The bands of CH and CN in stellar spectra

The upper limit of visibility in the spectral sequence of the CH band at λ4300 is found to be F8 (temperature about 6500°K). This value is considerably lower than has been adopted heretofore (classes F2 to A0; temperatures 7900° to 13000°K). The region occupied by the CH band is very rich in strong atomic lines and it is therefore not permissible to consider the general aspect of the Fraunhofer "G-band": the total intensity of the atomic lines greatly exceeds that of the molecular lines. The limit of visibility of the CN band at λ4200 is found to be at F8, in agreement with former estimates. The simultaneous disappearance of CH and CN, having heats of dissociation of 110 and 210 k cal/mol respectively, may be explained by the great abundance of H in stellar atmospheres.