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".[12] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[14] included a table of the first two collections of approved names, formally listing Alpha Ophiuchi as Rasalhague.[15]
PropertiesEdit
Alpha Ophiuchi is a binary star system with an orbital period of about 8.62 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. The primary component, Alpha Ophiuchi A, has a mass of about 2.4 times the mass of the Sun, while the secondary, Alpha Ophiuchi B, has 0.85 solar masses.[4] 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.[9] 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 milliarcseconds.[4]
This star system has a combined apparent magnitude of +2.08 and is located at a distance of about 48.6 light-years (14.9 parsecs) from the Earth. The stellar classification of A5 III indicates that the primary is a bluish-white giant star that has evolved away from the main sequence after consuming the hydrogen at its core. It is radiating about 25 times the luminosity of the Sun and has an effective temperature of about 8,000 K, giving it the characteristic white hue of an A-type star.[8][16]
The 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.[17]
RotationEdit
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 projected rotational velocity of 240 km s−1.[8] It is spinning at about 88.5% of the rate that would cause the star to break up.[18] This gives it an oblate spheroid shape with an equatorial bulge about 20% larger than the polar radius.[9] The polar radius is calculated to be 2.388 R☉ and the equatorial radius 2.858 R☉.[19]
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 9,384 K and the equatorial temperature 7,569 K.[19]
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 87.7° ± 0.4° to the line of sight from the Earth, so that it is being observed from nearly equator-on.[18] The apparent bolometric luminosity seen at this angle is 25.6 L☉, 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 black body, the true effective temperature of 8,336 K is different from the apparent effective temperature of 8,047 K.[19]
ReferencesEdit
^ abcdevan Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600
^ abcJohnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J
^Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819
^ abcdefHinkley, 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{{citation}}: CS1 maint: multiple names: authors list (link)
^Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick (eds.), "The Revision of the General Catalogue of Radial Velocities", Determination of Radial Velocities and Their Applications, Proceedings from IAU Symposium No. 30, University of Toronto: International Astronomical Union, 30: 57, Bibcode:1967IAUS...30...57E
^Gatewood, George (2005). "An Astrometric Study of the Binary Star α Ophiuchi". The Astronomical Journal. 130 (2): 809–814. Bibcode:2005AJ....130..809G. doi:10.1086/431723. ISSN 0004-6256.
^ abMalagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series, 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M
^ abcdeDeupree, 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
^ abcZhao, 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
^"RASALHAGUE -- Variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2011-12-25
^ abKunitzsch, 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. ISBN978-1-931559-44-7.
^"IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
^"Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
^, 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
^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
^ abZhao, 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
^ abcMonnier, 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.
External linksEdit
Kaler, James B., "RASALHAGUE (Alpha Ophiuchi)", Stars, University of Illinois, retrieved 2011-12-25
October 12, 2023
alpha, ophiuchi, ophiuchi, abbreviated, alpha, also, named, rasalhague, binary, star, brightest, star, constellation, ophiuchus, ophiuchilocation, ophiuchi, circled, observation, dataepoch, j2000, equinox, j2000constellation, ophiuchusright, ascension, 06945s,. Alpha Ophiuchi a Ophiuchi abbreviated Alpha Oph a Oph also named Rasalhague ˈ r ae s el h eɪ ɡ 11 12 is a binary star and the brightest star in the constellation of Ophiuchus a OphiuchiLocation of a Ophiuchi circled Observation dataEpoch J2000 Equinox J2000Constellation OphiuchusRight ascension 17h 34m 56 06945s 1 Declination 12 33 36 1346 1 Apparent magnitude V 2 07 2 CharacteristicsSpectral type A5 III 3 K5 7 V 4 U B color index 0 10 2 B V color index 0 15 2 AstrometryRadial velocity Rv 12 6 5 km sProper motion m RA 108 07 1 mas yr Dec 221 57 1 mas yrParallax p 67 13 1 06 mas 1 Distance48 6 0 8 ly 14 9 0 2 pc Absolute magnitude MV 1 248 6 Orbit 4 Period P 3 148 4 daysSemi major axis a 427 20 13 masEccentricity e 0 92 0 03Inclination i 125 6 9 Longitude of the node W 232 9 Periastron epoch T 2 452 888 53 JDArgument of periastron w secondary 162 14 Detailsa Oph AMass2 40 0 23 0 37 4 M Radius2 6 7 R Luminosity25 1 25 6 8 L Surface gravity log g 3 91 7 cgsTemperature7 880 8 050 8 KRotational velocity v sin i 240 8 km sAge0 77 0 03 9 Gyra Oph BMass0 85 0 06 0 04 4 M Other designationsRas Alhague Rasalhague 55 Ophiuchi BD 12 3252 FK5 656 HD 159561 HIP 86032 HR 6556 SAO 102932 10 Database referencesSIMBADdata Contents 