Metallicity and effective temperature of the secondary of RS Ophiuchi

¹ Astrophysics Group, Keele University, Keele, Staffordshire, ST5 5BG, UK e-mail: ae@astro.keele.ac.uk
² Main Astronomical Observatory of the National Academy of Sciences of Ukraine, 27 Zabolonnoho, Kyiv-127, 03680, Ukraine e-mail: [yp;yakovina]@mao.kiev.ua
³ Joint Astronomy Centre, 660 N. A'ohoku Place, University Park, Hilo, Hawaii 96720, USA e-mail: tkerr@jach.hawaii.edu
⁴ Department of Astronomy, 116 Church St. SE, University of Minnesota, Minneapolis, MN 55455, USA e-mail: chelsea@astro.umn.edu
⁵ The Aerospace Corporation, Mail Stop M2-266, PO Box 92957, Los Angeles, CA 90009-29957, USA e-mail: [David.K.Lynch;Richard.J.Rudy;Richard.L.Pearson;Ray.W.Russell]@aero.org
⁶ Department of Astronomy, Brigham Young University, N283 ESC, Provo, UT 84602, USA

Received: 6 September 2007
Accepted: 16 April 2008

Abstract

Context. The recurrent nova RS Ophiuchi undergoes nova eruptions every ~10-20 years as a result of thermonuclear runaway on the surface of a white dwarf close to the Chandrasekhar limit. Both the progress of the eruption and its aftermath depend on the (poorly known) composition of the red giant in the RS Oph system.

Aims. Our aim is to understand better the effect of the giant secondary on the recurrent nova eruption.

Methods. Synthetic spectra were computed for a grid of M-giant model atmospheres having a range of effective temperatures 3200 < T_eff < 4400 K, gravities 0 < log g < 1 and abundances -4 < [Fe/H] < 0.5, and fit to infrared spectra of RS Oph as it returned to quiescence after its 2006 eruption. We have modelled the infrared spectrum in the range 1.4-2.5m  to determine metallicity and effective temperature of the red giant.

Results. We find T_eff = 4100 ± 100 K, log g = 0.0 ± 0.5, [Fe/H] = 0.0 ± 0.5, [C/H] = -0.8 ± 0.2, [N/H] = +0.6 ± 0.3 in the atmosphere of the secondary, and demonstrate that inclusion of some dust “veiling” in the spectra cannot improve our fits.