Beryllium abundances and star formation in the halo and in the thick disk

Context. Beryllium is a pure product of cosmic ray spallation. This implies a relatively simple evolution in time of the beryllium abundance and suggests its use as a time-like observable. Aims. Our goal is to derive abundances of Be in a sample of 90 stars, the largest sample of halo and thick disk stars analyzed to date. We study the evolution of Be in the early Galaxy and its dependence on kinematic and orbital parameters, and investigate its use as a cosmochronometer. Abundances of Be, Fe, and α-elements of 73 stars are employed to study the formation of the halo and the thick disk of the Galaxy. Methods. Beryllium abundances are determined from high-resolution, high signal-to-noise UVES spectra with spectrum synthesis. Atmospheric parameters and abundances of α-elements are adopted from the literature. Lithium abundances are used to eliminate mixed stars from the sample. The properties of halo and thick disk stars are investigated in diagrams of log(Be/H) vs. [α/H], log(Be/H) vs. [Fe/H], and [α/Fe] vs. log(Be/H) and with orbital and kinematic parameters. Results. We present our observational results in various diagrams. (i) In a log(Be/H) vs. [Fe/H] diagram we find a marginal statistical detection of a real scatter, above what is expected from measurement errors, with a larger scatter among halo stars. The detection of the scatter is further supported by the existence of pairs of stars with identical atmospheric parameters and different Be abundances; (ii) in a log(Be/H) vs. [α/Fe] diagram, the halo stars separate into two components; one is consistent with predictions of evolutionary models, while the other has too high α and Be abundances and is chemically indistinguishable from thick disk stars. This suggests that the halo is not a single uniform population where a clear age-metallicity relation can be defined; (iii) In diagrams of Rmin vs. [α/Fe] and log(Be/H), the thick disk stars show a possible decrease in [α/Fe] with Rmin, whereas no dependence of Be with Rmin is seen. This anticorrelation suggests that the star formation rate was lower in the outer regions of the thick disk, pointing towards an inside-out formation. The lack of correlation for Be indicates that it is insensitive to the local conditions of star formation.

[1]  J. King.  The Evolution of Galactic Beryllium and Boron Traced by Magnesium and Calcium , 2001 .

[2]  The Galactic Thick Disk Stellar Abundances , 2000, astro-ph/0008075.

[3]  J. King.  The Galactic Evolution of Beryllium and Boron Revisited , 2001 .

[4]  Gang Zhao,et al.  Lithium abundances for 185 main-sequence stars - galactic evolution and stellar depletion of lithium , 2001 .

[5]  D. Macconnell,et al.  HST-FGS parallaxes of two high-velocity stars. , 1997 .

[6]  J. Fulbright.  Abundances and Kinematics of Field Halo and Disk Stars. I. Observational Data and Abundance Analysis , 2000, astro-ph/0006260.

[7]  D. Lambert,et al.  The abundance of boron in three halo stars , 1992 .

[8]  G. Fouts.  Candidates for spectroscopic binaries found in the Mount Wilson halo-mapping program , 1987 .

[9]  T. Beers,et al.  The Light Elements Be and B as Stellar Chronometers in the Early Galaxy , 2000, astro-ph/0002056.

[10]  Abundances for metal-poor stars with accurate parallaxes , I. Basic data , 2003, astro-ph/0303653.

[11]  R. G. Gratton,et al.  Early star formation in the Galaxy from beryllium and oxygen abundances , 2005 .

[12]  M. Bessell,et al.  Evolution of Beryllium Abundances in the Galactic Halo , 1992 .

[13]  S. Bergh.  What are SO galaxies , 1990 .

[14]  K. Fuhrmann.  Nearby stars of the Galactic disc and halo – IV , 2008 .

[15]  A. Boesgaard,et al.  Beryllium in the Hyades F and G Dwarfs from Keck HIRES Spectra , 2001, astro-ph/0109284.

[16]  R. G. Gratton,et al.  Beryllium in turnoff stars of NGC 6397: Early Galaxy spallation, cosmochronology and cluster formation , , 2004 .

[17]  B. Fields,et al.  The Revival of Galactic Cosmic-Ray Nucleosynthesis? , 1998, astro-ph/9809277.

[18]  M. Cassé,et al.  The Evolution of 9Be , 1990 .

[19]  Primordial nucleosynthesis and the abundances of beryllium and boron , 1992, astro-ph/9206002.

[20]  C. Deliyannis,et al.  Lithium and Lithium Depletion in Halo Stars on Extreme Orbits , 2005, astro-ph/0507625.

[21]  G. Hill,et al.  THE BINARY FREQUENCY OF EXTREME SUBDWARFS REVISITED. , 1985 .

[22]  S. Kawanomoto,et al.  Lithium Abundances of F-, G-, and K-Type Stars: Profile-Fitting Analysis of the Li I 6708 Doublet , 2005 .

