Astronomy and Astrophysics – Astrophysics
Scientific paper
2002-02-08
Mon.Not.Roy.Astron.Soc. 333 (2002) 231
Astronomy and Astrophysics
Astrophysics
Accepted for publication in MNRAS
Scientific paper
10.1046/j.1365-8711.2002.05406.x
We present lightcurves of four binary subdwarf B stars, Ton 245, Feige 11, PG1432+159 and PG1017-086. We also present new spectroscopic data for PG1017-086 from which we derive its orbital period, P=0.073d, and the mass function, f_m = 0.0010 +/- 0.0002 solar masses. This is the shortest period for an sdB binary measured to-date. The values of P and f_m for the other sdB binaries have been published elsewhere. We are able to exclude the possibility that the unseen companion stars to Ton 245, Feige 11 and PG1432+159 are main-sequence stars or sub-giant stars from the absence of a sinusoidal signal which would be caused by the irradiation of such a companion star, i.e., they show no reflection effect. The unseen companion stars in these binaries are likely to be white dwarf stars. By contrast, the reflection effect in PG1017-086 is clearly seen. The lack of eclipses in this binary combined with other data suggests that the companion is a low mass M-dwarf or, perhaps, a brown dwarf.
Heber Uli
Lawson Warrick A.
Marsh Thomas R.
Maxted Pierre F. L.
Morales-Rueda Luisa
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