Astron. Astrophys. 327, 1114-1122 (1997)

Long-term photometric flares patrol (1967-1977) on EV Lacertae: a clear evidence of a longitude concentrated flaring activity
in 1970 ^{* **}

G. Leto ¹, I. Pagano ², C.S. Buemi ³ and M. Rodonò <sup>2, 3

1</sup> Istituto di Radioastronomia C.N.R., Stazione VLBI, I-96017 Noto (SR), Italy
² Osservatorio Astrofisico di Catania, Viale A. Doria 6, I-95125 Catania, Italy
³ Istituto di Astronomia, Università di Catania, Viale A. Doria 6, I-95125 Catania, Italy

Received 10 April 1997 / Accepted 24 April 1997

Abstract

We report on a large sample of homogeneous photoelectric data obtained by monitoring the red dwarf flare star EV Lac. The data were collected in 10 years (1967-77) at Catania Astrophysical Observatory on Mt. Etna and consist of 212, 170, and 128 flares detected in the U, B and V band during total monitoring times of 903, 1013, and 864 hours, respectively.

The peak luminosity, the total energy emitted, the rise and decay times were measured for each flare. A statistical analysis of this data sample is presented.

A well defined phase modulation of the normalized flare occurrence rate in 1970 clearly suggests that, at that time, on EV Lac flaring activity was concentrated at a preferred longitude.

Key words: stars: EV Lac stars: flare; activity; rotation

* Based on observations collected at the "M.G. Fracastoro" mountain station of Catania Astrophysical Observatory, Italy
** Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

Send offprint requests to: G. Leto (gleto@ira.noto.cnr.it)

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Contents

• 1. Introduction
• 2. Observations and reduction method
  • 2.1. Flare monitoring data
  • 2.2. Rotation modulation data
• 3. Results
  • 3.1. Statistical analysis
    • 3.1.1. Flare energies and accumulated flare frequency distribution
    • 3.1.2. Flare occurence rate on time-scales of 1 .
    • 3.1.3. Color-color energy correlations
    • 3.1.4. Flare time-scales
    • 3.1.5. Correlation between flare colour indices
  • 3.2. Light curves
  • 3.3. Phase distribution of flare occurence
• 4. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998
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