Variable Star Observation By: Jessica Vaughn

Variable Stars What are variable stars? Variable stars are stars that change brightness. The brightness changes of these stars can range from a thousandth of a magnitude to as much as twenty magnitudes Variable stars are stars that change brightness. The brightness changes of these stars can range from a thousandth of a magnitude to as much as twenty magnitudes over periods of a fraction of a second to years, depending on the type of variable star , depending on the type of variable star. (AAVSO)

A Brief History of Variable Stars The first variable stars were discovered around 1600 Aristotle and other ancient philosophers taught that stars weren’t completely invariable. Some of the first variable stars were found by scientists from 1500- 1890. The latest edition of the General catalogue of Variable Stars (2003) lists nearly 40,000 variable stars in our own galaxy, as well as 10,000 in other galaxies, and over 10,000 'suspected' variables. (AAVSO)

What types of variable stars are there? There are two different types of variable stars and four main classes. Types of variable stars: Intrinsic Extrinsic

Pulsating and Eruptive stars Within the intrinsic group are two classes of stars: pulsating and eruptive. Pulsating variables are stars that show periodic expansion and contraction of their surface layers. (AAVSO)

Eruptive (Cataclysmic) variables Eruptive variables (also known as cataclysmic variables), as the name implies, are stars that have occasional violent outbursts caused by thermonuclear processes either in their surface layers or deep within their interiors. An example of a cataclysmic variable is a supernova.

Eclipsing binary and rotating stars Eclipsing binary and rotating stars are the two classes of stars within the extrinsic group. A binary star is a stellar system consisting of two stars orbiting around their center of mass.

Rotating stars Rotating stars are stars that show small changes in brightness due to dark or bright spots, or patches on their stellar system. Rotating stars are often binary systems.

Observing Variable Stars Variable stars can be observed through many ways such as photometry, spectrophotometry and spectroscopy. A light curve is more commonly used to observe a star’s brightness compared to non-variable stars of known magnitude.

Light Curve A light curve is a chart used to show the brightness of a star (in magnitude) verses time. The time is plotted in Julian date (JD). The magnitude is plotted on the Y-axis Time is plotted on the X-axis.

Why observe variable stars? By understanding variable stars and what makes them vary in brightness, scientists can start to understand other stars and their behavior. It also helps to find information on stellar properties.

More info There are various groups in the world that are studying variable stars. These are two I got information from. AAVSO ( American Association of Variable Star Observers ) BAA (British Astronomical Association)