The present work performs an asteroseismic study of a γ Doradus star member of the open cluster N... more The present work performs an asteroseismic study of a γ Doradus star member of the open cluster NGC 2506. This works conjugates the observational information of the star and the strong constraints imposed by the cluster memebership, with the latest developed theoretical asteroseismic tools for the modelling of this type of objects, in particular the Frequency Ratio Method (FRM) and Time-Dependent Convection (TDC), to study the γ Dor stars found in the NGC 2506 stellar cluster. The use of both techniques gives us the opportunity of constructing a self-consistent procedure, allowing the mode identification and improving the modelling of the γ Dor members of the cluster. In this work we present the result of the analysis of the first target of our project, showing the advantadge of modelling cluster member's γ Dor stars. This is the first step in a more ambitious project. In the near future, we plan to expand the study to other variable members of the NGC 2506 cluster. This will improve our knowledge of γ Dor pulsatorsand probe the self-consistency of our procedures.
It has been suggested that the detection of a wealth of very low amplitude modes in δ Sct stars w... more It has been suggested that the detection of a wealth of very low amplitude modes in δ Sct stars was only a matter of signal-to-noise ratio. Access to this treasure, impossible from the ground, is one of the scientific aims of the space mission CoRoT, developed and operated by CNES. This work presents the results obtained on HD 50844: the 140,016 datapoints allowed us to reach the level of 10 −5 mag in the amplitude spectra. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0-30 d −1. The initial guess that δ Sct stars have a very rich frequency content is confirmed. The spectroscopic mode identification gives theoretical support since very high-degree modes (up to ℓ=14) are identified. We also prove that cancellation effects are not sufficient in removing the flux variations associated to these modes at the noise level of the CoRoT measurements. The ground-based observations indicate that HD 50844 is an evolved star that is slightly underabundant in heavy elements, located on the Terminal Age Main Sequence. The predominant term (f 1 =6.92 d −1) has been identified as the fundamental radial mode combining ground-based photometric and spectroscopic data.
We present an improved version of the method of photometric mode identification based upon the in... more We present an improved version of the method of photometric mode identification based upon the inclusion of non-adiabatic eigenfunctions determined in the stellar atmosphere, according to the formalism recently proposed by Dupret et al. (2002). We apply our method to β Cephei, Slowly Pulsating B, δ Scuti and γ Doradus stars. Besides identifying the degree of the pulsating stars, our method is also a tool for improving the knowledge of stellar interiors and atmospheres, by imposing constraints on the metallicity for β Cephei and SPBs, the characteristics of the superficial convection zone for δ Scuti and γ Doradus stars and the limb-darkening law.
Monthly Notices of the Royal Astronomical Society: Letters, 2011
We present the results of the first theoretical non-radial non-adiabatic pulsational study of M d... more We present the results of the first theoretical non-radial non-adiabatic pulsational study of M dwarf stellar models with masses in the range 0.1 to 0.5 M⊙. We find the fundamental radial mode to be unstable due to an ǫ mechanism, caused by deuterium (D-) burning for the young 0.1 and 0.2 M⊙ models, by non-equilibrium He 3 burning for the 0.2 and 0.25 M⊙ models of 10 4 Myr, and by a flux blocking mechanism for the partially convective 0.4 and 0.5 M⊙ models once they reach the age of 500 Myr. The periods of the overstable modes excited by the D-burning are in the range 4.2 to 5.2 h for the 0.1 M⊙ models and is of order 8.4 h for the 0.2 M⊙ models. The periods of the modes excited by He 3 burning and flux blocking are in the range 23 to 40 min. The more massive and oldest models are more promising for the observational detection of pulsations, as their ratio of instability e-folding time to age is more favourable.
Monthly Notices of the Royal Astronomical Society, 2010
A spectroscopic analysis of Sloan Digital Sky Survey (SDSS) J160043.6+074802.9, a binary system c... more A spectroscopic analysis of Sloan Digital Sky Survey (SDSS) J160043.6+074802.9, a binary system containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields T eff = 70 000 ± 5000 K and log g = 5.25 ± 0.30, together with a most likely type of K3 V for the secondary star. We compare our results with atmospheric parameters derived by Fontaine et al. and in the context of existing evolution models for sdO stars. New and more extensive photometry is also presented which recovers most, but not all, frequencies found in an earlier paper. Therefore, it seems probable that some pulsation modes have variable amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO models show those having log g > 5.3 to be more likely to be unstable and capable of driving pulsation in the observed frequency range.
