Middleterm Flares in T Tau Stars of the Tau — Aur Complex

Light variations of different kinds appear to be one of the characteristic features of T Tau stars. They are mainly caused by changes in the continuum radiation. The availability of large observational databases makes it possible to investigate different patterns of variability such as stochastic, quasiperiodic and quasicyclic ones with typical time scales from days to years, as well as sporadic flare and fuorlike outbursts. Recent attempts in classification of the photometric variability of PMS-stars were made by Herbst (1994). In this paper, we study the observational results on flares in T Tau and related stars belonging to the Taurus-Auriga complex, which resemble that of ordinary flare stars. A census of T Tau stars with homogeneous observations of short and middleterm flares is presented in Table 1. Our selection criteria were: pre- and postilare levels of brightness ought to be quasiquiescent; the amplitude has to be more than 3 times the value of standard error; the duration of brightening does not exceed a few hundred minutes; the lightcurve shape should be similar to that of a typical flare. For convenience, all observational data in Table 1 are divided into 3 subgroups.

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