Asteroid sizes determined with thermophysical model and stellar occultations

¹ Astronomical Observatory Institute, Faculty of Physics and Astronomy, Adam Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
² Astronomical Institute, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 80 00 Prague 8, Czech Republic
³ Mt. Suhora Observatory, University of the National Education Commission, Podchorążych 2, 30-084 Cracow, Poland
⁴ Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, Konkoly Thege Miklós út 15–17, 1121 Budapest, Hungary
⁵ CSFK, MTA Centre of Excellence, Budapest, Konkoly Thege Miklós út 15–17, 1121 Hungary
⁶ MTA CSFK Lendület Near-Field Cosmology Research Group, Hungary
⁷ ELTE Eötvös Loránd University, Institute of Physics and Astronomy, 1117, Pázmány Péter sétány 1/A, Budapest, Hungary
⁸ Astronomy Department, Eötvös Loránd University, Pázmány P. s. 1/A, 1171 Budapest, Hungary
⁹ Observatório Nacional, R. Gen. José Cristino 77, São Cristóvão, 20921-400 Rio de Janeiro, RJ, Brazil
¹⁰ Grupo de Dinâmica Orbital e Planetologia, São Paulo State University, UNESP, Guaratinguetá, CEP 12516-410, São Paulo, Brazil
¹¹ International Occultation Timing Association/European Section e.V. (IOTA/ES), Am Brombeerhag 13, 30459 Hannover, Germany
¹² International Occultation Timing Association (IOTA) PO Box 20313 Fountain Hills, AZ 85269-0313, USA
¹³ Association T60, Observatoire Midi-Pyrénées, 14, avenue Edouard Belin, 31400 Toulouse, France
¹⁴ Korea Astronomy and Space Science Institute, 776 Daedeok-daero, Yuseong-gu, Daejeon 34055, Korea
¹⁵ Centro Astronónomico Hispano en Andalucía, Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Spain
¹⁶ MTA-ELTE Lendület “Momentum” Milky Way Research Group, Hungary
¹⁷ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹⁸ Maastricht University, Maastricht Science Programme, Maastricht, The Netherlands
¹⁹ Observatoire du Bois de Bardon, 16110 Taponnat, France
²⁰ Florida Space Institute, University of Central Florida, Orlando, FL, USA
²¹ Trans-Tasman Occultation Alliance (TTOA), Wellington, PO Box 3181, New Zealand
²² Instituto de Astrofísica de Canarias, C/ Vía Lactea, s/n, 38205 La Laguna, Tenerife, Spain
²³ Gran Telescopio Canarias (GRANTECAN), Cuesta de San José s/n, 38712, Breña Baja, La Palma, Spain
²⁴ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Toruń, ul. Grudziądzka 5, 87-100 Toruń, Poland
²⁵ Open University, School of Physical Sciences, The Open University, MK7 6AA, UK
²⁶ Hunters Hill Observatory, 7 Mawalan Street, Ngunnawal, ACT 2913, Australia
²⁷ Space sciences, Technologies and Astrophysics Research Institute, Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium
²⁸ British Astronomical Association, PO Box 702, Tonbridge TN9 9TX, UK
²⁹ Institute of Physics, Jan Kochanowski University, ul. Uniwersytecka 7, 25-406 Kielce, Poland
³⁰ Akdeniz University, Department of Space Sciences and Technologies, Antalya, Türkiye
³¹ Chungbuk National University, 1, Chungdae-ro, Seowon-gu, Cheongju-si, Chungcheongbuk-do, Republic of Korea
³² Czech Astronomical Society, Fričova 298, 251 65 Ondřejov, Czech Republic
³³ Observatory in Rokycany and Pilsen, p.o., Voldušská 721, 33701 Rokycany, Czech Republic
³⁴ Laboratory of Space Researches, Uzhhorod National University, Daleka st. 2a, 88000 Uzhhorod, Ukraine
³⁵ Observatoire de Nandrin, Société Astronomique de Liège, 17 Avenue des Platanes, 4000 Liège, Belgium
³⁶ Departamento de Astrofísica, Universidad de La Laguna – ULL, 38205 Tenerife, Spain
³⁷ NASA Johnson Space Center Astronomical Society, Houston, TX, USA
³⁸ Janusz Gil Institute of Astronomy, University of Zielona Góra, Szafrana 2, 65-516 Zielona Góra, Poland
³⁹ Japan Occultation Information Network (JOIN), Japan
⁴⁰ B-PHOT, Building F, Pleinlaan 2, 1050 Elsene, Brussels, Belgium
⁴¹ Blue Mountains Observatory, 94 Rawson Parade, Leura, NSW 2780, Australia
⁴² Institute of Theoretical Physics and Astronomy, Vilnius University, Saulėtekio al. 3, 10257 Vilnius, Lithuania
⁴³ Organ Mesa Observatory, 4438 Organ Mesa Loop, Las Cruces, NM 88011, USA
⁴⁴ Command Module Observatory, 121 W. Alameda Dr., Tempe, AZ 85282, USA
⁴⁵ Silesian University of Technology, Department of Electronics, Electrical Engineering and Microelectronics, Akademicka 16, 44-100 Gliwice, Poland
⁴⁶ Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
⁴⁷ Osservatorio Astronomico Via Nastro Verde 50, 80067, Sorrento (Na), Italy
⁴⁸ Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Carr. de San Vicente del Raspeig, s/n, 03690 San Vicente del Raspeig, Alicante, Spain
⁴⁹ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Carrer de Martí i Franquès, 1, 08028 Barcelona, Spain
⁵⁰ Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ, 86001 USA
⁵¹ Department of Physics, Adiyaman University, 02040 Adiyaman, Türkiye
⁵² Astrophysics Application and Research Center, Adıyaman University, Adiyaman 02040, Türkiye
⁵³ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁵⁴ Japan Spaceguard Association, Bisei Spaceguard Center, 1716-3, Okura, Bisei, Ibara, Okayama 714-1411 Japan
⁵⁵ Observatory, Vsetínská 78, Valašské Meziříčí, Czech Republic
⁵⁶ Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Cracow, Poland

