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See detailAn Asteroseismological Analysis of the Pulsating B Subdwarf Feige 48 Taking into Account Rotation
Van Grootel, Valérie ULg; Charpinet, Stéphane; Fontaine, Gilles et al

in Leaflet - Astronomical Society of the Pacific (2008, January), 392

We present a new analysis of the short period pulsating sdB star Feige 48 using the same observations as done in our previous work, but exploiting, this time, our new period-matching codes that include ... [more ▼]

We present a new analysis of the short period pulsating sdB star Feige 48 using the same observations as done in our previous work, but exploiting, this time, our new period-matching codes that include the rotation of the star. The pulsation spectrum of Feige 48 shows the signature of rotational splitting with a mean frequency spacing of about 28 μHz between the components of three different frequency multiplets. In addition, Feige 48 has been shown to be a member of a close binary system with an invisible (most likely a white dwarf) companion. Assuming various internal rotation laws, we are now able to fit all nine observed frequencies simultaneously, and not only the four m = 0 components that we identified a priori in our previous effort. For solid body rotation, our optimal model shows slightly different structural parameters than those obtained previously on the basis of purely spherical models. Interestingly, that optimal model is also characterized by a rotation period of 9.028 h, which falls exactly on the value of the orbital period found independently from spectroscopy, namely, 9.024 ± 0.072 h. This very strongly implies that Feige 48 is tidally locked, a suggestion quite consistent with theoretical expectations for such a close binary system. In the same vein, our investigations also demonstrate explicitly that the idea of a fast rotating core can be eliminated for Feige 48. [less ▲]

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See detailAn Asteroseismological Study of the Rapidly Pulsating Subdwarf B Star PG 0911+456
Randall, Suzanna K.; Green, Elizabeth M.; Van Grootel, Valérie ULg et al

in Leaflet - Astronomical Society of the Pacific (2008, January), 392

We present the analysis and interpretation of 57 hours of time-series photometry obtained with the new Mont4kccd on Mt. Bigelow, Arizona, for the rapidly pulsating sdB star PG 0911+456. Thanks to the ... [more ▼]

We present the analysis and interpretation of 57 hours of time-series photometry obtained with the new Mont4kccd on Mt. Bigelow, Arizona, for the rapidly pulsating sdB star PG 0911+456. Thanks to the impressively high S/N of the data we were able to extract 7 independent periodicities in the 140-200 s range with amplitudes down to 0.05 % of the mean stellar brightness. On the basis of these we performed an asteroseismological search for the optimal model and derived the star's fundamental parameters. Given that there are now 12 sdB stars for which asteroseismology has been performed, the results are starting to become significant from a statistical point of view and evolutionary trends are slowly emerging. [less ▲]

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See detailAsteroseismology and mode driving of the Herbig Ae star HD 104237
Dupret, Marc-Antoine ULg; Théado, S.; Böhm, T. et al

in 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 ▲]

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See detailAsteroseismology in action: a test of spin-orbit synchronism in the close binary system Feige 48
Van Grootel, Valérie ULg; Charpinet, Stéphane; Fontaine, Gilles et al

in Astronomy and Astrophysics (2008), 483

Aims. In this paper, we provide a test of spin-orbit synchronism in the close binary system Feige 48. This system is made of a rapidly pulsating subdwarf B (sdB) star with an unseen companion, most likely ... [more ▼]

