7332( 7) - 12/21/98 17:48 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7332 Version: 7 Check-in Date: 21-Dec-1998 17:47:47 1.Proposal Title: Improved Hubble Constant from the 0957+561 Gravitational Lens ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Gary Bernstein University of Michigan CoI: Phillippe Fischer University of Michigan N CoI: J. Anthony Tyson Lucent Technologies Bell Labs N CoI: George Rhee University of Nevada, Las Vegas N ------------------------------------------------------------------------------------ 5. Abstract We propose to image the gravitational lens system 0957+561 at least 1 mag deeper than previous HST data in order to detect more faint lensed structures. Previous WFPC2 imaging revealed two faint galaxies which appear to be lensed images of each other, plus a faint extended arc. The deeper image will permit more accurate reconstruction of the mass distribution in the lens. Because an accurate time delay is known for this lens, a better mass model translates directly to improved accuracy in the determination of the Hubble constant. With a deeper image, we should: (1) find the counter-images to the arc; (2) observe structure in the known lensed galaxy pair, thus determining the full relative magnification matrix between them; (3) likely detect at least one other multiply- imaged background galaxy; (4) better measure the positions of the existing features. The resulting extra constraints on the lens optics will give unprecedented accuracy in our knowledge of the dark matter distribution in the lens, and sho uld allow an H_0 determination to 10--15\ the STIS imager, this will only require 11 CVZ orbits. ------------------------------------------------------------------------------------ 7332( 7) - 12/21/98 17:48 - [ 2] Observations Description ------------------------ In order to calculate the exposure times we have used our cycle 5 WFPC2 data as a guide. We obtained 39000s in F555W on the Q0957+561 field which gave us a surface brightness noise of 26.0 V mag arcsec^-2 RMS on WFC pixels. The goal of the proposed observations is to achieve a surface brightness noise 2.5 times fainter on STIS pixels. To obtain the reduced noise with our original WFC setup would require a factor of 6.25 longer integration time. An additional factor of 4 is required to get to this noise level per STIS pixel, so at equal throughput we would require 25* more exposure time. According to the STIS manual, STIS+50CCD reaches 1.5 mag deeper than does the WFPC2+F555W (per PSF area) in equivalent integration time. This implies throughput greater by 3 mag, or a factor of 16. We will gain another factor of 2 in integration time over the WFPC2 observations by improving the PSF subtraction (see below). Therefore the total required exposure time is: 39, ksec * 25 * 1/1 6 * 1/2 = 30.5, ksec, which shoul d be broken up into 34 distinct 15 minute exposures. Our field is in the CVZ so we can observe 96 minutes per orbit. Therefore, we require 6 CVZ orbits (including overhead - dithers, readouts, etc.) to reach our limiting surface brightness in 50CCD. Additionally we require 4 orbits with F28X50LP. This image will have a limiting surface brightness 0.6 mag brighter than the 50CCD image and will provide rough color information for all but the faintest objects. The color information will aid in the identification of mutiply imaged galaxies. Therefore we require 10 orbits for our primary target. Because the lensed galaxies we are interested in are buried in the PSF wings of the A and B QSO images, we need to employ PSF subtraction in order to measure their properties. For our current data we are subtracting the A QSO image from the B image. This does a good job of removing the QSO images (see Figure 1), however, it leads to an increase in background noise of sqrt2. Additionally, faint galaxies near one quasar in t erfere with the view of galaxies near the other quasar. To combat this, and effectively double our integration time, we require 1 orbit to take multiple dithered short exposures of a nearby bright star for PSF subtraction of the QSO images. Therefore we require a total of 11 CVZ orbits. Real Time Justification ----------------------- Q0957+561 lies within the CVZ. The project is ideally suited to gain the doubled productivity from the CVZ because guide star reacquisition is needed only after passage through the South Atlantic Anomaly. The Call for Proposals shows two CVZ opportunities each more than twice the duration of our longest visit (8 orbits), placing us in the ``heart'' of the CVZ. Because the orbits are divided into 15 minute exposures, we will be able to de-weight those portions of the orbits with high background level. The goal of this HST proposal is to image deeply the strongly lensed regime (central $\approx10\arcsec$ radius) in Q0957+561 in order to find lensed galaxy pairs and thus provide more constraints on the small scale lens mass distribution. As discussed in the above Scientific Justification, this is insensitive to the slowly varying mass distribution of the underlying cluster. This must be contrained independently to determine $H_0$. We have carried out a weak lening study of the cluster (Fischer et al 1996) w hich contrains the cluster mass density at the 30% level (contributes 20% to the uncertainty in H$_0$). Pending are further deeper ground-based observations with the CFHT with the goal of reducing this uncertainty by up to a factor of two. The combination of the new weak lensing data and the new STIS data should yield H$_0$ with uncertainty in the range 10-15%. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7332( 7) - 12/21/98 17:48 - [ 3] Data Distribution Paper Products: Media: DAT Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7332( 7) - 12/21/98 17:48 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 0957+561 GALAXY, GRAVITATIONAL RA=10H 1M 20.93S +/- 1", DEC=55D J2000 Z = .355 V = 16+/-0.5 LENS, QUASAR, 53' 49.34" +/- 1" ELLIPTICAL 2 STAR STAR, UNDESIGNATED RA=8H 52M 34.13S +/- 1", DEC=-0D J2000 Z = .355 V = 9.17+/-0.5 39' 48.96" +/- 1" 7332( 7) - 12/21/98 17:48 - [ 5] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE GROUP 01, 02, 03 WITHIN 30 D ORIENT 138D TO 142D On Hold Comments: Additional Comments: We request that no telescope focuses occur between the three visits. Once visits are scheduled we would like to adjust orientation from nominal to minimize impact of diffraction spikes If possible we would like to utilize visible portions of orbit which are not LOW-SKY. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 0957+561 STIS/C ACCUM 50CCD MIRROR BINAXIS1=1,GAIN=1, 1 13.0 M EXPAND NO SPLIT LOW-SKY CD PATTERN=SPIRAL-DITH,STEP-SIZE=.25 ,NUM-POS=15,CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 7332( 7) - 12/21/98 17:48 - [ 6] Visit: 02 Visit Priority: Visit Requirements: PCS MODE FINE SAME ORIENT AS 01 GROUP 01, 02, 03 WITHIN 30 D On Hold Comments: Additional Comments: Once visits are scheduled we would like to adjust orientation from nominal to minimize impact of diffraction spikes. If possible we would like to utilize visible portions of orbit which are not LOW-SKY. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 0957+561 STIS/C ACCUM 50CCD MIRROR BINAXIS1=1,GAIN=1, 1 13.0 M EXPAND NO SPLIT LOW-SKY CD PATTERN=SPIRAL-DITH,STEP-SIZE=.25 ,NUM-POS=3,CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 20 0957+561 STIS/C ACCUM F28X50L MIRROR BINAXIS1=1,GAIN=1, 1 13.0 M EXPAND NO SPLIT LOW-SKY CD P PATTERN=SPIRAL-DITH,STEP-SIZE=.25 ,NUM-POS=12,CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 7332( 7) - 12/21/98 17:48 - [ 7] Visit: 03 Visit Priority: Visit Requirements: PCS MODE FINE GROUP 01, 02, 03 WITHIN 30 D 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 STAR STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO,GAIN=4 2 0.1 S MAX DUR CD ------------------------------------------------------------------------------------------------------------------------------------ 20 STAR STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO,GAIN=4 2 20 S MAX DUR CD ------------------------------------------------------------------------------------------------------------------------------------ 21 STAR STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO,GAIN=4,PATTERN=BOX, 1 20 S MAX DUR CD NUM-POS=4,SCALING-FACTOR=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 22 STAR STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO,GAIN=4,PATTERN=BOX, 1 2 S MAX DUR CD NUM-POS=4,SCALING-FACTOR=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 23 STAR STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO,GAIN=4,PATTERN=BOX, 1 20 S MAX DUR CD NUM-POS=4,SCALING-FACTOR=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 30 STAR STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO,GAIN=4 2 2.0 S MAX DUR CD ------------------------------------------------------------------------------------------------------------------------------------ 31 STAR STIS/C ACCUM F28X50L MIRROR CR-SPLIT=NO,GAIN=4 2 0.3 S MAX DUR CD P ------------------------------------------------------------------------------------------------------------------------------------ 32 STAR STIS/C ACCUM F28X50L MIRROR CR-SPLIT=NO,GAIN=4 2 5 S MAX DUR CD P ------------------------------------------------------------------------------------------------------------------------------------ 42 STAR STIS/C ACCUM F28X50L MIRROR CR-SPLIT=NO,GAIN=4,PATTERN=BOX, 1 5 S MAX DUR CD P NUM-POS=4,SCALING-FACTOR=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 7332( 7) - 12/21/98 17:48 - [ 8] Summary Form for Proposal 7332 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BINAXIS1=1 GAIN=1 PATTERN=SPIRAL-DITH STEP-SIZE=.25 NUM-POS=15 CR-SPLIT=NO NUM-POS=3 NUM-POS=12 GAIN=4 SCALING-FACTOR=0.5 NUM-POS=4 PATTERN=BOX ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE GROUP 01, 02, 03 WITHIN 30 D ORIENT 138D TO 142D EXPAND NO SPLIT LOW-SKY PCS MODE FINE SAME ORIENT AS 01 GROUP 01, 02, 03 WITHIN 30 D PCS MODE FINE GROUP 01, 02, 03 WITHIN 30 D MAX DUR ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names 0957+561 STAR ------------------------------------------------------------------------------------------------------------------------------------