Advertisement

Stellar jets: Spectral diagnostics and fluidodynamic models

  • F. Bacciotti
  • C. Chiuderi
  • G. Hirth
  • A. Natta
  • E. Oliva
Part V: Outflows—Theory
Part of the Lecture Notes in Physics book series (LNP, volume 465)

Abstract

We present a non-standard, straightforward procedure for a model-independent determination of crucial physical parameters of the linear section of stellar jets, such as the hydrogen ionization fraction x and the temperature T e of the emitting gas. The method can be easily applied to every Herbig-Haro jet for which the brightest red lines have been measured, even if the lines are not calibrated and the ratios are not corrected for reddening. In the cases of HH 34 and HH 111 we find x∼0.1 and T e∼6000. The momentum rates evaluated with the derived total number densities (N∼104 cm−3) give strong support to the picture in which the luminous jet is only the fastest and most ionized component of a wider neutral flow that, in turn, has the capability of accelerating a molecular outflow. The ionization fraction cannot be explained in terms of equilibrium processes reflecting the local physical conditions of the medium, however the recombination length scales turn out to be comparable to the linear extension of the most luminous part of the jets: the observed degree of ionization is most likely the remnant of the heating and the excitation occurred in the initial accelerating region. This picture is supported by our diagnostics of RW Aur’s optical jet, for which spatially resolved spectra have been taken: in this case the ionization fraction (around 10% again) is found to decrease slowly with distance from the star.

The combination of the time history of the ionization fraction, the proper radiative cooling, the recent observational evidence of a relative motion between the emitting gas and the pattern of bright knots, and the finding of multiple aligned bow-shocks in a single system, suggests that physical conditions consistent with the observed emission could be obtained through “mild” compressions of the central portion of the flow, caused by “damped” Kelvin-Helmoltz instabilities generated at the jet-ambient contact discontinuity. These compressions concentrate in smaller volumes the already available internal energy that is eventually radiated in optical and IR lines, unlike the weak shocks that actually increase the internal energy content by transforming the bulk kinetic energy into thermal random motions. A picture of this kind seems capable of resolving the long-standing problem of conciling the high supersonic velocity of the ionized material and the low excitation nature of the emission, and, at the same time, provides a very natural explanation for a number of observational constraints, not explicable in terms of the common shock excitation picture, among which the increase of the [SII]/Hα ratio along the jet and the disappearance of the optical emission after a characteristic scale length.

