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

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.

13 pages, 5 figures; accepted for publication in ApJ

References in corpus (9)

• New Grids of ATLAS9 Model Atmospheres
• Survival of a brown dwarf after engulfment by a red giant star
• A selection of hot subluminous stars in the GALEX survey II. Subdwarf atmospheric parameters
• Eclipse Timing Variation Analyses of Eccentric Binaries with Close Tertiaries in the Kepler field
• Hot subdwarfs from the ESO Supernova Ia Progenitor Survey: II. Atmospheric parameters of subdwarf O stars
• Dynamical masses, absolute radii and 3D orbits of the triply eclipsing star HD 181068 from Kepler photometry
• New binaries among UV-selected, hot subdwarf stars and population properties
• HD 183648: a Kepler eclipsing binary with anomalous ellipsoidal variations and a pulsating component
• The physical structure of planetary nebulae around sdO stars: Abell36, DeHt2, and RWT152

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