# Pluto's ephemeris from ground-based stellar occultations (1988-2016)

## TL;DR

This paper compiles and analyzes 19 stellar occultation observations of Pluto from 1988 to 2016, using Gaia data to refine Pluto's astrometric positions and update its ephemeris with milliarcsecond accuracy.

## Contribution

It provides a new, highly precise Pluto ephemeris based on occultation data and Gaia star positions, improving orbit predictions for future observations.

## Key findings

- Astrometric positions with 2-10 milliarcsecond accuracy derived from occultations.
- Updated Pluto ephemeris covering 2000-2020 with improved precision.
- Enhanced predictions for future stellar occultations.

## Abstract

From 1988 to 2016, several stellar occultations have been observed to characterize Pluto's atmosphere and its evolution (Meza et al, 2019). 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. We present Pluto's astrometric positions derived from 19 occultations from 1988 to 2016 (11 from Meza et al. (2019) and 8 from other publications). Using Gaia DR2 for the positions of the occulted stars, the accuracy of these positions is estimated to 2-10~milliarcsec depending on the observation circumstances. From these astrometric positions, we derive an updated ephemeris of Pluto's system barycentre using the NIMA code (Desmars et al., 2015). The astrometric positions are derived by fitting the occultation's light curves by a model of Pluto's atmosphere. The fits provide the observed position of the body's centre for a reference star position. Other publications usually provide circumstances of the occultation such as the coordinates of the stations, the timing, and the impact parameter (i.e. the closest distance between the station and the centre of the shadow). From these parameters, we use a procedure based on the Bessel method to derive an astrometric position. 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 milliarcsec level, over the period 2000-2020, allowing better predictions for future stellar occultations.