LOSVD Fitting (pPXF)

losvd_options = {
  "library"   : "IndoUS", # Options: IndoUS, Vazdekis2010
  "vel_const" :  {"bool":False, "val":0.0}, # Hold velocity constant?
  "disp_const":  {"bool":False, "val":250.0}, # Hold dispersion constant?
}