PACS Spectrometer Wavelength Calibration

Size: px

Start display at page:

Download "PACS Spectrometer Wavelength Calibration"

Eleanor Perry
5 years ago
Views:

1 PACS Spectrometer Wavelength Calibration H. Feuchtgruber Max-Planck-Institut für extraterrestrische Physik, Garching PACS WaveCal 1

Description of the Calibration Problem - Blue array: 400 pixels - Red array: 400 pixels - 2 different blue filters - 3 grating orders - Grating range: 32000-1064000 positions - Spectral

2 Description of the Calibration Problem - Blue array: 400 pixels - Red array: 400 pixels - 2 different blue filters - 3 grating orders - Grating range: positions - Spectral resolution elements: ~3650 (x sampling x int. time) 2x 47 x 47 Slit-width = solid line in lower left figure 1 st order 2 nd order 3 rd order Resolution (dashed) Slit-width (solid) 0 24 PACS WaveCal 2

3 PCD Requirements PCD sec : Required accuracy: Peak position to within 10-20% of a spectral resolution element PACS WaveCal 3

4 In-Flight Calibration The pre-launch statement of accuracy is still valid: 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) However: The pre-launch calibration has been obtained with an ideal extended absorption source and a reference measurement on the same source without the absorber. No such measurement can be carried out in-flight. PACS WaveCal 4

5 Calibration Method (1) = ; = = ; g LHe = µm; 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 = [steps/ ] δpix n = constant(n); n=[1,2,3,2 ] SCR PACS-2488 λ (n,pix,module) = i(gratpos/dgrat) i PACS WaveCal 5

Calculate model spectra (at expected PACS spectral resolution) for the wavelength range under investigation and define spectral intervals for correlation analysis (or fitting) Determine λ-calibration

6 Calculate model spectra (at expected PACS spectral resolution) for the wavelength range under investigation and define spectral intervals for correlation analysis (or fitting) Determine λ-calibration offsets for each interval Store 3rd order polynomial fit parameters for offsets vs. (gratpos/dgrat) for each pixel new = old + polynomial fit Fit 7 th order polynomial per pixel and grating blue=model, black=measurement Calibration Method (2) Analysis code (or CAP) is unchanged from FM ILT: Use HIPE to generate L0 products Use IDL code to derive new calibration parameters Output = ASCII files of polynomial coefficients for inclusion into pipeline correlation coeff. PACS WaveCal 6

7 Dependence on Source Position within Slit (1) Instrument boresight [Ra, Dec] slit 3 3 IC2501 raster: OBSIDs: , , Pixel 8 of module 12 at the 5 encircled raster positions Observed wavelength shifts are consistent with raster positions inside the slit Line shape asymmetries appear at off-center slit positions PACS WaveCal 7

8 Dependence on Source Position within Slit (2) Requirement Slit borders Pointing uncertainty IC2501 measurement 2D sim. Resulting profiles Poglitsch et al. 2010, A&A 518, L2 PACS WaveCal 8

9 Dependence on Source Position within Slit (3) Requirement Slit borders Pointing uncertainty IC2501 measurement Mars measurement Correlation Analysis: Model vs. Data 2D sim. 16 pixels of central spaxel; blue order 3 Resulting profiles 68% of pointings will fall within 1.8" of the target coordinates 98% of pointings will fall within 3.6" of the target coordinates 99.8% of pointings will fall within 5.4" of the target coordinates PACS WaveCal 9

10 Alignment Effects on -Calibration y 47 x 47 z 9.4 Blue PSF FWHM ~5.5 Uniform spatial weights across spectral pixels Non-uniform spatial weights across spectral pixels Wavelength Calibration 10

11 Alignment Effects on -Calibration Bright-Line Mode Nod A Single spectral pixels are color coded Different baselines for different spectral pixels Reasonable match for Nod A Significant offsets for Nod B Nod B Wavelength Calibration 11

12 Alignment Effects on -Calibration Bright-Line Mode Nod A Nod B Nod A Nod B After rebinning Wavelength Calibration 12

13 Pointing/Spatial Effects on -Calibration Observed wavelengths depend on point source position within the slit PACS WaveCal 13

