1. PACS SVR 38/9 Nov 2007 Wavelength Calibration1 FM ILT Spectrometer Wavelength Calibration Status Report H. Feuchtgruber, R. Vavrek

2. PACS SVR 38/9 Nov 2007 Wavelength Calibration2 Overview of Measurements (1) Nov/Dec 2006: FMILT1 - 2 short scans of water vapour cell and few laser lines measured (initial calibration done, report available) Mar 2007: FM ILT2 - Measured FIR-Laser lines [µm] (5 days): - CH 3 OH: [70.511638, 77.405660, 96.522408, 118.834107, 163.03352, 170.57637] x 5 chopper angles; - 13 CH 3 OH: [115.82324, 203.63577] x 5 chopper angles; - CH 3 18 OH: [134.6+-0.1, 162.647, 219.801] x 5 chopper angles; - Gas cell measurements (with Kapton foil) : - H 2 O: (27 hours) One Measurement consists of full scan vapour + full scan vacuum” Filter A (C=[0.1pF(blue), 1pF(red)] x 3 chopper angles Filter B (C=[0.1pF(blue), 0.2pF(red)] x 3 chopper angles - CO: (3 hours) Grating range scan pair: vacuum + CO gas at 1 chopper angle

3. PACS SVR 38/9 Nov 2007 Wavelength Calibration3 Overview of Measurements (2) June 2007: FMILT3 Gas cell measurements (without Kapton foil): - H2O: (9 hours) One Measurement consists of full scan vapour + full scan vacuum Filter A (C=[0.1pF(blue), 1pF(red)] x 1 chopper angle Filter B (C=[0.1pF(blue), 0.2pF(red)] x 1 chopper angle

4. PACS SVR 38/9 Nov 2007 Wavelength Calibration4 FIR Laser Setup TUFIR window Extended, but structured source with substantial contrast Substantial laser power variation (recorded within setup) Scan parameters Range: ~100-120 steps (up&down) Stepsize: 100 Readouts per ramp: 64 Ramps per position: 3

5. PACS SVR 38/9 Nov 2007 Wavelength Calibration5 Gas Absorption Setup Focus window Extended and controlled background source Source T=600°C (H 2 O) and T=400°C (CO) Absorption path ~56cm p= 9mBar (H 2 O) and p=70mBar (CO) Scan parameters - Range: 32000-1064000 - Stepsize: 200 - Readouts per ramp: 64 - Readouts per position: 3

6. PACS SVR 38/9 Nov 2007 Wavelength Calibration6 Calibration Method (1)  =  ;  =  =0.6253; g LHe =117.175µm; n=[1,2,3] ; pix=[1..16]  =  0 + (p 1 -1)*(gratpos/dgrat) + p 2 *(gratpos/dgrat) 2 + p 3 *(gratpos/dgrat) 3 with dgrat = 23301 [steps/  ] δpix n = constant(n); n=[1,2,3,2’]

7. PACS SVR 38/9 Nov 2007 Wavelength Calibration7 Calibration Method (2) Begin with calibration from FILT1 (few lines measured only) Calculate up/down corrected and divided spectra (gas/vacuum) for each pixel: F foreground (λ) + T gas (λ)*F background (λ) Ratio = F foreground (λ) + F background (λ) with F foreground (λ)  (20…50) x F background (λ) Calculate model spectra (at expected PACS spectral resolution) for the wavelength range under investigation and define spectral intervals for correlation analysis Determine λ-calibration offsets for each interval Store 3 rd order polynomial parameters fitted to offsets vs. (gratpos/dgrat) for each pixel  new =  old + polynomial fit Iterate previous steps (at least twice)

8. PACS SVR 38/9 Nov 2007 Wavelength Calibration8 Results A semi-automatic method to calibrate each pixel in each array is now available λ-calibration 3 rd order polynomials for all individual spectrometer pixels have been derived Separate sets of polynomials have been calculated for the 3 main PACS spectrometer bands and the “extra” band (2 nd order via filter A: 54-73µm) CO line positions are compliant with calibration based on water Laser positions largely compliant with calibration, however few single pixels show still some significant deviations  still to be corrected in a case by case analysis Laser lines may show peak-center variations due to actual position of laser spots within the slit. This is the initial uplink calibration for flight

