arXiv subjects

T. R. Bedding

Publications and source records attributed to T. R. Bedding.

At least 19 recordsLinked to original sources

arXiv2026

The Stellar Observations Network Group (SONG) -- A Legacy Archive of Stellar Time-Domain Spectroscopy

The Stellar Observations Network Group (SONG) network has operated for more than a decade, providing long-baseline, high-cadence spectroscopic observations of bright stars and the Sun. The observations, from 2014 through 2025, constitute a substantial archive of high-resolution spectra and precise radial velocities for a broad range of time-domain stellar astrophysics. We present an overview of the status, instrumentation, and scientific capabilities of the SONG network, and describe the scope and accessibility of the SONG Data Archive (SODA). We further illustrate the breadth of science enabled by SONG observations, including asteroseismology, stellar variability studies, binary-star characterisation, and exoplanet research. We summarise the operational status and observing strategies of the SONG facilities, describe the available data products and archive infrastructure, and outline procedures for accessing archival observations and proposing new observations within the SONG community framework. The SODA archive currently contains more than 580,000 spectra of 3091 stars obtained with SONG using either iodine-cell or Thorium-Argon wavelength calibration. The archive spans over a decade and includes extensive time-series data for bright targets across a wide range of stellar types and variability classes. Access to the archive is available to members of the SONG community, which remains open to new participants who agree to follow the community policies. The SONG archive has developed into a major long-baseline resource for stellar spectroscopy and radial-velocity time-series analysis. Continued expansion of the archive, together with coordinated observations obtained contemporaneously with TESS and future PLATO observations, is expected to enable new studies of stellar oscillations, variability, and exoplanet host stars through combined radial-velocity and photometric analyses.

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arXiv2026

Wildly Oscillating Stars -- Unexplained dense ridge-like frequency agglomerations in A and F type pulsators

We investigate the origin of the dense, ridge-like frequency clusters observed in a subset of A and F type pulsating stars, which we refer to as `wildly oscillating' stars (WOS). These agglomerated frequency regions occupy a confined part of the frequency spectrum, typically below the fundamental radial mode, and are not explained by pulsation theory. We analyse Kepler and TESS data, construct echelle diagrams, and perform searches for combination frequencies. We determine the fundamental radial mode in order to place the agglomerated regions in a seismic context. Rotational modulation is examined through phase-folded light curves and amplitude-phase analysis, and binarity and geometric modulation scenarios are tested. The WOS phenomenon is confined to a narrow region near the overlap of the delta Sct and gamma Dor instability strips. The observed ridge morphology and mode density cannot be reproduced by simple asymptotic g-mode behaviour, low-order p modes, binarity, or typical rotational splitting. In at least two stars, a significant fraction of peaks in the agglomerated region can be explained as nonlinear combination frequencies involving high-order g modes. However, these combinations require parent modes located within the agglomerated frequency band itself, indicating that intrinsic pulsation modes must be present there. Non-adiabatic stability calculations reproduce the classical instability domains but do not predict unstable modes with the observed density or organised ridge structure in the agglomerated region. The WOS appear to represent a pulsational regime not captured by current models of mode excitation or rotational modulation. The agglomerated frequency phenomenon requires a mechanism that selects or excites a confined intermediate-frequency band and produces organised ridge structures within a narrow region of stellar parameter space (abridged for arXiv).

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arXiv2026

Hipparcos period-luminosity relations for Miras and semiregular variables

We 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 Mira P-L relation and the second shifted to shorter periods by a factor of about 1.9. The second sequence only contains semiregular variables, while the Mira sequence contains both Miras and semiregulars. Several semiregular stars show double periods in agreement with both relations. The Whitelock evolutionary track is shown to fit the data, indicating that the semiregulars are Mira progenitors. The transition between the two sequences may correspond to a change in pulsation mode or to a change in the stellar structure. Large amplitude pulsations leading to classical Mira classification occur mainly near the tip of the local AGB luminosity function.

