Cepheid variable stars

Henrietta Leavitt, Harvard College Observatory, 1912, established the relation period-luminosity of Cepheid variable stars. Being a woman i.e. confined to the tedious and ridiculously paid work of examining photographic plates for the benefit of an all-male establishment, she would not be awarded credit for her milestone discovery... 

Cepheid variable Stars that have a periodic variation in their luminosity with a direct relation between the luminosity and the period. These stars are important distance markers. 

Way and Andromeda. A typical Cepheid variable star is anywhere from 5 to 20 times more massive than the Sun, and it shines 100 to 10,000 times brighter than the Sun. A Cepheid variable star may oscillate for a million years, which, I remind you, is the blink of an eye relative to the several-billion-year life span of most stars. ... 

In this chapter we also discussed the Cepheid variables, stars whose periods (the time for one cycle of dimness and brightness) are proportional to the stars luminosity. Using the distance modulus formula, this luminosity can be used to estimate interstellar and intergalactic distances. The American astronomer Henrietta Leavitt (1868-1921) discovered the relationship between period and luminosity in Cepheid variables (figure 7.9). I think of her on par with the... 

Cepheid variable star—type of star that varies in brightness as the star pulsates in size. Cephied variables are important distance yardsticks in establishing the distance to nearby galaxies. 

The emission of light from Cepheid stars has a characteristic light curve seen in Figure 4.14 for a Cepheid in the constellation of Perseus. The sawtooth pattern is characteristic of the class and enables the period of variation to be determined. The observation, however, that the luminosity and period are related has powerful consequences. The Cepheid variables fall into two classes type I classical Cepheids have periods of 5-10 days and type II have periods of 12-20 days. The two types of Cepheids initially caused problems when determining the luminosity-period relation but the relation has now been determined. Type I Cepheids follow the expression... 

A type II Cepheid variable is observed in the elliptical galaxy M49 in the Virgo cluster of galaxies with a period of 30 days. Calculate the absolute magnitude of this star. If the total flux on the Earth from the star is 4.2 x 10 22 W m-2, estimate the distance to the Virgo cluster. 

By identifying Cepheid variables in the globular clusters which gravitate around our own Galaxy, Harlow Shapley was able to measure their distance. He thus located their common centre and found it to be a considerable distance from us. It was clear that human beings inhabit the neighbourhood of a nondescript star, very far from the centre of the Milky Way. We are not even at the heart of our own stellar republic A second assault was thus made on human vanity, after the eviction of the Earth from the centre of the Universe. 

Cepheid variables 1-70 days Pulsating, large, luminous, yellow stars More than 700 known in Milky Way Distance markers out to 20 Mpc (66 million ly). 

Bob explained how by measuring Cepheid variables across our cosmos, astronomers have been able to accurately measure large distances between stars and between galaxies. Today, astronomers also search for exploding sun-like stars called Type la supernovae to estimate distances. Within a week of exploding, all Type la supernovae reach the same peak luminosity—about equal to 100 billion stars in a typical galaxy. Because the observed brightness of a supernova falls in proportion to its distance from Earth, astronomers can calculate... 

An alternative method based on following certain stars, known as Cepheid variables, allows measurement of much larger distances. The brightness of a Cepheid star fluctuates with a characteristic period of several days. 

As a star undergoes post-main sequence evolution, it may make several passes through the instability strip in the H-R diagram. There the star becomes variable, i.e. a Cepheid variable which alternately blows up and shrinks again causing an observable brightness variation. 

Halo most of the stars are in globular clusters, RR Lyrae star s (a group of variable stars like the Cepheids). They are about 11 billion years old and their distribution extends up to 2500 pc. Their metallicity relative to the Sun is 1/30. 

Cepheids stars with variable brightness whose period is related to their luminosity... 

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