78 research outputs found
A synthetic sample of short-cadence solar-like oscillators for TESS
NASA's Transiting Exoplanet Survey Satellite (TESS) has begun a two-year
survey of most of the sky, which will include lightcurves for thousands of
solar-like oscillators sampled at a cadence of two minutes. To prepare for this
steady stream of data, we present a mock catalogue of lightcurves, designed to
realistically mimic the properties of the TESS sample. In the process, we also
present the first public release of the asteroFLAG Artificial Dataset
Generator, which simulates lightcurves of solar-like oscillators based on input
mode properties. The targets are drawn from a simulation of the Milky Way's
populations and are selected in the same way as TESS's true Asteroseismic
Target List. The lightcurves are produced by combining stellar models,
pulsation calculations and semi-empirical models of solar-like oscillators. We
describe the details of the catalogue and provide several examples. We provide
pristine lightcurves to which noise can be added easily. This mock catalogue
will be valuable in testing asteroseismology pipelines for TESS and our methods
can be applied in preparation and planning for other observatories and
observing campaigns.Comment: 14 pages, 6 figures, accepted for publication in ApJS. Archives
containing the mock catalogue are available at
https://doi.org/10.5281/zenodo.1470155 and the pipeline to produce it at
https://github.com/warrickball/s4tess . The first public release of the
asteroFLAG Artificial Dataset Generator v3 (AADG3) is described at
https://warrickball.github.io/AADG3
Red Horizontal Branch stars: an asteroseismic perspective
Robust age estimates of red giant stars are now possible thanks to the
precise inference of their mass based on asteroseismic constraints. However,
there are cases where such age estimates can be highly precise yet very
inaccurate. An example is giants that have undergone mass loss or mass transfer
events that have significantly altered their mass. In this context, stars with
"apparent" ages significantly higher than the age of the Universe are
candidates as stripped stars, or stars that have lost more mass than expected,
most likely via interaction with a companion star, or because of the poorly
understood mass-loss mechanism along the red-giant branch. In this work we
identify examples of such objects among red giants observed by
, both at low ([Fe/H] ) and solar metallicity.
By modelling their structure and pulsation spectra, we find a consistent
picture confirming that these are indeed low-mass objects consisting of a He
core of and an envelope of . Moreover, we find that these stars are characterised by a rather
extreme coupling () between the pressure-mode and gravity-mode
cavities, i.e. much higher than the typical value for red clump stars,
providing thus a direct seismic signature of their peculiar structure. The
complex pulsation spectra of these objects, if observed with sufficient
frequency resolution, hold detailed information about the structural properties
of likely products of mass stripping, hence can potentially shed light on their
formation mechanism. On the other hand, our tests highlight the difficulties
associated with measuring reliably the large frequency separation, especially
in shorter datasets, with impact on the reliability of the inferred masses and
ages of low-mass Red Clump stars with e.g. K2 or TESS data.Comment: Accepted for publication in A&A Letter
TESS asteroseismology of the known red-giant host stars HD 212771 and HD 203949
International audienc
Amplification and PI3KCA Mutation in a Case of Sclerosing Rhabdomyosarcoma
A rare sclerosing variant of rhabdomyosarcoma characterized by prominent hyalinization and pseudovascular pattern has recently been described as a subtype biologically distinct from embryonal, alveolar, and pleomorphic forms. We present cytogenetic and molecular findings as well as experimental studies of an unusual case of sclerosing rhabdomyosarcoma. The primary lesion arose within the plantar subcutaneous tissue of the left foot of an otherwise healthy 23-year-old male who eventually developed pulmonary nodules despite systemic chemotherapy. Two genetic abnormalities identified in surgical and/or autopsy samples of the tumor were introduced into 10T1/2 murine fibroblasts to determine whether these genetic changes cooperatively facilitated transformation and growth. Cytogenetic analysis revealed a complex abnormal hyperdiploid clone, and MDM2 gene amplification was confirmed by fluorescence in situ hybridization. Cancer gene mutation screening using a combination of multiplexed PCR and mass spectroscopy revealed a PIK3CA exon 20 H1047R mutation in the primary tumor, lung metastasis, and liver metastasis. However, this mutation was not cooperative with MDM2 overexpression in experimental assays for transformation or growth. Nevertheless, MDM2 and PIK3CA are genes worthy of further investigation in patients with sclerosing rhabdomyosarcoma and might be considered in the enrollment of these patients into clinical trials of targeted therapeutics
Born to learn: The inspiration, progress, and future of evolved plastic artificial neural networks
Biological plastic neural networks are systems of extraordinary computational
capabilities shaped by evolution, development, and lifetime learning. The
interplay of these elements leads to the emergence of adaptive behavior and
intelligence. Inspired by such intricate natural phenomena, Evolved Plastic
Artificial Neural Networks (EPANNs) use simulated evolution in-silico to breed
plastic neural networks with a large variety of dynamics, architectures, and
plasticity rules: these artificial systems are composed of inputs, outputs, and
plastic components that change in response to experiences in an environment.
