Cold Dark Matter and the GD-1 Stellar Stream

0 Assigned ID: 845 ----- Attempting Submission 1 (Fri Apr 05 22:05:46 GMT 2019) ----- HST Phase I Proposal 845 (gd1.apt) successfully submitted. Receipt: # 845-1 ----- Attempting Submission 2 (Fri Apr 05 23:44:38 GMT 2019) ----- Decreased individual exposure times to comply with the increased GS acquisition overheads. 912033684 ----- Attempting Submission 1 (Tue Jul 23 14:02:22 GMT 2019) ----- ----- Attempting Submission 2 (Wed Jul 24 17:35:20 GMT 2019) ----- ----- Attempting Submission 3 (Wed Sep 18 18:37:07 GMT 2019) ----- ----- Attempting Submission 4 (Mon Sep 23 17:10:13 GMT 2019) ----- HST Phase II Proposal 15930 (PID15930.apt) successfully submitted. Receipt: # 15930-4 ----- Attempting Submission 5 (Mon Sep 23 17:43:02 GMT 2019) ----- ----- Attempting Submission 6 (Thu Dec 12 14:20:19 GMT 2019) ----- Cold Dark Matter and the GD-1 Stellar Stream We propose to use HST to characterize a dark-matter subhalo in the Milky Way. Tidally disrupted globular clusters create thin and kinematically cold stellar streams that are extremely sensitive to any gravitational perturbation. Orbiting in the Milky Way halo, these streams provide a unique opportunity to test for the presence of perturbing dark-matter subhalos. Gaps discovered along streams provide tentative evidence for dark matter influence, but their origin remains uncertain as stream gaps alone can be due to baryonic effects as well. Recently, Gaia observations of the GD-1 stellar stream have revealed a spur of stars associated with one of the gaps in the stream. Such features naturally arise when a stream encounters a massive perturber, and have a unique 3D kinematic signature. We propose here to measure precise proper motions in the perturbed region of GD-1. We will target eight fields with ACS/WFC and parallel-observe with WFC3/UVIS in two epochs. Proper motion accuracies near 3 km/s will be achieved by measuring the relative motion between stream stars and background galaxies using established techniques that have already been successfully applied to other objects in the Local Group (e.g., LMC/SMC, Leo I, M31, Sgr and Lethe streams). A passing subhalo is expected to introduce differences in tangential velocity between the stream and the spur, and our data will have the precision to resolve these kinematic offsets. Our results will definitively establish whether GD-1 features are a signature of a dark matter subhalo. If HST confirms the subhalo origin of the gap, it will measure the physical properties of the subhalo and rule out all reasonable alternatives. The ultimate goal of this multi-cycle program is to obtain sets of images separated by 2~3 years in time for measuring absolute proper motions of individual stars along the GD-1 stellar stream. In the Cycle 27 (this program), we will image 8 primary ACS/WFC + 8 parallel WFC3/UVIS = 16 fields in total. Each primary ACS/WFC field location was carefully chosen to target the densest region of the stream. Accordingly, our parallel WFC3/UVIS field locations were placed along the stream using the Visit Orientation special requirements. Each visit consists of 4 orbits, i.e., 3 orbits of F606W and 1 visit of F814W observations. Each F814W orbit consists of 1 short + 3 long exposures, and each F606W orbit consists of 1 short + 2 long exposures. The multband data will be used for constructing color-magnitude diagrams (CMDs) that will help identify the GD-1 stream members. To maximize the time baseline of the two cycles, we request all of our visits to be observed in the earlier period of Cycle 27 using the BEFORE Visit Timing Requirements. For all visits, we have also increased the SCHEDULEABILITY to 70 to allow wider observable windows. PI Ana Bonaca is an expert in tidal streams, having discovered one of the most distant cold streams and also theoretically explored what aspects of the Milky Way can be constrained from observations of tidal streams. Together with CoI Price-Whelan, she most recently discovered a sign of perturbation in the GD-1 stream using Gaia data. As a follow-up, she dynamically modeled the observed GD-1 features and showed they can be caused by a massive object passing by a stellar stream, which inspired this proposal. CoI Charlie Conroy is an expert in stellar population studies on scales from individual stars to most massive galaxies in the universe. He has plentiful experience with HST observations, and has most recently published a study of stellar variability in M51 from the ongoing HST project GO 14704. CoI David W. Hogg is an expert in data analysis, including experimental design and modeling of dynamical systems with noisy stars and complex selection functions, as well as precision imaging analysis. He was a part of the groundbreaking effort in understanding the dynamical theory of dark-matter interactions with cold stellar structures. CoI Nitya Kallivayalil is an expert in astrometry, whose inventive use of HST to measure proper motions of the LMC/SMC system has revolutionized our understanding of these objects. She has a career of experience in measuring proper motions with HST, and is the PI of an ongoing effort to measure precise proper motions