eta Ophiuchi

{{Starbox begin

| name = Eta Ophiuchi (Sabik)

}}

{{Starbox image

| image=

{{Location mark

|image=Ophiuchus constellation map.svg|alt=|float=center|width=280

|label=|position=right

}}

|caption=Location of η Ophiuchi (circled)

}}

{{Starbox observe

| epoch = J2000

| ra = {{RA|17|10|22.68689}}

| dec = {{DEC|–15|43|29.6639}}

| appmag_v = 2.43{{cite web | url=http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HR%202491 | title=Entry for HR 2491 | work=Bright Star Catalogue |edition=5th revised (Preliminary Version) |author1=Hoffleit, D. |author2=Warren, W. H. Jr. | date=1991 | publisher=CDS }} ID [http://vizier.u-strasbg.fr/viz-bin/Cat?V/50 V/50]. (3.05/3.27)

| constell = Ophiuchus

}}

{{Starbox character

| type = main sequence

| class = A2V + A2V

| b-v = +0.05

| u-b = +0.09

| variable =

}}

{{Starbox astrometry

| radial_v = −0.9

| prop_mo_ra = +40.13

| prop_mo_dec = +99.17

| parallax = 36.91

| p_error = 0.80

| parallax_footnote =

| absmag_v =

}}

{{Starbox orbit

| reference =

| period = {{val|87.77|0.28|0.24}}

| axis_unitless = {{Val|31.05|1.41|1.35|ul=au}}

| eccentricity = {{val|0.93077|0.00013|0.00012}}

| inclination = {{val|96.305|0.019|0.018}}

| node = {{val|39.241|0.011}}

| periastron = 2024.526

| periarg = {{val|275.90|0.10|0.11}}

}}

{{Starbox detail

| source =

| component1 = η Oph A (Sabik)

| mass = {{Val|2.25|0.18|0.09}}

| radius = {{Val|2.5|0.4}}

| luminosity = 35

| temperature = {{Val|9000|1250|750|fmt=commas}}

| metal = {{val|-0.01}} dex

| gravity = 3.74{{cite journal|bibcode= 2006AJ....132..161G|arxiv = astro-ph/0603770 |doi = 10.1086/504637 |title = Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc--The Southern Sample |journal = The Astronomical Journal |volume = 132 |pages = 161–170 |year = 2006 |last1 = Gray |first1 = R. O. |last2 = Corbally |first2 = C. J. |last3 = Garrison |first3 = R. F. |last4 = McFadden |first4 = M. T. |last5 = Bubar |first5 = E. J. |last6 = McGahee |first6 = C. E. |last7 = O'Donoghue |first7 = A. A. |last8 = Knox |first8 = E. R. |issue = 1 |s2cid = 119476992 }}

| rotational_velocity = 23

| age_myr = {{Val|500|210|280}}

| component2 = η Oph B

| mass2 = {{Val|2.03|0.02}}

| radius2 = {{Val|2.0|0.3|0.2}}

| temperature2 = {{Val|8700|450|fmt=commas}}

| luminosity2 = 21

| age_myr2 = {{Val|500|210|280}}

}}

{{Starbox catalog

| names = Sabik, 35 Oph, BD−15°4467, GCTP 3895.00, Gl 656.1A/B, HD 155125, HIP 84012, HR 6378, SAO 160332, WDS J17104-1544AB

}}

{{Starbox reference

| Simbad=HD+155125

}}

Eta Ophiuchi (η Ophiuchi, abbreviated Eta Oph, η Oph) is a binary star in the constellation of Ophiuchus. With a combined apparent magnitude of +2.43, it is the second-brightest of the constellation and one of the brightest stars in the night sky. Based on parallax measurements taken during the Hipparcos mission, it is approximately 88 light-years away.

Eta Ophiuchi is part of a multiple star system designated WDS J17104-1544. It itself is designated WDS J17104-1544AB and its two components WDS J17104-1544A (also called Sabik {{IPAc-en|'|s|ei|b|I|k}}, the traditional name for the system){{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

}}{{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars |publisher=IAU.org |access-date=27 February 2018}} and WDS J17104-1544B. The 'C' component is UCAC4 372-080717{{citation | title=UCAC4 372-080717 -- Star | work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=WDS+J17104-1544+C&submit=submit+id | access-date=2018-02-27 }} and 'D' is UCAC2 26022336.{{citation | title=UCAC2 26022336 -- Star | work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=WDS+J17104-1544+D&submit=submit+id | access-date=2018-02-27 }}

Nomenclature

η Ophiuchi (Latinised to Eta Ophiuchi) is the system's Bayer designation. WDS J17104-1544AB is its designation in the Washington Double Star Catalog. The designations of the two components as WDS J17104-1544 A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).{{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. }}

It bore the traditional name Sabik, from the Arabic السابق al-sābiq "the preceding one", of uncertain reference. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN){{citation

| url=https://www.iau.org/science/scientific_bodies/working_groups/280/

| title=IAU Working Group on Star Names (WGSN)

| publisher=International Astronomical Union

| access-date=22 May 2016 | postscript=. }} to catalogue and standardize proper names for stars. The WGSN approved the name Sabik for the component WDS J17104-1544 A on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.

