Search Publications
Physics and chemistry of ions in the pile-up region of comet P/Halley.
Altwegg, K.; Balsiger, H.; Geiss, J. +1 more
Measurements by the mass spectrometers onboard Giotto during the flyby at comet P/Halley showed a steep increase in the ion density outside the diamagnetic cavity at a distance of about 8000km from the nucleus (Balsiger et al. 1986a; Krankowsky et al. 1986). The maximum ion density was observed at a distance of 12000km from the nucleus rather than…
Hydra A: star formation and dust production in a cooling flow.
Norgaard-Nielsen, H. U.; Jorgensen, H. E.; Hansen, L.
Optical images and spectroscopy are presented for the radio galaxy Hydra A which contains a substantial flow of cooling X-ray gas. A young stellar population is observed as an excess light around the center showing blue colour and Balmer lines in absorption. The same area also exhibits strong optical emission lines. Our IUE spectra show Lyα and an…
A snapshot of the continuous emission of the active galactic nucleus in NGC 3783 from gamma-ray to radio wavelengths.
Altieri, B.; Glass, I. S.; Malkan, M. A. +21 more
With the aim of better understanding the physical processes that produce the continuous emission in active galactic nuclei (AGNs), a snapshot of the overall continuous energy distribution of NGC 3783, from γ-ray to radio wavelengths, has been obtained within the framework of the World Astronomy Days. The data collected in this campaign are from GR…
The ultraviolet absorption spectrum of the z=2.72 QSO HS 1700+6416. I. Results on heavy-element absorption systems.
Reimers, D.; Vogel, S.
We present the analysis of ultraviolet and optical spectra of the bright, high-redshift quasar HS 1700+6416. Ultraviolet observations in the range from 1150 to 3280A were obtained with the Faint Object Spectrograph (FOS) onboard the Hubble Space Telescope (HST) at a resolution of R=1300. The identification of the numerous absorption lines provides…
Infrared flux excesses from hot subdwarfs.
Ulla, A.; Thejll, P.; MacDonald, J.
Observations of 27 hot subdwarf stars and white dwarfs have been performed with an IR photometer in a search for excess fluxes in the JHK bands. 22 of the objects are observed for the first time in the infrared. In 11 of the stars a significant excess flux was found, 2 of which are new discoveries: GD 274 and GD 299. We confirm the suspicion of Mo…
Estimating the external accuracy of HIPPARCOS parallaxes by deconvolution.
Lindegren, L.
The external standard errors of a statistically homogeneous set of trigonometric parallaxes may be estimated from the distribution of small and negative parallax values. The paper describes a method using the Richardson-Lucy deconvolution algorithm combined with a fitting procedure to derive simultaneously an estimate of the distribution of true p…
Direct detection of a cometary nucleus with the Hubble Space Telescope.
Lamy, P. L.; Toth, I.
We report the unambiguous detection with the Planetary Camera of the Hubble Space Telescope of the nucleus of comet P/Faye 1991XXI during its last perihelion passage when it was at 0.6AU from the Earth. The high resolution of the HST allowed to discriminate the nucleus against the bright coma. The reduced V magnitude of the nucleus ranges between …
Spectral analysis of the hot DO white dwarf PG1034+001.
Werner, K.; Dreizler, S.; Wolff, B.
We present a non-LTE model atmosphere analysis of the hot DO white dwarf PG1034+001. It is based on archival HST GHRS spectra, on new optical medium resolution spectra and pointed ROSAT PSPC observations. The effective temperature is higher than previously thought (T_eff_=100000K, Logg=7.5). We determined abundances of carbon, nitrogen, and oxygen…
The β Pictoris circumstellar disk. XVII. Physical and chemical parameters of the disk.
Deleuil, M.; Ferlet, R.; Vidal-Madjar, A. +3 more
New high resolution spectroscopic observations in the visible as well as archival HST UV data are used to investigate some physical and chemical properties of the disk around β Pictoris . A number of circumstellar lines are detected for the first time: Fe I , as well as weak lines of Fe II , Mn II and Zn II . Reliable estimates of the total gaseou…
New global solution of Earth orientation parameters from optical astrometry in 1900-1990.
Pesek, I.; Vondrak, J.; Ron, C. +1 more
Astrometrically observed variations of latitude and Universal time with thirty instruments of different types, located at 19 observatories all over the world, are used to derive polar motion, UT1-TAI (since 1956) and celestial pole offset at 5-day intervals. The values based on the observations of individual stars are used, the model of least-squa…