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arXiv2025

Asteroseismic investigation of HD 140283: The Methuselah star

HD 140283 is a well-studied metal-poor subgiant and a Gaia benchmark star, often used for testing stellar models due to its proximity, brightness, and low metallicity ([Fe/H] = -2.3 dex). Here we present the first asteroseismic analysis of HD 140283, providing improved constraints on its fundamental properties. The star was observed by TESS in 20-second cadence during Sector 51. We extracted a custom light curve and performed a frequency analysis, revealing a rich spectrum of solar-like oscillations including mixed modes. These were combined with parameters from the literature to provide constraints on our model inference performed with BASTA. Using a dense grid of models, we find a mass of $0.75 \pm 0.01 \ \mathrm{M}_\odot$, a radius of $2.078 \substack{+0.012\\-0.011} \ \mathrm{R}_\odot$, and an age of $14.2 \pm 0.4$ Gyr, in agreement with the upper limit set by the age of the Universe within $1σ$. The observed frequency of maximum power, $\left(ν_\mathrm{max}\right)_\mathrm{obs} = 611.3 \pm 7.4 \ μ\mathrm{Hz}$, is significantly higher than predicted from standard scaling relations ($\left(ν_\mathrm{max}\right)_\mathrm{mod} = 537.2 \substack{+2.9\\-1.8} \ μ\mathrm{Hz}$), extending known deviations into the metal-poor regime. To our knowledge, the oscillations in HD 140283 have the highest $ν_\mathrm{max}$ of any metal-poor star to date, which will help to advance our understanding of oscillations in metal-poor stars in general. The results demonstrate the value of asteroseismology for precise age determination in old halo stars and taking custom abundances and opacities into account during the modelling is probably important for further improving models of such stars. In addition, a detailed characterisation of metal-poor stars, such as HD 140283, will also help advance our understanding of Population III stars and their impact on future stellar generations.

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arXiv2024

Expanding the frontiers of cool-dwarf asteroseismology with ESPRESSO. Detection of solar-like oscillations in the K5 dwarf $ε$ Indi

Fuelled by space photometry, asteroseismology is vastly benefitting the study of cool main-sequence stars, which exhibit convection-driven solar-like oscillations. Even so, the tiny oscillation amplitudes in K dwarfs continue to pose a challenge to space-based asteroseismology. A viable alternative is offered by the lower stellar noise over the oscillation timescales in Doppler observations. In this letter we present the definite detection of solar-like oscillations in the bright K5 dwarf $ε$ Indi based on time-intensive observations collected with the ESPRESSO spectrograph at the VLT, thus making it the coolest seismic dwarf ever observed. We measured the frequencies of a total of 19 modes of degree $\ell=0$--2 along with $ν_{\rm max}=5305\pm176\:{\rm μHz}$ and $Δν=201.25\pm0.16\:{\rm μHz}$. The peak amplitude of radial modes is $2.6\pm0.5\:{\rm cm\,s^{-1}}$, or a mere ${\sim} 14\%$ of the solar value. Measured mode amplitudes are ${\sim} 2$ times lower than predicted from a nominal $L/M$ scaling relation and favour a scaling closer to $(L/M)^{1.5}$ below ${\sim} 5500\:{\rm K}$, carrying important implications for our understanding of the coupling efficiency between pulsations and near-surface convection in K dwarfs. This detection conclusively shows that precise asteroseismology of cool dwarfs is possible down to at least the mid-K regime using next-generation spectrographs on large-aperture telescopes, effectively opening up a new domain in observational asteroseismology.

