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

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

Standard stars SED model

Data processing PACS photometry SPIRE photometry Mini-scan maps only (the science mode) Selected from : http://www.herschel.be/twiki/bin/view/Pacs/PacsPhotFluxCalibrationSources MMT degliching (disabled in PSF core) Standard high-pass filter (radius = 35 readouts) + photProject Aperture photometry, in r=20”: EEF = 0.949, 0.938, 0.897 from PICC-ME-TN-033 Colour correction : cc = 1.02, 1.03, 1.075 from PICC-ME-TN-036 SPIRE photometry Ratios measured/model from Tanya (e-mail 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 = 1.0113 * 0.9417, k350 = 1.0060 * 0.9582, k500 = 1.0065 * 0.9395

PACS: aperture photometry

Standard stars Herschel photometry

α Boo

γ Dra

γ Dra (2D gauss fitting)

γDra flux accuracy: blue: 1%

γDra flux accuracy: blue: 3.5%

α Tau

α Ceti

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

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

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

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 ?

Open issues

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 (0.5-15 Jy range only)