These systems may autonomously discover novel adaptive algorithms, and lead to
hypotheses on the emergence of biological adaptation. EPANNs have seen
considerable progress over the last two decades. Current scientific and
technological advances in artificial neural networks are now setting the
conditions for radically new approaches and results. In particular, the
limitations of hand-designed networks could be overcome by more flexible and
innovative solutions. This paper brings together a variety of inspiring ideas
that define the field of EPANNs. The main methods and results are reviewed.
Finally, new opportunities and developments are presented
AIMS - A new tool for stellar parameter determinations using asteroseismic constraints
A key aspect in the determination of stellar properties is the comparison of
observational constraints with predictions from stellar models. Asteroseismic
Inference on a Massive Scale (AIMS) is an open source code that uses Bayesian
statistics and a Markov Chain Monte Carlo approach to find a representative set
of models that reproduce a given set of classical and asteroseismic
constraints. These models are obtained by interpolation on a pre-calculated
grid, thereby increasing computational efficiency. We test the accuracy of the
different operational modes within AIMS for grids of stellar models computed
with the Li\`ege stellar evolution code (main sequence and red giants) and
compare the results to those from another asteroseismic analysis pipeline,
PARAM. Moreover, using artificial inputs generated from models within the grid
(assuming the models to be correct), we focus on the impact on the precision of
the code when considering different combinations of observational constraints
(individual mode frequencies, period spacings, parallaxes, photospheric
constraints,...). Our tests show the absolute limitations of precision on
parameter inferences using synthetic data with AIMS, and the consistency of the
code with expected parameter uncertainty distributions. Interpolation testing
highlights the significance of the underlying physics to the analysis
performance of AIMS and provides caution as to the upper limits in parameter
step size. All tests demonstrate the flexibility and capability of AIMS as an
analysis tool and its potential to perform accurate ensemble analysis with
current and future asteroseismic data yields.Comment: Accepted for publication in MNRAS. 17 pages, 17 figure
Age dating of an early Milky Way merger via asteroseismology of the naked-eye star ν Indi
Over the course of its history, the Milky Way has ingested multiple smaller satellite galaxies1. Although these accreted stellar populations can be forensically identified as kinematically distinct structures within the Galaxy, it is difficult in general to date precisely the age at which any one merger occurred. Recent results have revealed a population of stars that were accreted via the collision of a dwarf galaxy, called Gaia–Enceladus1, leading to substantial pollution of the chemical and dynamical properties of the Milky Way. Here we identify the very bright, naked-eye star ν Indi as an indicator of the age of the early in situ population of the Galaxy. We combine asteroseismic, spectroscopic, astrometric and kinematic observations to show that this metal-poor, alpha-element-rich star was an indigenous member of the halo, and we measure its age to be 11.0±0.7 (stat) ±0.8 (sys) billion years. The star bears hallmarks consistent with having been kinematically heated by the Gaia–Enceladus collision. Its age implies that the earliest the merger could have begun was 11.6 and 13.2 billion years ago, at 68% and 95% confidence, respectively. Computations based on hierarchical cosmological models slightly reduce the above limits
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
TOI-257b (HD 19916b): a warm sub-saturn orbiting an evolved F-type star
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 (43.9 ± 7.3 ), a radius of RP = 0.639 ± 0.013 (7.16 ± 0.15 ), bulk density of (cgs), and period . TOI-257b orbits a bright (V = 7.612 mag) somewhat evolved late F-type star with M* = 1.390 ± 0.046 , R* = 1.888 ± 0.033 , Teff = 6075 ± 90 , 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 sample 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
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