Variability of H α emission in young stellar objects in the cluster IC 348

Abstract

Abstract H α emission is one of the most prominent features of young stellar objects in the optical range, and importantly, the equivalent width (EW) of H α emission [EW(H α )] is used to characterise an evolutionary stage of young stars. The aim of this work is to identify and study the stellar objects with variable EW(H α ) in the young stellar cluster IC 348. We performed photometric and slit-less observations at several epochs in order to reveal the variable objects. Significant variability of EW(H α ) was found in 90 out of 127 examined stars. From all epochs of observations, 32 objects were classified as CTT (classical T Tauri) and 69 as WTT (weak-line T Tauri) objects. The fraction of the variables in these samples is ~60%. We also identified 20 stellar objects, which showed not only a significant variability of the EW, but which also change their apparent evolutionary stage (CTT ⇆ WTT). For six stars, H α line was observed in both emission and absorption. The analysis of data obtained over a wide wavelength range (from X-ray to mid-infrared) has shown that H α activity and the measure of its variability are in good agreement with the activity of stellar objects measured with its other parameters, such as X-ray radiation and the mass accretion rate. The EW(H α ) differs not only between objects at different evolutionary stages, but also between variable and non-variable objects. The variables in the CTT and WTT samples are more active than non-variables although they have almost the same evolutionary age. Another distinct difference between these variables and non-variables is their average masses. The variables from both CTT and WTT samples are noticeably more massive than non-variables. Our data confirm the assumption made for other star formation regions that the decay of accretion activity occurs more slowly for more massive CTT objects. Apparently, a similar trend is also present in WTT objects, which are at a later stage of evolution. The variability of the stellar objects, which change their evolutionary classes (CTT ⇆ WTT), at least in a fraction of them, is due to the fact that they are close binaries, which affects and modulates their H α emission activity.