Is β Pictoris b the transiting planet of November 1981?

¹ CNRS, UMR 7095, Institut d'Astrophysique de Paris, 98 boulevard Arago, 75014 Paris, France e-mail: lecaveli@iap.fr
² UPMC Univ. Paris 6, UMR 7095, Institut d'Astrophysique de Paris, 98 boulevard Arago, 75014 Paris, France

Received: 16 December 2008
Accepted: 8 January 2009

Abstract


In 1981, β Pictoris showed strong and rapid photometric variations that were attributed to the transit of a giant comet or a planet orbiting at several AUs. 
Recently, a candidate planet has been identified by imagery in the circumstellar disk of β Pictoris.
This planet, named β Pic b, is observed at a projected distance of 8 AU from the central star. It is therefore a plausible candidate for the photometric event observed in 1981. The coincidence of the observed position of the planet in November 2003 and the calculated position assuming that the 1981 transit is due to a planet orbiting at 8 AU is intriguing. Assuming that the planet that is detected on the image is the same as the object transiting in November 1981, we estimate ranges of possible orbital distances and periods. In the favored scenario, the planet orbits at ~8 AU and was seen close to its quadrature position in the 2003 images. In this case, most of the uncertainties are related to error bars on the position in 2003. Uncertainties related to the stellar mass and orbital eccentricity are also discussed. We find a semi-major axis in the range [7.6–8.7] AU and an orbital period in the range [15.9–19.5] years. We give predictions for imaging observations at quadrature in the southwest branch of the disk in future years (2011–2015). We also estimate possible dates for the next transits and anti-transits.