The observed mass loss vs. metallicity relation

1. The observed mass loss vs. metallicity relation Alex de Koter University of Amsterdam

2. The observed mass loss vs. metallicity relation Alex de Koter Rohied Mokiem, Chris Evans, S. Smartt, J. Puls, A. Herrero, F. Najarro, M.R. Villamariz University of Amsterdam

3. The problem of determining dM/dt(Z) • Large set of OB stars of sufficient baseline in Z • GAL, LMC, SMC • sampling of spectral sub-types and luminosity classes • Line blanketed, unified model atmospheres • dM/dt • Z • Homogeneous analysis • automated (well defined) method • realistic errors • Physics? among others: • clumping • velocity structure

4. Z diagnostics • Ideally… • stars (not nebulae)… • that reflect the composition of O stars for which dM/dt is determined (so, e.g. B V or O stars themselves)… • that do not show products of nucleosynthesis (no fast rotators, no Supergiants) • with sufficiently strong & abundant optical lines… (no fast rotators, high S/N) • of elements driving the wind (Fe dominant)

5. Z diagnostics • Unfortunately… • B V (and O themselves) have only few and weak optical Fe lines (still… Rolleston et al. 2003) • But… • Supergiants only show products of CNO - not too relevant for driving (e.g. Venn 1999) • one may resort to modeling UV spectrum, plenty Fe lines (Bouret et al. 2003) • Findings are… • AFG I + O(UV) →Fe = 0.2 Feʘ; B V → Fe = 0.3 Feʘ for SMC

6. dM/dt diagnostics • Hα, other optical lines (e.g. He II 4686) • difficult for low dM/dt (<~ few times 10-8 Mʘ/yr) • UV resonance lines • most sensitive dM/dt diagnostic • trace ions, sensitive to X-rays, shocks, atomic data • Radio flux • limited to Galactic stars

7. Detailed line-blanketed unified studies • FASTWIND (Puls et al. 2005) • dM/dt from Hα • H, He, Si explicit • fast & individual +/- errors • CMFGEN (Hillier & Miller 1998) • dM/dt from Hα and UV resonance lines • allows treatment of clumping • H, He, CNO, Si,S, Fe explicit • slow & typical errors

8. Detailed line-blanketed unified studies

9. Detailed line-blanketed unified studies

10. Analyzed sample of O stars

11. Analyzed sample of O stars

12. Homogeneous analysis • FASTWIND & CMFGEN compare well • good agreement, except for ionising flux < 400 A and He I singlets (Puls et al. 2005) • CMFGEN & TLUSTY compare well (Bouret et al. 2003) • would benefit from automated analysis

13. Automated method (Mokiem et al. 2005) • Genetic Algorithm based optimization • FASTWIND stellar atmosphere model • PIKAIA GA optimization (Charbonneau 1995) • Fitting of optical H,He lines and V magnitude • L, Teff, g, YHe, vsini, vturb, dM/dt,  • Homogeneous analysis of large samples

14. Optimization technique Teff g YHe vturb dM/dt  v

15. O5 If star example HeI 4471 HeII 4541HeII 4686 • GA method gives fit of at least the quality obtained by • experts in modelling • Well determined errors • Helps to resolve issues related to mass discrepancy • One fit per day

16. Clumping in O stars winds • Evidence for clumping in O stars • Eversberg et al. 1998, (stochastic substructure He II) • Crowther et al. 2002, Hillier et al. 2003 (PV) • Bouret et al. 2003 (O V 1371)

17. Clumping in O stars winds • dM/dt / √f ~ invariant • clumping leads to ↓ dM/dt • f ~ 0.01 – 0.2 • Clumping physics not well known (Owocki et al.) • radial behaviour f ? • potentially different “observed clumping” in V and I stars • interclumped medium? (assumed void) • dimension of clumps? (assumed to be small) • time dependence?

