11684( 5) - 24-Sep-2009 16:31:46 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11684 Version: 5 Check-in Time: 24-Sep-2009 16:31:46 STScI Edit Number: 0 Title The First Proper Motion Measurement for M31: Dynamics and Mass of the Local Group ------------------------------------------------------------------------------------ Type Cycle GO 17 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Roeland P. van der Marel Space Telescope Science Institute CoI: Dr. Jay Anderson Space Telescope Science Institute N CoI: Dr. Thomas M. Brown Space Telescope Science Institute N CoI: Dr. Puragra Guhathakurta University of California - Santa Cruz N ------------------------------------------------------------------------------------ Abstract We will perform observations to determine the proper motion of the Andromeda galaxy M31, which has been sought for almost a century without success. While challenging, this measurement has now become possible due to the availability of existing deep ACS/WFC images of several M31 fields. The requested second epoch images will yield the average shift of the M31 stars with respect to compact galaxies in the background. Our observing strategy uses six different fields (three primary and three coordinated parallel) with two different instruments (ACS and WFC3) to provide a maximum handle on possible systematic effects. The expected result will be sufficiently accurate to: (a) discriminate between different histories for the dynamics of the Local Group; (b) constrain the mass distribution of the Local Group; (c) determine the details of the expected future merger between M31 and the Milky Way; (d) infer the past interaction history between M31 and M33; (e) constrain the internal proper motion kinematics of the M31 spheroid, outer disk, and tidal stream; and (f) obtain a pilot estimate of the M31 distance through the method of rotational parallax. ------------------------------------------------------------------------------------ Observations Description ------------------------ To measure absolute PMs we will use compact background galaxies in the field of view (FOV) of M31 as stationary reference sources. We will measure the average motion of stars in M31 between epochs 1 and 2, with respect to these reference sources. Our analysis techniques and expected accuracies were described in the Phase I proposal. First epoch data are available from previous observing programs by PI T. Brown. The present project will obtain the second epoch data. One could use all exposure time with a single field and instrument, but then there would be no internal consistency checks on the results. So instead, we will study three different M31 fields with two different instruments (WFC3 and ACS). This will yield more or less the same random error, but in addition will constrain possible systematic errors. The target fields are the spheroid, disk, and tidal stream fields from Brown et al. (2003, 2006). These have similar stellar densities that 11684( 5) - 24-Sep-2009 16:31:46 - [ 2] provide acceptable crowding. The first epoch data were taken by Brown et al. in two filters, to make color magnitude diagrams that reach the M31 main sequence turn-off. These data are very deep (30--60 orbits per field per filter) so we already have excellent templates of all the usable reference background galaxies in the field. Moreover, the available broad-band colors and depth are sufficient for separating M31 stars, foreground stars, and background galaxies. For the second epoch it is therefore sufficient to take less deep data in only one of the filters. We will observe each field for 2 orbits with WFC3 and 1 orbit with ACS, all in the F606W filter. Individual exposures will be sub-pixel dithered and will last half an orbit. Tests have shown that the F606W filter provides the best astrometric handle on the background galaxies. The compact source detection efficiencies (taking into account pixel size, read noise, and throughput characteristics) of WFC3 and ACS are similar in this filter. Brown et al. (2003, 2006) also observed fields with WFPC2 in parallel with their primary ACS fields. We will use coordinated parallel observations (with ACS when WFC3 is primary, and vice versa) to cover exactly these same fields. We do not expect the same astrometric accuracy as for the primary fields, because of the lower depth with WFPC2, the larger pixel size, and the larger CTE. Nonetheless, this will yield another handle on possible systematic errors, in addition to the ones discussed below. For our primary ACS observations we request the same telescope orientation as for epoch 1. For our primary WFC3 observations we request the orientation that will align the parallel ACS field with the coordinated parallel WFPC2 fields of Brown et al. (2003, 2006). Possible systematic errors are difficult to quantify a priori, but our multi-faceted observing strategy should provide a good handle both on such errors as well as on field-to-field