Elemental high-precision abundances as function of stellar ages: Constrains on the Galactic chemical evolution

2017 ◽  
Vol 13 (S334) ◽  
pp. 376-377
Author(s):  
Marcelo Tucci Maia
Keyword(s):  
High Precision ◽  
Main Sequence ◽  
Chemical Elements ◽  
The Sun ◽  
Galactic Chemical Evolution ◽  
Special Group ◽  
Solar Mass ◽  
Differential Abundance ◽  
Stellar Ages ◽  
The Galaxy

AbstractSolar twins are a special group of stars that have spectra and stellar parameters very close to the Sun. Also having mass around 1 solar mass and roughly solar chemical composition, these stars follow a similar evolutionary path to the Sun, from the zero age main sequence to the end of their lives. Additional to that, the similarity between themselves permit us to obtain high-precision differential abundance and thus, very precise atmospheric parameters that allows a reliable estimation of their ages using the traditional isochronal method. Taking advantage of this very restrict group of stars we can better understand the effects of nucleosynthesis of chemical elements throughout the Galaxy and with this, finding constrains for its evolution.

scholarly journals Mass-loss varying luminosity and its implication to the solar evolution

2019 ◽  
Vol 15 (S356) ◽  
pp. 403-404
Author(s):  
Negessa Tilahun Shukure ◽  
Solomon Belay Tessema ◽  
Endalkachew Mengistu
Keyword(s):  
Standard Model ◽  
Mass Loss ◽  
Main Sequence ◽  
The Sun ◽  
Solar Mass ◽  
Solar Luminosity ◽  
Solar Evolution

AbstractSeveral models of the solar luminosity, , in the evolutionary timescale, have been computed as a function of time. However, the solar mass-loss, , is one of the drivers of variation in this timescale. The purpose of this study is to model mass-loss varying solar luminosity, , and to predict the luminosity variation before it leaves the main sequence. We numerically computed the up to 4.9 Gyrs from now. We used the solution to compute the modeled . We then validated our model with the current solar standard model (SSM). The shows consistency up to 8 Gyrs. At about 8.85 Gyrs, the Sun loses 28% of its mass and its luminosity increased to 2.2. The model suggests that the total main sequence lifetime is nearly 9 Gyrs. The model explains well the stage at which the Sun exhausts its central supply of hydrogen and when it will be ready to leave the main sequence. It may also explain the fate of the Sun by making some improvements in comparison to previous models.

scholarly journals A quantitative spectral analysis of 14 hypervelocity stars from the MMT survey

2018 ◽  
Vol 615 ◽  
pp. L5 ◽  
Author(s):  
A. Irrgang ◽  
S. Kreuzer ◽  
U. Heber ◽  
W. Brown
Keyword(s):  
Main Sequence ◽  
Galactic Center ◽  
Radial Velocities ◽  
Stellar Ages ◽  
The Galaxy ◽  
Quantitative Spectral Analysis ◽  
Kinematic Studies ◽  
Ejection Mechanism ◽  
Photometric Measurements ◽  
Stellar Masses

Context. Hypervelocity stars (HVSs) travel so fast that they may leave the Galaxy. The tidal disruption of a binary system by the supermassive black hole in the Galactic center is widely assumed to be their ejection mechanism. Aims. To test the hypothesis of an origin in the Galactic center using kinematic investigations, the current space velocities of the HVSs need to be determined. With the advent of Gaia’s second data release, accurate radial velocities from spectroscopy are complemented by proper motion measurements of unprecedented quality. Based on a new spectroscopic analysis method, we provide revised distances and stellar ages, both of which are crucial to unravel the nature of the HVSs. Methods. We reanalyzed low-resolution optical spectra of 14 HVSs from the MMT HVS survey using a new grid of synthetic spectra, which account for deviations from local thermodynamic equilibrium, to derive effective temperatures, surface gravities, radial velocities, and projected rotational velocities. Stellar masses, radii, and ages were then determined by comparison with stellar evolutionary models that account for rotation. Finally, these results were combined with photometric measurements to obtain spectroscopic distances. Results. The resulting atmospheric parameters are consistent with those of main sequence stars with masses in the range 2.5–5.0 M⊙. The majority of the stars rotate at fast speeds, providing further evidence for their main sequence nature. Stellar ages range from 90 to 400 Myr and distances (with typical 1σ-uncertainties of about 10–15%) from 30 to 100 kpc. Except for one object (B 711), which we reclassify as A-type star, all stars are of spectral type B. Conclusions. The spectroscopic distances and stellar ages derived here are key ingredients for upcoming kinematic studies of HVSs based on Gaia proper motions.

scholarly journals Age-related observations of low mass pre-main and young main sequence stars

2008 ◽  
Vol 4 (S258) ◽  
pp. 81-94 ◽  
Author(s):  
Lynne A. Hillenbrand
Keyword(s):  
Main Sequence ◽  
Rotation Period ◽  
Age Dating ◽  
Main Sequence Stars ◽  
Solar Mass ◽  
Age Related ◽  
Stellar Ages ◽  
Dating Methods ◽  
Low Mass ◽  
Lithium Depletion

