EDP Sciences
Free Access
Volume 433, Number 2, April II 2005
Page(s) L21 - L24
Section Letters
DOI https://doi.org/10.1051/0004-6361:200500025
Published online 22 March 2005

A&A 433, L21-L24 (2005)
DOI: 10.1051/0004-6361:200500025


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. Santos5

1  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 )

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 $M=0.092\pm0.009 \ M_\odot$ and $R=0.120^{+0.020}_{-0.013} \ R_\odot$, 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

SIMBAD Objects

© ESO 2005

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.