Coordinated thermal and optical observations of Trans-Neptunian object (20 000)Varuna from Sierra Nevada

¹ Observatoire de Paris, 5 place J. Janssen, 92195 Meudon, France
² I.R.A.M. 300 Av. de la Piscine, 38406 St-Martin d'Hères Cedex, France
³ Instituto de Astrofísica de Andalucia, CSIC, Camino Bajo de Huetor 24, 18080 Granada, Spain
⁴ I.R.A.M. Avda. Divina Pastora 7, 18012 Granada, Spain
⁵ Centro de Astronomia e Astrofísica da Universidade de Lisboa, 1349-018 Lisboa, Portugal

Corresponding author: E. Lellouch, emmanuel.lellouch@obspm.fr

Received: 11 June 2002
Accepted: 14 June 2002

Abstract

We report on coordinated thermal and optical measurements of trans-Neptunian object (20 000)Varuna obtained in January–February 2002, respectively from the IRAM 30-m and IAA 1.5 m telescopes. The optical data show a lightcurve with a period of  hr, a mean V magnitude of and a magnitude amplitude. They also tentatively indicate that the lightcurve is asymmetric and double-peaked. The thermal observations indicate a  mJy flux, averaged over the object's rotation. Combining the two datasets, we infer that Varuna has a mean 1060 km diameter and a mean 0.038 V geometric albedo, in general agreement with an earlier determination using the same technique.