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Title: 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 and 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 {sub H} in the hydrogen line formation region is constrained to 2 × 10{sup 10}-2 × 10{sup 11} cm{sup –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 excitationmore » 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.« less
Authors:
; ;  [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Five College Astronomy Department, Smith College, Northampton, MA 01063 (United States)
  2. Five College Astronomy Department, University of Massachusetts, Amherst, MA 01003 (United States)
  3. Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States)
  4. Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)
  5. Five College Astronomy Department, Mount Holyoke College, South Hadley, MA 01063 (United States)
Publication Date:
OSTI Identifier:
22341940
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 778; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; COMPARATIVE EVALUATIONS; DENSITY; DESIGN; ELECTRON DENSITY; EMISSION; EXCITATION; FORECASTING; HYDROGEN; IONIZATION; NEAR INFRARED RADIATION; PHOTONS; PROTOPLANETS; RECOMBINATION; SPECTRA; T TAURI STARS