ORCID Profile
0000-0001-5222-4661
Current Organisation
University of Sydney
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Astronomical and Space Sciences | Stellar Astronomy and Planetary Systems | Astronomy And Astrophysics | Galactic Astronomy | Astronomical and Space Instrumentation | Astronomical sciences | Stellar astronomy and planetary systems | Astrobiology | Theoretical Physics | Photonics, Optoelectronics and Optical Communications | Galactic astronomy
Expanding Knowledge in the Physical Sciences | Physical sciences | Computer software and services not elsewhere classified | Scientific instrumentation |
Publisher: American Astronomical Society
Date: 17-09-2019
Publisher: Oxford University Press (OUP)
Date: 19-05-2020
Abstract: The presence of mixed modes makes subgiants excellent targets for asteroseismology, providing a probe for the internal structure of stars. Here we study 36 Kepler subgiants with solar-like oscillations and report their oscillation mode parameters. We performed a so-called peakbagging exercise, i.e. estimating oscillation mode frequencies, linewidths, and litudes with a power spectrum model, fitted in the Bayesian framework and s led with a Markov chain Monte Carlo algorithm. The uncertainties of the mode frequencies have a median value of 0.180 μHz. We obtained seismic parameters from the peakbagging, analysed their correlation with stellar parameters, and examined against scaling relations. The behaviour of seismic parameters (e.g. Δν, νmax, ϵp) is in general consistent with theoretical predictions. We presented the observational p–g diagrams, namely γ1–Δν for early subgiants and ΔΠ1–Δν for late subgiants, and demonstrate their capability to estimate stellar mass. We also found a log g dependence on the linewidths and a mass dependence on the oscillation litudes and the widths of oscillation excess. This s le will be valuable constraints for modelling stars and studying mode physics such as excitation and d ing.
Publisher: American Astronomical Society
Date: 19-07-2011
Publisher: American Astronomical Society
Date: 16-01-2012
Publisher: EDP Sciences
Date: 27-11-2008
Publisher: American Astronomical Society
Date: 14-08-2020
Abstract: We present the discoveries of KELT-25 b (TIC 65412605, TOI-626.01) and KELT-26 b (TIC 160708862, TOI-1337.01), two transiting companions orbiting relatively bright, early A stars. The transit signals were initially detected by the KELT survey and subsequently confirmed by Transiting Exoplanet Survey Satellite (TESS) photometry. KELT-25 b is on a 4.40 day orbit around the V = 9.66 star CD-24 5016 ( K, M ⋆ = M ⊙ ), while KELT-26 b is on a 3.34 day orbit around the V = 9.95 star HD 134004 ( = K, M ⋆ = M ⊙ ), which is likely an Am star. We have confirmed the substellar nature of both companions through detailed characterization of each system using ground-based and TESS photometry, radial velocity measurements, Doppler tomography, and high-resolution imaging. For KELT-25, we determine a companion radius of R P = R J and a 3 σ upper limit on the companion’s mass of ∼64 M J . For KELT-26 b, we infer a planetary mass and radius of M P = and R P = R J . From Doppler tomographic observations, we find KELT-26 b to reside in a highly misaligned orbit. This conclusion is weakly corroborated by a subtle asymmetry in the transit light curve from the TESS data. KELT-25 b appears to be in a well-aligned, prograde orbit, and the system is likely a member of the cluster Theia 449.
Publisher: Oxford University Press (OUP)
Date: 26-07-2011
Publisher: American Astronomical Society
Date: 23-08-2011
Publisher: Oxford University Press (OUP)
Date: 06-09-2017
Publisher: American Astronomical Society
Date: 28-07-2008
DOI: 10.1086/591667
Publisher: American Astronomical Society
Date: 21-03-2007
DOI: 10.1086/517971
Publisher: Oxford University Press (OUP)
Date: 30-05-2013
DOI: 10.1093/MNRAS/STT802
Publisher: American Astronomical Society
Date: 30-08-2011
Publisher: SPIE-Intl Soc Optical Eng
Date: 2006
DOI: 10.1117/1.2148910
Publisher: Oxford University Press (OUP)
Date: 02-2010
Publisher: Oxford University Press (OUP)
Date: 03-04-2012
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-10-2013
Abstract: Stars with multiple coplanar planets have not been seen to show misalignments between the equatorial plane of the star and the orbital plane of the planets—a diagnostic of the dynamical history of planetary systems. Huber et al. (p. 331 ) analyzed the Kepler 56 planetary system, which contains a giant-sized and an intermediate-sized planet. The planets have orbits that are close to coplanar, but the planetary orbits are misaligned with the stellar equator. A third companion in a wide orbit, which could be another star or a planet, could explain the misaligned configuration.
Publisher: American Astronomical Society
Date: 29-03-2011
Publisher: Oxford University Press (OUP)
Date: 18-10-2019
Abstract: We report our survey of γ Dor stars from the 4-yr Kepler mission. These stars pulsate mainly in g modes and r modes, showing period-spacing patterns in the litude spectra. The period-spacing patterns are sensitive to the chemical composition gradients and the near-core rotation, hence they are essential for understanding the stellar interior. We identified period-spacing patterns in 611 γ Dor stars. Almost every star pulsates in dipole g modes, while about 30% of stars also show clear patterns for quadrupole g modes and 16% of stars present r mode patterns. We measure periods, period spacings, and the gradient of the period spacings. These three observables guide the mode identifications and can be used to estimate the near-core rotation rate. We find many stars are hotter and show longer period-spacing patterns than theory. Using the Traditional Approximation of Rotation (TAR), we inferred the asymptotic spacings, the near-core rotation rates, and the radial orders of the g and r modes. Most stars have a near-core rotation rate around 1 d−1and an asymptotic spacing around 4000 s. We also find that many stars rotate more slowly than predicted by theory for unclear reasons. 11 stars show rotational splittings with fast rotation rates. We compared the observed slope–rotation relation with the theory and find a large spread. We detected rotational modulations in 58 stars and used them to derive the core-to-surface rotation ratios. The interiors rotate faster than the cores in most stars, but by no more than 5%.
Publisher: EDP Sciences
Date: 26-09-2007
Publisher: IOP Publishing
Date: 02-2010
DOI: 10.1086/650399
Publisher: American Astronomical Society
Date: 27-06-2014
Publisher: American Society for Clinical Investigation
Date: 08-02-2018
Publisher: EDP Sciences
Date: 2017
Publisher: EDP Sciences
Date: 2008
DOI: 10.1051/EAS:0833004
Publisher: Wiley
Date: 16-02-2023
DOI: 10.1002/EPI4.12704
Abstract: Electroencephalogram (EEG) datasets from epilepsy patients have been used to develop seizure detection and prediction algorithms using machine learning (ML) techniques with the aim of implementing the learned model in a device. However, the format and structure of publicly available datasets are different from each other, and there is a lack of guidelines on the use of these datasets. This impacts the generatability, generalizability, and reproducibility of the results and findings produced by the studies. In this narrative review, we compiled and compared the different characteristics of the publicly available EEG datasets that are commonly used to develop seizure detection and prediction algorithms. We investigated the advantages and limitations of the characteristics of the EEG datasets. Based on our study, we identified 17 characteristics that make the EEG datasets unique from each other. We also briefly looked into how certain characteristics of the publicly available datasets affect the performance and outcome of a study, as well as the influences it has on the choice of ML techniques and preprocessing steps required to develop seizure detection and prediction algorithms. In conclusion, this study provides a guideline on the choice of publicly available EEG datasets to both clinicians and scientists working to develop a reproducible, generalizable, and effective seizure detection and prediction algorithm.
Publisher: American Astronomical Society
Date: 06-04-2011
Publisher: Oxford University Press (OUP)
Date: 20-01-2021
Abstract: HD 139614 is known to be a ∼14-Myr-old, possibly pre-main-sequence star in the Sco-Cen OB association in the Upper Centaurus-Lupus subgroup, with a slightly warped circumstellar disc containing ring structures hinting at one or more planets. The star’s chemical abundance pattern is metal-deficient except for volatile elements, which places it in the λ Boo class and suggests it has recently accreted gas-rich but dust-poor material. We identify seven dipole and four radial pulsation modes among its δ Sct pulsations using the TESS light curve and an échelle diagram. Precision modelling with the mesa stellar evolution and gyre stellar oscillation programs confirms it is on the pre-main sequence. Asteroseismic, grid-based modelling suggests an age of 10.75 ± 0.77 Myr, a mass of 1.52 ± 0.02 M ⊙, and a global metal abundance of Z = 0.0100 ± 0.0010. This represents the first asteroseismic determination of the bulk metallicity of a λ Boo star. The precise age and metallicity offer a benchmark for age estimates in Upper Centaurus–Lupus, and for understanding disc retention and planet formation around intermediate-mass stars.
Publisher: Springer Science and Business Media LLC
Date: 11-12-2009
Publisher: American Association for the Advancement of Science (AAAS)
Date: 08-04-2011
Abstract: The Kepler satellite reveals details of the oscillations patterns of an evolved star in an exotic triple-star system.
Publisher: American Astronomical Society
Date: 04-04-2013
Publisher: American Astronomical Society
Date: 10-05-2011
Publisher: American Astronomical Society
Date: 08-01-2013
Publisher: Oxford University Press (OUP)
Date: 15-05-2023
Abstract: In asteroseismology, the surface effect refers to a disparity between the observed and the modelled frequencies in stars with solar-like oscillations. It originates from improper modelling of the surface layers. Correcting the surface effect usually requires using functions with free parameters, which are conventionally fitted to the observed frequencies. On the basis that the correction should vary smoothly across the H–R diagram, we parameterize it as a simple function of surface gravity, effective temperature, and metallicity. We determine this function by fitting a wide range of stars. The absolute amount of the surface correction decreases with luminosity, but the ratio between it and νmax increases, suggesting the surface effect is more important for red giants than dwarfs. Applying the prescription can eliminate unrealistic surface correction, which improves parameter estimations with stellar modelling. Using two open clusters, we found a reduction of scatter in the model-derived ages for each star in the same cluster. As an important application, we provide a new revision for the Δν scaling relation that, for the first time, accounts for the surface correction. The values of the correction factor, fΔν, are up to 2 per cent smaller than those determined without the surface effect considered, suggesting decreases of up to 4 per cent in radii and up to 8 per cent in masses when using the asteroseismic scaling relations. This revision brings the asteroseismic properties into an agreement with those determined from eclipsing binaries. The new correction factor and the stellar models with the corrected frequencies are available at arallelpro/surface.
Publisher: American Astronomical Society
Date: 11-09-2020
Publisher: Cambridge University Press (CUP)
Date: 2005
DOI: 10.1071/AS04077
Abstract: The cold, dry, and stable air above the summits of the Antarctic plateau provides the best ground-based observing conditions from optical to sub-millimetre wavelengths to be found on the Earth. Pathfinder for an International Large Optical Telescope (PILOT) is a proposed 2 m telescope, to be built at Dome C in Antarctica, able to exploit these conditions for conducting astronomy at optical and infrared wavelengths. While PILOT is intended as a pathfinder towards the construction of future grand-design facilities, it will also be able to undertake a range of fundamental science investigations in its own right. This paper provides the performance specifications for PILOT, including its instrumentation. It then describes the kinds of projects that it could best conduct. These range from planetary science to the search for other solar systems, from star formation within the Galaxy to the star formation history of the Universe, and from gravitational lensing caused by exo-planets to that produced by the cosmic web of dark matter. PILOT would be particularly powerful for wide-field imaging at infrared wavelengths, achieving near diffraction-limited performance with simple tip–tilt wavefront correction. PILOT would also be capable of near diffraction-limited performance in the optical wavebands, as well be able to open new wavebands for regular ground-based observation, in the mid-IR from 17 to 40 μm and in the sub-millimetre at 200 μm.
