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Shantanu Desai, 01/08/2013 03:19 PM

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h1. Wiki
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This can be divided into 3 steps
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h2. Step 1 run modelfitting photometry
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you can find the scripts at /big/users/shantanu/VLTmfp/catalogs/runmfp_b.sh (for b band and so on)
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note that since initial catalogs will be uncalibrated , use -mag_zeropoint for b,I and z bands.
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The zeropoints for HST bands is :
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F606W 26.493mag, F814W 25.947mag.
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the sextractor param file used in the scripts is 
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/big/des_home/stable/etc/sex.param_sersic
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you can edit to remove params you don't need.
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h2. Step 2 Produce a matched catalog across all 4 bands
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This is the most tedious step.  Unfortunately you cannot run sextractor in dual image mode
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since coadds are of different size.
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The way I did it was to run a modified version of a code 
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used in DESDM called coadd_grabmatches. I first ran it to match R vs I band and then used
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that match catalog to match against z band and so on.
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A code to do this is at /home/moon/shantanu/desdm/devel/ImageProc/trunk/src/coadd_grabmatches_singleband.c
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There is one line in the code (below # 266) which needs to be changed depending upon number of coluns
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in input catalog.
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Once this is done you need to make a file with the matched magnitudes in all four bands
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(its possible to automate this script with some effort so that it does not need to be changed)
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h3. Step 3 Doing the stellar locus
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One you have the catalogs all you need to do is to do a fit by eye or quantitative to SED fits provided by Joerg.
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Here is my 2nd order polynomial  curve fit done to these relations
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1) b-R vs R-I
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b -R = -0.2904*x^2+1.319x +0.2941
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(where x=R-I)
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2) R-I vs I -z
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R-I = -1.016*x^2+ 3.532*x +0.1294
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where x=I-z
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3) b-R vs I-z
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R-I = -2.20378*x^2+ 3.96368*x +0.386878
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You can either use (1) & (2) or (2)  & (3) to get the zeropoints.
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I did the plotting in ROOT, but probably it can be done in any software.
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h4. Step 4 Rerun sextractor with the new zeropoints
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Same as (1) but use the new zeropoints now.
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h3. Direct calibration of I-band
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Joerg pointed out that I band can be directly calibrated using
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I_BESS = a0 + a1 * F814W + a2 * (F606W - F814W)
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with
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a0 = -1.009
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a1 =  1.067
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a2 = -0.001
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!{width: 10%}Izeropoint.png!
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This allows us to get direct calibration of I-zeropoint= 28.37+/- 0.02 (where error = sigma of fit/sqrt(no of points))
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We then recalibrated (b-R) vs (R-I)
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!{width: 10%}plotslrfit.png!
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Also a histogram wrt stellar locus
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!{width: 10%}slrhisto.png!
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the zeropoint for b band = 26.88
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h1. Results for other clusters
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h2. SPT-CLJ0102-4915
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I band zero-point = 28.52 +/- 0.0137
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b band zp = 26.87 +/- 0.016
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z band zp = 28.21 +/- 0.015 (I-0.31)
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h2. SPT-CLJ0533-5005
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I band  = 28.52 +/- 0.0123
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b band= 26.69 +/- 0.014
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z band = (I-z+0.4) = 28.12 +/- 0.006
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h3. SPT-CLJ0559-5249
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I-band 28.32 +/- 0.005
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b band 27.2 +/- 0.023
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z band (I-z+0.44) 27.88 +/- 0.0147
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h3. SPT-CLJ2331-5051
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I-band  28.32 +/- 0.012
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b-band 27.07 +/- 0.017
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z-band  I-z+0.42   27.9 +/- 0.013
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h4. SPT-CLJ2337-
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I-band 28.38 +/- 0.0123
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