6625( 8) - 11/13/96 09:48 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6625 Version: 8 Check-in Date: 13-Nov-1996 09:44:08 1.Proposal Title: The second-parameter effect and the formation history of the Milky Way Galaxy ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle STELLAR POPULATIONS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: ROBERTO BUONANNO OBSERVATORY OF ROME CoI: Carlo Corsi Observatory of Rome N CoI: Gianni Marconi Observatory of Rome N CoI: Vitali Fabrizio Observatory of Rome N CoI: Giulia Stratta University of Rome N CoI: Ferraro Francesco Observatory of Bologna N CoI: Bellazzini Michele Observatory of Bologna N CoI: Francesco Paresce ESO N ------------------------------------------------------------------------------------ 6. Abstract We propose to obtain HST V,I observations of a sample of Galactic globular clusters (GC's) in order to establish an unbiased correlation between the morphology of the horizontal branch (HB) and the age of the cluster (for fixed metallicity, the first parameter). After Searle and Zinn (1978) and Lee, Demarque and Zinn (1994, LDZ), it is widely accepted that differences in color between the HB's of GC's with the same metallicity can be explained in terms of differences in age (the candidate second parameter). On the other hand, according to Buonanno (1993) and Fusi Pecci et al. (1993), the HB-morphology is determined (perhaps with comparable weight) either by the age and by the cluster central mass density (the candidate third parameter). The problem is of substance because GC's classified as coeval by LDZ on the basis of their HB-morphology are, according to Buonanno (1993), different in age by 2-3 Gyrs and vice-versa. If this scenario is confirmed, the use of the HB-morphology as a clock must be revised and, in turn, the description of galaxy evolution could be modified. ------------------------------------------------------------------------------------ Observations Description ------------------------ WFPC2 observations of the galactic globular clusters NGC5897, NGC6626, NGC2298, NGC6535, NGC6101, will be taken using 2 filters, i.e. F555W, F814W. In particular the PC1 will be pointing the cluster center for each of the 2 filters, while the three WFC mosaics will map adjacent fields in the same bands. We plan to measure as many stars as possible near the TO because the standard errors of the color difference TO-RGB is roughly proportional to n^- 1/2, where n is the number of stars measured near the TO. Therefore with sigma_V-I ~eq 0.03 (conservative estimate), and n ~eq 100 the color difference TO-RGB will be determined with a precision of about 0.003 magnitudes, corresponding to an age uncertainty of ~0.3 Gyr. The observational strategy is to optimize the degree of completeness (down to a fixed magnitude limit, even at the very cluster center) and in particular the photometric quality of the individual measures. Hence, exposure times for each filter have been computed (using WFPC2 exposure time calculator at www.stsci.edu ) to be adequate to reach S/N=50 at about 2 mag below the turnoff, i.e. V ~ 22, in the wide band filters (VI), and to be subdivided into sets of appropriate sub-exposures short enough to avoid destructive blooming from the brightest (V~13) giants. In fact, strong charge transfer from highly saturated bright objects would prevent the detection and measure of fainter stars, so decreasing strongly the degree of completeness specially in the very crowded central regions. The exposure times have been computed by adopting a gain of 14 electrons/DN and the appropriate E(B-V) for each cluster to estimate the total exposure time (to obtain the desired S/N). We have also computed the maximum lenght of each sub-exposure (to avoid destructive blooming from bright giant stars at ~eq 90000 electrons/central px.) Considered the requirement of high statistics, our observations will be obtained with the PC1 chip centered on the clusters, while the WFs chips will observe the adiacent regions. Two broadband filters * ~ 0.9 hours/filters = 2 orbits for clusters NGC 5897, NGC 2298 and NGC 6101; two broadband filters * ~ 1.3 hours/filters = 3 orbits for clusters NGC 6535 and NGC 6626 for a grand total of 12 orbits. Real Time Justification ----------------------- We already have ground-based observations for the bright end of the clusters sample. These observations will allow a direct calibration of the HST targets, and add photometry of the brighter parts of the CMD. In addition, we will submit an ESO proposal to observe uncrowded stars which will be found on the WFPC2 chips in order to ceck HST calibrations. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: , ------------------------------------------------------------------------------------ 6625( 8) - 11/13/96 09:48 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5897 STELLAR RA=15H 17M 25.0S +/- 1.0",DEC=- J2000 SURF-BKG(V) = 20.60+/-0.2 CLUSTER,GLOBULAR 21D 0' 37.5" +/- 0.5" V = 13.0+/-0.1 CLUSTER, V = 16.25+/-0.1 V = 20.00+/-0.1 TYPE=K0 TYPE=F0 E(B-V) = 0.09+/-0.02 Comments: Flux1=central surface brightness in mag/arcsec-2 for ACQ only. Flux2, 3 and 4 are : V-magnitude of RGB tip, V-magnitude of HB and V-magnitude of TO for exposure time calculation. Spectral types are referred to flux2 and 4. 