scholarly journals Surveys for Field Carbon Stars in the Magellanic Clouds

1994 ◽  
Vol 161 ◽  
pp. 509-512 ◽  
Author(s):  
M. Azzopardi ◽  
E. Rebeirot ◽  
B.E. Westerlund
Keyword(s):  
Stellar Population ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Carbon Stars ◽  
Dwarf Spheroidal Galaxies ◽  
Giant Stars ◽  
Intermediate Mass Stars ◽  
Nearest Neighbours ◽  
The Mean ◽  
Red Giant

The Asymptotic Giant Branch (AGB) stage is the normal luminous phase of evolution of intermediate-mass stars (slightly less than 1 M ⊙ up to very roughly 3 M ⊙) and therefore the AGB stars play a noteworthy role in our understanding of the chemical evolution of galactic systems. Furthermore it is now generally accepted that the ratio of carbon (C) stars to late-type M giant stars can be used to estimate the mean metallicity of the stellar population of a system, or the change in metallicity from the inner to the outer parts of a galaxy. It is for these reasons among others that red giant stars have been searched for in nearby local group galaxies, principally in our nearest neighbours, the Magellanic Clouds and the dwarf spheroidal galaxies. This paper will be particularly devoted to the slitless spectroscopy surveys for carbon stars in the Magellanic Clouds.

scholarly journals Red Giant Stars: Comparison of Observations and Theory

1984 ◽  
Vol 108 ◽  
pp. 195-206
Author(s):  
Jeremy Mould
Keyword(s):  
Mass Loss ◽  
Parameter Space ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Carbon Stars ◽  
Giant Stars ◽  
Theoretical Investigations ◽  
Red Giant

Recent observations in both the field and the clusters of the Magellanic Clouds suggest a higher mass loss rate during or at the end of the asymptotic giant branch phase than previously supposed. Recent theoretical investigations offer an explanation for the frequency of carbon stars in the Clouds, but a rich parameter space remains to be explored, before detailed agreement can be expected.

scholarly journals Nucleosynthesis in Red Giant Stars

2002 ◽  
Vol 187 ◽  
pp. 57-69
Author(s):  
Nami Mowlavi
Keyword(s):  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Asymptotic Giant Branch Stars ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Giant Stars ◽  
Intermediate Mass Stars ◽  
Standard Models ◽  
Red Giant ◽  
Giant Branch Stars

The production of elements from helium-3 to fluorine in low- and intermediate-mass stars is reviewed and compared to chemical abundances observed at the surface of both red giant branch and asymptotic giant branch stars. It is highlighted that, while the trends predicted by standard models are generally well confirmed, many chemical abundances observed at the surface of red giants require the operation of non-standard mixing in the stellar interior. In addition, chemical abundance predictions from presently available asymptotic giant branch models further suffer from the uncertainties affecting the third dredge-up phenomenon, the source of neutrons and the hot bottom burning process.

scholarly journals Discovery of s-process enhanced stars in the LAMOST survey

2019 ◽  
Vol 490 (2) ◽  
pp. 2219-2227 ◽  
Author(s):  
Brodie J Norfolk ◽  
Andrew R Casey ◽  
Amanda I Karakas ◽  
Matthew T Miles ◽  
Alex J Kemp ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Selection Bias ◽  
Galactic Halo ◽  
Asymptotic Giant Branch ◽  
The Other ◽  
Data Driven ◽  
Giant Stars ◽  
Show Evidence ◽  
Data Driven Approach ◽  
Red Giant

