A model for collimated outflows in molecular clouds and the case of HH 7–11
Collimated outflows of high-velocity gas, with typical scale lengths of 0.01–0.2 pc, are often observed to be associated with linear chains of optical emission knots1, sometimes connected by faint nebulosities. The flows have been ascribed to the interaction between an energetic wind ejected by a young stellar object and circumstellar material. However, none of the acceleration and collimation mechanisms proposed so far can easily account for the most peculiar properties of the outflows, namely the almost constant spacing between the knots, their radial motion and the abrupt velocity changes along the flow, well illustrated by the prototype we use for our modelling, HH 7–11. We suggest here a new interpretation of the phenomenon, based on flows in a channel of variable cross-sectional area due to Kelvin–Helmholtz instabilities between the flow and the ambient medium; and present solutions of the Mach number equation for such a channel, which possess multiple critical points and shocks identified with the observed optical knots.
The exciting stars of Herbig-Haro objects
Accurate astrometry and infrared photometry are presented for 16 objects that are believed to represent the exciting stars for Herbig-Haro (HH) objects in their vicinities. These identifications are made on the bases of steeply rising energy distributions, proper motions of HH objects, alignment of sources with HH objects, or far-infrared emission. Exciting stars for the following HH objects are newly discovered or recognized: HH 17; HH 31; HH 32; HH 33 and 40; HH 34; HH 38 and 43; HH group 14 in NGC 2264; RNO 40; RNO 43; and GGD 33a, 33b, and 35. Geometrical alignments of some sources with HH objects support the view that young stars are capable of channeling kinetic energy into small solid angles, as does the fact that some sources are slightly displaced from the apices of fan nebulae (HH 17, R Mon, Haro 6-10). These exciting stars span a wide range of bolometric luminosity, although all are likely to be very young.
Microwave source with enhanced radiation power based on orbitron MASERs
We have proposed the design of high power microwave source in a vacuum tube based on the theory of negative mass instability. The proposed source does not operate based on a slow-wave structure but instead makes use of accelerated charged particles. In our structure, an electron emitter injects the charged particles into to the cavity. Emitted particles move around the anode, which leads to electron acceleration and emission of electromagnetic waves with a specific frequency. In this paper, we have enhanced the output power and frequency of microwave source by variation of particles initial energy and the number of anodes incorporating their specific arrangement and applied voltages. Working at room temperature, compactness, wide bandwidth, and tunability of output frequency are among the advantages of the proposed source.