Photometry with technique of Template Subtraction: personal experience.

Stefano ValentiPhysics Department of Ferrara – INAF Astronomical Observatory of Capodimonte

Padova-Asiago Supernova Group (http://web.pd.astro.it/supern/)

Other techniques

Aperture Photometry Isolated object

Photometry with PSF Fitting Not isolated object

measure the PSF Fit the object with the PSF

sn2004gt

Mark A

PSF

PSF (noao.digiphot.daophot.psf)

----------------------------------------------------------- on GRAPHIC display > a < to accept star, > d < to delete on IMAGE display > f < to fit PSF, > w < to write PSF fit, > q < to quit---------------------------------------------------------------Computing PSF for image: temp_SN97ab_281299_R9 stars read from temp_SN97ab_281299_R.mag

Star 1 rejected by userStar 2 has been added to the PSF star list X: 380.00 Y: 166.00 Mag: -7.644 Dmin: 6078.78 Dmax: 36255.29…...Star 9 has been added to the PSF star list X: 395.00 Y: 827.00 Mag: -4.913 Dmin: 6067.815 Dmax: 8494.79

8 PSF stars read from temp_SN97ab_281299_R.mag

Fitting function gauss norm scatter: 0.02782232

Analytic PSF fit Function: gauss X: 375. Y: 537.5 Height: 135507.7 Psfmag: -7.644 Par1: 2.375538 Par2: 1.847269

Computed 1 lookup table(s)

Writing PSF image temp_SN97ab_281299_R.psf.fitsWriting output PSF star list temp_SN97ab_281299_R.pstWriting output PSF star group file temp_SN97ab_281299_R.psg

ecpsf (package of SNOOPY) Cappellaro & Patat – Ledan software

allstar (noao.digiphot.daophot.allstar)

PSF, Magnitude of field stars, Aperture correction

sn2004gt

PSF PHOTOMETRY OF SN

ecsn (package of SNOOPY) Cappellaro & Patat – Ledan software

allstar (noao.digiphot.daophot.allstar)

Original image Residual image

PSF used for the fitDifference image

PSF used for the fit

Residual image

SN 2000cf

>>> input file ? (sn04gt_030105_R):

>>> reference FWHM ? (10.):

>>> aperture correction (ap-fit) ? (0.023):

************ background fit **********************

>>> mark corners of bg-region with >b<, exit >q<

Type b again to draw box.

>>> Order of function in x for bg fit ? (7):

>>> Order of function in y for bg fit ? (7):

>>> background fit OK ?

(yes):

>>> recentering for targets ?

(yes):

>>> Iterate on background ?

(no):

>>> Not yet happy ? Wish to adjust manually stellar peak ?

(no):

>>> Errors estimate (through artificial star experiment ?)

(no):

************************************************************

#id x_ori y_ori x y ap_ori ap_bgsub fit_mag err_art err_fit

SN1 395.617 737.999 52.617 51.999 -9.708 -8.809 -8.849 0 0.009

******************************************************

When we use template subtraction ?

Template subtraction Not isolated object Faint object

Scientific image, Scientific image without object, tool to make difference image, PSF, aperture correction

01-02-1998 12-12-1999 (filter R) 12-12-1999 (filter B)

SN1997ab

SN1997ab

HII regionSN1997ab

HII region

?

Result

SN1997ab 28-12-1999 Danish

Host Galaxy SN1997ab15-03-2004 Ekar

difference image

•Aperture photometry•Photometry with PSF fitting

Geometric Transformation To be compare the PSF of the two images To be compare the Flux scale of the two images

Subtraction with ISIS (or DIA)

n

nn v,uK)y,x(ay,x;v,uKer

ji/vun vuev,uK k

222 2

k,j,in

Ref = Reference Image (best seeing)Im = Program Image Ker = Kernel image (to be found)

j,i

jij,in yxby,xa

(C. Alard 2000; P.R. Wozniak 2001)

…the flux scaling factor is the sum of the local kernel …(C. Alard, 2000)

…the result is on the scale of the program image. I divide it by the norm of the kernel and express the flux in the units of the reference image…(P. Wozniak, private communication)

…the result is on the scale of the program image. I divide it by the norm of the kernel and express the flux in the units of the reference image…(P. Wozniak, private communication)

…the result is on the scale of the program image. I divide it by the norm of the kernel and express the flux in the units of the reference image…(P. Wozniak, private communication)

ISIS C. Alard http://www2.iap.fr/users/alard/package.html

DIA P.R. Wozniak http://www.astro.princeton.edu/~wozniak/dia/

)y,x(Diffy,x;v,uKer)v,u(fRey,xIm

Subtraction between two images ISIS or DIA

Program image Reference image

Geometric scaleScale the list of program images to the reference one

PSF

Flux Scale Flux Scale

Difference image

The difference images have the PSF of the program images

Flux Scale

(best seeing)

Subtraction between two images for SNe with SVSUB

Template

(image without SN)

Artificial stars experiment I

Difference imageGeometric scale

(immatch)

Target (image

with SN) Template

(image without SN)

Reference

(best seeing)

Target (image

with SN)

Reference

(best seeing)

FSF

PSF (daophot)

Make difference mrjphot (ISIS)Flux Scale

Artificial stars experiment II

Error of subtraction

Error of subtraction

Photometry (daophot)

PSF Photometry on difference image

PSF Photometry on difference image

?

?

