Astronomy:Alpha Persei

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Alpha Persei (Latinized from α Persei, abbreviated Alpha Per, α Per), formally named Mirfak[1] (pronounced /ˈmɜːrfæk/ or /ˈmɪərfæk/),[2] is the brightest star in the northern constellation of Perseus, outshining the constellation's best known star, Algol. Alpha Persei has an apparent visual magnitude of 1.8,[3] and is a circumpolar star when viewed from mid-northern latitudes.

Alpha Persei lies in the midst of a cluster of stars named as the eponymous Alpha Persei Cluster, or Melotte 20, which is easily visible in binoculars and includes many of the fainter stars in the constellation.[4] Determined distance using the trigonometric parallax, places the star 510 light-years (160 parsecs) from the Sun.[5]

Physical properties

The spectrum of Alpha Persei matches a stellar classification of F5 Ib,[6] revealing it to be a supergiant star in the latter stages of its evolution. It has a similar spectrum to Procyon A, though the latter star is much less luminous. This difference is highlighted in their spectral designation under the Yerkes spectral classification, published in 1943, where stars are ranked on luminosity as well as spectral typing. Procyon A is thus F5 IV,[7] a subgiant star. Since 1943, the spectrum of Alpha Persei has served as one of the stable anchor points by which other stars are classified.[8]

Alpha Persei has about 8.5[6] times the Sun's mass and has expanded to roughly 60[9] times the size of the Sun. It is radiating 5,000[4] times the luminosity of the Sun from its outer atmosphere at an effective temperature of 6,350 K,[6] which creates the yellow-white glow of an F-type star. In the Hertzsprung–Russell diagram, Alpha Persei lies inside the region in which Cepheid variables are found.[10] It is thus useful in the study of these stars, which are important standard candles.[4]

Unconfirmed exoplanet

In 2010 evidence was presented of a planet orbiting Mirfak. Radial velocity data from repeated observations of the star found a periodic variation with an amplitude of 70.8 ± 1.6 m/s. The proposed planet is estimated to have a minimum mass of approximately 6.6 times that of Jupiter and an orbital period of 128 days, but the claimed period may not be stable over 20 years so the exoplanet is considered doubtful. Rotational modulation due to surface activity such as starspots seem a more likely explanation of the radial velocity variations. In previous publications, periodic radial velocity variations of 87.7 or 77.7days have been reported but, these have not been confirmed.[11]

The Alpha Persei planetary system[11]
Companion
(in order from star)
Mass Semimajor axis
(AU)
Orbital period
(days)
Eccentricity Inclination Radius
b (unconfirmed) 6.6 ± 0.2 MJ 0.97? 128 ± 3 0.1 ± 0.04

Nomenclature

α Persei is the star's Bayer designation.

The star also bore the traditional names Mirfak and Algenib, which are Arabic in origin. The former, meaning 'Elbow' and also written Mirphak, Marfak or Mirzac, comes from the Arabic Mirfaq al-Thurayya, while Algenib, also spelt Algeneb, Elgenab, Gęnib, Chenib or Alchemb, is derived from الجنب al-janb, or الجانب al-jānib, 'the flank' or 'side'.[12][13] and was also the traditional name for Gamma Pegasi.[14] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[16] included a table of the first two batches of names approved by the WGSN; which included Mirfak for this star (Gamma Pegasi was given the name Algenib).

Hinali'i is the name of the star in Native Hawaiian astronomy. The name of the star is meant to commemorate a great tsunami and mark the beginning of the migration of Maui. According to some Hawaiian folklore, Hinali'i is the point of separation between the Earth and the sky that happened during the creation of the Milky Way.[17]

Assemani alluded to a title on the Borgian globe, Mughammid (مغمد), or Muliammir al Thurayya (ملىمرٱلطرى), the Concealer of the Pleiades, which, from its location, may be for this star.[12]

This star, together with γ Persei, δ Persei, η Persei, σ Persei and ψ Persei, has been called the Segment of Perseus.[12]

