Search Publications
New insights from a statistical analysis of IUE spectra of dwarf novae and nova-like stars. I. Inclination effects in lines and continua.
La Dous, Constanze
IUE observations of dwarf novae at maximum at quiescence and novalike objects at the high brightness state are analyzed for effects of the inclination angle on the emitted continuum and line radiation. A clear pattern in the continuum flux distribution is exhibited only by dwarf novae at maximum where some 80 percent of the non-double-eclipsing sy…
Structure, luminosity, and dynamics of the Venus thermosphere
Bougher, S. W.; Fox, J. L.
We review here observations and models related to the chemical and thermal structures, airglow and auroral emissions and dynamics of the Venus thermosphere, and compare empirical models of the neutral densities based in large part on in situ measurements obtained by the Pioneer Venus spacecraft. Observations of the intensities of emissions are imp…
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…
Optical and X-ray observations of AO PISCIUM and the origin of the spin pulse in intermediate polars.
Cropper, Mark; Hellier, Coel; Mason, Keith O.
Results are presented of three nights of time-resolved spectroscopic observations and of four Exosat X-ray observations of the AO Psc polar binary. It is found that the AO Psc has a magnetic field much weaker than that of the AM Her star and that it possesses an accretion disc extending inward to about 8 white-dwarf radii and outward to fill the R…
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…
Spectral energy distribution of compact planetary nebulae.
Kwok, S.; Zhang, C. Y.
The spectral energy distributions between 0.1 and 100 microns of 66 compact planetary nebulae are presented. The observed energy distributions are fitted with a model consisting of the stellar, nebular, and dust components. It is found that on the average, 38 +/-21, 25 +/-16, and 37 +/-14 percent of the emergent fluxes in the above wavelength rang…
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 …
On the Nature of the Symbiotic Binary CI Cygni
Stencel, R. E.; Kenyon, S. J.; Garcia, M. R. +4 more
An analysis of ultraviolet and optical spectroscopy is presented for the symbiotic binary CI Cyg. This system contains an M5 II asymptotic branch giant Mg of about 1.5 solar mass, transfering material at a few times 0.00001 solar mass/yr into a large accretion disk surrounding a main-sequence star with Mh of about 0.5 solar mass. A boundary layer …
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 …