Arcturus

Arcturus

Arcturus in the constellation of Boötes.
Observation data
Epoch J2000      Equinox J2000
Constellation Boötes
Pronunciation  /ɑrkˈtjʊərəs/
Right ascension 14h 15 m 39.7s[1]
Declination +19° 10' 56"[1]
Apparent magnitude (V) −0.04[1]
Characteristics
Spectral type K1.5IIIFe-0.5
Apparent magnitude (J) -2.25[1]
U−B color index 1.27
B−V color index 1.23
R−I color index 0.65
Variable type Variable star
Note (category: variability): H and K emission vary.
Astrometry
Radial velocity (Rv) +5 km/s
Proper motion (μ) RA: −1093.45 mas/yr
Dec.: −1999.40 mas/yr
Parallax (π) 88.98 ± 0.68 mas
Distance 36.7 ± 0.3 ly
(11.24 ± 0.09 pc)
Absolute magnitude (MV) −0.29
Details
Radius 25.7 ± 0.3[2] R☉
Luminosity 210 ± 10[3] L☉
Temperature 4,300[4] K
Metallicity 20–50% Sun
Rotational velocity (v sin i) <1.7 km/s
Other designations
Alramech, Abramech, α Boötis, 16 Boötes, HD 124897, HR 5340, BD+19°2777, GCTP 3242.00, GJ 541, LHS 48, and HIP 69673
Database references
SIMBAD data
Data sources:
Hipparcos Catalogue,
CCDM (2002),
Bright Star Catalogue (5th rev. ed.),
VizieR catalog entry

Arcturus ( /ɑrkˈtjʊərəs/; α Boo, α Boötis, Alpha Boötis) is the brightest star in the constellation Boötes. To the naked eye, orange-yellow Arcturus has a visual magnitude of −0.04, making it the brightest star in the northern hemisphere and the fourth brightest star in the night sky, after –1.46 magnitude Sirius, –0.86 magnitude Canopus and –0.27 magnitude Alpha Centauri. However, Alpha Centauri is a bright binary star, whose unresolved components to the naked eye are both fainter than Arcturus. This makes Arcturus the third brightest individual star, just ahead of Alpha Centauri A (α Cen A), whose visual magnitude is −0.01.

Arcturus is visible from both hemispheres in the sky, as it is located less than 20 degrees north of the celestial equator. The star culminates at midnight on about the 30th April, being visible during the northern spring or the southern autumn. From the northern hemisphere, an easy way to find Arcturus is to follow the arc of the handle of the Big Dipper. By continuing in this path, one can find Spica, "Arc to Arcturus, then speed to Spica." The star is also a member of the Local Interstellar Cloud.

Contents

Observational history

As one of the brightest stars in the sky, Arcturus has been significant to observers since antiquity. In Ancient Greece, the star's celestial activity was supposed to portend tempestuous weather. For citations, see Plautus Rudens prol. 71 and Lewis and Short's Latin Dictionary and its entry for Arcturus.

Prehistoric Polynesian navigators knew Arcturus as Hōkūleʻa, the "Star of Joy". Arcturus is the zenith star of the Hawaiian Islands. Using Hōkūleʻa and other stars, the Polynesians launched their double-hulled canoes from Tahiti and the Marquesas Islands. Traveling east and north they eventually crossed the equator and reached the latitude at which Arcturus would appear directly overhead in the summer night sky. Knowing they had arrived at the exact latitude of the island chain, they sailed due west on the trade winds to landfall. If Hōkūleʻa could be kept directly overhead, they landed on the southeastern shores of the Big Island of Hawaiʻi. For a return trip to Tahiti the navigators could use Sirius, the zenith star of that island. Since 1976, the Polynesian Voyaging Society's Hōkūle‘a has crossed the Pacific Ocean many times under navigators who have incorporated this wayfinding technique in their non-instrument navigation.

The Koori people of southeastern Australia knew Arcturus as Marpean-kurrk, and its appearance in the north signified the arrival of larvae of the wood-ant (a food item) in spring. The beginning of summer was marked by the star's setting with the sun in the west and the disappearance of the larvae. The star was also known as the mother of Djuit (Antares), and another star in Bootes, Weet-kurrk.[5]

Oscillations

As one of the brightest stars in the sky, Arcturus has been the subject of a number of studies in the emerging field of asteroseismology.

