omega Ophiuchi
{{Short description|Star in the constellation Ophiuchus}}
{{Starbox begin}}
{{Starbox image
| image =
{{Location mark
|image=Ophiuchus constellation map.svg|alt=|float=center|width=280
|label=|position=right
|mark=Red circle.svg|mark_width=12|mark_link=Omega Ophiuchi
|x=720|y=830
}}
| caption=Location of ω Ophiuchi (circled)
}}
{{Starbox observe
| epoch = J2000
| constell = Ophiuchus
| dec = {{DEC|−21|27|59.0120}}
}}
{{Starbox character
| type = main sequence
| class = ApSrEuCr or {{nowrap|A2 VpSrCrEu Ksn{{cite journal |bibcode=2014yCat....1.2023S |title=VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009- ) |last1=Skiff |first1=B. A. |journal=Vizier Online Data Catalog |date=2014 }}}}
| variable = α2 CVn
}}
{{Starbox astrometry
| parallax = 19.34
| p_error = 0.21
}}
{{Starbox detail
| mass = {{Val|2.25|0.13|0.35}}
| radius = {{Val|2.97|0.19}}
| gravity = {{Val|3.85|0.65|0.69}}
| age_myr = {{Val|860|150|110}}
| rotation = {{Val|2.3205|0.0002}} days
| temperature = {{Val|8150|250|fmt=commas}}
| luminosity = {{Val|34.7|1.6}}
| rotational_velocity = {{Val|32.2|1.4}}
}}
{{Starbox catalog
| names = {{odlist | B=ω Oph | F=9 Ophiuchi | BD=−21°4381 | FK5=3307 | HD=148898 | HIP=80975 | HR=6153 | SAO=184450 | GC=22221 }}
}}
{{Starbox reference
| Simbad = ome+Oph
}}
{{Starbox end}}
Omega Ophiuchi, which is Latinized from ω Ophiuchi, is a variable star in the equatorial constellation of Ophiuchus, located just to the north of the ecliptic near the western constellation border with Scorpius. It is a white-hued star that is faintly visible to the naked eye with an apparent visual magnitude that fluctuates around 4.45. Parallax measurements indicate it lies at a distance of about 168.6 light years from the Sun. It is drifting further away with a radial velocity of +2.5 km/s.
This is an Ap star with a stellar classification of ApSrEuCr, displaying strong abundance anomalies of the elements strontium, europium, and chromium. Abt and Morrell (1995) found a class of {{nowrap|A2 Vp(SrCrEu Ksn)}}, showing further an A-type main-sequence star with a Ca II line (singly-ionized calcium) having both sharp and broad components. It is an Alpha2 Canum Venaticorum variable, with its brightness ranging from magnitude 4.44 down to 4.51 over a period of 2.99 days. A strong magnetic field has been measured on the surface.
Omega Ophiuchi is around 860 million years old with a projected rotational velocity of 32.2 km/s and a rotation period of 2.3 days. It has 2.3 times the mass of the Sun and 3.0 times the Sun's radius. The star is radiating 35 times the luminosity of the Sun from its photosphere at an effective temperature of 8,150 K. It is a source of X-ray emission.
On 9 December 2017, it was occulted by Venus as viewed from the South Atlantic.{{cite book |date=2002 |first=Jan |last=Meeus |chapter=Mutual occultations of planets |pages=174–185 |title=More Mathematical Astronomy Morsels |isbn=0943396743 |url=https://falakmu.id/khgt/dokumen/More%20mathematical%20astronomy%20morsels%20(Jean%20Meeus)%20(Z-Library).pdf}}{{rp|165}}
This star has a significant change in its proper motion measurements over time, suggesting it may be an astrometric binary. The proposed companion is probably a compact star such as a white dwarf.
References
{{reflist|refs=
| title=ome Oph | access-date=2019-10-28 }}
| title=Magnetic fields in X-ray emitting A-type stars
| display-authors=1 | last1=Schröder | first1=C.
