Theta Librae

{{short description|Star in the constellation Libra}} {{Starbox begin | name = θ Librae }} {{Starbox image | image= {{Location mark |image=Libra constellation map.svg|alt=|float=center|width=240 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=θ Librae |x=184|y=439 }} |caption=Location of θ Librae (circled) }} {{Starbox observe | epoch = J2000 | ra = {{RA|15|53|49.53806}}<ref name=GaiaDR2/> | dec = {{DEC|−16|43|45.4582}}<ref name=GaiaDR2/> | appmag_v = 4.136<ref name=Liu2007/> | constell = [[Libra (constellation)|Libra]] }} {{Starbox character | type = [[red clump]]<ref name=Liu2007/> | class = G9IIIb<ref name=Keenan1989/> | b-v = +1.01<ref name=clpl99/> | u-b = +0.82<ref name=clpl99/> | variable = }} {{Starbox astrometry | radial_v = {{Val|4.56|0.25}}<ref name=Massarotti2008/> | prop_mo_ra = +100.33<ref name=GaiaDR2/> | prop_mo_dec = +135.02<ref name=GaiaDR2/> | parallax = 19.36 | p_error = 0.15 | parallax_footnote = <ref name=vanLeeuwen2007/> | absmag_v = 0.665<ref name=Liu2007/> }} {{Starbox detail | mass = 1.47<ref name=reffert2015/> | radius = 12.27<ref name=reffert2015/> | luminosity = 68.1<ref name=reffert2015/> | temperature = 4,739<ref name=reffert2015/> | metal_fe = −0.35<ref name=reffert2015/> | rotational_velocity = 0.0<ref name=Massarotti2008/> | gravity = 2.44<ref name=reffert2015/> | age_gyr = 3.4<ref name=reffert2015/> }} {{Starbox catalog | names = {{odlist | B=θ Lib | F=46 Librae | BD=−16°4174 | HD=142198 | HIP=77853 | HR=5908 | SAO=159563 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad = tet+Lib }} {{Starbox end}}

'''Theta Librae''' is a single<ref name=Eggleton2008/> [[star]] in the southern [[zodiac]] [[constellation]] of [[Libra (constellation)|Libra]], near the constellation border with [[Scorpius]]. Its name is a [[Bayer designation]] that is [[Romanization of Greek|Latinized]] from '''θ Librae''', and abbreviated Theta Lib or θ Lib. It is visible to the naked eye as a faint, orange-hued star with an [[apparent visual magnitude]] of 4.14.<ref name=Liu2007/> The distance to this star is approximately 168 [[light year]]s, as determined by [[stellar parallax|parallax]], and it is drifting further away with a [[radial velocity]] of 5 km/s.<ref name=Massarotti2008/> The position of this star near the [[ecliptic]] means it is subject to [[lunar occultation]]s.<ref name=Edwards1980/>

This object is an aging [[giant star]] with a [[stellar classification]] of G9IIIb.<ref name=Keenan1989/> Having exhausted the supply of hydrogen at its [[stellar core|core]], it has cooled and expanded; at present it has 12.3 times the girth of the Sun.<ref name=reffert2015/> The star has an estimated mass about 47% greater than the Sun. It is radiating about 68 times the [[luminosity of the Sun]] from its [[photosphere]] at an [[effective temperature]] of about {{val|4,739|fmt=commas|ul=K}}.<ref name=reffert2015/> It is probably on the [[red giant branch]], which indicates it is generating energy through [[hydrogen fusion]] in a shell outside an inert helium core.<ref name=reffert2015/> However, there is a 41% chance that it is a [[red clump]] giant on the [[horizontal branch]],<ref name=Liu2007/> which would mean it was somewhat older and less massive.<ref name=reffert2015/> It has sometimes been classified spectroscopically as a [[subgiant]], but detailed study shows that it is too cool and luminous to be on the [[subgiant branch]].<ref name=thoren2004/>

