View source for Alpha Herculis

{{Short description|Multiple star system in the constellation Hercules}}
{{Starbox begin
 | name = α Herculis
}}
{{Starbox image
 | image=
{{Location mark
|image=Hercules constellation map.svg|alt=|float=center|width=240
|label=|position=right
|mark=Red circle.svg|mark_width=10|mark_link=α Herculis
|x=596|y=896
}}
|caption=Location of α Herculis (circled)
}}
{{Starbox observe 2s
 | epoch      = J2000
 | constell = [[Hercules (constellation)|Hercules]]
 | component1 = A
 | ra1        = {{RA|17|14|38.853}}<ref name=tycho2/>
 | dec1       = {{DEC|+14|23|25.34}}<ref name=tycho2/>
 | appmag_v1  = 3.350<ref name=tycho2/> ({{Val|2.7|-|4.0}}<ref name=gcvs/>)
 | component2 = B
 | ra2        = {{RA|17|14|39.181}}<ref name=tycho2/>
 | dec2       = {{DEC|+14|23|23.98}}<ref name=tycho2/>
 | appmag_v2  = 5.322<ref name=tycho2/>
}}
{{Starbox character
 | component = A
 | type      = [[Asymptotic giant branch|AGB]]<ref name="moravveji"/>
 | class     = M5 Ib-II<ref name="moravveji"/>
 | b-v       = +1.45<ref name=ducati/>
 | u-b       = +1.01<ref name=ducati/>
 | variable  = [[Semiregular variable|SRc]]<ref name=gcvs/>
 | component2 = B
 | class2     = G8III + A9IV-V<ref name="moravveji"/>
 | b-v2       =
 | u-b2       =
 | variable2  =
}}
{{Starbox astrometry
 | prop_mo_ra  = −7.32<ref name="LEEUWEN"/>
 | prop_mo_dec = 36.07<ref name="LEEUWEN"/>
 | parallax = 9.07
 | p_error  = 1.32
 | parallax_footnote = <ref name="LEEUWEN"/>
 | absmag_v  = −2.3<ref name=huang/> + {{nowrap|1.8 + 2.8<ref name=reimers/>}}
}}
{{Starbox detail
 | component1 = A
 | mass   = {{Val|2.5|1.6|1.1}}<ref name=moravveji2011/>
 | radius = 284 ± 60, {{nowrap|{{Val|264|-|303}}}}<ref name="moravveji"/>
 | luminosity = {{Val|7244|-|9333|fmt=commas}}<ref name="moravveji"/>
 | temperature = {{Val|3155|-|3365|fmt=commas}}<ref name="moravveji"/>
 | metal  = 
 | gravity = {{Val|−0.41|0.19}}<ref name=aaa465_2_593/>
 | rotational_velocity = 
}}
{{Starbox detail|no_heading=y
 | component1 = Ba
 | mass   = ~2.5<ref name="moravveji"/>
 | radius =
 | luminosity = 126<ref name="moravveji"/>
 | temperature = 4,900<ref name="moravveji"/>
 | component2 = Bb
 | mass2   = ~2<ref name="moravveji"/>
 | radius2 =
 | luminosity2 = 26<ref name="moravveji"/>
 | temperature2 = 7,350<ref name="moravveji"/>
 | age_gyr2 = {{Val|0.41|-|1.25}}<ref name="moravveji"/>
}}
{{Starbox catalog
 |names=Ras Algethi, Rasalgethi, [[Bayer designation|α Her]], [[Flamsteed designation|64&nbsp;Her]], [[Bonner Durchmusterung|BD]]+14°3207, [[Hipparcos catalogue|HIP]]&nbsp;84345, [[Catalog of Components of Double and Multiple Stars|CCDM]]&nbsp;J17146+1424, [[American Association of Variable Star Observers|AAVSO]]&nbsp;1710+14, [[Washington Double Star Catalog|WDS]]&nbsp;J17146+1423<ref name="SIMBAD">{{cite simbad | title = alf Her | access-date = 2010-09-26 }}</ref>
 |component1=A
 |names1=[[Henry Draper Catalogue|HD]]&nbsp;156014, [[Harvard Revised catalogue|HR]]&nbsp;6406, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]]&nbsp;102680
 |component2=B
 |names2=[[Henry Draper Catalogue|HD]]&nbsp;156015, [[Harvard Revised catalogue|HR]]&nbsp;6407, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]]&nbsp;102681
}}
{{Starbox reference
 | Simbad=HIP+84345|sn=α Her
 | Simbad2=HD+156014|sn2=A
 | Simbad3=HD+156015|sn3=B
}}
{{Starbox end}}

'''Alpha Herculis''' ('''α Herculis''', abbreviated '''Alpha Her''', '''α Her'''), also designated '''Rasalgethi''' and '''64 Herculis''', is a [[Star system|multiple star system]] in the [[constellation]] of [[Hercules (constellation)|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 [[stellar parallax|parallax]] measurements obtained during the [[Hipparcos]] mission, it is approximately 360 [[light-year]]s (110&nbsp;[[parsec]]s) distant from the [[Sun]]. It is also close to another bright star [[Alpha Ophiuchi|Rasalhague]] in the vicinity.

