Patrick Gaulme | New Mexico State University (original) (raw)

Papers by Patrick Gaulme

Proceedings of the International Astronomical Union, 2010

The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and ... more The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the

Astronomy & Astrophysics, 2010

Context. HD 46375 is known to host a Saturn-like exoplanet orbiting at 0.04 AU from its host star... more Context. HD 46375 is known to host a Saturn-like exoplanet orbiting at 0.04 AU from its host star. Stellar light reflected by the planet was tentatively identified in the 34-day CoRoT run acquired in October-November 2008. Aims. We constrain the properties of the magnetic field of HD 46375 based on spectropolarimetric observations with the NARVAL spectrograph at the Pic du Midi observatory. In addition, we use a high-resolution NARVAL flux spectrum to contrain the atmospheric parameters. With these constraints, we perform an asteroseismic analysis and modelling of HD 46375 using the frequencies extracted from the CoRoT light curve. Methods. We used Zeeman Doppler imaging to reconstruct the magnetic map of the stellar surface. In the spectroscopic analysis we fitted isolated lines using 1D LTE atmosphere models. This analysis was used to constrain the effective temperature, surface gravity, and chemical composition of the star. To extract information about the p-mode oscillations, we used a technique based on the envelope autocorrelation function (EACF). Results. From the Zeeman Doppler imaging observations, we observe a magnetic field of ≈ 5 gauss. From the spectral analysis, HD 46375 is inferred to be an unevolved K0 type star with high metallicity [Fe/H] = +0.39. Owing to the relative faintness of the star (m hip = 8.05), the signal-to-noise ratio is too low to identify individual modes. However, we measure the p-mode excess power and large separation ∆ν 0 = 153.0 ± 0.7 µHz. Conclusions. We are able do constrain the fundamental parameters of the star thanks to spectrometric and seismic analyses. We conclude that HD 46375 is similar to a young version of α Cen B. This work is of special interest because of its combination of exoplanetary science and asteroseismology, which are the subjects of the current Kepler mission and the proposed Plato mission.

The Astrophysical Journal, 2011

Photometric observations made by the NASA Kepler Mission have led to a dramatic increase in the n... more Photometric observations made by the NASA Kepler Mission have led to a dramatic increase in the number of main-sequence and subgiant stars with detected solar-like oscillations. We present an ensemble asteroseismic analysis of 76 solar-type stars. Using frequencies determined from the Kepler time-series photometry, we have measured three asteroseismic parameters that characterize the oscillations: the large frequency separation (∆ν), the small frequency separation between modes of l = 0 and l = 2 (δν 02 ), and the dimensionless offset (ǫ). These measurements allow us to construct asteroseismic diagrams, namely the so-called C-D diagram of δν 02 versus ∆ν, and the recently reintroduced ǫ diagram. We compare the Kepler results with previously observed solar-type stars and with theoretical models. The positions of stars in these diagrams places constraints on their masses and ages. Additionally, we confirm the observational relationship between ǫ and T eff that allows for the unambiguous determination of radial order and should help resolve the problem of mode identification in F stars.

Astronomy and Astrophysics, 2010

Context. The present work deals with the detection of phase changes in an exoplanetary system. HD... more Context. The present work deals with the detection of phase changes in an exoplanetary system. HD 46375 is a solar analog known to host a non-transiting Saturn-mass exoplanet with a 3.0236 day period. It was observed by the CoRoT satellite for 34 days during the fall of 2008. Aims. We attempt to identify at optical wavelengths, the changing phases of the planet as it orbits its star. We then try to improve the star model by means of a seismic analysis of the same light curve and the use of ground-based spectropolarimetric observations. Methods. The data analysis relies on the Fourier spectrum and the folding of the time series. Results. We find evidence of a sinusoidal signal compatible in terms of both amplitude and phase with light reflected by the planet. Its relative amplitude is ∆F p /F ⋆ = [13.0, 26.8] ppm, implying an albedo A = [0.16, 0.33] or a dayside visible brightness temperature T b ≃ [1880, 2030] K by assuming a radius R = 1.1R Jup and an inclination i = 45 • . Its orbital phase differs from that of the radialvelocity signal by at most 2 σ RV . However, the tiny planetary signal is strongly blended by another signal, which we attribute to a telluric signal with a 1 day period. We show that this signal is suppressed, but not eliminated, when using the time series for HD 46179 from the same CoRoT run as a reference.

