Ball, Warrick Heinz

[["dc.bibliographiccitation.artnumber","A123"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","568"],["dc.contributor.author","Ball, Warrick H."],["dc.contributor.author","Gizon, Laurent"],["dc.date.accessioned","2017-09-07T11:49:44Z"],["dc.date.available","2017-09-07T11:49:44Z"],["dc.date.issued","2014"],["dc.description.abstract","Context. Space-based observations of solar-like oscillations present an opportunity to constrain stellar models using individual mode frequencies. However, current stellar models are inaccurate near the surface, which introduces a systematic difference that must be corrected.Aims. We introduce and evaluate two parametrizations of the surface corrections based on formulae given by Gough (1990, LNP, 367, 283). The first we call a cubic term proportional to ν3/ ℐ and the second has an additional inverse term proportional to ν-1/ ℐ, where ν and ℐ are the frequency and inertia of an oscillation mode.Methods. We first show that these formulae accurately correct model frequencies of two different solar models (Model S and a calibrated MESA model) when compared to observed BiSON frequencies. In particular, even the cubic form alone fits significantly better than a power law. We then incorporate the parametrizations into a modelling pipeline that simultaneously fits the surface effects and the underlying stellar model parameters. We apply this pipeline to synthetic observations of a Sun-like stellar model, solar observations degraded to typical asteroseismic uncertainties, and observations of the well-studied CoRoT target HD 52265. For comparison, we also run the pipeline with the scaled power-law correction proposed by Kjeldsen et al. (2008, ApJ, 683, L175).Results. The fits to synthetic and degraded solar data show that the method is unbiased and produces best-fit parameters that are consistent with the input models and known parameters of the Sun. Our results for HD 52265 are consistent with previous modelling efforts and the magnitude of the surface correction is similar to that of the Sun. The fit using a scaled power-law correction is significantly worse but yields consistent parameters, suggesting that HD 52265 is sufficiently Sun-like for the same power-law to be applicable.Conclusions. We find that the cubic term alone is suitable for asteroseismic applications and it is easy to implement in an existing pipeline. It reproduces the frequency dependence of the surface correction better than a power-law fit, both when comparing calibrated solar models to BiSON observations and when fitting stellar models using the individual frequencies. This parametrization is thus a useful new way to correct model frequencies so that observations of individual mode frequencies can be exploited."],["dc.identifier.doi","10.1051/0004-6361/201424325"],["dc.identifier.fs","609651"],["dc.identifier.gro","3147394"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10931"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/4989"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/312844/EU//SPACEINN"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","A new correction of stellar oscillation frequencies for near-surface effects"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A79"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","586"],["dc.contributor.author","Schunker, H."],["dc.contributor.author","Schou, J."],["dc.contributor.author","Ball, Warrick H."],["dc.contributor.author","Nielsen, M. B."],["dc.contributor.author","Gizon, Laurent"],["dc.date.accessioned","2017-09-07T11:48:42Z"],["dc.date.available","2017-09-07T11:48:42Z"],["dc.date.issued","2015"],["dc.description.abstract","Context. Radial differential rotation is an important parameter for stellar dynamo theory and for understanding angular momentum transport.Aims. We investigate the potential of using a large number of similar stars simultaneously to constrain their average radial differential rotation gradient: we call this “ensemble fitting”.Methods. We use a range of stellar models along the main sequence, each with a synthetic rotation profile. The rotation profiles are step functions with a step of ΔΩ = −0.35 μHz, which is located at the base of the convection zone. These models are used to compute the rotational splittings of the p modes and to model their uncertainties. We then fit an ensemble of stars to infer the average ΔΩ.Results. All the uncertainties on the inferred ΔΩ for individual stars are of the order 1 μHz. Using 15 stellar models in an ensemble fit, we show that the uncertainty on the average ΔΩ is reduced to less than the input ΔΩ, which allows us to constrain the sign of the radial differential rotation. We show that a solar-like ΔΩ ≈ 30 nHz can be constrained by an ensemble fit of thousands of main-sequence stars. Observing the number of stars required to successfully exploit the ensemble fitting method will be possible with future asteroseismology missions, such as PLATO. We demonstrate the potential of ensemble fitting by showing that any systematic differences in the average ΔΩ between F, G, and K-type stars larger than 100 nHz could be detected."],["dc.identifier.doi","10.1051/0004-6361/201527485"],["dc.identifier.gro","3147043"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/13440"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/4775"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Asteroseismic inversions for radial differential rotation of