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Timothy R. Bedding

Publications and source records attributed to Timothy R. Bedding.

At least 199 records · Page 11Linked to original sources
arXiv2008

Measurements of Stellar Properties through Asteroseismology: A Tool for Planet Transit Studies

Oscillations occur in stars of most masses and essentially all stages of evolution. Asteroseismology is the study of the frequencies and other properties of stellar oscillations, from which we can extract fundamental parameters such as density, mass, radius, age and rotation period. We present an overview of asteroseismic analysis methods, focusing on how this technique may be used as a tool to measure stellar properties relevant to planet transit studies. We also discuss details of the Kepler Asteroseismic Investigation -- the use of asteroseismology on the Kepler mission in order to measure basic stellar parameters. We estimate that applying asteroseismology to stars observed by Kepler will allow the determination of stellar mean densities to an accuracy of 1%, radii to 2-3%, masses to 5%, and ages to 5-10% of the main-sequence lifetime. For rotating stars, the angle of inclination can also be determined.

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arXiv2008

The amplitude of solar oscillations using stellar techniques

The amplitudes of solar-like oscillations depend on the excitation and damping, both of which are controlled by convection. Comparing observations with theory should therefore improve our understanding of the underlying physics. However, theoretical models invariably compute oscillation amplitudes relative to the Sun, and it is therefore vital to have a good calibration of the solar amplitude using stellar techniques. We have used daytime spectra of the Sun, obtained with HARPS and UCLES, to measure the solar oscillations and made a detailed comparison with observations using the BiSON helioseismology instrument. We find that the mean solar amplitude measured using stellar techniques, averaged over one full solar cycle, is 18.7 +/- 0.7 cm/s for the strongest radial modes (l=0) and 25.2 +/- 0.9 cm/s for l=1. In addition, we use simulations to establish an equation that estimates the uncertainty of amplitude measurements that are made of other stars, given that the mode lifetime is known. Finally, we also give amplitudes of solar-like oscillations for three stars that we measured from a series of short observations with HARPS (gamma Ser, beta Aql and alpha For), together with revised amplitudes for five other stars for which we have previously published results (alpha Cen A, alpha Cen B, beta Hyi, nu Ind and delta Pav).

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arXiv2008

Observing solar-like oscillations

The past few years have seen great progress in observing oscillations in solar-type stars, lying on or just above the main sequence. We review the most recent results, most of which were obtained using high-precision velocity measurements. We also briefly discuss observations of more evolved stars, namely G, K and M giants and supergiants.

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arXiv2007

Solar-like oscillations in the G2 subgiant beta Hydri from dual-site observations

We have observed oscillations in the nearby G2 subgiant star beta Hyi using high-precision velocity observations obtained over more than a week with the HARPS and UCLES spectrographs. The oscillation frequencies show a regular comb structure, as expected for solar-like oscillations, but with several l=1 modes being strongly affected by avoided crossings. The data, combined with those we obtained five years earlier, allow us to identify 28 oscillation modes. By scaling the large frequency separation from the Sun, we measure the mean density of beta Hyi to an accuracy of 0.6%. The amplitudes of the oscillations are about 2.5 times solar and the mode lifetime is 2.3 d. A detailed comparison of the mixed l=1 modes with theoretical models should allow a precise estimate of the age of the star.

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arXiv2007

Observations of solar-like oscillations

There has been tremendous progress in observing oscillations in solar-type stars. In a few short years we have moved from ambiguous detections to firm measurements. We briefly review the recent results, most of which have come from high-precision Doppler measurements. We also review briefly the results on giant and supergiant stars and the prospects for the future.

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arXiv2007

Asteroseismology from solar-like oscillations

There has been tremendous progress in observing oscillations in solar-type stars. In a few short years we have moved from ambiguous detections to firm measurements. We briefly review the recent results, most of which have come from high-precision Doppler measurements. We also review briefly the results on giant and supergiant stars and the prospects for the future.

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arXiv2006

Observations of solar-like oscillations

There has been tremendous progress in observing oscillations in solar-type stars. In a few short years we have moved from ambiguous detections to firm measurements. We review the recent results, most of which have come from high-precision Doppler measurements. We also review briefly the results on giant and supergiant stars and the prospects for the future.

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arXiv2006

Bayesian Inference from Observations of Solar-Like Oscillations

Stellar oscillations can provide a wealth of information about a star, which can be extracted from observed time series of the star's brightness or radial velocity. In this paper we address the question of how to extract as much information as possible from such a dataset. We have developed a Markov Chain Monte Carlo (MCMC) code that is able to infer the number of oscillation frequencies present in the signal and their values (with corresponding uncertainties), without having to fit the amplitudes and phases. Gaps in the data do not have any serious consequences for this method; in cases where severe aliasing exists, any ambiguity in the frequency determinations will be reflected in the results. It also allows us to infer parameters of the frequency pattern, such as the large separation Delta nu. We have previously applied this method to the star nu Indi (Bedding et al 2006), and here we describe the method fully and apply it to simulated datasets, showing that the code is able to give correct results even when some of the model assumptions are violated. In particular, the non-sinusoidal nature of the individual oscillation modes due to stochastic excitation and damping has no major impact on the usefulness of our approach.

