Disk Evolution of Young Stellar Objects in Lynds 1641

We study circumstellar disk evolution in young star forming regions under various environments, and here we present our recent results in Lynds 1641 located at Orion A cloud. Planet formation is one of the mechanisms for disk dispersal, however, other possible mechanisms include photoevaporation, grain growth, magneto-rotational instability, and close companion. In order to study disk dispersal mechanisms, we carried out multi-wavelength imaging and optical spectroscopic studies of young stellar objects (YSOs) in Lynds1641, and identified ?1390 YSOs. We followed up with optical spectroscopy using MMT/Hectospec and Hectochelle for low - high resolution spectroscopy. We summarize our recent findings from both imaging and spectroscopic analysis (Fang, Kim, van Boekel et al. 2013): we identifed 143 Class I sources, 131 Flat spectrum sources, 533 Class II sources, and 507 class III sources. Among the confirme YSOs, 46 of them are transition disks in L1641. We find that: (i) both clustered and isolated mode of star formation are seen in L1641; (ii) there are age differences in median age for different disk morphologies (?1.1Myr for optically thick disks, ?1.5Myr for trandision disks, and ?1.8Myr for diskless stars); (iii) ?80% of optically thick disks show accretion, while ?40-45% of transition disks show accretion; (iv) amplitude of accretion rate and variability for both optically thick disks and transition disks are similar; (v) accretion variability can account for about 0.6 dex in accretion rate vs. mass relation; and (vi) disk frequency of the L1641 region is about 50%.