Astronomy:Mimosa (star)

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Short description: Star in the constellation Crux
Mimosa
Crux constellation map.svg
Red circle.svg
Location of Mimosa (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Crux
Pronunciation /mɪˈmoʊsə/[1]
Right ascension  12h 47m 43.26877s[2]
Declination −59° 41′ 19.5792″[2]
Apparent magnitude (V) 1.25[3] (1.23 - 1.31)[4]
Characteristics
Spectral type B0.5 III[5] / B2V[6]
U−B color index −0.98[3]
B−V color index −0.23[3]
Variable type β Cep[5]
Astrometry
Radial velocity (Rv)+15.6[7] km/s
Proper motion (μ) RA: −42.97[2] mas/yr
Dec.: −16.18[2] mas/yr
Parallax (π)11.71 ± 0.98[2] mas
Distance280 ± 20 ly
(85 ± 7 pc)
Absolute magnitude (MV)−3.92[8]
Orbit[6]
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
Periastron epoch (T)2,449,879±38 HJD
Argument of periastron (ω)
(secondary)		293±9°
Details
A
Mass16[5] M☉
Radius8.4±0.6[5] R☉
Luminosity34,000[5] L☉
Surface gravity (log g)3.6±0.1[5] cgs
Temperature27,000±1,000[5] K
Metallicity [Fe/H]−0.08[9] dex
Rotation3.6 days[5]
Rotational velocity (v sin i)35[5] km/s
Age8 to 11[5] Myr
B
Mass10[6] M☉
Other designations
Mimosa[1] Becrux,[10], β Crucis, CPD−59°4451, FK5 481, HD 111123, HIP 62434, HR 4853, SAO 240259[11]
Database references
SIMBADdata

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 binary star or a possible 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 Greece 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.[12]

It bore the traditional names Mimosa and the historical name Becrux /ˈbeɪkrʌks/.[13] Mimosa, which is derived from the Latin for 'actor', may come from the flower of the same name.[14] Becrux is a modern contraction of the Bayer designation.[10] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[16] included a table of the first two batches of names approved by the WGSN; which included Mimosa for this star.

In Chinese, 十字架 (Shí Zì Jià), meaning Cross, refers to an asterism consisting of Acrux, Mimosa, Gamma Crucis, and Delta Crucis.[17] Consequently, Mimosa itself is known as 十字架三 (Shí Zì Jià sān, English: the Third Star of Cross.).[18]

Stellar system

The constellation Crux

Based on parallax measurements, Mimosa is located at a distance of 280 ly (86 pc) 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.[19] The pair orbit each other every 5 years with an estimated separation that varies from 5.4 to 12.0 Astronomical Units.[6] The system is only 8 to 11 million years old.[5]

The primary, β Crucis A, is a massive star with about 16 times the Sun's mass. The projected rotational velocity of this star is about 35 km s−1. However, the orbital plane of the pair is only about 10°, which probably means the inclination of the star's pole is also likely to be low. This suggests that the azimuthal rotational velocity is quite high, at about 120 km s−1. With a radius of about 8.4 times the radius of the Sun, this would mean the star has a rotational period of only about 3.6 days.[5]

A light curve for Beta Crucis, plotted from TESS data[20]

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. Owing to the first application of polarimetry it is the heaviest star with an age determined by asteroseismology.[21] The star has a stellar classification of B0.5 III, with the luminosity class of 'III' indicating that this is a giant star that has exhausted the supply of hydrogen at its core. 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.[22] It is generating a strong stellar wind and is losing about 10−8 M☉ 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, may be a main sequence star with a stellar class of B2.[6] In 2007, a third companion was announced, which may be a low mass, pre-main sequence star. The X-ray emission from this star was detected using the Chandra X-ray Observatory. 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.[23] 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.[24]

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.[25]

