  A survey of CO(3-2) emission from optically visible oxygen-rich Mira variable
stars within 500 pc of the sun was conducted. A molecular envelope was detected
surrounding 36 of the 66 stars examined. Some of these stars have lower outflow
velocities than any Miras previously detected in CO. The average terminal
velocity of the ejected material was 7.0 km/sec, about half the value found in
Miras selected by infrared criteria. None of the stars with spectral types
earlier than M 5.5 were detected. The terminal velocity increases as the
temperature of the stellar photosphere decreases, as would be expected for a
radiation driven wind. Mass loss rates for the detected objects were
calculated, and it was found that there is no correlation between the infrared
color of a Mira variable, and its mass loss rate. The mass loss rate is
correlated with the far infrared luminosity, although a few stars appear to
have extensive dust envelopes without any detectable molecular wind. A
power-law relationship is found to hold between the mass loss rate and the
terminal velocity of the ejected material. This relationship indicates that the
dust envelope should be optically thick in the near infrared and visible
regions of the spectrum when the outflow velocity is > 17 km/sec. At the low
end of the range of outflow velocities seen, the dust drift velocity may be
high enough to lead to the destruction of the grains via sputtering. Half of
the stars which were detected were re-observed in the CO(4-3) transition. A
comparison of the outflow velocities obtained from these observations with
those obtained by other investigators at lower frequencies shows no evidence
for gradual acceleration of the outer molecular envelope.
