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What are "short period pulsators?"

Variable stars are divided into categories, based on how and why they vary. One category of stars, the pulsating variables, change in brightness due to intrinsic (internal) changes that occur within the star. These pulsating variable stars are further divided into sub-categories. A short period pulsator (SPP for short) is a star that varies in brightness on the timescale of a few hours up to a tens of days as it grows and shrinks in size. These changes often follow a very regular pattern, repeating over and over from cycle to cycle. Short period pulsators include a number of different variable star types, including Cepheids, RR Lyrae stars, and delta Scuti stars.

In some cases poorly understood processes affect the regular pattern, causing the light curve to vary in height and shape from cycle to cycle. This variation in light curve, called the Blazhko effect after its discoverer, can become very large in some star. AR Herculis is an RR Lyrae star that shows a large Blazhko effect. The graph below shows the shape of the light curve around maximum brightness on 21 different nights, phased with the average pulsation period. Notice how the the height and broadness of the curve changes, and how the time of maximum brightness shifts.

About the AAVSO SPP Section

The AAVSO Short Period Pulsator Section targets all pulsating variable stars with periods in the range of hours to several weeks. This period range includes several important variable star classes like the Cepheids and RR Lyrae stars. More information about some types of short period pulsating stars is given on the SPP Star Classes page. Observations of all short period pulsating stars are welcome, but consult the SPP Program page for a list of interesting targets where additional observations are especially useful.

Several professional astronomers have graciously agreed to be advisers to the SPP section:

• Dr. Horace Smith at Michigan State University, a well-known RR Lyrae star expert
• Dr .Doug Welch at McMaster University, an expert on Cepheid stars
• Dr. Matt Templeton, staff scientist at the AAVSO

Gerry Samolyk and Shawn Dvorak serve as section leaders for the SPP.

About the AAVSO

The AAVSO (American Association of Amateur Variable Star Observers) is an international non-profit organization dedicated to studying variable stars of all types.

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Some short period pulsating stars have more than one period. These additional pulsation period(s) alternately interfere and reinforce each other, resulting in a very complex light curve. Multi-periodic stars like these must be observed frequently over weeks or months to provide enough data to measure the periods involved. There is also some evidence that the pulsation periods and amplitudes change over the span of years.