Articles de revues : « Stellar chemical abundances »

1

Tanaka, S., S. Kitamoto, T. Suzuki, K. Torii, M. F. Corcoran et W. Waldron. « Chemical Abundances of Early Type Stars ». Symposium - International Astronomical Union 188 (1998) : 224–25. http://dx.doi.org/10.1017/s007418090011486x.

Texte intégral

Résumé :

X-rays from early-type stars are emitted by the corona or the stellar wind. The materials in the surface layer of early-type stars are not contaminated by nuclear reactions in the stellar inside. Therefore, abundance study of the early-type stars provides us an information of the abundances of the original gas. However, the X-ray observations indicate low-metallicity, which is about 0.3 times of cosmic abundances. This fact raises the problem on the cosmic abundances.

Styles APA, Harvard, Vancouver, ISO, etc.

2

de Mijolla, Damien, et Melissa K. Ness. « Measuring Chemical Likeness of Stars with Relevant Scaled Component Analysis ». Astrophysical Journal 926, n^o 2 (1 février 2022) : 193. http://dx.doi.org/10.3847/1538-4357/ac46a0.

Texte intégral

Résumé :

Abstract Identification of chemically similar stars using elemental abundances is core to many pursuits within Galactic archeology. However, measuring the chemical likeness of stars using abundances directly is limited by systematic imprints of imperfect synthetic spectra in abundance derivation. We present a novel data-driven model that is capable of identifying chemically similar stars from spectra alone. We call this relevant scaled component analysis (RSCA). RSCA finds a mapping from stellar spectra to a representation that optimizes recovery of known open clusters. By design, RSCA amplifies factors of chemical abundance variation and minimizes those of nonchemical parameters, such as instrument systematics. The resultant representation of stellar spectra can therefore be used for precise measurements of chemical similarity between stars. We validate RSCA using 185 cluster stars in 22 open clusters in the Apache Point Observatory Galactic Evolution Experiment survey. We quantify our performance in measuring chemical similarity using a reference set of 151,145 field stars. We find that our representation identifies known stellar siblings more effectively than stellar-abundance measurements. Using RSCA, 1.8% of pairs of field stars are as similar as birth siblings, compared to 2.3% when using stellar-abundance labels. We find that almost all of the information within spectra leveraged by RSCA fits into a two-dimensional basis, which we link to [Fe/H] and α-element abundances. We conclude that chemical tagging of stars to their birth clusters remains prohibitive. However, using the spectra has noticeable gain, and our approach is poised to benefit from larger data sets and improved algorithm designs.

Styles APA, Harvard, Vancouver, ISO, etc.

3

Van der Swaelmen, M., V. Hill, F. Primas et A. A. Cole. « Chemical abundances in LMC stellar populations ». Astronomy & ; Astrophysics 560 (décembre 2013) : A44. http://dx.doi.org/10.1051/0004-6361/201321109.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

4

Pompéia, L., V. Hill, M. Spite, A. Cole, F. Primas, M. Romaniello, L. Pasquini, M. R. Cioni et T. Smecker Hane. « Chemical abundances in LMC stellar populations ». Astronomy & ; Astrophysics 480, n^o 2 (9 janvier 2008) : 379–95. http://dx.doi.org/10.1051/0004-6361:20064854.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

5

Leckrone, David S., Sveneric Johansson, Glenn M. Wahlgren, Charles R. Proffitt et Tomas Brage. « Stellar chemical abundances with the GHRS ». Physica Scripta T65 (1 janvier 1996) : 110–14. http://dx.doi.org/10.1088/0031-8949/1996/t65/015.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

6

Moya, A., L. M. Sarro, E. Delgado-Mena, W. J. Chaplin, V. Adibekyan et S. Blanco-Cuaresma. « Stellar dating using chemical clocks and Bayesian inference ». Astronomy & ; Astrophysics 660 (avril 2022) : A15. http://dx.doi.org/10.1051/0004-6361/202141125.

Texte intégral

Résumé :

Context. Dating stars is a major challenge with a deep impact on many astrophysical fields. One of the most promising techniques for this is using chemical abundances. Recent space- and ground-based facilities have improved the quantity of stars with accurate observations. This has opened the door for using Bayesian inference tools to maximise the information we can extract from them. Aims. Our aim is to present accurate and reliable stellar age estimates of FGK stars using chemical abundances and stellar parameters. Methods. We used one of the most flexible Bayesian inference techniques (hierarchical Bayesian models) to exceed current possibilities in the use of chemical abundances for stellar dating. Our model is a data-driven model. We used a training set that has been presented in the literature with ages estimated with isochrones and accurate stellar abundances and general characteristics. The core of the model is a prescription of certain abundance ratios as linear combinations of stellar properties including age. We gathered four different testing sets to assess the accuracy, precision, and limits of our model. We also trained a model using chemical abundances alone. Results. We found that our age estimates and those coming from asteroseismology, other accurate sources, and also with ten Gaia benchmark stars agree well. The mean absolute difference of our estimates compared with those used as reference is 0.9 Ga, with a mean difference of 0.01 Ga. When using open clusters, we reached a very good agreement for Hyades, NGC 2632, Ruprecht 147, and IC 4651. We also found outliers that are a reflection of chemical peculiarities and/or stars at the limit of the validity ranges of the training set. The model that only uses chemical abundances shows slightly worse mean absolute difference (1.18 Ga) and mean difference (−0.12 Ga).

Styles APA, Harvard, Vancouver, ISO, etc.

7

Sbordone, L., L. Monaco, S. Duffau, P. Bonifacio et E. Caffau. « A wide angle chemical survey of the Sagittarius dwarf Spheroidal galaxy ». Proceedings of the International Astronomical Union 14, S344 (août 2018) : 42–45. http://dx.doi.org/10.1017/s1743921318006804.

Texte intégral

Résumé :

AbstractWe present the status of an ongoing project to map the detailed chemical abundances of stars across the main body of the Sagittarius dwarf Spheroidal galaxy (Sgr dSph). The Sgr dSph is the closest known dwarf galaxy, and is being tidally destroyed by its interaction with the Milky Way (MW), leaving behind a massive stellar stream. Sgr dSph is a chemically outstanding object, with peculiar abundance ratios, clear center-outskirts abundance gradients, and spanning more than 3 orders of magnitude in metallicity. We present here detailed abundances from UVES@VLT spectra for more than 50 giants across 8 fields along the major and minor axes of Sgr dSph, and 5 more outside the galaxy main body, but possibly associated to its stellar stream.

Styles APA, Harvard, Vancouver, ISO, etc.

8

Tolstoy, Eline, et Kim Venn. « Stellar Abundances in Local Group Galaxies ». Highlights of Astronomy 13 (2005) : 548–53. http://dx.doi.org/10.1017/s1539299600016567.

Texte intégral

Résumé :

AbstractHere we describe some of our latest results from measuring detailed abundances in Local Group dwarf galaxies with the VLT. Combining spectroscopic abundances with Color-Magnitude diagrams allows the effective measurement of detailed chemical evolution with time in these galaxies. Although there are not yet significant numbers of individual stars observed in local group dwarf galaxies, the uniformity of the abundance patterns of the majority of stars in galaxies with very different star formation histories must hint at general properties of all star formation in these small systems.

Styles APA, Harvard, Vancouver, ISO, etc.

9

Matteucci, Francesca. « Chemical enrichment and feedback in low metallicity environments : constraints on galaxy formation ». Proceedings of the International Astronomical Union 4, S255 (juin 2008) : 134–41. http://dx.doi.org/10.1017/s1743921308024708.

