----- Attempting Submission 1 (Fri Jun 27 02:26:55 GMT 2008) ----- Assigned ID: 118 ----- Attempting Submission 1 (Thu Mar 06 07:04:31 GMT 2008) ----- The Main Sequence Luminosity Function of Low-Mass Globular Clusters Theoretical work indicates that the dynamical evolution of globular clusters of low mass and low central concentration is strongly determined by mass-loss processes, such as stellar evaporation and tidal stripping, that can eventually lead to cluster dissolution. In fact, mass loss and cluster disruption is now considered to be a viable explanation for the form of the faint end of the Milky Way globular cluster luminosity function. A clear observational demonstration of the prevalence of cluster mass-loss would have ramifications not only for the dynamical evolution of individual globular clusters and their internal stellar mass distributions, but also for the relationships between halo field and cluster stars and the properties of globular cluster systems in galaxies. Our previous WFPC2 imaging of the low-mass diffuse halo cluster Palomar 5 revealed a main sequence deficient in stars compared to other low-concentration globular clusters of much higher mass, consistent with there having been a considerable loss of stars from this system. But is Pal 5 typical of low-mass, low-concentration halo clusters? We propose to place the mass-loss scenario on a firm observational footing (or otherwise) by using WFC3 imaging to measure the main-sequence stellar mass functions of two of the lowest-mass lowest-concentration globular clusters in the Milky Way, AM-4 and Palomar 13, in order to search for analogous evidence of stellar depletion.
WFC3 imaging is required of two low-mass globular clusters. Exposures will be made in each of the F606W and F814W filters. With each cluster, one full orbit will be spent integrating in each of these two filters, for a total of four orbits in the program. Pointing will be such as to place the center of each cluster on the WFC3 detector center. Observations in each filter will consist of exposures made at four positions in a box configuration using the default WFC3-UVIS-DITHER-BOX pattern. No CR-SPLIT will be invoked since these dithered frames will allow for cosmic ray removal. RESOLVED STELLAR POPULATIONS 12 false 0.0 0.0 false false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER AM4 J2000 13 56 31.2000 -27 10 4.00 J2000 STELLAR CLUSTER GLOBULAR CLUSTER PALOMAR13 J2000 23 06 44.4000 +12 46 19.00 J2000 WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /u/graeme/props/cycle17/OP-cache/cycle17-v01.xml (Tic-Visit :proposal-id 11680 :visit-id "01" :proposal-version -1 :trans-version "20080609" :date "26-Jun-2008 19:16:38.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 2310000 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11680 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11680 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2931 :al-overhead-at-end 116 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3267 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11680 :visit-id "01" :orbit-number 2 :pcs-time 195 :si-vis-utilization 2931 :al-overhead-at-end 116 :internal-dur-at-end 670 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3267 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /u/graeme/props/cycle17/OP-cache/cycle17-v02.xml (Tic-Visit :proposal-id 11680 :visit-id "02" :proposal-version -1 :trans-version "20080609" :date "26-Jun-2008 19:16:54.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 2310000 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11680 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11680 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2911 :al-overhead-at-end 116 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11680 :visit-id "02" :orbit-number 2 :pcs-time 195 :si-vis-utilization 2911 :al-overhead-at-end 116 :internal-dur-at-end 670 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) true 2 0