explanation blue bibcodes open ADS page with paths to full text
Author name code: rosenthal
ADS astronomy entries on 2022-09-14
author:"Rosenthal, C."
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Title: Astropix: Everyone's New Portal to the Universe of Astronomical
Imagery
Authors: Hurt, Robert L.; Squires, G. K.; Llamas, J.; Rosenthal, C.;
Brinkworth, C. S.
2012AAS...21934703H Altcode:
Astropix is a new online repository for astronomical imagery that is
now available for everyone to use. Currently in a beta development
state, Astropix provides powerful ways to browse, search, and download
images, diagrams, artwork, and photographs from many astronomical
missions. The site is built around the Astronomical Visualization
Metadata (AVM) standard developed by the Virtual Astronomy Multimedia
Project (VAMP) that captures all the key descriptive information for
a public image, including color representations and astronomical and
sky coordinates. Existing image galleries containing AVM-tagged images
can easily supply them to Astropix, which downloads them, extracts
the metadata into its database, and generates versions of the images
at a variety of common sizes. Visitors to Astropix can search the
database using simple free-text queries, or use a structured search
(similar to "Smart Playlists" found in iTunes, for example). The
Astropix archive also features an Xquery-based method for posting
http queries and retrieving XML lists of matching imagery, allowing
for scripted access to the site. Current assets include imagery from
Spitzer, Chandra, ESO, Galex, Herschel, Hubble, Spitzer, and WISE,
with more on the way. Website: astropix.ipac.caltech.edu
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Title: Astropix: An Archive of Astronomical Images
Authors: Squires, Gordon K.; Hurt, R.; Rosenthal, C.; Llamas, J.;
Brinkworth, C.; Pyle, T.
2011AAS...21742003S Altcode: 2011BAAS...4342003S
In fall 2010, a new, central repository of astronomical images became
available at http://astropix.ipac.caltech.edu . Enabled by the Astronomy
Visualization Metadata (AVM) standard, this archive contains images
from NASA's Spitzer Space Telescope, Chandra, Hubble, WISE, GALEX,
and the Herschel Space Observatory. For the first time, an automated
registry is possible by populating contextual and informational
fields in the metadata of the images themselves. This presentation
will highlight the features of the archive, how to include your images
in the registry and applications enabled including dynamic websites,
kiosks, and mobile device applications.
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Title: Leveraging Metadata to Create Interactive Images... Today!
Authors: Hurt, Robert L.; Squires, G. K.; Llamas, J.; Rosenthal, C.;
Brinkworth, C.; Fay, J.
2011AAS...21742004H Altcode: 2011BAAS...4342004H
The image gallery for NASA's Spitzer Space Telescope has been newly
rebuilt to fully support the Astronomy Visualization Metadata (AVM)
standard to create a new user experience both on the website and in
other applications. We encapsulate all the key descriptive information
for a public image, including color representations and astronomical
and sky coordinates and make it accessible in a user-friendly form
on the website, but also embed the same metadata within the image
files themselves. Thus, images downloaded from the site will carry
with them all their descriptive information. Real-world benefits
include display of general metadata when such images are imported
into image editing software (e.g. Photoshop) or image catalog software
(e.g. iPhoto). More advanced support in Microsoft's WorldWide Telescope
can open a tagged image after it has been downloaded and display it
in its correct sky position, allowing comparison with observations
from other observatories. An increasing number of software developers
are implementing AVM support in applications and an online image
archive for tagged images is under development at the Spitzer Science
Center. Tagging images following the AVM offers ever-increasing
benefits to public-friendly imagery in all its standard forms (JPEG,
TIFF, PNG). The AVM standard is one part of the Virtual Astronomy
Multimedia Project (VAMP); http://www.communicatingastronomy.org
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Title: Theory and Simulations of Solar Atmosphere Dynamics
Authors: Stein, R. F.; Bogdan, T. J.; Carlsson, M.; Hansteen, V.;
McMurry, A.; Rosenthal, C. S.; Nordlund, Å.
