Mimosa (star)

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Template:Short description

Mimosa
Template:Location mark
Location of Mimosa (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Crux
Pronunciation Template:IPAc-en[1]
Right ascension Template:RA[2]
Declination Template:DEC[2]
Apparent magnitude (V) 1.25[3] (1.23 - 1.31)[4]
Characteristics
Spectral type B0.5 III[5]
U−B Template:Engvar −0.98[3]
B−V Template:Engvar −0.23[3]
Variable type β Cep[5]
Astrometry
Radial velocity (Rv)+15.6[6] km/s
Proper motion (μ) RA: −42.97[2] mas/yr
Dec.: −16.18[2] mas/yr
Parallax (π)11.71±0.98 mas[2]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)−3.92[7]
Orbit[8]
Primaryβ Crucis A
Companionβ Crucis B
Period (P)1828.0±2.5 days
Semi-major axis (a)8.7 AU
Eccentricity (e)0.38±0.09
Inclination (i)Script error: No such module "val".[9]°
Longitude of the node (Ω)Script error: No such module "val".[9]°
Periastron epoch (T)Script error: No such module "val".
Argument of periastron (ω)
(secondary)		293±9°
Details
A
MassScript error: No such module "val".[10] Template:Solar mass
RadiusScript error: No such module "val".[10] Template:Solar radius
LuminosityScript error: No such module "val".[11] Template:Solar luminosity
Surface gravity (log g)Script error: No such module "val".[5] cgs
Temperature28,840[11] K
Metallicity [Fe/H]−0.08[12] dex
RotationScript error: No such module "val". days[10]
Rotational velocity (v sin i)Script error: No such module "val".[10] km/s
AgeScript error: No such module "val".[10] Myr
B
MassScript error: No such module "val".[9] Template:Solar mass
Metallicity [Fe/H]{{{metal_fe2}}} dex
D
Mass0.78[9] Template:Solar mass
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Template:Odlist[13]
Database references
SIMBADdata

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Mimosa is the second-brightest object in the southern constellation of Crux (after Acrux), and the 20th-brightest star in the night sky. It has the Bayer designation β Crucis, which is Latinised to Beta Crucis and abbreviated Beta Cru or β Cru. Mimosa forms part of the prominent asterism called the Southern Cross. It is a triple star system.

Nomenclature

β Crucis (Latinised to Beta Crucis) is the system's Bayer designation. Although Mimosa is at roughly −60° declination, and therefore not visible north of 30° latitude, in the time of the ancient Greeks and Romans it was visible north of 40° due to the precession of equinoxes, and these civilizations regarded it as part of the constellation of Centaurus.[14]

It bore the traditional names Mimosa and the historical name Becrux Template:IPAc-en.[15] Mimosa, which is derived from the Latin for 'actor', may come from the flower of the same name.[16] Becrux is a modern contraction of the Bayer designation.[17] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[18] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[19] included a table of the first two batches of names approved by the WGSN; which included Mimosa for this star.

In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Cross, refers to an asterism consisting of Acrux, Mimosa, Gacrux, and δ Crucis.[20] Consequently, Mimosa itself is known as Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx).[21]

The Mursi people of Ethiopia call this star Thaadoi; it forms an asterism with δ Crucis (Imai), β Centauri (Waar), and α Centauri (Sholbi).[22]

Stellar system

File:Deep Crux wide field with fog.jpg
The constellation Crux

Based on parallax measurements, Mimosa is located at a distance of Script error: No such module "convert". from the Earth. In 1957, German astronomer Wulff-Dieter Heintz discovered that it is a spectroscopic binary with components that are too close together to resolve with a telescope.[23] The pair orbit each other every 5 years with an estimated separation that varies from 5.4 to 12.0 Astronomical Units.[8] The system is only 8 to 11 million years old.[5]

The primary, β Crucis A, has a stellar classification of B0.5 III,[5] classifying it as a blue giant that exausted the hydrogen supply at its core. Asteroseismic observations have measured its mass to be 15 times the Sun's mass, its radius to be between 7.3 and 8.9 times the Sun's radius and its age to be 11 million years—it is the most massive star with an age derived by this method.[10] Mimosa has sufficient mass to explode as a supernova, which might occur in roughly 6 million years.[16] The projected rotational velocity of this star is about 16 km s−1. Given that the inclination of the star's pole to the line of sight is 46°, the azimuthal rotational velocity is about 22 km s−1, resulting in a rotational period of 13 to 17 days.[10]

