The Molecular Spectrum of Sunspot Umbrae

By means of spectrographic analysis we have studied the molecular spectra in three sunspot umbrae. Our first step was to try to identify all the molecular lines in the spectral range 4900-6450 A using the method of coincidences. Because of the very high number of spectral lines per , this method may lead to spurious results; thus it was necessary to make various checks based on line or band intensities. Fourteen molecules have been studied; three of them (CN, MgH and TiO) were extensively analysed and provided reliable information about the rotational temperatures (3000 K in the largest umbra). In the same way we obtain an empirical curve of growth from the MgH lines that allowed us to estimate the Mg isotopic ratios. Our last step was to compute the equivalent widths of molecular lines using 's sunspot model and to compare the calculations with the observations; thus it was possible to confirm the model and also to evaluate several molecular parameters which were previously unknown (TiO oscfflator strengths in the cc system) or doubtful (MgH 8H - 8 system oscfflator strengths). We point out that all our results are consistent with a microturbulence velocity = 1 km/s in the largest sunspot. Key words: solar spectroscopy - sunspots - absorption band spectra - molecular identifications - molecular line intensity calculations - isotopes: isotopic abundance determination - vibrational oscfflator strength determination