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 Results 1-20 of 35. Search equation: (author:Godart, M%C3%A9lanie)OR(U196669) Sort: Issue date Author Title Filter: All documents types Scientific journals - Article - Short communication - Book review - Letter to the editor - Complete issue - OtherBooks - Book published as author, translator, etc. - Collective work published as editor or directorParts of books - Contribution to collective works - Contribution to encyclopedias, dictionaries... - Preface, postface, glossary...Scientific congresses and symposiums - Unpublished conference/Abstract - Paper published in a book - Paper published in a journal - PosterScientific conference in universities or research centersReports - Expert report - Internal report - External report - OtherDissertations and theses - Master of advanced studies dissertation - Master's dissertation - Doctoral thesis - Post doctoral thesisLearning materials - Course notes - OtherPatentCartographic materials - Single work - Part of another publicationComputer developments - Textual, factual or bibliographical database - Software - OtherE-prints/Working papers - First made available on ORBi - Already available on another siteDiverse speeches and writings - Article for general public - Conference given outside the academic context - Speech/Talk - Other     1 2   ASTA -- Theoretical Stellar Astrophysics and AsteroseismologyGodart, Mélanie Scientific conference (2017, September 15)Theoretical Stellar Physics and Asteroseismology The IACOB project. IV. New predictions for high-degree non-radial mode instability domains in massive stars and their connection with macroturbulent broadeningGodart, Mélanie ; Simón-Díaz, S.; Herrero, A. et alin Astronomy and Astrophysics (2016), 597Context. Asteroseismology is a powerful tool to access the internal structure of stars. Apart from the important impact of theoretical developments, progress in this field has been commonly associated ... [more ▼]Context. Asteroseismology is a powerful tool to access the internal structure of stars. Apart from the important impact of theoretical developments, progress in this field has been commonly associated with the analysis of time-resolved observations. Recently, the so-called macroturbulent broadening has been proposed as a complementary and less expensive way - in terms of observational time - to investigate pulsations in massive stars.
Aims: We assess to what extent this ubiquitous non-rotational broadening component which shapes the line profiles of O stars and B supergiants is a spectroscopic signature of pulsation modes driven by a heat mechanism.
Methods: We compute stellar main-sequence and post-main-sequence models from 3 to 70 M[SUB]⊙[/SUB] with the ATON stellar evolution code, and determine the instability domains for heat-driven modes for degrees ℓ = 1-20 using the adiabatic and non-adiabatic codes LOSC and MAD. We use the observational material compiled in the framework of the IACOB project to investigate possible correlations between the single snapshot line-broadening properties of a sample of ≈260 O and B-type stars and their location inside or outside the various predicted instability domains.
Results: We present an homogeneous prediction for the non-radial instability domains of massive stars for degree ℓ up to 20. We provide a global picture of what to expect from an observational point of view in terms of the frequency range of excited modes, and we investigate the behavior of the instabilities with respect to stellar evolution and the degree of the mode. Furthermore, our pulsational stability analysis, once compared to the empirical results, indicates that stellar oscillations originated by a heat mechanism cannot explain alone the occurrence of the large non-rotational line-broadening component commonly detected in the O star and B supergiant domain. Based on observations made with the Nordic Optical Telescope, operated by NOTSA, and the Mercator Telescope, operated by the Flemish Community, both at the Observatorio del Roque de los Muchachos (La Palma, Spain) of the Instituto de Astrofísica de Canarias. [less ▲]Detailed reference viewed: 14 (2 ULg) Apsidal motion in the massive binary HD 152218Rauw, Grégor ; Rosu, S.; Noels-Grötsch, Arlette et alin Astronomy and Astrophysics (2016), 594(A33), 1-12Massive binary systems are important laboratories in which to probe the properties of massive stars and stellar physics in general. In this context, we analysed optical spectroscopy and photometry of the ... [more ▼]Massive binary systems are important laboratories in which to probe the properties of massive stars and stellar physics in general. In this context, we analysed optical spectroscopy and photometry of the eccentric short-period early-type binary HD 152218 in the young open cluster NGC 6231. We reconstructed