[23]  L. Pasquini,et al.  Tracing mixing in stars: new beryllium observations of the open clusters NGC 2516, Hyades, and M 67 , 2007, 0705.2330.

[24]  F. Hoyle,et al.  Galactic Cosmic Ray Origin of Li, Be and B in Stars , 1970, Nature.

[25]  T. Kajino,et al.  Evolution of Beryllium and Boron in the Inhomogeneous Early Galaxy , 1999, astro-ph/9907182.

[26]  Abundances for metal-poor stars with accurate parallaxes - II. $\alpha-$elements in the halo , 2003, astro-ph/0305358.

[27]  A. Helmi,et al.  FASHIONABLY LATE? BUILDING UP THE MILKY WAY'S INNER HALO , 2008, 0804.2448.

[28]  Brant Robertson,et al.  Chemical Abundance Distributions of Galactic Halos and Their Satellite Systems in a ΛCDM Universe , 2006 .

[29]  A. Sandage,et al.  Evidence from the motions of old stars that the Galaxy collapsed. , 1962 .

[30]  Harold A. McAlister,et al.  ICCD Speckle Observations of Binary Stars. III. A Survey for Duplicity Among High Velocity Stars , 1987 .

[31]  Gerard Gilmore,et al.  Is beryllium in metal-poor stars of galactic or cosmological origin? , 1992, Nature.

[32]  A. Boesgaard,et al.  Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars , 2002 .

[33]  C. Deliyannis,et al.  Beryllium in Lithium-deficient F and G Stars , 1997 .

[34]  K. Lodders.  Solar System Abundances and Condensation Temperatures of the Elements , 2003 .

[35]  Harold A. McAlister,et al.  ICCD Speckle Observations of Binary Stars. X. A Further Survey for Duplicity Among the Bright Stars , 1987 .

[36]  F. Primas,et al.  The lithium content of the Galactic Halo stars , 2005 .

[37]  C. Brook,et al.  THE DUAL ORIGIN OF STELLAR HALOS , 2009, 0904.3333.

[38]  T. Beers,et al.  Beryllium Abundances in Halo Stars from Keck/HIRES Observations , 1999 .

[39]  K. Fuhrmann.  Nearby stars of the Galactic disk and halo. III. , 1998 .

[40]  C. Abia,et al.  9Be abundances in dwarfs of intermediate metal deficiency: Impications for galactic evolution , 1989 .

[41]  R. Blomme,et al.  Line formation in solar granulation VI. [Cl], Cl, CH and C2 lines and the photospheric C abundance , 2004, astro-ph/0410681.

[42]  H. Jahreiss,et al.  The third catalogue of nearby stars with special emphasis on wide binaries , 1988 .

[43]  A. Boesgaard.  Beryllium in Ultra-Lithium-Deficient Halo Stars: The Blue Straggler Connection , 2007, 0705.1551.

[44]  G. Preston,et al.  A Spectroscopic Analysis of 33 of the Most Metal-Poor Stars.I. , 1995 .

[45]  M. Cassé,et al.  Production and evolution of light elements in active star-forming regions , 1995, Nature.

[46]  Denmark,et al.  Atomic Diffusion and Mixing in Old Stars. I. Very Large Telescope FLAMES-UVES Observations of Stars in NGC 6397 , 2007, 0709.0639.

[47]  A. Boesgaard,et al.  Lithium in the Hyades Cluster , 1986 .

[48]  Bruce W. Carney,et al.  A Survey of Proper-Motion Stars. XVI. Orbital Solutions for 171 Single-lined Spectroscopic Binaries , 2002 .

[49]  P. Conti,et al.  Observations of the Lithium Content of Main-Sequence Stars in the Hyades. , 1965 .

[50]  S. Gawish,et al.  Gamma preirradiation and grafting of 2N-morpholino ethyl methacrylate onto polypropylene fabric , 1995 .

[51]  E. Armengaud,et al.  The Correlation of Lithium and Beryllium in F and G Field and Cluster Dwarf Stars , 2004 .

[52]  European Southern Observatory,et al.  First stars VII - Lithium in extremely metal poor dwarfs , 2007 .

[53]  R. Sutherland,et al.  Be-9 abundances in population II stars - Implications for light element nucleosynthesis , 1990 .

[54]  R. Schiavon,et al.  A library of high resolution synthetic stellar spectra from 300 nm to 1.8 μm with solar and α-enhanced composition , 2005, astro-ph/0505511.

[55]  S. S. Olivier,et al.  Stellar Companions to Stars with Planets , 2002, astro-ph/0207538.

[56]  D. Fabbian,et al.  Neutral oxygen spectral line formation revisited with new collisional data: large departures from LTE at low metallicity , 2009, 0902.4472.

[57]  P. Mazzali,et al.  Possible signature of hypernova nucleosynthesis in a beryllium-rich halo dwarf , 2008, 0801.0965.

