6614( 6) - 05/15/96 16:36 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6614 Version: 6 Check-in Date: 15-May-1996 16:31:07 1.Proposal Title: The Star Formation History of the Sagittarius Dwarf Spheroidal Galaxy ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle STELLAR POPULATIONS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Kenneth Mighell Columbia University CoI: Taft Armandroff Kitt Peak National Observatory N CoI: Ata Sarajedini Kitt Peak National Observatory N CoI: Andrew Layden McMaster University N CoI: Mario Mateo University of Michigan N CoI: Flavio Fusi Pecci Universita di Bologna N CoI: Francesco Ferraro Universita di Bologna N CoI: Roberto Buonanno Osservatorio Astronomico di Roma N ------------------------------------------------------------------------------------ 6. Abstract We propose WFPC2 observations that will provide deep VI color- magnitude diagrams of the field stellar population of the Sagittarius dwarf spheroidal galaxy which is the nearest galaxy to the Milky Way. We will determine the star formation history of the stellar populations from a) the location and distribution of stars near the main- sequence turnoff, b) the luminosities, colors, and metallicities of stars on the giant branch, c) the relation of horizontal-branch morphology to stellar ages and metallicities, and d) the stellar luminosity function near the main-sequence turnoff. This investigation will provide valuable information on the formation and evolution of dwarf spheroidal galaxies in the Local Group. ------------------------------------------------------------------------------------ 6614( 6) - 05/15/96 16:36 - [ 2] Observations Description ------------------------ We will observe four fields in the Sagittarius dwarf spheroidal galaxy and two background fields. We will spend two orbits per target field using the WFPC2 instrument with the F555W and F814W filters. We have 6 target fields and will use 12 primary orbits in 6 visits (2 orbits/visit). The first orbit of each visit will have 11 exposures : 6x160s (F555W) and 5x160s (F814W). The second orbit of each visit will have 4 exposures : 2x600s (F555W) and 2x500s (F814W). All exposures will be taken at ATD-GAIN=15 (high-gain) with CLOCKS=NO and CR- SPLIT=NO. The target SGR-DSPH1 is 12 arcmin north of the Sgr globular cluster M54 and was observed by Sarajedini & Layden (1995, AJ, 109, 1086). The target SGR-DSPH2 is 2 arcmin north of SGR-DSPH1. This will allow a 2 to 13 percent overlap depending on the orientation of the HST. The target SGR-DSPH3 is in the center of the field observed by Mateo et al. (1995, AJ, 109, 588). The target SGR-DSPH4 is 2 arcmin north of SGR-DSPH3. The target SGR-MWG1 is in the center of the Mateo \\et (1995) control field. The target SGR-MWG2 is two arcmin north of SGR-MWG1. The small amount of field overlap will allow us to measure measure many stars at two different locations within the WFPC2 instrument. This will allow us to determine the self-consistency of the WFPC2 photometry. Each 160- sec exposure pair of F555W and F814W will allow us to construct VI color- magnitude diagrams from ~1.3 mag above the horizontal branch (V_HB ~ 18.3 mag) to ~2.7 mag below an old 15 Gyr main-sequence turnoff (V_TO ~ 21.8 mag) assuming a minimum detection of signal-to-noise ratio S/N=5. All our S/N calculations assume a background level of V=20.0 mag/arcsec^2. Combining the photometry from three 160-sec exposure pairs together will allow us reach a limiting magnitude (S/N=5) of 24.7<=V<=25.4 mag (depending on the areal stellar density) which is at least 2.9 mag below the main-sequence turnoff of an old 15 Gyr stellar population. The final composite VI color-magnitude diagram will have a dynamic range of over 8 magnitudes from about 1.3 mag above the horizontal branch to at least 4 magnitudes (conservatively) below the main- sequence turnoff of the oldest stellar population in the Sgr dwarf spheroidal galaxy. Real Time Justification ----------------------- None. The supporting ground-based VI CCD observations already exist within our group. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6614( 6) - 05/15/96 16:36 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SGR-DSPH1 GALAXY, DWARF RA=18H 55M 03.30S +/- 0.01S, J2000 V = 17 SPHEROIDAL DEC=-30D 16' 42.0" +/- 0.1" B-V = 0.6 Comments: DO NOT USE THE GLOBULAR CLUSTER M54 AS A GUIDE STAR. 2 SGR-DSPH2 GALAXY, DWARF RA=18H 55M 03.30S +/- 0.01S, J2000 V = 17 SPHEROIDAL DEC=-30D 14' 42.0" +/- 0.1" B-V = 0.6 Comments: DO NOT USE THE GLOBULAR CLUSTER M54 AS A GUIDE STAR. 3 SGR-DSPH3 GALAXY, DWARF RA=19H 06M 11.00S +/- 0.01S, J2000 V = 17 SPHEROIDAL DEC=-30D 25' 22.0" +/- 0.1" B-V = 0.6 4 SGR-DSPH4 GALAXY, DWARF RA=19H 06M 11.00S +/- 0.01S, J2000 V = 17 SPHEROIDAL DEC=-30D 23' 22.0" +/- 0.1" B-V = 0.6 5 SGR-MWG1 GALAXY, SPIRAL RA=18H 33M 26.00S +/- 0.01S, J2000 V = 17 DEC=-40D 57' 57.0" +/- 0.1" B-V = 0.6 6 SGR-MWG2 GALAXY, SPIRAL RA=18H 33M 26.00S +/- 0.01S, J2000 V = 17 DEC=-40D 55' 57.0" +/- 0.1" B-V = 0.6 6614( 6) - 05/15/96 16:36 - [ 4] Visit: 01 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 SGR-DSPH1 WFPC2 IMAGE PC1-FIX F555W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 6 160S ------------------------------------------------------------------------------------------------------------------------------------ 17 SGR-DSPH1 WFPC2 IMAGE PC1-FIX F814W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 5 160S ------------------------------------------------------------------------------------------------------------------------------------ 21 SGR-DSPH1 WFPC2 IMAGE PC1-FIX F555W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 2 600S ------------------------------------------------------------------------------------------------------------------------------------ 