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Alpha Ophiuchi
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<h2 id="nomenclature">Nomenclature</h2> <p>The name Alpha Ophiuchi is a <a href="/facts/Romanisation/a4fl8fee">Romanisation</a> of the star's <a href="/facts/Bayer_designation/KU2DVT47">Bayer designation</a>, <i>α Ophiuchi</i>. It is also known by the traditional name <i>Rasalhague</i>, from the Arabic رأس الحواء <i>raʼs al-ḥawwāʼ</i> "the head of the serpent collector".<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> In 2016, the <a href="/facts/International_Astronomical_Union/GMFPImXo">International Astronomical Union</a> organized a <a href="/facts/IAU_Working_Group_on_Star_Names/EoRy108k">Working Group on Star Names</a> (WGSN)<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> included a table of the first two collections of approved names, formally listing Alpha Ophiuchi as <i>Rasalhague</i>.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p> <h2 id="properties">Properties</h2> <p>Alpha Ophiuchi is a <a href="/facts/Binary_star/TYlDe1bD">binary star</a> system with an orbital period of about 8.62 years. The orbital parameters were only poorly known until 2011 when observations using <a href="/facts/Adaptive_optics/D1vWeHK0">adaptive optics</a> produced a better orbital fit, allowing the individual masses of the two components to be determined.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> The orbital elements and masses were further improved in a 2021 study.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> The primary component, Alpha Ophiuchi A, has a mass of about 2.2 times the <a href="/facts/Solar_mass/j6Auhku8">mass of the Sun</a>, while the secondary, Alpha Ophiuchi B, has 0.82 solar masses.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> 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.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> The mass of the secondary suggests that it has a <a href="/facts/Stellar_classification/dYrIuK9H">stellar classification</a> in the range K5V to K7V, which indicates it is a <a href="/facts/Main_sequence/DJ3Wq8kd">main sequence</a> star that is still generating energy by the <a href="/facts/Thermonuclear_fusion/fzQUW49h">thermonuclear fusion</a> of hydrogen at its core. The pair reached <a href="/facts/Periastron/VaL6ow9w">periastron</a> passage, or closest approach, around April 19, 2012, when they had an angular separation of 50 <a href="/facts/Milliarcsecond/tybs6YGC">milliarcseconds</a>.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p><p>This star system has a combined <a href="/facts/Apparent_magnitude/7pCTF1Me">apparent magnitude</a> of +2.08 and is located at a distance of about 48.6 <a href="/facts/Light-year/IGc5NdQb">light-years</a> (14.9 <a href="/facts/Parsec/SwSsk57J">parsecs</a>) from the <a href="/facts/Earth/HLLmDfj0">Earth</a>. The <a href="/facts/Stellar_classification/dYrIuK9H">stellar classification</a> of A5IVnn indicates that the primary is a bluish-white <a href="/facts/Subgiant/wD7o7E2Q">subgiant</a> star that has evolved away from the main sequence after consuming the hydrogen at its core.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> It is radiating about 25 times the <a href="/facts/Solar_luminosity/CLG0r9bP">luminosity of the Sun</a> and has an <a href="/facts/Effective_temperature/RY30DaSY">effective temperature</a> of about 8,000 K, giving it the characteristic white hue of an A-type star.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a><a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p><p>The <a href="/facts/Stellar_spectrum/NDGQ7mmM">spectrum</a> 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.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> </p> <h3>Rotation</h3> <p>Alpha Ophiuchi A is a rapidly rotating star with a <a href="/facts/Stellar_rotation/N0VzIXLC">projected rotational velocity</a> of 240 km s−1.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> It is spinning at about 88.5% of the rate that would cause the star to break up.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> This gives it an <a href="/facts/Oblate_spheroid/GJyyLxQ7">oblate spheroid</a> shape with an equatorial bulge about 20% larger than the polar radius.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> The polar radius is calculated to be 2.388 R☉ and the equatorial radius 2.858 R☉.