Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986phdt.........4r&link_type=abstract
Ph.D. Thesis California Inst. of Tech., Pasadena.
Astronomy and Astrophysics
Astronomy
17
Astronomical Photometry, Astronomical Spectroscopy, Galactic Bulge, Galactic Nuclei, Giant Stars, K Stars, Kinematics, Late Stars, Milky Way Galaxy, Stellar Composition, Abundance, Color-Magnitude Diagram, Globular Clusters, Metals, Stellar Color
Scientific paper
Spectroscopy and photometry was obtained for 100 K giants in Baade's Window at l = 1 deg, b = -4 deg. The abundance distribution of the nuclear bulge K giants was derived relative to 45 stars of known abundance. The abundances run from -1 to nearly +1 dex, with a peak at 0.3 dex, or twice the solar abundance. Of the 88 stars with derived abundances, 22% exceeded the abundance of the most metal rich local K giants; 50% exceeded the solar abundance, and 10% were metal poor (less than -0.6 dex). Radial velocities were measured for 53 nuclear bulge K giants which also have derived abundances. Their velocity dispersion is 104 km/sec. The mean velocity is -19 + or - 14 km/sec. The abundance distribution function is found to be fit very well by the simple model of chemical evolution with complete gas consumption. No evidence was found that either the metal rich or metal poor stars follow the galactic rotation curve; hence neither population appears to be rotation supported. Optical and infrared photometry is presented for nuclear bulge K giants. The colors of these stars are shown to be too hot for their derived metal abundances. Analysis of color-magnitude diagrams in bulge fields at -4 deg (Baade's Window) and -8 deg shows that there cannot be a 1 Gyr old population of main sequence stars in the galactic bulge. A turnoff population is detected at -8 deg, and comparison with isochrones indicates that the population is older than 5 Gyr. For the first time, there is a clear indication of a horizontal branch, or globular cluster feature in the luminosity function of the galactic bulge.
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