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Systematic variations of interstellar linear polarization and growth of dust grains

A quantitative interpretation of the observed relation between the interstellar linear polarization curve parameters $K$ and $λ_{\max}$ characterizing the width and the wavelength of a polarization maximum, respectively, is given. The observational data available for 57 stars located in the dark clouds in Taurus, Chamaeleon, around the stars $ρ$ Oph and R CrA are considered. The spheroidal particle model of interstellar dust grains earlier applied to simultaneously interpret the interstellar extinction and polarization curves in a wide spectral range is utilized. The observed trend $K \approx 1.7 λ_{\max}$ is shown to be most likely related to a growth of dust grains due to coagulation rather than mantle accretion. The relation of the parameters $K$ and $λ_{\max}$ with an average size of silicate dust grains is discussed.