Theoretical Underpinnings: Modeling Stars

2017 ◽  
Author(s):  
Sarbani Basu ◽  
William J. Chaplin
Keyword(s):  
Thermal Equilibrium ◽  
Total Mass ◽  
Stellar Structure ◽  
Conservation Of Mass ◽  
Elemental Abundances ◽  
The Core ◽  
Self Consistent ◽  
Consistent Manner ◽  
Independent Variable ◽  
Stellar Oscillation

This chapter provides a brief description of the process of constructing models for the interpretation of stellar oscillation data. The equations of stellar structure are basically statements of conservation—of mass, momentum, and energy—along with the conditions required for thermal equilibrium. The equations of stellar structure are written with mass as the independent variable. Here, a star is divided into many mass shells, from the center at m = 0 to the surface at m = M, where M is the total mass of the star, and a model is obtained by solving the set of equations at each mass shell in a self-consistent manner. In addition, the chapter considers energy generation and how energy is transported from the core to the surface, as well as how elemental abundances change as a function of time.

scholarly journals The Vogt-Russell Theorem, and New Results on an Old Problem

1978 ◽  
Vol 80 ◽  
pp. 303-311
Author(s):  
Helmuth Kähler
Keyword(s):  
Existence And Uniqueness ◽  
Thermal Equilibrium ◽  
Equilibrium Configuration ◽  
Mathematical Proof ◽  
Stellar Structure

Half a centry ago Henry Norris Russell and Heinrich Vogt independently made a conjecture concerning the structure of spherical stars which are in hydrostatic and thermal equilibrium (Russell, 1927; Vogt, 1926). This conjecture has later come to be known as the Vogt-Russell theorem and is usually formulated as follows: The structure of a star is uniquely determined by the mass and the composition. In other words, the statement claims the existence and uniqueness of a stellar equilibrium configuration for given parameters mass and composition, and you may find what is called a mathematical proof in many textbooks on stellar structure.

scholarly journals Observations of Molecules in Stellar Atmospheres - Chemistry Near Thermal Equilibrium

1987 ◽  
Vol 120 ◽  
pp. 583-598
Author(s):  
David L. Lambert
Keyword(s):  
Thermodynamic Equilibrium ◽  
Thermal Equilibrium ◽  
Local Thermodynamic Equilibrium ◽  
Stellar Atmospheres ◽  
Red Giants ◽  
The Sun ◽  
Carbon Stars ◽  
General Review ◽  
Elemental Abundances

A general review is given of the astrophysical information obtainable from observations of molecules in stellar photospheres. Through selected examples, the use of molecules as thermometers (e.g., the OH 3 μm V-R lines in the Sun and α Ori) and as probes of the isotopic (e.g., iMg in metal-poor dwarfs, 12C/13C in cool carbon stars) and elemental abundances (e.g., CNO in red giants) is sketched. All of the (carefully) selected analyses assume that local thermodynamic equilibrium (LTE) prevails.

scholarly journals The Origin of the RS CVn Binaries

1976 ◽  
Vol 73 ◽  
pp. 381-387 ◽  
Author(s):  
P. Biermann ◽  
D. S. Hall
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Total Mass ◽  
Total Angular Momentum ◽  
Main Sequence ◽  
Be Stars ◽  
Large Space ◽  
Single Star ◽  
The Core ◽  
Thermal Phase

We consider six possible origins for the RS CVn binaries based on the following possibilities. RS CVn binaries might now be either pre-main-sequence or post-main-sequence. A pre-main-sequence binary might not always have been a binary but might have resulted from fission of a rapidly rotating single pre-main-sequence star. The main-sequence counterparts might be either single stars or binaries.To decide which of the six origins is possible, we consider the following observed data for the RS CVn binaries: total mass, total angular momentum, lack of observed connection with regions of star formation, large space density, kinematical age, and the visual companion of WW Dra. In addition we consider lifetimes and space densities of single stars and other types of binaries.The only origin possible is that the RS CVn binaries are in a thermal phase following fission of a main-sequence single star. In this explanation the single star had a rapidly rotating core which became unstable due to the core contraction which made it begin to evolve off the main sequence. The present Be stars might be examples of such parent single stars.

scholarly journals Analyses of the LMC Novae

1999 ◽  
Vol 190 ◽  
pp. 391-392
Author(s):  
Karen M. Vanlandingham ◽  
Greg J. Schwarz ◽  
Sumner Starrfield ◽  
Peter H. Hauschildt ◽  
Steven N. Shore ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Large Magellanic Cloud ◽  
Optical Spectra ◽  
Classical Novae ◽  
Preliminary Results ◽  
Elemental Abundances ◽  
Ultraviolet Spectra ◽  
The Past ◽  
Consistent Manner ◽  
Ism Abundances

