The Scattered Disk Population and the Oort Cloud     

Fernández  Julio A.  Gallardo  Tabaré  Brunini  Adrián 《Earth, Moon, and Planets》2003,92(1-4):43-48

The trans-Neptunian belt has been subject to a strong depletion that has reduced its primordial population by a factor of one hundred over the solar system's age. One by-product of such a depletion process is the existence of a scattered disk population in transit from the belt to other places, such as the Jupiter zone, the Oort cloud or interstellar space. We have integrated the orbits of the scattered disk objects (SDOs) so far discovered by 2500 Myr to study their dynamical time scales and the probability of falling in each of the end states mentioned above, paying special attention to their contribution to the Oort cloud. We found that their dynamical half-time is close to 2.5 Gyr and that about one third of the SDOs end up in the Oort cloud.  相似文献   

Potential of the VLTI for linking stellar frames to ICRF     

Gérard Daigne  Patrick Charlot  Christine Ducourant  Jean-François Lestrade 《Astrophysics and Space Science》2003,286(1-2):255-260

The question of positioning the optical counterparts of the ICRF quasars is outlined in the perspective of future space astrometry missions, which ultimately will bring a new realization of the ICRS in the optical range. Ground-based interferometry with a dual-field observing mode (PRIMA/VLTI),together with the missions DIVA and FAME, will have a key role in building an extragalactic reference frame in the optical/near-IR range with about the same accuracy as that of the present (VLBI) primary frame. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Light curve and O−C diagram analysis of RZ Cassiopeiae     

T. Hegedüs  K. Szatmáry  J. Vinkó 《Astrophysics and Space Science》1992,187(1):57-74

The aim of the present paper is to analyze the light variation as well as the period changes of the eclipsing binary RZ Cas. New photometric elements are computed using the frequency-domain method. The possibility of the light-time effect and the apsidal motion is discussed.  相似文献   

Adaptive Optics: Astronomical Results and Perspectives     

P. Léna 《Experimental Astronomy》1997,7(4):281-284

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Hα Photometry of Two Contact Binaries     

Szilárd Csizmadia  Zsolt Kővári  Péter Klagyivik 《Astrophysics and Space Science》2006,304(1-4):355-357

We carried out optical and Hα photometry of two contact binaries (V861 Herculis, EQ Tauri). The light curve modeling revealed stellar spots in both contact systems and strong Hα excess in the position of the observed stellar spots. A correlation was found between the V−R and R−H_α colour indices of V861 Her.  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   

Radon variations in a Hungarian village     

E. Tóth  F. Deak  C. S. Gyurkócza  Z. S. Kasztovszky  R. Kuczi  G. Marx  B. Nagy  S. Oberstedt  L. Sajó-Bohus  C. S. Sükösd  G. Toth  N. Vajda 《Environmental Geology》1997,31(1-2):123-127

 A steady radon exhalation is assumed in most publications. In a village of North-East Hungary, however, high radon concentrations have been measured, differing strongly in neighbouring houses and varying in time, due to the interplay of geochemical phenomena. Received: 20 November 1995 · Accepted: 18 June 1996  相似文献   

Bi-dimensional observation of waves near the mesopause at auroral latitudes     

J. Clairemidi  M. Hersé  G. Moreels 《Planetary and Space Science》1985,33(9):1013-1022

During a campaign of optical observations at high latitude, a bi-dimensional study of the wave structure of the OH layer has been performed in December 1981 from Sodankyla (Finland). This site is one of the three stations of the EISCAT ionosphere sounding system. It has been found that a wave field covering an area of 1 million km² may extend to latitudes as high as 70°N. The OH wave structure shows many similarities with noctilucent clouds. The fairly large horizontal wavelength, of the order of 40 km cannot easily be explained by a wave motion at an interface. The observed wave structure seems to be a result of the propagation of an internal gravity wave in the 80–100 km region. This wave structure was often recorded during the same time as an active aurora was present. As a result, it appears that the perturbation might be correlated with particle precipitations at auroral latitudes.  相似文献   

Polarization of Evolved Stars Envelopes     

C. Kahane  E. Viard  F. Ménard  P. Bastien  N. Manset 《Astrophysics and Space Science》1997,251(1-2):223-226

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X-ray and ultraviolet observations of AG Draconis during quiescence and outburst     

A. Cassatella  F. A. Córdova  M. Friedjung  J. Kenyon  L. Piro  R. Viotti 《Astrophysics and Space Science》1987,131(1-2):763-763

We describe the first X-ray monitoring of a symbiotic star during phases of enhanced activity. AG Dra is a Pop II object with a composite spectrum, characterized by a cool K-type component, prominent high ionization emission lines and a strong UV continuum which is attributed to a hot dwarf companion. Periodic variability of the UV radiation during minimum could be attributed to the orbital motion of the system. In April 1980 HEAO-2 detected an intense, soft X-ray flux from AG Dra, stronger than in other symbiotic stars. After one major outburst of November 1980, which continued until 1983, two more outbursts occurred in February 1985 and January 1986, and coordinated X-ray (EXOSAT) and ultraviolet (IUE) observations were organized to study the behaviour of AG Dra during different activity phases. EXOSAT observations made during decline after the 1985 outburst, revealed a weak X-ray flux in the Thin Lexan filter of the Low Energy dedtector. Observations made during minimum, in June and November 1985, at phases 0.22 and 0.50 of the UV light curve, disclosed the presence of an intense X-ray flux, which was not occulted in November. AG Dra was again observed with EXOSAT in February 1986 when the stellar luminosity was still at maximum. No X-ray flux was detected, in spite of the prominent, high ionization UV spectrum observed with IUE.A detailed discussion of the X-ray and ultraviolet results on AG Dra in the light of possible models is in progress.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.  相似文献