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  • 1
    Call number: M 91.0484
    In: Lecture notes in physics
    Type of Medium: Monograph available for loan
    Pages: X, 467 S. : 1 farb. Abb., zahlr. graph. Darst.
    ISBN: 3540530916
    Series Statement: Lecture notes in physics 367
    Language: English
    Location: Upper compact magazine
    Branch Library: GFZ Library
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  • 2
  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 82 (1983), S. 231-232 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have calculated eigenfrequencies of radial and nonradial p-mode oscillations with low harmonic index l (l = 0, 1, 2, 3, and 4) for a standard solar model with normal composition and appoximately the correct age. It is found that theoretical eigenfrequencies calculated for our standard model agree approximately with observed peaks in the power spectra for the full-disk five minute oscillation of the Sun (Claverie et al., 1980; Grec et al., 1983; Scherrer et al., 1983) in agreement with other recent works (Christensen-Dalsgaard and Gough, 1980; Scuflaire et al., 1981). However, there still remains a slight discrepancy between theory and observations in such a sense that the theoretical eigenfrequencies are slightly lower than observations (see Figure 1). Eigenfrequencies of nonradial p-modes with high degree l for the same model are also calculated for comparison with observations of the conventional five-minute oscillation with shorter horizontal wavelength. It is found that theoretical eigenfrequencies lie slightly above the observed ridges in the diagnostic (k, ω)-diagram, which is in accord with Ulrich and Rhodes (1977) and Berthomieu et al. (1980) because our standard model has a slightly shallow convective zone. It remains to be seen whether improvement in the equilibrium model can remove this small discrepancy, concurrently with a better agreement between theory and observation for the whole-disk oscillations of low degree. A full account of this work will be found in Shibahashi and Osaki (1981).
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 46 (1976), S. 323-346 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Numerical analysis has been carried out on the one-dimensional quasi-linear relaxation of a group of fast electrons travelling through the plasma. It is demonstrated that the electron velocity distribution of fast electrons tends to be a plateau form exciting the electron plasma waves and that the plasma waves are almost completely reabsorbed later by electrons arriving later. Both the velocity range and time interval in which quasi-plateau distribution is formed increase with distance from the origin of the fast electrons. There is no net energy loss of the electron cloud during the travel through the plasma if we neglect both the collisional losses and the scattering of plasma waves. Although the present computation is preliminary and limited to rather low beam density, we can see that the characteristics of both the electron beam and the plasma waves tend, with distance, to those of the analytical solution given by Ryutov and Sagdeev; though a modification to set a low velocity cutoff on the plasma waves due to the thermal electrons is necessary.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2016-07-29
    Description: We explore the detection limits of the phase modulation (PM) method of finding binary systems among multiperiodic pulsating stars. The method is an attractive way of finding non-transiting planets in the habitable zones of intermediate-mass stars, whose rapid rotation inhibits detections via the radial velocity (RV) method. While oscillation amplitudes of a few mmag are required to find planets, many  Scuti stars have these amplitudes. In suboptimal cases where the signal to noise of the oscillations is lower, low-mass brown dwarfs (~13 M Jup ) are detectable at orbital periods longer than about 1 yr, and the lowest mass main-sequence stars (0.1–0.2 M ) are detectable at all orbital periods where the PM method can be applied. We use purpose-written Markov chain Monte Carlo (MCMC) software for the calculation of the PM orbits, which offers robust uncertainties for comparison with RV solutions. Using Kepler data and ground-based RVs, we verify that these two methods are in agreement, even at short orbital periods where the PM method undersamples the orbit. We develop new theory to account for the undersampling of the time delays, which is also necessary for the inclusion of RVs as observational data in the MCMC software. We show that combining RVs with time delays substantially refines the orbits because of the complementarity of working in both the spatial (PM) and velocity (RV) domains simultaneously. Software outputs were tested through an extensive hare-and-hounds exercise, covering a wide range of orbital configurations including binaries containing two pulsators.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 6
    Publication Date: 2015-05-13
