A Color–Magnitude Diagram in the DDO Photometric System

A signature two-color diagram of the DDO photometric system plots C (45–48), which is sensitive to surface gravity for cool stars, versus C (42–45), which correlates with effective temperature. The extent to which this two-color diagram mimics a Hertzsprung–Russell diagram is explored. To this end, a color–magnitude diagram (CMD) that plots an absolute magnitude M 48 versus color C (42–45) is presented for a sample of field stars for which high-precision DDO photometry and Gaia DR3 parallaxes are available. Such a DDO CMD has seen little use to date.