Optimized photometric aperture for the seismology channel Fabio de Oliveira Fialho Michel Auvergne...

Optimized photometric aperture for the seismology channel

Fabio de Oliveira FialhoMichel Auvergne

2nd CoRoT-Brazil Workshop

03/11/2005 2nd CoRoT-Brazil Workshop2 2

On-board Software and Ground Segment Corrections (CMC)


Fixed Photometric Aperture

Goal: to find the mask with the minimum size in pixels and the lowest sensibility to the jitter effect , i. e., to optimize the SNR (Signal to Noise Ratio)

Masked ImagesImages


Jitter Contribution

Not corrected photometry

Jitter corrected photometry

JitterCorrection

MaskImages

(*)

(*)


Jitter CorrectionProblem Definition

Goal: to recover flux lost by jitter effect

Initial constraint: fixed photometric aperture

Mask Masked Image Photometry


Jitter Correction Method

Creation of correlation surface using the PSF model

Correction of flux

Correlation :

– Based on the PSF, identification of correlation surface between the mesured flux in the mask and the pointing error

– Correction of flux is performed using this surface and the pointing error

ii miic FyxKF ).,(


Jitter Correction Surface Creation

X Pointing Error

Y Pointing Error

Correction Surface

Mask

PSF Model


Jitter Correction Photometric Correction

X Pointing Error

Y Pointing Error

Photometric Correction

Not Corrected Photometry

Correction Surface


Jitter Correction Exemple

Not corrected, corrected and ideal photometry

Fourier spectra for corrected and ideal photometry


Jitter Correction Statistics – Star MV = 6

MV 6 Teff 5000 - SNR

0,9968010,997185

1,000000

flux de départ flux corrigée flux idéal

MV 6 Teff 5000 - variance

1,0064211,005656

1,000000


MV 6 Teff 5000 - moyenne

0,999996

1,0000011,000000


Not corrected and corrected photometry


MaskClassic Solution

...3,2,1,

)(

)()(

1

2

1

k

iN

iNk

N

Sk

inoiseph

k

i

ph

oise

ignal

PSF Model

SNR Curve


MaskHybrid Method

Analytic solution without jitter

Numeric solution with jitter

Photometry

PhotometricCorrection

Mask Definiton(pixel adding)

SNR’(k)

...3,2,1,

)(

)()(

1

2

1

k

iN

iNk

N

Sk

inoiseph

k

i

ph

oise

ignal


MaskResults – Star MV = 6

Initial Mask Edge Pixels Final Mask

Candidate Pixels SNR SNR with jitter


MaskSNR

SNR Gain - Optimal Mask

0,211

0,509

SISMO 6 SISMO 9

(%)


Conclusions

Jitter noise can be corrected in the SEISMO channel

Once pointing error becomes important, our ability to correct it will be taken in account to redefine masks

Jitter noise is not a critical issue for stars of magnitude 6 if the pointing error respects the specification )01.100656.1( 2

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Optimized photometric aperture for the seismology channel Fabio de Oliveira Fialho Michel Auvergne...

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