Sun-like stars: ensemble fits"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A25"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","582"],["dc.contributor.author","Appourchaux, Thierry"],["dc.contributor.author","Antia, H. M."],["dc.contributor.author","Ball, Warrick H."],["dc.contributor.author","Creevey, O. L."],["dc.contributor.author","Lebreton, Y."],["dc.contributor.author","Verma, K."],["dc.contributor.author","Vorontsov, S."],["dc.contributor.author","Campante, T. L."],["dc.contributor.author","Davies, G. R."],["dc.contributor.author","Gaulme, P."],["dc.contributor.author","Régulo, C."],["dc.contributor.author","Horch, E."],["dc.contributor.author","Howell, S. B."],["dc.contributor.author","Everett, M."],["dc.contributor.author","Ciardi, D."],["dc.contributor.author","Fossati, L."],["dc.contributor.author","Miglio, A."],["dc.contributor.author","Montalbán, J."],["dc.contributor.author","Chaplin, W. J."],["dc.contributor.author","García, R. A."],["dc.contributor.author","Gizon, Laurent"],["dc.date.accessioned","2017-09-07T11:48:37Z"],["dc.date.available","2017-09-07T11:48:37Z"],["dc.date.issued","2015"],["dc.description.abstract","Context. Solar-like oscillations have been observed by Kepler and CoRoT in many solar-type stars, thereby providing a way to probe stars using asteroseismology.Aims. The derivation of stellar parameters has usually been done with single stars. The aim of the paper is to derive the stellar parameters of a double-star system (HIP 93511), for which an interferometric orbit has been observed along with asteroseismic measurements.Methods. We used a time series of nearly two years of data for the double star to detect the two oscillation-mode envelopes that appear in the power spectrum. Using a new scaling relation based on luminosity, we derived the radius and mass of each star. We derived the age of each star using two proxies: one based upon the large frequency separation and a new one based upon the small frequency separation. Using stellar modelling, the mode frequencies allowed us to derive the radius, the mass, and the age of each component. In addition, speckle interferometry performed since 2006 has enabled us to recover the orbit of the system and the total mass of the system.Results. From the determination of the orbit, the total mass of the system is 2.34-0.33+0.45 M⊙. The total seismic mass using scaling relations is 2.47 ± 0.07 M⊙. The seismic age derived using the new proxy based upon the small frequency separation is 3.5 ± 0.3 Gyr. Based on stellar modelling, the mean common age of the system is 2.7–3.9 Gyr. The mean total seismic mass of the system is 2.34–2.53 M⊙  consistent with what we determined independently with the orbit. The stellar models provide the mean radius, mass, and age of the stars as RA = 1.82−1.87R⊙, MA = 1.25−1.39 M⊙, AgeA = 2.6–3.5 Gyr; RB = 1.22−1.25 R⊙, MB = 1.08−1.14 M⊙, AgeB = 3.35–4.21 Gyr. The models provide two sets of values for Star A: [1.25–1.27] M⊙ and [1.34–1.39] M⊙. We detect a convective core in Star A, while Star B does not have any. For the metallicity of the binary system of Z ≈ 0.02, we set the limit between stars having a convective core in the range [1.14–1.25] M⊙."],["dc.identifier.doi","10.1051/0004-6361/201526610"],["dc.identifier.gro","3146954"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/12450"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/4724"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","A seismic and gravitationally bound double star observed by Kepler"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A82"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","601"],["dc.contributor.author","White, Timothy R."],["dc.contributor.author","Benomar, O."],["dc.contributor.author","Aguirre, Victor Silva"],["dc.contributor.author","Ball, Warrick H."],["dc.contributor.author","Bedding, Timothy R."],["dc.contributor.author","Chaplin, W. J."],["dc.contributor.author","Christensen-Dalsgaard, Joergen"],["dc.contributor.author","Garcia, R. A."],["dc.contributor.author","Gizon, Laurent"],["dc.contributor.author","Stello, Dennis"],["dc.contributor.author","Aigrain, S."],["dc.contributor.author","Antia, H. M."],["dc.contributor.author","Appourchaux, T."],["dc.contributor.author","Bazot, M."],["dc.contributor.author","Campante, Tiago L."],["dc.contributor.author","Creevey, O. L."],["dc.contributor.author","Davies, G. R."],["dc.contributor.author","Elsworth, Yvonne P."],["dc.contributor.author","Gaulme, P."],["dc.contributor.author","Handberg, Rasmus"],["dc.contributor.author","Hekker, Saskia"],["dc.contributor.author","Houdek, Gunter"],["dc.contributor.author","Howe, R."],["dc.contributor.author","Huber, D."],["dc.contributor.author","Karoff, Christoffer"],["dc.contributor.author","Marques, J. P."],["dc.contributor.author","Mathur, S."],["dc.contributor.author","McQuillan, A."],["dc.contributor.author","Metcalfe, T. S."],["dc.contributor.author","Mosser, B."],["dc.contributor.author","Nielsen, M. B."],["dc.contributor.author","Regulo, C."],["dc.contributor.author","Salabert, D."],["dc.contributor.author","Stahn, Thorsten"],["dc.date.accessioned","2018-11-07T10:24:05Z"],["dc.date.available","2018-11-07T10:24:05Z"],["dc.date.issued","2017"],["dc.description.abstract","Binary star systems are important for understanding stellar structure and evolution, and are especially useful when oscillations can be detected and analysed with asteroseismology. However, only four systems are known in