2/18/16: SO/NOAO Joint Colloquium Series: Nuria Calvet, Univ. of Michigan

Title: Pre-Main Sequence Accretion Revisited, What Does it Tell Us About Disk Structure and Evolution?

Abstract:
The primordial disks around ~ 1- 10 Myr old stars are accreting matter onto the star and the rate of this process constrains their structure and evolution. Studies of low mass stellar populations with ages from 1 to 10 Myr indicate that some disks follow the expected evolutionary path of decreasing their mass accretion rates and masses as dust grows and settles, until photoevaporation sets in when the mass accretion rate is sufficiently low. However, the striking decrease of disk frequency with age cannot be explained by this evolution. Alternative evolutionary paths are exemplified by the transitional and pre-transitional disks, which are best explained by planet formation, now confirmed by direct imaging. These transitional disks are vigorously accreting mass onto their stars, which implies that their innermost regions are heavily depleted in dust. These possibilities suggest a number of questions, such as: are there many planets hidden in disks in which the inner regions have not yet had time to grow their dust? what is the structure of the innermost regions of full disks? do disks surviving to old age show indications of planet formation? I will present our work determining mass accretion rates and calculating structures with irradiated accretion disk models applied to populations of different ages that aim to address some of these questions.