MOPEX Online Manual
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APEX Modules: Aperture (Photometry)
Output Directory Keyword: OUTPUT_DIR
Default Output Directory: <output_dir>
Depends on: Detect
Important notes: The input image for this module is not set from within the parameter block, but by the keyword in the Global Parameters section of the namelist called use_background_subtracted_image_for_aperture. When using a sky annulus to subtract the background, it is recommended to use the original image as input rather than the background-subtracted one (i.e. use_background_subtracted_image_for_aperture = 0).
PURPOSE
-
This module calculates the flux(es) within the specified circular
aperture(s) for each source in the extract table. It will optionally
subtract a background value from a user-defined annulus. The annulus
value can be the mean, median or mode.
PARAMETER BLOCK
-
&APERTURE
N_Apertures = 1,
Aperture_Radius_1 = 5.0,,
Aperture_Radius_2 = 6.0,
Aperture_Radius_3 = 7.0,
Use_Annulus = 1,
Min_Number_Pixels = 10,
Annulus_Compute_Type = 'mode',
Inner_Radius = 15,
Outer_Radius = 25,
&END
INPUTS
N_Apertures: (int) Number of circular apertures to draw around each source, between 1 and 3.
Aperture_Radius_N: (float) Radius of aperture N in pixels.
Use_Annulus: (1,0) Switch to choose whether or not to subtract the background calculated from a user-defined annulus.
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: (char) The method used to compute the sky background. Choices are mean, 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.
OUTPUTS
- 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, turn this switch off:use_background_subtracted_image_for_aperture = 0in the command-line namelist, or uncheck it in Apex Settings in the GUI.
For more details, see Basic Concepts: Aperture Photometry.
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