scholarly journals Hydrodynamic Models of Low-Mass Pulsating Supergiants with Radiative Transfer

1989 ◽  
Vol 111 ◽  
pp. 264-264
Author(s):  
A.B. Foken
Keyword(s):  
Radiative Transfer ◽  
Variable Star ◽  
Stable Limit Cycle ◽  
Light Curves ◽  
Transfer Model ◽  
Stable Limit ◽  
Type Ii ◽  
Hydrodynamic Models ◽  
Stellar Pulsations ◽  
Low Mass

AbstractA method of calculating nonlinear stellar pulsations including nonstationary radiative transfer in a grey spherical atmosphere is described. With the help of this method eleven type II supergiant radiative models were constructed with masses of 0.6M⊙, luminosities ranging from 128L⊙ to 3123L⊙ and periods in the range from 1.123 to 46 days. A stable limit cycle was found to be accessible only by models with an effective temperature between 5700K and 6165K. The model with Te = 6165K is stable, whereas the models cooler than 5700K show nonregular behavior. Transition from strictly periodic to nonregular pulsation arises when M/R ≲ 0.018, due to high amplitudes, δr/r ≈ 1, and strong shocks in the atmosphere. The radiative transfer effects lead to some decay in the radial amplitude, as well as to a more significant decrease, about 0.6 magnitudes, in the light variation. A photometric comparison between the light curves of the models calculated with and without transfer and the observed light curve of the variable star No. 154 in M3 shows that the results predicted by the transfer model are in much better agreement with obervational data.

scholarly journals The influence of line opacity treatment in stella on supernova light curves

2020 ◽  
Vol 499 (3) ◽  
pp. 4312-4324
Author(s):  
Alexandra Kozyreva ◽  
Luke Shingles ◽  
Alexey Mironov ◽  
Petr Baklanov ◽  
Sergey Blinnikov
Keyword(s):  
Radiative Transfer ◽  
Spectral Synthesis ◽  
Broad Band ◽  
Light Curves ◽  
Radiation Hydrodynamics ◽  
Type Ii ◽  
Type Ia ◽  
The Impact ◽  
Supernovae Type Ia

ABSTRACT We systematically explore the effect of the treatment of line opacity on supernova light curves. We find that it is important to consider line opacity for both scattering and absorption (i.e. thermalization, which mimics the effect of fluorescence). We explore the impact of the degree of thermalization on three major types of supernovae: Type Ia, Type II-peculiar, and Type II-plateau. For this we use the radiative transfer code stella and analyse broad-band light curves in the context of simulations done with the spectral synthesis code artis and in the context of a few examples of observed supernovae of each type. We found that the plausible range for the ratio between absorption and scattering in the radiation hydrodynamics code stella is (0.8–1):(0.2–0), i.e. the recommended thermalization parameter is 0.9.

scholarly journals The Holling Type II Population Model Subjected to Rapid Random Attacks of Predator

2018 ◽  
Vol 2018 ◽  
pp. 1-10
Author(s):  
Jevgeņijs Carkovs ◽  
Jolanta Goldšteine ◽  
Kārlis Šadurskis
Keyword(s):  
Dynamical System ◽  
Population Model ◽  
Stable Limit Cycle ◽  
Time Interval ◽  
Stable Limit ◽  
Type Ii ◽  
Time Intervals ◽  
Average Motion ◽  
Trophic Function ◽  
Random Time Interval

We present the analysis of a mathematical model of the dynamics of interacting predator and prey populations with the Holling type random trophic function under the assumption of random time interval passage between predator attacks on prey. We propose a stochastic approximation algorithm for quantitative analysis of the above model based on the probabilistic limit theorem. If the predators’ gains and the time intervals between predator attacks are sufficiently small, our proposed method allows us to derive an approximative average dynamical system for mathematical expectations of population dynamics and the stochastic Ito differential equation for the random deviations from the average motion. Assuming that the averaged dynamical system is the classic Holling type II population model with asymptotically stable limit cycle, we prove that the dynamics of stochastic model may be approximated with a two-dimensional Gaussian Markov process with unboundedly increasing variances.

scholarly journals Star formation In Bright-Rimmed Clouds: a comparison of wind-driven triggering with millimeter observations

2006 ◽  
Vol 2 (S237) ◽  
pp. 409-409
Author(s):  
Christopher H. De Vries ◽  
G. Narayanan ◽  
R. L. Snell
Keyword(s):  
Star Formation ◽  
Radiative Transfer ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Hydrodynamic Models ◽  
Molecular Line ◽  
Model Based ◽  
Accurate Comparison ◽  
Cloud Cores ◽  
Shock Fronts

Bright-rimmed clouds (BRCs) are logical laboratories in which to study triggered star formation, however it is difficult in any single cloud to definitively show that star formation was triggered. In this study we compare the hydrodynamic models produced by Vanhala & Cameron (1998) that treat the problems of star-formation triggered by wind-driven implosion to millimeter and submillimeter molecular line observations of BRCs with embedded IRAS sources. These latter sources are derived from a catalog by Sugitani, Fukui, & Ogura (1991) In order to make an accurate comparison we implement a radiative transfer model based on the Sobolev or LVG approximation, and generate molecular line maps which can be directly compared to our observations. We observed several millimeter and submillimeter transitions of CO, C 18O, HCO+, and H13CO+ using the FCRAO, SMT, CSO, and SMA observatories (De Vries, Narayanan, & Snell 2002). We compare these observations with 3 hydrodynamic models of wind-driven shock fronts interacting with pre-existing, but unbound cloud cores. In two cases these model cores are triggered to collapse under the influence of the external wind.

FEEDBACK-INDUCED COMPLEX DYNAMICS IN A TWO-COMPONENT REGULATORY CIRCUIT

2012 ◽  
Vol 22 (03) ◽  
pp. 1250059 ◽  
Author(s):  
HUAHAI QIU ◽  
TIANSHOU ZHOU
Keyword(s):  
Negative Feedback ◽  
First Passage Time ◽  
Stable Limit Cycle ◽  
Feedback Loops ◽  
Type I ◽  
Stable Limit ◽  
Type Ii ◽  
Negative Feedback Loops ◽  
Two Component ◽  
Positive And Negative Feedback

Coupled positive and negative feedback loops form an essential building block of cellular signaling pathways, but the dynamics of such a system remain to be fully explored. Here, we systematically analyze a two-component circuit with interlinked positive and negative feedback loops, focusing on feedback-induced dynamics and their mechanisms. We show that feedbacks can induce monostability, oscillation, and excitability as well as the coexistence of two attractors (including that of two different stable steady states (called Type-I bistability) and that of both a stable steady state and a stable limit cycle (called Type-II bistability)). In particular for Type-II bistability, we find that feedback-controlled molecular noise can induce stochastic switching between two different attractors, and that the first passage time between them exhibits a multi-peak distribution. These investigations provide insights for understanding the biological functions of coupled positive and negative feedback circuits from the viewpoint of dynamics.

scholarly journals Synthetic observables for electron-capture supernovae and low-mass core collapse supernovae

2021 ◽  
Vol 503 (1) ◽  
pp. 797-814
Author(s):  
Alexandra Kozyreva ◽  
Petr Baklanov ◽  
Samuel Jones ◽  
Georg Stockinger ◽  
Hans-Thomas Janka
Keyword(s):  
Radiative Transfer ◽  
Light Curve ◽  
Electron Capture ◽  
Mass Range ◽  
Light Curves ◽  
Initial Mass ◽  
Core Collapse ◽  
Initial Composition ◽  
Solar Metallicity ◽  
Low Mass

ABSTRACT Stars in the mass range from 8 M⊙ to 10 M⊙ are expected to produce one of two types of supernovae (SNe), either electron-capture supernovae (ECSNe) or core-collapse supernovae (CCSNe), depending on their previous evolution. Either of the associated progenitors retain extended and massive hydrogen-rich envelopes and the observables of these SNe are, therefore, expected to be similar. In this study, we explore the differences in these two types of SNe. Specifically, we investigate three different progenitor models: a solar-metallicity ECSN progenitor with an initial mass of 8.8 M⊙, a zero-metallicity progenitor with 9.6 M⊙, and a solar-metallicity progenitor with 9 M⊙, carrying out radiative transfer simulations for these progenitors. We present the resulting light curves for these models. The models exhibit very low photospheric velocity variations of about 2000 km s−1; therefore, this may serve as a convenient indicator of low-mass SNe. The ECSN has very unique light curves in broad-bands, especially the U band, and does not resemble any currently observed SN. This ECSN progenitor being part of a binary will lose its envelope for which reason the light curve becomes short and undetectable. The SN from the 9.6 M⊙ progenitor exhibits also quite an unusual light curve, explained by the absence of metals in the initial composition. The artificially iron-polluted 9.6 M⊙ model demonstrates light curves closer to normal SNe IIP. The SN from the 9 M⊙ progenitor remains the best candidate for so-called low-luminosity SNe IIP like SN 1999br and SN 2005cs.

scholarly journals A Study of Period Doubling in a One-Zone Pulsating Stellar Model

1989 ◽  
Vol 111 ◽  
pp. 265-265
Author(s):  
A.B. Foken
Keyword(s):  
Degrees Of Freedom ◽  
Stable Limit Cycle ◽  
Period Doubling ◽  
Stellar Model ◽  
Zone Model ◽  
Stable Limit ◽  
Hydrodynamic Models ◽  
Excitation Rate ◽  
Return Map ◽  
Period Doubling Bifurcations

AbstractA simple one-zone model for nonlinear stellar pulsations is outlined and applied to the study of period doubling observed in some W Virginis and RV Tauri stars. The model reveals a number of period doubling bifurcations as the parameters are varied, similar to those found by Buchler & Kovacs in their series of hydrodynamic models. In the vicinity of a stable limit cycle, despite its large number of degrees of freedom, the model develops an essentially one-dimensional Poincaré’s return map, determining the modulation of the amplitude. The analysis of these maps confirmed that period doubling has its origin in a strong nonlinear increase of total energy losses per period as radial amplitude, δr/r, increases. An additional study of nearly periodic hydrodynamic models with P > 15 days, calculated including radiative transfer effects, shows that the rate of energy dissipation per period by shocks in the atmospheres increases rapidly with δr/r, whereas the excitation rate, δo, remains rather stable. This permitted us to construct an analytic return map for maxima of the total kinetic energy which clearly demonstrates the mechanism of successive period doubling as δo, the sole bifurcation parameter, grows monotonically.

Dynamics of a delayed competitive system affected by toxic substances with imprecise biological parameters

Filomat ◽  
2017 ◽  
Vol 31 (16) ◽  
pp. 5271-5293
Author(s):  
A.K. Pal ◽  
P. Dolai ◽  
G.P. Samanta
Keyword(s):  
Equilibrium Points ◽  
Stable Limit Cycle ◽  
Limit Cycle Oscillation ◽  
Toxic Substances ◽  
Stable Limit ◽  
Biological Parameters ◽  
Delay Model ◽  
Competitive System ◽  
Interval Numbers ◽  
Cycle Oscillation

In this paper we have studied the dynamical behaviours of a delayed two-species competitive system affected by toxicant with imprecise biological parameters. We have proposed a method to handle these imprecise parameters by using parametric form of interval numbers. We have discussed the existence of various equilibrium points and stability of the system at these equilibrium points. In case of toxic stimulatory system, the delay model exhibits a stable limit cycle oscillation. Computer simulations are carried out to illustrate our analytical findings.

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