Editor’s Note: For the remainder of 2024, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded articles published in AAS journals this year. The usual posting schedule will resume January 3rd.
The Orbit and Dynamical Mass of Polaris: Observations with the CHARA Array
Published August 2024
Main takeaway:
A research team led by Nancy Remage Evans (Smithsonian Astrophysical Observatory) used observations from the Center for High Angular Resolution Astronomy (CHARA) Array to deduce the mass of the North Star, Polaris. The team found the mass to be 5.13 ± 0.28 solar masses, which is about 50% more massive than previous estimates. The new data also show starspots on Polaris’s surface, which may explain some of the star’s properties.
Why it’s interesting:
Though a seemingly unwavering fixture in the northern night sky, Polaris is actually the nearest example of an important class of variable stars called Cepheids. The intrinsic luminosity of a Cepheid variable scales with the rate at which the star’s brightness varies. Thus, charting a Cepheid’s brightness over time provides a precise measure of the star’s luminosity. Comparing the intrinsic luminosity of the star to how bright the star appears then provides a way to measure the distance to the star. Cepheid variables are an important rung on the cosmic distance ladder, helping to measure the distances to far-off galaxies and even measure the rate of the universe’s expansion.
On amassing masses and spotting starspots:
Two reconstructions of Polaris’s surface, suggesting the presence of dark starspots. [Evans et al. 2024]
Citation
Nancy Remage Evans et al 2024 ApJ 971 190. doi:10.3847/1538-4357/ad5e7a