27 research outputs found
An Introduction to Data Analysis in Asteroseismology
A practical guide is presented to some of the main data analysis concepts and
techniques employed contemporarily in the asteroseismic study of stars
exhibiting solar-like oscillations. The subjects of digital signal processing
and spectral analysis are introduced first. These concern the acquisition of
continuous physical signals to be subsequently digitally analyzed. A number of
specific concepts and techniques relevant to asteroseismology are then
presented as we follow the typical workflow of the data analysis process,
namely, the extraction of global asteroseismic parameters and individual mode
parameters (also known as peak-bagging) from the oscillation spectrum.Comment: Lecture presented at the IVth Azores International Advanced School in
Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars
and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta,
Azores Islands, Portugal in July 201
Accurate fundamental parameters and detailed abundance patterns from spectroscopy of 93 solar-type Kepler targets
We present a detailed spectroscopic study of 93 solar-type stars that are
targets of the NASA/Kepler mission and provide detailed chemical composition of
each target. We find that the overall metallicity is well-represented by Fe
lines. Relative abundances of light elements (CNO) and alpha-elements are
generally higher for low-metallicity stars. Our spectroscopic analysis benefits
from the accurately measured surface gravity from the asteroseismic analysis of
the Kepler light curves. The log g parameter is known to better than 0.03 dex
and is held fixed in the analysis. We compare our Teff determination with a
recent colour calibration of V-K (TYCHO V magnitude minus 2MASS Ks magnitude)
and find very good agreement and a scatter of only 80 K, showing that for other
nearby Kepler targets this index can be used. The asteroseismic log g values
agree very well with the classical determination using Fe1-Fe2 balance,
although we find a small systematic offset of 0.08 dex (asteroseismic log g
values are lower). The abundance patterns of metals, alpha elements, and the
light elements (CNO) show that a simple scaling by [Fe/H] is adequate to
represent the metallicity of the stars, except for the stars with metallicity
below -0.3, where alpha-enhancement becomes important. However, this is only
important for a very small fraction of the Kepler sample. We therefore
recommend that a simple scaling with [Fe/H] be employed in the asteroseismic
analyses of large ensembles of solar-type stars.Comment: MNRAS, in press, 12 page
Asteroseismology from multi-month Kepler photometry: the evolved Sun-like stars KIC 10273246 and KIC 10920273
Seismic analysis of four solar-like stars observed during more than eight months by <i>Kepler</i>
Stellar activity cycles and contribution of the deep layers knowledge
It is believed that magnetic activity on the Sun and solar-type stars are
tightly related to the dynamo process driven by the interaction between
rotation, convection, and magnetic field. However, the detailed mechanisms of
this process are still incompletely understood. Many questions remain
unanswered, e.g.: why some stars are more active than others?; why some stars
have a flat activity?; why is there a Maunder minimum?; are all the cycles
regular? A large number of prox- ies are typically used to study the magnetic
activity of stars as we cannot resolve stellar discs. Recently, it was shown
that asteroseismology can also be used to study stellar activity, making it an
even more powerful tool. If short cycles are not so un- common, we expect to
detect many of them with missions such as CoRoT, Kepler, and possibly the PLATO
mission. We will review some of the latest results obtained with spectroscopic
measurements. We will show how asteroseismology can help us to better
understand the complex process of dynamo and illustrate how the CoRoT and
Kepler missions are revolutionizing our knowledge on stellar activity. A new
window is being opened over our understanding of the magnetic variability of
stars.Comment: 7 pages. To appear in Astrophysics and Space Science Proceedings
series of the 20th Stellar pulsation conference held in Granada (Spain) from
6 to 10 September 2011
TESS Reveals HD 118203 b to be a Transiting Planet
The exoplanet HD 118203 b, orbiting a bright (V = 8.05) host star, was discovered using the radial velocity method by da Silva et al., but was not previously known to transit. Transiting Exoplanet Survey Satellite (TESS) photometry has revealed that this planet transits its host star. Nine planetary transits were observed by TESS, allowing us to measure the radius of the planet to be 1.136-0.028 +0.029 R J, and to calculate the planet mass to be 2.166-0.079 +0.074 M J. The host star is slightly evolved with an effective temperature of T eff=5683-85 +84 K and a surface gravity of log\,g=3.889 0.018-0.017. With an orbital period of 6.134985-0.000030 +0.000029 days and an eccentricity of 0.314 ± 0.017, the planet occupies a transitional regime between circularized hot Jupiters and more dynamically active planets at longer orbital periods. The host star is among the 10 brightest known to have transiting giant planets, providing opportunities for both planetary atmospheric and asteroseismic studies
KOI-3158: The oldest known system of terrestrial-size planets
The first discoveries of exoplanets around Sun-like stars have fueled efforts to find ever smaller worlds evocative of Earth and other terrestrial planets in the Solar System. While gas-giant planets appear to form preferentially around metal-rich stars, small planets (with radii less than four Earth radii) can form under a wide range of metallicities. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe's history when metals were far less abundant. We report Kepler spacecraft observations of KOI-3158, a metal-poor Sun-like star from the old population of the Galactic thick disk, which hosts five planets with sizes between Mercury and Venus. We used asteroseismology to directly measure a precise age of 11.2 ± 1.0 Gyr for the host star, indicating that KOI-3158 formed when the Universe was less than 20 % of its current age and making it the oldest known system of terrestrial-size planets. We thus show that Earth-size planets have formed throughout most of the Universe's 13.8-billion-year history, providing scope for the existence of ancient life in the Galaxy
TOI-257b (HD 19916b): A warm sub-saturn orbiting an evolved F-type star
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 M J (43.9 ± 7.3, Mâ), a radius of RP = 0.639 ± 0.013 R J (7.16 ± 0.15, R â), bulk density of 0.65+0.12-0.11 (cgs), and period 18.38818 +0.00085 -0.00084 days. TOI-257b orbits a bright (V = 7.612 mag) somewhat evolved late F-type star with Mâ = 1.390 ± 0.046 rm M sun, Râ = 1.888 ± 0.033 Rsun, 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 âŒ71 day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars (âŒ100) 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
Die armenische Minderheit in der TĂŒrkei - zu den Entwicklungen seit den EU-Anpassungsreformen 2002 und 2003.
Donated by Klaus KreiserReprinted from : Orient 44. Jahrgang Heft 3, 200