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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.

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.

Context. The F8 star HD 181906 (effective temperature ${\sim}6300$K) was observed for 156 days by the CoRoT satellite during the first long run in the direction of the galactic centre. Analysis of the data reveals a spectrum of solar-like acoustic oscillations. However, the faintness of the target (mv= 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.

Context. The first asteroseismology results from CoRoT are presented, on a star showing Sun-like oscillations. We have analyzed a 60 day lightcurve of high-quality photometric data collected by CoRoT on the F5 V star HD 49933. The data reveal a rich spectrum of overtones of low-degree p modes.

Context. Asteroseismology of Sun-like stars is undergoing rapid expansion with, for example, new data from the CoRoT mission and continuation of ground-based campaigns. There is also the exciting upcoming prospect of NASA's Kepler mission, which will allow the asteroseismic study of several hundred Sun-like targets, in some cases for periods lasting up to a few years.

Aims. From observations of the K4III star βUMi we attempt to determine whether oscillations or any other form of variability is present.

Aims.We use 9.5-yr of BiSON Sun-as-a-star data to search for dependence of solar-cycle parameter changes on the angular degree, $\ell$, of the data. The nature of the Sun-as-a-star observations is such that for changes measured at fixed frequency, or for changes averaged across the same range in frequency, any $\ell$dependence present carries information on the latitudinal distribution of the agent (i.e., the activity) responsible for those changes.

We investigate the impact of a multi-site, ground-based observational window function on the extraction of estimates of the frequencies of low-angular-degree (low-$\ell$) solar p modes from decade-long datasets. To effect this study we have made use of some ≈$10~\rm yr$of full-disc, “Sun-as-a-star” Doppler velocity data collected by the Birmingham-Solar Oscillations Network (BiSON). A coherent combination of observations made by all six BiSON sites provided the principal time series of data. This set was then modulated by a whole series of different window functions and the resulting sets analyzed. The windows were made from different combinations and numbers of BiSON stations. We find that for the majority of low-$\ell$modes the bias in the frequencies given by the effects of the window function is not significant. However, for modes above ≈$3300~\rm \mu Hz$, and some $\ell=2$modes near ≈$2500~\rm \mu Hz$, the bias is important when the frequencies are extracted from long datasets.

Low-angular-degree (low-l) solar p modes provide a sensitive probe of the radiative interior and core of the Sun. Estimates of their centroid frequencies can be used to constrain the spherically symmetric structure of these deep-lying layers. The required data can be extracted from two types of observation: one where the modes are detected in integrated sunlight, i.e., a Sun-as-a-star view; and a second where the visible disc is imaged onto many pixels, and the collected images then decomposed into their constituent spherical harmonics. While the imaging strategy provides access to all of the individual components of a multiplet, the Sun-as-a-star technique is sensitive to only about two thirds of these (average over $l=0$to 3) with those modes that are detected having different levels of visibility. Because the various components can have contrasting spatial structure over the solar surface, they can respond very differently to changes in activity along the solar cycle. Since the Sun-as-a-star and resolved analyses take as input a different “subset” of modes, the extracted frequency estimates are expected to differ depending upon the phase of the cycle. Differences also arise from the types of models used to fit the modes. Here, we present expressions that allow the sizes of these differences to be predicted.

We have studied in detail the extraction of estimates of $\ell=2$p-mode frequencies from unresolved observations of the visible disc of the Sun. Examples of data of this type include ground-based observations made by the Birmingham Solar-Oscillations Network (BiSON), and space-borne observations made by the GOLF and VIRGO/SPM instruments on board the ESA/NASA SOHOsatellite. The fitting of the modes is complicated in practice by the asymmetric arrangement in frequency of the three components ($m=-2$, 0 and 2) that are prominent in such data. In order to investigate the effect of this we used a series of 10-yr artificial datasets into which varying degrees of asymmetry were introduced. The sets were designed to mimic the characteristics of the BiSON and GOLF data, and were analyzed both with and without the BiSON window function from the period 1992 through 2001. Since reliable estimates of the asymmetry have only recently been extracted from unresolved observations (Chaplin et al. [CITE]a) it has for a long time been standard practice to fit the $\ell=2$modes to a model that assumes a symmetrically arranged multiplet. We have tested the impact of this on the accuracy of the extracted frequencies. Furthermore, we demonstrate that asymmetric models can be successfully applied, provided the data are of sufficient length and quality. We also discuss the implications of our simulations for analyses of real solar data.

