Starspots on LO Pegasi

Students: Eva Mulloy ’22 and Tiyinoluwa Olushola-Alao ’23
Research Mentor: Bob Harmon (OWU Department of Physics and Astronomy)

In the night sky, stars appear to be pinpoints of light because they are so far away, so that we cannot produce detailed images of their surfaces like we can for the Sun. On the Sun we can see sunspots that are cooler and darker than the rest of the surface. Some other stars have starspots that are much larger than sunspots and cause the star’s brightness to change significantly as the star rotates and brings the starspots in and out of our view. We are specifically studying a star with prominent starspots called LO Pegasi, located in the constellation Pegasus. This project’s goal is to map the surface of LO Pegasi based on its brightness changes in 2021 and compare our results with those obtained from 2014-2020.

The goal of this project is to map the surface of the star LO Pegasi using information implied by its changes in brightness over a rotational period. LO Pegasi is a young, variable, main-sequence star of spectral type K about 81.7 light-years away from Earth with a rotation period of 10.153 hours. Due to its relatively rapid rotation, it exhibits a high level of magnetic activity. This causes starspots that are much larger than sunspots (solar starspots) on the Sun. Starspots are dark regions on the surface of a star caused by the suppression of convection in the plasma. This reduces the transport of energy into the starspot from the hotter layers below, causing it to be cooler than the surrounding surface. As LO Pegasi rotates, the brightness varies as starspots come in and out of view from Earth, with the star being dimmer when the starspots are in view. We took a series of digital images of LO Pegasi using a CCD camera through photometric B (blue), V (visual), R (red), and I (infrared) filters. We performed aperture photometry to measure the brightness of the star over time and then plotted the results to produce light curves. These light curves were then processed through a Light-curve Inversion (LI) program to map the surface of LO Pegasi to show changes in its starspots from 2014 to 2021.