Context. The CoRoT mission is in its third year of observation and the data from the second long ... more Context. The CoRoT mission is in its third year of observation and the data from the second long run in the galactic centre direction are being analysed. The solar-like oscillating stars that have been observed up to now have given some interesting results, specially concerning the amplitudes that are lower than predicted. We present here the results from the analysis of the star HD 170987. Aims. The goal of this research work is to characterise the global parameters of HD 170987. We look for global seismic parameters such as the mean large separation, maximum amplitude of the modes, and surface rotation because the signal-to-noise ratio in the observations do not allow us to measure individual modes. We also want to retrieve the stellar parameters of the star and its chemical composition. Methods. We have studied the chemical composition of the star using ground-based observations performed with the NARVAL spectrograph. We have used several methods to calculate the global parameters from the acoustic oscillations based on CoRoT data. The light curve of the star has been interpolated using inpainting algorithms to reduce the effect of data gaps. Results. We find power excess related to p modes in the range [400 -1200] µHz with a mean large separation of 55.2 ± 0.8 µHz with a probability above 95 % that increases to 55.9 ± 0.2 µHz in a higher frequency range [500 -1250] µHz and a rejection level of 1 %. A hint of the variation of this quantity with frequency is also found. The rotation period of the star is estimated to be around 4.3 days with an inclination axis of i = 50 • +20 −13 . We measure a bolometric amplitude per radial mode in a range [2.4 -2.9] ppm around 1000 µHz. Finally, using a grid of models, we estimate the stellar mass, M = 1.43 ± 0.05 M , the radius, R = 1.96 ± 0.046 R , and the age ∼2.4 Gyr.

Astronomy and Astrophysics, 2009

Context. The estimate of solar-like oscillation properties, such as their frequencies, amplitudes... more Context. The estimate of solar-like oscillation properties, such as their frequencies, amplitudes and lifetimes, is challenging because of their low amplitudes and will benefit from long and uninterrupted observing runs. The space telescope CoRoT allows us to obtain high-performance photometric data over a long and quasi continuous period. Among its main targets are stars for which we expect solar-like oscillations. Aims. HD 181420, an F2 main sequence star, has been observed by CoRoT during its first long run covering about 156 days. With this unprecedently high-quality set of data, our aim is to derive the p-mode parameters that can be used to probe the stellar interior. Methods. The CoRoT data obtained on HD 181420 is analysed using a classical Fourier approach for the search for the p mode signature. The p-mode parameters are then derived using global fitting of the power spectrum by a Lorentzian model, as used widely in the solar case. Results. From the p-mode frequencies, the mean value of the large spacing is estimated to be 75 μHz. The p-mode amplitudes are slightly less than 4 ppm with a line width of about 8 μHz at the maximum of the p modes. The inclination angle is estimated to be around 45 • . The large mode line-width combined with the observed mode spacing make it difficult to identify the = 2 modes and to estimate the rotational splitting. We explore two scenarios for the identification of the modes.

Astronomy and Astrophysics, 2009

Context. Solar-like oscillations have now been observed in several stars, thanks to ground-based ... more Context. Solar-like oscillations have now been observed in several stars, thanks to ground-based spectroscopic observations and space-borne photometry. CoRoT, which has been in orbit since December 2006, has observed the star HD49933 twice. The oscillation spectrum of this star has proven difficult to interpret. Aims. Thanks to a new timeseries provided by CoRoT, we aim to provide a robust description of the oscillations in HD49933, i.e., to identify the degrees of the observed modes, and to measure mode frequencies, widths, amplitudes and the average rotational splitting. Methods. Several methods were used to model the Fourier spectrum: Maximum Likelihood Estimators and Bayesian analysis using Markov Chain Monte-Carlo techniques. Results. The different methods yield consistent result, and allow us to make a robust identification of the modes and to extract precise mode parameters. Only the rotational splitting remains difficult to estimate precisely, but is clearly relatively large (several µHz in size).

Astronomy and Astrophysics, 2010

Context. The star HD 49385 is the first G-type solar-like pulsator observed in the seismology fie... more Context. The star HD 49385 is the first G-type solar-like pulsator observed in the seismology field of the space telescope CoRoT. The satellite collected 137 days of high-precision photometric data on this star, confirming that it presents solar-like oscillations. HD 49385 was also observed in spectroscopy with the NARVAL spectrograph in January 2009. Aims. Our goal is to characterize HD 49385 using both spectroscopic and seismic data. Methods. The fundamental stellar parameters of HD 49385 are derived with the semi-automatic software VWA, and the projected rotational velocity is estimated by fitting synthetic profiles to isolated lines in the observed spectrum. A maximum likelihood estimation is used to determine the parameters of the observed p modes. We perform a global fit, in which modes are fitted simultaneously over nine radial orders, with degrees ranging from ℓ = 0 to ℓ = 3 (36 individual modes). Results. Precise estimates of the atmospheric parameters (T eff , [M/H], log g) and of the v sin i of HD 49385 are obtained. The seismic analysis of the star leads to a clear identification of the modes for degrees ℓ = 0, 1, 2. Around the maximum of the signal (ν ≃ 1013 µHz), some peaks are found significant and compatible with the expected characteristics of ℓ = 3 modes. Our fit yields robust estimates of the frequencies, linewidths and amplitudes of the modes. We find amplitudes of ∼ 5.6 ± 0.8 ppm for radial modes at the maximum of the signal. The lifetimes of the modes range from one day (at high frequency) to a bit more than two days (at low frequency). Significant peaks are found outside the identified ridges and are fitted. They are attributed to mixed modes.

