7471( 10) - 08/04/97 09:27 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7471 Version: 10 Check-in Date: 04-Aug-1997 09:26:12 1.Proposal Title: STIS Snapshot Search for UV-bright High Redshift Quasars ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle QUASAR ABSORPTION LIN SNAP 7 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: PROF. DIETER Reimers UNIVERSITY OF HAMBURG CoI: Hans-J. Hagen Hamburger Sternwarte Y CoI: Lutz Wisotzki Hamburger Sternwarte N CoI: Peter Jakobsen Astrophysics Division, ESA/ESTEC N ------------------------------------------------------------------------------------ 6. Abstract We propose to carry out a snapshot survey of 6 new bright (B<18) high redshift (z>2) quasars from the Hamburg Bright Quasar Survey with the aim of probing their far-UV (Lambda1300 -1700) continuum fluxes. Our proposed technique is to use the G140L grating of STIS in a slitless mode, which should allow continuum flux as faint as F_Lambda ~eq 1 * 10^-16erg s^-1 cm^ -2 AA^-1 to be detected in a typical snapshot exposure time of approximately 10 minutes. Our objective is to identify further examples of the extremely rare z>2 quasars whose intrinsic brightness and exceptionally clear lines of sight conspire to make detailed follow-up far-UV absorption line studies feasible with HST and FUSE. Of special interest are the six new bright z>2.9 quasars in our sample which show no signs of strong absorption in their optical spectra, and for which the redshifted HeII Lambda304 line is accessible with HST. ------------------------------------------------------------------------------------ 7471( 10) - 08/04/97 09:27 - [ 2] Observations Description ------------------------ The objective of the proposed observations is to measure the far-UV (Lambda <~ 1700 Angstrom) continuum fluxes of our 6 new high redshift quasars in the hope that several of them will be comparable or exceed HS1700+6416 in brightness (F_Lambda >~ 1 * 10^-15erg s^-1 cm^-2 AA^-1), and that one of the new z>2.9 objects might turn out to be brighter than Q0302-003 and PKS 1935-692 (F_Lambda >~ 2 * 10^-16erg s^-1 cm^-2 AA^-1). The observing strategy we propose is to obtain short `snapshot' exposures of each of our quasars using the STIS far-UV MAMA detector and G140L grating in a `slitless' configuration. The CsI cathode of the STIS far-UV detector has significantly higher quantum efficiency than that of the FOC -- an advantage that still holds with the lowest resolution G140L grating inserted (the low throughput of the STIS prism renders this mode roughly equivalent FOC far-UV objective prism mode). Since we are only interested in a rough measure of the observable far-UV fluxes of the quasars under study, the uncertainty in wavelength calibration associated with working slitless is perfectly acceptable, as is the increased sky background in this mode. Previous experience with the slitless FOC prisms has shown that provided care is taken in measuring the quasar coordinates on the GASP system, targets can be positioned to an accuracy better than 1^ (~40 STIS pixels) through blind `point and shoot' target acquisition. This pointing accuracy corresponds to a wavelength zero point accuracy of DeltaLambda~eq25 Angstrom, which is wholly adequate for our purposes. Although the dispersion of the G140L grating (0.6 Angstrom per pixel - the lowest resolution mode available with STIS) is clearly overkill for the task at hand, provided the SrF_2 blocking filter is employed to suppress the dominant geocoronal Lyman alpha signal, the background signal can be reduced to such low levels that there is essentially no penalty associated with working at this dispersion. With the SrF_2 filter in place, the dominant source of residual background in the far- UV is OI Lambda1304 airglow emission, whose intensity for a typical (non-optimized) solar zenith distance is I_l~eq 2 kR (the zodiacal light signal is negligible at the short wavelengths and f/100 focal ratio of the STIS far-UV channel). This OI background emission yields an FUV- MAMA/G140L/F25SRF2 count rate of ~eq 8 * 10^ -4 counts s^-1 pixel^-1, which exceeds the advertised intrinsic detector background of ~eq 6 * 10^-5 counts s^-1 pixel^-1. The absolute faintest far-UV continuum quasar flux of interest is of order F_Lambda ~eq 1 * 10^-16erg s^-1 cm^-2 AA^-1 (i.e. half the brightness of Q0302-003 and PKS1935-692). This flux provides a signal count rate in the range ~eq 1-3 * 10^-3 counts s^-1 pixel row^-1 in the FUV-MAMA/G140L/F25SRF2 configuration. If we conservatively assume that the dispersed image is spread over ~eq 8 pixels (0.2^ ) perpendicular to the dispersion, the quasar