40 Eridani

For other stars with this Bayer designation, see ο Eridani.
40 Eridani / Keid
Location of 40 Eridani (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Eridanus
40 Eridani A
Right ascension 04h 15m 16.31962s[1]
Declination −07° 39′ 10.3308″[1]
Apparent magnitude (V) 4.43[2]
40 Eridani B
Right ascension 04h 15m 21.79572s[3]
Declination −07° 39′ 29.2040″[3]
Apparent magnitude (V) 9.52[4]
40 Eridani C
Right ascension 04h 15m 21.53600s[5]
Declination −07° 39′ 20.6946″[5]
Apparent magnitude (V) 11.17[4]
Characteristics
40 Eridani A
Spectral type K0.5V[6]
U−B color index +0.45[4]
B−V color index +0.82[2]
40 Eridani B
Spectral type DA4[4]
U−B color index +0.45[4]
B−V color index +0.03[4]
40 Eridani C
Spectral type M4.5eV[7]
U−B color index +0.83[4]
B−V color index +1.67[4]
Variable type Flare star[8]
Astrometry
40 Eridani A
Radial velocity (Rv)−42.47±0.12[1] km/s
Proper motion (μ) RA: −2,240.085 mas/yr[1]
Dec.: −3,421.809 mas/yr[1]
Parallax (π)199.6080 ± 0.1208 mas[1]
Distance16.340 ± 0.010 ly
(5.010 ± 0.003 pc)
Absolute magnitude (MV)5.93[9]
40 Eridani B
Radial velocity (Rv)−21[10] km/s
Proper motion (μ) RA: −2,236.169 mas/yr[3]
Dec.: −3,338.955 mas/yr[3]
Parallax (π)199.6911 ± 0.0512 mas[3]
Distance16.333 ± 0.004 ly
(5.008 ± 0.001 pc)
40 Eridani C
Radial velocity (Rv)−44.06±0.20[5] km/s
Proper motion (μ) RA: −2,247.183 mas/yr[5]
Dec.: −3,409.824 mas/yr[5]
Parallax (π)199.4516 ± 0.0692 mas[5]
Distance16.353 ± 0.006 ly
(5.014 ± 0.002 pc)
Orbit
Primary40 Eridani A
Companion40 Eridani BC
Period (P)~8,000[11] yr
Semi-major axis (a)~400[12] AU
Orbit[13]
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
Mass0.78±0.08[14] M☉
Radius0.804±0.006[15] R☉
Luminosity0.4±0.01[15] L☉
Surface gravity (log g)4.35±0.1[15] cgs
Temperature5126±30[15] K
Metallicity [Fe/H]−0.36±0.02[15] dex
Rotation~37–43[16] days
Rotational velocity (v sin i)1.23 ± 0.28[16] km/s
Age6.9±4.7[14] Gyr
40 Eridani B
Mass0.573±0.018[13] M☉
Radius0.014[17] R☉
Luminosity0.013[18] L☉
Temperature16,500[19] K
40 Eridani C
Mass0.271±0.001[20] M☉
Radius0.298±0.009[20] R☉
Luminosity0.00651±0.00013[20] L☉
Surface gravity (log g)~5.5[20] cgs
Temperature3,100[21] K
Age5.6[22] Gyr
1.8[23] Gyr
Other designations
ο2 Eri, 40 Eri, GJ 166, ADS 3093, CCDM J04153-0739
A: Keid[24], 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

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 by the Gaia mission, it is about 16.3 light-years from the Sun.

The primary star of the system, designated 40 Eridani A and named Keid,[24] 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.[25]: p73  It was again observed by Friedrich Struve in 1825 and by Otto Struve in 1851.[11][26]

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.[27] 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.[18]

  1. ^ a b c d e Cite error: The named reference GaiaDR3a was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference hip was invoked but never defined (see the help page).
  3. ^ a b c d Cite error: The named reference GaiaDR3b was invoked but never defined (see the help page).
  4. ^ a b c d e f g h Gliese Catalogue of Nearby Stars, preliminary 3rd ed., 1991. CDS ID V/70A.
  5. ^ a b c d e Cite error: The named reference GaiaDR3c was invoked but never defined (see the help page).
  6. ^ 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.
  7. ^ General Catalogue of Trigonometric Parallaxes, 4th ed., 1995. CDS ID I/238A.
  8. ^ 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.
  9. ^ Cite error: The named reference Holmberg2009 was invoked but never defined (see the help page).
  10. ^ 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.
  11. ^ a b Heintz, W. D. (1974). "Astrometric study of four visual binaries". Astronomical Journal. 79: 819. Bibcode:1974AJ.....79..819H. doi:10.1086/111614.
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  13. ^ a b Cite error: The named reference Mason2017 was invoked but never defined (see the help page).
  14. ^ a b Cite error: The named reference exoplanet was invoked but never defined (see the help page).
  15. ^ a b c d e Rains, Adam D.; et al. (April 2020). "Precision angular diameters for 16 southern stars with VLTI/PIONIER". Monthly Notices of the Royal Astronomical Society. 493 (2): 2377–2394. arXiv:2004.02343. Bibcode:2020MNRAS.493.2377R. doi:10.1093/mnras/staa282.
  16. ^ a b Cite error: The named reference Díaz2018 was invoked but never defined (see the help page).
  17. ^ 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. S2CID 122724497.
  18. ^ a b Keid Archived 2007-05-14 at the Wayback Machine, Jim Kaler, STARS web page, accessed 15/5/2007, 10/12/2011.
  19. ^ 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. S2CID 120006763.
  20. ^ a b c d Cite error: The named reference carmenes21 was invoked but never defined (see the help page).
  21. ^ 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.
  22. ^ 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.
  23. ^ Cite error: The named reference Bond_et_al_2017 was invoked but never defined (see the help page).
  24. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  25. ^ 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.
  26. ^ 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.
  27. ^ White Dwarfs, E. Schatzman, Amsterdam: North-Holland, 1958. , p. 1