for all satellites of the Milky Way (GO 14734). CoI Adrian Price-Whelan is an expert in the Milky Way dynamics, and has worked in areas spanning from signatures of orbital chaos in tidal streams to identification of binaries from sparse radial velocity data. Together with PI Bonaca, he most recently discovered a sign of perturbation in the GD-1 stream using Gaia data that inspired this proposal. CoIs Sangmo Tony Sohn and Roeland van der Marel have together with CoI Kallivayalil developed a set of techniques for obtaining proper motions with HST that will be used in executing this project. Stellar Populations 6 false true false false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER TIDAL TAIL NO J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER TIDAL TAIL NO J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER TIDAL TAIL NO J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER TIDAL TAIL NO J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER TIDAL TAIL NO J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER TIDAL TAIL NO J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER TIDAL TAIL NO J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER TIDAL TAIL NO J2000 J2000 ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W 1576102819413 The scheduling data was generated by CASM 27.2. CASM was run in Phase II mode. /private/var/folders/7q/8p7_k1q56vlfhxhm_v9tnb6m0004ph/T/OPVisit17432227733483370148.xml This is the visit for SPUR1 target field. This visit consists of 4 orbits. The first orbit is for obtaining F814W images for both the primary ACS/WFC + parallel WFC3/UVIS fields, while orbits 2-4 are for obtaining F606W images. We request specific orient ranges to position the primary+parallel fields parallel to the GD-1 stream which has a width of 0.5 deg FWHM. This will ensure that our target fields include as many GD-1 member stars as possible. Inidivual exposures will be dithered using a customized dither pattern designed for optimizing pixel-phase coverage via the POS TARG arguments. To fulfill our scientific goals, it is imperative to maxmimize the time baseline. We therefore added timing requirements so that the images are obtained as early in the cycle as possible. For this, we have also loosened the schedulability requirement to 70 to allow increased observable windows - the default schedulability would only allow 1~2 days of observable window, while our current schedulability allows about 12 days of windows. 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CASM was run in Phase II mode. /private/var/folders/7q/8p7_k1q56vlfhxhm_v9tnb6m0004ph/T/OPVisit11301390220983017054.xml This is the visit for SPUR2 target field. This visit consists of 4 orbits. The first orbit is for obtaining F814W images for both the primary ACS/WFC + parallel WFC3/UVIS fields, while orbits 2-4 are for obtaining F606W images. We request specific orient ranges to position the primary+parallel fields parallel to the GD-1 stream which has a width of 0.5 deg FWHM. This will ensure that our target fields include as many GD-1 member stars as possible. Inidivual exposures will be dithered using a customized dither pattern designed for optimizing pixel-phase coverage via the POS TARG arguments. To fulfill our scientific goals, it is imperative to maxmimize the time baseline. We therefore added timing requirements so that the images are obtained as early in the cycle as possible. For this, we have also loosened the schedulability requirement to 70 to allow increased observable windows - the default schedulability would only allow 1~2 days of observable window, while our current schedulability allows about 12 days of windows. 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CASM was run in Phase II mode. /private/var/folders/7q/8p7_k1q56vlfhxhm_v9tnb6m0004ph/T/OPVisit6913377855205383038.xml This is the visit for SPUR3 target field. This visit consists of 4 orbits. The first orbit is for obtaining F814W images for both the primary ACS/WFC + parallel WFC3/UVIS fields, while orbits 2-4 are for obtaining F606W images. We request specific orient ranges to position the primary+parallel fields parallel to the GD-1 stream which has a width of 0.5 deg FWHM. This will ensure that our target fields include as many GD-1 member stars as possible. Inidivual exposures will be dithered using a customized dither pattern designed for optimizing pixel-phase coverage via the POS TARG arguments. To fulfill our scientific goals, it is imperative to maxmimize the time baseline. We therefore added timing requirements so that the images are obtained as early in the cycle as possible. For this, we have also loosened the schedulability requirement to 70 to allow increased observable windows - the default schedulability would only allow 1~2 days of observable window, while our current schedulability allows about 12 days of windows. 