Processing of Processing of exoplanet full field exoplanet full field

imagesimagesFarid Karioty

CoRoT Week 12/06/2005

PlanPlan I. Already done:I. Already done:

Images correctionsImages corrections Stars identificationStars identification MGPDV (CoRoT Sight Geometric Model) updateMGPDV (CoRoT Sight Geometric Model) update PSF extraction from full field imagesPSF extraction from full field images

II. To be done:II. To be done: Masks assignmentMasks assignment Background windowsBackground windows Offset windows Offset windows Spectrum calculations for each star after mask Spectrum calculations for each star after mask

assignmentassignment

III. Remaining problemIII. Remaining problem Photometric precision of extracted PSFPhotometric precision of extracted PSF

IV. ConclusionIV. Conclusion

I. EXOWINDI. EXOWIND Inputs: Inputs:

3 full field images (equivalent exposition 3 full field images (equivalent exposition time is 30 min/ image)time is 30 min/ image)

EXODAT extractionsEXODAT extractions EXOBASKETEXOBASKET Theoretic PSF setTheoretic PSF set

Outputs: Outputs: 2 positions files of these stars for MGPDV 2 positions files of these stars for MGPDV

updateupdate XML assignment file of the masksXML assignment file of the masks

EXOWIND (IHM)EXOWIND (IHM)

Cosmic impacts Cosmic impacts correctioncorrection

Method:Method: 3 full field images, 30 minutes 3 full field images, 30 minutes

exposition eachexposition each For each pixel of the 3 imagesFor each pixel of the 3 images

Calculate the median for each pixel tripletCalculate the median for each pixel triplet If a pixel value exceeds mean value by more If a pixel value exceeds mean value by more

than 3σ, then it is replaced by the median than 3σ, then it is replaced by the median value of the 3 pixelsvalue of the 3 pixels

The 3 images are summedThe 3 images are summed

EMC correction EMC correction (crosstalk)(crosstalk)

Crosstalk: Crosstalk: Depends of seismology channel windowingDepends of seismology channel windowing Scrambling on the exoplanet channelScrambling on the exoplanet channel

Correction:Correction: Parasites positions are predictableParasites positions are predictable Values of the different scrambling sequences Values of the different scrambling sequences

are read in prescan pixels of the full field are read in prescan pixels of the full field imagesimages

An image containing the parasites is An image containing the parasites is generated & subtractedgenerated & subtracted

Crosstalk correctionCrosstalk correction(IHM)(IHM)

Offset correctionOffset correction

Method:Method: Calculate in prescan and overscan Calculate in prescan and overscan

pixels the offset values for each half pixels the offset values for each half CCDCCD

Subtraction of the measured offset Subtraction of the measured offset (possibility to choose between the value (possibility to choose between the value measured in the prescan or the measured in the prescan or the overscan pixels)overscan pixels)

Offset correctionOffset correction(IHM)(IHM)

Gain correctionGain correction

Method:Method: Reading in the BDE (calibration data Reading in the BDE (calibration data

base) of the gain values for each base) of the gain values for each channelchannel

Application of the multiplicative factor Application of the multiplicative factor for each half CCDfor each half CCD

Smearing correctionSmearing correction

Method :Method : Calculate the smearing value for each Calculate the smearing value for each

column of the imagecolumn of the image

Smearing subtractionSmearing subtraction

Background correctionBackground correction

Methods:Methods: Division of the image into sub-images in which Division of the image into sub-images in which

the minimum value is taken, then the minimum value is taken, then interpolation back to a 2048x2048 pixels interpolation back to a 2048x2048 pixels imageimage

Same method but the median value is usedSame method but the median value is used

Convolution method: convolution of the image Convolution method: convolution of the image by an enlarged Gaussian & fit by a 2by an enlarged Gaussian & fit by a 2ndnd degree degree polynomialpolynomial

Ravines : search of valleys in the imageRavines : search of valleys in the image

Background correctionBackground correction(IHM)(IHM)

