HD 220689

HD 220689 is a single[8] star in the equatorial constellation of Aquarius. It is a challenge to view with the naked eye, having an apparent visual magnitude of +7.74,[2] but is readily viewed with a pair of binoculars.[9] The star is located at a distance of 153 light years from the Sun based on parallax, and is drifting further away with a radial velocity of +12 km/s.[1] A survey in 2015 has ruled out the existence of any additional stellar companions at projected distances from 26 to 305 astronomical units.[8]

HD 220689
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Aquarius
Right ascension 23h 25m 52.99170s[1]
Declination –20° 36′ 57.6998″[1]
Apparent magnitude (V) +7.74[2]
Characteristics
Spectral type G3V[3]
B−V color index +0.603±0.002[2]
Astrometry
Radial velocity (Rv)+12.30±0.14[1] km/s
Proper motion (μ) RA: –15.328 mas/yr[1]
Dec.: –177.593 mas/yr[1]
Parallax (π)21.3074 ± 0.0236 mas[1]
Distance153.1 ± 0.2 ly
(46.93 ± 0.05 pc)
Absolute magnitude (MV)4.50[2]
Details[4]
Mass1.016±0.048 M☉
Radius1.068±0.047 R☉
Luminosity1.491±0.005[5] L☉
Surface gravity (log g)4.360±0.045 cgs
Temperature5,921±26 K
Metallicity [Fe/H]−0.07±0.10 dex
Rotation~29 d
Rotational velocity (v sin i)5.5[6] km/s
Age4.586±2.487 Gyr
Other designations
BD–21°6419, GC 32591, HD 220689, HIP 115662, SAO 191898, G 273-43[7]
Database references
SIMBADdata
Exoplanet Archivedata
Extrasolar Planets
Encyclopaedia		data

The stellar classification of HD 220689 is G3V,[3] matching a yellow hued G-type main-sequence star that is generating energy through core hydrogen fusion. It is roughly 4.6 billion years old and is spinning with a projected rotational velocity of 5.5 km/s,[6] giving it a rotation period of around 29 days.[4] The star has a similar size, mass, and elemental abundances as the Sun. It is radiating 1.5[5] times the luminosity of the Sun from its photosphere at an effective temperature of 5,921 K.[4]

Planetary system

From 1998 to 2012, the star was under observation from the CORALIE echelle spectrograph at La Silla Observatory. In 2012, a long-period, wide-orbiting exoplanet was deduced from radial velocity variations. This was published in November.[10] The maximum orbital period allowing for dynamic stability of a hypothetical inner planet is 3.9 years.[4] In 2023, the inclination and true mass of HD 220689 b were determined via astrometry.[11]

The HD 220689 planetary system[11]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(years)		 Eccentricity Inclination Radius
b 1.2+0.22
−0.11 MJ		 3.433+0.065
−0.064		 6.23+0.15
−0.14		 0.053+0.06
−0.037		 71+13
−18 or 109+18
−13°		 —

References
  1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  3. Houk, Nancy; Smith-Moore, M. (1978). Michigan catalogue of two-dimensional spectral types for the HD stars. Vol. 4. Ann Arbor: Dept. of Astronomy, University of Michigan. Bibcode:1988mcts.book.....H.
  4. Barbato, D.; et al. (August 2018). "Exploring the realm of scaled solar system analogues with HARPS". Astronomy & Astrophysics. 615: 21. arXiv:1804.08329. Bibcode:2018A&A...615A.175B. doi:10.1051/0004-6361/201832791. S2CID 119099721. A175.
  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.
  6. Luck, R. Earle (March 2018). "Abundances in the Local Region. III. Southern F, G, and K Dwarfs". The Astronomical Journal. 155 (3): 31. Bibcode:2018AJ....155..111L. doi:10.3847/1538-3881/aaa9b5. S2CID 125765376. 111.
  7. "HD 220689". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-01-02.
  8. Mugrauer, M.; Ginski, C. (12 May 2015). "High-contrast imaging search for stellar and substellar companions of exoplanet host stars". Monthly Notices of the Royal Astronomical Society. 450 (3): 3127–3136. Bibcode:2015MNRAS.450.3127M. doi:10.1093/mnras/stv771. Retrieved 19 June 2020.
  9. "The astronomical magnitude scale". International Comet Quarterly. Retrieved 2020-12-31.
  10. Marmier, M.; et al. (2013). "The CORALIE survey for southern extrasolar planets XVII. New and updated long period and massive planets". Astronomy and Astrophysics. 551. A90. arXiv:1211.6444. Bibcode:2013A&A...551A..90M. doi:10.1051/0004-6361/201219639. S2CID 59467665.
  11. Xiao, Guang-Yao; Liu, Yu-Juan; et al. (March 2023). "The Masses of a Sample of Radial-Velocity Exoplanets with Astrometric Measurements". Research in Astronomy and Astrophysics. arXiv:2303.12409.
  • "HD 220689 b". The Extrasolar Planet Encyclopedia. Retrieved 2021-01-02.
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