The VLT-FLAMES survey of massive stars: constraints on stellar evolution from the chemical compositions of rapidly rotating Galactic and Magellanic Cloud B-type stars

By I. Hunter, I. Brott, N. Langer, D. Lennon, P. Dufton, I. Howarth, R. Ryans, C. Trundle, Christopher H. Evans, A. D. Koter and 1 more. 2009

160 citations recorded by the source corpus.

Aims. We have previously analysed the spectra of 135 early B-type stars in the Large Magellanic Cloud (LMC) and found several groups of stars that have chemical compositions that conflict with the theory of rotational mixing. Here we extend this study to Galactic and Small Magellanic Cloud (SMC) metallicities. Methods. We provide chemical compositions for ~50 Galactic and ~100 SMC early B-type stars and compare these to the LMC results. These samples cover a range of projected rotational velocities up to ~300 km s-1 and hence are well suited to testing rotational mixing models. The surface nitrogen abundances are utilised as a probe of the mixing process since nitrogen is synthesized in the core of the stars and mixed to the surface. Results. In the SMC, we find a population of slowly rotating nitrogen-rich stars amongst the early B type core-hydrogen burning stars, which is comparable to that found previously in the LMC. The identification of non-enriched rapid rotators in the SMC is not possible due to the relatively high upper limits on the nitrogen abundance for the fast rotators. In the Galactic sample we find no significant enrichment amongst the core hydrogen-burning stars, which appears to be in contrast with the expectation from both rotating single-star and close binary evolution models. However, only a small number of the rapidly rotating stars have evolved enough to produce a significant nitrogen enrichment, and these may be analogous to the non-enriched rapid rotators previously found in the LMC sample. Finally, in each metallicity regime, a population of highly enriched supergiants is observed, which cannot be the immediate descendants of core-hydrogen burning stars. Their abundances are, however, compatible with them having gone through a previous red supergiant phase. Together, these observations paint a complex picture of the nitrogen enrichment in massive main sequence and supergiant stellar atmospheres, where age and binarity cause crucial effects. Whether rotational mixing is required to understand our results remains an open question at this time, but could be answered by identifying the true binary fraction in those groups of stars that do not agree with single-star evolutionary models.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/f0abef2395f048416efec002b23a825f5b84d3d0

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In Astronomy and Astrophysics

1. R. Hirschi
2. M. Limongi
3. A. Chieffi
4. G. Meynet
5. C. Conroy
6. S. Ekström
7. Benjamin D. Johnson
8. Andre Maeder

In Instrumentation

1. R. Hirschi
2. C. Conroy
3. Benjamin D. Johnson
4. A. Chieffi
5. M. Limongi
6. G. Meynet
7. S. Ekström
8. Andre Maeder

Citations in the corpus

• Chemical evolution with rotating massive star yields - I. The solar neighbourhood and the s-process elements (2018, methodology): “In the present case, a better calibration is adopted: the models fit the main trend of N abundance versus initial rotational velocity observed in a sample of stars taken from the FLAMES survey of the LMC (the so called Hunter diagram, Hunter et al. 2009), as originally done by Brott et al. (2011).”
• OPTICAL SPECTRA OF 73 STRIPPED-ENVELOPE CORE-COLLAPSE SUPERNOVAE (2014, background): “…in the near-infrared (NIR) that ought to be used, such as He i λ10830 and He i λ20581 (see discussion in Taubenberger et al. 2006; Modjaz et al. 2009; Hunter et al. 2009a; Valenti et al. 2011; Hachinger et al. 2012; Dessart et al. 2012), but these lines are outside the spectral wavelength range of…”
• MESA ISOCHRONES AND STELLAR TRACKS (MIST). I. SOLAR-SCALED MODELS (2016, background): “36 a compilation of data from Gies & Lambert (1992), Kilian (1992), Morel et al. (2008), and Hunter et al. (2009).”
• Classical Be stars (2013, background): “However, most of the chemical studies of Be stars (Dunstall et al. 2011) do not find such a pattern, and Hunter et al. (2009) pointed out in general that some stars may follow another chemical evolution path.”
• Presupernova Evolution and Explosive Nucleosynthesis of Rotating Massive Stars in the Metallicity Range −3 ≤ [Fe/H] ≤ 0 (2018, methodology): “Compared to our previous study, we also adopted a different approach to calibrate the rotation-induced mixing efficiency, which takes advantage now of the observations of the surface chemical composition of many B-stars in the LMC samples of the FLAMES survey (Hunter et al. 2009).”
• The VLT-FLAMES Tarantula Survey XXVII. Physical parameters of B-type main-sequence binary systems in the Tarantula nebula (2017, unknown): “In the Large Magellanic Cloud (LMC), Sana et al. (2013) estimated a fraction of 0.51 ± 0.04 for the O-type stellar population of the 30 Doradus regio observed in the VLT-FLAMES Tarantula survey (VFTS; Evans et al. 2011b, here-inafter Paper I).”
• A STELLAR ROTATION CENSUS OF B STARS: FROM ZAMS TO TAMS (2010, background): “There is a pressing need for observational results on a larger sample to help resolve questions surrounding the connection between rotation and birthplace density (Huang & Gies 2008; Wolff et al. 2008) and internal mixing (Ekström et al. 2008; Decressin et al. 2009; Hunter et al. 2009).”
• PRE-SUPERNOVA EVOLUTION OF ROTATING SOLAR METALLICITY STARS IN THE MASS RANGE 13–120 M☉ AND THEIR EXPLOSIVE YIELDS (2012, background): “…the various WR subtypes (Meynet & Maeder 2003, and references therein), the surface enhancement of He and N in MS stars (Mokiem et al. 2006, 2007; Hunter et al. 2009), the ratio of blue to red supergiants as a function of the metallicity (Langer & Maeder 1995), the peculiar chemical composition…”
• 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).”
• THE EFFECTS OF STELLAR ROTATION. II. A COMPREHENSIVE SET OF STARBURST99 MODELS (2014, background): “…mass loss cannot account for the second development: stars that should not have strong stellar winds during their main-sequence phases (typically 15 M stars) and thus should not display any changes in their surface abundances may actually show nitrogen surface enrichments (Hunter et al. 2009).”
• s-process production in rotating massive stars at solar and low metallicities (2015, background): “This is slightly lower than the peak of the velocity distribution, at υMW, peak = 225 km s−1, found for O- and B-type stars in the Milky Way (Dufton et al. 2006; Hunter et al. 2009).”
• The IACOB project - I. Rotational velocities in northern Galactic O- and early B-type stars revisited. The impact of other sources of line-broadening (2013, background): “…Sweden, in the Spanish Observatorio del Roque delos Muchachos of the Instituto de Astrofisica de Canarias. dance pattern observed in massive stars (e.g Hunter et al., 2009; Przybilla et al., 2010; Bouret et al., 2013), and (b) the eff ct of very extreme rotation in their evolution1 and final fate…”