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Abundance Ratios in Metal-Poor Globular Clusters: Deep Mixing and its Effect on Stellar Populations of the Galactic Halo

Published online by Cambridge University Press:  14 August 2015

Robert P. Kraft
Robert P. Kraft*
Affiliation:
UCO/Lick Observatory University of California, Santa Cruz, CA 95064

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Only a bit more than 25 years ago, it seemed possible to assume that all Galactic globular clusters were chemically homogeneous. There were indications that star-to-star Fe abundance variations existed in ω Cen, but this massive cluster appeared to be unique. Following Osborn’s (1971) initial discovery, Zinn’s (1973) observation that M92 asymptotic giant branch (AGB) stars had weaker G-bands than subgiants with equivalent temperatures provided the first extensive evidence that there might be variations in the abundances of the light elements in an otherwise “normal” cluster. Since then star-to-star variations in the abundances of C, N, O, Na, Mg and Al have been observed in all cases in which sample sizes have exceeded 5-10 stars, e.g., in clusters such as M92, M15, M13, M3, ω Cen, MIO and M5. Among giants in these clusters one finds large surface O abundance differences, and these are intimately related to differences of other light element abundances, not only of C and N, but also of Na, Mg and Al (cf. reviews by Suntzeff 1993, Briley et al 1994, and Kraft 1994). The abundances of Na and O, as well as Al and Mg, are anticorrelated. Prime examples are found among giants in M15 (Sneden et al 1997), M13 (Pilachowski et al 1996; Shetrone 1996a,b; and Kraft et al 1997) and ω Cen (Norris & Da Costa 1995a,b).

These observed anticorrelations almost certainly result from proton- capture chains that convert C to N, 0 to N, Ne to Na and Mg to Al in or near the hydrogen fusion layers of evolved cluster stars. But which stars? An appealing idea is that during the giant branch lifetimes of the low-mass stars that we now observe, substantial portions of the stellar envelopes have been cycled through regions near the H-burning shell where proton-capture nucleosynthesis can occur. This so-called “evolutionary” scenario involving deep envelope mixing in first ascent red giant branch (RGB) stars has been studied by Denissenkov & Denissenkova (1990), Langer & Hoffman (1995), Cavallo et al (1996, 1997) and Langer et al (1997). The mixing mechanism that brings proton-capture products to the surface is poorly understood (Denissenkov & Weiss 1996, Denissenkov et al 1997, Langer et al 1997), but deep mixing driven by angular momentum has been suggested (Sweigart & Mengel 1979, Kraft 1994, Langer & Hoffman 1995, Sweigart 1997).

Type
II. Joint Discussions
Information
Highlights of Astronomy , Volume 11 , Issue 1: Highlights of Astronomy. As presented at the XXIIIrd General Assembly of the IAU (Part A), 1997 , 1998 , pp. 53 - 57
Copyright
Copyright © Kluwer 1998

