Revised Stellar Parameters for V471 Tau, A Post-common Envelope Binary in the Hyades

TL;DR

This study refines the stellar and orbital parameters of the V471 Tau binary system using archival data, revealing gravitational microlensing effects during white dwarf transits and suggesting a merger origin for the white dwarf.

Contribution

It provides the first detection of white dwarf transits in V471 Tau and offers revised stellar parameters, highlighting the system's complex evolutionary history.

Findings

White dwarf transits detected via Gaussian process modeling.

White dwarf mass and temperature indicate a merger origin.

Transits affected by gravitational microlensing, constraining white dwarf mass.

Abstract

V471 Tau is a post-common-envelope binary consisting of an eclipsing DA white dwarf and a K-type main-sequence star in the Hyades star cluster. We analyzed publicly available photometry and spectroscopy of V471 Tau to revise the stellar and orbital parameters of the system. We used archival K2 photometry, archival Hubble Space Telescope spectroscopy, and published radial-velocity measurements of the K-type star. Employing Gaussian processes to fit for rotational modulation of the system flux by the main-sequence star, we recovered the transits of the white dwarf in front of the main-sequence star for the first time. The transits are shallower than would be expected from purely geometric occultations owing to gravitational microlensing during transit, which places an additional constraint on the white-dwarf mass. Our revised mass and radius for the main-sequence star is consistent with single-star evolutionary models given the age and metallicity of the Hyades. However, as noted previously in the literature, the white dwarf is too massive and too hot to be the result of single-star evolution given the age of the Hyades, and may be the product of a merger scenario. We independently estimate the conditions of the system at the time of common envelope that would result in the measured orbital parameters today.