Gacrux

Coordinates: Sky map 12h 31m 09.95961s, −57° 06′ 47.5684″
Source: Wikipedia, the free encyclopedia.
γ Crucis
Location of Gacrux, γ Crucis (circled)
Observation data
J2000.0
Constellation Crux
Right ascension 12h 31m 09.960s[1]
Declination −57° 06′ 47.568″[1]
Apparent magnitude (V) +1.64[2]
Characteristics
Spectral type M3.5 III[3]
Apparent magnitude (J) −1.99
U−B color index +1.78[2]
B−V color index +1.59[2]
Variable type SRV[3]
Distance
88.6 ± 0.4 ly
(27.2 ± 0.1 pc)
Absolute magnitude (MV)−0.52[5]
Details
Mass1.5±0.3[6] M☉
Radius120[7] R☉
Luminosity758[7] L☉
Temperature3,689[7] K
LTT
 4752
Database references
SIMBADdata

Gacrux

apparent visual magnitude of +1.63,[9] it is the 26th brightest star in the night sky. A line from the two "Pointers", Alpha Centauri through Beta Centauri, leads to within 1° north of this star. Using parallax measurements made during the Hipparcos mission, it is located at a distance of 88.6 light-years (27.2 parsecs) from the Sun.[1] It is the nearest M-type red giant star to the Sun.[10]

Nomenclature

The constellation Crux, with the reddish star Gacrux at the top of the constellation (north) in this image

γ Crucis (Latinised to Gamma Crucis) is the star's

precession of equinoxes. Oddly, it lacked a traditional name. The astronomer Ptolemy counted it as part of the constellation of Centaurus.[11] The historical name Gacrux was coined by astronomer Elijah Hinsdale Burritt (1794-1838).[12][13] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[15]
included a table of the first two batches of names approved by the WGSN; which included Gacrux for this star.

In Chinese astronomy, Gamma Crucis was known as 十字架一 (Shí Zì Jià yī, English: the First Star of Cross.).[16]

The people of

Aranda and Luritja tribe around Hermannsburg, Central Australia named Iritjinga, "The Eagle-hawk", a quadrangular arrangement comprising Gacrux, Delta Crucis (Imai), Gamma Centauri (Muhilfain) and Delta Centauri (Ma Wei).[17]

Among Portuguese-speaking peoples, especially in Brazil, it is also named Rubídea (or Ruby-like), in reference to its colour.[18]

Physical properties

Pulsation Periods[3]
Period
(days) 		Amplitude
(magnitude)
12.1 0.016
15.1 0.027
16.5 0.016
54.8 0.026
82.7 0.015
104.9 0.016

Gacrux has the MK system

red giant branch rather than the asymptotic giant branch.[10] Although only 50% more massive than the Sun,[6] at this stage the star has expanded to 120[7] times the Sun's radius. It is radiating roughly 760[7] times the luminosity of the Sun from its expanded outer envelope. With an effective temperature of 3,689 K,[7] the colour of Gacrux is a prominent reddish-orange, well in keeping with its spectral classification. It is a semi-regular variable with multiple periods.[3]
(See table at left.)

The atmosphere of this star is enriched with barium, which is usually explained by the transfer of material from a more evolved companion. Typically this companion will subsequently become a white dwarf.[19] However, no such companion has yet been detected. A +6.4 magnitude companion star lies about 2 arcminutes away at a position angle of 128° from the main star, and can be observed with binoculars. But it is only an optical companion,[20] which is about 400 light years distant from Earth.

In culture

Gacrux, Gamma Crucis.

Gacrux is represented in the flags of

Southern Cross
.

It is also featured on the flag of Brazil, along with 26 other stars, each of which represents a state. Gacrux represents the State of Bahia.[21] The position of the line passing through Gacrux and Acrux marks the local meridian of the sky observed from Rio de Janeiro, at 8:30 am on 15 November 1889, the time when the republic was formally ratified.[22]

See also

References

  1. ^
    S2CID 18759600
  2. ^
    Bibcode:2002yCat.2237....0D
    .
  3. ^
    S2CID 15358380
  4. Bibcode:1999VeARI..35....1W
  5. Bibcode:1999A&A...343..222E
  6. ^
    doi:10.1093/mnras/254.1.27
  7. ^
    S2CID 119364960
    .
  8. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  9. Bibcode:1966CoLPL...4...99J
    .
  10. ^
    S2CID 15830460
  11. ^ Richard Hinckley Allen, "Star Names: Their Lore and Meaning", Dover Press, 1963.
  12. ^ "Gacrux/Gamma Crucis 2?". SolStation.com. Retrieved 2011-11-03.
  13. ^ Lesikar, Arnold V. "Gacrux". Dome Of The Sky. Archived from the original on 2011-09-28. Retrieved 2011-11-03.
  14. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  15. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  16. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived January 30, 2011, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  17. ISBN 978-0-521-36575-8
  18. ^ da Silva Oliveira, R., "Crux Australis: o Cruzeiro do Sul", Artigos: Planetario Movel Inflavel AsterDomus.
  19. Bibcode:1997A&A...319..881G
  20. University of Illinois
    , retrieved 2012-03-03
  21. ^ Astronomy of the Brazilian Flag, FOTW Flags Of The World website
  22. ^ Flag of Brazil, World Afropedia

External links


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