Starspots of LO Pegasi, 2006-2016

Students: Mallory Cochran, Derek Shank, Nick Sweeney (Haverford College), and Oana Vesa (Albion College)
Mentor: Robert Harmon (Department of Physics and Astronomy)

Starspots are cooler, darker regions on stellar surfaces caused by strong magnetic fields. Our project focuses on observing the changes of the starspots over time on the star LO Pegasi, a star similar to the Sun 81 light years away that has starspots on it that are much larger than sunspots on the Sun. To do this, we are measuring the star’s changes in brightness as the starspots rotate into and out of view of Earth. Studying how starspots on other stars behave will aid in better understanding sunspots on the Sun and the magnetic processes behind them.

LO Pegasi is an ultrarotator (P = 10.1538 hr) and a young solar analog about 81 light years distant that exhibits large starspots on its surface. Starspots are regions of strong magnetic field that suppress convection on stellar surfaces. This causes the spots to be cooler and darker than their surroundings. Because starspots are darker, as the star rotates, starspots come into and out of view of Earth and vary the brightness of the star. The brightness variations of LO Pegasi were measured via differential aperture photometry, and light curves were produced through the B, V, R, and I photometric passbands using a 0.35-m Meade LX600 ACF telescope and a QSI 632wsg CCD camera. Then, an indirect photometric technique was employed to map the stellar surface. We present a study of the evolution of the starspots, including long-term changes in the size of the polar spot that we infer from year-to-year changes in the average brightness of the star.