^★ Corresponding author: antoine.choukroun@amu.edu.pl

Received: 11 March 2025
Accepted: 17 April 2025

Abstract

Context. The sizes of many asteroids, especially slowly rotating, low-amplitude targets, remain poorly constrained due to selection effects. These biases limit the availability of high-quality data, leaving size estimates reliant on spherical shape assumptions. Such approximations introduce significant uncertainties propagating, for example, into density determinations or thermophysical and compositional studies, affecting our understanding of asteroid properties.

Aims. This work targets poorly studied main-belt asteroids, for most of which no shape models were previously available. Using only high-quality, dense light curves, thermal infrared observations (systematically including WISE data), and stellar occultations, we aimed to produce reliable shape models and scale them using two independent techniques, allowing for size comparison at the end. We conducted two observing campaigns to achieve this: one to obtain dense photometric light curves and another to acquire multi-chord stellar occultations by these objects.

Methods. Shape and spin models were reconstructed using light curve inversion techniques. Sizes were determined via two methods: (1) advanced thermophysical modelling using the convex inversion thermophysical model (CITPM), which optimises spin and shape models to light curve data in the visible range together with infrared data, and (2) scaling the shape models with stellar occultations.

Results. We obtained precise sizes and shape models for 15 asteroids. CITPM and occultation-derived sizes agree within 5% for most cases, demonstrating the reliability of the modelling approach. Larger discrepancies are usually linked to incomplete occultation chord coverage. The study also provides insights into surface properties, including albedo, surface roughness and thermal inertia.

Conclusions. The use of high-quality data, coupled with an advanced TPM that uses both thermal and visible data while allowing the shape model to be adjusted according to both types of data, enabled us to determine sizes with precision comparable to those derived from multichord stellar occultations. We resolved substantial inconsistencies in previous size determinations for target asteroids, providing good input for future studies on asteroid densities and surface properties.