Differential Rotation In Sun Like Stars From Surface Variability And Asteroseismology

Thanks to helioseismology we know the internal rotation of the Sun as a function of radius and latitude. The presence of a shear at the base of the solar convection zone is thought to play a key role in the generation of magnetic fields. So far however, the internal rotation profiles of stars other than the Sun are unknown, and placing constraints on models of rotation and magnetic dynamos is therefore difficult.. The NASA Kepler mission has provided high-quality photometric data that can be used to study the rotation of stars with two different techniques; asteroseismology and surface acti...

In his PhD dissertation Martin Bo Nielsen performs observational studies of rotation in stars like the Sun. The interior rotation in stars is thought to be one of the driving mechanisms of stellar magnetic activity, but until now this mechanism was unconstrained by observational data. NASA’s Kepler space mission provides high-precision observations of Sun-like stars which allow rotation to be inferred using two independent methods: asteroseismology measures the rotation of the stellar interior, while the brightness variability caused by features on the stellar surface trace the rotation of its outermost layers. By combining these two techniques Martin Bo Nielsen was able to place upper limits on the variation of rotation with depth in five Sun-like stars. These results suggest that the interior of other Sun-like stars also rotate in much the same way as our own Sun.

First Published in 1989. Routledge is an imprint of Taylor & Francis, an informa company.

In his PhD dissertation Martin Bo Nielsen performs observational studies of rotation in stars like the Sun. The interior rotation in stars is thought to be one of the driving mechanisms of stellar magnetic activity, but until now this mechanism was unconstrained by observational data. NASA’s Kepler space mission provides high-precision observations of Sun-like stars which allow rotation to be inferred using two independent methods: asteroseismology measures the rotation of the stellar interior, while the brightness variability caused by features on the stellar surface trace the rotation of its outermost layers. By combining these two techniques Martin Bo Nielsen was able to place upper limits on the variation of rotation with depth in five Sun-like stars. These results suggest that the interior of other Sun-like stars also rotate in much the same way as our own Sun.

A complete and in-depth review of exoplanet research, covering the discovery methods, physics and theoretical background.

The Sun and stars rotate in di?erent ways and at di?erent velocity rates. The knowledge of how they rotate is important in understanding the formation and evolution of stars and their structure. The closest star to our Earth, the Sun, is a good laboratory to study in detail the rotation of a G star and allows to test new ideas and develop new techniques to study stellar rotation. More or less massive, more or lessevolved objects, however, can have averydi?erent rotation rate, structure and history. In recent years our understanding of the rotation of the Sun has greatly improved. The Sun has a well-known large-scale rotation, which can be m- sured thanks to visible features across the solar disk, such as sunspots, or via spectroscopy. In addition, several studies cast light on di?erential rotation in the convective zone and on meridional circulation in the radiative zone of the Sun. Even the rotation of the core of the Sun can now be studied thanks to various methods, such as dynamics of the gravitational moments and of course, helioseismology, through g-modes analysis. Moreover, the magnetic ?eld is strongly linked to the matter motions in the solar plasma. The solar magnetic ?eld can be measured only at the surface or in theupperlayers.Itistheproductoftheinternaldynamoorofthelocaldynamos if they exist – in any case magnetic ?eld and rotation cannot thus be separated.