We observed with the JVLA at 3.6 and 1.3 cm a sample of 11 proto-brown dwarf candidates in Taurus in a search for thermal radio jets driven by the most embedded brown dwarfs. We detected for the first time four thermal radio jets in proto-brown dwarf
candidates. We compiled data from UKIDSS, 2MASS, Spitzer, WISE and Herschel to build the Spectral Energy Distribution (SED) of the objects in our sample, which are similar to typical Class~I SEDs of Young Stellar Objects (YSOs). The four proto-brown dwarf candidates driving thermal radio jets also roughly follow the well-known trend of centimeter luminosity against bolometric luminosity determined for YSOs, assuming they belong to Taurus, although they present some excess of radio emission compared to the known relation for YSOs. Nonetheless, we are able to reproduce the flux densities of the radio jets modeling the centimeter emission of the thermal radio jets using the same type of models applied to YSOs, but with corresponding smaller stellar wind velocities and mass-loss rates, and exploring different possible geometries of the wind or outflow from the star. Moreover, we also find that the modeled mass outflow rates for the bolometric luminosities of our objects agree reasonably well with the trends found between the mass outflow rates and bolometric luminosities of YSOs, which indicates that, despite the excess centimeter emission, the intrinsic properties of proto-brown dwarfs are consistent with a continuation of those of very low mass stars to a lower mass range. Overall, our study favors the formation of brown dwarfs as a scaled-down version of low-mass stars.
Physical conditions in dense and cold regions of interstellar clouds favour the formation of ice mantles on the surfaces of interstellar grains. It is predicted that most of the gaseous species heavier than H2 or He will adsorb onto the grains and wi
ll disappear from the gas-phase, changing its chemistry, within 10^9/n_H years. Nonetheless, many molecules in molecular clouds are not completely depleted in timescales of 10^5 yr. Several speculative mechanisms have been proposed to explain why molecules stay in the gas phase, but up to now none are fully convincing. At the same time, these mechanisms are not mutually exclusive and we can still explore the effects of other possible processes. We speculate on the consequences of H2 coating of grains on the evaporation rates of adsorbed species. More experiments and simulations are needed to calculate the evaporation rate Eevap(X-H2).
