A very young and fast rotating shell star discovered in the eclipsing binary ZTF J200347.63+394429.8

TL;DR

This study characterizes a rapidly rotating shell star in an eclipsing binary, revealing its physical parameters, a surrounding decretion disk, and the evolutionary state of its companion, based on photometric data and stellar models.

Contribution

It provides detailed physical and evolutionary parameters of a young, fast-rotating shell star in an eclipsing binary, including the first characterization of its decretion disk.

Findings

Shell star has an equatorial radius of ~2.60 Rsun and rotates at ~430 km/s.

The binary system is approximately 1.8 million years old.

The companion is a helium white dwarf precursor with specific temperature and mass.

Abstract

A photometric study in combination with existing stellar models has revealed details of this eclipsing post-mass-transfer binary. The shell star has an equatorial/ polar radius of ~2.60/1.90 Rsun at an equatorial rotational velocity of ~430 km s-1, an effective mean temperature Teff of ~13300 K and a mass of ~3.42 Msun. This former accretor star is surrounded by a large decretion disk of ~47 Rsun. The secondary star is a helium white dwarf precursor with a radius of 0.98 Rsun, a Teff of ~17100 K and a mass of 0.29 Msun. The parameters of this former donor star indicate an age of the binary system of only ~1.8 Myr after the end of mass transfer. The results fit to a sub-solar metallicity of Z = 0.007.