High-dispersion spectroscopic study of solar twins: HIP 56948, HIP 79672, and HIP 100963*

Publications- Astronomical Society of Japan (Impact Factor: 2.07). 02/2009; 61(3). DOI: 10.1093/pasj/61.3.471
Source: arXiv


An intensive spectroscopic study was performed for three representative solar twins (HIP 56948, HIP 79672, and HIP 100963)
as well as for the Sun (Moon; reference standard), with intentions of (1) quantitatively discussing the relative-to-Sun similarities
based on the precisely established differential parameters and (2) investigating the reason that causes the Li abundance differences,
despite their similarities. It was concluded that HIP 56948 most resembles the Sun in every respect, including the Li abundance
(though not perfectly similar) among the three, and deserves the name of “closest-ever solar twin”, while HIP 79672 and HIP
100963 have a somewhat higher effective temperature and appreciably higher surface Li composition. While there is an indication
of Li being rotation-dependent, because the projected rotation in HIP 56948 (and the Sun) is slightly lower than the other
two, the rotational difference alone does not seem to be so large as to efficiently produce a marked change in Li. Rather,
this may be more likely to be attributed (at least partly) to a slight difference in $T_{\rm eff}$ via some $T_{\rm eff}$-sensitive Li-controlling mechanism. Since the abundance of Be was found to be essentially solar for all stars irrespective
of Li, any physical process causing the Li diversity should work only on Li without affecting Be.

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    ABSTRACT: The effective temperature of a stellar surface is a measure of the total energy and its correct characterization plays a central role in both theory and observations. Various effective temperature scales have been proposed in literature. Despite being such a long-lived tradition and the high internal precision usually achieved, systematic differences of order 100 K among various scales are still present, thus hindering much of a progress in the field. We present an Infrared Flux Method based investigation aimed to carefully assess the sources of such discrepancies and pin down their origin. We break the impasse among different scales by using a large set of solar twins, stars which are spectroscopically and photometrically identical to the Sun, to set the zero-point of the effective temperature scale to within few degrees. Our newly calibrated, precise and accurate temperature scale applies to dwarfs and subgiants, from super solar metallicities to the most metal poor stars currently known. The effect of using spectral energy distribution computed from 3D models in the Infrared Flux Method, as well as 3D synthetic colours are also briefly outlined.
    Preview · Article · Jan 2009
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    ABSTRACT: We analyze the non-standard mixing history of the solar twins HIP 55459, HIP 79672, HIP 56948, HIP 73815, and HIP 100963, to determine as precisely as possible their mass and age. We computed a grid of evolutionary models with non-standard mixing at several metallicities with the Toulouse-Geneva code for a range of stellar masses assuming an error bar of +-50K in Teff. We choose the evolutionary model that reproduces accurately the observed low lithium abundances observed in the solar twins. Our best-fit model for each solar twin provides a mass and age solution constrained by their Li content and Teff determination. HIP 56948 is the most likely solar-twin candidate at the present time and our analysis infers a mass of 0.994 +- 0.004 Msun and an age of 4.71 +-1.39 Gyr. Non-standard mixing is required to explain the low Li abundances observed in solar twins. Li depletion due to additional mixing in solar twins is strongly mass dependent. An accurate lithium abundance measurement and non-standard models provide more precise information about the age and mass more robustly than determined by classical methods alone. Comment: 10 pages, 5 figures, Accepted for publication in Astronomy and Astrophysics
    Full-text · Article · Apr 2009 · Astronomy and Astrophysics
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    ABSTRACT: For more than 140 years the chemical composition of our Sun has been considered typical of solar-type stars. Our highly differential elemental abundance analysis of unprecedented accuracy (~0.01 dex) of the Sun relative to solar twins, shows that the Sun has a peculiar chemical composition with a ~20% depletion of refractory elements relative to the volatile elements in comparison with solar twins. The abundance differences correlate strongly with the condensation temperatures of the elements. A similar study of solar analogs from planet surveys shows that this peculiarity also holds in comparisons with solar analogs known to have close-in giant planets while the majority of solar analogs without detected giant planets show the solar abundance pattern. The peculiarities in the solar chemical composition can be explained as signatures of the formation of terrestrial planets like our own Earth. Comment: Chemical Abundances in the Universe: Connecting First Stars to Planets. Proceedings IAU Symposium No. 265, 2009. K. Cunha, M. Spite & B. Barbuy, eds
    Preview · Article · Oct 2009 · Proceedings of the International Astronomical Union
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