UBV(RI )C photometry of Hipparcos red stars

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); delta <+10degrees; (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 25 pc, including five within 20 pc.