Resumo

RAGA, A. C.; WILLIAMS, D. A.  e  LIM, A. J.. The formation of H₂ in variable Herbig-Haro jets. Rev. mex. astron. astrofis [online]. 2005, vol.41, n.1, pp.137-146. ISSN 0185-1101.

The chains of aligned knots that define the beams of HH jets are sometimes observed both in atomic/ionic as well as in molecular (H₂) emission lines. We model such objects as jets with an ejection velocity time-variability, which produces internal working surfaces that travel down the jet beam. If this interpretation is indeed correct, then the presence of aligned H₂ knots is a sensitive indicator of the amplitude of the ejection velocity variability. We find that for variabilities with an amplitude of ~ 10 km s^-1, the internal working surfaces have appropriate conditions for H₂ to be formed (via negative and positive ion gas phase chemistry). We present axisymmetric gasdynamic+chemical numerical simulations which show that H₂ fractions as high as ~ 1-10% can be obtained, and that the resulting H₂ 1-0 S(1) emission can be substantially larger than the Hα emission. From our study, we conclude that the H₂ emission observed in the chains of knots along some HH jets could correspond to molecules formed in situ within the internal working surfaces that travel down the jet flow.

Palavras-chave : ISM [Herbing-Haro objects]; ISM [Jets and outflows]; ISM [Kinematics and dynamics].