scholarly journals Empirical relations for the sensitivities of solar-like oscillations to magnetic perturbations

2020 ◽  
Vol 496 (4) ◽  
pp. 4593-4605
Author(s):  
René Kiefer ◽  
Anne-Marie Broomhall
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Oscillation Mode ◽  
Magnetic Activity ◽  
Stellar Model ◽  
Asymptotic Giant Branch ◽  
Empirical Relations ◽  
Magnetic Perturbations ◽  
Best Fitting ◽  
Oscillation Frequencies

ABSTRACT Oscillation mode frequencies of stars are typically treated as static for a given stellar model. However, in reality they can be perturbed by time-varying sources such as magnetic fields and flows. We calculate the sensitivities of radial p-mode oscillations of a set of models for masses between 0.7 and 3.0 M⊙ from the main sequence to the early asymptotic giant branch. We fit these mode sensitivities with polynomials in fundamental stellar parameters for six stages of stellar evolution. We find that the best-fitting relations differ from those proposed in the literature and change between stages of stellar evolution. Together with a measure of the strength of the perturbation, e.g. of the level of magnetic activity, the presented relations can be used for assessing whether a star’s observed oscillation frequencies are likely to be close to the unperturbed ground state or whether they should be adjusted.

scholarly journals Comparisons between observational color-magnitude diagrams and synthetic cluster diagrams for young star clusters in the Magellanic Clouds

1984 ◽  
Vol 105 ◽  
pp. 83-87
Author(s):  
Stephen A. Becker ◽  
Grant J. Mathews ◽  
Wendee M. Brunish
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Star Clusters ◽  
Theoretical Models ◽  
Young Star ◽  
Asymptotic Giant Branch ◽  
Current Status ◽  
Large Numbers ◽  
Young Star Clusters ◽  
Convective Overshoot

Young star clusters (<3 × 108 yr) in the Maqellanic Clouds (MC) can be used to test the current status of the theory of stellar evolution as applied to intermediate and massive stars. The color-magnitude diagram of many young clusters in the MC shows, unlike the case of clusters in our Galaxy, large numbers of stars in both the main sequence and post main sequence evolutionary phases. Usina a arid of stellar evolution models, synthetic cluster H-R diagrams are constructed and compared to observed color-magnitude diagrams to determine the age, age spread, and composition for any given cluster. In addition, for those cases where the data is of high quality, detailed comparisons between theory and observation can provide a diagnostic of the accuracy of the stellar evolution models. Initial indications of these comparisons suggest that the theoretical models should be altered to include: a larger value for the mixing length parameter (α), a larger rate of mass loss during the asymptotic giant branch (AGB) phase, and possibly convective overshoot during the core burning phases.

scholarly journals The possible role of stellar mergers for the formation of multiple stellar populations in globular clusters

2019 ◽  
Vol 491 (1) ◽  
pp. 440-454 ◽  
Author(s):  
Long Wang ◽  
Pavel Kroupa ◽  
Koh Takahashi ◽  
Tereza Jerabkova
Keyword(s):  
Stellar Evolution ◽  
Globular Clusters ◽  
Main Sequence ◽  
Stellar Populations ◽  
Initial Mass Function ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Mass Star ◽  
Main Sequence Stars ◽  
Stellar Mergers

ABSTRACT Many possible scenarios for the formation of multiple stellar populations (MSPs) in globular clusters (GCs) have been discussed so far, including the involvement of asymptotic giant branch stars, fast-rotating main-sequence stars, very massive main-sequence stars and mass-transferring massive binaries based on stellar evolution modelling. But self-consistent, dynamical simulations of very young GCs are usually not considered. In this work, we perform direct N-body modelling of such systems with total masses up to 3.2 × 105 M⊙, taking into account the observationally constrained primordial binary properties, and discuss the stellar mergers driven both by binary stellar evolution and dynamical evolution of GCs. The occurrence of stellar mergers is enhanced significantly in binary-rich clusters such that stars forming from the gas polluted by merger-driven ejection/winds would appear as MSPs. We thus emphasize that stellar mergers can be an important process that connects MSP formation with star cluster dynamics, and that multiple MSP formation channels can naturally work together. The scenario studied here, also in view of a possible top-heavy initial mass function, may be particularly relevant for explaining the high mass fraction of MSPs (the mass budget problem) and the absence of MSPs in young and low-mass star clusters.

