The effects of rotation on stellar evolution are particularly important at low metallicity, when mass loss by stellar winds diminishes and the surface enrichment due to rotational mixing becomes relatively more pronounced than at high metallicities. Here we investigate the impact of rotation and metallicity on stellar evolution. Using similar physics as in our previous large grids of models at Z = 0.002 and Z = 0.014, we compute stellar evolution models with the Geneva code for rotating and nonrotating stars with initial masses (Mini) between 1.7 and 120 M⊙ and Z = 0.0004 (1/35 solar). This is comparable to the metallicities of the most metal poor galaxies observed so far, such as I Zw 18. Concerning massive stars, both rotating and nonrotating models spend most of their core-helium burning phase with an effective temperature higher than 8000 K. Stars become red supergiants only at the end of their lifetimes, and few red supergiants are expected. Our models predict very few to no classical Wolf–Rayet stars as a results of weak stellar winds at low metallicity. The most massive stars end their lifetimes as luminous blue supergiants or luminous blue variables, a feature that is not predicted by models with higher initial metallicities. Interestingly, due to the behavior of the intermediate convective zone, the mass domain of stars producing pair-instability supernovae is smaller at Z = 0.0004 than at Z = 0.002. We find that during the main sequence (MS) phase, the ratio between nitrogen and carbon abundances (N/C) remains unchanged for nonrotating models. However, N/C increases by factors of 10–20 in rotating models at the end of the MS. Cepheids coming from stars with Mini >  4 − 6 M⊙ are beyond the core helium burning phase and spend little time in the instability strip. Since they would evolve towards cooler effective temperatures, these Cepheids should show an increase of the pulsation period as a function of age.

Using the five‐factor personality model, the present study explored the influence of personality factors on sustained attention and perceived workload. Ninety‐six college‐aged participants were administered a 12 minute vigilance fast event rate task. Following the vigil, participants were asked to first, rate their perceived workload of the task using the NASA‐TLX, and then second, complete the NEO‐PI‐R personality inventory. Traditional measures of hits, false alarms, and reaction times were examined as well as the signal detection indices of perceptual sensitivity and response bias. Extraversion correlated with false alarms (r = 0.181; eta2 = 0.055) and conscientiousness correlated with both false alarms (r = −0.275, eta2 = 0.097) and perceptual sensitivity (r = 0.227, eta2 = 0.052). With regard to perceived workload, neuroticism was related to perceived frustration (r = 0.238, eta2 = 0.057). The findings are discussed in terms of theoretical implications, impact of task parameters, and practical applications. Copyright © 2002 John Wiley & Sons, Ltd.

GW190521 challenges our understanding of the late-stage evolution of massive stars and the effects of the pair instability in particular. We discuss the possibility that stars at low or zero metallicity could retain most of their hydrogen envelope until the pre-supernova stage, avoid the pulsational pair-instability regime, and produce a black hole with a mass in the mass gap by fallback. We present a series of new stellar evolution models at zero and low metallicity computed with the geneva and mesa stellar evolution codes and compare to existing grids of models. Models with a metallicity in the range 0–0.0004 have three properties that favour higher black hole (BH) masses. These are (i) lower mass-loss rates during the post main sequence phase, (ii) a more compact star disfavouring binary interaction, and (iii) possible H–He shell interactions which lower the CO core mass. We conclude that it is possible that GW190521 may be the merger of black holes produced directly by massive stars from the first stellar generations. Our models indicate BH masses up to 70–75 M⊙. Uncertainties related to convective mixing, mass loss, H–He shell interactions, and pair-instability pulsations may increase this limit to ∼85 M⊙.

Context. Grids of stellar models, computed with the same physical ingredients, allow one to study the impact of a given physics on a broad range of initial conditions and they are a key ingredient for modeling the evolution of galaxies. Aims. We present here a grid of single star models for masses between 0.8 and 120 M⊙, with and without rotation for a mass fraction of heavy element Z = 0.006, representative of the Large Magellanic Cloud (LMC). Methods. We used the GENeva stellar Evolution Code. The evolution was computed until the end of the central carbon-burning phase, the early asymptotic giant branch phase, or the core helium-flash for massive, intermediate, and low mass stars, respectively. Results. The outputs of the present stellar models are well framed by the outputs of the two grids obtained by our group for metallicities above and below the one considered here. The models of the present work provide a good fit to the nitrogen surface enrichments observed during the main sequence for stars in the LMC with initial masses around 15 M⊙. They also reproduce the slope of the luminosity function of red supergiants of the LMC well, which is a feature that is sensitive to the time-averaged mass loss rate over the red supergiant phase. The most massive black hole that can be formed from the present models at Z = 0.006 is around 55 M⊙. No model in the range of mass considered will enter into the pair-instability supernova regime, while the minimal mass to enter the region of pair pulsation instability is around 60 M⊙ for the rotating models and 85 M⊙ for the nonrotating ones. Conclusions. The present models are of particular interest for comparisons with observations in the LMC and also in the outer regions of the Milky Way. We provide public access to numerical tables that can be used for computing interpolated tracks and for population synthesis studies.

Context. Spectroscopic studies of Galactic O and B stars show that many stars with masses above 8 M⊙ have been observed in the Hertzsprung-Russell (HR) diagram just beyond the main-sequence (MS) band, as predicted by stellar models computed with a moderate overshooting. This may be an indication that the convective core sizes in stars in the upper part of the HR diagram are larger than predicted by these models. Aims. Combining stellar evolution models and spectroscopic parameters derived for a large sample of Galactic O and B stars with the inclusion of brand-new information about their projected rotational velocities, we reexamine the question of the convective core size in MS massive stars. Methods. We computed a grid of 120 different stellar evolutionary tracks with three initial rotations at solar metallicity (Z = 0.014), spanning a mass range from 7 to 25 M⊙, and combining different values for the initial rotation rate and overshooting parameter. For the rotating models, we considered two cases, one with a moderate and one with a strong angular momentum transport, the latter imposing a solid body rotation during most of the MS phase. We confront the results with two observed features: the position of the terminal age main sequence (TAMS) in the HR diagram and the decrease of the surface rotation when the surface gravity decreases at the end of the MS phase. Results. We confirm that for stars more massive than about 8 M⊙, the convective core size at the end of the MS phase increases more rapidly with the mass than in models computed with a constant step overshoot chosen to reproduce the main sequence width in the low mass range (around 2 M⊙). This conclusion is valid for both the cases of non-rotating models and rotating models either with a moderate or a strong angular momentum transport. The increase of the convective core mass with the mass obtained from the TAMS position is, however, larger than the one deduced from the surface velocity drop for masses above about 15 M⊙. Although the observations that are available at present cannot determine the best choice between the core sizes given by the TAMS and the velocity drop, we discuss various methods of escaping this dilemma. At the moment, comparisons with eclipsing binaries seem to favor the solution given by the velocity drop. Conclusions. While we confirm the need for larger convective cores at higher masses, we find tensions among different methods for stars more massive than 15 M⊙. The use of single-aged stellar populations (non-interacting binaries or stellar clusters) would be a great asset in resolving this tension.