2004ESASP.547...93S Altcode: 2004soho...13...93S
Numerical simulations are used to study the generation and propagation
of waves in the solar atmosphere. Solar p-mode oscillations are excited
by turbulent pressure work and entropy fluctuations (non-adiabatic gas
pressure work) near the solar surface. Interactions between short and
long period waves and radiative energy transfer control the formation of
shocks. The magnetic structure of the atmosphere induces coupling among
various MHD wave modes, with intense coupling and wave transformation
at the beta equal one surface, which likely is the location of the
so-called "magnetic canopy".
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Title: Waves in the Magnetized Solar Atmosphere. II. Waves from
Localized Sources in Magnetic Flux Concentrations
Authors: Bogdan, T. J.; Carlsson, M.; Hansteen, V. H.; McMurry, A.;
Rosenthal, C. S.; Johnson, M.; Petty-Powell, S.; Zita, E. J.; Stein,
R. F.; McIntosh, S. W.; Nordlund, Å.
2003ApJ...599..626B Altcode:
Numerical simulations of wave propagation in a two-dimensional
stratified magneto-atmosphere are presented for conditions that
are representative of the solar photosphere and chromosphere. Both
the emergent magnetic flux and the extent of the wave source are
spatially localized at the lower photospheric boundary of the
simulation. The calculations show that the coupling between the
fast and slow magneto-acoustic-gravity (MAG) waves is confined to
thin quasi-one-dimensional atmospheric layers where the sound speed
and the Alfvén velocity are comparable in magnitude. Away from this
wave conversion zone, which we call the magnetic canopy, the two MAG
waves are effectively decoupled because either the magnetic pressure
(B<SUP>2</SUP>/8π) or the plasma pressure (p=Nk<SUB>B</SUB>T)
dominates over the other. The character of the fluctuations observed
in the magneto-atmosphere depend sensitively on the relative location
and orientation of the magnetic canopy with respect to the wave source
and the observation point. Several distinct wave trains may converge
on and simultaneously pass through a given location. Their coherent
superposition presents a bewildering variety of Doppler and intensity
time series because (1) some waves come directly from the source while
others emerge from the magnetic canopy following mode conversion, (2)
the propagation directions of the individual wave trains are neither
co-aligned with each other nor with the observer's line of sight, and
(3) the wave trains may be either fast or slow MAG waves that exhibit
different characteristics depending on whether they are observed in
high-β or low-β plasmas (β≡8πp/B<SUP>2</SUP>). Through the
analysis of four numerical experiments a coherent and physically
intuitive picture emerges of how fast and slow MAG waves interact
within two-dimensional magneto-atmospheres.
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Title: Waves in the magnetised solar atmosphere
Authors: Rosenthal, Colin S.
2003safd.book...63R Altcode:
Oscillations and waves in the quiet and active solar atmosphere
constitute a zoo of distinct and overlapping phenomena: internetwork
oscillations, K-grains, running penumbral waves, umbral oscillations,
umbral flashes etc. The distinctive oscillation spectra associated
with the network, the internetwork, and sunspots and pores are a
strong indicator that the magnetic field has a significant dynamical
effect on wave motions. This immediately raises two questions I) Can
waves be used as diagnostic indicators of the magnetic field? and II)
Do the different properties of wave motions in various field geometries
have consequences for the efficiency of wave-heating in the atmosphere
and corona? I will discuss some new numerical calculations of wave
propagation in a variety of model atmospheres, which throw some light
on these questions.