Science, 2011

In addition to its search for extrasolar planets, the NASA Kepler mission provides exquisite data... more In addition to its search for extrasolar planets, the NASA Kepler mission provides exquisite data on stellar oscillations. We report the detections of oscillations in 500 solar-type stars in the Kepler field of view, an ensemble that is large enough to allow statistical studies of intrinsic stellar properties (such as mass, radius, and age) and to test theories of stellar evolution. We find that the distribution of observed masses of these stars shows intriguing differences to predictions from models of synthetic stellar populations in the Galaxy.

EAS Publications Series, 2005

Seismology is the only way to investigate the internal structure of the giant planets, with a lot... more Seismology is the only way to investigate the internal structure of the giant planets, with a lot of scientific implications such as high pressure physics and huge constraints on the scenario of solar system formation. As compared to other existing possibilities (ground based network, spacecraft), seismology of Jupiter will take a maximum benefit from the peculiarities of the Concordia station as an astronomical observatory. Indeed, the continuous temporal coverage for all the winter season, and the quality of the atmospheric seeing, are crucial parameters for this program. The jovian seismometer SYMPA, already used for network observations, is perfectly suitable for Dome C conditions. With the already existing small telescopes deployed in the frame of site testing program, seismology of Jupiter will constitute a excellent intermediate project with high scientific return, before the installation of large telescopes. In a second step, such an instrument could be a first light instrument for a 1.5 m class automatic telescope, which is to be developed as an individual stone for a large interferometer. With this diameter, the same scientific program on Saturn could also be achieved.

Astronomy and Astrophysics, 2009

Context. The CoRoT short runs give us the opportunity to observe a large variety of late-type sta... more Context. The CoRoT short runs give us the opportunity to observe a large variety of late-type stars through their solar-like oscillations. We report observations of the star HD 175726 that lasted for 27 days during the first short run of the mission. The time series reveals a high-activity signal and the power spectrum presents an excess due to solar-like oscillations with a low signal-to-noise ratio. Aims. Our aim is to identify the most efficient tools to extract as much information as possible from the power density spectrum.

Astronomische Nachrichten, 2010

Astron. Nachr. / AN 331, No. 9/10, 981 – 984 (2010) / DOI 10.1002/asna.201011440 ... Asteroseismo... more Astron. Nachr. / AN 331, No. 9/10, 981 – 984 (2010) / DOI 10.1002/asna.201011440 ... Asteroseismology of solar-type stars with Kepler: III. Ground-based data ... J. Molenda-˙Zakowicz 1,* , H. Bruntt 2 , S. Sousa 3 , A. Frasca 4 , K. Biazzo 5 , D. Huber 6 , M. Ireland 6 ,

Having started science operations in May 2009, the Kepler photometer has been able to provide exq... more Having started science operations in May 2009, the Kepler photometer has been able to provide exquisite data of solar-like stars. Five out of the 42 stars observed continuously during the survey phase show evidence of oscillations, even though they are rather faint (magnitudes from 10.5 to 12). In this paper, we present an overview of the results of the seismic analysis of 4 of these stars observed during more than eight months.

Astrophysical Journal, 2011

We use photometric observations of solar-type stars, made by the NASA Kepler Mission, to conduct ... more We use photometric observations of solar-type stars, made by the NASA Kepler Mission, to conduct a statistical study of the impact of stellar surface activity on the detectability of solar-like oscillations. We find that the number of stars with detected oscillations falls significantly with increasing levels of activity. The results present strong evidence for the impact of magnetic activity on the properties of near-surface convection in the stars, which appears to inhibit the amplitudes of the stochastically excited, intrinsically damped solar-like oscillations.

Monthly Notices of the Royal Astronomical Society, 2011

We present the asteroseismic analysis of 1948 F-, G-and K-type main-sequence and subgiant stars o... more We present the asteroseismic analysis of 1948 F-, G-and K-type main-sequence and subgiant stars observed by the NASA Kepler Mission. We detect and characterise solar-like oscillations in 642 of these stars. This represents the largest cohort of mainsequence and subgiant solar-like oscillators observed to date. The photometric observations are analysed using the methods developed by nine independent research teams. The results are combined to validate the determined global asteroseismic parameters and calculate the relative precision by which the parameters can be obtained. We correlate the relative number of detected solar-like oscillators with stellar parameters from the Kepler Input Catalog and find a deficiency for stars with effective temperatures in the range 5300 T eff 5700 K and a drop-off in detected oscillations in stars approaching the red edge of the classical instability strip. We compare the power-law relationships between the frequency of peak power, ν max , the mean large frequency separation, ∆ν, and the maximum mode amplitude, A max , and show that there are significant method-dependent differences in the results obtained. This illustrates the need for multiple complementary analysis methods to be used to assess the robustness and reproducibility of results derived from global asteroseismic parameters.

