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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Variable star | 6/10 | https://en.wikipedia.org/wiki/Variable_star | reference | science, encyclopedia | 2026-05-05T13:33:52.261350+00:00 | kb-cron |
==== Fast yellow pulsating supergiants ==== A fast yellow pulsating supergiant (FYPS) is a luminous yellow supergiant with pulsations shorter than a day. They are thought to have evolved beyond a red supergiant phase, but the mechanism for the pulsations is unknown. The class was named in 2020 through analysis of TESS observations.
==== Pulsating white dwarfs ====
These non-radially pulsating stars have short periods of hundreds to thousands of seconds with tiny fluctuations of 0.001 to 0.2 magnitudes. Known types of pulsating white dwarf (or pre-white dwarf) include the 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. GW Vir stars may be subdivided into DOV and PNNV stars.
==== BLAP variables ====
A Blue Large-Amplitude Pulsator (BLAP) is a very rare class of radially-pulsating star characterized by changes of 0.2 to 0.4 magnitudes with typical periods of 7 to 75 minutes. They are thought to be the small helium core of a red giant that has had the remainder of its atmosphere stripped away by a binary companion. It has been hypothesized that they are the long-sought surviving companions of Type Ia supernovae. Alternatively, they may form from the merger of two low-mass white dwarfs. BLAP are effectively pre-white dwarf bodies with an effective temperature between 20,000 and 35,000 K. Most of these objects are in the medium or late stage of helium fusion.
=== Eruptive variable stars === Eruptive variable stars show unpredictable brightness variations caused by material being lost from the star, or in some cases being accreted to it. Despite the name, these are distinguished from cataclysmic variables because the eruptions are due to non-thermonuclear processes.
==== Young stellar object ====
Protostars are young objects that have not yet completed the process of contraction from a gas nebula to a veritable star. During this phase, the object is deeply embedded in an optically thick envelope, so that the variability induced by the rapid accretion process is primarily visible in the infrared. Once the object has expelled most of this nascent cocoon of gas and dust, it stabilizes in mass and becomes a pre–main-sequence star that is contracting toward the main sequence. The luminosity of this object is derived from gravitational contraction. These objects often exhibit irregular brightness variations in association with strong magnetic fields.
Orion variables
Orion variables are young, hot pre–main-sequence stars usually embedded in nebulosity. They have irregular periods with amplitudes of several magnitudes. These irregular variables are so-named because many were first located in the Orion Nebula. A well-known subtype of Orion variables are the T Tauri variables. Variability of T Tauri stars is due to spots on the stellar surface and gas-dust clumps, orbiting in the circumstellar disks. This class of variables are subdivided into classical and weak-line T Tauri. The former display a typical emission line spectra, while the latter do not show strong emission lines and lack a strong stellar wind or accretion disk. The third class, Herbig Ae/Be stars, are the more massive form. The fourth are the RW Aurigae irregular variables that have similar properties but lack nearby nebulosity. These last irregular variables do display emission lines, providing evidence for circumstellar shells.
Herbig Ae/Be stars
Variability of more massive (2–8 solar mass) Herbig Ae/Be stars is thought to be due to gas-dust clumps, orbiting in the circumstellar disks. They can also occur due to cold spots on the photosphere or pulsations when crossing the instability strip. The optical variations are typically up to a magnitude in amplitude and occur on time scales of days to weeks. A particularly extreme example is UX Orionis, which is the prototype of "UXORs"; these protostars vary by 2 to 3 magnitudes.
FU Orionis variables
A small fraction of young stellar objects are eruptive. The two primary types are dubbed FUors and EXors, after their prototype stars, FU Orionis and EX Lupi. (There are also intermediate types and Fu Ori-like YSOs.) The two types differ in the amplitude and time scales of their outbursts. FUors reside in reflection nebulae and show sharp increases in their luminosity in the order of 5–6 magnitudes followed by a very slow decline. FU Orionis variables are of spectral type F or G and are possibly an evolutionary phase in the life of T Tauri stars. EXors exhibit flares like a FUor, but their duration is much shorter. They can exhibit brief flashes up to 5 magnitudes. Its possible these are the next stage in evolution following the FUor phase.
==== Giants and supergiants ==== Large, more luminous stars with lower surface gravity lose their matter relatively easily. Mass loss rates are greater in higher luminosity stars, with the stellar wind being propelled by radiation pressure, and in cool, low mass giants, by radiation pressure on dust grains and by pulsations. For this reason variability due to eruptions and mass loss is more common among giants and supergiants.
Luminous blue variables