Strömgren sphere

Target entity: Strömgren sphere
Context triple: [H II region, relatedTo, Strömgren sphere]

• A. Milne–Eddington approximation
  The Milne–Eddington approximation is a simplified model of stellar atmospheres that assumes constant physical properties with depth to make the radiative transfer equations analytically tractable.
• B. Eddington limit
  The Eddington limit is the maximum luminosity a star or accreting object can have before radiation pressure overcomes gravity and drives away its outer layers.
• C. Rosseland
  Rosseland is a Norwegian surname most notably associated with astrophysicist Svein Rosseland, a pioneer in theoretical astrophysics and radiative transfer.
• D. Bonnor–Ebert mass
  The Bonnor–Ebert mass is the maximum mass a pressure-confined, self-gravitating gas sphere can have while remaining in stable hydrostatic equilibrium before collapsing under its own gravity.
• E. Schwarzschild criterion
  The Schwarzschild criterion is a condition in astrophysics that determines when a star’s interior becomes convectively unstable, leading to energy transport by bulk motion of stellar material.
• F. None of above. chosen
• G. Unsure - the case is ambiguous/there is not enough information to decide.

Target entity: Strömgren sphere
Target entity description: A Strömgren sphere is a region of ionized hydrogen gas surrounding a hot, young star, formed where the star’s ultraviolet radiation balances the recombination of electrons and protons in the surrounding interstellar medium.

• A. Milne–Eddington approximation
  The Milne–Eddington approximation is a simplified model of stellar atmospheres that assumes constant physical properties with depth to make the radiative transfer equations analytically tractable.
• B. Eddington limit
  The Eddington limit is the maximum luminosity a star or accreting object can have before radiation pressure overcomes gravity and drives away its outer layers.
• C. Rosseland
  Rosseland is a Norwegian surname most notably associated with astrophysicist Svein Rosseland, a pioneer in theoretical astrophysics and radiative transfer.
• D. Bonnor–Ebert mass
  The Bonnor–Ebert mass is the maximum mass a pressure-confined, self-gravitating gas sphere can have while remaining in stable hydrostatic equilibrium before collapsing under its own gravity.
• E. Schwarzschild criterion
  The Schwarzschild criterion is a condition in astrophysics that determines when a star’s interior becomes convectively unstable, leading to energy transport by bulk motion of stellar material.
• F. None of above. chosen