This is a resubmission with corrections to visits 07/08. ----- Attempting Submission 1 (Mon Apr 23 17:39:48 GMT 2012) ----- ----- Attempting Submission 2 (Thu Apr 26 21:07:29 GMT 2012) ----- Proper Motions along the Sagittarius Stream: Constraining Milky Way Parameters and Dark Halo Shape The Sagittarius Stream is the brightest and most prominent stellar stream around the Milky Way (MW), and the only one with a widely agreed upon origin and parent galaxy (the Sgr dSph). It therefore provides a unique tracer to constrain the MW's dark halo. The position, width, distance, mean line-of-sight velocity, and velocity dispersion of the Stream have been mapped in various parts of the sky. Detailed N-body modeling by the CoIs has shown that conflicting past claims about the implied shape of MW dark halo were due to unnecessarily restrictive assumed dark halo geometries, which did not yield a simultaneous fit to all the data. But when a fully general triaxial geometry is allowed (as typical of CDM halos), the best fit is a near-oblate halo with its spin axis perpendicular to the MW disk. Further observational data are needed to validate or refute this very surprising result. We therefore propose to map for the first time the variation in proper motion along the Stream. The only existing measurements to date, obtained by the CoIs from 90 years of ground-based data, are restricted to the trailing side of the Stream, and have 10 times larger errorbars than achievable with HST. We will target four fields with ACS/WFC for which serendipitous first epoch observations exist in the Archive. Proper motion accuracies near 5 km/s will be achieved by measuring the relative motion between Stream stars and background galaxies, using established techniques developed by us in the context of ongoing programs. The results will provide a large improvement in our understanding of the MW dark halo, solar circular velocity, and Sgr dSph history. To measure the absolute proper motion of stars associated with the Sagittarius stream in the four target fields, we will use compact background galaxies in the field of view as stationary reference sources. We will measure the average motion of stars in each target field between epochs 1 and 2 with respect to their reference sources. Our analysis techniques and expected accuracies are described in the Phase I proposal. First epoch ACS data are available in the archive from previous observing programs. The present project will obtain the second epoch data. We will observe each target field for 4 orbits with ACS/WFC. We will use the I-band (F814W or F775W filter, depending on what was used in epoch 1) for astrometry and the V-band (F606W filter) to construct color-magntude diagrams (CMDs). Individual exposures will be dithered using customized patterns designed by J. Anderson (STScI) to maximize pixel phase coverage. We require that all of our images be obtained in 30 day windows so that they can be treated as single epoch data for astrometric analyses. During our second epoch observations, the WFC3/UVIS camera will be pointed ~6 arcmin away from our target fields. These parallel fields will be observed with F814W and F606W filters to construct CMDs and to study additional stellar population of the Sagittarius stream. RESOLVED STELLAR POPULATIONS 12 false 0.0 0.0 false false false false SUPPORTED STAR HALO J2000 J2000 STAR HALO J2000 J2000 STAR HALO J2000 J2000 STAR HALO J2000 J2000 ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W ACS/WFC Imaging No No F775W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W ACS/WFC Imaging No No F775W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W Timing link suitability includes constraints ([Group (01 02) Within 30.0 days]) The scheduling data was generated by CASM 20.0. CASM was run in Phase II mode. /private/var/folders/DR/DR3XeY4tHPau5MIJhCefBE++2h+/-Tmp-/OPVisit429620602830431187.xml This is the first visit for imaging SGRSTREAM-FIELD1. Two orbits are required to complete this visit. Since our goal is to measure proper motions of stars in the target field, our orientation is set to exactly match the previous observations of PID 9760. We adopt a customized dither pattern designed to optimally cover the pixel phase using the POS-TARG special requirements. We require that Visits 01 and 02 be observed in a 30 day window so that they can be treated as single epoch data for astrometric analysis. 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CASM was run in Phase II mode. /private/var/folders/DR/DR3XeY4tHPau5MIJhCefBE++2h+/-Tmp-/OPVisit8848291038785396135.xml This is the second visit for imaging SGRSTREAM-FIELD1. Two orbits are required to complete this visit. Since our goal is to measure proper motions of stars in the target field, our orientation is set to exactly match the previous observations of PID 9760. We adopt a customized dither pattern designed to optimally cover the pixel phase using the POS-TARG special requirements. We require that Visits 01 and 02 be observed in a 30 day window so that they can be treated as single epoch data for astrometric analysis. 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CASM was run in Phase II mode. /private/var/folders/DR/DR3XeY4tHPau5MIJhCefBE++2h+/-Tmp-/OPVisit1576605712607457213.xml This is the first visit for imaging SGRSTREAM-FIELD2. Two orbits are required to complete this visit. Since our goal is to measure proper motions of stars in the target field, our orientation is set to exactly match the previous observations of PID 10775. We adopt a customized dither pattern designed to optimally cover the pixel phase using the POS-TARG special requirements. We require that Visits 03 and 04 be observed in a 30 day window so that they can be treated as single epoch data for astrometric analysis. 1334656080000 281.820396 (Tic-Visit :proposal-id 12564 :visit-id "03" :proposal-version -1 :trans-version "20120125" :date "26-Apr-2012 17:06:38.