Nebulae associated with massive stars are excellent laboratories for studying the interaction of winds and ejecta with the interstellar medium. By studying the chemical compositions of ejecta-type nebulae, it is possible to identify the progenitor stars and thus test theories of massive star evolution. An analysis of some LBV nebulae in the LMC, using data obtained with the HST, has shown that their abundances are much lower than expected for current LBV wind material (see Smith et al. 1998 ApJ 503, 278). We therefore suggest that the nebulae were formed before the current unstable LBV phase, probably during a brief red supergiant phase (see Smith et al. 1997 MNRAS 290 265 ). Such an evolutionary stage is not predicted for the most massive and luminous stars that become LBVs, suggesting that revisions are required for our understanding of the evolution of massive stars. Other studies have focused on the LBV HR Car (Nota et al. 1997, ApJ 486 338) and the LBV candidate He 3-519 (Smith et al. 1994 A&A 281 833) .


We also investigate tests of current theoretical Lyman-continuum flux distributions using HII regions. Substantial progress has recently been made in incorporating heavy-element line blanketing in hot stars, with importance in extreme-ultraviolet (EUV) energy distributions. Recent results for O stars incorporating non-LTE effects result in improved agreement with observations of associated HII regions. For WR stars, Esteban et al. A&A 272, 299 (1993) identified significant discrepancies between non-LTE model fluxes and WNL ring nebulae, attributing discrepancies to the neglect of line blanketing. We have recently investigated whether new blanketed models for WR stars allow us to resolve these inconsistencies, for the WN8 star WR124 and its impressive ejecta-type nebula (M1-67: HST/WFPC2 Halpha image pictured to the left, courtesy Yves Grosdidier, Universite de Montreal) For M1-67, our recent study (Crowther et al. 1999, A&A 350, 1007 ps file) demontrates how the unblanketed model fluxes poorly reproduce the observed nebular properties, such as the electron temperature and and ionic ratios, while the line-blanketed flux provides excellent agreement with most observed nebular quantities. In particular, the absence of nebular OIII 5007 and the low Te are now reproduced. Differences in predicted [OIII] strengths can easily be understood since they depend on the flux shortward of the O+ edge at 353A. These results give us greater confidence in the validity of current Wolf-Rayet models, especially when models considering more complete blanketing become available in the near future.

Dust is found in a variety of astrophysical environments, including the `mild' conditions of carbon-rich Asymptotic Giant Branch (AGB) stars and the `harsh' environments of R Coronae Borealis (R CrB) stars and Wolf-Rayet (WR) stars, and is unique to late-type WC (WCL) stars in the latter. We obtained new observations of the WC9 star WR104 (Ve2-45) in 1996 July using the 2.5m INT, which revealed unprecedented spectral and photometric variations. Relative to previous observations we find a simultaneous visual fading by 1.1mag, plus the disappearance of high ionization spectral features (HeII, CIV) with low ionization features (HeI, CII) relatively unchanged. In we interpret this behaviour as obscuration of the inner WR wind by a dust cloud condensation analogous to R CrB stars, and recently proposed to explain occasional eclipses in other WC9 stars. Non-LTE model calculations for the WC9 component indicate a cloud diameter of at least 60 R(sun) (= 20 R(WC9)) - far smaller than in R CrB stars - probably formed at a radius beyond 300 R(sun) (= 100 R(WC9). We find the definite presence of a companion OB star which may facilitate the necessary conditions for dust formation via shocks (see Crowther, MNRAS 290, L59, 1997).

More recently, a team from the IR spatial Interferometry Group at Berkeley have used the giant 10m Keck telescope to obtain an IR (heat) image of WR104 that reveals an astonishing spiral structure. The image of WR 104 taken in April 1998 at the Keck I Telescope is shown here. A bar is drawn with a scale of 160 AU, which is approximately the diameter of the spiral. This scale corresponds to twice the diameter of the orbit of Pluto around the Sun. One AU is equal to 93 million miles and is the distance from the Earth to the Sun. The image is so small it is the same as seeing details on the head of a pin at a distance of 2 miles.

What is unusual about WR104 is that it is smoking like a chimney. The stellar wind is extremely dusty causing it to give off IR radiation. This dust has caused some headaches for astromomers. The intense radiation from the Wolf-Rayet star should incinerate the dust as soon as it is born; how do these snowflakes of dust survive the furnace?. But why do their images of this star look like a spiral? Binary stars, like planets, are in constant motion. And so, the dust nursery at the collision front between the stellar winds, is carried around with the natural orbital motion of the companion OB star, doing a complete rotation once every 220 days. The spiral shape is a consequence of material being swept radially outwards by the stellar wind from this rotating dust formation zone. This is the classic ``lawnsprinkler'' spiral where the water is always flowing straight away from the center, but as the system rotates the water looks like it is flowing in a spiral when you look from the top.

For more information see their groups Web pages.


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02-Dec-99 zuserver2.star.ucl.ac.uk