Confirming Accretion in Mylupi with UV-HST Observations

Abstract

The mass accretion rate is a crucial parameter for the study of the evolution of accretion discs around young low-mass stellar and substellar objects (YSOs), because it sets important constraints for disc evolution models and disc clearing mechanisms, and is a key quantity for the studies of Pre-Main Sequence (PMS) stellar evolution and planet formation. Low-mass PMS stars with transitional discs accreting at very low rates are likely in the final stages of inner disc evolution, and probably have already formed protoplanets. Hence, identifying and investigating such low accretors may help understanding planet formation. However, measurements of low accretion rates are challenging. In this work, we use UV-HST spectra to unambiguously confirm and investigate the accretion rate in the transitional YSO MYLup, an object previously classified as a weak or non-accretor based on optical spectra. The puzzle here is that the HST data provide a Macc value an order