GG Tauri: the fifth element ^{⋆,⋆⋆,⋆⋆⋆}

¹ Univ. Bordeaux, Laboratoire d’Astrophysique de Bordeaux, UMR 5804, 33270 Floirac, France
e-mail: emmanuel.difolco@obs.u-bordeaux1.fr
² CNRS, LAB, UMR 5804, 33270 Floirac, France
³ UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble UMR 5274, 38041 Grenoble, France
⁴ LESIA, CNRS/UMR-8109, Observatoire de Paris, UPMC, Université Paris Diderot, 5 place J. Janssen, 92195 Meudon, France
⁵ European Southern Observatory, 85748 Garching by München, Germany
⁶ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁷ IRAM, 300 rue de la piscine, 38406 Saint-Martin d’Hères, France
⁸ Department of Physics and Astronomy, Colgate University, 13 Oak Drive, Hamilton, NY 13346, USA
⁹ Space Telescope Science Institute, 3700 San Martin Dr. Baltimore, MD 21218, USA
e-mail: tbeck@stsci.edu; lubow@stsci.edu
¹⁰ Laboratoire AIM, CEA/DSM - CNRS - Université Paris Diderot, IRFU/SAP, 91191 Gif-sur-Yvette, France

Received: 19 February 2014
Accepted: 8 March 2014

Abstract

We aim at unveiling the observational imprint of physical mechanisms that govern planetary formation in young, multiple systems. In particular, we investigate the impact of tidal truncation on the inner circumstellar disks. We observed the emblematic system GG Tau at high-angular resolution: a hierarchical quadruple system composed of low-mass T Tauri binary stars surrounded by a well studied, massive circumbinary disk in Keplerian rotation. We used the near-IR 4-telescope combiner PIONIER on the VLTI and sparse-aperture-masking techniques on VLT/NaCo to probe this proto-planetary system at sub-au scales. We report the discovery of a significant closure-phase signal in H and K_s bands that can be reproduced with an additional low-mass companion orbiting GG Tau Ab, at a (projected) separation ρ = 31.7 ± 0.2 mas (4.4 au) and PA = 219.6 ± 0.3°. This finding offers a simple explanation for several key questions in this system, including the missing-stellar-mass problem and the asymmetry of continuum emission from the inner dust disks observed at millimeter wavelengths. Composed of now five co-eval stars with 0.02 ≤ M_⋆ ≤ 0.7 M_⊙, the quintuple system GG Tau has become an ideal test case to constrain stellar evolution models at young ages (few 10⁶ yr).