Publisher: BMJ
Date: 24-02-2016
Publisher: American Astronomical Society
Date: 21-09-2023
Publisher: American Astronomical Society
Date: 17-09-2012
Publisher: Oxford University Press (OUP)
Date: 15-05-2020
Abstract: Detailed modelling of stellar oscillations is able to give precise estimates for stellar ages, but the inferred results typically depend on the adopted model parameters used for the age inference. High-quality asteroseismic data with precise measurements of mixed modes are available for 36 Kepler subgiants. To obtain a handle on the robustness of the ages for these stars, we first study the dependencies of seismic ages on three model input parameters. We find that inferred ages do not change systematically with the helium fraction (Y) or the mixing-length parameter (αMLT) but depend strongly on the metallicity ([M/H]) of the model. The results indicate that age estimates of subgiants have less model dependence and hence are more reliable than those of main-sequence stars or red giants. We then model in idual oscillation frequencies of the same 36 Kepler subgiants, using observed metallicities, and obtain their ages with an average precision of ${\\sim}15{{\\ \\rm per\\ cent}}$. The comparison with previous age estimates with different stellar codes or input physics shows good agreement (mostly within 2σ). We hence suggest that seismology-determined ages of subgiants are not greatly model dependent.
Publisher: Oxford University Press (OUP)
Date: 29-01-2022
Abstract: We perform mode identification for five δ Scuti stars in the Pleiades star cluster, using custom light curves from K2 photometry. By creating échelle diagrams, we identify radial and dipole mode ridges, comprising a total of 28 radial and 16 dipole modes across the five stars. We also suggest possible identities for those modes that lie offset from the radial and dipole ridges. We calculate non-rotating stellar pulsation models to verify our mode identifications, finding good agreement within the age and metallicity constraints of the cluster. We also find that for all stars, the least dense models are preferred, reflecting the lower density of these oblate, rotating stars. Three of the five stars show rotationally split multiplets. We conclude that the s le shows promise for asteroseismic rotation rates, masses, and ages with rotating models in the future. Our preliminary modelling also indicates some sensitivity to the helium abundance.
Publisher: Oxford University Press (OUP)
Date: 25-05-2010
Publisher: American Astronomical Society
Date: 21-11-2017
Publisher: Oxford University Press (OUP)
Date: 30-12-2015
Publisher: Oxford University Press (OUP)
Date: 20-04-2019
Publisher: American Astronomical Society
Date: 21-10-2016
Publisher: American Astronomical Society
Date: 29-09-2006
DOI: 10.1086/508686
Publisher: American Astronomical Society
Date: 06-2018
Publisher: American Astronomical Society
Date: 03-01-0003
Publisher: Oxford University Press (OUP)
Date: 07-10-2015
Publisher: Cambridge University Press
Date: 13-01-2012
Publisher: SPIE-Intl Soc Optical Eng
Date: 2008
DOI: 10.1117/1.2831662
Publisher: American Astronomical Society
Date: 08-04-2013
Publisher: American Astronomical Society
Date: 14-02-2017
Publisher: Oxford University Press (OUP)
Date: 11-08-2003
Publisher: Oxford University Press (OUP)
Date: 09-2023
Publisher: American Astronomical Society
Date: 30-05-2019
Publisher: American Astronomical Society
Date: 10-07-2007
DOI: 10.1086/518593
Publisher: SPIE
Date: 27-08-2008
DOI: 10.1117/12.789783
Publisher: American Astronomical Society
Date: 11-2019
Publisher: EDP Sciences
Date: 04-2012
Publisher: American Astronomical Society
Date: 09-2003
DOI: 10.1086/377315
Publisher: American Astronomical Society
Date: 26-02-2013
Publisher: Oxford University Press (OUP)
Date: 13-10-2022
Abstract: Very little is known about the young planet population because the detection of small planets orbiting young stars is obscured by the effects of stellar activity and fast rotation, which mask planets within radial velocity and transit data sets. The few planets that have been discovered in young clusters generally orbit stars too faint for any detailed follow-up analysis. Here, we present the characterization of a new mini-Neptune planet orbiting the bright (V = 9) and nearby K2 dwarf star, HD 18599. The planet candidate was originally detected in TESS light curves from sectors 2, 3, 29, and 30, with an orbital period of 4.138 d. We then used HARPS and FEROS radial velocities, to find the companion mass to be 25.5$\\pm$4.6 $M_{\\oplus }$. When we combine this with the measured radius from TESS of 2.70$\\pm$0.05 $R_{\\oplus }$, we find a high planetary density of 7.1$\\pm$1.4 g cm$^{-3}$. The planet exists on the edge of the Neptune Desert and is the first young planet (300 Myr) of its type to inhabit this region. Structure models argue for a bulk composition to consist of 23 per cent H$_2$O and 77 per cent Rock and Iron. Future follow-up with large ground- and space-based telescopes can enable us to begin to understand in detail the characteristics of young Neptunes in the galaxy.
Publisher: Oxford University Press (OUP)
Date: 02-06-2022
Abstract: With the availability of large-scale surveys like Kepler and TESS, there is a pressing need for automated methods to classify light curves according to known classes of variable stars. We introduce a new algorithm for classifying light curves that compares 7000 time-series features to find those that most effectively classify a given set of light curves. We apply our method to Kepler light curves for stars with effective temperatures in the range 6500–10 000 K. We show that the s le can be meaningfully represented in an interpretable 5D feature space that separates seven major classes of light curves (δ Scuti stars, γ Doradus stars, RR Lyrae stars, rotational variables, contact eclipsing binaries, detached eclipsing binaries, and non-variables). We achieve a balanced classification accuracy of 82 per cent on an independent test set of Kepler stars using a Gaussian mixture model classifier. We use our method to classify 12 000 Kepler light curves from Quarter 9 and provide a catalogue of the results. We further outline a confidence heuristic based on probability density to search our catalogue and extract candidate lists of correctly classified variable stars.
Publisher: Springer Science and Business Media LLC
Date: 11-12-2008
Publisher: Oxford University Press (OUP)
Date: 10-06-2019
Abstract: We revisit the K -band period–luminosity (P–L) relations of Galactic red supergiants using Gaia Data Release 2 parallaxes and up to 70 yr of photometry from AAVSO and ASAS c aigns. In addition, we examine 206 LMC red supergiants using 50 yr of photometric data from the digitized Harvard Astronomical Plate Collection. We identified periods by computing power spectra and calculated the period–luminosity relations of our s les and compared them with the literature. Newly available data tighten the P–L relations substantially. Identified periods form two groups: one with periods of 300–1000 d, corresponding to pulsations, and another with Long Secondary Periods between 1000 and 8000 d. Among the 48 Galactic objects we find shorter periods in 25 stars and long secondary periods in 23 stars. In the LMC s le we identify 85 and 94 red supergiants with shorter and long secondary periods, respectively. The P–L relation of the Galactic red supergiants is in agreement with the red supergiants in both, the Large Magellanic Cloud and the Andromeda galaxy. We find no clear continuity between the known red giant period–luminosity sequences, and the red supergiant sequences investigated here.
Publisher: Oxford University Press (OUP)
Date: 15-06-2011
Publisher: EDP Sciences
Date: 13-12-2010
Publisher: American Astronomical Society
Date: 06-09-2012
Publisher: Springer Science and Business Media LLC
Date: 11-04-2016
DOI: 10.1038/NCOMMS11201
Abstract: Simulations predict that hot super-Earth sized exoplanets can have their envelopes stripped by photoevaporation, which would present itself as a lack of these exoplanets. However, this absence in the exoplanet population has escaped a firm detection. Here we demonstrate, using asteroseismology on a s le of exoplanets and exoplanet candidates observed during the Kepler mission that, while there is an abundance of super-Earth sized exoplanets with low incident fluxes, none are found with high incident fluxes. We do not find any exoplanets with radii between 2.2 and 3.8 Earth radii with incident flux above 650 times the incident flux on Earth. This gap in the population of exoplanets is explained by evaporation of volatile elements and thus supports the predictions. The confirmation of a hot-super-Earth desert caused by evaporation will add an important constraint on simulations of planetary systems, since they must be able to reproduce the dearth of close-in super-Earths.
Publisher: American Astronomical Society
Date: 03-2001
DOI: 10.1086/319139
Publisher: SPIE
Date: 12-09-2012
DOI: 10.1117/12.925838
Publisher: EDP Sciences
Date: 2015
Publisher: American Astronomical Society
Date: 23-02-2010
Publisher: American Astronomical Society
Date: 05-01-2023
Abstract: We analyzed 20 s cadence Transiting Exoplanet Survey Satellite time-series photometry of the exoplanet host star HR 8799 collected in Sector 56. The litude spectrum shows Gamma Doradus ( γ Dor) pulsations consistent with previous space-based photometry from MOST. Assuming that HR 8799 is a representative of γ Dor stars in the Kepler s le, the dominant dipole mode at 1.98 cycles day −1 implies a core rotation period of ∼0.7 day, which combined with v sin i and stellar radius measurements would result in a preliminary stellar inclination of ∼28° assuming rigid rotation. We find no significant residual photometric variation after removing the pulsation signal aside from a ∼9 days trend that is likely a systematic effect or an artifact from performing aggressive frequency subtraction in the presence of red noise.
Publisher: Oxford University Press (OUP)
Date: 02-11-2013
DOI: 10.1093/MNRAS/STS146
Publisher: Oxford University Press (OUP)
Date: 11-2004
Publisher: Oxford University Press (OUP)
Date: 07-10-2019
Abstract: We present the first asteroseismic results for δ Scuti and γ Doradus stars observed in Sectors 1 and 2 of the TESS mission. We utilize the 2-min cadence TESS data for a s le of 117 stars to classify their behaviour regarding variability and place them in the Hertzsprung–Russell diagram using Gaia DR2 data. Included within our s le are the eponymous members of two pulsator classes, γ Doradus and SX Phoenicis. Our s le 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 per cent for the relative litude suppression factor as a result of the redder TESS passband compared to the Kepler mission using a pulsating eclipsing binary system. Furthermore, our s le 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.
Publisher: Oxford University Press (OUP)
Date: 11-04-2005
Publisher: Oxford University Press (OUP)
Date: 13-07-2001
Publisher: EDP Sciences
Date: 23-12-2012
Publisher: American Astronomical Society
Date: 08-01-2014
DOI: 10.1086/523936
Publisher: Cambridge University Press (CUP)
Date: 08-2006
DOI: 10.1017/S1743921307011635
Abstract: The seismology and physics of localized structures beneath the surface of the Sun takes on a special significance with the completion in 2006 of a solar cycle of observations by the ground-based Global Oscillation Network Group (GONG) and by the instruments on board the Solar and Heliospheric Observatory ( SOHO ). Of course, the spatially unresolved Birmingham Solar Oscillation Network (BiSON) has been observing for even longer. At the same time, the testing of models of stellar structure moves into high gear with the extension of deep probes from the Sun to other solar-like stars and other multi-mode pulsators, with ever-improving observations made from the ground, the success of the MOST satellite, and the recently launched CoRoT satellite. Here we report the current state of the two closely related and rapidly developing fields of helio- and asteroseimology.
