Astron. Astrophys. 347, 508-517 (1999)

5. Conclusions

Using the multi-object spectrograph on the Schmidt telescope in Tautenburg, we have detected flares in ZAMSSs, wTTSs, and cTTSs. We thus conclude that there are flares on cTTSs that can be observed in the optical regime. This result is rather relieving as flares have been detected in cTTSs in the X-ray regime. The properties of these flares on stars of all three kinds are rather similar: All flares show a rapid increase, and a slow decay of the Balmer lines, and even the ratios are quite similar. We then derive criteria for the detection of such events, and derive the cumulative frequency diagram for flares on stars of the three classes of objects. We point out that the extinction is a problem for the observations of flares in the optical. We find that the difference of the intrinsic flare-frequency between cTTSs, and wTTSs is about a factor of two for the sample of stars observed.

Together with the fact that we observed flares on 80% of the wTTSs, this implies that a large flare activity is typical for both types pre-main sequence stars. Since only large flares could be detected, this also implies that large magnetic fields are common amongst young stars. In contrast to the T Tauri stars, the frequency (at a given energy) for flares on ZAMSSs seems to be an order of magnitude smaller than that for wTTSs.

© European Southern Observatory (ESO) 1999

Online publication: June 30, 1999
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