Alpha Arae

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Template:Short description

Alpha Arae
File:Ara constellation map.png
α Arae (Choo) in the constellation Ara.
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Ara
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) 2.93[2] (2.76 to 2.90)[3]
Characteristics
Spectral type B2 Vne[4]
U−B Template:Engvar −0.72[2]
B−V Template:Engvar −0.16[2]
R−I Template:Engvar −0.24[3]
Variable type BE[5]
Astrometry
Radial velocity (Rv)0[6] km/s
Proper motion (μ) RA: −33.27 mas/yr[1]
Dec.: −67.22 mas/yr[1]
Parallax (π)12.20±0.85 mas[1]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)−1.72[7]
Details
Mass9.6[8] Template:Solar mass
Radius4.5[9] Template:Solar radius
Luminosity (bolometric)5,800[8] Template:Solar luminosity
Surface gravity (log g)3.99[9] cgs
Temperature18,044[9] K
Rotational velocity (v sin i)375[10] km/s
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Template:Odlist[11][12][13]
Database references
SIMBADdata

Script error: No such module "Check for unknown parameters".

Alpha Arae, is the second brightest star in the southern constellation of Ara. Its name is a Bayer designation that is Latinized from α Arae, and abbreviated Alpha Ara or α Ara. With an average apparent visual magnitude 2.93,[2] it is readily visible to the naked eye from the southern hemisphere. This star is close enough to the Earth that its distance can be estimated using parallax data collected during the Hipparcos mission. It is around Template:Convert away, with a 7% margin of error. The visual magnitude of the star is diminished by 0.10 magnitudes as a result of extinction from intervening gas and dust.[9]

Properties

File:Alpha Arae.jpg
Artistic impression of the disk around Alpha Arae
File:AlphaAraLightCurve.png
A blue-light light curve for Alpha Arae, adapted from Cuypers et al. (1989)[14]

Alpha Arae has a stellar classification of B2 Vne,[4] indicating that it is a massive B-type main sequence star. The 'n' notation in the suffix indicates that the absorption lines in the star's spectrum appear spread out and nebulous because of the Doppler effect from rapid rotation. The measured projected rotational velocity has been measured as high as 375 km s−1.[10] Meilland et al. (2007) estimate the pole of the star is inclined by 55° to the line of sight, yielding an equatorial azimuthal velocity of 470 km s−1. This is close to the critical velocity where the star would start to break up.[8] The rapid rotation is causing a pronounced equatorial bulge of about 2.4–2.7 times the polar radius.[9]

It is a Be star, as indicated by the 'e' notation in the star's classification. This indicates that emission lines are observed in the spectrum, which is coming from a disk of material ejected from the star because of its rapid rotation.[15] In 2003 and 2005, Alpha Arae was observed by infrared interferometry, using the MIDI and AMBER instruments at the VLT Interferometer. The results, published in 2005 and 2007, appear to show that Alpha Arae is surrounded by a dense equatorial disk of material in Keplerian (rather than uniform) rotation, and that it is losing mass by a polar stellar wind with a terminal velocity of approximately 1,000 km/s. There is also some evidence that Alpha Arae is orbited by a companion at 0.7 AU.[8][16]

This star is around 9.6 times as massive as the Sun,[8] and has an average of 4.5 times its radius.[9] It is 5,800 times as luminous as the Sun,[8] its energy emitted from its outer envelope at an effective temperature of 18,044 K.[9] This heat gives Alpha Arae the blue-white hue that is characteristic of B-type stars. It is a variable star with a magnitude that varies between 2.76m and 2.90m.[3][11] The General Catalogue of Variable Stars classifies it only as BE, indicating that it is a variable Be star but not obviously a Gamma Cassiopeiae variable.[5] The International Variable Star Index defines it as GCAS + LERI, showing both rapid periodic variation and slow irregular eruptions.[17]

Alpha Arae has a visual companion star, CCDM J17318-4953B, located approximately 50 arcseconds away along a position angle of 168°, with an apparent visual magnitude of about 11.[12] The two stars appear close to each other by coincidence and are not physically close in space.[3]

In culture

With β and σ Ara it forms the Chinese asterism Choo (pinyin: chǔ, Script error: No such module "Lang".), "pestle" in traditional Chinese astronomy. It was the second star of Choo (Script error: No such module "Lang".), but R. H. Allen used the name Choo for this star only.[13] Patrick Moore lists Choo as a proper name for this star in his star catalogue of the constellation Ara.[18] This name is also given the French spelling Tchou.Script error: No such module "Unsubst". There is another Choo in the constellation Pegasus.

In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Pestle, refers to an asterism consisting of α Arae, σ Arae and β Arae.[19] Consequently, the Chinese name for α Arae itself is Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx).[20]

See also

References

Template:Reflist

External links

Template:Stars of Ara

Template:Authority control

  1. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named aaa474_2_653
  2. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named aj84_1713
  3. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named bsc1
  4. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named houk1978
  5. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named gcvs2
  6. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named rgcrv
  7. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Anderson2012
  8. ↑ a b c d e f Cite error: Invalid <ref> tag; no text was provided for refs named m07
  9. ↑ a b c d e f g Cite error: Invalid <ref> tag; no text was provided for refs named aaa505_2_687
  10. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named coapa239_1
  11. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named sb0
  12. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named wds
  13. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named allen
  14. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Cuypers
  15. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named ESO
  16. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Chesneau_et_al_2005
  17. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named vsx
  18. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named moore1983
  19. ↑ Template:In lang 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, Template:ISBN.
  20. ↑ Template:In lang 香港太空館 - 研究資源 - 亮星中英對照表 Template:Webarchive, Hong Kong Space Museum. Accessed on line November 23, 2010.
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