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40 Eridani is a triple star system in the constellation of Eridanus, abbreviated 40 Eri. It has the Bayer designation Omicron2 Eridani, which is Latinized from ο2 Eridani and abbreviated Omicron2 Eri or ο2 Eri. Based on parallax measurements taken during the Hipparcos mission, it is less than 17 light-years from the Sun.

For other stars with this Bayer designation, see ο Eridani.
40 Eridani
Location of 40 Eridani (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Eridanus
40 Eridani A
Right ascension 04h 15m 16.31963s[1]
Declination −07° 39′ 10.3404″[1]
Apparent magnitude (V) 4.43[1]
40 Eridani B
Right ascension 04h 15m 21.786s[2]
Declination −07° 39′ 29.22″[2]
Apparent magnitude (V) 9.52[3]
40 Eridani C
Right ascension 04h 15m 21.50s[4]
Declination −07° 39′ 22.3″[4]
Apparent magnitude (V) 11.17[3]
Characteristics
40 Eridani A
Spectral type K0.5V[5]
U−B color index +0.45[3]
B−V color index +0.82[1]
40 Eridani B
Spectral type DA4[3]
U−B color index +0.45[3]
B−V color index +0.03[3]
40 Eridani C
Spectral type M4.5eV[6]
U−B color index +0.83[3]
B−V color index +1.67[3]
Variable type Flare star[7]
Astrometry
40 Eridani A
Radial velocity (Rv)−43.0[8] km/s
Proper motion (μ) RA: −2,240.12[1] mas/yr
Dec.: −3,420.27[1] mas/yr
Parallax (π)199.6080 ± 0.1208 mas[9]
Distance16.340 ± 0.010 ly
(5.010 ± 0.003 pc)
Absolute magnitude (MV)5.93[10]
40 Eridani B
Radial velocity (Rv)−21[11] km/s
Proper motion (μ) RA: −2,228.3[2] mas/yr
Dec.: −3,377.1[2] mas/yr
Parallax (π)199.6911 ± 0.0512 mas[12]
Distance16.333 ± 0.004 ly
(5.008 ± 0.001 pc)
40 Eridani C
Radial velocity (Rv)−46[3] km/s
Proper motion (μ) RA: −2,250[13] mas/yr
Dec.: −3,408[13] mas/yr
Parallax (π)199.4516 ± 0.0692 mas[14]
Distance16.353 ± 0.006 ly
(5.014 ± 0.002 pc)
Orbit
Primary40 Eridani A
Companion40 Eridani BC
Period (P)~8,000[15] yr
Semi-major axis (a)~400[16] AU
Orbit[17]
Primary40 Eridani B
Companion40 Eridani C
Period (P)230.30±0.68 yr
Semi-major axis (a)6.930±0.050"
(~35 AU)
Eccentricity (e)0.4294±0.0027
Inclination (i)107.56±0.29°
Longitude of the node (Ω)151.44±0.12°
Periastron epoch (T)1847.7±1.1
Argument of periastron (ω)
(secondary)		318.4±1.1°
Details
40 Eridani A
Mass0.84 [8] M☉
Radius0.81[18] R☉
Luminosity0.457±0.002[19] L☉
Temperature5,300[8] K
Metallicity [Fe/H]−0.19[20] dex
Rotation~37–43[21] days
Rotational velocity (v sin i)1.23 ± 0.28[21] km/s
40 Eridani B
Mass0.573±0.018[17] M☉
Radius0.014[22] R☉
Luminosity0.013[23] L☉
Temperature16,500[24] K
40 Eridani C
Mass0.2036±0.0064[17] M☉
Radius0.31[18] R☉
Luminosity0.008[note 1] L☉
Temperature3,100[25] K
Age5.6[26] Gyr
Other designations
ο2 Eri, 40 Eri, GJ 166, ADS 3093, CCDM J04153-0739
A: Keid[27], BD−07° 780, HD 26965, HIP 19849, HR 1325, SAO 131063, LHS 23, LTT 1907
B: BD−07° 781, HD 26976, SAO 131065, G 160-060, LHS 24, LTT 1908
C: DY Eri, BD−07°781 C, LHS 25, LTT 1909
Database references
SIMBADA
B
C

