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The Elusive Nature of (early) R-stars

The Elusive Nature of (early) R-stars. Inma Domínguez. Tangata: L. Piersanti O. Straniero (INAF-OACT) C. Abia O. Zamora (UGR) R. Cabezón D. García-Senz (UPC). 10th Torino Workshop on AGB Nucleosynthesis: from Rutherford to Beatrice Hill Tinsley and beyond

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The Elusive Nature of (early) R-stars

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  1. The Elusive Nature of (early) R-stars Inma Domínguez Tangata: L. Piersanti O. Straniero (INAF-OACT) C. Abia O. Zamora (UGR) R. Cabezón D. García-Senz (UPC) 10th Torino Workshop on AGB Nucleosynthesis: from Rutherford to Beatrice Hill Tinsley and beyond January, 25-29, 2010 Chistchurch, New Zealand

  2. Observed properties • Low Luminosities ~ LC(N)/ 10 • Teff: 3800 – 4600 K C(N)  3500 K R-cool R-hot Not on the AGB  Core He-burning NIR C(N) R-cool • Not in Binary systems McClure 1997 (30% of  in binaries)  Previous merger R-hot Zamora et al. 2009

  3. [M/H]: 0  - 0.77 C/O: 0.8  3 12C/13C: 5  20 [N/Fe]: 0.1  1 (Li) : 0.5  1 No s-elements enhancement No evidence of O-depletion R-hot Chemical properties Li R-hot R-cool R-cool • He-burning & CN cycle Zamora et al. 2009

  4. Dominy 1984 Zamora et al. 2009 Chemical properties • Peculiar He-flash in a low mass RG  • Peculiar = mixing But NOT in the standard He-flash !! Most  do not modify their surface composition at the He-flash Dearborn et al. 2006 Lattanzio et al. 2006 Mocak et al. 2008-2009 Confirm by 3D HYDRO

  5. Carbon D-up Like 3-Dup / H-shell extinguishes X neutrinos “ad hoc” 0.4 M 0.4 M Angelou & Lattanzio 2008 Time Paczynski & Tremaine 1977 Increasing core-cooling by axions Domínguez et al. 1999 Increasing core-cooling by neutrinos But All  !! 12C/13C  !!

  6. Internal rotation in low mass stars Mengel & Gross, 1969 A series of flashes occurring progressively closer to the center NO MIXING Mfl  w min for w = 0.16 rad/s NO mixing !! Merger  Rotation

  7. Merger scenario: binary synthesis population Izzard et al. 2007 Number and location in the Galaxy of observed R-stars Dominant channel at [M/H] ~ 0  RG + He WD • Very common in nature Not studied in detail before 2 He WDs Iben 1990 (no rotation) Guerrero et al. 2004 (SPH) • Merging  Rotation  Different physical structure !!

  8. Selectingthe models RG + He WD (70 %) MRGcore 77 % 23 % too luminous !! (core mass ) Izzard et al. 2007

  9. Numerical Simulations Phases in the merging scenario: • Coalescence– Common envelope phase • Merging itself – Accretion disk around degenerate core • Accretion – Mass deposition onto the He core • 3D Hydrodynamical simulations - SPH: Merging • FRANEC: structures & accretion phase & evolution Coalescence (Population Synthesis) MRG : 1.4 1.3 1.2 MRGcore: 0.19 0.20 0.17 MWD: 0.2 0.15 0.38 Mfin : 0.76 0.75 0.78 Mcore: 0.5 0.36 0.55 A (R) : 20 20 16 masses in M Piersanti et al. 2010 (submitted)

  10. MWD = 0.15 M MRG_core = 0.2 M SPH RG 50000 WD 37000 resolve 104 in  SPH based on Monaghan 2005

  11. High accretion rates: 10-6 - 10-4 M /second • High angular velocities: core rigid rotation  ~ 0.036 rad/s • No He-burning (artificial viscosity ??) Tmax ~ 1.6 108 K  ~ 5280 g/cm3 nuc  hyd • in 2 hours Keplerian disk  evol. time-scales long

