Theta Hydrae

{{Short description|Binary star system in the constellation Hydra}} {{Starbox begin}} {{Starbox image | image = {{Location mark |image=Hydra constellation map.svg|alt=|float=center|width=300 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=θ Hydrae |x=820|y=100 }} | caption = Location of θ Hydrae (circled in red) }} {{Starbox observe | epoch = [[J2000.0]] | equinox = [[J2000.0]] ([[International Celestial Reference System|ICRS]]) | constell = [[Hydra (constellation)|Hydra]] | ra = {{RA|09|14|21.866}}<ref name=dr2/> | dec = {{DEC|+02|18|51.64}}<ref name=dr2/> | appmag_v = 3.888<ref name=Cousins1984/> }} {{Starbox character | class = {{nowrap|B9.5 V + DA 1.6}}<ref name=Holberg2013/> | b-v = −0.065<ref name=Cousins1984/> | u-b = −0.118<ref name=Cousins1984/> | r-i = | variable = }} {{Starbox astrometry | radial_v = {{Val|−10.7|0.3}}<ref name=Gontcharov2006/> | prop_mo_ra = +128.152<ref name=dr2/> | prop_mo_dec = −327.709<ref name=dr2/> | parallax = 28.4019 | p_error = 0.3682 | parallax_footnote = <ref name=dr2/> | absmag_v = +0.92<ref name=Anderson2012/> }} {{Starbox detail | source = | component1 = θ Hya A | mass = 2.52<ref name=Holberg2013/> | radius = | luminosity = 52<ref name=Anderson2012/> | temperature = {{Val|10099|145|fmt=commas}}<ref name=Wu2011/> | gravity = {{Val|3.80|0.08}}<ref name=Wu2011/> | metal_fe = {{Val|−0.42|0.09}}<ref name=Wu2011/> | rotational_velocity = 95<ref name=Zorec2012/> | age_myr = | component2 = θ Hya B | mass2 = 0.68<ref name=Burleigh1999/> or 1.21<ref name=Holberg2013/> | temperature2 = 30,700<ref name=Holberg2013/> }} {{Starbox catalog | names = [[Bayer designation|θ Hya]], 22 Hydrae, [[Durchmusterung|BD]]+02°2167, [[FK5]] 347, [[Henry Draper Catalogue|HD]] 79469, [[Hipparcos Catalogue|HIP]] 45336, [[Bright Star Catalogue|HR]] 3665, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]] 117527<ref name=SIMBAD/> }} {{Starbox reference | Simbad = tet+Hya }} {{starbox end}} '''Theta Hydrae''', [[Latinisation of names|Latinized]] from '''θ Hydrae''', is a [[binary star]]<ref name=Burleigh1999/> system in the [[constellation]] [[Hydra (constellation)|Hydra]]. It is visible to the naked eye with an [[apparent visual magnitude]] of 3.9.<ref name=Cousins1984/> The star system has a high [[proper motion]]<ref name=Burleigh1999/> with an annual [[stellar parallax|parallax shift]] of {{val|28.4|ul=mas}},<ref name=dr2/> indicating a distance of about {{val|115|ul=light years}}. Theta Hydrae forms a [[double star|double]] with a magnitude 9.9 star located at an [[angular separation]] of {{val|29|ul=arcseconds}}.<ref name=Privett2013/>

The primary component of this system is a [[B-type main sequence star]] with a [[stellar classification]] of B9.5 V.<ref name=Holberg2013/> It is a candidate [[Lambda Boötis star]], indicating it displays an underabundance of [[iron peak]] elements.<ref name=King1994/> However, it is also underabundant in oxygen, a characteristic not shared by other Lambda Boötis stars. Instead, it may be a [[Ap and Bp stars|peculiar B star]].<ref name=Baschek1969/>

An orbiting [[white dwarf]] companion was discovered in 1998 from its [[X-ray astronomy|X-ray emission]]. This [[degenerate star]] must have evolved from a progenitor that was once more massive than the current primary.<ref name=Burleigh1999/> Burleigh and Barstow (1999) gave a mass estimate of 0.68<ref name=Burleigh1999/> times the [[solar mass|mass of the Sun]], whereas Holberg et al. (2013) put it as high as 1.21<ref name=Holberg2013/> times the Sun's mass. The latter would put it beyond the theoretical upper limit for white dwarf remnants of typical single stars that did not undergo a merger or mass loss.<ref name=Vennes2008/>

==References== <references> <ref name=Anderson2012>{{citation | 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=119257644 | postscript=. }}</ref>

