arXiv:1301.1519v1 [astro-ph.SR] 8 Jan 2013 RG aebe ofimda Npoeiosfrsaswith for progenitors supergian SN 18 red as to Observationally, confirmed up been uncertain. have very (RSG) is event SN distances. cosmological to up traced be l can generally that a event (SN), nous sho core-collapse his- Their a the ener . with cosmic end the photons, of the into ionizing species mass in of chemical and players input the momentum, enormous key times their been through eight have tory about rare, although than , massive more Stars Introduction 1. ossetypeitteselrprmtr uha temper as such parameters stellar ( the predict consistently Un massive the of in impact understanding their the consequently in and deaths, gap their main stars, a & exposes Maeder observati theory between 2012; discrepancy and al. glaring et a (Ekström Such phase 2000). 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Key 2008ax. 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Jose n hi ie saSproa(N,a vn ffnaetli fundamental of event an (SN), Supernova a as lives their end uenv progenitors Supernova L te othe to etter nr hs.W ugs http I Ncudhv B sprog as LBV have could SN IIb type that suggest We phase. onary iverse. hrto ther yet, y hf nprdg,maigta rcino Bscudb th be could LBVs of fraction a that meaning paradigm, in shift uegat lesprin,o ofRytsaebfr th before stage Wolf-Rayet or supergiant, blue supergiant, n fsaswt nta assbten20 between masses initial with stars of ing ature umi- been ihrr,usal asv tr nw sLmnu leVa Blue Luminous as known stars massive unstable rare, with s ABSTRACT e 1 H19 avry wteln;e-mail: Switzerland; Sauverny, CH-1290 51, tes ia upr o eaieylwlmnst Bsexplodin LBVs low-luminosity relatively for support tical ons gy, ro- m- en ts rt l. o Bsa rgntr,n hoeia oe a e predicted yet had model theoretical no progenitors, as LBVs uigteRGpae oelyr ih xedteEdding- th the case, this exceed In might instabilities. s layers driving the possibly some of limit, ton phase, surface the RSG i variations beneath the of hydrogen t during Because of for (1988). level and al. ionization et (2001), the Jager al. de et from implemente phase Vink are RSG from rates loss prescription mass the radiative following The (1997). Maeder h rtclvlct o ra-p h rsrpinfrth for prescription The 40 di break-up. of tational for speed velocity rotational critical initial Th the and code. evolution solar stellar Geneva assume the with computed b (2012), will masses preparation). of in 2013, range al. full et the (Groh of elsewhere analysis reported The models. tating ln fsaswt nta assbten20 between masses initial mod with atmospheric stars and of evolution eling stellar coupled performed We models the of 2. SNe. as exploding before LBVs to similar spectra have Npoeio rmselreouinmdl,w rsn her atmospheric present transfer radiative we coupling models, t approach, evolution classify novel stellar properly a To from wind. progenitor stellar presenc SN the dense is of and layer because atmosphere this observations an the stage, by pre-SN directly the reached at especially However, face. eefe efcso h eut fte20 the of results the on focus we Hereafter nigta igesaswt nta asi h ag 20–25 range the theoret in mass surprising nature initial quite with the a stars into report single we insight that finding Here enormous gain progenitor. ha the to Letter, of this us in allows discuss spectrum we As a directl observations. condition be the can structure that to stellar spectrum fronted synthetic the a input generate to as able Using are 2012). with (Eks al. code 1998) et evolution stellar Miller Geneva the & with (Hillier performed those CMFGEN with done calculations E h vltoaymdl r hs rmEsrme al. et Ekström from those are models evolutionary The v tr:wns uflw tr:rotation stars: – outflows winds, stars: – ive ditor ff so coe usion o eebeayo h frmnindclasses aforementioned the of any resemble not o ffi insi ae rmZh 19)and (1992) Zahn from taken is cients prac nvrewd.Theoret- Universe-wide. mportance M ⊙ n 120 and [email protected] ril ubr ae1o 4 of 1 page number, Article M ⊙ xlso.We explosion. e efudthat found We . M sS nthe in SN as g M ⊙ n stage end e ⊙ n 25 and

