6555( 7) - 07/31/97 09:38 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6555 Version: 7 Check-in Date: 31-Jul-1997 09:37:20 1.Proposal Title: What causes the astigmatism in gravitational lenses? ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle COSMOLOGY GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: PAUL SCHECHTER MIT CoI: Marijn Franx Kapteyn Astronomical Institute N ------------------------------------------------------------------------------------ 6. Abstract Among multiply imaged quasars, those for which the shape of the lensing mass can be measured show surprisingly strong deviations from circular symmetry -- astigmatism in the gravitational lens. This astigmatism can be due to the flattening of lensing galaxy itself or due to tides from neighboring galaxies. Likewise it can be due to dark matter interior or exterior to the system's Einstein radius. In either case the implied flattenings and tides are larger than one would naively expect. Before the full potential of lenses can be exploited, the source of this astigmatism must be identified. We propose a direct search for the source of this astigmatism through deep HST imaging of the lensed objects. Such images will be used to measure the shape of the lensing galaxies in detail, and the matter distribution surrounding them. If the astigmatism is due to large scale structure, it should be measurable in the weak lensing (polarization) of nearby faint galaxies. These measurements provide a direct test of the two alternatives. ------------------------------------------------------------------------------------ 6555( 7) - 07/31/97 09:38 - [ 2] Observations Description ------------------------ We propose to do deep imaging of the lenses in the red (F814W). This is the reddest passband with reasonable throughput and good PSF monitoring. The passband is extensively used and has good calibrations. PG1115+80: The Einstein radius is about 1''. We propose 1 orbit of short exposures, and a series of long exposures. The short exposures will be taken on the PC chip, to measure the locations of the 4 QSO images accurately. The long exposures will be taken on the WF chip, so that we will be photon noise limited. The lensing galaxy is at a redshift of 0.295 and has an R magnitude of 19.8 (Angonin-Williame et al. 1993). An exposure time of 10,000 sec should give us a S/N of 10 at a surface brightness of 22.4 in I. The deep exposures will also produce independent point spread functions from the stellar images which are nearby, which are important for proper modeling of the PSF. In order to reduce the systematic errors in PSF fitting, the object will be shifted somewhat (dithered) between exposures. The total number of orbits is 6., 1608+657: The source is an extended galaxy, and the lens has been reported to be at z=0.6. We propose to take deep integrations to image the structure of source and lens. We propose to integrate for a total of 20,000 sec in F814W. This equals 9 orbits, unless the observations can be scheduled in the continuous viewing time-slot. We do not specifically request CVZ observing, because the total integration time is relatively short. The difficulty in scheduling CVZ may therefore offset the enhanced efficiency. We will obtain a S/N of 10 at a surface brightness of 22.8 in I. This is well matched to the redshift of the lens, at z=0.6., , omit 1413+117: The Einstein radius of this system is rather small, 0.6''. Contamination of the lens image by the star is therefore an additional worry. The main goal of the exposures is the detection of the lens, and its shape. Earlier images taken with WFPC2 indicate that the light from the QSO dominates the sky by a factor of XXX near the center. These images were taken with the WF chips. The implication is that it is better to image this system with the PC chip, since the photon noise from the QSO light will dominate the read noise. We propose to take 4 deep images in two passbands. The telescope will be shifted from one exposure to the other, so that calibration and the PSF modeling becomes more robust. References, , Angonin-Williame et al., 1993, ``Gravitational Lenses in the Universe'', ed. J. Surdej et al., (Liege: Universite de Liege), p.85. Real Time Justification ----------------------- PG1115+080 has been monitored by one of us (PLS) at MDM Observatory for the past four seasons. It shows small but highly significant variations in the flux ratios for the four components in each of two filters (Figure 2). The single greatest source of uncertainty and systematic error is the model for the surface brightness profile of the lensing galaxy, which blends with the 4 images of the QSO. The proposed HST data would permit substitution of an empirical model, or at the very least, would constrain the analytic model, for which the shape parameters are exceedingly difficult to obtain from groundbased data. With a perfect model the rms errors in the fainter components would be reduced from 8 millimag to 5 millimag on 5 minute V band exposures. This would apply both to data already taken and data yet to be taken. PLS will propose to monitor PG1115+080 intensively this coming