| Observation data EpochJ2000[1] EquinoxJ2000[1] | |
|---|---|
| Constellation | Scorpius |
| Right ascension | 16h 35m 13.83929s |
| Declination | −35° 43′ 28.7256″ |
| Apparent magnitude (V) | 6.64[2] |
| Characteristics | |
| Spectral type | B9V[3] + M5 + M4[4] |
| U−Bcolor index | −0.208±0.009[4] |
| B−Vcolor index | −0.049±0.007[4] |
| Astrometry | |
| Proper motion (μ) | RA: -9.701[1]mas/yr Dec.: -25.913[1]mas/yr |
| Parallax (π) | 6.8424±0.0475 mas[1] |
| Distance | 477 ± 3 ly (146 ± 1 pc) |
| Absolute magnitude (MV) | 0.292±0.080[4] |
| Orbit[4] | |
| Primary | HIP 81208 A |
| Companion | HIP 81208 B |
| Period (P) | 246.9+251.3 −95.4[5]yr |
| Semi-major axis (a) | 53.98+32.22 −15.00 AU |
| Eccentricity (e) | 0.33+0.26 −0.22 |
| Inclination (i) | 46.61+15.71 −19.47° |
| Orbit[4] | |
| Primary | HIP 81208 A |
| Companion | HIP 81208 C |
| Period (P) | 2232.4+4429.4 −1213.6[5]yr |
| Semi-major axis (a) | 234.27+168.65 −68.96 AU |
| Eccentricity (e) | 0.38+0.29 −0.26 |
| Inclination (i) | 128.16+19.47 −15.36° |
| Details | |
| HIP 81208 A | |
| Mass | 2.58±0.06[5] M☉ |
| Radius | 2.213±0.121[4] R☉ |
| Luminosity | 60.469±4.46[4] L☉ |
| Surface gravity (log g) | 4.201±0.011[4] cgs |
| Temperature | 10840±220[4] K |
| Age | 17+3 −4[4] Myr |
| HIP 81208 B | |
| Mass | 67+6 −7[4] MJup |
| Temperature | 2900[4] K |
| HIP 81208 C | |
| Mass | 0.135+0.010 −0.013[4] M☉ |
| Temperature | 3165+40 −60[4] K |
| Other designations | |
| CD−35°11037,Gaia DR3 6020514769906985728,GC 22284,HD 149274,HIP 81208,SAO 207794,PPM 295214,TIC 280474618,TYC 7357-207-1,GSC 07357-00207,2MASS J16351384-3543287[6] | |
| Database references | |
| SIMBAD | HIP 81208 |
HIP 81208 (HD 149274) is a youngtriple orquadruple[a] hierarchical star system in theconstellation ofScorpius. It consists of aB-type main sequence star (component A), abrown dwarf (B), and ared dwarf (C), the latter two distantly orbiting the primary star. The stars are part of theScorpius–Centaurus association.[7] In 2023, HIP 81208 C was found to be orbited by asubstellar object, which is at the border between being a massiveexoplanet and a low-mass brown dwarf. This made HIP 81208 the firststellarbinary with substellar objects orbiting both stellar components ever discovered bydirect imaging. With anapparent magnitude of 6.64, it is barely visible by the naked eye under dark skies.
The dominant component of the system, HIP 81208 A is a bright blue-white star with aspectral type of B9V, which is about 2.2 times larger, 2.6 times more massive, and 60 times more luminous than theSun. It is very young at only 17 million years old, less than 0.4% the age of theSolar System (4.6 billion years).[4]
In 2023, two smaller objects, respectively designated HIP 81208 B and C, were detected near the star using theSPHERE instrument at theVery Large Telescope inAntofagasta Region,Chile. They both have similarproper motions to HIP 81208 A, strongly supporting that the objects are physically bound to it.[4]
HIP 81208 B is a high-mass (67MJ) brown dwarf with aneffective temperature of 2,900 K (2,630 °C; 4,760 °F),[4] mostly due to residual heat from formation.[8] It orbits the primary star at a distance of 54 AU (8.1 billion km) once every 247years (albeit with a largemargin of error), close to theorbital period ofPluto (247.94 years[9]). HIP 81208 C orbits the star much farther at 234 AU (35.0 billion km) with a 2,242-year period, though its orbital parameters are also poorly constrained. It has a temperature of 3,165 K (2,892 °C; 5,237 °F), only slightly hotter than the brown dwarf.[4] Curiously, the orbits of the two companions are almostorthogonal to one another, and are probably in aKozai resonance with the host star.[4]
The 15th-magnitude star Gaia DR3 6020420074469092608 (2MASS J16360769-3543514), located at a separation of0.1823°, shares a similarparallax and proper motion with HIP 81208, and is potentially located within theHill sphere of the system. This hints at the possibility of a fourth stellar component even farther from the primary star than the confirmed two.[4]
In 2023, a previously unresolved object was identified in orbit of HIP 81208 C. The object, with a mass of 14.8MJ, is right at the boundary between exoplanets and brown dwarfs,[10] as it is close to the threshold fordeuterium fusion (~13MJ[11]). This made the HIP 81208 system the first binary between two stars (A, C) discovered by imaging where both stars are orbited by substellar companions (B, Cb).[12] It orbits the red dwarf host somewhere around 23 AU (3.4 billion km) distant with a period of roughly 285 years.[5]
HIP 81208 Cb is also unique in that it is unusually close to its host star for being a giant planet or brown dwarf companion to a late M-type star. Other objects of a similar nature, at least those that have been directly imaged, usually have a mass similar to that of the host star that a binary-like formation is likely, but HIP 81208 Cb is light enough that such a formation mode can be ruled out. The true formation of the object, however, remains inconclusive.[5]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| Cb | 14.8 ± 0.4 MJ | 23.04+13.88 −6.55 | 104100+107260 −40934 | — | — | 1.09[13] RJ |
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