24 Sextantis

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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[1] mas
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. ^ a b c d e 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. ^ a b c d e 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. ^ 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. ^ "24 Sextantis". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-09-17.
  6. ^ a b "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. doi:10.1093/mnras/stz345. Retrieved 28 April 2020.
  8. ^ Jean Schneider (2011). "Notes for star 24 Sex". Extrasolar Planets Encyclopaedia. Retrieved 30 September 2011.

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

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