SDSS-V LVM: Revealing the Physical and Chemical Structure of the Helix Nebula

We present a spatially contiguous spectroscopic analysis of the physical and chemical structure of the Helix Nebula (NGC 7293, PNG 036.1-57.1) using integral-field observations from the SDSS-V Local Volume Mapper (LVM). The nearly complete nebular coverage allows us to map extinction, electron density and temperature, ionisation structure, and chemical abundances within a common dataset. We reconstruct calibrated datacubes from the LVM row-stacked spectra and measure 41 optical emission lines from hydrogen, helium, and collisionally excited ions. The Helix is globally a low-density nebula, with characteristic electron densities of ∼102 cm−3, but shows a strongly structured thermal distribution. Te([O III]) exhibits a U-shaped radial profile, decreasing from the central cavity to intermediate radii and rising toward the outer nebula, while Te([N II]) increases outward and Te([O II]) decreases. These contrasting behaviours show that different diagnostics trace distinct ionisation zones. The spatially resolved abundance analysis yields a near-solar oxygen abundance, 12 + log (O/H) ≃ 8.7, consistent with an approximately chemically homogeneous nebula once ionisation structure is considered. Simulated long-slit extractions show that inferred O/H depends systematically on slit orientation and can remain biased after ionisation correction, demonstrating the importance of spatial coverage in strongly stratified nebulae. We also find sulfur systematically deficient relative to other α-elements, consistent with the planetary-nebula sulfur anomaly. These results highlight the power of wide-field integral-field spectroscopy for linking the thermal, ionisation, and chemical structure of extended planetary nebulae.