Accretion luminosity of Class I protostars

We have developed a new methodology to measure accretion luminosity using mid-infrared hydrogen recombination lines and applied it to a limited sample of Class I protostars in the Taurus and Ophiuchus star-forming regions. We adopted the commonly used assumption that the properties of disk-protostar accretion in Class I objects is similar to the disk-star accretion in Class II objects.

Using simultaneous observations of three hydrogen recombination lines, Br{gamma}, Pf{gamma}, and Br{alpha}, we derived the mean intrinsic line ratios, and we verified that these are constant across the probed range of photospheric and accretion properties. We established correlations between the line luminosities and accretion luminosity. We measured the extinction toward the line emission regions in Class I protostars, comparing the observed line ratios to the Class II mean values.