HR 5171: Difference between revisions
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{{Short description|Star in the constellation Centaurus}} |
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{{Starbox begin | |
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| name=HR 5171 |
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{{Starbox image |
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| image= |
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{{Location mark |
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|image=Centaurus constellation map.svg|alt=|float=center|width=280 |
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|label=|position=right |
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|mark=Red circle.svg|mark_width=8|mark_link=HR 5171 |
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|x=468|y=892 |
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}} |
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|caption=Location of HR 5171 (circled) |
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}} |
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{{Starbox observe 2s |
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| epoch=[[J2000.0]] |
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| constell=[[Centaurus (constellation)|Centaurus]] |
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| component1=A |
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| ra1={{RA|13|47|10.875}}<ref name=tycho2>{{cite journal|bibcode= 2000A&A...355L..27H|title= The Tycho-2 catalogue of the 2.5 million brightest stars|journal= Astronomy and Astrophysics|volume= 355|pages= L27|last1= Høg|first1= E.|last2= Fabricius|first2= C.|last3= Makarov|first3= V. V.|last4= Urban|first4= S.|last5= Corbin|first5= T.|last6= Wycoff|first6= G.|last7= Bastian|first7= U.|last8= Schwekendiek|first8= P.|last9= Wicenec|first9= A.|year= 2000|doi=10.1888/0333750888/2862|isbn= 0333750888}}</ref> |
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| dec1={{DEC|−62|35|23.06}}<ref name=tycho2/> |
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| appmag_v1=6.1 - 7.5<ref name="chesneau">{{cite journal|bibcode=2014A&A...563A..71C|arxiv=1401.2628v2|title=The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in the common envelope phase|journal=Astronomy & Astrophysics|volume=563|pages=A71|last1=Chesneau|first1=O.|last2=Meilland|first2=A.|last3=Chapellier|first3=E.|last4=Millour|first4=F.|last5=Van Genderen|first5=A. M.|last6=Nazé|first6=Y.|last7=Smith|first7=N.|last8=Spang|first8=A.|last9=Smoker|first9=J. V.|last10=Dessart|first10=L.|last11=Kanaan|first11=S.|last12=Bendjoya|first12=Ph.|last13=Feast|first13=M. W.|last14=Groh|first14=J. H.|last15=Lobel|first15=A.|last16=Nardetto|first16=N.|last17=Otero|first17=S.|last18=Oudmaijer|first18=R. D.|last19=Tekola|first19=A. G.|last20=Whitelock|first20=P. A.|last21=Arcos|first21=C.|last22=Curé|first22=M.|last23=Vanzi|first23=L.|s2cid=52108686|year=2014|doi=10.1051/0004-6361/201322421}}</ref> |
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| component2=B |
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| ra2={{RA|13|47|10.224}}<ref name=tycho2>{{cite journal|bibcode= 2000A&A...355L..27H|title= The Tycho-2 catalogue of the 2.5 million brightest stars|journal= Astronomy and Astrophysics|volume= 355|pages= L27|last1= Høg|first1= E.|last2= Fabricius|first2= C.|last3= Makarov|first3= V. V.|last4= Urban|first4= S.|last5= Corbin|first5= T.|last6= Wycoff|first6= G.|last7= Bastian|first7= U.|last8= Schwekendiek|first8= P.|last9= Wicenec|first9= A.|year= 2000|doi=10.1888/0333750888/2862|isbn= 0333750888}}</ref> |
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| dec2={{DEC|−62|35|17.40}}<ref name=tycho2/> |
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| appmag_v2=9.83<ref name=tycho2/> |
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}} |
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{{Starbox character |
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| component=A |
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| class=K0 0-Ia<ref name="keenan">{{Cite journal | last1 = Keenan | first1 = P. C. | last2 = McNeil | first2 = R. C. | doi = 10.1086/191373 | title = The Perkins catalog of revised MK types for the cooler stars | journal = The Astrophysical Journal Supplement Series | volume = 71 | pages = 245 | year = 1989 | bibcode = 1989ApJS...71..245K }}</ref> |
