X-shooter spectroscopy of young stellar objects. IV. Accretion in low-mass stars and substellar objects in Lupus

By J. Alcalá, A. Natta, C. Manara, L. Spezzi, B. Stelzer, A. Frasca, K. Biazzo, E. Covino, S. Randich, E. Rigliaco and 4 more. 2013

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We present X-Shooter/VLT observations of a sample of 36 accreting low-mass stellar and sub-stellar objects (YSOs) in the Lupus star forming region, spanning a range in mass from ~0.03 to ~1.2Msun, but mostly with 0.1Msun < Mstar < 0.5Msun. Our aim is twofold: firstly, analyse the relationship between excess-continuum and line emission accretion diagnostics, and, secondly, to investigate the accretion properties in terms of the physical properties of the central object. The accretion luminosity (Lacc), and from it the accretion rate (Macc), is derived by modelling the excess emission, from the UV to the near-IR, as the continuum emission of a slab of hydrogen. The flux and luminosity (Ll) of a large number of emission lines of H, He, CaII, etc., observed simultaneously in the range from ~330nm to 2500nm, were computed. The luminosity of all the lines is well correlated with Lacc. We provide empirical relationships between Lacc and the luminosity of 39 emission lines, which have a lower dispersion as compared to previous relationships in the literature. Our measurements extend the Pab and Brg relationships to Lacc values about two orders of magnitude lower than those reported in previous studies. We confirm that different methodologies to measure Lacc and Macc yield significantly different results: Ha line profile modelling may underestimate Macc by 0.6 to 0.8dex with respect to Macc derived from continuum-excess measures. Such differences may explain the likely spurious bi-modal relationships between Macc and other YSOs properties reported in the literature. We derive Macc in the range 2e-12 -- 4e-8 Msun/yr and conclude that Macc is proportional to Mstar^1.8(+/-0.2), with a dispersion lower by a factor of about 2 than in previous studies. A number of properties indicate that the physical conditions of the accreting gas are similar over more than 5 orders of magnitude in Macc.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/ce5f22dcf1b3eac97bff567aafed342b17d1dfbd

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Citations in the corpus

ALMA SURVEY OF LUPUS PROTOPLANETARY DISKS. I. DUST AND GAS MASSES (2016, methodology): “The age of Lupus is ∼1–2 Myr (Comerón 2008, and references therein) but may be as old as 3 ± 2 Myr (Alcalá et al. 2014).”
A STEEPER THAN LINEAR DISK MASS–STELLAR MASS SCALING RELATION (2016, background): “For these three young regions the relation is close to a power law of two: ˙ ( )*µM M 1.9 0.3 for Taurus (Herczeg & Hillenbrand 2008), ˙ ( )*µM M 1.8 0.2 for Lupus (Alcalá et al. 2014), and ˙ ( )*µM M 1.7 0.4 for ChamaeleonI (Manara et al. 2016a).”