Chemical enrichment of galaxies as the result of organic synthesis in evolved stars

2018 ◽  
Vol 14 (S343) ◽  
pp. 443-444
Author(s):  
Sun Kwok ◽  
SeyedAbdolreza Sadjadi ◽  
Yong Zhang
Keyword(s):  
Interstellar Medium ◽  
Organic Synthesis ◽  
Stellar Evolution ◽  
Solar Nebula ◽  
Spectroscopic Observations ◽  
Chemical Enrichment ◽  
Evolved Stars ◽  
The Galaxy ◽  
Organic Particles ◽  
Late Stages

AbstractInfrared spectroscopic observations have shown that complex organics with mixed aromatic-aliphatic structures are synthesized in large quantities during the late stages of stellar evolution. These organics are ejected into the interstellar medium and spread across the Galaxy. Due to the sturdy structures of these organic particles, they can survive through long journeys across the Galaxy under strong UV background and shock conditions. The implications that stellar organics were embedded in the primordial solar nebula is discussed.

scholarly journals Chemical enrichment from Wolf-Rayet stellar winds

1999 ◽  
Vol 193 ◽  
pp. 218-226
Author(s):  
Georges Meynet
Keyword(s):  
Angular Velocity ◽  
Interstellar Medium ◽  
Mass Loss ◽  
Solar Nebula ◽  
Cosmic Ray ◽  
Stellar Winds ◽  
Chemical Enrichment ◽  
Galactic Cosmic Ray ◽  
Loss Rates

Stellar winds contribute together with supernovae explosions to the chemical enrichment of the interstellar medium. We recall how the metallicity dependence of the stellar winds implies a metallicity dependence of the stellar yields. We show that an increase of the initial angular velocity has different effects than an increase of the mass loss rates. Wolf-Rayet stars appear as important sources of 19F and 26Al. They are the favoured candidates for the 22Ne anomaly observed in the Galactic cosmic ray sources. They may also have injected into the proto-solar nebula short-lived radionuclides as 26Al, 36Cl, 41Ca, 107Pd and 205Pb.

scholarly journals The ionization of galaxies by their planetary nebulae

2011 ◽  
Vol 7 (S283) ◽  
pp. 239-242 ◽  
Author(s):  
Grażyna Stasińska
Keyword(s):  
Interstellar Medium ◽  
Emission Line ◽  
Stellar Evolution ◽  
White Dwarf ◽  
Planetary Nebulae ◽  
Extragalactic Astronomy ◽  
Evolved Stars ◽  
Low Mass

AbstractRecent studies have shown that nuclei of planetary nebulae and their remnants (dubbed HOLMES for “hot low-mass evolved stars”) can easily explain two long-standing problems of extragalactic astronomy: the observed emission-line spectra of ellipticals and LINER-like galaxies and the ionization and heating of the diffuse interstellar medium in spirals. They are summarized in this contribution. It is emphasized that the computation of grids of stellar evolution models until the white dwarf stage is essential not only for the study of planetary nebulae but also for the study of the ionization of galaxies.

scholarly journals Molecular Evolution from AGB Stars to Planetary Nebulae

2011 ◽  
Vol 7 (S280) ◽  
pp. 203-215 ◽  
Author(s):  
Sun Kwok
Keyword(s):  
Chemical Synthesis ◽  
Stellar Evolution ◽  
Planetary Nebulae ◽  
Active Phase ◽  
Molecular Ions ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
The Galaxy ◽  
Short Time ◽  
Late Stages

AbstractThe late stages of stellar evolution from the Asymptotic Giant Branch (AGB) to planetary nebulae represent the most active phase of molecular synthesis in a star's life. Over 60 molecular species, including inorganics, organics, radicals, chains, rings, and molecular ions have been detected in the circumstellar envelopes of evolved stars. Most interestingly, complex organic compounds of aromatic and aliphatic structures are synthesized over very short time intervals after the end of the AGB. Also appeared during the post-AGB evolution are the unidentified 21 and 30 μm emission features, which are believed to originate from carbonaceous compounds.The circumstellar environment is an ideal laboratory for the testing of theories of chemical synthesis. The distinct spectral behavior among AGB stars, proto-planetary nebulae (PPN), and planetary nebulae (PN) and the short evolutionary time scales that separate these stages pose severe constraints on models. In this paper, we will present an observational summary of the chemical synthesis in the late stages of stellar evolution, discuss chemical and physical processes at work, and speculate on the possible effects these chemical products have on the Galaxy and the Solar System.

