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Analysis of Voyager Spectra of the beta Cephei Star nu Eridani
Stalio, R.; Morossi, C.; Polidan, R. S. +2 more
Voyager 500-1700 A spectrophotometric observations of the beta Cephei star nu Eri are presented and discussed. The Voyager observations were obtained in 1981 and cover six pulsation cycles of the star. These data are supplemented with a set of nine International Ultraviolet Explorer (IUE) SWP high-resolution observations covering one, earlier epoc…
Diffusive Shock Acceleration in the Presence of Current Sheets
Jokipii, J. R.; Kota, J.
We study the nature of diffusive shock acceleration in the presence of current sheets which are oriented normal to the shock, so that the drift along the sheets carries particles either away from or toward the shock plane. We consider a system with periodic regions of alternating magnetic field direction. This can be taken to be a very crude repre…
Analytic Lyman-Alpha Wing Diagnostics and the Chromospheric Excitation Balance in Cool Dwarfs
Gayley, K. G.
I show that the Lyman alpha wings of cool dwarfs can be understood in terms of a very simple model, based on a simplified representation of the chromospheric hydrogen excitation balance and approximate analytic wing diagnostics in partial redistribution. Much of the complexity of the radiation transfer in the partially coherent and steeply tempera…
Ultraviolet Photometry of Nova Cygni 1992 Obtained with the High Speed Photometer
Gallagher, J. S.; Nelson, M. J.; Percival, J. W. +6 more
In this Letter we present the first high-speed ultraviolet photometry of an active, classical nova, Nova Cygni 1992. The 45 minute observation shows significant evidence for power at frequencies that correspond to periods of about 565 and 900 s. Each of these periods has an amplitude of about 3 mmag. Since this data set is short, we cannot establi…
Optical Signatures of High-Redshift Galaxy Clusters
Charlot, Stephane; Evrard, August E.
We combine an N-body and gasdynamic simulation of structure formation with an updated population synthesis code to explore the expected optical characteristics of a high-redshift cluster of galaxies. We examine a poor (2 keV) cluster formed in a biased, cold dark matter cosmology and employ simple, but plausible, threshold criteria to convert gas …
Structural Parameters of Globular Clusters in the Fornax Cluster
Elson, Rebecca A. W.; Schade, David J.
We present measurements of the structural parameters of 24 globular cluster candidates with 19 < I < 22, ~4' from NGC 1399, the central giant elliptical galaxy in the Fornax cluster (distance modulus ~31). The data were obtained with the Hubble Space Telescope's Wide Field Camera prior to refurbishment. We use a two-dimensional model-fitting…
Nonthermal Pair Models, Reflection, and X-Ray Spectral Variability of Active Galaxies
Done, C.; Grandi, P.; Urry, C. M.
Standard nonthermal electron-positron pair cascades, including the effects of reflection from an accretion disk, can explain reasonably well the mean spectra of low-luminosity, Seyfert-type active galaxies. We test this model using the spectral variability observed by EXOSAT between 0.05 and 10 keV in five active galaxies: NGC 5548, 3C 120, 3C 273…
A Catalog of Intracluster Gas Temperatures
Forman, W.; Jones, C.; Vrtilek, S. D. +3 more
We have searched the Einstein Monitor Proportional Counter (MPC) data base for observations of clusters of galaxies. The MPC was a nonfocal plane instrument on board the Einstein Observatory and accumulated data during all pointed observations with the four focal plane instruments. By co-adding the MPC spectra obtained during all pointed observati…
Discovery of New Objects in the Orion Nebula on HST Images: Shocks, Compact Sources, and Protoplanetary Disks
O'Dell, C. R.; Wen, Zheng; Hu, Xihai
We have reduced and analyzed a set of narrow-band HST images of a portion of M42 south of the Trapezium. Many new emission-line sources were found, some quite long but so narrow that they are not seen on ground-based images. These include thin shells which are high-ionization shocks. The structure around Orion HH 3 is resolved into multiple compon…
Goddard High-Resolution Spectrograph Observations of the Local Interstellar Medium and the Deuterium/Hydrogen Ratio along the Line of Sight toward Capella
Ayres, Thomas R.; Savage, Blair D.; Brown, Alexander +6 more
HST Goddard High-Resolution Spectrograph observations of the 1216, 2600, and 2800 A spectral regions are analyzed for the spectroscopic binary system Capella, obtained at orbital phase 0.26 with 3.27-3.57 km/s resolution and high SNR. The column densities of H I, D I, Mg II, and Fe II for the local interstellar medium along this 12.5 pc line of si…