Important notes: The input image for this module is not set from within the parameter block, but in the APEX Settings module, using the parameter Use Background Subtracted Image For Aperture. When using a sky annulus to subtract the background, we recommend using the original image as input rather than the background-subtracted one (i.e. do not turn on the Use Background Subtracted Image For Aperture option).
PURPOSE
This module calculates the flux(es) within each specified circular aperture for each source in the extract table. It will optionally subtract a background value from a user-defined annulus. The background value can be set to the median or mode of the good pixels in the annulus. The aperture photometry is calculated using an exact algorithm to compute a fractional aperture-pixel overlap.
INPUT
Number of Apertures: (int) Number of circular apertures to draw around each source, between 1 and 5.
Aperture Radius N: (float) Radius of aperture N in pixels.
Min Number Pixels: (int) Minimum number of good pixels required in the annulus. If there are fewer, it will not subtract the background.
Annulus Compute Type: The method used to compute the sky background. Choices are median or mode of the good pixels in the background annulus.
Inner Radius: (float) Inner radius of annulus in pixels.
Outer Radius: (float) Outer radius of annulus in pixels.
Use Annulus: Check this box to subtract the background as calculated using a user-defined annulus.
COMMAND LINE INPUT
&APERTURE
N_Apertures = 3,
Aperture_Radius_1 = 5.0,
Aperture_Radius_2 = 6.0,
Aperture_Radius_3 = 7.0,
Min_Number_Pixels = 10,
Annulus_Compute_Type = 'mode',
Inner_Radius = 15,
Outer_Radius = 25,
Use_Annulus = 1,
&END
OUTPUT
Output Table (aperture.tbl): The aperture fluxes are written into the extract table, along with the number of bad pixels in each aperture. A separate aperture table is also created.
DISCUSSION
The default for this module is to work on median-filtered background-subtracted images if they are there. Because subtracting the background can be difficult, it is generally better to work on the original images, unless the background is complex or you are sure it has been correctly subtracted. To do this, uncheck the Use Background Subtracted Image for Aperture box in the APEX Settings module.
