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SPIRE Overview Bernhard Schulz, Nanyao Lu, Kevin Xu, Dave Shupe, Lijun Zhang, Arnie Schwartz

SPIRE Overview Bernhard Schulz, Nanyao Lu, Kevin Xu, Dave Shupe, Lijun Zhang, Arnie Schwartz NASA Herschel Science Center. Dust in our own Galaxy. PACS and SPIRE parallel mode observation of the galactic plane Two colors from two PACS bands and one color from three SPIRE bands. SPIRE ICC.

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SPIRE Overview Bernhard Schulz, Nanyao Lu, Kevin Xu, Dave Shupe, Lijun Zhang, Arnie Schwartz

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  1. SPIRE Overview Bernhard Schulz, Nanyao Lu, Kevin Xu, Dave Shupe, Lijun Zhang, Arnie Schwartz NASA Herschel Science Center

  2. Dust in our own Galaxy • PACS and SPIRE parallel mode observation of the galactic plane • Two colors from two PACS bands and one color from three SPIRE bands. SPIRE ICC

  3. M 81 M82 M81 40’ SPIRE 250/350 D=3.2 Mpc Chris Wilson and the SAG2 Consortium

  4. Beam Steering Mirror Telescope Beam SPIRE Optical Bench Spectrometer Cover Optical Bench Beam Splitter PLW Spectrometer Detector Box PMW Sorption Cooler SLW SSW PSW Optical Sub-bench FTS Mechanism S-Cal Photometer Detector Box Cone Support Photometer Cover The SPIRE Instrument Imaging Fourier Transform Spectrometer Simultaneous imaging observation of the whole spectral band 37 and 19 pixels Wavelength Range: 194-313, 303-671 m Resolution: 0.04, 0.24, 0.83 cm-1 Circular FOV 2.0‘ diameter, beams 17-21”, 29-42” Imaging Photometer Simultaneous observation in 3 bands 139, 88, and 43 pixels Wavelengths: 250, 350, 500 m / ~ 3 FOV 4' x 8', beams 18.1'', 25.2'', 36.6''

  5. SPIRE in the Herschel Focal Plane

  6. Components of the BDA Bolometer Pixels Single Bolometer Pixel Dark Pixel Absorber (Spiderweb) Load Resistors Heat Resistance Thermistor Base Plate

  7. D16 / T1 T1 / T1 A15 / T1 D15 / T1 A14 / T1 D14 / T1 Temperature Drifts PSW array [V] [sec] Most signal drifts come from temperature changes, as shown by the perfect correlation of thermistor pixel T1 and detector signals. The resistor pixel R1 does not vary with temperature. Signal is very stable after correction with thermistor signals (1/f knee < 10mHz).

  8. Feedhorn array 300-mK stage 2-K stage and interface to 2-K box Kevlar suspension Bolometer Detector Array (BDA)

  9. Chop +/- 130” Jiggle +/- 30” FWHM beams on the sky Beam separation  2l/D Beam FWHM l/D Beam Steering Mechanism Includes also PCAL calibration source that illuminates all detectors simultaneously. • Point source photometery • - 7 point jiggle, chop/nod • Spectrometer mapping • - No chop/nod

  10. Photometer

  11. Photometer Sensitivities HSpot provides more specific values depending on parameter selection

  12. Photometer Flux Calibration • Primary calibrator Neptune not available for most of PV. • Neptune model estimated absolute accuracy = ± 5% (correlated over the SPIRE range – i.e., whole spectrum moves up or down) • Current SPIRE pipeline uses interim calibration based on early observations of Ceres. • Current overall accuracy ± 15% • Neptune observations and non-linearity characterisation analysis completed. Pipeline implementation under way. • See SPIRE Observers’ Manual for further details

  13. Beam Profiles • Very close to Gaussian • Modeled and empirical beam profiles available

  14. 250 mm linear log Model (at 6” sampling) Compared to Mars Map Observed Modeled log some saturation in center

  15. A B Ghost as expected F E I J H G Simulated sky map over ~66degx66deg around boresight (log scale) of hot spots/stray paths C D Far Field Beam PSW OD136 • Hot Spot “I” verified with Jupiter in all 3 SPIRE wavelengths and by PACS with 2x2deg map in parallel mode. • PACS found attenuation 5*10-4 • Good and Bad news: Measurement consistent with telescope model • Low probability for Moon to enter, but observers should be wary of other bright sources close to telescope hot spots. Amplitude: ~0.74 (+/-10%) Extent, as fitted FWHM of the long dimension distribution: ~34.9arcmin (+/-10%) Width: ~6.5arcmin (+/-10%)

  16. ~4’ Fully sampled region Overlap region Scan 42.4o 42.4o Scan single step ~ 6” 348” Photometer AOT 7 point jiggle (point source) small map scan (large) map 126” chop + nod Scan map at speeds of 30 and 60 ”/sec is most efficient mode for large-area surveys. Parameters are optimized for full spatial sampling and uniform distribution of integration time. Cross scan capability(84.8o) 7-point jiggle for point source photometry, to compensate pointing error and under-sampling. Chopping and nodding at each jiggle position. Single cross scan at 84.8o replaces Jiggle map. Scan map at speeds of 30 and 60 ”/sec. Full spatial sampling in center of scans.

