Letter to the Editor

3D simulations of RS Ophiuchi: from accretion to nova blast ^*,**

¹ Observatoire de Genève, Université de Genève, 51 ch. des Maillettes, 1290 Sauvernay, Switzerland e-mail: walder@astro.phys.ethz.ch
² Institute for Astronomy, ETH Zürich, ETH-Zentrum, SEC D2, 8092 Zürich, Switzerland e-mail: folini@astro.phys.ethz.ch
³ Dipartimento di Fisica “Enrico Fermi”, Università di Pisa, largo Pontecorvo 3, Pisa 56127, Italy e-mail: shore@df.unipi.it
⁴ INFN/Pisa, largo Pontecorvo 3, Pisa 56127, Italy

Received: 3 March 2008
Accepted: 15 April 2008

Abstract

Context. The binary star system RS Ophiuchi is a recurrent nova, with outbursts occurring about every 22 years. It consists of a red giant star (RG) and a wind accreting white dwarf close to the Chandrasekhar limit. This system is considered a prime candidate for evolving into an SNIa. For its most recent outbursts in 1985 and 2006, exquisite multiwavelength observational data are available.

Aims. Deeper physical insight is needed regarding the inter-outburst accretion phase and the dynamical effects of the subsequent nova explosion in order to improve the interpretation of the observed data and to shed light on whether the system is an SNIa progenitor.

Methods. We present a 3D hydrodynamic simulation of the quiescent accretion with the subsequent explosive phase.

Results. The computed circumstellar mass distribution in the quiescent phase is highly structured with a mass enhancement in the orbital plane of about a factor of 2 as compared to the poleward directions. The simulated nova remnant evolves aspherically, propagating faster toward the poles. The shock velocities derived from the simulations agree with those derived from observations. For  km s^-1 and for nearly isothermal flows, we find that 10% of the mass lost by the RG is transfered to the WD. For an RG mass loss of  yr^-1, the orbit of the system decays by 3% per million years. With the derived mass transfer rate, multi-cycle nova models provide a qualitatively correct recurrence time, amplitude, and fastness of the nova.

Conclusions. Our 3D hydrodynamic simulations provide, along with the observations and nova models, the third ingredient for a deeper understanding of the recurrent novae of the RS Oph type. In combination with recent multi-cycle nova models, our results suggest that the WD in RS Oph will increase in mass. Several speculative outcomes then seem plausible. The WD may reach the Chandrasekhar limit and explode as an SN Ia. Alternatively, the mass loss of the RG could result in a smaller Roch volume, a common envelope phase, and a narrow WD + WD system. Angular momentum loss due to gravitational wave emission could trigger the merger of the two WDs and – perhaps – an SN Ia via the double degenerate scenario.