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ESO Large Program 165-L0263: Distances, Ages and Metal Abundances in Globular Cluster Dwarfs

ESO Large Program 165-L0263: Distances, Ages and Metal Abundances in Globular Cluster Dwarfs. Raffaele Gratton Osservatorio Astronomico di Padova, INAF, ITALY. ESO Large Program 165-L0263:. PI: R. Gratton co-authors: P. Bonifacio, A. Bragaglia, E. Carretta, V. Castellani,

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ESO Large Program 165-L0263: Distances, Ages and Metal Abundances in Globular Cluster Dwarfs

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  1. ESO Large Program 165-L0263:Distances, Ages and Metal Abundancesin Globular Cluster Dwarfs • Raffaele Gratton • Osservatorio Astronomico di Padova, INAF, ITALY

  2. ESO Large Program 165-L0263: 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, M. Zoccali VLT2 (Kueyen)+UVES 12 nights in June and September 2000 12 nights in August and October 2001 6 nights in August 2002

  3. Aims • Distances and Absolute Ages of Globular Clusters • The O-Na anticorrelation among globular cluster TO-stars • Lithium abundances in TO-stars and subgiants of globular clusters

  4. 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

  5. Stars selected for observations: TO stars and early subgiants (below the RGB clump)

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

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

  8. 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

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

  10. Comparison between Teff’s from H and from colours (calibration by Kurucz, model without overshooting) Zero point error 27 K r.m.s.=159 K Reddening zero point error: E(B-V)=0.008 (yielding an error of 0.04 mag in the distances and 0.5 Gyr on the ages)

  11. Our Teff scale agrees very well with that of Alonso et al. based on the IRFM Average difference is T(Us)-T(A)= 811 K (r.m.s.= 83 K, 58 stars) Eliminating nine outliers: r.m.s.= 38 K

  12. Results • Distances and Ages of Globular Clusters • 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 • Comparison between abundances in GC and field stars • Rotation of TO-stars in globular clusters

  13. Globular Cluster Ages • Absolute ages - lower limit to the age of the Universe - put formation of the Milky Way in a cosmological framework • Cluster distances: a step to the extragalactic distance scale • Relative Ages - GCs as probes to reconstruct early history of Galaxy formation

  14. Comparison between confidence range for globular cluster ages and values allowed by Universe geometry

  15. Costraints on the epoch of formation of globular clusters

  16. True distance modulus to the LMC according various methods

  17. Scenarios of MW formation • Dissipational collapse (Eggen, Sandage & Lynden Bell (1962) • Accretion (Searle & Zinn 1979) • Numerical models suggest that both mechanism may be active in a galaxy: the relative weight may be crucial in determining galaxy morphology (spiral vs elliptical)

  18. time Field stars • For field star • kinematics and • chemistry can be • used to show the • presence of two • metal-poor • populations: • a dissipative • collapse component • an accretion • component • (Gratton et al., in • preparation)

  19. End of Thick disk? Early phases of collapse? GC relative ages • Rosenberg et al. (1999): • metal-poor GCs all have the same age • some age spread for metal rich GCs

  20. Absolute Ages for GCs • TO luminosity • End of WD cooling sequence • Nucleocosmochronology Require distances

  21. End of WD cooling sequence Hansen et al. (2002): 12.70.7 Gyr for M4 However, De Marchi et al. (2002) analysis of this data only indicates an age larger than 10 Gyrs

  22. Nucleocosmochronology Cayrel et al., Nature, 409, 691, 2001 Age (143 Gyr) of the extremely metal-poor star CS31082-001 from nucleocosmochronology with first identification of UII lines

  23. Observational: • Distances: 0.07 mag 1 Gyr • Theoretical: • Microscopic diffusion: about 1 Gyr Uncertainties in ages from TO

  24. Distances to GCs Currently, the most accurate method is the main sequence fitting method In perspective, dynamical distances obtained combining proper motions and radial velocities (+ a dynamical model for the cluster) may provide distances accurate to a few percent within a few years from now

  25. Potentiality of GC dynamical distances:few per cent accuracy NGC6397 King et al. 1997

  26. Errors in dynamical distances Anderson & King (2002) showed that astrometric accuracy of about 1 mas can be achieved with WFPC2 on HST. Over 10 yrs, the accuracy on proper motion is equivalent to errors of about 2 km/s in the transverse motion of stars within GCs Coupled with radial velocities with accuracies of about 1 km/s for some hundred GC stars (with e.g. FLAMES), and a model for internal motions, this may yield distances accurate to a few per cent for most GCs

  27. Previous Globular Cluster distances from Main-Sequence fitting to local subdwarfs

  28. 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 Systematic effects and total error budget associated with previous MS fitting distances to Globular Clusters 2 Gyr

  29. Our results:

  30. Colour of the main sequence at MV=6 Line is not best fit, but the prediction of models by Chieffi & Straniero

  31. Reddenings toward NGC6397, NGC6752 and 47 Tuc Comparing the Teff-colour relations for field and cluster stars: Source E(B-V) NGC 6397 E(B-V) NGC6752 E(B-V)47Tuc (b-y) 0.1780.007 0.045 0.007 0.0210.005 (B-V) 0.1860.006 0.0350.007 0.0350.0091 average 0.1830.005 0.0400.005 0.0240.004 Harris 0.18 0.04 0.05 Schlegel et al maps 0.187 0.056 0.032 1 Including correction in the photometry by Hesser et al. suggested by Percival et al. 2002 Astro-ph 0203157: (B-V) = 1.091 (B-V)Hesser – 0.048