14 Jupiter 2x2 Raster on OD208 Wavelength shifts in spectral maps of 66.43µm H 2 O line [n,m]=[1,2] [n,m]=[2,2] [n,m]=[1,1] [n,m]=[2,1] PACS WaveCal 14

equatorial radius = 71492km ~ ±8km/s (mid hemisphere) - create

15 -Calibration Effects on Extended Sources PACS Spectral resolution at 66μm = 3850 = 78km/s Velocity structure of Jupiter: - period=9h55m - equatorial radius = 71492km ~ ±8km/s (mid hemisphere) - create velocity map of narrow stratospheric water lines +8km/s -8km/s PACS WaveCal 15

Calibration Workshop #2 18-20 Jan 2012 -Calibration Effects on Extended Sources PACS Spectral resolution at 66μm = 3850 = 78km/s Velocity structure of

16 Calibration Workshop # Jan Calibration Effects on Extended Sources PACS Spectral resolution at 66μm = 3850 = 78km/s Velocity structure of Jupiter: - period=9h55m - equatorial radius = 71492km ~ ±8km/s (mid hemisphere) - create velocity map of narrow stratospheric water lines PACS WaveCal 16

Calibration Workshop #2 18-20 Jan 2012 -Calibration Effects on Extended

of Jupiter: - period=9h55m - equatorial radius = 71492km ~ ±8km/s (mid

17 Calibration Workshop # Jan Calibration Effects on Extended Sources PACS Spectral resolution at 66μm = 3850 = 78km/s Velocity structure of Jupiter: - period=9h55m - equatorial radius = 71492km ~ ±8km/s (mid hemisphere) - create velocity map of narrow stratospheric water lines 16km/s PACS WaveCal 17

18 Calibration Observations for λ-stability PACS spectrometer observations of NGC6543 to monitor the stability of the wavelength calibration are contained in the calibration proposal RPSpecWave. Only nominal chop-nod line scan AORs are used The 6 observed lines are: Filter A: [NIII] 57μm, [OI]63μm, [OI]145μm Filter B: [OIII] 88μm, [NII]121μm, [CII]158μm ODs = [ 194, 235, 286, 319, 345, 373, 405, 457, 485, 550, 579, 598, 629, 656, 690, 716, 740, 774, 792, 819, 850, 882, 906, 938, 959] The semi-automatic analysis (on re-binned spectra) gives: Line centers Line widths Line peak Continuum The analysis has been run with standard calibration and Tel-normalization for the central spaxel only. PACS WaveCal 18

19 Calibration Observations on NGC6543 Covered Roll-angles ODs with NGC6543 λ-cal observations (OD194 - OD959) Hubble/Chandra composite PACS WaveCal 19

Calibration Observations on NGC6543 Remember the early

line flux [N III] 57µm integrated line flux [O I] / [N

important for the understanding of observed wavelength

20 Calibration Observations on NGC6543 Remember the early PACS spectral mapping results: [O I] 63µm integrated line flux [N III] 57µm integrated line flux [O I] / [N III] composite image Knowledge of source morphology is important for the understanding of observed wavelength shifts as a function of position angle. PACS WaveCal 20

21 Typical lines for OBSIDs: & [NIII] [OI] [OIII] OD286 [NII] [OI] [CII] PACS WaveCal 21

22 Line Peak Scale: ±10% Scale: ±80% Scale: ±10% Scale: ±30% Scale: ±50% Scale: ±30% PACS WaveCal 22

23 Trends in fitted line centers Herschel v-lsr variations: 1km/s Potential pointing changes! / for red lines is larger, but the lines are much fainter and also partly off-center PACS WaveCal 23

24 Concluding Remarks The absolute wavelength calibration is dominated by the spacecraft pointing and/or source structure The discussed phenomenology has also impact on spectrometer line profiles, line and continuum fluxes and relative spectral response functions Optimized observing strategy: Small maps provide more spatial information for a better understanding of the wavelength scale 50 routine calibration observations (up to OD959) to monitor the stability of the spectrometer wavelength scale have been successfully executed and analyzed. No instrumental degradation or trend affecting the wavelength calibration can be identified Observed scatter and trends in fitted line centers are explained by source morphology and satellite roll-angle, combined with the known shifts in wavelength scale due to the source position within the slit. Stability measurements on NGC6543 will continue at regular pace Related links: Poglitsch et al., 2010, A&A, 518, L PACS WaveCal 24

PACS Spectroscopy performance and calibration PACS Spectroscopy performance and calibration

1 of 18 PACS Spectroscopy performance and Prepared by Bart Vandenbussche With inputs by Alessandra Contursi Helmut Feuchtgruber Katrina Exter Christophe Jean Albrecht Poglitsch Elena Puga Pierre Royer