L’intelligence artificielle bien sûr Charbonnel, C.
Annales de cardiologie et d'angéiologie,
November 2020, 2020-11-00, Letnik:
69, Številka:
5
Journal Article
La cardio-oncologie est une spécialité de la cardiologie dont le but est de prévenir, identifier et prendre en charge les complications cardio-vasculaires liées aux traitements anticancéreux. Parmi ...ces complications, l’apparition d’une dysfonction cardiaque voire d’une insuffisance cardiaque clinique est une des plus inquiétantes. Elle va ainsi impacter la qualité de vie du patient et son pronostic, ceci expliquant l’importance de la prévention et de la détection. Cette mise au point a pour but de décrire les principaux traitements anticancéreux pouvant entraîner une dysfonction cardiaque et de mettre l’accent sur le rôle central de l’échocardiographie dans le suivi. Nous avons également essayé de donner au lecteur une meilleure compréhension de la conduite à tenir en cas de dysfonction cardiaque.
Cardio-oncology has recently been developed to prevent, identify and manage cardiovascular events in patients with cancer receiving cardiotoxic chemotherapy. Among cardiovascular complications of cancer therapy, myocardial dysfunction and heart failure are one of the most concerning issue. Since cardiotoxicity adversely affect quality of life and prognosis in cancer patients, its prevention, detection and treatment are crucial. This review aimed to describe the main chemotherapies able to induce myocardial dysfunction and to emphazise the pivotal role of echocardiography in the follow up. We also intent to provide to the lector a better understanding of what to do in case of cardiotoxicity.
Context.
Globular clusters (GCs) contain multiple stellar populations with peculiar chemical compositions. Pollution of the intracluster gas by an early population of fast-evolving stars is the most ...common scenario for explaining the observations. Stars with masses in excess of 1000
M
⊙
have recently been suggested as potential polluters.
Aims.
We investigate the spectral properties of proto-GCs that would host a supermassive star (SMS). Our main goal is to quantify how such a star would affect the integrated light of the cluster, and to study the detectability of such objects.
Methods.
We computed nonlocal thermal equilibirum atmosphere models for SMS with various combinations of stellar parameters (luminosity, effective temperature, and mass) and metallicities appropriate for GCs, and we predict their emergent spectra. Using these spectra, we calculated the total emission of young proto-GCs with SMS as predicted in a previously reported scenario, and we computed synthetic photometry in UV, optical, and near-IR bands, in particular for the
James Webb
Space Telescope (JWST).
Results.
At an effective temperature of 10 000 K, the spectrum of SMSs shows a Balmer break in emission. This feature is due to strong nonlocal thermal equilibrium effects (implied by the high luminosity) and is not observed in “normal” stars. The hydrogen lines also show a peculiar behavior, with Balmer lines in emission while higher series lines are in absorption. At 7000 K, the Balmer break shows a strong absorption. At high effective temperatures, the Lyman break is found in emission. Cool and luminous SMSs are found to dominate the integrated spectrum of the cluster, except for the UV range. The predicted magnitudes of these proto-GCs are mag
AB
∼ 28 − 30 between 0.7 and 8
μ
m and for redshifts
z
∼ 4 − 10, which is detectable with the JWST. The peculiar observational features of cool SMSs imply that they might in principle be detected in color-color diagrams that probe the spectral energy distribution below and above the Balmer break.
Conclusions.
Our results show that SMSs should be detectable in proto-GCs if they are luminous and relatively cool. They may be found through deep imaging with the JWST.
Context.
Open clusters provide unambiguous clues to understand the evolution of
7
Li at the surface of low-mass stars and its possible correlation with stellar rotation, which is a challenge for both ...stellar hydrodynamics and Galactic chemical evolution.
Aims.
We aim to quantify the efficiency of the transport processes for both angular momentum and chemicals that are required to explain simultaneously the observed behaviour of surface
7
Li (and
9
Be) and rotation as well as the internal rotation profiles inferred from helio- and asteroseismology in F- and G-type main sequence stars.
Methods.
We apply the model for the transport of angular momentum and chemicals that we tailored in a previous work for solar-type stars to an extended range of initial masses and metallicities corresponding to F- an G-type stars in a sample of 20 Galactic open clusters. We evaluate its ability to explain the
7
Li,
9
Be, and rotation periods observations. This model includes atomic diffusion, rotation-induced processes (for which we tested different prescriptions for shear turbulence), penetrative convection with a rotational dependence, parametric viscosity and turbulence, and magnetic braking.
Results.