Texte intégral

Résumé :

AbstractChemical evolution models for dwarf metal poor galaxies, including dwarf irregulars and dwarf spheroidals will be presented. The main ingredients necessary to build detailed models of chemical evolution including stellar nucleosynthesis, supernova progenitors, stellar lifetimes and stellar feedback will be discussed. The stellar feedback will be analysed in connection with the development of galactic winds in dwarf galaxies and their effects on the predicted abundances and abundance ratios. Model results concerning α-elements (O, Mg, Si, Ca), Fe and s-and r-process elements will be discussed and compared with the most recent observational data for metal poor galaxies of the Local Group. We will show how the study of abundance ratios versus abundances can represent a very powerful tool to infer constraints on galaxy formation mechanisms. In this framework, we will discuss whether, on the basis of their chemical properties, the dwarf galaxies of the Local Group could have been the building blocks of the Milky Way.

Styles APA, Harvard, Vancouver, ISO, etc.

10

Patrick, Lee R., Chris J. Evans, Ben Davies, Rolf-Peter Kudritzki, Maria Bergemann et Annette N. M. Ferguson. « Red Supergiants as Chemical Abundance Probes : The Local Group dwarf NGC6822 ». Proceedings of the International Astronomical Union 14, S344 (août 2018) : 213–16. http://dx.doi.org/10.1017/s174392131800649x.

Texte intégral

Résumé :

AbstractRed Supergiant Stars (RSGs) are important probes of stellar and chemical evolution in star-forming environments. They represent the brightest near-IR stellar components of external galaxies and probe the most recent stellar population to provide robust, independent abundance estimates. The Local Group dwarf irregular galaxy, NGC6822, is a reasonably isolated galaxy with an interesting structure and turbulent history. Using RSGs as chemical abundance probes, we estimate metallicities in the central region of NGC6822, finding a suggestion of a metallicity gradient (in broad agreement with nebular tracers), however, this requires further study for confirmation. With intermediate resolution Multi-object spectroscopy (from e.g. KMOS, EMIR, MOSFIRE) combined with state-of-the-art stellar model atmospheres, we demonstrate how RSGs can be used to estimate stellar abundances in external galaxies. In this context, we compare stellar and nebular abundance tracers in NGC 6822 and by combining stellar and nebular tracers we estimate an abundance gradient of −0.18 ± 0.05 dex/kpc.

Styles APA, Harvard, Vancouver, ISO, etc.

11

Venn, Kim A., Andreas Kaufer, Eline Tolstoy, Rolf-Peter Kudritzki, Norbert Przybilla, Stephen J. Smartt et Daniel J. Lennon. « Chemical abundances of massive stars in Local Group galaxies ». Symposium - International Astronomical Union 212 (2003) : 30–37. http://dx.doi.org/10.1017/s0074180900211613.

Texte intégral

Résumé :

The relative abundances of elements in galaxies can provide valuable information on the stellar and chemical evolution of a galaxy. While nebulae can provide abundances for a variety of light elements, stars are the only way to directly determine the abundances of iron-group and s-process and r-process elements in a galaxy. The new 8m and 10m class telescopes and high-efficiency spectrographs now make high-quality spectral observations of bright supergiants possible in dwarf galaxies in the Local Group. We have been concentrating on elemental abundances in the metal-poor dwarf irregular galaxies, NGC 6822, WLM, Sextants A, and GR 8. Comparing abundance ratios to those predicted from their star formation histories, determined from color-magnitude diagrams, and comparing those ratios between these galaxies can give us new insights into the evolution of these dwarf irregular galaxies. Iron-group abundances also allow us to examine the metallicities of the stars in these galaxies directly, which affects their inferred mass loss rates and predicted stellar evolution properties.

Styles APA, Harvard, Vancouver, ISO, etc.

12

Casali, G., L. Magrini, A. Frasca, A. Bragaglia, G. Catanzaro, V. D’Orazi, R. Sordo et al. « Stellar Population Astrophysics (SPA) with TNG ». Astronomy & ; Astrophysics 643 (27 octobre 2020) : A12. http://dx.doi.org/10.1051/0004-6361/202039176.

Texte intégral

Résumé :

Context. Open clusters are excellent tracers of the chemical evolution of the Galactic disc. The spatial distribution of their elemental abundances, through the analysis of high-quality and high-resolution spectra, provides insight into the chemical evolution and mechanisms of element nucleosynthesis in regions characterised by different conditions (e.g. star formation efficiency and metallicity). Aims. In the framework of the Stellar Population Astrophysics (SPA) project, we present new observations and spectral analysis of four sparsely studied open clusters located in the solar neighbourhood, namely Collinder 350, Gulliver 51, NGC 7044, and Ruprecht 171. Methods. We exploit the HARPS-N spectrograph at the TNG telescope to acquire high-resolution optical spectra for 15 member stars of four clusters. We derive stellar parameters (Teff, log g, [Fe/H] and ξ) using both the equivalent width (EW) analysis and the spectral fitting technique. We compute elemental abundances for light, α-, iron-peak, and n-capture elements using the EW measurement approach. We investigate the origin of the correlation between metallicity and stellar parameters derived with the EW method for the coolest stars of the sample (Teff < 4300 K). The correlation is likely due to the challenging continuum setting and to a general inaccuracy of model atmospheres used to reproduce the conditions of very cool giant stars. Results. We locate the properties of our clusters in the radial distributions of metallicity and abundance ratios, comparing our results with clusters from the Gaia-ESO and APOGEE surveys. We present the [X/Fe]−[Fe/H] and [X/Fe]−RGC trends for elements in common between the two surveys. Finally, we derive the C and Li abundances as a function of the evolutionary phase and compare them with theoretical models. Conclusions. The SPA survey, with its high-resolution spectra, allows us to fully characterise the chemistry of nearby clusters. With a single set of spectra, we provide chemical abundances for a variety of chemical elements, which are comparable to those obtained in two of the largest surveys combined. The metallicities and abundance ratios of our clusters fit very well in the radial distributions defined by the recent literature, reinforcing the importance of star clusters to outline the spatial distribution of abundances in our Galaxy. Moreover, the abundances of C and Li, modified by stellar evolution during the giant phase, agree with evolutionary prescriptions (rotation-induced mixing) for their masses and metallicities.

Styles APA, Harvard, Vancouver, ISO, etc.

13

Bresolin, Fabio. « Stellar vs. Hii region chemical abundances in nearby galaxies ». Proceedings of the International Astronomical Union 5, S265 (août 2009) : 233–36. http://dx.doi.org/10.1017/s1743921310000621.

Texte intégral

Résumé :

AbstractWe have obtained new spectrophotometric data for 28 Hii regions in the spiral galaxy NGC 300, a member of the nearby Sculptor Group. The detection of several auroral lines has allowed us to measure electron temperatures and direct chemical abundances for the whole sample. We determine for the first time in this galaxy a radial gas-phase oxygen abundance gradient based solely on auroral lines. The gradient corresponds to −0.077±0.006 dex kpc−1, which agrees very well with the galactocentric trend in metallicity obtained for 29 B and A supergiants in the same galaxy. The intercept of the regression for the nebular data virtually coincides with the intercept obtained from the stellar data. This result provides increased confidence on the direct method to determine extragalactic nebular abundances.

Styles APA, Harvard, Vancouver, ISO, etc.

14

Ishigaki, Miho N., Wako Aoki et Masashi Chiba. « Chemical differences and similarities among the kinematically selected thick disk, inner halo and outer halo stars ». Proceedings of the International Astronomical Union 9, S298 (mai 2013) : 71–76. http://dx.doi.org/10.1017/s1743921313006224.

