Astronomy and Astrophysics in the Gaia sky Proceedings IAU Symposium No. 330, 2017 A. Recio-Blanco, P. de Laverny, A.G.A. Brown & T. Prusti, eds. c  International Astronomical Union 2018 doi:10.1017/S1743921317006226 Prediction of stellar occultations by distant solar system bodies in the Gaia era Josselin Desmars 1 , Julio Camargo 2,5 , Bruno Sicardy 1 , Felipe Braga-Ribas 3,2,5 , Roberto Vieira-Martins 2,5 , Marcelo Assafin 4 , Diane B´ erard 1 and Gustavo Benedetti-Rossi 5 1 LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universit´ es, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cit´ e, 5 place Jules Janssen, 92195 Meudon, France, email: josselin.desmars@obspm.fr 2 Observat´ orio Nacional/MCT, R. General Jos´ e Cristino 77, RJ 20921-400 Rio de Janeiro, Brazil 3 Federal University of Technology-Paran´ a (UTFPR/DAFIS), Rua Sete de Setembro, 3165, CEP 80230-901, Curitiba, PR, Brazil 4 Observat´ orio do Valongo/UFRJ, Ladeira Pedro Antonio 43, RJ 20.080-090 Rio de Janeiro, Brazil 5 Laborat´ orio Interinstitucional de e-Astronomia - LIneA, Rua Gal. Jos´ e Cristino 77, Rio de Janeiro- RJ 20921-400, Brazil Abstract. Stellar occultations are a unique technique to access physical characteristics of distant solar system objects from the ground. They allow the measure of the size and the shape at kilometric level, the detection of tenuous atmospheres (few nanobars), and the investigation of close vicinity (satellites, rings) of Transneptunian objects and Centaurs. This technique is made successful thanks to accurate predictions of occultations. Accuracy of the predictions depends on the uncertainty in the position of the occulted star and the object’s orbit. The Gaia stellar catalogue (Gaia Collaboration (2017)) now allows to get accurate astrometric stellar positions (to the mas level). The main uncertainty remains on the orbit. In this context, we now take advantage of the NIMA method (Desmars et al.(2015)) for the orbit determination and of the Gaia DR1 catalogue for the astrometry. In this document, we show how the orbit determination is improved by reducing current and some past observations with Gaia DR1. Moreover, we also use more than 45 past positive occultations observed in the 2009-2017 period to derive very accurate astrometric positions only depending on the position of the occulted stars (about few mas with Gaia DR1). We use the case of (10199) Chariklo as an illustration. The main limitation lies in the imprecision of the proper motions which is going to be solved by the Gaia DR2 release. Keywords. Kuiper Belt, catalogs, astrometry, ephemerides, occultations. 1. Introduction Stellar occultations are a unique technique to access physical characteristics of distant solar system objects from the ground: size and shape at the kilometric level, tenuous atmospheres at few nanobars, and investigation of close vicinity (satellites, rings). This technique is successful thanks to accurate predictions of occultations depending on the precision of star’s position and the object’s orbit. Predictions of occultations by distant bodies is a difficult challenge. Indeed, good predictions require both accurate positions of the star and the body. As the objects are distant (from 15 to 90 au) and small in size (100-2000 km), the apparent size of the body is about 10 to 50 mas. A precision to the same level or less is required for good predictions. In comparison, 30 mas is equivalent to a coin of 1 euro seen at 200 km. 382 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921317006226 Downloaded from https://www.cambridge.org/core. IP address: 181.215.217.69, on 22 Apr 2020 at 04:37:33, subject to the Cambridge Core terms of use, available at