12270( 4) - 16-Aug-2010 16:17:52 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12270 Version: 4 Check-in Time: 16-Aug-2010 16:17:52 STScI Edit Number: 1 Title Proper Motion of Leo I: Constraining the Milky Way Mass ------------------------------------------------------------------------------------ Type Cycle GO 18 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Sangmo Tony Sohn Space Telescope Science Institute CoI: Dr. Roeland P. van der Marel Space Telescope Science Institute N CoI: Dr. Steven R. Majewski The University of Virginia N CoI: Ms. Gurtina Besla Harvard University N ------------------------------------------------------------------------------------ Abstract The mass of the Milky Way is one of the most poorly established Galactic parameters. One important reason for this problem stems from the uncertainty about the bound/unbound status of one particular object, Leo I, which has an unusually large radial velocity (v_hel = 283 km/s) at extreme distance (261 kpc). We propose to resolve this issue by measuring at high-precision the absolute proper motion of Leo I with HST. ACS/WFC F814W data that can be used as first epoch already exist in the archive. For the second epoch data, we request to obtain 6 more orbits with the same instrument and filter, yielding a 5 year time baseline. With proven techniques that use many compact background galaxies as astrometric reference sources, the predicted transverse velocity accuracy is only 26 km/s at the distance of Leo I. Our results will be accurate enough to address whether or not Leo I is bound. We will then perform new equilibrium modeling of the Milky Way satellite system to obtain an improved estimate of the Milky Way mass. We will also perform new N-body simulations of Leo I, constrained by the measured velocity, to fit simultaneously the orbit, extra-tidal features, and unusual star formation history. This will independently constrain the Milky Way mass. Only HST can achieve the required accuracy, and considerable progress can be made on these important issues with only a small investment of HST time. ------------------------------------------------------------------------------------ Observations Description ------------------------ To measure absolute PM of Leo I, we will use compact background galaxies in the field of view (FOV) as stationary reference sources. We will measure the average motion of stars in Leo I between epochs 1 and 2 with respect to these reference sources. Our analysis techniques and expected accuracies are described in the Phase I proposal. First epoch ACS data are available as part of previous observing programs by PI T. Smecker-Hane (Proposal 10520). The present project will obtain the second epoch data. The first epoch ACS data were obtained in two filters (F435W and F814W) to make deep color magnitude diagrams that reach well below the main sequence turn-off of Leo I. The available broad-band colors and depth are sufficient for separating Leo I stars, foreground stars, and background galaxies to first order. For the second epoch it is therefore sufficient to take data in only one of the filters. However, our analysis shows that the first epoch data are 12270( 4) - 16-Aug-2010 16:17:52 - [ 2] neither deep nor well-dithered enough to build high signal-to-noise and high resolution templates for the background galaxies. We will therefore use our deeper second epoch F814W data for building the templates. We will observe Leo I with the F814W filter using the same pointing and orientation used for the first epoch data. Individual exposures will be sub-pixel dithered and will last half an orbit. We will use customized dither patterns designed by Jay Anderson (STScI) to maximize the pixel phase coverage. We require that all of our images be obtained in a 21 day window so that they can be treated as single epoch data for astrometric analysis. During our second epoch observations, the WFC3/UVIS camera will be pointed ~6 arcmin away in the outer halo of Leo I. We will observe this field with F438W and F814W filters to construct a color-magnitude diagram of the outer halo. This will be used to determine stellar population gradients and the stellar halo density profile to constrain formation and evolutionary scenarios. Real Time Justification ----------------------- N/A Calibration Justification ------------------------- N/A Additional Comments ------------------- N/A ------------------------------------------------------------------------------------ 12270( 4) - 16-Aug-2010 16:17:52 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 LEO-I-DSPH