Wolf-Rayet stars as a diagnostic of internal mixing processes in massive mass losing stars

2006 ◽  
pp. 90-91
Author(s):  
N. Langer
Keyword(s):  
Mixing Processes ◽  
Internal Mixing

scholarly journals Light elements in massive single and binary stars

2009 ◽  
Vol 5 (S268) ◽  
pp. 411-420 ◽  
Author(s):  
N. Langer ◽  
I. Brott ◽  
M. Cantiello ◽  
S. E. de Mink ◽  
R. G. Izzard ◽  
...  
Keyword(s):  
Binary Stars ◽  
Main Sequence ◽  
Diagnostic Value ◽  
Light Elements ◽  
Main Sequence Stars ◽  
Mixing Processes ◽  
Transfer Event ◽  
Internal Mixing ◽  
Early Type Stars

AbstractWe highlight the role of the light elements (Li, Be, B) in the evolution of massive single and binary stars, which is largely restricted to a diagnostic value, and foremost so for the element boron. However, we show that the boron surface abundance in massive early type stars contains key information about their foregoing evolution which is not obtainable otherwise. In particular, it allows to constrain internal mixing processes and potential previous mass transfer event for binary stars (even if the companion has disappeared). It may also help solving the mystery of the slowly rotating nitrogen-rich massive main sequence stars.

scholarly journals Assessing hydrological effects of human interventions on coastal systems: numerical applications to the Venice Lagoon

2013 ◽  
Vol 17 (5) ◽  
pp. 1733-1748 ◽  
Author(s):  
C. Ferrarin ◽  
M. Ghezzo ◽  
G. Umgiesser ◽  
D. Tagliapietra ◽  
E. Camatti ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Venice Lagoon ◽  
Mixing Processes ◽  
Coastal System ◽  
Water Renewal ◽  
Internal Mixing ◽  
Renewal Time ◽  
Human Interventions ◽  
The Impact

Abstract. The hydrological consequences of historical, contemporary and future human activities on a coastal system were investigated by means of numerical models. The changes in the morphology of the Lagoon of Venice during the last century result from the sedimentological response to the combined effects of human interventions on the environment and global changes. This study focuses on changes from 1927 to 2012 and includes the changes planned for the protection of the city of Venice from storm surges and exceptional tides under future sea level rise scenarios. The application of a hydrodynamic model allowed for the analysis of the morphological effects on the lagoon circulation, the interaction with the sea and the internal mixing processes. The absolute values of the exchange between the lagoon and sea increased from 1927 to 2002 (from 3900 to 4600 m3 s−1), while the daily fraction of lagoon water volume exchanged decreased. At the same time, the flattening of the lagoon and loss of morphological heterogeneity enhanced the internal mixing processes driven by the tide and wind, reducing thus the overall water renewal time from 11.9 days in 1927 to 10.8 days in 2002. Morphological changes during the last decade reduced the water exchange through the inlets and induced an increase of the basin-wide water renewal time of 0.5 day. In the future, Venice Lagoon will evolve to a more restricted environment due to sea level rise, which increases the lagoon volume, and periodical closure of the lagoon from the sea during flooding events, which reduces the communication with the open sea. Therefore, the flushing capacity of the lagoon will decrease considerably, especially in its central part. Furthermore, some considerations on the impact of the hydromorphological changes on the ecological dynamics are proposed.

scholarly journals Constraints on stellar evolution from pulsations

1984 ◽  
Vol 105 ◽  
pp. 421-440
Author(s):  
Arthur N. Cox
Keyword(s):  
Stellar Evolution ◽  
Variable Stars ◽  
Mixing Processes ◽  
Rr Lyrae ◽  
Internal Mixing ◽  
Classical Cepheids ◽  
Basic Parameters ◽  
Effective Temperatures ◽  
The Many ◽  
Intrinsic Variable

Consideration of the many types of intrinsic variable stars, that is, those that pulsate, reveals that perhaps a dozen classes can indicate some constraints that affect the results of stellar evolution calculations, or some interpretations of observations. Many of these constraints are not very strong or may not even be well defined yet. In this review we discuss only the case for six classes: classical Cepheids with their measured Wesselink radii, the observed surface effective temperatures of the known eleven double-mode Cepheids, the pulsation periods and measured surface effective temperatures of three R CrB variables, the δ Scuti variable VZ Cnc with a very large ratio of its two observed periods, the nonradial oscillations of our sun, and the period ratios of the newly discovered double-mode RR Lyrae variables. Unfortunately, the present state of knowledge about the exact compositions; mass loss and its dependence on the mass, radius, luminosity, and composition; and internal mixing processes, as well as sometimes the more basic parameters such as luminosities and surface effective temperatures prevent us from applying strong constraints for every case where currently the possibility exists.

