{{Short description|Supergiant variable star in the constellation Centaurus}} {{starbox begin | name=SX Centauri }} {{Starbox image | image = [[Image:SXCenLightCurve.png|250px]] | caption = A [[Photometric_system#Photometric_letters|visual band]] [[light curve]] for SX Centauri, plotted from [[All Sky Automated Survey|''ASAS'']] data<ref name=ASASServer/> }} {{starbox observe | epoch=J2000 | constell=[[Centaurus]] | ra={{RA|12|21|12.5741}}<ref name=gaiadr2/> | dec={{DEC|-49|12|41.060}}<ref name=gaiadr2/> | appmag_v=9.1 to 12.4<ref name=GCVS/> }} {{starbox character | type=[[post-AGB]]<ref name=Deroo2006/> | class=F5G3/5Vp<ref name=Arneson2017/> | b-v = | u-b = | variable = [[RV Tauri variable|RV Tauri]] (RVB, RVb)<ref name=Maas2002/> }} {{starbox astrometry | radial_v=19.1 ± 0.4 km/s<ref name=Deroo2006/> | prop_mo_ra={{val|-14.357}}<ref name=gaiadr2/> | prop_mo_dec={{val|2.836}}<ref name=gaiadr2/> | parallax=0.2175 | p_error=0.0411 | parallax_footnote =<ref name=gaiadr2/> | dist_ly = | dist_pc = | absmag_v = −4.343<ref name=bodikiss/> }} {{Starbox orbit | reference = <ref name=Deroo2006/> | period_unitless = {{val|592|13}} days | periastron = 2,452,107 ± 10 JD | eccentricity = {{val|0.16|0.02}} | k1 = {{val|22.9|0.5}} }} {{Starbox detail | source = | component1 = Primary | mass = 0.6<ref name=Deroo2006/> | radius = {{val|61.1|14.7|9.8}}<ref name=bodikiss/> | luminosity = {{val|3,684|2,315|842|fmt=commas}}<ref name=bodikiss/> | gravity = 1.5<ref name=Maas2002/> | temperature = 6,000<ref name=bodikiss/> | metal_fe = -1.0<ref name=Maas2002/> | rotational_velocity = | age_myr = }} {{starbox catalog | names=[[Variable star designation|SX]] Centauri, [[Bonner Durchmusterung|CD]]-48 7357, [[Henry Draper Catalogue|HD]] 107439, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]] 223370<ref name=SIMBAD/> }} {{Starbox reference|Simbad=SX+Cen}} {{starbox end}}
'''SX Centauri''' is a [[variable star]] in the [[constellation]] [[Centaurus]]. A [[RV Tauri variable]], its [[light curve]] alternates between deep and shallow minima, varying its [[apparent magnitude]] from 9.1 to 12.4.<ref name=GCVS/> From the period-luminosity relationship, it is estimated to be around 1.6 [[parsec|kpc]] (5200 [[light-year]]s) from Earth.<ref name=Deroo2006/> [[Gaia Data Release 2]] gives a [[parallax]] of 0.2175 [[milliarcsecond|mas]], corresponding to distance of about {{val|4,600|ul=pc|fmt=commas}}.<ref name=gaiadr2/> [[Henrietta Leavitt]] announced the discovery of this variable star, in 1906, when it was called CPD-48° 4730.<ref name="Leavitt1906"/> It was given its [[variable star designation]], SX Centauri, in 1907.<ref name="Duner1907"/>
RV Tauri variables like SX Centauri are [[supergiant]] pulsating stars and a subtype of the population II [[Cepheid]]s. They are stars that have already passed the [[asymptotic giant branch]] (AGB) and are in the last stage of their evolution before becoming a [[planetary nebula]]. This transition phase is very fast, and may last for less than a thousand years.<ref name=Arneson2017/> SX Centauri is in the beginning of this process and is estimated to be leaving the AGB right now, or to have left the AGB a few decades ago. Its [[Stellar pulsation|pulsations]] are radial in nature and have a period of about 32.9 days (from deep minimum to deep minimum), causing the [[effective temperature]] of the star to vary between 5,000 and 6,500 [[kelvin|K]] and the radius between 21 and 29 [[solar radii]]. The radius seems to have the same value in both the primary and secondary minima, while the temperature shows a 500 K variation between minima.<ref name=Shenton1994/>
The spectrum of SX Centauri shows [[infrared excess]], indicating the presence of a [[circumstellar disk]] of hot dust around the star. [[Interferometry|interferometric]] observations constrained the diameter of the disk to less than 11 [[arcsecond]]s (18 [[astronomical unit|AU]] at the star's distance), indicating a very compact system.<ref name=Deroo2006/> The infrared emission is consistent with a hotter component (715 K) corresponding to 4% of the dust, and a colder one (244 K) corresponding to 96% of the dust. This material is composed mainly of [[amorphous carbon]] and [[graphite]] (83%), with the remainder being [[pyroxene]] and [[olivine]].<ref name=Arneson2017/> The disk is related to a depletion of refractory elements (with high condensation temperature) in the star's [[photosphere]]; this is caused by separation of gas from dust rich in refractories, followed by [[Accretion (astrophysics)|accretion]] of the gas by the star.<ref name=Maas2002/>
