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The Discovery of an X-Ray Burst and a Study of Aperiodic Variability from SMC X-1
Stella, L.; White, N. E.; Angelini, L.
The aperiodic X-ray variability of the 0.7 s X-ray pulsar SMC X-1 is investigated using five EXOSAT observations made in 1984 October and November. During the first observation an X-ray burst was observed, where the source count rate increased by a factor of ~ 3 in less than ~ 0.7 s, and then erratically decayed to the preburst level over ~ 80 s. …
The Ionization Structure of Planetary Nebulae. X. NGC 2392
Barker, Timothy
Spectrophotometric observations of emission-line intensities over the spectral range 1400 to 7200 A were made in six positions in the planetary nebula NGC 2392. Standard equations used to correct for the existence of elements in other than the optically observable ionization stages give consistent results for the different positions that are in ex…
On the X-Ray--emitting Boundary Layer of the Dwarf Nova VW Hydri
Mauche, Christopher W.; Polidan, Ronald S.; Wade, Richard A. +2 more
The temperature and luminosity of the boundary layer of VW Hyi are constrained to kT(BL) of about 10.5 eV, and L(BL) of about 6 x 10 to the 32nd (d/65 pc)squared ergs/sec. This is based on Voyager far- and extreme-ultraviolet spectrophotometry and a measurement of the column density of neutral hydrogen, combined with Exosat LE filter observations.…
The X-Ray Properties of GX 301-2 (4U 1223-62)
Haberl, F.
The X-ray luminosity of the X-ray binary pulsar GX 301 - 2 exhibits a strong maximum near periastron passage of the neutron star, or phase 0, but with the peak 0.05 in phase before. During the interval between phase 0.9 and 0.25, during periods when the absorption was high, the X-ray spectra indicate a strong low-energy excess that may be modeled …
First Results from the Faint Object Camera: High-Resolution Observations of the Central Object R136 in the 30 Doradus Nebula
Boksenberg, A.; Barbieri, C.; Weigelt, G. +16 more
R 136 is the luminous central object of the giant H II region 30 Doradus in the Large Magellanic Cloud. We report on the first high- resolution observations of RI 36 with the Faint Object Camera on board the Hubble Space Telescope. The physical nature of the brightest component R136a has been a matter of some controversy over the last few years. T…
Absolute Far-Ultraviolet Spectrophotometry of Hot Subluminous Stars from Voyager
Carone, T. E.; Holberg, J. B.; Polidan, R. S. +1 more
Observations, obtained with the Voyager ultraviolet spectrometers, are presented of absolute fluxes for two well-known hot subluminous stars: BD + 28 deg 4211, an sdO, and G191 - B2B, a hot DA white dwarf. Complete absolute energy distributions for these two stars, from the Lyman limit at 912 A to 1 micron, are given. For BD + 28 deg 4211, a singl…
Rapid Ultraviolet Variability in the BL Lacertae Object PKS 2155-304
Miller, H. R.; Warwick, R. S.; George, I. M. +6 more
This Letter reports the first clear evidence of a rapid change in the ultraviolet flux of a BL Lac object. Sophisticated analysis of 57 closely spaced IUE spectra yielded clear evidence of a ~12% drop in the ultra-violet flux of PKS 2155 - 304 over a 2 day period in 1989 October and a strong indication of a similar drop in a 5 hr period some three…
First Results from the Faint Object Camera: Images of the Gravitational Lens System G2237+0305
Barbieri, C.; Weigelt, G.; Nota, A. +16 more
Images of the gravitational lens system G2237+0305 have been obtained with the Faint Object Camera on board the Hubble Space Telescope. A preliminary analysis of these images is reported here and includes measurements of the relative positions and magnitudes of the lensed images of the QSO, and of the lensing galaxy. No evidence is found for a fif…
Criteria for the Spectral Classification of B Stars in the Ultraviolet
Sonneborn, George; Rountree, Janet
A set of criteria for the classification of G stars from UV spectra alone, using standards drawn form the optical region, is developed. About 100 stars having normal MK spectral types in the range B0-B8, III-V, have been classified. The UV spectral types are found to be very consistent with the optical MK types, implying that it is possible to do …
First Results from the Goddard High-Resolution Spectrograph: Spectroscopic Determination of Stellar Parameters of Melnick 42, an O3f Star in the Large Magellanic Cloud
Butler, K.; Kudritzki, R. P.; Puls, J. +8 more
GHRS and optical (ESO 3.6 m) observations of the O3f star Melnick 42 in the 30 Doradus complex are reported. A first analysis reveals that with a luminosity of 2.3 x 10^6^ L_sun_ and a present mass of 100 M_sun_, Melnick 42 is one of the most luminous and massive stars known. An estimate of abundances indicates that iron and oxygen are very likely…