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Altarf, β Cancri
Cancer constellation map.png
Altarf (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) 3.536 [1]
Spectral type K4III [1]
U−B color index -1.77 [1]
B−V color index -1.48 [1]
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
β Cancri, 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

Altarf (β Cnc, β Cancri, Tarf, Al Tarf) is the brightest star in the zodiacal constellation Cancer. At approximately 290 light years from earth, it has an apparent magnitude of +3.50 and absolute magnitude of -1.25 (visual).[1] The star is an orange K-type giant, about 48 times the radius of the Sun.[3]

The traditional name Tarf or Al Tarf (anglicized as Altarf), can be translated from Arabic as "end" or "edge".[3]

Altarf is known to have a fourteenth magnitude, red dwarf companion star. From its angular distance of 29 arcseconds, the companion's distance from its parent star is estimated at some 2600 AU, and has an orbital period of 76,000 years.[3]

In a paper published in the journal Astronomy & Astrophysics on May 12, 2014, evidence was presented of a planet orbiting Altarf. 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 orbit of 605 days.[5]

See also[edit]


  1. ^ a b c d e f g h i j k l "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. ^ a b c d 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/0611618Freely accessible. 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:1405.2127Freely accessible. Bibcode:2014A&A...566A..67L. doi:10.1051/0004-6361/201322608.