HST Studies of the Core of 47 Tucanae

Details HST Studies of the Core of 47 Tucanae HST Studies of the Core of 47 Tucanae

Nov 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aas...198.9505h&link_type=abstract

American Astronomical Society, 198th AAS Meeting, #95.05; Bulletin of the American Astronomical Society, Vol. 33, p.1182

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Scientific paper

The 8.3 day HST experiment described by R. L. Gilliland, et al. 2000 is aimed at detecting planetary transits in the globular cluster 47 Tucanae. An important by-product is a set of extremely deep WFPC2 images in F555W (V) and F814W (I) of the dense cluster core region. The effective exposure times in each of these bands is over 100,000 s, and extensive sub-pixel dithers between individual exposures supports the creation of 4x oversampled images in which the FWHM of the point spread function is < ~70 mas (PC) and < ~140 mas (WF CCDs). Limited use is made of the shorter exposure time F336W (U) data. This poster describes several studies underway using this outstanding data set. First is a study of mass segregation in the core of 47 Tuc using this extremely deep WFPC2 data set. The degree of mass segregation is characterized by the slope x of the best fitting stellar mass function, where x=+1.35 is the Salpeter value. The mass function slope is found to vary from x=-5 in the cluster center to x=-2 at the edge of the WFPC2 field of view at a radius around 100'', indicating extreme mass segregation in the core of 47 Tuc. We also examine nearly 100 blue stragglers in 47 Tuc's core. These include: a bright, strongly centrally concentrated population, and a faint population whose radial distribution is similar to that of the giants. The luminosity function and photometric properties of these two kinds of 47 Tuc blue stragglers are compared to predictions of blue straggler formation models. Blue stragglers are also discussed in relation to millisecond pulsars and other exotic objects in the cluster core. The binary sequence in 47 Tuc will be examined in future work. Funding has been provided via a NASA/STScI grant for GO-8267.

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