THE $MgH B^{\prime 2}\Sigma^{+} - X^{2}\Sigma^{+}$ TRANSITION: A NEW TOOL FOR STUDYING MAGNESIUM ISOTOPE ABUNDANCES
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Date
1999
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Publisher
Ohio State University
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 $^{24}MgH B^{\prime 2}\Sigma^{+} - X^{2}\Sigma^{-}$ transition in sunspot umbral spectra. Lines of the 0-7 and 1-8 bands in the uncluttered 7500 \AA region are the most obvious but $B^{\prime 2}\Sigma^{+} - X^{2}\Sigma^{+}$ lines have been tracked as far to the blue as 5300 \AA. Using the weak lines of the 0-7 band of the minor $^{25}MgH$ and $^{26}MgH$ isotopomers, the solar isotope ratio $^{24}Mg:^{25}Mg;^{26}Mg$ 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 $v^{\prime\prime}$ 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 $MgH B^{\prime 2}\Sigma^{+} - X^{2}\Sigma^{+}$ are much more clearly separated and much less blended than lines from strong $A^{2}\Pi - X^{2}\Sigma^{+}$ transition. The $B^{\prime 2}\Sigma^{+} - X^{2}\Sigma^{+}$ lines should prove useful in isotopic abundance analyses for stars where the $A^{2}II - X^{2}\Sigma^{+}$ transition is too strong to yield useful results.
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Author Institution: Kitt Peak National Observatory, National Optical Astronomy Observatories; Department of Chemistry, University of Waterloo