The Spectral Energy Distributions of White Dwarfs in 47 Tucanae: The Distance to the Cluster



Authors: Woodley, K. A.; Goldsbury, R.; Kalirai, J. S.; Richer, H. B.; Tremblay, P.-E.; Anderson, J.; Bergeron, P.; Dotter, A.; Esteves, L.; Fahlman, G. G.; and 6 coauthors


Abstract: We present a new distance determination to the Galactic globular cluster 47 Tucanae by fitting the spectral energy distributions of its white dwarfs (WDs) to pure hydrogen atmosphere WD models. Our photometric data set is obtained from a 121-orbit Hubble Space Telescope program using the Wide Field Camera 3 UVIS/IR channels, capturing F390W, F606W, F110W, and F160W images. These images cover more than 60 arcmin2 and extend over a radial range of 5-13.7 arcmin (6.5-17.9 pc) within the globular cluster. Using a likelihood analysis, we obtain a best-fitting unreddened distance modulus of (m - M)o = 13.36 ± 0.02 ± 0.06 corresponding to a distance of 4.69 ± 0.04 ± 0.13 kpc, where the first error is random and the second is systematic. We also search the WD photometry for infrared excess in the F160W filter, indicative of low-mass companions, and find no convincing cases within our sample.