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Published December 1, 2013 | Published + Submitted
Journal Article Open

Interpreting Near Infrared Hydrogen Line Ratios in T Tauri Stars


In accreting young stars, one of the prominent spectral features in the near-infrared is the Paschen and Brackett series in emission. We examine hydrogen line ratios for 16 classical T Tauri stars from SpeX spectra and assess the trends with veiling and accretion. The observed line ratios are compared with two theoretical models for line formation: (1) Baker & Menzel's Case B for radiative ionization and recombination and (2) a set of local line excitation calculations designed to replicate the conditions in T Tauri winds and magnetic accretion columns (KF). While the comparison between Case B and observed line ratios implies a wide range in electron density and temperature among the hydrogen line formation regions in T Tauri stars, the predictions of the local line excitation models give consistent results across multiple diagnostics. Under the assumptions of the local line excitation calculations, we find that n_H in the hydrogen line formation region is constrained to 2 × 10^(10)-2 × 10^(11) cm^(–3), where stars with higher accretion rates have densities at the higher end of this range. Because of uncertainties in extinction, temperature is not well delineated, but falls within the range expected for collisional excitation to produce the line photons. We introduce new diagnostics for assessing extinction based on near-infrared hydrogen line ratios from the local line excitation calculations.

Additional Information

© 2013 American Astronomical Society. Received 2013 June 12; accepted 2013 September 16; published 2013 November 12. We thank Greg Herczeg, Mike Peterson, and Hans Moritz Günther for useful discussions. Also, we thank our referee who made some very helpful comments. The authors reverently acknowledge the cultural significance of the Mauna Kea summit to the indigenous Hawaiian community. We are most fortunate to have had the opportunity to conduct observations with the IRTF from this mountain. Facility: IRTF(SpeX)

Attached Files

Published - 0004-637X_778_2_148.pdf

Submitted - 1309.4449v2.pdf


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