By Cristián Cortés, MAS Young Researcher and Professor of Metropolitan University of Educational Science UMCE

When we see the night sky, the stars appear to be static objects in the firmament, but in reality, they are much more than just colored dots. Fantastic phenomena occur in their atmospheres, such as spots, eruptions, stellar storms, and winds, which are similar to those that occur in the Sun.

These phenomena, as well as others occurring in the interiors of the stars, are strongly related to two fundamental parameters, the stellar rotation and the stellar angular momentum. However, these parameters were not well studied due to the difficulty of observing and modeling them. As a consequence, it was impossible to obtain values ​​of these parameters for large stellar samples that allow us to carry out a statistically robust study. Therefore, studies trying to characterize the stars theoretically and observationally do not consider these phenomena, so the usual models generated “stars” without the wealth of events that happen in their atmospheres. Moreover, even for the Sun there are still unresolved problems about its differential rotation (the speed of rotation is slower at its poles than at its equator), and the Sun rotates more slowly than most solar analog and solar twin stars, probably due to the way that the angular momentum was distributed in the planets of the Solar System. But many details of these processes, as well as of the connections between rotation and the Sun’s surface phenomena are still unknown.

Since the last decade the study of stellar rotation began to change when the space missions CoRoT and Kepler provided to the astronomical community with high quality data, allowing to detect several phenomena occurring in the atmospheres of hundreds of thousands of stars in our Milky Way. The camera sensitivity of these space telescopes to the star light changes, as well as the period of time the objects were observed, allowed us to find new planets in other stellar systems (about 3000 up to date), to identify new types of stars, as well as to detect variations in star brightness due to spots on its surface. Considering the stars rotate, then the spot will also rotate and therefore it is possible to know the period and the speed with which the star rotates. 

Despite the incredible and unique contribution of space missions,  their observations must complement with others  from Earth, which allow us to obtain other fundamental parameters, such as surface temperature, mass, age, and chemical composition. These parameters are generally determined by analyzing the spectral lines for different chemical elements present in their atmospheres, which are visible using spectrographs (optical devices that decompose light in their colors, such as when we see in the rainbow). In this sense the environmental conditions of Chile, as well as the installed instruments and telescopes, have allowed us to monitor the stars using different techniques, increasing the possibilities of a complete and detailed analysis.

Some research groups in the world are taking advantage of the information compiled by space missions and ground-based telescopes, which when combined with new computational models, new methods of analysis, and powerful computers, are helping us to understand how stellar rotation and stellar angular momentum impact the stellar life. For example, studies about the  stellar rotation on stars like the Sun, considering different stellar  ages, and with or without planetary systems, are allowing us to know how was and will be its evolution, as well as if the solar rotation is a product of how our Solar System was generated.

http://adsabs.harvard.edu/abs/2015A%26A…581A..68C