Alpha Fornacis

Alpha Fornacis (α Fornacis, abbreviated Alpha For, α For) is a binary star[12] system in the southern constellation of Fornax. It is the brightest star in the constellation and the only one brighter than magnitude 4.0. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 46 light-years (14 parsecs) distant from the Sun.

Alpha Fornacis

Location of α Fornacis (upper left).
Observation data
Epoch J2000      Equinox J2000
Constellation Fornax
Right ascension 3h 12m 04.5277s[1]
Declination –28° 59′ 15.425″[1]
Apparent magnitude (V) 3.85[2] (3.98/7.19)[3]
Characteristics
Spectral type F8IV[4]
U−B color index +0.082[5]
B−V color index +0.581[5]
Astrometry
Radial velocity (Rv)–20.5[6] km/s
Proper motion (μ) RA: 371.49[1] mas/yr
Dec.: 612.28[1] mas/yr
Parallax (π)71.4337 ± 0.1320 mas[7]
Distance45.66 ± 0.08 ly
(14.00 ± 0.03 pc)
Absolute magnitude (MV)3.08[8]
Orbit[3]
Period (P)269 yr
Semi-major axis (a)4.0″
Eccentricity (e)0.73
Inclination (i)81°
Longitude of the node (Ω)117°
Periastron epoch (T)1947
Argument of periastron (ω)
(secondary)		43°
Details
α For A
Mass1.33 ± 0.01[9] M☉
Radius2.04 ± 0.06[10] R☉
Luminosity4.87 ± 0.16[10] L☉
Surface gravity (log g)4.27[9] cgs
Temperature6,240[9] K
Metallicity [Fe/H]–0.20[9] dex
Rotational velocity (v sin i)3.9[10] km/s
Age2.9[11] Gyr
Other designations
α For, 12 Eridani, CD−29° 1177, GJ 127, HD 20010, HIP 14879, HR 963, SAO 168373, LTT 1512, 2MASS J03120443-2859156[2]
Database references
SIMBADdata

Its two components are designated Alpha Fornacis A (officially named Dalim /ˈdeɪlɪm/)[13] and B.

Nomenclature

α Fornacis (Latinised to Alpha Fornacis) is the system's Bayer designation. The designations of the two components as Alpha Fornacis A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[14] Formerly it was designated as the 12th of Eridanus (12 Eri) by Flamsteed.[15]

Indigenous Arabs had named both Alpha Eridani and Fomalhaut ظَلِيم al-ẓalīm, a local word for 'ostrich'. Later, Arabian astronomer would transfer the appellation to Theta Eridani, as they could not see those other stars from their location.[16] In recent times, Italian astronomer Giuseppe Piazzi applied it with the spelling Dalim to his "III 13" (= α For) in his Palermo Catalogue,[17][18][19] and Elijah Burritt labeled it Fornacis in his Atlas.[20]

In 2016, the IAU organized a Working Group on Star Names (WGSN)[21] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[22] It approved the name Dalim for the component Alpha Fornacis A on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[13]

Properties

Alpha Fornacis has a high proper motion[2] and the system displays an excess of infrared emission, which may indicate the presence of circumstellar material such as a debris disk.[23] The space velocity components of this star are (U, V, W) = (−35, +20, +30) km/s.[24] Approximately 350,000 years ago, Alpha Fornacis experienced a close encounter with the A-type main-sequence star Nu Horologii. The two came within an estimated 0.265 ly (0.081 pc) of each other, and both stars have debris disks.[25]

Alpha Fornacis A has a stellar classification of F8IV, where the luminosity class IV indicates this is a subgiant star that has just evolved off the main sequence.[26] It has 33% more mass than the Sun and is an estimated 2.9 billion years old.[9][11]

The secondary, Alpha Fornacis B, has been identified as a blue straggler, and has either accumulated material from, or merged with, a third star in the past. It is a strong source of X-rays and is 78% as massive as the Sun.[27]

