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PACS Spectrometer Spatial Calibration plan in PV phase

PACS Spectrometer Spatial Calibration plan in PV phase. A.Contursi D. Lutz and U. Klaas. GOALS. Spec. central pointing (Req. 4.1.1.PCD) ‏. FOV distortion (Req. 4.1.2 PCD) ‏. At module level. As function of chopper position. As function of wavelength. PSF determination (Req. 4.1.3 PCD) ‏.

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PACS Spectrometer Spatial Calibration plan in PV phase

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  1. PACS SpectrometerSpatial Calibration plan in PV phase A.Contursi D. Lutz and U. Klaas

  2. GOALS Spec. central pointing (Req. 4.1.1.PCD)‏ FOV distortion (Req. 4.1.2 PCD)‏ At module level As function of chopper position As function of wavelength PSF determination (Req. 4.1.3 PCD)‏ Ghosts (Req. 4.1.4 PCD)‏ Straylight (Req. 4.1.5 PCD)‏

  3. Spectrometer central pointing This is only a verification of the pointing for the spectrometer. The Herschel pointing is calibrated with PACS bolometer. 9 9 Req. 4.1.1 PCD

  4. Spectrometer central pointing MEASUREMENTS - Chopped 9×9 raster, - Step size= 1/4 of spectrometer pixel step size (2.35” assuming a spectral - pixel size = 9.4”), - Chopper throw = to 1.5’ , - Dwell time on each raster position= 12 s - Fixed grating position (77 and 154 μm), - Point source on Spec virtual aperture (module 12 BLUE), - Duration (XHSPOT)= 0.61 h. ANALYSIS and SIAM UPDATE - 2d Gaussian fit to get peak coordinates - Fed back to SIAM - New measurement to check the update ERRORS and DEPENDNCIES FROM SOLAR ASPECT ANGLES - Repetition on 7 other sources at different solar aspect angles Is this necessary or already done during CP? TOTAL DURATION - 9 measurements = 5.5 h

  5. Spectrometer central pointing SOURCES - No need to be perfectly point source but peak should be clear - Several hundreds Jys

  6. FOV DISTORTION AT Module level Req. 4.1.2 PCD

  7. FOV DISTORTION As function of chopper

  8. FOV DISTORTION As function of wavelength

  9. FOV DISTORTION MEASUREMENTS I - 27x27 chopped raster (as before but larger)‏ - Repeat minimum 5 chopper position, better all (Opt0,+/- Large, +/- Medium, +/- Small)‏ - Fixed grating (77 and 154 µm)‏ - Dwell time =12 sec per raster - Total duration= 18.5 h (26 h)‏ MEASUREMENT II - Chopped scan maps at fixed grating position. - Chop frequency =1 Hz - Chop throw = medium ( larger than the spectrometer FOV). - Scan speed =3”/sec - Off-position while chopping before and after scan map. - Leg length = 1.5', - # legs =31 legs - Leg distance = 3” - Source in the positive beam - Final map size = 1.5”×1.5” (bit larger than raster)‏ - Repeat minimum 5 chopper position, better all - Fixed grating (77 and 154 µm)‏ - Total duration=17.5 h (24.1 h)‏

  10. FOV DISTORTION SOURCES - Several hundreds Jys - If no point sources available, small extended OK but clear peak

  11. PSF CHARACTERIZATION Characterize the PSF profiles Check whether they are nominal at given wavelength Req. 4.1.3 PCD

  12. PSF CHARACTERIZATION MEASUREMENTS I (PSF in each spatial pixel at a given λ)‏ - 27x27 chopped raster (same as FOV distortion)‏ - 1 chopper position - Fixed grating position (77 and 154 µm)‏ - PSF in all pixels - Total duration =3.7 h MEASUREMENTS II (PSF in central module at other λ)‏ - 9×9 chopped raster (same as for pointing)‏ - Dwell time per raster position = 12 s - Raster step size in S/C x and y-direction = 2.5” - Source centered on the raster for the positive beam, - Chop throw = 1.5' - Off-positions while chopping before and after the raster. - Source centered on central module - Mapped area= 22”× 22” arcsec2 (to get at least the first Airy ring in the - diffraction limited case.)‏ - For 5 chopper deflections at 0, ±0.5’, ±1.5’. - Fixed grating positions at 55 / 110 μm and 90 / 180 μm. - Total duration = 1.5 h

  13. PSF CHARACTERIZATION SOURCES - Strictly point like source - Several hundred Jys - Best (and almost unique) candidate : Neptune !!!!!Constraints on observation period !!!! IMPORTANT NOTE If Neptune available in PV (unlikely) FOV distortion measurements give also PSFs measurements. No need to repeat big raster. Only 9x9 rasters needed

  14. SPECTROMETER GHOSTS Large map(s) to check the existence of ghosts. If found, characterize them ~100” Req. 4.1.4 PCD

  15. SPECTROMETER GHOSTS MEASUREMENT I - 50x50 chopped raster (same as FOV distortion)‏ - 1 chopper position - Fixed grating position (77 and 154 µm)‏ - total size = 188” - Large chopper throw - Total duration =14 h Further combinations of chopper deflections and wavelengths will be only implemented, if analysis of the available data sets suggests any dependence on chopper position or wavelength.

