Results 1 - 10 of 11192
Results 1 - 10 of 11192. Search took: 0.033 seconds
|Sort by: date | relevance|
[en] Instruments and techniques designed for registering the minute Doppler shifts arising from stellar radial velocity are examined. Particular attention is given to the photographic spectrographs, the high-dispersion spectrographs ('digital speedometers'), and the Palomar spectrometer. The principle of using radial-velocity masks is described, and the use of interferometers for radial-velocity measurements is discussed. Results are presented of radial velocity observations for HD 114762, HD 210647, and Epsilon Tauri, together with interpretations of these results
[en] The fundamental equations governing the self-similar dynamics of polytropic gaseous spheres are derived, and the asymptotic solutions are given. The solutions divide into cases with and without critical points in closed analogy with the solar wind solutions of Holzer and Axford (1970). Properties for solutions with critical points are discussed, and their behavior around the critical point is derived explicitly for n = 1. Numerical examples of self-similar solutions for n = 1 and n = 2 - gamma are presented, and the properties of the solutions are discussed. 11 references
[en] The stability to radial and nonradial perturbations of an extensive set of stellar dynamical models with the Plummer density law is investigated. Radial stability of a large subset of the models can be demonstrated using either a generalization of Antonov's (1962) sufficient criterion for isotropic systems, or a very simple criterion by Doremus and Feix (1973). Nonradial stability, and radial stability of models not satisfying Antonov's criterion, are tested with a mean-field N-body code. It is found that models near the limit of maximum radial velocity anisotropy are unstable to the formation of a bar. Models composed of nearly circular orbits are apparently stable. Of the three types of instability studied by Barnes, Goodman, and Hut (1985) in a family of generalized polytropes, only one, the radial-orbit instability, is active in these models. It is argued that the same is likely to be true in any family of spherical models with a density profile similar to those of real stellar systems. 26 references
[en] A diagram ''rotational velocity Vm - diameter D0'' obtained for a different types of galaxies is discussed. The value of Vm taken from rotation curves and from HI-line width WH are considered separately. Galaxies of an early (Sa-Sbc) types have in average a higher mean velocity of rotation than late-type galaxies of similar diameters. Velocities Vm obtained from WH for a giant SO - Sab-galaxies are often underestimated which may be caused by an asommetric clumply distribution of HI in these galaxies. The relation lnVm-lnD0 is nearly absent for galxies with D0>30 kpc: except a few cases Vm does not exceed 350 km/s for any value of D0
[en] The evolution and final stationary states of model galaxies consisting of a halo with a density of rho(r) approximately r-2 and rho(r) approximately r-4 and a disk of a finite thickness with N=200 particle-stars with an exponential surface density are investigated by numerical experiments. The instability of the bar mode is supressed when the ratio of the masses of the halo and disk Msub(H)/Msub(D)> or approximately 1. As far as this instability is concerned, the best stabilizing properties are possessed by the haloes most concentrated toward the center (rho approximately r-4 with a small size of the nucleus). With respect to the ratio of the radial velocity dispersion csub(r) to the circular velocity V, experiments agree with observational data in the Sun's vicinity at Msub(H)/Msub(D) approximately equal to 2 (within the sphere r<=10 kpc). The local stability criterion is obtained which takes into account both the smaller stability of nonaxisymmetrical perturbations in comparison with the axisymmetrical ones and the local characteristics of the disk parameter inhomogeneities. Comparison between the critical velocity dispersion in this criterion with the experimental one, csub(r), shows that the disk, as a result of the evolution, arrives at a state close to the stability boundary. In the region studied, Msub(H)/Msub(D)<=3, instability of bending oscillations of the disk is not detected
[en] We present the analysis of high-resolution optical spectroscopic observations of the zero-age main-sequence O star Herschel 36 spanning six years. This star is definitely a multiple system, with at least three components detected in its spectrum. Based on our radial-velocity (RV) study, we propose a picture of a close massive binary and a more distant companion, most probably in wide orbit about each other. The orbital solution for the binary, whose components we identify as O9 V and B0.5 V, is characterized by a period of 1.5415 ± 0.0006 days. With a spectral type O7.5 V, the third body is the most luminous component of the system and also presents RV variations with a period close to 498 days. Some possible hypotheses to explain the variability are briefly addressed and further observations are suggested.
[en] Critical velocities have been observed in an ultracold superfluid Fermi gas throughout the BEC-BCS crossover. A pronounced peak of the critical velocity at unitarity demonstrates that superfluidity is most robust for resonant atomic interactions. Critical velocities were determined from the abrupt onset of dissipation when the velocity of a moving one-dimensional optical lattice was varied. The dependence of the critical velocity on lattice depth and on the inhomogeneous density profile was studied
[en] We report the detection of a large mass planet orbiting around the K0 metal-rich subgiant HD38801 (V = 8.26) by precise radial velocity (RV) measurements from the Subaru Telescope and the Keck Telescope. The star has a mass of 1.36 Msun and a metallicity of [Fe/H] = +0.26. The RV variations are consistent with a circular orbit with a period of 696.0 days and a velocity semiamplitude of 200.0 m s-1, which yield a minimum mass for the companion of 10.7 MJUP and a semimajor axis of 1.71 AU. Such super-massive objects with very low eccentricities and periods of hundreds of days are uncommon among the ensemble of known exoplanets.
[en] We report the detection of eclipses in GJ 3236, a bright (I = 11.6), very low mass binary system with an orbital period of 0.77 days. Analysis of light and radial velocity curves of the system yielded component masses of 0.38 ± 0.02 Msun and 0.28 ± 0.02 Msun. The central values for the stellar radii are larger than the theoretical models predict for these masses, in agreement with the results for existing eclipsing binaries, although the present 5% observational uncertainties limit the significance of the larger radii to approximately 1σ. Degeneracies in the light curve models resulting from the unknown configuration of surface spots on the components of GJ 3236 currently dominate the uncertainties in the radii, and could be reduced by obtaining precise, multiband photometry covering the full orbital period. The system appears to be tidally synchronized and shows signs of high activity levels as expected for such a short orbital period, evidenced by strong Hα emission lines in the spectra of both components. These observations probe an important region of mass-radius parameter space around the predicted transition to fully convective stellar interiors, where there are a limited number of precise measurements available in the literature.