Showing results 21 to 34 of 34
  Space observations of B stars with CoRoT; Miglio, Andrea  ; et alin Communications in Asteroseismology (2009), 158 We present the preliminary results of the exploration of pulsating B stars observed with the CoRoT space mission. The previously known group of Slowly Pulsating B stars gains a substantial amount of new ... [more ▼] We present the preliminary results of the exploration of pulsating B stars observed with the CoRoT space mission. The previously known group of Slowly Pulsating B stars gains a substantial amount of new candidates, offering the opportunity to test stellar models beyond individual cases. Besides these well-defined stars, the analysis of other B star candidate pulsators hints towards the presence of different variability behaviour, co-existing in the same space in terms of the timescale of the variations and location in the (Teff, logg) diagram. [less ▲] Detailed reference viewed: 21 (6 ULg)First asteroseismic results from CoRoT; ; et al in Communications in Asteroseismology (2008), 156 About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first ... [more ▼] About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first results to illustrate how these data of unprecedented quality shed a new light on the field of stellar seismology. [less ▲] Detailed reference viewed: 24 (13 ULg) First asteroseismic results from CoRoT; ; et al in Communication in Asteroseismology (2008), 157 About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first ... [more ▼] About one year after the end of the first observational run and six months after the first CoRoT data delivery, we comment the data exploitation progress for different types of stars. We consider first results to illustrate how these data of unprecedented quality shed a new light on the field of stellar seismology. [less ▲] Detailed reference viewed: 2 (2 ULg)Impact of the new solar abundances on the calibration of the PMS binary system RS Chamaeleontis; ; et al in Astronomy and Astrophysics (2007), 473 Context: In a recent work, we tried to obtain a calibration of the two components of the pre-main sequence binary system RS Cha by means of theoretical stellar models. We found that the only way to ... [more ▼] Context: In a recent work, we tried to obtain a calibration of the two components of the pre-main sequence binary system RS Cha by means of theoretical stellar models. We found that the only way to reproduce the observational parameters of RS Cha with standard stellar models is to decrease the initial abundances of carbon and nitrogen derived from the GN93 solar mixture of heavy elements by a few tenths of dex. Aims: In this work, we aim to reproduce the observational properties of the RS Cha stars with stellar evolution models based on the new AGS05 solar mixture recently derived from a three-dimensional solar model atmosphere. The AGS05 mixture is depleted in carbon, nitrogen and oxygen with respect to the GN93 mixture. Methods: We calculated new stellar models of the RS Cha components using the AGS05 mixture and appropriate opacity tables. We sought models that simultaneously satisfy the observations of the two components (masses, radii, luminosities, effective temperatures and metallicity). Results: We find that it is possible to reproduce the observational data of the RS Cha stars with AGS05 models based on standard input physics. From these models, the initial helium content of the system is YË 0.255 and its age is Ë 9.13 ± 0.12 Myr. [less ▲] Detailed reference viewed: 3 (0 ULg)Calibration of the Pre-Main Sequence Binary System RS Cha: Impact of the Initial Chemical Mixture; ; et al in IAU Symposium (2007, August 01) Accurate observational data are available for the eclipsing double-lined spectroscopic binary system RS Cha, composed of two stars in the pre-main sequence stage of evolution: masses, radii, luminosities ... [more ▼] Accurate observational data are available for the eclipsing double-lined spectroscopic binary system RS Cha, composed of two stars in the pre-main sequence stage of evolution: masses, radii, luminosities and effective temperatures of each component and metallicity of the system. This allows to build pre-main sequence stellar models representing the components of RS Cha and to constrain them in terms of physical ingredients, initial chemical composition and age.We present stellar models we have calculated using the CESAM stellar evolution code for different sets of physical inputs (opacities, nuclear reaction rates, etc.) and different initial parameters (global metallicity, helium abundance, individual abundances of heavy elements). We discuss their ability to reproduce the observational constraints simultaneously for the two components. We focus on the impact on the models of the chemical mixture adopted and we propose a calibration for the RS Cha system providing an estimate of its age and initial helium abundance. [less ▲] Detailed reference viewed: 1 (1 ULg)Asteroseismology and mode driving of the Herbig Ae star HD 104237Dupret, Marc-Antoine ; ; et alin Communications in Asteroseismology (2007), 150 Eight pulsation frequencies were detected in the Herbig Ae star HD 104237 during two observational campaigns in 1999 -- 2000 (Böhm et al. 2004). Moreover, Böhm et al. (in preparation) detected recently in ... [more ▼] Eight pulsation frequencies were detected in the Herbig Ae star HD 104237 during two observational campaigns in 1999 -- 2000 (Böhm et al. 2004). Moreover, Böhm et al. (in preparation) detected recently in their data two independent signatures of a signal at 95 hr that corresponds probably to rotational modulation. We present here a seismic study of this Pre-Main Sequence star based on these observations. Different possible interpretations of the pulsation spectrum are considered. The driving of the pulsation modes is not explained by standard models, the observed frequencies being too high for delta Scuti-type pulsations. We consider the effect of He accumulation in its partial ionization zones as a possible explanation for this driving. [less ▲] Detailed reference viewed: 4 (2 ULg)Calibration of the pre-main sequence RS Chamaleontis binary system; ; et al in Astronomy and Astrophysics (2007), 465 Context: The calibration of binary systems with accurately known masses and/or radii provides powerful tools to test stellar structure and evolution theory and to determine the age and helium content of ... [more ▼] Context: The calibration of binary systems with accurately known masses and/or radii provides powerful tools to test stellar structure and evolution theory and to determine the age and helium content of stars. We study the eclipsing double-lined spectroscopic binary system RS Cha, for which we have accurate observations of the parameters of both stars (masses, radii, luminosities, effective temperatures and metallicity). Aims: We have calculated several sets of stellar models for the components of the RS Cha system, with the aim of reproducing simultaneously the available observational constraints and to estimate the age and initial helium abundance of the system. Methods: Using the CESAM stellar evolution code, we model both components starting from the initial mass and metallicity and adjusting the input parameters and physics in order to satisfy the observational constraints. Results: We find that the observations cannot be reproduced if we assume that the abundance ratios are solar but they are satisfied if carbon and nitrogen are depleted in the RS Cha system with respect to the Sun. This is in accordance with the abundances observed in other young stars. The RS Cha system is in an evolutionary stage at the end of the PMS phase where models are not strongly sensitive to various physical uncertainties. However we show that the oscillations of these two stars, which have been detected, would be able to discriminate between different options in the physical description of this evolutionary phase. [less ▲] Detailed reference viewed: 1 (1 ULg)The Seismology Programme of CoRoT; ; et al in Proceedings of "The CoRoT Mission Pre-Launch Status - Stellar Seismology and Planet Finding (2006, November 01) We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working ... [more ▼] We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working Group. With a few illustrative examples, we show how CoRoT data will help to address various problems associated with present open questions of stellar structure and evolution. [less ▲] Detailed reference viewed: 43 (32 ULg)Seismic study of the Herbig Ae star HD 104237Dupret, Marc-Antoine ; ; et alin Communications in Asteroseismology (2006), 147 HD 104237 is the brightest Herbig Ae star, and as such a pre-main sequence (PMS) star. It is also a spectroscopic binary with determined orbital parameters. It was observed in 1999-2000 at SAAO and Mt ... [more ▼] HD 104237 is the brightest Herbig Ae star, and as such a pre-main sequence (PMS) star. It is also a spectroscopic binary with determined orbital parameters. It was observed in 1999-2000 at SAAO and Mt Stromolo and 1888 Echelle spectra were obtained. From these observations, 8 pulsation frequencies were detected among which 5 with very high confidence (Böhm et al. 2004). We present here a preliminary seismic study based on these observations. We also consider the problem of the excitation of the observed modes and show, as an important result of our study, that HD 104237 is not a delta Sct type pulsator. [less ▲] Detailed reference viewed: 7 (1 ULg)RS Cha, a binary system suitable for testing stellar physics modeling during the pre-main sequence phase.; ; et al in Memorie della Società Astronomica Italiana : Journal of the Italian Astronomical Society (2006), 77 We use accurate spectroscopic data of the pre-main sequence eclipsing binary system RS Cha to redetermine masses and radii of both components and to measure the metallicity of the system. Knowing all ... [more ▼] We use accurate spectroscopic data of the pre-main sequence eclipsing binary system RS Cha to redetermine masses and radii of both components and to measure the metallicity of the system. Knowing all fundamental parameters of both stars we are