9. PACS SVR 38/9 Nov 2007 Wavelength Calibration9 Data Quality (1) Typical data used during correlation analysis single pixel

10. PACS SVR 38/9 Nov 2007 Wavelength Calibration10 Data Quality (2) single pixel rebinned module

11. PACS SVR 38/9 Nov 2007 Wavelength Calibration11 Accuracies PCD V8.0 (sec. 4.2.1): Required accuracy: “Peak position to within 10-20% of a spectral resolution element” In general the requirement is met throughout all bands however at band borders, due to leakage effects and lower S/N the calibration accuracy (in terms of σ over all pixels) is closer to 20% of a spectral resolution element, while in band centers, σ values even better than 10% are obtained. σ=stdev(all_pixels residual λ-shift vs. model) Absolute verification against Laser and CO lines Relative verification by combining all pixels Be aware: relative position of point sources within slit can have significant effect

12. PACS SVR 38/9 Nov 2007 Wavelength Calibration12 Remarks Depth of grating scans (normalized to line scan AOT):3 rd order (2.5h), 2 nd ’ order (2.5h), 2 nd order (2.8h),1 st order (3.6h); (time1st= 58steps × 0.75sec × 2updown × 3numres × 2vapvac × 25modules / 3600sec ) HDO lines are detected (abundance ~3e-4; partial pressure 2.7e-6 bar) CO spectra show residual lines from water contamination Faintest lines ~3e-18W/m 2 C=1pF C=0.1pF C=0.2pF n=3, 2’ n=1 n=2 Leak models

13. PACS SVR 38/9 Nov 2007 Wavelength Calibration13 Depth of grating scans (normalized to line scan AOT):3 rd order (2.5h), 2 nd ’ order (2.5h), 2 nd order (2.8h),1 st order (3.6h); (time1 st = 58steps × 0.75s × 2updown × 3numres × 2vapvac × 25modules / 3600s) HDO lines are detected (abundance ~3e-4; partial pressure 2.7e-6 bar) CO spectra show residual lines from water contamination Faintest lines ~3e-18W/m 2 Remarks

14. PACS SVR 38/9 Nov 2007 Wavelength Calibration14

15. PACS SVR 38/9 Nov 2007 Wavelength Calibration15 Verification with Laser Lines Expected Line centers and slit widths overplotted

16. PACS SVR 38/9 Nov 2007 Wavelength Calibration16 Next Steps / Open Work Investigate/recalibrate few outlying pixels found during verification against Laser lines. The reason is essentially the poor S/N in the measurements during FM ILT 2. Calibrate –L/+L chopper throws, spot checks indicate that there is no significant change in calibration… Provide Report and Calfiles (version as of this report provided for PACS spectrometer pipeline) Check calibration and eventually recalibrate for FMILT 3 measurements

17. PACS SVR 38/9 Nov 2007 Wavelength Calibration17 Instrumental Profile (1) For more details see report by R. Vavrek

18. PACS SVR 38/9 Nov 2007 Wavelength Calibration18 Instrumental Profile (2)

19. PACS SVR 38/9 Nov 2007 Wavelength Calibration19 Wavelength Calibration in Flight (1) Observing modes: –Use standard SpecRangeScan AOT –Use Wave_Cal mode with pointing request Suitable target list : - PICC-ME-TN-013, ”Use of late type stars for PACS wavelength calibration”, (D. Lutz) -“Photometric and Spectroscopic Calibration of Herschel Instruments with Planets and Satellites”, (Th. Encrenaz, R. Moreno, A. Coustenis) –Uranus(H 2 O), Neptune(H 2 O, CO), Saturn(H 2 O, NH 3, PH 3 ) –Jupiter (H 2 O, NH 3, PH 3 ; fills entire 5x5 field of view !)

20. PACS SVR 38/9 Nov 2007 Wavelength Calibration20 Wavelength Calibration in Flight (2) Start PV Start Routine Ops Target visibilities (HSPOT)