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Astron. Astrophys. 318, 467-471 (1997)

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A major optical flare on the recently discovered X-ray active dMe star G 102-21

I. Pagano 1, R. Ventura 1, M. Rodonò 1, 2, G. Peres 3 and G. Micela 3

1 Osservatorio Astrofisico di Catania, Città Universitaria, I-95125 Catania, Italy
2 Istituto di Astronomia, Università degli Studi, viale A. Doria 6, I-95125 Catania, Italy
3 Istituto e Osservatorio Astronomico di Palermo, Palazzo dei Normanni, I-90134 Palermo, Italy

Received 2 December 1994 / Accepted 6 July 1996


During the course of UBV photoelectric measurements made at the Catania Astrophysical Observatory we have observed an unusually intense optical flare on the nearby M dwarf G 102-21, the optical counterpart of a strong X-ray source recently detected by ROSAT.

The amplitude of the magnitude increase ([FORMULA] mag) and the total energy release in the UBV bands ([FORMULA] erg) put this event among the strongest flares ever detected on UV Ceti-type stars. The U-B and B-V colours of the flare emission did not significantly change during most of the flare development. While the B-V is quite a typical colour for stellar flares, the U-B is much bluer when compared with typical values given in literature. This unusually strong ultraviolet component of the flare emission, together with the very fast flare decay, suggest a possible flare site close to the limb. We find that the observed amount of flare energy could be explained by the fast release of energy stored in a magnetic filament located in between the two G 102-21 stellar components, with a surface magnetic field [FORMULA] 3600 G.

The characteristics of the quiescent optical emission are also discussed.

Key words: stars: activity – stars: flare – stars: G 102-21 – X-rays: stars

Send offprint requests to: I. Pagano, ipagano@astrct.ct.astro.it

© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998