= PGC55 =

pgc55 
 * RA:  0.15583   
 * Dec: 33.60094  
 * Ra = 0.67 (arcmin)
 * Rb = 0.20 (arcmin)
 * PA = 13.12 (degrees)

# position angle (PA)  [Degrees: Up=0, Left=90]"
{{{
run_sex <root> <ra> <dec>
./run_sex.csh pgc55_g 0.15583 33.60094
}}}

= SExtractor first outputs = 

||filter || Mag || X0 || Y0 || RA || DEC || Re || Ra  || Rb  || b/a || PA  || 
|| || mag || pix || pix || deg || deg || arcmin || arcmin || arcmin ||  ||  deg || 

|| pgc55_u || 16.99 || 458.3 || 459.6 || 0.1555 || 33.6014 || 0.17 || 0.75 || 0.20 || 0.27 || 9.30 || 
|| pgc55_g || 16.11 || 457.8 || 459.1 || 0.1555 || 33.6013 || 0.15 || 0.67 || 0.20 || 0.30 || 13.12 || 
|| pgc55_r || 15.75 || 457.8 || 458.3 || 0.1555 || 33.6013 || 0.14 || 0.65 || 0.20 || 0.31 || 13.20 || 
|| pgc55_i || 15.53 || 457.8 || 457.8 || 0.1555 || 33.6012 || 0.14 || 0.65 || 0.20 || 0.31 || 13.53 || 
|| pgc55_z || 15.38 || 458.0 || 457.8 || 0.1555 || 33.6012 || 0.15 || 0.50 || 0.14 || 0.28 || 12.21 || 



GLGA-qa

{{{
minskywid = 27. / as_pix	 ; 27 arcsec is minimum sky width
factor = 1.5                     ;  1.5 default
skyinner = factor*semimajor
skyouter = semimajor*sqrt(1+factor^2) > (skyinner+minskywid)  


Sigma multiplier for thresshold (default =  2.5): 2.0
Magnitude faint limit (default =  24.0): 25
}}}

I increased the aperture size, until the difference between APR and ASY magnitudes are less than 0.05 mag.

= SKY =

 * u
{{{
final sky/px, skyerr/px     [mJy/px]:    0.00068215   0.00010009  ds/s = ~15%
final musky, muskyerr  [AB mag/as^2]:     22.304     0.159
}}}

 * g
{{{
final sky/px, skyerr/px     [mJy/px]:    0.00083100   0.00003426  ds/s = ~4%
final musky, muskyerr  [AB mag/as^2]:     22.090     0.045
}}}

 * r
{{{
final sky/px, skyerr/px     [mJy/px]:    0.00194121   0.00005404  ds/s = ~3%
final musky, muskyerr  [AB mag/as^2]:     21.168     0.030
}}}

 * i
{{{
final sky/px, skyerr/px     [mJy/px]:    0.00371400   0.00009490  ds/s = ~3%
final musky, muskyerr  [AB mag/as^2]:     20.464     0.028
}}}

 * z
{{{
final sky/px, skyerr/px     [mJy/px]:    0.01061923   0.00031765  ds/s = ~3%
final musky, muskyerr  [AB mag/as^2]:     19.323     0.032
}}}

[[Image(pgc55_sdss_profile.jpg)]] [[Image(pgc55_sdss_images.jpg)]]

----

= Changing the sky aperture =

Now, I keep everything the same but the size of the inner aperture


{{{
minskywid = 27. / as_pix	 ; 27 arcsec is minimum sky width
factor = 2.0                     ;  1.5 default
skyinner = factor*semimajor
skyouter = semimajor*sqrt(1+factor^2) > (skyinner+minskywid)  
}}}


= SKY =

 * u
{{{
final sky/px, skyerr/px     [mJy/px]:    0.00068317   0.00010508  ds/s = ~15%
final musky, muskyerr  [AB mag/as^2]:     22.302     0.167
}}}

 * g
{{{
final sky/px, skyerr/px     [mJy/px]:    0.00083044   0.00003543  ds/s = ~4%
final musky, muskyerr  [AB mag/as^2]:     22.090     0.046
}}}

 * r
{{{
final sky/px, skyerr/px     [mJy/px]:    0.00193863   0.00005487  ds/s = ~3%
final musky, muskyerr  [AB mag/as^2]:     21.170     0.031
}}}

 * i
{{{
final sky/px, skyerr/px     [mJy/px]:    0.00371275   0.00009834  ds/s = ~3%
final musky, muskyerr  [AB mag/as^2]:     20.464     0.029
}}}

 * z
{{{
final sky/px, skyerr/px     [mJy/px]:    0.01062065   0.00033289  ds/s = ~3%
final musky, muskyerr  [AB mag/as^2]:     19.323     0.034
}}}


----

 * left-top :  factor = 2.0  i.e. expand by 100%
 * right-bottom:  factor = 1.5  i.e. expand by  50% (original)

[[Image(pgc55_sdss_profile_factor2.jpg)]]  [[Image(pgc55_sdss_profile.jpg)]]


----

Knowing the fact that estimated error for the background level is <~5%:

 * left-top: Adding 1% to the estimated sky value
{{{
IDL code: sdss_radprof.pro
skyint = 1.01*skyint     ; ehsan-edit
}}}

 * right-bottom: original

[[Image(pgc55_sdss_profile_sky1percent.jpg)]]  [[Image(pgc55_sdss_profile.jpg)]]

Left panel shows that, the sensitivity to the sky background is too high and probably the estimated precession for the sky background level is wrong. 

Final conclusion up to this point (for pgc55): If the profile looks good, we can claim that we've got to the precession of 5% in magnitude (e.g. 0.05 mag).
Slightly changing the position angle (7 degrees) and axial ratio does not change 0.05 mag precession.


----

= GLGA Mask

[[Image(pgc55_glga_mask.png)]] 

----


Archangel:

{{{
sky = 0.000827037089005
skysig = 2.71460323481e-06
}}}

pgc55_profile1.png

rm pgc55_g.clean pgc55_g.xml
xml_archangel -c pgc55_g archangel
xml_archangel -e pgc55_g sky 0.00083100    
xml_archangel -e pgc55_g skysig 0.00003426