Monthly Notices of the Royal Astronomical Society, 2004
We present the results of a three-continent multisite photometric campaign carried out on the Alg... more We present the results of a three-continent multisite photometric campaign carried out on the Algol-type eclipsing binary system RZ Cas, in which the primary component has recently been discovered to be a δ Sct-type pulsator. The present observations include, for the first time, complete simultaneous Strömgren uvby light curves together with a few Crawford Hβ data collected around the orbital phase of the first quadrature. The new observations confirm the pulsational behaviour of the primary component. A detailed photometric analysis, based on these observations, is presented for both binarity and pulsation. The results indicate a semidetached system where the secondary fills its Roche lobe. The appearance of the light curves reveals the presence of the mass stream from the secondary component and a hotspot where this stream impacts on the surface of the primary star. There are also some indications of chromospheric activity in the secondary. On the other hand, the pulsational behaviour out-of-primary eclipse can be well described with only one frequency at 64.1935 cd −1 similar to the main peak found by Ohshima et al. The existence of multiperiodicity is not confirmed in our data. Concerning the mode identification, our results indicate non-radial pulsation in a high radial order (n = 6), with l = 2, |m| = 1, 2 as the most suitable. However, additional effects must be taken into account in the predictions. Moreover, the pulsation amplitude in the u band is larger than in b and v, which is unusual among the δ Sct-type variables. This can be explained as due to pulsation in a high n value and close to the blue edge of the δ Sct region. On the other hand, the early data of Ohshima et al. have also been analysed and similar results are found concerning the frequency content and pulsational amplitude. Finally, a revision of all the photometric out-of-primary-eclipse data sets available in the literature is made together with some additional unpublished data leading to interesting findings relative to changes taking place in the pulsation amplitudes and frequencies from season to season. Furthermore, multiperiodicity is probably present in some epochs.
Observations of the pulsations of stars can be used to infer their interior structure and test th... more Observations of the pulsations of stars can be used to infer their interior structure and test theoretical models. The main sequence γ Doradus (Dor) and δ Scuti (Sct) stars with masses 1.2-2.5 M ⊙ are particularly useful for these studies. The γ Dor stars pulsate in high-order g modes with periods of order 1 day, driven by convective blocking at the base of their envelope convection zone. The δ Sct stars pulsate in low-order g and p modes with periods of order 2 hours, driven by the κ mechanism operating in the He ii ionization zone. Theory predicts an overlap region in the Hertzsprung-Russell diagram between instability regions, where 'hybrid' stars pulsating in both types of modes should exist. The two types of modes with properties governed by different portions of the stellar interior provide complementary model constraints. Among the known γ Dor and δ Sct stars, only four have been confirmed as hybrids. Now, analysis of combined Quarter 0 and Quarter 1 Kepler data for hundreds of variable stars shows that the frequency spectra are so rich that there are practically no pure δ Sct or γ Dor pulsators, i.e. essentially all of the stars show frequencies in both the δ Sct and γ Dor frequency range. A new observational classification scheme is proposed that takes into account the amplitude as well as the frequency, and is applied to categorize 234 stars as δ Sct, γ Dor, δ Sct/γ Dor or γ Dor/δ Sct hybrids.
The forthcoming data expected from space missions such as CoRoT require the capacity of the avail... more The forthcoming data expected from space missions such as CoRoT require the capacity of the available tools to provide accurate models whose numerical precision is well above the expected observational errors. In order to secure that these tools meet the specifications, a team has been established to test and, when necessary, to improve the codes available in the community. The CoRoT evolution and seismic tool activity (ESTA) has been set up with this mission. Several groups have been involved. The present paper describes the motivation and the organisation of this activity, providing the context and the basis for the presentation of the results that have been achieved so far. This is not a finished task as future even better data will continue to demand more precise and complete tools for asteroseismology.
HD 172189 is a spectroscopic eclipsing binary system with a rapidly-rotating pulsating δ Scuti co... more HD 172189 is a spectroscopic eclipsing binary system with a rapidly-rotating pulsating δ Scuti component. It is also a member of the open cluster IC 4756. These combined characteristics make it an excellent laboratory for asteroseismic studies. To date, HD 172189 has been analysed in detail photometrically but not spectroscopically. For this reason we have compiled a set of spectroscopic data to determine the absolute and atmospheric parameters of the components. We determined the radial velocities (RV) of both components using four different techniques. We disentangled the binary spectra using KOREL, and performed the first abundance analysis on both disentangled spectra. By combining the spectroscopic results and the photometric data, we obtained the component masses, 1.8 and 1.7 M , and radii, 4.0 and 2.4 R , for inclination i = 73.2 • , eccentricity e = 0.28, and orbital period Π = 5.70198 days. Effective temperatures of 7600 K and 8100 K were also determined. The measured v sin i are 78 and 74 km s −1 , respectively, giving rotational periods of 2.50 and 1.55 days for the components. The abundance analysis shows [Fe/H] =-0.28 for the primary (pulsating) star, consistent with observations of IC 4756. We also present an assessment of the different analysis techniques used to obtain the RVs and the global parameters.