the spectra of the individual stars using a disentangling code. The individual spectra were then compared with synthetic spectra obtained with the CMFGEN model atmosphere code. We furthermore analysed the light curve of the binary and used it to constrain the orbital inclination and to derive absolute masses of (19.8 ± 1.5) and (15.0 ± 1.1) M⊙. Combining radial velocity measurements from over 60 yr, we show that the system displays apsidal motion at a rate of (2.04 ± .24)°/yr. Solving the Clairaut-Radau equation, we used stellar evolution models, obtained with the CLES code, to compute the internal structure constants and to evaluate the theoretically predicted rate of apsidal motion as a function of stellar age and primary mass. In this way, we determine an age of 5.8 ± 0.6 Myr for HD 152218, which is towards the higher end of, but compatible with, the range of ages of the massive star population of NGC 6231 as determined from isochrone fitting. [less ▲]Detailed reference viewed: 42 (3 ULg) Leaky-wave-induced disks around Be stars: a pulsational analysis on their formationGodart, Mélanie ; Shibahashi, Hiromoto; Dupret, Marc-Antoine et alin New windows on massive stars: asteroseismology, interferometry, and spectropolarimetry, Proceedings of the International Astronomical Union, IAU Symposium, Volume 307 (2015, January 01)Be stars are B-type stars near the main sequence which undergo episodic mass loss events detected by emission lines, whose line shape and intensity vary with a timescale of the order of decades ... [more ▼]Be stars are B-type stars near the main sequence which undergo episodic mass loss events detected by emission lines, whose line shape and intensity vary with a timescale of the order of decades. Spectroscopic observations show a large rotation velocity such that one of the prevailing scenarios for the formation of the equatorial disk consists in an increasing equatorial rotation velocity to the break-up limit where gravity is challenged by the centrifugal force. We investigate here a new scenario recently suggested by Ishimatsu & Shibahashi (2013), in which the transport of angular momentum through the photosphere would be achieved by leaky waves, keeping the rotation velocity still below the break-up limit. [less ▲]Detailed reference viewed: 8 (1 ULg) Pulsations in hot supergiantsGodart, Mélanie ; Grotsch-Noels, Arlette; Dupret, Marc-Antoine et alin Precision Asteroseismology, Proceedings of the International Astronomical Union, IAU Symposium, Volume 301 (2014, February 01)Massive stars are the cosmic engines that shape and drive our Universe. Many issues such as their formation, their stability and the mass loss effects, are far from being completely understood. Recent ... [more ▼]Massive stars are the cosmic engines that shape and drive our Universe. Many issues such as their formation, their stability and the mass loss effects, are far from being completely understood. Recent ground-based and space observations have shown pulsations in massive MS and post-MS stars, such as acoustic and gravity modes excited by the κ-mechanism and even solar-like oscillations. Theoretical studies emphasized the presence of strange modes in massive models, and recent theoretical analyses have shown that hot supergiants can pulsate in oscillatory convective modes. We review the instability domains of massive stars as well as their excitation mechanisms and present the latest results. [less ▲]Detailed reference viewed: 13 (3 ULg) CoRoT Observations of O Stars: Diverse Origins of VariabilityBlomme, R.; Briquet, Maryline ; Degroote, P. et alin Astronomical Society of the Pacific Conference Series (2013, January 01)Six O-type stars were observed continuously by the CoRoT satellite during a 34.3-day run. The unprecedented quality of the data allows us to detect even low-amplitude stellar pulsations in some of these ... [more ▼]Six O-type stars were observed continuously by the CoRoT satellite during a 34.3-day run. The unprecedented quality of the data allows us to detect even low-amplitude stellar pulsations in some of these stars (HD 46202 and the binaries HD 46149 and Plaskett's star). These cover both opacity-driven modes and solar-like stochastic oscillations, both of importance to the asteroseismological modeling of O stars. Additional effects can be seen in the CoRoT light curves, such as binarity and rotational modulation. Some of the hottest O-type stars (HD 46223, HD 46150 and HD 46966) are dominated by the presence of red-noise: we speculate that this is related to a sub-surface convection zone. [less ▲]Detailed reference viewed: 53 (20 ULg) Theoretical Instability Domains of Massive StarsGodart, Mélanie ; Dupret, Marc-Antoine ; Noels-Grötsch, Arlette et alin ASP Conference Proceeding, Vol. 462, 27 (2012, September 01)Massive stars are characterized by a large radiation