Radiative Accelerations for Evolutionary Model Calculations

1998 ◽  
Vol 492 (2) ◽  
pp. 833-842 ◽  
Author(s):  
J. Richer ◽  
G. Michaud ◽  
F. Rogers ◽  
C. Iglesias ◽  
S. Turcotte ◽  
...  
Keyword(s):  
Evolutionary Model ◽  
Model Calculations

scholarly journals The Naming of Stars and the Study of Protostars

1993 ◽  
Vol 137 ◽  
pp. 810-811
Author(s):  
D.R.O. Morrison
Keyword(s):  
Monte Carlo ◽  
Particle Physics ◽  
Evolutionary Model ◽  
Model Calculations ◽  
Monte Carlo Studies ◽  
Physical Principles

AbstractThe logic of naming stars could be based more on physical principles as happened in the naming of resonances in Particle Physics. A possible system might be based on extensive Monte Carlo studies of protostars followed by standard Stellar Evolutionary Model calculations.

scholarly journals Dredge-Up in Asymptotic Giant Branch Stars

1999 ◽  
Vol 191 ◽  
pp. 47-52 ◽  
Author(s):  
N. Mowlavi
Keyword(s):  
Evolutionary Model ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Model Calculations ◽  
The Third ◽  
Giant Branch Stars

The third dredge-up phenomenon in asymptotic giant branch stars, responsible for the formation of C stars, is discussed based on detailed evolutionary model calculations. The structural readjustment of the star as dredge-up proceeds is analyzed, and its consequences on dredge-up predictions discussed. The question of how to obtain dredge-up in asymptotic giant branch models is also addressed. It is stressed, in particular, that the modeling of dredge-up requires some sort of extra-mixing to be applied below the envelope if the local Schwarzschild criterion is used to delimit convective zones.

scholarly journals Mass loss from pulsating cool stars

2008 ◽  
Vol 4 (S252) ◽  
pp. 259-260
Author(s):  
Qian Wang ◽  
Lee Anne Willson ◽  
Steven Kawaler
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Evolutionary Model ◽  
Theoretical Models ◽  
Observation Data ◽  
Loss Mechanism ◽  
Model Calculations ◽  
Cool Stars ◽  
Evolutionary Studies

AbstractIt has long been clear that most, if not all, of the mass loss experienced by stars from 0.8 to 8 solar masses occurs near the tip of the AGB and/or the RGB. Evolutionary studies have incorporated empirical mass loss laws but theoretical models suggest quite different dependence of mass loss rate on stellar parameters. We are combining evolutionary model calculations with ISUEVO with mass loss modeling using the Bowen code in a systematic study of final stages of stellar evolution. We mapped the RGB (without steady mass loss) to the “Death Zone” as a function of mixing length, mass, and metallicity. We compared these results with observation data from Origlia. We are investigating a possible mass loss mechanism through companions as a complement to mass loss through pulsation. By the end of the project we expect to provide a reliable prescription for AGB mass loss.

scholarly journals Evolutionary Period Changes in ω Centauri!?

2000 ◽  
Vol 176 ◽  
pp. 254-254 ◽  
Author(s):  
Johanna Jurcsik
Keyword(s):  
Evolutionary Model ◽  
Past Century ◽  
Model Calculations ◽  
The Past ◽  
Evolutionary Changes

AbstractThe periods of most of the RRab stars in ω Centauri have increased during the past century at the same rate as evolutionary model calculations predict. This result raises the possibility that evolutionary changes in the periods are directly observed in this cluster.

scholarly journals Outbursts by Low-Mass White Dwarfs in Symbiotic Variables

1992 ◽  
Vol 151 ◽  
pp. 439-440
Author(s):  
Edward M. Sion ◽  
Christian J. Ready
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Evolutionary Model ◽  
Terminal Velocity ◽  
High Rate ◽  
High Dispersion ◽  
Absorption Feature ◽  
Intensity Level ◽  
Model Calculations ◽  
Low Mass