The primary star of the system, designated 40 Eridani A and named Keid,[27] is easily visible to the naked eye. It is orbited by a binary pair whose two components are designated 40 Eridani B and C, and which were discovered on January 31, 1783, by William Herschel.[28]: p73  It was again observed by Friedrich Struve in 1825 and by Otto Struve in 1851.[15][29]

In 1910, it was discovered that although component B was a faint star, it was white in color. This meant that it had to be a small star; in fact it was a white dwarf, the first discovered.[30] Although it is neither the closest white dwarf, nor the brightest in the night sky, it is by far the easiest to observe; it is nearly three magnitudes brighter than Van Maanen's Star, the nearest solitary white dwarf, and unlike the companions of Procyon and Sirius it is not swamped in the glare of a much brighter primary.[23]


Nomenclature


40 Eridani is the system's Flamsteed designation and ο² Eridani (Latinised to Omicron2 Eridani) its Bayer designation. The designations of the sub-components – 40 Eridani A, B and C – derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[31] 40 Eridani C also bears the variable star designation DY Eridani.

The system bore the traditional name Keid derived from the Arabic word قيض (alqayḍ) meaning "the eggshells," alluding to its neighbour Beid (Arabic "egg").[32] In 2016, the IAU organized a Working Group on Star Names (WGSN)[33] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[34] It approved the name Keid for the component 40 Eridani A on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.[27]


Properties


Amateur photo of 40 Eridani
Amateur photo of 40 Eridani

40 Eridani A is a main-sequence dwarf of spectral type K1, 40 Eridani B is a 9th magnitude white dwarf of spectral type DA4, and 40 Eridani C is an 11th magnitude red dwarf flare star of spectral type M4.5e. When component B was a main-sequence star, it is thought to have been the most massive member of the system, but ejected most of its mass before it became a white dwarf.[citation needed] B and C orbit each other approximately 400 AU from the primary star, A.[16] Their orbit has a semimajor axis of 35 AU and is rather elliptical with an orbital eccentricity of 0.410).[15]

As seen from the 40 Eridani system, the Sun is a 3.4-magnitude star in Hercules, near the border with Serpens Caput.[note 2]


Potential for life


The habitable zone of 40 Eridani A, where a planet could exist with liquid water, is near 0.68 AU from A. At this distance a planet would complete a revolution in 223 Earth days (according to the third of Kepler's laws) and 40 Eridani A would appear nearly 20%[note 3] wider than the Sun does on Earth. An observer on a planet in the 40 Eridani A system would see the B-C pair as unusually bright white and reddish-orange stars in the night sky – magnitudes −8 and −6, slightly brighter than the appearance of Venus seen from Earth as the evening star.

It is unlikely that habitable planets exist around 40 Eridani B because they would have been sterilized by its evolution into a white dwarf. As for 40 Eridani C, it is prone to flares, which cause large momentary increases in the emission of X-rays as well as visible light. This would be lethal to Earth-type life on planets near the flare star.[16]


Planetary system


In 2018, a planet was discovered orbiting 40 Eridani A with a minimum mass of 8.47±0.47 Earth masses.[35] The planet has an orbit of 42 days, and lies considerably interior to the habitable zone, receiving nine times more stellar flux than Earth, which is an even greater stellar flux amount than Mercury, the innermost planet in the Solar System, on average receives from the Sun. It is one of the closest Super-Earths known.

A 2021 study found that the radial velocity signal corresponding to 40 Eridani Ab was likely an artifact of the stellar rotation, making the planet a false positive.[36]

The 40 Eridani A planetary system[35]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b (unconfirmed) 8.47 ± 0.47 M🜨 0.22446±0.00004 42.378 ± 0.01 days 0.04+0.05
−0.03		 — —

See also



Notes


  1. From L=4πR2σTeff4, where L is the luminosity, R is the radius, Teff is the effective surface temperature and σ is the Stefan–Boltzmann constant.
  2. From 40 Eridani the Sun would appear on the diametrically opposite side of the sky at the coordinates RA=16h 15m 16.32s, Dec=07° 39′ 10.34″, which is located near the border of Hercules (constellation) and Serpens Caput, the closest bright star being Alpha Serpentis. The absolute magnitude of the Sun is 4.85, so, at a distance of 5.04 parsecs, the Sun would have an apparent magnitude .
  3. From where h is the apparent height, d is the distance of the object, and a is the actual size of the object.

