A new spectral classification system for the earliest O stars: definition of type O2

High-quality, blue-violet spectroscopic data are collected for 24 stars that have been classified as type O3 and that display the hallmark N IV and N V lines. A new member of the class is presented; it is the second known in the Cyg OB2 association, and only the second in the northern hemisphere. New digital data are also presented for several of the other stars. Although the data are inhomogeneous, the uniform plots by subcategory reveal some interesting new relationships. Several issues concerning the classification of the hottest O-type spectra are discussed, and new digital data are presented for the five original O3 dwarfs in the Carina Nebula, in which the N IV, N V features are very weak or absent. New spectral types O2 and O3.5 are introduced here as steps toward resolving these issues. The relationship between the derived absolute visual magnitudes and the spectroscopic luminosity classes of the O2–O3 stars shows more scatter than at later O types, at least partly because some overluminous dwarfs are unresolved multiple systems, and some close binary systems of relatively low luminosity and mass emulate O3 supergiant spectra. However, it also appears that the behavior of He II λ4686, the primary luminosity criterion at later O types, responds to other phenomena in addition to luminosity at spectral types O2–O3. There is evidence that these spectral types may correspond to an immediate pre-WN phase, with a correspondingly large range of luminosities and masses. A complete census of spectra classified into the original O3 subcategories considered here (not including intermediate O3/WN types or O3 dwarfs without N IV, N V features) totals 45 stars; 34 of them belong to the Large Magellanic Cloud and 20 of the latter to 30 Doradus

On the multiplicity of the O-star Cyg OB2 #8A and its contribution to the gamma-ray source 3EG J2033+4118

We present the results of an intensive spectroscopic campaign in the optical waveband revealing that Cyg OB2 #8A is an O6 + O5.5 binary system with a period of about 21.9 d. Cyg OB2 #8A is a bright X-ray source, as well as a non-thermal radio emitter. We discuss the binarity of this star in the framework of a campaign devoted to the study of non-thermal emitters, from the radio waveband to gamma-rays. In this context, we attribute the non-thermal radio emission from this star to a population of relativistic electrons, accelerated by the shock of the wind-wind collision. These relativistic electrons could also be responsible for a putative gamma-ray emission through inverse Compton scattering of photospheric UV photons, thus contributing to the yet unidentified EGRET source 3EG J2033+4118.Comment: 8 pages, 4 figures, conference on "The Multiwavelength Approach to Gamma-Ray Sources", to appear in Ap&S

An ultra-high-resolution study of the interstellar medium towards Orion

We report ultra-high-resolution observations graphic of Na I, Ca II, K I, CH and CH+ for interstellar sightlines towards 12 bright stars in Orion. These data enable the detection of many more absorption components than previously recognized, providing a more accurate perspective on the absorbing medium. This is especially so for the line of sight to the Orion nebula, a region not previously studied at very high resolution. Model fits have been constructed for the absorption-line profiles, providing estimates for the column density, velocity dispersion and central velocity for each constituent velocity component. A comparison between the absorption occurring in sightlines with small angular separations has been used, along with comparisons with other studies, to estimate the line-of-sight velocity structures. Comparisons with earlier studies have also revealed temporal variability in the absorption-line profile of ζ Ori, highlighting the presence of small-scale spatial structure in the interstellar medium on scales of ≈10 au. Where absorption from both Na0 and K0 is observed for a particular cloud, a comparison of the velocity dispersions measured for each of these species provides rigorous limits on both the kinetic temperature and turbulent velocity prevailing in each cloud. Our results indicate the turbulent motions to be subsonic in each case

First results from the UHRF: ultra-high-resolution observations of atomic interstellar lines towards ζ Ophiuchi

We present ultra-high-resolution observations of optical interstellar lines towards ζOph obtained during the commissioning phase of the new Ultra-High-Resolution Facility (UHRF) at the AAT. The UHRF has achieved its design resolving power of R≈106, and has very clearly resolved hyperfine splitting in three of the 11 identified Na I D-line velocity components towards ζ Oph. In addition, the intrinsic line profiles of the 3s-4p Na I doublet at 3302 Å have been measured for the first time. 12 velocity components are identified in the interstellar Ca II K-line absorption profile, of which seven have definite velocity counterparts in the Na I profile. Three of the Na I velocity components have b-values which correspond to a gas temperature of about 200 K, for the case of pure thermal broadening. The strongest component in the sightline (-14.8 km s-1) was found to have a b-value of 0.6+0.2−0.1kms−1⁠, corresponding to a temperature of 500 K. If a true gas kinetic temperature of 54 K is assumed to apply to this component, from the H2 rotational excitation temperature previously measured for the ζ Oph sightline, then the observed Na I and Fe I line profiles both imply an rms turbulent velocity of 0.4 km s-1 within the cloud, just less than the local sound speed. The observed Ca II linewidths are all significantly larger than those of the corresponding Na I components. The Ca IIcomponents are interpreted as arising from warm neutral material (intercloud medium) surrounding cooler clouds, while half of the Na I components arise from cool clouds and half arise from warm intercloud material. The measured Na I/CaII column density ratios, and the inferred temperatures, are consistent with a model in which calcium is heavily depleted on to grains in cool clouds but is restored to the gas phase by impact desorption in the warm intercloud medium

The ultra-high-resolution facility at the Anglo-Australian telescope

The Ultra-High-Resolution Facility (UHRF) has been commissioned at the coudé focus of the Anglo-Australian Telescope (AAT), and provides a resolving power of R≈106. This is the highest spectral resolution ever obtained by an optical astronomical spectrograph, and is intended mainly for astrophysical studies of cool interstellar clouds. This paper describes the development of this ambitious project, which includes diffraction-limited optical components, very tight specification for the optical configuration, and a new type of image slicer which allows ultra-high-resolution work towards faint stars. Astrophysical results from the first observing runs are presented to demonstrate the performance in terms of both resolution and throughput

On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)