BVI CCD Photometry of the Globular Cluster 47 Tuc

Details BVI CCD Photometry of the Globular Cluster 47 Tuc BVI CCD Photometry of the Globular Cluster 47 Tuc

1998-06-25

arxiv.org/abs/astro-ph/9806343v1

1998, Acta Astronomica, 48, 439

Astronomy and Astrophysics

Astrophysics

submitted to Acta Astronomica, 16 pages, 8 figures; full paper with all 11 figures and tables with the BVI photometry are avai

Scientific paper

We present $BVI$ photometry for about 16000 stars from a 220 arcmin$^{2}$ field centered 8 arcmin 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\pm 0.005 $mag. This in turn implies distance modulus of the cluster $(m-M)_{0,47Tuc}=13.32\pm 0.03\pm 0.036 $mag (statistical plus systematic error), if we adopt $M_{I,m}=-0.23 \pm 0.03 $mag for the average absolute luminosity of {\em Hipparcos}-calibrated clump giants, following Paczy\'nski & Stanek and Stanek & 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.

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