[58]  M. Spite,et al.  The Light Elements and their Evolution , 2000 .

[59]  R. Zinn,et al.  Compositions of halo clusters and the formation of the galactic halo , 1978 .

[60]  A. Ardeberg,et al.  Orbital elements for double stars of Population II. The system HD 29907 , 1996 .

[61]  J. Thorburn,et al.  Beryllium Abundances of Six Halo Stars , 1996 .

[62]  Beatriz Barbuy,et al.  A grid of synthetic spectra and indices Fe5270, Fe5335, Mgb and Mg$_\mathsf{2}$ as a function of stellar parameters and [ $\mathsf{\alpha}$/Fe] , 2003 .

[63]  M. Pinsonneault,et al.  Hubble Space Telescope Beryllium Abundances in the α Centauri System , 1997 .

[64]  Piercarlo Bonifacio,et al.  The primordial lithium abundance , 1997 .

[65]  Beryllium in Disk and Halo Stars: Evidence for a Beryllium Dispersion in Old Stars* , 2005, astro-ph/0512317.

[66]  Spain.,et al.  Beryllium abundances in stars hosting giant planets , 2002, astro-ph/0202456.

[67]  Y. Yoshii,et al.  A New Model for the Evolution of Light Elements in an Inhomogeneous Galactic Halo , 2000, astro-ph/0010108.

[68]  J. S. Wright,et al.  Discovery of an "alpha" Element-Poor Halo Star in a Search for Very Low- Metallicity Disk Stars , 1997 .

[69]  Ingemar Furenlid,et al.  Solar flux atlas from 296 to 1300 nm , 1985 .

[70]  M. Mayor,et al.  The Geneva–Copenhagen Survey of the Solar Neighbourhood , 2004, Publications of the Astronomical Society of Australia.

[71]  Michael Perryman,et al.  Astronomical Applications of Astrometry: The Hipparcos and Tycho Catalogues , 2008 .

[72]  T. Beers,et al.  Ultra-Lithium-deficient Halo Stars and Blue Stragglers: A Common Origin? , 2000, astro-ph/0010413.

[73]  S. Ryan,et al.  Lithium in Short-Period Tidally Locked Binaries: A Test of Rotationally Induced Mixing , 1995 .

[74]  F. Castelli,et al.  Round Table Summary: Problems in Modelling Stellar Atmospheres , 2003 .

[75]  D. S. Balsara,et al.  From First Stars to the Spite Plateau: A Possible Reconciliation of Halo Stars Observations with Predictions from Big Bang Nucleosynthesis , 2006, astro-ph/0603553.

[76]  N. Prantzos,et al.  Production and evolution of LiBeB isotopes in the galaxy , 1993 .

[77]  M. Asplund.  Line formation in solar granulation V. Missing UV-opacity and the photospheric Be abundance , 2003, astro-ph/0312291.

[78]  Coryn A. L. Bailer-Jones,et al.  Two stellar components in the halo of the Milky Way , 2007, Nature.

[79]  E. Tolstoy,et al.  Stellar Chemical Signatures and Hierarchical Galaxy Formation , 2004, astro-ph/0406120.

[80]  D. Sokoloff,et al.  Anomalous persistence of bisymmetric magnetic structures in spiral galaxies , 1997 .

[81]  Gemini-Phoenix infrared high-resolution abundance analysis of five giants in the bulge globular cluster NGC 6553 , 2003, astro-ph/0309552.

[82]  Roger A. Bell,et al.  Shallow mixing in the solar photosphere inferred from revised beryllium abundances , 1998, Nature.

[83]  C. Ledoux,et al.  The UVES Paranal Observatory Project: A Library of High- Resolution Spectra of Stars across the Hertzsprung-Russell Diagram , 2003 .

[84]  Li and Be depletion in metal-poor subgiants , 2005, astro-ph/0512293.

[85]  F. Ferrini,et al.  Galactic Chemical Evolution of Lithium: Interplay between Stellar Sources , 2001, astro-ph/0105558.

[86]  F. Ferrini,et al.  Evolution of Li, Be, and B in the Galaxy , 2001, astro-ph/0110327.

[87]  A. Boesgaard.  Galactic evolution of beryllium , 1993 .

[88]  Bernard Delabre,et al.  Design, construction, and performance of UVES, the echelle spectrograph for the UT2 Kueyen Telescope at the ESO Paranal Observatory , 2000, Astronomical Telescopes and Instrumentation.

[89]  J. B. Laird,et al.  A Survey of Proper-Motion Stars. XV. Orbital Solutions for 34 Double-lined Spectroscopic Binaries , 2002 .

[90]  B. Carney,et al.  A Survey of Proper-Motion Stars. XIV. Spectroscopic Binaries among Metal-poor Field Blue Stragglers , 2001 .