  17. The SPIRE Photometer in HSpot Sensitivity Repetitions AOT Mode Time Map Size Scan Speed Confusion Noise Offset Orientation

  18. SPIRE Geometry PACS SPIRE Overlap region Overlap region 42.4o 42.4o PACS Geometry Scan Scan 155” orth. 168” nom. 155” orth. 168” nom. Considerable redundancy for SPIRE due to smaller scan distance needed by PACS arrays. Samplerate lowered from 16 to 10Hz. Even field coverage for PACS. Additional frame averaging needed to keep data rate down. Blue array frames are averaged by additional factor two compared to PACS only mode. Parallel Mode SPIRE and PACS • Scan maps at speeds of 20 and 60”/sec with PACS and SPIRE active in parallel are useful for large-area surveys. • The distance between PACS and SPIRE apertures is 21 arcmin. • Two almost orthogonal (84.8o) directions for cross scanning are available.

  19. SPIRE PACS PACS SPIRE ~21’ Parallel Mode SPIRE and PACS

  20. Spectrometer

  21. FTS Optics (simplified) SMEC spectrometer mechanism Telescope input SSW Filter Beam Splitter Beam Splitter Filter SCAL IR source to null telescope background SLW Mach-Zehnder type design broad band intensity beam splitters (200-700mm) two input ports and two output ports no sensitivity to polarisation of incident radiation

  22. FTS Scan Mechanism • Double parallelogram carriage with toothless gear • Moiré fringe position measurement system (0.1 mm accuracy) • Continuous scan ability used • Nominal speed: 0.5 mm s-1 • Signal frequency range 3 - 10 Hz • 3.8-cm travel

  23. High Spectral Resolution Medium Low Optical Path Difference 0 SSW FWHM SLW FWHM SMEC Scans & Spectral Map Coverage Differences in SMEC scan pattern for different spectral resolutions. Sparse Full Intermediate no jiggling 4 point jiggle 16 point jiggle BSM used to increase filling factor (no chopping)

  24. Unapodized Line Profile Ds = 0.04 cm-1 Sinc Function Ds = 0.24 cm-1 Ds = 0.83 cm-1 Spectral Resolution

  25. Spectrometer Sensitivity • In-flight sensitivity is significantly better than pre-launch estimates • Improvement factor of 2 – 3 at present - May get better still as data processing and RSRF characterisation are further improved • Reasons for better sensitivity - Telescope is less emissive - Lower background allows second-port calibrator to be switched off – further reduction in photon noise - Detectors are running slightly colder than assumed - FTS model is complex with a number of uncertainties, so a “pessimism factor” was applied pre-launch

  26. Spectrometer Sensitivities • So far, sensitivities are limited by systematic noise associated with channel fringing and imperfect RSRF removal. • Noise currently integrates down as NReps1/2 for up to ~ 2500 s (~ 20 repeats) in high-res mode, then more slowly. • Better data processing will improve basic sensitivity and allow noise to integrate down. • No change to AOT implementation will be needed, so longer integrations can be scheduled now.

  27. Spectrometer Flux Calibration • Currently: • SSW: 10 – 20% • SLW: ~ 30% • Better for stronger sources • Will improve with better modelling of instrument emission • Default calibration in all channels for extended sources • Point source calibration available for central detectors

  28.  Good agreement in overlap region for point sources - Beamsize difference will affect extended sources  Short-wavelength overlap for cross calibration with PACS 200 mm Overlap Between Bands

  29. MeasuredBroadband FTS Beams SSW D4SLW C3 Beams • Broad-band FWHM for center detectors • SSW D4: 19 ± 1” • SLW C3: 35 ± 1.5”

  30. Overlapping spectrometer arrays projected on the sky Spectrometer AOT example 3 x 3 map Spectral Resolution • High0.04 cm-1 • Medium 0.25 cm-1 • Low 0.83 cm-1 • High & Low 0.04/0.83 cm-1 unvignetted beam Image Sampling • Sparse • Intermediate any combination allowed • Full Pointing Mode • Single Pointing Each color shows the unvignetted beams of the same array for all sampling positions (jiggles) at one raster position. • Raster Pointing

  31. The SPIRE Spectrometer in HSpot Sensitivity Image Sampling Spectral Resolution Pointing Mode Repeats Time

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