scholarly journals Supernovae and their Evolution in a Low Metallicity ISM

2008 ◽  
Vol 4 (S255) ◽  
pp. 175-181
Author(s):  
Roger A. Chevalier
Keyword(s):  
Mass Loss ◽  
Interaction Region ◽  
High Mass ◽  
Initial Mass ◽  
Dust Formation ◽  
Core Collapse ◽  
Early Type ◽  
Low Metallicity ◽  
Early Type Stars ◽  
Loss Rates

AbstractObservations of core collapse supernovae and their progenitors generally support expectations of increasing mass loss with increasing initial mass. Mass loss rates are expected to decline at lower metallicity, and there are prospects for directly testing this for the red supergiant progenitors of Type IIP supernovae. However, there are indications that mass loss rates for high mass early type stars may be overestimated and that there are mass loss mechanisms that do not decline at lower metallicity. In this case, there may be supernova emission from strong circumstellar interaction even at low metallicity. Although there is evidence for dust formation in freely expanding ejecta of supernovae, the quantities are relatively small. Another promising site of dust formation is the circumstellar interaction region, but this should occur in only a fraction of supernovae.

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 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 Wolf-Rayet stars in starbursts: Effects of a change of mass loss rate

1995 ◽  
Vol 163 ◽  
pp. 318-319
Author(s):  
G. Meynet
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
High Mass ◽  
New Models ◽  
Theoretical Predictions ◽  
High Mass Loss ◽  
Low Metallicity ◽  
Loss Rates

We present here starburst models based on the most recent grids of stellar evolutionary tracks obtained by the Geneva group. These new models, computed with enhanced mass loss rates during the main sequence and the Wolf-Rayet WNL phases, very well reproduce the luminosities, surface abundances and statistics of WR stars (Maeder & Meynet 1994). This change of the mass loss rates considerably affects the way the WR stars, born in a starburst's episode, are distributed among the different WR subtypes. We compare the theoretical predictions with recent observations and conclude that: (1) to reproduce the high observed ratios of WNL to O-type stars, a flat IMF seems to be required; and (2) the models which reproduce the best the observed characteristics of WR stars, i.e., those computed with an enhanced mass loss rate, can also account for the observed properties of the WR populations observed in starbursts. Moreover, the possible presence of numerous WC stars found in the low metallicity He2-10 A starburst by Vacca and Conti (1992), can only be accounted for when the high mass loss rate stellar models are used.

scholarly journals Wolf-Rayet stars in I Zw 18

1999 ◽  
Vol 193 ◽  
pp. 606-607
Author(s):  
Francoid Legrand ◽  
Daniel Kunth ◽  
Jean-René Roy ◽  
J. Miguel Mas-Hesse ◽  
Jeremy R. Walsh
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
High Mass ◽  
Starburst Galaxy ◽  
Individual Stars ◽  
Binary Channel ◽  
High Mass Loss ◽  
Low Metallicity ◽  
Loss Rates ◽  
Integrated Luminosity

Wolf-Rayet stars have been detected in the NW region of the metal–poor starburst galaxy I Zw 18. The integrated luminosity and FWHM of the bumps at 4650 Å and 5808 Å are consistent with the presence of a few individual stars of WC4 or WC5 type. The unexpected presence of WC stars in such a low-metallicity galaxy could, however, be explained by high mass loss rates, or alternatively favor a binary channel for WR formation. WC stars could also account for the strong and narrow He II 4686Å emission line which peaks co-spatially with the WR bump emission (see Schaerer 1996).

scholarly journals Mass loss rates of OB stars derived from infrared observations

1981 ◽  
Vol 59 ◽  
pp. 51-56 ◽  
Author(s):  
E.G. Tanzi ◽  
M. Tarenghi ◽  
N. Panagia
Keyword(s):  
Mass Loss ◽  
Near Infrared ◽  
Broad Band ◽  
Early Type ◽  
Model Calculations ◽  
Infrared Observations ◽  
Ob Stars ◽  
Wide Range ◽  
Early Type Stars ◽  
Loss Rates

