Variability of the NGC 1333 IRAS 4A Outflow: Molecular Hydrogen and Silicon Monoxide Images

The NGC 1333 region was observed in the H2 1-0 S(1) line. The H2 images covera 5' x 7' region around IRAS 4. Numerous H2 emission features were detected.The northeast-southwest bipolar outflow driven by IRAS 4A was studied bycombining the H2 images with SiO maps published previously. The SiO-H2 outflowsare continuous on the southwestern side but show a gap on the northeasternside. The southwestern outflow lobe curves smoothly, and the position angleincreases with the distance from the driving source. The base and the outer tipof the northeastern outflow lobe are located at positions opposite to thecorresponding parts of the southwestern lobe. This point-symmetry suggests thatthe outflow axis may be drifting or precessing clockwise in the plane of thesky and that the cause of the axis drift may be intrinsic to the outflowengine. The axis drift model is supported by the asymmetric lateral intensityprofile of the SiO outflow. The axis drift rate is about 0.011 deg yr-1. Themiddle part of the northeastern outflow does not exactly follow the pointsymmetry because of the superposition of two different kinds of directionalvariability: the axis drift of the driving source and the deflection by a densecore. The axis drift model provides a good explanation for the large deflectionangle of the northeastern outflow. Other H2 emission features around the IRAS 4region are discussed briefly. Some of them are newly found outflows, and someare associated with outflows already known before