- page 1 PACS Phil Appleton on behalf of the NHSC/HSC and the PACS ICC ; especially Bart Vandenbussche and Pierre Royer (KUL Belgium) Instrument Performance and Calibration of the Pacs Spectrometer

- page 2 PACS PACS Spectrometer Integral Field Spectrometer 5x5 pixels 1 pixel = 9.4” FOV 47”x47” Simultaneous Blue (55-98  m) Red (  m) coverage M82 showing IFU scale and example of a simple map GeGa Two (25 x 16) arrays Stressed and un- stressed A GRATING DESIGN PROVIDES THREE ORDERS The PACS grating disperses light from 5 slices of the image using reimaging mirrors

- page 3 PACS Photoconductor Arrays (Spectrometer) 3 CRE Two 25x16 pixel filled arrays Extrinsic photoconductors (Ge:Ga, stressed/unstressed) Integrated cryogenic readout electronics (CRE) Near-background- noise limited performance expected

- page 4 PACS HIPE ONLINE HELP SYSTEM HAS LINKS TO ALL THE MANUALS: There is much on performance here

- page 5 PACS ● Spatial calibration – Implications for chopped measurements & raster step sizes ● Wavelength calibration – Wavelength shift with pointing offset in cross-slit dimension – spectral ranges & leakage ● Flux calibration – Stability, transients – Effects of Pointing Jitter on flux measured in central pixel – Saturation limits ● Achieved Sensitivity Topics Covered Today

- page 6 PACS Spatial Calibration

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- page 9 PACS TELESCOPE BACKGROUND REMOVAL TRICKY

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- page 13 PACS Wavelength Calibration

- page 14 PACS Wavelength calibration 14 Use water vapor lines to provide initial wavelength calibration Neptune in-orbit measurements

- page 15 PACS ● In-orbit measurements of Jupiter, Mars and In-orbit measurements of Jupiter, Mars and late-type stars confirm ground calibration late-type stars confirm ground calibration accurate to ~1/3 rd resolution element co- added spectra ● Wavelength Calibration is updated using observations of Neptune from in flight data ● Spectral resolution as expected Wavelength calibration

- page 16 PACS Spectral distortions in the Cross-slit direction: Case of point line source 9.4 arcsecs 48 arcsecs Central Slit of IFU effect of moving across slit THE 5 x 5 SPAXALS of the PACS IFU

- page 17 PACS Profile shape depends on position in cross-slit direction—best profile when centered in slit

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- page 24 PACS Flux Calibration See also discussion in Section 4.9 of the PACS Observer Manual

- page 25 PACS ● Pipeline 6.0 RC2 uses a nominal absolute response and relative spectral response determined on ground (from Calibration Tree ver. 8 and later includes scale factors and new flat-field; In Pipeline type >print calTree for version.) ● No use of internal calibration block for absolute calibration yet. Work is ongoing to incorporate this. ● In-orbit measurements of flux calibrators (asteroids, Neptune, Uranus, fiducial stars) indicates point source calibration accuracy of 30% absolute, relative in band 10% blue and 20% red (P. Royer: December 2010 Calibration Workshop). Incorporation of internal calibrators will likely reduce to 15-20% absolute when implemented. Flux calibration

- page 26 PACS Flux Calibration

- page 27 PACS Calibration Sources compared with Models - Models Convolved with the PACS-Spec instrumental profile - Primary stellar calibrators: γDra, αTau, Sirius Models from L. Decin, accuracy ~ 5% - Asteroids: model provided for each cal-OBSID by T. Mueller Adapted to time of observation Typical uncertainties 5-10% - Planets: Neptune and Uranus: models from R. Moreno, Model uncertainty 1-2%, absolute uncertainty 5% New Neptune model (v3). Corrected for solid angle, as seen from Herschel at T. Obs

- page 28 PACS Current Status All flux calib. Measurements OBS / Model Calibrators RMS ~ 10% in all bands Reproducibility RMS ~ 6-9% OUTLIERS MAY BE AN EFFECT OF POINTING

