Alpha Herculis

Coordinates: Sky map 17h 14m 38.858s, +14° 23′ 25.20″
Source: Wikipedia, the free encyclopedia.
α Herculis
Location of α Herculis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
A
Right ascension 17h 14m 38.853s[1]
Declination +14° 23′ 25.34″[1]
Apparent magnitude (V) 3.350[1] (2.7–4.0[2])
B
Right ascension 17h 14m 39.181s[1]
Declination +14° 23′ 23.98″[1]
Apparent magnitude (V) 5.322[1]
Characteristics
A
Evolutionary stage AGB[3]
Spectral type M5 Ib-II[3]
U−B color index +1.01[4]
B−V color index +1.45[4]
Variable type
SRc[2]
B
Spectral type G8III + A9IV-V[3]
Distance
approx. 360 ly
(approx. 110 pc)
Absolute magnitude (MV)−2.3[6] + 1.8 + 2.8[7]
Details
A
Mass2.5+1.6
−1.1[8] M☉
Radius284 ± 60, 264–303[3] R☉
Luminosity7,244–9,333[3] L☉
Surface gravity (log g)−0.41±0.19[9] cgs
Temperature3,155–3,365[3] K
Ba
Gyr
HR 6407, SAO
 102681
Database references
SIMBADα Her
A
B

Alpha Herculis (α Herculis, abbreviated Alpha Her, α Her), also designated 64 Herculis, is a multiple star system in the constellation of Hercules. Appearing as a single point of light to the naked eye, it is resolvable into a number of components through a telescope. It has a combined apparent magnitude of 3.08, although the brightest component is variable in brightness. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 360 light-years (110 parsecs) distant from the Sun. It is also close to another bright star Rasalhague in the vicinity.

System

A view of Alpha Herculis in a small telescope. The components A and B are resolved with angular separation of 4.64'' (in 2020).

Alpha Herculis is a triple star system. The primary (brightest) of the three stars, designated α1 Herculis or α Herculis A, is a pulsating variable star on the asymptotic giant branch (AGB), and is the second nearest AGB star after Mira. The primary star forms a visual binary pair with a second star, which is itself a spectroscopic binary.[3]

Alpha Herculis also forms the A and B components of a wider system designated WDS J17146+1423, with two additional faint visual companions designated WDS J17146+1423C and D.[11] The two fainter stars are far more distant than the triple system.[12]

Nomenclature

α Herculis (Latinised to Alpha Herculis) is the system's Bayer designation; α1 and α2 Herculis, those of its two visible components. 64 Herculis is the system's Flamsteed designation. WDS J17146+1423 is the wider system's designation in the Washington Double Star Catalog. The designations of Alpha Herculis' main components as Alpha Herculis A and B and the wider system's four components as WDS J17146+1423A, B, C and D, together with the spectroscopic pair - Alpha Herculis Ba and Bb - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[13]

Alpha Herculis bore the traditional name Rasalgethi or Ras Algethi (

Arabic: رأس الجاثي ra‘is al-jāthī 'Head of the Kneeler').[14] 'Head' comes from the fact that in antiquity Hercules was depicted upside down on maps of the constellation. In 2016, the IAU organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN approved the name Rasalgethi for the component Alpha Herculis A (α1) on 30 June 2016 and it is now so included in the List of IAU-approved Star Names.[15]

The term ra's al-jaθiyy or Ras al Djathi appeared in the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, which was translated into Latin as Caput Ingeniculi.[16]

In Chinese astronomy, Alpha Herculis is called 帝座, Pinyin: Dìzuò, meaning 'Emperor's Seat'. The star is seen as marking itself, and stands alone in the center of the Emperor's Seat asterism, Heavenly Market enclosure (see: Chinese constellations).[17] 帝座 (Dìzuò) was westernized into Ti Tso by R.H. Allen, with the same meaning [18]

Properties

A light curve for Alpha Herculis A, plotted from data published by Wasatonic (1997)[19]

Alpha Herculis A and B are more than 500

bright giant, but radial velocity measurements suggest a companion with a period of the order of a decade.[11] B's two components are a primary yellow giant star and a secondary, yellow-white dwarf star in a 51.578 day orbit.[20]

Alpha Herculis A is an

interferometer
as 34 ± 0.8
mas, or 0.034 arcseconds.[21] At its estimated distance of 110 parsecs this corresponds to a radius of about 280 million kilometers (or 170 million miles), which is roughly 400 R☉ or 1.87 AU.[a] If Alpha Herculis were at the center of the Solar System its radius would extend past the orbit of Mars at 1.5 AU but not quite as far as the asteroid belt. The red giant is estimated to have started its life with about 2.175-3.250 M☉.[3]

Alpha Herculis A has been specified as a standard star for the spectral class M5 Ib-II.

semiregular variable with complex changes in brightness with periods ranging from a few weeks to many years. The most noticeable variations occur at timescales of 80–140 days and at 1,000 - 3,000 days. The strongest detectable period is 128 days.[22] The full range in brightness is from magnitude 2.7 to 4.0,[2] but it usually varies over a much smaller range of around 0.6 magnitudes.[22]

Notes

  1. ^ To determine Rasalgethi's radius in terms of solar units, the calculations begin with the formula for angular diameter as follows:
    where δ equals Rasalgethi's angular diameter in
    AU
    , and DR the Distance from Earth in parsecs. If one knows the angular diameter and the Distance, then one can solve for dR as follows:
    .
    To obtain Rasalgheti's radius:
    .
    Converting into Solar units, 1
    AU = 149,597,871 km and the mean radius of the Sun
    = 696,000 km, hence the calculation:
    (rounded).

References

  1. ^
    ISBN 0333750888
    .
  2. ^
    Bibcode:2009yCat....102025S
    .
  3. ^
    S2CID 117872505
    .
  4. ^
    Bibcode:2002yCat.2237....0D
    .
  5. ^
    S2CID 18759600
    .
  6. S2CID 119286159
    .
  7. Bibcode:1977A&A....61..217R
    .
  8. Bibcode:2011ASPC..445..163M
    .
  9. S2CID 55901104
  10. ^ "alf Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2010-09-26.
  11. ^ a b "Washington Double Star Catalog". United States Naval Observatory. Archived from the original on 2011-02-14. Retrieved 2018-07-10.
  12. doi:10.1051/0004-6361/201833051
    .
  13. arXiv:1012.0707 [astro-ph.SR
    ].
  14. ^ Kurt Vonnegut. "Constellations: Hercules 'the Strongman'". The BBC (British Broadcasting Corporation). Retrieved 2010-11-14.
  15. ^ a b "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  16. doi:10.1093/mnras/55.8.429
    .
  17. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 25 日 Archived 2021-04-21 at the Wayback Machine
  18. ^ Richard Hinckley Allen: Star Names — Their Lore and Meaning: Hercules
  19. Bibcode:1997JAVSO..26....1W
    . Retrieved 18 December 2022.
  20. ^
    doi:10.1086/146152
    .
  21. doi:10.1086/116033
    .
  22. ^
    doi:10.1086/322153
    .

External links


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