Looking for outflows from brown dwarfs

Abstract

First evidences of IR excess and disk mass accretion (strong H$\alpha$ emission) around brown dwarfs seem to indicate the existence of circumstellar disks around these sub-stellar objects. Nothing is known at the present time about outflows which potentially might be launched from brown dwarfs, although jets are typically associated with the accretion in standard T Tauri star disks. In this paper we calculate the H$\alpha$ emission of internal working surfaces produced by a radiative jet in a neutral and in a photoionized environment as a function of the jet parameters (the ejection velocity $v_j$, shock velocity $v_s$, mass loss rate ${\dot M}$ and radius $r_j$ of the jet) and we provide estimates of the H$\alpha$ luminosity for the parameters of ``standard'' Herbig-Haro (HH) jets from T Tauri stars and for the parameters expected for jets from BDs. Interestingly, we find that while the mass loss rates associated with jets from BDs are found to be two orders of magnitude lower than the mass loss rates associated with ``standard'' HH jets (from T Tauri stars), their velocities are likely to be similar. Based on our calculations, we discuss the conditions in which jets from BDs can be detected and we conclude that the H$\alpha$ luminosities of internal working surfaces of jets from BDs in a photoionized environment should have only one order of magnitude lower than the H$\alpha$ luminosities of T Tauri jets in a neutral environment.