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131.
132.
Ján Budaj † 《Monthly notices of the Royal Astronomical Society》1999,310(2):419-427
We reveal sufficient evidence that the physical characteristics of Ap stars are related to binarity. The Ap star peculiarity [represented by the Δ( V 1- G ) value and magnetic field strength] diminishes with eccentricity, and it may also increase with orbital period ( P orb ). This pattern, however, does not hold for large orbital periods. A striking gap that occurs in the orbital period distribution of Ap binaries at 160–600 d might well mark a discontinuity in the above-mentioned behaviour. There is also an interesting indication that the Ap star eccentricities are relatively lower than those of corresponding B9–A2 normal binaries for P orb >10 d . All this gives serious support to the pioneering idea of Abt & Snowden concerning a possible interplay between the magnetism of Ap stars and their binarity. Nevertheless, we argue instead in favour of another mechanism, namely that it is binarity that affects magnetism and not the opposite, and suggest the presence of a new magnetohydrodynamical mechanism induced by the stellar companion and stretching to surprisingly large P orb . 相似文献
133.
S. A. Lamzin 《Astronomy Letters》2000,26(9):589-599
The ultraviolet spectra of the stars RY Tau and HD 115043 from the Hubble Space Telescope are analyzed. RY Tau belongs to the classical T Tauri stars, while HD 115043 is a young (t~3×108 years), chromospherically active star. The most intense emission lines were identified, and their fluxes were measured. Low-resolution spectra of RY Tau and HD 115043 in the wavelength range 1160–1760 Å exhibit almost the same set of emission lines. However, first, the luminosity of RY Tau in these lines is approximately a factor of 300 higher than that of HD 115043, and, second, the relative line intensities differ greatly. The intensity ratio of the C IV λ1550, Si IV λ1400, and NV λ1240 doublet components is close to 1: 2 in the spectra of both stars. Judging by the continuum energy distribution, the spectral type of RY Tau is later than that of HD 115043. Synchronous flux variability in the C IV λ1550 and He II λ1640 lines in a time of ~20 min was detected in RY Tau. The flux rise in these lines was accompanied by a redshift of the intensity peak in the profiles by~50 km s?1. Intermediate-resolution spectra are used to study line profiles in the spectrum of RY Tau. In particular, the profiles of (optically thin) Si III]λ1892 and C III]λ1909 lines were found to be asymmetric and about 300 km s?1 in width. The (optically thick) C IV λ1550 doublet lines have similar profiles. The Mg II λ2800 doublet lines are also asymmetric, but their shape is different: they consist of a broad (?750 km s?1 at the base) emission component on which an interstellar absorption line shifted from the line symmetry center by about 20 km s?1 is superimposed. The intensity ratio of the Mg II λ2800 doublet components is?1.4. Whether there are molecular hydrogen lines in the spectrum of RY Tau is still an open question. It is shown that the emission lines in the ultraviolet spectrum of RY Tau cannot originate in a hydrostatically equilibrium chromosphere. It is argued that quasi-steady accretion of circumstellar matter is responsible for the emission. 相似文献
134.
Wen-Yuan Cui Bo Zhang Ya-Min Quan Gui-De Zhou Yan-Ping Chen 《Astrophysics and Space Science》2008,314(4):351-359
Taking account of the metallicity dependence of the s-process nucleosynthesis in the AGB stars, we adopted the wind accretion
model with the condition of total angular momentum conservation and used the Monte-Carlo method to study the variations and
the distributions of the orbital elements of the mild and strong Ba stars. The calculated results show that the level of heavy-element
overabundance in a Ba star depends on the orbital period. Since there is a strong dependence of s-process yields on the initial
stellar metallicity of the AGB star and a strong increase of the s-process yields in AGB stars with decreasing metallicity,
the calculated results strongly suggest that the initial metallicity of the Ba star systems is another important parameter
for the level of heavy-element overabundance in a Ba star. The strong Ba stars generally have lower metallicities than mild
Ba stars. The masses of AGB progenitor and Ba star are other two parameters which also have some impact on the heavy-element
overabundance in the Ba star. 相似文献
135.
