8706( 5) - 07/17/00 10:12 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8706 Version: 5 Check-in Date: 17-Jul-2000 09:54:34 1.Proposal Title: Phoenix: ``halo/disk'' structures in dwarf galaxies ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Antonio Aparicio Instituto de Astrofisica de Canarias CoI: Dr. David Marti nez-Delgado Instituto de Astrofi sica de Canarias N ------------------------------------------------------------------------------------ 5. Abstract Hierarchical clustering scenarios for galaxy formation predict that dwarf galaxies are the first to be formed and that they are building blocks of larger galaxies. We propose here to measure the spatial structure and the stellar age and metallicity distribution of the Phoenix dwarf galaxy to give support or reject such scenarios. The kind of detailed study we propose can only be carried on in nearby dwarfs and using the HST. We intend to obtain very deep V and I color-magnitude diagrams reaching the oldest MS turn-offs of a central and an outer field of Phoenix. Applying our techniques based on synthetic color-magnitude diagrams, we will determine the stellar population (age and metallicity distribution) gradients as a function of the galactocentric distance. Combined with our previous ground-based study of the galaxy, this will provide evidences of whether or not Phoenix has a real ``disk/halo'' structure and will allow to trace out the early phases of its evolution. ------------------------------------------------------------------------------------ 8706( 5) - 07/17/00 10:12 - [ 2] Observations Description ------------------------ sectionGeneral description and time calculation We require observations of one field placed outside the core radius of Phoenix, at ~eq 4' from the center in the region labeled B in Marti nez-Delgado Etal (1999), along the major axis of the external component of the galaxy. Besides this, we need to extend the already done observations of the central part of Phoenix to reach both in this and in the outer region, the magnitude of the oldest turn-offs (M_I=+3) with good photometric accuracy. The requested observations are based on what we have obtained for Leo I. Our analysis of the central part of this galaxy (Gallart Etal 1999) has been done with a nominal S/N~eq 19 at M_I=+3, as given by the WFPC2 exposure calculator assuming a spectral type G5 for the turn-off stars and a surface brightness of the background stellar light of V=24.0. At the distance of Phoenix, M_I=+3 implies I=26. To reach S/N=20 at this magnitude, total exposure times of 11000 sec in F555W and 14000 sec in F814W are needed. These are the times we need for the outer field. The central part of the galaxy has been already observed with 4700 sec in both filters. Hence, we need supplementary exposures of 6300 sec in F555W and 9300 sec in F814W for the central field. This will means 6* 1200 sec and 8* 1200 in F555W and F814W respectively in the central field and 10* 1200 and 12* 1200 in the outer filed. Short exposures of 200 sec in both filters will be necessary to obtain the photometry of the brightest stars in the external field. sectionVisits and orbits While the separation between both fields is larger than 2', two visits are required, one for each field. Low-sky restriction is required for the long exposures. However, the guide stars acquisition, the last over-head as well as part (if any) of the short-time integrations can be done without this restriction. For the declination of Phoenix, 45 min are available per orbit with the low-sky restriction and 55 without it. This means that 2* 1250 sec integrations can be done in every typical orbit (no short integration). In one orbit per filter and per field, 2* 1100+200 sec will be obtained. 7 orbits will be necessary for the central field and 11 orbits for the outer field. Each set will make up a visit. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8706( 5) - 07/17/00 10:12 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PHOENIX-DISK GALAXY, Dwarf RA=1H 51M 6.3S +/- 0.1S, DEC=- J2000 V = 13.2+/-0.5 Spheroidal, disk 44D 26' 40.9" +/- 0.1", PLATE- B-V = 0.61+/-0.2 ID=04FJ E(B-V) = 0.02+/-0.2 Coordinate Source: GUIDE_STAR_CATALOG Comments: V and (B-V) refer to integrated apparent magnitude. 2 PHOENIX-HALO GALAXY, Dwarf RA=1H 51M 8.2S +/- 0.1S, DEC=- J2000 V = 13.2+/-0.5 Spheroidal, halo 44D 24' 3.9" +/- 0.1", PLATE- B-V = 0.61+/-0.2 ID=04FJ E(B-V) = 0.02+/-0.2 Coordinate Source: GUIDE_STAR_CATALOG Comments: V and (B-V) refer to integrated apparent magnitude. 