Epoch J2000 Equinox J2000
|Right ascension||03h 47m 29.077s|
|Declination||24° 06′ 18.49″|
|Apparent magnitude (V)||2.87|
|U−B color index||−0.34|
|B−V color index||−0.09|
|Radial velocity (Rv)||5.40 km/s|
|Proper motion (μ)||RA: 19.34 ± 0.39 mas/yr
Dec.: -43.67 ± 0.33 mas/yr
|Parallax (π)||8.09 ± 0.42 mas|
|Absolute magnitude (MV)||-2.62|
|Surface gravity (log g)||3.047 cgs|
|Rotational velocity (v sin i)||149 km/s|
Alcyone (η Tau, η Tauri, Eta Tauri) is a star system in the constellation Taurus. It is the brightest star in the Pleiades open cluster, which is a young cluster, aged at around 100 million years. Alcyone is approximately 440 light years from Earth. It is named after the mythological figure Alcyone, one of the mythological Pleiades. It is known as 昴宿六 (the Sixth Star of the Hairy Head) in Chinese.
Alcyone is the brightest member of the nearby Pleiades open cluster. There are a number of fainter stars very close to it, all most probably also member of the same cluster. The Catalog of Components of Double and Multiple Stars lists three companions: B is 24 Tau, a magnitude 6.28 A0 main sequence star 117" away; C is V647 Tau, a δ Sct variable star; and D is a magnitude 9.15 F3 main sequence star. V647 Tau varies from magnitude +8.25 to +8.30 over 1.13 hours.
The Washington Double Star Catalog lists a further four companions, all fainter than 11th magnitude, and also describes component D as itself double with two nearly equal components separated by 0.30".
The main star, Alcyone A, consists of three components, the brightest being a B-type giant star. The closest companion has a very low mass and is less than 1 milli-arcsecond away, with a likely orbital period just over four days. The other star is about half the mass of the giant and they are separated by 0.031 arcseconds, or about the distance from the Sun to Jupiter, orbiting in about 830 days.
The main star, known as Alcyone A, is a blue-white B-type giant similar to many of the other B-type stars in the Pleiades cluster. It has an apparent magnitude of +2.87 (absolute magnitude = −2.39), and a radius almost 10 times that of the Sun. Its temperature is approximately 13,000 K giving it a total luminosity that is 2,400 times solar. The spectral type of B7IIIe indicates that emission lines are present in its spectrum. Like many Be stars, Alcyone A has a high rotational velocity of 149 km/s, which has created a gaseous disk flung into orbit around the star from its equator.
- Lists of stars in the constellation Taurus
- White Tiger of The West
- Class B Stars
- Be stars
- Shell star
- Circumstellar disk
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