SPECTROSCOPY OVERVIEW

1. SPECTROSCOPY OVERVIEW This cycle is directed to ASTRONOMERS Develops through a logical path which goes from conception to construction and operations of the instrument The Science Case: High Resolution Spectroscopy of (cool) stars Basic tools for specifications and verification One example of similar design and different implementations: UVES, FEROS, HARPS Successful Program: VLT instrumentation Aspects of Optical design (B. Delabre) L. Pasquini July 2002

2. SPECTROSCOPY Science Cases Science cases: Why do we want to have a new instrument ? Which science to address? Which Outstanding problems to solve ? How ? Which Telescope ? Which fraction of the time is available ? Related questions: Which community will serve ? What is already available to them ? What is the state of art ? The competition ? The alternatives? Some Practical Aspects: Feasibility, Financial, Timescale L. Pasquini July 2002

3. SPECTROSCOPY WHY H-R Spectroscopy ? Spectroscopy brings the largest amount of information. The best (and in some case unique) way of making physics. From Zoccali et al. 2002, search for CN - CH variations in Globular Clusters L. Pasquini July 2002

4. SPECTROSCOPY Cool Stars: Some Topics Detailed Chemical Abundance: Distance Scale , Stellar Populations, Star Formation History, Chemical Evolution, Age of the Galaxy Primordial Nucleosynthesis: Li, Be abundance Stellar Interior: Diffusion, Mixing, oscillations .. Accurate Radial velocities : Dynamics of complex systems, Binaries, Exo- Planets, short and long term variations Rotation & magnetic fields: Activity, Dynamo, Solar-stellar connection, Angular Momentum evolution... L. Pasquini July 2002

5. The chemical evolution of Globular Clusters: some unexpected (?) results with VLT ESO Large Programme, PI: Raffaele Gratton (PD)

6. Content - Distances to globular clusters and impact on ages: short and long distance scales - Star-to-star chemical inhomogeneities: the Na-O anticorrelation - Lithium abundances - ESO Large Program 165-L0263

7. Distances to globular clusters and impact on ages: short and long distance scales

8. Comparison between confidence range for globular clusters ages and values allowed by Universe geometry

9. True distance modulus to the LMC according various methods

10. Globular cluster distances from Main-Sequence fitting to local subdwarfs

11. Systematic effects and total error budget associated with the MS fitting distances to Globular Clusters Effect (m-M) Malmquist bias negligible Lutz-Kelker correction 0.02 Binaries (in the field) 0.02 Binaries (in clusters) 0.03 Photometric calibrations (0.01 mag) 0.04  Reddening scale (0.015 mag) 0.07  Metallicity scale (0.1 dex) 0.08  Total uncertainty (1 ) 0.12 Reddening free Teff calibration

12. Star-to-star chemical inhomogeneities: the Na-O anticorrelation

13. Variations in the strength of CH and CN bands Noticed since early seventies (Osborn 1971) from DDO photometry and spectroscopy Bimodal distribution along the RGB (Norris & Smith 1980s) Variations among MS stars in 47 Tuc (Briley et al. 1994) NGC6752

14. Kraft, Sneden and coworkers: The O-Na anticorrelation for giants in globular clusters

15. From Langer et al. 1993 Presence of elements processed through the complete CNO-cycle. At these temperatures 22Ne+p  23Na (Denissenkov & Denissenkova 1990; Langer & Hoffman 1995; Cavallo et al. 1996). At higher temperatures, also 26Mg+p  27Al

16. Mixing episodes along the RGB evolution of small mass stars A first mixing episode occurs at the base of the RGB, due to the inward penetration of the outer convective envelope in regions where some H-burning (through uncomplete CN-cycle) occurred during the latest phases of MS evolution (first dredge-up: Iben 1964). First dredge up causes only minor effect in metal-poor stars At the same phases, dilution (by a factor of ~20) of the surface Li abundance occurs

