Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...491..233p&link_type=abstract
Astrophysical Journal v.491, p.233
Astronomy and Astrophysics
Astronomy
20
Galaxies: Magellanic Clouds, Ism: Planetary Nebulae: Individual Alphanumeric: N66, Stars: Evolution, Stars: Mass Loss, Stars: Wolf-Rayet
Scientific paper
Hubble Space Telescope, IUE, and ground-based observations of the central star of the LMC planetary nebula N66 (CS N66), obtained in different epochs, are presented. Since 1990, CS N66 has displayed remarkable short- and long-term spectroscopic and photometric changes amounting to more than 3 mag in the optical. Expanding model atmospheres have been constructed to fit observations from different epochs. Fits provide the chemical composition, the fundamental stellar parameters L*, T*, R*, the mass-loss rate, and the wind velocity. From our best models we find that CS N66 is a very luminous He star (X/Y <= 0.1), with a small amount of N, undergoing a violent and unstable mass-loss event. The photospheric chemical abundances correspond to the equilibrium CNO nuclear burning values, while the nebula has a normal chemical composition. Models fitting data from different epochs indicate that the fundamental stellar parameters remain constant with time, with values log (L*/L&sun;) = 4.53 +/- 0.10, T* = 93,300 K, and R* = 0.71 R&sun;. The short- and long-term stellar variations are produced by large changes in the mass-loss rate, which varies by large factors, from M dot <=8x10^{-7} M&sun; yr-1 in 1983 (preoutburst epoch) to M dot =2.5x10^{-5} M&sun; yr-1 in early 1995 (maximum stellar brightness). No evidence was found to support the suggestion that the outburst was due to a late thermal pulse. We propose that the event taking place in CS N66 was produced by an atmospheric instability similar to that triggering the giant eruptions of Population I luminous blue variable stars. The possible mechanism causing the atmospheric instability is briefly discussed.
Hamann Wolf-Rainer
Koesterke Lars
Maza Jose
Mendez Roberto H.
Peimbert Manuel
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