Looking for Outflows from Brown Dwarfs

Abstract

Initial evidence of IR excess and disk mass accretion (strong Halphaemission) around brown dwarfs (BDs) seems to indicate the existence ofcircumstellar disks around these substellar objects. Nothing is known atpresent about outflows that might be launched from BDs, although jetsare typically associated with the accretion in the case of standard TTauri star disks. In this paper we calculate the Halpha emission ofinternal working surfaces produced by a radiative jet in a neutral andin a photoionized environment as a function of the jet parameters ( theejection velocity v(j), shock velocity v(s), mass-loss rate. M, andradius r(j) of the jet), and we provide estimates of the Halphaluminosity for the parameters of ``standard'' Herbig-Haro (HH) jets fromT Tauri stars and for the parameters expected for jets from BDs.Interestingly, we find that while the mass-loss rates associated withjets from BDs are 2 orders of magnitude lower than the mass-loss ratesassociated with ``standard'' HH jets (from T Tauri stars), theirvelocities are likely to be similar. Based on our calculations, wediscuss the conditions in which jets from BDs can be detected, and weconclude that the Halpha luminosities of internal working surfaces ofjets from BDs in a photoionized environment should be only 1 order ofmagnitude lower than the Halpha luminosities of T Tauri jets in aneutral environment.