Publisher: IOP Publishing
Date: 26-09-2019
Publisher: American Astronomical Society
Date: 22-10-2021
Publisher: Oxford University Press (OUP)
Date: 11-08-2017
Publisher: EDP Sciences
Date: 11-2003
Publisher: Oxford University Press (OUP)
Date: 28-02-2022
Abstract: Red giant asteroseismology can provide valuable information for studying the Galaxy as demonstrated by space missions like CoRoT and Kepler. However, previous observations have been limited to small data sets and fields of view. The TESS mission provides far larger s les and, for the first time, the opportunity to perform asteroseimic inference from full-frame images full-sky, instead of narrow fields and pre-selected targets. Here, we seek to detect oscillations in TESS data of the red giants in the Kepler field using the 4-yr Kepler results as a benchmark. Because we use 1–2 sectors of observation, our results are representative of the typical scenario from TESS data. We detect clear oscillations in ∼3000 stars with another ∼1000 borderline (low S/N) cases. In comparison, best-case predictions suggest ∼4500 detectable oscillating giants. Of the clear detections, we measure Δν in 570 stars, meaning a ∼20 per cent Δν yield (14 per cent for one sector and 26 per cent for two sectors). These yields imply that typical (1–2 sector) TESS data will result in significant detection biases. Hence, to boost the number of stars, one might need to use only νmax as the seismic input for stellar property estimation. However, we find little bias in the seismic measurements and typical scatter is about 5–6 per cent in νmax and 2–3 per cent in Δν. These values, coupled with typical uncertainties in parallax, Teff, and [Fe/H] in a grid-based approach, would provide internal uncertainties of 3 per cent in inferred stellar radius, 6 per cent in mass, and 20 per cent in age for low-luminosity giant stars. Finally, we find red giant seismology is not significantly affected by seismic signal confusion from blending for stars with Tmag ≲ 12.5.
Publisher: Oxford University Press (OUP)
Date: 09-05-2015
DOI: 10.1093/MNRAS/STV868
Publisher: American Astronomical Society
Date: 31-10-2019
Publisher: Wiley
Date: 10-2007
Publisher: American Astronomical Society
Date: 31-01-2012
Publisher: Oxford University Press (OUP)
Date: 30-06-2022
Abstract: We study 119 B stars located in the Scorpius–Centaurus Association using data from NASA’s TESS Mission. We see pulsations in 81 stars (68 per cent) across the full range of effective temperatures. In particular, we confirm previous reports of low-frequency pulsations in stars whose temperatures fall between the instability strips of SPB stars (slowly pulsating B stars) and δ Scuti stars. By taking the stellar densities into account, we conclude that these cannot be p modes and confirm previous suggestions that these are probably rapidly rotating SPB stars. We also confirm that they follow two period–luminosity relations that are consistent with prograde sectoral g modes that are dipole (l = m = 1) and quadrupole (l = m = 2), respectively. One of the stars (ξ2 Cen) is a hybrid pulsator that shows regular spacings in both g and p modes. We confirm that α Cru has low- litude p-mode pulsations, making it one of the brightest β Cephei stars in the sky. We also find several interesting binaries, including a very short-period heartbeat star (HD 132094), a previously unknown eclipsing binary (π Lup), and an eclipsing binary with high- litude tidally driven pulsations (HR 5846). The results clearly demonstrate the power of TESS for studying variability in stellar associations.
Publisher: American Astronomical Society
Date: 24-02-2014
Publisher: Wiley
Date: 17-06-2022
DOI: 10.1111/INM.13031
Abstract: This qualitative exploratory study explored nurses' mental health and coping strategies working with suspected and confirmed COVID‐19 patients in Brunei Darussalam. Eleven focus group discussions were conducted between October 2020 and January 2021, involving 75 participants. Three themes emerged: ‘COVID‐19 roller‐coaster transitional journey’ explained the different psychological responses of the journey of the nurses from merely hearing about COVID‐19 from far to the invasion of the virus and community outbreak in the country ‘Mind my mind and heart’ share experiences of the nurses in terms of their mental health and emotional responses and ‘the psychosocial system’ described the coping mechanisms of the nurses throughout the COVID‐19 pandemic. Nurses' mental health and coping strategies during the COVID‐19 pandemic influenced how they provided care and performed other tasks, which should not be taken for granted. Nurses employed psychosocial coping methods at the different phases of the COVID‐19 pandemic and support from family, friends, the public, and the governmental level. This research is fundamental as a basis for other countries to design psychological interventions during this yet unsettled COVID‐19 pandemic.
Publisher: EDP Sciences
Date: 12-2004
Publisher: Oxford University Press (OUP)
Date: 29-01-2018
DOI: 10.1093/MNRAS/STY222
Publisher: Oxford University Press (OUP)
Date: 13-02-2019
DOI: 10.1093/MNRAS/STZ432
Publisher: Cambridge University Press (CUP)
Date: 08-2006
DOI: 10.1017/S1743921307004310
Abstract: We have analysed publicly available MACHO observations of 6833 variable stars in the Large Magellanic Cloud, classified as eclipsing binaries. After finding that a significant fraction of the s le was misclassified, we redetermined periods and variability class for all stars, producing a clean s le of 3031 eclipsing binaries. We have investigated their distribution in the period-color-luminosity space, which was used, for ex le, to assign a foreground probability to every object and establish new period-luminosity relations to selected types of eclipsing stars. We found that the orbital period distribution of LMC binaries is very similar to those of the SMC and the Milky Way. We have also determined the rate of period change for every star using the O-C method, discovering about 40 eclipsing binaries with apsidal motion, 45 systems with cyclic period changes and about 80 stars with parabolic O-C diagrams. In a few objects we discovered gradual litude variation, which can be explained by changes in the orbital inclination caused by a perturbing third body in the system.
Publisher: Oxford University Press (OUP)
Date: 25-09-2023
Publisher: Springer Science and Business Media LLC
Date: 2002
Publisher: Cambridge University Press (CUP)
Date: 05-2008
DOI: 10.1017/S1743921308026537
Abstract: 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.
Publisher: American Astronomical Society
Date: 15-09-2011
Publisher: Oxford University Press (OUP)
Date: 04-05-2017
Publisher: Oxford University Press (OUP)
Date: 28-12-2020
Abstract: We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA’s Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to be of planetary origin based on radial velocity observations. An analysis of the TESS photometry, the Minerva-Australis, FEROS, and HARPS radial velocities, and the asteroseismic data of the stellar oscillations reveals that TOI-257b has a mass of MP = 0.138 ± 0.023 $\\rm {M_J}$ (43.9 ± 7.3 $\\, M_{\\rm \\oplus}$), a radius of RP = 0.639 ± 0.013 $\\rm {R_J}$ (7.16 ± 0.15 $\\, \\mathrm{ R}_{\\rm \\oplus}$), bulk density of $0.65^{+0.12}_{-0.11}$ (cgs), and period $18.38818^{+0.00085}_{-0.00084}$ $\\rm {days}$. TOI-257b orbits a bright (V = 7.612 mag) somewhat evolved late F-type star with M* = 1.390 ± 0.046 $\\rm {M_{sun}}$, R* = 1.888 ± 0.033 $\\rm {R_{sun}}$, Teff = 6075 ± 90 $\\rm {K}$, and vsin i = 11.3 ± 0.5 km s−1. Additionally, we find hints for a second non-transiting sub-Saturn mass planet on a ∼71 day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars (∼100) that have been characterized with asteroseismology. Warm sub-Saturns are rare in the known s le of exoplanets, and thus the discovery of TOI-257b is important in the context of future work studying the formation and migration history of similar planetary systems.
Publisher: American Astronomical Society
Date: 31-03-2010
Publisher: American Astronomical Society
Date: 03-2023
Abstract: The Transiting Exoplanet Survey Satellite (TESS) mission searches for new exoplanets. The observing strategy of TESS results in high-precision photometry of millions of stars across the sky, allowing for detailed asteroseismic studies of in idual systems. In this work, we present a detailed asteroseismic analysis of the giant star HD 76920 hosting a highly eccentric giant planet ( e = 0.878) with an orbital period of 415 days, using five sectors of TESS light curve that cover around 140 days of data. Solar-like oscillations in HD 76920 are detected around 52 μ Hz by TESS for the first time. By utilizing asteroseismic modeling that takes classical observational parameters and stellar oscillation frequencies as constraints, we determine improved measurements of the stellar mass (1.22 ± 0.11 M ⊙ ), radius (8.68 ± 0.34 R ☉ ), and age (5.2 ± 1.4 Gyr). With the updated parameters of the host star, we update the semimajor axis and mass of the planet as a = 1.165 ± 0.035 au and M p sin i = 3.57 ± 0.22 M Jup . With an orbital pericenter of 0.142 ± 0.005 au, we confirm that the planet is currently far away enough from the star to experience negligible tidal decay until being engulfed in the stellar envelope. We also confirm that this event will occur within about 100 Myr, depending on the stellar model used.
Publisher: EDP Sciences
Date: 02-10-2007
Publisher: Oxford University Press (OUP)
Date: 04-12-2021
Abstract: Oscillating eclipsing Algols (oEAs) are remarkable systems that 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 Transiting Exoplanet Survey Satellite 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 $3.52 \\times 10^{-9}\\, {\\rm M}_\\odot$ yr−1 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, 12 doublets spaced by 2forb were detected from which we infer that this star is a tidally tilted pulsator. A mean p-mode frequency spacing of ≈7.2 d−1 was found as well.
Publisher: EDP Sciences
Date: 26-11-2014
Publisher: Oxford University Press (OUP)
Date: 03-07-2018
Publisher: Oxford University Press (OUP)
Date: 11-10-2019
Publisher: Oxford University Press (OUP)
Date: 21-12-2009
Publisher: American Astronomical Society
Date: 09-02-2011
Publisher: Springer Science and Business Media LLC
Date: 14-04-2022
Publisher: Springer Science and Business Media LLC
Date: 2016
DOI: 10.1038/NATURE16171
Abstract: Magnetic fields play a part in almost all stages of stellar evolution. Most low-mass stars, including the Sun, show surface fields that are generated by dynamo processes in their convective envelopes. Intermediate-mass stars do not have deep convective envelopes, although 10 per cent exhibit strong surface fields that are presumed to be residuals from the star formation process. These stars do have convective cores that might produce internal magnetic fields, and these fields might survive into later stages of stellar evolution, but information has been limited by our inability to measure the fields below the stellar surface. Here we report the strength of dipolar oscillation modes for a s le of 3,600 red giant stars. About 20 per cent of our s le show mode suppression, by strong magnetic fields in the cores, but this fraction is a strong function of mass. Strong core fields occur only in red giants heavier than 1.1 solar masses, and the occurrence rate is at least 50 per cent for intermediate-mass stars (1.6-2.0 solar masses), indicating that powerful dynamos were very common in the previously convective cores of these stars.
