{{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 | component1 = A | ra1 = {{RA|17|14|38.853}}<ref name=tycho2/> | dec1 = {{DEC|+14|23|25.34}}<ref name=tycho2/> | appmag_v1 = {{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 = 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 = 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, α Her, 64 Her, BD+14°3207, HIP 84345, CCDM J17146+1424, AAVSO 1710+14, WDS J17146+1423<ref name="SIMBAD">{{cite simbad | title = alf Her | access-date = 2010-09-26 }}</ref> |component1=A |names1=HD 156014, HR 6406, SAO 102680 |component2=B |names2=HD 156015, HR 6407, SAO 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 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. Five degrees east-south-east of Rasalgethi lies Rasalhague, the brightest star in Ophiuchus. These stars may be among the closest-lying pair of alpha stars in the entire sky. Despite the star designated as "alpha", it is actually the 5th brightest star in Hercules.
== System == 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 J17146+1423, with two additional faint visual companions designated WDS 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'' (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 multiple star systems, 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 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, 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 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 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 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 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 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 == <references> <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> </references>
==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}}
Category:Double stars Category:Hercules (constellation) Herculis, Alpha Herculis, 064 Category:Triple star systems Rasalgethi Category:M-type bright giants Category:G-type giants Category:F-type main-sequence stars 6406 7 084345 156014 5 BD+14 3207 Category:Semiregular variable stars Category:M-type supergiants Category:Asymptotic-giant-branch stars