Astron. Astrophys. 343, 213-221 (1999)

Circumstellar emission and flares on FK Comae Berenices

Analysis and modelling of Balmer and He i D3 line variations ^*

J.M. Oliveira ^1,2 and B.H. Foing <sup>1,3

1</sup> ESA Space Science Department, ESTEC/SCI-SO, P.O. Box 299, 2200 AG Noordwijk, The Netherlands (e-mail: joana@so.estec.esa.nl; bfoing@estec.esa.nl)
² Centro de Astrofísica da Universidade do Porto, Rua das Estrelas s/n, P-4150 Porto, Portugal
³ Institut d'Astrophysique Spatiale, CNRS/Univ. Paris XI, Bât. 121, Campus d'Orsay, F-91405 Orsay Cedex, France

Received 27 August 1998 / Accepted 1 December 1998

Abstract

We present results on spectroscopic observations of the fast-rotating active giant FK Comae, obtained mainly with the ESA-MUSICOS spectrograph at the Isaac Newton Telescope (INT) in 1996 and 1997 and also with the Aurélie spectrograph at the Observatoire de Haute Provence (OHP) in 1997. The profiles analysed are those of the Balmer, H and H, and He i D3 ( 5876 Å) lines.

We analyse the Balmer line variability and phase behaviour. We confirm these lines as highly variable, with excess emission that originates from extended structures and exhibits clear signs of rotational modulation. We have described the line profiles for two distinct states of activity, using different modelling approaches. Similar techniques were applied to the He i D3 spectra.

A large flare event lasting several days was detected in both Balmer lines and in the He i D3 line. The energy released during this flare in H is of the order of 10³⁷ erg, making it the largest H flare reported on a cool star.

Our results confirm the extreme complexity of the circumstellar environment of FK Comae. The activity level of this star is quite variable demanding different approaches to the line profile analysis.

Key words: line: profiles stars: late-type stars: individual: FK Comae stars: flare stars: circumstellar matter stars: activity

* Based on observations obtained at the Isaac Newton Telescope with the ESA-MUSICOS spectrograph and at the Observatoire de Haute Provence with the Aurélie spectrograph.

Send offprint requests to: J.M. Oliveira, ESTEC address (joana@so.estec.esa.nl)

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Contents

• 1. Introduction
• 2. Observations and data reduction
  • 2.1. Artificial template for excess spectra
• 3. Results from May 96 line profiles
  • 3.1. Low activity Balmer extended emission
  • 3.2. Modelling of circumstellar emission
• 4. Results from May/June 97 line profiles
  • 4.1. Multi-component analysis
  • 4.2. The Balmer lines fitted components
    • 4.2.1. Velocity curves analysis
    • 4.2.2. Comparison of H and H components
  • 4.3. The He i D3 line profiles
  • 4.4. The 16 May 97 long-duration giant flare event
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999
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