Abstract
We draw attention to the singularly peculiar photometric properties of the 9.5-day Cepheid FN Aql. An initial study of its color-color plots shows an unusually wide trajectory in the (U – B)-(B – V) diagnostic plane. A closer investigation reveals that the photometric residuals around fits to the individual mean light curves are highly correlated, decreasing in amplitude as a function of increasing wavelength. That correlation and trend suggest time-variable dust extinction; however, the grain properties must be different from the general interstellar medium. FN Aql is an IRAS source and also appears in the proto-planetary nebulae candidate in the 1989 listing of Volk & Kwok. The source of the changing extinction is probably localized and intrinsic to the Cepheid itself, possibly a wind. Further photometric studies of this peculiar Cepheid are recommended.
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