Texte intégral

Résumé :

AbstractChemical diversity among metal-poor stars in the old stellar components in the Milky Way (MW), namely the thick disk and stellar halo, provides clues to understanding the early chemodynamical evolution of our Galaxy. We present our results on a homogeneous chemical abundance analysis for nearby metal-poor stars likely belonging to the MW thick disk, inner and outer stellar halos. Abundances of alpha, sodium, iron-peak and neutron-capture elements in the sample stars have been estimated using high-resolution (R 50000) spectra obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. The derived abundances are used to examine differences and similarities in elemental abundance ratios among the kinematically defined thick disk, inner and outer halo subsamples in the metallicity range of −3.3 < [Fe/H] < −0.5. We show that, in the metallicity range of [Fe/H] < −2, the three subsamples are similar in most of the elemental abundances. On the other hand, in the higher metallicities, particularly in [Fe/H] > −1.5, the thick disk and the inner/outer halo subsamples show systematically different abundance ratios for some elements including alpha, sodium, zinc and europium. A modest difference in the sodium and zinc abundances between the inner- and outer halo subsamples is also identified. The observed distinct abundances of some elements among the three subsamples implies that their constituent stars originally formed in progenitor systems that have experienced different star formation and chemical enrichment histories.

Styles APA, Harvard, Vancouver, ISO, etc.

15

Deal, M., M. J. Goupil, J. P. Marques, D. R. Reese et Y. Lebreton. « Chemical mixing in low mass stars ». Astronomy & ; Astrophysics 633 (24 décembre 2019) : A23. http://dx.doi.org/10.1051/0004-6361/201936666.

Texte intégral

Résumé :

Context. When modelling stars with masses higher than 1.2 M⊙ with no observed chemical peculiarity, atomic diffusion is often neglected because, on its own, it causes unrealistic surface abundances compared with those observed. The reality is that atomic diffusion is in competition with other transport processes. Rotation is one of the processes able to prevent excessively strong surface abundance variations. Aims. The purpose of this study is to quantify the opposite or conjugated effects of atomic diffusion (including radiative acceleration) and rotationally induced mixing in stellar models of low mass stars, and to assess whether rotational mixing is able to prevent the strong abundance variations induced by atomic diffusion in F-type stars. Our second goal is to estimate the impact of neglecting both rotational mixing and atomic diffusion in stellar parameter inferences for stars with masses higher than 1.3 M⊙. Methods. Using the Asteroseismic Inference on a Massive Scale (AIMS) stellar parameter inference code, we infer the masses and ages of a set of representative artificial stars for which models were computed with the Code d’Evolution Stellaire Adaptatif et Modulaire (CESTAM; the T stands for Transport) evolution code, taking into account rotationally induced mixing and atomic diffusion, including radiative acceleration. The observed constraints are asteroseismic and classical properties. The grid of stellar models used for the optimization search include neither atomic diffusion nor rotationally induced mixing. The differences between real and retrieved parameters then provide an estimate of the errors made when neglecting transport processes in stellar parameter inference. Results. We show that for masses lower than 1.3 M⊙, rotation dominates the transport of chemical elements and strongly reduces the effect of atomic diffusion, with net surface abundance modifications similar to solar values. At higher mass, atomic diffusion and rotation are competing equally. Above 1.44 M⊙, atomic diffusion dominates in stellar models with initial rotation lower than 80 km s−1 producing a chemical peculiarity which is not observed in Kepler Legacy stars. This indicates that a transport process of chemical elements is missing, probably linked to the missing transport process of angular momentum needed to explain rotation profiles in solar-like stars. Importantly, neglecting rotation and atomic diffusion (including radiative acceleration) in the models, when inferring the parameters of F-type stars, may lead to respective errors of ≈5%, ≈2.5%, and ≈25% for stellar masses, radii, and ages. Conclusions. Atomic diffusion (including radiative acceleration) and rotational mixing should be taken into account in stellar models in order to determine accurate stellar parameters. When atomic diffusion and shellular rotation are both included, they enable stellar evolution codes to reproduce the observed metal and helium surface abundances for stars with masses up to 1.4 M⊙ at solar metallicity. However, if rotation is actually uniform for these stars (as observations seem to indicate), then an additional chemical mixing process is needed together with a revised formulation of rotational mixing. For higher masses, an additional mixing process is needed in any case.

Styles APA, Harvard, Vancouver, ISO, etc.

16

De Silva, G. M., K. C. Freeman et J. Bland-Hawthorn. « Chemically tagging the Galactic disk : abundance patterns of old open clusters ». Proceedings of the International Astronomical Union 4, S254 (juin 2008) : 133–38. http://dx.doi.org/10.1017/s1743921308027506.

Texte intégral

Résumé :

AbstractThe long term goal of large-scale chemical tagging is to use stellar elemental abundances as a tracer of dispersed substructures of the Galactic disk. The identification of such lost stellar aggregates and exploring their chemical properties will be key in understanding the formation and evolution of the disk. Present day stellar structures such as open clusters and moving groups are the ideal testing grounds for the viability of chemical tagging, as they are believed to be the remnants of the original larger star-forming aggregates. We examine recent high resolution abundance studies of open clusters to explore the various abundance trends and reassess the prospects of large-scale chemical tagging.

Styles APA, Harvard, Vancouver, ISO, etc.

17

Boeche, Corrado. « The RAVE harvest : from the relation between abundances and kinematic of the Milky Way stars to tools for the abundance analysis of the spectra ». Proceedings of the International Astronomical Union 9, S298 (mai 2013) : 292–97. http://dx.doi.org/10.1017/s1743921313006480.

Texte intégral

Résumé :

AbstractRAVE is a spectroscopic survey of the Milky Way which collected more than 500,000 stellar spectra of nearby stars in the Galaxy. The RAVE consortium analysed these spectra to obtain radial velocities, stellar parameters and chemical abundances. These data, together with spatial and kinematic information like positions, proper motions, and distance estimations, make the RAVE database a rich source for galactic archaeology. I present recent investigations on the chemo-kinematic relations and chemical gradients in the Milky Way disk using RAVE data and compare our results with the Besançon models. I also present the code SPACE, an evolution of the RAVE chemical pipeline, which integrates the measurements of stellar parameters and chemical abundances in one single process.

Styles APA, Harvard, Vancouver, ISO, etc.

18

Mao, Junjie, Jelle de Plaa, Jelle S. Kaastra, Ciro Pinto, Liyi Gu, François Mernier, Hong-Liang Yan, Yu-Ying Zhang et Hiroki Akamatsu. « Nitrogen abundance in the X-ray halos of clusters and groups of galaxies ». Astronomy & ; Astrophysics 621 (19 décembre 2018) : A9. http://dx.doi.org/10.1051/0004-6361/201730931.

Texte intégral

Résumé :

Context. Chemical abundances in the X-ray halos (also known as the intracluster medium, ICM) of clusters and groups of galaxies can be measured via prominent emission line features in their X-ray spectra. Elemental abundances are footprints of time-integrated yields of various stellar populations that have left their specific abundance patterns prior to and during the cluster and group evolution. Aim. We aim to constrain nitrogen abundances in the CHEmical Evolution RGS Sample (CHEERS), which contains 44 nearby groups and clusters of galaxies, to gain a better understanding of their chemical enrichment. Method. We examined the high-resolution spectra of the CHEERS sample and took various systematic effects in the spectral modelling into account. We compared the observed abundance ratios with those in the Galactic stellar populations and also with predictions from stellar yields (low- and intermediate-mass stars, massive stars, and degenerate stars). Results. The nitrogen abundance can only be well constrained (≳3σ) in one cluster of galaxies and seven groups of galaxies. The [O/Fe] – [Fe/H] relation of the ICM is comparable to that for the Galaxy, while the [N/Fe] and [N/O] ratios of the ICM are both higher than in the Galaxy. Future studies on nitrogen radial distributions are required to tell whether the obtained higher [N/Fe] and [N/O] ratios are biased as a result of the small extraction region (r/r500 ≲ 0.05) that we adopt here. Since abundances of odd-Z elements are more sensitive to the initial metallicity of stellar populations, accurate abundance measurements of N, Na, and Al are required to better constrain the chemical enrichment in the X-ray halos of clusters and groups of galaxies.