The Astrophysical Journal Supplement Series, 2014

We use asteroseismic data obtained by the NASA Kepler mission to estimate the fundamental propert... more We use asteroseismic data obtained by the NASA Kepler mission to estimate the fundamental properties of more than 500 main-sequence and sub-giant stars. Data obtained during the first 10 months of Kepler science operations were used for this work, when these solar-type targets were observed for one month each in survey mode. Stellar properties have been estimated using two global asteroseismic parameters and complementary photometric and spectroscopic data. Homogeneous sets of effective temperatures, T eff , were available for the entire ensemble from complementary photometry; spectroscopic estimates of T eff and [Fe/H] were available from a homogeneous analysis of ground-based data on a subset of 87 stars. We adopt a grid-based analysis, coupling six pipeline codes to 11 stellar evolutionary grids. Through use of these different grid-pipeline combinations we allow implicitly for the impact on the results of stellar model dependencies from commonly used grids, and differences in adopted pipeline methodologies. By using just two global parameters as the seismic inputs we are able to perform a homogenous analysis of all solar-type stars in the asteroseismic cohort, including many targets for which it would not be possible to provide robust estimates of individual oscillation frequencies (due to a combination of low signal-to-noise ratio and short dataset lengths). The median final quoted uncertainties from consolidation of the grid-based analyses are for the full ensemble (spectroscopic subset) approximately 10.8% (5.4%) in mass, 4.4% (2.2%) in radius, 0.017 dex (0.010 dex) in log g, and 4.3% (2.8%) in mean density. Around 36% (57%) of the stars have final age uncertainties smaller than 1 Gyr. These ages will be useful for ensemble studies, but should be treated carefully on a star-bystar basis. Future analyses using individual oscillation frequencies will offer significant improvements on up to 150 stars, in particular for estimates of the ages, where having the individual frequency data is most important.

Seismology applied to giant planets could drastically change our understanding of their deep inte... more Seismology applied to giant planets could drastically change our understanding of their deep interiors, as it has happened with the Earth, the Sun, and many main-sequence and evolved stars. The study of giant planets' composition is important for understanding both the mechanisms enabling their formation and the origins of planetary systems, in particular our own. Unfortunately, its determination is complicated by the fact that their interior is thought not to be homogeneous, so that spectroscopic determinations of atmospheric abundances are probably not representative of the planet as a whole. Instead, the determination of their composition and structure must rely on indirect measurements and interior models. Giant planets are mostly fluid and convective, which makes their seismology much closer to that of solar-like stars than that of terrestrial planets. Hence, helioseismology techniques naturally transfer to giant planets. In addition, two alternative methods can be used: ph...

Astronomy and Astrophysics, 2009

Context. The F8 star HD 181906 (effective temperature ∼ 6300 K) was observed for 156 days by the ... more Context. The F8 star HD 181906 (effective temperature ∼ 6300 K) was observed for 156 days by the CoRoT satellite during the first long run in the centre direction. Analysis of the data reveals a spectrum of solar-like acoustic oscillations. However, the faintness of the target (m v =7.65) means the signal-to-noise (S/N) in the acoustic modes is quite low, and this low S/N leads to complications in the analysis. Aims. To extract global variables of the star as well as key parameters of the p modes observed in the power spectrum of the lightcurve. Methods. The power spectrum of the lightcurve, a wavelet transform and spot fitting have been used to obtain the average rotation rate of the star and its inclination angle. Then, the autocorrelation of the power spectrum and the power spectrum of the power spectrum were used to properly determine the large separation. Finally, estimations of the mode parameters have been done by maximizing the likelihood of a global fit, where several modes were fit simultaneously. Results. We have been able to infer the mean surface rotation rate of the star (∼4 µHz) with indications of the presence of surface differential rotation, the large separation of the p modes (∼87 µHz), and therefore also the "ridges" corresponding to overtones of the acoustic modes.

The Astrophysical Journal

Red-giant stars are an incredible source of information for testing models of stellar evolution, ... more Red-giant stars are an incredible source of information for testing models of stellar evolution, as asteroseismology has opened up a window into their interiors. Such insights are a direct result of the unprecedented data from space missions Kepler and CoRoT as well as recent theoretical advances. Eclipsing binaries are also fundamental astrophysical objects, and when coupled with asteroseismology, binaries would provide two independent methods to obtain masses and radii and exciting opportunities to develop highly constrained stellar models. The possibility of discovering pulsating red giants in eclipsing binary systems is therefore an important goal that could potentially offer very robust characterization of these systems. Hitherto, only 1 case has been discovered with Kepler. We cross-correlated the detected red-giant and eclipsing-binary catalogs from Kepler data to find candidate systems. Light-curve modeling and mean asteroseismic properties are combined to yield measurements...

The Astrophysical Journal

Among 19 red-giant stars belonging to eclipsing binary systems that have been identified in Keple... more Among 19 red-giant stars belonging to eclipsing binary systems that have been identified in Kepler data, 15 display solar-like oscillations. We study whether the absence of mode detection in the remaining 4 is an observational bias or possibly evidence of mode damping that originates from tidal interactions. A careful analysis of the corresponding Kepler light curves shows that modes with amplitudes that are usually observed in red giants would have been detected if they were present. We observe that mode depletion is strongly associated with short-period systems, in which stellar radii account for 16-24 % of the semi-major axis, and where red-giant surface activity is detected. We suggest that when the rotational and orbital periods synchronize in close binaries, the red-giant component is spun up, so that a dynamo mechanism starts and generates a magnetic field, leading to observable stellar activity. Pressure modes would then be damped as acoustic waves dissipate in these fields.