Publisher: American Astronomical Society
Date: 12-2022
Abstract: The study of young associations is essential for building a complete record of local star formation processes. The Fornax–Horologium association (FH), including the χ 1 Fornacis cluster, represents one of the nearest young stellar populations to the Sun. This association has recently been linked to the Tuc-Hor, Carina, and Columba associations, building an extensive “Austral Complex” almost entirely within 150 pc. Using Gaia astrometry and photometry in addition to new spectroscopic observations, we perform the deepest survey of FH to date, identifying over 300 candidate members, nearly doubling the known population. By combining this s le with literature surveys of the other constituent populations, we produce a contiguous stellar population covering the entire Austral Complex, allowing the definitions of subpopulations to be reassessed along with connections to external populations. This analysis recovers new definitions for FH, Tuc-Hor, Columba, and Carina, while also revealing a connection between the Austral complex and the Sco-Cen-affiliated Platais 8 cluster. This suggests that the Austral complex may be just a small component of a much larger and more erse star formation event. Computing ages and tracing stellar populations back to formation reveals two distinct nodes of cospatial and continuous formation in the Austral Complex, one containing Tuc-Hor, and the other containing FH, Carina, and Columba. This mirrors recent work showing similar structure elsewhere, suggesting that these nodes, which only emerge through the use of traceback, may represent the clearest discrete unit of local star formation, and a key building block needed to reconstruct larger star-forming events.
Publisher: American Astronomical Society
Date: 02-2022
Abstract: The four-year Kepler mission collected long-cadence images of the open clusters NGC 6791 and NGC 6819, known as “superst s”. Each superst region is a 200 pixel square that captures thousands of cluster members, plus foreground and background stars, of which only the brightest were targeted for long- or short-cadence photometry during the Kepler mission. Using image subtraction photometry, we have produced light curves for every object in the Kepler Input Catalog that falls on the superst s. The Increased Resolution Image Subtraction (IRIS) catalog includes light curves for 9150 stars, and contains a wealth of new data: 8427 of these stars were not targeted at all by Kepler, and we have increased the number of available quarters of long-cadence data for 382 stars. The catalog is available as a high-level science product on MAST, with both raw photometric data for each quarter and corrected light curves for all available quarters for each star. We also present an introduction to our implementation of image subtraction photometry and the open-source IRIS pipeline, alongside an overview of the data products, systematics, and catalog statistics.
Publisher: American Astronomical Society
Date: 29-10-2019
Publisher: Oxford University Press (OUP)
Date: 31-07-2022
Abstract: We have used NASA’s TESS mission to study catalogued δ Scuti stars. We examined TESS light curves for 434 stars, including many for which few previous observations exist. We found that 62 are not δ Scuti pulsators, with most instead showing variability from binarity. For the 372 δ Scuti stars, we provide a catalogue of the period and litude of the dominant pulsation mode. Using Gaia DR3 parallaxes, we place the stars in the period–luminosity (P–L) diagram and confirm previous findings that most stars lie on a ridge that corresponds to pulsation in the fundamental radial mode, and that many others fall on a second ridge that is a factor two shorter in period. This second ridge is seen more clearly than before, thanks to the revised periods and distances. We demonstrate the value of the P–L diagram in distinguishing δ Scuti stars from short-period RR Lyrae stars, and we find several new ex les of high-frequency δ Scuti stars with regular sequences of overtone modes, including XX Pyx and 29 Cyg. Finally, we revisit the s le of δ Scuti stars observed by Kepler and show that they follow a tight period–density relation, with a pulsation constant for the fundamental mode of Q = 0.0315 d.
Publisher: American Astronomical Society
Date: 03-2016
Publisher: American Astronomical Society
Date: 14-04-2015
Publisher: Oxford University Press (OUP)
Date: 24-12-2021
Abstract: Mass-loss by red giants is an important process to understand the final stages of stellar evolution and the chemical enrichment of the interstellar medium. Mass-loss rates are thought to be controlled by pulsation-enhanced dust-driven outflows. Here, we investigate the relationships between mass-loss, pulsations, and radiation, using 3213 luminous Kepler red giants and 13 5000 ASAS–SN semiregulars and Miras. Mass-loss rates are traced by infrared colours using 2MASS and Wide-field Infrared Survey Explorer(WISE) and by observed-to-model WISE fluxes, and are also estimated using dust mass-loss rates from literature assuming a typical gas-to-dust mass ratio of 400. To specify the pulsations, we extract the period and height of the highest peak in the power spectrum of oscillation. Absolute magnitudes are obtained from the 2MASS Ks band and the Gaia DR2 parallaxes. Our results follow. (i) Substantial mass-loss sets in at pulsation periods above ∼60 and ∼100 d, corresponding to Asymptotic-Giant-Branch stars at the base of the period-luminosity sequences C′ and C. (ii) The mass-loss rate starts to rapidly increase in semiregulars for which the luminosity is just above the red-giant-branch tip and gradually plateaus to a level similar to that of Miras. (iii) The mass-loss rates in Miras do not depend on luminosity, consistent with pulsation-enhanced dust-driven winds. (iv) The accumulated mass-loss on the red giant branch consistent with asteroseismic predictions reduces the masses of red-clump stars by 6.3 per cent, less than the typical uncertainty on their asteroseismic masses. Thus mass-loss is currently not a limitation of stellar age estimates for galactic archaeology studies.
Publisher: American Astronomical Society
Date: 07-2007
DOI: 10.1086/517994
Publisher: AIP
Date: 2008
DOI: 10.1063/1.2993676
Publisher: American Astronomical Society
Date: 07-12-2016
Publisher: Oxford University Press (OUP)
Date: 22-06-2020
Abstract: The study of planet occurrence as a function of stellar mass is important for a better understanding of planet formation. Estimating stellar mass, especially in the red giant regime, is difficult. In particular, stellar masses of a s le of evolved planet-hosting stars based on spectroscopy and grid-based modelling have been put to question over the past decade with claims they were overestimated. Although efforts have been made in the past to reconcile this dispute using asteroseismology, results were inconclusive. In an attempt to resolve this controversy, we study four more evolved planet-hosting stars in this paper using asteroseismology, and we revisit previous results to make an informed study of the whole ensemble in a self-consistent way. For the four new stars, we measure their masses by locating their characteristic oscillation frequency, νmax, from their radial velocity time series observed by SONG. For two stars, we are also able to measure the large frequency separation, Δν, helped by extended SONG single-site and dual-site observations and new Transiting Exoplanet Survey Satellite observations. We establish the robustness of the νmax-only-based results by determining the stellar mass from Δν, and from both Δν and νmax. We then compare the seismic masses of the full ensemble of 16 stars with the spectroscopic masses from three different literature sources. We find an offset between the seismic and spectroscopic mass scales that is mass dependent, suggesting that the previously claimed overestimation of spectroscopic masses only affects stars more massive than about 1.6 M⊙.
Publisher: American Astronomical Society
Date: 10-2022
Abstract: 51 Eri is well known for hosting a directly imaged giant planet and for its membership to the β Pictoris moving group. Using 2 minute cadence photometry from the Transiting Exoplanet Survey Satellite (TESS), we detect multiperiodic variability in 51 Eri that is consistent with pulsations of Gamma Doradus ( γ Dor) stars. We identify the most significant pulsation modes (with frequencies between ∼0.5 and 3.9 cycles day −1 and litudes ranging between ∼1 and 2 mmag) as dipole and quadrupole gravity modes, as well as Rossby modes, as previously observed in Kepler γ Dor stars. Our results demonstrate that previously reported variability attributed to stellar rotation is instead likely due to γ Dor pulsations. Using the mean frequency of the ℓ = 1 gravity modes, together with empirical trends of the Kepler γ Dor population, we estimate a plausible stellar core rotation period of 0.9 − 0.1 + 0.3 days for 51 Eri. We find no significant evidence for transiting companions around 51 Eri in the residual light curve. The detection of γ Dor pulsations presented here, together with follow-up observations and modeling, may enable the determination of an asteroseismic age for this benchmark system. Future TESS observations would allow a constraint on the stellar core rotation rate, which in turn traces the surface rotation rate, and thus would help clarify whether or not the stellar equatorial plane and orbit of 51 Eri b are coplanar.
Publisher: Oxford University Press (OUP)
Date: 29-01-2015
Publisher: American Astronomical Society
Date: 09-08-2016
Publisher: Oxford University Press (OUP)
Date: 19-07-2018
Publisher: Oxford University Press (OUP)
Date: 21-08-2001
Publisher: Oxford University Press (OUP)
Date: 07-2004
Publisher: American Astronomical Society
Date: 10-04-2020
Publisher: American Astronomical Society
Date: 25-07-2012
Publisher: American Astronomical Society
Date: 08-2023
Abstract: This paper reports the estimated stellar parameters of 1153 Kepler red giant branch stars determined with asteroseismic modeling. We use radial-mode oscillation frequencies, gravity-mode period spacings, Gaia luminosities, and spectroscopic data to characterize these stars. Compared with previous studies, we find that the two additional observed constraints, i.e., the gravity-mode period spacing and luminosity, significantly improve the precision of fundamental stellar parameters. The typical uncertainties are 2.9% for the mass, 11% for the age, 1.0% for the radius, 0.0039 dex for the surface gravity, and 0.5% for the helium core mass, making this the best-characterized large s le of red giant stars available to date. With better characterizations for these red giants, we recalibrate the seismic scaling relations and study the surface term on the red giant branch. We confirm that the surface term depends on the surface gravity and effective temperature, but there is no significant correlation with metallicity.
Publisher: American Astronomical Society
Date: 03-04-2014
Publisher: Springer Science and Business Media LLC
Date: 13-01-2020
Publisher: Oxford University Press (OUP)
Date: 05-11-2018
Publisher: Springer Science and Business Media LLC
Date: 07-12-2011
DOI: 10.1038/NATURE10612
Abstract: When 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. Convection takes place over much of the star's radius. Conservation of angular momentum requires that the cores of these stars rotate faster than their envelopes indirect evidence supports this. Information about the angular-momentum distribution is inaccessible to direct observations, but it can be extracted from the effect of rotation on oscillation modes that probe the stellar interior. Here we report an increasing rotation rate from the surface of the star to the stellar core in the interiors of red giants, obtained using the rotational frequency splitting of recently detected 'mixed modes'. By comparison with theoretical stellar models, we conclude that the core must rotate at least ten times faster than the surface. This observational result confirms the theoretical prediction of a steep gradient in the rotation profile towards the deep stellar interior.
