C and N abundances among 47 Tucanae main-sequence stars

The nature of AN-band strangth variations among upper MS stars in 47 Tuc is characterized, with particular emphasis on the results from the main-sequence (MS) stars. The CTIO 4-m telescope, RC spectrograph, and '2D-Frutti' detector were used to obtain spectra for 20 stars. The observed C and N abundance variations are impossible to reproduce with the assumptions of mixing involving only C-N-processed material and initial C and N abundances appropriate to either the CN-normal stars or the solar ratio. Adding the possibility of the O-N-cycle mixing will allow total C + N + O to be conserved. The C and N abundance differences are very similar to the differences observed among the more luminous cluster stars. Any discussion of mechanisms for altering the surface C, N, and O abundances of evolved stars must allow for a significant population of upper-MS stars with strong CN bands. 51 refs