A slowly accreting ~10 Myr old transitional disk in Orion OB1a

Abstract

Here we present the Spitzer IRS spectrum of CVSO 224, the sole transitional disk located within the ~10 Myr old 25 Orionis group in Orion OB1a. A model fit to the spectral energy distribution of this object indicates a ~7 AU inner disk hole that contains a small amount of optically thin dust. In previous studies, CVSO 224 had been classified as a weak-line T Tauri star based on its Halpha equivalent width, but here we find an accretion rate of 7x10^-11 Msun/yr based on high-resolution Hectochelle data. CVSO 224's low mass accretion rate is in line with photoevaporative clearing theories. However, the Spitzer IRS spectrum of CVSO 224 has a substantial mid-infrared excess beyond 20microns which indicates that it is surrounded by a massive outer disk. Millimeter measurements are necessary to constrain the mass of the outer disk around CVSO 224 in order to confirm that photoevaporation is not the mechanism behind creating its inner disk hole.