The molecular core associated with HH 25-26: Contraction or expansion?

We mapped the star formation region HH 25-26 IR in the NH3(1, 1) and (2, 2) transitions using the VLA in its D configuration. The study has been made with 5″ angular resolution and 0.3 km s-1 velocity resolution. As has been seen before, there is an elongated NH3 core that lies perpendicular to the molecular outflow as traced in high-velocity CO emission. In this experiment, the NH3 core is resolved, showing a central cavity and a number of distinct velocity features. Heating is seen at the position where the velocity features overlap spatially, and on the edges of the cavity, which is also seen as a reflection nebula with evidence for shock excitation. We have also detected what appears to be a new 1.3 cm continuum source on the wall of the cavity, associated with a 2.2 μm point source and jetlike structure. It is not clear at this time whether this is a truly continuum emission or high-velocity ammonia emission. The overall kinematics is complicated. A velocity gradient can be seen, together with the signatures for expanding or contracting motions. We consider here two possible models: (a) a disk or ring structure, slowly rotating and contracting, and (b) an expanding cavity. © 1996. The American Astronomical Society. All rights reserved.