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991.
I. V. Chilingarian P. Prugniel O. K. Sil'chenko V. L. Afanasiev 《Monthly notices of the Royal Astronomical Society》2007,376(3):1033-1046
We present the first 3D observations of a diffuse elliptical galaxy (dE). The good quality data (S/N up to 40) reveal the kinematical signature of an embedded stellar disc, reminiscent of what is commonly observed in elliptical galaxies, though similarity of their origins is questionable. Colour map built from Hubble Space Telescope Advanced Camera for Surveys (ACS) images confirms the presence of this disc. Its characteristic scale (about 3 arcsec =250 pc) is about a half of galaxy's effective radius, and its metallicity is 0.1–0.2 dex larger than the underlying population. Fitting the spectra with synthetic single stellar populations (SSP), we found an SSP-equivalent age of 5 Gyr and nearly solar metallicity [Fe/H] =−0.06 dex. We checked that these determinations are consistent with those based on Lick indices, but have smaller error bars. The kinematical discovery of a stellar disc in dE gives additional support to an evolutionary link from dwarf irregular galaxies due to stripping of the gas against the intracluster medium. 相似文献
992.
E.M. Poulter J.K. Hargreaves G.J. Bailey R.J. Moffet 《Planetary and Space Science》1981,29(8):869-883
The principal advance of the ATS-6 satellite beacon experiment was the ability to deduce continuously the electron content along the entire slant path from ground-based measurements of the signal group delay. This feature has been exploited in conjunction with the more usual Faraday rotation technique to separate the total electron content into ionospheric and protonospheric components. The physical validity of the deduced quantities is investigated using a mathematical model of the plasmasphere in which integration of the time-dependent continuity and momentum equations for oxygen and hydrogen ions along selected L shells yields the ion concentrations and field-aligned fluxes. The ion concentrations are then integrated along the propagation path to various ground stations from ATS-6 to give computed values for comparison with observations. The mathematical model is used with different sets of atmospheric parameters to investigate the significance of ionospheric and protonospheric contents as derived from beacon data.The calculated electron concentrations are able to reproduce mid-latitude equinoctial electron content observations. The shape parameters τ and F can also be simulated by day, but night-time values do not match the observations well, a greater protonospheric content being required. The calculations show that the quantity Np, which is readily derived from ATS-6 observations, may be interpreted as the slant H+ content above some fixed height in the case of some stations (but not others) if the plasmasphere is reasonably full. The total slant content of H+ is approx. twice the value of Np, though it appears that for the Lancaster raypath a closer relationship exists between Np and the H+ tube content at L = 1.8. In general,Np is most closely related to the tube content for an L value slightly greater than the minimum L intersected along the raypath. 相似文献
993.
A filter composed of a crossed pair of doubly refracting crystals and a polaroid, mounted at the focal plane of the telescope, divides each star image into two images of constant intensity ratio. It is shown that such a filter arrangement is capable of providing reliable photographic calibration for stellar photometry. 相似文献
994.
Values for the ratio of total to selective absorption are estimated from optical measurements on Cepheids, their radial velocities, and an assumed rotational velocity model of the Galaxy. It is shown that there is no systematic variation ofR with galactic longitude on the basis of these measurements. 相似文献
995.
The free-convection flow of an incompressible and viscous fluid past an exponentially accelerated infinite vertical plate is analysed. The Laplace transform method is used to obtain the expressions for velocity and skin-friction. The effect of various parameters, occuring into the problem, is discussed with the help of graphs and table. 相似文献
996.
A magnetospheric cavity model is presented to explain self-pulsing and frequency modulation of ducted whistler waves associated with triggered emissions. Partial reflection of these waves at the ends of the duct suggests such a magnetospheric cavity analogous to a laser cavity. 相似文献
997.
P. K. Seidelmann G. H. Kaplan K. J. Johnston C. M. Wade 《Celestial Mechanics and Dynamical Astronomy》1984,34(1-4):39-48
The weak thermal emission from the largest minor planets can be detected and measured at all points around their orbits at microwave frequencies using the Very Large Array (VLA). Position determinations of astrometric quality have been obtained, and flux measurements have provided size estimates. When enough precise positional observations have been accumulated, the orbits of the minor planets and the Earth can be determined. This will allow the equinox to be located within the radio reference frame, providing a truly fundamental coordinate system for radio source positions. It will also provide a means of relating the optical and radio (quasar) coordinate systems.The National Radio Astronomy Observatory is operated by Associated Universities, Incorporated, under contract with the National Science Foundation. 相似文献
998.
New theoretical emission line ratios for the Be-sequence ions Mgix and Sixi are presented. A comparison with observational data for two solar flares and an active region loop obtained with the Harvard EUV spectrometer and NRL XUV spectroheliograph aboard Skylab reveals that these plasmas are in ionization equilibrium at coronal temperatures. Unfortunately most of the density diagnostics are not particularly useful under solar plasma conditions, as they vary only slightly over the electron density range 108–1013cm–3. However the Sixi ratioI(3
P
e
2 -3
P
o
2)/I(3
P
o
1 –1
S
e
0) is density sensitive in the range 108 to 1010cm–3, which is representative of electron densities found in solar active regions or small flares. 相似文献
999.
Shivamoggi (1983) has used the method of strained coordinates in investigating the nonlinear Rayleigh-Taylor instability problem. After incorporating the corrections pointed out by Malik and Singh (1983) he obtained a revised expression for the nonlinear cut off wavenumber which separates the region of stability from that of instability. 相似文献
1000.
C.K. Goertz 《Planetary and Space Science》1984,32(11):1387-1392
Several observations near moving arcs require particle acceleration in nonstationary electric fields. We suggest that kinetic Alfvén waves play a significant role in the acceleration process. The characteristic properties of kinetic Alfvén waves are summarized and the Hasegawa and Mima (1976) solitary kinetic Alfvén waves are described. The resonant coupling of large-scale surface waves to the kinetic Alfvén wave is discussed. Finally, we show that kinetic Alfvén waves can reasonably well explain the observations of what has hence been called “electrostatic” shocks. 相似文献