The barium stars

McClure, R. D.

doi:10.1086/131310

Cited by 73 publications

(56 citation statements)

References 17 publications

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“…This has been confirmed by McClure (1983McClure ( , 1984 and Udry et al (1998a,b). Böhm-Vitense (1980) and Böhm-Vitense & Johnson (1985) observed an ultraviolet excess in the barium stars ζ CAP and ξ Ceti, which could be explained by white dwarf companions.…”

Section: Introductionsupporting

confidence: 61%

Analysis of 26 barium stars

Allen

Barbuy

2006

A&A

157

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Context. We present a detailed analysis of 26 barium stars, including dwarf barium stars, providing their atmospheric parameters (T eff , log g, [Fe/H], v t ), and elemental abundances. Aims. We aim at deriving gravities and luminosity classes of the sample stars, in particular to confirm the existence of dwarf barium stars. Accurate abundances of chemical elements were derived. We present the abundance ratios between nucleosynthetic processes, by using Eu and Ba as representatives of the r-and s-processes. Methods. High-resolution spectra were obtained with the FEROS spectrograph at the ESO-1.52 m Telescope, along with photometric data with Fotrap at the Zeiss telescope at the LNA. The atmospheric parameters were derived in an iterative way, with temperatures obtained from colour-temperature calibrations. The abundances were derived using spectrum synthesis for Li, Na, Al, α-, iron-peak, s-, and r-element atomic lines, and for C and N molecular lines. Results. Atmospheric parameters in the range 4300 < T eff < 6500, −1.2 < [Fe/H] < 0.0, and 1.4 ≤ log g < 4.6 were derived, confirming that our sample contains giants, subgiants, and dwarfs. The abundance results obtained for Li, Al, Na, α-, and iron-peak elements for the sample stars show that they are compatible with the values found in the literature for normal disk stars in the same range of metallicities. Enhancements of C, N, and heavy elements relative to Fe, that characterise barium stars, were derived and showed that [X/Ba]

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Section: Introductionsupporting

confidence: 61%

Analysis of 26 barium stars

Allen

Barbuy

2006

A&A

157

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“…This is the explanation for blue stragglers in clusters (McCrea 1964), Ba-stars, and extrinsic C-stars (McClure et al 1980;McClure 1984;McClure & Woodsworth 1990). Different signatures can be observed, depending on when and how much mass was transferred from the donor (in our case the WD).…”

Section: Abundance Analysismentioning

confidence: 74%

“…Bidelman (1985) obtained a frequency between 0.5 and 1%. Most Ba-stars are in binary systems with orbital periods typically longer than 100 days but shorter than 10 years (McClure et al 1980;McClure 1984;McClure & Woodsworth 1990), though Jorissen et al (1998) reported a few cases with periods outside this range. Orbits typically have low but nonzero eccentricity, because they are most likely not produced by Roche-lobe overflow; the origin is probably due to stellar wind.…”

Section: Discussionmentioning

confidence: 99%

Astrophysical false positives in direct imaging for exoplanets: a white dwarf close to a rejuvenated star

Zurlo

Vigan

Hagelberg

et al. 2013

A&A

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Context. As is the case for all techniques involved in the research for exoplanets, direct imaging has to take into account the probability of so-called astrophysical false positives, which are phenomena that mimic the signature of the objects we are seeking. Aims. In this work we present the case of a false positive found during a direct-imaging survey conducted with VLT/NACO. A promising exoplanet candidate was detected around the K2-type star HD 8049 in July 2010. Its contrast of ∆H = 7.05 at 1.57 arcsec allowed us to assume a 35 M Jup companion at 50 projected AU, for the nominal system age and heliocentric distance. Methods. To check whether it was gravitationally bound to the host star, as opposed to an unrelated background object, we re-observed the system one year later and concluded a high probability of a bound system. We also used radial velocity measurements of the host star, spanning a time range of ∼30 yr, to constrain the companion's mass and orbital properties, as well as to probe the host star's spectral age indicators and general spectral energy distribution. We also obtained U-band imaging with EFOSC and near-infrared spectroscopy for the companion. Results. Combining all these information we conclude that the companion of HD 8049 is a white dwarf (WD) with temperature T eff = 18 800 ± 2100 K and mass M WD = 0.56 ± 0.08 M . The significant radial velocity trend combined with the imaging data indicates that the most probable orbit has a semi-major axis of about 50 AU. The discrepancy between the age indicators speaks against a bona-fide young star. The moderately high level of chromospheric activity and fast rotation, mimicking the properties of a young star, might be induced by the exchange of mass with the progenitor of the WD. This example demonstrates some of the challenges in determining accurate age estimates and identifications of faint companions.

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“…Most of the stars for which no radial velocity variability was found belonged to the mild barium class. A firm conclusion was not possible although they mostly seemed to be members of a binary system (McClure 1984).…”

Section: The Mild Barium Starsmentioning

confidence: 96%

Abundance analysis of barium and mild barium stars

Smiljanić¹,

Mello²,

Silva³

2007

A&A

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Aims. We compare and discuss abundances and trends in normal giants, mild barium, and barium stars, searching for differences and similarities between barium and mild barium stars that could help shed some light on the origin of these similar objects. Also, we search for nucleosynthetic effects possibly related to the s-process that were observed in the literature for elements like Cu in other types of s-process enriched stars. Methods. High signal to noise, high resolution spectra were obtained for a sample of normal, mild barium, and barium giants.Atmospheric parameters were determined from the Fe i and Fe ii lines. Abundances for Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, Eu, and Gd, were determined from equivalent widths and model atmospheres in a differential analysis, with the red giant Vir as the standard star. Results. The different levels of s-process overabundances of barium and mild barium stars were earlier suggested to be related to the stellar metallicity. Contrary to this suggestion, we found in this work no evidence of barium and mild barium having a different range in metallicity. However, comparing the ratio of abundances of heavy to light s-process elements, we found some evidence that they do not share the same neutron exposure parameter. The exact mechanism controlling this difference is still not clear. As a by-product of this analysis we identify two normal red giants misclassified as mild barium stars. The relevance of this finding is discussed. Concerning the suggested nucleosynthetic effects possibly related to the s-process, for elements like Cu, Mn, V and Sc, we found no evidence for an anomalous behavior in any of the s-process enriched stars analyzed here. However, further work is still needed since a clear [Cu/Fe] vs. [Ba/Fe] anticorrelation exists for other s-process enriched objects.

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The barium stars

Cited by 73 publications

References 17 publications

Analysis of 26 barium stars

Analysis of 26 barium stars

Astrophysical false positives in direct imaging for exoplanets: a white dwarf close to a rejuvenated star

Abundance analysis of barium and mild barium stars

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