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Title: Waves in magnetic flux concentrations: The critical role of
mode mixing and interference
Authors: Bogdan, T. J.; Rosenthal, C. S.; Carlsson, M.; Hansteen, V.;
McMurry, A.; Zita, E. J.; Johnson, M.; Petty-Powell, S.; McIntosh,
S. W.; Nordlund, Å.; Stein, R. F.; Dorch, S. B. F.
2002AN....323..196B Altcode:
Time-dependent numerical simulations of nonlinear wave propagation
in a two-dimensional (slab) magnetic field geometry show wave mixing
and interference to be important aspects of oscillatory phenomena in
starspots and sunspots. Discrete sources located within the umbra
generate both fast and slow MHD waves. The latter are compressive
acoustic waves which are guided along the magnetic field lines and
steepen into N-waves with increasing height in the spot atmosphere. The
former are less compressive, and accelerate rapidly upward through the
overlying low-beta portion of the umbral photosphere and chromosphere
(beta equiv 8pi p/ B<SUP>2</SUP>). As the fast wave fronts impinge
upon the beta ~ 1 penumbral “magnetic canopy" from above, they
interfere with the outward-propagating field-guided slow waves, and
they also mode convert to (non-magnetic) acoustic-gravity waves as
they penetrate into the weak magnetic field region which lies between
the penumbral canopy and the base of the surrounding photosphere. In
a three-dimensional situation, one expects additional generation,
mixing and interference with the remaining torsional Alfvén waves.
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Title: Waves in the Magnetized Solar Atmosphere. I. Basic Processes
and Internetwork Oscillations
Authors: Rosenthal, C. S.; Bogdan, T. J.; Carlsson, M.; Dorch,
S. B. F.; Hansteen, V.; McIntosh, S. W.; McMurry, A.; Nordlund, Å.;
Stein, R. F.
2002ApJ...564..508R Altcode:
We have modeled numerically the propagation of waves through magnetic
structures in a stratified atmosphere. We first simulate the propagation
of waves through a number of simple, exemplary field geometries in
order to obtain a better insight into the effect of differing field
structures on the wave speeds, amplitudes, polarizations, direction
of propagation, etc., with a view to understanding the wide variety of
wavelike and oscillatory processes observed in the solar atmosphere. As
a particular example, we then apply the method to oscillations in the
chromospheric network and internetwork. We find that in regions where
the field is significantly inclined to the vertical, refraction by
the rapidly increasing phase speed of the fast modes results in total
internal reflection of the waves at a surface whose altitude is highly
variable. We conjecture a relationship between this phenomenon and the
observed spatiotemporal intermittancy of the oscillations. By contrast,
in regions where the field is close to vertical, the waves continue
to propagate upward, channeled along the field lines but otherwise
largely unaffected by the field.
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Title: Wave Propagation in a Magnetized Atmosphere
Authors: Bogdan, T. J.; Rosenthal, C. S.; Carlsson, M.; McIntosh,
S.; Dorch, S.; Hansteen, V.; McMurry, A.; Nordlund, Å; Stein, R. F.
2001AGUSM..SH41A01B Altcode:
Numerical simulations of MHD wave propagation in plane-parallel
atmospheres threaded by non-trivial potential magnetic fields will be
presented, and their implications for understanding distinctions between
intranetwork and internetwork oscillations will be discussed. Our
findings basically confirm the conjecture of McIntosh et al. (2001,
ApJ 548, L237), that the two-dimensional surface where the Alfvén
and sound speeds coincide (i.e., where the plasma-β , the ratio of
gas to magnetic pressure, is of order unity) plays a fundamental
role in mediating the conversion between the fast-, intermediate-
(Alfvén), and slow-Magneto-Atmospheric-Gravity (MAG) waves. For
example, upward-propagating acoustic waves generated at the base of
the internetwork photosphere suffer significant downward reflection
when they encounter this β ≈ 1 surface. Close to the network, this
surface descends from the upper chromosphere and low corona (which
pertains in the internetwork cell interiors) down into the photosphere,
and so chromospheric oscillation `shadows' are predicted to surround
the network. In the network, strong vertical magnetic fields further
depress the β ≈ 1 surface below the surface layers where the
(magnetic field-aligned) acoustic waves (i.e., slow MAG-waves) are
generated. For frequencies in excess of the cutoff frequency, these
acoustic waves suffer little reflection from the overlying atmosphere
and they steepen as they progress upward.
