2023PASJ...75.1280O

H4-1 is a planetary nebula (PN) located in the Galactic halo, and is notably carbon-rich and one of the most metal-deficient PNe in the Milky Way. To unveil its progenitor evolution through accurate measurement of the gas mass, we conducted a comprehensive investigation of H4-1, using the newly obtained Seimei/KOOLS-IFU spectra and multiwavelength spectro-photometry data. The emission-line images generated from the KOOLS-IFU data cube successfully resolve the ellipsoidal nebula and the equatorial flattened disk that are frequently seen in bipolar PNe evolved from massive progenitors. By a fully data-driven method, we directly derived the seven elemental abundances, the gas-to-dust mass ratio, and the gas and dust masses based on our own distance scale. By comparing the observed quantities with both the photoionization model and the binary nucleosynthesis model, we conclude that the progenitors of initial masses of 1.87 M$_{\odot }$ and 0.82 M$_{\odot }$ are second-generation stars formed ∼4 Gyr after the Big Bang that have undergone mass transfers and a binary merger, and have ultimately evolved into a PN showing unique chemical abundances. Our binary model successfully reproduces the observed abundances and also explains the evolutionary time scale of H4-1.