Hot Subdwarf Stars Observed in Lamost Dr1—atmospheric Parameters From Single-Lined Spectra

Abstract

We present a catalog of 166 spectroscopically identified hot subdwarf stars from LAMOST DR1, 44 of which show the characteristics of cool companions in their optical spectra. Atmospheric parameters of 122 non-composite spectra subdwarf stars were measured by fitting the profiles of hydrogen (H) and helium (He) lines with synthetic spectra from non-LTE model atmospheres. Most of the sdB stars scatter near the Extreme Horizontal Branch in the T eff − log g diagram and two well defined groups can be outlined. A clustering of He-enriched sdO stars appears near T eff = 45 000 K and log(g) = 5.8. The sdB population separates into several nearly parallel sequences in the T eff −He abundance diagram with clumps corresponding to those in the T eff − log g diagram. Over 38 000 K (sdO) stars show abundance extremes, they are either He-rich or He-deficient and we observe only a few stars in the −1 < log(y) < 0 abundance range. With increasing temperature these extremes become less prominent and the He abundance approaches to log(y) ∼ −0.5. A unique property of our sample is that it covers a large range in apparent magnitudes and galactic latitudes, therefore it contains a mix of stars from different populations and galactic environments. Our results are consistent with the findings of Hirsch (2009) and we conclude that He-rich and He-deficient sdB stars (log(y) < 1) probably origin from different populations. We also find that most sdO and sdB stars lie in a narrow strip in the luminosity and helium abundance plane, which suggests that these atmospheric parameters are correlated.

The population of hot subdwarf stars studied withGaia

“…This fraction is not complete, because only papers containing larger samples of sdO/B stars A50, page 4 of 11 have been taken into account (Heber et al 1984;Bixler et al 1991;Saffer et al 1994Saffer et al , 1997Maxted et al 2001;Edelmann et al 2003;Lisker et al 2005;Ströer et al 2007;Hirsch 2009;Østensen et al 2010a;Nemeth et al 2012;Geier et al 2013Geier et al , 2015bKupfer et al 2015;Luo et al 2016;Kepler et al 2016).…”

“…In addition, we added the sample of sdO/Bs selected from the Guide Star and the Galaxy Evolution Explorer (GALEX) catalogs by Vennes et al (2011), the samples of Oreiro et al (2011) and Perez-Fernandez et al (2016) selected using Virtual observatory tools and multiband photometry, and the first sample of sdO/Bs discovered by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) survey (Luo et al 2016). Those samples are considered the most important ones to date and should cover more than 90% of the currently known sdO/Bs in the field.…”

Evolution Models of Helium White Dwarf–Main-sequence Star Merger Remnants

“…10). We compile a sample of all known iHe-rich hot subdwarfs (those with n He = 10-90%; Edelmann 2003;Naslim et al 2010Naslim et al , 2011Németh et al 2012;Naslim et al 2013;Jeffery et al 2016;Luo et al 2016). Fig.…”

Searching for hot subdwarf stars from the LAMOST Spectra. II. Pure spectroscopic identification method for hot subdwarfs

“…Thanks to large surveys over the past decade a significant number of previously unknown hot subdwarfs have been catalogued, e.g., Kepler (∅stensen et al 2010), Galaxy Evolution Explorer (GALEX, Vennes et al 2011;Németh et al 2012;Kawka et al 2015), the Sloan Digital Sky Survey (SDSS, Geier et al 2015;Kepler et al 2015Kepler et al , 2016 and the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) survey (Luo et al 2016). ∅stensen (2006) compiled a widely used hot subdwarf database by searching extensive literatures, in which more than 2300 hot subdwarf stars are archived.…”