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| Observation data Epoch J2000.0 Equinox J2000.0 |
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|---|---|
| Constellation | Crux |
| Right ascension | 12h 31m 9.9s |
| Declination | -57° 06′ 48″ |
| Apparent magnitude (V) | 1.59 |
| Characteristics | |
| Spectral type | M4III |
| U-B color index | 1.77 |
| B-V color index | 1.60 |
| Astrometry | |
| Radial velocity (Rv) | +20.6 km/s |
| Proper motion (μ) | RA: 27.94 mas/yr Dec.: -264.33 mas/yr |
| Parallax (π) | 37.09 ± 0.67 mas |
| Distance | 88 ± 2 ly (27 ± 0.5 pc) |
| Absolute magnitude (MV) | -0.56 |
| Details | |
| Mass | 3 M☉ |
| Radius | 113 R☉ |
| Luminosity | 1,500 L☉ |
| Temperature | 3,400 K |
| Other designations | |
| Database references | |
| SIMBAD | data |
Gamma Crucis (γ Cru / γ Crucis), often named Gacrux, is a red giant star approximately 88 light-years away in the constellation of Crux. The star is the third-brightest star in Crux (the Southern Cross) and one of the brightest stars in the nighttime sky. A line from the two "Pointers", Alpha Centauri through Beta Centauri leads to within a few degrees of this star.
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Physical Properties
Gamma Crucis is a binary star, 88 light years distant from Earth. The main star is of apparent magnitude +1.6 and spectral classification M4 III. Its +6.4 magnitude white companion star (spectral classification A3) lies about 2 arcminutes away at an angle of 128 degrees from the main star, and can be observed with binoculars. But it is only an optical companion, who is about 400 light years distant from Earth. The colour of Gamma Crucis A is a prominent reddish-orange, well in keeping with its spectral classification.
Gacrux has evolved off of the main sequence to become a red giant star, and may even be evolving past the helium-burning stage. It is also semi-variable with a period of about 90 days. The atmosphere is enriched with barium, which is likely due to neutron emission from an undetected white dwarf companion.
Etymology
Since Gamma Crucis is at roughly −60° declination, it is only visible south of the Tropic of Cancer and likely never received an ancient traditional name. Thus, "Gacrux" is simply a combination of the "Ga" in Gamma plus Crux. It is known as 十字架一 ('First Star of the Cross') in Chinese.
See also
External links
- "Gacrux/Gamma Crucis 2". SolStation. Retrieved on 2008-09-10.
