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8 Ursae Minoris

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8 Ursae Minoris / Baekdu
Observation data
Epoch J2000      Equinox
Constellation Ursa Minor
Right ascension 14h 56m 48.35230s[1]
Declination 74° 54′ 03.3212″[1]
Apparent magnitude (V) 6.835[2]
Characteristics
Evolutionary stage Red clump[3]
Spectral type G8III[4]
Astrometry
Radial velocity (Rv)−9.55[1] km/s
Proper motion (μ) RA:  13.139[1] mas/yr
Dec.:  3.578[1] mas/yr
Parallax (π)6.1278 ± 0.0142 mas[1]
Distance532 ± 1 ly
(163.2 ± 0.4 pc)
Absolute magnitude (MV) 0.82[5]
Details
Mass1.51±0.06[3] M☉
Radius10.73±0.14[3] R☉
Luminosity52.9±5.9[3] L☉
Surface gravity (log g)2.53[1] cgs
Temperature4,847±100[3] K
Metallicity [Fe/H]−0.03±0.02[6] dex
Rotation100–200 d[3]
Age377[1] Myr
Other designations
Baekdu, HD 133086, HIP 73136, BD 75 547, 2MASS J14564834 7454032, WDS J14568 7454A, Gaia DR3 1700658653802527104[7]
Database references
SIMBADdata

8 Ursae Minoris is a 7th-magnitude red clump star in Ursa Minor. The star is unusually rich in lithium, with an abundance of A = 2.0±0.2 dex.[8][9][3]

In the 2019 NameExoWorlds competition, the star was assigned to contestants in South Korea. It was named Baekdu after Paektu Mountain, the tallest mountain in North Korea.[10][11]

Planetary system

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One exoplanet was discovered in 2015 by the Bohyunsan Optical Astronomy Observatory.[12] It has a tight 93-day orbit at a distance of about 0.5 AU, which is unusually close for a giant host star — it should have been consumed during a previous expansion to 0.7 AU.[13][14] It is officially named Halla after Hallasan, the tallest mountain in South Korea.[10][14] There is also a stellar activity cycle of 65 days, and possibly a second companion orbiting at a distance of at least 5 AU.[3]

The 8 Ursae Minoris planetary system
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b / Halla ≥ 1.65±0.06 MJ 0.462±0.006 93.31±0.06 0.062±0.18 — —

A 2023 study suggests that 8 Ursae Minoris was initially a binary star with star masses of 1.23 and 0.86 M☉. When the heavier star reached the end of the main sequence about 4.2–5.6 Gyr, it expanded until it dumped all of its mass onto the secondary and became a helium white dwarf. The other star eventually engulfed this white dwarf at around 8.6 Gyr, causing helium burning to start prematurely and forming the star that we know today. The planet may have survived the episode as a former circumbinary planet, or it may have formed from material ejected during the stellar merger. 8 Ursae Minoris is now in the red clump stage, and the planet will eventually be engulfed once it reaches the asymptotic giant branch.[3]

Research published in May 2024 used three different methods to determine the age of 8 Ursae Minoris and came up with an estimate of 1.9–3.5 Gyr. This is much younger than the approximately 9 Gyr age required for the theory that the presence of the planet so close to 8 Ursae Minoris can be explained by a stellar merger. The researchers also estimated a new mass for the star of 1.7 solar masses, making it more compact. This would allow for the planet to orbit slightly further from the star, making its existence less of a mystery.[15]