    Description: There are many Slowly Pulsating B (SPB) stars and Dor stars in the Kepler mission data set. The light curves of these pulsating stars have been classified phenomenologically into stars with symmetric light curves and with asymmetric light curves. In the same effective temperature ranges as the Dor and SPB stars, there are variable stars with downward light curves that have been conjectured to be caused by spots. Among these phenomenological classes of stars, some show ‘frequency groups’ in their amplitude spectra that have not previously been understood. While it has been recognized that non-linear pulsation gives rise to combination frequencies in a Fourier description of the light curves of these stars, such combination frequencies have been considered to be a only a minor constituent of the amplitude spectra. In this paper, we unify the Fourier description of the light curves of these groups of stars, showing that many of them can be understood in terms of only a few base frequencies, which we attribute to g-mode pulsations, and combination frequencies, where sometimes a very large number of combination frequencies dominate the amplitude spectra. The frequency groups seen in these stars are thus tremendously simplified. We show observationally that the combination frequencies can have amplitudes greater than the base frequency amplitudes, and we show theoretically how this arises. Thus for some Dor and SPB stars, combination frequencies can have the highest observed amplitudes. Among the B stars are pulsating Be stars that show emission lines in their spectra from occasional ejection of material into a circumstellar disc. Our analysis gives strong support to the understanding of these pulsating Be stars as rapidly rotating SPB stars, explained entirely by g-mode pulsations.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 7
    Publication Date: 2015-05-22
    Description: Continuous and precise space-based photometry has made it possible to measure the orbital frequency modulation of pulsating stars in binary systems with extremely high precision over long time spans. Frequency modulation caused by binary orbital motion manifests itself as a multiplet with equal spacing of the orbital frequency in the Fourier transform. The amplitudes and phases of the peaks in these multiplets reflect the orbital properties, hence the orbital parameters can be extracted by analysing such precise photometric data alone. We derive analytically the theoretical relations between the multiplet properties and the orbital parameters, and present a method for determining these parameters, including the eccentricity and the argument of periapsis, from a quintuplet or a higher order multiplet. This is achievable with the photometry alone, without spectroscopic radial velocity measurements. We apply this method to Kepler mission data of KIC 8264492, KIC 9651065, and KIC 10990452, each of which is shown to have an eccentricity exceeding 0.5. Radial velocity curves are also derived from the Kepler photometric data. We demonstrate that the results are in good agreement with those obtained by another technique based on the analysis of the pulsation phases.
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    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 8
    Publication Date: 2015-05-24
    Description: We present the latest developments to the phase modulation method for finding binaries among pulsating stars. We demonstrate how the orbital elements of a pulsating binary star can be obtained analytically, that is, without converting time delays to radial velocities by numerical differentiation. Using the time delays directly offers greater precision, and allows the parameters of much smaller orbits to be derived. The method is applied to KIC 9651065, KIC 10990452 and KIC 8264492, and a set of the orbital parameters is obtained for each system. Radial velocity curves for these stars are deduced from the orbital elements thus obtained.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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  • 9
    Publication Date: 2014-08-30
    Description: We report an analysis of high time resolution spectra of the chemically peculiar Ap star KIC 10195926 obtained with the Subaru telescope. We find that the star has low overabundances of rare earth elements compared with other rapidly oscillating Ap stars. We found only upper limits for pulsations from spectral lines of rare earth and other chemical elements. Pulsation was found only for the narrow core of the Hα line with an amplitude of 171 ± 41 m s –1 and with the frequency corresponding to photometric frequency obtained from Kepler observations.
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  • 10
    Publication Date: 2015-01-15
    Description: High-resolution spectroscopy with the Subaru High Dispersion Spectrograph, and Swift ultraviolet photometry are presented for the pulsating extreme helium star V652 Her. Swift provides the best relative ultraviolet photometry obtained to date, but shows no direct evidence for a shock at ultraviolet or X-ray wavelengths. Subaru has provided high spectral and high temporal resolution spectroscopy over six pulsation cycles (and eight radius minima). These data have enabled a line-by-line analysis of the entire pulsation cycle and provided a description of the pulsating photosphere as a function of optical depth. They show that the photosphere is compressed radially by a factor of at least 2 at minimum radius, that the phase of radius minimum is a function of optical depth and the pulse speed through the photosphere is between 141 and 239 km s –1 (depending how measured) and at least 10 times the local sound speed. The strong acceleration at minimum radius is demonstrated in individual line profiles; those formed deepest in the photosphere show a jump discontinuity of over 70 km s –1 on a time-scale of 150 s. The pulse speed and line profile jumps imply a shock is present at minimum radius. These empirical results provide input for hydrodynamical modelling of the pulsation and hydrodynamical plus radiative transfer modelling of the dynamical spectra.
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    Electronic ISSN: 1365-2966
    Topics: Physics
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