Improving white dwarfs as chronometers with Gaia parallaxes and spectroscopic metallicities

Abstract

White dwarfs (WDs) offer unrealized potential in solving two problems in astrophysics: stellar age accuracy and precision. WD cooling ages can be inferred from surface temperatures and radii, which can be constrained with precision by high quality photometry and parallaxes. Accurate and precise Gaia parallaxes along with photometric surveys provide information to derive cooling and total ages for vast numbers of WDs. Here we analyse 1372 WDs found in wide binaries with MS companions, and report on the cooling and total age precision attainable in these WD+MS systems. The total age of a WD can be further constrained if its original metallicity is known, because the main-sequence (MS) progenitor lifetime depends on metallicity at fixed mass, yet metallicity is unavailable via spectroscopy of the WD. We show that incorporating spectroscopic metallicity constraints from 38 wide binary MS companions substantially decreases internal uncertainties in WD total ages compared to a uniform constraint. Averaged over the 38 stars in our sample, the total (internal) age uncertainty improves from 21.04% to 16.77% when incorporating the spectroscopic constraint. Higher mass WDs yield better total age precision; for 8 WDs with zero age main sequence masses $\ge$ 2.0 solar masses, the mean uncertainty in total ages improves from 8.61% to 4.54% when incorporating spectroscopic metallicities. We find that it is often possible to achieve 5% total age precision for WDs with progenitor masses above 2.0 solar masses if parallaxes with $\le$ 1% precision and Pan-STARRS $g,r$, and $i$ photometry with $\le$ 0.01 mag precision are available.

14 pages, 9 figure, accepted for publication in The Astrophysical Journal

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