6561( 3) - 02/23/96 11:29 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6561 Version: 3 Check-in Date: 23-Feb-1996 11:20:30 1.Proposal Title: Ages of Extreme-metallicity Inner Galaxy Globular Clusters ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle STELLAR POPULATIONS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Laura Fullton Space Telescope Science Institute CoI: Bruce Carney University of North Carolina N CoI: John Laird Bowling Green State University N CoI: Suchitra Balachandran National Air and Space Museum N CoI: Peter Stetson Dominion Astrophysical Observatory N ------------------------------------------------------------------------------------ 6. Abstract We will observe the most metal-poor globular cluster within 3 kpc of the Galactic Center (NGC 6287, Fe/H = -2.05) with WFPC2 to obtain main-sequence photometry suitable for deriving its age. Because of its extreme nature, this object will provide information that cannot be inferred from previous HST globular cluster studies. A comparison of the age of NGC 6287 with the ages of low-metallicity clusters at larger Galactocentric distances will reveal if clusters in the higher density environment near the Galactic Center formed before their outer halo counterparts. We are pursuing ground-based optical spectroscopy to measure this cluster's Fe/H and alpha/Fe abundances precisely, which will also provide complementary chronological information. Adequate photometric observations of NGC 6287 cannot be obtained from the ground, although it is within spectroscopic reach. ------------------------------------------------------------------------------------ 6561( 3) - 02/23/96 11:29 - [ 2] Observations Description ------------------------ We propose to observe NGC 6287 with WFPC2 during Cycle 6 to construct a V(F555W), I(F814W) color-magnitude diagram. We must attain photometric precision of 1% at the cluster's main-sequence turnoff (MSTO) to derive an age to a precision of 1 Gyr (or better), and formation timescales of 1 Gyr or less are astrophysically relevant. The horizontal branch of NGC 6287 is near V ~ 17.5 (Stetson & West, 1994, PASP, 106, 726), and the cluster's MSTO should therefore be near V ~ 21 mag. E(B-V) = 0.55 mag. We can attain 0.01 mag precision one magnitude below the MSTO with exposure times of 1000(F555W)/600(F814W) seconds. Several shorter exposures will also be taken to delinate the cluster's horizontal and red giant branches. Our detailed exposure list is as follows: F555W: 2x5 sec, 3x50 sec, 3x1000 sec F814W: 2x2.3 sec, 3x35 sec, 3x600 sec As have previous investigators, we wish to obtain several dithered images with the given exposure times to help overcome problems associated with undersampling of the point-spread function and to enable recovery from cosmic rays and bad pixels. This can be done within 3 HST orbits. We also have enough time to take a few short F439W exposures to provide three- color photometry of stars above the level of the HB to help map out the reddening variations across the FOV observed by Stetson & West (op. cit.). Two such exposures are possible in the allotted time: F439W: 1x60 sec, 1x230 sec Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6561( 3) - 02/23/96 11:29 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6287 STELLAR CLUSTER, RA=17H 05M 09.42S +/- 0.03S, 2000 V=-208 V = 24 GLOBULAR CLUSTER DEC=-22D 42' 29.6" +/- 0.5", B-V = 1.15 PLATE-ID=06PP Comments: THE TARGET FLUX LEVEL REFERS TO THE FAINT MAIN SEQUENCE STARS IN THE CLUSTER. 6561( 3) - 02/23/96 11:29 - [ 4] Visit: 01 Visit Requirements: ORIENT 270D TO 360D On Hold Comments: Additional Comments: POSITION ANGLE OF U3 AXIS SHOULD BE 45 DEGREES WEST OF NORTH, WITH RANGE +/ - 45D. THE OPTIMAL ORIENT FOR THIS TARGET IS 315D. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC6287 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 2 5S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 12 NGC6287 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 35S SAME POS AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 13 NGC6287 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 50S SAME POS AS 11 ------------------------------------------------------------------------------------------------------------------------------------ 14 NGC6287 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 600S SAME POS AS 11 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 15 NGC6287 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 1000S SAME POS AS 11 END ORBIT; ------------------------------------------------------------------------------------------------------------------------------------ 21 NGC6287 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 2 2.3S POS TARG 0.0, 0.15 ------------------------------------------------------------------------------------------------------------------------------------ 22 NGC6287 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 35S SAME POS AS 21 ------------------------------------------------------------------------------------------------------------------------------------ 23 NGC6287 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 50S SAME POS AS 21 ------------------------------------------------------------------------------------------------------------------------------------ 24 NGC6287 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO 1 60S SAME POS AS 21 ------------------------------------------------------------------------------------------------------------------------------------ 25 NGC6287 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 600S SAME POS AS 21 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 26 NGC6287 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 1000S SAME POS AS 21 END ORBIT; ------------------------------------------------------------------------------------------------------------------------------------ 31 NGC6287 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 35S POS TARG 0.15, 0.15 ------------------------------------------------------------------------------------------------------------------------------------ 32 NGC6287 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 50S SAME POS AS 31 ------------------------------------------------------------------------------------------------------------------------------------ 33 NGC6287 WFPC2 IMAGE PC1-FIX F439W CR-SPLIT=NO 1 230S SAME POS AS 31 ------------------------------------------------------------------------------------------------------------------------------------ 34 NGC6287 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 600S SAME POS AS 31 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 35 NGC6287 WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=NO 1 1000S SAME POS AS 31 END ORBIT; ------------------------------------------------------------------------------------------------------------------------------------ 6561( 3) - 02/23/96 11:29 - [ 5] Summary Form for Proposal 6561 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 270D TO 360D POS TARG 0.0, 0.0 SAME POS AS 11 SAME POS AS 11 EXPAND SAME POS AS 11 END ORBIT; POS TARG 0.0, 0.15 SAME POS AS 21 SAME POS AS 21 EXPAND SAME POS AS 21 END ORBIT; POS TARG 0.15, 0.15 SAME POS AS 31 SAME POS AS 31 EXPAND SAME POS AS 31 END ORBIT; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W F439W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6287 ------------------------------------------------------------------------------------------------------------------------------------