scholarly journals Fast and Automated Peak Bagging with DIAMONDS (FAMED)

2020 ◽  
Vol 640 ◽  
pp. A130
Author(s):  
E. Corsaro ◽  
J. M. McKeever ◽  
J. S. Kuszlewicz
Keyword(s):  
Main Sequence ◽  
Oscillation Mode ◽  
Asymptotic Giant Branch ◽  
Helium Burning ◽  
Mode Identification ◽  
Wide Range ◽  
Oscillation Modes ◽  
Red Giant ◽  
Stellar Properties ◽  
Subgiant Stars

Stars of low and intermediate mass that exhibit oscillations may show tens of detectable oscillation modes each. Oscillation modes are a powerful tool to constrain the internal structure and rotational dynamics of the star, hence allowing one to obtain an accurate stellar age. The tens of thousands of solar-like oscillators that have been discovered thus far are representative of the large diversity of fundamental stellar properties and evolutionary stages available. Because of the wide range of oscillation features that can be recognized in such stars, it is particularly challenging to properly characterize the oscillation modes in detail, especially in light of large stellar samples. Overcoming this issue requires an automated approach, which has to be fast, reliable, and flexible at the same time. In addition, this approach should not only be capable of extracting the oscillation mode properties of frequency, linewidth, and amplitude from stars in different evolutionary stages, but also able to assign a correct mode identification for each of the modes extracted. Here we present the new freely available pipeline FAMED (Fast and AutoMated pEak bagging with DIAMONDS), which is capable of performing an automated and detailed asteroseismic analysis in stars ranging from the main sequence up to the core-helium-burning phase of stellar evolution. This, therefore, includes subgiant stars, stars evolving along the red giant branch (RGB), and stars likely evolving toward the early asymptotic giant branch. In this paper, we additionally show how FAMED can detect rotation from dipolar oscillation modes in main sequence, subgiant, low-luminosity RGB, and core-helium-burning stars.

Stellar Evolution, Mass Loss and Nucleosynthesis on the Asymptotic Giant Branch

1981 ◽  
Vol 4 (2) ◽  
pp. 145-148
Author(s):  
P. R. Wood
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Horizontal Branch ◽  
Helium Burning ◽  
Red Giant ◽  
Hr Diagram

In this review, I will be concentrating on problems related to the evolution of stars on the asymptotic giant branch (AGB). AGB stars are defined as stars which have completed core helium burning and have subsequently developed degenerate carbon/oxygen cores surrounded by hydrogen and helium burning shells; such stars have main sequence masses M≤9 M⊙ (Paczynski 1971; Becker and Iben 1980). In the HR diagram most AGB stars sit on the red giant branch. An exception to this rule occurs in Population II systems, where the AGB stars evolve asymptotically to the red giant branch from the blue side as the luminosity increases after completion of core helium burning on the horizontal branch.

scholarly journals The slowly pulsating B-star 18 Pegasi: A testbed for upper main sequence stellar evolution

2016 ◽  
Vol 591 ◽  
pp. L6 ◽  
Author(s):  
A. Irrgang ◽  
A. Desphande ◽  
S. Moehler ◽  
M. Mugrauer ◽  
D. Janousch
Keyword(s):  
Stellar Evolution ◽  
Main Sequence

scholarly journals Carbon stars as standard candles – II. The median J magnitude as a distance indicator

2020 ◽  
Vol 501 (1) ◽  
pp. 933-947
Author(s):  
Javiera Parada ◽  
Jeremy Heyl ◽  
Harvey Richer ◽  
Paul Ripoche ◽  
Laurie Rousseau-Nepton
Keyword(s):  
Luminosity Function ◽  
Asymptotic Giant Branch ◽  
Distance Modulus ◽  
Asymptotic Giant Branch Stars ◽  
Luminosity Functions ◽  
Best Fitting ◽  
Distance Indicator ◽  
Ngc 6822 ◽  
The Given ◽  
Giant Branch Stars

