode: 2006ESASP.624E.127J
Altcode: 2006soho...18E.127J
No abstract at ADS
Title: Low-frequency magneto-acoustic waves in the solar chromosphere
Authors: Jefferies, S. M.; McIntosh, S. W.; Armstrong, J. D.; Bogdan,
T. J.; Cacciani, A.; Fleck, B.
Bibcode: 2006ESASP.624E..16J
Altcode: 2006soho...18E..16J
No abstract at ADS
Title: Magnetoacoustic Portals and the Basal Heating of the Solar
Chromosphere
Authors: Jefferies, Stuart M.; McIntosh, Scott W.; Armstrong, James
D.; Bogdan, Thomas J.; Cacciani, Alessandro; Fleck, Bernhard
Bibcode: 2006ApJ...648L.151J
Altcode:
We show that inclined magnetic field lines at the boundaries of
large-scale convective cells (supergranules) provide ``portals''
through which low-frequency (<5 mHz) magnetoacoustic waves can
propagate into the solar chromosphere. The energy flux carried by
these waves at a height of 400 km above the solar surface is found
to be a factor of 4 greater than that carried by the high-frequency
(>5 mHz) acoustic waves, which are believed to provide the dominant
source of wave heating of the chromosphere. This result opens up
the possibility that low-frequency magnetoacoustic waves provide a
significant source of energy for balancing the radiative losses of
the ambient solar chromosphere.
Title: Observing the Modification of the Acoustic Cutoff Frequency
by Field Inclination Angle
Authors: McIntosh, Scott W.; Jefferies, Stuart M.
Bibcode: 2006ApJ...647L..77M
Altcode:
We use observations of a sunspot from the Transition Region and
Coronal Explorer (TRACE) spacecraft to demonstrate observationally
the modification of the acoustic cutoff frequency in the lower solar
chromosphere by the changing the inclination of the magnetic field as
first predicted theoretically by Bel & Leroy.
Title: Low-frequency magneto-acoustic waves in the solar chromosphere
Authors: Jefferies, S. M.; McIntosh, S. W.; Armstrong, J. D.; Cacciani,
A.; Bogdan, T. J.; Fleck, B.
Bibcode: 2006IAUJD...3E..62J
Altcode:
We demonstrate that low-frequency (< 5 mHz) propagating
magneto-acoustic waves provide a larger source of energy for balancing
the radiative losses of the solar chromosphere than their high-frequency
(> 5 mHz) counterparts. The low-frequency waves, which are normally
evanescent in the solar atmosphere, are able to propagate through
"acoustic portals" that exist in areas of strong, significantly
inclined (> 30° with respect to the vertical), magnetic field. Such
conditions are found both in active regions and at the boundaries of
supergranules. The latter implies that acoustic portals are omnipresent
over the solar surface and throughout the magnetic activity cycle,
an essential prerequisite for any baseline heating mechanism.
Title: Low-frequency Magneto-acoustic Waves In The Solar Chromosphere
Authors: Fleck, Bernard; Jefferies, S. M.; McIntosh, S. W.; Armstrong,
J. D.; Cacciani, A.; Bogdan, T. J.
Bibcode: 2006SPD....37.0206F
Altcode: 2006BAAS...38..662F
We demonstrate that low-frequency (< 5 mHz) propagating
magneto-acoustic waves provide a larger source of energy for balancing
the radiative losses of the solar chromosphere than their high-frequency
(> 5 mHz) counterparts. The low-frequency waves, which are normally
evanescent in the solar atmosphere, are able to propagate through
"acoustic portals” that exist in areas of strong, significantly
inclined (> 30° with respect to the vertical), magnetic field. Such
conditions are found both in active regions and at the boundaries of
supergranules. The latter implies that acoustic portals are omnipresent
over the solar surface and throughout the magnetic activity cycle,
an essential prerequisite for any baseline heating mechanism.
Title: A Calcium-Based Magneto-Optical Filter
Authors: Rodgers, W.; Murphy, N.; Jefferies, S. M.
Bibcode: 2005AGUSMSH13C..13R
Altcode:
The magneto-optical filter, MOF [1], has been used for imaged Doppler
and magnetic field observations of the Sun for nearly three decades. The
strengths of the MOF lie in its wavelength stability, its narrow
pass-band (approx. 0.005nm) and high throughput. Until recently, its
main limitation has been that it has only been available for use with
the Na I (sodium) and K I (potassium) D-lines. We will discuss some
developments in the technology for building the vapor cells for the
MOF and will show preliminary results for a calcium-based MOF. The Ca I
line at 422nm is formed in the mid-chromosphere and can thus provide a
probe for velocity and magnetic field information for this region. [1]
Cacciani and Fofi, Solar Phys. 59, 1978
Title: Acoustic Mapping of the Magnetic Canopy in the Solar
Chromosphere
Authors: Jefferies, S. M.; Armstrong, J. D.; Cacciani, A.; Finsterle,
W.; McIntosh, S. W.
Bibcode: 2005AGUSMSH13C..11J
Altcode:
We show that high-frequency acoustic waves can be used to map the
location where the gas and magnetic pressures of the plasma in the
solar chromosphere are comparable. This transition region, which can be
considered as a "magnetic canopy" where MHD waves can transform from one
type into another, is believe to play a key role in the flow of mass
and energy through the chromosphere. Results will be presented from
the analysis of 18 (uninterrupted) hours of simultaneous, full-disk,
velocity observations using the Ni (676 nm), K (770 nm) and Na (589 nm)
Fraunhofer lines (with the SOHO/MDI and MOTH/South Pole instruments),
and 106 (uninterrupted) hours of K and Na data (from the MOTH/South
Pole instrument). The MOTH data were acquired every 10 seconds and the
MDI data every 60 seconds. This work was funded by awards OPP-0087541
and OPP-0338251 from the National Science Foundation.
Title: A new Instrument for High-cadence, Multi-height Observations
of the Velocity and Magnetic Fields of the Full Solar Disk
Authors: Jefferies, S. M.; Armstrong, J. D.; Cacciani, A.; Giebink,
C. A.; Rodgers, W.; Murphy, N.
Bibcode: 2005AGUSMSH13C..12J
Altcode:
We will describe a new instrument that is being built to measure the
velocity, intensity and line-of-sight magnetic fields of the full solar
disk, simultaneously at four heights in the solar atmosphere with a
resolution of 4 arc-seconds and a cadence of 10 seconds. The heart of
the instrument is the magneto-optical filter [1] that can be operated
using vapor cells containing K, Na, Ca and He. The instrument is also
designed to have a high-resolution imaging mode that will provide 1
arc-second resolution over a FOV of 450x450 square arc-seconds. The
instrument is scheduled for deployment to South Pole during the Austral
summer of 2005/2006. This work is funded by award OPP-0338251 from the
National Science Foundation. [1] Cacciani & Fofi, Solar Phys 59,
179 (1978)
Title: Travel Time and Phase Analysis of Waves in the Lower Solar
Chromosphere
Authors: Fleck, B.; Armstrong, J.; Cacciani, A.; de Pontieu, B.;
Finsterle, W.; Jefferies, S. M.; McIntosh, S. W.; Tarbell, T. D.
Bibcode: 2005AGUSMSH13C..04F
Altcode:
In an effort to better understand how the chromospheric plasma and
magnetic fields are guiding, converting and dissipating acoustic waves,
we analyze high-cadence time series taken in Na I D2 589.0 nm and K I
769.9 nm that were obtained with the Magneto Optical Filters at Two
Heights (MOTH) experiment at the South Pole in January 2003. These
data are complemented by a very high spatial resolution time series
taken in Na D with the Swedish Vacuum Solar Telescope in June 1992. The
travel time maps, power maps, and phase diagrams show some unexpected
behaviour, in particular in and around active regions.
Title: Modeling Solar Oscillation Power Spectra. I. Adaptive Response
Function for Doppler Velocity Measurements
Authors: Vorontsov, Sergei V.; Jefferies, Stuart M.
Bibcode: 2005ApJ...623.1202V
Altcode:
Improving the accuracy and resolution of helioseismic inversions
calls for more accurate modeling of the observational p-mode power
spectra from which the solar oscillation frequencies are traditionally
measured. We present a new technique of calculating the response
function (leakage matrix) for Doppler velocity measurements that is
based largely on an analytical description of the relevant instrumental
and physical effects. The computational efficiency of the new approach
allows us to implement the response function in an adaptive manner:
i.e., the compensation for instrumental or optical distortions of
unknown magnitude can be performed as a part of the spectral fitting
procedure.
Title: Helioseismology from South Pole: Past, Present, and Future
Authors: Jefferies, Stuart M.
Bibcode: 2005HiA....13..966J
Altcode:
No abstract at ADS
Title: Diagnostic of the Solar Atmosphere through Two Level Doppler
and Magnetic Measurements
Authors: Cacciani, A.; Rapex, P.; Massa, F.; Briguglio, R.; Jefferies,
S. M.; Finsterle, W.; Giebink, C.; Knox, A.
Bibcode: 2005EAS....14..269C
Altcode:
This contribution describes our solar project at the Antarctic sites
of Baia Terranova, South Pole and Dome-C. The project is based on a
multi-level helioseismology analysis, aimed to study, for the first
time, the local properties of the solar atmosphere. In addition,
we plan to detect the presence of Alfvèn waves in and around the
active regions, as an energy transfer vehicle from sunspots towards
the corona. The technology used is the well known compact, stable,
relatively unexpensive and still improving MOF (Magneto-Optical Filter).
Title: Global Helioseismic Metrology
Authors: Jefferies, S. M.; Vorontsov, S. V.; Giebink, C.
Bibcode: 2004ESASP.559..254J
Altcode: 2004soho...14..254J
No abstract at ADS
Title: Acoustic Waves Reveal the Magnetic Topology of the Solar
Atmosphere
Authors: Finsterle, W.; Jefferies, S. M.; Cacciani, A.; Rapex, P.
Bibcode: 2004ESASP.559..223F
Altcode: 2004soho...14..223F
No abstract at ADS
Title: An Alternative Interpretation of the Double-Ridge Structure
in the - Frequency Time-Distance Autocorrelation Function?
Authors: Sekii, T.; Shibahashi, H.; Jefferies, S. M.
Bibcode: 2004ESASP.559..619S
Altcode: 2004soho...14..619S
No abstract at ADS
Title: Helioseismic Mapping of the Magnetic Canopy in the Solar
Chromosphere
Authors: Finsterle, W.; Jefferies, S. M.; Cacciani, A.; Rapex, P.;
McIntosh, S. W.