Aims. In this paper, we provide a test of spin-orbit synchronism in the close binary system Feige 48. This system is made of a rapidly pulsating subdwarf B (sdB) star with an unseen companion, most likely a white dwarf. The presence of nonradial oscillations offers the opportunity to infer the inner profile and period of rotation of the primary star through asteroseismology. This constitutes the key element for testing spin-orbit synchronism in depth, since stellar internal layers are inaccessible to traditional techniques. Methods. We carried out a new asteroseismic analysis of Feige 48 following the so-called “forward modeling” approach. This is done with our latest optimization algorithms, which have been updated to incorporate the effect of stellar rotation on pulsations, assuming various internal rotation laws. In this analysis, the simultaneous match of all the frequencies observed in Feige 48 leads objectively to the full identification of the pulsation modes through the determination of the indices k, l, m. It also leads to determining the structural and rotational parameters of Feige 48. Results. Our optimal model, obtained with a solid-body rotation law, is characterized by a spin period of 9.028 ± 0.480 h. This value is remarkably similar to the system’s orbital period of 9.024 ± 0.072 h, measured independently from radial velocity variations. We further demonstrate that the hypothesis of differential rotation of the core – including a fast rotating core – must be eliminated for Feige 48. Conclusions. These results strongly imply that Feige 48 rotates as a solid body in a tidally locked system. This constitutes the first explicit demonstration of spin-orbit synchronism in a binary star by asteroseismic means. [less ▲]

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See detailAsteroseismology of beta Cephei stars
Thoul, Anne ULg

Scientific conference (2011, October)

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See detailAsteroseismology of B stars
Thoul, Anne ULg

in Communications in Asteroseismology (2009), 159

Numerous B stars on the main sequence are found to be variable. These stars have a relatively simple structure, and yet they present some very interesting challenges. It is important to understand these ... [more ▼]

Numerous B stars on the main sequence are found to be variable. These stars have a relatively simple structure, and yet they present some very interesting challenges. It is important to understand these stars before we can expect to be able to understand stars which have a more complicated internal structure. Asteroseismology of B stars has made considerable progress in the last few years, thanks to the observations obtained from large multisite campaigns, and it is now possible to determine global parameters for these stars such as their masses, ages, metallicities, with very high accuracy. Many variable B stars are also observed with the CoRoT space mission, and statistical studies may become possible in the near future. Detailed studies of the oscillation spectra of β Cephei stars have already allowed to put some limits on the overshooting parameter, and this overshooting parameter is found to vary from one star to the next. Some β Cephei stars are found to present differential rotation in their envelopes, while others are compatible with solid body rotation. Some B stars present nitrogen enhancement, even though they are very slow rotators. The instability strips of B stars differ depending on the composition and the opacity tables adopted. Microscopic diffusion and radiative accelerations could produce an accumulation of iron-group elements in some layers of these stars. Hybrid pulsators, showing both β Cephei and SPB pulsations have been observed. Some of the best observed stars have pulsation spectra which still cannot be reproduced by modelling. Here I review the present status of the observations and of the modelling of β Cephei stars, emphasizing both the successes reached and the questions and problems which remain open today. [less ▲]

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See detailAsteroseismology of B stars with MESA
Thoul, Anne ULg

Conference (2013, December)

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See detailAsteroseismology of beta Cephei stars: effects of the chemical composition
Thoul, Anne ULg

Conference (2007, August)

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See detailAsteroseismology of delta Scuti Stars: Problems and Prospects
Goupil, Marie-José; Dupret, Marc-Antoine ULg; Samadi, R. et al

in 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 ▲]

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See detailAsteroseismology of evolved stars: from hot B subdwarfs to white dwarfs
Van Grootel, Valérie ULg; Fontaine, G.; Charpinet, S. et al

Conference (2014, September)

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See detailAsteroseismology of HD 129929: Core Overshooting and Nonrigid Rotation
Aerts, C.; Thoul, Anne ULg; Daszynska, J. et al

in Science (2003), 300

We have gathered and analyzed 1493 high-quality multicolor Geneva photometric data taken over 21 years of the B3V star HD 129929. We detect six frequencies, among which appear the effects of rotational ... [more ▼]

We have gathered and analyzed 1493 high-quality multicolor Geneva photometric data taken over 21 years of the B3V star HD 129929. We detect six frequencies, among which appear the effects of rotational splitting with a spacing of ~0.0121 cycles per day, which implies that the star rotates very slowly. A nonadiabatic analysis of the oscillations allows us to constrain the metallicity of the star to Z â [0.017,0.022], which agrees with a similar range derived from spectroscopic data. We provide evidence for the occurrence of core convective overshooting in the star, with alpha[SUB]ov[/SUB] = 0.10 +/- 0.05, and we rule out rigid rotation. [less ▲]

