Evolutionary stages and disk properties of young stellar objects in the Perseus cloud

We investigated the evolutionary stages and disk properties of 211 young stellar objects (YSOs) across the Perseus cloud by modeling their broadband optical to mid-infrared (IR) spectral energy distribution (SED). Our optical gri photometry data were obtained from the recently finished Purple Mountain Observatory Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center (XSTPS-GAC). About 81% of our sample fall into the Stage II phase which is characterized by having optically thick disks, while 14% into the Stage I phase characterized by having significant infalling envelopes, and the remaining 5% into the Stage III phase characterized by having optically thin disks. The median stellar age and mass of the Perseus YSOs are 3.1 Myr and 0.3 M-circle dot respectively. By exploring the relationships among the turnoff wave bands lambda(turnoff) (longward of which significant IR excesses above the stellar photosphere are observed), the excess spectral index alpha(excess) as determined for lambda > lambda(turnoff), and the disk inner radius R-in (determined from SED modeling) for YSOs at different evolutionary stages, we found that the median and standard deviation of alpha(excess) for YSOs with optically thick disks tend to increase with lambda(turnoff), especially at lambda(turnoff) >= 5.8 mu m, whereas the median fractional dust luminosities L-dust/L star tend to decrease with increasing lambda(turnoff). This points to an inside-out process of disk clearing for small dust grains. Moreover, a positive correlation between alpha(excess) and R-in was found at alpha(excess) greater than or similar to 0 and R-in greater than or similar to 10 x the dust sublimation radius R-sub, irrespective of lambda(turnoff), L-dust/L star and disk flaring. This suggests that the outer disk flaring either does not evolve synchronously with the inside-out disk clearing of small dust grains or has little appreciable influence on the spectral slopes at lambda less than or similar to 24 mu m. About 23% of our YSO disks are classified as transitional disks, which have lambda(turnoff) = 5.8 mu m and L-dust/L star > 10(-3). The transitional disks and full disks occupy distinctly different regions on the L-dust/L star vs. alpha(excess) diagram. Taking L-dust/L star as an approximate discriminator of disks with (>0.1) and without (<0.1) considerable accretion activity, we found that 65% and 35% of the transitional disks may be consistent with being dominantly cleared by photoevaporation and dynamical interaction with giant planets respectively. None of our transitional disks have alpha(excess) (<0.0) or L-dust/L star (>0.1) values that would otherwise be suggestive of disk clearing dominanted by grain growth.National Natural Science Foundation of China (NSFC) [11390373]; China Postdoctoral Science Foundation [2013M530008]; CAS-CONICYT Postdoctoral Fellowship; NSFC [11203081]SCI(E)中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)ARTICLEhongxin@pku.edu.cn; yugao@pmo.ac.cn; mfang.cn@gmail.com8,SI1294-13241