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| b-v=+2.499<ref name=tycho2/> |
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| u-b= |
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| variable=[[Eclipsing Variable Star|EB]] + [[Luminous blue variable|SDOR?]]<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> |
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}} |
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{{Starbox character|no_heading=y |
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| component=B |
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| class=B0 Ibp<ref name=pah>{{cite journal|bibcode=2015A&A...583A..98V|arxiv=1509.07421|title=An early detection of blue luminescence by neutral PAHs in the direction of the yellow hypergiant HR 5171A?|journal=Astronomy & Astrophysics|volume=583|pages=A98|last1=Van Genderen|first1=A. M.|last2=Nieuwenhuijzen|first2=H.|last3=Lobel|first3=A.|s2cid=56270146|year=2015|doi=10.1051/0004-6361/201526392}}</ref> |
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| b-v=+0.39<ref name=tycho2/> |
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| u-b= |
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| variable= |
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}} |
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{{Starbox astrometry |
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| radial_v=−38.20<ref>{{cite journal|bibcode=2006AstL...32..759G|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|last1=Gontcharov|first1=G. A.|s2cid=119231169|year=2006|doi=10.1134/S1063773706110065|arxiv = 1606.08053 }}</ref> |
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| prop_mo_ra=−5.649<ref name=dr2/> |
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| prop_mo_dec=−1.483<ref name=dr2/> |
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| parallax=0.3658 |
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| p_error=0.1239 |
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| parallax_footnote=<ref name=dr2>{{cite DR2|5865517646532509568}}</ref> |
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| dist_ly=4,900 – 11,700 |
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| dist_pc=1,500<ref name=van>{{cite journal|bibcode=2019A&A...631A..48V|title=Pulsations, eruptions, and evolution of four yellow hypergiants|last1=van Genderen|first1=A. M.|last2=Lobel|first2=A.|last3=Nieuwenhuijzen|first3=H.|last4=Henry|first4=G. W.|last5=De Jager|first5=C.|last6=Blown|first6=E.|last7=Di Scala|first7=G.|last8=Van Ballegoij|first8=E. J.|s2cid=203836020|journal=Astronomy and Astrophysics|year=2019|volume=631|pages=A48|doi=10.1051/0004-6361/201834358|arxiv=1910.02460}}</ref> – 3,600<ref name=chesneau /> |
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| absmag_v=−9.2<ref name=humphreys>{{cite journal|bibcode=1978ApJS...38..309H|title=Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way|journal=Astrophysical Journal|volume=38|pages=309|last1=Humphreys|first1=R. M.|year=1978|doi=10.1086/190559}}</ref> + −5.8<ref name=humphreys1971>{{cite journal|bibcode=1971ApJ...167L..35H|title=High-luminosity G supergiants|journal=Astrophysical Journal|volume=167|pages=L35|last1=Humphreys|first1=R. M.|last2=Strecker|first2=D. W.|last3=Ney|first3=E. P.|year=1971|doi=10.1086/180755}}</ref> |
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}} |
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{{Starbox orbit |
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| primary=Aa |
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| name=Ab |
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| reference=<ref name=chesneau /> |
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| period_unitless={{val|1,304|6|fmt=commas}} days |
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| axis_unitless={{solar radius|2,028 - 2,195}} |
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| eccentricity=0 |
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| inclination=>60 |
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}} |
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{{Starbox detail |
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| source= |
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|component1=Aa |