In Chinese, 天船 (Tiān Chuán), meaning Celestial Boat, refers to an asterism consisting of α Persei, γ Persei, δ Persei, η Persei, μ Persei, ψ Persei, 48 Persei and HD 27084. Consequently, the Chinese name for α Persei itself is 天船三 (Tiān Chuán sān, English: the Third Star of Celestial Boat.)[18]

References

  1. "IAU Catalog of Star Names". http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt. Retrieved 28 July 2016. 
  2. "Mirfak". Merriam-Webster Dictionary. https://www.merriam-webster.com/dictionary/Mirfak. 
  3. Mermilliod, J. C.; Mayor, M.; Udry, S. (July 2008), "Red giants in open clusters. XIV. Mean radial velocities for 1309 stars and 166 open clusters", Astronomy and Astrophysics 485 (1): 303–314, doi:10.1051/0004-6361:200809664, Bibcode2008A&A...485..303M 
  4. 4.0 4.1 4.2 Kaler, James B., "Mirfak", Stars (University of Illinois), http://stars.astro.illinois.edu/sow/mirfak.html, retrieved 2012-03-14 
  5. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode2007A&A...474..653V 
  6. 6.0 6.1 6.2 Lyubimkov, Leonid S. et al. (February 2010), "Accurate fundamental parameters for A-, F- and G-type Supergiants in the solar neighbourhood", Monthly Notices of the Royal Astronomical Society 402 (2): 1369–1379, doi:10.1111/j.1365-2966.2009.15979.x, Bibcode2010MNRAS.402.1369L 
  7. Ramanamurthy, G. (2007), Biographical Dictionary of Great Astronomers, Sura Books, p. 167, ISBN 978-81-7478-697-5 
  8. Garrison, R. F. (December 1993), "Anchor Points for the MK System of Spectral Classification", Bulletin of the American Astronomical Society 25: 1319, Bibcode1993AAS...183.1710G, http://www.astro.utoronto.ca/~garrison/mkstds.html, retrieved 2012-02-04 
  9. Nordgren, Tyler E. et al. (December 1999), "Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer", The Astronomical Journal 118 (6): 3032–3038, doi:10.1086/301114, Bibcode1999AJ....118.3032N, http://digitalcommons.wcupa.edu/cgi/viewcontent.cgi?article=1008&context=phys_facpub 
  10. Mérand, Antoine et al. (August 2007), "Extended Envelopes around Galactic Cepheids. III. Y Ophiuchi and α Persei from Near-Infrared Interferometry with CHARA/FLUOR", The Astrophysical Journal 664 (2): 1093–1101, doi:10.1086/518597, Bibcode2007ApJ...664.1093M 
  11. 11.0 11.1 Lee, B. -C; Han, I.; Park, M. -G.; Kim, K. -M.; Mkrtichian, D. E. (2012). "Detection of the 128-day radial velocity variations in the supergiant α Persei. Rotational modulations, pulsations, or a planet?". Astronomy and Astrophysics 543: A37. doi:10.1051/0004-6361/201118539. Bibcode2012A&A...543A..37L. 
  12. 12.0 12.1 12.2 Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications. p. 331. ISBN 978-0-486-21079-7. https://archive.org/details/starnamestheirlo00alle/page/331. Retrieved 2012-09-04. 
  13. Davis Jr., G. A. (October 1944), "The Pronunciations, Derivations, and Meanings of a Selected List of Star Names", Popular Astronomy 52 (3): 14, Bibcode1944PA.....52....8D 
  14. Pegasus
  15. "IAU Working Group on Star Names (WGSN)". https://www.iau.org/science/scientific_bodies/working_groups/280/. Retrieved 22 May 2016. 
  16. "Bulletin of the IAU Working Group on Star Names, No. 1". http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf. Retrieved 28 July 2016. 
  17. "Astronomer charts skies in Hawaiian", Mālamalama, the Magazine of the University of Hawai'i System 29 (2): 8, May 2004, http://www.hawaii.edu/malamalama/archive/downloads/0405_all.pdf, retrieved 2012-03-14 
  18. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 11 日

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