Context. Helioseismology has enabled us to better understand the solar interior, while also allowing us to better constrain solar models. But now is a tremendous epoch for asteroseismology as space ...missions dedicated to studying stellar oscillations have been launched within the last years (MOST and CoRoT). CoRoT has already proved valuable results for many types of stars, while Kepler, which was launched in March 2009, will provide us with a huge number of seismic data very soon. This is an opportunity to better constrain stellar models and to finally understand stellar structure and evolution. Aims. The goal of this research work is to estimate the global parameters of any solar-like oscillating target in an automatic manner. We want to determine the global parameters of the acoustic modes (large separation, range of excited pressure modes, maximum amplitude, and its corresponding frequency), retrieve the surface rotation period of the star and use these results to estimate the global parameters of the star (radius and mass). Methods. To prepare for the arrival and the analysis of hundreds of solar-like oscillating stars, we have developed a robust and automatic pipeline, which was partially adapted from helioseismic methods. The pipeline consists of data analysis techniques, such as Fast Fourier Transform, wavelets, autocorrelation, as well as the application of minimisation algorithms for stellar-modelling. Results. We apply our pipeline to some simulated lightcurves from the asteroFLAG team and the Aarhus-asteroFLAG simulator, and obtain results that are consistent with the input data to the simulations. Our strategy gives correct results for stars with magnitudes below 11 with only a few 10% of bad determinations among the reliable results. We then apply the pipeline to the Sun and three CoRoT targets. In particular we determine the large separation and radius of the Sun, HD49933, HD181906, and HD181420.
The first public release of long-cadence stellar photometric data collected by the NASA Kepler mission has now been made available. In this paper, we characterize the red giant (G-K) stars in this ...large sample in terms of their solar-like oscillations. We use published methods and well-known scaling relations in the analysis. Just over 70 per cent of the red giants in the sample show detectable solar-like oscillations, and from these oscillations we are able to estimate the fundamental properties of the stars. This asteroseismic analysis reveals different populations: low-luminosity H-shell burning red giant branch stars, cool high-luminosity red giants on the red giant branch and He-core burning clump and secondary-clump giants.
Rotation is expected to have an important influence on the structure and the evolution of stars. However, the mechanisms of angular momentum transport in stars remain theoretically uncertain and very ...complex to take into account in stellar models. To achieve a better understanding of these processes, we desperately need observational constraints on the internal rotation of stars, which until very recently was restricted to the Sun. In this paper, we report the detection of mixed modes-i.e., modes that behave both as g modes in the core and as p modes in the envelope-in the spectrum of the early red giant KIC 7341231, which was observed during one year with the Kepler spacecraft. By performing an analysis of the oscillation spectrum of the star, we show that its non-radial modes are clearly split by stellar rotation and we are able to determine precisely the rotational splittings of 18 modes. We then find a stellar model that reproduces very well the observed atmospheric and seismic properties of the star. We use this model to perform inversions of the internal rotation profile of the star, which enables us to show that the core of the star is rotating at least five times faster than the envelope. This will shed new light on the processes of transport of angular momentum in stars. In particular, this result can be used to place constraints on the angular momentum coupling between the core and the envelope of early red giants, which could help us discriminate between the theories that have been proposed over the last few decades.
The solar low-degree low-frequency modes of oscillation are of particular interest as their frequencies can be measured with very high precision and hence provide good constraints on seismic models. ...Here we detect and characterize these valuable measures of the solar interior from a 22 yr Birmingham Solar Oscillations Network data set. We report mode frequencies, line widths, heights, amplitudes, and rotational splitting, all with robust uncertainties. The new values of frequency, rotational splitting, amplitude, and line width we provide will help place new constraints on hydrostatic and rotational structure, plus diagnostics of near-surface convection. Further to this, by assuming simple power laws, we extrapolate mode properties to lower frequencies. We demonstrate that the low-l low-frequency p modes have a low signal-to-noise ratio and that this cannot be overcome simply by continued observation. It will be necessary to observe the Sun in novel ways to 'beat' the intrinsic granulation noise.
