1. INAF-Osservatorio Astronomico di Padova Dipartimento di Astronomia, Università di Padova

2. Bologna, June 13th 20032 Team Timothy Beers - Michigan State University Eugenio Carretta - Osservatorio Astronomico di Padova Norbert Chriestlieb – Hamburger Sternewarte Judith Cohen – California Institute of Technology Raffaele Gratton - Osservatorio Astronomico di Padova Jennifer Johnson – DAO Solange Ramirez - California Institute of Technology

3. Bologna, June 13th 20033 Metal poor CH stars III s-process elements rich Three kinds of CH stars? II r-process elements rich I Normal n-capture elements Surveys of metal-deficient stars find a large number of stars with strong CH bands Explanation analogous to classical CH stars

4. Bologna, June 13th 20034 s-process rich case: binary scenario s-process enrichment attributed to accretion of shell processed material from AGB companion Explains increasing frequency of such stars with decreasing [Fe/H]

5. Bologna, June 13th 20035 What can we learn from CEMP? Constraints on nucleosynthesis at low Z Constraints on the IMF

6. Bologna, June 13th 20036 Constraints on the IMF Surveys find ~30% CEMP at [Fe/H]<-2.5 dex ~30% IMS Almost flat IMF at low Z? CNO and ¹²C/¹³C Binary fraction ~60% ~50% of CH stars s-process binaries IMF works for Ba and classical CH stars!

7. Bologna, June 13th 20037 Further constraints on the IMF Indications on mass distributions from orbital informations C, N, O abundances and ¹²C/¹³C

8. Bologna, June 13th 20038 Nucleosynthesis s and r-process at low Z Early galactic chemical evolution

9. Bologna, June 13th 20039 Metal poor CH stars Surveys of metal-deficient stars (HK, Beers et al.; HES Wisotzki et al. etc) find a large number of stars with strong CH bands 8 “new” spectra 1 CH star Keck Pilot program HE0024-2523 V=14.91 (B-V )0= 0.39

10. Bologna, June 13th 200310 Keck pilot progra 8 candidate extremely metal poor stars observed 1 CH star HE0024-2523 V=14.913 (B-V) 0 = 0.391 Teff=6625K, log(g)=4.3dex [Fe/H]=-2.7

11. Measuring C and N abundance Broadened lines [C/Fe]=2.6±0.1dex [N/Fe]=2.1±0.1dex

12. Bologna, June 13th 200312 [C/Fe]=2.6 [C/Fe]=2.5 [C/Fe]=2.7 Smoothed spectrum Unsmoothed spectrum Another CH spectrum

13. CH:yet another synthetic spectrum

14. Bologna, June 13th 200314 Isotopic C abundance Best fit for ¹²C/¹³C=6 Best fit for ¹²C/¹³C=5

15. Bologna, June 13th 200315 Isotopic C abundance

16. Measuring N abundance [N/Fe]=2.0[N/Fe]=2.1[N/Fe]=2.2 [N/Fe]=2.1±0.1dex

17. Bologna, June 13th 200317 Radial velocity curve Hires & Uves data Palomar Data

18. Bologna, June 13th 200318 Radial velocity curve Hires & Uves data Palomar Data Orbital Parameters P=(3.413±0.001)dTo(MJD)=(52066.921±0.006)d G=(-178.7±0.5) km/s K=(52.0±0.6) km/s e=0 asini=(2.442±0.029)10e6 km f(m)=(0.0498±0.002) M sun

19. Bologna, June 13th 200319 Rotational velocity vsini=(9.7±1.5) km/s measured from our spectra From orbital parameters + few assumptions expected synchrone velocity: Vsini syn= <(13.5±3.9)km/s Compatible!!

20. Bologna, June 13th 200320 Rotational velocity: method Cross-correlation technique FWHM vs vsini relation calibrated using previously studied stars Also useful for detecting contami- nated spectra

21. Bologna, June 13th 200321 What do we infer from this information? P<<P ch ~100d Circular orbit Synchrone orbit Common envelope phase

22. Bologna, June 13th 200322 Lithium abundance and rotation Upper limit: logε (Li) =1.5 Low Li abundance As in Ryan et al(2002) rotating stars

23. Bologna, June 13th 200323 s and r process elements [Ba/Fe]=1.4±0.2 [Eu/Fe]<1.1 dex If Ba r-process: [Eu/Fe]=2.2 [Pb/Fe]=3.3±0.2 dex

24. Bologna, June 13th 200324 Could Ba be from r-process? Upper limit to Eu [Eu/Fe]=1.1 dex If Ba produced by r-process [Eu/Fe]=2.2

25. Bologna, June 13th 200325 Third peak elements: Pb Best fit for line 3683.4 Å with [Pb/Fe]=3.4 dex Best fit for line 4057.8 Å with [Pb/Fe]=3.2 dex [Pb/Fe]=3.3±0.2 dex

26. Bologna, June 13th 200326 Extremely high Pb LP 625-44 [Pb/Fe]=2.55 [Fe/H]=-2.71 LP 706-7 [Pb/Fe]=2.28 [Fe/H]=-2.74 In the sun: Fe/Pb=3 10e5 This star: Fe/Pb=100

27. Bologna, June 13th 200327 Abundances summary Teff=6625K log(g)=4.3 [Fe/H]=-2.7 v t =1.4 km/s [Fe/H]-2.700.1032a [C/Fe]2.60.1syn [N/Fe]2.10.1syn [O/Fe]0.41a [Mg/Fe]0.70.13a [Al/Fe]0.3..1a [Si/Fe]0.3..1a [Ca/Fe]0.60.23a [ScII/Fe]0.40.13a [Ti/Fe]0.360.0514a [Cr/Fe]-0.50.22a [Mn/Fe]-0.20.12a [SrII/Fe]0.30.22a [BaII/Fe]1.40.23a [EuII/Fe]<1.1syn [Pb/Fe]3.30.1syn C/O100syn N/O8syn ¹²C/¹³C61syn

28. Bologna, June 13th 200328 Is theory able to explain these values? A preliminary model Gallino et al. (private communication) Dilution factor 10 Standard pocket M(¹³C)=4 10e-6 M sun at top of He intershell Model for [Fe/H]=-2.6 M=1.5M sun Mass of the evolved companion

29. Existing sample 10 stars Vr variables Vr constant No info on Vr Updated

30. Updated sample

31. Bologna, June 13th 200331 Conclusions Sample too limited to draw conclusions Abundance analysis and radial velocity infos are both crucial This object is clearly a case of s-process rich, binary star: enrichment through mass transfer from an AGB companion

32. Bologna, June 13th 200332 Work in progress 7 UVES spectra 5 Keck spectra 4 TNG spectra Abundance analysis Vrad monitoring 2-4 spectra for ~30 objects

33. Bologna, June 13th 200333 Conclusions This object is clearly a case of s-process rich, binary star: enrichment through mass transfer from an AGB companion Not easy to explain at the same time ¹²C/¹³C, C/O and abundance pattern Strong observational constraints

34. Bologna, June 13th 200334 Future perspectives Widen the sample (~15 to ~40) of high res high S/N analysis (already obtained data for 13 objects) Vr measurements for ~60 objects