Radio Observations of Rapidly Rotating F { M Dwarf Stars in thePleiadesJeremy

We report deep 3.6 cm radio observations of six very rapidly rotating late-type dwarf stars in the Pleiades open cluster, distributed in spectral class from F9 to M0. This study, supplemented by our previous radio detections of three G8-K2 dwarfs in the Pleiades (Lim & White 1995; hereinafter LW95), completes our small census of Pleiades ultrafast rotators with spectral types spanning the range occupied by convective solar-type stars. We report the discovery of quasi-steady radio emission from the G1 dwarf H II 253, almost identical in eeective temperature to the Sun, and also from the G8 dwarf H II 1136, which was previously found to be a strong aring source by LW95. The quasi-steady radio luminosity of both these stars was 2 10 15 ergs Hz ?1 s ?1 , similar to that of the K0 and K2 dwarfs previously detected by LW95. We connrm the single nondetection reported by LW95, that of the K2 dwarf H II 3163, at a signiicantly lower lumi-nosity threshold of 8:5 10 14 ergs Hz ?1 s ?1. At this luminosity threshold, none of the other stars, which have spectral types of F9, K7, and M0, were detected. As the number of stars studied and the number of observations per star are small, we can only draw tentative conclusions at this stage. Nevertheless, our study does show that at least some solar-type stars in the Pleiades display quasi-steady radio emission at a luminosity similar to their equally rapidly rotating but relatively nearby proper motion counterparts in the Local Association. In their quasi-steady state, the most radio luminous solar-type stars in the Pleiades span the spectral class range early-G to early-K. This range also encompasses the most X-ray luminous solar-type stars in the cluster. The failure to detect stars with { 2 { spectral types later than K2 is consistent with the idea that the quasi-steady radio luminosity of solar-type stars in the Pleiades, like their quiescent X-ray luminosity, decreases towards later spectral types.