SPITZER SPECTROSCOPY OF THE TRANSITION OBJECT TW Hya

Journal Article · Sat Mar 20 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/712/1/274· OSTI ID:21394273

Najita, Joan R; Strom, Stephen E ^[1]; Carr, John S ^[2]; Watson, Dan M ^[3]; Pascucci, Ilaria ^[4]; Hollenbach, David; Gorti, Uma ^[5]; Keller, Luke ^[6]

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1. National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719 (United States)
2. Naval Research Laboratory, Code 7211, Washington, DC 20375 (United States)
3. University of Rochester, Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States)
4. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
5. SETI Institute, 515 North Whisman Road, Mountain View, CA 94043 (United States)
6. Department of Physics, Ithaca College, Ithaca, NY 14850 (United States)

We report sensitive Spitzer IRS spectroscopy in the 10-20 {mu}m region of TW Hya, a nearby T Tauri star. The unusual spectral energy distribution of the source, that of a 'transition object', indicates that the circumstellar disk in the system has experienced significant evolution, possibly as a result of planet formation. The spectrum we measure is strikingly different from that of other classical T Tauri stars reported in the literature, displaying no strong emission features of H{sub 2}O, C{sub 2}H{sub 2}, or HCN. The difference suggests that the inner planet formation region ({approx}<5 AU) of the gaseous disk has evolved physically and/or chemically away from the classical T Tauri norm. Nevertheless, TW Hya does show a rich spectrum of emission features of atoms (H I, [Ne II], and [Ne III]) and molecules (H{sub 2}, OH, CO{sub 2}, HCO{sup +}, and possibly CH{sub 3}), some of which are also detected in classical T Tauri spectra. The properties of the neon emission are consistent with an origin for the emission in a disk irradiated by X-rays (with a possible role for additional irradiation by stellar EUV). The OH emission we detect, which also likely originates in the disk, is hot, arising from energy levels up to 23,000 K above ground, and may be produced by the UV photodissociation of water. The H I emission is surprisingly strong, with relative strengths that are consistent with case B recombination. While the absence of strong molecular emission in the 10-20 {mu}m region may indicate that the inner region of the gaseous disk has been partly cleared by an orbiting giant planet, chemical and/or excitation effects may be responsible instead. We discuss these issues and how our results bear on our understanding of the evolutionary state of the TW Hya disk.

• OSTI ID: 21394273
• Journal Information: Astrophysical Journal, Vol. 712, Issue 1; Other Information: DOI: 10.1088/0004-637X/712/1/274; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CARBON DIOXIDE
DISSOCIATION
EMISSION
ENERGY LEVELS
ENERGY SPECTRA
HYDROCYANIC ACID
HYDROGEN
MATTER
NEON
PHOTOLYSIS
PLANETS
PROTOPLANETS
SPECTROSCOPY
T TAURI STARS
WATER
X RADIATION
BINARY STARS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
DECOMPOSITION
ELECTROMAGNETIC RADIATION
ELEMENTS
ERUPTIVE VARIABLE STARS
FLUIDS
GASES
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INORGANIC COMPOUNDS
IONIZING RADIATIONS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
RADIATIONS
RARE GASES
SPECTRA
STARS
VARIABLE STARS