Search Publications
Lensing galaxies: light or dark?
Fassnacht, C. D.; Jackson, N.; Wilkinson, P. N. +4 more
In a recent paper, Hawkins (1997) argues on the basis of statistical studies of double-image gravitational lenses and lens candidates that a large population of dark lenses exists and that these outnumber galaxies with more normal mass-to-light ratios by a factor of 3:1. If correct, this is a very important result for many areas of astronomy inclu…
Spectral analysis of the extreme helium star LSS3184
Heber, U.; Drilling, J. S.; Jeffery, C. S.
LSS3184 is a hydrogen-deficient, early B-type giant, recently found to pulsate with a period of 2.5 hours. Its photospheric parameters have been derived from optical high-resolution spectra by the method of fine analysis. The principal results are T_eff=23300 K, log g=3.35, {n_H}/{n_He}simle0.00015, {n_C}/{n_He}=0.003, {n_N}/{n_He}=0.0005, and {n_…
HST - GHRS observations of CO and CI fill in the beta -Pictoris circumstellar disk
Feldman, P. D.; Ferlet, R.; Jolly, A. +7 more
GHRS-EchA and G160M spectra of beta -Pictoris have been obtained in the 1400-1600 Angstroms range. A detailed analysis of the CO A-X (0-0, 1-0, 2-0) bands and of the CI lambda 1561 Angstroms multiplet is presented. A column density of the order of 2 10(15) cm(-2) is found for both species. For CO, the rotational temperature is found close to 20 K …
Abundances of UV bright stars in globular clusters. I. ROA 5701 in omega Centauri and Barnard 29 in M 13
Heber, U.; Moehler, S.; Lemke, M. +1 more
Two UV brights stars in globular clusters, ROA 5701 (omega Cen) and Barnard 29 (M 13) are analysed from high-resolution UV and optical spectra. The main aim is the measurement of iron abundances from UV spectra obtained with the HST-GHRS. In addition atmospheric parameters and abundances for He, C, N, O, and Si are derived from optical spectra (ES…
The spectral variability of the cool hypergiant rho Cassiopeiae
Lobel, A.; Parker, J. Wm.; de Jager, C. +3 more
We checked the change of the effective temperature with the atmospherical pulsation of rho Cas from combined analyses of optical spectra of 1993-95 and IUE spectra of 1979-81. We find an upper range for bigtriangleup T_eff =~ 750 K over a period of 16-17 months. We present a thorough study of the related absorption line profile changes from which …
HS0507+0434: a double DA degenerate with a ZZCeti component
Reimers, D.; Dreizler, S.; Heber, U. +6 more
HS0507+0434 and HS2240+1234 are two new common proper motion pairs of DA white dwarfs, discovered by the Hamburg Quasar Survey. Our model atmosphere analysis shows that HS0507+0434A has an effective temperature of 20000K and is remarkably young (tau_cool < 1Gyr) compared to the average cooling time of all known wide double degenerates (~ 3Gyr).…
Infrared lasers in the circumstellar disk of MWC 349
Quirrenbach, A.; Martin-Pintado, J.; Thum, C. +1 more
Observations of hydrogen recombination lines were made with the Infrared Space Observatory (ISO) towards the star MWC349, where the alpha -transitions at short millimeter and submillimeter wavelengths have been found to be masers. All alpha -line s in the ISO wavelength range from 2.4 to 190mu m (quantum numbers n=4 to 15) were detected. We find t…
A new determination of the local distribution of interstellar NaI
Crifo, F.; Lallement, R.; Welsh, B. Y.
We present galactic maps of the distribution of neutral sodium absorption column density using the newly determined Hipparcos satellite distances for a total of 290 stars lying within 250pc of the Sun. These maps now replace those originally presented in Welsh {et al./} (1994). The Local Bubble is now seen to be a neutral gas-free cavity (nH<…
Pulsation in lambda Bootis stars
Strassmeier, K. G.; Handler, G.; Garrido, R. +7 more
In this paper we present a further step in applying asteroseismic techniques to the group of lambda Bootis stars which can be characterized as nonmagnetic A to F-type Population I dwarfs with significant (surface) underabundances of Fe-peak elements. Since no conclusive theory explaining the origin of the observed abundance anomalies exists, an ex…
The nature of some doubtful open clusters as revealed by HIPPARCOS
Baumgardt, H.
We discuss the nature of some galactic open clusters by using proper motions and parallaxes from the Hipparcos and ACT catalogues. We show that the clusters Collinder 399, Upgren 1, NGC 1252 and Melotte 227 do not exist. Collinder 132 is found to be mainly composed out of members of an OB association, but there may be a star cluster present in thi…