We have studied solar-like oscillations in ~800 red giant stars using Kepler long-cadence photometry. The sample includes stars ranging in evolution from the lower part of the red giant branch to the ...helium main sequence. We investigate the relation between the large frequency separation ( Delta *D Delta *n) and the frequency of maximum power ( Delta *nmax) and show that it is different for red giants than for main-sequence stars, which is consistent with evolutionary models and scaling relations. The distributions of Delta *nmax and Delta *D Delta *n are in qualitative agreement with a simple stellar population model of the Kepler field, including the first evidence for a secondary clump population characterized by M 2 M and Delta *nmax 40-110 Delta *mHz. We measured the small frequency separations Delta *d Delta *n02 and Delta *d Delta *n01 in over 400 stars and Delta *d Delta *n03 in over 40. We present C-D diagrams for l = 1, 2, and 3 and show that the frequency separation ratios Delta *d Delta *n02/ Delta *D Delta *n and Delta *d Delta *n01/ Delta *D Delta *n have opposite trends as a function of Delta *D Delta *n. The data show a narrowing of the l = 1 ridge toward lower Delta *nmax, in agreement with models predicting more efficient mode trapping in stars with higher luminosity. We investigate the offset in the asymptotic relation and find a clear correlation with Delta *D Delta *n, demonstrating that it is related to fundamental stellar parameters. Finally, we present the first amplitude- Delta *nmax relation for Kepler red giants. We observe a lack of low-amplitude stars for Delta *nmax 110 Delta *mHz and find that, for a given Delta *nmax between 40 and 110 Delta *mHz, stars with lower Delta *D Delta *n (and consequently higher mass) tend to show lower amplitudes than stars with higher Delta *D Delta *n.
The solar analogues 16 Cyg A and B are excellent asteroseismic targets in the Kepler field of view and together with a red dwarf and a Jovian planet form an interesting system. For these more evolved ...Sun-like stars we cannot detect surface rotation with the current Kepler data but instead use the technique of asteroseimology to determine rotational properties of both 16 Cyg A and B. We find the rotation periods to be ... and ..., and the angles of inclination to be ... and ..., for A and B, respectively. Together with these results we use the published mass and age to suggest that, under the assumption of a solar-like rotation profile, 16 Cyg A could be used when calibrating gyrochronology relations. In addition, we discuss the known 16 Cyg B star-planet eccentricity and measured low obliquity which is consistent with Kozai cycling and tidal theory. (ProQuest: ... denotes formulae/symbols omitted.)
The Birmingham Solar Oscillations Network (BiSON) has provided high-quality high-cadence observations from as far back in time as 1978. These data must be calibrated from the raw observations into ...radial velocity and the quality of the calibration has a large impact on the signal-to-noise ratio of the final time series. The aim of this work is to maximize the potential science that can be performed with the BiSON data set by optimizing the calibration procedure. To achieve better levels of signal-to-noise ratio, we perform two key steps in the calibration process: we attempt a correction for terrestrial atmospheric differential extinction; and the resulting improvement in the calibration allows us to perform weighted averaging of contemporaneous data from different BiSON stations. The improvements listed produce significant improvement in the signal-to-noise ratio of the BiSON frequency–power spectrum across all frequency ranges. The reduction of noise in the power spectrum will allow future work to provide greater constraint on changes in the oscillation spectrum with solar activity. In addition, the analysis of the low-frequency region suggests that we have achieved a noise level that may allow us to improve estimates of the upper limit of g-mode amplitudes.
Context. Asteroseismic surface gravity values can be important for determining spectroscopic stellar parameters. The independent log (g) value from asteroseismology can be used as a fixed value in ...the spectroscopic analysis to reduce uncertainties because log (g) and effective temperature cannot be determined independently from spectra. Since 2012, a combined analysis of seismically and spectroscopically derived stellar properties has been ongoing for a large survey with SDSS/APOGEE and Kepler. Therefore, knowledge of any potential biases and uncertainties in asteroseismic log (g) values is now becoming important. Aims. The seismic parameter needed to derive log (g) is the frequency of maximum oscillation power (νmax). Here, we investigate the influence on the derived log (g) values of νmax derived with different methods. The large frequency separation between modes of the same degree and consecutive radial orders (Δν) is often used as an additional constraint for determining log (g). Additionally, we checked the influence of small corrections applied to Δν on the derived values of log (g). Methods. We use methods extensively described in the literature to determine νmax and Δν together with seismic scaling relations and grid-based modelling to derive log (g). Results. We find that different approaches to derive oscillation parameters give results for log (g) with small, but different, biases for red-clump and red-giant-branch stars. These biases are well within the quoted uncertainties of ~0.01 dex (cgs). Corrections suggested in the literature to the Δν scaling relation have no significant effect on log (g); however, somewhat unexpectedly, method specific solar reference values induce biases close to the uncertainties, which is not the case when canonical solar reference values are used.
Asteroseismology of solar-type stars has an important part to play in the exoplanet program of the NASA Kepler Mission. Precise and accurate inferences on the stellar properties that are made ...possible by the seismic data allow very tight constraints to be placed on the exoplanetary systems. Here, we outline how to make an estimate of the detectability of solar-like oscillations in any given Kepler target, using rough estimates of the temperature and radius, and the Kepler apparent magnitude.
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