Astronomy & Astrophysics

Free access article

A&A 368, 994-1005 (2001)
DOI: 10.1051/0004-6361:20010068

Physical parameters of sdB stars from spectral energy distributions

R. Aznar Cuadrado and C. S. Jeffery

Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
e-mail: csj@star.arm.ac.uk

(Received 21 July 2000 / Accepted 4 January 2001 )

Abstract
The atmospheric parameters of 34 hot subdwarf B stars have been obtained using a combination of 61 short and long-wave IUE spectra, together with new and existing optical and infrared photometric data. Using a grid of high-gravity helium-deficient model atmospheres and a $\chi^{2}$ -minimization procedure, 15 single sdB stars and 19 composite systems, containing a hot subdwarf B star and a cool main-sequence companion, were analyzed. From the ( ${\rm log} L$ - ${\rm log} T_{\rm eff}$ ) diagram of our results, we conclude that the majority of the cool companions to our sample of binary sdB stars are main sequence stars, in the range of 4000 < T_eff / K< 6000 and mass 0.8 < M/ $M_{\odot} < 1.3$ . The lower limit on detectability of cool stars in composite sdB of our sample is ~3600 K, corresponding to a spectral type of M1 or later (Lang 1992).

Key words: stars: formation, early-type, subdwarfs, fundamental parameters (luminosities, temperatures) -- binaries: spectroscopic

Offprint request: R. Aznar Cuadrado, rea@star.arm.ac.uk

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