40 Eridani
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| Observation data Epoch J2000.0 (ICRS) |
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|---|---|---|---|
| Constellation | Eridanus | ||
| Right ascension | 04h 15m | 04h 15m | 04h 15m |
| 16.320s[1] | 21.786s[2] | 21.50s[3] | |
| Declination | −07° 39′ | −07° 39′ | −07° 39′ |
| 10.34″[1] | 29.22″[2] | 22.3″[3] | |
| Apparent magnitude (V) | 4.43[1] | 9.52[4] | 11.17[4] |
| Characteristics | |||
| Spectral type | K1V[1] | DA4[4] | M4.5eV[5] |
| U-B color index | 0.45[4] | -0.68[4] | 0.83[4] |
| B-V color index | 0.82[1] | 0.03[4] | 1.67[4] |
| Variable type | None[6] | None | Flare star[6][7] |
| Astrometry | |||
| Radial velocity (Rv) | -43.0 km/s[8] | -46 km/s[4] | |
| Proper motion, RA (μα cos δ) | -2239.72 mas/yr[1] | -2228.3 mas/yr[2] | -2237 mas/yr[3] |
| Proper motion, Dec. (μδ) | -3420.35 mas/yr[1] | -3377.1 mas/yr[2] | -3411 mas/yr[3] |
| Parallax (π) | 198.26 ± 0.84 mas[1] | ||
| Distance | 16.45 ± 0.07 ly (5.04 ± 0.02 pc) |
||
| Absolute magnitude (MV) | 5.92 | 11.01 | 12.66 |
| Details | |||
| Mass | 0.84 M☉[8] | 0.50 M☉[9][10] | 0.20 M☉[11] |
| Radius | 0.81 R☉[11] | 0.014 R☉[10] | 0.31 R☉[11] |
| Luminosity | 0.4L☉[12] | 0.013 L☉[12] | 0.008 L☉[13] |
| Temperature | 5,200 K[8] | 16,500 K[9] | 3,100 K[14] |
| Age | 4·109 to 12·109 years[15] | ||
| Orbits | |||
| Secondary/primary | BC/A | C/B | |
| Period (P) | ~8000 yr[16] | 252.1 yr[16] | |
| Semimajor axis (a) | ~400 AU[17] | 6.943" (~35 AU)[16] | |
| Eccentricity (e) | 0.410[16] | ||
| Inclination (i) | 108.9°[16] | ||
| Longitude of node (Ω) | 150.9°[16] | ||
| Periastron epoch (T) | 1849.6[16] | ||
| Argument of periastron (ω) | 327.8°[16] | ||
| Other designations | |||
|
A: Keid, ο2 Eri A, o2 Eridani A, 40 Eri A, ADS 3093A, BD -07°780, CCDM J04153-0739A, GCTP 945, GJ 166 A, HD 26965, HIP 19849, HR 1325, LHS 23, LTT 1907, SAO 131063, STF 518A.
B: ο2 Eri B, o2 Eridani B, 40 Eri B, ADS 3093B, BD -07°781A, CCDM J04153-0739B, G 160-060, GCTP 945, GJ 166 B, HD 26976, LHS 24, LTT 1908, SAO 131065, WD 0413-077, STF 518B. C: DY Eri[6], DY Eridani, ο2 Eri C, o2 Eridani C, 40 Eri C, ADS 3093C, BD -07°781B, BD -07°781C, CCDM J04153-0739C, GCTP 945, GJ 166 C, LHS 25, LTT 1909, STF 518C; also, see entries for B. |
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40 Eridani (also known as Omicron2 Eridani, or Keid, from the Arabic word qayd, (egg) shells) is a triple star system less than 16.5 light years away from Earth.[12] It is in the constellation Eridanus. The primary star of the system, 40 Eridani A, is easily visible to the naked eye. The pair 40 Eridani B/C was discovered on January 31, 1783 by William Herschel.[18], p. 73 It was again observed by Friedrich Georg Wilhelm Struve in 1825 and by Otto Wilhelm von Struve in 1851.[19][16] 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.[20], p. 1
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[edit] General information
40 Eridani A is an red-orange main sequence dwarf of spectral type K1. Its two companion stars, 40 Eridani B and 40 Eridani C, are a 9th magnitude white dwarf (spectral type DA4) and an 11th magnitude red dwarf flare star (spectral type M4.5e) which has the variable star designation DY Eridani. Presumably, while B was a main sequence star, it was the most massive member of the system, but ejected most of its mass before it became a white dwarf.[12] B and C orbit each other approximately 400 astronomical units from the primary star, A.[17] 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).[16]
[edit] Potential for life
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.[17] 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 -4.7) It is extremely unlikely that habitable planets exist around the B star: planets circling 40 Eri B would likely have been destroyed or sterilized by its evolution into a white dwarf. As for 40 Eri 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 a planet in the habitable zone.[17]
[edit] Star Trek affiliation
40 Eridani was the star system of the Vulcans in Star Trek, though not canonized until the fourth season (2004-2005) of Star Trek: Enterprise.[21]
[edit] References
- ^ a b c d e f g h Hipparcos Catalogue; CDS ID I/239. Astrometric data updated from J1991.25 to J2000.0.
