8295( 3) - 02/16/99 11:33 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8295 Version: 3 Check-in Date: 16-Feb-1999 11:32:32 1.Proposal Title: Anomalously Blue Giants: Possible Precursurs to Subdwarf B Stars ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle SNAP 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Brian Chaboyer Steward Observatory CoI: Dr. Elizabeth Green Steward Observatory Y CoI: Dr. Wayne Landsman Raytheon STX Corporation N ------------------------------------------------------------------------------------ 5. Abstract Subdwarf B (sdB) stars are evolved hot stars (24000 to 35000K) that are commonly found in the field of our Galaxy and have recently been identified in old disk, metal-rich clusters. They are likely to be one of the most important contributors to the upturn in the far-ultraviolet (FUV) flux exhibited by many elliptical galaxies and the bulge of M31. It is believed that sdB stars are core helium burning stars with very thin hydrogen envelopes. The mechanism which stripped the hydrogen envelope is not currently known. We propose that sdB stars are formed due to binary interactions. In particular, they have evolved from anomalously blue giants, which in turn have evolved from blue stragglers. These `blue' giants have been recently identified by us in NGC 188 and 6791, and are 0.1 -- 0.2 mag bluer in B-V than the normal red giant stars in each cluster. If our theory is correct, a significant fraction of these giants will have white dwarf companions that could be detected in t he FUV. We propose to test this scenario in a snapshot program to obtain STIS FUV images of a dozen of the bluer giants in both clusters. The giants themselves emit a negligible amount of FUV flux and would be undetectable without a hot companion. Confirmation of the presence of hot companions would lend strong support to the theory that the anomalous giants are the binary precursors to the sdB stars. ------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 2] Observations Description ------------------------ The goal of this project is to image a number of anomalously blue giants in NGC 6791 and NGC 188 to see if they have He white dwarf secondaries, similar to the anomalous giant S1040 in M67 which was detected by the Ultraviolet Imaging Telescope (Landsman et al. 1998). The anomalous giants in NGC 188 and NGC 6791 are spread over a wide area on the sky, and only one of these giants will be in each STIS field of view. The He white dwarf secondary (S1040) discovered by Landsman et al. (1998) in M67 has an unreddened flux of ~ 2* 10^-15 erg cm^-2 s^-1 A^-1 at 1600 Angstrom. NGC 6791 is 5.1 times farther away than M67 (reducing the flux by a factor of 26) and the increased reddening reduces the FUV flux by a further factor of 3, implying that a white dwarf similar to S1040 in NGC 6791 would have a flux of ~ 2.5* 10^-17, erg cm^-2 s^-1 A^-1. Using the STIS exposure time calculator and the F25SRF2 filter with the FUV MAMA leads to an estimated exposure time of 410 s for a de te ction with S/N = 10. However, the He white dwarf FUV flux is a strong function of its unknown mass and age. Based upon theoretical He WD models, the FUV flux can easily vary by a factor of 8 depending on its mass and age. For this reason, we are requesting 1440 s exposures on each of the anomalously blue giants in NGC 6791. This exposure time would allow us to detect He white dwarfs up to 5 times fainter than our nominal case, with S/N = 5. The total spacecraft time for each snapshot would be 35 minutes. Due to its lower reddening and distance, the He white dwarfs which we are hoping to detect in NGC 188 would be about 5 times brighter than those in NGC 6791. For this reason, we are requesting somewhat shorter exposures times, 540 s in NGC 188. The total spacecraft time for each snapshot of an anomalously blue giant in NGC 188 would be 20 minutes. We have identified 5 anomalous giants in NGC 6791 which based upon their location in the color magnitude diagram (Fig. 1) are likely to have the youngest He white