Gacrux
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Star Gacrux (γ Crucis) |
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Observation dates equinox : J2000.0 , epoch : J2000.0 |
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| Constellation | southern Cross | ||||||||||||||||||
| Right ascension | 12 h 31 m 10 s | ||||||||||||||||||
| declination | -57 ° 06 ′ 48 ″ | ||||||||||||||||||
| Apparent brightness | 1.59 likes | ||||||||||||||||||
| Typing | |||||||||||||||||||
| B − V color index | +1.59 | ||||||||||||||||||
| U − B color index | +1.78 | ||||||||||||||||||
| R − I index | +1.41 | ||||||||||||||||||
| Spectral class | M3.5 III | ||||||||||||||||||
| Variable star type | semi-regular | ||||||||||||||||||
| Astrometry | |||||||||||||||||||
| Radial velocity | (+21.0 ± 0.1) km / s | ||||||||||||||||||
| parallax | (36.83 ± 0.18) mas | ||||||||||||||||||
| distance | (88.6 ± 0.4) ly (27.2 ± 0.1) pc |
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| Visual absolute brightness M vis | −0.6 mag | ||||||||||||||||||
| Proper movement | |||||||||||||||||||
| Rec. Share: | (+28.23 ± 0.14) mas / a | ||||||||||||||||||
| Dec. portion: | (−265.08 ± 0.12) mas / a | ||||||||||||||||||
| Physical Properties | |||||||||||||||||||
| Dimensions | 3 M ☉ | ||||||||||||||||||
| radius | approx. 110 R ☉ | ||||||||||||||||||
| Luminosity |
1500 L ☉ |
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| Effective temperature | 3400 K | ||||||||||||||||||
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Other names and catalog entries |
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Gacrux ( portmanteau of "Gamma" and "Crux") is the name of the star γ Crucis (Gamma Crucis) in the constellation of the Southern Cross , whose dritthellster star he is. Gacrux is only visible from the southern hemisphere. Its name is likely to have been introduced by the astronomer Elijah Hinsdale Burritt (1794–1838) by contracting his Bayer name .
With an apparent magnitude of 1.59 mag, Gacrux is the 25th brightest star in the sky. Gacrux is a red giant belonging to the spectral class M3.5. Its distance from the sun is about 90 light years ( Hipparcos database), its absolute brightness about −0.6 mag. The dimensions of the red giant are estimated to be about 3 solar masses, 110 solar diameters and (taking into account its infrared radiation) 1500 times the solar luminosity.
Gacrux is a double star . Its companion is a 6.4 mag bright blue-white star of the spectral class A3 and is located 129 " from the main component. It can already be observed in prism binoculars . It was previously assumed that it was a physical, i.e. gravitationally bound binary star, but according to more recent observations, the system represents an optical double star, with the companion Gamma Crucis B with about 400 light years being more than four times as far as the main star from the Sun. Gacrux also has two other optical companions.
The main star is a semi-regular variable whose brightness fluctuates by a few tenths of a magnitude with a not very constant period of a little less than 90 days. He loses mass due to a strong, variable stellar wind . It has evolved from a B star in the main sequence to a red giant and is now likely to be in a phase beyond the helium burn. Since barium and other elements can be found in its atmosphere , it is likely to be surrounded by a previously invisible white dwarf , which has emerged from a more massive (physical) companion. It had already expanded into a red giant earlier and repelled its outer atmosphere as a planetary nebula , with heavy elements of its interior contaminating today's main component Gamma Crucis A.
See also
Web links
Individual evidence
- ↑ a b c Hipparcos catalog (ESA 1997)
- ↑ a b c Bright Star Catalog
- ↑ Pulkovo radial velocities for 35493 HIP stars
- ↑ a b c Hipparcos, the New Reduction (van Leeuwen, 2007)
- ↑ estimated from apparent brightness and distance