82 G. Eridani

Coordinates: Sky map 04h 31m 11.52059s, +58° 58′ 37.4806″
Source: Wikipedia, the free encyclopedia.
This article is about e Eridani. It is not to be confused with ε Eridani.
82 G. Eridani
Location of 82 G. Eridani (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Eridanus
Right ascension 03h 19m 55.651s[1]
Declination −43° 04′ 11.22″[1]
Apparent magnitude (V) 4.254[2]
Characteristics
Spectral type G6 V[3]
U−B color index +0.22[4]
B−V color index +0.71[4]
Distance
19.704 ± 0.009 ly
(6.041 ± 0.003 pc)
Absolute magnitude (MV)5.34[2]
Details
Gyr
LTT 1583[4]
Database references
Exoplanet Archive
data
ARICNSdata

82 G. Eridani (HD 20794, HR 1008, e Eridani) is a star 19.7 light-years (6.0 parsecs) away from Earth in the constellation Eridanus. It is a main-sequence star with a stellar classification of G6 V, and it hosts a system of at least three planets and a dust disk.

Observation

In the southern-sky catalog Uranometria Argentina, 82 G. Eridani (often abbreviated to 82 Eridani)

Benjamin Gould, is a southern celestial hemisphere analog of the more famous Flamsteed catalog, and uses a similar numbering scheme. 82 G. Eridani, like other stars near the Sun, has held on to its Gould designation, even while other more distant stars have not.[citation needed
]

Properties

This star is slightly smaller and less massive than the Sun, making it marginally dimmer than the Sun in terms of luminosity; it is about a third more luminous than Tau Ceti or Alpha Centauri B. The projected equatorial rotation rate (v sin i) is 4.0 km/s,[9] compared to 2 km/s for the Sun. However, this value is likely overestimated and explained by the limitation of the spectrograph used. When observed by HARPS, a v sin i smaller than 2 km/s is found, compatible with a slow-rotating or inclined star. Such observation would also match the lack of a reliable rotational period detection and the absence of any magnetic cycle.[13]

82 G. Eridani is a high-velocity star—it is moving quickly compared to the average—and hence is probably a member of

Population II, generally older stars whose motions take them well outside the plane of the Milky Way. Like many other Population II stars, 82 G. Eridani is somewhat metal-deficient (though much less deficient than many), and is older than the Sun. It has a relatively high orbital eccentricity of 0.40 about the galaxy, ranging between 4.6 and 10.8 kiloparsecs from the core. Estimates of the age of this star ranged from 6 to 12 billion years.[10][14]

This star is located in a region of low-density

space velocity of 101 km/s, with the bow shock advancing at more than Mach 3 through the ISM.[15]

Planetary system

An infrared excess was discovered around the star by the Infrared Space Observatory at 60 μm,[16] but was not later confirmed by the Spitzer Space Telescope, in 2006. However, in 2012, a dust disk was found around the star,[17] by the Herschel Space Observatory. While not well-constrained, if assumed to have a similar composition to 61 Virginis' dust disk, it has a semi-major axis of 19 AU.[18]

On August 17, 2011, European astronomers announced the discovery of three planets orbiting 82 G. Eridani. The mass range of these planets classifies them as

equilibrium temperature for the most distant planet, based on an assumed Bond albedo of 0.3, would be about 388 K (115 °C); significantly above the boiling point of water.[5]

The number of planets in the system remains uncertain, and continued observation of the star will be required to determine the exact nature of the planetary system. At the time of planet c's detection, it exerted the lowest gravitational perturbation. There was also a similarity noted between its orbital period and the rotational period of the star. For these reasons the discovery team were somewhat more cautious regarding the verity of its candidate planet status than for the other two.[5]

Using the TERRA algorithm, developed by Guillem Anglada-Escudé and R. Paul Butler in 2012, to describe better and filter out noise interference to extract more precise radial velocity measurements, a team of scientists led by Fabo Feng, in 2017, provided evidence for up to three more planets. One such candidate, of Neptune mass, 82 G. Eridani f, may orbit in the habitable zone of the star. The team also believe that, using these noise reduction techniques, they are able to better quantify the descriptions for the earlier 3 exoplanets, but only have weak evidence of 82 G. Eridani c.[19]

A study in 2023 could only confirm planets b & d, and did not significantly detect the other planet candidates. In particular, the statistical significance of planet c would be expected to increase with additional data; the fact that this has not happened casts doubt on its existence. The 40-day radial velocity signal may instead be tied to the stellar rotation. The additional three candidates found in 2017 (e, f, g) could not be confirmed or refuted.[20]: 23, 44  Another 2023 study also only confirmed b & d out of the previous planet candidates (referring to them as b & c), but also detected a potential third planet farther from the star than any of the previous candidates.[13]

The 82 Eridani planetary system[18][13][a]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
Hot dust ≲0.1 AU — —
b ≥2.0±0.2 M🜨 0.13±0.01 18.32±0.01 0.09+0.08
−0.06 		— —
d ≥4.7±0.4 M🜨 0.37±0.01 89.58+0.09
−0.10 		0.13±0.07 — —
(unconfirmed) ≥6.6+0.6
−0.7 M🜨 		1.36±0.03 644.6+9.9
−7.7 		0.40±0.07 — —
Dust disk ~19–~30 AU — —

Planned observation missions

82 G. Eridani (GJ 139) was picked as a Tier 1 target star for NASA's proposed Space Interferometry Mission (SIM) mission to search for terrestrial-sized or larger planets,[21] which was cancelled in 2010.

See also

  • Map analysis of the 1961 Zeta Reticuli Incident
    (a purported alien abduction)

Notes

  1. ^ The Cretignier et al. 2023 reference used here refers to the 90-day planet as "c" and the new 640-day candidate as "d".[13] Previous publications refer to the 90-day planet as "d", with "c" referring to a 40-day candidate that is likely a false positive.[20] Additional candidates found by Feng et al. 2017[19] are not included here as they are not detected by more recent studies.

References

  1. ^
    S2CID 244398875
    . Gaia DR3 record for this source at VizieR.
  2. ^
    S2CID 118577511
  3. doi:10.1086/191373
    .
  4. ^
    Centre de Données astronomiques de Strasbourg
    , retrieved 2007-07-26
  5. ^
    S2CID 15088852
  6. doi:10.1086/190905
    — See the table on p. 653.
  7. S2CID 119459291
  8. ^
    S2CID 18173201
  9. ^
    doi:10.1051/0004-6361:200810377[permanent dead link
    ]
  10. ^
    S2CID 27151456
  11. Bibcode:2004yCat.4027....0K
    .
  12. ^ Gould, Benjamin Apthorp (1879), Uranometria Argentina: brightness and position of every fixed star, down to the seventh magnitude, within one hundred degrees of the South Pole, Resultados, Universidad Nacional de Córdoba Observatorio Astronómico, vol. 1, Observatorio Nacional Argentino, pp. 159–160 Coordinates are for the 1875 equinox.
  13. ^
    S2CID 261076243
    .
  14. Bibcode:1973A&A....29..165H
  15. doi:10.1086/172505
  16. Bibcode:2000A&A...357..533D
    .
  17. S2CID 54056835
    .
  18. ^
    S2CID 53638901
    .
  19. ^
    S2CID 119084078
    .
  20. ^
    doi:10.3847/1538-3881/acc067
    .
  21. ^ McCarthy, Chris (2005). "SIM Planet Search Tier 1 Target Stars". San Francisco State University. Archived from the original on 2007-08-10. Retrieved 2007-07-26.

External links

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