Finding planets is a major occupation for many observers, and it is made complicated by the imperfections in stellar surfaces. A planet may only block a fraction of a percent of a star’s light as it crosses in front of it. A star spot, caused by the star’s tangled magnetic field, can cause a significantly larger variation in the star’s brightness. 

Luckily, starspots come and go with time, whereas planets should keep eclipsing over and over like clockwork. Waiting for those recurring transits, however, is annoying, and pretty much everyone agrees a better way to separate the starspots from the passing planet is needed. You can’t separate a star from its spots, but in a new paper in The Astronomical Journal, researchers led by Rachael Roettenbacher point out how you can at least identify the spots. According to Rottenbacher: Our techniques pull together three different types of contemporaneous observations to focus on understanding the star and what its surface looks like. From one of the data sets, we create a map of the surface that allows us to reveal more detail in the radial velocity data as we search for signals from small planets.

Researchers have been studying starspots on giant stars like Betelgeuse for some time, but this research has made it possible to see spots on a sunlike star for the first time. This work looked at a sunlike star and required combining spectra from the EXPRES instrument on TESS with images from the CHARA interferometric telescope array. Together, this data allowed astronomers to reproduce the starspots on the star and determine its rotation rate.

By the way, they did this work looking at Epsilon Eridani, which according to some sources is the home star of the planet Vulcan from Star Trek lore. That just makes me happy, but really has no baring on the science except isn’t it cool to know the system actually has planets?

More Information

Yale press release

“EXPRES. III. Revealing the Stellar Activity Radial Velocity Signature of ε Eridani with Photometry and Interferometry,” Rachael M. Roettenbacher et al., accepted to The Astronomical Journal (preprint on arxiv.org)