We present a study based on more than 2500 uvby-measurements collected on HD 172189, a new eclips... more We present a study based on more than 2500 uvby-measurements collected on HD 172189, a new eclipsing binary system with a δ Sct-type pulsating component that belongs to the open cluster IC 4756. The great interest of this object lies in that three important characteristics coexist: cluster membership, binarity and pulsation. Its binarity and the δ Sct-type pulsations of one component were detected in the course of several Strömgren photometric campaigns. The frequency analysis of all the uvby out-of-eclipse data reveals a clear frequency of 19.5974 cd −1 as well as the existence of other high values in the range 18-20 cd −1. We have also carried out a first evaluation of the binary parameters and determined a value of 5.702 d for the orbital period. An additional potential interest of HD 172189 resides in its location in the field of view of the COROT mission and, therefore, this star is an excellent candidate for becoming a target for asteroseismology.
Aims. This work presents the results obtained by CoRoT on HD 50844, the only δ Sct star observed ... more Aims. This work presents the results obtained by CoRoT on HD 50844, the only δ Sct star observed in the CoRoT initial run (57.6 d). The aim of these CoRoT observations was to investigate and characterize for the first time the pulsational behaviour of a δ Sct star, when observed at a level of precision and with a much better duty cycle than from the ground. Methods. The 140 016 datapoints were analysed using independent approaches (SigSpec software and different iterative sine-wave fittings) and several checks performed (splitting of the timeseries in different subsets, investigation of the residual light curves and spectra). A level of 10 −5 mag was reached in the amplitude spectra of the CoRoT timeseries. The space monitoring was complemented by ground-based high-resolution spectroscopy, which allowed the mode identification of 30 terms. Results. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0-30 d −1. All the crosschecks confirmed this new result. The initial guess that δ Sct stars have a very rich frequency content is confirmed. The spectroscopic mode identification gives theoretical support since very high-degree modes (up to = 14) are identified. We also prove that cancellation effects are not sufficient in removing the flux variations associated to these modes at the noise level of the CoRoT measurements. The ground-based observations indicate that HD 50844 is an evolved star that is slightly underabundant in heavy elements, located on the Terminal Age Main Sequence. Probably due to this unfavourable evolutionary status, no clear regular distribution is observed in the frequency set. The predominant term (f 1 = 6.92 d −1) has been identified as the fundamental radial mode combining ground-based photometric and spectroscopic data.
Context. BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a v... more Context. BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a very complex frequency spectrum is detected, with a number of independent nonradial modes excited, unusual among the high-amplitude pulsators in the Lower Classical Instability Strip. Aims. An extensive and detailed study has been carried out to investigate the pulsational content and properties of this object. Methods. The analysis is based on 283 h of CCD observations obtained in the Johnson V filter, during a long multisite photometric campaign carried out along the Northern autumn-winter of 2005-2006. Additionally, multicolour BI photometry was also collected to study the phase shifts and amplitude ratios, between light curves obtained in different filters, for modal discrimination of the main excited modes. Results. The detailed frequency analysis revealed a very rich and dense pulsational content consisting of 25 significant peaks, 22 of them corresponding to independent modes: one is the already known main periodicity f 0 = 25.5765 cd −1 (∆V = 153 mmag) and the other 21 are excited modes showing very small amplitudes. Some additional periodicities are probably still remaining in the residuals. This represents the most complex spectrum ever detected in a high-amplitude pulsator of this type. The majority of the secondary modes suspected from earlier works are confirmed here and, additionally, a large number of new peaks are detected. The amplitude of the main periodicity f 0 seems to be stable during decades, but the majority of the secondary modes show strong amplitude changes from one epoch to another. The suspected fundamental radial nature of the main periodicity of BL Cam is confirmed, while the secondary peak f 1 = 25.2523 cd −1 is identified as a nonradial mixed mode g 4 with = 1. The radial double-mode nature, claimed by some authors for the main two frequencies of BL Cam, is not confirmed. Nevertheless, the frequency f 6 = 32.6464 cd −1 could correspond to the first radial overtone.