Publisher: American Astronomical Society
Date: 29-04-2019
Publisher: Oxford University Press (OUP)
Date: 13-08-2018
Publisher: EDP Sciences
Date: 03-2010
Publisher: Oxford University Press (OUP)
Date: 02-2002
Publisher: American Astronomical Society
Date: 11-2005
DOI: 10.1086/462401
Publisher: Oxford University Press (OUP)
Date: 21-06-2009
Publisher: Oxford University Press (OUP)
Date: 23-06-2018
Publisher: Oxford University Press (OUP)
Date: 28-03-2016
DOI: 10.1093/MNRAS/STW705
Publisher: Oxford University Press (OUP)
Date: 13-11-2006
Publisher: Oxford University Press (OUP)
Date: 05-2004
Publisher: EDP Sciences
Date: 05-2017
Publisher: Oxford University Press (OUP)
Date: 20-05-2014
DOI: 10.1093/MNRAS/STU765
Publisher: American Astronomical Society
Date: 03-04-2012
Publisher: EDP Sciences
Date: 20-09-2011
Publisher: EDP Sciences
Date: 2012
Publisher: American Astronomical Society
Date: 15-06-2020
Publisher: Springer Science and Business Media LLC
Date: 09-2011
DOI: 10.1038/NATURE10389
Abstract: Delta Scuti (δSct) stars are opacity-driven pulsators with masses of 1.5-2.5 M⊙, their pulsations resulting from the varying ionization of helium. In less massive stars such as the Sun, convection transports mass and energy through the outer 30 per cent of the star and excites a rich spectrum of resonant acoustic modes. Based on the solar ex le, with no firm theoretical basis, models predict that the convective envelope in δSct stars extends only about 1 per cent of the radius, but with sufficient energy to excite solar-like oscillations. This was not observed before the Kepler mission, so the presence of a convective envelope in the models has been questioned. Here we report the detection of solar-like oscillations in the δSct star HD187547, implying that surface convection operates efficiently in stars about twice as massive as the Sun, as the ad hoc models predicted.
Publisher: EDP Sciences
Date: 2015
Publisher: Springer Science and Business Media LLC
Date: 20-02-2013
DOI: 10.1038/NATURE11914
Abstract: Since the discovery of the first exoplanets, it has been known that other planetary systems can look quite unlike our own. Until fairly recently, we have been able to probe only the upper range of the planet size distribution, and, since last year, to detect planets that are the size of Earth or somewhat smaller. Hitherto, no planets have been found that are smaller than those we see in the Solar System. Here we report a planet significantly smaller than Mercury. This tiny planet is the innermost of three that orbit the Sun-like host star, which we have designated Kepler-37. Owing to its extremely small size, similar to that of the Moon, and highly irradiated surface, the planet, Kepler-37b, is probably rocky with no atmosphere or water, similar to Mercury.
Publisher: Oxford University Press (OUP)
Date: 27-02-2020
Abstract: Measuring phase modulation in pulsating stars has proven to be a highly successful way of finding binary systems. The class of pulsating main-sequence A and F variables, known as δ Scuti stars consists of particularly good targets for this, and the Kepler s le of these has been almost fully exploited. However, some Keplerδ Scuti stars have incorrect temperatures in stellar properties catalogues, and were missed in previous analyses. We used an automated pulsation classification algorithm to find 93 new δ Scuti pulsators among tens of thousands of F-type stars, which we then searched for phase modulation attributable to binarity. We discovered 10 new binary systems and calculated their orbital parameters, which we compared with those of binaries previously discovered in the same way. The results suggest that some of the new companions may be white dwarfs.
Publisher: EDP Sciences
Date: 2015
Publisher: Oxford University Press (OUP)
Date: 12-10-2019
Abstract: Asteroseismology is a promising tool to study Galactic structure and evolution because it can probe the ages of stars. Earlier attempts comparing seismic data from the Kepler satellite with predictions from Galaxy models found that the models predicted more low-mass stars compared to the observed distribution of masses. It was unclear if the mismatch was due to inaccuracies in the Galactic models, or the unknown aspects of the selection function of the stars. Using new data from the K2 mission, which has a well-defined selection function, we find that an old metal-poor thick disc, as used in previous Galactic models, is incompatible with the asteroseismic information. We use an importance-s ling framework, which takes the selection function into account, to fit for the metallicities of a population synthesis model using spectroscopic data. We show that spectroscopic measurements of [Fe/H] and [α/Fe] elemental abundances from the GALAH survey indicate a mean metallicity of log (Z/Z⊙) = −0.16 for the thick disc. Here Z is the effective solar-scaled metallicity, which is a function of [Fe/H] and [α/Fe]. With the revised disc metallicities, for the first time, the theoretically predicted distribution of seismic masses show excellent agreement with the observed distribution of masses. This indirectly verifies that the asteroseismic mass scaling relation is good to within five per cent. Assuming the asteroseismic scaling relations are correct, we estimate the mean age of the thick disc to be about 10 Gyr, in agreement with the traditional idea of an old α-enhanced thick disc.
Publisher: Oxford University Press (OUP)
Date: 06-08-2020
Abstract: We systematically searched for gravity- and Rossby-mode period spacing patterns in Kepler eclipsing binaries with γ Doradus pulsators. These stars provide an excellent opportunity to test the theory of tidal synchronization and angular momentum transport in F- and A-type stars. We discovered 35 systems that show clear patterns, including the spectroscopic binary KIC 10080943. Combined with 45 non-eclipsing binaries with γ Dor components that have been found using pulsation timing, we measured their near-core rotation rates and asymptotic period spacings. We find that many stars are tidally locked if the orbital periods are shorter than 10 d, in which the near-core rotation periods given by the traditional approximation of rotation are consistent with the orbital period. Compared to the single stars, γ Dor stars in binaries tend to have slower near-core rotation rates, likely a consequence of tidal spin-down. We also find three stars that have extremely slow near-core rotation rates. To explain these, we hypothesize that unstable tidally excited oscillations can transfer angular momentum from the star to the orbit, and slow the star below synchronism, a process we refer to as ‘inverse tides’.
Publisher: Oxford University Press (OUP)
Date: 05-2005
Publisher: EDP Sciences
Date: 21-01-2201
Publisher: Oxford University Press (OUP)
Date: 09-12-0001
Publisher: Oxford University Press (OUP)
Date: 11-08-2002
Publisher: EDP Sciences
Date: 2012
Publisher: American Association for the Advancement of Science (AAAS)
Date: 03-08-2012
Abstract: In our solar system, the rocky planets have very distinct orbits from those of the gas giants. Carter et al. (p. 556 , published online 21 June) report on a planetary system where this pattern does not apply, posing a challenge to theories of planet formation. Data from the Kepler space telescope reveal two planets with radically different densities orbiting the same star with very similar orbital periods. One planet has a rocky Earth-like composition and the other is akin to Neptune.
Publisher: American Astronomical Society
Date: 02-12-2011
Publisher: Cambridge University Press (CUP)
Date: 12-2005
DOI: 10.1017/S1743921306004649
Abstract: We report the major highlights of variable star research within the past three years. This overview is limited to intrinsically variable stars, because the achievements in variable star research stemming from binarity, or multiplicity in general, is covered by the summary report of Commissions 26 and 42.
Publisher: Oxford University Press (OUP)
Date: 18-04-2018
DOI: 10.1093/MNRAS/STY898
Publisher: Oxford University Press (OUP)
Date: 29-03-2018
DOI: 10.1093/MNRAS/STY784
Publisher: American Astronomical Society
Date: 31-10-2012
Publisher: American Astronomical Society
Date: 27-04-2016
Publisher: Oxford University Press (OUP)
Date: 04-2009
Publisher: Cambridge University Press (CUP)
Date: 08-2006
DOI: 10.1017/S1743921307000270
Abstract: Asteroseismology—using stellar oscillations to study the interiors of stars—is a relatively new and growing research field in astrophysics. Oscillations are found in stars of most masses and essentially all stages of evolution. Their frequencies are determined by the internal sound speed and density structure of the star, as well as rotation, convection processes and possibly effects of magnetic fields. Recent developments have led to a breakthrough in our ability to study the details of cores of solar-like stars and it is foreseen that a number of key science questions will be addressed through the analysis of frequencies and other properties of stellar oscillations. In this paper we review some of the latest results from asteroseismology of solar-like stars, with the focus on properties of convection.
Publisher: American Astronomical Society
Date: 10-2014
Publisher: Oxford University Press (OUP)
Date: 11-05-2012
Publisher: American Astronomical Society
Date: 10-05-2006
DOI: 10.1086/501418
Publisher: The Open Journal
Date: 10-07-2020
DOI: 10.21105/JOSS.02125
Publisher: Springer Science and Business Media LLC
Date: 2003
Publisher: EDP Sciences
Date: 11-2010
Publisher: American Astronomical Society
Date: 03-2022
Abstract: This paper presents a correction to the scaling relations for red giant stars using model-based masses and radii. We measure radial-mode frequencies from Kepler observations for 3642 solar-like oscillators on the red giant branch and use them to characterize the stars with grid-based modeling. We determine fundamental stellar parameters with good precision: the typical uncertainty is 4.5% for mass, 16% for age, 0.006 dex for surface gravity, and 1.7% for radius. We also achieve good accuracy for estimated masses and radii, based on a comparison with those determined for eclipsing binaries. We find a systematic offset of ∼15% in mass and ∼7% in radius between the modeling solutions and the scaling relations. Further investigation indicates that these offsets are mainly caused by a systematic bias in the Δ ν scaling relation: the original scaling relation underestimates the Δ ν value by ∼4%, on average, and it is important to correct for the surface term in the calibration. We find no significant offset in the ν max scaling relation, although a clear metallicity dependence is seen and we suggest including a metallicity term in the formulae. Lastly, we calibrate new scaling relations for red giant stars based on observed global seismic parameters, spectroscopic effective temperatures and metallicities, and modeling-inferred masses and radii.
Publisher: Oxford University Press (OUP)
Date: 18-04-2019
Publisher: EDP Sciences
Date: 03-2005
Publisher: American Astronomical Society
Date: 27-01-2017
Publisher: Oxford University Press (OUP)
Date: 05-02-2007
Publisher: Cambridge University Press (CUP)
Date: 2003
DOI: 10.1071/AS03025
Abstract: 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 in idual stars. We conclude that the study of solar-like oscillations from the ground and space has an exciting future.
Publisher: American Astronomical Society
Date: 12-2011
Publisher: BMJ
Date: 10-08-2017
Publisher: Oxford University Press (OUP)
Date: 13-06-2019
Abstract: We perform a search for rapidly oscillating Ap stars in the Kepler long-cadence data, where true oscillations above the Nyquist limit of 283.21 $\\mu$Hz can be reliably distinguished from aliases as a consequence of the barycentric time corrections applied to the Kepler data. We find evidence for rapid oscillations in six stars: KIC 6631188, KIC 7018170, KIC 10685175, KIC 11031749, KIC 11296437, and KIC 11409673, and identify each star as chemically peculiar through either pre-existing classifications or spectroscopic measurements. For each star, we identify the principal pulsation mode, and are able to observe several additional pulsation modes in KIC 7018170. We find that KIC 7018170 and KIC 11409673 both oscillate above their theoretical acoustic cut-off frequency, whilst KIC 11031749 oscillates at the cut-off frequency within uncertainty. All but KIC 11031749 exhibit strong litude modulation consistent with the oblique pulsator model, confirming their mode geometry and periods of rotation.