Working in progress [mrjphot aga(DIA)]

Template

(image without SN)

Difference image

Target

(image with SN) Template

(image without SN)Reference

Target

(image with SN)Reference

We know the FSFIt’s possible to select witch star use to make difference

Artificial stars experiment I

Geometric scale

(immatch)

FSF

PSF (daophot)

Make difference mrjphot (ISIS)Flux Scale

Artificial stars experiment II

Error of subtraction

Error of subtraction

Photometry (daophot)

PSF Photometry on difference image

PSF Photometry on difference image

Scaling Factor for images of one telescope

FSF

FSF

B

Scaling Factor for difference telescope

FSFFSF

FSF

HG

In the subtraction between two images we lose the information about the color term

B

Little Example SN2001ge

SN2001gf

SN2001gf SN2001ge

Geometric scale14-02-2000 Danish

15-03-2004 Ekar 1.82m14-02-2000 Danish

15-03-2004 Ekar 1.82m

15-03-2004 Ekar 1.82m after Geometric scale

Geomap: Compute geometric transforms using coordinate lists (cl.images.immatch)Gregister: Register 1-D or 2-D images using the geomap transforms (cl.images.immatch)

ISIS (C. Alard 2000) & DIA (P.R. Wozniak 2000) : use the same technique without find stars manually.

• Time • PSF of the two images (noao.digiphot.daophot.psf)• Photometry of sequence stars (noao.digiphot.daophot.allstar)

Target Template

mrjphot (ISIS)PARAMETERS

nstamps_x 9 /*** Number of stamps along X axis ***/ nstamps_y 9 /*** Number of stamps along Y axis***/ sub_x 1 /*** Number of sub_division of the image along X axis ***/ sub_y 1 /*** Number of sub_division of the image along Y axis ***/ half_mesh_size 10 /*** Half kernel size ***/ half_stamp_size 15 /*** Half stamp size ***/ deg_bg 2 /** degree to fit differential bakground variations **/ saturation 60000 /** degree to fit background varaitions **/ pix_min 5. /*** Minimum vaue of the pixels to fit ****/ min_stamp_center 130 /*** Minimum value for object to enter kernel fit *****/ ngauss 3 /*** Number of Gaussians ****/ deg_gauss1 6 /*** Degree associated with 1st Gaussian ****/ deg_gauss2 4 /*** Degree associated with 2nd Gaussian ****/ deg_gauss3 2 /*** Degree associated with 3rd Gaussian ****/ sigma_gauss1 0.7 /*** Sigma of 1st Gaussian ****/ sigma_gauss2 1.5 /*** Sigma of 2nd Gaussian ****/ sigma_gauss3 2.5 /*** Sigma of 3rd Gaussian ****/ deg_spatial 2 /*** Degree of the fit of the spatial variations of the Kernel ****/

stampsub_x

The difference image have the flux scale of the reference

)y,x(Diffy,x;v,uKer)v,u(fRey,xIm

Artificial experiment I

---------------------------------------------------------->>> Give position for artificial stars for calibration(> x < then > q <)artificial star magnitude for calibration (-5.):OUTPUT IMAGE: _targart.fits Added Star: 1 - X: 686.00 Y: 201.00 Mag: -5.000 Added Star: 2 - X: 706.00 Y: 255.00 Mag: -5.000 Added Star: 3 - X: 560.00 Y: 274.00 Mag: -5.000 Added Star: 4 - X: 546.00 Y: 277.00 Mag: -5.000 Added Star: 5 - X: 434.00 Y: 148.00 Mag: -5.000********************************************************-4.880-4.869-4.888-4.884-4.890-4.886-4.892>>> zero point mag difference = 0.12 >>> error = 0.00 ********************************************************.... min-max rejection ....-4.892-4.869-4.8856 0.0038470768111717 5 >>> zero point mag difference = 0.11 >>> error = 0.00 ********************************************************

Difference image

Target + artif. starsTarget

addstar (noao.digiphot.daophot.addstar)

Artificial experiment II---------------------------------------------------------->>> radius of circle inside of which background is not calculated in unit of FWHM ? (3.): >>> half-lenght of square to cut in unit of FWHM ? (6): >>> Give position for artificial stars for error estimates(> x < then > q <)zero magnitude difference between target and template (0.1144): artificial star magnitude for error estimate (-1.3158180721099):OUTPUT IMAGE: _targart.fits Added Star: 1 - X: 682.00 Y: 493.00 Mag: -1.430 Added Star: 2 - X: 517.00 Y: 361.00 Mag: -1.430 ….********************************************************-1.3538180721099-1.5208180721099 ….>>> average magnitude = -1.40 >>> error = 0.07 ********************************************************.... min-max rejection ....-1.3876180721099 0.03703646851414 5 >>> average magnitude = -1.39 >>> error = 0.04 ********************************************************!!! zero 0.11+/- 0.04, err = 0.04 # id ap_original ap_bgsub fit_mag err_art err_fit# SN_FIT SN1 -1.3734 -1.3984 -1.4302180721099 0.03703646851414 0.059

Target + artif. stars

Difference image

addstar (noao.digiphot.daophot.addstar)

Subtraction with ISIS (or DIA)

iiiii y,x;v,uKer)v,u(fRey,xIm 2

n

nn v,uK)y,x(ay,x;v,uKer

ji/vun vuev,uK k

222 2

k,j,in

Ref = Reference Image (best seeing)Im = Program Image Ker = Kernel image (to be found)

j,i

jij,in yxby,xa

(C. Alard 2000; P.R. Wozniak 2001)

…the flux scaling factor is the sum of the local kernel …(C. Alard, 2000)

…the result is on the scale of the program image. I divide it by the norm of the kernel and express the flux in the units of the reference image…(P. Wozniak, private communication)

…the result is on the scale of the program image. I divide it by the norm of the kernel and express the flux in the units of the reference image…(P. Wozniak, private communication)

…the result is on the scale of the program image. I divide it by the norm of the kernel and express the flux in the units of the reference image…(P. Wozniak, private communication)

ISIS http://www2.iap.fr/users/alard/package.html

DIA http://www.astro.princeton.edu/~wozniak/dia/