<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> </p><p>Because of the oblateness and rapid spin, the <a href="/facts/Surface_gravity/Q5QVbA7e">surface gravity</a> at the pole is higher than at the equator. An effect known as <a href="/facts/Gravity_darkening/Jp1fuYDa">gravity darkening</a> means that the temperature at the poles is also higher than at the equator. The polar temperature is calculated to be 9,384 K and the equatorial temperature 7,569 K.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> </p><p>The energy radiated by an oblate star is higher along its axis of rotation because of the larger projected area and the <a href="/facts/Stefan%25E2%2580%2593Boltzmann_law/vA4tbwKC">Stefan–Boltzmann law</a>. The axis of rotation of α Ophiuchi is inclined about 87.7° ± 0.4° to the line of sight from the Earth, so that it is being observed from nearly equator-on.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> The apparent <a href="/facts/Bolometric_luminosity/1tdhpk9l">bolometric luminosity</a> seen at this angle is 25.6 <a href="/facts/Solar_luminosity/CLG0r9bP">L☉</a>, but the true luminosity of the star is thought to be 31.3 L☉. Since a star's effective temperature is simply the temperature which would produce its total energy output from a <a href="/facts/Black_body/f0fHghDy">black body</a>, the true effective temperature of 8,336 K is different from the apparent effective temperature of 8,047 K.<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Vega/G3wJwhhl">Vega</a>, <a href="/facts/Altair/avsmInG0">Altair</a> and <a href="/facts/Alderamin/UjeEsuUD">Alderamin</a>, stars similar to Alpha Ophiuchi A in physical characteristics</li> <li><a href="/facts/List_of_nearest_bright_stars/CHHePdRq">List of nearest bright stars</a></li> <li><a href="/facts/List_of_nearest_stars_by_spectral_type/Juq4E4KE">List of nearest A-type stars</a></li></ul> <h2 id="external-links">External links</h2> <ul><li>Kaler, James B., <a href="http://stars.astro.illinois.edu/sow/rasalhague.html">"RASALHAGUE (Alpha Ophiuchi)"</a>, <i>Stars</i>, University of Illinois, retrieved 2011-12-25</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>also /-ˈheɪɡjuː/ or /-ˈheɪɡwiː/. "Rasalhague". Merriam-Webster.com Dictionary. Merriam-Webster. <a href="/wiki/Help:IPA/English" target="_blank">/wiki/Help:IPA/English</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7. <a href="978-1-931559-44-7" target="_blank">978-1-931559-44-7</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7. <a href="978-1-931559-44-7" target="_blank">978-1-931559-44-7</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016. <a href="https://www.iau.org/science/scientific_bodies/working_groups/280/" target="_blank">https://www.iau.org/science/scientific_bodies/working_groups/280/</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016. <a href="http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf" target="_blank">http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>"Stars Pronunciation Guide". Space.com. Retrieved 2017-06-25. <a href="https://www.space.com/3250-stars-pronunciation-guide.html" target="_blank">https://www.space.com/3250-stars-pronunciation-guide.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Hinkley, Sasha; et al. (January 2011), "Establishing α Oph as a Prototype Rotator: Improved Astrometric Orbit", The Astrophysical Journal, 726 (2): 104, arXiv:1010.4028, Bibcode:2011ApJ...726..104H, doi:10.1088/0004-637X/726/2/104, S2CID 50830196 <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Gardner, Tyler; Monnier, John D.; Fekel, Francis C.; Williamson, Michael; Baron, Fabien; Hinkley, Sasha; Ireland, Michael; Kraus, Adam L.; Kraus, Stefan; Roettenbacher, Rachael M.; Schaefer, Gail; Sturmann, Judit; Sturmann, Laszlo; ten Brummelaar, Theo (2021-11-01). "Establishing α Oph as a Prototype Rotator: Precision Orbit with New Keck, CHARA, and RV Observations". The Astrophysical Journal. 921: 41. arXiv:2107.02844. Bibcode:2021ApJ...921...41G. doi:10.3847/1538-4357/ac1172. ISSN 0004-637X. <a href="https://doi.org/10.3847%2F1538-4357%2Fac1172" target="_blank">https://doi.org/10.3847%2F1538-4357%2Fac1172</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Gardner, Tyler; Monnier, John D.; Fekel, Francis C.; Williamson, Michael; Baron, Fabien; Hinkley, Sasha; Ireland, Michael; Kraus, Adam L.; Kraus, Stefan; Roettenbacher, Rachael M.; Schaefer, Gail; Sturmann, Judit; Sturmann, Laszlo; ten Brummelaar, Theo (2021-11-01). "Establishing α Oph as a Prototype Rotator: Precision Orbit with New Keck, CHARA, and RV Observations". The Astrophysical Journal. 