Results for "Timothy R. Bedding"

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Hipparcos Luminosities and AsteroseismologyOct 31 2000Asteroseismology involves using the resonant frequencies of a star to infer details about its internal structure and evolutionary state. Oscillation frequencies are most useful when accompanied by accurate measurements of the more traditional stellar ... More
Optical and infrared interferometryNov 29 2000Interferometric techniques are at the forefront of modern astronomical instrumentation. A new generation of instruments are either operating or nearing completion, including arrays of small telescopes as well as the ``big guns'' (VLTI and Keck). A number ... More
Prospects for observing pulsating red giants with the MONS Star TrackersMar 17 2000K and M giants show variability on timescales from years down to days and possibly even hours. I discuss the contribution that can be made with high-precision photometry that will be obtained by the MONS Star Trackers. These include observations of flare-like ... More
Solar-like Oscillations: An Observational PerspectiveJul 08 2011Solar-like oscillations are excited stochastically by convection. They occur in stars with an outer convection zone, which includes the Sun and other stars on the lower main sequence, as well as cool subgiants and red giants. This chapter reviews the ... More
Introduction to InterferometrySep 12 1996This tutorial gives a general introduction to optical and infrared interferometry, specifically addressing two questions: `Can I use VLTI to observe my favourite object?' and `What will it tell me?' The observables measured by an interferometer are fringe ... More
The Orbit of the Binary Star Delta ScorpiiMay 22 1993Although delta Scorpii is a bright and well-studied star, the details of its multiplicity have remained unclear. Here we present the first diffraction-limited image of this 0.12 arcsec binary star, made using optical interferometry, and resolve the confusion ... More
Solar-like oscillations in semiregular variablesSep 18 2002Sep 25 2002Power 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 ... More
Amplitudes of solar-like oscillations: a new scaling relationApr 08 2011Solar-like oscillations are excited by near-surface convection and are being observed in growing numbers of stars using ground and space-based telescopes. We have previously suggested an empirical scaling relation to predict their amplitudes (Kjeldsen ... More
The MONS Star TrackersMar 17 2000The MONS satellite will have two Star Trackers to sense the spacecraft attitude, and we plan to use them as scientific instruments to perform high-precision photometry of thousands of stars. We briefly describe the current plans for the Star Trackers ... More
Solar-like Oscillations (Invited Review)May 22 2003Aug 22 2003The 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 ... More
Solar-like oscillations: the search goes onSep 29 1997Despite numerous attempts and many hours of telescope time, there has so far been no confirmed detection of solar-like oscillations in any star except the Sun. We review recent efforts, with particular emphasis on the technique of monitoring equivalent ... More
Observing solar-like oscillationsApr 04 1997We review techniques for measuring stellar oscillations in solar-type stars. Despite great efforts, no unambiguous detections have been made. A new method, based on monitoring the equivalent widths of strong lines, shows promise but is yet to be confirmed. ... More
Observations of solar-like oscillationsMay 10 2007There 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 ... More
Current status of AsteroseismologyNov 19 2000Oscillation frequencies are the most accurate properties one can measure for a star, potentially allowing detailed tests of stellar models and evolution theories. We briefly review asteroseismology for two classes of stars. In delta Scuti variables, the ... More
Scaled oscillation frequencies and echelle diagrams as a tool for comparative asteroseismologyJan 27 2010We describe a method for comparing the frequency spectra of oscillating stars. We focus on solar-like oscillations, in which mode frequencies generally follow a regular pattern. On the basis that oscillation frequencies of similar stars scale homologously, ... More
Asteroseismology from solar-like oscillationsFeb 19 2007There 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 ... More
Observations of solar-like oscillationsSep 28 2006There 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. ... More
Measurements of Stellar Properties through Asteroseismology: A Tool for Planet Transit StudiesJul 03 2008Oscillations 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, ... More
