A detailed analysis of barium oxide molecular lines in sunspot umbral spectra

Abstract

It is essential to know the composition of atoms or molecules present in the astrophysical objects concerned to determine the physical and chemical nature of a solar or stellar region. With the aim to identify them clearly, we therefore analyzed the rotational lines of eleven bands of the A 1Σ–X 1Σ+ system and three bands of the A ′1Π–X 1Σ+ system of the barium oxide (BaO) molecule in high-resolution sunspot umbra spectra provided by the National Solar Observatory, Kitt Peak, in the visible and infrared wavenumber range 13 600 – 25 000 cm−1. We confirm rotational lines in several bands of the BaO molecule by following the line identification technique, in which the positive result of chance coincidences is observed. We additionally confirmed the BaO molecule in sunspots by evaluating the rotational temperature. The equivalent widths for the well-resolved lines have been observed in the spectra, and accordingly, the rotational temperature of the band systems were determined by plotting the graph between J(J+1) and log(W/J). The estimated effective rotational temperature values for the bands of A–X and A′–X vary from 1000 to 3500 K, which agrees well with the reported temperatures obtained by identifying other diatomic molecules in sunspot umbrae. The present work therefore provides clear evidence of the existence of the BaO molecule in sunspot umbral regions.