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《New Astronomy》2015
The absolute dimensions of the components of the eccentric eclipsing binary KL CMa have been determined. The solution of light and radial velocity curves of high ( Å) and intermediate ( Å) resolution spectra yielded masses M1 = 3.55 ± 0.27 M⊙, M2 = 2.95 ± 0.24 M⊙ and radii R1 = 2.37 ± 0.09 R⊙, R2 = 1.70 ± 0.1 R⊙ for primary and secondary components, respectively. The system consists of two late B-type components at a distance of 220 ± 20 pc for an estimated reddening of .The present study provides an illustration of spectroscopy’s crucial role in the analysis of binary systems in eccentric orbits. The eccentricity of the orbit () of KL CMa is found to be bigger than the value given in the literature (). The apsidal motion rate of the system has been updated to a new value of , which indicates an apsidal motion period of yrs, two times slower than given in the literature. Using the absolute dimensions of the components yielded a relatively weak relativistic contribution of . The observed internal-structure component () is found to be in agreement with its theoretical value ().Both components of the system are found very close to the zero-age main-sequence and theoretical isochrones indicate a young age ( Myr) for the system. Analysis of the spectral lines yields a faster rotation ( km s−1) for the components than their synchronization velocities ( km s−1, km s−1). 相似文献
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Using available astrometric and radial velocity data, the space velocities of cataclysmic variables (CVs) with respect to Sun were computed and kinematical properties of various sub-groups of CVs were investigated. Although observational errors of systemic velocities (γ) are high, propagated errors are usually less than computed dispersions. According to the analysis of propagated uncertainties of the computed space velocities, available sample was refined by removing the systems with the largest propagated uncertainties so that the reliability of the space velocity dispersions was improved. Having a dispersion of for the space velocities, CVs in the current refined sample (159 systems) are found to have 5 ± 1 Gyr mean kinematical age. After removing magnetic systems from the sample, it is found that non-magnetic CVs (134 systems) have a mean kinematical age of 4 ± 1 Gyr. According to 5 ± 1 and 4 ± 1 Gyr kinematical ages implied by 52 ± 8 and 45 ± 7 km s?1 dispersions for non-magnetic systems below and above the period gap, CVs below the period gap are older than systems above the gap, which is a result in agreement with the standard evolution theory of CVs. Age difference between the systems below and above the gap is smaller than that expected from the standard theory, indicating a similarity of the angular momentum loss time scales in systems with low-mass and high-mass secondary stars. Assuming an isotropic distribution, velocity dispersions of non-magnetic CVs below and above the period gap are calculated and . The small difference of velocity dispersions between the systems below and above the gap may imply that magnetic braking does not operate in the detached phase, during which the system evolves from the post-common envelope orbit into contact. 相似文献
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We study intensity oscillations near the apex of a coronal loop to find the signature of MHD oscillations. We analyse the time series of the strongest Fe XII 195.12 Å image data, observed by 40″ SLOT of the EUV Imaging Spectrometer (EIS) onboard the Hinode spacecraft. Using a standard wavelet tool, we produce power spectra of intensity oscillations at location ‘’ near the apex of a clearly visible coronal loop. We detect intensity oscillations of a period of ≈322 s with a probability of 96%. This oscillation period of ≈322 s is found to be in good agreement with theory of the (second) harmonics of standing slow acoustic oscillations of . We detect, for the first time, the observational signature of multiple (first and second) harmonics of slow acoustic oscillations in the non-flaring coronal loop. Such oscillations have been observed in the past in hot and flaring coronal loops only, but have been predicted recently to exist in comparatively cooler and non-flaring coronal loops as well. We find the periodicities ～497 s and ～592 s with the probability 99–100% at the ‘L1’ and ‘L2’ locations, respectively, near the clearly visible western footpoint of the loop. We interpret these oscillations to be likely associated with the first harmonics (fundamental mode) of slow acoustic oscillations. Using the period ratios , we estimate the density scale heights in the EUV loop as ～10 Mm and 21 Mm, respectively, in which the latter value (～21 Mm) is compared well with the loop half length. We also find an evidence of propagating bright blob at its lower bound sub-sonic speed of ≈6.4 km/s, suggesting that they are caused by the mass flow from one end to the other in the coronal loop. We also suggest that standing oscillations, and propagating bright blobs caused probably by the pulse of plasma flow, co-exist in comparatively cooler and non-flaring coronal loop. 相似文献