6105( 8) - 03/05/97 12:53 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6105 Version: 8 Check-in Date: 04-Mar-1997 14:44:36 1.Proposal Title: Primary distance measurement to the Virgo Cluster ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Galaxies & Clusters GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: WILLIAM E. HARRIS McMaster University CoI: Patrick R. Durrell Department of Physics and Astronomy, N McMaster University CoI: Michael J. Pierce Department of Astronomy, Indiana N University CoI: Jeff Secker Department of Physics and Astronomy, N McMaster University ------------------------------------------------------------------------------------ 6. Abstract The I-band luminosity of the brightest red giant stars in old, metal-poor, halo populations, M_I(tip), is a primary standard candle accurate to +/-0.1 mag, and offers several distinct advantages over other Population II distance indicators. A critical feature of M_I(tip) is that the metallicity of the galaxy's underlying halo population must be less than Fe/H ~ -0.7 dex. However, giant elliptical galaxies like those at the core of the Virgo Cluster possess a metal-rich stellar halo; as a result, any M_I(tip) distance to the Virgo core which is based upon these giant galaxies will suffer an intrinsic bias towards larger distance if compared to local, metal-poor calibrators. We will use WFPC2 in I to resolve the brightest RGB stars in two metal-poor nucleated dwarf ellipticals near M87 (the cD galaxy at the center of the main Virgo Cluster core). Because of its high intrinsic precision, reliance on basic stellar physics, and independence from the current collection of secondary distance estimators, the resulting M_I(tip) Virgo distance will be the most nearly definitive to date, providing a stepping stone to more remote clusters and (eventually) H_0. ------------------------------------------------------------------------------------ 6105( 8) - 03/05/97 12:53 - [ 2] Observations Description ------------------------ We will use WFPC2 with the F814W (``wide I'') filter, which will maximize throughput while preserving a well defined photometric bandpass. The absolute magnitude of the metal- poor RGB tip is at M_I = -4.0 +/- 0.1. If (m-M)(Virgo) = 31.0, we expect the brightest red giants to resolve at I=27.0, corresponding to V=29.0. We will center the PC1 CCD field at a nominal radius from the center of the dE,N galaxy which is equivalent to a V surface brightness of ~26.8 mag per sq arcsec, which simulations show will yield several hundred resolved RGB stars across the frame with no severe crowding problems. We will carry out the CCD photometry with DAOPHOT III (ALLFRAME), by far the best code for crowded field photometry. A sophisticated maximum-likelihood code has been developed to fit a model luminosity function to the data, simultaneously incorporating photometric incompleteness, photometric error, and background contamination: This will be used to fit the steep upturn in the LF at the giant branch tip and to deduce the tip magnitude. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 6105( 8) - 03/05/97 12:53 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 VCC1104 GALAXY, DWARF RA=12H 28M 31.4S +/- 2",DEC=12D J2000 V = V = 29.0 ELLIPTICAL 49' 38" +/- 2",PLATE-ID=00IY +1704 B-V = 1.6 Comments: TARGET V MAGNITUDE CORRESPONDS TO BRIGHTEST RED GIANTS IN GALAXY 2 VCC1407 GALAXY,DWARF ELLIPTICAL RA=12H 32M 4.33S +/- 2",DEC=11D J2000 V = +941 V = 29.0 52' 45" +/- 2",PLATE-ID=00IY B-V = 1.6 Comments: TARGET V MAGNITUDE CORRESPONDS TO BRIGHTEST RED GIANTS IN GALAXY 6105( 8) - 03/05/97 12:53 - [ 4] Visit: 01 Visit Requirements: ORIENT 105D TO 105D On Hold Comments: Additional Comments: ORIENT 45D TO 105D NUCLEUS OF GALAXY SHOULD FALL WITHIN WF3. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 12 VCC1104 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 2400 S END ORBIT EXPAND Comments: EXPOSURES 12-17 ARE A 6 STEP SEQUENCE AROUND A HEXAGONAL PATTERN WITH 2.5 PX STEPS ------------------------------------------------------------------------------------------------------------------------------------ 13 VCC1104 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 2600 S POS TARG 0.115,0.115 END ORBIT EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 14 VCC1104 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 2600 S POS TARG 0.115,0.230 END ORBIT EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 15 VCC1104 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 2600 S POS TARG 0.0,0.345 END ORBIT EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 16 VCC1104 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 2600 S POS TARG -0.115,0.230 END ORBIT EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 17 VCC1104 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 2600 S POS TARG -0.115,0.115 END ORBIT EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 6105( 8) - 03/05/97 12:53 - [ 5] Visit: 02 Visit Requirements: ORIENT 105D TO 105D On Hold Comments: Additional Comments: SAME ORIENT AS 01 NUCLEUS OF GALAXY SHOULD FALL WITHIN WF3. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 22 VCC1104 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 2400 S END ORBIT EXPAND Comments: EXPOSURES 22-27 ARE A 6 STEP SEQUENCE AROUND A HEXAGONAL PATTERN WITH 2.5 PX STEPS ------------------------------------------------------------------------------------------------------------------------------------ 23 VCC1104 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 2600 S POS TARG 0.115,0.115 END ORBIT EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 24 VCC1104 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 2600 S POS TARG 0.115,0.230 END ORBIT EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 25 VCC1104 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 2600 S POS TARG 0.0,0.345 END ORBIT EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 26 VCC1104 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 2600 S POS TARG -0.115,0.230 END ORBIT EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 27 VCC1104 WFPC2 IMAGE PC1-FIX F814W CR-SPLIT=NO 1 2600 S POS TARG -0.115,0.115 END ORBIT EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 6105( 8) - 03/05/97 12:53 - [ 6] Summary Form for Proposal 6105 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Galaxies & Clusters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 105D TO 105D END ORBIT EXPAND POS TARG 0.115,0.115 END ORBIT EXPAND POS TARG 0.115,0.230 END ORBIT EXPAND POS TARG 0.0,0.345 END ORBIT EXPAND POS TARG -0.115,0.230 END ORBIT EXPAND POS TARG -0.115,0.115 END ORBIT EXPAND ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names VCC1104 ------------------------------------------------------------------------------------------------------------------------------------