2019/08/27 by J. M. Alcalá, J. M. Alcala', C. F. Manara +7 · 1 citation
Physics and Astronomy · #Accretion (finance) #Accretion disc #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Emission spectrum #Luminosity #Space Telescope Imaging Spectrograph #Spectral line #Spectrograph #Spitzer Space Telescope #Telescope #astro-ph.SR
paper · pdf · doi:10.1051/0004-6361/201935657
published as A&A 629, A108 (2019) · 13 pager, 8 figures, two tables
openalex publication_date 2019/08/27 · arxiv created 2019/08/28 · openalex created_date 2019/09/05 · arxiv updated 2019/09/18 · openalex updated_date 2026/08/06
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 λ 1549 Å doublet is 4.1 × 10 −4 L ⊙ . Using scalings between accretion luminosity, L acc , and C IV luminosity from the literature, we derive L acc ~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 H 2 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 Ṁ acc estimates exists that is not ascribable to variability. The mass accretion rate inferred from the revisited L acc estimate is Ṁ 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.