We are grateful to Bo Reipurth for his help in the early phase of the project. We would like to thank France Allard for communicating the synthetic colours derived from the model spectra of M dwarfs to us. We are grateful to Pat Hartigan for his helpful referee's comments. WB was supported by a student fellowship of the European Southern Observatory and by Harald W. Yorke and the Deutsche Forschungsgemeinschaft (DFG) under grant Yo 5/16-1. This research has made use of the Simbad database, operated at CDS, Strasbourg, France, and NASA's Astrophysics Data System Abstract Server.
© European Southern Observatory (ESO) 1997
Online publication: June 30, 1998