The VLT FLAMES Survey of Massive Stars: Rotation and Nitrogen Enrichment as the Key to Understanding Massive Star Evolution

By I. Hunter, I. Brott, D. Lennon, N. Langer, P. Dufton, C. Trundle, S. Smartt, A. D. Koter, Christopher H. Evans, R. Ryans. 2007

141 citations recorded by the source corpus.

Rotation has become an important element in evolutionary models of massive stars, specifically via the prediction of rotational mixing. Here we study a sample of stars, including rapid rotators, to constrain such models and use nitrogen enrichments as a probe of the mixing process. Chemical compositions (C, N, O, Mg, and Si) have been estimated for 135 early B-type stars in the Large Magellanic Cloud with projected rotational velocities up to ~300 km s-1 using a non-LTE TLUSTY model atmosphere grid. Evolutionary models, including rotational mixing, have been generated attempting to reproduce these observations by adjusting the overshooting and rotational mixing parameters and produce reasonable agreement with 60% of our core hydrogen burning sample. We find (excluding known binaries) a significant population of highly nitrogen-enriched intrinsic slow rotators (vsin i ≲ 50 km s-1) incompatible with our models (~20% of the sample). Furthermore, while we find fast rotators with enrichments in agreement with the models, the observation of evolved (log g < 3.7 dex) fast rotators that are relatively unenriched (a further ~20% of the sample) challenges the concept of rotational mixing. We also find that 70% of our blue supergiant sample cannot have evolved directly from the hydrogen-burning main sequence. We are left with a picture where invoking binarity and perhaps fossil magnetic fields is required to understand the surface properties of a population of massive main-sequence stars.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/8138afdc8954def92c40450b6b3c7a2098aa70b7

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In Astronomy and Astrophysics

1. Selma de Mink
2. N. Langer
3. Michela Mapelli
4. Robert G. Izzard
5. Ilya Mandel
6. S. Smartt
7. C. Conroy
8. N. Smith

Citations in the corpus

• MESA ISOCHRONES AND STELLAR TRACKS (MIST). I. SOLAR-SCALED MODELS (2016, background): “…with/without surface nitrogen enrichment, and some authors even find that de-projected velocities show no statistically significant correlation with surface nitrogen abundances (e.g, Hunter et al. 2008; Brott et al. 2011b; Rivero González et al. 2012; Bouret et al. 2013; Aerts et al. 2014).”
• INTERNAL GRAVITY WAVES IN MASSIVE STARS: ANGULAR MOMENTUM TRANSPORT (2013, background): “Hunter et al. (2008) show that more than 10% of their sampled stars are enhanced in nitrogen without rapid rotation, while 20% of their stars are rapidly rotating without showing any significant nitrogen enhancement.”
• The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 M⊙ stellar mass limit (2010, background): “However, the VLT FLAMES survey has highlighted some discrepancies between models and observations (Hunter et al. 2008), questioning the efficiency of rotation-induced mixing.”
• THE GALACTIC O-STAR SPECTROSCOPIC SURVEY. I. CLASSIFICATION SYSTEM AND BRIGHT NORTHERN STARS IN THE BLUE-VIOLET AT R ∼ 2500 (2011, background): “The relationship between rotational velocity and surface nitrogen enrichment in massive stars is a subject of considerable current interest (Maeder & Meynet 2000; Hunter et al. 2008, 2009).”
• Merging binary black holes formed through chemically homogeneous evolution in short-period stellar binaries (2015, background): “It should also be noted that the direct comparison of trends between the measured projected rotation rates and surface nitrogen abundances has raised questions concerning rotational mixing (Hunter et al. 2008; Maeder et al. 2009; Brott et al. 2011b).”
• Rotational mixing in massive binaries - Detached short-period systems (2009, methodology): “The Galactic model with an equatorial velocity of 230 km s−1 shows nitrogen enhancements up to about 0.3 dex, while in the SMC model the N abundance increases by up to approximately 0.8 dex.”
• The Observer's Guide to the Gamma-Ray Burst-Supernova Connection (2016, background): “The FLAMES survey [385] observed over 100 O- and B-type stars in the Large Magellanic Cloud (LMC) and the Milky Way galaxy and showed the presence of a group of rapidly rotating stars that were enriched with nitrogen at their surfaces.”
• Classical Be stars (2013, background): “This was confirmed observationally: O, B, and Be stars rotate faster in the SMC than in the LMC, and in the LMC faster than in the MW (Keller 2004; Hunter et al. 2008; Martayan et al. 2006a, 2007b).”
• The VLT-FLAMES Tarantula Survey XXVII. Physical parameters of B-type main-sequence binary systems in the Tarantula nebula (2017, unknown): “This has lead other authors (Hunter et al. 2008; Brott et al. 2011b; Grin et al. 2016) to question whether all the low-v e sin i single stars with high nitrogen abundances found in other single-star samples can be rapid rotators viewed at low angles of incidence.”
• Formation and dynamical evolution of multiple stellar generations in globular clusters (2008, background): “…have not been studied, and a recent VLT FLAMES survey of massive stars, studying the nitrogen abundance and the rotational velocity of 135 B-type stars in the LMC (Hunter et al. 2008), has found a number of unenriched fast rotators and cast some doubt on the efficiency of rotational mixing.”
• Sub-surface convection zones in hot massive stars and their observable consequences (2009, methodology): “7, we show the microturbulent velocities for the LMC stars of Hunter et al. (2008b) versus the stellar surface gravity.”
• THE ROTATION RATES OF MASSIVE STARS: THE ROLE OF BINARY INTERACTION THROUGH TIDES, MASS TRANSFER, AND MERGERS (2012, background): “Additional evidence for the importance of close binary evolution in the sample of Hunter et al. (2008a) comes from the star-by-star analysis of Köhler et al. (2012).”
• Progenitors of Core-Collapse Supernovae (2009, methodology): “These convincingly suggest a spectral type of B3I, a Teff ≃ 15750 (from the calibration of LMC B-supergiants Trundle et al. 2007) and hence log L/L⊙= 5.1 ± 0.1.”
• The Wolf-Rayet stars in the Large Magellanic Cloud - A comprehensive analysis of the WN class (2014, background): “One may also mention here the work of Hunter et al. (2008), who determined the chemical composition of 135 early B-type stars in the LMC to test the prediction of rotationally induced mixing.”
• THE INCIDENCE OF STELLAR MERGERS AND MASS GAINERS AMONG MASSIVE STARS (2013, background): “This questions whether the observed nitrogen abundances are the result of rotational mixing processes operating in isolated rotating stars, or whether they are the result of binary interaction processes (Hunter et al. 2008).”