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We analyze the variability in accretion-related emission lines for 40Classical T Tauri stars to probe the extent of accretion variations in youngstellar objects. Our analysis is based on multi-epoch high-resolution spectrafor young stars in Tau-Aur and Cha I. For all stars, we obtain typically fourspectra, covering timescales from hours to months. As proxies for the accretionrate, we use the H-alpha 10% width and the CaII-8662 line flux. We find thatwhile the two quantities are correlated, their variability amplitude is not.Converted to accretion rates, the CaII fluxes indicate typical accretion ratechanges of 0.35 dex, with 32% exceeding 0.5 dex, while H-alpha 10% widthsuggests changes of 0.65 dex, with 66% exceeding 0.5 dex. We conclude that CaIIfluxes are a more robust quantitative indicator of accretion than H-alpha 10%width, and that intrinsic accretion rate changes typically do not exceed 0.5dex on timescales of days to months. The maximum extent of the variability isreached after a few days, suggesting that rotation is the dominant cause ofvariability. We see a decline of the inferred accretion rates towards laterspectral types, reflecting the dM/dt vs. M relationship. There is a gap betweenaccretors and non-accretors, pointing to a rapid shutdown of accretion. Weconclude that the ~2 orders of magnitude scatter in the dM/dt vs. Mrelationship is dominated by object-to-object scatter instead of intrinsicsource variability.

How Variable is Accretion in Young Stars?