Ephemeris defaults to DE440

[vhaasteren]

When reading a par file with load_pulsar, there is an option to set ephem which defaults to DE440. This is problematic when the EPHEM is set in the par file already, because then the wrong ephemeris is used.

Physically one could argue that using the latest ephemeris is always best, especially when simulating data, but this default overwriting the value in the par file violates the principle of least surprise.

[bencebecsy]

Yes, that's a good point. The two places I see where we actually use ephem is pint.toa.get_TOAs when reading in the pulsar and for setting up and enterprise Pulsar object for saving it. Are those smart enough that if we call them without an ephem specified they will just use what's in the par file?

Maybe the default should be None in which case we could call these without ephem specified and print out a note that we are using whatever's in the par file. But if the user specifies a specific ephem we can use that.