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VODIA V ST O megaCAM D ifference I mage A nalysis

VODIA V ST O megaCAM D ifference I mage A nalysis. Silvio Leccia AW-OAC team. Overview: Original DIA. The DIA is a software written by P.R.Wozniak based on the Alard & Lupton optimal PSF matching algorithm. AGA step: Image Subtraction.

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VODIA V ST O megaCAM D ifference I mage A nalysis

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  1. VODIA VST OmegaCAM Difference Image Analysis Silvio Leccia AW-OAC team Leiden, 17 November 2005

  2. Overview: Original DIA The DIA is a software written by P.R.Wozniak based on the Alard & Lupton optimal PSF matching algorithm Leiden, 17 November 2005

  3. AGA step: Image Subtraction • Once the REFerence frame is created it is convoluted with a kernel (spatially variable in general) in order to match as close as possible each image. This convoluted image is then subtracted to the current frame, producing a serie of subtracted images. The Algorithm • A list of objects is found on the REF (domains) • A list of objects is found on the single image (domains) • It matchs the domains and calculates the kernels (3 Gaussians of costant widths multipied by polynomials) • It produces the difference image Leiden, 17 November 2005

  4. Getvar step: variable objects detection • The program starts by rejecting some fraction of the frames with the worst seeing (in our case 10%) • The pixel is declared as variable if one of these two conditions are met: • 1. There are at least 3 consecutive points departing at least 3σ from the base line in the same direction (up or down), or • 2. There are at least 10 points in total departing at least 4σ from the base line in the same direction, not necessarily consecutive. Leiden, 17 November 2005

  5. Phot Step: Photometry • For each variable object the program performs both profile and aperture photometry on difference images keeping the centroid fixed • The format of the catalog is : • Flux – profile photometry • Flux error – profile photometry • Flux – aperture photometry • Flux error – aperture photometry • Background • FWHW of the PSF profile • Where: • Pi is PSF for pixel i • fi flux for pixel i on differece images • fi,0 flux for pixel on original images • G is Gain and Leiden, 17 November 2005

  6. VODIA: new functionalities • Added in Aga: • Mask for each input image • The kernel can be calculated using an external list of objects • Added in Getvar: • Ascii catalogs of variable objects • Psf image is created and saved (QC check) • VAR images are saved • Added in Phot: • Ascii light curves • Errors now include also read-out noise Leiden, 17 November 2005

  7. VODIA: how it works on the BEOWULF Software Hardware MASTER storage wcs2pix prepare Network SWITCH mstack Node 1 BeoRunner getpsf Node 2 aga getvar phot Node n lc Leiden, 17 November 2005

  8. Step 1: cut all images using the astrometric solution MASTER storage wcs2pix prepare Network SWITCH mstack Node 1 BeoRunner getpsf Node 2 aga getvar phot Node n lc Leiden, 17 November 2005

  9. Step 2: split the images in sub frames and copy them on nodes MASTER storage wcs2pix prepare Network SWITCH mstack Node 1 BeoRunner getpsf Node 2 aga getvar phot Node n lc Leiden, 17 November 2005

  10. Step 3: mstack the subframes indipendently on the nodes MASTER storage wcs2pix prepare Network SWITCH mstack Node 1 BeoRunner getpsf Node 2 aga getvar phot Node n lc Leiden, 17 November 2005

  11. TESTs • 69 Images VLT-FORS – GC 2kx2k B Band • 46 Images WFI – Carina 8kx9k B Band • 15 Images WFI – OACDF 7kx7k V Band Beo0/1 – 2 Master + 8 nodes Beo2 – 1 Master + 16 nodes * it depends from the threshold in Getvar Leiden, 17 November 2005

  12. VLT-FORS Images Leiden, 17 November 2005

  13. VLT-FORS Image VLT-FORS difference Image Leiden, 17 November 2005

  14. Testing VODIA and comparing the results with other methods(red=VODIA, black=ALLFRAME, cyan=Munich IS) Leiden, 17 November 2005

  15. Testing VODIA and comparing the results with other methods(red=VODIA, black=ALLFRAME, cyan=Munich IS) Leiden, 17 November 2005

  16. Testing VODIA and comparing the results with other methods(red=VODIA, black=ALLFRAME, cyan=Munich IS) Leiden, 17 November 2005

  17. Testing with Simulated Images Aobs/Aorig1.05 Leiden, 17 November 2005

  18. Exercise • 68 images 500x500 pixel • Run VODIA in the AWE • Second part: • Change parameters of getvar and run only the final steps of VODIA (getvar and phot) in order to try to have different (better?) results. Leiden, 17 November 2005

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