Gone with the Molecular Wind: Photoevaporation in the Compact Dust Disk around CX Tau

Abstract

We present Keck NIRSPEC+AO high-resolution (R ∼ 25,000), mid-infrared (M-band: 4.6–5.2 μm) spectra of the protoplanetary disk CX Tau. CX Tau provides an ideal laboratory to study inner disk chemistry in a disk where the signs of radial drift of pebbles are present in the form of a compact mm dust disk and extended gas disk. Our data covers many ¹²CO v = 1–0 ro-vibrational transitions, in addition to ¹³CO and ¹²CO v = 2–1. We find no evidence for CO emission in the inner disk of CX Tau at the level of 8 × 10¹⁶ cm^‑2, but do detect narrow, blueshifted absorption at ∼‑6 km s^‑1. A rotation diagram analysis shows that the gas temperature ranges from about 10 to 350 K, with column densities ∼9 × 10¹⁵ and 3 × 10¹⁷ cm^‑2, respectively. In addition to our Keck-NIRSPEC spectra, we create line maps from archival JWST-MIRI IFU data using custom JDISCS reduction techniques. These maps show spatially extended (∼500 au) H₂ and [ Ne II]. The blueshifted CO absorption and extended H₂ and [Ne II] are evidence of a photoevaporative disk wind. We estimate a wind mass-loss rate from the H₂ S(1) line of ∼10^‑9 M _⊙ yr^‑1, which is approximately equal to the stellar accretion rate and suggests that CX Tau is in the early stages of disk dispersal.