1. Padova-Asiago Supernova Group (http://web.pd.astro.it/supern/)
Photometry with technique of Template Subtraction: personal experience.
Stefano Valenti
Physics Department of Ferrara – INAF Astronomical Observatory of Capodimonte
Padova-Asiago Supernova Group (

2. Other techniques Aperture Photometry Photometry with PSF Fitting
Isolated object
Photometry with PSF Fitting
Not isolated object
measure the PSF
Fit the object with the PSF
Mark A
sn2004gt

3. PSF ecpsf (package of SNOOPY)
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_R
9 stars read from temp_SN97ab_281299_R.mag
Star 1 rejected by user
Star 2 has been added to the PSF star list
X: Y: Mag: Dmin: Dmax:
…...
Star 9 has been added to the PSF star list
X: Y: Mag: Dmin: Dmax:
8 PSF stars read from temp_SN97ab_281299_R.mag
Fitting function gauss norm scatter:
Analytic PSF fit
Function: gauss X: Y: Height: Psfmag:
Par1: Par2:
Computed 1 lookup table(s)
Writing PSF image temp_SN97ab_281299_R.psf.fits
Writing output PSF star list temp_SN97ab_281299_R.pst
Writing output PSF star group file temp_SN97ab_281299_R.psg
PSF (noao.digiphot.daophot.psf)
allstar (noao.digiphot.daophot.allstar)
PSF, Magnitude of field stars, Aperture correction
ecpsf (package of SNOOPY)
Cappellaro & Patat – Ledan software

4. PSF PHOTOMETRY OF SN allstar (noao.digiphot.daophot.allstar)
PSF used for the fit
Difference image
Residual image
>>> 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 ?
>>> Iterate on background ?
(no):
>>> Not yet happy ? Wish to adjust manually stellar peak ?
>>> Errors estimate (through artificial star experiment ?)
************************************************************
#id x_ori y_ori x y ap_ori ap_bgsub fit_mag err_art err_fit SN
******************************************************
sn2004gt
SN 2000cf
Original image
Residual image
PSF used for the fit
ecsn (package of SNOOPY)
Cappellaro & Patat – Ledan software

5. When we use template subtraction ?
Not isolated object
Faint object
Scientific image, Scientific image without object, tool to make difference image, PSF, aperture correction
SN1997ab
HII region
SN1997ab
HII region ?
SN1997ab
(filter R)
(filter B)

6. Result Geometric Transformation
SN1997ab
Danish
Host Galaxy SN1997ab
Ekar
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
difference image

7. Subtraction with ISIS (or DIA)
ISIS C. Alard
DIA P.R. Wozniak
Ref = Reference Image (best seeing)
Im = Program Image
Ker = Kernel image (to be found)
…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)
(C. Alard 2000; P.R. Wozniak 2001)

8. Subtraction between two images ISIS or DIA
Program image
Reference image
Difference image
(best seeing)
Geometric scale
Scale the list of program images to the reference one
PSF
Flux Scale
The difference images have the PSF of the program images
Flux Scale
Flux Scale

9. Subtraction between two images for SNe with SVSUB
Difference image
Geometric scale
(immatch)
PSF (daophot)
Make difference mrjphot (ISIS)
Photometry (daophot)
Artificial stars experiment I
Artificial stars experiment II
Target (image with SN)
Reference
(best seeing)
Flux Scale
PSF Photometry on difference image
Error of subtraction
Template
(image without SN)
Target (image with SN)
PSF Photometry on difference image
Error of subtraction
Template
(image without SN)
Reference
(best seeing) ?
FSF ?

