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The Fractional Ionization in Molecular Cloud Cores

Published online by Cambridge University Press:  25 May 2016

Paola Caselli
Paola Caselli*
Affiliation:
Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy

Abstract

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Ions and electrons play a key role in the chemical and dynamical evolution of interstellar clouds. Gas phase ion–molecule reactions are major chemical routes to the formation of interstellar molecules. The ionization degree determines the coupling between the magnetic field and the molecular gas through ion–neutral collisions, and thus regulates the rate of star formation. In the theoretical determination of the degree of ionization we run into several sources of uncertainty, including the poorly known cosmic ray flux and metal depletion within the cores, the penetration of UV radiation deep into regions of high visual extinction due to cloud inhomogeneities, and the ionization rate increase in the proximity of young stellar objects which may be strong X–ray emitters. Observational estimates of electron (or ion) fractions x(e) (≡ n(e)/n(H2), where n(e) and n(H2) are the electron and molecular hydrogen number densities, respectively) in dense cloud cores are thus of considerable interest. In this paper, I will review recent improvements in the estimates of the ion fraction in dense cores and point out the difficulties in determining x(e).

Type
Part 1. Chemistry in Pre-Stellar Cores and Low-Mass Star-Forming Regions
Information
Symposium - International Astronomical Union , Volume 197: Astrochemistry: From Molecular Clouds to Planetary Systems , 2000 , pp. 41 - 50
Copyright
Copyright © Astronomical Society of the Pacific 2000 

