65 research outputs found
Asteroseismologie van ɣ Doradus sterren met de Kepler ruimtemissie
No full textRecently, Tkachenko et al. (2013) proposed a sample of 70 main sequencestars in the Kepler field of view, which show Gamma Doradus variability. For all stars we have long time series of Kepler space-based photometry available, as well as ground-based high-resolution spectroscopy. By developing and applying analysis tools for both, we can derive diagnosticsfrom the data, which in turn can be compared with those deduced from theoretical models (computed with e.g. the GYRE code in combination with the stellar evolution code MESA). Such detailed seismic modelling of the stars individually and of the sample as a whole will allow us to deepen our understanding of both stellar pulsations and stellar evolution.status: Publishe
Stellar evolution in motion: Period spacings in γ Doradus stars
No full textThe years of available space-based photometry have led to the detection the dense oscillation frequency spectra for γ Doradus stars. Theory predicts the presence of non-uniform period spacing series in these frequency spectra, which contain information on the interior stellar structure. We have therefore developed a new method, based on the theoretical expectations and the observational spectroscopic studies, which allows us to detect such spacing patterns. The technique has a high success rate, with detections for ~60 % of the studied targets, though a notable deficiency is the inability to determine values for the degree l and the azimuthal order m
Four bright eclipsing binaries with γ Doradus pulsating components: CM Lac, MZ Lac, RX Dra, and V2077 Cyg
No full textsponsorship: TVR gratefully acknowledges support from the Research Foundation Flanders (FWO) under grant agreement N.12ZB620N. We thank Johanna Molenda-.Zakowicz for sending us her RV measurements for V2077 Cyg, and Dominic Bowman and the anonymous referee for discussions and comments. The TESS data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute (STScI). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support to MAST for these data is provided by the NASA Office of Space Science via grant NAG5-7584 and by other grants and contracts. Funding for the TESS mission is provided by the NASA Explorer Program. This research has made use of the SIMBAD data base, operated at CDS, Strasbourg, France; the SAO/NASA Astrophysics Data System; and the VizieR catalogue access tool, CDS, Strasbourg, France. (Research Foundation Flanders (FWO)|12ZB620N, NASA|NAS5-26555, NASA Office of Space Science|NAG5-7584, NASA Explorer Program)status: Publishe
Porcien respiratory coronavirus : voorkomen, pathogenese en klinisch belang /
No full textMaster in de diergeneeskund
Constraining magnetic fields in intermediate-mass main-sequence stars with asteroseismology
No full textThis is the digital version of the poster presented by Jordan Van Beeck at the Nederlandse Astronomenconferentie (NAC), 2019. (https://www.astro.rug.nl/nac2019/)
Additional information can be found in the references, for which we provide a link to the corresponding NASA astrophysics data system (ADS) pages:
[1]: https://ui.adsabs.harvard.edu/abs/2019arXiv190301426P/abstract
[2]: https://ui.adsabs.harvard.edu/abs/2018MNRAS.475..879T/abstract
[3]: https://ui.adsabs.harvard.edu/abs/2019arXiv190305620P/abstract
[4]: https://ui.adsabs.harvard.edu/abs/2010A&A...517A..58D/abstract</p
The Interior Angular Momentum of Core Hydrogen Burning Stars from Gravity-mode Oscillations
No full text© 2017. The American Astronomical Society. All rights reserved. A major uncertainty in the theory of stellar evolution is the angular momentum distribution inside stars and its change during stellar life. We compose a sample of 67 stars in the core hydrogen burning phase with a log g value from high-resolution spectroscopy, as well as an asteroseismic estimate of the near-core rotation rate derived from gravity-mode oscillations detected in space photometry. This assembly includes 8 B-type stars and 59 AF-type stars, covering a mass range from 1.4 to 5M o , i.e., it concerns intermediate-mass stars born with a well-developed convective core. The sample covers projected surface rotation velocities v sin i ∈ [9, 242] km s -1 and core rotation rates up to 26 μHz, which corresponds to 50% of the critical rotation frequency. We find deviations from rigid rotation to be moderate in the single stars of this sample. We place the near-core rotation rates in an evolutionary context and find that the core rotation must drop drastically before or during the short phase between the end of the core hydrogen burning and the onset of core helium burning. We compute the spin parameter, which is the ratio of twice the rotation rate to the mode frequency (also known as the inverse Rossby number), for 1682 gravity modes and find the majority (95%) to occur in the sub-inertial regime. The 10 stars with Rossby modes have spin parameters between 14 and 30, while the gravito-inertial modes cover the range from 1 to 15.sponsorship: C.A. and T.V.R. are grateful for the kind hospitality and opportunity