Finding the lost siblings of the Sun Cheng Liu Lund Observatory Collaborators: S. Feltzing, G. Ruchti, T. Bensby, L. Lindegren Lund Observatory A. Brown Leiden University S. Portegies Zwart University of Amsterdam Tuesday, February 11, 14
Introduction--I • Most stars form within embedded clusters • Stars were born with the Sun in an open cluster (<100 Myr) called solar siblings • Properties of parent cluster: three observations • Gas planets spread out r ~ 30 AU in solar system • Ordered planetary orbits and excited orbits of Kuiper Belt objects • Short-lived radioactive isotopes found within meteorite 10 3 M pc − 3 < ρ c < 10 5 M pc − 3 Estimated properties of 4000 < N < 10 5 parent cluster: R ~1 − 3 pc Lada & Lada 2003, Adams 2010, Portegies Zwart et al. 2009 Tuesday, February 11, 14
Introduction--II Simulations: * Birthplace of the Sun is ~2.8 kpc further outer * Derive phase-space distribution of solar siblings axisymmetric + velocity dispersion 10000 5000 birth place y [pc] 0 GC Sun -5000 -10000 -10000 -5000 0 5000 10000 x [pc] About 10-60 siblings within 100 pc from the Sun Portegies Zwart et al. 2009 Tuesday, February 11, 14
Introduction--II Simulations: * Have chance to find solar siblings in solar vicinity axisymmetric + velocity dispersion Two spiral arms 10000 Sun 5000 birth place y [pc] 0 GC Sun -5000 -10000 -10000 -5000 0 5000 10000 x [pc] Mishurov & Acharova 2011 Tuesday, February 11, 14
Introduction--III • Solar siblings have the common origin with the Sun: kinematics, metallicities, elemental abundances, and stellar ages • Kinematics information could be lost caused by spiral arms, while chemical abundances are preserved in star’s atmosphere • Homogeneous chemical signatures of members of parental cluster allow us to tag the Sun’s siblings (Chemical tagging) • Determine the birth place of the Sun and better understand the mechanisms of the radial migration in the Galactic disk Freeman & Bland-Hawthorn 2002; Mitschang et al. 2013 Tuesday, February 11, 14
Our sample • The methodology developed in Brown et al. (2010) is used to select candidates from the Hipparcos Catalogue − 5 Hipparcos • selection criteria of phase-space colour cut observed Parallax: 0 ̟ ≥ 10 mas Relative parallax: M V ∧ σ ̟ / ̟ ≤ 0 . 1 Proper motion: ∧ µ ≤ 6 . 5 mas yr − 1 5 • exclude very young stars with colours bluer than (B-V)=0.4 10 0 0.5 1 1.5 (B − V) • 57 candidates were selected, while high resolution (>48000) and SNR (>150) spectra (UVES, FIES, FEROS) of 33 targets were observed Tuesday, February 11, 14
Spectral analysis Stellar parameters • SME (Spectroscopy Made Easy) is used to determine Teff, logg, [Fe/H], Vsini and elemental abundances • Initial model atmosphere: Teff and logg were calibrated from photometric and astrometric data ( [Fe/H]=0 ) • The Sun and other 4 stars, with well-known Teff and logg and high resolution spectra, are used to construct a homogeneous line list Jofre et al. 2013 G d 1 5617 . 910 MgH 5615 . 045 MgH 5615 . 489 MgH 5615 . 489 MgH 5615 . 521 MgH 5616 . 906 MgH 5617 . 358 MgH 5618 . 393 MgH 5618 . 875 MgH 5619 . 526 MgH 5619 . 995 MgH 5620 . 279 MgH 5620 . 654 MgH 5620 . 673 MgH 5620 . 799 MgH 5620 . 923 F e 1 5615 . 644 F e 1 5618 . 632 F e 1 5619 . 225 F e 1 5619 . 595 079672_SME C2 5615 . 441 C2 5615 . 926 C2 5616 . 156 C2 5616 . 172 C2 5616 . 269 C2 5616 . 317 C2 5617 . 198 C2 5617 . 750 C2 5617 . 870 C2 5617 . 924 C2 5618 . 061 C2 5619 . 649 C2 5619 . 658 C2 5619 . 808 1.0 1.0 0.0 0.8 0.8 -0.1 0.6 0.6 Residuals Intensity 0.4 0.4 -0.2 0.2 0.2 HIP 79672: Teff=5796, logg=4.34, [Fe/H]=0.058 -0.3 0.0 0.0 5616 5616 5616 5617 5617 5617 5618 5618 5618 5619 5619 5619 5620 5620 5620 Wavelength Tuesday, February 11, 14
