11680( 2) - 27-Jun-2008 12:50:30 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11680 Version: 2 Check-in Time: 27-Jun-2008 12:50:30 STScI Edit Number: 0 Title The Main Sequence Luminosity Function of Low-Mass Globular Clusters ------------------------------------------------------------------------------------ Type Cycle GO 17 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Graeme H. Smith University of California - Santa Cruz CoI: Dr. Carl Grillmair Jet Propulsion Laboratory N CoI: Ms. Sarah L. Martell University of California - Santa Cruz N ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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. Real Time Justification ----------------------- Calibration Justification ------------------------- 11680( 2) - 27-Jun-2008 12:50:30 - [ 2] Additional Comments ------------------- ------------------------------------------------------------------------------------ 11680( 2) - 27-Jun-2008 12:50:30 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 STAR-CLUS-13 STELLAR CLUSTER, RA=13H56M21.2000S +/- 1.0", J2000 V = 27.0 5621-271004 GLOBULAR CLUSTER DEC=-27D10'4.00" +/- 1.0" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 2 STAR-CLUS-23 STELLAR CLUSTER, RA=23H06M44.4000S +/- 1.0", J2000 V = 27.0 0644+124619 GLOBULAR CLUSTER DEC=+12D46'19.00" +/- 1.0" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 11680( 2) - 27-Jun-2008 12:50:30 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 11680( 2) - 27-Jun-2008 12:50:30 - [ 5] 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 STAR-CLUS-1 WFC3/UVI ACCUM UVIS F606W CR-SPLIT=NO 1 615 S PATTERN 1 1-2 35621-27100 S 4 ------------------------------------------------------------------------------------------------------------------------------------ 2 STAR-CLUS-1 WFC3/UVI ACCUM UVIS F814W CR-SPLIT=NO 1 620 S 35621-27100 S 4 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ STAR-CLUS-135621-27 1 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 N/A 1004 S STAR-CLUS-135621-27 1 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 N/A 1004 S STAR-CLUS-135621-27 1 WFC3/UVI ACCUM UVIS F606W 3 none none none 2 N/A 1004 S STAR-CLUS-135621-27 1 WFC3/UVI ACCUM UVIS F606W 4 none none none 2 N/A 1004 S STAR-CLUS-135621-27 2 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 N/A 1004 S STAR-CLUS-135621-27 2 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 N/A 1004 S STAR-CLUS-135621-27 2 WFC3/UVI ACCUM UVIS F814W 3 none none none 2 N/A 1004 S STAR-CLUS-135621-27 2 WFC3/UVI ACCUM UVIS F814W 4 none none none 2 N/A 1004 S 11680( 2) - 27-Jun-2008 12:50:30 - [ 6] Visit: 02 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 STAR-CLUS-2 WFC3/UVI ACCUM UVIS F606W CR-SPLIT=NO 1 610 S PATTERN 1 1-2 30644+12461 S 9 ------------------------------------------------------------------------------------------------------------------------------------ 2 STAR-CLUS-2 WFC3/UVI ACCUM UVIS F814W CR-SPLIT=NO 1 615 S 30644+12461 S 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 | ------------------------------------------------------------------------------------------------------------------------------------ STAR-CLUS-230644+12 1 WFC3/UVI ACCUM UVIS F606W 1 none none none 1 N/A 4619 S STAR-CLUS-230644+12 1 WFC3/UVI ACCUM UVIS F606W 2 none none none 1 N/A 4619 S STAR-CLUS-230644+12 1 WFC3/UVI ACCUM UVIS F606W 3 none none none 2 N/A 4619 S STAR-CLUS-230644+12 1 WFC3/UVI ACCUM UVIS F606W 4 none none none 2 N/A 4619 S STAR-CLUS-230644+12 2 WFC3/UVI ACCUM UVIS F814W 1 none none none 1 N/A 4619 S STAR-CLUS-230644+12 2 WFC3/UVI ACCUM UVIS F814W 2 none none none 1 N/A 4619 S STAR-CLUS-230644+12 2 WFC3/UVI ACCUM UVIS F814W 3 none none none 2 N/A 4619 S STAR-CLUS-230644+12 2 WFC3/UVI ACCUM UVIS F814W 4 none none none 2 N/A 4619 S 11680( 2) - 27-Jun-2008 12:50:30 - [ 7] Summary Form for Proposal 11680 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1-2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names STAR-CLUS-135621-271004, STAR-CLUS-230644+124619 ------------------------------------------------------------------------------------------------------------------------------------