Adding New Filters Documentation

[kfosdick]

Hello,

I wanted to confirm, as suggested in issue #46, that modifying the FILTER_LIST, magsun.dat, and filter_lambda_eff.dat files is important when adding new filters to python-fsps. My code gave non-physical results until I added information for my custom filters into these files.

Would it be possible to add documentation about adding new filters to the python-fsps documentation page, since the filter-adding process is different than that for FSPS? This might help others avoid this issue in the future, especially those who have less experience with github.

Thank you!

[jurgenpopp]

Hi, in addition to the above comment, is there any documentation about how the transmission data for the filters are normalised or transformed from sources like https://cosmos.astro.caltech.edu/page/filterset or http://svo2.cab.inta-csic.es/theory/fps/ ? The values differ between allfilters.dat and transmission data from the external sources and I am wondering what I am missing here...?

Cheers!

[bd-j]

Hi @jurgenpopp,

Sorry, there is not detailed information on the transmission curve sources beyond this. I note that for FSPS the overall normalization is not important, as detector signal is computed relative to a standard (f_nu=3631Jy for AB or a Vega spectrum). In some cases the transmission curves may have been altered to account for unit differences (signal per energy vs signal per photon). In other cases this may be due to updates that have not been incorporated into FSPS.

FWIW I often find it more straightforward to use FSPS for providing spectra and then obtain magnitudes via a separate filter projection package focused on this task, e.g. pyphot, sedpy, or pysynphot