Search Publications
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…
Hubble Space Telescope Observations of Circumnuclear Star-Forming Rings in NGC 1097 and NGC 6951
Filippenko, Alexei V.; Ho, Luis C.; Barth, Aaron J. +1 more
We have obtained new and archival Hubble Space Telescope V-band images of kiloparsec-sized circumnuclear star-forming rings in the barred spiral galaxies NGC 1097 and NGC 6951, both of which contain active nuclei. The images resolve the rings into two-armed spirals composed of bright knots located on the outer edges of prominent dust lanes. The tw…
Measuring the Hubble Constant with the Hubble Space Telescope
Freedman, Wendy L.; Mould, Jeremy R.; Kennicutt, Robert C., Jr.
The spectacular success of the Hubble Space Telescope (HST) repair mission now makes it possible to realize one of the astrophysical goals for which the HST was designed. Despite recent progress in ground-based measurements of the distance scale, the value of the Hubble constant remains uncertain at the +/- 20%-30% level. The incompatibility of hi…
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…
RE J0317-853: the hottest known highly magnetic DA white dwarf
Jordan, S.; Barstow, M. A.; O'Donoghue, D. +3 more
We report the discovery of a new highly magnetic DA white dwarf, RE J0317-853, through its detection as an EUV source by the ROSAT Wide Field Camera. A combination of far-UV and optical spectra indicates that the star has an effective temperature ~=50000K, making it the hottest known white dwarf with a measurable magnetic field. Furthermore, the m…
The Dense Galactic Starburst NGC 3603. I. HST/FOS Spectroscopy of Individual Stars in the Core and the source of Ionization and Kinetic Energy
Walborn, Nolan R.; Drissen, Laurent; Moffat, Anthony F. J. +1 more
We present spectrograms of 14 individual luminous stars in RD 97950, the core (r≤4"=0.12 pc) of the dense galactic starburst NGC 3603, obtained with the Faint Object Spectrograph aboard the refurbished Hubble Space Telescope. In a volume of less than a cubic light year, three luminous hydrogen-rich WNL+abs stars cohabit with six O3 stars [includin…
White Dwarf Standard Stars: G191-B2B, GD 71, GD 153, HZ 43
Colina, Luis; Bohlin, Ralph C.; Finley, David S.
Three additional white dwarfs, GD 71, GD 153, and HZ 43, covering a wide range in effective temperature, have been observed with HST faint object spectrograph (FOS) to check the G191 -B2B white dwarf based absolute calibration of HST instruments. The FOS spectrophotometry of the three additional white dwarfs agree with model spectra to ∼2%. The FO…
Detection of Compact Ultraviolet Nuclear Emission in LINER Galaxies
Filippenko, Alexei V.; Ho, Luis C.; Maoz, Dan +4 more
Low-ionization nuclear emission-line regions (LINERs), which exist in a large fraction of galaxies, may be the least luminous manifestation of quasar activity. As such, they may make possible the study of the AGN phenomenon in the nearest galaxies. The nature of LINERs has, however, remained controversial because an AGN-like nonstellar continuum s…
Radio to X-ray energy distribution of BL Lacertae objects.
Giommi, P.; Micol, A.; Ansari, S. G.
We present multifrequency spectra of a large number of radio and X-ray selected BL Lacertae objects constructed using non-simultaneous archival data. The data were obtained using the European Space Information System (ESIS) and are from several radio and optical catalogues, the IRAS Faint Source Catalogue, the Einstein and the EXOSAT databases. Th…