Spectral analysis of 636 white dwarf - M star binaries from the Sloan Digital Sky Survey

TL;DR

This paper catalogs 857 WD-M star binaries from SDSS DR6, performs spectral analysis on 636 systems to derive stellar parameters, and investigates their physical and orbital characteristics, revealing insights into binary evolution and stellar populations.

Contribution

It provides a comprehensive spectral analysis of WD-M binaries, including parameter estimation, spatial separation, and identification of substellar companions, expanding understanding of binary system properties.

Findings

Spectral analysis of 636 systems yields stellar parameters and distances.

Identification of 41 optically resolved systems with estimated orbital periods.

Detection of 70 candidate substellar companions and 24.4% of systems with active M dwarfs.

Abstract

We present a catalog of 857 white dwarf (WD)-M binaries from the sixth data release (DR6) of the Sloan Digital Sky Survey (SDSS), most of which were previously identified. For 636 of them, we complete a spectral analysis and derive the basic parameters of their stellar constituents and their distances from Earth. We attempt to measure fundamental parameters of these systems by completing spectral analyses. We use a Chi^2 minimization technique to decompose each combined spectrum and derive independent parameter estimates for its components. Forty-one of the stellar duets in our spectroscopic sample are optically resolved in their respective SDSS images. For these systems, we also derive a minimum true spatial separation and a lower limit to their orbital periods, typically which are some 10^4 yr. Spectra of 167 stellar duets show significant hydrogen emission and in most cases no additional He i or He ii features. We also find that 20 of the 636 WDs are fitted to be DOs, with 16 measured to have T_eff around 40,000 K. Furthermore, we identify 70 very low-mass objects, which are secondaries of masses smaller than about 0.1 solar masses, to be candidate substellar companions. Although various selection effects may play a role, the fraction 6.4 % of WD-M star binaries with orbital separations of around 500 AU is a criterion for evolutionary models of stellar binary systems. Active M dwarfs are likely present in 155 Balmer-emitting systems, corresponding to a fraction of 24.4 %. The excess of cool DOs is most likely due to additional WDs in the DB-DO T_eff range, for which no detailed fitting was completed. The trend of the M stars being closer to Earth than the WD component is probably due to an underestimation of the theoretical M star radii.