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Infrared study of the eta Chamaeleontis cluster and the longevity of circumstellar discs

A-Ran Lyo·Warrick A. Lawson·Eric M. Mamajek·Eric D. Feigelson·Eon-Chang Sung·Lisa A. Crause
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Abstract

We have analyzed JHKL observations of the stellar population of the ~9 Myr-old eta Chamaeleontis cluster. Using infrared (IR) colour-colour and colour-excess diagrams, we find the fraction of stellar systems with near-IR excess emission is 0.60 pm 0.13 (2_sigma). This results implies considerably longer disc lifetimes than found in some recent studies of other young stellar clusters. For the classical T Tauri (CTT) and weak-lined T Tauri (WTT) star population, we also find a strong correlation between the IR excess and H_alpha emission. The IR excesses of these stars indicate a wide range of star-disc activity; from a CTT star showing high levels of accretion, to CTT - WTT transition objects with evidence for some on-going accretion, and WTT stars with weak or absent IR excesses. Of the 15 known cluster members, 4 stars with IR excesses delta(K-L) > 0.4 mag are likely experiencing on-going accretion owing to strong or variable optical emission. The resulting accretion fraction (0.27 pm 0.13; 2_sigma) shows that the accretion phase, in addition to the discs themselves, can endure for at least ~10 Myr.

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A-Ran Lyo, Warrick A. Lawson, Eric M. Mamajek, Eric D. Feigelson, Eon-Chang Sung, Lisa A. Crause. 2002-09-27. Infrared study of the eta Chamaeleontis cluster and the longevity of circumstellar discs. https://doi.org/10.1046/j.1365-8711.2003.06084.x

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