Publisher: Oxford University Press (OUP)
Date: 21-12-2021
Abstract: Asteroseismic scaling relations are often used to derive stellar masses and radii, particularly for stellar, exoplanet, and Galactic studies. It is therefore important that their precisions are known. Here we measure the intrinsic scatter of the underlying seismic scaling relations for Δν and νmax, using two sharp features that are formed in the H–R diagram (or related diagrams) by the red giant populations. These features are the edge near the zero-age core-helium-burning phase, and the strong clustering of stars at the so-called red giant branch bump. The broadening of those features is determined by factors including the intrinsic scatter of the scaling relations themselves, and therefore it is capable of imposing constraints on them. We modelled Kepler stars with a Galaxia synthetic population, upon which we applied the intrinsic scatter of the scaling relations to match the degree of sharpness seen in the observation. We found that the random errors from measuring Δν and νmax provide the dominating scatter that blurs the features. As a consequence, we conclude that the scaling relations have intrinsic scatter of $\\sim 0.5$ (Δν), $\\sim 1.1$ (νmax), $\\sim 1.7$ (M), and $\\sim 0.4{{\\ \\rm per\\ cent}}$ (R), for the SYD pipeline measured Δν and νmax. This confirms that the scaling relations are very powerful tools. In addition, we show that standard evolution models fail to predict some of the structures in the observed population of both the HeB and RGB stars. Further stellar model improvements are needed to reproduce the exact distributions.
Publisher: Springer Science and Business Media LLC
Date: 03-2011
DOI: 10.1038/NATURE09935
Abstract: Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell. Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion. Outstanding issues in our understanding of red giants include uncertainties in the amount of mass lost at the surface before helium ignition and the amount of internal mixing from rotation and other processes. Progress is h ered by our inability to distinguish between red giants burning helium in the core and those still only burning hydrogen in a shell. Asteroseismology offers a way forward, being a powerful tool for probing the internal structures of stars using their natural oscillation frequencies. Here we report observations of gravity-mode period spacings in red giants that permit a distinction between evolutionary stages to be made. We use high-precision photometry obtained by the Kepler spacecraft over more than a year to measure oscillations in several hundred red giants. We find many stars whose dipole modes show sequences with approximately regular period spacings. These stars fall into two clear groups, allowing us to distinguish unambiguously between hydrogen-shell-burning stars (period spacing mostly ∼ 50 seconds) and those that are also burning helium (period spacing ∼ 100 to 300 seconds).
Publisher: American Astronomical Society
Date: 26-05-2010
Publisher: Springer Science and Business Media LLC
Date: 13-05-2020
Publisher: American Association for the Advancement of Science (AAAS)
Date: 08-04-2011
Abstract: Using asteroseismology—the study of stellar oscillations, it is possible to probe the interior of stars and to derive stellar parameters, such as mass and radius (see the Perspective by Montgomery ). Based on asteroseismic data from the NASA Kepler mission, Chaplin et al. (p. 213 ) detected solarlike oscillations in 500 solartype stars in our Galaxy. The distribution of the radii of these stars matches that expected from stellar evolution theory, but the distribution in mass does not, which challenges our knowledge of star formation rates, the mass of forming stars, and the models of the stars themselves. Derekas et al. (p. 216 ) report the detection of a triple-star system comprising a red giant star and two red dwarfs. The red giant star, instead of the expected solarlike oscillations, shows evidence for tidally induced oscillations driven by the orbital motion of the red dwarf pair. Finally, Beck et al. (p. 205 ) describe unusual oscillations from a red giant star that may elucidate characteristics of its core.
Publisher: American Astronomical Society
Date: 06-01-2012
Publisher: EDP Sciences
Date: 17-11-2003
Publisher: American Astronomical Society
Date: 24-10-4220
Abstract: Asteroseismology of bright stars has become increasingly important as a method to determine the fundamental properties (in particular ages) of stars. The Kepler Space Telescope initiated a revolution by detecting oscillations in more than 500 main-sequence and subgiant stars. However, most Kepler stars are faint and therefore have limited constraints from independent methods such as long-baseline interferometry. Here we present the discovery of solar-like oscillations in α Men A, a naked-eye ( V = 5.1) G7 dwarf in TESS’s southern continuous viewing zone. Using a combination of astrometry, spectroscopy, and asteroseismology, we precisely characterize the solar analog α Men A ( T eff = 5569 ± 62 K, R ⋆ = 0.960 ± 0.016 R ⊙ , M ⋆ = 0.964 ± 0.045 M ⊙ ). To characterize the fully convective M dwarf companion, we derive empirical relations to estimate mass, radius, and temperature given the absolute Gaia magnitude and metallicity, yielding M ⋆ = 0.169 ± 0.006 M ⊙ , R ⋆ = 0.19 ± 0.01 R ⊙ , and T eff = 3054 ± 44 K. Our asteroseismic age of 6.2 ± 1.4 (stat) ± 0.6 (sys) Gyr for the primary places α Men B within a small population of M dwarfs with precisely measured ages. We combined multiple ground-based spectroscopy surveys to reveal an activity cycle of P = 13.1 ± 1.1 yr for α Men A, a period similar to that observed in the Sun. We used different gyrochronology models with the asteroseismic age to estimate a rotation period of ∼30 days for the primary. Alpha Men A is now the closest ( d = 10 pc) solar analog with a precise asteroseismic age from space-based photometry, making it a prime target for next-generation direct-imaging missions searching for true Earth analogs.
Publisher: American Astronomical Society
Date: 20-12-2005
DOI: 10.1086/497530
Publisher: American Astronomical Society
Date: 23-05-2014
Publisher: American Astronomical Society
Date: 30-01-2017
Publisher: American Astronomical Society
Date: 30-01-2017
Publisher: Springer Science and Business Media LLC
Date: 21-12-2023
Publisher: American Astronomical Society
Date: 09-09-2022
Abstract: With long data sets available for asteroseismology from space missions, it is sometimes necessary to deal with time series that have large gaps. This is becoming particularly relevant for TESS, which is revisiting many fields on the sky every two years. Because solar-like oscillators have finite mode lifetimes, it has become tempting to close large gaps by shifting time st s. Using actual data from the Kepler Mission, we show that this results in artificial structures in the power spectrum that compromise the measurements of mode frequencies and linewidths.
Publisher: Oxford University Press (OUP)
Date: 11-05-2007
Publisher: American Astronomical Society
Date: 29-02-2012
Publisher: Oxford University Press (OUP)
Date: 11-05-2010
Publisher: Wiley
Date: 06-06-2023
DOI: 10.1002/EPI4.12766
Abstract: Anxiety and depression are common comorbidities in people living with epilepsy. Emerging research suggests that these conditions may even predate epilepsy onset. This review aimed to summarize the prevalence of clinically significant anxiety and depressive symptoms in people with first seizures and newly diagnosed epilepsy, as well as clinicodemographic factors associated with these symptoms. A scoping literature review was performed. OVID Medline and Embase were searched from January 1, 2000, through May 1, 2022. Articles of interest were selected based on predetermined inclusion and exclusion criteria. From 1836 studies identified on screening, 16 met eligibility criteria and were included in the review. Clinically significant anxiety and depressive symptoms, as determined by validated cutoff scores for anxiety and depression screening instruments, were common in people with first seizures (range 13–28%) and newly diagnosed epilepsy (range 11–45%). They were associated with a range of clinicodemographic factors including past psychiatric history and trauma, personality traits, self‐esteem, and stigma profiles. There is substantial evidence that clinically significant anxiety and depressive symptoms are often present at the time and shortly following the first seizure or epilepsy diagnosis. Future research is needed to better understand the complex interactions between these common psychiatric comorbidities, new‐onset seizure disorders, and certain clinicodemographic characteristics. This knowledge may inform targeted and holistic treatment approaches.
Publisher: EDP Sciences
Date: 08-2012
Publisher: EDP Sciences
Date: 2017
Publisher: Public Library of Science (PLoS)
Date: 07-05-2014
Publisher: Oxford University Press (OUP)
Date: 11-07-2007
Publisher: American Astronomical Society
Date: 06-2006
DOI: 10.1086/502964
Publisher: Springer Science and Business Media LLC
Date: 04-2012
DOI: 10.1038/NATURE10935
Abstract: An intermediate-mass star ends its life by ejecting the bulk of its envelope in a slow, dense wind. Stellar pulsations are thought to elevate gas to an altitude cool enough for the condensation of dust, which is then accelerated by radiation pressure, entraining the gas and driving the wind. Explaining the amount of mass loss, however, has been a problem because of the difficulty of observing tenuous gas and dust only tens of milliarcseconds from the star. For this reason, there is no consensus on the way sufficient momentum is transferred from the light from the star to the outflow. Here we report spatially resolved, multiwavelength observations of circumstellar dust shells of three stars on the asymptotic giant branch of the Hertzsprung-Russell diagram. When imaged in scattered light, dust shells were found at remarkably small radii (less than about two stellar radii) and with unexpectedly large grains (about 300 nanometres in radius). This proximity to the photosphere argues for dust species that are transparent to the light from the star and, therefore, resistant to sublimation by the intense radiation field. Although transparency usually implies insufficient radiative pressure to drive a wind, the radiation field can accelerate these large grains through photon scattering rather than absorption--a plausible mass loss mechanism for lower- litude pulsating stars.
Publisher: American Association of Physics Teachers (AAPT)
Date: 03-2200
DOI: 10.1119/1.3052072
Abstract: We investigate a variation of the simple double pendulum in which the two point masses are replaced by square plates. The double square pendulum exhibits richer behavior than the simple double pendulum and provides a convenient demonstration of nonlinear dynamics and chaos. It is also an ex le of an asymmetric compound double pendulum, which has not been studied in detail. We obtain the equilibrium configurations and normal modes of oscillation and derive the equations of motion, which are solved numerically to produce Poincaré sections. We show how the behavior varies from regular motion at low energies, to chaos at intermediate energies, and back to regular motion at high energies. We also show that the onset of chaos occurs at a significantly lower energy than for the simple double pendulum.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 08-04-2011
Abstract: Measurements of 500 Sun-like stars show that their properties differ from those predicted by stellar population models.
Publisher: Oxford University Press (OUP)
Date: 27-08-2010
Publisher: American Astronomical Society
Date: 27-07-2017
Publisher: American Astronomical Society
Date: 02-09-2009
Publisher: EDP Sciences
Date: 2015
Publisher: Oxford University Press (OUP)
Date: 12-2009
Publisher: Cambridge University Press (CUP)
Date: 2009
DOI: 10.1071/AS08051
Abstract: PILOT (the Pathfinder for an International Large Optical Telescope) is a proposed 2.5-m optical/infrared telescope to be located at Dome C on the Antarctic plateau. The atmospheric conditions at Dome C deliver a high sensitivity, high photometric precision, wide-field, high spatial resolution, and high-cadence imaging capability to the PILOT telescope. These capabilities enable a unique scientific potential for PILOT, which is addressed in this series of papers. The current paper presents a series of projects dealing with the nearby Universe that have been identified as key science drivers for the PILOT facility. Several projects are proposed that examine stellar populations in nearby galaxies and stellar clusters in order to gain insight into the formation and evolution processes of galaxies and stars. A series of projects will investigate the molecular phase of the Galaxy and explore the ecology of star formation, and investigate the formation processes of stellar and planetary systems. Three projects in the field of exoplanet science are proposed: a search for free-floating low-mass planets and dwarfs, a program of follow-up observations of gravitational microlensing events, and a study of infrared light-curves for previously discovered exoplanets. Three projects are also proposed in the field of planetary and space science: optical and near-infrared studies aimed at characterising planetary atmospheres, a study of coronal mass ejections from the Sun, and a monitoring program searching for small-scale Low Earth Orbit satellite debris items.
