Abstract
Aims. The aims of our study are to improve the orbital elements of the giant and to derive the spectroscopic orbit for the white dwarf companion of the symbiotic system RS Oph. Spectral variations related to the 2006 outburst are also studied. Methods. We performed an analysis of about seventy optical and near infrared spectra of RS Oph that were acquired between 1998 and June 2008. The spectroscopic orbits were obtained by measuring the radial velocities of the cool component absorption lines and the broad Hα emission wings, which seem to be associated with the hot component. A set of cF-type absorption lines were also analyzed for a possible connection with the hot component motion. Results. A new period of 453.6 days and a mass ratio, q = M g /M h = 0.59 ± 0.05 were determined. Assuming a massive white dwarf as the hot component (M h = 1.2-1.4 M ⊙ ) the red giant mass is Mg = 0.68-0.80 M ⊙ and the orbit inclination, i = 49°-52°. The cF-type lines are not associated with either binary component, and are most likely formed in the material streaming towards the hot component. We also confirm the presence of the LiI doublet in RS Oph and its radial velocities fit very well to the M-giant radial velocity curve. Regardless of the mechanism involved to produce lithium, its origin is most likely from within the cool giant rather than material captured by the giant at the time of the nova explosion. The quiescent spectra reveal a correlation of the H I and He I emission line fluxes with the monochromatic magnitudes at 4800 A, indicating that the hot component activity is responsible for those flux variations. We also discuss the spectral characteristics around 54-55 and 240 days after the 2006 outburst. In April 2006 most of the emission lines present a broad pedestal with a strong and narrow component at about -20 km s -1 and two other extended emission components at -200 and +150 km s -1 . These components could originate in a bipolar gas outflow supporting the model of a bipolar shock-heated shell expanding through the cool component wind perpendicularly to the binary orbital plane. Our observations also indicate that the cF absorption system was disrupted during the outburst, and restored about 240 days after the outburst, which is consistent with the resumption of accretion.
Highlights
RS Oph is a recurrent symbiotic nova in which a white dwarf near the Chandrasekhar limit orbits inside the outer wind of a red giant
The most recent outburst began on 2006 February 12 and multifrequency observations confirmed the current model for the outburst in which the massive white dwarf accretes material from the red giant until a thermonuclear runaway ensues and high velocity gas is ejected from the white dwarf
Adopting v sin i = 11.7 ± 1.5 km s−1 (Zamanov et al 2007) and Kg = 17.1 ± 0.6 km s−1 (Table 2) results in qmin = 0.68 ± 0.1. This lower limit is surprisingly close to the mass ratio derived from the radial velocity curves, and indicates that either the giant is filling its Roche lobe (RL) – the actual q should be equal to qmin – or that its measured rotational velocity is faster than the synchronized value
Summary
RS Oph is a recurrent symbiotic nova in which a white dwarf near the Chandrasekhar limit orbits inside the outer wind of a red giant. Dobrzycka & Kenyon (1994, hereafter DK94) continued monitoring the radial velocities of RS Oph during quiescence They separated their echelle spectra into sets of M-type and A-type absorption lines, both of which resulted in a period of 460 days. The Atype radial velocity curve was shifted by 0.37 relative to the M giant solution and it was not associated with the hot component motion They concluded that their results are more reasonable if they only considered the circular orbit of the cool giant. The longer period was in agreement with P = 2283 days given by Oppenheimer & Mattei (1993) but it did not appear in their radial velocity analysis so it could not be associated with the orbital motion.
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