Pluto’s ephemeris from ground-based stellar occultations (1988–2016)

¹ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
e-mail: josselin.desmars@obspm.fr
² Observatório do Valongo/UFRJ, Ladeira Pedro Antonio 43, Rio de Janeiro, RJ 20080-090, Brazil
³ Observatório Nacional/MCTIC, Laboratório Interinstitucional de e-Astronomia-LIneA and INCT do e-Universo, Rua General José Cristino 77, Rio de Janeiro 20921-400, Brazil
⁴ Federal University of Technology – Paraná (UTFPR/DAFIS), Rua Sete de Setembro 3165, 80230-901 Curitiba, Brazil
⁵ Escola SESC de Ensino Médio, Avenida Ayrton Senna 5677, Rio de Janeiro, RJ 22775-004, Brazil
⁶ UNESP – São Paulo State University, Grupo de Dinâmica Orbital e Planetologia, 12516-410 Guaratinguetá, Brazil
⁷ Geneva Observatory, 1290 Sauverny, Switzerland
⁸ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain

Received: 21 December 2018
Accepted: 8 March 2019

Abstract

Context. From 1988 to 2016, several stellar occultations have been observed to characterise Pluto’s atmosphere and its evolution. From each stellar occultation, an accurate astrometric position of Pluto at the observation epoch is derived. These positions mainly depend on the position of the occulted star and the precision of the timing.

Aims. We present 19 Pluto’s astrometric positions derived from occultations from 1988 to 2016. Using Gaia DR2 for the positions of the occulted stars, the accuracy of these positions is estimated at 2−10 mas, depending on the observation circumstances. From these astrometric positions, we derive an updated ephemeris of Pluto’s system barycentre using the NIMA code.

Methods. The astrometric positions were derived by fitting the light curves of the occultation by a model of Pluto’s atmosphere. The fits provide the observed position of the centre for a reference star position. In most cases other publications provided the circumstances of the occultation such as the coordinates of the stations, timing, and impact parameter, i.e. the closest distance between the station and centre of the shadow. From these parameters, we used a procedure based on the Bessel method to derive an astrometric position.

Results. We derive accurate Pluto’s astrometric positions from 1988 to 2016. These positions are used to refine the orbit of Pluto’system barycentre providing an ephemeris, accurate to the milliarcsecond level, over the period 2000−2020, allowing for better predictions for future stellar occultations.