arXiv subjects

A. Palacios

Publications and source records attributed to A. Palacios.

At least 19 recordsLinked to original sources

arXiv2025

Very massive stars at low metallicity: evolution, synthetic spectroscopy, and impact on the integrated light of starbursts

We study the spectroscopic appearance of very massive stars and their effect on the integrated light of starbursts at low metallicity (Z). We adopt two frameworks for the mass loss rates of VMS: in one case we assume no Z dependence, in the other case we assume a linear scaling with Z. We compute evolutionary models for masses 150, 200, 250 and 300 Msun at Z=0.2, 0.1 and 0.01 Zsun. We compute the associated synthetic spectra at selected points along the evolutionary tracks. Finally we build population synthesis models including VMS. We find that the evolution of VMS critically depends on the assumptions regarding mass loss rates. In case of no Z dependence VMS remain hot for all their lifetime. Conversely when mass loss rates are reduced because of lower Z VMS follow a classical evolution towards the red part of the HR diagram. VMS display HeII 1640 emission in most phases of their evolution, except when they become too cool. This line is present in the integrated light of population synthesis models down to 0.1 Zsun whatever the star formation history, and is also sometimes seen at Z=0.01 Zsun. HeII 1640 is weaker in models that include a Z scaling of the mass loss rates. The optical spectra of starbursts, especially the Wolf-Rayet bumps, sometimes display VMS signatures when these stars are present. At low Z, adding VMS to population synthesis models produces more ionising photons down to 45 eV. At higher energy the ionising flux depends on age, Z, assumption regarding VMS mass loss rates, and on the very short phases at the end of VMS evolution. HeII ionising fluxes large enough to produce some amount of nebular HeII 4686 emission can be produced under specific circumstances. Our models are able to reproduce qualitatively and sometimes also quantitatively the UV spectra of star-forming regions. However we are not able to clearly identify which mass loss framework is favoured.

astro-ph.SR↗

arXiv2024

He-enriched STAREVOL models for globular cluster multiple populations. Self-consistent isochrones from ZAMS to the TP-AGB phase

A common property of globular clusters (GC) is to host multiple populations characterized by peculiar chemical abundances. Recent photometric studies suggest that the He content could vary between the populations of a GC by up to $\Delta$He $\sim$ 0.13, in mass fraction. The initial He content impacts the evolution of low-mass stars by ultimately modifying their lifetimes, luminosity, temperatures, and, more generally, the morphology of post-RGB evolutionary tracks in the Hertzsprung-Russell diagram. We present new physically accurate isochrones with different initial He-enrichments and metallicities, with a focus on the methods implemented to deal with the post-RGB phases. The isochrones are based on tracks computed with the stellar evolution code STAREVOL for different metallicities (Z = 0.0002, 0.0009, 0.002, and 0.008) and with different He-enrichment (from 0.25 to 0.6 in mass fraction). We describe the effect of He-enrichment on the morphology of the isochrones and test these by comparing the predicted number counts of HB and AGB stars with those of selected GCs. Comparing the number ratios, we find that our new theoretical ones agree with the observed values within $1\sigma$ in most cases. The work presented here sets the ground for future studies on stellar populations in globular clusters, in which the abundances of light elements in He-enhanced models will rely on different assumptions for the causes of this enrichment. The developed methodology permits the computation of isochrones from new stellar tracks with non-canonical stellar processes. The checked number counts ensure that, at least in this reference set, the contribution of the luminous late stages of stellar evolution to the integrated light of a GC is represented adequately.

astro-ph.SR↗

arXiv2024

Evidence for Very Massive Stars in extremely UV-bright star-forming galaxies at $z \sim 2.2-3.6$

