Leavitt's Cepheid Variables


General Description

This simulation allows the user to explore the relationship between period and apparent magnitude for Cepheid variables in the Magellanic Clouds, first discovered by Henrietta Levitt in 1912. The main window displays a photographic negative of a star field. When the simulation is played, the main window displays an animated sequence of photo negatives taken at 1 day intervals. Each star field contains one Cepheid variable star, which can be identified by its changing size in the photographic negative.

A tool for measuring the apparent magnitude of the Cepheid variable (or any other star) is included. In addition, the user can display a plot of apparent magnitude versus time (known as a light curve), modulo a specified test period. A slider is provided to adjust the value of the test period. When the test period corresponds to the actual period of the Cepheid variable the plot will display a single full period of variation in apparent magnitude (although the data is noisy, so there is some scatter in the light curve).

Resetting the simulation generates a new star field with a new Cepheid variable. By measuring the period and median apparent magnitude of many Cepheid variables, and constructing a plot of magnitude versus period, the user can discover a relation between period and apparent magnitude like the one found by Leavitt for the variable stars in the Small Magellanic Cloud.


Photographic Negative Frame

This frame displays a series of photographic negative of a star field. The user can measure apparent magnitudes of these stars, identify the variable star, and get a rough estimate of the variable's period in this frame.

Light Curve Frame

This frame displays a plot of the Cepheid variable's apparent magnitude as a function of time, modulo a specified test period. The user can use the Min and Max settings to specify a range of possible periods, and then use the slider to search for the correct period. When the test period is equal to the actual period of the variable the plot will display a single full period of the light curve (with some noise).
Todd K. Timberlake (ttimberlake@berry.edu)