Castor (star)
Sextuple star system in Gemini / From Wikipedia, the free encyclopedia
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Castor is the second-brightest object in the zodiac constellation of Gemini. It has the Bayer designation α Geminorum, which is Latinised to Alpha Geminorum and abbreviated Alpha Gem or α Gem. With an apparent visual magnitude of 1.58, it is one of the brightest stars in the night sky. Castor appears singular to the naked eye, but it is actually a sextuple star system organized into three binary pairs. Although it is the 'α' (alpha) member of the constellation, it is fainter than 'β' (beta) Geminorum, Pollux.
Quick Facts Observation data Epoch J2000 Equinox J2000, Pronunciation ...
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Gemini |
Pronunciation | /ˈkæstər/[1] |
A | |
Right ascension | 07h 34m 35.863s[2] |
Declination | +31° 53′ 17.79″[2] |
Apparent magnitude (V) | 1.93[2] |
B | |
Right ascension | 07h 34m 36.100s[2] |
Declination | +31° 53′ 18.57″[2] |
Apparent magnitude (V) | 2.97[2] |
C | |
Right ascension | 07h 34m 37.584s[2] |
Declination | +31° 53′ 17.8160″[2] |
Apparent magnitude (V) | 9.83[2] |
Characteristics | |
A | |
Spectral type | A1V + dM1e[3] |
B−V color index | +0.03[4] |
B | |
Spectral type | Am + dM1e[3] |
B−V color index | +0.04[4] |
C | |
Spectral type | dM1e + dM1e[3] |
U−B color index | +1.04[5] |
B−V color index | +1.49[5] |
Variable type | BY Dra[6] |
Astrometry | |
AB | |
Radial velocity (Rv) | 5.40[7] km/s |
Proper motion (μ) | RA: –191.45[8] mas/yr Dec.: –145.19[8] mas/yr |
Parallax (π) | 64.12 ± 3.75 mas[8] |
Distance | 51 ± 3 ly (15.6 ± 0.9 pc) |
Absolute magnitude (MV) | +0.986 / +1.886[4] |
C | |
Radial velocity (Rv) | +2.5[9] km/s |
Proper motion (μ) | RA: –201.490[10] mas/yr Dec.: –97.104[10] mas/yr |
Parallax (π) | 66.2323 ± 0.0511 mas[10] |
Distance | 49.24 ± 0.04 ly (15.10 ± 0.01 pc) |
Absolute magnitude (MV) | +8.950[11] |
Details | |
α Geminorum Aa | |
Mass | 2.37[12] M☉ |
Radius | 2.089[12] R☉ |
Surface gravity (log g) | 4.2[13] cgs |
Temperature | 10,286[14] K |
Rotational velocity (v sin i) | 18[15] km/s |
Age | 290[12] Myr |
α Geminorum Ba | |
Mass | 1.79[12] M☉ |
Radius | 1.648[12] R☉ |
Surface gravity (log g) | 4.0[13] cgs |
Temperature | 8,842[14] K |
Rotational velocity (v sin i) | 33[15] km/s |
α Geminorum Ca/Cb (components are identical) | |
Mass | 0.5992[11] M☉ |
Radius | 0.6191[11] R☉ |
Luminosity | 0.0733[11] L☉ |
Surface gravity (log g) | 4.6317[11] cgs |
Temperature | 3,820[11] K |
Metallicity [Fe/H] | ~0.0[11] dex |
Rotational velocity (v sin i) | 37[11] km/s |
Age | 370[11] Myr |
Orbit[12] | |
Primary | α Geminorum A |
Companion | α Geminorum B |
Period (P) | 459 yr |
Semi-major axis (a) | 6.722″ |
Eccentricity (e) | 0.338 |
Inclination (i) | 115.1° |
Longitude of the node (Ω) | 41.3° |
Periastron epoch (T) | 2436785 |
Argument of periastron (ω) (secondary) | 251.84° |
Orbit[16] | |
Primary | α Geminorum Aa |
Companion | α Geminorum Ab |
Period (P) | 9.2128 days |
Eccentricity (e) | 0.5 |
Periastron epoch (T) | 2427543.938 |
Argument of periastron (ω) (primary) | 266.4° |
Semi-amplitude (K1) (primary) | 12.9 km/s |
Orbit[16] | |
Primary | α Geminorum Ba |
Companion | α Geminorum Bb |
Period (P) | 2.9283 days |
Periastron epoch (T) | 2427501.703 |
Argument of periastron (ω) (primary) | 94.7° |
Semi-amplitude (K1) (primary) | 31.9 km/s |
Orbit[16] | |
Primary | α Geminorum AB |
Companion | α Geminorum C |
Period (P) | 14,000 yr |
Orbit[11] | |
Primary | α Geminorum Ca |
Companion | α Geminorum Cb |
Period (P) | 0.814 days |
Eccentricity (e) | 0 |
Inclination (i) | 86.29 ± 0.10° |
Longitude of the node (Ω) | 7.315° |
Semi-amplitude (K1) (primary) | 121.0 km/s |
Semi-amplitude (K2) (secondary) | 119.0 km/s |
Other designations | |
A: BD+32°1581A, HD 60179, HR 2891, PLX 1785.00 | |
B: BD+32°1581B, HD 60178, HR 2890 | |
C: YY Geminorum, BD+32°1582 | |
Database references | |
SIMBAD | data |
Castor A | |
Castor B | |
Castor C (YY Gem) |
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