Search Publications
HIPPARCOS distance calibrations for 9 open clusters
van Leeuwen, Floor
Parallaxes have been determined for 9 nearby open clusters in order to derive a composite, age resolved, HR diagram. An age-luminosity relation was found to exist for main-sequence stars. A suggested 1 mas error in the Hipparcos parallax for the Pleiades, to explain the difference with the ground-based photometric distance estimate, seems unlikely…
2.4-197 mu m spectroscopy of OH/IR stars: the IR characteristics of circumstellar dust in O-rich environments
Waters, L. B. F. M.; Omont, A.; Barlow, M. J. +4 more
Infrared spectra of a number of evolved O-rich stars have been obtained with the Short- and Long- Wavelength spectrometers on board the Infrared Space Observatory. The very broad wavelength coverage (2.4-197 mu m) obtained by combining observations made with the two spectrometers includes practically all of the flux emitted by the sources, and all…
An ultra-deep ISOCAM observation through a cluster-lens
Altieri, B.; Aussel, H.; Elbaz, D. +10 more
We present results of ultra-deep ISOCAM observations through a cluster-lens at 7mu m and 15mu m with the Infrared Space Observatory (ISO) satellite. These observations reveal a large number of luminous Mid-Infrared (MIR) sources. Cross-identification in the optical and Near-Infrared (NIR) wavebands shows that about half of the 7 mu m sources are c…
The ISO spectrum of the young star HD 142527
Waters, L. B. F. M.; de Koter, A.; Waelkens, C. +2 more
We present a detailed analysis of SWS (2.35-45 mu m) and LWS (43-200 mu m) spectra obtained with the Infrared Space Observatory (ISO) (Kessler et al. 1996) of the dusty circumstellar disk surrounding the isolated young Fe star HD 142527. Two dust populations can be clearly discriminated: a warm component which is dominated by very strong silicate …
Laboratory studies of thermally processed H_2O-CH_3OH-CO_2 ice mixtures and their astrophysical implications
van Dishoeck, E. F.; Whittet, D. C. B.; Schutte, W. A. +7 more
Data of the Infrared Space Observatory ISO have strongly influenced the current view of interstellar ice chemistry. ISO and ground-based results have confirmed that the most abundant ice species in warm regions close to massive protostars are H_2O, CO_2, and CH_3OH. Ice segregation in those environments reflects the extensive thermal processing of…
Barium abundances in cool dwarf stars as a constraint to s- and r-process nucleosynthesis
Bikmaev, I.; Mashonkina, L.; Gehren, T.
We revise barium abundances in 11 cool stars with metallicities ranging from -2.65 to 0.05. The results are based on differential NLTE model atmosphere analyses of spectra that have a typical S/N of 200 and a resolution of 40000 or 60000. To minimize systematic errors of theoretical modeling and to be sure that elemental surface abundances are not…
HST/NICMOS2 observations of the HD 141569 A circumstellar disk
Ménard, F.; Mouillet, D.; Augereau, J. C. +1 more
We report the first resolved scattered light images of the circumstellar dust disk around the old Pre-Main Sequence star da. The disk seen in HST/NICMOS2 images shapes a bright annulus inclined at 37.5degr +/- 4.5degr from edge-on. This ring peaks at 325+/-10 AU from the star with a characteristic width of ~ 150 AU. At 1.6 mu m, the dust grains sc…
Long- and short-term variability in O-star winds. II. Quantitative analysis of DAC behaviour
Kaper, L.; Henrichs, H. F.; Nichols, J. S. +1 more
A quantitative analysis of time series of ultraviolet spectra from a sample of 10 bright O-type stars (cf. Kaper et al. \cite{KH96}, Paper I) is presented. Migrating discrete absorption components (DACs), responsible for the observed variability in the UV resonance doublets, are modeled. To isolate the DACs from the underlying P Cygni lines, a met…
High-precision VLBI astrometry of radio-emitting stars
Lestrade, J. -F.; Preston, R. A.; Jones, D. L. +5 more
Multiple-epoch phase-referenced VLBI observations of 11 radio-emitting stars have been conducted as part of an astrometric program to link the Hipparcos optical reference frame to the radio extragalactic reference frame. We present the VLBI positions, proper motions and trigonometric parallaxes from this program in the ICRF (International Celestia…
SUMER observations of Doppler shift in the quiet Sun and in an active region
Doyle, J. G.; Teriaca, L.; Banerjee, D.
The UV spectral lines formed at transition region temperatures in the solar atmosphere, show a prevailing redshifted emission. Using the Solar Ultraviolet Measurements of Emitted Radiation spectrometer flown on the Solar and Heliospheric Observatory spacecraft, we measure the amount of line shift as a function of the temperature for several spectr…