[KIDS] QC coadds for KiDS-INT-DR2

[Gijs Verdoes Kleijn]

Dear Lino and Fedor,

Thanks for this analysis. I think it is an insightful comparison to test 
homogeneity over coadds. I have included these results in the release 
table on photometric homogeneity. I propose to put this comparison also 
in the synoptic table plots.

A few points follow below.
Best wishes, Gijs

Op 2-12-2012 3:51, aniello grado schreef:
>   Dear Gijs and Jelte,
>
>   As agreed in the last teleconf we made the comparison between SDSS
>   (catalogs provided by Mario) and KIDS catalogues (from the catalogs
>   group) for the coadds flagged as zero.  For the SDSS we adopt the
>   psfmag beeing interested in comparing stars magnitudes. For the KIDS
>   we adopt the aperture magnitude at 20 pixels,  an aperture corrections
>   was calculated as the difference between mag_auto and mag_aper for the
>   stars with magnitude between 16 and 17. This is indeed a very crude
>   aperture correction and somehow arbitrary choice but in this way we
>   have a consistent view of systematic offset between SDSS and KIDS.
>   Clearly the final test would be to evaluate PSF magnitudes on KIDS!!
>   The range in ra and dec was divided in 25 intervals and the median of
>   the magnitudes difference between SDSS and KIDS was calculated.
What's the typical #stars per interval?
>   We select high signal to noise stars  which have a psfmagerr < 0.03.
>   Indeed we perform the tests for all the 52 coadds and this is what you
>   get in the attached tar.
>   The first plot shows the delta mag as function of RA. Overplotted is
>   the line interpolating the median values. The same as function of DEC.
>   The last plot shows in arbitrary colors the deltamag vs RA and DEC
>   (just to have a 2D impression of systematics trends).
Systematics seem mild but also seem chip-related often. Shows we have 
handle to improve homogeneity further.
> As bonus track in the next mail you will get an animated gif of such
> plots (too big to be attached here).
>
>   Also is attached a file with tile_name min, max and max-min median
>   magnitude differences between SDSS and KIDS. The last column (max-min)
>   gives an indication about the biggest difference of a median filtered
>   magnitude variation in the field of view compared to SDSS. The file
> is ordered as increasing (max-min).
Will be interesting to compare to the KiDS-internal counterpart 
measurement. Currently this can come from min-max analysis in KiDS-KiDS 
coadd-overlaps. Gives a baseline on homogeneity from edge to edge in the 
OmegaCAM mosaic. Later on ATLAS-KiDS will add more "baselines" within 
mosaic to test homogeneity over.
Best wishes, Gijs

>   In particular for the flagged zero coadds we have:
>
>                                  vs  dec           vs  ra
>   KIDS_139.0_-1.5_i    0.026           0.019
>   KIDS_184.0_-1.5_i    0.039           0.029
>   KIDS_184.0_1.5_u    0.048           0.050
>   KIDS_184.0_1.5_i     0.022           0.037
>   KIDS_185.0_-1.5_r    0.035          0.048
>   KIDS_186.0_-0.5_u   0.040          0.044
>   KIDS_186.0_0.5_i     0.029          0.043
>
> This indicate that for the flag=0 coadds there are no big problems
> from a photometric point of view. Other tests on limiting magnitudes
> in particular regions or morphological studies on galaxies in such
> regions should be performed.  Also should be noted that for some u
> band coadds a big max deviation is found. This is due to problems in
> the SDSS catalog. A simple check like psfmag vs RA and DEC shows a
> region where the mags jump by 5-6 mags. In those regions the psfmagerr
> is anomalous big (~1 mag) but still to small compared to the true
> systematic error.
>
>   Fedor and Lino
>
>
>> Also we evaluate the
>>
>> --
>> <<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>
>>
>> Aniello Grado, PhD
>>
>> Ricercatore Astronomo
>> INAF- Osservatorio Astronomico di Capodimonte
>> Via Moiariello 16 80131 Napoli
>> ITALIA
>> Tel: 0039 0815575547
>> Fax: 0039 0815575433
>>
>> <<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>
>
>

-- 
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|dr Gijs Verdoes Kleijn         |   astronomer                     |
|e-mail: verdoes at astro.rug.nl   |   OmegaCEN / Kapteyn Institute / |
|www: www.astro.rug.nl/~verdoes |   Target                         |
|tel: +31-50-3638326            |   University of Groningen        |
|mobile: +31-654658050          |   postal address:                |
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