What is a characteristic of F-type stars?

F-type stars are characterized by their spectral classification, which indicates a certain temperature range and composition. One significant characteristic of F-type stars is the presence of neutral metal absorption lines, which arise from elements like iron and magnesium in the stellar atmosphere. This is due to the relatively high temperatures of F-type stars (between approximately 6,000 and 7,500 Kelvin), which allows for the ionization of hydrogen but still retains enough neutral atoms to produce these important spectral lines.

The presence of neutral metal absorption lines is crucial for astronomers as it provides insights into the star's composition and helps in determining its age, metallicity, and evolution. In contrast, as the temperature increases in other star types, such as G-type or hotter stars, the prevalence of neutral lines diminishes as ionization increases.

The other choices do not accurately represent characteristics of F-type stars. For instance, the Balmer lines, associated with hydrogen, do not continue to increase; instead, they are strongest in A-type stars and start to decrease in F-type. Similarly, F-type stars do exhibit Ca II absorption lines, contrary to the suggestion that they lack them. Finally, while He II absorption lines may be observed in hotter O-type stars, they are not the