The MUCHFUSS project – searching for hot subdwarf binaries with massive unseen companions
Dr. Karl Remeis-Observatory & ECAP, Astronomical Institute,
Friedrich-Alexander University Erlangen-Nuremberg,
2 Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
3 Institute of Astronomy, K.U.Leuven, Celestijnenlaan 200D, 3001 Heverlee, Belgium
4 Department of Physics, University of Warwick, Conventry CV4 7AL, UK
5 Centre of Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
6 Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599-3255, USA
7 Australian Astronomical Observatory, PO Box 296, Epping, NSW, 1710, Australia
Received: 1 July 2010
Accepted: 19 March 2011
The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding sdBs with compact companions like supermassive white dwarfs (M > 1.0 M⊙), neutron stars or black holes. The existence of such systems is predicted by binary evolution theory and recent discoveries indicate that they are likely to exist in our Galaxy. A determination of the orbital parameters is sufficient to put a lower limit on the companion mass by calculating the binary mass function. If this lower limit exceeds the Chandrasekhar mass and no sign of a companion is visible in the spectra, the existence of a massive compact companion is proven without the need for any additional assumptions. We identified about 1100 hot subdwarf stars from the SDSS by colour selection and visual inspection of their spectra. Stars with high velocities have been reobserved and individual SDSS spectra have been analysed. In total 127 radial velocity variable subdwarfs have been discovered. Binaries with high RV shifts and binaries with moderate shifts within short timespans have the highest probability of hosting massive compact companions. Atmospheric parameters of 69 hot subdwarfs in these binary systems have been determined by means of a quantitative spectral analysis. The atmospheric parameter distribution of the selected sample does not differ from previously studied samples of hot subdwarfs. The systems are considered the best candidates to search for massive compact companions by follow-up time resolved spectroscopy.
Key words: binaries: spectroscopic / subdwarfs
Based on observations at the Paranal Observatory of the European Southern Observatory for programme number 081.D-0819. Based on observations at the La Silla Observatory of the European Southern Observatory for programme number 082.D-0649. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). Based on observations with the William Herschel Telescope operated by the Isaac Newton Group at the Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias on the island of La Palma, Spain.
Tables 2–4 and Appendix A are available in electronic form at http://www.aanda.org
© ESO, 2011