Imaging ejecta from the final flash star V605 Aquilae

Abstract

Aims. We investigated the cloud of ejecta resulting from the mass loss associated with the final helium shell flash in V605 Aql. Methods. V605 Aql was imaged at high spatial resolution in both optical emission lines and the infrared continuum using HST/WFPC2 and Gemini/Hokupa' a+QUIRC, respectively. The He I 10 830 A spectrum was also observed. Results. The obscuring circumstellar shell, whose effects were first seen in 1923, is shown to be a disk with extended structure, including knots. The morphology of the V605 Aql circumstellar shell is discussed as an 80 year old in an evolutionary sequence consisting of recent, as well as much older, final flash objects. Conclusions. The obscuration of V605 Aql by dust marked the emergence of the hot white dwarf remnant from an optically thick pseudo-photosphere. This white dwarf drives a 2500 km s -1 wind principally in one plane resulting in a circumstellar disk. Where the wind encounters the circumstellar disk, He I 10 830 A emission is created, and hot, ∼ 1500 K, grains are generated. Grains exit the disk at 350 K, and the accompanying gas then expands at ∼ 140 km s -1 . The strong concentration of the mass loss to the disk suggests the white dwarf is now rotating rapidly. There is convincing evidence in the literature that this process is also seen in V4334 Sgr and is still going on in the old final flash objects A30 and A78.