PhoSim Tutorial 5: How to Simulate Different Telescopes

Another complex use of PhoSim is to simulate other telescopes. There are a set of files called the instrument and site characteristics (ISC). By default, PhoSim points to the files in data/generic. The generic telescope is a simple 1 meter parabolic telescope with a 1k x 1k sensor. Other implemented designs can be simulated using the -i option as:

phosim catalog -i instrument

Here instrument is a directory that is in the data directory. This could be one of the currently implemented observatories or a custom instrument that you create.

The same scene through multiple telescopes is then very straight-forward. An example of this is a 150 second exposure through the Rubin LSST, WIYN ODI, and JWST NIRCAM instruments that use the following commands.

phosim examples/large_catalog_long_exposure -i lsst -c examples/nocosmics

phosim examples/large_catalog_long_exposure -i wiyn_odi -c examples/nocosmics

phosim examples/large_catalog_long_exposure -i nircam_sw_a -c examples/nocosmics

The Rubin LSST image:

Rubin (LSST) Simulation with PhoSim

The WIYN image:

WIYN Simulation with PhoSim

The JWST NirCAM image:

JWST Simulation with PhoSim

In this way, the same scene has been generated through multiple telescopes, and there are very different output images. The PSF, plate scale, background level, and overall intensity will be the most obvious differences, but many other details will make the images different. Notice the same three bright stars appear in a line on these images. In the JWST image they fit in the whole chip whereas they are near the center of the LSST and WIYN images reflecting the various different plate scales and field of views. The differences in background levels, PSF sizes, and plate scales leads to differing source detection limits.