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Where Do Lbvs Come From? …And Where Do WR Stars Come From?

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Where Do Lbvs Come From? …And Where Do WR Stars Come From? Where do LBVs come from? …and where do WR stars come from? Nathan Smith UC Berkeley LBV WNH Peter (WNH) 120 M Stan (LBV) YHG WR 60 M RSG LBV B[e] 35 M 20 M LBV WNH 120 M YHG WR 60 M RSG LBV B[e] 35 M O star WR WNH LBV 20 M ? Luminous WNH stars: pre-LBV or post LBV? WNH stars: WR-like features (em. lines), but… • more luminous H • they have H • cooler no H 1. WNH stars as “transitional WR stars” O WR Short “pit stop” on the way to WR; beginning of core He burning. (some models even skip the LBV phase) 2. WNH stars as “O stars on steroids”… GUILT BY ASSOCIATION: WNH stars in massive young H II regions. HIGH LUMINOSITY/HIGH Mdot: H-rich pre-LBVs approaching the end of core- H burning (e.g., Crowther et al. 1995; Drissen et al. 1995; de Koter et al. 1997; Lamers et al. 1994; Hamann et al. 2006; Moffat & Seggewiss 1979). CONTINUITY IN SPECTRAL TYPES: O, O((f)), O(f), Of?fpe+* etc., WNH (Walborn et al. 1971, 1973, 1974, 1975, ‘76, ‘77, ‘78, ‘79…2002; Conti 1976). (WNH) Walborn (1971) 2. WNH stars as “O stars on steroids”… GUILT BY ASSOCIATION: WNH stars in massive young H II regions. HIGH LUMINOSITY/HIGH Mdot: H-rich pre-LBVs approaching the end of core- H burning (e.g., Crowther et al. 1995; Drissen et al. 1995; de Koter et al. 1997; Lamers et al. 1994; Hamann et al. 2006; Moffat & Seggewiss 1979). CONTINUITY IN SPECTRAL TYPES: O, O((f)), O(f), Of?fpe+* etc., WNH (Walborn et al. 1971, 1973, 1974, 1975, ‘76, ‘77, ‘78, ‘79…2002; Conti 1976). Why call them “WNH stars”? Smith & Conti (2007, ApJ, 679, 1467) (as opposed to WNL, WN6ha, WN7h, Ofpe/WN9, WNEh, etc.) They are not REAL Wolf-Rayet stars: they have hydrogen, more massive, cooler… _________________________________ WNH is short-hand for a group of semi-evolved, very luminous O-stars with strong winds. Spectral type for any individual star (WN6ha etc) still applies…phew! SNe: Type I or Type II? WNH stars are not SN Ib progenitors _________________________________ Like the term “LBV”. Unspecific, but arguably useful, and introduced by someone we all know. LBV = (S Doradus var., Hubble-Sandage var., η Car var., α Car var., P Cygni stars., Ofpe/WN9, WN11, BSG, blue hypergiant, B0.5 Ia+, LBV candidates, etc.) WNH STARS AS MASSIVE PRE-LBVs . Smith & Conti (2007, ApJ, 679, 1467) • WNH stars have high masses • WN/WC stars have low mass <25 M Very different M distribution from H-free WN/WC stars, even with big uncertainties. Spectroscopic masses mostly from Hamann, Gräfner, & Liermann WR20a (2006), but also from Crowther & Dessart (1998) and de Koter et al. (1997) for Carina, NGC3603, 30 Dor. Binary masses from many different sources (van der Hucht et al. 2001 plus several others). Most WNH stars are not “transitional” Wolf-Rayet stars. H no H WNH (WNL+H) STARS AS MASSIVE PRE-LBVs Smith & Conti (2007, ApJ, 679, 1467) Hydrogen mass fractions XH of WNH stars compared to LBVs: Two different studies of WNH stars: roughly same XH values, …but luminosities differ by about 0.3 dex (luminosities from Hamann et al. 2006 are higher). FEEDBACK: MASS LOSS AND EVOLUTION Mass loss depends on previous mass loss: Mass-loss rates change if we account for FEEDBACK due to previous mass loss. L=L(t) steadily increases during core-H burning. M=M(t) decreases, so Γ~L/M is increasing. M ≠ constant…. M = M ( t , L , Γ ) . M(t) t=0 2.5-3 Myr Feedback FEEDBACK: MASS LOSS AND EVOLUTION Mass loss depends on previous mass loss: From CAK theory, line driven winds should follow: 1 $1+ • % # ( + M " L ' * & 