Revisiting the Formation of HeH$^+$ in the Planetary Nebula NGC 7027

TL;DR

This study recalculates the rate coefficients for HeH$^+$ formation in planetary nebulae using multiple methods, confirming previous results and reinforcing the understanding of this process's robustness relevant to NGC 7027.

Contribution

It provides new, consistent calculations of HeH$^+$ formation rates using three different theoretical approaches, validating earlier findings and addressing recent conflicting claims.

Findings

New calculations agree with past results for 800-20,000 K

Confirms robustness of HeH$^+$ formation rate estimates

Supports previous models of HeH$^+$ abundance in NGC 7027

Abstract

From four independent calculations using three different theoretical approaches, rate coefficients for the formation of HeH$^+$ via the radiative association of He$^+$ and H were computed. Good agreement is found between our new calculations and prior results obtained two decades ago for kinetic temperatures between $\sim$800 and 20,000 K. This finding is inconsistent with a recent claim in the literature of a wide variation in published values and establishes the robustness of our knowledge of this process for the formation of HeH$^+$. The implications of the current results to the first detection of HeH$^+$ and its modeled abundance in the planetary nebula NGC 7027 are discussed.