HD 162020

HD 162020 is a star in the southern constellation of Scorpius with a likely red dwarf companion. It has an apparent visual magnitude of 9.10,[2] which is too faint to be visible to the naked eye. The distance to this system is 102 light-years (31 parsecs) based on stellar parallax.[1] It is drifting closer to the Sun with a radial velocity of −27 km/s,[4] and is predicted to come to within ~18 light-years in 1.1 million years.[11]

HD 162020
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 17h 50m 38.35575s[1]
Declination −40° 19′ 06.0723″[1]
Apparent magnitude (V) 9.10[2]
Characteristics
Spectral type K3V[3]
B−V color index 0.964±0.066[2]
Astrometry
Radial velocity (Rv)−26.55±2.30[4] km/s
Proper motion (μ) RA: +19.412 mas/yr[1]
Dec.: −25.799 mas/yr[1]
Parallax (π)31.8624 ± 0.0622 mas[1]
Distance102.4 ± 0.2 ly
(31.38 ± 0.06 pc)
Absolute magnitude (MV)6.76[2]
Orbit[5]
Period (P)8.4282388+0.0000014
−0.0000026 d
Semi-major axis (a)0.0859±0.0010 AU
Eccentricity (e)0.28126±0.00057
Inclination (i)177.273+0.030
−0.027°
Longitude of the node (Ω)288.93+0.67
−0.73°
Periastron epoch (T)2457393.1874+0.0026
−0.0023
Argument of periastron (ω)
(secondary)		28.70+0.13
−0.12°
Semi-amplitude (K1)
(primary)		1.8112+0.0013
−0.0016 km/s
Details[5]
Mass0.797±0.042 M☉
Radius0.770±0.017 R☉
Luminosity0.413+0.056
−0.050 L☉
Surface gravity (log g)4.567±0.028 cgs
Temperature5,270+190
−180 K
Metallicity [Fe/H]−0.18+0.17
−0.19 dex
Rotational velocity (v sin i)1.9[6] km/s
Age5.7±4.7 Gyr[7]
3.1±2.7[8] Gyr
HD 162020 b
Mass0.39±0.02[9] M☉
Mass410.8+5.8
−5.3 MJup
Other designations
CD−40°11894, HD 162020, HIP 87330, PPM 763039[10]
Database references
SIMBADdata
Exoplanet Archivedata

This is an ordinary K-type main-sequence star with a stellar classification of K3V.[3] The age estimate is poorly constrained but it appears to have an intermediate age of several billion years. However, the activity level suggests a younger star; the rotation rate of the star may have been increased through synchronization with the companion, resulting in a higher than normal activity for its age.[6] X-ray emission has been detected from this star.[12]

HD 162020 has 74%[7] of the mass of the Sun and 73%[4] of the Sun's radius. The abundance of iron is roughly the same as the Sun, suggesting a similar metallicity. It is radiating just 25.8% of the luminosity of the Sun from its photosphere at an effective temperature of 4,801 K.[4] The star is spinning with a projected rotational velocity of 1.9 km/s.[6]

Companion

HD 162020 b is a companion, initially thought to be a brown dwarf, with a minimum mass of 15.0 MJ. At the time of discovery, the actual mass was undetermined since the orbital inclination was not known. This object orbits very close to the star at a distance of 0.075 AU with an eccentricity (ovalness) of 0.277. The object's distance from the star ranges from 0.054 to 0.096 AU. It has an extremely high semi-amplitude of 1,813 m/s. The discovery was announced on April 15, 2000 by the Geneva Extrasolar Planet Search Team.[13][6]

Despite the presence of this massive object in an eccentric orbit around the star, computer modelling done in 2017 (when the object was still thought to be a brown dwarf) showed it is still theoretically possible for an Earth-mass exoplanet to be occupying a dynamically-stable orbit in the habitable zone of this star.[14]

An astrometric measurement of this object's true mass was published in 2022 as part of Gaia DR3, revealing it to be 0.39 M☉ and thus likely a red dwarf star.[9] A full orbital solution was published in 2023.[5]

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. Torres, C. A. O.; et al. (December 2006). "Search for associations containing young stars (SACY). I. Sample and searching method". Astronomy and Astrophysics. 460 (3): 695–708. arXiv:astro-ph/0609258. Bibcode:2006A&A...460..695T. doi:10.1051/0004-6361:20065602. S2CID 16080025.
  4. 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.
  5. Unger, N.; Ségransan, D.; et al. (October 2023). "Exploring the Brown Dwarf Desert with Precision Radial Velocities and Gaia DR3 Astrometric Orbits". Astronomy & Astrophysics. arXiv:2310.02758.
  6. Udry, M.; et al. (2002). "The CORALIE survey for southern extra-solar planets VIII. The very low-mass companions of HD 141937, HD 162020, HD 168443, HD 202206: Brown dwarfs or "superplanets"?". Astronomy and Astrophysics. 390 (1): 267–279. arXiv:astro-ph/0202458. Bibcode:2002A&A...390..267U. doi:10.1051/0004-6361:20020685. S2CID 9389274.
  7. Delgado Mena, E.; et al. (April 2019). "Abundance to age ratios in the HARPS-GTO sample with Gaia DR2. Chemical clocks for a range of [Fe/H]". Astronomy & Astrophysics. 624: 24. arXiv:1902.02127. Bibcode:2019A&A...624A..78D. doi:10.1051/0004-6361/201834783. S2CID 90259810. A78.
  8. Bonfanti, A.; Ortolani, S.; Nascimbeni, V. (2016). "Age consistency between exoplanet hosts and field stars". Astronomy & Astrophysics. 585: A5, 14 pp. arXiv:1511.01744. Bibcode:2016A&A...585A...5B. doi:10.1051/0004-6361/201527297. S2CID 53971692.
  9. Gaia Collaboration; et al. (June 2023). "Gaia Data Release 3: Stellar multiplicity, a teaser for the hidden treasure". Astronomy & Astrophysics. 674: A34. arXiv:2206.05595. Bibcode:2023A&A...674A..34G. doi:10.1051/0004-6361/202243782.
  10. "HD 162020". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-04-02.
  11. Bailer-Jones, C.A.L.; et al. (2018). "New stellar encounters discovered in the second Gaia data release". Astronomy & Astrophysics. 616: A37. arXiv:1805.07581. Bibcode:2018A&A...616A..37B. doi:10.1051/0004-6361/201833456. S2CID 56269929.
  12. Poppenhaeger, K.; Schmitt, J. H. M. M. (July 2011). "A Correlation Between Host Star Activity and Planet Mass for Close-in Extrasolar Planets?". The Astrophysical Journal. 735 (1): 5. arXiv:1106.0189. Bibcode:2011ApJ...735...59P. doi:10.1088/0004-637X/735/1/59. S2CID 11359940. 59.
  13. "Exoplanets Galore!" (Press release). Garching, Germany: European Southern Observatory. April 15, 2000. Retrieved December 30, 2012.
  14. Agnew, Matthew T.; Maddison, Sarah T.; Thilliez, Elodie; Horner, Jonathan (2017). "Stable habitable zones of single Jovian planet systems". Monthly Notices of the Royal Astronomical Society. 471 (4): 4494–4507. arXiv:1706.05805. Bibcode:2017MNRAS.471.4494A. doi:10.1093/mnras/stx1449. S2CID 119227856.
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