n 120 and c enitors, riables S 2013 ESO radiative e ted that M con- y / ,we s, of % ⊙ ro- e wind tröm ving M of e ical M not ro- tar he he ey ⊙ n ⊙ d e e - . Letter to the Editor Letter to the Editor .Teft frttn 20–25 rotating of fate The 3. LBVs resembling still spectra model pre-SN the with tained, me di the significant in no changes layer, are reasonable ing here For reached approach. this conclusions loo of the dependent progenitor However, SN colder. the or make hotter the would at CMF- which the the surface, change hydrostatic between would point solutions Geneva merging and the GEN solutions of structure location stellar the Geneva the Changing envel and stellar CMFGEN evolu- the the of analyz Geneva structure merge range temperature parameter the the the by use in the We 2001 used here). al. adopt et that Vink we (from as consistency, code abu recipe tion For surface rate CMFGEN. and mass-loss in mass, same luminosity, input radius, as the dances, as such tions, ril ubr ae2o 4 of 2 page number, Article eeassume here iue1sosteeouinr rcso oaigmsies 20 massive of rotating masses of initial tracks with evolutionary the shows 1 Figure rmKdizi&Pl 20) idcupn sicue with ( included factor is filling clumping veloc Wind volume escape terminal a (2000). the wind Puls with The & scaling Kudritzki the speed. from using sonic two computed the The is of velocity atmosphere. 0.75 the at of merge portion solutions subsonic the for computed ilr19) o h yrdnmc ftewn,w suea assume we wind, the of hydrodynamics standard the (Hillier For CMFGEN 1998). code Miller transfer eq radiative thermodynamical atmospheric non-local rium, blanketed, line full metric, whic (2005). models, al. our et in Loon three van of from factor observations a the by matches increased is loss mass h r-Nsae h 20 the stage, pre-SN the 1 3 asv tr,sc sBGadLV,aefudi hsrneof range this in found are LBVs, and T BSG as such stars, massive ol aesgetdaBG(ae on (based BSG a suggested have would yea iulmnmm ent htHe that note we spectral minimum, WN11h a visual spectra display at synthetic may type the LBVs some in While present stage. also pre-SN main are 1993), the al. str that et as Stahl see such LBVs, clearly of can He of spectrum H, optical One spectrum the LBV. the in other present ra reproduce any features mass-loss to or rate, tuned Car rotation velocity AG terminal mass, initial wind have or not do models also 2. we Fig. in spectrum, Carinae LBV AG LBV observed prototypical typical the display illustr a To of optical modeling. morphology synthetic atmospheric pre-SN the the our shows with 2 computed Figure spectra stars. WR or BSG, t Cote ta.19) eotie httemorphologic the that obtained We inappropri- 1995). late be al. the would et with WN11h) (Crowther - classification ate (WN9h WR types a spectral therefore, possible and, emission in tes(rhe l 09,;Hlire l 98 aar 200 20 the Najarro of 1998; morphology