The Size, Shape, Albedo, Density, and Atmospheric Limit of Transneptunian Object (50000) Quaoar from Multi-chord Stellar Occultations

F. Braga-Ribas (1) , B. Sicardy (1) , J. Ortiz (2) , E. Lellouch (1) , G. Tancredi , J. Lecacheux (1) , R. Vieira-Martins (3, 4) , J. I B Camargo (3) , M. Assafin (5) , R. Behrend (6) , F. Vachier (4) , F. Colas (4) , N. Morales , A. Maury (7) , M. Emilio (8) , A. Amorim (9) , E. Unda-Sanzana (10) , S. Roland (11) , S. Bruzzone , L. Almeida , C. Rodrigues , C. Jacques (12) , R. Gil-Hutton (13) , L. Vanzi , A. Milone (14) , W. Schoenell , R. Salvo , L. Almenares , E. Jehin (15) , J. Manfroid (16) , S. Sposetti (17) , P. Tanga (18) , A. Klotz (19) , E. Frappa (20) , P. Cacella , J. Colque , C. Neves , E. Alvarez , M. Gillon (21) , E. Pimentel , B. Giacchini , F. Roques (1) , T. Widemann (1) , V. Magalhães , A. Thirouin (22) , R. Duffard (22) , R. Leiva (23) , I. Toledo (24) , J. Capeche , W. Beisker (25) , J. Pollock (26) , C. Cedeño Montaña , K. Ivarsen , D. Reichart , J. Haislip , A. Lacluyze

1 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
2 CTM-ETSIM - Cátedra de Tecnología de la Madera. Departamento de Ingeniería Forestal
3 Observatorio Nacional [Rio de Janeiro]
4 IMCCE - Institut de Mécanique Céleste et de Calcul des Ephémérides
5 Observatório do Valongo/UFRJ [Rio de Janeiro]
6 ObsGE - Observatoire Astronomique de l'Université de Genève
7 SPACE - San Pedro de Atacama Celestial Explorations
8 Universidade Estadual de Ponta Grossa
9 Institute Patology and Imunology Molecular, Fac Ciencias
10 Instituto de Astronomıa
11 IPCM - Institut Parisien de Chimie Moléculaire
12 Observatório CEAMIG-REA
13 UNSJ - Universidad Nacional de San Juan [Argentine]
14 INPE - Instituto Nacional de Pesquisas Espaciais
15 ESO - European Southern Observatory
16 Institut d'Astrophysique et de Géophysique [Liège]
17 Gnosca Observatory
18 CASSIOPEE - Laboratoire de Cosmologie, Astrophysique Stellaire & Solaire, de Planétologie et de Mécanique des Fluides
19 IRAP - Institut de recherche en astrophysique et planétologie
20 Euraster
21 IDES - Interactions et dynamique des environnements de surface
22 IAA - Instituto de Astrofísica de Andalucía
23 SwRI - Southwest Research Institute [Boulder]
24 JAO - Joint ALMA Observatory
25 IOTA ES - International Occultation Timing Association European Section
26 Department of Physics and Astronomy [Boone]

We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord occultation observed on 2012 October 15. If the timing of the five chords obtained in 2011 were correct, then Quaoar would possess topographic features (crater or mountain) that would be too large for a body of this mass. An alternative model consists in applying time shifts to some chords to account for possible timing errors. Satisfactory elliptical fits to the chords are then possible, yielding an equivalent radius R equiv = 555 ± 2.5 km and geometric visual albedo pV = 0.109 ± 0.007. Assuming that Quaoar is a Maclaurin spheroid with an indeterminate polar aspect angle, we derive a true oblateness of $\epsilon = 0.087^{+0.0268}_{-0.0175}$, an equatorial radius of $569^{+24}_{-17}$ km, and a density of 1.99 ± 0.46 g cm–3. The orientation of our preferred solution in the plane of the sky implies that Quaoar's satellite Weywot cannot have an equatorial orbit. Finally, we detect no global atmosphere around Quaoar, considering a pressure upper limit of about 20 nbar for a pure methane atmosphere.

Mots clés: planets and satellites: fundamental parameters; planets and satellites: atmospheres; occultations; Kuiper belt objects: individual: 50000 Quaoar

Domaines: Physique [physics]; Astrophysique [astro-ph]

F. Braga-Ribas, B. Sicardy, J. Ortiz, E. Lellouch, G. Tancredi, et al.. The Size, Shape, Albedo, Density, and Atmospheric Limit of Transneptunian Object (50000) Quaoar from Multi-chord Stellar Occultations. The Astrophysical Journal, 2013, 773 (1), pp.26. ⟨10.1088/0004-637X/773/1/26⟩. ⟨hal-02539916⟩