The multichord stellar occultation on 2019 October 22 by the trans-Neptunian object (84922) 2003 VS₂^★

¹ Instituto de Astrofísica de Andalucía - Consejo Superior de Investigaciones Científicas, Glorieta de la Astronomía S/N, 18008 Granada, Spain
e-mail: mvara@iaa.es
² LESIA, Observatoire de Paris, Université PSL, Sorbonne Université, Université de Paris, CNRS, 92190 Meudon, France
³ Laboratório Interinstitucional de e-Astronomia - LIneA & INCT do e-Universo, Rua Gal. José Cristino 77, Bairro Imperial de São Cristóvão, Rio de Janeiro (RJ), Brazil
⁴ UNESP - São Paulo State University, Grupo de Dinámica Orbital e Planetologia, Guaratinguetá, SP 12516-410, Brazil
⁵ Astronomical Institute of the Romanian Academy, 5 Cu¸itul de Argint, 040557 Bucharest, Romania
⁶ Instituto de Astrofísica de Canarias (IAC), C/Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁷ Observatório Nacional/MCTI, Rio de Janeiro (RJ), Brazil, Rua Gal. José Cristino 77, Bairro Imperial de São Cristóvão, Rio de Janeiro (RJ), Brazil
⁸ Florida Space Institute, UCF, 12354 Research Parkway, Partnership 1 building, Room 211, Orlando, USA
⁹ naXys, University of Namur, 8 Rempart de la Vierge, Namur 5000, Belgium
¹⁰ Department of astronomy, Faculty of Mathematics, University of Belgrade, Studentski trg 16, 11000 Belgrade, Serbia
¹¹ Humboldt Research Fellow, Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
¹² Astronomical Observatory, Volgina 7, 11000 Belgrade, Serbia
¹³ Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, Sofia, Bulgaria
¹⁴ ROASTERR-1 Observatory, L04 Cluj Napoca, Romania
¹⁵ Stardust Observatory, L13 Brasov, Romania
¹⁶ Astroclubul Bucureşti, Bucharest, Romania
¹⁷ Stardreams Observatory, L16 Vălenii de Monte, Romania
¹⁸ Romanian Academy - Cluj-Napoca Branch, Astronomical Observatory Cluj-Napoca, Romania
¹⁹ University of Craiova, Craiova, Romania
²⁰ Institutul de Stiinte Spatiale (ISS), Atomistilor 409, C.P.: 23 Magurele 077125, Ilfov, Romania
²¹ Societatea Română pentru Astronomie Culturală (SRPAC), Timisoara, Romania
²² Federal University of Technology - Paraná (UTFPR/DAFIS), Curitiba, Brazil
²³ Institut Polytechnique des Sciences Avancées IPSA, 63 boulevard de Brandebourg, 94200 Ivry-sur-Seine, France
²⁴ Institut de Mécanique Céleste et de Calcul des Éphémérides, IMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ Paris 06, Univ. Lille, 77 Av. Denfert-Rochereau, 75014 Paris, France
²⁵ Universidade Federal do Rio de Janeiro, Observatorio do Valongo, Rio de Janeiro, Brazil
²⁶ Astronomical Institute of the Slovak Academy of Sciences, 059 60 Tatranska Lomnica, Slovakia
²⁷ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, 1121 Budapest, Konkoly Thege Miklos ut 15-17, Hungary
²⁸ Osservatorio Astrofísico di Catania (OACt-INAF), Via S. Sofia 78, 95123 Catania, Italy
²⁹ ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, Szombathely, Hungary
³⁰ MTA-ELTE Exoplanet Research Group, 9700 Szombathely, Szent Imre h. u. 112, Hungary
³¹ Mt. Suhora Observatory, Pedagogical University of Cracow Limanowa County, Poland
³² Isaac Newton Group of Telescopes, Santa Cruz de La Palma, Spain
³³ Osservatorio Astronomico di Monte Agliale, Via Cune Motrone, Borgo a Mozzano, Italy
³⁴ PDlink Observatory, Cadca, Slovakia
³⁵ INAF - Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34143 Trieste, Italy
³⁶ Gruppo Astrofili Massesi, EAON, Massa, Italy
³⁷ International Occultation Timing Association - European Section (IOTA/ES), Germany
³⁸ Ia cu Stele, Bucharest, Romania
³⁹ Crni Vrh Observatory, Crni Vrh nad Idrijo, Slovenia
⁴⁰ Faculty of Mathematics and Physics, University of Ljubljana, Slovenia
⁴¹ Dark Sky Slovenia, Savlje 89, 1000 Ljubljana, Slovenia

Received: 21 July 2021
Accepted: 7 April 2022

Abstract

Context. Stellar occultations have become one of the best techniques to gather information about the physical properties of trans-Neptunian objects (TNOs), which are critical objects for understanding the origin and evolution of our Solar System.

Aims. The purpose of this work is to determine, with better accuracy, the physical characteristics of the TNO (84922) 2003 VS₂ through the analysis of the multichord stellar occultation on 2019 October 22 and photometric data collected afterward.

Methods. We predicted, observed, and analyzed the multichord stellar occultation of the Second Gaia Data Release (Gaia DR2) source 3449076721168026624 (m_υ = 14.1 mag) by the plutino object 2003 VS₂ on 2019 October 22. We performed aperture photometry on the images collected and derived the times when the star disappeared and reappeared from the observing sites that reported a positive detection. We fit the extremities of such positive chords to an ellipse using a Monte Carlo method. We also carried out photometric observations to derive the rotational light curve amplitude and rotational phase of 2003 VS2 during the stellar occultation. Combining the results and assuming a triaxial shape, we derived the 3D shape of 2003 VS2.

Results. Out of the 39 observatories involved in the observational campaign, 12 sites, located in Bulgaria (one), Romania (ten), and Serbia (one), reported a positive detection; this makes it one of the best observed stellar occultations by a TNO so far. Considering the rotational phase of 2003 VS₂ during the stellar occultation and the rotational light curve amplitude derived (Am = 0.264 ± 0.017 mag), we obtained a mean area-equivalent diameter of D_Aeq = 545 ± 13 km and a geometric albedo of 0.134 ± 0.010. By combining the rotational light curve information with the stellar occultation results, we derived the best triaxial shape for 2003 VS2, which has semiaxes a = 339 ± 5 km, b = 235 ± 6 km, and c = 226 ± 8 km. The derived aspect angle of 2003 VS₂ is θ = 59^° ± 2^° or its supplementary θ = 121^° ± 2^°, depending on the north-pole position of the TNO. The spherical-volume equivalent diameter is D_Veq = 524 ± 7 km. If we consider large albedo patches on its surface, the semi-major axis of the ellipsoid could be ~ 10 km smaller. These results are compatible with the previous ones determined from the single-chord 2013 and four-chord 2014 stellar occultations and with the effective diameter and albedo derived from Herschel and Spitzer data. They provide evidence that 2003 VS₂’s 3D shape is not compatible with a homogeneous triaxial body in hydrostatic equilibrium, but it might be a differentiated body and/or might be sustaining some stress. No secondary features related to rings or material orbiting around 2003 VS2 were detected.