On the Correlation between CO Absorption and Far‐Ultraviolet Nonlinear Extinction toward Galactic OB Stars

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Abstract
A sample of 59 sight lines to reddened Galactic OB stars was examined for correlations of the strength of the CO Fourth Positive (A1Π-X1Σ+) absorption band system with the ultraviolet interstellar extinction curve parameters. We used archival high-dispersion NEWSIPS IUE spectra to measure the CO absorption for comparison with parametric fits of the extinction curves from the literature. A strong correlation with the nonlinear far-UV curvature term was found with greater absorption, normalized to E(B-V), being associated with more curvature. A weaker trend with the linear extinction term was also found. Mechanisms for enhancing CO in dust environments exhibiting high nonlinear curvature are discussed.
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