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See detailAsteroseismology of hot B subdwarf stars
Charpinet, Stéphane; Van Grootel, Valérie ULg; Brassard, Pierre et al

in EPJ Web of Conferences (2013, March), 43

Nonradial pulsations in Extreme Horizontal Branch stars (also known as hot B subdwarfs or sdB stars) offer strong opportunities to study through asteroseismology the structure and internal dynamics of ... [more ▼]

Nonradial pulsations in Extreme Horizontal Branch stars (also known as hot B subdwarfs or sdB stars) offer strong opportunities to study through asteroseismology the structure and internal dynamics of stars in this intermediate stage of stellar evolution. Most sdB stars directly descend from former red giants and are expected to evolve straight into white dwarfs after core helium exhaustion. They thus represent the most direct link between these two stages. Their properties should therefore reflect both the outcome of the core evolution of red giant stars and the initial state for a fraction of the white dwarfs. We review the status of this field after a decade of efforts to exploit both p-mode and g-mode pulsating sdB stars as asteroseismic laboratories. From the discoveries of these two classes of pulsators in 1997 and 2003, respectively, up to the current epoch of data gathering of unprecedented quality from space, a lot of progress has been made in this area and prospects for future achievements look very promising. [less ▲]

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See detailAsteroseismology of OB stars with CoRoT
Degroote, P.; Aerts, C.; Samadi, R. et al

in Astronomische Nachrichten (2010), 331

The CoRoT satellite is revolutionizing the photometric study of massive O-type and B-type stars. During its long runs, CoRoT observed the entire main sequence B star domain, from typical hot β Cep stars ... [more ▼]

The CoRoT satellite is revolutionizing the photometric study of massive O-type and B-type stars. During its long runs, CoRoT observed the entire main sequence B star domain, from typical hot β Cep stars, via cooler hybrid p- and g-mode pulsators to the SPB stars near the edge of the instability strip. CoRoT lowers the sensitivity barrier from the typical mmag-precision reached from the ground, to the μmag-level reached from space. Within the wealth of detected and identified pulsation modes, relations have been found in the form of multiplets, combination of frequencies, and frequency- and period spacings. This wealth of observational evidence is finally providing strong constraints to test current models of the internal structure and pulsations of hot stars. Aside from the expected opacity driven modes with infinite lifetime, other unexpected types of variability are detected in massive stars, such as modes of stochastic nature. The simultaneous observation of all these light curve characteristics implies a challenge for both observational asteroseismology and stellar modelling. 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. [less ▲]

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See detailAsteroseismology of old open clusters with Kepler: direct estimate of the integrated red giant branch mass-loss in NGC 6791 and 6819
Miglio, A.; Brogaard, K.; Stello, D. et al

in Monthly Notices of the Royal Astronomical Society (2012), 419

Mass-loss of red giant branch (RGB) stars is still poorly determined, despite its crucial role in the chemical enrichment of galaxies. Thanks to the recent detection of solar-like oscillations in G-K ... [more ▼]