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Title: An Observational Manifestation of Magnetoatmospheric Waves
in Internetwork Regions of the Chromosphere and Transition Region
Authors: McIntosh, S. W.; Bogdan, T. J.; Cally, P. S.; Carlsson, M.;
Hansteen, V. H.; Judge, P. G.; Lites, B. W.; Peter, H.; Rosenthal,
C. S.; Tarbell, T. D.
2001ApJ...548L.237M Altcode:
We discuss an observational signature of magnetoatmospheric waves in
the chromosphere and transition region away from network magnetic
fields. We demonstrate that when the observed quantity, line or
continuum emission, is formed under high-β conditions, where β is
the ratio of the plasma and magnetic pressures, we see fluctuations in
intensity and line-of-sight (LOS) Doppler velocity consistent with the
passage of the magnetoatmospheric waves. Conversely, if the observations
form under low-β conditions, the intensity fluctuation is suppressed,
but we retain the LOS Doppler velocity fluctuations. We speculate that
mode conversion in the β~1 region is responsible for this change in
the observational manifestation of the magnetoatmospheric waves.
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Title: Waves in the Magnetised Solar Atmosphere
Authors: Rosenthal, C. S.; Carlsson, M.; Hansteen, V.; McMurry,
A.; Bogdan, T. J.; McIntosh, S.; Nordlund, A.; Stein, R. F.; Dorch,
S. B. F.
2001IAUS..203..170R Altcode:
We have simulated the propagation of magneto-acoustic disturbances
through various magneto-hydrostatic structures constructed to mimic
the solar magnetic field. As waves propagate from regions of strong
to weak magnetic field and vice-versa different types of wave modes
(transverse and longitudinal) are coupled. In closed-field geometries
we see the trapping of wave energy within loop-like structures. In
open-field regions we see wave energy preferentially focussed away
from strong-field regions. We discuss these oscillations in terms
of various wave processes seen on the Sun - umbral oscillations,
penumbral running waves, internetwork oscillations etc.
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Title: Numerical Modeling of the Absorption and Scattering of Acoustic
Radiation by Sunspots
Authors: Rosenthal, C. S.; Julien, K. A.
2000ApJ...532.1230R Altcode:
We present numerical calculations of the scattering of acoustic-gravity
waves by a model sunspot consisting of an inhomogeneous, vertically
magnetized region embedded in a polytropically stratified layer. The
calculations show the transformation of incoming f-mode and p-mode
power into downward-propagating, slow magnetoacoustic waves resulting
in substantial absorption of incident f-modes and first-order p-modes
and indicating that the slow-mode transformation model is a viable
explanation for the observed absorption. In addition to absorption,
we find large scattering phase shifts for the f-modes. Phase shifts
are small for all p-modes. Coupling between modes of different
radial order is generally small. The remaining differences between
our results and the observations may constitute evidence that,
if the mode transformation picture is correct, real sunspots must
deviate significantly from the simple unidirectional field geometry
we use here. In particular, we suggest that a sunspot consisting of a
bundle of fibrils, in each of which the magnetic flux density increases
rapidly with depth, would reproduce more closely the measured strong
absorption and scattering of p-modes.
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Title: Convective contributions to the frequencies of solar
oscillations
Authors: Rosenthal, C. S.; Christensen-Dalsgaard, J.; Nordlund, Å.;
Stein, R. F.; Trampedach, R.
