{{Short description|Blue-hued star in the constellation Hydra}} {{Starbox begin}} {{Starbox image | image = {{Location mark |image=Hydra constellation map.svg|alt=|float=center|width=320 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=ο Hydrae |x=425|y=500 }} | caption = Location of ο Hydrae (circled in red) }} {{Starbox observe | epoch = [[J2000.0]] | equinox = [[J2000.0]] ([[International Celestial Reference System|ICRS]]) | constell = [[Hydra (constellation)|Hydra]]<ref name=Anderson2012/> | ra = {{RA|11|40|12.78970}}<ref name=vanLeeuwen2007/> | dec = {{DEC|−34|44|40.7733}}<ref name=vanLeeuwen2007/> | appmag_v = 4.70<ref name=Mermilliod1986/> }} {{Starbox character | type = [[main sequence]]<ref name=Zorec2012/> | class = B9 V<ref name=Houk1982/> | b-v = −0.08<ref name=Mermilliod1986/> | u-b = −0.20<ref name=Mermilliod1986/> | r-i = | variable = }} {{Starbox astrometry | radial_v = +5.9<ref name=fk6_3/> | prop_mo_ra = −43.24<ref name=vanLeeuwen2007/> | prop_mo_dec = −1.61<ref name=vanLeeuwen2007/> | parallax = 7.27 | p_error = 0.16 | parallax_footnote = <ref name=vanLeeuwen2007/> | absmag_v = −0.99<ref name=Anderson2012/> }} {{Starbox detail | source = | mass = {{Val|3.56|0.04}}<ref name=Zorec2012/> | radius = 5.5<ref name=tic/> | luminosity = 309<ref name=Zorec2012/> | temperature = 10,495<ref name=Zorec2012/> | gravity = 2.87<ref name=oelkers2018/> | metal_fe = | rotation = 27.2 days<ref name=oelkers2018/> | rotational_velocity = 160<ref name=Zorec2012/> | age_myr = 252<ref name=gontcharov2012/> }} {{Starbox catalog | names = [[Bayer designation|ο Hya]], [[Durchmusterung|CD]]−34°7610, [[FK5]] 439, [[Henry Draper Catalogue|HD]] 101431, [[Hipparcos Catalogue|HIP]] 56922, [[Bright Star Catalogue|HR]] 4494, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]] 202695<ref name=SIMBAD/> }} {{Starbox reference | Simbad = omi+Hya }} {{starbox end}} '''Omicron Hydrae''' ('''ο Hya''') is the [[Bayer designation]] for a solitary<ref name=Eggleton2008/> [[star]] in the equatorial [[constellation]] [[Hydra (constellation)|Hydra]]. At one time it bore the [[Flamsteed designation]] '''25 Crateris''', but this is no longer used by astronomers so as to avoid confusion.<ref name=Wagman1987/> With an [[apparent visual magnitude]] of 4.70,<ref name=Mermilliod1986/> this star is visible to the naked eye. Based upon an annual [[stellar parallax|parallax shift]] of 7.27 [[milliarcsecond|mas]],<ref name=vanLeeuwen2007/> it is located around 449 [[light year]]s from the [[Sun]].
This is a [[B-type main sequence star]] with a [[stellar classification]] of B9 V.<ref name=Houk1982/> It has completed an estimated {{Val|98.4|1.1|u=%}} of its lifetime on the [[main sequence]]. With 3.56<ref name=Zorec2012/> times the [[Solar mass|mass of the Sun]], it radiates 309 times the [[solar luminosity|Sun's luminosity]] from its [[stellar atmosphere|outer atmosphere]] at an [[effective temperature]] of 10,495 K.<ref name=Zorec2012/> The rate of spin is relatively high, with a [[projected rotational velocity]] of 160 km/s.<ref name=Zorec2012/>
==References== <references> <ref name=vanLeeuwen2007>{{citation | title=Validation of the new Hipparcos reduction | last1=van Leeuwen | first1=F. | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–664 | date=2007 | arxiv=0708.1752 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | s2cid=18759600 | postscript=. }}</ref>
<ref name=Anderson2012>{{cite XHIP|56922|mode=cs2|postscript=.}}</ref>
<ref name=oelkers2018>{{citation |postscript=. |bibcode=2018AJ....155...39O |title=Variability Properties of Four Million Sources in the TESS Input Catalog Observed with the Kilodegree Extremely Little Telescope Survey |last1=Oelkers |first1=Ryan J. |last2=Rodriguez |first2=Joseph E. |last3=Stassun |first3=Keivan G. |last4=Pepper |first4=Joshua |last5=Somers |first5=Garrett |last6=Kafka |first6=Stella |last7=Stevens |first7=Daniel J. |last8=Beatty |first8=Thomas G. |last9=Siverd |first9=Robert J. |last10=Lund |first10=Michael B. |last11=Kuhn |first11=Rudolf B. |last12=James |first12=David |last13=Gaudi |first13=B. Scott |journal=The Astronomical Journal |date=2018 |volume=155 |issue=1 |page=39 |doi=10.3847/1538-3881/aa9bf4 |doi-access=free |arxiv=1711.03608 }}</ref>
