yr) T Tauri star DM Tau. The
kinematic pattern and line profiles obtained from 
CO J=2--1 and
CO J=2--1 are consistent with a disk inclined about 
from
face-on, with a rotation axis at PA 
, and orbiting a
central star with a systemic velocity of 
. All
detected lines can be well fitted by a simple Keplerian disk model
with outer radius 
AU, mean temperature about 15 K, and
standard isotopic ratios. If the CO abundance is normal, the total
disk mass is 
.
Such a mass is small compared to that derived from mm and sub-mm
continuum emission (
). This can be explained either
by CO depletion, or by an anomalous gas-to-dust ratio, or by the
existence of a dense, compact, optically thick core which dominates the
mm continuum emission. The size derived for such a core is consistent
with the size of the current solar system. In all cases, our results
indicate that significant amount of gas still exists several Myr after
star formation.