CN and CH Variations Near the 47 Tucanae Main Sequence

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Session 74 -- Globular Clusters
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[74.13] CN and CH Variations Near the 47 Tucanae Main Sequence

J. E. Hesser (DAO/HIA/NRC), G. H. Smith, M. Bolte (UCO/Lick Observatory), R. A. Bell (U. Maryland), M. M. Briley (U. Texas)

Observations of blue CN and CH band strengths among a random sample of main sequence turn-off stars $(+4.0 < M_{V} < +4.5)$ in the globular cluster 47 Tuc (NGC 104, C0021-723) were made with the CTIO 4-m telescope and Argus fiber spectrograph for the purpose of determining the ratio of CN-strong to CN-weak stars and investigating the behavior of CH relative to CN. Of the 20 turn-off stars, 12 were found to be CN-strong while 8 appear to be CN-weak. This ratio of CN-strong to CN-weak stars is comparable to the ratios found among the more luminous 47 Tuc stars. Moreover, a general anticorrelation between CN and CH is also apparent.

\par These observations imply that there is little change in the overall distribution of CN and CH with evolutionary state, although the present sample of turnoff region stars is admittedly small. The apparent similarity in behavior among highly evolved giants and the present sample appears difficult to reconcile with stellar interior mixing theories for the origin of the range and the anticorrelation of CN and CH band strengths, unless such mixing has taken place during an evolutionary state prior to the main sequence turnoff. This requirement contrasts sharply with the properties of standard stellar evolution models of low mass stars, for which the calculated surface C and N abundances are not altered from their initial values prior to the giant branch phase of evolution. Arguably the most natural interpretation of the observed CN and CH variations is that they reflect an initial inhomogeneity within the material out of which the 47 Tuc stars formed.

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