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Variable Stars Help (page 2)

By — McGraw-Hill Professional
Updated on Sep 17, 2011

RR Lyrae Variables

There are other types of variables besides eclipsing binaries and Cepheids. RR Lyrae variables are bluish stars and are on average, about 40 times as bright as the Sun. The term comes from the location, in the constellation Lyra, of one of the best-known stars of this kind.

RR Lyrae variables have regular, constant cycles of pulsation, usually with periods of about half an Earth day. They tend to be found in large clusters of stars and in the halo of stars surrounding the Milky Way. Because of their locations, they are always far away and require a telescope to be observed. They, like Cepheids, can be used as distance-measuring beacons.

Mira Variables

Both the Cepheid and RR Lyrae variable stars physically expand and shrink in size as their brightness changes. Another sort of variable, called a Mira variable , oscillates without any apparent change in size. Mira variable stars are named after a certain red giant, Mira , in the constellation Cetus. Mira’s brightness varies with a period of about a year and fluctuates between the eighth and the third visual magnitudes. Thus, at its peak, it is about 100 times as bright as it is at the minimum in its cycle. Because of their long periods, Mira stars are sometimes called long-period variables (LPVs).

Astronomers think that Mira variable stars do not expand and contract in radius, as do the Cepheid or the RR Lyrae variables. The increase in brilliance occurs faster than the decline. While Mira, the first variable of this type to be discovered (in 1596), varies by 5 visual magnitudes, some Mira variables have brightness ranges of only 2 or 3 magnitudes, whereas others can change by up to 10 magnitudes. Mira variables are believed to be old stars that have depleted much of their hydrogen and are fusing helium atoms. These stars contain heavier elements as well; most of them are rich in elemental carbon, and some contain large amounts of elemental oxygen.

Practice problems of this concept can be found at: Stars and Nebulae Practice Problems

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