24 Sextantis
Observation data
Epoch J2000      Equinox J2000
Constellation Sextans
Right ascension 10h 23m 28.3694s[1]
Declination –00° 54′ 08.0772″[1]
Apparent magnitude (V) 6.61 ± 0.04[2]
Characteristics
Spectral type K0 IV[3]
B−V color index 0.92 ± 0.01[2]
Astrometry
Radial velocity (Rv)7.08 ± 0.16[4] km/s
Proper motion (μ) RA: 65.220±0.167[1] mas/yr
Dec.: −36.272±0.244[1] mas/yr
Parallax (π)13.8488 ± 0.1298 mas[1]
Distance236 ± 2 ly
(72.2 ± 0.7 pc)
Absolute magnitude (MV)2.17 ± 0.06[2]
Details[2]
Mass1.54 ± 0.08 M☉
Radius4.9 ± 0.08 R☉
Luminosity14.6 ± 0.1 L☉
Surface gravity (log g)3.5 ± 0.1 cgs
Temperature5,098 ± 44 K
Metallicity [Fe/H]−0.03 ± 0.04 dex
Rotational velocity (v sin i)2.77 ± 0.5 km/s
Age2.7 ± 0.4 Gyr
Other designations
BD−00° 2332, HD 90043, HIP 50887, SAO 137532[5]
Database references
SIMBADdata

24 Sextantis, often abbreviated as 24 Sex, is the Flamsteed designation of a 7th-magnitude star located approximately 236 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

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.[6] 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.[6] The planetary system was found to be unstable in 2019.[7]

The 24 Sextantis planetary system[8]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b ≥1.99+0.26
−0.38 MJ		 1.333+0.004
−0.009		 452.8+2.1
−4.5		 0.09+0.14
−0.06		 — —
c ≥0.86+0.35
−0.26 MJ		 2.08+0.05
−0.02		 883+32
−14		 0.29+0.16
−0.09		 — —

See also

References

  1. 1 2 3 4 5 Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. 1 2 3 4 5 Johnson, John Asher; et al. (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. 1 2 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, S2CID 121883397
  5. ↑ "24 Sextantis". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-09-17.
  6. 1 2 "Astronomers find planets in unusually intimate dance around dying star". Astronomy Magazine. July 29, 2010. Retrieved 2011-01-13.
  7. ↑ Agnew, Matthew T; Maddison, Sarah T; Horner, Jonathan; Kane, Stephen R (June 2019). "Predicting multiple planet stability and habitable zone companions in the TESS era". Monthly Notices of the Royal Astronomical Society. 485 (4): 4703–4725. arXiv:1901.11297. doi:10.1093/mnras/stz345. Retrieved 28 April 2020.
  8. ↑ Jean Schneider (2011). "Notes for star 24 Sex". Extrasolar Planets Encyclopaedia. Archived from the original on August 4, 2010. Retrieved 30 September 2011.
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