2 NGC6626 STELLAR RA=18H 24M 32.9S +/- 1.0",DEC=- J2000 SURF-BKG(V) = 15.99+/-0.2 CLUSTER,GLOBULAR 24D 52' 12.0" +/- 0.5" V = 12.90+/-0.15 CLUSTER, V = 15.60+/-0.1 V = 19.4+/-0.15 E(B-V) = 0.37+/-0.05 TYPE=K0 TYPE=F0 Comments: Flux1=central surface brightness in mag/arcsec-2 for ACQ only. Flux2, 3 and 4 are : V-magnitude of RGB tip, V-magnitude of HB and V-magnitude of TO for exposure time calculation. Spectral types are referred to flux2 and 4. 3 NGC2298 STELLAR RA=06H 48M 59.2S +/- 1.0",DEC=- J2000 SURF-BKG(V) = 18.98+/-0.2 CLUSTER,GLOBULAR 36D 0' 19.0" +/- 0.5" V = 13.0+/-0.1 CLUSTER, V = 16.20+/-0.1 V = 20.00+/-0.15 E(B-V) = 0.15+/-0.03 TYPE=K0 TYPE=F0 Comments: Flux1=central surface brightness in mag/arcsec-2 for ACQ only. Flux2, 3 and 4 are : V-magnitude of RGB tip, V-magnitude of HB and V-magnitude of TO for exposure time calculation. Spectral types are referred to flux2 and 4. 4 NGC6535 STELLAR RA=18H 3M 50.7S +/- 1.00",DEC=- J2000 SURF-BKG(V) = 21.28+/-0.2 CLUSTER,GLOBULAR 00D 17' 49.0" +/- 0.5" V = 12.90+/-0.1 CLUSTER, V = 15.85+/-0.1 V = 19.60+/-0.1 E(B-V) = 0.33+/-0.05 TYPE=K0 TYPE=F0 Comments: Flux1=central surface brightness in mag/arcsec-2 for ACQ only. Flux2, 3 and 4 are : V-magnitude of RGB tip, V-magnitude of HB and V-magnitude of TO for exposure time calculation. Spectral types are referred to flux2 and 4. 6625( 8) - 11/13/96 09:48 - [ 2] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6101 STELLAR RA=16H 25M 48.6S +/- 1.0",DEC=- J2000 SURF-BKG(V) = 20.30+/-0.2 CLUSTER,GLOBULAR 72D 12' 6.0" +/- 0.5" V = 13.2+/-0.05 CLUSTER, V = 16.76+/-0.08 V = 20.3+/-0.1 E(B-V) = 0.04+/-0.03 TYPE=K0 TYPE=F0 Comments: Flux1=central surface brightness in mag/arcsec-2 for ACQ only. Flux2, 3 and 4 are : V-magnitude of RGB tip, V-magnitude of HB and V-magnitude of TO for exposure time calculation. Spectral types are referred to flux2 and 4. 6625( 8) - 11/13/96 09:48 - [ 3] Visit: 01 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC2298 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 2.60 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=3 Comments: 3 exposures of 3 sec each to avoid blooming from V=13 KO stars. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC2298 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 100 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=6 Comments: 3 + 3 exposures of 160 sec each to reach SNR 50 ~ 2 mag below turnoff stars. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC2298 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15,DITHER-TYPE=LINE, 1 2.60 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=2 Comments: 2 exposures of 3 sec each to avoid blooming from V=13 KO stars. ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC2298 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15,DITHER-TYPE=LINE, 1 160 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=4 Comments: 2 + 2 exposures of 200 sec each to reach SNR 50 ~ 2 mag below turnoff stars ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC2298 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15 1 260 S Comments: 1 exposure of 300 sec to reach SNR 40 ~ 2 mag below turnoff stars ------------------------------------------------------------------------------------------------------------------------------------ 6625( 8) - 11/13/96 09:48 - [ 4] Visit: 02 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5897 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 2.60 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=3 Comments: 3 exposures of 3 sec each to avoid blooming from V=13 KO stars. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC5897 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 100 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=6 Comments: 3 + 3 exposures of 140 sec each to reach SNR 50 ~ 2 mag below turnoff stars ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC5897 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15,DITHER-TYPE=LINE, 1 2.60 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=2 Comments: 2 exposures of 3 sec each to avoid blooming from V=13 KO stars. ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC5897 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15,DITHER-TYPE=LINE, 1 160 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=4 Comments: 2 + 2 exposures of 180 sec each to reach SNR 50 ~ 2 mag below turnoff stars ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC5897 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15 1 200 S Comments: 1 exposures of 230 sec to fill the orbit ------------------------------------------------------------------------------------------------------------------------------------ 6625( 8) - 11/13/96 09:48 - [ 5] Visit: 03 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6101 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 3 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=2 Comments: 2 exposures of 3 sec each to avoid blooming from V=13.2 KO stars. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6101 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 160 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=6 Comments: 3 + 3 exposures of 160 sec each to reach SNR 50 ~ 2 mag below turnoff stars ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6101 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15 1 160 S Comments: 1 exposures of 160 sec to fill the orbit. ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6101 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15,DITHER-TYPE=LINE, 1 3 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=3 Comments: 3 exposures of 3 sec each to avoid blooming from V=13.2 KO stars. ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6101 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15,DITHER-TYPE=LINE, 1 200 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=4 Comments: 2 + 2 exposures of 200 sec each to reach SNR 50 ~ 2 mag below turnoff stars ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6101 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15 1 350 S Comments: 1 exposure of 350 sec to reach SNR 40 ~ 2 mag below turnoff stars ------------------------------------------------------------------------------------------------------------------------------------ 6625( 8) - 11/13/96 09:48 - [ 6] Visit: 04 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6535 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15,DITHER-TYPE=LINE, 1 160 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=6 Comments: 3 + 3 exposures of 200 sec each to reach SNR 50 ~ 2 mag below turnoff stars ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6535 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15,DITHER-TYPE=LINE, 1 2.60 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=3 Comments: 3 exposures of 3 sec each to avoid blooming from V=12.9 KO stars. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6535 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15 3 180 S Comments: 3 exposures of 200 sec each to reach SNR 50 ~ 2 mag below turnoff stars ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6535 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 2.60 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=3 Comments: 3 exposures of 3 sec each to avoid blooming from V=12.9 KO stars. ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6535 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 140 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=4 Comments: 4 exposures of 160 sec each to reach SNR 50 ~ 2 mag below turnoff stars ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6535 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 140 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=4 Comments: 4 exposures of 160 sec each to reach SNR 50 ~ 2 mag below turnoff stars ------------------------------------------------------------------------------------------------------------------------------------ 6625( 8) - 11/13/96 09:48 - [ 7] Visit: 05 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6626 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15,DITHER-TYPE=LINE, 1 160 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=6 Comments: 3 + 3 exposures of 200 sec each to reach SNR 50 ~ 2 mag below turnoff stars ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6626 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15,DITHER-TYPE=LINE, 1 2.60 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=3 Comments: 3 exposures of 3 sec each to avoid blooming from V=12.9 KO stars. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6626 WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=15 3 180 S Comments: 3 exposures of 200 sec each to reach SNR 50 ~ 2 mag below turnoff star ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6626 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 2.60 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=3 Comments: 3 exposures of 3 sec each to avoid blooming from V=12.9 KO stars. ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6626 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 140 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=4 Comments: 4 exposures of 160 sec each to reach SNR 50 ~ 2 mag below turnoff star ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6626 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 140 S DITHER-LINE-SPACING=0.1767, DITHER-LINE-STEPS=4 Comments: 4 exposures of 160 sec each to reach SNR 50 ~ 2 mag below turnoff star ------------------------------------------------------------------------------------------------------------------------------------ 6625( 8) - 11/13/96 09:48 - [ 8] Summary Form for Proposal 6625 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=15 DITHER-TYPE=LINE DITHER-LINE-SPACING=0.1767 DITHER-LINE-STEPS=3 DITHER-LINE-STEPS=6 DITHER-LINE-STEPS=2 DITHER-LINE-STEPS=4 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC2298 NGC5897 NGC6101 NGC6535 NGC6626 ------------------------------------------------------------------------------------------------------------------------------------