difference image analysis at oac groningen, 1st dec 2004 aw-oac team

Difference Image Analysis Difference Image Analysis at OACat OAC

Groningen, 1st Dec 2004Groningen, 1st Dec 2004 AW-OAC teamAW-OAC team


• The DIA is a software written by P.R.Wozniak The DIA is a software written by P.R.Wozniak based on the Alard & Lupton optimal PSF matching based on the Alard & Lupton optimal PSF matching algorithm.algorithm.

• DIA was originally created to search variable DIA was originally created to search variable objects on the OGLE-II bugle microlensing dataobjects on the OGLE-II bugle microlensing data

• The original version is not well documented The original version is not well documented (parameters optimization is not easy) and it is (parameters optimization is not easy) and it is optimized for OGLE data optimized for OGLE data

• We present a modified version that includes:We present a modified version that includes:– New tool to prepare the images using the astrometryNew tool to prepare the images using the astrometry– New functionalities in the core (masks, external domains)New functionalities in the core (masks, external domains)– Python interface to send processes on a BEOWULF clusterPython interface to send processes on a BEOWULF cluster– New tool to study the candidates (ascii catalogues, light New tool to study the candidates (ascii catalogues, light

curves, frequency analysis, phase diagrams, stamps)curves, frequency analysis, phase diagrams, stamps)


Overview: Original DIAOverview: Original DIACross_regrid*Cross_regrid* Registration and correction of input imagesRegistration and correction of input images

mstackmstack Creation of the reference image with best Creation of the reference image with best seeing framesseeing frames

getpsfgetpsf Global PSF on REF (used in getvar and phot Global PSF on REF (used in getvar and phot steps)steps)

Aga **Aga ** Creates difference images Creates difference images

Getvar **Getvar ** Finds variable candidatesFinds variable candidates

Phot **Phot ** Light Curve with PSF and aperture Light Curve with PSF and aperture photometry on the difference imagesphotometry on the difference images

* Not used in the new version

** New functionalities added


AGA step: Image SubtractionAGA step: Image Subtraction

• Once the reference frame ref.fits is created it is convoluted with a Once the reference frame ref.fits is created it is convoluted with a

kernel (spatially variable in general) in order to match as close as kernel (spatially variable in general) in order to match as close as

possible each image. This convoluted image is then subtracted to possible each image. This convoluted image is then subtracted to

the current frame, producing a serie of subtracted images. the current frame, producing a serie of subtracted images.

The AlgorithmThe Algorithm

• A list of objects is found on the REF (domains)A list of objects is found on the REF (domains)

• A list of objects is found on the single image (domains) A list of objects is found on the single image (domains)

• It matchs the domains and calculates the kernels It matchs the domains and calculates the kernels (3 Gaussians of costant widths multipied by (3 Gaussians of costant widths multipied by polynomials)polynomials)

• The best solution is taken to produce the difference The best solution is taken to produce the difference imageimage


Getvar step: variable objects detectionGetvar step: variable objects detection

Variable objects are detected using some preliminary variability measurements based on the entire serie of difference images for a given field. Final measurements are made only for these candidates.

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.

NB: The extension to other types of variables is straightforward!


Phot Step: PhotometryPhot Step: Photometry

For each variable object the program performs both profile and aperture For each variable object the program performs both profile and aperture photometry on difference images keeping the centroid fixedphotometry on difference images keeping the centroid fixed

The format of the catalog is :The format of the catalog is :

1.1. Flux – profile photometry Flux – profile photometry

2.2. Flux error – profile photometryFlux error – profile photometry

3.3. Flux – aperture photometry Flux – aperture photometry

4.4. Flux error – aperture photometryFlux error – aperture photometry

5.5. Background Background

6.6. FWHW of the PSF profileFWHW of the PSF profile

)/(

)/(22

2

iii

iii ipsf P

Pfa

)/(

122iii

psf P

api rr

iiap fa

i

iap2

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

G

fii

0,2


New DIA Version: step 1 wcs2pixNew DIA Version: step 1 wcs2pix

• A C program that reads A C program that reads astrometric informations from astrometric informations from the headers (CRVAL,CRPIX,CD) the headers (CRVAL,CRPIX,CD) and through the WCS library and through the WCS library finds the common part of the finds the common part of the images.images.

• The WCS library is also used to The WCS library is also used to extract the object coordinates in extract the object coordinates in alfa e delta from the output files.alfa e delta from the output files.


New DIA Version: new New DIA Version: new functionalitiesfunctionalities

Added in Aga:Added in Aga:• Mask for each input imageMask for each input image• The kernel can be calculated using an The kernel can be calculated using an

external list of objectsexternal list of objects

Added in Getvar:Added in Getvar:• Ascii catalogs of variable objectsAscii catalogs of variable objects• Psf image is created and saved (QC check)Psf image is created and saved (QC check)• VAR and ABS images are saved (see ISIS)VAR and ABS images are saved (see ISIS)

Added in Phot:Added in Phot:• Ascii light curves with phasesAscii light curves with phases


