PhoSim Tutorial 6: How to Create a Custom Catalog

Custom catalogs can be created by adding lists of objects that you want PhoSim to simulate. For example, the following catalog simulates 3 different stars (point sources) with flat SEDs and different brightnesses.

rightascension 0

declination 0

object 0 0.01 0.0 18 ../sky/sed_flat.txt 0 0 0 0 0 0 star none none

object 0 0.00 0.01 16 ../sky/sed_flat.txt 0 0 0 0 0 0 star none none

object 0 0.01 0.01 14 ../sky/sed_flat.txt 0 0 0 0 0 0 star none none

This results in an image as:

Three Stars with PhoSim

The most important parameters are the right ascension/declination (third and fourth column) and the source magnitude (fifth column). The flat SED filename is a standard spectral energy distribution that has a constant number of photons per wavelength bin. Note that the SEDs are referenced relative to the SEDs directory in the data directory. 

The next 6 numbers are used for the redshift and the weak lensing distortion that we cover in other tutorials. The star parameter establishes the object as a point source. We cover other spatial models in other tutorials. Finally, the dust absorption is turned off by the last two keywords.

The full documentation of the object format is found in the User Catalog Documentation.

Another useful option for very large catalogs or catalogs that are used in different contexts is the includeobj command. Here instead of specifying the objects in the catalog file, instead the file is referenced from the includeobj command. The command can be used many times, for example, to separate kinds of objects and then have a range of observing configurations (filter/pointing) for simulations of the same objects. The catalog can also be gzipped and PhoSim will directly read the catalog in compressed form. Thus, arbitrarily large catalogs can be efficiently stored. This is particularly useful for grid computing where transferring large catalogs across the grid in principle take more time than running PhoSim making the computation I/O bound.