Editing Alpha Ophiuchi

{{Short description|Star in the constellation Ophiuchus}}
{{Starbox begin
| name=α Ophiuchi
}}
{{Starbox image
 | image=
{{Location mark
|image=Ophiuchus constellation map.svg|alt=|float=center|width=240
|label=|position=right
|mark=Red circle.svg|mark_width=10|mark_link=α Ophiuchi
|x=411|y=116
}}
|caption=Location of α Ophiuchi (circled)
}}
{{Starbox observe
| epoch = J2000
| ra    = {{RA|17|34|56.06945}}<ref name=aaa474_2_653/>
| dec   = {{DEC|+12|33|36.1346}}<ref name=aaa474_2_653/>
| appmag_v = 2.07<ref name=clpl4/>
| constell = [[Ophiuchus]]
}}
{{Starbox character
| class = A5IVnn<ref name=":0"/> / K5–7&nbsp;V<ref name=apj726_2_104/>
| b-v   = +0.15<ref name=clpl4/>
| u-b   = +0.10<ref name=clpl4/>
| variable =
}}
{{Starbox astrometry
| radial_v = +12.6<ref name=rgcrv/>
| prop_mo_ra  = +108.07<ref name=aaa474_2_653/>
| prop_mo_dec = −221.57<ref name=aaa474_2_653/>
| parallax = 67.13
| p_error  = 1.06
| parallax_footnote = <ref name=aaa474_2_653/>
| absmag_v = +1.248<ref name="Gatewood2005"/>
}}
{{Starbox orbit
| reference = <ref name=Gardner2021/>
| period_unitless = {{val|3139.72|0.28|fmt=commas}}&nbsp;days
| axis_unitless = {{val|409.8|0.3|ul=mas}}
| eccentricity = {{val|0.93912|0.00013}}
| inclination = {{val|130.679|0.067}}
| node = {{val|236.86|0.16}}
| periastron = {{val|2456028.2|fmt=commas|u=[[Julian Date|JD]]}}
| periarg = {{val|170.21|0.23}}
| k1 = {{val|12.7|0.2}}
| k2 = {{val|33.74|0.35}}
}}
{{Starbox detail
| component1 = α Oph A
| mass     = {{val|2.20|0.06}}<ref name=Gardner2021/>
| radius   = {{val|2.858|0.015|u=solar radius}} (equatorial)<br />{{val|2.388|0.013}} (polar)<ref name=monnier/>
| luminosity  = {{val|31.3|0.96}}<ref name=monnier/>
| temperature = {{val|7569|124|fmt=commas|u=K}} (equatorial)<br />{{val|9384|154|fmt=commas}} (polar)<ref name=monnier/>
| gravity  = 3.91<ref name=aass85_3_1015/>
| metal_fe =
| rotational_velocity = {{val|239|12}}<ref name=monnier/>
| rotation = 0.61<ref name=monnier/> days
| age_gyr  =  {{val|0.77|0.03}}<ref name=apj701_1_209/>
| component2 = α Oph B
| mass2    = {{val|0.824|0.023}}<ref name=Gardner2021/>
}}
{{Starbox catalog
| names=Ras Alhague, Rasalhague, 55 Ophiuchi, [[Bonner Durchmusterung|BD]]+12°3252, [[FK5]] 656, [[Henry Draper catalogue|HD]] 159561, [[Hipparcos catalogue|HIP]]&nbsp;86032, [[Harvard Revised catalogue|HR]] 6556, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]] 102932.<ref name=SIMBAD/>
}}
{{Starbox reference
|Simbad=alf+Oph
}}
{{Starbox end}}

'''Alpha Ophiuchi''' ('''α Ophiuchi''', abbreviated '''Alpha Oph''', '''α Oph'''), also named '''Rasalhague''' {{IPAc-en|'|r|æ|s|@l|h|ei|g}},<ref>also {{IPAc-en|-|'|h|ei|g|juː}} or {{IPAc-en|-|'|h|ei|g|w|iː}}. <br/>{{MW|Rasalhague}}</ref><ref name=Kunitzsch>{{cite book
  |last1=Kunitzsch |first1=Paul
  |last2=Smart |first2=Tim
  |date = 2006  |edition = 2nd rev.
  |title = A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations
  |publisher = Sky Pub |location = Cambridge, Massachusetts
  |isbn = 978-1-931559-44-7
}}</ref> is a [[binary star]] and the brightest star in the [[constellation]] of [[Ophiuchus]].

