Observations of the pulsations of stars can be used to infer their interior structure and test theoretical models. The main-sequence γ Doradus (Dor) and δ Scuti (Sct) stars with masses 1.2-2.5 M ...SUBsun/SUB are particularly useful for these studies. The γ Dor stars pulsate in high-order g-modes with periods of order 1 day, driven by convective blocking at the base of their envelope convection zone. The δ Sct stars pulsate in low-order g- and p-modes with periods of order 2 hr, driven by the κ mechanism operating in the He II ionization zone. Theory predicts an overlap region in the Hertzsprung-Russell diagram between instability regions, where "hybrid" stars pulsating in both types of modes should exist. The two types of modes with properties governed by different portions of the stellar interior provide complementary model constraints. Among the known γ Dor and δ Sct stars, only four have been confirmed as hybrids. Now, analysis of combined Quarter 0 and Quarter 1 Kepler data for hundreds of variable stars shows that the frequency spectra are so rich that there are practically no pure δ Sct or γ Dor pulsators, i.e., essentially all of the stars show frequencies in both the δ Sct and the γ Dor frequency range. A new observational classification scheme is proposed that takes into account the amplitude as well as the frequency and is applied to categorize 234 stars as δ Sct, γ Dor, δ Sct/γ Dor or γ Dor/δ Sct hybrids.
We use asteroseismic data obtained by the NASA Kepler mission to estimate the fundamental properties of more than 500 main-sequence and sub-giant stars. Data obtained during the first 10 months of ...Kepler science operations were used for this work, when these solar-type targets were observed for one month each in survey mode. Stellar properties have been estimated using two global asteroseismic parameters and complementary photometric and spectroscopic data. Homogeneous sets of effective temperatures, Tsubeff , were available for the entire ensemble from complementary photometry; spectroscopic estimates of Tsubeff and Fe/H were available from a homogeneous analysis of ground-based data on a subset of 87 stars. We adopt a grid-based analysis, coupling six pipeline codes to 11 stellar evolutionary grids. Future analyses using individual oscillation frequencies will offer significant improvements on up to 150 stars, in particular for estimates of the ages, where having the individual frequency data is most important.
Asteroseismology of solar-type stars has an important part to play in the exoplanet program of the NASA Kepler Mission. Precise and accurate inferences on the stellar properties that are made ...possible by the seismic data allow very tight constraints to be placed on the exoplanetary systems. Here, we outline how to make an estimate of the detectability of solar-like oscillations in any given Kepler target, using rough estimates of the temperature and radius, and the Kepler apparent magnitude.
Fluoroscopic and electrocardiographic (ECG) criteria for the documentation of pacing lead positioning (apical and alternative sites) have been described, but data regarding their accuracy are ...lacking.
Fifty patients (27 men; mean age, 76 ± 9 years) with permanent right ventricular (RV) pacing leads were included. RV lead position was classified as apical, mid septal, mid RV free wall, RV outflow tract (RVOT) septal, or RVOT free wall. Exact anatomic lead position was documented using three-dimensional (3D) transthoracic echocardiography (TTE). Cohen's κ coefficient was used to assess agreement between fluoroscopic or ECG criteria and 3D TTE.
True lead positions were as follows: 15 apical, 24 mid septal, three mid RV free wall, and eight RVOT septal wall; no leads were implanted into the RVOT free wall. Fluoroscopy (κ = 0.56; 95% confidence interval CI, 0.37-0.76) and electrocardiography (κ = 0.43; 95% CI, 0.25-0.60) had moderate overall agreement with 3D TTE. Fluoroscopy had moderate agreement with 3D TTE for apical (κ = 0.57; 95% CI, 0.32-0.83), mid septal (κ = 0.48; 95% CI, 0.25-0.72), and mid free wall sites (κ = 0.54; 95% CI, 0.08-1.00) and moderate to good agreement for the RVOT septal wall (κ = 0.61; 95% CI, 0.30-0.90). Fluoroscopy misclassified as mid septal six of the 15 RV apical leads. ECG criteria had moderate agreement with 3D TTE for apical positions (κ = 0.55; 95% CI, 0.34-0.77) and RVOT sites (κ = 0.47; 95% CI, 0.21-0.73). Electrocardiography misclassified as apical 10 and as RVOT six of the 24 mid septal leads.
Fluoroscopic and ECG criteria are only moderately accurate in discriminating between RV apical, mid septal, mid free wall, and RVOT pacing sites. These data suggest that both fluoroscopy and electrocardiography may not be adequate techniques for the correct documentation of RV pacing lead position for routine clinical practice or research purposes.
Recently the number of main-sequence and subgiant stars exhibiting solar-like oscillations that are resolved into individual mode frequencies has increased dramatically. While only a few such data ...sets were available for detailed modeling just a decade ago, the Kepler mission has produced suitable observations for hundreds of new targets. This rapid expansion in observational capacity has been accompanied by a shift in analysis and modeling strategies to yield uniform sets of derived stellar properties more quickly and easily. We use previously published asteroseismic and spectroscopic data sets to provide a uniform analysis of 42 solar-type Kepler targets from the Asteroseismic Modeling Portal. We find that fitting the individual frequencies typically doubles the precision of the asteroseismic radius, mass, and age compared to grid-based modeling of the global oscillation properties, and improves the precision of the radius and mass by about a factor of three over empirical scaling relations. We demonstrate the utility of the derived properties with several applications.
We have measured solar-like oscillations in red giants using time-series photometry from the first 34 days of science operations of the Kepler Mission. The light curves, obtained with 30 minute ...sampling, reveal clear oscillations in a large sample of G and K giants, extending in luminosity from the red clump down to the bottom of the giant branch. We confirm a strong correlation between the large separation of the oscillations (Δν) and the frequency of maximum power (νmax). We focus on a sample of 50 low-luminosity stars (νmax > 100 μHz, L <~ 30 L sun) having high signal-to-noise ratios and showing the unambiguous signature of solar-like oscillations. These are H-shell-burning stars, whose oscillations should be valuable for testing models of stellar evolution and for constraining the star formation rate in the local disk. We use a new technique to compare stars on a single échelle diagram by scaling their frequencies and find well-defined ridges corresponding to radial and non-radial oscillations, including clear evidence for modes with angular degree l = 3. Measuring the small separation between l = 0 and l = 2 allows us to plot the so-called C-D diagram of δν02 versus Δν. The small separation δν01 of l = 1 from the midpoint of adjacent l = 0 modes is negative, contrary to the Sun and solar-type stars. The ridge for l = 1 is notably broadened, which we attribute to mixed modes, confirming theoretical predictions for low-luminosity giants. Overall, the results demonstrate the tremendous potential of Kepler data for asteroseismology of red giants.
In addition to its search for extrasolar planets, the NASA Kepler mission provides exquisite data on stellar oscillations. We report the detections of oscillations in 500 solar-type stars in the ...Kepler field of view, an ensemble that is large enough to allow statistical studies of intrinsic stellar properties (such as mass, radius, and age) and to test theories of stellar evolution. We find that the distribution of observed masses of these stars shows intriguing differences to predictions from models of synthetic stellar populations in the Galaxy.
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