Editing Triangulum (section)

===Stars===
Three stars make up the long narrow triangle that gives the constellation its name. The brightest member is the white [[giant star]] Beta Trianguli of [[apparent magnitude]] 3.00,<ref name=garfinckle1997/> lying 127 [[light-year]]s distant from Earth.<ref>{{cite web |url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Beta+trianguli&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = Beta Trianguli |work = SIMBAD Astronomical Database|publisher=Centre de Données astronomiques de Strasbourg |access-date = 29 August 2013}}</ref> It is actually a [[spectroscopic binary]] system; the primary is a white star of spectral type A5IV with 3.5 times the mass of the Sun that is beginning to expand and evolve off the main sequence. The secondary is poorly known, but calculated to be a yellow-white [[F-type main-sequence star]] around 1.4 solar masses. The two orbit around a common [[Center of mass|centre of gravity]] every 31 days, and are surrounded by a [[debris disk|ring of dust]] that extends from 50 to 400&nbsp;[[Astronomical unit|AU]] away from the stars.<ref>{{cite journal|author =Kennedy, G. M.|author2 =Wyatt, M. C.|author3 = Sibthorpe, B.|author4 = Phillips, N. M.|author5 = Matthews, B.|author6 = Greaves, J. S.|date=2012|title=Coplanar Circumbinary Debris Disks|journal=[[Monthly Notices of the Royal Astronomical Society]]|volume=426|issue=3|pages=2115–28|bibcode=2012MNRAS.426.2115K|doi=10.1111/j.1365-2966.2012.21865.x|doi-access =free|arxiv = 1208.1759 |s2cid =59408005}}</ref>

The second-brightest star, the yellow-white [[subgiant]] star Alpha Trianguli (3.41<sup>m</sup>) with a close dimmer companion, is also known as Caput Trianguli or Ras al Muthallath, and is at the apex of the [[triangle]]. It lies around 7 degrees north-northwest of [[Alpha Arietis]].<ref name="motz">{{cite book |last1=Motz |first1=Lloyd |author-link1=Lloyd Motz |last2=Nathanson |first2=Carol |title=The Constellations: An Enthusiast's Guide to the Night Sky |publisher=Aurum Press |location=London, United Kingdom |date=1991 |pages=310–12 |isbn=1-85410-088-2}}</ref> Making up the triangle is [[Gamma Trianguli]], a [[A-type main sequence star|white main sequence star]] of spectral type A1Vnn of apparent magnitude 4.00 about 112 light-years from Earth.<ref name=sb1>{{cite web |url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Gamma+Trianguli&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title=Gamma Trianguli |work=[[SIMBAD|SIMBAD Astronomical Database]] |publisher=Centre de Données astronomiques de Strasbourg |access-date=25 May 2013}}</ref> It is around double the size of and around 33 times as luminous as the sun and rotates rapidly. Like Beta, it is surrounded by a dusty debris disk, which has a radius 80 times the distance of the Earth from the Sun.<ref name=apj660_2_1556>{{citation | last1=Rhee | first1=Joseph H. | last2=Song | first2=Inseok | last3=Zuckerman | first3=B. | last4=McElwain | first4=Michael | title=Characterization of Dusty Debris Disks: The IRAS and Hipparcos Catalogs | journal=The Astrophysical Journal | volume=660 | issue=2 | pages=1556–71 |date=May 2007 | doi=10.1086/509912 | bibcode=2007ApJ...660.1556R |arxiv = astro-ph/0609555 | s2cid=11879505 }}</ref> Lying near Gamma and forming an optical triple system with it are [[Delta Trianguli|Delta]] and [[7 Trianguli]]. Delta is a [[binary star#Spectroscopic binaries|spectroscopic binary]] system composed of two [[G-type main-sequence star|yellow main sequence stars]] of similar dimensions to the Sun that lies 35 light-years from Earth. The two stars orbit each other every ten days and are a mere 0.1 AU apart.<ref name=kalerdeltatri>{{cite web |url=http://stars.astro.illinois.edu/sow/deltatri.html |title=Delta Trianguli |last=Kaler |first=Jim |author-link=Jim Kaler |work=Stars |publisher=University of Illinois |access-date=16 June 2013}}</ref> This system is the closest in the constellation to the Earth.<ref name=bagnall/> Only of magnitude 5.25, 7 Trianguli is much further away at around 280 light-years distant from Earth.<ref>{{cite web |url = http://simbad.u-strasbg.fr/simbad/sim-id?Ident=7+Trianguli&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = 7 Trianguli |work = SIMBAD Astronomical Database|publisher=Centre de Données astronomiques de Strasbourg |access-date = 29 August 2013}}</ref>

