Letter to the Editor

Evidence for a co-moving sub-stellar companion of GQ Lup

¹ Astrophysikalisches Institut, Universität Jena, Schillergäßchen 2-3, 07745 Jena, Germany e-mail: rne@astro.uni-jena.de
² Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
³ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany

Received: 6 October 2004
Accepted: 27 March 2005

Abstract

We present a companion of the ≤2 Myr young classical T Tauri star GQ Lup in the Lupus star forming region at  pc from imaging, astrometry, and spectroscopy. With direct K-band imaging using VLT/NACO, we detected an object 6 mag fainter than GQ Lup located west of it. Compared to images obtained 2 to 5 years earlier with Subaru/CIAO and HST/PC, this object shares the proper motion of GQ Lup by 5 and , respectively, hence it is a co-moving companion. Its color is consistent with a spectral type early to mid L. Our NACO K-band spectrum yields spectral type M9-L4 with H₂O and CO absorption, consistent with the new GAIA-Dusty template spectrum for to 3 and  K with ~2 R_jup radius at ∼140 pc, hence few Jupiter masses. Using the theoretical models from Wuchterl & Tscharnuter (2003), Burrows et al. (1997), and Baraffe et al. (2002), the mass lies between 1 and 42 Jupiter masses.