Albireo
From Wikipedia, the free encyclopedia
 Albireo's position, lower right corner. The cross-like figure is the Northern Cross. The blue line shows the boundaries of the constellation the Swan. |
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| Observation data Equinox J2000 |
|
|---|---|
| Constellation | Cygnus |
| Right ascension | 19h 30m 43.3s |
| Declination | +27° 57' 35" |
| Apparent magnitude (V) | 3.08/5.10 |
| Characteristics | |
| Spectral type | (K3 II + B8 V) |
| U-B color index | 0.62 |
| B-V color index | 1.13 |
| Variable type | ? |
| Astrometry | |
| Radial velocity (Rv) | -24.0 km/s |
| Proper motion (μ) | RA: -7.09 mas/yr Dec.: -5.667 mas/yr |
| Parallax (π) | 8.46 ± 0.58 mas |
| Distance | 385 ly (118 pc) |
| Absolute magnitude (MV) | -2.28/-0.26 |
| Details | |
| Mass | 5/3.3 M☉ |
| Radius | 55.6/3.1 R☉ |
| Luminosity | 950/190 L☉ |
| Temperature | 4,300/12,100 K |
| Metallicity | ? |
| Rotation | ?/0.6d |
| Age | ? years |
| Other designations | |
Albireo (β Cyg / β Cygni / Beta Cygni) is the third brightest star in the constellation Cygnus. Although it has the Bayer designation "beta", it is actually fainter than Gamma Cygni.
Since Cygnus is "the swan", and Albireo is located at the head of the swan, it is sometimes called the "beak star". It also forms the "Northern Cross" along with Deneb, Delta Cygni and Epsilon Cygni.
The name of the star originates in misunderstandings and bad translations. The name of the star was originally Minqār al-Dajājah, "the hen's beak," as in Arab texts. Latin scholars misunderstood and thought that the name came from a kind of herb, and translated it into ab ireo ("from ireus"). Later this was treated as a misprint of an Arabic term and transcribed as al-bireo.
Albireo is 385 light years away from the Earth. With bare eyes Albireo seems like a single star. However, when viewed with a telescope it readily resolves into a double star, one yellow (apparent magnitude 3.1), the other blue (apparent magnitude 5.1). Separated by 34 seconds of arc, the two components provide one of the best contrasting double stars in the sky due to their different colors.
They had been considered as merely optical double, not orbiting around a common point as a true binary star system would be. However, in spite of the large distance between them, it has been shown that they are a true binary system.
The brighter, yellow member of the pair, Beta Cygni A, is itself a close binary.
[edit] Albireo as a triple Star
The brighter A component of the wide pair was itself resolved as a binary star using large telescopes and image processing techniques (speckle interferometry) in 1976. Some fifty measurements since then have shown a position-angle change between the stars of about 50 degrees, which is not yet sufficient to yield an orbital determination. The current separation of around 0.4 arcseconds is tantalizingly close to the limit which visual observations through instruments of at least 20" in size under very rare perfect conditions of seeing can resolve.
