Arcturus
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Boötes |
Pronunciation
|
/ɑːrkˈtjʊərəs/ |
Right ascension | 14h 15m 39.7s[1] |
Declination | +19° 10′ 56″[1] |
Apparent magnitude (V) | −0.05[2] |
Characteristics | |
Spectral type | K1.5 III Fe−0.5[3] |
Apparent magnitude (J) | −2.25[2] |
U−B color index | +1.28[2] |
B−V color index | +1.23[2] |
R−I color index | +0.65[2] |
Note (category: variability): | H and K emission vary. |
Absolute magnitude (MV) | −0.30±0.02[6] |
Details | |
Gyr | |
GCTP 3242.00 | |
Database references | |
SIMBAD | data |
Data sources: | |
Arcturus is the brightest
Located relatively close at 36.7 light-years from the Sun, Arcturus is a red giant of spectral type K1.5III—an aging star around 7.1 billion years old that has used up its core hydrogen and evolved off the main sequence. It is about the same mass as the Sun, but has expanded to 25 times its size and is around 170 times as luminous. Its diameter is 35 million kilometres.
Nomenclature
The traditional name Arcturus is Latinised from the ancient Greek Ἀρκτοῦρος (Arktouros) and means "Guardian of the Bear",[9] ultimately from ἄρκτος (arktos), "bear"[10] and οὖρος (ouros), "watcher, guardian".[11]
The designation of Arcturus as α Boötis (Latinised to Alpha Boötis) was made by Johann Bayer in 1603. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN, which included Arcturus for α Boötis.[12][13]
Observation
With an
Arcturus is visible from both of
Ptolemy described Arcturus as subrufa ("slightly red"): it has a B-V color index of +1.23, roughly midway between Pollux (B-V +1.00) and Aldebaran (B-V +1.54).[15]
Physical characteristics
Based upon an annual
Arcturus is moving rapidly (122 km/s or 270,000 mph) relative to the Sun, and is now almost at its closest point to the Sun. Closest approach will happen in about 4,000 years, when the star will be a few hundredths of a light-year closer to Earth than it is today. (In antiquity, Arcturus was closer to the centre of the constellation.
With an absolute magnitude of −0.30, Arcturus is, together with Vega and Sirius, one of the most luminous stars in the Sun's neighborhood. It is about 110 times brighter than the Sun in visible light wavelengths, 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. With a near-infrared J band magnitude of −2.2, only Betelgeuse (−2.9) and R Doradus (−2.6) are brighter. The lower output in visible light is due to a lower efficacy as the star has a lower surface temperature than the Sun.
There have been suggestions that Arcturus might be a member of a binary system with a faint, cool companion, but no companion has been directly detected.[7] In the absence of a binary companion, the mass of Arcturus cannot be measured directly, but models suggest it is slightly greater than that of the Sun. Evolutionary matching to the observed physical parameters gives a mass of 1.08±0.06 M☉,[7] while the oxygen isotope ratio for a first dredge-up star gives a mass of 1.2 M☉.[21] Given the star's evolutionary state, it is expected to have undergone significant mass loss in the past.[22] The star displays magnetic activity that is heating the coronal structures, and it undergoes a solar-type magnetic cycle with a duration that is probably less than 14 years. A weak magnetic field has been detected in the photosphere with a strength of around half a gauss. The magnetic activity appears to lie along four latitudes and is rotationally modulated.[23]
Arcturus is estimated to be around 6 to 8.5 billion years old,[7] but there is some uncertainty about its evolutionary status.[24] Based upon the color characteristics of Arcturus, it is currently ascending the red-giant branch and will continue to do so until it accumulates a large enough degenerate helium core to ignite the helium flash.[7] It has likely exhausted the hydrogen from its core and is now in its active hydrogen shell burning phase. However, Charbonnel et al. (1998) placed it slightly above the horizontal branch, and suggested it has already completed the helium flash stage.[24]
Spectrum
Arcturus has
The spectrum shows a dramatic transition from
Astronomers term "metals" those elements with higher
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
Asteroseismological measurements allow direct calculation of the mass and radius, giving values of 0.8±0.2 M☉ and 27.9±3.4 R☉. This form of modelling is still relatively inaccurate, but a useful check on other models.[31]
Possible planetary system
Hipparcos satellite astrometry 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 humans' current ability to make it out. Recent results remain inconclusive, but do support the marginal Hipparcos detection of a binary companion.[32]
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
Mythology
One astronomical tradition associates Arcturus with the mythology around
Aratus in his Phaenomena said that the star Arcturus lay below the belt of Arctophylax, and according to Ptolemy in the Almagest it lay between his thighs.[35]
An alternative lore associates the name with the legend around Icarius, who gave the gift of wine to other men, but was murdered by them, because they had had no experience with intoxication and mistook the wine for poison. It is stated this Icarius, became Arcturus, while his dog, Maira, became Canicula (Procyon), although "Arcturus" here may be used in the sense of the constellation rather than the star.[36]
Cultural significance
As one of the brightest stars in the sky, Arcturus has been significant to observers since antiquity.
