Close binary is an astronomical term.Fan YiChild starAffecting the evolution of another child starphysical doubleCan be called close binary.In fact, people oftenSpectroscopic binaryAnd photometric binaries (the latter includesEclipsing binary）They are collectively called close binary stars.Visible to the naked eyeCapella﹑CornucopiaDalingwu and Jiantaier are close binary stars.
In the vast universe, stars are a huge family.In this huge group, more than half of the stars are binary stars, and some are triads.Among them, close binary stars are the most concerned type because they show very active physical phenomena.
Specifically, there are strong H and K spectral line emission of H and Ca II, X-ray emission, chromospheric activity, large area sunspot activity, stellar wind loss, flares, and orbital period changes.In addition, according to whether it is full of the Roche lobes, binary stars can also be divided into three categories: separated binary stars, semi connected binary stars and connected binary stars.
Research value
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Close binary is a kind of celestial body that exists universally in the stellar world, some of which can provide reliable physical parameters;Some can provide important clues of stellar evolution;Some can be used to study the inner density distribution of stars, the characteristics of matter around stars, stellar windaccretion ProcessQuality communicationAnd so on.
Internal structure of neutron star and white dwarf:
Internal Structure Diagram of White Dwarf
classification
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1. The classification of close binary stars is often based on the classification method of Roche geometry.In 1955, Kopar divided binaries into three categories according to whether the volume of the sub star filled the Roche lobe:
(1) Detached binary: the two sub stars are not full of Roche lobes (the volume is smaller than the corresponding critical volume of Roche);
(2) Semi detached binary: one of the two sub stars is full of Roche lobes;
(3) Contact binary: two sub stars are full of Roche petals.[1]
2. Close binaries can be divided into eclipse binaries and spectral binaries according to different observation methods.Eclipsing binaries are suitable for photometric observation because their total apparent brightness changes periodically due to the mutual eclipse of their sub stars.In particular, when the orbital inclination of the eclipsing binary (the angle between the normal of the orbital plane and the direction of the observer's line of sight) is close to 90 degrees, it will produce large eclipse depth and total eclipse (platform eclipse) characteristics, which is conducive to accurate measurement of various parameters of the eclipsing binary.According to the shape type of light curve (or LC), eclipsing binaries can be divided into big Ling type (Algol type, symbol EA), gradual stage type (Tianqin beta type, symbol EB) and big bear type W (W UMa type, symbol EW). Their characteristics are as follows: EA type, the light curve can clearly distinguish between out of eclipse and eclipse, the change of out of eclipse part is relatively gentle or unchanged, and the change of eclipse part is relatively steep;EB type, the light curve changes continuously, and the depth of primary and secondary food varies greatly;EW type, light curve changes continuously, and the depth of primary and secondary food is almost the same.The above classifications sometimes have no obvious boundaries.
Observation method
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Observation mode
Observations of close binary stars include infrared, visible, ultraviolet photometric radiation and spectrum, and radio and X-ray radiation.The best way to study a close binary star is to observe it from the radio wavelength to the X-ray wavelength.
Processing and analysis methods of observation data
The mutual rotation of binary stars produces eclipse phenomenon and the change of apparent velocity, so we can measure and analyze the close binary stars by photometry and spectroscopic methods.Through these two methods, we can not only obtain the orbital parameters of the close binary, such as the orbital inclination, the distance between the two sub stars, but also obtain the absolute parameters of the two sub stars, such as the mass, radius, and so on.These parameters are the basis of our analysis of the properties of close binary stars.[2]
Research History
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Information
When a sub star in a close binary is full of its critical plane, its matter should flow to another sub star on a large scale (if the latter is not full of its critical plane), causing mass transfer (more generally, called mass exchange), which has a huge impact on the evolution of close binary.
