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Massive stars have a strong impact on their surroundings, in particular when they produce a core-collapse supernova at the end of their evolution. In these proceedings, we review the general evolution of massive stars and their properties at collapse as well as the transition between massive and intermediate-mass stars. We also summarise the effects of metallicity and rotation. We then discuss some of the major uncertainties in the modelling of massive stars, with a particular emphasis on the treatment of convection in 1D stellar evolution codes. Finally, we present new 3D hydrodynamic simulations of convection in carbon burning and list key points to take from 3D hydrodynamic studies for the development of new prescriptions for convective boundary mixing in 1D stellar evolution codes.
We present the first detailed three-dimensional hydrodynamic implicit large eddy simulations of turbulent convection for carbon burning. The simulations start with an initial radial profile mapped from a carbon burning shell within a 15 M⊙ stellar evolution model. We considered 4 resolutions from 1283 to 10243 zones. These simulations confirm that convective boundary mixing (CBM) occurs via turbulent entrainment as in the case of oxygen burning. The expansion of the boundary into the surrounding stable region and the entrainment rate are smaller at the bottom boundary because it is stiffer than the upper boundary. The results of this and similar studies call for improved CBM prescriptions in 1D stellar evolution models.
A few core collapse supernovae progenitors have been found to be yellow or blue supergiants. Weshall discuss possible scenarios involving single and close binary evolution allowing to explain this kind of corecollapse supernova progenitors. According to stellar models for both single and close binaries, blue supergiants, at theend of their nuclear lifetimes and thus progenitors of core collapse supernovae, present very different characteristicsfor what concerns their surface compositions, rotational surface velocities and pulsational properties with respect toblue supergiants in their core helium burning phase. We discuss how the small observed scatter of the flux-weightedgravity-luminosity (FWGL) relation of blue supergiants constrains the evolution of massive stars after the Main-Sequence phase and the nature of the progenitors of supernovae in the mass range between 12 and 40 solarmasses. The present day observed surface abundances of blue supergiants, of their pulsational properties, as well asthe small scatter of the FWGL relation provide strong constraints on both internal mixing and mass loss in massivestars and therefore on the end point of their evolution.
The recent detection in archival HST images of an object at the the location of supernova (SN) iPTF13bvn may represent the first direct evidence of the progenitor of a Type Ib SN. The object's photometry was found to be compatible with a Wolf-Rayet pre-SN star mass of ≈ 11 M⊙. However, based on hydrodynamical models we show that the progenitor had a pre-SN mass of ≈ 3.5 M⊙ and that it could not be larger than ≈ 8 M⊙. We propose an interacting binary system as the SN progenitor and perform evolutionary calculations that are able to self-consistently explain the light-curve shape, the absence of hydrogen, and the pre-SN photometry. Our models also predict that the remaining companion is a luminous O-type star of significantly lower flux in the optical than the pre-SN object. A future detection of such star may be possible and would provide the first robust progenitor identification for a Type-Ib SN.
We present preliminary results of the determination of fundamental parameters of single O-type stars in the MiMeS survey. We present the sample and we focus on surface CNO abundances, showing how they change as stars evolve off the zero-age main sequence.
Here we present the report on the “Nainital–Cape survey” research project aiming to search for and study the pulsational variability of main-sequence chemically peculiar (CP) stars. For this study, the time-series photometric observations of the sample stars were carried out at the 1.04 m ARIES telescope (India), while the high-resolution spectroscopic and spectro-polarimetric observations were carried out at the the 6.0 m Russian telescope. Under this project, we have recently found clear evidence of photometric variability in the Am star HD 73045, which is likely to be pulsating in nature with a period of about 36 min, hence adding a new member to the family of the δ Scuti pulsating variables that have peculiar abundances.
Globular clusters are among the oldest structures in the Universe and they host today low-mass stars and no gas. However, there has been a time when they formed as gaseous objects hosting a large number of short-lived, massive stars. Many details on this early epoch have been depicted recently through unprecedented dissection of low-mass globular cluster stars via spectroscopy and photometry. In particular, multiple populations have been identified, which bear the nucleosynthetic fingerprints of the massive hot stars disappeared a long time ago. Here we discuss how massive star archeology can be done through the lense of these multiple populations.
