8652( 2) - 12/12/00 11:31 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8652 Version: 2 Check-in Date: 06-Mar-2000 12:43:03 1.Proposal Title: Evolution of the Extinction Curve ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Alain Smette NASA Goddard Space Flight Center CoI: Dr. Jean-Francois Claeskens Institut d'Astrophysique et de N Geophysique, ULg CoI: Ph.D. student Christophe Jean Institut d'Astrophysique et de N Geophysique, ULg CoI: Dr. Serge Khmil Institut d'Astrophysique et de N Geophysique, ULg CoI: Prof. Jean Surdej Institut d'Astrophysique et de N Geophysique, ULg ------------------------------------------------------------------------------------ 5. Abstract The extinction curve has been determined precisely in only a few galaxies: the Milky Way (MW), the Large and Small Magellanic clouds (LMC and SMC). It has also been determined towards several starburst galaxies, but its significance then depends on the precise star-gas-dust geometry. There is no general agreement on a model to explain its characteristics; laboratory experiments fail to reproduce the famous 2175Angstrom feature under the conditions of the popular silicate-graphite model. The MW, LMC and SMC extinction curves are generally used to bracket extinction curves in other galaxies. Extinction by dust influences the determination of the Hubble constant from cepheids, of Omega_\mathrm M and Lambda using Type Ia Supernovae or gravitational lenses, of the cosmological density of gas and star formation history and the origin the Cosmic Infrared Background. A larger sample of extinction curves is thus urgently needed. Recently, Jean & Surdej (1998) described a method to recover the extinction curve based on high signal-to-noise, low- resolution spectra of the multiple images of gravitationally lensed quasars. Here, we apply this method to a quadruply imaged quasars in order to recover the extinction curve of a galaxy with redshift close to 0.7. We will also measure the HI column density along each line-of-sight to each component in order to estimate the gas-to-dust ratio. ------------------------------------------------------------------------------------ 8652( 2) - 12/12/00 11:31 - [ 2] Observations Description ------------------------ We propose to obtain high signal-to-noise (after binning), low-resolution PRISM, G430L and G750L slitless spectra of a quadruply imaged quasar in order to recover the extinction curve of the lensing galaxy over a wide spectral range. Since the 4 point sources (plus the lensing galaxy) are located within 3'' from each other, they make an excellent target to exploit the good spatial resolution of the HST. In addition, we would like to determine the extinction curve all the way from the optical to the UV, which is only possible with a space telescope. The choice of these dispersion elements is then natural: the PRISM is the most efficient dispersion element in the UV; G430L and G750L are the low-resolution gratings available in the optical. In order to increase the S/N, the data from G430L and G750L will be binned on chip 2x2. A higher value is risky because of the high cosmic ray rate. The optimal exposure time of individual exposures in order to reach the highest S/N for the STIS CCD in presence of cosmic rays (Smette and Hill 1999, STIS Post-Launch Quick- Look Analysis and SMOV Reports \#60) is close to the 800s obtained by splitting the orbit in 3 exposures. The determination of the total exposure time is constrained by the requirement that data, rebinned further in pixels of ~ 30Angstrom\ reach a S/N ~30 per (rebinned) pixel. Example of a recovered extinction law is shown in Fig reffig:ext.ps. A similar constrain fixes the observing time required for the PRISM observations. Note that the PRISM NUV- MAMA spectrum can be rebinned at will without much loss as the dark count rate is small. Using SIM\_STIS developed at GSFC, we find that one orbit per dispersion element leads to the required S/N for a V = 19.5 object with a power -law typical for a QSO (f_Nu \propto nu^-1.8). RX J0911+0551 is a quadruply imaged QSO (Burud et al. 1998, ApJ 501, L5) with redshift z=2.8 (Bade et al. 1997, A&A 317, L13). The lensing galaxy has been detected and its redshift is estimated between 0.6 and 0.8 from its photometric colors (Burud et al.). Three images form an arc and the smallest angular separation is 0.48''. Differential extinction between 3 components has already been reported (Burud et al.), making this lensed system an excellent candidate to determine the extinction law as well as the unknown lens redshift. There is probably a galaxy cluster close to the lens. The V magnitude of the indivual components range between ~ 18.7 and ~ 20.0 (estimated from Bade et al. and Burud et al.). Thanks also to the sensitivity of the STIS CCD, images will also allow to (i) precisely fix the relative positions of the images and their magnitudes (which allow for an additional check on the flux calibration of the spectra), (ii) reveal the presence of any additional component, (iii) and the morphology of the lensing galaxy. Special orientation is needed to prevent any overlapping of the spectra. The observations will provide in addition the spectra of any (relatively bright) galaxy in the field. Each of the 3 allocated visits follow the same structure: first a 60s image of the field is obtained, which allows to determine the position of the components in the field, and thus allows to fix the zero-point of the wavelength calibration. However, we also need to obtain an image of the slit on the CCD for the same reason. Each orbit will then provide spectra in each of the 3 selected dispersive elements. Each orbit ends by a wavelength calibration. We have selected 2 narrow Position Angles which allow to have the spectra of each of the 4 QSO components and of the lensing galaxy without overlap. The minimal separation between any two spectra is at least 4 pixels. PAs are [18.8, 22.3]. The values of ORIENT are obtained by adding 45D or 225D to these values. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8652( 2) - 12/12/00 11:31 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 RXJ0911+0551 GALAXY, QSO, RA=09H 11M 27.62S +/- 2.", J2000 V = 18.5+/-0.5 GRAVITATIONAL LENS DEC=5D 50' 53.55" +/- 2.", PLATE I = 18.14+/-0.08 -ID=03R7 Coordinate Source: GSC_SURVEY_PLATE 8652( 2) - 12/12/00 11:31 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type STIS-ALONG-SLIT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 1.5 Coordinate_Frame POS-TARG Pattern_Orient 90 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 8652( 2) - 12/12/00 11:31 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 63.8D TO 67.30D ORIENT 243.800D TO 247.300D On Hold Comments: Additional Comments: Spectral observations of the quadruply lensed quasar RXJ0911-0551. I: STIS- NUV-MAMA/PRISM observations. (110) CCD image of the field. 1 CR-SPLIT=NO image totaling 60s is taken. It will be used to precisely know the location of each component (120) Image of the slit on the CCD. The TUNGSTEN LAMP is switched on in order to get an image of a narrow 52x0.1 slit on the CCD. (130) PRISM, NUV-MAMA observations in TIME-TAG mode, which can be useful if the background changes significantly during the observations. The BUFFER- TIME value should not increase the overhead. The F25QTZ filter is preferred in order to have the images at focus, which is necessary to properly extract the spectra, while at the same time reducing the sky background to a level much below the dark counts. (140) Wavelength calibration. The DUMP (of exposure 130) and the WAVECAL should be done in occultation. Aperture 52x0.1 is not accepted by RPS2. II STIS-CCD-G430L observations (210) CCD imag e of the field. (230) G430L, CCD observations in ACCUM mode. The specially allowed 6X6 aperture is preferred in order to decrease the sky background. The observations are split into 3 exposures at different positions along the slit. (240) Wavelength calibration. The DUMP (of exposure 230) and the WAVECAL should be done in occultation. Aperture 52x0.1 is not accepted by RPS2. III STIS-CCD/G750L observations (310) CCD image of the field. (330) G750L, CCD observations in ACCUM mode. The specially allowed 6X6 aperture is preferred in order to decrease the sky background. The observations are split into 3 exposures at different positions along the slit. (340) Wavelength calibration. The DUMP (of exposure 330) and the WAVECAL should be done in occultation. Aperture 52x0.1 is not accepted by RPS2. Additional note: RPS2 requires a fringe flat: however, it makes little sense in slitless of wide slit mode. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 110 RXJ0911+055 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 60 S MAX DUR 60S 1 CD Comments: CCD image of the field. 1 CR-SPLIT=NO image totaling 60s is taken. It will be used to precisely know the location of each component. ------------------------------------------------------------------------------------------------------------------------------------ 120 NONE STIS/C ACCUM 52X0.1 MIRROR CR-SPLIT=NO,LAMP=TUNGSTEN, 1 1 S CD WAVECAL=NO Comments: CCD image of a 52x0.1 slit. The aperture (52x0.1) is not accepted by RPS2. TARGET-NAME = NONE is normally not accepted for a GO proposal. Optional parameter LAMP=TUNGSTEN is not accepted by RPS2 for a GO proposal. ------------------------------------------------------------------------------------------------------------------------------------ 130 RXJ0911+055 STIS/N TIME-TA F25QTZ PRISM 2125 BUFFER-TIME=200 1 2320 S 1 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8652( 2) - 12/12/00 11:31 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 140 WAVE STIS/N ACCUM 52X0.1 PRISM 2125 1 DEF END ORBIT UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 210 RXJ0911+055 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 60 S MAX DUR 60S 1 CD ------------------------------------------------------------------------------------------------------------------------------------ 230 RXJ0911+055 STIS/C ACCUM 6X6 G430L 4300 CR-SPLIT=NO,BINAXIS1=2,BINAXIS2=2 1 670 S PATTERN 1 230 1 CD Comments: 3 exposures at different positions along the slit ------------------------------------------------------------------------------------------------------------------------------------ 240 WAVE STIS/C ACCUM 52X0.1 G430L 4300 1 DEF END ORBIT CD ------------------------------------------------------------------------------------------------------------------------------------ 310 RXJ0911+055 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=NO 1 60 S MAX DUR 60S 1 CD ------------------------------------------------------------------------------------------------------------------------------------ 330 RXJ0911+055 STIS/C ACCUM 6X6 G750L 7751 CR-SPLIT=NO,BINAXIS1=2,BINAXIS2=2 1 670 S PATTERN 1 330 1 CD Comments: 3 exposures at different positions along the slit ------------------------------------------------------------------------------------------------------------------------------------ 340 WAVE STIS/C ACCUM 52X0.1 G750L 7751 1 DEF END ORBIT CD ------------------------------------------------------------------------------------------------------------------------------------ 8652( 2) - 12/12/00 11:31 - [ 7] Summary Form for Proposal 8652 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD 52X0.1 F25QTZ 6X6 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO WAVECAL=NO BUFFER-TIME=200 BINAXIS2=2 BINAXIS1=2 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 63.8D TO 67.30D ORIENT 243.800D TO 247.300D MAX DUR 60S END ORBIT PATTERN 1 230 PATTERN 1 330 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR PRISM G430L G750L ------------------------------------------------------------------------------------------------------------------------------------ Target Names RXJ0911+0551 NONE WAVE ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 2125 4300 7751 ------------------------------------------------------------------------------------------------------------------------------------