HST spectra reveal accretion in MY Lupi Journal Article uri icon



  • 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). We revisit the case of MY Lup, an object where VLT/X-shooter data suggested a negligible mass accretion rate, and show it to be accreting on a level similar to other Class II YSOs in Lupus based on Hubble Space Telescope (HST) observations. In our HST-Cosmic Origins Spectrograph (HST-COS) and -Space Telescope Imaging Spectrograph (HST-STIS) spectra, we find many emission lines, as well as substantial far-ultraviolet (FUV) continuum excess emission, which can be ascribed to active accretion. The total luminosity of the C IV λ1549 Å doublet is 4.1 × 10−4 L. Using scalings between accretion luminosity, Lacc, and C IV luminosity from the literature, we derive Lacc ~2 × 10−1 L, which is more than an order of magnitude higher than the upper limit estimated from the X-shooter observations. We discuss possible reasons for the X-shooter-HST discrepancy, the most plausible being that the low contrast between the continuum excess emission and the photospheric+chromospheric emission at optical wavelengths in MY Lup hampered detection of excess emission. The luminosity of the FUV continuum and C IV lines, strong H2 fluorescence, and a “1600 A Bump” place MY Lup in the class of accreting objects with gas-rich discs. So far, MY Lup is the only peculiar case in which a significant difference between the HST and X-shooter acc estimates exists that is not ascribable to variability. The mass accretion rate inferred from the revisited Lacc estimate is acc ~ 1(; −0.5+1.5; ) × 10−8 M yr−1. This value is consistent with the typical value derived for accreting YSOs of similar mass in Lupus and points to less clearing of the inner disc than indicated by near- and mid-infrared observations. This is confirmed by Atacama Large Millimeter Array (ALMA) data, which show that the gaps and rings seen in the sub-millimetre are relatively shallow.

publication date

  • September 1, 2019

Full Author List

  • Alcalá JM; Manara CF; France K; Schneider CP; Arulanantham N; Miotello A; Günther HM; Brown A

Other Profiles

Additional Document Info

start page

  • A108

end page

  • A108


  • 629