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    First Detection Of Near-Infrared Line Emission From Organics In Young Circumstellar Disks

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    Date
    2012-03
    Author
    Mandell, Avi M.
    Bast, Jeanette
    van Dishoeck, Ewine F.
    Blake, Geoffrey A.
    Salyk, Colette
    Mumma, Michael J.
    Villanueva, Geronimo
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    Abstract
    We present an analysis of high-resolution spectroscopy of several bright T Tauri stars using the CRIRES spectrograph on the Very Large Telescope and NIRSPEC spectrograph on the Keck Telescope, 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 similar to 500 at 3 mu m, 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 local thermal equilibrium (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 that the molecular emission originates from within a narrow region in the inner disk (R < 1 AU).
    Department
    Astronomy
    Subject
    line: profiles
    planets and satellites: formation
    protoplanetary disks
    stars: low-mass
    t-tauri stars
    planet-forming region
    midinfrared molecular-emission
    spitzer spectroscopic survey
    protoplanetary disks
    stellar objects
    co
    emission
    mass stars
    ab-aurigae
    gas
    astronomy & astrophysics
    URI
    http://hdl.handle.net/2152/35016
    xmlui.dri2xhtml.METS-1.0.item-citation
    Mandell, Avi M., Jeanette Bast, Ewine F. Van Dishoeck, Geoffrey A. Blake, Colette Salyk, Michael J. Mumma, and Geronimo Villanueva. "First detection of Near-infrared line emission from organics in young circumstellar disks." The Astrophysical Journal, Vol. 747, No. 2 (Mar., 2012): 92.
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