Cepheid Variables: The Breathing Stars

Introduction

Cepheid Variables are basically those stars that witness changes or fluctuations in their brightness. Cepheid variable are those special sort of variable stars which are extremely hot and massive. Their mass equals to five times that of the sun and are well known for their efficiency to pulsate and vary both in diameter and temperature. The name Cepheid variable has been derived from Delta Cephei, a variable star in the cepheus constellation, which were the first CV to be identified. During pulsation period, CVs undergo certain changes when it comes to temperature and diameter, where temperature varies from (5500-6600k) diameter depreciates by (-15%) periodically expanding and contracting. This the reason these are called breathing stars.

Types of CVs

Depending upon the difference in their mass and age, Cepheid Variables are of two types: Classical Cepheids and type 2 cepheids.

Classical Cepheids are those stars that are 4-20 times more massive than the sun and around 1000 times more luminous (yellow bright supergiants). Type 2 are around half the mass of the sun.

Recently, Anomalous Cepheids which are unable to fit in any of the classes, have been identified. They have high luminosity but small pulsating time, and higher masses than type 2.

Their use in Astronomy

Cepheids are in general used in determining astronomical distances. These are often referred as standard candles because if one observes its period (the time for which it glows), their absolute brightness can be determined. These stars pulsate because whenever a Cepheid gets compressed, it becomes opaque. The photons which are trapped inside the Cepheid heats the gas and increases the temperature. On heating, the gas expands and gets transparent. In the meantime photon escapes and the gas cools making the star pulsate.

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