Molecules in Cool Stars: The A2Π − X2Σ+ and the B2Σ+ − X2Σ+ Band Systems of CaCl

Abstract

Cool red giant stars exhibit absorption bands of calcium monochloride (CaCl) in the optical region. In this work, the bands of CaCl corresponding to the A ^2 Π − X ^2 Σ ^+ transition with ${v}^{{\prime} }\leqslant $ 4 and v ″ ≤ 4, and B ^2 Σ ^+ − X ^2 Σ ^+ transition with ${v}^{{\prime} }\leqslant $ 2 and v ″ ≤ 2 are rotationally analyzed with PGOPHER, a multipurpose program for simulating and fitting molecular spectra. All bands were analyzed using high-resolution absorption spectra collected at the National Solar Observatory in 1985, calibrated with atomic lines from a high-resolution emission spectrum obtained in a separate hollow cathode experiment. The results are compared with previous laser-induced fluorescence measurements. Overall, the accuracy of spectroscopic constants for the A ^2 Π and B ^2 Σ ^+ states is improved. Scaled transition dipole moment calculations were used to obtain line strengths. Line lists are provided with Einstein A coefficients and oscillator strengths, which can be used to determine CaCl stellar abundances. Additionally, isotope splittings allowed us to estimate band origins for the ^40 Ca ^37 Cl isotopologue based on band-head positions.

Keywords

• Spectral line lists
• Laboratory astrophysics