Author name code: rosenthal ADS astronomy entries on 2022-09-14 author:"Rosenthal, C." ------------------------------------------------------------------------ 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. Bibcode: 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 Title: Astropix: An Archive of Astronomical Images Authors: Squires, Gordon K.; Hurt, R.; Rosenthal, C.; Llamas, J.; Brinkworth, C.; Pyle, T. Bibcode: 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. Title: Leveraging Metadata to Create Interactive Images... Today! Authors: Hurt, Robert L.; Squires, G. K.; Llamas, J.; Rosenthal, C.; Brinkworth, C.; Fay, J. Bibcode: 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 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. Bibcode: 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". 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. Bibcode: 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 (B2/8π) or the plasma pressure (p=NkBT) 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/B2). 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. Title: Waves in the magnetised solar atmosphere Authors: Rosenthal, Colin S. Bibcode: 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. 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. Bibcode: 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/ B2). 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. 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. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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. Title: Numerical Modeling of the Absorption and Scattering of Acoustic Radiation by Sunspots Authors: Rosenthal, C. S.; Julien, K. A. Bibcode: 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. Title: Convective contributions to the frequencies of solar oscillations Authors: Rosenthal, C. S.; Christensen-Dalsgaard, J.; Nordlund, Å.; Stein, R. F.; Trampedach, R. Bibcode: 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. 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. Bibcode: 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. Title: Peaks and Troughs in Helioseismology: The Power Spectrum of Solar Oscillations Authors: Rosenthal, C. S. Bibcode: 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. Title: p-Mode Line-Shapes in Theory and Practice Authors: Rosenthal, C. S. Bibcode: 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. 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. Bibcode: 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. 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. Bibcode: 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. Title: Convective Effects on Mode Frequencies Authors: Rosenthal, C. S. Bibcode: 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. Title: SCORe'96 : Solar Convection and Oscillations and their Relationship Authors: Pijpers, F. P.; Christensen-Dalsgaard, J.; Rosenthal, C. S. Bibcode: 1997ASSL..225.....P Altcode: 1997scor.proc.....P No abstract at ADS Title: The Forward Problem in Sunspot Seismology Authors: Rosenthal, Colin S.; Julien, Keith A. Bibcode: 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. Title: The interfacial F mode in a spherical solar model Authors: Rosenthal, C. S.; Christensen-Dalsgaard, J. Bibcode: 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. Title: Convective Perturbations to Solar Oscillations: the f-MODE Authors: Rosenthal, C. S.; Christensen-Dalsgaard, Jorgen; Nordlund, Ake; Trampedach, Regner Bibcode: 1995ESASP.376b.453R Altcode: 1995soho....2..453R; 1995help.confP.453R No abstract at ADS 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. Bibcode: 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. 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. Bibcode: 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. Title: The Role of Photospheric Magnetic Fields in the Variation of Solar Oscillation Eigenfrequencies Authors: Rosenthal, C. S. Bibcode: 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. Title: The Solar f-Mode as an Interfacial Mode at the Chromosphere-Corona Transition Authors: Rosenthal, C. S.; Gough, D. O. Bibcode: 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. Title: When is an F-Mode not an F-Mode Authors: Rosenthal, C. S.; Gough, D. O. Bibcode: 1993ASPC...42..185R Altcode: 1993gong.conf..185R No abstract at ADS Title: Absorption of Acoustic Waves by Sunspots - Part Two Authors: Rosenthal, C. S. Bibcode: 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. Title: Absorption of Acoustic Waves in Monolithic and Fibril Sunspot Models Authors: Rosenthal, C. S. Bibcode: 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. Title: Scattering and multiple scattering of acoustic waves in a stratified medium. Authors: Rosenthal, C. S.; Gough, Douglas O. Bibcode: 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. Title: Small-Telescope Photoelectric Data Acquisition at Pace University Authors: Engelbrektson, S.; Dick, J. B.; Kwietniak, K. T.; Rosenthal, C. Bibcode: 1985BAAS...17..511E Altcode: No abstract at ADS