In ancient Mesopotamia, it was linked to the god Enlil, and also known as Shudun, "yoke",[19] or SHU-PA of unknown derivation in the Three Stars Each Babylonian star catalogues and later MUL.APIN around 1100 BC.[37]
In ancient Greek the star is found in ancient astronomical literature, e.g. Hesiod's Work and Days, circa 700 BC,[19] as well as Hipparchus's and Ptolemy's star catalogs. The folk-etymology connecting the star name with the bears (Greek: ἄρκτος, arktos) was probably invented much later.[citation needed] It fell out of use in favour of Arabic names until it was revived in the Renaissance.[38]
In Arabic, Arcturus is one of two stars called al-simāk "the uplifted ones" (the other is Spica). Arcturus is specified as السماك الرامح as-simāk ar-rāmiħ "the uplifted one of the lancer". The term Al Simak Al Ramih has appeared in Al Achsasi Al Mouakket catalogue (translated into Latin as Al Simak Lanceator).[39] This has been variously romanized in the past, leading to obsolete variants such as Aramec and Azimech. For example, the name Alramih is used in Geoffrey Chaucer's A Treatise on the Astrolabe (1391). Another Arabic name is Haris-el-sema, from حارس السماء ħāris al-samā’ "the keeper of heaven".[40][41][42] or حارس الشمال ħāris al-shamāl’ "the keeper of north".[43]
In Indian astronomy, Arcturus is called Swati or Svati (Devanagari स्वाति, Transliteration IAST svāti, svātī́), possibly 'su' + 'ati' ("great goer", in reference to its remoteness) meaning very beneficent. It has been referred to as "the real pearl" in Bhartṛhari's kāvyas.[44]
In
The
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 Hawaii. For a return trip to Tahiti the navigators could use Sirius, the zenith star of that island. Since 1976, the Polynesian Voyaging Society's Hōkūleʻa has crossed the Pacific Ocean many times under navigators who have incorporated this wayfinding technique in their non-instrument navigation.
Arcturus had several other names that described its significance to indigenous Polynesians. In the Society Islands, Arcturus, called Ana-tahua-taata-metua-te-tupu-mavae ("a pillar to stand by"), was one of the ten "pillars of the sky", bright stars that represented the ten heavens of the Tahitian afterlife.[48] In Hawaii, the pattern of Boötes was called Hoku-iwa, meaning "stars of the frigatebird". This constellation marked the path for Hawaiʻiloa on his return to Hawaii from the South Pacific Ocean.[49] The Hawaiians called Arcturus Hoku-leʻa.[50] It was equated to the Tuamotuan constellation Te Kiva, meaning "frigatebird", which could either represent the figure of Boötes or just Arcturus.[51] However, Arcturus may instead be the Tuamotuan star called Turu.[52] The Hawaiian name for Arcturus as a single star was likely Hoku-leʻa, which means "star of gladness", or "clear star".[53] In the Marquesas Islands, Arcturus was probably called Tau-tou and was the star that ruled the month approximating January. The Māori and Moriori called it Tautoru, a variant of the Marquesan name and a name shared with Orion's Belt.[54]
In Inuit astronomy, Arcturus is called the Old Man (Uttuqalualuk in Inuit languages) and The First Ones (Sivulliik in Inuit languages).[55]
The
Early-20th-century Armenian scientist
In popular culture
In Ancient Rome, the star's celestial activity was supposed to portend tempestuous weather, and a personification of the star acts as narrator of the prologue to Plautus' comedy Rudens (circa 211 BC).[58][59]
The Kāraṇḍavyūha Sūtra, compiled at the end of the 4th century or beginning of the 5th century, names one of Avalokiteśvara's meditative absorptions as "The face of Arcturus".[60]
One of the possible etymologies offered for the name "Arthur" assumes that it is derived from "Arcturus" and that the late 5th to early 6th-century figure on whom the myth of King Arthur is based was originally named for the star.[59][61][62][63][64][65]
In the
Arcturus's light was employed in the mechanism used to open the 1933 Chicago World's Fair. The star was chosen as it was thought that light from Arcturus had started its journey at about the time of the previous Chicago World's Fair in 1893 (at 36.7 light-years away, the light actually started in 1896).[67]
At the height of the American Civil War, President Abraham Lincoln observed Arcturus through a 9.6-inch refractor telescope when he visited the Naval Observatory in Washington, DC, in August, 1863.[68]
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Further reading
- Harper, Graham M.; et al. (June 2022), "The Wind Temperature and Mass-loss Rate of Arcturus (K1.5 III)", The Astrophysical Journal, 932 (1): 57, S2CID 249880096, 57.