Over the entire range of masses, metallicities, and ages explored, we reproduce the evolution of the surface rotation rates and predict, for the first time, the observed anti-correlation between the surface rotation rate and
7
Li depletion as a consequence of the penetrative convection prescription. The
7
Li behaviour and its evolution with time is well reproduced for G-type stars. However, the ability of the model to reproduce the so-called
7
Li dip centred around ∼6600 K strongly depends on the adopted prescriptions for shear turbulence. It also requires a stellar mass dependence for the parametric viscosity adopted for the transport of angular momentum, similar to the behaviour predicted for the generation and luminosity of internal gravity waves generated by stellar convective envelopes. Finally, the model predicts internal rotation profiles in good agreement with asteroseismic constraints in main sequence stars.
Conclusions.
We provide an efficient way to model G-type stars of different ages and metallicities successfully. However, the
7
Li and
9
Be dip constraints urgently call for further hydrodynamical studies to better model turbulence in stars, and for the exploration of physical processes such as tachocline mixing for the transport of chemicals and internal gravity waves for the transport of angular momentum. Finally, additional data for the internal rotation and for
9
Be in main sequence low-mass stars are definitively needed.
Context. Understanding the angular momentum evolution of stars is one of the greatest challenges of modern stellar physics. Aims. We study the predicted rotational evolution of solar-type stars from ...the pre-main sequence to the solar age with 1D rotating evolutionary models including physical ingredients. Methods. We computed rotating evolution models of solar-type stars including an external stellar wind torque and internal transport of angular momentum following the method of Maeder and Zahn with the code STAREVOL. We explored different formalisms and prescriptions available from the literature. We tested the predictions of the models against recent rotational period data from extensive photometric surveys, lithium abundances of solar-mass stars in young clusters, and the helioseismic rotation profile of the Sun. Results. We find a best-matching combination of prescriptions for both internal transport and surface extraction of angular momentum. This combination provides a very good fit to the observed evolution of rotational periods for solar-type stars from early evolution to the age of the Sun. Additionally, we show that fast rotators experience a stronger coupling between their radiative region and the convective envelope. Regardless of the set of prescriptions, however, we cannot simultaneously reproduce surface angular velocity and the internal profile of the Sun or the evolution of lithium abundance. Conclusions. We confirm the idea that additional transport mechanisms must occur in solar-type stars until they reach the age of the Sun. Whether these processes are the same as those needed to explain recent asteroseismic data in more advanced evolutionary phases is still an open question.
Aims.Numerous spectroscopic observations provide compelling evidence for a non-canonical mixing process that modifies the surface abundances of Li, C and N of low-mass red giants when they reach the ...bump in the luminosity function. Eggleton and collaborators have proposed that a molecular weight inversion created by the 3He(3He, 2p)4He reaction may be at the origin of this mixing, and relate it to the Rayleigh-Taylor instability. We argue that one is actually dealing with a double diffusive instability referred to as thermohaline convection and we discuss its influence on the red giant branch. Methods.We compute stellar models of various initial metallicities that include thermohaline mixing, which is treated as a diffusive process based on the prescription given originally by Ulrich for the turbulent diffusivity produced by the thermohaline instability in stellar radiation zones. Results.Thermohaline mixing simultaneously accounts for the observed behaviour of the carbon isotopic ratio and of the abundances of Li, C and N in the upper part of the red giant branch. It significantly reduces the 3He production with respect to canonical evolution models as required by measurements of 3He/H in galactic HII regions. Conclusions.Thermohaline mixing is a fundamental physical process that must be included in stellar evolution modeling.
Context. With the ever growing number of detected and confirmed exoplanets, the probability of finding a planet that looks like the Earth increases continuously. While it is clear that the presence ...of a planet in the habitable zone does not imply the planet is habitable, a systematic study of the evolution of the habitable zone is required to account for its dependence on stellar parameters. Aims. In this article, we aim to provide the community with the dependence of the habitable zone upon the stellar mass, metallicity, rotation, and for various prescriptions of the limits of the habitable zone. Methods. We use stellar evolution models computed with the code STAREVOL, which includes the most current physical mechanisms of internal transport of angular momentum and external wind braking, to study the evolution of the habitable zone and the continuously habitable zone limits. Results. The stellar parameters mass and metallicity affect the habitable zone limits most dramatically. Conversely, for a given stellar mass and metallicity, stellar rotation has only a marginal effect on these limits and does not modify the width of the habitable zone. Moreover, and as expected in the main-sequence phase and for a given stellar mass and metallicity, the habitable zone limits remain almost constant, and this confirms the usual assumptions of a relative constancy of these limits during that phase. The evolution of the habitable zone limits is also correlated to the evolution of the stellar activity (through the Rossby number), which depends on the stellar mass considered. While the magnetic activity has negligible consequence in the case of more massive stars, these effects may have a strong impact on the habitability of a planet around M-dwarf stars. Thus, stellar activity cannot be neglected and may have a strong impact on the development of life during the early stage of the continuously habitable zone phase of low-mass stars. Using observed trends of stellar magnetic field strength, we also constrain the planetary magnetic field (at the zero order) required for a sufficient magnetospheric protection during the whole stellar evolution. Conclusions. We explain for the first time the systematic dependence of planet habitability on stellar parameters along the full evolution of low- and intermediate-mass stars. These results can be used as physical inputs for a first order estimation of exoplanetary habitability.
