We present high‐sensitivity 2 × 4 arcmin2 maps of the J= 2→1 rotational lines of SiO, CO, 13CO and C18O, observed towards the filamentary infrared dark cloud (IRDC) G035.39−00.33. Single‐pointing spectra of the SiO J= 2→1 and J= 3→2 lines towards several regions in the filament are also reported. The SiO images reveal that SiO is widespread along the IRDC (size ≥2 pc), showing two different components: one bright and compact arising from three condensations (N, E and S) and the other weak and extended along the filament. While the first component shows broad lines (linewidths of ∼4–7 km s−1) in both SiO J= 2→1 and SiO J= 3→2, the second one is only detected in SiO J= 2→1 and has narrow lines (∼0.8 km s−1). The maps of CO and its isotopologues show that low‐density filaments are intersecting the IRDC and appear to merge towards the densest portion of the cloud. This resembles the molecular structures predicted by flow‐driven, shock‐induced and magnetically‐regulated cloud formation models. As in outflows associated with low‐mass star formation, the excitation temperatures and fractional abundances of SiO towards N, E and S increase with velocity from ∼6 to 40 K and from ∼10−10 to ≥10−8, respectively, over a velocity range of ∼7 km s−1. Since 8 μm and 24 μm sources and/or extended 4.5 μm emission are detected in N, E and S, broad SiO is likely produced in outflows associated with high‐mass protostars. The excitation temperatures and fractional abundances of the narrow SiO lines, however, are very low (∼9 K and ∼10−11, respectively), and consistent with the processing of interstellar grains by the passage of a shock with vs∼ 12 km s−1. This emission could be generated (i) by a large‐scale shock, perhaps remnant of the IRDC formation process, (ii) by decelerated or recently processed gas in large‐scale outflows driven by 8‐ and 24‐μm sources or (iii) by an undetected and widespread population of lower mass protostars. High‐angular‐resolution observations are needed to disentangle between these three scenarios.

We report on the results of four XMM–Newton observations separated by about ten days from each other of Cyg OB2 #8A [O6If + O5.5III(f)]. This massive colliding wind binary is a very bright X‐ray emitter — one of the first X‐ray emitting O‐stars discovered by the Einstein satellite — as well as a confirmed non‐thermal radio emitter whose binarity was discovered quite recently. The X‐ray spectrum between 0.5 and 10.0 keV is essentially thermal, and is best fitted with a three‐component model with temperatures of about 3, 9 and 20 MK. The X‐ray luminosity corrected for the interstellar absorption is rather large, i.e. about 1034 erg s−1. Compared to the ‘canonical’LX/Lbol ratio of O‐type stars, Cyg OB2 #8A was a factor of 19–28 overluminous in X‐rays during our observations. The EPIC spectra did not reveal any evidence for the presence of a non‐thermal contribution in X‐rays. This is not unexpected considering that the simultaneous detections of non‐thermal radiation in the radio and soft X‐ray (below 10.0 keV) domains is unlikely. Our data reveal a significant decrease in the X‐ray flux from apastron to periastron with an amplitude of about 20 per cent. Combining our XMM–Newton results with those from previous ROSAT‐PSPC and ASCA‐SIS observations, we obtain a light curve suggesting a phase‐locked X‐ray variability. The maximum emission level occurs around phase 0.75, and the minimum is probably seen shortly after the periastron passage. Using hydrodynamic simulations of the wind–wind collision, we find a high X‐ray emission level close to phase 0.75, and a minimum at periastron as well. The high X‐ray luminosity, the strong phase‐locked variability and the spectral shape of the X‐ray emission of Cyg OB2 #8A revealed by our investigation point undoubtedly to X‐ray emission dominated by colliding winds.

We present the first results from the B-fields In STar-forming Region Observations (BISTRO) survey, using the Sub-millimetre Common-User Bolometer Array2 camera, with its associated polarimeter (POL-2), on the James Clerk Maxwell Telescope in Hawaii. We discuss the survey's aims and objectives. We describe the rationale behind the survey, and the questions thatthe survey will aim to answer. The most important of these is the role of magnetic fields in the star formation process on the scale of individual filaments and cores in dense regions. We describe the data acquisition and reduction processes for POL-2, demonstrating both repeatability and consistency with previous data. We present a first-look analysis of the first results from the BISTRO survey in the OMC1 region. We see that the magnetic field lies approximately perpendicular to the famous "integral filament" in the densest regions of that filament. Furthermore, we see an "hourglass" magnetic field morphology extending beyond the densest region of the integral filament into the less-dense surrounding material, and discuss possible causes for this. We also discuss the more complex morphology seen along the Orion Bar region. We examine the morphology of the field along the lower-density northeastern filament. We find consistency with previous theoretical models that predict magnetic fields lying parallel to low-density, non-self-gravitating filaments, and perpendicular to higher-density, self-gravitating filaments.

Whenever the N = (2, 2) supersymmetry algebra of non-linear σ-models in two dimensions does not close off-shell, a holomorphic two-form can be defined. The only known superfields providing candidate auxiliary fields to achieve an off-shell formulation are semi-chiral fields. Such a semi-chiral description is only possible when the two-form is constant. Using an explicit example, hyperKähler manifolds, we show that this is not always the case. Finally, we give a concrete construction of semi-chiral potentials for a class of hyper-Kähler manifolds using the duality exchanging a pair consisting of a chiral and a twistedchiral superfield for one semi-chiral multiplet.

We examine the role of the gravitational instability in an isothermal, self-gravitating layer threaded by magnetic fields on the formation of filaments and dense cores. Using a numerical simulation, we follow the non-linear evolution of a perturbed equilibrium layer. The linear evolution of such a layer is described in the analytic work of Nagai et al. We find that filaments and dense cores form simultaneously. Depending on the initial magnetic field, the resulting filaments form either a spiderweb-like network (for weak magnetic fields) or a network of parallel filaments aligned perpendicular to the magnetic field lines (for strong magnetic fields). Although the filaments are radially collapsing, the density profile of their central region (up to the thermal scale height) can be approximated by a hydrodynamical equilibrium density structure. Thus, the magnetic field does not play a significant role in setting the density distribution of the filaments. The density distribution outside of the central region deviates from the equilibrium. The radial column density distribution is then flatter than the expected power law of r −4 and similar to filament profiles observed with Herschel. Our results do not explain the near constant filament width of ∼0.1pc. However, our model does not include turbulent motions. It is expected that the accretion-driven amplification of these turbulent motions provides additional support within the filaments against gravitational collapse. Finally, we interpret the filamentary network of the massive star forming complex G14.225-0.506 in terms of the gravitational instability model and find that the properties of the complex are consistent with being formed out of an unstable layer threaded by a strong, parallel magnetic field.