Radio emission

Helium is the second most abundant element in the visible Universe and accordingly there is a mass of data from optical and radio emission lines in nebulae, optical emission lines from the solar chromosphere and prominences and absorption lines in spectra of hot stars. Further estimates are derived more indirectly by applying theories of stellar structure, evolution and pulsation. However, because of the relative insensitivity of Tp to cosmological parameters, combined with the need to allow for additional helium from stellar nucleosynthesis in most objects, the requirements for accuracy are very severe better than 5 per cent to place cosmological limits on Nv and better still to place interesting constraints on t] or One can, however, assert with confidence that there is a universal floor to the helium abundance in observed objects corresponding to 0.23 < Fp < 0.25. 

Fig. 6.1. Stellar nursery in the constellation of Orion. Molecular clouds A and B were detected by their radio emissions. They appear to have given birth to several generations of stars (la, It and Ic).

Also, one classical question is whether dust formation initiates mass-loss or whether dust is formed as a result of mass-loss. It is to be noted that the latter process may be rather easy, once mass-loss occurs by another mechanism. This problem can be examined on the basis of recent observations of CO radio emission lines, by which stellar mass-loss rate has been determined with better accuracy than by any other method for a large sample of red giant stars, and terminal flow velocities have also been determined with high accuracy( e.g.,Knapp,Morris,1985). The result revealed that the momentum in the stellar wind and that in the stellar radiation do not necessarily show good correlation(e.g.,Zuckerman,Dyck,1986). Also, a necessary condition for the winds to be accelerated by radiation pressure on dust( Mv [Pg.160]

The successful models for the ultraviolet spectra of previous SN II consider the emission from a substantial circumstellar layer (Fransson et al. 1984), such as might be expected around a red supergiant with a slow dense wind. The absence of these features makes it unlikely that SK -69 202 had such a wind immediately before the explosion, although It does not rule out a wind at an earlier stage of evolution. The picture in which SN 1987a has a low density circumstellar envelope is consistent with the weak, brief radio emission (Turtle et al 1987) and the absence of early X-ray flux (Makino 1987) as described by Chevalier and Fransson (1987). 

The discovery of a prompt radio burst is related to the epoch of shock break-out was an important Australian contribution to the studies of SN1987A. The burst lasted for only about a week, (Turtle et al. ), and can be understood in terms of free-free absorption of synchrotron emission (Storey and Manchester). The location of this radio emission was probably in the shocked stellar wind region of the star, with the free-free absorption arising from within this layer. The thickness of the emitting layer was estimated at only 4.8% of the radius, which would be consistent with a power law density distribution of matter with an index of 11.8. Since the first week, the radio emission continued to fade (despite some other reports to the contrary), becoming effectively unobservable at 843MHz after about 50 days. 

In the final discussion G. R. Burbidge stressed that the problems of energy conversion from a primary energy source to the form of relativistic particles needed for the radio emission are entirely unsolved. In particular, the production of cosmic ray particles requires an acceleration mechanism, of an efficiency at least a few orders of magnitude larger than that of the best man-made accelerators.109... 

Fracto-emission (FE) is the emission of particles and photons accompanying deformation and fracture. These emissions typically include electrons (EE), positive ions (PIE), neutral atoms and molecules, including both ground state neutrals (NE) and excited neutrals (NE ), visible photons (phE)—also called triboluminescence in this context, and long wavelength electromagnetic radiation (RE radio emission). 

In certain situations, FE could prove useful in the remote detection of fracture. An unusual radio emission observed at several widely space receivers six days before the Great Chilean Earthquake of May 22,1960, has led Warwick, Stoker, and Meyer to speculate that stress induced microfracture along the Chilean fault was the source of this emission (38). More recent observations of RE some hours to tens of minutes before earthquakes have been made by Soviet researchers (39). Nitsan has surveyed a number of minerals for fracture related RE and has concluded that quartz-bearing rocks were sources of rather intense RE (IS). Under similar conditions, rocks not containing quartz (basalts, obsidians, limestones) did not yield detectable RE. Therefore, RE is expected to be a strong function of the mineral content (quart or non-quartz bearing formations). Formation structure (the presence of previously pulverized material, state of stress and strain) is also expect to affect RE intensity. 