AbstractThis overview summarizes the age dating methods available for young sub-solar mass stars. Pre-main sequence age diagnostics include the Hertzsprung-Russell (HR) diagram, spectroscopic surface gravity indicators, and lithium depletion; asteroseismology is also showing recent promise. Near and beyond the zero-age main sequence, rotation period or vsiniand activity (coronal and chromospheric) diagnostics along with lithium depletion serve as age proxies. Other authors in this volume present more detail in each of the aforementioned areas. Herein, I focus on pre-main sequence HR diagrams and address the questions: Do empirical young cluster isochrones match theoretical isochrones? Do isochrones predict stellar ages consistent with those derived via other independent techniques? Do the observed apparent luminosity spreads at constant effective temperature correspond to true age spreads? While definitive answers to these questions are not provided, some methods of progression are outlined.

scholarly journals The AMBRE project: searching for the closest solar siblings

2018 ◽  
Vol 619 ◽  
pp. A130 ◽  
Author(s):  
V. Adibekyan ◽  
P. de Laverny ◽  
A. Recio-Blanco ◽  
S. G. Sousa ◽  
E. Delgado-Mena ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Chemical Characterization ◽  
Isotopic Ratios ◽  
The Sun ◽  
Chemical Abundances ◽  
Carbon Isotopic ◽  
Yield Information ◽  
Stellar Ages ◽  
The Galaxy ◽  
Astrometric Data

Context. Finding solar siblings, that is, stars that formed in the same cluster as the Sun, will yield information about the conditions at the Sun’s birthplace. Finding possible solar siblings is difficult since they are spread widely throughout the Galaxy. Aims. We search for solar sibling candidates in AMBRE, the very large spectra database of solar vicinity stars. Methods. Since the ages and chemical abundances of solar siblings are very similar to those of the Sun, we carried out a chemistry- and age-based search for solar sibling candidates. We used high-resolution spectra to derive precise stellar parameters and chemical abundances of the stars. We used these spectroscopic parameters together with Gaia DR2 astrometric data to derive stellar isochronal ages. Gaia data were also used to study the kinematics of the sibling candidates. Results. From about 17 000 stars that are characterized within the AMBRE project, we first selected 55 stars whose metallicities are closest to the solar value (−0.1 ≤ [Fe/H] ≤ 0.1 dex). For these stars we derived precise chemical abundances of several iron-peak, α- and neutron-capture elements, based on which we selected 12 solar sibling candidates with average abundances and metallicities between −0.03 and 0.03 dex. Our further selection left us with four candidates with stellar ages that are compatible with the solar age within observational uncertainties. For the two of the hottest candidates, we derived the carbon isotopic ratios, which are compatible with the solar value. HD 186302 is the most precisely characterized and probably the most probable candidate of our four best candidates. Conclusions. Very precise chemical characterization and age estimation is necessary to identify solar siblings. We propose that in addition to typical chemical tagging, the study of isotopic ratios can give further important information about the relation of sibling candidates with the Sun. Ideally, asteroseismic age determinations of the candidates could solve the problem of imprecise isochronal ages.

Developing an astrophysical line list for Keck/Nirspec observations of red giants in the Galactic centre

2017 ◽  
Vol 13 (S334) ◽  
pp. 372-373 ◽  
Author(s):  
B. Thorsbro ◽  
N. Ryde ◽  
R. M. Rich ◽  
M. Schultheis ◽  
T. K. Fritz ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Wavelength Region ◽  
Galactic Centre ◽  
Red Giants ◽  
The Sun ◽  
Galactic Chemical Evolution ◽  
Line List ◽  
Stellar Spectroscopy ◽  
Near Ir ◽  
The Galaxy

AbstractA major avenue in the study of the Galaxy is the investigation of stellar populations and Galactic chemical evolution by stellar spectroscopy. Due to the dust obscuration, stars in the centre of the Galaxy can only be observed in the near-IR wavelength region. However, existing line lists in this wavelength region are demonstratively not of good enough quality for use in stellar spectroscopy. In response to this, we have developed an empirical astrophysical line list in the K-band based on modelling against the Sun and testing against Arcturus. Of ca. 700 identified interesting lines about 570 lines have been assigned empirically determined values.

scholarly journals Nucleosynthesis in Massive Population II Stars

1978 ◽  
Vol 80 ◽  
pp. 375-378
Author(s):  
David S. P. Dearborn ◽  
Virginia Trimble
Keyword(s):  
Heavy Element ◽  
Main Sequence ◽  
Massive Stars ◽  
Galactic Chemical Evolution ◽  
Initial Composition ◽  
Lower Mass ◽  
First Stars ◽  
The Galaxy ◽  
History Of ◽  
Metal Abundances

