S-type Stars: LaO Line List for the B²Σ⁺–X²Σ⁺ Band System

Abstract

LaO bands are a characteristic feature in the spectrum of cool S-type stars. La is made primarily by the s-process during the asymptotic giant branch phase of stellar evolution. The B2Σ+–X2Σ+ and A2Π–X2Σ+ band systems can be used to determine the La abundances in cool S stars. The bands of the B2Σ+–X2Σ+ with v ′ and v ′ ′ ≤ 5 have been rotationally analyzed from an emission spectrum from a carbon furnace. Line strengths are calculated using an ab initio transition dipole function, corrected using experimental lifetimes. We provide a line list for the B2Σ+–X2Σ+ band system that can be used to determine La abundances.

S-type Stars: Line List for the A2Π–X2Σ+ Band System of LaO

“…The experimental observations were as described in our B 2 Σ + -X 2 Σ + analysis (Bernath et al 2022). In brief, the LaO spectrum was recorded in emission from a carbon tube furnace with the Fourier transform spectrometer associated with the McMath-Pierce Solar Telescope on Kitt Peak in Arizona.…”

“…Internally contracted multireference configuration interaction calculations (ic-MRCI; ) have been performed with the MOLPRO quantum chemistry package (Werner et al 2012(Werner et al , 2019 to calculate the electric TDM curve for the A 2 Π-X 2 Σ + transition. A detailed description of the method, basis sets, and active space is given in our previous work on the B 2 Σ + -X 2 Σ + transition (Bernath et al 2022). The transition matrix elements of the electric dipole moment operator were obtained using the wave functions calculated as in Bernath et al (2022) for the X 2 Σ + state and through a state-averaged complete active space self-consistent field (SA-CASSCF) orbital optimization involving the two low-lying 2 Π interacting states for the A 2 Π state.…”

“…A detailed description of the method, basis sets, and active space is given in our previous work on the B 2 Σ + -X 2 Σ + transition (Bernath et al 2022). The transition matrix elements of the electric dipole moment operator were obtained using the wave functions calculated as in Bernath et al (2022) for the X 2 Σ + state and through a state-averaged complete active space self-consistent field (SA-CASSCF) orbital optimization involving the two low-lying 2 Π interacting states for the A 2 Π state. A biorthogonal orbital transformation has been applied for this calculation.…”

“…The structure of the X 2 Σ + state is well known from the work of Childs et al (1986), Törring et al (1988), Steimle &Virgo (2002), andBernath et al (2022). The rotational energy levels of the ground X 2 Σ + state display b βs coupling because the Fermi contact parameter (b) that describes the hyperfine interaction is much larger than the spin-rotation interaction parameter, γ (Bacis et al 1973;Steimle & Virgo 2002;Brown & Carrington 2003;Bernath et al 2022). The spectroscopic parameters for the ground state (X 2 Σ + ) are described in Bernath et al (2022) and these values are used in this analysis for the X 2 Σ + state.…”

“…The ground X 2 Σ + state is well characterized by microwave (Törring et al 1988;Suenram et al 1990) and radio frequency spectroscopy (Childs et al 1986). More recently, the LaO ionization potential of 5.2446 eV has been measured by Cao et al (2021), and the B 2 Σ + -X 2 Σ + system has been reanalyzed (Bernath et al 2022), including a line list calculation.…”