Kapteyn's Star

Coordinates: Sky map 05h 11m 41s, −45° 01′ 06″
Source: Wikipedia, the free encyclopedia.
Kapteyn's Star
Pictor
Observation data
Epoch J2000      Equinox J2000
Constellation Pictor
Right ascension 05h 11m 40.58984s[1]
Declination −45° 01′ 06.3617″[1]
Apparent magnitude (V) 8.853±0.008[2]
Characteristics
Spectral type sdM1[3] or M1.5V[2][4]
U−B color index +1.21[5]
B−V color index 1.57±0.012[2]
Variable type BY Dra[6]
Distance
12.8308 ± 0.0008 ly
(3.9339 ± 0.0003 pc)
Absolute magnitude (MV)10.89[3]
Details
Gyr
LTT 2200[5]
Database references
SIMBADThe star
planet b
planet c

Kapteyn's Star is a class M1 red subdwarf about 12.83 light-years from Earth in the southern constellation Pictor; it is the closest halo star to the Solar System. With an apparent magnitude of nearly 9 it is visible through binoculars or a telescope.[9]

Its diameter is 30% of the Sun's, but its luminosity just 1.2% that of the Sun. It may have once been part of the globular cluster Omega Centauri, itself the likely core of a dwarf galaxy swallowed up by the Milky Way in the distant past. The discovery of two planets—Kapteyn b and Kapteyn c—was announced in 2014,[10] but had a mixed history of rejections and confirmations, until a 2021 study refuted both planets. The "planets" are in fact artifacts of the star's rotation and activity.[7]

History of observations

Jacobus Cornelius Kapteyn, the Dutch astronomer who discovered Kapteyn's Star

Attention was first drawn to what is now known as Kapteyn's Star by the Dutch astronomer

arcseconds away from the absent star's position. It became clear that the star had a very high proper motion of more than 8 arcseconds per year and had moved significantly. Later, CPD-44 612 came to be referred to as Kapteyn's Star[14] although equal credit should be accorded to Robert Innes.[15] At the time of its discovery it had the highest proper motion of any star known, dethroning Groombridge 1830. In 1916, Barnard's Star was found to have an even larger proper motion.[14][16][17] In 2014, two super-Earth planet candidates in orbit around the star were announced,[10] but later refuted.[7]

Characteristics

sine function that best fits
the data.

Based upon

moving group of stars that share a common trajectory through space, named the Kapteyn moving group.[20] Based upon their element abundances, these stars may once have been members of Omega Centauri, a globular cluster that is thought to be the remnant of a dwarf galaxy that merged with the Milky Way. During this process, the stars in the group, including Kapteyn's Star, may have been stripped away as tidal debris.[17][21][22]

Comparison with Sun, Jupiter and Earth

Kapteyn's Star is between one quarter and one third the size and mass of the Sun and has a much cooler

star spots into and out of the line of sight with respect to the Earth.[6]

The star has a mass of 0.27 M☉, a radius of 0.29 R☉ and has about 1.2% of the Sun's luminosity. It has a surface temperature of 3,550 K and is roughly 11 billion years old.[10] In comparison, the Sun is about 4.6 billion years old[25] and has a surface temperature of 5,778 K.[26] Stars like Kapteyn's Star have the ability to live up to 100–200 billion years, ten to twenty times longer than the Sun will live.[27]

Search for planets

In 2014, Kapteyn's Star was announced to host two planets, Kapteyn b and Kapteyn c, based on

habitable planet, estimated to be 11 billion years old,[10] while Kapteyn c was described as beyond the host star's habitable zone.[29][30][10]

Kapteyn b was thought to make a complete orbit around its parent star about every 48.62 days at a distance of 0.17 AU, with an eccentricity of 0.21, meaning its orbit is mildly elliptical. Kapteyn c was thought to orbit with a period of 121.5 days at a distance of 0.31 AU, with an eccentricity of 0.23. Both planets were thought to be super-Earths, with minimum masses of 4.8 and 7.0 ME, respectively.[10]