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arXiv2021

Mass transfer and tidally tilted pulsation in the Algol-type system TZ Dra

Oscillating eclipsing Algols (oEAs) are remarkable systems which allow us to determine accurate fundamental stellar parameters (mass, radius) and probe the stellar interiors through pulsations. TZ\,Dra is an oEA system containing a $δ$ Scuti component. To examine particular characteristics of such close systems including pulsations and mass transfer, we present a detailed photometric and spectroscopic study of TZ\,Dra. With the analysis of high-resolution spectra, the orbital parameters were determined by the radial velocity analysis and the atmospheric parameters were derived for the primary component. The binary modelling and the pulsational frequency analysis was carried out using the TESS data set. The H$α$ line profiles show the signature of mass transfer from the cool to the hot binary component. The conclusion of mass transfer/mass loss in the system was supported by the analysis of the orbital period changes. As a result, it was found that there is $3.52 \times 10^{-9}$ $M_\odot$/year mass loss from the system most probably through the hotspot and stellar winds. Additionally, most pulsation frequencies originating from the primary component were found to be spaced by harmonics of the orbital frequencies in particular, twelve doublets spaced by $2f_{\rm orb}$ were detected from which we infer that this star a tidally tilted pulsator. A mean p-mode frequency spacing of $\approx 7.2 $d$^{-1}$ was found as well.

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arXiv2020

The Pulsation Properties of $λ$ Bootis Stars I. The Southern TESS Sample

We analyse TESS light curves for 70 southern $λ$ Boo stars to identify binaries and to determine which of them pulsate as $δ$ Scuti stars. We find two heartbeat stars and two eclipsing binaries among the sample. We calculate that 81 percent of $λ$ Boo stars pulsate as $δ$ Sct variables, which is about twice that of normal stars over the same parameter space. We determine the temperatures and luminosities of the $λ$ Boo stars from photometry and Gaia DR2 parallaxes. A subset of 40 $λ$ Boo stars have 2-min TESS data, reliable temperatures and luminosities, and $δ$ Sct pulsation. We use Petersen diagrams (period ratios), échelle diagrams and the period--luminosity relation to identify the fundamental mode in 20 of those 40 stars and conclude that a further 8 stars are not pulsating in this mode. For the remaining 12, the fundamental mode cannot be unambiguously identified. Further mode identification is possible for 12 of the fundamental mode pulsators that have regular sequences of pulsation overtones in their échelle diagrams. We use stellar evolution models to determine statistically that the $λ$ Boo stars are only superficially metal weak. Simple pulsation models also better fit the observations at a metallicity of $Z=0.01$ than at $Z=0.001$. The TESS observations reveal the great potential of asteroseismology on $λ$ Boo stars, for determining precise stellar ages and shedding light on the origin(s) of the $λ$ Boo phenomenon.

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arXiv2020

The BRITE-SONG of Aldebaran -- Stellar Music in three voices

Solar-like oscillations in red-giant stars are now commonly detected in thousands of stars with space telescopes such as the NASA Kepler mission. Parallel radial velocity and photometric measurements would help to better understand the physics governing the amplitudes of solar-like oscillators. Yet, most target stars for space photometry are too faint for light-demanding ground-based spectroscopy. The BRITE Constellation satellites provide a unique opportunity of two-color monitoring of the flux variations of bright luminous red giants. Those targets are also bright enough to be monitored with high-resolution spectrographs on small telescopes, such as the SONG Network. In these proceedings, we provide a first overview of our comprehensive, multi-year campaign utilizing both BRITE and SONG to seismically characterize Aldebaran, one of the brightest red giants in the sky. Because luminous red giants can be seen at large distances, such well-characterized objects will serve as benchmark stars for galactic archeology.

