Brackett emission lines in young star APOGEE sp.

Upon impacting the stellar surface, the shocked gas recombines and emits hydrogen spectral lines. To characterize the density and temperature of the gas within these accretion streams, we measure equivalent widths of Brackett (Br)11-20 emission lines detected in 1101 APOGEE spectra of 326 likely pre-main-sequence accretors.

For sources with multiple observations, we measure median epoch-to-epoch line strength variations of 10% in Br11 and 20% in Br20. We also fit the measured line ratios to predictions of radiative transfer models by Kwan & Fischer. We find characteristic best-fit electron densities of n_e_=10^11^-10^12^cm-3, and excitation temperatures that are inversely correlated with electron density (from T~5000K for n_e_~10^12^cm^-3^ to T~12500K at n_e_~10^11^cm^-3^).