40 Eridani
![Sky map](http://upload.wikimedia.org/wikipedia/commons/thumb/e/e4/Jupiter_and_moon.png/20px-Jupiter_and_moon.png)
Observation data 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] | |
Absolute magnitude (MV) | 5.93[9] | |
40 Eridani B | ||
Distance | 16.353 ± 0.006 ly (5.014 ± 0.002 pc) | |
Argument of periastron (ω)(secondary) | 318.4±1.1° | |
Details | ||
40 Eridani A | ||
Gyr | ||
40 Eridani B | ||
Gyr | ||
LTT 1909 | ||
Database references | ||
SIMBAD | A | |
B | ||
C |
40 Eridani is a
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]
Nomenclature
40 Eridani is the system's
The system bore the traditional name Keid derived from the Arabic word قيض (alqayḍ) meaning "the eggshells," alluding to its neighbour Beid (Arabic "egg").[29] In 2016, the IAU organized a Working Group on Star Names (WGSN)[30] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire
Properties
![](http://upload.wikimedia.org/wikipedia/commons/thumb/e/e2/40_Eridani.png/220px-40_Eridani.png)
40 Eridani A is a
As seen from the 40 Eridani system, the Sun is a 3.4-magnitude star in
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 2] 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.[12]
Search for planets
40 Eridani A shows periodic radial velocity variations, which were suggested to be caused by a planetary companion. The 42-day period is close to the stellar rotation period, which made the possible planetary nature of the signal difficult to confirm.[16] A 2018 study found that most evidence supports a planetary origin for the signal,[14] but this has remained controversial, with a 2021 study characterizing the signal as a false positive.[32] As of 2022, the cause of the radial velocity variations remained inconclusive.[33]
Further studies in 2023[34]: 23–24, 44 and 2024 concluded that the radial velocity signal very likely does originate from stellar activity, and not from a planet.[35]
The candidate planet would have had a minimum mass of 8.47±0.47 M🜨, and lie considerably interior to the habitable zone, receiving nine times more stellar flux than Earth, which is an even greater amount than Mercury, the innermost planet in the Solar System, on average receives from the Sun.[14]
In fiction
In the Star Trek franchise, the planet Vulcan orbits 40 Eridani A.[36] Vulcan has been referenced in relation to the real-life search for exoplanets in this system.[37][35] The hypothetical planet 40 Eridani A b is also mentioned in the book Project Hail Mary as the home of the eponymous Eridian species.[38]
Notes
- 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 .
- ^ From where h is the apparent height, d is the distance of the object, and a is the actual size of the object.
References
- ^ S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ S2CID 18759600.
- ^ S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ CDS ID V/70A.
- ^ S2CID 244398875. Gaia DR3 record for this source at VizieR.
- S2CID 119476992.
- CDS ID I/238A.
- Bibcode:2009yCat....102025S.
- S2CID 118577511.
- Bibcode:1967IAUS...30...57E.
- ^ doi:10.1086/111614.
- ^ a b c "40 Eridani 3 (Omicron² Eridani)". solstation.com. Archived from the original on 30 September 2023. Retrieved 2018-02-06.
- ^ S2CID 119080080, 200.
- ^ .
- .
- ^ S2CID 119404519.
- S2CID 122724497.
- ^ a b Keid Archived 2007-05-14 at the Wayback Machine, Jim Kaler, STARS web page, accessed 15/5/2007, 10/12/2011.
- S2CID 120006763.
- ^ ISSN 0004-6361
- doi:10.1086/190905.
- S2CID 27151456.
- ^ S2CID 119257982. 16.
- ^ a b c "Naming Stars". IAU.org. Retrieved 16 December 2017.
- S2CID 186209747.
- Bibcode:1926BAN.....3..128V.
- ^ White Dwarfs, E. Schatzman, Amsterdam: North-Holland, 1958. , p. 1
- arXiv:1012.0707 [astro-ph.SR].
- ^ "Beid". stars.astro.illinois.edu.
- ^ "Working Group on Star Names (WGSN)". Working Groups. International Astronomical Union. Retrieved 22 May 2016.
- ^ Working Group on Star Names Triennial Report (2015-2018) (PDF) (Report). International Astronomical Union. 2018. p. 5. Retrieved 2018-07-14.
- S2CID 235186973.
- S2CID 246285610.
- .
- ^ .
- ^ Sallie Baliunas; Gene Roddenberry; et al. "Vulcan's Sun". Archived from the original on August 29, 2009. Retrieved 2011-04-21.
- . Retrieved 2018-09-20.
- ISBN 978-0-593-13520-4.
External links
- Keid at Jim Kaler's STARS.
- Omicron(2) Eridani entry at the Internet Stellar Database.