Pulsating white dwarf

A pulsating white dwarf is a white dwarf star whose luminosity changes because of special kinds of shaking inside it. These stars are very dense and small, but they can shake in ways that make their brightness go up and down. Scientists study these changes to learn more about what is happening deep inside these stars.

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, usually between 1% and 30%, over times of a few minutes to more than an hour. By watching these changes, scientists can learn amazing things about the inside of white dwarfs using a method called asteroseismological studies. This helps us understand how these stars live and evolve after their big explosions.

DAV stars

Early scientists thought white dwarfs might change brightness every about 10 seconds, but they couldn’t see it happen in the 1960s. The first white dwarf found to change brightness was HL Tau 76. In 1965 and 1966, Arlo U. Landolt saw it vary in about 12.5 minutes. This change happens because of special waves inside the star, called gravity wave pulsations.

Later, another white dwarf named Ross 548 showed the same kind of change. In 1972, it was named ZZ Ceti. This name is used for a group of white dwarfs that change brightness, called DAV stars. These stars, which have hydrogen in their atmospheres, change 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 figured out that certain white dwarf stars with helium around them and very hot temperatures might shine in a special way. They looked and found one star, GD 358, that changed its brightness. This was the first time they predicted a new group of these changing stars before seeing them. By 1985, this star was named V777 Her, and it also names this group of stars. These stars are very hot, with temperatures around 25,000K.

GW Virginis stars

GW Vir stars are a special kind of star that changes 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, and their atmospheres are made mostly of helium, carbon, and oxygen.

The changes in brightness happen because of vibrations inside the star, and these vibrations can last from about 300 to 5,000 seconds. Scientists first tried to understand why these vibrations happen in the 1980s, and they thought it might be because of a process called the κ-mechanism. This process involves carbon and oxygen, but they thought it wouldn’t work if helium was present. However, we now know that these vibrations can still happen even when helium is there.

DQV stars

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