Proceedings of the International Astronomical Union, 2010

The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and ... more The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the

Astronomy & Astrophysics, 2010

Context. HD 46375 is known to host a Saturn-like exoplanet orbiting at 0.04 AU from its host star... more Context. HD 46375 is known to host a Saturn-like exoplanet orbiting at 0.04 AU from its host star. Stellar light reflected by the planet was tentatively identified in the 34-day CoRoT run acquired in October-November 2008. Aims. We constrain the properties of the magnetic field of HD 46375 based on spectropolarimetric observations with the NARVAL spectrograph at the Pic du Midi observatory. In addition, we use a high-resolution NARVAL flux spectrum to contrain the atmospheric parameters. With these constraints, we perform an asteroseismic analysis and modelling of HD 46375 using the frequencies extracted from the CoRoT light curve. Methods. We used Zeeman Doppler imaging to reconstruct the magnetic map of the stellar surface. In the spectroscopic analysis we fitted isolated lines using 1D LTE atmosphere models. This analysis was used to constrain the effective temperature, surface gravity, and chemical composition of the star. To extract information about the p-mode oscillations, we used a technique based on the envelope autocorrelation function (EACF). Results. From the Zeeman Doppler imaging observations, we observe a magnetic field of ≈ 5 gauss. From the spectral analysis, HD 46375 is inferred to be an unevolved K0 type star with high metallicity [Fe/H] = +0.39. Owing to the relative faintness of the star (m hip = 8.05), the signal-to-noise ratio is too low to identify individual modes. However, we measure the p-mode excess power and large separation ∆ν 0 = 153.0 ± 0.7 µHz. Conclusions. We are able do constrain the fundamental parameters of the star thanks to spectrometric and seismic analyses. We conclude that HD 46375 is similar to a young version of α Cen B. This work is of special interest because of its combination of exoplanetary science and asteroseismology, which are the subjects of the current Kepler mission and the proposed Plato mission.

The Astrophysical Journal, 2011

Photometric observations made by the NASA Kepler Mission have led to a dramatic increase in the n... more Photometric observations made by the NASA Kepler Mission have led to a dramatic increase in the number of main-sequence and subgiant stars with detected solar-like oscillations. We present an ensemble asteroseismic analysis of 76 solar-type stars. Using frequencies determined from the Kepler time-series photometry, we have measured three asteroseismic parameters that characterize the oscillations: the large frequency separation (∆ν), the small frequency separation between modes of l = 0 and l = 2 (δν 02 ), and the dimensionless offset (ǫ). These measurements allow us to construct asteroseismic diagrams, namely the so-called C-D diagram of δν 02 versus ∆ν, and the recently reintroduced ǫ diagram. We compare the Kepler results with previously observed solar-type stars and with theoretical models. The positions of stars in these diagrams places constraints on their masses and ages. Additionally, we confirm the observational relationship between ǫ and T eff that allows for the unambiguous determination of radial order and should help resolve the problem of mode identification in F stars.

Astronomy and Astrophysics, 2010

Context. The present work deals with the detection of phase changes in an exoplanetary system. HD... more Context. The present work deals with the detection of phase changes in an exoplanetary system. HD 46375 is a solar analog known to host a non-transiting Saturn-mass exoplanet with a 3.0236 day period. It was observed by the CoRoT satellite for 34 days during the fall of 2008. Aims. We attempt to identify at optical wavelengths, the changing phases of the planet as it orbits its star. We then try to improve the star model by means of a seismic analysis of the same light curve and the use of ground-based spectropolarimetric observations. Methods. The data analysis relies on the Fourier spectrum and the folding of the time series. Results. We find evidence of a sinusoidal signal compatible in terms of both amplitude and phase with light reflected by the planet. Its relative amplitude is ∆F p /F ⋆ = [13.0, 26.8] ppm, implying an albedo A = [0.16, 0.33] or a dayside visible brightness temperature T b ≃ [1880, 2030] K by assuming a radius R = 1.1R Jup and an inclination i = 45 • . Its orbital phase differs from that of the radialvelocity signal by at most 2 σ RV . However, the tiny planetary signal is strongly blended by another signal, which we attribute to a telluric signal with a 1 day period. We show that this signal is suppressed, but not eliminated, when using the time series for HD 46179 from the same CoRoT run as a reference.

