Search Publications
Toward Unbiased Determination of the Redshift Evolution of Lyman-Alpha Forest Clouds
Lu, Limin; Zuo, Lin
The possibility of using D_A_, the mean depression of a quasar spectrum due to Lyα forest absorption, to study the number density evolution of the Lyα forest clouds is examined in some detail. Current D_A_ measurements are made against a continuum that is a power- law extrapolation from the continuum longward of Lyα emission. Compared to the line-…
Concurrent X-Ray and Optical Observations of Two Dwarf Novae during Eruption
Raymond, J. C.; Vrtilek, S. D.; Silber, A.
The dwarf novae SU UMa and RU Peg were each observed with the ROSAT Observatory during outburst. SU UMa was also observed twice between outbursts. The spectrum of SU UMa during quiescence is well fitted by a 2.1 keV thermal bremsstrahlung model with a Gaussian line at 0.97 keV absorbed by a column density of 1.4 x 1020/sq cm. During the…
Markarian 315: A Test Case for the Active Galactic Nucleus--Merger Hypothesis?
MacKenty, John W.; Wilson, Andrew S.; Griffiths, Richard E. +2 more
Using the Hubble Space Telescope Wide Field/Planetary Camera, we have detected a diffuse continuum knot in the inner regions of the Seyfert galaxy Markarian 315. This knot may be a remnant nucleus. It is associated with a complex, ringlike structure in both the continuum and ionized gas emission. We have measured the kinematics of the ionized gas …
The Linear Polarization of 3C 345 in the Ultraviolet
Boyd, Patricia T.; Impey, C. D.; Nelson, M. J. +9 more
The linear polarization of 3C 345, a superluminal radio source and OVV quasar, was observed in two bandpasses in the ultraviolet (centered at 2160 A and 2770 A) in 1993 April using the High Speed Photometer on the Hubble Space Telescope. The quasar is significantly polarized in the UV (p > 5%). Ground-based polarimetry was obtained 11 days late…
Ultraviolet Observations of the Gamma-Ray Blazar 3C 279 following the Gamma-Ray Flare of 1991 June
Vestrand, W. Thomas; Bonnell, Jerry T.; Stacy, J. Gregory
Ultraviolet observations of the gamma-ray blazar 3C 279 were carried out in 1991 July with the International Ultraviolet Explorer (IUE) satellite, 28 days after the outburst of intense gamma-ray emission detected from this source with the high-energy EGRET instrument aboard the Compton Gamma-Ray Observatory. IUE observations were conducted over th…
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…