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Astron. Astrophys. 362, 281-288 (2000)

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1. Introduction

Magnetic chemically peculiar (MCP) stars can produce radio emission at centimetric wavelengths. This radio emission is consistent with gyrosynchrotron emission from continuous ejected, mildly relativistic nonthermal particles trapped in the magnetosphere (Drake et al. 1987).

MCP stars are characterized by mainly dipolar magnetic fields, whose strength steeply decreases with the stellar distance, and thus each radio frequency is expected to be emitted in a well localized stellar shell of the circumstellar region. Since the dipole axis is tilted with respect to the rotation axis, Leone (1991) suggested that the observed radio emission from MCP stars should be periodically variable. Combining their own observations with Drake et al. (1987) and Phillips & Lestrade (1988) data, Leone & Umana (1993) have shown that the 6 cm density fluxes of HD 37017 and HD 37479 vary with the stellar rotation period. The coincidence of radio maxima with the extrema of the effective magnetic field lead Leone & Umana to suggest that radio emitting regions are located above the magnetic poles. The variability of the 6 cm emission with the rotational period and has been also observed for the MCP star HD 133880 by Lim et al. (1996).

We have monitored along the rotational period CU Vir (= HD 124224) with the Very Large Array (VLA) at four frequencies. This star is particularly suitable for studying the radio emission from MCP stars because of its small distance (80 pc), very short rotational period (0.52 days) and reversing magnetic field. Here we present the behavior of the 1.4 GHz radiation whose properties are compatible with cyclotron maser emission.

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© European Southern Observatory (ESO) 2000

Online publication: October 30, 19100