Flash-assisted deep mixing in globular cluster red giants

被引:26
作者
Aikawa, M [1 ]
Fujimoto, MY [1 ]
Kato, K [1 ]
机构
[1] Hokkaido Univ, Dept Phys, Sapporo, Hokkaido 0600810, Japan
关键词
convection; globular clusters : general; nuclear reactions; nucleosynthesis; abundances; stars : abundances; stars : evolution;
D O I
10.1086/323054
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We discuss a new model of deep mixing in red giants caused by shell flashes triggered by the inward penetration of hydrogen into the helium core. The objective is to explain the large star-to-star variations of proton-capture elements that are observed among globular cluster red giants (Fujimoto, Aikawa, & Kato). The characteristics of this mixing model are explored by computing the products of nucleosynthesis during hydrogen shell flashes in red giants. It is shown that, during sufficiently strong flashes, both Mg-24 and Na-23 are depleted by burning. For moderately and very metal-poor clusters, the burned Mg-24 is converted mostly into Al-27. Thus, the model not only resolves the difficulties arising from the observed underabundance of Mg-24, but also removes the problem of sodium overproduction, which would otherwise accompany the aluminum enrichment observed. For moderately metal-poor cluster giants, Mg-25 and Mg-26 survive with nearly scaled-solar abundances, while for very metal-poor cluster giants, all the magnesium isotopes are depleted and aluminum also burns appreciably into Si-28. For metal-rich cluster giants, shell flashes are quenched before Mg-25 and Mg-26 can burn to synthesize aluminum. These properties agree well with the manner in which observed abundance anomalies vary with cluster metallicity, including the absence of large Al-enrichments for red giants in metal-rich clusters. From a detailed comparison with observed abundances in M13 giants, we deduce constraints on the strength of the mixing mechanism responsible for the inward penetration of hydrogen into the helium core. We discuss further implications of the present results, in particular the importance of star-star interactions for the proper understanding of the evolution of stars in globular clusters.
引用
收藏
页码:937 / 956
页数:20
相关论文
共 64 条
[1]   A compilation of charged-particle induced thermonuclear reaction rates [J].
Angulo, C ;
Arnould, M ;
Rayet, M ;
Descouvemont, P ;
Baye, D ;
Leclercq-Willain, C ;
Coc, A ;
Barhoumi, S ;
Aguer, P ;
Rolfs, C ;
Kunz, R ;
Hammer, JW ;
Mayer, A ;
Paradellis, T ;
Kossionides, S ;
Chronidou, C ;
Spyrou, K ;
Degl'Innocenti, S ;
Fiorentini, G ;
Ricci, B ;
Zavatarelli, S ;
Providencia, C ;
Wolters, H ;
Soares, J ;
Grama, C ;
Rahighi, J ;
Shotter, A ;
Rachti, ML .
NUCLEAR PHYSICS A, 1999, 656 (01) :3-183
[2]  
ARNOULD M, 1995, STELLAR EVOLUTION WH, P17
[3]  
BAILYN CD, 1995, ARA A, V33, P113
[4]   Sodium abundance variations in main-sequence stars of the globular cluster 47 Tucanae [J].
Briley, MM ;
Smith, VV ;
Suntzeff, NB ;
Lambert, DL ;
Bell, RA ;
Hesser, JE .
NATURE, 1996, 383 (6601) :604-606
[5]   Carbon and nitrogen abundance variations on the main sequence of 47 Tucanae [J].
Cannon, RD ;
Croke, BFW ;
Bell, RA ;
Hesser, JE ;
Stathakis, RA .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1998, 298 (02) :601-624
[6]   CARBON AND NITROGEN ABUNDANCES IN GIANT STARS OF THE METAL-POOR GLOBULAR CLUSTER-M92 [J].
CARBON, DF ;
LANGER, GE ;
BUTLER, D ;
KRAFT, RP ;
SUNTZEFF, NB ;
KEMPER, E ;
TREFZGER, CF ;
ROMANISHIN, W .
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 1982, 49 (02) :207-258
[7]   THERMONUCLEAR REACTION-RATES .5. [J].
CAUGHLAN, GR ;
FOWLER, WA .
ATOMIC DATA AND NUCLEAR DATA TABLES, 1988, 40 (02) :283-334
[8]   Aluminum abundances, deep mixing, and the blue-tail second-parameter effect in the globular clusters M3 and M13 [J].
Cavallo, RM ;
Nagar, NM .
ASTRONOMICAL JOURNAL, 2000, 120 (03) :1364-1383
[9]   The production of sodium and aluminum in globular cluster red giant stars [J].
Cavallo, RM ;
Sweigart, AV ;
Bell, RA .
ASTROPHYSICAL JOURNAL, 1996, 464 (01) :L79-L82
[10]   Proton-capture nucleosynthesis in globular cluster red giant stars [J].
Cavallo, RM ;
Sweigart, AV ;
Bell, RA .
ASTROPHYSICAL JOURNAL, 1998, 492 (02) :575-595