- page 29 PACS Sensitivity of Flux Calibration Pointing Drift PACS Spectrometer PSF at 70  m PACS Spectrometer PSF at 150  m

- page 30 PACS Sensitivity to Pointing Monte-Carlo Model PSF 74 m APE 2” → large <0 excursions 1 st nod cycle ~ 6% rms (→ outliers) → av % of Max Flux (Implicitely Included in our calibration!) The Spatial Relative Pointing Error (SRPE) is measure to be around arcsecs (Table 2.4 of the Herschel Obs. Manual

- page 31 PACS Sensitivity to Pointing Monte-Carlo Model PSF 74 m APE 1” → large <0 excursions 1 st nod cycle ~ 1% rms (→ outliers) → av % of Max Flux The ability to reconstruct the correct flux thus depends on the relative pointing error The goal is to get this down to about 1.4

- page 32 PACS Chopping Transient Transient f1('background' flux) f2 (source flux) ON source (f1+f2) → OFF source (Background f1) → Chopping For bright sources corrections are necessary to account for the transient that occurs as you chop “on” the source. For bright sources corrections are necessary to account for the transient that occurs as you chop “on” the source. When you chop on and off a bright source there is evidence of transients. Source takes time to reach maximum When you chop on and off a bright source there is evidence of transients. Source takes time to reach maximum

- page 33 PACS ● Awaiting proper correction, transients in chopping pattern lead to uncertainties when comparing PACS fluxes. Will be corrected in 7.0 builds of HIPE ● In SED scan mode signal varies with relative spectral response → awaiting transient correction, broadband SED shape not reliable. Transients in chopping pattern

- page 34 PACS SED Mode has some issues with continuum shape that is being worked by the Leuven team. OBSERVED AFTER SCALING strong residuals remain MODEL

- page 35 PACS There is some hope! A method is being developed that uses the telescope in the sky position as a “reference” rather than an assumed nominal response plus and RSRF. This method is called the telescope normalization method It requires a good knowledge of the spectrum of the telescope emission

- page 36 PACS Spectrometer Flux Calibration36 Spectral Normalization: Will only work with Chop-Nod Principle S = “Normalized” spectrum. Units [Telescope] T = Tel. Spectrum. Units [Jy] S x T = Spectrum in Jy Implicit instantaneous drifts correction Independent of RSRF Currently not part of the pipeline Research ongoing by Johan Oloffson and Joroen Bouwman in Heidelberg.

- page 37 PACS Herschel Telescope Emission is assumed smooth This is a plot from the Calibration Tree See excellent topics and details on calibration tree and how to plot various cal files like the RSRF etc in: or get to it from our nhscsci.ipac.caltech.edu Key Calibration Hot Topics Links

- page 38 PACS Spectrometer Flux Calibration38 Spectral Normalisation: Example Default reduction Normalisation on Neptune OD389 Normalisation on Neptune OD373

- page 39 PACS Choice of 4 Capacitances Recently PACS Spectrometer automatically chooses one of 4 capacitances to avoid saturation on bright sources (Need very bright sources to trigger this). In HSpot Line Fluxes ACTUALLY AFFECT WHICH CAP USED Has Implications for AORS in a single band when more than one line is specified. Best to group bright and faint lines in a single order into separate AORs if you approach saturation HSpot will warn when you cross a boundary

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- page 41 PACS Faint-Line Chop/Nod Sensitivity is very much as predicted before launch Rms sensitivities are measured for a 400s and 440s total execution time in the blue and red respectively (Nyquist binning applied) See Sect of the PACS OM for more plots for different modes.

- page 42 PACS New Unchopped mode does quite well in comparison with Chop/Nod (See Dario Fadda’s talk later in meeting).

- page 43 PACS Conclusions  PACS is performing well, and with some caveats, according to expectations.  Biggest area of improvement will use of internal calibration block for flux calibration and better understanding of effects of pointing.  SED/large range scans still have problems with shape of continuum. Work proceeds on a number of fronts to try to reduce it.  Some of these corrections will eventually become incorporated into HIPE!