Letters to the Editor

High angular resolution detection of β Pictoris b at 2.18 μm^⋆

¹ UJF-Grenoble 1 / CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble 38041, France
² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: bonnefoy@mpia-hd.mpg.de
³ LESIA, Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon, France
⁴ Space Telescope Science Institute, 3700 San Martin Drive Baltimore, MD 21218, USA
⁵ Centre de Recherche Astronomique de Lyon, 46 allée d’Italie, 69364 Lyon Cedex 7, France
⁶ European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁷ European Southern Observatory, Karl Schwarzschild St 2, 85748 Garching, Germany

Received: 29 November 2010
Accepted: 25 January 2011

Abstract

Context. A giant planet was recently discovered around the young star β Pictoris. This planet is the closest to its parent star ever imaged. With an estimated mass of about 9 M_Jup and separation of 8–15 AU, it explains most of the peculiarities of β Pictoris  and its disk.

Aims. Previous detections were made in the L′ band (3.8 μm) and at 4.05 μm. We recorded new K_s-band data (2.18 μm) in order to measure its color and get an additional estimate of its mass and effective temperature

Methods. Angular differential K_s-band images of β Pictoris were recorded with NaCo in March and April 2010.

Results. The companion is detected at K_s. This independently confirms the physical nature of β Pictoris b inferred from the L′ and NB_4.05 bands. The increase of the projected separation between October–December 2009 and April 2010 observations is consistent within error bars with the expected orbital motion. Using the absolute K_s photometry, “hot start” evolutionary models predict a mass of 7–11 M_Jup in agreement with previous estimates. Moreover, this mass is compatible with T_eff = 1700 ± 300 K derived from the comparison of the K_s − L′ color with those generated using synthetic spectra.