Determining stellar accretion rates from Paα and Brβ emission lines with JWST NIRSpec

In this Letter, we present the first systematic spectroscopic measurements of the near-infrared (NIR) hydrogen recombination lines Paschen alpha ( Pa α λ = 1.875 μm) and Brackett beta ( Br β λ = 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 Br γ 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: 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 to establishing rough estimates of the accretion rates for large samples of PMS stars with JWST.