8769( 2) - 02/28/00 10:48 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8769 Version: 2 Check-in Date: 28-Feb-2000 10:48:20 1.Proposal Title: The red giant stellar population in two nearby low-metallicity blue compact dwarf galaxies ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Trinh Thuan The University of Virginia CoI: Dr. Yuri Izotov Main Astronomical Observatory N ------------------------------------------------------------------------------------ 5. Abstract We wish to obtain deep V and I WFPC2 images of two nearby metal-deficient blue compact dwarf (BCD) galaxies UGC 4483 (Z_\odot/23) and NGC 2366 \equiv Mrk 71 (Z_\odot/13). Our main goal is to detect the red giant stellar population in these resolved BCDs to study their evolutionary history and constrain their ages. Are they young or old? On the basis of chemical evolution arguments, we have argued that all galaxies with Z < Z_\odot/20 are young with ages < 100 Myr, while those with Z > Z_\odot/20 are older. The high spatial resolution of the WFPC2 will allow to detect stars ~ 3 mag fainter than the red giant tip in UGC 4483 and NGC 2366, both members of the M81 group at a distance of 3.44 Mpc, and determine stellar ages directly through color-magnitude diagrams. If our chemical evolution arguments are correct, then UGC 4483 should not possess a red giant population and not be older than ~ 100 Myr, while such a population should be present in NGC 2366. ------------------------------------------------------------------------------------ 8769( 2) - 02/28/00 10:48 - [ 2] Observations Description ------------------------ We wish to obtain V(F555W) and I(F814W) PC1 and WF3 images of the 2 metal- deficient galaxies UGC 4483 and NGC 2366. For UGC 4483 and NGC 2366 which are both in the M81 group at a distance of 3.44 Mpc (m-M = 27.7), red giant stars are expected to be in the range V ~ 25 - 27.5 mag and I ~ 24 - 26.5 mag. To get signal-to-noise ratio of 10 for stars with V = 27.5 mag and I = 26.5 mag, 3.5 orbits in V and 2.5 orbits in I (a total of 6 orbits) are necessary for UGC 4483, and 2.5 orbits in V and 1.5 orbit in I (a total of 4 orbits) are needed for NGC 2366, counting overhead. We wish to orient the main body of the 2 BCDs (the position angle of NGC 2366 is 25 degrees and that of UGC 4483 is 162 degrees) along the diagonal joining the centers of the PC1 and WF3 chips. The brightest HII region at the SW edge of NGC 2366, and at the NW edge of UGC 4483 is to be placed near the edge of the PC1 chip. Each exposure will be split into several subexposures to allow for cosmic ray removal. Real Time Justification ----------------------- None Calibration Justification ------------------------- None Additional Comments ------------------- ------------------------------------------------------------------------------------ 8769( 2) - 02/28/00 10:48 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 MRK71 GALAXY, DWARF COMPACT RA=07H 28M 43.5S +/- 0.2S, J2000 V = 13.8+/-0.1 DEC=69D 11' 33.4" +/- 1", PLATE- B-V = 0.3+/-0.1 ID=01KS 2 UGC4483 GALAXY, DWARF COMPACT RA=08H 37M 3.4S +/- 0.2S, J2000 V = 15.7+/-0.1 DEC=69D 46' 42.1" +/- 1", PLATE- B-V = 0.3+/-0.1 ID=01L1 8769( 2) - 02/28/00 10:48 - [ 4] Visit: 10 Visit Priority: Visit Requirements: ORIENT 195D TO 215D On Hold Comments: Additional Comments: The brightest HII region at the SW edge of the galaxy NGC 2366 is placed near the edge of PC1. The mainbody of the galaxy NGC2366 with P.A.=+25 deg is oriented along the diagonals of PC1 and WF3 chips (see Special Requirement). Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 MRK71 WFPC2 IMAGE PC1 F555W 5398 CR-SPLIT=0.5 1 45 M ------------------------------------------------------------------------------------------------------------------------------------ 2 MRK71 WFPC2 IMAGE PC1 F555W 5398 CR-SPLIT=0.5 1 47 M ------------------------------------------------------------------------------------------------------------------------------------ 3 MRK71 WFPC2 IMAGE PC1 F555W 5398 CR-SPLIT=NO 1 23 M ------------------------------------------------------------------------------------------------------------------------------------ 4 MRK71 WFPC2 IMAGE PC1 F814W 7921 CR-SPLIT=NO 1 23 M ------------------------------------------------------------------------------------------------------------------------------------ 5 MRK71 WFPC2 IMAGE PC1 F814W 7921 CR-SPLIT=0.5 1 47 M ------------------------------------------------------------------------------------------------------------------------------------ 8769( 2) - 02/28/00 10:48 - [ 5] Visit: 20 Visit Priority: Visit Requirements: ORIENT 332D TO 352D On Hold Comments: Additional Comments: The brightest HII region at the NW edge of the galaxy is placed near the edge of PC1. The mainbody of the galaxy with P.A.=+162 deg is oriented along the diagonals of PC1 and WF3 chips. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 4 UGC4483 WFPC2 IMAGE PC1 F555W 5398 CR-SPLIT=0.5 1 45 M ------------------------------------------------------------------------------------------------------------------------------------ 5 UGC4483 WFPC2 IMAGE PC1 F555W 5398 CR-SPLIT=0.5 1 47 M ------------------------------------------------------------------------------------------------------------------------------------ 6 UGC4483 WFPC2 IMAGE PC1 F555W 5398 CR-SPLIT=0.5 1 47 M ------------------------------------------------------------------------------------------------------------------------------------ 7 UGC4483 WFPC2 IMAGE PC1 F555W 5398 CR-SPLIT=NO 1 23 M ------------------------------------------------------------------------------------------------------------------------------------ 8 UGC4483 WFPC2 IMAGE PC1 F814W 7921 CR-SPLIT=NO 1 23 M ------------------------------------------------------------------------------------------------------------------------------------ 9 UGC4483 WFPC2 IMAGE PC1 F814W 7921 CR-SPLIT=0.5 1 47 M ------------------------------------------------------------------------------------------------------------------------------------ 10 UGC4483 WFPC2 IMAGE PC1 F814W 7921 CR-SPLIT=0.5 1 47 M ------------------------------------------------------------------------------------------------------------------------------------ 8769( 2) - 02/28/00 10:48 - [ 6] Summary Form for Proposal 8769 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=0.5 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 195D TO 215D ORIENT 332D TO 352D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names MRK71 UGC4483 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 5398 7921 ------------------------------------------------------------------------------------------------------------------------------------