Name: Keivan Stassun

Institution: Vanderbilt University

e-mail: keivan.stassun(no-spam)vanderbilt.edu

Partner Country: USA

Science Meeting: Yes

User Meeting: Yes

NGO Staff Meeting: No

Presentation: Yes

Format: Oral

Title: Empirical Constraints on the Formation and Structure of Young, Low-Mass Stars and Brown Dwarfs

Abstract:

We report on recent progress and future prospects in two broad areas of research centered around the formation of low-mass pre-main-sequence stars and brown dwarfs. First, we will summarize efforts to directly and accurately measure the fundamental physical properties (masses, radii, luminosities) of young low-mass stars and brown dwarfs as critical tests of theoretical evolutionary tracks. Second, we will discuss the broad problem of magnetic-field generation and X-ray production in these objects, emphasizing results from the recent Chandra Orion Ultradeep Project. We synthesize this work to provide observational constraints on the internal structure of young, low-mass stars and brown dwarfs. Combining the empirically determined fundamental physical parameters with lithium abundances and X-ray tracers of magnetic activity, we discuss the evidence for magnetically suppressed convection in very young stars and brown dwarfs. Using recently discovered eclipsing binary stars and brown dwarfs as exemplars, we discuss the possible effects of strong magnetic fields on the ages derived from theoretical pre-main-sequence evolutionary tracks, and discuss the implications for observational tests of star- and brown-dwarf formation models. For example, the recently discovered brown-dwarf eclipsing binary 2M0535-05 exhibits a surprising reversal of temperature with mass. This can be taken as evidence for non-coeval formation of the brown dwarfs---supporting ejection models of brown dwarf formation---or as evidence of strong magnetic fields altering energy transport in a coeval system. Resolving these scenarios will thus be critical to calibrating theoretical evolutionary tracks and stellar ages, and to testing theories of brown-dwarf formation mechanisms.