Bibcode: 2004ApJ...613L.185F
Altcode:
We determine the three-dimensional topography of the magnetic canopy
in and around active regions by mapping the propagation behavior of
high-frequency acoustic waves in the solar chromosphere.
Title: Seismology of the solar atmosphere
Authors: Finsterle, Wolfgang; Jefferies, Stuart M.; Cacciani,
Alessandro; Rapex, Paolo; Giebink, Cynthia; Knox, Allister; DiMartino,
Vincenzo
Bibcode: 2004SoPh..220..317F
Altcode:
We describe a new instrument for seismically probing the properties
of the Sun's lower atmosphere, and present some first results from
an observational campaign carried out at the geographic South Pole
during the austral summer of 2002/2003. A preliminary analysis of the
data (simultaneous, high-cadence observations of the velocity signals
from the photosphere and low chromosphere) shows that the well-known
suppression of acoustic power in regions of strong magnetic field, and
enhancement of high-frequency power around active regions (acoustic
halos), are both consistent with a spreading out of the magnetic
field lines with increasing height in the atmosphere. The data have
also revealed some unexpected wave behavior. First, evanescent-like
waves are found at frequencies substantially above the acoustic
cut-off frequency in regions of intermediate magnetic field. Second,
upward- and downward-propagating waves are detected in areas of strong
magnetic field such as sunspots and plage: even at frequencies below
the acoustic cut-off frequency. Third, the wave behavior in regions
of strong magnetic field can change over periods of a few hours from
propagating to evanescent. While we have no concrete explanation for the
first two results, the latter result opens up the question of whether
sound waves are involved in short-term events such as flares or CME's.
Title: A New Way to Model the Solar Oscillation ℓ−ν Power
Spectrum
Authors: Jefferies, Stuart M.; Vorontsov, Sergei V.
Bibcode: 2004SoPh..220..347J
Altcode:
We present a new approach for the precise and accurate forward modeling
of the solar oscillation ℓ−ν power spectrum. The approach is
designed to provide the basis for a streamlined solar seismic inversion
without measurements of the p-mode frequencies. The new strategy
represents a paradigm change in how information is extracted from the
oscillation spectrum. It also represents a step toward the ideal case
of inferring the Sun's properties directly from the raw observations.
Title: How Well Can We Infer the Properties of the Solar Acoustic
Sources?
Authors: Jefferies, Stuart M.; Severino, Giuseppe; Moretti,
Pier-Francesco; Oliviero, Maurizio; Giebink, Cynthia
Bibcode: 2003ApJ...596L.117J
Altcode:
Measurements of the p-mode line asymmetry in the solar oscillation
velocity power spectrum have been used on several occasions to infer
the properties of the acoustic sources. These inferences are based on
the assumption that, unlike the observed intensity signal, the velocity
signal does not contain a nonresonant (background) component that is
correlated with the p-mode signal. Line asymmetry measurements have also
been used to draw inferences on the nature of the correlated background
signal that is present in intensity observations. By simultaneously
modeling the observed velocity and intensity power spectra and the
intensity-velocity cross spectrum, we enforce strict observational
constraints on the properties of the fitting model. We find that in
order to accurately describe the observed data, we have to include
a correlated background component in both our models for the V and
I signals at low frequencies. Our results also show that we cannot
uniquely determine the acoustic source depth for low-frequency waves
or the detailed properties of the correlated background signals. It
appears that further physical and/or observational constraints are
needed before we can obtain this information.
Title: A new instrument for sounding the solar atmosphere
Authors: Cacciani, A.; Jefferies, S. M.; Finsterle, W.; Rapex, P.;
Knox, A.; Giebink, C.; di Martino, V.
Bibcode: 2003ESASP.517..243C
Altcode: 2003soho...12..243C
A new instrument based on Magneto-Optical Filters (MOFs) (Cacciani
et al., 1994) will be used to simultaneously map the line-of-sight
velocity at two heights in the solar atmosphere. Simultaneous Doppler
images of 5 arc-seconds resolution will be taken in the K I (7699 Å)
and Na I D2 (5890 Å) lines, which are separated by a few
hundred kilometers in the solar atmosphere (Grossman-Doerth, 1994). By
cross correlating the signals of the K and Na channels we will be able
to determine the travel time and thus the propagation speed of sound
waves in the solar atmosphere. The experiment will be run at the South
Pole during austral summer of 2002/2003.
Title: Comments on inferring the properties of the solar acoustic
sources by modeling the velocity and/or intensity fluctuations
Authors: Jefferies, Stuart M.; Moretti, Pier-Francesco; Oliviero,
Maurizio; Giebink, Cynthia
Bibcode: 2003ESASP.517..311J
Altcode: 2003soho...12..311J
We model the observed velocity and intensity power spectra and the
intensity-velocity cross-spectrum using an updated version of the
Severino et al. (2001) model that includes the effects of the acoustic
source. We find that in order to accurately describe the data it
is necessary to include a correlated background component in both
the V and I signals at low frequencies, and in the I signal at high
frequencies. Preliminary results show that even using the new model we
can not uniquely determine the phase that is related to the acoustic
source depth at low frequencies, or the amplitudes and phases of the
individual correlated background signals. It appears that further
physical or observational constraints are needed before we can obtain
this information.
Title: Seismology of the Solar Atmosphere
Authors: Finsterle, Wolfgang; Rapex, Paolo; Jefferies, Stuart M.;
Cacciani, Alessandro; Giebink, Cynthia; Knox, Allister
Bibcode: 2003IAUJD..12E..18F
Altcode:
We use full-disk Dopplergrams simultaneously acquired using the K1
(770 nm) and Na D2 (589 nm) Fraunhofer lines to examine the acoustic
properties of Sun's atmosphere. We present preliminary results of the
use of acoustic waves with frequencies beyond the cut-off frequency for
the solar atmosphere (~ 5mHz) to map the spatial and temporal changes
in the vertical wave travel time between the mid-chromosphere and
low-photosphere over a period of a single solar rotation. These types
of maps should provide a strong constraint for models of the solar
atmosphere . The data used for the analysis were obtained at South
Pole during January 2003 and represent four uninterrupted stretches
of between 46 and 106 hours.
Title: A two color pupil imaging method to detect stellar oscillations
Authors: Cacciani, A.; Dolci, M.; Jefferies, S. M.; Finsterle, W.;
Fossat, E.; Sigismondi, C.; Cesario, L.; Bertello, L.; Varadi, F.
Bibcode: 2003MSAIS...2..172C
Altcode:
Observations of stellar intensity oscillations from the ground are
strongly affected by intensity fluctuations caused by the atmosphere
(scintillation). However, by using a differential observational method
that images the pupil of the telescope in two colors at the same
time on a single CCD, we can partially compensate for this source of
atmospheric noise (which is color dependant) as well as other problems,
such as guiding and saturation. Moreover, by placing instruments at
different locations (eg. Dome C and South Pole) we can further reduce
the atmospheric noise contribution by using cross-spectral methods,
such as Random Lag Singular Cross-Spectrum Analysis (RLSCA). (We
also decrease the likelihood of gaps in the data string due to
bad weather). The RLSCA method is well suited for extracting common
oscillatory components from two or more observations, including their
relative phases. We have evaluated the performance of our method
using real data from SOHO. We find that our differential algorithm can
recover the absolute amplitudes of the solar intensity oscillations
with an efficiency of 70%. We are currently carrying out tests using a
number of telescopes, including Big Bear, Mt. Wilson, Teramo and Milano,
while waiting for the South Pole and Dome C sites to become available.
Title: CONCORDIASTRO/Italy: A Solar High-Resolution Observation
Program at Dome-C
Authors: Severino, G.; Andretta, V.; Berrilli, F.; Cascone, E.;
Centrone, M.; Criscuoli, S.; Del Moro, D.; Ermolli, I.; Giorgi, F.;
Jefferies, S. M.; Magri, M.; Moretti, P. F.; Oliviero, M.; Parisi,
L.; V; Porzio; Smaldone, L. A.; Straus, Th.
Bibcode: 2003MSAIS...2..181S
Altcode:
CONCORDIASTRO is the Nice-Napoli joint project for site
testing of the Dome C for solar and stellar astronomy in the
visible. CONCORDIASTRO/Italy is the solar physics part of this project,
whose the Napoli team has the principal responsibility. Beyond the
well-known interest for the helioseismology, CONCORDIASTRO/Italy pointed
out that, because of its special atmospheric conditions, Dome C promises
to be one of the best sites on Earth to perform high-resolution solar
physics. Here we review the basis for this statement and the solar
observations program planned by CONCORDIASTRO/Italy.
Title: Helioseismology from South Pole: Past, Present and Future
Authors: Jefferies, Stuart M.
Bibcode: 2003IAUSS...2E..15J
Altcode:
From the early 1980's through to the middle of the 1990's helioseismic
observations from South Pole played a significant role in improving
our understanding of the Sun's interior. Not only with fundamental
measurements such as the determination of the internal sound speed
and rotational profiles but also with the development of important
techniques such as time-distance analysis. However the advent of global
networks of observing sites and space-based instruments in the mid-1990s
eventually led to the end of this ""golden era"" for South Pole Solar
Observatory (SPSO) for traditional helioseismology. The Austral
summer of 2002/2003 saw the ressurection of SPSO for a new generation
of helioseismic observations to probe the characteristics of the solar
atmosphere. This paper describes these new observations and discusses
how they might evolve in the future.
Title: a New way to Model the Solar Oscillation Power Spectrum
Authors: Jefferies, Stuart M.; Vorontsov, Sergei V.
Bibcode: 2003IAUJD..12E..33J
Altcode:
We will present a new technique for directly characterizing large
regions of the solar oscillation velocity power spectrum using a solar
seismic model. We will discus the implications of this paradigm change
in how information is extracted from the oscillation spectrum.
Title: Mapping the Sound Speed Structure of the Sun's Atmosphere
Authors: Cacciani, A.; Jefferies, S. M.; Finsterle, W.; Giebink, C.;
Knox, A.; Rapex, P.; Subrizi, B.; Cesario, L.
