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Hubble Space Telescope observations of M31 associations
Magnier, Eugene A.; Lewin, Walter H. G.; van Paradijs, Jan +2 more
We have used HST WFPC-2 observations of five fields along the eastern spiral arm regions of M31 to study the stellar populations. We use fits to stellar models to determine extinction individually for the stars in OB associations in these fields. The range of extinction within each cluster is the major constraint on our ability to determine accura…
Mass determination of astrometric binaries with Hipparcos. I. Theory and simulation
Mignard, F.; Martin, C.; Froeschle, M.
The analysis of the observations of double stars made by the ESA satellite Hipparcos has involved a very specific processing to derive the relevant astrometric parameters. This required to distinguish between several categories of double stars according to the separation and orbital motion. We show that for close pairs with orbital period less tha…
Far-Ultraviolet Absorption Lines in the Remnant of SN 1006
Sarazin, Craig L.; Crenshaw, D. Michael; Fesen, Robert A. +3 more
We have obtained a far-ultraviolet spectrum (1150-1600 Å) of a hot subdwarf star behind the remnant of supernova 1006 with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope. The high-quality spectrum is used to test previous identifications of the strong absorption features discovered with the International Ultraviolet Explorer. Th…
The Mass of the Classical Cepheid S Muscae
Carpenter, Kenneth; Robinson, Richard; Beck-Winchatz, Bernhard +2 more
A good determination of the mass-luminosity relation for evolved stars on blue loops can determine the degree of excess mixing in the interiors of their main-sequence companions. In this study we determine the dynamical mass of the Cepheid binary S Muscae. This can be combined with its known luminosity and be fitted on evolutionary tracks to deter…
Extreme Ultraviolet Photometry and Spectroscopy of BL Hydri
Vennes, Stéphane; Szkody, Paula; Howell, Steve B. +2 more
We have analyzed Extreme Ultraviolet Explorer (EUVE) observations of BL Hyi obtained during a high-accretion state in 1995 October. The light curve obtained with the Deep Survey instrument reveals a broad hump covering the phases in which both poles have been known to be active in X-ray emission. In contrast to the X-ray, both poles contribute a c…
Correlation between variability time scale and X-ray spectral index in AGN.
Wilms, J.; Staubert, R.; Koenig, M.
We have analysed EXOSAT ME X-ray light curves of a sample of AGN assuming a stochastic process in these sources. The result is a significant anti-correlation between the relaxation timescale τ, derived from this stochastic model fit, and the photon index {GAMMA} of the X-ray spectrum. This establishes for the first time a relationship between vari…
On the interpretation of the extinction curves of R Coronae Borealis stars
Zubko, V. G.
The available extinction curves for some RCB stars (R CrB, RY Sgr, MV Sgr and V348 Sgr) have been analysed, making use of the method of regularization for solution of ill-posed problems. This approach allows an estimate of dust grain sizes responsible for fadings of RCB stars. A model involving graphite grains is shown to be preferable for the exp…
Timing the eclipse of HD185510
Simon, Theodore; Jeffery, C. Simon
HD185510 (=V1379 Aql) is an eclipsing double-lined RS CVn binary containing a K0 III/IV giant and a hot subluminous companion. An International Ultraviolet Explorer (IUE) ultraviolet light curve has been obtained through the eclipse of the companion with an average time resolution of one measurement every 19min. This was sufficient to resolve all …
Properties of hydromagnetic waves in the polar caps: ulysses
Forsyth, R.; Balogh, A.; Tsurutani, B. T. +3 more
Properties of the large amplitude Alfvén waves which are a dominant feature of the high latitude solar wind have been studied during the pole-to-pole passage of Ulysses. In addition, an effort has begun to identify magnetosonic waves at high latitude in spite of their expected small amplitude and the presence of the large amplitude Alfvén waves. T…
Alfvénic fluctuations in fast and slow solar winds
Orlando, S.; Peres, G.; Rosner, R. +1 more
We compute properties of Alfvénic fluctuations within a wide frequency range (i.e., 10-6s-1<~f<~10-2s-1) in both high- and low-speed magnetized radial solar winds. In particular, the radial and frequency variations of the normalized cross helicity σc, the Alfvén ratio <script>R<…