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 3437840 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12564 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12564 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2942 :al-overhead-at-end 116 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12564 :visit-id "03" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3053 :al-overhead-at-end 116 :internal-dur-at-end 1015 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) true 2 0 Timing link suitability includes constraints ([Group (03 04) Within 30.0 days]) The scheduling data was generated by CASM 20.0. CASM was run in Phase II mode. /private/var/folders/DR/DR3XeY4tHPau5MIJhCefBE++2h+/-Tmp-/OPVisit7858578439555945082.xml This is the second visit for imaging SGRSTREAM-FIELD2. Two orbits are required to complete this visit. Since our goal is to measure proper motions of stars in the target field, our orientation is set to exactly match the previous observations of PID 10775. We adopt a customized dither pattern designed to optimally cover the pixel phase using the POS-TARG special requirements. We require that Visits 03 and 04 be observed in a 30 day window so that they can be treated as single epoch data for astrometric analysis. 1334673134000 281.820396 (Tic-Visit :proposal-id 12564 :visit-id "04" :proposal-version -1 :trans-version "20120125" :date "26-Apr-2012 17:06:42.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 3437840 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12564 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12564 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2942 :al-overhead-at-end 116 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12564 :visit-id "04" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3053 :al-overhead-at-end 116 :internal-dur-at-end 1015 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) true 2 0 Timing link suitability includes constraints ([Group (05 06) Within 30.0 days]) The scheduling data was generated by CASM 20.0. CASM was run in Phase II mode. /private/var/folders/DR/DR3XeY4tHPau5MIJhCefBE++2h+/-Tmp-/OPVisit3017364451145272721.xml This is the first visit for imaging SGRSTREAM-FIELD3. Two orbits are required to complete this visit. Since our goal is to measure proper motions of stars in the target field, our orientation is set to exactly match the previous observations of PID 10417. We adopt a customized dither pattern designed to optimally cover the pixel phase using the POS-TARG special requirements. For each visit we will do a set of 6-point dithering. We require that Visits 05 and 06 be observed in a 30 day window so that they can be treated as single epoch data for astrometric analysis. (Tic-Visit :proposal-id 12564 :visit-id "05" :proposal-version -1 :trans-version "20120125" :date "26-Apr-2012 17:06:44.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 3437840 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12564 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12564 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2901 :al-overhead-at-end 116 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12564 :visit-id "05" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3012 :al-overhead-at-end 108 :internal-dur-at-end 1015 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) true 2 0 Timing link suitability includes constraints ([Group (05 06) Within 30.0 days]) The scheduling data was generated by CASM 20.0. CASM was run in Phase II mode. /private/var/folders/DR/DR3XeY4tHPau5MIJhCefBE++2h+/-Tmp-/OPVisit6139796157926303710.xml This is the second visit for imaging SGRSTREAM-FIELD3. Two orbits are required to complete this visit. Since our goal is to measure proper motions of stars in the target field, our orientation is set to exactly match the previous observations of PID 10417. We adopt a customized dither pattern designed to optimally cover the pixel phase using the POS-TARG special requirements. For each visit we will do a set of 6-point dithering. We require that Visits 05 and 06 be observed in a 30 day window so that they can be treated as single epoch data for astrometric analysis. (Tic-Visit :proposal-id 12564 :visit-id "06" :proposal-version -1 :trans-version "20120125" :date "26-Apr-2012 17:06:49.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 3437840 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12564 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12564 :visit-id "06" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2901 :al-overhead-at-end 116 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12564 :visit-id "06" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3012 :al-overhead-at-end 116 :internal-dur-at-end 1015 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) true 2 0 Timing link suitability includes constraints ([Group (07 08) Within 30.0 days]) The scheduling data was generated by CASM 20.0. CASM was run in Phase II mode. /private/var/folders/DR/DR3XeY4tHPau5MIJhCefBE++2h+/-Tmp-/OPVisit2489391476392654126.xml This is the first visit for imaging SGRSTREAM-FIELD4. Two orbits are required to complete this visit. Since our goal is to measure proper motions of stars in the target field, our orientation is set to exactly match the previous observations of PID 10417. We adopt a customized dither pattern designed to optimally cover the pixel phase using the POS-TARG special requirements. We require that Visits 07 and 08 be observed in a 30 day window so that they can be treated as single epoch data for astrometric analysis. 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CASM was run in Phase II mode. /private/var/folders/DR/DR3XeY4tHPau5MIJhCefBE++2h+/-Tmp-/OPVisit267322108308014336.xml This is the first visit for imaging SGRSTREAM-FIELD4. Two orbits are required to complete this visit. Since our goal is to measure proper motions of stars in the target field, our orientation is set to exactly match the previous observations of PID 10417. We adopt a customized dither pattern designed to optimally cover the pixel phase using the POS-TARG special requirements. We require that Visits 07 and 08 be observed in a 30 day window so that they can be treated as single epoch data for astrometric analysis. 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