Distant White Dwarfs in the US Naval Observatory Flagstaff Station Parallax Sample

TL;DR

This study provides new precise parallax measurements for 214 white dwarfs, analyzes their properties using spectral energy distributions, and identifies candidates for binaries, dust disks, and halo membership, enhancing understanding of local white dwarf populations.

Contribution

It offers a comprehensive parallax dataset for white dwarfs, combined with multi-wavelength photometry and spectroscopy, and introduces classifications for binaries and dust disk candidates.

Findings

Good agreement with Gaia DR2 parallaxes, minor systematic offset.

Identification of 26 new white dwarf classifications.

Detection of candidate unresolved binaries and dust disk systems.

Abstract

This paper presents new trigonometric parallaxes and proper motions for 214 stars. The measurements were made at the US Naval Observatory Flagstaff Station (NOFS) between 1989 and 2017, and the average uncertainty in the parallax values is 0.6 mas. We find good agreement with Gaia Data Release 2 measurements for the stars in common, although there may be a small systematic offset similar to what has been found by other investigators. The sample is matched to catalogs and the literature to create a photometric dataset which spans the ultraviolet to the mid-infrared. New mid-infrared photometry is obtained for nineteen stars from archived Spitzer mosaics. New optical spectroscopy is presented for seven systems and additional spectra were obtained from the literature. We identify a sub-sample of 179 white dwarfs (WDs) at distances of 25 - 200 pc. Their spectral energy distributions (SEDs) are analyzed using model atmospheres. The models reproduce the entire flux-calibrated SED very well and provide the atmospheric chemical composition, temperature, surface gravity, mass and cooling age of each WD. Twenty-six WDs are newly classified and twelve systems are presented as candidate unresolved binaries. We confirm one WD+red dwarf system and identify two WDs as candidate dust disk systems. Twelve old and high-velocity systems are identified as candidate thick disk or halo objects. The WDs in the sample generally have Galactic disk-like ages of < 8 Gyr and masses close to the canonical 0.6 M_Sun.