The Evolution of Protoplanetary Disks: Probing the Inner Disk of Very Low Accretors

July 2018 • 2018ApJ...861...73T

Authors • Thanathibodee, Thanawuth • Calvet, Nuria • Herczeg, Gregory • Briceño, César • Clark, Catherine • Reiter, Megan • Ingleby, Laura • McClure, Melissa • Maucó, Karina • Hernández, Jesús

Abstract • We report FUV, optical, and NIR observations of three T Tauri stars in the Orion OB1b subassociation with Hα equivalent widths consistent with low or absent accretion and various degrees of excess flux in the mid-infrared. We aim to search for evidence of gas in the inner disk in HST Advanced Camera for Surveys/Solar Blind Channel spectra, and to probe the accretion flows onto the star using Hα and He I λ10830 in spectra obtained at the Magellan and SOAR telescopes. At the critical age of 5 Myr, the targets are at different stages of disk evolution. One of our targets is clearly accreting, as shown by redshifted absorption at freefall velocities in the He I line and wide wings in Hα however, a marginal detection of FUV H₂ suggests that little gas is present in the inner disk, although the spectral energy distribution indicates that small dust still remains close to the star. Another target is surrounded by a transitional disk, with an inner cavity in which little sub-micron dust remains. Still, the inner disk shows substantial amounts of gas, accreting onto the star at a probably low but uncertain rate. The third target lacks both a He I line or FUV emission, consistent with no accretion or inner gas disk; its very weak IR excess is consistent with a debris disk. Different processes occurring in targets with ages close to the disk dispersal time suggest that the end of the accretion phase is reached in diverse ways.

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Catherine Clark

JPL Postdoctoral Fellow