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

Derekas, Aliz and Németh, Péter and Southworth, J. and Borkovits, Tamás and Sárneczky, Krisztián and Pál, András and Csák, Balázs and Kiss, L. László and Vida, Krisztián and Szabó M., Gyula and Kriskovics, Levente (2015) A new sdO+dM binary with extreme eclipses and reflection effect. ASTROPHYSICAL JOURNAL, 808 (2). ISSN 1538-4357

Preview

Text 1505.06487.pdf Available under License Creative Commons Attribution. Download (710kB) | Preview

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.

Actions (login required)

Edit Item