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arXiv2006

Solar-like oscillations in the metal-poor subgiant nu Indi: constraining the mass and age using asteroseismology

Asteroseismology is a powerful method for determining fundamental properties of stars. We report the first application to a metal-poor object, namely the subgiant star nu Ind. We measured precise velocities from two sites, allowing us to detect oscillations and infer a large frequency separation of Delta_nu = 24.25 +/- 0.25 microHz. Combining this value with the location of the star in the H-R diagram and comparing with standard evolutionary models, we were able to place constraints on the stellar parameters. In particular, our results indicate that nu Ind has a low mass (0.85 +/- 0.04 M_sun) and is at least 9 Gyr old.

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arXiv2005

Observing solar-like oscillations: recent results

We review recent progress in observations of ground-based oscillations. Excellent observations now exist for a few stars (alpha Cen A and B, mu Ara), while there is some controversy over others (Procyon, eta Boo). We have reached the stage where single-site observations are of limited value and where careful planning is needed to ensure the future of asteroseismology.

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arXiv2005

Solar-like oscillations in alpha Centauri B

We have made velocity observations of the star alpha Cen B from two sites, allowing us to identify 37 oscillation modes with l=0-3. Fitting to these modes gives the large and small frequency separations as a function of frequency. The mode lifetime, as measured from the scatter of the oscillation frequencies about a smooth trend, is similar to that in the Sun. Limited observations of the star delta Pav show oscillations centred at 2.3 mHz with peak amplitudes close to solar. We introduce a new method of measuring oscillation amplitudes from heavily-smoothed power density spectra, from which we estimated amplitudes for alpha Cen A and B, beta Hyi, delta Pav and the Sun. We point out that the oscillation amplitudes may depend on which spectral lines are used for the velocity measurements.

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arXiv2003

A Tight Upper Limit on Oscillations in the Ap star Epsilon Ursae Majoris from WIRE Photometry

Observations of Epsilon UMa obtained with the star tracker on the Wide Field Infrared Explorer (WIRE) satellite during a month in mid-2000 are analyzed. This is one of the most precise photometry of an Ap star. The amplitude spectrum is used to set an upper limit of 75 parts per million for the amplitude of stellar pulsations in this star unless it accidentally oscillates with a single mode at the satellite orbit, its harmonics or their one day aliases. This is the tightest limit put on the amplitude of oscillations in an Ap star. As the rotation period of Epsilon UMa is relatively short (5.1 d), it cannot be argued that the observations were made at a wrong rotational phase. Our results thus support the idea that some Ap stars do not pulsate at all.

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arXiv2003

Ultra-high-precision velocity measurements of oscillations in alpha Cen A

We have made differential radial velocity measurements of the star alpha Cen A using two spectrographs, UVES and UCLES, both with iodine absorption cells for wavelength referencing. Stellar oscillations are clearly visible in the time series. After removing jumps and slow trends in the data, we show that the precision of the velocity measurements per minute of observing time is 0.42 m/s for UVES and 1.0 m/s for UCLES, while the noise level in the Fourier spectrum of the combined data is 1.9 cm/s. As such, these observations represent the most precise velocities ever measured on any star apart from the Sun.

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arXiv2003

Solar-like Oscillations (Invited Review)

The five-minute oscillations in the Sun have provided a wealth of information about the solar interior. After many attempts, positive detections of similar oscillations in solar-type stars have now been made. This review discusses the properties of solar-like oscillations, the methods used to observe them and the results on individual stars. We conclude that the study of solar-like oscillations from the ground and space has an exciting future.

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arXiv2002

Solar-like oscillations in semiregular variables

Power spectra of the light curves of semiregular variables, based on visual magnitude estimates spanning many decades, show clear evidence for stochastic excitation. This supports the suggestion by Christensen-Dalsgaard et al. (2001) that oscillations in these stars are solar-like, i.e., stochastically excited by convection, with mode lifetimes ranging from years to decades.

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arXiv2002

Evidence for Solar-like Oscillations in Arcturus (Alpha Boo)

Observations of the red giant Arcturus (Alpha Boo) obtained with the star tracker on the Wide Field Infrared Explorer (WIRE) satellite during a baseline of 19 successive days in 2000 July-August are analysed. The power spectrum has a significant excess of power at low-frequencies. The highest peak is at about 4.1 micro-Hz, which is in agreement with the ground-based radial velocity and photometry study of Belmonte et al. (1990a; 1990b). The variability of Arcturus can be explained by sound waves, but it is not clear whether these are coherent p-mode oscillations.

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arXiv2000

Evidence for solar-like oscillations in beta Hydri

We have made a clear detection of excess power, providing strong evidence for solar-like oscillations in the G2 subgiant beta Hyi. We observed this star over five nights with the UCLES echelle spectrograph on the 3.9-m Anglo-Australian Telescope, using an iodine absorption cell as a velocity reference. The time series of 1196 velocity measurements shows an rms scatter of 3.30 m/s, and the mean noise level in the amplitude spectrum at frequencies above 0.5 mHz is 0.11 m/s. We see a clear excess of power centred at 1.0 mHz, with peak amplitudes of about 0.5 m/s, in agreement with expectations for this star. Fitting the asymptotic relation to the power spectrum indicates the most likely value for the large separation is 56.2 microHz, also in good agreement with the known properties of beta Hyi.

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