References

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  1. ^ a b c d e f g h 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. ^ 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. ^ a b c d e f g h i Hon, Marc; Huber, Daniel; Rui, Nicholas Z.; Fuller, Jim; Veras, Dimitri; Kuszlewicz, James S.; Kochukhov, Oleg; Stokholm, Amalie; Rørsted, Jakob Lysgaard; Yıldız, Mutlu; Orhan, Zeynep Çelik; Örtel, Sibel; Jiang, Chen; Hey, Daniel R.; Isaacson, Howard; Zhang, Jingwen; Vrard, Mathieu; Stassun, Keivan G.; Shappee, Benjamin J.; Tayar, Jamie; Claytor, Zachary R.; Beard, Corey; Bedding, Timothy R.; Brinkman, Casey; Campante, Tiago L.; Chaplin, William J.; Chontos, Ashley; Giacalone, Steven; Holcomb, Rae; Howard, Andrew W.; Lubin, Jack; MacDougall, Mason; Montet, Benjamin T.; Murphy, Joseph M. A.; Ong, Joel; Pidhorodetska, Daria; Polanski, Alex S.; Rice, Malena; Stello, Dennis; Tyler, Dakotah; Van Zandt, Judah; Weiss, Lauren M. (2023). "A close-in giant planet escapes engulfment by its star". Nature. 618 (7967): 917–920. arXiv:2306.15877. Bibcode:2023Natur.618..917H. doi:10.1038/s41586-023-06029-0. PMID 37380688. S2CID 259275140.
  4. ^ Abt, Helmut A. (2004). "Spectral Classification of Stars in A Supplement to the Bright Star Catalogue". The Astrophysical Journal Supplement Series. 155 (1): 175–177. Bibcode:2004ApJS..155..175A. doi:10.1086/423803.
  5. ^ 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.
  6. ^ Goda, Shohei; Matsuo, Taro (2019). "Multiple Populations of Extrasolar Gas Giants". The Astrophysical Journal. 876 (1): 23. arXiv:1903.05317. Bibcode:2019ApJ...876...23G. doi:10.3847/1538-4357/ab0f9c. S2CID 119096144.
  7. ^ "* 8 UMi". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2023-06-29.
  8. ^ Kumar, Yerra Bharat; Reddy, Bacham E.; Lambert, David L. (20 March 2011). "Origin of Lithium Enrichment in K Giants". The Astrophysical Journal. 730 (1): L12. arXiv:1102.2299. Bibcode:2011ApJ...730L..12K. doi:10.1088/2041-8205/730/1/L12. S2CID 118383042.
  9. ^ Gao, Jun; Zhu, Chunhua; Yu, Jinlong; Liu, Helei; Lu, Xizhen; Shi, Jianrong; Lü, Guoliang (December 2022). "Li-rich and super Li-rich giants produced by element diffusion". Astronomy & Astrophysics. 668: A126. arXiv:2210.13152. Bibcode:2022A&A...668A.126G. doi:10.1051/0004-6361/202243871. S2CID 253098085.
  10. ^ a b "Approved names". NameExoworlds. Archived from the original on 2019-12-19. Retrieved 2020-01-02.
  11. ^ "International Astronomical Union | IAU". www.iau.org. Archived from the original on 2022-12-05. Retrieved 2020-01-02.
  12. ^ Lee, B.-C.; Park, M.-G.; Lee, S.-M.; Jeong, G.; Oh, H.-I.; Han, I.; Lee, J. W.; Lee, C.-U.; Kim, S.-L.; Kim, K.-M. (December 2015). "Search for exoplanet around northern circumpolar stars: Four planets around HD 11755, HD 12648, HD 24064, and 8 Ursae Minoris⋆". Astronomy & Astrophysics. 584: A79. arXiv:1509.09012. Bibcode:2015A&A...584A..79L. doi:10.1051/0004-6361/201527076. S2CID 119294400.
  13. ^ Timmer, John (28 June 2023). "Planet that shouldn't exist found". Ars Technica. Archived from the original on 7 November 2023. Retrieved 29 June 2023.
  14. ^ a b Strickland, Ashley (2023-06-28). "Scientists spot a planet that shouldn't exist". CNN. Archived from the original on 2023-08-17. Retrieved 2023-06-29.
  15. ^ Hensley, Kerry (2024-05-10). "Astronomers Reopen the Mystery of a Planet That Shouldn't Exist". AAS Nova. Archived from the original on 2024-05-25. Retrieved 2024-05-25.
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