1. PACS / SPIRE cross-calibration on prime fidicial standard stars
ESAC, December 2010
Bruno Altieri

2. Objectives
Investigate cross-calibration on PACS & SPIRE photometers on stable flux calibrators :
Herschel fiducial standard stars :
Independent view on the PACS photometric calibration (see T.Müller/M.Nielbock) from a user’s perspective.
Only scan mapping

3. Standard stars SED model

4. Data processing PACS photometry SPIRE photometry
Mini-scan maps only (the science mode)
Selected from :
MMT degliching (disabled in PSF core)
Standard high-pass filter (radius = 35 readouts) + photProject
Aperture photometry, in r=20”:
EEF = 0.949, 0.938, from PICC-ME-TN-033
Colour correction :
cc = 1.02, 1.03, from PICC-ME-TN-036
SPIRE photometry
Ratios measured/model from Tanya ( Dec.8, 2010)
Previously derived from Luca Conversi photometry, very consistent except for one star.
Are we using the same model version ?
Except for γDra (George Bendo & Luca Conversi photometry)
k250 = * , k350 = * , k500 = *

5. PACS: aperture photometry

6. Standard stars Herschel photometry

7. α Boo

8. γ Dra

9. γ Dra (2D gauss fitting)

10. γDra flux accuracy: blue: 1%

11. γDra flux accuracy: blue: 3.5%

12. α Tau

13. α Ceti

14. β Peg: normalization problem by ~10% ?
HPF=15/25
 Photometry too low by ~2% 

15.  Photometry too low by ~2%
β And (no SPIRE)
HPF=15/25
 Photometry too low by ~2% 

16. Sirius: PACS colour term to be investigated
HPF=15/25
 Photometry too low by ~2% 

17. Open issues PACS: SPIRE: background subtraction
Highpass filtering still filtering out some flux ?
2-3% increase when going from 15 to 35 in blue/green bands
Non-linear effect with flux.
MADmap returns 9% higher fluxes in the red (N. Billot, PICC-NHSC-TR-028, November 2010)
Do the advertised EEF factors apply for an observation reduced with a different hp-filter width than PICC-ME-TN-033 ?
PICC-ME-TN-033 (v0.1 Sep. 2009), hp-filter radius lower, but masked regions larger …
Background subtraction in the PSF wings ?
Deglitching disables in PSF core, some upward flux bias ?
Move to 2nd order deglitching
SPIRE: background subtraction
Map based versus timeline fitting ?

18. Open issues

19. Conclusions
No obvious overall systematics in PACS/SPIRE cross-calibration - from the prime fiducial stars only.
But some systematics seen for some stars,
e.g. β Peg PACS excess
SPIRE 500μm excesses (αBoo & γDra)
Hence the standard deviation for a given band is dominated by the fiducial star model and not by measurement uncertainties.
Flux calibration :
PACS: photometry possibly to high by ~3% in green and blue,
SPIRE: OK within errors
SPIRE rising excess towards long wavelengths (500μm) seems to be true
PACS : no trend with time and flux ( Jy range only)