Beta Cephei variableBeta Cephei variables, also known as Beta Canis Majoris stars, are variable stars that exhibit small rapid variations in their brightness due to pulsations of the stars' surfaces, thought due to the unusual properties of iron at temperatures of 200,000 K in their interiors. These stars are usually hot blue-white stars of spectral class B and should not be confused with Cepheid variables, which are named after Delta Cephei and are luminous supergiant stars.
Mira variableMira variables (; named for the prototype star Mira) are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wavelengths. They are red giants in the very late stages of stellar evolution, on the asymptotic giant branch (AGB), that will expel their outer envelopes as planetary nebulae and become white dwarfs within a few million years.
Rapidly oscillating Ap starRapidly oscillating Ap stars (roAp stars) are a subtype of the Ap star class that exhibit short-timescale rapid photometric or radial velocity variations. The known periods range between 5 and 23 minutes. They lie in the δ Scutiinstability strip on the main sequence. DiscoveryThe first roAp star to be discovered was HD 101065 (Przybylski's Star) in 1961.
Cepheid variableA Cepheid variable () is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period (typically 1–100 days) and amplitude. Cepheids are important cosmic benchmarks for scaling galactic and extragalactic distances; a strong direct relationship exists between a Cepheid variable's luminosity and its pulsation period.
Instability stripThe unqualified term instability strip usually refers to a region of the Hertzsprung–Russell diagram largely occupied by several related classes of pulsating variable stars: Delta Scuti variables, SX Phoenicis variables, and rapidly oscillating Ap stars (roAps) near the main sequence; RR Lyrae variables where it intersects the horizontal branch; and the Cepheid variables where it crosses the supergiants.
Pulsating white dwarfA pulsating white dwarf is a white dwarfstar whose luminosityvaries due to non-radial gravity wave pulsations within itself. Known types of pulsating white dwarfs include DAV, or ZZ Ceti, stars, with hydrogen-dominated atmospheres and the spectral type DA; DBV, or V777 Her, stars, with helium-dominated atmospheres and the spectral type DB; and GW Vir stars, with atmospheres dominated by helium, carbon, and oxygen, and the spectral type PG 1159.RR Lyrae variableRR Lyrae variables are periodic variable stars, commonly found in globular clusters and other old stellar populations in galaxies. They are used as standard candles to measure (extra) galactic distances, assisting with the cosmic distance ladder. This class is named after the prototype and brightest example, RR Lyrae.
MetallicityIn astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-dark) matter in the universe is either hydrogen or helium, and astronomers use the word metals as convenient shorthand for all elements except hydrogen and helium. This word-use is distinct from the conventional chemical or physical definition of a metal as an electrically conducting element.
KappaHistoryArchaic local variants Diacritics and other symbolsDiacriticsάὰᾶἀἁᾱᾰϊᾳσ̌LigaturesϗϛNumerals (Attic)ϛ (6)ϟ (90)ϡ (900) Related topicsUse as scientific symbolsOrthographyRomanizationCyrillizationKappa (; uppercase Κ, lowercase κ or cursiveϰ; Greek: κάππα, káppa) is the tenth letter of the Greek alphabet, representing the voiceless velar plosiveIPA: sound in Ancient and Modern Greek. In the system of Greek numerals, Kʹ has a value of 20.
Stellar structureStellar structure models describe the internal structure of a star in detail and make predictions about the luminosity, the color and the future evolution of the star. Different classes and ages of stars have different internal structures, reflecting their elemental makeup and energy transport mechanisms.
Variable starStar whose brightness fluctuates, as seen from EarthComparison of VLT-SPHERE images of Betelgeuse taken in January 2019 and December 2019, showing the changes in brightness and shape. Betelgeuse is an intrinsically variable star.A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time.
AsteroseismologyAsteroseismology is the study of oscillations in stars. Stars have many resonant modes and frequencies, and the path of sound waves passing through a star depends on the local speed of sound, which in turn depends on local temperature and chemical composition.*As an Amazon Associate I earn from qualifying purchases.