Letter to the Editor

First stellar occultation by the Galilean moon Europa and upcoming events between 2019 and 2021

¹ Observatório Nacional/MCTIC, R. General José Cristino 77, Rio de Janeiro 20921-400, Brazil
e-mail: morgado.fis@gmail.com
² Laboratório Interinstitucional de e-Astronomia - LIneA & INCT do e-Universo, Rua Gal. José Cristino 77, Rio de Janeiro 20921-400, Brazil
³ Observatório do Valongo/UFRJ, Ladeira Pedro Antonio 43, Rio de Janeiro 20080-090, Brazil
⁴ UNESP – São Paulo State University, 12516-410 Guaratinguetá, São Paulo, Brazil
⁵ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, USA
⁶ IMCCE, Observatoire de Paris, PSL Research University, CNRS-UMR 8028, Sorbonne Universités, UPMC, Univ. Lille 1, 77 Av. Denfert-Rochereau, 75014 Paris, France
⁷ Federal University of Technology – Paraná (UTFPR/DAFIS), Av. Sete de Setembro, 3165, CEP 80230-901 Paraná, Brazil
⁸ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
⁹ San Pedro de Atacama Celestial Explorations, Casilla 21, San Pedro de Atacama, Chile
¹⁰ Unioeste, Avenida Tarquínio Joslin dos Santos 1300, Foz do Iguaçu 85870-650 Paraná, Brazil
¹¹ Polo Astronômico Casimiro Montenegro Filho/FPTI-BR, Avenida Tancredo Neves 6731, Foz do Iguaçu 85867-900 Paraná, Brazil
¹² Observatório SONEAR, Brazil
¹³ Dogsheaven Observatory, SMPW Q25 CJ1 LT10B Brasilia, Brazil
¹⁴ Research Center of Astronomy, Francisco J. Duarte (CIDA). 264, 5101-A Mérida, Venezuela
¹⁵ Instituto de Física/UFRGS, Porto Alegre 91501-970, Brazil

Received: 20 March 2019
Accepted: 24 May 2019

Abstract

Context. Bright stellar positions are now known with an uncertainty below 1 mas thanks to Gaia DR2. Between 2019–2020, the Galactic plane will be the background of Jupiter. The dense stellar background will lead to an increase in the number of occultations, while the Gaia DR2 catalogue will reduce the prediction uncertainties for the shadow path.

Aims. We observed a stellar occultation by the Galilean moon Europa (J2) and propose a campaign for observing stellar occultations for all Galilean moons.

Methods. During a predicted period of time, we measured the light flux of the occulted star and the object to determine the time when the flux dropped with respect to one or more reference stars, and the time that it rose again for each observational station. The chords obtained from these observations allowed us to determine apparent sizes, oblatness, and positions with kilometre accuracy.

Results. We present results obtained from the first stellar occultation by the Galilean moon Europa observed on 2017 March 31. The apparent fitted ellipse presents an equivalent radius of 1561.2 ± 3.6 km and oblatenesses 0.0010 ± 0.0028. A very precise Europa position was determined with an uncertainty of 0.8 mas. We also present prospects for a campaign to observe the future events that will occur between 2019 and 2021 for all Galilean moons.

Conclusions. Stellar occultation is a suitable technique for obtaining physical parameters and highly accurate positions of bright satellites close to their primary. A number of successful events can render the 3D shapes of the Galilean moons with high accuracy. We encourage the observational community (amateurs included) to observe the future predicted events.