Volume 643, November 2020
|Number of page(s)||15|
|Section||Planets and planetary systems|
|Published online||13 November 2020|
A multi-chord stellar occultation by the large trans-Neptunian object (174567) Varda★
LESIA UMR-8109, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité,
5 place Jules Janssen,
2 naXys, University of Namur, Rempart de la Vierge, Namur 5000, Belgium
3 Federal University of Technology – Paraná (UTFPR / DAFIS), Curitiba, Brazil
4 Observatório Nacional/MCTIC, Rio de Janeiro, Brazil
5 Laboratório Interinstitucional de e-Astronomia – LineA, Rua Gal. José Cristino 77, Rio de Janeiro, RJ 20921-400, Brazil
6 Instituto de Astrofísica de Andalucía, IAA-CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
7 Institut Polytechnique des Sciences Avancées IPSA, 63 boulevard de Brandebourg, 94200 Ivry-sur-Seine, France
8 IMCCE-CNRS UMR8028, Observatoire de Paris, PSL Université, Sorbonne Université, 77 Av. Denfert-Rochereau, 75014 Paris, France
9 Université de la Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
10 International Occultation Timing Association (IOTA), PO Box 7152, WA 98042, USA
11 College of Southern Idaho, Idaho, USA
12 NASA Johnson Space Center Astronomical Society, Houston, TX, USA
13 Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder, CO 80302, USA
14 University of Colorado, Boulder, Colorado, USA
15 Observatório do Valongo/UFRJ, Rio de Janeiro, Brazil
16 UNESP – São Paulo State University, Grupo de Dinâmica Orbital e Planetologia, Guaratinguetá, SP 12516-410, Brazil
17 Tangra Observatory (E24), St. Clair, Australia
18 California Polytechnic State University, San Luis Obispo, CA, USA
19 Calipatria High School, Calipatria, CA, USA
20 Euraster, 1 rue du tonnelier, 46100 Faycelles, France
21 Jimginny Observatory (W08), Naperville, IL, USA
22 Universidade Estadual de Ponta Grossa (UEPG), Ponta Grossa, Brazil
Accepted: 22 July 2020
Context. We present results from the first recorded stellar occultation by the large trans-Neptunian object (174567) Varda that was observed on September 10, 2018. Varda belongs to the high-inclination dynamically excited population, and has a satellite, Ilmarë, which is half the size of Varda.
Aims. We determine the size and albedo of Varda and constrain its 3D shape and density.
Methods. Thirteen different sites in the USA monitored the event, five of which detected an occultation by the main body. A best-fitting ellipse to the occultation chords provides the instantaneous limb of the body, from which the geometric albedo is computed. The size and shape of Varda are evaluated, and its bulk density is constrained using Varda’s mass as is known from previous works.
Results. The best-fitting elliptical limb has semi-major (equatorial) axis of (383 ± 3) km and an apparent oblateness of 0.066 ± 0.047, corresponding to an apparent area-equivalent radius R′equiv = (370±7) km and geometric albedo pv = 0.099 ± 0.002 assuming a visual absolute magnitude HV = 3.81 ± 0.01. Using three possible rotational periods for the body (4.76, 5.91, and 7.87 h), we derive corresponding MacLaurin solutions. Furthermore, given the low-amplitude (0.06 ± 0.01) mag of the single-peaked rotational light-curve for the aforementioned periods, we consider the double periods. For the 5.91 h period (the most probable) and its double (11.82 h), we find bulk densities and true oblateness of ρ = (1.78 ± 0.06) g cm−3, ɛ = 0.235 ± 0.050, and ρ = (1.23 ± 0.04) g cm−3, ɛ = 0.080 ± 0.049. However, it must be noted that the other solutions cannot be excluded just yet.
Key words: methods: observational / occultations / Kuiper belt objects: individual: Varda
Astrometric data of Varda acquired between 2013 and 2019 and used for the prediction as well as the photometric data associated with Fig. 3b are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/643/A125
© D. Souami et al. 2020
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