The (0,0) Band of the -System of TiO in the Umbral Spectrum: The Isotopic Abundances of Ti

Photoelectric spectra of the γ -system of TiO in sunspot umbrae are examined for the presence of the less abundant stable isotopes of Ti. From comparisons of computed spectra with observations in the wavelength region of minimum line density (7065–7085 A), the solar and terrestrial abundances of 46, 47, 49, 50Ti relative to 48Ti are shown to be equal to within ± 30 per cent. Analysis of 48TiO lines yields a value for the band oscillator strength: $$f\,0,0\,=\,0\cdot034$$ with an adopted dissociation energy of TiO of 7 · 2 e V and the model umbral atmosphere proposed by Stellmacher and Wiehr. A significant dependence of the f -value on dissociation energy and model atmosphere is found. Line profiles in the α- and γ -systems require a microturbulent velocity of $${\xi }_\text{t}\,=\,1\cdot2\pm 0\cdot1\,\text{km}\,\text{s}^{-1}$$ .