Context. The CoRoT mission is in its third year of observation and the data from the second long ... more Context. The CoRoT mission is in its third year of observation and the data from the second long run in the galactic centre direction are being analysed. The solar-like oscillating stars that have been observed up to now have given some interesting results, specially concerning the amplitudes that are lower than predicted. We present here the results from the analysis of the star HD 170987. Aims. The goal of this research work is to characterise the global parameters of HD 170987. We look for global seismic parameters such as the mean large separation, maximum amplitude of the modes, and surface rotation because the signal-to-noise ratio in the observations do not allow us to measure individual modes. We also want to retrieve the stellar parameters of the star and its chemical composition. Methods. We have studied the chemical composition of the star using ground-based observations performed with the NARVAL spectrograph. We have used several methods to calculate the global parameters from the acoustic oscillations based on CoRoT data. The light curve of the star has been interpolated using inpainting algorithms to reduce the effect of data gaps. Results. We find power excess related to p modes in the range [400 -1200] µHz with a mean large separation of 55.2 ± 0.8 µHz with a probability above 95 % that increases to 55.9 ± 0.2 µHz in a higher frequency range [500 -1250] µHz and a rejection level of 1 %. A hint of the variation of this quantity with frequency is also found. The rotation period of the star is estimated to be around 4.3 days with an inclination axis of i = 50 • +20 −13 . We measure a bolometric amplitude per radial mode in a range [2.4 -2.9] ppm around 1000 µHz. Finally, using a grid of models, we estimate the stellar mass, M = 1.43 ± 0.05 M , the radius, R = 1.96 ± 0.046 R , and the age ∼2.4 Gyr.

Astronomy and Astrophysics, 2009

Context. The estimate of solar-like oscillation properties, such as their frequencies, amplitudes... more Context. The estimate of solar-like oscillation properties, such as their frequencies, amplitudes and lifetimes, is challenging because of their low amplitudes and will benefit from long and uninterrupted observing runs. The space telescope CoRoT allows us to obtain high-performance photometric data over a long and quasi continuous period. Among its main targets are stars for which we expect solar-like oscillations. Aims. HD 181420, an F2 main sequence star, has been observed by CoRoT during its first long run covering about 156 days. With this unprecedently high-quality set of data, our aim is to derive the p-mode parameters that can be used to probe the stellar interior. Methods. The CoRoT data obtained on HD 181420 is analysed using a classical Fourier approach for the search for the p mode signature. The p-mode parameters are then derived using global fitting of the power spectrum by a Lorentzian model, as used widely in the solar case. Results. From the p-mode frequencies, the mean value of the large spacing is estimated to be 75 μHz. The p-mode amplitudes are slightly less than 4 ppm with a line width of about 8 μHz at the maximum of the p modes. The inclination angle is estimated to be around 45 • . The large mode line-width combined with the observed mode spacing make it difficult to identify the = 2 modes and to estimate the rotational splitting. We explore two scenarios for the identification of the modes.

Astronomy and Astrophysics, 2009

Context. Solar-like oscillations have now been observed in several stars, thanks to ground-based ... more Context. Solar-like oscillations have now been observed in several stars, thanks to ground-based spectroscopic observations and space-borne photometry. CoRoT, which has been in orbit since December 2006, has observed the star HD49933 twice. The oscillation spectrum of this star has proven difficult to interpret. Aims. Thanks to a new timeseries provided by CoRoT, we aim to provide a robust description of the oscillations in HD49933, i.e., to identify the degrees of the observed modes, and to measure mode frequencies, widths, amplitudes and the average rotational splitting. Methods. Several methods were used to model the Fourier spectrum: Maximum Likelihood Estimators and Bayesian analysis using Markov Chain Monte-Carlo techniques. Results. The different methods yield consistent result, and allow us to make a robust identification of the modes and to extract precise mode parameters. Only the rotational splitting remains difficult to estimate precisely, but is clearly relatively large (several µHz in size).

Astronomy and Astrophysics, 2010

Context. The star HD 49385 is the first G-type solar-like pulsator observed in the seismology fie... more Context. The star HD 49385 is the first G-type solar-like pulsator observed in the seismology field of the space telescope CoRoT. The satellite collected 137 days of high-precision photometric data on this star, confirming that it presents solar-like oscillations. HD 49385 was also observed in spectroscopy with the NARVAL spectrograph in January 2009. Aims. Our goal is to characterize HD 49385 using both spectroscopic and seismic data. Methods. The fundamental stellar parameters of HD 49385 are derived with the semi-automatic software VWA, and the projected rotational velocity is estimated by fitting synthetic profiles to isolated lines in the observed spectrum. A maximum likelihood estimation is used to determine the parameters of the observed p modes. We perform a global fit, in which modes are fitted simultaneously over nine radial orders, with degrees ranging from ℓ = 0 to ℓ = 3 (36 individual modes). Results. Precise estimates of the atmospheric parameters (T eff , [M/H], log g) and of the v sin i of HD 49385 are obtained. The seismic analysis of the star leads to a clear identification of the modes for degrees ℓ = 0, 1, 2. Around the maximum of the signal (ν ≃ 1013 µHz), some peaks are found significant and compatible with the expected characteristics of ℓ = 3 modes. Our fit yields robust estimates of the frequencies, linewidths and amplitudes of the modes. We find amplitudes of ∼ 5.6 ± 0.8 ppm for radial modes at the maximum of the signal. The lifetimes of the modes range from one day (at high frequency) to a bit more than two days (at low frequency). Significant peaks are found outside the identified ridges and are fitted. They are attributed to mixed modes.

