Presentation on theme: "Probing the first stars with metal poor stars"— Presentation transcript:
1Probing the first stars with metal poor stars T. SivaraniIndian Institute of Astrophysics, Bangalore
2Chemical abundances of metal poor stars Probing the first stars – Stellar archeologyLooking for the fossil records of early star formation and Galaxy evolutionIn metal poor systems of Milky way and its satellite galaxies.Complementary to high redshift observations (IGM, GRB, SNs)Nature of First starsEarly IMFFormation of Milky wayConnection between halo stars and satellite dwarf galaxieshalo stars and globular clusters
5Definitions [Fe/H] = log(N(Fe)/N(H)) –log(N(Fe)/N(H))ʘ [Fe/H] = Solar metallicity[Fe/H] = Halo or (PopII)[Fe/H] ~ Metal poor Globular clusters[Fe/H] < Extreme metal poor (EMP) stars[Fe/H] < Hyper metal poor (HMP) stars[C/Fe] > Carbon enhance metal poor (CEMP) starsMetal poor DLA ~ (Kobayashi et al. 2011)Metal poor LLS < (Fumagali et al. 2011)
6Chemical tagging as tool to probe the First starsFe-peak – SN Ia, core collapse SN, PISN (Massive and low mass stars)Alpha elements (Mg, Ca) – Core collapse SN (massive stars)s-process – AGB stars (0.8-3Msun), weak s-process in massive starsr-process – Core collapse SN (10-25 Msun)carbon – primarily low mass AGBs, fast rotating massive star wind(only in low metallicities)Nitrogen – RGB, AGB stars, massive star winds (solve the problem of primary nitrogen in IGM)
7Metallicity distribution of the early Halo stars Komiya et al. 2007
9Carbon enhancement at low metallcities ~1000 EMP stars are observed in the Galactic halo.12~25% of EMP stars show carbon enhancement (CEMP).[C/Fe]I talk about EMP star.In this talk,I call stars of metallicity [Fe/H] = -2.5 or less EMP stars (and distinguish them from Pop2 stars and zero metal pop3 stars. )As you know, EMP star is a nearby probe into early universe.However, we can observe only low mass EMP star still alive.Large fraction of EMP stars show enhancement of the surface carbon abundance.I focus on these CEMP stars.Aoki et al. (2000,2004, 2008) ,Sivarani et al (2003), (2006),Lucatello et al. (2004),Goswami et al.(2005),Cohen et al.(2006),Jonsell et al (2007)[Fe/H]9
10SDSS Sample SDSS calibration stars ~ 30,000 Z < 10 kpc Kinematics and [C/Fe] abundances were derivedCarollo et al (2012)Sivarani, Carollo, Beers & Lai 201210
12Increasing carbon rich stars at low [Fe/H] Z > 5kpc - to avoid contamination frommilky way metal weak thick disk stars
13CEMP frequency at different Galactic scale height IMF depends on another parameter other than metallicity,Carollo et al (2012)
14The CMB influence the IMF of EMP stars? At low redshift,Z = Zmin = 10 K is set by metal and dust cooling.But at high z,the CMB itself is the minimum gas temperature!z = 5, 10, T_CMB = 16, 30, 57 KM_c = 2, 6, 17 MsunThus stars formed early in MW history, at z>5,should be affectedEnhanced AGB fraction at low metallicity and at larger distances from the Galactic planeTumlinson 2006
15AGB yields at Z = 10^-4 (Lugaro et al 2004, Karakas & Lattanzio (2008) 15
16HBB burning AGB stars in the Halo Sivarani et al. (2007)16
17Carbon in the inner and outer halo of the Galaxy
18CEMP fraction in ultra faint dwarf satellite galaxies Lai et al. 2011Zucker et al. 200618
19Carbon at high redshifts DLA at z=2.3 [Fe/H] = -3.0, [C/Fe] = 1.53AGBs can not contribute to IGM earlier than z=1.8 (Kobayashi et al. 2011)Faint SN (with fallback)? (Nomoto et al.)Massive star wind (Meynet et al.) - Nitrogen has to be highIGM abundances Primary nitrogen production at high redshifts
20Globular cluster and Halo connection Extended tail ~ -5.0many stars < -2.5C-normal/C-richGlobular clustersLowest metallicity ~ -2.5C-poor N-richr-process similar to haloNa-O anticorrelation pollution of hydrogen burning products
23Indo-SA collaboration Search for metal poor stars with 1-2m facilities in India:Target selection: GALEX, SDSS, 2MASS and WISEUVIT will be ideal with MgIIhk narrow band filterIdentifying milkway substructure with UVIT:Dwarf satellites, halo streamsCombining the classification based on the broad band SEDs and narrowband filters to identify over densities in RV.Identification of High velocity stars.Follow up metal poor stars:SALT RSS spectrograph -C,N, Fe-peak, alpha abundances-NH lines (3380A), CH 4350, MgH, CaII Triplet R=1000s-process and r-process (R=10000)Multi object capabilities will be ideal to study metal poor stars in thedwarf satellites and globular clusters and streams.
24Indo-SA collaboration HRS at SALTOrigin of r-process – universality of r-processU and Th abundances – cosmic chronometryPrimordial Lithium abundances- Lithium in inner and outer halo starsBeryillum abundances in outer halo starsprobing the pre-galactic magnetic fieldsOxygen, s-process and isotopic ratiosNIR spectroscopy: Flourine, 17O/18O ratios massive versus IM pollution in GCs.
25Signature of EMP AGB star Pb enhancementSignature of EMP AGB starCS[Fe/H] = -2.7[Pb/Fe] = 2.9Binary 342 daysS-process enhancement in the early GalaxySivarani et al. 200425
26Summary Stellar archeology is an ideal tool to study, The milestones of Early star formationFirst starsTransition of Top heavy to normal mode – CMB based IMFChemical and kinematical origin of early galaxy.Primordial LithiumCosmic ray spallation and magnetfields – Beryillium1-2m telescopes in India and UVIT
29Gradual change in the CMB-IMF evolution? ConclusionsCMB would have provided a temperature floor for the minimum gas temperature.Influenced the majority of stars formed at redshifts between z = 3-6, and probably even to higher redshift.Five signatures of CMB-regulated star formation are:Higher supernova rate than predicted at high redshiftSystematic discrepancy between direct and indirect measurementsof the high redshift star formation rate3)Lack of surviving globular clusters that formed at high metallicity and high redshift4) More rapid rise in the metallicity of cosmic gas than is predicted by current simulations5) Enhancement in the abundances of α elements such as O and Mg at metallicities −2 [Fe/H] −0.5.Gradual change in the CMB-IMF evolution?
30Metallicities in perspective Fumagali et al (2011)