What can be inferred about the absorption lines in O-type stars?

O-type stars are the hottest and most massive stars in the spectrum classification system. Their surface temperatures typically exceed 30,000 Kelvin. Due to their high temperatures, O-type stars exhibit a very ionized atmosphere, which affects the presence and variety of absorption lines in their spectra.

The correct inference is that O-type stars have few absorption lines present. This is due to the fact that many of the heavier elements are fully ionized at such high temperatures, preventing them from producing the strong absorption lines typically seen in cooler stars. Hydrogen, while it does produce some prominent lines, is less prominent compared to other spectral types, leading to a reduced overall number of observable absorption lines.

While O-type stars can show a few absorption features due to hydrogen and some ionized metals, the key aspect is that the lines are not as abundant as in cooler stars, making the overall spectrum appear less complex. This characteristic aligns with the classification of O-type stars as exhibiting fewer absorption features in their spectra.