1$ #) Adopting =0.5, then: α • % # ( M " L ' * & 1$ #) ! ___________________________________ Assume L(t), M0, Mdot0 ------ --- calculate M(t), Mdot(t), Γ(t)=L/L ! Edd . • Moderately clumped winds (fc ≈ 4) taking Mdot0 from Repolust et al. (2004) . M2 = M1 − M2 × (t2-t1) FEEDBACK: MASS LOSS AND EVOLUTION Mass loss depends on previous mass loss: From CAK theory, line driven winds should follow: 1 $1+ • % # ( + M " L ' * & 1$ #) Adopting =0.5, then: α • % # ( M " L ' * & 1$ #) ! ___________________________________ (we ignored rotation…mixing…) ! Can the mass-loss rates be even lower? That might delay or prolong the LBV phase…. • LBVs are generally not in young clusters . • Type IIn SNe from LBVs LBVs on the upper HR Diagram L L ! = * ~ * L M Luminous Blue Variables Edd * • Eta Car Γ=0.9 • Pistol * WNH . Sher 25 Γ=0.6 + Wolf-Rayet (WC, WN) B[e] RSGs . SN1987A Smith, Vink, & de Koter (2004) MS LBVs on the upper HR Diagram L L ! = * ~ * L M Luminous Blue Variables Edd * • Eta Car Γ=0.9 • Pistol * WNH . Sher 25 =0.6 log L/L =5.8 Γ + Wolf-Rayet (WC, WN) . VY CMa Bistability Jump RSGs . SN1987A Smith, Vink, & de Koter (2004) MS …so where do WR stars come from? LBV WNH 120 M YHG WR 60 M RSG LBV B[e] 35 M 20 M • WR stars in low-Z galaxies SMC, IC10, I Zw18, etc. • All GRBs known to be associated with SNe are Type Ic in low metallicity galaxies. • WR star binary fractions in SMC, LMC, and Milky Way are not convincingly different…so RLOF/binary tidal stripping is not sole cause of WR stars at low Z (Moffat et al.). Need to be able to make H-free WR stars without shedding angular momentum and without binaries, and process must not depend strongly on metallicity. …This requires that line-driven winds DO NOT dominate mass loss (instead: continuum-driven LBV eruptions? Critical rotation? RSG winds?). OBSERVED MASSES OF LBV NEBULAE In circumstellar shells around other LBVs and LBV candidates, a mass of ~10 M is typical for 6 stars with L>10 L. In Eta Carinae, at least, we know this is ejecta from a single outburst. Smith & Owocki (2006) ApJ Letters, 645, L45 P Cygni: the other nebula from a Galactic giant LBV eruption that was actually observed. The historical light curve of P Cygni (see several papers by Meaburn et al.) Smith & Hartigan MASS: 2006, ApJ, 638, 1045 [Fe II] 1.644 um NICFPS From [Fe II] lines: ~1200 M=0.1-0.2 M yr old . M=0.01 M/yr 400 yr { KE=1e47 ergs Mass and KE similar to 1890 outburst of Eta Car’s Little Ginsburg, Smith, & Bally (in prep.) Homunculus. DO LBVs EXPLODE AS SUPERNOVAE? They are supposed to be a very brief (few × 104 yr) transition phase at the end of core-H burning and start of core-He burning... BUT, Nevertheless: Massive stars seem to be exploding with H envelopes anyway. (see Smith & Owocki 2006; Smith 2006, 2007; Kotak & Vink 2006; Gal Yam et al. 2007; Smith et al. 2007, 2008; Trundle et al. 2008,etc.) very luminous SNe IIn, progenitor wind speeds, progenitor detections We would need the overall LBV phase to be stretched out, and to have the characteristic LBV variability and eruptions be intermittent. That scenario would predict a large number of “dormant” LBVs. (WNH?) In fact, dormant LBVs or “LBV candidates” may be numerous... Remember P Cygni? (see Massey et al. 2007, AJ, 134, 2474) Where do LBVs come from? …and where do WR stars come from? At non-zero metallicity, all stars with M0 ≥ 30-40 M WR SN Ib/c FALSE Also: LBVs are apparently NOT just a brief ~104 yr interlude between H and He burning Instead, with M0 ≥ 40 M SN IIn O Of WNH LBV (WNH) WN/WC SN Ib/c With M < 40 M , 0 What the heck? RSG, YHG Initial mass? Metallicity? Rotation? Binaries? LBV eruptions?.
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