Bibcode: 2003MSAIS...2..190C
Altcode:
We describe an instrument for seismically probing the acoustic
properties of the Sun's lower atmosphere. The instrument, which
is based on magneto-optical filter technology, acquires full-disk
Dopplergrams simultaneously in the K D1 (770 nm) and Na D2 (589
nm) Fraunhofer lines. The Dopplergrams have a spatial resolution
of ~5 arc secs and are recorded at a cadence of one frame every 10
seconds, average from 16 frames per second. These data allow us to
use acoustic waves with frequencies beyond the cut-off frequency for
the solar atmosphere (~5mHz) to map the spatial and temporal changes
in the vertical wave travel time between the mid-chromosphere and the
low-photosphere. These types of maps will provide a strong constraint
for models of the solar atmosphere and possibly study early warnings
for explosive phenomena. We present some preliminary results from
observations made at the geographical South Pole during the 2002/2003
Austral summer. We also discuss our program for the next campaign
with instrumental improvements as far as a third level Dopplergram and
magnetographic capability. We also consider cloning the instrument for
Dome C in order to further minimize atmospheric noise and gaps in the
data string due to bad weather.
Title: Imaging through turbid media: post processing using blind
deconvolution
Authors: Jefferies, Stuart M.; Schulze, Kathy J.; Matson, Charles L.;
Hege, E. Keith; Stoltenberg, Kurt
Bibcode: 2001SPIE.4490..282J
Altcode:
How to obtain sharp images when viewing through a turbid medium
is a problem that arises in a number of applications, including
optical biomedical imaging and optical surveillance in the presence
of clouds. The main problem with this type of imagery is that it is
difficult to accurately characterize the turbid medium sufficiently
well to generate a point spread function that can be used to deconvolve
the blurred data (and thus increase the resolution). We discuss the
use of blind deconvolution as a means of estimating both the blur-free
target and the system point spread function. We compare restorations
obtained using a non-linear blind deconvolution algorithm with those
obtained using a linear backpropagation algorithm. Preliminary results
indicate that the blind deconvolution algorithm produces the more
visually pleasing restorations. Moreover, it does so without requiring
any prior knowledge of the characteristics of the turbid medium, or
of what the blur-free target should look like: an important advance
over the backpropagation algorithm.
Title: The Solar Intensity-Velocity Cross Spectrum: A Powerful
Diagnostic for Helioseismology
Authors: Severino, G.; Magrì, M.; Oliviero, M.; Straus, Th.;
Jefferies, S. M.
Bibcode: 2001ApJ...561..444S
Altcode:
We show that the solar intensity-velocity cross spectrum provides
a sensitive diagnostic for the interaction between the oscillatory
and nonoscillatory components of the solar velocity and intensity
signals. In particular, we demonstrate that to simultaneously model the
V and I power spectra, the I-V coherence spectrum, and the I-V phase
difference spectrum requires a coherent, correlated background signal
and a coherent, uncorrelated signal in both intensity and velocity. We
speculate that these signals may be related to the ``acoustic events''
observed recently by Goode and colleagues. We also show why caution
should be exercised in the interpretation of model fit parameters
based only on measurements of the velocity or intensity power spectra,
or both: specifically, the parameters associated with the oscillation
source characteristics.
Title: Multi-Wavelength Observations of Solar Fine-Structure with
High Spatial Resolution (CD-ROM Directory: contribs/denker)
Authors: Denker, C.; Spirock, T. J.; Jefferies, S. M.; Chen, H.;
Marquette, W. H.; Wang, H.; Goode, P. R.
Bibcode: 2001ASPC..223..607D
Altcode: 2001csss...11..607D
No abstract at ADS
Title: New approach to Rayleigh guide beacons
Authors: Lloyd-Hart, Michael; Jefferies, Stuart M.; Hege, E. Keith;
Angel, J. Roger P.
Bibcode: 2000SPIE.4007..277L
Altcode:
We present analysis and numerical simulations of a new method to
sense atmospheric wavefront distortion in real time with Rayleigh
beacons. Multiple range-gated images of a single pulse from the laser
are used to determine each phase map, providing an advantage over
other methods in that photon noise is substantially reduced for a given
brightness of the beacon. A laser at about 350 nm projects collimated
pulses of light adjacent to the telescope. Rayleigh-scattered light from
each pulse is recorded through the full telescope aperture in a sequence
of video frames, each a few microseconds long. Images are captured as
the pulse approaches and passes through the height at which the camera
is focused. Phase diversity is thus naturally introduced between the
frames. An iterative algorithm is used to extract the pupil-plane
phases from the recorded intensity distributions. We anticipate that
such beacons are likely to be valuable in future advanced systems for
adaptive optics on very large telescopes with multiple laser beacons
and deformable mirrors that aim to provide a large corrected field of
view by tomography of the atmospheric turbulence.
Title: Two-dimensional Modeling of the Solar Oscillation l-ν Power
Spectrum
Authors: Meunier, Nadège; Jefferies, Stuart M.
Bibcode: 2000ApJ...530.1016M
Altcode:
We describe an algorithm which can accurately model the spatial-temporal
l-ν solar oscillation power spectrum over large ranges in frequency
(ν) and degree (l). We show how modeling in two dimensions provides
a better representation of the observed spectrum than can be obtained
with traditional one-dimensional approaches. The gain comes from
using more of the observed signal to constrain the model and improved
descriptions of the solar background spectrum and the signal leakage
between different spatial scales. We discuss the level of systematic
error that can be expected in the solar oscillation mode frequency
data published to date.
Title: I-V phase difference and gain analysis of GONG full-disk data
Authors: Oliviero, M.; Severino, G.; Straus, T.; Jefferies, S. M.;
Appourchaux, T.
Bibcode: 2000MmSAI..71..999O
Altcode:
No abstract at ADS
Title: Object-independent point spread function and wavefront phase
estimation
Authors: Christou, Julian C.; Jefferies, Stuart M.; Hege, E. Keith
Bibcode: 1999SPIE.3762..201C
Altcode:
We demonstrate the recovery, without a priori object knowledge,
of the unknown object and point spread functions (PSFs) from
multiframe focal-plane data. By modeling the object Fourier spectrum
as an unprejudiced linear combination of the cross-spectra of the
measurements and the PSFs, we significantly reduce the number of
degrees-of- freedom for the blind deconvolution problem.
Title: Improving the signal-to-noise ratio in solar oscillation
spectra
Authors: García, R. A.; Jefferies, S. M.; Toner, C. G.; Pallé, P. L.
Bibcode: 1999A&A...346L..61G
Altcode:
We describe a data analysis technique for helioseismology that
provides a reduction in the contamination of the solar oscillation
spectrum from incoherent noise. We show that the technique allows:
(i) a significant improvement in the signal-to-noise ratio for the
modes in the oscillation power spectrum, and (ii) the solar velocity
background spectrum to be observed at low frequencies using ground-based
observations.
Title: Increasing the Visibility of Solar Oscillations
Authors: Toner, C. G.; Jefferies, S. M.; Toutain, T.
Bibcode: 1999ApJ...518L.127T
Altcode:
Recent calculations by Toutain, Berthomieu, & Provost predict that
low-degree p- and g-modes should produce large continuum intensity
perturbations close to the solar limb. Analysis of 72 hr of spatially
resolved, full-disk, continuum intensity images of the Sun--obtained
with the Solar Oscillations Investigation/Michelson Doppler Imager
instrument on board the Solar and Heliospheric Observatory--verifies
the theoretical prediction for the p-mode signal. The p-mode amplitude
for observations of the solar limb is found to be more than twice that
for observations of the solar disk. In addition, the low-frequency
background level is substantially reduced over that measured using
a full-disk analysis. The combination of these two effects suggests
that observing the solar limb signal could significantly enhance our
chances of detecting g-modes and low-frequency p-modes.
Title: Observational Constraints on Models of the Solar Background
Spectrum
Authors: Straus, Th.; Severino, G.; Deubner, F. -L.; Fleck, B.;
Jefferies, S. M.; Tarbell, T.
Bibcode: 1999ApJ...516..939S
Altcode:
We discuss the properties of the solar background signal as observed in
high-quality, l-ν power and phase difference spectra of the continuum
(C), velocity (V), and line intensity (I) fluctuations of the Ni
I 6768 Å line. These spectra were generated from high-resolution
images acquired by the Michelson Doppler Imager on board SOHO. We
confirm that the background signal in the velocity power spectra can be
reproduced by a composite model with two quasi-stationary components,
describing large-scale and small-scale convective motions, and a
periodic component. The line and continuum intensity power spectra
require additional quasi-stationary and periodic components. The
extra quasi-stationary component dominates the intensity and
continuum background signals over the spectral region where the I-V
phase difference spectra show essentially constant negative phase
difference: i.e., below and in between the p-mode ridges (called the
plateau-interridge regime by Deubner et al.). Since the I-V phase
between the p-mode ridges is not random, the solar background beneath
the p-modes must be considered as coherent. We thus speculate that
the negative phase regime may be the manifestation of a correlated
background. Such a background has been proposed to explain the opposite
sense of the asymmetries of the p-mode line profiles in velocity and
brightness oscillations.
Title: Space and Time Analysis of the Solar Photospheric Dynamics
at Moderate-l Values
Authors: Oliviero, M.; Severino, G.; Straus, Th.; Jefferies, S. M.;
Appourchaux, T.
Bibcode: 1999ApJ...516L..45O
Altcode:
A space-time analysis of 36 days' worth of full-disk intensity and
velocity images, obtained by the Global Oscillation Network Group,
is used to produce a high-resolution l-ν phase-difference spectrum
for the spectral range (4<=l<=2000, 0<=ν<=8.3 mHz). This
is the first time a phase-difference spectrum has been produced for
intermediate-l values. The phase differences on the p-mode ridges
are found to linearly increase from ~65° at 2 mHz up to ~95°
at 4.7 mHz. Only near 3.9 mHz are the differences close to 90°,
the theoretically expected phase for adiabatic evanescent waves. The
phases between the ridges exhibit a steplike behavior in frequency with
negative values at low frequency and positive values (greater than 90°)
at high frequency. The negative phase values are consistent with the
extension to low- and moderate-l values of the plateau-interridge regime
discovered by Deubner et al. in 1990. However, positive phase values,
which represent higher phase for the solar background than for the
acoustic modes, were not expected. An understanding of this observed
phase-difference behavior will improve our knowledge of the nature of
the solar background and its interaction with the acoustic p-modes.
Title: High-Frequency Peaks in the Power Spectrum of Solar Velocity
Observations from the GOLF Experiment
Authors: García, R. A.; Pallé, P. L.; Turck-Chièze, S.; Osaki,
Y.; Shibahashi, H.; Jefferies, S. M.; Boumier, P.; Gabriel, A. H.;
Grec, G.; Robillot, J. M.; Roca Cortés, T.; Ulrich, R. K.