over gas pressure ratio. With increasing stellar initial mass, they suffer stronger stellar winds, and the induced mass-loss affects the evolution and ... [more ▼]Massive stars are characterized by a large radiation over gas pressure ratio. With increasing stellar initial mass, they suffer stronger stellar winds, and the induced mass-loss affects the evolution and internal structure on the main sequence and on the post-main sequence. Recent ground-based observations and space missions have shown the presence of pulsations in massive stars, such as acoustic and gravity modes excited by the κ-mechanism and even solar-like oscillations. Strange modes could also be excited in the most massive stars (Aerts et al. 2010). We computed evolutionary tracks and non-adiabatic frequencies for initial masses ranging from 15 to 70 M[SUB]&sun;[/SUB] on the main sequence and on the post-main sequence taking mass loss into account and we discuss in this paper the results for 25 M[SUB]&sun;[/SUB] models. [less ▲]Detailed reference viewed: 31 (2 ULg) Unveiling the internal structure and evolution of massive stars through their pulsation modesGodart, Mélanie Doctoral thesis (2011)Stars in the night sky are not as quiet as they seem. A human being wandering on Earth few billions years ago would have seen a different night sky, with different stars forming different constellations ... [more ▼]Stars in the night sky are not as quiet as they seem. A human being wandering on Earth few billions years ago would have seen a different night sky, with different stars forming different constellations. Moving forward in time, he would have been the witness of stellar evolution as some stars would have suddenly shined while others disappeared forever. Hard to realize at a time scale of human life, stars are born, evolve, and die in a limited lifetime which can last only a few million years for the most massive to trillion years for the less massive. Fortunately, it is not necessary to wait that long to study the formation and evolution of stars. Stellar evolution can be studied on shorter time scales, on thousands of stars, at various evolutionary stages. This is of great importance as stars shape the Universe and produce the chemical elements at the origin of life. Probing the internal structure of stars is however very challenging due to the opacity barrier of their superficial layers. One way to get around this issue is to study and interpret stellar pulsations. As seismologists extract information about Earth interior trough the study of earthquakes, asteroseismologists can study the internal structure of stars by studying their oscillations. In this thesis, this technique is used to study the internal structure and evolution of massive stars which are at least eight times more massive than our Sun and which have a spectral type between O and B. The first part of this work is devoted to the determination of the $\kappa$-mechanism instability domains for massive stars. In order to extend the computations to the post-main sequence phase of evolution, we develop a numerical technique in which the non-adiabatic computations for the stellar core are made, independently than for the envelope, within the quasi-adiabatic and the asymptotic treatment. In a second step, we investigate the pulsations modes in O main sequence stars and in B post-main sequence stars. The presence of g-modes in post-main sequence stars is closely related to the internal structure of the star and we study the effects of several physical factors on the occurrence of these modes. Finally, the last part of this work is dedicated to the characterization of strange mode pulsations. In particular, we focus on strange modes having an adiabatic counterpart, which are trapped into a superficial cavity. The effect of the model atmosphere on the excitation is investigated in addition to the characterization of their eigenfunctions. [less ▲]Detailed reference viewed: 54 (18 ULg) Variability in the CoRoT photometry of three hot O-type stars. HD 46223, HD 46150, and HD 46966Blomme, R.; Mahy, Laurent ; Catala, C. et alin Astronomy and Astrophysics (2011), 533Context. The detection of pulsational frequencies in stellar photometry is required as input for asteroseismological modelling. The second short run (SRa02) of the CoRoT mission has provided photometric ... [more ▼]Context. The detection of pulsational frequencies in stellar photometry is required as input for asteroseismological modelling. The second short run (SRa02) of the CoRoT mission has provided photometric data of unprecedented quality and time-coverage for a number of O-type stars.
Aims: We analyse the CoRoT data corresponding to three hot O-type stars, describing the properties of their light curves and search for pulsational frequencies, which we then compare to theoretical model predictions.