<ref name=tic>{{citation |postscript=. |bibcode=2019AJ....158..138S |title=The Revised TESS Input Catalog and Candidate Target List |last1=Stassun |first1=Keivan G. |last2=Oelkers |first2=Ryan J. |last3=Paegert |first3=Martin |last4=Torres |first4=Guillermo |last5=Pepper |first5=Joshua |last6=De Lee |first6=Nathan |last7=Collins |first7=Kevin |last8=Latham |first8=David W. |last9=Muirhead |first9=Philip S. |last10=Chittidi |first10=Jay |last11=Rojas-Ayala |first11=Bárbara |last12=Fleming |first12=Scott W. |last13=Rose |first13=Mark E. |last14=Tenenbaum |first14=Peter |last15=Ting |first15=Eric B. |last16=Kane |first16=Stephen R. |last17=Barclay |first17=Thomas |last18=Bean |first18=Jacob L. |last19=Brassuer |first19=C. E. |last20=Charbonneau |first20=David |last21=Ge |first21=Jian |last22=Lissauer |first22=Jack J. |last23=Mann |first23=Andrew W. |last24=McLean |first24=Brian |last25=Mullally |first25=Susan |last26=Narita |first26=Norio |last27=Plavchan |first27=Peter |last28=Ricker |first28=George R. |last29=Sasselov |first29=Dimitar |last30=Seager |first30=S. |journal=The Astronomical Journal |date=2019 |volume=158 |issue=4 |page=138 |doi=10.3847/1538-3881/ab3467 |doi-access=free |arxiv=1905.10694 |display-authors=1 }}</ref>
<ref name=gontcharov2012>{{citation |postscript=. |bibcode=2012AstL...38..771G |title=Dependence of kinematics on the age of stars in the solar neighborhood |last1=Gontcharov |first1=G. A. |journal=Astronomy Letters |date=2012 |volume=38 |issue=12 |page=771 |doi=10.1134/S1063773712120031 |arxiv=1606.08814 }}</ref>
<ref name=fk6_3>{{citation | display-authors=1 | last1=Wielen | first1=R. | last2=Schwan | first2=H. | last3=Dettbarn | first3=C. | last4=Lenhardt | first4=H. | last5=Jahreiß | first5=H. | last6=Jährling | first6=R. | last7=Khalisi | first7=E. | title=Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions | work=Veröffentlichungen Astronomisches Rechen-Institut Heidelberg | publisher=Verlag G. Braun | publication-place=Karlsruhe | issue=37 | pages=1–308 | isbn=3-7650-0536-3 | date=2000 | volume=37 | bibcode=2000VeARI..37....1W | postscript=. }}</ref>
<ref name=Eggleton2008>{{citation | last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A. | title=A catalogue of multiplicity among bright stellar systems | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=389 | issue=2 | pages=869–879 | date=September 2008 | doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | bibcode=2008MNRAS.389..869E | arxiv=0806.2878 | s2cid=14878976 | postscript=. }}</ref>
<ref name=Houk1982>{{citation | last1=Houk | first1=N. | title=Michigan Catalogue of Two-dimensional Spectral Types for the HD stars | volume=3 | year=1982 | publication-place=Ann Arbor, MI | publisher=Department of Astronomy, University of Michigan | bibcode=1982mcts.book.....H | postscript=. }}</ref>
<ref name=Mermilliod1986>{{citation | last1=Mermilliod | first1=J.-C. | title=Compilation of Eggen's UBV data, transformed to UBV (unpublished) | journal=Catalogue of Eggen's UBV Data | year=1986 | publisher=[[SIMBAD]] | bibcode=1986EgUBV........0M | postscript=. }}</ref>
<ref name=Wagman1987>{{citation | last=Wagman | first=M. | postscript=. | title=Flamsteed's Missing Stars | journal=Journal for the History of Astronomy | volume=18 | page=216 |date=August 1987 | issue=3 | bibcode=1987JHA....18..209W | doi=10.1177/002182868701800305 | s2cid=118445625 }}</ref>
<ref name=Zorec2012>{{citation | last1=Zorec | first1=J. | last2=Royer | first2=F. | title=Rotational velocities of A-type stars. IV. Evolution of rotational velocities | journal=Astronomy & Astrophysics | volume=537 | page=A120 |date=January 2012 | doi=10.1051/0004-6361/201117691 | bibcode=2012A&A...537A.120Z | arxiv=1201.2052 | s2cid=55586789 | postscript=. }}</ref>
<ref name=SIMBAD>{{cite simbad | title=* omi Hya | access-date=2017-01-06 }}</ref> </references>
{{Stars of Hydra|state=collapsed}}
[[Category:B-type main-sequence stars]] [[Category:Hydra (constellation)]] [[Category:Bayer objects|Hydrae, Omicron]] [[Category:Henry Draper Catalogue objects|101431]] [[Category:Hipparcos objects|056922]] [[Category:Bright Star Catalogue objects|4494]] [[Category:Flamsteed objects|Crateris, 25]] [[Category:Durchmusterung objects|CD-34 07610]]