dwarfs and offer the be st chance for detection by STIS. Due to its decreased metallicity, the giant branch lifetimes in NGC 188 are shorter (implying younger white dwarfs). Thus, we propose to observe 7 anomalous giants in this cluster. Accordingly, we are requesting 12 snapshot observations. The main scientific goal of this proposal would be met if at least 2 stars in NGC 6791 and 4 stars in NGC 188 are actually observed. Note that the fainter anomalous giants in each cluster are most likely to have the youngest, and therefore the UV- brightest white dwarf companions. The use of the FUV MAMA with the F25SRF2 gives us the maximum sensitivity to possible white dwarf secondaries, while ensuring that the anomalous giants will contribute negligible flux. The Ultraviolet Imaging Telescope 1600 A images of NGC 188 and NGC 6791 have been searched by us, and we have verified that no bright FUV sources are in the STIS field of view for each of our selected targets. Thus, all of our fields pass the str ic t bright object limit imposed upon STIS FUV MAMA observations. Due to the small (25"x 25") field of view of the STIS MAMA detector, we require guide star acquisitions with Fine Lock. This overhead has been included in our total spacecraft time for each snapshot. We waive our rights to a proprietary data-rights period. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 3] Data Distribution Paper Products: NO Media: DAT Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6791- STAR, K III-I RA=19H 20M 45.17S +/- 0.01S, J2000 V = 15.956+/-0.005 192045+37443 DEC=37D 44' 29.74" +/- 0.1", B-V = 1.162+/-0.008 0 PLATE-ID=037K V-I = 1.160+/-0.009 E(B-V) = 0.10+/-0.03 Comments: UIT 1620 A image shows no sources within 170 arcsec of target position to sensitivity limit of 8.3e-16 erg cm -2 s-1 A-1. 2 NGC6791- STAR, K III-I RA=19H 21M 3.91S +/- 0.01S, J2000 V = 15.948+/-0.003 192104+37460 DEC=37D 46' 2.10" +/- 0.1", B-V = 1.118+/-0.007 2 PLATE-ID=037K B-V = 0.10+/-0.03 Comments: UIT 1620 A image shows no sources within 55 arcsec of target position to sensitivity limit of 8.3e-16 erg cm -2 s-1 A-1. 3 NGC6791- STAR, K III-I RA=19H 21M 7.18S +/- 0.01S, J2000 V = 14.605+/-0.006 192107+37443 DEC=37D 44' 35.74" +/- 0.1", B-V = 1.265+/-0.007 6 PLATE-ID=037K E(B-V) = 0.10+/-0.03 Comments: UIT 1620 A image shows no sources within 100 arcsec of target position to sensitivity limit of 8.3e-16 erg cm -2 s-1 A-1. 4 NGC6791- STAR, K III-I RA=19H 20M 40.54S +/- 0.01S, J2000 V = 14.929+/-0.005 192041+37511 DEC=37D 51' 9.96" +/- 0.1", E(B-V) = 0.10+/-0.03 0 PLATE-ID=037K B-V = 1.267+/-0.007 V-I = 1.340+/-0.011 Comments: UIT 1620 A image shows no sources within 110 arcsec of target position to sensitivity limit of 8.3e-16 erg cm -2 s-1 A-1. 5 NGC6791- STAR, K III-I RA=19H 20M 46.11S +/- 0.01S, J2000 V = 14.384+/-0.005 192046+37475 DEC=37D 47' 54.69" +/- 0.1", B-V = 1.269+/-0.006 5 PLATE-ID=037K E(B-V) = 0.10+/-0.03 Comments: UIT 1620 A image shows no sources within 25 arcsec of target position to sensitivity limit of 8.3e-16 erg cm -2 s-1 A-1. 6 NGC188- STAR, K III-I RA=0H 42M 35.65S +/- 0.01S, J2000 V = 13.630+/-0.007 004236+85132 DEC=85D 13' 25.75" +/- 0.1", E(B-V) = 0.09+/-0.03 6 PLATE-ID=00A5 B-V = 0.955+/-0.010 Comments: UIT 1520 A image shows no sources within 45 arcsec of target position to sensitivity limit of 1.2e-15 erg cm -2 s-1 A-1. 7 NGC188- STAR, K III-I RA=0H 30M 47.12S +/- 0.01S, J2000 V = 13.43+/-0.05 003047+85070 DEC=85D 7' 0.01" +/- 0.1", PLATE E(B-V) = 0.09+/-0.03 0 -ID=00A5 B-V = 0.96+/-0.1 Comments: Nothing visible in USNO-A2 catalog within 30 arcsec radius of target to limits O=21 and E=20, fainter than bright limit of V=19.3 for an O5V star. 8 NGC188- STAR, K III-I RA=0H 46M 39.43S +/- 0.01S, J2000 V = 11.684+/-0.007 004639+85233 DEC=85D 23' 33.95" +/- 0.1", E(B-V) = 0.09+/-0.03 4 PLATE-ID=00A5 B-V = 1.174+/-0.010 Comments: UIT 1520 A image shows no sources within 270 arcsec of target position to sensitivity limit of 1.2e-15 erg cm -2 s-1 A-1. 