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METALLICITIES FOR OLD STELLAR-SYSTEMS FROM CA II TRIPLET STRENGTHS IN MEMBER GIANTS
被引:174
作者:
ARMANDROFF, TE
[1
]
DACOSTA, GS
[1
]
机构:
[1] ANGLO AUSTRALIAN OBSERV,EPPING,NSW 2121,AUSTRALIA
关键词:
D O I:
10.1086/115769
中图分类号:
P1 [天文学];
学科分类号:
0704 ;
摘要:
Spectra of a large sample of giants in six well-studied Galactic globular clusters have been used to investigate the utility of Ca II triplet line strengths as an abundance indicator. We find the most appropriate diagram for abundance analysis is that in which the sum of the equivalent widths of the two stronger triplet lines is plotted against V - V(HB). This diagram shows good abundance sensitivity, particularly for abundances less than approximately [Fe/H] = - 1.2 dex. At higher abundances, however, there is a loss of sensitivity and the interpretation is complicated by possible changes in the [Ca/Fe] ratio. We do not have, at this stage, sufficient data to resolve this ambiguity. Nevertheless the calibration provided by the standard clusters is used to derive abundances from spectra of giants in Eridanus, Pal 12, and the Carina dwarf spheroidal galaxy. The abundance derived for Eridanus, [Fe/H] = - 1.41 +/- 0.11 dex, agrees well with earlier determinations based on giant branch photometry while that for Carina, [Fe/H] = - 1.52 +/- 0.13 dex, is somewhat higher. We argue, however, that the Carina abundance determinations from giant branch photometry have been affected by the age difference between the bulk of the Carina population and that of the calibrating globular clusters. For Pal 12, our calibration formally yields an abundance of [Fe/H] approximately - 0.6 dex. However, the applicability of this value depends critically on the assumption that [Ca/Fe] in this cluster is similar to that in the nearest calibrating cluster, 47 Tuc. If instead [Ca/Fe] in Pal 12 exceeds that of 47 Tuc, the resulting [Fe/H] value for Pal 12 would be closer to the values near - 1.0 dex derived from giant branch photometry. The Pal 12 spectra also yield a much improved radial velocity for this cluster, 29 +/- 2 km/s.
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页码:1329 / 1337
页数:9
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