HD 200964

HD 200964 is a 7th magnitude star located approximately 237 light-years away in the constellation of Equuleus. It is a K-type subgiant with 44% more mass than the Sun, but cooler. At the age of 3 billion years, it indicates that it is an evolved A-type star. At a magnitude of 6.64, this star is too faint to be seen with the naked eye for most people, but binoculars would make it easy to see this star. Only people with a very clear eyesight and very dark sky can barely see this star.

HD 200964
Observation data
Epoch J2000      Equinox J2000
Constellation Equuleus
Right ascension  21h 06m 39.8424s[1]
Declination +03° 48′ 11.2240″[1]
Apparent magnitude (V) +6.64
Characteristics
Spectral type K0 IV
Astrometry
Proper motion (μ) RA: 94.608[1] mas/yr
Dec.: 50.604[1] mas/yr
Parallax (π)13.7469 ± 0.0455[1] mas
Distance237.3 ± 0.8 ly
(72.7 ± 0.2 pc)
Details[2]
Mass1.45 M☉
Radius4.92 R☉
Surface gravity (log g)3.22 cgs
Temperature4982 K
Age3.3 Gyr
Other designations
10 G. Equ, BD+03°4501, HIP 104202, SAO 126546[3]
Database references
SIMBADdata

The star is known to have two giant extrasolar planets.[4]

Planetary system

On July 26, 2010 the California and Carnegie Planet Search team announced the discovery of two planets around HD 200964 along with two planets around 24 Sextantis.[5] The inner planet is nearly twice as massive as Jupiter and takes 614 days to orbit the star in a circular orbit at the average distance of 1.60 AU (240 Gm). The outer planet is 9/10 the mass of Jupiter and takes 825 days to orbit eccentrically around the star at the average distance of 1.95 AU (292 Gm).

Due to the close proximity of the two planets to each other the discoverers only found stable orbits near the 4:3 resonance, meaning that every time the outer planet orbits the star three times, the inner planet orbits the star four times. The two planets are separated by only 0.35 AU. Because of the small separation between the two massive planets, the gravitational tugs between the two planets is nearly 3 million times greater than the gravitational force between Earth and Mars, 700 times larger than that between Earth and the Moon, and 4 times larger than the pull of the Sun on Earth.[5][4] After additional radial velocity measurements were taken stable solutions in the 7:5 and 3:2 mean-motion resonances were found in addition to the 4:3 mean-motion resonance. The 7:5 configuration currently provides the best match to the measurements.[2]

There is evidence of a possible third planet in the system with a period of ~7 days however the three planet model of the system is only slightly better than the two planet model.[2]

The HD 200964 planetary system[6]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b ≥1.85+0.14
−0.08 MJ		 1.601 ± 0.002 613.8+1.3
−1.4		 0.04+0.04
−0.02		 — 0.85 RJ
c ≥0.90+0.12
−0.06 MJ		 1.950+0.008
−0.005		 825.0+3.1
−5.1		 0.181+0.024
−0.017		 — 0.85 RJ

See also

References
  1. 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. Rosenthal, M. M.; et al. (2019). "Measuring the Orbital Parameters of Radial Velocity Systems in Mean-motion Resonance: A Case Study of HD 200964". The Astronomical Journal. 158 (4). 136. arXiv:1908.04789. Bibcode:2019AJ....158..136R. doi:10.3847/1538-3881/ab3b02.
  3. "HD 200964". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-09-15.
  4. 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.
  5. "Astronomers find planets in unusually intimate dance around dying star". Astronomy Magazine. July 29, 2010. Retrieved 2011-01-13.
  6. "Notes for star 24 Sex". The Extrasolar Planets Encyclopaedia. Retrieved 2011-01-13.

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