A&A 506, 927-934 (2009)
DOI: 10.1051/0004-6361/200912098

Constraining the orbit of the possible companion to  Pictoris

New deep imaging observations

A.-M. Lagrange¹, M. Kasper², A. Boccaletti³, G. Chauvin¹, D. Gratadour³, T. Fusco⁴, D. Ehrenreich¹, D. Apai⁵, D. Mouillet¹, and D. Rouan<sup>3

1</sup>  Laboratoire d'Astrophysique de l'Observatoire de Grenoble, Université Joseph Fourier, CNRS (UMR 5571), BP 53, 38041 Grenoble, France,
    e-mail: anne-marie.lagrange@obs.ujf-grenoble.fr
²  European Southern Observatory, Karl Schwarzschild Straße, 2, 85748 Garching bei München, Germany
³  Laboratoire d'Études Spatiales et d'Instrumentation en Astrophysique, Observatoire de Paris, CNRS (UMR 8109), Université Pierre et Marie Curie, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France
⁴  Office National d'Études et de Recherches Aérospatiales, 29 avenue de la Division Leclerc, 92322 Châtillon, France
⁵  Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

Received 18 March 2009/ Accepted 9 June 2009

Abstract
Context. We recently reported on the detection of a possible planetary mass companion to  Pictoris at a projected separation of 8 AU from the star, using data taken in November 2003 with NaCo, the adaptive-optics system installed on the Very Large Telescope UT4. Even though no second epoch detection was available, there are strong arguments to favor a gravitationally bound companion rather than a background object. If confirmed and located at a physical separation of 8 AU, this companion would be the closest planet ever imaged, and above all, could have formed via core-accretion. Its apparent magnitude would indicate a typical temperature of ~1500 K and a mass of ~8 M_Jup. Interestingly, a planet with such characteristics would explain the main morphological and dynamical peculiarities of the  Pic system.
Aims. Our goal was to re-observe  Pic five years later to again detect the companion or, in the case of a non-detection, constrain its orbit.
Methods. Deep adaptive-optics L'-band direct images of  Pic  as well as K_s-band Four Quadrant Phase Mask coronagraph images with were recorded with NaCo.
Results. No point-like signal with the brightness of the companion candidate (apparent magnitudes L' = 11.2 or K_s 12.5) was detected at projected distances down to 6.5 AU in the present data from the star (by comparison, the same limit was reached at 5.5 AU in the better quality November 2003 data). As expected, the non detection does not allow us to rule out a background companion from an observational point of view. We show that the non detection is consistent with orbital motion. Using these data and previous -band data obtained in 2004, we place strong constraints on the possible orbits of the companion.

Key words: instrumentation: adaptive optics -- stars: early-type -- stars: planetary systems -- stars: individual:  Pictoris

© ESO 2009

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