A SPITZER SURVEY OF MID-INFRARED MOLECULAR EMISSION FROM PROTOPLANETARY DISKS. I. DETECTION RATES
- California Institute of Technology, Division of Geological and Planetary Sciences, MS 150-21, Pasadena, CA 91125 (United States)
- Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712 (United States)
- Naval Research Laboratory, Code 7211, Washington, DC 20375 (United States)
- National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719 (United States)
We present a Spitzer InfraRed Spectrometer search for 10-36 {mu}m molecular emission from a large sample of protoplanetary disks, including lines from H{sub 2}O, OH, C{sub 2}H{sub 2}, HCN, and CO{sub 2}. This paper describes the sample and data processing and derives the detection rate of mid-infrared molecular emission as a function of stellar mass. The sample covers a range of spectral type from early M to A, and is supplemented by archival spectra of disks around A and B stars. It is drawn from a variety of nearby star-forming regions, including Ophiuchus, Lupus, and Chamaeleon. Spectra showing strong emission lines are used to identify which lines are the best tracers of various physical and chemical conditions within the disks. In total, we identify 22 T Tauri stars with strong mid-infrared H{sub 2}O emission. Integrated water line luminosities, where water vapor is detected, range from 5 x 10{sup -4} to 9 x 10{sup -3} L{sub sun}, likely making water the dominant line coolant of inner disk surfaces in classical T Tauri stars. None of the five transitional disks in the sample show detectable gaseous molecular emission with Spitzer upper limits at the 1% level in terms of line-to-continuum ratios (apart from H{sub 2}), but the sample is too small to conclude whether this is a general property of transitional disks. We find a strong dependence on detection rate with spectral type; no disks around our sample of 25 A and B stars were found to exhibit water emission, down to 1%-2% line-to-continuum ratios, in the mid-infrared, while more than half of disks around late-type stars (M-G) show sufficiently intense water emission to be detected by Spitzer, with a detection rate approaching 2/3 for disks around K stars. Some Herbig Ae/Be stars show tentative H{sub 2}O/OH emission features beyond 20 {mu}m at the 1%-2% level, however, and one of them shows CO{sub 2} in emission. We argue that the observed differences between T Tauri disks and Herbig Ae/Be disks are due to a difference in excitation and/or chemistry depending on spectral type and suggest that photochemistry may be playing an important role in the observable characteristics of mid-infrared molecular line emission from protoplanetary disks.
- OSTI ID:
- 21460091
- Journal Information:
- Astrophysical Journal, Vol. 720, Issue 1; Other Information: DOI: 10.1088/0004-637X/720/1/887; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
CARBON DIOXIDE
EMISSION
HYDROCYANIC ACID
INFRARED SPECTROMETERS
LUMINOSITY
PHOTOCHEMISTRY
PROTOPLANETS
STAR EVOLUTION
T TAURI STARS
WATER
WATER VAPOR
BINARY STARS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMISTRY
ERUPTIVE VARIABLE STARS
EVOLUTION
FLUIDS
GASES
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INORGANIC COMPOUNDS
MEASURING INSTRUMENTS
OPTICAL PROPERTIES
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SPECTROMETERS
STARS
VAPORS
VARIABLE STARS