Our Sun. III. Present and Future

Sackmann, I. J.; Boothroyd, Arnold I.; Kraemer, K. E.

doi:10.1086/173407

Cited by 246 publications

(228 citation statements)

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“…F and G dwarf stars are especially reliable tracers as their expected lifetimes on the main sequence, burning hydrogen to helium in their centres, are similar to, or possibly even longer than, the current age of the Galaxy. For instance, a solar-type star will spend around 10 Gyr on the main sequence (e.g., Sackmann et al 1993). During this time its atmosphere is untouched by internal nuclear processes.…”

Section: Introductionmentioning

confidence: 99%

Exploring the Milky Way stellar disk

Bensby

Feltzing

Oey

2014

A&A

1,063

227

1,612

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Aims. The aim of this paper is to explore and map the age and abundance structure of the stars in the nearby Galactic disk. Methods. We have conducted a high-resolution spectroscopic study of 714 F and G dwarf and subgiant stars in the Solar neighbourhood. The star sample has been kinematically selected to trace the Galactic thin and thick disks to their extremes, the metal-rich stellar halo, sub-structures in velocity space such as the Hercules stream and the Arcturus moving group, as well as stars that cannot (kinematically) be associated with either the thin disk or the thick disk. The determination of stellar parameters and elemental abundances is based on a standard 1-D LTE analysis using equivalent width measurements in high-resolution (R = 40 000 − 110 000) and high signal-to-noise (S /N = 150 − 300) spectra obtained with FEROS on the ESO 1.5-m and 2.2-m telescopes, SOFIN and FIES on the Nordic Optical Telescope, UVES on the ESO Very Large Telescope, HARPS on the ESO 3.6-m telescope, and MIKE on the Magellan Clay telescope. NLTE corrections for individual Fe i lines were employed in every step of the analysis. Results. We present stellar parameters, stellar ages, kinematical parameters, orbital parameters, and detailed elemental abundances for O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, and Ba for 714 nearby F and G dwarf stars. Our data show that there is an old and α-enhanced disk population, and a younger and less α-enhanced disk population. While they overlap greatly in metallicity between −0.7 < [Fe/H] +0.1, they show a bimodal distribution in [α/Fe]. This bimodality becomes even clearer if stars where stellar parameters and abundances show larger uncertainties (T eff 5400 K) are discarded, showing that it is important to constrain the data set to a narrow range in the stellar parameters if small differences between stellar populations are to be revealed. We furthermore find that the α-enhanced population has orbital parameters placing the stellar birthplaces in the inner Galactic disk while the low-α stars mainly come from the outer Galactic disk, fully consistent with the recent claims of a short scale-length for the α-enhanced Galactic thick disk. We have also investigated the properties of the Hercules stream and the Arcturus moving group and find that neither of them present chemical or age signatures that could point to that they are disrupted clusters or extragalactic accretion remnants from ancient merger events. Instead, they are most likely dynamical features originating within the Galaxy. We furthermore have discovered that a standard 1-D, LTE analysis, utilising ionisation and excitation balance of Fe i and Fe ii lines produces a flat lower main sequence. As the exact cause for this effect is unclear we chose to apply an empirical correction. Turn-off, and more evolved, stars, appears to be un-affected.

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Section: Introductionmentioning

confidence: 99%

Exploring the Milky Way stellar disk

Bensby

Feltzing

Oey

2014

A&A

1,063

227

1,612

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“…Initially focusing on the future of the solar system (Sackmann et al 1993;Duncan & Lissauer 1998), a number of theoretical studies have shown that a fraction of planets can survive the red-giant stage Table 1 is available in electronic form at http://www.aanda.org of their host stars (Villaver & Livio 2007, 2009Nordhaus et al 2010;Mustill & Villaver 2012). The ensuing long-term orbital evolution is complex and may lead to planet ejections or collisions (Debes & Sigurdsson 2002;Veras et al 2011;Voyatzis et al 2013).…”

