I want to use the 'GFM_StellarPhotometrics' field for star particles in a given snapshot, but it seems not to work, both in TNG100-1 and TNG100-3.
I call star particles as:
stars=il.snapshot.loadSubset(basePath, 18, 'stars', fields=fields_s)
but python gives me this error (not only for THIS snapshot) :
Exception: Particle type  does not have field [GFM_StellarPhotometrics]
Hope you can help me.
Snapshot 18 is a "mini" snapshot, so the GFM_StellarPhotometrics is not available - it only exists for "full" snapshots.
The reason we skipped this in mini snapshots is that, in general, people may prefer other methods/tools to generate photometry from star particles, and this can be done at any snapshot using the stored (birth time, metallicity, and initial mass) of each stellar population. You can use the BC03 models, or e.g. FSPS or any other stellar population synthesis code.
ok, thank you very much. What do you mean for mini snapshot, also that there are less particles compared to full snapshots?
By "mini" we mean that they contain only a subset of fields (for all particles). The snapshot organization is described more on the data specifications page.