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Template:PAGEBANNER:Aldebaran b Planet.png Artist's impression of Aldebaran's suspected planetary companion, Aldebaran B or Alpha Tauri B.

Taurus constellation map.svg
The position of Aldebaran in the Taurus constellation.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Taurus
Pronunciation /ælˈdɛbərən/[1][2]
Right ascension 04h 35m 55.23907s[3]
Declination +16° 30′ 33.4885″[3]
Apparent magnitude (V) 0.86[4] (0.75-0.95)[5]
Evolutionary stage Red giant branch
Spectral type K5 III[6]
Apparent magnitude (J) −2.095[7]
U−B color index +1.92[4]
B−V color index +1.44[4]
Variable type LB[5]
Radial velocity (Rv)+54.26±0.03[8] km/s
Proper motion (μ) RA: 63.45±0.84[3] mas/yr
Dec.: −189.94±0.65[3] mas/yr
Parallax (π)49.97 ± 0.75[9] mas
Distance65.3 ± 1.0 ly
(20.0 ± 0.3 pc)
Absolute magnitude (MV)−0.641±0.034[9]
Mass1.16±0.07[10] M
Radius44.13±0.84[11] R
Diameter44.13±0.84[11] D
Luminosity518±32[11] L
Surface gravity (log g)1.59[11] cgs
Temperature3,910[11] K
Metallicity [Fe/H]−0.15±0.2[12] dex
Rotation643 days[13]
Other designations
87 Tauri, Alpha Tauri, BD+16°629, GJ 171.1, GJ 9159, HD 29139, HIP 21421, HR 1457, SAO 94027
Database references

Aldebaran, designated Alpha Tauri (in Icons-flag-gr.png Greek letters: α Tauri, abbreviated Alpha Tau, α Tau), is a red giant star located about 65 light-years away from the Sun and Earth in the constellation Taurus and the 14th brightest overall, though it slowly varies in apparent magnitude between magnitude 0.75 and 0.95. It is believed that Aldebaran hosts a planet several times the size of Jupiter. The planetary exploration probe Pioneer 10 is currently heading in the general direction of the star and should make pass by the star in two million years.[14]

Physical properties

Size comparison between Aldebaran and the Sun

Aldebaran is classified as a K5 type star, which indicates it is an orange-hued giant star that has evolved off the main sequence of the Hertzsprung–Russell diagram after exhausting all of the hydrogen at its core. The collapse of the centre of the star into a degenerate helium core has ignited a shell of hydrogen outside the core, bringing Aldebaran to being a red giant on the red giant branch (RGB). It has expanded to 44 times the diameter of the Sun,[11] equivalent to approximately 61 million kilometres. Measurements by the Hipparcos satellite and other reliable sources put Aldebaran around 65 light years away.[9] On the other hand, asteroseismology has determined that it is about 17% more massive than the Sun,[10] yet it shines with over 425 times the Sun's luminosity due to the expanded diameter. Aldebaran is only a slightly variable star, of the slow irregular variable type LB. It varies by about 0.2 in apparent magnitude from 0.75 to 0.95.[5] With a near-infrared J band magnitude of −2.1, only Betelgeuse (−2.9), R Doradus (−2.6), and Arcturus (−2.2) are brighter.[7]

Planetary companion

In 1993, radial velocity measurements of Aldebaran, along with the similar red and orange giants Arcturus and Pollux showed that Aldebaran exhibited a long-period radial velocity oscillation, which could be interpreted as a potential substellar companion. The measurements for Aldebaran implied a companion with a minimum mass around 11.4 times that of Jupiter in a 643-day orbit at a separation of 2 astronomical units in a mildly eccentric orbit. However, all three stars surveyed showed similar oscillations yielding somewhat similar companion masses, and the authors concluded that the variation was likely to be exclusive to the star itself rather than due to the gravitational effect of an orbiting planet.[15]

Sun's position viewed from this star

If the sun were to be observed from this star, it would be an almost invisible 6.4 magnitude star located between the Ophiuchus and Scorpius constellations.

See also


  1. Oxford Dictionary: Aldebaran
  2. Merriam-Webster: Aldebaran
  3. 3.0 3.1 3.2 3.3 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653. arXiv:0708.1752. Bibcode 2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  4. 4.0 4.1 4.2 Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues 2237: 0. Bibcode 2002yCat.2237....0D.
  5. 5.0 5.1 5.2 Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  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: 161. arXiv:astro-ph/0603770. Bibcode 2006AJ....132..161G. doi:10.1086/504637.
  7. 7.0 7.1 Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T. et al. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally published in: 2003yCat.2246....0C 2246. Bibcode 2003yCat.2246....0C.
  8. Famaey, B.; Jorissen, A.; Luri, X.; Mayor, M.; Udry, S.; Dejonghe, H.; Turon, C. (2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters". Astronomy and Astrophysics 430: 165. arXiv:astro-ph/0409579. Bibcode 2005A&A...430..165F. doi:10.1051/0004-6361:20041272.
  9. 9.0 9.1 9.2 Gatewood, George (July 2008). "Astrometric Studies of Aldebaran, Arcturus, Vega, the Hyades, and Other Regions". The Astronomical Journal 136 (1): 452–460. Bibcode 2008AJ....136..452G. doi:10.1088/0004-6256/136/1/452.
  10. 10.0 10.1 Lua error in Module:Citation/CS1 at line 876: attempt to call method 'sub' (a nil value).
  11. 11.0 11.1 11.2 11.3 11.4 Piau, L; Kervella, P; Dib, S; Hauschildt, P (February 2011). "Surface convection and red-giant radius measurements". Astronomy and Astrophysics 526: A100. arXiv:1010.3649. Bibcode 2011A&A...526A.100P. doi:10.1051/0004-6361/201014442.
  12. Decin, L; Vandenbussche, B; Waelkens, C; Decin, G; Eriksson, K; Gustafsson, B; Plez, B; Sauval, A. J (March 2003). "ISO-SWS calibration and the accurate modelling of cool-star atmospheres. IV. G9 to M2 stars". Astronomy and Astrophysics 400 (2): 709–729. arXiv:astro-ph/0207653. Bibcode 2003A&A...400..709D. doi:10.1051/0004-6361:20021786.
  13. Koncewicz, R.; Jordan, C. (January 2007). "OI line emission in cool stars: calculations using partial redistribution". Monthly Notices of the Royal Astronomical Society 374 (1): 220–231. Bibcode 2007MNRAS.374..220K. doi:10.1111/j.1365-2966.2006.11130.x.
  14. Nieto, Michael Martin; Anderson, John D. (January 2007). "Search for a solution of the Pioneer anomaly". Contemporary Physics 48 (1): 41–54. arXiv:0709.3866. Bibcode 2007ConPh..48...41N. doi:10.1080/00107510701462061.
  15. Hatzes, A.; Cochran, W. (1993). "Long-period radial velocity variations in three K giants". The Astrophysical Journal 413 (1): 339–348. Bibcode 1993ApJ...413..339H. doi:10.1086/173002.

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