Here are some notes I made on Apr15,2018. I
Development notes for usno_photcal with wcs-calibrated image:
20180206T022042.6_acm_sci_proc.fits
% usno_photcal ./S/20180206T022042.6_acm_sci_proc.fits Y
arg1 - Name of FITS image (can be full path)
arg2 - run in debug mode (Y/N)
I'm set up to run this in:
/home/sco/play
/home/sco/A_wcsf/zp0
At the most basic level I need a star with standard (USNO) and
instrumental magnitudes.
Recall my mido magnitude: MAG30ZP = 30.0 - 2.5 log (F)
where F is the sky-subtracted total signal in aperture (in ADU)
For a basic test set, when I use "Blue 16.0" I get 5 stars. I
remove the stars labeled: 2,3,4
I also add one sky box.
At the end of this, I get the following table: midodata.2.table (see midodata.2.parlab)
# Contents of: midodata.2
Col01 = X pixels (aperture X center)
Col02 = Y pixels (aperture Y center)
Col03 = X center, pixels (intensity weighted centroid)
Col04 = Y center, pixels (intensity weighted centroid)
Col05 = magnitude (assuming zp=30)
Col06 = Average value per pixel in aperture
Col07 = Average value per pixel in annulus
Col08 = number of pixels in aperture
Col09 = Peak pixel value (no bkg-sub, image ADU)
Col10 = marker code (1=circle,2=box,3=ellipse)
203.26 264.65 202.57 263.56 17.066 180.301 41.740 1076.0 4114.00 1 # star 1
516.98 624.06 517.31 624.67 15.703 527.447 43.506 1081.0 14402.50 1 # star 5
555.84 446.55 553.31 443.36 21.982 39.476 39.337 11550.0 983.50 2
Recall that star name is the line number in the cdfp file = 20180206T022042.6_acm_sci_proc-usno.cdfp
I can retrieve the standard mag values with the routine:
% cdfp_getline.sh 20180206T022042.6_acm_sci_proc-usno.cdfp Blue 1
15.8000
% cdfp_getline.sh 20180206T022042.6_acm_sci_proc-usno.cdfp Blue 5
cdfp_getline.sh 20180206T022042.6_acm_sci_proc-usno.cdfp Blue 5
14.0800
**** Just looking at the cdfp file I see that these are correct.
Hence, the ZP values are:
Star MAG30ZP MAGSTAN
1 17.066 15.800
5 15.703 14.080
To see how Mag20ZP is computed in the code:
SCOLIB m2048ims.f
measure_circle_simple compuets Npix Average SIGMA MERR min max TCOUNT (=total flux)
measure_aper_wbkg (m2048ims.f:1052) like above, but handles the local sky subtraction
I use measure_circle_simple in mido.f (mopo code)
measure_aper_wbkg In this routine I gather both the aperture and annulus stats.
Here is the code I use to get the magnitude in aperture:
c predict background in aperture (line 1289 i m2048ims.f)
Tap_bkg = xnp*averageA
Tfcorr = sum - Tap_bkg
xMagZP30 = -99.0
if( Tfcorr.gt.0.0 ) xMagZP30 = 30.0 - 2.5*alog10(Tfcorr)
where,
c sum = total flux in aperture
c xnp = number of pixels in aperture
c xnpA = number of pixels in annulus
c averageA = average flux per pixel in annulus
======================================================================================================================
In my example for star 1, here are the values as they appear in the *.info file:
Nap = 1076.0 / Number of pixels in aperture
AVann = 41.73976898 / Average pixel value in annulus # this is averageA
AVap = 180.30111694 / Average pixel value in aperture # average in aperture ----> in midodata2 table
Tap = 0.19400400000000E+06 / Total summed pixel flux in aperture # total sum = 194004.000
MagZP30 = 17.0664 / BKG-corrected aperture magnitude (ZP=30)
======================================================================================================================
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Here I confirm how my mag is computed
Tap_bkg = 1076.0 * 41.7397 = 44909.98
what I write to my table is average pixel value in aperture (not the sum total)
AVap = 180.3011
sum = 194004.0
Nap = 1076
Do I get the same average? Avap = 194004 / 1076.0 = 180.301 Yes!!!!
Total flux = 1076.0 * 180.3011 = 194003.98
To get total sky subtracted flux from my midodata2 values alone?
Flux in ap due to sky = 44909.98
Total flux in ap = 194003.98
Total ap flux above sky = 149094.0 adu
mag = 30 - 2.5 log( 149094.0 )
= 30 - 2.5 (5.1735)
= 30 - 12.9337
Mag30 = 17.0663 Yes!!!! This is what was stored above.
So, here is my midodata2 table line with variabe names as column headings:
Mag30 Avap AVann Bpix
203.26 264.65 202.57 263.56 17.066 180.301 41.740 1076.0 4114.00 1
So, star_flux = (180.301-41.740) * 1076
= 138.561 * 1076
= 149091.636
Hence,
Mag30ZP = 30 - 2.5 * log(149091.636)
= 30 - 2.5 * 5.17345
= 30 - 12.93362
= 17.066 **** This is the magnitude reported in the midodata2 table!!!!
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
In m2048ims.f line 1201 I compute
average = -999.0
if( xnp.gt.0.0 ) average = sum/xnp
where xnp = 1076 sum = Tap
======================
Where I packed the values:
# Number of pixels in aperture
ncd=ncd+1
kw = "Nap "
com = "Number of pixels in aperture "
keyword(ncd) = kw
comhold(ncd) = com
write(b20,1200) xnp
# Store the total sum in aperture
ncd=ncd+1
kw = "Tap "
com = "Total summed pixel flux in aperture "
keyword(ncd) = kw
comhold(ncd) = com
write(b20,1202) sum
# Store the average in background annulus
ncd=ncd+1
kw = "AVann "
com = "Average pixel value in annulus "
keyword(ncd) = kw
comhold(ncd) = com
write(b20,1201) averageA
b20hold(ncd) = b20
--------------------------
# I store both the average in apertur and the sum total
# Store the average in aperture
ncd=ncd+1
kw = "AVap "
com = "Average pixel value in aperture "
keyword(ncd) = kw
comhold(ncd) = com
write(b20,1201) average
b20hold(ncd) = b20
# Store the summed total in aperture
ncd=ncd+1
kw = "Tap "
com = "Total summed pixel flux in aperture "
keyword(ncd) = kw
comhold(ncd) = com
write(b20,1202) sum
b20hold(ncd) = b20
--------------------------
# Finally, I store the background -subtracted magnitude
ncd=ncd+1
kw = "MagZP30 "
com = "BKG-corrected aperture magnitude (ZP=30) "
keyword(ncd) = kw
comhold(ncd) = com
write(b20,1203) xMagZP30
b20hold(ncd) = b20