LLOYD WALLACE, KENNETH HINKLE, Kitt Peak National Observatory, National Optical Astronomy Observatories, Tucson, AZ 85726; EDWARD G. LEE AND PETER F. BERNATH, Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
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'2 + - X2 + transition in sunspot umbral spectra. Lines of the 0-7 and 1-8 bands in the uncluttered 7500 Å~ region are the most obvious but B'2 + - X2 + lines have been tracked as far to the blue as 5300 Å. Using the weak lines of the 0-7 band of the minor 25MgH and 26MgH isotopomers, 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'2 + - X2 + are much more clearly separated and much less blended than lines from strong A2 -X2 + transition. The B'2 + - X2 + lines should prove useful in isotopic abundance analyses for stars where the A2 -X2 + transition is too strong to yield useful results.