HD 131399

SPHERE image of HD 131399 A (top left), B and C (bottom right), and the background object (center) Credit: ESO/K. Wagner et al.
Observation data Epoch J2000      Equinox J2000
Constellation	Centaurus
Right ascension	14h 54m 25.30919s[1]
Declination	−34° 08′ 34.0412″[1]
Apparent magnitude (V)	7.07[2]
Characteristics
Spectral type	A1V + G + K[3]
Astrometry
Radial velocity (Rv)	0.30 ± 1.3[4] km/s
Distance	351+15 −12 ly (107.9+4.5 −3.7[5] pc)
A
Proper motion (μ)	RA: −30.702[6] mas/yr Dec.: −30.774[6] mas/yr
Parallax (π)	9.7480 ± 0.0357 mas[6]
Distance	335 ± 1 ly (102.6 ± 0.4 pc)
Absolute magnitude (MV)	1.89[7]
BC
Proper motion (μ)	RA: −31.523[8] mas/yr Dec.: −31.047[8] mas/yr
Parallax (π)	9.3021 ± 0.0633 mas[8]
Distance	351 ± 2 ly (107.5 ± 0.7 pc)
Orbit[3]
Primary	A
Companion	BC
Period (P)	3556 ± 36 yr
Semi-major axis (a)	3.56 ± 0.03″ (349 ± 28 au)
Eccentricity (e)	0.13 ± 0.05
Inclination (i)	45 to 65°
Longitude of the node (Ω)	265 ± 20[note 1]°
Periastron epoch (T)	B 502 ± 33
Argument of periastron (ω) (secondary)	145.3 ± 15[note 2]°
Details
Age	21.9+4.1 −3.8[5] Myr
HD 131399 A
Mass	1.95+0.08 −0.06[7] M☉
Radius	1.51+0.13 −0.10[7] R☉
Luminosity	14.8+2.6 −2.2[7] L☉
Surface gravity (log g)	4.37±0.10[7] cgs
Temperature	9,200±100[7] K
Rotational velocity (v sin i)	26±2[7] km/s
HD 131399 B
Mass	0.95±0.04[5] M☉
Surface gravity (log g)	4.40±0.03[5] cgs
Temperature	4,890+190 −170[5] K
HD 131399 C
Mass	0.35±0.04[5] M☉
Surface gravity (log g)	4.45±0.05[5] cgs
Temperature	3,460±60[5] K
Other designations
CD−33°10153, HD 131399, HIP 72940, SAO 206071
Database references
SIMBAD	data

HD 131399 is a star system in the constellation of Centaurus. Based on the system's electromagnetic spectrum, it is located around 350 light-years (107.9 parsecs) away.^[5] The total apparent magnitude is 7.07,^[5] but because of interstellar dust between it and the Earth, it appears 0.22 ± 0.09 magnitudes dimmer than it should be.^[5]

The brightest star, is a young A-type main-sequence star, and further out are two lower-mass stars.^[3] A Jupiter-mass planet or a low-mass brown dwarf was once thought to be orbiting the central star, but this has been ruled out.^[5][9]

The brightest star in the HD 131399 system is designated HD 131399 A. Its spectral type is A1V,^[3] and it is 2.08 times as massive as the Sun.^[5] The two lower-mass stars are designated HD 131399 B and C, respectively. B is a G-type main-sequence star, while HD 131399 C is a K-type main-sequence star.^[3] Both stars are less massive than the Sun.^[5]

HD 131399 B and C are located very close to each other, and the two orbit each other at about 10 AU.^[10] In turn, the B-C pair orbits the central star A at a distance of 349 astronomical units (au). This orbit takes about 3,600 years to complete, and it has an eccentricity of about 0.13^[3] The entire system is about 21.9 million years old.^[5]

One paper has reported that HD 131399 A has a companion in an inclined 10-day orbit with a semi-major axis of 0.1 AU.^[11] HD 131399 A has been described as a "nascent Am star"; although it has a very slow projected rotation rate and would be expected to show chemical peculiarities, its spectrum is relatively normal, possibly due to its young age.^[7]

The claimed discovery of a massive planet, named HD 131399 Ab, was announced in a paper published in the journal Science.^[3] The object was imaged using the SPHERE imager of the Very Large Telescope at the European Southern Observatory, located in the Atacama Desert of Chile, and announced in a July 2016 paper in the journal Science.^[3][12] It was thought to be a T-type object with a mass of 4 ± 1 M_J,^[3] but its orbit would have been unstable, causing it to be ejected between the primary's red giant phase and white dwarf phase.^[13] This was the first exoplanet candidate to be discovered by SPHERE. The image was created from two separate SPHERE observations: one to image the three stars and one to detect the faint planet.^[14] After its discovery, the team unofficially named the system "Scorpion-1" and the planet "Scorpion-1b", after the survey that prompted its discovery, the Scorpion Planet Survey (principal investigator: Daniel Apai).^[15]

In May 2017, observations made by the Gemini Planet Imager and including a reanalysis of the SPHERE data suggest that this target is, in fact, a background star. This object's spectrum seems to be like that of a K-type or M-type dwarf, not a T-type object as first thought. It also initially appeared to be associated with HD 131399, but this was because of its unusually high proper motion (in the top 4% fastest-moving stars).^[5] After subsequent data published in 2022 confirmed that the object is a background star, the paper announcing the putative discovery was retracted.^[9][16]