10788( 3) - 04/20/07 07:04 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10788 Version: 3 Check-in Time: 20-Apr-2007 11:03:51 STScI Edit Number: 0 Title Probing the Central Dark Mass Concentration of the Collapsed-Core Globular Cluster M15 ------------------------------------------------------------------------------------ Type Cycle Parallel Pointing Tolerance GO 15 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Haldan N. Cohn Indiana University System CoI: Dr. Phyllis M. Lugger Indiana University System N CoI: Dr. Jay Anderson Rice University N CoI: Dr. Adrienne Cool San Francisco State University N ------------------------------------------------------------------------------------ Abstract We plan to probe the central dark mass concentration in the collapsed-core globular cluster M15 by analyzing the structure of its central stellar cusp with the highest possible angular resolution. The rapid rise of M/L toward the center of M15 can be alternatively explained by a central concentration of several thousand compact remnants (heavy white dwarfs and neutron stars) or instead by the presence of an intermediate-mass black hole (IMBH) of a few thousand solar masses. We propose to obtain one orbit of highly dithered WFPC2 F555W (V) imaging to supplement the available ACS/HRC F435W (B) imaging from GO-10401. This will allow us (1) to improve the constraints on the radius of the as yet unresolved core and (2) to investigate the relation between cusp slope and stellar mass, the form of which depends on the size and mix of the remnant population and on whether or not an IMBH is present. We will compare the central cusp structure with predictions from both Fokker-Planck and GRAPE-6 N-body models, with and without IMBHs, to constrain the nature of the intriguing dark mass concentration. ------------------------------------------------------------------------------------ 10788( 3) - 04/20/07 07:04 - [ 2] Observations Description ------------------------ We have selected a sequence of WFPC2 F555W exposures to image the center of M15 with the highest possible angular resolution by using an optimized 3x3 dither pattern. This sequence consists of one 8s short exposure and 9 x 30s long exposures. The 8s exposure length ensures that no star in the PC1 field saturates. The 9 x 30s exposure sequence provides sufficient photometric depth to reach at least 4 mag below the main-sequence turnoff, while ensuring that no star in the critical central region saturates. We have specified the 15e/DN gain channel to increase the effective dynamic range and thus maximize the possible exposure length. We have selected a set of 9 separate dither positions for each of the 30s exposures that provide a dense sampling of the subpixel phase space over the WFPC2 field, with the subpixel sampling optimized for the PC1 field. The dither pattern also provides multipixel steps, to increase photometric accuracy. The short exposure will be taken at the same position as the final long exposure. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 10788( 3) - 04/20/07 07:04 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC7078 STELLAR CLUSTER, RA=21H29M58.3000S +/- 0.1", J2000 V = 13.5 GLOBULAR CLUSTER DEC=+12D10'1.00" +/- 0.1" (brightest star in field) Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the NED database. The position was updated to GSC2/ICRS. 10788( 3) - 04/20/07 07:04 - [ 4] Visit: 01 Visit Priority: 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 NGC7078 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 30 S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC7078 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 30 S POS TARG 0.1827, 0.5632 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC7078 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 30 S POS TARG 0.3653, 1.1264 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC7078 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 30 S POS TARG 0.5632, 0.1827 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC7078 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 30 S POS TARG 0.7459, 0.7459 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC7078 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 30 S POS TARG 0.9285, 1.3091 ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC7078 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 30 S POS TARG 1.1264, 0.3653 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC7078 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 30 S POS TARG 1.3091, 0.9285 ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC7078 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 30 S POS TARG 1.4918, 1.4918 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC7078 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 8 S SAME POS AS 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC7078 1 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A NGC7078 2 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A NGC7078 3 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A NGC7078 4 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A NGC7078 5 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A NGC7078 6 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A NGC7078 7 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A NGC7078 8 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A NGC7078 9 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A NGC7078 10 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A 10788( 3) - 04/20/07 07:04 - [ 5] Summary Form for Proposal 10788 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG 0.1827, 0.5632; POS TARG 0.3653, 1.1264; POS TARG 0.5632, 0.1827; POS TARG 0.7459, 0.7459; POS TARG 0.9285, 1.3091; POS TARG 1.1264, 0.3653; POS TARG 1.3091, 0.9285; POS TARG 1.4918, 1.4918; SAME POS AS 9; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC7078 ------------------------------------------------------------------------------------------------------------------------------------