Hipparcos parallaxes for eta Boo and kappa_2 Boo: two successes for asteroseismologySep 01 1997The release of the Hipparcos catalogue provides an opportunity to check results from asteroseismology. Here we show that Hipparcos parallaxes for two stars are in good agreement with oscillation results. For eta Boo, a probable detection of solar-like ... More
A search for solar-like oscillations in alpha Cen AOct 31 1997Dec 03 1997We have been using a new method to search for solar-like oscillations that involves measuring temperature changes via their effect on the equivalent widths of the Balmer hydrogen lines. We observed alpha Cen A over six nights in 1995 with the 3.9-metre ... More
Correcting stellar oscillation frequencies for near-surface effectsJul 11 2008In helioseismology, there is a well-known offset between observed and computed oscillation frequencies. This offset is known to arise from improper modeling of the near-surface layers of the Sun, and a similar effect must occur for models of other stars. ... More
Hipparcos calibration of the tip of the Red Giant BranchAug 20 2009We have detected the tip of the Red Giant Branch (TRGB) in the solar neighborhood using near infrared photometry from the 2MASS and DIRBE catalogs, and revised Hipparcos parallaxes. We confirm that the revised Hipparcos parallaxes are superior to the ... More
Asteroseismic analysis of solar-mass subgiants KIC 6442183 and KIC 11137075 observed by KeplerJun 03 2015Jun 05 2015Asteroseismology provides a powerful way to constrain stellar parameters. Solar-like oscillations have been observed on subgiant stars with the \emph{Kepler\/} mission. The continuous and high-precision time series enables us to carry out a detailed asteroseismic ... More
Bayesian Inference from Observations of Solar-Like OscillationsAug 26 2006Stellar 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 ... More
A planet in an 840-d orbit around a Kepler main-sequence A star found from phase modulation of its pulsationsAug 09 2016Aug 11 2016We have detected a 12 M$_{\rm Jup}$ planet orbiting in or near the habitable zone of a main-sequence A star via the pulsational phase shifts induced by orbital motion. The planet has an orbital period of $840\pm20$ d and an eccentricity of 0.15. All known ... More
Finding binaries from phase modulation of pulsating stars with Kepler. IV. Detection limits and radial velocity verificationJul 26 2016Aug 01 2016We explore the detection limits of the phase modulation (PM) method of finding binary systems among multi-periodic pulsating stars. The method is an attractive way of finding non-transiting planets in the habitable zones of intermediate mass stars, whose ... More
Asteroseismology of main-sequence F stars with \textit{Kepler}: overcoming short mode lifetimesFeb 14 2019Asteroseismology is a powerful way of determining stellar parameters and properties of stars like the Sun. However, main-sequence F-type stars exhibit short mode lifetimes relative to their oscillation frequency, resulting in overlapping radial and quadrupole ... More
Calculating asteroseismic diagrams for solar-like oscillationsSep 15 2011With the success of the Kepler and CoRoT missions, the number of stars with detected solar-like oscillations has increased by several orders of magnitude, for the first time we are able to perform large-scale ensemble asteroseismology of these stars. ... More
Photometry Using Kepler "Superstamps" of Open Clusters NGC 6791 & NGC 6819Sep 24 2013The Kepler space telescope has proven to be a gold mine for the study of variable stars. Unfortunately, Kepler only returns a handful of pixels surrounding each star on the target list, which omits a large number of stars in the Kepler field. For the ... More
A unifying explanation of complex frequency spectra of gamma Dor, SPB and Be stars: combination frequencies and highly non-sinusoidal light curvesApr 16 2015There are many Slowly Pulsating B (SPB) stars and gamma Dor stars in the Kepler Mission data set. The light curves of these pulsating stars have been classified phenomenologically into stars with symmetric light curves and with asymmetric light curves. ... More
Finding binaries among Kepler pulsating stars from phase modulation of their pulsationsApr 22 2014We present a method for finding binaries among pulsating stars that were observed by the Kepler Mission. We use entire four-year light curves to accurately measure the frequencies of the strongest pulsation modes, then track the pulsation phases at those ... More
