Massive unseen companions to hot faint underluminous stars from SDSS (MUCHFUSS) - Analysis of seven close subdwarf B binaries

TL;DR

This study analyzes seven close subdwarf B binary stars from SDSS, aiming to find systems with massive unseen companions like white dwarfs, neutron stars, or black holes, confirming the efficiency of their selection method.

Contribution

First detailed analysis of seven sdB binaries with potential massive companions, demonstrating the effectiveness of the target selection method for such systems.

Findings

All seven binaries have parameters consistent with core helium-burning stars.

Most companions are likely white dwarfs, with one confirmed by light-curve analysis.

Target selection method is efficient in identifying high-mass companion candidates.

Abstract

The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding hot subdwarf stars with massive compact companions like massive white dwarfs (M > 1.0 Msun), neutron stars or stellar mass black holes. The existence of such systems is predicted by binary evolution theory and recent discoveries indicate that they exist in our Galaxy. First results are presented for seven close binary sdBs with short orbital periods ranging from 0.21 d to 1.5 d. The atmospheric parameters of all objects are compatible with core helium-burning stars. The companions are most likely white dwarfs. In one case the companion could be shown to be a white dwarf by the absence of light-curve variations. However, in most cases late type main sequence stars cannot be firmly excluded. Comparing our small sample with the known population of close sdB binaries we show that our target selection method aiming at massive companions is efficient. The minimum companion masses of all binaries in our sample are high compared to the reference sample of known sdB binaries.