Alpha Herculis
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| Observation data Equinox J2000 |
|
|---|---|
| Constellation | Hercules |
| Right ascension | 17h 14m 38.80s |
| Declination | +14° 23′ 25.0″ |
| Apparent magnitude (V) | 3.48 / 5.4 |
| Characteristics | |
| Spectral type | M5IIver / (G5III+F2V) |
| U-B color index | |
| B-V color index | 1.44 |
| Variable type | Semiregular |
| Astrometry | |
| Proper motion (μ) | RA: -6.71 mas/yr Dec.: 32.78 mas/yr |
| Parallax (π) | 8.53 ± 2.03 mas |
| Distance | approx. 380 ly (approx. 120 pc) |
| Other designations | |
| Database references | |
| SIMBAD | data |
Alpha Herculis (α Her / α Herculis) is a multiple star in the constellation Hercules. It also has the traditional name Ras Algethi or Rasalgethi (Arabic: رأس الجاثي ra's al-jaθiyy Head of the Kneeler), and the Flamsteed designation 64 Herculis.
When viewed through a telescope, this system is resolved into two components designated α1 and α2. These two components are more than 500 astronomical units apart, with an estimated orbital period of approximately 3600 years. α1 is a relatively massive red bright giant. α2 is actually a double star system with a primary yellow giant star and a secondary, yellow-white dwarf star. (These components are sometimes designated α Herculis A, Ba and Bb, respectively.)
The angular diameter of the red giant α1 has been measured with an interferometer as 34 ± 0.8 milli-arcseconds, or 0.034 arcseconds.[1] At an estimated distance of 120 parsecs, this corresponds to a radius of about 300 million kilometers (or 188 million miles),[2] or 400 times the size of the Sun. It has a total of about 14 solar masses,[3] and has emitted a sparse, gaseous envelope that extends at least 90 astronomical units.[4]
The star is located at the bottom of the constellation. The traditional name "Head" comes from the fact that in the antiquity Hercules was depicted upside on the constellation maps.
[edit] References
- ^ Benson, J. A.; Dyck, H. M.; Mason, W. L.; Howell, R. R.; Ridgway, S. T.; Dixon, D. J. (1991). "The infrared angular diameter of Alpha Herculis measured with a Michelson interferometer". Astronomical Journal 102: 2091-2097. Retrieved on 2007-03-08.
- ^ Kaler, Jim. Rasalgethi. University of Illinois. Retrieved on 2007-03-07.
- ^ Hoffleit, D. (1982). The Bright Star Catalogue, 4th Revised Edition, Yale University Observatory. Retrieved on 2007-03-07. —See note 6406.
- ^ Deutsch, Armin J. (1956). "The Circumstellar Envelope of Alpha Herculis.". Astrophysical Journal 123: 210-227. Retrieved on 2007-02-04.
[edit] See also
[edit] External links
- Dome-of-theSky entry (Retrieved 2 February 2007)
- Alcyone entry (Retrieved 2 February 2007)
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