al. spectral the et that Hillier show 2009a,b; results Our al. among 316285, et HDE Cygni, (Groh P LBV others Carinae, of HR spectra Carinae, AG observed as the such to similar remarkably are models criter 2012). abundance Georgy chemical from the using (WNL, classification WN 25 . . ⋆ 9 2 xldn sTp ISN II Type as exploding M and eueteotusfo h eeaselrsrcuecalcula structure stellar Geneva the from outputs the use We ocmueteotu pcr eue h peial sym- spherically the used we spectra output the compute To h iiaiisaecnpcos seilybcueour because especially conspicuous, are similarities The tiigy efudta h r-Nsnhtcsetao ou of spectra synthetic pre-SN the that found we Strikingly, × × ⊙ 10 10 i n N and , r-Nmdl smrel di markedly is models pre-SN L 5 5 ⋆ β nteasneo pcrm ovninlwisdom conventional spectrum, a of absence the In . tp a with law -type L L ⊙ ⊙ f bu le qae nFg1.Svrlcassof classes Several Fig.1). in squares filled (blue hl h 25 the while ii = ie ihPCgipols(rhe l 2009b; al. et (Groh profiles P-Cygni with lines 0 . 1. 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LBVs of results, reminiscent similar type expect we qualitatively atm changes, the e of the extension 2008; the and Hamann change sphere could & which (Gräfener 2011), limit al. et Eddington Vink the near a loss mass- be Humphreys mass assumed Our may 2011; 2006). al. rates Owocki et loss & phe- Smith Groh LBV 1994; 2012; the Davidson in al. & factor key et surpa a (Gräfener be (or to nomenon to seems proximity limit the Eddington the that of) and recall evolution We stellar calculations. the tral in rat used mass-loss prescribed velocities the wind-terminal wind supports t turn t the of in from of because which resulting occurs lution, layers ratio This subsonic luminosity-to-mass 20). deep high of relatively the depth optical in parameter Rosseland 0.90 a Eddington (at – the th 0.85 that high equ around hydrostatic indicates so is in modeling is star star Our the the hold of rium. longer luminosity not could the which the at limit a limit, aeadwn emnlvlct.I atclr h modeled ( the rate particular, mass-loss high In relatively have velocity. terminal wind and rate oteW phase. WR still the could to LBVs high-luminosity while evolution, stellar L f20 of 1. Fig. o idtria eoiy( velocity terminal wind low log( 1. model Table in The summarized are LBVs. stage in pre-SN encountered the at typically properties values with line in end eaae lse.Orrslsse oidct tha indicate (log( to LBVs seem luminosity results Our we classes. represent separated LBVs defined, high-luminosity and low- whether unclear perneo h Npoeio srgltdntol by only not regulated is progenitor SN the of appearance layer. envelope last the at a those phases to squa evolutionary refer filled representative Blue and break-up. stage, for pre-SN velocity the critical initial the The of (2012). 40% al. is et Ekström in calculated and diagram ⋆