A search for non-pulsating, chemically normal stars in the $δ$ Scuti instability strip using Kepler dataDec 23 2014We identify stars in the $\delta$ Sct instability strip that do not pulsate in p modes at the 50-$\mu$mag limit, using Kepler data. Spectral classification and abundance analyses from high-resolution spectroscopy allow us to identify chemically peculiar ... More
Time-series Spectroscopy of EC14026 Stars: Preliminary ResultsNov 05 1999We have obtained time-series spectra for the pulsating hot subdwarf (sdB) PG1605+072. Previous time-series photometry of this star has shown maximum amplitude variations of about 0.1 mag and at least 50 periods. The pulsator has the largest amplitude ... More
Asteroseismology of 16000 Kepler red giants: Global oscillation parameters, Masses, and radiiFeb 13 2018The Kepler mission has provided exquisite data to perform an ensemble asteroseismic analysis on evolved stars. In this work we systematically characterize solar-like oscillations and granulation for 16,094 oscillating red giants, using end-of-mission ... More
Asteroseismology of 16000 Kepler Red Giants: Global Oscillation Parameters, Masses, and RadiiFeb 13 2018Apr 03 2018The Kepler mission has provided exquisite data to perform an ensemble asteroseismic analysis on evolved stars. In this work we systematically characterize solar-like oscillations and granulation for 16,094 oscillating red giants, using end-of-mission ... More
Echelle diagrams and period spacings of g modes in gamma Doradus stars from four years of Kepler observationsNov 07 2014We use photometry from the Kepler Mission to study oscillations in gamma Doradus stars. Some stars show remarkably clear sequences of g modes and we use period echelle diagrams to measure period spacings and identify rotationally split multiplets with ... More
Binary star detectability in $Kepler$ data from phase modulation of different types of oscillationsMay 11 2016Detecting binary stars in photometric time series is traditionally done by measuring eclipses. This requires the orbital plane to be aligned with the observer. A new method without that requirement uses stellar oscillations to measure delays in the light ... More
Erratum: "Oscillations in Arcturus from WIRE photometry" (ApJ, 591, L151 [2003])Aug 25 2003The value of the mode lifetime given in the first paragraph of the Discussion should be divided by 2pi and is therefore 2.0 days rather than 13 days.
Testing Newtonian Gravity with AAOmega: Mass-to-Light Profiles of Four Globular ClustersAug 05 2009Testing Newtonian gravity in the weak-acceleration regime is vital to our understanding of the nature of the gravitational interaction. It has recently been claimed that the velocity dispersion profiles of several globular clusters flatten out at large ... More
Testing Newtonian Gravity with AAOmega: Mass-To-Light Profiles and Metallicity Calibrations From 47 Tuc and M55Oct 05 2009Globular clusters are an important test bed for Newtonian gravity in the weak-acceleration regime, which is vital to our understanding of the nature of the gravitational interaction. Recent claims have been made that the velocity dispersion profiles of ... More
Asteroseismology of 1523 misclassified red giants using $\textit{Kepler}$ dataAug 20 2016We analysed solar-like oscillations in 1523 $\textit{Kepler}$ red giants which have previously been misclassified as subgiants, with predicted $\nu_{\rm max}$ values (based on the Kepler Input Catalogue) between 280$\mu$Hz to 700$\mu$Hz. We report the ... More
Automated extraction of oscillation parameters for Kepler observations of solar-type starsOct 15 2009The recent launch of the Kepler space telescope brings the opportunity to study oscillations systematically in large numbers of solar-like stars. In the framework of the asteroFLAG project, we have developed an automated pipeline to estimate global oscillation ... More
Finding binaries from phase modulation of pulsating stars with Kepler: V. Orbital parameters, with eccentricity and mass-ratio distributions of 341 new binariesNov 30 2017The orbital parameters of binaries at intermediate periods ($10^2$--$10^3$ d) are difficult to measure with conventional methods and are very incomplete. We have undertaken a new survey, applying our pulsation timing method to {\it Kepler} light curves ... More
Asteroseismic measurement of slow, nearly-uniform surface-to-core rotation in the main sequence F star KIC 9244992Dec 17 2014We have found a rotationally split series of core g-mode triplets and surface p-mode multiplets in a main sequence F star, KIC 9244992. Comparison with models shows that the star has a mass of about 1.45 M$_\odot$, and is at an advanced stage of main ... More
