42 Draconis

42 Draconis / Fafnir

42 Draconis in optical light
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Draco
Right ascension	18^h 25^m 59.13696^s[1]
Declination	+65° 33′ 48.5313″[1]
Apparent magnitude (V)	4.82[2]
Characteristics
Spectral type	K1.5 III[2]
B−V color index	1.187
Astrometry
Radial velocity (Rv)	31.75±0.12[1] km/s
Proper motion (μ)	RA: +105.816 mas/yr[1] Dec.: −26.846 mas/yr[1]
Parallax (π)	11.056 ± 0.0841 mas[1]
Distance	295 ± 2 ly (90.4 ± 0.7 pc)
Absolute magnitude (MV)	–0.108
Details
Mass	0.879±0.050[2] M☉
Radius	21.25+0.41 −0.43[3] R☉
Luminosity	142.55±5.77[2] L☉
Surface gravity (log g)	1.86±0.04[4] cgs
Temperature	4,367±46[4] K
Metallicity [Fe/H]	−0.45±0.02[4] dex
Age	13.19±1.92[2] Gyr
Other designations
Fafnir, BD+65° 1271, GC 25212, HD 170693, HIP 90344, HR 6945, SAO 17888, PPM 20916, GCRV 10941
Database references
SIMBAD	data
Exoplanet Archive	data

42 Draconis (abbreviated 42 Dra), formally named Fafnir (/ˈfɑːvnər/ or /ˈfɑːfnɪər/),^[5][6] is a 5th magnitude K-type giant star located approximately 295 light years away in the constellation of Draco. As of 2009, an extrasolar planet (designated 42 Draconis b, later named Orbitar) is thought to be orbiting the star.

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 northern pole star of Venus.^[7]

Nomenclature

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.^[8] The process involved public nomination and voting for the new names.^[9] In December 2015, the IAU announced the winning names were Fafnir for this star and Orbitar for its planet.^[10]

The winning names were submitted by the Brevard Astronomical Society of Brevard County, Florida, United States.^[11] 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.^[12]

In 2016, the IAU organized a Working Group on Star Names (WGSN)^[13] to catalog and standardize proper names for stars. In its first bulletin of July 2016,^[14] 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.^[6]

Planetary system

42 Draconis b was discovered in 2009. It is an example of a super-Jupiter.^[15] However, the existence of this planet was questioned in 2021.^[16]

The 42 Draconis planetary system^[15]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b (Orbitar) (disputed)	≥3.88 ± 0.85 MJ	1.19 ± 0.01	479.1 ± 6.2	0.38 ± 0.06	—	—

See also

• HD 139357
• Iota Draconis
• Lists of exoplanets

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. 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.
3. Baines, Ellyn K.; Armstrong, J. Thomas; Schmitt, Henrique R.; Zavala, R. T.; Benson, James A.; Hutter, Donald J.; Tycner, Christopher; Van Belle, Gerard T. (2018), "Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer", The Astronomical Journal, 155 (1): 30, arXiv:1712.08109, Bibcode:2018AJ....155...30B, doi:10.3847/1538-3881/aa9d8b, S2CID 119427037.
4. Soubiran, C.; Creevey, O. L.; Lagarde, N.; Brouillet, N.; Jofré, P.; Casamiquela, L.; Heiter, U.; Aguilera-Gómez, C.; Vitali, S.; Worley, C.; de Brito Silva, D. (2024-02-01), "Gaia FGK benchmark stars: Fundamental Teff and log g of the third version", Astronomy and Astrophysics, 682: A145, Bibcode:2024A&A...682A.145S, doi:10.1051/0004-6361/202347136, ISSN 0004-6361 42 Draconis' database entry at VizieR.
5. "Fafnir". Merriam-Webster.com Dictionary. Merriam-Webster.
6. "IAU Catalog of Star Names". Retrieved 28 July 2016.
7. ""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.
8. NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. IAU.org. 9 July 2014
9. "NameExoWorlds The Process". Archived from the original on 2015-08-15. Retrieved 2015-09-05.
10. Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.
11. Website
12. "NameExoWorlds The Approved Names". Archived from the original on 2018-02-01. Retrieved 2015-12-18.
13. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
14. "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
15. 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.
16. 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.

External links

• Jean Schneider (2011). "Notes for star 42 Dra". Extrasolar Planets Encyclopaedia. Archived from the original on August 19, 2009. Retrieved 3 October 2011.