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X-ray spectrum of the BL Lacertae object PKS 2155-304.
Koyama, K.; Warwick, R. S.; Makishima, K. +4 more
The BL Lacertae object PKS 2155-304 was observed with Ginga for two days in May 1987. The 2-35 keV intensity showed a significant variability, the most rapid change being a 30 percent increase in 3 hr. The X-ray spectrum was described by a single power-law model with photon spectral index ranging between 2.7 and 2.9, but the power-law slope showed…
Mechanisms of dust emission from the surface of a cometary nucleus
Spohn, T.; Thiel, K.; Krankowsky, D. +9 more
Cometary nuclei consist of mixtures of ices and non-volatile particulates in mass proportions of similar magnitudes. Dust is carried by the gas drag of the sublimating ices. Gas drag from free expansion of the gases from the nucleus dominates the acceleration of dust particles after their release from the surface. Significant gas pressure can buil…
Stellar wind velocities and luminosities of O stars.
Stalio, R.; Bernabeu, G.; Magazzu, A.
Stellar wind velocities (v-edge not greater than v-infinity) for 110 O stars are calculated. The spectral types in the sample range from O3 through B0; all luminosity classes are represented. Stars from clusters and associations (extreme Population I) as well as field stars are considered. There is a weak evidence of higher v-edge for extreme Popu…
Far-Ultraviolet Spectrophotometry of SPICA
Snow, Theodore P.; Cook, Timothy A.; Cash, Webster
A spectrum of the star Spica (Alpha Virginis) from 960 to 1270 A was recorded by a rocket-borne spectrograph March 13, 1988. The spectrum, which has 3.4 A resolution, shows a much sharper drop-off in intensity near 1050 A than similar measurements made by the Voyager UVS, but is in good agreement with the spectrum obtained by Brune et al. in a 197…
The Binary Companion of the Classical Cepheid AW Per
Evans, Nancy Remage
An analysis of IUE spectra of the companion of AW Per shows it to be an extreme BpSi/HeW star with a spectral type of B7 V to B8 V. The flux of the composite spectrum from 1200 A through V is found to be well matched by F7 Ib and B8 V standard stars with Delta M(V) = 3.1 mag. The results suggest that the mass of the Cepheid must be greater than 4.…
Rotational modulation and flares on RS Canum Venaticorum and BY Draconis stars. XII. Near-to-simultaneous high resolution UV and optical observations of II Pegasi during July 1984.
Doyle, J. G.; Byrne, P. B.; Marang, F. +4 more
Nearly simultaneous high resolution ground-based optical and IUE satellite UV spectroscopy and an optical light curve of the RS CVn star II Peg are presented. It is shown that the chromospheric and transition region radiative losses of the star in July 1984 are lower than previously recorded means. The flux in the Lyman-alpha line is estimated and…
An X-ray and optical study of the low-mass X-ray source 4U 1556-605.
Motch, C.; Beuermann, K.; Pakull, M. W. +1 more
Partly simultaneous EXOSAT and optical observations of the low-mass X-ray binary 4U 1556-605 are presented. X-ray flux variations of relatively small amplitude (about 20 percent) are accompanied by a significant hardening of the X-ray spectrum. This behavior is investigated in the framework of several currently proposed spectral models. The optica…
An Interpretation of the Line Profile Variations in the IUE Spectrum of the Wolf-Rayet Binary gamma 2 Velorum
Sahade, Jorge; Brandi, Estela; Ferrer, Osvaldo E.
An analysis of the variable profiles of the high-temperature resonance lines of Si IV in the IUE spectrum of gamma(2) Vel has made it possible to describe these profiles as a superposition of two different profiles, namely, a P Cygni profile that remains practically stationary throughout the orbital cycle and an absorption profile that moves back …
Line Identifications in the Ultraviolet Spectrum of 31 Cygni
Bauer, Wendy Hagen; Stencel, Robert E.
Line identifications are presented for the Zeta Aur-type eclipsing binary system 31 Cyg (K4 Ib + B4 V). The rich absorption spectrum observed during chromospheric eclipse has been nearly completely identified. This list will be useful in analyzing spectra of related binaries, such as 32 Cyg and VV Cep. The large number of line transitions contribu…
High-resolution Hα spectroscopy of the bright RS CVn system HR 7275.
Eker, Zeki
HR 7275 is a bright, long-period (28 day), single-lined RS CVn binary. High-resolution (0.36 A) and good signal-to-noise ratio echelle spectra do not show any clear evidence of the secondary in the system on spectral lines. Also, absence of a continuum on a low-resolution UV spectrum (IUE merged log) and the known mass function imply a main-sequen…