Binaries discovered by the SPY project I. HE 1047-0436: a subdwarf B + white dwarf system

TL;DR

This paper reports the discovery of a binary system consisting of a subdwarf B star and a white dwarf, with detailed orbital parameters, atmospheric properties, and implications for supernova progenitors.

Contribution

First detection of a subdwarf B + white dwarf binary system with detailed orbital and stellar parameters using the SPY survey.

Findings

Orbital period of 1.213253 days and semi-amplitude of 94 km/s.

Minimum companion mass of 0.44 solar masses, likely a white dwarf.

System's total mass approaches the Chandrasekhar limit but will merge after several Hubble times.

Abstract

In the course of our search for double degenerate binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY - SPY) we discovered that the sdB star HE 1047-0436 is radial velocity variable. The orbital period of 1.213253d, a semi-amplitude of 94km/s, and a minimum mass of the invisible companion of 0.44Msol are derived from the analysis of the radial velocity curve. We use an upper limit on the projected rotational velocity of the sdB star to constrain the system inclination and the companion mass to M>0.71Msol, bringing the total mass of the system closer to the Chandrasekhar limit. However, the system will merge due to loss of angular momentum via gravitational wave radiation only after several Hubble times. Atmospheric parameters and metal abundances are also derived. The resulting values are typical for sdB stars.