Assigned ID: 736
----- Attempting Submission 1 (Fri Feb 24 21:41:52 GMT 2012) -----
----- Attempting Submission 2 (Wed Feb 29 01:12:10 GMT 2012) -----This is an updated version meant to fix an issue with guide star availability.----- Attempting Submission 2 (Fri Aug 03 20:52:21 GMT 2012) -----Completing the Empirical White Dwarf Cooling Sequence: Hot White Dwarfs in 47 TucanaeIn 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.Our observing plan allows us to observe with both WFC3/UVIS and ACS/WFC simultaneously.
In order to reach our required depth to include hot WDs greater than 30,000K, we will observe for a total of 1040sec in F225W, followed by 1130sec in F336W with 2 exposures in each filter This will be similarly done with F475W (981sec) and F555W (982sec) with ACS. The individual exposure times are long enough to allow the buffer to be dumped in parallel to our subsequent exposure. Obtaining just 2 exposures in each filter will not compromise the data as our parallel
exposures with WFC3/UVIS from our Cycle 17 project also only included two exposures in each of the two UVIS filters. With these exposure times, we will be able to reach a S/N > 100 for 30,000K WDs in 47 Tuc, E(B-V)=0.04, and using a standard HST star spectra of GD71 (32,300K DA WD).
In total we observe 10 fields with each camera, 1 orbit each, for a total request of 10 orbits.
Our time estimates in WFC3 include a 6 minute guide star acquisition for each orbit, image overheads of 2.6 minutes for the first exposure and 2.1 minutes for the second exposure in F225W and F336W. In ACS, our time estimates include a 6 minute guide star acquisition, image overheads of 4 minutes for the first exposure and 2.5 minutes for the second exposure in F475W and F555W. Our total observing times are 40.4 minutes in WFC3 and 44 minutes in ACS. Both of these times are well below the reduced visibility of 51 minutes per orbit in Cycle 20 due to our target's right ascension.RESOLVED STELLAR POPULATIONS12false0.00.0falsefalsefalsefalseSUPPORTEDSTELLAR CLUSTERGLOBULAR CLUSTERJ2000J2000STELLAR CLUSTERGLOBULAR CLUSTERJ2000J2000STELLAR CLUSTERGLOBULAR CLUSTERJ2000J2000STELLAR CLUSTERGLOBULAR CLUSTERJ2000J2000STELLAR CLUSTERGLOBULAR CLUSTERJ2000J2000STELLAR CLUSTERGLOBULAR CLUSTERJ2000J2000STELLAR CLUSTERGLOBULAR CLUSTERJ2000J2000STELLAR CLUSTERGLOBULAR CLUSTERJ2000J2000STELLAR CLUSTERGLOBULAR CLUSTERJ2000J2000STELLAR CLUSTERGLOBULAR CLUSTERJ2000J2000WFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF336WACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF555WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF336WACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF555WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF336WACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF555WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF336WACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF555WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF336WACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF555WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF336WACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF555WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF336WACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF555WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF336WACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF555WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF336WACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF555WWFC3/UVISImagingNoNoF225WWFC3/UVISImagingNoNoF336WACS/WFCImagingNoNoF435WACS/WFCImagingNoNoF555WThe scheduling data was generated by CASM 20.2.CASM was run in Phase II mode.(Tic-Visit
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