References


  1. van Leeuwen, F. (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. Second U.S. Naval Observatory CCD Astrograph Catalog (UCAC-2); CDS ID I/289.
  3. Gliese Catalogue of Nearby Stars, preliminary 3rd ed., 1991. CDS ID V/70A.
  4. Salim, Samir; Gould, Andrew (2003). "Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog". The Astrophysical Journal. 582 (2): 1011–1031. arXiv:astro-ph/0206318. Bibcode:2003ApJ...582.1011S. doi:10.1086/344822. S2CID 19035401.; CDS ID J/ApJ/582/1011.
  5. Gray, R. O.; Corbally, C. J.; Garrison, R. F.; McFadden, M. T.; Bubar, E. J.; McGahee, C. E.; O'Donoghue, A. A.; Knox, E. R. (2006). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample". The Astronomical Journal. 132 (1): 161–170. arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637. S2CID 119476992.
  6. General Catalogue of Trigonometric Parallaxes, 4th ed., 1995. CDS ID I/238A.
  7. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: B/gcvs. Bibcode:2009yCat....102025S.
  8. HD 26965, database entry, Geneva-Copenhagen Survey of Solar neighbourhood, J. Holmberg et al., 2007, CDS ID V/117A, accessed on line November 19, 2008; described in Nordström, B; Mayor, M; Andersen, J; Holmberg, J; Pont, F; Jørgensen, B. R; Olsen, E. H; Udry, S; Mowlavi, N (2004). "The Geneva-Copenhagen survey of the Solar neighbourhood". Astronomy & Astrophysics. 418 (3): 989–1019. arXiv:astro-ph/0405198. Bibcode:2004A&A...418..989N. doi:10.1051/0004-6361:20035959. S2CID 11027621.
  9. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  10. Holmberg, J.; et al. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191, S2CID 118577511.
  11. Evans, D. S (1967). "The Revision of the General Catalogue of Radial Velocities". Determination of Radial Velocities and Their Applications. 30: 57. Bibcode:1967IAUS...30...57E.
  12. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  13. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  14. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  15. Heintz, W. D. (1974). "Astrometric study of four visual binaries". Astronomical Journal. 79: 819. Bibcode:1974AJ.....79..819H. doi:10.1086/111614.
  16. "40 Eridani 3 (Omicron² Eridani)". solstation.com. Retrieved 2018-02-06.
  17. Mason, Brian D.; et al. (November 2017), "Binary Star Orbits. V. The Nearby White Dwarf/Red Dwarf Pair 40 Eri BC", The Astronomical Journal, 154 (5): 9, arXiv:1707.03635, Bibcode:2017AJ....154..200M, doi:10.3847/1538-3881/aa803e, S2CID 119080080, 200.
  18. Catalogue of nearest stars until 10pc, V. A. Zakhozhaj. Revised 1996. CDS ID V/101.
  19. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  20. Cayrel de Strobel, G.; Hauck, B.; Francois, P.; Thevenin, F.; Friel, E.; Mermilliod, M.; Borde, S. (1992). "A catalogue of Fe/H determinations". Astronomy & Astrophysics (1991 ed.). 95: 273–336. Bibcode:1992A&AS...95..273C.
  21. Díaz, Matías R.; Jenkins, James S.; Tuomi, Mikko; Butler, R. Paul; Soto, Maritza G.; Teske, Johanna K.; Feng, Fabo; Shectman, Stephen A.; Arriagada, Pamela; Crane, Jeffrey D.; Thompson, Ian B.; Vogt, Steven S. (2018). "The test case of HD26965: Difficulties disentangling weak Doppler signals from stellar activity". The Astronomical Journal. 155 (3): 126. arXiv:1801.03970. Bibcode:2018AJ....155..126D. doi:10.3847/1538-3881/aaa896. S2CID 119404519.
