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ticle talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikimedia commons wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia star that has a supergiant luminosity class with a spectral type of f or g a yellow supergiant ysg is a star generally of spectral type f or g having a supergiant luminosity class e g ia or ib they are stars that have evolved away from the main sequence expanding and becoming more luminous image of polaris one of the yellow supergiants nearest to earth yellow supergiants are hotter and smaller than red supergiants naked eye examples include polaris alpha leporis alpha persei delta canis majoris and iota¹ scorpii many of them are variable stars mostly pulsating cepheids such as δ cephei itself hertzsprung russell diagram spectral type o b a f g k m l t brown dwarfs white dwarfs red dwarfs subdwarfs main sequence dwarfs subgiants giants red giants blue giants bright giants supergiants red supergiant hypergiants absolute magni tude m v spectrum edit yellow supergiants generally have spectral types of f and g although sometimes late a or early k stars are included 1 2 3 these spectral types are characterised by hydrogen lines that are very strong in class a weakening through f and g until they are very weak or absent in class k calcium h and k lines are present in late a spectra but stronger in class f and strongest in class g before weakening again in cooler stars lines of ionised metals are strong in class a weaker in class f and g and absent from cooler stars in class g neutral metal lines are also found along with ch molecular bands 4 the massive rsgc1 cluster contains 14 red supergiants and one yellow supergiant 5 supergiants are identified in the yerkes spectral classification by luminosity classes ia and ib with intermediates such as iab and ia ab sometimes being used these luminosity classes are assigned using spectral lines that are sensitive to luminosity historically the ca h and k line strengths have been used for yellow stars as well as the strengths of various metal lines 6 the neutral oxygen lines such as the 777 3 nm triplet have also been used since they are extremely sensitive to luminosity across a wide range of spectral types 7 modern atmospheric models can accurately match all the spectral line strengths and profiles to give a spectral classification or even skip straight to the physical parameters of the star but in practice luminosity classes are still usually assigned by comparison against standard stars 4 some yellow supergiant spectral standard stars 8 f0 ib α leporis f2 ib 89 herculis f5 ib α persei f8 ia δ canis majoris g0 ib μ persei g2 ib α aquarii g5 ib 9 pegasi g8 ib ε geminorum properties edit size comparison of the sun yellow supergiants polaris and alpha leporis arneb and numerous red giants yellow supergiants have a relatively narrow range of temperatures corresponding to their spectral types from about 4 000 k to 7 000 k 9 their luminosities range from about 1 000 l upwards with the most luminous stars exceeding 100 000 l the high luminosities indicate that they are much larger than the sun from about 30 r to several hundred r 10 the masses of yellow supergiants vary greatly from less than the sun for stars such as w virginis to 20 m or more e g v810 centauri corresponding surface gravities log g cgs are around 1 2 for high mass supergiants but can be as low as 0 for low mass supergiants 9 11 yellow supergiants are rare stars much less common than red supergiants and main sequence stars in m31 andromeda galaxy 16 yellow supergiants are seen associated with evolution from class o stars of which there are around 25 000 visible 12 variability edit light curve of delta cephei a yellow supergiant classical cepheid variable many yellow supergiants are in a region of the hr diagram known as the instability strip because their temperatures and luminosities cause them to be dynamically unstable most yellow supergiants observed in the instability strip are cepheid variables named for δ cephei which pulsate with well defined periods that are related to their luminosities this means they can be used as standard candles for determining the distance of stars knowing only their period of variability cepheids with longer periods are cooler and more luminous 13 two distinct types of cepheid variable have been identified which have different period luminosity relationships classical cepheid variables are young massive population i stars type ii cepheids are older population ii stars with low masses including w virginis variables bl herculis variables and rv tauri variables the classical cepheids are more luminous than the type ii cepheids with the same period 14 r coronae borealis variables are often yellow supergiants but their variability is produced by a different mechanism from the cepheids at irregular intervals they become obscured