Program: GN-2009B-Q-76

We propose to use Gemini's GMOS in the multi-ob ject mode to measure spectral types of those members of the young stellar cluster NGC 2264 (RA = 7 hs, DEC = +10 deg) with known rotation periods and undetermined spectral types in order to construct a very clean sample of M3 and later type stars. We will use this sample, in combination with Spitzer data from our Cycle-5 program to study the role circumstellar disks play in the angular momentum evolution of very low-mass, pre-main-sequence (PMS) stars. This pro ject is a continuation of our studies of disk regulation in higher mass stars (M2.5 and earlier types), in which we have shown the first unambiguous correlation between stellar rotation and the presence of a circumstellar disk (Cieza & Baliber, 2006,2007), thereby settling the long standing debate on whether or not star-disk interaction regulate the angular momentum evolution of PMS stars (e.g., Attridge & Herbst, 1992, Makidon et al. 2004, Lamm et al. 2005). There is a sharp break in the behavior of rotation period distributions for stars earlier and later than type M2.5, suggesting a significant change in the efficiency or nature of the angular momentum transfer mechanism at this boundary. Our main goals are to establish whether or not disk regulation is operating in low-mass stars and to investigate any differences between the star-disk interaction parameters of high-mass and low-mass stars. We have already obtained spectra of most of our sample with the wide-field multi-fiber spectrograph on the MMT (through NOAO community access time). However, since some of the time was lost to the weather, we couldn't observe one of the fiber configurations, corresponding to 65 objects in our sample. Given the spatial distribution of the targets and the 305 field of view of GMOS, we will need 15 masks/pointings to observe 50 of them.