THE ASTROPHYSICAL JOURNAL, 439:983-990, 1995 February 1

         CORRELATIONS BETWEEN THE FLARING RADIO EMISSION AND STARSPOT
                          DISTRIBUTION OF UX ARIETIS

                             NICHOLAS M. ELIAS II
United States Naval Observatory, Astronomy Department, Interferometry Division;
  and NRL/USNO Optical Interferometer Project, 3450 Massachusetts Avenue, NW,
                           Washington, DC 20392-5420

                              ANDREAS QUIRRENBACH
     NRL/USNO Optical Interferometer Project; and Max-Planck-Institut fur
            Extraterrestrische Physik, Giessenbachstrasse, D-85748
                        Garching bei Muenchen, Germany

              ARNO WITZEL, CHRISTIAN E. NAUNDORF, AND RALF WEGNER
          Max-Planck-Institut fur Radioastronomie, Auf dem Huegel 69,
                             D-53121 Bonn, Germany

                                      AND

                     EDWARD F. GUINAN AND GEORGE P. McCOOK
        Villanova University, Astronomy Department, Villanova, PA 19085


                                   ABSTRACT

       We have observed UX Arietis at C band (6 cm) for 3 weeks with four
    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
    Neidhoefer, Massi, & Chiuderi-Drago (1993, A&A, 278, L51).
       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 ~ 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, ApJ, 388,
    27) and Lim et al. (1994, ApJ, 430, 332) for the single K0 V star AB
    Dor.
       We make the following conclusions from our observations.  First, the
    episodes of long-term (~hours to days) radio flaring were modulated by
    stellar eclipses.  Second, the flares were located close to the
    starspot groups.  Third, the sizes of the flares were comparable to
    sizes of the starspot groups, which is consistent with nonthermal
    emission of brightness temperature T_b ~ 10^10-10^13 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.

    Subject headings: radio continuum: stars -- stars: flare -- stars:
                      individual (UX Arietis)