Kerstin Weis

Ring Nebula and Bipolar Outflows Associated with the B1.5 Supergiant Sher 25 in NGC 3603

We have identified a ring-shaped emission-line nebula and a possible bipolar outflow centered on the B1.5 supergiant Sher 25 in the Galactic giant H II region NGC 3603 (distance 6 kpc). The clumpy ring around Sher 25 appears to be tilted by 64° against the plane of the sky. Its semimajor axis (position angle ≈ 165°) is 69 long, which corresponds to a ring diameter of 0.4 pc. The bipolar outflow filaments, presumably located above and below the ring plane on either side of Sher 25, show a separation of ≈ 0.5 pc from the central star. High-resolution spectra show that the ring has a systemic velocity of VLSR = +19 km s-1 and a deprojected expansion velocity of 20 km s-1, and that one of the bipolar filaments has an outflow speed of ~83 km s-1. The spectra also show a high [N II]/Hα ratio, suggestive of strong N enrichment. Sher 25 must be an evolved blue supergiant (BSG) past the red supergiant (RSG) stage. We find that the ratio of equatorial to polar mass-loss rate during the RSG phase was ≈ 16. We discuss the results in the framework of RSG-BSG wind evolutionary models. We compare Sher 25 to the progenitor of SN 1987A, which it resembles in many aspects.

High velocity structures in, and the X-ray emission from the LBV nebula around

The Luminous Blue Variable star η Carinae is one of the most massive stars known. It underwent a giant eruption in 1843 in which the Homunculus nebula was created. ROSAT and ASCA data indicate the existence of a hard and a soft X-ray component which appear to be spatially distinct: a softer diffuse shell of the nebula around η Carinae and a harder point-like source centered on the star η Car. Astonishingly the morphology of the X-ray emission is very different from the optical appearance of the nebula. We present a comparative analysis of optical morphology, the kinematics, and the diffuse soft X-ray structure of the nebula around η Carinae. Our kinematic analysis of the nebula shows extremely high expansion velocities. We find a strong correlation between the X-ray emission and the knots in the nebula and the largest velocities, i.e. the X-ray morphology of the nebula around η Carinae is determined by the interaction between material streaming away from η Car and the ambient medium.

\eta

We have selected the seven most well-defined Wolf-Rayet (WR) ring nebulae in the Large Magellanic Cloud (LMC), Br 2, 10, 13, 40a, 48, 52, and 100, to study their physical nature and evolutionary stages. New CCD imaging and echelle observations have been obtained for five of these nebulae; previous photographic imaging and echelle observations are available for the remaining two nebulae. Using the nebular dynamics and abundances, we find that the Br 13 nebula is a circumstellar bubble, and that the Br 2 nebula may represent a circumstellar bubble merging with a fossil main-sequence interstellar bubble. The nebulae around Br 10, 52, and 100 all show influence of the ambient interstellar medium. Their regular expansion patterns suggest that they still contain significant amounts of circumstellar material. Their nebular abundances would be extremely interesting, as their central stars are WC5 and WN3–WN4 stars whose nebular abundances have not been derived previously. Intriguing and tantalizing implications are obtained from comparisons of the LMC WR ring nebulae with ring nebulae around Galactic WR stars, Galactic LBVs, LMC LBVs, and LMC BSGs; however, these implications may be limited by small-number statistics. A SNR candidate close to Br 2 is diagnosed by its large expansion velocity and nonthermal radio emission. There is no indication that Br 2s ring nebula interacts dynamically with this SNR candidate.

Carinae

The most massive stars, those with ZAMS masses above 50 M⊙, evolve into Luminous Blue Variables (LBVs) within 3 × 106 years (Langer et al. 1994) when they reach the empirical upper boundary in the Hertzsprung-Russell diagram (which is known as the Humphreys-Davidson limit; Humphreys & Davidson 1994). Winds with high mass-loss rates (~10−4 M⊙yr−1) and giant eruptions during the short (25,000 years) LBV phase lead to the formation of nebulae around these objects, the so-called LBV-nebulae (LBVN).