Criticism of recent calculations of common envelope ejection     

Noam Soker  Amos Harpaz 《Monthly notices of the Royal Astronomical Society》2003,343(2):456-458

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Parameters affecting maximum fluid transport in large aperture fractures   总被引：1，自引：0，他引：1  

Maria Ines Dragila  Noam Weisbrod   《Advances in water resources》2003,26(12):1219-1228

We present results of laboratory experiments to study the behavior of liquids moving in unsaturated wide-aperture fractures. A 5-mm-thick glass plate cut with a 1.7-mm aperture was used as a fractured rock analog to study behavior of film and capillary droplet flow modes. Flow rates ranged between 0.6 and 6.0 ml/min. Variability in the ambient barometric pressure, resulting from weather conditions, seemed to play a role in the natural selection of flow mode. For droplet mode, constant input conditions resulted in highly variable transport properties within the fracture. The advancing meniscus exhibited a dynamic contact angle that was a function of the droplet speed and much larger than the static contact angle. Flow rate was reduced due to the larger contact angle. Analytical expressions for droplet velocity and flow capacity are presented as a function of the dynamic rather than the static contact angle.  相似文献   

Uplifted cool gas and heating by mixing in cooling flows     

Shlomi Hillel  Noam Soker 《天文和天体物理学研究(英文版)》2018,(7)

We analyze our earlier three-dimensional hydrodynamical numerical simulation of jet-inflated bubbles in cooling flow clusters, and find that dense gas that was not heated by the jets' activity and that resides around the hot jet-inflated bubbles can be identified as uplifted gas as observed in some clusters.During the build up of the dense gas around the hot bubble, mixing of hot bubble gas with other regions of the intracluster medium(ICM) heats the ICM. The vortices that mix the ICM with the hot bubble gas also excite shock waves, sound waves and turbulence. Sound waves, shocks, turbulence and uplifted gas might be easier to detect than the mixing process and hence attract more attention, but we argue that the contributions of these processes to the heating of the ICM do not add up to the level of contribution of the mixing-heating process.  相似文献   

Hydraulic Connections Among Subaquifers of the Coastal Plain Aquifer, Israel   总被引：5，自引：0，他引：5  

Ronit Nativ  Noam Weisbrod 《Ground water》1994,32(6):997-1007

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Inflight Calibration of the NEAR Multispectral Imager: II. Results from Eros Approach and Orbit     

Scott MurchieMark Robinson  Deborah DomingueHan Li  Louise ProckterS.Edward Hawkins III  William OwenBeth Clark  Noam Izenberg 《Icarus》2002,155(1):229-243

During the Near-Earth Asteroid Rendezvous (NEAR) spacecraft's investigation of asteroid 433 Eros, inflight calibration measurements from the multispectral imager (MSI) have provided refined knowledge of the camera's radiometric performance, pointing, and light-scattering characteristics. Measurements while at Eros corroborate most earlier calibration results, although there appears to be a small, gradual change in instrument dark current and flat field due to effects of aging in the space environment. The most pronounced change in instrument behavior, however, is a dramatic increase in scattered light due to contaminants accumulated on the optics during unscheduled fuel usage in December 1998. Procedures to accurately quantify and to remediate the scattered light are described in a companion paper (Li et al. 2002, Icarus155, 00-00). Acquisition of Eros measurements has clarified the relative, filter-to-filter, radiometric performance of the MSI. Absolute radiometric calibration appears very well constrained from flight measurements, with an accuracy of ∼5%. Pointing relative to the spacecraft coordinate system can be determined from the temperature of the spacecraft deck with an accuracy of ∼1 pixel.  相似文献   

Detection of Temperature-Dependent Spectral Variation on the Asteroid Eros and New Evidence for the Presence of an Olivine-Rich Silicate Assemblage     

Paul G. LuceyJohn Hinrichs  Mary KellyDennis Wellnitz  Noam IzenbergScott Murchie  Mark RobinsonBeth E. Clark  James F. Bell III 《Icarus》2002,155(1):181-188

