DRAVG test on SN 2009kf photometry (MT Botticella)

We are working on photometry of the the SN PS1-0609001 (2009kf) and we have been looking at the newly released MD08 images (stacks for each epoch).

Several immediate problems :

-masked areas

the stacks have a lot of masked areas and sometimes the SN host galaxy is hidden (see fig stacks, stacks_2,stacks_3 in the green circle the SN host galaxy).

If you look at some of the not saturated stars (for example the green ringed stars in fig Stars_ppStack.jpg) they have mask "blocks" sitting on top of them. The masks are not symmetrical, nor simply on the highest pixel value, but are irregular shapes, sitting over part of the psf.

These were several of the comparison stars for the SN photometry and we can not use them to calibrate the SN mag. There are masked areas all over the images. These masks are mostly (but not always) associated with moderately bright stars - but the star cores are not saturated (we know this from comparisons with other images, and other stars in the field). The profiles of the same stars on stacked images obtained with IRAF with median combine and crreject are different

-background

We are using the template subtraction technique to remove the signal of the host galaxy. The SN residual on difference image is nice but it is impossible to obtain an accurate measurement because of the background around the residual.

We collected some images from the Liverpool telescope and you can see the two difference images obtained with the same procedure (right images from the LT (stacked with IRAF) left images from PS1 (stacked with IPP). We also found a bigger scatter between the zero points in the PS1 images with respect the LT images. Here some numbers relative to the same sequence stars

13/10/09 z band LT

id fwhm ph_mag fit_mag fiterr zp

1 5.0 -4.379 -4.589 0.007 22.43 2 5.0 -2.990 -2.858 0.025 22.41 5 5.0 -5.597 -5.613 0.005 22.42 6 5.0 -5.043 -5.092 0.005 22.40 7 5.0 -5.350 -5.418 0.004 22.41 8 5.0 -5.168 -5.287 0.005 22.41

PS1 (target and template are obtained stacking 8 PS1 images)

16/06/09 z band

id fwhm ph_mag fit_mag fiterr zp

1 7.0 -6.42 -6.45 0.006 24.30 2 7.0 -4.63 -4.62 0.006 24.10 5 7.0 -7.47 -7.49 0.003 24.29 6 7.0 -6.89 -6.91 0.002 24.15 7 7.0 -8.28 -7.19 0.003 24.19 8 7.0 -7.1 -7.13 0.003 24.25

We tried to combine the warps available with IRAF and to obtain some measurements on these new stacks. In this case the measure is easier and the scatter is reduced.

PS1 (target and template images are obtained stacking warps with IRAF)

130609 z band

id fwhm ph_mag fit_mag fiterr zp

1 6.2 -6.466 -6.544 0.011 24.38 2 6.2 -4.657 -4.739 0.019 24.22 5 6.2 -7.451 -7.554 0.011 24.36 6 6.2 -6.783 -6.962 0.011 24.27 7 6.2 -7.892 -7.288 0.011 24.28

160609 z band

id fwhm ph_mag fit_mag fiterr zp

1 6.9 -6.421 -6.395 0.007 24.23 2 6.9 -4.402 -4.614 0.018 24.09 5 6.9 -7.453 -7.405 0.005 24.21 6 6.9 -6.871 -6.828 0.005 24.18 7 6.9 -7.158 -7.151 0.006 24.14 8 6.9 -7.107 -7.070 0.006 24.19