  The NGC 1333 IRAS 4A protobinary was observed in the ammonia (2, 2) and (3,
3) lines and in the 1.3 cm continuum with a high resolution (about 1.0 arcsec).
The ammonia maps show two compact sources, one for each protostar, and they are
probably protostellar accretion disks. The disk associated with IRAS 4A2 is
seen nearly edge-on and shows an indication of rotation. The A2 disk is
brighter in the ammonia lines but dimmer in the dust continuum than its sibling
disk, with the ammonia-to-dust flux ratios different by about an order of
magnitude. This difference suggests that the twin disks have surprisingly
dissimilar characters, one gas-rich and the other dusty. The A2 disk may be
unusually active or hot, as indicated by its association with water vapor
masers. The existence of two very dissimilar disks in a binary system suggests
that the formation process of multiple systems has a controlling agent lacking
in the isolated star formation process and that stars belonging to a multiple
system do not necessarily evolve in phase with each other.
