! Proposal 6734, submission 1 ! PI: Annette Ferguson ! Received Fri Feb 9 12:40:27 EST 1996 ! From: ferguson@skysrv.Pha.Jhu.EDU ! +====================+ ! | PED OUTPUT PRODUCT | ! +====================+ ! ! /home/haggis/ferguson/tex/proposals/hst/1995/phase2/6734.prop ! Generated by PREPROCESSOR, version 6.0e ! Date: Fri Feb 9 12:05:04 EST 1996 Proposal_Information Title: REVEALING THE STELLAR POPULATION(S) OF ANDROMEDA IV Proposal_Category: GO Scientific_Category: STELLAR POPULATIONS Cycle: 6 Investigators PI_Name: Annette Ferguson PI_Institution: Johns Hopkins University CoI_Name: Rosemary Wyse CoI_Institution: Johns Hopkins University Contact: CoI_Name: Jay Gallagher CoI_Institution: University of Wisconsin--Madison Contact: 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. Questions Observing_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: Fixed_Targets Target_Number: 1 Target_Name: ANDROMEDA-IV Alternate_Names: Description: EXT-CLUSTER,OPEN CLUSTER, Position: RA=00H 42M 32.44S +/- 0.5",DEC=40D 34' 16.46" +/- 1.0" !PLATE-ID=06PI Equinox: J2000.0 RV_or_Z: V = -373. RA_PM: Dec_PM: Epoch: Annual_Parallax: Flux: SURF(V) = 25.0+/-0.5 E(B-V) = 0.31+/-0.2 Comments: Solar_System_Targets Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: ORIENT 140D TO 160D On_Hold_Comments: Visit_Comments: Exposure_Number: 10 Target_Name: ANDROMEDA-IV Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F555W Wavelength: Optional_Parameters: ATD-GAIN=7,CR-SPLIT=NO Number_of_Iterations: 2 Time_Per_Exposure: 1300S Special_Requirements: POS TARG 27.60,14.04 Comments: Exposure_Number: 20 Target_Name: ANDROMEDA-IV Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F555W Wavelength: Optional_Parameters: DITHER-LINE-SPACING=0.2828,DITHER-TYPE=LINE,ATD-GAIN=7,CR-SPLIT=no Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: SAME POS AS 10 Comments: Exposure_Number: 30 Target_Name: ANDROMEDA-IV Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F555W Wavelength: Optional_Parameters: ATD-GAIN=7,CR-SPLIT=no Number_of_Iterations: 1 Time_Per_Exposure: 1000S Special_Requirements: SAME POS AS 10 Comments: Exposure_Number: 50 Target_Name: ANDROMEDA-IV Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F814W Wavelength: Optional_Parameters: ATD-GAIN=7,CR-SPLIT=0.5 Number_of_Iterations: 1 Time_Per_Exposure: 1300S Special_Requirements: SAME POS AS 10 Comments: Exposure_Number: 60 Target_Name: ANDROMEDA-IV Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F814W Wavelength: Optional_Parameters: ATD-GAIN=7,CR-SPLIT=no,DITHER-TYPE=LINE,DITHER-LINE-SPACING=0.2828 Number_of_Iterations: 1 Time_Per_Exposure: 1200S Special_Requirements: SAME POS AS 10 Comments: Exposure_Number: 70 Target_Name: ANDROMEDA-IV Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F814W Wavelength: Optional_Parameters: ATD-GAIN=7,CR-SPLIT=no Number_of_Iterations: 2 Time_Per_Exposure: 800S Special_Requirements: SAME POS AS 10 Comments: Exposure_Number: 90 Target_Name: ANDROMEDA-IV Config: WFPC2 Opmode: IMAGE Aperture: WF3-FIX Sp_Element: F814W Wavelength: Optional_Parameters: ATD-GAIN=7,CR-SPLIT=no Number_of_Iterations: 1 Time_Per_Exposure: 900S Special_Requirements: SAME POS AS 10 Comments: Data_Distribution ! 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