[[Iota Trianguli]] is a double star whose components can be separated by medium-sized telescopes into a strong yellow and a contrasting pale blue star. Both of these are themselves close binaries.<ref>{{cite book|author=Burnham, Robert Jr. |date=1978 |title=Burnham's Celestial Handbook |url=https://archive.org/details/burnhamscelestia02robe |url-access=registration |publisher= Dover Publications |location=New York, New York |isbn= 0-486-24065-7}}</ref> [[X Trianguli]] is an [[binary star#Eclipsing binaries|eclipsing binary]] system that ranges between magnitudes 8.5 and 11.2 over a period of 0.97 days.<ref name="levy05">{{cite book|last=Levy|first=David H.|title=David Levy's Guide to Variable Stars|publisher=Cambridge University Press|location=Cambridge, United Kingdom|date=2005|page=227|isbn=0-521-60860-0|url=https://books.google.com/books?id=Df9d8FBagqEC&q=%22X+trianguli%22&pg=PA227}}</ref> [[RW Trianguli]] is a [[cataclysmic variable star]] system composed of a [[white dwarf]] primary and an [[K-type main-sequence star|orange main sequence star]] of spectral type K7 V. The former is drawing off matter from the latter, forming a prominent [[accretion disc]]. The system is around 1076 light-years distant.<ref>{{cite journal|author =Groot, Paul J.|author2 =Rutten, Rene G.M.|author3 =van Paradijs, Jan  |date=2004|title=A Spectrophotometric Study of RW Trianguli|journal=Astronomy & Astrophysics|volume=417|pages=283–91| doi=10.1051/0004-6361:20031771|arxiv = astro-ph/0401029 |bibcode = 2004A&A...417..283G |s2cid =15078798}}</ref>

[[R Trianguli]] is a [[Mira variable|long period (Mira) variable]] that ranges from magnitude 6.2 to 11.7 over a period of 267 days.<ref name="levy05"/> It is a [[red giant]] of spectral type M3.5-8e, lying around 960 light-years away.<ref>{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=R+Tri&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = R Trianguli – Variable Star of Mira Ceti type |work = SIMBAD Astronomical Database|publisher=Centre de Données astronomiques de Strasbourg |access-date = 21 July 2013}}</ref> [[HD 12545]], also known as XX Trianguli, is
an orange giant of spectral type K0III around 520 light-years distant with a visual magnitude of 8.42.<ref name=sbxx>{{cite web |url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD+12545&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title=XX Trianguli – Variable of RS CVn type |work=[[SIMBAD|SIMBAD Astronomical Database]] |publisher=Centre de Données astronomiques de Strasbourg |access-date=26 July 2013}}</ref> A huge [[starspot]] larger than the diameter of the Sun was detected on its surface in 1999 by astronomers using [[Doppler imaging]].<ref>{{cite journal|bibcode=1999A&A...347..225S|title=Doppler imaging of stellar surface structure. XI. The super starspots on the K0 giant HD 12545: Larger than the entire Sun|journal=Astronomy and Astrophysics|volume=347|pages=225|last1=Strassmeier|first1=K. G|year=1999}}</ref>

Two [[star system]]s appear to have [[exoplanet|planets]]. [[HD 9446]] is a Sun-like star around 171 light-years distant that has two planets of masses 0.7 and 1.8 times that of [[Jupiter]], with orbital periods of 30 and 193 days respectively.<ref name=aaa513>{{cite journal |doi=10.1051/0004-6361/200913790 |last1=Hébrard |first1=Guillaume |last2=Bonfils |first2=Xavier |last3=Ségransan |first3=Damien |last4=Moutou |first4=Claire |last5=Delfosse |first5=Xavier |last6=Bouchy |first6=François |last7=Boisse |first7=Isabelle |last8=Arnold |first8=Luc |date=2010 |title=The SOPHIE Search for Northern Extrasolar Planets: II. A Multi-planet System Around HD 9446 |journal=Astronomy & Astrophysics |volume=513 |pages=A69 |url=http://www.aanda.org/articles/aa/full_html/2010/05/aa13790-09/aa13790-09.html |bibcode=2010A&A...513A..69H |arxiv=1001.0682 |s2cid=119306916 }}</ref> [[HD 13189]] is an orange giant of spectral type K2II about 2–7 times as massive as the Sun with a planetary or [[brown dwarf]] companion between 8 and 20 times as massive as Jupiter, which takes 472 days to complete an orbit. It is one of the largest stars discovered to have a planetary companion.<ref name=aaa437_2_743>{{cite journal  | last1=Hatzes | first1=A. P. | last2=Guenther | first2=E. W. | last3=Endl | first3=M. | last4=Cochran | first4=W. D. | last5=Döllinger | first5=M. P. | last6=Bedalov | first6=A. | title=A giant planet around the massive giant star HD 13189 | journal=[[Astronomy and Astrophysics]] | date=2005 | volume=437 | issue=2 | pages=743–51 | doi=10.1051/0004-6361:20052850 | bibcode=2005A&A...437..743H| url=http://www.aanda.org/articles/aa/pdf/2005/26/aa2850-05.pdf | doi-access=free }}</ref><!-- cites previous two sentences -->