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Register a new userSpatially Extended Brackett Gamma Emission in the Environments of Young Stars
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Tracy L. Beck
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The majority of atomic hydrogen Br{gamma} emission detected in the spectra of young stellar objects (YSOs) is believed to arise from the recombination regions associated with the magnetospheric accretion of circumstellar disk material onto the forming star. In this paper, we present the results of a K-band IFU spectroscopic study of Br{gamma} emission in eight young protostars: CW Tau, DG Tau, Haro 6-10, HL Tau, HV Tau C, RW Aur, T Tau and XZ Tau. We spatially resolve Br{gamma} emission structures in half of these young stars and find that most of the extended emission is consistent with the location and velocities of the known Herbig-Haro flows associated with these systems. At some velocities through the Br{gamma} line profile, the spatially extended emission comprises 20% or more of the integrated flux in that spectral channel. However, the total spatially extended Br{gamma} is typically less than ~10% of the flux integrated over the full emission profile. For DG Tau and Haro 6-10 S, we estimate the mass outflow rate using simple assumptions about the hydrogen emission region, and compare this to the derived mass accretion rate. We detect extended Br{gamma} in the vicinity of the more obscured targets in our sample and conclude that spatially extended Br{gamma} emission may exist toward other stars, but unattenuated photospheric flux probably limits its detectability.
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We present multiple epochs of near-IR spectroscopy for a sample of 25 young stars, including T Tauri, Herbig Ae/Be, and FU Ori objects. Using the FSPEC instrument on the Bok 90-inch telescope, we obtained K-band spectra of the BrGamma transition of hydrogen, with a resolution of ~3500. Epochs were taken over a span of >1 year, sampling time-spacings of roughly one day, one month, and one year. The majority of our targets show BrGamma emission, and in some cases these are the first published detections. Time-variability is seen in approximately half of the targets showing BrGamma emission. We compare the observed variability with expectations for rotationally-modulated accretion onto the central stars and time-variable continuum emission or extinction from matter in the inner disk. Our observations are not entirely consistent with models of rotationally-modulated magnetospheric accretion. Further monitoring, over a larger number of epochs, will facilitate more quantitative constraints on variability timescales and amplitudes, and a more conclusive comparison with theoretical models.
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