Extremely low-mass white dwarf stars observed in Gaia DR2 and LAMOST DR8

TL;DR

This study uses LAMOST spectra and Gaia data to identify and analyze extremely low-mass white dwarfs, discovering 21 new candidates and confirming their potential as binary systems, demonstrating LAMOST's effectiveness in probing ELM WDs.

Contribution

First application of LAMOST spectra to study ELM white dwarfs, identifying new candidates and validating the method's potential for characterizing these stars.

Findings

Identified 21 new high-probability ELM WDs.

Confirmed LAMOST spectra's utility in studying ELM WDs.

Detected radial velocity variability indicating binary systems.

Abstract

We present the first results from our ongoing project to study extremely low mass (ELM) white dwarfs (WDs) ($M$ $\leq$ 0.3$M_{\sun}$) with the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) spectra. Based on the LAMOST DR8 spectral database, we analyzed 136 ELM WD candidates selected from $\it Gaia$ DR2 data and 12 known objects previously identified by the ELM Survey. The atmospheric parameters and radial velocities of these stars were obtained by fitting the LAMOST low-resolution spectra. After comparing the atmospheric parameters of the 12 known objects from this work to the results reported by the ELM Survey, we demonstrated the potential of LAMOST spectra in probing into the nature of ELM WDs. Based on the atmospheric parameters and $\it Gaia$ EDR3 data, we identified 21 new high-probability ELM WDs with masses $M$ $\leq$ 0.3$M_{\sun}$ and parallax estimates that agree to within a factor of 3. Two of them, J0338+4134 and J1129+4715, show significant radial velocity variability and are very likely to be binary systems containing at least one ELM WD.