6106( 0) - 07/18/95 20:03 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6106 Version: ********** Check-in Date: ********** 1.Proposal Title: The Formation of the Galaxy: Ages for Globular Clusters in the Remote Halo ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Stellar Populations GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: James E. Hesser Dominion Astrophysical Observatory CoI: Peter B. Stetson Dominion Astrophysical Observatory N CoI: Don A. VandenBerg University of Victoria N CoI: Sidney van den Bergh Dominion Astrophysical Observatory N CoI: Roger A. Bell University of Maryland N CoI: Michael Bolte University of California at Santa Cruz N CoI: Howard E. Bond Space Telescope Science Institute N CoI: Gregory G. Fahlman University of British Columbia N CoI: William E. Harris McMaster University N CoI: Robert D. McClure Dominion Astrophysical Observatory N CoI: Harvey B. Richer University of British Columbia N ------------------------------------------------------------------------------------ 6. Abstract We propose HST imaging observations that will allow us to measure the age of the globular cluster Eridanus, located in the distant halo of the Milky Way. This object is one of the five known globular clusters with Galactocentric distances larger than 75 kpc. We are already observing three others (NGC 2419, Pal 3, and Pal 4) during Cycle 4. The Cycle 5 observations of Eridanus will help complete our program aimed at mapping the ages of far-halo clusters relative to nearby globulars (R ~ 10 kpc) with a precision of 1 Gyr or better. This age comparison is an essential component of reconstructing early Galactic formation history, and is complementary to ongoing HST programs being carried out by other groups to measure ages of globular clusters in the Galactic bulge. ------------------------------------------------------------------------------------ 6106( 0) - 07/18/95 20:03 - [ 2] Observations Description ------------------------ WFPC2 exposures will be taken in the standard V (F555W) and I (F814W) bandpasses, on the distant-halo globular cluster Eridanus. 3 short exposures (3 x 180 sec) and 6 long exposures (3 x 1200 sec, 3 x 1100 sec) in V will be taken, along with 3 short (3 x 230 sec) and 8 long (4 x 1200 sec, 4 1100 sec) in I. Sub-pixel shifts will be used between each long exposure for cosmic-ray removal. Two very bright stars flanking the cluster imply that a fairly narrow range of camera orientations is required. We specify a nominal orientation angle for WFPC2 of 315 +/- 20 degrees (see Visit_Comments). Please note that this nominal angle may also be shifted 90 deg either clockwise or counterclockwise, i.e. to values of 45 +/- 20 degrees, or 225 +/- 20 degrees. In each case, the pointing aperture (WF2, WF3, or WF4) is chosen so that the center of the target cluster will be located in the southeast corner of the WFPC2 array. This range of orientations is listed to increase scheduling flexibility as much as possible. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: Howard Bond (CoI)*Space Telescope Science Institute*ext. 4718*bond@stsci.edu Ship Via: Howard Bond wil Email: , ------------------------------------------------------------------------------------ 6106( 0) - 07/18/95 20:03 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ERIDANUS STELLAR CLUSTER, RA=4H 24M 44.4S +/- 1", DEC=-21D J2000 V = -24 V = 27.5 GLOBULAR CLUSTER 11' 15" +/- 1", PLATE-ID=04LR B-V = 0.6 Comments: THE TARGET FLUX LEVEL REFERS TO THE FAINT MAIN SEQUENCE STARS IN THE CLUSTER. 6106( 0) - 07/18/95 20:03 - [ 4] Visit: 01 Visit Requirements: ORIENT 295D TO 335D On Hold Comments: Additional Comments: POSITION ANGLE OF U3 AXIS SHOULD BE 45 DEGREES WEST OF NORTH, WITH RANGE +/ - 20D. A NOMINAL ORIENTATION EITHER +90D OR -90D FROM THE GIVEN VALUE IS ALSO ACCEPTABLE. IF +90D DIFFERENT, THEN WE REQUIRE ORIENT 35D TO 65D AND APERTURE = WF2-FIX FOR ALL EXPOSURES. IF -90D DIFFERENT, THEN WE REQUIRE ORIENT 205D TO 245D AND APERTURE = WF4-FIX FOR ALL EXPOSURES. