MOPEX Online Manual

Source Estimate

PURPOSE

Performs point source estimation using PRF-fitting. Fits the input image with the PRF to estimate fluxes and refine positions of the point-source candidates from the detection list. If Max_Number_PS>1, the module will attempt to do an "active" deblend on the detections that cannot be successfully fit.

PARAMETER BLOCK

&SOURCESTIMATE
 InputType = 'image_list',
 Fitting_Area_X = 5,
 Fitting_Area_Y = 5,
 Max_Number_PS = 1,
 Chi_Threshold = 3,
 N_Edge = 4,
 Max_N_Iteration = 1000,
 Max_N_Success_Iteration = 0,
 MinimizeFtol = 0.001,
 MinimizeFtolSuccess = 0.00001,
 DitherPixelFraction = 0.1,
 DitherFluxFraction = 0.8,
 DeblendDitherPixelFraction = 1.,
 Background_Fit = 0,
 Random_Fit = 0,
 Chi2_Improvement = 1.,
 PRF_ResampleX_Factor = 4,
 PRF_ResampleY_Factor = 4,
 Normalization_Radius = 44,
&END

INPUTS

Input Type: "image_list" for apex_1frame.pl; "tile_map" for apex.pl

Fitting_Area_X,Y(int): Size of the area in the input image to be fit with the PRF, in input image pixels. If not given, the detection table is expected to have FitX and FitY columns, whose content is used for the same purpose. These columns can be created with the Fit Radius module. If Fitting_Area_X(Y) are set then this will override the output of the module Fit Radius. In order to use the Fit Radius results, make sure that you do not include these parameters in the Source Estimate parameter block.



Max_Number_PS(int): Maximum number of point sources to use in an attempt to deblend a detection (active de-blending).

Chi_Threshold(float): Maximum acceptable value of χ²/dof (degrees of freedom).

N_Edge(int): Positive number excludes point sources within N_Edge pixels of the edge of the input image from fitting. A negative number appends an edge around the input images N_Edge pixels wide to include the point sources into the fitting.

Max_N_Iteration(int): Termination criterion for the maximum number of iterations to reach Chi_Threshold.

Max_N_Success_Iteration(int): Termination criterion for the maximum number of iterations after Chi_Threshold has been reached.

MinimizeFtol(float): Termination criterion for the relative change in χ²/dof to achieve before Chi_Threshold is reached.

MinimizeFtolSuccess(float): Termination criterion for the relative change in χ²/dof to achieve after Chi_Threshold is reached.

DitherPixelFraction(float): See PRF Fitting.

DitherFluxFraction(float): See PRF Fitting.

DeblendDitherPixelFraction(float): Same as DitherFluxFraction but applied during active deblending.

Background_Fit(int): Switch on (=1) to fit a constant background under the point source in the fitting area. Default is off (=0). You may wish to use this module if your field is very crowded. If this option is not turned on, you are relying on the results of the Extract MedFilter module to subtract the background.

Random_Fit(int): Switch on (=1) to give the minimization routine a random start, so that the results of fitting on the same set of data will not be identical for every run.

Chi2_Improvement(float): Acceptable change in χ²/dof for incremented number of point sources in active deblending.

PRF_ResampleX,Y_Factor(int): Ratio of the input image pixel size to the PRF pixel size.

Normalization_Radius(int): PRF flux is normalized within this radius (in PRF pixels). By default, the PRF is normalized to the whole PRF array.

OUTPUTS

Table (*_extract_raw.tbl): The preliminary extract table, which includes the fluxes and improved positions of the point sources, along with other parameters characterizing the fit. Details of the output parameters are given in the description of Select.

DISCUSSION

IMPORTANT: APEX normalizes the PRF before fitting. If Normalization_Radius is specified in the Source Estimate module block, the normalization is peformed over the pixels within that radius (IN PRF PIXEL UNITS) from the center of the PRF. If Normalization_Radius is not specified, APEX will normalize over the available range that the central PRF covers in the PRF FITS file. The central PRF is defined as the one lined up on the center pixel of the PRF FITS file, and corresponds to the response one gets if a photon hits the center of a pixel. Getting correct PRF-fitted absolute fluxes requires having the correct PRF normalization for your data!

Set Fitting_Area_X,Y if Fit_Radius is not run. If Fitting_Area_X(Y) are set then this will override the output of the module Fit Radius. In order to use the Fit Radius results, make sure that you do not include these parameters in the Source Estimate parameter block.

In general, it is better to keep Background_Fit turned off, as it is difficult to get a robust measure of the background within the small fitting area that is best for PRF fitting.