On the correlation between CO absorption and far-ultraviolet nonlinear extinction toward Galactic OB stars

A sample of 59 sight lines to reddened Galactic OB stars was examined for c orrelations of the strength of the CO Fourth Positive (A(1)Pi-X(1)Sigma(+)) 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 cu rves from the literature. A strong correlation with the nonlinear far-UV cu rvature term was found with greater absorption, normalized to E(B - V), bei ng associated with more curvature. A weaker trend with the linear extinctio n term was also found. Mechanisms for enhancing CO in dust environments exh ibiting high nonlinear curvature are discussed.