KI diagnostic capabilities for M dwarfs

For the optical doublet we use only the red line, since the blue line is often contaminated by telluric correction artefacts. Both doublets have a dominant photospheric component in inactive stars and can be used as tracers of effective temperature and gravity.

For M dwarfs later than M5.0V the optical doublet lines develop an emission core. The line is often correlated to H{alpha} for stars with H{alpha} in emission and anticorrelated for stars with H{alpha} in absorption. The near-infrared doublet lines very rarely show correlation/anti-correlation to H{alpha}.