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 ERIDANUS WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 3 180S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 12 ERIDANUS WFPC2 IMAGE WF3-FIX F814W CR-SPLIT=NO 3 230S SAME POS AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 21 ERIDANUS WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 1200S SAME POS AS 11 Comments: EXPOSURES 21-26 ARE A 6-STEP SEQUENCE WITH 1.5-PIXEL (WF) STEPS IN A HEXAGONAL PATTERN ------------------------------------------------------------------------------------------------------------------------------------ 22 ERIDANUS WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 1100S POS TARG 0.15, 0.15 END ORBIT; EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 23 ERIDANUS WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 1200S POS TARG 0.15, 0.30 ------------------------------------------------------------------------------------------------------------------------------------ 24 ERIDANUS WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 1100S POS TARG 0.0, 0.45 END ORBIT; EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 25 ERIDANUS WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 1200S POS TARG -0.15, 0.30 ------------------------------------------------------------------------------------------------------------------------------------ 26 ERIDANUS WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 1100S POS TARG -0.15, 0.15 END ORBIT; EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 31 ERIDANUS WFPC2 IMAGE WF3-FIX F814W CR-SPLIT=NO 1 1200S SAME POS AS 11 Comments: EXPOSURES 31-38 ARE AN 8-STEP SEQUENCE WITH 1.5-PIXEL SHIFTS IN AN OCTAGONAL PATTERN ------------------------------------------------------------------------------------------------------------------------------------ 32 ERIDANUS WFPC2 IMAGE WF3-FIX F814W CR-SPLIT=NO 1 1100S POS TARG 0.15, 0.0 END ORBIT; EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 33 ERIDANUS WFPC2 IMAGE WF3-FIX F814W CR-SPLIT=NO 1 1200S POS TARG 0.30, 0.15 ------------------------------------------------------------------------------------------------------------------------------------ 34 ERIDANUS WFPC2 IMAGE WF3-FIX F814W CR-SPLIT=NO 1 1100S POS TARG 0.30, 0.30 END ORBIT; EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 35 ERIDANUS WFPC2 IMAGE WF3-FIX F814W CR-SPLIT=NO 1 1200S POS TARG 0.15, 0.45 ------------------------------------------------------------------------------------------------------------------------------------ 36 ERIDANUS WFPC2 IMAGE WF3-FIX F814W CR-SPLIT=NO 1 1100S POS TARG 0.0, 0.45 END ORBIT; EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 37 ERIDANUS WFPC2 IMAGE WF3-FIX F814W CR-SPLIT=NO 1 1200S POS TARG -0.15, 0.30 ------------------------------------------------------------------------------------------------------------------------------------ 38 ERIDANUS WFPC2 IMAGE WF3-FIX F814W CR-SPLIT=NO 1 1100S POS TARG -0.15, 0.15 END ORBIT; EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 6106( 0) - 07/18/95 20:03 - [ 5] Summary Form for Proposal 6106 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Stellar Populations ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 295D TO 335D POS TARG 0.0, 0.0 SAME POS AS 11 POS TARG 0.15, 0.15 END ORBIT; EXPAND POS TARG 0.15, 0.30 POS TARG 0.0, 0.45 END ORBIT; EXPAND POS TARG -0.15, 0.30 POS TARG -0.15, 0.15 END ORBIT; EXPAND POS TARG 0.15, 0.0 END ORBIT; EXPAND POS TARG 0.30, 0.15 POS TARG 0.30, 0.30 END ORBIT; EXPAND POS TARG 0.15, 0.45 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ERIDANUS ------------------------------------------------------------------------------------------------------------------------------------