scholarly journals Wolf-Rayet stars as a diagnostic of internal mixing processes in massive mass losing stars

1988 ◽  
Vol 108 ◽  
pp. 90-91
Author(s):  
N. Langer
Keyword(s):  
Observational Data ◽  
Stellar Evolution ◽  
Chemical Structure ◽  
Large Scale ◽  
Massive Stars ◽  
The Other ◽  
Large Uncertainty ◽  
Mixing Processes ◽  
Internal Mixing ◽  
Convective Core

Massive stars (MZAMS ≳ 30 M⊙) develop during their observable hydrostatic evolutionary phases — i.e. central H- and He-burning — three different large scale convective zones, which are: 1) The H-burning convective core, 2) the intermediate convective shell (ICZ) above the hydrogen shell source, which forms at time of hydrogen exhaustion, and 3) the He-burning convective core. The spatial extent of these convective regions, wherein the chemical structure is rapidly homogenised, can be predicted from theory only with a large uncertainty. Different assumptions on the efficiency of these mixing processes in stellar evolution calculations lead to quite different evolutionary pictures for massive stars, especially regarding their Wolf-Rayet (WR) phases. On the other side, many observational data concerning WR stars became available in recent years. For this reason, we attempt to perform a comparison of theoretical evolutionary sequences with observed properties of WR stars in order to derive restrictions on the efficiency of the three mixing processes mentioned above.

scholarly journals Rotation: a fundamental parameter of massive stars

1997 ◽  
Vol 189 ◽  
pp. 343-348 ◽  
Author(s):  
N. Langer ◽  
A. Heger ◽  
J. Fliegner
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Large Fraction ◽  
Reasonable Doubt ◽  
Close Binary ◽  
Fundamental Parameter ◽  
Mixing Processes ◽  
B Stars ◽  
Internal Mixing ◽  
Rule Out

Massive stars are rapid rotators. Equatorial rotation velocities span the range vrot = 100–400 km s−1, with B stars rotating closest to their break-up speed vcrit (Howarth et al. 1997). During the last decade, many observations have revealed unusual surface abundances that may require additional internal mixing (beyond that of simple convection and overshooting) for their explanation, most important helium and nitrogen enrichment in main sequence O and B stars (Gies & Lambert 1992), in the SN 1987A progenitor (Fransson et al. 1989), and boron depletions in main sequence B stars (Venn et al. 1996). In particular the latter observations clearly point towards internal mixing and rule out a close binary origin of the abundance peculiarities (Fliegner et al. 1996). Altogether, the occurrence of some form of additional mixing responsible for altering the surface abundances in a large fraction, if not all massive stars appears to be beyond reasonable doubt, and mixing processes due to rotation are the most natural explanation.

scholarly journals Supernova progenitors as a test for stellar physics

2015 ◽  
Vol 11 (A29B) ◽  
pp. 217-217
Author(s):  
Cyril Georgy
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
Point Of View ◽  
Theoretical Point ◽  
Mixing Processes ◽  
End Points ◽  
Evolutionary Path ◽  
Internal Mixing ◽  
The Way

AbstractThe evolution of massive stars after the main sequence is not very well known from a theoretical point of view. Recent studies have shown that the way internal mixing processes, such as rotation and convection, are implemented in stellar evolution codes lead to significant discrepancies between the predictions of these codes. Particularly, the end-points of stellar evolution can be considerably different, making hard to understand the evolutionary path the lead to the observed supernovae progenitors.

scholarly journals Evolution of massive stars: main sequence and close to it

1993 ◽  
Vol 137 ◽  
pp. 426-436
Author(s):  
Norbert Langer
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Nuclear Data ◽  
Mass Range ◽  
Sequence Evolution ◽  
Mixing Processes ◽  
Convective Mixing ◽  
Internal Mixing ◽  
The Status ◽  
Standard Models

AbstractWe discuss the status of current models for the early evolutionary stages of stars in the initial mass range 10-40 M⊙. Effects of the pre-main sequence evolution, mass loss, internal mixing, and changes in atomic and nuclear data are outlined and confronted with several basic observational facts, which are unexplained by standard models. We conclude that especially internal mixing processes deserve much more attention in future investigations, and we show why convective mixing may be less efficient than generally assumed, but more mixing should be present in the radiative zones of at least a fraction of all massive stars.

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