We present a comprehensive analysis of the presence of very massive stars (VMS > $100 M_{\odot}$) in the integrated spectra of 13 UV-bright star-forming galaxies at $2.2 \lesssim z \lesssim 3.6$ taken with the Gran Telescopio Canarias (GTC). These galaxies have very high UV absolute magnitudes ($M_{\rm UV} \simeq -24$), intense star formation (SFR $ \simeq 100-1000$ $M_{\odot}$ yr$^{-1}$), and metallicities in the range of 12+log(O/H) $\simeq8.10-8.50$ inferred from strong rest-optical lines. The GTC rest-UV spectra reveal spectral features indicative of very young stellar populations with VMS, such as strong P-Cygni line profiles in the wind lines N~{\sc v} $λ1240$ and C~{\sc iv} $λ1550$ along with intense and broad He~{\sc ii} $λ1640$ emission with $EW_{0}$ $\simeq 1.40-4.60$ Å, and FWHM $\simeq 1150-3170$ $km \ s^{-1}$. A Comparison with known VMS-dominated sources and typical galaxies without VMS reveals that some UV-bright galaxies closely resemble VMS-dominated clusters (e.g., R136 cluster). The presence of VMS is further supported by a quantitative comparison of the observed strength of the He~{\sc ii} emission with population synthesis models with and without VMS, where models with VMS are clearly preferred. Employing an empirical threshold for $EW_{0}$ (\heii) $\geq 3.0$ Å, along with the detection of other VMS-related spectral profiles (N~{\sc iv} $λ1486, 1719$), we classify nine out of 13 UV-bright galaxies as VMS-dominated sources. This high incidence of VMS-dominated sources in the UV-bright galaxy population ($\approx 70\%$) contrasts significantly with the negligible presence of VMS in typical $L_{\rm UV}^{*}$ LBGs at similar redshifts ($<1\%$). Our results thus indicate that VMS are common in UV-bright galaxies, suggesting a different initial mass function (IMF) with upper mass limits between $175 M_{\odot}$ and $475 M_{\odot}$.

astro-ph.GA↗

arXiv2024

Attosecond metrology of 2D charge distribution in molecules

Photoionization as a half-scattering process is not instantaneous. Usually, time delays in photoionization are of the order of few tens of attoseconds (1 as = 10$^{-18}$ s). While going from a single atom to a nano-object, one can expect the delay to increase since the photoelectron scatters over a larger distance. Here, we show that this is no longer valid in the case of planar systems. Using attosecond interferometry, we find that the time delay in a 2D carbon-based molecule, naphthalene, is significantly smaller compared to its 3D diamond-like counterpart, adamantane. The measured time delay carries the signature of the spatial distribution of the hole created in the residual molecular cation, allowing us to obtain its dimensions with angstrom accuracy. Our findings offer novel opportunities for tracking and manipulating ultrafast charge transport in molecular materials.

physics.chem-ph↗

arXiv2023

A long-term study of the magnetic field and activity in the M giant RZ Ari

We present a detailed long-term study of the single M6 III giant RZ~Ari to obtain direct and simultaneous measurements of the magnetic field, activity indicators, and radial velocity in order to infer the origin of its activity. We study its magnetic activity in the context of stellar evolution, and for this purpose, we also refined its evolutionary status and Li abundance. In general, for the M giants, little is known about the properties of the magnetic activity and its causes. RZ~Ari posses the strongest surface magnetic field of the known Zeeman-detected M giants and is bright enough to allow a deep study of its surface magnetic structure. The results are expected to shed light on the activity mechanism in these stars.

astro-ph.SR↗

arXiv2022

Two-color polarization control on angularly resolved attosecond time delays

Measured photoionization time delays may exhibit large variations as a function of the emission angles, even for spherically symmetric targets, as shown in recent RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) experiments. The contributions from different pathways to the two-photon quantum channels can already explain the observed phase jumps that shape those angular distributions. Here, we propose a simple analytical model to describe angularly-resolved RABBITT spectra as a function of the relative polarization angle between the ionizing attosecond pulse train and the assisting IR field. We demonstrate that the angular dependencies of the measured delays can be analytically predicted and the position of the phase jumps reduced to the analysis of a few relevant parameters.

