Spectroscopy of Hot Stars in the Galactic Halo. II. The Identification and Classification of Horizontal-Branch and Other A-Type Stars

Details Spectroscopy of Hot Stars in the Galactic Halo. II. The Identification and Classification of Horizontal-Branch and Other A-Type Stars Spectroscopy of Hot Stars in the Galactic Halo. II. The Identification and Classification of Horizontal-Branch and Other A-Type Stars

May 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aj....117.2308w&link_type=abstract

The Astronomical Journal, Volume 117, Issue 5, pp. 2308-2328.

Astronomy and Astrophysics

Astronomy

62

Galaxy: Halo, Stars: Horizontal-Branch, Stars: Population Ii

Scientific paper

We discuss a spectroscopic and photometric technique that enables the identification and classification of field horizontal-branch (FHB) and other A-type stars, even from relatively low signal-to-noise ratio medium-resolution spectra. This technique makes use of broadband UBV colors predicted from model atmosphere calculations and Balmer line profiles and Ca II K equivalent widths determined from synthetic spectra to estimate the physical parameters T_eff, log g, and [Fe/H] for stars in the effective temperature range 6000-10,000 K. A comparison of our method with high signal-to-noise ratio spectra of standard stars indicates a scatter in the derived parameters of sigma(T_eff)=+/-250 K, sigma(log g)=+/-0.14 dex, and sigma([Fe/H])=+/-0.12 dex. This precision allows for a separation of low surface gravity FHB and other, generally higher surface gravity, A-type (and somewhat later) stars. We also develop a synthetic-template comparison technique, which is very effective in the identification of metallic-line and peculiar A-type stars. A detailed investigation of the influence of noise in the spectra on the determination of physical parameters shows that, for spectra with signal-to-noise ratios in the range 10