A search for distant stars in the Milky Way Galaxy's halo and thick disk
The author has observed 247 faint (13.3 mag. < V < 17.9 mag.) stars with B-V {le} 1.00 in one square degree near the North Galactic Pole. Most of these stars are distant, lying in either the Galactic halo or thick disk, and allow a study of these two populations in siu, with no kinematic or metallicity bias. For all 247 stars, spectra yield {omega} velocities, and for over half the stars, Stroemgren photometry gives luminosities, distances, and metallicities. Even though it was selected with no kinematic or metallicity criteria, the sample consists predominantly of thick disk and halo stars: the velocity dispersion of the total sample is 62 km/sec. For the stars with known distances and metallicities, three populations appear: a thin disk at solar metallicities, a thick disk ranging in metallicity from (Fe/H) = {minus}0.5 to (Fe/H) = {minus}1.0 with a velocity dispersion {sigma}{sub w} of 30-35 km/sec, and a halo with metallicity (Fe/H) < {minus}1 and a velocity dispersion {sigma}{sub {omega}} of 60 km/sec. However, stars with unknown distances and metallicities - have {sigma}{sub {omega}} = 80 km/sec, suggesting that the more distant halo has a velocity dispersion considerably in excess of 60 km/sec. If bound to the Galaxy, one faint distant high-velocity giant star implies that the mass of the Galaxy out to 30 kpc must be at least 1.4 {times} 10{sup 11} M{sub {center dot}}. Another faint star, blue in color but of unknown luminosity and distance, implies that the Galactic mass out to 30 kpc must be at least 3 {times} 10{sup 10} M{sub {center dot}}, if the star is on the horizontal branch.
- Research Organization:
- Harvard Univ., Cambridge, MA (United States)
- OSTI ID:
- 5051131
- Resource Relation:
- Other Information: Thesis (Ph.D)
- Country of Publication:
- United States
- Language:
- English
Similar Records
Portrait of a dark horse: a photometric and spectroscopic study of the ultra-faint Milky Way satellite Pegasus III
The Milky Way Tomography with SDSS. 2. Stellar Metallicity