Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5386 Report Date: 18-Jul-95:17:16 Version: ********** Check-in Date: ********** 1.Proposal Title: STELLAR POPULATIONS OF THE LEO II DWARF SPHEROIDAL GALAXY ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID COOL STARS GO Sub Category STELLAR POPULATIONS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Kenneth J Mighell COLUMBIA UNIVERSITY USA 212-854-6899 ------------------------------------------------------------------------------------ 7. Abstract We propose to obtain deep V and I photometry of the Leo II dwarf spheroidal galaxy using the WFPC2 and the F555W and F791 filters. We will produce a deep HR diagram of this Local Group galaxy which will be analyzed to determine its age and star formation history. This galaxy has luminous carbon stars and an anomalously red horizontal branch which indicates the presence of at least some intermediate age stars, and suggests that Leo II is younger than the Draco and Ursa Minor dwarf spheroidals. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 4.08 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: WF/PC ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5386 PI: Kenneth J Mighell Proposal Title: STELLAR POPULATIONS OF THE LEO II DWARF SPHEROIDAL GALAXY ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Kenneth J Mighell 1770 USA R. Michael Rich 1770 USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. Leo II has a distance modulus (m-M)=21.85 (Demers & Harris 1983). An intermediate-age turnoff would occur at V=25; an old trunoff at V=26. We seek (V- I) color errors less than 0.30 mag for a F0 star at V=27. A 4800 second exposure in F555W gives S/N=7.9 and a 4800 second exposure in F791W gives S/N=5.1. The combined color error is 0.28 mag. Filter: F555W has QT_integral = 0.0250 Star: V=27, F0 star has AB_V=0.030 (average of 500 and 600 nm) Stellar flux: I=(2.5E+11)*(QT_integral)*10**(-0.4(V+AB_V))=0.096 e/sec Sky: WF -> V=27.1 (Leo II is near the ecliptic), AB_V = 0.035 Sky flux: B=(2.5E+11)*(QT_integral)*10**(- 0.4(V+AB_V))=0.087 e/sec Total Exposure: T=4800 sec S/N correction: C=0.261 (WF Center & Corner, avgerage of 400 and 800 nm) S/N=I*SQRT((T*C)/(B+I))= 7.9 in 4800 sec Filter: F791W has QT_integral = 0.0169 Star: V=27, F0 star has AB_V=0.080 (800 nm) Stellar flux: I=(2.5E+11)*(QT_integral)*10**(-0.4(V+AB_V))=0.062 e/sec Sky: WF -> V=27.1 (Leo II is near the ecliptic), AB_V = -0.55 Sky flux: B=(2.5E+11)*(QT_integral)*10**(-0.4(V+AB_V))=0.101 e/sec Total Exposure: T=4800 sec S/N correction: C=0.226 (WF Center & Corner, 800 nm) S/N=I*SQRT((T*C)/(B+I))= 5.1 in 4800 sec We will take 2x80 sec exposures with ATD-GAIN=15 and 4x1200 sec exposures with ATD-GAIN=7 for both filters (F555W and F791W). The short high -gain exposures increase the dynamic range of the long low-gain exposures. We would like all the exposures to be taken together as one group with only interruptions due to Earth occultations (GROUP 1-4 NO GAP). We would like all exposures to be made at the same position in the sky with the same telescope roll angle (SAME POS FOR 2-4 AS 1). Each 1200 second exposure will be split in half (CR-SPLIT=0.5) to minimize cosmic-ray contamination. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. See answer to question 4.a. on the HST Cycle 4 proposal general form. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. ------------------------------------------------------------------------------------ 9. Description of previous HST work. See answer to question 9. on the HST Cycle 4 proposal general form. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). See answer to question 10. on the HST Cycle 4 proposal general form. ------------------------------------------------------------------------------------ 11. Address Information Page 3 Name: KENNETH J MIGHELL Category: PI Institution: 1770 Address: DEPT. OF ASTRONOMY COLUMBIA UNIVERSITY 538 WEST 120TH STREET City: NEW YORK State: NY Zip Code: 10027 Country: USA Telephone: 212-854-6899 Telex (or e-mail): MIGHELL@FIGARO.PHYS.COLUMBIA.EDU ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 5386 [ 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-II E, 308 RA = 11H 13M 32.00S +/- 2000.0 1 V=12.4 0.10S, 2 B-V=1.0 DEC = +22D 09' 30" +/- 0.10" Comments: POSITION CHOSEN TO AVOID BRIGHT STAR NEAR THE CENTER OF THE GALAXY ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5386 [ 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-II WFPC2 IMAGE PC1 F555W ATD-GAIN=15 2 80S 7.9 1 1 CYCLE 4 CR-SPLIT=NO 4800S PCS MODE F ------------------------------------------------------------------------------------------------------------------------------------ 2 LEO-II WFPC2 IMAGE PC1 F555W ATD-GAIN=7 4 1200S 7.9 1 1 CYCLE 4 CR-SPLIT=0.5 1200S PCS MODE F CR- TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 LEO-II WFPC2 IMAGE PC1 F814W ATD-GAIN=15 2 80S 5.1 1 1 CYCLE 4 CR-SPLIT=NO 4800S PCS MODE F ------------------------------------------------------------------------------------------------------------------------------------ 4 LEO-II WFPC2 IMAGE PC1 F814W ATD-GAIN=7 4 1200S 5.1 1 1 CYCLE 4 CR-SPLIT=0.5 4800S PCS MODE F CR- GROUP 1-4 NO GAP TOLERANCE=0.0 SAME POS FOR 2-4 AS 1 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5386 [ 6] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=15 CR-SPLIT=NO ATD-GAIN=7 CR-SPLIT=0.5 CR-TOLERANCE=0.0 ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 4.08 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COOL STARS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4; PCS MODE F; GROUP 1-4 NO GAP; SAME POS FOR 2-4 AS 1; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names LEO-II ------------------------------------------------------------------------------------------------------------------------------------