Methods: We determine the amplitude spectrum of the data, using the Lomb-Scargle and a multifrequency HMM-like technique. Frequencies are extracted by prewhitening, and their significance is evaluated under the assumption that the light curve is dominated by red noise. We search for harmonics, linear combinations, and regular spacings among these frequencies. We use simulations with the same time sampling as the data as a powerful tool to judge the significance of our results. From the theoretical point of view, we use the MAD non-adiabatic pulsation code to determine the expected frequencies of excited modes.
Results: A substantial number of frequencies is listed, but none can be convincingly identified as being connected to pulsations. The amplitude spectrum is dominated by red noise. Theoretical modelling shows that all three O-type stars can have excited modes, but the relation between the theoretical frequencies and the observed spectrum is not obvious.
Conclusions: The dominant red noise component in the hot O-type stars studied here clearly points to a different origin than the pulsations seen in cooler O stars. The physical cause of this red noise is unclear, but we speculate on the possibility of sub-surface convection, granulation, or stellar wind inhomogeneities being responsible. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany and Spain.Tables 2-4 are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/533/A4 [less ▲]Detailed reference viewed: 28 (2 ULg) Pulsations in massive stars: effect of the atmosphere on the strange mode pulsationsGodart, Mélanie ; Dupret, Marc-Antoine ; Noels-Grötsch, Arlette et alin Proceedings of the International Astronomical Union (2011), 272Recent space observations with CoRoT and ground-based spectroscopy have shown the presence of different types of pulsations in OB stars. These oscillations could be due to acoustic and gravity modes ... [more ▼]Recent space observations with CoRoT and ground-based spectroscopy have shown the presence of different types of pulsations in OB stars. These oscillations could be due to acoustic and gravity modes, solar-like oscillations or even other pulsations of large growth rates. We present a first attempt at interpreting the latter as strange modes. [less ▲]Detailed reference viewed: 21 (4 ULg) Seismic modelling of OB starsDupret, Marc-Antoine ; Godart, Mélanie ; Belkacem, Kevin et alin Proceedings of the International Astronomical Union (2011), 272A review of the ability of asteroseismology to probe the internal physics of OB stars is presented. The main constraints that can be obtained from the frequency spectrum in p- and g-modes pulsators are ... [more ▼]A review of the ability of asteroseismology to probe the internal physics of OB stars is presented. The main constraints that can be obtained from the frequency spectrum in p- and g-modes pulsators are discussed. Next, we consider energetic aspects of the pulsations in OB stars and show how such study also allows to constrain their internal physics. The cases of p-mixed modes (β Cep stars), g-modes (SPB stars), strange modes and stochastically excited modes are considered. [less ▲]Detailed reference viewed: 13 (1 ULg) Theoretical instability domains in the upper part of the HR diagramGodart, Mélanie Conference (2011, March)Massive stars are characterized by a large radiation over gaz pressure ratio and a large temperature over density ratio. With increasing stellar initial mass, they suffer stronger stellar winds which ... [more ▼]Massive stars are characterized by a large radiation over gaz pressure ratio and a large temperature over density ratio. With increasing stellar initial mass, they suffer stronger stellar winds which plays an important role in the chemical enrichment of the galaxies. The induced mass loss affects also the evolution and internal structure of massive stars on the main sequence (MS) and on the post-main sequence phase (post-MS). Recent ground-based observations and space missions have shown the presence of pulsations in massive stars, such as accouctic and gravity modes excited by the $\kappa$-mechanism and even solar-like oscillations. Strange modes could also found to be excited in the most massive stars. $\kappa$-mechanism instability domains are presented for the upper HR diagram (up to $70$M$_{odot}$) on the MS and on the post-MS. We compute evolutionary tracks and non-adiabatic frequencies for different input parameters such as the metallicity, the mass loss rate and the overshooting parameter. [less ▲]Detailed reference viewed: 27 (8 ULg) The multiplicity of O-type stars in NGC 2244Mahy, Laurent ; Rauw, Grégor ; Martins, F. et alin Bulletin de la Societe Royale des Sciences de Liege (2011), 80The investigation of the multiplicity of massive stars is crucial to determine a robust binary fraction but also for understanding the physical properties of these objects. In this contribution, we will ... [more ▼]The investigation of the multiplicity of massive stars is crucial to determine a robust binary fraction