Modelling Kepler Red Giants in Eclipsing Binaries:Calibrating the Mixing Length Parameter with AsteroseismologyDec 05 2017Stellar models rely on a number of free parameters. High-quality observations of eclipsing binary stars observed by Kepler offer a great opportunity to calibrate model parameters for evolved stars. Our study focuses on six Kepler red giants with the goal ... More
Asteroseismology of KIC 7107778: a binary comprising almost identical subgiantsJan 27 2018We analyze an asteroseismic binary system: KIC 7107778, a non-eclipsing, unresolved target, with solar-like oscillations in both components. We used \emph{Kepler} short cadence time series spanning nearly two years to obtain the power spectrum. Oscillation ... More
AAOmega Observations of 47 Tucanae: Evidence for a Past Merger?Feb 03 2010The globular cluster 47 Tucanae is well studied but it has many characteristics that are unexplained, including a significant rise in the velocity dispersion profile at large radii, indicating the exciting possibility of two distinct kinematic populations. ... More
Oscillation frequencies and mode lifetimes in alpha Centauri AJun 21 2004We analyse our recently-published velocity measurements of alpha Cen A (Butler et al. 2004). After adjusting the weights on a night-by-night basis in order to optimize the window function to minimize sidelobes, we extract 42 oscillation frequencies with ... More
Evidence for solar-like oscillations in beta HydriDec 20 2000We 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 ... More
AAOmega spectroscopy of 29 351 stars in fields centered on ten Galactic globular clustersApr 13 2011May 02 2011Galactic globular clusters have been pivotal in our understanding of many astrophysical phenomena. Here we publish the extracted stellar parameters from a recent large spectroscopic survey of ten globular clusters. A brief review of the project is also ... More
A close halo of large transparent grains around extreme red giant starsApr 12 2012Intermediate-mass stars end their lives by ejecting the bulk of their envelope via a slow dense wind back into the interstellar medium, to form the next generation of stars and planets. Stellar pulsations are thought to elevate gas to an altitude cool ... More
Ultra-high-precision velocity measurements of oscillations in alpha Cen ANov 17 2003We 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 ... More
MORE ON SOLAR-LIKE OSCILLATIONS IN ETA BOOMar 14 1995We recently reported strong evidence for solar-like oscillations in the G0 IV star eta Boo (Kjeldsen et al. 1995, AJ 109, 1313). We measured small temperature fluctuations produced by oscillations through their effect on the equivalent widths of the Balmer ... More
Amplitudes of Stellar Oscillations: The Implications for AsteroseismologyMar 08 1994There are no good predictions for the amplitudes expected from solar-like oscillations in other stars. In the absence of a definitive model for convection, which is thought to be the mechanism that excites these oscillations, the amplitudes for both velocity ... More
Large amplitude change in spot-induced rotational modulation of the Kepler Ap star KIC 2569073Jul 18 2017An investigation of the 200 $\times$ 200 pixel 'superstamp' images of the centres of the open clusters NGC 6791 and NGC 6819 allows for the identification and study of many variable stars that were not included in the Kepler target list. KIC 2569073 (V=14.22), ... More
Evidence for compact binary systems around Kepler red giantsMay 01 2017We present an analysis of 168 oscillating red giants from NASA's $Kepler$ mission that exhibit anomalous peaks in their Fourier amplitude spectra. These peaks result from ellipsoidal variations which are indicative of binary star systems, at frequencies ... More
Solving the mode identification problem in asteroseismology of F stars observed with KeplerMay 02 2012Asteroseismology of F-type stars has been hindered by an ambiguity in identification of their oscillation modes. The regular mode pattern that makes this task trivial in cooler stars is masked by increased linewidths. The absolute mode frequencies, encapsulated ... More
Asteroseismology: a powerful tool to complement planet transitsFeb 02 2007Feb 05 2007The study of stellar oscillations - asteroseismology - has revolutionized our understanding of the physical properties of the Sun, and similar potential for other stars has been demonstrated in recent years. In particular, asteroseismic studies can constrain ... More