Bibcode: 1998ApJ...504L..51G
Altcode:
The power spectrum of more than 630 days of full-disk solar velocity
data, provided by the GOLF spectrophotometer aboard the Solar and
Heliospheric Observatory, has revealed the presence of modelike
structure well beyond the acoustic cutoff frequency for the solar
atmosphere (νac~5.4 mHz). Similar data produced by
full-disk instruments deployed in Earth-based networks (BiSON and
IRIS) had not shown any peak structure above νac: this
is probably due to the higher levels of noise that are inherent in
Earth-based experiments. We show that the observed peak structure
(νac<=ν<=7.5 mHz) can be explained by a simple
two-wave interference model if the high-frequency waves are partially
reflected at the back side of the Sun.
Title: Acoustic interferometry of the solar atmosphere: p-modes with
frequencies near the `acoustic cut-off'
Authors: Vorontsov, S. V.; Jefferies, S. M.; Duval, T. L., Jr.;
Harvey, J. W.
Bibcode: 1998MNRAS.298..464V
Altcode:
High-frequency p-mode intensity data, obtained from the South Pole in
1987, 1988, 1990 and 1994, show a sharp variation in the phase-shift
function and in the frequency spacings near 5.5 mHz. Using a simple
theoretical model, we demonstrate that this behaviour is caused by an
acoustic resonance in the atmosphere between the excitation source and
the upper reflection level. We discuss the diagnostic properties of this
resonance, which is sensitive to the acoustic reflectivity of the solar
atmosphere and to the location and parity of the excitation source. When
applied to the solar data, our model indicates that the average acoustic
reflectivity increases with increasing solar activity. The model also
shows that the acoustic source has composite parity and is located
within one pressure scaleheight of the base of the photosphere.
Title: Active optical fringe tracking at the NPOI
Authors: Benson, James A.; Mozurkewich, David; Jefferies, Stuart M.
Bibcode: 1998SPIE.3350..493B
Altcode:
The Navy Prototype Optical Interferometer is routinely used to measure
visibility amplitudes and closure phase for stellar objects at optical
wavelengths. In this poster we describe the fringe data collection
aspects and the real time algorithm that enables us to actively track
fringes with the instrument.
Title: Estimated Mode Parameters from the Fitting of GONG Spectra
Authors: Hill, F.; Anderson, E.; Howe, R.; Jefferies, S. M.; Komm,
R.; Toner, C.
Bibcode: 1998ESASP.418..231H
Altcode: 1998soho....6..231H
The estimation of mode parameters is a critical step in the helioseismic
data reduction process. Several estimation methods are currently in
use, and a comparison of the resulting frequencies from a common data
set shows small, yet significant, differences. This suggests that the
fitting procedures can introduce systematic errors. These errors will
affect subsequent inversions of the data. For example, the presence of
a high-latitude jet in the solar rotation rate appears to depend on the
type of spectral fitting used to estimate the splitting coefficients. In
addition, as the available helioseismic observations have improved,
it has become apparent that several effects have been neglected in the
peak fitting techniques. These effects include line profile asymmetry,
coupling between the background and the mode signal, fine details in
the leakage matrix, and the differences in the oscillation spectrum
when observed in Doppler velocity or total intensity. Here we report
on the latest GONG fitting methods and present the resulting mode
parameter estimates. The GONG fitting technique now includes improved
mode quality assurance checks and asymmetrical line profiles. Currently
under development are multi-dimensional fitting, multi-taper time
series analysis, background/mode coupling, simultaneous fitting
of velocity and intensity spectra, and the inclusion of a leakage
matrix. The improvements have resulted in higher-quality frequency
estimates that are now being computed for 108-day long time series
spaced by 36 days. After completion, each frequency table is made
freely available to the helioseismic community.
Title: High-frequency (Pseudo-) modes
Authors: Jefferies, S. M.
Bibcode: 1998IAUS..185..415J
Altcode:
I will review the properties of the solar oscillation powerspectrum at
frequencies near and above the acoustic cut-off frequency (~5.3 mHz). In
particular, I will show how the line profiles of the high-frequency
``pseudo-modes'' are affected by the properties of the acoustic
source and the solar atmosphere, and by changes in the level of solar
activity. Finally, I will examine the potential of the pseudo-modes
to provide a tomography of the solar chromosphere.
Title: Modeling the Solar Oscillation l-v Power Spectrum
Authors: Meunier, N.; Jefferies, S. M.
Bibcode: 1998ESASP.418..267M
Altcode: 1998soho....6..267M
We have developed a ``two-dimensional'' algorithm which simultaneously
models the ell- ν spectrum over several n-values and a wide
range of ell-values. In addition to the estimation of the line
profile parameters, the algorithm also allows a determination of the
spatial response function for the observations. This is an important
improvement over algorithms which either rely on theoretical leakage
matrix calculations, or use many extra free parameters to model the
features due to spatial leakage. Using intensity data obtained at
the South Pole, and velocity data from GONG and MDI, we show that 2-D
modeling allows significant increases in the precision of the measured
line profile parameters for peaks with low peak-to-background ratios.
Title: Searching for g-modes at the Solar Limb
Authors: Toner, C. G.; Jefferies, S. M.
Bibcode: 1998IAUS..185...55T
Altcode:
The detection and measurement of solar g-modes is of significant
importance in the study of the internal structure of the Sun. The g-mode
signal in intensity is predicted to peak very close to the solar limb
(T. Toutain, private communication). We are developing a technique which
differences the signal in a narrow annulus very close to the limb from
the signal in an adjacent (interior) annulus in order to remove the
solar background ``noise'' signal and thus enhance the probability of
detecting g-modes. Here we present our preliminary results.
Title: Oscillatory Signals Near the Solar Limb
Authors: Toner, C. G.; Jefferies, S. M.
Bibcode: 1998ESASP.418..345T
Altcode: 1998soho....6..345T
A recent calculation by T. Toutain predicts that the solar p-mode and
g-mode amplitudes in intensity should peak near the solar limb. We
use full-disk intensity images of the Sun, obtained at the South Pole
and with the SOI/MDI instrument on board SOHO, to explore how the
oscillation signal varies near the solar limb. We divide each observed
image into narrow annuli and then average in equally spaced bins in
azimuthal angle. By computing the 2-D FFT of the time series of these
``sector-annulus'' data we can generate ``k-ω'' diagrams for each
annulus. Here we present our results.
Title: The Solar Background Spectrum: a Gold Mine of Information
Authors: Severino, G.; Straus, Th.; Jefferies, S. M.
Bibcode: 1998ESASP.418...53S
Altcode: 1998soho....6...53S
We discuss the properties of the intensity-velocity (I-V) phase
difference spectra generated from 15 hours of high resolution MDI
observations. These spectra provide a spectacular demonstration of the
wealth of untapped information that is available on the nature of the
solar background. In this context, the regimes of coherent phase in
between the modes (``interridges'') and between the f mode and the
Lamb waves (``plateau''), first discovered by Deubner et al. 1990,
is of extreme interest. Understanding the background is important for
several reasons: (i) it contains information about the convection
processes and the wave propagation characteristics of the solar
atmosphere in addition to that provided by the resonant oscillations,
(ii) its interaction with the p-modes may explain why the sense of the
asymmetry in the p-mode line profiles depends on the dynamic variable
observed (Roxburgh & Vorontsov 1997, Nigam et al. 1998), (iii)
estimates for the p-mode line asymmetries are sensitive to errors in
the background determination, and (iv) the background limits the g-mode
and low frequency p-mode visibilities. We also propose a new model
for the solar background which uses the observed phase information:
previous models (e.g. Harvey 1985) are restricted to power information
only. Currently, our model is limited to low frequencies (1 mHz <=
ν <= 3.5 mHz) and intermediate to high ell values, however, it
still demonstrates the potential of the phase information to improve
our estimates of the background components of both the velocity and
intensity signals. A superposition of a correlated background and the
p-mode signal succeeds in reproducing the observed I-V phase transition
from negative (background) to positive (p-mode) values. Moreover,
the model suggests that the background is responsible for the values
of I-V phase, equal to or less than the adiabatic values observed in
the low photosphere (Hill et al, 1991).
Title: Sounding the Sun's Chromosphere
Authors: Jefferies, S. M.; Osaki, Y.; Shibahashi, H.; Harvey, J. W.;
D'Silva, S.; Duvall, T. L., Jr.
Bibcode: 1997ApJ...485L..49J
Altcode:
Time-distance analysis of solar acoustic waves with frequencies above
the nominal atmospheric acoustic cutoff frequency (~5.3 mHz) shows
partial reflection of the waves at both the Sun's photosphere and a
layer located higher in the atmosphere. This result supports recent
reports of chromospheric modes.
Title: Searching for G-MODES at the Solar Limb
Authors: Toner, C. G.; Jefferies, S. M.
Bibcode: 1997SPD....28.0209T
Altcode: 1997BAAS...29..894T
The detection and measurement of solar g-modes is of significant
importance in the study of the internal structure of the Sun. The
g-mode signal in intensity is predicted to peak very close to the solar
limb. To enhance the probability of detecting g-modes, we have tried to
reduce the solar background ``noise'' signal by differencing the signal
in a narrow annulus at the solar limb from the signal in an adjacent
(interior) annulus. We will present some preliminary results from a
study of Ca K-line intensity observations obtained at the South Pole
during the austral summer of 1995/95.
Title: Restoration of Long-Exposure Full-Disk Solar Intensity Images
Authors: Toner, C. G.; Jefferies, S. M.; Duvall, T. L.
Bibcode: 1997ApJ...478..817T
Altcode:
We describe an algorithm for restoring full-disk solar intensity images
blurred by a smooth, quasi-stationary point-spread function (PSF). For
Earth-based observations, this type of data can be obtained by using
exposure times that are much longer than the redistribution time of
the atmosphere. Using simulated data for a wide range of observing
conditions, we show that the algorithm restores data in such a way
that the RMS difference between an original, unblurred image and the
restored image is typically less than 1.0%. Thus, we substantially
improve the photometric precision. The simulations also show that under
``reasonable'' seeing conditions (<~4"), exposure times of 5-10 s are
adequate to produce smooth calibratable PSFs if the observing instrument
uses a centroid-shifting tip/tilt wavefront correction. The algorithm
determines the PSF for each observation directly from the recorded
image and does not require separate measurements of point sources.
Title: Helioseismic Tomography
Authors: D'Silva, Sydney; Duvall, Thomas L., Jr.; Jefferies, Stuart
M.; Harvey, John W.