1999A&A...351..689R Altcode: 1998astro.ph..3206R
Differences between observed and theoretical eigenfrequencies of the Sun
have characteristics which identify them as arising predominantly from
properties of the oscillations in the vicinity of the solar surface:
in the super-adiabatic, convective boundary layer and above. These
frequency differences may therefore provide useful information about
the structure of these regions, precisely where the theory of solar
structure is most uncertain. In the present work we use numerical
simulations of the outer part of the Sun to quantify the influence
of turbulent convection on solar oscillation frequencies. Separating
the influence into effects on the mean model and effects on the
physics of the modes, we find that the main model effects are due
to the turbulent pressure that provides additional support against
gravity, and thermal differences between average 3-D models and 1-D
models. Surfaces of constant pressure in the visible photosphere are
elevated by about 150 km, relative to a standard envelope model. As a
result, the turning points of high-frequency modes are raised, while
those of the low-frequency modes remain essentially unaffected. The
corresponding gradual lowering of the mode frequencies accounts for
most of the frequency difference between observations and standard
solar models. Additional effects are expected to come primarily from
changes in the physics of the modes, in particular from the modulation
of the turbulent pressure by the oscillations.
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Title: Effects of line asymmetries on the determination of solar
internal structure
Authors: Rabello-Soares, M. C.; Christensen-Dalsgaard, J.; Rosenthal,
C. S.; Thompson, M. J.
1999A&A...350..672R Altcode: 1999astro.ph..8250R
Despite the strong evidence that the peaks in the spectrum of solar
oscillations are asymmetric, most determinations of mode frequencies
have been based on fits of symmetric Lorentzian profiles to the Fourier
or power spectra of oscillation time strings. The systematic errors
resulting from neglecting the line asymmetry could have serious effects
on inversions for the solar internal structure and rotation. Here we
analyse artificial data based on simple models of the intrinsic line
asymmetry, using GONG mode parameters with asymmetries found by one
of us (Rosenthal \cite{rosenthal2}). By fitting Lorentzians to the
resulting spectra, we estimate the likely properties of the errors
introduced in the frequencies. We discuss whether these frequency
shifts have a form similar to the near-surface layers uncertainties
and are therefore suppressed in the solar structure inversion. We also
estimate directly their contribution, if any, in the solar sound-speed
and density determinations using the SOLA technique.
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Title: Peaks and Troughs in Helioseismology: The Power Spectrum of
Solar Oscillations
Authors: Rosenthal, C. S.
1998ApJ...508..864R Altcode: 1998astro.ph..4035R
I present a matched-wave asymptotic analysis of the driving of solar
oscillations by a general localized source. The analysis provides a
simple mathematical description of the asymmetric peaks in the power
spectrum in terms of the relative locations of eigenmodes and troughs in
the spectral response. It is suggested that the difference in measured
phase function between the modes and the troughs in the spectrum
will provide a key diagnostic of the source of the oscillations. I
also suggest a form for the asymmetric line profiles to be used in the
fitting of solar power spectra. Finally, I present a comparison between
the numerical and asymptotic descriptions of the oscillations. The
numerical results bear out the qualitative features suggested by
the asymptotic analysis but suggest that numerical calculations of
the locations of the troughs will be necessary for a quantitative
comparison with the observations.
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Title: p-Mode Line-Shapes in Theory and Practice
Authors: Rosenthal, C. S.
1998ESASP.418..957R Altcode: 1998soho....6..957R; 1998astro.ph..7065R
I present an asymptotic analysis of the driving of p-modes by an
arbitrary source in a generic solar-like stratified layer. The model
produces strong line-asymmetries, especially at low frequencies, and
implies a particular form for the asymmetric profile. I will present a
comparison of the asymptotic results with numerical calculations for
a simple model. I will also show results from a fitting of the new
profile to recent data, including an estimate of the frequency errors
resulting from neglecting the asymmetry in the fitting process.
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Title: Tests of Convective Frequency Effects with SOI/MDI High-Degree
Data
Authors: Rosenthal, C. S.; Christensen-Dalsgaard, J.; Kosovichev,
A. G.; Nordlund, A. A.; Reiter, J.; Rhodes, E. J., Jr.; Schou, J.;
Stein, R. F.; Trampedach, R.