Yu. A. Fadeyev 《Astronomy Letters》2007,33(2):103-112
We present the results of solving the radiative transfer equation for the Stokes vector in the case of light scattering by
spherical forsterite dust particles in an axisymmetric circumstellar envelope of a red giant. We have assumed that the surfaces
of constant scattering-particle density are prolate or oblate spheroids, the particle density decreases with radius as N
d ∝ r
−2, and the dust particles at the inner boundary of the envelope are in thermal equilibrium with the stellar emission at solid-phase
evaporation temperature T
ev = 800 K. In the wavelength range 0.27 μm ≤ λ ≤ 1 μm, particles with radii 0.03 μm ≲ a ≲ 0.2 μm make a major contribution to the linear polarization of the stellar emission. The increase in scattering efficiency factor
with decreasing wavelength λ is mainly responsible for the growth of polarization toward the short wavelengths known from
observations. However, at a mean number of scatterings 1.2 ≤ N
sca ≤ 1.6, the polarization ceases to grow due to depolarization effects and decreases rapidly as the wavelength decreases further.
The wavelength of the polarization maximum is determined mainly by two quantities: the particle radius and the mass loss rate.
The upper limits for the degree of linear polarization in the case of light scattering in circumstellar dust envelopes with
the geometries of prolate and oblate spheroids are p ≈ 3 and 5%, respectively. The polarization for light scattering by enstatite particles is higher than that for light scattering
by forsterite particles approximately by 0.3%.
Original Russian Text ? Yu.A. Fadeyev, 2007, published in Pis’ma v Astronomicheskiĭ Zhurnal, 2007, Vol. 33, No. 2, pp. 123–133. 相似文献
136.
M. Spavone E. Iodice R. Calvi D. Bettoni G. Galletta G. Longo P. Mazzei G. Minervini 《Monthly notices of the Royal Astronomical Society》2009,393(1):317-328
In this paper, we present a detailed study of the peculiar early-type galaxy NGC 1947. The main goal of this work is to constrain the dynamical status and the formation history of NGC 1947 by comparing the observed properties with the predictions derived from different galaxy formation scenarios. To this aim, we derived the photometric and kinematical properties of NGC 1947. Due to the presence of an extended dust lane, which crosses the galaxy centre along the photometric minor axis, we used near-infrared (NIR) images ( J and K bands) to derive an accurate analysis of the stellar light distribution. Optical images (in the V and R bands) are used to derive the colour profiles and colour maps to study the structure of the dust lane. The observed kinematics confirm the presence of two components with decoupled angular momentum: gas and dust rotate along the minor axis, while the rotation velocities of the stars are observed along the major axis. The complex structure observed in NGC 1947 supports the hypothesis that some kind of interactions happened in the evolution of this object. We analysed two alternatives: a merging process and an accretion event. We discussed how the observed properties strongly suggest that the decoupled ring of gas and dust has been accreted from outside. 相似文献
137.
138.
139.
P.Y. LUKYANOV O.I. PETROV A.A. GURULEV A.O. ORLOV S.D. KRYLOV K.A. SHEGRINA and S.V. TSYRENZHAPOV 《《地质学报》英文版》2014,88(Z1):20-22
正1 Introduction Soda Lake Doroninskoye(Uleoti District of Transbaikalian Region,Russia)belongs to a rare type of meromictic basins.For meromictic basins,the vertical stratification in the form of sufficiently thin water layers with significantly differing physical and chemical properties is typical,as well as peculiar biota.The main characteristics of the lake Doroninskoye are: 相似文献
140.
Due to a combination of rapid expansion and changes in chemical composition, the optical spectrum of V4334 Sgr changed rapidly between discovery in 1996 Februaryand extinction during 1999. As one of the most rapidly evolving stars ever observed, optical spectroscopy must answer a range of important questions.The development of the optical spectrum and its implications are discussedthrough a review of published literature. A previously unpublished sequence of spectra from near discovery through 1996 demonstrates the thermal evolution of V4334 Sgr, while detailed analysis of an unpublished echelle spectrumobtained in 1996 May raises questions about the model atmospheres used to date.As a result, requirements for future models of the atmosphere of V4334 Sgr are analysed. The future evolution of V4334 Sgr and the dispersion of its dustycocoon are briefly discussed. 相似文献