* Broad velocity features appear on the high velocity (NE) and the low velocity (SW) side of the narrow dark cloud line. The central position profile is symmetrically broadened. The contour map of the broad velocity emission reveals two symmetric lobes about IRS-5. Each lobe extends 0.5 pc, if we assume a distance of 160 pc to L1551.

    * ¹²CO emission is not optically thick. There is evidence for this from the enhancement of the 2-1 CO intensity at positions SW of the infrared source. The ratio of the antenna temperatures of the lines gives T_ex(2-1) ~ 8-35 K.

    * Assuming that the CO/H₂ ratio is 5*10^-5, the gas column density is ~10²⁰cm^-2. The total mass of gas in the NE and SW lobes is 0.1 M_SUN and 0.2 M_SUN, respectively. This calculation agrees with 0.7 M_SUN, the swept up mass estimated by assuming that the average density away from the core is 1000 cm^-3.
 
 

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