Physical properties of the trans-Neptunian object (38628) Huya from a multi-chord stellar occultation

¹ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 - Granada, Spain
e-mail: psantos@iaa.es
² LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, France
³ Astronomical Institute of the Romanian Academy, 5 Cuţitul de Argint, 040557 Bucharest, Romania
⁴ Instituto de Astrofísica de Canarias (IAC), C/Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁵ 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
⁶ UNESP – São Paulo State University, Grupo de Dinãmica Orbital e Planetologia, Guaratinguetá, SP 12516-410, Brazil
⁷ Observatório Nacional/MCTI, Rua Gal. José Cristino 77, Bairro Imperial de São Cristóvão, Rio de Janeiro (RJ), Brazil
⁸ Universidade Federal do Rio de Janeiro – Observatório do Valongo, Ladeira Pedro Antônio 43, CEP 20.080-090 Rio de Janeiro, RJ, Brazil
⁹ Institut Polytechnique des Sciences Avancées IPSA, 63 boulevard de Brandebourg, 94200 Ivry-sur-Seine, France
¹⁰ Institut de Mécanique Céleste et de Calcul des Éphémérides, IMCCE, Observatoire de Paris, PLS Research University, CNRS, Sorbonne Universités, UPMC Univ Paris 06, Univ. Lille, 77 Av. Denfert-Rochereau, 75014 Paris, France
¹¹ Federal University of Technology – Paraná (UTFPR/Curitiba), Brazil
¹² Florida Space Institute, University of Central Florida, Orlando, FL, USA
¹³ ISTEK Belde Observatory, Turkey
¹⁴ Department of Astronomy and Space Sciences, University of Ege, Turkey
¹⁵ Faculty of Physics, University of Bucharest, 405, Atomistilor Street, 077125 Magurele, Ilfov, Romania
¹⁶ Ataturk University, Astrophysics Research & Application Center (ATASAM), 25240 Erzurum, Turkey
¹⁷ Akdeniz University, Faculty of Sciences, Department of Space Sciences and Technologies, 07058 Antalya, Turkey
¹⁸ TÜBITAK National Observatory, Akdeniz University Campus, 07058 Antalya, Turkey
¹⁹ School of Physics and Astronomy and Wise Observatory, Tel Aviv University, Israel
²⁰ Department of Astronomy and Space Sciences, Science Faculty, Erciyes University, 38030 Melikgazi, Kayseri, Turkey
²¹ Particle Physics and Astrophysics Department, Weizmann Institute of Science, Israel
²² Astronomical Observatory “Amiral Vasile Urseanu” Bucharest, Romania
²³ Space Sciences and Solar Energy Research and Application Center (UZAYMER), Çukurova University, Adana, Turkey
²⁴ Space Observation and Research Center, Çağ University, Mersin, Turkey
²⁵ Ege University, Faculty of Science, Department of Physics, 35100 Bornova, Izmir, Turkey
²⁶ Ataturk University, Science Faculty, Department of Astronomy & Space Sciences, 25240 Erzurum, Turkey
²⁷ Astronomical Observatory “Victor Anestin” Bacau, Romania
²⁸ Astroclubul Bucurefti, Romania
²⁹ Stardust Observatory, Brasov, Romania
³⁰ St. George Observatory, Ploieşti, Romania
³¹ Ia cu Stele, Romania
³² Stardreams Observatory, Valenii de Munte, Romania
³³ ROASTERR-1 Observatory, Cluj-Napoca, Romania
³⁴ Galaţi Astronomical Observatory, “Răsvan Angheluţă” Museum Complex of Natural Sciences, 6A, Regiment 11 Siret Street, 800340, Galaţi, Romania
³⁵ Tiraspol State University, 5, Ghenadie Iablocikin Street, 2069 Chisinǎu, Republic of Moldova
³⁶ Asociatia Astroclubul Quasar, Romania
³⁷ Romanian Academy, Cluj-Napoca Branch, Astronomical Observatory Cluj-Napoca, Str. Cirefilor, Nr. 19, 400487, Cluj-Napoca, Romania
³⁸ Barlad Observatory, Romania
³⁹ Institute of Astronomy, V.N. Karazin Kharkiv National University, Ukraine
⁴⁰ QOS Observatory, National Space Facilities Control and Test Center, Ukraine
⁴¹ Section of Astrophysics, Astronomy and Mechanics, Department of Physics, National and Kapodistrian University of Athens, 15784 Zografos, Athens, Greece
⁴² Astronomical Observatory of Odessa I.I. Mechnikov National University, Shevchenko Park, Odessa 65014 Ukraine
⁴³ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network (ELKH), 1121 Budapest, Konkoly Thege Miklós út 15–17, Hungary
⁴⁴ ELTE Eötvös Loránd University, Institute of Physics, Budapest Hungary
⁴⁵ Çanakkale Onsekiz Mart University, Faculty of Arts and Sciences, Department of Physics, 17020 Çanakkale, Turkey
⁴⁶ Çanakkale Onsekiz Mart University, Astrophysics Research Center and Ulupinar Observatory, 17020 Çanakkale, Turkey
⁴⁷ Northolt Branch Observatories, UK
⁴⁸ Sainte Marie, La Réunion, France
⁴⁹ Agrupació Astronòmica de Sabadell, Barcelona, Spain
⁵⁰ International Occultation Timing Association–European Section (IOTA-ES), Germany
⁵¹ Almalex Observatory, Leeds, UK
⁵² Les Makes, La Réunion, France
⁵³ Ellinogermaniki Agogi Observatory, Athens, Greece
⁵⁴ Ondokuz Mayis University Observatory, Space Research Center, 55200, Kurupelit, Samsun, Turkey
⁵⁵ Laboratory of Space Researches, Uzhhorod National University, Uzhhorod, Daleka Str., 2A, Uzhhorod, 88000, Ukraine
⁵⁶ Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University, Sloneczna 36,, 60-286 Poznań, Poland
⁵⁷ Mt. Suhora Observatory, Pedagogical University, ul. Podchorazych 2, PL-30-084 Krakow, Poland
⁵⁸ Department of Physics, Faculty of Science and Arts, Inönü University, Malatya, Turkey
⁵⁹ Astronomical Observatory, Institute of Theoretical Physics and Astronomy, Vilnius University, Sauletekio av. 3, 10257 Vilnius, Lithuania
⁶⁰ Janusz Gil Institute of Astronomy, University of Zielona Góra, Prof. Szafrana 2, PL-65-516 Zielona Góra, Poland

