Cirrus Color Variations Due to Enhanced Radiation Fields

We have investigated the variations in 12/100, 25/100, 60/100, and 12/25 μm colors for seven main-sequence B stars and three F and G supergiants associated with infrared cirrus. All sources displayed an increase in 60/100 color above the background cirrus color. In two of the sources, ɛ Apodis and HR 890, the 12/100 and 25/100 colors decline toward the embedded star in a similar fashion to the IR colors of S264 and the Rosette Nebula. Current grain models composed of equilibrium-heated submicron grains, transiently heated small grains, and polycyclic aromatic hydrocarbons cannot account for the color variations observed around ɛ Aps and HR 890. The supergiants exhibited 12/100 and 25/100 increases, suggesting that the color deficits observed for the B stars are due to an enhancement in the soft UV component of the radiation field only. A candidate explanation for the color variations is a conglomerate small grain component, composed of very small grains and/or large molecules, that is fragmented in the enhanced radiation field around ɛ Aps and HR 890.