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Variable Stars

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Kato Douglas

on 19 April 2010

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Transcript of Variable Stars

What is a variable star? A star that has a detectable change in brightness which is
often accompained by other physical changes -whether
the changes are due to variations in the star's actual luminosity
or to variations in the amount of the star's light that is blocked
from reaching Earth. Variable stars can be divided into two major types:
extrinsic and intrinsic. There are two main groups of extrinsic variables:
rotating stars and eclipsing stars. are those stars in which the variability in brightness occurs because of the occultation of one star by another (eclipsing binary) or rotation of a star that has dark or bright spots on its surface, similar to sunspots. are those stars in which the variability of brightness occurs because of physical change in or on the star itself. Extrinsic variables Intrinsic variables Intrinsic stars are divided into two classes: pulsating and eruptive. 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. Rotating stars
are binary systems of stars with an orbital plane lying near the line-of-sight of the observer. Eclipsing Binary Stars Pulsating stars are stars that show periodic expansion and contraction of their surface layers. The brightness peaks every 50 days. Pulsations may be radial or non-radial. Eruptive stars
(also known as Cataclysmic) are stars that have occasional violent outbursts caused by thermonuclear processes either in their surface layers or deep within their interiors. There are four types of pulsating stars: cepheids, RR Lyrae, RV Tauri
& Long-period variables. Cepheids are rare, highly luminous (supergiant), yellow variable stars. pulsate with periods of a few days to months, and their radii change by several million kilometers (30%) in the process. They are up to 4 times more luminous than Type II Cepheids. (Around 1.5 magnitudes higher) There are two classes of cepheids: Type I Classical & Type II W Virginis Type I Classical Cepheids Type II W Virginis Cepheids are typically 1.5 magnitudes fainter than Type I cepheids and have a mass of less than 1 solar mass. They also have a distinctive light curve with a variation of 0.3 to 1.2 magnitude and a bump on the decline side. RR Lyrae are short-period, pulsating, white giant stars, usually of spectral class A. RV Tauri are yellow supergiants having a characteristic light variation with alternating deep and shallow minima. Long Period Variables (LPVs) are giant red variables that show characteristic emission lines. There are two types of long period variables: mira variable and semiregular variables. Mira Long Period Variables long regular pulsation periods in the range between 80 to 1000 days and grand light variations, from 2.5 magnitudes up to 11 Semiregular Long Period Variables are giants and supergiants showing appreciable periodicity accompanied by intervals of irregular light variation. There are many types of eruptive stars: Supernovae, novae, recurrent novae, darf novae, symbiotic stars and R Coronae Borealis Supernovae are massive stars that show sudden, dramatic, and final magnitude increases as a result of a catastrophic stellar explosion. Novae are close binary systems that consist of a main sequence, Sun-like star and a white dwarf. They increase in brightness by 7 to 16 magnitudes in a matter of one to several hundred days. After the outburst, the star fades slowly to the initial brightness over several years or decades. Recurrent Novae are objects similar to novae, but have two or more slightly smaller-amplitude outbursts during their recorded history. These are close binary systems made up of a Sun-like star, a white dwarf, and an accretion disk surrounding the white dwarf. Dwarf Novae Symbiotic are close binary systems that consist of a red giant and a hot blue star, both embedded in nebulosity. 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. V838 Monocerotis is a red variable star in the constellation Monoceros. The star experienced a major outburst that was observed in early 2002. Mozilla Firefox (browser) released in 2004. Variable Stars By: Kate Douglas April 19th, 2010 Works Cited http://en.wikipedia.org/wiki/Variable_star#Extrinsic_variable_stars
"The Cosmic Perspective" 6th Edition - Bennett, Donahue, Schneider & Voit
"Understanding Variable Stars" - John R. Percy
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