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| mass=27 - 36<ref name=wittkowski>{{cite journal|bibcode=2017A&A...597A...9W|arxiv=1610.01927|title=VLTI/AMBER spectro-interferometry of the late-type supergiants V766 Cen (=HR 5171 A), σ Oph, BM Sco, and HD 206859|journal=Astronomy & Astrophysics|volume=597|pages=A9|last1=Wittkowski|first1=M.|last2=Arroyo-Torres|first2=B.|last3=Marcaide|first3=J. M.|last4=Abellan|first4=F. J.|last5=Chiavassa|first5=A.|last6=Guirado|first6=J. C.|s2cid=55679854|year=2017|doi=10.1051/0004-6361/201629349}}</ref><ref name=wittkowski2017/> |
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| radius=1,060 – 1,160,<ref name=van/> {{nowrap|{{val|1,315|fmt=commas}}<ref name=chesneau /> – 1,575<ref name=wittkowski2017/>}} |
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| luminosity=200,000 – 251,000,<ref name=van/> {{nowrap|{{val|630,000|60,000|55,000|fmt=commas}}<ref name=wittkowski/>}} |
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| temperature={{val|4,287|760|fmt=commas}}<ref name=wittkowski/> {{nowrap|(3,855<ref name=vangenderen/> - 5,012<ref name=van/>)}} |
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| metal_fe= |
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| gravity={{val|-0.5|0.6}}<ref name=wittkowski/> |
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| rotational_velocity= |
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| age_myr=3.5<ref name=karr>{{cite journal|bibcode=2009ApJ...697..133K|arxiv=0903.0934|title=Gum 48d: An Evolved H II Region with Ongoing Star Formation|journal=The Astrophysical Journal|volume=697|pages=133–147|last1=Karr|first1=J. L.|last2=Manoj|first2=P.|last3=Ohashi|first3=N.|s2cid=17962808|year=2009|issue=1|doi=10.1088/0004-637X/697/1/133}}</ref> |
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|component2=Ab |
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| mass2={{val|5|15|3}}<ref name=wittkowski2017/> |
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| radius2=312 - 401,<ref name=chesneau /> {{nowrap|{{val|650|150}}<ref name=wittkowski2017>{{cite journal|bibcode=2017A&A...606L...1W|arxiv=1709.09430|title=Multi-epoch VLTI-PIONIER imaging of the supergiant V766 Cen: Image of the close companion in front of the primary|journal=Astronomy & Astrophysics|volume=1709|pages=L1|last1=Wittkowski|first1=M|last2=Abellan|first2=F. J|last3=Arroyo-Torres|first3=B|last4=Chiavassa|first4=A|last5=Guirado|first5=J. C|last6=Marcaide|first6=J. M|last7=Alberdi|first7=A|last8=De Wit|first8=W. J|last9=Hofmann|first9=K.-H|last10=Meilland|first10=A|last11=Millour|first11=F|last12=Mohamed|first12=S|last13=Sanchez-Bermudez|first13=J|s2cid=54740936|date=28 September 2017|doi=10.1051/0004-6361/201731569}}</ref>}} |
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| luminosity2= |
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| temperature2=4,800 - 5,200<ref name=chesneau /> |
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| metal_fe2= |
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| gravity2= |
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| rotational_velocity2= |
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| age_myr2= |
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}} |
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{{Starbox detail|no_heading=y |
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|component2=B |
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| mass2= |
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| radius2= |
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| luminosity2=160,000<ref name=kaler>{{cite web|url = http://stars.astro.illinois.edu/sow/v766cen.html|title = V766 Centauri|author = Jim Kaler|access-date = 2015-11-21}}</ref> |
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| temperature2=26,000<ref name=pah/> |
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| metal_fe2= |
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| gravity2=3.0 - 3.5<ref name=pah/> |
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| rotational_velocity2= |
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| age_myr2=4<ref name=karr>{{cite journal|bibcode=2009ApJ...697..133K|arxiv=0903.0934|title=Gum 48d: An Evolved H II Region with Ongoing Star Formation|journal=The Astrophysical Journal|volume=697|pages=133–147|last1=Karr|first1=J. L.|last2=Manoj|first2=P.|last3=Ohashi|first3=N.|s2cid=17962808|year=2009|issue=1|doi=10.1088/0004-637X/697/1/133}}</ref> |
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}} |
