5939( 7) - 03/14/96 14:19 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5939 Version: 7 Check-in Date: 14-Mar-1996 13:53:26 1.Proposal Title: Evolution in the Isotropic Properties of BL Lac Objects ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle AGN GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: C. Megan Urry Space Telescope Science Institute CoI: Riccardo Scarpa Osservatorio Astronomico di Padova N CoI: Aldo Treves SISSA/ISAS N CoI: Joseph E. Pesce Space Telescope Science Institute Y CoI: Renato Falomo Osservatorio Astronomico di Padova N CoI: Mauro Giavalisco Space Telescope Science Institute N CoI: Rita M. Sambruna Space Telescope Science Institute N ------------------------------------------------------------------------------------ 6. Abstract Although high quality imaging of a few local BL Lac objects shows they are in giant elliptical galaxies, nothing is known about host galaxies at higher redshifts. Similarly, nearby BL Lac objects appear to be in rich clusters of galaxies but little is known about the evolution of these environments. Some nearby BL Lacs have close companions (r~<2''), possibly indicating that interactions are important the BL Lac phenomenon. There is disagreement about whether local z<0.3 and distant (z>0.5) BL Lac objects are the same thing or the latter are more closely related to quasars. The host galaxies and environments of local objects support the idea that BL Lacs are aligned versions of low-luminosity (FRI) radio galaxies, the so-called ``unified scheme,'' but as FRIs are only observed locally the extension of this scheme to higher redshift is unclear. We propose to study the host galaxies and environments of four radio-selected BL Lac objects from a well-defined, complete sample at high redshift (0.5 < z < 1), to measure evolution in the isotropic properties of BL Lac objects and to determine whether the low- and high-redshift BL Lacs are similar or are distinct classes. No comparable HST data exist or are planned for any BL Lac objects. ------------------------------------------------------------------------------------ 5939( 7) - 03/14/96 14:19 - [ 2] Observations Description ------------------------ We propose WFPC2 images in one filter, F814w (which corresponds approximately to V at the median sample redshift). We will obtain several short exposures to get the central point source without saturating the detector, and several medium and long ones to get the galaxy fuzz. The medium exposure is calculated to, at most (depending on the variability of the point source), saturate the central pixel. The longer exposure should, at most, cause the first pixel to bleed. We will rotate the telescope between sets of exposures (short, medium, long, roll, short, medium, long. It is imperative that for each target the 2 visits are in consecutive orbits. The point source will be centered in the PC to get the best resolution in the inner part of the galaxy; the WF chips will give the environments (0.5-0.6 Mpc projected distance from the BL Lac object). Our integration times should be more than sufficient to get a S/N ratio of 3 at the 24 mag/arcsec^2 isophote, which is sufficient to determine the host galaxy properties. The filter chosen is frequently used; no special calibration exposures are required but PSF monitoring in this filter would greatly enhance our program. Real Time Justification ----------------------- We have no special scheduling requirements. Calibration Justification ------------------------- We have no special calibration requirments. PSF monitoring in the PC with the F814W filter would help us better subtract the nuclear point source, which is expected to be the limiting factor in detecting the host galaxy. Additional Comments ------------------- We require the spacecraft to roll between sets of observations (one set of short exposure, medium exposure, and long exposure per orbit). It is imperative that for each target the two visits are sequential, in consecutive orbits with nothing intervening but the roll. ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: *Joe Pesce*STSCI*3700 San Martin Drive*Baltimore, MD. 21218 Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5939( 7) - 03/14/96 14:19 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 QSO0828+493 GALAXY,BL Lac RA=08H 32M 23.2S +/- 0.5S, J2000 Z = V = 18.5+/-1.0 DEC=+49D 13' 21.0" +/- 0.5" 0.548 2 PKS1538+149 GALAXY,BL Lac RA=15H 40M 49.5S +/- 0.5S, J2000 Z = V = 17.1+/-1.3 DEC=+14D 47' 45.9" +/- 0.5" 0.605 3 QSO1823+568 GALAXY,BL Lac RA=18H 24M 07.1S +/- 0.5S, J2000 Z = V = 18.4+/-1.0 DEC=+56D 51' 01.5" +/- 0.5" 0.664 4 QSO1308+326 GALAXY,BL Lac RA=13H 10M 28.7S +/- 0.5S, J2000 Z = V = 19.0+/-4.0 DEC=+32D 20' 43.8" +/- 0.5" 0.997 5939( 7) - 03/14/96 14:19 - [ 4] Visit: 01 Visit Requirements: SEQ 1-2 WITHIN 100M On Hold Comments: Additional Comments: Visits 1 and 2 MUST be consecutive Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 QSO0828+493 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 30S SEQuence 1-6 NON-INTerruptible SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 2 QSO0828+493 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 30S SAME POSition AS 1; SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 3 QSO0828+493 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 300S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 4 QSO0828+493 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 300S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 5 QSO0828+493 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 600S SAME POSition AS 1; SPLIT=NO Comments: target will be saturated ------------------------------------------------------------------------------------------------------------------------------------ 6 QSO0828+493 