Science, 2011

In addition to its search for extrasolar planets, the NASA Kepler mission provides exquisite data... more In addition to its search for extrasolar planets, the NASA Kepler mission provides exquisite data on stellar oscillations. We report the detections of oscillations in 500 solar-type stars in the Kepler field of view, an ensemble that is large enough to allow statistical studies of intrinsic stellar properties (such as mass, radius, and age) and to test theories of stellar evolution. We find that the distribution of observed masses of these stars shows intriguing differences to predictions from models of synthetic stellar populations in the Galaxy.

EAS Publications Series, 2005

Seismology is the only way to investigate the internal structure of the giant planets, with a lot... more Seismology is the only way to investigate the internal structure of the giant planets, with a lot of scientific implications such as high pressure physics and huge constraints on the scenario of solar system formation. As compared to other existing possibilities (ground based network, spacecraft), seismology of Jupiter will take a maximum benefit from the peculiarities of the Concordia station as an astronomical observatory. Indeed, the continuous temporal coverage for all the winter season, and the quality of the atmospheric seeing, are crucial parameters for this program. The jovian seismometer SYMPA, already used for network observations, is perfectly suitable for Dome C conditions. With the already existing small telescopes deployed in the frame of site testing program, seismology of Jupiter will constitute a excellent intermediate project with high scientific return, before the installation of large telescopes. In a second step, such an instrument could be a first light instrument for a 1.5 m class automatic telescope, which is to be developed as an individual stone for a large interferometer. With this diameter, the same scientific program on Saturn could also be achieved.

Astronomy and Astrophysics, 2009

Context. The CoRoT short runs give us the opportunity to observe a large variety of late-type sta... more Context. The CoRoT short runs give us the opportunity to observe a large variety of late-type stars through their solar-like oscillations. We report observations of the star HD 175726 that lasted for 27 days during the first short run of the mission. The time series reveals a high-activity signal and the power spectrum presents an excess due to solar-like oscillations with a low signal-to-noise ratio. Aims. Our aim is to identify the most efficient tools to extract as much information as possible from the power density spectrum.

Astronomische Nachrichten, 2010

Astron. Nachr. / AN 331, No. 9/10, 981 – 984 (2010) / DOI 10.1002/asna.201011440 ... Asteroseismo... more Astron. Nachr. / AN 331, No. 9/10, 981 – 984 (2010) / DOI 10.1002/asna.201011440 ... Asteroseismology of solar-type stars with Kepler: III. Ground-based data ... J. Molenda-˙Zakowicz 1,* , H. Bruntt 2 , S. Sousa 3 , A. Frasca 4 , K. Biazzo 5 , D. Huber 6 , M. Ireland 6 ,

Having started science operations in May 2009, the Kepler photometer has been able to provide exq... more Having started science operations in May 2009, the Kepler photometer has been able to provide exquisite data of solar-like stars. Five out of the 42 stars observed continuously during the survey phase show evidence of oscillations, even though they are rather faint (magnitudes from 10.5 to 12). In this paper, we present an overview of the results of the seismic analysis of 4 of these stars observed during more than eight months.

Astrophysical Journal, 2011

We use photometric observations of solar-type stars, made by the NASA Kepler Mission, to conduct ... more We use photometric observations of solar-type stars, made by the NASA Kepler Mission, to conduct a statistical study of the impact of stellar surface activity on the detectability of solar-like oscillations. We find that the number of stars with detected oscillations falls significantly with increasing levels of activity. The results present strong evidence for the impact of magnetic activity on the properties of near-surface convection in the stars, which appears to inhibit the amplitudes of the stochastically excited, intrinsically damped solar-like oscillations.

Monthly Notices of the Royal Astronomical Society, 2011

We present the asteroseismic analysis of 1948 F-, G-and K-type main-sequence and subgiant stars o... more We present the asteroseismic analysis of 1948 F-, G-and K-type main-sequence and subgiant stars observed by the NASA Kepler Mission. We detect and characterise solar-like oscillations in 642 of these stars. This represents the largest cohort of mainsequence and subgiant solar-like oscillators observed to date. The photometric observations are analysed using the methods developed by nine independent research teams. The results are combined to validate the determined global asteroseismic parameters and calculate the relative precision by which the parameters can be obtained. We correlate the relative number of detected solar-like oscillators with stellar parameters from the Kepler Input Catalog and find a deficiency for stars with effective temperatures in the range 5300 T eff 5700 K and a drop-off in detected oscillations in stars approaching the red edge of the classical instability strip. We compare the power-law relationships between the frequency of peak power, ν max , the mean large frequency separation, ∆ν, and the maximum mode amplitude, A max , and show that there are significant method-dependent differences in the results obtained. This illustrates the need for multiple complementary analysis methods to be used to assess the robustness and reproducibility of results derived from global asteroseismic parameters.

