seb on 24-Feb-2011 16:26:44 GMT about New M dwarfs in solar neighborhood (Riaz+, 2006)
The authors
have been using the TiO5 features in the spectra to derive both the spectral type (linear relation, equation 1) and the absolute J magnitude (section 5.2). But they use two different relations for deriving M_J, and these two relations are not continuous: there is a nearly 2mag break around TiO5 value 0.4.
And this TiO5 value corresponds to M4 spectral types with the relation 1 they have adopted.
This gives two "populations" of M4V stars, depending on the TiO5 value : distances are derived from the observed magnitude and the computed (with a discontinuity) M_J, giving a sharp discontinuity in distance estimates for M4 stars.
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View annotation on catalogue J/AJ/132/866