The relationship between spectral line strength and gravity is complex and not straightforward. The equivalent width of spectral lines, such as Ca II, is influenced by multiple factors including oscillator strength, elemental abundance, temperature, and pressure. Changes in a star's gravity affect atmospheric pressure, which in turn alters the structure of the star's atmosphere and its spectral class. The intricacies of radiative transfer and pressure broadening further complicate the relationship between gravity and spectral line characteristics.
PREREQUISITESAstronomers, astrophysicists, and students studying stellar spectroscopy and the effects of gravity on spectral line characteristics.
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.Angela G said:what kind of processes affects the strength of a line if we change the gravity of a star?