類星體環境乃屬高溫且活耀，但形成塵埃的條件為溫度需小於2000K，因此，一般而言，在類型體環境下，極難形成塵埃。在過去的推論中，便認為類星體周遭的灰塵乃自老舊恆星或是AGB stars 所噴發出來的。

然而，在2002年，Elvis et al.提出一套模型解釋，其解釋在類星體風中，仍有些環境條件和AGB stars是很接近的，那這樣的環境下，便可利於灰塵形成。2007年，Markwick-Kemper et al. 用了Spitzer-IRS 所得到的PG2112+059 data做分析，得到了其中可能組成的成分。

本研究便由此處再做延伸，分別找了五個radio-quiet 類星體(PG 2112+059, PG 0043+039, PG 1211+143, PG 1351+640 and PG 0050+124.)作為目標，再用常見的六種宇宙中的成分做比對，發展出新的方式去分析這些數值，嘗試著在結果中觀察類星體成分比例是否受到類星體風大小的影響，以期望證實2002年Elvis et al.所提出之模型是否正確。

Forming dust is difficult, it needs a high density and low temperature (<2000K) environment. Therefore, where the dust in the torus around Active Galactic Nuclei (AGN) comes from is an interesting question. It could be processed interstellar dust, or, as Elvis et al (2002) proposed, it could be formed in the wind lifting off the accretion disk. Assuming this is the case, we can analyze the composition of this dust using mid-IR spectroscopy (Markwick-Kemper
et al., 2007).
Silicate features have been detected in emission at 9.7 and 18 µm and have been seen in the spectrum of several quasars and AGN (Siebenmorgen et al., 2005; Sturm et al., 2005; Hao et al., 2005; Shi et al., 2006; Markwick-Kemper et al., 2007).
In this study, we fit the Spitzer Space Telescope InfraRed Spectrograph (IRS) data of AGN with a power-law continuum model, and an optically thin dust component. We use the opacities for six different species (Alumina(Al2O3),
Periclase(MgO), PAHs, Fe-rich Amorphous Olivine, Fe-poor Amorphous Olivine, and Forsterite(Mg2SiO4)) calculated from laboratory data using a Continuous Distribution of Ellipsoids (CDE) or Mie Theory (Mie). Fitting the spectra with this model, we can identify the dust features in the spectrum to determine the composition of the dust around AGN. We have successfully applied the model to PG 2112+059, then we use the same model to analyze other radio-quiet quasars: two BAL quasars with strong winds, PG 2112+059 and PG 0043+039; three non-BAL or mini-BAL, PG 1211+143,
PG 1351+640 and PG 0050+124.

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