scholarly journals The Effects of Magnetic Fields on Period Changes, Mass Transfer and Evolution of Algol Binaries

1989 ◽  
Vol 107 ◽  
pp. 311-322
Author(s):  
C. T. Bolton

AbstractVariations in the magnetic pressure and flux blocking by starspots during the magnetic cycle of the cool semidetached component of an Algol binary may cause cyclic changes in the quadrupole moment and moment of inertia of the star which can cause alternate period changes. Since several different processes and timescales are involved, the orbital period changes may not correlate strongly with the indicators of magnetic activity. The structural changes in the semidetached component can also modulate the mass transfer rate. Sub-Keplerian velocities, supersonic turbulence, and high temperature regions in circumstellar material around the accreting star may all be a consequence of magnetic fields embedded in the flow. Models for the evolution of Algols which include the effects of angular momentum loss (AML) through a magnetized wind may have underestimated the AML rate by basing it on results from main sequence stars. Evolved stars appear to have higher AML rates, and there may be additional AML in a wind from the accretion disk.

1991 ◽  
Vol 130 ◽  
pp. 336-341
Author(s):  
David F. Gray

AbstractEvolved stars tell us a great deal about dynamos. The granulation boundary shows us where solar-type convection begins. Since activity indicators also start at this boundary, it is a good bet that solar-type convection is an integral part of dynamo activity for all stars. The rotation boundary tells us where the magnetic fields of dynamos become effective in dissipating angular momentum, and rotation beyond the boundary tells us the limiting value needed for a dynamo to function. The observed uniqueness of rotation rates after the rotation boundary is crossed can be understood through the rotostat hypothesis. Quite apart from the reason for the unique rotation rate, its existence can be used to show that magnetic activity of giants is concentrated to the equatorial latitudes, as it is in the solar case. The coronal boundary in the H-R diagram is probably nothing more than a map of where rotation becomes too low to sustain dynamo activity.


Author(s):  
V. Krivodubskij

The sources of energy of solar activity are analyzed. The primary source of solar energy is the core of the Sun, where as a result of the reactions of thermonuclear fusion, energy is released in the form of γ-quanta and neutrino particles that propagate outward. At approaching the surface, the temperature is rapidly decreasing and at the same time the opacity of the substance of the radiation zone steadily increases, resulting in the creation of conditions for the emergence of a convective energy transfer at a distance from surface of about 0.3 radius of the Sun. Above this boundary lies a layer called the convection zone. The existence and localization of the convection zone of the Sun is determined by two reasons: the first – the structural (radiative) temperature gradient increases due to increased opacity when the temperature drops; the second – the adiabatic gradient of the temperature of the floating elements reduces its value in the zones of partial ionization of hydrogen and helium. It is the convection zone that plays the role of the landfill, where the main processes are born, which are responsible for the cyclic manifestations of the Sun’s activity. However, part of the convective flow of energy coming from the interior of the Sun, accumulates and is carried upwards in the “magnetic form”. An important specific property of magnetic energy transfer is manifested in cyclic changes in most of the phenomena generated by magnetic fields, which are called magnetic activity of the Sun. The main mechanism providing the cyclic nature of the fluctuations of magnetic activity is the turbulent dynamo, localized in the convection zone. The most favorable place for the generation of a toroidal magnetic field, on which the intensity of spot formation depends, are the deep layers near the bottom of the convection zone, covering the layer of permeable convection (convective overshoot layer) and the tachocline. Overshoot creates the necessary conditions for the formation of a layer of long retention maintenance of magnetic fields, whereas in the tachocline, due to the sharp decrease in angular velocity in the presence of a weak poloidal field, a powerful toroidal field is effectively generated. Parker buoyancy of this field dominates over the effects of anti-buoyancy. Therefore, eventually, toroidal field rises to the surface and forms magnetic bipolar groups of sunspots. An important factor of physical processes in the deep layers is also the meridional flow directed to the equator, which, within the framework of the hydromagnetic dynamo model, provides the migration of toroidal fields from high latitudes to low ones. The author’s recent studies on the role of the deep layers of the solar convection zone in explaining the observed phenomenon of double peaks of the cycle of sunspots are noted.


1983 ◽  
Vol 102 ◽  
pp. 133-147 ◽  
Author(s):  
R.W. Noyes

It is now firmly established that lower main sequence (LMS) stars show a qualitative correlation between rotation rate and chromospheric and coronal emission. By analogy with the Sun, the emission is believed to be intimately associated with surface magnetic fields. This association is especially close on the Sun for the Ca II H and K lines, for which the spatial correlation between chromospheric emission and photospheric fields is essentially one-to-one down to scales at least as fine as a few arcseconds and for which the emission flux from an area on the Sun is approximately proportional to the total magnetic flux passing through the same area in the underlying photosphere (Leighton 1959; Skumanich, Smythe, and Frazier 1975; Frazier 1971). The extension of the association to other LMS stars, while based on appeal to analogy, has been strengthened by recent detections of strong magnetic fields covering large fraction of the surface area of chromospherically active stars (see review by Marcy in this symposium).


2003 ◽  
Vol 68 (11) ◽  
pp. 2080-2092 ◽  
Author(s):  
Martin Keppert ◽  
Josef Krýsa ◽  
Anthony A. Wragg

The limiting diffusion current technique was used for investigation of free convective mass transfer at down-pointing up-facing isosceles triangular surfaces of varying length and inclination. As the mass transfer process, copper deposition from acidified copper(II) sulfate solution was used. It was found that the mass transfer rate increases with inclination from the vertical to the horizontal position and decreases with length of inclined surface. Correlation equations for 7 angles from 0 to 90° were found. The exponent in the ShL-RaL correlation ranged from 0.247 for the vertical case, indicating laminar flow, to 0.32 for inclinations of 60 to 90°, indicating mixed or turbulent flow. The general correlation ShL = 0.358(RaL sin θ)0.30 for the RaL sin θ range from 7 × 106 to 2 × 1011 and inclination range from 15 to 90° was obtained.


2000 ◽  
Vol 55 (7) ◽  
pp. 1257-1267 ◽  
Author(s):  
Tiruta-Barna Ligia ◽  
Barna Radu ◽  
Moszkowicz Pierre ◽  
Bae Hae-Ryong

RSC Advances ◽  
2016 ◽  
Vol 6 (111) ◽  
pp. 109978-109982 ◽  
Author(s):  
Young-Kee Kim ◽  
Sung-Yeob Lee ◽  
Byung-Keun Oh

In an enzyme process using a gas substrate, the enhanced gas liquid mass transfer rate of the gas substrate by methyl-functionalized mesoporous nanoparticles could improve the productivity.


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