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

¹ Institut für Astronomie und Astrophysik, Kepler Center for Astro and Particle Physics, Eberhard Karls Universität, 72076 Tübingen, Germany
e-mail: emma.whelan@astro.uni-tuebingen.de
² INAF-Osservatorio Astronomico di Capodimonte, via Moiariello, 16, 80131 Napoli, Italy
³ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ INAF-Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
⁵ Dipartimento di Fisica e Chimica, Università di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
⁶ INAF-Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
⁷ ASI Science Data Center, Via del Politecnico snc, 00133 Rome, Italy
⁸ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland

Received: 25 April 2014
Accepted: 19 August 2014

Abstract

As the number of observed brown dwarf outflows is growing it is important to investigate how these outflows compare to the well-studied 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 blue-shifted 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 constrain Ṁ_out/Ṁ_acc. The outflow is spatially resolved in the [S ii] 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 outflow Ṁ_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. Thus Ṁ_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.