9479( 4) - 12/09/02 16:28 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9479 Version: 4 Check-in Date: 09-Dec-2002 16:27:36 1.Proposal Title: The Field Stellar Populations of M33's Outer Halo ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Ata Sarajedini University of Florida CoI: Dr. Doug Geisler Universidad de Concepcion N CoI: Dr. Robert Schommer Cerro Tololo InterAmerican Observatory N CoI: Mr. Paul Harding University of Arizona N ------------------------------------------------------------------------------------ 5. Abstract In cycle 5, we observed 10 globular clusters in the halo of M33 with HST/WFPC2. For each cluster, we have constructed VI color-magnitude diagrams (CMDs) that reach some 2 magnitudes below the horizontal branch (HB). Although their mean metallicity is <~ngleFe/H\rangle= -1.27 +/- 0.11, 80\ possess completely red HB morphologies, much redder than comparable globular clusters in the halo of the Milky Way. Furthermore, these M33 halo globulars therefore suffer from the `second parameter effect' where another parameter in addition to metallicity is influencing the HB morphology. If interpreted in terms of age, this leads us to the surprising conclusion that the epoch of halo formation in M33 was significantly more extended as compared with the Milky Way. Of course, this conclusion is based only on the properties of the halo clusters in M33. As a result, we propose to investigate the properties of the halo field stars in M33. Our approach involves the construction of VI color-magnitude diagrams for 3 fields located at projected distances of 7 kpc, 8 kpc, and 9 kpc from the center of M33. From the color-magnitude diagrams, we will measure the mean metallicity, metallicity dispersion, and horizontal branch morphology of the field halo stars in M33. These properties will be compared with those of the M33 halo globular clusters as well as the halo populations of the Milky Way and M31. ------------------------------------------------------------------------------------ 9479( 4) - 12/09/02 16:28 - [ 2] Observations Description ------------------------ We will use the ACS in WFC mode to image three halo fields in M33. One of the fields is coincident with the Mould & Kristian (1986) field while the other two are progressively further away from the center of M33 with overlaps to allow the calibration of all of the data to the same photometric system. Based on our existing WFPC2 photometry, we estimate needing S/N = 20 at the level of the horizontal branch (V ~ 25.5, I ~ 25.0) in order to unequivocally measure the morphology and magnitude of the HB. Using the ETC for ACS (WFC, F606W & F814W, S/N=20, Kurucz F0V spectrum, default aperture size, V=25.5 & I=25.0, E(B- V)=0.1, average Zodiacal light, average Bright Earth, 8 e-/ADU, CR-SPLIT=2), we find that we require 900s of exposure time in F606W and 1500s in F814W. For M33, the visibility period is 53 minutes. Each orbit will consist of 6 minutes for guide star acquisition, 1 (CR-SPLIT=2) 900 sec exposure in the F606W filter, 20 sec for a <1.25" dither, 1 (CR-SPLIT=2) 1500 sec exposure in the F814W filter, and 6.5 minutes for overhead. One of these exposure times can potentially be increased if some of the instrument overhead can be done during earth occultation of our fields. The images will be reduced in the same way as our WFPC2 images of the cluster fields. We have a great deal of experience in doing crowded field PSF fitting photometry using the DAOPHOT/ALLFRAME software package; we will apply this reduction method to the ACS data as well. We estimate being able to reach a limiting magnitude of V=27.6 (I=27.0) with S/N~3.5. This will allow us to detect an extended blue HB located as much as 2 magnitudes below the nominal HB level. In addition, we will be able to reach the main sequence turnoff of a 3 Gyr population, if it exists. To optimize the observing efficiency of HST, we plan to specify a range of possible spacecraft roll angles in order to obtain coordinated parallel observations with NICMOS/NIC2, WFPC2 (by turning off auto-parallels with HRC), and STIS/CCD. Using the Visual Target Tuner, we have already checked the feasibility of this strategy. The intent is to use NICMOS, WFPC2, and STIS to image the outer disk of M33 in the IR and optical bands and thus construct J--K with NICMOS (e.g. Stephens et al. 2001), V--I with WFPC2, and B--R (e.g. Gregg & Minniti 1997) color-magnitude diagrams for these fields. Judging from the NICMOS CMDs of M31 globulars published by Stephens et al. (2001), our own WFPC2 observations, and using the STIS ETC, we estimate reaching a magnitude of R~26.5 with STIS, V~27 with WFPC2, and K~21.4 with NICMOS. These would be analyzed using the same techniques described above and will yield valuable information on the star formation history of the M33 disk. Real Time Justification ----------------------- Calibration Justification ------------------------- Real_Time_Justification Additional Comments ------------------- ------------------------------------------------------------------------------------ 9479( 4) - 12/09/02 16:28 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC598-HALO1 EXT-STAR, AGB STAR, RR RA=1H 35M 18.25S +/- 1.0", J2000 V = 180 V = 18 LYRAE