Hertzsprung-Russell diagram and mass distribution of barium stars

With the availability of parallaxes provided by the Tycho-Gaia Astrometric Solution, it is possible to construct the Hertzsprung-Russell diagram (HRD) of barium and related stars with unprecedented accuracy. A direct result from the derived HRD is that subgiant CH stars occupy the same region as barium dwarfs, contrary to what their designations imply. By comparing the position of barium stars in the HRD with STAREVOL evolutionary tracks, it is possible to evaluate their masses, provided the metallicity is known. We used an average metallicity [Fe/H] = -0.25 and derived the mass distribution of barium giants. The distribution peaks around 2.5 Msun with a tail at higher masses up to 4.5 Msun. This peak is also seen in the mass distribution of a sample of normal K and M giants used for comparison and is associated with stars located in the red clump. When we compare these mass distributions, we see a deficit of low-mass (1 - 2 Msun) barium giants. This is probably because low-mass stars reach large radii at the tip of the red giant branch, which may have resulted in an early binary interaction. Among barium giants, the high-mass tail is however dominated by stars with barium indices of less than unity, based on a visual inspection of the barium spectral line; that is, these stars have a very moderate barium line strength. We believe that these stars are not genuine barium giants, but rather bright giants, or supergiants, where the barium lines are strengthened because of a positive luminosity effect. Moreover, contrary to previous claims, we do not see differences between the mass distributions of mild and strong barium giants.

[1]  Observatoire de la Côte d'Azur,et al.  Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties , 2016, 1609.04172.

[2]  C. Barache,et al.  Gaia Data Release 1: Astrometry - one billion positions, two million proper motions and parallaxes , 2016, 1609.04303.

[3]  A. Jorissen,et al.  The mass-ratio and eccentricity distributions of barium and S stars, and red giants in open clusters , 2016, 1608.04949.

[4]  G. Gontcharov.  3D interstellar extinction map within the nearest kiloparsec , 2016, 1606.09483.

[5]  C. Soubiran,et al.  The PASTEL catalogue: 2016 version , 2016, 1605.07384.

[6]  F. Roig,et al.  Chemical abundances and kinematics of barium stars , 2016, 1604.03031.

[7]  A. Karakas,et al.  STELLAR YIELDS FROM METAL-RICH ASYMPTOTIC GIANT BRANCH MODELS , 2016, 1604.02178.

[8]  H. Winckel,et al.  Chemical abundance study of two strongly s-process enriched post-AGB stars in the LMC: J051213.81-693537.1 and J051848.86-700246.9 , 2015, 1508.01091.

[9]  Lennart Lindegren,et al.  The Tycho-Gaia astrometric solution. How to get 2.5 million parallaxes with less than one year of Gaia data , 2014, 1412.8770.

[10]  H. Boffin.  Mass Transfer by Stellar Wind , 2014, 1406.3473.

[11]  D. O. Astronomy,et al.  Exploring the Milky Way stellar disk - A detailed elemental abundance study of 714 F and G dwarf stars in the solar neighbourhood , 2013, 1309.2631.

[12]  Paul M. Brunet,et al.  The Gaia mission , 2013, 1303.0303.

[13]  N. Mowlavi,et al.  Grids of stellar models with rotation - I. Models from 0.8 to 120 M⊙ at solar metallicity (Z = 0.014) , 2011, 1110.5049.

[14]  W. Aoki,et al.  The s process: Nuclear physics, stellar models, and observations , 2010, 1012.5218.

[15]  R. Izzard,et al.  White-dwarf kicks and implications for barium stars , 2010, 1008.3818.

[16]  O. Zamora,et al.  The chemical composition of carbon stars. The R-type stars , 2009, 0909.4222.

[17]  M. Asplund,et al.  The chemical composition of the Sun , 2009, 0909.0948.

[18]  M. Arnould,et al.  Production of 26Al by super-AGB stars , 2008 .

[19]  Kjell Eriksson,et al.  A grid of MARCS model atmospheres for late-type stars. I. Methods and general properties , 2008, 0805.0554.

