Gliese 521

Gliese 521 is a double star in the northern constellation of Canes Venatici. The system is located at a distance of 43.6 light-years from the Sun based on parallax measurements, but is drawing closer with a radial velocity of −65.6 km/s. It is predicted to come as close as 4.814 pc from the Sun in 176,900 years. This star is too faint to be visible to the naked eye, having an apparent visual magnitude of +10.26 and an absolute magnitude of 10.24.

The primary is an M-type main-sequence star with a stellar classification of M1V. It is only about half the size and mass of the Sun. The star is rotating slowly with a projected rotational velocity of 0.85 km/s and a rotation period of roughly 49.5 days. The star has a lower metal-content compared to the Sun. It is radiating just 3% of the luminosity of the Sun from its photosphere at an effective temperature of 3,493 K.

A faint stellar companion was announced by E. Jódar and associates in 2013. The companion has an angular separation of $−65.72$ along a position angle of 352.1°$−42.332$° from the primary. This is equivalent to a projected separation of $389.167$.

Search for planets
According to Marcy & Benitz (1989) detected a possible periodicity of 510 days, inferring the possible presence of a massive planetary object with minimum mass of 12 times that of Jupiter in highly eccentric orbit (e=0.6). So far the planet has not been confirmed. A radial velocity study of the star during the period 2013–2017 initially found a promising signal, but this disappeared when additional data was collected and was instead attributed to magnetic activity.