Near-Infrared Spectroscopic Study

of AA TauLogan R. Brown

Erika L. Gibb

Nathan X. Roth

University of Missouri – St. Louis

© Bill Saxton, NRAO / AUI / NSF

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

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

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)

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)

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)

Henning & Semenov 2013

Near-IR

Mid-IR

(Sub)millimeter

Portion of the observed spectra

Error envelope plotted in grey, telluric model in pink

Schematic representation of the line-of-sight geometry for the inner region of T Tauri star disk. (McJunkin et al. 2013)

Portion of the observed spectra

Error envelope plotted in grey, telluric model in pink

001-000 blue, 011-010 purple, 020-000 brown, 100-000 red, 110-010 green, OH tick marks

Single temperature, LTE model

001-000 blue, 011-010 purple, 020-000 brown, 100-000 red, 110-010 green, OH tick marks

Single temperature, LTE model

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)

Fractional abundance of H2O as a function of disk radius and height up to a radius of 10 AU (Walsh et al. 2010)

Fractional abundance of H2O as a function of disk radius and height up to a radius of 10 AU (Walsh et al. 2010)

See Brown et al. 2013 for discussion of modeling

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

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