Search Publications
The D/H and ^18^O/^16^O ratios in water from comet P/Halley.
Eberhardt, P.; Krankowsky, D.; Hodges, R. R. +1 more
From a detailed evaluation of the ion currents measured by the Neutral Mass Spectrometer (NMS) on the Giotto spaceprobe in the 17.5amu/e to 21.5amu/e mass range inside the contact surface of P/Halley we derive the cometary ion densities for masses 18amu/e to 21amu/e. From these we calculate the deuterium and ^18^O abundances in the H_3_O^+^ ion to…
Fundamental parameters of Wolf-Rayet stars. III. The evolutionary status of WNL stars.
Schmutz, W.; Hillier, D. J.; Crowther, P. A. +1 more
New high S/N optical observations of 9 Galactic WNL (WN7-8) stars are presented. The spectra have been analysed using tailored non-LTE model atmospheres by Crowther et al. (1994c). Here we use the derived stellar parameters and abundances for a thorough investigation of the evolutionary status and mass-loss properties of WNL stars. We have identif…
Local Cloud structure from HST-GHRS
Ferlet, R.; Vidal-Madjar, A.; Lallement, R. +2 more
Echelle spectra at high resolution (λ/{DELTA}λ= 90,000) of the nearby stars α Aql (Altaie r), α Lyr (Vega), α Cen and δ Cas, have been obtained with the Goddard High-Resolution Spectrograph (GHRS) on board the Hubble Space Telescope (HST), during the cycles 1 and 3. In all but one spectra, interstellar Fe II and Mg II absorption lines are detected…
Excess Hα emission in chromospherically active binaries.
Montes, D.; Fernandez-Figueroa, M. J.; de Castro, E. +1 more
We study the behaviour of the excess Hα emission in a sample of 51 chromospherically active binary systems (RS CVn and BY Dra classes), of different activity levels. This sample include the 27 stars analysed by Fernandez-Figueroa et al. (1994) and the new observations of 24 systems described by Montes et al. (1994b). By using the spectral subtract…
Fundamental parameters of Wolf-Rayet stars. I. Ofpe/WN9 stars.
Hillier, D. J.; Crowther, P. A.; Smith, L. J.
A detailed study has been carried out for 4 LMC Ofpe/WN9 (`slash') stars, and the sole Galactic WN9 star WR108 (HDE 313846), using new high S/N spectroscopy and archive UV and near-IR spectroscopy. Our observations reveal that photospheric Of features such as HeIIλ4542 are absent from the optical spectra of our sampled stars. All observed optical …
The white dwarf in AM Herculis.
Gänsicke, B. T.; Beuermann, K.; de Martino, D.
We present orbital phase-resolved UV spectroscopy of AM Herculis in its high and low state obtained with the IUE satellite. We derive the effective temperatures and sizes of the accretion-heated polecap in both states. We also estimate the effective temperature and radius of the white dwarf. The spot is hotter in the high state, but always covers …
Spectroscopy of HD77581 and the mass of VELA X-1.
van Kerkwijk, M. H.; van Paradijs, J.; Zuiderwijk, E. J. +3 more
We present new high-resolution, high signal-to-noise optical spectra of HD77581, the optical counterpart of the X-ray source Vela X-1, and determine radial velocities from these spectra, as well as from high-resolution IUE spectra and from digitized photographic spectra. The measured velocities show strong deviations from a pure Keplerian radial-v…
X-ray outburst of the peculiar Seyfert galaxy IC 3599^*^.
Beuermann, K.; de Martino, D.; Bade, N. +4 more
We report optical, soft X-ray, and UV observations of the peculiar Seyfert galaxy IC 3599 using data obtained with ROSAT and IUE. Most remarkably, we discovered a rapid decrease of the X-ray flux by a factor of about 100 within one year and a more gradual decrease thereafter. The X-ray spectrum of IC3599 was soft at flux maximum and became even so…
Physical and chemical structure of the IC 63 nebula. II. Chemical models.
van Dishoeck, E. F.; Spaans, M.; Black, J. H. +2 more
Chemical models are presented for the photon dominated region (PDR) IC 63, a small isolated molecular cloud located close to the B0.5 IVpe star γ Cas for which we have presented observations of various molecular species in an earlier paper, and for which observations of ionized and neutral atomic carbon, as well as additional CO observations, are …
Discovery of an ultrasoft transient ROSAT AGN: WPVS 007.
de Martino, D.; Grupe, D.; Mannheim, K. +3 more
We have identified the ROSAT source RX J0039.2-5117 with the previously almost unknown 'narrow line' Seyfert 1 galaxy WPVS007 (z = 0.028). The X-ray source displays quite unusual properties for an AGN. It was bright and ultrasoft in the ROSAT All-Sky Survey (RASS) and found at a level lower by a factor of ~400 in PSPC count rate in 1993. The impli…