Context. The high accuracy of space data increased the number of the periodicities determined for... more Context. The high accuracy of space data increased the number of the periodicities determined for pulsating variable stars, but the mode identification is still a critical point in the non-asymptotic regime. Aims. We use regularities in frequency spacings for identifying the pulsation modes of the recently discovered δ Sct star ID 102749568. Methods. In addition to analysing CoRoT light curves (15 252 datapoints spanning 131 days), we obtained and analysed both spectroscopic and extended multi-colour photometric data. We applied standard tools (MUFRAN, Period04, SigSpec, and FAMIAS) for time-series analysis. Results. A satisfactory light-curve fit was obtaining by means of 52 independent modes and 15 combination terms. The frequency spacing revealed distinct peaks around large (25.55-31.43 μHz), intermediate (9.80, 7.66 μHz), and low (2.35 μHz) separations. We directly identified 9 modes, and the l and n values of other three modes were extrapolated. The combined application of spectroscopy, multi-colour photometry, and modelling yielded the precise physical parameters and confirmed the observational mode identification. The large separation constrained the log g and related quantities. The dominant mode is the radial first overtone.
Many questions are still open regarding the structure and the dynamics of the solar core. By cons... more Many questions are still open regarding the structure and the dynamics of the solar core. By constraining more this region in the solar evolution models, we can reduce the incertitudes on some physical processes and on momentum transport mechanisms. A first big step was made with the detection of the signature of the dipole-gravity modes in the Sun, giving a
From the recent work of the Evolution and Seismic Tools Activity (ESTA, Monteiro et al., 2006; Le... more From the recent work of the Evolution and Seismic Tools Activity (ESTA, Monteiro et al., 2006; Lebreton et al., 2008), whose Task 2 is devoted to compare pulsational frequencies computed using most of the pulsational codes available in the asteroseismic community, the dependence of the theoretical frequencies with non-physical choices is now quite well fixed. To ensure that the accuracy of the computed frequencies is of the same order of magnitude or better than the observational errors, some requirements in the equilibrium models and the numerical resolutions of the pulsational equations must be followed. In particular, we have verified the numerical accuracy obtained with the Saclay seismic model, which is used to study the solar g-mode region (60 to 140µHz). We have compared the results coming from the Aarhus adiabatic pulsation code (ADIPLS), with the frequencies computed with the Granada Code (GraCo) taking into account several possible choices. We have concluded that the present equilibrium models and the use of the Richardson extrapolation ensure an accuracy of the order of 0.01µHz in the determination of the frequencies, which is quite enough for our purposes.
Monthly Notices of the Royal Astronomical Society, 2010
We present the first description of mode trapping for sdO models. Mode trapping of gravity modes ... more We present the first description of mode trapping for sdO models. Mode trapping of gravity modes caused by the He/H chemical transition is found for a particular model, providing a selection effect for high radial order trapped modes. Low-and intermediate-radial order p-modes (mixed modes with a majority of nodes in the Pmode region) are found to be trapped by the C-O/He transition, but with no significant effects on the driving. This region seems to have also a subtle effect on the trapping of low radial order g-modes (mixed modes with a majority of nodes in the G-mode region), but again with no effect on the driving. We found that for mode trapping to have an influence on the driving of sdO modes (1) the mode should be trapped in a way that the amplitude of the eigenfunctions is lower in a damping region and (2) in this damping region significant energy interchange has to be produced.
Monthly Notices of the Royal Astronomical Society, 2010
We have explored the possibility of driving pulsation modes in models of sdO stars in which the e... more We have explored the possibility of driving pulsation modes in models of sdO stars in which the effects of element diffusion, gravitational settling and radiative levitation have been neglected so that the distribution of iron-peak elements remains uniform throughout the evolution. The stability of these models was determined using a nonadiabatic oscillations code. We analysed 27 sdO models from 16 different evolutionary sequences and discovered the first ever sdO models capable of driving high-radial order g-modes. In one model, the driving is by a classical κ-mechanism due to the opacity bump from iron-peak elements at temperature ∼ 200, 000 K. In a second model, the driving result from the combined action of κ-mechanisms operating in three distinct regions of the star: (i) a carbon-oxygen partial ionization zone at temperature ∼ 2 10 6 K, (ii) a deeper region at temperature ∼ 2 10 7 K, which we attribute to ionization of argon, and (iii) at the transition from radiative to conductive opacity in the core of the star.
Monthly Notices of the Royal Astronomical Society, 2013
The overstability of the fundamental radial mode in M dwarf models was theoretically predicted re... more The overstability of the fundamental radial mode in M dwarf models was theoretically predicted recently by Rodríguez-López et al. The periods were found to be in the ranges ∼25-40 min and ∼4-8 h, depending on stellar age and excitation mechanism. We have extended our initial M dwarf model grid in mass, metallicity and mixing length parameter. We have also considered models with boundary conditions from PHOENIX NEXTGEN atmospheres to test their influence on the pulsation spectra. We find instability of non-radial modes with radial orders up to k = 3, degree = 0-3, including p-and g-modes, with the period range extending from 20 min up to 11 h. Furthermore, we find theoretical evidence of the potential of M dwarfs as solar-like oscillators.