Bibcode: 1996ApJ...471.1030D
Altcode:
"Helioseismic tomography" is a method using observations to construct
slices of the Sun's internal structure. It is based on a reduction of
observations to time-distance surfaces and hypersurfaces. We present
a procedure for measuring time-distance surfaces and hypersurfaces,
and thereby a method of studying localized inhomogeneities in the
interior of the Sun, such as abnormalities in the sound speed (e.g., a
thermal shadow, Parker 1987a), or local subsurface flows, or magnetic
fields. We also present a simulation of measuring time-distance
surfaces and illustrate how to measure the size of an inhomogeneity,
its location in depth, and the deviation of its sound speed compared
to its local surroundings.
Title: Doppler Acoustic Diagnostics of Subsurface Solar Magnetic
Structure
Authors: Lindsey, C.; Braun, D. C.; Jefferies, S. M.; Woodard, M. F.;
Fan, Y.; Gu, Y.; Redfield, S.
Bibcode: 1996ApJ...470..636L
Altcode:
We used the Bartol-NSO-NASA South Pole helioseismic observations of 1991
January to probe the subsurface structure of active regions to depths
of ∼15,000 km. The helioseismic signature we particularly examine is
intended to register acoustic Doppler effects caused by horizontal flows
associated with the active region. We propose to show that the Doppler
acoustic signature of horizontal flows is particularly well suited
for deep subsurface diagnostics in terms of vertical discrimination
of the structure. This study is based primarily on observations of
NOAA Active Regions 6431, 6432, 6440, and 6442 between 1991 January
1 and January 8. We interpret the acoustic signatures we find in
terms of a general outflow of the solar medium surrounding the active
region. The acoustic signatures are strongly dependent on wavenumber,
which suggests an outflow that is quite weak near the surface, the upper
4000 km of the subphotosphere, but which increases strongly with depth
to velocities of several hundred meters per second at 15,000 km. This
depth profile evolves rapidly as the active region matures. Young
active regions show a strong outflow signature for waves that explore
depths between 4000 and 8000 km. As the active region matures, the
outflow vacates these intermediate layers and submerges to depths
mostly below 8000 km. We examine the location of AR 6442 for a
possible preemergence signature. We also show evidence for extended,
relatively superficial flows in the quiet Sun between the active region
bands directed roughly into the active region bands.
Title: Dynamics of the Chromospheric Network: Mobility, Dispersal,
and Diffusion Coefficients
Authors: Schrijver, Carolus J.; Shine, Richard A.; Hagenaar, Hermance
J.; Hurlburt, Neal E.; Title, Alan M.; Strous, Louis H.; Jefferies,
Stuart M.; Jones, Andrew R.; Harvey, John W.; Duvall, Thomas L., Jr.
Bibcode: 1996ApJ...468..921S
Altcode:
Understanding the physics behind the dispersal of photo spheric magnetic
flux is crucial to studies of magnetoconvection, dynamos, and stellar
atmospheric activity. The rate of flux dispersal is often quantified by
a diffusion coefficient, D. Published values of D differ by more than a
factor of 2, which is more than the uncertainties allow. We propose that
the discrepancies between the published values for D are the result of
a correlation between the mobility and flux content of concentrations of
magnetic flux. This conclusion is based on measurements of displacement
velocities of Ca II K mottles using an uninterrupted 2 day sequence
of filtergrams obtained at the South Pole near cycle minimum. We
transform the Ca II K intensity to an equivalent magnetic flux density
through a power-law relationship defined by a comparison with a nearly
simultaneously observed magnetogram. One result is that, wherever the
network is clearly defined in the filtergrams, the displacement vectors
of the mottles are preferentially aligned with the network, suggesting
that network-aligned motions are more important to field dispersal than
deformation of the network pattern by cell evolution. The rms value
of the inferred velocities, R = <|v|2>½,
decreases with increasing flux, Φ, contained in the mottles, from R
≍ 240 m s-1 down to 140 s-1. The value of R(Φ)
appears to be independent of the flux surrounding the concentration,
to the extreme that it does not matter whether the concentration is
in a plage or in the network. The determination of a proper effective
diffusion coefficient requires that the function R(Φ) be weighted
by the number density n(Φ) of mottles that contain a total flux. We
find that n(Φ) decreases exponentially with Φ and propose a model
of continual random splitting and merging of concentrations of flux to
explain this dependence. Traditional methods used to measure D tend to
be biased toward the larger, more sluggish flux concentrations. Such
methods neglect or underestimate the significant effects of the
relatively large number of the more mobile, smaller concentrations. We
argue that the effective diffusion coefficient for the dispersal of
photo spheric magnetic flux is ∼600 km2 s-1.
Title: Helioseismic Measurements of Subsurface Outflows From Sunspots
Authors: Braun, D. C.; Fan, Y.; Lindsey, C.; Jefferies, S. M.
Bibcode: 1996AAS...188.6911B
Altcode: 1996BAAS...28Q.937B
We measure the mean frequencies of acoustic waves propagating toward
and away from sunspots employing a spot-centered Fourier-Hankel
decomposition of p-mode amplitudes as measured from observations made at
the South Pole in 1988 and 1991. There is a significant frequency shift
between the inward and outward traveling waves which is consistent with
the Doppler effect of a radial outflow from the sunspots. For p-modes
of temporal frequencies of 3 mHz it is observed that the frequency
shift decreases slightly with spatial frequency, for modes with degree
l between 160 to 600. From the l dependence of the frequency shift, we
infer that the mean radial outflow within the observed annular region
(which extends between 30 and 137 Mm from the spots) increases nearly
linearly with depth, reaching a magnitude of about 200 m/s at a depth
of 20 Mm. This outflow exhibits properties similar to flows recently
reported by Lindsey, et al. (1996 ApJ submitted) using spatially
sensitive local helioseismic techniques. This work is supported by
NSF Grant AST 9496171 and NASA Grant NAGW-4143.
Title: Diagnostics of a Subsurface Radial Outflow From a Sunspot
Authors: Braun, D. C.; Fan, Y.; Lindsey, C.; Jefferies, S. M.
Bibcode: 1996astro.ph..3078B
Altcode:
We measure the mean frequencies of acoustic waves propagating toward
and away from a sunspot employing a spot-centered Fourier-Hankel
decomposition of p-mode amplitudes as measured from a set of
observations made at the South Pole in 1991. We demonstrate that
there is a significant frequency shift between the inward and outward
traveling waves which is consistent with the Doppler effect of a radial
outflow from the sunspot. For p-modes of temporal frequencies of 3
mHz it is observed that the frequency shift decreases slightly with
spatial frequency, for modes with degree l between 160 to 600. From
the l dependence of the frequency shift, we infer that the mean radial
outflow within the observed annular region (which extends between 30 and
137 Mm from the spot) increases nearly linearly with depth, reaching a
magnitude of about 200 m/s at a depth of 20 Mm. This outflow exhibits
properties similar to flows recently reported by Lindsey, et al. (1996)
using spatially sensitive local helioseismic techniques.
Title: Downflows under sunspots detected by helioseismic tomography
Authors: Duvall, T. L.; D'Silva, S.; Jefferies, S. M.; Harvey, J. W.;
Schou, J.
Bibcode: 1996Natur.379..235D
Altcode:
SUNSPOTS are areas of cooler gas and stronger magnetic fields in the
Sun's photosphere (its 'surface'), but just how they form and are
maintained has long been a puzzle. It has been proposed1
that small vertical magnetic flux tubes, generated deep within the Sun,
develop downflows around them when they emerge at the surface. The
downflows bring together a large number of flux tubes in a cluster
to form a sunspot, which behaves as a single flux bundle as long as
the downflows bind the flux tubes together. Until now, however,
it has not been possible to test this model with subsurface
observations. Here we use the recently developed technique of
travel-time helioseismology2 to detect the presence of
strong downflows beneath both sunspots and the bright features known
as plages. The flows have a velocity of ~2 kms-1, and they
persist to a depth of about 2,000 km. The data suggest, however, that
the vertical magnetic field can be a coherent flux bundle only to a
depth of ~600 km; below this depth it is possible that the downflows
hold together a loose collection of flux tubes to maintain the sunspots
that we see.
Title: Speckle deconvolution imaging using an iterative algorithm
Authors: Christou, Julian C.; Hege, E. Keith; Jefferies, Stuart M.
Bibcode: 1995SPIE.2566..134C
Altcode:
We present an application of an iterative deconvolution algorithm
to speckle interferometric data. This blind deconvolution algorithm
permits the recovery of the target distribution when the point spread
function is either unknown or poorly known. The algorithm is applied to
specklegrams of the multiple star systems, and the results for (zetz)
UMa are compared to shift-and-add results for the same data. The
linearity of the algorithm is demonstrated and the signal-to-noise
ratio of the reconstruction is shown to grow as the square root of
the number of specklegrams used. This algorithm does not require the
use of an unresolved target for point spread function calibration.
Title: Mapping Wave Speed in the Outer Convection Zone
Authors: Duvall, T. L., Jr.; Jefferies, S. M.; Harvey, J. W.
Bibcode: 1995SPD....26..105D
Altcode: 1995BAAS...27..950D
No abstract at ADS
Title: Restoring Full Disk Solar Images
Authors: Toner, C. G.; Jefferies, S. M.
Bibcode: 1994AAS...185.4403T
Altcode: 1994BAAS...26.1377T
The Modulation Transfer Function (MTF) for a full-disk solar intensity
image can be estimated using the zero crossing properties of the
Fourier Transform of the image (Toner & Jefferies 1993). We show
that the MTF can be used to restore an image for the adverse effects of
the earth's atmosphere and the measurement instrument's optics. The
restoration process can be approximated for the special case of
helioseismic analysis by using the estimated MTFs, after calibration
onto a spherical harmonic degree l scale, to correct the time series
of spherical harmonic transform coefficients.
Title: Use of Acoustic Wave Travel-Time Measurements to Probe the
Near-Surface Layers of the Sun
Authors: Jefferies, S. M.; Osaki, Y.; Shibahashi, H.; Duvall, T. L.,
Jr.; Harvey, J. W.; Pomerantz, M. A.
