1999/05/01 by Ronald Wilhelm, Timothy C. Beers, Richard O. Gray +1 · 103 citations
Physics and Astronomy · #Astronomical spectroscopy #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Balmer series #Emission spectrum #Galactic halo #Galaxy #Geometry #Halo #Horizontal branch #Line (geometry) #Metallicity #Physics #Spectral line #Spectroscopy #Stars #Stellar atmosphere #Stellar, planetary, and galactic studies
paper · pdf · doi:10.1086/300824
published in The Astronomical Journal 117(5), 2308-2328 (Institute of Physics)
openalex publication_date 1999/05/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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 σ( T eff ) = ±250 K, σ(log g ) = ±0.14 dex, and σ([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 < S/N < 20, the scatter in estimated surface gravity, σ(log g ) = ±0.25 dex, is sufficiently small to keep the noise-induced misclassification rate for the hot stars we consider to less than 10%. Effective temperatures of precision σ( T eff ) = ±225 K and metallicities of precision σ([Fe/H]) = ±0.3 dex can be obtained.