Optimizing Weights for the Detection of Stellar Oscillations: Application to alpha Centauri A and B, and beta HydriJan 23 2009We have recently developed a new method for adjusting weights to minimize sidelobes in the spectral window. Here we show the results of applying this method to published two-site velocity observations of three stars (alpha Cen A, alpha Cen B and beta ... More
Time-series spectroscopy of the rapidly oscillating Ap star HR 3831Apr 28 2000We present time-series spectroscopy of the rapidly oscillating Ap star HR 3831. This star has a dominant pulsation period of 11.7 minutes and a rotation period of 2.85 days. We have analysed 1400 intermediate-resolution spectra of the wavelength region ... More
Hipparcos period-luminosity relations for Miras and semiregular variablesAug 17 1998We present period-luminosity diagrams for nearby Miras and semiregulars, selecting stars with parallaxes better than 20 per cent and well-determined periods. Using K-band magnitudes, we find two well-defined P-L sequences, one corresponding to the standard ... More
Photometric biases due to stellar blending: implications for measuring distances, constraining binarity and detecting exoplanetary transitsJan 24 2005We investigate blending, binarity and photometric biases in crowded-field CCD imaging. For this, we consider random blend losses, which correspond to the total number of stars left undetected in unresolved blends. We present a simple formula to estimate ... More
Replicated Echelle Diagrams in Asteroseismology: A Tool for Studying Mixed Modes and Avoided CrossingsSep 27 2011In oscillating stars, mixed modes have p-mode character in the envelope and g-mode character in the core. They are observed in subgiants and red giants, in which the large density gradient outside the core effectively divides the star into two coupled ... More
New methods for masked-aperture and speckle interferometryJan 18 1999Diffraction-limited images can be obtained with a large optical telescope using interferometry. One such method for objects of sufficient brightness is non-redundant masking (NRM), in which observations are made through a pupil mask that contains an array ... More
Solar-like oscillations in the metal-poor subgiant nu Indi: constraining the mass and age using asteroseismologyApr 21 2006Asteroseismology 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 ... More
Modeling Kepler Observations of Solar-like Oscillations in the Red-giant Star HD 186355Sep 05 2011Nov 28 2011We have analysed oscillations of the red giant star HD 186355 observed by the NASA Kepler satellite. The data consist of the first five quarters of science operations of Kepler, which cover about 13 months. The high-precision time-series data allow us ... More
Standing on the shoulders of Dwarfs: the Kepler asteroseismic LEGACY sample II - radii, masses, and agesNov 27 2016Nov 29 2016We use asteroseismic data from the Kepler satellite to determine fundamental stellar properties of the 66 main-sequence targets observed for at least one full year by the mission. We distributed tens of individual oscillation frequencies extracted from ... More
Tidally Induced Oscillations and Orbital Decay in Compact Triple-Star SystemsNov 29 2012Jan 28 2013We investigate the nature of tidal effects in compact triple-star systems. The hierarchical structure of a triple system produces tidal forcing at high frequencies unobtainable in binary systems, allowing for the tidal excitation of high frequency p-modes ... More
Standing on the shoulders of Dwarfs: the Kepler asteroseismic LEGACY sample II - radii, masses, and agesNov 27 2016Dec 02 2016We use asteroseismic data from the Kepler satellite to determine fundamental stellar properties of the 66 main-sequence targets observed for at least one full year by the mission. We distributed tens of individual oscillation frequencies extracted from ... More
Asteroseismology of the open clusters NGC 6791, NGC 6811, and NGC 6819 from nineteen months of Kepler photometryMay 17 2012Aug 07 2012We studied solar-like oscillations in 115 red giants in the three open clusters NGC 6791, NGC 6811, and NGC 6819, based on photometric data covering more than 19 months with NASA's Kepler space telescope. We present the asteroseismic diagrams of the asymptotic ... More
Standing on the shoulders of Dwarfs: the $Kepler$ asteroseismic LEGACY sample I - oscillation mode parametersDec 01 2016The advent of space-based missions like $Kepler$ has revolutionized the study of solar-type stars, particularly through the measurement and modeling of their resonant modes of oscillation. Here we analyze a sample of 66 $Kepler$ main-sequence stars showing ... More