References
  1. Perryman, M. A. C.; et al. (April 1997). "The HIPPARCOS Catalogue". Astronomy & Astrophysics. 323: L49–L52. Bibcode:1997A&A...323L..49P.
  2. "LHS 1515 -- High proper-motion Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2010-05-10.
  3. Hartkopf, W. I.; et al. (June 30, 2006), Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory, archived from the original on 2017-08-01, retrieved 2017-06-02.
  4. Favata, F.; Micela, G.; Sciortino, S. (July 1997). "The [Fe/H] distribution of a volume limited sample of solar-type stars and its implications for galactic chemical evolution". Astronomy and Astrophysics. 323: 809–818. Bibcode:1997A&A...323..809F.
  5. Rakos, K. D.; et al. (February 1982). "Photometric and astrometric observations of close visual binaries". Astronomy and Astrophysics Supplement Series. 47: 221–235. Bibcode:1982A&AS...47..221R.
  6. Evans, D. S. (June 20–24, 1966). "The Revision of the General Catalogue of Radial Velocities". In Batten, Alan Henry; Heard, John Frederick (eds.). Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30. University of Toronto: International Astronomical Union. Bibcode:1967IAUS...30...57E.
  7. 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.
  8. Holmberg, J.; et al. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191, S2CID 118577511.
  9. Santos, N. C.; Israelian, G.; Mayor, M. (July 2001). "The metal-rich nature of stars with planets". Astronomy and Astrophysics. 373 (3): 1019–1031. arXiv:astro-ph/0105216. Bibcode:2001A&A...373.1019S. doi:10.1051/0004-6361:20010648. S2CID 119347084.
  10. Bruntt, H.; et al. (July 2010), "Accurate fundamental parameters for 23 bright solar-type stars", Monthly Notices of the Royal Astronomical Society, 405 (3): 1907–1923, arXiv:1002.4268, Bibcode:2010MNRAS.405.1907B, doi:10.1111/j.1365-2966.2010.16575.x, S2CID 118495267
  11. Nordström, B.; Mayor, M.; Andersen, J.; Holmberg, J.; Pont, F.; Jørgensen, B. R.; Olsen, E. H.; Udry, S.; Mowlavi, N. (May 2004). "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs". Astronomy and Astrophysics. 418 (3): 989–1019. arXiv:astro-ph/0405198. Bibcode:2004A&A...418..989N. doi:10.1051/0004-6361:20035959. S2CID 11027621. See VizierR catalogue V/130.
  12. Söderhjelm, Staffan (January 1999). "Visual binary orbits and masses POST HIPPARCOS". Astronomy and Astrophysics. 341: 121–140. Bibcode:1999A&A...341..121S.
  13. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  14. Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  15. Wagman, Morton (2003). Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others. Blacksburg, Virginia: The McDonald & Woodward Publishing Company. Bibcode:2003lslm.book.....W. ISBN 978-0-939923-78-6.
  16. Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. pp. 36–37. ISBN 978-1-931559-44-7.
  17. Piazzi, G, ed. (1814). Praecipuarum Stellarum Inerrantium Positiones Mediae Ineunte Saeculo XIX: ex Observationibus Habitis in Specula Panormitana ab anno 1792 ad annum 1813. Palermo. p. 21.
  18. Kunitzsch, P. (1959). Arabische Sternnamen in Europa. Wiesbaden: Otto Harrassowitz. p. 155.
  19. Laffitte, R. (2005). Héritages arabes: Des noms arabes pour les étoiles (2éme revue et corrigée ed.). Paris: Librairie Orientaliste Paul Geunthner / Les Cahiers de l'Orient. p. 229.
  20. Burritt, E. H. (1835). Atlas, Designed to Illustrate the Geography of the Heavens (new ed.). New York: F. J. Huntington. plate III.
  21. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  22. "WG Triennial Report (2015–2018) – Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  23. Oudmaijer, Rene D.; et al. (December 1992). "SAO stars with infrared excess in the IRAS Point Source Catalog". Astronomy and Astrophysics Supplement Series. 96 (3): 625–643. Bibcode:1992A&AS...96..625O.
  24. Gliese, W. (1969). "Catalogue of Nearby Stars". Veröffentlichungen des Astronomischen Rechen-Instituts Heidelberg. 22: 1. Bibcode:1969VeARI..22....1G.
  25. Deltorn, J.-M.; Kalas, P. (2001). "Search for Nemesis Encounters with Vega, ε Eridani, and Fomalhaut". In Ray Jayawardhana; Thomas Greene (eds.). Young Stars Near Earth: Progress and Prospects. ASP Conference Series. Vol. 244. San Francisco: Astronomical Society of the Pacific. p. 227. arXiv:astro-ph/0105284. Bibcode:2001ASPC..244..227D. ISBN 1-58381-082-X.
  26. Lopez, Bruno; Schneider, Jean; Danchi, William C. (July 2005). "Can Life Develop in the Expanded Habitable Zones around Red Giant Stars?". The Astrophysical Journal. 627 (2): 974–985. arXiv:astro-ph/0503520. Bibcode:2005ApJ...627..974L. doi:10.1086/430416. S2CID 17075384.
  27. Fuhrmann, K.; Chini, R. (August 2015), "Multiplicity among F-type Stars. II", The Astrophysical Journal, 809 (1): 19, Bibcode:2015ApJ...809..107F, doi:10.1088/0004-637X/809/1/107, 107.
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