The VLT-FLAMES survey of massive stars: evolution of surface N abundances and effective temperature scales in the Galaxy and Magellanic Clouds

AbstractOne of the challenges for stellar astrophysics is to reach the point at which we can undertake reliable spectral synthesis of unresolved populations in young, star-forming galaxies at high redshift. Here I summarise recent studies of massive stars in the Galaxy and Magellanic Clouds, which span a range of metallicities commensurate with those in high-redshift systems, thus providing an excellent laboratory in which to study the role of environment on stellar evolution. I also give an overview of observations of luminous supergiants in external galaxies out to a remarkable 6.7 Mpc, in which we can exploit our understanding of stellar evolution to study the chemistry and dynamics of the host systems.

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The properties of early-type stars in the Magellanic Clouds

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308028664 ◽

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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The excess of cool supergiants from contemporary stellar evolution models defies the metallicity-independent Humphreys-Davidson limit

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab383 ◽

2021 ◽

Author(s):

Avishai Gilkis ◽

Tomer Shenar ◽

Varsha Ramachandran ◽

Adam S Jermyn ◽

Laurent Mahy ◽

...

Keyword(s):

Stellar Evolution ◽

Massive Stars ◽

Magellanic Clouds ◽

Rotation Rates ◽

Mixing Parameters ◽

Synthetic Populations ◽

The Galaxy ◽

Effective Temperatures ◽

The Impact

Abstract The Humphreys-Davidson (HD) limit empirically defines a region of high luminosities (log10(L/L⊙) ≳ 5.5) and low effective temperatures (Teff ≲ 20 kK) on the Hertzsprung-Russell Diagram in which hardly any supergiant stars are observed. Attempts to explain this limit through instabilities arising in near- or super-Eddington winds have been largely unsuccessful. Using modern stellar evolution we aim to re-examine the HD limit, investigating the impact of enhanced mixing on massive stars. We construct grids of stellar evolution models appropriate for the Small and Large Magellanic Clouds (SMC, LMC), as well as for the Galaxy, spanning various initial rotation rates and convective overshooting parameters. Significantly enhanced mixing apparently steers stellar evolution tracks away from the region of the HD limit. To quantify the excess of over-luminous stars in stellar evolution simulations we generate synthetic populations of massive stars, and make detailed comparisons with catalogues of cool (Teff ≤ 12.5 kK) and luminous (log10(L/L⊙) ≥ 4.7) stars in the SMC and LMC. We find that adjustments to the mixing parameters can lead to agreement between the observed and simulated red supergiant populations, but for hotter supergiants the simulations always over-predict the number of very luminous (log10(L/L⊙) ≥ 5.4) stars compared to observations. The excess of luminous supergiants decreases for enhanced mixing, possibly hinting at an important role mixing has in explaining the HD limit. Still, the HD limit remains unexplained for hotter supergiants.

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The initial mass function for massive stars in the Galaxy and the Magellanic Clouds

The Astrophysical Journal ◽

10.1086/162439 ◽

1984 ◽

Vol 284 ◽

pp. 565 ◽

Cited By ~ 269

Author(s):

R. M. Humphreys ◽

D. B. McElroy

Keyword(s):

Massive Stars ◽

Mass Function ◽

Magellanic Clouds ◽

Initial Mass Function ◽

Initial Mass ◽

The Galaxy

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The Metallicity Dependence of the Mass Loss of Early-Type Massive Stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308020322 ◽

2007 ◽

Vol 3 (S250) ◽

pp. 39-46

Author(s):

Alex de Koter

Keyword(s):

Mass Loss ◽

Metal Content ◽

Massive Stars ◽

Magellanic Clouds ◽

Stellar Winds ◽

Early Type ◽

The Galaxy ◽

Early Type Stars ◽

Good Agreement ◽

Comprehensive Study

AbstractWe report on a comprehensive study of the wind properties of 115 O- and early B-type stars in the Galaxy and the Large Magellanic Clouds. This work is part of the VLT/FLAMES Survey of Massive Stars. The data is used to construct the empirical dependence of the mass-loss in stellar winds on the metal content of their atmospheres. The metal content of early-type stars in the Magellanic Clouds is discussed. Assuming a power-law dependence of mass loss on metal content, Ṁ ∝ Zm, we find m = 0.83 ± 0.16 from an analysis of the wind momentum luminosity relation (Mokiem et al. 2007b). This result is in good agreement with the prediction m = 0.69 ± 0.10 by Vink et al. (2001). Though the scaling agrees, the absolute empirical value of mass loss is found to be a factor of two higher than predictions. This may be explained by a modest amount of clumping in the outflows of the objects studied.

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Massive stars in the galaxy and the magellanic clouds - Clues to stellar evolution

Publications of the Astronomical Society of the Pacific ◽

10.1086/131419 ◽

1984 ◽

Vol 96 ◽

pp. 779 ◽

Cited By ~ 4

Author(s):

C. D. Garmany

Keyword(s):

Stellar Evolution ◽

Massive Stars ◽

Magellanic Clouds ◽

The Galaxy

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Interstellar gas around WO stars in the Galaxy and the Magellanic Clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900201113 ◽

1991 ◽

Vol 148 ◽

pp. 438-439

Author(s):

Tatiana A. Lozinskaya

Keyword(s):

Massive Stars ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Magellanic Clouds ◽

Stellar Winds ◽

Small Magellanic Cloud ◽

Interstellar Gas ◽

The Galaxy

The four oxygen-sequence WR stars, Sand 1 in the Small Magellanic Cloud (SMC), Sand 2 in the Large Magellanic Cloud (LMC), and WR 102 and WR 142 in the Galaxy represent the latest stage of the evolution of massive stars (Sanduleak 1971, Barlow and Hummer 1982, Moffatet al.1985). We have shown WR 102 to be a stripped CO core of a supermassive star (Dopitaet al.1990), probably seen only several thousand years before a SN explosion. The four stars are characterized by extremely energetic stellar winds –Vw from 4500 to 7400 km/s (Barlow and Hummer 1982, Dopitaet al.1990, Torreset al.1986). Examination of the environments of WO stars leads to the conclusion that the four objects appear to be associated with optical and/or IR shell-like structures, although the short WO-superwind does not prevail in the shell's formation.

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The Stellar Population in the SMC Region N76B

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000016994 ◽

1983 ◽

Vol 5 (2) ◽

pp. 238-241 ◽

Cited By ~ 1

Author(s):

P. Seal ◽

A.R. Hyland

Keyword(s):

Stellar Population ◽

Milky Way ◽

Massive Stars ◽

Magellanic Clouds ◽

Birth Rates ◽

Infrared Observations ◽

The Galaxy ◽

Optical Wavelengths

The Magellanic Clouds are the nearest major extragalactic objects to the Milky Way. The study of young giants or supergiants in the Clouds enables us to obtain information regarding the birth rates and evolution of young massive stars in those systems, free from biases inherent in similar studies in the Galaxy. Although the Magellanic Clouds have been studied by an extremely large number of research workers at optical wavelengths, it is only recently that significant infrared observations have also been undertaken (e.g., Glass 1979, McGregor and Hyland 1981, Cohen et al. 1982). Cool supergiants in the SMC have been studied optically by Humphreys (1979). She found that most are very metal deficient, and should be classified spectroscopically as M0.

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