HD 131399

HD 131399 is a star system in the constellation of Centaurus. Based on the system's electromagnetic spectrum, it is located around 351 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][note 3]

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
Proper motion (μ) RA: -29.69[1] mas/yr
Dec.: -31.52[1] mas/yr
Parallax (π)10.20 ± 0.70[1] mas
Distance351+15
−12 ly
(107.9+4.5
−3.7[5] pc)
Orbit[3]
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[5]
Age21.9+4.1
−3.8 Myr
HD 131399 A
Mass2.08+0.12
−0.11 M☉
Surface gravity (log g)4.32 ± 0.01 cgs
Temperature9480+420
−410 K
HD 131399 B
Mass0.95 ± 0.04 M☉
Surface gravity (log g)4.40 ± 0.03 cgs
Temperature4890+190
−170 K
HD 131399 C
Mass0.35 ± 0.04 M☉
Surface gravity (log g)4.45 ± 0.05 cgs
Temperature3460 ± 60 K
Other designations
CD−33° 10153, HD 131399, HIP 72940, SAO 206071
Database references
SIMBADdata

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]

Stellar system

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.[6] 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]

Planetary system
Artist's impression of HD 131399 Ab, before it was found to be a background star.

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.[7][8] It was thought to be a T-type object with a mass of 4 ± 1 MJ,[3] but its orbit would have been unstable, causing it to be ejected between the primary's red giant phase and white dwarf phase.[9] 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.[10] 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).[11]

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]

Characteristics

The planet was thought to be about 16 million years old, with a mass of 4 (± 1) MJ (Jupiter masses), and a temperature of 850 K (577 °C; 1,070 °F) (± 50 K), which would make it one of the coldest and least massive directly-imaged exoplanets.[6] Its atmosphere was shown to contain both water and methane through the use of near-infrared spectroscopy (1.4-1.6 μm).[8] Scientists believed it was unlikely that the planet harbored life due to it being gaseous. The planet was said to have "no liquid water, extremely powerful winds, and no surface; just below the uppermost layer of the atmosphere it rains liquid iron droplets."[12] One orbit of HD 131399 Ab was thought to take 550 years.[8][7]

References
  1. van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
  2. Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
  3. Wagner, K.; Apai, D.; Kasper, M.; Kratter, K.; McClure, M.; Robberto, M.; Beuzit, J.-L. (2016). "Direct imaging discovery of a Jovian exoplanet within a triple-star system". Science. 353 (6300): 673–8. arXiv:1607.02525. Bibcode:2016Sci...353..673W. doi:10.1126/science.aaf9671. PMID 27386921. S2CID 206650422.
  4. Kharchenko, N. V.; et al. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776. S2CID 119323941.
  5. Nielsen, Eric L.; et al. (2017). "Evidence that the Directly-Imaged Planet HD 131399 Ab is a Background Star". The Astronomical Journal. 154 (6): 218. arXiv:1705.06851. Bibcode:2017AJ....154..218N. doi:10.3847/1538-3881/aa8a69. S2CID 55138870.
  6. "HD 131399Ab: Astronomers Find Super-Jupiter in Triple-Star System | Astronomy | Sci-News.com". Retrieved 8 July 2016.
  7. "This strange new planet has three suns". CBS News. 7 July 2016. Retrieved 7 July 2016.
  8. Wagner, Kevin (7 July 2016). "Direct imaging discovery of a Jovian exoplanet within a triple-star system". Science. 353 (6300): 673–8. arXiv:1607.02525. Bibcode:2016Sci...353..673W. doi:10.1126/science.aaf9671. PMID 27386921. S2CID 206650422.
  9. Veras, Dimitri; Mustill, Alexander J.; Gänsicke, Boris T. (2017). "The unstable fate of the planet orbiting the a star in the HD 131399 triple stellar system". Monthly Notices of the Royal Astronomical Society. 465 (2): 1499. arXiv:1611.00007. Bibcode:2017MNRAS.465.1499V. doi:10.1093/mnras/stw2821. S2CID 73723946.
  10. [email protected]. "A Surprising Planet with Three Suns". ESO. Retrieved 7 July 2016.
  11. Miller, Michael (12 April 2017). "UC mountaineer, galactic explorer". UC Magazine. University of Cincinnati. Retrieved 3 May 2017.
  12. "16-million-year-old planet with three suns discovered". MSN. 8 July 2016.

Notes
  1. There are two solutions; the other one is 75 ± 10°.
  2. There are two solutions; the other one is 310 ± 10°.
  3. See Interstellar extinction.
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