which solar-like oscillations are detected in both components. Here, we analyse the fifth such system, HD 176465, which was observed by Kepler. We carefully analysed the system's power spectrum to measure individual mode frequencies, adapting our methods where necessary to accommodate the fact that both stars oscillate in a similar frequency range. We also modelled the two stars independently by fitting stellar models to the frequencies and complementary parameters. We are able to cleanly separate the oscillation modes in both systems. The stellar models produce compatible ages and initial compositions for the stars, as is expected from their common and contemporaneous origin. Combining the individual ages, the system is about 3.0 +/- 0.5 Gyr old. The two components of HD 176465 are young physically-similar oscillating solar analogues, the first such system to be found, and provide important constraints for stellar evolution and asteroseismology."],["dc.identifier.doi","10.1051/0004-6361/201628706"],["dc.identifier.isi","000402313500082"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/15004"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/42591"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","PUB_WoS_Import"],["dc.publisher","Edp Sciences S A"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/338251/EU//STELLARAGES"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Kepler observations of the asteroseismic binary HD 176465"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A14"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","592"],["dc.contributor.author","Reese, Daniel R."],["dc.contributor.author","Chaplin, W. J."],["dc.contributor.author","Davies, G. R."],["dc.contributor.author","Miglio, Andrea"],["dc.contributor.author","Antia, H. M."],["dc.contributor.author","Ball, Warrick H."],["dc.contributor.author","Basu, S."],["dc.contributor.author","Buldgen, G."],["dc.contributor.author","Christensen-Dalsgaard, Joergen"],["dc.contributor.author","Coelho, Hugo R."],["dc.contributor.author","Hekker, Saskia"],["dc.contributor.author","Houdek, Gunter"],["dc.contributor.author","Lebreton, Yveline"],["dc.contributor.author","Mazumdar, Anupam"],["dc.contributor.author","Metcalfe, T. S."],["dc.contributor.author","Aguirre, Victor Silva"],["dc.contributor.author","Stello, Dennis"],["dc.contributor.author","Verma, Kuldeep"],["dc.date.accessioned","2018-11-07T10:10:38Z"],["dc.date.available","2018-11-07T10:10:38Z"],["dc.date.issued","2016"],["dc.description.abstract","Context. Detailed oscillation spectra comprising individual frequencies for numerous solar-type stars and red giants are either currently available, e.g. courtesy of the CoRoT, Kepler, and K2 missions, or will become available with the upcoming NASA TESS and ESA PLATO 2.0 missions. The data can lead to a precise characterisation of these stars thereby improving our understanding of stellar evolution, exoplanetary systems, and the history of our galaxy. Aims. Our goal is to test and compare different methods for obtaining stellar properties from oscillation frequencies and spectroscopic constraints. Specifically, we would like to evaluate the accuracy of the results and reliability of the associated error bars, and to see where there is room for improvement. Methods. In the context of the SpaceInn network, we carried out a hare-and-hounds exercise in which one group, the hares, simulated observations of oscillation spectra for a set of ten artificial solar-type stars, and a number of hounds applied various methods for characterising these stars based on the data produced by the hares. Most of the hounds fell into two main groups. The first group used forward modelling (i.e. applied various search/optimisation algorithms in a stellar parameter space) whereas the second group relied on acoustic glitch signatures. Results. Results based on the forward modelling approach were accurate to 1:5% (radius), 3.9% (mass), 23% (age), 1.5% (surface gravity), and 1.8% (mean density), as based on the root mean square difference. Individual hounds reached different degrees of accuracy, some of which were substantially better than the above average values. For the two 1 M-circle dot stellar targets, the accuracy on the age is better than 10% thereby satisfying the requirements for the PLATO 2.0 mission. High stellar masses and atomic diffusion (which in our models does not include the effects of radiative accelerations) proved to be sources of difficulty. The average accuracies for the acoustic radii of the base of the convection zone, the He II ionisation, and the Gamma(1) peak located between the two He ionisation zones were 17%, 2.4%, and 1.9%, respectively. The results from the forward modelling were on average more accurate than those from the glitch fitting analysis as the latter seemed to be affected by aliasing problems for some of the targets. Conclusions. Our study indicates that forward modelling is the most accurate way of interpreting the pulsation spectra of solar-type stars. However, given its model-dependent nature, this method needs to be complemented by model-independent results from, e.g. glitch analysis. Furthermore, our results indicate that global rather than local optimisation algorithms should be used in order to obtain robust error bars."],["dc.identifier.doi","10.1051/0004-6361/201527987"],["dc.identifier.isi","000384722600072"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/14281"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/39895"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/312844/EU/Exploitation