High-resolution Fourier Transform Spectrometer sunspot umbral spectra of the National Solar Observatory/National Optical Astronomy Observatory at Kitt Peak were used to detect rotational lines from 19 electronic transition bands of the molecules LaO, ScO and VO, in the wavenumber range of 11 775 to 20 600 cm −1 . The presence of lines from the following transitions is confirmed: 0) and B 2 Σ + -X 2 Σ + (0, 0) of ScO; and C 4 Σ − -X 4 Σ − (0, 1; 1, 0; 0, 2) and (2, 0) of VO. However, the presence of A 2 Π r3/2 -X 2 Σ + (0, 0) and C 2 Π r3/2 -A 2 r5/2 (0, 0; 1, 1) of LaO and C 4 Σ − -X 4 Σ − (0, 0) of VO are found to be doubtful because the lines are very weak, and detections are difficult owing to heavy blending by strong rotational lines of other molecules. Equivalent widths are measured for well-resolved lines and, thereby, the effective rotational temperatures are estimated for the systems for which the presence is confirmed.

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The physical conditions of celestial objects can be analyzed using the spectrum of atoms or molecules present in the object. The present work focuses on the spectroscopic analysis of astrophysically significant molecule AlF. The evaluation of Franck-Condon (FC) factors andr-centroids is done by a numerical integration procedure using the suitable potential energy curves forC1Σ+-A1Σ+,b3Σ+-a3Πr,c3Σ-a3Πr, andf3Π-a3Πrband systems of AlF molecule. The intensity of various bands is discussed with the help of derived FC factors. The band degradation and the nature of potential energy curves are studied usingr-centroid values. The vibrational temperature of sunspot is estimated to be around 1220 ± 130 K which falls in the reported temperature range of cold sunspots.