1 Nomenclature 2 Properties 2 1 Rotation 3 References 4 External linksNomenclature EditThe name Alpha Ophiuchi is a Romanisation of the star s Bayer designation a Ophiuchi It is also known by the traditional name Rasalhague from the Arabic رأس الحواء raʼs al ḥawwaʼ the head of the serpent collector 12 In 2016 the International Astronomical Union organized a Working Group on Star Names WGSN 13 to catalog and standardize proper names for stars The WGSN s first bulletin of July 2016 14 included a table of the first two collections of approved names formally listing Alpha Ophiuchi as Rasalhague 15 Properties EditAlpha Ophiuchi is a binary star system with an orbital period of about 8 62 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 The primary component Alpha Ophiuchi A has a mass of about 2 4 times the mass of the Sun while the secondary Alpha Ophiuchi B has 0 85 solar masses 4 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 9 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 milliarcseconds 4 This star system has a combined apparent magnitude of 2 08 and is located at a distance of about 48 6 light years 14 9 parsecs from the Earth The stellar classification of A5 III indicates that the primary is a bluish white giant star that has evolved away from the main sequence after consuming the hydrogen at its core It is radiating about 25 times the luminosity of the Sun and has an effective temperature of about 8 000 K giving it the characteristic white hue of an A type star 8 16 The 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 17 Rotation Edit nbsp 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 projected rotational velocity of 240 km s 1 8 It is spinning at about 88 5 of the rate that would cause the star to break up 18 This gives it an oblate spheroid shape with an equatorial bulge about 20 larger than the polar radius 9 The polar radius is calculated to be 2 388 R and the equatorial radius 2 858 R 19 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 9 384 K and the equatorial temperature 7 569 K 19 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 a 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 18 The apparent bolometric luminosity seen at this angle is 25 6 L 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 black body the true effective temperature of 8 336 K is different from the apparent effective temperature of 8 047 K 19 References Edit a b c d e van Leeuwen F November 2007 Validation of the new Hipparcos reduction Astronomy and Astrophysics 474 2 653 664 arXiv 0708 1752 Bibcode 2007A amp A 474 653V doi 10 1051 0004 6361 20078357 S2CID 18759600 a b c Johnson H L et al 1966 UBVRIJKL photometry of the bright stars Communications of the Lunar and Planetary Laboratory 4 99 99 Bibcode 1966CoLPL 4 99J Cowley A et al April 1969 A study of the bright A stars I A catalogue of spectral classifications Astronomical Journal 74 375 406 Bibcode 1969AJ 74 375C doi 10 1086 110819 a b c d e f Hinkley Sasha et al January 2011 Establishing a 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 Template Citation html title Template Citation citation a CS1 maint multiple names authors list link Evans D S June 20 24 1966 Batten Alan Henry Heard John Frederick eds The Revision of the General Catalogue of Radial Velocities Determination of Radial Velocities and Their Applications Proceedings from IAU Symposium No 30 University of Toronto International Astronomical Union 30 57 Bibcode 1967IAUS 30 57E Gatewood George 2005 An Astrometric Study of the Binary Star a Ophiuchi The Astronomical Journal 130 2 809 814 Bibcode 2005AJ 130 809G doi 10 1086 431723 ISSN 0004 6256 a b Malagnini M L Morossi C November 1990 Accurate absolute luminosities effective temperatures radii masses and surface gravities for a selected sample of field stars Astronomy and Astrophysics Supplement Series 85 3 1015 1019 Bibcode 1990A amp AS 85 1015M a b c d e Deupree Robert G November 2011 Theoretical p Mode Oscillation Frequencies for the Rapidly Rotating d Scuti Star a 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 b c Zhao M et al August 2009 Imaging and Modeling Rapidly Rotating Stars a Cephei and a 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 RASALHAGUE Variable Star SIMBAD Centre de Donnees astronomiques de Strasbourg retrieved 2011 12 25 also ˈ h eɪ ɡ juː or ˈ h eɪ ɡ w iː Rasalhague Merriam Webster Dictionary a b 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 IAU Working Group on Star Names WGSN Retrieved 22 May 2016 Bulletin of the IAU Working Group on Star Names No 1 PDF Retrieved 28 July 2016 Stars Pronunciation Guide Space com Retrieved 2017 06 25 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 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 b Zhao M et al February 2010 Rivinius Th Cure M eds Imaging and Modeling Rapid Rotators a Cep and a Oph The Interferometric View on Hot Stars Revista Mexicana de Astronomia y Astrofisica Serie de Conferencias 38 117 118 Bibcode 2010RMxAC 38 117Z a b c 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 d Scuti Star Rasalhague a 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 External links EditKaler James B RASALHAGUE Alpha Ophiuchi Stars University of Illinois retrieved 2011 12 25 Retrieved from https en wikipedia org w index php title Alpha Ophiuchi amp oldid 1154748510, wikipedia, wiki, book, books, library,