17. Role of the molecular weight barrier The maximum inward penetration of the outer convective envelope at the base of the RGB creates a discontinuity in molecular weight (-barrier) that prevents further mixing, until is canceled by the outward expansion of the H-burning shell (RGB clump) (Sweigart & Mengel 1979; Charbonnel 1994). Further mixing (due e.g. to meridional circulations activated by core rotation is possible only after the RGB clump

18. Molecular weight-barrier along the RGB (from Charbonnel et al. 1998)

19. Field stars conform this theoretical paradigma (Gratton et al. 2000) However abundances of O and Na are not affected: mixing is not deep enough to reach regions where complete CNO cycle occurs

20. There is a systematic difference between field and cluster stars. Important: this might be correlated with the 2nd parameter effect - Systematic different core-rotation  core and total mass at He-flash - Mixing of He It may also affect HB magnitudes (and then distance scales) Possible hints for a correlation between the 2nd parameter and the Na-O anticorrelation may be suggested by these graphs by Carretta et al. (1996)

21. What is going on in cluster stars? There are mainly two scenarios: - Deep mixing episodes: may only occur along the RGB, after the clump (temperature is not large enough in TO-stars) - Accretion: should be present independent of the evolutionary phase (the material comes from now extincted TP AGB stars, undergoing hot bottom burning). Accretion might occur: . on protostars (Cottrell & Da Costa) . on already formed stars (D’Antona, Gratton & Chieffi) Not distinguishable from observations of bright giants Observations of stars fainter than the clump

22. Lithium abundances

23. Lithium abundances and primordial nucleosynthesis (figure from Suzuki et al. 2000)

24. Lithium abundances from halo stars on the Spite’s paletau (data from Suzuki et al. 2000)

25. Main concern: Surface Li depletion due to sedimentation due to some mixing (figure from Vauclair & Charbonnel 1998)

26. Role of globular clusters We may compare abundances in TO and subgiants looking for costraints about sedimentation: - comparing abundances in TO-stars and subgiants  effects of sedimentation should be canceled when the outer convective envelope penetrates inward (dilution is independent of diffusion) - elements other than Li provide costraints on effects of sedimentation Comparison between abundances for TO-stars and subgiants

27. Previous observations of Li in globular clusters (figure from Charbonnel et al. 2000) GC stars: filled symbols: Deliyannis et al. open symbols: Pasquini & Molaro Castilho et al. Field stars

28. Previous observations of Li in globular clusters Li abundances in NGC6397 stars from Castilho et al. (2000)

29. ESO Large Program 165-L0263:Distances, Ages and Metal Abundancesin Globular Cluster Dwarfs PI: R. Gratton co-authors: P. Bonifacio, A. Bragaglia, E. Carretta, V. Castellani, M. Centurion, A. Chieffi, R. Claudi, G. Clementini, F. D’Antona, S. Desidera, P. Francois, F. Grundhal, S. Lucatello, P. Molaro, L. Pasquini, C. Sneden, M. Spite, F. Spite, O. Straniero VLT2 (Kueyen)+UVES 12 nights in June and September 2000 12 nights in August and October 2001

30. OBSERVATIONS

31. Clusters selected for observations The closest globular clusters (but M4 for which differential reddening is important) cluster V(TO) [Fe/H] NGC6397 16.4 -1.82 NGC6752 17.2 -1.42 47 Tuc 17.6 -0.70

32. NGC 6397 and NGC 6752 - Stars selected for observations: 14 TO stars and 12 subgiants (below the RGB clump) in NGC6397 and NGC6752

33. 47 Tucanae - Stars selected for observations: 3 TO stars and 8 subgiants (below the RGB clump)

34. Field star sample: 34 metal-poor stars with good parallaxes from the Hipparcos satellite Green points: single stars Red squares: binaries

35. ANALYSIS

36. Our spectra have R~40,000, and S/N~80-100 for stars in NGC6397, S/N~20-60 for stars in NGC 6752 and 47 Tucanae.. The spectral range is 3500-9000 Å. We show the correlation between EWs measured with an authomatic procedure on spectra of two TO stars in NGC6752 (upper panel) and NGC6397 (lower panel) Typical errors are 3 mÅ for stars in NGC 6397, and 5 mÅ for stars in NGC 6752 and 47 Tucanae Accurate EWs can be derived from our spectra