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{{Starbox catalog |
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| names=[[Variable star designation|V766]] Cen, [[Harvard Revised catalogue|HR]] 5171, [[Henry Draper Catalogue|HD]] 119796, [[Hipparcos catalogue|HIP]] 67261, [[Smithsonian Astrophysical Observatory catalogue|SAO]] 252448, [[Cordoba Durchmusterung|CD]]−61°3988, [[Washington Double Star Catalog|WDS]] J13472-6235, [[AAVSO]] 1340-62 |
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}} |
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{{Starbox reference |
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|Simbad=V766+Centauri |
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}} |
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{{Starbox end}} |
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'''HR 5171''', also known as '''V766 Centauri''', is a [[triple star system]] in the [[constellation]] [[Centaurus (constellation)|Centaurus]], either 5,000 or 12,000 light years from Earth. It is said to contain either an extreme [[red supergiant]] (RSG) or recent post-red supergiant (Post-RSG) [[yellow hypergiant]] (YHG), both of which suggest it is one of the [[List of largest known stars|largest known stars]]. The star's diameter is uncertain but likely to be between 1,100 and 1,600 times that of the Sun. It is a [[contact binary]], sharing a common envelope of material with a smaller yellow supergiant and secondary star, the two orbiting each other every 1,304 ± 6 days. There is also said to be a third star orbiting the contact binary further out in the system. |
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==System== |
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[[File:Potw1740a.tif|thumb|left|upright=1.4|[[Interferometry|Interferometric]] images showing the passage of the companion in front of the primary]] |
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The HR 5171 system contains at least three stars. The primary A is an [[eclipsing binary]] (components Aa and Ab, or A and C in the [[Catalog of Components of Double and Multiple Stars]]) with two yellow stars in contact and orbiting in 1,304 days. The companion has been detected directly by [[optical interferometry]], and is approximately one third the size of the [[hypergiant]] primary. The two stars are in the [[common envelope]] phase where material surrounding both stars rotates synchronously with the stars themselves. |
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Component B, located 9.4 [[arcsecond]]s away from the primary, is a [[blue supergiant]] with the spectral type B0.<ref name=pah/> It is a highly luminous massive star in itself but [[Visual magnitude|visually]] three [[magnitude (astronomy)|magnitude]]s fainter than the yellow hypergiant. The projected separation between the hypergiant primary and the blue supergiant is 35,000 AU, although their actual separation could be larger.<ref name=chesneau/> |
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==Observational history== |
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HR 5171 was named by inclusion in the [[Harvard Revised catalogue]], later published as the [[Bright Star Catalogue]]. It was the 5171th entry in the catalogue, listed with a visual magnitude of 6.23 and [[K-type star|K-type spectral type]].<ref name="hr">{{cite journal|bibcode=1908AnHar..50....1P|title=Revised Harvard photometry : A catalogue of the positions, photometric magnitudes and spectra of 9110 stars, mainly of the magnitude 6.50, and brighter observed with the 2 and 4 inch meridian photometers|journal=Annals of the Astronomical Observatory of Harvard College |volume=50|last1=Pickering|first1=Edward Charles|year=1908|page=1}}</ref> HR 5171 was catalogued as a [[double star]] in 1927.<ref name="sds">{{cite journal|bibcode=1927sdsc.book.....I|title=Southern double star catalogue -19 deg. To -90 deg|journal=Johannesburg|last1=Innes|first1=R. T. A.|last2=Dawson|first2=B. H.|last3=Van Den Bos|first3=W. H.|year=1927}}</ref> |
