Publication Date:
2013-02-28
Description:
We announce the discovery of a new eclipsing hot subdwarf B + M dwarf binary, EC 10246–2707, and present multicolour photometric and spectroscopic observations of this system. Similar to other HW Vir-type binaries, the light curve shows both primary and secondary eclipses, along with a strong reflection effect from the M dwarf; no intrinsic light contribution is detected from the cool companion. The orbital period is 0.118 507 9936 ± 0.000 000 0009 d, or about 3 h. Analysis of our time series spectroscopy reveals a velocity semi-amplitude of K 1 = 71.6 ± 1.7 km s –1 for the sdB and best-fitting atmospheric parameters of T eff = 28 900 ± 500 K, log g = 5.64 ± 0.06 and log N (He)/ N (H) = –2.5 ± 0.2. Although we cannot claim a unique solution from modelling the light curve, the best-fitting model has an sdB mass of 0.45 M and a cool companion mass of 0.12 M . These results are roughly consistent with a canonical-mass sdB and M dwarf separated by a ~ 0.84 R . We find no evidence of pulsations in the light curve and limit the amplitude of rapid photometric oscillations to 〈0.08 per cent. Using 15 yr of eclipse timings, we construct an observed minus calculated (O – C) diagram but find no statistically significant period changes; we rule out $|\dot{P}| 〉 7.2 \times 10^{-12}$ . If EC 10246–2707 evolves into a cataclysmic variable, its period should fall below the famous cataclysmic variable period gap.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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