[20]  R. P. Butler,et al.  Beyond the Iron Peak: r- and s-Process Elemental Abundances in Stars with Planets , 2008, 0804.3354.

[21]  M. Cuntz,et al.  A critical test of empirical mass loss formulas applied to individual giants and supergiants , 2007, astro-ph/0702172.

[22]  Lionel Siess,et al.  Evolution of massive AGB stars: I.Carbon burning phase , 2006 .

[23]  M. Skrutskie,et al.  The Two Micron All Sky Survey (2MASS) , 2006 .

[24]  Usa,et al.  The origin and chemical evolution of carbon in the Galactic thin and thick discs , 2006, astro-ph/0601130.

[25]  I. Hachisu,et al.  Wind accretion in binary stars II. Angular momentum loss , 2005 .

[26]  C. Pereira.  Spectroscopic Verification of Barium Dwarf Candidates: The Analysis of HD 8270, HD 13551, and HD 22589 , 2005 .

[27]  David R. Alexander,et al.  Low-Temperature Opacities , 2005, astro-ph/0502045.

[28]  S. Udry,et al.  Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data: Revisiting the concept of superclusters , 2004, astro-ph/0409579.

[29]  Flagstaff,et al.  UBVRI photometric sequences for symbiotic stars , 2002, astro-ph/0208316.

[30]  P. Marigo.  Asymptotic Giant Branch evolution at varying surface C/O ratio: effects of changes in molecular opacities , 2002, astro-ph/0203036.

[31]  G. Knapp,et al.  Reprocessing the Hipparcos data for evolved giant stars II. Absolute magnitudes for the R-type carbon stars ⋆ , 2001, astro-ph/0103141.

[32]  J. Weingartner,et al.  Dust Grain-Size Distributions and Extinction in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud , 2001 .

[33]  J. Weingartner,et al.  Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and SMC , 2000, astro-ph/0008146.

[34]  L. Girardi,et al.  Population effects on the red giant clump absolute magnitude, and distance determinations to nearby galaxies , 2000, astro-ph/0007343.

[35]  A. Jorissen,et al.  Re-processing the Hipparcos Transit Data and intermediate astrometric data of spectroscopic binaries: I. Ba, CH and Tc-poor S stars , 2000, astro-ph/0006175.

[36]  R. Wing.  The Carbon Star Phenomenon , 2000 .

[37]  F. Bonnarel,et al.  The SIMBAD astronomical database. The CDS reference database for astronomical objects , 2000, astro-ph/0002110.

[38]  L. Girardi,et al.  Evolutionary tracks and isochrones for low- and intermediate-mass stars: From 0.15 to 7 , and from to 0.03 , 1999, astro-ph/9910164.

[39]  R. Mcclure.  THE R STARS: CARBON STARS OF A DIFFERENT KIND , 1997, astro-ph/9701066.

[40]  Forrest J. Rogers,et al.  Updated Opal Opacities , 1996 .

[41]  P. Podsiadlowski,et al.  The formation of barium and CH stars and related objects , 1995 .

[42]  P. Wood,et al.  Evolution of Low- and Intermediate-Mass Stars to the End of the Asymptotic Giant Branch with Mass Loss , 1993 .

[43]  H. Bond,et al.  Subgiant CH stars. II: Chemical compositions and the evolutionary connection with barium stars , 1991 .

[44]  P. K. Lu.  Taxonomy of barium stars , 1991 .

[45]  R. Mcclure,et al.  The Binary Nature of the Barium and CH Stars. III. Orbital Parameters , 1990 .

[46]  P. K. Lu,et al.  A catalog of spectral classification and photometry of Barium stars. , 1983 .

[47]  R. Mcclure,et al.  The binary nature of the barium stars. , 1980 .

[48]  B. Warner.  The Barium Stars , 1965 .

[49]  P. C. Keenan,et al.  The Ba II Stars. , 1951 .

[50]  P. C. Keenan.  The Spectra of CH Stars , 1942 .

[51]  Jean Kovalevsky,et al.  Astronomical Applications of Astrometry: The Hipparcos and Tycho Catalogues , 2008 .

[52]  A. Baranne,et al.  Coravel— A new tool for radial velocity measurements , 1979 .