These non-MK types consist of two parts: (1) a notation for the particular system, which depends on the degree of line weakening - we adopt here three systems, (m-1), (m-2), and (m-3), for progressively greater line weakening; and (2) a spectral type in the particular system. The latter is evocative of the MK System, but uses small letters instead of capitals, and the type is enclosed in square brackets; these emphasize the fact that the types are not on the MK System.
The types then are:
Dr. Abt and the writer are now engaged in setting up complete systems for the above three categories of line weakening. In this connection, it must be emphasized that such types as those shown above are independent of similar MK types; these types cannot be used with the calibrations for MK types; and completely new calibrations for luminosity and intrinsic color will have to be carried out when a sufficient number of stars have been classified on the new system.