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

A Correlation between Rotation Period and Disk Presence in the ONC and NGC 2264

First Author:
Nairn Baliber
Email: baliber AT lcogt.net
LCOGT and UCSB
Santa Barbara, CA USA

Abstract

Observations of PMS star rotation periods reveal slow rotators in young clusters of various ages, indicating that angular momentum is somehow removed from these rotating masses as they contract onto the main sequence. Using the disk identification capability of Spitzer Space Telescope data, we have studied the angular momentum history of pre-main-sequence (PMS) stars in the young Orion Nebula Cluster and NGC 2264. Once mass effects and sensitivity biases are removed, an unambiguous correlation between PMS star rotation periods and the presence of a circumstellar disk for stars with spectral type M2 and earlier is revealed, providing clear evidence that star-disk interaction regulates PMS star angular momentum. Because Spitzer data allows the populations of stars with and without disks to be separated accurately, a quantitative analysis of the angular momentum history of these clusters is now underway using Monte Carlo simulations. Parameters such as disk release timescales, angular momentum transfer efficiency, and fractions of stars released by their disks as a function of time can be constrained. We present our observational results, preliminary results from our ongoing numerical simulations, and discuss future work to study the same effect in stars of spectral type M3 and later in NGC 2264 with Spitzer Cycle 5 data.