Final Remarks: Connections between Chemical and Dynamical Evolution

1977 ◽  
Vol 45 ◽  
pp. 309-319
Author(s):  
Beatrice M. Tinsley
Keyword(s):  
Interstellar Medium ◽  
Chemical Evolution ◽  
Dynamical Evolution ◽  
Theoretical Background ◽  
Dynamical Processes ◽  
Chemical Enrichment ◽  
The Galaxy ◽  
History Of

Dynamical processes strongly affect the chemical enrichment of gas in galaxies, so abundances in stars and the Interstellar medium can be used as probes of the dynamical history of the Galaxy. By way of tying together some diverse points, rather than summarizing the conference, I shall discuss some examples of connections between chemical and dynamical evolution. The first section of this paper mentions some of the well-known ways in which dynamical processes can affect chemical evolution, in order to outline a theoretical background to the use of abundances as clues to dynamics.

scholarly journals MUSE unravels the ionisation and origin of metal-enriched absorbers in the gas halo of a z = 2.92 radio galaxy

2019 ◽  
Vol 625 ◽  
pp. A102 ◽  
Author(s):  
S. Kolwa ◽  
J. Vernet ◽  
C. De Breuck ◽  
M. Villar-Martín ◽  
A. Humphrey ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Radio Galaxy ◽  
Stellar Winds ◽  
Chemical Enrichment ◽  
Velocity Shift ◽  
The Galaxy ◽  
Spatially Extended ◽  
Nitrogen Abundance ◽  
Circumgalactic Medium ◽  
Projected Distance

We have used the Multi-Unit Spectroscopic Explorer (MUSE) to study the circumgalactic medium (CGM) of a z = 2.92 radio galaxy, MRC 0943−242 by parametrising its emitting and absorbing gas. In both Lyα λ1216 and He II λ1640 lines, we observe emission with velocity shifts of Δv ≃ −1000 km s−1 from the systemic redshift of the galaxy. These blueshifted components represent kinematically perturbed gas that is aligned with the radio axis, and is therefore a signature of jet-driven outflows. Three of the four known Lyα absorbers in this source are detected at the same velocities as C IV λλ1548, 1551 and N V λλ1239, 1243 absorbers, proving that the gas is metal-enriched more so than previously thought. At the velocity of a strong Lyα absorber which has an H I column of NH I/cm−2 = 1019.2 and velocity shift of Δv ≃ −400 km s−1, we also detect Si II λ1260 and Si II λ1527 absorption, which suggests that the absorbing gas is ionisation bounded. With the added sensitivity of this MUSE observation, we are more capable of adding constraints to absorber column densities and consequently determining what powers their ionisation. To do this, we obtain photoionisation grid models in CLOUDY which show that AGN radiation is capable of ionising the gas and producing the observed column densities in a gas of metallicity of Z/Z⊙ ≃ 0.01 with a nitrogen abundance a factor of 10 greater than that of hydrogen. This metal-enriched absorbing gas, which is also spatially extended over a projected distance of r ≳ 60 kpc, is likely to have undergone chemical enrichment through stellar winds that have swept up metals from the interstellar-medium and deposited them in the outer regions of the galaxy’s halo.

THE HELIUM CONTENT OF THE GALAXY

1965 ◽  
Vol 43 (9) ◽  
pp. 1616-1635 ◽  
Author(s):  
J. W. Truran ◽  
C. J. Hansen ◽  
A. G. W. Cameron
Keyword(s):  
Interstellar Medium ◽  
Stellar Evolution ◽  
Pure Hydrogen ◽  
Stellar Content ◽  
Initial Composition ◽  
Solar Mass ◽  
Helium Content ◽  
Numerical Studies ◽  
The Galaxy ◽  
Time Changes

It is usually assumed in modern theories of nucleosynthesis that the initial composition of the galaxy was pure hydrogen. The large solar and stellar content of helium has appeared to present a difficulty for such an assumption. This paper examines the problem. Numerical studies are made of the time changes in the compositions of stars and the interstellar medium as a result of stellar evolution. It is concluded that the large helium content of the sun and recently formed stars can be produced only as a result of the evolution of stars of approximately solar mass. Hence the initial hydrogen hypothesis requires a large age for the galaxy ([Formula: see text] years). The content of long-lived radioactivities in the interstellar medium is also followed as a function of time. It is found that the ratios of radioactivities are very insensitive functions of time and are approximately those observed in the solar system when the helium content is satisfactory. However, it is also concluded that these ratios give little useful information about cosmochronology.

scholarly journals Spectra of the Central Stars of Planetary Nebulae

1968 ◽  
Vol 34 ◽  
pp. 339-354 ◽  
Author(s):  
Lawrence H. Aller
Keyword(s):  
Observational Data ◽  
Stellar Evolution ◽  
Planetary Nebulae ◽  
Spectral Energy ◽  
Spectral Energy Distributions ◽  
Energy Distributions ◽  
Spectroscopic Observations ◽  
Theoretical Investigations ◽  
Late Stages ◽  
Central Stars

The central stars of planetary nebulae represent seemingly well-defined late stages of stellar evolution. Theoretical investigations with predictions of evolutionary tracks impose difficult requirements for observational data. Measurements of spectral energy distributions, of colors, and of magnitudes, and spectroscopic observations are all urgently needed.

scholarly journals The Contribution of Hipparcos to the Study of the Stellar Metal-Rich Population in the Solar Neighbourhood

