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A&A 433, L21-L24 (2005)
DOI: 10.1051/0004-6361:200500025
Letter
A planet-sized transiting star around OGLE-TR-122
Accurate mass and radius near the hydrogen-burning limit
F. Pont1, C. H. F. Melo2, F. Bouchy3, 4, S. Udry1, D. Queloz1, M. Mayor1 and N. C. Santos51 Observatoire de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
e-mail: frederic.pont@obs.unige.ch
2 European Southern Observatory, Casilla 19001, Santiago 19, Chile
3 Laboratoire d'Astrophysique de Marseille, Traverse du Siphon, BP 8, 13376 Marseille Cedex 12, France
4 Observatoire de Haute Provence, 04870 St Michel l'Observatoire, France
5 Centro de Astronomia e Astrofísica da Universidade de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
(Received 28 January 2005 / Accepted 12 February 2005 )
Abstract
We report the discovery and characterisation of OGLE-TR-122b, the smallest main-sequence star to date with a direct radius determination. OGLE-TR-122b transits around its solar-type primary every 7.3-days. With
and
, it is by far the smallest known eclipsing M-dwarf. The derived mass and radius for OGLE-TR-122b are in agreement with the theoretical expectations. OGLE-TR-122b is the first observational evidence that stars can indeed have radii comparable or even smaller than giant planets. In such cases, the photometric signal is exactly that of a transiting planet and the true nature of the companion can only be determined with high-resolution spectroscopy.
Key words: stars: low-mass, brown-dwarfs -- stars: fundamental parameters -- stars: binaries -- binaries: eclipsing
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