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	17h 14m 38.853s
Declination	+14° 23′ 25.0″
Apparent magnitude (V)	3.350 (2.7 - 4.0)
	B
Right ascension	17h 14m 39.181s
Declination	+14° 23′ 23.98″
Apparent magnitude (V)	5.322
Characteristics
A
Spectral type	M5 Ib-II
U−B color index	+1.01
B−V color index	+1.45
Variable type	SRc
B
Spectral type	G8III + A9IV-V
Astrometry
Proper motion (μ)	RA: -6.71 mas/yr ; Dec.: 32.78 mas/yr
Parallax (π)	9.07 ± 1.32 mas
Distance	approx. 360 ly ; (approx. 110 pc)
Absolute magnitude (MV)	−2.3 + 1.8 + 2.8
Details
A
Mass	2.5 M☉
Radius	264 - 303 R☉
Luminosity	7,244 - 9,333 L☉
Surface gravity (log g)	−0.41 ± 0.19 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 Her, α Herculis) is a multiple star system in the constellation Hercules. It has the traditional name Rasalgethi or Ras Algethi (Arabic: رأس الجاثي ra's al-jaθiyy Head of the Kneeler), and the Flamsteed designation 64 Herculis.^[11] The traditional name "Head" comes from the fact that in antiquity Hercules was depicted upside down on the constellation maps.

The term ra's al-jaθiyy or Ras al Djathi was appeared in the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, which was translated into Latin as Caput Ingeniculi.^[12]

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 Emperor's Seat asterism, Heavenly Market enclosure (see : Chinese constellations).^[13] 帝座 (Dìzuò) was westernized into Ti Tso by R.H. Allen, with the same meaning ^[14]

Properties

The primary star, α¹ Her, 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.^[15] At an estimated distance of 110 parsecs from Hipparcos,^[5]^[6]^[16] this corresponds to a radius of about 280 million kilometers (or 170 million miles), which is roughly 400 R_☉ or 1.87 AU.^{[note 1]} If Rasalgethi were at the center of our 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.^[17]

Star system

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 in a 51.578 day orbit. (These components are sometimes designated α Herculis A, Ba and Bb, respectively.)^[18]

Notes

^ To determine the Rasalgheti'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 we know the angular diameter and the Distance, then we 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).

References

^ ^a ^b ^c ^d ^e ^f 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.
^ ^a ^b 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.
^ ^a ^b ^c ^d 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.
^ ^a ^b 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.
^ ^a ^b ^c ^d 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
^ ^a ^b ^c ^d van Leeuwen, F (November 2007). "Hipparcos, the New Reduction". Astronomy and Astrophysics. 474 (2). Centre de Données astronomiques de Strasbourg: 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
^ ^a ^b "SIMBAD query result:NAME RASALGETHI -- Semi-regular pulsating Star". Centre de Données astronomiques de Strasbourg. Retrieved 2010-09-26.
^ 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.
^ 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.
^ 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
^ Kurt Vonnegut. "Constellations: Hercules 'the Strongman'". The BBC (British Broadcasting Corporation). Retrieved 2010-11-14.
^ 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.
^ Template:Zh icon AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 25 日
^ Richard Hinckley Allen: Star Names — Their Lore and Meaning: Hercules
^ 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.
^ 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
^ Deutsch, Armin J. (March 1956). "The Circumstellar Envelope of Alpha Herculis". Astrophysical Journal. 123: 210–227. Bibcode:1956ApJ...123..210D. doi:10.1086/146152.
^ 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.

External links

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

[NOTERADIUS-17] To determine the Rasalgheti'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 we know the angular diameter and the Distance, then we 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).

[tycho2-1] ^ ^a ^b ^c ^d ^e ^f 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.

[gcvs-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.

[moravveji-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.

[ducati-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.

[aaa323_L49-5] 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

[LEEUWEN-6] van Leeuwen, F (November 2007). "Hipparcos, the New Reduction". Astronomy and Astrophysics. 474 (2). Centre de Données astronomiques de Strasbourg: 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.

[SIMBAD-7] "SIMBAD query result:NAME RASALGETHI -- Semi-regular pulsating Star". Centre de Données astronomiques de Strasbourg. Retrieved 2010-09-26.

[huang-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.

[reimers-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.

[aaa465_2_593-10] 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

[BBC1-11] Kurt Vonnegut. "Constellations: Hercules 'the Strongman'". The BBC (British Broadcasting Corporation). Retrieved 2010-11-14.

[12] 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.

[13] Template:Zh icon AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 25 日

[14] Richard Hinckley Allen: Star Names — Their Lore and Meaning: Hercules

[BENSON-15] 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.

[GSM-16] 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

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

[msc-19] 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.

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Observation data Epoch J2000 Equinox J2000
Historical view of the Hercules constellation showing Rasalgethi as the α star and "Head of the Kneeler"
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
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 mas^[5]^[6]
Distance	approx. 360 ly (approx. 110 pc)
Absolute magnitude (M_V)	−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

Properties

Star system

See also

Notes

References

External links