Bibcode: 1994ApJ...434..795J
Altcode:
The variation of solar p-mode travel times with cyclic frequency
nu is shown to provide information on both the radial variation of
the acoustic potential and the depth of the effective source of the
oscillations. Observed travel-time data for waves with frequency
lower than the acoustic cutoff frequency for the solar atmosphere
(approximately equals 5.5 mHz) are inverted to yield the local acoustic
cutoff frequency nuc as a function of depth in the outer
convection zone and lower atmosphere of the Sun. The data for waves
with nu greater than 5.5 mHz are used to show that the source of the
p-mode oscillations lies approximately 100 km beneath the base of the
photosphere. This depth is deeper than that determined using a standard
mixing-length calculation.
Title: Application of multiframe iterative blind deconvolution for
diverse astronomical imaging
Authors: Christou, Julian C.; Hege, E. Keith; Jefferies, Stuart M.;
Keller, Christoph U.
Bibcode: 1994SPIE.2200..433C
Altcode: 1994aisi.conf..433C
We present applications of a recently developed iterative blind
deconvolution algorithm to both simulated and real data. The
applications demonstrate the algorithm's performance for a wide range
of astronomical imaging. We demonstrate the effectiveness of using
multiple observations of the same object convolved with different
point spread functions. We also show the extension of the algorithm
to phase retrieval when the object Fourier amplitude is available.
Title: Limits on Coronal Reflection Using High-Frequency Solar
Oscillations
Authors: Kumar, P.; Fardal, M. A.; Jefferies, S. M.; Duvall, T. L.,
Jr.; Harvey, J. W.; Pomerantz, M. A.
Bibcode: 1994ApJ...422L..29K
Altcode:
Acoustic waves in the Sun with frequencies above about 5.3 mHz can
propagate in the chromosphere. We examine imaged solar intensity data
for evidence of reflection of these waves in the upper chromosphere,
where the temperature increases by a large factor over a short
distance. Our method is to compare the observed and theoretically
derived frequency spacings between peaks in the power spectrum. We find
that our theoretical frequencies provide the best fit to the data when
the reflection in the upper atmosphere is eliminated. In particular, the
model of Kumar (1993b), which includes the source depth, and radiative
damping, in the calculation of power spectra but ignores chromospheric
reflection, gives peak frequencies that are in good agreement with
the observations. For acoustic waves of frequency greater than 6 mHz
we put an upper limit to the reflectivity of chromosphere and corona,
using our method, of about 10%. At a given spherical harmonic degree,
the frequency spacing between peaks in the data generally decreases
with increasing frequency, because the lower turning point of the
waves is moving inward. However, between 5 and 5.5 mHz the frequency
spacing increases slightly. This feature is probably associated
with the acoustic cutoff frequency in the solar atmosphere, i.e., it
indicates a transition from trapped waves to propagating waves. We
are able to reproduce the observed behavior by a crude modeling of
the solar atmosphere. Further study of these peaks should provide an
independent way of exploring the mean structure of the solar atmosphere,
particularly around the temperature minimum region.
Title: Blind Deconvolution of HST Simulated Data
Authors: Christou, J. C.; Jefferies, S. M.; Robison, M. W.
Bibcode: 1994rhis.conf..212C
Altcode:
No abstract at ADS
Title: Some Recent Advances in Iterative Blind Deconvolution
(Invited Review)
Authors: Jefferies, Stuart M.
Bibcode: 1994ASPC...64..619J
Altcode: 1994csss....8..619J
No abstract at ADS
Title: Accurate Measurement of the Geometry for a Full-Disk Solar
Image and Estimation of the Observational Point Spread Function
Authors: Toner, C. G.; Jefferies, S. M.
Bibcode: 1993ApJ...415..852T
Altcode:
We present a new method for accurately determining the geometry for
full-disk solar intensity images that is insensitive to changes in
the observational point spread function. The method exploits the
zero-crossing properties of the Fourier transform of an observed
image to recover the image's true dimensions and to reconstruct an
azimuthally averaged estimate for the point spread function. Simulations
show that the undistorted image dimensions can be reproduced to better
than 0.01 of a resolution element, and that the point spread function
can be recovered to within 5% at low spatial frequencies and 15% at
high spatial frequencies. Preliminary tests with real data confirm
the results from the simulations and show the method to be robust.
Title: Restoration of Astronomical Images by Iterative Blind
Deconvolution
Authors: Jefferies, Stuart M.; Christou, Julian C.
Bibcode: 1993ApJ...415..862J
Altcode:
We have developed a modified version of the Iterative Blind
Deconvolution (IBD) algorithm of Lane, applicable to different types
of astronomical data. Besides using positivity, convolution, and
support constraints, we have also applied band-limit, multiple image,
and Fourier modulus constraints. By using all the available image
constraining information, we are able to successfully recover object
and point spread function information from noisy data. The algorithm's
performance under controlled conditions using simulated data for a
binary source object, a compact multiple quasi-point source object,
and an extended object with low contrast are demonstrated. The ability
of the algorithm to restore information beyond the conventional cutoff
frequency is also demonstrated. Results are presented for infrared
speckle imaging of (1) the nearby binary star Gl 914, which resolves
the secondary component into two stars, and (2) the asteroid 4 Vesta. We
also present results for "direct" imaging data in the form of a visible
high-resolution image of Capella and an infrared adaptively corrected
image of the Galactic center.
Title: Prospects in Helioseismic Holography
Authors: Lindsey, C. A.; Braun, D. C.; Jefferies, S. M.
Bibcode: 1993BAAS...25.1220L
Altcode:
No abstract at ADS
Title: Time-Distance Helioseismology
Authors: Duvall, T. L., Jr.; Jefferies, S. M.; Harvey, J. W.;
Pomerantz, M. A.
Bibcode: 1993BAAS...25.1220D
Altcode:
No abstract at ADS
Title: Asymmetries of Solar Oscillation Line Profiles
Authors: Duvall, T. L., Jr.; Jefferies, S. M.; Harvey, J. W.; Osaki,
Y.; Pomerantz, M. A.
Bibcode: 1993ApJ...410..829D
Altcode:
Asymmetries of the power spectral line profiles of solar global
p-modes are detected in full-disk intensity observations of the Ca
II K Fraunhofer line. The asymmetry is a strong function of temporal
frequency being strongest at the lowest frequencies observed and
vanishing near the peak of the power distribution. The variation with
spherical harmonic degree is small. The asymmetry is interpreted in
terms of a model in which the solar oscillation cavity is compared
to a Fabry-Perot interferometer with the source slightly outside
the cavity. A phase difference between an outward direct wave and
a corresponding inward wave that passes through the cavity gives
rise to the asymmetry. The asymmetry is different in velocity and
intensity observations. Neglecting the asymmetry when modeling the
power spectrum can lead to systematic errors in the measurement of
mode frequencies of as much as 10 exp -4 of the mode frequency. The
present observations and interpretation locate the source of the
oscillations to be approximately 60 km beneath the photosphere, the
shallowest position suggested to date.
Title: Time-distance helioseismology
Authors: Duvall, T. L., Jr.; Jefferies, S. M.; Harvey, J. W.;
Pomerantz, M. A.
Bibcode: 1993Natur.362..430D
Altcode:
THE application of seismology to the study of the solar interior1,
2(helioseismology) has advanced almost solely by the prediction
and measurement of the Sun's frequencies of free oscillation, or
normal modes. Direct measurement of the travel times and distances
of individual acoustic waves-the predominant approach in terrestrial
seismology3-would appear to be more difficult in view of the
number and stochastic nature of solar seismic sources. Here, however,
we show that it is possible to extract time-distance information from
temporal cross-correlations of the intensity fluctuations on the solar
surface. This approach opens the way for seismic studies of local
solar phenomena, such as subsurface in homogeneities near sunspots,
and should help to refine global models of the internal velocity
stratification in the Sun.
Title: The P-Mode Scattering Properties of a Sunspot
Authors: Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr.; Jefferies,
S. M.; Harvey, M. A.; Pomerantz, J. W.
Bibcode: 1993ASPC...42...77B
Altcode: 1993gong.conf...77B
No abstract at ADS
Title: Local Helioseismology of Subsurface Structure
Authors: Lindsey, C.; Braun, D. C.; Jefferies, S. M.
Bibcode: 1993ASPC...42...81L
Altcode: 1993gong.conf...81L
No abstract at ADS
Title: Solar G-Mode Signatures in P-Mode Signals
Authors: Kennedy, J. R.; Jefferies, S. M.; Hill, F.
Bibcode: 1993ASPC...42..273K
Altcode: 1993gong.conf..273K
No abstract at ADS
Title: Chromospheric Oscillations and the Background Spectrum
Authors: Harvey, J. W.; Duvall, T. L., Jr.; Jefferies, S. M.;
Pomerantz, M. A.
Bibcode: 1993ASPC...42..111H
Altcode: 1993gong.conf..111H
No abstract at ADS
Title: Accurate Measurement of the Geometry for a Full-Disk Solar
Image and Estimation of the Observational Point Spread Function
Authors: Toner, C. G.; Jefferies, S. M.
Bibcode: 1993ASPC...42..433T
Altcode: 1993gong.conf..433T
No abstract at ADS
Title: Restoration of Astronomical Images by Blind Iterative
Deconvolution
Authors: Jefferies, S. M.; Christou, J. C.
Bibcode: 1992AAS...181.1308J
Altcode: 1992BAAS...24.1140J
Image degradation, whether due to turbulent atmospheric motion and/or
inherent defects in imaging optics, causes attenuation and/or loss of
the high-spatial frequency content of astronomical images. Knowledge
of a point spread function (Psf) permits restoration of these spatial
frequencies. However, not all Psf's are well behaved and can vary
both in time and also location across the image. Thus optimal image
restoration requires both the object and Psf to be restored from a
``blurred'' image. This is known as blind deconvolution. In this paper
we describe an algorithm that incorporates a priori image information
as constraints for deconvolution by error metric minimization using a
conjugate gradient technique. We demonstrate the effectiveness of this
algorithm to recover a complex object and Psf using simulated speckle
interferometric data under different signal-to-noise conditions for
both single and multiple frame input. We present astronomical results
using both speckle interferometric data, e.g. near-infrared images of 4
Vesta, and direct near-infrared images of the Galactic Center obtained
using an adaptive tip-tilt secondary. This work was supported by the
NSF through grants DPP 89-17626, AST 88-22465 and AST 92-03336.
Title: Local Acoustic Diagnostics of the Solar Interior
Authors: Braun, D. C.; Lindsey, C.; Fan, Y.; Jefferies, S. M.