- Isidoro-García, L.; et al. (January 2022), "Theoretical lifetimes and Stark broadening parameters for visible-infrared spectral lines of V I in Arcturus", Monthly Notices of the Royal Astronomical Society, 509 (3): 4538–4554, .
- Kushniruk, Iryna; Bensby, Thomas (November 2019), "Disentangling the Arcturus stream", Astronomy & Astrophysics, 631: A47, S2CID 202558933, A47.
- Wood, M. P.; et al. (February 2018), "Vanadium Transitions in the Spectrum of Arcturus", The Astrophysical Journal Supplement Series, 234 (2): 25, S2CID 119356096, 25.
- Küker, M.; Rüdiger, G. (January 2011), "Differential rotation and meridional flow of Arcturus", Astronomische Nachrichten, 332 (1): 83, .
- Lacour, S.; et al. (July 2008), "The limb-darkened Arcturus: imaging with the IOTA/IONIC interferometer", Astronomy and Astrophysics, 485 (2): 561–570, S2CID 18853087.
- Brown, Kevin I. T.; et al. (June 2008), "Long-Term Spectroscopic Monitoring of Arcturus", The Astrophysical Journal, 679 (2): 1531–1540, S2CID 121170557.
- Tarrant, N. J.; et al. (November 2007), "Asteroseismology of red giants: photometric observations of Arcturus by SMEI", Monthly Notices of the Royal Astronomical Society: Letters, 382 (1): L48–L52, S2CID 5666311.
- Brown, Kevin I. T. (February 2007), "Long-Term Spectroscopic and Precise Radial Velocity Monitoring of Arcturus", The Publications of the Astronomical Society of the Pacific, 119 (852): 237, S2CID 121637958.
- Gray, David F.; Brown, Kevin I. T. (August 2006), "The Rotation of Arcturus and Active Longitudes on Giant Stars", The Publications of the Astronomical Society of the Pacific, 118 (846): 1112–1118, S2CID 120918694.
- Cohen, Martin; et al. (June 2005), "Far-Infrared and Millimeter Continuum Studies of K Giants: α Bootis and α Tauri", The Astronomical Journal, 129 (6): 2836–2848, S2CID 119419198.
- Navarro, Julio F.; et al. (January 2004), "The Extragalactic Origin of the Arcturus Group", The Astrophysical Journal, 601 (1): L43–L46, S2CID 10638792.
- Retter, Alon; et al. (July 2003), "Oscillations in Arcturus from WIRE Photometry", The Astrophysical Journal, 591 (2): L151–L154, S2CID 119083930.
- Ryde, N.; et al. (November 2002), "Detection of Water Vapor in the Photosphere of Arcturus", The Astrophysical Journal, 580 (1): 447–458, S2CID 7672420.
- Griffin, R. E. M.; Lynas-Gray, A. E. (June 1999), "The Effective Temperature of Arcturus", The Astronomical Journal, 117 (6): 2998–3006, S2CID 120907426.
- Turner, Nils H.; et al. (May 1999), "Adaptive Optics Observations of Arcturus using the Mount Wilson 100 Inch Telescope", The Publications of the Astronomical Society of the Pacific, 111 (759): 556–558, S2CID 2441153.
- Griffin, R. F. (October 1998), "Arcturus as a double star", The Observatory, 118: 299–301, Bibcode:1998Obs...118..299G.
- Quirrenbach, A.; et al. (August 1996), "Angular diameter and limb darkening of Arcturus.", Astronomy and Astrophysics, 312: 160–166, Bibcode:1996A&A...312..160Q.
External links