1996A&A...310..271L

Predicted mass-loss rates for magnetic chemically peculiar stars seem to exclude the possibility that the observed centimetric radiation is due to free-free emission mechanism. This class of stars shows large scale organized dipolar magnetic fields. Because of the steep radial dependence of the field strength, it can be assumed that each observed radio frequency is emitted in a shell of the circumstellar region whose localization depends on the dipole strength and the emission mechanism. We have observed several CP stars at 1.3, 2, 6 and 20 cm with the Very Large Array to determine how each circumstellar layer emits centimetric radiation. Since the selected stars shown different magnetic dipole strengths, we have observed the radio emission from circumstellar regions which are either very close to or far from the CP star. The radio spectra of HD37017, HD37479, and HD124224 decrease with the increasing wavelength. The radio spectra of HD142301 and HD215441 extend longward of a cutoff wavelength, indicating the presence of inner shells that are either weakly emitting or whose emission is suppressed. For gyrosynchtron emission, the observed radio spectra have been used to constrain the dimension of the emitting region for the observed frequencies. Three of the brightest radio CP stars have been observed with SEST, with the aim of extending the observed radio spectrum to the mm range. Only an upper limit was determined for the flux density of any of the observed stars at 1.3mm. This yields an upper limit for the mass-loss, assuming that the mm radiation is due to free-free emission from the expanding wind.