Not-So-Simple Stellar Populations in Star Clusters

Not-So-Simple Stellar Populations in Star Clusters
Author: Chengyuan Li
Publisher: Springer
Total Pages: 132
Release: 2017-09-19
Genre: Science
ISBN: 9811056811

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This book focuses on understanding the stellar populations of massive star clusters and aims to investigate the origin, evolution and properties of binary systems, their collision products, as well as the general characteristics (e.g. ages, metal content) of stellar population(s) in star clusters. It introduces the basic background knowledge of various stellar populations in star clusters as well as their formation, interaction and evolution and offers high impact observational results on our understanding of the formation and evolution mode of star clusters. Based on these discoveries, this book proposes a series of future projects that can shed light on these topics. The research introduced in this book reveals key features of star clusters formation and by extension how all stars formed in our universe.

Multiple Populations in Globular Clusters of the Galactic Bulge

Multiple Populations in Globular Clusters of the Galactic Bulge
Author: Justin Arras Kader
Publisher:
Total Pages: 0
Release: 2022
Genre: Galactic bulges
ISBN:

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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.

Old Stellar Populations

Old Stellar Populations
Author: Santi Cassisi
Publisher: John Wiley & Sons
Total Pages: 506
Release: 2013-08-29
Genre: Science
ISBN: 3527665544

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The book discusses the theoretical path to decoding the information gathered from observations of old stellar systems. It focuses on old stellar systems because these are the fossil record of galaxy formation and provide invaluable information ont he evolution of cosmic structures and the universe as a whole. The aim is to present results obtained in the past few years for theoretical developments in low mass star research and in advances in our knowledge of the evolution of old stellar systems. A particularly representative case is the recent discovery of multiple stellar populations in galactic globular clusters that represents one of the hottest topics in stellar and galactic astrophysics and is discussed in detail. Santi Cassisi has authored about 270 scientific papers, 150 of them in peer-reviewed journals, and the title Evolution of Stars and Stellar Populations.

Ages of LMC Star Clusters from Their Integrated Properties

Ages of LMC Star Clusters from Their Integrated Properties
Author: Randa Asa'd
Publisher:
Total Pages: 163
Release: 2012
Genre:
ISBN:

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Star Clusters are the building blocks of galaxies. Determining their ages gives us information about the formation history of their hosting galaxies. For far-away galaxies, star clusters are not resolved. Only their integrated properties can be observed. Both integrated photometry and integrated spectra have been used as age indicators of stellar clusters. The Large Magellanic Cloud (LMC) is a perfect galaxy to test these methods of age determination, because its clusters are close enough to see their individual stars, but also far enough away so that each cluster can be observed as a whole. This work first shows that the traditional methods of using the integrated broad-band photometry for age determination are highly inaccurate. This is attributed primarily to two things. First, the UBV integrated broad-band aging methods require matching a cluster with an expected model prediction of the cluster colors as a function of age. The biggest problem we find is the stellar clusters in our sample do not typically lie on the model line based on their known age and extinction. That is to say, real cluster colors often do not match the model colors and can be found some distance from expected model values. A second issue, which has been previously documented in numerous studies, is the strong degeneracy between age and extinction in the UBV color-color plane. Certainly, providing more photometric bands will reduce degeneracy between age and reddening. Better yet, if extinction can be independently determined, we show that ages from methods based on integrated broad-band colors will more closely match those obtained from more accurate methods based on stellar photometry. But the underlying issue remains. Simple stellar population models often do not accurately represent the colors of real stellar clusters due to the incomplete and stochastic sampling of the stellar mass function in low and moderate mass stellar clusters. On the other hand, integrated spectra provide better age predictions than broad-band photometry in the wavelength range 3626' 6248 A when compared with high resolution computational models. I obtained the integrated spectra of 20 clusters that didn't have integrated spectra in the optical range, or they have never been observed before. Using ths sample and 7 other clusters from the literature I show that the statistical Kolmogorov-Smirnov (KS) test can better find the closest match between the observed spectrum and theoretical model than the traditional Chi squared. Finally, I present a new software routine that efficiently predicts the age of a star cluster given its optical integrated spectrum compared to spectra generated by computational models.

Evolution of Stars and Stellar Populations

Evolution of Stars and Stellar Populations
Author: Maurizio Salaris
Publisher: John Wiley & Sons
Total Pages: 386
Release: 2005-12-13
Genre: Science
ISBN: 9780470092224

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Evolution of Stars and Stellar Populations is a comprehensive presentation of the theory of stellar evolution and its application to the study of stellar populations in galaxies. Taking a unique approach to the subject, this self-contained text introduces first the theory of stellar evolution in a clear and accessible manner, with particular emphasis placed on explaining the evolution with time of observable stellar properties, such as luminosities and surface chemical abundances. This is followed by a detailed presentation and discussion of a broad range of related techniques, that are widely applied by researchers in the field to investigate the formation and evolution of galaxies. This book will be invaluable for undergraduates and graduate students in astronomy and astrophysics, and will also be of interest to researchers working in the field of Galactic, extragalactic astronomy and cosmology. comprehensive presentation of stellar evolution theory introduces the concept of stellar population and describes "stellar population synthesis" methods to study ages and star formation histories of star clusters and galaxies presents stellar evolution as a tool for investigating the evolution of galaxies and of the universe in general

Stellar populations as building blocks of galaxies : proceedings of the 241th symposium of the International Astronomical Union held in La Palma, Tenerife, Spain, December 10-16, 2006

Stellar populations as building blocks of galaxies : proceedings of the 241th symposium of the International Astronomical Union held in La Palma, Tenerife, Spain, December 10-16, 2006
Author: International Astronomical Union. Symposium
Publisher: Cambridge University Press
Total Pages: 628
Release: 2007
Genre: Double stars
ISBN: 9780521863506

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Light Elements in the Universe (IAU S268)

Light Elements in the Universe (IAU S268)
Author: International Astronomical Union. Symposium
Publisher: Cambridge University Press
Total Pages: 528
Release: 2010-05-13
Genre: Science
ISBN: 9780521765060

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IAU Symposium 268 presents an overview of the most recent observational and theoretical research on the formation and evolution of light elements in the Universe: H, He, Li, Be, B, and their isotopes. Astrophysicists from a variety of subfields discuss recent developments that will improve our understanding of the light elements and provide important clues to stellar and galactic evolution, Big Bang nucleosynthesis, and cosmology. Striking observational progress has been achieved recently through the advent of next generation ground- and space-based telescopes, such as the cosmic microwave background experiments that allow the accurate determination of the baryon density of the Universe. New theoretical breakthroughs in describing stellar interiors and the chemical evolution of complex systems and the remaining challenges in this field are also addressed. This critical review is a useful resource for all those interested in the chemical evolution of the Universe.