A principal component analysis approach to the morphology of Planetary Nebulae

Abstract

Principal Component Analysis (PCA) is a well-known technique used to decorrelate a set of vectors. It has been applied to explore the star formation history of galaxies or to determine distances of mass-lossing stars. Here we apply PCA to the optical data of Planetary Nebulae (PNe) with the aim of extracting information about their morphological differences. Preliminary analysis of a sample of 55 PNe with known abundances and morphology shows that the second component (PC2), which results from a relation produced by the parameters log(N/O), initial and final mass of PNe, is depending on the morphology of PNe. It has been found that when log(N/O) < -0.18 the PNe's nitrogen is low independently on the oxygen abundance for either Bipolar (B), Elliptical (E) or Round (R) PNe. An interesting result is that both E and R PNe have log(N/O) < 0 while only B PNe show negative and positive values. Consequently, B PNe are expected to have higher nitrogen values than the E and R PNe. Following that and a second sample of 35 PNe, n_{e} is also found to be higher in B PNe. Also, in all PNe morphologies PC2 appears to have a minimum at 0.89 and PNe's initial mass at 2.6 solar masses. 5-D diagrams between PCAs components and physical parameters are also presented. More results will follow while simple models will be applied in order to try to give a physical meaning to the components.