11-12 Gyr old White Dwarfs 30 parsecs Away

TL;DR

This study analyzes two of the oldest known white dwarfs in the solar neighborhood, determining their ages, compositions, and distances, and confirming their status as halo stars with ages around 11 billion years.

Contribution

It provides detailed atmospheric modeling and precise measurements for two ancient white dwarfs, enhancing understanding of stellar evolution and galactic halo composition.

Findings

Both stars are approximately 11 billion years old.

J1102 is a hydrogen-atmosphere white dwarf at 3830 K.

WD0346 has a mixed H/He atmosphere at 3650 K.

Abstract

We present a detailed model atmosphere analysis of two of the oldest stars known in the solar neighborhood, the high proper motion white dwarfs SDSS J110217.48+411315.4 (hereafter J1102) and WD 0346+246 (hereafter WD0346). We present trigonometric parallax observations of J1102, which places it at a distance of only 33.7 +- 2.0 pc. Based on the state of the art model atmospheres, optical, near-, mid-infrared photometry, and distances, we constrain the temperatures, atmospheric compositions, masses, and ages for both stars. J1102 is an 11 Gyr old (white dwarf plus main-sequence age), 0.62 Msol white dwarf with a pure H atmosphere and Teff = 3830 K. WD0346 is an 11.5 Gyr old, 0.77 Msol white dwarf with a mixed H/He atmosphere and Teff = 3650 K. Both stars display halo kinematics and their ages agree remarkably well with the ages of the nearest globular clusters, M4 and NGC 6397. J1102 and WD0346 are the closest examples of the oldest halo stars that we know of.