Line Strengths of Rovibrational and Rotational Transitions in the X$^2\Pi$ Ground State of OH

TL;DR

This paper presents a comprehensive new line list for OH ground state rovibrational and rotational transitions, including accurate line positions and intensities, with applications to stellar oxygen abundance measurements.

Contribution

It introduces a new, detailed line list with improved molecular constants and intensities based on high-level ab initio calculations, extending temperature coverage and enhancing astrophysical analyses.

Findings

Good agreement with experimental lifetimes and line ratios

Extended temperature range for partition functions (5-6000 K)

Accurate oxygen abundance determinations in stars

Abstract

A new line list including positions and absolute intensities (in the form of Einstein $A$ values and oscillator strengths) has been produced for the OH ground X\DP\ state rovibrational (Meinel system) and pure rotational transitions. All possible transitions are included with v$\primed$ and v$\Dprimed$ up to 13, and $J$ up to between 9.5 and 59.5, depending on the band. An updated fit to determine molecular constants has been performed, which includes some new rotational data and a simultaneous fitting of all molecular constants. The absolute line intensities are based on a new dipole moment function, which is a combination of two high level ab initio calculations. The calculations show good agreement with an experimental v=1 lifetime, experimental $\mu_\mathrm{v}$ values, and $\Delta$v=2 line intensity ratios from an observed spectrum. To achieve this good agreement, an alteration in the method of converting matrix elements from Hund's case (b) to (a) was made. Partitions sums have been calculated using the new energy levels, for the temperature range 5-6000 K, which extends the previously available (in HITRAN) 70-3000 K range. The resulting absolute intensities have been used to calculate O abundances in the Sun, Arcturus, and two red giants in the Galactic open and globular clusters M67 and M71. Literature data based mainly on [O I] lines are available for the Sun and Arcturus, and excellent agreement is found.