10. Working in progress [mrjphot aga(DIA)]
Difference image
Geometric scale
(immatch)
PSF (daophot)
Make difference mrjphot (ISIS)
Photometry (daophot)
Artificial stars experiment I
Artificial stars experiment II
Flux Scale
Target
(image with SN)
Reference
PSF Photometry on difference image
Error of subtraction
Template
(image without SN)
Target
(image with SN)
PSF Photometry on difference image
Template
(image without SN)
Reference
Error of subtraction
FSF
It’s possible to select witch star use to make difference
We know the FSF

11. Scaling Factor for images of one telescopeB
FSF
FSF

12. Scaling Factor for difference telescopeHG B
FSF
FSF
FSF
In the subtraction between two images we lose the information about the color term

13. Little Example
SN2001ge
SN2001gf
SN2001ge
SN2001gf

14. Geometric scale 14-02-2000 Danish 15-03-2004 Ekar 1.82m
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)
Ekar 1.82m after Geometric scale
Target Template
Danish
Ekar 1.82m
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)

15. mrjphot (ISIS) PARAMETERS sub_x stamp
nstamps_x /*** Number of stamps along X axis ***/
nstamps_y /*** 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 /** 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_gauss /*** Degree associated with 1st Gaussian ****/
deg_gauss /*** Degree associated with 2nd Gaussian ****/
deg_gauss /*** Degree associated with 3rd Gaussian ****/
sigma_gauss /*** Sigma of 1st Gaussian ****/
sigma_gauss /*** Sigma of 2nd Gaussian ****/
sigma_gauss /*** Sigma of 3rd Gaussian ****/
deg_spatial 2 /*** Degree of the fit of the spatial variations of the Kernel ****/
sub_x
stamp
The difference image have the flux scale of the reference

16. 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: Y: Mag:
Added Star: 2 - X: Y: Mag:
Added Star: 3 - X: Y: Mag:
Added Star: 4 - X: Y: Mag:
Added Star: 5 - X: Y: Mag:
********************************************************
-4.880
-4.869
-4.888
-4.884
-4.890
-4.886
-4.892
>>> zero point mag difference =
>>> error =
.... min-max rejection ....
>>> zero point mag difference =
Target
Target + artif. stars
Difference image
addstar (noao.digiphot.daophot.addstar)

17. 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 ( ):
OUTPUT IMAGE: _targart.fits
Added Star: 1 - X: Y: Mag:
Added Star: 2 - X: Y: Mag: ….
********************************************************
>>> average magnitude =
>>> error =
.... min-max rejection ....
>>> average magnitude =
>>> error =
!!! zero / , err =
# id ap_original ap_bgsub fit_mag err_art err_fit
# SN_FIT SN
Target + artif. stars
Difference image
addstar (noao.digiphot.daophot.addstar)

18. …the flux scaling factor is the sum of the local kernel …(C
…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 letters)
ISIS (C. Alard 2000) & DIA (P.R. Wozniak 2000)
Maximize a cross correlation function

19. Measure the strumental magnitude on the difference image
Register the images
Calculate the PSF
Subtract the images
Measure the strumental magnitude on the difference image
Apparent magnitude
Estimate error
Choice the reference image (image with best PSF)
photometric scale =
reference image
geometric scale =
target
Difference image
photometry scale of reference
Geometric scale = target
Stefano Valenti - RTN Winter school - asiago 2005

20. Subtraction between two images
Program image
Reference image
Geometric scale
Difference image
PSF
Photometric Constants
Exposure time
Airmass
Photometric Constants
Exposure time
Airmass ?

21. Subtraction between two images for SNe
Difference image
Geometric scale
(immatch)
PSF
( daophot)
Photometric Constants
Exposure time
Airmass
Target (image with SN)
Reference
Template (image without SN)
Target (image with SN)
Template (image without SN)
Reference
I prefer that the difference image have the same characteristics of the target
I have to control that the FSF is that what I want.
Why I want to know the FSF ?

22. Working in progress mrjphot (ISIS) aga (DIA)
ISIS program is difficult to read.
If we know the FSF we have to use an experiment of artificial stars.
We know the FSF in DIA.
DIA program is written well and it’s possible to do easily some change

23. Subtraction with ISIS (or DIA)
Ref = Reference Image (best seeing)
Im = Program Image
Ker = Kernel image (to be found)
…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)
(C. Alard 2000; P.R. Wozniak 2001)
ISIS
DIA