29 November 2001 CfA Colloquium


Title: Challenges in Star Formation

Speaker: Lee Hartmann

Abstract:

Substantial progress has been made in understanding star formation over the last decade. In this talk I focus on two areas at the forefront of current research: disk evolution and its implications for planet formation; and initial conditions for protostellar collapse. We have evidence for the dust growth and/or settling expected as the first stage of planet formation in the standard model, though spatial constraints on this process are poor. The observation that substantial amounts of disk material are accreted during the T Tauri phase poses a significant challenge to understanding planet formation and migration. A key issue is whether massive planets really open up clean gaps in the disk, or whether some material may accrete through gaps into the inner disk. I suggest that the rapid protostellar cloud collapse needed to form massive stars requires non-equilibrium cloud core formation, which in turn are a natural consequence of dynamic, flow-driven molecular cloud formation and evolution. Recent studies suggest that the frequency of very low mass stars and brown dwarfs in the low-density Taurus star forming cloud is much smaller than in other regions. These results suggest that the stellar initial mass function may best be understood as a combination of competitive accretion at high masses and Jeans fragmentation at low masses.

References for students:

Hartmann, Ballesteros, & Bergin 2001, astro-ph/0108023

Bonnell et al. 2001, MNRAS, 324, 573

Kastner et al. 1997, Science, 277, 67

Wilner et al. 2000, ApJ, 534, L101

Lunch with the students will be on Friday, November 30 at 12:00 in A-101.