Mass-loss of red giant branch (RGB) stars is still poorly determined, despite its crucial role in the chemical enrichment of galaxies. Thanks to the recent detection of solar-like oscillations in G-K giants in open clusters with Kepler, we can now directly determine stellar masses for a statistically significant sample of stars in the old open clusters NGC 6791 and 6819. The aim of this work is to constrain the integrated RGB mass-loss by comparing the average mass of stars in the red clump (RC) with that of stars in the low-luminosity portion of the RGB [i.e. stars with L≲L(RC)]. Stellar masses were determined by combining the available seismic parameters ν[SUB]max[/SUB] and Δν with additional photometric constraints and with independent distance estimates. We measured the masses of 40 stars on the RGB and 19 in the RC of the old metal-rich cluster NGC 6791. We find that the difference between the average mass of RGB and RC stars is small, but significant [? (random) ±0.04 (systematic) M[SUB]&sun;[/SUB]]. Interestingly, such a small ? does not support scenarios of an extreme mass-loss for this metal-rich cluster. If we describe the mass-loss rate with Reimers prescription, a first comparison with isochrones suggests that the observed ? is compatible with a mass-loss efficiency parameter in the range 0.1 ≲η≲ 0.3. Less stringent constraints on the RGB mass-loss rate are set by the analysis of the ˜2 Gyr old NGC 6819, largely due to the lower mass-loss expected for this cluster, and to the lack of an independent and accurate distance determination. In the near future, additional constraints from frequencies of individual pulsation modes and spectroscopic effective temperatures will allow further stringent tests of the Δν and ν[SUB]max[/SUB] scaling relations, which provide a novel, and potentially very accurate, means of determining stellar radii and masses. [less ▲]

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See detailAsteroseismology of red-clump stars with CoRoT and Kepler
Miglio, Andrea ULg; Montalban Iglesias, Josefa ULg; Eggenberger, P. et al

in AIP Conference Proceedings (2009), 1170

The availability of asteroseismic constraints for a large number of red giants with CoRoT and, in the near future with Kepler, paves the way for detailed studies of populations of galactic-disk red giants ... [more ▼]

The availability of asteroseismic constraints for a large number of red giants with CoRoT and, in the near future with Kepler, paves the way for detailed studies of populations of galactic-disk red giants. We investigate which information on the observed population can be recovered by the distribution of the observed seismic constraints: the frequency of maximum power of solar-like oscillations (νmax) and the large frequency separation (Δν). We use the distribution of νmax and of Δν observed by CoRoT in nearly 800 red giants in the first long observational run, as a tool to investigate the properties of galactic red-giant stars through the comparison with simulated distributions based on synthetic stellar populations. We can clearly identify the bulk of the red giants observed by CoRoT as red-clump stars, i.e. post-flash core-He-burning stars. The distribution of νmax and of Δν give us access to the distribution of the stellar radius and mass, and thus represent a most promising probe of the age and star formation rate of the disk, and of the mass-loss rate during the red-giant branch. This approach will be of great utility also in the interpretation of forthcoming surveys of variability of red giants with CoRoT and Kepler. In particular, an asteroseismic mass estimate of clump stars in the old-open clusters observed by Kepler, would represent a most valuable observational test of the poorly known mass-loss rate on the giant branch, and of its dependence on metallicity. [less ▲]

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See detailAsteroseismology of solar-type stars with Kepler I: Data analysis
Karoff, C.; Chaplin, W. J.; Appourchaux, T. et al

in Astronomische Nachrichten (2010), 331

We report on the first asteroseismic analysis of solar-type stars observed by Kepler. Observations of three G-type stars, made at one-minute cadence during the first 33.5 days of science operations ... [more ▼]

We report on the first asteroseismic analysis of solar-type stars observed by Kepler. Observations of three G-type stars, made at one-minute cadence during the first 33.5 days of science operations, reveal high signal-to-noise solar-like oscillation spectra in all three stars: About 20 modes of oscillation can clearly be distinguished in each star. We discuss the appearance of the oscillation spectra, including the presence of a possible signature of faculae, and the presence of mixed modes in one of the three stars. [less ▲]

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See detailAsteroseismology of solar-type stars with Kepler: III. Ground-based data
Molenda-Żakowicz, J.; Bruntt, H.; Sousa, S. et al

in Astronomische Nachrichten (2010), 331

We report on the ground-based follow-up program of spectroscopic and photometric observations of solar-like asteroseismic targets for the Kepler space mission. These stars constitute a large group of more ... [more ▼]

