Free Access
Volume 408, Number 2, September III 2003
Page(s) 663 - 673
Section Stellar atmospheres
Published online 17 November 2003

A&A 408, 663-673 (2003)
DOI: 10.1051/0004-6361:20030987

Photometric variability of a young, low-mass brown dwarf

M. R. Zapatero Osorio1, J. A. Caballero2, V. J. S. Béjar2 and R. Rebolo2, 3

1  LAEFF-INTA, PO Box 50727, 28080 Madrid, Spain
2  Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
3  Consejo Superior de Investigaciones Científicas, Spain

(Received 7 March 2003 / Accepted 16 June 2003 )

We report differential I-band and J-band photometry of S Ori 45, a cool (spectral type M8.5), young (1-8 Myr) brown dwarf of the $\sigma$ Orionis cluster with a likely mass estimated at around 20 times the mass of Jupiter. We detect variability (amplitudes ranging from 34 to 81 mmag) and observe a modulation at a period of 2.5-3.6 h in both optical and near-infrared light curves. The most recent optical data set, however, presents a modulation at the very short period of 46.4 $\pm$ 1.5 min, which remains a mystery. The origin of the 2.5-3.6 h modulation is analyzed in terms of various scenarios: inhomogeneous features (dust clouds or magnetically induced dark spots) co-rotating with the object's surface, and presence of an unseen very low-mass companion that is steadily transferring mass to the primary. Because of the very young age of the object and its persistent strong H $\alpha$ emission, the possible presence of an accreting disk is also discussed. If the period of a few hours is related to rotation, our results suggest that $\sigma$ Orionis low-mass brown dwarfs are rotating faster than more massive cluster brown dwarfs at a rate consistent with their theoretically inferred masses and radii, implying that all of these objects have undergone similar angular momentum evolution.

Key words: stars: low mass, brown dwarfs -- stars: rotation -- stars: pre-main sequence -- stars: formation

Offprint request: M. R. Zapatero Osorio,

SIMBAD Objects

© ESO 2003

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.