Luminosity, Radius and Wind Budget of the Central Star of IC 418

This paper computes a self-contained budget for IC 418 from published observational values, with every derived number produced by the deposited computation script. IC 418, the Spirograph Nebula, surrounds one of the coolest central stars of any bright planetary nebula. At an effective temperature near thirty-seven thousand kelvin the star is still on the early, nearly constant-luminosity portion of its track, and the nebula around it is correspondingly young and compact. The stellar radius and gravity computed from the published luminosity and temperature show a star that has contracted substantially since leaving the asymptotic giant branch but has not yet reached white-dwarf dimensions. The headline results are: luminosity_Lsun = 7.7e+03; effective_temperature_K = 3.7e+04; stellar_radius_Rsun = 2.14; surface_gravity_m_s2 = 36.1; log_g_cgs = 3.56; core_mass_Msun = 0.6; nebular_age_yr = 4889. The radius is larger and the gravity lower than in nebulae with hotter central stars, exactly the ordering the evolutionary tracks predict. The nebular dynamical age is short, consistent with a star that began ionising its surroundings only recently. Because the star is still heating, the nebula is expected to brighten in high-ionisation lines over coming centuries, a slow prediction that follows directly from the track position adopted here. The calculation is presented with its inputs, relations and sensitivities stated openly, so that any revised distance, density or stellar parameter can be substituted and the verdict recomputed directly.