GQ Leonis

GQ Leonis is a variable star located in the zodiac constellation of Leo, close to the second-magnitude star Denebola. With an apparent magnitude of 10.8, it is too faint to be seen by the naked eye but observable using a telescope with an aperture of or larger. It is situated at a distance of according to Gaia EDR3 parallax measurements, and is advancing towards the Solar System at a heliocentric radial velocity of −12.121 km/s.

Physical properties

This is a K-type main-sequence star with the spectral type K5Ve, where the "e" suffix denotes the presence of emission lines. It is considered to be a field star, not part of any star cluster. It is expected to have a radius of about 0.8, and shines at an effective temperature of, giving it an orange hue. It is poorer in heavy elements than the Sun with a metallicity of −0.171, meaning it has 10^−0.171 ≈ 67% the Sun's iron content. Age estimates vary between publications, but the consensus is that it is young and very active, as evidenced by strong emission in the calcium H and K lines and the Balmer series. The star is also a source of X-rays and extreme ultraviolet radiation.

In 2001, the star was reported to show low-amplitude photometric variations with a period of 4.45 days. It was suspected that the star was a BY Draconis variable due to the period paired with the X-ray and EUV emissions. This was confirmed in 2004 in a paper which also newly classified HD 77191 and V573 Puppis as BY Dra variables. The star received its variable-star designation GQ Leonis in 2003.

Slow fluctuations are known to occur in the star's radial velocity. In a 2019 study, a period was mentioned to fit the observed variations, but other periods remain possible. This object is also a visual binary, designated MET 57Aa/Ab in the Washington Double Star Catalog, with a separation of 0.25 arcseconds and a period of roughly 45 years. Additionally, an optical component exists 9.5 arcseconds away.