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= = =Explain the types of variable stars and be able to find an example of each type online.=

Almost all of the following information can be obtained from the [|AAVSO] website and the [|Australia Telescope Outreach and Education] website.

**__The groups, classes, and types of variable stars__**
There are two groups of variable stars that divide variable stars into their different stars. The two groups are intrinsic variables and extrinsic variables.


 * Intrinsic variables** are those in which the change in brightness is due to some change within the star itself such as in pulsating stars like the Cepheids.


 * Extrinsic variables** are those in which the light output changes due to some process external to the star itself. The most common example of these are the eclipsing binaries.

There are four classes of variable stars. There are two classes of intrinsic variable stars. They are pulsating stars and eruptive or cataclysmic stars. There are different types of pulsating stars, which include Cepheids, RR Lyrae, RV Tauri, and Long-Period Variables. Within the eruptive or cataclysmic stars there are different types of this group. They include Supernovae, Novae, Recurrent Novae, Dwarf Novae, symbiotic stars, and R Coronae Borealis. There are two classes of extrinsic variables, eclipsing binaries and rotating variables.

**__Explaining of the classes and types of variable stars__**

 * Intrinsic Variables**

__Pulsating Stars__: are stars that show periodic expansion and contraction of their surface layers. Pulsations may be radial or non-radial. A radially pulsating star remain spherical in shape, while a star experiencing non-radial pulsations may deviate from a sphere periodically.
 * Cepheids are very luminous, massive variables with periods of 1 -70 days. They have a rapid rise in brightness, but then a slow decline of brightness.
 * Type I Classical Cepheids have a period of between 5 -10 days and an amplitude range of 0.5 - 2.0 magnitudes in visible light. They have distinctive light curves.
 * Type II //W Virgins// type Cepheids are intrinsically less luminous by 1.5 - 2 magnitudes and have typical periods of 12 - 30 days. They display a well-defined period-luminosity relationship that can be used for distance determination.
 * RR Lyrae are older giant stars usually found in globular clusters and have very short periods of about 1.5 hours to a day.
 * RV Tauri are yellow supergiants with distinctive light curves showing alternating deep and shallow minima with the period equal to the time between two successive deep minima. (Minima meaning the minimum of the light curve. For more information look at the section on light curves.)
 * Long-Period are giant red variables that show characteristic emission lines and have periods of months to years.
 * //Mira// type stars have long periods, ranging from about 80 to 1,000 days, varying by 2.5 to 10 magnitudes visually. Their high luminosities mean they can, at maximum brightness, be detected at large distances.
 * Semiregular stars show some periodicity and variations in brightness also exhibit irregularities where they appear to be stable. They are giant and supergiant stars with periods ranging from a few days to several years and the change in brightness is typically less than two magnitudes. Light curves have a variety of shapes.

__Eruptive or Cataclysmic Stars__: exhibit significant and rapid changes in their luminosity due to violent outbursts caused by processes within the star. Some event, as implied by the term cataclysmic result in the destruction of the star whilst others can reoccur one or more times.
 * Supernovae are massive stars that show sudden, dramatic, and final magnitude increases as a result of a catastrophic stellar explosion.
 * Novae are characterized by a rapid and unpredictable rise in brightness of 7 - 16 magnitudes within a few days. The eruptive event is followed by a steady decline back to the pre-nova magnitude over a few months. This suggests that the event causing the nova does not destroy the original star.
 * Recurrent Novae are similar to novae with a change in magnitude of 7 - 16 and a period of outburst of up to about 200 days. They show two or more outburst over recorded observations.
 * Dwarf Novae are intrinsically faint stars that exhibit a sudden increase in brightness by 2 to 5 magnitudes over a few days with intervals of weeks or months between outbursts.
 * //U Geminorum// are stars that have a stillness at minimum light that suddenly brighten. The duration of outburst is generally from 5 to 20 days.
 * //Z Camelopardalis// systems show cyclic variations, interrupted by intervals of constant brightness called standstills. These standstills last the equivalent of several cycles, with the star stuck at the brightness approximately one-third of the way from maximum to minimum.
 * //SU Ursae Majoris// systems have two distinct kinds of outbursts: one is faint, frequent, and short, with duration of 1 to 2 days; the other super outburst is bright, less frequent, and long, with duration of 10 to 20 days.
 * Symbiotic Stars are close binary systems consist of a red giant and a hot blue star, both embedded in nebulosity. They show nova-like outbursts, up to three magnitudes in amplitude.
 * R Coronae Borealis are rare, luminous, hydrogen-poor, carbon-rich, variables that spend most of their time at maximum light, occasionally fading as much as nine magnitudes at irregular intervals. They then slowly recover to their maximum brightness after a few months to a year.


 * Extrinsic Variables**

__Eclipsing Binaries__: are binary systems of stars with an orbital plane lying near the line-of-sight of the observer. The components periodically eclipse one another, causing a decrease in the apparent brightness of the system as seen by the observer. The period of the eclipse, which coincides with the orbital period of the system, can range from minutes to years.

__Rotating Variables__: show small changes in light that may be due to dark or bright spots, or patches on their stellar surfaces (starspots). Rotating stars are often binary systems.

__Examples of Each Type of Star__

 * Intrinsic Variables**

__Pulsating Stars -__ Cepheid RR Lyrae - RW Dra RV Tauri - R Scuti in Scutum Long Period Variables
 * Type I Classical Cepheid - Eta Aquilae
 * Type II //W Virginis// Star - BL Herculis
 * //Mira// Type – Omicron Ceti
 * Semiregular - Betelgeuse, Alpha Orionis

__Cataclysmic or Eruptive Stars -__

Supernovae - SN 1604 Novae - Nova 1670 Vulpeculae Recurrent Novae - RS Ophiuchi Dwarf Novae Symbiotic Stars - R Aquarii R Coronae Borealis – XX Cam and R CrB itself
 * U Geminorum - SS Cygni
 * Z Camelopardalis stars
 * SU Ursae Majoris stars


 * Extrinsic Variables**

Eclipsing Binaries - Zeta Aurigae Rotating Variables - Altair

http://www.aavso.org/vstar/types.shtml http://outreach.atnf.csiro.au/education/senior/astrophysics/variable_types.html http://jumk.de/astronomie/special-stars/index.shtml [|http://www.seds.org/~spider/spider/Vars/vars.html] http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1996PASP..108..225C&db_key=AST&page_ind=1&data_type=GIF&type=SCREEN_VIEW&classic=YES
 * //References://**