==References== <references>

<ref name=SIMBAD>{{cite simbad | title=tet Lib | accessdate=2017-06-19 }}</ref>

<ref name=Edwards1980>{{cite journal | title=Photoelectric observations of lunar occultations. XI. | last1=Edwards | first1=D. A. | last2=Evans | first2=D. S. | last3=Fekel | first3=F. C. | last4=Smith | first4=B. W. | display-authors=1 | journal=Astronomical Journal | volume=85 | pages=478–489 | date=April 1980 | doi=10.1086/112700 | bibcode=1980AJ.....85..478E }}</ref>

<ref name=Keenan1989>{{cite journal | last1=Keenan | first1=Philip C. | last2=McNeil | first2=Raymond C. | title=The Perkins catalog of revised MK types for the cooler stars | journal=The Astrophysical Journal Supplement Series | volume=71 | pages=245 | year=1989 | doi=10.1086/191373 | bibcode=1989ApJS...71..245K }}</ref>

<ref name=Massarotti2008>{{citation | last1=Massarotti | first1=Alessandro | last2=Latham | first2=David W. | last3=Stefanik | first3=Robert P. | last4=Fogel | first4=Jeffrey | title=Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity | display-authors=1 | journal=The Astronomical Journal | volume=135 | issue=1 | pages=209–231 | date=January 2008 | doi=10.1088/0004-6256/135/1/209 | bibcode=2008AJ....135..209M | s2cid=121883397 | doi-access=free }}</ref>

<ref name=vanLeeuwen2007>{{cite journal | 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 }}</ref>

<ref name=Eggleton2008>{{cite journal | 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 | arxiv=0806.2878 | doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | s2cid=14878976 }}</ref>

<ref name=Liu2007>{{cite journal | display-authors=1 | last1=Liu | first1=Y. J. | last2=Zhao | first2=G. | last3=Shi | first3=J. R. | last4=Pietrzyński | first4=G. | last5=Gieren | first5=W. | title=The abundances of nearby red clump giants | journal=Monthly Notices of the Royal Astronomical Society | volume=382 | issue=2 | pages=553–66 | date=2007 | bibcode=2007MNRAS.382..553L | doi=10.1111/j.1365-2966.2007.11852.x | doi-access=free }}</ref>

<ref name=clpl99>{{Cite journal | last1=Johnson | first1=H. L. | last2=Iriarte | first2=B. | last3=Mitchell | first3=R. I. | last4=Wisniewskj | first4=W. Z. | display-authors=1 | title=UBVRIJKL photometry of the bright stars | journal=Communications of the Lunar and Planetary Laboratory | volume=4 | issue=99 | date=1966 | page=99 | bibcode=1966CoLPL...4...99J }}</ref>

<ref name=reffert2015>{{cite journal |bibcode=2015A&A...574A.116R |title=Precise radial velocities of giant stars. VII. Occurrence rate of giant extrasolar planets as a function of mass and metallicity |journal=Astronomy and Astrophysics |volume=574 |pages=A116 |last1=Reffert |first1=Sabine |last2=Bergmann |first2=Christoph |last3=Quirrenbach |first3=Andreas |last4=Trifonov |first4=Trifon |last5=Künstler |first5=Andreas |year=2015 |arxiv=1412.4634 |doi=10.1051/0004-6361/201322360 |s2cid=59334290 }}</ref>

<ref name=thoren2004>{{cite journal |bibcode=2004A&A...425..187T |title=Subgiants as probes of galactic chemical evolution |journal=Astronomy and Astrophysics |volume=425 |pages=187–206 |last1=Thorén |first1=P. |last2=Edvardsson |first2=B. |last3=Gustafsson |first3=B. |year=2004 |arxiv=astro-ph/0407260 |doi=10.1051/0004-6361:20040421 |s2cid=2116895 }}</ref>

</references>

{{Stars_of_Libra}}  {{DEFAULTSORT:Theta Librae}} [[Category:G-type giants]] [[Category:Horizontal-branch stars]]  [[Category:Libra (constellation)]] [[Category:Bayer objects|Librae, Theta]] [[Category:Durchmusterung objects]] [[Category:Flamsteed objects|Librae, 46]] [[Category:Henry Draper Catalogue objects|142198]] [[Category:Hipparcos objects|077853]] [[Category:Bright Star Catalogue objects|5908]]