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Near-Infrared Spectroscopic Study
of AA TauLogan R. Brown
Erika L. Gibb
Nathan X. Roth
University of Missouri – St. Louis
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© Bill Saxton, NRAO / AUI / NSF
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Observations
High-resolution (λ/Δλ ∼ 25,000), near-infrared spectroscopic data obtained 2010 Feb 23 using NIRSPEC at Keck II (McLean et al. 1998)
Observations range from 2860 cm-1 to 3477 cm-1, chosen to cover many transitions of OH and Water
Reduced using a standard method: dark subtracted, flat fielded, cleaned of hot and dead pixels, spectrally and spatially straightened (Bonev 2005, DiSanti et al. 2001)
Telluric model fit to and subtracted from reduced spectra
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AA Tau
Fairly typical Classical T Tauri Star: K7 spectral type
Well-know, shows strong H-alpha emission and IR excesses indicating the presence of a gaseous and dusty accretion disc
Undergoes periodic eclipses caused by a warped inner disk structure
CO absorption studied in the 2 micron region
Water and prebiotic molecules observed in emission in the Mid-IR
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Comparison of the observed spectrum of AA Tauri to the combined model spectrum. All the unlabeled features are rotational transitions of H2O. (Carr & Najita 2008)
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AA Tau Inclination
Warped inner disc structure producing periodic eclipses
Period of eclipses used to calculate equatorial rotation velocity (8.22 ± 0.03 d)
Coupled with measured v sin i (11.3 ± 0.7 km s-1)
Calculated inclination of 70o ± 10o
(Donati et al. 2010)
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Red = 75o (traces top of dark lane), orange = 72o, yellow = 70o, blue = 68o inclination (traces bottom of dark lane. Derived i = 71o ± 1o. (Cox et al. 2013)
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Henning & Semenov 2013
Near-IR
Mid-IR
(Sub)millimeter
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Portion of the observed spectra
Error envelope plotted in grey, telluric model in pink
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Schematic representation of the line-of-sight geometry for the inner region of T Tauri star disk. (McJunkin et al. 2013)
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Portion of the observed spectra
Error envelope plotted in grey, telluric model in pink
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001-000 blue, 011-010 purple, 020-000 brown, 100-000 red, 110-010 green, OH tick marks
Single temperature, LTE model
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001-000 blue, 011-010 purple, 020-000 brown, 100-000 red, 110-010 green, OH tick marks
Single temperature, LTE model
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CO spectrum from HL Tau. The broad emission features result from hot CO gas near the star. The narrow absorption features that are superposed on these emission features have a lower rotational temperature indicating colder gas along the line of sight. (Brittain et al. 2005)
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Fractional abundance of H2O as a function of disk radius and height up to a radius of 10 AU (Walsh et al. 2010)
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Fractional abundance of H2O as a function of disk radius and height up to a radius of 10 AU (Walsh et al. 2010)
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See Brown et al. 2013 for discussion of modeling
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Going Forward
Apply the developed emission line model with disk appropriate line profile
Simultaneously modeling emission and absorption
Finalize temperature and column density
Search for and identify other species such as HCN
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Acknowledgments
NASA Missouri Space Grant Consortium
NSF’s Stellar Astronomy program
The American Recovery and Reinvestment Act of 2009
NASA Exobiology and Evolutionary Biology program
W.M. Keck Observatory
The cultural role and reverence that the summit of Mauna Kea has with the indigenous Hawaiian community