Styles APA, Harvard, Vancouver, ISO, etc.

19

Yushchenko, V., V. Gopka, A. V. Yushchenko, A. Shavrina, Ya Pavlenkо et S. Vasil’eva. « ACTINIUM ABUNDANCES IN STELLAR ATMOSPHERES ». Odessa Astronomical Publications 34 (3 décembre 2021) : 70–73. http://dx.doi.org/10.18524/1810-4215.2021.34.244288.

Texte intégral

Résumé :

This paper presents a study of radioactive actinium in the atmospheres of stars located in galaxies with different chemical evolution history – namely, Przybylski's Star (HD 101065) in the Milky Way and the red supergiant PMMR27 in the Small Magellanic Cloud; it also reports the findings of the previous research of the red supergiant RM 1-667 in the Large Magellanic Cloud and the red giant BL138 in the Fornax dwarf spheroidal galaxy. The actinium abundance is close to that of uranium in the atmospheres of certain stars in the Milky Way’s halo and in the atmosphere of Arcturus. The following actinium abundances have been obtained (in a scale of lg N(H) = 12): for the red supergiants PMMR27 and RM 1- 667 lg N(Ac) = -1.7 and lg N(Ac) = -1.3, respectively, and for the red giant BL138 lg N(Ac) = -1.6. The actinium abundance in the atmosphere of Przybylski's Star (HD 101065) is lg N(Ac) = `0.94±0.09, which is more than two orders of magnitude higher than those in the atmospheres of the other studied stars.

Styles APA, Harvard, Vancouver, ISO, etc.

20

Swastik, C., Ravinder K. Banyal, Mayank Narang, P. Manoj, T. Sivarani, S. P. Rajaguru, Athira Unni et Bihan Banerjee. « Galactic Chemical Evolution of Exoplanet Hosting Stars : Are High-mass Planetary Systems Young ? » Astronomical Journal 164, n^o 2 (19 juillet 2022) : 60. http://dx.doi.org/10.3847/1538-3881/ac756a.

Texte intégral

Résumé :

Abstract The imprints of stellar nucleosynthesis and chemical evolution of the galaxy can be seen in different stellar populations, with older generation stars showing higher α-element abundances and the later generations becoming enriched with iron-peak elements. The evolutionary connections and chemical characteristics of circumstellar disks, stars, and their planetary companions can be inferred by studying the interdependence of planetary and host star properties. Numerous studies in the past have confirmed that high-mass giant planets are commonly found around metal-rich stars, while the stellar hosts of low-mass planets have a wide range of metallicity. In this work, we analyzed the detailed chemical abundances for a sample of >900 exoplanet hosting stars drawn from different radial velocity and transit surveys. We correlate the stellar abundance trends for α- and iron-peak elements with the planets’ mass. We find the planet mass–abundance correlation to be primarily negative for α-elements and marginally positive or zero for the iron-peak elements, indicating that stars hosting giant planets are relatively younger. This is further validated by the age of the host stars obtained from isochrone fitting. The later enrichment of protoplanetary material with iron and iron-peak elements is also consistent with the formation of the giant planets via the core accretion process. A higher metal fraction in the protoplanetary disk is conducive to rapid core growth, thus providing a plausible route for the formation of giant planets. This study, therefore, indicates that the observed trends in stellar abundances and planet mass are most likely a natural consequence of Galactic chemical evolution.

Styles APA, Harvard, Vancouver, ISO, etc.

21

Tissera, P. B., et D. G. Lambas. « Chemical Abundances and Hierarchical Clustering ». Symposium - International Astronomical Union 217 (2004) : 264–65. http://dx.doi.org/10.1017/s0074180900197682.

Texte intégral

Résumé :

In this contribution we study the chemical enrichment of the interstellar medium and stellar population of the building blocks of current typical galaxies in the field, in cosmological hydrodynamics simulations. The simulations include detailed modeling of chemical enrichment by SNIa and SNII In our simulations the missing metal problem is caused by chemical elements being locked up in stars, in the central regions (or bulges) mainly. Supernova energy feedback could help to reduce this concentration by expelling metals to the intergalactic medium.

Styles APA, Harvard, Vancouver, ISO, etc.

22

Semenova, Ekaterina, Maria Bergemann, Morgan Deal, Aldo Serenelli, Camilla Juul Hansen, Andrew J. Gallagher, Amelia Bayo et al. « The Gaia-ESO survey : 3D NLTE abundances in the open cluster NGC 2420 suggest atomic diffusion and turbulent mixing are at the origin of chemical abundance variations ». Astronomy & ; Astrophysics 643 (novembre 2020) : A164. http://dx.doi.org/10.1051/0004-6361/202038833.

Texte intégral

Résumé :

Context. Atomic diffusion and mixing processes in stellar interiors influence the structure and the surface composition of stars. Some of these processes cannot yet be modelled from the first principles, and they require calibrations. This limits their applicability in stellar models used for studies of stellar populations and Galactic evolution. Aims. Our main goal is to put constraints on the stellar structure and evolution models using new refined measurements of the chemical composition in stars of a Galactic open cluster. Methods. We used medium-resolution, 19 200 ≤ R ≤ 21 500, optical spectra of stars in the open cluster NGC 2420 obtained within the Gaia-ESO survey. The sample covers all evolutionary stages from the main sequence to the red giant branch. Stellar parameters were derived using a combined Bayesian analysis of spectra, 2MASS photometry, and astrometric data from Gaia DR2. The abundances of Mg, Ca, Fe, and Li were determined from non-local thermodynamic equilibrium (NLTE) synthetic spectra, which were computed using one-dimensional (1D) and averaged three-dimensional (3D) model atmospheres. We compare our results with a grid of Code d’Evolution Stellaire Adaptatif et Modulaire (CESTAM) stellar evolution models, which include atomic diffusion, turbulent, and rotational mixing. Results. We find prominent evolutionary trends in the abundances of Fe, Ca, Mg, and Li with the mass of the stars in the cluster. Furthermore, Fe, Mg, and Ca show a depletion at the cluster turn-off, but the abundances gradually increase and flatten near the base of the red giant branch. The abundance trend for Li displays a signature of rotational mixing on the main sequence and abrupt depletion on the sub-giant branch, which is caused by advection of Li-poor material to the surface. The analysis of abundances combined with the CESTAM model predictions allows us to place limits on the parameter space of the models and to constrain the zone in the stellar interior, where turbulent mixing takes place.

Styles APA, Harvard, Vancouver, ISO, etc.

23

Boeche, C., A. Vallenari et S. Lucatello. « SP_Ace v1.4 and the new GCOG library for deriving stellar parameters and elemental abundances ». Astronomy & ; Astrophysics 645 (janvier 2021) : A35. http://dx.doi.org/10.1051/0004-6361/202038973.

Texte intégral

Résumé :

Context. Ongoing and future massive spectroscopic surveys will collect very large numbers (106–107) of stellar spectra that need to be analyzed. Highly automated software is needed to derive stellar parameters and chemical abundances from these spectra. Aims. We present the new version of SP_Ace (Stellar Parameters And Chemical abundances Estimator) a code that derives stellar parameters and elemental abundance from stellar spectra. The new version covers a larger spectral resolution interval (R = 2000−40 000) and its new library covers bluer wavelengths (4800–6860 Å). Methods. SP_Ace relies on the General-Curve-Of-Growth (GCOG) library based on 6700 absorption lines whose oscillator strengths were calibrated astrophysically. We developed the calibration method and applied it to all the lines. From the new line list obtained we build the GCOG library, adopting an improved method to correct for the opacity of the neighboring lines. We implemented a new line profile for the code SP_Ace that better reproduces that of synthetic spectra. This new version of SP_Ace and the GCOG library has been tested on synthetic and real spectra to establish the accuracy and precision of the derived stellar parameters. Results. SP_Ace can derive the stellar parameters Teff, log g, [M/H], and chemical abundances with satisfactory results; the accuracy depends on the spectral features that determine the quality, such as spectral resolution, signal-to-noise ratio, and wavelength coverage. Systematic errors were identified and quantified where possible. The source code is publicly available.

