High-Resolution Mid-Infrared Spectroscopy of GV Tau N: Surface Accretion and Detection of Ammonia in a Young Protoplanetary Disk

Abstract

Physical processes that redistribute or remove angular momentum from protoplanetary disks can drive mass accretion onto the star and affect the outcome of planet formation. Despite ubiquitous evidence that protoplanetary disks are engaged in accretion, the process(es) responsible remain unclear. Here we present evidence for redshifted molecular absorption in the spectrum of a Class I source that indicates rapid inflow at the disk surface. High resolution mid-infrared spectroscopy of GV Tau N reveals a rich absorption spectrum of individual lines of C2H2, HCN, NH3, and water. From the properties of the molecular absorption, we can infer that it carries a significant accretion rate (~ 1e-8 to 1e-7 Msun/yr), comparable to the stellar accretion rates of active T Tauri stars. Thus we may be observing disk accretion in action. The results may provide observational evidence for supersonic "surface accretion flows," which have been found in MHD simulations of magnetized disks. The observed spectra also represent the first detection of ammonia in the planet formation region of a protoplanetary disk. With ammonia only comparable in abundance to HCN, it cannot be a major missing reservoir of nitrogen. If, as expected, the dominant nitrogen reservoir in inner disks is instead N2, its high volatility would make it difficult to incorporate into forming planets, which may help to explain the low nitrogen content of the bulk Earth.

55 pages, 18 figures, accepted for publication in the Astrophysical Journal

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Cited by in corpus (7)

• ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) VI: Accretion shocks in the disk of DG Tau and HL Tau
• Effect of MHD wind-driven disk evolution on the observed sizes of protoplanetary disks
• H${}_2$S observations in young stellar disks in Taurus
• Radiative Nonideal MHD Simulations of Inner Protoplanetary Disks: Temperature Structures, Asymmetric Winds, and Episodic Surface Accretion
• A rich molecular chemistry in the gas of the IC 348 star cluster of the Perseus Molecular Cloud
• Ammonia, carbon dioxide and the non-detection of the 2152 cm${}^{-1}$ CO band
• Protoplanetary Disk Chemistry