6813( 4) - 05/07/96 15:28 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6813 Version: 4 Check-in Date: 07-May-1996 15:25:31 1.Proposal Title: The Oldest Star Clusters of Local Group Irregular Galaxies ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle STELLAR POPULATIONS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Paul Hodge University of Washington CoI: Mario Mateo University of Michigan N CoI: Toby Smith University of Washington N ------------------------------------------------------------------------------------ 6. Abstract Globular clusters of spiral and elliptical galaxies are well- studied and they have provided much information on the early histories of these types of galaxies. For irregular galaxies, however, very little is known about the globular clusters and other old clusters. The only irregulars for which much globular cluster research has been carried out are the Magellanic Clouds, and they are probably anomalous because of the interactions of the Clouds with the Milky Way Galaxy (MWG). We are proposing to investigate globular and other old clusters in two Local Group irregular galaxies: WLM and NGC 6822. The WLM globular appears from the limited available photometry to be a normal, massive old globular, possibly similar to the classical globulars of the MWG. The "Hubble clusters" of NGC 6822, which were identified as possible clusters by Hubble, on the other hand, are of lower luminosity, though their colors indicate that they are old. Study of these rare objects will be enlightening about the early history of irregular galaxies. ------------------------------------------------------------------------------------ 6813( 4) - 05/07/96 15:28 - [ 2] Observations Description ------------------------ We propose to obtain color-magnitude diagrams of the six clusters in the V and I pass-bands in order to determine their ages and approximate abundances. Using the filters specified above, the data can be converted through well-known transformations to the Johnson-Cousins V and I, which photometric system has become a common one for the study of old stellar systems. The exposures will be divided into shorter sections to facilitate identifying cosmic rays. For the clusters in NGC 6822 and IC 1613, which have nearly the same apparent distance moduli of 24.5, we will need to reach V magnitudes at least 1.5 magnitudes below the horizontal branch or red giant clump in order to discern the CMD characteristics. To have a S/N of 10 at V = 26, exposures will need to be 90 minutes per filter (the stars are sufficiently red that the necessary exposures are nearly the same in spite of the decreased sensitivity at the position of the F814W filter). Thus we will need three orbits per cluster. For WLM, the apparent distance modulus is 0.4 magnitudes fainter, and thus to achieve the same accuracy, we will need four orbits. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6813( 4) - 05/07/96 15:28 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 WLM-STARCLUS EXT-CLUSTER,GLOBULAR RA=00H 01M 49.52S +/- 0.05S, J2000 V = 16.06 CLUSTER DEC=-15D 27' 31.1" +/- 0.1", B-V = 0.58 PLATE-ID=024M 2 NGC6822- EXT-CLUSTER,GLOBULAR RA=19H 44M 52.18S +/- 0.05S, J2000 V = 17.04 STARCLUS-HIV CLUSTER DEC=-14D 51' 58.0" +/- 0.1", B-V = 0.78 PLATE-ID=00CN 3 NGC6822- EXT-CLUSTER,GLOBULAR RA=19H 44M 53.67S +/- 0.05S, J2000 V = 16.11 STARCLUS-HVI CLUSTER DEC=-14D 49' 11.8" +/- 0.1", B-V = 0.54 PLATE-ID=00CN 4 NGC6822- EXT-CLUSTER,GLOBULAR RA=19H 44M 55.85S +/- 0.05S, J2000 V = 16.28 STARCLUS- CLUSTER DEC=-14D 48' 55.8" +/- 0.1", B-V = 0.57 HVII PLATE-ID=00CN 5 NGC6822- EXT-CLUSTER,GLOBULAR RA=19H 44M 58.33S +/- 0.05S, J2000 V = 17.37 STARCLUS- CLUSTER DEC=-14D 43' 13.8" +/- 0.1", B-V = 0.75 HVIII PLATE-ID=00CN 6813( 4) - 05/07/96 15:28 - [ 4] Visit: 01 Visit Requirements: ORIENT 298D TO 58D 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 WLM-STARCLU WFPC2 IMAGE PC1-FIX F555W CR-SPLIT=0.482 1 5400S S ------------------------------------------------------------------------------------------------------------------------------------ 11 WLM-STARCLU WFPC2 IMAGE PC1-FIX F814W 1 5400S S ------------------------------------------------------------------------------------------------------------------------------------ 6813( 4) - 05/07/96 15:28 - [ 5] 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC6822-STA WFPC2 IMAGE PC1-FIX F555W 1 3900S RCLUS-HIV ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC6822-STA WFPC2 IMAGE PC1-FIX F814W 1 3900S RCLUS-HIV ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC6822-STA WFPC2 IMAGE PC1-FIX F555W 1 3900S RCLUS-HVI ------------------------------------------------------------------------------------------------------------------------------------ 21 NGC6822-STA WFPC2 IMAGE PC1-FIX F814W 1 3900S RCLUS-HVI ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC6822-STA WFPC2 IMAGE PC1-FIX F555W 1 3900S RCLUS-HVII ------------------------------------------------------------------------------------------------------------------------------------ 31 NGC6822-STA WFPC2 IMAGE PC1-FIX F814W 1 3900S RCLUS-HVII ------------------------------------------------------------------------------------------------------------------------------------ 40 NGC6822-STA WFPC2 IMAGE PC1-FIX F555W 1 3900S RCLUS-HVIII ------------------------------------------------------------------------------------------------------------------------------------ 41 NGC6822-STA WFPC2 IMAGE PC1-FIX F814W 1 3900S RCLUS-HVIII ------------------------------------------------------------------------------------------------------------------------------------ 6813( 4) - 05/07/96 15:28 - [ 6] Summary Form for Proposal 6813 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=0.482 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 298D TO 58D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names WLM-STARCLUS NGC6822-STARCLUS-HIV NGC6822-STARCLUS-HVI NGC6822-STARCLUS-HVII NGC6822-STARCLUS-HVIII ------------------------------------------------------------------------------------------------------------------------------------