<ref name=Privett2013>{{citation | title=The Constellation Observing Atlas | series=The Patrick Moore Practical Astronomy Series | first1=Grant | last1=Privett | first2=Kevin | last2=Jones | publisher=Springer Science & Business Media | year=2013 | isbn=978-1461476481 | page=104 | bibcode=2013coa..book.....P | postscript=. | url=https://books.google.com/books?id=uN69BAAAQBAJ&pg=PA104 }}</ref>

<ref name=Baschek1969>{{citation | title=The Chemical Composition of the Lambda Bootis Stars | last1=Baschek | first1=Bodo | last2=Searle | first2=Leonard | journal=Astrophysical Journal | postscript=. | volume=155 | page=537 | date=February 1969 | doi=10.1086/149890 | bibcode=1969ApJ...155..537B | doi-access=free }}</ref>

<ref name=Wu2011>{{citation | display-authors=1 | last1=Wu | first1=Yue | last2=Singh | first2=H. P. | last3=Prugniel | first3=P. | last4=Gupta | first4=R. | last5=Koleva | first5=M. | title=Coudé-feed stellar spectral library – atmospheric parameters | journal=Astronomy and Astrophysics | volume=525 | page=A71 | date=January 2011 | doi=10.1051/0004-6361/201015014 | bibcode=2011A&A...525A..71W | postscript=. | arxiv=1009.1491 | s2cid=53480665 }}</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=Gontcharov2006>{{citation | last1=Gontcharov | first1=G. A. | 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 | date=November 2006 | doi=10.1134/S1063773706110065 | bibcode=2006AstL...32..759G | postscript=. |arxiv = 1606.08053 | s2cid=119231169 }}</ref>

<ref name=King1994>{{citation | last1=King | first1=J. R. | postscript=. | title=Accretion from Circumstellar Discs and the Lambda-Bootis Phenomenon | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=269 | issue=1 | pages=209–217 | date=July 1994 | bibcode=1994MNRAS.269..209K | doi=10.1093/mnras/269.1.209 | url=http://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=1236&context=physastro_pubs| doi-access=free }}</ref>

<ref name=Vennes2008>{{citation | title=On the empirical evidence for the existence of ultramassive white dwarfs | last1=Vennes | first1=S. | last2=Kawka | first2=A. | journal=Monthly Notices of the Royal Astronomical Society | volume=389 | issue=3 | pages=1367–1374 | date=September 2008 | doi=10.1111/j.1365-2966.2008.13652.x | doi-access=free | bibcode=2008MNRAS.389.1367V | arxiv=0806.4742 | s2cid=15349194 | postscript=. }}</ref>

<ref name=Burleigh1999>{{citation | title=Theta Hya: spectroscopic identification of a second B star+white dwarf binary | last1=Burleigh | first1=M. R. | last2=Barstow | first2=M. A. | journal=Astronomy and Astrophysics | volume=341 | pages=795–798 | date=January 1999 | bibcode=1999A&A...341..795B | arxiv=astro-ph/9810113 | postscript=. }}</ref>

<ref name=Holberg2013>{{citation | title=Where are all the Sirius-like binary systems? | display-authors=1 | last1=Holberg | first1=J. B. | last2=Oswalt | first2=T. D. | last3=Sion | first3=E. M. | last4=Barstow | first4=M. A. | last5=Burleigh | first5=M. R. | journal=Monthly Notices of the Royal Astronomical Society | volume=435 | issue=3 | pages=2077–2091 | date=November 2013 | doi=10.1093/mnras/stt1433 | doi-access=free | bibcode=2013MNRAS.435.2077H | arxiv=1307.8047 | postscript=. }}</ref>

<ref name=Cousins1984>{{citation | last1=Cousins | first1=A. W. J. | title=Standardization of Broadband Photometry of Equatorial Standards | journal=South African Astronomical Observatory Circulars | volume=8 | page=59 | date=1984 | bibcode=1984SAAOC...8...59C | postscript=. }}</ref>

<ref name=SIMBAD>{{cite simbad | title=tet Hya | accessdate=2017-01-04 | postscript=. }}</ref>

==External links== *{{citation | title=Theta Hydrae | work=Stars | publisher=University of Illinois | last1=Kaler | first1=James B. | date=May 8, 2015 | url=http://stars.astro.illinois.edu/sow/thetahya.html | accessdate=2016-01-04 | postscript=. }}

[[Category:B-type main-sequence stars]] [[Category:Spectroscopic binaries]] [[Category:White dwarfs]] [[Category:Hydra (constellation)]] [[Category:Bayer objects|Hydrae, Theta]] [[Category:Durchmusterung objects|BD+02 2167]] [[Category:Flamsteed objects|Hydrae, 22]] [[Category:Henry Draper Catalogue objects|079469]] [[Category:Hipparcos objects|045336]] [[Category:Bright Star Catalogue objects|3665]] [[Category:Lambda Boötis stars]]