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Published March 1, 2005 | Submitted + Published
Journal Article Open

A Long-lived Accretion Disk around a Lithium-depleted Binary T Tauri Star


We present a high-dispersion optical spectrum of St 34 and identify the system as a spectroscopic binary with components of similar luminosity and temperature (both M3 ± 0.5). Based on kinematics, signatures of accretion, and location on an H-R diagram, we conclude that St 34 is a classical T Tauri star belonging to the Taurus-Auriga T association. Surprisingly, however, neither component of the binary shows Li I λ6708 absorption, the most universally accepted criterion for establishing stellar youth. In this uniquely known instance, the accretion disk appears to have survived longer than the lithium-depletion timescale. We speculate that the long-lived accretion disk is a consequence of the sub-AU separation companion tidally inhibiting, although not preventing, circumstellar accretion. Comparisons with pre-main-sequence evolutionary models imply, for each component of St 34, a mass of 0.37 ± 0.08 M_☉ and an isochronal age of 8 ± 3 Myr, which is much younger than the predicted lithium-depletion timescale of ~25 Myr. Although a distance 38% closer than that of Taurus-Auriga or a hotter temperature scale could reconcile this discrepancy at 21-25 Myr, similar discrepancies in other systems and the implications of an extremely old accreting Taurus-Auriga member suggest instead a possible problem with evolutionary models. Regardless, the older age implied by St 34's depleted lithium is the first compelling evidence of a substantial age spread in this region. Additionally, since St 34's coeval comembers with early M spectral types would likewise fail the lithium test for youth, current membership lists may be incomplete.

Additional Information

© 2005 The American Astronomical Society. Received 25 October 2004 Accepted 12 January 2005 Published 31 January 2005 We thank I. Baraffe, A. Ghez, and J. Stauffer for helpful discussions, and are grateful to E. Mamajek for generously providing valuable kinematic information and insight. We appreciate the data provided by the NASA/IPAC Infrared Science Archive, and the privilege to observe on the revered summit of Mauna Kea.

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Published - White_2005_ApJ_621_L65.pdf

Submitted - 0501307.pdf


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