Determining stellar accretion rates from Pa_α and Br_β emission lines with JWST NIRSpec

In this letter we present the first systematic spectroscopic measurements of the Near-InfraRed (NIR) hydrogen recombination lines Pa_α (λ = 1.875 μ m) and Br_β (λ = 2.626 μ m), produced by pre-main sequence (PMS) stars. These stars, consisting of T Tauri and Herbig AeBe stars are located in the massive Galactic star-formation region NGC 3603. The measurements were obtained from JWST NIRSpec, using multi-object spectroscopy (MOS) mode. Utilising existing empirical relations between L_acc and L_Br_γ, we have 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: log_10( L_acc/L_⊙) = 1.42 (± 0.18) ×log_10( L_Pa_α/L_⊙) + 3.33 (± 0.42) and log_10( L_acc/L_⊙) = 1.47 (± 0.18) ×log_10( L_Br_β/L_⊙) + 4.60 (± 0.57). These new relationships are key for roughly estimating the accretion rates for large samples of PMS stars with JWST.