Search Publications
The Local LY alpha Forest: Association of Clouds with Superclusters and Voids
Carilli, Chris; Donahue, Megan; Shull, J. Michael +2 more
The Goddard High Resolution Spectrograph aboard the Hubble Space Telescope was used with the G160M grating to obtain high-resolution (0.2 Å) spectra of three very bright active galactic nuclei located behind voids in the nearby distribution of bright galaxies (i.e., CfA and Arecibo redshift survey regions). A total of eight definite (≥ 4 σ) Lyα ab…
Very Low Mass Stars and White Dwarfs in NGC 6397
Paresce, Francesco; de Marchi, Guido; Romaniello, Martino
Deep Wide Field/Planetary Camera 2 (WFPC2) images in wide bands centered at 606 and 802 nm were taken with the Hubble Space Telescope (HST) 4.6 min from the center of the galactic globular cluster NGC 6397. The images were used to accurately position approximately 2120 stars detected in the field on a color magnitude diagram down to a limiting mag…
The Striking Near-Infrared Morphology of the Inner Region in M100
Knapen, J. H.; Peletier, R. F.; de Jong, R. S. +3 more
New optical and near-infrared (NIR) X-band images of the inner 3 kpc region of the nearby Virgo spiral M100 (NGC 4321) display remarkable morphological changes with wavelength. While in the optical the light is dominated by a circumnuclear zone of enhanced star formation, the morphological features in the 2.2 micron image correspond to a newly dis…
Multiwavelength Monitoring of the BL Lacertae Object PKS 2155-304. IV. Multiwavelength Analysis
Maraschi, L.; Tagliaferri, G.; Pian, E. +47 more
Simultaneous X-ray, ultraviolet, optical, infrared, and radio monitoring data were used to test and constrain models of continuum emission from the BL Lacertae object PKS 2155-304. Intensively sampled ultraviolet and soft X-ray light curves showed a clear temporal correlation, with the X-rays leading the ultraviolet by 2-3 hr. This lag was found t…
Hubble Space Telescope Sample of Radio-loud Quasars: Ultraviolet Spectra of the First 31 Quasars
Netzer, H.; Ferland, G. J.; Browne, I. W. A. +6 more
We report the first results from a continuing program to investigate the multifrequency spectrophotometric and other properties of a sample of about 50 radio-loud quasars in the redshift range ∼0.3-1.3. Here we present spectrophotometric data of high signal-to-noise ratio (≳20 in the continuum) of the first 31 radio-loud quasars, over the waveleng…
HST Observations of the Ring around SN 1987A
Chevalier, Roger A.; Kirshner, Robert P.; Lundqvist, Peter +1 more
Hubble Space Telescope observations of SN 1987A show that the circumstellar material near the supernova forms a clumpy elliptical ring. We analyze six epochs of images made with the Faint Object Camera imaging the lines of [O III] and Hβ over the interval 1990 August-1993 October, and three epochs of observations with the Planetary Camera in the c…
Large size of Lyman-α gas clouds at intermediate redshifts
Morris, Simon L.; Weymann, Ray J.; Foltz, Craig B. +2 more
THE Lyman-α absorption lines observed in the spectra of quasars are thought to be caused by intervening clouds of atomic hydrogen, the origin and physical nature of which are still unknown. These clouds might be structures confined by the pressure of the surrounding intergalactic medium1, relicts of density fluctuations in the early Uni…
Spectroscopy of HD77581 and the mass of VELA X-1.
van Kerkwijk, M. H.; van Paradijs, J.; Zuiderwijk, E. J. +3 more
We present new high-resolution, high signal-to-noise optical spectra of HD77581, the optical counterpart of the X-ray source Vela X-1, and determine radial velocities from these spectra, as well as from high-resolution IUE spectra and from digitized photographic spectra. The measured velocities show strong deviations from a pure Keplerian radial-v…
X-ray outburst of the peculiar Seyfert galaxy IC 3599^*^.
Beuermann, K.; de Martino, D.; Bade, N. +4 more
We report optical, soft X-ray, and UV observations of the peculiar Seyfert galaxy IC 3599 using data obtained with ROSAT and IUE. Most remarkably, we discovered a rapid decrease of the X-ray flux by a factor of about 100 within one year and a more gradual decrease thereafter. The X-ray spectrum of IC3599 was soft at flux maximum and became even so…
Interplanetary Shock Waves: ULYSSES Observations In and Out of the Ecliptic Plane
Balogh, A.; Forsyth, R. J.; Burton, M. E. +4 more
Between its launch in October 1990 and the end of 1993, approximately 160 fast collisionless shock waves were observed in the solar wind by the Ulysses space probe. During the in-ecliptic part of the mission, to February 1992, the observed shock waves were first caused mainly by solar transient events following the solar maximum and the reorganisa…