SIMBAD references

We present homogeneous and standardized UBV (RI)_C photometry for nearly 550 M stars selected from the Hipparcos satellite data base using the following selection criteria: lack of obvious variability (no Hipparcos variability flag); δ<+10°; (V-I)>1.7; and V magnitude fainter than about 7.6. Comparisons are made between the current photometry, other ground-based data sets and Hipparcos photometry. We use linear discriminant analysis to determine a luminosity segregation criterion for late-type stars, and principal component analysis to study the statistical structure of the colour indices and to calibrate absolute magnitude in terms of (V-I) for the dwarf stars. Various methods are used to determine the mean absolute magnitude of the giant stars. We find 10 dwarf stars, apparently previously unrecognized (prior to Hipparcos) as being within 25pc, including five within 20pc.