Two Hydrogen-Deficient Planetary Nuclei with Recent Mass-Loss Events: V605 Aql and Lo 4

Abstract

V605 Aquilae, central star of the ancient planetary nebula Abell 58, had evolved to the top of the white‐dwarf cooling sequence before undergoing a very late thermal pulse around 1919. V605 Aql is now embedded in a compact, dusty, hydrogen‐deficient nebula, which has been imaged by HST in 1991, 2001, and 2009. We detect angular expansion, consistent with ejection in 1919. Emission‐line images of the compact nebula show a clumpy structure, bisected by a dark band, indicating a toroidal morphology. The dark band appears to be aligned with the major axis of the large surrounding PN. Continuum images reveal the hot central star, seen through substantial extinction.The hydrogen‐deficient, pulsating central star of the PN Longmore 4 normally has the spectrum of a PG 1159‐type white dwarf. In 1992, Werner et al. discovered that the spectrum had temporarily changed to that of an emission‐line [WCE] star. I have monitored the spectrum of Lo 4 since 2003; out of 70 spectra, three have shown mass‐loss outbursts similar to the one seen in 1992, each event lasting for only a few days. There is still no convincing explanation for these remarkable events.