ORCID Profile
0000-0001-8654-9499
Current Organisation
CNRS
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Publisher: EDP Sciences
Date: 10-2012
Publisher: Oxford University Press (OUP)
Date: 04-11-2014
Publisher: American Astronomical Society
Date: 14-10-2015
Publisher: EDP Sciences
Date: 21-12-2018
DOI: 10.1051/0004-6361/201732433
Abstract: Context . The Gaia -ESO Public Spectroscopic Survey using FLAMES at the VLT has obtained high-resolution UVES spectra for a large number of giant stars, allowing a determination of the abundances of the key chemical elements carbon and nitrogen at their surface. The surface abundances of these chemical species are known to change in stars during their evolution on the red giant branch (RGB) after the first dredge-up episode, as a result of the extra mixing phenomena. Aims . We investigate the effects of thermohaline mixing on C and N abundances using the first comparison between the Gaia -ESO survey [C/N] determinations with simulations of the observed fields using a model of stellar population synthesis. Methods . We explore the effects of thermohaline mixing on the chemical properties of giants through stellar evolutionary models computed with the stellar evolution code STAREVOL. We include these stellar evolution models in the Besançon Galaxy model to simulate the [C/N] distributions determined from the UVES spectra of the Gaia -ESO survey and to compare them with the observations. Results . Theoretical predictions including the effect of thermohaline mixing are in good agreement with the observations. However, the field stars in the Gaia -ESO survey with C and N abundance measurements have a metallicity close to solar, where the efficiency of thermohaline mixing is not very large. The C and N abundances derived by the Gaia -ESO survey in open and globular clusters clearly show the impact of thermohaline mixing at low metallicity, which explains the [C/N] value observed in lower mass and older giant stars. Using independent observations of carbon isotopic ratio in clump field stars and open clusters, we also confirm that thermohaline mixing should be taken into account to explain the behaviour of 12 C/ 13 C as a function of stellar age. Conclusions . Overall, the current model including thermohaline mixing is able to reproduce very well the C and N abundances over the whole metallicity range investigated by the Gaia -ESO survey data.
Publisher: American Astronomical Society
Date: 14-08-2017
Publisher: EDP Sciences
Date: 11-2016
Publisher: Cambridge University Press (CUP)
Date: 08-2015
DOI: 10.1017/S1743921316000946
Abstract: Research on the structure and dynamics of the Galactic System covers a large field of research, from formation scenarios to long-term evolution and secular processes. Today we speak of near-field cosmology where the oldest parts of the Galaxy are used to probe back to early times, e.g. studying the chemical signatures of the oldest star clusters and dwarf galaxies to learn about the byproducts of the first stars. Some of the most detailed work relates to the structure of the dark matter and baryons in order to compare with expectation from N-body models. Secular processes have been identified (e.g. stellar migration) where material within the Galaxy is being reorganized by dynamical resonances and feedback processes.
Publisher: American Astronomical Society
Date: 07-04-2014
Publisher: EDP Sciences
Date: 04-2014
Publisher: American Astronomical Society
Date: 28-07-2015
Publisher: Oxford University Press (OUP)
Date: 12-07-2013
DOI: 10.1093/MNRAS/STT927
Publisher: American Astronomical Society
Date: 25-06-2020
Abstract: This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the Southern Hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey and new data from the SPectroscopic IDentification of ERosita Survey programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library “MaStar”). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17).
Publisher: American Astronomical Society
Date: 04-11-2014
Publisher: EDP Sciences
Date: 29-10-2019
DOI: 10.1051/0004-6361/201935369
Abstract: We report the serendipitous discovery of a nitrogen-rich, mildly metal-poor ([Fe/H] = −1.08) giant star in a single-lined spectroscopic binary system found in the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) survey, Data Release 14 (DR14). Previous work has assumed that two percent of halo giants with unusual elemental abundances have been evaporated from globular clusters, but other origins for their abundance signatures, including binary mass transfer, must also be explored. We present the results of an abundance reanalysis of the APOGEE-2 high-resolution near-infrared spectrum of 2M12451043+1217401 with the Brussels Automatic Stellar Parameter (BACCHUS) automated spectral analysis code. We manually re-derive the main element families, namely light elements (C, N), elements (O, Mg, Si), the iron-peak element (Fe), s -process element (Ce), and light odd-Z element (Al). Our analysis confirms the N-rich nature of 2M12451043+1217401, which has a [N/Fe] ratio of +0.69, and shows that the abundances of C and Al are slightly discrepant from those of a typical mildly metal-poor red giant branch star, but exhibit Mg, Si, O and s -process abundances (Ce) of typical field stars. We also detect a particularly large variability in the radial velocity of this star over the period of the APOGEE-2 observations the most likely orbit fit to the radial velocity data has a period of 730.89 ± 106.86 days, a velocity semi- litude of 9.92 ± 0.14 km s −1 , and an eccentricity of ∼0.1276 ± 0.1174. These data support the hypothesis of a binary companion, which has probably been polluted by a now-extinct asymptotic giant branch star.
Publisher: American Astronomical Society
Date: 29-06-2017
Publisher: Oxford University Press (OUP)
Date: 09-2016
Publisher: American Astronomical Society
Date: 29-08-2023
Abstract: We present new maps of the Milky Way disk showing the distribution of metallicity ([Fe/H]), α -element abundances ([Mg/Fe]), and stellar age, using a s le of 66,496 red giant stars from the final data release (DR17) of the Apache Point Observatory Galactic Evolution Experiment survey. We measure radial and vertical gradients, quantify the distribution functions for age and metallicity, and explore chemical clock relations across the Milky Way for the low- α disk, high- α disk, and total population independently. The low- α disk exhibits a negative radial metallicity gradient of −0.06 ± 0.001 dex kpc −1 , which flattens with distance from the midplane. The high- α disk shows a flat radial gradient in metallicity and age across nearly all locations of the disk. The age and metallicity distribution functions shift from negatively skewed in the inner Galaxy to positively skewed at large radius. Significant bimodality in the [Mg/Fe]–[Fe/H] plane and in the [Mg/Fe]–age relation persist across the entire disk. The age estimates have typical uncertainties of ∼0.15 in log(age) and may be subject to additional systematic errors, which impose limitations on conclusions drawn from this s le. Nevertheless, these results act as critical constraints on galactic evolution models, constraining which physical processes played a dominant role in the formation of the Milky Way disk. We discuss how radial migration predicts many of the observed trends near the solar neighborhood and in the outer disk, but an additional more dramatic evolution history, such as the multi-infall model or a merger event, is needed to explain the chemical and age bimodality elsewhere in the Galaxy.
No related grants have been discovered for Annie Robin.