Multicolour time series photometry of four short-period weak-lined T Tauri stars

The paper describes continuous photometric monitoring of four pre-main-sequence stars, probable members of young stellar associations. Measurements, covering at least four nights per star, were obtained by cycling through several filters. The data could be used to choose between aliases of rotation periods quoted in the literature. As expected, the amplitudes of sinusoidal variations decline with increasing wavelength, mildly enough to indicate the presence of coolspots on the stellar surfaces. Variability amplitudes can dwindle from a 0.1mag level to virtually zero on a time-scale of one or two days. A flare observed in CD-36 3202 is discussed in some detail, and a useful mathematical model for its shape is introduced. It is demonstrated that accurate colour indices (sigma < 5-6 mmag, typically) can be derived from the photometry. The magnitude variations as measured through different filters are linearly related. This is exploited to calculate spot temperatures (800-1150K below photospheric for the different stars) and the ranges of variation of the spot filling factors (roughly 10-20 per cent). The available All Sky Automated Survey measurements of the stars are analysed, and it is concluded that there is good evidence for differential rotation in all four stars.