White Dwarfs in Wide Binary Systems as Reliable Age Calibrators

TL;DR

This work addresses the challenge of deriving precise stellar ages by leveraging white dwarfs in wide WD+MS binaries as reliable age calibrators. It argues that WD cooling ages, combined with progenitor lifetimes tied to the IFMR, can yield robust system ages, but IFMR uncertainties hinder accuracy; focusing on massive WDs with $M \gtrsim 0.7\,M_{\odot}$ minimizes progenitor lifetimes and metallicity effects. The authors employ a MRBIN Monte Carlo framework with BSE and La Plata WD cooling sequences to forecast the population of WD+MS binaries observable by LSST within ~3 kpc, predicting ~40,500 LSST-accessible systems, including ~13,000 with $M \ge 0.7\,M_{\odot}$ and ~8,600 at $g_{LSST} \le 23$, with massive-WD progenitors having $\lesssim 0.5$ Gyr lifetimes and total ages up to $9$ Gyr. They conclude that realizing these measurements requires a new, dedicated facility with $\gtrsim 10$ m aperture and high multiplexing to obtain WD spectra ($R \simeq 2{,}000$ over $3600$–$10{,}000$ Å) and MS companion spectra ($R \gtrsim 15{,}000$ in three bands), enabling precise WD ages to calibrate the Milky Way’s age–metallicity, age–velocity dispersion, and age–rotation–activity relations.

Abstract

Deriving precise stellar ages is a challenging task. Consequently, age-dependent relations - such as the age-metallicity and age-velocity dispersion relations of the Milky Way, or the age-rotation-activity relation of low-mass stars - are subject to potentially large uncertainties, despite the well-defined trends observed at the population level. White dwarfs, the most common stellar remnants, follow a relatively simple and well-understood cooling process. When found in wide binary systems with main-sequence companions, they can therefore provide the much-needed precise age estimates. The total age of such systems depends not only on the white dwarf cooling time but also on the lifetime of the main-sequence progenitor. Estimating this lifetime requires knowledge of the progenitor mass, which is typically inferred by adopting an initial-to-final mass relation. However, the observational constraints on this relation are still poorly defined, introducing a source of uncertainty in white dwarf age determinations. To mitigate this issue, we focus on a large sample of massive white dwarfs (>~0.7 Msun), for which the main-sequence progenitor lifetime is negligible. These white dwarfs are intrinsically faint and therefore require specialized facilities for adequate follow-up observations. In this white paper, we outline the instrumentation requirements needed to observe the forthcoming population of massive white dwarfs in our Galaxy.

Figures (2)

• Figure 1: Left: $Gaia$ DR3 HR diagram for the synthetic WD+MS binaries within 3 kpc. Dark red shows all systems accessible by LSST ($\simeq$40 500), dark yellow those containing massive white dwarfs ($M\geq0.7$ M$_{\odot}$; $\simeq13\,000$ objects) and dark green those with g$_\mathrm{LSST}\leq23$ ($\simeq8\,600$ objects). The solid red and blue lines indicate the cooling sequences of a 0.5 and a 0.7 M$_{\odot}$ white dwarf, respectively. The synthetic massive white dwarfs (yellow, green) are spread above and below these limits due to extinction and parallax uncertainties considered by our code. Right: their $g_\mathrm{LSST}$ magnitudes as a function of distance.
• Figure 2: White dwarf progenitor (left) and total (right) ages for the synthetic WD+MS binaries. Colors are as in Figure \ref{['f-surveys']}.