<i>uvby</i>-<i>β</i>photometry of high-velocity and metal-poor stars

Schuster, W. J.; Moitinho, A.; Márquez, A.; Parrao, L.; Covarrubias, E

doi:10.1051/0004-6361:20053796

Cited by 85 publications

(152 citation statements)

References 98 publications

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“…We found, in accordance with other studies (e.g., Haywood 2006;Schuster et al 2006), that stars with kinematics typical of the thick disk show an age-metallicity relation such that more metal-rich stars on average are younger than the less metal-poor stars in the sample. The stars older than about 8 Gyr in Fig.…”

Section: Age-metallicity Relations?supporting

confidence: 92%

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: Age-metallicity Relations?supporting

confidence: 92%

Exploring the Milky Way stellar disk

Bensby

Feltzing

Oey

2014

A&A

1,063

227

1,612

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“…This is shown in Fig. 11 where the model at ∼ 1.9 Gyr after the perturbation is compared to a combination of the observational samples by Nordström et al (2004) and Schuster et al (2006). The separation of the induced velocity streams due to this "disk ringing" could be related to the time of the last merger impact, suggesting an event ∼ 1.9 Gyr ago.…”

Section: Constraining Recent Merger Eventsmentioning

confidence: 91%

Constraining the Milky Way assembly history with Galactic Archaeology

Minchev

2016

Astron Nachr

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The aim of Galactic Archaeology is to recover the evolutionary history of the Milky Way from its present day kinematical and chemical state. Because stars move away from their birth sites, the current dynamical information alone is not sufficient for this task. The chemical composition of stellar atmospheres, on the other hand, is largely preserved over the stellar lifetime and, together with accurate ages, can be used to recover the birthplaces of stars currently found at the same Galactic radius. In addition to the availability of large stellar samples with accurate 6D kinematics and chemical abundance measurements, this requires detailed modeling with both dynamical and chemical evolution taken into account. An important first step is to understand the variety of dynamical processes that can take place in the Milky Way, including the perturbative effects of both internal (bar and spiral structure) and external (infalling satellites) agents. We discuss here (1) how to constrain the Galactic bar, spiral structure, and merging satellites by their effect on the local and global disc phase-space, (2) the effect of multiple patterns on the disc dynamics, and (3) the importance of radial migration and merger perturbations for the formation of the Galactic thick disc. Finally, we discuss the construction of Milky Way chemo-dynamical models and relate to observations.

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“…The large number of stars in our sample allows us to group stars in metallicity and determine the age of that population very accurately if there is a coeval dominant population (Unavane, Wyse & Gilmore 1996;Schuster et al 2006;Jofré & Weiss 2011). This way of determining ages relies on using the colour (or temperature) of the main sequence turn-off of the population, which presents a sharp edge in the temperature distribution.…”

Section: Introductionmentioning

confidence: 99%

On the relative ages of the α-rich and α-poor stellar populations in the Galactic halo

Hawkins

Jofré

Gilmore

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We study the ages of α-rich and α-poor stars in the halo using a sample of F and G dwarfs from the Sloan Digital Sky Survey (SDSS). To separate stars based on [α/Fe], we have developed a new semi-empirical spectral-index based method and applied it to the low-resolution, moderate signal-to-noise SDSS spectra. The method can be used to estimate the [α/Fe] directly providing a new and widely applicable way to estimate [α/Fe] from low-resolution spectra. We measured the main-sequence turnoff temperature and combined it with the metallicities and a set of isochrones to estimate the age of the α-rich and α-poor populations in our sample. We found all stars appear to be older than 8 Gyr confirming the idea that the Galactic halo was formed very early on. A bifurcation appears in the age-metallicity relation such that in the low metallicity regime the α-rich and α-poor populations are coeval while in the high metallicity regime the α-rich population is older than the α-poor population. Our results indicate the α-rich halo population, which has shallow age-metallicity relation, was formed in a rapid event with high star formation, while the α-poor stars were formed in an environment with a slower chemical evolution timescale.

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uvby-βphotometry of high-velocity and metal-poor stars

Cited by 85 publications

References 98 publications

Exploring the Milky Way stellar disk

Exploring the Milky Way stellar disk

Constraining the Milky Way assembly history with Galactic Archaeology

On the relative ages of the α-rich and α-poor stellar populations in the Galactic halo

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