921: 41. arXiv:2107.02844. Bibcode:2021ApJ...921...41G. doi:10.3847/1538-4357/ac1172. ISSN 0004-637X. <a href="https://doi.org/10.3847%2F1538-4357%2Fac1172" target="_blank">https://doi.org/10.3847%2F1538-4357%2Fac1172</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Zhao, M.; et al. (August 2009), "Imaging and Modeling Rapidly Rotating Stars: α Cephei and α Ophiuchi", The Astrophysical Journal, 701 (1): 209–224, arXiv:0906.2241, Bibcode:2009ApJ...701..209Z, doi:10.1088/0004-637X/701/1/209, S2CID 554145 <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Hinkley, Sasha; et al. (January 2011), "Establishing α Oph as a Prototype Rotator: Improved Astrometric Orbit", The Astrophysical Journal, 726 (2): 104, arXiv:1010.4028, Bibcode:2011ApJ...726..104H, doi:10.1088/0004-637X/726/2/104, S2CID 50830196 <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>"alf Oph". SIMBAD. Retrieved December 23, 2023. <a href="https://simbad.cds.unistra.fr/mobile/object.html?object_name=alf+Oph" target="_blank">https://simbad.cds.unistra.fr/mobile/object.html?object_name=alf+Oph</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Deupree, Robert G. (November 2011), "Theoretical p-Mode Oscillation Frequencies for the Rapidly Rotating δ Scuti Star α Ophiuchi", The Astrophysical Journal, 742 (1): 9, arXiv:1110.1345, Bibcode:2011ApJ...742....9D, doi:10.1088/0004-637X/742/1/9, S2CID 118433889 <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>"The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 18, 2012, retrieved 2012-01-16 <a href="https://web.archive.org/web/20120318151427/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html" target="_blank">https://web.archive.org/web/20120318151427/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Redfield, Seth; Kessler-Silacci, Jacqueline E.; Cieza, Lucas A. (June 2007), "Spitzer Limits on Dust Emission and Optical Gas Absorption Variability around Nearby Stars with Edge-on Circumstellar Disk Signatures", The Astrophysical Journal, 661 (2): 944–971, arXiv:astro-ph/0703089, Bibcode:2007ApJ...661..944R, doi:10.1086/517516, S2CID 42241365 <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Deupree, Robert G. (November 2011), "Theoretical p-Mode Oscillation Frequencies for the Rapidly Rotating δ Scuti Star α Ophiuchi", The Astrophysical Journal, 742 (1): 9, arXiv:1110.1345, Bibcode:2011ApJ...742....9D, doi:10.1088/0004-637X/742/1/9, S2CID 118433889 <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>Zhao, M.; et al. (February 2010), Rivinius, Th.; Curé, M. (eds.), "Imaging and Modeling Rapid Rotators: α Cep and α Oph", The Interferometric View on Hot Stars, Revista Mexicana de Astronomía y Astrofísica, Serie de Conferencias, 38: 117–118, Bibcode:2010RMxAC..38..117Z <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>Zhao, M.; et al. (August 2009), "Imaging and Modeling Rapidly Rotating Stars: α Cephei and α Ophiuchi", The Astrophysical Journal, 701 (1): 209–224, arXiv:0906.2241, Bibcode:2009ApJ...701..209Z, doi:10.1088/0004-637X/701/1/209, S2CID 554145 <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>Monnier, J. D; Townsend, R. H. D; Che, X; Zhao, M; Kallinger, T; Matthews, J; Moffat, A. F. J (2010). "Rotationally Modulated g-modes in the Rapidly Rotating δ Scuti Star Rasalhague (α Ophiuchi)". The Astrophysical Journal. 725 (1): 1192–1201. arXiv:1012.0787. Bibcode:2010ApJ...725.1192M. doi:10.1088/0004-637X/725/1/1192. S2CID 51105576. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Monnier, J. D; Townsend, R. H. D; Che, X; Zhao, M; Kallinger, T; Matthews, J; Moffat, A. F. J (2010). "Rotationally Modulated g-modes in the Rapidly Rotating δ Scuti Star Rasalhague (α Ophiuchi)". The Astrophysical Journal. 725 (1): 1192–1201. arXiv:1012.0787. Bibcode:2010ApJ...725.1192M. doi:10.1088/0004-637X/725/1/1192. S2CID 51105576. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>Zhao, M.; et al. (February 2010), Rivinius, Th.; Curé, M. (eds.), "Imaging and Modeling Rapid Rotators: α Cep and α Oph", The Interferometric View on Hot Stars, Revista Mexicana de Astronomía y Astrofísica, Serie de Conferencias, 38: 117–118, Bibcode:2010RMxAC..38..117Z <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> <li id="fn:22"><p>Monnier, J. D; Townsend, R. H. D; Che, X; Zhao, M; Kallinger, T; Matthews, J; Moffat, A. F. J (2010). "Rotationally Modulated g-modes in the Rapidly Rotating δ Scuti Star Rasalhague (α Ophiuchi)". The Astrophysical Journal. 725 (1): 1192–1201. arXiv:1012.0787. Bibcode:2010ApJ...725.1192M. doi:10.1088/0004-637X/725/1/1192. S2CID 51105576. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></p></li> </ol>