23 SGR-DSPH1 WFPC2 IMAGE PC1-FIX F814W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 2 500S ------------------------------------------------------------------------------------------------------------------------------------ 6614( 6) - 05/15/96 16:36 - [ 5] Visit: 02 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 SGR-DSPH2 WFPC2 IMAGE PC1-FIX F555W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 6 160S ------------------------------------------------------------------------------------------------------------------------------------ 17 SGR-DSPH2 WFPC2 IMAGE PC1-FIX F814W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 5 160S ------------------------------------------------------------------------------------------------------------------------------------ 21 SGR-DSPH2 WFPC2 IMAGE PC1-FIX F555W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 2 600S ------------------------------------------------------------------------------------------------------------------------------------ 23 SGR-DSPH2 WFPC2 IMAGE PC1-FIX F814W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 2 500S ------------------------------------------------------------------------------------------------------------------------------------ 6614( 6) - 05/15/96 16:36 - [ 6] Visit: 03 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 SGR-DSPH3 WFPC2 IMAGE PC1-FIX F555W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 6 160S ------------------------------------------------------------------------------------------------------------------------------------ 17 SGR-DSPH3 WFPC2 IMAGE PC1-FIX F814W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 5 160S ------------------------------------------------------------------------------------------------------------------------------------ 21 SGR-DSPH3 WFPC2 IMAGE PC1-FIX F555W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 2 600S ------------------------------------------------------------------------------------------------------------------------------------ 23 SGR-DSPH3 WFPC2 IMAGE PC1-FIX F814W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 2 500S ------------------------------------------------------------------------------------------------------------------------------------ 6614( 6) - 05/15/96 16:36 - [ 7] Visit: 04 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 SGR-DSPH4 WFPC2 IMAGE PC1-FIX F555W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 6 160S ------------------------------------------------------------------------------------------------------------------------------------ 17 SGR-DSPH4 WFPC2 IMAGE PC1-FIX F814W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 5 160S ------------------------------------------------------------------------------------------------------------------------------------ 21 SGR-DSPH4 WFPC2 IMAGE PC1-FIX F555W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 2 600S ------------------------------------------------------------------------------------------------------------------------------------ 23 SGR-DSPH4 WFPC2 IMAGE PC1-FIX F814W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 2 500S ------------------------------------------------------------------------------------------------------------------------------------ 6614( 6) - 05/15/96 16:36 - [ 8] Visit: 05 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 SGR-MWG1 WFPC2 IMAGE PC1-FIX F555W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 6 160S ------------------------------------------------------------------------------------------------------------------------------------ 17 SGR-MWG1 WFPC2 IMAGE PC1-FIX F814W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 5 160S ------------------------------------------------------------------------------------------------------------------------------------ 21 SGR-MWG1 WFPC2 IMAGE PC1-FIX F555W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 2 600S ------------------------------------------------------------------------------------------------------------------------------------ 23 SGR-MWG1 WFPC2 IMAGE PC1-FIX F814W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 2 500S ------------------------------------------------------------------------------------------------------------------------------------ 6614( 6) - 05/15/96 16:36 - [ 9] Visit: 06 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 SGR-MWG2 WFPC2 IMAGE PC1-FIX F555W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 6 160S ------------------------------------------------------------------------------------------------------------------------------------ 17 SGR-MWG2 WFPC2 IMAGE PC1-FIX F814W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 5 160S ------------------------------------------------------------------------------------------------------------------------------------ 21 SGR-MWG2 WFPC2 IMAGE PC1-FIX F555W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 2 600S ------------------------------------------------------------------------------------------------------------------------------------ 23 SGR-MWG2 WFPC2 IMAGE PC1-FIX F814W CLOCKS=NO,ATD-GAIN=15,CR-SPLIT=NO 2 500S ------------------------------------------------------------------------------------------------------------------------------------ 6614( 6) - 05/15/96 16:36 - [ 10] Summary Form for Proposal 6614 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CLOCKS=NO ATD-GAIN=15 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names SGR-DSPH1 SGR-DSPH2 SGR-DSPH3 SGR-DSPH4 SGR-MWG1 SGR-MWG2 ------------------------------------------------------------------------------------------------------------------------------------