82 research outputs found
Mode Mixing and Rotational Splittings: I. Near-Degeneracy Effects Revisited
Rotation is typically assumed to induce strictly symmetric rotational
splitting into the rotational multiplets of pure p- and g-modes. However, for
evolved stars exhibiting mixed modes, avoided crossings between different
multiplet components are known to yield asymmetric rotational splitting,
particularly for near-degenerate mixed-mode pairs, where notional pure p-modes
are fortuitiously in resonance with pure g-modes. These near-degeneracy effects
have been described in subgiants, but their consequences for the
characterisation of internal rotation in red giants has not previously been
investigated in detail, in part owing to theoretical intractability. We employ
new developments in the analytic theory of mixed-mode coupling to study these
near-resonance phenomena. In the vicinity of the most p-dominated mixed modes,
the near-degenerate intrinsic asymmetry from pure rotational splitting
increases dramatically over the course of stellar evolution, and depends
strongly on the mode mixing fraction . We also find that a linear
treatment of rotation remains viable for describing the underlying p- and
g-modes, even when it does not for the resulting mixed modes undergoing these
avoided crossings. We explore observational consequences for potential
measurements of asymmetric mixed-mode splitting, which has been proposed as a
magnetic-field diagnostic. Finally, we propose improved measurement techniques
for rotational characterisation, exploiting the linearity of rotational effects
on the underlying p/g modes, while still accounting for these mixed-mode
coupling effects.Comment: 21 pages, 13 figures. Accepted to Ap
Horizontal shear instabilities in rotating stellar radiation zones:II. Effects of the full Coriolis acceleration
Stellar interiors are the seat of efficient transport of angular momentum all
along their evolution. Understanding the dependence of the turbulent transport
triggered by the shear instabilities due to the differential rotation in
stellar radiation zones is mandatory. Indeed, it constitutes one of the
cornerstones of the rotational transport and mixing theory which is implemented
in stellar evolution codes to predict the rotational and chemical evolutions of
stars. We investigate horizontal shear instabilities in stellar radiation zones
by considering the full Coriolis acceleration with both the dimensionless
horizontal component and the vertical component . We performed a
linear stability analysis for a horizontal shear flow with a hyperbolic tangent
profile, both numerically and asymptotically using the WKBJ approximation. As
in the traditional approximation, we identified the inflectional and inertial
instabilities. The inflectional instability is destabilized as
increases and its maximum growth rate increases significantly, while the
thermal diffusivity stabilizes the inflectional instability similarly to the
traditional case. The inertial instability is also strongly affected; for
instance, the inertially unstable regime is extended in the non-diffusive limit
as , where is the dimensionless
Brunt-V\"ais\"al\"a frequency. More strikingly, in the high-thermal-diffusivity
limit, it is always inertially unstable at any colatitude except at
the poles (i.e., ). Using the asymptotic and
numerical results, we propose a prescription for the effective turbulent
viscosities induced by the instabilities to be possibly used in stellar
evolution models. The characteristic time of this turbulence is short enough to
redistribute efficiently angular momentum and mix chemicals in the radiation
zones.Comment: Accepted in A&
New U-Pb ages for syn-orogenic magmatism in the SW sector of the Ossa Morena Zone (Portugal)
The Ossa-Morena Zone (OMZ) is a major geotectonic unit within the Iberian Massif (which constitutes an important segment of the European Variscan Belt) and one of its distinguishing features is the presence of a noteworthy compositional diversity of plutonic rocks. In the SW sector of the OMZ, the tonalitic Hospitais intrusion (located to the W of Montemor-o-Novo) is considered a typical example of syn-orogenic magmatism, taking into account that both the long axis of the plutonic body and its mesoscopic foliation are oriented parallel to the Variscan WNW-ESE orientation. Another relevant feature of the Hospitais intrusion is the occurrence of mafic microgranular enclaves within the main tonalite. In previous works (Moita et al., 2005; Moita, 2007), it was proposed that: (1) the Hospitais intrusion is part of a calc-alkaline suite, represented by a large number of intrusions in this sector of the OMZ, ranging from gabbros to granites; (2) the enclaves are co-genetic to the host tonalite in the Hospitais pluton.
