6660( 5) - 10/28/96 10:03 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6660 Version: 5 Check-in Date: 28-Oct-1996 10:00:32 1.Proposal Title: White Dwarf Distance and Precision Age for Globular Clusters ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle COOL STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: ANAGELA BRAGAGLIA OSSERVATORIO ASTRONOMICO DI BOLOGNA CoI: Francesco Ferraro Osservatorio di Bologna N CoI: Alvio Renzini European Southern Observatory N CoI: Sergio Ortolani Osservatorio di Padova N CoI: Eugenio Carretta Osservatorio di Bologna N CoI: Gianni Marconi Osservatorio di Roma N CoI: Jay B. Holberg Lunar and Planetary Laboratory N CoI: Ralph Bohlin Space Telescope Science Institute N CoI: R. Michael Rich Columbia University N CoI: Roberto Gilmozzi ESO N CoI: Francois Wesemael Universite de Montreal N ------------------------------------------------------------------------------------ 6. Abstract This proposal is the natural complement of our Cycle 4 and 5 programs aimed at using the White Dwarf cooling sequence for the calibration of the globular cluster distance scale, the determination of accurate distances being a critical prerequisite for the estimate of reliable cluster ages. In Cycle 4 we obtained data on NGC6752, while in Cycle 5 we got images of 47Tuc. These two clusters will test whether there really exists a measurable age difference between the metal poor and the metal rich clusters, as has been inferred from some horizontal branch luminosity - metallicity calibration. While reducing our Cycle 4 data we have realized that a few short exposures would greatly help to accurately subtract the wings of the heavily saturated images in the field of view, hence to improve the accuracy of the faint star fotometry in the crowded field of the cluster. We therefore apply for one orbit for each of the two clusters in order to get shallow images of our Cycle 4 and 5 fields. The observed cooling sequences for the clusters (for DA and non-DA WDs) will then be fit to the corresponding FCSs to determine the cluster distance moduli. Moreover, directly fitting to each other the WD cooling sequences of the two clusters will provide very accurate relative distances (hence ages). ------------------------------------------------------------------------------------ Observations Description ------------------------ We need to observe the 2 clusters in exactly the SAME positions given for the Cycle 4 (i.e. 125" from the center for NGC6752) and Cycle 5 (i.e. 300" from the center for 47Tuc) and with the SAME position angles. We wish to measure with high photometric precision the Turn Off region (at a V mag level of ~ 17.5 for both clusters). This means to be able to measure stars about 2 mag above/belove the TO, avoiding saturation and too low S/N. For this program, we are using the U, B, V, I filters (BVI for NGC6752 and UVI for NGC104). For B, V, I we require at least 3 exposure each, to remove cosmics and increase the photometric accuracy. The U filter exposures have a lower priority, and we will take only the ones fitting into the sigle orbit. The exposure times have been computed from the general formula in the WFPC2 Handbook, and Biretta (March 9, 1995) with a change related to the read-out-noise. The following table illustrates the computed exposure times and S/N for both clusters, since their distance moduli and E(B-V) are very similar (respectively: 13.1, 0.03 for NGC6752, and 13.3, 0.04 for 47Tuc). -------------------------------------- band exptime S/N S/N S/N (sec) (V=14.5) (TO) (V=21) -------------------------------------- V 20 - 70 15 I 20 - 90 15 B 300 - 90 15 U 120 55 25 - ------------------------------ -------- Real Time Justification ----------------------- No special scheduling required. The two clusters could be observed in CVZ, but we do not strictly require it. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: , ------------------------------------------------------------------------------------ 6660( 5) - 10/28/96 10:03 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6752-TO STELLAR CLUSTER, RA=19H 6M 36.6S +/- 1",DEC=-60D B1950 V = 17.5 GLOBULAR CLUSTER 6' 10.5" +/- 1",REGION B-V = 0.4 E(B-V) = 0.04 Comments: Flux of Turn Off from Main Sequence 2 NGC104-TO STELLAR RA=00H 22M 40.0S +/- 0.01S,DEC=- J2000 V = 17.5 CLUSTER,GLOBULAR 72D 4' 0.0" +/- 0.1",REGION B-V = 0.4 CLUSTER, E(B-V) = 0.04 Comments: Flux of Turn Off from Main Sequence 6660( 5) - 10/28/96 10:03 - [ 2] Visit: 01 Visit Requirements: ORIENT 259D TO 262D On Hold Comments: Additional Comments: SAME ORIENT AS EXPOSURES IN ID 5439 (PA 80.5, ORIENT 260.5) Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6752-TO WFPC2 IMAGE WFALL F555W CLOCKS=YES,ATD-GAIN=15 2 120 S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6752-TO WFPC2 IMAGE WFALL F555W CLOCKS=YES,ATD-GAIN=15 1 20 S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6752-TO WFPC2 IMAGE WFALL F814W CLOCKS=YES,ATD-GAIN=15 2 120 S ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6752-TO WFPC2 IMAGE WFALL F814W CLOCKS=YES,ATD-GAIN=15 1 20 S ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6752-TO WFPC2 IMAGE WFALL F439W CLOCKS=YES,ATD-GAIN=15, 1 1100 S CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6752-TO WFPC2 IMAGE WFALL F439W CLOCKS=YES,ATD-GAIN=15 1 230 S ------------------------------------------------------------------------------------------------------------------------------------ 6660( 5) - 10/28/96 10:03 - [ 3] Visit: 02 Visit Requirements: ORIENT 22.2D TO 25.2D On Hold Comments: Additional Comments: SAME ORIENT AS EXPOSURES IN ID 6114 (PA 203.7, ORIENT 23.7) Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC104-TO WFPC2 IMAGE WFALL-F F555W CLOCKS=YES,ATD-GAIN=15 2 120 S IX ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC104-TO WFPC2 IMAGE WFALL-F F555W CLOCKS=YES,ATD-GAIN=15 2 20 S IX ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC104-TO WFPC2 IMAGE WFALL-F F814W CLOCKS=YES,ATD-GAIN=15, 2 120 S IX CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC104-TO WFPC2 IMAGE WFALL-F F814W CLOCKS=YES,ATD-GAIN=15 2 20 S IX ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC104-TO WFPC2 IMAGE WFALL-F F336W CLOCKS=YES,ATD-GAIN=15, 2 600 S IX CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 6660( 5) - 10/28/96 10:03 - [ 4] Summary Form for Proposal 6660 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CLOCKS=YES ATD-GAIN=15 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COOL STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 259D TO 262D ORIENT 22.2D TO 25.2D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W F439W F336W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6752-TO NGC104-TO ------------------------------------------------------------------------------------------------------------------------------------