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CASM was run in Phase II mode. /private/var/folders/7q/8p7_k1q56vlfhxhm_v9tnb6m0004ph/T/OPVisit874080993514721398.xml This is the visit for SPUR4 target field. This visit consists of 4 orbits. The first orbit is for obtaining F814W images for both the primary ACS/WFC + parallel WFC3/UVIS fields, while orbits 2-4 are for obtaining F606W images. We request specific orient ranges to position the primary+parallel fields parallel to the GD-1 stream which has a width of 0.5 deg FWHM. This will ensure that our target fields include as many GD-1 member stars as possible. Inidivual exposures will be dithered using a customized dither pattern designed for optimizing pixel-phase coverage via the POS TARG arguments. To fulfill our scientific goals, it is imperative to maxmimize the time baseline. We therefore added timing requirements so that the images are obtained as early in the cycle as possible. For this, we have also loosened the schedulability requirement to 70 to allow increased observable windows - the default schedulability would only allow 1~2 days of observable window, while our current schedulability allows about 12 days of windows. 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CASM was run in Phase II mode. This is the visit for STREAME1 target field. This visit consists of 2 orbits. The first orbit is for obtaining F814W images for both the primary ACS/WFC + parallel WFC3/UVIS fields, while the second orbit is for obtaining F606W images. We request specific orient ranges to position the primary+parallel fields parallel to the GD-1 stream which has a width of 0.5 deg FWHM. This will ensure that our target fields include as many GD-1 member stars as possible. Inidivual exposures will be dithered using a customized dither pattern designed for optimizing pixel-phase coverage via the POS TARG arguments. To fulfill our scientific goals, it is imperative to maxmimize the time baseline. We therefore added timing requirements so that the images are obtained as early in the cycle as possible. For this, we have also loosened the schedulability requirement to 70 to allow increased observable windows - the default schedulability would only allow 1~2 days of observable window, while our current schedulability allows about 12 days of windows. 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CASM was run in Phase II mode. This is the visit for STREAME1 target field. This visit consists of 2 orbits. Both orbits are for obtaining F606W images. We request specific orient ranges to position the primary+parallel fields parallel to the GD-1 stream which has a width of 0.5 deg FWHM. This will ensure that our target fields include as many GD-1 member stars as possible. Inidivual exposures will be dithered using a customized dither pattern designed for optimizing pixel-phase coverage via the POS TARG arguments. To fulfill our scientific goals, it is imperative to maxmimize the time baseline. We therefore added timing requirements so that the images are obtained as early in the cycle as possible. For this, we have also loosened the schedulability requirement to 70 to allow increased observable windows - the default schedulability would only allow 1~2 days of observable window, while our current schedulability allows about 12 days of windows. 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CASM was run in Phase II mode. /private/var/folders/7q/8p7_k1q56vlfhxhm_v9tnb6m0004ph/T/OPVisit16759683466956920184.xml This is the visit for STREAME2 target field. This visit consists of 4 orbits. The first orbit is for obtaining F814W images for both the primary ACS/WFC + parallel WFC3/UVIS fields, while orbits 2-4 are for obtaining F606W images. We request specific orient ranges to position the primary+parallel fields parallel to the GD-1 stream which has a width of 0.5 deg FWHM. This will ensure that our target fields include as many GD-1 member stars as possible. Inidivual exposures will be dithered using a customized dither pattern designed for optimizing pixel-phase coverage via the POS TARG arguments. To fulfill our scientific goals, it is imperative to maxmimize the time baseline. We therefore added timing requirements so that the images are obtained as early in the cycle as possible. For this, we have also loosened the schedulability requirement to 70 to allow increased observable windows - the default schedulability would only allow 1~2 days of observable window, while our current schedulability allows about 12 days of windows. 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CASM was run in Phase II mode. /private/var/folders/7q/8p7_k1q56vlfhxhm_v9tnb6m0004ph/T/OPVisit14071382640830593367.xml This is the visit for STREAMW1 target field. This visit consists of 4 orbits. The first orbit is for obtaining F814W images for both the primary ACS/WFC + parallel WFC3/UVIS fields, while orbits 2-4 are for obtaining F606W images. We request specific orient ranges to position the primary+parallel fields parallel to the GD-1 stream which has a width of 0.5 deg FWHM. This will ensure that our target fields include as many GD-1 member stars as possible. Inidivual exposures will be dithered using a customized dither pattern designed for optimizing pixel-phase coverage via the POS TARG arguments. To fulfill our scientific goals, it is imperative to maxmimize the time baseline. We therefore added timing requirements so that the images are obtained as early in the cycle as possible. For this, we have also loosened the schedulability requirement to 70 to allow increased observable windows - the default schedulability would only allow 1~2 days of observable window, while our current schedulability allows about 12 days of windows. (Tic-Visit :proposal-id 15930 :visit-id "07" :proposal-version -1 :trans-version "20190514" :date "11-Dec-2019 17:34:04.