PhoSim Tutorial 14: How to Use Different Spectral Energy Distributions

Step 1: Getting SEDs

These catalogs use this library of SEDs, which can be used with PhoSim, that are curated by the Spanish Virtual Observatory and the Space Telescope Institute. After downloading and untarring, these SEDs should be put into the directory data/SEDs

Step 2: Making Catalogs

Catalog 1

Catalog 2

Catalog 3

The spectral energy distribution of every entry in the catalog can be customized. The objects automatically generated from the stars and galaxies commands have unique, realistic SEDs. You can customize the SEDs in a number of different ways. An example of this is these three simple catalogs below, which generate an M star, a Sun-like star, and an O star. 

Step 3: Running phosim

We then generated images using 3 separate phosim commands with -c examples/nobackground. Then a 3 color image can be made with the following command:

Step 4: Opening in DS9

To view your three color image in ds9:

Here is an example of a generated image where a clear chromatic differences of the 3 stars can be seen.

Creating your own SEDs

SEDs can also be made easily. A PhoSim formatted SED is two columns. The first column is the wavelength in nanometers. The second column is the flux in ergs per square centimeters per second per angstroms. An example of a simple SED is as follows:

The overall flux normalization is not important as the normalization is defined on a object by object basis, and not in the SED. PhoSim therefore automatically renormalizes every SED. The wavelength grid does not have to be uniform, either, and can also start and stop at any wavelength where the spectrum is relevant. The files can also remain gzipped to reduce space, and PhoSim will read the files while gzipped. 

A monochromatic SED would simply be one line: