GQ Lupi

GQ Lupi

A visual band light curve for GQ Lupi. The main plot (from ASAS data), shows the long-term variability, and the inset plot (adapted from Broeg et al.) shows the short-term periodic brightness variation.
Observation data Epoch J2000.0      Equinox ICRS
Constellation	Lupus
GQ Lupi A
Right ascension	15h 49m 12.1054s
Declination	−35° 39′ 05.058″
Apparent magnitude (V)	11.3–14.3
GQ Lupi C
Right ascension	15h 49m 13.3078s
Declination	−35° 39′ 11.761″
Apparent magnitude (V)	19.72
Characteristics
GQ Lupi A
Evolutionary stage	Pre-main sequence
Spectral type	K7Ve
B−V color index	0.96
Variable type	T Tauri variable
GQ Lupi C
Evolutionary stage	Pre-main sequence
Spectral type	M4
Astrometry
GQ Lupi A
Radial velocity (Rv)	−3.6±1.3 km/s
Proper motion (μ)	RA: −14.133 mas/yr Dec.: −23.329 mas/yr
Parallax (π)	6.4893±0.0289 mas
Distance	503 ± 2 ly (154.1 ± 0.7 pc)
GQ Lupi C
Proper motion (μ)	RA: −14.508 mas/yr Dec.: −23.862 mas/yr
Parallax (π)	5.7229±0.3559 mas
Distance	570 ± 40 ly (170 ± 10 pc)
Position (relative to GQ Lupi A)
Component	GQ Lupi C
Projected separation	2430 AU
Details
GQ Lupi A
Mass	1.03±0.05 M☉
Radius	1.75+0.06 −0.07 R☉
Luminosity	1.05+0.27 −0.22 L☉
Surface gravity (log g)	3.7 cgs
Temperature	4306±35 K
Rotation	8.45±0.20 days
Rotational velocity (v sin i)	5.66±0.02 km/s
Age	2.8+1.8 −1.1 Myr
GQ Lupi C
Mass	0.15±0.05 M☉
Radius	0.87±0.20 R☉
Luminosity	0.07±0.02 L☉
Temperature	3230±101 K
Rotational velocity (v sin i)	13±6 km/s
Other designations
GQ Lup, WDS J15492-3539
GQ Lupi A: CD−35°10525, 2MASS J15491210-3539051
GQ Lupi C: 2MASS J15491331-3539118
Database references
SIMBAD	GQ Lupi A
SIMBAD	GQ Lupi C

GQ Lupi is a possible binary star system in the constellation Lupus. The system is young, with an age of a few million years (for comparison, the Solar System is roughly 4.6 billion years old), and is within the Lupus I star-forming region, which is part of the Scorpius–Centaurus association.

Stellar system

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. The spectral type is K7Ve, with the 'e' indicating emission lines in the spectrum, which in classical T Tauri stars such as GQ Lupi results from an extensive surrounding disk. The star has 1.03 times the mass of the Sun and 1.75 times the Sun's radius, with an effective temperature of 4306 K. Its age is estimated at 2.8+1.8
−1.1 million years. This star is surrounded by a circumstellar disk with a major axis of 59±12 AU.

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.

Substellar companion

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. 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".