Ground-based CCD trigonometric parallax determinations with formal errors in the range 0.5<=epsilon_ π <=1.5 mas can now readily be obtained for stars as faint as R ~ 20 from only 3--4 years of observations. As a result, some 45 lower-luminosity (10.0<MV<15.7) stars with Pop.II characteristics (i.e., either marked subluminosity and/or Vtan >=180 km/sec) now have absolute magnitudes determined to +/-0.22 mag (pi /epsilon_ π=10). An additional 25 Pop.II stars have determinations good to +/-0.4 mag (pi /epsilon_ π=5). These 70 stars form a rather loose sequence in the MV versus V-I diagram, falling as much as 2.5 mag below the locus of the young disk stars. MMT spectrophotometry (lambda lambda4700 -8700 Angstroms; ~ 18 Angstroms resolution) has been obtained for 19 of the more extreme stars and qualitatively confirms their very metal-poor abundances. Detailed abundance estimates await improved model atmosphere calculations, at which point a quantitative connection can be established to the more luminous sdF-G stars. An estimate of the local Pop.II luminosity function will be presented based on a 1/Vmax analysis of the LHS stars with delta >=-20deg and mu >=0.8 arcsec/yr.
American Astronomical Society Meeting Abstracts #184
- Pub Date:
- May 1994