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Titolo:
Stellar evolution with rotation. VII. Low metallicity models and the blue to red supergiant ratio in the SMC
Autore:
Maeder, A; Meynet, G;
Indirizzi:
Observ Geneva, CH-1290 Sauverny, Switzerland Observ Geneva Sauverny Switzerland CH-1290 CH-1290 Sauverny, Switzerland
Titolo Testata:
ASTRONOMY & ASTROPHYSICS
fascicolo: 2, volume: 373, anno: 2001,
pagine: 555 - 571
SICI:
1432-0746(200107)373:2<555:SEWRVL>2.0.ZU;2-V
Fonte:
ISI
Lingua:
ENG
Soggetto:
SMALL-MAGELLANIC-CLOUD; THERMONUCLEAR REACTION-RATES; MASS-LOSS RATES; HELIUM ABUNDANCE; STAR EVOLUTION; HR DIAGRAMS; GRIDS; CLUSTERS; GALAXIES; WIND;
Keywords:
stars : evolution; stars : rotation; supergiant; magellanic clouds;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
68
Recensione:
Indirizzi per estratti:
Indirizzo: Maeder, A Observ Geneva, CH-1290 Sauverny, Switzerland Observ Geneva Sauverny Switzerland CH-1290 uverny, Switzerland
Citazione:
A. Maeder e G. Meynet, "Stellar evolution with rotation. VII. Low metallicity models and the blue to red supergiant ratio in the SMC", ASTRON ASTR, 373(2), 2001, pp. 555-571

Abstract

We calculate a grid of models with and without the effects of axial rotation for massive stars in the range of 9 to 60 M-. and metallicity Z = 0.004 appropriate for the SMC. Remarkably, the ratios Omega/Omega (crit) of the angular velocity to the break-up angular velocity grow strongly during the evolution of high mass stars, contrary to the situation at Z = 0.020. The reason is that at low Z, mass loss is smaller and the removal of angular momentum during evolution much weaker, also there is an efficient outward transport of angular momentum by meridional circulation. Thus, a much larger fraction of the stars at lower Z reach break-up velocities and rotation may thus be a dominant effect at low Z. The models with rotation well account forthe long standing problem of the large numbers of red supergiants observedin low Z galaxies, while current models with mass loss were predicting no red supergiants. We discuss in detail the physical effects of rotation which favour a redwards evolution in the HR diagram. The models also predict large N enrichments during the evolution of high mass stars. The predicted relative N-enrichments are larger at Z lower than solar and this is in very good agreement with the observations for A-type supergiants in the SMC.

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Documento generato il 11/07/20 alle ore 16:47:34