==Nomenclature==

The name Alpha Ophiuchi is a [[Romanisation]] of the star's [[Bayer designation]], ''α Ophiuchi''.  It is also known by the traditional name ''Rasalhague'', from the Arabic رأس الحواء ''raʼs al-ḥawwāʼ'' "the head of the serpent collector".<ref name=Kunitzsch/> In 2016, the [[International Astronomical Union]] organized a [[IAU Working Group on Star Names|Working Group on Star Names]] (WGSN)<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}}</ref> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<ref name="WGSN1">{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf | title=Bulletin of the IAU Working Group on Star Names, No. 1 |access-date=28 July 2016}}</ref> included a table of the first two collections of approved names, formally listing Alpha Ophiuchi as ''Rasalhague''.<ref>{{Cite news|url=https://www.space.com/3250-stars-pronunciation-guide.html|title=Stars Pronunciation Guide|work=Space.com|access-date=2017-06-25}}</ref>

==Properties==

Alpha Ophiuchi is a [[binary star]] system with an orbital period of about 8.62&nbsp;years. The orbital parameters were only poorly known until 2011 when observations using [[adaptive optics]] produced a better orbital fit, allowing the individual masses of the two components to be determined.<ref name=apj726_2_104/> The orbital elements and masses were further improved in a 2021 study.<ref name=Gardner2021/> The primary component, Alpha Ophiuchi A, has a mass of about 2.2 times the [[solar mass|mass of the Sun]], while the secondary, Alpha Ophiuchi B, has 0.82 solar masses.<ref name=Gardner2021/> Estimates of the mass of the primary by other means range from a low of 1.92 to 2.10 solar masses, up to 2.84 or even 4.8 solar masses.<ref name=apj701_1_209/> The mass of the secondary suggests that it has a [[stellar classification]] in the range K5V to K7V, which indicates it is a [[main sequence]] star that is still generating energy by the [[thermonuclear fusion]] of hydrogen at its core. The pair reached [[periastron]] passage, or closest approach, around April 19, 2012, when they had an angular separation of 50&nbsp;[[milliarcsecond]]s.<ref name=apj726_2_104/>

This star system has a combined [[apparent magnitude]] of +2.08 and is located at a distance of about {{Convert|48.6|ly|pc|abbr=off|lk=on}} from the [[Earth]]. The [[stellar classification]] of A5IVnn indicates that the primary is a bluish-white [[subgiant]] star that has evolved away from the main sequence after consuming the hydrogen at its core.<ref name=":0">{{Cite web |title=alf Oph |url=https://simbad.cds.unistra.fr/mobile/object.html?object_name=alf+Oph |access-date=December 23, 2023 |website=SIMBAD}}</ref> It is radiating about 25 times the [[solar luminosity|luminosity of the Sun]] and has an [[effective temperature]] of about 8,000&nbsp;K, giving it the characteristic white hue of an A-type star.<ref name=apj742_1_9/><ref name=csiro/>

The [[stellar spectrum|spectrum]] of Alpha Ophiuchi shows an anomalously high level of absorption of the lines for singly-ionized calcium (Ca II). However, this is likely the result of interstellar matter between the Earth and the star, rather than a property of the star or circumstellar dust.<ref name=apj661_2_944/>