In the past 10 years, 6 classical novae have been observed in the Large Magellanic Cloud (LMC). We have begun a study of these objects using ultraviolet spectra obtained by IUE and optical spectra from nova surveys. We are using the results of this study to further our understanding of novae and stellar evolution.Our study includes analysis of both the early, optically thick spectra using model atmospheres (Hauschildt et al. 1992), and the later nebular spectra using optimization of photoionization codes (Ferland 1996; James & Roos 1993). By analysing all the LMC novae in a consistent manner, we can compare their individual results and use their combined properties to calibrate Galactic novae. In addition, our studies can be used to determine the elemental abundances of the nova ejecta, the amount of mass ejected, and the contribution of novae to the ISM abundances. To date we have analysed Nova LMC 1988#1 (Schwarz et al. 1998) and Nova LMC 1990#1 (Vanlandingham et al. 1999), and have obtained preliminary results for Nova LMC 1991. The results of this work are presented in this poster.

scholarly journals Direct simulation on nonlinear thermokinetic phenomena due to induced-charge electroosmosis

2018 ◽  
Vol 855 ◽  
pp. 736-769 ◽  
Author(s):  
Hideyuki Sugioka
Keyword(s):  
Electric Field ◽  
Vortex Flow ◽  
Direct Simulation ◽  
General Phenomenon ◽  
Dielectric Particles ◽  
Self Consistent ◽  
Physics Simulation ◽  
Normal Diffusion ◽  
Consistent Manner ◽  
The Stokes Equation

Previously, we proposed a novel mechanism to produce a nonlinear thermokinetic phenomenon (NTKP) around a metal cylinder in an electrolyte on the basis of analytical discussion. In this study, by using a non-steady direct multi-physics simulation technique based on the Stokes equation coupled with the electroosmotic equation that considers normal diffusion, electrophoresis and thermal diffusion, we directly verify the NTKP and show that the original driving force is the excess ions pressed on the particle by the thermokinetic force and that the NTKP vortex flow around the particle is generated by the interaction between the excess ion and the electric field that is made by the excess ions and/or the Seebeck electric field due to the blocking boundary condition on the wall. Namely, two types of NTKP exist and they are explained in a self-consistent manner by our new theory. In addition, through the discussion of a dielectric particle, we show that the NTKP is a general phenomenon that can be found in both metal and dielectric particles. We believe that our findings provide a new unified viewpoint to understand complex thermokinetic phenomena near metal and dielectric particles.

Research on Heat Transfer Characteristics of the Thermometric Sphere in HTR-10

2018 ◽  
Author(s):  
Shiyan Sun ◽  
Youjie Zhang ◽  
Yanhua Zheng ◽  
Xiang Fang ◽  
Xiaoyong Yang
Keyword(s):  
Heat Transfer ◽  
Thermal Equilibrium ◽  
Reactor Core ◽  
Fluid Temperature ◽  
Heat Transfer Characteristics ◽  
Pebble Bed ◽  
The Core ◽  
Temperature Measuring ◽  
Transfer Characteristics ◽  
Metal Wires

During the operation of the High Temperature Gas-cooled Reactor (HTGR), the hot-spot temperature in the reactor core must be lower than the maximum permissible temperature of the fuel elements and the materials of construction, so that the reactor kept safe. However, no fixed temperature-measuring devices can be set in a pebble-bed core. A special spherical temperature-measuring device is adopted to make sure it brings as small impact to the reactor operation as possible. There are several metal wires with different melting points inside. The graphite thermometric balls will be put onto the top of HTR-10 reactor core, and they record and reflect the highest temperature in different positions in the core when flowing in the pebble bed. Before the reactor core temperature-measuring experiment of HTR-10, we must study the heat transfer characteristics of the graphite thermometric sphere to find out the relationship of the melting conditions and the temperature in the reactor core. A 3-D model of the graphite thermometric ball is established, and CFD method is adopted to research and figure out the thermal equilibrium time and temperature difference between the metal wires in the ball and the hot fluid outside the balls. Multiple situations are simulated, and the heat transfer process of the thermometric sphere is comprehensively studied. The heat convection is certified the most important aspect. Thermal equilibrium can be achieved within 19 minutes, far shorter than the period while the spheres flowing through the core. The simulation results can also applied to derive the thermal fluid temperature backward.

Experimentation in the Study of Religion and Politics

2019 ◽  
Author(s):  
Paul A. Djupe ◽  
Amy Erica Smith
Keyword(s):  
Public Life ◽  
Religion And Politics ◽  
Experimental Methods ◽  
Potential Effect ◽  
Religious Groups ◽  
Treatment Groups ◽  
Political Beliefs ◽  
The Core ◽  
Political Outcome ◽  
Independent Variable

Experiments in religion and politics model a communication system with three elements: who (the sample) is exposed to what (the treatment) and with what potential effect (the outcome). Most experiments in religion and politics focus on one of three types of samples: clergy, the faithful within certain religious groups, or all citizens within a polity. At the core of the experiment is the randomized treatment: an independent variable that the researcher manipulates and randomly assigns to treatment groups that are supposed to be equivalent in all other respects. Certain kinds of treatments tend to be associated with certain kinds of hypothesized outcomes. That is, most experiments in religion and politics involve investigating either (a) how a randomized treatment related to religion affects a political outcome or (b) how a randomized treatment related to politics affects a religious outcome. There are several types of religious treatments that closely mirror the actual insertion of religion into public life: manipulating candidates’ religious affiliations, behavior, and rhetoric; manipulating appeals attributed to religious elites and institutions; priming subjects’ own religious or political beliefs or manipulating other religious attributes of subjects; manipulating the characteristics of other citizens; and manipulating religious institutional cues received by clergy. Experimental methods are everywhere now in the study of religion and politics and provide clear benefits for understanding how religion and politics interact. Perhaps most importantly, the method imposes intellectual rigor, helping scholars pin down theoretically and empirically the precise mechanisms involved in the mutual impact between religion and politics. In addition, experimental control enables scholars to assert more confidently the direction of influence among variables that in the real world plausibly influence each other.