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arXiv2019

The first view of $δ$ Scuti and $γ$ Doradus stars with the TESS mission

We present the first asteroseismic results for $δ$ Scuti and $γ$ Doradus stars observed in Sectors 1 and 2 of the TESS mission. We utilise the 2-min cadence TESS data for a sample of 117 stars to classify their behaviour regarding variability and place them in the Hertzsprung-Russell diagram using Gaia DR2 data. Included within our sample are the eponymous members of two pulsator classes, $γ$ Doradus and SX Phoenicis. Our sample of pulsating intermediate-mass stars observed by TESS also allows us to confront theoretical models of pulsation driving in the classical instability strip for the first time and show that mixing processes in the outer envelope play an important role. We derive an empirical estimate of 74% for the relative amplitude suppression factor as a result of the redder TESS passband compared to the Kepler mission using a pulsating eclipsing binary system. Furthermore, our sample contains many high-frequency pulsators, allowing us to probe the frequency variability of hot young $δ$ Scuti stars, which were lacking in the Kepler mission data set, and identify promising targets for future asteroseismic modelling. The TESS data also allow us to refine the stellar parameters of SX Phoenicis, which is believed to be a blue straggler.

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arXiv2019

Oscillations in the Sun with SONG: Setting the scale for asteroseismic investigations

Context. We present the first high-cadence multi-wavelength radial-velocity observations of the Sun-as-a-star, carried out during 57 consecutive days using the stellar échelle spectrograph at the Hertzsprung SONG Telescope operating at the Teide Observatory. Aims. The aim was to produce a high-quality data set and reference values for the global helioseismic parameters {ν_{max}}, and {Δν} of the solar p-modes using the SONG instrument. The obtained data set or the inferred values should then be used when the scaling relations are applied to other stars showing solar-like oscillations which are observed with SONG or similar instruments. Methods. We used different approaches to analyse the power spectrum of the time series to determine {ν_{max}}; simple Gaussian fitting and heavy smoothing of the power spectrum. {Δν} was determined using the method of autocorrelation of the power spectrum. The amplitude per radial mode was determined using the method described in Kjeldsen et al. (2008). Results. We found the following values for the solar oscillations using the SONG spectrograph: {ν_{max}} = 3141 {\pm} 12 μHz, {Δν} = 134.98 {\pm} 0.04 μHz and an average amplitude of the strongest radial modes of 16.6 {\pm} 0.4 cm/s. These values are consistent with previous measurements with other techniques.

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arXiv2019

The Asteroseismic Target List (ATL) for solar-like oscillators observed in 2-minute cadence with the Transiting Exoplanet Survey Satellite (TESS)

We present the target list of solar-type stars to be observed in short-cadence (2-min) for asteroseismology by the NASA Transiting Exoplanet Survey Satellite (TESS) during its 2-year nominal survey mission. The solar-like Asteroseismic Target List (ATL) is comprised of bright, cool main-sequence and subgiant stars and forms part of the larger target list of the TESS Asteroseismic Science Consortium (TASC). The ATL uses Gaia DR2 and the Extended Hipparcos Compilation (XHIP) to derive fundamental stellar properties, calculate detection probabilities and produce a rank-ordered target list. We provide a detailed description of how the ATL was produced and calculate expected yields for solar-like oscillators based on the nominal photometric performance by TESS. We also provide publicly available source code which can be used to reproduce the ATL, thereby enabling comparisons of asteroseismic results from TESS with predictions from synthetic stellar populations.

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arXiv2018

Surface correction of main sequence solar-like oscillators with the $Kepler$ LEGACY sample

Poor modelling of the surface regions of solar-like stars causes a systematic discrepancy between the observed and model pulsation frequencies. We aim to characterise this frequency discrepancy for main sequence solar-like oscillators for a wide range of initial masses and metallicities. We fit stellar models to the observed mode frequencies of the 67 stars, including the Sun, in the $Kepler$ LEGACY sample, using three different empirical surface corrections. The three surface corrections we analyse are a frequency power-law, a cubic frequency term divided by the mode inertia, and a linear combination of an inverse and cubic frequency term divided by the mode inertia. We construct a grid of stellar evolution models using the stellar evolution code MESA and calculate mode frequencies using GYRE. We scale the frequencies of each stellar model by an empirical calculated homology coefficient, which greatly improves the robustness of our grid. We calculate stellar parameters and surface corrections for each star using the average of the best-fitting models from each evolutionary track, weighted by the likelihood of each model. The resulting model stellar parameters agree well with an independent reference, the $\texttt{BASTA}$ pipeline. However, we find that the adopted physics of the stellar models has a greater impact on the fitted stellar parameters than the choice of correction method. We find that scaling the frequencies by the mode inertia improves the fit between the models and observations. The inclusion of the inverse frequency term produces substantially better model fits to lower surface gravity stars.