BeoRunner

wcs2pix

prepare

mstack

getpsf

aga

getvar

phot

MASTER

Node 2

Node 1

Node nlc

storage

Software Hardware

The New DIA Version: how it works on the BEOWULF

Network SWITCH


BeoRunner

wcs2pix

prepare

mstack

getpsf

aga

getvar

phot

MASTER

Node 2

Node 1

Node nlc

storage

Step 1: cut all images using the astrometric solution

Network SWITCH


BeoRunner

wcs2pix

prepare

mstack

getpsf

aga

getvar

phot

MASTER

Node 2

Node 1

Node nlc

storage

Step 2: split the images in sub frames and copy them on nodes

Network SWITCH


BeoRunner

wcs2pix

prepare

mstack

getpsf

aga

getvar

phot

MASTER

Node 2

Node 1

Node nlc

storage

Step 3: mstack the subframes indipendently on the nodes

Network SWITCH


BeoRunner

wcs2pix

prepare

mstack

getpsf

aga

getvar

phot

MASTER

Node 2

Node 1

Node nlc

storage

Step 4: getpsf

Network SWITCH


BeoRunner

wcs2pix

prepare

mstack

getpsf

aga

getvar

phot

MASTER

Node 2

Node 1

Node nlc

storage

Step 5: aga

Network SWITCH


BeoRunner

wcs2pix

prepare

mstack

getpsf

aga

getvar

phot

MASTER

Node 2

Node 1

Node nlc

storage

Step 6: getvar

Network SWITCH


BeoRunner

wcs2pix

prepare

mstack

getpsf

aga

getvar

phot

MASTER

Node 2

Node 1

Node nlc

storage

Step 7: phot

Network SWITCH


BeoRunner

wcs2pix

prepare

mstack

getpsf

aga

getvar

phot

MASTER

Node 2

Node 1

Node nlc

storage

Step 8: lc

Network SWITCH


LC Step: Analysis of the LC Step: Analysis of the resultsresultsFor each variable candidate the software produces a light curve in a file called LC_NAMEFIELD_Xpixel_Ypix_alfa_delta-subframe.data

An automatic Fourier transform is done and an ascii file is created with An automatic Fourier transform is done and an ascii file is created with frequency, power and s/n ratio (power/standard deviation). This file is called frequency, power and s/n ratio (power/standard deviation). This file is called as the LC file plus Max=…_fre=…_sn=… in order to have the main as the LC file plus Max=…_fre=…_sn=… in order to have the main informations directly in the filename.informations directly in the filename.

The frequency of the max peak is used to add a phase column.The frequency of the max peak is used to add a phase column.


The format of the LIGHT CURVE The format of the LIGHT CURVE

1.1. Flux – profile photometry Flux – profile photometry

2.2. Flux error – profile Flux error – profile photometryphotometry

3.3. Flux – apeture photometry Flux – apeture photometry

4.4. Flux error – aperture Flux error – aperture photometryphotometry

5.5. Background Background

6.6. FWHM of the PSF ProfileFWHM of the PSF Profile

7.7. MJD-OBSMJD-OBS

8.8. PHASE PHASE

)/(

)/(22

2

iii

iii ipsf P

Pfa

)/(

122iii

psf P

api rr

iiap fa

i

iap2

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

G

fii

0,2


6969

2kx2k2kx2k1515

7kx7k7kx7k4646

8kx9k8kx9k

wcs2pixwcs2pix 1m1m 14m14m

prepareprepare 1m1m 3m3m 21m21m

mstackmstack 3s3s 10s10s 1m10s1m10s

getpsfgetpsf 2s2s 5s5s 10s10s

agaaga 3m3m 3m50s3m50s 19m31s19m31s

Getvar*Getvar* 10s10s 14s14s 1m37s1m37s

Phot *Phot * 3s3s 10s10s 1m7s1m7s

Lc*Lc* 8s8s 12s12s 1m1m

TOTALTOTAL 4m26s4m26s 8m42s8m42s 59m3559m35ss

TESTsTESTs• 69 Images VLT-FORS – GC 2kx2k B Band69 Images VLT-FORS – GC 2kx2k B Band• 46 Images WFI – Carina 8kx9k B Band46 Images WFI – Carina 8kx9k B Band• 15 Images WFI – OACDF 7kx7k V Band15 Images WFI – OACDF 7kx7k V Band

Beo2 – 1 Master + 16 nodesBeo0/1 – 2 Master + 8 nodes

6969

2kx2k2kx2k1515

7kx7k7kx7k

wcs2pixwcs2pix 1m15s1m15s

prepareprepare 2m2m 8m8m

mstackmstack 10s10s 37s37s

getpsfgetpsf 7s7s 12s12s

agaaga 4m20s4m20s 5m23s5m23s

Getvar*Getvar* 1m11s1m11s 1m591m59

Phot*Phot* 59s59s 1m321m32

Lc*Lc* 2m2m 1m1m

TOTALTOTAL 6m47s6m47s 19m5819m58

* it depends from the threshold in Getvar


VLT-FORS ImagesVLT-FORS Images


VLT-FORS ImageVLT-FORS Image VLT-FORS difference VLT-FORS difference ImageImage


Light curves: VLT-FORSLight curves: VLT-FORS


Light curves: WFI-Light curves: WFI-CarinaCarina



Light curves: WFI-Light curves: WFI-CarinaCarinaLight curves: WFI-Light curves: WFI-CarinaCarina


An object from the OACDFAn object from the OACDF


Other Light curves from FORS data

Other Light curves WFI-CARINA data


Open Points:Open Points:

• Improve the throughput in the preparation stepsImprove the throughput in the preparation steps

• Photometry (PSF, aperture on original images) Photometry (PSF, aperture on original images) and relative amplitudes.and relative amplitudes.

• User ManualUser Manual

• AW integrationAW integration

difference image analysis at oac groningen, 1st dec 2004 aw-oac team

Documents

difference images getvar

new version

difference image analysis

original images g

reference image

serie of subtracted

convoluted image

difference imagesaga