Identification of Zirconium Oxide molecular lines in the sunspot umbral spectra

► The presence of ZrO molecular lines indicates the temperature range and the molecular strength of the sunspots. ► The newly identified ZrO molecular lines are non-negligible components in the sunspot umbrae. ► The estimated rotational temperature helps to confirm the presence of ZrO molecular lines in the sunspot spectrum. The ZrO molecule has been detected in sunspot umbrae through the identification of following laboratory molecular transitions: 1Σ+−X1Σ+ (0,0), A3Φ2−X2Δ1 (0,0), A3Φ3−X2Δ2 (0,0), A3Φ4−X2Δ3 (0,0), B3Π2−X3Δ3 (0,0), B3Π1−X3Δ2 (0,0) and B3Π0−X3Δ1 (0,0) in red – infrared region using high resolution, visible range Fourier Transform Spectrum of sunspot umbra observed at the National Solar Observatory in Kitt Peak (NSO/KP). Much new identification has been made in the searched spectral wavenumber region from 16650cm−1 to 18007cm−1 of sunspot spectrum. Equivalent widths of well resolved lines, versus rotational quantum number J have been used to determine the effective rotational temperature for seven bands of the ZrO molecule. This result agrees well with the temperatures derived for other molecules’ presence in sunspot umbrae. It is evident that ZrO molecular lines are formed in higher layers of the atmosphere of relatively “cold” sunspots.