Correlation among extinction efficiency and other parameters in an aggregate dust model

Abstract

We study the extinction properties of highly porous BCCA dust aggregates in a wide range of complex refractive indices ($1.4 \le n \le 2.0$, $0.001 \le k \le 1.0$) and wavelength ($0.11\mu m \le \lambda \le 3.4\mu m$). An attempt has been made for the first time to investigate the correlation among extinction efficiency ($Q_{ext}$), the composition of dust aggregates ($n, k$), the wavelength of radiation ($\lambda$) and size parameter of the monomers ($x$). If $k$ is fixed at any value between 0.001 and 1.0, $Q_{ext}$ increases with increase of $n$ from 1.4 to 2.0. $Q_{ext}$ and $n$ are correlated via \emph{linear} regression when the cluster size is small whereas the correlation is \emph{quadratic} at moderate and higher sizes of the cluster. This feature is observed at all wavelengths (UV to optical to infrared). We also find that the variation of $Q_{ext}$ with $n$ is very small when $\lambda$ is high. When $n$ is fixed at any value between 1.4 and 2.0, it is observed that $Q_{ext}$ and $k$ are correlated via polynomial regression equation (of degree 1, 2, 3 or 4), where the degree of the equation depends on the cluster size, $n$ and $\lambda$. The correlation is linear for small size and quadratic/cubic/quartic for moderate and higher sizes. We have also found that $Q_{ext}$ and $x$ are correlated via a polynomial regression (of degree 3,4 or 5) for all values of $n$. The degree of regression is found to be $n$ and $k$-dependent. The set of relations obtained from our work can be used to model interstellar extinction for dust aggregates in a wide range of wavelengths and complex refractive indices.