Belmonte et al. (1990) carried out a radial velocity (Doppler shift of spectral lines) study of the star in April and May 1988, which showed variability with a frequency of the order of a few microhertz, the highest peak corresponding to 4.3 μHz (2.7 days) with an amplitude of 60 ms−1, with a frequency separation of ~5 μHz. They suggested that the most plausible explanation for the variability of Arcturus is stellar oscillations.

It is believed that the surface of the star oscillates slightly, a common feature of red giant stars. In the case of Arcturus, this was an interesting discovery as it is known that the redder (more towards or within the M spectral class) a giant gets, the more variable it will be. Extreme cases like Mira undergo large swings over hundreds of days; Arcturus is not very red and is a borderline case between variability and stability with its short period and tiny range.

System

Arcturus is a type K1.5 IIIpe orange giant star—the letters "pe" stand for "peculiar emission," which indicates that the spectrum of light given off by the star is unusual and full of emission lines. This is not too uncommon in red giants, but Arcturus has a particularly strong case of the phenomenon. It is at least 110 times visually more luminous than the Sun, but this underestimates its strength as much of the "light" it gives off is in the infrared; total (bolometric) power output is about 180 times that of the Sun. The lower output in visible light is due to a lower efficacy as the star has a lower surface temperature than the Sun.

Arcturus is notable for its high proper motion, larger than any first magnitude star in the stellar neighborhood other than α Centauri. It is moving rapidly (122 km/s) relative to the solar system, and is now almost at its closest point to the Sun. Closest approach will happen in about 4000 years, when the star will be a few hundredths of a light year closer to Earth than it is today. Arcturus is thought to be an old disk star, and appears to be moving with a group of 52 other such stars, known as the Arcturus stream. Its mass is hard to exactly determine, but may be slightly larger than that of the Sun[6] (1.1-0.4+0.6 solar mass). Arcturus is likely to be considerably older than the Sun, and much like how the Sun will be in its red giant phase.

According to the Hipparcos satellite, Arcturus is 36.7 light years (11.3 parsecs) from Earth, relatively close in astronomical terms. Hipparcos also suggested that Arcturus is a binary star, with the companion about twenty times dimmer than the primary and orbiting close enough to be at the very limits of our current ability to make it out. Recent results remain inconclusive, but do support the marginal Hipparcos detection of a binary companion.[7]

Claims of a planetary system

In 1993, radial velocity measurements of Aldebaran, Arcturus and Pollux showed that Arcturus exhibited a long-period radial velocity oscillation, which could be interpreted as a substellar companion. This substellar object would be nearly 12 times the mass of Jupiter and be located roughly within Earth's orbital zone, at 1.1 Astronomical Units. However, all three stars surveyed showed similar oscillations yielding similar companion masses, and the authors concluded that the variation was likely to be intrinsic to the star rather than due to the gravitational effect of a companion. So far no substellar companion has been confirmed.[8]

Names and cultural significance

The name of the star derives from Ancient Greek Αρκτοῦρος (Arktouros) and means "Guardian of the Bear",[9] ultimately from ἄρκτος (arktos), "bear"[10] + οὖρος (ouros), "watcher, guardian".[11] This is a reference to it being the brightest star in the constellation Boötes (of which it forms the left foot), which is next to the Greater and Lesser Bears, Ursa Major and Ursa Minor.

In Arabic, it is one of two stars called al-simāk "the uplifted one", the other being Spica. Arcturus, then, is السماك الرامح as-simāk ar-rāmiħ "the uplifted one of the lancer". The term Al Simak Al Ramih was appeared in Al Achsasi Al Mouakket catalogue, which was translated into Latin as Al Simak Lanceator.[12] This has been variously romanized in the past, leading to obsolete variants such as Aramec and Azimech. The name Alramih is used in Geoffrey Chaucer's Treatise on the Astrolabe of 1391. Another Arabic name is Haris-el-sema, from حارس السماء ħāris al-samā’ "the keeper of heaven."[13][14][15] or حارس ألشمل ħāris al-shamāl’ "the keeper of north."[16]

In Chinese astronomy, Arcturus is called Da Jiao (大角, Great Horn, Pinyin: Dàjiǎo), because it is the brightest star in the Chinese constellation called Jiao Xiu (角宿, Pinyin: Jiǎo Xiǔ). And later, it become a part of Kang Xiu (亢宿, Pinyin: Kàng Xiǔ), which is also a Chinese constellation. In Inuit astronomy, Arcturus is called the Old Man (Uttuqalualuk in Inuit) and The First Ones (Sivulliik in Inuit). In Indian tradition, Arcturus is known as Svati, and is eponymous of one of the nakshatras (lunar mansions) of Hindu astrology. In Indonesia, Arcturus is called Bintang Biduk (Star of boat).