We present a study of the impact of a ground-based, multi-station window function on estimates of the power and damping of low-$\ell$solar pmodes extracted from fits to resonant structure in the frequency domain. The window functions come from six-site observations made by the Birmingham Solar-Oscillations Network (BiSON) over the 10-yr period beginning 1991 January. Two strategies were adopted. In the first, we used an 800-d time series of continuous observations made by the GOLF instrument on board the ESA/NASASOHO satellite. These data were modulated by a variety of BiSON window functions, with fractional duty cycles ranging from ~0.4 to ~0.8, and the resulting series analyzed. In the second we generated artificial 10-yr time series and studied the effect on these of the complete BiSON window.

Context. Successful inference from asteroseismology relies on at least two factors: that the oscillations in the stars have amplitudes large enough to be clearly observable, and that the oscillations themselves be stable enough to enable precise measurements of mode frequencies and other parameters. Solar-like p modes are damped by convection, and hence the stability of the modes depends on the lifetime.Aims. We seek a simple scaling relation between the mean lifetime of the most prominent solar-like p modes in stars, and the fundamental stellar parameters.Methods. We base our search for a relation on the use of stellar equilibrium and pulsation computations of a grid of stellar models, and the first asteroseismic results on lifetimes of main-sequence, sub-giant and red-giant stars.Results. We find that the mean lifetimes of all three classes of solar-like stars scale like?Teff-4(where?Teffis the effective temperature). When this relation is combined with the well-known scaling relation of Kjeldsen & Bedding for mode amplitudes observed in narrow-band intensity observations, we obtain the unexpected result that the height (the maximum power spectral density) of mode peaks in the frequency power spectrum scales as?g-2(where?g is the surface gravity). As it is the mode height (and not the amplitude) that fixes the?S/N at which the modes can be measured, and as?g changes only slowly along the main sequence, this suggests that stars cooler than the Sun might be as good targets for asteroseismology as their hotter counterparts. When observations are instead made in Doppler velocity, our results imply that mode height does increase with increasing effective temperature.?

Solar p-mode frequencies vary with solar activity. It is important to take this into account when comparing the frequencies observed from epochs that span different regions of the solar cycle. We present details of how to correct observed p-mode frequencies for the effects of the solar cycle. We describe three types of correction. The first allows mode frequencies to be corrected to a nominal activity level, such as the canonical quiet-Sun level. The second accounts for the effect on the observed mode frequencies, powers, and damping rates of the continually varying solar cycle and is pertinent to frequencies obtained from very long data sets. The third corrects for Sun-as-a-star observations not seeing all components of the modes. Suitable combinations of the three correction procedures allow the frequencies obtained from different sets of data to be compared and enable activity-independent inversions of the solar interior. As an example of how to apply the corrections we describe those used to produce a set of definitive Sun-as-a-star frequencies.

Aims. From observations of the K4III star ??UMi we attempt to determine whether oscillations or any other form of variability is present. Methods. A high-quality photometric time series of ?1000?days in length obtained from the SMEI instrument on the Coriolis satellite is analysed. Various statistical tests were performed to determine the significance of features seen in the power density spectrum of the light curve. Results. Two oscillations with frequencies 2.44 and 2.92??Hz have been identified. We interpret these oscillations as consecutive overtones of an acoustic spectrum, implying a large frequency spacing of 0.48 ?Hz. Using derived asteroseismic parameters in combination with known astrophysical parameters, we estimate the mass of ??UMi to be 1.3 ?0.3?M?. Peaks of the oscillations in the power density spectrum show width, implying that modes are stochastically excited and damped by convection. The mode lifetime is estimated at 18?9?days.

Aims. As g-mode pulsators, gamma-Doradus-class stars may na?vely be expected to show a large number of modes. Taking advantage of the long photometric time-series generated by the solar mass ejection imager (SMEI) instrument, we have studied the star gamma Doradus to determine whether any other modes than the three already known are present at observable amplitude.Methods. High-precision photometric data from SMEI taken between April?2003 and March?2006 were subjected to periodogram analysis with the PERIOD04 package.Results. We confidently determine three additional frequencies at?1.39, 1.87, and 2.743?d-1. These are above and beyond the known frequencies of?1.320, 1.364, and 1.47?d-1.Conclusions. Two of the new frequencies, at 1.39 and 1.87?d-1, are speculated to be additional modes of oscillation, with the third frequency at 2.743-1a possible combination frequency.

Context.The evolved main-sequence Sun-like stars KIC 10273246 (F-type) and KIC 10920273 (G-type) were observed with the NASA Kepler satellite for approximately ten months with a duty cycle in excess of 90%. Such continuous and long observations are unprecedented for solar-type stars other than the Sun.

Context.The CoRoT mission has provided thousands of red-giant light curves. The analysis of their solar-like oscillations allows us to characterize their stellar properties.

