Unprecedented Star Cluster Study May Offer View of Planet Formation and Our Solar System’s Own Early Beginnings

The observations were presented at the American Astronomical Society (AAS) meeting in Washington, DC. on January 11 by William Herbst, the John Monroe Van Vleck Professor of Astronomy and chair the astronomy department (pictured at right), Gabriel Roxby ‘06, a Wesleyan undergraduate involved in the study, and Eric Williams, the systems manager of the Van Vleck observatory.

The Wesleyan team analyzed 500 stars in the Orion Nebula Cluster (ONC) which is approximately 500 pc or 1600 light years from earth. The data from the stars were collected by faculty and graduate and undergraduate students during a continuous 14-year period. The observations gave the astronomers the unique opportunity to track the long-term behavior of these stars concurrently with their subtle changes over short timescales.

The findings presented at the AAS meeting detail the discovery of a large number of young T Tauri stars with intriguing patterns in brightness variation over both short and long timescales. One star discovered, Trapezium 093/JW#669, became of particular interest because it seemed to grow brighter then fainter in a remarkably steady pattern with a possible period of about 10 years. This is an extremely long cycle, given that it rotates every 1.18 days.

One theory suggests the presence of a disk of dust and rock orbiting the star. Such a circumstellar disk would have to contain a large clump, such as a planet or proto-planet, in order to obscure the light of the star at certain times and not others. Another possible explanation for the brightness fluctuations may be that the star is experiencing magnetic cycles akin to those seen in our Sun, where its magnetic field becomes stronger and weaker over time, causing the total area covered by sunspots to grow and shrink. Another theory is that the phenomenon is being caused by the presence of a young fully-formed gas-giant planet akin to Jupiter.

Whatever the cause, the observations by the Wesleyan researchers may offer significant insights into our own solar system’s origins. Trapezium 093/JW#669 bears a strong resemblance to a younger version of the Sun, and it may be undergoing processes similar to those in the Sun’s early history. Further investigation may reveal whether these or other explanations can account for this star’s long and regular period.

This active star-forming region is a promising area for observations because of its relative nearby distance and its large population of T Tauri stars, which are typically young (about 1 million years old).

The study also offers a new perspective on the changes that occur in T Tauri stars over many years. For the first time a large collection of long-term light curves for a vast sample of young variable stars has been gathered. The sample can be used to further analyze general trends among these stars, as well as locate other unique stars that may help to shed light on the genesis of our own Solar System.

The data were obtained using Wesleyan’s 0.6 meter (24 inch) Perkin telescope. Researchers used differential photometry to calculate stars’ alterations in brightness from night to night by comparing the variable stars to a few stars in each field known to have relatively unchanging brightness. They used these calculations to plot “light curves,” or diagrams of the change in brightness over time, for each star.