New Observations of Quaoar

THE SIZE, SHAPE, ALBEDO, DENSITY, AND ATMOSPHERIC LIMIT OF TRANSNEPTUNIAN OBJECT (50000) QUAOAR FROM MULTI-CHORD STELLAR OCCULTATIONS

Authors:

1. F. Braga-Ribas (a,b,bb)
2. B. Sicardy (b,c)
3. J. L. Ortiz (d)
4. E. Lellouch (b)
5. G. Tancredi (e)
6. J. Lecacheux (b)
7. R. Vieira-Martins (a,f,g)
8. J. I. B. Camargo (a)
9. M. Assafin (g)
10. R. Behrend (h)
11. F. Vachier (f)
12. F. Colas (f)
13. N. Morales (d)
14. A. Maury (i)
15. M. Emilio (j)
16. A. Amorim (k)
17. E. Unda-Sanzana (l)
18. S. Roland (e)
19. S. Bruzzone (e)
20. L. A. Almeida (m)
21. C. V. Rodrigues (m)
22. C. Jacques (n)
23. R. Gil-Hutton (o)
24. L. Vanzi (p)
25. A. C. Milone (m)
26. W. Schoenell (d,k)
27. R. Salvo (e)
28. L. Almenares (e)
29. E. Jehin1 (g)
30. J. Manfroid (q)
31. S. Sposetti (r)
32. P. Tanga1 (i)
33. A. Klotz (t)
34. E. Frappa (u)
35. P. Cacella (u)
36. J. P. Colque (l)
37. C. Neves (j)
38. E. M. Alvarez (v)
39. M. Gillon (q)
40. E. Pimentel (n)
41. B. Giacchini (n)
42. F. Roques (b)
43. T. Widemann (b)
44. V. S. Magalhães (m)
45. A. Thirouin (d)
46. R. Duffard (d)
47. R. Leiva1 (f)
48. I. Toledo (x)
49. J. Capeche (e)
50. W. Beisker (y)
51. J. Pollock (z)
52. C. E. Cedeño Montaña (m)
53. K. Ivarsen (aa)
54. D. Reichart (aa)
55. J. Haislip (aa)
56. A. Lacluyze (aa)

Affiliations:

a. Observatório Nacional, Rio de Janeiro, Brazil

b. Observatoire de Paris, LESIA, F-92195 Meudon, France

c. Université Pierre et Marie Curie, F-75252 Paris, France

d. Instituto de Astrofísica de Andalucía-CSIC, E-18080 Granada, Spain

e. Observatorio Astronomico Los Molinos, Montevideo U-12400, Uruguay

f. Observatoire de Paris, IMCCE, F-75014 Paris, France

g. Observatório do Valongo/UFRJ, Rio de Janeiro, Brazil

h. Observatoire de Genève, Sauverny, Switzerland

i. San Pedro de Atacama Celestial Explorations, San Pedro de Atacama, Chile

j. Universidade Estadual de Ponta Grossa, Ponta Grossa, Brazil

k. Universidade Federal de Santa Catarina, Florianópolis, Brazil

l. Unidad de Astronomía, Universidad de Antofagasta, Antofagasta, Chile

m. Instituto Nacional de Pesquisas Espaciais, DAS, São José dos Campos, Brazil

n. Centro de Estudos Astronômicos de Minas Gerais (CEAMIG), Belo Horizonte, Brazil

o. Complejo Astronómico El Leoncito and San Juan National University, San Juan, Argentina

p. Department of Electrical Engineering and Center of Astro-Engineering, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile

q. Institut d'Astrophysique de l'Université de Liége, B-4000 Liège, Belgium

r. Gnosca Observatory, Gnosca, Switzerland

s. Laboratoire Lagrange, Université de Sophia Antipolis, Observatoire de la Côte d'Azur, CNRS UMS7293, F-06304 NICE Cedex 4, France

t. Université de Toulouse, UPS-OMP, IRAP, F-31000 Toulouse, France

u. Euraster, 1B cours J. Bouchard, F-42000 St-Etienne, France

v. Rede de Astronomia Observacional, Brasilia, Brazil

w. Observatorio Los Algarrobos, Salto, Uruguay

x. Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile

y. International Occultation Timing Association-European Section, D-30459 Hannover, Germany

z. Department of Physics and Astronomy, Appalachian State University, Boone, NC 28608, USA

aa. Physics and Astronomy Department, University of North Carolina, Chapel Hill, NC, USA

bb. Current address: Rua General José Cristino, 77, CEP 20921-400, Rio de Janeiro, RJ, Brazil.

Abstract:

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.

In the future, with this many authors, I am not going to reformat.  Good grief.