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Near-infrared integral-field spectroscopy of the companion to GQ Lupi
Context: The first substellar companion of possibly planetary massaround a normal star, GQ Lup, has been directly imaged (Neuhäuseret al. 2005, A&A, 435, L13). Besides the unknown formation history,the mass of such an object is a criterion to decide about its truenature. Aims: We aim to determine the physical properties of the GQ Lupcompanion - effective temperate (T_eff) and surface gravity (log{g}),and thus its mass independently from evolutionary models. Methods: Weuse the adaptive optics integral-field spectrograph SINFONI at the VLTfor near-infrared spectroscopy from 1.1 to 2.5 μm with a resolutionof R = 2500-4000. We compare these spectra with synthetic atmosphericmodels (GAIA v2.0 cond). Results: From the complete set of spectra wefind a consistent effective temperature and surface gravity of T_eff =2650 ± 100 K and log{g} = 3.7 ± 0.5 dex. Combined with aslightly revised luminosity of log{L/Lȯ} = -2.25± 0.24 dex for the companion, we determine a radius of R =3.50+1.50-1.03 {R_Jup} and thus a mass of 25{M_Jup}. The uncertainty of this value is rather high. Due to the largeuncertainty of the surface gravity, the mass could range from 4 to 155{M_Jup}. By comparing the paramaters of the companion of GQ Lup to theones of 2MASS J05352184-0546085, published by Stassunet al. (2006, Nature, 440, 311), we conclude that the companion to GQLup A has a mass lower than 36 ± 3 {M_Jup}.Based on observations collected at the European Southern Observatory,Chile, in programmes 275.C-5033(A) and 077.C-0264(A).
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