37. Analysis procedure strictly identical for field and cluster stars Teff’s from spectra: - Balmer line profiles  Reddening free

38. Comparison between Teff’s from H and from colours (calibration by Kurucz, model without overshooting) Green points: single stars Red squares: binaries Mean offset: -6827 K r.m.s.=159 K Reddening zero point error: E(B-V)=0.008

39. Our Teff scale agrees quite well with that of Alonso et al. based on the IRFM Average difference is T(Us)-T(A)=2912 K (r.m.s.= 78 K, 42 stars) Eliminating five outliers: T(Us)-T(A)=0.906T(A) +564 K (r.m.s.= 35 K, 37 stars)

40. Results • Impact of microscopic diffusion on models of low mass stars • The O-Na anticorrelation among globular cluster TO-stars • Lithium abundances in TO-stars and subgiants of globular clusters • Distances and Ages of Globular Clusters • Comparison between abundances in GC and field stars • Rotation of TO-stars in globular clusters

41. Impact of microscopic diffusion on models of low mass stars

42. Impact of microscopic diffusion on models of low mass stars Microscopic diffusion is a basic physical mechanism, that should be included in stellar models It causes sedimentation of heavy elements, mainly He; in low mass (M~0.8 M0), metal-poor ([Fe/H]-2) stars near the TO, also O and Fe are expected to be depleted significantly The net effects of sedimentation are: - ages are reduced by about 10% - Li abundances may be significantly reduced with respect to the original value Our observations of TO and subgiants in NGC6397 (M~0.8 M0, [Fe/H]=-2.0) allow to costrain sedimentation effects

43. Abundances in stars of NGC6397 Star S/N [Fe/H] [O/Fe] TO-stars 1543 91 -2.02 0.16 1622 82 -2.02 0.11 1905 92 -2.06 0.11 201432 97 -2.00 0.08 202765 59 -2.02 0.21 <> -2.020.01 Subgiants 669 91 -2.01 0.26 793 105 -2.04 <0.26 206810 85 -2.10 0.48 <> -2.050.03

44. Prediction of models with microscopic diffusion (0.8 Mo) Model [Fe/H] TO-subgiants Castellani et al. 2001 -0.25 for [Fe/H]= -2.0 Salasnich et al. 2000 -0.29 for [Fe/H]= -1.3 -0.78 for [Fe/H]= -2.3 Chieffi & Straniero 1997 -0.38 for [Fe/H]= -2.3 NGC6397 +0.030.04 for [Fe/H]= -2.0 Conclusion: Models predict much larger sedimentation due to microscopic diffusion than actually observed. There should be some mechanism that prevents sedimentation

45. The O-Na anticorrelation among globular cluster stars

46. The O-Na anticorrelation among globular cluster stars There are mainly two scenarios: - Deep mixing episodes: may only occur along the RGB (temperature is not large enough in TO-stars) - Pollution: should be present independent of the evolutionary phase (the material comes from now extincted TP AGB stars, undergoing hot bottom burning). Pollution might occur: . on protostars (Cottrell & Da Costa) . on already formed stars (D’Antona, Gratton & Chieffi) Our observations of TO-stars in NGC6752 (a cluster which exhibits a clear O-Na among giants) allows to make a definitive test on the deep mixing scenarios

47. Na doublet at 8183-94 Å in TO-stars of NGC6752 (these stars have virtually identical atmospheric parameters) There is a clear star-to-star variation in Na abundances

48. OI triplet at 7771-75 Å in TO-stars of NGC6752. These stars have virtually identical atmospheric parameters. There is a clear star-to-star variation in O-abundances, anticorrelated with variations in Na abundances

49. The O-Na anticorrelation among stars in NGC6752. Filled squares: TO stars Empty squares: subgiants. The observed anticorrelation is very similar to that observed in giants

50. The correlation between the Strömgren c1 index and the Na abundance among stars in NGC6752. Filled squares: TO stars Empty squares: subgiants The c1 index is correlated with Na abundances among subgiants.