Multiple stellar populations in Magellanic Cloud clusters – VI. A survey of multiple sequences and Be stars in young clusters

Milone, A. P.; Marino, A. F.; Criscienzo, M. Di; D’Antona, Francesca; Bedin, L. R.; Costa, Guglielmo; Piotto, G.; Tailo, M.; Dotter, Aaron; Angeloni, R.; Anderson, Jay; Jerjen, Helmut; Li, C; Dupree, A. K.; Granata, V.; Lagioia, E. P.; Mackey, A. D.; Nardiello, D.; Vesperini, Enrico

doi:10.1093/mnras/sty661

Cited by 105 publications

(207 citation statements)

References 67 publications

(111 reference statements)

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“…We have compared our CMD, which includes also the core He-burning loop, with isochrones of rotating models from the Geneva stellar models database 4 (Georgy et al 2014), provided by the SYCLIST code. We took into account the work done by Milone et al (2018), in which they show the presence of two families of stars in NGC 330, the bluest formed by non-rotating stars with an age compatible with 32 Myr (in agreement with our results), the reddest by rotating stars with angular velocity ω = 0.9ω c and age around 40 Myr, representing 40-55% of MS stars. As shown in Fig.…”

Section: Effect Of Stellar Rotationsupporting

confidence: 79%

MUSE Observations of NGC330 in the Small Magellanic Cloud: Helium Abundance of Bright Main-sequence Stars*

Carini

Biazzo

Brocato

et al. 2020

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We present observations of the most bright main sequence stars in the Small Magellanic Cloud stellar cluster NGC 330 obtained with the integral field spectrograph MUSE@VLT. The use of this valuable instrument allows us to study both photometric and spectroscopic properties of stellar populations of this young star cluster.The photometric data provide us a precise color magnitude diagram, which seems to support the presence of two stellar populations of ages of ≈ 18 Myr and ≈ 30 Myr assuming a metallicity of Z = 0.002.Thanks to the spectroscopic data, we derive helium abundance of 10 main sequence stars within the effective radius R eff = 20 of NGC 330, thus leading to an estimation of (He) = 10.93 ± 0.05 (1σ).The helium elemental abundances of stars likely belonging to the two possible stellar populations, do not show differences or dichotomy within the uncertainties. Thus, our results suggest that the two stellar populations of NGC 330, if they exist, share similar original He abundances.If we consider stellar rotation velocity in our analysis, a coeval (30 Myr) stellar population, experiencing different values of rotation, cannot be excluded. In this case, the mean helium abundance < (He) > rot obtained in our analysis is 11.00 ± 0.05 dex. We also verified that possible NLTE effects cannot be identified with our analysis because of the spectral resolution and they are within our derived abundance He uncertainties.Moreover, the analysis of the He abundance as a function of the distance from the cluster center of the observed stars do not show any correlation.

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Section: Effect Of Stellar Rotationsupporting

confidence: 79%

MUSE Observations of NGC330 in the Small Magellanic Cloud: Helium Abundance of Bright Main-sequence Stars*

Carini

Biazzo

Brocato

et al. 2020

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“…7 show that most of the observed Hα emitters are redder than the ordinary main sequence stars. This segregation is not a unique feature to NGC 330, with many LMC and SMC clusters exhibiting the same trait (Milone et al 2018). Telting et al (1998) have suggested through observations of Be stars whose spectra show rapid switching between containing emission lines and not, that the decretion disc can contribute up to 40% of a Be star's flux.…”

Section: Fast Rotators In the Colour-magnitude Diagrammentioning

confidence: 96%

“…To compare the models with observations of the SMC open cluster NCG 330 (Milone et al 2018) in the colour-magnitude diagram, the bolometric luminosities and effective temperature are converted to absolute magnitudes in the Hubble Space Telescope Wide-Field Camera 3 filters F814W and F336W by interpolating tables based on synthetic stellar spectra (Girardi et al 2002). The values of distance modulus and reddening adopted are (m − M) = 18.92 and E(B − V) = 0.06 respectively.…”