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In 1956, HR 5171 was recorded at magnitude 6.4, spectral type G5p, and profoundly reddened.<ref name="stoy">{{cite journal|bibcode=1956MNSSA..15...96S|title=Photoelectric Magnitudes and Colours for 270 Southern Stars|journal=Monthly Notes of the Astronomical Society of South Africa|volume=15|pages=96|last1=Stoy|first1=R. H.|year=1956}}</ref> In 1966 Corben recorded it as magnitude 6.51 and spectral type G5p, and noted it as being variable. A 1969 catalogue records a visual magnitude of 5.85 and a spectral type of A7V, presumably a case of mistaken identity.<ref name="cowley">{{cite journal|bibcode=1969AJ.....74..375C|title=A study of the bright A stars. I. A catalogue of spectral classifications|journal=Astronomical Journal|volume=74|pages=375|last1=Cowley|first1=A.|last2=Cowley|first2=C.|last3=Jaschek|first3=M.|last4=Jaschek|first4=C.|year=1969|doi=10.1086/110819}}</ref> In 1971, HR 5171 A was identified as a G8 hypergiant, reddened by over three magnitudes of [[interstellar extinction]] and also by half a magnitude of extinction from circumstellar material.<ref name=humphreys1971/> In 1979 it was confirmed as one of the brightest known stars with an absolute visual magnitude (M<sub>V</sub>) of −9.2.<ref name=humphreys/> The G8 spectral type was later adjusted to K0 0-Ia in the revised MK system, meeting the criteria of highly luminous supergiants.<ref name="mk">{{cite journal|bibcode=1980ApJS...42..541K|title=Revised MK spectral types for G, K, and M stars|journal=Astrophysical Journal Supplement Series|volume=42|pages=541|last1=Keenan|first1=P. C.|last2=Pitts|first2=R. E.|year=1980|doi=10.1086/190662}}</ref> |
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In 1973 HR 5171 was formally recognised as variable star V766 Centauri, based on Corben's 1966 catalogue.<ref name="ibvs">{{cite journal|bibcode=1973IBVS..834....1K|title=59th Name-List of Variable Stars|journal=Information Bulletin on Variable Stars|volume=834|pages=1|last1=Kukarkin|first1=B. V.|last2=Kholopov|first2=P. N.|last3=Kukarkina|first3=N. P.|last4=Perova|first4=N. B.|year=1973}}</ref> At the time it was considered a "cool S Doradus variable", a class including stars such as [[Rho Cassiopeiae]] that are now known as the yellow hypergiants. These variables are usually classified as semi-regular (SRd) due to variations which are sometimes well-defined, at other times nearly constant, and may show unpredictable fading. A detailed study showed variability in both brightness and spectral type with possible periods developing from 430 days to 494 days. Surface temperature was calculated to vary from nearly 5,000K to below 4,000K.<ref name="vangenderen">{{cite journal|bibcode=1992A&A...257..177V|title=Light variations of massive stars (Alpha Cygni variables). XII - the photometric history of the G8Ia(+) hypergiant V766 CEN (= HR 5171A) during the years 1953-1991 and its interpretation|journal=Astronomy and Astrophysics|volume=257|pages=177|last1=Van Genderen|first1=A. M.|year=1992}}</ref> |
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In a 2014 paper, VLTI observations directly determined an unexpectedly large size for HR 5171 and revealed that it is a [[contact binary]]. A shell of material around the star has also been directly imaged.<ref name=chesneau /> In 2016, VLTI observations showed an even larger radius and an unexpectedly cool temperature for a K0 hypergiant.<ref name=wittkowski/> Further interferometry imaged the secondary star transiting the primary.<ref name=wittkowski2017/> |
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==Distance== |
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[[File:The field around yellow hypergiant star HR 5171.jpg|thumb|left|upright=1.1|Combined optical and infrared image of HR 5171<br /><small>([[European Southern Observatory|ESO]]/[[Digitized Sky Survey|Digitized Sky Survey 2]])</small>]] |
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HR 5171 appears near the centre of the [[HII Region]] Gum 48d, a ring of material ionised most likely by one or both of the visible HR 5171 stars. The stars and the nebulosity all show similar space motions that would place them in the [[Centaurus Arm|Centaurus spiral arm]] about 4,000 parsecs (4 kpc) away from Earth. It is apparently part of an extensive [[molecular cloud]] complex with a distance between 3.2 kpc and 5.5 kpc from Earth. Gum 48d would require one or two [[O-type star]]s to be [[ionization|ionised]], presumably one or both of the HR 5171 stars a few million years ago. Its age is calculated to be 3.5 million years, one of the oldest known HII regions.<ref name=karr/> |