variations in M31 internal kinematics. Using WFC3 in epoch 2 has the advantage of providing a new detector that is relatively free of Charge Transfer Efficiency (CTE) effects. The disadvantage is that we will have to calculate PMs by comparison of data from different instruments. While this has the potential to introduce low-level systematic errors, we have already performed studies that show that such cross-instrument comparisons can be done to high accuracy. By contrast, using ACS in epoch 2 has the disadvantage that it now has significant CTE degradation, which affects astrometry at low but important levels. By comparing the second epoch ACS and WFC3 results, and their dependence on detector y-position, we will be able to perform a low-level correction for CTE effects in both the second and the first epoch data. The large number of M31 stars of different brightnesses will also constrain the differential CTE between the first and second epoch. The data need to be corrected for geometric distortion. For ACS this is calibrated and stable with time to better than 0.005 pixels. However, any instabilities at this level would only affect our 11684( 5) - 24-Sep-2009 16:31:46 - [ 3] results to much lower levels. This is because we will compare the position of each galaxy only to its local neighboring stars. Therefore, we are sensitive only to the highest spatial frequencies of any geometric distortion uncertainty. Moreover, averaging of many galaxies at different positions in the FOV will further reduce these uncertainties. Being a new instrument, no distortion calibration exists yet for WFC3. However, calibration observations will be obtained soon after SM4 that should allow a calibration of similar accuracy as what we have obtained in the past for ACS. We request that visit 4 be scheduled early in Cycle 17. This 1-orbit visit contains ACS observations of the M31 spheroid field. This is the only field for which we have already analyzed the epoch 1 data in some detail. Early receipt and analysis of the visit 4 data will allow us to do a quick sanity check on the results, and identify possible problems, if any. If problems are identified then we will tweak the other visits if necessary. Real Time Justification ----------------------- N/A Calibration Justification ------------------------- N/A Additional Comments ------------------- N/A ------------------------------------------------------------------------------------ 11684( 5) - 24-Sep-2009 16:31:46 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 M31-SPHEROID GALAXY, DISK, HALO, RA=00H46M7.8020S +/- 0.1", J2000 V = -301 V = 3.44 +/- 0.03 1 SPIRAL DEC=+40D42'28.21" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 2 M31-OUTERDIS GALAXY, DISK, HALO, RA=00H49M9.6070S +/- 0.1", J2000 V = -301 V = 3.44 +/- 0.03 K1 SPIRAL DEC=+42D44'51.15" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 3 M31-TIDALSTR GALAXY, DISK, HALO, RA=00H44M16.9601S +/- 0.1", J2000 V = -301 V = 3.44 +/- 0.03 EAM1 SPIRAL DEC=+39D47'31.63" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 4 M31-SPHEROID GALAXY, DISK, HALO, RA=00H46M8.1358S +/- 0.1", J2000 V = -301 V = 3.44 +/- 0.03 2 SPIRAL DEC=+40D42'38.37" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 5 M31-OUTERDIS GALAXY, DISK, HALO, RA=00H49M9.7732S +/- 0.1", J2000 V = -301 V = 3.44 +/- 0.03 K2 SPIRAL DEC=+42D45'3.26" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 6 M31-TIDALSTR GALAXY, DISK, HALO, RA=00H44M17.5102S +/- 0.1", J2000 V = -301 V = 3.44 +/- 0.03 EAM2 SPIRAL DEC=+39D47'21.74" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 11684( 5) - 24-Sep-2009 16:31:46 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO Pattern_Comments: This is the default pattern WFC3-UVIS-DITHER-BOX. It shifts by (0, 0), (4.0, 1.5), (2.5, 4.0), and (-1.5, 2.5) pixels. See Section 8.4.4 of the P2PI. ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.149 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 34.25 Angle_Between_Sides Center_Pattern NO Pattern_Comments: This is the 2-point sub-pixel pattern for ACS from http://www.stsci.edu/hst/acs/proposing/dither/ACS-WFC-DITHER-LINE.html It shifts by (2.5 , 1.5) pixels. ------------------------------------------------------------------------------------------------------------------------------------ 11684( 5) - 24-Sep-2009 16:31:46 - [ 6] Visit: 01 Visit Requirements: SCHED 50%; ORIENT 255.070404D TO 255.070404 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M31-SPHEROI WFC3/UVI ACCUM UVIS F606W CR-SPLIT=NO 1 1360 S PATTERN 1 1-2; PAR 2 D1 S see below WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY ACS/WFC ACCUM WFC F606W CR-SPLIT=NO 1 1200 S see below ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ M31-SPHEROID1 1 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 1379.0 S S M31-SPHEROID1 1 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 1379.0 S S M31-SPHEROID1 1 WFC3/UVI ACCUM UVIS F606W 3 none none none 2 1450.0 S S M31-SPHEROID1 