Bibcode: 1992ApJ...392..739B
Altcode:
Two diagnostic utilities, acoustic power maps, and surface acoustic
flux maps are used to explore the local diagnostics of magnetic field
structure in the solar interior. The acoustic power maps, constructed
from 50 hr of continuous K-line intensity images, show three general
features: acoustic power deficits at 3 mHz corresponding to surface
magnetic flux, acoustic power enhancements at 6 mHz surrounding the
exterior of magnetic regions, and occasional power deficits at 3 mHz
which extend beyond magnetic regions visible on the surface to regions
of quiet-sun. Surface acoustic flux vector maps of two active regions
were constructed for two 6-hr time-series of Dopplergrams. Both maps
show the divergence of 3-mHz acoustic flux into surface magnetic
structures and also sources and sinks of wave energy which are not
associated with surface features.
Title: Scattering of p-Modes by a Sunspot
Authors: Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J.; Jefferies,
S. M.; Harvey, J. W.; Pomerantz, M. A.
Bibcode: 1992ApJ...391L.113B
Altcode:
The acoustic scattering properties of a large sunspot are determined
from a Fourier-Hankel decomposition of p-mode amplitudes as measured
from a 68-hr subset of a larger set of observations made at the
South Pole in 1988. It is shown that significant improvement in the
measurement of p-mode scattering amplitudes results from the increased
temporal frequency resolution provided by these data. Scattering
phase shifts are unambiguously determined for the first time, and the
dependence of the p-mode phase shift and absorption with wavenumber
and frequency is presented.
Title: Prospects in Acoustic Holography of the Solar Interior
Authors: Lindsey, C.; Braun, D. C.; Fan, Y.; Jefferies, S. M.
Bibcode: 1992AAS...180.1703L
Altcode: 1992BAAS...24..753L
Acoustic power maps of the solar surface show strong evidence
of magnetic structure crossing the solar equator not far beneath
the photosphere to connect the active latitude bands. These maps,
generated using the Bartol-NSO-NASA South Pole Observations show long
finger-like acoustic shadows we think are caused by absorption of
acoustic energy by the submerged magnetic structure. These features
suggest a solar interior magnetic structure quite different from any
previously expected. These new results open the prospect of a new and
powerful solar interior diagnostic based on acoustic holography.
Title: Accurate Measurement of the Radius of Full-Disk Solar
Intensity Images
Authors: Toner, C. G.; Jefferies, S. M.
Bibcode: 1992AAS...180.1707T
Altcode: 1992BAAS...24..754T
No abstract at ADS
Title: Scattering of p-Modes by a Sunspot
Authors: Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J.; Jefferies,
S. M.; Harvey, J. W.; Pomerantz, M. A.
Bibcode: 1992AAS...180.0604B
Altcode: 1992BAAS...24..737B
For the first time the scattering phase shifts of solar p-modes
from a sunspot have been unambiguously determined. This is made
possible by the recent availability of long duration, high duty
cycle observations. The results presented here are determined from a
Fourier-Hankel decomposition of p-mode amplitudes as measured from a
68 hr subset of a larger set of observations made at the South Pole in
1988. In addition to the detection of the phase shifts, the quality of
the data allows the dependence of the p-mode scattering and absorption
with azimuthal order, spatial wavenumber and temporal frequency to
be independently determined. Thus, unlike previous observations, our
measurements of absorption and phase shifts do not represent averages
over a range of p-modes. With this information we have for the first
time a complete description of the acoustic scattering amplitudes
from a large sunspot. Interpretation of these observations requires a
suitable theory of the interaction of p-modes and sunspots. However,
with the complete scattering amplitudes now available one may apply
inverse scattering algorithms, based on a few simplifying assumptions,
to deduce a 3-dimensional map of the scattering strength of the active
region. This offers the hope that general information about subsurface
morphology of active regions might be gained even without a detailed
understanding of the physical scattering processes involved. DCB is
supported by Air Force URI grant AFOSR-90-0116. The South Pole program
is supported in part by National Science Foundation grants DPP87-15791
and 89-17626, and by the Solar Physics Branch of the Space Physics
Division of NASA.
Title: Helioseismology from South Pole: Surprises from Near the
Solar Surface
Authors: Jefferies, S. M.; Pomerantz, M. A.; Duvall, T. L.; Harvey,
J. W.
Bibcode: 1992AnJUS..27..322J
Altcode:
No abstract at ADS
Title: Characteristics of Intermediate-Degree Solar p-Mode Line Widths
Authors: Jefferies, S. M.; Duvall, T. L., Jr.; Harvey, J. W.; Osaki,
Y.; Pomerantz, M. A.
Bibcode: 1991ApJ...377..330J
Altcode:
Measurements of the p-mode linewidths over the frequency range v =
1.87-4.93 mHz and degree range 1 = 1-150 are presented. The linewidth
is observed to vary with mode frequency and degree. The variation with
frequency is consistent with the observations of Libbrecht although
the measurements are systematically narrower. The frequency variation
has been explained in terms of radiative and convective damping
of the modes. The observed variation with degree resolves previous
contradictory results and is shown to exceed the 1/S variation that is
expected in theoretical grounds. Here S is the travel time of a mode
from its lower turning point in the solar interior, to its reflection
at the solar surface. The deviations from a 1/S variation suggest that
there are two possible damping mechanisms, in addition to radiative
and convective damping, that affect the modes.
Title: Measurements of High-Frequency Solar Oscillation Modes
Authors: Duvall, T. L., Jr.; Harvey, J. W.; Jefferies, S. M.;
Pomerantz, M. A.
Bibcode: 1991ApJ...373..308D
Altcode:
The spatial-temporal spectrum of solar oscillations exhibits modelike
structure at frequencies above the nominal photospheric acoustic cutoff
of about 5.3 mHz. The linewidth and frequency of these features are
measured as functions of degree from high-quality spectra obtained from
observations made at the geographic South Pole. From 5.3 to 6.5 mHz the
linewidths are relatively constant with a value of about 70 microHz,
approximately one-half the frequency difference between modes of the
same degree but successive values of radial order number. This width
is larger than can be accounted for by simple considerations of the
leakage of trapped acoustic waves. The frequencies of the high-frequency
modes adhere to a simple dispersion law if one uses a substantially
larger effective phase shift that applies at lower frequencies. The
frequency variation of this phase shift changes markedly above the
acoustic cutoff frequency.
Title: A Simple Method for Correcting Spatially Resolved Solar
Intensity Oscillation Observations for Variations in Scattered Light
Authors: Jefferies, S. M.; Duvall, T. L., Jr.
Bibcode: 1991SoPh..132..215J
Altcode:
A measurement of the intensity distribution in an image of the solar
disk will be corrupted by a spatial redistribution of the light that
is caused by the Earth's atmosphere and the observing instrument. If
the precise form of the spatial point spread function is known and
can be modeled, then the observed image can be corrected for its
effects. However, accurate modeling of the spatial point spread
function, which can be considered as composed of a `blurring'
component and a `scattering' component (Zwaan, 1965), is difficult
and the correction for its effects is computationally expensive.
Title: The Solar Equatorial Internal Rotation Rate Estimated from
Combined South Pole and NSO/Sac Peak Helioseismic Data Sets
Authors: Hill, F.; Jefferies, S. M.; Pomerantz, M. A.; Duvall, T. L.,
Jr.; Harvey, J. W.
Bibcode: 1991BAAS...23.1050H
Altcode:
No abstract at ADS
Title: Characteristics of Intermediate-Degree Solar p-mode Line Widths
Authors: Duvall, T. L., Jr.; Jefferies, S. M.; Harvey, J. W.; Osaki,
Y.; Pomerantz, M. A.
Bibcode: 1991BAAS...23.1032D
Altcode:
No abstract at ADS
Title: Helioseismology from South Pole: 1990 High Resolution Campaign
Authors: Jefferies, S. M.; Pomerantz, M. A.; Duvall, T. L.; Harvey,
J. W.
Bibcode: 1991AnJUS..26..285J
Altcode:
No abstract at ADS
Title: Modeling of Solar Oscillation Power Spectra
Authors: Anderson, Edwin R.; Duvall, Thomas L., Jr.; Jefferies,
Stuart M.
Bibcode: 1990ApJ...364..699A
Altcode:
To produce accurate estimates of the line-profile parameters of a
model used to represent the spectral features in a solar oscillation
power spectrum, it is necessary to (1) select the appropriate
probability density function when deriving the maximum-likelihood
function to be employed for the parameter estimation and (2) allow
for the redistribution of spectral power caused by gaps in the data
string. This paper describes a maximum-likelihood method for estimating
the model parameters (based on the observed power spectrum statistics)
that accounts for redistribution of spectral power caused by gaps in
the data string, by convolving the model with the power spectrum of the
observed window function. The accuracy and reliability of the method
were tested using both artificial and authentic solar oscillation power
spectrum data. A comparison of this method with various least-squares
techniques is also presented.
Title: Observed Characteristics of High-Frequency Solar Global
Oscillations
Authors: Harvey, J. W.; Duvall, T. L., Jr.; Jefferies, S. M.;
Pomerantz, M. A.
Bibcode: 1990BAAS...22..896H
Altcode:
No abstract at ADS
Title: What are the Observed High-Frequency Solar Acoustic Modes?
Authors: Kumar, P.; Duvall, T. L., Jr.; Harvey, J. W.; Jefferies,
S. M.; Pomerantz, M. A.; Thompson, M. J.
Bibcode: 1990LNP...367...87K
Altcode: 1990psss.conf...87K
Jefferies et al. (1988) observe discrete peaks up to 7mHz in the power
spectra of their intermediate degree solar intensity oscillation data
obtained at South Pole. This is perhaps surprising since waves with
frequency greater than the acoustic cut-off frequency at the temperature
minimum ( 5.5mHz), unlike their lower frequency counterparts, are not
trapped in the solar interior. We propose that the observed peaks are
associated with what are principally progressive waves emanating from
a broad-band acoustic source. The geometrical effect of projecting
observations of these progressive waves onto spherical harmonics
then gives rise to peaks in the power spectra. The frequencies and
amplitudes of the peaks will depend on the spatial characteristics of
the source. Partial reflections in the solar atmosphere modify the power
spectra, but in this picture they are not the primary reason for the
appearance of the peaks. We estimate the frequency and power which would
be expected from this model and compare it with the observations. We
argue that these high frequency mock-modes are not overstable, and
that they are excited by acoustic emission from turbulent convection.
Title: Observations of p-Mode Absorption in Active Regions
Authors: Braun, D. C.; Duvall, T. L., Jr.; Jefferies, S. M.
