The following is a comparison of the outputs, returned values and user options for this module versus imexamine in IRAF
How do the numerical results compare with the IRAF version? This is a little harder to judge with cursor centering. Visual comparison of the resulting plots shows good agreement, as well as some random checks of the photometry and statistical return methods.
IRAF “m” key:
–> imexam
# SECTION NPIX MEAN MEDIAN STDDEV MIN MAX
[584:588,697:701] 25 46533. 51314. 10281. 21215. 56186.
imexam “m” key (with cursor location flooring):
[583:588,695:700] median: 51458.000000
imexam only shows one statistic at a time. The same function call may be used to show the results from any valid numpy function, it will return an attribute error for invalid functions. For example, if you edit the defaults dictionary for the “m” key:
viewer.mimexam()
{'function': ['report_stat'],
'region_size': [5, 'region size in pixels to use'],
'stat': ['median',
'which numpy stat to return [median,min,max...must map to a numpy func]']}
viewer.exam.report_stat_pars["stat"][0] = "max" <---- will report np.max for the array
[584:589,695:700] amax: 56186.000000
viewer.exam.report_stat_pars["stat"][0] = "mean" <---- will report np.mean for the array
[583:588,694:699] mean: 45412.878906
viewer.exam.report_stat_pars["stat"][0]="std"
[583:588,694:699] std: 10706.179688
IRAF “a” key:
# COL LINE COORDINATES
# R MAG FLUX SKY PEAK E PA BETA ENCLOSED MOFFAT DIRECT
585.81 698.16 585.81 698.16
17.51 8.86 2.858E6 10840. 45443. 0.03 -64 8.32 5.23 7.10 5.83
imexam “a” key (using the defaults):
xc=586.138728 yc=697.990516
x y radius flux mag(zpt=25.00) sky fwhm
586.14 697.99 5 1508664.63 9.55 11160.89 6.03
The “xc” and “yc” returns are the gaussian fit centers, as well as the FWHM from the fit. If we set the values to be similar to what IRAF.imexamine used, we can see the numbers are closer, the radius for the apertures are floored though before being sent to photutil:
viewer.aimexam()
{'center': [True, 'Center the object location using a 2d gaussian fit'],
'function': ['aperphot'],
'radius': [5, 'Radius of aperture for star flux'],
'skyrad': [15, 'Distance to start sky annulus is pixels'],
'subsky': [True, 'Subtract a sky background?'],
'width': [5, 'Width of sky annulus in pixels'],
'zmag': [25.0, 'zeropoint for the magnitude calculation']}
viewer.exam.aperphot_pars["radius"][0]=17.5
xc=586.213790 yc=697.501845
x y radius flux mag(zpt=25.00) sky fwhm
586.21 697.50 17 2565167.11 8.98 11162.83 6.02
This one differs the most from the IRAF result. Instead of showing the fit profile of the star out to the specified radius, I chose to instead plot the curve of growth along the same radius. Users can still look at the fit profile of the star using the 1D gaussian option. The two options seemed to provide similar information in IRAF and the added curve of growth information should extend the usefulness in this python package. By default, imexam prints the data point values to the screen.
imexam prints the plotted data to the screen
xc=254.175307 yc=238.815292
radii:[ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25]
flux:[30934.408146022368, 114046.22547367863, 177389.39089718129, 202243.23883521429, 213454.31429635832, 219322.32530913973, 223395.73606952291, 226248.48319652156, 228435.17955336376, 230380.36766761239, 232201.61496279205, 234076.75246054522, 236123.10410712915, 238158.7402636983, 240158.23945478137, 241891.71717447872, 243568.62690102594, 245329.38157960901, 247033.98100633049, 248685.62548291287, 250207.19453966396, 251513.40886564567, 252770.43217266718, 253758.53886851895, 254644.90939720051]
Keep in mind that python is 0-index and IRAF returns 1-index arrays, so the equivalent IRAF plot of 587 is really 588:
.
An added benefit in the python package is that you can zoom in and out of the plots using the window controls, below is a zoomed in area of the column plot as it appears in the window:
These plots are representative for both the column and line versions
imexam prints the fit information to the screen
xc=585.660034 yc=697.499370
(585,697) mean=585.900, fwhm=5.653
The default viewing angle for this package was set to that the axis are easiest to read, the user may choose a different azimuthal value as well. The most fancy imexam surface plot is displayed, the user can alter it with the available options.