Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 1B095

Young Stellar Objects in Lynds 1641: Disks and Accretion

Fang, Min (Universidad Autónoma de Madrid; Purple Mountain Observatory)
Kim, Jinyoung Serena (Steward Observatory, University of Arizona)
van Boekel, Roy (Max-Planck Institute for Astronomy)
Sicilia-Aguilar, Aurora (Universidad Autónoma de Madrid)
Henning, Thomas (Max-Planck Institute for Astronomy)
Flaherty, Kevin (Steward Observatory, University of Arizona)

We investigate the young stellar objects (YSOs) in the Lynds~1641 (L1641) cloud using multi-wavelength data including Spitzer, WISE, 2MASS, and XMM covering ~1390 YSOs across a range of evolutionary stages. In addition, we targeted a sub-sample of YSOs for optical spectroscopy with the MMT/Hectospec and the MMT/Hectochelle. We use this data, along with archival photometric data, to derive spectral types, masses, ages and extinction values. We also use the H_alpha and H_beta lines to derive accretion rates. We calculate the disk fraction as N(II)/N(II+III), where N(II) and N(III) are numbers of Class\\,II and Class\\,III sources, respectively, and obtain a disk fraction of ~50% in L1641. We find that the disk frequency is almost constant as a function of stellar mass with a slight peak at log(M_*/M_sun)~-0.25. The analysis of multi-epoch data indicates that the accretion variability of YSOs cannot explain the two orders of magnitude of scatter for YSOs with similar masses in the M_acc vs. M_* plot. Forty-six new transition disk objects are confirmed in our spectroscopic survey and we find that the fraction of transition disks that are actively accreting is lower than for optically thick disks (40-45% vs. 77-79% respectively). We confirm our previous result that the accreting YSOs with transition disks have a similar median accretion rate to normal optically thick disks. Analyzing the age distributions of various populations, we find that the diskless YSOs are statistically older than the YSOs with optically-thick disks and the transition disk objects have a median age which is intermediate between the two populations.

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