Constraining Temperature and Density of Accretion Flows in T Tauri Stars from Brackett Line Ratios

Young stellar objects known as T Tauri Stars (TTSs) are low-mass, pre-main sequence stars with strong hydrogen emission lines. These emission lines are thought to originate in the accretion of disk material, which is dominated by the stellar magnetopshere. In this magnetospheric accretion model, gas in the circumstellar disk is captured by magnetic field lines and funneled onto the stellar surface, creating a shock. Hydrogen Brackett emission lines trace this shocked material and can be used determine the density and temperature of the accretion flows. Brackett lines (Br10-Br18) were located within the high resolution, near infrared spectra of 165 TTSs from the Immersion Grating INfrared Spectrometer (H and K band coverage at R~45,000). The lines were extinction corrected, fit, and integrated to calculate the total flux. A Bootstrap Monte Carlo simulation was run for each measurement to calculate the associated uncertainties. Line ratios relative to Br10 were calculated and compared with a Case B recombination method using a reduced chi squared test. The measurements best fit higher model temperatures and densities than previous attempts using low resolution spectra. These results are in better agreement with the predictions of magnetospheric accretion models.