Light Curves of Variable Stars

Overview

Variable stars are stars that undergo a change in brightness over time, due to either intrinsic processes or external factors.
A light curve is a graph that displays the change in a star’s brightness over time, typically, the vertical axis represents the star’s brightness, and the horizontal axis represents time.

Intrinsic variables change brightness due to internal processes. Examples are pulsating variables and eruptive variables.
Pulsating variables change brightness due to expansion and contraction on regular intervals. Their light curves have a regular pattern.
Cepheid variables and RR Lyrae stars are types of pulsating variables. Cepheids have periods of several days to months while RR Lyrae stars have periods of a few hours to a day.
The period-luminosity relationship of Cepheid variables and RR Lyrae stars is a crucial tool in distance measurement in astronomy.
Eruptive variables are stars that change brightness because of flares or eruptions. Their light curve pattern is irregular and unpredictable.

Extrinsic variables change brightness because of external factors like binary star systems or circumstellar clouds.
Eclipsing binaries are binary star systems where one star passes in front of the other from our line of sight, causing a dip in the overall brightness. Their light curves have a distinctive pattern of regular dips.
Rotating variables change brightness due to the variation in emitted light as they rotate. If the star has dark spots or is not spherical, it can cause variations in brightness, creating a periodic light curve.

By meticulously analysing the light curve of a variable star, astronomers can deduce valuable information about the star like its period, physical shape, and nature of variability.
The curve’s shape, such as whether it is regular or irregular, smooth or jagged, can indicate what type of variable star it represents.
The star’s period can be determined by finding the time it takes for its brightness to complete a full cycle of change.

Understanding light curves and the behaviour of variable stars allows astronomers to make inferences about a star’s properties and its life cycle.
Light curves provide invaluable support to other astronomical tools and methods such as distance measurement, search for exoplanets, and the exploration of stellar evolution.