Mapping the Local Halo: Statistical Parallax Analysis of SDSS Low-Mass Subdwarfs

TL;DR

This study uses statistical parallax to analyze nearly 2,000 low-mass subdwarfs from SDSS, revealing their kinematic properties, metallicity dependence, and providing tools for future surveys to identify halo stars.

Contribution

It introduces refined color-magnitude and metallicity relations for low-mass subdwarfs, enhancing their use as tracers of the stellar halo in future surveys.

Findings

Subdwarfs share kinematics with the inner halo and thick disk.

Color-magnitude relations depend on metallicity parameter zeta.

Developed a photometric metallicity parameter delta(g-r).

Abstract

We present a statistical parallax study of nearly 2,000 M subdwarfs with photometry and spectroscopy from the Sloan Digital Sky Survey. Statistical parallax analysis yields the mean absolute magnitudes, mean velocities and velocity ellipsoids for homogenous samples of stars. We selected homogeneous groups of subdwarfs based on their photometric colors and spectral appearance. We examined the color-magnitude relations of low-mass subdwarfs and quantified their dependence on the newly-refined metallicity parameter, zeta. We also developed a photometric metallicity parameter, delta(g-r), based on the g-r and r-z colors of low-mass stars and used it to select stars with similar metallicities. The kinematics of low-mass subdwarfs as a function of color and metallicity were also examined and compared to main sequence M dwarfs. We find that the SDSS subdwarfs share similar kinematics to the inner halo and thick disk. The color-magnitude relations derived in this analysis will be a powerful tool for identifying and characterizing low-mass metal-poor subdwarfs in future surveys such as GAIA and LSST, making them important and plentiful tracers of the stellar halo.