9719( 5) - 05/19/03 11:36 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9719 Version: 5 Check-in Date: 19-May-2003 11:35:33 1.Proposal Title: Metallicity Spreads in M31 Globular Clusters ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 12 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Dr. Terry Bridges Anglo-Australian Observatory CoI: Dr. Pascale Jablonka Observatoire de Paris - Section de Meudon N CoI: Dr. Ata Sarajedini University of Florida N CoI: Dr. Georges Meylan Space Telescope Science Institute N CoI: Prof. S. George Djorgovski California Institute of Technology N ------------------------------------------------------------------------------------ 5. Abstract Our recent deep HST photometry of the M31 halo globular cluster (GC) Mayall~II, also called G1, has revealed a red-giant branch with a clear spread that we attribute to an intrinsic metallicity dispersion of at least 0.4 dex in [Fe/H]. The only other GC exhibiting such a metallicity dispersion is Omega Centauri, the brightest and most massive Galactic GC, whose range in [Fe/H] is about 0.5 dex. These observations are obviously linked to the fact that both G1 and Omega Cen are bright and massive GC, with potential wells deep enough to keep part of their gas, which might have been recycled, producing a metallicity scatter among cluster stars. These observations dramatically challenge the notion of chemical homogeneity as a defining characteristic of GCs. It is critically important to find out how common this phenomenon is and how it can constrain scenarios/models of GC formation. The obvious targets are other bright and massive GCs, which exist in M31 but not in our Galaxy where Omega Cen is an isolated giant. We propose to acquire, with ACS/HRC, deep imaging of 3 of the brightest M31 GCs for which we have observed velocity dispersion values similar to those observed in G1 and Omega Cen. A sample of GCs with chemical abundance dispersions will provide essential information about their formation mechanism. This would represent a major step for the studies of the origin and evolution of stellar populations. ------------------------------------------------------------------------------------ 9719( 5) - 05/19/03 11:36 - [ 2] Observations Description ------------------------ We will observe 3 massive M31 globular clusters using the F606W and F814W filters. We have been allocated 6 orbits total, or 2 orbits per cluster. We wish to reach one magnitude fainter than the cluster horizontal branch, ie. V~26.3 and I~25.3, with a S/N ~ 10. G78 is located South-East of the M31 center mostly along the major axis, while G213 and G280 are located South-West of the center and closer to the galaxy minor axis. Each cluster will be centered on the HRC, and we will use the ACS-HRC-DITHER-BOX pattern with default spacing to improve the spatial resolution and remove cosmic rays. For each cluster, at each of the 4 dither positions, we will obtain 505/715 sec exposures in F606W/F814W. Over 2 orbits, we thus get total exposures of 2020/2860 sec in F606W/F814W. The ACS ETC shows that this will yield a S/N of 11 to V=26.3, I=25.3. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9719( 5) - 05/19/03 11:36 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC224-G78 EXT-CLUSTER, GLOBULAR RA=00H41M1.14S +/- 0.1", J2000 V = 14.2 CLUSTER DEC=+41D13'45.4" +/- 0.1" Coordinate Source: Other_Source: Mike Rich (priv. comm.) Comments: Vlim = 26.3, Vlim= limiting V magnitude (1 mag below HB) llim = 25.3, Ilim = limiting I magnitude (1 mag below HB) 2 NGC224-G213 EXT-CLUSTER, GLOBULAR RA=00H43M14.34S +/- 0.1", J2000 V = 14.5 CLUSTER DEC=+41D07'20.7" +/- 0.1" Coordinate Source: Other_Source: Mike Rich (priv. comm.) Comments: Vlim= 26.3, Vlim= limiting V magnitude (1 mag below HB) llim=25.3, Ilim= limiting I magnitude (1 mag below HB) 3 NGC224-G280 EXT-CLUSTER, GLOBULAR RA=00H44M29.51S +/- 0.1", J2000 V = 14.3 CLUSTER DEC=+41D21'35.5" +/- 0.1" Coordinate Source: Other_Source: Mike Rich (priv. comm.) Comments: Vlim= 26.3, Vlim= limiting V magnitude (1 mag below HB) llim= 25.3, Ilim= limiting I magnitude (1 mag below HB) 9719( 5) - 05/19/03 11:36 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-HRC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.15 Coordinate_Frame POS-TARG Pattern_Orient 19.89 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 9719( 5) - 05/19/03 11:36 - [ 5] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC224-G213 ACS/HR ACCUM HRC F606W CR-SPLIT=NO,GAIN=2 1 505 S PATTERN 1 1-2 C ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC224-G213 ACS/HR ACCUM HRC F814W CR-SPLIT=NO,GAIN=2 1 715 S C ------------------------------------------------------------------------------------------------------------------------------------ 9719( 5) - 05/19/03 11:36 - [ 6] Visit: 02 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC224-G78 ACS/HR ACCUM HRC F606W CR-SPLIT=NO,GAIN=2 1 505 S PATTERN 1 1-2 C ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC224-G78 ACS/HR ACCUM HRC F814W CR-SPLIT=NO,GAIN=2 1 715 S C ------------------------------------------------------------------------------------------------------------------------------------ 9719( 5) - 05/19/03 11:36 - [ 7] Visit: 03 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC224-G280 ACS/HR ACCUM HRC F606W CR-SPLIT=NO,GAIN=2 1 505 S PATTERN 1 1-2 C ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC224-G280 ACS/HR ACCUM HRC F814W CR-SPLIT=NO,GAIN=2 1 715 S C ------------------------------------------------------------------------------------------------------------------------------------ 9719( 5) - 05/19/03 11:36 - [ 8] Summary Form for Proposal 9719 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures HRC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/HRC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO GAIN=2 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1-2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC224-G213 NGC224-G78 NGC224-G280 ------------------------------------------------------------------------------------------------------------------------------------