ABSTRACT We introduce a new distance determination method using carbon-rich asymptotic giant branch stars (CS) as standard candles and the Large and Small Magellanic Clouds (LMC and SMC) as the fundamental calibrators. We select the samples of CS from the ((J − Ks)0, J0) colour–magnitude diagrams, as, in this combination of filters, CS are bright and easy to identify. We fit the CS J-band luminosity functions using a Lorentzian distribution modified to allow the distribution to be asymmetric. We use the parameters of the best-fitting distribution to determine if the CS luminosity function of a given galaxy resembles that of the LMC or SMC. Based on this resemblance, we use either the LMC or SMC as the calibrator and estimate the distance to the given galaxy using the median J magnitude ($\overline{J}$) of the CS samples. We apply this new method to the two Local Group galaxies NGC 6822 and IC 1613. We find that NGC 6822 has an ‘LMC-like’ CS luminosity function, while IC 1613 is more ‘SMC-like’. Using the values for the median absolute J magnitude for the LMC and SMC found in Paper I we find a distance modulus of μ0 = 23.54 ± 0.03 (stat) for NGC 6822 and μ0 = 24.34 ± 0.05 (stat) for IC 1613.

scholarly journals New models for the rapid evolution of the central star of the Stingray Nebula

2021 ◽  
Author(s):  
T M Lawlor
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Planetary Nebula ◽  
Rapid Evolution ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Initial Mass ◽  
Thermal Pulse ◽  
The Past ◽  
New Models

Abstract We present stellar evolution calculations from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) phase for models of initial mass 1.2 M⊙ and 2.0 M⊙ that experience a Late Thermal Pulse (LTP), a helium shell flash that occurs following the AGB and causes a rapid looping evolution between the AGB and PN phase. We use these models to make comparisons to the central star of the Stingray Nebula, V839 Ara (SAO 244567). The central star has been observed to be rapidly evolving (heating) over the last 50 to 60 years and rapidly dimming over the past 20–30 years. It has been reported to belong to the youngest known planetary nebula, now rapidly fading in brightness. In this paper we show that the observed timescales, sudden dimming, and increasing Log(g), can all be explained by LTP models of a specific variety. We provide a possible explanation for the nebular ionization, the 1980’s sudden mass loss episode, the sudden decline in mass loss, and the nebular recombination and fading.

scholarly journals Constraints on pre-main-sequence evolution from stellar pulsations

2013 ◽  
Vol 9 (S301) ◽  
pp. 137-144
Author(s):  
M. P. Casey ◽  
K. Zwintz ◽  
D. B. Guenther
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Sequence Evolution ◽  
B Stars ◽  
Stellar Pulsations ◽  
Pms Stars

AbstractPulsating pre-main-sequence (PMS) stars afford the earliest opportunity in the lifetime of a star to which the concepts of asteroseismology can be applied. PMS stars should be structurally simpler than their evolved counterparts, thus (hopefully!) making any asteroseismic analysis relatively easier. Unfortunately, this isn't necessarily the case. The majority of these stars (around 80) are δ Scuti pulsators, with a couple of γ Doradus, γ Doradus – δ Scuti hybrids, and slowly pulsating B stars thrown into the mix. The majority of these stars have only been discovered within the last ten years, with the community still uncovering the richness of phenomena associated with these stars, many of which defy traditional asteroseismic analysis.A systematic asteroseismic analysis of all of the δ Scuti PMS stars was performed in order to get a better handle on the properties of these stars as a group. Some strange results have been found, including one star pulsating up to the theoretical acoustic cut-off frequency of the star, and a number of stars in which the most basic asteroseismic analysis suggests problems with the stars' positions in the Hertzsprung-Russell diagram. From this we get an idea of the\break constraints — or lack thereof — that these results can put on PMS stellar evolution.

scholarly journals Tracing early stellar evolution with asteroseismology: pre-main sequence stars in NGC 2264

2015 ◽  
Vol 101 ◽  
pp. 01010 ◽  
Author(s):  
Konstanze Zwintz ◽  
Luca Fossati ◽  
Tatiana Ryabchikova ◽  
David Guenther ◽  
Conny Aerts
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Main Sequence Stars

scholarly journals Oscillation mode linewidths and heights of 23 main-sequence stars observed byKepler

2014 ◽  
Vol 566 ◽  
pp. A20 ◽  
Author(s):  
T. Appourchaux ◽  
H. M. Antia ◽  
O. Benomar ◽  
T. L. Campante ◽  
G. R. Davies ◽  
...  
Keyword(s):  
Main Sequence ◽  
Oscillation Mode ◽  
Main Sequence Stars
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