We report on the ground-based follow-up program of spectroscopic and photometric observations of solar-like asteroseismic targets for the Kepler space mission. These stars constitute a large group of more than a thousand objects which are the subject of an intensive study by the Kepler Asteroseismic Science Consortium Working Group 1 (KASC WG-1). In the current work we will discuss the methods we use to determine the fundamental stellar atmospheric parameters using high-quality stellar spectra. These provide essential constraints for the asteroseismic modelling and make it possible to verify the parameters in the Kepler Input Catalogue (KIC). [less ▲]

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See detailAsteroseismology of the beta Cep star HD 129929. I. Observations, oscillation frequencies and stellar parameters
Aerts, C.; Waelkens, C.; Daszynska-Daszkiewicz, J. et al

in Astronomy and Astrophysics (2004), 415

We have gathered and analysed a timeseries of 1493 high-quality multicolour Geneva photometric data of the B3V beta Cep star HD 129929. The dataset has a time base of 21.2 years. The occurrence of a ... [more ▼]

We have gathered and analysed a timeseries of 1493 high-quality multicolour Geneva photometric data of the B3V beta Cep star HD 129929. The dataset has a time base of 21.2 years. The occurrence of a beating phenomenon is evident from the data. We find evidence for the presence of at least six frequencies, among which we see components of two frequency multiplets with an average spacing of Ë 0.0121 c d[SUP]-1[/SUP] which points towards very slow rotation. This result is in agreement with new spectroscopic data of the star and also with previously taken UV spectra. We provide the amplitudes of the six frequencies in all seven photometric filters. The metal content of the star is Z=0.018± 0.004. All these observational results will be used to perform detailed seismic modelling of this massive star in a subsequent paper. Based on data gathered with the Swiss 0.7m telescope equipped with the photometer P7 of the Geneva Observatory and with the FEROS spectrograph attached to the ESO 2.2 m telescope, both situated at La Silla in Chile; the reduced photometric multicolour data are provided in Table 1, which is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/415/241 [less ▲]

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See detailAsteroseismology of the beta Cep star HD 129929. II. Seismic constraints on core overshooting, internal rotation and stellar parameters
Dupret, Marc-Antoine ULg; Thoul, Anne ULg; Scuflaire, Richard ULg et al

in Astronomy and Astrophysics (2004), 415

We perform a detailed seismic study of the beta Cep star HD 129929. Our analysis is based on the recent derivation of six pulsation frequencies. These frequencies are unambiguously identified from the ... [more ▼]

We perform a detailed seismic study of the beta Cep star HD 129929. Our analysis is based on the recent derivation of six pulsation frequencies. These frequencies are unambiguously identified from the seismic modelling and the photometric amplitudes to be the radial fundamental, the l=1, p[SUB]1[/SUB] triplet, two consecutive components of the l=2, g[SUB]1[/SUB] quintuplet. A non-adiabatic analysis allows us to constrain the metallicity of the star to Z \in [0.016, 0.022]. In addition, the fitting of three independent frequencies, two of which correspond to axisymmetric (m=0) modes, allows us to constrain the core overshooting parameter to alpha[SUB]ov[/SUB]=0.10 ± 0.05, as well as the other global parameters of the star. Finally, from the observation of the l=1 triplet and part of the l=2 quintuplet, we derive constraints on the internal rotation of this star. [less ▲]

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See detailAsteroseismology of the Beta Cephei star HD 129929. Effects of a change in the metal mixture
Thoul, Anne ULg; Scuflaire, Richard ULg; Ausseloos, M. et al

in Communications in Asteroseismology (2004), 144

We show that the constraints on the mass and on the rotation law in the envelope of the Beta Cephei star HD129929 are robust against a change in the metal mixture. The constraints on the metallicity and ... [more ▼]

We show that the constraints on the mass and on the rotation law in the envelope of the Beta Cephei star HD129929 are robust against a change in the metal mixture. The constraints on the metallicity and on the overshooting parameter, however, are dependent on the assumed metal mixture. [less ▲]

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