Precise predictions of stellar occultations by Pluto , Charon , Nix and Hydra for 2008 - 2015 , ⋆ , ⋆ ⋆ , ⋆ ⋆ ⋆ , †

Context. Investigation of transneptunian objects, including Pluto and its satellites, by stellar occultations. Aims. Derive precise, astrometric predictions for stellar occultations by Pluto and its satellites Charon, Hydra and Nix for 2008–2015. Construct an astrometric star catalog in the UCAC2 system covering Plutos sky path. Methods. We have carried out in 2007 an observational program at the ESO2p2/WFI instrument covering the sky path of Pluto from 2008 to 2015. Astrometry of 110 GB of images was made by using the Platform for Reduction of Astronomical Images Automatically (PRAIA). By relatively simple astrometric techniques, we have treated the overlapping observations and derived a Field Distortion Pattern for the WFI mosaic of CCDs to within 50 mas precision. Results. Positions were obtained in the UCAC2 frame with errors of 50 mas for stars up to magnitude R = 19, and 25 mas up to R = 17. New stellar proper motions were also determined using 2MASS and USNO B1.0 catalog positions as first epoch. We have generated 2252 predictions of stellar occultations by Pluto, Charon, Hydra and Nix for 2008–2015. An astrometric catalog with proper motions was produced, containing 2.24 million stars covering Plutos sky path with 30 width. Its magnitude completeness is about R = 18–19 with limit about R = 21. Based on past 2005–2008 occultations successfully predicted, recorded and fitted, a linear drift with time in declination with regard to DE418/plu017 ephemerides was determined for Pluto and used in the current predictions. For offset (mas) = A∗( t(yr)−2005.0 )+B, we find A = +30.5 ±4.3 mas yr and B = −31.5 ±11.3 mas, with standard deviation of 14.4 mas for the offsets. For these past occultations, prediction and follow up observations were made with the 0.6m and 1.6m telescopes at the Laboratório Nacional de Astrof́ısica/Brazil. Conclusions. Here, recurrent issues in stellar occultation predictions were addressed and properly overcome: body ephemeris offsets, catalog zero-point position errors and Field-of-View size, long term predictions and stellar proper motions, faint-visual versus bright-infrared stars, star/body astrometric follow up. In particular, we highlight the usefulness of the obtained astrometric catalog as a reference frame for star/body astrometric follow up before and after future events involving the Pluto system. Besides, it also furnishes useful photometric information for field stars in the flux calibration of observed light curves. Updates on the ephemeris offsets and candidate star positions (geometric conditions of predictions and finding charts) are made available in a continuous basis by the group at http://www.lesia.obspm.fr/perso/bruno-sicardy/.