ABSTRACT Here we present the discovery of 895 s-process-rich candidates from 454 180 giant stars observed by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) using a data-driven approach. This sample constitutes the largest number of s-process enhanced stars ever discovered. Our sample includes 187 s-process-rich candidates that are enhanced in both barium and strontium, 49 stars with significant barium enhancement only and 659 stars that show only a strontium enhancement. Most of the stars in our sample are in the range of effective temperature and log g typical of red giant branch (RGB) populations, which is consistent with our observational selection bias towards finding RGB stars. We estimate that only a small fraction (∼0.5 per cent) of binary configurations are favourable for s-process enriched stars. The majority of our s-process-rich candidates (95 per cent) show strong carbon enhancements, whereas only five candidates (<3  per cent) show evidence of sodium enhancement. Our kinematic analysis reveals that 97 per cent of our sample are disc stars, with the other 3 per cent showing velocities consistent with the Galactic halo. The scaleheight of the disc is estimated to be $z_{\rm h}=0.634 \pm {0.063}\, \mathrm{kpc}$, comparable with values in the literature. A comparison with yields from asymptotic giant branch (AGB) models suggests that the main neutron source responsible for the Ba and Sr enhancements is the 13C(α,n)16O reaction. We conclude that s-process-rich candidates may have received their overabundances via mass transfer from a previous AGB companion with an initial mass in the range $1\!-\!3\, \mathrm{M}_{\odot }$.

29. Stellar Spectra (Spectres Stellaires)

1991 ◽  
Vol 21 (1) ◽  
pp. 309-326
Keyword(s):  
Milky Way ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Dynamical Interaction ◽  
Stellar Spectra ◽  
Luminous Blue Variables ◽  
Classical Novae ◽  
Giant Stars ◽  
Red Giant ◽  
Sydney Australia

In the triennium under review, from the late second half of 1987 to the early second half of 1990, Commission 29 has sponsored or cosponsored the following IAU Conferences: Coll. No. 106, “Evolution of Peculiar Red Giant Stars,” Bloomington, Indiana, July 1988; CoU. No. 114, “White Dwarfs,” Hanover, New Hamsphire, August 1988; Coll. No. 113, “Physics of Luminous Blue Variables,” Val Morin, Quebec, August 1988; Coll. No. 122, “Physics of Classical Novae,” Madrid, Spain, June 1989; Symp. No. 143, “Wolf-Rayet Stars and Interrelations with Other Massive Stars in Galaxies,” Denpasar, Indonesia, June 1990; Symp. No 148, “The Magellanic Clouds and their Dynamical Interaction with the Milky Way,” Sydney, Australia, July 1990; Symp. No. 145, “Evolution of Stars: the Photospheric Abundance Connection,” Druzba, Bulgaria. August 1990.

scholarly journals Models of stellar population at high redshift, as constrainedby PN yields and luminosity function

2015 ◽  
Vol 11 (A29B) ◽  
pp. 26-32
Author(s):  
C. Maraston
Keyword(s):  
Luminosity Function ◽  
Stellar Population ◽  
High Redshift ◽  
Spectral Energy Distribution ◽  
Population Models ◽  
Asymptotic Giant Branch ◽  
Theoretical Modelling ◽  
Spectral Energy ◽  
Evolutionary Stage ◽  
Intermediate Mass Stars

AbstractThe stellar phase of Thermally-Pulsating Asymptotic giant branch is the last major evolutionary stage of intermediate-mass stars which afterwards evolve into planetary nebulae. The TP-AGB phase is affected by mass-loss and instabilities which notoriously make its theoretical modelling uncertain. This review focuses on the effects such modelling has on stellar population models for galaxies, with particular focus on the high-z Universe where galaxies are young and contain a large number of short-living TP-AGB stars. I shall present the models, discuss how different prescriptions for the treatment of the TP-AGB affect the theoretical integrated spectral energy distribution and how these compare to galaxy data, and discuss implications for the PN nebulae luminosity function stemming from the various assumptions. Finally I shall discuss the inclusion of hot evolved stars on stellar population models and how they compare to data for old galaxies at our present time.

scholarly journals Observations of Lithium in red giant stars

2009 ◽  
Vol 5 (S268) ◽  
pp. 301-309
Author(s):  
Verne V. Smith
Keyword(s):  
Stellar Evolution ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Asymptotic Giant Branch Stars ◽  
Multiple Sources ◽  
Lithium Abundance ◽  
Giant Stars ◽  
Red Giant ◽  
First Time ◽  
Giant Branch Stars

