2022ApJ...925L...4T

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 V 605 Aql that unveil for the first time the spatio-kinematic distribution of the molecular material associated with a born-again star. Both the continuum and molecular line emission exhibit a clumpy ring-like structure with a total extent of ≃1'' 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 ∼ 90 km s^–1 and an inclination i ≃ 60° with respect to the line of sight. The observations also reveal a compact high-velocity component, v_exp ∼ 280 km s^–1, that is aligned perpendicularly to the expanding disk. This component is interpreted as a bipolar outflow with a kinematical age τ <= 20 yr, which could either be material that is currently being ejected from V 605 Aql, or 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 _dust ∼ 0.2-8 x 10^–3 M _☉, depending on the dust absorption coefficient. The mass of the CO is M _CO ≃ 1.1 x 10^–5 M _☉, which is more than three orders of magnitude larger than the mass of the other detected molecules. We estimate a ¹²C/¹³C ratio of 5.6 ± 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.