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arXiv2018

Interferometric diameters of five evolved intermediate-mass planet-hosting stars measured with PAVO at the CHARA Array

Debate over the planet occurrence rates around intermediate-mass stars has hinged on the accurate determination of masses of evolved stars, and has been exacerbated by a paucity of reliable, directly-measured fundamental properties for these stars. We present long-baseline optical interferometry of five evolved intermediate-mass ($\sim\,1.5\,\mathrm{M}_\odot$) planet-hosting stars using the PAVO beam combiner at the CHARA Array, which we combine with bolometric flux measurements and parallaxes to determine their radii and effective temperatures. We measured the radii and effective temperatures of 6 Lyncis ($5.12\pm0.16\,\mathrm{R}_\odot$, $4949\pm58\,\mathrm{K}$), 24 Sextantis ($5.49\pm0.18\,\mathrm{R}_\odot$, $4908\pm65\,\mathrm{K}$), $κ$ Coronae Borealis ($4.77\pm0.07\,\mathrm{R}_\odot$, $4870\pm47\,\mathrm{K}$), HR 6817 ($4.45\pm0.08\,\mathrm{R}_\odot$, $5013\pm59\,\mathrm{K}$), and HR 8641 ($4.91\pm0.12\,\mathrm{R}_\odot$, $4950\pm68\,\mathrm{K}$). We find disagreements of typically 15 per cent in angular diameter and $\sim$200 K in temperature compared to interferometric measurements in the literature, yet good agreement with spectroscopic and photometric temperatures, concluding that the previous interferometric measurements may have been affected by systematic errors exceeding their formal uncertainties. Modelling based on BaSTI isochrones using various sets of asteroseismic, spectroscopic, and interferometric constraints tends to favour slightly ($\sim$15 per cent) lower masses than generally reported in the literature.

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arXiv2018

An astrophysical interpretation of the remarkable g-mode frequency groups of the rapidly rotating $γ$ Dor star, KIC 5608334

The Fourier spectrum of the $γ$-Dor variable KIC 5608334 shows remarkable frequency groups at $\sim$3, $\sim$6, $\sim$9, and 11--12\,d$^{-1}$. We explain the four frequency groups as prograde sectoral g modes in a rapidly rotating star. Frequencies of intermediate-to-high radial order prograde sectoral g modes in a rapidly rotating star are proportional to $|m|$ (i.e., $ν\propto |m|$) in the co-rotating frame as well as in the inertial frame. This property is consistent with the frequency groups of KIC 5608334 as well as the period vs. period-spacing relation present within each frequency group, if we assume a rotation frequency of $2.2$\,d$^{-1}$, and that each frequency group consists of prograde sectoral g modes of $|m| = 1, 2, 3,$ and 4, respectively. In addition, these modes naturally satisfy near-resonance conditions $ν_i\approxν_j+ν_k$ with $m_i=m_j+m_k$. We even find exact resonance frequency conditions (within the precise measurement uncertainties) in many cases, which correspond to combination frequencies.