  16. SPECTROMETER GHOSTS MEASUREMENT II - Very large scan map - Chopper frequency = 1 Hz - Chopper throw = 3' - Scan speed = 3”/sec - Off-position while chopping before and after the scan map - Leg length = 3' - # legs = 45 - Leg distance = 4” - Source in the positive beam, would give a - Final map size = 3'x3' (~3 times the 27x27 raster size)‏ - Scan map repetition = 8 - Fixed grating position at 77 and 154 µm - Total duration = 8 h The use of the scan was first thought to be more efficient than rasters to observe large areas. This turned out not to be true if measurements are not too long.

  17. SPECTROMETER GHOSTS UNIFYING PSF AND GHOSTS MEASUREMENTS - The scan map is 5 h shorter than the raster. - But since ghosts have to be done on point sources too, we can combine the PSF measurements at chopper = 0 with the ghosts measurements. Instead of having 8+3.7 ~ 12h we would have 14h SOURCES - Strictly Point sources, as isolated as possible and with clean background. - Very bright (1000 Jy) (Neptune still the best candidate!)‏

  18. STRAYLIGHT 5 strips (scan map) around very very bright source (i.e. Jupiter)‏ repeat the same measurement w/o source X = Jupiter movements @ 30 Oct 2009 Req. 4.1.5 PCD

  19. STRAYLIGHT MEASUREMENTS - 5 strips around Jupiter (Jupiter moves ~ 3' per day)‏ - Each strip = unchopped scan maps - Leg length =15' - # legs = 4 - Leg separation = 30” - Scan speed = 3”/sec - Repeat maps twice to disentangle glitch effects and increase S/N. - Point to a clean off-position before after scan. - Strips orientation in TRUE sky coordinates to avoid Jupiter - If e.g.. Jupiter is selected fix grating at prominent line so that instantaneous spectrum of any intensity feature could support origin by Jupiter. - Repeat same types of measurements with Jupiter far away. - Total duration = 19 h Rasters would be too long due to overheads!

  20. CANDIDATES SOURCES PLANETS Best candidates: small and bright! @ 154 µm ~ 250 Jy ~ 600 Jy ~ 1.5e4 Jy ~ 2.5e4 Jy PV

  21. CANDIDATES SOURCES Neptune (best candidate for brightness and size) BUT basically not visible during PV Uranus(good for brightness not for PSF measurements)‏ is visible most of PV. We could use Uranus for all Spectrometer Spatial Calibration measurements but PSFs. We still need other than Uranus sources for the Central Pointing dependency from the solar aspect angle.

  22. CANDIDATES SOURCES Neptune 27x27 raster lasts 3.7 h If we observe where v<0.5”/h Neptune moves ~ 2.3” in the all raster. Start to become significant for PSF. Velocity (arcsec/hour)‏ 0.5”/h Uranus Velocity (arcsec/hour)‏ 0.5”/h Days since 1 May 2009

  23. CANDIDATES SOURCES Planets can be observed as Fixed objects: not advisable for PSF Moving object: tracking must be good reduction could become an issue Point like candidates Not moving objects: reduction much more straightforward They might be not point sources after all. They will be checked with photometer

  24. Proposed strategy SOURCES Use point like candidates for all but PSF and ghosts measurements. (The important requirement is to get the intensity peak)‏ Use Neptune ONLY for PSF and ghosts, as moving target. Since this will be observed after PV at that point in time we might have: 1) gained experience for reduction strategy 2) have s/w available for reduction Type of measurements Since scanning does not seem to be significantly more efficient than rastering, do scanning only when rastering is prohibitive (i.e. Straylight). Try to double some observations with both techniques for exploration purposes (FOV Distortion).

  25. Summary measurements Spec Central Pointing: 9 9x9 rasters , total time = 5.5 h source with good peak FOV distortion: 7 (each chop position) 27x27 rasters , total time = 26 h 5 scan maps, total time = 17.5 h source with good peak PSF and Ghosts: 6 27x27 rasters (all chop but center) total time = 16.2h One 50x50 raster at chop=0, total time 13.2 h 2 9x9 rasters at chop 0 at other λ, total time = 1.5 h Source: Neptune (POST PV !!!) Straylight : 5 scan maps, total time =19h TOTAL SPEC SPATIAL CALIBRATION CAMPAIGN DURATION: ~99 h ( 68 h in PV, 31 h after PV)‏

  26. CONCLUSIONS Time expensive campaign. Raster type data format already known (analysis “should” be straightforward)‏ Scan map never tried. Moreover no such pointing mode is available for spectrometer science data. This means no piece of s/w is available neither. If scan map can be reduced at a desired precision level, we will have the following advantages: 1) have redundant data for the spatial calibration 2) the possibility to introduce this mode for the spectrometer later in the mission.....

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