According to the conventional wisdom, the first stars formed in our Galaxy, including the massive ones responsible for most heavy element synthesis, must have had metal abundances much lower than solar. They may also have had somewhat lower helium abundances, corresponding to an enrichment ΔY/ΔZ = 2.7 ± 1.0 over the history of the Galaxy, a larger ratio than is readily accounted for by standard (Arnett-type) supernovae (Hacyan et al. 1977) or by mass shed from lower mass stars (Gingold 1977). But early nucleosynthesis must have occurred in stars with Pop II compositions. Several authors (Ezer and Cameron 1969; Cary 1974; Chiosi and Nasi 1974; Trimbleet al. 1973) have modelled and evolved such stars, but none of the studies followed the stars far enough from the main sequence to be able to say anything very quantitative about their contribution to galactic chemical evolution. We address here the question of the effects of initial composition upon helium and heavy element production in massive stars.

scholarly journals Mathematical model for the 0.5 billion years aged Sun

2000 ◽  
pp. 35-40
Author(s):  
E. Tatomir
Keyword(s):  
Energy Source ◽  
Mathematical Model ◽  
Numerical Integration ◽  
Main Sequence ◽  
Solar Model ◽  
System Of Equations ◽  
The Sun ◽  
Solar Mass ◽  
Proton Proton ◽  
Close Vicinity

An algorithm is given for constructing evolutionary tracks for a star with the mass equal to one solar mass. The presented model can be applied to the stars belonging to the inferior main sequence, which have the proton-proton reaction as energy source and present a radiative core and a convective shell. This paper presents an original way of solving the system of equations corresponding to the radiative nucleus by using Taylor?s series in close vicinity to the center of the Sun. It also presents the numerical integration and the results for a 0.5 billion years aged solar model.

The nearby spiral density-wave structure of the Galaxy: line-of-sight velocities of the Gaia DR2 main-sequence A, F, G, and K stars

2020 ◽  
Vol 493 (2) ◽  
pp. 2111-2126
Author(s):  
Evgeny Griv ◽  
Michael Gedalin ◽  
I-Chun Shih ◽  
Li-Gang Hou ◽  
Ing-Guey Jiang
Keyword(s):  
Main Sequence ◽  
Density Wave ◽  
Wave Structure ◽  
Wave Pattern ◽  
Line Of Sight ◽  
The Sun ◽  
Density Waves ◽  
Spiral Density Waves ◽  
The Galaxy ◽  
Spiral Arm

ABSTRACT Distances and velocities of $\approx \!2400\, 000$ main-sequence A, F, G, and K stars are collected from the second data release of ESA's Gaia astrometric mission. This material is analysed to find evidence of radial and azimuthal systematic non-circular motions of stars in the solar neighbourhood on the assumption that the system is subject to spiral density waves (those produced by a spontaneous disturbance, a central bar, or an external companion), developing in the Galactic disc. Data analysis of line-of-sight velocities of $\approx \!1500\, 000$ stars selected within 2 kpc from the Sun and 500 pc from the Galactic mid-plane with distance accuracies of <10 per cent makes evident that a radial wavelength of the wave pattern is 1.1–1.6 kpc and a phase of the wave at the Sun’s location in the Galaxy is 55°–95°. Respectively, the Sun is situated at the inner edge of the nearest Orion spiral arm segment. Thus, the local Orion arm is a part of a predominant density-wave structure of the system. The spiral structure of the Galaxy has an oscillating nature corresponding to a concept of the Lin–Shu-type moderately growing in amplitude, tightly wound, and rigidly rotating density waves.

scholarly journals A Dynamical Investigation of Nine Wide Visual Double Stars in the Neighbourhood of the Sun

1995 ◽  
Vol 166 ◽  
pp. 396-396
Author(s):  
A.A. Kisselev ◽  
L.G. Romanenko
Keyword(s):  
Observational Data ◽  
Radial Velocities ◽  
The Sun ◽  
Orbital Elements ◽  
Solar Mass ◽  
Double Stars ◽  
Visual Double Stars ◽  
The Family ◽  
The Galaxy ◽  
Elliptical Motion

The dynamical states of nine wide visual double stars (ADS 7251, 10329, 10386, 10759 [psi Dra], 11061 [40&41 Dra], 11632, 12169, 12815 [16 Cyg]) are considered. The 20-30 – year series of photographic observations obtained with the Pulkovo 26-inch refractor (Kisselev et al., 1988) supported by the data of relative radial velocities of the components and parallaxes are used. On this base the vectors of relative spatial positions and velocities of the components are determined or estimated with confidence. Families of orbits, satisfying observational data are determined by assuming stability of motions in the systems. The orbits of three nearby binaries ADS 7251, 11632 and 61 Cyg were calculated earlier by classical methods and belong to the family mentioned above. Thus the authenticity of our analysis is proved (Kisselev, Kiyaeva, 1980). It is shown that elliptical motion in the couples ADS 10759 and 11061 could be explained only if an additional (hidden) mass exists. This mass consists of one solar mass for the first couple and two solar masses for the second one. The dynamical orbital elements of the binaries belonging to each family may differ greatly, but the geometrical elements are fairly stable. The orientation of the orbit planes of binaries with respect to the Galaxy plane is determined. In one half of the cases the orbital planes are approximately orthogonal to that of our Galaxy.

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