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Radial velocities of the IUE calibration stars

Stickland, D. J.

Precise equatorial coordinates of double and multiple systems : an astronomical support to the HIPPARCOS mission.

Pannunzio, R.; Lattanzi, M. G.; Morbidelli, R. +3 more

Results are presented on determinations of precise positions (to the accuracy required for their possible inclusion in the Hipparcos Input Catalogue) of 623 double and multiple stars (126 of them newly discovered) from the measurement of 39 plates taken at the ESO and the Astronomical Observatory of Torino, obtained between 1984 and 1987. The tabl…

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…

Chemical Heterogeneity and Mineralogy of Halley's Dust

Kissel, J.; Schulze, H.

It is commonly assumed that comets are pristine bodies which still contain relatively unaltered material from the beginning of our solar system. Therefore, in March 1986 the chemical composition of Halley's dust particles was investigated by time- of-flight mass spectrometers on board the Vega 1 & 2 and Giotto spacecraft using the high relativ…

Comparison of HIPPARCOS results obtained on different dates on the same great circle

Schrijver, Hans

The results on great circles that have been scanned by Hipparcos on dates separated by several months are compared. The differences in the abscissae, after correction for known proper motions and parallaxes show a noise and a systematic effect that correspond to expected inaccuracies in proper motions and parallaxes. Instrumental terms related to …

The Orbital Parameters and the IUE Spectrum of the Single-lined Spectroscopic Binary HD 698

Sahade, Jorge; Barba, Rodolfo; Kondo, Yoji

IUE observations of the spectroscopic binary HD 698 show that its continuous spectrum corresponds to that of a B5 III-II object and that, even in the ultraviolet, the object is single-lined. The spectrum displays several sets of lines, all in absorption, where features can be distinguished that partake of the orbital motion of the B5 component, li…

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…

Reliability of the HIPPARCOS input catalogue tested by the 'first look'.

Arenou, F.; Crifo, F.; Gomez, A. +2 more

The reliability of the Input Catalogue is one of the keys for the success of the Hipparcos mission. As the Input Catalogue is a catalog made of very heterogeneous sources, many systematic reliability tests were conducted to eliminate errors on identifications, position, magnitude, etc. In March 1991, half of the Input Catalogue had already been ch…

How fast is the evolution of the diffuse ultraviolet cosmic background radiation ?

Stanek, Krzysztof Z.

Lyα absorption lines observed in Hubble Space Telescope UV spectra of 3C 273 have neutral hydrogen column densities comparable with those of z ~ 2 quasars. Assuming the standard pressure-confined model of Lyα clouds, we use this fact to determine the evolution of UV background radiation for z < 2. We find that to fit the data the UV background …

Supernova distance measurements suggest an older, larger Universe.

Schwarzschild, Bertram

Three determinations of the Hubble constant from supernova observations are reviewed and compared to existing data on the age and size of the universe. Type-Ia supernovae are used as standard candles in all of the calculations, and the observations were made with the Hubble Space Telescope Wide-field and Planetary Camera. Hubble diagrams for the t…