PACS Instrument Performance and Calibration of the Pacs

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

PACS Spectrometer Integral Field Spectrometer 5 x 5 pixels 1 pixel = 9. 4” FOV 47”x 47” PACS A GRATING DESIGN PROVIDES THREE Simultaneous Blue (55 -98 m) Red (102 -210 m) coverage Ge. Ga Two (25 x 16) arrays Stressed and unstressed M 82 showing IFU scale and example of a simple map - page 2 The PACS grating disperses light from 5 slices of the image using reimaging mirrors

Photoconductor Arrays (Spectrometer)PACS • Two 25 x 16 pixel filled arrays • Extrinsic photoconductors (Ge: Ga, stressed/unstressed) • Integrated cryogenic readout electronics (CRE) • Near-backgroundnoise limited performance expected CRE - page 3 3

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

PACS Topics Covered Today ● 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 - page 5

PACS Spatial Calibration - page 6

PACS - page 7

PACS - page 8

PACS Y K IC R T L D N U O R G S E L TE - page 9 E P CO K C BA M E R A V O

PACS QFWHM = 5" (8. 5, 12. 7) at 70 (120, 180) m - page 10

PACS - page 11

PACS - page 12

PACS Wavelength Calibration - page 13

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

PACS Wavelength calibration ● In-orbit measurements of Jupiter, Mars and 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 - page 15

Spectral distortions in the Cross. PACS slit direction: Case of point line source 48 arcsecs THE 5 x 5 SPAXALS of the PACS IFU Central Slit of IFU - page 16 effect of moving across slit 9. 4 arcsecs

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

PACS - page 18

PACS - page 19

PACS - page 20

PACS - page 21

PACS - page 22

PACS - page 23

PACS Flux Calibration See also discussion in Section 4. 9 of the PACS Observer Manual - page 24

PACS Flux calibration ● Pipeline 6. 0 RC 2 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 cal. Tree 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. - page 25

PACS Flux Calibration - page 26

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 (v 3). Corrected for solid angle, as seen from Herschel at T. Obs - page 27

PACS Current Status All flux calib. Measurements OBS / Model F O T Y A M BE AN C E F F E S R IE G L T TIN U O IN PO - page 28 Calibrators RMS ~ 10% in all bands Reproducibility RMS ~ 6 -9%

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

PACS Sensitivity to Pointing Monte-Carlo • Model PSF 74 �m • APE 2” → large <0 excursions 1 st nod cycle ~ 6% rms (→ outliers) → av. 92 -93% of Max Flux (Implicitely Included in our calibration!) - page 30 The Spatial Relative Pointing Error (SRPE) is measure to be around 1. 5 -2. 4 arcsecs (Table 2. 4 of the Herschel Obs. Manual http: //herschel. esac. esa. int/Docs/Herschel/html/observatory. html)

PACS Sensitivity to Pointing Monte-Carlo • Model PSF 74 �m • APE 1” → large <0 excursions 1 st nod cycle ~ 1% rms (→ outliers) → av. 97 -98% of Max Flux - page 31 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

PACS Chopping Transient When you chop on and off a bright source there is evidence of transients. Source takes time to reach maximum Chopping ON source (f 1+f 2) → OFF source (Background f 1) → Transient • f 1('background' flux) • f 2 (source flux) - page 32 For bright sources corrections are necessary to account for the transient that occurs as you chop “on” the source.

PACS Transients in chopping pattern ● 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. - page 33

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

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 35

PACS 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 36 Spectrometer Flux Calibration 36

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: http: //www. herschel. be/twiki/pub/Public/Pacs. Documentation/The_PACS_Calibration_Framework_-_issue_0. 10. pdf or get to it from our nhscsci. ipac. caltech. edu Key Calibration Hot Topics Links - page 37

PACS Spectral Normalisation: Example Default reduction - page 38 Spectrometer Flux Calibration Normalisation on Neptune OD 389 Normalisation on Neptune OD 373 38

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 - page 39

PACS - page 40

PACS Faint-Line Chop/Nod Sensitivity is very much as predicted before launch Rms sensitivities are measured for a 400 s and 440 s total execution time in the blue and respectively (Nyquist binning applied) See Sect. 4. 10 of the PACS OM for more plots for different modes. - page 41

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

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