Styles APA, Harvard, Vancouver, ISO, etc.

24

Mena, E. Delgado, M. Tsantaki, V. Zh. Adibekyan, S. G. Sousa, N. C. Santos, J. I. González Hernández et G. Israelian. « Abundance ratios & ; ages of stellar populations in HARPS-GTO sample ». Proceedings of the International Astronomical Union 12, S330 (avril 2017) : 156–59. http://dx.doi.org/10.1017/s1743921317006081.

Texte intégral

Résumé :

AbstractIn this work we present chemical abundances of heavy elements (Z>28) for a homogeneous sample of 1059 stars from HARPS planet search program. We also derive ages using parallaxes from Hipparcos and Gaia DR1 to compare the results. We study the [X/Fe] ratios for different populations and compare them with models of Galactic chemical evolution. We find that thick disk stars are chemically disjunt for Zn adn Eu. Moreover, the high-alpha metal-rich population presents an interesting behaviour, with clear overabundances of Cu and Zn and lower abundances of Y and Ba with respect to thin disk stars. Several abundance ratios present a significant correlation with age for chemically separated thin disk stars (regardless of their metallicity) but thick disk stars do not present that behaviour. Moreover, at supersolar metallicities the trends with age tend to be weaker for several elements.

Styles APA, Harvard, Vancouver, ISO, etc.

25

Wang, Liang, Yujuan Liu, Gang Zhao et Bun'ei Sato. « Stellar Parameters and Chemical Abundances of G Giants ». Publications of the Astronomical Society of Japan 63, n^o 5 (25 octobre 2011) : 1035–46. http://dx.doi.org/10.1093/pasj/63.5.1035.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

26

Walton, N. A., J. R. Walsh, G. Jacoby et R. F. Peletier. « The chemical abundances of Planetary Nebulae in Centaurus-A (NGC 5128) ». Symposium - International Astronomical Union 180 (1997) : 478. http://dx.doi.org/10.1017/s0074180900131808.

Texte intégral

Résumé :

Abundances in early-type galaxies are measured from the analysis of stellar spectra (e.g. colour indices, Peletier et al, 1990). The presence of many planetary nebulae (PN) in early-type galaxies provides an independent measure of abundances for the old stellar population and allows the spread in abundances to be sampled at a range of galacto-centric distances. PN are feasible for this project since the nebular O, Ne and S abundances in most PN reflect that of the progenitor star.

Styles APA, Harvard, Vancouver, ISO, etc.

27

Jugaku, Jun. « Main Sequence Abundances : Observational Aspects ». International Astronomical Union Colloquium 108 (1988) : 2. http://dx.doi.org/10.1017/s0252921100093313.

Texte intégral

Résumé :

AbstractAlthough once it was thought that main-sequence stars are remarkably homogeneous with respect to their chemical composition, the upper main-sequence stars (30000 > Te > 7000) show a variaety of chemically peculiar stars besides the so-called normal stars. Those include the Am, Ap, λ Bootis, He-deficient, and He-rich stars. This review summarizes the current data, which are necessary to construct and test the theoretical models of these stars. In the second half of the review we concentrate on Li. In the lower main-sequecnce stars abundances of Li have been determined in hundreds of stars. Some of the remarkable results are: (1) A uniform upper abundance value irrespective of stellar effective temperature, (2) abundance gap in the F stars of the Hyades, and (3) increasing depletion with smaller stellar mass for the Hyades.

Styles APA, Harvard, Vancouver, ISO, etc.

28

Liu, F., M. Asplund, D. Yong, S. Feltzing, A. Dotter, J. Meléndez et I. Ramírez. « Chemical (in)homogeneity and atomic diffusion in the open cluster M 67 ». Astronomy & ; Astrophysics 627 (juillet 2019) : A117. http://dx.doi.org/10.1051/0004-6361/201935306.

Texte intégral

Résumé :

Context. The benchmark open cluster M 67 is known to have solar metallicity and an age similar to that of the Sun. It thus provides us with a great opportunity to study the properties of solar twins, as well as the evolution of Sun-like stars. Aims. Previous spectroscopic studies of M 67 reported possible subtle changes in stellar surface abundances throughout the stellar evolutionary phase, namely the effect of atomic diffusion. In this study we attempt to confirm and quantify more precisely the effect of atomic diffusion, and to explore the level of chemical (in)homogeneity in M 67. Methods. We presented a strictly line-by-line differential chemical abundance analysis of two groups of stars in M 67: three turn-off stars and three subgiants. Stellar atmospheric parameters and elemental abundances were obtained with very high precision using the Keck/HIRES spectra. Results. The subgiants in our sample show negligible abundance variations (≤0.02 dex), which implies that M 67 was born chemically homogeneous. We note that there is a significant abundance difference (~0.1–0.2 dex) between subgiants and turn-off stars, which can be interpreted as the signature of atomic diffusion. Qualitatively stellar models with diffusion agree with the observed abundance results. Some turn-off stars do not follow the general pattern, which suggests that in some cases diffusion can be inhibited, or they might have undergone some sort of mixing event related to planets. Conclusions. Our results pose additional challenges for chemical tagging when using turn-off stars. In particular, the effects of atomic diffusion, which could be as large as 0.1–0.2 dex, must be taken into account in order for chemical tagging to be successfully applied.

Styles APA, Harvard, Vancouver, ISO, etc.

29

Hinkel, Natalie R., Patrick A. Young et Caleb H. Wheeler III. « A Concise Treatise on Converting Stellar Mass Fractions to Abundances to Molar Ratios ». Astronomical Journal 164, n^o 6 (18 novembre 2022) : 256. http://dx.doi.org/10.3847/1538-3881/ac9bfa.

Texte intégral

Résumé :

Abstract Understanding stellar composition is fundamental not only to our comprehension of the Galaxy, especially chemical evolution, but it can also shed light on the interior structure and mineralogy of exoplanets, which are formed from the same material as their host stars. Unfortunately, the underlying mathematics describing stellar mass fractions and stellar elemental abundances is difficult to parse, is fragmented across the literature, and contains vexing omissions that makes any calculation far from trivial, especially for nonexperts. In this treatise, we present a clear mathematical formalism and clarification of inherent assumptions and normalizations within stellar composition measurements, which facilitates the conversion from stellar mass fractions to elemental abundances to molar ratios, including error propagation. We also provide an example case study of HIP 544 to further illustrate the provided equations. Given the important chemical association between stars, as well as the interdisciplinary relationship between stars and their planets, it is vital that stellar mass fractions and abundance data be more transparent and accessible to people within different subfields and scientific disciplines.

Styles APA, Harvard, Vancouver, ISO, etc.

30

Truran, James W. « Chemical Evolution of Galaxies : Abundance Trends and Implications ». Symposium - International Astronomical Union 145 (1991) : 13–19. http://dx.doi.org/10.1017/s0074180900227228.

Texte intégral

Résumé :

Recent spectroscopic studies of the elemental abundance patterns associated with extremely metal deficient field halo stars and globular cluster stars are briefly reviewed. These metal deficient stellar populations have been found to be characterized by abundance patterns which differ quite distinctly from those of solar system abundances, but are consistent with the view that they reflect primarily the nucleosynthesis products of the evolution of massive stars and associated Type II supernovae. Guided by our current knowledge of nucleosynthesis as a function of stellar mass occurring in stars and supernovae, we identify some interesting constraints upon theories of the formation and early history of our Galaxy.

