2018ApJ...863...13G

We analyze Herschel Space Observatory observations of 104 young stellar objects with protoplanetary disks in the ∼1.5 Myr star-forming region Lynds 1641 (L1641) within the Orion A Molecular Cloud. We present spectral energy distributions from the optical to the far-infrared including new photometry from the Herschel Photodetector Array Camera and Spectrometer at 70 µm. Our sample, taken as part of the Herschel Orion Protostar Survey, contains 24 transitional disks, 8 of which we identify for the first time in this work. We analyze the full disks (FDs) with irradiated accretion disk models to infer dust settling properties. Using forward modeling to reproduce the observed n_KS-[70]_ index for the FD sample, we find the observed disk indices are consistent with models that have depletion of dust in the upper layers of the disk relative to the midplane, indicating significant dust settling. We perform the same analysis on FDs in Taurus with Herschel data and find that Taurus is slightly more evolved, although both samples show signs of dust settling. These results add to the growing literature that significant dust evolution can occur in disks by ∼1.5 Myr.