2002/11/13 by F. Kerber, Nor Pirzkal, N. Pirzkal +5 · 1 citation
Physics and Astronomy · #Astro and Planetary Science #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atomic physics #Ejecta #Galaxy #Helium #Interstellar medium #Ion #Ionization #Photoionization #Physics #Planetary nebula #Spectral line #Stars #Stellar, planetary, and galactic studies #Supernova #astro-ph
paper · pdf · doi:10.1086/345773
published as Astrophys.J. 581 (2002) L39-L42 · 11 pages, 2 figures. Accepted by ApJL
arxiv created 2002/11/13 · openalex publication_date 2002/12/02 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
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 multiobject spectroscopy, we have found spatially extended (~2'') emission from [N II], [O I], [O II], and very faint Hα and [S II]. In the [N II] (λλ6548, 6583) lines, we have identified two components located at velocities -350 ± 50 and +200 ± 50 km s -1 , relative to V4334 Sgr itself. The full width of the [N II] λ6583 feature at zero intensity corresponds to a velocity spread of ~1500 km s -1 . On the basis of the available data, it is not possible to conclusively determine the mechanism of ionization. Both photoionization, from a rapidly evolving central star, and shock excitation, resulting from 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 toward 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.