physics.atom-ph↗

arXiv2022

Spectroscopic evolution of very massive stars at Z = 1/2.5 Zsun

Stars with masses in excess of 100 Msun are observed in the Local Universe, but they remain rare objects. Because of the shape of the mass function, they are expected to be present only in the most massive and youngest clusters. They may thus be formed in number in highly star-forming galaxies. Very massive stars (VMSs) experience strong stellar winds that are stronger than those of their less massive OB-type counterparts. These strong winds therefore need to be taken into account in evolutionary models and synthetic spectra to properly predict the appearance of VMS. We present evolutionary models computed with the code STAREVOL. They include a recent mass-loss recipe that is relevant for VMSs. We subsequently calculated atmosphere models and synthetic spectra along the resulting tracks with the code CMFGEN. We studied stars with masses between 150 and 400 Msun and focused on a metallicity Z=1/2.5Zsun. We studied the impact of our VMS spectra on the spectral energy distribution of young starbursts. We show that the optical and UV range is dominated by HeII 4686 and HeII 1640 emission for almost the entire main-sequence evolution of VMSs, in contrast to less massive stars. In the UV spectral range, carbon, nitrogen, and iron lines shape the spectra of VMSs, which appear for most of their evolution as WNh objects. The morphology of the synthetic spectra is similar to that of VMSs in the Large Magellanic Cloud. We show that stars with masses higher than 100 Msun emit nearly as much light as all other stars in young starbursts. The integrated UV spectrum of these starbursts is significantly affected by the presence of VMSs.

astro-ph.SR↗

arXiv2020

Lithium depletion and angular momentum transport in solar-type stars

Transport processes occurring in the radiative interior of solar-type stars are evidenced by the surface variation of light elements, in particular Li, and the evolution of their rotation rates. For the Sun, inversions of helioseismic data indicate that the radial profile of angular velocity in its radiative zone is nearly uniform, which implies the existence of angular momentum transport mechanisms. While there are many independent transport models for angular momentum and chemical species, there is a lack of self-consistent theories that permit stellar evolution models to simultaneously match the present-day observations of solar lithium abundances and radial rotation profiles. We explore how additional transport processes can improve the agreement between evolutionary models of rotating stars and observations. We constrain the resulting models by simultaneously using the evolution of the surface rotation rate and Li abundance in the solar-type stars of open clusters, and the solar surface and internal rotation profile as inverted from helioseismology. We show the relevance of penetrative convection for the depletion of Li. The rotational dependence of the depth of penetrative convection yields an anti-correlation between the initial rotation rate and Li depletion in our models of solar-type stars that is in agreement with the observed trend. Simultaneously, the addition of an ad hoc vertical viscosity leads to efficient transport of angular momentum between the core and the envelope. We also self-consistently compute for the first time the thickness of the tachocline and find that it is compatible with helioseismic estimations. However, the main sequence depletion of Li in solar-type stars is only reproduced when adding a parametric turbulent mixing below the convective envelope. The need for additional transport processes in stellar evolution models is confirmed.

astro-ph.SR↗

arXiv2020

Spectroscopic evolution of massive stars near the main sequence at low metallicity

We present synthetic spectra and SEDs computed along evolutionary tracks at Z=1/5 Zsun and Z=1/30 Zsun, for masses between 15 and 150 Msun. We predict that the most massive stars all start their evolution as O2 dwarfs at sub-solar metallicities. The fraction of lifetime spent in the O2V phase increases at lower metallicity. The distribution of dwarfs and giants we predict in the SMC accurately reproduces the observations. Supergiants appear at slightly higher effective temperatures than we predict. More massive stars enter the giant and supergiant phases closer to the ZAMS, but not as close as for solar metallicity. This is due to the reduced stellar winds at lower metallicity. Our models with masses higher than ~60 Msun should appear as O and B stars, whereas these objects are not observed, confirming a trend reported in the recent literature. At Z=1/30 Zsun, dwarfs cover a wider fraction of the MS and giants and supergiants appear at lower effective temperatures than at Z=1/5 Zsun. The UV spectra of these low-metallicity stars have only weak P-Cygni profiles. HeII 1640 sometimes shows a net emission in the most massive models, with an equivalent width reaching ~1.2 A. For both sets of metallicities, we provide synthetic spectroscopy in the wavelength range 4500-8000 A. This range will be covered by the instruments HARMONI and MOSAICS on the ELT and will be relevant to identify hot massive stars in Local Group galaxies with low extinction. We suggest the use of the ratio of HeI 7065 to HeII 5412 as a diagnostic for spectral type. We show that this ratio does not depend on metallicity. Finally, we discuss the ionizing fluxes of our models. The relation between the hydrogen ionizing flux per unit area versus effective temperature depends only weakly on metallicity. The ratios of HeI and HeII to H ionizing fluxes both depend on metallicity, although in a slightly different way.

