Complex sentence: Having the rotation period of 5--6 days, HIP 13044 is a fast rotating star for its type, perhaps because it had swallowed its inner planets during its red giant phase.
Split into simpler sentences: Having the rotation period of 5--6 days, HIP 13044 is a fast rotating star for its type. It is possible that this is because it may have swallowed inner planets during its red giant phase.