by dust condensation around the star and their brightness drops dramatically 15 evolution edit evolution of a 5 m star showing a blue loop and post agb track across the yellow supergiant region supergiants are stars that have evolved away from the main sequence after exhausting the hydrogen in their cores yellow supergiants are a heterogenous group of stars crossing the standard categories of stars in the hr diagram at various different stages of their evolution stars more massive than 8 12 m spend a few million years on the main sequence as class o and early b stars until the dense hydrogen in their cores becomes depleted then they expand and cool to become supergiants they spend a few thousand years as a yellow supergiant while cooling then spend one to four million years as a red supergiant typically supergiants make up less than 1 of stars though different proportions in the visible early eras of the universe the relatively brief phases and concentration of matter explains the rarity of these stars 16 some red supergiants undergo a blue loop temporarily re heating and becoming yellow or even blue supergiants before cooling again stellar models show that blue loops rely on particular chemical makeups and other assumptions but they are most likely for stars of low red supergiant mass while cooling for the first time or when performing a sufficiently extended blue loop yellow supergiants will cross the instability strip and pulsate as classical cepheid variables with periods around ten days and longer 17 18 intermediate mass stars leave the main sequence by cooling along the subgiant branch until they reach the red giant branch stars more massive than about 2 m have a sufficiently large helium core that it begins fusion before becoming degenerate these stars will perform a blue loop for masses between about 5 m and 12 m the blue loop can extend to f and g spectral types at luminosities reaching 1 000 l these stars may develop supergiant luminosity classes especially if they are pulsating when these stars cross the instability strip they will pulsate as short period cepheids blue loops in these stars can last for around 10 million years so this type of yellow supergiant is more common than the more luminous types 19 20 stars with masses similar to the sun develop degenerate helium cores after they leave the main sequence and ascend to the tip of the red giant branch where they ignite helium in a flash they then fuse core helium on the horizontal branch with luminosities too low to be considered supergiants stars leaving the blue half of the horizontal branch to be classified in the asymptotic giant branch agb pass through the yellow classifications and will pulsate as bl herculis variables such yellow stars may be given a supergiant luminosity class despite their low masses but assisted by luminous pulsation in the agb thermal pulses from the helium fusing shell of stars may cause a blue loop across the instability strip such stars will pulsate as w virginis variables and again may be classified as relatively low luminosity yellow supergiants 14 when the hydrogen fusing shell of a low or intermediate mass star of the agb nears its surface the cool outer layers are rapidly lost which causes the star to heat up eventually becoming a white dwarf these stars have masses lower than the sun but luminosities that can be 10 000 l or higher so they will become yellow supergiants for a short time post agb stars are believed to pulsate as rv tauri variables when they cross the instability strip 21 the evolutionary status of yellow supergiant r coronae borealis variables is unclear they may be post agb stars reignited by a late helium shell flash or they could be formed from white dwarf mergers 22 it is expected that first time yellow supergiants mature to the red supergiant stage without any supernova the cores of some post red supergiant yellow supergiants might collapse and trigger a supernova a handful of supernovae have been associated with apparent yellow supergiant progenitors that are not luminous enough to be post red supergiants if these are confirmed then an explanation must be found for how a star of moderate mass still with a helium core would cause a core collapse supernova the obvious candidate in such cases is always some form of binary interaction 23 based on reports from chinese astronomers in the 2nd 1st century bc the red supergiant betelgeuse was described as yellow hinting it may have been a yellow supergiant at the time 24 25 yellow hypergiants edit main article yellow hypergiant particularly luminous and unstable yellow supergiants are often grouped into a separate class of stars called the yellow hypergiants these are mostly thought to be post red supergiant stars very massive stars that have lost a considerable portion of their outer layers and are now evolving towards becoming blue supergiants and wolf rayet stars 26 