of Space Data for Innovative Helio- and Asteroseismology/SPACEINN"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/267864/EU/ASTERoseismic Investigations with SONG and Kepler/ASTERISK"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/338251/EU/Accurate ages of stars/StellarAges"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","SpaceInn hare-and-hounds exercise: Estimation of stellar properties using space-based asteroseismic data"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A105"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","564"],["dc.contributor.author","Hekker, Saskia"],["dc.contributor.author","Ball, Warrick H."],["dc.date.accessioned","2018-11-07T09:41:47Z"],["dc.date.available","2018-11-07T09:41:47Z"],["dc.date.issued","2014"],["dc.description.abstract","Context. Recently, the CoRoT target HD 175272 (F5V), which shows a weak signal of solar-like oscillations, was modelled by a differential asteroseismic analysis (Ozel et al. 2013, A&A, 558, A79) relative to a seismically similar star, HD 181420 (F2V), for which there is a clear signature of solar-like oscillations. The results provided by Ozel et al. indicate the possibility of HD 175272 having subsolar mass, while being of the order of 1000 K hotter than the Sun. This seems unphysical - standard stellar evolution theory generally does not predict solar-metallicity stars of subsolar mass to be hotter than about 6000 K - and calls for a reanalysis of this star. Aims. We aim to compare the performance of differential asteroseismic analysis with that of grid-based modelling. Methods. We use two sets of stellar model grids and two grid-fitting methods to model HD 175272 and HD 181420 using their effective temperatures, metallicities, large frequency separations (Delta v), and frequencies of maximum oscillation power (v(max)) as observational constraints. Results. We find that we are able to model both stars with parameters that are both mutually compatible and comparable with other modelling efforts. Hence, with modest spectroscopic and asteroseismic inputs, we obtain reasonable estimates of stellar parameters. In the case of HD 175272, the uncertainties of the stellar parameters from our grid-based modelling are smaller, and hence more physical, than those reported in the differential analysis. For both stars, the models have significantly lower values of v(max) than the reported observed values. Furthermore, when using the asymptotic large frequency separation as opposed to the scaling relation to compute Delta v, we find that our modelling results are significantly more self-consistent when v(max) is ignored. Conclusions. Grid-based modelling is a useful tool even in cases of weak solar-like oscillations. It provides more precise and more realistic results than obtained with differential seismology. The difference in the observed and modelled values of v(max) indicates that the four observational constraints are not fully consistent with the stellar models used here, with v(max) most likely to be the inconsistent constraint for these two stars."],["dc.identifier.doi","10.1051/0004-6361/201323121"],["dc.identifier.fs","609711"],["dc.identifier.isi","000334671000105"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10918"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/33808"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/338251/EU//STELLARAGES"],["dc.relation.issn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Grid-based seismic modelling at high and low signal-to-noise ratios HD 181420 and HD 175272"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A159"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","592"],["dc.contributor.author","Ball, Warrick H."],["dc.contributor.author","Beeck, B."],["dc.contributor.author","Cameron, R. H."],["dc.contributor.author","Gizon, Laurent"],["dc.date.accessioned","2017-09-07T11:48:37Z"],["dc.date.available","2017-09-07T11:48:37Z"],["dc.date.issued","2016"],["dc.description.abstract","Context. Space-based observations of solar-like oscillators have identified large numbers of stars in which many individual mode frequencies can be precisely measured. However, current stellar models predict oscillation frequencies that are systematically affected by simplified modelling of the near-surface layers. Aims. We use three-dimensional radiation hydrodynamics simulations to better model the near-surface equilibrium structure of dwarfs with spectral types F3, G2, K0 and K5, and examine the differences between oscillation mode frequencies computed in stellar models with and without the improved near-surface equilibrium structure. Methods. We precisely match stellar models to the simulations’ gravities and effective temperatures at the surface, and to the temporally- and horizontally-averaged densities and pressures at their deepest points. We then replace the near-surface structure with that of the averaged simulation and compute the change in the oscillation mode frequencies. We also fit the differences using several parametric models currently available in the literature. Results. The surface effect in the stars of solar-type and later is qualitatively similar and changes steadily with decreasing effective temperature. In particular, the point of greatest frequency difference decreases slightly as a fraction of the acoustic cut-off frequency