Received: 14 June 2021
Accepted: 30 April 2022

Abstract

Context. As part of our international program aimed at obtaining accurate physical properties of trans-Neptunian objects (TNOs), we predicted a stellar occultation by the TNO (38628) Huya of the star Gaia DR2 4352760586390566400 (m_G = 11.5 mag) on March 18, 2019. After an extensive observational campaign geared at obtaining the astrometric data, we updated the prediction and found it favorable to central Europe. Therefore, we mobilized half a hundred of professional and amateur astronomers in this region and the occultation was finally detected by 21 telescopes located at 18 sites in Europe and Asia. This places the Huya event among the best ever observed stellar occultation by a TNO in terms of the number of chords.

Aims. The aim of our work is to determine an accurate size, shape, and geometric albedo for the TNO (38628) Huya by using the observations obtained from a multi-chord stellar occultation. We also aim to provide constraints on the density and other internal properties of this TNO.

Methods. The 21 positive detections of the occultation by Huya allowed us to obtain well-separated chords which permitted us to fit an ellipse for the limb of the body at the moment of the occultation (i.e., the instantaneous limb) with kilometric accuracy.

Results. The projected semi-major and minor axes of the best ellipse fit obtained using the occultation data are (a′, b′) = (217.6 ± 3.5 km, 194.1 ± 6.1 km) with a position angle for the minor axis of P′ = 55.2° ± 9.1. From this fit, the projected area-equivalent diameter is 411.0 ± 7.3 km. This diameter is compatible with the equivalent diameter for Huya obtained from radiometric techniques (D = 406 ± 16 km). From this instantaneous limb, we obtained the geometric albedo for Huya (p_V = 0.079 ± 0.004) and we explored possible three-dimensional shapes and constraints to the mass density for this TNO. We did not detect the satellite of Huya through this occultation, but the presence of rings or debris around Huya was constrained using the occultation data. We also derived an upper limit for a putative Pluto-like global atmosphere of about p_surf = 10 nbar.