A spectroscopic and proper motion search of Sloan digital Sky Survey: red subdwarfs in binary systems

TL;DR

This study identifies and analyzes red subdwarfs in binary systems using SDSS data, revealing their binary fraction, spectral properties, and kinematics to aid in stellar classification and evolution models.

Contribution

The paper presents the first large-scale search for red subdwarfs in binary systems, including new discoveries and relationships between spectral types and magnitudes.

Findings

30 red subdwarfs in wide binary systems discovered.

Binary fraction estimated at approximately 10%.

Spectral type and magnitude relationships derived for subdwarfs.

Abstract

Red subdwarfs in binary systems are crucial for both model calibration and spectral classification. We search for red subdwarfs in binary systems from a sample of high proper motion objects with Sloan digital Sky Survey spectroscopy. We present here discoveries from this search, as well as highlight several additional objects of interest. We find 30 red subdwarfs in wide binary systems including: two with spectral type of esdM5.5, 6 companions to white dwarfs and 3 carbon enhanced red subdwarfs with normal red subdwarf companions. 15 red subdwarfs in our sample are partially resolved close binary systems. With this binary sample, we estimate the low limit of the red subdwarf binary fraction of ~ 10%. We find that the binary fraction goes down with decreasing masses and metallicities of red subdwarfs. A spectroscopic esdK7 subdwarf + white dwarf binary candidate is also reported. 30 new M subdwarfs have spectral type of >= M6 in our sample. We also derive relationships between spectral types and absolute magnitudes in the optical and near-infrared for M and L subdwarfs, and we present an M subdwarf sample with measured U, V, W space velocities.