8141( 4) - 09/22/99 09:20 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8141 Version: 4 Check-in Date: 22-Feb-1999 14:21:07 1.Proposal Title: High Quality WFPC2 Photometry for 3 Intermediate age LMC Clusters with Multiple (?) Turnoffs ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: R. Rich University of California - Los Angeles CoI: Dr. Michael Shara Space Telesope Science Institute N CoI: Dr. S. Michael Fall Space Telesope Science Institute N CoI: Mr. David Zurek Space Telesope Science Institute N ------------------------------------------------------------------------------------ 5. Abstract In the course of analyzing photometry from a snapshot survey of Magellanic globular clusters, we discovered 3 clusters with apparent double turnoffs. If the fainter of the two possible turnoffs is the actual main sequence turnoff point, then the clusters would fall in the putative LMC age gap from 4 to 12 Gyr. However, our team has been reluctant to proceed with publication until better data could be obtained: we have never seen such peculiar turnoffs in any of the more than 40 Magellanic clusters we have reduced. The double turnoffs could be caused either by mergers, multiple bursts within a cluster, or a bimodal metallicity distribution. We can test other explanations, e.g. binary populations and convective overshoot. Given the very short original exposures, we are requesting 6 orbits to obtain deep, high quality photometry of these clusters in order to explain this phenomenon. ------------------------------------------------------------------------------------ 8141( 4) - 09/22/99 09:20 - [ 2] Observations Description ------------------------ Our original survey images were short (few hundred seconds) in F450W (B) and F555W (V) with the goal of discovering blue stragglers near the cluster cores. We are now seeking to get much better turnoff photometry and we propose to work in V and I. This also gives us an independent check on the reality of the doubled turnoffs. Our goal is to reach S/N > 100 at V=22.5 in order to reach below the vertical turnoff region. The WFPC2 exposure time calculator indicates that 2100 sec in F555W and about 2700 sec in F814W are needed. This amount of time is available in 2 orbits and will provide us data of the quality we need. Real Time Justification ----------------------- None Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: NO Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8141( 4) - 09/22/99 09:20 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC2121 EXT-CLUSTER, GLOBULAR RA=05H 48M 12.7S +/- 0.1S, DEC=- J2000 V = 22.0 CLUSTER 71D 28' 47" +/- 1.0" B-V = 0.5 8141( 4) - 09/22/99 09:20 - [ 4] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE 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 NGC2121 WFPC2 IMAGE PC1-FIX F814W DITHER-TYPE=BOX 1 400 S ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC2121 WFPC2 IMAGE PC1-FIX F336W 1 300 S EXPAND NO SPLIT MAX DUR 150.0% ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC2121 WFPC2 IMAGE PC1-FIX F555W DITHER-TYPE=BOX 1 400 S ------------------------------------------------------------------------------------------------------------------------------------ 40 NGC2121 WFPC2 IMAGE PC1-FIX F336W 1 300 S EXPAND MAX DUR 150.0% NO SPLIT ------------------------------------------------------------------------------------------------------------------------------------ 8141( 4) - 09/22/99 09:20 - [ 5] Summary Form for Proposal 8141 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters DITHER-TYPE=BOX ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE EXPAND NO SPLIT MAX DUR 150.0% EXPAND MAX DUR 150.0% NO SPLIT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F336W F555W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC2121 ------------------------------------------------------------------------------------------------------------------------------------