Section: Introductionmentioning

confidence: 99%

The frequency of planetary debris around young white dwarfs

Koester

Gänsicke

Farihi

2014

A&A

455

531

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Context. Heavy metals in the atmospheres of white dwarfs are thought in many cases to be accreted from a circumstellar debris disk, which was formed by the tidal disruption of a rocky planetary body within the Roche radius of the star. The abundance analysis of photospheric elements and conclusions about the chemical composition of the accreted matter are a new and promising method of studying the composition of extrasolar planetary systems. However, ground-based searches for metal-polluted white dwarfs that rely primarily on the detection of the Ca ii K line become insensitive at T eff > 15 000 K because this ionization state depopulates.Aims. We present the results of the first unbiased survey for metal pollution among hydrogen-atmosphere (DA type) white dwarfs with cooling ages in the range 20-200 Myr and 17 000 K < T eff < 27 000 K. Methods. The sample was observed with the Cosmic Origins Spectrograph on board the Hubble Space Telescope in the far ultraviolet range between 1130 and 1435 Å. The atmospheric parameters were obtained using these spectra and optical observations from the literature. Element abundances were determined using theoretical models, which include the effects of element stratification due to gravitational settling and radiative levitation. Results. We find 48 of the 85 DA white dwarfs studied, or 56% show traces of heavy elements. In 25 stars (showing only Si and occasionally C), the elements can be explained by radiative levitation alone, although we argue that accretion has very likely occurred recently. The remaining 23 white dwarfs (27%), however, must be currently accreting. Together with previous studies from the ground and adopting bulk Earth abundances for the debris, accretion rates range from a few 10 5 g s −1 to a few 10 8 g s −1 , with no evident trend in cooling age from ≈40 Myr to ≈2 Gyr. Only a single, modest case of metal pollution (Ṁ < 10 6 g s −1 ) is found among ten white dwarfs with T eff > 23 000 K, in excellent agreement with the absence of infrared excess from dust around these warmer stars. The median, main sequence progenitor of our sample corresponds to an A-type star of ≈2 M , and we find 13 of 23 white dwarfs descending from main sequence 2-3 M , late B-and A-type stars to be currently accreting. Only one of 14 targets with M wd > 0.8 M is found to be currently accreting, which suggests a large fraction of these stars result from double-degenerate mergers, and the merger disks do not commonly reform large planetesimals or otherwise pollute the remnant. We reconfirm our previous finding that two 625 Myr Hyades white dwarfs are currently accreting rocky planetary debris. Conclusions. At least 27% of all white dwarfs with cooling ages 20-200 Myr are accreting planetary debris, but that fraction could be as high as ≈50%. At T eff > 23 000 K, the luminosity of white dwarfs is probably sufficient to vaporize circumstellar dust grains, so no stars with strong metal-pollution are found. Planetesimal disruption events should occur in this cooling age and temper...

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“…For instance, a solar type star will spend ∼11 Gyr on the main sequence (e.g. Sackmann et al 1993) during which their atmospheres are untouched by internal nuclear processes of the star (e.g. Iben 1991).…”

Section: Introductionmentioning

confidence: 99%

Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars

Bensby¹,

Johnson

Cohen³

et al. 2009

A&A

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Aims. Our aims are twofold. First we aim to evaluate the robustness and accuracy of stellar parameters and detailed elemental abundances that can be derived from high-resolution spectroscopic observations of microlensed dwarf and subgiant stars. We then aim to use microlensed dwarf and subgiant stars to investigate the abundance structure and chemical evolution of the Milky Way Bulge. Contrary to the cool giant stars, with their extremely crowded spectra, the dwarf stars are hotter, their spectra are cleaner, and the elemental abundances of the atmospheres of dwarf and subgiant stars are largely untouched by the internal nuclear processes of the star. Methods. We present a detailed elemental abundance analysis of OGLE-2008-BLG-209S, the source star of a new microlensing event towards the Bulge, for which we obtained a high-resolution spectrum with the MIKE spectrograph on the Magellan Clay telescope. We have performed four different analyses of OGLE-2008-BLG-209S. One method is identical to the one used for a large comparison sample of F and G dwarf stars, mainly thin and thick disc stars, in the Solar neighbourhood. We have also re-analysed three previous microlensed dwarf stars OGLE-2006

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Our Sun. III. Present and Future

Cited by 246 publications

References 0 publications

Exploring the Milky Way stellar disk

Exploring the Milky Way stellar disk

The frequency of planetary debris around young white dwarfs

Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars

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