Chemical Abundances and Dust in the Halo Planetary Nebula K648 in M15: Its Origin and Evolution Based on an Analysis of Multiwavelength Data

Abstract

We report on an investigation of the extremely metal-poor and C-rich planetary nebula (PN) K648 in M15 using the UV to far-infrared data obtained using Subaru, the Hubble Space Telescope, the Far Ultraviolet Spectroscopic Explorer, Spitzer, and Herschel. We determined the nebular abundances of 10 elements. The enhancement of F ([F/H] = +0.96) is comparable to that of the halo PN BoBn1. The central stellar abundances of seven elements are determined. The stellar C/O ratio is similar to the nebular C/O ratios from recombination lines and from collisionally excited lines (CELs) within error, and the stellar Ne/O ratio is also close to the nebular CEL Ne/O ratio. We found evidence of carbonaceous dust grains and molecules including Class B 6-9 and 11.3 μm polycyclic aromatic hydrocarbons and the broad 11 μm feature. The profiles of these bands are similar to those of the C-rich halo PNe H4-1 and BoBn1. Based on the theoretical model, we determined the physical conditions of the gas and dust and their masses, i.e., 0.048 and 4.95 × 10^-7 {{M}_⊙ }, respectively. The observed chemical abundances and gas mass are in good agreement with an asymptotic giant branch nucleosynthesis model prediction for stars with an initial 1.25 {{M}_⊙ } plus a 2.0 × 10^-3 {{M}_⊙ } partial mixing zone (PMZ) and stars with an initial mass of 1.5 {{M}_⊙ } without a PMZ. The core mass of the central star is approximately 0.61-0.63 {{M}_⊙ }. K648 is therefore likely to have evolved from a progenitor that experienced coalescence or tidal disruption during the early stages of evolution, and became a ∼1.25-1.5 {{M}_⊙ } blue straggler.