GQ Lupi

The primary component is designated GQ Lupi A, and was referred to simply as GQ Lupi before the discovery of the secondary stellar companion. It is a T Tauri star, with a variable apparent magnitude ranging from 11.3 at brightest and 14.3 at faintest.^[3] The spectral type is K7Ve, with the 'e' indicating emission lines in the spectrum,^[8] which in classical T Tauri stars such as GQ Lupi results from an extensive surrounding disk.^[3] The star has 1.03 times the mass of the Sun^[12] and 1.75 times the Sun's radius, with an effective temperature of 4306 K.^[12] Its age is estimated at 2.8+1.8
−1.1 million years.^[14] This star is surrounded by a circumstellar disk with a major axis of 59±12 AU.^[12]

In 2020, a low-mass companion of GQ Lupi was discovered at a separation of about 16 arcseconds, or 2400 AU. Designated 2MASS J15491331-3539118 in the 2MASS catalogue, it is a young stellar object that is likely gravitationally bound to the primary star, although the low quality of the companion's proper motion and parallax does not allow for a definitive conclusion. It is estimated to be approximately 15% the Sun's mass and 87% the Sun's radius. It has an effective temperature of about 3230 K, indicating that it is a red dwarf with the spectral type M4.^[10]

In 2005, Ralph Neuhäuser and his colleagues reported a substellar object, GQ Lupi b, orbiting the star. Along with 2M1207b, this was one of the first extrasolar planet candidates to be directly imaged. The image was made with the VLT telescope at Paranal Observatory, Chile, on June 25, 2004. Depending on its mass and the definition of a planet, GQ Lupi b may or may not be considered a planet.^[20] As of 2006, the International Astronomical Union Working Group on Extrasolar Planets described GQ Lupi b as a "possible planetary-mass companion to a young star".^[21]