HD 42936

HD 42936, also known as DMPP-3, is a star located in the southern circumpolar constellation Mensa. With an apparent magnitude of 9.1, it is too faint to be detected with the naked eye but can be seen with a telescope. The star is relatively close at a distance of about 153 ly but is receding with a heliocentric radial velocity of $35.64$.

HD 42936 is an early K-type star with the blended luminosity class of a main sequence star and a subgiant. At present it has 87% the mass of the Sun and 91% the radius of the Sun. The object shines at 51% the luminosity of the Sun from its photosphere at an effective temperature of 5,138 K, which gives it an orangish yellow glow. HD 42936 has iron abundance 151% that of the Sun, meaning it is metal enriched despite an age of 10.9 billion years.

HD 42936 has a very low mass companion star in a close orbit, approaching to $506.89 d$ at periastron.

Planetary system
In 2019, a radial velocity analysis carried out by a team of astronomers led by astronomer John R. Barnes of the Dispersed Matter Planet Project (DMPP) confirmed the existence of a super-Earth in orbit around DMPP-3 A. Planets in close binary star systems such as this are rare.

A follow-up study in 2023 refined the parameters of the planet and companion star, and detected two additional radial velocity signals. One of these could be caused by a second, Earth-mass planet closer to the star, but the other, 800-day signal cannot be caused by an orbiting body because the companion star would make its orbit unstable. The study concludes that the 800-day signal must be caused by stellar activity, but if not for the companion star it could have been considered a likely planet, which has implications for other radial velocity planet detections.