On detection of BaO molecular lines in sunspot spectrum

Context

Spectral lines of diatomic molecules are perfect tools for studying the structure of sunspots and their temperature layers and magnetic sensitive absorption features, which are typically higher than in atomic lines. The integrated intensities of a few bands in the rotational structure of the astrophysically significant $A^1{\Sigma }^{+}-X^1{\Sigma }^{+}$and $A{}^{\prime 1}\Pi -X^1{\Sigma }^{+}$ systems of barium monoxide (BaO) have been measured experimentally using band spectra. An analysis of the prominent lines of (0, 0; 1, 1; 2, 2) bands of $A^1{\Sigma }^{+}-X^1{\Sigma }^{+}$transition and (0, 0; 1, 1; 2, 2) bands of $A{}^{\prime 1}\Pi -X^1{\Sigma }^{+}$transition with those of sunspot umbral spectrum. The effective rotational temperatures of the $A{}^{\prime 1}\Pi -X^1{\Sigma }^{+}$transition of BaO in the sunspot umbral spectrum are found to be in the range of 1600 K to 3200 K.

Aims

An analysis of BaO prominent rotational molecular lines of $A^1{\Sigma }^{+}-X^1{\Sigma }^{+}$and $A{}^{\prime 1}\Pi -X^1{\Sigma }^{+}$transition with those of sunspot umbral spectral lines. To find the significant values of radiative transition parameters, vibrational temperature and the effective rotational temperature of the molecule in celestial objects.

Methods

Calibrated the rotational structure of molecular band heads and lines for and $A^1{\Sigma }^{+}-X^1{\Sigma }^{+}$and $A{}^{\prime 1}\Pi -X^1{\Sigma }^{+}$ransitions in laboratory spectrum using most precise Hartmann's technique. High resolution FTS sunspot umbral spectra from NSO/Kitt Peak were used to detect rotational molecular lines due to the $A{}^{\prime 1}\Pi -X^1{\Sigma }^{+}$transition of the BaO molecule using the method of line coincidence. The effective rotational temperature was derived from the variation of equivalent width $\left(W\right)$ with rotational quantum number $\left(J\right)$ of spectrally well resolved rotational lines of a band in umbral spectrum. The triangular profile approximation method was used to estimate the equivalent width of the well resolved spectral lines.

Results

The effective rotational temperatures of the $A{}^{\prime 1}\Pi -X^1{\Sigma }^{+}$transition of BaO in the sunspot umbral spectrum are found to be in the range of 1600 K to 3200 K. It is compared with other results with a view to obtaining useful physical parameters. This is an evidence to ascertain the possible presence of BaO molecule in solar spectrum in different layers.

Conclusions

Unblended rotational lines due to the band of BaO, provide a good range of temperatures for the study of absorbing layers in umbral spectra. The $A{}^{\prime 1}\Pi -X^1{\Sigma }^{+}$transition of BaO molecular lines is found to be very sensitive to effective temperature. Radiative transition parameters data of these lines, in contrast to intensity measurements, provide us with more direct and detailed information to study the coolest parts of sunspot umbrae.