The present work performs an asteroseismic study of a γ Doradus star member of the open cluster N... more The present work performs an asteroseismic study of a γ Doradus star member of the open cluster NGC 2506. This works conjugates the observational information of the star and the strong constraints imposed by the cluster memebership, with the latest developed theoretical asteroseismic tools for the modelling of this type of objects, in particular the Frequency Ratio Method (FRM) and Time-Dependent Convection (TDC), to study the γ Dor stars found in the NGC 2506 stellar cluster. The use of both techniques gives us the opportunity of constructing a self-consistent procedure, allowing the mode identification and improving the modelling of the γ Dor members of the cluster. In this work we present the result of the analysis of the first target of our project, showing the advantadge of modelling cluster member's γ Dor stars. This is the first step in a more ambitious project. In the near future, we plan to expand the study to other variable members of the NGC 2506 cluster. This will improve our knowledge of γ Dor pulsatorsand probe the self-consistency of our procedures.
It has been suggested that the detection of a wealth of very low amplitude modes in δ Sct stars w... more It has been suggested that the detection of a wealth of very low amplitude modes in δ Sct stars was only a matter of signal-to-noise ratio. Access to this treasure, impossible from the ground, is one of the scientific aims of the space mission CoRoT, developed and operated by CNES. This work presents the results obtained on HD 50844: the 140,016 datapoints allowed us to reach the level of 10 −5 mag in the amplitude spectra. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0-30 d −1. The initial guess that δ Sct stars have a very rich frequency content is confirmed. The spectroscopic mode identification gives theoretical support since very high-degree modes (up to ℓ=14) are identified. We also prove that cancellation effects are not sufficient in removing the flux variations associated to these modes at the noise level of the CoRoT measurements. The ground-based observations indicate that HD 50844 is an evolved star that is slightly underabundant in heavy elements, located on the Terminal Age Main Sequence. The predominant term (f 1 =6.92 d −1) has been identified as the fundamental radial mode combining ground-based photometric and spectroscopic data.
We present an improved version of the method of photometric mode identification based upon the in... more We present an improved version of the method of photometric mode identification based upon the inclusion of non-adiabatic eigenfunctions determined in the stellar atmosphere, according to the formalism recently proposed by Dupret et al. (2002). We apply our method to β Cephei, Slowly Pulsating B, δ Scuti and γ Doradus stars. Besides identifying the degree of the pulsating stars, our method is also a tool for improving the knowledge of stellar interiors and atmospheres, by imposing constraints on the metallicity for β Cephei and SPBs, the characteristics of the superficial convection zone for δ Scuti and γ Doradus stars and the limb-darkening law.
Monthly Notices of the Royal Astronomical Society: Letters, 2011
We present the results of the first theoretical non-radial non-adiabatic pulsational study of M d... more We present the results of the first theoretical non-radial non-adiabatic pulsational study of M dwarf stellar models with masses in the range 0.1 to 0.5 M⊙. We find the fundamental radial mode to be unstable due to an ǫ mechanism, caused by deuterium (D-) burning for the young 0.1 and 0.2 M⊙ models, by non-equilibrium He 3 burning for the 0.2 and 0.25 M⊙ models of 10 4 Myr, and by a flux blocking mechanism for the partially convective 0.4 and 0.5 M⊙ models once they reach the age of 500 Myr. The periods of the overstable modes excited by the D-burning are in the range 4.2 to 5.2 h for the 0.1 M⊙ models and is of order 8.4 h for the 0.2 M⊙ models. The periods of the modes excited by He 3 burning and flux blocking are in the range 23 to 40 min. The more massive and oldest models are more promising for the observational detection of pulsations, as their ratio of instability e-folding time to age is more favourable.
Monthly Notices of the Royal Astronomical Society, 2010
A spectroscopic analysis of Sloan Digital Sky Survey (SDSS) J160043.6+074802.9, a binary system c... more A spectroscopic analysis of Sloan Digital Sky Survey (SDSS) J160043.6+074802.9, a binary system containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields T eff = 70 000 ± 5000 K and log g = 5.25 ± 0.30, together with a most likely type of K3 V for the secondary star. We compare our results with atmospheric parameters derived by Fontaine et al. and in the context of existing evolution models for sdO stars. New and more extensive photometry is also presented which recovers most, but not all, frequencies found in an earlier paper. Therefore, it seems probable that some pulsation modes have variable amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO models show those having log g > 5.3 to be more likely to be unstable and capable of driving pulsation in the observed frequency range.
