Alpha Herculis

Alpha Herculis

Historical view of the Hercules constellation showing Rasalgethi as the α star and "Head of the Kneeler"
Observation data Epoch J2000      Equinox J2000
Constellation	Hercules
A
Right ascension	17^h 14^m 38.853^s[1]
Declination	+14° 23′ 25.0″[1]
Apparent magnitude (V)	3.350[1] (2.7 - 4.0[2])
B
Right ascension	17^h 14^m 39.181^s[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]
Astrometry
Proper motion (μ)	RA: -6.71[5][6][7] mas/yr Dec.: 32.78[5][6][7] mas/yr
Parallax (π)	9.07 ± 1.32[5][6] mas
Distance	approx. 360 ly (approx. 110 pc)
Absolute magnitude (MV)	−2.3[8] + 1.8 + 2.8[9]
Details^[3]
A
Mass	2.5 M☉
Radius	264 - 303 R☉
Luminosity	7,244 - 9,333 L☉
Surface gravity (log g)	−0.41 ± 0.19[10] cgs
Temperature	3,155 - 3,365 K
Ba
Mass	~2.5 M☉
Luminosity	126 L☉
Temperature	4,900 K
Bb
Mass	~2 M☉
Luminosity	26 L☉
Temperature	7,350 K
Age	0.41 - 1.25 Gyr
Other designations
Ras Algethi, Rasalgethi, α Her, 64 Her, BD+14°3207, HIP 84345, CCDM J17146+1424, AAVSO 1710+14
A: HD 156014, HR 6406, SAO 102680
B: HD 156015, HR 6407, SAO 102681
Database references
SIMBAD	data

Alpha Herculis (α Herculis, abbreviated Alpha Her, α Her), also designated 64 Herculis, is a multiple star system in the constellation of Hercules. When viewed through a telescope, this system is resolved into a number of components, the brightest one of which has been named Rasalgethi.^[11]

Nomenclature

α Herculis (Latinised to Alpha Herculis) is the system's Bayer designation and 64 Herculis its Flamsteed designation. The two components are designated α¹ Herculis (the brightest of the two) and α² Herculis. The latter is itself a binary star and all three stars are sometimes designated α Herculis A, Ba and Bb, respectively.^[12]

The system bore the traditional name Rasalgethi or Ras Algethi (Arabic: رأس الجاثي ra‘is al-jāthī‎‎ 'Head of the Kneeler').^[13] 'Head' comes from the fact that in antiquity Hercules was depicted upside down on maps of the constellation. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)^[14] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016^[15] included a table of the first two batches of names approved by the WGSN; which included Rasalgethi for α¹ Herculis.

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, Rasalgethi is called 帝座, Pinyin: Dìzuò, meaning 'Emperor's Seat', this star is 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

α¹ and α² Herculis 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's two components are a primary yellow giant star and a secondary, yellow-white dwarf star in a 51.578 day orbit.

α¹ Herculis is an asymptotic giant branch (AGB) star, a luminous red giant that has both hydrogen and helium shells around a degenerate carbon-oxygen core. Its angular diameter has been measured with an interferometer as 34 ± 0.8 mas, or 0.034 arcseconds.^[19] At an estimated distance of 110 parsecs from the Sun determined by Hipparcos,^[5][6][20] this corresponds to a radius of about 280 million kilometers (or 170 million miles), which is roughly 400 R_☉ or 1.87 AU.^[21] If Rasalgethi 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] Like most type M stars near the end of their lives, Rasalgethi is experiencing a high degree of stellar mass loss creating a sparse, gaseous envelope that extends at least 90 astronomical units.^[22]

See also

• List of largest known stars
• Lists of stars in the constellation Hercules
• Betelgeuse mass loss
• Spectral types F, G & M