1998ESASP.418..521R Altcode: 1998astro.ph..7066R; 1998soho....6..521R
Advances in hydrodynamical simulations have provided new insight into
the effects of convection on the frequencies of solar oscillations. As
more accurate observations become available, this may lead to an
improved understanding of the dynamics of convection and the interaction
between convection and pulsation (Rosenthal et al. 1999). Recent
high-resolution observations from the SOI/MDI instrument on the
SOHO spacecraft have provided the so-far most-detailed observations
of high-degree modes of solar oscillations, which are particularly
sensitive to the near-surface properties of the Sun. Here we present
preliminary results of a comparison between these observations and
frequencies computed for models based on realistic simulations of
near-surface convection. Such comparisons may be expected to help
in identifying the causes for the remaining differences between the
observed frequencies and those of solar models.
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Title: Effects of Line Asymmetries on the Determination of Solar
Oscillation Frequencies
Authors: Christensen-Dalsgaard, J.; Rabello-Soares, M. C.; Rosenthal,
C. S.; Thompson, M. J.
1998ESASP.418..147C Altcode: 1998soho....6..147C
Despite the strong evidence that the peaks in the spectrum of solar
oscillations are asymmetric, most determinations of mode frequencies
have been based on fits of symmetric Lorentzian profiles to the Fourier
or power spectra of oscillation time strings. The systematic errors
resulting from neglecting the line asymmetry could have serious effects
on inversions for the solar internal structure and rotation. Here we
analyze artificial data based on simple models of the intrinsic line
asymmetry. By fitting Lorentzians to the resulting spectra, we estimate
the likely properties of the errors introduced in the frequencies and
consider the possible effects on the inversions.
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Title: Convective Effects on Mode Frequencies
Authors: Rosenthal, C. S.
1997ASSL..225..145R Altcode: 1997scor.proc..145R
It is well known that the principal cause of the differences between
measured and theoretical solar oscillation frequencies lies close to
the solar surface, particularly in the narrow strongly-superadiabatic
region. I shall discuss the details of these frequency residuals,
and attempts to explain their existence by invoking structural
changes in solar models and/or novel physics in the Sun or the
oscillations. In general it will be found that, given the best atomic
physics, hydrodynamics, and mode-physics available, the discrepancy
between theory and observation can be considerably reduced compared
to that found in simpler calculations. However there still remains a
significant discrepancy which apparently indicates that the required
perturbation to the solar structure is shallower than that implied by
hydrodynamical simulation. In addition, no complete theory exists for
the behaviour of significantly non-radial modes, of which the {\it
f}\/-modes provide the paramount example.
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Title: SCORe'96 : Solar Convection and Oscillations and their
Relationship
Authors: Pijpers, F. P.; Christensen-Dalsgaard, J.; Rosenthal, C. S.
1997ASSL..225.....P Altcode: 1997scor.proc.....P
No abstract at ADS
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Title: The Forward Problem in Sunspot Seismology
Authors: Rosenthal, Colin S.; Julien, Keith A.
1997SPD....28.0208R Altcode: 1997BAAS...29..894R
Observations of the interaction of p -modes with sunspots show strong
absorption and scattering which each show a systematic pattern of
variation as a function of frequency and wavenumber. Our goal of
inferring the sub-surface structure of sunspots from such data has been
difficult to achieve because of the many complexities involved in the
wave/spot interaction. However, the basic wave-transformation processes
involved are now relatively well understood. We have therefore proceeded
to the next step of constructing a fully two-dimensional numerical
model of the interaction of solar oscillations with a sunspot. In
a simple slab geometry, in which the field is everywhere vertical,
we find that modes confined to the region close to the surface show
absorption and scattering profiles comparable to those measured on the
Sun. However, deeper modes pass through our model sunspot virtually
unaffected. We conclude that our basic mode-transformation mechanism
can adequately explain the properties of real sunspots, but that the
actual structure of a sunspot must involve a magnetic field which
increases substantially with depth below the photosphere if it is to
explain the strength of the observed interaction.
