Correlations between the flaring radio emission and starspot distribution of UX ARIETIS

Abstract

We have observed UX Arietis at C band (6 cm) for 3 weeks with four Very Long Array (VLA) antennas. The temporal coverage during the program was approximately three scans per day. A few days into the VLA program, UX Ari began a radio flaring period which lasted for at least 2 weeks. All the radio fluxes were above the system noise during this episode, but the largest values (up to 270 mJy) occurred close to 0.0 phase. This phasing is confirmed by the UX Ari radio observations of Neidhofer, Massi & Chiuderi-Drago (1993). Visible-band light curves of UX Ari were obtained both during and after our radio observations; the peak-to-peak variation in all filters was approximately equal to 0.2 mag. The light curves indicate that the maximum starspot visibility occurred very close to 0.0 phase, the same phase as the radio maxima. Closer comparison of our radio and optical light curves indicates that they are almost perfectly anticorrelated. A similar radio/optical correlation has been found by Lim et al (1992) and Lim et al (1994) for the single KO V star and AB Dor. We make the following conclusions from our observations. First, the episodes of long-term (approximately hours to days) radio flaring were modulated by stellar eclipes. Second, the flares were located close to the starspot groups. Third, the sizes were compared to sized of the starspot groups, which is consistent with nonthermal emission of brightness temperature T_b approximately 1010-13 K. Fourth, the radio emission arose only from the midlatitude starspot groups. Last, the radio flares emitted their radiation nearly normal to the stellar surface.

Correlations between the flaring radio emission and starspot distribution of UX ARIETIS

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