Variable Star Discoveries
During its inaugural year, the Calvin College Astronomy Camp, part of Calvin’s Academic Camps for Excellence, included a search for variable stars among the camp’s activities. The 7th-10th graders searched 20 fields of view, each of which was imaged continuously through the course of a night. After searching over 1000 stars, the students found six candidate variables, stars whose brightness was never previously known to vary. After follow-up observations from the Calvin-Rehoboth Robotic Observatory in New Mexico, the students were able to follow up the discovery and determine the nature of most of the systems: two pulsating stars known as RR Lyraes, one partially eclipsing binary star system, and two contact binary systems. The final discovery remains unclassified, pending further observations.
The Calvin Astronomy Camp
Given the strong interest in astronomy among young students and the unique capabilities of Calvin's twin robotic observatories, the Department of Physics and Astronomy decided to offer an astronomy camp to middle and high school students. The camp activities included building a small telescope, creating full color astronomical pictures, observing through Calvin's 16-inch telescope, and performing the search for new variable stars. With great success in its first year, the Astronomy Camp will continue and expand in future years, offering specialized camp sessions based on student age and interest.
Understanding the Variability
Variable stars are among some of the most interesting objects in our sky. Typically stars maintain a constant brightness for most of their lifetime, but variable stars can change brightness dramatically over the course of just a few hours. This variability is an indicator of a complex and dynamic system. The key to understanding variables is carefully measuring the brightness of the star over a number of nights. The first task is to find out whether the variations repeat with a regular period, and to find out the length of that period. The next task is to plot the brightness as a function of the phase of that period--a plot that is called a light curve. The shape of the light curve provides clues to the physical nature of the star.
|V1704-11||6.470 hour||contact binary|
|V1707-11||10.909 hour||RR Lyrae|
|V2011+12||24.870 hour||eclipsing binary|
|V2012+12||9.398 hour||contact binary|
|V2038-07||15.384 hour||RR Lyrae|
[Click on any figure or photo to see a larger version.]
Two of the discoveries are pulsating stars known as RR Lyras. These stars show a characteristic light curve with a sharp rise in brightness followed by a slow gradual dimming. Although we do not yet have enough data to fix their periods, typical values range from 10 to 20 hours.
Eclipsing binary stars
One discovery is a partially eclipsing binary star. This is a pair of stars orbiting very close to each other, with an orientation that is just right so that one star will block or eclipse the other when it is in front, causing a temporary drops in brightness. The shape and depth of the eclipses are indicators of the separation distance, shape, and temperature of the binary stars. In our system, the one eclipse is deeper than the other, indicating one star is hotter than the other.
Contact binary stars
Two of the discoveries are contact binary stars. These are like the eclipsing binary stars except that the two stars are so close to each other that their outer atmospheres overlap, resulting in a dumbbell shape. We recognize this by the rounded nature of the light curve. Compare how much more angular the eclipsing binary light curve looks.
posted 7/2/2010 by L. Molnar & A. Vanden Heuvel
updated 9/14/2010 by L. Molnar