NOAO/KPNO--NSO,

DEPARTMENT OF ASTRONOMY

AND STEWARD OBSERVATORY

AND NRAO

The University of Arizona

<><><><><><><><><><><><><><><><><><>

JOINT COLLOQUIUM

<><><><><><><><><><><><><><><><><><>

presents

• Dr. Gibor Basri

of the

• University of California, Berkeley, Department of Astronomy

who will present a talk entitled

• "Baby Brown Dwarfs (Very Low Mass T Tauri Stars)"

Abstract:

The best opportunity to observe extremely low-mass objects comes when they are very young. This is when they are at their brightest, and even high resolution spectra can be obtained of them. This is also the time to best probe formation mechanisms for substellar objects - while they are still underway. I summarize 3 years of a program to obtain echelle spectra of the faintest objects in some nearby star-forming regions. I discuss the evidence for, and frequency of, accretion signatures from the lowest mass stars down to the planet/brown dwarf boundary. The rotations and magnetic activity of these objects differ from field brown dwarfs.

We show that echelle spectra enable us to get good determinations of both temperature and surface gravity. Given these, and the fact that the objects are in clusters, we can determine their masses independently of evolutionary models. We find that our lowest mass objects may be below the fusion boundary. We can also make critical tests of those models. There are substantial deviations from the model predictions at the lowest masses (models predict gravities that are higher than observed, or the ages of these objects are far too young when estimated from the models). We discuss possible reasons for this discrepancy, and conclude that the initialization of deuterium burning in the models may require modification.

• on Thursday, November 20, 2003

• at 4:00 p.m.

• in Steward Observatory Lecture Hall-Room N210

Refreshments at 3:30 p.m. in the Lobby