Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5350 Report Date: 18-Jul-95:17:13 Version: ********** Check-in Date: ********** 1.Proposal Title: THE FOSSIL RECORD OF STAR FORMATION IN THE LEO I AND FORNAX DWARF GALAXIES: CYCLE 4 MEDIUM ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID COOL STARS GO Sub Category ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Edward W Olszewski STEWARD OBSERVATORY USA (602)621-1973 ------------------------------------------------------------------------------------ 7. Abstract Deep galaxy counts and redshift surveys have uncovered evidence that many dwarf systems may have undergone enhancements in their star formation rates between redshifts of 0.3 to 1.0 (roughly 2-7 Gyr ago). The fossil record of such bursts must exist in the present-day stellar populations of galaxies if this interpretation is correct. We propose HST WF/PC-2 observations of two of the most distant dwarf spheroidal galaxies orbiting the Milky Way -- Leo I and Fornax -- to search for quantitative evidence of such intermediate-age bursts. These galaxies are of particular interest because recent ground-based observations have provided strong circumstantial evidence for the presence of significant intermediate-age populations in both systems. The analysis of our proposed deep V and I band HST WF/PC-2 observations of these galaxies shall involve methods that have been successfully used to determine the star-formation history of field stars in the Large Magellanic Cloud. The capabilities of HST are essential to reach sufficiently faint stars in both galaxies, and to cope with the extremely crowded fields in the cores of the Leo I and Fornax dwarf spheroidal galaxies. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 4.05 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: WF/PC ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5350 PI: Edward W Olszewski Proposal Title: THE FOSSIL RECORD OF STAR FORMATION IN THE LEO I AND FORNAX DWARF GALAXIES: CYCLE 4 MEDIUM ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Edward W Olszewski 1212 USA Myung Gyoon Lee 6630 KOREA Mario Mateo 2660 USA Wendy Freedman 3030 USA Paul Hodge 3760 USA Mike Keane 1552 USA Abi Saha 3470 USA Nick Suntzeff 4720 USA Ian Thompson 3030 USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. We are going to take 3 identical exposures in each filter with CR-SPLIT=NO, and a pair of short exposures. It does not matter whether the triad of V exposures is taken before or after the triad of I exposures (F555W and F814W) but the three exposures should be taken one after the other. Once a roll angle is defined it should be the same for all of the 3+3+1+1 exposures. Coordinates are not critical. We provide coordinates tied into GASP images sent to us a year or so ago for other purposes. We have chosen a region near the center of the galaxy as devoid of "bright" stars as possible, but to an accuracy of a couple of arcsec (probably a larger number than that, actually) it doesnt matter. We put the given coords on the center of the PC chip. We will be using our own cosmic ray removal techniques, which is why CR-SPLIT=NO. We want the longest possible triad of exposures. As we say elsewhere, we did extensive calling and checking to ensure that we were to use F814W as our I filter, despite the strong statements in the TAC report. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. Extensive ground-based observations of Leo I and Fornax have been attempted with 4m-class telescopes over the past few years. These data consistently fail to reach to faint enough levels in the cores of these relatively crowded systems to pursue the analysis required to determine the star formation histories of these galaxies. HST is required to obtain deep photometry in the crowded cores in order to study sufficient numbers of stars for statistically meaningful results. The mean spacing between stars with the HST data will be of order 10x the FWHM, while from the ground it will never be better than 2-3x the FWHM. At the 10x level, even aperture photometry should work, while at 2x even simultaneous psf fitting becomes problematic. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. All we require is that the 3 V exposures be as identical as possible so that we can median-filter them to get rid of cosmic rays. Once an orientation is chosen for the first exposure it should be the same for all subsequent exposures. It's hard to imagine that they shouldnt all be taken as close together in time as possible. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. We need no special calibrations. Page 3 ------------------------------------------------------------------------------------ 8. Additional comments or special requests. After extensive discussions with "STSCI" and Hugh Harris it became apparent that the Cool Star TAC had changed its mind, and F814W is the I filter of choice. ------------------------------------------------------------------------------------ 9. Description of previous HST work. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Lots of computers. Lots of telescope time. ------------------------------------------------------------------------------------ 11. Address Information Name: Edward W Olszewski Category: PI Institution: 1212 Address: Steward Observatory University of Arizona City: Tucson State: AZ Zip Code: 85721 Country: US Telephone: 602 621 2288 Telex (or e-mail): edo@as.arizona.edu ------------------------------------------------------------------------------------ Name: Category: CON Institution: Address: City: State: Zip Code: Country: Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 5350 [ 4] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 LEO-I LEO I E, RA = 10H 08M 26.58S +/-0.1S, J2000. 1 SURF(V)=22.3 +/- 0.2 DWARF 308 DEC = +12D 18' 33.4" +/-1.0" SPEHEROIDAL GALAXY ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5350 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LEO-I WFPC2 IMAGE PC1-FIX F555W 5407 CR-SPLIT=NO 3 1900S 1 1 CYCLE 4 / 1-4 CLOCKS=NO GROUP 1-4 NO GAP SAME POS FOR 2-4 AS 1 Comments: "SAME POS" HERE MEANS THAT ALL 8 EXPOSURES IN THE FOUR GROUPS WILL BE TAKEN AT THE SAME POSITION AND ORIENTATION. EXPOSURES 3 AND 4 ARE SHORT VERSIONS OF 1 AND 2 ------------------------------------------------------------------------------------------------------------------------------------ 2 LEO-I WFPC2 IMAGE PC1-FIX F814W 7940 CR-SPLIT=NO 1 1600S 1 1 CLOCKS=NO ------------------------------------------------------------------------------------------------------------------------------------ 2.1 LEO-I WFPC2 IMAGE PC1-FIX F814W 7940 CR-SPLIT=NO 1 1600S 1 1 CLOCKS=NO ------------------------------------------------------------------------------------------------------------------------------------ 2.2 LEO-I WFPC2 IMAGE PC1-FIX F814W 7940 CR-SPLIT=NO 1 1600S 1 1 CLOCKS=NO ------------------------------------------------------------------------------------------------------------------------------------ 3 LEO-I WFPC2 IMAGE PC1-FIX F555W 5407 CR-SPLIT=NO 1 350S 1 1 CLOCKS=NO Comments: SHORT EXPOSURE FOR GROUND-BASED TIE-IN ------------------------------------------------------------------------------------------------------------------------------------ 4 LEO-I WFPC2 IMAGE PC1-FIX F814W 7940 CR-SPLIT=NO 1 300S 1 1 CLOCKS=NO Comments: SHORT EXPOSURE FOR GROUND-BASED TIE-IN ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5350 [ 6] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO CLOCKS=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 4.05 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COOL STARS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4 / 1-4; GROUP 1-4 NO GAP; SAME POS FOR 2-4 AS 1; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names LEO-I LEO I DWARF SPEHEROIDAL GALAXY ------------------------------------------------------------------------------------------------------------------------------------