but also for understanding the physical properties of these objects. In this contribution, we will present the main results from our long-term spectroscopic survey devoted to the young open cluster NGC 2244. We discuss the spectral classification, the projected rotational velocity (v sin{i}) and the multiplicity of O-stars. The stellar and wind parameters of each star, obtained using the CMFGEN atmosphere code, help us to better constrain the individual properties of these objects. Several of these stars were observed by the CoRoT satellite (SRa02) in the Asteroseismology channel. This intensive monitoring and the unprecedented quality of the light curves allow us to shed a new light on these objects. [less ▲]Detailed reference viewed: 25 (2 ULg) Plaskett's star: analysis of the CoRoT photometric dataMahy, Laurent ; Gosset, Eric ; Baudin, F. et alin Astronomy and Astrophysics (2011), 525Context. The second short run (SRa02) of the CoRoT space mission for asteroseismology was partly devoted to stars belonging to the Mon OB2 association. An intense monitoring has been performed on Plaskett ... [more ▼]Context. The second short run (SRa02) of the CoRoT space mission for asteroseismology was partly devoted to stars belonging to the Mon OB2 association. An intense monitoring has been performed on Plaskett's star (HD 47129) and the unprecedented quality of the light curve allows us to shed new light on this very massive, non-eclipsing binary system.
Aims: We particularly aimed at detecting periodic variability that might be associated with pulsations or interactions between both components. We also searched for variations related to the orbital cycle that could help to constrain the inclination and the morphology of the binary system.
Methods: We applied an iterative Fourier-based prewhitening and a multiperiodic fitting procedure to analyse the time series and extract the frequencies of variations from the CoRoT light curve. We describe the noise properties to tentatively define an appropriate significance criterion and, in consequence, to only point out the peaks at a certain significance level. We also detect the variations related to the orbital motion and study them with the NIGHTFALL programme.
Results: The periodogram computed from Plaskett's star CoRoT light curve mainly exhibits a majority of peaks at low frequencies. Among these peaks, we highlight a list of 43 values, notably including two different sets of harmonic frequencies whose fundamental peaks are located at about 0.07 and 0.82 d[SUP]-1[/SUP]. The former represents the orbital frequency of the binary system, whilst the latter could probably be associated with non-radial pulsations. The study of the 0.07 d[SUP]-1[/SUP] variations reveals a hot spot most probably situated on the primary star and facing the secondary.
Conclusions: The investigation of this unique dataset constitutes a further step in the understanding of Plaskett's star. These results provide a first basis for future seismic modelling and put forward the probable existence of non-radial pulsations in Plaskett's star. Moreover, the fit of the orbital variations confirms the problem of the distance of this system which was already mentioned in previous works. A hot region between both components renders the determination of the inclination ambiguous. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany and Spain.Table 2 is only available in electronic form at http://www.aanda.org [less ▲]Detailed reference viewed: 53 (5 ULg) Overshooting and semiconvection: structural changes and asteroseismic signaturesNoels-Grötsch, Arlette ; Montalban Iglesias, Josefa ; Miglio, Andrea et alin Astrophysics & Space Science (2010), 328Overshooting and semiconvection are two poorly known mechanisms which affect the extent and the efficiency of chemical mixing outside classical convection zones in stars. We discuss the uncertainties and ... [more ▼]Overshooting and semiconvection are two poorly known mechanisms which affect the extent and the efficiency of chemical mixing outside classical convection zones in stars. We discuss the uncertainties and the inferences of those processes in main sequence stars burning hydrogen in a convective core. We then focus on the asteroseismic signatures of partially or fully mixed zones surrounding the convective core, through the detailed shape of the induced chemical composition profile. We emphasize the potential power of asteroseismology to determine the internal structure of stars and thus to help us understand the physical processes at work inside the stars. [less ▲]Detailed reference viewed: 24 (9 ULg) Pulsations in O and B starsGodart, Mélanie Conference (2010, June)Detailed reference viewed: 25 (6 ULg) Periodic mass-loss episodes due to an oscillation mode with variable amplitude in the hot supergiant HD 50064Aerts, C.; Lefever, K.; Baglin, A. et alin Astronomy and Astrophysics (2010), 513
Aims: We aim to interpret the photometric and spectroscopic variability of the luminous blue variable supergiant HD 50064 (V = 8.21).
