Background Part 2: Variable Stars Variable stars are those that change their lum

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Background Part 2: Variable Stars Variable stars are those that change their luminosity with time. They tend to be found in the Instability Strip on the HR Diagram. More information can be found at this Cosmos site (http://www.astronomy.swin.edu.au/cosmos/VInstability+Strip); at trip (http://en.wikipedia.org/wikil a.org/wiki/instability_strip), Variable Stars (http://en.wikipedia.org/wiki/Variable star), RR Lyrae Variables (http://en.wikipedia.org/wiki/RR Lyrae_variable),and related links; as well as in your lecture textbook. Questions Part 2: Variable Stars 5. Are the ZZ Ceti variable stars also giant stars? If not, what type of star are they Proofing errors were found. Click to correct

Explanation / Answer

5. ZZ Ceti are a class of variable white dwarf star. Falling in the instability strip of the Hertzsprung-Russell diagram these stars pulsate with periods of minutes. Hertzsprung-Russell diagram which contains many different types of variable stars (RR Lyrae, Cepheid variable, W Virginis and ZZ Ceti stars all reside in the instability strip).

6.RR Lyrae: Pulsating Variable Star. Recognizable by the characteristic shapes of their light curves.RR Lyrae stars all pulsate similarly with only small differences in period between them.Observed periods range from about 0.5 to 1 day .Low mass horizontal-branch stars lie within the lower portion of the instability strip on the H-R diagram. variables are periodic variable stars, commonly found in globular clusters. They are used as standard candles to measure (extra)galactic distances, as a part of the cosmic distance ladder. This class of variable star is named after the prototype and brightest example, RR Lyrae.

Harlow Shapley determined the position of the Sun in the galaxy by measuring the distances to 93 globular clusters of stars.He measured the apparent brightness and pulsation periods of RR Lyrae stars in the cluster.

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