Searching for White Dwarf Candidates Formed Through Binary evolution in Star Clusters

TL;DR

This paper addresses how WD formation channels manifest in star clusters by leveraging Gaia 5D astrometry to identify 439 WD candidates in 117 open clusters. It quantifies the binary-evolution contribution with a probabilistic framework, finding 244 candidates (including 49 high-confidence 5D members) likely formed through binary interactions, aided by Monte Carlo delineation of $P_{ ext{bin}}$ values and cluster ages. WD parameters (mass, $T_{ ext{eff}}$, $ ext{log }g$, cooling ages) are inferred via WD_models, with total ages $t_{ ext{tot}}$ computed by combining cooling ages and MS lifetimes through the IFMR and MIST tracks; uncertainties are propagated through 1000 realizations. The results reveal a substantial deficit of WDs compared with single-star evolution predictions across all age bins, suggesting significant WD escape from clusters possibly driven by natal kicks, alongside observational incompleteness and WD cooling physics effects; the findings underscore binary evolution’s role in cluster WD populations and motivate targeted follow-up spectroscopy and IFMR studies.

Abstract

White dwarfs (WDs), the evolutionary endpoints of most stars, can form through both single-star and binary channels. While single-star evolutionary models enable reliable WD age estimates, binary evolution introduces interactions that can accelerate WD formation and result in a variety of exotic WDs, which may exhibit strong magnetic fields, rapid rotation, or even serve as potential gravitational wave sources. Such systems offer valuable insights into magnetic field generation, angular momentum evolution, and compact object physics. Star clusters, with their approximately coeval populations, allow precise age determination of member WDs. If a WD's total age derived from single-star evolution exceeds that of its host cluster, it likely indicates a binary origin. In this study, we use \textit{Gaia} 5D astrometry to identify 439 WD candidates in 117 open clusters, with 244 likely formed via binary evolution. We discuss the possibility of dynamical ejection for WDs meeting only 2D (proper motion space) membership criteria. Spectroscopic observations further reveal a subset with strong magnetic fields and rapid rotation, supporting their binary evolutionary origin.

Figures (8)

• Figure 1: The distribution of WDs belonging to OCs on the CMD. Primarily vertical tracks show mass models Bedard2020ApJ...901...93B from 0.21 $M_{\odot}$ to 1.29 $M_{\odot}$ .
• Figure 2: The spatial distribution, kinematic parameters, and CMD of candidate cluster members from Hunt2024AA...686A..42H, along with the selected WD candidates. The main plot is the CMD of the cluster, in which gray points represent the OC member stars selected by Hunt2024AA...686A..42H, while black points indicate the WDs we identified as belonging to the cluster. Red squares denote WDs previously identified in the literature as cluster members. Inset (a): Spatial distribution of cluster members and WDs. Inset (b): Proper motion distribution of cluster members and WDs. Inset (c): Parallax distribution of cluster members and WDs. Inset (d): CMD for WD members in cluster. The tracks represent mass models with 0.21 $M_{\odot}$ and 1.29 $M_{\odot}$. In each inset, black dashed lines indicate the $1\sigma$ and $3\sigma$ ranges. Crosses, triangles, and pentagrams denote WDs satisfying the 2D, 3D, and 5D selection criteria, respectively. The color bar represents the probability of a binary origin.
• Figure 3: RSG5-WD light curve. The period of RSG5-WD is 6.556 minutes.
• Figure 4: The SDSS spectrumKleinman2013ApJS..204....5K (top panel) and the Gemini spectrumRicher2021ApJ...912..165R (bottom panel) of Gaia EDR3 1992469104239732096. Each panel's inset shows the spectrum near the $\text{H}\alpha$ absorption line. In the top panel, the black dashed line indicates the position of the Zeeman split.
• Figure 5: LAMOST spectrum of Gaia EDR3 119677790531181056 Guo2015MNRAS.454.2787G.