HH 212: The most beautiful protostellar jet known to date
We report the discovery of the most symmetric embedded twin-exhaust jet known to date. It is located in a dense molecular star forming core in Orion, not far from the famous Horsehead Nebula, and is about 0.3 pc long on either side. Each side contains an inner series of spatially resolved knots (with inter-knot emission) and an outer series of giant bow-shocks, all seen in the v=1−0 S(1) line of shock excited H2 at 2.12 μm. Each pair of bow-shocks represents a distinct ejection event, lasting of the order of 300 yr. The regular spacing of the inner knots (of order 0.01 pc) which are almost perfectly matched on opposite sides of this bipolar jet, provide the strongest evidence yet for a physical model of a time-variable pulsed jet, with a period of (small) velocity variations as short as 30 yr. The high degree of symmetry also allows us to see that the two opposite halves of the jet are not completely co-linear and that there is a 1–2 degree asymmetry angle. The jet (named HH 212) originates from a very cold infrared and mm-continuum source, i.e., a very young embedded stellar object with a luminosity about 15 L ⊙, likely to be powered by accretion from an edge-on disk. Furthermore, the position of the exciting source as inferred from the symmetry of the jet coincides very well with the position of a compact radio H2O maser, this maser being the origin of our initial interest in this cold IRAS source.
KeywordsProper Motion Circumstellar Disk Exciting Source Cloud Core IRAS Point Source Catalog
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