Styles APA, Harvard, Vancouver, ISO, etc.

31

Costa, Roberto D. D., Walter J. Maciel et Thais E. P. Idiart. « Primordial helium abundance of the SMC : a view from intermediate mass stars ». Proceedings of the International Astronomical Union 5, S268 (novembre 2009) : 173–74. http://dx.doi.org/10.1017/s1743921310004047.

Texte intégral

Résumé :

AbstractHelium abundances were derived for a sample of planetary nebulae of the Small Magellanic Cloud. These abundances were corrected from the chemical evolution of the galaxy as well as from stellar nucleosynthesis, and the primordial helium abundance then was estimated for the sample. Results indicate that the resulting average value for the sample is consistent with the expected values for primordial helium from SBBN and other values derived from HII regions in different stellar systems, even varying the enrichment ratio within its uncertainty range.

Styles APA, Harvard, Vancouver, ISO, etc.

32

De Silva, G. M., K. C. Freeman et J. Bland-Hawthorn. « Reconstructing Fossil Sub-structures of the Galactic Disk : Clues from Abundance Patterns of Old Open Clusters and Moving Groups ». Publications of the Astronomical Society of Australia 26, n^o 1 (2009) : 11–16. http://dx.doi.org/10.1071/as08019.

Texte intégral

Résumé :

AbstractThe long term goal of large-scale chemical tagging is to use stellar elemental abundances as a tracer of dispersed substructures of the Galactic disk. The identification of such lost stellar aggregates and the exploration of their chemical properties will be key in understanding the formation and evolution of the disk. Present day stellar structures such as open clusters and moving groups are the ideal testing grounds for the viability of chemical tagging, as they are believed to be the remnants of the original larger star-forming aggregates. Until recently, high accuracy elemental abundance studies of open clusters and moving groups having been lacking in the literature. In this paper we examine recent high resolution abundance studies of open clusters to explore the various abundance trends and reasses the prospects of large-scale chemical tagging.

Styles APA, Harvard, Vancouver, ISO, etc.

33

Fanelli, C., L. Origlia, E. Oliva, E. Dalessandro, A. Mucciarelli et N. Sanna. « Stellar population astrophysics (SPA) with the TNG ». Astronomy & ; Astrophysics 660 (30 mars 2022) : A7. http://dx.doi.org/10.1051/0004-6361/202142492.

Texte intégral

Résumé :

Context. The Perseus complex in the outer disk of the Galaxy hosts a number of clusters and associations of young stars. Gaia is providing a detailed characterization of their kinematic structure and evolutionary properties. Aims. Within the SPA Large Program at the TNG, we secured HARPS-N and GIANO-B high-resolution optical and near-infrared (NIR) spectra of the young red supergiant (RSG) stars in the Perseus complex in order to obtain accurate radial velocities, stellar parameters, and detailed chemical abundances. Methods. We used spectral synthesis to best fit hundreds of atomic and molecular lines in the spectra of the observed 27 RSGs. We obtained accurate estimates of the stellar temperature, gravity, micro- and macroturbulence velocities, and chemical abundances for 25 different elements. We also measured the 12C/13C abundance ratio. Results. Our combined optical and NIR chemical study provides homogeneous half-solar iron with a low dispersion, about solar-scaled abundance ratios for the iron-peak, alpha-, and other light elements, and a low enhancement of Na, K, and neutron-capture elements. This is consistent with the thin-disk chemistry traced by older stellar populations at a similar galactocentric distance of about 10 kpc. We inferred an enhancement of N and a depletion of C and of the 12C/13C isotopic abundance ratio that are consistent with mixing processes in the stellar interiors during the RSG evolution.

Styles APA, Harvard, Vancouver, ISO, etc.

34

Anders, F., C. Chiappini, B. X. Santiago, G. Matijevič, A. B. Queiroz, M. Steinmetz et G. Guiglion. « Dissecting stellar chemical abundance space with t-SNE ». Astronomy & ; Astrophysics 619 (novembre 2018) : A125. http://dx.doi.org/10.1051/0004-6361/201833099.

Texte intégral

Résumé :

In the era of large-scale Galactic astronomy and multi-object spectroscopic stellar surveys, the sample sizes and the number of available stellar chemical abundances have reached dimensions in which it has become difficult to process all the available information in an effective manner. In this paper we demonstrate the use of a dimensionality-reduction technique (t-distributed stochastic neighbour embedding; t-SNE) for analysing the stellar abundance-space distribution. While the non-parametric non-linear behaviour of this technique makes it difficult to estimate the significance of any abundance-space substructure found, we show that our results depend little on parameter choices and are robust to abundance errors. By reanalysing the high-resolution high-signal-to-noise solar-neighbourhood HARPS-GTO sample with t-SNE, we find clearer chemical separations of the high- and low-[α/Fe] disc sequences, hints for multiple populations in the high-[α/Fe] population, and indications that the chemical evolution of the high-[α/Fe] metal-rich stars is connected with the super-metal-rich stars. We also identify a number of chemically peculiar stars, among them a high-confidence s-process-enhanced abundance-ratio pair (HD 91345/HD 126681) with very similar ages and v X and v Y velocities, which we suggest have a common birth origin, possibly a dwarf galaxy. Our results demonstrate the potential of abundance-space t-SNE and similar methods for chemical-tagging studies with large spectroscopic surveys.

Styles APA, Harvard, Vancouver, ISO, etc.

35

Martins, F., L. Mahy et A. Hervé. « Properties of six short-period massive binaries : A study of the effects of binarity on surface chemical abundances ». Astronomy & ; Astrophysics 607 (novembre 2017) : A82. http://dx.doi.org/10.1051/0004-6361/201731593.

Texte intégral

Résumé :

Context.A significant percentage of massive stars are found in multiple systems. The effect of binarity on stellar evolution is poorly constrained. In particular, the role of tides and mass transfer on surface chemical abundances is not constrained observationally.Aims.The aim of this study is to investigate the effect of binarity on the stellar properties and surface abundances of massive binaries.Methods.We performed a spectroscopic analysis of six Galactic massive binaries. We obtained the spectra of individual components via a spectral disentangling method and subsequently analyzed these spectra by means of atmosphere models. The stellar parameters and CNO surface abundances were determined.Results.Most of these six systems are comprised of main-sequence stars. Three systems are detached, two are in contact, and no information is available for the sixth system. For 11 out of the 12 stars studied, the surface abundances are only mildly affected by stellar evolution and mixing. The surface abundances are not different from those of single stars within the uncertainties. The secondary of XZ Cep is strongly chemically enriched. Considering previous determinations of surface abundances in massive binary systems suggests that the effect of tides on chemical mixing is limited, whereas the mass transfer and removal of outer layers of the mass donor leads to the appearance of chemically processed material at the surface, although this is not systematic. The evolutionary masses of the components of our six systems are on average 16.5% higher than the dynamical masses. Some systems seem to have reached synchronization, while others may still be in a transitory phase.

Styles APA, Harvard, Vancouver, ISO, etc.

36

Aoki, Wako. « Stellar elemental abundances constraining nucleosynthesis and chemical evolution of the universe ». EPJ Web of Conferences 260 (2022) : 07002. http://dx.doi.org/10.1051/epjconf/202226007002.

Texte intégral

Résumé :

Measurements of elemental abundances of stars in the Milky Way and surrounding dwarf galaxies in the past few decades have been providing useful constraints on modeling the nucleosynthesis and chemical evolution. Recent large spectroscopic surveys combined with studies on dynamical motions of stars in the Milky Way reveal connections between chemical enrichment and galaxy formation. This paper provides a brief overview of the recent update of the understanding of the distribution of elemental abundances and remaining issues for key elements, mostly focusing on the low metallicity range which should reflect nucleosynthesis by massive stars and early chemical evolution. This covers the abundance ratios of α-elements, iron-peak elements, and neutron-capture elements which have been measured for a large number of metal-poor stars.

