Theta Hydri
{{short description|Star in the constellation Hydrus}}
{{Starbox begin}}
{{Starbox observe
| epoch = J2000.0
| constell = Hydrus
}}
{{Starbox character
| r-i =
| variable =
}}
{{Starbox astrometry
| radial_v = {{Val|+12.3|1.6}}
| prop_mo_ra = +27.256
| prop_mo_dec = +16.598
| parallax = 6.4996
| p_error = 0.0619
}}
{{Starbox detail
| source =
| mass =
| radius =
| metal_fe =
| rotational_velocity =
}}
{{Starbox catalog
| names = {{odlist | B=θ Hyi | CPD=−72°219 | FK5=113 | HD=19400 | HIP=14131 | HR=939 | SAO=255945 | WDS=J03023-7154AB }}
}}
{{Starbox reference
| Simbad = tet+Hyi
}}
{{starbox end}}
Theta Hydri, Latinized from θ Hydri, is a blue-white hued star in the southern constellation of Hydrus. It is faintly visible to the naked eye with an apparent visual magnitude of +5.53. Based upon an annual parallax shift of {{val|6.50|ul=mas}} as seen from Earth, it is located approximately {{val|502|ul=light years}}. At that distance, the visual magnitude of the star is diminished by an extinction of 0.10 due to interstellar dust. It is moving away from the Sun with a radial velocity of {{val|+12.3|u=km/s}}.
A stellar classification of B8 III/IV suggests it is an evolving B-type star showing mixed traits of a subgiant or giant star. It is a PGa star – a sub-class of the higher temperature chemically peculiar stars known as mercury-manganese stars (HgMn stars). That is, it displays a rich spectra of singly-ionized phosphorus and gallium, in addition to ionized mercury and manganese. As such, Theta Hydri forms a typical example of this type. The absorption lines for these ionized elements are found to vary, most likely as the result of uneven surface distribution combined with the star's rotation. It is a helium-weak star, having helium lines that are anomalously weak for its spectral type. A weak and variable longitudinal magnetic field has been detected.
There is a nearby companion star of class A0 IV located at an angular separation of {{val|0.1|ul=arc seconds}} along a position angle of 179°, as of 2002. Schöller et al. (2010) consider this to be a visual companion, although Eggleton and Tokovinin (2008) listed the pair as a probable binary star system.
References
{{reflist|refs=
{{Cite Gaia EDR3|4645479443883933824}}
| title=Multiplicity of late-type B stars with HgMn peculiarity
| last1=Schöller | first1=M. | last2=Correia | first2=S.
| last3=Hubrig | first3=S. | last4=Ageorges | first4=N.
| journal=Astronomy and Astrophysics | display-authors=1
| volume=522 | id=A85 | pages=12 | date=November 2010
| doi=10.1051/0004-6361/201014246 | bibcode=2010A&A...522A..85S | arxiv=1010.3643| s2cid=119273467 }}
| title=Spatial distribution and kinematics of OB stars
| last1=Gontcharov | first1=G. A.
| journal=Astronomy Letters
| volume=38 | issue=11 | pages=694−706 | date=November 2012
| doi=10.1134/S1063773712110035 | bibcode=2012AstL...38..694G
| arxiv=1606.09028 | s2cid=255202762 | postscript=. }}
| last1=de Bruijne | first1=J. H. J. | last2=Eilers | first2=A.-C.
| title=Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project
| journal=Astronomy & Astrophysics
| volume=546 | id=A61 | pages=14 | date=October 2012
| doi=10.1051/0004-6361/201219219 | bibcode=2012A&A...546A..61D
| arxiv=1208.3048 | s2cid=59451347 | postscript=. }}
| 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
| bibcode=2008MNRAS.389..869E | doi=10.1111/j.1365-2966.2008.13596.x
| doi-access=free | arxiv=0806.2878 | s2cid=14878976 | postscript=. }}
| last1=Alonso | first1=M. S. | last2=López-García | first2=Z.
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| title=Elemental abundance studies of CP stars. The helium-weak stars HD 19400, HD 34797 and HD 35456*
| journal=Astronomy and Astrophysics | display-authors=1
| volume=402 | pages=331−334 | date=April 2003 | postscript=.
| doi=10.1051/0004-6361:20030222 | bibcode=2003A&A...402..331A | doi-access=free }}
| display-authors=1 | last1=Hubrig | first1=S.
| last2=Castelli | first2=F. | last3=González | first3=J. F.
| last4=Carroll | first4=T. A. | last5=Ilyin | first5=I.
| last6=Schöller | first6=M. | last7=Drake | first7=N. A.
| last8=Korhonen | first8=H. | last9=Briquet | first9=M.
| title=Abundance analysis, spectral variability, and search for the presence of a magnetic field in the typical PGa star HD 19400
| journal=Monthly Notices of the Royal Astronomical Society
| volume=442 | issue=4 | pages=3604−3615 | date=August 2014
| doi=10.1093/mnras/stu1122 | doi-access=free | bibcode=2014MNRAS.442.3604H | arxiv=1406.1927}}
| title=XHIP: An extended hipparcos compilation
| last1=Anderson | first1=E. | last2=Francis | first2=Ch.
| journal=Astronomy Letters
| volume=38 | issue=5 | pages=331 | year=2012
| bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015
| arxiv=1108.4971 | s2cid=255204555 | postscript=. }}
| last1=Johnson | first1=H. L. | last2=Mitchell | first2=R. I.
| last3=Iriarte | first3=B. | last4=Wisniewski | first4=W. Z.
| title=UBVRIJKL photometry of the bright stars
| journal=Communications of the Lunar and Planetary Laboratory
| volume=4 | issue=99 | date=1966 | page=99 | display-authors=1
| bibcode=1966CoLPL...4...99J | postscript=. }}
| title=Michigan catalogue of two-dimensional spectral types for the HD stars
| last1=Houk | first1=N. | last2=Cowley | first2=A. P.
| publication-place=Ann Arbor, Michigan | volume=1
| publisher=Dept. of Astronomy, University of Michigan
| year=1975 | bibcode=1975mcts.book.....H | postscript=. }}
| doi=10.3847/1538-4357/ac3335 | year=2022
| title=Rotation Signature of TESS B-type Stars. A Comprehensive Analysis
| last1=Barraza | first1=L. F. | last2=Gomes | first2=R. L.
| last3=Messias | first3=Y. S. | last4=Leão | first4=I. C.
| last5=Almeida | first5=L. A. | last6=Janot-Pacheco | first6=E.
| last7=Brito | first7=A. C. | last8=Brito | first8=F. A. C.
| last9=Santana | first9=J. V. | last10=Gonçalves | first10=N. S.
| last11=Das Chagas | first11=M. L. | last12=Teixeira | first12=M. A.
| last13=De Medeiros | first13=J. R. | last14=Canto Martins | first14=B. L.
| journal=The Astrophysical Journal | display-authors=1
| volume=924 | issue=2 | page=117 | arxiv=2202.01022
| bibcode=2022ApJ...924..117B | s2cid=246030494 | doi-access=free
}}
| title=tet Hyi | accessdate=2017-10-13 | postscript=. }}
}}
{{Stars of Hydrus|state=collapsed}}
{{DEFAULTSORT:Theta Hydri}}
Category:Mercury-manganese stars