HD 212771

HD 212771, also named Lionrock, is a solitary star in the southern zodiac constellation Aquarius. It has an apparent magnitude of 7.60,^[2] making it readily visible with binoculars but not the naked eye. Parallax measurements place the object at a distance of 364 light years,^[1] and is currently receding with a radial velocity of 15 km/s.^[5]

HD 212771 / Lionrock

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Aquarius
Right ascension	22h 27m 03.072s[1]
Declination	−17° 15′ 49.164″[1]
Apparent magnitude (V)	7.6±0.01[2]
Characteristics
Spectral type	G8 IV[3]
U−B color index	+0.54[4]
B−V color index	+0.88[2]
Astrometry
Radial velocity (Rv)	14.9±0.03[5] km/s
Proper motion (μ)	RA: −85.892 mas/yr[1] Dec.: −104.042 mas/yr[1]
Parallax (π)	8.9648 ± 0.0314 mas[1]
Distance	364 ± 1 ly (111.5 ± 0.4 pc)
Absolute magnitude (MV)	2.04[6]
Details[7]
Mass	1.42±0.07 M☉
Radius	4.44±0.13 R☉
Luminosity	11.67±0.57 L☉
Surface gravity (log g)	3.263±0.010 cgs
Temperature	5,065±75 K
Metallicity [Fe/H]	−0.09±0.01[8] dex
Age	2.90±0.47 Gyr
Other designations
BD−17°6526, HD 212771, HIP 110813, SAO 165086
Database references
SIMBAD	data
Exoplanet Archive	data

HD 212771 has a stellar classification of G8 IV,^[3] indicating that it is a subgiant evolving towards the red giant branch after being an F-type main-sequence star for 1.7 billion years.^[8] It has 142% the mass of the Sun and 4.4 times its radius. It radiates at 11.67 solar luminosities from its slightly enlarged photosphere at an effective temperature of 5,065 K,^[7] giving it a yellow-hue. Unlike most planetary hosts, HD 212771 is slightly metal deficient, and spins with a projected rotational velocity of about 2 km/s.^[8]

Planetary system

In 2010, a group of astronomers at the Keck Observatory surveyed several subgiant stars for extrasolar planets via Doppler spectroscopy They happened to find a massive Jupiter-like planet orbiting HD 212771.^[9]

HD 212771 is named Lionrock. The name was selected in the NameExoWorlds campaign by Hong Kong, during the 100th anniversary of the IAU. It is named after the Lion Rock. The planet is named Victoriapeak, after the Victoria Peak.^[10][11]

The HD 212771 planetary system^[12]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b / Victoriapeak	≥2.39±0.27 MJ	1.19±0.13	381±1	0.076±0.051	—	—

References

1. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
2. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (March 2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H. ISSN 0004-6361.
3. Houk, N.; Smith-Moore, M. (1988). Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Volume 4, Declinations -26°.0 to -12°.0. Vol. 4. Bibcode:1988mcts.book.....H.
4. Paunzen, E. (May 2022). "Catalogue of stars measured in the Geneva seven-colour photometric system". Astronomy & Astrophysics. 661: A89. arXiv:2111.04810. Bibcode:2022A&A...661A..89P. doi:10.1051/0004-6361/202142355. eISSN 1432-0746. ISSN 0004-6361.
5. Jofré, E.; Petrucci, R.; Saffe, C.; Saker, L.; Artur de la Villarmois, E.; Chavero, C.; Gómez, M.; Mauas, P. J. D. (26 January 2015). "Stellar parameters and chemical abundances of 223 evolved stars with and without planets". Astronomy & Astrophysics. 574: A50. arXiv:1410.6422. Bibcode:2015A&A...574A..50J. doi:10.1051/0004-6361/201424474. eISSN 1432-0746. ISSN 0004-6361.
6. Anderson, E.; Francis, Ch. (May 2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331–346. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. ISSN 1063-7737. S2CID 255204555.
7. Campante, Tiago L.; Corsaro, Enrico; Lund, Mikkel N.; Mosser, Benoît; Serenelli, Aldo; Veras, Dimitri; Adibekyan, Vardan; Antia, H. M.; Ball, Warrick; Basu, Sarbani; Bedding, Timothy R.; Bossini, Diego; Davies, Guy R.; Mena, Elisa Delgado; García, Rafael A. (October 2019). "TESS Asteroseismology of the Known Red-giant Host Stars HD 212771 and HD 203949". The Astrophysical Journal. 885 (1): 31. arXiv:1909.05961. Bibcode:2019ApJ...885...31C. doi:10.3847/1538-4357/ab44a8. ISSN 0004-637X.
8. Ghezzi, L. (June 2018), "Retired A Stars Revisited: An Updated Giant Planet Occurrence Rate as a Function of Stellar Metallicity and Mass", The Astrophysical Journal, 860 (2): 18, arXiv:1804.09082, Bibcode:2018ApJ...860..109G, doi:10.3847/1538-4357/aac37c, S2CID 118969017
9. Johnson, John Asher; Howard, Andrew W.; Bowler, Brendan P.; Henry, Gregory W.; Marcy, Geoffrey W.; Wright, Jason T.; Fischer, Debra A.; Isaacson, Howard (June 2010). "Retired A Stars and Their Companions. IV. Seven Jovian Exoplanets from Keck Observatory1". Publications of the Astronomical Society of the Pacific. 122 (892): 701–711. arXiv:1003.3445. Bibcode:2010PASP..122..701J. doi:10.1086/653809. eISSN 1538-3873. ISSN 0004-6280.
10. "Approved names". NameExoworlds. Retrieved 2020-01-02.
11. "International Astronomical Union | IAU". www.iau.org. Retrieved 2020-01-02.
12. Luhn, Jacob K.; Bastien, Fabienne A.; Wright, Jason T.; Johnson, John A.; Howard, Andrew W.; Isaacson, Howard (20 March 2019). "Retired A Stars and Their Companions. VIII. 15 New Planetary Signals around Subgiants and Transit Parameters for California Planet Search Planets with Subgiant Hosts". The Astronomical Journal. 157 (4): 149. arXiv:1811.03043. Bibcode:2019AJ....157..149L. doi:10.3847/1538-3881/aaf5d0. eISSN 1538-3881.