===Rotation===
[[File:Eso0316c.tif|thumb|left|upright=1.2|A rapidly-rotating star is distorted into an [[oblate spheroid]] bulging at the equator and hotter at the poles.]]
Alpha Ophiuchi A is a rapidly rotating star with a [[stellar rotation|projected rotational velocity]] of 240&nbsp;km&nbsp;s<sup>−1</sup>.<ref name=apj742_1_9/>  It is spinning at about 88.5% of the rate that would cause the star to break up.<ref name=rmaa38_117/>  This gives it an [[oblate spheroid]] shape with an equatorial bulge about 20% larger than the polar radius.<ref name=apj701_1_209/>  The polar radius is calculated to be {{solar radius|2.388|;ink=y}} and the equatorial radius {{solar radius|2.858}}.<ref name=monnier/>

Because of the oblateness and rapid spin, the [[surface gravity]] at the pole is higher than at the equator.  An effect known as [[gravity darkening]] means that the temperature at the poles is also higher than at the equator.  The polar temperature is calculated to be {{val|9,384|u=K|fmt=commas}} and the equatorial temperature {{val|7,569|u=K|fmt=commas}}.<ref name=monnier/>

The energy radiated by an oblate star is higher along its axis of rotation because of the larger projected area and the [[Stefan–Boltzmann law]].  The axis of rotation of α Ophiuchi is inclined about {{nowrap|87.7° ± 0.4°}} to the line of sight from the Earth, so that it is being observed from nearly equator-on.<ref name=rmaa38_117/>  The apparent [[bolometric luminosity]] seen at this angle is {{solar luminosity|25.6|link=y}}, but the true luminosity of the star is thought to be {{solar luminosity|31.3}}.  Since a star's effective temperature is simply the temperature which would produce its total energy output from a [[black body]], the true effective temperature of {{val|8,336|u=K|fmt=commas}} is different from the apparent effective temperature of {{val|8,047|u=K|fmt=commas}}.<ref name=monnier/>

==See also==
* [[Vega]], [[Altair]] and [[Alderamin]], stars similar to Alpha Ophiuchi A in physical characteristics
* [[List of nearest bright stars]]
* [[List of nearest stars by spectral type#List of nearest A-type stars|List of nearest A-type stars]]

==References==
{{reflist|30em|refs=

<ref name=aaa474_2_653>{{citation | title=Validation of the new Hipparcos reduction | last=van Leeuwen | first=F. | journal=Astronomy and Astrophysics | volume=474 | issue=2 |date=November 2007 | pages=653–664 | doi=10.1051/0004-6361:20078357 | bibcode=2007A&A...474..653V |arxiv = 0708.1752 | s2cid=18759600 }}</ref>

<ref name=rgcrv>{{citation | last=Evans | first=D. S. | date=June 20–24, 1966 | editor1-last=Batten | editor1-first=Alan Henry | editor2-last=Heard | editor2-first=John Frederick | title=The Revision of the General Catalogue of Radial Velocities | journal=Determination of Radial Velocities and Their Applications, Proceedings from IAU Symposium No. 30 | volume=30 | page=57| location=University of Toronto | publisher=[[International Astronomical Union]] | bibcode=1967IAUS...30...57E }}</ref>

<!-- <ref name=aj74_375>{{citation | display-authors=1 | last1=Cowley | first1=A. | last2=Cowley | first2=C. | last3=Jaschek | first3=M. | last4=Jaschek | first4=C. | title=A study of the bright A stars. I. A catalogue of spectral classifications | journal=Astronomical Journal | volume=74 | pages=375–406 |date=April 1969 | doi=10.1086/110819 | bibcode=1969AJ.....74..375C }}</ref> -->

