----- Submission 1 (Fri May 19 18:49:55 GMT 2006) ----- ----- Attempting Submission 2 (Wed Apr 18 20:37:41 GMT 2007) ----- Phase II Proposal 10788 (GO10788_2007_04) successfully submitted. ----- Attempting Submission 3 (Wed Apr 18 20:40:40 GMT 2007) ----- Assigned ID: 675 ----- Submission 1 (Sat Jan 28 00:49:36 GMT 2006) ----- 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.

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. RESOLVED STELLAR POPULATIONS 12 false 0.0 false false false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the NED database. The position was updated to GSC2/ICRS. (brightest star in field) MESSIER-015 M15 J2000 21 29 58.4000 +12 10 1.00 J2000 ACS/HRC Imaging No No F555W /mnt/data/cohn/hst/proposals/cycle15/Phase_II_WFPC2/OP-cache/GO10788_2007_04-v01.xml 1176922299388 (Tic-Visit :proposal-id 10788 :visit-id "01" :proposal-version -1 :trans-version "20070325" :date "18-Apr-2007 14:51:39.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 448160 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10788 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10788 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2700 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3137 :pcs-gap 0 ) true 1 0 /tmp/OPVisit45733.xml 1176918554138