4 Conclusions

Most of the slow rotators found among the M-type asteroids have one or more of the classification parameters differing from the typical ones for the M-type population. For others radar observations, or spectra in the near infrared, show that they do not have the properties representative for the M-type population. The slow rotators dicussed above should therefore probably not be classified as type M. The enlarged data of spin rates of M-type asteroids confirms and strengthens the conclusion that asteroids of taxonomic type M spin faster than those of similar sizes of types S and C.

Acknowledgements

We thank E. Braatz and Yu. Krugly for their help with the observations. The Kharkiv team was partly supported by the Ukrainian State Foundation of Fundamental Research (grant N 2.4/314). I. Belskaya is grateful to Uppsala University for financing her visit at the Uppsala observatory. J. Piironen wishes to thank NorFA foundation for financial support.