1. Eli Kasai
NASSP Masters 2011
UCT
SAAO
Thesis: SN Ia Rate in Intermediate-Redshift
Galaxy Clusters
Supervisor: Dr Steve Crawford
Co-supervisor: Prof Bruce Bassett

2. OUTLINE
 SN Ia rate measurement
• Importance
 Physical Processes
• Single and Double degenerate
 Image Subtraction Algorithm
• IRAF
 Automated Image Subtraction Algorithm
• ISIS (Alard & Lupton, 1998)

3. Importance SN Ia rate measurements
 Progenitor Models
 Delay Time Distribution
 Iron Abundance in the ICM
 Intra-cluster stellar component tracer
 Cosmology
• Improved cosmological parameters

4. Physical Processes




5. Image Subtraction Algorithm – IRAF
 Measure FWHM of few stars
 Convolve images to seeing of worst frame
 tw05.R186.1001.fits > conv_tw05.R186.s23.fits

6. Image Subtraction Algorithm – IRAF cont...
 tw05.R128.1004.fits > conv_tw05.R128.1004.s23.fits

7. Image Subtraction Algorithm – IRAF cont...
 Scale flux of convolved reference frame to match the rest
of the convolved frames
 Flux conv_tw05.R186.1001.s23.fits = Flux conv_tw05.R128.1004.s23.fits

8. Image Subtraction Algorithm – IRAF cont...
 Subtract scaled convolved reference from each convolved image
 Normalize difference image with Poisson fluctuations > S/N image

9. Automated Subtraction Algorithm – ISIS
 Measure FWHM of few stars - IRAF
 Crop out common area > 3600 x 3600 - Python script

10. Automated Subtraction Algorithm – ISIS cont...
 Produce 900 x 900 cutouts (for MS0451) – Python script
 Apply automated subtraction steps

11. Automated Subtraction Algorithm – ISIS cont...
 interp.csh
 image registration – match coordinates to reference frame
 ref.csh
 composite reference frame
 subtract.csh
 mrj_phot C code, convolution kernel modeling, difference images
 detect.csh
 normalize subtracted images with photon noise
 find.csh
 positions of candidate transients
 phot.csh
 light curve production

12. Automated subtraction steps – ISIS cont...
 Mosaic the sub-images to produce complete difference
image – Python script

13. Automated Subtraction Algorithm – ISIS cont...
 Left: difference sub-image
 Centre: difference sub-image normalized by poisson fluctuations
 Right: positions of variables located by “find.csh”

14. Transients found by both Algorithm in the same images
Top row: Iraf Algorithm
Bottom row: ISIS algorithm

15. Comparison of the algorithms,
Left – IRAF; Right – ISIS
 Time span from image convolution to differencing
 IRAF algorithm ~ 1 week
 ISIS automated algorithm ~ 3 - 4 hours

16. THANK YOU

17. References
 Alard C. & Lupton, R. H. 1998, ApJ, 503, 325
 Alard, C. 2000, A&A, 144, 363
 Barbary et al. 2011, arXiv:1010.5786v3
 Dilday et al. 2010, ApJ, 715, 1021
 Maoz & Avishay 2004, MNRAS, 347, 951
 Sand et al. 2008, AJ, 135, 1917
 Sharon et al. 2010, ApJ, 718, 876