A. C. Raga,1 D. A. Williams,2 A. J. Lim3
1 Instituto de Ciencias Nucleares, UNAM, Apdo. Postal 70-543, 04510 México, D. F., México (raga@nuclecu.unam.mx).
2 Department of Physics and Astronomy, UCL, Gower St., London, WC1E 6BT, United Kingdom (daw@star.ucl.ac.uk).
3 Department of Applied Mathematics, University of Leeds, LS2 9JT, United Kingdom (ajl@ast.leeds.ac.uk).
Received 2004 November 15 ]]> Accepted 2005 January 31
RESUMEN
Las cadenas de nudos alineados que definen los haces de los chorros HH a veces son observadas tanto en líneas atómicas/iónicas como en líneas moleculares (de H2). Modelamos estos objetos como chorros con una velocidad de expulsión dependiente del tiempo, la cual produce superficies de trabajo internas que viajan a lo largo del chorro. Si esta interpretación es correcta, entonces la presencia de nudos alineados de H2 es un indicador de alta sensibilidad de las amplitudes de la variabilidad en la expulsión. Encontramos que para variabilidades con amplitudes de ~ 10 km s-1, las superficies de trabajo internas tienen condiciones apropiadas para que se forme H2 (mediante química de iones negativos y positivos en la fase gaseosa). Presentamos simulaciones axisimétricas hidrodinámicas+químicas que muestran que fracciones de H2 de hasta ~ 1-10% pueden ser obtenidas, y que la emisión de H2 1-0 S(1) resultante puede ser substancialmente más alta que la emisión de Hα. De nuestro estudio, concluímos que la emisión de H2 observada en las cadenas de nudos de algunos chorros HH podrían corresponder a moléculas formadas in situ dentro de superficies de trabajo internas que viajan a lo largo del chorro.
ABSTRACT
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.
Key Words: ISM: Herbing-Haro objects — ISM: Jets and outflows — ISM: Kinematics and dynamics.
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]]>ACKNOWLEDGMENTS
AR acknowledges support from the CONACyT grants 36572-E, 41320-F and 43103-F and the DGAPA (UNAM) grants IN 112602 and IN 111803. AJL acknowledges support from PPARC for a postdoctoral research assistantship, and DAW is grateful to the Leverhulme Trust for a travel grant. AR acknowledges I. Diaz for his support with the computing facilities with which the numerical simulations were carried out. We thank an anonymous referee for relevant comments.
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