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 537S SAME POSition AS 1; END ORBIT; EXPAND; SPLIT=NO MAXimum DURation 1200S; Comments: target will be saturated. This is ok. ------------------------------------------------------------------------------------------------------------------------------------ 5939( 7) - 03/14/96 14:19 - [ 5] Visit: 02 Visit Requirements: ORIENTation 20D TO 20.5D FROM 1; On Hold Comments: Additional Comments: Visits 1 and 2 MUST be consecutive Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 QSO0828+493 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 30S SEQuence 1-6 NON-INTerruptible SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 2 QSO0828+493 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 30S SAME POSition AS 1; SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 3 QSO0828+493 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 300S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 4 QSO0828+493 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 300S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 5 QSO0828+493 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 600S SAME POSition AS 1; SPLIT=NO Comments: target will be saturated ------------------------------------------------------------------------------------------------------------------------------------ 6 QSO0828+493 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 537S SAME POSition AS 1; END ORBIT; EXPAND; SPLIT=NO MAXimum DURation 1200S; Comments: target will be saturated. This is ok. ------------------------------------------------------------------------------------------------------------------------------------ 5939( 7) - 03/14/96 14:19 - [ 6] Visit: 03 Visit Requirements: SEQ 3-4 WITHIN 100M On Hold Comments: Additional Comments: Visits 3 and 4 MUST be consecutive Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 10S SEQuence 1-8 NON-INTerruptible SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 2 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 10S SAME POSition AS 1; SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 3 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 50S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 4 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 50S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 5 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 50S SAME POSition AS 1; SPLIT=NO Comments: target will be saturated ------------------------------------------------------------------------------------------------------------------------------------ 6 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 400S SAME POSition AS 1; EXPAND; SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 7 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 400S SAME POSition AS 1; SPLIT=NO Comments: target will be saturated. This is ok. ------------------------------------------------------------------------------------------------------------------------------------ 8 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 400S SAME POSition AS 1; END ORBIT; EXPAND; SPLIT=NO MAXimum DURation 1200S; Comments: target will be saturated. This is ok. ------------------------------------------------------------------------------------------------------------------------------------ 5939( 7) - 03/14/96 14:19 - [ 7] Visit: 04 Visit Requirements: ORIENTation 20D TO 20.5D FROM 3; On Hold Comments: Additional Comments: Visits 3 and 4 MUST be consecutive Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 10S SEQuence 1-8 NON-INTerruptible SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 2 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 10S SAME POSition AS 1; SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 3 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 50S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 4 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 50S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 5 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 50S SAME POSition AS 1; SPLIT=NO Comments: target will be saturated ------------------------------------------------------------------------------------------------------------------------------------ 6 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 400S SAME POSition AS 1; SPLIT=NO Comments: target will be saturated. This is OK. ------------------------------------------------------------------------------------------------------------------------------------ 7 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 400S SAME POSition AS 1; SPLIT=NO Comments: target will be saturated. This is OK. ------------------------------------------------------------------------------------------------------------------------------------ 8 PKS1538+149 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 400S SAME POSition AS 1; END ORBIT; EXPAND; SPLIT=NO MAXimum DURation 1200S; Comments: target will be saturated. This is ok. ------------------------------------------------------------------------------------------------------------------------------------ 5939( 7) - 03/14/96 14:19 - [ 8] Visit: 05 Visit Requirements: SEQ 5-6 WITHIN 100M On Hold Comments: Additional Comments: Visits 5 and 6 MUST be consecutive Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 QSO1823+568 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 30S SEQuence 1-6 NON-INTerruptible SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 2 QSO1823+568 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 30S SAME POSition AS 1; SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 3 QSO1823+568 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 250S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 4 QSO1823+568 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 