Hot Horizontal Branch Stars in the Galactic Bulge. I

Abstract

We present the first results of a survey of blue horizontal branch (BHB) stars in the Galactic bulge. 164 candidates with 15 < V < 17.5 in a field 7.5deg from the Galactic Center were observed in the blue at 2.4A FWHM resolution with the AAT 2dF spectrograph. Radial velocities were measured for all stars. For stars with strong Balmer lines, their profiles were matched to theoretical spectrum calculations to determine stellar temperature Teff and gravity log g; matches to metal lines yielded abundances. CTIO UBV photometry then gave the reddening and distance to each hot star. Reddening was found to be highly variable, with E(B-V) from 0.0 to 0.55 around a mean of 0.28. Forty-seven BHB candidates were identified with Teff >= 7250K, of which seven have the gravities of young stars, three are ambiguous, and 37 are HB stars. They span a wide metallicity range, from solar to 1/300 solar. The warmer BHB's are more metal-poor and loosely concentrated towards the Galactic center, while the cooler ones are of somewhat higher metallicity and closer to the center. Their red B-V colors overlap main-sequence stars, but the U-B vs. B-V diagram separates them until E(B-V) > 0.5. We detect two cool solar-metallicity HB stars in the bulge of our own Galaxy, the first such stars known. Still elusive are their hot counterparts, the metal-rich sdB/O stars causing excess UV light in metal-rich galaxies; they have V ~ 20.5 in the Bulge.

29 pages, 4 figures (the third with 4 panels, the fourth with 2 panels). To appear in the Astrophysical Journal v571n1, Jan. 20, 2000. Abstract is shortened here, and figures compressed

References in corpus (3)

• Far-Ultraviolet Radiation from Elliptical Galaxies
• Striking Photospheric Abundance Anomalies in Blue Horizontal-Branch Stars in Globular Cluster M13
• A New Spin on the Problem of HB Gaps: Stellar Rotation along the Blue Horizontal Branch of Globular Cluster M13

Cited by in corpus (8)

• Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
• Milky Way demographics with the VVV survey. IV. PSF photometry from almost one billion stars in the Galactic bulge and adjacent southern disk
• The Origins and Evolutionary Status of B Stars Found Far From the Galactic Plane I: Composition and Spectral Features
• Blue Horizontal Branch Stars in Old, Metal-Rich Stellar Systems
• Clusters AgeS Experiment. Hot subdwarfs and luminous white dwarf candidates in the field of the globular cluster M4
• Searching for merger debris in the Galactic halo: Chemodynamical evidence based on local blue HB stars
• VVV Survey of Blue Horizontal-Branch Stars in the Bulge-Halo Transition Region of the Milky Way
• A Survey for EHB Stars in the Galactic Bulge