Volume 433, Number 2, April II 2005
|Page(s)||L21 - L24|
|Published online||22 March 2005|
Letter to the Editor
A planet-sized transiting star around OGLE-TR-122*
Accurate mass and radius near the hydrogen-burning limit
Observatoire de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland e-mail: email@example.com
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
Accepted: 12 February 2005
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
© ESO, 2005
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