HD 162020

HD 162020 is a star in the southern constellation of Scorpius with a brown 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 101 light years based on stellar parallax.[1] It is drifting closer to the Sun with a radial velocity of −27 km/s,[1] and is predicted to come to within ~18 light-years in 1.1 million years.[8]

HD 162020
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 17h 50m 38.35457s[1]
Declination −40° 19′ 06.0801″[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[1] km/s
Proper motion (μ) RA: +20.276[1] mas/yr
Dec.: −25.320[1] mas/yr
Parallax (π)32.4128 ± 0.0745[1] mas
Distance100.6 ± 0.2 ly
(30.85 ± 0.07 pc)
Absolute magnitude (MV)6.76[2]
Details
Mass0.741±0.019 M☉[4]
0.75±0.01[5] M☉
Radius0.73+0.02
−0.01 R☉[1]
0.68±0.01[5] R☉
Luminosity0.258±0.001 L☉[1]
0.22±0.01[5] L☉
Surface gravity (log g)4.76±0.25[6]
4.63±0.01[5] cgs
Temperature4,801+39
−52[1] K
Metallicity [Fe/H]0.01±0.11[6] dex
Rotational velocity (v sin i)1.9[6] km/s
Age5.7±4.7 Gyr[4]
3.1±2.7[5] Gyr
Other designations
CD−40°11894, HD 162020, HIP 87330, PPM 763039[7]
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.[9]

HD 162020 has 74%[4] of the mass of the Sun and 73%[1] 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.[1] The star is spinning with a projected rotational velocity of 1.9 km/s.[6]

Companion
HD 162020 b
Discovery
Discovered byUdry et al.
Discovery dateApril 15, 2000[10]
Doppler Spectroscopy
Orbital characteristics
00,751 AU (1.123×1011 km)
Eccentricity0.277 ± 0.02
8.428198 ± 0.000056 d
2451990.6768 ± 0.0050
28.40 ± 0.23
Semi-amplitude1,813 ± 4
Physical characteristics
Mass>15.0 MJ

    HD 162020 b is a brown dwarf companion with a minimum mass of at least 15.0 MJ. The actual mass is undetermined since the orbital inclination is not known. This planetar 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 km/s. The discovery was announced on April 15, 2000 by the Geneva Extrasolar Planet Search Team.[10][6]

    Despite the presence of this massive object in an eccentric orbit around the star, computer modelling shows it is still theoretically possible for an Earth-mass exoplanet to be occupying a dynamically-stable orbit in the habitable zone of this star.[11]

    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. 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. 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. A78.
    5. 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.
    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.
    7. "HD 162020". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-04-02.
    8. 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.
    9. 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. 59.
    10. "Exoplanets Galore!" (Press release). Garching, Germany: European Southern Observatory. April 15, 2000. Retrieved December 30, 2012.
    11. 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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