Search results for "Solar system"
showing 10 items of 43 documents
An idealized mechanism for the orbital migration of protoplanets
1993
We report here how the action of radiation forces on small solid particles in a circumstellar disc could induce a suitable mechanism for orbital migration of protoplanets. The ratio of radiation-to-gravitational forces acting on a particle depends on its physical and chemical properties. As a consequence of this fact, we show that different particles following the same trajectory would move with different velocities. Sufficiently large bodies, insensitive to radiation forces, would accrete dust particles that are moving more slowly, thus spiralling towards the central star and transporting mass and angular momentum from the outer to the inner parts of the circumstellar disc. In the case of …
Actinides in the Source of Cosmic Rays and the Present Interstellar Medium
2003
The abundances of the actinide elements in the cosmic rays can provide critical constraints on the major sites of their acceleration. Using recent calculations of the r-process yields in core collapse supernovae, we have determined the actinide abundances averaged over various assumed time intervals for their supernova generation and their cosmic-ray acceleration. Using standard Galactic chemical evolution models, we have also determined the expected actinide abundances in the present interstellar medium. From these two components, we have calculated the U/Th and other actinide abundances expected in the supernova-active cores of superbubbles, as a function of their ages and mean metallicit…
The Extremely Metal‐poor, Neutron Capture–rich Star CS 22892‐052: A Comprehensive Abundance Analysis
2003
High-resolution spectra obtained with three ground-based facilities and the Hubble Space Telescope (HST) have been combined to produce a new abundance analysis of CS 22892-052, an extremely metal-poor giant with large relative enhancements of neutron-capture elements. A revised model stellar atmosphere has been derived with the aid of a large number of Fe-peak transitions, including both neutral and ionized species of six elements.Several elements, including Mo, Lu, Au, Pt and Pb, have been detected for the first time in CS 22892-052, and significant upper limits have been placed on the abundances of Ga, Ge, Cd, Sn, and U in this star. In total, abundance measurements or upper limits have b…
Extraterrestrial Mössbauer Spectroscopy
2011
To understand the origin of the Solar system and the origin of Life itself is one of the longest standing goals of human thought. Our Sun and its planets have formed out of an interstellar cloud which collapsed due to gravitational forces, forming a disk shaped so-called protosolar nebula, with the young star in the centre. Such disk shaped and dust grain containing protosolar nebulae have been observed. One of them is surrounding the young star Beta pictoris [1, 2]. Silicates, carbon and metal grains, oxides and sulfides should have been present. One of the important elements with relatively high abundance is iron. It is believed that simple molecules, such as water (H2O), carbon monoxide …
A view of extraterrestrial soils
2009
International audience; The nature of soils on celestial bodies other than Earth is a growing area of research in planetary geology. However, disagreement over the significance of these deposits arises in part due to the lack of a unified concept and definition of soil in the literature. The pragmatic definition “medium for plant growth” is taken by some to imply the necessity of biota for soil to exist, and has been commonly adopted in the planetary science community. In contrast, a more complex and informative definition bases on scientific theory: soil is the (bio)geochemically/physically altered material at the surface of a planetary body that encompasses surficial extraterrestrial tell…
Mhd-Modeling of the Propagation of a Coronal Mass Ejection
2005
Hydrodynamic modeling of the propagation of a density perturbation launched upwards in the solar corona has been shown to explain some features of a Coronal Mass Ejection (CME) observed in detail with the SoHO/UVCS, but left open the questions of the evidence of thermal insulation of the CME and of its large expansion factor. We investigate whether the interaction with the coronal magnetic field is able to explain these aspects, by performing magnetohydrodynamic simulations. We solve the ideal MHD equations for a fully ionized compressible plasma with different assumptions on the ambient magnetic field, using the FLASH code. We include the effect of the directional thermal conduction. Preli…
ON THE “SOLAR SYSTEM SMALL BODIES” ASTROPLATE PROJECT OF THE UKRAINIAN VIRTUAL OBSERVATORY
2019
The UkrVO Joint Digital Archive of astro- plates and the newest digitized data processing services al- lowed us to form a new approach for the creation of catalogs of astrometric and photometric characteristics of the Solar System bodies. Given this, the main goal of this approach was not only to complete the processing with the best possi- ble accuracy of high-quality and unprocessed earlier photo- graphic observations of the Solar System bodies but also to find new original data from these observations. As a result, more than 6,500 new astrometric positions and stellar magnitudes of asteroids, and 3,036 positions of outer planets (Pluto, Uranus, Neptune, Saturn, Jupiter) and their satelli…
BALDONE OBSERVATORY IN THE CIRCLES OF TIME
2019
1957 – The first laboratory building, known as the White House, was built near Baldone on the Riekstu hill, in the territory of the next Observatory. 01.01.1958 – The Astronomy Sector was separated from the Institute of Physics and commenced independent activi- ty as the Laboratory of Astrophysics at the Latvian Acade- my of Sciences (LAS). In 1967, with the decision of the Presidium of the Latvian SSR LAS the Laboratory of As- trophysics was transformed into the Radioastrophysic Ob- servatory at LAS. Under the leadership of the first director, Janis Ikaunieks, an instrumental observation base develops – a 1.2m Schmidt telescope was installed in 1966 for opti- cal observations. The project …
The endpoint of the rp-process
1997
Abstract The endpoint of rp-process nucleosynthesis in X-ray bursts determines the fuel consumption, the energy generation, and the abundance pattern of the produced nuclei. To investigate the time structure of rp-process nucleosynthesis, we used a nuclear reaction network including nuclei from H to Sn. We found that if 2p-capture reactions are included, the synthesis of nuclei heavier than Kr proceeds faster than previously thought. Therefore, in most X-ray bursts large amounts of nuclei in the A=80–100 region are expected to be produced. With an escape factor of about 1%, X-ray bursts could account for the large observed solar system abundances of the light p-nuclei like 92 Mo and 96 Ru t…
A model for predicting the potential diffusion of solar energy systems in complex urban environments
2011
Abstract The necessity to reduce greenhouse gases emission produced by energy building consumptions and to cut the energy bill (mainly due to the use of fossil sources) leads to the employment of renewable energy sources in new planned scenarios. In particular, more and more often municipal energy and environmental plans pay great attention to the possibilities of employment of the solar technologies at urban scale. Solar thermal and photovoltaic (PV) systems are, by far, the most suitable tools to be utilized in urban areas. Obviously, the proper adoption of such systems in buildings does call for the availability of calculation methods suitable to provide the actual level of exploitation …