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Early calculations based on the assumed luminosity of HR 5171B gave a distance of 3.2 kpc and 3.2 magnitudes of interstellar [[Extinction (astronomy)|extinction]]. Comparison of HR 5171A with similar stars in the [[Magellanic Clouds]] imply a distance of 3.7 kpc. An average distance based on all these calculations is 3.6 kpc,<ref name=humphreys1971/> which is still the widely accepted distance although there are reasons to think it could be closer.<ref name=pah/> |
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Gum 48d is also catalogued as RCW 80, although the designation RCW 80 is sometimes used for the more distant [[supernova remnant]] G309.2-00.6 which overlaps it.<ref name=pah/> The [[open cluster]] [[NGC 5281]] lies 19' from HR 5171, projected against the supernova remnant but only about 1,200 parsecs from Earth.<ref name="snr">{{cite journal|bibcode=2007ApJ...659..407S|arxiv=astro-ph/0607551|title=A Multiwavelength Study of 1WGA J1346.5-6255: A New γ Cas Analog Unrelated to the Background Supernova Remnant G309.2-00.6|journal=The Astrophysical Journal|volume=659|pages=407–418|last1=Safi-Harb|first1=Samar|last2=Ribó|first2=Marc|last3=Butt|first3=Yousaf|last4=Matheson|first4=Heather|last5=Negueruela|first5=Ignacio|last6=Lu|first6=Fangjun|last7=Jia|first7=Shumei|last8=Chen|first8=Yong|s2cid=15997425|year=2007|issue=1|doi=10.1086/512055}}</ref> |
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==Spectrum== |
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The [[Astronomical spectroscopy|spectrum]] of HR 5171 is easily separated into a luminous yellow star and a hot blue supergiant. The third component, HR 5171Ab, is not resolved and its [[Stellar classification|spectral type]] is uncertain. Both stars show 3-4 magnitudes of reddening due to dust extinction. |
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The yellow star has been defined as the spectral standard for K0 0-Ia stars.<ref name=mk/> It shows the general features of a late G or early K supergiant, but with a number of peculiarities. High luminosity is indicated by the strength of the 421.5 nm [[Cyanogen|CN]] break and the existence of the infrared [[oxygen]] triplet. It also shows a large [[infrared excess]] and exceptionally strong [[silicate]] absorption, both caused by a dust shell condensed out of material ejected from the star.<ref name=humphreys1971/> An unusual blue excess near 383.8 nm may be due to [[polycyclic aromatic hydrocarbon]] (PAH) luminescence.<ref name=pah/> The spectrum is strongly influenced by the extended atmosphere of the star, with strong [[emission line]]s formed in the [[stellar wind]] and the [[continuous spectrum|continuum]] forming in an extended region rather than at the sharp surface of a [[photosphere]]. The star effectively has a pseudo-photosphere hiding the true surface of the star.<ref name=chesneau/> |
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The blue companion has been classified as B0 Ibp, a hot supergiant of normal luminosity, with some uncertainty. The spectral peculiarity code indicates that its [[absorption line]]s are less sharp than normal for a star of its type.<ref name=humphreys1971/> |
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==Variability== |
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{{more sources needed|section|date=October 2019}} |
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HR 5171 shows erratic changes in brightness and [[Color index|colour]]. HR 5171B is apparently stable, with the changes being due to physical changes in the hypergiant star, variations in the envelope, and [[eclipse]]s between the two close companions. |
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The primary and secondary minima have depths of 0.21 and 0.14 magnitudes respectively at visual wavelengths. The light curve shows almost continuous variation due to the contact nature of the system, but there is a distinct flat bottom to the secondary minimum where the secondary passes in front of the primary. The shape of the eclipse [[light curve]] suggests that the orbit is almost edge on to Earth, and that the secondary is slightly hotter than the primary. |
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The eclipses occur against a background of intrinsic variations. Statistically, the system has a mean magnitude of 6.54 and average variations of 0.23 magnitude over a period from the middle of the 20th century until 2013, but within this there are decades with relatively little variation and others which are much more active. Three deep minima have been observed, in 1975, 1993, and 2000, with the brightness dropping below 7th magnitude each time for around a year. Colour changes at these minima suggest a transfer of luminosity from the visual to the [[infrared]], either as a result of cooling or recycling by the surrounding envelope. Following the deep minima, smaller brightness peaks are observed. Overall, the variability in brightness has been much stronger since 2000. |
