Abstract
We have identified lines from the 0-3, 0-4, 0-5, 0-6, 0-7, 1-3, 1-4, 1-7, and 1-8 bands of the 24MgH B' 2Σ+-X 2Σ+ transition in sunspot umbral spectra. Lines of the 0-7 and 1-8 bands in the uncluttered 7500 A region are the most obvious, but B' 2Σ+-X 2Σ+ lines have been tracked as far to the blue as 5300 A. In combination with weak lines of the 0-7 bands of the 25MgH and 26MgH isotopes, the solar isotope ratio 24Mg:25Mg:26Mg has been measured as 76:12:12, in agreement with the much better determined terrestrial ratio 79:10:11. The intensity distribution of bands with v'' from 4 to 8 has been measured and found to show no anomalies; the excitation temperature of 3100 K agrees well with a value of 3200 K determined from SiO in a sunspot spectrum. The lines of the MgH B' 2Σ+-X 2Σ+ transition are much more cleanly separated and much less blended than lines from the stronger A 2Π-X 2Σ+ transition. The B' 2Σ+-X 2Σ+ lines should prove useful in isotopic abundance analyses for stars where the A 2Π-X 2Σ+ transition is too strong to yield useful results.
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