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| journal=Contributions of the Astronomical Observatory Skalnaté Pleso
| volume=38 | issue=2 | pages=447–448 | date=April 2008
| arxiv=0712.0173 | bibcode=2008CoSka..38..447S }}
| title=A volume-limited survey of mCP stars within 100 pc - I. Fundamental parameters and chemical abundances
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| journal=Monthly Notices of the Royal Astronomical Society
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| doi=10.1093/mnras/sty3105 | doi-access=free | arxiv=1811.05633
| bibcode=2019MNRAS.483.2300S | s2cid=119089236 | display-authors=1 }}
| title=A volume-limited survey of mCP stars within 100 pc II: rotational and magnetic properties
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| last3=Power | first3=J. | last4=Neiner | first4=C.
| journal=Monthly Notices of the Royal Astronomical Society
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| doi=10.1093/mnras/sty2895 | doi-access=free | arxiv=1811.05635
| bibcode=2019MNRAS.483.3127S | s2cid=119415579 | display-authors=1 }}
| last1=Houk | first1=Nancy | last2=Smith-Moore | first2=M.
| title=Michigan catalogue of two-dimensional spectral types for the HD stars
| volume=4 | location=Ann Arbor | year=1978
| publisher=Dept. of Astronomy, University of Michigan
| bibcode=1988mcts.book.....H }}
| last1=Abt | first1=Helmut A. | last2=Morrell | first2=Nidia I.
| title=The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
| journal=Astrophysical Journal Supplement
| volume=99 | pages=135 | year=1995
| bibcode=1995ApJS...99..135A | doi=10.1086/192182 | doi-access=free }}
| display-authors=1 | last1=Samus | first1=N. N.
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| title=General Catalogue of Variable Stars
| version=5.1 | journal=Astronomy Reports
| year=2017 | volume=61 | issue=1 | pages=80–88
| bibcode=2017ARep...61...80S | doi=10.1134/S1063772917010085 | s2cid=125853869 }}
| arxiv=0708.1752 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357
| title=Validation of the new Hipparcos reduction
| journal=Astronomy and Astrophysics
| volume=474 | issue=2 | pages=653–664 | year=2007
| last1=Van Leeuwen | first1=F.
| s2cid=18759600 }} [http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HIP%2080975 Vizier catalog entry]
| last1=Ducati | first1=J. R.
| title=VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system
| journal=CDS/ADC Collection of Electronic Catalogues
| volume=2237 | year=2002 | bibcode=2002yCat.2237....0D }}
| doi=10.1134/S1063773706110065 | bibcode=2006AstL...32..759G | arxiv=1606.08053
| title=Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system
| journal=Astronomy Letters
| volume=32 | issue=11 | pages=759–771 | year=2006
| last1=Gontcharov | first1=G. A. | s2cid=119231169 }}
| bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015 | arxiv=1108.4971
| title=XHIP: An extended hipparcos compilation
| journal=Astronomy Letters
| volume=38 | issue=5 | pages=331 | year=2012
| last1=Anderson | first1=E. | last2=Francis | first2=Ch.
| s2cid=119257644 }} [http://vizier.u-strasbg.fr/viz-bin/VizieR-4?-source=V/137D/XHIP&HIP=80975 Vizier catalog entry]
| bibcode=2016A&A...591A.118S | doi=10.1051/0004-6361/201628497 |arxiv=1605.07384
| title=The PASTEL catalogue: 2016 version
| journal=Astronomy & Astrophysics
| volume=591 | pages=A118 | year=2016
| last1=Soubiran | first1=Caroline | last2=Le Campion | first2=Jean-François
| last3=Brouillet | first3=Nathalie | last4=Chemin | first4=Laurent | s2cid=119258214 }}
}}
{{Stars of Ophiuchus}}
{{DEFAULTSORT:Omega Ophiuchi}}
Category:A-type main-sequence stars