Completing the Empirical White Dwarf Cooling Sequence: Hot White Dwarfs in 47 Tucanae

In HST Cycle 17 we obtained panchromatic imaging data in 47 Tuc covering the UV through to the IR over 60 square arcmins in 14 different fields. From the UV data obtained with WFC3 we were able to construct an empirical white dwarf cooling sequence and compare it with various theoretical models. The data exhibited a sharp break in slope at 20,000K. Cooler than this it followed the expected Mestel slope of -0.4 in Log Temperatue vs Log Age and above this temperature the slope was somewhat more gentle {-0.2}. The number of white dwarfs detected with temperatures above 30,000K {only 10} was too small to constrain the slope of the cooling sequence at the very hot end. This is because hot white dwarfs cool quite quickly and are thus rare objects. This segment of the cooling sequence is of great interest as white dwarfs are expected to cool mainly by neutrino emission at these hot temperatures. An empirical cooling sequence extending well into this region containing 100 white dwarfs above 30,000K, will allow us to test several predictions of neutrino physics and possibly provide a hint whether axions are produced in processes similar to those that manufacture neutrinos.