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arXiv2017

The γ Dor stars as revealed by Kepler : A key to reveal deep-layer rotation in A and F stars

The γ Dor pulsating stars present high-order gravity modes, which make them important targets in the intermediate-and low-mass main-sequence region of the Hertzsprung-Russell diagram. Whilst we have only access to rotation in the envelope of the Sun, the g modes of γ Dor stars can in principle deliver us constraints on the inner layers. With the puzzling discovery of unexpectedly low rotation rates in the core of red giants, the γ Dor stars appear now as unique targets to explore internal angular momentum transport in the progenitors of red giants. Yet, the γ Dor pulsations remain hard to detect from the ground for their periods are close to 1 day. While the CoRoT space mission first revealed intriguing frequency spectra, the almost uninterrupted 4-year photometry from the Kepler mission eventually shed a new light on them. It revealed regularities in the spectra, expected to bear signature of physical processes, including rotation, in the shear layers close to the convective core. We present here the first results of our effort to derive exploitable seismic diagnosis for mid- to fast rotators among γ Dor stars. We confirm their potential to explore the rotation history of this early phase of stellar evolution.

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arXiv2017

Asteroseismic masses of retired planet-hosting A-stars using SONG

To better understand how planets form, it is important to study planet occurrence rates as a function of stellar mass. However, estimating masses of field stars is often difficult. Over the past decade, a controversy has arisen about the inferred occurrence rate of gas-giant planets around evolved intermediate-mass stars -- the so-called `retired A-stars'. The high masses of these red-giant planet hosts, derived using spectroscopic information and stellar evolution models, have been called into question. Here we address the controversy by determining the masses of eight evolved planet-hosting stars using asteroseismology. We compare the masses with spectroscopic-based masses from the Exoplanet Orbit Database that were previously adopted to infer properties of the exoplanets and their hosts. We find a significant one-sided offset between the two sets of masses for stars with spectroscopic masses above roughly 1.6Msun, suggestive of an average 15--20% overestimate of the adopted spectroscopic-based masses. The only star in our sample well below this mass limit is also the only one not showing this offset. Finally, we note that the scatter across literature values of spectroscopic-based masses often exceed their formal uncertainties, making it comparable to the offset we report here.

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arXiv2017

Beyond the Kepler/K2 bright limit: variability in the seven brightest members of the Pleiades

The most powerful tests of stellar models come from the brightest stars in the sky, for which complementary techniques, such as astrometry, asteroseismology, spectroscopy, and interferometry can be combined. The K2 Mission is providing a unique opportunity to obtain high-precision photometric time series for bright stars along the ecliptic. However, bright targets require a large number of pixels to capture the entirety of the stellar flux, and bandwidth restrictions limit the number and brightness of stars that can be observed. To overcome this, we have developed a new photometric technique, that we call halo photometry, to observe very bright stars using a limited number of pixels. Halo photometry is simple, fast and does not require extensive pixel allocation, and will allow us to use K2 and other photometric missions, such as TESS, to observe very bright stars for asteroseismology and to search for transiting exoplanets. We apply this method to the seven brightest stars in the Pleiades open cluster. Each star exhibits variability; six of the stars show what are most-likely slowly pulsating B-star (SPB) pulsations, with amplitudes ranging from 20 to 2000 ppm. For the star Maia, we demonstrate the utility of combining K2 photometry with spectroscopy and interferometry to show that it is not a 'Maia variable', and to establish that its variability is caused by rotational modulation of a large chemical spot on a 10 d time scale.

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arXiv2017

First Results From The Hertzsprung Song Telescope: Asteroseismology Of The G5 Subgiant Star {\Mu}Her

We report the first asteroseismic results obtained with the Hertzsprung SONG Telescope from an extensive high-precision radial-velocity observing campaign of the subgiant muHerculis. The data set was collected during 215 nights in 2014 and 2015. We detected a total of 49 oscillation modes with l values from 0 to 3, including some l = 1 mixed modes. Based on the rotational splitting observed in l = 1 modes, we determine a rotational period of 52 days and a stellar inclination angle of 63 degrees. The parameters obtained through modeling of the observed oscillation frequencies agree very well with independent observations and imply a stellar mass between 1.11 and 1.15M_sun and an age of 7.8+/-0.4 Gyr. Furthermore, the high-quality data allowed us to determine the acoustic depths of the He II ionization layer and the base of the convection zone.

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