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

Abstract

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⊙ respectively. By exploring the relationships among the turnoff wave bands λ_(turnoff) (longward of which significant IR excesses above the stellar photosphere are observed), the excess spectral index α_(excess) as determined for λ > λ_(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 α_(excess) for YSOs with optically thick disks tend to increase with λ_(turnoff), especially at λ_(turnoff) ≥5.8 μm, whereas the median fractional dust luminosities L_(dust)/L* tend to decrease with increasing λ_(turnoff). This points to an inside-out process of disk clearing for small dust grains. Moreover, a positive correlation between α_(excess) and R_(in) was found at α_(excess) 0 and R_(in) 10 × the dust sublimation radius R_(sub), irrespective of λ_(turnoff), L_(dust)/L* 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 λ 24 μm. About 23% of our YSO disks are classified as transitional disks, which have λ_(turnoff) ≥ 5.8 μm and L_(dust)/L* > 10^(−3). The transitional disks and full disks occupy distinctly different regions on the L_(dust)/L* vs. α_(excess) diagram. Taking L_(dust)/L* 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 α_(excess) (<0.0) or L_(dust)/L* (>0.1) values that would otherwise be suggestive of disk clearing dominanted by grain growth.

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