In this paper we report briefly on a study of the mass loss of early type stars in the infrared. Up to now near infrared (1.25 - 4.8 μ ) broad band photometry of 70 southern OB stars of various luminosity class has been secured. Program stars have been selected, among those bright enough in the infrared to give a suitable photometric accuracy, in order to cover a wide range of spectral types (Fig. 1).37 stars are found to exhibit emission in excess over a blackbody photospheric continuum, which is interpreted in terms of gas ejected in the form of an accelerated wind. By means of model calculations the corresponding mass loss rates are derived. The obtained values compare well with those determined indipendently by various Authors for stars in common. Our data show that mass loss rates increase with luminosity and are a decreasing function of surface gravity.

scholarly journals The evolution of red supergiants to supernovae

2016 ◽  
Vol 12 (S329) ◽  
pp. 59-63
Author(s):  
Emma R. Beasor ◽  
Ben Davies
Keyword(s):  
Mass Loss ◽  
Early Stage ◽  
Initial Mass ◽  
Core Collapse ◽  
Circumstellar Material ◽  
Core Collapse Supernova ◽  
Evolved Stars ◽  
Circumstellar Extinction ◽  
Red Supergiants ◽  
Loss Rates

AbstractWith red supergiants (RSGs) predicted to end their lives as Type IIP core collapse supernova (CCSN), their behaviour before explosion needs to be fully understood. Mass loss rates govern RSG evolution towards SN and have strong implications on the appearance of the resulting explosion. To study how the mass-loss rates change with the evolution of the star, we have measured the amount of circumstellar material around 19 RSGs in a coeval cluster. Our study has shown that mass loss rates ramp up throughout the lifetime of an RSG, with more evolved stars having mass loss rates a factor of 40 higher than early stage RSGs. Interestingly, we have also found evidence for an increase in circumstellar extinction throughout the RSG lifetime, meaning the most evolved stars are most severely affected. We find that, were the most evolved RSGs in NGC2100 to go SN, this extra extinction would cause the progenitor’s initial mass to be underestimated by up to 9M⊙.

Empirical ionization fractions in the winds and the determination of mass-loss rates for early-type stars

1980 ◽  
Vol 242 ◽  
pp. L33 ◽  
Author(s):  
H. J. G. L. M. Lamers ◽  
R. Gathier ◽  
T. P. Snow
Keyword(s):  
Mass Loss ◽  
Early Type ◽  
Early Type Stars ◽  
Loss Rates

scholarly journals Chemical Abundances of Early Type Stars

1998 ◽  
Vol 188 ◽  
pp. 224-225
Author(s):  
S. Tanaka ◽  
S. Kitamoto ◽  
T. Suzuki ◽  
K. Torii ◽  
M.F. Corcoran ◽  
...  
Keyword(s):  
Surface Layer ◽  
Stellar Wind ◽  
Nuclear Reactions ◽  
X Rays ◽  
Early Type ◽  
Chemical Abundances ◽  
X Ray ◽  
Low Metallicity ◽  
Early Type Stars

X-rays from early-type stars are emitted by the corona or the stellar wind. The materials in the surface layer of early-type stars are not contaminated by nuclear reactions in the stellar inside. Therefore, abundance study of the early-type stars provides us an information of the abundances of the original gas. However, the X-ray observations indicate low-metallicity, which is about 0.3 times of cosmic abundances. This fact raises the problem on the cosmic abundances.

scholarly journals The properties of early-type stars in the Magellanic Clouds

2008 ◽  
Vol 4 (S256) ◽  
pp. 325-336
Author(s):  
Christopher J. Evans
Keyword(s):  
Physical Properties ◽  
Mass Loss ◽  
Temperature Scale ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Early Type ◽  
The Past ◽  
The Galaxy ◽  
Stellar Temperature ◽  
Early Type Stars

AbstractThe past decade has witnessed impressive progress in our understanding of the physical properties of massive stars in the Magellanic Clouds, and how they compare to their cousins in the Galaxy. I summarise new results in this field, including evidence for reduced mass-loss rates and faster stellar rotational velocities in the Clouds, and their present-day compositions. I also discuss the stellar temperature scale, emphasizing its dependence on metallicity across the entire upper-part of the Hertzsprung-Russell diagram.

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