(star that varies in magnitude)
A variable star (or just a variable) is a star which becomes dimmer
and brighter over time as seen from Earth. This
can be due to changes in the star such as brightening
or enlarging, or through a change in whatever the
light must pass through to reach us.
Stars generally are at least slightly variable,
such as the 0.1% variability of the Sun over the solar cycle.
The term microvariable indicates a star showing very slight
variability, e.g., small enough that multiple observations must be
made to preclude instrument variability and random errors.
The term rotational modulation indicates the repeating pattern
of variability that is a signature of starspots.
Some general classes:
- pulsating variable star - grow larger and smaller.
- eruptive variable star - stellar flares, etc.
- cataclysmic variable star - significant explosions such as novae.
- rotating variable star - e.g., showing/hiding star spots.
- eclipsing binary.
- semiregular variable.
- irregular variable.
- intrinsic variable - due to internal features (e.g., pulsation).
- extrinsic variable - due to surface or external features (e.g., rotation, shape, binary star appearance).
Variation may be something that occurs in less than the course
of a day (intraday variable or IDV) or for some pulsating stars,
a variation period longer than 30 or so days (a long period variable
or LPV) or even over spans of years such as FU Orionis stars.
Some of the specific types:
- Cepheid variable - oscillates between being physically larger and smaller.
- W Virginis variable - specific type of Cepheid variable: 10-20 day period, spectral type F6 to K2.
- RR Lyrae variable - somewhat similar to a cepheid.
- protostars such as T-Tauri star and FU Orionis stars (both sometimes termed Orion variables).
- polar or AM Herculis star - binary star with accretion of mass from a red dwarf to a white dwarf with a significant magnetic field.
- intermediate polar or DQ Herculis star - similar to a polar if the magnetic field is weaker or the stars are further apart.
- BY Draconis variable (or BY Draconis star or just BY) - apparently starspots produce their variability.
- RS Canum Venaticorum variable (or RS Canum Venaticorum star) - like BY Draconis variables that are also close binary stars.
- Alpha² Canum Venaticorum variable (or α² Canum Venticorum variable or ACV) - a type of early star that varies in brightness across its surface, showing variability as it rotates.
- flare star - shows quick variations, e.g., in minutes - generally an M dwarf (examples: Wolf 359 and Barnard's Star).
- W Ursae Majoris variable or eclipsing W Ursae Majoris (EW) - type of eclipsing contact binary of low mass stars.
- Beta Cephei variable (BCEP or BCE or Beta Canis Majoris star) - has a type of small rapid variation.
- Algol variable or eclipsing Algol (EA) - eclipsing binary with peculiar characteristics.
- Beta Lyrae variable or eclipsing Beta Lyrae (EB) - type of eclipsing binary with two massive stars in contact.
- Gamma Cassiopeiae variable (GCAS) - type of star with long-term variations ascribed to a varying decretion disk.
- PV Telescopii variable (PVTEL) - type of pulsating supergiant.
- R Coronae Borealis variable (RCB) - type of eruptive variable.
- S Doradus variable (SDOR) - type of eruptive variable.
- SX Arietis variable (SXARI) - type of B-type rotating variable.
- SX Phoenicis variable (SXPHE) - type of pulsating variable.
- U Geminorum variable (UG) - type of cataclysmic variable star, aka a dwarf nova.
- Z Andromedae variable (ZAND) - type of eruptive variable.
- Z Andromedae with eclipses (ZANDE) - a Z Andromedae variable that is also an eclipsing binary.
- rotating ellipsoidal variable - close binary star non-spherical through gravitational inter-attraction, showing varying amounts of surface toward us.
- FK Comae Berenices variable - rotating star with large cool areas.
The details of the observed variation offer clues to the sources
of variation, often revealing or confirming models of stellar structure
for the given star, for its particular variable-star type, and for
stars in general. In this sense, variable stars are analogous to
binary stars, which also serve as windows into stellar detail.
(star type,transient type,variable)
Referenced by pages:
AD Leonis (AD Leo)
asymptotic giant branch (AGB)
Algol (Beta Per)
AU Microscopii (AU Mic)
Bibliographic Catalog of Variable Stars (BCVS)
Cepheid variable (CEP)
cataclysmic variable star (CV)
eclipsing binary (E)
Frank Ross's Catalog (Ross)
FU Orionis star (FUor)
General Catalogue of Variable Stars (GCVS)
Hubble constant (H0)
kappa mechanism (κ-mechanism)
luminous blue variable (LBV)
LaSilla-QUEST Variability Survey (LSQ)
Messier 15 (M15)
main sequence star (MS)
New Catalogue of Suspected Variable Stars (NSV)
partial ionization zone
planetary nebula (PN)
RR Lyrae variable (RRL)
shell star (sh)
T-Tauri star (TTS)
variable star designation
Whole Earth Telescope (WET)