Context.The star HD 52265is a G0V metal-rich exoplanet-host star observed in the seismology field of the CoRoT space telescope from November 2008 to March 2009. The satellite collected 117 days of high-precision photometric data on this star, showing that it presents solar-like oscillations. HD 52265 was also observed in spectroscopy with the Narval spectrograph at the same epoch.Aims.We characterise HD 52265 using both spectroscopic and seismic data. Methods.The fundamental stellar parameters of HD 52265 were derived with the semi-automatic software VWA, and the projected rotational velocity was estimated by fitting synthetic profiles to isolated lines in the observed spectrum. The parameters of the observed p modes were determined with a maximum-likelihood estimation. We performed a global fit of the oscillation spectrum, over about ten radial orders, for degrees l= 0 to 2. We also derived the properties of the granulation, and analysed a signature of the rotation induced by the photospheric magnetic activity.Results.Precise determinations of fundamental parameters have been obtained: Teff= 6100    ±    60   K, log g= 4.35    ±    0.09,  [M/H]  = 0.19    ±    0.05, as well as \hbox{$\vsini=3.6^{+0.3}_{-1.0}\kms$}. We have measured a mean rotation period Prot= 12.3    ±    0.15 days, and find a signature of differential rotation. The frequencies of 31 modes are reported in the range 1500–2550    μHz. The large separation exhibits a clear modulation around the mean value \hbox{$\Dnu=98.3\,\pm\,0.1~\muHz$}. Mode widths vary with frequency along an S-shape with a clear local maximum around 1800    μHz. We deduce lifetimes ranging between 0.5 and 3 days for these modes. Finally, we find a maximal bolometric amplitude of about 3.96    ±    0.24 ppm for radial modes.

Context.Four open clusters are present in the Kepler field of view and timeseries of nearly a year in length are now available. These timeseries allow us to derive asteroseismic global oscillation parameters of red-giant stars in the three open clusters NGC 6791, NGC 6819 and NGC 6811. From these parameters and effective temperatures, we derive masses, radii and luminosities for the clusters as well as field red giants. Aims.We study the influence of evolution and metallicity on the observed red-giant populations. Methods.The global oscillation parameters are derived using different published methods and the effective temperatures are derived from 2MASS colours. The observational results are compared with BaSTI evolution models.Results.We find that the mass has significant influence on the asteroseismic quantities Δνvs. νmaxrelation, while the influence of metallicity is negligible, under the assumption that the metallicity does not affect the excitation/damping of the oscillations. The positions of the stars in the H-R diagram depend on both mass and metallicity. Furthermore, the stellar masses derived for the field stars are bracketed by those of the cluster stars. Conclusions.Both the mass and metallicity contribute to the observed difference in locations in the H-R diagram of the old metal-rich cluster NGC 6791 and the middle-aged solar-metallicity cluster NGC 6819. For the young cluster NGC 6811, the explanation of the position of the stars in the H-R diagram challenges the assumption of solar metallicity, and this open cluster might have significantly lower metallicity [Fe/H] in the range  − 0.3 to  − 0.7 dex. Also, nearly all the observed field stars seem to be older than NGC 6811 and younger than NGC 6791.

The growing interest in solar twins is motivated by the possibility of comparing them directly to the Sun. To carry on this kind of analysis, we need to know their physical characteristics with precision. Our first objective is to use asteroseismology and interferometry on the brightest of them: 18 Sco. We observed the star during 12 nights with HARPS for seismology and used the PAVO beam-combiner at CHARA for interferometry. An average large frequency separation 134.4 ± 0.3 μHz and angular and linear radiuses of 0.6759 ± 0.0062 mas and 1.010 ± 0.009 R⊙were estimated. We used these values to derive the mass of the star, 1.02 ± 0.03 M⊙.

Aims.The CoRoT and Kepler satellites have provided thousands of red-giant oscillation spectra. The analysis of these spectra requires efficient methods of identifying all eigenmode parameters.

Context.The large number of stars for which uninterrupted high-precision photometric timeseries data are being collected with Kepler and CoRoT initiated the development of automated methods to analyse the stochastically excited oscillations in main-sequence, subgiant and red-giant stars.

Context.Clear power excess in a frequency range typical for solar-type oscillations in red giants has been detected in more than 1000 stars, which have been observed during the first 138 days of the science operation of the NASA Kepler satellite. This sample includes stars in a wide mass and radius range with spectral types G and K, extending in luminosity from the bottom of the giant branch up to high-luminous red giants, including the red bump and clump. The high-precision asteroseismic observations with Kepler provide a perfect source for testing stellar structure and evolutionary models, as well as investigating the stellar population in our Galaxy.