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

Bologna, June 13th 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

Bologna, June 13th 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

Bologna, June 13th 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]

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

Bologna, June 13th 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!

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

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

Bologna, June 13th 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 HE V=14.91 (B-V )0= 0.39

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

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

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

CH:yet another synthetic spectrum

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

Bologna, June 13th Isotopic C abundance

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

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

Bologna, June 13th Radial velocity curve Hires & Uves data Palomar Data Orbital Parameters P=(3.413±0.001)dTo(MJD)=( ±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

Bologna, June 13th 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!!

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

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

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

Bologna, June 13th 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

Bologna, June 13th 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

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

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

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

Bologna, June 13th 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

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

Updated sample

Bologna, June 13th 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

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

Bologna, June 13th 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

Bologna, June 13th 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