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Home > Variable star

 Contents
1 Double star observations
2 Intrinsic variables
2.1 Pulsating variables
2.1.1 Cepheid variables
2.1.2 W Virginis stars
2.1.3 δ Scuti stars
2.1.4 RR Lyrae stars
2.1.5 RV Tauri stars
2.1.6 Mira variables
2.1.7 Semiregular variables and Irregular variableAn irregular variable is a type of variable star in which variations in brightness show no regular periodicity. There are two main sub-types of irregular variable eruptive irregular variables and pulsating irregular variables.s
2.2 Cataclysmic variables
2.2.1 SupernovaRemnant of Kepler's Supernova, SN 1604. A supernova is a type of stellar explosion which appears to result in the creation of a new star upon the celestial sphere. Nova" is Latin for "new"). The "super" prefix distinguishes this from a nova, which also ine
2.2.2 Novae
2.2.3 Dwarf novae
2.2.4 R Coronae Borealis stars
2.2.5 Flare stars
3 Extrinsic variables
3.1 Eclipsing binaries
3.2 Planetary eclipses
3.3 Rotating stars
4 Variable star nomenclature
5 See also
6 External link
Most stars are of nearly constant luminosity. Our own Sun is a good example of one which goes through relatively little variation in brightness (usually about 0.1% over an 11 year solar cycle). Many stars, however, undergo significant variations in luminosity, and these are known as variable stars. Variable stars may either intrinsic or extrinsic.

1 Double star observations

Double stars are generally analysed using photometry and photospectrometry . Observations of their brightness compared to non-variable stars of known magnitude can be used to establish a light curve. For regular variables, the period of variation and its amplitude can be very well established; for many variable stars, though, these quantities may vary slowly over time, or even from one period to the next. Peak brightnesses in the light curve are known as maxima, while troughs are known as minima.

2 Intrinsic variables

These are stars which have intrinsic variations in brightness, that is the star itself gets brighter and dimmer. This category can itself be divided into two subgroups: pulsating and cataclysmic (or eruptive) variables. Examples of types within these divisions are given below.

2.1 Pulsating variables

2.1.1 Cepheid variables

Main article: Cepheid variable

One of the most important types of variables star are Cepheid variables, yellow giant stars which undergo pulsations with very regular periods. They are named after Delta Cephei , the first of the class to be discovered, and have periods ranging from about a day to several weeks.

Cepheids are important because they are a type of standard candle. Their luminosity is directly related to their period of variation, with a slight dependence on metallicity as well. The longer the pulsation period, the more luminous the star. Once this period-luminosity relationship is calibrated, this means that by observing the periods of Cepheids, their luminosity can be established. Their distance is then easily found from their apparent brightness. Observations of Cepheid variables are very important for determining distances to galaxies within the Local Group.

2.1.2 W Virginis stars

These are very similar to Cepheids, but belong to Population II and so have a lower metallicity and hence a slightly different period-luminosity relationship.

2.1.3 δ Scuti stars

These are similar to Cepheids but rather fainter, and with shorter periods. They were once known as Dwarf Cepheids. They often show many superimposed periods, which combine to form an extremely complex light curve.

2.1.4 RR Lyrae stars

These stars are somewhat similar to Cepheids, but are not as luminous. They are older than cepheids, belonging to Population II. They are common in globular clusters, and were occasionally referred to in the past as cluster Cepheids. They also have a well established period-luminosity relationship, and so are also useful distance indicators.

2.1.5 RV Tauri stars

These are yellow supergiant stars which have alternating deep and shallow minima. This double-peaked variation typically has periods of 30-100 days. Superimposed on this variation, there may be long-term variations over periods of several years.

2.1.6 Mira variables

Mira variables are very cool red supergiants, which are undergoing very large pulsations. Over periods usually of many months, they may brighten by several magnitudeThe apparent magnitude m of a star, planet or other heavenly body is a measure of its apparent brightness; that is, the amount of light received from the object. Hundred times less bright (e. the same object ten times as far) corresponds to an apparent mas before fading again. MiraMira Omicron Ceti, is an oscillating variable star. The first non- supernova variable star discovered, excepting the odd Eta Carinae, it is the brightest periodic variable in the sky that is not visible during part of its cycle. Mira was discovered (or at itself, also known as Omicron Ceti, varies in brightness from almost 2nd magnitude to as faint as 9th magnitude.

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Topics: Variable Star, Double Star Observations, Intrinsic Variables...

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