Beta Crucis
 Location of β Crucis (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Crux |
| Right ascension | 12h 47m 43.26877s |
| Declination | –59° 41′ 19.5792″ |
| Apparent magnitude (V) | 1.25(1.23 - 1.31) |
| Characteristics | |
| Spectral type | B0.5 III / B2V |
| U−B color index | –0.98 |
| B−V color index | –0.23 |
| Variable type | β Cep |
| Astrometry | |
| Radial velocity (Rv) | +15.6 km/s |
| Proper motion (μ) |
RA: –42.97 mas/yr Dec.: –16.18 mas/yr |
| Parallax (π) | 11.71 ± 0.98mas |
| Distance | 280 ± 20 ly (85 ± 7 pc) |
| Details | |
| A | |
| Mass | 16 M☉ |
| Radius | 8.4 ± 0.6 R☉ |
| Luminosity | 34,000 L☉ |
| Surface gravity (log g) | 3.6 ± 0.1 cgs |
| Temperature | 27,000 ± 1,000 K |
| Metallicity [Fe/H] | –0.08 dex |
| Rotation | 3.6 days |
| Rotational velocity (v sin i) | 35 km/s |
| Age | 8 to 11 million years |
| B | |
| Mass | 10 M☉ |
| Orbit | |
| Companion | β Cru B |
| Period (P) | 1828.0 ± 2.5 days |
| Semi-major axis (a) | 8.7 AU |
| Eccentricity (e) | 0.38 ± 0.09 |
| Periastron epoch (T) | 2449879 ± 38 |
|
Argument of periastron (ω) (secondary) |
293 ± 9° |
| Other designations | |
| Database references | |
| SIMBAD | data |
Beta Crucis (β Crucis, abbreviated Beta Cru, β Cru), also named Mimosa, is a binary star system; the second-brightest star in the constellation of Crux (after Alpha Crucis or Acrux) and the 19th-brightest star in the night sky. It forms part of the prominent asterism called the Southern Cross.
β Crucis (Latinised to Beta Crucis) is the system's Bayer designation. Although Beta Crucis 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.
It bore the traditional names Mimosa and the historical name Becrux. Mimosa, which is derived from the Latin for 'actor', may come from the flower of the same name.Becrux is a modern contraction of the Bayer designation. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 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 Beta Crucis, Gamma Crucis, Alpha Crucis and Delta Crucis. Consequently, Beta Crucis itself is known as 十字架三 (Shí Zì Jià sān, English: the Third Star of Cross.).
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