Search Publications
Accurate optical-to-radio registration of Seyfert galaxies with HST images. Absolute astrometry of HST images.
Macchetto, F. D.; Capetti, A.; Lattanzi, M. G.
We propose a method to obtain accurate absolute astrometry of Hubble Space Telescope images. Ground based images are used to link HST images to standard astrometric stars defining the optical frame of reference. The method has been used to register optical images of the Seyfert 2 galaxy NGC 5929 to the corresponding radio maps, allowing the explor…
The discovery of a new massive O-type close binary: tau CMa (HD 57061), based on HIPPARCOS and Walraven photometry
van Leeuwen, F.; van Genderen, A. M.
We present an interpretation of Hipparcos Hp and Walraven VBLUW photometry of the brightest star in the open cluster NGC 2362 (although not necessarily associated with this cluster), HD 57061 (30tau CMa, HR 2782, HIP 35415). In this multiple system the central component consist of a visual double star, two O-type stars separated by 0\farcs 151, wh…
Zero-metallicity very low mass stars as halo dark matter.
Kerins, E. J.
Hubble Space Telescope (HST) limits on the amount of halo dark matter (DM) in the form of very low-mass (VLM) stars close to the hydrogen-burning limit have been interpreted as excluding such stars as viable candidates. However, these limits assume that the stars are smoothly distributed and have at least the metallicity of Population II stars, wh…
HIPPARCOS parallaxes and the nature of δ Scuti stars.
Hog, E.; Petersen, J. O.
Hipparcos parallaxes give new tests of the nature of δ Sct variables. For many individual stars accurate distances are now available, i.e. directly determined luminosities and radii can be used to test theoretical models. Of particular interest are the at present very unclear relations between high-amplitude δ Sct stars and the much more abundant …
Correlated X-ray spectral and fast-timing behaviour of 4U 1636-53.
van der Klis, M.; Prins, S.
We present a study of the persistent X-ray emission from the low-mass X-ray binary 4U 1636-53 based on the entire archival EXOSAT ME data set. We performed a homogeneous analysis of all five EXOSAT observations in terms of the correlated rapid X-ray variability and X-ray spectral properties by means of power spectra, and colour-colour and hardness…
HIPPARCOS distances of X-ray selected stars: implications on their nature as stellar population.
Micela, G.; Favata, F.; Sciortino, S.
We present the parallaxes, measured by Hipparcos, for a sample of X-ray selected stars. The stars belong to the stellar sample of the Einstein Extended Medium Sensitivity Survey. They are all at galactic latitude |b|>20deg, and are generally far away from known star forming regions. Several of these stars show lithium abundance and activity lev…
Calibrating horizontal-branch stars with Hipparcos.
de Boer, K. S.; Tucholke, H. -J.; Schmidt, J. H. K.
Parallaxes from the Hipparcos satellite allow for the first time to calibrate parameters of horizontal-branch (HB) like stars based on geometric distances. The authors present absolute magnitudes and luminosities for 8 such stars. Using Teff and log g values available from the literature, they also can calculate the mass of the HB stars…
Abundances of the ^3^He star 3 CEN A (B5 IIIp) from ultraviolet IUE spectra.
Hack, M.; Parthasarathy, M.; Castelli, F.
High resolution (0.010-0.025nm) IUE ultraviolet spectra of the peculiar ^3^He star 3 Cen A were analyzed in the whole 120-320nm region. Abundances were derived from the comparison of the observed and computed spectra. For computing spectra a Kurucz ATLAS9 model with parameters T_eff_=17500K, logg=3.8, and microturbulent velocity ξ=0km/s was adopte…
On the history of star formation in the bar of the Large Magellanic Cloud.
Gustafsson, B.; Ardeberg, A.; Linde, P. +1 more
With the HST PC and uvby photometry, we investigate evolutionary signatures in a field in the centre of the LMC Bar. Field stars close to the turn off point in the HR diagram are used for a study of ages and evolution of the stellar populations dominating the Bar as well as for determination of the abundance of heavy elements. Including fainter st…
Oxygen-rich Mira variables: near-infrared luminosity calibrations. Populations and period-luminosity relations.
Luri, X.; Barthes, D.; Mattei, J. A. +2 more
HIPPARCOS astrometric and kinematical data of oxygen-rich Mira variables are used to calibrate absolute near-infrared magnitudes and kinematic parameters. Two sets of near-infrared magnitudes compiled from different authors are used: broad-band K and narrow-band photometric measurements at 1.04µm (104 filter). Three distinct classes of stars…