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We describe high spectral resolution, high dynamic range integral field spectroscopy of IC 418 covering the spectral range 3300-8950 Å and compare with earlier data. We determine line fluxes, derive chemical abundances, provide a spectrum of the central star and determine the shape of the nebular continuum. Using photoionization models, we derive the reddening function from the nebular continuum and recombination lines. The nebula has a very high inner ionization parameter. Consequently, radiation pressure dominates the gas pressure and dust absorbs a large fraction of ionizing photons. Radiation pressure induces increasing density with radius. From a photoionization analysis we derive central star parameters; log Teff = 4.525 K, log L*/L⊙ = 4.029, log g = 3.5 and using stellar evolutionary models we estimate an initial mass of 2.5 < M/M⊙ < 3.0. The inner filamentary shell is shocked by the rapidly increasing stellar wind ram pressure, and we model this as an externally photoionized shock. In addition, a shock is driven into the pre-existing asymptotic giant branch (AGB) stellar wind by the strong D-Type ionization front developed at the outer boundary of the nebula. From the dynamics of the inner mass-loss bubble and from stellar evolutionary models, we infer that the nebula became ionized in the last 100-200 yr, but evolved structurally during the ~2000 yr since the central star evolved off the AGB. The estimated current mass-loss rate (̈M = 3.8 × 10-8 M⊙ yr-1) and terminal velocity (v∞ ~ 450 km s-1) are sufficient to excite the inner mass-loss bubble. While on the AGB, the central star lost mass at ̈M = 2.1 × 10-5 M⊙ yr-1 with outflow velocity ~14 km s-1. [ABSTRACT FROM AUTHOR]

ABSTRACT In an attempt to remove the systematic errors which have plagued the calibration of the H ii region abundance sequence, we have theoretically modelled the extragalactic H ii region sequence. We then used the theoretical spectra so generated in a double-blind experiment to recover the chemical abundances using both the classical electron temperature + ionization correction factor technique and the technique which depends on the use of strong emission lines (SELs) in the nebular spectrum to estimate the abundance of oxygen. We find a number of systematic trends, and we provide correction formulae which should remove systematic errors in the electron temperature + ionization correction factor technique. We also provide a critical evaluation of the various semi-empirical SEL techniques. Finally, we offer a scheme which should help to eliminate systematic errors in the SEL-derived chemical abundance scale for extragalactic H ii regions. [ABSTRACT FROM AUTHOR]

Context. Analysis of published [Oiii] and [Siii] temperatures measurements of emission line objects consisting of Hii galaxies, giant extragalactic Hii regions, Galactic Hii regions, and Hii regions from the Magellanic Clouds reveal that the [Oiii] temperatures are higher than the corresponding values from [S iii] in most objects with gas metallicities in excess of 0.2 solar. For the coolest nebulae (the highest metallicities), the [O iii] temperature excess can reach ∼3000K. Aims. We look for an explanation for these temperature differences and explore the parameter space of models with the aim of reproducing the observed trend of TOiii > TS iii in Hii regions with temperatures below 14 000 K. Methods. Using standard photoionization models, we varied the ionization parameter, the hardness of the ionizing continuum, and the gas metallicities in order to characterize how models behave with respect to the observations. We introduced temperature inhomogeneities and varied their mean squared amplitude t2.We explored the possibility of inhomogeneities in abundances by combining two models of widely different metallicity. We calculated models that consider the possibility of a non-Maxwell-Boltzmann energy distribution (a κ-distribution) for the electron energies. We also considered shock heating within the photoionized nebula. Results. Simple photoionization calculations yield nearly equal [Oiii] and [Siii] temperatures in the domain of interest. Hence these models fail to reproduce the [Oiii] temperature excess. Models that consider temperature inhomogeneities, as measured by the mean squared amplitude t2, also fail in the regime where TOiii < 14 000 K. Three options remain that can reproduce the observed excess in TOiii temperatures: (1) large metallicity inhomogeneities in the nebula; a (2) κ-distribution for the electron energies; and (3) shock waves that propagate in the photoionized plasma at velocities ∼60 km s-1. Conclusions. The observed nebular temperatures are not reproduced by varying the input parameters in the pure photoionization case nor by assuming local temperature inhomogeneities. We find that (1) metallicity inhomogeneities of the nebular gas; (2) shock waves of velocities <∼60 km s-1 propagating in a photoionized plasma; and (3) an electron energy distribution given by a κ-distribution are successful in reproducing the observed excess in the [Oiii] temperatures. However, shock models require proper 3D hydrodynamical simulations to become a fully developed alternative while models with metallicity inhomogeneities appear to fail in metal-poor nebulae, since they result in TO++ rec >∼ TOiii. [ABSTRACT FROM AUTHOR]

The periodic spectroscopic events in η Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision (WWC) boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of η Carinae with five Southern telescopes during the 2009 low-excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II λ4686 emission line (L ~ 310 L⊙)just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the WWC region. Clumps in the primary's wind probably explain the flare-like behavior of both the X-ray and He II λ4686 light curves. After a short-lived minimum, He II λ4686 emission rises again to a new maximum, when X-rays are still absent or very weak. We interpret this as a collapse of the WWC onto the "surface" of the secondary star, switching off the hard X-ray source and diminishing the WWC shock cone. The recovery from this state is controlled by the momentum balance between the secondary's wind and the clumps in the primary's wind. [ABSTRACT FROM AUTHOR]

Using an optically-unbiased selection process based on the HIPAS S neutral hydrogen survey, we have identified a sample of over 170 spatially isolated, gas-rich dwarf galaxies in the southern hemisphere with cz between 350 and 1500 km s 1, with R-band luminosities and HI masses less than the Small Magellanic Cloud, most of which lack spectroscopic data. This paper summarises our survey criteria and procedures and nebular abundance measurements using the WiFeS IFU on the ANU 2.3 m telescope. (See longer version on astro.ph.) [ABSTRACT FROM AUTHOR]