<ref name=Gardner2021>{{Cite journal |last1=Gardner |first1=Tyler |last2=Monnier |first2=John D. |last3=Fekel |first3=Francis C. |last4=Williamson |first4=Michael |last5=Baron |first5=Fabien |last6=Hinkley |first6=Sasha |last7=Ireland |first7=Michael |last8=Kraus |first8=Adam L. |last9=Kraus |first9=Stefan |last10=Roettenbacher |first10=Rachael M. |last11=Schaefer |first11=Gail |last12=Sturmann |first12=Judit |last13=Sturmann |first13=Laszlo |last14=ten Brummelaar |first14=Theo |date=2021-11-01 |title=Establishing α Oph as a Prototype Rotator: Precision Orbit with New Keck, CHARA, and RV Observations |journal=The Astrophysical Journal |volume=921 |pages=41 |doi=10.3847/1538-4357/ac1172 |doi-access=free |bibcode=2021ApJ...921...41G |issn=0004-637X|arxiv=2107.02844 }}</ref>

<ref name=clpl4>{{citation | display-authors=1 | last1=Johnson | first1=H. L. | last2=Iriarte | first2=B. | last3=Mitchell | first3=R. I. | last4=Wisniewskj | first4=W. Z. | title=UBVRIJKL photometry of the bright stars | journal=Communications of the Lunar and Planetary Laboratory | volume=4 | issue=99 | page=99 | date=1966 | bibcode=1966CoLPL...4...99J }}</ref>

<ref name=SIMBAD>{{citation | title=RASALHAGUE -- Variable Star | work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Alpha+Ophiuchi | access-date=2011-12-25 }}</ref>

<ref name=monnier>{{cite journal|doi=10.1088/0004-637X/725/1/1192|arxiv=1012.0787|title=Rotationally Modulated g-modes in the Rapidly Rotating δ Scuti Star Rasalhague (α Ophiuchi)|journal=The Astrophysical Journal|volume=725|issue=1|pages=1192–1201|year=2010|last1=Monnier|first1=J. D|last2=Townsend|first2=R. H. D|last3=Che|first3=X|last4=Zhao|first4=M|last5=Kallinger|first5=T|last6=Matthews|first6=J|last7=Moffat|first7=A. F. J|bibcode=2010ApJ...725.1192M|s2cid=51105576}}</ref>

<ref name=apj726_2_104>{{citation | display-authors=1 | last1=Hinkley | first1=Sasha | last2=Monnier | first2=John D. | last3=Oppenheimer | first3=Ben R. | last4=Roberts | first4=Lewis C. Jr. | last5=Ireland | first5=Michael | last6=Zimmerman | first6=Neil | last7=Brenner | first7=Douglas | last8=Parry | first8=Ian R. | last9=Martinache | first9=Frantz | title=Establishing α Oph as a Prototype Rotator: Improved Astrometric Orbit | journal=The Astrophysical Journal | volume=726 | issue=2 | page=104 |date=January 2011 | doi=10.1088/0004-637X/726/2/104 | bibcode=2011ApJ...726..104H |arxiv = 1010.4028 | s2cid=50830196 }}</ref>

<ref name=apj742_1_9>{{citation | last1=Deupree | first1=Robert G. | title=Theoretical p-Mode Oscillation Frequencies for the Rapidly Rotating δ Scuti Star α Ophiuchi | journal=The Astrophysical Journal | volume=742 | issue=1 | page=9 |date=November 2011 | doi=10.1088/0004-637X/742/1/9 | bibcode=2011ApJ...742....9D |arxiv = 1110.1345 | s2cid=118433889 }}</ref>


<ref name=rmaa38_117>{{citation | display-authors=1 | last1=Zhao | first1=M. | last2=Monnier | first2=J. D. | last3=Pedretti | first3=E. | last4=Thureau | first4=N. | last5=Mérand | first5=A. | last6=Ten Brummelaar | first6=T. | last7=McAlister | first7=H. | last8=Ridgway | first8=S. T. | last9=Turner | first9=N. | title=Imaging and Modeling Rapid Rotators: α Cep and α Oph | department=The Interferometric View on Hot Stars | editor1-first=Th. | editor1-last=Rivinius | editor2-first=M. | editor2-last=Curé | journal=Revista Mexicana de Astronomía y Astrofísica, Serie de Conferencias | volume=38 | pages=117–118 |date=February 2010 | bibcode=2010RMxAC..38..117Z }}</ref>

