We have added post-flashes to all exposures in Visits 01, 02, and 04, in order to improve the CTE
performance, based on concerns raised by the Visit 03 data. We also slightly adjusted the exposure times
downward, due to the overheads for the post-flashes.
--Resubmitted by H. E. Bond, 10/19/2012.----- Attempting Submission 1 (Fri Oct 19 04:51:51 GMT 2012) -----There is a warning upon submission about a Visibility Overrun in Visit 03, but this observation has already been made.The True Origin of Hypervelocity StarsWe propose to obtain WFC3 images of 4 hypervelocity stars in the Galactic halo, in order to conclusively establish their origin. This will be a final epoch of a long-term program to measure precise proper motions in an absolute inertial frame. The origin of these unique stars with extremely large positive radial velocities, in excess of the escape speed from the Galaxy, is consistent only with being ejected by the massive black hole at the Galactic center. Reconstructing the full three-dimensional space motion of these stars, through astrometric proper motions, provides a unique opportunity to measure the shape of the triaxial dark matter halo, at larger distances than is afforded by tidal streams. In Cycles 15 and 17 our team obtained two epochs of observations for these stars with ACS. The accuracy of the proper motion measurement was affected by the CTE degradation in ACS and the unexpected change in the PSF after SM4. The CTE error of HVS3 was unfortunately amplified by the need to use different guide stars and take the second-epoch observations at a 180 degree different orientation. We request third-epoch observations for 4 targets with WFC3 to double the proper motion baseline to 5-6 years and to reduce the systematic error using our newly-developed CTE correction. The new measurement will conclusively confirm or reject the Galactocentric origin of HVSs.These are 3rd-epoch images of 4 hypervelocity stars, aimed at determining precise proper motions relative to background galaxies. The 1st and 2nd epochs were observed with ACS, but for the 3rd epoch we are changing to WFC3/UVIS.
We will spend 2 orbits on each of the 4 targets. During the first orbit, we take dithered exposures centered around the center of the UVIS1 chip, and during the 2nd orbit they are dithered around the center of the UVIS2 chip. We have specified ORIENT angles such that the long direction of the chips will be parallel to what we used for the long direction of the ACS chips at the 1st and 2nd epochs. We also use the same filters that were used with ACS (F814W for 3 of the stars, F850LP for one of them). The AFTER dates are set so that we will observed about 3 years since the more recent ACS observation.RESOLVED STELLAR POPULATIONS12false0.00.0falsefalsefalsefalseSUPPORTEDSTARBPHALOHVS1J2000J2000STARBPHALOHVS2US708J2000J2000STARBPHALOHVS3J2000J2000STARBPHALOHVS4J2000J2000WFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF606WThe scheduling data was generated by CASM 20.2.CASM was run in Phase II mode./var/tmp/OPVisit5007801520232794592.xml(Tic-Visit
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