A star shows only weak hydrogen absorption lines even though its composition is…
PHYSICS · Single correct · A Level · Physics · Particles and radiation · Particles and radiation
Problem
A star shows only weak hydrogen absorption lines even though its composition is similar to that of the Sun. Which explanation is most consistent with this observation?
(a) The star is cooler than the Sun, so most hydrogen atoms remain in the ground state and therefore cannot participate in Balmer absorption, making the lines appear weak
(b) The star rotates so rapidly that Doppler broadening spreads the hydrogen absorption over a wide range of wavelengths until it is no longer discernible as distinct Balmer lines
(c) The star is significantly hotter than the Sun, so most hydrogen atoms are ionized and therefore cannot absorb Balmer photons
(d) Hydrogen emission from the star’s hot chromosphere fills in the photospheric Balmer absorption features, causing the hydrogen lines to appear weak in the observed spectrum