RT Andromedae

Lore & Background

RT Andromedae is a close eclipsing binary system consisting of a G-type main-sequence star slightly more massive than the Sun and a K-type main-sequence star slightly less massive. It varies in apparent visual magnitude from 9.83 at minimum brightness to 8.97 at maximum, with a period of 0.6289216 days. The light curve exhibits secular variations of period and minima.

According to Pribulla et al. (2000), the changes in variability could be ascribed to a third object in the system, with even a possible fourth. Its minimum mass is estimated to be 5 percent the mass of the Sun (roughly 50 times the mass of Jupiter), with an orbital period close to 75 years and an eccentricity thought to be fairly high at 0.56. Such an object could likely turn out to be a brown dwarf or even a massive jovian planet.

However, a recent paper of Manzoori (2009) noticed that there is a decreasing trend in the orbital period, so magnetic braking could explain better the evolution of this orbital system. The system is estimated to be 323 light-years (99.0 parsecs) away.

Reader's Guide

RT Andromedae holds significance as an RS Canum Venaticorum variable, a class of close eclipsing binaries that exhibit starspot activity and orbital period changes. Its secular variations in period and minima have made it a subject of study for understanding stellar evolution in binary systems. The article presents two competing explanations for these variations: the presence of a third (or even fourth) body with a minimum mass of 5 percent the mass of the Sun, possibly a brown dwarf or massive jovian planet, with an orbital period near 75 years and high eccentricity; or magnetic braking, as suggested by a decreasing trend in the orbital period noted by Manzoori (2009). This unresolved dispute highlights the complexity of interpreting period changes in close binaries. The system's legacy lies in its role as a test case for distinguishing between dynamical perturbations from additional companions and intrinsic stellar magnetic effects, contributing to broader knowledge of binary star evolution and the potential for substellar companions.

Did You Know?

• The system varies from magnitude 9.83 at minimum to 8.97 at maximum with a period of 0.6289216 days.
• Manzoori (2009) proposed magnetic braking as an alternative explanation for the orbital period decrease.