0 2.5 5.01 Gyr 4.47 Gyr 1 3.16 Gyr 3 2 3 3.5 4 log g M V 5 4 6 4.5 7 8 (a) (b) 5 9 3.8 3.7 3.6 3.8 3.7 3.6 log( T eff ) log( T eff ) • Stellar ages are estimated from Y2 isochrones by maximising probability distribution functions • 17 stars have solar metallicity, while the age of 4 candidates (HIP 10786, 30344, 40317 and 112584) are consistent with the solar age within one-sigma • Systematic errors: ▵ T ~ 60K, ▵ logg ~ -0.07dex, ▵ [Fe/H] ~ 0.06dex Demarque et al. 2004, Bensby et al. 2011 Tuesday, February 11, 14
Elemental abundances [X/Fe]=[X/H]-[Fe/H] 0.2 0.2 [Mg/Fe] [Na/Fe] 0 0 − 0.2 − 0.2 − 0.3 − 0.2 − 0.1 0 0.1 0.2 0.3 − 0.3 − 0.2 − 0.1 0 0.1 0.2 0.3 [Fe/H] [Fe/H] 0.2 0.2 [Al/Fe] [Si/Fe] 0 0 − 0.2 − 0.2 − 0.3 − 0.2 − 0.1 0 0.1 0.2 0.3 − 0.3 − 0.2 − 0.1 0 0.1 0.2 0.3 [Fe/H] [Fe/H] 0.2 0.2 [Ca/Fe] [Ti/Fe] 0 0 − 0.2 − 0.2 − 0.3 − 0.2 − 0.1 0 0.1 0.2 0.3 − 0.3 − 0.2 − 0.1 0 0.1 0.2 0.3 [Fe/H] [Fe/H] 0.2 0.2 [Cr/Fe] [Ni/Fe] 0 0 − 0.2 − 0.2 − 0.3 − 0.2 − 0.1 0 0.1 0.2 0.3 − 0.3 − 0.2 − 0.1 0 0.1 0.2 0.3 [Fe/H] [Fe/H] • Flat trends for most of elements with abundances close to the solar abundances, while [Al/Fe] and [Ni/Fe] show a transition • Uncertainty of abundances are between 0.05 and 0.08 dex Tuesday, February 11, 14
Chemical tagging • Mitschang et al. (2013) defined a metric to quantify chemical difference between two stars using element abundances (Nc = 9) N C C − A j | A i C | � δ C = ω C N C C • P c that a probability of two stars belong to the same δ C cluster responds to • Confidence limit of probability P lim = 90 percent Tuesday, February 11, 14
Process to identify solar siblings calculate for any one δ C star and the Sun non-cluster possible stars P c < 90 cluster stars re-calculate for δ C any two stars cluster stars cluster detection P c > 90 confidence P clus Tuesday, February 11, 14
Results • Three sibling candidates (HIP 7764, 21158 and 40317) and the Sun may be from a dissolved cluster based on chemical tagging • The cluster detection confidence is P clue = 94 percent • 4 stars (HIP 10786, 30344, 40317 and 112584) are consistent with the solar metallicity and age within one- sigma • Only star -HIP 40317- could be the lost sibling of the Sun ([Fe/H]=0.04, Age ~ 4.4 Gyrs, and P c > 90) Tuesday, February 11, 14
Conclusion • Chemical tagging is a powerful technical to detect dissolved cluster • Very small fraction of candidates (1/33 ≃ 0.03) are solar siblings • The selection criteria developed in Brown et al. (2010) are not optimal • Since a smooth and axisymmetric Galactic potential has been used to model stellar orbits in Brown’s work, a more realistic potential could prove more efficient at finding solar siblings • If our results are true, then only few solar siblings left because of perturbation from the spiral arms or inner bar Tuesday, February 11, 14
Thanks for listening! Tuesday, February 11, 14
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