AbstractConnections between observations of the lithium abundance in various types of red giants and stellar evolution are discussed here. The emphasis is on three main topics; 1) the depletion of Li as stars ascend the red giant branch for the first time, 2) the synthesis of 7Li in luminous and massive asymptotic giant branch stars via the mechanism of hot-bottom burning, and 3) the possible multiple sources of excess Li abundances found in a tiny fraction of various types of G and K giants.

scholarly journals Small amplitude variable red giants

2006 ◽  
Vol 2 (S239) ◽  
pp. 379-381
Author(s):  
D. R. Xiong ◽  
L. Deng
Keyword(s):  
Small Amplitude ◽  
Turning Point ◽  
Magellanic Clouds ◽  
Photometric Data ◽  
Red Giants ◽  
Giant Stars ◽  
Dependent Theory ◽  
Long Time ◽  
Non Local ◽  
Red Giant

AbstractSmall amplitude variable red giants were discovered long time ago (Eggen 1969, Henry et al. 2000, Jorison et al. 1997). The revolutionary turning point for the study of this type of variable was due to the work of Wood (2000) and Soszyński et al. (2004) based on the very large stellar sample of the Magellanic clouds MACHO project and OGLE photometric data. By using our non-local time-dependent theory of convection (Xiong 1989), we carried out a linear stability survey for red giants with initial mass of M = 1 − 3M⊙. Explanations for the observed variabilities and analysis of mode identifications in red giant stars are presented in this work.

scholarly journals γ Doradus stars as a test of angular momentum transport models

2019 ◽  
Vol 626 ◽  
pp. A121 ◽  
Author(s):  
R.-M. Ouazzani ◽  
J. P. Marques ◽  
M.-J. Goupil ◽  
S. Christophe ◽  
V. Antoci ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Evolutionary Models ◽  
Intermediate Mass ◽  
Angular Momentum Transport ◽  
Rotation Rates ◽  
Giant Stars ◽  
Intermediate Mass Stars ◽  
Red Giant ◽  
Core Rotation

Helioseismology and asteroseismology of red giant stars have shown that distribution of angular momentum in stellar interiors, and the evolution of this distribution with time remains an open issue in stellar physics. Owing to the unprecedented quality and long baseline of Kepler photometry, we are able to seismically infer internal rotation rates in γ Doradus stars, which provide the main-sequence counterpart to the red-giants puzzle. Here, we confront these internal rotation rates to stellar evolution models which account for rotationally induced transport of angular momentum, in order to test angular momentum transport mechanisms. On the one hand, we used a stellar model-independent method developed by our team in order to obtain accurate, seismically inferred, buoyancy radii and near-core rotation for 37 γ Doradus stars observed by Kepler. We show that the stellar buoyancy radius can be used as a reliable evolution indicator for field stars on the main sequence. On the other hand, we computed rotating evolutionary models of intermediate-mass stars including internal transport of angular momentum in radiative zones, following the formalism developed in the series of papers started by Zahn (1992, A&A, 265, 115), with the CESTAM code. This code calculates the rotational history of stars from the birth line to the tip of the RGB. The initial angular momentum content has to be set initially, which is done here by fitting rotation periods in young stellar clusters. We show a clear disagreement between the near-core rotation rates measured in the sample and the rotation rates obtained from the evolutionary models including rotationally induced transport of angular momentum following Zahn’s prescriptions. These results show a disagreement similar to that of the Sun and red giant stars in the considered mass range. This suggests the existence of missing mechanisms responsible for the braking of the core before and along the main sequence. The efficiency of the missing mechanisms is investigated. The transport of angular momentum as formalized by Zahn and Maeder cannot explain the measurements of near-core rotation in main-sequence intermediate-mass stars we have at hand.

scholarly journals A CFH12K Survey of Red Giant Stars in the M81 Group

2004 ◽  
Vol 217 ◽  
pp. 90-91 ◽  
Author(s):  
Patrick R. Durrell ◽  
Megan E. DeCesar ◽  
Robin Ciardullo ◽  
Denise Hurley-Keller ◽  
John J. Feldmeier
Keyword(s):  
Asymptotic Giant Branch ◽  
Wide Field ◽  
Agb Stars ◽  
Field Sampling ◽  
Giant Stars ◽  
Tidal Tail ◽  
Dimensional Distribution ◽  
Red Giant ◽  
The Many ◽  
Tidal Tails

