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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…
The COS-B X-ray observations of X-ray binaries
van der Klis, M.
The observational information on X-ray binaries that was collected with the 80 cm2 auxiliary X-ray detector onboard the COS-B gamma-ray satellite is reviewed. The results illustrate that in the study of X-ray binaries observations of long duration are extremely effective, even when using a small instrument.
Ultraviolet Colors of Old LMC Clusters
Cowley, A. P.; Hartwick, F. D. A.
New ultraviolet spectra for five red LMC globular clusters have been obtained with IUE. These have been supplemented with archival spectra for eleven old LMC clusters. These data strengthen and extend the UV-color vs. age relation for clusters older than 10^9 years, but do not offer much precision in age determination, presumably because the ultra…
Determination of the optical or physical nature of wide visual binaries by means of two-dimensional conditional probabilities
Brosche, P.; Denis-Karafistan, A.; Denis, C.
A sample consisting of 888 wide visual double stars with known relative proper motions has been processed for the HIPPARCOS input catalog. Brosche et al. (1992) applied two separate criteria on this list to discriminate statistically between physical and optical pairs. The first of these criteria uses the number density contrast, the second the ra…