Resumen

RAGA, A. C.; WILLIAMS, D. A.  y  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.

Palabras llave : ISM [Herbing-Haro objects]; ISM [Jets and outflows]; ISM [Kinematics and dynamics].

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