HST WFPC2 Observations of CN Band Strengths Near the Core of 47 Tucanae

We present HST WFPC2 photometry, taken in the F390N and F410M filters, of stars brighter than V = 17 near the core of 47 Tuc. This cluster, and every Galactic globular cluster studied to date, exhibits large star-to-star variations in the light element abundances of its members, particularly with regard to C and N. As the F390N filter includes the 388.3nm CN feature, we have developed a 390-410 color and employed it to assess CN band strengths. Preliminary analysis with corresponding synthetic spectra indicates significant CN band strength differences present to the base of the subgiant branch (as has been noted by several other studies). However, there does not appear to be an excess of CN-strong stars in the central region of the cluster as previously hinted at by more limited ground based spectroscopic and photometric surveys (and suggested to be evidence of a primordial/external origin to the observed inhomogeneities). We also note our model 390-410 colors reveal this system to be sensitive to CN band formation in cluster stars over a wide range of luminosity and metallicity. Support for this work was provided by NASA through grant number GO-08339.01-A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.