Synergistic Ground and Space Based Observations of the Core of 47 TUC

Details Synergistic Ground and Space Based Observations of the Core of 47 TUC Synergistic Ground and Space Based Observations of the Core of 47 TUC

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.4306b&link_type=abstract

American Astronomical Society, 181st AAS Meeting, #43.06; Bulletin of the American Astronomical Society, Vol. 24, p.1187

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Scientific paper

We describe a procedure to analyze HST images and deep ground based images of dense stellar fields together to extract information unobtainable from either one alone. The method involves using astrometry derived from HST frames to constrain the photometry of ground based images. If the positions are known in advance from HST imaging, the regular point spread functions and extremely high S/N obtainable from the ground allow photometry of very dense fields comparable to that from HST alone. Since the ground based images are substantially larger in spatial extent, and can be made repeatedly over long time-bases, comparisons between inner and outer regions and studies of variability can be carried out in this way which would be unacceptably time consuming to do from space alone. We find that a CLEAN type algorithm is better than using the ALLSTAR routine in DAOPHOT, probably because the latter requires an a priori estimate of the sky background. We apply this procedure to a sum of 40 ground based images in each of B and V of the center of 47 Tuc. The ground based data were taken at the CTIO 0.9m, with a Tek 1024x1024 chip covering 6.7'. We have used both archival FOC images of the center of the cluster, and PC data from Guhathakurta et al. (AJ in press). We find a sequence of stars one magnitude above the horizontal branch; these stars can also be seen in the CMD of Guhathakurta et al. The strong apparent central concentration of these objects suggests that they are not simply asymptotic giant branch stars, but may be related to the large blue straggler population recently discovered with HST in the center of 47 Tuc (Paresce et al. 1991, Nature 352, 297). In particular, we speculate that they may be evolved horizontal branch stars of ~ 1.5 solar masses, descended from blue stragglers. Further analysis of these stars, and of other features of the color magnitude diagram, are in progress.

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