References

  1. ↑ 1.0 1.1 "IAU Catalog of Star Names". http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V 
  3. ↑ 3.0 3.1 3.2 Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99): 99, Bibcode: 1966CoLPL...4...99J 
  4. ↑ Samus, N. N. et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S 1: 02025. Bibcode: 2009yCat....102025S. 
  5. ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 5.12 5.13 5.14 Cohen, David H. et al. (June 2008), "Chandra spectroscopy of the hot star βCrucis and the discovery of a pre-main-sequence companion", Monthly Notices of the Royal Astronomical Society 386 (4): 1855–1871, doi:10.1111/j.1365-2966.2008.13176.x, Bibcode: 2008MNRAS.386.1855C 
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Aerts, C. et al. (January 1998), "Evidence for binarity and multiperiodicity in the beta Cephei star beta Crucis", Astronomy and Astrophysics 329: 137–146, Bibcode: 1998A&A...329..137A 
  7. ↑ Evans, D. S. (June 20–24, 1966). "Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30". in Batten, Alan Henry; Heard, John Frederick. 30. University of Toronto: International Astronomical Union. 57. Bibcode: 1967IAUS...30...57E. 
  8. ↑ Kaltcheva, N. T.; Golev, V. K.; Moran, K. (2014), "Massive stellar content of the Galactic supershell GSH 305+01−24", Astronomy & Astrophysics 562: A69, doi:10.1051/0004-6361/201321454, Bibcode: 2014A&A...562A..69K 
  9. ↑ Kilian, J. (February 1994), "Chemical abundances in early B-type stars. 5: Metal abundances and LTE/NLTE comparison", Astronomy and Astrophysics 282 (3): 867–873, Bibcode: 1994A&A...282..867K 
  10. ↑ 10.0 10.1 Hoffleit, Dorrit; Jaschek, Carlos (1991). "The Bright star catalogue". New Haven. Bibcode: 1991bsc..book.....H. 
  11. ↑ "HD 93521". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+93521. 
  12. ↑ Wilkinson, Susan (2007), Mimosa: The Life and Times of the Ship That Sailed to Patagonia, Y Lolfa, pp. 56–57, ISBN 978-0-86243-952-1, https://books.google.com/books?id=OscUpqaBzPoC&pg=PA56 
  13. ↑ "Audio Pronunciation Guide". Simulation Curriculum Corp.. 2009. https://www.starrynighteducation.com/resources_pronunciation.html. 
  14. ↑ "MIMOSA (Beta Crucis)", Stars (university of Illinois), http://www.astro.uiuc.edu/~kaler/sow/mimosa.html, retrieved 2011-12-30 
  15. ↑ "IAU Working Group on Star Names (WGSN)". https://www.iau.org/science/scientific_bodies/working_groups/280/. 
  16. ↑ "Bulletin of the IAU Working Group on Star Names, No. 1". http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf. 
  17. ↑ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN:978-986-7332-25-7.
  18. ↑ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 , Hong Kong Space Museum. Accessed on line November 23, 2010.
  19. ↑ Heintz, W. D. (October 1957), "The radial velocity variation of beta Crucis", The Observatory 77: 200, Bibcode: 1957Obs....77..200H 
  20. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html. 
  21. ↑ Cotton, D. V.; Buzasi, D. B; Aerts, C.; Bailey, J. et al. (2021), "Polarimetric detection of non-radial oscillation modes in the β Cephei star β Crucis", Nature Astronomy 6: 154–164, doi:10.1038/s41550-021-01531-9, https://www.nature.com/articles/s41550-021-01531-9 
  22. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16 
  23. ↑ Rizzuto, Aaron; Ireland, Michael; Robertson, J. G. (October 2011), "Multidimensional Bayesian membership analysis of the Sco OB2 moving group", Monthly Notices of the Royal Astronomical Society 416 (4): 3108–3117, doi:10.1111/j.1365-2966.2011.19256.x, Bibcode: 2011MNRAS.416.3108R. 
  24. ↑ "Astronomy of the Brazilian Flag". FOTW Flags Of The World website. https://flagspot.net/flags/br_astro.html. 
  25. ↑ "Mighty Ships". DiscoveryHD.ca. CTV Global Media. http://www.discoveryhd.ca/shows/showdetails.aspx?sid=9955. 

External links

Coordinates: Sky map 12h 47m 43.26877s, −59° 41′ 19.5792″



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