  12. FRANEC: accretion phase & evolution Accretion – Mass deposition onto the He core 10-5 M /yr (Eddington limit) Assume: inner core & expanded envelope decoupled (different time-scales, presence of the accretion disk) masses in M MRG : 1.4 1.3 1.2 MRGcore: 0.19 0.20 0.17 MWD: 0.2 0.15 0.38 Mfin : 0.76 0.75 0.78 Mcore: 0.5 0.36 0.55 Piersanti et al. 2010 (submitted) Different assumptions: • Angular momentum deposited by the accreted matter • Angular momentum transport efficiency into the accreting He-core No-rotation Rigid-rotation Differential-rotation

  13. After accretion During accretion 10-5 M /yr NO He-burning He-ignition No rotation acc << dif central ignition Diff. rotation 0. 0.1 0.2 0.3 0.4 0.5 M/M 0. 0.1 0.2 0.3 0.4 0.5 M/M Piersanti et al. 2010

  14. After accretion  H-burning active  No mixing Differential rotation No rotation Rigid rotation 104 107 109 100 100 0.6 0.4 0.5 0.1 0.1

  15. Accretion is the main physical mechanism driving the evolution of the  inner core & expanded envelope decoupled acc << diff compression  local T  No He-burning • After accretion – evolutionary time-scales longer thermal energy diffuses inward  whole core T  (less degenerate) re-ignition of H-burning shell He-ignition closer to the center He-flash less strong • Rotation “modulates” that behaviour: T    MHe-core  vs standard single RGB No-rotrig-rotdif-rot MHe 0.400.410.47 Mig 0.12 0.04 0.00 Mf 0.24 0.36 0.45 bigger If MHeWD  ?? inner

  16. “massive” He-WDs ? RG + He WD MRGcore Number is OK 77 % 23 % Zamora et al. 2009 40% of the sample wrongly classified too luminous !! (core mass ) Izzard et al. 2007

  17. MWD =0.38 M MRG =1.20 M (MRGcore =0.17 M) • At the end of accretion • TMAX = 1.28 108 K BUT • = 6500 g/cm3 Mild He-flashes within He-core Mild flashes For MWD  weak He-flashes Isolated by accretion disk Piersanti et al. 2010

  18. Merging of a RG + He-WD in common envelope • is very common in nature (Izzard et al. 2007) • We have studied the final outcome: • Physical structure very different from standard single RGB (T,  and rotation) • physical conditions do not favour external or stronger He-flashes • NO mixing of C-rich material into the envelope • (early) R-stars progenitors still missing

  19. C-rich RR Lyrae Tohunga !!! Wallerstein et al. 2009 Mixing at the He-flash ?? Wallerstein et al. 2009 [Fe/H] [C/Fe] [N/Fe] [O/Fe] C/O KP Cyg + 0.18 0.52 0.90 -0.07 1.7 UY CrB - 0.40 0.65 1.26 + 0.59 0.83 R-hot -0.28 0.53 0.60 (?) 1.6 No s-elements • 12C from He-burning • 13C from proton captures over 12C • 14N from proton captures over 13C H mixes with 12C (Pop. III) How ??

  20. The Nature of (early) R-stars ?? Te Araroa (long way) runangaka pai (Excellent meeting) Kia Ora (Good luck/Good health)

  21. The Nature of R-stars ??still Elusive Te Araroa (long way) runangaka pai (Excellent meeting) Kia Ora (Good luck/Good health)

  22. Population III stars • He-convective zone into H-rich layers • H-ingestion • Two convective shells • Convective envelope into N and C-rich regions 12C/13C C-rich N-rich Hollowell, Iben, Fugimoto, 1990 Picardi et al. 2004 Cristallo et al. 2007 Schlattl et al. 2002 D-up H-ingestion He-ignition close to H/He H-shell less efficient  Lack of CNO elements

  23. 2 He-WDs of MWD = 0.4 M The maximum temperature  thermonuclear flash Tmax = 2 108 K Tmax = 1.6 108 K Guerrero, García-Berro, Isern, 2004

  24. Rotation Differential Rigid

  25. No rotation

  26. Galactic distribution

  27. Galactic distribution

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