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Session 97 - Planetary Nebulae.
Display session, Thursday, January 16
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\sc ii region NGC 3603 (distance 6 kpc). The clumpy ring around Sher #25 appears to be tilted by 64^\circ against the plane of the sky. Its semi-major axis (position angle \approx 165^\circ) is 6.9'' 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 \approx 0.5 pc from the central star.
High-resolution spectra show that the ring has a systemic velocity of v_LSR = +19 km s^-1 and a de-projected expansion velocity of 20 km s^-1, and that one of the bipolar filaments has an outflow speed of \sim83 km s^-1. The spectra also show a high [N\sc ii]/H\alpha ratio, suggestive of strong N enrichment. Sher #25 must be an evolved blue supergiant (BSG) past the red supergiant (RSG) stage. We discuss the results in the framework of RSG--BSG wind evolutionary models.
We compare Sher #25 to the progenitor of SN\,1987\,A, which it resembles in many aspects.
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