astro-ph.SR↗

arXiv2020

Attosecond timing of electron emission from a molecular shape resonance

Shape resonances in physics and chemistry arise from the spatial confinement of a particle by a potential barrier. In molecular photoionization, these barriers prevent the electron from escaping instantaneously, so that nuclei may move and modify the potential, thereby affecting the ionization process. By using an attosecond two-color interferometric approach in combination with high spectral resolution, we have captured the changes induced by the nuclear motion on the centrifugal barrier that sustains the well-known shape resonance in valence-ionized N$_2$. We show that despite the nuclear motion altering the bond length by only $2\%$, which leads to tiny changes in the potential barrier, the corresponding change in the ionization time can be as large as $200$ attoseconds. This result poses limits to the concept of instantaneous electronic transitions in molecules, which is at the basis of the Franck-Condon principle of molecular spectroscopy.

physics.chem-ph↗

arXiv2019

Lithium in red giant stars: Constraining non-standard mixing with large surveys in the Gaia era

Lithium is extensively known to be a good tracer of non-standard mixing processes occurring in stellar interiors. We present the results of a new large Lithium survey in red giant stars and combine it with surveys from the literature to probe the impact of rotation-induced mixing and thermohaline double-diffusive instability along stellar evolution. We determined the surface Li abundance for a sample of 829 giant stars with accurate Gaia parallaxes for a large sub-sample (810 stars) complemented with accurate Hipparcos parallaxes (19 stars). The spectra of our sample of northern and southern giant stars were obtained in three ground-based observatories (OHP, ESO-La Silla, Mc Donald). We determined the atmospheric parameters (Teff, log(g), [Fe/H]), and the Li abundance. We used Gaia parallaxes and photometry to determine the luminosity of our objects and we estimated the mass and evolution status of each sample star with a maximum-likelihood technique using stellar evolution models computed with the STAREVOL code. We compared the observed Li behaviour with predictions from stellar models, including rotation and thermohaline mixing. The same approach was used for stars from selected Li surveys from the literature. Rotation-induced mixing accounts nicely for the lithium behaviour in stars warmer than about 4200K, independently of the mass domain. For stars with masses lower than 2Msun thermohaline mixing leads to further Li depletion below the Teff of the RGB bump (about 4000K), and on the early AGB, as observed. Depending on the definition we adopt, we find between 0.8 and 2.2% of Li-rich giants in our new sample. Gaia puts a new spin on the understanding of mixing processes in stars, and our study confirms the importance of rotation-induced processes and of thermohaline mixing. However asteroseismology is required to definitively pinpoint the actual evolution status of Li-rich giants.

astro-ph.SR↗

arXiv2019

First grids of low-mass stellar models and isochrones with self-consistent treatment of rotation : From 0.2 to 1.5 M_\odot at 7 metallicities from PMS to TAMS

We present an extended grid of state-of-the art stellar models for low-mass stars including updated physics (nuclear reaction rates, surface boundary condition, mass-loss rate, angular momentum transport, torque and rotation-induced mixing prescriptions). We aim at evaluating the impact of wind braking, realistic atmospheric treatment, rotation and rotation-induced mixing on the structural and rotational evolution from the pre-main sequence to the turn-off. Using the STAREVOL code, we provide an updated PMS grid. We compute stellar models for 7 different metallicities, from [Fe/H] = -1 dex to [Fe/H] = +0.3 dex with a solar composition corresponding to $Z=0.0134$. The initial stellar mass ranges from 0.2 to 1.5\Ms with extra grid refinement around one solar mass. We also provide rotating models for three different initial rotation rates (slow, median and fast) with prescriptions for the wind braking and disc-coupling timescale calibrated on observed properties of young open clusters. The rotational mixing includes an up-to-date description of the turbulence anisotropy in stably stratified regions. The overall behaviour of our models at solar metallicity -- and its constitutive physics -- is validated through a detailed comparison with a variety of distributed evolutionary tracks. The main differences arise from the choice of surface boundary conditions and initial solar composition. The models including rotation with our prescription for angular momentum extraction and self-consistent formalism for angular momentum transport are able to reproduce the rotation period distribution observed in young open clusters over a broad mass-range. These models are publicly available and may be used to analyse data coming from present and forthcoming asteroseismic and spectroscopic surveys such as Gaia, TESS and PLATO.

astro-ph.SR↗

arXiv2018

Disappearance of the extended main sequence turn-off in intermediate age clusters as a consequence of magnetic braking