Monthly Notices of the Royal Astronomical Society, 2004
We present the results of a three-continent multisite photometric campaign carried out on the Alg... more We present the results of a three-continent multisite photometric campaign carried out on the Algol-type eclipsing binary system RZ Cas, in which the primary component has recently been discovered to be a δ Sct-type pulsator. The present observations include, for the first time, complete simultaneous Strömgren uvby light curves together with a few Crawford Hβ data collected around the orbital phase of the first quadrature. The new observations confirm the pulsational behaviour of the primary component. A detailed photometric analysis, based on these observations, is presented for both binarity and pulsation. The results indicate a semidetached system where the secondary fills its Roche lobe. The appearance of the light curves reveals the presence of the mass stream from the secondary component and a hotspot where this stream impacts on the surface of the primary star. There are also some indications of chromospheric activity in the secondary. On the other hand, the pulsational behaviour out-of-primary eclipse can be well described with only one frequency at 64.1935 cd −1 similar to the main peak found by Ohshima et al. The existence of multiperiodicity is not confirmed in our data. Concerning the mode identification, our results indicate non-radial pulsation in a high radial order (n = 6), with l = 2, |m| = 1, 2 as the most suitable. However, additional effects must be taken into account in the predictions. Moreover, the pulsation amplitude in the u band is larger than in b and v, which is unusual among the δ Sct-type variables. This can be explained as due to pulsation in a high n value and close to the blue edge of the δ Sct region. On the other hand, the early data of Ohshima et al. have also been analysed and similar results are found concerning the frequency content and pulsational amplitude. Finally, a revision of all the photometric out-of-primary-eclipse data sets available in the literature is made together with some additional unpublished data leading to interesting findings relative to changes taking place in the pulsation amplitudes and frequencies from season to season. Furthermore, multiperiodicity is probably present in some epochs.
Observations of the pulsations of stars can be used to infer their interior structure and test th... more Observations of the pulsations of stars can be used to infer their interior structure and test theoretical models. The main sequence γ Doradus (Dor) and δ Scuti (Sct) stars with masses 1.2-2.5 M ⊙ are particularly useful for these studies. The γ Dor stars pulsate in high-order g modes with periods of order 1 day, driven by convective blocking at the base of their envelope convection zone. The δ Sct stars pulsate in low-order g and p modes with periods of order 2 hours, driven by the κ mechanism operating in the He ii ionization zone. Theory predicts an overlap region in the Hertzsprung-Russell diagram between instability regions, where 'hybrid' stars pulsating in both types of modes should exist. The two types of modes with properties governed by different portions of the stellar interior provide complementary model constraints. Among the known γ Dor and δ Sct stars, only four have been confirmed as hybrids. Now, analysis of combined Quarter 0 and Quarter 1 Kepler data for hundreds of variable stars shows that the frequency spectra are so rich that there are practically no pure δ Sct or γ Dor pulsators, i.e. essentially all of the stars show frequencies in both the δ Sct and γ Dor frequency range. A new observational classification scheme is proposed that takes into account the amplitude as well as the frequency, and is applied to categorize 234 stars as δ Sct, γ Dor, δ Sct/γ Dor or γ Dor/δ Sct hybrids.
The forthcoming data expected from space missions such as CoRoT require the capacity of the avail... more The forthcoming data expected from space missions such as CoRoT require the capacity of the available tools to provide accurate models whose numerical precision is well above the expected observational errors. In order to secure that these tools meet the specifications, a team has been established to test and, when necessary, to improve the codes available in the community. The CoRoT evolution and seismic tool activity (ESTA) has been set up with this mission. Several groups have been involved. The present paper describes the motivation and the organisation of this activity, providing the context and the basis for the presentation of the results that have been achieved so far. This is not a finished task as future even better data will continue to demand more precise and complete tools for asteroseismology.
HD 172189 is a spectroscopic eclipsing binary system with a rapidly-rotating pulsating δ Scuti co... more HD 172189 is a spectroscopic eclipsing binary system with a rapidly-rotating pulsating δ Scuti component. It is also a member of the open cluster IC 4756. These combined characteristics make it an excellent laboratory for asteroseismic studies. To date, HD 172189 has been analysed in detail photometrically but not spectroscopically. For this reason we have compiled a set of spectroscopic data to determine the absolute and atmospheric parameters of the components. We determined the radial velocities (RV) of both components using four different techniques. We disentangled the binary spectra using KOREL, and performed the first abundance analysis on both disentangled spectra. By combining the spectroscopic results and the photometric data, we obtained the component masses, 1.8 and 1.7 M , and radii, 4.0 and 2.4 R , for inclination i = 73.2 • , eccentricity e = 0.28, and orbital period Π = 5.70198 days. Effective temperatures of 7600 K and 8100 K were also determined. The measured v sin i are 78 and 74 km s −1 , respectively, giving rotational periods of 2.50 and 1.55 days for the components. The abundance analysis shows [Fe/H] =-0.28 for the primary (pulsating) star, consistent with observations of IC 4756. We also present an assessment of the different analysis techniques used to obtain the RVs and the global parameters.
