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Title: Evolution of Protoplanetary Disks in the Orion A Star-Forming Region 2013-10-23
- Speaker : Dr. Kim, Kyoung Hee
- Date : 2013-10-23 16:00 ~ 17:30
- Location : JYS #331-2
We present our investigation of the characteristics of Class II protoplanetary disks in Orion A star-forming region. Our major goal is to analyze a large sample of protoplanetary disks with near- and mid-IR spectra, by statistical approaches, to understand protoplanetary disk evolution in Orion A. For this work, 303 protoplanetary disks in Orion A region observed by IRS/Spitzer and the follow-up observation of 120 objects from SpeX/IRTF are used to reveal the characteristics of Class II disks in Orion A.
For clues on environmental effects on disk evolution and planet formation, we compare the disk properties and dust properties of Orion A disks to that of Taurus disks and examine trends with respect to position within Orion A. We extract spectral indices, equivalent widths, and integrated fluxes from IRS spectra of Class II objects in Orion A which pertain to disk structure and dust composition. We measure mass accretion rates using hydrogen recombination lines in SpeX spectra of our targets. Utilizing the properties, we analyze the general distribution of properties of disks in ONC, L1641, and Taurus from their histograms.
Our main findings are as follows. (1)Transitional disks ? those protoplanetary disks for which deficits of infrared excess signify sharp-edged gaps in the dust distribution ? are produced gravitationally by companions to the central star. (2) From the high frequency (>20%) of transitional disks and the similar vertical structure of the Orion A disks to those of Taurus, we infer that giant planet formation and dust sedimentation is well under way, if not complete, even in the youngest Class II objects. (3) Less grain processing ? crystallization and growth of grains to diameter of 1?10 μm ? has occurred among the dust grains in the Orion A disks than in Taurus. The time scales for dust processing must therefore lie in the range of ages of the nearby clouds like Orion, NGC 1333, Taurus, Ophiuchus and Chamaeleon. (4) We detected PAH emission at 6?14 μm from disks around low-mass and low-luminosity young stars, excited externally by UV from the Trapezium stars. (5) As others have found for the Trapezium region of Orion, the disks of the surrounding Orion Nebular Cluster suffer reduced emission at long infrared wavelengths. The reduction tracks distance from the most luminous Trapezium star, θ1 Ori C, so this appears to be the effect of UV oblation of the outer part of the disks.
For clues on environmental effects on disk evolution and planet formation, we compare the disk properties and dust properties of Orion A disks to that of Taurus disks and examine trends with respect to position within Orion A. We extract spectral indices, equivalent widths, and integrated fluxes from IRS spectra of Class II objects in Orion A which pertain to disk structure and dust composition. We measure mass accretion rates using hydrogen recombination lines in SpeX spectra of our targets. Utilizing the properties, we analyze the general distribution of properties of disks in ONC, L1641, and Taurus from their histograms.
Our main findings are as follows. (1)Transitional disks ? those protoplanetary disks for which deficits of infrared excess signify sharp-edged gaps in the dust distribution ? are produced gravitationally by companions to the central star. (2) From the high frequency (>20%) of transitional disks and the similar vertical structure of the Orion A disks to those of Taurus, we infer that giant planet formation and dust sedimentation is well under way, if not complete, even in the youngest Class II objects. (3) Less grain processing ? crystallization and growth of grains to diameter of 1?10 μm ? has occurred among the dust grains in the Orion A disks than in Taurus. The time scales for dust processing must therefore lie in the range of ages of the nearby clouds like Orion, NGC 1333, Taurus, Ophiuchus and Chamaeleon. (4) We detected PAH emission at 6?14 μm from disks around low-mass and low-luminosity young stars, excited externally by UV from the Trapezium stars. (5) As others have found for the Trapezium region of Orion, the disks of the surrounding Orion Nebular Cluster suffer reduced emission at long infrared wavelengths. The reduction tracks distance from the most luminous Trapezium star, θ1 Ori C, so this appears to be the effect of UV oblation of the outer part of the disks.