The purported planets were thought to be close to a 5:2 period commensurability, but resonances could not be confirmed. Dynamical integration of the orbits suggested[10] that the pair of planets are in a dynamical state called apsidal co-rotation, which usually implies that the system is dynamically stable over long time scales.[31] Guinan et al. (2016) suggested that the present day star could potentially support life on Kapteyn b, but that the planet's atmosphere may have been stripped away when the star was young (~0.5 Gyr) and highly active.[2] The announcement of the planetary system was accompanied by a science-fiction short-story, "Sad Kapteyn", written by writer Alastair Reynolds.[32]

However, subsequent research by Robertson et al. (2015) found that the orbital period of Kapteyn b is an integer fraction (1/3) of their estimated stellar rotation period, and thus the planetary signal is most likely an artifact of stellar activity. The authors did not rule out the existence of Kapteyn c, calling for further observation.[33] This refutation was questioned by the team that published the exoplanet discovery paper.[34] Guinan et al. (2016) (as well as earlier authors) found a lower value for the stellar rotation, which lended support to the original planetary finding.[2]

In 2021, a new analysis found no evidence for either planet, and found that the observed radial velocity signals are in fact artifacts of the star's rotation and activity, after the rotational period of the star was refined, with a rotational period very similar to that of candidate c.[7] There is currently no evidence for planets orbiting Kapteyn's Star.

See also

References

  1. ^
    S2CID 244398875
    . Gaia DR3 record for this source at VizieR.
  2. ^
    S2CID 119283541
    , 81.
  3. ^
    doi:10.1111/j.1365-2966.2009.16182.x
  4. S2CID 14786643
    .
  5. ^
    Centre de Données astronomiques de Strasbourg, archived
    from the original on 2016-03-03, retrieved 2009-10-14.
  6. ^ a b "VZ Pic", General Catalogue of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia, archived from the original on 2011-09-27, retrieved 2009-10-14
  7. ^
    S2CID 232110395
    .
  8. doi:10.1111/j.1365-2966.2010.16827.x
  9. ^ "Kapteyn b and c: Two Exoplanets Found Orbiting Kapteyn's Star". Sci-News. Archived from the original on 3 August 2014. Retrieved 23 July 2014.
  10. ^
    S2CID 67807856
  11. doi:10.1002/asna.18981450906
    .
  12. Centre de Données astronomiques de Strasbourg
    .
  13. ^ "Resultados del Observatorio Nacional Argentino, vol. 7, pg.98". Archived from the original on 2019-04-21. Retrieved 2019-04-21.
  14. ^ a b c Kaler, James B. (2002), "Kapteyn's Star", The Hundred Greatest Stars, Copernicus Books, pp. 108–109.
  15. ^ Gill, D. (1899). "On the Discovery of a Certain Proper Motion". The Observatory: 99–101.
  16. doi:10.1086/104156
    .
  17. ^
    doi:10.1051/0004-6361:20042287
    .
  18. S2CID 59039482
    , A35.
  19. S2CID 15907478
    .
  20. doi:10.1086/118210
  21. S2CID 119217292
  22. ^ "Backward star ain't from round here", New Scientist, November 4, 2009, archived from the original on May 25, 2015, retrieved September 2, 2017
  23. S2CID 15664454
  24. ^ The abundance is given by taking the metallicity to the power of 10. From Woolf and Wallerstein (2005), [M/H] ≈ –0.86 dex. Thus:
    10−0.86 = 0.138
  25. ^ Cain, Fraser (16 September 2008). "How Old is the Sun?". Universe Today. Archived from the original on 18 August 2010. Retrieved 19 February 2011.
  26. ^ Cain, Fraser (September 15, 2008). "Temperature of the Sun". Universe Today. Archived from the original on 29 August 2010. Retrieved 19 February 2011.
  27. Bibcode:2004RMxAC..22...46A
    .
  28. ^ Wall, Mike (3 June 2014). "Found! Oldest Known Alien Planet That Might Support Life". Space.com. Retrieved 10 January 2015.
  29. ^ David Dickinson, Discovered: Two New Planets for Kapteyn’s Star (June 4, 2014).
  30. ^ Kapteyn's Star at SolStations.com.
  31. S2CID 85449365
  32. ^ "Sad Kapteyn", Science fiction story released with the announcement of planetary system, Jun 4, 2014, archived from the original on June 6, 2014, retrieved 2014-06-04
  33. S2CID 117871083
    , L22.
  34. S2CID 14348277
    .

Further reading

External links



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