Calibration of the CH and CN variations among main-sequence stars in M71 and in M13

被引:38
作者
Briley, MM [1 ]
Cohen, JG
机构
[1] Univ Wisconsin, Dept Phys, Oshkosh, WI 54901 USA
[2] CALTECH, Palomar Observ, Pasadena, CA 91125 USA
关键词
globular clusters : general; globular clusters : individual (M71; M13); stars : evolution; stars : abundances;
D O I
10.1086/321115
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
An analysis of the CN and CH band strengths measured in a large sample of M71 and M13 main-sequence stars by Cohen is undertaken using synthetic spectra to quantify the underlying C and N abundances. In the case of M71 it is found that the observed CN and CH band strengths are best matched by the identical C/N/O abundances which fit the bright giants, implying: (1) little if any mixing is taking place during red giant branch ascent in M71, and (2) a substantial component of the C and N abundance inhomogeneities is in place before the main-sequence turn-off. The unlikelihood of mixing while on the main sequence requires an explanation for the abundance variations which lies outside the present stars (primordial inhomogeneities or intracluster self enrichment). For M13 it is shown that the 3883 Angstrom CN bands are too weak to be measured in the spectra for any reasonable set of expected compositions. A similar situation exists for CH as well. However, two of the more luminous program stars do appear to have C abundances considerably greater than those found among the bright giants, thereby suggesting deep mixing has taken place on the M13 red giant branch.
引用
收藏
页码:242 / 247
页数:6
相关论文
共 35 条
[1]  
Bell R. A., 1978, Astronomy and Astrophysics Supplement Series, V34, P229
[2]   THE CALIBRATION OF SYNTHETIC COLORS [J].
BELL, RA ;
PALTOGLOU, G ;
TRIPICCO, MJ .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1994, 268 (03) :771-792
[3]   THE EFFECTIVE TEMPERATURES AND COLORS OF G-STAR AND K-STAR [J].
BELL, RA ;
GUSTAFSSON, B .
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1989, 236 (03) :653-707
[4]  
BELL RA, 1983, APJ, V269, P508
[5]   OXYGEN-ENHANCED MODELS FOR GLOBULAR-CLUSTER STARS .2. ISOCHRONES AND LUMINOSITY FUNCTIONS [J].
BERGBUSCH, PA ;
VANDENBERG, DA .
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 1992, 81 (01) :163-220
[6]   C AND N ABUNDANCES AMONG 47 TUCANAE MAIN-SEQUENCE STARS [J].
BRILEY, MM ;
HESSER, JE ;
BELL, RA .
ASTROPHYSICAL JOURNAL, 1991, 373 (02) :482-496
[7]   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
[8]   CN and CH band strengths of 283 47 Tucanae giants [J].
Briley, MM .
ASTRONOMICAL JOURNAL, 1997, 114 (03) :1051-1059
[9]   ANTICORRELATED CN AND CH VARIATIONS ON THE 47-TUCANAE MAIN-SEQUENCE TURNOFF [J].
BRILEY, MM ;
HESSER, JE ;
BELL, RA ;
BOLTE, M ;
SMITH, GH .
ASTRONOMICAL JOURNAL, 1994, 108 (06) :2183-2192
[10]  
BRILEY MM, 2001, IN PRESS AJ