Seimei KOOLS-IFU mapping of the gas and dust distributions in Galactic PNe: the origin and evolution of DdDm1

Abstract

We conduct a detailed study of the planetary nebula (PN) DdDm1 in the Galactic halo field. DdDm1 is a metal-deficient and the most carbon-poor PN (C/O = 0.11 +/- 0.02) identified in the Galaxy. We aim to verify whether it evolved into a PN without experiencing the third dredge-up (TDU) during the thermal pulse asymptotic giant branch (AGB) phase and to investigate its origin and evolution through accurate measurements of the physical parameters of the nebula and its central star. We perform a comprehensive investigation of DdDm1 using multiwavelength spectra. The KOOLS-IFU emission line images achieve ~0.9 arcsec resolution, resolving the elliptical nebula and revealing a compact spatial distribution of the [Fe III] line compared to the [O III] line, despite their similar volume emissivities. This indicates that iron, with its higher condensation temperature than oxygen, is easily incorporated into dust grains such as silicate, making the iron abundance estimate prone to underestimation. Using a fully data-driven approach, we directly derive ten elemental abundances, the gas-to-dust mass ratio, and the gas and dust masses based on our own heliocentric distance scale (19.4 kpc) and the emitting volumes of gas and dust. Our analysis reveals that DdDm1 is a unique PN evolved from a single star with an initial mass of ~1.0 Msun and a metallicity Z of 0.18 Zsun. Thus, DdDm1 is the only known PN that is confirmed to have evolved without experiencing TDUs. The photoionization model reproduces all observed quantities in excellent agreement with predictions from AGB nucleosynthesis, post-AGB evolution, and AGB dust production models. Our study provides new insights into the internal evolution of low-mass and metal-deficient stars like DdDm1 and highlights the role of PN progenitors in the chemical enrichment of the Galaxy.