Spectroscopic Observations of Distant Horizontal-Branch Stars in the Halo of the Galaxy

Details Spectroscopic Observations of Distant Horizontal-Branch Stars in the Halo of the Galaxy Spectroscopic Observations of Distant Horizontal-Branch Stars in the Halo of the Galaxy

Aug 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999noao.prop..166b&link_type=abstract

NOAO Proposal ID #1999B-0166

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Scientific paper

We propose to complete a program of medium-resolution spectroscopy for a sample of some 600 distant (10 ≤ d ≤ 25 kpc) candidate field horizontal-branch (FHB) stars identified from the Hamburg/ESO objective- prism survey. Based on the 200 FHB/A candidates already observed at CTIO, and the remaining 400 candidates we request time for in the present proposal, the photometric data already in hand, and additional photometry which we plan to obtain this fall at ESO (time already allocated) and McDonald Observatory, we will derive estimates of abundance, temperature, and surface gravity (with accuracies sufficient to distinguish FHB stars from other A-type stars in the halo), and measure radial velocities accurate to 10 km/s. These distant FHB stars will be used in combination with a recently-completed sample of some 700 near- to intermediate-distance FHB stars to place strong constraints on the nature of the orbital distributions of stars in the Galactic halo. In particular, we hope to test a model for which we already have some observational evidence, that the velocity ellipsoid of stellar populations in the Galaxy changes from radially-dominated to tangentially-dominated as the Galactocentric distance increases. Furthermore, we hope to establish the existence of a proposed counter- rotating population of stars in the ``high halo'' of the Galaxy. Both of these results are crucial for development of a model for the formation of the Milky Way, and other galaxies like it.

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