Letters to the Editor

First astronomical unit scale image of the GW Orionis triple system

Direct detection of a new stellar companion

¹ European Southern Observatory, Alonso de Cordova 3107 Vitacura, Casilla 19001, Santiago de Chile 19, Chile
e-mail: jpberger@eso.org
² IPAG, CNRS/UMR 5571, Université J. Fourier, BP-53, 38041 Grenoble Cedex, France
³ University of Michigan, 941 Dennison Building, 500 Church Street, Ann Arbor, MI 48109-1090.e, USA
⁴ California Institute of Technology, 770 S. Wilson Ave. MS 100-22 Pasadena, CA 91125, USA
⁵ University of St. Andrews, Scotland, UK
⁶ JPL, California Institute of Technology, M/S 301-355, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
⁷ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁸ Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁹ CEA-DRT-LETI, 17 rue des Martyrs, 38054 Grenoble, France
¹⁰ W. M. Keck Observatory, 65-1120 Mamalahoa Hwy, Kamuela, HI 96743, USA
¹¹ University of Massachusetts, Department of Astronomy, Amherst, MA 01003 4610, USA
¹² IAS, CNRS/UMR 8617, Université Paris-Sud, 91405 Orsay, France
¹³ CRAL Observatoire de Lyon 9 avenue Charles André, 69561 Saint Genis Laval, France

Received: 27 November 2010
Accepted: 1 March 2011

Abstract

Context. Young and close multiple systems are unique laboratories to probe the initial dynamical interactions between forming stellar systems and their dust and gas environment. Their study is a key building block to understanding the high frequency of main-sequence multiple systems. However, the number of detected spectroscopic young multiple systems that allow dynamical studies is limited. GW Orionis is one such system. It is one of the brightest young T Tauri stars and is surrounded by a massive disk.

Aims. Our goal is to probe the GW Orionis multiplicity at angular scales at which we can spatially resolve the orbit.

Methods. We used the IOTA/IONIC3 interferometer to probe the environment of GW Orionis with an astronomical unit resolution in 2003, 2004, and 2005. By measuring squared visibilities and closure phases with a good UV coverage we carry out the first image reconstruction of GW Ori from infrared long-baseline interferometry.

Results.We obtained the first infrared image of a T Tauri multiple system with astronomical unit resolution. We show that GW Orionis is a triple system, resolve for the first time the previously known inner pair (separation ρ ~ 1.4 AU) and reveal a new more distant component (GW Ori C) with a projected separation of  ~ 8 AU with direct evidence of motion. Furthermore, the nearly equal (2:1) H-band flux ratio of the inner components suggests that either GW Ori B is undergoing a preferential accretion event that increases its disk luminosity or that the estimate of the masses has to be revisited in favour of a more equal mass-ratio system that is seen at lower inclination.

Conclusions. Accretion disk models of GW Ori will need to be completely reconsidered because of this outer companion C and the unexpected brightness of companion B.