Bibcode: 1990LNP...367..181B
Altcode: 1990psss.conf..181B
We present here a summary of results on the interaction of p-modes with
solar active regions based on observations made at the Kitt Peak Solar
Vacuum Telescope and the geographic South Pole. A travelling wave
decomposition of p-modes is performed in a cylindrical coordinate
system centered on the active regions. Significant absorption of
p-mode wave power is observed to occur in all of the regions and
is a function of horizontal wavenumber () - increasing linearly
with k up to some maximum value and remaining constant for higher
wavenumbers. The maximum fractional absorption of incident power
is about 0.2 for small pores and 0.4 for typical isolated sunspots
(radius = 15 Mm). A maximum of 70% absorption is seen in the large
sunspot group of March 1989 (radius = 60 Mm). No convincing variation
of the absorption with temporal frequency (i.e. radial order) is seen,
although not entirely ruled out considering the relative errors involved
with the power measurements. No significant difference in the amount
of p-mode absorption is detected between equal 3-hour time intervals
before and after a class X4 flare in the March 1989 region. No excess
of outgoing waves following the time of the flare is detected. These
observations do not support the suggestion that large flares may excite
observable acoustic waves in the photosphere.
Title: Helioseismology from South Pole: Solar Cycle Connection
Authors: Jefferies, S. M.; Pomerantz, M. A.; Duvall, T. L.; Harvey,
J. W.
Bibcode: 1990AnJUS..25..271J
Altcode:
No abstract at ADS
Title: Helioseismology from the South Pole: Results from the 1987
Campaign
Authors: Jefferies, S. M.; Duvall, T. L., Jr.; Harvey, J. W.;
Pomerantz, M. A.
Bibcode: 1990LNP...367..135J
Altcode: 1990psss.conf..135J
This paper presents some results on the frequencies and line widths
of features in solar p-mode spectra obtained from 460 hours of
observations made at South Pole in 1987. To investigate the possibility
of temporal variations in these quantities, a comparison is made with
measurements obtained from data taken in 1981. The differences between
the frequencies measured from the 1981 and 1987 data sets appear to be
independent of both frequency (2.4 v 4.8 mHz) and degree (3 98). The
mean difference (v 1981 - v 1987) averaged. over v and is found to be
224 ± 19 nl1z. The line width measurements display the same variation
with v as that previously reported (Libbrecht 1988a), an increase
with ℓ (Duvall et ad. 1988) and with solar activity. Measurement of
the rotational splittings of sectoral modes (m = ±ℓ) in the range
(3 ≤ ℓ ≤ 15), shows no indication of a dependence on the depth
of the lower turning points of these modes.
Title: Linewidths of low-degree acoustic modes of the sun
Authors: Elsworth, Y.; Isaak, G. R.; Jefferies, S. M.; McLeod, C. P.;
New, R.
Bibcode: 1990MNRAS.242..135E
Altcode:
Estimates of the spectral linewidths of low degree (l = 0 and l = 1),
5-min p-modes obtained from Doppler shift observations in 1984 (63 d)
and 1986 (63 d) are reported. The observed linewidths increase from
0.5 micro-Hz at 2000 micro-Hz to 3 micro-Hz at 3800 micro-Hz for l =
0. Comparison with other data suggests that for a given frequency the
linewidth increases with increasing values of l. On the assumption
that the linewidth is substantially due to damping processes, the
linewidths are consistent with e-folding times between 3.7 and 0.6 d.
Title: A Solar Tracking Platform for Use at the South Pole
Authors: Jefferies, S. M.; Pfeiffer, R.; Pomerantz, M. A.; Schulman,
L.; Ball, W.
Bibcode: 1990AIPC..198..222J
Altcode: 1989AIPC..198..222J; 1990asan.conf..222J
The design and performance of a solar tracking platform specifically
built to capitalize on the outstanding observing conditions available
at the geographic South Pole are described. Attention is given to a
description of the apparatus and the principles of operation. Results
reported were obtained using a CCD camera with 260 x 260 pixels to
collect full disk solar images that were integrated over 75 sec before
being recorded.
Title: Rotational Splitting of the Low-Degree Solar P-Modes
Authors: Jefferies, S. M.; Duvall, T. L., Jr.; Harvey, J. W.;
Pomerantz, M. A.
Bibcode: 1989BAAS...21..831J
Altcode:
No abstract at ADS
Title: The 160 Minute Solar Oscillation: an Artifact?
Authors: Elsworth, Y. P.; Jefferies, S. M.; McLeod, C. P.; New, R.;
Palle, P. L.; van der Raay, H. B.; Regulo, C.; Roca Cortes, T.
Bibcode: 1989ApJ...338..557E
Altcode:
Analysis of data obtained over the years 1980-1985 are analyzed to show
that the period of the 160-minute signal is indeed 160.00 minutes. It is
demonstrated that this signal may be simulated by a slightly distorted
diurnal sine wave such as that occasioned by differential atmospheric
extinction.
Title: Helioseismology from the South Pole: 1987 Results and 1988
Campaign
Authors: Jefferies, S. M.; Pomerantz, M. A.; Duvall, T. L.; Harvey,
J. W.
Bibcode: 1989AnJUS..24..244J
Altcode:
No abstract at ADS
Title: Helioseismology from the South Pole: comparison of 1987 and
1981 results.
Authors: Jefferies, S. M.; Pomerantz, M. A.; Duvall, T. L., Jr.;
Harvey, J. W.; Jaksha, D. B.
Bibcode: 1988ESASP.286..279J
Altcode: 1988ssls.rept..279J
Full disk images with ≡10 arc sec pixels and filtered to a ≡7 Å
passband centered on the Ca II K line were obtained from the geographic
South Pole in 1981 and 1987. In 1981, about 50 hours of essentially
uninterrupted data were obtained. In 1987, three such runs were
obtained over a period of 325 hours for a duty cycle of about 47%. The
1987 observations are characterized by a much lower level of solar
activity than 1981, a much improved CCD camera, considerably better
image stability and a varying amount of instrumental scatter. The 1987
data have a substantially better signal-to-noise ratio than the 1981
data so that oscillations with degrees from 0 to 150 and frequencies
from 2 to 7 mHz are well observed. The observations were reduced to
spectra in l, m and ν. This paper presents a comparison of p-mode
frequencies measured in 1981 and 1987 and coefficients of Legendre
polynomial expansions of frequency shifts caused by solar rotation. The
authors also study the time behavior of systematic frequency shifts
which depend upon m but which do not arise from rotation.
Title: Linewidth of low degree acoustic modes of the Sun.
Authors: Elsworth, Y. P.; Isaak, G. R.; Jefferies, S. M.; McLeod,
C. P.; New, R.; Palle, Pere L.; Regulo, C.; Roca Cortés, Teodoro
Bibcode: 1988ESASP.286...27E
Altcode: 1988ssls.rept...27E
Estimates of the spectral linewidths of low degree (l = 0 and l = 1),
"5 minute" p-modes obtained from Doppler shift observations in 1984,
1986 and 1987 are reported. The observed linewidths increase from 0.5
μHz at 2000 μHz to 3.8 μHz at 4300 μHz for l = 0. Comparison with
other data suggest that for a given frequency the linewidth increases
with increasing l value. On the assumption that the linewidth is
substantially due to damping processes the linewidths are consistent
with e-folding times between 3.7 and 0.5 days.
Title: Frequency stability of solar oscillations
Authors: Jefferies, S. M.; Pallé, P. L.; van der Raay, H. B.; Régulo,
C.; Roca Cortés, T.
Bibcode: 1988Natur.333..646J
Altcode:
Changes in the internal structure of the Sun over the 11-year
magnetic activity cycle could be reflected in the eigenfrequencies
of the acoustic p-modes. The first tentative experimental evidence
was presented in 19841 and subsequently an analysis
of ACRIM solar intensity data2 suggested a decrease of
frequencies of the 5-min solar p-modes between 1980 and 1984 of ~0.4
μHz. Recently3-6 further experimental data have provided
conflicting results; frequency increases, decreases and stability have
all been reported.
Title: Splitting of the Low L Solar P-Modes
Authors: Jefferies, S. M.; McLeod, C. P.; van der Raay, H. B.; Palle,
P. L.; Roca-Cortes, T.
Bibcode: 1988IAUS..123...25J
Altcode:
An analysis of full disc line of sight velocity data yield line
splitting values of the low l-value non-radial modes. Possible
variations of the line splitting with the solar cycle are investigated.
Title: Solar Cycle Dependence of Solar P-Modes
Authors: Isaak, G. R.; Jefferies, S. M.; McLeod, C. P.; New, R.;
van der Raay, H. B.; Palle, P. L.; Regulo, C.; Roca-Cortes, T.
Bibcode: 1988IAUS..123..201I
Altcode:
Data obtained at Izaña (Tenerife) and Haleakala (Maui), using optical
resonant scattering with a potassium vapour cell over the years 1980 -
84, are used to determine the frequencies of the low l p modes. Possible
variation in these frequencies with the solar cycle are investigated.
Title: Variations in the Mean Line-Of Velocity of the Sun - 1976-1985
Authors: Jimenez, A.; Palle, P. L.; Regulo, C.; Roca-Cortes, T.;
Elsworth, Y. P.; Isaak, G. R.; Jefferies, S. M.; McLeod, C. P.; New,
R.; van der Raay, H. B.
Bibcode: 1988IAUS..123..215J
Altcode:
Measurements of the line of sight velocity of the sun with respect to
earth have been obtained at Izaña (Tenerife) during the years 1976 to
1985. The mean values found for each year show a trend of ≡30 m/s from
minimum to maximum. Their mean value is of 583.1±0.2 m/s which is 92%
of the gravitational redshift predicted by theory and their variation
seems to be related to the solar cycle with the clear exception of 1985.
Title: Experience in Operating a Limited Global Network of Stations
Measuring Full-Disc Oscillations of the Sun
Authors: Elsworth, Y. P.; Isaak, G. R.; Jefferies, S. M.; McLeod,
C. P.; New, R.; van der Raay, H. B.; Palle, P. L.; Regulo, C.;
Roca-Cortes, T.
Bibcode: 1988IAUS..123..535E
Altcode:
Details are given about the operation of a two station network and of
a new semi-automatic station which has recently been added. Comparison
is made with predicted duty cycles. A possible way of quantifying the
sky quality is also given.
Title: Helioseismology from the South Pole: 1987 Campaign
Authors: Jefferies, S. M.; Pomerantz, M. A.; Duvall, T. L.; Harvey,
J. W.; Jaksha, D.
Bibcode: 1988AnJUS..23..191J
Altcode:
No abstract at ADS