able to test stellar physics modeling during the PMS phase. We find no evidence that our models are deficient. Accurate detection of modes and measurements of periods of the recently discovered pulsations in both components are required to constrain more severely the physical description of PMS stellar models.. [less ▲] Detailed reference viewed: 10 (2 ULg)The life of stars and their planets; ; et al in Favata, F.; Sanz-Forcada, J.; Giménez, A. (Eds.) et al 39TH ESLAB Symposium on Trends in Space Science and Cosmic Vision 2020 (2005, December 01) We lack a reliable scenario for the formation and evolution of stars and their planetary systems, involving key factors such as magnetic fields and turbulence. We present the case for a mission concept ... [more ▼] We lack a reliable scenario for the formation and evolution of stars and their planetary systems, involving key factors such as magnetic fields and turbulence. We present the case for a mission concept that will clarify these problems and give us a global view of the evolution of combined star and planetary systems. This will be achieved by simultaneously addressing the search for planetary transits in front of a large number of stars, including many nearby stars, the study of their internal structure and evolution via asteroseismology, and that of their magnetic activity, via UV monitoring. [less ▲] Detailed reference viewed: 3 (0 ULg)RS Cha, a spectroscopic binary system as a test of stellar physics modeling during the pre-main sequence phase; ; et al in SF2A-2005: Semaine de l'Astrophysique Francaise (2005, December 01) New spectra of the PMS eclipsing binary RS Cha obtained with the GIRAFFE spectrograph at the SAAO, allowed us to measure the metallicity and new masses of both components of RS Cha. The system is ... [more ▼] New spectra of the PMS eclipsing binary RS Cha obtained with the GIRAFFE spectrograph at the SAAO, allowed us to measure the metallicity and new masses of both components of RS Cha. The system is therefore observationally well constrained, and modelling both stars (both with masses around 1.8 M[SUB]o[/SUB]) at the same (young) age is a severe challenge for stellar evolutionary codes. We find no evidence that our models are deficient. However accurate detection of modes and measurements of periods of the recently discovered pulsations in both components are required to constrain more severely the physical description of PMS stellar models. [less ▲] Detailed reference viewed: 5 (2 ULg)Asteroseismology of delta Scuti Stars: Problems and Prospects; Dupret, Marc-Antoine ; et alin Journal of Astrophysics & Astronomy (2005), 26 We briefly outline the state-of-the-art seismology of delta Scuti stars from a theoretical point of view: why is it so difficult a task? The recent theoretical advances in the field that these ... [more ▼] We briefly outline the state-of-the-art seismology of delta Scuti stars from a theoretical point of view: why is it so difficult a task? The recent theoretical advances in the field that these difficulties have influenced are also discussed. [less ▲] Detailed reference viewed: 10 (2 ULg)Abundance analysis of targets for the COROT/MONS asteroseismology missions. II. Abundance analysis of the COROT main targets; ; et al in Astronomy and Astrophysics (2004), 425 One of the goals of the ground-based support program for the COROT and MONS/RÖMER satellite missions is to characterize suitable target stars for the part of the missions dedicated to asteroseismology. We ... [more ▼] One of the goals of the ground-based support program for the COROT and MONS/RÖMER satellite missions is to characterize suitable target stars for the part of the missions dedicated to asteroseismology. We present the detailed abundance analysis of nine of the potential COROT main targets using the semi-automatic software VWA. For two additional COROT targets we could not perform the analysis due to the high rotational velocity of these stars. For five stars with low rotational velocity we have also performed abundance analysis by a classical equivalent width method in order to test the reliability of the VWA software. The agreement between the different methods is good. We find that it is necessary to measure abundances extracted from each line relative to the abundances found from a spectrum of the Sun in order to remove systematic errors. We have constrained the global atmospheric parameters T[SUB]eff[/SUB], log g, and [Fe/H] to within 70-100 K, 0.1-0.2 dex, and 0.1 dex for five stars which are slow rotators (v sin i < 15 km s[SUP]-1[/SUP]). For most of the stars we find good agreement with the parameters found from line depth ratios, H alpha lines, Strömgren indices, previous spectroscopic studies, and also log g determined from the HIPPARCOS parallaxes. For the fast rotators (v sin i > 60 km s[SUP]-1[/SUP]) it is not possible to constrain the atmospheric parameters. Based on observations obtained with the 193 cm telescope at Observatoire de Haute Provence, France. [less ▲] Detailed reference viewed: 19 (3 ULg)
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