to perform part of this research at the Kavli Institute of Theoretical Physics, University of California at Santa Barbara, USA. The research leading to these results has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 670519: MAMSIE), from the Research Foundation Flanders (FWO, grant agreements G.0B69.13 and V4.272.17N), and from the National Science Foundation of the United States under grant NSF PHY11-25915. (European Research Council (ERC) under the European Union's Horizon research and innovation program from the Research Foundation Flanders (FWO)|670519, European Research Council (ERC) under the European Union's Horizon research and innovation program from the Research Foundation Flanders (FWO)|G.0B69.13, European Research Council (ERC) under the European Union's Horizon research and innovation program from the Research Foundation Flanders (FWO)|V4.272.17N, National Science Foundation of the United States|NSF PHY11-25915)status: Publishe
Physical properties of the eclipsing binary KIC 9851944 and analysis of its tidally-perturbed p- and g-mode pulsations
No full textStars that are both pulsating and eclipsing offer an important opportunity to
better understand many of the physical phenomena that occur in stars, because
it is possible to measure the pulsation frequencies of stars for which the
masses and radii are known precisely and accurately. KIC 9851944 is a
double-lined detached eclipsing binary containing two F-stars which show both
pressure and gravity mode pulsations. We present an analysis of new
high-resolution spectroscopy of the system and high quality light curves from
the Kepler and TESS space missions. We determine the masses and effective
temperatures of the stars to 0.6% precision, and their radii to 1.0% and 1.5%
precision. The secondary component is cooler, but larger and more massive than
the primary so is more evolved; both lie inside the {\delta} Scuti and {\gamma}
Doradus instability strips. We measure a total of 133 significant pulsation
frequencies in the light curve, including 14 multiplets that each contain
between 3 and 19 frequencies. We find evidence for tidal perturbations to some
of the p- and g-modes, attribute a subset of the frequencies to either the
primary or secondary star, and measure a buoyancy radius and near-core
rotational frequency for the primary component. KIC 9851944 is mildly
metal-rich and MIST isochrones from the MESA evolutionary code agree well with
the observed properties of the system for an age of 1.25 Gyr.Comment: 28 pages, 29 figure
Seismic diagnosis for rapidly rotating upper-main-sequence g-mode pulsators: the combined effects of the centrifugal acceleration and differential rotation
No full textSpace-based asteroseismology has revolutionised our understanding of stellar structure, evolution, mixing, and rotation. In particular, intermediate-mass, main-sequence g-mode pulsators like gamma-Dor and slowly pulsating B-type (SPB) stars allow us to probe rotation and mixing at their convective core/radiative envelope interface with a high precision. This constitutes a gold mine for our global understanding of stellar rotation and related mixing. To fully exploit the information that is provided by detected g-mode pulsations, it is crucial to improve our understanding of how stellar rotation influences g-modes in rapidly rotating stars for which the action of the Coriolis and the centrifugal accelerations have to be taken into account.
In this framework, the Traditional Approximation of Rotation (hereafter TAR) provides a flexible treatment of the adiabatic propagation of gravity modes modified by rotation (i.e. gravito-inertial modes including Rossby modes which propagate under the combined action of the buoyancy force and the Coriolis acceleration), which is extensively used for intensive seismic forward modelling. However, it has been built on the restrictive assumptions of spherical uniformly rotating stars. In this work, we generalise the TAR to take into account simultaneously the centrifugal deformation and differential rotation. We determine the validity domain of this generalised TAR using the state-of-the-art 2D stellar structure and evolution code ESTER. We then demonstrate how these new physics affect the pulsation-period spacings between consecutive g-mode pulsations, which are a common diagnostic that allow us to probe rotation and the chemicals mixing, for instance by convective overshoot or penetration, at the core boundary. We show that the effects induced by the centrifugal acceleration and the differential rotation are detectable using high-precision asteroseismic data. Finally, we discuss how this work can be generalised in a near future to include the effects of stellar magnetic fields and how it will lead to more realistic and accurate asteroseismic modelling of OBA-type stars
Internal rotation and buoyancy travel time of 60 gamma Doradus stars from uninterrupted TESS light curves spanning 352 days
No full textDescription:
Electronic versions of Table A.1 and A.2 from the Appendix of
Garcia et al. (2022b), as well as all analysed g-mode period-spacing
patterns from this work.