Styles APA, Harvard, Vancouver, ISO, etc.

37

Berlanas, S. R., A. Herrero, F. Comerón, S. Simón-Díaz, M. Cerviño et A. Pasquali. « Oxygen and silicon abundances in Cygnus OB2 ». Astronomy & ; Astrophysics 620 (29 novembre 2018) : A56. http://dx.doi.org/10.1051/0004-6361/201833989.

Texte intégral

Résumé :

Context. Cygnus OB2 is a rich OB association in the Galaxy located at only ∼1.4 kpc from us which has experienced intense star formation in the last 20–25 Myr. Its stellar population shows a correlation between age and Galactic longitude. Exploring the chemical composition of its stellar content we will be able to check the degree of homogeneity of the natal molecular cloud and possible effects of self-enrichment processes. Aims. Our aim is to determine silicon and oxygen abundances for a sample of eight early-type slow rotators (with rotational velocities below 80 km s−1) in Cygnus OB2 in order to check possible inhomogeneities across the whole association and whether there exists a correlation of chemical composition with Galactic longitude. Methods. We have performed a spectroscopic analysis of a sample of late O and early B stars with low rotational velocity in Cygnus OB2, which have been chosen so as to cover the whole association area. We have carried out an analysis based on equivalent widths of metal lines, the wings of the H Balmer lines and FASTWIND stellar atmosphere models to determine their stellar fundamental parameters (effective temperature and surface gravity) as well as the silicon and oxygen surface abundances. Results. We derive a rather homogeneous distribution of silicon and oxygen abundances across the region, with average values of 12 + log(Si/H) = 7.53 ± 0.08 dex and 12 + log(O/H) = 8.65 ± 0.12 dex. Conclusions. We find a homogeneous chemical composition in Cygnus OB2 with no clear evidence for significant chemical self-enrichment, despite indications of strong stellar winds and possible supernovae during the history of the region. Comparison with different scenarios of chemical enrichment by stellar winds and supernovae point to star forming efficiencies not significantly above 10%. The degree of homogeneity that we find is consistent with the observed Milky Way oxygen gradient based on H II regions. We also find that the oxygen scatter within Cygnus OB2 is at least of the same order than among H II regions at similar Galactocentric distance.

Styles APA, Harvard, Vancouver, ISO, etc.

38

Saffe, C., P. Miquelarena, J. Alacoria, J. F. González, M. Flores, M. Jaque Arancibia, D. Calvo, E. Jofré et A. Collado. « KELT-17 : a chemically peculiar Am star and a hot-Jupiter planet ». Astronomy & ; Astrophysics 641 (septembre 2020) : A145. http://dx.doi.org/10.1051/0004-6361/202038843.

Texte intégral

Résumé :

Context. There is very little information to be found in the literature regarding the detection of planets orbiting chemically peculiar stars. Aims. Our aim is to determine the detailed chemical composition of the remarkable planet host star KELT-17. This object hosts a hot-Jupiter planet with 1.31 MJup detected by transits, and it is one of the more massive and rapidly rotating planet hosts seen to date. We set out to derive a complete chemical pattern for this star, in order to compare it with those of chemically peculiar stars. Methods. We carried out a detailed abundance determination in the planet host star KELT-17 via spectral synthesis. Stellar parameters were estimated iteratively by fitting Balmer line profiles and imposing the Fe ionization balance using the SYNTHE program together with plane-parallel ATLAS12 model atmospheres. Specific opacities for an arbitrary composition and microturbulence velocity vmicro were calculated through the opacity sampling (OS) method. The abundances were determined iteratively by fitting synthetic spectra to metallic lines of 16 different chemical species using SYNTHE. The complete chemical pattern of KELT-17 was compared to the recently published average pattern of Am stars. We estimated the stellar radius using two methods: a) comparing the synthetic spectral energy distribution with the available photometric data and the Gaia parallax, and b) using a Bayesian estimation of stellar parameters using stellar isochrones. Results. We found over-abundances of Ti, Cr, Mn, Fe, Ni, Zn, Sr, Y, Zr, and Ba, together with subsolar values of Ca and Sc. Notably, the chemical pattern agrees with those recently published for Am stars, making KELT-17 the first exoplanet host whose complete chemical pattern is unambiguously identified with this class. The stellar radius derived by two different methods agrees to each other and with those previously obtained in the literature.

Styles APA, Harvard, Vancouver, ISO, etc.

39

Katime Santrich, Orlando J., et Silvia Rossi. « High-resolution spectroscopy of giant stars in the open clusters IC 4651 and IC 4725 ». Canadian Journal of Physics 95, n^o 9 (septembre 2017) : 862–68. http://dx.doi.org/10.1139/cjp-2016-0912.

Texte intégral

Résumé :

Open clusters are important astrophysical laboratories to study the stellar formation and evolution and to verify the disk structure of the Milky Way. We present calculations of stellar atmospheric parameters and s-process abundances for nine giant stars in the galactic open clusters IC 4651 and IC 4725. These objects have their memberships confirmed from dynamic studies and chemical analysis. The high-resolution spectra are available in the FEROS ESO archive. We have applied a line by line analysis relative to Juno solar spectrum to determine the stellar atmospheric parameters and chemical abundances of Y II, Zr I, La II, Ce II, and Nd II under the local thermal equilibrium hypothesis. The obtained results were compared to the literature values. The derived s-process abundance pattern agrees with the most recent behaviors reported for giant stars in galactic open clusters.

Styles APA, Harvard, Vancouver, ISO, etc.

40

Khalack, V., et F. LeBlanc. « Project VeSElkA : Vertical Stratification of Element Abundances in CP stars ». Advances in Astronomy and Space Physics 5, n^o 1 (2015) : 3–10. http://dx.doi.org/10.17721/2227-1481.5.3-10.

Texte intégral

Résumé :

A new research project on spectral analysis which aims to characterize the vertical stratification of element abundances in stellar atmospheres of chemically peculiar (CP) stars, is discussed in detail. Some results on detection of vertical abundance stratification in several slowly rotating main sequence CP stars are presented and considered as an indicator of the effectiveness of the atomic diffusion mechanism responsible for the observed peculiarities of chemical abundances. This study is carried out in the frame of Project VeSElkA (Vertical Stratification of Elements Abundance) for which 34 slowly rotating CP stars have been observed with the ESPaDOnS spectropolarimetre at CFHT.

Styles APA, Harvard, Vancouver, ISO, etc.

41

Nissen, P. E. « Progress in High S/N Spectroscopy and its Importance for Stellar Modelling ». International Astronomical Union Colloquium 137 (1993) : 108–21. http://dx.doi.org/10.1017/s0252921100017590.

Texte intégral

Résumé :

AbstractRecent advances in high S/N spectroscopy are reviewed with particular emphasis on new data for the abundances of chemical elements of importance for the modelling of stellar interiors.It seems well established that young, nearby B-type stars have abundances of CNO elements that are about a factor of two lower than in the Sun except for a small fraction of nitrogen-rich stars. The existence of such stars among main sequence stars remains to be explained.Among normal A-type stars (excluding Am and Ap stars) large deviations from solar abundance ratios occur with interesting anticorrelations of the abundances of C and Si. This suggests that diffusion processes and/or gas-dust separation of the chemical elements in the protostellar cloud play an important rôle.

Styles APA, Harvard, Vancouver, ISO, etc.

42

Marino, Anna F. « Chemical abundances of multiple stellar populations in massive globular clusters ». Proceedings of the International Astronomical Union 12, S316 (août 2015) : 267–74. http://dx.doi.org/10.1017/s1743921315009485.

