Stellar models: firm evidence, open questions and future developments

AbstractDuring this last decade our knowledge of the evolutionary properties of stars has significantly improved. This result has been achieved thanks to our improved understanding of the physical behavior of stellar matter in the thermal regimes characteristic of the different stellar mass ranges and/or evolutionary stages.This notwithstanding, the current generation of stellar models is still affected by several, not negligible, uncertainties related to our poor knowledge of some thermodynamical processes and nuclear reaction rates, as well as the efficiency of mixing processes. These drawbacks have to be properly taken into account when comparing theory with observations, to derive evolutionary properties of both resolved and unresolved stellar populations.In this paper we review the major sources of uncertainty along the main evolutionary stages, and emphasize their impact on population synthesis techniques.

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An investigation of fine sediment mixing within free-flowing and surcharged manholes

Water Science & Technology ◽

10.2166/wst.1998.0052 ◽

1998 ◽

Vol 37 (1) ◽

pp. 215-222

Author(s):

I. Guymer ◽

R. O'Brien ◽

O. Mark ◽

P. Dennis

Keyword(s):

Dead Zone ◽

Laser Induced Fluorescence ◽

Fine Sediment ◽

Longitudinal Dispersion ◽

Qualitative Description ◽

Suspended Material ◽

Mixing Processes ◽

Future Developments ◽

Mixing Effects ◽

Sediment Mixing

Previous studies of the effects of manholes on longitudinal dispersion has concentrated on the spreading of solutes. This papers presents new data describing the influence of a surcharged and free-flowing manhole structure on the longitudinal dispersion of a fine suspended material. The effects of benching within the manhole structure are also illustrated. Laser Induced Fluorescence (LIF) techniques have been used to provide a qualitative description of the mixing processes present within a surcharged manhole. Nephelometric results have provided estimates of the parameters required to simulate the mixing effects using either increase in variance or aggregated dead zone techniques. A preliminary attempt at describing these observations using available software is discussed and recommendations for future developments are made.

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A Large Stellar Evolution Database for Population Synthesis Studies. II. Stellar Models and Isochrones for an α‐enhanced Metal Distribution

The Astrophysical Journal ◽

10.1086/501344 ◽

2006 ◽

Vol 642 (2) ◽

pp. 797-812 ◽

Cited By ~ 413

Author(s):

Adriano Pietrinferni ◽

Santi Cassisi ◽

Maurizio Salaris ◽

Fiorella Castelli

Keyword(s):

Stellar Evolution ◽

Metal Distribution ◽

Population Synthesis ◽

Stellar Models

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TP-AGB stars in population synthesis models

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310002498 ◽

2009 ◽

Vol 5 (S262) ◽

pp. 36-43 ◽

Cited By ~ 2

Author(s):

Paola Marigo ◽

Léo Girardi ◽

Alessandro Bressan ◽

Bernhard Aringer ◽

Marco Gullieuszik ◽

...

Keyword(s):

Mass Loss ◽

Stellar Evolution ◽

Magellanic Clouds ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Population Synthesis ◽

Future Developments ◽

First Results ◽

Nearby Galaxies ◽

The Subject

AbstractIn spite of its relevance, the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) phase is one of the most uncertain phases of stellar evolution, and a major source of disagreement between the results of different population synthesis models of galaxies. I will briefly review the existing literature on the subject, and recall the basic prescriptions that have been used to fix the contribution of TP-AGB stars to the integrated light of stellar populations. The simplicity of these prescriptions greatly contrasts with the richness of details provided by present-day databases of AGB stars in the Magellanic Clouds, which are now being extended to other nearby galaxies. I will present the first results of an ongoing study aimed at simulating photometry, chemistry, pulsation, mass loss, dust properties of AGB star populations in resolved and un-resolved galaxies. We test our predictions against observations from various surveys of the Magellanic Clouds (DENIS, 2MASS, OGLE, MACHO, Spitzer, and AKARI). I will discuss the implications and outline the plan of future developments.