signal needs to be detected on top of a ~3 times higher background signal of ~eq 6 * 10^-3 counts s^-1 pixel row^-1. Hence integrating for a typical snapshot exposure time of ~eq600 s and binning the spectrum over ~eq40 pixel rows (corresponding to the absolute wavelength uncertainty), one expects in this worst case each DeltaLambda~eq25 Angstrom wavelength bin to contain ~eq25-75 quasar counts on top of ~eq150 background counts, i.e. a detection at the S/N~eq1.9-5.0 level per wavelength bin. It is evident that the sensitivity of the proposed observing mode is very well matched to the problem at hand, and that there should be little problem locating and extracting the signals of any unabsorbed quasars from the slitless exposures. The proposed observations require Fine Lock pointing control since gyro-only control would lead to smearing of the dispersed signal on top of the background and too great a loss in sensitivity. We request the standard one year proprietary period for the data. Lastly, we note for completeness that since our highest redshift target is at z=3.15, the necessity for using the SrF_2 blocking filter means that the Lambda = 1150-1300 Angstrom region in which the HeII Lambda304 line resides for 2.8 < z < 3.3 is not directly sampled by our slitless spectra. Nonetheless, since the likelihood of encountering a strong Lyman limit system at low redshift z<~0.5 is rather modest, any quasar that shows a strong flux at lambda~eq1300 Angstrom has a very good chance of also being detectable at lower wavelengths. Real Time Justification ----------------------- None Calibration Justification ------------------------- Additional Comments ------------------- Ground-based slit spectra and redshifts of all our targets have already been obtained. ------------------------------------------------------------------------------------ 7471( 10) - 08/04/97 09:27 - [ 3] Data Distribution Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7471( 10) - 08/04/97 09:27 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HE0340-2612 GALAXY,QSO RA=03H 42M 27.79S +/- 0.07S,DEC= J2000 Z=3.08 V = 16.5 -26D 2' 43.2" +/- 1",PLATE- B-V = 1 ID=027X 2 HS1111+7915 GALAXY,QSO RA=11H 14M 57.72S +/- J2000 Z=3.05 V = 16.9 0.4S,DEC=78D 59' 8.7" +/- B-V = 1. 1",PLATE-ID=02D3 3 HS1140+3508 GALAXY,QSO RA=11H 43M 8.89S +/- J2000 Z=3.13 V = 16.8 0.08S,DEC=34D 52' 22.1" +/- B-V = 0.7 1",PLATE-ID=01PX 4 CSO0118 GALAXY,QSO RA=12H 0M 6.19S +/- J2000 Z=2.98 V = 16.1 0.08S,DEC=31D 26' 30.2" +/- B-V = 0.5 1",PLATE-ID=01TE 5 HS1248+7102 GALAXY,QSO RA=12H 50M 28.87S +/- J2000 Z=2.99 V = 17.3 0.2S,DEC=70D 46' 38.7" +/- B-V = 0.7 1",PLATE-ID=01L4 6 HE2318-1107 GALAXY,QSO RA=23H 21M 28.66S +/- 0.07S,DEC= J2000 Z=2.95 V = 17 -10D 51' 22.3" +/- 1",PLATE- B-V = 0.5 ID=00WQ 7471( 10) - 08/04/97 09:27 - [ 5] Visit: 01 Visit Requirements: PCS MODE FINE 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 HE0340-2612 STIS/F ACCUM F25SRF2 G140L 1425 1 600 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7471( 10) - 08/04/97 09:27 - [ 6] Visit: 02 Visit Requirements: PCS MODE FINE 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 HS1111+7915 STIS/F ACCUM F25SRF2 G140L 1425 1 600 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7471( 10) - 08/04/97 09:27 - [ 7] Visit: 03 Visit Requirements: PCS MODE FINE 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 HS1140+3508 STIS/F ACCUM F25SRF2 G140L 1425 1 600 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7471( 10) - 08/04/97 09:27 - [ 8] Visit: 04 Visit Requirements: PCS MODE FINE 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 CSO0118 STIS/F ACCUM F25SRF2 G140L 1425 1 600 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7471( 10) - 08/04/97 09:27 - [ 9] Visit: 05 Visit Requirements: PCS MODE FINE 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 HS1248+7102 STIS/F ACCUM F25SRF2 G140L 1425 1 600 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7471( 10) - 08/04/97 09:27 - [ 10] Visit: 06 Visit Requirements: PCS MODE FINE 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 HE2318-1107 STIS/F ACCUM F25SRF2 G140L 1425 1 600 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7471( 10) - 08/04/97 09:27 - [ 11] Summary Form for Proposal 7471 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category SNAP ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category QUASAR ABSORPTION LINES ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names HE0340-2612 HS1111+7915 HS1140+3508 CSO0118 HS1248+7102 HE2318-1107 ------------------------------------------------------------------------------------------------------------------------------------