Astronomy & Astrophysics

Free access article

A&A 464, 119-126 (2007)
DOI: 10.1051/0004-6361:20066609

AMBER/VLTI interferometric observations of the recurrent Nova RS Ophiuchii 5.5 days after outburst

O. Chesneau¹, N. Nardetto^{1, 2}, F. Millour^{3, 4}, C. Hummel⁵, A. Domiciano de Souza³, D. Bonneau¹, M. Vannier^{5, 6}, F. Rantakyrö⁵, A. Spang¹, F. Malbet⁴, D. Mourard¹, M. F. Bode⁷, T. J. O'Brien⁸, G. Skinner⁹, R. G. Petrov³, P. Stee¹, E. Tatulli¹⁰, and F. Vakili³

¹ Laboratoire Gemini, UMR 6203 Observatoire de la Côte d'Azur/CNRS, BP 4229, 06304 Nice Cedex 4, France
e-mail: Olivier.Chesneau@obs-azur.fr
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Laboratoire Universitaire d'Astrophysique de Nice, UMR 6525 Université de Nice - Sophia Antipolis/CNRS, Parc Valrose, 06108 Nice Cedex 2, France
⁴ Laboratoire d'Astrophysique de Grenoble, UMR 5571 Université Joseph Fourier/CNRS, BP 53, 38041 Grenoble Cedex 9, France
⁵ European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁶ Departamento de Astronomia, Universidad de Chile, Chile
⁷ Astrophysics Research Institute, Liverpool John Moores University, Birkenhead, CH41 1LD, UK
⁸ Jodrell Bank Observatory, School of Physics and Astronomy, Univ. of Manchester, Macclesfield, SK11 9DL, UK
⁹ CESR, 31028 Toulouse, France and Univ. P. Sabatier, 31062 Toulouse, France
¹⁰ INAF - Osservatorio Astrofisico di Arcetri, Istituto Nazionale di Astrofisica, Largo E. Fermi 5, 50125 Firenze, Italy

(Received 20 October 2006 / Accepted 13 November 2006 )

Abstract
Aims.We report on spectrally dispersed interferometric AMBER/VLTI observations of the recurrent nova RS Oph five days after the discovery of its outburst on 2006 Feb. 12.
Methods.Using three baselines ranging from 44 to 86 m, and a spectral resolution of $\lambda/\delta\lambda=1500$ , we measured the extension of the milliarcsecond-scale emission in the K band continuum and in the Br $\gamma$ and He I $2.06~\mu$ m lines, allowing us to get an insight into the kinematics of the line forming regions. The continuum visibilities were interpreted by fitting simple geometric models consisting of uniform and Gaussian ellipses, ring and binary models. The visibilities and differential phases in the Br $\gamma$ line were interpreted using skewed ring models aiming to perform a limited parametric reconstruction of the extension and kinematics of the line forming region.
Results.The limited uv coverage does not allow discrimination between filled models (uniform or Gaussian ellipses) and rings. Binary models are discarded because the measured closure phase in the continuum is close to zero. The visibilities in the lines are at a low level compared to their nearby continuum, consistent with a more extended line forming region for He I $2.06~\mu$ m than Br $\gamma$ . The ellipse models for the continuum and for the lines are highly flattened ( $b/a\sim0.6$ ) and share the same position angle ( ${\rm PA}\sim140^{\circ}$ ). Their typical Gaussian extensions are $3.1\times1.9~{\rm mas}$ , $4.9\times2.9~{\rm mas}$ and $6.3\times3.6~{\rm mas}$ for the continuum, Br $\gamma$ and He I $2.06~\mu$ m lines, respectively. Two radial velocity fields are apparent in the Br $\gamma$ line: a slow expanding ring-like structure ( $v_{\rm rad}\leq1800~{\rm km\,s}^$ ), and a fast structure extended in the E-W direction ( $v_{\rm rad}\sim 2500{-}3000~{\rm km\,s}^$ ), a direction that coincides with the jet-like structure seen in the radio. These results confirm the basic fireball model, contrary to the conclusions of other interferometric observations conducted by Monnier et al. (2006a, ApJ, 647, L127).

Key words: techniques: interferometric -- techniques: high angular resolution -- stars: novae, cataclysmic variables -- stars: individual: RS Oph -- stars: circumstellar matter -- stars: mass-loss