TU Ursae Majoris, an RR Lyrae variable star, is known to exhibit an unusual property: its pulsation period ( the time it takes to complete an entire cycle of variation in brightness) is uniform over time This characteristic suggests that the star may be orbiting a companion which cannot be seen visually. RR Lyrae variables in such binary systems are fairly rare, so those which are discovered offer astronomers important insights into the evolution and mass of RR Lyrae stars. Earlier research depended on analysis of the star’s light curve to derive an orbit. In contrast, this experiment set out to use velocity measurements, some of which were directly obtained for this project, to determine whether or not TU Ursae Majoris is in fact a binary star.

Velocity data covering 39 years were obtained from both prior scientific research and direct observations. Observations were taken using the 61-inch telescope at the Harvard-Smithsonian Center for Astrophysics’ (CfA) Oak Ridge Observatory; hose taken during 1998 were specifically for this project. Data were fitted to pulsation curves and average velocities were determined to ascertain the long term pattern of velocity. Computer programs, analyzing this pattern, confirmed that an orbit could be fitted to the available data. The result was an estimated orbit of 7453 days or 20.4 years. Highly consistent with earlier light curve based findings.