u lob h tla idpoete,sc stemass-los the as such properties, wind stellar the by also but Log (luminosity/solar ) M hr isi ewe u oesadLV r h chem- the are LBVs and models our between kinship third A nadto osetocpcsmlrte,bt h 20 the both similarities, spectroscopic to addition In h aatcLV pnarneo uioiis with luminosities, of range a span LBVs Galactic The L 4.6 4.8 5.0 5.2 5.4 5.6 ⋆ M ⊙ / ⊙ L oaigmdl r xrml ls oteEddington the to close extremely are models rotating ⊙ n 25 and 4.8 ) M vltoaytak frttn oeswt nta masses initial with models rotating of tracks Evolutionary ≃ ⊙ 5 oe,teH n bnacs(.4ad0.0075 and (0.74 abundances N and He the model, (O6V) . 2 M 20 M ff 25 M − ⊙ 4.6 cietmeaue oee,frreasonable for However, temperature. ective tslrmtliiy(Z metallicity solar at 6 O • ff O • . ce ytedsic rpriso stellar of properties distinct the by ected Cake l 05.Osrainly tis it Observationally, 2005). al. et (Clark 5 (O7.5V) L ⋆ / 4.4 Log (temperature/K) L ⊙ v (LBV) ) ∞ ≃ ∼ (LBV) 5 4.2 7 o30k s km 320 to 270 . 2 M ˙ − ∼ 5 = 1 . )aeteedonsof endpoints the are 5) .1) hw nteHR the in shown 0.014), 4.0 − 4 × 10 3.8 v Z=0.014 − − rot 5 1 /v M ,wihare which ), crit eindicated. re oainrate rotation ⊙ e indicate res =0.4 yr (RSG) (RSG) M eevo- he 3.6 − T pectral evolve sand es 1 low- t ⋆ ⊙ spec- ssing and ) stars ilib- and and 3). he ll- o- at Γ e s Groh, Meynet & Ekström: LBVs as unexpected Supernova progenitors

