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Hot subdwarf binaries from the MUCHFUSS project Analysis of 12 new systems and a study of the short-period binary population

Kupfer T, Geier S, Heber U, Ostensen RH, Barlow BN, Maxted PFL, Heuser C, Schaffenroth V, Gaensicke BT (2015)

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Publication Status: Published

Publication Type: Journal article

Publication year: 2015

Journal

Publisher: EDP SCIENCES S A

Book Volume: 576

Article Number: ARTN A44

DOI: 10.1051/0004-6361/201425213

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 M-circle dot), 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. We present orbital and atmospheric parameters and put constraints on the nature of the companions of 12 close hot subdwarf B star (sdB) binaries found in the course of the MUCHFUSS project. The systems show periods between 0.14 and 7.4 days. In nine cases the nature of the companions cannot be constrained unambiguously whereas three systems most likely have white dwarf companions. We find that the companion to SDSS J083006.17+475150.3 is likely to be a rare example of a low-mass helium-core white dwarf. SDSS J095101.28+034757.0 shows an excess in the infrared that probably originates from a third companion in a wide orbit, which makes this system the second candidate hierarchical triple system containing an sdB star. SDSS J113241.58-063652.8 is the first helium deficient sdO star with a confirmed close companion. This study brings to 142 the number of sdB binaries with orbital periods of less than 30 days and with measured mass functions. We present an analysis of the minimum companion mass distribution and show that it is bimodal. One peak around 0.1 M-circle dot corresponds to the low-mass main sequence (dM) and substellar companions. The other peak around 0.4 M-circle dot corresponds to the white dwarf companions. The derived masses for the white dwarf companions are significantly lower than the average mass for single carbon-oxygen white dwarfs. In a T-eff - log g diagram of sdB+dM companions, we find signs that the sdB components are more massive than the rest of the sample. The full sample was compared to the known population of extremely low-mass white dwarf binaries as well as short-period white dwarfs with main sequence companions. Both samples show a significantly different companion mass distribution indicating either different selection effects or different evolutionary paths. We identified 16 systems where the dM companion will fill its Roche Lobe within a Hubble time and will evolve into a cataclysmic variable; two of them will have a brown dwarf as donor star. Twelve systems with confirmed white dwarf companions will merge within a Hubble time, two of them having a mass ratio to evolve into a stable AMCVn-type binary and another two which are potential supernova Ia progenitor systems. The remaining eight systems will most likely merge and form RCrB stars or massive C/O white dwarfs depending on the structure of the white dwarf companion.

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APA:

Kupfer, T., Geier, S., Heber, U., Ostensen, R.H., Barlow, B.N., Maxted, P.F.L.,... Gaensicke, B.T. (2015). Hot subdwarf binaries from the MUCHFUSS project Analysis of 12 new systems and a study of the short-period binary population. Astronomy & Astrophysics, 576. https://doi.org/10.1051/0004-6361/201425213

MLA:

Kupfer, Thomas, et al. "Hot subdwarf binaries from the MUCHFUSS project Analysis of 12 new systems and a study of the short-period binary population." Astronomy & Astrophysics 576 (2015).

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