The age of the Milky Way inner halo

Kalirai, Jason

doi:10.1038/nature11062

Cited by 104 publications

(106 citation statements)

References 28 publications

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“…Because these stars most likely belong to the Galactic halo (see below), we used tracks with Z = 0.001. We derived M = 0.54 M for all O(H)-type stars, which agrees well within the error limits with the mean mass of 0.551 ± 0.005 M of H-rich halo white dwarfs (Kalirai 2012).…”

Section: Masses Luminosities and Distancessupporting

confidence: 67%

Radial velocity variable, hot post-AGB stars from the MUCHFUSS project

Reindl¹,

Geier

Kupfer

et al. 2016

A&A

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In the course of the MUCHFUSS project we recently discovered four radial velocity (RV) variable, hot (T eff ≈ 80 000−110 000 K) post-asymptotic giant branch (AGB) stars. Among them, we found the first known RV variable O(He) star, the only second known RV variable PG 1159 close binary candidate, as well as the first two naked (i.e., without planetary nebula (PN)) H-rich post-AGB stars of spectral type O(H) that show significant RV variations. We present a non-LTE spectral analysis of these stars along with one further O(H)-type star whose RV variations were found to be not significant. We also report the discovery of a far-infrared excess in the case of the PG 1159 star. None of the stars in our sample displays nebular emission lines, which can be explained well in terms of a very late thermal pulse evolution in the case of the PG 1159 star. The "missing" PNe around the O(H)-type stars seems strange, since we find that several central stars of PNe have much longer post-AGB times. Besides the non-ejection of a PN, the occurrence of a late thermal pulse, or the re-accretion of the PN in the previous post-AGB evolution offer possible explanations for those stars not harbouring a PN (anymore). In the case of the O(He) star J0757, we speculate that it might have been previously part of a compact He transferring binary system. In this scenario, the mass transfer must have stopped after a certain time, leaving behind a low-mass close companion that may be responsible for the extreme RV shift of 107.0 ± 22.0 km s −1 that was measured within only 31 min.

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Section: Masses Luminosities and Distancessupporting

confidence: 67%

Radial velocity variable, hot post-AGB stars from the MUCHFUSS project

Reindl¹,

Geier

Kupfer

et al. 2016

A&A

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“…This is a fundamental technique in white dwarf research and astrophysics, such as in studies of galactic clusters and the halo (see, e.g., Hansen 1999;Fontaine et al 2001;Dobbie et al 2006;Hansen et al 2007;Kalirai 2012). There is still much interest to improve our understanding of the model atmospheres and the mass-radius relation of DA stars.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic analysis of DA white dwarfs with 3D model atmospheres

Tremblay

Ludwig

Steffen

et al. 2013

A&A

214

334

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We present the first grid of mean three-dimensional (3D) spectra for pure-hydrogen (DA) white dwarfs based on 3D model atmospheres. We use CO 5 BOLD radiation-hydrodynamics 3D simulations instead of the mixing-length theory for the treatment of convection. The simulations cover the effective temperature range of 6000 < T eff (K) < 15 000 and the surface gravity range of 7 < log g < 9 where the large majority of DAs with a convective atmosphere are located. We rely on horizontally averaged 3D structures (over constant Rosseland optical depth) to compute 3D spectra. It is demonstrated that our 3D spectra can be smoothly connected to their 1D counterparts at higher and lower T eff where the 3D effects are small. Analytical functions are provided in order to convert spectroscopically determined 1D effective temperatures and surface gravities to 3D atmospheric parameters. We apply our improved models to well studied spectroscopic data sets from the Sloan Digital Sky Survey and the White Dwarf Catalog. We confirm that the so-called high-log g problem is not present when employing 3D spectra and that the issue was caused by inaccuracies in the 1D mixing-length approach. The white dwarfs with a radiative and a convective atmosphere have derived mean masses that are the same within ∼0.01 M , in much better agreement with our understanding of stellar evolution. Furthermore, the 3D atmospheric parameters are in better agreement with independent T eff and log g values from photometric and parallax measurements.

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“…In this context, the stellar halo is of paramount importance to reveal the early stages of the Milky Way because these stars are mostly very old and metal-poor (e.g. McWilliam 1997; Unavane, Wyse & Gilmore 1996;Helmi 2008;Jofré & Weiss 2011;Kalirai 2012).…”

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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The age of the Milky Way inner halo

Cited by 104 publications

References 28 publications

Radial velocity variable, hot post-AGB stars from the MUCHFUSS project

Radial velocity variable, hot post-AGB stars from the MUCHFUSS project

Spectroscopic analysis of DA white dwarfs with 3D model atmospheres

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

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