SX Centauri is a [[spectroscopic binary]], having a companion star with an [[orbital period]] of 592 days and an [[orbital eccentricity]] of 0.16. This companion has a mass estimated between 1.4 and 1.9 [[solar mass]]es and is probably an unevolved [[main sequence]] star. The system must have interacted in the past when the primary was a [[red giant]], which is likely related to the formation of disk.<ref name=Deroo2006/> All RV Tauri stars with dust disks are believed to be part of a binary system.<ref name=Manick2017/>
Slow periodic variations in the mean brightness of SX Centauri have been detected, leading the star to be classified as an RV Tauri star of the photometric class b (RVb). The period of this variation is approximately equal to the orbital period of the system. This phenomenon can be explained as variation of the circumstellar [[Extinction (astronomy)|extinction]] during the orbital motion of the disk.<ref name=Maas2002/>
==References== <references> <ref name=ASASServer>{{cite web |title=ASAS All Star Catalogue |url=http://www.astrouw.edu.pl/asas/?page=aasc |publisher=The All Sky Automated Survey |access-date=8 December 2021}}</ref>
<ref name=SIMBAD>{{cite web | title=V* SX Cen -- Variable Star of RV Tau type | work=SIMBAD | publisher=[[Centre de Données astronomiques de Strasbourg]] | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=SX+Centauri | access-date=2017-12-01 }}</ref>
<ref name=GCVS>{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref>
<ref name="Duner1907">{{cite journal |last1=Dunér |last2=Hartwig |last3=Müller |title=Benennung von neu entdeckten veränderlichen Sternen (in German)|journal=Astronomische Nachrichten |date=November 1907 |volume=176 |issue=12 |pages=181–194 |doi=10.1002/asna.19071761202 |url=https://articles.adsabs.harvard.edu/pdf/1907AN....176..181. |access-date=14 January 2025}}</ref>
<ref name="Leavitt1906">{{cite journal |last1=Leavitt |first1=Henrietta S. |last2=Pickering |first2=Edward C. |title=Thirty-Six New Variable Stars |journal=Harvard College Observatory Circular |bibcode=1906HarCi.122....1L |date=November 1906 |volume=122 |pages=1–4 |url=https://articles.adsabs.harvard.edu/pdf/1906HarCi.122....1L |access-date=14 January 2025}}</ref>
<ref name=gaiadr2>{{cite DR2|6127031608094036864}}</ref>
<ref name=Manick2017>{{cite journal|author=Manick, Rajeev |author2=Van Winckel, Hans |author3=Kamath, Devika |author4=Hillen, Michel |author5=Escorza, Ana|title=Establishing binarity amongst Galactic RV Tauri stars with a disc|journal=Astronomy & Astrophysics|volume=597|pages=A129, 18 pp|date=January 2017|bibcode=2017A&A...597A.129M|doi=10.1051/0004-6361/201629125|arxiv=1610.00506|s2cid=119242786 }}</ref>
<ref name=Maas2002>{{cite journal|author=Maas, T. |author2=Van Winckel, H. |author3=Waelkens, C.|title=RU Cen and SX Cen: Two strongly depleted RV Tauri stars in binary systems. The RV Tauri photometric b phenomenon and binarity|journal=Astronomy and Astrophysics|volume=386|pages=504–516|date=May 2002|bibcode=2002A&A...386..504M|doi=10.1051/0004-6361:20020209|doi-access=free}}</ref>
<ref name=Arneson2017>{{cite journal|display-authors=etal|author=Arneson, R. A.|title=A SOFIA FORCAST Grism Study of the Mineralogy of Dust in the Winds of Proto-planetary Nebulae: RV Tauri Stars and SRd Variables|journal= The Astrophysical Journal|volume=843|issue=1|pages=article 51, 22 pp|date=July 2017|bibcode=2017ApJ...843...51A|doi=10.3847/1538-4357/aa75cf|arxiv=1706.00445|s2cid=53460498 |doi-access=free }}</ref>
<ref name=Deroo2006>{{cite journal|display-authors=etal|author=Deroo, P.|title=Resolving the compact dusty discs around binary post-AGB stars using N-band interferometry|journal=Astronomy and Astrophysics|volume=450|issue=1|pages=181–192|date=April 2006|bibcode=2006A&A...450..181D|doi=10.1051/0004-6361:20054300|arxiv=astro-ph/0601169|s2cid=15338413}}</ref>
<ref name=Shenton1994>{{cite journal|display-authors=etal|author=Shenton, M.|title=Multiwavelength observations of RV Tauri stars. 4: SX Centauri|journal=Astronomy and Astrophysics|volume=292|issue=1|pages=102–114|date=December 1994|bibcode=1994A&A...292..102S}}</ref>
<ref name=bodikiss>{{cite journal|arxiv=1901.01409|last1=Bódi|first1=A.|title=Physical properties of galactic RV Tauri stars from Gaia DR2 data|last2=Kiss|first2=L. L.|journal=The Astrophysical Journal|year=2019|volume=872|issue=1 |page=60|doi=10.3847/1538-4357/aafc24|bibcode=2019ApJ...872...60B |s2cid=119099605 |doi-access=free }}</ref> </references>
{{Stars of Centaurus}}
[[Category:Centaurus]] [[Category:Objects with variable star designations|Centauri, SX]] [[Category:RV Tauri variables]] [[Category:Spectroscopic binaries]] [[Category:Henry Draper Catalogue objects|107439]] [[Category:Durchmusterung objects]]