Search Publications
Evidence Signaling the Start of Enhanced Counterjet Flow in the Symbiotic System R Aquarii
Kafatos, M.; Michalitsianos, A. G.; Perez, M.
The velocity struture of strong far-UV emission lines observed in the symbiotic variable R Aqr suggests the start of new jet activity which will probably culminate in the appearance of a series of intense nebular emission knots within a decade. This is indicated by a systematic redward wavelength drift of emission lines, which we have followed wit…
Analysis of the IUE Satellite and the Ground-based Observations of SW Lacertae
Lee, Woo Baik; Jeong, Jang Hae; Kang, Yong Woon +1 more
We present UBV observations of SW Lacertae obtained in 1988. We classify all previous light curves into three groups according to their maxima. The International Ultraviolet Explorer (IUE) spectra of SW Lacertae are used for ultraviolet photometry and for a variation study of chromspheric activity. Five light curves between the wavelengths of 2600…
Searching for Hard X-Ray Directivity during the Rise, Peak, and Decay Phases of Solar Flares
Li, Peng
We have identified 72 large solar flares (peak counting rates more than 1000 counts/s) observed by Hard X-ray Burst Spectroscopy (HXRBS) on-board the Solar Maximum Mission (SMM). Using a database of these flares, we have studied hard X-ray (50-850 keV) spectral center-to-limb variation and its evolution with time. The major results are the followi…
Active Galactic Nuclei. V. X-Ray Variability and the Black Hole Cluster Paradigm
Pacholczyk, A. G.; Stoeger, W. R.
A random superposition of elementary luminosity bursts of rectangular or triangular shape produces X-ray luminosity flicker curves characterized by features corresponding to those observed in the X-ray- variable Seyfert galaxies and other active galactic nuclei. Such luminosity events could be produced by accretion processes resulting from tidal d…
A Search for Ultraviolet Circumstellar Gas Absorption Features in alpha Piscis Austrinus (Fomalhaut), A Possible beta Pictoris--like System
Kondo, Yoji; Cheng, K. -P.; Bruhweiler, Fred C.
Archival high-dispersion International Ultraviolet Explorer (IUE) spectra have been used to search for circumstellar gas absorption features in alpha PsA (A3 V), a nearby (6.7 pc) proto-planetary system candidate. Recent sub-millimeter mapping observations around the region of alpha PsA indicate a spatially resolved dust disk like the one seen aro…
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 …