STAR, HORIZONTAL DEC=30D 28' 57.7" +/- 1.0" B-V = 0.6 BRANCH STAR E(B-V) = 0.1 Coordinate Source: Other_Source: VTT Comments: FLUX DATA REPRESENT PROPERTIES OF BRIGHTEST STARS IN THIS FIELD 2 NGC598-HALO2 EXT-STAR, AGB STAR, RR RA=1H 35M 31.71S +/- 1.0", J2000 V = 180 V = 18 LYRAE STAR, HORIZONTAL DEC=30D 28' 6.5" +/- 1.0" B-V = 0.6 BRANCH STAR E(B-V) = 0.1 Coordinate Source: Other_Source: VTT Comments: FLUX DATA REPRESENT PROPERTIES OF BRIGHTEST STARS IN THIS FIELD 3 NGC598-HALO3 EXT-STAR, AGB STAR, RR RA=1H 35M 46.01S +/- 1.0", J2000 V = 180 V = 18 LYRAE STAR, HORIZONTAL DEC=30D 27' 2.2" +/- 1.0" B-V = 0.6 BRANCH STAR E(B-V) = 0.1 Coordinate Source: Other_Source: VTT Comments: FLUX DATA REPRESENT PROPERTIES OF BRIGHTEST STARS IN THIS FIELD 9479( 4) - 12/09/02 16:28 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 60.0D TO 70.0D 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 NGC598-HALO ACS/WF ACCUM WFC F606W CR-SPLIT=2,GAIN=2,PAREXP=NONE 1 760 S PAR 2-4 WITH 1 1 C ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFPC2 IMAGE WFALL-F F606W ATD-GAIN=7 2 147 S IX ------------------------------------------------------------------------------------------------------------------------------------ 3 ANY STIS/C ACCUM 50CCD MIRROR GAIN=4 1 787 S CD ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY NIC2 MULTIAC NIC2 F110W SAMP-SEQ=STEP128,NSAMP=17 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC598-HALO ACS/WF ACCUM WFC F814W CR-SPLIT=2,GAIN=2,PAREXP=NONE 1 1400 S POS TARG 0.12, 0.12 PAR 1 C 6-8 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFPC2 IMAGE WFALL-F F814W ATD-GAIN=7 2 587 S IX ------------------------------------------------------------------------------------------------------------------------------------ 7 ANY STIS/C ACCUM F28X50L MIRROR GAIN=4 1 1587 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY NIC2 MULTIAC NIC2 F222M SAMP-SEQ=STEP128,NSAMP=22 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 9479( 4) - 12/09/02 16:28 - [ 5] Visit: 02 Visit Priority: Visit Requirements: ORIENT 60.0D TO 70.0D 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 NGC598-HALO ACS/WF ACCUM WFC F606W CR-SPLIT=2,GAIN=2,PAREXP=NONE 1 760 S PAR 2-4 WITH 1 2 C ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFPC2 IMAGE WFALL-F F606W ATD-GAIN=7 2 147 S IX ------------------------------------------------------------------------------------------------------------------------------------ 3 ANY STIS/C ACCUM 50CCD MIRROR GAIN=4 1 787 S CD ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY NIC2 MULTIAC NIC2 F110W SAMP-SEQ=STEP128,NSAMP=17 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC598-HALO ACS/WF ACCUM WFC F814W CR-SPLIT=2,GAIN=2,PAREXP=NONE 1 1400 S POS TARG 0.12, 0.12 PAR 2 C 6-8 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFPC2 IMAGE WFALL-F F814W ATD-GAIN=7 2 587 S IX ------------------------------------------------------------------------------------------------------------------------------------ 7 ANY STIS/C ACCUM F28X50L MIRROR GAIN=4 1 1587 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY NIC2 MULTIAC NIC2 F222M SAMP-SEQ=STEP128,NSAMP=22 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 9479( 4) - 12/09/02 16:28 - [ 6] Visit: 03 Visit Priority: Visit Requirements: ORIENT 60.0D TO 70.0D 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 NGC598-HALO ACS/WF ACCUM WFC F606W CR-SPLIT=2,GAIN=2,PAREXP=NONE 1 760 S PAR 2-4 WITH 1 3 C ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFPC2 IMAGE WFALL-F F606W ATD-GAIN=7 2 147 S IX ------------------------------------------------------------------------------------------------------------------------------------ 3 ANY STIS/C ACCUM 50CCD MIRROR GAIN=4 1 787 S CD ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY NIC2 MULTIAC NIC2 F110W SAMP-SEQ=STEP128,NSAMP=17 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC598-HALO ACS/WF ACCUM WFC F814W CR-SPLIT=2,GAIN=2,PAREXP=NONE 1 1400 S POS TARG 0.12, 0.12 PAR 3 C 6-8 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFPC2 IMAGE WFALL-F F814W ATD-GAIN=7 2 587 S IX ------------------------------------------------------------------------------------------------------------------------------------ 7 ANY STIS/C ACCUM F28X50L MIRROR GAIN=4 1 1587 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY NIC2 MULTIAC NIC2 F222M SAMP-SEQ=STEP128,NSAMP=22 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 9479( 4) - 12/09/02 16:28 - [ 7] Summary Form for Proposal 9479 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC WFALL-FIX 50CCD NIC2 F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC WFPC2 STIS/CCD NIC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM IMAGE MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2 GAIN=2 PAREXP=NONE ATD-GAIN=7 GAIN=4 NSAMP=17 NSAMP=22 SAMP-SEQ=STEP128 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 60.0D TO 70.0D PAR 2-4 WITH 1 POS TARG 0.12, 0.12 PAR 6-8 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W MIRROR F110W F814W F222M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC598-HALO1 ANY NGC598-HALO2 NGC598-HALO3 ------------------------------------------------------------------------------------------------------------------------------------