Abstract:
Context. Gamma Doradus (hereafter gamma Dor) stars are gravity-mode
pulsators whose periods carry information about the internal structure of
the star. These periods are especially sensitive to the internal rotation
and chemical mixing, two processes that are currently not well constrained
in the theory of stellar evolution.
Aims. We aim to identify the pulsation modes and deduce the internal
rotation and buoyancy travel time for 106 gamma Dor stars observed
by the TESS mission in its southern continuous viewing zone (hereafter
S-CVZ). We rely on 140 previously detected period-spacing patterns, that is,
series of (near-)consecutive pulsation mode periods.
Methods. We used the asymptotic expression to compute gravity-mode
frequencies for ranges of the rotation rate and buoyancy travel time that
cover the physical range in γ Dor stars. Those frequencies were fitted to
the observed period-spacing patterns by minimizing a custom cost function.
The effects of rotation were evaluated using the traditional approximation
of rotation, using the stellar pulsation code GYRE.
Results. We obtained the pulsation mode identification, internal rotation
and buoyancy travel time for 60 TESS gamma Dor stars. For the remaining 46
targets, the detected patterns are either too short or contained too many
missing modes for unambiguous mode identification, and longer light curves
are required. For the successfully analysed stars, we found that
period-spacing patterns from 1-yr long TESS light curves can constrain the
internal rotation and buoyancy travel time to a precision of 0.03 d^{−1} and
400s, respectively, which is about half as precise as literature results
based on 4-yr Kepler light curves of gamma Dor stars.The research leading to these results has received funding from the the KU\,Leuven Research Council (grant C16/18/005: PARADISE) and from the BELgian federal Science Policy Office (BELSPO) through PRODEX grants for the Gaia and PLATO space missions. TVR gratefully acknowledges support from the Research Foundation Flanders (FWO) under grant agreement N12ZB620N
Probing the physics in the core boundary layers of the double-lined B-type binary KIC4930889 from its gravito-inertial modes
No full textStellar evolution models of B-type stars are still uncertain in terms of
internal mixing properties, notably in the area between the convective core and
the radiative envelope. This impacts age determination of such stars in
addition to the computation of chemical yields produced at the end of their
life. We investigated the thermal and chemical structure and rotation rate in
the near-core boundary layer of the double-lined B-type binary KIC4930889 from
its four-year Kepler light curve, ground-based spectroscopy, and Gaia
astrometry. We computed grids of 1D stellar structure and evolution models for
different mixing profiles and prescriptions of the temperature gradient in the
near-core region. We examined the preferred prescription and the near-core
rotation rate using 22 prograde dipole modes detected by Kepler photometry. We
employed a Mahalanobis distance merit function and considered various nested
stellar model grids, rewarding goodness of fit but penalising model complexity.
Furthermore, we found a preference for either an exponentially decaying mixing
profile in the near-core region or absence of additional near-core mixing, but
found no preference for the temperature gradient in this region. The frequency
(co)variances of our theoretical predictions are much larger than the errors on
the observed frequencies. This forms the main limitation on further
constraining the individual parameters of our models. Additionally,
non-adiabatic pulsation computations of our best models indicate a need for
opacity enhancements to accurately reproduce the observed mode excitation. The
eccentric close binary system KIC4930889 proves to be a promising target to
investigate additional physics in close binaries by developing new modelling
methods with the capacity to include the effect of tidal interactions for full
exploitation of all detected oscillation modes.Comment: Accepted for publication in A&A, 20 pages, 14 figures, 10 table
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