Validation of the Exoplanet Kepler-21b using PAVO/CHARA Long-Baseline InterferometryFeb 23 2012Mar 09 2012We present long-baseline interferometry of the Kepler exoplanet host star HD179070 (Kepler-21) using the PAVO beam combiner at the CHARA Array. The visibility data are consistent with a single star and exclude stellar companions at separations ~1-1000 ... More
Stellar populations in NGC 5128 with the VLT: evidence for recent star formationSep 24 2001We resolve stars of the nearest giant elliptical galaxy NGC 5128 using VLT with FORS1 and ISAAC. We construct deep U, V and Ks color-magnitude and color-color diagrams in two different halo fields (in the halo and in the north-eastern diffuse shell). ... More
Long Period Variables in NGC 5128: II. Near-IR propertiesSep 12 2003Long Period Variable stars are ubiquitous among the bright red giant branch stars in NGC 5128. Mostly they are found to be brighter than the tip of the first ascent giant branch with magnitudes ranging from about K=19 to K=21.5. They have periods between ... More
Asteroseismology of the Hyades red giant and planet host epsilon TauJan 18 2019Asteroseismic analysis of solar-like stars allows us to determine physical parameters such as stellar mass, with a higher precision compared to most other methods. Even in a well-studied cluster such as the Hyades, the masses of the red giant stars are ... More
An Optical Interferometer with Wavelength DispersionApr 04 1994MAPPIT is an optical interferometer installed at the coude focus of the 3.9-m Anglo-Australian Telescope. The instrument combines non-redundant masking with wavelength dispersion and is able to record fringes simultaneously over a wide bandwidth. For ... More
Observing solar-like oscillationsFeb 04 2008The 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 ... More
Observing solar-like oscillations: recent resultsOct 14 2005We 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 ... More
A search for solar-like oscillations and granulation in alpha Cen ANov 19 1998We report the most sensitive search yet made for solar-like oscillations. We observed the star alpha Cen A in Balmer-line equivalent widths over six nights with both the 3.9m Anglo-Australian Telescope and the ESO 3.6m telescope. We set an upper limit ... More
Mode switching in the nearby Mira-like variable R DoradusAug 28 1998We discuss visual observations spanning nearly 70 years of the nearby semiregular variable R Doradus. Using wavelet analysis, we show that the star switches back and forth between two pulsation modes having periods of 332 days and about 175 days, the ... More
Studies of Mira and semiregular variables using visual databasesNov 05 1999We use wavelets to investigate period and amplitude changes in Mira and semiregular variables and found a variety of behaviours. Period and amplitude changes often go together, perhaps because changes in amplitude are causing period changes via non-linear ... More
Red variables in the OGLE-II data base -- III. Constraints on the three-dimensional structures of the LMC and SMCFeb 22 2005We present an analysis of the 3-D structure of the Magellanic Clouds, using period-luminosity (P-L) relations of pulsating red giants in the OGLE-II sample. By interpreting deviations from the mean P-L relations as distance modulus variations, we examine ... More
Do red giants have short mode lifetimes?Oct 18 2005We show evidence that the red giant star ksi Hya has an oscillation mode lifetime, tau, of about 2 days significantly shorter than predicted by theory (tau = 17 days, Houdek & Gough 2002). If this is a general trend of red giants it would limit the prospects ... More
The evolution of the Mira variable R HydraeMar 20 2002The Mira variable R Hydrae is well known for its declining period, which Wood & Zarro (1981) attributed to a possible recent thermal pulse. Here we investigate the long-term period evolution, covering 340 years, going back to its discovery in AD 1662. ... More
The extended atmosphere and evolution of the RV Tau star R ScutiMar 14 2002We analyze ISO/SWS spectra of the RV Tau star R Scuti. The infrared spectra are dominated by H2O emission bands. The near- and mid-infrared excess is attributed to H2O; the dust contribution is less important. We also identify CO, SiO and CO2 bands. The ... More
Oscillation mode lifetimes in ksi Hydrae: Will strong mode damping limit asteroseismology of red giant stars?Nov 11 2005We introduce a new method to measure frequency separations and mode lifetimes of stochastically excited and damped oscillations, so-called solar-like oscillations. Our method shows that velocity data of the red giant star ksi Hya (Frandsen et al. 2002) ... More
