M-TYPE ASTEROIDS

Observations of asteroids of type M have been one of my interests for a long time. In a recent paper in

Astron. & Astrophysics, Suppl. Ser. 131, 55-62

the results from photometric lightcurve observations of nine M-type asteroids are presented. New rotation periods were determined for 6 asteroids: 217 Eudora (12.54 h), 322 Phaeo (17.56 h), 572 Rebekka (5.65 h), 757 Portland (6.58 h), 857 Glasenappia (8.23 h) and 872 Holda (7.20 h). B-V colour measurements of seventeen previously unclassified asteroids add seven asteroids to the known M-type population. An excess of fast rotators among M-type asteroids compared to asteroids of other taxonomic types is evident. The six asteroids with slow spin rates, but hitherto classified as M, are shown to have classification parameters untypical for the M-type population. In the three figures below the normalized distributions of the spin rates are given for asteroids belonging to taxonomic types M, S and C.


Claes-Ingvar Lagerkvist