On the effective temperature of AlC molecular lines in sunspot umbral spectra
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ORIGINAL ARTICLE
On the effective temperature of AlC molecular lines in sunspot umbral spectra R. Sindhan1,2 · P. Sriramachandran3 · R. Shanmugavel3 · S. Ramaswamy1
Received: 30 January 2018 / Accepted: 8 September 2020 / Published online: 30 September 2020 © Springer Nature B.V. 2020
Abstract In the present work, a significant rotational lines of the B 4 − –X 4 − (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 A4 − –X 4 − and B 4 − –X 4 − 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 − –X 4 − (0, 0) band system is most intense (qv v = 0.741). For the B 4 − state, the radiative lifetime of v = 0 level is found as 103.93 ns. The effective vibrational temperature of the A4 − –X 4 − and B 4 − –X 4 − 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. Keywords Molecular data · Electronic transition moment · Sunspot umbrae · Rotational temperature · Vibrational temperature · AlC molecule
B S. Ramaswamy
[email protected] P. Sriramachandran [email protected]
1
Physics Research Centre, N.M.S.S.V.N. College, Madurai – 625 019, India
2
Madurai Kamaraj University Constituent College, Kappalur, Thirumangalam – 625 008, India
3
Physics Research Centre, V.H.N.S.N. College, Virudhunagar – 626 001, India
1 Introduction The aluminum carbide (AlC) molecule is astrophysically significant, because diatomic carbon molecules like C2 , CN, CH and CO have been identified in the stars of globular clusters (Kraft 1979) and in the spectra of sunspots, late stars, comets and interstellar atmospheres (Amiot 1983 and Sriramachandran et al. 2016). Also the diatomic aluminumbased molecules have been found in the emission spectra of sunspots and in the carbon rich star IRC+10216 (Cernicharo and Guelin 1987; Cernicharo 1997; Turner 1995, and Sriramachandran et al. 2013). Cernicharo et al. (1989) have noted the presence of silicon monocarbide (SiC) in IRC+10216. The silane molecule (SiH4 ) has been an important compound of the dust shell surrounding the carbon rich stars (Barrett 1978 and Goldhaber and Betz 1984). Knight et al. (1990) have reported the first experimental evidence showing that the AlC molecule has a X 4 − ground state and AlC2 is in a X 2 A1 state. After that, Brazier (1993) has observed the B 4 − –X 4 − band system of the AlC radical near 22,0
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