The Astrophysical Journal Supplement Series, 2014

We use asteroseismic data obtained by the NASA Kepler mission to estimate the fundamental propert... more We use asteroseismic data obtained by the NASA Kepler mission to estimate the fundamental properties of more than 500 main-sequence and sub-giant stars. Data obtained during the first 10 months of Kepler science operations were used for this work, when these solar-type targets were observed for one month each in survey mode. Stellar properties have been estimated using two global asteroseismic parameters and complementary photometric and spectroscopic data. Homogeneous sets of effective temperatures, T eff , were available for the entire ensemble from complementary photometry; spectroscopic estimates of T eff and [Fe/H] were available from a homogeneous analysis of ground-based data on a subset of 87 stars. We adopt a grid-based analysis, coupling six pipeline codes to 11 stellar evolutionary grids. Through use of these different grid-pipeline combinations we allow implicitly for the impact on the results of stellar model dependencies from commonly used grids, and differences in adopted pipeline methodologies. By using just two global parameters as the seismic inputs we are able to perform a homogenous analysis of all solar-type stars in the asteroseismic cohort, including many targets for which it would not be possible to provide robust estimates of individual oscillation frequencies (due to a combination of low signal-to-noise ratio and short dataset lengths). The median final quoted uncertainties from consolidation of the grid-based analyses are for the full ensemble (spectroscopic subset) approximately 10.8% (5.4%) in mass, 4.4% (2.2%) in radius, 0.017 dex (0.010 dex) in log g, and 4.3% (2.8%) in mean density. Around 36% (57%) of the stars have final age uncertainties smaller than 1 Gyr. These ages will be useful for ensemble studies, but should be treated carefully on a star-bystar basis. Future analyses using individual oscillation frequencies will offer significant improvements on up to 150 stars, in particular for estimates of the ages, where having the individual frequency data is most important.

Seismology applied to giant planets could drastically change our understanding of their deep inte... more Seismology applied to giant planets could drastically change our understanding of their deep interiors, as it has happened with the Earth, the Sun, and many main-sequence and evolved stars. The study of giant planets' composition is important for understanding both the mechanisms enabling their formation and the origins of planetary systems, in particular our own. Unfortunately, its determination is complicated by the fact that their interior is thought not to be homogeneous, so that spectroscopic determinations of atmospheric abundances are probably not representative of the planet as a whole. Instead, the determination of their composition and structure must rely on indirect measurements and interior models. Giant planets are mostly fluid and convective, which makes their seismology much closer to that of solar-like stars than that of terrestrial planets. Hence, helioseismology techniques naturally transfer to giant planets. In addition, two alternative methods can be used: ph...

Astronomy and Astrophysics, 2009

Context. The F8 star HD 181906 (effective temperature ∼ 6300 K) was observed for 156 days by the ... more Context. The F8 star HD 181906 (effective temperature ∼ 6300 K) was observed for 156 days by the CoRoT satellite during the first long run in the centre direction. Analysis of the data reveals a spectrum of solar-like acoustic oscillations. However, the faintness of the target (m v =7.65) means the signal-to-noise (S/N) in the acoustic modes is quite low, and this low S/N leads to complications in the analysis. Aims. To extract global variables of the star as well as key parameters of the p modes observed in the power spectrum of the lightcurve. Methods. The power spectrum of the lightcurve, a wavelet transform and spot fitting have been used to obtain the average rotation rate of the star and its inclination angle. Then, the autocorrelation of the power spectrum and the power spectrum of the power spectrum were used to properly determine the large separation. Finally, estimations of the mode parameters have been done by maximizing the likelihood of a global fit, where several modes were fit simultaneously. Results. We have been able to infer the mean surface rotation rate of the star (∼4 µHz) with indications of the presence of surface differential rotation, the large separation of the p modes (∼87 µHz), and therefore also the "ridges" corresponding to overtones of the acoustic modes.

The Astrophysical Journal

Red-giant stars are an incredible source of information for testing models of stellar evolution, ... more Red-giant stars are an incredible source of information for testing models of stellar evolution, as asteroseismology has opened up a window into their interiors. Such insights are a direct result of the unprecedented data from space missions Kepler and CoRoT as well as recent theoretical advances. Eclipsing binaries are also fundamental astrophysical objects, and when coupled with asteroseismology, binaries would provide two independent methods to obtain masses and radii and exciting opportunities to develop highly constrained stellar models. The possibility of discovering pulsating red giants in eclipsing binary systems is therefore an important goal that could potentially offer very robust characterization of these systems. Hitherto, only 1 case has been discovered with Kepler. We cross-correlated the detected red-giant and eclipsing-binary catalogs from Kepler data to find candidate systems. Light-curve modeling and mean asteroseismic properties are combined to yield measurements...

The Astrophysical Journal

Among 19 red-giant stars belonging to eclipsing binary systems that have been identified in Keple... more Among 19 red-giant stars belonging to eclipsing binary systems that have been identified in Kepler data, 15 display solar-like oscillations. We study whether the absence of mode detection in the remaining 4 is an observational bias or possibly evidence of mode damping that originates from tidal interactions. A careful analysis of the corresponding Kepler light curves shows that modes with amplitudes that are usually observed in red giants would have been detected if they were present. We observe that mode depletion is strongly associated with short-period systems, in which stellar radii account for 16-24 % of the semi-major axis, and where red-giant surface activity is detected. We suggest that when the rotational and orbital periods synchronize in close binaries, the red-giant component is spun up, so that a dynamo mechanism starts and generates a magnetic field, leading to observable stellar activity. Pressure modes would then be damped as acoustic waves dissipate in these fields.