Improved Neutron-Capture Element Abundances in Planetary Nebulae

TL;DR

This study improves the accuracy of neutron-capture element abundance measurements in planetary nebulae by combining high-resolution spectroscopy with new atomic data, addressing previous uncertainties in ionization corrections.

Contribution

It presents a comprehensive approach integrating deep spectroscopy and atomic data to enhance abundance determinations of n-capture elements in planetary nebulae.

Findings

Detection of multiple ions of Se, Br, Kr, Rb, and Xe in PNe

Development of new atomic data for ionization corrections

Potential for more accurate n-capture element abundances

Abstract

Spectroscopy of planetary nebulae (PNe) provides the means to investigate s-process enrichments of neutron(n)-capture elements that cannot be detected in asymptotic giant branch (AGB) stars. However, accurate abundance determinations of these elements present a challenge. Corrections for unobserved ions can be large and uncertain, since in many PNe only one ion of a given n-capture element has been detected. Furthermore, the atomic data governing the ionization balance of these species are not well-determined, inhibiting the derivation of accurate ionization corrections. We present initial results of a program that addresses these challenges. Deep high resolution optical spectroscopy of ~20 PNe has been performed to detect emission lines from trans-iron species including Se, Br, Kr, Rb, and Xe. The optical spectral region provides access to multiple ions of these elements, which reduces the magnitude and importance of uncertainties in the ionization corrections. In addition, experimental and theoretical efforts are providing determinations of the photoionization cross-sections and recombination rate coefficients of Se, Kr, and Xe ions. These new atomic data will make it possible to derive robust ionization corrections for these elements. Together, our observational and atomic data results will enable n-capture element abundances to be determined with unprecedented accuracy in ionized nebulae.