We have investigated the nature of P Cygni-like features in the high resolution IUE spectra of the symbiotic variables BF Cyg and EG And by looking for orbital phase-dependent variations in the structure and velocity of the C IV (1550 Å) resonance doublet in 10 archival IUE high-dispersion spectra of these systems and by comparing their profiles with P Cygni-like features seen in IUE high-dispersion spectra of other symbiotic stars. For BF Cyg, we find maximal P Cygni absorption equivalent widths and terminal velocities of ~ 900 mÅ and ~ −240 km s−1 respectively, full emission velocity widths at the 10% intensity level of 300–400 km s−1, depending on phase, Φ, variations in the width of the P Cygni absorption, shortward velocity shifts of the C IV emission line in all but two orbital phases, relative to the C IV velocity at Φ = 0.01, and absorption sub-structure within the C IV P Cygni lines which coincide in velocity from image to image. In EG And the C IV P Cygni absorption equivalent width is, on average, 300 mÅ with a terminal velocity of −217 km s−1 (which includes the systemic radial velocity contribution of -93 km s−1). The presence in one image, of a strong absorption feature at He II (1640), having a precise velocity coincidence with the C IV P Cygni absorption component, suggests that the absorbing material responsible for both line features is associated with outflow and P Cygni self-absorption from the vicinity of the hot component. In both BF Cyg and EG And, the structure and behavior of the P Cygni profiles may rule out their origin in the red giant wind or in an expanding circumbinary shell. Our results support the hot component wind interpretation of Mikolajewska et al. (1989). Motivated by the low-mass white dwarf shown to be present in BF Cyg (Mikolajewska et al. 1989), we have carried out quasi-static evolutionary model calculations with accretion onto a 0.55 M⊙ white dwarf accreting at the rate 2 × 10−8 M⊙ yr−1. The sequence of 3800 quasi-static models, the first to be reported for a low-mass hot white dwarf (Mwd < 0.8 M⊙) accreting at a high rate, yields an unexpected outburst behavior in response to accretion at that rate, when compared to evolutionary sequences with accretion onto higher mass white dwarfs. A series of three major thermonuclear shell flashes and one lower energy shell flash is revealed with the timescale during outburst and the inter-outburst timescale substantially shorter than expected for a 0.55 M⊙ white dwarf. Preliminary results on other sequences are also reported. Implications for the observations of symbiotic systems thought to contain low-mass white dwarfs, are discussed.

Why do people believe in a zero-sum economy?

2018 ◽  
Vol 41 ◽  
Author(s):  
Samuel G. B. Johnson
Keyword(s):  
Perspective Taking ◽  
Evolutionary Model ◽  
Everyday Experience ◽  
Coalitional Psychology ◽  
The Face ◽  
Zero Sum

AbstractZero-sum thinking and aversion to trade pervade our society, yet fly in the face of everyday experience and the consensus of economists. Boyer & Petersen's (B&P's) evolutionary model invokes coalitional psychology to explain these puzzling intuitions. I raise several empirical challenges to this explanation, proposing two alternative mechanisms – intuitive mercantilism (assigning value to money rather than goods) and errors in perspective-taking.

Effects of Ambipolar Diffusion on Prominence Thread Models

1994 ◽  
Vol 144 ◽  
pp. 315-321 ◽  
Author(s):  
M. G. Rovira ◽  
J. M. Fontenla ◽  
J.-C. Vial ◽  
P. Gouttebroze
Keyword(s):  
Energy Balance ◽  
Transition Region ◽  
Ambipolar Diffusion ◽  
Line Profiles ◽  
Balance Equations ◽  
Model Calculations ◽  
Partial Frequency ◽  
Frequency Redistribution ◽  
Partial Frequency Redistribution ◽  
Theoretical Structure

AbstractWe have improved previous model calculations of the prominence-corona transition region including the effect of the ambipolar diffusion in the statistical equilibrium and energy balance equations. We show its influence on the different parameters that characterize the resulting prominence theoretical structure. We take into account the effect of the partial frequency redistribution (PRD) in the line profiles and total intensities calculations.

Influence of stable iodine on the uptake of the thyroid – model vs. experiment

2001 ◽  
Vol 40 (01) ◽  
pp. 31-37 ◽  
Author(s):  
U. Wellner ◽  
E. Voth ◽  
H. Schicha ◽  
K. Weber
Keyword(s):  
Time Course ◽  
Compartment Model ◽  
The Body ◽  
Iodine Uptake ◽  
Model Calculations ◽  
Physiological Conditions ◽  
Iodine Supply ◽  
Predicted Values ◽  
The Individual ◽  
Stable Iodine

Summary Aim: The influence of physiological and pharmacological amounts of iodine on the uptake of radioiodine in the thyroid was examined in a 4-compartment model. This model allows equations to be derived describing the distribution of tracer iodine as a function of time. The aim of the study was to compare the predictions of the model with experimental data. Methods: Five euthyroid persons received stable iodine (200 μg, 10 mg). 1-123-uptake into the thyroid was measured with the Nal (Tl)-detector of a body counter under physiological conditions and after application of each dose of additional iodine. Actual measurements and predicted values were compared, taking into account the individual iodine supply as estimated from the thyroid uptake under physiological conditions and data from the literature. Results: Thyroid iodine uptake decreased from 80% under physiological conditions to 50% in individuals with very low iodine supply (15 μg/d) (n = 2). The uptake calculated from the model was 36%. Iodine uptake into the thyroid did not decrease in individuals with typical iodine supply, i.e. for Cologne 65-85 μg/d (n = 3). After application of 10 mg of stable iodine, uptake into the thyroid decreased in all individuals to about 5%, in accordance with the model calculations. Conclusion: Comparison of theoretical predictions with the measured values demonstrated that the model tested is well suited for describing the time course of iodine distribution and uptake within the body. It can now be used to study aspects of iodine metabolism relevant to the pharmacological administration of iodine which cannot be investigated experimentally in humans for ethical and technical reasons.

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