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The variations in infrared brightness compared to visual brightness correspond quite well to the light curve, suggesting that brightness changes are related to colour or extinction changes, but there has been a secular trend in the [[UBV photometric system|B-V]] colour index. From 1942 until 1982, B-V steadily increased from around 1.8 to 2.6. Since then it has been approximately constant. This does not appear to be related to reddening as it is independent of the visual magnitude, so it suggests a change in the star itself. The most likely change is that the hypergiant has been cooling and increasing in size. |
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The variations are erratic, but a strong 657-day periodicity was noticed in [[Hipparcos]] photometry of HR 5171. More recent variations showed the strongest periodicity at around 3,300 days, but also showed other periods including one at 648 days. This persistent periodicity through all other variations is due to the eclipses twice every 1,304 days.<ref name=chesneau/> |
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It is classified in the [[General Catalogue of Variable Stars]] as a possible [[S Doradus]] variable, as well as an eclipsing variable.<ref name=gcvs/> |
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==Properties== |
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[[Image:HR 5171A.jpg|Artist's impression of HR 5171 and its companion star|thumb|left|upright=1.2]] |
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The angular diameter of HR 5171A has been published three times using measurements from the [[Very Large Telescope]], twice with the [[AMBER (Very Large Telescope)|AMBER]] interferometer and once with the [[AMBER (Very Large Telescope)|PIONIER]] interferometer. In all cases, an unexpectedly large diameter was found, between about 3.3 and 4.1 mas, well over {{solar radius|1,000}} at the accepted distance of 3.6 kpc. |
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The earliest AMBER interferometry was at a range of [[infrared]] wavelengths in March 2012. The best-fit model was a sharply-defined uniform disk with a small bright spot towards its edge, all surrounded by a fainter extended envelope. The uniform disk, taken to be the photosphere of the larger star, was 3.39 mas across, corresponding to a radius of {{convert|1,315 ± 260|solar radius|km au|lk=on}}. The size of the smaller disk, assumed to be the secondary star, was not well-defined.<ref name=chesneau/> The second set of AMBER observations were made in the [[K band (infrared)|K-band]] in April 2014. The best fits for a uniform disk and the Rosseland radius of a model atmosphere were almost identical at 3.87 mas and 3.86 mas respectively, corresponding to a radius of {{convert|1,492 ± 540|solar radius|au|lk=on|abbr=on}}.<ref name=wittkowski/> The PIONIER observations were made across six different infrared wavelengths during 2016 and 2017. [[Aperture synthesis]] was used to produce an image of HR 5171 at three different phases of the orbit. In two of the images, the secondary star is visible in front of the primary, and in the third it is expected to be behind the primary and was not visible. Modelled as a Rosseland stellar atmosphere surrounded by an extended uniform disk, the photosphere was found to be between 3.3 mas and 4.8 mas. Overall, the radius of the primary was calculated to be {{convert|1,575 ± 400|solar radius|au|lk=on|abbr=on}} and {{convert|650 ± 150|solar radius|km|lk=on|abbr=on}} for the secondary.<ref name=wittkowski2017/> The radii are statistically consistent with each other, but more representative of an extreme [[red supergiant]] rather than a [[yellow hypergiant]]. It is unclear whether this is due to binary interaction or misinterpretation of the unusual and highly reddened spectrum.<ref name=chesneau/> |