season (15 minutes every two nights) using the WIYN telescope in its queue scheduled mode., \\epsfxsize=6.5truein 71 40 555 328both2.ps Figure 2. Figure 2a we shows the variability of A1 + A2 of PG1115+080 relative to Vanderriest's star F over the course of 40 months. Figure 2b shows the ratio C/(A1 + A2) as observed at V and I. All of the points are derived from averages of at least 3 frames taken with the Hiltner Telescope, with the exception of 1994 April V point, obtained from a single exposure, and the filled symbol, obtained at CTIO. This latter point was obtained at the same time, 1992 April, as point labeled ``1''. The agreement of these two, obtained with different seeing and different sampling using different instruments, supports the conclusion that the variation in C/(A1+A2) is real and not the result of systematic error., Calibration Justification ------------------------- Real_Time_Justification Additional Comments ------------------- ------------------------------------------------------------------------------------ 6555( 7) - 07/31/97 09:38 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: ------------------------------------------------------------------------------------ 6555( 7) - 07/31/97 09:38 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PG1115+080 GALAXY, GRAVITATIONAL RA=11H 15M 41.49S +/- .001S, B1950 Z=0.3 V = 17 LENS DEC=08D02' 23.2" +/- 0.01" B-V = 0.5 Comments: Position from PS. 2 PG1115+080- STAR RA=11H 15M 44.98S +/- .001S, B1950 Z=0. V = 16 STARB DEC=08D02' 21.7" +/- 0.01" B-V = 0.7 Comments: STAR for PSF on WF, QSO on PC. Position from PS. 3 PG1115+080- STAR RA=11H 15M 38.48S +/- .001S, B1950 Z=0. V = 17 STARC DEC=08D02' 52.3" +/- 0.01" B-V = 1.0 Comments: STAR for PSF on WF, QSO on PC. Position from PS. 4 QSO- GALAXY, GRAVITATIONAL RA=16H 09M 13.956S +/- .001S, J2000 Z=1 V = 21.5 160913+65322 LENS DEC=65D32' 28.97" +/- 0.01" B-V = 1.0 Comments: position from Myers et al ApJL 447, L6. 6555( 7) - 07/31/97 09:38 - [ 5] Visit: 01 Visit Requirements: ORIENT 271D TO 272D On Hold Comments: Additional Comments: two guide stars requested. Don't change ORIENT without notifying PI. The ORIENT can be changed by the PI if it helps schedulability. email PI about all changes: schech@achernar.mit.edu. Background sky as low as possible. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 PG1115+080 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 1000 S POS TARG -10, -10 IX Comments: 4 exposures in 2 orbits, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 2 PG1115+080 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 1100 S POS TARG -10.55, -10 IX Comments: 4 exposures in 2 orbits, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 3 PG1115+080 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 1100 S POS TARG -10, -10.55 IX Comments: 4 exposures in 2 orbits, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 4 PG1115+080 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 1200 S POS TARG -10.55, -10.55 IX Comments: 4 exposures in 2 orbits, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 10 PG1115+080- WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 30 S POS TARG -10, -10 STARB IX Comments: short exposure. Unsaturated on PC ------------------------------------------------------------------------------------------------------------------------------------ 11 PG1115+080- WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 400 S POS TARG -10, -10 STARB IX Comments: 4 exposures in 1 orbit, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 12 PG1115+080- WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 400 S POS TARG -10.55, -10 STARB IX Comments: 4 exposures in 1 orbit, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 6555( 7) - 07/31/97 09:38 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 13 PG1115+080- WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 400 S POS TARG -10, -10.55 STARB IX Comments: 4 exposures in 1 orbit, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 14 PG1115+080- WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 400 S POS TARG -10.55, -10.55 STARB IX Comments: 4 exposures in 1 orbit, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 6555( 7) - 07/31/97 09:38 - [ 7] Visit: 02 Visit Requirements: ORIENT 123D TO 124D On Hold Comments: Additional Comments: two guide stars requested. Don't change ORIENT without notifying PI. The ORIENT can be changed by the PI if it helps schedulability. email PI about all changes: schech@achernar.mit.edu. Background sky as low as possible. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 PG1115+080 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 1000 S POS TARG -10, -10 IX Comments: 4 exposures in 2 orbits, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 2 PG1115+080 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 1100 S POS TARG -10.55, -10 IX Comments: 4 exposures in 2 orbits, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 3 PG1115+080 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 1100 S POS TARG -10, -10.55 IX Comments: 4 exposures in 2 orbits, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 4 PG1115+080 WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 1200 S POS TARG -10.55, -10.55 IX Comments: 4 exposures in 2 orbits, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 10 PG1115+080- WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 30 S POS TARG -10, -10 STARC IX Comments: short exposure. Unsaturated on PC. Don't lenthen this. ------------------------------------------------------------------------------------------------------------------------------------ 11 PG1115+080- WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 1100 S POS TARG -10, -10 STARC IX Comments: 4 exposures in 1 orbit, with 2D dithering with POS TARG ------------------------------------------------------------------------------------------------------------------------------------ 12 PG1115+080- WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 1100 S POS TARG -10.55, -10 STARC IX Comments: 4 exposures in 1 orbit, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 20 PG1115+080- WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 30 S POS TARG -10.55, -10.55 STARC IX Comments: short exposure. Unsaturated on PC ------------------------------------------------------------------------------------------------------------------------------------ 6555( 7) - 07/31/97 09:38 - [ 8] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 21 PG1115+080- WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 1100 S POS TARG -10.55, -10.55 STARC IX Comments: 4 exposures in 1 orbit, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 22 PG1115+080- WFPC2 IMAGE WFALL-F F814W CR-SPLIT=NO 1 1100 S POS TARG -10, -10.55 STARC IX Comments: 4 exposures in 1 orbit, with 2D dithering with POS TARG Dither of 0.55 arcsec=5.5 WFPC pixels and 12.5 PC pixels ------------------------------------------------------------------------------------------------------------------------------------ 6555( 7) - 07/31/97 09:38 - [ 9] Visit: 03 Visit Requirements: On Hold Comments: Additional Comments: two guide stars required. email PI about all changes: schech@achernar.mit.edu. Background sky should be as low as possible. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 QSO-160913+ WFPC2 IMAGE PC1 F814W CR-SPLIT=NO 1 2800 S POS TARG 0., 0. 65322 Comments: 4 exposures in 4 orbits per passband. Dither of 5 PC pixels. POS TARG driven. ------------------------------------------------------------------------------------------------------------------------------------ 2 QSO-160913+ WFPC2 IMAGE PC1 F814W CR-SPLIT=NO 1 2900 S POS TARG 0., 0. 65322 Comments: 4 exposures in 4 orbits per passband. Dither of 5 PC pixels. POS TARG driven. ------------------------------------------------------------------------------------------------------------------------------------ 3 QSO-160913+ WFPC2 IMAGE PC1 F606W CR-SPLIT=NO 1 2900 S POS TARG 0., 0. 65322 Comments: 4 exposures in 4 orbits per passband. Dither of 5 PC pixels. POS TARG driven. ------------------------------------------------------------------------------------------------------------------------------------ 4 QSO-160913+ WFPC2 IMAGE PC1 F606W CR-SPLIT=NO 1 2900 S POS TARG 0., 0. 65322 Comments: 4 exposures in 4 orbits per passband. Dither of 5 PC pixels. POS TARG driven. ------------------------------------------------------------------------------------------------------------------------------------ 11 QSO-160913+ WFPC2 IMAGE PC1 F814W CR-SPLIT=NO 1 2900 S POS TARG 0.22, 0.22 65322 Comments: 4 exposures in 4 orbits per passband. Dither of 5 PC pixels. POS TARG driven. ------------------------------------------------------------------------------------------------------------------------------------ 12 QSO-160913+ WFPC2 IMAGE PC1 F814W CR-SPLIT=NO 1 2900 S POS TARG 0.22, 0.22 65322 Comments: 4 exposures in 4 orbits per passband. Dither of 5 PC pixels. POS TARG driven. ------------------------------------------------------------------------------------------------------------------------------------ 13 QSO-160913+ WFPC2 IMAGE PC1 F606W CR-SPLIT=NO 1 2900 S POS TARG 0.22, 0.22 65322 Comments: 4 exposures in 4 orbits per passband. Dither of 5 PC pixels. POS TARG driven. ------------------------------------------------------------------------------------------------------------------------------------ 14 QSO-160913+ WFPC2 IMAGE PC1 F606W CR-SPLIT=NO 1 2900 S POS TARG 0.22, 0.22 65322 Comments: 4 exposures in 4 orbits per passband. Dither of 5 PC pixels. POS TARG driven. ------------------------------------------------------------------------------------------------------------------------------------ 6555( 7) - 07/31/97 09:38 - [ 10] Summary Form for Proposal 6555 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COSMOLOGY ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 271D TO 272D POS TARG -10, -10 POS TARG -10.55, -10 POS TARG -10, -10.55 POS TARG -10.55, -10.55 ORIENT 123D TO 124D POS TARG 0., 0. POS TARG 0.22, 0.22 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names PG1115+080 PG1115+080-STARB PG1115+080-STARC QSO-160913+65322 ------------------------------------------------------------------------------------------------------------------------------------