18. Modified Wind Momentum log (dM/dt * v∞ * √R) = x log (L/Lʘ) + log Do x = 1/(α-δ) = 0 (all thin) … 1 (all thick)

19. Modified Wind Momentum Theory – no rotation, clumping, spherical outflow -predicts a unique relation, for fixed metal content (Vink et al. 2000, Pauldrach et al. 2003, Puls et al. 2003) log (dM/dt * v∞ * √R) = x log (L/Lʘ) + log Do x = 1/(α-δ) = 0 (all thin) … 1 (all thick)

20. Galactic O stars

21. Galactic O stars

22. Galactic O stars → Repolust et al. 2004

23. LMC O stars

24. LMC O stars

25. SMC O stars

26. SMC O stars

27. Steep turn in MWM at log(L/Lʘ) < 5.25 Bouret et al. 2003

28. Steep turn in MWM at log(L/Lʘ) < 5.25 Bouret et al. 2003 not even corrected for clumping!

29. Why this break-down at low L?? • NOT: bi-stability jump, as this causes a jump up in dM/dt • 2 early B I stars that do not appear to obey the turn-down may be at ``cool side’’, having higher dM/dt due to different set op driving lines

30. Why this break-down at low L?? • Perhaps derived rates are wrong… • ionization predictions depend on X-rays (shocks), treatment of clumping, atomic data • discrepancy Hα and UV dM/dt determination • uncertainties in v∞ • Perhaps predictions are wrong… • for low density winds Sobolev approx. for line force may break down (Owocki & Puls 1999) • ion decoupling (→ Krticka & Kubat) • Perhaps low dM/dt stars have a different nature • Vz stars

31. Steep turn in MWM at log(L/Lʘ) < 5.25 Martins et al. 2005

32. Steep turn in MWM at log(L/Lʘ) < 5.25

33. SMC O stars

34. GAL, LMC, SMC O stars

35. GAL, LMC, SMC O stars

36. Conclusions & Remarks • Number of O stars analyzed rapidly increasing • multi-object spectroscopy (such as FLAMES program) • automated fitting • fast codes • Model atmosphere codes in good agreement • Not clear whether dM/dt diagnostics in agreement in low-brightness O stars • UV vs Hα problem

37. Conclusions & Remarks • dM/dt(Z) in terms of MWM(Z) • appears to be a ``kink’’ in MWM slope at log(L/Lʘ) ~ 5.25, not predicted by current theory, leading to much lower dM/dt • ``uncorrected’’ supergiants yield ~0.4 dex higher dM/dt than Vink et al. predictions • bright OB stars: dM/dt ~ Z-m, m ~ 0.7-0.9 (corrected for v∞(Z) following Leitherer et al. 1992), in agreement with theory

38. Conclusions & Remarks • If clumping important… • dM/dt of O stars may all (?) be overestimated by factors ~3

39. End

40. End

41. Large sample analysis • Fundamental parameters of massive stars • ~100 analyzed until now • Multi-object spectrographs • VLT-Flames Survey • ~100 hours VLT time • Galactic, SMC and LMC fields • will double total number of analyzed stars • calibration of fundamental parameters • requires an automated method

42. How can we study massive stars?

43. HeI 4471 He II He I Hγ How can we study massive stars?

44. Optimization technique Teff g YHe vturb dM/dt  v

45. The automated method • FASTWIND stellar atmosphere model • Puls et al. 2005, A&A, 435, 669 • PIKAIA genetic algorithm optimization • Charbonneau1995, ApJS, 101, 309 • Fitting of optical hydrogen and helium lines • Teff, g, YHe, vsini, vturb, dM/dt, 

46. The observed mass loss vs. metallicity relation Alex de Koter University of Amsterdam

47. O5 If star example HeI 4471 HeII 4541HeII 4686

48. evolutionary mass (Mʘ) spectroscopic mass (Mʘ) First results • Galactic sample analysis • 12 early type stars • previously analyzed “by eye” • Spectroscopic mass • g, R Mspec • Evolutionary mass • Teff, L, evolutionary track Mevol

49. Vz Stars

50. In conclusion • The method works • 12 object galactic sample fitted • good agreement with earlier analyses • improved determination of fundamental parameters • Currently applied to a sample of ~100 stars • VLT Flames survey