Search Publications
3C 390.3: Modeling Variable Profile Humps
Veilleux, Sylvain; Zheng, Wei; Grandi, Steven A.
A comparison of the Hα and Hβ profiles of the radio galaxy 3C 390.3 at different epochs shows that the Hβ/Hα ratio is significantly higher in the line "humps" than in the rest of the profiles. No humps are found in the Lyα profile, although Lyα is as broad as the Balmer lines. Therefore, the profile humps are probably produced in a region of highe…
Accretion Mechanisms in the Be/X-Ray Transient System A0535+26
Stella, L.; Motch, C.; Janot-Pacheco, E. +1 more
We present four EXOSAT observations of the Be/X-ray transient pulsar HDE 245770/A0535+26 obtained at various phases of the 111d period. On all occasions, a faint X-ray flux is detected from the source (Fx = 1.5-3.0 × 10-10 ergs cm-2 s-1) which corresponds to Lx (1-20 keV) = 2.5 × 10…
First Results from the Goddard High-Resolution Spectrograph: Elemental Abundances in the Diffuse Clouds toward XI Persei
Ebbets, Dennis C.; Sembach, Kenneth R.; Savage, Blair D. +4 more
An analysis is presented of high-resolution observations of ultraviolet interstellar absorption lines of dominant ion stages arising in the diffuse clouds toward Xi Per obtained with the Goddard High-Resolution Spectrograph. A detection of the weak intersystem line of semiforbidden C II 2325 A is reported. For C, O, and Mg, column densities are de…
Interstellar Gas Phase Abundance of Carbon, Oxygen, Nitrogen, Copper, Gallium, Germanium, and Krypton toward zeta Ophiuchi
Ebbets, Dennis C.; Savage, Blair D.; Cardelli, Jason A.
An analysis of weak (less than 10 mA) UV interstellar absorption line data obtained for the line of sight to the O9.5 IV star Zeta Oph is presented. Measurements of weak semiforbidden lines of N I, O I, Cu II, and a new UV detection of Na I are reported along with a small upper limit for C II. Interstellar detections of Ga II, Ge II, and Kr I are …
The Postcollapse Core of M15 Imaged with the HST Planetary Camera
Schneider, Donald P.; Lauer, Tod R.; Faber, S. M. +12 more
It is shown here that, despite the severe spherical aberration present in the HST, the Wide Field/Planetary Camera (WFPC) images still present useful high-resolution information on M15, the classic candidate for a cluster with a collapsed core. The stars in M15 have been resolved down to the main-sequence turnoff and have been subtracted from the …
First Results from the Goddard High-Resolution Spectrograph: High-Resolution Observations of the 1942 Angstrom Resonance Line of HG II in the Chemically Peculiar B Star, chi LUPI
Wahlgren, Glenn M.; Leckrone, David S.; Johansson, Sveneric G.
The Goddard High-Resolution Spectrograph on the HST has been used to obtain high S/N observations of the sharp-lined, Hg- and Pt-rich B-type star, Chi Lupi, with a resolving power of 87,000. The observations reveal a level of spectroscopic detail never before observed at ultraviolet wavelengths for any star other than the sun. Concentrating on the…
Observations of Scorpius X-1 with IUE: Ultraviolet Results from a Multiwavelength Campaign
Raymond, J. C.; Lewin, W. H. G.; Mitsuda, K. +5 more
IUE UV results are presented for the low-mass X-ray binary Sco X-1. Models that predict UV continuum emission from the X-ray-heated surface from the companion star and from an X-ray illuminated accretion disk are adjusted for parameters intrinsic to Sco X-1, and fitted to the data. X-ray heating is found to be the dominant source of UV emission; t…
The Core of the Nearby S0 Galaxy NGC 7457 Imaged with the HST Planetary Camera
Lauer, Tod R.; Faber, S. M.; Currie, Douglas G. +12 more
We have observed the nearby S0 galaxy NGC 7457 with the Planetary Camera of the Hubble Space Telescope. Spatial structure is observable at the diffraction-limited resolution of the 2.4 m HST primary despite the effects of spherical aberration. The central distribution of starlight appears consistent with a γ ~ -1.0 power law for r < 600 pc, plu…
The Onset of Chromospheric Activity among the A and F Stars
Simon, Theodore; Landsman, Wayne
Results are reported from a search for an upper boundary for the onset of main-sequence star activity based on a quest for high-temperature UV line emission in a large collection of IUE spectra. It is shown that strong chromospheric emission is common among early F dwarf and subgiant stars. At its brightest, the emission is equal to that of the mo…
Shot Model Parameters for Cygnus X-1 through Phase Portrait Fitting
Swank, J. H.; Szymkowiak, A. E.; Lochner, James C.
Shot models for systems having about 1/f power density spectrum are developed by utilizing a distribution of shot durations. Parameters of the distribution are determined by fitting the power spectrum either with analytic forms for the spectrum of a shot model with a given shot profile, or with the spectrum derived from numerical realizations of t…