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A Minor Outburst during the Quiescent Period of the Symbiotic Star Ch-Cygni
Hack, Margherita; Aydin, Cemal
We have studied a few optical spectra of the symbiotic star CH Cygni obtained in the period January 1990-June 1991, which indicate that a mild increase of activity occurred between July and December 1990. This increase of activity is confirmed by the IUE observations made in the same period. In fact, in this period of time, we have observed an inc…
Detection of Rs-Canum Type Systems by Doublet 2800 MGII
Gurzadian, G. A.; Cholakian, V. G.
The problem of the detection or discovery of RS CVn-type close binary systems with the aid of the magnesium emission doublet 2800 MgII is discussed. On the example of a star, HD 102077, the possibility of such an approach is shown. The determining factor is the magnitude of the measureless parameterR(MgII), that is, the relative power of the magne…
Stellar Wind Velocities and the Radiation-Driven Winds Theory for O-Stars
Bernabeu, G.
In this paper we have carried out an analysis of the predictions of the radiatively driven stellar winds theories on 63 stars belonging to clusters or associations. The spectral types in our sample range from O3 to B0 and all classes of luminosity are considered. The study has been carried out starting from the relationship between the stellar-win…
The Ultraviolet Spectrum of the Binary System Sz-Piscium
Mathioudakis, M.; Danezis, E.; Theodossiou, E. +1 more
In this paper we study the far-UV as well as the UV spectrum of the spectroscopic binary system SZ Psc in the wavelength ranges λλ1235–1950 Å and λλ2710–3090 Å, respectively, from spectra obtained with the International Ultraviolet Explorer (IUE). The UV spectrum of SZ Psc is mainly an emission spectrum. The short wavelength region includes emissi…
Analysis of Neckel and Chini Standard Stars in the UBVRI Photometric System
Oriol, R.
This paper studies the list of 60 faint standard stars of Neckel and Chini (1980) in theUBVRI Johnson photometric system. These standards have been used due to the collaboration in the HIPPARCOS project of our department, but this work was made in parallel of this and the results were not used. We have re-reduced the standard stars using our own m…
X-ray VS He ii λ1640 Å correlation of II Peg
Esendemir, A.; Alev, H. M.
The HeII λ1640 Å emission feature on the IUE spectra of II Peg has been compared with the observed X-ray flux. The atmospheric activity level is determined by comparing the several diagnostic line intensities with the solar case.
The Far Ultraviolet Spectrum of the Be-Star Ax-Monocerotis
Danezis, E.; Laskarides, P. G.; Theodossiou, E.
In this paper we study the main features of the far UV spectrum of the binary star AX Mon, observed with the IUE satellite at phase 0.568. Ions indicating a large range of ionization stages, going fromCI,OI,NI toSIV,CIV,NV are present. The spectrum is dominated by shell absorption lines of FeII, FeIII, SiIII,CII, AlII, MgII and NiII. Two satellite…
Modern Photographic Catalogue Work - Aspects of Observing Techniques and Reduction Methods
de Vegt, Chr.
The consequent application of present optical technology for the construction of substantially improved instrumentation in photographic astrometry and the application of rigorous reduction techniques provide all means for the construction of new, global position catalogs with a precision of a few 0.01 arcsec. At the same time the limiting magnitud…
Objectives of ground-based astrometry after HIPPARCOS
Kovalevsky, J.
After a short summary of the results expected from the HIPPARCOS mission, the author gives several examples illustrating the needs that will arise afterwards in order to maintain the level of precision achieved and to extend it to many more objects. Three domains are particularly dealt with in this paper:The maintenance of the HIPPARCOS reference …
Doublet 2800 Mg II in close binary systems
Perez, M.; Gurzadian, G. A.
It is shown that the emission ultraviolet doublet 2800 MgII in radio stars, actually in close binary systems, do not have chromospheric origin, but is generated in the space between the components of the system, filled by clouds or streams of two types — emission (A) and absorption (B). It is shown also that the strongly deformed or distorted form…