8295( 3) - 02/16/99 11:33 - [ 5] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC188- STAR, K III-I RA=0H 34M 14.32S +/- 0.01S, J2000 V = 12.98+/-0.02 003414+85261 DEC=85D 26' 14.15" +/- 0.1", E(B-V) = 0.09+/-0.03 4 PLATE-ID=00A5 B-V = 0.96+/-0.02 Comments: UIT 1520 A image shows no sources within 60 arcsec of target position to sensitivity limit of 1.2e-15 erg cm -2 s-1 A-1. 10 NGC188- STAR, K III-I RA=0H 47M 56.29S +/- 0.01S, J2000 V = 11.951+/-0.010 004756+85145 DEC=85D 14' 57.29" +/- 0.1", E(B-V) = 0.09+/-0.03 7 PLATE-ID=00A5 B-V = 1.133+/-0.013 Comments: UIT 1520 A image shows no sources within 90 arcsec of target position to sensitivity limit of 1.2e-15 erg cm -2 s-1 A-1. 11 NGC188- STAR, K III-I RA=0H 45M 22.83S +/- 0.01S, J2000 V = 13.931+/-0.007 004523+85123 DEC=85D 12' 37.48" +/- 0.1", E(B-V) = 0.09+/-0.03 7 PLATE-ID=00A5 B-V = 0.923+/-0.010 Comments: UIT 1520 A image shows no sources within 215 arcsec of target position to sensitivity limit of 1.2e-15 erg cm -2 s-1 A-1. 12 NGC188- STAR, K III-I RA=0H 55M 45.63S +/- 0.01S, J2000 V = 10.916+/-0.016 005546+85122 DEC=85D 12' 21.00" +/- 0.1", E(B-V) = 0.09+/-0.03 1 PLATE-ID=00A5 B-V = 1.376+/-0.018 Comments: UIT 1520 A image shows no sources within 560 arcsec of target position to sensitivity limit of 1.2e-15 erg cm -2 s-1 A-1. 8295( 3) - 02/16/99 11:33 - [ 6] Visit: 01 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6791-192 STIS/F ACCUM F25SRF2 MIRROR 1 24 M 045+374430 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 7] Visit: 02 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6791-192 STIS/F ACCUM F25SRF2 MIRROR 1 24 M 104+374602 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 8] Visit: 03 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6791-192 STIS/F ACCUM F25SRF2 MIRROR 1 24 M 107+374436 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 9] Visit: 04 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6791-192 STIS/F ACCUM F25SRF2 MIRROR 1 24 M 046+374755 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 10] Visit: 05 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6791-192 STIS/F ACCUM F25SRF2 MIRROR 1 24 M 041+375110 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 11] Visit: 06 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC188-0042 STIS/F ACCUM F25SRF2 MIRROR 1 9 M 36+851326 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 12] Visit: 07 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC188-0030 STIS/F ACCUM F25SRF2 MIRROR 1 9 M 47+850700 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 13] Visit: 08 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC188-0046 STIS/F ACCUM F25SRF2 MIRROR 1 9 M 39+852334 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 14] Visit: 09 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC188-0034 STIS/F ACCUM F25SRF2 MIRROR 1 9 M 14+852614 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 15] Visit: 10 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC188-0047 STIS/F ACCUM F25SRF2 MIRROR 1 9 M 56+851457 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 16] Visit: 11 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC188-0045 STIS/F ACCUM F25SRF2 MIRROR 1 9 M 23+851237 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 17] Visit: 12 Visit Priority: 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 ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC188-0055 STIS/F ACCUM F25SRF2 MIRROR 1 9 M 46+851221 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8295( 3) - 02/16/99 11:33 - [ 18] Summary Form for Proposal 8295 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F25SRF2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category SNAP ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6791-192045+374430 NGC6791-192104+374602 NGC6791-192107+374436 NGC6791-192046+374755 NGC6791-192041+375110 NGC188-004236+851326 NGC188-003047+850700 NGC188-004639+852334 NGC188-003414+852614 NGC188-004756+851457 NGC188-004523+851237 NGC188-005546+851221 ------------------------------------------------------------------------------------------------------------------------------------