References

Bell, R.A., Dickens, R.J., Gustafsson, B. 1979, ApJ, 229, 604.Google Scholar
Bell, R.A. & Dickens, R. 1980, ApJ, 242, 657.Google Scholar
Bolton, A.J. & Eggleton, P.P. 1973, A&A, 24, 429.Google Scholar
Briley, M.M., Bell, R.A., Hoban, S., Dickens, R.J. 1990, ApJ, 359, 307.Google Scholar
Briley, M.M. & Smith, G.H. 1993, PASP, 105, 1260.Google Scholar
Briley, M.M., Bell, R.A., Hesser, J.E., Smith, G.H. 1994, Can. J. Phys., 72, 772.Google Scholar
Briley, M.M., Smith, V.V., Suntzeff, N.B., Lambert, D.L., Bell, R.A., Hesser, J.E. 1996, Nature, 383, 604.Google Scholar
Brown, J.A., Wallerstein, G., Oke, J.B. 1991, AJ, 101, 1693.Google Scholar
Buonanno, R., Buscema, G., Fusi Pecci, F., Richer, H.B., Fahlman, G.G. 1990, AJ, 100, 1811.Google Scholar
Carbon, D.F., Langer, G.E., Butler, D., Kraft, R.P., Trefzer, Ch., Suntzeff, N.B. 1982, ApJS, 49, 207.Google Scholar
Cavallo, R.M., Swcigart, A.V., Bell, R.A. 1996 ApJ, 464, L79.Google Scholar
Cavallo, R.M., Pilachowski, C.A., Rebolo, R. 1997 PASP, 109, 226.Google Scholar
Da Costa, G., Armandroff, T.E., Norris, J.E. 1992, AJ, 104, 154.Google Scholar
Denissenkov, P.A. & Denissenkova, S.N. 1990, Sov. Aitr. Lett., 16, 275.Google Scholar
Denissenkov, P.A. & Weiss, A. 1996, A&A, 308, 773.Google Scholar
Denissenkov, P.A., Weiss, A., Wagenhuber, J. 1997, A&A, 320, 115.Google Scholar
Dickens, R., Bell, R.A., Gustafsson, B. 1979, ApJ, 232, 428.Google Scholar
Dorman, B., 1992, ApJS, 80, 701.Google Scholar
Gratton, R.G. & Ortolani, S. 1988, A&AS, 73, 137.Google Scholar
Kinman, T.D., Suntzeff, N.B., Kraft, R.P. 1994, AJ, 108, 1722.Google Scholar
Kraft, R.P. 1994, PASP, 106, 553.Google Scholar
Kraft, R.P., Sneden, C., Langer, G.E., Prosser, C.F. 1992, AJ, 104, 645.Google Scholar
Kraft, R.P., Sneden, C., Langer, G.E., Shetrone, M.D. 1993, AJ, 106, 1490.Google Scholar
Kraft, R.P., Sneden, C., Langer, G.E., Shetrone, M.D., Bolte, M. 1995, AJ, 109, 2586.Google Scholar
Kraft, R.P., Sneden, C., Smith, G.H., Shetrone, M.D., Langer, G.E., Pilachowski, C.A. 1997, AJ, 113, 279.Google Scholar
Laird, J.B. et al 1993, ASP Conf. Ser. 48, 95.Google Scholar
Langer, G.E., Kraft, R.P., Carbon, D.F., Friel, E., Oke, J.B. 1986, PASP, 98, 473.Google Scholar
Langer, G.E. & Hoffman, R. 1995, PASP, 107, 1177.Google Scholar
Langer, G.E., Hoffman, R.E., Zaidins, C.S. 1997, PASP, 109, 244.Google Scholar
Lee, Y.-W., Demarque, P., Zinn, R. 1988, Calibration of Stellar Ages, ed. Philip, A.G.D. (Schenectady, Davis), 149.Google Scholar
Lee, Y.-W., Demarque, P., Zinn, R. 1994, ApJ, 423, 248.Google Scholar
Moehler, S., Heber, U., de Boer, K.S. 1995, A&A, 294, 65.Google Scholar
Norris, J.E. & Da Costa, G.S. 1995a, ApJ, 441, L81.Google Scholar
Norris, J.E. & Da Costa, G.S. 1995b, ApJ, 447, 680.Google Scholar
Osborn, W. 1971, Observatory, 91, 223.Google Scholar
Peterson, R.C. 1983, ApJ, 275, 737.Google Scholar
Peterson, R.C., Rood, R.T., Crocker, D.A. 1995, ApJ, 453, 214.Google Scholar
Pilachowski, C., Sneden, C., Kraft, R.P., Langer, G.E. 1996, AJ, 112, 545.Google Scholar
Preston, G.W., Schectman, S.A., Beers, T.C. 1991, ApJ, 375, 121.Google Scholar
Richer, H.B. et al 1996, ApJ, 463, 602.Google Scholar
Rood, R. 1973, ApJ, 184, 815.Google Scholar
Sandage, A.R. & Wildey, R. 1967, ApJ, 150, 469.Google Scholar
Searle, L. & Zinn, R. 1978, ApJ, 225, 357.Google Scholar
Shetrone, M.D. 1996a, AJ, 112, 1517.Google Scholar
Shetrone, M.D. 1996b, AJ, 112, 2639.Google Scholar
Smith, G.H., Shetrone, M.D., Bell, R.A., Churchill, C.W., Briley, M.M. 1996, AJ, 112, 1511.Google Scholar
Smith, G.H., Shetrone, M.D., Briley, M.M., Churchill, C.W., Bell, R.A. 1997, PASP, 109, 236.Google Scholar
Smith, G.H., Kraft, R.P., Sneden, C., Shetrone, M.D., Fullbright, J. 1997, AJ, (submitted).Google Scholar
Smith, V.V. 1996, private comm.Google Scholar
Sneden, C., Pilachowski, C.A., Vandenberg, D.A. 1986, ApJ, 311, 826.Google Scholar
Sneden, C., Kraft, R.P., Prosser, C.F., Langer, G.E., Langer, G.E. 1992, AJ, 104, 2121.Google Scholar
Sneden, C., Kraft, R.P., Langer, G.E., Prosser, C.F., Shetrone, M.D. 1994, AJ, 107, 1773.Google Scholar
Sneden, C., Kraft, R.P., Shetrone, M.D., Smith, G.H., Laner, G.E., Prosser, C. 1997, AJ, (in press).Google Scholar
Stetson, P.B., Hesser, J.E., Smith, G.H., Vandenberg, D.A., Bolte, M. 1989, AJ, 97, 1360.Google Scholar
Stetson, P.B., Vandenberg, D.A., Boite, M. 1996, PASP, 108, 560.Google Scholar
Suntzeff, N.B. 1993, ASP Conf. Ser. 48, 167.Google Scholar
Sweigart, A.V. 1997, ApJ, 474, L23.Google Scholar
Sweigart, A.V. & Mengel, J.G. 1979, ApJ, 229, 624.Google Scholar
Trefzger, C. F., Langer, G.E., Carbon, D.F., Suntzeff, N.B., Kraft, R.P. 1983, ApJ, 266, 144.Google Scholar
van den Bergh, S. 1967, AJ, 72, 70.Google Scholar
von Rudloff, I.R., Vandenberg, D.A., Hartwick, F.D.A. 1988, ApJ, 324, 840.Google Scholar
Zaidins, C. & Langer, G.E. 1997, PASP, 109, 252.Google Scholar
Zinn, R. 1973, ApJ, 182, 183.Google Scholar
Zinn, R. 1993, ASP Conf. Ser. 48, 38.Google Scholar