BVI CCD Photometry of the Globular Cluster 47Tuc

Abstract

We present BVI photometry for about 16000 stars from a 220 square arcmin field centered 8arcmin East of the center of 47 Tuc. We have identified eight likely blue stragglers located in the outer parts of the cluster. Four of these objects are easy targets for spectroscopic studies with ground-based telescopes. Six candidates for blue horizontal branch stars were identified. However, it is possible that all or most of them belong in fact to the SMC halo. One faint blue star being candidate for a cataclysmic variable was found close to the cluster center. The average I-band magnitude for stars forming the red giant branch clump is determined at I_0=13.09+/-0.005 mag. This in turn implies distance modulus of the cluster (m-M)_{0,47Tuc}=13.32+/-0.03+/-0.036 mag (statistical plus systematic error), if we adopt M_{I,m}=-0.23+/-0.03 mag for the average absolute luminosity of Hipparcos-calibrated clump giants, following Paczynski and Stanek and Stanek and Garnavich. This distance modulus of 47 Tuc is lower by 0.2-0.25 mag than its recent estimates based on Hipparcos parallaxes for subdwarfs. We discuss possible reasons for this discrepancy. The photometric data are available through the anonymous ftp service.