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On the effective temperature of AlC molecular lines in sunspot umbral spectra

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Abstract

In the present work, a significant rotational lines of the \(B^{4}\Sigma ^{-} \mbox{--} X^{4}\Sigma ^{ -} \) (\(0,0\)) band system of the AlC molecule were identified in high resolution FTS sunspot umbral spectra in the region from 22,450 to 22,600 cm−1. Among the well-resolved identified lines, the rotational temperatures have been estimated to be 4018 K for photosphere and 3722 K for a hot umbra. Hence, the estimated effective rotational temperatures provide evidence for the possible presence of the AlC molecule in a sunspot umbra. The radiative transition parameters for \(A^{4}\Pi ^{ -} \mbox{--} X^{4}\Sigma ^{ -} \) and \(B^{4}\Sigma ^{ -} \mbox{--} X^{4}\Sigma ^{ -} \) systems of the AlC molecule have been estimated for experimentally known vibrational levels using the Rydberg–Klein–Rees (RKR) potential. The Franck-Condon (FC) factor of \(B^{4}\Sigma ^{ -} \mbox{--} X^{4}\Sigma ^{ -} \) (\(0,0\)) band system is most intense (\(q_{v'v''} = 0.741\)). For the \(B^{4}\Sigma ^{ -}\) state, the radiative lifetime of \(v'=0\) level is found as 103.93 ns. The effective vibrational temperature of the \(A^{4}\Pi ^{ -} \mbox{--} X^{4}\Sigma ^{ -} \) and \(B^{4}\Sigma ^{ -} \mbox{--} X^{4}\Sigma ^{ -} \) band systems of the AlC molecule is 3981 K and 2706 K, respectively. Therefore, the effective vibrational temperature and radiative transition parameters help us to ascertain the possible presence of the AlC molecule in the solar atmosphere.

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Acknowledgements

The sunspot spectra used in this study are taken from the technical reports of the National Solar Observatory, operated by the Association of Universities in Astronomy, Inc. (AURA), under a cooperative agreement with the National Science Foundation.

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Correspondence to S. Ramaswamy.

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Sindhan, R., Sriramachandran, P., Shanmugavel, R. et al. On the effective temperature of AlC molecular lines in sunspot umbral spectra. Astrophys Space Sci 365, 157 (2020). https://doi.org/10.1007/s10509-020-03866-7

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  • DOI: https://doi.org/10.1007/s10509-020-03866-7

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