6734( 5) - 02/19/96 16:26 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6734 Version: 5 Check-in Date: 19-Feb-1996 11:28:57 1.Proposal Title: REVEALING THE STELLAR POPULATION(S) OF ANDROMEDA IV ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle STELLAR POPULATIONS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Annette Ferguson Johns Hopkins University CoI: Rosemary Wyse Johns Hopkins University N CoI: Jay Gallagher University of Wisconsin--Madison N ------------------------------------------------------------------------------------ 6. Abstract Andromeda IV is an enigmatic object, first identified by van den Bergh (1972), during his photographic survey for dwarf spheroidal galaxy companions to M31, as either an `old star cloud' in the outer disk of M31, or possibly a background dwarf galaxy. We here propose deep WFPC2 V and I imaging of And IV to V>~ 27, which will resolve stars down to M_V ~ +3, and determine main sequence turnoffs of <~ 5 * 10^9yr. The mean color of the red giant branch will provide a mean metallicity estimate, while the width constrains the dispersion in metallicity. The AGB and BHB stars provide further age and metallicity constraints. A reliable distance is necessary to establish the location of And IV in the M31 disk; this will be obtained from the I--band magnitude of the tip of the RGB. Ground-based observations are hampered by the proximity of a relatively bright star and by the combination of faintness and crowding in And IV. The extant ground-based CCD photometry for this object, to V ~ 23 (Jones 1993), have been interpreted as representing a young population with a narrow range of ages, an `unusually large' open cluster. And IV may be large enough that it could represent the transition stage between a single- age star cluster, and a self-enriched, many-generation stellar system. If indeed in the disk of M31, And IV lies beyond 4 disk scalelengths, a typical `edge' of optical disks. It thus could provide a unique example of a large star cluster in the outer regions of a disk, where there is little on-going or past star formation. ------------------------------------------------------------------------------------ 6734( 5) - 02/19/96 16:26 - [ 2] Observations Description ------------------------ We estimate we require 2.5 orbits per V and I filter. From experience with WFPC2 on-orbit we expect to reach stars with V ~ 27.5 with S/N ratio of ~12. This calculation is for an idealized case--with scattered light and digitization noise, we can predict that our limit for S/N>10 photometry will be in the V~ 27 range with gain setting of 7. Similarly, our F814W ``I" S/N 10 limit is approximately I=25.5 for a moderately red star. These should allow study of the AGB, RGB and main sequence stars down to M_V ~ +3. We will dither by a few pixels in integral pixel shift mode, between same filter exposures, to optimise S/N on faint stars. There is a bright star close to the center of our target. We estimated the star's brightness from the size of its image on the POSS, finding B ~ 10.5. It lies ~ 0.5arcmin from the center of And IV, so that the roll angle would preferably be chosen to place this star outside of the PC FOV, while keeping the center of And IV on the PC. Real Time Justification ----------------------- None Gallagher has access to the WIYN telescope, and we will attempt B and U band imaging of this object. However, as noted earlier, the bright star presents a problem for ground- based observations. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6734( 5) - 02/19/96 16:26 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ANDROMEDA-IV EXT-CLUSTER,OPEN RA=00H 42M 32.44S +/- J2000.0 V = - SURF(V) = 25.0+/-0.5 CLUSTER, 0.5",DEC=40D 34' 16.46" +/- 1.0" 373. E(B-V) = 0.31+/-0.2 6734( 5) - 02/19/96 16:26 - [ 4] Visit: 01 Visit Requirements: ORIENT 140D TO 160D 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 ANDROMEDA- WFPC2 IMAGE WF3-FIX F555W ATD-GAIN=7,CR- 2 1300S POS TARG 27.60,14.04 IV SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 20 ANDROMEDA- WFPC2 IMAGE WF3-FIX F555W DITHER-LINE- 1 1200S SAME POS AS 10 IV SPACING=0.2828, DITHER- TYPE=LINE,ATD- GAIN=7,CR- Comments: SPLIT=no ------------------------------------------------------------------------------------------------------------------------------------ 30 ANDROMEDA- WFPC2 IMAGE WF3-FIX F555W ATD-GAIN=7,CR- 1 1000S SAME POS AS 10 IV SPLIT=no ------------------------------------------------------------------------------------------------------------------------------------ 50 ANDROMEDA- WFPC2 IMAGE WF3-FIX F814W ATD-GAIN=7,CR- 1 1300S SAME POS AS 10 IV SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 60 ANDROMEDA- WFPC2 IMAGE WF3-FIX F814W ATD-GAIN=7,CR- 1 1200S SAME POS AS 10 IV SPLIT=no,DITHER - TYPE=LINE,DITHE R-LINE- Comments: SPACING=0.2828 ------------------------------------------------------------------------------------------------------------------------------------ 70 ANDROMEDA- WFPC2 IMAGE WF3-FIX F814W ATD-GAIN=7,CR- 2 800S SAME POS AS 10 IV SPLIT=no ------------------------------------------------------------------------------------------------------------------------------------ 90 ANDROMEDA- WFPC2 IMAGE WF3-FIX F814W ATD-GAIN=7,CR- 1 900S SAME POS AS 10 IV SPLIT=no ------------------------------------------------------------------------------------------------------------------------------------ 6734( 5) - 02/19/96 16:26 - [ 5] Summary Form for Proposal 6734 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=7 CR-SPLIT=NO DITHER-TYPE=LINE CR-SPLIT=0.5 DITHER-LINE-SPACING=0.2828 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 140D TO 160D POS TARG 27.60,14.04 SAME POS AS 10 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ANDROMEDA-IV ------------------------------------------------------------------------------------------------------------------------------------