HIPPARCOS and the Spectroscopic Distance to Local Halo Stars
Abstract
We are currently extending the study of "Nearby stars of the Galactic disk and halo I & II" (Fuhrmann 1998 & 2000) to a sample of metal-poor halo stars out to about 500 pc. Our ultimate aim is to derive spectroscopic ages for these stars. The basis of our analysis are spectra with R between 40,000 and 60,000 and signal-to-noise ratios (after co-addition) above 200 at Hα. These spectra were acquired using FOCES on the 2.2 m telescope at Calar Alto in 1999. Some of the brighter halo stars have significant Hipparcos parallaxes against which we can cross-check our method of gravity determination. For halo stars down to [m/H] ~-2 (to which the strong line method is applicable) the resulting gravities are practically free of systematics when compared to Hipparcos. From 150 pc outward, the spectroscopic uncertainty in distance is smaller than the astrometric one. The question of whether or not metal-poor stars require a temperature label and/or temperature-depth structure different from that of the Sun and solar-metallicity stars may be addressed in the context of non-LTE ionization equilibria of e. g. iron or calcium.
- Publication:
-
Astronomische Gesellschaft Meeting Abstracts
- Pub Date:
- 2000
- Bibcode:
- 2000AGM....16..P58K