scholarly journals Relative importance of convective uncertainties in massive stars

2020 ◽  
Vol 496 (2) ◽  
pp. 1967-1989 ◽  
Author(s):  
Etienne A Kaiser ◽  
Raphael Hirschi ◽  
W David Arnett ◽  
Cyril Georgy ◽  
Laura J A Scott ◽  
...  
Keyword(s):  
Convective Zone ◽  
Stellar Structure ◽  
Convective Boundary ◽  
Hydrogen Burning ◽  
Surface Evolution ◽  
Boundary Mixing ◽  
The Core ◽  
Boundary Location ◽  
Parameter Values ◽  
The Impact

ABSTRACT In this work, we investigate the impact of uncertainties due to convective boundary mixing (CBM), commonly called ‘overshoot’, namely the boundary location and the amount of mixing at the convective boundary, on stellar structure and evolution. For this we calculated two grids of stellar evolution models with the MESA code, each with the Ledoux and the Schwarzschild boundary criterion, and vary the amount of CBM. We calculate each grid with the initial masses of 15, 20, and $25\, \rm {M}_\odot$. We present the stellar structure of the models during the hydrogen and helium burning phases. In the latter, we examine the impact on the nucleosynthesis. We find a broadening of the main sequence with more CBM, which is more in agreement with observations. Furthermore, during the core hydrogen burning phase there is a convergence of the convective boundary location due to CBM. The uncertainties of the intermediate convective zone remove this convergence. The behaviour of this convective zone strongly affects the surface evolution of the model, i.e. how fast it evolves redwards. The amount of CBM impacts the size of the convective cores and the nucleosynthesis, e.g. the 12C to 16O ratio and the weak s-process. Lastly, we determine the uncertainty that the range of parameter values investigated introduces and we find differences of up to $70{{\ \rm per\ cent}}$ for the core masses and the total mass of the star.

scholarly journals N and Fe-Peak Elemental Abundances from IUE Co-Added Spectra of Hg-Mn and Normal Stars

1993 ◽  
Vol 138 ◽  
pp. 154-160
Author(s):  
Scott W. Roby ◽  
Saul J. Adelman ◽  
David S. Leckrone ◽  
Charles Cowley ◽  
Glenn M. Wahlgren
Keyword(s):  
Optical Spectra ◽  
High Quality ◽  
Term Study ◽  
Data Set ◽  
B Stars ◽  
Elemental Abundances ◽  
Long Term Study ◽  
Self Consistent ◽  
Good Agreement

AbstractLeckrone and Adelman have established an IUE observing strategy that has yielded co-added spectra with enhanced S/N ratios for several A and B stars. New observations by Roby and Adelman using the same technique have added two new Hg-Mn stars into this sample. We have begun a long-term study of elemental abundances in this uniform, high-quality set of IUE spectra for 13 stars. We report on the first stages of this project: abundances for N, Cr, Mn, Fe, Co, and Ni. The study of the Fe- peak elements show that our data set can provide accurate abundances and that abundances obtained from UV and optical spectra often are in good agreement. This study provides the groundwork for self-consistent abundance analyses of more exotic elements in our long term project.

Planetesimal Capture by an Evolving Giant Gaseous Protoplanet

2012 ◽  
Vol 8 (S293) ◽  
pp. 263-269
Author(s):  
Morris Podolak ◽  
Nader Haghighipour
Keyword(s):  
Mass Distribution ◽  
Total Mass ◽  
Size Composition ◽  
Giant Planets ◽  
The Core ◽  
Last Stage ◽  
Core Accretion ◽  
Gaseous Envelope ◽  
Gas Drag ◽  
Probability Of Capture

AbstractBoth the core-accretion and disk-instability models suggest that at the last stage of the formation of a gas-giant, the core of this object is surrounded by an extended gaseous envelope. At this stage, while the envelope is contracting, planetesimals from the protoplanetary disk may be scattered into the protoplanets atmosphere and deposit some or all of their materials as they interact with the gas. We have carried out extensive simulations of approximately 104 planetesimals interacting with a envelope of a Jupiter-mass protoplanet including effects of gas drag, heating, and the effect of the protoplanets extended mass distribution. Simulations have been carried out for different radii and compositions of planetesimals so that all three processes occur to different degrees. We present the results of our simulations and discuss their implications for the enrichment of ices in giant planets. We also present statistics for the probability of capture (i.e. total mass-deposition) of planetesimals as a function of their size, composition, and closest approach to the center of the protoplanetary body.

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