Cosmic rays residing in galaxy clusters produce several astrophysical signatures among which there are diffuse synchrotron radio emission, ICS of CMB (and other background) photons which are then moved to higher frequencies... 

The Galactic Centre could provide a smoking gun" with radio synchrotron, 7-ray and v data annihilations measure cold dark matter where Milky Way formation began inside-out", some 12 Gyr ago. Accretion models onto the central black hole fail to give sufficient low frequency radio or gamma ray emission to account for the observed fluxes from SagA, and it is tempting to invoke a more exotic alternative. For example, the low frequency radio emission can be explained by spike-enhanced self-absorbed synchrotron emission,... 

The radio emission from Sgr A is easily explained by thermal emission of hot matter falling into the black hole. However, contrary to many of the similar black holes observed at the center of external galaxies, our galactic black hole does not emit intensely in the X-ray band, and it is controversial if it emits gamma-rays. Models for such quiet black holes do exist, however, such as those involving advection-dominated accretion flows (ADAFs). 

Like many red dwarfs, Proxima or Alpha Centauri C is a flare star. Flare stars can brighten suddenly to many times their normal luminosity. The cause is thought to be a sudden and intense outburst of radiation on or above the star s surface. An increase in radio emission is often detected simultaneously with the optical outburst. 

Information regarding the interiors of the giant planets from the presence of magnetic fields became available iDeginning in 1950 with the detection of radio-emissions from Jupiter at... 

The recent ai roach of large comets such as IP/Halley, C71996 B2 Hyakutake, and C/1995 Ol Hale-Bopp to the Earth provided a good opportunity to investigate the detailed composition of cometary ices by various methods such as mass spectrometry, infrared spectroscopy, and radio emission. The composition of interstellar ices is compared with that of the cometary ices in Table 9.3. It is striking that cometary and interstellar ices have quite comparable relative molecular abundances. 

ANITA will use radio emission from the cascade induced by a neutrino interaction within the Antarctic ice cap to detect UHE neutrino interactions that occur within a million square km area. The remarkable transparency of Antarctic ice to radio waves makes this experiment possible, and the enormous volume of ice that can be simultaneously monitored leads to an unparalleled sensitivity to neutrinos in the energy range of 0.1 to 100 EeV. Three separate... 

The radio emission from HII regions can also be a tracer of the SFR. 

Other applications include the use of polyesters in gaskets, printer rolls, flexible insulation and as binders for mica. Polyester resin putty, when applied to hardened white cement filled tile seams, ensures toughness and smoothness. Polyester resins containing niobium carbide nanoparticles have been used in the production of radio wave absorbing materials. These materials can be used as protective screens, coverings or coating material to mask equipment from radio detection. They are also used to protect personnel from radio emissions, and as a radio wave absorbing label for security papers and documents. 

The quasars are quasi-star (i.e., similar) sources of radio emission their mass and diameter exceed those of the Sun by tens million times the energy of radiation exceeds the total energy of radiation of several galaxies. 

The aurora is associated with electromagnetic waves over a wide frequency range, including X-rays, visible, EUV, UV, and IR emissions as well as VLF and ULF radio emissions. Thus, the visible emissions constitute only a small part of the spectrum. In addition, the aurora is associated with intense VLF radio waves that can be observed only... 

The aurora is aeeompanied by various VLF radio emissions that carmot be observed by radio devices on the ground. The diseharge-eutrent-carrying eleetrons are accelerated in the auroral potential structure, which is located at an altitude of 10,000 km above the aurora (see Section VI). This potential structure was discovered... 

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