Methanol in the L1551 Circumbinary Torus

Abstract

We report observations of gaseous methanol in an edge-on torus surrounding the young stellar object L1551 IRS 5. The peaks in the torus are separated by ∼10,000 AU from L1551 IRS 5 and contain ∼0.03 M⊕of cold CH3OH. We infer that the CH3OH abundance increases in the outer part of the torus, probably as a result of methanol evaporation from dust grain surfaces heated by the shock luminosity associated with the shocks associated with the jets of an externally located X-ray source. Any methanol released in such a cold environment will rapidly freeze again, spreading CH3OH throughout the circumbinary torus to nascent dust grains, planetesimals, and primitive bodies. These observations probe the initial chemical conditions of matter infalling onto the disk. © 2006. The American Astronomical Society. All rights reserved.