Fitparameters¶
PySME can use a wide variety of fitparameters, however there are a few things to consider.
How to specify fitparameters¶
Fitparameters can either be passed to ‘pysme.solve.solve’ or as part of the sme structure. When in doubt the explicitly passed values overwrite the structure. Fitparameters are passed using their names as strings (e.g. ‘teff’ or ‘logg’), which are usually straightforward. There are however a few more tricky ones for individual abundances and linelist parameters.
Abundances Individual abundances are passed using strings of the form ‘abund {El}’ where ‘El’ is the short form element we want to fit (e.g. ‘Mg’). PySME supports the fitting of all elements up to ‘Es’. Alternatively you can also use the element number, i.e. the charge number, instead. E.g. ‘3’ for Lithium
Linelist For linelist parameters use ‘linelist {nr} {p}’, where ‘nr’ is the index in the linelist and ‘p’ is the name of the parameter (e.g. ‘gflog’). Parameters of the long format (e.g. lande_upper) can only be varied for a long format linelist. For a list of the linelist parameters, see Linelist.
Bounds¶
Most parameters have bounds. PySME gets the bounds of each parameter from the specified atmosphere grid if possible. It also only allows for positive turbulence velocities for example.
Continuum and Radial velocities¶
It might be logical to think that the continuum and especially the radial velocity is a regular fitparameters. However there are several options about how to handle them (see Radial velocity and Continuum). It is therefore recommended to use ‘cscale_flag’ and ‘vrad_flag’ to specify the desired fitting method. If ‘vrad’ is passed as a fitparameter it is equivalent to ‘vrad_flag’ = ‘each’, and if ‘cont’ is passed it is the same as ‘cscale_flag’ = ‘linear’.