Accretion in Young Stellar/Substellar Objects

We present a study of accretion in a sample of 45 young, low-mass objects in a variety of star-forming regions and young associations, about half of which are likely substellar. Based primarily on the presence of broad, asymmetric Hα emission, we have identified 13 objects (~30% of our sample) that are strong candidates for ongoing accretion. At least three of these are substellar. We do not detect significant continuum veiling in most of the accretors with late spectral types (M5-M7). Accretion shock models show that lack of measurable veiling allows us to place an upper limit to the mass accretion rates of ≲10^-10 M_☉ yr^-1. Using magnetospheric accretion models with appropriate (sub)stellar parameters, we can successfully explain the accretor Hα emission-line profiles and derive quantitative estimates of accretion rates in the range 10^-12 M_☉ yr^-1 < < 10^-9 M_☉ yr^-1. There is a clear trend of decreasing accretion rate with stellar mass, with mean accretion rates declining by 3-4 orders of magnitude over ~1-0.05 M_☉.