We present a study based on more than 2500 uvby-measurements collected on HD 172189, a new eclips... more We present a study based on more than 2500 uvby-measurements collected on HD 172189, a new eclipsing binary system with a δ Sct-type pulsating component that belongs to the open cluster IC 4756. The great interest of this object lies in that three important characteristics coexist: cluster membership, binarity and pulsation. Its binarity and the δ Sct-type pulsations of one component were detected in the course of several Strömgren photometric campaigns. The frequency analysis of all the uvby out-of-eclipse data reveals a clear frequency of 19.5974 cd −1 as well as the existence of other high values in the range 18-20 cd −1. We have also carried out a first evaluation of the binary parameters and determined a value of 5.702 d for the orbital period. An additional potential interest of HD 172189 resides in its location in the field of view of the COROT mission and, therefore, this star is an excellent candidate for becoming a target for asteroseismology.
Aims. This work presents the results obtained by CoRoT on HD 50844, the only δ Sct star observed ... more Aims. This work presents the results obtained by CoRoT on HD 50844, the only δ Sct star observed in the CoRoT initial run (57.6 d). The aim of these CoRoT observations was to investigate and characterize for the first time the pulsational behaviour of a δ Sct star, when observed at a level of precision and with a much better duty cycle than from the ground. Methods. The 140 016 datapoints were analysed using independent approaches (SigSpec software and different iterative sine-wave fittings) and several checks performed (splitting of the timeseries in different subsets, investigation of the residual light curves and spectra). A level of 10 −5 mag was reached in the amplitude spectra of the CoRoT timeseries. The space monitoring was complemented by ground-based high-resolution spectroscopy, which allowed the mode identification of 30 terms. Results. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0-30 d −1. All the crosschecks confirmed this new result. The initial guess that δ Sct stars have a very rich frequency content is confirmed. The spectroscopic mode identification gives theoretical support since very high-degree modes (up to = 14) are identified. We also prove that cancellation effects are not sufficient in removing the flux variations associated to these modes at the noise level of the CoRoT measurements. The ground-based observations indicate that HD 50844 is an evolved star that is slightly underabundant in heavy elements, located on the Terminal Age Main Sequence. Probably due to this unfavourable evolutionary status, no clear regular distribution is observed in the frequency set. The predominant term (f 1 = 6.92 d −1) has been identified as the fundamental radial mode combining ground-based photometric and spectroscopic data.
Context. BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a v... more Context. BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a very complex frequency spectrum is detected, with a number of independent nonradial modes excited, unusual among the high-amplitude pulsators in the Lower Classical Instability Strip. Aims. An extensive and detailed study has been carried out to investigate the pulsational content and properties of this object. Methods. The analysis is based on 283 h of CCD observations obtained in the Johnson V filter, during a long multisite photometric campaign carried out along the Northern autumn-winter of 2005-2006. Additionally, multicolour BI photometry was also collected to study the phase shifts and amplitude ratios, between light curves obtained in different filters, for modal discrimination of the main excited modes. Results. The detailed frequency analysis revealed a very rich and dense pulsational content consisting of 25 significant peaks, 22 of them corresponding to independent modes: one is the already known main periodicity f 0 = 25.5765 cd −1 (∆V = 153 mmag) and the other 21 are excited modes showing very small amplitudes. Some additional periodicities are probably still remaining in the residuals. This represents the most complex spectrum ever detected in a high-amplitude pulsator of this type. The majority of the secondary modes suspected from earlier works are confirmed here and, additionally, a large number of new peaks are detected. The amplitude of the main periodicity f 0 seems to be stable during decades, but the majority of the secondary modes show strong amplitude changes from one epoch to another. The suspected fundamental radial nature of the main periodicity of BL Cam is confirmed, while the secondary peak f 1 = 25.2523 cd −1 is identified as a nonradial mixed mode g 4 with = 1. The radial double-mode nature, claimed by some authors for the main two frequencies of BL Cam, is not confirmed. Nevertheless, the frequency f 6 = 32.6464 cd −1 could correspond to the first radial overtone.