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Physics under the bonnet of a stellar evolution code

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316006189 ◽

2015 ◽

Vol 11 (A29B) ◽

pp. 600-607

Author(s):

Richard J. Stancliffe

Keyword(s):

Magnetic Fields ◽

Stellar Evolution ◽

Reaction Rates ◽

Computational Method ◽

Atomic Diffusion ◽

Stellar Models ◽

Convective Boundaries ◽

The Way

AbstractJust how good are modern stellar models? Providing a rigorous assessment of the uncertainties is difficult because of the multiplicity of input physics. Some of the ingredients are reasonably well-known (like reaction rates and opacities). Others are not so good, with convection standing out as a particularly obvious example. In some cases, it is not clear what the ingredients should be: what role do atomic diffusion, rotation, magnetic fields, etc. play in stellar evolution? All this is then compounded by computational method. In converting all this physics into something we can implement in a 1D evolution code, we are forced to make choices about the way the equations are solved, how we will treat mixing at convective boundaries, etc. All of this can impact the models one finally generates. In this review, I will attempt to assess the uncertainties associated with the ingredients and methods used by stellar evolution modellers, and what their impacts may be on the science that we wish to do.

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Binary Population and Spectral Synthesis

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317003192 ◽

2016 ◽

Vol 12 (S329) ◽

pp. 396-396

Author(s):

J. J. Eldridge ◽

E. R. Stanway ◽

L. Xiao ◽

L. A. S. McClelland ◽

J. C. Bray ◽

...

Keyword(s):

Spectral Synthesis ◽

Stellar Populations ◽

Population Synthesis ◽

Single Star ◽

Individual Stars ◽

Star Models ◽

Theoretical Predictions ◽

Version 2.0 ◽

Stellar Models ◽

Better Than

AbstractWe have recently released version 2.0 of the Binary Population and Spectral Synthesis (BPASS) population synthesis code. This is designed to construct the spectra and related properties of stellar populations built from ~200,000 detailed, individual stellar models of known age and metallicity. The output products enable a broad range of theoretical predictions for individual stars, binaries, resolved and unresolved stellar populations, supernovae and their progenitors, and compact remnant mergers. Here we summarise key applications that demonstrate that binary populations typically reproduce observations better than single star models.

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Calibration of the Pre-Main Sequence Binary System RS Cha: Impact of the Initial Chemical Mixture

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307006059 ◽

2006 ◽

Vol 2 (S240) ◽

pp. 652-657

Author(s):

E. Alecian ◽

Y. Lebreton ◽

M.-J. Goupil ◽

M.-A. Dupret ◽

C. Catala

Keyword(s):

Binary System ◽

Main Sequence ◽

Reaction Rates ◽

Helium Abundance ◽

Chemical Mixture ◽

Spectroscopic Binary ◽

Initial Chemical Composition ◽

Effective Temperatures ◽

Stellar Models ◽

The Impact

AbstractAccurate observational data are available for the eclipsing double-lined spectroscopic binary system RS Cha, composed of two stars in the pre-main sequence stage of evolution: masses, radii, luminosities and effective temperatures of each component and metallicity of the system. This allows to build pre-main sequence stellar models representing the components of RS Cha and to constrain them in terms of physical ingredients, initial chemical composition and age.We present stellar models we have calculated using the CESAM stellar evolution code for different sets of physical inputs (opacities, nuclear reaction rates, etc.) and different initial parameters (global metallicity, helium abundance, individual abundances of heavy elements). We discuss their ability to reproduce the observational constraints simultaneously for the two components. We focus on the impact on the models of the chemical mixture adopted and we propose a calibration for the RS Cha system providing an estimate of its age and initial helium abundance.

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Transport and Exchange Processes in the Atmosphere over Mountainous Terrain: Perspectives and Challenges for Observational and Modelling Systems, from Local to Climate Scales

Atmosphere ◽

10.3390/atmos12020199 ◽

2021 ◽

Vol 12 (2) ◽

pp. 199

Author(s):

Dino Zardi ◽

Mathias W. Rotach

Keyword(s):

Complex Terrain ◽

Recent Progress ◽

Future Research ◽

Mountainous Terrain ◽

Special Issue ◽

Atmospheric Processes ◽

Multi Scale ◽

Future Developments ◽

Open Questions ◽

Exchange Processes

This Editorial offers an overview of the results presented in the series of coordinated articles included in the Atmosphere special issue on Atmospheric Processes over Complex Terrain. In particular, the variety of approaches and methods, as well as the main outcomes of recent progress in the field, are outlined, along with open questions and challenges for future developments. The possible outreach of future research in the field is also pointed out, especially in connection with the ongoing international cooperation initiative Multi-scale transport and exchange processes in the atmosphere over mountains programme and experiment (TEAMx).

