Physics of late M, L and T dwarfs

Ultracool atmospheres and brown dwarf meteorology

Known effective temperatures of substellar objects are approximately in the range from 3000 K (the youngest, most massive brown dwarfs) to 750 K (the oldest field brown dwarfs and the least massive, young isolated giant exoplanets). Physics on these cool atmospheres is far from being completely understood.

The photometric variability of L and T dwarfs has been subject of study in a few recent studies (Bailer-Jones and Mundt 1999, 2001; Terndrup et al. 1999; Clarke, Tinney and Covey 2002, Gelino et al. 2002), mostly performed in the optical region. Through optical and near-infrared continuous monitoring we can study: 1) the amplitude of variability associated with atmospheric changes over time scales from minutes to several hours of a sample of late-M, L and T dwarfs; 2) the presence of accretion disks in very young, low-mass objects; 3) the search for cool companions in wide orbits, after combining our series of observations to produce deep images; 4) the search for transits of low mass brown dwarfs or planetary companions in very close orbits.

Our refereed publications

Photometric variability of young brown dwarfs in the sigma Orionis open cluster
Caballero, J. A.; Béjar, V. J. S.; Rebolo, R.; Zapatero Osorio, M. R.
2004, A&A, 424, 857

Photometric variability of a young, low-mass brown dwarf
Zapatero Osorio, M. R.; Caballero, J. A.; Béjar, V. J. S.; Rebolo, R.
2003, A&A, 408, 663

On the interpretation of the optical spectra of L-type dwarfs
Pavlenko, Ya.; Zapatero Osorio, M. R.; Rebolo, R.
2000, A&A, 355, 245

The rotation period of a very low-mass star in alpha Persei
Martin, E. L.; Zapatero-Osorio, M. R.
1997, MNRAS, 286, L 17

Formation of lithium lines in very cool dwarfs
Pavlenko, Y. V.; Rebolo, R.; Martin, E. L.; Garcia Lopez, R. J.
1995, A&A, 303, 807

Previous refereed publications

Pre-main sequence lithium burning. 1: Weak T Tauri stars
Martin, E. L.; Rebolo, R.; Magazzu, A.; Pavlenko, Ya. V.
1994, A&A, 282, 503