It bore the traditional namesMimosa and the historical nameBecrux/ˈbeɪkrʌks/.[16]Mimosa, which is derived from theLatin for 'actor', may come fromthe flower of the same name.[17]Becrux is a modern contraction of the Bayer designation.[13] In 2016, theInternational Astronomical Union organized aWorking 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 includedMimosa for this star.
InChinese,十字架 (Shí Zì Jià), meaningCross, refers to an asterism consisting ofAcrux, Mimosa,Gacrux, andδ Crucis.[20] Consequently, Mimosa itself is known as十字架三 (Shí Zì Jià sān, English:the Third Star of Cross).[21]
Based onparallax measurements, Mimosa is located at a distance of 280 ly (86 pc) from theEarth. In 1957, German astronomerWulff-Dieter Heintz discovered that it is aspectroscopic binary with components that are too close together to resolve with atelescope.[23] The pair orbit each other every 5 years with an estimated separation that varies from 5.4 to 12.0Astronomical Units.[8] The system is only 8 to 11 million years old.[5]
The primary, β Crucis A, has astellar classification of B0.5 III,[5] classifying it as ablue giant that exausted thehydrogen supply at itscore.Asteroseismic observations have measured its mass to be 15 times theSun's mass, its radius to be between 7.3 and 8.9 times theSun'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 asupernova, which might occur in roughly 6 million years.[17] Theprojected rotational velocity of this star is about16 km s−1. Given that the inclination of the star's pole to the line of sight is 46°, theazimuthal rotational velocity is about22 km s−1, resulting in a rotational period of 13 to 17 days.[10]
β Crucis A is a knownβ Cephei variable, although with aneffective temperature of about 27,000 K it is at the hot edge of theinstability strip where such stars are found. It has three different pulsation modes, none of which areradial. 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 10−8M☉ per year, or the equivalent of themass 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 amain sequence star with a stellar class of B2, based on the non-detection of its spectrum, and a mass of 10 M☉.[8] Later observations by theSPHERE 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 theChandra 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 itscommon 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 370arcseconds, 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 theScorpius–Centaurus association.[26] This is astellar association of stars that share a common origin.[5]
A vessel namedMV Becrux is used to export live cattle from Australia to customers in Asia. An episode dedicated to the vessel features in the television documentary seriesMighty Ships.[28]
^abcJohnson, 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.
^Samus, N. N.; Durlevich, O. V.; 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.
^Evans, D. S. (June 20–24, 1966). "The Revision of the General Catalogue of Radial Velocities". In Batten, Alan Henry; Heard, John Frederick (eds.).Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30.Determination of Radial Velocities and Their Applications. Vol. 30. University of Toronto: International Astronomical Union. p. 57.Bibcode:1967IAUS...30...57E.
^abcAerts, 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.
^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.
^"The Colour of Stars".Australia Telescope, Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. December 21, 2004. Archived fromthe original on 2012-03-18. Retrieved2012-01-16.