HeI- -HI -HI -HI -HI -NII -NII -NII -NII -NII -NII -SiII -SiII -SiII -SiII -HeI -HeI -HeI -HeI -HeI -HeI -HeI -SiIII -FeII 15 -FeIII

pre-SN 25 Msun rot. model

10 pre-SN 20 Msun rot. model

Normalized Flux 5

AG Car observations 2002-Jul-04

0 4000 4500 5000 5500 6000 6500 Wavelength (Angstrom) Letter to the Editor

Fig. 2. Synthetic optical spectra of the 20 M⊙ (black) and 25 M⊙ (blue) rotating models at the pre-SN stage. The flux has been continuum- normalized and offset for clarity. The strongest spectral features are identified. We also show the observed spectrum of the prototypical LBV AG Carinae obtained in 2002 July 04 (green), when the star had an effective temperature of 16400 K (Groh et al. 2009b). Note that AG Car has a higher luminosity than the pre-SN models, and is shown only to illustrate the morphology of a typical LBV spectrum. We note the remarkable similarity between our synthetic spectra and a typical LBV spectrum. This suggests that some LBV stars are caught just before the explosion.

by mass fraction, respectively) are remarkably similar to those of 20 M⊙: O7.5V → BSG → RSG → BSG/BHG → LBV → SN; LBVs (e.g. Clark et al. 2009). The 25 M⊙ model predicts a more 25 M⊙: O6V → OSG → RSG → OSG/WNL → LBV → SN. chemically enriched surface with He and N (0.92 and 0.016 by Our models indicate that the pre-mortem LBV phase is short mass fraction, respectively) and, as expected, its spectrum shows (∼ 5000 years), which is consistent with the observed rarity stronger He I and N II lines than that of the 20 M⊙ model or the of LBVs (Clark et al. 2005; Humphreys & Davidson 1994; van LBV observations. Still, the 25 M⊙ model spectrum looks more Genderen 2001). The 20 M⊙ and 25 M⊙ models lose most of similar to LBVs than to any other class of massive stars. their mass at the RSG phase (8.7 M⊙ and 9.6 M⊙ respectively), We note that the LBV classification is phenomenological, which enables the star to have the aforementioned surface prop- where one of the following properties has to be present. Either erties required to show an LBV spectrum at pre-death. Thus, the star shows S-Doradus type variability, or giant eruptions of mass loss at the RSG phase has a key impact in the subsequent several solar masses must have occurred (Humphreys & David- evolution (see Georgy 2012). son 1994; van Genderen 2001). Therefore, had the SN model Let us look at the expected properties of the SN arising from progenitors been observed, they would technically be classified the explosion of these low-luminosity LBVs. For this purpose, as “candidate LBVs", since none of the above phenomenaare in- we investigate the chemical composition of the star before the cluded in our calculations. Despite semantics, here we show that explosion. Figure 3 shows the chemical structure of our 20 M⊙ the model SN progenitors are alike stars in the quite rare LBV rotating model at the end of the core C burning phase. The star phase in many aspects, such as spectral appearance, proximity to consists of a He-rich core containing 94% of the total mass and the Eddington limit, and chemical abundances at the surface. extending over slightly more than 10% of the total radius of the One may wonder why the rotating model explodes as an star, surrounded by a very shallow H-rich envelope containing LBV, while the corresponding non-rotating model 20 M⊙ does about 6% of the mass and extending over about 90% of the total not evolve back to the blue and explodes as a RSG, showing a radius. We see that very little amountof H remainsat the surface. ff type IIP SN. This is mainly an e ect of rotational mixing which According to Georgy et al. (2012), the 20 M⊙ model presents produces a larger He-core. The He-core is the inner part of the a very nice fit with the observed characteristics of the core- star, enclosed in the first layer encountered going deeper into the collapse SN 2008ax (Crockett et al. 2008). These are (a) a CO ∼ star where the He mass fraction is greater than 0.75. It is a core mass between 4 and 5 M⊙ (the model gives 4.73 M⊙), (b) a ff well known e ect that the larger is the mass fraction of the total small amount of hydrogenin the ejecta (the model gives 0.02 M⊙ mass occupied by the He-core, the bluer is the position of the of H) and (c) theestimated position of theprogenitorin thecolor- star in the HR diagram (Giannone 1967). In our rotating 20 M⊙ diagram (Fig. 10 of Georgy et al. 2012). Our revised model, the He-core encompasses 100% of the total mass, while colors for the rotating 20 M⊙ model (B − V = −0.14) confirms in the non-rotating corresponding model, it encompasses only the very good agreement. SN 2008ax was found to be a type IIb, 71%. Hence the difference of position in the HR diagram. i.e. an event which transitions from type II to Ib. This suggests that type IIb SN could have an LBV as progenitor, and a prime example could be SN 2008ax. 4. Implications for massive star evolution Thus, for the rotating 20 M⊙ model, one would expect that Our results indicate that for rotating massive stars with initial the SN progenitor, which has an LBV-type spectrum, will ex- masses between 20–25 M⊙, a previously unreported evolution- plodeas a type IIb SN. The 25 M⊙ model presents a very similar ary sequence occurs. The star appears at the Zero-Age Main Se- structure as the one shown in Fig. 3, thus will likely explode as a quence as late-type O star (O6V to O7.5V), evolving to a BSG/O type IIb SN too. Because the progenitor star has significant mass supergiant (OSG), a RSG, a BSG/blue (BHG, for loss during the RSG phase and crosses the infamous “Yellow the 20 M⊙ model) or O supergiant (OSG)/WNL (for the 25 M⊙ Void" in the HR diagram (de Jager 1998), enhanced mass loss model), and finally appearing as an LBV before the SN event, may have occurred in both phases. As a consequence, this would