Publisher: Oxford University Press (OUP)
Date: 24-05-2016
Abstract: We study the δ Scuti – red giant (RG) binary KIC 9773821, the first double-pulsator binary of its kind. It was observed by Kepler during its 4-yr mission. Our aims are to ascertain whether the system is bound, rather than a chance alignment, and to identify the evolutionary state of the RG via asteroseismology. An extension of these aims is to determine a dynamical mass and an age prior for a δ Sct star, which may permit mode identification via further asteroseismic modelling. We determine spectroscopic parameters and radial velocities (RVs) for the RG component using HERMES@Mercator spectroscopy. Light arrival-time delays from the δ Sct pulsations are used with the red-giant RVs to determine that the system is bound and to infer its orbital parameters, including the binary mass ratio. We use asteroseismology to model the in idual frequencies of the red giant to give a mass of $2.10^{+0.20}_{-0.10}$ M⊙ and an age of $1.08^{+0.06}_{-0.24}$ Gyr. We find that it is a helium-burning secondary clump star, confirm that it follows the standard $\\nu _{\\rm max}$ scaling relation, and confirm its observed period spacings match their theoretical counterparts in the modelling code mesa. Our results also constrain the mass and age of the δ Sct star. We leverage these constraints to construct δ Sct models in a reduced parameter space and identify four of its five pulsation modes.
Publisher: American Astronomical Society
Date: 04-02-2014
Publisher: American Astronomical Society
Date: 14-01-2016
Publisher: American Astronomical Society
Date: 28-10-2011
Publisher: Oxford University Press (OUP)
Date: 11-08-2020
Abstract: The λ Boo stars are chemically peculiar A-type stars whose abundance anomalies are associated with the accretion of metal-poor material. We searched for λ Boo stars in the Southern hemisphere in a targeted spectroscopic survey of metal-weak and emission-line stars. Obtaining spectra for 308 stars and classifying them on the MK system, we found or co-discovered 24 new λ Boo stars. We also revised the classifications of 11 known λ Boo stars, one of which turned out to be a chemically normal rapid rotator. We show that stars previously classified in the literature as blue horizontal branch stars or emission-line A stars have a high probability of being λ Boo stars, although this conclusion is based on small-number statistics. Using WISE infrared fluxes, we searched our targets for infrared excesses that might be attributable to protoplanetary or debris discs as the source of the accreted material. Of the 34 λ Boo stars in our s le, 21 at various main-sequence ages have infrared excesses, confirming that not all λ Boo stars are young.
Publisher: EDP Sciences
Date: 28-07-2015
Publisher: EDP Sciences
Date: 03-05-2011
Publisher: American Astronomical Society
Date: 08-2008
DOI: 10.1086/589142
Publisher: American Astronomical Society
Date: 02-2009
Publisher: Springer Science and Business Media LLC
Date: 28-06-2023
Publisher: American Astronomical Society
Date: 04-08-2015
Publisher: Oxford University Press (OUP)
Date: 28-02-2023
Abstract: We present the discovery and characterization of six short-period, transiting giant planets from NASA’s Transiting Exoplanet Survey Satellite (TESS) -- TOI-1811 (TIC 376524552), TOI-2025 (TIC 394050135), TOI-2145 (TIC 88992642), TOI-2152 (TIC 395393265), TOI-2154 (TIC 428787891), and TOI-2497 (TIC 97568467). All six planets orbit bright host stars (8.9 & G & 11.8, 7.7 & K & 10.1). Using a combination of time-series photometric and spectroscopic follow-up observations from the TESS Follow-up Observing Program Working Group, we have determined that the planets are Jovian-sized (RP = 0.99--1.45 RJ), have masses ranging from 0.92 to 5.26 MJ, and orbit F, G, and K stars (4766 ≤ Teff ≤ 7360 K). We detect a significant orbital eccentricity for the three longest-period systems in our s le: TOI-2025 b (P = 8.872 d, 0.394$^{+0.035}_{-0.038}$), TOI-2145 b (P = 10.261 d, e = $0.208^{+0.034}_{-0.047}$), and TOI-2497 b (P = 10.656 d, e = $0.195^{+0.043}_{-0.040}$). TOI-2145 b and TOI-2497 b both orbit subgiant host stars (3.8 & log g & .0), but these planets show no sign of inflation despite very high levels of irradiation. The lack of inflation may be explained by the high mass of the planets $5.26^{+0.38}_{-0.37}$ MJ (TOI-2145 b) and 4.82 ± 0.41 MJ (TOI-2497 b). These six new discoveries contribute to the larger community effort to use TESS to create a magnitude-complete, self-consistent s le of giant planets with well-determined parameters for future detailed studies.
Publisher: Oxford University Press (OUP)
Date: 29-04-2019
Publisher: Oxford University Press (OUP)
Date: 14-01-2022
Abstract: We present an analysis of the eclipsing single-lined spectroscopic binary system α Dra based on photometry from the Transiting Exoplanet Survey Satellite (TESS) mission and newly acquired spectroscopic measurements. Recently discovered to have eclipses in the TESS data, at a magnitude of V = 3.7, α Dra is now one of the brightest detached eclipsing binary (EB) systems known. We obtain the parameters of this system by simultaneously fitting the TESS light curve in conjunction with radial velocities (RVs) acquired from the SONG spectrograph. We determine the fractional radii (R/a) for the primary and secondary components of the system to be 0.0479 $\\, \\pm \\,$ 0.0003 and 0.0226 $\\, \\pm \\,$ 0.0005, respectively. We constrain the temperature, mass, and luminosity (log(L/L⊙)) of the primary to be $9975\\, \\pm \\, 125$ K, $3.7\\, \\pm \\, 0.1$ M⊙, and $2.49\\, \\pm \\, 0.02$, respectively, using isochrone fitting. Although the secondary is too faint to appear in the spectra, the obtained mass function and observed inclination yields a secondary minimum mass of $M_2=2.5\\, \\pm \\, 0.1$ M⊙, which suggests that it is an A2V type star. We were unable to obtain RVs of the secondary, and are only able to see a weak highly rotationally broadened absorption line, indicating that the secondary is rapidly rotating (vsin i ∼ 200 km s−1). We also perform an abundance analysis of the primary star for 21 chemical elements. We find a complex abundance pattern, with a few elements having mild underabundances while the majority have solar abundances. We make available the python code used in this paper to facilitate future modelling of EBs. anhey/adra
Publisher: EDP Sciences
Date: 26-04-1020
Publisher: Oxford University Press (OUP)
Date: 11-11-2006
Publisher: American Astronomical Society
Date: 15-05-2012
Publisher: Oxford University Press (OUP)
Date: 11-2002
Publisher: Oxford University Press (OUP)
Date: 21-08-2005
Publisher: Oxford University Press (OUP)
Date: 09-06-2016
Publisher: Oxford University Press (OUP)
Date: 11-04-2003
Publisher: Oxford University Press (OUP)
Date: 08-01-2013
DOI: 10.1093/MNRAS/STS511
Publisher: Oxford University Press (OUP)
Date: 17-08-2017
Publisher: Springer Science and Business Media LLC
Date: 04-2004
Publisher: American Astronomical Society
Date: 14-03-2019
Publisher: Springer Science and Business Media LLC
Date: 05-2015
Publisher: Oxford University Press (OUP)
Date: 11-02-2009
Publisher: American Astronomical Society
Date: 25-10-2010
Publisher: EDP Sciences
Date: 18-05-2011
Publisher: EDP Sciences
Date: 2015
Publisher: Wiley
Date: 18-03-2021
DOI: 10.1111/EPI.16871
Abstract: This study was undertaken to identify factors that predict discordance between the screening instruments Neurological Disorders Depression Inventory for Epilepsy (NDDI‐E) and Generalized Anxiety Disorder scale (GAD‐7), and diagnoses made by qualified psychiatrists among patients with seizure disorders. Importantly, this is not a validation study rather, it investigates clinicodemographic predictors of discordance between screening tests and psychiatric assessment. Adult patients admitted for inpatient video‐electroencephalographic monitoring completed eight psychometric instruments, including the NDDI‐E and GAD‐7, and psychiatric assessment. Patients were grouped according to agreement between the screening instrument and psychiatrists’ diagnoses. Screening was "discordant" if the outcome differed from the psychiatrist's diagnosis, including both false positive and false negative results. Bayesian statistical analyses were used to identify factors associated with discordance. A total of 411 patients met inclusion criteria mean age was 39.6 years, and 55.5% ( n = 228) were female. Depression screening was discordant in 33% of cases ( n = 136/411), driven by false positives ( n = 76/136, 56%) rather than false negatives ( n = 60/136, 44%). Likewise, anxiety screening was discordant in one third of cases ( n = 121/411, 29%) due to false positives ( n = 60/121, 50%) and false negatives ( n = 61/121, 50%). Seven clinical factors were predictive of discordant screening for both depression and anxiety: greater dissociative symptoms, greater patient‐reported adverse events, subjective cognitive impairment, negative affect, detachment, disinhibition, and psychoticism. When the analyses were restricted to only patients with psychogenic nonepileptic seizures (PNES) or epilepsy, the rate of discordant depression screening was higher in the PNES group ( n = 29, 47%) compared to the epilepsy group ( n = 70, 30%, Bayes factor for the alternative hypothesis = 4.65). Patients with seizure disorders who self‐report a variety of psychiatric and other symptoms should be evaluated more thoroughly for depression and anxiety, regardless of screening test results, especially if they have PNES and not epilepsy. Clinical assessment by a qualified psychiatrist remains essential in diagnosing depressive and anxiety disorders among such patients.
Publisher: Oxford University Press (OUP)
Date: 08-12-2018
Publisher: American Astronomical Society
Date: 10-01-2014
Publisher: Oxford University Press (OUP)
Date: 24-07-2015
Publisher: American Astronomical Society
Date: 19-10-2021
Publisher: American Astronomical Society
Date: 25-10-2011
Publisher: American Astronomical Society
Date: 20-01-2022
Abstract: We present an analysis of the first 20 second cadence light curves obtained by the TESS space telescope during its extended mission. We find improved precision of 20 second data compared to 2 minute data for bright stars when binned to the same cadence (≈10%–25% better for T ≲ 8 mag, reaching equal precision at T ≈ 13 mag), consistent with pre-flight expectations based on differences in cosmic-ray mitigation algorithms. We present two results enabled by this improvement. First, we use 20 second data to detect oscillations in three solar analogs ( γ Pav, ζ Tuc, and π Men) and use asteroseismology to measure their radii, masses, densities, and ages to ≈1%, ≈3%, ≈1%, and ≈20% respectively, including systematic errors. Combining our asteroseismic ages with chromospheric activity measurements, we find evidence that the spread in the activity–age relation is linked to stellar mass and thus the depth of the convection zone. Second, we combine 20 second data and published radial velocities to recharacterize π Men c, which is now the closest transiting exoplanet for which detailed asteroseismology of the host star is possible. We show that π Men c is located at the upper edge of the planet radius valley for its orbital period, confirming that it has likely retained a volatile atmosphere and that the “asteroseismic radius valley” remains devoid of planets. Our analysis favors a low eccentricity for π Men c ( .1 at 68% confidence), suggesting efficient tidal dissipation ( Q / k 2,1 ≲ 2400) if it formed via high-eccentricity migration. Combined, these early results demonstrate the strong potential of TESS 20 second cadence data for stellar astrophysics and exoplanet science.