In the Harry Potter series, Arcturus is the middle name of the brother of Sirius Black, Regulus Arcturus Black, or R.A.B., as he is known.

Myths

This bright star is the subject of numerous ancient and modern myths.

See also

References

  1. ^ a b c d "Arcturus (HD 124897)". SIMBAD Astronomical Database. http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Arcturus. Retrieved 2011-11-27. 
  2. ^ Angular diameters of stars from the Mark III optical interferometer., MOZURKEWICH D.; ARMSTRONG J.T.; HINDSLEY R.B.; QUIRRENBACH A.; HUMMEL C.A.; HUTTER D.J.; JOHNSTON K.J.; HAJIAN A.R.; ELIAS II N.M.; BUSCHER D.F.; SIMON R.S., Astron. J., 126, 2502-2520 (2003)
  3. ^ Based upon the values for temperature and radius in combination with the Stefan–Boltzmann law.
  4. ^ Oxygen abundances in halo giants. V. Giants in the fairly metal-rich globular cluster M 71., SNEDEN C.; KRAFT R.P.; LANGER G.E.; PROSSER C.F.; SHETRONE M.D, Astron. J., 107, 1773-1785 (1994)
  5. ^ Mudrooroo (1994). Aboriginal mythology : an A-Z spanning the history of aboriginal mythology from the earliest legends to the present day. London: HarperCollins. p. 5. ISBN 1855383063. 
  6. ^ Ayres, T. R. & Johnson, H. R., ApJ, 1977, Vol 214, P410-417
  7. ^ Verhoelst, T.; Bordé, P. J.; Perrin, G.; Decin, L.; Eriksson, K.; Ridgway, S. T.; Schuller, P. A.; Traub, W. A. et al. (2005). "Is Arcturus a well-understood K giant?". Astronomy & Astrophysics 435: 289. arXiv:astro-ph/0501669. Bibcode 2005A&A...435..289V. doi:10.1051/0004-6361:20042356 , and see references therein.
  8. ^ Hatzes, A., Cochran, W. (August, 1993). "Long-period radial velocity variations in three K giants". The Astrophysical Journal 413 (1): 339–348. Bibcode 1993ApJ...413..339H. doi:10.1086/173002. 
  9. ^ Αρκτοῦρος, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
  10. ^ ἄρκτος, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
  11. ^ οὖρος, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
  12. ^ Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society 55: 429. Bibcode 1895MNRAS..55..429K. 
  13. ^ List of the 25 brightest stars, website of the Jordanian Astronomical Society, accessed March 28, 2007.
  14. ^ Richard Hinckley Allen, Star-names and their meanings (1936), p. 100-101.
  15. ^ Hans Wehr (J.M. Cowan ed.), A dictionary of modern written Arabic (1994).
  16. ^ Davis Jr., G. A., "The Pronunciations, Derivations, and Meanings of a Selected List of Star Names,"Popular Astronomy, Vol. LII, No. 3, Oct. 1944, p. 13.
  17. ^ "Century of Progress World's Fair, 1933-1934". University of Illinois-Chicago. 2008-01. http://collections.carli.illinois.edu/cdm4/item_viewer.php?CISOROOT=/uic_cop&CISOPTR=45&CISOBOX=1&REC=1. Retrieved 2009-09-06. 
  18. ^ Mudrooroo (1994). Aboriginal mythology : an A-Z spanning the history of aboriginal mythology from the earliest legends to the present day. London: HarperCollins. p. 5. ISBN 1855383063. 
  19. ^ Law of Time (Jose Arguelles’ official website)--Timeship Earth 2013—"Arcturus Remembered"—Transmission by “Pan Agent”:

External links

Coordinates: 14h 15m 39.7s, +19° 10′ 56″

Stars of Boötes
Bayer
Flamsteed
Nearby
  • Wolf 498
  • ξ
  • SDSS J1416+13