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

Bound States of the q-Deformed AdS5 x S5 Superstring S-matrix

The investigation of the q deformation of the S-matrix for excitations on the string world sheet in AdS5 x S5 is continued. We argue that due to the lack of Lorentz invariance the situation is more subtle than in a relativistic theory in that the nature of bound states depends on their momentum. At low enough momentum |p|<E the bound states transform in the anti-symmetric representation of the super-algebra symmetry and become the solitons of the Pohlmeyer reduced theory in the relativistic limit. At a critical momentum |p|=E they become marginally unstable, and at higher momenta the stable bound states are in the symmetric representation and become the familiar magnons in the string limit as q->1. This subtlety fixes a problem involving the consistency of crossing symmetry with the relativistic limit found in earlier work. With mirror kinematics, obtained after a double Wick rotation, the bound state structure is simpler and there are no marginally unstable bound states.Comment: 25 page

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

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

VLTI/MIDI 10 micron interferometry of the forming massive star W33A

We report on resolved interferometric observations with VLTI/MIDI of the massive young stellar object (MYSO) W33A. The MIDI observations deliver spectrally dispersed visibilities with values between 0.03 and 0.06, for a baseline of 45m over the wavelength range 8-13 micron. The visibilities indicate that W33A has a FWHM size of approximately 120AU (0.030'') at 8 micron which increases to 240AU at 13 micron, scales previously unexplored among MYSOs. This observed trend is consistent with the temperature falling off with distance. 1D dust radiative transfer models are simultaneously fit to the visibility spectrum, the strong silicate feature and the shape of the mid infrared spectral energy distribution (SED). For any powerlaw density distribution, we find that the sizes (as implied by the visibilities) and the stellar luminosity are incompatible. A reduction to a third of W33A's previously adopted luminosity is required to match the visibilities; such a reduction is consistent with new high resolution 70 micron data from Spitzer's MIPSGAL survey. We obtain best fits for models with shallow dust density distributions of r^(-0.5) and r^(-1.0) and for increased optical depth in the silicate feature produced by decreasing the ISM ratio of graphite to silicates and using optical grain properties by Ossenkopf et al. (1992).Comment: 4 pages, 4 figures. Accepted for ApJ letter

Velocity dependence of friction and Kramers relaxation rates

We study the influence of the velocity dependence of friction on the escape of a Brownian particle from the deep potential well ($E_{b} \gg k_{B}T$, $E_{b}$ is the barrier height, $k_{B}$ is the Boltzmann constant, $T$ is the bath temperature). The bath-induced relaxation is treated within the Rayleigh model (a heavy particle of mass $M$ in the bath of light particles of mass $m\ll M$) up to the terms of the order of $O(\lambda^{4})$, $\lambda^{2}=m/M\ll1$. The term $\sim 1$ is equivalent to the Fokker-Planck dissipative operator, and the term $\sim \lambda^{2}$ is responsible for the velocity dependence of friction. As expected, the correction to the Kramers escape rate in the overdamped limit is proportional to $\lambda^{2}$ and is small. The corresponding correction in the underdamped limit is proportional to $\lambda^{2}E_{b}/(k_{B}T)$ and is not necessarily small. We thus suggest that the effects due to the velocity-dependent friction may be of considerable importance in determining the rate of escape of an under- and moderately damped Brownian particle from a deep potential well, while they are of minor importance for an overdamped particle