5979( 12) - 09/21/95 11:14 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5979 Version: 12 Check-in Date: ********** 1.Proposal Title: The Mass Distribution Lensing QSO : 0957+561: The Hubble Constant ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Quasars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: George Rhee University of Nevada Las Vegas CoI: Tony Tyson AT&T Bell Laboratories N CoI: Gary Bernstein University of Michigan N CoI: Phil Fischer AT&T Bell Laboratories N ------------------------------------------------------------------------------------ 6. Abstract We propose to use HST with WFPC2 in order to carry out deep imaging of the lensing cluster of the double quasar Q0957+561. This will significantly improve the estimate we have made of the Hubble constant using this double quasar. We will determine the gravitational potential of the cluster in which the lensing galaxy is located. The most accurate way to do this is to take very deep images of the cluster and measure the gravitational lens distortion of the blue background galaxy population. The confirmation of distortions in the lensed background galaxies inferred from ground- based observations at CFHT and KPNO, particularly in several small blue galaxies seen near the QSO and one apparent arc, will allow us to produce a high quality map of the cluster mass distribution, thereby reducing the largest unknown in the determination of H_0 via the gravitational lens time delay method. In addition, there is a possibility that WFPC2 images may reveal the presence of giant thin arcs, particularly if the mass falls off faster than isothermal. These thin arcs if observed would provide an additional strong constraint on the mass distribution models. We wish to emphasize that measuring the Hubble constant in this manner is complementary to the standard distance ladder methods. ------------------------------------------------------------------------------------ 5979( 12) - 09/21/95 11:14 - [ 2] Observations Description ------------------------ In order to accurately measure the ellipticity of the blue galaxies we must go fainter in surface brightness than normally required for photometry. We require a 1-sigma surface brighness sensitivity of 27.0 - 27.5 V mag/sq.arcsec in the inner 30-50 WFC2 pixels of the blue arclets, which leads to 12 hr (16 orbits) of total exposure in V. We will do 2 color imaging with WFPC2. Although we already have color information from our deep ground based data, we will take a deep V-band image and a shorter R exposure. We just need enough R WFC2 images to distinguish red stars on top of blue arcs. The filters best suited to do this (based on throughput figures in the WFPC2 Instrument Handbook) are the F450W (wide B), F569W, and F702W (wide R) filters. The faint blue galaxies which we wish to image have a spectrum in the optical similar to an F0 star. This is in agreement with mild evolution models. We will look for arclets at a B magnitude of 26. The colors of the arclets imply from Table 6.1 of the WFPC2 handbook an AB correction of 0.06 magnitudes at 450nm and 0.05 magnitudes at 700nm. The seeing deconvolved CFHT data and the HST MDS data give a mean half light radius of 0sec point 05 for galaxies around magnitude 24-25 with at least 50\ area for half the light at magnitude 26. Using equations 6.1 and Tables 6.1 and 6.2 we infer 205 electrons in 2900s for a 26 V magnitude galaxy at 450nm and 456 electrons for the same galaxy and integration time at 702nm. We calculate signal to noise per pixel since we are doing surface photometry. Note that ellipse fitting averages pixels and will increase our signal to noise. Assuming a flat profile for the galaxies we get 2e/pixel/1s at 450nm although based on extrapolations from the MDS survey data it could be as much as 5e/pixel/s. For the sky background at high ecliptic latitudes (tables 6.1 and 6.3) we infer 21e/pixel/s. This same calculation for the wide V band filter F569W leads to over 7e/pixel/s in the center of a typical faint blue galaxy, with a sky background of 40e/pixel/s (plus 22.4e for dark current and 5.2^2e for readnoise) at high ecliptic latitude. Since our deep ground- based data is in the V band, we therefore chose this for the HST observation, based on these calculations. Calculating signal-to-noise based on the data above we get a S/N of 0.6 in 1s seconds per pixel inside the half light radius. We thus need 25 2900s exposures to get a signal-to-noise of 3 per pixel at the half light point. We can get two 2900s exposures per orbits for a total of 13 orbits. Note however that there are many sources inside the WFC field at magnitude 26 and we get significant signal from pixels inside the half light radius. We calculate a S/N of 0.8 per pixel in the central 30 pixels of a 26 V mag galaxy in 2900s in the F569W filter. Cycle 2 and 3 data for arclets in A370 (10 hours WFC1 r band) and for CL0024 (6 hours WFC1 r band) and the cycle 4 data now coming in are consistent with these calculations. We also request 7 orbits with F702W as explained above. We request 16 orbits in with filter F569W and 7 orbits with filter F702W. We will take 4 exposures per orbit. This will give a sufficient number of exposures to both eliminate the radiation events, to reach sufficient S/N for ellipticity determination of the lensed background galaxies near the QSO position, and enable us to detect faint projected red stars. Real Time Justification ----------------------- none As indicated above we have obtained the best quality ground based deep imaging in V. We plan further CFHT imaging in I to get further color data, complimenting our KPNO 4m J-R color data. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 5979( 12) - 09/21/95 11:14 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5979( 12) - 09/21/95 11:14 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 0957+561B GALAXY, QUASAR, RA=09H 57M 57.42S +/- 0.001S, 1950 Z=1.41 V=17.3 GRAVITATIONAL LENS DEC=56D 08' 16.4" +/- 0.02" 5979( 12) - 09/21/95 11:14 - [ 5] Visit: 01 Visit Requirements: ORIENT 305D to 325D GROUP 1-2 WITHIN 21D On Hold Comments: Additional Comments: It would be great if this could be done in the CVZ Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 0957+561B WFPC2 IMAGE WF3-FIX F555W 1 80S POS TARG +1.10, +1.10 ------------------------------------------------------------------------------------------------------------------------------------ 2 0957+561B WFPC2 IMAGE WF3-FIX F555W 1 80S POS TARG +0.00, +0.00 ------------------------------------------------------------------------------------------------------------------------------------ 3 0957+561B WFPC2 IMAGE WF3-FIX F814W 1 160S POS TARG +1.10, +1.10 ------------------------------------------------------------------------------------------------------------------------------------ 4 0957+561B WFPC2 IMAGE WF3-FIX F814W 1 160S POS TARG +0.00, +0.00 ------------------------------------------------------------------------------------------------------------------------------------ 5 0957+561B WFPC2 IMAGE WF3-FIX F814W 1 500S POS TARG +0.00, +1.10 ------------------------------------------------------------------------------------------------------------------------------------ 6 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG +0.00, +0.00 ------------------------------------------------------------------------------------------------------------------------------------ 7 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG +0.00, +1.10 ------------------------------------------------------------------------------------------------------------------------------------ 8 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG +0.00, +2.20 ------------------------------------------------------------------------------------------------------------------------------------ 9 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG +0.00, -1.10 ------------------------------------------------------------------------------------------------------------------------------------ 10 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG +0.00, -2.20 ------------------------------------------------------------------------------------------------------------------------------------ 11 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG +1.10, +2.20 ------------------------------------------------------------------------------------------------------------------------------------ 12 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG +1.10, +0.00 ------------------------------------------------------------------------------------------------------------------------------------ 5979( 12) - 09/21/95 11:14 - [ 6] Visit: 02 Visit Requirements: SAME ORIENT AS 1 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 0957+561B WFPC2 IMAGE WF3-FIX F814W CR-SPLIT=NO 1 900S POS TARG +2.20, +2.20 ------------------------------------------------------------------------------------------------------------------------------------ 2 0957+561B WFPC2 IMAGE WF3-FIX F814W CR-SPLIT=NO 1 900S POS TARG +2.20, 0.00 ------------------------------------------------------------------------------------------------------------------------------------ 3 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG +2.20, -1.10 ------------------------------------------------------------------------------------------------------------------------------------ 4 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG +2.20, -2.20 ------------------------------------------------------------------------------------------------------------------------------------ 5 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG +2.20, +1.10 ------------------------------------------------------------------------------------------------------------------------------------ 6 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG -1.10, +0.00 ------------------------------------------------------------------------------------------------------------------------------------ 7 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG -1.10, +1.10 ------------------------------------------------------------------------------------------------------------------------------------ 8 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG -1.10, +2.20 ------------------------------------------------------------------------------------------------------------------------------------ 9 0957+561B WFPC2 IMAGE WF3-FIX F555W CR-SPLIT=NO 1 2300S POS TARG -1.10, -1.10 ------------------------------------------------------------------------------------------------------------------------------------ 5979( 12) - 09/21/95 11:14 - [ 7] Summary Form for Proposal 5979 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Quasars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 305D to 325D GROUP 1-2 WITHIN 21D POS TARG +1.10, +1.10 POS TARG +0.00, +0.00 POS TARG +0.00, +1.10 POS TARG +0.00, +2.20 POS TARG +0.00, -1.10 POS TARG +0.00, -2.20 POS TARG +1.10, +2.20 POS TARG +1.10, +0.00 SAME ORIENT AS 1 POS TARG +2.20, +2.20 POS TARG +2.20, 0.00 POS TARG +2.20, -1.10 POS TARG +2.20, -2.20 POS TARG +2.20, +1.10 POS TARG -1.10, +0.00 POS TARG -1.10, +1.10 POS TARG -1.10, +2.20 POS TARG -1.10, -1.10 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names 0957+561B ------------------------------------------------------------------------------------------------------------------------------------