bmodel -- Build a model image from the results of isophotal analysis.
bmodel table output
The bmodel task creates a 2-dimensional image file containing a noiseless photometric model of a source image (referred to here as the "parent" image). The model is built from the results of isophotal analysis generated by the isophote fitting task, ellipse.
The bmodel task is a script that calls, in sequence, tasks tsort and trebin from the ttools package to create a temporary table with an interpolated version of the original input table. This temporary table is then fed to the hidden task model, which creates the actual model.
All information needed for building the model image is in the table created by ellipse, including the parent image name and section, when applicable.
The modelling interval is specified by the parameters fulltable, minsma and maxsma. fulltable should be normally set to yes, so the task will ignore minsma and maxsma and will use instead the full range of semi-major axis lengths included in the table. Care must be taken when using explicitly minimum and/or maximum values, because trebin can also extrapolate from the original data, and meaningless results may be generated in some cases. minsma and maxsma should, in general, be inside the interval of good photometry available in the original table. The interpolation technique is specified by the parameter interp.
Outside the measured region the output image pixels are filled with a constant value supplied by the backgr task parameter.
If the highar parameter has the value "yes", the 3rd and 4th harmonics from the photometry are added to the model. This option is most useful when working close to the central intensity peak (SMA < 10 pixels). As explained in Jedrzejewski's paper (Mon.Not.R.Astr.Soc., 226, 747, 1987), the sampling at small radii is prone to introduce a "boxy" (cos 4*theta) component. More accurate modelling at the central region is generally achieved when including this component.
The modelling algorithm was evaluated with high signal-to-noise synthetic galaxy images. Residuals galaxy-model are usually close to 1-2% at the 5 pixel radius, around 0.5% at the 10 pixel radius, and smaller than 0.2% at radii larger than 20 pixels. These results are for spline table interpolation, which was found to generate the smaller residuals.
The ttools package must be loaded before this task can run.
- table [file name]
- STSDAS table generated by the ellipse task.
- output [file name]
- Output model image created by this task.
- (parent) [file name]
- The original source image analyzed by the ellipse task, i.e., the input used by ellipse. Parameter should normally be left empty.
- (fulltable = yes) [boolean]
- Use full range of semi-major axis from table ?
- (maxsma = 1.0) [real, min=0.0]
- Maximum model semi-major axis.
- (backgr = 0.0) [real]
- Background value to be stored in pixels outside maxsma.
- (interp = "spline") [string, allowed values: nearest |
- linear | poly3 | spline]
Interpolation technique used by the task trebin.
- (highar = no) [boolean]
- Add 3rd and 4th harmonics to the model?
- (verbose = no) [boolean]
- Print the semi-major axis being processed ?
This task was written by I.Busko