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42 Draconis

Coordinates: Sky map 18h 25m 59.1381s, +65° 33′ 48.530″
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(Redirected from Orbitar)
42 Draconis / Fafnir

42 Draconis in optical light
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Draco[1]
Right ascension 18h 25m 59.13696s[2]
Declination +65° 33′ 48.5313″[2]
Apparent magnitude (V) 4.82[3]
Characteristics
Spectral type K1.5 III[3]
B−V color index 1.18[1]
Astrometry
Radial velocity (Rv)31.75±0.12[2] km/s
Proper motion (μ) RA: +105.816 mas/yr[2]
Dec.: −26.846 mas/yr[2]
Parallax (π)11.056±0.0841 mas[2]
Distance295 ± 2 ly
(90.4 ± 0.7 pc)
Absolute magnitude (MV)−0.10[1]
Details[4]
Mass1.07±0.01 M☉
Radius19.78±0.17 R☉
Luminosity129.26+1.77
−1.05 L☉
Surface gravity (log g)1.9±0.02 cgs
Temperature4,449+11
−17 K
Metallicity [Fe/H]−0.43±0.01 dex
Rotation554±142 d
(~479 or ~690 d)
Rotational velocity (v sin i)1.76±0.45 km/s
Age9.49±1.76[5] Gyr
13.19±1.92[3] Gyr
Other designations
Fafnir, BD+65°1271, GC 25212, HD 170693, HIP 90344, HR 6945, SAO 17888, PPM 20916, GCRV 10941
Database references
SIMBADdata
Exoplanet Archivedata

42 Draconis (abbreviated 42 Dra), formally named Fafnir (/ˈfɑːvnər/ or /ˈfɑːfnɪər/),[6][7] is a 5th magnitude K-type giant star located approximately 295 light-years away in the constellation of Draco. An exoplanet (designated 42 Draconis b, later named Orbitar) was once thought to be orbiting the star, but its existence has since been refuted.[4]

Of spectral type K1.5III, the star has a mass similar to the Sun but with a radius 22 times greater. It is a metal-poor star with metallicity as low as 35% that of the Sun and its age is 9.49 billion years. It is the southern pole star of Venus.[8]

A 2019 study using Gaia DR2 data found a companion star to 42 Draconis, about half the Sun's mass, at a separation of 24 arcseconds, corresponding to 2220 AU.[9]

Nomenclature

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42 Draconis is the star's Flamsteed designation. Following its discovery the planet was designated 42 Draconis b. In July 2014 the International Astronomical Union launched NameExoWorlds, a process for giving proper names to certain exoplanets and their host stars.[10] The process involved public nomination and voting for the new names.[11] In December 2015, the IAU announced the winning names were Fafnir for this star and Orbitar for its planet.[12]

The winning names were submitted by the Brevard Astronomical Society of Brevard County, Florida, United States.[13] Fafnir was a Norse mythological dwarf who turned into a dragon, it is also the name of a fictional planet in Larry Niven's Known Space universe of similar description, ('Draco' is Latin for 'dragon'); Orbitar is a contrived word paying homage to the space launch and orbital operations of NASA.[14]

In 2016, the IAU organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. In its first bulletin of July 2016,[16] the WGSN explicitly recognized the names of exoplanets and their host stars approved by the Executive Committee Working Group Public Naming of Planets and Planetary Satellites, including the names of stars adopted during the 2015 NameExoWorlds campaign. This star is now so entered in the IAU Catalog of Star Names.[7]

Disproven planet

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"Orbitar" redirects here. For the video game weapon, see Kid Icarus: Uprising.

The discovery of 42 Draconis b (later named Orbitar) by the radial velocity method was announced in 2009. It was thought to be a super-Jupiter, with a minimum mass 4 times that of Jupiter, an orbital period of 479 days, and an eccentricity of 0.38.[5] However, the existence of this planet was questioned in a 2021 study by the same authors, which found that more recent radial velocity measurements were inconsistent with the proposed planetary orbit.[17] With further observations, by 2025 the planet hypothesis could be conclusively ruled out.[4] The star appears to have intrinsic radial velocity variations that mimic a planetary companion, as observed in other giant stars such as Gamma Draconis and Aldebaran.[4]

In a 2024 study, 42 Draconis b was listed as one of several doubtful planets around giant stars, along with other named planets around 14 Andromedae and 41 Lyncis.[18] With the 2025 refutation, it is now the second named exoplanet to be conclusively disproven, after Fomalhaut b (Dagon) in 2020.[19]

See also

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References

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  1. ^ a b c 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. XHIP record for this object at VizieR.
  2. ^ a b c d e 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.
  3. ^ a b c Ligi, R.; et al. (February 2016), "Radii, masses, and ages of 18 bright stars using interferometry and new estimations of exoplanetary parameters", Astronomy & Astrophysics, 586: 23, arXiv:1511.03197, Bibcode:2016A&A...586A..94L, doi:10.1051/0004-6361/201527054, S2CID 15941645, A94.
  4. ^ a b c d Hatzes, Artie P.; Perdelwitz, Volker; et al. (May 2025). "No Planet around the K Giant Star 42 Draconis". Astronomy & Astrophysics. arXiv:2505.05260.
  5. ^ a b Döllinger, M. P.; et al. (2009). "Planetary companion candidates around the K giant stars 42 Draconis and HD 139 357". Astronomy and Astrophysics. 499 (3): 935–942. arXiv:0903.3593. Bibcode:2009A&A...499..935D. doi:10.1051/0004-6361/200810837. S2CID 15677079.
  6. ^ "Fafnir". Merriam-Webster.com Dictionary. Merriam-Webster.
  7. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016.
  8. ^ ""Is Polaris the north star for all the other planets just like it is for Earth?" | Planetarium | University of Southern Maine". usm.maine.edu. Archived from the original on 2022-11-03. Retrieved 2022-07-12.
  9. ^ Mugrauer, M. (December 2019). "Search for stellar companions of exoplanet host stars by exploring the second ESA-Gaia data release". Monthly Notices of the Royal Astronomical Society. 490 (4): 5088–5102. Bibcode:2019MNRAS.490.5088M. doi:10.1093/mnras/stz2673.
  10. ^ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. IAU.org. 9 July 2014
  11. ^ "NameExoWorlds The Process". Archived from the original on 2015-08-15. Retrieved 2015-09-05.
  12. ^ Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.
  13. ^ Website
  14. ^ "NameExoWorlds The Approved Names". Archived from the original on 2018-02-01. Retrieved 2015-12-18.
  15. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  16. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  17. ^ Döllinger, M. P.; Hartmann, M. (September 2021). "A Sanity Check for Planets around Evolved Stars". The Astrophysical Journal Supplement Series. 256 (1): 10. Bibcode:2021ApJS..256...10D. doi:10.3847/1538-4365/ac081a. S2CID 237369556.
  18. ^ Spaeth, Dane; Reffert, Sabine; et al. (September 2024). "Non-radial oscillations mimicking a brown dwarf orbiting the cluster giant NGC 4349 No. 127". Astronomy & Astrophysics. 689: A91. arXiv:2407.21583. Bibcode:2024A&A...689A..91S. doi:10.1051/0004-6361/202450163.
  19. ^ Gáspár, András; Rieke, George H. (April 20, 2020). "New HST data and modeling reveal a massive planetesimal collision around Fomalhaut". PNAS. 117 (18): 9712–9722. arXiv:2004.08736. Bibcode:2020PNAS..117.9712G. doi:10.1073/pnas.1912506117. PMC 7211925. PMID 32312810.
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