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The luminosity has been calculated from [[Spectral energy distribution|spectral energy distribution (SED)]] fitting to be {{solar luminosity|630,000}}, assuming a distance of 3.7 kpc and 3.2 magnitudes of interstellar extinction.<ref name=humphreys/> This is considerably more luminous than expected for any red supergiant and extreme even for a yellow hypergiant.<ref name=pah/> The [[effective temperature]] derived from matching [[infrared]] spectra is 5,000 K,<ref name=chesneau/> while the temperature calculated from a radius of {{solar radius|1,490}} and luminosity of {{solar luminosity|630,000}} is 4,290 ± 760 K.<ref name=wittkowski/> |
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The close secondary HR 5171 Ab is a luminous yellow star with a radius about a third that of the primary star and an almost identical temperature. From the shape of the eclipse light curve, it is 12% as luminous as the primary and slightly hotter. It is much less massive, estimated at only a tenth of the mass of the primary. Its exact properties can only be predicted from models since it is barely resolved from its larger companion and its spectrum cannot be distinguished.<ref name=chesneau/> |
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The hot companion HR 5171 B is a B0 supergiant, 316,000 times as luminous as the Sun according to a 1992 paper. Although it is about half the [[bolometric luminosity]] of HR 5171A, it is three magnitudes fainter as much of its radiation is in the [[ultraviolet]]. |
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==Evolution== |
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The evolutionary history of HR 5171A is complicated by its uncertain and unusual physical properties and binary companion. As a single star with a temperature of 4,290 K, its properties correspond to a non-rotating star with an initial mass of {{solar mass|32 - 40}}, or possibly a rotating star of initial mass {{solar mass|25}}, which is several million years old and near its coolest temperature and largest size. Such stars are too massive to produce type II-P [[supernova]]e at the red supergiant stage and will evolve to higher temperatures, likely producing a different type of supernova explosion.<ref name=wittkowski/> With a temperature of 5,000 K, it would be a slightly more evolved star, having left the red supergiant phase. The primary star is probably undergoing wind [[roche lobe]] overflow (WRLOF) with a portion of the material being transferred to the secondary. This is a possible evolutionary path to a stripped-envelope [[Wolf-Rayet star|Wolf-Rayet binary system]]. The interaction between the pair should spin up the primary to [[synchronous rotation]], which is a possible path to fast-spinning [[luminous blue variable]]s or [[B(e) stars|B[e] stars]].<ref name=chesneau/> |
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==References== |
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{{reflist}} |
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==External links== |
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* [https://www.eso.org/public/images/potw1740a/ VLTI Revisits the Largest Yellow Hypergiant Ever Discovered] www.eso.org |
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{{Stars of Centaurus}} |
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{{DEFAULTSORT:HR 5171}} |
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[[Category:Centaurus (constellation)]] |
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[[Category:K-type hypergiants]] |
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[[Category:Objects with variable star designations|Centauri, V766]] |
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[[Category:Henry Draper Catalogue objects|119796]] |
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[[Category:HR objects|5171]] |
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[[Category:Eclipsing binaries]] |
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[[Category:B-type supergiants]] |
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[[Category:Hipparcos objects|067261]] |
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[[Category:Triple star systems]] |
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[[Category:Durchmusterung objects]] |
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[[Category:TIC objects]] |
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Revision as of 17:11, 29 November 2021
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