STF 307 (Eta Persei) is a triple physical system located around 880 light-years away. The primary component is a supergiant of spectral type K3I with a mass of about 8 solar masses and a radius of 173 solar radii. It is likely a spectroscopic binary. The companion is HD237009, a blue-white main sequence star of spectral type B9V. The components likely form a CPM pair, with their mutual distance estimated at 11,500 AU and an estimated orbital period of 350,000 years. However, this has not been confirmed.

103mm - Eta Persei is a wide, easily resolvable pair even in small telescopes. The primary component appears clearly orange, and the companion has a bluish appearance next to it. Overall, this system, along with its surroundings, is visually very attractive.