Velocities of Magneto-Elastic and Magneto-Electron Waves in Dark Molecular Clouds

We present analytic and numerical estimates for group velocity of wave motions in two models of cold interstellar medium presumably constituting the interior of cores of magnetically supported dark molecular clouds. Namely, in the model of gas-based ferrocolloidal soft matter and in the model of noncompensated electron magnetoplasma. The predictions of these models are given in juxtaposition with data on recent Zeeman measurements of the molecular linewidths detected from dark central regions of star-forming interstellar clouds.     

Observational Indicators of Formation Excitation of H2

Theoretical predictions by Farebrother et al. and Meijer et al. of rovibrational excitation probabilities in H₂ arising from formation by Eley-Rideal processes on a graphite surface are incorporated into a model of the chemistry and excitation of interstellar H₂. The model includes the usual radiative and collisional pumping of H₂ rotational and vibrational states, in addition to the formation processes. Predictions are made for HH₂ rovibrational emission line intensities for representative points in diffuse and in dark interstellar clouds. We find that – if all the interstellar HH₂ is formed by this Eley-Rideal process – then the consequences of formation pumping, as distinct from collisional and radiative pumping, should be clearly evident in both cases. In particular, we predict a clear spectral signature of this direct HH₂ formation process on graphite, distinct from radiative and collisional pumping; this signature should be evident in both diffuse and dark clouds; but the emissivity for dark clouds is predicted to be some 500 times greater than that in diffuse clouds in which the dense material may be embedded. An observational search for this signature in two dark cloud sources was made, but a preliminary analysis of the data did not yield a detection. The implications of and possible reasons for this preliminary conclusion are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gas-Dynamical Models of Star-forming Regions

This article describes some of the techniques used to include various micro-processes in numerical gas-dynamic simulations. These techniques are then used in simulations of photo-evaporating clumps, H₂ level populations and time dependent shocks/jets. This revised version was published online in July 2006 with corrections to the Cover Date.     

Shocked molecular gas towards the supernova remnant G359.1–0.5 and the Snake

We have found a bar of shocked molecular hydrogen (H₂) towards the OH(1720 MHz) maser located at the projected intersection of supernova remnant (SNR)  G359.1–0.5  and the non-thermal radio filament known as the Snake. The H₂ bar is well aligned with the SNR shell and almost perpendicular to the Snake. The OH(1720 MHz) maser is located inside the sharp western edge of the H₂ emission, which is consistent with the scenario in which the SNR drives a shock into a molecular cloud at that location. The spectral line profiles of ¹²CO, HCO⁺ and CS towards the maser show broad-line absorption, which is absent in the ¹³CO spectra and most probably originates from the pre-shock gas. A density gradient is present across the region and is consistent with the passage of the SNR shock, while the H₂ filament is located at the boundary between the pre-shock and post-shock regions.     

Shocked gas around Cepheus A: evidence for multiple outflows from H2S and SO2 observations

The Cepheus A star-forming region has been investigated through a multiline H₂S and SO₂ survey at millimetre wavelengths. Large-scale maps and high-resolution line profiles reveal the occurrence of several outflows. Cep A East is associated with multiple mass-loss processes: in particular, we detect a 0.6-pc jet-like structure which shows for the first time that the Cep A East young stellar objects are driving a collimated outflow moving towards the south.
The observed outflows show different clumps associated with definitely different H₂S/SO₂ integrated emission ratios, indicating that the gas chemistry in Cepheus A has been altered by the passage of shocks. H₂S appears to be more abundant than SO₂ in high-velocity clumps, in agreement with chemical models. However, we also find quite small H₂S linewidths, suggestive of regions where the evaporated H₂S molecules had enough time to slow down but not to freeze out on to dust grains. Finally, comparison between the line profiles indicates that the excitation conditions increase with the velocity, as expected for a propagation of collimated bow shocks.