Methods: CoRoT space photometry and follow-up high ... [more ▼]
Aims: We aim to interpret the photometric and spectroscopic variability of the luminous blue variable supergiant HD 50064 (V = 8.21).
Methods: CoRoT space photometry and follow-up high-resolution spectroscopy with a time base of 137 d and 169 d, respectively, was gathered, analysed, and interpreted using standard time series analysis and light curve modelling methods, as well as spectral line diagnostics.
Results: The space photometry reveals one period of 37 d, which undergoes a sudden amplitude change with a factor 1.6. The pulsation period is confirmed in the spectroscopy, which additionally reveals metal line radial velocity values differing by 30 km s[SUP]-1[/SUP] depending on the spectral line and on the epoch. We estimate T[SUB]eff[/SUB] 13 500 K, log g 1.5 from the equivalent width of Si lines. The Balmer lines reveal that the star undergoes episodes of changing mass loss on a time scale similar to the changes in the photometric and spectroscopic variability, with an average value of log dot{M} â -5 (in M_È¯ yr[SUP]-1[/SUP]). We tentatively interpret the 37 d period as the result of a strange mode oscillation. Based on high-resolution spectroscopy assembled with the CORALIE spectrograph attached to the 1.2 m Euler telescope at La Silla, Chile and on CoRoT space-based photometry. The CoRoT space mission was developed and is operated by the French space agency CNES, with the participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.Postdoctoral Fellow of the Fund for Scientific Research of Flanders (FWO), Belgium. [less ▲]Detailed reference viewed: 13 (3 ULg) Collective pulsational velocity broadening due to gravity modes as a physical explanation for macroturbulence in hot massive starsAerts, C.; Puls, J.; Godart, Mélanie et alin Astronomy and Astrophysics (2009), 508Aims. We aimed at finding a physical explanation for the occurrence of macroturbulence in the atmospheres of hot massive stars, a phenomenon found in observations for more than a decade but that remains ... [more ▼]Aims. We aimed at finding a physical explanation for the occurrence of macroturbulence in the atmospheres of hot massive stars, a phenomenon found in observations for more than a decade but that remains unexplained.
Methods: We computed time series of line profiles for evolved massive stars broadened by rotation and by hundreds of low-amplitude nonradial gravity-mode pulsations which are predicted to be excited for evolved massive stars.
Results: In general, line profiles based on macrotubulent broadening can mimic those subject to pulsational broadening. In several cases, though, good fits require macroturbulent velocities that pass the speed of sound for realistic pulsation amplitudes. Moreover, we find that the rotation velocity can be seriously underestimated by using a simple parameter description for macroturbulence rather than an appropriate pulsational model description to fit the line profiles.
Conclusions: We conclude that macroturbulence is a likely signature of the collective effect of pulsations. We provide line diagnostics and their typical values to decide whether or not pulsational broadening is present in observed line profiles, as well as a procedure to avoid an inaccurate estimation of the rotation velocity. [less ▲]Detailed reference viewed: 29 (2 ULg) Theoretical amplitudes and lifetimes of non-radial solar-like oscillations in red giantsDupret, Marc-Antoine ; Belkacem, Kevin ; Samadi, Réza et alin Astronomy and Astrophysics (2009), 506Context: Solar-like oscillations have been observed in numerous red giants from ground and from space. An important question arises: could we expect to detect non-radial modes probing the internal ... [more ▼]Context: Solar-like oscillations have been observed in numerous red giants from ground and from space. An important question arises: could we expect to detect non-radial modes probing the internal structure of these stars?
Aims: We investigate under what physical circumstances non-radial modes could be observable in red giants; what would be their amplitudes, lifetimes and heights in the power spectrum (PS)?
Methods: Using a non-radial non-adiabatic pulsation code including a non-local time-dependent treatment of convection, we compute the theoretical lifetimes of radial and non-radial modes in several red giant models. Next, using a stochastic excitation model, we compute the amplitudes of these modes and their heights in the PS.