references edit chiosi cesare maeder andré 1986 the evolution of massive stars with mass loss annual review of astronomy and astrophysics 24 329 375 bibcode 1986ara a 24 329c doi 10 1146 annurev aa 24 090186 001553 giridhar s ferro a parrao l 1997 elemental abundances and atmospheric parameters of seven f g supergiants publications of the astronomical society of the pacific 109 1077 bibcode 1997pasp 109 1077g doi 10 1086 133978 drout maria r massey philip meynet georges 2012 the yellow and red supergiants of m33 the astrophysical journal 750 2 97 arxiv 1203 0247 bibcode 2012apj 750 97d doi 10 1088 0004 637x 750 2 97 s2cid 119160120 1 2 gray richard o corbally christopher 2009 stellar spectral classification stellar spectral classification by richard o gray and christopher j corbally princeton university press bibcode 2009ssc book g figer donald f mackenty john w robberto massimo smith kester najarro francisco kudritzki rolf p herrero artemio 2006 discovery of an extraordinarily massive cluster of red supergiants the astrophysical journal 643 2 1166 arxiv astro ph 0602146 bibcode 2006apj 643 1166f doi 10 1086 503275 s2cid 18241900 morgan william wilson keenan philip childs kellman edith 1943 an atlas of stellar spectra with an outline of spectral classification chicago bibcode 1943assw book m faraggiana r gerbaldi m van t veer c floquet m 1988 behaviour of o i triplet lambda 7773 astronomy and astrophysics 201 259 bibcode 1988a a 201 259f garcia b 1989 a list of mk standard stars bulletin d information du centre de données stellaires 36 27 bibcode 1989bicds 36 27g 1 2 parsons s b 1971 effective temperatures intrinsic colours and surface gravities of yellow supergiants and cepheids monthly notices of the royal astronomical society 152 121 131 bibcode 1971mnras 152 121p doi 10 1093 mnras 152 1 121 burki g 1978 the semi period luminosity color relation for supergiant stars astronomy and astrophysics 65 357 bibcode 1978a a 65 357b gonzalez guillermo lambert david l giridhar sunetra 1997 abundance analyses of the field rv tauri variables ep lyrae dy orionis ar puppis and r sagittae the astrophysical journal 479 1 427 440 bibcode 1997apj 479 427g doi 10 1086 303852 drout maria r massey philip meynet georges tokarz susan caldwell nelson 2009 yellow supergiants in the andromeda galaxy m31 the astrophysical journal 703 1 441 460 arxiv 0907 5471 bibcode 2009apj 703 441d doi 10 1088 0004 637x 703 1 441 s2cid 16955101 majaess d j turner d g lane d j 2009 characteristics of the galaxy according to cepheids monthly notices of the royal astronomical society 398 1 263 270 arxiv 0903 4206 bibcode 2009mnras 398 263m doi 10 1111 j 1365 2966 2009 15096 x s2cid 14316644 1 2 wallerstein g cox a n 1984 the population ii cepheids astronomical society of the pacific 96 677 bibcode 1984pasp 96 677w doi 10 1086 131406 asplund m gustafsson b lambert d l rao n k 2000 the r coronae borealis stars atmospheres and abundances astronomy and astrophysics 353 287 bibcode 2000a a 353 287a meynet g maeder a 2000 stellar evolution with rotation v changes in all the outputs of massive star models astronomy and astrophysics 361 101 arxiv astro ph 0006404 bibcode 2000a a 361 101m meynet georges georgy cyril hirschi raphael maeder andré massey phil przybilla norbert nieva m fernanda 2011 red supergiants luminous blue variables and wolf rayet stars the single massive star perspective société royale des sciences de liège 80 266 arxiv 1101 5873 bibcode 2011bsrsl 80 266m meynet georges ekstrom sylvia maeder andré eggenberger patrick saio hideyuki chomienne vincent haemmerlé lionel 2013 models of rotating massive stars impacts of various prescriptions studying stellar rotation and convection lecture notes in physics vol 865 pp 3 22 arxiv 1301 2487v1 bibcode 2013lnp 865 3m doi 10 1007 978 3 642 33380 4_1 isbn 978 3 642 33379 8 s2cid 118342667 pols onno r schröder klaus peter hurley jarrod r tout christopher a eggleton peter p 1998 stellar evolution models for z 0 0001 to 0 03 monthly notices of the royal astronomical society 298 2 525 bibcode 1998mnras 298 525p doi 10 1046 j 1365 8711 1998 01658 x girardi l bressan a bertelli g chiosi c 2000 evolutionary tracks and isochrones for low and intermediate mass stars from 0 15 to 7 msun and from z 0 0004 to 0 03 astronomy and astrophysics supplement 141 3 371 383 arxiv astro ph 9910164 bibcode 2000a as 141 371g doi 10 1051 aas 2000126 s2cid 14566232 van winckel hans 2003 post agb stars annual review of astronomy and astrophysics 41 391 427 bibcode 2003ara a 41 391v doi 10 1146 annurev astro 41 071601 170018 clayton geoffrey c geballe t r herwig falk fryer christopher asplund martin 2007 very large excesses of 18o in hydrogen deficient carbon and r coronae borealis stars evidence for white dwarf mergers the astrophysical journal 662 2 1220 1230 arxiv astro ph 0703453 bibcode 2007apj 662 1220c doi 10 1086 518307 s2cid 12061197 bersten m ...