1998 ◽  
Vol 11 (1) ◽  
pp. 566-566
Author(s):  
G. Cayrel de Strobel ◽  
C. Soubiran ◽  
Y. Lebreton
Keyword(s):  
High Resolution ◽  
Interstellar Medium ◽  
Evolved Stars ◽  
Spectroscopic Analyses ◽  
The Galaxy ◽  
Solar Metallicity ◽  
Metal Abundances ◽  
The Mean ◽  
Effective Temperatures ◽  
Absolute Magnitudes

The ‘1996 Edition’ of the Catalogue of [Fe/H] determinations by Cayrel de Strobel et al. (1997, A&A S 124,1) and two recent papers by Castro et al. (1997, AJ Vol.114, N.1) and by Feltzing and Gustafsson (A&A in press) have made possible to increase in the theoretical HR diagram (log Teff, Mbol the number of SMR stars. The SMR Stars of this new enlarged sample had to have reliable absolute magnitudes, coming all from Hipparcos parallaxes, precise bolometric corrections, effective temperatures and metal abundances from high resolution detailed spectroscopic analyses. With the help of an appropriate grid of isochrones computed by Lebreton (1997, Perryman et al. A&A, in press), ‘turn-off ages’could then be attributed to the slightly evolved stars (subgiants) of the sample. The (log Teff, Mbol) diagram constituted by the new sample of SMR stars, shows that the conclusions in a former paper by Cayrel de Strobel (1987, A&AJ 8,141) remain valid: the SMR stars areold stars in spite of their higher than solar metallicity. The result, that metal-rich stars were in the mean old stars, was interpreted in the 1987 paper as due to a more chemical uniformity of the nowadays interstellar medium of the Galaxy with respect of the older much more active interstellar medium.

scholarly journals Lithium survey in evolved stars observed in the sacy project

2009 ◽  
Vol 5 (S266) ◽  
pp. 368-368
Author(s):  
B. L. Canto Martins ◽  
S. Vieira ◽  
C. A. O. Torres ◽  
G. R. Quast ◽  
L. da Silva ◽  
...  
Keyword(s):  
Chemical Abundance ◽  
Echelle Spectrograph ◽  
Chemical Enrichment ◽  
Physical Mechanisms ◽  
Evolved Stars ◽  
Stellar Formation ◽  
The Galaxy ◽  
First Results ◽  
Subgiant Stars

AbstractThe primary goal of the sacy project (Search for Associations Containing Young Stars) was to identify possible associations of stars younger than the Pleiades association among optical counterparts of ROSAT X-ray-bright sources. The study of the chemical abundance in stars located in regions of stellar formation is extremely important to understand stellar nucleo-synthesis, the physical mechanisms controlling mixing in stellar interiors, and chemical enrichment in the Galaxy. The present work highights the first results of a chemical-abundance study of evolved stars identified in the sacy survey. For this, we performed a detailed spectroscopic analysis for the determination of atmospheric parameters and Li abundance for a sample of giant and subgiant stars. The observations were carried out with high resolution using the FEROS (R = 48 000) échelle spectrograph. We measured the stellar parameters (Teff, log g, vmic, [Fe/H]) from LTE analysis in the complete range of 420-1100 nm. Li abundance was derived from the region around the lithium line at 6707.78 Å for the entire sample of stars.

scholarly journals Inferring the parallax of Westerlund 1 from Gaia DR2

2019 ◽  
Vol 492 (2) ◽  
pp. 2497-2509 ◽  
Author(s):  
Mojgan Aghakhanloo ◽  
Jeremiah W Murphy ◽  
Nathan Smith ◽  
John Parejko ◽  
Mariangelly Díaz-Rodríguez ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Bayesian Model ◽  
Main Sequence ◽  
Zero Point ◽  
Star Cluster ◽  
Initial Mass ◽  
Data Release ◽  
The Galaxy ◽  
Late Stages ◽  
Gaia Dr2

ABSTRACT Westerlund 1 (Wd1) is potentially the largest star cluster in the Galaxy. That designation critically depends upon the distance to the cluster, yet the cluster is highly obscured, making luminosity-based distance estimates difficult. Using Gaia Data Release 2 (DR2) parallaxes and Bayesian inference, we infer a parallax of $0.35^{+0.07}_{-0.06}$ mas corresponding to a distance of $2.6^{+0.6}_{-0.4}$ kpc. To leverage the combined statistics of all stars in the direction of Wd1, we derive the Bayesian model for a cluster of stars hidden among Galactic field stars; this model includes the parallax zero-point. Previous estimates for the distance to Wd1 ranged from 1.0 to 5.5 kpc, although values around 5 kpc have usually been adopted. The Gaia DR2 parallaxes reduce the uncertainty from a factor of 3 to 18 per cent and rules out the most often quoted value of 5 kpc with 99 per cent confidence. This new distance allows for more accurate mass and age determinations for the stars in Wd1. For example, the previously inferred initial mass at the main-sequence turn-off was around 40 M⊙; the new Gaia DR2 distance shifts this down to about 22 M⊙. This has important implications for our understanding of the late stages of stellar evolution, including the initial mass of the magnetar and the LBV in Wd1. Similarly, the new distance suggests that the total cluster mass is about four times lower than previously calculated.

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