I How Does Gravity Affect Spectral Line Strength?

[Angela G]

TL;DR Summary

Hello,

I wonder if someone please could explain what the relationship between a spectral line strength and gravity is? Does the equivalent width of e.g. Ca II decrease with increasing gravity? what kind of processes affects the strength of a line if we change the gravity of a star?
Hope you can help me

 

[WernerQH]

what kind of processes affects the strength of a line if we change the gravity of a star?

There is no simple relationship. The equivalent width of a spectral line depends on the oscillator strength (an atomic parameter), the elemental abundance, temperature (ionization states) and pressure, and can only be obtained by solving a complicated radiation transport problem in a model atmosphere. The pressure depends, of course, on the star's gravity and determines the structure of its atmosphere and the spectral class. Electron and gas pressure have an influence on the line shape (causing "pressure broadening"), but the resulting line width is not simply proportional to the pressure because of the intricacies of radiative transfer. Spectral lines are formed in layers with temperature and pressure gradients.

Hope this helps. :-)

 

[Angela G]

Thank you very much!