  22. Provencal, J. L.; Shipman, H. L.; Høg, Erik; Thejll, P. (1998). "Testing the White Dwarf Mass-Radius Relation with HIPPARCOS". The Astrophysical Journal. 494 (2): 759. Bibcode:1998ApJ...494..759P. CiteSeerX 10.1.1.44.7051. doi:10.1086/305238.
  23. Keid Archived 2007-05-14 at the Wayback Machine, Jim Kaler, STARS web page, accessed 15/5/2007, 10/12/2011.
  24. Finley, David S.; Koester, Detlev; Basri, Gibor (1997). "The Temperature Scale and Mass Distribution of Hot DA White Dwarfs". The Astrophysical Journal. 488 (1): 375–396. Bibcode:1997ApJ...488..375F. doi:10.1086/304668.
  25. Johnson, H. M.; Wright, C. D. (1983). "Predicted infrared brightness of stars within 25 parsecs of the sun". Astrophysical Journal Supplement Series. 53: 643. Bibcode:1983ApJS...53..643J. doi:10.1086/190905.
  26. Mamajek, Eric E.; Hillenbrand, Lynne A. (November 2008). "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics". The Astrophysical Journal. 687 (2): 1264–1293. arXiv:0807.1686. Bibcode:2008ApJ...687.1264M. doi:10.1086/591785. S2CID 27151456.
  27. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  28. Herschel, William (1785). "Catalogue of Double Stars. By William Herschel, Esq. F. R. S". Philosophical Transactions of the Royal Society of London. 75: 40–126. Bibcode:1785RSPT...75...40H. doi:10.1098/rstl.1785.0006. JSTOR 106749. S2CID 186209747.
  29. Van Den Bos, W. H. (1926). "The orbit and the masses of 40 Eridani BC". Bulletin of the Astronomical Institutes of the Netherlands. 3: 128. Bibcode:1926BAN.....3..128V.
  30. White Dwarfs, E. Schatzman, Amsterdam: North-Holland, 1958. , p. 1
  31. Hessman, F.V.; Dhillon, V.S.; Winget, D.E.; Schreiber, M.R.; Horne, K.; Marsh, T.R.; et al. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  32. "Beid". stars.astro.illinois.edu.
  33. "Working Group on Star Names (WGSN)". Working Groups. International Astronomical Union. Retrieved 22 May 2016.
  34. Working Group on Star Names Triennial Report (2015-2018) (PDF) (Report). International Astronomical Union. 2018. p. 5. Retrieved 2018-07-14.
  35. Ma, Bo; et al. (2018). "The first super-Earth Detection from the High Cadence and High Radial Velocity Precision Dharma Planet Survey". Monthly Notices of the Royal Astronomical Society. 480 (2): 2411. arXiv:1807.07098. Bibcode:2018MNRAS.480.2411M. doi:10.1093/mnras/sty1933.
  36. Rosenthal, Lee J.; Fulton, Benjamin J.; Hirsch, Lea A.; Isaacson, Howard T.; Howard, Andrew W.; Dedrick, Cayla M.; Sherstyuk, Ilya A.; Blunt, Sarah C.; Petigura, Erik A.; Knutson, Heather A.; Behmard, Aida; Chontos, Ashley; Crepp, Justin R.; Crossfield, Ian J. M.; Dalba, Paul A.; Fischer, Debra A.; Henry, Gregory W.; Kane, Stephen R.; Kosiarek, Molly; Marcy, Geoffrey W.; Rubenzahl, Ryan A.; Weiss, Lauren M.; Wright, Jason T. (2021). "The California Legacy Survey. I. A Catalog of 178 Planets from Precision Radial Velocity Monitoring of 719 Nearby Stars over Three Decades". The Astrophysical Journal Supplement Series. 255 (1): 8. arXiv:2105.11583. Bibcode:2021ApJS..255....8R. doi:10.3847/1538-4365/abe23c. S2CID 235186973.



На других языках

[de] Keid

40 Eridani, auch als ο2 Eridani (Omicron2 Eridani) oder Keid (von dem arabischen Wort القيض, DMG al-qaiḍ ‚Eierschale‘) bekannt, ist ein Dreifachsternsystem und etwa 16,3 Lichtjahre von der Erde entfernt.
- [en] 40 Eridani

[ru] 40 Эридана

40 Эрида́на или Омикрон² Эридана — близкая к Земле тройная звёздная система в созвездии Эридана. Находится на расстоянии 16,45 световых лет (5,04 пк) от Солнца.


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