New ZZ Ceti stars from the LAMOST survey

Abstract

The spectroscopic sky survey carried out by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) provides the largest stellar spectra library in the world until now. A large number of new DA white dwarfs had been identified based on the LAMOST spectra. The effective temperature ($T_{\mathrm{eff}}$) and surface gravity ($\log g$) of most DA white dwarfs were determined and published in the catalogs, e.g. Zhao et al. (2013), Rebassa-Mansergas et al. (2015), Gentile Fusillo et al. (2015) and Guo et al. (2015). We selected ZZ Ceti candidates from the published catalogs by considering whether their $T_{\mathrm{eff}}$ are situated in the ZZ Ceti instability strip. The follow-up time-series photometric observations for the candidates were performed in 2015 and 2016. Four stars: LAMOST J004628.31+343319.90, LAMOST J062159.49+252335.9, LAMOST J010302.46+433756.2 and LAMOST J013033.90+273757.9 are finally confirmed to be new ZZ Ceti stars. They show dominant peaks with amplitudes rising above the 99.9% confidence level in the amplitude spectra. As LAMOST J004628.31+343319.90 has an estimated mass of $\sim$ 0.40 $M_{\odot }$ and LAMOST J013033.90+273757.9 has a mass of $\sim$ 0.45 $M_{\odot }$ derived from their $\log g$ values, these two stars are inferred to be potential helium-core white dwarfs.

arXiv comment15 pages, 8 figures, 3 tables, accepted for publication in ApJ

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• Ground based observation of ZZ Ceti stars and the discovery of four new variables
• Uncovering the chemical structure of the pulsating low-mass white dwarf SDSS J115219.99+024814.4
• Seismic test of the mass-radius relationship of hydrogen-atmospheric white dwarf stars