Identification of Identification of saturated starssaturated stars

Method :Method : Histogram of the image => selection of the Histogram of the image => selection of the

saturation thresholdsaturation threshold

Research in the image of saturation Research in the image of saturation domains (adjacent pixels with values domains (adjacent pixels with values greater to the chosen saturation threshold)greater to the chosen saturation threshold)

Identification of these stars (automatic Identification of these stars (automatic identification & manual module for the identification & manual module for the stars where a doubt persists e.g. 2 close stars where a doubt persists e.g. 2 close saturated stars)saturated stars)

Identification of saturated Identification of saturated starsstars (IHM)(IHM)

Stars identificationStars identification Identification of about 20 bright Identification of about 20 bright

slightly contaminated stars of the same slightly contaminated stars of the same spectral typespectral type

Update of CCD position in the MGPDV Update of CCD position in the MGPDV (translation & rotation)(translation & rotation)

Identification of 100 to 500 stars (still Identification of 100 to 500 stars (still of the same spectral type)of the same spectral type)

Distortion update of the MGPDVDistortion update of the MGPDV

Stars identification (2)Stars identification (2) Method:Method:

Projection of the catalogue on the CCD (selection Projection of the catalogue on the CCD (selection of the stars with these 3 parameters: mgr, of the stars with these 3 parameters: mgr, contamination, spectral type)contamination, spectral type)

For each star: calculation of the subpixel shift For each star: calculation of the subpixel shift between the star position on the CCD and it’s between the star position on the CCD and it’s position given by the catalogue & the MGPDV position given by the catalogue & the MGPDV (correlation method)(correlation method)

If the shift is less than a user-defined limit If the shift is less than a user-defined limit (depending on the knowledge of CCD position & (depending on the knowledge of CCD position & distortion coefficients in the MGPDV) & if the distortion coefficients in the MGPDV) & if the correlation is greater to a user-defined threshold, correlation is greater to a user-defined threshold, then the star is identifiedthen the star is identified

Stars identificationStars identification(IHM)(IHM)

PSF extractionPSF extraction Method:Method:

Selection in the catalogue of the stars corresponding to Selection in the catalogue of the stars corresponding to the PSF spectral type to extractthe PSF spectral type to extract the maximum magnitude of these “PSF stars” (MGR min = MGR the maximum magnitude of these “PSF stars” (MGR min = MGR

sat)sat) the maximum contamination level of these starsthe maximum contamination level of these stars

Choice of the number of sub-domains in the image (1 Choice of the number of sub-domains in the image (1 extracted PSF by sub-domain and spectral type)extracted PSF by sub-domain and spectral type)

Summation of the stack of PSF stars after subpixel Summation of the stack of PSF stars after subpixel recenteringrecentering

Filtering by an ellipsoidal Gaussian to decrease the Filtering by an ellipsoidal Gaussian to decrease the background noise (residuals of the corrections, other background noise (residuals of the corrections, other fainter stars…)fainter stars…)

PSF extraction (IHM)PSF extraction (IHM)

Extracted PSFExtracted PSF

II. Masks assignmentII. Masks assignment

Method: Method: For each EXOBASKET star:For each EXOBASKET star:

PSF fittingPSF fitting Fitted PSF = signal, remaining = noiseFitted PSF = signal, remaining = noise Stack of images for the attribution procedureStack of images for the attribution procedure XML file of the masks assignmentsXML file of the masks assignments

But: it is crucial to know precisely the PSFBut: it is crucial to know precisely the PSF

III. Unsolved problemIII. Unsolved problem

Photometric precision of the extracted Photometric precision of the extracted PSF :PSF : Important remainders, maximum errors ≈ Important remainders, maximum errors ≈

20%20%

Too much important imprecision for a PSF fitToo much important imprecision for a PSF fit

assignment quality is decreasedassignment quality is decreased

A deconvolution method is being implementedA deconvolution method is being implemented

IV. ConclusionIV. Conclusion

Images corrections: OKImages corrections: OK

Identification of the saturated stars and of Identification of the saturated stars and of the saturation magnitude: OKthe saturation magnitude: OK

Identification of the stars: OKIdentification of the stars: OK

PSF extraction: not totally solved but the PSF extraction: not totally solved but the deconvolution method seems to give deconvolution method seems to give better resultsbetter results