Author : Justin Arras Kader
Release : 2022
Genre : Galactic bulges
Kind : eBook
Book Rating : /5 ( reviews)
Book Synopsis Multiple Populations in Globular Clusters of the Galactic Bulge by : Justin Arras Kader
Download or read book Multiple Populations in Globular Clusters of the Galactic Bulge written by Justin Arras Kader. This book was released on 2022. Available in PDF, EPUB and Kindle. Book excerpt: Globular clusters are a class of very old, massive, spherical, gravitationally bound star cluster which likely play an important, but as of yet unknown, role in the formation and evolution of galaxies. These clusters had been regarded as the archetypical example of simple stellar populations, with all stars having been born at the same time from the same star-forming gaseous material. One of the major predictions of such a model is that the stars in the cluster should have identical abundances, save for inhomogeneities caused by self-enrichment of red giant atmospheres via mixing of material processed in the inner layers of the evolved stars up to their surface. However, in several pivotal studies at the turn of the 21st century, star-to-star variations in atmospheric chemical abundance were discovered among unevolved stars on the main sequence of several Galactic globular clusters, prompting acceptance of a multiple populations model. It has since been demonstrated that almost all Galactic globular clusters harbor multiple populations. Several of the most popular models envision a first generation of stars forming in the protocluster with primordial abundances, followed by formation of a second generation out of intracluster material polluted with light element products of the CNO cycle (along with the NeNa- and MgAl-chain) processes. In these scenarios, the ejecta of SNe, which include Fe and other heavy elements, attains escape velocity and does not contribute to the abundances of the second generation. However, the complexity of the observed chemical trends has so far eluded comprehensive explanation, and there is still no unified model for the origin of multiple populations in globular clusters.In this dissertation, we seek to provide key constraints on competing models of the origin of multiple populations in globular clusters by studying the relative fraction of stars of different generations, and their distribution, among 14 inner Milky Way clusters which span a wide range in mass, dynamical age, and orbital characteristics. This work was made possible by use of the Blanco DECam Bulge Survey point source catalog, providing deep, wide-field, NUV-NIR broadband photometry for more than 250 million stars toward the southern Galactic bulge. Proper motions for many of the stars were available after cross-matching the photometric catalog with Gaia EDR3, which allowed for the creation of high resolution extinction maps toward the target clusters. The extinction maps allowed us to correct the photometry for the effects of differential reddening, which can be quite severe toward the Galactic bulge. By taking advantage of the de-reddened u-band, we showed that the Blanco photometry is capable of separating cluster red giant stars based on their N (Na) abundance, enabling wide-field studies of the populations in these clusters with large number statistics. With this preferentially metal-rich sample, we were able to test whether the well-known correlations between the properties of the populations and their parent clusters hold true at higher metallicity. We were also able to compare wide-field distributions of the cluster multiple populations with orbital and internal dynamical properties of the parent clusters, which are on preferentially disruptive orbits, in order to test dynamical models of the evolution of multiple populations.
