Detail Line-blanketed spherically extended model atmospheres of hot luminous stars with and without winds Bibliografi Author: Aufdenberg, Jason Paul ; Starrfield, Sumner (Advisor) Topik: PHYSICS; ASTRONOMY AND ASTROPHYSICS Bahasa: (EN )    ISBN: 0-599-67027-4     Penerbit: Arizona State University     Tahun Terbit: 2000     Jenis: Theses - Dissertation Fulltext: 9962935.pdf (0.0B; 0 download) Abstract Spherical, hydrostatic, non-local thermodynamic equilibrium (non-LTE) metal line-blanketed model atmospheres have been employed to reproduce the spectral energy distributions of the bright B-type giant stars Beta and Epsilon Canis Majoris, including the extreme ultraviolet where previous models have failed. The combination of spherical geometry and line-blanketing produces significantly different model temperature structures and synthetic extreme ultraviolet spectra relative to otherwise similar plane-parallel geometry models. The synthetic spectra are compared to the observed spectral energy distributions of these B stars in absolute units, a rarity in stellar atmosphere analyses. A full grid of O- and early B-type model stellar atmospheres has been constructed and comparisons with hydrostatic, plane-parallel, LTE line-blanketing models show that these models predict consistently higher ionizing fluxes, particularly at lower effective temperatures. Models for hot, luminous stars and their winds have been developed which unify the inner hydrostatic layers with the outer dynamic layers of the atmosphere into a single structure. These models include the effects of full non-LTE metal line-blanketing in both the computation of the model atmosphere plus wind and the synthetic spectrum. Models of this type have been developed for comparison with the spectral energy distribution and detailed spectrum of the A-type supergiant Alpha Cygni. A synthetic spectrum has been computed which is able to match the observed spectral energy distribution in absolute units from 120 nm to 3.6 cm reasonably well. These models predict that Alpha Cyg's expanding envelope is only partially ionized, which leads to a steeper spectral slope than predicted in the fully ionized case commonly applied to hotter O- and B-type stars. Non-LTE model structures and line formation in the ultraviolet suggest mass-loss rates 50 times larger than in the LTE studies. Using recently available observational data, the uncertainty in Alpha Cyg's effective temperature has been reduced, its mass-loss rate has been constrained, and lower limits to its radius, luminosity, gravity, and mass have been determined. In addition, a scheme for the computation of a radiation-driven wind has been developed which solves the one-dimensional momentum equation and computes the velocity field from the run of temperature, density, and radiative acceleration with depth through solutions of the radiative transfer and hydrodynamic equations. Opini Anda Klik untuk menuliskan opini Anda tentang koleksi ini! Lihat Sejarah Pengadaan  Konversi Metadata   Kembali

Copyright © 2006, 2007 Unika Atma Jaya, all rights reserved