Spectrometer Wavelength Calibration Report

1. FM ILT Spectrometer Wavelength Calibration Status ReportH. Feuchtgruber Wavelength Calibration

2. 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): • - CH3OH: [70.511638, 77.405660, 96.522408, 118.834107, • 163.03352, 170.57637] x 5 chopper angles; • - 13CH3OH: [115.82324, 203.63577] x 5 chopper angles; • - CH318OH: [134.6+-0.1, 162.647, 219.801] x 5 chopper angles; • - Gas cell measurements (with Kapton foil) : • - H2O: (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 Wavelength Calibration

3. 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 Wavelength Calibration

4. 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 Wavelength Calibration

5. Gas Absorption Setup • Focus window • Extended and controlled background source • Source T=600°C (H2O) and T=400°C (CO) • Absorption path ~56cm • p= 9mBar (H2O) and p=70mBar (CO) • Scan parameters • - Range: 32000-1064000 • - Stepsize: 200 • - Readouts per ramp: 64 • - Readouts per position: 3 Wavelength Calibration

6. Calibration Method (1) =; ==0.6253; gLHe=117.175µm; n=[1,2,3] ; pix=[1..16]  = 0+ (p1-1)*(gratpos/dgrat) + p2*(gratpos/dgrat)2 + p3*(gratpos/dgrat)3 with dgrat = 23301 [steps/] δpixn = mean[δpixn,FILT1(module)] Wavelength Calibration

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

8. Results • A semi-automatic method to calibrate each pixel in each array has been developed • λ-calibration 3rd 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 (2nd 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  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 Wavelength Calibration

9. Data Quality (1) single pixel Typical data used during correlation analysis Wavelength Calibration

10. Data Quality (2) single pixel rebinned module Wavelength Calibration

11. 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 Wavelength Calibration

12. Remarks • Depth of grating scans (normalized to line scan AOT):3rd order (2.5h), 2nd’ order (2.5h), • 2nd order (2.8h),1st order (3.6h); • (time1st= 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/m2 Wavelength Calibration

13. Expected Line centers and slit widths overplotted Verification with Laser Lines Wavelength Calibration

14. 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 Wavelength Calibration

15. 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(H2O), Neptune(H2O, CO), Saturn(H2O, NH3, PH3) • Jupiter (H2O, NH3, PH3 ; fills entire 5x5 field of view !) Wavelength Calibration

16. Wavelength Calibration in Flight (2) • Target Visibilities in their 1st two windows (HSPOT): Start PV Start Routine Ops Mars 18-Aug-09 – 9-Dec-09 Wavelength Calibration