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Predicting drug safety and communicating risk: benefits of a Bayesian approach

10.1101/193169 ◽

2017 ◽

Author(s):

Stanley E Lazic ◽

Nicholas Edmunds ◽

Christopher E. Pollard

Keyword(s):

Bayesian Methods ◽

External Information ◽

Pharmaceutical Companies ◽

Drug Discovery And Development ◽

Sources Of Uncertainty ◽

Open Questions ◽

Clear Link ◽

Diverse Data ◽

Bayesian Machine Learning

AbstractDrug toxicity is a major source of attrition in drug discovery and development. Pharmaceutical companies routinely use preclinical data to predict clinical outcomes and continue to invest in new assays to improve predictions. However, there are many open questions about how to make the best use of available data, combine diverse data, quantify risk, and communicate risk and uncertainty to enable good decisions. The costs of suboptimal decisions are clear: resources are wasted and patients may be put at risk. We argue that Bayesian methods provide answers to all of these problems and use hERG-mediated QT prolongation as a case study. Benefits of Bayesian machine learning models include intuitive probabilistic statements of risk that incorporate all sources of uncertainty, the option to include diverse data and external information, and visualisations that have a clear link between the output from a statistical model and what this means for risk. Furthermore, Bayesian methods are easy to use with modern software, making their adoption for safety screening straightforward. We include R and Python code to encourage the adoption of these methods.

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s-Processing in Asymptotic Giant Branch Stars in the Light of Revised Neutron-Capture Cross Sections

Universe ◽

10.3390/universe7070239 ◽

2021 ◽

Vol 7 (7) ◽

pp. 239

Author(s):

Diego Vescovi ◽

René Reifarth

Keyword(s):

Cross Sections ◽

Neutron Capture ◽

Reaction Rates ◽

Asymptotic Giant Branch ◽

Asymptotic Giant Branch Stars ◽

Capture Cross ◽

Magnetic Buoyancy ◽

Stellar Models ◽

Pocket Formation ◽

Capture Cross Sections

Current AGB stellar models provide an adequate description of the s-process nucleosynthesis that occurs. Nonetheless, they still suffer from many uncertainties related to the modeling of the 13C pocket formation and the adopted nuclear reaction rates. For many important s-process isotopes, a best set of neutron-capture cross sections was recently re-evaluated. Using stellar models prescribing that the 13C pocket is a by-product of magnetic-buoyancy-induced mixing phenomena, s-process calculations were carried out with this database. Significant effects are found for a few s-only and branching point isotopes, pointing out the need for improved neutron-capture cross section measurements at low energy.

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[Fe/H] and lithium Abundance for Detached Eclipsing Binaries

International Astronomical Union Colloquium ◽

10.1017/s0252921100017711 ◽

1993 ◽

Vol 137 ◽

pp. 177-179

Author(s):

J.V. Clausen

Keyword(s):

Globular Clusters ◽

Reaction Rates ◽

Eclipsing Binaries ◽

The Sun ◽

Lithium Abundance ◽

Unique Role ◽

Pulsating Stars ◽

Stellar Models ◽

New Generation ◽

Metal Ratios

We are now seeing a new generation of stellar models based on the recent opacity tables by Rogers and Iglesias (1992). Various changes in other important physical ingredients like nuclear reaction rates, convection parameters, mass loss rates, helium/metal ratios, relative abundances of heavy elements etc. are also included. Besides the Sun the most obvious objects for confrontation of the new grids with observations are binary components, pulsating stars, and well-studied open and globular clusters. Among these candidates the detached, double-lined eclipsing binaries play a unique role as our only source of absolute dimensions which 1) can be considered valid for single stars and 2) are accurate enough for serious tests of the input physics of modern stellar models.

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