Letter to the Editor

The two rings of (50000) Quaoar

¹ Observatório Nacional/MCTI, R. General José Cristino 77, CEP 20921-400 Rio de Janeiro, RJ, Brazil
e-mail: chrystianpereira@on.br
² Laboratório Interinstitucional de e-Astronomia – LIneA, Rio de Janeiro, RJ, Brazil
³ LESIA, Observatoire de Paris, Université PSL, Sorbonne Université, Université de Paris, CNRS, 92190 Meudon, France
⁴ Universidade Federal do Rio de Janeiro – Observatório do Valongo, Ladeira Pedro Antônio 43, CEP 20.080-090 Rio de Janeiro, RJ, Brazil
⁵ Federal University of Technology – Paraná (UTFPR-Curitiba), Rua Sete de Setembro, 3165, CEP 80230-901 Curitiba, PR, Brazil
⁶ Florida Space Institute, UCF, 12354 Research Parkway, Partnership 1 Building, Room 211, Orlando FL, USA
⁷ Instituto de Astrofísica de Andalucía – Consejo Superior de Investigaciones Científicas, Glorieta de la Astronomía S/N, 18008 Granada, Spain
⁸ Departments of Astronomy, and of Earth and Planetary Science, 501, Campbell Hall, University of California, Berkeley, CA 94720, USA
⁹ naXys, Department of Mathematics, University of Namur, Rue de Bruxelles 61, 5000 Namur, Belgium
¹⁰ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
¹¹ Space Telescope Science Institute, Baltimore MD, USA
¹² Aix Marseille Université, CNRS, CNES, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
¹³ Canada-France-Hawaii Telescope, 65-1238 Mamalahoa Highway, Kamuela, HI 96743, USA
¹⁴ Institut Polytechnique des Sciences Avancées IPSA, 63 boulevard de Brandebourg, 94200 Ivry-sur-Seine, France
¹⁵ 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, France
¹⁶ Akdeniz University, Faculty of Sciences, Department of Space Sciences and Technologies, 07058 Antalya, Turkey
¹⁷ TÜBİTAK National Observatory, Akdeniz University Campus, 07058 Antalya, Turkey
¹⁸ Institute of Physics, Federal University of Uberlândia, Uberlândia-MG, Brazil
¹⁹ UNESP – São Paulo State University, Grupo de Dinâmica Orbital e Planetologia, CEP 12516-410, Guaratinguetá, SP, Brazil
²⁰ Universidade Estadual de Ponta Grossa, O.A. – DEGEO, Ponta Grossa, PR, Brazil
²¹ Internationale Amateursternwarte (IAS) e. V., Mittelstr. 6, 15749 Mittenwalde, Germany
²² International Occultation Timing Association – European Section (IOTA/ES), Am Brombeerhag 13, 30459 Hannover, Germany
²³ Département de Physique and Observatoire du Mont-Mégantic, Université de Montréal, C.P. 6128, Succ. Centre-ville, Montréal, H3C 3J7 Québec, Canada
²⁴ Institut Trottier de Recherche sur les exoplanètes, Université de Montréal, Montreal, Canada
²⁵ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
²⁶ Gemini Observatory/NSF’s NOIRLab, Hilo HI, USA
²⁷ Cabrillo College Astronomy, Aptos, CA, USA
²⁸ Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA
²⁹ International Occultation Timing Association (IOTA), Topeka, KS, USA
³⁰ California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, USA
³¹ Universidad Nacional Autónoma de México, Instituto de Astronomía, AP 106, Ensenada, 22800 BC, Mexico
³² University of Oregon, Eugene, OR, USA
³³ CanCON – Canadian Collaborative Occultation Network, Canada
³⁴ NASA Ames Research Center, Moffett Field, California, USA & NASA Exoplanet Science Institute, Caltech/IPAC, Mail Code 100-22, Pasadena, CA, USA
³⁵ University of New Haven, Dept. of Mathematics and Physics, 300 Boston Post Road, West Haven, CT 06477, USA
³⁶ Academia Sinica Institute of Astronomy and Astrophysics, 11F of AS/NTU Astronomy-Mathematics Building, No.1, Sec. 4, Roosevelt Road Taipei 10617, Taiwan, ROC
³⁷ University of Colorado, 2000 Colorado Avenue, Boulder, CO 80309, USA
³⁸ Planetary Plasma and Atmospheric Research Center, Graduate School of Science, Tohoku University, 6-3 Aramaki -aza-aoba, Aoba-ku, Sendai 980-8578, Japan
³⁹ Department of Physics and Astronomy, University of Victoria, Building, 3800 Finnerty Road, Victoria, BC V8P 5C2, Canada
⁴⁰ Unistellar, 5 allée Marcel Leclerc, bâtiment B, 13008 Marseille, France
⁴¹ SETI Institute, Carl Sagan Center, Suite 200, 339 Bernardo Avenue, Mountain View, CA 94043, USA
⁴² Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA
⁴³ Research and Education Collaborative Occultation Network, USA
⁴⁴ Purdue University Northwest, Department of Chemistry and Physics, Hammond, IN, USA
⁴⁵ University of Virginia, Department of Astronomy, PO Box 400325 Charlottesville, VA 22904, USA
⁴⁶ Private Observatory, PA, USA
⁴⁷ Instituto de Astrofísica de Canarias, University of La Laguna, Tenerife, Spain
⁴⁸ Dept. Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
⁴⁹ School of Medicine Department of Basic Sciences University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahata, Kitakyusyu 807-8555, Japan
⁵⁰ Planetary Exploration Research Center, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan
⁵¹ Naylor Observatory, Lewisberry, PA, USA

Received: 9 March 2023
Accepted: 17 April 2023

Abstract

Context. Quaoar is a classical trans-Neptunian object (TNO) with an area-equivalent diameter of 1100 km and an orbital semi-major axis of 43.3 astronomical units. Based on stellar occultations observed between 2018 and 2021, an inhomogeneous ring (Q1R, i.e., Quaoar’s first ring) has been detected around this body.

Aims. A new stellar occultation by Quaoar was observed on August 9, 2022, with the aim of improving Quaoar’s shape models and the physical parameters of Q1R, while searching for additional material around the body.

Methods. The occultation provided nine effective chords across Quaoar, pinning down its size, shape, and astrometric position. Large facilities, such as Gemini North and the Canada-France-Hawaii Telescope (CFHT), were used to obtain high acquisition rates and signal-to-noise ratios. The light curves were also used to characterize the Q1R ring (radial profiles and orbital elements).

Results. Quaoar’s elliptical fit to the occultation chords yields the limb with an apparent semi-major axis of 579.5 ± 4.0 km, apparent oblateness of 0.12 ± 0.01, and area-equivalent radius of 543 ± 2 km. Quaoar’s limb orientation is consistent with Q1R and Weywot orbiting in Quaoar’s equatorial plane. The orbital radius of Q1R is refined to a value of 4057 ± 6 km. The radial opacity profile of the more opaque ring profile follows a Lorentzian shape that extends over 60 km, with a full width at half maximum (FWHM) of ∼5 km and a peak normal optical depth of 0.4. Besides the secondary events related to the already reported rings, new secondary events detected during the August 2022 occultation in three different data sets are consistent with another ring around Quaoar with a radius of 2520 ± 20 km, assuming the ring is circular and co-planar with Q1R. This new ring has a typical width of 10 km and a normal optical depth of ∼0.004. Just as Q1R, it also lies outside Quaoar’s classical Roche limit.