Jackoyo 2102 B000510-B Ni As 500 Im F8 V M0 D
This source lists the second (companion?) star as a M0 D versus an MO V. How to account for the discrepancy between this source and the source you (esampson) used? Is it a typo? A different classification system being used?
The "D" in M0 D means that the star is implied to be a white dwarf (or Degenerate Dwarf - the cooling remnant of a dead stellar core), whereas M0 V would be a red main-sequence star (also called a Red Dwarf, but that is only refering to the fact that it is a small normal star).
The World Generation Systems in CT and MT generated an anomolously high number of degenerate (white) dwarf companion stars (and almost all of them "M-type"). They were all over the place. In reality, only about 6% (~1 in 20) of the stars we actually observe are degenerate (white) dwarfs. Therefore, at some point Traveller reclassified all of the anomolous degenerate (white) dwarfs as Red Main-sequence Dwarfs to resolve the issue (I know they did this in GT, but I believe it was also done in either TNE:1200 or TNE:1248 as well). T20 genertaes them as Red Main-sequence Dwarfs too.
The M0 V classification is the one that should be prefered, if you are going with the most recent Traveller info (and the most realisitic).
Also, to my knowledge, there are no observed M-type degenerate dwarfs at all (the Universe isn't old enough for any white dwarfs to have cooled to that temperature, as far as we know). The coldest observed seem to be early K-type.
And as an aside, the O, B, A, F, G, K, M system is not actually used to classify white dwarfs, but it works within Traveller to maintain consistency and simplicity.