Types of Variable Stars

There are several main types of variable stars – eclipsing, Cepheids, and semi-regular/irregular. Some of these have sub types, which are named after the first discovered star in the class.

β Lyra. This type is a close binary. The two orbiting stars are so close to each other that one of them (or both stars) has shape no longer spherical, but more like a pear. This makes the dips in the light curve to be wider.

β Persei (Algol). Both stars are fairly well separated and the light curve has sharper dips.

Here is how both systems and their light curves look like.

beta_lyra

β Lyra

algol

Algol

Eclipsing variables have fixed periods and the shape of their light curves do not change.

Cepheids

The progenitor of this type is δ Cepheus. This class has one very important to astronomy feature. For all cepheids there is a relation between their periods and luminosities. This was very important astronomical discovery, because by knowing the luminosity, the astronomers could calculate the distance to the Cepheid. Their light curves look more or less like this one:

cepheid

Semi-regulars and irregulars

Semi-regular variable stars have light curve’s shapes that vary every cycle. These stars are typically giants that are not very stable. Very often such stars could have periods that change slightly.

Irregular, we can call such variables, that do not have constant period nor shape of their light curves. Some could stay at some magnitude for days, others for years, before a change in the brightness occurs.

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