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Title: The interfacial F mode in a spherical solar model
Authors: Rosenthal, C. S.; Christensen-Dalsgaard, J.
1995MNRAS.276.1003R Altcode:
The solar f modes are a branch of oscillations characterized by a
close correspondence between their measured dispersion relation and
that predicted for a pure surface gravity wave: omega^2=gk where g
is the surface gravity of the Sun. However, there is now substantial
evidence for deviations from this simple behaviour. We consider the
hypothesis of Rosenthal & Gough that the f modes are characterized
better as an interfacial wave propagating at the chromosphere-corona
transition. Using a standard solar interior model, a semi-empirical
atmospheric model, and a parametrized transition region model as our
equilibrium state, we solve the linearized oscillation equations for
the interfacial f mode. We find that the frequencies of the interfacial
f mode differ from those of the classical f mode only at very high
degrees. We conclude that the interfacial f-mode theory may be the
correct explanation for the very high-degree data, but that some other
mechanism is required to explain the lower degree data.
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Title: Convective Perturbations to Solar Oscillations: the f-MODE
Authors: Rosenthal, C. S.; Christensen-Dalsgaard, Jorgen; Nordlund,
Ake; Trampedach, Regner
1995ESASP.376b.453R Altcode: 1995soho....2..453R; 1995help.confP.453R
No abstract at ADS
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Title: Seismology of the Solar Surface Regions
Authors: Rosenthal, C. S.; Christensen-Dalsgaard, J.; Houdek, G.;
Monteiro, M. J. P. F. G.; Nordlund, A.; Trampedach, R.
1995ESASP.376b.459R Altcode: 1995soho....2..459R; 1995help.confP.459R
We investigate the influence of dynamical and nonadiabatic affects
ocurring in the superadiabatic region near the top of the solar
convetcion zone on the frequencies of solar p modes. Taking as our
baseline a standard hydrostatic solar model, we calculate frequency
changes resulting from a number of different formalisms, involving
modifications of the superadiabatic temperature gradient, turbulent
pressure and/or nonadiabatic effects. We compare these various
methods of calculating the effect of convection on solar-oscillation
eigenfrequencies with each other and with the measured frequency
residuals.
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Title: Near-surface Effects in Modelling Oscillations of Eta Boo
Authors: Christensen-Dalsgaard, J.; Bedding, T. R.; Houdek, G.;
Kjeldsen, H.; Rosenthal, C.; Trampedach, H.; Monteiro, M. J. P. F. G.;
Nordlund, A.
1995ASPC...83..447C Altcode: 1995IAUCo.155..447C; 1995aasp.conf..447C; 1995astro.ph..3106C
Following the report of solar-like oscillations in the G0 V star eta
Boo (Kjeldsen et al. 1995, AJ 109, 1313), a first attempt to model the
observed frequencies was made by Christensen-Dalsgaard et al. (1995, ApJ
Letters, in press). This attempt succeeded in reproducing the observed
frequency separations, although there remained a difference of about
10 microHz between observed and computed frequencies. In those models,
the near-surface region of the star was treated rather crudely. Here we
consider more sophisticated models that include non-local mixing-length
theory, turbulent pressure and nonadiabatic oscillations.
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Title: The Role of Photospheric Magnetic Fields in the Variation of
Solar Oscillation Eigenfrequencies
Authors: Rosenthal, C. S.
1995ApJ...438..434R Altcode:
The frequencies of solar oscillations have been found to be higher at
the peak of the solar cycle, their variation being consistent with that
expected from a change in the solar structure confined to the Sun's
outer layers. In this work, a technique is introduced for estimating
the effect of the highly inhomogeneous photospheric magnetic field on
solar oscillation eigenfrequencies, and its results are compared with
the solar data. It is found that the observed steep rise in frequency
shift at low frequency and the leveling of or decline at high frequency
are well reproduced by the model. The correct order of magnitude for the
frequency changes is also reproduced, at least at low frequency. The
model implies a particular functional form for the variation of the
frequency changes with order and degree, and it is suggested that
future advances in observation and theory will therefore allow this
model to be confirmed or refuted.
