HD 166724

HD 166724 is a star in the southern constellation of Corona Australis. It is invisible to the naked eye with an apparent visual magnitude of +9.33.[2] The star is located at a distance of 148 light-years (45 parsecs) from the Sun based on parallax, but is drifting closer with a radial velocity of −18 km/s.[1] It is predicted to come as close as 97.0 light-years in around 1.2 million years from now.[2] The star has an absolute magnitude of 6.20.[2]

HD 166724
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Corona Australis
Right ascension 18h 13m 59.67590s[1]
Declination –42° 34′ 31.3558″[1]
Apparent magnitude (V) +9.33[2]
Characteristics
Spectral type K0IV/V[3]
B−V color index 0.861±0.032[2]
Astrometry
Radial velocity (Rv)−17.51±0.20[1] km/s
Proper motion (μ) RA: +36.061 mas/yr[1]
Dec.: –80.180 mas/yr[1]
Parallax (π)22.0344 ± 0.0177 mas[1]
Distance148.0 ± 0.1 ly
(45.38 ± 0.04 pc)
Absolute magnitude (MV)6.20[2]
Details[4]
Mass0.81±0.02 M☉
Radius0.80+0.01
−0.02[5] R☉
Luminosity0.388±0.001[5] L☉
Surface gravity (log g)4.43±0.08 cgs
Temperature5,101+50
−41[5] K
Metallicity [Fe/H]−0.09±0.03 dex
Age4.0±3.8 Gyr
Other designations
CD–42° 13019, HD 166724, HIP 89354[6]
Database references
SIMBADdata
Exoplanet Archivedata
Extrasolar Planets
Encyclopaedia		data

The stellar classification of HD 166724 is K0IV/V,[3] showing blended features of a K-type main-sequence star with a more evolved subgiant star. It is slightly active with chromospheric activity being demonstrated by an emission peak in the Ca II K absorption line.[4] The age of the star is poorly constrained, but it is spinning slowly with a period of around 30 days.[4] It has 81% of the mass of the Sun and 80%[4] of the Sun's girth. The star is radiating 39%[5] of the luminosity of the Sun from its photosphere at an effective temperature of 5,101 K.[4]

Planetary system

From 1998 to 2012, the star was under observance from the CORALIE echelle spectrograph at La Silla Observatory. In 2012, a long-period, wide-orbiting exoplanet was deduced by radial velocity variations. This was published in November. The discoverers noted that HD 166724 b is among "the three most eccentric planets with a period larger than 5 years" alongside HD 98649 b and HD 219077 b; but unlike them, too dim as a candidate for direct imaging with current technology. The reason for this high orbital eccentricity is unknown.[4] In 2023, the inclination and true mass of HD 166724 b were determined via astrometry.[7]

The HD 166724 planetary system[7]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(years)		 Eccentricity Inclination Radius
b 3.8+0.65
−0.29 MJ		 5.17+0.38
−0.49		 13.0+1.4
−1.8		 0.729+0.018
−0.017		 68+15
−16 or 112+16
−15°		 —

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 (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 2, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1978mcts.book.....H
  4. 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.
  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. "HD 166724". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-03-21.
  7. Xiao, Guang-Yao; Liu, Yu-Juan; et al. (May 2023). "The Masses of a Sample of Radial-Velocity Exoplanets with Astrometric Measurements". Research in Astronomy and Astrophysics. 23 (5): 055022. arXiv:2303.12409. Bibcode:2023RAA....23e5022X. doi:10.1088/1674-4527/accb7e.
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