BU Crucis
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 The star cluster NGC 4755. BU Crucis is the bright blue star just above and to the right of the centre. Credit: ESO/Y. Beletsky | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Crux |
| Right ascension | 12h 53m 37.62181s[1] |
| Declination | −60° 21′ 25.3912″[1] |
| Apparent magnitude (V) | 6.80 - 6.90[2] |
| Characteristics | |
| Spectral type | B2 Ia[3] |
| U−B color index | −0.67[4] |
| B−V color index | +0.20[4] |
| Variable type | Eclipsing?[2] |
| Astrometry | |
| Radial velocity (Rv) | −17.00[5] km/s |
| Proper motion (μ) | RA: −4.643[6] mas/yr Dec.: −1.050[6] mas/yr |
| Parallax (π) | 0.4441±0.0330 mas[6] |
| Distance | 7,300 ± 500 ly (2,300 ± 200 pc) |
| Absolute magnitude (MV) | −7.00[3] |
| Details | |
| Mass | 29.2[3] M☉ |
| Radius | 41.6[3] R☉ |
| Luminosity | 275,000[3] L☉ |
| Surface gravity (log g) | 2.65[3] cgs |
| Temperature | 20,600[3] K |
| Rotational velocity (v sin i) | 75[7] km/s |
| Age | 5.6[3] Myr |
| Other designations | |
| BU Cru, CD−59°4458, HD 111934, HIP 62913, 2MASS J12533761-6021254 | |
| Database references | |
| SIMBAD | data |
BU Crucis (HD 111934) is a variable star in the open cluster NGC 4755, which is also known as the Kappa Crucis Cluster or Jewel Box Cluster.
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BU Cru is one of the brightest members of the NGC 4775 open cluster, better known as the Jewel Box Cluster.[8] It forms the right end of the bar of the prominent letter "A" asterism at the centre of the cluster. The cluster is part of the larger Centaurus OB1 association and lies about 8,500 light years away.
The cluster, and BU Crucis itself, is just to the south-east of β Crucis, the lefthand star of the famous Southern Cross.
Properties
BU Crucis is a B2 bright supergiant (luminosity class Ia). It is 275,000 times the luminosity of the sun, partly due to its higher temperature over 20,000 K, and partly to being forty times larger than the sun. The κ Crucis cluster has a calculated age of 11.2 million years, and BU Crucis itself around five million years.[3]
