First images of the molecular gas around a born-again star revealed by ALMA

Abstract

Born-again stars allow probing stellar evolution in human timescales and provide the most promising path for the formation of hydrogen-deficient post-asymptotic giant branch objects, but their cold and molecular components remain poorly explored. Here we present ALMA observations of V605 Aql that unveil for the first time the spatio-kinematic distribution of the molecular material associated to a born-again star. Both the continuum and molecular line emission exhibit a clumpy ring-like structure with a total extent of $\approx$1${}^{\prime \prime }$ in diameter. The bulk of the molecular emission is interpreted as being produced in a radially-expanding disk-like structure with an expansion velocity v${}_{\exp }$$\sim$90 km s${}^{-1}$ and an inclination $i$$\approx$60${}^{\circ }$ with respect to the line-of-sight. The observations also reveal a compact high-velocity component, v${}_{\exp }$$\sim$280 km s${}^{-1}$, that is aligned perpendicularly to the expanding disk. This component is interpreted as a bipolar outflow with a kinematical age $\tau$$\lesssim$20 yr, which could either be material that is currently being ejected from V605 Aql, or it is being dragged from the inner parts of the disk by a stellar wind. The dust mass of the disk is in the range $M_{\mathrm{dust}}$$\sim$0.2-8$\times$10${}^{-3}$ M${}_{\odot }$, depending on the dust absorption coefficient. The mass of the CO is $M_{\mathrm{CO}}$$\approx$1.1$\times 10^{-5}$ $M_{\odot }$, which is more than three orders of magnitude larger than the mass of the other detected molecules. We estimate a ${}^{12}$C/${}^{13}$C ratio of 5.6$\pm$0.6, which is consistent with the single stellar evolution scenario in which the star experienced a very late thermal pulse instead of a nova-like event as previously suggested.

9 pages, 5 Figures; accepted to ApJL

References in corpus (8)

• V605 Aql: The Older Twin of Sakurai's Object
• The Spitzer IRS view of V4334 Sgr (Sakurai's Object)
• Expansion of hydrogen-poor knots in the born-again planetary nebulae A30 and A78
• Abell 30 -- A Binary Central Star Among the Born-Again Planetary Nebulae
• Carbon dust in the evolved born-again planetary nebulae A30 and A78
• The infrared view of dust and molecules around V4334 Sgr (Sakurai's Object): a 20-year retrospective
• WR 72: a born-again planetary nebula with hydrogen-poor knots
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Cited by in corpus (1)

• A primer on the formation and evolution of hydrogen deficient Central Stars of Planetary Nebulæ and Related Objects