Search Publications
A Far-Ultraviolet Flare on a Pleiades G Dwarf
Linsky, J. L.; Basri, G. S.; Antiochos, S. K. +9 more
The Hubble Space Telescope/Faint Object Spectrograph (HST/FOS) recorded a remarkable transient brightening in the C IV lambda lambda 1548,50 emissions of the rapidly rotating Pleiades G dwarf H II 314. On the one hand the 'flare' might be a rare event luckily observed; on the other hand it might be a bellwether of the coronal heating in very young…
An EXOSAT Detection of the Transient X-Ray Pulsar GRO J1008-57
Shrader, C. R.; Schultz, A. B.; Macomb, D. J.
The hard X-ray transient, GRO J1008-57, was discovered during a bright outburst in 1993 July by the Burst and Transient Source Experiment (BATSE) instrument on board the Compton Gamme-Ray Observatory (CGRO). There are no published reports of previous emission from this 93.6 sec X-ray pulsar. Recent optical results have suggested a Be star as the c…
Transition in the X-Ray Light Curve of the AM Herculis System V834 Centauri (E1405-451): 1985--1986 EXOSAT Observations
Sambruna, Rita M.; Treves, Aldo; Maraschi, Laura +2 more
We analyze the EXOSAT observations of the AM Herculis system V834 Centauri (E1405-451), taken in 1985 March and 1986 August. Archival UV data, simultaneous with the 1986 observations, are also considered. The soft X-ray light curve has a double humped structure, with total eclipse at phi approximately 0.0. It differs significantly from that observ…
A Study of the Ultraviolet Absorption Lines through the Complete Galactic Halo by the Analysis of HST Faint Object Spectrograph Spectra of Active Galactic Nuclei. I.
Cohen, Ross D.; Shull, J. Michael; Stocke, John T. +7 more
The ultraviolet (1150-2850 A) spectra of a number of active galactic nuclei (AGNs) observed with the Hubble Space Telescope Faint Object Spectrograph (FOS) have been used to study the properties of the Galactic halo. The objects that served as probes are 3C 273, PKS 0454-220, PG 1211+143, CSO 251, Ton 951, and PG 1351+640. The equivalent widths of…
Evolution of Lyman-Alpha Clouds at Low Redshifts
Ikeuchi, Satoru; Murakami, Izumi
We examine the evolution of an intergalactic gas cloud confined by the gravity of cold dark matter in the minihalo model. Assuming that the evolution of the diffuse ultraviolet (UV) flux follows a power law function of the form (1 + Z)alphai^ with a change in exponent at redshift z_c_ and a constant comoving number density of gas clouds…
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…