New Light on Young Stars:
Spitzer's View of Circumstellar Disks

The Masses of Transition Circumstellar Disks:
Observational Support for Photoevaporation Models

First Author:
Lucas Cieza
Email: lcieza AT ifa.hawaii.edu
IfA / University of Hawaii
Honolulu, HI 96814 USA

Abstract

We report deep Sub-Millimeter Array (SMA) observations of a sample of 25 Pre-Main-Sequence (PMS) stars that show evidence for inner disk evolution (i.e., decreased levels of near- and mid-IR excess and/or weak accretion). These observations measure the mass of the cold outer disk (r ~20-100 AU)across every evolutionary stage of the inner disk (r < 10 AU) as determined by the IR Spectral Energy Distributions (SEDs). We find that only targets with high mid-IR excesses are detected and have disk masses in the 1-5 M_Jup range, while most of our objects remain undetected to sensitivity levels of M_DISK~ 0.1-1 M_Jup. To put these results in a more general context, we collected publicly available data to construct the optical to millimeter wavelength SEDs of over 130 additional PMS stars. We find that the near-IR and mid-IR emission remain optically thick in objects whose disk masses span 2 orders of magnitude(~0.5-50 M_Jup). Taken together, these results imply that, in general, inner disks start to dissipate only after the outer disk has been significantly depleted of mass. This provides strong support for photoevaporation being one of the dominant processes driving disk evolution.