State variable (astrophysics)
In astrophysics , stars are characterized by several quantities of state . These include above all the mass , the radius and the luminosity of the stars, but also variables that can be derived from them such as the density or the acceleration due to gravity on the surface.
They are an essential resource not only for astrophysics , but also for the methods of stellar statistics . For example, they are included as important data in the galactic calibration fields of the 250 Selected Areas .
The primary state variables also include proper motion , rotation , magnetic field and the chemical composition of the stars.
Since the fixed stars can only be perceived as points from the earth, the state variables of the stars are usually only determined indirectly. For example, the surface temperature of the stars is determined from which spectral lines occur in which frequency, for which the stars are classified according to spectral types .
The dependencies of the state variables are shown in state diagrams, such as B. the Hertzsprung-Russell diagram , which plots the absolute brightness over the spectral types and in which lines or bands for the various luminosity classes can be seen, from which it can be deduced which stage of development the star is currently in.
Web links
- State variables of stars Website of the University of Göttingen (accessed on March 27, 2018.)
- Seminar lecture: State variables of the stars Website of the University of Regensburg, Oliver Viehmann, Supervisor: Prof. Dr. Wolfgang Gebhardt (PDF file, 0.25 MB, accessed on March 27, 2018.)
- Status variable Spektrum.de: Lexicon of Astronomy (Accessed March 27, 2018.)
- Presentation slides for the seminar presentation ( memento from February 14, 2015 in the Internet Archive ) Stephan Koopmans, Birgitta Müller, website of the Max Planck Institute for Astrophysics (presentation slides, PDF, 1.2 MB)