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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 areprobably protostellar accretion disks. The disk associated with IRAS 4A2 isseen nearly edge-on and shows an indication of rotation. The A2 disk isbrighter in the ammonia lines but dimmer in the dust continuum than its siblingdisk, with the ammonia-to-dust flux ratios different by about an order ofmagnitude. This difference suggests that the twin disks have surprisinglydissimilar characters, one gas-rich and the other dusty. The A2 disk may beunusually active or hot, as indicated by its association with water vapormasers. The existence of two very dissimilar disks in a binary system suggeststhat the formation process of multiple systems has a controlling agent lackingin the isolated star formation process and that stars belonging to a multiplesystem do not necessarily evolve in phase with each other.

Ammonia Imaging of the Disks in the NGC 1333 IRAS 4A Protobinary System