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Title: The Solar f-Mode as an Interfacial Mode at the
Chromosphere-Corona Transition
Authors: Rosenthal, C. S.; Gough, D. O.
1994ApJ...423..488R Altcode:
Observations of the solar f-mode at intermediate and high spherical
harmonic degree show substantial departures from the dispersion relation
expected for a pure surface gravity oscillation. We suggest that the
waves are reflected by the high density gradient in the region of the
chromosphere-corona transition and are therefore characterized better
as interfacial modes localized near the transition. An analytical
calculation, for a simple model in which the transition is treated as
a discontinuity, shows that such modes have a dispersion relation with
the correct qualitative features to explain the observations. However,
quantitative agreement is not possible for reasonable parameter
values. We next consider a more general atmospheric structure with
a continuous stratification for which asymptotic frequency estimates
are obtained. These are compared with direct numerical solutions of
the differential equations. The frequencies are found to give a much
closer quantitative agreement with the observations. We suggest that
f-mode seismology might be used to obtain direct information about
the average structure of the solar atmosphere and transition region.
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Title: When is an F-Mode not an F-Mode
Authors: Rosenthal, C. S.; Gough, D. O.
1993ASPC...42..185R Altcode: 1993gong.conf..185R
No abstract at ADS
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Title: Absorption of Acoustic Waves by Sunspots - Part Two
Authors: Rosenthal, C. S.
1992SoPh..139...25R Altcode:
Observations of the scattering of acoustic waves by sunspots show a
substantial deficit in scattered power relative to incident power. A
number of calculations have attempted to model this process in terms
of absorption at the magnetohydrodynamic Alfvén resonance. The
results presented here extend these calculations to the case of a
highly structured axisymmetric translationally invariant flux-tube
embedded in a uniform atmosphere. The fractional energy absorbed is
calculated for models corresponding to flux-tubes of varying radius,
mean flux-density and location below the photosphere. The effects of
twist are also included.
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Title: Absorption of Acoustic Waves in Monolithic and Fibril Sunspot
Models
Authors: Rosenthal, C. S.
1990SoPh..130..313R Altcode:
It has been hypothesized that the observation of substantial absorption
of acoustic power in the vicinity of sunspots may be explained by
the transformation of acoustic oscillations into highly damped shear
Alfvén waves in thin resonant layers. Analytical estimates of the
efficiency of this process (Hollweg, 1988) are compared with direct
one-dimensional numerical simulations of absorption by a magnetic
barrier in a viscous medium. After slight modification, the estimate
is found to give a good approximation to the numerical absorption rate.
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Title: Scattering and multiple scattering of acoustic waves in a
stratified medium.
Authors: Rosenthal, C. S.; Gough, Douglas O.
1988ESASP.286..457R Altcode: 1988ssls.rept..457R
Bogdan and Zweibel have studied the effect on wave propagation of
scattering from an ensemble of vertical magnetic flux tubes in a
stratified atmosphere, using the WKB approximation. The authors analyse
the effect of an ensemble of general axisymmetric scatterers on acoustic
waves in a stratified atmosphere, without using the WKB approximation,
and obtain a dispersion relation valid for small filling factors. The
properties of this dispersion relation are studied for scattering
from density inhomogeneities in a two-layer model atmosphere. It is
found that increased strafication tends to decrease the frequency
perturbation induced by a population of cylindrical inhomogeneities.
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Title: Small-Telescope Photoelectric Data Acquisition at Pace
University
Authors: Engelbrektson, S.; Dick, J. B.; Kwietniak, K. T.; Rosenthal,
C.
1985BAAS...17..511E Altcode:
No abstract at ADS