Keywords

Ionization Fraction Momentum Rate Bipolar Outflow Spectral Diagnostics Diagnostic Diagram 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Appl, S., and Camezind, M., 1992, ApJ 256, 354.ADSGoogle Scholar
  2. Bacciotti, F., Chiuderi, C. and Oliva, E., A&A, 296, 185Google Scholar
  3. Bacciotti, F., Hirth, G.A. and Natta, A., 1995, A&A, in pressGoogle Scholar
  4. Blondin, J.M. Fryxell, B.A., and Königl, A., 1990, ApJ 360, 370.CrossRefADSGoogle Scholar
  5. Bodo, G., Trussoni, E., Massaglia, S., and Ferrari, A. 1993, in Proc. of the 6th International Workshop of the OAC on Stellar Jets and Bipolar Outflows, L. Errico and A. Vittone eds., Dordrecht, p. 307.Google Scholar
  6. Butler, K., and Dalgarno, A., 1979, ApJ 234, 765.CrossRefADSGoogle Scholar
  7. Bührke, T., Mundt, R., and Ray, T., 1988, A&A 200, 99.ADSGoogle Scholar
  8. Coleman, C.S., 1990, MNRAS 244, 35.ADSzbMATHGoogle Scholar
  9. Eislöffel, J., 1993, in Proc. of the 6th International Workshop of the OAC on Stellar Jets and Bipolar Outflows, L. Errico and A. Vittone eds., Dordrecht p. 283.Google Scholar
  10. Eislöffel, J., and Mundt, R., 1992, A&A 263, 292 (EM).ADSGoogle Scholar
  11. Eislöffel, J., and Mundt, R., 1994, A&A 284, 530.ADSGoogle Scholar
  12. Franck, A., and Mellema, G., 1994, A&A 289, 937ADSGoogle Scholar
  13. Franck, A., and Mellema, G., 1994, ApJ 430, 800CrossRefADSGoogle Scholar
  14. Giovanardi, C., Natta, A., and Palla, F., 1987, A & AS 70, 269.ADSGoogle Scholar
  15. Hartigan, P., Raymond, J., 1993, ApJ 409, 705.CrossRefADSGoogle Scholar
  16. Hartigan, P., Morse, J., Raymond, J., 1994, ApJ 436, 125.CrossRefADSGoogle Scholar
  17. Hirth, G.A., Mundt, R. and Solf, J., 1994a, A&A 285, 929.ADSGoogle Scholar
  18. Hirth, G.A., Mundt, R., Solf, J., and Ray, T., 1994b, ApJ 427, L99CrossRefADSGoogle Scholar
  19. Hummer, D.G., and Storey, P.J., 1987, MNRAS 224, 801.ADSGoogle Scholar
  20. Kofman, L., and Raga, A.C., 1992, ApJ 390, 359.CrossRefADSGoogle Scholar
  21. Masson, C.R., Chernin, L.M., 1993, ApJ 414, 230.CrossRefADSGoogle Scholar
  22. Mendoza, C. 1983, in IAU Symposium: “Planetary Nebulae”, Vol. 103Google Scholar
  23. Mundt, R., 1993, in Proc. of the 6th International Workshop of the OAC on Stellar Jets and Bipolar Outflows, L. Errico and A. Vittone eds., Dordrecht, p. 91.Google Scholar
  24. Mundt, R., Ray, T.P., and Raga, A.C., 1991, A&A 252, 740.ADSGoogle Scholar
  25. Norman, M.L., Smarr, L., and Winkler, K.H., 1985, in Numerical Astrophysics, eds. J. Centrella, J. LeBlanc, and R. Bowes, (Boston, Jones & Bartlett), p. 88.Google Scholar
  26. Oliva, E., Moorwood, A.F.M., and Danziger, I.J., 1989, A&A, 214, 307ADSGoogle Scholar
  27. Peimbert, M., Storey, P.J., and Torres-Peimbert, S., 1994 Rev. Mex. Astron. Astrofis. 29, 211.ADSGoogle Scholar
  28. Raga, A.C., 1991 in “The Physics of Star Formation and Early Stellar Evolution”, eds. C.J. Lada and N.D. Kylafis, Kluwer Academic, Dordrecht, p. 247.Google Scholar
  29. Raga, A.C., 1992, private communication.Google Scholar
  30. Raga, A.C., and Cabrit, S., 1993, A&A 278, 267.ADSGoogle Scholar
  31. Raga, A.C., Cantó, J., Binette, L., and Calvet, N., 1990, ApJ 364, 601.CrossRefADSGoogle Scholar
  32. Raga, A.C., and Kofman, L., 1992, ApJ 386, 222.CrossRefADSGoogle Scholar
  33. Raga, A.C., Mundt, R., and Ray, T.P., 1991, A&A 252, 733.ADSGoogle Scholar
  34. Ray, T.P., 1993, in Proc. of the 6th International Workshop of the OAC on Stellar Jets and Bipolar Outflows, L. Errico and A. Vittone eds., Dordrecht, p. 241.Google Scholar
  35. Reipurth, B., 1991 in “The Physics of Star Formation and Early Stellar Evolution”, eds. C.J. Lada and N.D. Kylafis, Kluwer Academic, Dordrecht, p. 497.Google Scholar
  36. Reipurth, B., and Heathcote, S.R., 1991, A&A 246, 511.ADSGoogle Scholar
  37. Reipurth, B., and Heathcote, S.R., 1992, A&A 257, 693.ADSGoogle Scholar
  38. Reipurth, B., and Heathcote, S., 1993, in “Astrophysical jets”, D. Burgarella, M. Livio and C. O’Dea eds. (Cambridge University Press).Google Scholar
  39. Reipurth, B., Raga, A.C., and Heathcote, S.R., 1992, ApJ 392, 145 (RRH).CrossRefADSGoogle Scholar
  40. Stone, J.M., and Norman, M.L., 1993, ApJ 413, 198.CrossRefADSGoogle Scholar
  41. Walter, D.K., Dufour, R.J., and Hester, J.J., 1992, ApJ 397, 196.CrossRefADSGoogle Scholar
  42. Yue, Z.Y., and Winnewisser, G., 1993, in Proc. of the 6th International Workshop of the OAC on Stellar Jets and Bipolar Outflows, L. Errico and A. Vittone eds., Dordrecht, p. 283.Google Scholar

Copyright information

© Springer-Verlag 1996

Authors and Affiliations

  • F. Bacciotti
    • 1
  • C. Chiuderi
    • 2
  • G. Hirth
    • 3
  • A. Natta
    • 4
  • E. Oliva
    • 4
  1. 1.Observatoire de la Côte d’AzurNice Cedex 4France
  2. 2.Dipartimento di Astronomia e Scienza dello SpazioUniversità di FirenzeFirenzeItaly
  3. 3.Max-Planck-Institut für AstronomieHeidelbergGermany
  4. 4.Osservatorio Astrofisico di ArcetriFirenzeItaly

Personalised recommendations