GALAXY, DWARF RA=10H08M22.5000S +/- 0.1", J2000 V = 11.2 SPHEROIDAL DEC=+12D18'6.00" +/- 0.1" Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 12270( 4) - 16-Aug-2010 16:17:52 - [ 4] Visit: 01 Visit Requirements: ORIENT 314.0D TO 315.0 D; GROUP 01, 02, 03 WITHIN 21D On Hold Comments: Additional Comments: This is the first visit for imaging the Leo I Dwarf Spheroidal Galaxy. Two orbits are required to complete this visit. Since our goal is to measure proper motions of stars in the target galaxy, our orientation is set to exactly match the previous observations of PID 10520. We adopt a customized dither pattern designed by Jay Anderson (STScI) to optimally cover the pixel phase using the POS-TARG special requirements. For each visit we will do a set of 4-point dithering. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LEO-I-DSPH ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=NO 1 1267 S POS TARG 0.0000, 0.0000; GS ACQ SCENARIO BASE1B3; SEQ 1-4 NON-INT; PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 LEO-I-DSPH WFC3/UVI ACCUM UVIS F814W CR-SPLIT=NO 1 1326 S S ------------------------------------------------------------------------------------------------------------------------------------ 3 LEO-I-DSPH ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=NO 1 1267 S POS TARG 0.1740, 0.1850; PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 LEO-I-DSPH WFC3/UVI ACCUM UVIS F438W CR-SPLIT=NO 1 1367 S S ------------------------------------------------------------------------------------------------------------------------------------ 5 LEO-I-DSPH ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=NO 1 1361 S POS TARG 0.3232, 0.1235; SEQ 5-8 NON-INT; PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 LEO-I-DSPH WFC3/UVI ACCUM UVIS F814W CR-SPLIT=NO 1 1371 S S ------------------------------------------------------------------------------------------------------------------------------------ 7 LEO-I-DSPH ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=NO 1 1360 S POS TARG 0.1005, 0.3305; PAR 8 WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 LEO-I-DSPH WFC3/UVI ACCUM UVIS F438W CR-SPLIT=NO 1 1466 S S ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ LEO-I-DSPH 1 ACS/WFC ACCUM WFCENTER F814W none none none none 1 N/A LEO-I-DSPH 2 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S LEO-I-DSPH 3 ACS/WFC ACCUM WFCENTER F814W none none none none 1 N/A 12270( 4) - 16-Aug-2010 16:17:52 - [ 5] 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 | ------------------------------------------------------------------------------------------------------------------------------------ LEO-I-DSPH 4 WFC3/UVI ACCUM UVIS F438W none none none none 1 N/A S LEO-I-DSPH 5 ACS/WFC ACCUM WFCENTER F814W none none none none 2 N/A LEO-I-DSPH 6 WFC3/UVI ACCUM UVIS F814W none none none none 2 N/A S LEO-I-DSPH 7 ACS/WFC ACCUM WFCENTER F814W none none none none 2 N/A LEO-I-DSPH 8 WFC3/UVI ACCUM UVIS F438W none none none none 2 N/A S 12270( 4) - 16-Aug-2010 16:17:52 - [ 6] Visit: 02 Visit Requirements: ORIENT 314.0D TO 315.0 D; GROUP 02, 01, 03 WITHIN 21D On Hold Comments: Additional Comments: This is the second visit for imaging the Leo I Dwarf Spheroidal Galaxy. Two orbits are required to complete this visit. We request that the orientation be exactly the same as that for Visit 01. 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 4-point dithering. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LEO-I-DSPH ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=NO 1 1267 S POS TARG 0.5030, 0.0460; GS ACQ SCENARIO BASE1B3; SEQ 1-4 NON-INT; PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 LEO-I-DSPH WFC3/UVI ACCUM UVIS F814W CR-SPLIT=NO 1 1326 S S ------------------------------------------------------------------------------------------------------------------------------------ 3 LEO-I-DSPH ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=NO 1 1267 S POS TARG 0.6770, 0.2310; PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 LEO-I-DSPH WFC3/UVI ACCUM UVIS F438W CR-SPLIT=NO 1 1367 S S ------------------------------------------------------------------------------------------------------------------------------------ 5 LEO-I-DSPH ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=NO 1 1363 S POS TARG 0.8262, 0.1695; SEQ 5-8 NON-INT; PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 LEO-I-DSPH WFC3/UVI ACCUM UVIS F814W CR-SPLIT=NO 1 1371 S S ------------------------------------------------------------------------------------------------------------------------------------ 7 LEO-I-DSPH ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=NO 1 1364 S POS TARG 0.6035, 0.3765; PAR 8 WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 LEO-I-DSPH WFC3/UVI ACCUM UVIS F438W CR-SPLIT=NO 1 1462 S S ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ LEO-I-DSPH 1 ACS/WFC ACCUM WFCENTER F814W none none none none 1 N/A LEO-I-DSPH 2 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S LEO-I-DSPH 3 ACS/WFC ACCUM WFCENTER F814W none none none none 1 N/A 12270( 4) - 16-Aug-2010 16:17:52 - [ 7] 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 | ------------------------------------------------------------------------------------------------------------------------------------ LEO-I-DSPH 4 WFC3/UVI ACCUM UVIS F438W none none none none 1 N/A S LEO-I-DSPH 5 ACS/WFC ACCUM WFCENTER F814W none none none none 2 N/A LEO-I-DSPH 6 WFC3/UVI ACCUM UVIS F814W none none none none 2 N/A S LEO-I-DSPH 7 ACS/WFC ACCUM WFCENTER F814W none none none none 2 N/A LEO-I-DSPH 8 WFC3/UVI ACCUM UVIS F438W none none none none 2 N/A S 12270( 4) - 16-Aug-2010 16:17:52 - [ 8] Visit: 03 Visit Requirements: ORIENT 314.0D TO 315.0 D; GROUP 03, 01, 02 WITHIN 21D On Hold Comments: Additional Comments: This is the third visit for imaging the Leo I Dwarf Spheroidal Galaxy. Two orbits are required to complete this visit. We request that the orientation be exactly the same as that for Visit 01. 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 4-point dithering. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LEO-I-DSPH ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=NO 1 1267 S POS TARG 0.1180, 0.5180; GS ACQ SCENARIO BASE1B3; SEQ 1-4 NON-INT; PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 LEO-I-DSPH WFC3/UVI ACCUM UVIS F814W CR-SPLIT=NO 1 1326 S S ------------------------------------------------------------------------------------------------------------------------------------ 3 LEO-I-DSPH ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=NO 1 1267 S POS TARG 0.2920, 0.7030; PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 LEO-I-DSPH WFC3/UVI ACCUM UVIS F438W CR-SPLIT=NO 1 1367 S S ------------------------------------------------------------------------------------------------------------------------------------ 5 LEO-I-DSPH ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=NO 1 1363 S POS TARG 0.4412, 0.6415; SEQ 5-8 NON-INT; PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 LEO-I-DSPH WFC3/UVI ACCUM UVIS F814W CR-SPLIT=NO 1 1371 S S ------------------------------------------------------------------------------------------------------------------------------------ 7 LEO-I-DSPH ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=NO 1 1364 S POS TARG 0.2185, 0.8485; PAR 8 WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 LEO-I-DSPH WFC3/UVI ACCUM UVIS F438W CR-SPLIT=NO 1 1462 S S ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ LEO-I-DSPH 1 ACS/WFC ACCUM WFCENTER F814W none none none none 1 N/A LEO-I-DSPH 2 WFC3/UVI ACCUM UVIS F814W none none none none 1 N/A S LEO-I-DSPH 3 ACS/WFC ACCUM WFCENTER F814W none none none none 1 N/A 12270( 4) - 16-Aug-2010 16:17:52 - [ 9] 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 | ------------------------------------------------------------------------------------------------------------------------------------ LEO-I-DSPH 4 WFC3/UVI ACCUM UVIS F438W none none none none 1 N/A S LEO-I-DSPH 5 ACS/WFC ACCUM WFCENTER F814W none none none none 2 N/A LEO-I-DSPH 6 WFC3/UVI ACCUM UVIS F814W none none none none 2 N/A S LEO-I-DSPH 7 ACS/WFC ACCUM WFCENTER F814W none none none none 2 N/A LEO-I-DSPH 8 WFC3/UVI ACCUM UVIS F438W none none none none 2 N/A S 12270( 4) - 16-Aug-2010 16:17:52 - [ 10] Summary Form for Proposal 12270 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS, WFCENTER ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GROUP 01, 02, 03 WITHIN 21D, GROUP 02, 01, 03 WITHIN 21D, GROUP 03, 01, 02 WITHIN 21D, GS ACQ SCENARIO BASE1B3, ORIENT 314.0D TO 315.0 D, PAR 2 WITH 1, PAR 4 WITH 3, PAR 6 WITH 5, PAR 8 WITH 7, POS TARG 0.0000, 0.0000, POS TARG 0.1005, 0.3305, POS TARG 0.1180, 0.5180, POS TARG 0.1740, 0.1850, POS TARG 0.2185, 0.8485, POS TARG 0.2920, 0.7030, POS TARG 0.3232, 0.1235, POS TARG 0.4412, 0.6415, POS TARG 0.5030, 0.0460, POS TARG 0.6035, 0.3765, POS TARG 0.6770, 0.2310, POS TARG 0.8262, 0.1695, SEQ 1-4 NON-INT, SEQ 5-8 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F438W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names LEO-I-DSPH ------------------------------------------------------------------------------------------------------------------------------------