40 Eridani ABC

Star type
g A: K1
g B: DA4
g C: M4.5 Ve

Distance from Earth
g 16.38 ly

Star Service No.
g NA

Age
g A: 4.109 Gy to 12.109 Gy
g B: 4.109 Gy to 12.109 Gy

g C: 4.109 Gy to 12.109 Gy
Diameter/Mass/Temp (xSol)
g A: 85%; 89%; 5,200 K
g B: 2%; 50%; 16,500 K
g C: 28%; 19.5%; 3,100 K

Brightness (xSol)
g A: 36%
g B: 33/10,000th
g C: 7/10,000th

Metallicity
g A: 46 percent to 102 percent as enriched as Sol with elements heavier than hydrogen
g B: NA
g C: NA

Comparison to Sol
g See illustration

Picture of star
g A: See picture
g A-B-C: See picture

Star system features
g B: First white dwarf discovered
g C: Strong X-ray emission

Known planets
g A: No brown dwarf or large Jupiter or Saturn class planet in the triple star system thus far
g B: None
g C: None

Habitable zone
g A: The habitable zone of 40 Eri A, where a planet could exist with liquid water, is near 0.61 AU from A. At this distance a planet would complete a revolution in 203 earth days, and A would appear about 30% wider than Sol does on Earth. An observer on a planet in the 40 Eri A system would see the B/C pair as unusually bright (magnitudes -8 and -6) white and red stars in the night sky. This is not bright enough to diminish the darkness at night, though they would be visible during daytime. (By comparison, Earth's full moon is magnitude -12.6, and Venus at its brightest is -4.). An expedition to a terrestrial planet around this star might conduct studies to determine of there is a geological record of the red giant winds from 40 Eridani C before it became a white dwarf; ice ages due to the dusty space caused by Star C's red giant phase is one possibility.
g B: The current water zone is centered around 0.06 AU which would require an orbital period of about 7.8 days. It is extremely unlikely that habitable planets exist around the B star as planets circling 40 Eri B would likely have been destroyed or sterilized by its evolution into a white dwarf.
g C: Its water zone is 0.03 AU (which has an orbital period of only about 4.3 days. The star is prone to flares, however, which cause large momentary increases in the emission of X-rays as well as visible light.This would be lethal to a planet in the habitable zone.

Orbital map
g See map
g Star A and the binary pair BC have a wide separation of about 418 AUs and an orbital period of some 8,000 years
g B and C orbit each other approximately 400 astronomical units from the primary star, A. Their orbit has a semimajor axis of 35 AU (which is also the approximate average distance between B and C) and is rather elliptical (eccentricity 0.410).

View from star
g A: See sky map
g B: NA but nearly identical to Star A (except for lack of Star A and Star C in sky)
g C: NA but nearly identical to Star A (except for lack of Star A and Star B in sky)

Nearby stars
(Star systems with 10 light years)
g LHS 1723: 3.8 ly
g Hip 15689: 4.4 ly
g BD-03 1123: 6.2 ly
g Epsilon Eridani: 6.4 ly
g LTT 17897: 8.1 ly
g LP 944-20: 8.2 ly (brown dwarf)
g Teegarden's Star: ~8.7 ly
g L 730-18 ABC; 8.9 ly
g G 99-44: 9.1 ly
g Ross 614 AB: 9.1 ly
g Ross 47: 9.3 ly
g Gliese 229; 9.8 ly

Map locating star system
g See stellar map (listed as ο2 Eri)

Location in Earth sky
g In the northernmost part of Constellation Eridanus, the River, northeast of Zaurak, Gamma Eridani. Star A is visible in the night sky.

Other names
g Keid
g A: HD 26965
g A: ο2 Eri A
g A: o2 Eridani A
g A: 40 Eri A
g ADS 3093A
g BD -07°780
g CCDM J04153-0739A
g GCTP 945
g GJ 166 A
g A: HIP 19849
g A: HR 1325
g LHS 23
g A: LTT 1907
g SAO 131063
g STF 518A
g A-B: 40 Omicron 2
g A-B-C: HIP 19849
g B: ο2 Eri B
g B: o2 Eridani B
g B: 40 Eri B
g B: ADS 3093B
g B: BD -07°781A
g B: CCDM J04153-0739B
g B: G 160-060
g B: GCTP 945
g B: GJ 166 B
g B: HD 26976
g B: LHS 24
g B: LTT 1908
g B: SAO 131065
g B: WD 0413-077
g B: STF 518B
g C: DY Eri
g C: DY Eridani
g C: ο2 Eri C
g C: o2 Eridani C
g C: 40 Eri C
g C: ADS 3093C
g C: BD -07°781B
g C: BD -07°781C
g C: CCDM J04153-0739C
g C: GCTP 945
g C: GJ 166 C
g C: LHS 25
g C: LTT 1909
g C: STF 518C

Sci-fi mentions
g 40 Eridani A is the location of the planet Vulcan, home of the Vulcan species. Although this was never stated on any TV show or film, both the authorized Star Trek book "Star Trek: Star Charts" and Gene Roddenberry gave this location. In addition, Commander Tucker's statement in Star Trek: Enterprise that Vulcan is 16 light years from Earth confirms this.

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