Extended MS turn-offs are features commonly found in the colour-magnitude diagrams of young and intermediate age (less than about 2 Gyr) massive star clusters, where the MS turn-off is broader than can be explained by photometric uncertainties, crowding, or binarity. Rotation is suspected to be the cause of this feature, by accumulating fast rotating stars, strongly affected by gravity darkening and rotation-induced mixing, near the MS turn-off. This scenario successfully reproduces the tight relation between the age and the actual extent in luminosity of the extended MS turn-off of observed clusters. Below a given mass (dependent on the metallicity), stars are efficiently braked early on the MS due to the interaction of stellar winds and the surface magnetic field, making their tracks converge towards those of non-rotating tracks in the HRD. When these stars are located at the turn-off of a cluster, their slow rotation causes the extended MS turn-off feature to disappear. We investigate the maximal mass for which this braking occurs at different metallicities, and determine the age above which no extended MS turn-off is expected in clusters. Our models predict that the extended MS turn-off phenomenon disappears at ages older than about 2 Gyr. There is a trend with the metallicity, the age at which the disappearance occurs becoming older at higher metallicity. These results are robust between the two codes used in this work, despite some differences in the input physics and in particular in the detailed description of rotation-induced internal processes and of angular momentum extraction by stellar winds. Comparing our results with clusters in the LMC and Galaxy shows a very good fit to the observations. This strengthens the rotation scenario to explain the cause of the extended MS turn-off phenomenon.

astro-ph.SR↗

arXiv2018

Seismic probing of the first dredge-up event through the eccentric red-giant & red-giant spectroscopic binary KIC9163796

Binaries in double-lined spectroscopic systems provide a homogeneous set of stars. Differences of parameters, such as age or initial conditions, which otherwise would have strong impact on the stellar evolution, can be neglected. The observed differences are determined by the difference in stellar mass between the two components. The mass ratio can be determined with much higher accuracy than the actual stellar mass. In this work, we aim to study the eccentric binary system KIC9163796, whose two components are very close in mass and both are low-luminosity red-giant stars from four years of Kepler space photometry and high-resolution spectroscopy with Hermes. Mass and radius of the primary were determined through asteroseismology to be 1.39+/-0.06 Mo and 5.35+/-0.09 Ro, resp. From spectral disentangling the mass ratio was found to be 1.015+/-0.005 and that the secondary is ~600K hotter than the primary. Evolutionary models place both components, in the early and advanced stage of the first dredge-up event on the red-giant branch. From theoretical models of the primary, we derived the internal rotational gradient. From a grid of models, the measured difference in lithium abundance is compared with theoretical predictions. The surface rotation of the primary is determined from the Kepler light curve and resembles the orbital period within 10 days. The radial rotational gradient between the surface and core is found to be 6.9+2.0/-1.0. The agreement between the surface rotation with the seismic result indicates that the full convective envelope is rotating quasi-rigidly. The models of the lithium abundance are compatible with a rigid rotation in the radiative zone during the main sequence. Because of the many constraints offered by oscillating stars in binary systems, such objects are important test beds of stellar evolution.

astro-ph.SR↗

arXiv2018

Imaging the square of the correlated two-electron wave function of a hydrogen molecule

The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometrical structure, others the electron density or electron orbitals. Molecules are many-body systems for which the correlation between the constituents is decisive and the spatial and the momentum distribution of one electron depends on those of the other electrons and the nuclei. Such correlations have escaped direct observation by imaging techniques so far. Here, we implement an imaging scheme which visualizes correlations between electrons by coincident detection of the reaction fragments after high energy photofragmentation. With this technique, we examine the H2 two-electron wave function in which electron-electron correlation beyond the mean-field level is prominent. We visualize the dependence of the wave function on the internuclear distance. High energy photoelectrons are shown to be a powerful tool for molecular imaging. Our study paves the way for future time resolved correlation imaging at FELs and laser based X-ray sources.

physics.atom-ph↗

arXiv2017

The evolution of surface magnetic fields in young solar-type stars II: The early main sequence (250-650 Myr)