Evidence for Granulation and Oscillations in Procyon from Photometry with the WIRE satelliteApr 21 2005Apr 25 2005We report evidence for the granulation signal in the star Procyon A, based on two photometric time series from the star tracker on the WIRE satellite. The power spectra show evidence of excess power around 1 milliHz, consistent with the detection of p-modes ... More
Colour ratios of pulsation amplitudes in red giantsJun 04 2003We have analysed the three-colour photometry of 34 pulsating red giants that was published by Percy, Wilson and Henry (2001). As is common with semiregulars, many of these stars have long secondary periods (LSPs) of several years, in addition to the usual ... More
Photometry of Very Bright Stars with Kepler and K2 Smear DataSep 30 2015High-precision time series photometry with the Kepler satellite has been crucial to our understanding both of exoplanets, and via asteroseismology, of stellar physics. After the failure of two reaction wheels, the Kepler satellite has been repurposed ... More
Testing the Asteroseismic Mass Scale Using Metal-Poor Stars Characterized with APOGEE and KeplerMar 07 2014Fundamental stellar properties, such as mass, radius, and age, can be inferred using asteroseismology. Cool stars with convective envelopes have turbulent motions that can stochastically drive and damp pulsations. The properties of the oscillation frequency ... More
Kepler-432: a red giant interacting with one of its two long period giant planetsNov 17 2014Apr 20 2015We report the discovery of Kepler-432b, a giant planet ($M_b = 5.41^{+0.32}_{-0.18} M_{\rm Jup}, R_b = 1.145^{+0.036}_{-0.039} R_{\rm Jup}$) transiting an evolved star $(M_\star = 1.32^{+0.10}_{-0.07} M_\odot, R_\star = 4.06^{+0.12}_{-0.08} R_\odot)$ ... More
Solar-like oscillations in the G2 subgiant beta Hydri from dual-site observationsMar 29 2007May 15 2007We 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 ... More
Fast core rotation in red-giant stars revealed by gravity-dominated mixed modesDec 13 2011When the core hydrogen is exhausted during stellar evolution, the central region of a star contracts and the outer envelope expands and cools, giving rise to a red giant, in which convection occupies a large fraction of the star. Conservation of angular ... More
Kepler-93b: A Terrestrial World Measured to within 120 km, and a Test Case for a New Spitzer Observing ModeMay 14 2014We present the characterization of the Kepler-93 exoplanetary system, based on three years of photometry gathered by the Kepler spacecraft. The duration and cadence of the Kepler observations, in tandem with the brightness of the star, enable unusually ... More
Asteroseismology and Gaia: Testing Scaling Relations Using 2200 Kepler Stars with TGAS ParallaxesMay 12 2017We present a comparison of parallaxes and radii from asteroseismology and Gaia DR1 (TGAS) for 2200 Kepler stars spanning from the main sequence to the red giant branch. We show that previously identified offsets between TGAS parallaxes and distances derived ... More
The GALAH Survey and Gaia DR2: (Non)existence of five sparse high-latitude open clustersJul 02 2018Sparse open clusters can be found at high galactic latitudes where loosely populated clusters are more easily detected against the lower stellar background. Because most star formation takes place in the thin disk, the observed population of clusters ... More
Sounding open clusters: asteroseismic constraints from Kepler on the properties of NGC 6791 and NGC 6819Feb 10 2011We present initial results on some of the properties of open clusters NGC 6791 and NGC 6819 derived from asteroseismic data obtained by NASA's Kepler mission. In addition to estimating the mass, radius and log g of stars on the red-giant branch of these ... More
Accretion disk models and their X-ray reflection signatures. I. Local spectraMay 31 2000X-ray illumination of accretion disks is an invaluable diagnostic of the structure of these disks because of the associated iron K$\alpha$ emission. Here we point out that the resulting reflected spectra depend very sensitively on the geometry of the ... More
Moonshots for agingJan 13 2019As the global population ages, there is increased interest in living longer and improving quality of life in later years. However studying aging is expensive and time-consuming. And despite successes in extending lifespan in model organisms there still ... More
Angular Diameters of Compact Planetary NebulaeSep 14 1993We have obtained H$\alpha$ CCD images of 21 compact planetary nebulae in the galactic bulge. All objects are resolved and, after deconvolving the seeing disk, we find diameters of 1--2$''$ with typical uncertainties of 20\%. The values are generally in ... More