* Astronomy

Blobrana · L

RE: HD 140283

Blobrana · L

Title: HD 140283: A Star in the Solar Neighborhood that Formed Shortly After the Big Bang
Authors: Howard E. Bond (1 and 2), Edmund P. Nelan (2), Don A. VandenBerg (3), Gail H. Schaefer (4), Dianne Harmer (5) ((1) Pennsylvania State University, (2) Space Telescope Science Institute, (3) University of Victoria, (4) CHARA Array, Georgia State University, (5) NOAO)

HD 140283 is an extremely metal-deficient and high-velocity subgiant in the solar neighborhood, having a location in the HR diagram where absolute magnitude is most sensitive to stellar age. Because it is bright, nearby, unreddened, and has a well-determined chemical composition, this star avoids most of the issues involved in age determinations for globular clusters. Using the Fine Guidance Sensors on the Hubble Space Telescope, we have measured a trigonometric parallax of 17.15 ± 0.14 mas for HD 140283, with an error one-fifth of that determined by the Hipparcos mission. Employing modern theoretical isochrones, which include effects of helium diffusion, revised nuclear reaction rates, and enhanced oxygen abundance, we use the precise distance to infer an age of 14.46 ± 0.31 Gyr. The quoted error includes only the uncertainty in the parallax, and is for adopted surface oxygen and iron abundances of [O/H] = -1.67 and [Fe/H] = -2.40. Uncertainties in the stellar parameters and chemical composition, especially the oxygen content, now contribute more to the error budget for the age of HD 140283 than does its distance, increasing the total uncertainty to about ±0.8 Gyr. Within the errors, the age of HD 140283 does not conflict with the age of the Universe, 13.77 ± 0.06 Gyr, based on the microwave background and Hubble constant, but it must have formed soon after the big bang.

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Blobrana · L

Nearby star is almost as old as the Universe

Astronomers have discovered a Methuselah of stars - a denizen of the Solar System's neighbourhood that is at least 13.2 billion years old and formed shortly after the Big Bang.
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Blobrana · L

Title: Origin of the heavy elements in HD 140283. Measurement of europium abundance
Authors: C. Siqueira Mello (1 and 2), B. Barbuy (1), M. Spite (2), F. Spite (2) ((1) IAG, Universidade de São Paulo, Brazil, (2) GEPI, Observatoire de Paris, Meudon, France)

HD 140283 is a nearby (V=7.7) subgiant metal-poor star, extensively analysed in the literature. Although many spectra have been obtained for this star, none showed a signal-to-noise (S/N) ratio high enough to enable a very accurate derivation of abundances from weak lines. The detection of europium proves that the neutron-capture elements in this star originate in the r-process, and not in the s-process, as recently claimed in the literature. Based on the OSMARCS 1D LTE atmospheric model and with a consistent approach based on the spectrum synthesis code Turbospectrum, we measured the europium lines at 4129 {\AA} and 4205 {\AA}, taking into account the hyperfine structure of the transitions. The spectrum, obtained with a long exposure time of seven hours at the Canada-France-Hawaii Telescope (CFHT), has a resolving power of 81000 and a S/N ratio of 800 at 4100 {\AA}. We were able to determine the abundance A(Eu)=-2.35 dex, compatible with the value predicted for the europium from the r-process. The abundance ratio [Eu/Ba]=+0.58 dex agrees with the trend observed in metal-poor stars and is also compatible with a strong r-process contribution to the origin of the neutron-capture elements in HD 140283.

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