There is a large change in surface rotation rates of sun-like stars on the pre-main sequence and early main sequence. Since these stars have dynamo driven magnetic fields, this implies a strong evolution of their magnetic properties over this time period. The spin-down of these stars is controlled by interactions between stellar winds and magnetic fields, thus magnetic evolution in turn plays an important role in rotational evolution. We present here the second part of a study investigating the evolution of large-scale surface magnetic fields in this critical time period. We observed stars in open clusters and stellar associations with known ages between 120 and 650 Myr, and used spectropolarimetry and Zeeman Doppler Imaging to characterize their large-scale magnetic field strength and geometry. We report 15 stars with magnetic detections here. These stars have masses from 0.8 to 0.95 Msun, rotation periods from 0.326 to 10.6 days, and we find large-scale magnetic field strengths from 8.5 to 195 G with a wide range of geometries. We find a clear trend towards decreasing magnetic field strength with age, and a power-law decrease in magnetic field strength with Rossby number. There is some tentative evidence for saturation of the large-scale magnetic field strength at Rossby numbers below 0.1, although the saturation point is not yet well defined. Comparing to younger classical T Tauri stars, we support the hypothesis that differences in internal structure produce large differences in observed magnetic fields, however for weak lined T Tauri stars this is less clear.

astro-ph.SR↗

arXiv2017

The magnetic strip(s) in the advanced phases of stellar evolution - Theoretical convective turnover timescale and Rossby number for low- and intermediate-mass stars up to the AGB at various metallicities

Recent spectropolarimetric observations of otherwise ordinary G, K, and M giants revealed localized magnetic strips in the HRD coincident with the regions where the first dredge-up and core He-burning occur. We seek to understand the origin of magnetic fields in such late-type giant stars. In analogy with late-type dwarf stars, we focus primarily on parameters known to influence the generation of magnetic fields in the outer convective envelope. We compute the classical dynamo parameters along the evolutionary tracks of low- and intermediate-mass stars at various metallicities using stellar models that have been extensively tested by spectroscopic and asteroseismic observations. These include convective turnover timescales and convective Rossby numbers, computed from the PMS to the tip of the RGB or the early AGB. To investigate the effects of the very extended outer convective envelope, we compute these parameters both for the entire convective envelope and locally, that is, at different depths within the envelope. We also compute the turnover timescales and corresponding Rossby numbers for the convective cores of intermediate-mass stars on the main sequence. Our models show that the Rossby number of the convective envelope becomes lower than unity in the well-delimited locations of the Hertzsprung-Russell diagram where magnetic fields have indeed been detected. We show that alpha-omega dynamo processes might not be continuously operating, but that they are favored in the stellar convective envelope at two specific moments along the evolution tracks, that is, during the first dredge-up at the base of the RGB and during central helium burning in the helium-burning phase and early-AGB. This general behavior can explain the so-called magnetic strips recently discovered by dedicated spectropolarimetric surveys of evolved stars.

astro-ph.SR↗

arXiv2016

Spectroscopic evolution of massive stars on the main sequence

We provide an observational view of evolutionary models in the Hertzsprung--Russell diagram, on the main sequence. For that we computed evolutionary models with the code STAREVOL for 15 < M/Msun < 100. We subsequently calculated atmosphere models at specific points along the evolutionary tracks, using the code CMFGEN. Synthetic spectra obtained in this way were classified as if they were observational data. We tested our spectral classification by comparison to observed spectra of various stars. We also compared our results with empirical data of a large number of OB stars. We obtain spectroscopic sequences along evolutionary tracks. In our computations, the earliest O stars (O2-3.5) appear only above ~50 Msun. For later spectral types, a similar mass limit exists, but is lower. A luminosity class V does not correspond to the entire main sequence. This only holds for the 15 Msun track. As mass increases, a larger portion of the main sequence is spent in luminosity class III. Above 50 Msun, supergiants appear before the end of core-hydrogen burning. Dwarf stars do not occur on the zero-age main sequence above 80 Msun. Consequently, the distribution of luminosity class V in the HR diagram cannot be used to constrain the size of the convective core. The distribution of dwarfs and giants in the HR diagram agrees well with the location of stars analyzed by means of quantitative spectroscopy. For supergiants, there is a slight discrepancy in the sense that luminosity class I is observed slightly earlier than our predictions. This is mainly due to wind densities that affect the luminosity class diagnostic lines. We predict an upper mass limit for dwarf stars (~60 Msun) that is found consistent with the rarity of O2V stars in the Galaxy. Stars with WNh spectral type are not predicted by our models. Stronger winds are required to produce the characteristic emission lines of these objects.

astro-ph.SR↗