A spectroscopic study of flares on T Tauri and zero-age main-sequence stars

Using a multi-object spectrograph on the Schmidt telescope in Tautenburg, we study the flare-activity of T Tauri stars and of zero-age main sequence stars. The sample comprises both classical, and weak-line T Tauri stars (cTTSs, wTTSs) in the Taurus-Auriga star forming region, as well as zero-age mainsequence stars (ZAMSSs) in the open cluster α Persei. The properties of the flares detected on V 486 Per in the α Persei region, and on the Weak-Line T Tauri stars V 819 Tau and V 410 Tau are rather similar: All events show a rapid increase and a slow decay of the strength of the Balmer lines, and all events have similar flux-ratios of Hγ to Hβ. An event which shares these properties has also been detected in the cTTS FN Tau, and we correspondingly interpret it as a magnetic flare. Using the properties of observed flares as criteria for the detection of such events, we study the frequency of flares in the three classes of objects. Using these criteria, we detected flares on 80% of the wTTSs, on 56% of the cTTSs, and on 16% of the ZAMSSs. We find that the intrinsic flare rate is only about a factor of two smaller for cTTSs than for wTTSs for our sample of stars, and for flares with energies ≥ 2 1032 erg in Hβ. We thus conclude that a strong flare activity is a common property of both types of T Tauri stars. In contrast to the T Tauri stars, we find a drastically lower flare rate for the zero-age main sequence stars.