Binaries discovered by the SPY project V. GD 687 - a massive double degenerate binary progenitor that will merge within a Hubble time

Abstract

Aims. The ESO SN Ia Progenitor Survey (SPY) aims at finding merging double degenerate binaries as candidates for supernova type Ia (SN Ia) explosions. A white dwarf merger has also been suggested to explain the formation of rare types of stars like R CrB, extreme helium or He sdO stars. Here we present the hot subdwarf B binary GD 687, which will merge in less than a Hubble time. Methods. The orbital parameters of the close binary have been determined from time resolved spectroscopy. Since GD 687 is a single-lined binary, the spectra contain only information about the subdwarf primary and its orbit. From high resolution spectra the projected rotational velocity was derived. Assuming orbital synchronisation, the inclination of the system and the mass of the unseen companion were constrained. Results. The derived inclination is $i=39.3_{-5.6}^{+6.2}{}^{\circ }$. The mass $M_2=0.71_{-0.21}^{+0.22}{M}_{\odot }$ indicates that the companion must be a white dwarf, most likely of C/O composition. This is only the fourth case that an sdB companion has been proven to be a white dwarf unambiguously. Its mass is somewhat larger than the average white dwarf mass, but may be as high as $0.93M_{\odot }$ in which case the total mass of the system comes close to the Chandrasekhar limit. Conclusions. GD 687 will evolve into a double degenerate system and merge to form a rare supermassive white dwarf with a mass in excess of solar. A death in a sub-Chandrasekhar supernova is also conceivable.

6 pages, 4 figures, A&A accepted

References in corpus (3)

• The hot subdwarf B + white dwarf binary KPD 1930+2752 - a Supernova Type Ia progenitor candidate
• Modeling the System Parameters of 2M1533+3759: A New Longer-Period Low-Mass Eclipsing sdB+dM Binary
• First Results from the Swarms Survey. SDSS 1257+5428: A Nearby, Massive White Dwarf Binary with a Likely Neutron Star or Black Hole Companion

Cited by in corpus (29)

• Observational clues to the progenitors of Type-Ia supernovae
• Hot subluminous stars
• Progenitors of type Ia supernovae
• The Long-Term Evolution of Double White Dwarf Mergers
• Type Ia Supernova Explosions in Binary Systems: A Review
• The ELM Survey. II. Twelve Binary White Dwarf Merger Systems
• Mass-accreting white dwarfs and type Ia supernovae
• Hot subdwarf binaries from the MUCHFUSS project - Analysis of 12 new systems and a study of the short-period binary population
• Three-dimensional simulations of the interaction between Type Ia supernova ejecta and their main sequence companions
• The MUCHFUSS project - Searching for hot subdwarf binaries with massive unseen companions: Survey, target selection and atmospheric parameters
• The ELM Survey. III. A Successful Targeted Survey for Extremely Low Mass White Dwarfs
• Hot subdwarf stars in close-up view I. Rotational properties of subdwarf B stars in close binary systems and nature of their unseen companions
• New binaries among UV-selected, hot subdwarf stars and population properties
• The formation of neutron star systems through accretion-induced collapse in white-dwarf binaries
• Hot subdwarfs in close binaries observed from space I: orbital, atmospheric, and absolute parameters and the nature of their companions
• Where are the double-degenerate progenitors of type Ia supernovae?
• A Catalogue of Potential Post Common Envelope Binaries
• Massive unseen companions to hot faint underluminous stars from SDSS (MUCHFUSS) - Analysis of seven close subdwarf B binaries
• The violent white dwarf merger scenario for the progenitors of type Ia supernovae
• Stellar wind models of subluminous hot stars
• Using large spectroscopic surveys to test the double degenerate model for Type Ia supernovae
• Some constraints on the lower mass limit for double-degenerate progenitors of Type Ia supernovae
• Single magnetic white dwarfs with Balmer emission lines: A small class with consistent physical characteristics as possible signposts for close-in planetary companions
• Orbital solutions of eight close sdB binaries and constraints on the nature of the unseen companions
• Binaries discovered by the SPY survey VI. Discovery of a low mass companion to the hot subluminous planetary nebula central star EGB\,5 - A recently ejected common envelope?
• Hot subdwarfs in close binaries observed from space II: Analysis of the light curves
• MUCHFUSS - Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS
• Angular momentum transfer between oscillations and rotation in subdwarf B hybrid pulsators
• Discovery and analysis of three magnetic hot subdwarf stars: evidence for merger-induced magnetic fields