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 7448608 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15930 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15930 :visit-id "07" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2669 :al-overhead-at-end 80 :internal-dur-at-end 1015 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3052 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15930 :visit-id "07" :orbit-number 2 :pcs-time 302 :si-vis-utilization 2660 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3052 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15930 :visit-id "07" :orbit-number 3 :pcs-time 302 :si-vis-utilization 2660 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3052 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15930 :visit-id "07" :orbit-number 4 :pcs-time 302 :si-vis-utilization 2660 :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 3052 :pcs-gap 0 ) true 4 0 1576103721737 Timing link suitability includes constraints ([Group (81 82) Within 30.0 days]) The scheduling data was generated by CASM 27.2. CASM was run in Phase II mode. /private/var/folders/7q/8p7_k1q56vlfhxhm_v9tnb6m0004ph/T/OPVisit6108554989747698140.xml This is the visit for STREAMW2 target field. This visit consists of 2 orbits. The first orbit is for obtaining F814W images for both the primary ACS/WFC + parallel WFC3/UVIS fields, while the second orbit is for obtaining F606W images. We request specific orient ranges to position the primary+parallel fields parallel to the GD-1 stream which has a width of 0.5 deg FWHM. This will ensure that our target fields include as many GD-1 member stars as possible. Inidivual exposures will be dithered using a customized dither pattern designed for optimizing pixel-phase coverage via the POS TARG arguments. To fulfill our scientific goals, it is imperative to maxmimize the time baseline. We therefore added timing requirements so that the images are obtained as early in the cycle as possible. For this, we have also loosened the schedulability requirement to 70 to allow increased observable windows - the default schedulability would only allow 1~2 days of observable window, while our current schedulability allows about 12 days of windows. (Tic-Visit :proposal-id 15930 :visit-id "81" :proposal-version -1 :trans-version "20190514" :date "11-Dec-2019 17:35:21.0" :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 4010800 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15930 :visit-id "81" :obset-id "81" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15930 :visit-id "81" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2669 :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 3052 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15930 :visit-id "81" :orbit-number 2 :pcs-time 302 :si-vis-utilization 2660 :al-overhead-at-end 0 :internal-dur-at-end 699 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3052 :pcs-gap 0 ) true 2 0 1576103785359 Timing link suitability includes constraints ([Group (81 82) Within 30.0 days]) The scheduling data was generated by CASM 27.2. CASM was run in Phase II mode. /private/var/folders/7q/8p7_k1q56vlfhxhm_v9tnb6m0004ph/T/OPVisit16638925442739896602.xml This is the visit for STREAMW2 target field. This visit consists of 2 orbits. Both orbits are for obtaining F606W images. We request specific orient ranges to position the primary+parallel fields parallel to the GD-1 stream which has a width of 0.5 deg FWHM. This will ensure that our target fields include as many GD-1 member stars as possible. Inidivual exposures will be dithered using a customized dither pattern designed for optimizing pixel-phase coverage via the POS TARG arguments. To fulfill our scientific goals, it is imperative to maxmimize the time baseline. We therefore added timing requirements so that the images are obtained as early in the cycle as possible. For this, we have also loosened the schedulability requirement to 70 to allow increased observable windows - the default schedulability would only allow 1~2 days of observable window, while our current schedulability allows about 12 days of windows. (Tic-Visit :proposal-id 15930 :visit-id "82" :proposal-version -1 :trans-version "20190514" :date "11-Dec-2019 17:36:25.0" :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 3437808 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15930 :visit-id "82" :obset-id "82" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15930 :visit-id "82" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2629 :al-overhead-at-end 14 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3052 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15930 :visit-id "82" :orbit-number 2 :pcs-time 302 :si-vis-utilization 2660 :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 3052 :pcs-gap 0 ) true 2 0