# Where are Cepheid variables on H-R diagram?

## Where are Cepheid variables on H-R diagram?

Cepheids occupy an elon- gated horizontal instability strip on the H-R diagram as massive stars transition from the main sequence to the giant and supergiant branches. RR Lyrae variables are older pulsating white giants with low metallicity.

## How would you describe the Cepheid variable?

A Cepheid variable (/ˈsɛfiːɪd, ˈsiːfiːɪd/) is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.

What are the two 2 main variables of the Hertzsprung-Russell diagram?

Developed independently in the early 1900s by Ejnar Hertzsprung and Henry Norris Russell, it plots the temperature of stars against their luminosity (the theoretical HR diagram), or the colour of stars (or spectral type) against their absolute magnitude (the observational HR diagram, also known as a colour-magnitude …

What does the Hertzsprung-Russell diagram tell us?

The Hertzsprung-Russell diagram shows the relationship between a star’s temperature and its luminosity. It is also often called the H-R diagram or colour-magnitude diagram.

### Why is it called the instability strip?

It turns out that there is a certain region of the HR diagram where stars having that combination of temperature and luminosity also have the proper conditions for this pulsation to occur. That region is called the instability strip, and is labeled in the schematic HR diagram below.

### Why do Cepheids pulsate?

But why does the star pulsate at all?? When a Cepheid is compressed, it becomes opaque. Photons are trapped inside, heating the gas and increasing its pressure. The high-pressure gas expands, becoming transparent. Photons escape, the gas cools, the pressure drops.

How can a Cepheid variable indicate distance?

Through observations of Cepheid variables, astronomers have determined the distances to other galaxies. They compare the Cepheid variable’s apparent brightness with its intrinsic brightness. The difference between observed and actual brightness yields the distance.

What does the Hertzsprung-Russell diagram show?

The Hertzsprung–Russell diagram, abbreviated as H–R diagram, HR diagram or HRD, is a scatter plot of stars showing the relationship between the stars’ absolute magnitudes or luminosities versus their stellar classifications or effective temperatures. More simply, it plots a star’s luminosity (brightness) against its temperature (color).

#### What is a Cepheid variable?

Cepheid variables also fall on the instability strip, at higher luminosities. The H-R diagram can be used by scientists to roughly measure how far away a star cluster or galaxy is from Earth.

#### Where are most stars located on a Hertzsprung Russell diagram?

On plotting a Hertzsprung-Russell diagram, the region occupied by most stars in the diagram is along a line. This line is referred to as the main sequence. The second-most concentration of stars is along a horizontal branch.

How did Heinrich Hertzsprung determine the magnitude of stars?

Hertzsprung noted that stars described with narrow lines tended to have smaller proper motions than the others of the same spectral classification. He took this as an indication of greater luminosity for the narrow-line stars, and computed secular parallaxes for several groups of these, allowing him to estimate their absolute magnitude.