Kenneth Whight
British Astronomical Association, UK
A Single Layer Thermal Equilibrium Stellar Photosphere Model for Analysing Spectral Absorption Line Profiles
Abstract:
In this paper I will present the details of a simple single layer thermal equilibrium stellar photosphere model that can be used in the analysis of a single Hydrogen Balmer absorption line to estimate a photosphere’s:- pressure, thickness and rotational parameters. Having characterised a particular photosphere in this way, profiles of other lines in the Balmer series can then be predicted. Further, knowing the thickness of a particular photosphere allows elemental relative abundances to be estimated from the analysis of a single line from a spectral series of a particular element.
The method uses a linear absorption model employing the concept of “thermal equilibrium photon capture cross-sections” constructed from the Planck and Boltzmann functions together with the Einstein A coefficients of a particular spectral series. These cross-sections are employed in the linear absorption model in combination with Temperature (Gaussian), Pressure (Lorentz) and Rotation spreading functions. These spreading functions capture the “dynamics” of a given photosphere by determining the distribution of atoms that can interact with a photon as a function of wavelength.
The model is validated by analysis of the Solar photosphere and comparison of the resulting parameter estimates to published data for the Sun. Results for other stars will be presented including, Deneb, Vega and the blue component of Albireo.
The simplicity of the model necessarily results in some stars being better modelled than others but the model could be extended to one admitting multi-layers at varying temperatures in the expectation of extending the class of well modelled stars.