== System ==
[[File:Double star Alpha Hercules.jpg|left|thumb|A view of Alpha Herculis in a small telescope. The components A and B are resolved with angular separation of 4.64<nowiki>''</nowiki> (in 2020).]]
Alpha Herculis is a triple star system.  The primary (brightest) of the three stars, designated α<sup>1</sup> Herculis or α Herculis A, is a pulsating variable star on the [[asymptotic giant branch]] (AGB). The primary star forms a visual binary pair with a second star, which is itself a spectroscopic binary.<ref name=moravveji/>

Alpha Herculis also forms the A and B components of a wider system <!-- system? --> designated WDS&nbsp;J17146+1423, with two additional faint [[double star|visual companions]] designated WDS&nbsp;J17146+1423C and D.<ref name="WDS"/>  The two fainter stars are far more distant than the triple system.<ref name=dr2cd/>

==Nomenclature==

''α Herculis'' ([[Latinisation of names|Latinised]] to ''Alpha Herculis'') is the system's [[Bayer designation]]; ''α<sup>1</sup>'' and ''α<sup>2</sup> 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 [[Star system|multiple star system]]s, and adopted by the [[International Astronomical Union]] (IAU).<ref name="planetnaming"/>

Alpha Herculis bore the traditional name ''Rasalgethi'' or ''Ras Algethi'' ({{langx|ar|رأس الجاثي ra‘is al-jāthī}} 'Head of the Kneeler').<ref name="BBC1"/> 'Head' comes from the fact that in antiquity Hercules was depicted upside down on maps of the constellation. In 2016, the IAU organized a [[IAU Working Group on Star Names|Working Group on Star Names]] (WGSN)<ref name="WGSN"/> to catalog and standardize proper names for stars. The WGSN approved the name ''Rasalgethi'' for the component Alpha Herculis A (α<sup>1</sup>) on 30 June 2016 and it is now so included in the List of IAU-approved Star Names.<ref name="WGSN"/>

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''.<ref name=Knobel/>

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 (astronomy)|asterism]], [[Heavenly Market enclosure]] (see: [[Chinese constellations]]).<ref name=aeea/> 帝座 (Dìzuò) was westernized into ''Ti Tso'' by R.H. Allen, with the same meaning <ref name=RHA/>

== Properties ==
[[File:AlphaHerLightCurve.png|thumb|left|A [[light curve]] for Alpha Herculis A, plotted from data published by Wasatonic (1997)<ref name=Wasatonic/>]]
Alpha Herculis A and B are more than 500 [[astronomical unit|AU]] apart, with an estimated [[orbital period]] of approximately 3600 years.{{cn|date=December 2022}} A presents as a relatively massive red [[bright giant]], but [[radial velocity]] measurements suggest a companion with a period of the order of a decade.<ref name="WDS"/> B's two components are a primary yellow [[giant star]] and a secondary, yellow-white [[dwarf star]] in a 51.578 day orbit.<ref name=deutsch/>

Alpha Herculis A is an [[asymptotic giant branch]] (AGB) star, a luminous red giant that has both hydrogen and helium shells around a degenerate carbon-oxygen core. It is the second nearest AGB star to the Sun. Its radius [[stellar pulsation|pulsates]] between 264 and 303 solar radii. At its minimum, the [[effective temperature]] is of {{convert|3155|K|C|abbr=on|lk=in}} 
and the luminosity is of 7,200 [[solar luminosity|solar luminosities]], while at its maximum the temperature is of {{convert|3365|K|C|abbr=on}} and the luminosity is of 9,330 solar luminosities.<ref name="moravveji"/> If Alpha Herculis were at the center of the [[Solar System]] its radius would extend past the orbit of [[Earth]] at 1.23{{snd}}1.4 [[astronomical unit|AU]] but not quite as far as the orbit of [[Mars]] or the [[asteroid belt]]. The red giant is estimated to have started its life with about {{solar mass|2.175-3.250}}.<ref name="moravveji"/>

