First Detection of Near-Infrared Line Emission from Organics in Young Circumstellar Disks

Abstract

We present an analysis of high-resolution spectroscopy of several bright T Tauri stars using the VLT/CRIRES and Keck/NIRSPEC spectrographs, revealing the first detections of emission from HCN and C2H2 in circumstellar disks at near-infrared wavelengths. Using advanced data reduction techniques we achieve a dynamic range with respect to the disk continuum of ~500 at 3 microns, revealing multiple emission features of H2O, OH, HCN, and C2H2. We also present stringent upper limits for two other molecules thought to be abundant in the inner disk, CH4 and NH3. Line profiles for the different detected molecules are broad but centrally peaked in most cases, even for disks with previously determined inclinations of greater than 20 degrees, suggesting that the emission has both a Keplerian and non-Keplerian component as observed previously for CO emission. We apply two different modeling strategies to constrain the molecular abundances and temperatures: we use a simplified single-temperature LTE slab model with a Gaussian line profile to make line identifications and determine a best-fit temperature and initial abundance ratios, and we compare these values with constraints derived from a detailed disk radiative transfer model assuming LTE excitation but utilizing a realistic temperature and density structure. Abundance ratios from both sets of models are consistent with each other and consistent with expected values from theoretical chemical models, and analysis of the line shapes suggests the molecular emission originates from within a narrow region in the inner disk (R < 1 AU).

Accepted to the Astrophysical Journal

References in corpus (15)

• Protoplanetary Disk Structures in Ophiuchus
• UV excess measures of accretion onto young very low-mass stars and brown dwarfs
• Structure and evolution of pre-main sequence circumstellar disks
• Spectro-astrometric imaging of molecular gas within protoplanetary disk gaps
• H2O and OH gas in the terrestrial planet-forming zones of protoplanetary disks
• On the formation of H-alpha line emission around classical T Tauri stars
• Line Emission from Gas in Optically Thick Dust Disks around Young Stars
• Spatial mapping of ices in the Oph-F core: A direct measurement of CO depletion and the formation of CO2
• Formation of Water in the Warm Atmospheres of Protoplanetary Disks
• Formation of simple organic molecules in inner T Tauri disks
• Investigating grain growth in disks around southern T Tauri stars at millimetre wavelengths
• Formation of Organic Molecules and Water in Warm Disk Atmospheres
• Warm HCN, C2H2, and CO in the disk of GV Tau
• TEXES Observations of Pure Rotational H2 Emission From AB Aurigae
• Rotational Line Emission from Water in Protoplanetary Disks

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