This corrects the formula for astrometric precision with sky+detector noise and uses slightly different numbers
out of the ETC calculator. Just 3 sentences are altered with no change in conclusion or request.1310759913Assigned ID: 895
----- Attempting Submission 1 (Fri Apr 11 21:52:37 GMT 2014) -----
HST Phase I Proposal 895 (lgs3_a.apt) successfully submitted.
----- Attempting Submission 2 (Mon Apr 14 14:20:27 GMT 2014) -----
HST Phase I Proposal 895 (lgs3_a.apt) successfully submitted.The only changes are on the pos targ offsets in an attempt to sample the subpixel PSF more accurately.69737886----- Attempting Submission 1 (Wed Jul 23 22:21:29 GMT 2014) -----
----- Attempting Submission 2 (Thu Jul 24 18:00:12 GMT 2014) -----The Proper Motion of M31 Vast Plane Galaxy LGS3We propose to measure the proper motion of Local Group dwarf galaxy LGS-3 with a 10 year baseline provided by existing first epoch ACS imaging. An HST-determined proper motion can both constrain the mass of M31 to 20% and test whether LGS-3 is indeed a part of the recently discovered thin plane of M31 dwarf galaxies (Ibata et al., 2013). If it is, we will trace its orbit backwards in time to understand the origin of this plane; how it formed, how it persists, and why all of the blueshifted members are on one side of M31 and the redshifted members are on the other side.
The long HST baseline and the fact that the field is extra rich in background galaxies that can define an excellent reference frame will allow a second epoch of deep images in the ACS to reach a proper motion error of about 7 - 8 microas/yr in each angular component. At the distance of LGS-3, Gaia is unlikely to detect any stars, making this a measurement that can only be made by HST.
There are two important reasons to learn the 3-d velocity of this particular galaxy. The distance of LGS-3 from M31 is known to 2% accuracy, and modeling indicates that LGS 3 is falling nearly radially toward M31 with proper motion amplitude of ~60 microas/yr (Shaya & Tully, 2014). Therefore, a proper motion that refines this value can constrain the mass of M31 to 20% and through the Local Group timing argument, will also constrain the mass of the MW to 30%. LGS 3 happens to be in a recently discovered thin plane of dwarf galaxies. It is important to get the 3-d velocity of at least one of these to discriminate between different theories about the origin of such planes of galaxies or else to point to new possibilities.This dwarf galaxy will be observed to obtain a proper motion by comparing the centroid of its stars with what they were in 2005 (proposal 10505). We will want to position the ACS as closely as possible to how it was positioned in 2005 (each orbit is a little different).COSMOLOGYDefaultfalsefalsefalsefalsefalseSUPPORTEDGALAXYDWARF SPHEROIDALThis object was generated by the targetselector and retrieved from the SIMBAD database.LGS3J2000J2000Total V-mag = 14.3ACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WC:\Users\eshaya\Dropbox\HST\Cycle22\OP-cache\lgs3GO22_PhaseII-v01.xmlThe scheduling data was generated by CASM 22.2.CASM was run in Phase II mode.(Tic-Visit
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)true20All of the exposure are set to be as long as possible and still give reasonable flexibility for scheduling days. But, we are happy to have longer exposures if possible. The orientation should be as close as possible to the orientation maintained in proposal 10505 in 2005 which was reported as 241.0. The set of pos-targ offsets for visits 1 to 3 mostly tries to repeat what happened in the execution of proposal 10505 as indicated by measuring a bright star in the archival images.C:\Users\eshaya\Dropbox\HST\Cycle22\OP-cache\lgs3GO22_PhaseII-v02.xmlThe scheduling data was generated by CASM 22.2.CASM was run in Phase II mode.(Tic-Visit
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