References

Allamandola, L.J., Tielens, A.G.G.M., & Barker, J.R. 1989, ApJS, 71, 733 CrossRefGoogle Scholar
Anderson, I.M., Caselli, P., Haikala, L.K., & Harju, J. 1999, A&A, 347, 983 Google Scholar
André, P., Ward–Thompson, D., & Motte, F. 1996, A&A, 314, 625 Google Scholar
Bergin, E.A., Plume, R., Williams, J.P., & Myers, P.C. 1999, ApJ, 512, 724 CrossRefGoogle Scholar
Butner, H.M., Lada, E.A., & Loren, R.B. 1995, ApJ, 448, 207 CrossRefGoogle Scholar
Caselli, P., Walmsley, C.M., Tafalla, M., Dore, L., & Myers, P.C. 1999, ApJ, 523, L165 CrossRefGoogle Scholar
Caselli, P., Walmsley, C.M., Terzieva, R., & Herbst, E. 1998, ApJ, 499, 234 (CWTH) CrossRefGoogle Scholar
Caselli, P., Walmsley, M., Galli, D., Tafalla, M., & Myers, P.C. 2000, in preparation Google Scholar
Dalgarno, A. & Lepp, S. 1984, ApJ, 287, L47 CrossRefGoogle Scholar
de Boisanger, C., Helmich, F.P., & van Dishoeck, E.F. 1996, A&A, 310, 315 Google Scholar
Feigelson, E.D. & Montmerle, T. 1999, ARA&A, 37, 363 Google Scholar
Fisk, L.A. & Wenzel, K.-P. 1998, Space Science Reviews, 83, 179 CrossRefGoogle Scholar
Fukui, Y. & Hayakawa, S. 1981, in 17th International Cosmic Ray Conference, 2, 226 Google Scholar
Graedel, T.E., Langer, W.D., & Frerking, M.A. 1982, ApJS, 48, 321 CrossRefGoogle Scholar
Grosso, N., Montmerle, T., Feigelson, E.D., André, P., Casanova, S., & Gregorio–Hetem, J. 1997, Nature, 387, 56 CrossRefGoogle Scholar
Guélin, M., Langer, W.D., & Wilson, R.W. 1982, A&A, 107, 107 Google Scholar
Hartquist, T.W., Caselli, P., Rawlings, J.M.C., Ruffle, D.P., & Williams, D.A. 1998, in The Molecular Astrophysics of Stars and Galaxies, eds. Hartquist, T.W. & Williams, D.A., Clarendon Press, Oxford, 101 CrossRefGoogle Scholar
Hartquist, T.W., Doyle, H.T., & Dalgarno, A. 1978, A&A, 68, 65 Google Scholar
Hartquist, T.W. & Morfill, G.E. 1983, ApJ, 266, 271 CrossRefGoogle Scholar
Hartquist, T.W. & Morfill, G.E. 1994, Ap&SS, 216, 223 Google Scholar
Herbst, E. & Leung, C.M. 1989, ApJS, 69, 271 CrossRefGoogle Scholar
Jones, A.P. & Williams, D.A. 1985, MNRAS, 217, 413 CrossRefGoogle Scholar
Kramer, C., Alves, J., Lada, C.J., Lada, E.A., Sievers, A., Ungerecths, H., & Walmsley, C.M. 1999, A&A, 342, 257 Google Scholar
Larsson, M., et al. 1996, A&A, 309, L1 Google Scholar
Lee, H.-H., Bettens, R.P.A., & Herbst, E. 1996, A&AS, 119, 111 Google Scholar
Lepp, S. & Dalgarno, A. 1988, ApJ, 324, 553 CrossRefGoogle Scholar
Lepp, S. & Dalgarno, A. 1996, A&A, 306, L21 Google Scholar
Linsky, J.L., Diplas, A., Wood, B.E., Brown, A., Ayres, T.R., & Savage, B.D. 1995, ApJ, 451, 335 CrossRefGoogle Scholar
Lucas, R. & Liszt, H. 1996, A&A, 307, 237 Google Scholar
McCall, B.J., Geballe, T.R., Hinkle, K.H., & Oka, T. 1999, ApJ, 522, 338 CrossRefGoogle Scholar
McKee, C.F. 1989, ApJ, 345, 782 CrossRefGoogle Scholar
Millar, T.J., Bennet, A., & Herbst, E. 1989, ApJ, 340, 906 CrossRefGoogle Scholar
Myers, P.C. & Khersonsky, V.K. 1995, ApJ, 442, 186 CrossRefGoogle Scholar
Ohashi, N., Lee, S.W., Wilner, D.J., & Hayashi, M. 1999, ApJ, 518, L41 CrossRefGoogle Scholar
Ozawa, H., Nagase, F., Ueda, Y., Dotani, T., & Ishida, M. 1999, ApJ, 523, L81 CrossRefGoogle Scholar
Pratap, P., Dickens, J.E., Snell, R.L., Miralles, M.P., Bergin, E.A., Irvine, W.M., & Schloerb, F.P. 1997, ApJ, 486, 862 CrossRefGoogle Scholar
Ruffle, D.P., Hartquist, T.W., Taylor, S.D., & Williams, D.A. 1997, MNRAS, 291, 235 CrossRefGoogle Scholar
Shu, F.H., Adams, F.C., & Lizano, S. 1987, ARA&A, 25, 23 Google Scholar
Tafalla, M., Mardones, D., Myers, P.C., Caselli, P., Bachiller, R., & Benson, P.J. 1998, ApJ, 504, 900 CrossRefGoogle Scholar
Tielens, A.G.G.M. & Allamandola, L.J. 1987, in Interstellar Processes, eds. Hollenbach, D.J. & Thronson, H.A. Jr. (Dordrecht: Kluwer), 397 CrossRefGoogle Scholar
Turner, B.E. 1995, ApJ, 449, 653 CrossRefGoogle Scholar
Watson, W.D. 1977, CNO Isotopes in Astrophysics, ed. Audouze, J., Reidel Publ. (Dordrecht)Google Scholar
Ward–Thompson, D., Motte, F., & André, P. 1999, MNRAS, 305, 143 CrossRefGoogle Scholar
Williams, J.P., Bergin, E.A., Caselli, P., Myers, P.C., & Plume, R. 1998, ApJ, 503, 689 CrossRefGoogle Scholar
Williams, J.P., Myers, P.C., Wilner, D.J., & Di Francesco, J. 1999, ApJ, 513, L61 CrossRefGoogle Scholar
Wootten, A., Loren, R.B., & Snell, R.L. 1982, ApJ, 255, 160 CrossRefGoogle Scholar
Wootten, A., Snell, R.L., & Glassgold, A.E. 1979, ApJ, 234, 876 CrossRefGoogle Scholar