“variable star”的概念、定义、翻译、参考文献-科学参考

variable star

Physics

A star that varies in brightness (see luminosity). This variation, which can be regular or irregular, can be due either to changes in internal conditions (an example of this being a pulsating star in which the variation in brightness is due to the star expanding and contracting) or due to external reasons, such as a star being eclipsed by another star (or stars). Changes in brightness of a star occur both in its early stages and close to its death. Extreme examples of variable stars are nova and supernova. Observations of variable stars provide important information concerning the mass, size, structure, temperature, and evolution of stars. There are more than 25 000 variable stars known, some of which can be seen with the naked eye. The time-scale from maximum to minimum brightness varies from less than a second to a few years.

Astronomy

Any star that varies in brightness. Two broad categories are recognized: extrinsic variables, which vary for a mechanical reason (e.g. eclipses or rotation); and intrinsic variables, which undergo a real change in luminosity of either an individual star or some element in a binary system. Certain stars may combine both forms of variation. The standard reference for the classification of types of variable stars and their nomenclature is the General Catalogue of Variable Stars (GCVS). As of 2017, the total of designated variables in our Galaxy was over 50 000, and more than 200 000 if suspected variables are included.
The classification of variable stars was originally based upon the form of their light-curve, its amplitude (1), and periodicity (or lack of it). Increasingly, however, the physical mechanisms that underlie the different forms of variation, or the physical structure of the stars (and binaries) are used to define six groups of variables, each with specific features. The groups are subdivided into individual types of variation, often named after specific stars, and commonly referred to by capital-letter abbreviations, as listed in Table 8, Appendix. Some stars exhibit more than one form of variability, in which case a combined abbreviation is used, such as E+UG, BY+UV, or EA+UV+BY. Eclipsing binaries are classified in three ways: by their light curve, their physical characteristics, and the evolutionary state of their components. For these, combined abbreviations of the form E/DM, EA/DS/RS, EB/AR, EW/KW are used.
Eruptive variables exhibit unpredictable changes in the form of flares or fades, most of which originate in chromospheric or coronal activity. The group includes flare stars, Gamma Cassiopeiae stars, Orion variables, R Coronae Borealis stars, and T Tauri stars.
Pulsating variables expand and contract or experience wave-like motion of the surface because of fluctuations in the flow of energy from their interiors. Notable examples are Cepheid variables, Mira stars, RR Lyrae stars, RV Tauri stars, semiregular variables, and ZZ Ceti stars.
Rotating variables are a small group whose variations arise from non-uniform surface brightness or ellipsoidal shape.
Cataclysmic variables generally exhibit powerful outbursts with a sudden release of energy. The group includes novae, dwarf novae, and supernovae, and should not be confused with eruptive variables.
Eclipsing variables are binary stars which exhibit partial or total eclipses of one or both components. They are subdivided, on the basis of the shape of the light-curve, into Algol stars, Beta Lyrae stars, and W Ursae Majoris stars. This group also includes some systems that do not eclipse, but where the distorted shape of the components produce fluctuations in the light-curve.
Optically variable X-ray sources bear many similarities to cataclysmic variables (specifically to cataclysmic binaries). The optical variations are often induced by the X-ray variability. Two examples are the AM Herculis stars (or polars) and the HZ Herculis stars (or X-ray pulsars).

Space Exploration

A star whose brightness changes, either regularly or irregularly, over a period ranging from a few hours to months or years. The Cepheid variables regularly expand and contract in size every few days or weeks.
Stars that change in size and brightness at less precise intervals include long-period variables, such as the red giant Mira in the constellation Cetus (period about 331 days), and irregular variables, such as some red supergiants.
Eruptive variables emit sudden outbursts of light. Some suffer flares on their surfaces, while others, such as a nova, result from transfer of gas between a close pair of stars. A supernova is the explosive death of a star. In an eclipsing binary, the variation is due not to any change in the star itself but to the periodic eclipse of a star by a close companion. The different types of variability are closely related to different stages of stellar evolution.

