Acrux
Star in the constellation Crux / From Wikipedia, the free encyclopedia
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Acrux is the brightest star in the southern constellation of Crux. It has the Bayer designation α Crucis, which is Latinised to Alpha Crucis and abbreviated Alpha Cru or α Cru. With a combined visual magnitude of +0.76, it is the 13th-brightest star in the night sky. It is the most southerly star of the asterism known as the Southern Cross and is the southernmost first-magnitude star, 2.3 degrees more southerly than Alpha Centauri.[14] This system is located at a distance of 321 light-years from the Sun.[1][15]
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Crux |
Pronunciation | /ˈeɪkrʌks/[citation needed] |
Right ascension | 12h 26m 35.89522s[1] |
Declination | −63° 05′ 56.7343″[1] |
Apparent magnitude (V) | 0.76[2] (1.33 + 1.75)[3] |
Characteristics | |
Spectral type | B0.5IV + B1V[4] |
B−V color index | −0.26[2] |
Variable type | β Cep[5] |
Astrometry | |
Radial velocity (Rv) | −11.2 / −0.6[6] km/s |
Proper motion (μ) | RA: −35.83[1] mas/yr Dec.: −14.86[1] mas/yr |
Parallax (π) | 10.13 ± 0.50 mas[1] |
Distance | 320 ± 20 ly (99 ± 5 pc) |
Absolute magnitude (MV) | −3.77[7] (−2.2 + −2.7[8]) |
Orbit[9] | |
Primary | α Crucis Aa |
Companion | α Crucis Ab |
Period (P) | 75.7794±0.0037 d |
Eccentricity (e) | 0.46±0.03 |
Periastron epoch (T) | 2,417,642.3±1.6 JD |
Argument of periastron (ω) (secondary) | 21±6° |
Semi-amplitude (K1) (primary) | 41.7±1.2 km/s |
Details | |
α1 | |
Mass | 17.80 + 6.05[3] M☉ |
Radius | 7.8[10] R☉ |
Luminosity | 25,000[11] L☉ |
Temperature | 24,000[12] K |
Rotational velocity (v sin i) | 120[12] km/s |
α2 | |
Mass | 15.52[3] M☉ |
Radius | 5.4 R☉ |
Luminosity | 16,000[11] L☉ |
Temperature | 28,000[12] K |
Rotational velocity (v sin i) | 200[12] km/s |
Age | 10.8[13] Myr |
Other designations | |
α1 Cru: Acrux, 26 G. Crucis, FK5 462, GC 16952, HD 108248, HR 4730 | |
α2 Cru: 27 G. Crucis, GC 16953, HD 108249, HR 4731, 2MASS J12263615-6305571 | |
Database references | |
SIMBAD | α Cru |
α1 Cru | |
α2 Cru |
To the naked eye Acrux appears as a single star, but it is actually a multiple star system containing six components. Through optical telescopes, Acrux appears as a triple star, whose two brightest components are visually separated by about 4 arcseconds and are known as Acrux A and Acrux B, α1 Crucis and α2 Crucis, or α Crucis A and α Crucis B. Both components are B-type stars, and are many times more massive and luminous than the Sun. α1 Crucis is itself a spectroscopic binary with components designated α Crucis Aa (officially named Acrux, historically the name of the entire system)[16][17] and α Crucis Ab. Its two component stars orbit every 76 days at a separation of about 1 astronomical unit (AU).[11] HR 4729, also known as Acrux C, is a more distant companion, forming a triple star through small telescopes. C is also a spectroscopic binary, which brings the total number of stars in the system to at least five.