The primary has been specified as a standard star for the spectral class M5 Ib-II.<ref name="moravveji"/> Like most [[Stellar classification#Class M|type M]] stars near the end of their lives, Alpha Herculis is experiencing a high degree of [[stellar mass loss]] creating a sparse, gaseous envelope that extends at least 930 AU.<ref name=deutsch/> It is a [[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.<ref name=percy/> The full range in brightness is from magnitude 2.7 to 4.0,<ref name=gcvs/> but it usually varies over a much smaller range of around 0.6 magnitudes.<ref name=percy/>
{{clear left}}

== References ==
{{reflist|refs=

<ref name=RHA>[https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Hercules*.html Richard Hinckley Allen: Star Names — Their Lore and Meaning: Hercules]</ref>

<ref name=aeea>{{in lang|zh}} [http://aeea.nmns.edu.tw/2006/0606/ap060625.html AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 25 日] {{Webarchive|url=https://web.archive.org/web/20210421134546/http://aeea.nmns.edu.tw/2006/0606/ap060625.html |date=2021-04-21 }}</ref>

<ref name=Knobel>{{cite journal
 | last=Knobel | first=E. B.
 | title=Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket
 | journal=[[Monthly Notices of the Royal Astronomical Society]]
 | volume=55 | issue=8
 | page=429 |date=June 1895
 | bibcode=1895MNRAS..55..429K | doi=10.1093/mnras/55.8.429| doi-access=free}}</ref>

<ref name="WGSN">{{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN) | access-date=22 May 2016 | archive-date=10 June 2016 | archive-url=https://web.archive.org/web/20160610172014/https://www.iau.org/science/scientific_bodies/working_groups/280/ | url-status=dead }}</ref>

<ref name="BBC1">{{cite web
  |title=Constellations: Hercules 'the Strongman'
  |publisher=The BBC (British Broadcasting Corporation)
  |author=Kurt Vonnegut
  |url=https://h2g2.com/edited_entry/A29778916
  |access-date=2010-11-14}}</ref>

<ref name="planetnaming">{{cite arXiv |title=On the naming convention used for multiple star systems and extrasolar planets |date=2010 |eprint=1012.0707 |class=astro-ph.SR |last1= Hessman |first1=F. V. |last2= Dhillon |first2=V. S. |last3= Winget |first3=D. E. |last4= Schreiber |first4=M. R. |last5= Horne |first5=K. |last6= Marsh |first6=T. R. |last7= Guenther |first7=E. |last8= Schwope |first8=A. |last9= Heber |first9=U. }}</ref>

<ref name=dr2cd>{{cite DR2}}</ref>

<ref name="WDS">{{cite web | url=http://ad.usno.navy.mil/wds/ | title=Washington Double Star Catalog | publisher=United States Naval Observatory | access-date=2018-07-10 | archive-url=https://web.archive.org/web/20110214155533/http://ad.usno.navy.mil/wds/ | archive-date=2011-02-14 | url-status=dead }}</ref>

<ref name=reimers>{{cite journal|bibcode=1977A&A....61..217R |title=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 |journal=Astronomy and Astrophysics |volume=61 |pages=217 |last1=Reimers |first1=D. |year=1977 }}</ref>

<ref name=gcvs>{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref>

<ref name=ducati>{{cite journal|bibcode=2002yCat.2237....0D|title=VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system|journal=CDS/ADC Collection of Electronic Catalogues|volume=2237|last1=Ducati|first1=J. R.|year=2002}}</ref>

<ref name=huang>{{cite journal|bibcode=2012A&A...547A..62H|arxiv=1210.7893|title=A catalogue of Paschen-line profiles in standard stars|journal=Astronomy & Astrophysics|volume=547|pages=A62|last1=Huang|first1=W.|last2=Wallerstein|first2=G.|last3=Stone|first3=M.|year=2012|doi=10.1051/0004-6361/201219804|s2cid=119286159}}</ref>

<ref name="moravveji">{{cite journal|bibcode=2013AJ....146..148M|arxiv=1308.1632|title=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|journal=The Astronomical Journal|volume=146|issue=6|pages=148|last1=Moravveji|first1=Ehsan|last2=Guinan|first2=Edward F.|last3=Khosroshahi|first3=Habib|last4=Wasatonic|first4=Rick|year=2013|doi=10.1088/0004-6256/146/6/148|s2cid=117872505}}</ref>

