Building blocks in hierarchical clustering scenarios and their connection with damped Lyα systems     

Sofía A. Cora  Patricia B. Tissera †  Diego G. Lambas ‡  Mirta B. Mosconi 《Monthly notices of the Royal Astronomical Society》2003,343(3):959-970

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Terminal Outflow Velocities from the Mass-Losing AGB Stars     

A. Kučinskas 《Astrophysics and Space Science》1997,251(1-2):231-234

We have calculated terminal gas outflow velocities from the circumstellar shells of the AGB stars. Our results confirm that, in case of the stationary dust driven winds, the dynamics of the outflow is governed essentially by the dust properties and stellar luminosities, while only marginally by other stellar parameters. Although being far from comprehensive, our calculations also indicate that the dust driven winds may only occur in cool, luminous, low mass objects. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Radar observations of the Geminid meteoroid stream     

G. Cevolani  G. Bortolotti  L. Foschini  C. Franceschi  G. Grassi  G. Trivellone  A. Hajduk  V. Porubčan 《Earth, Moon, and Planets》1995,68(1-3):247-255

Continuous radio-wave monitoring of the Geminid activity in December 1992 and 1993 by using a forward scatter (FS) bistatic radar over the Bologna-Lecce baseline (700 km) in Italy, reveals peculiar structural aspects of the stream in terms of signal amplitude-rate and duration-rate dependence. The observational results of the Geminid display obtained in the two consecutive years with differentiated peak levels of transmitted power, exhibit different time distributions of underdense meteors against the signal received power. Both sets of the data relative to the peak activity in December 12–14, show reflection properties of Geminids which are atypical if compared with echoes from cometary-type showers, with really high echo counts at mid-upper levels of the peak received power. An assymmetric curve of activity of the Geminids complex is evidenced, with the peak flux of smaller particles occurring earlier than that of larger ones.  相似文献   

Interplanetary dust particles and solar radiation     

J. Klačka 《Earth, Moon, and Planets》1994,64(2):125-132

The problem of the action of the solar radiation on the motion of interplanetary dust particle is discussed. Differences between the action of electromagnetic solar radiation and that of the solar wind are explained not only from the point of view of the physical nature of these phenomena but also from the point of view of dust particle's orbital evolution. As for the electromagnetic solar radiation, general equation of motion for the particle is written and the most important consequences are: (i) the process of inspiralling toward the Sun is not the only possible motion - even spiralling from the Sun is also possible, and, (ii) the orbital plane of the particle (its inclination) may change in time. As for the solar wind, the effect corresponding to the fact that solar wind particles spread out from the Sun in nonradial direction causes that the process of inspiralling toward the Sun is in more than 50% less effective than for radial spread out; in the region of the asteroid belt (long period orbits) the process of inspiralling is changed into offspiralling. Also shift in the perihelion of dust particle's orbit exists.  相似文献   

Testing the consistency of the Starburst scenario for active galactic nuclei     

María Luisa García Vargas  Angeles Díaz  Roberto Terlevich  Elena Terlevich 《Astrophysics and Space Science》1993,205(1):77-84

In the frame of the Starburst Model, we show that the evolution of a massive stellar cluster in a high metallicity environment can reproduce the observed emission-line spectrum and the UV-optical Spectral Energy Distribution of the Seyfert 2 galaxies and LINERs. We apply the results of our models to three objects: NGC 5506, NGC 5643 and Mk 348.  相似文献   

Chemical Enrichment of the Intra-Cluster Medium     

SofÍa A. Cora  Simon D.M. White 《Astrophysics and Space Science》2003,284(2):425-428

We investigate the metal enrichment of the intra-cluster medium by using a method that combines N-Body simulations and a semi-analytic model (SAM) of galaxy formation. The cluster of galaxies is simulated in a flat, low density universe, with a numerical resolution that allows the detection of substructures in the dark matter background of the cluster. The phenomenological approach used to model the physical processes involved in the galaxy formation and metal production is applied to the substructures found in the dark matter halos detected at different redshifts. Details of the chemical implementation in the SAM and first results related to the mean properties of the baryonic matter components are presented. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

The estimate of the deceleration in the earth's rotation due to the sun     

Milan Burša 《Earth, Moon, and Planets》1992,56(1):57-60

The tidal long-term decrease in the angular velocity of the Earth's rotation has been estimated on the basis of the angular momentum tidal balance in the Earth-Moon-Sun system. The observed (LLR) tidal long-term decrease in the Moon's mean motion, the apparent secular acceleration in the mean longitude of the Sun and the long-term decrease in the 2nd degree zonal geopotential parameter were used.Presented at the XXth General Assembly of the I.A.G., Vienna, August 15, 1991.  相似文献   

Results from several persistent train spectra intercompared     

J. Rajchl  J. Bočcek  D. Očenáš  J. Škvarka  P. Zimnikoval  H. Murayama  K. Ohtsuka 《Earth, Moon, and Planets》1995,68(1-3):479-486

Some results following from two contemporary photographical programs (Slovakia and Japan) for persistent meteor train spectra are compared. It shows that even though both programs are not too different according to their lenses and films used, the spectral interval detected is very different. In this respect prism as a dispersion element is more favourable than the grating with blaze wavelength near 610 nm. However, some results previously assumed as typicai for presented persistent trains-e.g. the forbidden Herzberg O₂ emission, the NO₂ continuum and OH red emissions-seem to be substanciated especially due to higher and linear dispersion of those grating spectra.  相似文献   

Radiative association in Li+H revisited: the role of quasi-bound states     

O. J. Bennett  A. S. Dickinson  T. Leininger  F. X. Gadéa 《Monthly notices of the Royal Astronomical Society》2003,341(1):361-368

The role in radiative association of narrow resonances arising from quasi-bound levels is examined. For the rate coefficient the contribution from such levels is readily calculated in terms of the Einstein A -coefficient from bound rovibrational levels generated using a suitable alternative boundary condition. By locating systematically all the quasi-bound levels, an enhancement by more than an order of magnitude of the rate coefficient for Li(2s) + H(1s) association above about 600 K is obtained. The effect on the LiH abundance in the early Universe is no more than an increase of a factor of 3 for limited ranges of values of the redshift. For the Li(2p) state the effect of narrow resonances appears to have been taken into account in previous calculations.  相似文献   

Beam Mode Expansion of Corrugated Conical Horns with Phase Correcting Lens: Application to Radioastronomy Receivers     

E. García  L. De Haro  C. O'Sullivan  G. Cahill  J. A. López Fernández  F. Tercero  B. Galocha  J. L. Besada 《Experimental Astronomy》2003,15(3):173-193

A classical radioastronomy receiver is fed with a corrugated horn and an independent lens, both placed in a cryostat to lower the noise temperature. The beam is focused and directed using a combination of elliptical and plane mirrors. This paper proposes modifying the initial feeding system by placing the lens onto the horn aperture, thereby allowing a size reduction of the horn and lens, and a simplification of their mechanical design. The profiled lens is shaped to correct the phase error on the horn aperture. A quasi-optical model of the horn-plus-lens system has been developed using a Beam Mode Expansion (BME). Results using both a hyperbolic-planar lens and a spherical-elliptical lens, as well as results obtained by using Geometrical Optics (GO) with a Kirchoff–Huygens integration to get the far-field pattern, have been compared with measurements. As a direct application, a full focusing system for the new 40-m radiotelescope at the “Centro Astronómico de Yebes” is presented for the 22, 30 and 45 GHz bands. This paper has developed a QO model for a corrugated conical horn with a phase-correcting lens. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献