The work initially started as a test to retrace the Shen & Ho (2014) Quasar Main Sequence diagram where they claimed that the parameter RFeII, which defines the Eigenvector 1 (EV1) is driven by the Eddington ratio alone. We subsequently construct a refined (error and redshift limited) sample from the original Shen et al. 2011 QSO catalogue. Based on our hypothesis - the main driver of the Quasar Main Sequence is the maximum of the accretion disk temperature defined by the Big Blue Bump on the Spectral Energy Distribution. We select the four extreme sources that have RFeII $geq$ 4.0 and use the SED modelling code CIGALE to fit the multi-band photometric data for these sources. We also perform detailed spectral fitting including the FeII pseudo-continuum to estimate and compare the value of RFeII for them. We show the metallicity dependent FeII strength in the context of this study.
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