Pulsating white dwarf

A pulsating white dwarf is a white dwarf star whose luminosity changes because of special shaking inside it. These stars are very small and dense, and their brightness can go up and down.

There are several types of pulsating white dwarfs. One kind is called DAV, or ZZ Ceti, stars. These have mostly hydrogen in their outer layers. Another type is DBV, or V777 Her, stars, which have more helium. There are also stars called GW Vir, which have layers of helium, carbon, and oxygen. These stars are special because they have not yet become true white dwarfs.

All of these stars change their brightness by small amounts over times of a few minutes to more than an hour. By watching these changes, scientists can learn more about the inside of white dwarfs using a method called asteroseismological studies. This helps us understand how these stars change after their big explosions.

DAV stars

Scientists used to think white dwarfs could change brightness every 10 seconds, but they couldn’t see it in the 1960s. The first white dwarf seen to change brightness was HL Tau 76. In 1965 and 1966, Arlo U. Landolt noticed it changed every 12.5 minutes. This happens because of special waves inside the star, called gravity wave pulsations.

Later, another white dwarf named Ross 548 also showed this kind of change. In 1972, it was named ZZ Ceti. This name is now used for a group of white dwarfs that change brightness, called DAV stars. These stars, which have hydrogen in their atmospheres, change brightness between 30 seconds and 25 minutes. They are found within a specific temperature range. Studying these changes helps scientists learn about the age of the galactic disk.

DBV stars

In 1982, scientists discovered that some white dwarf stars with helium around them and very high temperatures might shine in a special way. They found one star, GD 358, that changed its brightness. This was the first time they found a new group of these changing stars before they were seen. By 1985, this star was named V777 Her, and it also gave its name to this group of stars. These stars are very hot, with temperatures around 25,000K.

GW Virginis stars

GW Vir stars are special stars that change in brightness. They are called "pre-white dwarfs" because they are not quite white dwarfs yet, but are on their way to becoming one. These stars are very hot, with temperatures between 75,000 K and 200,000 K. Their atmospheres are made mostly of helium, carbon, and oxygen.

The changes in brightness happen because of vibrations inside the star. These vibrations can last from about 300 to 5,000 seconds. Scientists first tried to understand why these vibrations happen in the 1980s. They thought it might be because of a process called the κ-mechanism. We now know that these vibrations can still happen even when helium is present.

DQV stars

Scientists have found a special kind of star called a white dwarf, made mostly of carbon. Some of these stars might shine in a special way, called pulsating, when their temperatures are just right. Observations from McDonald Observatory suggest that one star, named SDSS J142625.71+575218.3, could be the first of these new pulsating stars, called DQV stars. It might also be two stars orbiting each other with a ring of carbon and oxygen between them.