UNSPECIFIED (2006) Subdwarf B binaries in the Edinburgh-Cape survey. In: 2nd Meeting on Hot Subdwarf Stars and Related Objects, JUN 06-10, 2005, Santa Cruz de la Palma, SPAIN.

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Abstract

We give an update of the results of a campaign to obtain orbital solutions of subdwarf B stars from the Edinburgh-Cape survey (Stobie et al. 1997). To date we have obtained blue spectra of 40 subdwarf B stars from the Edinburgh-Cape catalogue using the grating spectrograph at the 1.9 m Radcliffe telescope at the South African Astronomical Observatory. We find that 17 out of these 40 are certain binaries with a few other objects showing radial velocity variations of small amplitude. The binary fraction found in our sample, after correcting for our binary detection efficiency, is 48%. We have secured the orbital parameters for 4 of the 17 systems and narrowed down the orbits of another 7 to a small range of periods. Out of the four subdwarf B binaries for which we have determined the orbital solution, three have orbital periods that, according to population synthesis studies by Han et al. (2003), suggest they have been formed via a common envelope ejection channel. The masses of the companions, assuming a canonical mass of 0.5 M-circle dot for the subdwarf B star, suggest that they are probably white dwarfs. We observed the shortest period binary (3 h) of the three, to search for indications of modulation in the lightcurve due to irradiation of the companion by the subdwarf B star. No indications of reflection effect were found confirming that the companion is indeed a white dwarf. The fourth system with measured orbital parameters shows an orbital period that could correspond to a subdwarf B binary formed either via the common envelope ejection channel or the stable Roche Lobe overflow channel. The aim of the this study: to obtain an independent, statistically significant sample of subdwarf B binaries, with solved orbits, based purely upon the Edinburgh-Cape survey to avoid the uncertain biases of the Palomar-Green and other surveys, is underway.

Item Type:	Conference Item (UNSPECIFIED)
Subjects:	Q Science > QB Astronomy
Journal or Publication Title:	BALTIC ASTRONOMY
Publisher:	INST THEORETICAL PHYSICS ASTRONOMY
ISSN:	1392-0049
Date:	2006
Volume:	15
Number:	2
Number of Pages:	4
Page Range:	pp. 187-190
Publication Status:	Published
Title of Event:	2nd Meeting on Hot Subdwarf Stars and Related Objects
Location of Event:	Santa Cruz de la Palma, SPAIN
Date(s) of Event:	JUN 06-10, 2005
URI:	http://wrap.warwick.ac.uk/id/eprint/33637

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