Returns LCOGT optical filter characteristics
This primitive is suitable for LCOGT optical photometry.
The filter name comes from the user header ORAC_FILTER.
The recognised filters have names ending with U, B, V, R, I, up, gp, rp, ip, zp, zs and Y.
The mean extinction coefficients are: U: 0.53, B: 0.27, V: 0.14, R: 0.10, I: 0.05, u’: 0.56, g’: 0.20, r’:0.11, i’: 0.05, z’: 0.04 and Y: 0.03. Zero extinction applies to any other filter. Effective wavelengths are from Bessell (1998); extinction is from AJP’s loc_m1_assm.c code as of 2012/05/08 for ELP; M1 inst. zeropoints are from AJP’s loc_m1_assm.c code as of 2012/05/08 for 1m0 kb72.