Molecular and Ionised Gas Motions in the Compact HII region G29.96-0.02

We present a new observation of the compact HII region, G29.96-0.02, that allows us to compare the velocity structure in the ionised gas and surrounding molecular gas directly. This allows us to remove most of the remaining ambiguity about the nature of this source. In particular, the comparison of the velocity structure present in the 4S-3P HeI lines with that found in the 1-0 S(1) of molecular hydrogern convincingly rules out a bow shock as being important to the kinematics of this source. Our new observation therefore agrees with our previous conclusion, drawn from a velocity resolved HI Br gamma map, that most of the velocity structure in G29.96-0.02 can largely be explained as a result of a champagne flow model. We also find that the best simple model must invoke a powerful stellar wind to evacuate the `head' of the cometary HII region of ionised gas. However, residual differences between model and data tend to indicate that no single simple model can adequately explain all the observed features.Comment: 10 pages, 4 postscript figures. To be published in MNRA

Infrared Helium-Hydrogen Line Ratios as a Measure of Stellar Effective Temperature

We have observed a large sample of compact planetary nebulae in the near-infrared to determine how the 2^1P-2^1S HeI line at 2.058um varies as a function of stellar effective temperature, Teff. The ratio of this line with HI Br g at 2.166um has often been used as a measure of the highest Teff present in a stellar cluster, and hence on whether there is a cut-off in the stellar initial mass function at high masses. However, recent photoionisation modelling has revealed that the behaviour of this line is more complex than previously anticipated. Our work shows that in most aspects the photoionisation models are correct. In particular, we confirm the weakening of the 2^1P-2^1S as Teff increases beyond 40000K. However, in many cases the model underpredicts the observed ratio when we consider the detailed physical conditions in the individual planetary nebulae. Furthermore, there is evidence that there is still significant 2^1P-2^1S HeI line emission even in the planetary nebulae with very hot (Teff>100000K) central stars. It is clear from our work that this ratio cannot be considered as a reliable measure of effective temperature on its own.Comment: 24 pages 11 figures (in 62 separate postscript files) Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Near Infrared Spectra of Compact Planetary Nebulae

This paper continues our study of the behaviour of near infrared helium recombination lines in planetary nebula. We find that the 1.7007um 4^3D-3^3P HeI line is a good measure of the HeI recombination rate, since it varies smoothly with the effective temperature of the central star. We were unable to reproduce the observed data using detailed photoionisation models at both low and high effective temperatures, but plausible explanations for the difference exist for both. We therefore conclude that this line could be used as an indicator of the effective temperature in obscured nebula. We also characterised the nature of the molecular hydrogen emission present in a smaller subset of our sample. The results are consistent with previous data indicating that ultraviolet excitation rather than shocks is the main cause of the molecular hydrogen emission in planetary nebulae.Comment: Accepted for publication in MNRA

On partial order semantics for SAT/SMT-based symbolic encodings of weak memory concurrency

Concurrent systems are notoriously difficult to analyze, and technological advances such as weak memory architectures greatly compound this problem. This has renewed interest in partial order semantics as a theoretical foundation for formal verification techniques. Among these, symbolic techniques have been shown to be particularly effective at finding concurrency-related bugs because they can leverage highly optimized decision procedures such as SAT/SMT solvers. This paper gives new fundamental results on partial order semantics for SAT/SMT-based symbolic encodings of weak memory concurrency. In particular, we give the theoretical basis for a decision procedure that can handle a fragment of concurrent programs endowed with least fixed point operators. In addition, we show that a certain partial order semantics of relaxed sequential consistency is equivalent to the conjunction of three extensively studied weak memory axioms by Alglave et al. An important consequence of this equivalence is an asymptotically smaller symbolic encoding for bounded model checking which has only a quadratic number of partial order constraints compared to the state-of-the-art cubic-size encoding.Comment: 15 pages, 3 figure

Vermiforichnus (Polychaeta) Borings in Paraspirifer Bownockeri (Brachiopoda: Devonian)

Author Institution: Department of Geology, Bowling Green UniversityShells of Paraspirifer bownockeri (Stewart) from the Silica Formation, Middle Devonian of northwestern Ohio, commonly contain numerous borings of a polychaete worm forming the endolithic trace fossil Vermiforichnus clarki Cameron (1969a) which can be exposed by acidizing the specimens. The borings are most abundant on the brachial valve, and their surface openings tend to be concentrated along major growth lines thence extending dominantly in the general direction of the beaks of the valves. Infestations of the polychaete occurred at 2 different time intervals as indicated by the spacing of the borings on 2 major growth lines with renewed shell growth between them. Growth of the host was severely reduced immediately following the infestation and in some areas damage to the mantle caused deformation in the shell of the host

IR Dust Bubbles: Probing the Detailed Structure and Young Massive Stellar Populations of Galactic HII Regions

We present an analysis of wind-blown, parsec-sized, mid-infrared bubbles and associated star-formation using GLIMPSE/IRAC, MIPSGAL/MIPS and MAGPIS/VLA surveys. Three bubbles from the Churchwell et al. (2006) catalog were selected. The relative distribution of the ionized gas (based on 20 cm emission), PAH emission (based on 8 um, 5.8 um and lack of 4.5 um emission) and hot dust (24 um emission) are compared. At the center of each bubble there is a region containing ionized gas and hot dust, surrounded by PAHs. We identify the likely source(s) of the stellar wind and ionizing flux producing each bubble based upon SED fitting to numerical hot stellar photosphere models. Candidate YSOs are also identified using SED fitting, including several sites of possible triggered star formation.Comment: 37 pages, 17 figure

Scattering and Unitarity Methods in Two Dimensions

The standard unitarity-cut method is applied to several massive two-dimensional models, including the world-sheet AdS5×S5 superstring, to compute 2→2 scattering S-matrices at one loop from tree level amplitudes. Evidence is found for the cut-constructibility of supersymmetric models, while for models without supersymmetry (but integrable) the missing rational terms can be interpreted as a shift in the coupling