- ^ a b c d Second U.S. Naval Observatory CCD Astrograph Catalog (UCAC2); CDS ID I/289.
- ^ a b c d Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog, Samir Salim and Andrew Gould, Astrophysical Journal 582, #2 (January 2003), pp. 1011–1031; CDS ID J/ApJ/582/1011.
- ^ a b c d e f g h i Gliese Catalogue of Nearby Stars, preliminary 3rd ed., 1991. CDS ID V/70A.
- ^ General Catalogue of Trigonometric Parallaxes, 4th ed., 1995. CDS ID I/238A.
- ^ a b c 40 Eri A is misidentified by SIMBAD as being the flare star DY Eri. DY Eri is 40 Eri C. See the GCVS entry for 40 Eri.
- ^ Combined General Catalogue of Variable Stars (GCVS), v. 4.2. CDS ID II/250.
- ^ a b c The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ~14 000 F and G dwarfs, B. Nordström, M. Mayor, J. Andersen, J. Holmberg, F. Pont, B. R. Jørgensen, E. H. Olsen, S. Udry, and N. Mowlavi, Astronomy and Astrophysics 418 (May 2004), pp. 989–1019; CDS ID J/A+A/418/989.
- ^ a b The Temperature Scale and Mass Distribution of Hot DA White Dwarfs, David S. Finley, Detlev Koester, and Gibor Basri, Astrophysical Journal 488 (October 10, 1997), pp. 375–396.
- ^ a b Testing the White Dwarf Mass-Radius Relation with HIPPARCOS, J. L. Provencal, H. L. Shipman, Erik Hog, and P. Thejll, Astrophysical Journal 494 (February 20, 1998), pp. 759–767.
- ^ a b c Catalogue of nearest stars until 10pc, V. A. Zakhozhaj. Revised 1996. CDS ID V/101.
- ^ a b c d Keid, Jim Kaler, STARS web page, accessed May 15, 2007.
- ^ From L=4πR2σTeff4.
- ^ Predicted infrared brightness of stars within 25 parsecs of the sun, H. M. Johnson and C. D. Wright, Astrophysical Journal Supplement 53 (November 1983), pp. 643–711.
- ^ Age determinations of main-sequence stars: combining different methods, R. Lachaume, C. Dominik, T. Lanz, and H. J. Habing, Astronomy and Astrophysics 348 (August 1999), pp. 897–909.
- ^ a b c d e f g h i j Astrometric study of four visual binaries, W. D. Heintz, Astronomical Journal 79, #7 (July 1974), pp. 819–825.
- ^ a b c d 40 (Omicron2) Eridani 3 at solstation.com, accessed May 15, 2007.
- ^ Catalogue of Double Stars, William Herschel, Philosophical Transactions of the Royal Society of London 75 (1785), pp. 40–126
- ^ The orbit and the masses of 40 Eridani BC, W. H. van den Bos, Bulletin of the Astronomical Institutes of the Netherlands 3, #98 (July 8, 1926), pp. 128–132.
- ^ White Dwarfs, E. Schatzman, Amsterdam: North-Holland, 1958.
- ^ Vulcan system, Memory Alpha. Accessed on line March 17, 2008.
[edit] See also
[edit] External links
- Keid at Jim Kaler's STARS.
- 40 (Omicron2) Eridani 3 at solstation.com.
- Omicron(2) Eridani entry at the Internet Stellar Database.
