Author : Elena-Ruxandra Cojocaru
Publisher :
ISBN 13 :
Total Pages : 157 pages
Book Rating : 4.:/5 (112 download)
Book Synopsis Population Synthesis Studies of the White Dwarfs of the Galactic Disk and Halo by : Elena-Ruxandra Cojocaru
Download or read book Population Synthesis Studies of the White Dwarfs of the Galactic Disk and Halo written by Elena-Ruxandra Cojocaru and published by . This book was released on 2017 with total page 157 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the evolutionary end-point of most main-sequence stars, white dwarfs can be used to infer important properties concerning the formation and evolution of the different Galactic stellar populations. Population synthesis methods, when correlated with the excellent quality of modern white dwarf cooling tracks, can prove to be a powerful tool for further exploring the information offered by observed samples of white dwarfs. Possible applications may include estimating the age and history of stellar populations, measuring the local stellar formation rate and stellar density, constraining the local content of baryonic matter, examining intrinsic aspects of single and binary stellar evolution and exploring different progenitor scenarios for type Ia supernovae. In this thesis we studied the white dwarf populations of the Galactic disk and halo and our work was focused on four main objectives. The first was to analyze the effects of stellar metallicity on the white dwarf luminosity function of the Galactic disk. We use our Monte Carlo population synthesis code to produce synthetic samples of white dwarfs which we later compare to two relatively large observational samples, from the Sloan Digital Sky Survey (SDSS) and SuperCosmos Sky Survey (SSS). For each of the two cases, we implement the corresponding observational selection criteria. We first explore the impact of varying the fraction of white dwarfs with hydrogen-deficient atmospheres and of using alternative sets of cooling tracks. We then test different age-metallicity relations, considering the impact of progenitor metallicity throughout the entire evolution of the star. Our second objective was to determine the luminosity, mass and cumulative age functions derived from a sample of disk white dwarfs identified by the LAMOST Sky Survey of the Galactic Anti-Center. We initially compute the observed functions and then the theoretical ones, according to series of initial assumptions, using our population synthesis code. We derive values for the local space density and formation rate of hydrogen-rich white dwarfs and analyze the possible causes behind the apparent excess of massive white dwarfs identified in the observed mass function. The next objective of this thesis was to revisit the halo white dwarf luminosity function, modeling the halo white dwarf population using a self-consistent prescription for very low metallicity progenitors. We pass the synthetic sample through a series of filters that reproduce the selection criteria employed in culling the observed sample of halo white dwarfs from the SSS. Given that for very low-metallicity progenitors residual hydrogen burning can become a significant source of energy, we test two different sets of cooling tracks, one that incorporates residual hydrogen burning and another where this phenomenon is artificially ignored. Finally, our last study consisted in modeling the sample of white dwarf-main sequence binaries in the Galactic disk. We compare our simulations to the largest and most recent catalog of white dwarf-main sequence binaries from the SDSS and we provide a detailed account of observational biases and errors. We use this sample to constrain several important inputs for binary formation and evolution, namely the initial mass ratio distribution and the common envelope efficiency parameter. To conclude, the work presented in this thesis testifies to the versatility of using white dwarf populations for constraining different properties of the Galactic disk and halo. The methodology described here can be used in future studies of this kind, with a myriad of new applications, especially given than in the near future a noticeable improvement in terms of the size and quality of observed white dwarf catalogs is expected.