and the overall scale of the surface effect decreases. The surface effect in the hot, F3-type star follows the same trend in scale (i.e. it is larger in magnitude) but shows a different overall variation with mode frequency. We find that a two-term fit using the cube and inverse of the frequency divided by the mode inertia is best able to reproduce the surface terms across all four spectral types, although the scaled solar term and a modified Lorentzian function also match the three cooler simulations reasonably well. Conclusions. Three-dimensional radiation hydrodynamics simulations of near-surface convection can be averaged and combined with stellar structure models to better predict oscillation mode frequencies in solar-like oscillators. Our simplified results suggest that the surface effect is generally larger in hotter stars (and correspondingly smaller in cooler stars) and of similar shape in stars of solar type and cooler. However, we cannot presently predict whether this will remain so when other components of the surface effect are included."],["dc.identifier.doi","10.1051/0004-6361/201628300"],["dc.identifier.gro","3146958"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/14283"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/4725"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","MESA meets MURaM"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A10"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","582"],["dc.contributor.author","Nielsen, M. B."],["dc.contributor.author","Schunker, H."],["dc.contributor.author","Gizon, Laurent"],["dc.contributor.author","Ball, Warrick H."],["dc.date.accessioned","2017-09-07T11:48:42Z"],["dc.date.available","2017-09-07T11:48:42Z"],["dc.date.issued","2015"],["dc.identifier.doi","10.1051/0004-6361/201526615"],["dc.identifier.gro","3147029"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/12442"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/4767"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.publisher","EDP Sciences"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Constraining differential rotation of Sun-like stars from asteroseismic and starspot rotation periods"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A24"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","586"],["dc.contributor.author","Schunker, H."],["dc.contributor.author","Schou, Jesper"],["dc.contributor.author","Ball, Warrick H."],["dc.date.accessioned","2018-11-07T10:18:36Z"],["dc.date.available","2018-11-07T10:18:36Z"],["dc.date.issued","2016"],["dc.description.abstract","Aims. We quantify the effect of observational spectroscopic and asteroseismic uncertainties on regularised least squares (RLS) inversions for the radial differential rotation of Sun-like and subgiant stars. Methods. We first solved the forward problem to model rotational splittings plus the observed uncertainties for models of a Sun-like star, HD 52265, and a subgiant star, KIC 7341231. We randomly perturbed the parameters of the stellar models within the uncertainties of the spectroscopic and asteroseismic constraints and used these perturbed stellar models to compute rotational splittings. We experimented with three rotation profiles: solid body rotation, a step function, and a smooth rotation profile decreasing with radius. We then solved the inverse problem to infer the radial differential rotation profile using a RLS inversion and kernels from the best-fit stellar model. We also compared RLS, optimally localised average (OLA) and direct functional fitting inversion techniques. Results. We found that the inversions for Sun-like stars with solar-like radial differential rotation profiles are insensitive to the uncertainties in the stellar models. The uncertainties in the splittings dominate the uncertainties in the inversions and solid body rotation is not excluded. We found that when the rotation rate below the convection zone is increased to six times that of the surface rotation rate the inferred rotation profile excluded solid body rotation. We showed that when we reduced the uncertainties in the splittings by a factor of about 100, the inversion is sensitive to the uncertainties in the stellar model. With the current observational uncertainties, we found that inversions of subgiant stars are sensitive to the uncertainties in the stellar model. Conclusions. Our findings suggest that inversions for the radial differential rotation of subgiant stars would benefit from more tightly constrained stellar models. We conclude that current observational uncertainties make it difficult to infer radially resolved features of the rotation profile in a Sun-like star using inversions with regularisation. In Sun-like stars, the insensitivity of the inversions to stellar model uncertainties suggests that it may be possible to perform ensemble inversions for the average radial differential rotation of many stars with a range of stellar types to better constrain the inversions."],["dc.description.sponsorship","Deutsche Forschungsgemeinschaft (DFG) [SFB 963/1]"],["dc.identifier.doi","10.1051/0004-6361/201525937"],["dc.identifier.isi","000369715900035"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/13439"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/41482"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Asteroseismic inversions for radial differential rotation of Sun-like stars: Sensitivity to uncertainties"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]