0 Assigned ID: 1667 ----- Attempting Submission 1 (Fri Mar 01 19:24:19 GMT 2013) ----- 0 ----- Attempting Submission 1 (Fri Jun 07 17:28:44 GMT 2013) ----- Proper Motions along the Orphan Stream: Finding the Parent, Orbit, and Milky Way Halo Shape Stellar streams in the Milky Way (MW) support the view that much of its halo was formed hierarchically via the tidal disruption of dwarf galaxies and globular clusters. These streams are unique dynamical tracers of the dark matter halo, and provide strong tests of galaxy formation models. The Orphan Stream, discovered in the SDSS survey area, is closer, colder, and fainter than the better known Sagittarius (Sgr) Stream, and it has no known parent galaxy. It therefore allows a study of the less-massive objects that built up the MW halo. Lack of proper motion (PM) data limits our understanding of stream orbits and MW dark halo properties. HST's excellent astrometric accuracy can now address this, as demonstrated by our ongoing Sgr Stream study. We propose here to map the PM variation along the Orphan Stream. We will target four fields with ACS/WFC for which serendipitous first-epoch observations exist in the Archive with 10-12 yr time baselines. PM accuracies near 6 km/s will be achieved by measuring the relative motion between stream stars and background galaxies, using techniques developed by us for other successful PM programs (e.g., LMC/SMC, Leo I, M31). We will interpret the results using dynamical calculations and N-body models, using our techniques already developed for modeling the Sgr and Magellanic Streams. Our study will yield the orbit of the Orphan Stream, which in turn may allow us to identify its progenitor (if not already entirely disrupted). The orbit will also strongly constrain the shape and mass of the MW dark halo, especially when combined with our ongoing studies of other streams. To measure the absolute proper motion of stars associated with the Orphan stellar 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/WFC 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. These are specificied using POS TARGs on the individual exposures; no pre-specified patterns are used. To maximize the overlapping area and to minimize systematics dependent on location on the detector, we request the same orientations and coordinates as used by the first-epoch observations. We also require that each target field be imaged 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 also the stellar population of the Orphan stellar stream. Finally, to mitigate the impact of CTE in our science which is important for astrometric analyses, we will use the FLASH optional parameters on all of the ACS and WFC3 exposures. RESOLVED STELLAR POPULATIONS Default false 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 F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F775W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F775W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W /Users/tsohn/Dropbox/HST Phase II/PID13443-OrphanStream/OP-cache/PID13443-v01.xml Timing link suitability includes constraints ([Group (01 02) Within 30.0 days]) The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. This is the first visit for imaging ORPHAN-STREAM-1 field. 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 9468. 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. This is the second visit for imaging ORPHAN-STREAM-1 field. 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 9468. 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. This is the first visit for imaging ORPHAN-STREAM-2 field. 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 9575. 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. 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CASM was run in Phase II mode. This is the second visit for imaging ORPHAN-STREAM-2 field. 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 9575. 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. 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CASM was run in Phase II mode. This is the first visit for imaging ORPHAN-STREAM-3 field. 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 9984. We adopt a customized dither pattern designed to optimally cover the pixel phase using the POS-TARG special requirements. 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 13443 :visit-id "05" :proposal-version -1 :trans-version "20130502" :date "07-Jun-2013 11:39:48.0" :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 13443 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13443 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2849 :al-overhead-at-end 30 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3187 :pcs-gap 0 ) (Tic-Orbit :proposal-id 13443 :visit-id "05" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2965 :al-overhead-at-end 0 :internal-dur-at-end 1015 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3187 :pcs-gap 0 ) true 2 0 /Users/tsohn/Dropbox/HST Phase II/PID13443-OrphanStream/OP-cache/PID13443-v06.xml Timing link suitability includes constraints ([Group (05 06) Within 30.0 days]) The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. This is the second visit for imaging ORPHAN-STREAM-3 field. 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 9984. We adopt a customized dither pattern designed to optimally cover the pixel phase using the POS-TARG special requirements. 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. 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CASM was run in Phase II mode. This is the first visit for imaging ORPHAN-STREAM-4 field. 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 9877. 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. This is the second visit for imaging ORPHAN-STREAM-4 field. 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 9877. 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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