[KIDS] KIDSCAT mag lim implementation

[Gijs Verdoes Kleijn]

Dear Francesco et al,

Many thanks for the input Francesco. I bring this conversation now into 
the mailinglist space to ease following the discussion.

On 11/21/2012 09:42 AM, Francesco La Barbera wrote:
> Dear All,
>
> I just finished to implement the limiting mag computation for KIDS 
> catalogs within
> KIDSCAT. I'm including Gijs and Jelte in cc here so that they are 
> real-time updated, and
> can contribute to the discussion/provide comments of course.
>
> I ran the procedure for all 52 fields. The procedure produces a single 
> plot, with SNR as a function
> of 2'' diameter mag. One example is attached here, for the 
> field KIDS_185.0_1.5.r.
> Black points are all good (flag==0) objects in the field. In red you 
> can see the median trend, while
> the blue curve is the analytic fit
> p_1*flux/(p_2*flux+p_3)
> where p_1, p_2, and p_3 are free fitting parameters.
Looks good! Could you share the script you are using? Then Hugo and I 
will make a python version of it as part of the QC script for sourcelists.

The series of 4 (5?) curves are due to discrete steps in integration 
times due to the dither pattern, right?
The displacement in magnitude seem in rough agreement with that idea:
 >>> -2.5*math.log10(4/5.)
0.24227503252014099
 >>> -2.5*math.log10(3/5.)
0.55462187404089092
 >>> -2.5*math.log10(1/5.)
1.7474250108400469
 >>> -2.5*math.log10(2/5.)
0.99485002168009395

>
> The analytic fit is used to compute the typical mag corresponding to 
> SNR_LIMIT=5 (see dashed and
> solid black lines in the plot). This is our limiting mag.
> The procedure also computes the same kind of limit but for different 
> SNR_LIMIT(i.e. 10 and 15). These
> values are stored in an ascii file (MLIM.dat), into the subdirectory 
> OUTPUT_RES.
Good. Please store the analytic fit parameters as well. Those will come 
in handy.
>
> I made some tests according to what we mentioned some time ago:
> 1) I can confirm that computing SNR from either FLUXERR or MAGERR 
> doesn't make any difference at all (just a sanity check);
Good.
> 2) using different detection tresholds does not change significantly 
> the mag lim estimates; the second attached plot
> shows the effect of decreasing DETECT_TRESH from 2.5 to 2.0 for the 
> same fit as in the example. The mag lim goes
> from 24.77 to 24.78!!
Good to know MAG_APER at 2" diameter is very insensitive to this change 
in DETECT_THRESH. That might be different for e..g, MAG_ISO. For now I 
think it is enough to restrict the lim. mag. analysis to MAG_APER with 
2". For those we have predictions we can compare to (in KiDS proposal). 
KiDS team meeting is a good opportunity if/how we need to extend the 
lim. mag. analysis.
Best wishes, Gijs
>
> Pls, lemme know whatever comment/suggestion you have. Also, do we 
> want/need compute other limiting mags
> (e.g. using MAGAUTO/different apertures)???
>
> Cheers,
> Francesco
>

-- 
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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:                |
|                               |   Kapteyn Astronomical Institute |
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