In Chinese, this star is considered part of {{lang|zh|天市左垣}} ({{lang|zh-Latn|Tiān Shì Zuǒ Yuán}}), meaning Left Wall of Heavenly Market Enclosure, which refers to an asterism representing eleven old states in China that mark the left borderline of the enclosure, consisting of Eta Ophiuchi, Delta Herculis, Lambda Herculis, Mu Herculis, Omicron Herculis, 112 Herculis, Zeta Aquilae, Theta Serpentis, Eta Serpentis, Nu Ophiuchi and Xi Serpentis.{{in lang|zh}} 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, {{ISBN|978-986-7332-25-7}}. Consequently, the Chinese name for Eta Ophiuchi itself is {{lang|zh|天市左垣十一}} ({{lang|zh-Latn|Tiān Shì Zuǒ Yuán shíyī}}, {{langx|en|the Eleventh Star of Left Wall of Heavenly Market Enclosure}}), representing the state Song (宋).{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_s.htm 香港太空館 - 研究資源 - 亮星中英對照表] {{webarchive |url=https://web.archive.org/web/20100818141141/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_s.htm |date=August 18, 2010 }}, Hong Kong Space Museum. Accessed on line November 23, 2010.{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/e_research_chinengstarzone_b.htm#HeavenlyMarketEnclosure English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name] {{webarchive |url=https://web.archive.org/web/20100810114313/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/e_research_chinengstarzone_b.htm#HeavenlyMarketEnclosure |date=August 10, 2010 }}, Hong Kong Space Museum. Accessed on line November 23, 2010.

=Namesake=

USS Sabik (AK-121) was a United States Navy Crater class cargo ship named after the star.

Properties

Eta Ophiuchi consists on two A-type main-sequence stars, currently fusing hydrogen into helium at their core. The primary, of apparent magnitude +3.05, has about 2.5 times the Sun's radius and 2.25 times its mass, with an effective temperature around 9,000 K. The secondary, of apparent magnitude +3.27, is 2 times as large and massive than the Sun, with an effective temperature of 8,700 K. The estimated age of the system is 500 million years, albeit with significant uncertainty.

The stars take 87.8 years to complete an orbit, which is highly elliptical: While the semi-major axis is 31 astronomical units, the high orbital eccentricity of 0.931 take them to a distance of 2.15 au during their closest apporach (the periastron); the last of such occurring in 2024. Such large eccentricity hindered accurate measurements of the stellar mass with the Kepler's third law, until observations with the Very Large Telescope during the most recent periastron accurately determined orbital elements such as the eccentricity, hence a considerable mass sum for A2V-type stars.

References

{{Reflist|refs=

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

{{citation | last=Wilson | first=Ralph Elmer | date=1953 | title=General Catalogue of Stellar Radial Velocities | journal=Washington | pages=0 | publisher=Carnegie Institution of Washington | location=Washington | bibcode=1953GCRV..C......0W }}

{{citation | last1=Royer | first1=F. | last2=Zorec | first2=J. | last3=Gómez | first3=A. E. | title=Rotational velocities of A-type stars. III. Velocity distributions | journal=Astronomy and Astrophysics | volume=463 | issue=2 | pages=671–682 |date=February 2007 | doi=10.1051/0004-6361:20065224 | bibcode=2007A&A...463..671R |arxiv = astro-ph/0610785 | s2cid=18475298 }}

{{Citation |last=Waisberg |first=Idel |last2=Klein |first2=Ygal |last3=Katz |first3=Boaz |title=Which is the most eccentric binary known? Insights from the 2023/4 pericenter passages of Zeta Boötis and Eta Ophiuchi |date=2025-04-24 |arxiv=2504.17858 }}

[http://stars.astro.illinois.edu/sow/sabik.html Sabik]. stars.astro.illinois.edu. Retrieved July 1, 2024.

{{citation | last1=Docobo | first1=J. A. | last2=Ling | first2=J. F. | title=Orbits and System Masses of 14 Visual Double Stars with Early-Type Components | journal=The Astronomical Journal | volume=133 | issue=4 | pages=1209–1216 |date=April 2007 | doi=10.1086/511070 | bibcode=2007AJ....133.1209D | s2cid=120821801 | doi-access=free }}

}}

Ophiuchi, Eta

Category:Binary stars

Category:A-type main-sequence stars