Publisher: EDP Sciences
Date: 2015
Publisher: Oxford University Press (OUP)
Date: 19-08-2016
Publisher: Oxford University Press (OUP)
Date: 07-02-2013
DOI: 10.1093/MNRAS/STT059
Publisher: Cambridge University Press (CUP)
Date: 09-2011
DOI: 10.1017/S1743921312000142
Abstract: During the last 10 years we have seen a revolution in the quality and quantity of data for time-series photometry. The two satellites MOST and WIRE were the precursors for dedicated time-series missions. CoRoT (launched in 2006) has now observed more than 100,000 targets for exoplanet studies and a few hundred stars for asteroseismology, while Kepler (launched in 2009) is producing extended time-series data for years, aiming to discover Earth-size planets in or near the habitable zone. We discuss the accuracy of some of the parameters one may extract from the high-quality data from such photometric space missions, including the prospects for detecting oscillation-period changes due to real-time stellar evolution.
Publisher: Oxford University Press (OUP)
Date: 06-07-2016
Publisher: Oxford University Press (OUP)
Date: 05-12-2018
Publisher: American Astronomical Society
Date: 27-04-2023
Abstract: Asteroseismology is playing an increasingly important role in the characterization of red giant host stars and their planetary systems. Here, we conduct detailed asteroseismic modeling of the evolved red giant branch (RGB) hosts KOI-3886 and ι Draconis, making use of end-of-mission Kepler (KOI-3886) and multisector TESS ( ι Draconis) time-series photometry. We also model the benchmark star KIC 8410637, a member of an eclipsing binary, thus providing a direct test to the seismic determination. We test the impact of adopting different sets of observed modes as seismic constraints. Inclusion of ℓ = 1 and 2 modes improves the precision of the stellar parameters, albeit marginally, compared to adopting radial modes alone, with 1.9%–3.0% (radius), 5%–9% (mass), and 19%–25% (age) reached when using all p -dominated modes as constraints. Given the very small spacing of adjacent dipole mixed modes in evolved RGB stars, the sparse set of observed g -dominated modes is not able to provide extra constraints, further leading to highly multimodal posteriors. Access to multiyear time-series photometry does not improve matters, with detailed modeling of evolved RGB stars based on (lower-resolution) TESS data sets attaining a precision commensurate with that based on end-of-mission Kepler data. Furthermore, we test the impact of varying the atmospheric boundary condition in our stellar models. We find the mass and radius estimates to be insensitive to the description of the near-surface layers, at the expense of substantially changing both the near-surface structure of the best-fitting models and the values of associated parameters like the initial helium abundance, Y i . Attempts to measure Y i from seismic modeling of red giants may thus be systematically dependent on the choice of atmospheric physics.
Publisher: IOP Publishing
Date: 10-2015
DOI: 10.1086/683103
Publisher: EDP Sciences
Date: 24-02-2006
Publisher: Oxford University Press (OUP)
Date: 23-10-2017
Publisher: Oxford University Press (OUP)
Date: 31-01-2020
Abstract: While long-period variables (LPVs) have been extensively investigated, especially with MACHO and OGLE data for the Magellanic Clouds, there still exist open questions in their pulsations regarding the excitation mechanisms, radial order, and angular degree assignment. Here, we perform asteroseismic analyses on LPVs observed by the 4-year Kepler mission. Using a cross-correlation method, we detect unambiguous pulsation ridges associated with radial fundamental modes (n = 1) and overtones (n ≥ 2), where the radial order assignment is made using theoretical frequencies and observed frequencies. Our results confirm that the litude variability seen in semiregulars is consistent with oscillations being solar-like. We identify that the dipole modes, l = 1, are dominant in the radial orders of 3 ≤ n ≤ 6, and that quadrupole modes, l = 2, are dominant in the first overtone n = 2. A test of seismic scaling relations using Gaia DR2 parallaxes reveals the possibility that the relations break down when νmax ≲ 3 $\\mu {\\rm Hz}$ (R ≳ 40 R⊙, or log $\\rm L/L_{\\odot }$ ≳ 2.6). Our homogeneous measurements of pulsation litude and period for 3213 LPVs will be valuable for probing effects of pulsation on mass-loss, in particular in those stars with periods around 60 d, which has been argued as a threshold of substantial pulsation-triggered mass-loss.
Publisher: Oxford University Press (OUP)
Date: 21-11-2009
Publisher: Wiley
Date: 22-11-2010
Abstract: We present a brief overview of the history of attempts to obtain a clear detection of solar‐like oscillations in cluster stars, and discuss the results on the first clear detection, which was made by the Kepler Asteroseismic Science Consortium (KASC) Working Group 2 (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Publisher: American Astronomical Society
Date: 14-03-2013
Publisher: EDP Sciences
Date: 27-06-2012
Publisher: Wiley
Date: 22-11-2010
Abstract: We report on the ground‐based follow‐up program of spectroscopic and photometric observations of solar‐like asteroseismic targets for the Kepler space mission. These stars constitute a large group of more than a thousand objects which are the subject of an intensive study by the Kepler Asteroseismic Science Consortium Working Group 1 (KASC WG‐1). In the current work we will discuss the methods we use to determine the fundamental stellar atmospheric parameters using high‐quality stellar spectra. These provide essential constraints for the asteroseismic modelling and make it possible to verify the parameters in the Kepler Input Catalogue (KIC) (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Publisher: American Astronomical Society
Date: 2007
DOI: 10.1086/508766
Publisher: Oxford University Press (OUP)
Date: 08-05-2020
Abstract: 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 s le. We calculate that 81 per cent 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.
Publisher: Oxford University Press (OUP)
Date: 03-10-2013
Publisher: Springer Science and Business Media LLC
Date: 04-2013
DOI: 10.1038/NATURE12067
Publisher: Springer Science and Business Media LLC
Date: 04-2004
Publisher: American Astronomical Society
Date: 03-2023
Abstract: We studied 89 A- and F-type members of the Pleiades open cluster, including five escaped members. We measured projected rotational velocities ( v sin i ) for 49 stars and confirmed that stellar rotation causes a broadening of the main sequence in the color–magnitude diagram. Using time-series photometry from NASA’s TESS Mission (plus one star observed by Kepler/K2), we detected δ Scuti pulsations in 36 stars. The fraction of Pleiades stars in the middle of the instability strip that pulsate is unusually high (over 80%), and their range of effective temperatures agrees well with theoretical models. On the other hand, the characteristics of the pulsation spectra are varied and do not correlate with stellar temperature, calling into question the existence of a useful ν max relation for δ Scutis, at least for young main-sequence stars. By including δ Scuti stars observed in the Kepler field, we show that the instability strip is shifted to the red with increasing distance by interstellar reddening. Overall, this work demonstrates the power of combining observations with Gaia and TESS for studying pulsating stars in open clusters.
Publisher: EDP Sciences
Date: 17-11-2015
Publisher: Oxford University Press (OUP)
Date: 08-2002
Publisher: EDP Sciences
Date: 07-2006
Publisher: Elsevier BV
Date: 2003
Publisher: American Astronomical Society
Date: 05-12-1111
Publisher: Oxford University Press (OUP)
Date: 16-01-2015
Publisher: American Astronomical Society
Date: 14-04-2011
Publisher: Oxford University Press (OUP)
Date: 30-04-2008
DOI: 10.1111/J.1365-2966.2008.13167.X
Abstract: We have used the Sydney University Stellar Interferometer to measure the angular diameter of α Cir. This is the first detailed interferometric study of a rapidly oscillating A (roAp) star, α Cir being the brightest member of its class. We used the new and more accurate Hipparcos parallax to determine the radius to be 1.967 ± 0.066 R⊙. We have constrained the bolometric flux from calibrated spectra to determine an effective temperature of 7420 ± 170 K. This is the first direct determination of the temperature of an roAp star. Our temperature is at the low end of previous estimates, which span over 1000 K and were based on either photometric indices or spectroscopic methods. In addition, we have analysed two high-quality spectra of α Cir, obtained at different rotational phases and we find evidence for the presence of spots. In both spectra we find nearly solar abundances of C, O, Si, Ca and Fe, high abundance of Cr and Mn, while Co, Y, Nd and Eu are overabundant by about 1 dex. The results reported here provide important observational constraints for future studies of the atmospheric structure and pulsation of α Cir.
Publisher: American Astronomical Society
Date: 10-02-2009
Publisher: American Astronomical Society
Date: 10-10-2004
DOI: 10.1086/423484
Publisher: Cambridge University Press (CUP)
Date: 08-2014
DOI: 10.1017/S174392131301497X
Abstract: The 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 open clusters NGC 6791 and NGC 6819, Kepler also reads out larger superst s which contain complete images of the central region of each cluster. These cluster images can potentially be used to study additional stars in the open clusters. We present preliminary results from using traditional photometric techniques to identify and analyze additional variable stars from these images.
Publisher: Wiley
Date: 22-11-2010
Abstract: We present our preliminary results of the modelling of the F5 star Procyon A. The frequencies predicted by our models are compared with the frequencies extracted through a global fit to the power spectrum obtained by the latest ground‐based observations, which provides two different mode identification scenarios (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Publisher: EDP Sciences
Date: 2015
Publisher: EDP Sciences
Date: 19-05-2007
Publisher: Oxford University Press (OUP)
Date: 04-2003
Publisher: Oxford University Press (OUP)
Date: 26-05-2011
Publisher: EDP Sciences
Date: 19-04-2011
Publisher: Oxford University Press (OUP)
Date: 02-2004
Start Date: 03-2010
End Date: 03-2014
Amount: $300,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 05-2013
End Date: 12-2016
Amount: $300,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2014
End Date: 12-2014
Amount: $151,962.00
Funder: Australian Research Council
View Funded ActivityStart Date: 02-2004
End Date: 12-2007
Amount: $32,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2017
End Date: 03-2020
Amount: $270,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2021
End Date: 12-2024
Amount: $390,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 04-2005
End Date: 12-2008
Amount: $215,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2023
End Date: 12-2027
Amount: $2,497,216.00
Funder: Australian Research Council
View Funded ActivityStart Date: 01-2012
End Date: 12-2015
Amount: $355,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 02-2015
End Date: 07-2018
Amount: $760,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2007
End Date: 12-2013
Amount: $1,280,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2019
End Date: 12-2020
Amount: $159,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 05-2002
End Date: 11-2005
Amount: $289,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 03-2004
End Date: 04-2008
Amount: $240,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2015
End Date: 12-2018
Amount: $443,900.00
Funder: Australian Research Council
View Funded ActivityStart Date: 06-2016
End Date: 12-2018
Amount: $800,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2009
End Date: 12-2009
Amount: $350,000.00
Funder: Australian Research Council
View Funded Activity