The geometry of the close environment of SV Piscium as probed by VLTI/MIDI^⋆

¹ Department of AstrophysicsUniversity of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
e-mail: daniela.klotz@univie.ac.at
² Department of Physics and Astronomy, Division of Astronomy and Space Physics, Uppsala University, Box 516, 75120 Uppsala, Sweden
³ Onsala Space Observatory, Dept. of Earth and Space Sciences, Chalmers University of Technology, 43992 Onsala, Sweden

Received: 18 October 2011
Accepted: 17 April 2012

Abstract

Context. SV Psc is an asymptotic giant branch (AGB) star surrounded by an oxygen-rich dust envelope. The mm-CO line profile of the object’s outflow shows a clear double-component structure. Because of the high angular resolution, mid-IR interferometry may give strong constraints on the origin of this composite profile.

Aims. The aim of this work is to investigate the morphology of the environment around SV Psc using high-angular resolution interferometry observations in the mid-IR with the Very Large Telescope MID-infrared Interferometric instrument (VLTI/MIDI).

Methods. Interferometric data in the N-band taken at different baseline lengths (ranging from 32–64 m) and position angles (73–142°) allow a study of the morphology of the circumstellar environment close to the star. The data are interpreted on the basis of 2-dimensional, chromatic geometrical models using the fitting software tool GEM-FIND developed for this purpose.

Results. The results favor two scenarios: (i) the presence of a highly inclined, optically thin, dusty disk surrounding the central star; (ii) the presence of an unresolved binary companion at a separation of 13.7^+4.2_-4.8 AU and a position angle of 121.8°^+15.4°_-24.5° NE. The derived orbital period of the binary is 38.1^+20.4_-22.6 yr. This detection is in good agreement with hydrodynamic simulations showing that a close companion could be responsible for the entrainment of the gas and dust into a circumbinary structure.