On the spatial distribution of luminous blue variables in the M33 galaxy

Abstract

In the current paper, we present a study of the spatial distribution of luminous blue variables (LBVs) and various LBV candidates (cLBVs) with respect to OB associations in the M33 galaxy. The identification of blue star groups was based on the LGGS data and was carried out by two clustering algorithms with initial parameters determined during simulations of random stellar fields. We have found that the distribution of distances to the nearest OB association obtained for the LBV/cLBV sample is close to that for massive stars with $M_{\rm init}>20\,M_\odot$ and Wolf-Rayet stars. This result is in good agreement with the standard assumption that luminous blue variables represent an intermediate stage in the evolution of the most massive stars. However, some objects from the LBV/cLBV sample, particularly Fe$\,$II-emission stars, demonstrated severe isolation compared to other massive stars, which, together with certain features of their spectra, implicitly indicates that the nature of these objects and other LBVs/cLBVs may differ radically.