Accretion-ejection connection in the young brown dwarf candidate ISO-ChaI 217

Abstract

As the number of observed brown dwarf outflows is growing it is important to investigate how these outflows compare to the wellstudied jets from young stellar objects. A key point of comparison is the relationship between outflow and accretion activity and in particular the ratio between the mass outflow and accretion rates (Ṁ out /Ṁ acc ). The brown dwarf candidate ISO-ChaI 217 was discovered by our group, as part of a spectro-astrometric study of brown dwarfs, to be driving an asymmetric outflow with the blueshifted lobe having a position angle of ∼20 • . The aim here is to further investigate the properties of ISO-ChaI 217, the morphology and kinematics of its outflow, and to better constrainṀ out /Ṁ acc . The outflow is spatially resolved in the [S ] λλ6716, 6731 lines and is detected out to ∼1. 6 in the blue-shifted lobe and 1 in the red-shifted lobe. The asymmetry between the two lobes is confirmed although the velocity asymmetry is less pronounced with respect to our previous study. Using thirteen different accretion tracers we measure log (Ṁ acc ) [M /yr] = −10.6 ± 0.4. As it was not possible to measure the effect of extinction on the ISO-ChaI 217 outflowṀ out was derived for a range of values of A v , up to a value of A v = 2.5 mag estimated for the source extinction. The logarithm of the mass outflow (Ṁ out ) was estimated in the range −11.7 to −11.1 for both jets combined. ThusṀ out /Ṁ acc [M /yr] lies below the maximum value predicted by magneto-centrifugal jet launching models. Finally, both model fitting of the Balmer decrements and spectro-astrometric analysis of the Hα line show that the bulk of the H I emission comes from the accretion flow.

Jets from young stars and brown dwarfs

“…Projects are currently under-way to complete the goal of constrainingṀ out /Ṁ acc in BDs. See Whelan et al (2014) for a description of these results.…”

“…If this is confirmed to be the case, it would be relevant to BD formation as it could be invoked to explain why BDs never accrete enough mass for hydrogen fusion to begin. However, this result will not be confirmed until the kind of investigation discussed in Whelan et al (2014) has been completed for a significant number of young BDs with outflows. A second property unique to BD outflows is that the proper motion of the BD itself could be comparable to the proper motion of the outflow.…”

“…The work of measuring this important ratio in BDs has begun and while the first results suggested that this ratio may be higher in BDs than CTTSs (Whelan et al 2009b), recent new investigations have demonstrated that various biases can strongly influence these measurements (Whelan et al 2014). This is well illustrated if we consider the case of the very low mass star (VLMS) Par-Lup3-4.…”

X-shooter study of accretion in Chamaeleon I

“…One of them is a well-known edge-on target, ESO-Hα 574, which was analyzed by Bacciotti et al (2011) and is not discussed here, since the stellar and accretion parameters of edge-on targets are too uncertain to be included in the analysis. The other, ISO-ChaI 217, is a a well-known brown dwarf with a jet (Whelan et al 2014) and is included in our sample. With respect to the ALMA sample, our sample includes 2 additional targets.…”

Episodic accretion in binary protostars emerging from self-gravitating solar mass cores

“…The great number of physical parameters involved in setting the initial conditions in molecular cloud cores makes the phenomenon of star formation interesting as well as complex enough to explore in every detail. In addition to physical processes like episodic accretion onto young embedded protostars (Fendt 2009), many other exciting features of star formation exist, such as protostellar jets (Vorobyov and Basu 2015;Lee 2015) observed during the accretion phase of protostars (Whelan et al 2014) and in the absence of efficient angular momentum transport mechanisms (Attwood et al 2009;Walch et al 2012). The fundamental cause of episodic accretion is still unclear (Stamatellos et al 2012).…”