Beta Cancri

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Al Tarf, β Cancri
Cancer constellation map.png
Al Tarf 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) 3.536 [1]
Spectral type K4III [1]
U−B color index -1.77 [1]
B−V color index -1.48 [1]
Variable type  ?
Radial velocity (Rv) 22.94 [1] km/s
Proper motion (μ) RA: -46.80 [1] mas/yr
Dec.: −48.65 [1] mas/yr
Parallax (π) 11.23 ± 0.97[1] mas
Distance 290 ± 30 ly
(89 ± 8 pc)
Absolute magnitude (MV) -1.21
Radius 48 ± 4[2] R
Luminosity 660[3] L
Surface gravity (log g) 1.51[4] cgs
Temperature 4,039[4] K
Metallicity -0.12[4]
Rotational velocity (v sin i) 8[1] km/s
Other designations
Altarf, Al Tarf, Tarf, 17 Cancri, HR 3249, HD 69267, BD+09°1917, FK5 312, HIP 40526, SAO 116569, GC 11254, ADS 6704, CCDM 08165+0911
Database references

Beta Cancri (β Cnc, β Cancri) is the brightest star in the constellation Cancer. It has the traditional name Tarf or Al Tarf (Altaraf), certainly a derivation from Arabic الطرف aṭ-ṭaraf "the eye" or طرفة aṭ-ṭarfah "the glance (of Leo)". It is approximately 290 light years from Earth.

This is an orange K-type giant, about 49 times the radius of the Sun, with an apparent magnitude of +3.50 and absolute magnitude of -1.25 (visual). It has a faint, fourteenth magnitude, red dwarf companion star located 29 arcseconds away. A planet, Beta Cancri b, was discovered on May 13, 2014.[5]

See also[edit]


  1. ^ a b c d e f g h i j k "SIMBAD query result: NSV 3973 -- Variable Star". Centre de Données astronomiques de Strasbourg. Retrieved 2010-02-23. 
  2. ^ Nordgren, Tyler E. et al., Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer, The Astronomical Journal 118 (6): 3032–303, Bibcode:1999AJ....118.3032N, doi:10.1086/301114 
  3. ^ Kaler, James B. "AL TARF (Beta Cancri)". Stars. University of Illinois. Retrieved 2010-02-23. 
  4. ^ a b c Cenarro, A. J.; Peletier, R. F., et al (2007). "Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters". Monthly Notices of the Royal Astronomical Society (PDF) 374 (2): 664–690. arXiv:astro-ph/0611618. Bibcode:2007MNRAS.374..664C. doi:10.1111/j.1365-2966.2006.11196.x. 
  5. ^ 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. id.A67. arXiv:1405.2127. Bibcode:2014A&A...566A..67L. doi:10.1051/0004-6361/201322608.