Context. The high accuracy of space data increased the number of the periodicities determined for... more Context. The high accuracy of space data increased the number of the periodicities determined for pulsating variable stars, but the mode identification is still a critical point in the non-asymptotic regime. Aims. We use regularities in frequency spacings for identifying the pulsation modes of the recently discovered δ Sct star ID 102749568. Methods. In addition to analysing CoRoT light curves (15 252 datapoints spanning 131 days), we obtained and analysed both spectroscopic and extended multi-colour photometric data. We applied standard tools (MUFRAN, Period04, SigSpec, and FAMIAS) for time-series analysis. Results. A satisfactory light-curve fit was obtaining by means of 52 independent modes and 15 combination terms. The frequency spacing revealed distinct peaks around large (25.55-31.43 μHz), intermediate (9.80, 7.66 μHz), and low (2.35 μHz) separations. We directly identified 9 modes, and the l and n values of other three modes were extrapolated. The combined application of spectroscopy, multi-colour photometry, and modelling yielded the precise physical parameters and confirmed the observational mode identification. The large separation constrained the log g and related quantities. The dominant mode is the radial first overtone.
Many questions are still open regarding the structure and the dynamics of the solar core. By cons... more Many questions are still open regarding the structure and the dynamics of the solar core. By constraining more this region in the solar evolution models, we can reduce the incertitudes on some physical processes and on momentum transport mechanisms. A first big step was made with the detection of the signature of the dipole-gravity modes in the Sun, giving a
From the recent work of the Evolution and Seismic Tools Activity (ESTA, Monteiro et al., 2006; Le... more From the recent work of the Evolution and Seismic Tools Activity (ESTA, Monteiro et al., 2006; Lebreton et al., 2008), whose Task 2 is devoted to compare pulsational frequencies computed using most of the pulsational codes available in the asteroseismic community, the dependence of the theoretical frequencies with non-physical choices is now quite well fixed. To ensure that the accuracy of the computed frequencies is of the same order of magnitude or better than the observational errors, some requirements in the equilibrium models and the numerical resolutions of the pulsational equations must be followed. In particular, we have verified the numerical accuracy obtained with the Saclay seismic model, which is used to study the solar g-mode region (60 to 140µHz). We have compared the results coming from the Aarhus adiabatic pulsation code (ADIPLS), with the frequencies computed with the Granada Code (GraCo) taking into account several possible choices. We have concluded that the present equilibrium models and the use of the Richardson extrapolation ensure an accuracy of the order of 0.01µHz in the determination of the frequencies, which is quite enough for our purposes.
Monthly Notices of the Royal Astronomical Society, 2010
We present the first description of mode trapping for sdO models. Mode trapping of gravity modes ... more We present the first description of mode trapping for sdO models. Mode trapping of gravity modes caused by the He/H chemical transition is found for a particular model, providing a selection effect for high radial order trapped modes. Low-and intermediate-radial order p-modes (mixed modes with a majority of nodes in the Pmode region) are found to be trapped by the C-O/He transition, but with no significant effects on the driving. This region seems to have also a subtle effect on the trapping of low radial order g-modes (mixed modes with a majority of nodes in the G-mode region), but again with no effect on the driving. We found that for mode trapping to have an influence on the driving of sdO modes (1) the mode should be trapped in a way that the amplitude of the eigenfunctions is lower in a damping region and (2) in this damping region significant energy interchange has to be produced.
Monthly Notices of the Royal Astronomical Society, 2010
We have explored the possibility of driving pulsation modes in models of sdO stars in which the e... more We have explored the possibility of driving pulsation modes in models of sdO stars in which the effects of element diffusion, gravitational settling and radiative levitation have been neglected so that the distribution of iron-peak elements remains uniform throughout the evolution. The stability of these models was determined using a nonadiabatic oscillations code. We analysed 27 sdO models from 16 different evolutionary sequences and discovered the first ever sdO models capable of driving high-radial order g-modes. In one model, the driving is by a classical κ-mechanism due to the opacity bump from iron-peak elements at temperature ∼ 200, 000 K. In a second model, the driving result from the combined action of κ-mechanisms operating in three distinct regions of the star: (i) a carbon-oxygen partial ionization zone at temperature ∼ 2 10 6 K, (ii) a deeper region at temperature ∼ 2 10 7 K, which we attribute to ionization of argon, and (iii) at the transition from radiative to conductive opacity in the core of the star.
Monthly Notices of the Royal Astronomical Society, 2013
The overstability of the fundamental radial mode in M dwarf models was theoretically predicted re... more The overstability of the fundamental radial mode in M dwarf models was theoretically predicted recently by Rodríguez-López et al. The periods were found to be in the ranges ∼25-40 min and ∼4-8 h, depending on stellar age and excitation mechanism. We have extended our initial M dwarf model grid in mass, metallicity and mixing length parameter. We have also considered models with boundary conditions from PHOENIX NEXTGEN atmospheres to test their influence on the pulsation spectra. We find instability of non-radial modes with radial orders up to k = 3, degree = 0-3, including p-and g-modes, with the period range extending from 20 min up to 11 h. Furthermore, we find theoretical evidence of the potential of M dwarfs as solar-like oscillators.
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Papers by A. Moya