Algol variable
The concept of Algolsterne (short Algol ) describes both a class of eclipsing stars whose brightness is little or no change in the maximum, as well as a group of interacting binary stars. Both classes of stars named after their prototype Algol in the constellation Perseus.
Eclipsing binary star Algol type
Algolsterne ( GCVS nomenclature abbreviation: EA) is a binary star system consisting of two spherical or slightly ellipsoidal deformed by centrifugal single stars. The orbital plane is in the room so that the stars cover each other as they orbit and thereby less radiation reaches the earth. The time of beginning and end of a minimum is clearly defined in Algolsternen in contrast to the Beta Lyrae stars and W Ursae Majoris stars, which show a continuous change of light due to the strong deformation of the stars in these binary systems.
Between the minima of the brightness of the eclipsing Algol -type stars remains approximately constant. A slight change in brightness may be the result of a reflection effect, elliptical deformation of the star components or intrinsic variability. The periods of Algolsternen be between about 0.2 and about 10,000 days, with the longest known period holds with 27 years of Star Almaaz in the constellation Auriga. The amplitude of the changes in brightness during the Algolsternen can be up to several magnitudes large.
The Algol - stars were named after the star Algol in the constellation Perseus, the first ( 1669 through Geminianus Montanari ) discovered eclipsing binaries. In total there are now several thousand stars of this type are known.
Interacting Binary Stars from Algol type
The second star class named Algolsterne describes binary stars in which a less massive star has evolved as a mass richer star. This is in contrast to the stellar evolution of single stars, which runs faster with increasing mass and is also known as Algol paradox. In a narrower sense, it is a binary star system consisting of a BA main sequence star and a cooler FG giant star, with the cool giant fills its Roche limit volume. This Algolsterne often show that the more massive star rotates faster than the orbital period of the binary system. In some Algolsternen a mass flow can be demonstrated by the lower-mass companion to a hot spot on the supernova. In the hot spot, the matter strikes the atmosphere is converted into kinetic and thermal energy. The now less massive star originally had the greater mass and has evolved from the main sequence. He began to expand until it has exceeded the Roche limit volume. If this limit is exceeded matter flows to the companion and within a short period there is a mass reversal. Therefore, further developed in the Algolphase after rapid mass transfer of the less massive star and the more massive rotating at high speed due to the transfer of angular momentum between the two stars. In the observable phase, the mass transfer from the developed subgiant or giant to the heavy main sequence star, an increase of railway orbital period should occur. However, analysis of the behavior of Algolsternen often show cyclic period changes both with decreasing and anwachsender orbital period, the cause of which may be located in the magnetic activity of the mass -giving component.
In the stable phase after the rapid mass transfer of the formerly more massive star is a cool supergiant with an extended atmosphere with convective energy transport. At the same time the speed of rotation of the lower Riesens is quite high because of the bound rotation in close binary systems. A fast differential rotation in combination with a convective atmosphere through the MGD to a pronounced magnetic activity at Algolsternen, which is manifested in the form of flares in the radio and X-ray radiation as well as by emission lines of the Balmer series. For long-period Algolsternen are also temporary accretion disks have been found that do not always lie in the orbital plane of the binary system. These deviations can not be explained by a simple model, which take into account only the gravitational and centrifugal forces. The gas masses outside the orbital plane to be associated with the magnetic activity of the mass -giving star:
- Due to coronal ejections
- Magnetic fields on the subgiant interact with the ioniserten matter that flows through the L1 Lagrange point
- Akkretiertes gas is deflected out of the plane of the web, because, is at the point at which the gas flow impinges on the primary star, a backwater
- A Superhump - similar phenomenon has been detected in radio observations. Probably, the gas flow is deflected by a helical magnetic field in the vicinity of the mass donor. Since the early stars have no intrinsic magnetic field, these magnetic field lines are likely to be generated by the plasma current itself.