Scaling slowly rotating asteroids with stellar occultations^★

¹ Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Sloneczna 36, 60-286 Poznań, Poland
e-mail: am@amu.edu.pl
² Astronomical Institute, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 180 00 Prague 8, Czech Republic
³ Mt. Suhora Observatory, Pedagogical University, Podchorążych 2, 30-084 Cracow, Poland
⁴ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network (ELKH), 1121 Budapest, Konkoly Thege Miklós út 15-17, 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, 1117, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁸ Astronomy Department, Eötvös Loránd University, Pázmány P. s. 1/A, 1171 Budapest, Hungary
⁹ Observatorio Nacional, R. Gen. José Cristino 77, Säo Cristövão, 20921-400, Rio de Janeiro, RJ, Brazil
¹⁰ EURASTER, 8 rue du Tonnelier, 46100 Faycelles, France
¹¹ International Occultation Timing Association/European Section, Am Brombeerhag 13, 30459 Hannover, Germany
¹² International Occultation Timing Association (IOTA), PO Box 7152, WA 98042, USA
¹³ Institute of Theoretical Physics and Astronomy, Vilnius University, Saulėtekio al. 3, 10257 Vilnius, Lithuania
¹⁴ Japanese Occultation Information Network, Japan
¹⁵ Geneva Observatory, 1290 Sauverny, Switzerland
¹⁶ Les Engarouines Observatory, 84570 Mallemort-du-Comtat, France
¹⁷ Association T60, Observatoire Midi-Pyrénées, 14 avenue Édouard Belin, 31400 Toulouse, France
¹⁸ Collonges Observatory, 90 allée des Résidences, 74160 Collonges, France
¹⁹ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Toruń, ul. Grudziądzka 5, 87-100 Toruń, Poland
²⁰ Departamento de Sistema Solar, Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
²¹ Observatoire du Bois de Bardon, 16110 Taponnat, France
²² Arecibo Observatory, University of Central Florida, HC-3 Box 53995, Arecibo, PR 00612, USA
²³ Instituto de Astrofisica de Canarias, C/ Via Lactea, s/n, 38205 La Laguna, Tenerife, Spain
²⁴ Gran Telescopio Canarias (GRANTECAN), Cuesta de San José s/n, 38712, Brena Baja, La Palma, Spain
²⁵ Open University, School of Physical Sciences, The Open University, MK7 6AA, UK
²⁶ Trans-Tasman Occultation Alliance (TTOA), Wellington, PO Box 3181, New Zealand
²⁷ Hunters Hill Observatory, 7 Mawalan Street, Ngunnawal, ACT 2913, Australia
²⁸ Space sciences, Technologies and Astrophysics Research Institute, Université de Liège, Allée du Août 4000 Liège, Belgium
²⁹ British Astronomical Association, Burlington House, Piccadilly, Mayfair, London W1J 0DU, UK
³⁰ Institute of Physics, Jan Kochanowski University, ul. Uniwersytecka 7, 25-406 Kielce, Poland
³¹ Chungbuk National University, 1, Chungdae-ro, Seowon-gu, Cheongju-si, Chungcheongbuk-do, Republic of Korea
³² Korea Astronomy and Space Science Institute, 776 Daedeok-daero, Yuseong-gu, Daejeon 34055, Korea
³³ Laboratory of Space Researches, Uzhhorod National University, Daleka st. 2a, 88000, Uzhhorod, Ukraine
³⁴ Departamento de Astrofisica, Universidad de La Laguna - ULL, Tenerife, Spain
³⁵ NASA Johnson Space Center Astronomical Society, Houston, TX 77058, USA
³⁶ Blue Mountains Observatory, 94 Rawson Parade, Leura NSW 2780, Australia
³⁷ Organ Mesa Observatory, 4438 Organ Mesa Loop, Las Cruces, NM 88011, USA
³⁸ Command Module Observatory, 121 W. Alameda Dr., Tempe, AZ 85282, USA
³⁹ Silesian University of Technology, Department of Electronics, Electrical Engineering and Microelectronics, Akademicka 16, 44-100 Gliwice, Poland
⁴⁰ Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA
⁴¹ Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
⁴² Department of Physics, Adiyaman University, 02040 Adiyaman, Turkey
⁴³ Observatory, Vsetínská 78, 757 01 Valašské Meziříčí, Czech Republic
⁴⁴ Kepler Institute of Astronomy, University of Zielona Góra, Lubuska 2, 65-265 Zielona Góra, Poland

Received: 20 February 2023
Accepted: 28 August 2023

Abstract

Context. As evidenced by recent survey results, the majority of asteroids are slow rotators (spin periods longer than 12 h), but lack spin and shape models because of selection bias. This bias is skewing our overall understanding of the spins, shapes, and sizes of asteroids, as well as of their other properties. Also, diameter determinations for large (>60 km) and medium-sized asteroids (between 30 and 60 km) often vary by over 30% for multiple reasons.

Aims. Our long-term project is focused on a few tens of slow rotators with periods of up to 60 h. We aim to obtain their full light curves and reconstruct their spins and shapes. We also precisely scale the models, typically with an accuracy of a few percent.

Methods. We used wide sets of dense light curves for spin and shape reconstructions via light-curve inversion. Precisely scaling them with thermal data was not possible here because of poor infrared datasets: large bodies tend to saturate in WISE mission detectors. Therefore, we recently also launched a special campaign among stellar occultation observers, both in order to scale these models and to verify the shape solutions, often allowing us to break the mirror pole ambiguity.

Results. The presented scheme resulted in shape models for 16 slow rotators, most of them for the first time. Fitting them to chords from stellar occultation timings resolved previous inconsistencies in size determinations. For around half of the targets, this fitting also allowed us to identify a clearly preferred pole solution from the pair of two mirror pole solutions, thus removing the ambiguity inherent to light-curve inversion. We also address the influence of the uncertainty of the shape models on the derived diameters.

Conclusions. Overall, our project has already provided reliable models for around 50 slow rotators. Such well-determined and scaled asteroid shapes will, for example, constitute a solid basis for precise density determinations when coupled with mass information. Spin and shape models in general continue to fill the gaps caused by various biases.