8135( 3) - 09/25/01 12:00 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8135 Version: 3 Check-in Date: 10-Feb-1999 14:09:01 1.Proposal Title: Spectroscopy of Gravitational Lens Candidates from the HST Survey of BL Lac Objects ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Riccardo Scarpa European Southern Observatory - Chile CoI: Dr. C. Megan Urry Space Telescope Science Institute N CoI: Dr. Rachel L. Webster University of Melbourne N CoI: Mr Matthew O'Dowd University of Melbourne N CoI: Dr. Renato Falomo Padova Observatory N CoI: Dr. Aldo Treves Milan University N ------------------------------------------------------------------------------------ 5. Abstract We propose spectroscopic observations of two new gravitational lens candidates, 0502+675 and 1440+122, discovered in our HST R-band snapshot survey of ~100 BL Lac objects. Each contains a double point source with separation of only 0.3 arcsec. In each case, a candidate for the lensing galaxy is also found. For 0502+675, a subsequent NICMOS H-band image shows that the two point sources have similar R-H colors. STIS long-slit spectra of each point source will determine whether these candidates are lenses and also measure the redshift of the possible lensing galaxy. Due to the small image separation, HST spatial resolution is essential. These two sources, if confirmed as lenses, are particularly valuable for estimating H_0 because of the large amplitude and rapid flux variability that characterize BL Lac objects. ------------------------------------------------------------------------------------ 8135( 3) - 09/25/01 12:00 - [ 2] Observations Description ------------------------ Target Properties beginitemize em 0502+675: two point sources separated by 0.3 arcsec, with magnitudes V=17.9 mag and V=19.4 mag. Orienting the slit at P.A. 30^degrees, a single telescope pointing is sufficient to obtain the spectrum of both components. em 1440+122: two large galaxies with similar luminosity (V~ 17.5 mag) separated by 2.53 arcsec; one point source centered in galaxy ``A'', with V=17.3 mag; a second point source 0.29 arcsec to the east, with V=20.1 mag. Orienting the slit at P.A. 260^degrees, all 4 will be observed at once. enditemize Instrument Set-Up We propose STIS low resolution spectroscopy over a broad wavelength range, using the CCD, first-order gratings G750L and G430L, and the 52X0.2 aperture. The broad wavelength range is needed to increase the probability of detecting multiple spectral features. The G750L and G430L gratings, spanning 3500--10200 Angstrom, with spectral resolution of 4.9 and 2.7Angstrom/pixel, respectively, are sufficient for dete cting the most common features obs erved in BL Lac spectra, including HAlpha and OIII (Scarpa & Falomo 1997, Stocke & Rector 1997). In addition, if either source is located behind the galaxy, an absorption feature due to the foreground galaxy might be observed. To reliably identify spectral features, we also need a signal-to- noise ratio of at least 10 for the faintest component, V~ 20 in both cases. The 52X0.2 arcsec slit was selected as the optimal compromise between throughput and spectral resolution. With this combination of slit and grating, the FWHM of the point-source spectrum is ~lt 2 pixels (or ~ 0.01 arcsec), much smaller than the binary separation. Required Orbits. For a point source with V=20 mag and power low spectrum appropriate for a BL Lac, the required exposure time to achieve a signal-to- noise ratio of 10 with grating G750L at 7500 Angstrom, where the sensitivity is close to the maximum, is ~ 1000 sec according to the STIS exposure time calculator. To ensure S/N~gt 10 in the whole range from 5400 to 9500 Angstrom, the re q uired exposure time is ~ 2000 sec. Similarly, an exposure time of ~ 2000 sec is required to achieve S/N=10 at 4000Angstrom\ with grating G430L. The overhead for guide star acquisition and target acquisition for a point source of V~18 mag (the brightest of the two components) is ~ 9+8=17 min. At the declination of our targets, the orbit durations are 57 and 52 minutes for 0502+675 and 1440+122, respectively. Hence, the required possible exposure times require two orbits per source, for a total request of 4 orbits. Real Time Justification ----------------------- A specific telescope roll angle is required in order to properly orient the spectrograph slit, as specified above. A contemporaneous flat field will be needed to remove fringes. We are proposing VLA observations of both lenses. Existing VLA observations of 1440+122 (Perlman et al. 1994) had insufficient resolution (~1-2 arcsec). Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8135( 3) - 09/25/01 12:00 - [ 3] Data Distribution Paper Products: YES Media: DAT Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8135( 3) - 09/25/01 12:00 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 0502+675 GALAXY, BL LAC RA=05H 7M 56.254S +/- 0.1", J2000 V = 19.4+/-1 DEC=67D 37' 24.33" +/- 0.1" 2 1440+122 GALAXY, BL LAC, RA=14H 42M 48.351S +/- 0.1", J2000 V = 20.1+/-0.5 INTERACTING GALAXY, DEC=12D 0' 40.50" +/- 0.1" GRAVITATIONAL LENS 8135( 3) - 09/25/01 12:00 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 65D TO 71D ORIENT 245D TO 251D 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 0502+675 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 5 S ONBOARD ACQ FOR 30, 40 CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 0502+675 STIS/C ACQ/PEA 52X0.2 MIRROR 1 5 S ONBOARD ACQ FOR 30, 40 CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 0502+675 STIS/C ACCUM 52X0.2 G750L 7751 CR-SPLIT=3,GAIN=1 1 32 M CD ------------------------------------------------------------------------------------------------------------------------------------ 40 CCDFLAT STIS/C ACCUM 52X0.2 G750L 7751 2 DEF CD ------------------------------------------------------------------------------------------------------------------------------------ 50 0502+675 STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=4,GAIN=1 1 50 M SAME POS AS 30 CD ------------------------------------------------------------------------------------------------------------------------------------ 8135( 3) - 09/25/01 12:00 - [ 6] Visit: 02 Visit Priority: Visit Requirements: ORIENT 127.1D TO 127.1D ORIENT 307.1D TO 307.1D 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 1440+122 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 5 S ONBOARD ACQ FOR 30 CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 1440+122 STIS/C ACQ/PEA 52X0.2 MIRROR 1 5 S ONBOARD ACQ FOR 30 CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 1440+122 STIS/C ACCUM 52X0.2 G750L 7751 CR-SPLIT=3,GAIN=1 1 28 M CD ------------------------------------------------------------------------------------------------------------------------------------ 40 CCDFLAT STIS/C ACCUM 52X0.2 G750L 7751 2 DEF CD ------------------------------------------------------------------------------------------------------------------------------------ 50 1440+122 STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=3,GAIN=1 1 48 M SAME POS AS 30 CD ------------------------------------------------------------------------------------------------------------------------------------ 8135( 3) - 09/25/01 12:00 - [ 7] Summary Form for Proposal 8135 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT GAIN=1 CR-SPLIT=4 CR-SPLIT=3 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 65D TO 71D ORIENT 245D TO 251D ONBOARD ACQ FOR 30, 40 SAME POS AS 30 ORIENT 127.1D TO 127.1D ORIENT 307.1D TO 307.1D ONBOARD ACQ FOR 30 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G750L G430L ------------------------------------------------------------------------------------------------------------------------------------ Target Names 0502+675 CCDFLAT 1440+122 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 7751 4300 ------------------------------------------------------------------------------------------------------------------------------------