Measurements of secular period change probe real-time stellar evolution of classical Cepheids making these measurements powerful constraints for stellar evolution models, especially when coupled with interferometric measurements. In this work, we present stellar evolution models and measured rates of period change for two Galactic Cepheids: Polaris and l Carinae, both important Cepheids for anchoring the Cepheid Leavitt law (period-luminosity relation). The combination of previously-measured parallaxes, interferometric angular diameters and rates of period change allows for predictions of Cepheid mass loss and stellar mass. Using the stellar evolution models, We find that l Car has a mass of about 9 M⊙ consistent with stellar pulsation models, but is not undergoing enhanced stellar mass loss. Conversely, the rate of period change for Polaris requires including enhanced mass-loss rates. We discuss what these different results imply for Cepheid evolution and the mass-loss mechanism on the Cepheid instability strip.
We investigate the physical properties of large-scale wind structures around massive hot stars with radiatively-driven winds. We observe Discrete Absorption Components (DACs) in optical He i P Cygni lines of the LBV binary MWC 314 (Porb = 60.8 d). The DACs are observed during orbital phases when the primary is in front of the secondary star. They appear at wind velocities between −100 km s−1 and −600 km s−1 in the P Cyg profiles of Hei λ5875, λ6678, and λ4471, signaling high-temperature expanding wind regions of enhanced density and variable outflow velocity. The DACs can result from wave propagation linked to the orbital motion near the low-velocity wind base. The He i lines indicate DAC formation close to the primary's surface in high-temperature wind regions in front of its orbit, or in dynamical wind regions confined between the binary stars. We observed the DACs with Mercator-HERMES on 5 Sep 2009, 5 May 2012, and 6 May 2014 when the primary is in front of the secondary star. XMM-Newton observations of 6 May 2014 significantly detected MWC 314 in X-rays at an average rate of ~0.015 cts s−1.
The B fields in OB stars (BOB) survey is an ESO large programme collecting spectropolarimetric observations for a large number of early-type stars in order to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars. As of July 2014, a total of 98 objects were observed over 20 nights with FORS2 and HARPSpol. Our preliminary results indicate that the fraction of magnetic OB stars with an organised, detectable field is low. This conclusion, now independently reached by two different surveys, has profound implications for any theoretical model attempting to explain the field formation in these objects. We discuss in this contribution some important issues addressed by our observations (e.g., the lower bound of the field strength) and the discovery of some remarkable objects.
Stochastic gravity waves have been recently detected and characterised in stars thanks to space asteroseismology and they may play an important role in the evolution of stellar angular momentum. In this context, the observational study of the CoRoT hot Be star HD 51452 suggests a potentially strong impact of rotation on stochastic excitation of gravito-inertial waves in rapidly rotating stars. In this work, we present our results on the action of the Coriolis acceleration on stochastic wave excitation by turbulent convection. We study the change of efficiency of this mechanism as a function of the waves' Rossby number and we demonstrate that the excitation presents two different regimes for super-inertial and sub-inertial frequencies. Consequences for rapidly rotating early-type stars and the transport of angular momentum in their interiors are discussed.
Formation of massive stars (M > 8 M⊙) is still not well understood and lacks of observational constraints. We observed 7 MYSO candidates using the NIFS spectrometer at Gemini North Telescope to study the accretion process at high angular resolution (~ 50 mas) and very closer to the central star. Preliminary results for 2 sources have revealed circumstellar structures traced by Brackett-Gamma, CO lines and extended H2 emission. Both sources present kinematics in the CO absorption lines, suggesting rotating structures. The next step will derive the central mass of each source by applying a keplerian model for these CO features.
We produced a model grid of rotating main and post-main sequence stars with the Geneva Stellar Evolution Code (GENEC). The initial chemical composition is tailored to compare with observations of early OB type stars in the Large Magellanic Cloud (LMC) and the grid covers stellar masses in the range of 7 ≤ M/M⊙ ≤ 15 and initial velocity between 0 km s−1 ≤ v sin(i) ≤ 300 km s−1. The model grid has been used to determine the changes in the surface Nitrogen abundances during the star evolution and the results have been compared with observations.
Stellar evolution models predict that rotation induces the mixing of chemical species, with the subsequent surface abundance anomalies relative to single non-rotating models, even during the main sequence (MS) evolution. The lack of measurable nitrogen surface enrichment in MS rotating stars, such as Be stars, has been interpreted as being in conflict with evolutionary models (e.g. Lennon et al. 2005; Hunter et al. 2008). In order to have an insight on the kind of ambient we do or we do not expect to find enriched rotating stars, we use our new population synthesis code, to produce synthetic intermediate-mass stellar populations fully accounting for stellar rotation effects, and study their evolution in time.
