12274( 4) - 22-Aug-2011 19:15:44 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12274 Version: 4 Check-in Time: 22-Aug-2011 19:15:44 STScI Edit Number: 0 Title Proper motion study of M54: an intermediate-mass black hole in the nucleus of the Sagittarius Dwarf Galaxy? ------------------------------------------------------------------------------------ Type Cycle GO 18 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Roeland P. van der Marel Space Telescope Science Institute CoI: Dr. Jay Anderson Space Telescope Science Institute N CoI: Dr. Rodrigo Ibata Universite de Strasbourg I N ------------------------------------------------------------------------------------ Abstract Intermediate Mass Black Holes (IMBHs) are objects of considerable astrophysical significance, and the centers of globular clusters may be our best chance of detecting them. Tentative evidence has been presented for, e.g., G1, Omega Cen, and M54. These are all suspected to be the remnant nuclei of disrupted dwarf galaxies, with M54 residing at the center of the Sagittarius dwarf galaxy. IMBHs in these clusters could indicate an important connection between globular cluster black holes and the super-massive black holes known to exist in galactic nuclei. However, the line-of-sight velocity studies from which the IMBH evidence was obtained are not clear-cut. We have demonstrated that HST proper motion studies can provide much better constraints. We recently published 170, 000 proper motions for Omega Cen, and our modeling of the results significantly weakened the case for an IMBH. Here we propose a similar study for M54. Ground-based spectroscopy by one of us found a peak in velocity dispersion which could be fit by either a 10^4 solar mass IMBH or an anisotropic velocity distribution; it also found a surprising offset between the kinematic and star count centers. The proposed proper motions will validate and refine our knowledge of the dispersion peak; they will directly measure the anisotropy through the ratio of radial and tangential proper motions; and they will allow an improved determination of the kinematic center from the proper motion dispersion field. We will derive a high quality proper motion catalog of thousands of stars to put strong new constraints on the M54 cluster dynamics, structure, and possible presence of an IMBH. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will observe M54 with the WFC3/UVIS, with the F438W filter, using the subarray mode, for 2 orbits. Our observation strategy will be focused on the core of the cluster, for two reasons. First, the core is where an IMBH would reside and leave its mark. Second, the velocity dispersion in M54 drops with radius. Outside the core the proper motion velocity dispersion would be hard to measure, because it becomes comparable to our expected random errors. The choice of a blue filter is motivated by the fact that it reduces the prominence of the brightest red giant stars in the images. The choice of WFC3/UVIS over ACS/WFC is motivated by three considerations: WFC3/UVIS has a smaller pixel size, better blue sensitivity, and higher cosmetic quality (very little charge transfer efficiency degradation). The choice of subarray 12274( 4) - 22-Aug-2011 19:15:44 - [ 2] mode reduces overheads associated with buffer dumps, therefore allowing for more exposure time and exposures per orbit. We are planning 10 2048x2048 exposures, per orbit. The resulting field of view (FOV; 80x 80 arcsec) is more than sufficient to cover the M54 core (core radius equals 7 arcsec, half-mass radius equals 30 arcsec). The FOV will overlap 100% with the epoch 1 ACS/WFC data from GO-10775, independent of the telescope orientation. The 20 total exposures are split over 10 positions. At each position we will obtain one short (30s) and one long (200-300s) exposure. The 10 positions were chosen by Jay Anderson based on the output of custom scripts. Real Time Justification ----------------------- N/A Calibration Justification ------------------------- N/A Additional Comments ------------------- N/A ------------------------------------------------------------------------------------ 12274( 4) - 22-Aug-2011 19:15:44 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 M54 STELLAR CLUSTER, RA=18H55M3.3300S +/- 0.1", J2000 V = 8.37 GLOBULAR CLUSTER, DEC=-30D28'47.50" +/- 0.1" NUCLEUS Reference Frame: ICRS Comments: Distance is 26.8 kpc. ------------------------------------------------------------------------------------------------------------------------------------ 12274( 4) - 22-Aug-2011 19:15:44 - [ 4] Visit: 01 Visit Requirements: 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 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 200 S POS TARG 10.40000, S C-SUB see below 9.00000 ------------------------------------------------------------------------------------------------------------------------------------ 2 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 30 S SAME POS AS 1 S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 3 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 200 S POS TARG 18.06040, S C-SUB see below 2.57210 ------------------------------------------------------------------------------------------------------------------------------------ 4 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 30 S SAME POS AS 3 S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 5 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 200 S POS TARG 12.13650, S C-SUB see below -0.84810 ------------------------------------------------------------------------------------------------------------------------------------ 