250S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 5 QSO1823+568 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 600S SAME POSition AS 1; SPLIT=NO Comments: target will be saturated ------------------------------------------------------------------------------------------------------------------------------------ 6 QSO1823+568 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 552S SAME POSition AS 1; END ORBIT; EXPAND; SPLIT=NO MAXimum DURation 1200S; Comments: target will be saturated. This is ok. ------------------------------------------------------------------------------------------------------------------------------------ 5939( 7) - 03/14/96 14:19 - [ 9] Visit: 06 Visit Requirements: ORIENTation 20D TO 20.5D FROM 5; On Hold Comments: Additional Comments: Visits 5 and 6 MUST be consecutive Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 QSO1823+568 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 30S SEQuence 1-6 NON-INTerruptible SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 2 QSO1823+568 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 30S SAME POSition AS 1; SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 3 QSO1823+568 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 250S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 4 QSO1823+568 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 250S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 5 QSO1823+568 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 600S SAME POSition AS 1; SPLIT=NO Comments: target will be saturated ------------------------------------------------------------------------------------------------------------------------------------ 6 QSO1823+568 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 552S SAME POSition AS 1; END ORBIT; EXPAND; SPLIT=NO MAXimum DURation 1200S; Comments: target will be saturated. This is ok. ------------------------------------------------------------------------------------------------------------------------------------ 5939( 7) - 03/14/96 14:19 - [ 10] Visit: 07 Visit Requirements: SEQ 7-8 WITHIN 100M On Hold Comments: Additional Comments: Visits 7 and 8 MUST be consecutive Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 QSO1308+326 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 50S SEQuence 1-6 NON-INTerruptible SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 2 QSO1308+326 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 50S SAME POSition AS 1; SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 3 QSO1308+326 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 300S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 4 QSO1308+326 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 300S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 5 QSO1308+326 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 500S SAME POSition AS 1; SPLIT=NO Comments: target will be saturated ------------------------------------------------------------------------------------------------------------------------------------ 6 QSO1308+326 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 492S SAME POSition AS 1; END ORBIT; EXPAND; SPLIT=NO MAXimum DURation 600S; Comments: target will be saturated. This is ok. ------------------------------------------------------------------------------------------------------------------------------------ 5939( 7) - 03/14/96 14:19 - [ 11] Visit: 08 Visit Requirements: ORIENTation 20D TO 20.5D FROM 7; On Hold Comments: Additional Comments: Visits 7 and 8 MUST be consecutive Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 QSO1308+326 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 50S SEQuence 1-6 NON-INTerruptible SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 2 QSO1308+326 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 50S SAME POSition AS 1; SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 3 QSO1308+326 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 300S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 4 QSO1308+326 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 300S SAME POSition AS 1; SPLIT=NO Comments: target may be saturated ------------------------------------------------------------------------------------------------------------------------------------ 5 QSO1308+326 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 500S SAME POSition AS 1; SPLIT=NO Comments: target will be saturated ------------------------------------------------------------------------------------------------------------------------------------ 6 QSO1308+326 WFPC2 IMAGE PC1-FIX F814W 7940 CLOCKS=NO,CR- 1 492S SAME POSition AS 1; END ORBIT; EXPAND; SPLIT=NO MAXimum DURation 600S; Comments: target will be saturated. This is ok. ------------------------------------------------------------------------------------------------------------------------------------ 5939( 7) - 03/14/96 14:19 - [ 12] Summary Form for Proposal 5939 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CLOCKS=NO CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category AGN ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SEQ 1-2 WITHIN 100M SEQuence 1-6 NON-INTerruptible SAME POSition AS 1; SAME POSition AS 1; END ORBIT; EXPAND; MAXimum DURation 1200S; ORIENTation 20D TO 20.5D FROM 1; SEQ 3-4 WITHIN 100M SEQuence 1-8 NON-INTerruptible SAME POSition AS 1; EXPAND; ORIENTation 20D TO 20.5D FROM 3; SEQ 5-6 WITHIN 100M ORIENTation 20D TO 20.5D FROM 5; SEQ 7-8 WITHIN 100M SAME POSition AS 1; END ORBIT; EXPAND; MAXimum DURation 600S; ORIENTation 20D TO 20.5D FROM 7; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names QSO0828+493 PKS1538+149 QSO1823+568 QSO1308+326 ------------------------------------------------------------------------------------------------------------------------------------