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Parallaxes and the Hertzsprung-Russell diagram for the preliminary HIPPARCOS solution H30
Grewing, M.; Evans, D. W.; Lindegren, L. +20 more
We outline the principles by which absolute trigonometric parallaxes have been derived from the first 30 months of data acquired by the Hipparcos astrometry satellite. Distributions of the parallaxes and formal errors of more than one hundred thousand stars are presented, indicating median standard errors of about 1.5milliarcsec (mas). Tests which…
Galactic wind and Lyman α emission in the blue compact galaxy Haro 2 = MKN 33.
Mas-Hesse, J. M.; Kunth, D.; Sargent, W. L. W. +1 more
We have observed with the Goddard High-Resolution Spectrometer on board the Hubble Space Telescope the blue compact galaxy Haro 2 in two wavelength regions around Lyman α and O I 1302A. We have detected redshifted absorptions in those lines as well as in lines of N I, Si II and Si III, in front of the hot stars ionizing the central H II region of …
ROSAT observations of γ Velorum (WC8+O9I). I. The discovery of colliding-wind X-ray emission.
Willis, A. J.; Schild, H.; Stevens, I. R.
We present an analysis of 13 X-ray (0.1-2.5keV) observations of γ Velorum obtained with the XRT+PSPC on the ROSAT satellite. The first set of 10 observations were obtained in our Guest Observer AO2 programme, with 9 at roughly 8-day intervals in the 78^d^.5 binary period, providing nearly complete phase coverage. Of these, the last two (secured at…
The interstellar void in the direction to ɛ CMa: local clouds and hot gas.
Ferlet, R.; Vidal-Madjar, A.; Lemoine, M. +2 more
We analyse HST GHRS observations of the interstellar medium in the direction to ɛ CMa, the strongest EUV source in the sky, located in a region deficient in neutral gas. The line of sight contains three main absorption components resolved in the high resolution Ech B observations. Three weak components are also detected. We derive their heliocentr…
Properties of the WO Wolf-Rayet stars.
Barlow, M. J.; Storey, P. J.; Kingsburgh, R. L.
We present optical spectrophotometry for five WO Wolf-Rayet stars, three of them in our own Galaxy and one in each of the SMC and LMC. IUE ultraviolet spectrophotometry has also been obtained for the two Magellanic Cloud WO stars, including a high resolution spectrum for one of them. Quantitative spectral typing criteria are defined for WO subtype…
Ultraviolet observations of galaxies in nearby clusters. III. Star-forming galaxies in the Coma cluster.
Laget, M.; Donas, J.; Milliard, B.
In a field of 1deg radius centered in the Coma cluster of galaxies, UV (λ=2000A) observations with a 40-cm balloon-borne imaging telescope (FOCA) have provided a list of 442 UV sources brighter than m_UV_=18, which are identified in the Godwin et al. (1983) catalogue. 254 are identified as galaxies, 178 as star-like objects and 10 as galaxy-star p…
Zero-point and external errors of HIPPARCOS parallaxes
Arenou, F.; Lindegren, L.; Turon, C. +4 more
A good knowledge of both accuracy and precision of the Hipparcos parallaxes is one of the keys for their future scientific use. For this purpose, the Hipparcos preliminary parallaxes, as obtained after the processing of the first 30 months of Hipparcos data, are compared to various ground-based parallax estimates, using astrometric, photometric an…
Linking the HIPPARCOS Catalogue to the extragalactic reference system.
Lindegren, L.; Kovalevsky, J.
We present an overview of the methods currently planned to link the Hipparcos reference system to the conventional extragalactic reference system, as defined by VLBI observations. The link programme consists of VLBI and connected element interferometry of radio stars, separation measurements with the Hubble Space Telescope, photographic observatio…
Low mass stars in globular clusters. II. The mass function of M15.
Paresce, F.; de Marchi, G.
We have used the WFPC2 on board HST to investigate the stellar population in a field located 4.6' NW of the center of the globular cluster M15 by means of deep imaging in wide bands centered at 606 and 812nm. A total of 7770 stars are accurately classified by two-color photometry to form a color-magnitude diagram extending down to a limiting magni…
B[e] phenomenon extending to lower luminosities in the Magellanic Clouds.
Zickgraf, F. -J.; Wolf, B.; Gummersbach, C. A.
An analysis of the four recently discovered B[e] stars HenS35, S59, S93, and S137 in the Large Magellanic Cloud has been carried out using low-resolution IUE spectra, ESO 3.6-m CASPEC spectra, and ESO 0.5-m and 1-m UBV and JHK photometry, respectively. LTE model atmospheres have been fitted to the observed continuum energy distributions in order t…