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Mapping of the PSF to large radii » History » Version 14

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Emmanuel Bertin, 11/13/2013 12:23 PM


Mapping of the PSF to large radii

We stack star images with SNRs>100 (20 in the u-band) in each channel (excluding CCD # 61) using reduced images DECam_00180620-25, DECam_00180721-32, and normalizing all exposures to the flux in a ring with diameter 6"<⌀<9". The central 5" are affected by saturation so we merge the stacked star images with the PSFEx model obtained from the concatenation of DECam central CCDs (#28 and #35); basically all pixels at radius <3" are replaced with the PSFEx model while the outer pixels are from the stacked star images, scaled to match the PSFEx model in the ring with diameter 6"<⌀<9". The results are "average" PSF images with a 0.263" pixel scale, normalized to 1 inside a disk with diameter ⌀=6", and with a dynamic range that reaches about 15 magnitudes (~120dB):

channel u g r i z Y
PSF image (N is up, E is left) Stacked PSF model in the u band Stacked PSF model in the g band Stacked PSF model in the r band Stacked PSF model in the i band Stacked PSF model in the z band Stacked PSF model in the Y band
PSF isophotes [mag.arcsec⁻²] Isophotes of the stacked PSF model in the u band Isophotes of the stacked PSF model in the g band Isophotes of the stacked PSF model in the r band Isophotes of the stacked PSF model in the i band Isophotes of the stacked PSF model in the z band Isophotes of the stacked PSF model in the Y band
FITS file psf_u.fits.gz psf_g.fits.gz psf_r.fits.gz psf_i.fits.gz psf_z.fits.gz psf_Y.fits.gz
Seeing 0.99" 0.92" 0.83" 0.75" 0.77" 0.77"
Mag offset from ⌀=60" to ⌀=6" 0.0061 0.0049 0.0041 0.0040 0.0116 0.0516
Surface brightness μ as a function of distance d Stacked PSF profile in the u band Stacked PSF profile in the g band Stacked PSF profile in the r band Stacked PSF profile in the i band Stacked PSF profile in the z band Stacked PSF profile in the Y band
μ at d = 30" [mag.arcsec⁻²]* 15.69 16.15 16.42 16.57 14.92 13.33
μ at d = 60" [mag.arcsec⁻²]* 17.80 18.49 18.94 19.13 16.90 16.15

* Extrapolation based on best-fitting bi-Moffat model.