<ref name=tycho2>{{cite journal|bibcode=2000A&A...355L..27H|title=The Tycho-2 catalogue of the 2.5 million brightest stars|journal=Astronomy and Astrophysics|volume=355|pages=L27|last1=Høg|first1=E.|last2=Fabricius|first2=C.|last3=Makarov|first3=V. V.|last4=Urban|first4=S.|last5=Corbin|first5=T.|last6=Wycoff|first6=G.|last7=Bastian|first7=U.|last8=Schwekendiek|first8=P.|last9=Wicenec|first9=A.|year=2000|doi=10.1888/0333750888/2862|isbn=0333750888}}</ref>

<ref name=Wasatonic>{{cite journal |last1=Wasatonic |first1=Richard P. |title=Photoelectric Photometry of TX Psc, Alpha Her A, Omicron Cet, and RT Cyg |journal=The Journal of the American Association of Variable Star Observers |date=January 1997 |volume=26 |issue=1 |pages=1–13 |url=https://app.aavso.org/jaavso/article/1637/ |bibcode=1997JAVSO..26....1W |access-date=18 December 2022}}</ref>

<ref name=percy>{{cite journal|doi=10.1086/322153|bibcode=2001PASP..113..983P|title=Long-TermVRIPhotometry of Small-Amplitude Red Variables. I. Light Curves and Periods|journal=Publications of the Astronomical Society of the Pacific|volume=113|issue=786|pages=983|year=2001|last1=Percy|first1=John R|last2=Wilson|first2=Joseph B|last3=Henry|first3=Gregory W|doi-access=free}}</ref>

<ref name=deutsch>{{cite journal | last=Deutsch | first=Armin J. | title=The Circumstellar Envelope of Alpha Herculis | journal=Astrophysical Journal |date=March 1956 | volume=123 | pages=210–227 | doi=10.1086/146152 | bibcode=1956ApJ...123..210D}}</ref>

<ref name=aaa465_2_593>{{citation | last1=Schröder | first1=K.-P. | last2=Cuntz | first2=M. | title=A critical test of empirical mass loss formulas applied to individual giants and supergiants | journal=Astronomy and Astrophysics | volume=465 | issue=2 | pages=593–601 |date=April 2007 | doi=10.1051/0004-6361:20066633 | bibcode=2007A&A...465..593S |arxiv = astro-ph/0702172 | s2cid=55901104 }}</ref>

<ref name="LEEUWEN">{{cite journal | title=Hipparcos, the New Reduction | last1=van Leeuwen | first1=F |date=November 2007 | pages=653–664 | issue=2 | volume=474 | doi=10.1051/0004-6361:20078357 | journal=Astronomy and Astrophysics | bibcode=2007A&A...474..653V |arxiv = 0708.1752 | s2cid=18759600 }}</ref>

<ref name=moravveji2011>{{cite journal |bibcode=2011ASPC..445..163M |title=On the Mass and Evolutionary Status of the Bright Red AGB Supergiant α<SUP>1</SUP> Herculis |last1=Moravveji |first1=E. |last2=Guinan |first2=E. F. |last3=Sobouti |first3=Y. |journal=Why Galaxies Care About Agb Stars Ii: Shining Examples and Common Inhabitants |year=2011 |volume=445 |page=163 }}</ref>

}}

==External links==
*An Atlas of the Universe: [http://www.atlasoftheuniverse.com/orbits.html Multiple Star Orbits]
*Upside down Hercules showing Alpha Herculisethi as the head: [https://web.archive.org/web/20110401031408/http://www.ne.jp/asahi/stellar/scenes/seiza_e/her.htm Hercules]

{{Sky|17|14|38.858|+|14|23|25.20|1000000}}
{{Stars of Hercules}}
{{Portal bar|Astronomy|Stars|Outer space}}
{{DEFAULTSORT:Alpha Herculis}}
[[Category:Double stars]]
[[Category:Hercules (constellation)]]
[[Category:Bayer objects|Herculis, Alpha]]
[[Category:Flamsteed objects|Herculis, 064]]
[[Category:Triple star systems]]
[[Category:Stars with proper names|Rasalgethi]]
[[Category:M-type bright giants]]
[[Category:G-type giants]]
[[Category:F-type main-sequence stars]]
[[Category:Bright Star Catalogue objects|6406 7]]
[[Category:Hipparcos objects|084345]]
[[Category:Henry Draper Catalogue objects|156014 5]]
[[Category:Durchmusterung objects|BD+14 3207]]
[[Category:Semiregular variable stars]]
[[Category:M-type supergiants]]
[[Category:Asymptotic-giant-branch stars]]