File:BetaCruLightCurve.png
A light curve for Beta Crucis, plotted from TESS data[24]

β Crucis A is a known β Cephei variable, although with an effective temperature of about 27,000 K it is at the hot edge of the instability strip where such stars are found. It has three different pulsation modes, none of which are radial. The periods of all three modes are in the range of 4.03–4.59 hours. The high temperature of the star's outer envelope is what gives the star the blue-white hue that is characteristic of B-type stars.[25] It is generating a strong stellar wind and is losing about Template:Solar mass per year, or the equivalent of the mass of the Sun every 100 million years. The wind is leaving the system with a velocity of 2,000 km s−1 or more.[5]

The secondary, β Crucis B, was thought to be a main sequence star with a stellar class of B2, based on the non-detection of its spectrum, and a mass of Template:Solar mass.[8] Later observations by the SPHERE imager have shown it to have a mass of only 1.9 times that of the Sun. Its orbit is close to edge-on, which is not consistent with the inclination of the primary star's rotation axis; however, the position angles of both suggest that they're aligned.[9]

In 2007, a second companion was announced, which may be a pre-main sequence star 0.78 times the Sun's mass. With the assigned designation of β Crucis D, the X-ray emission from this star was detected using the Chandra X-ray Observatory.[5] It is likely on the post-T Tauri stage of its evolution, as opposed to the primary star which has already left the main sequence. From its common proper motion, it was confirmed to be bound to the system by a 2023 study. While its orbit has not been measured, it probably has a high inclination, and its position angle is similar to that of the inner AB pair, suggesting that both orbits are mutually aligned.[9]

Two other stars, located at angular separations of 44 and 370 arcseconds, are likely optical companions that are not physically associated with the system. The β Crucis system may be a member of the Lower Centaurus–Crux sub-group of the Scorpius–Centaurus association.[26] This is a stellar association of stars that share a common origin.[5]

In culture

Mimosa is represented in the flags of Australia, New Zealand, Samoa and Papua New Guinea as one of five stars making up the Southern Cross.[5] It is also featured in the flag of Brazil, along with 26 other stars, each of which represents a state. Mimosa represents the State of Rio de Janeiro.[27]

A vessel named MV Becrux is used to export live cattle from Australia to customers in Asia. An episode dedicated to the vessel features in the television documentary series Mighty Ships.[28]

References

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  5. ↑ a b c d e f g h i Script error: No such module "Citation/CS1".
  6. ↑ Script error: No such module "citation/CS1".
  7. ↑ Script error: No such module "Citation/CS1".
  8. ↑ a b c Script error: No such module "Citation/CS1".
  9. ↑ a b c d e f Script error: No such module "Citation/CS1".
  10. ↑ a b c d e f g Script error: No such module "Citation/CS1".
  11. ↑ a b Script error: No such module "Citation/CS1".
  12. ↑ Script error: No such module "Citation/CS1".
  13. ↑ Template:Cite simbad
  14. ↑ Script error: No such module "citation/CS1".
  15. ↑ Script error: No such module "citation/CS1".
  16. ↑ a b Script error: No such module "citation/CS1".
  17. ↑ Script error: No such module "Citation/CS1".
  18. ↑ Script error: No such module "citation/CS1".
  19. ↑ Script error: No such module "citation/CS1".
  20. ↑ 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.
  21. ↑ 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.
  22. ↑ Script error: No such module "citation/CS1".
  23. ↑ Script error: No such module "Citation/CS1".
  24. ↑ Script error: No such module "citation/CS1".
  25. ↑ Script error: No such module "citation/CS1".
  26. ↑ Script error: No such module "Citation/CS1".
  27. ↑ Script error: No such module "citation/CS1".
  28. ↑ Script error: No such module "citation/CS1".

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External links

Template:Stars of Crux Template:Authority control Template:Sky

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