Data obtained by the near-infrared spectrometer carried by the NEAR-Shoemaker spacecraft show that the spectral properties of the asteroid Eros vary with temperature. The manner in which they vary demonstrates that the mineral olivine is a major constituent of the surface. The near-IR temperature-dependent spectral properties of Eros in the northern hemisphere, and for two individual regions on the surface, show clear evidence of the presence of the mineral olivine and are a close match to the temperature-spectral behavior of LL-type ordinary chondrite meteorites. While the presence of other olivine-rich meteorites cannot be excluded, H-type ordinary chondrites are clearly too pyroxene-rich to be permitted as a major surface component of Eros. The results of the thermal-spectral analysis are consistent with results from analysis of conventional reflectance spectra of the asteroid and contribute unambiguous detection of olivine to the understanding of the surface composition of Eros.  相似文献   

Magnetic activity in stellar merger products     

Noam Soker  Romuald Tylenda 《Monthly notices of the Royal Astronomical Society》2007,375(3):909-912

We study the expected X-ray luminosity of stellar merger products several years after merger. The X-ray emission is assumed to result from magnetic activity. The extended envelope of the merger product possesses a large convective region and it is expected to rotate fast. The rotation and convection might give rise to an efficient dynamo operation; therefore we expect strong magnetic activity. Using well-known relations connecting magnetic activity and X-ray luminosity in other types of magnetically active stars, we estimate that the strong X-ray luminosity will start several years after merger, will reach a maximum of L _x∼ 3 × 10³⁰ erg s⁻¹, and will slowly decline on a time-scale of ∼100 yr. We predict that X-ray emission from V838 Mon which erupted in 2002 will be detected in 2008 with 20 h of observation.  相似文献   

Spinning-up the envelope before entering a common envelope phase     

Ealeal Bear  Noam Soker 《New Astronomy》2010,15(5):483-490

We calculate the orbital evolution of binary systems where the primary star is an evolved red giant branch (RGB) star, while the secondary star is a low-mass main sequence (MS) star or a brown dwarf. The evolution starts with a tidal interaction that causes the secondary to spiral-in. Than either a common envelope (CE) is formed in a very short time, or alternatively the system reaches synchronization and the spiraling-in process substantially slows down. Some of the latter systems later enter a CE phase. We find that for a large range of system parameters, binary systems reach stable synchronized orbits before the onset of a CE phase. Such stable synchronized orbits allow the RGB star to lose mass prior to the onset of the CE phase. Even after the secondary enters the giant envelope, the rotational velocity is high enough to cause an enhanced mass-loss rate. Our results imply that it is crucial to include the pre-CE evolution when studying the outcome of the CE phase. We find that many more systems survive the CE phase than would be the case if these preceding spin-up and mass-loss phases had not been taken into account. Although we have made the calculations for RGB stars, the results have implications for other evolved stars that interact with close companions.  相似文献   

Wind accretion by a binary stellar system and disc formation     

Noam Soker 《Monthly notices of the Royal Astronomical Society》2004,350(4):1366-1372

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The departure of η Carinae from axisymmetry and the binary hypothesis     

Noam Soker 《Monthly notices of the Royal Astronomical Society》2001,325(2):584-588

I argue that the large-scale departure from axisymmetry of the η Carinae nebula can be explained by the binary star model of η Carinae. The companion diverts the wind blown by the primary star, by accreting from the wind and possibly by blowing its own collimated fast wind (CFW). The effect of these processes depends on the orbital separation, and hence on the orbital phase of the eccentric orbit. The variation of the mass outflow from the binary system with the orbital phase leads to a large-scale departure from axisymmetry along the equatorial plane, as is observed in η Carinae. I further speculate that such a companion may have accreted a large fraction of the mass that was expelled in the Great Eruption of 1850 and the Lesser Eruption of 1890. The accretion process was likely to form an accretion disc, with the formation of a CFW, or jets, on the two sides of the accretion disc. The CFW may have played a crucial role in the formation of the two lobes.  相似文献