Aims.Galactic globular cluster (GC) stars exhibit abundance patterns that are not shared by their field counterparts, e.g. the well-documented O-Na and Mg-Al anticorrelations. Recent spectroscopic ...observations of GC turnoff stars have provided compelling evidence that these abundance anomalies were already present in the gas from which the observed stars formed. A widely held hypothesis is that the gas was “polluted” by stars that were more massive (and evolving faster) than the presently observed low-mass stars. In the framework of this “self-enrichment” scenario for GCs, we present a new method of deriving the initial mass function (IMF) of the polluters, by using the O/Na abundance distribution. Methods.We focus on NGC 2808, a GC for which the largest sample of O and Na abundance determinations is presently available. We use the abundance distribution of O/Na to derive the amount of polluted material with respect to the original composition. We explore two scenarios in detail for the self-enrichment of the cluster, which differ by the assumptions made on the composition of the polluter ejecta. In each case we consider two classes of possible “culprits”: massive asymptotic giant branch (AGB) stars (4-9 $M_{\odot}$) and winds of massive stars (WMS) in the mass range 10-100 $M_{\odot}$. Results.We obtain upper limits for the slope of the IMF (assumed to be given by a power-law) of the stars initially more massive than the present turnoff mass. We also derive lower limits for the amount of stellar residues in NGC 2808. Conclusions.We find that the polluter IMF had to be much flatter than the presently observed IMFs in stellar clusters, which agrees with the results of two other GC IMF determination methods, which we also discuss. Likewise, we find that the present mass of the GC should be totally dominated by stellar remnants if the polluters were AGB stars, which is not the case if the culprits are WMS. We critically analyse the advantages and shortcomings of each potential polluter class and find the WMS scenario more attractive.
Context. Rotation is one of the key physical mechanisms that deeply impact the evolution of stars. Helio- and asteroseismology reveal a strong extraction of angular momentum from stellar radiation ...zones over the whole Hertzsprung–Russell diagram. Aims. Turbulent transport in differentially rotating, stably stratified stellar radiation zones should be carefully modelled and its strength evaluated. Stratification and rotation imply that this turbulent transport is anisotropic. So far only phenomenological prescriptions have been proposed for the transport in the horizontal direction. This, however, constitutes a cornerstone in current theoretical formalisms for stellar hydrodynamics in evolution codes. We aim to improve its modelling. Methods. We derived a new theoretical prescription for the anisotropy of the turbulent transport in radiation zones using a spectral formalism for turbulence that takes simultaneously stable stratification, rotation, and a radial shear into account. Then, the horizontal turbulent transport resulting from 3D turbulent motions sustained by the instability of the radial differential rotation is derived. We implemented this framework in the stellar evolution code STAREVOL and quantified its impact on the rotational and structural evolution of solar metallicity low-mass stars from the pre-main-sequence to the red giant branch. Results. The anisotropy of the turbulent transport scales as N4τ2/(2Ω2), N and Ω being the buoyancy and rotation frequencies respectively and τ a time characterizing the source of turbulence. This leads to a horizontal turbulent transport of similar strength in average that those obtained with previously proposed prescriptions even if it can be locally larger below the convective envelope. Hence the models computed with the new formalism still build up too steep internal rotation gradients compared to helioseismic and asteroseismic constraints. As a consequence, a complementary transport mechanism such as internal gravity waves or magnetic fields is still needed to explain the observed strong transport of angular momentum along stellar evolution. Conclusions. The new prescription links for the first time the anisotropy of the turbulent transport in radiation zones to their stratification and rotation. This constitutes important theoretical progress and demonstrates how turbulent closure models should be improved to get firm conclusions on the potential importance of other processes that transport angular momentum and chemicals inside stars along their evolution.
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