POISSON project

Abstract

Context. We present the results of the analysis of low-resolution optical-near IR spectroscopy (0.6-2.4 μm) of a sample (47 sources) of Class I and Class II young stellar objects in the Chamaeleon I and II star-forming clouds. These data are part of the POISSON project (Protostellar Optical-Infrared Spectral Survey On NTT). Aims. The aim of the observations is to determine the accretion luminosity (L acc ) and mass accretion rate (Ṁ acc ) of the sources through the analysis of the detected emission features. Taking advantage of the wide wavelength range covered by our spectra, we also aim at verifying the reliability and consistency of the existing empirical relationships connecting emission line luminosity and L acc . Methods. We employ five different tracers ([O i] λ6300, Hα, Ca ii λ8542, Paβ, and Brγ) to derive the accretion luminosity, and critically discuss the various determinations in the light of the source properties. Results. The tracers provide L acc values characterised by different scatters when plotted as a function of L * . The Brγ relation appears to be the most reliable, because it gives the minimum dispersion of L acc over the entire range of L * , whereas the other tracers, in particular Hα, provide much more scattered L acc results, which are not expected for the homogeneous sample of targets we are observing. The direct comparison between L acc (Brγ) and the accretion luminosity obtained from the other four tracers also shows systematic differences in the results provided by the empirical relationships. These may probably be ascribed to different excitation mechanisms that contribute to the line emission, which may vary between our sample and those where the relationships have been calibrated, which were mostly based on observations in Taurus. Adopting the accretion luminosities estimates derived from the Brγ line, we infer L acc in the range 0.1 L * -1 L * for all sources, andṀ acc of the order 10 −7 − 10 −9 M yr −1 , in the range of values commonly obtained for Class II objects. The mass accretion rates derived in Cha I are roughly proportional to M 2 * , in agreement with the results found in other low-mass star-forming regions. We find that the discrepancies observed in the case of L acc (Brγ) and L acc (Paβ) can be related to different intrinsic Paβ/Brγ ratios. The derived ratios point to the existence of two different emission modalities, one that agrees with predictions of both wind and accretion models, the other suggesting optically thick emission from relatively small regions (10 21 -10 22 cm 2 ) with gas at low temperatures (<4000 K), the origin of which needs additional investigation.

POISSON project

“…4.4.2 and Table 7), with Class I, Flat, and Class II represented as dots, squares, and triangles, respectively. As already observed by several authors (e.g., Muzerolle et al 1998;Natta et al 2006;Antoniucci et al 2011), L acc increases with L * . In our sample there is a large scatter of L acc /L * values for objects with similar L * values, i.e.…”

“…In this framework, we have undertaken a combined optical/IR unbiased spectroscopic survey on a flux-limited sample of selected Class I/II sources, located in six different nearby clouds (namely Cha I & II, L 1641, Serpens, Lupus, Vela, and Corona Australis; see, Antoniucci et al 2011, hereafter Paper I), using the EFOSC2/SOFI instruments on the ESO-NTT (POISSON: Protostellar Objects IR-optical Spectral Survey On NTT). In Paper I we presented the results of the Cha I & II regions, comparing L acc determinations from the different tracers, and discussing the reliability and consistency of the different empirical relationships considered.…”

X-shooter spectroscopy of young stellar objects

“…The trend found by Natta et al (2004) shows a good correlation over the whole range of masses from few tens of Jupiter masses to about one solar mass. Our new data confirm the trend found by Natta et al (2004) and reinforce the strength of this line as an accretion indicator, agreeing with the results found by Antoniucci et al (2011), who also tested the reliability of this indicator as accretion tracer.…”

X-Shooter study of accretion in Chamaeleon I

“…This mass accretion rate (Ṁ acc , e.g., Hartmann et al 1998) may be compared to the stellar and disk properties to test the predictions of models of disk evolution. Relations between the accretion luminosity (L acc ) and stellar luminosity (L , e.g., Natta et al 2006;Clarke & Pringle 2006;Rigliaco et al 2011a;Manara et al 2012) and betweenṀ acc and stellar mass (M , e.g., Muzerolle et al 2003;Mohanty et al 2005;Natta et al 2006;Herczeg & Hillenbrand 2008;Antoniucci et al 2011Antoniucci et al , 2014Manara et al 2012;Alcalá et al 2014;Ercolano et al 2014;Frasca et al 2015) are frequently derived to examine the dependence of accretion on the properties of the central star. Accretion has sometimes been found to correlate with age (e.g., Hartmann et al 1998;Sicilia-Aguilar et al 2010;Antoniucci et al 2014), although ages of individual young stars in a given This work is based on observations made with ESO Telescopes at the Paranal Observatory under programme ID 084.C-1095 and 094.C-0913.…”

“…Recent studies have also demonstrated that L acc 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). Therefore, measuringṀ acc from the luminosity of emission lines is a method that is being extensively used in the literature (e.g., Mohanty et al 2005;Natta et al 2006;Fang et al 2009;Costigan et al 2012;Antoniucci et al 2011Antoniucci et al , 2014Biazzo et al 2014).…”