Determining stellar accretion rates from Pa_α and Br_β emission lines with JWST NIRSpec: Accretion of pre-main-sequence stars in NGC 3603

In this Letter, we present the first systematic spectroscopic measurements of the near-infrared (NIR) hydrogen recombination lines Paschen alpha (Pa_αλ = 1.875 µm) and Brackett beta (Br_βλ = 2.626 µm), produced by pre-main-sequence (PMS) stars. Such stars include T Tauri and Herbig AeBe stars, located in the massive Galactic star-forming region NGC 3603. We used measurements obtained from JWST NIRSpec, using multi-object spectroscopy (MOS) mode. Based on the existing empirical relations between L_acc and L_Brγ from the literature, we used our new measurements to formulate, for the first time, an empirical relationship between the accretion luminosity, L_acc, of the stars and the line luminosities, L_line, of both Pa_α and Br_β. These relationships are: log₁₀(Equation presented) = 1.42(±0.18) × log₁₀(Equation presented) + 3.33(±0.42) and log₁₀(Equation presented) = 1.47(±0.18) × log₁₀(Equation presented) + 4.60(±0.57). These new relationships are key to establishing rough estimates of the accretion rates for large samples of PMS stars with JWST.