1 WFC3/UVI ACCUM UVIS F606W 4 none none none 2 1450.0 S S ANY 2 ACS/WFC ACCUM WFC F606W 1 none none none 1 1290.0 S ANY 2 ACS/WFC ACCUM WFC F606W 2 none none none 1 1240.0 S ANY 2 ACS/WFC ACCUM WFC F606W 3 none none none 2 1420.0 S ANY 2 ACS/WFC ACCUM WFC F606W 4 none none none 2 1320.0 S 11684( 5) - 24-Sep-2009 16:31:46 - [ 7] Visit: 02 Visit Requirements: ORIENT 247.085007D TO 247.085007 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M31-OUTERDI WFC3/UVI ACCUM UVIS F606W CR-SPLIT=NO 1 1400 S PATTERN 1 1-2; PAR 2 SK1 S see below WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY ACS/WFC ACCUM WFC F606W CR-SPLIT=NO 1 1280 S see below ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ M31-OUTERDISK1 1 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 1420.0 S S M31-OUTERDISK1 1 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 1420.0 S S M31-OUTERDISK1 1 WFC3/UVI ACCUM UVIS F606W 3 none none none 2 1491.0 S S M31-OUTERDISK1 1 WFC3/UVI ACCUM UVIS F606W 4 none none none 2 1491.0 S S ANY 2 ACS/WFC ACCUM WFC F606W 1 none none none 1 1340.0 S ANY 2 ACS/WFC ACCUM WFC F606W 2 none none none 1 1280.0 S ANY 2 ACS/WFC ACCUM WFC F606W 3 none none none 2 1460.0 S ANY 2 ACS/WFC ACCUM WFC F606W 4 none none none 2 1340.0 S 11684( 5) - 24-Sep-2009 16:31:46 - [ 8] Visit: 03 Visit Requirements: SCHED 40%; ORIENT 21.922609D TO 36.922609 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M31-TIDALST WFC3/UVI ACCUM UVIS F606W CR-SPLIT=NO 1 1350 S PATTERN 1 1-2; PAR 2 REAM1 S see below WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY ACS/WFC ACCUM WFC F606W CR-SPLIT=NO 1 1230 S see below ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ M31-TIDALSTREAM1 1 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 1379.0 S S M31-TIDALSTREAM1 1 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 1379.0 S S M31-TIDALSTREAM1 1 WFC3/UVI ACCUM UVIS F606W 3 none none none 2 1450.0 S S M31-TIDALSTREAM1 1 WFC3/UVI ACCUM UVIS F606W 4 none none none 2 1450.0 S S ANY 2 ACS/WFC ACCUM WFC F606W 1 none none none 1 1300.0 S ANY 2 ACS/WFC ACCUM WFC F606W 2 none none none 1 1230.0 S ANY 2 ACS/WFC ACCUM WFC F606W 3 none none none 2 1420.0 S ANY 2 ACS/WFC ACCUM WFC F606W 4 none none none 2 1290.0 S 11684( 5) - 24-Sep-2009 16:31:46 - [ 9] Visit: 04 Visit Requirements: SCHED 40%; ORIENT 75.070404D TO 75.070404 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M31-SPHEROI ACS/WFC ACCUM WFC F606W CR-SPLIT=NO 1 1200 S PATTERN 2 1-2; PAR 2 D2 see below WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W CR-SPLIT=NO 1 1200 S S see below ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ M31-SPHEROID2 1 ACS/WFC ACCUM WFC F606W 1 none none none 1 1289.0 S M31-SPHEROID2 1 ACS/WFC ACCUM WFC F606W 2 none none none 1 1289.0 S ANY 2 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 1349.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 1299.0 S S 11684( 5) - 24-Sep-2009 16:31:46 - [ 10] Visit: 05 Visit Requirements: SCHED 40%; ORIENT 67.085007D TO 67.085007 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M31-OUTERDI ACS/WFC ACCUM WFC F606W CR-SPLIT=NO 1 1200 S PATTERN 2 1-2; PAR 2 SK2 see below WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W CR-SPLIT=NO 1 1200 S S see below ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ M31-OUTERDISK2 1 ACS/WFC ACCUM WFC F606W 1 none none none 1 1289.0 S M31-OUTERDISK2 1 ACS/WFC ACCUM WFC F606W 2 none none none 1 1289.0 S ANY 2 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 1349.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 1299.0 S S 11684( 5) - 24-Sep-2009 16:31:46 - [ 11] Visit: 06 Visit Requirements: ORIENT 201.922609D TO 201.922609 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M31-TIDALST ACS/WFC ACCUM WFC F606W CR-SPLIT=NO 1 1290 S PATTERN 2 1-2; PAR 2 REAM2 see below WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFC3/UVI ACCUM UVIS F606W CR-SPLIT=NO 1 1300 S S see below ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ M31-TIDALSTREAM2 1 ACS/WFC ACCUM WFC F606W 1 none none none 1 1299.0 S M31-TIDALSTREAM2 1 ACS/WFC ACCUM WFC F606W 2 none none none 1 1299.0 S ANY 2 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 1359.0 S S ANY 2 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 N/A S 11684( 5) - 24-Sep-2009 16:31:46 - [ 12] Summary Form for Proposal 11684 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS, WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 201.922609D TO 201.922609 D, ORIENT 21.922609D TO 36.922609 D, ORIENT 247.085007D TO 247.085007 D, ORIENT 255.070404D TO 255.070404 D, ORIENT 67.085007D TO 67.085007 D, ORIENT 75.070404D TO 75.070404 D, PAR 2 WITH 1, PATTERN 1 1-2, PATTERN 2 1-2, SCHED 40%, SCHED 50% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ANY, M31-OUTERDISK1, M31-OUTERDISK2, M31-SPHEROID1, M31-SPHEROID2, M31-TIDALSTREAM1, M31-TIDALSTREAM2 ------------------------------------------------------------------------------------------------------------------------------------