In this study, zircon populations from one sample of the main tonalite (MM-17) and one sample of the associated enclave (MM-17E) were analysed by ID-TIMS for U-Pb geochronology. In each sample, three fractions of nice glassy, euhedral, long prismatic and inclusion free crystals were analysed. The results from the three fractions of MM-17 yielded a 206Pb/238U age of 337.0 ± 2.0 Ma. Similarly, for the enclave MM-17E a 206Pb/238U zircon age of 336.5 ± 0.47 Ma was obtained. These identical ages, within error, are in agreement with a common parental magma for the tonalite and mafic granular enclaves.
Similar U-Pb ages have been reported in previous works for plutonic and metamorphic events in this region (e.g.: Pereira et al., 2009; Antunes et al., 2011). Furthermore, also in the SW sector of the OMZ, palaeontological studies (Pereira et al., 2006; Machado & Hladil, 2010) carried out in Carboniferous sedimentary basins containing intercalated calc-alkaline volcanics (Santos et al., 1987; Chichorro, 2006) have shown that they are mainly of Visean age. Therefore, magmatism displaying features typical of continental arc setting seems to have been active in this part of the OMZ during the Lower Carboniferous times
FliPer<sub>Class</sub>:in search of solar-like pulsators among TESS targets
The NASA's Transiting Exoplanet Survey Satellite (TESS) is about to provide
full-frame images of almost the entire sky. The amount of stellar data to be
analysed represents hundreds of millions stars, which is several orders of
magnitude above the amount of stars observed by CoRoT, Kepler, or K2 missions.
We aim at automatically classifying the newly observed stars, with near
real-time algorithms, to better guide their subsequent detailed studies. In
this paper, we present a classification algorithm built to recognise solar-like
pulsators among classical pulsators, which relies on the global amount of power
contained in the PSD, also known as the FliPer (Flicker in spectral Power
density). As each type of pulsating star has a characteristic background or
pulsation pattern, the shape of the PSD at different frequencies can be used to
characterise the type of pulsating star. The FliPer Classifier
(FliPer) uses different FliPer parameters along with the effective
temperature as input parameters to feed a machine learning algorithm in order
to automatically classify the pulsating stars observed by TESS. Using noisy
TESS simulated data from the TESS Asteroseismic Science Consortium (TASC), we
manage to classify pulsators with a 98% accuracy. Among them, solar-like
pulsating stars are recognised with a 99% accuracy, which is of great interest
for further seismic analysis of these stars like our Sun. Similar results are
obtained when training our classifier and applying it to 27 days subsets of
real Kepler data. FliPer is part of the large TASC classification
pipeline developed by the TESS Data for Asteroseismology (T'DA) classification
working group.Comment: 8 pages, 6 figures, accepted to A&
Asteroseismology with the Roman Galactic Bulge Time-Domain Survey
Asteroseismology has transformed stellar astrophysics. Red giant
asteroseismology is a prime example, with oscillation periods and amplitudes
that are readily detectable with time-domain space-based telescopes. These
oscillations can be used to infer masses, ages and radii for large numbers of
stars, providing unique constraints on stellar populations in our galaxy. The
cadence, duration, and spatial resolution of the Roman galactic bulge
time-domain survey (GBTDS) are well-suited for asteroseismology and will probe
an important population not studied by prior missions. We identify photometric
precision as a key requirement for realizing the potential of asteroseismology
with Roman. A precision of 1 mmag per 15-min cadence or better for saturated
stars will enable detections of the populous red clump star population in the
Galactic bulge. If the survey efficiency is better than expected, we argue for
repeat observations of the same fields to improve photometric precision, or
covering additional fields to expand the stellar population reach if the
photometric precision for saturated stars is better than 1 mmag.