单词	variable star
释义	variable star Physics A star that varies in brightness (see luminosity). This variation, which can be regular or irregular, can be due either to changes in internal conditions (an example of this being a pulsating star in which the variation in brightness is due to the star expanding and contracting) or due to external reasons, such as a star being eclipsed by another star (or stars). Changes in brightness of a star occur both in its early stages and close to its death. Extreme examples of variable stars are nova and supernova. Observations of variable stars provide important information concerning the mass, size, structure, temperature, and evolution of stars. There are more than 25 000 variable stars known, some of which can be seen with the naked eye. The time-scale from maximum to minimum brightness varies from less than a second to a few years. Astronomy Any star that varies in brightness. Two broad categories are recognized: extrinsic variables, which vary for a mechanical reason (e.g. eclipses or rotation); and intrinsic variables, which undergo a real change in luminosity of either an individual star or some element in a binary system. Certain stars may combine both forms of variation. The standard reference for the classification of types of variable stars and their nomenclature is the General Catalogue of Variable Stars (GCVS). As of 2017, the total of designated variables in our Galaxy was over 50 000, and more than 200 000 if suspected variables are included. The classification of variable stars was originally based upon the form of their light-curve, its amplitude (1), and periodicity (or lack of it). Increasingly, however, the physical mechanisms that underlie the different forms of variation, or the physical structure of the stars (and binaries) are used to define six groups of variables, each with specific features. The groups are subdivided into individual types of variation, often named after specific stars, and commonly referred to by capital-letter abbreviations, as listed in Table 8, Appendix. Some stars exhibit more than one form of variability, in which case a combined abbreviation is used, such as E+UG, BY+UV, or EA+UV+BY. Eclipsing binaries are classified in three ways: by their light curve, their physical characteristics, and the evolutionary state of their components. For these, combined abbreviations of the form E/DM, EA/DS/RS, EB/AR, EW/KW are used. Eruptive variables exhibit unpredictable changes in the form of flares or fades, most of which originate in chromospheric or coronal activity. The group includes flare stars, Gamma Cassiopeiae stars, Orion variables, R Coronae Borealis stars, and T Tauri stars. Pulsating variables expand and contract or experience wave-like motion of the surface because of fluctuations in the flow of energy from their interiors. Notable examples are Cepheid variables, Mira stars, RR Lyrae stars, RV Tauri stars, semiregular variables, and ZZ Ceti stars. Rotating variables are a small group whose variations arise from non-uniform surface brightness or ellipsoidal shape. Cataclysmic variables generally exhibit powerful outbursts with a sudden release of energy. The group includes novae, dwarf novae, and supernovae, and should not be confused with eruptive variables. Eclipsing variables are binary stars which exhibit partial or total eclipses of one or both components. They are subdivided, on the basis of the shape of the light-curve, into Algol stars, Beta Lyrae stars, and W Ursae Majoris stars. This group also includes some systems that do not eclipse, but where the distorted shape of the components produce fluctuations in the light-curve. Optically variable X-ray sources bear many similarities to cataclysmic variables (specifically to cataclysmic binaries). The optical variations are often induced by the X-ray variability. Two examples are the AM Herculis stars (or polars) and the HZ Herculis stars (or X-ray pulsars). Space Exploration A star whose brightness changes, either regularly or irregularly, over a period ranging from a few hours to months or years. The Cepheid variables regularly expand and contract in size every few days or weeks. Stars that change in size and brightness at less precise intervals include long-period variables, such as the red giant Mira in the constellation Cetus (period about 331 days), and irregular variables, such as some red supergiants. Eruptive variables emit sudden outbursts of light. Some suffer flares on their surfaces, while others, such as a nova, result from transfer of gas between a close pair of stars. A supernova is the explosive death of a star. In an eclipsing binary, the variation is due not to any change in the star itself but to the periodic eclipse of a star by a close companion. The different types of variability are closely related to different stages of stellar evolution.
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