We present preliminary results from a survey of molecular H2 (2.12 μm) emission in massive young stellar objects (MYSO) candidates selected from the Red MSX Source survey. We observed 354 MYSO candidates through the H2 S(1) 1-0 transition (2.12 μm) and an adjacent continuum narrow-band filters using the Spartan/SOAR and WIRCam/CFHT cameras. The continuum-subtracted H2 maps were analyzed and extended H2 emission was found in 50% of the sample (178 sources), and 38% of them (66) have polar morphology, suggesting collimated outflows. The polar-like structures are more likely to be driven on radio-quiet sources, indicating that these structures occur during the pre-ultra compact H ii phase. We analyzed the continuum images and found that 54% (191) of the sample displayed extended continuum emission and only ~23% (80) were associated to stellar clusters. The extended continuum emission is correlated to the H2 emission and those sources within stellar clusters does display diffuse H2 emission, which may be due to fluorescent H2 emission. These results support the accretion scenario for massive star formation, since the merging of low-mass stars would not produce jet-like structures. Also, the correlation between jet-like structures and radio-quiet sources indicates that higher inflow rates are required to form massive stars in a typical timescale less than 105 years.
It is now well established that a fraction of the massive (M > 8 M⊙) star population hosts strong, organised magnetic fields, most likely of fossil origin. The details of the generation and evolution of these fields are still poorly understood. The BinaMIcS project takes an important step towards the understanding of the interplay between binarity and magnetism during the stellar formation and evolution, and in particular the genesis of fossil fields, by studying the magnetic properties of close binary systems. The components of such systems are most likely formed together, at the same time and in the same environment, and can therefore help us to disentangle the role of initial conditions on the magnetic properties of the massive stars from other competing effects such as age or rotation. We present here the main scientific objectives of the BinaMIcS project, as well as preliminary results from the first year of observations from the associated ESPaDOnS and Narval spectropolarimetric surveys.
The MiMeS project demonstrated that a small fraction of massive stars (around 7%) presents large-scale, stable, generally dipolar magnetic fields at their surface. These fields that do not present any evident correlations with stellar mass or rotation are supposed to be fossil remnants of the initial phases of stellar evolution. They result from the relaxation to MHD equilibrium states, during the formation of stable radiation zones, of initial fields resulting from a previous convective phase. In this work, we present new theoretical results, where we generalize previous studies by taking rotation into account. The properties of relaxed fossil fields are compared to those obtained when rotation is ignored. Consequences for magnetic fields in the radiative envelope of rotating early-type stars and their stability are finally discussed.
The Westerlund 1 Galactic cluster hosts an eclectic mix of coeval massive stars. At a modest distance of 4–5 kpc, it offers a unique opportunity to study the resolved stellar content of a young (~5 Myr) high mass (5·104M⊙) star cluster. With the aim of testing single-star evolutionary predictions, and revealing any signatures of binary evolution, we discuss on-going analyses of NTT/SOFI near-IR spectroscopy of Wolf-Rayet stars in Westerlund 1. We find that late WN stars are H-poor compared to their counterparts in the Milky Way field, and nearly all are less luminous than predicted by single-star Geneva isochrones at the age of Westerlund 1.
Be star phenomenology is strongly associated with their viscous circumstellar disks. Recently, models became available for the temporal evolution of these disks when subject to variable mass ejection rates. In this contribution we will discuss how these dynamical disk models, modeled with the radiative transfer code HDUST, can be used for constraining fundamental disk parameters, such as the α viscosity parameter, and we will report on an ongoing effort to model light curves of a large number of stars.
We present the first results of our analysis of the famous variable star, WR6 (HD50896). Using IUE ultraviolet data and an ESPaDOnS spectropolarimetric survey of this star, we plan to determine possible variation of the stellar and wind parameters during the different phases using the radiative transfer code CMFGEN. After the detection of parameter's modifications as a function of the phase, we will analyse deeper the origin of these variability (for example, CIRs?). In the present poster we show the first results of our analysis of the variability and the first step of the stellar parameter determination of the average spectrum of this star.