X-ray and He I 1.0830μm emission from protostellar jets

Abstract

Context. The high energies of protostellar jets, implied by recent observations of X-rays from such flows, came very much as a surprise. Inferred shock velocities are considerably higher than what was previously known, hence putting even larger energy demands on the driving sources of the jets. The statistics of X-ray emitting jets are still poor, yet a few cases exist which seem to imply a correlation between the presence of He I 1.0830 µm emission and X-ray radiation in a given source. Aims. This tentative correlation needs confirmation and explanation. If the jet regions of He I 1.0830 µm emission are closely associated with those producing X-rays, high resolution infrared spectroscopy can be used to observationally study the velocity fields in the hot plasma regions of the jets. This would provide the necessary evidence to test and further develop theoretical models of intermediately fast (>500−1500 km s −1 ) interstellar shock waves. Methods. The HH 154 jet flow from the embedded protostellar binary L 1551 IRS 5 provides a case study, since adequate IR and X-ray spectroscopic data are in existence. The thermal X-ray spectrum is fed into a photoionization code to compute, in particular, the line emission of He I and H I and to account for the observed unusual line intensity ratios.Results. The advanced model is capable of accounting for most observables, but shows also major weaknesses. It seems not unlikely that these could, in principle, be overcome by a time dependent hydrodynamical calculation with self-consistent cooling. However, such sophisticated model development is decisively beyond the scope of the present work. Conclusions. Continued X-ray observations, coordinated with simultaneous high resolution infrared spectroscopy, are highly desirable.

ISOobservation of molecular hydrogen and fine-structure lines in the photodissociation region IC���63

“…The discrepancy stems mostly from uncertainties in PDR codes (Röllig et al 2007). However, there is a possibility that the O i (63 μm) is absorbed by foreground material (Liseau 2006). An increase in O i (63 μm) will result in a higher O i (63 μm)/C ii ratio and therefore a higher gas density.…”