Notes

References

1. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27. Bibcode:2000A&A...355L..27H.
2. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
3. Moravveji, Ehsan; Guinan, Edward F.; Khosroshahi, Habib; Wasatonic, Rick (2013). "The Age and Mass of the α Herculis Triple-star System from a MESA Grid of Rotating Stars with 1.3 <= M/M ⊙ <= 8.0". The Astronomical Journal. 146 (6): 148. arXiv:1308.1632. Bibcode:2013AJ....146..148M. doi:10.1088/0004-6256/146/6/148.
4. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
5. Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; et al. (July 1997), "The Hipparcos Catalogue", Astronomy and Astrophysics, 323: L49–L52, Bibcode:1997A&A...323L..49P
6. van Leeuwen, F (November 2007). "Hipparcos, the New Reduction". Astronomy and Astrophysics. Centre de Données astronomiques de Strasbourg. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
7. "SIMBAD query result:NAME RASALGETHI -- Semi-regular pulsating Star". Centre de Données astronomiques de Strasbourg. Retrieved 2010-09-26.
8. Huang, W.; Wallerstein, G.; Stone, M. (2012). "A catalogue of Paschen-line profiles in standard stars". Astronomy & Astrophysics. 547: A62. arXiv:1210.7893. Bibcode:2012A&A...547A..62H. doi:10.1051/0004-6361/201219804.
9. Reimers, D. (1977). "On the absolute scale of mass-loss in red giants. I - Circumstellar absorption lines in the spectrum of the visual companion of Alpha-1 HER". Astronomy and Astrophysics. 61: 217. Bibcode:1977A&A....61..217R.
10. Schröder, K.-P.; Cuntz, M. (April 2007), "A critical test of empirical mass loss formulas applied to individual giants and supergiants", Astronomy and Astrophysics, 465 (2): 593–601, arXiv:astro-ph/0702172, Bibcode:2007A&A...465..593S, doi:10.1051/0004-6361:20066633
11. "IAU Catalog of Star Names". Retrieved 28 July 2016.
12. Tokovinin, A. A. (1997). "MSC - a catalogue of physical multiple stars". Astronomy & Astrophysics Supplement Series. 124: 75. Bibcode:1997A&AS..124...75T. doi:10.1051/aas:1997181.
13. Kurt Vonnegut. "Constellations: Hercules 'the Strongman'". The BBC (British Broadcasting Corporation). Retrieved 2010-11-14.
14. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
15. "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
16. Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society. 55 (8): 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
17. (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 25 日
18. Richard Hinckley Allen: Star Names — Their Lore and Meaning: Hercules
19. Benson, J. A.; Dyck, H. M.; Mason, W. L.; Howell, R. R.; Ridgway, S. T.; et al. (December 1991). "The infrared angular diameter of Alpha Herculis measured with a Michelson interferometer". Astronomical Journal. 102: 2091–2097. Bibcode:1991AJ....102.2091B. doi:10.1086/116033.
20. Perryman, Michael (2010), The Making of History's Greatest Star Map, Astronomers’ Universe, Heidelberg: Springer-Verlag, doi:10.1007/978-3-642-11602-5, ISBN 978-3-642-11601-8
21. To determine Rasalgethi's radius in terms of solar units, the calculations begin with the formula for angular diameter as follows:

    ${\begin{smallmatrix}{\delta }={\frac {d_{R}}{D_{R}}}\end{smallmatrix}}$

    where δ equals Rasalgethi's angular diameter in arcseconds, d_R the star's diameter in AU, and D_R the Distance from Earth in parsecs. If one knows the angular diameter and the Distance, then one can solve for d_R as follows:

    ${\begin{smallmatrix}d_{R}=\delta \cdot D_{R}={0.034}\cdot 110.0=3.740AU\end{smallmatrix}}$.

    To obtain Rasalgheti's radius:

    ${\begin{smallmatrix}R_{R}={\left({{\frac {d_{R}}{2}}}\right)}={\left({{\frac {3.740}{2}}}\right)}=1.870AU\end{smallmatrix}}$.

    Converting into Solar units, 1 AU = 149,597,871 km and the mean radius of the Sun = 696,000 km, hence the calculation:

    ${\begin{smallmatrix}d_{B}={\left(1.87AU\right)}{\left({{\frac {149,597,871km}{696,000km}}}\right)}=280,000,000km=402R_{{\odot }}\end{smallmatrix}}$ (rounded).

22. Deutsch, Armin J. (March 1956). "The Circumstellar Envelope of Alpha Herculis". Astrophysical Journal. 123: 210–227. Bibcode:1956ApJ...123..210D. doi:10.1086/146152.

External links

• An Atlas of the Universe: Multiple Star Orbits
• Upside down Hercules showing Rasalgethi as the head: Hercules

Coordinates: 17^h 14^m 38.858^s, +14° 23′ 25.20″