10430( 3) - 10/22/04 08:53 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 10430 Version: 3 Check-in Date: 22-Oct-2004 12:52:06 1.Proposal Title: Identifying the Major Star Formation Epoch(s) in the Outlying M31 Dwarf Spheroidal Companion Cassiopeia ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle 4. Parallel Pointing Tolerance GO 13 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. Taft E. Armandroff National Optical Astronomy Observatories, AURA CoI: Prof. Gary Stewart Da Costa Australian National University Y CoI: Dr. George Jacoby National Optical Astronomy Observatories, N AURA CoI: Dr. Barton John Pritzl Macalester College N ------------------------------------------------------------------------------------ 6. Abstract The Galaxy's dwarf spheroidal (dSph) companions show a surprising diversity in the epochs of their major star formation episodes, which extend from ~15 to ~1 Gyr. For Galactic dSphs there is correlation between Galactocentric distance and the prominence of intermediate-age (~2-10 Gyr) populations; the dSphs with extended star formation lie at larger Galactocentric distance. This correlation may also apply to M31's dSph companions. Our WFPC2 data (Da Costa et al. 2000) show that And II lies at a true distance of between 160 and 230 kpc from M31, comparable to the Galactocentric distances of the Galaxy's outer dSphs satellites, and further than the other M31 Companions studied in detail so far. This dSph shows convincing evidence for an intermediate-age (~6-9 Gyr) population, which the other well-studied M31 dSphs lack. Only the recently discovered M31 dSphs companions And VI and Cassiopeia lie at larger distances from the center of M31 than And II. The pri mary aim of this proposal is to determine a color-magnitude diagram for the Cassiopeia dSph which reaches below the horizontal branch. With these data we will constrain the epoch of the main star formation episode in Cassiopeia, adding to our knowledge of how star formation in dwarf galaxies is affected by the presence of a larger neighbor. Additional results will include measurement of the true distance from M31, mean abundance, abundance dispersion, and the variable star content. With these observations, the investigation of the stellar populations down to the horizontal branch of the known M31 dSphs with HST will be complete. ------------------------------------------------------------------------------------ 10430( 3) - 10/22/04 08:53 - [ 2] Observations Description ------------------------ The required color-magnitude diagrams will be derived from multiple exposures carried out with ACS-WFC using the F555W (V) and F435W (B) filters. The center of Cas will be placed on the nominal center of the ACS-WFC field. We require the F555W and F435W frames to taken with the same, or nearly the same, orientation so that most stars in the field are imaged through both filters. We have broken the 12 orbit allocation into three 4 orbit visits. In order to preserve the maximum number of stars for the final combined color-magnitude diagram, use of the SAME ORIENT and GROUP WITHIN special requirements is necessary. The GROUP WITHIN time as been set at 7 DAYS as previous experience suggests this should not generate any particular scheduling difficulties. The 7 day interval is a compromise between easing the scheduling of the program and minimizing aliasing in the period determination for any RR Lyrae variables found. For the first and third visits the observations have been set up as follows: (a) 4 x 1200sec F555W (CR-SPLIT=2) over the standard ACS-WFC-DITHER- BOX dither pattern. (b) 4 x 1200sec F450W as for (a) For the second visit the observations use the F435W filter only ( we require 8 orbits of integration with F435W but only 4 with F555W). (a) 4 x 1200sec F435W (CR-SPLIT=2) over the standard ACS-WFC-DITHER-BOX dither pattern. (b) 4 x 1200sec F435W as for (a) but with a small POS-TARG move to further improve the discrimination between hot pixels and cosmis-ray hits. For both the second and third visits the entire pattern is shifted slightly relative to the first visit with POS TARG. We have found that this approach allows us to reliably determine the (internal) photometric uncertainties. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 10430( 3) - 10/22/04 08:53 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 CASSIOPEIA GALAXY, DWARF RA=23H26M31.0000S +/- 1", J2000 V = 12.9 SPHEROIDAL DEC=+50D41'31.00" +/- 1" Brightest individual target stars have V~22.4 and B~24.1 Coordinate Source: IMAGE_TIED_TO_GSC_FRAME 10430( 3) - 10/22/04 08:53 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.265 Line_Spacing 0.187 Coordinate_Frame POS-TARG Pattern_Orient 20.67 Angle_Between_Sides 69.05 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 10430( 3) - 10/22/04 08:53 - [ 5] Visit: 01 Visit Priority: Visit Requirements: GROUP 01, 02, 03 WITHIN 7.0D 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 CASSIOPEIA ACS/WFC ACCUM WFC F555W 1 1200 S PATTERN 1 1 see below ------------------------------------------------------------------------------------------------------------------------------------ 2 CASSIOPEIA ACS/WFC ACCUM WFC F435W 1 1200 S PATTERN 1 2 see below ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ CASSIOPEIA 1 ACS/WFC ACCUM WFC F555W 1 none none 1 1 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F555W 1 none none 2 1 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F555W 2 none none 1 1 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F555W 2 none none 2 1 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F555W 3 none none 1 2 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F555W 3 none none 2 2 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F555W 4 none none 1 2 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F555W 4 none none 2 2 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 1 none none 1 3 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 1 none none 2 3 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 2 none none 1 3 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 2 none none 2 3 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 3 none none 1 4 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 3 none none 2 4 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 4 none none 1 4 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 4 none none 2 4 600.0 S 10430( 3) - 10/22/04 08:53 - [ 6] Visit: 02 Visit Priority: Visit Requirements: SAME ORIENT AS 01 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 CASSIOPEIA ACS/WFC ACCUM WFC F435W 1 1200 S POS TARG 2.5, 2.5; see below PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 CASSIOPEIA ACS/WFC ACCUM WFC F435W 1 1200 S POS TARG 2.5,-2.5; see below PATTERN 1 2 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 1 none none 1 1 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 1 none none 2 1 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 2 none none 1 1 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 2 none none 2 1 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 3 none none 1 2 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 3 none none 2 2 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 4 none none 1 2 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 4 none none 2 2 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 1 none none 1 3 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 1 none none 2 3 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 2 none none 1 3 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 2 none none 2 3 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 3 none none 1 4 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 3 none none 2 4 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 4 none none 1 4 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F435W 4 none none 2 4 600.0 S 10430( 3) - 10/22/04 08:53 - [ 7] Visit: 03 Visit Priority: Visit Requirements: SAME ORIENT AS 01 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 CASSIOPEIA ACS/WFC ACCUM WFC F435W 1 1200 S POS TARG -2.5,-2.5; see below PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 CASSIOPEIA ACS/WFC ACCUM WFC F555W 1 1200 S POS TARG -2.5,-2.5; see below PATTERN 1 2 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 1 none none 1 1 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 1 none none 2 1 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 2 none none 1 1 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 2 none none 2 1 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 3 none none 1 2 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 3 none none 2 2 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 4 none none 1 2 600.0 S CASSIOPEIA 1 ACS/WFC ACCUM WFC F435W 4 none none 2 2 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F555W 1 none none 1 3 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F555W 1 none none 2 3 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F555W 2 none none 1 3 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F555W 2 none none 2 3 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F555W 3 none none 1 4 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F555W 3 none none 2 4 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F555W 4 none none 1 4 600.0 S CASSIOPEIA 2 ACS/WFC ACCUM WFC F555W 4 none none 2 4 600.0 S 10430( 3) - 10/22/04 08:53 - [ 8] Summary Form for Proposal 10430 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GROUP 01, 02, 03 WITHIN 7.0D PATTERN 1 1 PATTERN 1 2 SAME ORIENT AS 01 POS TARG 2.5, 2.5; PATTERN 1 1 POS TARG 2.5,-2.5; PATTERN 1 2 POS TARG -2.5,-2.5; PATTERN 1 1 POS TARG -2.5,-2.5; PATTERN 1 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F435W ------------------------------------------------------------------------------------------------------------------------------------ Target Names CASSIOPEIA ------------------------------------------------------------------------------------------------------------------------------------