PhoSim Tutorial 12: How to Create Custom Moving Objects

Objects that move on long timescales (hours/days/years/centuries) can be handled by simply making two catalogs and changing the right ascension and declination of the object in the second catalog. However, objects that move on short timescales (seconds/minutes) may move enough that its position changes during an exposure. This is particularly true for asteroids, comets, and satellites.

In PhoSim, this is handled by several spatial models. A simple example is a moving point source that is specified by a catalog as:

rightascension 0

declination 0

object 0 0.0 0.0 10 ../sky/sed_flat.txt 0 0 0 0 0 0 movingpoint 10.0 30.0 none none

Here the object will move 10 arcseconds every second in time. The position angle of the motion is 30 degrees. The resulting image is:

Notice the wiggling shape of the pattern is not caused by the object itself, but rather the turbulence and tracking in PhoSim that keeps the track from being straight.

There are more complex models: moving disk, moving sphere, and moving reflected sphere that are specified on the instance catalog page. An example of the moving reflected sphere is given by this catalog:

rightascension 0

declination 0

object 0 0.0 0.0 10 ../sky/sed_flat.txt 0 0 0 0 0 0 movingpoint 10.0 30.0 1.0 1.0 none none

The corresponding image is:

Here more details of the source's illumination pattern is visible.