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SUMMARY:Early Evolution of Very Low Mass Stars and Brown Dwarfs: A consist
 ent scenario based on episodic accretion? - Isabelle Baraffe (Exeter)
DTSTART:20111121T160000Z
DTEND:20111121T170000Z
UID:TALK32786@talks.cam.ac.uk
CONTACT:Henrik Latter
DESCRIPTION:I will present evolutionary models for young low mass stars an
 d brown dwarfs\ntaking into account episodic phases of accretion at early 
 stages of evolution\,\na scenario supported by recent large surveys of emb
 edded protostars. An\nevolution including short episodes of vigorous accre
 tion can explain the\nobserved luminosity spread in HR diagrams of star fo
 rming regions at ages of a\nfew Myr\, for objects ranging from a few Jupit
 er masses to a few tenths of a\nsolar mass. The gravitational contraction 
 of these accreting objects strongly\ndeparts from the standard Hayashi tra
 ck at constant Teff. The obtained\nluminosity spread at 1 Myr in the HR di
 agram is equivalent to what can be\nmisinterpreted as a ~ 10 Myr age sprea
 d for non-accreting objects. I will show\nthat a consistent scenario based
  on the coupling between accretion burst models\nand stellar evolution cal
 culations can also explain observations of Fu Ori\nobjects\, and in partic
 ular the expansion of their central star. Our results\nsuggest a link betw
 een the fraction of accretion energy absorbed by the\nprotostar and the ac
 cretion burst intensity\, suggesting the existence of a\nthreshold in accr
 etion rate where a transition from ”cold” to ”hot” accretion\noccu
 rs. This transition may stem from a change in the accretion geometry\, lik
 e\na transition from magnetospheric or thin disk to thick disk accretion. 
 These\ncalculations bear important consequences on our understanding of st
 ar formation\nand early stages of evolution and on the determination of th
 e IMF for young (≤\na few Myr) clusters.
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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