Knowledge Bank

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 $\mathrm{<mrow\; data-mjx-texclass="ORD">24</mrow>}MgHB\prime 2\Sigma +-X2\Sigma -$ 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 $B\prime 2\Sigma +-X2\Sigma +$ lines have been tracked as far to the blue as 5300 \AA. Using the weak lines of the 0-7 band of the minor $\mathrm{<mrow\; data-mjx-texclass="ORD">25</mrow>}MgH$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">26</mrow>}MgH$ isotopomers, the solar isotope ratio $\mathrm{<mrow\; data-mjx-texclass="ORD">24</mrow>}Mg:25Mg;26Mg$ 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 $v\prime \prime$ 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 $MgHB\prime 2\Sigma +-X2\Sigma +$ are much more clearly separated and much less blended than lines from strong $A2\Pi -X2\Sigma +$ transition. The $B\prime 2\Sigma +-X2\Sigma +$ lines should prove useful in isotopic abundance analyses for stars where the $A2II-X2\Sigma +$ transition is too strong to yield useful results.