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arXiv · 1505.06487

A new sdO+dM binary with extreme eclipses and reflection effect

A. Derekas·P. Nemeth·J. Southworth·T. Borkovits·K. Sarneczky·A. Pal·B. Csak·D. Garcia-Alvarez·P. F. L. Maxted·L. L. Kiss·K. Vida·Gy. M. Szabo·L. Kriskovics
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Abstract

We report the discovery of a new totally-eclipsing binary (RA=06:40:29.11; Dec=+38:56:52.2; J=2000.0; Rmax=17.2 mag) with an sdO primary and a strongly irradiated red dwarf companion. It has an orbital period of Porb=0.187284394(11) d and an optical eclipse depth in excess of 5 magnitudes. We obtained two low-resolution classification spectra with GTC/OSIRIS and ten medium-resolution spectra with WHT/ISIS to constrain the properties of the binary members. The spectra are dominated by H Balmer and He II absorption lines from the sdO star, and phase-dependent emission lines from the irradiated companion. A combined spectroscopic and light curve analysis implies a hot subdwarf temperature of Teff(spec) = 55 000 +/- 3000K, surface gravity of log g(phot) = 6.2 +/- 0.04 (cgs) and a He abundance of log(nHe/nH) = -2.24 +/- 0.40. The hot sdO star irradiates the red-dwarf companion, heating its substellar point to about 22 500K. Surface parameters for the companion are difficult to constrain from the currently available data: the most remarkable features are the strong H Balmer and C II-III lines in emission. Radial velocity estimates are consistent with the sdO+dM classification. The photometric data do not show any indication of sdO pulsations with amplitudes greater than 7mmag, and Halpha-filter images do not provide evidence of the presence of a planetary nebula associated with the sdO star.

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A. Derekas, P. Nemeth, J. Southworth, T. Borkovits, K. Sarneczky, A. Pal, B. Csak, D. Garcia-Alvarez, P. F. L. Maxted, L. L. Kiss, K. Vida, Gy. M. Szabo, L. Kriskovics. 2015-05-24. A new sdO+dM binary with extreme eclipses and reflection effect. https://doi.org/10.1088/0004-637x%2F808%2F2%2F179

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