6 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 30 S SAME POS AS 5 S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 7 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 200 S POS TARG 5.40000, S C-SUB see below 0.33970 ------------------------------------------------------------------------------------------------------------------------------------ 8 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 30 S SAME POS AS 7 S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 9 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 200 S POS TARG 1.00310, S C-SUB see below 5.57980 ------------------------------------------------------------------------------------------------------------------------------------ 10 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 30 S SAME POS AS 9 S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 11 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 200 S POS TARG 1.00310, S C-SUB see below 12.42020 ------------------------------------------------------------------------------------------------------------------------------------ 12 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 30 S SAME POS AS 11 S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 13 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 200 S POS TARG 5.40000, S C-SUB see below 17.66030 ------------------------------------------------------------------------------------------------------------------------------------ 14 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 30 S SAME POS AS 13 S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 12274( 4) - 22-Aug-2011 19:15:44 - [ 5] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 15 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 200 S POS TARG 12.13650, S C-SUB see below 18.84810 ------------------------------------------------------------------------------------------------------------------------------------ 16 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 30 S SAME POS AS 15 S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 17 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 200 S POS TARG 18.06040, S C-SUB see below 15.42790 ------------------------------------------------------------------------------------------------------------------------------------ 18 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 30 S SAME POS AS 17 S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 19 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 200 S POS TARG 20.40000, S C-SUB see below 9.00000 ------------------------------------------------------------------------------------------------------------------------------------ 20 M54 WFC3/UVI ACCUM UVIS2-2K2 F438W CR-SPLIT=NO 1 30 S SAME POS AS 19 S C-SUB ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ M54 1 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 1 234.0 S S 2C-SUB M54 2 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 1 N/A S 2C-SUB M54 3 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 1 234.0 S S 2C-SUB M54 4 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 1 N/A S 2C-SUB M54 5 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 1 234.0 S S 2C-SUB M54 6 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 1 N/A S 2C-SUB M54 7 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 1 234.0 S S 2C-SUB M54 8 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 1 N/A S 2C-SUB M54 9 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 1 234.0 S S 2C-SUB M54 10 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 1 N/A S 2C-SUB M54 11 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 2 256.0 S S 2C-SUB 12274( 4) - 22-Aug-2011 19:15:44 - [ 6] 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 | ------------------------------------------------------------------------------------------------------------------------------------ M54 12 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 2 N/A S 2C-SUB M54 13 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 2 256.0 S S 2C-SUB M54 14 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 2 N/A S 2C-SUB M54 15 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 2 256.0 S S 2C-SUB M54 16 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 2 N/A S 2C-SUB M54 17 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 2 256.0 S S 2C-SUB M54 18 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 2 N/A S 2C-SUB M54 19 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 2 256.0 S S 2C-SUB M54 20 WFC3/UVI ACCUM UVIS2-2K F438W none none none none 2 N/A S 2C-SUB 12274( 4) - 22-Aug-2011 19:15:44 - [ 7] Summary Form for Proposal 12274 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-2K2C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG 1.00310, 12.42020, POS TARG 1.00310, 5.57980, POS TARG 10.40000, 9.00000, POS TARG 12.13650, -0.84810, POS TARG 12.13650, 18.84810, POS TARG 18.06040, 15.42790, POS TARG 18.06040, 2.57210, POS TARG 20.40000, 9.00000, POS TARG 5.40000, 0.33970, POS TARG 5.40000, 17.66030, SAME POS AS 1, SAME POS AS 11, SAME POS AS 13, SAME POS AS 15, SAME POS AS 17, SAME POS AS 19, SAME POS AS 3, SAME POS AS 5, SAME POS AS 7, SAME POS AS 9 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F438W ------------------------------------------------------------------------------------------------------------------------------------ Target Names M54 ------------------------------------------------------------------------------------------------------------------------------------