X-shooter spectroscopy of young stellar objects: I - Mass accretion rates of low-mass T Tauri stars in \sigma Orionis

By E. Rigliaco, A. Natta, L. Testi, S. Randich, J. Alcalá, E. Covino, B. Stelzer. 2012

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We present high-quality, medium resolution X-shooter/VLT spectra in the range 300-2500 nm for a sample of 12 very low-mass stars in the Orionis cluster. The sample includes eight stars with evidence of disks from Spitzer and four without, with masses ranging from 0.08 to 0.3 M . The aim of this first paper is to investigate the reliability of the many accretion tracers currently used to measure the mass accretion rate in low-mass, young stars and the accuracy of the correlations between these secondary tracers (mainly accretion line luminosities) found in the literature. We use our spectra to measure the accretion luminosity from the continuum excess emission in the UV and visual; the derived mass accretion rates range from 10 9 M yr 1 down to 5 10 11 M yr 1 , allowing us to investigate the behavior of the accretion-driven emission lines in very-low mass accretion rate regimes. We compute the luminosity of ten accretion-driven emission lines, from the UV to the near-IR, all obtained simultaneously. In general, most of the secondary tracers correlate well with the accretion luminosity derived from the continuum excess emission. We recompute the relationships between the accretion luminosities and the line luminosities, we confirm the validity of the correlations given in the literature, with the possible exception of H . Metallic lines, such as the CaII IR triplet or the Na I line at 589.3 nm, show a larger dispersion. When looking at individual objects, we find that the Hydrogen recombination lines, from the UV to the near-IR, give good and consistent measurements of Lacc often in better agreement than the uncertainties introduced by the adopted correlations. The average Lacc derived from several Hydrogen lines, measured simultaneously, have a much reduced error. This suggests that some of the spread in the literature correlations may be due to the use of non-simultaneous observations of lines and continuum. Three stars in our sample deviate from this behavior, and we discuss them individually.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/f54f693d4809580e0853eddd7cfd7180913fec4b

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Citations in the corpus

A spectroscopic survey of Herbig Ae/Be stars with X-shooter – I. Stellar parameters and accretion rates (2015, background): “This UV-excess has been measured in both brown dwarfs (Herczeg & Hillenbrand 2008; Herczeg, Cruz & Hillenbrand 2009; Rigliaco et al. 2012) and CTTs (Calvet et al. 2004; Gullbring et al. 2000; Calvet et al. 2004; Ingleby et al. 2013).”
ACCRETION RATES FOR T TAURI STARS USING NEARLY SIMULTANEOUS ULTRAVIOLET AND OPTICAL SPECTRA (2013, background): “…by either a single temperature and density in treatments of the shock as a slab (Valenti et al. 1993; Gullbring et al. 1998; Herczeg & Hillenbrand 2008; Rigliaco et al. 2012), or a single energy flux in the accretion column for accretion shock models (Calvet & Gullbring 1998, see Section 3.4).”
Magellan Adaptive Optics Imaging of PDS 70: Measuring the Mass Accretion Rate of a Young Giant Planet within a Gapped Disk (2018, methodology): “Briefly, the calculation follows the conversion from Hα luminosity, to accretion luminosity, to accretion rate as outlined in Rigliaco et al. (2012).”
An ALMA Survey of Protoplanetary Disks in the σ Orionis Cluster (2017, methodology): “Spectral types were primarily taken from the homogenous sample of low-resolution optical spectra analyzed in Hernández et al. (2014), but supplemented with those from medium-resolution VLT/X-Shooter spectra when available from Rigliaco et al. (2012).”
Accretion onto Pre-Main-Sequence Stars (2016, methodology): “Direct measurements of accretion rates have been made for intermediate-mass and HAeBe stars (Calvet et al. 2004, Donehew & Brittain 2011, Mendigutia et al. 2011, Fairlamb et al. 2015) down to the substellar regime (e.g., Herczeg et al. 2009, Rigliaco et al. 2012, Zhou et al. 2014).”
X-Shooter study of accretion in Chamaeleon I (2015, methodology): “Recent studies have also demonstrated that Lacc derived from several emission lines measured simultaneously lead to results compatible, although with a larger scatter, with more direct methods (Rigliaco et al. 2012; Alcalá et al. 2014).”