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Freshly ionized matter around the final Helium shell flash object V4334 Sgr (Sakurai's object)

F. Kerber·N. Pirzkal·Orsola De Marco·M. Asplund·G. C. Clayton·M. R. Rosa
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Abstract

We report on the discovery of recently ionized hydrogen-deficient gas in the immediate circumstellar environment of the final helium shell flash star V4334 Sgr (Sakurai's object). On spectra obtained with FORS2 multi-object spectroscopy we have found spatially extended (about 2") emission from [N II], [O I], [O II] and very faint Halpha and [S II]. In the [N II] (ll6548,83) lines we have identified two components located at velocities -350 +/-50 and +200 +/-50 km/s, relative to V4334 Sgr itself. The full width of the [N II] l6583 feature at zero intensity corresponds to a velocity spread of about 1500 km/s. Based on the available data it is not possible to conclusively determine the mechanism of ionization. Both photo-ionization, from a rapidly evolving central star, and shock excitation, as the result of the collision of the fast ouflows with slower circumstellar matter, could account for the observed lines. The central star is still hidden behind strong dust absorption, since only a faint highly reddened continuum is apparent in the spectra. Theory states that it will become hotter and will retrace its post-asymptotic giant branch evolution towards the planetary nebula domain. Our detection of the ionized ejecta from the very late helium shell flash marks the beginning of a new phase in this star's amazingly rapid evolution.

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F. Kerber, N. Pirzkal, Orsola De Marco, M. Asplund, G. C. Clayton, M. R. Rosa. 2002-11-13. Freshly ionized matter around the final Helium shell flash object V4334 Sgr (Sakurai's object). https://doi.org/10.1086/345773

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