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Astron. Astrophys. 341, 595-601 (1999)

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Flaring loop structures at VLBI scale in UX Arietis

E. Franciosini 1, M. Massi 2,3, J.M. Paredes 4 and R. Estalella 4

1 Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Florence, Italy
2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
3 Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
4 Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647, E-08028 Barcelona, Spain

Received 21 July 1998 / Accepted 21 October 1998


We report the results of three VLBI observations at 5 GHz of the active binary system UX Ari. Observations have been made during five consecutive days with the aim of studying the variations of the source structure during the decay phase of a flare.

We find that during the observations UX Ari was undergoing a low-energy flare (peak flux [FORMULA] mJy) with a decay time of a few days. The maps show a clear variation of the source structure with time. The visibility function and the maps can be reproduced using two gaussian components of angular dimensions [FORMULA] mas, whose relative position changes. Since the observations have been made at different orbital phases, we interpret the observed variations of the source structure as due to two distinct flaring loops that are seen in different positions as the star rotates.

Key words: stars: binaries: close – stars: flare – stars: individual: UX Ari – radio continuum: stars

Send offprint requests to: E. Franciosini (francio@arcetri.astro.it)

© European Southern Observatory (ESO) 1999

Online publication: December 4, 1998