Texte intégral

Résumé :

AbstractMultiple stellar populations in the Milky Way globular clusters manifest themselves with a large variety. Although chemical abundance variations in light elements, including He, are ubiquitous, the amount of these variations is different in different globulars. Stellar populations with distinct Fe, C+N+O and slow-neutron capture elements have been now detected in some globular clusters, whose number will likely increase. All these chemical features correspond to specific photometric patterns. I review the chemical+photometric features of the multiple stellar populations in globular clusters and discuss how the interpretation of data is being more and more challenging. Very excitingly, the origin and evolution of globular clusters is being a complex puzzle to compose.

Styles APA, Harvard, Vancouver, ISO, etc.

43

Majewski, Steven R., Mei-Yin Chou, Katia Cunha, Verne V. Smith, Richard J. Patterson et David Martínez-Delgado. « Chemical Fingerprinting and Chemical Analysis of Galactic Halo Substructure ». Proceedings of the International Astronomical Union 5, S265 (août 2009) : 364–65. http://dx.doi.org/10.1017/s1743921310000943.

Texte intégral

Résumé :

AbstractWe present high-resolution spectroscopic measurements of the abundances of the α-like element titanium (Ti) and s-process elements yttrium (Y) and lanthanum (La) for M giant candidates of (a) the Sagittarius (Sgr) dwarf spheroidal + tidal tail system, (b) the Triangulum-Andromeda (TriAnd) Star Cloud, and (c) the Galactic Anticenter Stellar Structure (GASS, or Monoceros Stream). All three systems show abundance patterns unlike the Milky Way but typical of dwarf galaxies. The Sgr system abundance patterns resemble those of the Large Magellanic Cloud. GASS/Mon chemically resembles Sgr but is distinct from TriAnd, a result that does not support previous suggestions that TriAnd is a piece of the Monoceros Stream.

Styles APA, Harvard, Vancouver, ISO, etc.

44

Yana Galarza, Jhon, Jorge Meléndez, Diego Lorenzo-Oliveira, Adriana Valio, Henrique Reggiani, Marília Carlos, Geisa Ponte, Lorenzo Spina, Raphaëlle D. Haywood et Davide Gandolfi. « The effect of stellar activity on the spectroscopic stellar parameters of the young solar twin HIP 36515 ». Monthly Notices of the Royal Astronomical Society : Letters 490, n^o 1 (7 octobre 2019) : L86—L90. http://dx.doi.org/10.1093/mnrasl/slz153.

Texte intégral

Résumé :

ABSTRACT Spectroscopic equilibrium allows us to obtain precise stellar parameters in Sun-like stars. It relies on the assumption of the iron excitation and ionization equilibrium. However, several works suggest that magnetic activity may affect chemical abundances of young active stars, calling into question the validity of this widely used method. We have tested, for the first time, variations in stellar parameters and chemical abundances for the young solar twin HIP 36515 (∼0.4 Gyr), along its activity cycle. This star has stellar parameters very well established in the literature and we estimated its activity cycle in ∼6 yr. Using HARPS spectra with high resolving power (115 000) and signal-to-noise ratio (∼270), the stellar parameters of six different epochs in the cycle were estimated. We found that the stellar activity is strongly correlated with the effective temperature, metallicity, and microturbulence velocity. The possibility of changes in the Li i 6707.8 Å line due to flares and star-spots was also investigated. Although the core of the line profile shows some variations with the stellar cycle, it is compensated by changes in the effective temperature, resulting in a non-variation of the Li abundance.

Styles APA, Harvard, Vancouver, ISO, etc.

45

Marigo, Paola. « Theoretical abundances in Planetary Nebulae ». Symposium - International Astronomical Union 180 (1997) : 257. http://dx.doi.org/10.1017/s007418090013075x.

Texte intégral

Résumé :

A semi-analytical model has been constructed to calculate the TP-AGB evolution of low-and intermediate-mass stars (Marigo et al. 1996), starting from the first thermal pulse until the complete ejection of the envelope by stellar winds. We estimate the changes in the chemical composition of the envelope due to different processes: (i) the intershell nucleosynthesis and convective dredge-up; (ii) envelope burning in the most massive AGB stars (M ≥ 3–4M⊙); (iii) mass loss by stellar winds.

Styles APA, Harvard, Vancouver, ISO, etc.

46

Prugniel, Philippe, et Mina Koleva. « Spectral models of stellar populations resolved in chemical abundances ». Proceedings of the International Astronomical Union 7, S284 (septembre 2011) : 16–19. http://dx.doi.org/10.1017/s1743921312008629.

Texte intégral

Résumé :

AbstractWe present model spectra of stellar populations with variable chemical composition. We derived the [α/Fe] abundance ratio of the stars of the most important libraries (ELODIE, CFLIB and MILES) using full spectrum fitting and we generated PEGASE.HR models resolved in [α/Fe]. We used a semi-empirical approach that combines the observed spectra with synthetic stellar spectra. We tested the models using them to derive [α/Fe] in galaxies and star clusters using full spectrum fitting. The present models are available from http://ulyss.univ-lyon1.fr

Styles APA, Harvard, Vancouver, ISO, etc.

47

Sneden, Christopher, James E. Lawler, Elizabeth A. Den Hartog et Michael E. Wood. « Atomic Data for Stellar Nucleosynthesis ». Proceedings of the International Astronomical Union 11, A29A (août 2015) : 287–90. http://dx.doi.org/10.1017/s1743921316003069.

Texte intégral

Résumé :

AbstractStellar chemical composition analyses can only yield reliable abundances if the atomic transition parameters are accurately determined. During the last couple of decades a renewed emphasis on laboratory spectroscopy has produced large sets of useful atomic transition probabilities for species of interest to stellar spectroscopists. In many cases the transition data are of such high quality that they play little part in the abundance uncertainties. We summarize the current state of atomic parameters, highlighting the areas of satisfactory progress and noting places, where further laboratory progress will be welcome.

Styles APA, Harvard, Vancouver, ISO, etc.

48

Boeche, C., M. C. Smith, E. K. Grebel, J. Zhong, J. L. Hou, L. Chen et D. Stello. « LAMOST DR1 : Stellar Parameters and Chemical Abundances with SP_Ace ». Astronomical Journal 155, n^o 4 (4 avril 2018) : 181. http://dx.doi.org/10.3847/1538-3881/aab5af.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

49

García Pérez, Ana E., Carlos Allende Prieto, Jon A. Holtzman, Matthew Shetrone, Szabolcs Mészáros, Dmitry Bizyaev, Ricardo Carrera et al. « ASPCAP : THE APOGEE STELLAR PARAMETER AND CHEMICAL ABUNDANCES PIPELINE ». Astronomical Journal 151, n^o 6 (23 mai 2016) : 144. http://dx.doi.org/10.3847/0004-6256/151/6/144.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

50

Roederer, Ian U., Christopher Sneden, Ian B. Thompson, George W. Preston et Stephen A. Shectman. « Detailed Chemical Abundances in a Metal-Poor Stellar Stream ». Proceedings of the International Astronomical Union 5, S265 (août 2009) : 368–69. http://dx.doi.org/10.1017/s1743921310000967.

Texte intégral

Résumé :

AbstractWe have observed 9 bright metal-poor stars whose kinematics suggest they are members of a stellar stream in the vicinity of the Solar neighborhood. These 9 stars exhibit no star-to-star dispersion in their [X/Fe] ratios for the α and Fe-peak elements, and the neutron-capture elements suggest mild enrichment by the main r-process. The abundance patterns seen in this stream are very similar to those found in the metal-poor globular cluster M15, and the kinematics of M15 are similar to those of the stream, suggesting that these two groups of stars may have shared a common origin.

Styles APA, Harvard, Vancouver, ISO, etc.

Articles de revues sur le sujet « Stellar chemical abundances »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres