scholarly journals Pulsation and its rôle for circumstellar features

1989 ◽  
Vol 106 ◽  
pp. 369-369
Author(s):  
A. Heske
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Circumstellar Matter ◽  
Single Component ◽  
Molecular Gas ◽  
Spectral Features ◽  
Evolutionary Models ◽  
Circumstellar Envelopes ◽  
Infrared Wavelengths ◽  
Loss Rates

Circumstellar envelopes of cool giants and supergiants contain atomic and molecular gas, and dust. The charateristic spectral features of these different components can be observed at optical (atoms), at radio (molecules) and at infrared wavelengths (dust). Since the detection of circumstellar matter around giants and supergiants most studies concentrated on detemining mass loss rates from observations of a single component assuming steady mass loss during late stellar evolution. Nevertheless, the IRAS colour colour diagramme and evolutionary models rather point to a non steady evolution during the mass loss phase of the star.

scholarly journals ENHANCED MASS LOSS RATES IN RED SUPERGIANTS AND THEIR IMPACT ON THE CIRCUMSTELLAR MEDIUM

2019 ◽  
Vol 55 (2) ◽  
pp. 161-175
Author(s):  
L. Hernández-Cervantes ◽  
B. Pérez-Rendón ◽  
A. Santillán ◽  
G. García-Segura ◽  
C. Rodríguez-Ibarra
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Gas Dynamics ◽  
Numerical Experiments ◽  
Evolutionary Models ◽  
Solar Composition ◽  
Red Supergiants ◽  
The Impact ◽  
Circumstellar Medium ◽  
Loss Rates

In this work, we present models of massive stars between 15 and 23 M⊙ , with enhanced mass loss rates during the red supergiant phase. Our aim is to explore the impact of extreme red supergiant mass-loss on stellar evolution and on their circumstellar medium. We computed a set of numerical experiments, on the evolution of single stars with initial masses of 15, 18, 20 and, 23 M⊙ , and solar composition (Z = 0.014), using the numerical stellar code BEC. From these evolutionary models, we obtained time-dependent stellar wind parameters, that were used explicitly as inner boundary conditions in the hydrodynamical code ZEUS-3D, which simulates the gas dynamics in the circumstellar medium (CSM), thus coupling the stellar evolution to the dynamics of the CSM. We found that stars with extreme mass loss in the RSG phase behave as a larger mass stars.

scholarly journals ISOCAM and DENIS Survey of 0.5 square degrees in the Bar of the LMC. Detection of the whole TP-AGB Star Population

1999 ◽  
Vol 191 ◽  
pp. 561-566
Author(s):  
C. Loup ◽  
E. Josselin ◽  
M.-R. Cioni ◽  
H.J. Habing ◽  
J.A.D.L. Blommaert ◽  
...  
Keyword(s):  
Mass Loss ◽  
High Mass ◽  
Evolutionary Models ◽  
Agb Stars ◽  
Complete Sample ◽  
High Mass Loss ◽  
Low Mass ◽  
The One ◽  
Good Agreement ◽  
Loss Rates

We surveyed 0.5 square degrees in the Bar of the LMC with ISOCAM at 4.5 and 12 μm, and with DENIS in the I, J, and Ks bands. Our goal was to build a complete sample of Thermally-Pulsing AGB stars. Here we present the first analysis of 0.14 square degrees. In total we find about 300 TP-AGB stars. Among these TP-AGB stars, 9% are obscured AGB stars (high mass-loss rates); 9 of them were detected by IRAS, and only 1 was previously identified. Their luminosities range from 2 500 to 14 000 L⊙, with a distribution very similar to the one of optical TP-AGB stars (i.e. those with low mass-loss rates). Such a luminosity distribution, as well as the percentage of obscured stars among TP-AGB stars, is in very good agreement with the evolutionary models of Vassiliadis & Wood (1993) if most of the TP-AGB stars that we find have initial masses smaller than 1.5 to 2 M⊙.

The final 105 years of stellar AGB evolution in the presence of a pulsating, dust-induced “superwind”

1999 ◽  
Vol 191 ◽  
pp. 389-394
Author(s):  
K.-P. Schröder ◽  
J.M. Winters ◽  
E. Sedlmayr
Keyword(s):  
Radiative Transfer ◽  
Mass Loss ◽  
Stellar Evolution ◽  
Mass Range ◽  
Initial Mass ◽  
Temperature Sensitive ◽  
Dust Formation ◽  
Time Step ◽  
Thermal Pulse ◽  
Loss Rates

We have computed mass-loss histories and tip-AGB stellar evolution models in the presence of a dust-induced, carbon-rich “superwind”, in the initial mass-range of 1.1 to about 2.5 solar masses and for nearly solar composition (X=0.28, Y=0.70, Z=0.02). Consistent, actual mass-loss rates are used in each time-step, based on pulsating and “dust-driven” stellar wind models for carbon-rich stars (Fleischer et al. 1992) which include a detailed treatment of dust-formation, radiative transfer and wind acceleration. Our tip-AGB mass-loss rates reach about 4 · 10−5M⊙yr−1 and become an influencial factor of stellar evolution.Heavy outflows of 0.3 to 0.6 M⊙ within only 2 to 3·104 yrs, exactly as required for PN-formation, occur with tip-AGB models of an initial stellar mass Mi ≳ 1.3M⊙. The mass-loss of our “superwind” varies strongly with effective temperature (Ṁ ∝ T−8eff, see Arndt et al. 1997), reflecting the temperature-sensitive micro-physics and chemistry of dust-formation and radiative transfer on a macroscopic scale. Furthermore, a thermal pulse leads to a very short (100 to 200 yrs) interruption of the “superwind” of these models.For Mi ≲ 1.1M⊙, our evolution models fail to reach the (Eddington-like) critical luminosity Lc required by the radiatively driven wind models, while for the (initial) mass-range in-between, with the tip-AGB luminosity LtAGB near Lc, thermal pulses drive bursts of “superwind”, which could explain the outer shells found with some PN's. In particular, a burst with a duration of only 800 yrs and a mass-loss of about 0.03 M⊙, occurs right after the last AGB thermal pulse of a model with Mi ≈ 1.1M⊙. There is excellent agreement with the thin CO shells found by Olofsson et al. (e.g., 1990, 1998) around some Mira stars.

scholarly journals Stellar Winds and Mass-Loss Rates from Be Stars

1982 ◽  
Vol 98 ◽  
pp. 377-385 ◽  
Author(s):  
Theodore P. Snow
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Stellar Winds ◽  
Be Stars ◽  
Line Profiles ◽  
Sample Group ◽  
Show Evidence ◽  
Acceleration Zone ◽  
Low Levels ◽  
Loss Rates

Resonance-line profiles of SiIII and SiIV lines in 22 B and Be stars have been analyzed in the derivation of mass-loss rates. Of the 19 known Be or shell stars in the sample group, all but one show evidence of winds. It is argued that for stars of spectral type B1.5 and later, SiIII and SiIV are the dominant stages of ionization, and this conclusion, together with theoretical fits to the line profiles, leads to mass-loss rates between 10-11 and 3 × 10-9 for the stars. The rate of mass loss does not correlate simply with stellar parameters, and probably is variable with time. The narrow FeIII shell lines often seen in the ultraviolet spectra of Be stars may arise at low levels in the wind, below the strong acceleration zone. The mass-loss rates from Be stars are apparently insufficient to affect stellar evolution.

scholarly journals Massive stars burning helium: the numbers of WR stars and red supergiants in galaxies

1981 ◽  
Vol 59 ◽  
pp. 283-287
Author(s):  
A. Maeder
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Short Note ◽  
Evolutionary Models ◽  
Helium Burning ◽  
Red Supergiants ◽  
Low Mass ◽  
Age Sequence ◽  
Carbon Burning ◽  
Loss Rates

We have calculated evolutionary models of massive stars in the range 15-120 Mʘ from the zero-age sequence up to the end of the carbon burning stage (Maeder, 1981). Three sets of models with different mass loss rates Ṁ have been computed; the adopted parametrisation of Ṁ is fitted on the observations and thus the expression for Ṁ differs according to the location of the stars in the HRD.In this short note we concentrate on the location of the He-burning stars in the HRD. The helium burning phase, which lasts 8 to 10% of the MS phase, is spent mainly as red supergiants (RSG) and as WR stars (note that for low mass loss, the time spent as A-G supergiants becomes longer).

scholarly journals A new mass-loss rate prescription for red supergiants

2020 ◽  
Vol 492 (4) ◽  
pp. 5994-6006 ◽  
Author(s):  
Emma R Beasor ◽  
Ben Davies ◽  
Nathan Smith ◽  
Jacco Th van Loon ◽  
Robert D Gehrz ◽  
...  
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Substantial Effect ◽  
Evolutionary Models ◽  
Total Mass Loss ◽  
Red Supergiants ◽  
Current Mass ◽  
The Impact ◽  
Loss Rates

ABSTRACT Evolutionary models have shown the substantial effect that strong mass-loss rates ($\dot{M}$s) can have on the fate of massive stars. Red supergiant (RSG) mass-loss is poorly understood theoretically, and so stellar models rely on purely empirical $\dot{M}$–luminosity relations to calculate evolution. Empirical prescriptions usually scale with luminosity and effective temperature, but $\dot{M}$ should also depend on the current mass and hence the surface gravity of the star, yielding more than one possible $\dot{M}$ for the same position on the Hertzsprung–Russell diagram. One can solve this degeneracy by measuring $\dot{M}$ for RSGs that reside in clusters, where age and initial mass (Minit) are known. In this paper we derive $\dot{M}$ values and luminosities for RSGs in two clusters, NGC 2004 and RSGC1. Using newly derived Minit measurements, we combine the results with those of clusters with a range of ages and derive an Minit-dependent $\dot{M}$ prescription. When comparing this new prescription to the treatment of mass-loss currently implemented in evolutionary models, we find models drastically overpredict the total mass-loss, by up to a factor of 20. Importantly, the most massive RSGs experience the largest downward revision in their mass-loss rates, drastically changing the impact of wind mass-loss on their evolution. Our results suggest that for most initial masses of RSG progenitors, quiescent mass-loss during the RSG phase is not effective at removing a significant fraction of the H-envelope prior to core-collapse, and we discuss the implications of this for stellar evolution and observations of SNe and SN progenitors.

scholarly journals Mass-losing AGB Stars in the LMC

2000 ◽  
Vol 177 ◽  
pp. 145-151
Author(s):  
Jacco Th. Van Loon ◽  
Albert A. Zijlstra ◽  
Patricia A. Whitelock ◽  
Cecile Loup ◽  
L.B.F.M. Waters
Keyword(s):  
Mass Loss ◽  
Optical Depth ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Carbon Stars ◽  
Infrared Study ◽  
Tentative Evidence ◽  
Loss Rates

We show the results of an infrared study of a sample of heavily obscured AGB stars in the LMC. Both carbon-rich and oxygen-rich mass-losing AGB stars can be found at both high and low luminosities, but the percentage of carbon stars decreases with increasing luminosity. The optical depth of the circumstellar envelopes also decreases with increasing luminosity, while the mass-loss rates are (nearly) constant with luminosity. We also show tentative evidence for having found the first post-AGB stars in the LMC.

scholarly journals The luminosity distribution of RSGs to test their mass-loss rate

2015 ◽  
Vol 11 (A29B) ◽  
pp. 454-454 ◽  
Author(s):  
Cyril Georgy ◽  
Sylvia Ekström
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Massive Star ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Red Supergiants ◽  
Loss Rates

AbstractThe red supergiant phase is an important phase of the evolution of massive star, as it mostly determines its final stages. One of the most important driver of the evolution during this phase is mass loss. However, the mass-loss rates prescription used for red supergiants in current stellar evolution models are still very inaccurate.Varying the mass-loss rate makes the star evolve for some time in yellow/blue regions of the HRD, modifying the number of RSGs in some luminosity ranges. Figure 1 shows how the luminosity distribution of RSGs is modified for various mass-loss prescriptions. This illustrates that it is theoretically possible to determine at least roughly what is the typical mass loss regime of RSGs in a stellar evolution perspective.

scholarly journals The theory of winds in early type stars

1981 ◽  
Vol 59 ◽  
pp. 125-130 ◽  
Author(s):  
A.G. Hearn
Keyword(s):  
Mass Loss ◽  
Spectral Type ◽  
Stellar Evolution ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Optical Measurements ◽  
Early Type ◽  
Large Uncertainty ◽  
Early Type Stars ◽  
Loss Rates

I assume that the purpose of this review of the theory of winds from early type stars is to summarize the way in which the mass loss rate of a star may be included in a calculation of stellar evolution. Let me summarize my conclusions. It is not possible. One can only use estimates of mass loss rates obtained from the observations. Even these give a large uncertainty. The observed mass loss rates for different stars of the same spectral type vary. Further the mass loss rates obtained by different methods for the same star differ. An extreme example of this is 9 Sgr. The mass loss rate derived from the radio observations is forty times greater than that derived from the U.V. and optical measurements (Abbott et al. 1980).

scholarly journals Stellar masers, circumstellar envelopes and supernova remnants

2007 ◽  
Vol 3 (S242) ◽  
pp. 236-245
Author(s):  
Athol J. Kemball
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Supernova Remnants ◽  
Stellar Mass ◽  
Stellar Atmospheres ◽  
Late Type ◽  
Open Future ◽  
Circumstellar Envelopes ◽  
Recent Advances

AbstractThis paper reviews recent advances in the study or circumstellar masers and masers found toward supernova remnants. The review is organized by science focus area, including the astrophysics of extended stellar atmospheres, stellar mass-loss processes and outflows, late-type evolved stellar evolution, stellar maser excitation and chemistry, and the use of stellar masers as independent distance estimators. Masers toward supernova remnants are covered separately. Recent advances and open future questions in this field are explored.

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