  32. Main sequence fitting distance to NGC6397 and NGC6752 NGC6397 E(B-V) 0.1830.005 [Fe/H] -2.030.04 NGC6752 E(B-V) 0.0400.005 [Fe/H] -1.42 0.04 47 Tucanae E(B-V) 0.0240.004 [Fe/H] -0.660.04

  33. Main parameters for NGC6397, NGC6752 and 47 Tuc Parameter NGC6397 NGC6752 47 Tuc [Fe/H] -2.030.04 -1.430.04 -0.66 0.04 [/Fe] 0.340.02 0.290.02 0.300.02 [M/H] -1.790.04 -1.220.04 -0.45 0.04 (m-M)V 12.57 13.38 13.47 (from B-V) (m-M)V 12.62 13.15 13.57 (from b-y) (m-M)V 12.600.08 13.260.08 13.520.08 (average) (m-M)V 12.580.08 13.240.08 13.500.08 (bin. corr) V(TO) 16.560.02 17.390.03 17.680.05 (new measure) V(HB) 13.110.10 13.840.10 14.130.10 (using Rosenberg V) MV(TO) 3.980.08 4.150.08 4.180.08 MV(HB) 0.530.13 0.600.13 0.630.13 Age (Gyr)14.21.1 14.11.1 11.51.1(No diffusion) Age (Gyr)13.81.1 13.71.1 11.11.1(Diffusion).

  34. Comparison with previous data:Main Sequence Fitting Method [Fe/H] E(B-V) (m-M)V NGC 6397 Reid 1998 -1.82 0.19 12.830.15 Us -2.030.04 0.1830.005 12.580.08 NGC6752 Reid 1998 -1.42 0.04 13.280.15 Carretta 2000 -1.43 0.0350.005 13.340.04 Us -1.430.04 0.0400.005 13.240.08 47 Tucanae Reid 1998 -0.70 0.04 13.680.15 Carretta 2000 -0.67 0.0550.007 13.570.09 Percival 2002 -0.67 0.0550.007 13.370.11 Us -0.660.04 0.0240.004 13.500.08

  35. Comparison with other data:White Dwarf cooling sequence Distances from white dwarf cooling sequence are independent on metallicity, but have a dependence on reddening similar to that from Main Sequence Fitting NGC 6752 Renzini et al. 1996 E(B-V)=0.04 0.02 13.170.030.10 Us 0.0400.005 13.240.020.08 47 Tucanae Zoccali et al. 2001 E(B-V)=0.0550.02 13.270.030.10 Us 0.0240.004 13.500.020.08

  36. The age difference between 47 Tuc and the two other clusters is real? A similar age difference is given by the horizontal method The horizontal age parameter is from Rosenberg et al.

  37. Relative ages from Rosenberg et al. 1999 8 Gyr 10 Gyr End of Thick disk? 12 Gyr 14 Gyr Early phases of collapse? Calibration of Relative ages from the horizontal method

  38. Systematic effects and total error budget associatedwith 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 Reddening scale (0.008 mag) 0.04  Metallicity scale (0.04 dex) 0.03  Total uncertainty (1 ) 0.07 Reddening free Teff calibration 1 Gyr

  39. Model Error Budget

  40. Absolute Age Error Budget • Distance modulus 0.07 mag 1.0 Gyr • Model uncertainties (Carretta et al. 2000): 0.6 Gyr • Chaboyer et al. (2001): ages are likely 4% smaller due to diffusion • Best age estimate: 13.7 0.8 0.6 Gyr • This corresponds to a redshift of z4 and very likely >1

  41. Epoch of formation of GCs z>3 for the oldest GCs z>1.3 for the youngest GCs

  42. Limit on M M <0.57 at 95%

  43. HB and RR Lyrae magnitudes Mv(HB) = (0.220.05)([Fe/H]+1.5)+(0.560.07) This distance scale is 0.12 mag shorter than that previously obtained from the Main Sequence Fitting Method (Carretta et al. 2000) It is 0.03 mag shorter than the best distance scale proposed by Carretta et al. (2000)

  44. Clementini et al. 2003 Dependence of the RR Lyrae magnitude on metallicity for variables in the bar of the LMC (photometric data from the Danish 1.5 m telescope and spectroscopic data from FORS1 at VLT UT1)

  45. Distance estimates for the LMC

  46. Old Comparison between various distance estimates for the LMC New

  47. Microscopic diffusion Microscopic diffusion is a basic physical mechanism, that should be included in stellar models It is needed to adequately reproduce the run of the sound speed within the solar interior as derived from helioseismogical data

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

  49. Effects of microscopic diffusion Diffusion causes sedimentation of heavy elements, mainly He Timescale for sedimentation is given by:   K Mcz /(M Tcz3/2) where K is a constant, Mcz is the mass and Tcz the temperature at the base of the convective envelope, and M the star mass

  50. Due to the low mass of the convective envelope, 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 Observations of TO and subgiants in NGC6397 (M~0.8 M0, [Fe/H]=-2.0) allow to costrain sedimentation effects

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