Section: Population Synthesismentioning

confidence: 99%

The single star path to Be stars

Hastings

Wang

Langer

2020

A&A

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Context. Be stars are rapidly rotating B main sequence stars, which show line emission due to an outflowing disc. By studying the evolution of rotating single star models, we can assess their contribution to the observed Be star populations. Aims. We identify the main effects which are responsible for single stars to approach critical rotation as functions of initial mass and metallicity, and predict the properties of populations of rotating single stars. Methods. We perform population synthesis with single star models of initial masses ranging between 3 and 30 M , initial equatorial rotation velocities between 0 and 600 km s −1 at compositions representing the Milky Way, Large and Small Magellanic Clouds. These models include efficient core-envelope coupling mediated by internal magnetic fields and correspond to the maximum efficiency of Be star production. We predict Be star fractions and the positions of fast rotating stars in the colour-magnitude diagram. Results. We identify stellar wind mass-loss and the convective core mass fraction as the key parameters which determine the time dependance of the stellar rotation rates. Using empirical distributions of initial rotational velocities, our single star models can reproduce the trends observed in Be star fractions with mass and metallicity. However, they fail to produce a significant number of stars rotating very close to critical. We also find that rapidly rotating Be stars in the Magellanic Clouds should have significant surface nitrogen enrichments, which may be in conflict with abundance determinations of Be stars.Conclusions. Single star evolution may explain the high number of Be stars if 70 to 80% of critical rotation would be sufficient to produce the Be phenomenon. However even in this case, the unexplained presence of many Be stars far below the cluster turn-off indicates the importance of the binary channel for Be star production.

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“…Correspondingly uncertain is the number of predicted OB+BH binaries. However, Wang et al (2020) have shown that the distribution of the sizable Be population of NGC 330 (Milone et al 2018) in the colour-magnitude diagram is well reproduced by detailed binary evolution models. In order to explain their number, however, the condition for stable mass transfer would have to be relaxed such that merging is prevented in more systems.…”

Section: Mass Transfer Efficiencymentioning

confidence: 99%

Properties of OB star−black hole systems derived from detailed binary evolution models

Langer

Schürmann

Stoll

et al. 2020

A&A

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Context. The recent gravitational wave measurements have demonstrated the existence of stellar mass black hole binaries. It is essential for our understanding of massive star evolution to identify the contribution of binary evolution to the formation of double black holes. Aims. A promising way to progress is investigating the progenitors of double black hole systems and comparing predictions with local massive star samples such as the population in 30 Doradus in the Large Magellanic Cloud (LMC). Methods. To this purpose, we analyse a large grid of detailed binary evolution models at LMC metallicity with initial primary masses between 10 and 40 M , and identify which model systems potentially evolve into a binary consisting of a black hole and a massive main sequence star. We then derive the observable properties of such systems, as well as peculiarities of the OB star component. Results. We find that ∼3% of the LMC late O and early B stars in binaries are expected to possess a black hole companion, when assuming stars with a final helium core mass above 6.6 M to form black holes. While the vast majority of them may be X-ray quiet, our models suggest that these may be identified in spectroscopic binaries, either by large amplitude radial velocity variations ( ∼ > 50 km s −1 ) and simultaneous nitrogen surface enrichment, or through a moderate radial velocity ( ∼ > 10 km s −1 ) and simultaneously rapid rotation of the OB star. The predicted mass ratios are such that main sequence companions could be excluded in most cases. A comparison to the observed OB+WR binaries in the LMC, Be/X-ray binaries, and known massive BH binaries supports our conclusion. Conclusions. We expect spectroscopic observations to be able to test key assumptions in our models, with important implications for massive star evolution in general, and for the formation of double-black hole mergers in particular.

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Multiple stellar populations in Magellanic Cloud clusters – VI. A survey of multiple sequences and Be stars in young clusters

Cited by 105 publications

References 67 publications

MUSE Observations of NGC330 in the Small Magellanic Cloud: Helium Abundance of Bright Main-sequence Stars*

MUSE Observations of NGC330 in the Small Magellanic Cloud: Helium Abundance of Bright Main-sequence Stars*

The single star path to Be stars

Properties of OB star−black hole systems derived from detailed binary evolution models

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