8706( 5) - 07/17/00 10:12 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFPC2-LINE Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.3535 Coordinate_Frame POS-TARG Pattern_Orient 45 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 8706( 5) - 07/17/00 10:12 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 70D TO 75D 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 PHOENIX-DIS WFPC2 IMAGE WFALL-F F555W 5398 CR-SPLIT=NO,ATD-GAIN=15 2 1200.00 K IX ------------------------------------------------------------------------------------------------------------------------------------ 12 PHOENIX-DIS WFPC2 IMAGE WFALL-F F555W 5398 CR-SPLIT=NO,ATD-GAIN=15 1 1200.00 PATTERN 1 12 K IX ------------------------------------------------------------------------------------------------------------------------------------ 8706( 5) - 07/17/00 10:12 - [ 6] Visit: 02 Visit Priority: Visit Requirements: SAME ORIENT AS 01 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 ------------------------------------------------------------------------------------------------------------------------------------ 14 PHOENIX-DIS WFPC2 IMAGE WFALL-F F814W 7921 CR-SPLIT=NO,ATD-GAIN=15 1 1200.00 PATTERN 1 14 K IX ------------------------------------------------------------------------------------------------------------------------------------ 15 PHOENIX-DIS WFPC2 IMAGE WFALL-F F814W 7921 CR-SPLIT=NO,ATD-GAIN=15 1 1200.00 PATTERN 1 15 K IX ------------------------------------------------------------------------------------------------------------------------------------ 8706( 5) - 07/17/00 10:12 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 110 PHOENIX-HAL WFPC2 IMAGE WFALL-F F555W 5398 ATD-GAIN=15 1 100.00 O IX ------------------------------------------------------------------------------------------------------------------------------------ 120 PHOENIX-HAL WFPC2 IMAGE WFALL-F F555W 5398 CR-SPLIT=NO,ATD-GAIN=15 2 1100.00 O IX ------------------------------------------------------------------------------------------------------------------------------------ 130 PHOENIX-HAL WFPC2 IMAGE WFALL-F F555W 5398 CR-SPLIT=NO,ATD-GAIN=15 1 1200.00 PATTERN 1 130 O IX ------------------------------------------------------------------------------------------------------------------------------------ 140 PHOENIX-HAL WFPC2 IMAGE WFALL-F F555W 5398 CR-SPLIT=NO,ATD-GAIN=15 1 1200.00 PATTERN 1 140 O IX ------------------------------------------------------------------------------------------------------------------------------------ 8706( 5) - 07/17/00 10:12 - [ 8] Visit: 04 Visit Priority: Visit Requirements: SAME ORIENT AS 03 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 ------------------------------------------------------------------------------------------------------------------------------------ 140 PHOENIX-HAL WFPC2 IMAGE WFALL-F F814W 7921 CR-SPLIT=NO,ATD-GAIN=15 1 100.00 O IX ------------------------------------------------------------------------------------------------------------------------------------ 150 PHOENIX-HAL WFPC2 IMAGE WFALL-F F814W 7921 CR-SPLIT=NO,ATD-GAIN=15 2 1100.00 O IX ------------------------------------------------------------------------------------------------------------------------------------ 160 PHOENIX-HAL WFPC2 IMAGE WFALL-F F814W 7921 CR-SPLIT=NO,ATD-GAIN=15 2 1200.00 O IX ------------------------------------------------------------------------------------------------------------------------------------ 170 PHOENIX-HAL WFPC2 IMAGE WFALL-F F814W 7921 CR-SPLIT=NO,ATD-GAIN=15 1 1200.00 PATTERN 1 170 O IX ------------------------------------------------------------------------------------------------------------------------------------ 180 PHOENIX-HAL WFPC2 IMAGE WFALL-F F814W 7921 CR-SPLIT=NO,ATD-GAIN=15 1 1200.00 PATTERN 1 180 O IX ------------------------------------------------------------------------------------------------------------------------------------ 8706( 5) - 07/17/00 10:12 - [ 9] Summary Form for Proposal 8706 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFALL-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 70D TO 75D PATTERN 1 12 SAME ORIENT AS 01 PATTERN 1 14 PATTERN 1 15 PATTERN 1 130 PATTERN 1 140 SAME ORIENT AS 03 PATTERN 1 170 PATTERN 1 180 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names PHOENIX-DISK PHOENIX-HALO ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 5398 7921 ------------------------------------------------------------------------------------------------------------------------------------