CCD Parallaxes for 309 Late-type Dwarfs and Subdwarfs

TL;DR

This paper presents updated CCD parallaxes for 309 late-type dwarf and subdwarf stars, including photometry and analysis of their properties, with implications for understanding their distances, classifications, and potential halo membership.

Contribution

It provides the largest uniform set of CCD parallaxes for late-type dwarfs and subdwarfs, with new photometry and analysis of their kinematics and classifications.

Findings

Identification of possible halo subdwarfs based on velocity and luminosity.

Detection of astrometric perturbations indicating potential companions.

Comparison of new parallaxes with previous measurements for consistency.

Abstract

New, updated, and/or revised CCD parallaxes determined with the Strand Astrometric Reflector at the Naval Observatory Flagstaff Station (NOFS) are presented. Included are results for 309 late-type dwarf and subdwarf stars observed over the 30+ years that the program operated. For 124 of the stars, parallax determinations from other investigators have already appeared in the literature and we compare the different results. Also included here is new or updated $VI$ photometry on the Johnson-Kron-Cousins system for all but a few of the faintest targets. Together with 2MASS $JHK_s$ near-infrared photometry, a sample of absolute magnitude versus color and color versus color diagrams are constructed. Since large proper motion was a prime criterion for targeting the stars, the majority turn out to be either M-type subdwarfs or late M-type dwarfs. The sample also includes 50 dwarf or subdwarf L-type stars, and four T dwarfs. Possible halo subdwarfs are identified in the sample based on tangential velocity, subluminosity, and spectral type. Residuals from the solutions for parallax and proper motion for several stars show evidence of astrometric perturbations.