Beta Cancri

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β Cancri
Cancer constellation map.svg
Red circle.svg
β Cancri is the bottom right star in the "crab"
Observation data
Epoch J2000      Equinox J2000
Constellation Cancer
Right ascension 08h 16m 30.9206s[1]
Declination +09° 11′ 07.961″[1]
Apparent magnitude (V) 3.50 - 3.58[2]
Spectral type K4III Ba1[3]
U−B color index +1.77[4]
B−V color index +1.48[4]
Variable type Suspected[2]
Radial velocity (Rv)22.94[5] km/s
Proper motion (μ) RA: −46.80[1] mas/yr
Dec.: −48.65[1] mas/yr
Parallax (π)11.23 ± 0.97 mas[1]
Distance290 ± 30 ly
(89 ± 8 pc)
Absolute magnitude (MV)−1.218[6]
Radius61[7] R
Luminosity871[7] L
Surface gravity (log g)1.5[7] cgs
Temperature3,990[7] K
Rotational velocity (v sin i)6.9[7] km/s
Other designations
Tarf, β Cancri, 17 Cancri, HR 3249, HD 69267, BD+09°1917, FK5 312, HIP 40526, SAO 116569, GC 11254, ADS 6704, CCDM 08165+0911, WDS J08165+0911A.[8]
Database references

Beta Cancri (β Cancri, abbreviated Beta Cnc, β Cnc), also named Tarf /ˈtɑːrf/,[9] is the brightest star in the zodiacal constellation of Cancer. It has an apparent visual magnitude of +3.5[2] and an absolute magnitude of −1.2.[6] Based on parallax measurements obtained during the Hipparcos mission, it is approximately 290 light-years distant from the Sun.[1] An exoplanet, designated Beta Cancri b, is believed to be orbiting the star.[10]

Beta Cancri has a companion listed and together they are designated WDS J08165+0911. As the primary, Beta Cancri bears the designation WDS J08165+0911A.[8] The companion is designated WDS J08165+0911B.[11]


β Cancri (Latinised to Beta Cancri) is the star's Bayer designation. WDS J08165+0911A is its designation in the Washington Double Star Catalog.[8]

The star bore the traditional name of Al Tarf (anglicized as Altarf[12]), which can be translated from the Arabic as "end" or "edge".[13] In 2016, the IAU organized a Working Group on Star Names (WGSN)[14] to catalog and standardize proper names for stars. The WGSN approved the name Tarf for Beta Cancri on 1 June 2018 and it is now so included in the List of IAU-approved Star Names.[9]


A light curve for Beta Cancri, plotted from Hipparcos data[15]

Beta Cancri is an orange K-type giant, about 50 times the radius of the Sun.[13] It is a Barium star, a type of cool giant showing enhanced abundances of Barium.[16] It is also suspected to vary slightly in brightness.[2] Koen and Laurent analyzed the Hipparcos data for Beta Cancri and found in that data set its brightness varied with an amplitude of 0.0054 magnitudes over a period of 6.00565 days.[17]

The companion is a red dwarf of the fourteenth magnitude. From its angular distance of 29 arcseconds, the companion's distance from Beta Cancri is estimated at some 2600 AU, with an orbital period of 76,000 years.[13]


In 2014 evidence was presented of a planet orbiting Beta Cancri. Using radial velocity data from repeated observations of the star, the planet is estimated to have a minimum mass of approximately 7.8 times that of Jupiter, and an orbital period of 605 days.[10]

The Beta Cancri planetary system[18]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b 7.8 ± 0.8 MJ 1.7 ± 0.1 605.2 ± 4.0 0.08 ± 0.02


  1. ^ a b c d e f Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
  2. ^ a b c d 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. Bibcode:2009yCat....102025S.
  3. ^ Lu, Phillip K. (1991). "Taxonomy of barium stars". Astronomical Journal. 101: 2229. Bibcode:1991AJ....101.2229L. doi:10.1086/115845.
  4. ^ a b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  5. ^ 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. S2CID 17804304.
  6. ^ a b Cassatella, A.; Altamore, A.; Badiali, M.; Cardini, D. (2001). "On the Wilson-Bappu relationship in the Mg II k line". Astronomy and Astrophysics. 374 (3): 1085–1091. arXiv:astro-ph/0106070. Bibcode:2001A&A...374.1085C. doi:10.1051/0004-6361:20010816. S2CID 16286422.
  7. ^ a b c d e f Massarotti, Alessandro; Latham, David W.; Stefanik, Robert P.; Fogel, Jeffrey (2008). "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity". The Astronomical Journal. 135 (1): 209–231. Bibcode:2008AJ....135..209M. doi:10.1088/0004-6256/135/1/209.
  8. ^ a b c "bet Cnc -- High proper-motion Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2018-06-26
  9. ^ a b "Naming Stars". Retrieved 18 June 2018.
  10. ^ a b Lee, B.-C.; Han, I.; Park, M.-G.; Mkrtichian, D. E.; Hatzes, A. P.; Kim, K.-M. (2014). "Planetary companions in K giants β Cancri, μ Leonis, and β Ursae Minoris". Astronomy & Astrophysics. 566: A67. arXiv:1405.2127. Bibcode:2014A&A...566A..67L. doi:10.1051/0004-6361/201322608. S2CID 118631934.
  11. ^ "UCAC4 496-050758 -- Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2018-06-26
  12. ^ Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H. 5050. Bibcode:1995yCat.5050....0H.
  13. ^ a b c Kaler, James B. "AL TARF (Beta Cancri)". Stars. University of Illinois. Retrieved 2010-02-23.
  14. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  15. ^ "Light Curve". Hipparcos ESA. ESA. Retrieved 17 February 2022.
  16. ^ Gomez, A. E.; Luri, X.; Grenier, S.; Prevot, L.; Mennessier, M. O.; Figueras, F.; Torra, J. (1997). "Absolute magnitudes and kinematics of barium stars". Astronomy and Astrophysics. 319: 881. Bibcode:1997A&A...319..881G.
  17. ^ Koen, Chris; Laurent, Eyer (March 2002). "New periodic variables from the Hipparcos epoch photometry". Monthly Notices of the Royal Astronomical Society. 331 (1): 45–59. arXiv:astro-ph/0112194. Bibcode:2002MNRAS.331...45K. doi:10.1046/j.1365-8711.2002.05150.x.
  18. ^ "Notes on beta Cnc b". Extrasolar Planets Encyclopaedia. Retrieved 28 February 2017.