Other
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21933709c&link_type=abstract
American Astronomical Society, AAS Meeting #219, #337.09
Other
Scientific paper
Classical T Tauri stars (CTTSs) are young stars still surrounded by circumstellar accretion disks. The currently accepted theory for how matter is accreted onto the central star from the disk is magnetospheric accretion: stellar magnetic fields truncate the disk at 3R*-6R* and channel material from the disk onto the surface of the star at near free-fall velocities. The infalling material heats up as it impacts the stellar photosphere and emits strongly at optical and UV wavelengths, creating excess emission that can veil the underlying stellar spectrum. We determine mass accretion rates for 35 stars in the 3 Myr old open cluster NGC 2264 and test specific relationships between the stellar and accretion parameters as predicted by the current magnetospheric accretion theory. To find accretion rates, we model the excess accretion emission using an isothermal, pure hydrogen slab in LTE. The observed spectrum is then fit by a combination of the slab emission and a non--accreting stellar template, each of which is subject to a model-dependent reddening value. The final fits provide estimates of the stellar mass, radius, filling factor of the accretion column on the stellar surface, and mass accretion rates. Our observations are well fit by this simple treatment of the excess emission. Using the stellar parameters and accretion rates from the fits, we find an excellent correlation (r=.90) for the relationship predicted by a modified version of the Shu et al. (1994) magnetospheric accretion theory. The modified theory relaxes the stellar dipole magnetic field requirement in favor of a random surface geometry. Our results support the conclusion that magnetospheric accretion governs the mass accretion in CTTSs. Comparisons with accretion rates derived from U-band photometry are also presented. This work is supported by NASA Origins of Solar Systems grant NNX08AH86G.
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