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Optical and UV spectroscopy of blue horizontal branch stars in the globular cluster NGC 6752.
Boksenberg, A.; Danziger, J.; Caloi, V. +4 more
Optical and far-UV spectra have been obtained for blue HB stars on both sides of the observed luminosity gap in NGC 6752. On this basis effective temperatures and absolute bolometric magnitudes are derived for six stars above the gap and four stars below it. The authors find that stars above the gap arrange themselves along a ZAHB locus. Across th…
The soft X-ray superoutburst of VW Hydri.
Heise, J.; van der Woerd, H.; Bateson, F.
The dwarf nova VW Hyi has been monitored with Exosat, during and shortly after the optical superoutburst of November 1983. VW Hyi appears to be a very soft X-ray emitter, and is marginally detected in the hard (1 to 6 keV) X-ray range. The soft X-ray emission increased by two orders of magnitude during outburst, with the dominant emission at wavel…
The accretion of supergiant wind material onto the hot companion in zeta Aurigae binaries.
Reimers, D.; Che-Bohnenstengel, A.
This paper is an attempt to interpret the behaviour of the high excitation C IV and Si IV resonance lines in the course of a period of the Zeta Aurigae binary systems. Three distinct phenomena have been observed: shock front emission, accretion wake absorption and accretion disc emission. At the C IV and Si IV emission regions the electron tempera…
The ultraviolet variability of the symbiotic star HBV 475. III. The periodicity of HBV 475.
Schmutz, W.; Vogel, M.; Nussbaumer, H.
The symbiotic star HBV 475 (= V1329 Cyg) shows periodic variations in its spectrum, both in flux and in the wavelength positions of the emission lines. New IUE observations, extending to the October 1985 flux maximum, allow an improved period and phase determination. The periodic variation of the line profiles are interpreted as being due to illum…
Mass loss from central stars of planetary nebulae : the nucleus of NGC6543.
Grewing, M.; Bianchi, L.; Cerrato, S.
Low and high resolution spectra of the nucleus of NGC 6543 were analyzed in the UV range (1150-3200 A). From the continuum energy distribution, the extinction towards this object was estimated to be E(B - V) = 0.08, and an effective temperature (80,000 K) was derived for the central star by comparison with pure-He model atmospheres for hot high gr…
Distribution of MG II in the local interstellar medium towards eight cool giants.
Molaro, P.; Beckman, J. E.; Vladilo, G.
A study of IUE spectra of eight cool G4-K0 giants shows evidence of interstellar Mg II absorption in all the stars but Delta Dra. Sharp features are detected in the emission wings of four stars, while only strong asymmetries of the emission profiles are noted in three cases. In all the cases studied, the interstellar absorption features fall very …
Semidetached Systems - Evolutionary Viewpoints and Observational Constraints
De Greve, J. P.
The present knowledge on the evolution of semidetached systems is reviewed. Characteristics of observed systems are discussed and general properties tested by the behaviour of theoretical models. New models of mass accreting companion stars are computed. The accretion phase is divided into a fast and slow phase with an accretion rate depending on …
Abundances in the planetary nebula NGC 6153.
Pottasch, S. R.; Mo, J.; Dennefeld, M.
Spectra in the visual, infrared and ultraviolet, of the planetary nebula NGC 6153 are presented. They are analysed to obtain the abundance and physical conditions in the nebula. It is found that NGC 6153 is a very unusual nebula, its abundance of many elements being higher than any other nebula.
Ultraviolet and visual variability of theta CrB during a normal B-phase following a shell phase (1980-1985).
Stalio, R.; Peters, G. J.; Doazan, V. +6 more
Based on far-UV and visual observations made between 1980 and 1985, the phenomena characterizing the end of a shell phase of Theta-CrB, and the normal B-phase following it, are described as part of a long-term study of Be stars. The strength, shape, and velocity of the C IV, Si IV, and Al III resonance lines, and the Fe III lines of low excitation…
A study of the upper atmosphere of Uranus using the IUE
Encrenaz, T.; Atreya, S. K.; Romani, P. N. +2 more
The 1750 Å band of C2H2 has been detected in an IUE spectrum of Uranus recorded in 1980. The derived C2H2 column density is 6.8±3.4×1016cm-2. Eddy diffusion coefficients of 104cm2s-1 or smaller at the homopause result in an abundance of photochemical…