Volume 561, January 2014
|Number of page(s)||43|
|Section||Stellar structure and evolution|
|Published online||17 December 2013|
X-shooter spectroscopy of young stellar objects
1 INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
2 INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
3 INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
4 INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
5 INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
6 INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
7 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
8 Department of Planetary Science, Lunar and Planetary Lab. University of Arizona, 1629, E. University Blvd, 85719, Tucson, AZ, USA
9 DIAS/Dublin Institute for Advanced Studies, Burlington Road, 15 Dublin 4, Ireland
10 ASI-Science Data Centre, via Galileo Galilei, 00044 Frascati, Italy
11 Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching, Germany
Received: 10 July 2013
Accepted: 3 October 2013
We present VLT/X-shooter observations of a sample of 36 accreting low-mass stellar and substellar objects (YSOs) in the Lupus star-forming region, spanning a range in mass from ~0.03 to ~1.2 M⊙, but mostly with 0.1 M⊙<M⋆< 0.5 M⊙. Our aim is twofold: firstly, to 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 in turn the accretion rate (Ṁacc), was derived by modelling the excess emission from the UV to the near-infrared as the continuum emission of a slab of hydrogen. We computed the flux and luminosity (Lline) of many emission lines of H , He , and Ca ii, observed simultaneously in the range from ~330 nm to 2500 nm. 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 than relationships previously reported in the literature. Our measurements extend the Paβ and Brγ relationships to Lacc values about two orders of magnitude lower than those reported in previous studies. We confirm that different methodologies of measuring Lacc and Ṁacc yield significantly different results: Hα line profile modelling may underestimate Ṁacc by 0.6 to 0.8 dex with respect to Ṁacc derived from continuum-excess measures. These differences may explain the probably spurious bi-modal relationships between Ṁacc and other YSOs properties reported in the literature. We derived Ṁacc in the range 2 × 10-12–4 × 10-8 M⊙ yr-1 and conclude that Ṁacc ∝ M⋆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 Ṁacc, confirming previous suggestions that the geometry of the accretion flow controls the rate at which the disc material accretes onto the central star.
Key words: stars: pre-main sequence / stars: low-mass / accretion, accretion disks / line: formation / line: identification / open clusters and associations: individual: Lupus
Based on observations collected at the European Souther Observatory at Paranal, under programs 084.C-0269(A), 085.C-0238(A), 086.C-0173(A), 087.C-0244(A) and 089.C-0143(A).
Tables 1–4 and Appendices are available in electronic form at http://www.aanda.org
© ESO, 2013
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