We present the preliminary results of a wide-field photometric survey of individual red giant branch (RGB) and asymptotic giant branch (AGB) stars in the M81 group, performed with the CFH12K mosaic camera of the CFHT. We use deep VI images of 0.65 sq. deg. of sky to map out the two-dimensional distribution of intragroup stars and to search for stars associated with the many HI tidal tails in the group. We place an upper limit on the presence of metal-poor RGB stars in a field located 50-80 kpc from M81, and derive an ‘intragroup’ fraction of < 2%. In a field sampling the M81-NGC3077 HI tidal tail, we find blue stars associated with some of the tidal features, including 2 clumps which we tentatively describe as tidal dwarf candidates. These objects are ~ 1 kpc in size, and, based on their color-magnitude diagrams, have formed stars as recently as ~ 30 – 70 Myr ago, long after the group's most recent interactions.

scholarly journals Chemical composition of giant stars in the open cluster IC 4756

2018 ◽  
Vol 615 ◽  
pp. A165 ◽  
Author(s):  
Vilius Bagdonas ◽  
Arnas Drazdauskas ◽  
Gražina Tautvaišienė ◽  
Rodolfo Smiljanic ◽  
Yuriy Chorniy
Keyword(s):  
Chemical Elements ◽  
Open Cluster ◽  
Theoretical Models ◽  
Open Clusters ◽  
Galactic Chemical Evolution ◽  
Element Abundances ◽  
Giant Stars ◽  
Thin Disc ◽  
The Mean ◽  
Red Giant

Context. Homogeneous investigations of red giant stars in open clusters contribute to studies of internal evolutionary mixing processes inside stars, which are reflected in abundances of mixing-sensitive chemical elements like carbon, nitrogen, and sodium, while α- and neutron-capture element abundances are useful in tracing the Galactic chemical evolution. Aims. The main aim of this study is a comprehensive chemical analysis of red giant stars in the open cluster IC 4756, including determinations of 12C∕13C and C/N abundance ratios, and comparisons of the results with theoretical models of stellar and Galactic chemical evolution. Methods. We used a classical differential model atmosphere method to analyse high-resolution spectra obtained with the FEROS spectrograph on the 2.2 m MPG/ESO Telescope. The carbon, nitrogen, and oxygen abundances, 12C∕13C ratios, and neutron-capture element abundances were determined using synthetic spectra, and the main atmospheric parameters and abundances of other chemical elements were determined from equivalent widths of spectral lines. Results. We have determined abundances of 23 chemical elements for 13 evolved stars and 12C∕13C ratios for six stars of IC 4756. The mean metallicity of this cluster, as determined from nine definite member stars, is very close to solar – [Fe/H] = − 0.02 ± 0.01. Abundances of carbon, nitrogen, and sodium exhibit alterations caused by extra-mixing: the mean 12C∕13C ratio is lowered to 19 ± 1.4, the C/N ratio is lowered to 0.79 ± 0.05, and the mean [Na/Fe] value, corrected for deviations from the local thermodynamical equilibrium encountered, is enhanced by 0.14 ± 0.05 dex. We compared our results to those by other authors and theoretical models. Conclusions. Comparison of the α-element results with the theoretical models shows that they follow the thin disc α-element trends. Being relatively young (~ 800 Myr), the open cluster IC 4756 displays a moderate enrichment of s-process-dominated chemical elements compared to the Galactic thin disc model and confirms the enrichment of s-process-dominated elements in young open clusters compared to the older ones. The r-process-dominated element europium abundance agrees with the thin disc abundance. From the comparison of our results for mixing-sensitive chemical elements and the theoretical models, we can see that the mean values of 12C∕13C, C/N, and [Na/Fe] ratios lie between the model with only the thermohaline extra-mixing included and the model which also includes the rotation-induced mixing. The rotation was most probably smaller in the investigated IC 4756 stars than 30% of the critical rotation velocity when they were on the main sequence.

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