Asteroseismology is relatively insensitive to the timing of the observations
during the mission, and the prime red clump targets can be observed in a single
70 day campaign in any given field. Complementary stellar characterization,
particularly astrometry tied to the Gaia system, will also dramatically expand
the diagnostic power of asteroseismology. We also highlight synergies to Roman
GBTDS exoplanet science using transits and microlensing.Comment: Roman Core Community Survey White Paper, 3 pages, 4 figure
Asteroseismology with the Roman Galactic Bulge Time-Domain Survey
Asteroseismology has transformed stellar astrophysics. Red giant asteroseismology is a prime example, with oscillation periods and amplitudes that are readily detectable with time-domain space-based telescopes. These oscillations can be used to infer masses, ages and radii for large numbers of stars, providing unique constraints on stellar populations in our galaxy. The cadence, duration, and spatial resolution of the Roman galactic bulge time-domain survey (GBTDS) are well-suited for asteroseismology and will probe an important population not studied by prior missions. We identify photometric precision as a key requirement for realizing the potential of asteroseismology with Roman. A precision of 1 mmag per 15-min cadence or better for saturated stars will enable detections of the populous red clump star population in the Galactic bulge. If the survey efficiency is better than expected, we argue for repeat observations of the same fields to improve photometric precision, or covering additional fields to expand the stellar population reach if the photometric precision for saturated stars is better than 1 mmag. Asteroseismology is relatively insensitive to the timing of the observations during the mission, and the prime red clump targets can be observed in a single 70 day campaign in any given field. Complementary stellar characterization, particularly astrometry tied to the Gaia system, will also dramatically expand the diagnostic power of asteroseismology. We also highlight synergies to Roman GBTDS exoplanet science using transits and microlensing
The K2 Galactic Archaeology Program Data Release 3: Age-abundance Patterns in C1–C8 and C10–C18
© 2022. The Author(s). Published by the American Astronomical Society. Content from this work may be used under the terms of the Creative Commons Attribution 4.0 license. https://creativecommons.org/licenses/by/4.0/Abstract: We present the third and final data release of the K2 Galactic Archaeology Program (K2 GAP) for Campaigns C1–C8 and C10–C18. We provide asteroseismic radius and mass coefficients, κ R and κ M , for ∼19,000 red giant stars, which translate directly to radius and mass given a temperature. As such, K2 GAP DR3 represents the largest asteroseismic sample in the literature to date. K2 GAP DR3 stellar parameters are calibrated to be on an absolute parallactic scale based on Gaia DR2, with red giant branch and red clump evolutionary state classifications provided via a machine-learning approach. Combining these stellar parameters with GALAH DR3 spectroscopy, we determine asteroseismic ages with precisions of ∼20%–30% and compare age-abundance relations to Galactic chemical evolution models among both low- and high-α populations for α, light, iron-peak, and neutron-capture elements. We confirm recent indications in the literature of both increased Ba production at late Galactic times as well as significant contributions to r-process enrichment from prompt sources associated with, e.g., core-collapse supernovae. With an eye toward other Galactic archeology applications, we characterize K2 GAP DR3 uncertainties and completeness using injection tests, suggesting that K2 GAP DR3 is largely unbiased in mass/age, with uncertainties of 2.9% (stat.) ± 0.1% (syst.) and 6.7% (stat.) ± 0.3% (syst.) in κ R and κ M for red giant branch stars and 4.7% (stat.) ± 0.3% (syst.) and 11% (stat.) ± 0.9% (syst.) for red clump stars. We also identify percent-level asteroseismic systematics, which are likely related to the time baseline of the underlying data, and which therefore should be considered in TESS asteroseismic analysis.Peer reviewedFinal Published versio
Detection and Characterization of Oscillating Red Giants: First Results from the TESS Satellite
Since the onset of the "space revolution" of high-precision high-cadence photometry, asteroseismology has been demonstrated as a powerful tool for informing Galactic archeology investigations. The launch of the NASA Transiting Exoplanet Survey Satellite (TESS) mission has enabled seismic-based inferences to go full sky-providing a clear advantage for large ensemble studies of the different Milky Way components. Here we demonstrate its potential for investigating the Galaxy by carrying out the first asteroseismic ensemble study of red giant stars observed by TESS. We use a sample of 25 stars for which we measure their global asteroseimic observables and estimate their fundamental stellar properties, such as radius, mass, and age. Significant improvements are seen in the uncertainties of our estimates when combining seismic observables from TESS with astrometric measurements from the Gaia mission compared to when the seismology and astrometry are applied separately. Specifically, when combined we show that stellar radii can be determined to a precision of a few percent, masses to 5%-10%, and ages to the 20% level. This is comparable to the precision typically obtained using end-of-mission Kepler data
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