Article number, page 3 of 4 Letter to the Editor ril ubr ae4o 4 of 4 page number, Article Notes. 1. Table eprtr rdu)o h ae hr h osln optic Rosseland the where layer the of (radius) temperature oso N rmsaswt nta asaoe25 above mass initial with stars from SNe 2007). of (Smith 1987A tors SN of case mod the in the of as to LBVs here, comparable have compute progenitors, we to as proposed masses initial been 2007). modest have al. et SNe (Smith some 2006gy SN Interestingly, and 2009) Leonard & (Gal-Yam etda Npoeioshdteriiilms orycon- othe poorly while ( 2008), mass stars al. massive sug- very initial et LBVs to (Trundle linked their the 2005gj were SN of had as Some progenitors such strained, masses. SN initial as of gested range co a progenitors the from that indicates come progenitors SN coul be can wave IIb. LBVs blast type a SN of the instead SN with IIn type interaction a its produce velo and slow dense, material, with ity medium circumstellar H-rich a produce n h usqetS vn frttn tr ihiiilma initial with stars rotating collapse of 20 core event between SN precede subsequent immediately the LBVs and to similar spectrum previous evolution the LBV. an follow as would o explode fraction range and significant discussed mass a this that expect in would stars one Thus, phase. MS 1 n 0 ms s km 209 and 217 (25 h 0ad25 and 20 the o-oaigmdl xld saRG(20 RSG a as birth, explode at mass velocities models exact rotational non-rotating the of low- on distribution of depends and number SN limits The as explode scenario. that l star LBVs of single luminosity a explosions in for LBVs support luminosity theoretical unexpected provide uioiyLVa h r-Nsaeaebu,with blue, are stage pre-SN the at LBV luminosity eJgr . iuehizn . a e uh,K .1988, A. K. Hucht, der van & H., Nieuwenhuijzen, 293, 145 C., A&A, 8, Jager, 1995, Rev., de A&A J. L. 1998, M C. Smith, 2008, al. Jager, & et J., de D. J., S. Hillier, 2 A., Smartt, 435, P. J., A&A, Crowther, J. 2005, Eldridge, A. M., Arkharov, A& R. & 2009, Crockett, M., al. V. et Larionov, M., S., V. J. Larionov, Clark, A., P. Crowther, S., J. Clark, References availabl Gr CMFGEN Goetz making for referee, Hillier the John and thank comments We tailed Foundation. Science National i Acknowledgements. the of tip the just revealed berg. have could L for progenitors progenitors evidence SN previous as being the LBVs and detection, low-luminosity awaiting with be could progenit SNe luminous of more population obser the a obvious detecting the towards Given bias 2012). vational al. et Mauerhan 2009; Leonard to tween eLV,a nS 05lad20i ( 2009ip and 2005gl proposed SN been have in that as progenitors LBVs, SN be of those than fainter − 1 − hl u oessild o upr Bsa progeni- as LBVs support not do still models our While h silsac)osrainleiec htsget th suggests that evidence observational scarce) (still The nsmay u e hoeia nigi htsaswith stars that is finding theoretical key our summary, In osdrda h envlcte fsc tr uigthe during stars such of velocities mean the as considered M 0 . 1 hyas aeaslt antdsi h -adbe- V-band the in magnitudes absolute have also They 11. ( 00711. 1 10.5 7.1 20.0 M 5096863 8.6 9.6 25.0 ⊙ (a) M M .W oeta h ieaeaerttoa eoiisof velocities rotational average time the that note We ). ini rpriso h Npoeiosfo oaigmdl tsol at models rotating from progenitors SN the of Properties ⊙ V rmEsrme l (2012). al. et Ekström From ( ) = M M − ⊙ M 6 M prog . H sspotdb nAbzoeFlosi fteSwiss the of Fellowship Ambizione an by supported is JHG n 25 and and 8 ⊙ ⊙ Mr (10 (Myr) ) . a − oesdrn h anSqec M)are (MS) Sequence Main the during models 1 hsi oprbet h sa 0 km 200 usual the to comparable is This . Age − M 7 . a .Teevle r he magnitudes three are values These 2. ⊙ u oespeitta h low- the that predict models Our . L 5 ⋆ . . > 05 94 533. 1 38.1 35.3 19540 20355 9 59 00 844. 4 47.0 28.4 20000 25790 2 a L (b) ⊙ 50 K K ( (K) (K) ) endhr stetmeaue(ais ftels ae ft of layer last the of (radius) temperature the as here Defined M M T ⊙ V ⋆ ,sc sS 2005gl SN as such ), a,b − ∼ M ⊙ RS 9,L5 391, NRAS, rWNL or ) 0 a-a & Gal-Yam 10; ,57 1555 507, A, T B 172 e e. de- for aefener, &S 2 259 72, A&AS, − ff 39 c ldphi qa o2 to equal is depth al V M ic the since = ⊙ R they , − / R ⋆ LBV BVs 0 a,b ⊙ ow- ors, uld . ce- ( ) els 14 to ss c- rmtlct,wihhv nLVsetu n xld sS II SN as explode and spectrum LBV an have which metalicity, ar ly rs at d f - R phot R ik .S,Mirs .E,Atois,B,e l 01 A&A, 369 2011, A&A, 115 al. 2001, 265, et M. A&A, B., L. 1992, Anthonisse, G. J.-P. E., J. Zahn, L. H. Muijres, Lamers, S., & J. A., Vink, Koter, de S., J. Vink, ile,D . rwhr .A,Njro . ulro,A. Fullerton, & F., Najarro, L10 A., 531, P. A&A, 6 Crowther, 2011, ApJ, J., S. 2009b, D. J. al. Hillier, Vink, et 46 & A., 736, H. Damineli, ApJ, J. 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