omicron Hydrae
{{Short description|Blue-hued star in the constellation Hydra}}
{{Starbox begin
| name = Omicron Hydrae
}}
{{Starbox observe
| epoch = J2000.0
| constell = Hydra
| dec = {{DEC|−34|44|40.7733}}
}}
{{Starbox character
| r-i =
| variable =
}}
{{Starbox astrometry
| parallax = 7.27
| p_error = 0.16
}}
{{Starbox detail
| source =
| metal_fe =
}}
{{Starbox catalog
| names = ο Hya, CD−34°7610, FK5 439, HD 101431, HIP 56922, HR 4494, SAO 202695
}}
{{Starbox reference
| Simbad = omi+Hya
}}
{{starbox end}}
Omicron Hydrae (ο Hya) is the Bayer designation for a solitary star in the equatorial 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. With an apparent visual magnitude of 4.70, this star is visible to the naked eye. Based upon an annual parallax shift of 7.27 mas, it is located around 449 light years from the Sun.
This is a B-type main sequence star with a stellar classification of B9 V. It has completed an estimated {{Val|98.4|1.1|u=%}} of its lifetime on the main sequence. With 3.56 times the mass of the Sun, it radiates 309 times the Sun's luminosity from its outer atmosphere at an effective temperature of 10,495 K. The rate of spin is relatively high, with a projected rotational velocity of 160 km/s.
References
{{reflist|refs=
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| volume=37 | bibcode=2000VeARI..37....1W | postscript=. }}
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| arxiv=0806.2878 | s2cid=14878976 | postscript=. }}
| 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=. }}
| 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| title=Compilation of Eggen's UBV data, transformed to UBV (unpublished)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=. }}
| 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 }}
| 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=. }}
| title=* omi Hya
| access-date=2017-01-06 }}
}}
{{Stars of Hydra|state=collapsed}}
{{DEFAULTSORT:Omicron Hydrae}}
Category:B-type main-sequence stars