24 Sextantis

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24 Sextantis
Observation data
Epoch 2000      Equinox 2000
Constellation Sextans
Right ascension 10h 23m 28.37066s[1]
Declination –00° 54′ 08.0888″[1]
Apparent magnitude (V) 6.61 ± 0.04[2]
Spectral type K0 IV[3]
B−V color index 0.92 ± 0.01[2]
Radial velocity (Rv)7.08 ± 0.16[4] km/s
Proper motion (μ) RA: +66.21[1] mas/yr
Dec.: –34.92[1] mas/yr
Parallax (π)12.91 ± 0.38[1] mas
Distance253 ± 7 ly
(77 ± 2 pc)
Absolute magnitude (MV)2.17 ± 0.06[2]
Mass1.54 ± 0.08[2] M
Radius4.9 ± 0.08[2] R
Luminosity14.6 ± 0.1[2] L
Surface gravity (log g)3.5 ± 0.1[2] cgs
Temperature5,098 ± 44[2] K
Metallicity [Fe/H]−0.03 ± 0.04[2] dex
Rotational velocity (v sin i)2.77 ± 0.5[2] km/s
Age2.7 ± 0.4[2] Gyr
Other designations
BD−00° 2332, HD 90043, HIP 50887, SAO 137532.
Database references

24 Sextantis, often abbreviated as 24 Sex, is the Flamsteed designation of a 7th-magnitude star located approximately 253 light years away in the constellation of Sextans. At an apparent visual magnitude of 6.61,[2] this star can only be viewed from rural skies under good seeing conditions.

At the age of 2.8 billion years, it has reached an evolutionary stage called a subgiant star, having a stellar classification of K0 IV.[3] Previously it was an A-type main sequence star before using up the hydrogen at its core. It has 54% more mass than the Sun, but the outer envelope has become cooler than the Sun's as it slowly expands into a giant star.

The star is known to have two giant extrasolar planets.

Planetary system[edit]

On July 26, 2010 the California and Carnegie Planet Search team announced the discovery of two planets around 24 Sextantis along with two planets around HD 200964.[5] The inner planet is twice as massive as Jupiter and takes 453 days to orbit the star in a circular orbit at the average distance of 1.33 AU (199 Gm). The outer planet is 5/6 the mass of Jupiter and takes 883 days to orbit eccentrically around the star at the average distance of 2.08 AU (312 Gm).

The two planets are in a 2:1 resonance, meaning that the outer planet orbits the star once every time when the inner planet orbits the star twice. These two jovian planets are dancing around each other gravitationally.[5]

The 24 Sextantis planetary system[6]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b ≥1.99+0.26
c ≥0.86+0.35

See also[edit]


  1. ^ a b c d e van Leeuwen, F. (November 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
  2. ^ a b c d e f g h i j k l Johnson, John Asher; et al. (January 2011), "Retired a Stars and Their Companions. VI. A Pair of Interacting Exoplanet Pairs Around the Subgiants 24 Sextanis and HD 200964", The Astronomical Journal, 141 (1): 16, arXiv:1007.4552, Bibcode:2011AJ....141...16J, doi:10.1088/0004-6256/141/1/16
  3. ^ a b Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Bibcode:1999MSS...C05....0H.
  4. ^ Massarotti, Alessandro; et al. (January 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
  5. ^ a b "Astronomers find planets in unusually intimate dance around dying star". Astronomy Magazine. July 29, 2010. Retrieved 2011-01-13.
  6. ^ Jean Schneider (2011). "Notes for star 24 Sex". Extrasolar Planets Encyclopaedia. Retrieved 30 September 2011.

Coordinates: Sky map 10h 23m 28s, −00° 54′ 08″