The two bright stars that make up Sentinel II rotate rapidly around each other, once every 12.9 days.And there is a strong flow of material constantly thrown from the main star.Some of these thrown substances may run intocompanionThe matter surrounding a star that forms nearby.Some may break away from the wholebinary star And the flying maninterstellarSpace.
historical background
Kepenhahn and Wigt of the Federal Republic of Germany, Paczynski of Poland,CzechoslovakiaIn the late 1960s, Pravitz et al. made a pioneering theoretical study on the mass exchange evolution of close binary stars.If one of the sub stars in the disjoint binary composed of two main sequence stars has a large mass, then when this sub star evolves to be full of its critical plane (that is, when it starts to make mass transfer), it will at least appear "fishy"?Zhixiewen s its central hydrogen is still playing a nuclear reaction;Or the central hydrogen has "burned" and the central helium has not started "burning";Or the central helium has "burned" and the carbon has not yet started "burning".These three cases are called the A case, B case and C case of the mass exchange evolution of close binary respectively.
Starting from these basic concepts, astronomers made a lot of theoretical calculations for various forms of close binary stars in the 1970s.For example, in explaining the "evolution oddity" of the five type eclipsed binary stars of Daling (i.e., the smaller sub stars seem to evolve faster), explaining the basic parameters of the "enigma" Gradual Two, explaining some B-type emission binary stars, and simulating someX-ray binaryandRadio pulsarEncouraging achievements have been made in the evolution history of binary stars and other work.However, in order to better explain the measured phenomena, it is necessary to break the restrictions of a series of simplified assumptions in the earlier theoretical work, such as taking into account the non spherical shape of the sub star, the eccentricity of the orbit, the non conservation of the total mass and the total angular momentum, the wind and radiation pressure, rotation and magnetic field, and the occurrence of sub starsSupernovaThe asymmetry of the outbreak and so on.The research on the evolution of close binary is obviously an arduous and meaningful work.
Theoretical aspects
The important task in theory is to use the concepts of mass exchange and mass loss of close binary stars to explain the change of light changing period of some eclipsing binary stars and explain the change of light changing period of some eclipsing binary starsGas ringThe formation and change of and many of theDwarf nova﹑Supernova﹑NovaThe explosion of close binary stars andRadio binaryPhenomenon and so on.Many people have used hydrodynamics instead of particle mechanics to deal with the matter exchange problem in close binary stars.Many people attach importance to the physical problems of accretion disks, and great progress has been made in the research of explosive binaries and X-ray binaries.The problem of changing the orbital period of close binary stars due to gravitational waves has also been studied.
In 1978, J.H. Taylor reported that the observed orbital period shortening of the radio pulsar binary PSR1913+16 was very consistent with the theoretical value of the orbital period shortening caused by gravitational waves. Many people believed that this was the first time to find the measured evidence of the existence of gravitational waves.In recent years, the research on the mechanical and physical problems of connected binaries represented by W Ursa Major is also very enthusiastic.Some close binary stars (such as Cygnus X-1) may have the problem of "black holes". The relationship between close binary stars and solar and stellar activities, and the interaction between the wind of two sub stars have long or are attracting the attention and research of astronomers.
Measured aspects
In the 1970s, rapid progress was made in the field measurement of close binary stars.For example, we foundX-rayDouble star, X-raypulseStar binary (including extragalactic), radio binary, radio pulsar binary, optical pulsar binary andCompact celestial body(e.gWhite dwarf﹑neutron star, black hole) (such as Capella, five mausoleums, and RS in the constellation Hound);Confirm the stable X-ray source with the strongest apparent flow in a certain bandscorpioX-1 YesSpectroscopic binary；Negative eclipsed binary V78 isGlobular clusterCentaurThe members of ω (so that the question of whether there are binary stars in Extreme Star Family II is raised again);Found a batchBeagleRS type radio and X-ray binary;Discovery andursa majorW-type very different early type large mass, high luminosity new type connected binary stars (if it contains a pairBlue giant（Supergiant）OfCygnusV729）；Measure the classicMonospectral spectroscopic binaryThe spectral line of the other child star in the, which determines that these binary stars are bispectral binary stars;Polarization method is used to calculate the orbital inclination of close binary;wait.
Bibliography
H.C.Thomas，Consequences of mass transfer in close binary systems，Annual Review of Astronomy and Astrophysics， Vol.15，p.127 ，Annual Reviews Inc.，Palo Alto，1977.
J.Sahade and F.Wood，Interacting Binary Stars，Pergamon Press，Oxford，1978.
Z. Kopal ，Dynamics of Close Binary Systems，D.Reidel Pub Cou.，Dordrecht，Holland，1978.