<ref name=apj661_2_944>{{citation | last1=Redfield | first1=Seth | last2=Kessler-Silacci | first2=Jacqueline E. | last3=Cieza | first3=Lucas A. | title=Spitzer Limits on Dust Emission and Optical Gas Absorption Variability around Nearby Stars with Edge-on Circumstellar Disk Signatures | journal=The Astrophysical Journal | volume=661 | issue=2 | pages=944–971 |date=June 2007 | doi=10.1086/517516 | bibcode=2007ApJ...661..944R |arxiv = astro-ph/0703089 | s2cid=42241365 }}</ref>

<ref name=apj701_1_209>{{citation | display-authors=1 | last1=Zhao | first1=M. | last2=Monnier | first2=J. D. | last3=Pedretti | first3=E. | last4=Thureau | first4=N. | last5=Mérand | first5=A. | last6=ten Brummelaar | first6=T. | last7=McAlister | first7=H. | last8=Ridgway | first8=S. T. | last9=Turner | first9=N. | title=Imaging and Modeling Rapidly Rotating Stars: α Cephei and α Ophiuchi | journal=The Astrophysical Journal | volume=701 | issue=1 | pages=209–224 |date=August 2009 | doi=10.1088/0004-637X/701/1/209 | bibcode=2009ApJ...701..209Z |arxiv = 0906.2241 | s2cid=554145 }}</ref>

<ref name=csiro>{{citation|title=The Colour of Stars |date=December 21, 2004 |work=Australia Telescope, Outreach and Education |publisher=Commonwealth Scientific and Industrial Research Organisation |url=http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |access-date=2012-01-16  |archive-url=https://web.archive.org/web/20120318151427/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |archive-date=March 18, 2012 }}</ref>

<ref name=aass85_3_1015>{{citation | last1=Malagnini | first1=M. L. | last2=Morossi | first2=C. | title=Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars | journal=Astronomy and Astrophysics Supplement Series | volume=85 | issue=3 | pages=1015–1019 |date=November 1990 | bibcode=1990A&AS...85.1015M }}</ref>

<ref name="Gatewood2005">{{cite journal|last1=Gatewood|first1=George|title=An Astrometric Study of the Binary Star α Ophiuchi|journal=The Astronomical Journal|volume=130|issue=2|date=2005|pages=809–814|issn=0004-6256|doi=10.1086/431723|bibcode = 2005AJ....130..809G |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}}</ref>

<ref name="WGSN1">{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf | title=Bulletin of the IAU Working Group on Star Names, No. 1 |access-date=28 July 2016}}</ref>

}}

==External links==
*{{citation | first1=James B. | last1=Kaler | title=RASALHAGUE (Alpha Ophiuchi) | work=Stars | publisher=University of Illinois | url=http://stars.astro.illinois.edu/sow/rasalhague.html | access-date=2011-12-25 }}

{{Sky|17|34|56.06945|+|12|33|36.1346}}
{{Stars of Ophiuchus}}

{{DEFAULTSORT:Alpha Ophiuchi}}
[[Category:Bayer objects|Ophiuchi, Alpha]]
[[Category:Ophiuchus]]
[[Category:Stars with proper names|Rasalhague]]
[[Category:Flamsteed objects|Ophiuchi, 55]]
[[Category:Hipparcos objects|086032]]
[[Category:K-type main-sequence stars]]
[[Category:Binary stars]]
[[Category:Bright Star Catalogue objects|6556]]
[[Category:Henry Draper Catalogue objects|159561]]
[[Category:Durchmusterung objects|BD+12 3252]]
[[Category:A-type subgiants]]